Transverse Spectra Research Articles

Star-coupled Hindmarsh–Rose neural network with chemical synapses

We analyze the patterns like synchrony, desynchrony, and Drum head mode in a network of Hindmarsh–Rose (HR) neurons interacting via chemical synapse in unidirectional and bidirectional star topology. A two-coupled system has been studied for synchronization by varying the coupling strength and the parameter describing the activation and inactivation of the fast ion channel. The transverse Lyapunov exponent spectrum is plotted to observe the point of transition from desynchrony to synchrony. The synchronized, desynchronized, and drum head mode regions are observed when the neurons are connected in unidirectional and bidirectional coupling configurations. A detailed analysis about the time evolution of membrane potential corresponding to each region is presented. The annihilation of synchronized region and the expansion of drum head mode region in bidirectional coupling is discussed using parameter space. Our work provides finer insight into the existence and stability of Drum head mode and is useful for designing communication networks.

Black hole elasticity and gapped transverse phonons in holography

We study the elastic response of planar black hole (BH) solutions in a simple class of holographic models with broken translational invariance. We compute the transverse quasi-normal mode spectrum and the propagation speed of the lowest energy mode. We find that the speed of the lowest mode relates to the BH rigidity modulus as dictated by elasticity theory. This allows to identify these modes as transverse phonons — the pseudo Goldstone bosons of spontaneously broken translational invariance. In addition, we show that these modes have a mass gap controlled by an explicit source of the translational symmetry breaking. These results provide a new confirmation that the BHs in these models do exhibit solid properties that become more manifest at low temperatures. Also, by the AdS/CFT correspondence, this allows to extend the standard results from the effective field theory for solids to quantum-critical materials.

Intense and Collimated Supercontinuum Generation Using Microlens Array

A method of high power supercontinuum (SC) generation is proposed, in which femtosecond pulses are focused into a transparent medium using a microlens array (MLA). The MLA combining a telescopic system is used to form long-path multiple filaments inside the medium, and another symmetrically arranged telescopic system and MLA are used to collimate of the emitting multiple SC beams from filaments. The reshaped stable SC beam shows a Gaussian intensity transverse distribution and similar spectra and chirp properties with that generated by single filament, while the pulse energy can be increased by more than two orders.

Phosphorylation-Dependent Effects on the Structural Flexibility of Phosphoglucosamine Mutase from Bacillus anthracis.

Phosphoglucosamine mutase (PNGM) is an evolutionarily conserved bacterial enzyme in the peptidoglycan biosynthetic pathway, catalyzing the reversible conversion between glucosamine 1- and 6-phosphate. Previous structural studies of PNGM from the pathogen Bacillus anthracis revealed its dimeric assembly and highlighted the rotational mobility of its C-terminal domain. Recent studies of two other enzymes in the same superfamily have demonstrated the long-range effects on the conformational flexibility associated with phosphorylation of the conserved, active site phosphoserine involved in phosphoryl transfer. Building on this work, we use a combination of experimental and computational studies to show that the active, phosphorylated version of B. anthracis PNGM has decreased flexibility relative to its inactive, dephosphorylated state. Limited proteolysis reveals an enhanced and accelerated cleavage of the dephosphorylated enzyme. 15N transverse relaxation-optimized NMR spectra corroborate a conformational adjustment with broadening and shifts of peaks relative to the phospho-enzyme. Electrostatic calculations indicate that residues in the mobile, C-terminal domain are linked to the phosphoserine by lines of attraction that are absent in the dephosphorylated enzyme. Phosphorylation-dependent changes in protein flexibility appear linked with the conformational change and enzyme mechanism in PNGM, establishing this as a conserved theme in multiple subgroups of the diverse α-d-phosphohexomutase superfamily.

Collinear spin density wave order and anisotropic spin fluctuations in the frustrated J1−J2 chain magnet NaCuMoO4(OH)

The phase diagram of the quasi-one-dimensional magnet NaCuMoO$_4$(OH) is established through single-crystal NMR and heat-capacity measurements. The $^{23}$Na and $^1$H NMR experiments indicate a spiral and a collinear spin-density-wave (SDW) order below and above $B_c$ = 1.5-1.8 T, respectively. Moreover, in the paramagnetic state above the SDW transition temperature, the nuclear spin-lattice relaxation rate $1/T_1$ indicates anisotropic spin fluctuations that have gapped excitations in the transverse spectrum but gapless ones in the longitudinal spectrum. These static and dynamic properties are well described by a theoretical model assuming quasi-one-dimensional chains with competing ferromagnetic nearest-neighbor interactions $J_1$ and antiferromagnetic next-nearest-neighbor interactions $J_2$ ($J_1$-$J_2$ chains). Because of the excellent crystal quality and good one dimensionality, NaCuMoO$_4$(OH) is a promising compound to elucidate the unique physics of the frustrated $J_1$-$J_2$ chain.

Dynamics of bound magnon pairs in the quasi-one-dimensional frustrated magnet LiCuVO4

We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic fields 10--34 T, in which the ground state has spin-density-wave order. The spin fluctuations in the paramagnetic phase exhibit striking anisotropy with respect to the magnetic field. The transverse excitation spectrum probed by $^{51}$V nuclei has an excitation gap, which increases with field. On the other hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with lowering temperature, but tend to be suppressed with increasing field. Such anisotropic spin dynamics and its field dependence agree with the theoretical predictions and are ascribed to the formation of bound magnon pairs, a remarkable consequence of the frustration between ferromagnetic nearest neighbor and antiferromagnetic next-nearest-neighbor interactions.

Inversion of the permeability of a tight gas reservoir with the combination of a deep Boltzmann kernel extreme learning machine and nuclear magnetic resonance logging transverse relaxation time spectrum data

In view of the low accuracy of the existing nuclear magnetic-resonance (NMR) logging permeability model in tight sandstone reservoirs, we derive a relationship between the NMR [Formula: see text] spectrum and permeability based on the transverse relaxation theory of NMR and the Kozeny-Carman equation. We determined the reasons for the low accuracy of the model through the theoretical analysis. We have developed the deep Boltzmann kernel extreme learning machine (DBKELM) to improve the deep-learning algorithm and to predict the reservoir permeability based on NMR logging with a deep Boltzmann machine (DBM). We use the permeability data of 200 rock specimens in a tight gas reservoir in a certain area and the corresponding [Formula: see text] spectra from NMR logging for modeling. We apply the model to the evaluation of permeability in this area. The results show that the accuracy of the deep-learning algorithm is higher than that of the existing NMR logging permeability model and the shallow layer machine-learning model. Furthermore, the accuracy of the DBKELM that we have developed is higher than that of the DBM, which indicates that DBKELM is more suitable for the prediction of reservoir permeability. Therefore, deep-learning theory can be effectively used in oil exploration and development, and it can improve the interpretation accuracy of reservoir parameters. These findings contribute to the interpretation of reservoir parameters.

Emergence and Evolution of the k Gap in Spectra of Liquid and Supercritical States.

Fundamental understanding of strongly interacting systems necessarily involves collective modes, but their nature and evolution is not generally understood in dynamically disordered and strongly interacting systems such as liquids and supercritical fluids. We report the results of extensive molecular dynamics simulations and provide direct evidence that liquids develop a gap in a solidlike transverse spectrum in the reciprocal space, with no propagating modes between zero and a threshold value. In addition to the liquid state, this result importantly applies to the supercritical state of matter. We show that the emerging gap increases with the inverse of liquid relaxation time and discuss how the gap affects properties of liquid and supercritical states.

Probing the electronic structure of Ni–Mn–In–Si based Heusler alloys thin films using magneto-optical spectra in martensitic and austenitic phases

Thin films of Ni52Mn35−xIn11+xSi2 were fabricated by magnetron sputtering on MgO (001) single crystal substrates. Magnetization as function of temperature for Ni52Mn35In11Si2 exhibits features consistent with a magnetostructural transition (MST) from an austenitic phase to a martensitic phase, similar to the bulk material. We observed that the martensitic transformation is externally sensitive to small changes in chemical composition and stoichiometry. It has been found that thin films of Ni52Mn34−xIn11+xSi2 with x=0 and 1 undergo a temperature-induced MST or remain in a stable austenitic phase, respectively. Comparison of magneto-optical transverse Kerr effect spectra obtained at 0.5–4.0eV in the 35–300K temperature interval reveal insignificant differences between the martensitic and austenite phases. We found that the field and temperature dependencies of the transverse Kerr effect are quite different from the magnetization behavior, which is attributed to magnetic inhomogeneity across the films. To elucidate the effects of magnetostructural phase transitions on the electronic properties, we performed density functional calculations of the magneto-optical Kerr effect.

Density of states from mode expansion of the self-dynamic structure factor of a liquid metal.

We show that by exploiting multi-Lorentzian fits of the self-dynamic structure factor at various wave vectors it is possible to carefully perform the Q→0 extrapolation required to determine the spectrum Z(ω) of the velocity autocorrelation function of a liquid. The smooth Q dependence of the fit parameters makes their extrapolation to Q=0 a simple procedure from which Z(ω) becomes computable, with the great advantage of solving the problems related to resolution broadening of either experimental or simulated self-spectra. Determination of a single-particle property like the spectrum of the velocity autocorrelation function turns out to be crucial to understanding the whole dynamics of the liquid. In fact, we demonstrate a clear link between the collective mode frequencies and the shape of the frequency distribution Z(ω). In the specific case considered in this work, i.e., liquid Au, analysis of Z(ω) revealed the presence, along with propagating sound waves, of lower frequency modes that were not observed before by means of dynamic structure factor measurements. By exploiting ab initio simulations for this liquid metal we could also calculate the transverse current-current correlation spectra and clearly identify the transverse nature of the above mentioned less energetic modes. Evidence of propagating transverse excitations has actually been reported in various works in the recent literature. However, in some cases, like the present one, these modes are difficult to detect in density fluctuation spectra. We show here that the analysis of the single-particle dynamics is able to unveil their presence in a very effective way. The properties here shown to characterize Z(ω), and the information in it contained therefore allow us to identify it with the density of states (DoS) of the liquid. We demonstrate that only nonhydrodynamic modes contribute to the DoS, thus establishing its purely microscopic origin. Finally, as a by-product of this work, we provide our estimate of the self-diffusion coefficient of liquid gold just above melting.

The hadron production inπ−-C interaction at 40 GeV/c and QCD phase transition

In this paper, we proposed to study the phase transition process to use the new pair of variables, the temperature T and the cumulative number n c (T, n c ). We considered the transverse energy spectra of protons and π − -mesons produced in π − -C interactions at 40 GeV/c as a function of cumulative number n c (or four-dimensional momentum transfer t) and the baryonic chemical potential μ b (√ t ). Obtained results indicate the possible appearance of QCD phase transition of nuclear matter.

Acquired Demyelinating Syndromes in Children

Collectively, pediatric acquired demyelinating syndromes encompass a diverse clinical spectrum and include disorders such as multiple sclerosis (MS), acute disseminated encephalomyelitis, acute transverse myelitis, optic neuritis, and neuromyelitis optica spectrum disorders (NMOSDs). Acquired demyelination may occur as a monophasic illness or represent chronic demyelinating disease (such as MS or NMOSD) and thus prompt identification and classification is essential for proper treatment and guidance. As such, approximately 3% of all patients affected by MS experience their first attack during childhood. In general, one quarter of children diagnosed with an acute demyelinating syndrome will be ultimately confirmed to have MS. The likelihood that an incident demyelinating attack represents the first attack of MS is increased in adolescents, females, patients with positive cerebrospinal fluid oligoclonal bands, and those with clinically silent T2 bright and T1 hypointense lesions on brain magnetic resonance imaging at onset. Early therapeutic intervention for MS and NMOSD is recommended to reduce relapses, modify relapse severity, and, it is hoped, limit future disability and reduce demyelination-related central nervous system injury. Of particular clinical relevance in children, there are many mimics of demyelinating disease that must be considered.

Experimental investigation on modulation of homogeneous and isotropic turbulence in the presence of single particle using time-resolved PIV

Turbulence modulation of a nearly isotropic flow field due to the presence of single glass particles, with diameters in the range of 1−8mm (~10–77 times the Kolmogorov scale), was studied experimentally in an oscillating grid apparatus. Particle image velocimetry (PIV) was used to obtain the instantaneous, two-dimensional velocity field for grid Reynolds number, Reg, varying from 1080 to 10,800. Fluctuating velocity components, flow field length scales, energy dissipation rates, turbulence intensity modulation and energy spectra were determined. An apparent increase of ~2–25% in the turbulence fluctuating velocity in the inertial subrange was noted compared with the fluid-only system. Presence of the particle led to enhancement in the flow field isotropy ratio and this ratio was found to be more dependent on the particle size compared with grid Reynolds number. The integral length scale for both fluid-only and fluid–particle systems exhibited a decreasing power law dependency on the grid Reynolds number. A critical ratio (0.41) of particle size to integral length scale was obtained which demarcated the regime of attenuation and enhancement of turbulence intensity and found to be valid for general grid turbulence in multiparticle systems as well. Energy dissipation rate was observed to increase with increase in particle size. Both longitudinal and transverse energy spectrum exhibited less steep slope than −5/3 in the presence of particle which was reasoned to the production of turbulence in the inertial subrange region. Energy enhancements from large scale to smaller scale were explained by the dissipative spectrum which showed maximum energy enhancement in the inertial subrange followed by a decaying trend. In general, the role of a particle in modulating turbulence was explained through possible wake oscillation and vortex shedding due to boundary layer separation on the particle surface and interaction with bulk eddies.

Using Fourier Transform Near-Infrared Spectroscopy to Predict the Mechanical Properties of Thermally Modified Southern Pine Wood.

This study seeks to estimate the mechanical properties of thermally modified wood (TMW) by using near-infrared (NIR) spectroscopy to measure 80 samples in three-point bending tests. Near-infrared spectra collected from the transverse, radial, and tangential sections of wood, coupled with chemometric techniques, were used to predict the mechanical properties of southern pine wood, from which NIR models were constructed based on partial least squares and corresponding cross-validation. The coefficient of determination between NIR transverse section spectra, as well as two mechanical properties of wood samples, modulus of rupture (MOR) and modulus of elasticity (MOE), were above 0.92 and greater than values for other sections. Spectral data from the transverse sections were richer than data from other sections, and thus, a model based on transverse sections better predicts the mechanical properties of wood. A close relationship between the values for mechanical properties (MOE and MOR) and the NIR spectra of thermally modified southern pine wood can be demonstrated, which provides the potential to predict the mechanical properties of untreated and thermally modified wood.

Molecular Spectrum Capture by Tuning the Chemical Potential of Graphene.

Due to its adjustable electronic properties and effective excitation of surface plasmons in the infrared and terahertz frequency range, research on graphene has attracted a great deal of attention. Here, we demonstrate that plasmon modes in graphene-coated dielectric nanowire (GNW) waveguides can be excited by a monolayer graphene ribbon. What is more the transverse resonant frequency spectrum of the GNW can be flexibly tuned by adjusting the chemical potential of graphene, and amplitude of the resonance peak varies linearly with the imaginary part of the analyte permittivity. As a consequence, the GNW works as a probe for capturing the molecular spectrum. Broadband sensing of toluene, ethanol and sulfurous anhydride thin layers is demonstrated by calculating the changes in spectral intensity of the propagating mode and the results show that the intensity spectra correspond exactly to the infrared spectra of these molecules. This may open an effective avenue to design sensors for detecting nanometric-size molecules in the terahertz and infrared regimes.

INFLUENCE OF THE NONLINEARITY PARAMETER ON THE SOLAR WIND SUB-ION MAGNETIC ENERGY SPECTRUM: FLR–LANDAU FLUID SIMULATIONS

ABSTRACT The cascade of kinetic Alfvén waves (KAWs) at sub-ion scales in the solar wind is simulated numerically using a fluid approach that retains ion and electron Landau damping, together with ion finite Larmor radius (FLR) corrections. Assuming initially equal and isotropic ion and electron temperatures, and an ion beta equal to unity, different simulations are performed by varying the propagation direction and the amplitude of KAWs that are randomly driven at a transverse wavenumber k 0 such that k 0 d i = 0.18 ?> (where d i is the proton inertial length), in order to maintain a prescribed level of turbulent fluctuations. The resulting turbulent regimes are characterized by the nonlinearity parameter, defined as the ratio of the characteristic times of Alfvén wave propagation and of the transverse nonlinear dynamics. The corresponding transverse magnetic energy spectra display power laws with exponents spanning a range of values consistent with spacecraft observations. The meandering of the magnetic field lines and the homogenization of ion temperature along these lines are shown to be related to the strength of the turbulence, measured by the nonlinearity parameter. The results are interpreted in terms of a recently proposed phenomenological model where the homogenization process along field lines induced by Landau damping plays a central role.

THE IMPACT OF NONLINEAR STRUCTURE FORMATION ON THE POWER SPECTRUM OF TRANSVERSE MOMENTUM FLUCTUATIONS AND THE KINETIC SUNYAEV–ZEL’DOVICH EFFECT

ABSTRACT Cosmological transverse momentum fields, whose directions are perpendicular to Fourier wave vectors, induce temperature anisotropies in the cosmic microwave background via the kinetic Sunyaev–Zel’dovich (kSZ) effect. The transverse momentum power spectrum contains the four-point function of density and velocity fields, ⟨ δ δ vv ⟩ . ?> In the post-reionization epoch, nonlinear effects dominate in the power spectrum. We use perturbation theory and cosmological N-body simulations to calculate this nonlinearity. We derive the next-to-leading order expression for the power spectrum with a particular emphasis on the connected term that has been ignored in the literature. While the contribution from the connected term on small scales ( k > 0.1 h Mpc − 1 ?> ) is subdominant relative to the unconnected term, we find that its contribution to the kSZ power spectrum at ℓ = 3000 ?> at z < 6 ?> can be as large as ten percent of the unconnected term, which would reduce the allowed contribution from the reionization epoch ( z > 6 ?> ) by twenty percent. The power spectrum of transverse momentum on large scales is expected to scale as k 2 as a consequence of momentum conservation. We show that both the leading and the next-to-leading order terms satisfy this scaling. In particular, we find that both of the unconnected and connected terms are necessary to reproduce k 2.

RADMAP: Simple probes for rapid assessment of complex reactivity: A method and case studies on the reaction of hydrogen atoms with unsaturated organic molecules

RADMAP, an open source program, allows for rapid analysis and visualization of the earliest stages of reactions between any molecule and a monoatomic probe (i.e., H*, H+, H−, Br*, or any other monoatomic species) using ab initio methods. This program creates non-planar potential energy surfaces of the initial interaction between a molecule of interest and the monoatomic probe. These surfaces can be used to both predict the site of addition as well as provide a qualitative estimate for the relative proportion of the formation of adducts; therefore, it gives insight into both the reactivity and the kinetic stability of a molecule. The program presents a way to quickly predict the number of signals anticipated in transverse field muon spin resonance spectra as well as their relative intensities.

Modelling of the turbulent energy decay based on the finite-difference and spectral methods

The work deals with the modeling of turbulent energy using finite-difference and spectral methods. Simulation of the turbulent process is based on the filtered three-dimensional unsteady Navier-Stokes equations, for the closure of the main equation the dynamic model is used. The mathematical model is solved numerically, the equation of motion is solved by a finite-difference method, the equation for pressure is solved by spectral method. Also new algorithm for the numerical solution of the Poisson equation for finding pressure is developed. In the results of simulation, the change of turbulent kinetic energy over the time, the integral length scale, the change of longitudinal-transverse correlation functions are obtained, and longitudinal and transverse one-dimensional spectra are defined.

Time-resolved neurite mechanics by thermal fluctuation assessments

In the absence of simple noninvasive measurements, the knowledge of temporal and spatial variations of axons mechanics remains scarce. By extending thermal fluctuation spectroscopy (TFS) to long protrusions, we determine the transverse amplitude thermal fluctuation spectra that allow direct and simultaneous access to three key mechanics parameters: axial tension, bending flexural rigidity and plasma membrane tension. To test our model, we use PC12 cell protrusions—a well-know biophysical model of axons—in order to simplify the biological system under scope. For instance, axial and plasma membrane tension are found in the range of nano Newton and tens of pico Newtons per micron respectively. Furthermore, our results shows that the TFS technique is capable to distinguish quasi-identical protrusions. Another advantage of our approach is the time resolved nature of the measurements. Indeed, in the case of long term experiments on PC12 protrusions, TFS has revealed large temporal, correlated variations of the protrusion mechanics, displaying extraordinary feedback control over the axial tension in order to maintain a constant tension value.