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1
Fox, M., F. Herman, S. D. Willett, and D. A. May. "A linear inversion method to infer exhumation rates in space and time from thermochronometric data." Earth Surface Dynamics Discussions 1, no. 1 (July 19, 2013): 207–59. http://dx.doi.org/10.5194/esurfd-1-207-2013.
Повний текст джерелаАнотація:
Abstract. We present a formal inverse procedure to extract exhumation rates from spatially distributed low temperature thermochronometric data. Our method is based on a Gaussian linear inversion approach in which we define a linear problem relating exhumation rate to thermochronometric age with rates being parameterized as variable in both space and time. The basis of our linear forward model is the fact that the depth to the "closure isotherm" can be described as the integral of exhumation rate, ė, from the cooling age to the present day. For each age, a one-dimensional thermal model is used to calculate a characteristic closure temperature, and is combined with a spectral method to estimate the conductive effects of topography on the underlying isotherms. This approximation to the four-dimensional thermal problem allows us to calculate closure depths for datasets that span large spatial regions. By discretizing the integral expressions into time intervals we express the problem as a single linear system of equations. In addition, we assume that exhumation rates vary smoothly in space, and so can be described through a spatial correlation function. Therefore, exhumation rate history is discretized over a set of time intervals, but is spatially correlated over each time interval. We use an a priori estimate of the model parameters, in order to invert this linear system and obtain the maximum likelihood solution for the exhumation rate history. An estimate of the resolving power of the data is also obtained by computing the a posteriori variance of the parameters, and by analyzing the resolution matrix. Finally, we illustrate our inversion procedure using examples from the literature.
2
Malizia, Angela, Mariateresa Fiocchi, Lorenzo Natalucci, Vito Sguera, John B. Stephen, Loredana Bassani, Angela Bazzano, Pietro Ubertini, Elena Pian, and Antony J. Bird. "INTEGRAL View of TeV Sources: A Legacy for the CTA Project." Universe 7, no. 5 (May 7, 2021): 135. http://dx.doi.org/10.3390/universe7050135.
Повний текст джерелаАнотація:
Investigations that were carried out over the last two decades with novel and more sensitive instrumentation have dramatically improved our knowledge of the more violent physical processes taking place in galactic and extra-galactic Black-Holes, Neutron Stars, Supernova Remnants/Pulsar Wind Nebulae, and other regions of the Universe where relativistic acceleration processes are in place. In particular, simultaneous and/or combined observations with γγ-ray satellites and ground based high-energy telescopes, have clarified the scenario of the mechanisms responsible for high energy photon emission by leptonic and hadronic accelerated particles in the presence of magnetic fields. Specifically, the European Space Agency INTEGRAL soft γγ-ray observatory has detected more than 1000 sources in the soft γγ-ray band, providing accurate positions, light curves and time resolved spectral data for them. Space observations with Fermi-LAT and observations that were carried out from the ground with H.E.S.S., MAGIC, VERITAS, and other telescopes sensitive in the GeV-TeV domain have, at the same time, provided evidence that a substantial fraction of the cosmic sources detected are emitting in the keV to TeV band via Synchrotron-Inverse Compton processes, in particular from stellar galactic BH systems as well as from distant black holes. In this work, employing a spatial cross correlation technique, we compare the INTEGRAL/IBIS and TeV all-sky data in search of secure or likely associations. Although this analysis is based on a subset of the INTEGRAL all-sky observations (1000 orbits), we find that there is a significant correlation: 39 objects (∼20% of the VHE γγ-ray catalogue) show emission in both soft γγ-ray and TeV wavebands. The full INTEGRAL database, now comprising almost 19 years of public data available, will represent an important legacy that will be useful for the Cherenkov Telescope Array (CTA) and other ground based large projects.
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Fox, M., F. Herman, S. D. Willett, and D. A. May. "A linear inversion method to infer exhumation rates in space and time from thermochronometric data." Earth Surface Dynamics 2, no. 1 (January 28, 2014): 47–65. http://dx.doi.org/10.5194/esurf-2-47-2014.
Повний текст джерелаАнотація:
Abstract. We present a formal inverse procedure to extract exhumation rates from spatially distributed low temperature thermochronometric data. Our method is based on a Gaussian linear inversion approach in which we define a linear problem relating exhumation rate to thermochronometric age with rates being parameterized as variable in both space and time. The basis of our linear forward model is the fact that the depth to the "closure isotherm" can be described as the integral of exhumation rate, ..., from the cooling age to the present day. For each age, a one-dimensional thermal model is used to calculate a characteristic closure temperature, and is combined with a spectral method to estimate the conductive effects of topography on the underlying isotherms. This approximation to the four-dimensional thermal problem allows us to calculate closure depths for data sets that span large spatial regions. By discretizing the integral expressions into time intervals we express the problem as a single linear system of equations. In addition, we assume that exhumation rates vary smoothly in space, and so can be described through a spatial correlation function. Therefore, exhumation rate history is discretized over a set of time intervals, but is spatially correlated over each time interval. We use an a priori estimate of the model parameters in order to invert this linear system and obtain the maximum likelihood solution for the exhumation rate history. An estimate of the resolving power of the data is also obtained by computing the a posteriori variance of the parameters and by analyzing the resolution matrix. The method is applicable when data from multiple thermochronometers and elevations/depths are available. However, it is not applicable when there has been burial and reheating. We illustrate our inversion procedure using examples from the literature.
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Mishchenko, T. M. "Methodology and Models of Combined Modeling of Electromagnetic Pro-cesses in Electric Traction Systems." Science and Transport Progress. Bulletin of Dnipropetrovsk National University of Railway Transport, no. 2(92) (April 15, 2021): 40–49. http://dx.doi.org/10.15802/stp2021/237404.
Повний текст джерелаАнотація:
Purpose. The main purpose of the work is the development of identification models and a new method of modeling electromagnetic processes in electric traction systems with simultaneous consideration of all its subsystems, as well as several feeder zones of the electrified section. Methodology. To achieve this purpose, the methods of mathematical modelling, the basics of the theory of random processes and the methodology of their probabilistic-statistical processing, the methods for solving integral equations and analysis of electric traction circuits in electric traction systems are used. Findings. The requirements to be met by an adequate, stochastic identification model of electric traction devices are established. The solution of Fredholm’s integral correlation equation of the first kind is performed. The analytical expression of the identification dynamic model of the electric locomotive DE–1 is obtained and its adequacy is checked. The methodology of combined modeling of electromagnetic processes in devices and subsystems of electric traction systems is developed and presented tabularly. Originality. For the first time it is proposed to use the pulse transition function as identification models of traction substation and traction network with electric rolling stock in predictive modeling of electromagnetic and electric power processes in electric traction systems. A new method has been developed, a method of complex modeling of electromagnetic and electric power processes in the system of electric traction with simultaneous consideration of all its subsystems, as well as several inter-substation zones of the electrified section. For the first time, a method of partitioning the correlation functions for solving an integral correlation equation has been proposed, which allows defining a pulse transition function as an identification model of any subsystem of an electric traction system. Practical value. The developed identification models and the method of combined modeling make it possible to predict electromagnetic processes simultaneously in all feeder zones of the electrified section of the electric traction system. The obtained identification model of the electric locomotive DE–1 can be adapted with its subsequent use in modeling processes in the traction circuits of electric locomotives of other types. The method of factorization of correlation functions used in solving the Volterra integral correlation equation of the first kind (convolution type) can be adapted to the solution of other integral equations, which describe the processes in electric traction systems.
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Rodionova, Irina A., and Uliana V. Mizerovskaya. "Correlation Between the Level of Socio-economic Development and the Use of the Information and Communication Technologies." Studies of the Industrial Geography Commission of the Polish Geographical Society 22 (June 1, 2013): 93–103. http://dx.doi.org/10.24917/20801653.22.6.
Повний текст джерелаАнотація:
During recent decades, the rate of structural shifts in the world economy has been especially fast. One of the factors used to influence these processes was to actively develop hi-tech industries and information and communication technologies. With the course of time, the level of informatization of society becomes a defining factor for a country’s competitiveness and predefines its ability to integrate into the global economy. The article characterizes the readiness of different countries to make a move to an innovative way of development based on analysis of combined rating tables that contain integral indices of society’s informatization level. The level of accomplishment of the task to form an innovative type of economy can be assessed in the link between implementation of science and technology progress achievements (i.e.: through the use of information and communication technologies) and the level of socio-economic development of the world countries. Current positions held by Russia and Poland according to some integral indices are also being analyzed.
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Hu, Heng, Yunchang Cao, Chuang Shi, Yong Lei, Hao Wen, Hong Liang, Manhong Tu, et al. "Analysis of the Precipitable Water Vapor Observation in Yunnan–Guizhou Plateau during the Convective Weather System in Summer." Atmosphere 12, no. 8 (August 23, 2021): 1085. http://dx.doi.org/10.3390/atmos12081085.
Повний текст джерелаАнотація:
The ERA5 reanalysis dataset of the European Center for Medium-Range Weather Forecasts (ECMWF) in the summers from 2015 to 2020 was used to compare and analyze the features of the precipitable water vapor (PWV) observed by six ground-based Global Navigation Satellite System (GNSS) meteorology (GNSS/MET) stations in the Yunnan–Guizhou Plateau. The correlation coefficients of the two datasets ranged between 0.804 and 0.878, the standard deviations ranged between 4.686 and 7.338 mm, and the monthly average deviations ranged between −4.153 and 9.459 mm, which increased with the altitude of the station. Matching the quality-controlled ground precipitation data with the PWV in time and space revealed that most precipitation occurred when the PWV was between 30 and 65 mm and roughly met the normal distribution. We used the vertical integral of divergence of moisture flux (∇p) and S-band Doppler radar networking products combined with the PWV to study the convergence and divergence process and the water vapor delivery conditions during the deep convective weather process from August 24 to 26, 2020, which can be used to analyze the real-time observation capability and continuity of PWV in small-scale and mesoscale weather processes. Furthermore, the 1 h precipitation and the cloud top temperature (ctt) data at the same site were used to demonstrate the effect of PWV on the transit of convective weather systems from different time–space scales.
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Hacar, A., M. Tafalla, J. Forbrich, J. Alves, S. Meingast, J. Grossschedl, and P. S. Teixeira. "An ALMA study of the Orion Integral Filament." Astronomy & Astrophysics 610 (February 2018): A77. http://dx.doi.org/10.1051/0004-6361/201731894.
Повний текст джерелаАнотація:
Aim. We have investigated the gas organization within the paradigmatic Integral Shape Filament (ISF) in Orion in order to decipher whether or not all filaments are bundles of fibers. Methods. We combined two new ALMA Cycle 3 mosaics with previous IRAM 30m observations to produce a high-dynamic range N2H+ (1-0) emission map of the ISF tracing its high-density material and velocity structure down to scales of 0.009 pc (or ~2000 AU). Results. From the analysis of the gas kinematics, we identify a total of 55 dense fibers in the central region of the ISF. Independently of their location in the cloud, these fibers are characterized by transonic internal motions, lengths of ~0.15 pc, and masses per unit length close to those expected in hydrostatic equilibrium. The ISF fibers are spatially organized forming a dense bundle with multiple hub-like associations likely shaped by the local gravitational potential. Within this complex network, the ISF fibers show a compact radial emission profile with a median FWHM of 0.035 pc systematically narrower than the previously proposed universal 0.1 pc filament width. Conclusions. Our ALMA observations reveal complex bundles of fibers in the ISF, suggesting strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. The fibers show identical dynamic properties in both low- and high-mass regions, and their widespread detection in nearby clouds suggests a preferred organizational mechanism of gas in which the physical fiber dimensions (width and length) are self-regulated depending on their intrinsic gas density. Combining these results with previous works in Musca, Taurus, and Perseus, we identify a systematic increase of the surface density of fibers as a function of the total mass per-unit-length in filamentary clouds. Based on this empirical correlation, we propose a unified star-formation scenario where the observed differences between low- and high-mass clouds, and the origin of clusters, emerge naturally from the initial concentration of fibers.
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Kamraj, Nikita, Murray Brightman, Fiona A. Harrison, Daniel Stern, Javier A. García, Mislav Baloković, Claudio Ricci, et al. "X-Ray Coronal Properties of Swift/BAT-selected Seyfert 1 Active Galactic Nuclei." Astrophysical Journal 927, no. 1 (March 1, 2022): 42. http://dx.doi.org/10.3847/1538-4357/ac45f6.
Повний текст джерелаАнотація:
Abstract The corona is an integral component of active galactic nuclei (AGNs) which produces the bulk of the X-ray emission above 1–2 keV. However, many of its physical properties and the mechanisms powering this emission remain a mystery. In particular, the temperature of the coronal plasma has been difficult to constrain for large samples of AGNs, as constraints require high-quality broadband X-ray spectral coverage extending above 10 keV in order to measure the high-energy cutoff, which provides constraints on the combination of coronal optical depth and temperature. We present constraints on the coronal temperature for a large sample of Seyfert 1 AGNs selected from the Swift/BAT survey using high-quality hard X-ray data from the NuSTAR observatory combined with simultaneous soft X-ray data from Swift/XRT or XMM-Newton. When applying a physically motivated, nonrelativistic disk-reflection model to the X-ray spectra, we find a mean coronal temperature kT e = 84 ± 9 keV. We find no significant correlation between the coronal cutoff energy and accretion parameters such as the Eddington ratio and black hole mass. We also do not find a statistically significant correlation between the X-ray photon index, Γ, and Eddington ratio. This calls into question the use of such relations to infer properties of supermassive black hole systems.
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Senior, K., J. Kouba, and J. Ray. "Status and Prospects for Combined GPS LOD and VLBI UT1 Measurements." Artificial Satellites 45, no. 2 (January 1, 2010): 57–73. http://dx.doi.org/10.2478/v10018-010-0006-7.
Повний текст джерелаАнотація:
Status and Prospects for Combined GPS LOD and VLBI UT1 Measurements A Kalman filter was developed to combine VLBI estimates of UT1-TAI with biased length of day (LOD) estimates from GPS. The VLBI results are the analyses of the NASA Goddard Space Flight Center group from 24-hr multi-station observing sessions several times per week and the nearly daily 1-hr single-baseline sessions. Daily GPS LOD estimates from the International GNSS Service (IGS) are combined with the VLBI UT1-TAI by modeling the natural excitation of LOD as the integral of a white noise process (i.e., as a random walk) and the UT1 variations as the integration of LOD, similar to the method described by Morabito et al. (1988). To account for GPS technique errors, which express themselves mostly as temporally correlated biases in the LOD measurements, a Gauss-Markov model has been added to assimilate the IGS data, together with a fortnightly sinusoidal term to capture errors in the IGS treatments of tidal effects. Evaluated against independent atmospheric and oceanic axial angular momentum (AAM + OAM) excitations and compared to other UT1/LOD combinations, ours performs best overall in terms of lowest RMS residual and highest correlation with (AAM + OAM) over sliding intervals down to 3 d. The IERS 05C04 and Bulletin A combinations show strong high-frequency smoothing and other problems. Until modified, the JPL SPACE series suffered in the high frequencies from not including any GPS-based LODs. We find, surprisingly, that further improvements are possible in the Kalman filter combination by selective rejection of some VLBI data. The best combined results are obtained by excluding all the 1-hr single-baseline UT1 data as well as those 24-hr UT1 measurements with formal errors greater than 5 μs (about 18% of the multi-baseline sessions). A rescaling of the VLBI formal errors, rather than rejection, was not an effective strategy. These results suggest that the UT1 errors of the 1-hr and weaker 24-hr VLBI sessions are non-Gaussian and more heterogeneous than expected, possibly due to the diversity of observing geometries used, other neglected systematic effects, or to the much shorter observational averaging interval of the single-baseline sessions. UT1 prediction services could benefit from better handling of VLBI inputs together with proper assimilation of IGS LOD products, including using the Ultra-rapid series that is updated four times daily with 15 hr delay.
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CELANI, ANTONIO, MARCO MARTINS AFONSO, and ANDREA MAZZINO. "Point-source scalar turbulence." Journal of Fluid Mechanics 583 (July 4, 2007): 189–98. http://dx.doi.org/10.1017/s0022112007006520.
Повний текст джерелаАнотація:
The statistics of a passive scalar randomly emitted from a point source is investigated analytically for the Kraichnan ensemble. Attention is focused on the two-point equal-time scalar correlation function, a statistical indicator widely used both in experiments and in numerical simulations. The only source of inhomogeneity/anisotropy is the injection mechanism, the advecting velocity being here statistically homogeneous and isotropic. The main question we address is on the possible existence of an inertial range of scales and a consequent scaling behaviour. The question arises from the observation that for a point source the injection scale is formally zero and the standard cascade mechanism cannot thus be taken for granted. We find from first principles that an intrinsic integral scale, whose value depends on the distance from the source, emerges as a result of sweeping effects. For separations smaller than this integral scale a standard forward cascade occurs. This is characterized by a Kolmogorov–Obukhov power-law behaviour as in the homogeneous case, except that the dissipation rate is also dependent on the distance from the source. Finally, we also find that the combined effect of a finite inertial-range extent and of inhomogeneities causes the emergence of subleading anisotropic corrections to the leading isotropic term, that are here quantified and discussed.
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Puga, Alejandro J., and John C. LaRue. "Normalized dissipation rate in a moderate Taylor Reynolds number flow." Journal of Fluid Mechanics 818 (March 29, 2017): 184–204. http://dx.doi.org/10.1017/jfm.2017.47.
Повний текст джерелаАнотація:
Time-resolved velocity measurements are obtained using a hot-wire in a nearly homogeneous and isotropic flow downstream of an active grid for a range of Taylor Reynolds numbers from$191$to$659$. It is found that the dimensionless dissipation rate,$C_{\unicode[STIX]{x1D716}}$, is nearly a constant for sufficiently high values of Taylor Reynolds number,$R_{\unicode[STIX]{x1D706},u_{q}}$, and is approximately equal to$0.87$. This value is approximately$5\,\%$less than the value reported by Boset al.(Phys. Fluids, vol. 19 (4), 2007, 045101), which is obtained using DNS/LES (direct numerical simulation combined with large eddy simulation) for decaying homogeneous and isotropic turbulence, and is in excellent agreement with the active grid experiment of Thormann & Meneveau (Phys. Fluids, vol. 26 (2), 2014, 025112.). The results presented herein show that deviation from isotropy may cause inconsistencies in the computation of$C_{\unicode[STIX]{x1D716}}$. As a result, it is suggested that the velocity scale be the square root of the turbulence kinetic energy. The integral length scale measurements obtained from the longitudinal velocity correlation are in close agreement with the integral length scale measured from the peak of the energy spectrum,$\unicode[STIX]{x1D705}E_{11}(\unicode[STIX]{x1D705})$, where$\unicode[STIX]{x1D705}$is the wavenumber and$E_{11}(\unicode[STIX]{x1D705})$is the one-dimensional power spectrum of the downstream velocity.
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Antipov, O. I., and A. V. Zakharov. "COMBINING METHODS OF FREQUENCY FILTERING AND NONLINEAR ANALYSIS FOR SOMNOLOGICAL STUDY OF EEG SIGNALS." Science and Innovations in Medicine 1, no. 3 (September 15, 2016): 45–50. http://dx.doi.org/10.35693/2500-1388-2016-0-3-45-50.
Повний текст джерелаАнотація:
Aim - combined use of frequency and nonlinear analysis methods for obtaining hypnograms by analyzing electroencephalographic (EEG) signals during somnological studies. Methods. Frequency filtering methods were used for preliminary treatment of EEG signals before the following nonlinear analysis. As non-linear methods of analysis we used fractal methods of deterministic chaos, such as Hurst’s method of the normalized amplitude, approximate entropy method, calculation of the correlation integral by Grassberger and Procaccia’s method. For the possibility of applying the last two methods we used quasi phase space recovery method according to the Taken’s theorem. As a result of non-linear analysis we obtained hypnograms reflecting the transition between the stages of sleep in patients undergoing somnological examination. To assess the reliability of the results, they were compared to the hypnograms obtained by the classical method based on the rules of Rehchaffen and Keyls. Also the problems associated with the occurrence of various types of interference were considered and methods for reducing their influence on the final results were suggested. Results. We can conclude that using these methods with appropriate selection of the parameters, employing the necessary normalization of raw data, and averaging the results allow us to obtain hypnogram having a full match of defined phases of sleep for about half of the periods recorded by EEG. To obtain these results it is sufficient to use only one channel of EEG recording.
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Wang, Fang, Zhao Liu, Shanshan Shang, Yuelei Qin, and Bihu Wu. "Vitality continuation or over-commercialization? Spatial structure characteristics of commercial services and population agglomeration in historic and cultural areas." Tourism Economics 25, no. 8 (April 26, 2019): 1302–26. http://dx.doi.org/10.1177/1354816619837129.
Повний текст джерелаАнотація:
In recent years, with rapid urbanization and development of tourism, historic and cultural areas have become characterized by strong vitality. However, a dilemma has arisen concerning their over-commercialization. In this study, 17 Chinese historic and cultural areas, and their surroundings within a radius of 1.5 km, were selected for research. Then, the spatial structure and population agglomeration associated with points of interest (POIs), including commercial service POIs and tourist attraction POIs, were analyzed, resulting in five principal findings. (1) In China, commercial services in historic and cultural areas have become an integral part of tourist attractions. (2) The relationships between the spatial structures of commercial service POIs and tourist attraction POIs can be classified into five types: fully encircled clustering, semi-surrounding clustering, overlapping clustering, contiguous clustering, and separate clustering. (3) Based on a POI kernel density analysis, historic and cultural areas can generally be classified into three categories: commercial service oriented areas, tourist attraction oriented areas, and commerce–tourism complexes. (4) The results illustrated that population agglomeration and spatial patterns of the POIs were tightly coupled; and this correlation was very consistent. The authors found that while living, shopping, and catering services were attractive in isolation, tourist attractions, accommodation, and leisure services often combined to form a shared space to attract business. The research results also provided insights into maintaining the balance between community life and commercial development of historic and cultural areas.
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Maseda, Michael V., Jarle Brinchmann, Marijn Franx, Roland Bacon, Rychard J. Bouwens, Kasper B. Schmidt, Leindert A. Boogaard, et al. "The MUSE Hubble Ultra Deep Field Survey." Astronomy & Astrophysics 608 (November 29, 2017): A4. http://dx.doi.org/10.1051/0004-6361/201730985.
Повний текст джерелаАнотація:
The C III] λλ1907, 1909 emission doublet has been proposed as an alternative to Lyman-α in redshift confirmations of galaxies at z ≳ 6 since it is not attenuated by the largely neutral intergalactic medium at these redshifts and is believed to be strong in the young, vigorously star-forming galaxies present at these early cosmic times. We present a statistical sample of 17 C III]-emitting galaxies beyond z ~ 1.5 using ~30 h deep VLT/MUSE integral field spectroscopy covering 2 square arcminutes in the Hubble Deep Field South (HDFS) and Ultra Deep Field (UDF), achieving C III] sensitivities of ~ 2 × 10-17 erg s-1 cm-2 in the HDFS and ~ 7 × 10-18 erg s-1 cm-2 in the UDF. The rest-frame equivalent widths range from 2 to 19 Å. These 17 galaxies represent ~3% of the total sample of galaxies found between 1.5 ≲ z ≲ 4. They also show elevated star formation rates, lower dust attenuation, and younger mass-weighted ages than the general population of galaxies at the same redshifts. Combined with deep slitless grism spectroscopy from the HST/WFC3 in the UDF, we can tie the rest-frame ultraviolet C III] emission to rest-frame optical emission lines, namely [O III] λ5007, finding a strong correlation between the two. Down to the flux limits that we observe (~ 1 × 10-18 erg s-1 cm-2 with the grism data in the UDF), all objects with a rest-frame [O III] λλ4959, 5007 equivalent width in excess of 250 Å, the so-called extreme emission line galaxies, have detections of C III] in our MUSE data. More detailed studies of the C III]-emitting population at these intermediate redshifts will be crucial to understand the physical conditions in galaxies at early cosmic times and to determine the utility of C III] as a redshift tracer.
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Gan, Tingting, Nanjing Zhao, Gaofang Yin, Min Chen, Xiang Wang, and Hui Hua. "Preconcentration with Chlorella vulgaris combined with energy dispersive X-ray fluorescence spectrometry for rapid determination of Cd in water." Royal Society Open Science 7, no. 5 (May 2020): 200182. http://dx.doi.org/10.1098/rsos.200182.
Повний текст джерелаАнотація:
Freshwater green algae Chlorella vulgaris was selected as an adsorbent, and a simple, rapid, economical and environmentally friendly method for the detection of heavy metal Cd in water samples based on preconcentration with C. vulgaris combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry was proposed. Chlorella vulgaris could directly and rapidly adsorb Cd 2+ without any pretreatment, and the maximum adsorption efficiency could be obtained when the contact time was 1 min with an optimal pH of 10. The obtained Cd-enriched thin samples after preconcentration with C. vulgaris by suction filtration of reaction solution had very good uniformity, which could be directly measured by EDXRF spectrometry, and the net integral fluorescence intensity of Cd K α characteristic peak had a very good linear relationship with the initial concentration of Cd in the range of 0.703–74.957 µg ml −1 with a correlation coefficient of 0.9979. When the Cd thin samples with a Cd-enriched region of 15.1 mm in diameter were formed by the developed preconcentration method with suction filtration of 10 ml reaction solution, the detection limit of this method was 0.0654 µg ml −1 , which was lower than the maximum allowable discharge concentration of Cd in various industrial wastewaters. The proposed method was simple to operate, and could effectively remove the influence of matrix effect of water samples and effectively improve the sensitivity and stability of EDXRF spectrometry directly detecting heavy metals in water samples, which was successfully applied to detect Cd in real water samples with satisfactory results, and the recoveries ranged from 94.80% to 116.94%. Moreover, this method can be applied to the rapid detection and early warning of excessive Cd in discharged industrial wastewaters. This work will provide a methodological basis for the development of rapid and online monitoring technology and instrument of heavy metal pollutants in water.
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Wiesemeyer, H., R. Güsten, K. M. Menten, C. A. Durán, T. Csengeri, A. M. Jacob, R. Simon, J. Stutzki, and F. Wyrowski. "Unveiling the chemistry of interstellar CH." Astronomy & Astrophysics 612 (April 2018): A37. http://dx.doi.org/10.1051/0004-6361/201731810.
Повний текст джерелаАнотація:
Context. The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a “canonical” CH abundance needs to be addressed. Aim. The N = 2 ← 1 ground state transition of CH at λ149 μm has become accessible to high-resolution spectroscopy thanks to the German Receiver for Astronomy at Terahertz Frequencies (GREAT) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at λ560 μm , environments forming massive stars can be analyzed. For this we present a case study on the “proto-Trapezium” cluster W3 IRS5. Methods. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. Results. In diffuse gas, at lower densities a quiescent ion-neutral chemistry alone cannot account for the observed abundance of CH. Unlike the production of HF, for CH+ and CH, vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path. However, CH remains a valuable tracer for molecular gas in environments reaching from diffuse clouds to sites of high-mass star formation.
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Pessa, I., E. Schinnerer, F. Belfiore, E. Emsellem, A. K. Leroy, A. Schruba, J. M. D. Kruijssen, et al. "Star formation scaling relations at ∼100 pc from PHANGS: Impact of completeness and spatial scale." Astronomy & Astrophysics 650 (June 2021): A134. http://dx.doi.org/10.1051/0004-6361/202140733.
Повний текст джерелаАнотація:
Aims. The complexity of star formation at the physical scale of molecular clouds is not yet fully understood. We investigate the mechanisms regulating the formation of stars in different environments within nearby star-forming galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) sample. Methods. Integral field spectroscopic data and radio-interferometric observations of 18 galaxies were combined to explore the existence of the resolved star formation main sequence (Σstellar versus ΣSFR), resolved Kennicutt–Schmidt relation (Σmol. gas versus ΣSFR), and resolved molecular gas main sequence (Σstellar versus Σmol. gas), and we derived their slope and scatter at spatial resolutions from 100 pc to 1 kpc (under various assumptions). Results. All three relations were recovered at the highest spatial resolution (100 pc). Furthermore, significant variations in these scaling relations were observed across different galactic environments. The exclusion of non-detections has a systematic impact on the inferred slope as a function of the spatial scale. Finally, the scatter of the Σmol. gas + stellar versus ΣSFR correlation is smaller than that of the resolved star formation main sequence, but higher than that found for the resolved Kennicutt–Schmidt relation. Conclusions. The resolved molecular gas main sequence has the tightest relation at a spatial scale of 100 pc (scatter of 0.34 dex), followed by the resolved Kennicutt–Schmidt relation (0.41 dex) and then the resolved star formation main sequence (0.51 dex). This is consistent with expectations from the timescales involved in the evolutionary cycle of molecular clouds. Surprisingly, the resolved Kennicutt–Schmidt relation shows the least variation across galaxies and environments, suggesting a tight link between molecular gas and subsequent star formation. The scatter of the three relations decreases at lower spatial resolutions, with the resolved Kennicutt–Schmidt relation being the tightest (0.27 dex) at a spatial scale of 1 kpc. Variation in the slope of the resolved star formation main sequence among galaxies is partially due to different detection fractions of ΣSFR with respect to Σstellar.
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Flagey, N., A. F. McLeod, L. Aguilar, and S. Prunet. "Wide field-of-view study of the Eagle Nebula with the Fourier transform imaging spectrograph SITELLE at CFHT." Astronomy & Astrophysics 635 (March 2020): A111. http://dx.doi.org/10.1051/0004-6361/201833690.
Повний текст джерелаАнотація:
Context. We present the very first wide-field, 11′ by 11′, optical spectral mapping of M 16, one of the most famous star-forming regions in the Galaxy. The data were acquired with the new imaging Fourier transform spectrograph SITELLE mounted on the Canada-France-Hawaii Telescope (CFHT). We obtained three spectral cubes with a resolving power of 10 000 (SN1 filter), 1500 (SN2 filter) and 600 (SN3 filter), centered on the iconic Pillars of Creation and the HH 216 flow, covering the main optical nebular emission lines, namely [O II]λ3726,29 (SN1), Hβ, [O III]λ4959,5007 (SN2), [N II]λ6548,84, Hα, and [S II]λ6717,31 (SN3). Aims. We validate the performance, calibration, and data reduction of SITELLE, and analyze the structures in the large field-of-view in terms of their kinematics and nebular emission. Methods. We compared the SITELLE data to MUSE integral field observations and other spectroscopic and narrow-band imaging data to validate the performance of SITELLE. We computed gas-phase metallicities via the strong-line method, performed a pixel-by-pixel fit to the main emission lines to derive kinematics of the ionized gas, computed the mass-loss rate of the Eastern pillar (also known as the Spire), and combined the SITELLE data with near-infrared narrow-band imaging to characterize the HH 216 flow. Results. The comparison with previously published fluxes demonstrates very good agreement. We disentangle the dependence of the gas-phase metallicities (derived via abundance-tracing line ratios) on the degree of ionization and obtain metallicities that are in excellent agreement with the literature. We confirm the bipolar structure of HH 216, find evidence for episodic accretion from the source of the flow, and identify its likely driving source. We compute the mass-loss rate Ṁ of the Spire pillar on the East side of the H II region and find excellent agreement with the correlation between the mass-loss rate and the ionizing photon flux from the nearby cluster NGC 6611.
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Herenz, Edmund Christian, Matthew Hayes та Claudia Scarlata. "Deciphering the Lyman α blob 1 with deep MUSE observations". Astronomy & Astrophysics 642 (жовтень 2020): A55. http://dx.doi.org/10.1051/0004-6361/202037464.
Повний текст джерелаАнотація:
Context. Lyman α blobs (LABs) are large-scale radio-quiet Lyman α (Lyα) nebula at high-z that occur predominantly in overdense proto-cluster regions. In particular, there is the prototypical SSA22a-LAB1 at z = 3.1, which has become an observational reference for LABs across the electromagnetic spectrum. Aims. We want to understand the powering mechanisms that drive the LAB so that we may gain empirical insights into the galaxy-formation processes within a rare dense environment at high-z. Thus, we need to infer the distribution, the dynamics, and the ionisation state of LAB 1’s Lyα emitting gas. Methods. LAB 1 was observed for 17.2 h with the VLT/MUSE integral-field spectrograph. We produced optimally extracted narrow band images, in Lyαλ1216, He IIλ1640, and we tried to detect C IVλ1549 emission. By utilising a moment-based analysis, we mapped the kinematics and the line profile characteristics of the blob. We also linked the inferences from the line profile analysis to previous results from imaging polarimetry. Results. We map Lyα emission from the blob down to surface-brightness limits of ≈6 × 10−19 erg s−1 cm−2 arcsec−2. At this depth, we reveal a bridge between LAB 1 and its northern neighbour LAB 8, as well as a shell-like filament towards the south of LAB 1. The complexity and morphology of the Lyα profile vary strongly throughout the blob. Despite the complexity, we find a coherent large-scale east-west velocity gradient of ∼1000 km s−1 that is aligned perpendicular to the major axis of the blob. Moreover, we observe a negative correlation of Lyα polarisation fraction with Lyα line width and a positive correlation with absolute line-of-sight velocity. Finally, we reveal He II emission in three distinct regions within the blob, however, we can only provide upper limits for C IV. Conclusions. Various gas excitation mechanisms are at play in LAB 1: ionising radiation and feedback effects dominate near the embedded galaxies, while Lyα scattering contributes at larger distances. However, He II/Lyα ratios combined with upper limits on C IV/Lyα are not able to discriminate between active galactic nucleus ionisation and feedback- driven shocks. The alignment of the angular momentum vector parallel to the morphological principal axis appears to be at odds with the predicted norm for high-mass halos, but this most likely reflects that LAB 1 resides at a node of multiple intersecting filaments of the cosmic web. LAB 1 can thus be thought of as a progenitor of a present-day massive elliptical within a galaxy cluster.
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Han, Leran, Chunmei Wang, Tao Yu, Xingfa Gu, and Qiyue Liu. "High-Precision Soil Moisture Mapping Based on Multi-Model Coupling and Background Knowledge, Over Vegetated Areas Using Chinese GF-3 and GF-1 Satellite Data." Remote Sensing 12, no. 13 (July 2, 2020): 2123. http://dx.doi.org/10.3390/rs12132123.
Повний текст джерелаАнотація:
This paper proposes a combined approach comprising a set of methods for the high-precision mapping of soil moisture in a study area located in Jiangsu Province of China, based on the Chinese C-band synthetic aperture radar data of GF-3 and high spatial-resolution optical data of GF-1, in situ experimental datasets and background knowledge. The study was conducted in three stages: First, in the process of eliminating the effect of vegetation canopy, an empirical vegetation water content model and a water cloud model with localized parameters were developed to obtain the bare soil backscattering coefficient. Second, four commonly used models (advanced integral equation model (AIEM), look-up table (LUT) method, Oh model, and the Dubois model) were coupled to acquire nine soil moisture retrieval maps and algorithms. Finally, a simple and effective optimal solution method was proposed to select and combine the nine algorithms based on classification strategies devised using three types of background knowledge. A comprehensive evaluation was carried out on each soil moisture map in terms of the root-mean-square-error (RMSE), Pearson correlation coefficient (PCC), mean absolute error (MAE), and mean bias (bias). The results show that for the nine individual algorithms, the estimated model constructed using the AIEM (mv1) was significantly more accurate than those constructed using the other models (RMSE = 0.0321 cm³/cm³, MAE = 0.0260 cm³/cm³, and PCC = 0.9115), followed by the Oh model (m_v5) and LUT inversion method under HH polarization (mv2). Compared with the independent algorithms, the optimal solution methods have significant advantages; the soil moisture map obtained using the classification strategy based on the percentage content of clay was the most satisfactory (RMSE = 0.0271 cm³/cm³, MAE = 0.0225 cm³/cm³, and PCC = 0.9364). This combined method could not only effectively integrate the optical and radar satellite data but also couple a variety of commonly used inversion models, and at the same time, background knowledge was introduced into the optimal solution method. Thus, we provide a new method for the high-precision mapping of soil moisture in areas with a complex underlying surface.
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Yeung, Betty. "BGA Board Level Reliability Analysis & Optimization." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2015, DPC (January 1, 2015): 000958–72. http://dx.doi.org/10.4071/2015dpc-tp51.
Повний текст джерелаАнотація:
The solder joint reliability of semiconductor package interconnects to printed circuit boards is critical for product durability. A dominant failure mode is solder fatigue due to the CTE mismatch between the BGA component and PCB at thermal cycling. However, it is well known that other factors can impact fatigue behavior and time to failure such as solder joint geometry, die geometry, solder system, etc. Finite element modeling (FEM) and simulation can play an integral role in providing deeper insight into the impact of these package parameters on the overall assembly. However, a major challenge of accurately modeling these systems includes simulation of multiple length scales from the package, substrate, and solder joints. The FEM approach addressing these can lead to reduced cycle time, accurate simulation, and improved package performance. In this work, the finite element modeling and simulation procedure is demonstrated for a BGA package at accelerated temperature cycling conditions. At the component level, key details regarding the properties and constituents of the BGA package mold compound and substrate are established by coupling measured experimental warpage data and finite element modeling. Comparison of simulated & Thermoire measurements shows excellent agreement at the package level, with warpage correlation achieved over the entire temperature range. At the assembly level, the truncated sphere model is used to arrive at precise solder joint profiles for accurate representation to tie the package to the board. The combined validated package-level results and solder joint profiles are employed towards a subsequent thermo-mechanical analysis of the full BGA assembly. The entire simulation procedure is demonstrated for a BGA design, where inelastic creep and reliability test data are compared. High strain regions in the solder joint array are shown to compare closely with regions of failure from experimental reliability test data. The validated FEM model allows for extrapolating to similar package conditions allowing faster design cycle time and less time consuming experimental work.
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Krychkov, Igor, Gennady Slukin, and Valery Chapursky. "Space-time signal processing in MIMO antennas system with the Earth surface reflections." ITM Web of Conferences 30 (2019): 15013. http://dx.doi.org/10.1051/itmconf/20193015013.
Повний текст джерелаАнотація:
The generalized correlation integral for space-time signal processing at the output of a MIMO antenna system radio altimeter in the Earth’s surface reflections presence is obtained. The results of calculation of one-dimensional cross-section of the generalized correlation integral at an elevation angle with a known target range and two-dimensional crosssection of the generalized correlation integral «horizontal range-height» for specific surface reflection coefficient are presented.
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Jelbart, Jane E., Pauline M. Ross, and Rod M. Connolly. "Patterns of small fish distributions in seagrass beds in a temperate Australian estuary." Journal of the Marine Biological Association of the United Kingdom 87, no. 5 (October 2007): 1297–307. http://dx.doi.org/10.1017/s0025315407053283.
Повний текст джерелаАнотація:
Beds of the seagrass Zostera capricorni are an integral part of the estuarine landscape along the east coast of Australia, forming an important habitat for juvenile fish. Seagrass beds can vary in their size, shape and patchiness of seagrass cover as well as their distance from the estuary mouth. We tested for a correlation between these features and small fish assemblages in seagrass. Fifteen beds were selected from three size-categories (small, 980 to 2300 m2; medium, 3375 to 4090 m2; and large, 5335 to 6630 m2). We found that the size of beds, the patchiness of seagrass cover and location within the estuary (distance from estuary mouth) were all related to differences in fish assemblages. There were greater densities of fish species in small (10.3 ±0.79 species .net-1) compared to medium (7.6 ±0.6) and large (8.2 ±0.5) beds. This occurred regardless of bed placement within the estuary, its patchiness or time of sampling (day and night). The fish assemblages within seagrass beds also changed as bed distance to estuary mouth increased. Six species had greater densities in beds closer to the estuary mouth, while only two species were in greater densities far from the mouth. Fish assemblages were different between beds with patchy and continuous cover, although total densities of all fish species combined were similar. There were greater densities of four species in continuous beds compared to two species that were greater in patchy beds. Overall, an important finding was that even small patchy seagrass beds contain greater densities of small fish species than larger beds with continuous seagrass cover.
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Storonova, O. A., A. S. Trukhmanov, A. A. Makushina, A. V. Paraskevova, and V. T. Ivashkin. "New Parameters for Impedance–pH Monitoring in Diagnosing Gastroesophageal Reflux Disease and Predicting its Severity." Russian Journal of Gastroenterology, Hepatology, Coloproctology 29, no. 2 (May 16, 2019): 35–44. http://dx.doi.org/10.22416/1382-4376-2019-29-2-35-44.
Повний текст джерелаАнотація:
Aim. The present articleidentifies possible correlations between new parameters for impedance–pH monitoring, such as mean nocturnal baseline impedance (MNBI); post-reflux swallow-induced peristaltic wave index (PSPW); and the main parameter, acid exposure time (AET), as well as esophageal motor function. The authors set out to assess the values of MNBI and the PSPW index as additional criteria improving the diagnostic efficacy of impedance-pH monitoring, the completeness of clinical phenotyping of gastroesophageal reflux disease (GERD), as well as determining the probability of a more severe disease course. Materials and methods. A total of 60 patients aged 19 to 71 (mean age 44.7 years) participated in the study: 30 patients with erosive reflux disease (ERD), 30 with non-erosive reflux disease (NERD) and 20 healthy volunteers aged 26 to 65 (mean age 45.2 years). All of them underwent 24-hour combined esophageal impedance–pH monitoring (Gastroscan-IAM, JSC RPE Istok-Sistema, Fryazino) and high-resolution esophageal manometry using a 22-channel water-perfusion catheter (Solar GI MMS, The Netherlands). The authors studied such parameters as AET, GER number, MNBI level, PSPW index, distal contractile integral (DCI), resting pressure in the lower esophageal sphincter (LES), peristaltic break. Statistical processing was performed using Statistica for Windows 10.0 (StatSoft Inc.) and Prism 8 (GraphPad).Results. The examination of patients revealed that MNBI, the PSPW index and DCI significantly decrease with the development of more severe GERD (r = -0.79; p = 0.0000, r = -0.4; p = 0.0002, r = -0.49; p = 0.0000, respectively). A negative correlation was found between AET and the PSPW index (r = -0.38; p = 0.0003) and the MNBI level (r = -0.59; p = 0.0000). A correlation was determined between the value of MNBI and the following parameters: LES resting pressure (r = 0.26; p = 0.0006), DCI (r = 0.35; p = 0.00004), peristaltic break (r = -0.21; p = 0.007), the PSPW index (r = 0.41; p = 0.0000), and GER number (r = -0.59; p = 0.0). A correlation between the PSPW index and DCI (r = 0.22; p = 0.001) was found as well.In the group of ERD patients, the median values of PSPW and MNBI constitute 0.23 [0.17; 0.33] and 1.13 [0.63; 1.53], respectively. Also, a correlation between AET and the MNBI level was found in this group of patients (r=-0.53; p=0.000036). In turn, MNBI correlated with LES resting pressure (r = 0.46; p = 0.0004), DCI (r = 0.36; p = 0.005), peristaltic break (r = -0.37; p = 0.004), and GER number (r = -0,42; p = 0,0000).In the group of NERD patients, the median values of PSPW and MNBI constitute 0.56 [0.51; 0.75] and 3.3 [2.57; 4.8], respectively. A correlation was also found between the MNBI level and AET (r = -0.35; p = 0.005), GER number (r = -0.39; p = 0.00005), as well as between AET and the PSPW index (r = -0.26; p = 0.0000).In the control group, the median values of PSPW and MNBI constitute 0.42 [0.3; 0.5] and 5.83 [5.21; 6.48], respectively. A statistically significant difference (p = 0.02) was found between the median values of MNBI in patients with ERD, NERD, and the control group. A statistically significant difference (p = 0.0) between the median values of the PSPW index in patients with ERD, NERD and the control group was found as well.Conclusions. The revealed correlations between AET, esophageal motor function and new parameters for impedance-pH monitoring allow them to be used as additional criteria improving the diagnostic efficacy of impedance-pH monitoring and the completeness of GERD clinical phenotyping. A decrease in the level of these parameters in patients reflects the probability of a more severe disease course.
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Zhang, Yun, Ziyu Yan, Shuhu Yang, Wanting Meng, Siqi Gu, Jin Qin, Yanling Han, and Zhonghua Hong. "Research on Shore-Based River Flow Velocity Inversion Model Using GNSS-R Raw Data." Remote Sensing 14, no. 5 (February 26, 2022): 1170. http://dx.doi.org/10.3390/rs14051170.
Повний текст джерелаАнотація:
Global navigation satellite system reflectometry technology (GNSS-R) is rarely used for river flow velocity inversion, and in particular, there is currently no research using the BeiDou Navigation Satellite System reflectometry technology (BDS-R) for river flow velocity inversion. In this paper, a carrier phase observation of river flow velocity inversion model is proposed. The interference phase is the integral of the Doppler frequency. The raw intermediate frequency (IF) data sets are processed through an open-loop method to obtain the Doppler frequency observation generated by river flow and then realize velocity inversion. The shore-based river current measurement was conducted on the south bank of Dashengguan Yangtze River in Nanjing city, Jiangsu Province, for nearly two hours on 22 April 2021. After realizing the inversion of river flow velocity in GPS L1, the combined inversion of BDS B1I GEO satellite and IGSO satellite is realized for the first time, which demonstrates the feasibility of river flow velocity inversion using BDS reflected signals. Compared with the real river flow velocity, the GPS L1 PRN 4 (1st period) inversion precision reaches up to 0.028 m/s (mean absolute error, MAE) and 0.036 m/s (root mean square error, RMSE). In parallel, BDS GEO 2 inversion precision can reach 0.048 m/s (MAE) and 0.063 m/s (RMSE), and BDS IGSO 10 inversion precision is 0.061 m/s (MAE) and 0.073 m/s (RMSE). These results illustrate that satellite elevation change rate and distance between specular points and current meter may have a negative effect on the accuracy of river flow velocity inversion. Specular points obstructed by obstacles or too far from the velocity meter may introduce uncertain error in both MAE and RMSE. Neither the satellite elevation nor the signal strength has an obvious correlation with inversion precision, which is consistent with the theoretical principle.
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HILBORN, ROBERT C., and MINGZHOU DING. "OPTIMAL RECONSTRUCTION SPACE FOR ESTIMATING CORRELATION DIMENSION." International Journal of Bifurcation and Chaos 06, no. 02 (February 1996): 377–81. http://dx.doi.org/10.1142/s0218127496000126.
Повний текст джерелаАнотація:
In this paper we consider the estimation of the correlation dimension from a scalar chaotic time series using delay coordinates. Past work has shown that there appears to be a reconstruction space for which the correlation integral has the longest scaling region. We give a firmer foundation to this idea by developing a theory that estimates the dimension of this “optimal” reconstruction space in terms of dynamical quantities such as the largest Lyapunov exponent.
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Slavkovic, Zoran, Dusica Stamenkovic, Veselin Geric, Milic Veljovic, Nebojsa Ivanovic, Slobodan Todorovic, Predrag Maric, and Menelaos Karanikolas. "Combined spinal-epidural technique: Single-space vs double distant space technique." Vojnosanitetski pregled 70, no. 10 (2013): 953–58. http://dx.doi.org/10.2298/vsp1310953s.
Повний текст джерелаАнотація:
Background/Aim. Several combined spinal-epidural (CSE) anesthesia techniques have been described. This study was designed to compare the single space (?needle-throughneedle?) technique (SST) and the double distant space technique (DDS) with regards to the time needed for the procedure, patient discomfort during the procedure and patient's preference technique. Methods. This prospective, randomized single-blind study included 156 patients undergoing colorectal surgery under general anesthesia and CSE. All neuraxial blocks were performed before general anesthesia induction. DDS group of patients had thoracic epidural catheter placed at T6-7 or T7-8, followed by subarachnoid injection at the L2-3 interspace. The SST group of patients had a single injection using the needle-through-needle technique (Espocan? needle) at L2-3. The epidural catheter was used for postoperative analgesia for 72 hours. Body habitus, spinal anatomy and spinal landmarks were assessed preoperatively. The number of epidural and spinal punctures, the feeling that the dura is perforated (dural perforation click) and the time needed to perform CSE were also recorded. Complications during epidural catheter placement and perioperative and postoperative epidural catheter function and patient preference for the anesthetic procedure were recorded. Results. Epidural and subarachnoid spaces were successfully identified in all the patients. Duration of CSE procedure, the number of spinal punctures, dural click feeling and the effects of test dose did not differ between the groups. The patients in both groups (90% of DDS and 87% of SST) would choose CSE as preferred method in the future. The CSE procedure was painful for 16% of DDS vs 20% of SST patients. A significant correlation between time needed for CSE technique performance and body habitus (r = 0.338, p < 0.01), spinal landmarks (r = 0.452, p < 0.001) and anatomy (r = 0.265, p < 0.05) was found in the SST group. There was no correlation between the number of epidural/spinal punctures and epidural bacteriological findings. There was no correlation between the patients? choice of the CSE technique and the number of spinal punctures, duration of CSE procedure and epidural catheter stay. Conclusion. The two CSE techniques did not differ with regards to the procedure time and patient's preference. Procedure time correlated with body habitus, spinal landmarks and the anatomy in the SST group.
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Beghein, Yves, Kristof Cools, Hakan Bagci, and Daniël De Zutter. "A Space-Time Mixed Galerkin Marching-on-in-Time Scheme for the Time-Domain Combined Field Integral Equation." IEEE Transactions on Antennas and Propagation 61, no. 3 (March 2013): 1228–38. http://dx.doi.org/10.1109/tap.2012.2226553.
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Wang, Bing Cheng, and Zhao Hui Ren. "General Fractal Dimension Calculation of Vibration Signal Based on Correlation Integral." Applied Mechanics and Materials 34-35 (October 2010): 1269–73. http://dx.doi.org/10.4028/www.scientific.net/amm.34-35.1269.
Повний текст джерелаАнотація:
Four different fault signals are simulated and collected which are oil whip fault signal, rub-impact fault signal, rub- oil whip coupling fault signal and rub - loose coupling fault signal in the lab. According to the Restructuring the theory of phase space, in foundation of the optimal delay time τ and the embedding dimension d, phase space is restructured to the time sequence of different fault. Simultaneously in connection with the general fractal theory and its algorithm, author has conducted the analysis and study, and the correlation integral is used to the concrete calculation of general fractal dimension, fractal dimensions of four kind of fault are calculated separately by this calculation method. The research goal is attempting to explore one new calculation method of general fractal dimension to improve accuracy and increase the degree of differentiation, to provide the basis for the analysis of the fault signal.
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Su, Fei, Honghui Dong, Limin Jia, Zhao Tian, and Xuan Sun. "Space–time correlation analysis of traffic flow on road network." International Journal of Modern Physics B 31, no. 05 (February 9, 2017): 1750027. http://dx.doi.org/10.1142/s0217979217500278.
Повний текст джерелаАнотація:
Space–time correlation analysis has become a basic and critical work in the research on road traffic congestion. It plays an important role in improving traffic management quality. The aim of this research is to examine the space–time correlation of road networks to determine likely requirements for building a suitable space–time traffic model. In this paper, it is carried out using traffic flow data collected on Beijing’s road network. In the framework, the space–time autocorrelation function (ST-ACF) is introduced as global measure, and cross-correlation function (CCF) as local measure to reveal the change mechanism of space–time correlation. Through the use of both measures, the correlation is found to be dynamic and heterogeneous in space and time. The finding of seasonal pattern present in space–time correlation provides a theoretical assumption for traffic forecasting. Besides, combined with Simpson’s rule, the CCF is also applied to finding the critical sections in the road network, and the experiments prove that it is feasible in computability, rationality and practicality.
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Its, A. R., A. G. Izergin, V. E. Korepin, and N. A. Slavnov. "DIFFERENTIAL EQUATIONS FOR QUANTUM CORRELATION FUNCTIONS." International Journal of Modern Physics B 04, no. 05 (April 1990): 1003–37. http://dx.doi.org/10.1142/s0217979290000504.
Повний текст джерелаАнотація:
The quantum nonlinear Schrödinger equation (one dimensional Bose gas) is considered. Classification of representations of Yangians with highest weight vector permits us to represent correlation function as a determinant of a Fredholm integral operator. This integral operator can be treated as the Gelfand-Levitan operator for some new differential equation. These differential equations are written down in the paper. They generalize the fifth Painlève transcendent, which describe equal time, zero temperature correlation function of an impenetrable Bose gas. These differential equations drive the quantum correlation functions of the Bose gas. The Riemann problem, associated with these differential equations permits us to calculate asymp-totics of quantum correlation functions. Quantum correlation function (Fredholm determinant) plays the role of τ functions of these new differential equations. For the impenetrable Bose gas space and time dependent correlation function is equal to τ function of the nonlinear Schrödinger equation itself, For a penetrable Bose gas (finite coupling constant c) the correlator is τ-function of an integro-differentiation equation.
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Коржова, Наталья, and Natalya Korzhova. "PHARMACOECONOMIC ANALYSIS OF THE EFFECTIVENESS OF ANTIBIOTIC THERAPY OF NOSOCOMIAL PNEUMONIA." Bulletin physiology and pathology of respiration 1, no. 62 (December 15, 2016): 28–34. http://dx.doi.org/10.12737/23247.
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There was performed a prospective pharmacoeconomic study of effectiveness of different variants of antibacterial therapy in 118 patients diagnosed with nosocomial pneumonia who were treated in specialized departments of General hospital to identify the most effective treatment regimens from the point of view of pharmacoeconomics. Taking into account the characteristics of the local microbiological pattern and the spectrum of sensitivity to antibiotics of the most commonly encountered microorganisms in this hospital there were selected the drugs that have high activity against these pathogens. The patients were divided into groups: the first group (n=57) included the patients with early nosocomial pneumonia including 37 patients receiving combination therapy with Levofloxacin and Ceftazidime, 20 patients with Amoxiclav monotherapy; the second group (n=61) consisted of patients with later nosocomial pneumonia; 34 patients had combined treatment with Amikacin and Cefoperazone/Sulbactam, 27 patients had Imipenem monotherapy. The evaluation and analysis of clinical effectiveness with the method "cost-effectiveness" were done. It was found out that in all compared groups there is a high effectiveness of antibacterial drugs starting from 61%. The highest integral factor of clinical efficacy was in the group of Imipenem (86.1%), then in the group of Levofloxacin and Ceftazidime (71.5%), in the group of Amikacin and Cefoperazon/Sulbactam (70%), in the group of Amoxiclav (61%). Noteworthy is that only in the group of Imipenem there was no need for additional antibacterial therapy and there was short term treatment. While analyzing the cost-effectiveness correlation, it was found out that the least cost per unit of effectiveness was the cost of treatment with the combination of Levofloxacin and Ceftazidime for patients with early nosocomial pneumonia and the cost of therapy with Amikacin and Cefoperazon/Sulbactam in patients with late nosocomial pneumonia. Despite the high cost of a single dose, there was a reduction in the cost while using Imipenem due to the decrease of the time of treatment of patients in the hospital and the intensive care unit and no expenses for additional antibacterial drugs. Imipenem can be used as monotherapy as an alternative to the standard combination therapy in severe nosocomial pneumonia, primarily in patients located in intensive care unit.
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Povstenko, Y. Z. "Fundamental Solutions to Time-Fractional Advection Diffusion Equation in a Case of Two Space Variables." Mathematical Problems in Engineering 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/705364.
Повний текст джерелаАнотація:
The fundamental solutions to time-fractional advection diffusion equation in a plane and a half-plane are obtained using the Laplace integral transform with respect to timetand the Fourier transforms with respect to the space coordinatesxandy. The Cauchy, source, and Dirichlet problems are investigated. The solutions are expressed in terms of integrals of Bessel functions combined with Mittag-Leffler functions. Numerical results are illustrated graphically.
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Aghili, A. "Analytic solutions of fractional ODEs and PDEs." Asian-European Journal of Mathematics 13, no. 02 (October 23, 2018): 2050032. http://dx.doi.org/10.1142/s1793557120500321.
Повний текст джерелаАнотація:
In this work, it is shown that the combined use of exponential operators and integral transforms provides a powerful tool to solve space fractional partial differential equation with non-constant coefficients in three dimensions. Also, a variety of Lamb–Bateman singular integral equation and a non-homogeneous time fractional Kd.V of order [Formula: see text] are solved. Constructive examples are also provided.
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PAULUS, MARTIN P., JAMES B. KADTKE, and FREDERICK V. MENKELLO. "STATISTICAL MECHANICS OF BIOLOGICAL AND OTHER COMPLEX EXPERIMENTAL TIME SERIES: ASSESSING GEOMETRICAL AND DYNAMICAL PROPERTIES." International Journal of Bifurcation and Chaos 03, no. 03 (June 1993): 717–27. http://dx.doi.org/10.1142/s0218127493000623.
Повний текст джерелаАнотація:
Biological and other experimental time series often exhibit complex and possibly chaotic behavior that may not be completely deterministic or completely random. Particularly problematic is the fact that measures of chaos such as the dynamical or geometrical invariants, e.g. the correlation dimension, Lyapunov exponents, or Kolmogorov entropy, often cannot be calculated from short, noisy, and possibly highly discretized experimental time series. Here, it is argued that nonrandom structure in the data may be uncovered by using a conceptual framework based on statistical mechanics and the standard correlation integral as a computational tool. A new use of the generalized correlation integral is proposed to assess statistically the occurrence of nonrandom spatiotemporal patterns in experimental data. We argue that nonrandomness of a time series can be assessed by the statistics of the topology of the reconstructed state space distribution, which we quantify via the generalized correlation integral. This approach provides a simple, graphical tool which can yield immediate information about the length scales and sequence lengths where the data may appear to be different from random, and also may provide a data classification tool based on spatiotemporal patterns. We demonstrate the usefulness of this approach using several numerical examples, including data from experimental biological systems. Finally, we propose that particular characteristics of such patterns imply considerable macroscopic information about the behavior of the generating system, and qualitative changes in the time series.
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Liu, Jian, and William H. Miller. "Real time correlation function in a single phase space integral beyond the linearized semiclassical initial value representation." Journal of Chemical Physics 126, no. 23 (June 21, 2007): 234110. http://dx.doi.org/10.1063/1.2743023.
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Zagorodniuk, Oksana, Maryna Gomeniuk, and Liudmyla Maliuga. "MANAGEMENT OF ECONOMIC SECURITY OF HORTICULTURAL ENTERPRISES IN UKRAINE." Baltic Journal of Economic Studies 8, no. 2 (March 25, 2022): 68–77. http://dx.doi.org/10.30525/2256-0742/2022-8-2-68-77.
Повний текст джерелаАнотація:
The current state of economic security of horticultural enterprises in Ukraine, functioning in the agro-industrial complex of Ukraine, indicates the presence of a large number of internal and external threats that arise in the process of their financial and economic activities. Most horticultural enterprises have an insufficient level of economic security. The purpose of the study is to substantiate the algorithm of economic security management of horticultural enterprises of Ukraine. Methodology. During the study the following methods were used: analysis and synthesis (to critically comprehend the theoretical provisions of economic security); system analysis (to substantiate the economic security management system of horticultural enterprises and its subsystems); expert method (to determine the weights in the integral index of internal economic security of horticultural enterprise); methods of statistical (correlation and regression) analysis (to check the sensitivity of horticultural enterprises of Ukraine to changes in macroeconomic and other indicators); graphic and tabular methods (to visualize the results of the study). Results. The authors pay special attention to the presence of internal and external threats to the economic security of horticultural enterprises. The authors have developed a protocol for managing internal and external economic security of horticultural enterprises as a set of successive stages, which will ensure the achievement of the target level of economic security. The article substantiates the methodological approach to the assessment of internal economic security of horticultural enterprise on the basis of relative indicators, which are combined into five components. The article substantiates methodological approach to the assessment of external economic security of horticultural enterprise on the basis of four macro-indicators. Practical implications. The proposed protocol of economic security management of horticultural enterprise can be used as a technology of enterprise management to ensure its stable development. The proposed method for assessing internal and external economic security can be used by a horticultural enterprise. Value/originality. Improved the theoretical and applied bases of the study of economic security of agricultural enterprises on the example of horticultural enterprises. The methodological foundations of internal and external assessment of the economic security of enterprises were developed. The protocol of economic security management of horticultural enterprise is developed for the first time. The protocol includes interconnected and sequential stages and is adaptive to modern conditions of financial and economic activity of horticultural enterprises.
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Adebanjo, Ibukunoluwa Adetutu, Yekeen Olajide Olasoji, and Micheal Olorunfunmi Kolawole. "Space-Time Trellis Coding with Equalization." European Journal of Engineering Research and Science 4, no. 9 (September 27, 2019): 207–11. http://dx.doi.org/10.24018/ejers.2019.4.9.1412.
Повний текст джерелаАнотація:
As we are entering the 5G era, high demand is made of wireless communication. Consistent effort has been ongoing in multiple-input multiple-output (MIMO) systems, which provide correlation on temporal and spatial domain, to meet the high throughput demand. To handle the characteristic nature of wireless channel effectively and improve the system performance, this paper considers the combination of diversity and equalization. Space-Time trellis code is combined with single-carrier modulation using two-choice equalization techniques, namely: minimum mean squared error (MMSE) equalizer and orthogonal triangular (QR) detection. MMSE gives an optimal balance between noise enhancement and net inter-symbol interference (ISI) in the transmitted signal. Use of these equalizers provides the platform of investigating the bit error rate (BER) and the pairwise error probability (PEP) at the receiver, as well as the effect of cyclic prefix reduction on the receivers. It was found that the MMSE receiver outperforms the QR receiver in terms of BER, while in terms of PEP; the QR receiver outperforms the MMSE receiver. When a cyclic prefix reduction test was carried out on both receivers, it yields a significant reduction in BER of both receivers but has no significant effect on the overall performance.
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Adebanjo, Ibukunoluwa Adetutu, Yekeen Olajide Olasoji, and Micheal Olorunfunmi Kolawole. "Space-Time Trellis Coding with Equalization." European Journal of Engineering and Technology Research 4, no. 9 (September 27, 2019): 207–11. http://dx.doi.org/10.24018/ejeng.2019.4.9.1412.
Повний текст джерелаАнотація:
As we are entering the 5G era, high demand is made of wireless communication. Consistent effort has been ongoing in multiple-input multiple-output (MIMO) systems, which provide correlation on temporal and spatial domain, to meet the high throughput demand. To handle the characteristic nature of wireless channel effectively and improve the system performance, this paper considers the combination of diversity and equalization. Space-Time trellis code is combined with single-carrier modulation using two-choice equalization techniques, namely: minimum mean squared error (MMSE) equalizer and orthogonal triangular (QR) detection. MMSE gives an optimal balance between noise enhancement and net inter-symbol interference (ISI) in the transmitted signal. Use of these equalizers provides the platform of investigating the bit error rate (BER) and the pairwise error probability (PEP) at the receiver, as well as the effect of cyclic prefix reduction on the receivers. It was found that the MMSE receiver outperforms the QR receiver in terms of BER, while in terms of PEP; the QR receiver outperforms the MMSE receiver. When a cyclic prefix reduction test was carried out on both receivers, it yields a significant reduction in BER of both receivers but has no significant effect on the overall performance.
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Cao, Le. "A New Method to Calculate Induced Current of Thin Wire over Anisotropic Ground under HPM." International Journal of Antennas and Propagation 2019 (February 26, 2019): 1–8. http://dx.doi.org/10.1155/2019/4270395.
Повний текст джерелаАнотація:
The time response analysis of wire structures is often carried out in free space or isotropic half-space, but the real ground is usually layered and has anisotropic properties. In this paper, the induced current of a thin wire over layered anisotropic half-space under a high-power microwave (HPM) is calculated by using the time-domain integral equation (TDIE) method. The reflection coefficient of a layered anisotropic medium is obtained by the general transmitting matrix (GTM) method combined with Fourier transform. The variation of the induced current on the thin wire under different incident conditions is analyzed.
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Taiwo Ajiboye, Aye, Jayeola Femi Opadiji, Abdulrahman Olalekan Yusuf, Olusogo Joshua Popoola, Esther Toyin Olawole, and Olalekan Femi Adebayo. "New methods for proportional-integral controller design for time-delay systems." Indonesian Journal of Electrical Engineering and Computer Science 28, no. 3 (October 7, 2022): 1437. http://dx.doi.org/10.11591/ijeecs.v28.i3.pp1437-1450.
Повний текст джерелаАнотація:
The development of structured methods for proportional-integral (PI) controller design for systems with time delay are proposed in this article. Several PI controller design methods for time-delay systems have been reported. However, combining two or more methods to form new ones have not been given serious attention. The system stability region in the controller parameters space was determined by plotting the stability boundaries. In this study, the controller gains were first obtained using genetic algorithm (GA), weighted geometric center (WGC), and centroid of convex stability region (CCSR). Thereafter, these gains were combined by finding the centroids of lines joining any of the two gain locations, and triangle whose vertices are the location of the three gains in the convex stability region, thus yielding four additional methods, M1, M2, M3, and M4. Compared to a particular existing method, some of the proposed methods yield faster response speed at the expense of reference input tracking, while the reverse is the case for others. Any of the proposed methods (M1, M2, M3, and M4) can be selected depending on the system performance specifications.
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Ivanov, Alexander A., Irina V. Alexandrova, and Dmitri V. Alexandrov. "Phase transformations in metastable liquids combined with polymerization." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2143 (March 4, 2019): 20180215. http://dx.doi.org/10.1098/rsta.2018.0215.
Повний текст джерелаАнотація:
This paper is concerned with the theory of nucleation and growth of crystals in a metastable polymer melt with allowance for the polymerization of a monomer. A mathematical model consisting of the heat balance equation, equations governing the particle-radius distribution function and the polymerization degree is formulated. The exact steady-state analytical solutions are found. In the case of unsteady-state crystallization with polymerization, the particle-size distribution function is determined analytically for different space–time regions by means of the Laplace transform. Two functional integro-differential equations governing the dimensionless temperature and polymerization degree are deduced. These equations are solved by means of the saddle-point technique for the evaluation of a Laplace-type integral. The time-dependent distribution function, temperature and polymerization degree at different polymerization rates and nucleation kinetics are derived with allowance for the main contribution to the Laplace-type integral. In addition, the general analytical solution by means of the saddle-point technique and an example showing how to construct the analytical solutions in particular cases are given in the appendices. The analytical method developed in the present paper can be used to describe the similar phase transition phenomena in the presence of chemical reactions. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.
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Sámano-Robles, Ramiro. "A Space-Time Correlation Model for MRC Receivers in Rayleigh Fading Channels." Technologies 8, no. 3 (July 22, 2020): 41. http://dx.doi.org/10.3390/technologies8030041.
Повний текст джерелаАнотація:
This paper presents a statistical model for maximum ratio combining (MRC) receivers in Rayleigh fading channels enabled with a temporal combining process. This means that the receiver effectively combines spatial and temporal branch components. Therefore, the signals that will be processed by the MRC receiver are collected not only across different antennas (space), but also at different instants of time. This suggests the use of a retransmission, repetition or space-time coding algorithm that forces the receiver to store signals in memory at different instants of time. Eventually, these stored signals are combined after a predefined or dynamically optimized number of time-slots or retransmissions. The model includes temporal correlation features in addition to the space correlation between the signals of the different components or branches of the MRC receiver. The derivation uses a frequency domain approach (using the characteristic function of the random variables) to obtain closed-form expressions of the statistics of the post-processing signal-to-noise ratio (SNR) under the assumption of equivalent correlation in time and equivalent correlation in space. The described methodology paves the way for the reformulation of other statistical functions as a frequency-domain polynomial root analysis problem. This is opposed to the infinite series approach that is used in the conventional methodology using directly the probability density function (PDF). The results suggest that temporal diversity is a good complement to receivers with limited spatial diversity capabilities. It is also shown that this additional operation could be maximized when the temporal diversity is adaptive (i.e., activated by thresholds of SNR), thus leading to a better resource utilization.
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Wang, Deng, Yang Liu, Hong Li, and Zhichao Fang. "Second-Order Time Stepping Scheme Combined with a Mixed Element Method for a 2D Nonlinear Fourth-Order Fractional Integro-Differential Equations." Fractal and Fractional 6, no. 4 (April 2, 2022): 201. http://dx.doi.org/10.3390/fractalfract6040201.
Повний текст джерелаАнотація:
In this article, we study a class of two-dimensional nonlinear fourth-order partial differential equation models with the Riemann–Liouville fractional integral term by using a mixed element method in space and the second-order backward difference formula (BDF2) with the weighted and shifted Grünwald integral (WSGI) formula in time. We introduce an auxiliary variable to transform the nonlinear fourth-order model into a low-order coupled system including two second-order equations and then discretize the resulting equations by the combined method between the BDF2 with the WSGI formula and the mixed finite element method. Further, we derive stability and error results for the fully discrete scheme. Finally, we develop two numerical examples to verify the theoretical results.
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Xu, Xiaoyong, and Fengying Zhou. "Crank-Nicolson orthogonal spline collocation method combined with WSGI difference scheme for the two-dimensional time-fractional diffusion-wave equation." Open Mathematics 18, no. 1 (March 5, 2020): 67–86. http://dx.doi.org/10.1515/math-2020-0007.
Повний текст джерелаАнотація:
Abstract In this paper, a discrete orthogonal spline collocation method combining with a second-order Crank-Nicolson weighted and shifted Grünwald integral (WSGI) operator is proposed for solving time-fractional wave equations based on its equivalent partial integro-differential equations. The stability and convergence of the schemes have been strictly proved. Several numerical examples in one variable and in two space variables are given to demonstrate the theoretical analysis.
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Jiang, Yong Xiang, Bing Du, Pan Zhang, San Peng Deng, and Yu Ming Qi. "The Research of Chaos Time Series on Chatter Signal Recognition." Key Engineering Materials 584 (September 2013): 137–41. http://dx.doi.org/10.4028/www.scientific.net/kem.584.137.
Повний текст джерелаАнотація:
The online detecting of chatter is the key technology to improve the machining quality. Based on the nonlinear chaos control theory in discrete dynamic system, the processing vibration signal discrete time series is taken as system nonlinear input, the C-C algorithm and correlation integral was used to determine appropriate embedding dim m and time delay τ. Then the phase space is reconstructed by discrete vibration signal. In milling chatters experiment, the time series analysis method is used to get the phase diagram before and after chatter. The chatter phase chart shows the characteristics of chaos and recognized the milling chatter.
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Wang, Xiao Li, Hui Juan Wang, and Ying Ga Wu. "Time-Space Distribution Characteristics of Nitrogen in Surface Sediment from the Inner Mongolia of the Yellow River." Advanced Materials Research 1092-1093 (March 2015): 996–1000. http://dx.doi.org/10.4028/www.scientific.net/amr.1092-1093.996.
Повний текст джерелаАнотація:
Time-space distribution characteristics of nitrogen in surface sediment from the Inner Mongolia of the Yellow River were investigated using the sequential extraction method. Sedimentary nitrogen were fractionized into four forms: ion exchange nitrogen (IEF-N), nitrogen combined with carbonate (CF-N), nitrogen combined with iron-manganese oxide (IMOF-N), organic nitrogen and combined with sulfides (OSF-N). The rank order according to the mean concentration of N-fraction in surface sediments from the Inner Mongolia of the Yellow River was OSF-N > IMOF-N > IEF-N > CF-N and the N-fraction content in surface sediments of autumn was higher than that of spring. Moreover, the different degrees of positive correlation between different morphological transformation nitrogen forms and the sum of TN, TP, CEC and organic matter of 12 sediment samples.
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Du, Z. L. "The correlation between solar and geomagnetic activity – Part 3: An integral response model." Annales Geophysicae 29, no. 6 (June 15, 2011): 1005–18. http://dx.doi.org/10.5194/angeo-29-1005-2011.
Повний текст джерелаАнотація:
Abstract. An integral response model is proposed to describe the relationship between geomagnetic activity (aa index) and solar activity (represented by sunspot number Rz): The aa at a given time t is the integral of Rz at past times (t'&leq;t) multiplied by an exponential decay factor of the time differences (e−(t−t')/τ), where τ is the decay time scale (~40 months). The correlation coefficient of aa with the reconstructed series based on this model (rf=0.85) is much higher than that of aa with Rz (r0=0.61). If this model is applied to each solar cycle, the correlation coefficient will be higher (rf=0.95). This model can naturally explain some phenomena related to aa and Rz, such as (i) the significant increase in the aa index (and its baseline) over the twentieth century; (ii) the longer lag times of aa to Rz at solar cycle maxima than at minima; and (iii) the variations in the correlations related to solar and Hale cycles. These results demonstrate that aa depends not only on the present Rz but also on past values. The profile of aa can be better predicted from Rz by this model than by point-point correspondence.
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Li, Shilong, Xiaolei Yang, and Yu Lv. "Predictive capability of the logarithmic law for roughness-modeled large-eddy simulation of turbulent channel flows with rough walls." Physics of Fluids 34, no. 8 (August 2022): 085112. http://dx.doi.org/10.1063/5.0098611.
Повний текст джерелаАнотація:
Direct numerical simulation (DNS) and large-eddy simulation (LES) resolving roughness elements are computationally expensive. LES employing the logarithmic law as the wall model, without the need to resolve the flow at the roughness element scale, provides an efficient alternative for simulating turbulent flows over rough walls. In this work, we evaluate the predictive capability of the roughness-modeled LES by comparing its predictions with those from the roughness-resolved DNS for turbulent channel flows with rough walls. A good agreement is observed for the mean streamwise velocity. The Reynolds stresses predicted by the roughness-modeled LES also reasonably agree with the roughness-resolved predictions. Differences, on the other hand, are observed for the dispersive Reynolds stresses, integral scales, and space-time correlations. The roughness-modeled LES fails to predict the dispersive stresses as one can expect. In the outer layer, the integral length scale predicted by the roughness-modeled LES is lower than the roughness-resolved prediction, which cannot be improved by refining the grid. As for the space-time correlations, discrepancies are shown for the streamwise velocity fluctuations, with a faster decay of the correlation in the outer layer observed in the roughness-modeled predictions. Examination of the space-time correlation using the elliptic approximation model shows that the roughness-modeled LES underpredicts the convection velocity in the near wall region while overpredicting the sweeping velocity in the outer layer with no improvements observed when refining the grid.
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Song, Yong, Chengjin Zhang, and Hai Liu. "Method of Quantitative Analysis for Multirobot Cooperative Hunting Behaviors." Mathematical Problems in Engineering 2016 (2016): 1–7. http://dx.doi.org/10.1155/2016/4370635.
Повний текст джерелаАнотація:
The kinematic behavior of mobile robots can be represented as functions of time. During the operation of a multirobot system, the orbit of a special robot is recorded. The embedding dimension and the delay time are chosen based on the correlation integral method. A chaotic attractor equivalent to the original system is reconstructed in phase space. The multirobot system can be adequately described based on the phase space information, and the dynamic system states can be forecast based on this information. The eigenvalues of the attractor are calculated including the maximum Lyapunov exponent and correlation dimension. The robot collective behavior is described and analyzed quantitatively based on the eigenvalues. The critical factor that affects the interaction of robots is investigated based on quantified parameters. Our analysis results can be used to improve the understanding of robot interaction mechanisms.