Articles de revues : « Magnitude-Frequency Curve »

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Sung, J. H., E. S. Chung et K. S. Lee. « Development of streamflow drought severity- and magnitude-duration-frequency curves using the threshold level method ». Hydrology and Earth System Sciences Discussions 10, n^o 12 (3 décembre 2013) : 14675–704. http://dx.doi.org/10.5194/hessd-10-14675-2013.

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Abstract. This study developed a comprehensive method to quantify streamflow drought severity and magnitude based on a traditional frequency analysis. Two types of curve were developed: the streamflow drought severity-duration-frequency (SDF) curve and the streamflow drought magnitude-duration-frequency (MDF) curve (e.g., a rainfall intensity-duration-frequency curve). Severity was represented as the total water deficit volume for the specific drought duration, and magnitude was defined as the daily average water deficit. The variable threshold level method was introduced to set the target instream flow requirement, which can significantly affect the streamflow drought severity and magnitude. The four threshold levels utilized were fixed, monthly, daily, and desired yield for water use. The threshold levels for the desired yield differed considerably from the other levels and represented more realistic conditions because real water demands were considered. The streamflow drought severities and magnitudes from the four threshold methods could be derived at any frequency and duration from the generated SDF and MDF curves. These SDF and MDF curves are useful in designing water resources systems for streamflow drought and water supply management.

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Kusumastuti, D. I., I. Struthers, M. Sivapalan et D. A. Reynolds. « Threshold effects in catchment storm response and the occurrence and magnitude of flood events : implications for flood frequency ». Hydrology and Earth System Sciences Discussions 3, n^o 5 (23 octobre 2006) : 3239–77. http://dx.doi.org/10.5194/hessd-3-3239-2006.

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Abstract. The aim of this paper is to illustrate the effects of selected catchment storage thresholds upon runoff behaviour, and specifically their impact upon flood frequency. The analysis is carried out with the use of a stochastic rainfall model, incorporating rainfall variability at intra-event, inter-event and seasonal timescales, as well as infrequent summer tropical cyclones, coupled with deterministic rainfall-runoff models that incorporate runoff generation by both saturation excess and subsurface stormflow mechanisms. Changing runoff generation mechanisms (i.e. from subsurface flow to surface runoff) associated with a given threshold (i.e. saturation storage capacity) are shown to be manifested in the flood frequency curve as a break in slope. It is observed that the inclusion of infrequent summer storm events increases the temporal frequency occurrence and magnitude of surface runoff events, in this way contributing to steeper flood frequency curves, and an additional break in the slope of the flood frequency curve. The results of this study highlight the importance of thresholds on flood frequency, and provide insights into the complex interactions between rainfall variability and threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves.

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Kusumastuti, D. I., I. Struthers, M. Sivapalan et D. A. Reynolds. « Threshold effects in catchment storm response and the occurrence and magnitude of flood events : implications for flood frequency ». Hydrology and Earth System Sciences 11, n^o 4 (20 août 2007) : 1515–28. http://dx.doi.org/10.5194/hess-11-1515-2007.

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Abstract. The aim of this paper is to illustrate the effects of selected catchment storage thresholds upon runoff behaviour, and specifically their impact upon flood frequency. The analysis is carried out with the use of a stochastic rainfall model, incorporating rainfall variability at intra-event, inter-event and seasonal timescales, as well as infrequent summer tropical cyclones, coupled with deterministic rainfall-runoff models that incorporate runoff generation by both saturation excess and subsurface stormflow mechanisms. Changing runoff generation mechanisms (i.e. from subsurface flow to surface runoff) associated with a given threshold (i.e. saturation storage capacity) is shown to be manifested in the flood frequency curve as a break in slope. It is observed that the inclusion of infrequent summer storm events increases the temporal frequency occurrence and magnitude of surface runoff events, in this way contributing to steeper flood frequency curves, and an additional break in the slope of the flood frequency curve. The results of this study highlight the importance of thresholds on flood frequency, and provide insights into the complex interactions between rainfall variability and threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves.

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Shu, Mengying, Bijie Yang, Mingyang Yang, Ricardo F. Martinez-Botas et Kangyao Deng. « Investigation on the unsteadiness of centrifugal compressor exposed to pulsating backpressure ». Proceedings of the Institution of Mechanical Engineers, Part D : Journal of Automobile Engineering 235, n^o 8 (9 janvier 2021) : 2212–25. http://dx.doi.org/10.1177/0954407020984593.

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Centrifugal compressor is exposed to pulsating backpressure due to the movement of intake valves in internal combustion engine. The performance of compressor deviates from the steady performance map, which affects the matching between turbocharger and engine. The behavior of compressor system at pulsation conditions are investigated via an in-house developed 1D unsteady code validated by experimental results. The influence of pulse frequency, magnitude and compressor characteristic curve on the compressor transient responses, including filling-emptying effect and wave dynamics, are analyzed. Results show that the strength of wave dynamics grows stronger with the increasing of pulse frequency, while the strength of filling-emptying effect increases first then decreases. The rise of pulse magnitude results in an almost linearly increasing of filling-emptying effect, while it can hardly affect the wave dynamics. Furthermore, the influence of pulsation magnitude and frequency represents the influence of local pressure gradient, and a correlation as quadratic curve can be evaluated between the pressure gradient and compressor unsteadiness. On the other hand, the influence of operating point, including the average mass flow rate and the slope of characteristic curve, is confirmed to be evidently smaller, comparing to the influence of pulsation frequency and magnitude. This study is helpful to estimate the behavior of compressor and the discrepancy of performance when operating at unsteady environment or matched with engine.

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Xu, Lan Shu, Yi Cheng, Yu Yu Li et Rui Li. « Study of Errors on Larch Wood Pyrolysis Kinetic Analysis ». Advanced Materials Research 1096 (avril 2015) : 243–47. http://dx.doi.org/10.4028/www.scientific.net/amr.1096.243.

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Errors was generate when use integral methods to calculate pyrolysis kinetic. It was analyzed by considered the effects of methods and reaction orders. A α-T curve was established for the error discussion depending on basic kenotic theory. For analysis methods, both single curve and multiple curve methods can obtain reliable activation energy values (≤3%), but the error of frequency factor was significant (up to 40%). Frequency factor is sensitive to intercept changing and is also to reaction order. Magnitude error could show if reaction order deviates to true value.

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Song, Lei, JoAnn McGee et Edward J. Walsh. « Development of Cochlear Amplification, Frequency Tuning, and Two-Tone Suppression in the Mouse ». Journal of Neurophysiology 99, n^o 1 (janvier 2008) : 344–55. http://dx.doi.org/10.1152/jn.00983.2007.

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It is generally believed that the micromechanics of active cochlear transduction mature later than passive elements among altricial mammals. One consequence of this developmental order is the loss of transduction linearity, because an active, physiologically vulnerable process is superimposed on the passive elements of transduction. A triad of sensory advantage is gained as a consequence of acquiring active mechanics; sensitivity and frequency selectivity (frequency tuning) are enhanced and dynamic operating range increases. Evidence supporting this view is provided in this study by tracking the development of tuning curves in BALB/c mice. Active transduction, commonly known as cochlear amplification, enhances sensitivity in a narrow frequency band associated with the “tip” of the tuning curve. Passive aspects of transduction were assessed by considering the thresholds of responses elicited from the tuning curve “tail,” a frequency region that lies below the active transduction zone. The magnitude of cochlear amplification was considered by computing tuning curve tip-to-tail ratios, a commonly used index of active transduction gain. Tuning curve tip thresholds, frequency selectivity and tip-to-tail ratios, all indices of the functional status of active biomechanics, matured between 2 and 7 days after tail thresholds achieved adultlike values. Additionally, two-tone suppression, another product of active cochlear transduction, was first observed in association with the earliest appearance of tuning curve tips and matured along an equivalent time course. These findings support a traditional view of development in which the maturation of passive transduction precedes the maturation of active mechanics in the most sensitive region of the mouse cochlea.

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Şenol, Bilal, et Uğur Demiroğlu. « Fractional order proportional derivative control for first order plus time delay plants : achieving phase and gain specifications simultaneously ». Transactions of the Institute of Measurement and Control 41, n^o 15 (25 juin 2019) : 4358–69. http://dx.doi.org/10.1177/0142331219857397.

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The aim of the method in this paper is to achieve desired gain and phase specifications for robustness and performance of first order plus time delay plants. The previously proposed method “frequency frame”, implemented for tuning fractional order proportional integral controllers, is applied on such plants controlled with a fractional order proportional derivative controller. Four specifications of gain and phase are considered in the Bode plot inspired from an ideal system. The frame is drawn enclosing the magnitude and phase curves limited by gain and phase crossover frequencies. Then, the size of the frame is tuned to provide loop-shaping of the curves to meet desired properties. The iso-damping property is achieved by shaping the phase curve. Similarly, numerous studies in the literature work on robustness achievement by loop shaping the phase curve of the Bode plot. However, the “frequency frame” approach is a new perspective in controller tuning. Two examples are illustratively given to prove the proposed method. Plants in the examples are also considered to be due to load disturbances. Simulation results and effects of the method are clearly explained.

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Guthrie, R. H., et S. G. Evans. « Magnitude and frequency of landslides triggered by a storm event, Loughborough Inlet, British Columbia ». Natural Hazards and Earth System Sciences 4, n^o 3 (4 août 2004) : 475–83. http://dx.doi.org/10.5194/nhess-4-475-2004.

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Abstract. One hundred and one landslides were documented across 370km2 following a rainstorm that swept the British Columbia coastline on 18 November 2001. Despite the regional nature of the storm, the landslides were spaced close together, even within the study area. Landslide clustering is attributed to high intensity storm cells too small to be recorded by the general hydrometric network. The evidence nicely corroborates previous historical studies that reached similar conclusions, but against which there was no modern analog analyzed for coastal British Columbia. Magnitude-cumulative frequency data plotted well on a power law curve for landslides greater than 10000m2, however, below that size several curves would fit. The rollover effect, a point where the data is no longer represented by the power law, therefore occurs at about 1.5 orders of magnitude higher than the smallest landslide. Additional work on Vancouver Island has provided evidence for rollovers at similar values. We propose that the rollover is a manifestation of the physical conditions of landslide occurrence and process uniformity. The data was fit to a double Pareto distribution and P-P plots were generated for several data sets to examine the fit of that model. The double Pareto model describes the bulk of the data well, however, less well at the tails. For small landslides (<650m2) this may still be a product of censoring. Landscape denudation from the storm was averaged over the study area and equal to 2mm of erosion. This is more than an order of magnitude larger than the annual rate of denudation reported by other authors for coastal British Columbia, but substantially less than New Zealand. The number is somewhat affected by the rather arbitrary choice of a study area boundary.

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Al-Gburi, Ahmed Jamal Abdullah, Zahriladha Zakaria, Norhanani Abd Rahman, Syah Alam et Maizatul Alice Meor Said. « A Compact and Low-Profile Curve-Feed Complementary Split-Ring Resonator Microwave Sensor for Solid Material Detection ». Micromachines 14, n^o 2 (3 février 2023) : 384. http://dx.doi.org/10.3390/mi14020384.

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A compact and low-profile curve-feed complementary split-ring resonator (CSRR) microwave sensor for solid material detection is presented in this article. The curve-feed CSRR sensor was developed based on the CSRR configuration with triple rings (TRs) designed together, utilizing a high-frequency structure simulator (HFSS) microwave studio. The designed curve-feed CSRR sensor resonates at 2.5 GHz, performs in transmission mode, and senses shift in frequency. Four varieties of the sample under tests (SUTs) were simulated and measured. These SUTs are Air (without SUT), Roger 5880, Roger 4350, FR4, and detailed sensitivity analysis is being performed for the resonant band at 2.5 GHz. The finalized CSRR curve-feed sensor was integrated with defective ground structure (DGS) to deliver high-performance characteristics in microstrip circuits, which leads to a high Q-factor magnitude. The presented curve-feed sensor has a Q-factor of 520 at 2.5 GHz, with high sensitivity of about 1.072. The relationship between loss tangent, permittivity, and Q-factor at the resonant frequency has been compared and discussed. These disseminated outcomes make the suggested sensor ideal for characterizing solid materials.

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Yin, Yilin, Zhenghong Yang et Meilun Shi. « Analytical Expression of Complex Modulus for Viscoelastic Material ». International Journal of Applied Mechanics 12, n^o 05 (juin 2020) : 2050048. http://dx.doi.org/10.1142/s1758825120500489.

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Transfer functions in the linear dynamic system theory are applied to characterize dynamic mechanical properties of viscoelastic materials. Correlation between transfer functions and typical rheological models and fractional derivative ones are briefly introduced. The transfer function of a rheological model may be expressed in terms of multiplication of factored polynomials. The frequency–response data are presented in the form of a Bode plot of magnitude, from which a transfer function can be established. The characteristic times can be conveniently identified via the corner frequencies of asymptotes of the magnitude curve. Dynamic frequency sweep results for a typical viscoelastic solid are presented to illustrate the use of the Bode diagram method for parameter identification.

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Li, Dajun, Aihua Weng, Yue Yang, Song Han et Yu Tang. « Magnitude-phase Relationship behind Controlled-source Electromagnetic Field Revealed by Nyquist Diagrams ». Journal of Environmental and Engineering Geophysics 22, n^o 4 (décembre 2017) : 365–73. http://dx.doi.org/10.2113/jeeg22.4.365.

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We present a means of processing data from frequency-domain controlled-source electromagnetic method observations via a Nyquist diagram. For a controlled-source electromagnetic field in the frequency domain, the x component of the electric field and the y and z components of the magnetic fields were chosen for discussion. Typical 1-D models and a 3-D model, which have a single anomalous body embedded in a half space, have been used to calculate the complex electromagnetic fields. The corresponding Nyquist diagrams have been plotted and analyzed. The diagrams can reveal the magnitude-phase frequency characteristics of an electromagnetic field and can be used to guide data processing by considering the constraints of the intrinsic connection between amplitude and phase. The results further show that: (1) the Nyquist diagrams of both electric and magnetic responses, varying from low to high frequencies, are all characterized by continuous, single-direction, clockwise spiral curves; (2) for the magnetic field, the opening direction of the Nyquist curve is upward for the y and downward for the z components, regardless of the change in resistivity; (3) for the electric fields, the resistivity changes also lead the spiral structure to take on complicated shapes, such as a snail-like shape or a W, and the starting points of the Nyquist curves depend on the variations in the resistivity with depth. According to the aforementioned rules, we can obtain reliable and reasonably complex field data during the data processing of frequency-domain controlled-source electromagnetic method, which lays a foundation for 3-D frequency-domain data inversion.

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Struthers, I., et M. Sivapalan. « Theoretical investigation of process controls upon flood frequency : role of thresholds ». Hydrology and Earth System Sciences Discussions 3, n^o 5 (26 octobre 2006) : 3279–319. http://dx.doi.org/10.5194/hessd-3-3279-2006.

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Abstract. Traditional statistical approaches to flood frequency inherently assume homogeneity and stationarity in the flood generation process. This study illustrates the impact of heterogeneity associated with threshold non-linearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour. For a simplified, non-threshold (i.e. homogeneous) scenario, flood frequency can be characterised in terms of rainfall frequency, the characteristic response time of the catchment, and storm intermittency, modified by the relative strength of evaporation. The flood frequency curve is then a consistent transformation of the rainfall frequency curve, and could be readily described by traditional statistical methods. The introduction of storage thresholds, namely a field capacity storage and a catchment storage capacity, however, results in different flood frequency "regions" associated with distinctly different rainfall-runoff response behaviour and different process controls. The return period associated with the transition between these regions is directly related to the frequency of threshold exceedence. Where threshold exceedence is relatively rare, statistical extrapolation of flood frequency on the basis of short historical flood records risks ignoring this heterogeneity, and therefore significantly underestimating the magnitude of extreme flood peaks.

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Struthers, I., et M. Sivapalan. « A conceptual investigation of process controls upon flood frequency : role of thresholds ». Hydrology and Earth System Sciences 11, n^o 4 (6 juillet 2007) : 1405–16. http://dx.doi.org/10.5194/hess-11-1405-2007.

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Abstract. Traditional statistical approaches to flood frequency inherently assume homogeneity and stationarity in the flood generation process. This study illustrates the impact of heterogeneity associated with threshold non-linearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour. For a simplified, non-threshold (i.e. homogeneous) scenario, flood frequency can be characterised in terms of rainfall frequency, the characteristic response time of the catchment, and storm intermittency, modified by the relative strength of evaporation. The flood frequency curve is then a consistent transformation of the rainfall frequency curve, and could be readily described by traditional statistical methods. The introduction of storage thresholds, namely a field capacity storage and a catchment storage capacity, however, results in different flood frequency "regions" associated with distinctly different rainfall-runoff response behaviour and different process controls. The return period associated with the transition between these regions is directly related to the frequency of threshold exceedence. Where threshold exceedence is relatively rare, statistical extrapolation of flood frequency on the basis of short historical flood records risks ignoring this heterogeneity, and therefore significantly underestimating the magnitude of extreme flood peaks.

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Zhang, Xiang, Wu, Feng, Shi, Hu et Zhao. « Finite Element Simulation Study of Ultrasonic Vibration-Assisted Tensile High-Volume Fraction SiCp/Al Composite ». Materials 12, n^o 23 (21 novembre 2019) : 3841. http://dx.doi.org/10.3390/ma12233841.

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Silicon carbide particle-reinforced aluminum matrix composite (SiCp/Al) has been widely used in the military and aerospace industry due to its special performance; however, there remain many problems in the processing. The present paper introduces an ultrasonic vibration tensile apparatus and a composite tensile specimen and performs Abaqus finite element simulation on high-volume SiCp/Al. The results show that the stress-strain curve increases linearly during conventional tensile strength; the intermittent vibration tensile strength is similar to the full course vibration tensile strength: The magnitude of the stress reduction increases as the amplitude of the ultrasound increases and the vibration frequency increases. The tensile rate is inversely proportional to the magnitude of the stress reduction, and in the ultrasonic parameters, the amplitude has the greatest influence on the magnitude of the stress reduction, followed by the tensile rate; additionally, the frequency has the least influence on the magnitude of the stress reduction. The experimental results show that the simulation results are consistent with the experimental results.

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Liu, Yang, Liming Wu, Tianqi Sun, Pengfei Zhang, Xi Fang, Liyun Cheng et Bin Jiang. « A Comprehensive Comparison of Period Extraction Algorithms for Asteroids with Long Term Observation ». Universe 7, n^o 11 (10 novembre 2021) : 429. http://dx.doi.org/10.3390/universe7110429.

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The light curve period of an asteroid plays an important role in determining the rotation period, the collision evolution and the YORP effect. There are many period extraction algorithms used to find the light curve period of asteroids with long term observation, which are mainly based on the frequency, time and time–frequency domains. This paper presents a comprehensive and unparalleled comparison of the popular algorithms based on the DAMIT (Database of Asteroid Models from Inversion Techniques) data set to show the statistical results. Considering the quoted period, absolute magnitude, diameter, albedo, time span and number of observations, we analyze the accuracy of five popular methods using the light curve data of 2902 asteroids. We find that although the performance of all the algorithms varies little, Phase Dispersion Minimization (PDM) performs better, followed by Lomb-Scargle (LS), while Conditional Entropy (CE) is not better than the others under certain conditions. We also analyze the cases which are more suitable for searching by frequencies or by periods.

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Nowicka, Barbara. « Estimation of the Degree of Extremality of High-Water Flows in Selected Rivers in Poland in 1971–2006 ». Miscellanea Geographica 14, n^o 1 (1 décembre 2010) : 169–76. http://dx.doi.org/10.2478/mgrsd-2010-0015.

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Abstract The paper presents the results of estimation and comparison of risk of extreme floods on rivers of various hydrological regime. The hypothesis that extreme events occur with the same frequency in all rivers was rejected. The limit between extreme and common floods on 30 rivers from different geographical regions of Poland was defined on the basis of standardized flow-duration curve in 1971-2006. These analyses resulted in designing five curve groups. Four measures of flood magnitude have been proposed. The time distribution of extreme events during the last decades was estimated for the most dynamic rivers.

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Chen, Guang Chao, B. Li, Yu Mei Tong, Fan Xiu Lu et Jin Hyo Boo. « Mechanical and Electrical Properties of Boron-Oxygen-Nitrogen Film as Buffer Layer ». Key Engineering Materials 336-338 (avril 2007) : 2586–88. http://dx.doi.org/10.4028/www.scientific.net/kem.336-338.2586.

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BON film was fabricated as buffer layer by radio frequency plasma enhanced metal-organic chemical vapor deposition with 100 kHz frequency and trimethyl borate precursor. The typical binding energy of each element is 191.5 eV of B1s, 399.4 eV of N1s, and 531.2 eV of O1s in the films detected by XPS. HRTEM showed the film contained amorphous composition and nano-sized crystalline particles. Electrical properties of films were characterized by I–V curve. The order-magnitude of electric conductivity was measured as several tens (·cm)-1. The hardness of BON film was ~ 10 GPa.

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Kawazumi, Hirofumi, et Edward S. Yeung. « Resonant Cell Laser-Based Photoacoustic Densitometer for Thin-Layer Chromatography ». Applied Spectroscopy 42, n^o 7 (septembre 1988) : 1228–31. http://dx.doi.org/10.1366/0003702884430074.

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Photoacoustic spectroscopy was applied to the in situ densitometry of thin-layer chromatographic plates. Fast laser-scanning detection with signal enhancement was demonstrated at a resonant frequency of the cell. The use of phase difference between signal and background provided higher signal-to-noise ratios. Detection limit for Orange G was 170 pg, and the analytical curve was linear over three orders of magnitude.

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Grover, Patrick L., Donald H. Burn et Juraj M. Cunderlik. « A comparison of index flood estimation procedures for ungauged catchments ». Canadian Journal of Civil Engineering 29, n^o 5 (1 octobre 2002) : 734–41. http://dx.doi.org/10.1139/l02-065.

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Flood frequency analysis is used by water resources professionals to estimate the probability of exceedence associated with a flood of a given magnitude. The estimation of flood frequencies is important because they are used in the planning and design of hydraulic structures, in flood-plain management, and in reservoir operation. The index flood method is commonly used to develop a flood frequency curve that relates flood magnitude to flood rarity. This method involves scaling a dimensionless flood frequency curve by the index flood. The index flood is a middle-sized flood for which the mean or median of the flood data series is typically used. When the catchment of interest is ungauged, statistical models, such as multiple regression, are often used to relate the index flood to catchment descriptors. In this study six different parameter estimation techniques and three regionalization techniques are compared in terms of ability to predict the index flood for an ungauged catchment. A case study employing a split-sample experiment with data from catchments in Ontario, Canada, was used to evaluate the approaches. The models were assessed using three performance indices to evaluate the capability to predict the index flood for 20 stations. The dimensionless nonlinear model outperformed all of the other parameter estimation techniques for each of the three indices selected. The performance was improved through the use of geostatistical residual mapping, however, the improvement was small. The residual mapping was found to greatly improve the estimates obtained using ordinary least-squares regression.Key words: index flood, flood frequency analysis, regression, residual mapping, geostatistics.

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Fuzessery, Z. M., et J. C. Hall. « Role of GABA in shaping frequency tuning and creating FM sweep selectivity in the inferior colliculus ». Journal of Neurophysiology 76, n^o 2 (1 août 1996) : 1059–73. http://dx.doi.org/10.1152/jn.1996.76.2.1059.

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1. We examined the role of gamma-aminobutyric acid (GABA)-mediated inhibition in shaping excitatory tuning curves and creating selectivity for frequency-modulated (FM) sweeps in 29 neurons in the central nucleus of the inferior colliculus (ICC) of the pallid bat, with the use of single-unit recording coupled with the iontophoretic application of bicuculline methiodide (BIC), an antagonist of GABAA receptors. 2. BIC increased response magnitude 2 to 6 times over pretreatment levels in > 80% of neurons tested, and converted > 50% of nonmonotonic intensity-rate functions to monotonic or plateaued functions, demonstrating that GABAergic input normally limited response magnitude and inhibited responses at higher intensities. BIC typically had little effect on response thresholds, except in more specialized neurons that normally responded poorly to tones. In these cases, BIC disinhibited the neurons' responses to tones and lowered excitatory thresholds as much as 25 dB. 3. We examined the effects of BIC application on both excitatory and inhibitory tuning curves (measured with simultaneous 2-tone inhibition) to determine whether inhibitory curves were GABA mediated and whether removal of this inhibition was accompanied by an expansion of the excitatory curve. BIC had variable effects on the width of excitatory curves. In most cases, excitatory curves were at least slightly broadened, and expanded into regions previously occupied by inhibitory curves. In most cases, excitatory curves were at least slightly broadened, and expanded into regions previously occupied by inhibitory curves. However, in a few cases, inhibitory curves could be eliminated without an expansion of the excitatory curve. The greatest effect was seen in neurons with closed excitatory tuning curves; blocking GABAergic input caused the curves to open, allowing the neurons to respond at higher intensities. 4. Approximately 50% of the neurons in the ICC tuned to the spectrum of the bat's downward FM sweeping biosonar pulse respond preferentially to downward FM sweeps and not to upward sweeps, tones, or noise. In all neurons tested, BIC at least partially destroyed selectivity for sweep direction. This destruction could occur, however, without a loss of response exclusivity; in some cases, the neurons still did not respond to tones or noise. These results suggest that response selectivity for a species-specific signal is created by GABAergic input to ICC neurons. These results are used to suggest a mechanism that creates selectivity for FM sweep direction.

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Zhan, Tianyi, Jiali Jiang, Jianxiong Lu, Yaoli Zhang et Jianmin Chang. « Frequency-dependent viscoelastic properties of Chinese fir (Cunninghamia lanceolata) under hygrothermal conditions. Part 1 : moisture adsorption ». Holzforschung 73, n^o 8 (26 juillet 2019) : 727–36. http://dx.doi.org/10.1515/hf-2018-0208.

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AbstractTo elucidate the frequency-dependent viscoelasticity of wood under a moisture non-equilibrium state, changes in stiffness and damping as a function of frequency were investigated during the moisture adsorption process. The moisture adsorption processes were carried out at six temperatures (30–80°C) and three relative humidity levels (30, 60 and 90% RH). During the moisture adsorption process, the wood stiffness decreased, and damping increased with the increment of moisture content (MC). Regardless of the moisture adsorption time, the wood stiffness increased, and damping decreased with the increasing testing frequency. Based on the re-organized Williams-Landel-Ferry (WLF) model, the time-moisture superposition (TMS) relation was assumed to be applicable for developing a master curve of wood stiffness during the moisture adsorption process. The frequency ranges of the stiffness master curves spanned from 16 to 23 orders of magnitude at temperatures ranging from 30 to 80°C. However, the TMS relation was not able to predict the wood damping properties during the moisture adsorption process due to the multi-relaxation system of the wood and the non-proportional relationship between free volume and MC at transient moisture conditions.

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Sun, Yanwei, Qingyun Li, Furong Yu, Mingwei Ma et Cundong Xu. « Assessing Hydrological Performances of Bioretention Cells to Meet the LID Goals ». Sustainability 15, n^o 5 (26 février 2023) : 4204. http://dx.doi.org/10.3390/su15054204.

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BRCs (bioretention cells), one of many low-impact development (LID) practices, are increasingly utilized to lessen the amount of runoff while simultaneously improving the runoff quality. Because the goal of BRCs and LID designs, in general, is to mimic or replicate the pre-development hydrology, it is critical to evaluate the hydrologic and ecologic performances of the BRC facility from the perspective of replicating the pre-development hydrology. The metrics developed in this study were intended to represent the hydrologic regime including the runoff volume control metrics, peak flow frequency exceedance curve, and flow duration curve. We also used a hydrological indicator of T0.5, the fraction of a multi-year period in which the flow exceeds the 0.5-year return period storm to represent the performances regarding downstream ecology. The indicators were compared to their pre-development values to determine how closely they reflected and replicated the pre-development state. A long-term stormwater management model (SWMM) model was developed to examine conditions before and after development and water movement in BRCs. When the BRCs facilities areas are 5% of the entire impervious study area, key findings show that: (1) BRCs have significant runoff volume control performances. (2) The peak flow frequency exceedance curve with BRCs could fully match the pre-development scenario for minor rainfall events compared to the 0.1-year storm. Flow duration curves with BRCs showed that, the frequency, magnitude, and duration of small flows that occurred for more than 90% of the total time closely matched those of pre-development hydrology. (3) T0.5 with BRCs showed significant improvement compared with the value of the area with no BRCs and was close to the pre-development T0.5. The findings presented in this study indicated the significant performance of BRCs in improving downstream ecology.

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Tadmor, Y., et D. J. Tolhurst. « The effect of threshold on the relationship between the receptive-field profile and the spatial-frequency tuning cure in simple cells of the cat's striate cortex ». Visual Neuroscience 3, n^o 5 (novembre 1989) : 445–54. http://dx.doi.org/10.1017/s0952523800005940.

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AbstractIt is believed that spatial summation in most simple cells is a linear process. If this were so, then the Fourier transform of a simple cell's line weighting function should predict the cell's spatial frequency tuning curve. We have compared such predictions with experimental measurements and have found a consistent discrepancy: the predicted tuning curve is much too broad. We show qualitatively that this kind of discrepancy is consistent with the well-known threshold nonlinearity shown by most cortical cells. We have tested quantitatively whether a response threshold could explain the observed disagreements between predictions and measurements: a least-squares minimization routine was used to fit the inverse Fourier Transform of the measured frequency tuning curve to the measured line weighting function. The fitting procedure permitted us to introduce a threshold to the reconstructed line weighting function. The results of the analysis show that, for all of the cells tested, the Fourier transforms produced better predictions when a response threshold was included in the model. For some cells, the actual magnitude of the response threshold was measured independently and found to be compatible with that suggested by the model. The effects of nonlinearities of spatial summation are considered.

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Shih, I., A. L. Li, W. W. Lam, C. X. Qiu, L. Ngo Phong et B. Tremblay. « Low-frequency noise in RF-sputtered Pb-doped 2223 phase BiSrCaCuO thin films ». Canadian Journal of Physics 72, n^o 5-6 (1 mai 1994) : 270–73. http://dx.doi.org/10.1139/p94-040.

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Noise measurements were carried out on RF-sputtered Pb-doped 2223 phase BiSrCaCuO superconducting thin films. No definite relationship between noise and bias current was observed in the superconducting state, however, a square-current dependence of noise was found in the normal state. The magnitude of the noise in the BiSrCaCuO films at room temperature was one to five orders of magnitude larger than that in a normal metal. Near the tail of the resistance transition, noise peaks were observed that were 3–12 K below the maximum of the derivative resistance–temperature curve. Noise dependence on frequency shows an approximate 1/f relation in both normal and superconducting states. The origin of the noise in the normal state is believed to be due to thermal fluctuation or resistance fluctuation and the larger noise near zero TC is possibly caused by grain boundaries in the films.

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Basso, S., G. Botter, R. Merz et A. Miniussi. « PHEV ! The PHysically-based Extreme Value distribution of river flows ». Environmental Research Letters 16, n^o 12 (1 décembre 2021) : 124065. http://dx.doi.org/10.1088/1748-9326/ac3d59.

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Abstract Magnitude and frequency are prominent features of river floods informing design of engineering structures, insurance premiums and adaptation strategies. Recent advances yielding a formal characterization of these variables from a joint description of soil moisture and daily runoff dynamics in river basins are here systematized to highlight their chief outcome: the PHysically-based Extreme Value (PHEV) distribution of river flows. This is a physically-based alternative to empirical estimates and purely statistical methods hitherto used to characterize extremes of hydro-meteorological variables. Capabilities of PHEV for predicting flood magnitude and frequency are benchmarked against a standard distribution and the latest statistical approach for extreme estimation, by using both an extensive observational dataset and long synthetic series of streamflow generated for river basins from contrasting hydro-climatic regions. The analyses outline the domain of applicability of PHEV and reveal its fairly unbiased capabilities to estimate flood magnitudes with return periods much longer than the sample size used for calibration in a wide range of case studies. The results also emphasize reduced prediction uncertainty of PHEV for rare floods, notably if the flood magnitude-frequency curve displays an inflection point. These features, arising from the mechanistic understanding embedded in the novel distribution of the largest river flows, are key for a reliable assessment of the actual flooding hazard associated to poorly sampled rare events, especially when lacking long observational records.

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Bloot, S., J. R. Callingham et B. Marcote. « Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep ». Monthly Notices of the Royal Astronomical Society 509, n^o 1 (18 octobre 2021) : 475–88. http://dx.doi.org/10.1093/mnras/stab2976.

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ABSTRACT Apep is the brightest and most luminous non-thermal colliding-wind binary by over an order of magnitude. It has been suggested from infrared observations that one of the Wolf–Rayet stars in Apep is launching an anisotropic wind. Here we present radio observations of Apep from 0.2 to 20 GHz taken over 33 yr. The spectrum reveals an extremely steep turnover in the flux density at low frequencies, where the flux density decreases by two orders of magnitude over only 325 MHz of bandwidth. This exponential decline is best described by free–free absorption, with a turnover frequency at 0.54 ± 0.01 GHz. Above the turnover, the spectrum is well described by a power-law and a high-frequency cut-off likely caused by inverse-Compton cooling. The light curve of Apep shows significant variation over the observing period, with Apep brightening by over 50 mJy in a span of 25 yr at 1.4 GHz. Models that assume spherical winds do not replicate all of the structure evident in the radio light curve. We derived a model that allows one of the winds in the system to be anisotropic. This anisotropic model recovers most of the structure of the light curve and is a significantly better statistical fit to the data than the spherical wind model. We suggest such a result is independent support that one of the Wolf–Rayet stars in Apep is launching an anisotropic wind. If the anisotropic wind model is correct, we predict a ∼25 per cent decrease of the 1.4 GHz flux density of Apep over the next 5 yr.

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Martin, Louis. « Holocene sea-level history along eastern-southeastern Brazil ». Anuário do Instituto de Geociências 26 (1 janvier 2003) : 13–24. http://dx.doi.org/10.11137/2003_0_13-24.

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Relative sea-level curves have been delineated for several sectors of the Brazilian coast. In order to have homogeneous and consistent curves, very short segments of the coastline with the same framework are considered. To minimize systematic errors tied to the particular nature of an indicator, we use the maximum number of different indicators available from former positions of relative sea level. These sea-level curves show that, during the last 7000 years, the central Brazilian coast has been subjected to a submergence phase which lasted until 5100 14C yr BP (5600 cal yr BP), followed by a drop in sea level. This drop in sea level was not continuous but was interrupted by two high-frequency oscillations. The Salvador curve, the most detailed, can be used as a reference for the central portion of the Brazilian coastline. It is now presented with corrections for isotopic fractionation and reservoir effects as well as calibrations for astronomical ages. Additional supporting evidence for the existence of high-frequency oscillations is provided. They are of the same magnitude as is predicted for the future under greenhouse conditions. These data will help us to understand how the coastal systems will respond to these sea-level changes.

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Kreyling, Juergen, Rhena Schumann et Robert Weigel. « Soils from cold and snowy temperate deciduous forests release more nitrogen and phosphorus after soil freeze–thaw cycles than soils from warmer, snow-poor conditions ». Biogeosciences 17, n^o 15 (13 août 2020) : 4103–17. http://dx.doi.org/10.5194/bg-17-4103-2020.

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Abstract. The effects of global warming are most pronounced in winter. A reduction in snow cover due to warmer atmospheric temperature in formerly cold ecosystems, however, could counteract an increase in soil temperature by reduction of insulation. Thus, soil freeze–thaw cycles (FTCs) might increase in frequency and magnitude with warming, potentially leading to a disturbance of the soil biota and release of nutrients. Here, we assessed how soil freeze–thaw magnitude and frequency affect short-term release of nutrients in temperate deciduous forest soils by conducting a three-factorial gradient experiment with ex situ soil samples in climate chambers. The fully crossed experiment included soils from forests dominated by Fagus sylvatica (European beech) that originate from different winter climate (mean coldest month temperature range ΔT>4 K), a range of FTC magnitudes from no (T=4.0 ∘C) to strong (T=-11.3 ∘C) soil frost, and a range of FTC frequencies (f=0–7). We hypothesized that higher FTC magnitude and frequency will increase the release of nutrients. Furthermore, soils from cold climates with historically stable winter soil temperatures due to deep snow cover will be more responsive to FTCs than soils from warmer, more fluctuating winter soil climates. FTC magnitude and, to a lesser extent, also FTC frequency resulted in increased nitrate, ammonium, and phosphate release almost exclusively in soils from cold, snow-rich sites. The hierarchical regression analyses of our three-factorial gradient experiment revealed that the effects of climatic origin (mean minimum winter temperature) followed a sigmoidal curve for all studied nutrients and was modulated either by FTC magnitude (phosphate) or by FTC magnitude and frequency (nitrate, ammonium) in complex twofold and, for all studied nutrients, in threefold interactions of the environmental drivers. Compared to initial concentrations, soluble nutrients were predicted to increase to 250 % for nitrate (up to 16 µg NO3-N kg−1DM), to 110 % for ammonium (up to 60 µg NH4-N kg−1DM), and to 400 % for phosphate (2.2 µg PO4-P kg−1DM) at the coldest site for the strongest magnitude and highest frequency. Soils from warmer sites showed little nutrient release and were largely unaffected by the FTC treatments except for above-average nitrate release at the warmest sites in response to extremely cold FTC magnitude. We suggest that currently warmer forest soils have historically already passed the point of high responsiveness to winter climate change, displaying some form of adaptation either in the soil biotic composition or in labile nutrient sources. Our data suggest that previously cold sites, which will lose their protective snow cover during climate change, are most vulnerable to increasing FTC frequency and magnitude, resulting in strong shifts in nitrogen and phosphorus release. In nutrient-poor European beech forests of the studied Pleistocene lowlands, nutrients released over winter may be leached out, inducing reduced plant growth rates in the following growing season.

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Kim, Chulhee, D. H. McNamara, Kent A. Feltz et C. G. Christensen. « A Photometric and Spectrographic Study of SX Phœnicis ». International Astronomical Union Colloquium 139 (1993) : 380–81. http://dx.doi.org/10.1017/s0252921100117968.

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AbstractNew simultaneous photometric (uvbyβ) and spectrographic observations of SX Phe are described. Analysis of the light variation frequency spectrum is performed and the oscillation modes are investigated. After separating the light curves and radial velocity curve, atmospheric and physical parameters corresponding to each different oscillation mode were determined. Intrinsic (b – y), m1, and c1 values used in conjunction with a model-atmosphere grid yield a mean effective temperature < Teff > = 7590K, a mean surface gravity, < logg > = 4.02, and [Fe/H]= -0.47 for the first period. The pulsation theory and stellar model sequences yield bolometric magnitude of mass of 1.4 M⊙ and age of 2.0 Gyrs. It was found that these atmospheric parameters are almost independent upon different oscillation mode. The radial-velocity data indicates a mean radial velocity of -37km/s and a total velocity amplitude range of 38km/s.

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Alifov, A. A. « About mixed forced, parametric and self-oscillations by limited excitation and delayed elasticity ». PNRPU Mechanics Bulletin, n^o 3 (15 décembre 2020) : 12–19. http://dx.doi.org/10.15593/perm.mech/2020.3.02.

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Mixed forced, parametric, and self-oscillations are considered if there is a delay in the elastic force in the system. A dynamic model is a friction self-oscillation system describing the frictional self-oscillations that occur in many technical systems for various purposes (metal-cutting machines, textile equipment, brakes and a number of other engineering objects). The operation of the system is supported by the energy source of limited power. For the analysis we used the method of straight linearization which is easier than the known methods of analysis of nonlinear systems, has no time-consuming and complex approximations of different orders, provides an opportunity to obtain the final design ratios regardless of the specific type and degree of nonlinearity, thus reducing labor costs and time by several orders of magnitude. By using this method, we obtained solutions of a nonlinear system of differential equations describing the system's motion. The equations of non-stationary and stationary movements are derived. To analyze the stability of stationary movements, the stability conditions based on the Routh-Hurwitz criteria are compiled. Calculations were performed to obtain information about the effect of delay on the oscillation modes. It is shown that the delay affects both the magnitude of the amplitude and the location of the amplitude-frequency curve in the frequency range depending on the magnitude of the delay, the amplitude curve is shifted to the region of lower frequencies. The stability of stationary oscillations depends both on the energy source characteristics and lag value. The interaction of the oscillating system and the energy source leads to a number of effects, both in the presence and absence of the lag. However, their course may be different depending on the lag value.

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Allaire, P. E., R. L. Fittro, E. H. Maslen et W. C. Wakefield. « Measured Force/Current Relations in Solid Magnetic Thrust Bearings ». Journal of Engineering for Gas Turbines and Power 119, n^o 1 (1 janvier 1997) : 137–42. http://dx.doi.org/10.1115/1.2815537.

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When magnetic bearings are employed in a pump, compressor, turbine, or other rotating machine, measurement of the current in the bearing coils provides knowledge of the forces imposed on the bearings. This can be a significant indicator of machine problems. Additionally, magnetic bearings can be utilized as a load cell for measuring impeller forces in test rigs. The forces supported by magnetic bearings are directly related to the currents, air gaps, and other parameters in the bearings. This paper discusses the current/force relation for magnetic thrust bearings. Force versus current measurements were made on a particular magnetic bearing in a test rig as the bearing coil currents were cycled at various time rates of change. The quasi-static force versus current relations were measured for a variety of air gaps and currents. The thrust bearing exhibits a hysteresis effect, which creates a significant difference between the measured force when the current is increasing as compared to that when the current is decreasing. For design current loops, 0.95 A to 2.55 A, at the time rate of change of 0.1 A/s, the difference between increasing and decreasing current curves due to hysteresis ranged from 4 to 8 percent. If the bearing is operated in small trajectories about a fixed (nonzero) operation point on the F/I (force/current) curve, the scatter in the measurement error could be expected to be on the order of 4 percent. A quasi-static nonlinear current/force equation was developed to model the data and curve-fit parameters established for the measured data. The effects of coercive force and iron reluctance, obtained from conventional magnetic materials tests, were included to improve the model, but theoretically calculated values from simple magnetic circuit theory do not produce accurate results. Magnetic fringing, leakage, and other effects must be included. A sinusoidal perturbation current was also imposed on the thrust bearing. Force/current magnitude and phase angle values versus frequency were obtained for the bearing. The magnitude was relatively constant up to 2 Hz but then decreased with frequency. The phase lag was determined to increase with frequency with value of 16 deg at 40 Hz. This effect is due to eddy currents, which are induced in the solid thrust-bearing components.

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Galiatsatou, Panagiota, et Christos Iliadis. « Intensity-Duration-Frequency Curves at Ungauged Sites in a Changing Climate for Sustainable Stormwater Networks ». Sustainability 14, n^o 3 (21 janvier 2022) : 1229. http://dx.doi.org/10.3390/su14031229.

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Intensity-duration-frequency (IDF) curves representing the variation of the magnitude of extreme rainfall events with a return period and storm duration are widely used in hydrologic infrastructure design, flood risk management projects, and climate change impact studies. However, in many locations worldwide, short-duration rainfall-observing sites with long records do not exist. This paper introduces a new methodological framework for extracting IDF curves at ungauged sites transferring information from gauged ones with a relatively homogeneous extreme rainfall climate. This methodology is grounded on a simple scaling concept based on the multifractal behaviour of rainfall. A nonstationary Generalized Extreme Value (GEV) distribution fitted to annual rainfall monthly maxima at the ungauged site using a moving-time window approach is also applied to consider effects of a changing climate on IDF curve construction. An application is presented at the study site of Fourni, Crete, to derive IDF curves under changing climate conditions and present implications of the proposed methodology in the design of a sustainable stormwater network. The methodology introduced in this work results in increased rainfall extremes up to 20.5%, while the newly designed stormwater network is characterised by increased diameters of its primary conduits, compared to the ones resulting under fully stationary conditions.

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Kusumastuti, Cilcia, Prasetio Sudjarwo, Marvin Christhie et Timotius Krisna. « Intensity-Duration-Frequency (IDF) Curve and the Most Suitable Method to Determine Flood Peak Discharge in Upper Werba Sub-Watershed ». Civil Engineering Dimension 21, n^o 2 (18 octobre 2019) : 70–75. http://dx.doi.org/10.9744/ced.21.2.70-75.

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Design flood is one of the important factors for flood risk assessment and water infrastructures planning and development in a certain location. There are several methods to estimate it, one method which has been commonly and widely use is using flood frequency analysis. This research aims to develop Intensity-Duration-Frequency (IDF) curves in Upper Werba Sub-Watershed, West Papua Province, Indonesia, to estimate design rainfall intensity. The design rainfall intensity is used to estimate peak of flood discharge using Rational Formula in the sub-watershed. Other methods, i.e. Soil Conservation Service and Nakayasu Synthetic Unit Hydrograph are also presented in this paper to provide comparison of the estimated peak of flood discharge. The result shows that the Rational method provide the closest magnitude of estimated flood discharge in Upper Werba Sub-Watershed to the observed streamflow. Therefore, it is suggested that the Rational method can be used for water infrastructure planning and development in the sub-watershed.

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Peng, Li En, et Rui Guo. « Transmission Study on Dynamic Characteristics of Front Suspension LCA Bushing ». Advanced Materials Research 605-607 (décembre 2012) : 1249–52. http://dx.doi.org/10.4028/www.scientific.net/amr.605-607.1249.

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This paper simplified the wheel-Lower Control Arm-frame system into a two DOFs vibration system and analyzed its transmission characteristics by modeling the LCA rubber bushing in Kelvin-Voigt model, Zener model and Berg model, respectively. The results show that the system with Berg model shows obvious amplitude-dependent characteristics. Its magnitude and frequency at the peak of the transmission curve change as the excitation amplitude changes. The system with Kelvin-Voigt model or Zener model shows none amplitude-dependent characteristics. It’s more effective and more exact to model the LCA rubber bushing in Berg model than the others.

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Doi, Manh Van, et Jongho Kim. « Addressing Climate Internal Variability on Future Intensity-Duration-Frequency Curves at Fine Scales across South Korea ». Water 13, n^o 20 (12 octobre 2021) : 2828. http://dx.doi.org/10.3390/w13202828.

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Designing water infrastructure requires information about the magnitude and frequency of upcoming rainfall. A limited range of data offers just one of many realizations that occurred in the past or will occur in the future; thus, it cannot sufficiently explain climate internal variability (CIV). In this study, future relationships among rainfall intensity (RI), duration, and frequency (called the IDF curve) are established by addressing the CIV and tail characteristics with respect to frequency. Specifically, 100 ensembles of 30-year time series data were created to quantify that uncertainty. Then, the tail characteristics of future extreme rainfall events were investigated to determine whether they will remain similar to those in the present. From the RIs computed for control and future periods under two emission scenarios, following are the key results. Firstly, future RI will increase significantly for most locations, especially near the end of this century. Secondly, the spatial distributions and patterns indicate higher RI in coastal areas and lower RI for the central inland areas of South Korea, and those distributions are similar to those of the climatological mean (CM) and CIV. Thirdly, a straightforward way to reveal whether the tail characteristics of future extreme rainfall events are the same as those in the present is to inspect the slope value for the factor of change (FOC), mFOC. Fourthly, regionalizing with nearby values is very risky when investigating future changes in precipitation frequency estimates. Fifthly, the magnitude of uncertainty is large when the data length is short and gradually decreases as the data length increases for all return periods, but the uncertainty range becomes much greater as the return period becomes large. Lastly, inferring future changes in RI from the CM is feasible only for small return periods and at locations where mFOC is close to zero.

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Doi, Manh Van, et Jongho Kim. « Addressing Climate Internal Variability on Future Intensity-Duration-Frequency Curves at Fine Scales across South Korea ». Water 13, n^o 20 (12 octobre 2021) : 2828. http://dx.doi.org/10.3390/w13202828.

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Designing water infrastructure requires information about the magnitude and frequency of upcoming rainfall. A limited range of data offers just one of many realizations that occurred in the past or will occur in the future; thus, it cannot sufficiently explain climate internal variability (CIV). In this study, future relationships among rainfall intensity (RI), duration, and frequency (called the IDF curve) are established by addressing the CIV and tail characteristics with respect to frequency. Specifically, 100 ensembles of 30-year time series data were created to quantify that uncertainty. Then, the tail characteristics of future extreme rainfall events were investigated to determine whether they will remain similar to those in the present. From the RIs computed for control and future periods under two emission scenarios, following are the key results. Firstly, future RI will increase significantly for most locations, especially near the end of this century. Secondly, the spatial distributions and patterns indicate higher RI in coastal areas and lower RI for the central inland areas of South Korea, and those distributions are similar to those of the climatological mean (CM) and CIV. Thirdly, a straightforward way to reveal whether the tail characteristics of future extreme rainfall events are the same as those in the present is to inspect the slope value for the factor of change (FOC), mFOC. Fourthly, regionalizing with nearby values is very risky when investigating future changes in precipitation frequency estimates. Fifthly, the magnitude of uncertainty is large when the data length is short and gradually decreases as the data length increases for all return periods, but the uncertainty range becomes much greater as the return period becomes large. Lastly, inferring future changes in RI from the CM is feasible only for small return periods and at locations where mFOC is close to zero.

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Jeng, Fuh-Cherng, Brandie Nance, Karen Montgomery-Reagan et Chia-Der Lin. « Exponential Modeling of Frequency-Following Responses in American Neonates and Adults ». Journal of the American Academy of Audiology 29, n^o 02 (février 2018) : 125–34. http://dx.doi.org/10.3766/jaaa.16135.

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AbstractThe scalp-recorded frequency-following response (FFR) has been widely accepted in assessing the brain’s processing of speech stimuli for people who speak tonal and nontonal languages. Characteristics of scalp-recorded FFRs with increasing number of sweeps have been delineated through the use of an exponential curve-fitting model in Chinese adults; however, characteristics of speech processing for people who speak a nontonal language remain unclear.This study had two specific aims. The first was to examine the characteristics of speech processing in neonates and adults who speak a nontonal language, to evaluate the goodness of fit of an exponential model on neonatal and adult FFRs, and to determine the differences, if any, between the two groups of participants. The second aim was to assess effective recording parameters for American neonates and adults.This investigation employed a prospective between-subject study design.A total of 12 American neonates (1–3 days old) and 12 American adults (24.1 ± 2.5 yr old) were recruited. Each neonate passed an automated hearing screening at birth and all adult participants had normal hearing and were native English speakers.The English vowel /i/ with a rising pitch contour (117–166 Hz) was used to elicit the FFR. A total of 8,000 accepted sweeps were recorded from each participant. Three objective indices (Frequency Error, Tracking Accuracy, and Pitch Strength) were computed to estimate the frequency-tracking acuity and neural phase-locking magnitude when progressively more sweeps were included in the averaged waveform. For each objective index, the FFR trends were fit to an exponential curve-fitting model that included estimates of asymptotic amplitude, noise amplitude, and a time constant.Significant differences were observed between groups for Frequency Error, Tracking Accuracy, and Pitch Strength of the FFR trends. The adult participants had significantly smaller Frequency Error (p < 0.001), better Tracking Accuracy (p = 0.001), and larger Pitch Strength (p = 0.003) values than the neonate participants. The adult participants also demonstrated a faster rate of improvement (i.e., a smaller time constant) in all three objective indices compared to the neonate participants. The smaller time constants observed in adults indicate that a larger number of sweeps will be needed to adequately assess the FFR for neonates. Furthermore, the exponential curve-fitting model provided a good fit to the FFR trends with increasing number of sweeps for American neonates (mean r 2 = 0.89) and adults (mean r 2 = 0.96).Significant differences were noted between the neonatal and adult participants for Frequency Error, Tracking Accuracy, and Pitch Strength. These differences have important clinical implications in determining when to stop a recording and the number of sweeps needed to adequately assess the frequency-encoding acuity and neural phase-locking magnitude in neonates and adults. These findings lay an important foundation for establishing a normative database for American neonates and adults, and may prove to be useful in the development of diagnostic and therapeutic paradigms for neonates and adults who speak a nontonal language.

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Pailoplee, Santi, et Chitti Palasri. « CU-PSHA : A MATLAB Software for Probabilistic Seismic Hazard Analysis ». Journal of Earthquake and Tsunami 08, n^o 04 (octobre 2014) : 1450008. http://dx.doi.org/10.1142/s1793431114500080.

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In this study, an open source MATLAB software, called CU-PSHA, is developed in order to analyze probabilistic earthquake hazards. This software aims to provide a user friendly and flexible tool for evaluating reliable earthquake hazard estimates. With the CU-PSHA, the probability of distances between the earthquake sources and the study site can be estimated. Two choices for the estimation of earthquake frequency–magnitude distribution, the exponential magnitude distribution and the characteristic earthquake models, are provided. Some strong ground–motion attenuation models are available for both shallow crustal and subduction zone earthquakes. The probability of exceedance of any individual given ground shaking value can be obtained, allowing the display of a seismic hazard curve. In addition with the supplementary MATLAB scripts, this CU-PSHA software can be employed in general seismic hazard mapping, for both ground shaking level and probability of occurrence, in any specific given time span.

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Darmayadi, Danna, et Iman Satyarno. « Finite element modeling of masonry wall with mortar 1pc : 4 lime : 10 sand under lateral force ». MATEC Web of Conferences 258 (2019) : 05019. http://dx.doi.org/10.1051/matecconf/201925805019.

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This paper gives a detailed presentation of three-dimensional Finite Element Model that has been constructed for Masonry Wall under lateral force by using Abaqus software. This research aimed to investigate the behavior of Masonry Walls under lateral force and developed load-displacement curve. From the result that The numerical model using the Abaqus Software can represent the load-displacement curve of Masonry Walls due to lateral forces, Numerical Results with the Abaqus Software obtained that the magnitude of the load on condition of Plastic is 82.13 KN and experimental results obtained of 81 KN. There is a difference of 1.4%, Based on Abaqus Software with Numerical results obtained a compressive strength of masonry wall fm = 1.8 MPa with a modulus of elasticity = 150 MPa, Calculation of the natural frequency of structures with Abaqus Software is obtained as the difference of 2.13-2.92% with the test results Hakas (2017)

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Steele, A. W., et G. M. Hieftje. « A Modulated Sample-Introduction System for ICP-Atomic Emission Spectrometry ». Applied Spectroscopy 40, n^o 8 (novembre 1986) : 1127–31. http://dx.doi.org/10.1366/0003702864507710.

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A modulated sample-introduction device for use in inductively coupled plasma emission spectrometry has been constructed and evaluated. With this device, the flow of aerosol to the excitation source is modulated by applying at a specific frequency a pressure pulse to the nebulizer chamber; the use of frequency-selective detection then permits efficient signal recovery. Unfortunately, background emission from the ICP was also found to be modulated at the sample-introduction frequency; the magnitude of background modulation depends on the depth of sample modulation and the types of spectral features present at the analytical line of interest. The sample-modulation device discriminated best between analyte emission and continuum background radiation, but performed most poorly when OH band emission was the dominant background interference. The construction and operation of the device are described and its performance for several elements is evaluated in terms of detection limits, S/B enhancement, and working-curve linearity.

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Layton, H. E., E. Bruce Pitman et Leon C. Moore. « Spectral properties of the tubuloglomerular feedback system ». American Journal of Physiology-Renal Physiology 273, n^o 4 (1 octobre 1997) : F635—F649. http://dx.doi.org/10.1152/ajprenal.1997.273.4.f635.

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A simple mathematical model was used to investigate the spectral properties of the tubuloglomerular feedback (TGF) system. A perturbation, consisting of small-amplitude broad-band forcing, was applied to simulated thick ascending limb (TAL) flow, and the resulting spectral response of the TGF pathway was assessed by computing a power spectrum from resulting TGF-regulated TAL flow. Power spectra were computed for both open- and closed-feedback-loop cases. Open-feedback-loop power spectra are consistent with a mathematical analysis that predicts a nodal pattern in TAL frequency response, with nodes corresponding to frequencies where oscillatory flow has a TAL transit time that equals the steady-state fluid transit time. Closed-feedback-loop spectra are dominated by the open-loop spectral response, provided that γ, the magnitude of feedback gain, is less than the critical value γc required for emergence of a sustained TGF-mediated oscillation. For γ exceeding γc, closed-loop spectra have peaks corresponding to the fundamental frequency of the TGF-mediated oscillation and its harmonics. The harmonics, expressed in a nonsinusoidal waveform for tubular flow, are introduced by nonlinear elements of the TGF pathway, notably TAL transit time and the TGF response curve. The effect of transit time on the flow waveform leads to crests that are broader than troughs and to an asymmetry in the magnitudes of increasing and decreasing slopes. For feedback gain magnitude that is sufficiently large, the TGF response curve tends to give a square waveshape to the waveform. Published waveforms and power spectra of in vivo TGF oscillations have features consistent with the predictions of this analysis.

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Jia, J. H., J. Y. Du, Y. Wang et H. X. Hua. « Investigation of the wall friction in the pipe induced by the oscillating flow ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 222, n^o 3 (1 mars 2008) : 387–92. http://dx.doi.org/10.1243/09544062jmes730.

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The wall friction induced by the oscillating flow of the fractional derivative Maxwell viscoelastic fluid in the pipe is investigated. The velocity and the shear stress solutions of the flow are solved. The friction is derived from the shear stress expression and analysed by numerical simulation. From analysis, it is found that the friction amplitude exhibits resonance-like phenomena. Moreover, the number of the resonance-like peaks, the enhancement magnitude, and the resonance-like frequency of the same order vary with the pipe radius and rheological parameters of fluids. When the radius overtakes the critical value, the friction curve monotonously decreases, and when the radius is big enough, the enhancement disappears.

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Kaida, Hideki, et Naoto Kihara. « FRAGILITY EVALUATION METHODOLOGY FOR TSUNAMI-BORNE DEBRIS IMPACT ». Coastal Engineering Proceedings, n^o 36v (28 décembre 2020) : 9. http://dx.doi.org/10.9753/icce.v36v.currents.9.

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In the safe design and risk assessment of structures in coastal area, it is important to consider tsunami-borne debris impact. Recently, probabilistic analysis has become the preferred form of analysis because of the large aleatory and epistemic uncertainties associated with tsunami effects, which are not captured in deterministic scenario-based assessments. By performing both a probabilistic tsunami hazard assessment (PTHA) and a tsunami fragility assessment (TFA) on structures, their annual failure frequency can be determined. The TFA involves evaluation of the response (e.g. debris impact force exerted on the structure) and the capacity of the structure to resist tsunami effects. Then, a fragility curve shows conditional damage probability of the structure for the tsunami magnitude (e.g., discrete tsunami height around the focused area). This study proposes a TFA methodology for tsunami-borne debris impact, as this has not yet been sufficiently established. Evaluation of the impact speed and impact probability of debris considering various uncertainties in the response evaluation are described in particular detail. Moreover, an assessment of a coastal industrial site was performed and fragility curves and the annual failure frequency of structures against debris impact were shown.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/es-ny8eIUfc

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Orem, Caitlin A., et Jon D. Pelletier. « Constraining frequency–magnitude–area relationships for rainfall and flood discharges using radar-derived precipitation estimates : example applications in the Upper and Lower Colorado River basins, USA ». Hydrology and Earth System Sciences 20, n^o 11 (8 novembre 2016) : 4483–501. http://dx.doi.org/10.5194/hess-20-4483-2016.

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Abstract. Flood-envelope curves (FECs) are useful for constraining the upper limit of possible flood discharges within drainage basins in a particular hydroclimatic region. Their usefulness, however, is limited by their lack of a well-defined recurrence interval. In this study we use radar-derived precipitation estimates to develop an alternative to the FEC method, i.e., the frequency–magnitude–area-curve (FMAC) method that incorporates recurrence intervals. The FMAC method is demonstrated in two well-studied US drainage basins, i.e., the Upper and Lower Colorado River basins (UCRB and LCRB, respectively), using Stage III Next-Generation-Radar (NEXRAD) gridded products and the diffusion-wave flow-routing algorithm. The FMAC method can be applied worldwide using any radar-derived precipitation estimates. In the FMAC method, idealized basins of similar contributing area are grouped together for frequency–magnitude analysis of precipitation intensity. These data are then routed through the idealized drainage basins of different contributing areas, using contributing-area-specific estimates for channel slope and channel width. Our results show that FMACs of precipitation discharge are power-law functions of contributing area with an average exponent of 0.82 ± 0.06 for recurrence intervals from 10 to 500 years. We compare our FMACs to published FECs and find that for wet antecedent-moisture conditions, the 500-year FMAC of flood discharge in the UCRB is on par with the US FEC for contributing areas of ∼ 102 to 103 km2. FMACs of flood discharge for the LCRB exceed the published FEC for the LCRB for contributing areas in the range of ∼ 103 to 104 km2. The FMAC method retains the power of the FEC method for constraining flood hazards in basins that are ungauged or have short flood records, yet it has the added advantage that it includes recurrence-interval information necessary for estimating event probabilities.

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Orem, C. A., et J. D. Pelletier. « Constraining frequency-magnitude-area relationships for precipitation and flood discharges using radar-derived precipitation estimates : example applications in the Upper and Lower Colorado River Basins, USA ». Hydrology and Earth System Sciences Discussions 12, n^o 11 (10 novembre 2015) : 11739–82. http://dx.doi.org/10.5194/hessd-12-11739-2015.

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Abstract. Flood-envelope curves (FEC) are useful for constraining the upper limit of possible flood discharges within drainage basins in a particular hydroclimatic region. Their usefulness, however, is limited by their lack of a well-defined recurrence interval. In this study we use radar-derived precipitation estimates to develop an alternative to the FEC method, i.e. the frequency-magnitude-area-curve (FMAC) method, that incorporates recurrence intervals. The FMAC method is demonstrated in two well-studied U.S. drainage basins, i.e. the Upper and Lower Colorado River basins (UCRB and LCRB, respectively), using Stage III Next-Generation-Radar (NEXRAD) gridded products and the diffusion-wave flow-routing algorithm. The FMAC method can be applied worldwide using any radar-derived precipitation estimates. In the FMAC method, idealized basins of similar contributing area are grouped together for frequency-magnitude analysis of precipitation intensity. These data are then routed through the idealized drainage basins of different contributing areas, using contributing-area-specific estimates for channel slope and channel width. Our results show that FMACs of precipitation discharge are power-law functions of contributing area with an average exponent of 0.79 ± 0.07 for recurrence intervals from 10 to 500 years. We compare our FMACs to published FECs and find that for wet antecedent-moisture conditions, the 500-year FMAC of flood discharge in the UCRB is on par with the US FEC for contributing areas of ~ 102 to 103 km2. FMACs of flood discharge for the LCRB exceed the published FEC for the LCRB for contributing areas in the range of ~ 102 to 104 km2. The FMAC method retains the power of the FEC method for constraining flood hazards in basins that are ungauged or have short flood records, yet it has the added advantage that it includes recurrence interval information necessary for estimating event probabilities.

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JI, XU, et ERKAN OTERKUS. « Physical mechanism of ice/structure interaction ». Journal of Glaciology 64, n^o 244 (28 février 2018) : 197–207. http://dx.doi.org/10.1017/jog.2018.5.

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ABSTRACTTo obtain the effect of velocity and structural natural frequency (structural stiffness) on ice failure, an extended dynamic Van der Pol-based single degree-of-freedom ice/structure interaction model is developed. Three basic modes of response were reproduced: intermittent crushing, frequency lock-in and continuous crushing. Further analysis on the physical mechanism of ice/structure interaction is presented on the basis of feedback mechanism and energy mechanism, respectively. Internal effect and external effect from ice and structure were both explained in the feedback branch. Based on reproduced results, energy exchanges at different configurations are computed from the energy conservation using the first law of thermodynamics. A general conclusion on the predominant type of vibration when the ice velocity increases during the interaction process is forced, self-excited and forced in each of the three modes of responses. Ice force variations also show that there is more impulse energy during the lock-in range. Moreover, ice-induced vibration demonstrates an analogy of friction-induced self-excited vibration. Finally, the similarity between strain-stress curve and Stribeck curve shows that static and kinetic friction force variations are attributed to ice force characteristic, and can be used to explain the lower effective pressure magnitude during continuous crushing than the peak pressure during intermittent crushing.

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Ortega, J. A., et G. Garzón. « A contribution to improved flood magnitude estimation in base of palaeoflood record and climatic implications – Guadiana River (Iberian Peninsula) ». Natural Hazards and Earth System Sciences 9, n^o 1 (26 février 2009) : 229–39. http://dx.doi.org/10.5194/nhess-9-229-2009.

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Abstract. The Guadiana River has a significant record of historical floods, but the systematic data record is only 59 years. From layers left by ancient floods we know about we can add new data to the record, and we can estimate maximum discharges of other floods only known by the moment of occurrence and by the damages caused. A hydraulic model has been performed in the area of Pulo de Lobo and calibrated by means of the rating curve of Pulo do Lobo Station. The palaeofloods have been dated by means of 14C y 137Cs. As non-systematic information has been used in order to calculate distribution functions, the quantiles have changed with respect to the same function when using systematic information. The results show a variation in the curves that can be blamed on the human transformations responsible for changing the hydrologic conditions as well as on the latest climate changes. High magnitude floods are related to cold periods, especially at transitional moments of change from cold to warm periods. This tendency has changed from the last medium-high magnitude flood, which took place in a systematic period. Both reasons seem to justify a change in the frequency curves indicating a recent decrease in the return period of big floods over 8000 m3 s−1. The palaeofloods indicate a bigger return period for the same water level discharge thus showing the river basin reference values in its natural condition previous to the transformation of the basin caused by anthropic action.

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Zhu, Kaiguang, Zining Yu, Chengquan Chi, Mengxuan Fan et Kaiyan Li. « Negentropy anomaly analysis of the borehole strain associated with the <i>M</i><sub>s</sub> ; 8.0 Wenchuan earthquake ». Nonlinear Processes in Geophysics 26, n^o 4 (23 octobre 2019) : 371–80. http://dx.doi.org/10.5194/npg-26-371-2019.

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Abstract. A large earthquake of 8.0 magnitude occurred on 12 May 2008, 14:28 UTC, with the epicentre in Wenchuan. To investigate the pre-earthquake anomalous strain changes, negentropy is introduced to borehole strain data for three locations, approximated by skewness and kurtosis, revealing the non-Gaussianity of recorded fluctuations. We separate the negentropy anomalies from the background by Otsu's method and accumulate the anomaly frequency on different scales. The results show that the long-term cumulative frequency of negentropy anomalies follows a sigmoid behaviour, while the inflection point of the fitting curve is close to the occurrence of the earthquake. For the short-term analysis before the earthquake, there are two cumulative acceleration phases. To further verify the correlation with the earthquake, we compare our findings for different time periods and stations and rule out the possible influence of meteorological factors. We consider the negentropy analysis to exhibit potential for studying pre-earthquake anomalies.

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Herrera, Michael A., Istvan Szunyogh et Joseph Tribbia. « Forecast Uncertainty Dynamics in the THORPEX Interactive Grand Global Ensemble (TIGGE) ». Monthly Weather Review 144, n^o 7 (1 juillet 2016) : 2739–66. http://dx.doi.org/10.1175/mwr-d-15-0293.1.

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Abstract This paper employs local linear, spatial spectral, and Lorenz curve–based diagnostics to investigate the dynamics of uncertainty in global numerical weather forecasts in the NH extratropics. The diagnostics are applied to ensembles in the THORPEX Interactive Grand Global Ensemble (TIGGE). The initial growth of uncertainty is found to be the fastest at the synoptic scales (zonal wavenumbers 7–9) most sensitive to baroclinic instability. At later forecast times, the saturation of uncertainties at the synoptic scales and the longer sustainable growth of uncertainty at the large scales lead to a gradual shift of the wavenumber of the dominant uncertainty toward zonal wavenumber 5. At the subsynoptic scales, errors saturate as predicted by Lorenz’s classic theory. While the ensembles capture the general characteristics of the uncertainty dynamics efficiently, there are locations where the predicted magnitude and structure of uncertainty have considerable time-mean errors. In addition, the magnitude of systematic errors in the prediction of the uncertainty increases with increasing forecast time. These growing systematic errors are dominated by errors in the prediction of low-frequency changes in the large-scale flow.

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Ibenbrahim, Aomar, James Ni, Stephen Salyards et Inayat M. Ali. « Induced Seismicity of The Tarbela Reservoir, Pakistan ». Seismological Research Letters 60, n^o 4 (1 octobre 1989) : 185–97. http://dx.doi.org/10.1785/gssrl.60.4.185.

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Abstract Earthquakes with local magnitudes from 0.0 to 4.9 recorded by the Tarbela seismic network, in Pakistan, between 1973 and 1982 have been used to study the reservoir-induced seismicity. A comparison between the pre-impounding and the post-impounding seismicity shows a dramatic decrease in the latter. The sharp decrease in seismicity is not related to the reservoir filling since it started two months before the first impounding and affected a very large area extending more than 100 km away from the reservoir. Statistical analyses of the distributions of earthquakes that occurred within the 20-km radial zone centered on the reservoir indicate that earthquakes in the magnitude range 0.0–1.9 are not randomly distributed in time, while larger events (2≤ML <5 ) have a random temporal distribution. Further analysis of the occurrence of larger magnitude earthquakes indicates that there is no simple relationship between their occurrence and the reservoir loading. On the other hand the cross-correlation of the frequency of non-random small-sized events in a 20-km radial zone with the monthly reservoir water level shows that there is a 160-day lag between the two time-series. This time lag, equivalent to a 180° phase shift between the water level curve and the event curve, indicates that the frequency of microearthquakes is reduced when the reservoir level is at high stand and vice-versa. An elastic model consisting of a two-dimensional rectangular load predicts that the effect of reservoir loading alone is to suppress the pre-existing seismicity directly beneath the Tarbela reservoir, while the effect of unloading the reservoir is to lead to a partial recovery of seismicity. The positive correlation between the frequency of earthquakes and the low reservoir water level could be explained mostly by the elastic effects of reservoir unloading. A gradual increase in the seismicity in regions as far as 100 km from the reservoir started in 1979 (five years after the first reservoir filling) and appears not to be a consequence of the slow diffusion of water to hypocentral depths; rather it reflects the long-term behavior of seismicity in the Pakistan Himalayas.

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