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1
Chaplin, W. J., Y. Elsworth, G. R. Isaak, C. P. McLeod, B. A. Miller e R. New. "A Search for ℓ = 2 Asymmetries in Bison Data". Symposium - International Astronomical Union 185 (1998): 169–70. http://dx.doi.org/10.1017/s0074180900238527.
Testo completoAbstract (sommario):
An in-depth discussion of the analysis presented here can be found in an up-coming paper (Chaplin et al., 1997).The presence of a magnetic field will raise the degeneracy in ℓ of the resonant p-mode oscillations, via perturbations resulting from the Lorentz force. These degeneracyraising effects will give rise to asymmetric mode-multiplet structures. Both Gough & Thompson (1990). and Dziembowski & Goode (1997) have addressed the implications and potential complications that might result from such phenomena. Here, in an attempt to reveal the presence of an asymmetric frequency structure in the low-degree ℓ = 2 modes, i.e. to measure the asymmetries
2
Philidet, J., K. Belkacem, H. G. Ludwig, R. Samadi e C. Barban. "Velocity-intensity asymmetry reversal of solar radial p-modes". Astronomy & Astrophysics 644 (dicembre 2020): A171. http://dx.doi.org/10.1051/0004-6361/202038222.
Testo completoAbstract (sommario):
The development of space-borne missions has significantly improved the quality of the measured spectra of solar-like oscillators. Their p-mode line profiles can now be resolved, and the asymmetries inferred for a variety of stars other than the Sun. However, it has been known for a long time that the asymmetries of solar p-modes are reversed between the velocity and the intensity spectra. Understanding the origin of this reversal is necessary in order to use asymmetries as a tool for seismic diagnosis. For stars other than the Sun, only the intensity power spectrum is sufficiently resolved to allow for an estimation of mode asymmetries. We recently developed an approach designed to model and predict these asymmetries in the velocity power spectrum of the Sun and to successfully compare them to their observationally derived counterpart. In this paper we expand our model and predict the asymmetries featured in the intensity power spectrum. We find that the shape of the mode line profiles in intensity is largely dependent on how the oscillation-induced variations of the radiative flux are treated, and that modelling it realistically is crucial to understanding asymmetry reversal. Perturbing a solar-calibrated grey atmosphere model, and adopting the quasi-adiabatic framework as a first step, we reproduce the asymmetries observed in the solar intensity spectrum for low-frequency modes. We conclude that, unlike previously thought, it is not necessary to invoke an additional mechanism (e.g. non-adiabatic effects, coherent non-resonant background signal) to explain asymmetry reversal. This additional mechanism is necessary, however, to explain asymmetry reversal for higher-order modes.
3
Regan, Marc A., e Krishnan Mahesh. "Adjoint sensitivity and optimal perturbations of the low-speed jet in cross-flow". Journal of Fluid Mechanics 877 (22 agosto 2019): 330–72. http://dx.doi.org/10.1017/jfm.2019.582.
Testo completoAbstract (sommario):
The tri-global stability and sensitivity of the low-speed jet in cross-flow are studied using the adjoint equations and finite-time horizon optimal disturbance analysis at Reynolds number $Re=2000$, based on the average velocity at the jet exit, the jet nozzle exit diameter and the kinematic viscosity of the jet, for two jet-to-cross-flow velocity ratios $R=2$ and $4$. A novel capability is developed on unstructured grids and parallel platforms for this purpose. Asymmetric modes are more important to the overall dynamics at $R=4$, suggesting increased sensitivity to experimental asymmetries at higher $R$. Low-frequency modes show a connection to wake vortices. Adjoint modes show that the upstream shear layer is most sensitive to perturbations along the upstream side of the jet nozzle. Lower frequency downstream modes are sensitive in the cross-flow boundary layer. For $R=2$, optimal analysis reveals that for short time horizons, asymmetric perturbations dominate and grow along the counter-rotating vortex pair observed in the cross-section. However, as the time horizon increases, large transient growth is observed along the upstream shear layer. When $R=4$, the optimal perturbations for short time scales grow along the downstream shear layer. For long time horizons, they become hybrid modes that grow along both the upstream and downstream shear layers.
4
Deheuvels, S., R. M. Ouazzani e S. Basu. "Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants". Astronomy & Astrophysics 605 (settembre 2017): A75. http://dx.doi.org/10.1051/0004-6361/201730786.
Testo completoAbstract (sommario):
Context. The Kepler space mission has made it possible to measure the rotational splittings of mixed modes in red giants, thereby providing an unprecedented opportunity to probe the internal rotation of these stars. Aims. Asymmetries have been detected in the rotational multiplets of several red giants. This is unexpected since all the red giants whose rotation profiles have been measured thus far are found to rotate slowly, and low rotation, in principle, produces symmetrical multiplets. Our aim here is to explain these asymmetries and find a way of exploiting them to probe the internal rotation of red giants. Methods. We show that in the cases where asymmetrical multiplets were detected, near-degeneracy effects are expected to occur, because of the combined effects of rotation and mode mixing. Such effects have not been taken into account so far. By using both perturbative and non-perturbative approaches, we show that near-degeneracy effects produce multiplet asymmetries that are very similar to the observations. We then propose and validate a method based on the perturbative approach to probe the internal rotation of red giants using multiplet asymmetries. Results. We successfully apply our method to the asymmetrical l = 2 multiplets of the Kepler young red giant KIC 7341231 and obtain precise estimates of its mean rotation in the core and the envelope. The observed asymmetries are reproduced with a good statistical agreement, which confirms that near-degeneracy effects are very likely the cause of the detected multiplet asymmetries. Conclusions. We expect near-degeneracy effects to be important for l = 2 mixed modes all along the red giant branch (RGB). For l = 1 modes, these effects can be neglected only at the base of the RGB. They must therefore be taken into account when interpreting rotational splittings and as shown here, they can bring valuable information about the internal rotation of red giants.
5
Wilcox, R. S., L. R. Baylor, A. Bortolon, M. Knolker, C. J. Lasnier, D. Shiraki, I. Bykov et al. "Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D". Nuclear Fusion 62, n. 2 (22 dicembre 2021): 026017. http://dx.doi.org/10.1088/1741-4326/ac3b8b.
Testo completoAbstract (sommario):
Abstract Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25%–50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.
6
Woo, K. M., R. Betti, C. A. Thomas, C. Stoeckl, K. Churnetski, C. J. Forrest, Z. L. Mohamed et al. "Analysis of core asymmetries in inertial confinement fusion implosions using three-dimensional hot-spot reconstruction". Physics of Plasmas 29, n. 8 (agosto 2022): 082705. http://dx.doi.org/10.1063/5.0102167.
Testo completoAbstract (sommario):
Three-dimensional effects play a crucial role during the hot-spot formation in inertial confinement fusion (ICF) implosions. A data analysis technique for 3D hot-spot reconstruction from experimental observables has been developed to characterize the effects of low modes on 3D hot-spot formations. In nuclear measurements, the effective flow direction, governed by the maximum eigenvalue in the velocity variance of apparent ion temperatures, has been found to agree with the measured hot-spot flows for implosions dominated by mode [Formula: see text]. Asymmetries in areal-density ( ρR) measurements were found to be characterized by a unique cosine variation along the hot-spot flow axis. In x-ray images, a 3D hot-spot x-ray emission tomography method was developed to reconstruct the 3D hot-spot plasma emissivity using a generalized spherical-harmonic Gaussian function. The gradient-descent algorithm was used to optimize the mapping between the projections from the 3D hot-spot emission model and the measured x-ray images along multiple views. This work establishes a platform to analyze 3D low-mode core asymmetries in ICF.
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Bugnet, L., V. Prat, S. Mathis, A. Astoul, K. Augustson, R. A. García, S. Mathur, L. Amard e C. Neiner. "Magnetic signatures on mixed-mode frequencies". Astronomy & Astrophysics 650 (giugno 2021): A53. http://dx.doi.org/10.1051/0004-6361/202039159.
Testo completoAbstract (sommario):
Context. The discovery of moderate differential rotation between the core and the envelope of evolved solar-like stars could be the signature of a strong magnetic field trapped inside the radiative interior. The population of intermediate-mass red giants presenting surprisingly low-amplitude mixed modes (i.e. oscillation modes that behave as acoustic modes in their external envelope and as gravity modes in their core) could also arise from the effect of an internal magnetic field. Indeed, stars more massive than about 1.1 solar masses are known to develop a convective core during their main sequence. The field generated by the dynamo triggered by this convection could be the progenitor of a strong fossil magnetic field trapped inside the core of the star for the remainder of its evolution. Aims. Observations of mixed modes can constitute an excellent probe of the deepest layers of evolved solar-like stars, and magnetic fields in those regions can impact their propagation. The magnetic perturbation on mixed modes may therefore be visible in asteroseismic data. To unravel which constraints can be obtained from observations, we theoretically investigate the effects of a plausible mixed axisymmetric magnetic field with various amplitudes on the mixed-mode frequencies of evolved solar-like stars. Methods. First-order frequency perturbations due to an axisymmetric magnetic field were computed for dipolar and quadrupolar mixed modes. These computations were carried out for a range of stellar ages, masses, and metallicities. Conclusions. We show that typical fossil-field strengths of 0.1 − 1 MG, consistent with the presence of a dynamo in the convective core during the main sequence, provoke significant asymmetries on mixed-mode frequency multiplets during the red giant branch. We provide constraints and methods for the detectability of such magnetic signatures. We show that these signatures may be detectable in asteroseismic data for field amplitudes small enough for the amplitude of the modes not to be affected by the conversion of gravity into Alfvén waves inside the magnetised interior. Finally, we infer an upper limit for the strength of the field and the associated lower limit for the timescale of its action in order to redistribute angular momentum in stellar interiors.
8
Alexander, D. E. "Wind tunnel studies of turns by flying dragonflies". Journal of Experimental Biology 122, n. 1 (1 maggio 1986): 81–98. http://dx.doi.org/10.1242/jeb.122.1.81.
Testo completoAbstract (sommario):
High-speed movies of dragonflies turning in flight on flexible tethers show that there are two distinct modes of turning. In the ‘conventional’ mode, dragonflies use left-right asymmetries in the wing stroke amplitude, and occasionally in the angle of attack, to produce more lift and thrust on one side than the other. This causes the animal to roll into a bank, so that the lift vector has a sideward component; this sideward component produces the turn, much as in an airplane. This type of turn is probably most useful during fast forward flight. The second mode of turning in the ‘yaw turn’. Yaw turns are accomplished without banking, and the dragonfly's long axis may turn more than 90 degrees in the period of two wing strokes. The kinematics of this turn could not be as closely analysed, but it appears that dragonflies use drag on the inner wing upstroke and the outer wing downstroke to turn, much like pivoting a rowing boat. This turn may be hampered by drag on the abdomen during fast forward flight and would be most useful at low speeds or during hovering.
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CAZACU, Emil, e Lucian PETRESCU. "ASPECTE CALITATIVE ȘI CANTITATIVE ALE FENOMENUL DE FEROREZONANȚĂ ÎN INSTALAȚIILE ELECTRICE DE JOASĂ TENSIUNE". "ACTUALITĂŢI ŞI PERSPECTIVE ÎN DOMENIUL MAŞINILOR ELECTRICE (ELECTRIC MACHINES, MATERIALS AND DRIVES - PRESENT AND TRENDS)" 2020, n. 1 (10 febbraio 2021): 1–14. http://dx.doi.org/10.36801/apme.2020.1.8.
Testo completoAbstract (sommario):
The phenomenon of ferroresonance is generated by the interaction between nonlinear magnetic devices and capacitive elements in an electrical installation in which losses are reduced and which are constantly supplied by at least one energy source. Feroresonance is manifested by the appearance of overvoltages and overcurrents in the installation with strongly distorted waveforms. Also, the phenomenon is accompanied by other disturbances of the quality of electricity (voltage fluctuations, asymmetries, noise, etc.), which propagate in the network affecting the proper functioning of the entire installation. In addition, unlike linear resonance, ferroresonance allows the manifestation of several stable states (modes) for the same parameters of the network, these being imposed by the initial conditions in the installation and the moment of occurrence of the phenomenon. Thus, the vulnerability to low resonance of a low voltage installation has become an indicator of electricity quality. This paper presents a procedure for calculating and investigating this phenomenon based on the analysis of numerical solutions of systems of differential equations (nonlinear and non-autonomous), which models the transient phenomena that initiate the appearance of ferroresonance (usually switching processes). Also, modern means of investigation are used (3D visualizations in the phase plan or Poincaré diagrams), imposed by the difficulty of the quantitative analysis both in dynamic regime and in stationary regime of ferroresonance. In addition, methods and procedures are proposed to mitigate the effects of the ferroresonance phenomenon on equipment or network elements in electrical distribution installations.
10
Hall, H. G. "Parental analysis of introgressive hybridization between African and European honeybees using nuclear DNA RFLPs." Genetics 125, n. 3 (1 luglio 1990): 611–21. http://dx.doi.org/10.1093/genetics/125.3.611.
Testo completoAbstract (sommario):
Abstract African honeybees, introduced into Brazil 33 years ago, have spread through most of South and Central America and have largely replaced the extant European bees. Due to a paucity of genetic markers, genetic interactions between European and African bees are not well understood. Three restriction fragment length polymorphisms (RFLPs), detected with random, nuclear DNA probes, are described. The polymorphisms are specific to bees of European descent, possibly specific to certain European races. Each European marker was found present at a high frequency in U.S. colonies but absent in South African bees. Previous mitochondrial DNA studies of neotropical bees have revealed negligible maternal gene flow from managed European apiaries into feral African populations. The findings reported here with nuclear DNA show paternal gene flow between the two but suggest asymmetries in levels of introgressive hybridization. Managed colonies in southern Mexico, derived from European maternal lines, showed diminished levels of the European nuclear markers, reflecting significant hybridization with African drones. The European alleles were present only at low frequencies in feral swarms from the same area. The swarms were of African maternal descent. In Venezuelan colonies, also derived from African maternal lines, the European markers were almost totally absent. The results point to limited paternal introgression from European colonies into the African honeybee populations. These findings dispute other views regarding modes of Africanization.
11
Churnetski, K., K. M. Woo, W. Theobald, P. B. Radha, R. Betti, V. Gopalaswamy, I. V. Igumenshchev et al. "Three-dimensional hot-spot x-ray emission tomography from cryogenic deuterium–tritium direct-drive implosions on OMEGA". Review of Scientific Instruments 93, n. 9 (1 settembre 2022): 093530. http://dx.doi.org/10.1063/5.0098977.
Testo completoAbstract (sommario):
A three-dimensional model of the hot-spot x-ray emission has been developed and applied to the study of low-mode drive asymmetries in direct-drive inertial confinement fusion implosions on OMEGA with cryogenic deuterium–tritium targets. The steady-state model assumes an optically thin plasma and the data from four x-ray diagnostics along quasi-orthogonal lines of sight are used to obtain a tomographic reconstruction of the hot spot. A quantitative analysis of the hot-spot shape is achieved by projecting the x-ray emission into the diagnostic planes and comparing this projection to the measurements. The model was validated with radiation-hydrodynamic simulations assuming a mode-2 laser illumination perturbation resulting in an elliptically shaped hot spot, which was accurately reconstructed by the model using synthetic x-ray images. This technique was applied to experimental data from implosions in polar-direct-drive illumination geometry with a deliberate laser-drive asymmetry, and the hot-spot emission was reconstructed using spherical-harmonic modes of up to ℓ = 3. A 10% stronger drive on the equator relative to that on the poles resulted in a prolate-shaped hot spot at stagnation with a large negative A2,0 coefficient of A2,0 = −0.47 ± 0.03, directly connecting the modal contribution of the hot-spot shape with the modal contribution in laser-drive asymmetry.
12
Lettry, J., A. Vnuchenko, S. Bertolo, C. Mastrostefano, M. O'Neil, F. di Lorenzo, Y. Coutron et al. "Correlation of H- beam properties to Cs-coverage". Journal of Instrumentation 18, n. 06 (1 giugno 2023): C06023. http://dx.doi.org/10.1088/1748-0221/18/06/c06023.
Testo completoAbstract (sommario):
Abstract A caesiated RF driven source delivers H- ions that, after stripping at the end of the 160 MeV H- linear injector, provides protons to CERN's accelerator complex including LHC, where the protons reached a record energy of 6.8 TeV. In Caesiated RF sources, H- ions are produced via dissociative attachment of electrons onto roto-vibrationally excited H2-molecules (volume) and re-emission as negative ions of protons or hydrogen atoms colliding on a low work function caesiated molybdenum plasma electrode (surface). During initial caesiation, the production mechanism evolves from the initial Cs-free volume production to a predominant surface production mode; the observed stunning reduction of co-extracted electrons is concomitant to an increase of the H- ion current to RF-power yield. This paper describes the evolution of the beam-profile at today's operational beam intensities of 35 mA for various ratios of volume and surface ion-origin. The presence of surface produced ions occurring on a conical plane is characterized by the electron to ion ratio and by measurement of the Cs-coverage of the molybdenum plasma electrode down to a fraction of a monolayer. Angular distributions are extracted from beam profile and Beam Emission Spectroscopy (BES) measurements. These experimental results provide an initial comparison to beam formation simulation that, at a later stage, could be coupled to beam transport software packages. The paper focuses on the caaesiation transient to present experimental evidence for 3D beam formation studies, it provides insight into the mixing of volume and surface production modes, reduction of co-extracted electrons and Cs-coverage. The paper also establishes magnetic field induced asymmetries in the beam's current density.
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Singh, A. K., A. K. Sinha, R. Rajaram e B. M. Pathan. "Storm-time longitudinally propagating asymmetric modes at low latitudes". Annales Geophysicae 30, n. 1 (13 gennaio 2012): 131–41. http://dx.doi.org/10.5194/angeo-30-131-2012.
Testo completoAbstract (sommario):
Abstract. The westward flowing toroidal ring current at about 2–7 RE in the Earth's equatorial plane consists of symmetric and asymmetric parts. Zonal mean of H disturbances from longitudinally distributed low latitude stations represents the symmetric contribution, whereas departure from the zonal mean gives local time dependent asymmetric component at each of the stations. Through a standard analysis of closely spaced low latitude geomagnetic data we demonstrate 24 h periodicity in the asymmetric component of the storm-time ring current, which is related to the changing local time due to rotation of the Earth. Detailed examination of shorter period oscillations, when observed globally, often show westward propagating modes. Eastward propagating mode was also observed in one case. Based on satellite and radar observations covering a narrow longitude region, westward and eastward propagating modes had been reported in earlier studies. In this study, we report that similar propagating modes which are available on global scale, can be identified using ground-based magnetometer data. These globally propagating modes, observed from ground-based studies, find obvious practical application in diagnostics of the magnetosphere, especially the ring current region. Simultaneous use of satellite and ground-based data should establish the morphology of such modes.
14
Giovannettone, Jason P., e Ana P. Barros. "A Remote Sensing Survey of the Role of Landform on the Organization of Orographic Precipitation in Central and Southern Mexico". Journal of Hydrometeorology 9, n. 6 (1 dicembre 2008): 1267–83. http://dx.doi.org/10.1175/2008jhm947.1.
Testo completoAbstract (sommario):
Abstract Data from NASA’s TRMM satellite and NOAA’s GOES satellites were used to survey the orographic organization of cloud precipitation in central and southern Mexico during the monsoon with two main objectives: 1) to investigate large-scale forcing versus local landform controls, and 2) to compare the results with previous work in the Himalayas. At large scales, the modes of spatial variability of cloudiness were estimated using the empirical orthogonal function (EOF) analysis of GOES brightness temperatures. Terrain modulation of synoptic-scale high-frequency variability (3–5- and 6–9-day cycles normally associated with the propagation of easterly waves) was found to cause higher dispersion in the EOF spectrum, with the first mode explaining less than 30% of the spatial variability in central and southern Mexico as opposed to 50% and higher in the Himalayas. A detailed analysis of the first three EOFs for 1999, an average La Niña year with above average rainfall, and for 2001, a weak La Niña year with below average rainfall, shows that landform (mountain peaks and land–ocean contrast) and large-scale circulation (moisture convergence) alternate as the key controls of regional hydrometeorology in dry and wet years, or as active and break (midsummer drought) phases of the monsoon, respectively. The diurnal cycle is the dominant time scale of variability in 2001, as it is during the midsummer drought in all years. Strong variability at time scales beyond two weeks is only present during the active phases of the monsoon. At the river basin scale, the data show increased cloudiness over the mountain ranges during the afternoon, which moves over the low-lying regions at the foot of the major orographic barriers [the Sierra Madre Occidental (SMO)/Sierra Madre del Sur (SMS) and Trans-Mexican Volcanic Belt (TMVB)], specifically the Balsas and the Rio de Santiago basins at nighttime and in the early morning. At the ridge–valley scale (∼100–200 km), robust day–night (ridge–valley) asymmetries suggest strong local controls on cloud and precipitation, with convective activity along the coastal region of the SMO and topographically forced convection at the foothills of headwater ridges in the Altiplano and the SMS. These day–night spatial shifts in cloudiness and precipitation are similar to those found in the Himalayas at the same spatial scales.
15
Yang, Fuxiang, Fangchao Dang, Xingjun Ge, Juntao He, Jinchuan Ju e Xiaoping Zhang. "Excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier with cascaded single-gap bunching cavities". AIP Advances 12, n. 11 (1 novembre 2022): 115219. http://dx.doi.org/10.1063/5.0112068.
Testo completoAbstract (sommario):
The excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier (RKA) with cascaded single-gap bunching cavities are analyzed in this paper. Through theoretical analysis and simulated verification, we find that the asymmetric modes of cascaded single-gap bunching cavities have low external quality factors, the same resonant frequencies, and negative beam-loading conductance ratios so that they are easily excited by the electron beam. To solve this issue, a feasible method is proposed in this paper to suppress the asymmetric modes of cascaded single-gap bunching cavities, under the conditions of decreasing their coupling coefficients and increasing the frequency separation, choosing an appropriate drift tube length between them. These improved bunching cavities are further examined in an X-band coaxial RKA by 3D particle-in-cell simulation, which shows that high power microwaves with a power of 0.8 GW are generated corresponding to an efficiency of 40%. Furthermore, there is no asymmetric mode competition during 150 ns of simulation time.
16
Moënne-Loccoz, Victor, Isabelle Trébinjac, Nicolas Poujol e Pierre Duquesne. "Low frequency stall modes of a radial vaned diffuser flow". Mechanics & Industry 20, n. 8 (2019): 805. http://dx.doi.org/10.1051/meca/2020026.
Testo completoAbstract (sommario):
The present paper aims at providing an experimental analysis of the path to surge of a centrifugal compressor stage designed and built by Safran Helicopter Engines. Depending on the rotation speed of the compressor, two distinct flow patterns are observed in the radial diffuser at stabilized operating points near the surge, an asymmetric and a symmetric pattern. At medium rotation speed, the alternate pattern consisting of a two-channel pattern in the radial diffuser develops. One passage over two is stalled, the adjacent passage is free and this pattern replicates over the whole circumference while pulsing at a frequency of roughly 12 Hz which is close to the Helmholtz frequency of the test rig. By lowering the rotation speed, the two-channel pattern fades away and gives way to a periodical behavior of the radial diffuser passages called symmetric mode. The flow in each channel is identical presenting a stalled behavior pulsating in phase at a higher frequency of roughly 42 Hz. The two 12 Hz and 42 Hz modes are described and their existences are imputed to a lock-in of the natural frequencies of the instabilities with the acoustic modes of the test rig.
17
CHANG, NGEE-PONG, DA-XI LI e J. PÉREZ MERCADER. "ON THE ZERO COSMOLOGICAL CONSTANT SUGRA AND THE ASYMMETRIC ORBIFOLD". International Journal of Modern Physics A 04, n. 02 (gennaio 1989): 287–326. http://dx.doi.org/10.1142/s0217751x89000121.
Testo completoAbstract (sommario):
In this paper, we give a brief review of the orbifold compactification of Superstrings and describe how the spectrum of zero-modes determines the structure of the 'low'-energy compactified theory. We show how the asymmetric orbifold can lead to a 'low'-energy N = 1 SUGRA theory that continues to have a zero cosmological constant even after supersymmetry is broken. We discuss the implications the asymmetric orbifold can have for a new scenario of the hierarchy of compactification scales.
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Wang, Zhi Hong, Dong Yan Xie, Bao He Yuan, Xian Sheng Liu, Wen Bo Song, Bin Yuan e Er Jun Liang. "Synthesis, Thermal Expansion Properties and Raman Spectroscopic Study of Ca1-xSrxZr4P6O24 Ceramics". Advanced Materials Research 415-417 (dicembre 2011): 1023–27. http://dx.doi.org/10.4028/www.scientific.net/amr.415-417.1023.
Testo completoAbstract (sommario):
A simplified method with much lower time and energy costs is presented for the rapid synthesis of low thermal expansion materials of CaZr4P6O24, SrZr4P6O24 and their solid solution Ca0.5Sr0.5Zr4P6O24. The coefficients of thermal expansion of CaZr4P6O24, SrZr4P6O24 and Ca0.5Sr0.5Zr4P6O24 are measured to be -1.45×10-6, 2.1×10-6 and 0.26×10-6, respectively. Raman spectroscopic study confirms the formation of the solid solution of Ca0.5Sr0.5Zr4P6O24 though its symmetric and asymmetric stretching modes are obviously broadened with respect to those of CaZr4P6O24 and SrZr4P6O24 due to the lattice deformation by incorporation of Ca2+ and Sr2+ with different cation size. The shifts of the asymmetric stretching Raman modes and the librational/translational modes with temperature in Ca0.5Sr0.5Zr4P6O24 are between those in CaZr4P6O24 and SrZr4P6O24, suggesting a cancelling effect of Ca2+ and Sr2+ cations in the thermal expansion of Ca0.5Sr0.5Zr4P6O24.
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Kholiddinov, I. Kh, G. F. Musinova, M. E. Yulchiev, Z. Z. Tuychiev e M. M. Kholiddinova. "Modeling Of Calculation Of Voltage Unbalance Factor Using Simulink (Matlab)". American Journal of Engineering And Techonology 02, n. 10 (31 ottobre 2020): 33–37. http://dx.doi.org/10.37547/tajet/volume02issue10-07.
Testo completoAbstract (sommario):
This paper presents the problem of power quality in asymmetric modes in low-voltage electrical networks. The modeling of determination of power value, voltages and currents and, accordingly, their symmetric components, using the Simulink package in the MatLab program is shown.
20
Mousa, Hana Mohammed. "Simulation of An Asymmetric TM Metamaterial Waveguide Absorber". JOURNAL OF ADVANCES IN PHYSICS 4, n. 3 (26 giugno 2014): 585–94. http://dx.doi.org/10.24297/jap.v4i3.2013.
Testo completoAbstract (sommario):
This paper tackles the simulation of an asymmetric  TM mode absorption  in a lossy metamaterial (left-handed) slab (LHM) sandwiched between a lossy substrate and coverd by a losseless dielectric cladding. The asymmetry solutions of the eigen value equation describe lossy –guided modes with complex –valued propagation constants . The dispersion relations , normalized field and the longitudinal attenuation were numerically solved for a given set of parameters: frequency range; film’s thicknesses; and TM mode order. I found out that high order modes which are guided in thinner films are generally have more loss of power than low-order modes since the mode attenuation along z-axis increases to negative values by the mode's order increase and the film thickness decrease . Moreover,  LHM , at incident wavelength =1.9, refractive index=and at thickness ,   guides the power better than RHM or metal one. This LHM  is appropriate for solar cell applications. For arbitrary LHM, at frequency band of wavelengt(600, 700 to 1200 )nm,  the best absorption is attained at longer wavelengths and for lower order modes at wider films.
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Bichurin, Mirza, Oleg Sokolov, Sergey Ivanov, Viktor Leontiev, Dmitriy Petrov, Gennady Semenov e Vyacheslav Lobekin. "Physics of Composites for Low-Frequency Magnetoelectric Devices". Sensors 22, n. 13 (25 giugno 2022): 4818. http://dx.doi.org/10.3390/s22134818.
Testo completoAbstract (sommario):
The article discusses the physical foundations of the application of the linear magnetoelectric (ME) effect in composites for devices in the low-frequency range, including the electromechanical resonance (EMR) region. The main theoretical expressions for the ME voltage coefficients in the case of a symmetric and asymmetric composite structure in the quasi-static and resonant modes are given. The area of EMR considered here includes longitudinal, bending, longitudinal shear, and torsional modes. Explanations are given for finding the main resonant frequencies of the modes under study. Comparison of theory and experimental results for some composites is given.
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Nolasco, Mariela M., Paulo J. A. Ribeiro-Claro e Pedro D. Vaz. "Vibrational Dynamics in crystalline 4-(dimethylamino) benzaldehyde: Inelastic Neutron Scattering and Periodic DFT Study". Materials 15, n. 2 (8 gennaio 2022): 475. http://dx.doi.org/10.3390/ma15020475.
Testo completoAbstract (sommario):
The structure and dynamics of crystalline 4-(dimethylamino) benzaldehyde, 4DMAB, are assessed through INS spectroscopy combined with periodic DFT calculations. The excellent agreement between experimental and calculated spectra is the basis for a reliable assignment of INS bands. The external phonon modes of crystalline 4DMAB are quite well described by the simulated spectrum, as well as the modes involving low-frequency molecular vibrations. Crystal field splitting is predicted and observed for the modes assigned to the dimethylamino group. Concerning the torsional motion of methyl groups, four individual bands are identified and assigned to specific methyl groups in the asymmetric unit. The torsional frequencies of the four methyl groups in the asymmetric unit fall in a region of ca. 190 ± 20 cm−1, close to the range of values observed for methyl groups bonding to unsaturated carbon atoms. The hybridization state of the X atom in X-CH3 seems to play a key role in determining the methyl torsional frequency.
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Dai, Peng, Shuyu Liu, Shiqi Fang e Zheng Gong. "Optimal Asymmetric Duty Modulation for Dual Active Bridge Converters with DC Blocking Capacitors". Energies 16, n. 18 (18 settembre 2023): 6674. http://dx.doi.org/10.3390/en16186674.
Testo completoAbstract (sommario):
Aiming at the optimization of current stress with low voltage ratio and full ZVS, a control method combining variable duty cycle and phase shift was proposed based on dual active bridge (DAB) converters with DC blocking capacitors. By adding DC bias to the DC blocking capacitors, asymmetric duty modulation (ADM) can adjust the bias as needed. Based on the theoretical analysis of steady-state operation, the operating modes can be divided into eight modes. According to the features of each mode, equivalent circuits are established. The transmission power and the boundary of zero-voltage-switching (ZVS) are deduced through a detailed analysis of each mode. Based on the theoretical deduction, ADM is more suitable for a low voltage ratio. Verified by experiment, optimized asymmetric duty modulation (OADM) can increase efficiency by 3.58%, 6.57%, 8.81%, and 10.33% compared with DPS when P is equal to 0.36 and m is equal to 0.4, 0.3, 0.2, and 0.1, respectively. Using this method, the current stress of the converter is lighter than that under regular modulation when the voltage ratio m ≤ 0.5 with full ZVS.
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Bichurin, Mirza, Oleg Sokolov, Sergey Ivanov, Viktor Leontiev, Vyacheslav Lobekin, Gennady Semenov e Yaojin Wang. "Modeling the Converse Magnetoelectric Effect in the Low-Frequency Range". Sensors 24, n. 1 (27 dicembre 2023): 151. http://dx.doi.org/10.3390/s24010151.
Testo completoAbstract (sommario):
This article is devoted to the theory of the converse magnetoelectric (CME) effect for the longitudinal, bending, longitudinal-shear, and torsional resonance modes and its quasi-static regime. In contrast to the direct ME effect (DME), these issues have not been studied in sufficient detail in the literature. However, in a number of cases, in particular in the study of low-frequency ME antennas, the results obtained are of interest. Detailed calculations with examples were carried out for the longitudinal mode on the symmetric and asymmetric structures based on Metglas/PZT (LN); the bending mode was considered for the asymmetric free structure and structure with rigidly fixed left-end Metglas/PZT (LN); the longitudinal-shear and torsional modes were investigated for the symmetric and asymmetric free structures based on Metglas/GaAs. For the identification of the torsion mode, it was suggested to perform an experiment on the ME structure based on Metglas/bimorphic LN. All calculation results are presented in the form of graphs for the CME coefficients.
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Solway, J., T. H. Rossing, A. F. Saari e J. M. Drazen. "Expiratory flow limitation and dynamic pulmonary hyperinflation during high-frequency ventilation". Journal of Applied Physiology 60, n. 6 (1 giugno 1986): 2071–78. http://dx.doi.org/10.1152/jappl.1986.60.6.2071.
Testo completoAbstract (sommario):
Dynamic hyperinflation of the lungs occurs during high-frequency oscillatory ventilation (HFOV) and has been attributed to asymmetry of inspiratory and expiratory impedances. To identify the nature of this asymmetry, we compared changes in lung volume (VL) observed during HFOV in ventilator-dependent patients with predictions of VL changes from electrical analogs of three potential modes of impedance asymmetry. In the patients, when a fixed oscillatory tidal volume was applied at a low mean airway opening pressure (Pao), which resulted in little increase in functional residual capacity, progressively greater dynamic hyperinflation was observed as HFOV frequency, (f) was increased. When mean Pao was raised so that resting VL increased, VL remained at this level during HFOV as f was increased until a critical f was reached; above this value, VL increased further with f in a fashion nearly parallel to that observed when low mean Pao was used. Three modes of asymmetric inspiratory and expiratory impedance were modeled as electrical circuits: 1) fixed asymmetric resistance [Rexp greater than Rinsp]; 2) variable asymmetric resistance [Rexp(VL) greater than Rinsp, with Rexp(VL) decreasing as VL increased]; and 3) equal Rinsp and Rexp, but with superimposed expiratory flow limitation, the latter simulated using a bipolar transistor as a descriptive model of this phenomenon. The fixed and the variable asymmetric resistance models displayed a progressive increase of mean VL with f at either low or high mean Pao. Only the expiratory flow limitation model displayed a dependence of dynamic hyperinflation on mean Pao and f similar to that observed in our patients. We conclude that expiratory flow limitation can account for dynamic pulmonary hyperinflation during HFOV.
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Denisov, V. N., A. A. Zakhidov, R. Danieli, G. Ruani, R. Zamboni, C. Taliani, K. Imaeda, K. Yakushi, H. Inokuchi e Y. Achiba. "EVIDENCE FOR JAHN-TELLER COUPLING AND FANO RESONANCE OF LOWER Hg MODES IN K3C60 AND Rb3C60 FILMS FROM RAMAN SCATTERING". International Journal of Modern Physics B 06, n. 23n24 (dicembre 1992): 4019–24. http://dx.doi.org/10.1142/s0217979292002127.
Testo completoAbstract (sommario):
The Raman scattering study of superconducting thin films of A 3 C 60 (A=K,Rb) carried out upon laser excitations at 1.16 and 2.41 eV have revealed the significant broadening and Fano-lineshapes of several low energy H g intramolecular modes with relative intensities and widths depending on excitation energies. The most interesting feature of the 1.16 eV excited spectrum is the wide asymmetric band at 400 cm −1 which can be assigned by Fano-shape fitting to enormously broadened H g (2) mode red shifted compared to its bare frequency of 408 cm −1. The narrowing of all lower H g modes in insulating A 6 C 60 phase indicates strong electron-phonon coupling of this Jahn-Teller modes in x =3 phase and suggests that this low energy vibrations are contributing to superconducting pairing. However the possibility to interpret the wide band at 400 cm −1 as the maximum of electronic background can not be ruled out yet and is supported by our preliminary observations of its disappearance at low temperature below T c .
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GRANADO-CRIADO, JOSE M., MIGUEL A. VEGA-RODRÍGUEZ, JOSE M. CHAVES-GONZALEZ, JUAN M. SANCHEZ-PEREZ e JUAN A. GOMEZ-PULIDO. "LOW POWER CONSUMPTION SECURITY PLATFORM FOR INDUSTRIAL COMMUNICATIONS USING AN MPSOC". Journal of Circuits, Systems and Computers 22, n. 05 (9 maggio 2013): 1350029. http://dx.doi.org/10.1142/s0218126613500291.
Testo completoAbstract (sommario):
This work presents a novel security platform for industrial communications using a nine-MicroBlaze MPSoC. This platform has low power consumption and cost, therefore, it is very appropriate for embedded systems, where restrictions on cost and power consumption have to be fulfilled. This system uses the RSA asymmetric algorithm combined with the AES symmetric algorithm, which was developed using two encryption modes, ECB and CBC. In this way, the platform makes possible to combine different algorithms and modes in function of the necessities of speed and security required. Furthermore, due to the implementation of standard algorithms (AES and RSA) and modes (ECB and CBC), this platform can be connected to the Internet, and can even use secure protocols as SSL.
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Naumov, Igor V., Sergey V. Podyachikh e Andrey V. Bastron. "The Power Quality Improving and its Losses Reducing with Balancing Devices". IOP Conference Series: Earth and Environmental Science 979, n. 1 (1 febbraio 2022): 012160. http://dx.doi.org/10.1088/1755-1315/979/1/012160.
Testo completoAbstract (sommario):
Abstract The method, algorithms, modeling, calculations and analysis the 0.38 kV electric network operation with unbalancing power consumption are considered. It is noted that the 0.38 kV electric networks, being electric low observability networks, are largely characterized by low power quality, which is accompanied by additional losses. An electric network model with a distributed load is presented. The current and voltage asymmetry indicators calculating method is developed, and the specialized balancing device parameters are determined. Bas ed on the obtained expressions, using Matlab technologies, the calculating asymmetric modes program was developed. The studied indicators were calculated for the created electric network model with symmetric and asymmetric loads. The balancing device influence degree on the quality indicators stabilization and the electrical energy additional losses reduction is established.
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Ly, Anh Hung, e Quang Doan Le. "Geometrical effect on behavior of thin-walled cylindrical tubes subjected to low velocity impact load". Science and Technology Development Journal 19, n. 3 (30 settembre 2016): 34–42. http://dx.doi.org/10.32508/stdj.v19i3.550.
Testo completoAbstract (sommario):
Geometrical effect on deformation of thinwalled cylindrical tubes subjected to low velocity impact load is conducted using numerical simulation. The cylindrical tube models are made by 6060-T5 Aluminum with difference of diameter (D), thickness (h) and length (L). If ratios of D/h and L/D are changed, deformation modes are also varied as symmetric, asymmetric, mix or buckling. Two sets of trigger applied to model to activate deformation modes. Results obtained from numerical simulation agree very well with experimental results published in the international journal articles. The formula indicated relationship between the nondimension mean crushing force Pm/M0 and D/h is also proposed.
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Wang, Yang, e Sonya Legg. "Enhanced Dissipation of Internal Tides in a Mesoscale Baroclinic Eddy". Journal of Physical Oceanography 53, n. 10 (ottobre 2023): 2293–316. http://dx.doi.org/10.1175/jpo-d-23-0045.1.
Testo completoAbstract (sommario):
Abstract The dissipation of low-mode internal tides as they propagate through mesoscale baroclinic eddies is examined using a series of numerical simulations, complemented by three-dimensional ray tracing calculations. The incident mode-1 internal tide is refracted into convergent energy beams, resulting in a zone of reduced energy flux in the lee of the eddy. The dissipation of internal tides is significantly enhanced in the upper water column within strongly baroclinic (anticyclonic) eddies, exhibiting a spatially asymmetric pattern, due to trapped high-mode internal tides. Where the eddy velocity opposes the internal tide propagation velocity, high-mode waves can be trapped within the eddy, whereas high modes can freely propagate away from regions where eddy and internal wave velocities are in the same direction. The trapped high modes with large vertical shear are then dissipated, with the asymmetric distribution of trapping leading to the asymmetric distribution of dissipation. Three-dimensional ray tracing solutions further illustrate the importance of the baroclinic current for wave trapping. Similar enhancement of dissipation is also found for a baroclinic cyclonic eddy. However, a barotropic eddy is incapable of facilitating robust high modes and thus cannot generate significant dissipation of internal tides, despite its strong velocities. Both energy transfer from low to high modes in the baroclinic eddy structure and trapping of those high modes by the eddy velocity field are therefore necessary to produce internal wave dissipation, a conclusion confirmed by examining the sensitivity of the internal tide dissipation to eddy radius, vorticity, and vertical scale. Significance Statement The oceanic tides drive underwater waves at the tidal frequency known as internal tides. When these waves break, or dissipate, they can lead to mixing of oceanic heat and salt which impacts the ocean circulation and climate. Accurate climate predictions require computer models that correctly represent the distribution of this mixing. Here we explore how an oceanic eddy, a swirling vortex of order 100–400 km across, can locally enhance the dissipation of oceanic internal tides. We find that strong ocean eddies can be hotspots for internal tide dissipation, for both clockwise and anticlockwise rotating vortices, and surface-enhanced eddies are most effective at internal tide dissipation. These results can improve climate model representations of tidally driven mixing, leading to more credible future predictions.
31
Albertsson, Martin, B. Gillis Carlsson, Thomas Døssing, Peter Möller, Jørgen Randrup e Åberg Sven. "Fission modes in fermium isotopes with Brownian shape-motion model". EPJ Web of Conferences 223 (2019): 01002. http://dx.doi.org/10.1051/epjconf/201922301002.
Testo completoAbstract (sommario):
Fission-fragment mass and total-kinetic-energy distributions following fission of the fermium isotopes 256,258,260Fm at low excitation energy have been calculated using the Brownian shape-motion model. A transition from asymmetric fission in 256Fm to symmetric fission in 258Fm is obtained. The total-kinetic-energy distributions for the three isotopes show radically different behaviour due to varying contributions from different fission modes, with a double-humped distribution for 258Fm.
32
Orobengoa, Danel, Cesar Capillas, Mois I. Aroyo e J. Manuel Perez-Mato. "AMPLIMODES: symmetry-mode analysis on the Bilbao Crystallographic Server". Journal of Applied Crystallography 42, n. 5 (8 settembre 2009): 820–33. http://dx.doi.org/10.1107/s0021889809028064.
Testo completoAbstract (sommario):
AMPLIMODESis a computer program available on the Bilbao Crystallographic Server that can perform a symmetry-mode analysis of any distorted structure of displacive type. The analysis consists in decomposing the symmetry-breaking distortion present in the distorted structure into contributions from different symmetry-adapted modes. Given the high- and the low-symmetry structures,AMPLIMODESdetermines the atomic displacements that relate them, defines a basis of symmetry-adapted modes, and calculates the amplitudes and polarization vectors of the distortion modes of different symmetry frozen in the structure. The program uses a mode parameterization that is as close as possible to the crystallographic conventions, expressing all quantities for the asymmetric unit of the low-symmetry structure. Distorted structures are often related to their higher-symmetry counterparts by temperature- and/or pressure-driven phase transitions, ferroic phase transitions being a particular example. The automatic symmetry-mode analysis performed byAMPLIMODEScan be very useful for establishing the driving mechanisms of such structural phase transitions or the fundamental instabilities at the origin of the distorted phases.
33
Кочаровская, Е. Р., e Вл В. Кочаровский. "Структура и особенности автомодуляции сверхизлучательных состояний в асимметричном резонаторе Фабри-Перо". Физика и техника полупроводников 57, n. 5 (2023): 348. http://dx.doi.org/10.21883/ftp.2023.05.56202.29k.
Testo completoAbstract (sommario):
The dependence of the structure and stability of strongly asymmetric stationary states of a superradiant laser with a slightly asymmetric low-Q Fabry-Perot cavity on its length, reflection factors of mirrors, and pumping level is studied. The states are related to a self-consistent inhomogeneous half-wavelength population inversion grating. The possibility of the existence of two dynamic phase transitions from a stationary (monochromatic) state of this type to a nonstationary one is established: 1) a dissipative superradiant transition to a regime with a quasi-continuous lasing spectrum (in a weakly asymmetric cavity) and 2) a self-modulation transition to a regime with a discrete lasing spectrum. It is shown that the latter can be caused by excitation of both polariton and electromagnetic laser modes due to resonant Rabi oscillations of active centers with a sufficiently long phase relaxation time.
34
Ibraheem AlQadi, Ibraheem AlQadi. "Investigation of Flow Around a Slender Body at High Angles of Attack". journal of King Abdulaziz University Engineering Sciences 30, n. 1 (1 febbraio 2019): 51–61. http://dx.doi.org/10.4197/eng.30-1.4.
Testo completoAbstract (sommario):
A numerical investigation of flow around a slender body at high angles of attack is presented. Large eddy simulation of the flow around an ogive-cylinder body at high angles of attack is carried out. Asymmetric vortex flow was observed at angles of attack of α = 55◦ and 65◦ . The results showed that the phenomenon is present in the absence of artificial geometrical or flow perturbation. Contrary to the accepted notion that flow asymmetry is due to a convective instability, the development of vortex asymmetry in the absence of perturbations indicates the existence of absolute instability. An investigation of the unsteady flow field was carried out using dynamic mode decomposition. The analysis identified two distinct unsteady modes; high-frequency mode and low-frequency mode. At angle of attack 45◦ the high-frequency mode is dominant in the frontal part of the body and the low-frequency mode is dominant at the rear part. At α = 55◦ , the highfrequency mode is dominant downstream of vortex breakdown. At α = 65◦ , the spectrum shows a wide range of modes. Reconstruction of the dynamical modes shows that the low-frequency mode is associated with the unsteady wake and the high-frequency mode is associated with unsteady shear layer.
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GUBANKOVA, ELENA. "EXOTIC SUPERFLUIDITY IN COLD ATOMS". International Journal of Modern Physics A 25, n. 02n03 (30 gennaio 2010): 637–46. http://dx.doi.org/10.1142/s0217751x10048925.
Testo completoAbstract (sommario):
We derived the low energy effective action for the collective modes in asymmetric fermionic systems with attractive interaction. We obtained the phase diagram in terms of the chemical potentials. It features a stable gapless superfluidity with one Fermi surface on the BEC side of the resonance. Also we predict a sharp increase in outer core of a vortex, i.e. vortex size, upon entering into the gapless phase. This may serve as a signature of a gapless phase.
36
Miller, D. R., O. H. Han e P. W. Bohn. "Quantitative Raman Spectroscopy of Homogeneous Molecular Profiles in Optical Waveguides via Direct Measurement". Applied Spectroscopy 41, n. 2 (febbraio 1987): 245–48. http://dx.doi.org/10.1366/000370287774986886.
Testo completoAbstract (sommario):
Quantitative measurements of Raman scattering from three-layer asymmetric slab dielectric waveguides made of organic macromolecular materials have been obtained from homogeneous distributions of scatterers as a function of mode by direct measurement of all mode-dependent quantities. For low-order modes, precision of the Raman intensity is limited to ∼5% by uncertainty in the measurement of the coupling coefficient, γ; while for high-order modes, precision was limited at the same level by uncertainty in the integrated electric field due to film-thickness variations. Observation of Raman instead of Rayleigh scatter vs. distance in the waveguide allowed measurement of the optical loss function, α, to be made down to 0.2 dB/cm with less than 1% uncertainty, so it is never the limiting factor.
37
Кочаровская, Е. Р., А. В. Мишин, Вл В. Кочаровский e В. В. Кочаровский. "Поляритонный резонанс в автомодуляции асимметричного состояния сверхизлучающего лазера". Физика и техника полупроводников 56, n. 7 (2022): 651. http://dx.doi.org/10.21883/ftp.2022.07.52755.10.
Testo completoAbstract (sommario):
Based on the numerical solution to the semiclassical Maxwell-Bloch equations in a one-dimensional model of a superradiant laser with a low-Q symmetric Fabry-Perot cavity, a comparative analysis of the spectrum of polariton modes of the linearized problem and the discrete spectrum of the of quasi-monochromatic generation with weak self-modulation under the condition of strong spontaneous mirror symmetry breaking of the counterpropagating electromagnetic waves, population inversion and polarization of an active medium is carried out. It is shown that the main frequencies of resonant self-modulation of a steady asymmetric superradiant phase state are close to the frequencies of polariton modes that are calculated in the linearized problem for the average level of the population inversion taken from the nonlinear problem and have small decay rates.
38
A, Manoranjan, e Christober Asir Rajan C. "Design and Analsyis of 31-Level Asymmetric Cascaded H-Bridge Multilevel Inverter with Reduced Number of Switches". Bulletin of Scientific Research 2, n. 2 (6 ottobre 2020): 14–28. http://dx.doi.org/10.34256/bsr2023.
Testo completoAbstract (sommario):
A new multilevel inverter with less no of power switches is proposed. This is based on cascaded H-bridge topology. The design and analysis of 31-level reduced switch inverter with different modes of operation are presented in this paper. The proposed inverter is asymmetric in nature and it uses unequal DC voltage sources. PD-PWM modulation technique has been used here to get proper switching. The proposed idea has been validated through simulation and the received results provides better efficiency, less low order harmonics and less switching losses.
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Lanzerstorfer, Daniel, e Hendrik C. Kuhlmann. "Global stability of multiple solutions in plane sudden-expansion flow". Journal of Fluid Mechanics 702 (16 maggio 2012): 378–402. http://dx.doi.org/10.1017/jfm.2012.184.
Testo completoAbstract (sommario):
AbstractThe two-dimensional, incompressible flow in a plane sudden expansion is investigated numerically for a systematic variation of the geometry, covering expansion ratios (steps-to-outlet heights) from $0. 25$ to $0. 95$. By means of a three-dimensional linear stability analysis global temporal modes are scrutinized. In a symmetric expansion the primary bifurcation is stationary and two-dimensional, breaking the mirror symmetry with respect to the mid-plane. The secondary asymmetric flow experiences a secondary instability to different three-dimensional modes, depending on the expansion ratio. For a moderately asymmetric expansion only one of the two secondary flows (the connected branch) is realized at low Reynolds numbers. Since the perturbed secondary flow does not deviate much from the symmetric secondary flow, both secondary stability boundaries are very close to each other. For very small and very large expansion ratios an asymptotic behaviour is found for suitably scaled critical Reynolds numbers and wavenumbers. Representative instabilities are analysed in detail using an a posteriori energy transfer analysis to reveal the physical nature of the instabilities. Depending on the geometry, pure centrifugal and elliptical amplification processes are identified. We also find that the basic flow can become unstable due to the effects of flow deceleration, streamline convergence and high shear stresses, respectively.
40
LI, TIANJUN, e WEI LIAO. "LOW ENERGY GAUGE UNIFICATION THEORY". Modern Physics Letters A 17, n. 36 (30 novembre 2002): 2393–407. http://dx.doi.org/10.1142/s0217732302009131.
Testo completoAbstract (sommario):
Because of the problems arising from the fermion unification in the traditional grand unified theory and the mass hierarchy between the four-dimensional Planck scale and weak scale, we suggest the low energy gauge unification theory with low high-dimensional Planck scale. We discuss the nonsupersymmetric SU(5) model on M4 × S1/Z2 × S1/Z2 and the supersymmetric SU(5) model on M4 × S1/(Z2 × Z2′) × S1/(Z2 × Z2′). The SU(5) gauge symmetry is broken by the orbifold projection for the zero modes, and the gauge unification is accelerated due to the SU(5) asymmetric light KK states. In our models, we forbid the proton decay, still keep the charge quantization, and automatically solve the fermion mass problem. We also comment on the anomaly cancellation and other possible scenarios for low energy gauge unification.
41
Katsumoto, Yukiteru, Daisuke Adachi, Harumi Sato e Yukihiro Ozaki. "Usefulness of a Curve Fitting Method in the Analysis of Overlapping Overtones and Combinations of CH Stretching Modes". Journal of Near Infrared Spectroscopy 10, n. 1 (gennaio 2002): 85–91. http://dx.doi.org/10.1255/jnirs.325.
Testo completoAbstract (sommario):
This paper reports the usefulness of a curve fitting method in the analysis of NIR spectra. NIR spectra in the 7500–5500 cm−1 (1333–1818 nm) region were measured for water–methanol, water–ethanol and water–1-propanol mixtures with alcohol concentrations of 0–100 wt% at 25°C. The 6000–5600 cm−1 (1667–1786 nm) region, where the overtones and combinations of CH3 and CH2 stretching modes are expected to appear, shows significant band shifts with the increase in the alcohol content. To analyse the concentration-dependent spectral changes, a curve fitting method was utilised, and the results were compared with those obtained previously by a second derivative method. It was found that the first overtones of CH3 asymmetric and symmetric stretching modes of alcohols show a downward shift by about 15–30 cm−1 with the increase in the concentration of alcohols. The shifts are much larger for water–methanol mixtures than for water–ethanol and water–1-propanol mixtures. The first overtones and combinations of CH2 stretching modes of ethanol and 1-propanol also show a small downward shift. These shifts support our previous conclusion that there is an intermolecular “CH⃛O” interaction between the methyl group and water in the water–alcohol mixtures. The curve fitting method provided more feasible results for the band shifts than the second derivative method. It was revealed from the curve fitting method that the first overtone of the CH3 asymmetric stretching mode of water–methanol, water–ethanol and water–1-propanol mixtures shows different concentration-dependent plots. The first overtone of CH3 asymmetric stretching mode of water–methanol mixtures shifts more rapidly in the high methanol concentration range while that of water–1-propanol concentration shifts more markedly in the low 1-propanol concentration range. That of water–ethanol mixtures shows an intermediate trend. Based upon these differences structural differences among the three kinds of water–alcohol mixtures are discussed.
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Antonov, Alexander I., Dmitry Yu Rudy, Alexander A. Ruppel e Elena Yu Ruppel. "CONSIDERATION OF THE CRITERION OF THE INFLUENCE OF ASYMMETRIC LOAD ON VOLTAGE DISTORTION IN A 10 kV NETWORK FOR RECOMMENDATIONS FOR REDUCING VOLTAGE ASYMMETRY". Vestnik Chuvashskogo universiteta, n. 3 (29 settembre 2022): 12–20. http://dx.doi.org/10.47026/1810-1909-2022-3-12-20.
Testo completoAbstract (sommario):
To date, there is a fairly large number of electrical equipment that is a source of asymmetric modes of operation in medium and low voltage electrical networks. This electrical equipment can create conductive low-frequency electromagnetic interference in electrical networks by the coefficient of voltage asymmetry in the reverse sequence. Studying the methodological basis of research on the theory of conductive low-frequency interference, it was found that when switching from one adjacent electrical network to another (for example, from a 0.4 kV network to a 10 kV network and vice versa) potential for conductive low-frequency interference decreases, i.e. the interference is partially suppressed by a certain amount. This amount is called the criterion determining the changes of the voltage asymmetry coefficient values in the reverse sequence in the transition of conductive low-frequency electromagnetic interference to the adjacent network. The purpose of this article is to develop a mathematical model for the study of network parameters affecting voltage asymmetry in the reverse sequence, which is reduced to a method for determining the value of the criterion for the effect of an asymmetric load on voltage distortion in a 10 kV network for recommendations for reducing voltage asymmetry. The article describes in detail the method of calculating this value and how it can be used to form recommendations for reducing voltage asymmetry. Scientific novelty of the study consists in the fact that an empirical mathematical model has been obtained that determines the criterion for the influence of an asymmetric load in a low-voltage network, the impact on which makes it possible to improve the electromagnetic situation in a 10 kV electrical network. This parameter can be taken into account when designing elements of electrical networks to determine the electromagnetic environment.
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Subramaniam, S., M. J. Lance, C. J. Rawn, B. C. Chakoumakos e A. J. Rondinone. "Raman spectroscopic studies on structure I and structure IItrimethylene oxide hydrate". Canadian Journal of Physics 83, n. 9 (1 settembre 2005): 941–49. http://dx.doi.org/10.1139/p05-040.
Testo completoAbstract (sommario):
Raman spectra were collected from structure I (sI) and structure II (sII) trimethylene oxide (TMO) hydrates at various temperatures and used to assign the vibrational modes, investigate the ordering of TMO molecules inside the cage structure, and to determine possible interactions between the guest and the host lattice. Only Raman spectra from sI hydrate could be analyzed since the low concentration of TMO prevented sII peaks from being resolved. Comparison of the Raman spectra of liquid, solid, and enclathrated TMO (sI) showed Raman shifts to higher wave numbers for the enclathrated TMO; mainly among the ring modes. The ring and (or) skeletal modes around 930 cm1 and the asymmetric CH2 stretching mode around 2970 cm1, showed shifts greater than 10 cm1. These observed changes are interpreted on the basis of the "loose-cage tight-cage" model, which interprets the shift as arising from strain induced by the hydrate cage on the guest TMO molecules in the 62 cages. In addition, variable temperature Raman studies, in the temperatures ranging from 103 to 203 K, showed no evidence of ordering and (or) reorientation of host molecules. PACS No.: 78.30.-j
44
Krishnan, Hrisheekesh, Amit Agrawal e Atul Sharma. "On the wake response of a square cylinder subjected to an inline nonharmonic forcing". AIP Advances 12, n. 8 (1 agosto 2022): 085225. http://dx.doi.org/10.1063/5.0092386.
Testo completoAbstract (sommario):
In this work, we study the effect of two spectrally simple nonharmonic inline forcing waveforms on the wake response of a square cylinder. The characteristics of wake response under nonharmonic forcing were studied and compared to wake response under harmonic forcing for a constant Reynolds number 100. By varying the relative strength of the spectral components and the secondary frequency of the nonharmonic forcing of the inflow, an asymmetric modulated wake and an asymmetric 2P + 2S wake were observed for a two-tone nonharmonic forcing. These modes combine the features of the wake response of individual spectral components. In some regions of the parameter space, the wake response did not correlate well with the spectral components of harmonic forcing. An amplitude-modulated forcing was also studied. For amplitude-modulated forcing, the additional frequency component did not affect the wake structure. This observation indicates that the wake may act as a low pass filter for inline flow frequency components above the natural vortex shedding frequency.
45
Sarmast, Sasan, Reza Dadfar, Robert F. Mikkelsen, Philipp Schlatter, Stefan Ivanell, Jens N. Sørensen e Dan S. Henningson. "Mutual inductance instability of the tip vortices behind a wind turbine". Journal of Fluid Mechanics 755 (26 agosto 2014): 705–31. http://dx.doi.org/10.1017/jfm.2014.326.
Testo completoAbstract (sommario):
AbstractTwo modal decomposition techniques are employed to analyse the stability of wind turbine wakes. A numerical study on a single wind turbine wake is carried out focusing on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier–Stokes equations using the actuator line (ACL) method to simulate the wake behind the Tjæreborg wind turbine. The wake is perturbed by low-amplitude excitation sources located in the neighbourhood of the tip spirals. The amplification of the waves travelling along the spiral triggers instabilities, leading to breakdown of the wake. Based on the grid configurations and the type of excitations, two basic flow cases, symmetric and asymmetric, are identified. In the symmetric setup, we impose a 120° symmetry condition in the dynamics of the flow and in the asymmetric setup we calculate the full 360° wake. Different cases are subsequently analysed using dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD). The results reveal that the main instability mechanism is dispersive and that the modal growth in the symmetric setup arises only for some specific frequencies and spatial structures, e.g. two dominant groups of modes with positive growth (spatial structures) are identified, while breaking the symmetry reveals that almost all the modes have positive growth rate. In both setups, the most unstable modes have a non-dimensional spatial growth rate close to $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\pi /2$ and they are characterized by an out-of-phase displacement of successive helix turns leading to local vortex pairing. The present results indicate that the asymmetric case is crucial to study, as the stability characteristics of the flow change significantly compared to the symmetric configurations. Based on the constant non-dimensional growth rate of disturbances, we derive a new analytical relationship between the length of the wake up to the turbulent breakdown and the operating conditions of a wind turbine.
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Guan, Xueyuan, Shunshun Tong, Jianfeng Wang, Xiangjun Zhang e Yushun Liu. "High Gain Millimeter-Wave Transmitarray Antenna Based on Asymmetric U-Shaped Metasurface Using Characteristic Mode Analysis". International Journal of RF and Microwave Computer-Aided Engineering 2023 (9 febbraio 2023): 1–8. http://dx.doi.org/10.1155/2023/6513623.
Testo completoAbstract (sommario):
An asymmetric U-shaped millimeter-wave (MMW) metasurface (MS) transmitarray (TA) antenna is proposed based on characteristic mode analysis (CMA). The CMA of U-type unit shows two modes in the required frequency band and excites these two modes with a certain phase difference, so that the transmittance of the unit in the working band is greater than 0.8. The difference of lens unit is 360° by controlling the size change of the unit, and the transmission array is designed according to the phase distribution of the array. Through optimization simulation, the total size of the lens is 92.4 × 92.4 mm2, composed of 21 × 21 components and focal ratio of 0.85. The feed source is a SIW antenna, and then, the MS converts the quasispherical wave emitted from this feed source into a plane wave. The measured results show that the peak gain at 28 GHz is 22.3 dBi, the gain bandwidth at 3 dB is 5.8°, and the radiation efficiency is 81.6%. Due to the high gain and low-cost design, the proposed MS transmitarray antenna is suitable for MMW communication.
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Xu, Wei, Jingchang Nan e Mingming Gao. "Compact Broadband Circularly Polarized CPW-Fed Antenna with Characteristic Mode Analysis". International Journal of Antennas and Propagation 2022 (10 gennaio 2022): 1–11. http://dx.doi.org/10.1155/2022/9002700.
Testo completoAbstract (sommario):
A compact circularly polarized (CP) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). A ring patch with a gap and two arc-shaped metallic stubs as the radiator is analyzed and optimized by CMA to figure out the orthogonal modes and operating frequency band for potential good axial ratio (AR) performance. The studies of these CP modes provide a physical insight into the property of broadband circular polarization. Such an in-depth understanding paves the way for the proposal of novel CP antenna with separation between the design of radiator and feeding network. A 50-Ω coplanar waveguide (CPW) is introduced and placed appropriately to excite the desired modes based on the information from CMA, which employs two asymmetric ground planes to improve the performance in terms of AR and impedance matching. The antenna with a compact size of 0.71λ0 × 0.76λ0 × 0.038λ0 (λ0 is the free-space wavelength at the center frequency of the 3-dB AR bandwidth) is fabricated and measured for validation. The realized gain varies from 1.6 to 3.1 dBic over the operating bandwidth characterized by the measured 10-dB impedance bandwidth of 83.8% (3.98–9.72 GHz) and 3-dB AR bandwidth of 70.3% (4.59–9.57 GHz), respectively.
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Nolan, David S. "Three-dimensional instabilities in tornado-like vortices with secondary circulations". Journal of Fluid Mechanics 711 (19 settembre 2012): 61–100. http://dx.doi.org/10.1017/jfm.2012.369.
Testo completoAbstract (sommario):
AbstractTornadoes and other intense atmospheric vortices are known to occasionally transition to a flow structure with multiple vortices within their larger circulations. This phenomenon has long been ascribed to fluid dynamical instability of the inner-core circulation, and many previous studies have diagnosed low-wavenumber unstable modes in tornado-like vortices that resemble the observed structures. However, relatively few of these studies have incorporated the strong vertical motions of the inner-core circulation into the stability analysis, and no stability analyses have been performed using a complete, frictionally driven secondary circulation with strong radial inflow near the surface. Stability analyses are presented using the complete circulations generated from idealized simulations of tornado-like vortices. Fast-growing unstable modes are found that are consistent with the asymmetric structures present in these simulations. Attempts to correlate the structures and locations of these modes with instability conditions for vortices with axial jets derived by Howard & Gupta and by Leibovich & Stewartson produce only mixed results. Analyses of perturbation energy growth show that interactions between eddy fluxes and the radial shear of the azimuthal wind contribute very little to the growth of the dominant modes. Rather, the radial shear of the vertical wind and the vertical shear of the vertical wind (corresponding to deformation in the axial direction) are the primary energy sources for perturbation growth. Relatively weak axisymmetric instabilities are also identified that have some similarity to symmetric oscillations that have been observed in tornadoes.
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Stewart, Peter S. "Instabilities in flexible channel flow with large external pressure". Journal of Fluid Mechanics 825 (24 luglio 2017): 922–60. http://dx.doi.org/10.1017/jfm.2017.404.
Testo completoAbstract (sommario):
We examine the stability of laminar high-Reynolds-number flow through an asymmetric flexible-walled channel driven by a fixed upstream flux and subject to a (large) uniform external pressure. We construct a long-wavelength, spatially one-dimensional model using a flow profile assumption, modelling the flexible wall as a thin tensioned membrane subject to a large axial pre-stress. We numerically construct the non-uniform static shape of the flexible wall and consider its stability using both a global eigensolver and numerical simulation of the nonlinear governing equations. The system admits multiple static solutions, including a highly collapsed steady state where the membrane has a single constriction which increases with increasing external pressure. We demonstrate that the non-uniform static state is unstable to two distinct (infinite) families of normal modes which we characterise in the limit of large external pressure. In particular, there is a family of low-frequency oscillatory modes which each persist to low membrane tensions, where the most unstable mode has an oscillating membrane profile which is outwardly bulged at the centre of the domain with a narrow constriction at the downstream end. In addition, there is a family of high-frequency oscillatory modes which are each unstable beyond a critical value of the tension within a two-branch neutral curve. Unstable modes along the lower branch of the neutral curve are sustained by a leading-order balance between unsteady inertia and the restoring force of membrane tension along the channel. In addition, we elucidate the mechanism of energy transfer to sustain the self-excited oscillations: oscillations decrease the mean maximal constriction of the channel over a period, which reduces the overall dissipation of the mean flow and releases energy to sustain the instability. Fully nonlinear simulations indicate that as the Reynolds number increases these unstable normal modes can grow supercritically into sustained large-amplitude ‘slamming’ oscillations, where the membrane is periodically drawn very close to the opposite rigid wall before recovering.
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Toshev, Sherzod, Shaxnoza Tosheva, Abror Saodullaev e Sevara Tengelova. "Mathematical and simulation modeling of a synchronous generator for micro hydroelectric and low-speed wind power plants". E3S Web of Conferences 497 (2024): 01008. http://dx.doi.org/10.1051/e3sconf/202449701008.
Testo completoAbstract (sommario):
In this article, in conditions where environmental deterioration and energy shortages are observed throughout the world, a mathematical model for improving and developing new types of synchronous generators for low-speed wind power plants and micro-hydroelectric power plants is developed free of charge extraction of running water and simulation processes. As a result of mathematical and simulation modeling of a synchronous generator, it is based on the analysis of electromagnetic processes and the study of improvement issues to ensure its efficient operation at low speeds. In mathematical modeling, the electromagnetic processes of a low-speed synchronous generator were analyzed using mathematical equations. For this purpose, mathematical and simulation models of an improved generator designed for low speed were developed and research was carried out. The article creates a mathematical model based on the Park-Gorev equations of asymmetric modes of a synchronous generator designed to generate electricity from low-speed wind and freely flowing water. The mathematical model of the generator was expressed in the Simulink package and a simulation model was built, research was carried out and characteristics were obtained.