Absence Of Oscillations Research Articles

Experimental Investigation of the Heaving Motion Effect on Critical Heat Flux Phenomena and Wall Temperature Fluctuation Using R134a for Floating Nuclear Applications

This study experimentally investigated the flow boiling critical heat flux (CHF) under heaving conditions pertinent to floating nuclear power plants (FNPPs). Experiments were conducted using R134a to simulate the operational pressure of pressurized water reactors, extending the CHF database to a pressure range of 5 to 18 MPa. The tested heaving motion reached up to 0.6 g of maximum acceleration, with a period that varied from 3 to 5.3 s. A parametric trend involving mass flux, critical quality, and motion conditions was analyzed through extensive tests encompassing static and heaving conditions. The results showed that CHF reduction was observed due to the effect of heaving acceleration, even in the absence of oscillations in other thermal-hydraulic factors. The CHF reduction was up to 9% in the present experimental conditions. The heaving motion effect was prominent under two specific thermal-hydraulic conditions: when the critical quality was close to zero and when it exceeded the value of 0.6. Furthermore, an examination of wall temperature responses suggested that a longer period of heaving motion can lead to an earlier occurrence of CHF. This fundamental effort was conducted to enhance the understanding of the CHF mechanism under motion conditions, with the aim of contributing to the safe and efficient design of FNPPs.

Transverse electric waves in three-layered waveguide structure with a parabolic spatial profile of the dielectric constant, optical linear and nonlinear layers

A three-layered waveguide structure containing the Kerr nonlinear medium separated by an optical linear interlayer from a parabolic graded-index layer is considered. Exact solutions of the wave equation corresponding to several types of transverse electric waves existing in different ranges of values of the effective refractive index are found. The types of waves differ from each other by the presence or absence of oscillations in the interlayer and in the graded-index layer, as well as the form of attenuation in a nonlinear medium. The wave types obtained can be divided into two main groups. The first group includes such waves that can propagate with an arbitrarily varying effective refractive index in the allowable range of values. The second one includes such waves that can propagate at certain discrete values of the effective refractive index. Such values of the effective refractive index of waveguide modes are determined by the wavelength of the incident ray, difference between the dielectric constants of a parabolic graded-index layer, and its width. Even and odd waveguide modes are described separately. Field oscillations can be observed only in the interlayer for waves of the first group. Field oscillations can also be observed in the graded-index layer for waves of the second group. The field profile is a self-focusing nonlinear medium flatter than in a defocusing one for all types of waves. An increase in the same parameters has a different effect on the profiles of the different types of waves. The possibility of controlling the distribution of the wave energy between the layers of the waveguide structure by changing the angle of incidence is shown.

Proton Gradient Regulation 5 is required to avoid photosynthetic oscillations during light transitions.

The production of ATP and NADPH by the light reactions of photosynthesis and their consumption by the Calvin-Benson-Bassham (CBB) cycle and other downstream metabolic reactions requires careful regulation. Environmental shifts perturb this balance, leading to photo-oxidative stress and losses in CO2 assimilation. Imbalances in the production and consumption of ATP and NADPH manifest themselves as transient instability in the chlorophyll fluorescence, P700, electrochromic shift, and CO2 uptake signals recorded on leaves. These oscillations can be induced in wild-type plants by sudden shifts in CO2 concentration or light intensity; however, mutants exhibiting increased oscillatory behaviour have yet to be reported. This has precluded an understanding of the regulatory mechanisms employed by plants to suppress oscillations. Here we show that the Arabidopsis pgr5 mutant, which is deficient in Proton Gradient Regulation 5 (PGR5)-dependent cyclic electron transfer (CET), exhibits increased oscillatory behaviour. In contrast, mutants lacking the NADH-dehydrogenase-like-dependent CET are largely unaffected. The absence of oscillations in the hope2 mutant which, like pgr5, lacks photosynthetic control and exhibits high ATP synthase conductivity, ruled out loss of these photoprotective mechanisms as causes. Instead, we observed slower formation of the proton motive force and, by inference, ATP synthesis in pgr5 following environmental perturbation, leading to the transient reduction of the electron transfer chain and photosynthetic oscillations. PGR5-dependent CET therefore plays a major role in damping the effect of environmental perturbations on photosynthesis to avoid losses in CO2 fixation.

Absence of magnetic order and emergence of unconventional fluctuations in the Jeff=12 triangular-lattice antiferromagnet YbBO3

We present the ground state properties of a new quantum antiferromagnet, ${\mathrm{YbBO}}_{3}$, in which the isotropic ${\mathrm{Yb}}^{3+}$ triangular layers are separated by a nonmagnetic layer of partially occupied B and O(2) sites. The magnetization and heat capacity data establish a spin-orbit entangled effective spin ${J}_{\mathrm{eff}}=\frac{1}{2}$ state of ${\mathrm{Yb}}^{3+}$ ions at low temperatures, interacting antiferromagnetically with an intralayer coupling $J/{k}_{\mathrm{B}}\ensuremath{\simeq}0.53$ K. The absence of oscillations and a $1/3$ tail in the zero-field muon asymmetries rules out the onset of magnetic long-range order as well as spin freezing down to 20 mK. An anomalous broad maximum in the temperature-dependent heat capacity with an unusually reduced value and a broad anomaly in the zero-field muon depolarization rate centered at ${T}^{*}\ensuremath{\simeq}0.7J/{k}_{\mathrm{B}}$ provide compelling evidence for a wide fluctuating regime $(0.2\ensuremath{\lesssim}T/J\ensuremath{\le}1.5)$ with slow relaxation. We infer that the fluctuating regime is a universal feature of highly frustrated triangular-lattice antiferromagnets while the absence of magnetic long-range order is due to perfect two-dimensionality of the spin lattice protected by nonmagnetic site disorder.

Comparison of turbulence models for solving problems of swirling jet flows

There are several turbulence models that can be used to solve the swirling jet problems, which are typical turbulence problems. A comparison of these models allows us to determine which one is better suited for a given task. When comparing turbulence models for the swirling jet problem, the most important criteria are the accuracy and stability of the solution. Accuracy is assessed by comparison with experimental data or other numerical methods, and stability is assessed by the absence of oscillations and convergence of the solution. In addition, it is also important to consider the computational complexity of each model and its applicability to a specific problem. The swirling flow in a nozzle is studied in the article using various turbulence models (SA, k-ε, k-ω, L-VEL, v2-f, yPlus, SST). To evaluate the performance of different CFD (Computational Fluid Dynamics) turbulence models, their numerical results for velocity profiles are compared with known experimental data.

РОЗВ'ЯЗАННЯ ПОЗИЦІЙНИХ ЗАДАЧ ПРИ МОДЕЛЮВАННІ МОНОТОННИХ КРИВИХ ЛІНІЙ

The paper considers the development of the method of variable discrete geometric modeling of curved lines with a monotonous change in curvature. The discretely represented curve (DRC) being modeled is represented by an ordered set of points that belong to them and the differential geometric characteristics of the curve. These characteristics must be ensured during the modeling process. The curve is formed by thickening, which involves determining the initial point series of intermediate points. At the same time, we believe that the starting points are set without error and do not change their position during the modeling process. The problem of the mutual location of the DRC and an arbitrary straight line has been solved: determining the point of intersection or contact of a curve with a straight line. The solution of the problems considered in the work involves determining the area of a possible solution based on the conditions imposed on the curve: the absence of oscillation, the given order of smoothness, the dynamics of changes in the tangent positions and the values ​​of the radii of curvature along the curves, etc. In the process of modeling, the area of a possible solution is refined. The proposed algorithms can be used to form surfaces according to the given differential-geometric conditions on the basis of the framework, the linear elements of which are flat DRCs. Algorithms allow you to match the characteristics of the curves that define the mesh discrete frame of the surface. This makes it possible to ensure the intersection of curved lines belonging to different families of lines in the process of successive thickenings, and to control the dynamics of changes in positions tangent to the surface. Modeling the surface involves the thickening of the DRC, which are the elements of the surface frame, and the increase of these elements - the thickening of the linear frame. The elements of the model are the lines formed on the basis of the original nodes (output DRCs) and the lines formed on the basis of the original point series consisting of points of condensation of the original DRCs (condensation DRCs). The surface will be considered defined if all the DRCs that make up the frame of the surface are formed with an error that does not exceed the specified value. Key words: discretely represented curve, region of curve location, second order of smoothness, monotonicity of curvature change.

Microtransplantation of Postmortem Native Synaptic mGluRs Receptors into Xenopus Oocytes for Their Functional Analysis.

Metabotropic glutamate receptors (mGluRs) are membrane receptors that play a central role in the modulation of synaptic transmission and neuronal excitability and whose dysregulation is implicated in diverse neurological disorders. Most current understanding about the electrophysiological properties of such receptors has been determined using recombinant proteins. However, recombinant receptors do not necessarily recapitulate the properties of native receptors due to the lack of obligated accessory proteins, some of which are differentially expressed as function of developmental stage and brain region. To overcome this limitation, we sought to microtransplant entire synaptosome membranes from frozen rat cortex into Xenopus oocytes, and directly analyze the responses elicited by native mGluRs. We recorded ion currents elicited by 1 mM glutamate using two electrodes voltage clamp. Glutamate produced a fast ionotropic response (6 ± 0.3 nA) in all microtransplanted oocytes (n = 218 oocytes) and a delayed oscillatory response (52 ± 7 nA) in 73% of them. The participation of Group 1 mGluRs was confirmed by the presence of metabotropic oscillations during the administration of (±)-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD; Group 1 mGluR agonist), and the absence of oscillations during co-administration of N-(1-adamantyl)quinoxaline-2-carboxamide (NPS 2390; Group 1 mGluR antagonist). Since both mGluR1 and mGluR5 belong to Group 1 mGluRs, further investigation revealed that mGluR1 antagonism with LY 456236 has little effect on metabotropic oscillations, while mGluR5 antagonism with 100 µM AZD 9272 has significant reduction of metabotropic currents elicited by ACPD and glutamate. We confirmed the expression of mGluR1 and mGluR5 in native synaptosomes by immunoblots, both of which are enhanced when compared to their counterpart proteins in rat cortex tissue lysates. Finally, these results demonstrate the merit of using microtransplantation of native synaptosomes for the study of mGluRs and the contribution of mGluR5 to the metabotropic glutamate signaling, providing a better tool for the understanding of the role of these receptors in neurological disorders.

An efficient numerical scheme for fractional characterization of MHD fluid model

How to precisely characterize the fractional modeling and physical treatment is an ongoing challenge in fluid mechanics and numerical techniques, especially in nonlinear complex models. A model study is conducted to report fractional time-dependent mixed convection incompressible fluid flow inside a channel. The physical system is under the impacts of viscous dissipation, electrical and magnetic fields. Three fractional operators Atangana Baleanu Caputo (ABC), Caputo Fabrizio (CF), and classical Caputo (CC) are involved into the temporal derivative. Transformations are used to convert the physical model into equivalent fractional partial differential equations (FPDEs). The computational code is developed for finite difference schemes and code validation is made for different fractional operators. The simulations have been performed to check the appropriate fractional operator and a comparison is made to check the accuracy and efficiency. Additionally, a set of graphs is asserted to show the velocity and temperature distribution for various values of parameters. Velocity is analyzed as decreasing function with an enhancement in the Rayleigh number while the higher fractional parameter (α) causes a dominant drop. A dropped velocity is analyzed in the absence of oscillation and enhanced velocity for higher oscillation, while a more dominant increment in the velocity is noted when Λ0 is non-zero. A decrease in the thermal layer is observed for higher Pe, and a more dominant impact is noted for smaller values of the fractional parameter. The pattern of the thermal profile is observed enhancing when there is an involvement of radiative parameter while lower temperature distribution is noted in the absence of the radiative term.

Stability performance of series coupled natural circulation system with different operating procedures

Series coupled natural circulation system with the last loop being an open-air loop finds application as an infinite mission time passive decay heat removal system in nuclear power plants and solar thermal systems. Hence the stability behavior of series coupled rectangular loops with horizontal heater and horizontal cooler orientation was experimentally studied. The loop was subjected to various operating procedures viz., start up from rest, power raising from a stable steady state and power step down from an unstable state to witness that the stability threshold was not a unique value, thus confirming the existence of a hysteresis phenomenon. The stability threshold enhancement of the system with orifice plates was maximum for the lowest orifice diameter. The coupled system was chosen with an unstable first loop and the instability was found to transmit from loop#1 to the subsequent loops. However, the oscillation amplitude was highly attenuated and seemed to be nearly stable in the 2nd and 3rd loop without any flow reversals even when the first loop was unstable with chaotic bidirectional pulsing. In case of bi-directional pulsing in loop#1, the heat exchanger between the first two loops operated alternatively in co-current and counter-current mode with no change in the flow direction of loop#2. A delay in the flow initiation was found for start-up from rest, which increased from the first loop to the last loop and decreased with the increase in power input. Further, the numerical simulation with the one-dimensional model reproduced the oscillatory behavior in loop#1, with the predicted stability threshold being considerably lower compared to the experiments. The attenuation of the oscillations in the loop#2 as observed in the experiments could be reproduced. Predicted transients showed practically no oscillations in loop#3 corroborating the experimental observations. The attenuation of the oscillations in loop#2 and the absence of oscillations in loop#3 were attributed to the damping caused by the wall and also due to the higher Lt/D ratio in loop#2 and a vertical air flow channel in loop#3 respectively. The phase plots indicated a near periodic oscillation compared to the highly chaotic pattern in the experiments, presumably due to the higher power at which instability was observed in the experiments. The deviations were also due to the secondary flows being generated in the large diameter loop as the simulation was based on 1D along with the heat loss being neglected.

Evolutionary divergence of anaphase spindle mechanics in nematode embryos constrained by antagonistic pulling and viscous forces.

Cellular functions such as cell division are remarkably conserved across phyla. However, the evolutionary principles of cellular organization that drive them are less well explored. Thus, an essential question remains: to what extent do cellular parameters evolve without altering the basic functions they sustain? Here we have observed six different nematode species for which the mitotic spindle is positioned asymmetrically during the first embryonic division. Whereas the C. elegans spindle undergoes oscillations during its displacement, the spindle elongates without oscillations in other species. We asked which evolutionary changes in biophysical parameters could explain differences in spindle motion while maintaining a constant output. Using laser microsurgery of the spindle, we revealed that all species are subjected to cortical pulling forces of varying magnitudes. Using a viscoelastic model to fit the recoil trajectories and with an independent measurement of cytoplasmic viscosity, we extracted the values of cytoplasmic drag, cortical pulling forces, and spindle elasticity for all species. We found large variations in cytoplasmic viscosity, whereas cortical pulling forces and elasticity were often more constrained. In agreement with previous simulations, we found that increased viscosity correlates with decreased oscillation speeds across species. However, the absence of oscillations in some species despite low viscosity can only be explained by smaller pulling forces. Consequently, we find that spindle mobility across the species analyzed here is characterized by a tradeoff between cytoplasmic viscosity and pulling forces normalized by the size of the embryo. Our work provides a framework for understanding mechanical constraints on evolutionary diversification of spindle mobility.

Exclusion of the Possibility of "False Ripples" From Ripple Band High-Frequency Oscillations Recorded From Scalp Electroencephalogram in Children With Epilepsy.

AimRipple-band epileptic high-frequency oscillations (HFOs) can be recorded by scalp electroencephalography (EEG), and tend to be associated with epileptic spikes. However, there is a concern that the filtration of steep waveforms such as spikes may cause spurious oscillations or “false ripples.” We excluded such possibility from at least some ripples by EEG differentiation, which, in theory, enhances high-frequency signals and does not generate spurious oscillations or ringing.MethodsThe subjects were 50 pediatric patients, and ten consecutive spikes during sleep were selected for each patient. Five hundred spike data segments were initially reviewed by two experienced electroencephalographers using consensus to identify the presence or absence of ripples in the ordinary filtered EEG and an associated spectral blob in time-frequency analysis (Session A). These EEG data were subjected to numerical differentiation (the second derivative was denoted as EEG″). The EEG″ trace of each spike data segment was shown to two other electroencephalographers who judged independently whether there were clear ripple oscillations or uncertain ripple oscillations or an absence of oscillations (Session B).ResultsIn Session A, ripples were identified in 57 spike data segments (Group A-R), but not in the other 443 data segments (Group A-N). In Session B, both reviewers identified clear ripples (strict criterion) in 11 spike data segments, all of which were in Group A-R (p < 0.0001 by Fisher’s exact test). When the extended criterion that included clear and/or uncertain ripples was used in Session B, both reviewers identified 25 spike data segments that fulfilled the criterion: 24 of these were in Group A-R (p < 0.0001).DiscussionWe have demonstrated that real ripples over scalp spikes exist in a certain proportion of patients. Ripples that were visualized consistently using both ordinary filters and the EEG″ method should be true, but failure to clarify ripples using the EEG″ method does not mean that true ripples are absent.ConclusionThe numerical differentiation of EEG data provides convincing evidence that HFOs were detected in terms of the presence of such unusually fast oscillations over the scalp and the importance of this electrophysiological phenomenon.

The Efficiency of the Electro-Oxidation of Small Organic Molecules: Oscillations and Mechanism

Many hydrogen-carriers have been considered for the direct use in fuel cells and also in the electrochemical reform, where they are oxidized instead of water at lower potentials. We have investigated the electro-oxidation of formaldehyde, formic acid, methanol, and ethanol,[1] and of ethylene glycol, glycerol, and glucose[2] on polycrystalline platinum in acidic media, and compare the activity under conventional and oscillatory regimes. The comparison is carried out by different means and generalized by the use of simple identical experimental conditions in all cases. The activity along slow potentiodynamic curves, inferred by the peak current, decreases in the following sequence: formaldehyde ~ formic acid > methanol > ethanol ~ ethylene glycol > glucose > glycerol. The ubiquitous occurrence of potential oscillations under galvanostatic regime is associated with excursions of the electrode potentials to lower values, which noticeably decreases the overpotential of the anodic reaction, when compared to that in the absence of oscillations. Considerable enhancement in the power density was observed in an idealized fuel cell operated with those fuels when operated under oscillatory regime. Furthermore, the spontaneous periodic self-cleaning processes, present important advantages to the use of autonomous oscillations to reach both higher and long-term activities, and stability [3]. The discussion of these half-cell studies is complemented with experiments with proton exchange membrane fuel cells, namely direct liquid fuel cells (DLFCs). We have investigated the effect of temperature on DLFCs under conventional and oscillatory conditions.[4] Methanol, formic acid, ethanol, and dimethyl ether (DME) were used as fuels and identical experimental conditions were used in all cases. Some findings observed in half-cells are also observed in the DLFCs studied, but few peculiarities of the experimental configuration adopted in the later arise. Finally, mechanistic aspects underlying the observed dynamics are discussed.[1] M. V. F. Delmonde, L. F. Sallum, N. Perini, E. R. Gonzalez, R. Schlögl, H. Varela, J. Phys. Chem. C 120 (2016) 22365.[2] G. B. Melle, T. A. Ferreira, R. L. Romano, H. Varela, in preparation (2020).[3] J. A. Nogueira, P. P. Lopes, N. M. Markovic, H. Varela, Electrochem. Commun. 121 (2020) 106853.[4] J.A. Nogueira, H. Varela, Energy Fuels 34 (2020) 12995.

Neutrino-4 anomaly: Oscillations or fluctuations?

We present a deep study of the Neutrino-4 data aimed at finding the statistical significance of the large-mixing short-baseline neutrino oscillation signal claimed by the Neutrino-4 collaboration at more than 3σ. We found that the results of the Neutrino-4 collaboration can be reproduced approximately only by neglecting the effects of the energy resolution of the detector. Including these effects, we found that the best fit is obtained for a mixing that is even larger, close to maximal, but the statistical significance of the short-baseline neutrino oscillation signal is only about 2.7σ if evaluated with the usual method based on Wilks' theorem. We show that the large Neutrino-4 mixing is in strong tension with the KATRIN, PROSPECT, STEREO, and solar νe bounds. Using a more reliable Monte Carlo simulation of a large set of Neutrino-4-like data, we found that the statistical significance of the Neutrino-4 short-baseline neutrino oscillation signal decreases to about 2.2σ. We also show that it is not unlikely to find a best-fit point that has a large mixing, even maximal, in the absence of oscillations. Therefore, we conclude that the claimed Neutrino-4 indication in favor of short-baseline neutrino oscillations with very large mixing is rather doubtful.

Experimental study of the effect of air oscillations on vapor diffusion in a channel of variable cross-section and in a granular medium

The diffusion of 2-propanol vapor in the air in a channel of variable radius and in a porous medium composed of spheres of equal diameter under longitudinal oscillations is experimentally studied. In the experiments, vapor concentration at the top and bottom of the channel (or porous medium) is constant. In the absence of oscillations, mass transfer along the channel (or porous medium) is carried out due to molecular diffusion. When air oscillations are imposed, additional mass transfer effects are activated, namely, Taylor dispersion and convective mass transfer due to steady vortex flows. In the studied range of frequencies and amplitudes, the total mass transfer exceeds molecular diffusion by one order of magnitude. In a channel of variable radius, mass is transferred mainly due to the steady vortex flows (convective mass transfer) arising in the viscous boundary layer due to the inhomogeneity of the amplitude of air oscillations in narrow and wide sections of the channel. In a porous medium, Taylor dispersion plays a major role while the convective mass transfer makes minor contribution.

Comparison and Speed Control of DC Motor and DC Servomotor Using IMC Based PID Controller

IMC based PID controllers are being used to speed control of DC motor and DC servomotor in industry. As this controller offer good performance comparitive to conventional controllers like PI, PID and Ziegler Nichols frequency method controllers. This paper presents the speed control of the DC motor and DC servomotor using PI, PID, Ziegler Nichols method and IMC-PID controllers, to realize the optimization of control action. A mathematical calculation of DC motor and DC servomotor has developed and simulations are carried out in MATLAB/ Simulink environment. From the results, it is observed that time domain parameters like rise time 0.6 secs, settling time 2 secs, speed for peak over shoot 1450, peak amplitude 1, with no oscillations using IMC-PID controller on DC motor. And for DC servomotor its rise time is 0.3 seconds, settling time is 1 second, speed for peak overshoot 1450 rpm, peak amplitude 1 with absence of oscillations by using IMC-PID controller

Simulation of the Ignition and Detonation of Methane–Air Mixtures behind a Reflected Shock Wave

A physical and mathematical model, computational algorithms, and calculation results are presented for the ignition and detonation of methane–air combustible mixtures behind a reflected shock wave. The one-dimensional, unsteady equations of gas dynamics, supplemented with the equations of chemical kinetics, are solved numerically with the grid-characteristic and Godunov methods. An original modification of the simplified kinetic mechanism is used to describe the combustion of methane in air. The results of calculations of the ignition delay time of the combustible mixture are compared with the experimental and calculated data reported by other authors, and the results of calculations of the occurrence and propagation of the detonation wave are presented. The modes of the propagation of a detonation wave with a constant velocity and in oscillatory mode are obtained. The velocity of the detonation wave in the absence of oscillations accurately corresponds to the velocity of the overcompressed detonation wave obtained from the solution of the Rankine–Hugoniot equations under the assumption that the flow is frozen in front of the shock wave and equilibrial behind the shock wave and that the gas velocity behind the shock wave is zero.

Electrostatic theory of irregular conductance oscillations through a quantum constriction under quantized Hall conditions

Abstract We propose a semi-classical explanation to the conductance oscillations ( δ G ) observed at gate-controlled quantum dots under quantized Hall conditions. Our approach is based on the self-consistent screening theory of the quantum Hall effect and δ G originates either from the interference of electrons or from charging effects. In the interference regime electrons acquire an Aharonov–Bohm phase while propagating coherently along the evanescent incompressible stripes at a particular filling factor, where the stripes enclose a magnetic flux. The charging regime finds its ground in Coulomb blocked, where the transport electron generates an additional energy scale to conductance oscillations. Combining these two regimes, we found that the period of conductance oscillations in magnetic field ( Δ B ) may increase, decrease or remain constant at different filling factors, as observed in the experiments. In addition it is shown that, a gate potential can shift the incompressible stripe along the gated edge spatially, thereby changing the enclosed flux, and can induce δ G with a period Δ V g . We demonstrate that our formulation is able to generate the superimposed Δ B - Δ V g interferences in stripe or checkerboard patterns in agreement with experiments. We can account for further salient and peculiar features of experimental observations for example the surprising absence of oscillations at certain filling factors.

Evidence of Overtone Interference in Fundamental‐Mode Rayleigh Wave Phase and Amplitude Measurements

AbstractWe present evidence that measurements of minor‐arc fundamental‐mode (FM) Rayleigh waves experience interference from major‐arc overtones, resulting in travel‐time and amplitude measurements oscillating along a ray path. The oscillations are present in synthetic seismograms generated in a 3‐D Earth model via SPECFEM3D_GLOBE and in a 1‐D Earth model by mode summation. The absence of oscillations in synthetics containing only the FM indicates that the oscillations originate from higher‐mode interference. This interference is present across multiple measurement techniques, including multi‐channel cross correlation, phase‐matched filtering, and cluster analysis. Experiments with 1‐D synthetics suggest that contamination from interference is largest at epicentral distances greater than around 120 degrees, where record sections of seismograms show the major‐arc overtones intersecting the minor‐arc FM Rayleigh wave. The short wavelength of the interference pattern means it is only observable with dense station spacing and high data quality, which may explain why it has not, to our knowledge, been previously recognized. We show the interference is visible in real data. Its overall impact on phase‐velocity maps is probably minor due to many measurements from shorter path lengths less prone to interference bias. However, phase‐velocity maps constructed only from measurements at epicentral distances prone to interference exhibit significant noise and poor agreement with maps from measurements that include all path lengths; the issue is especially problematic for approaches that use differential travel times between nearby stations. Accounting for interference may diminish noise in measurements and improve the accuracy of images of the upper mantle.

High mobility control of an omnidirectional platform for gait rehabilitation after stroke.

We present a novel control method for an omnidirectional robotic platform for gait training. This mobile platform or "walker" provides trunk support and allows unrestricted motion of the pelvis simultaneously. In addition to helping the user maintain balance and preventing falls, the walker combines two types of therapeutic intervention: forward propulsion of the trunk and partial body weight support (BWS). The core of the walker's control is an admittance controller that maximizes the platform's horizontal mobility by optimizing the virtual mass of the admittance model. Said mass represents the best tradeoff between a low-frequency oscillation mode that becomes more damped as the virtual mass decreases, and a high-frequency mode that becomes less damped simultaneously and hence could destabilize the system. Forward propulsion of the trunk is aided by a horizontal force that is modulated with the patient's gait speed and turning rate to ensure easy adaptation. BWS is provided by a second, independent admittance controller that generates a spring-like upward force. In an initial study, a stroke patient was able to walk stably in the platform, as evidenced by the absence of oscillations associated with an excessively low virtual mass. A progressive increase in the patient's self-selected speed, along with greater uniformity in the instantaneous velocity, suggest that forward propulsion was effective in compensating the patient's own propulsion deficit.

Nonoscillatory Phase Coding and Synchronization in the Bat Hippocampal Formation

Hippocampal theta oscillations were proposed to be important for multiple functions, including memory and temporal coding of position. However, previous findings from bats have questioned these proposals by reporting absence of theta rhythmicity in bat hippocampal formation. Does this mean that temporal coding is unique to rodent hippocampus and does not generalize to other species? Here, we report that, surprisingly, bat hippocampal neurons do exhibit temporal coding similar to rodents, albeit without any continuous oscillations at the 1-20Hz range. Bat neurons exhibited very strong locking to the non-rhythmic fluctuations of the field potential, such that neurons were synchronized together despite the absence of oscillations. Further, some neurons exhibited "phase precession" and phase coding of the bat's position-with spike phases shifting earlier as the animal moved through the place field. This demonstrates an unexpected type of neural coding in the mammalian brain-nonoscillatory phase coding-and highlights the importance of synchrony and temporal coding for hippocampal function across species.