Spike Configuration Research Articles

Magnons and spikes for N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2 linear quivers and their non-Abelian T-duals

We compute the spectra associated with various semiclassical string states that propagate over N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2 Gaiotto-Maldacena backgrounds. As an interesting special case, for the Abelian T- dual solution, we discover giant magnon and single spike configurations while imposing appropriate boundary conditions. However, for Sfetsos-Thompson backgrounds, one has to adopt a different string embedding which reveals “modified” dispersion relations both for magnons and spikes. These results boil down into the standard dispersion relations in the limit when the rank of the associated SU(Nc) color gauge group becomes large enough. We further generalize our analysis in the presence of flavor D6 branes. Our analysis reveals a new set of dispersion relations, which shows that both magnons and spikes are ceased to exist in the presence of flavor excitations.

Heat flux and aerodynamics drag reduction of a hypersonic flow with the different tips of the taper spike design parabolic nose cone

The primary engineering challenge in the realm of supersonic aircraft design lies in the effective management of aero-heating and drag. This study delves into a numerical exploration of flow characteristics at Mach number 5.8, specifically focusing on the aerodynamic performance of actively modified the leading edge of the spike configurations. These configurations encompass bi-conic, parabolic, ogive, elliptical, spherical, and flat-tapered spikes attached to parabolic nose cones. The investigation is carried out at a zero-degree angle of attack, with a particular emphasis on their abilities to reduce aerodynamic drag, heating, and skin friction. Analysis of velocity vectors and contour geometries offers insights into flow patterns, and the presence of shock phenomena in front of the various tapered spike geometries. A comparative examination of these different tip-tapered spike designs on the parabolic nose cone reveals that the flat-tapered spike exhibits superior performance in terms of heat mitigation and reduction in aerodynamic drag. This can potentially be attributed to specific inflow and shock features near both the tip and the base of the spike on the parabolic nose cone, including aspects such as flow deceleration and the presence of strong and weak shock waves. These characteristics likely contribute to the observed reductions in both heating and aerodynamic drag.

Numerical Analysis and Design Optimization Of Bluff Body Using Spike

The drag force caused on the re-entry vehicle and for missile, cursing at supersonic speed will result in Aerodynamic heating of the body. To minimize the aerodynamic heating and drag, designing of bluff body is an important aspect. This paper deals with the design optimization of bluff body using spike. Computational studies have been made in ANSYS FLUENT to obtain the effect of spike shape and length over a bluff body at supersonic Mach number of 2 at zero angle of attack. In this paper numerical analysis on conical bluff body integrated with different spike configurations were carried out using ANSYS software packages. Computations have been made on three spike configurations i.e., sharp, blunt and aerospike of different lengths. Larger the recirculation zone, reduces coefficient of drag. It has been observed that with an increase in spike length the pressure fluctuations increase and with the change in shape to blunt spike and sharp spike the fluctuations decrease.

Coronavirus peplomer charge heterogeneity

Recent advancements in viral hydrodynamics afford the calculation of the transport properties of particle suspensions from first principles, namely, from the detailed particle shapes. For coronavirus suspensions, for example, the shape can be approximated by beading (i) the spherical capsid and (ii) the radially protruding peplomers. The general rigid bead-rod theory allows us to assign Stokesian hydrodynamics to each bead. Thus, viral hydrodynamics yields the suspension rotational diffusivity, but not without first arriving at a configuration for the cationic peplomers. Prior work considered identical peplomers charged identically. However, a recent pioneering experiment uncovers remarkable peplomer size and charge heterogeneities. In this work, we use energy minimization to arrange the spikes, charged heterogeneously to obtain the coronavirus spike configuration required for its viral hydrodynamics. For this, we use the measured charge heterogeneity. We consider 20 000 randomly generated possibilities for cationic peplomers with formal charges ranging from 30 to 55. We find the configurations from energy minimization of all of these possibilities to be nearly spherically symmetric, all slightly oblate, and we report the corresponding breadth of the dimensionless rotational diffusivity, the transport property around which coronavirus cell attachment revolves.

Tensor network approach to 2D Lorentzian quantum Regge calculus

We demonstrate a tensor renormalization group (TRG) calculation for a two-dimensional Lorentzian model of quantum Regge calculus (QRC). This model is expressed in terms of a tensor network by discretizing the continuous edge lengths of simplicial manifolds and identifying them as tensor indices. The expectation value of space-time area, which is obtained through the higher-order TRG method, nicely reproduces the exact value. The Lorentzian model does not have the spike configuration that was an obstacle in the Euclidean QRC, but it still has a length-divergent configuration called a pinched geometry. We find a possibility that the pinched geometry is suppressed by checking the average edge length squared in the limit where the number of simplices is large. This implies that the Lorentzian model may describe smooth geometries, although the investigation of the higher moments is required to make the statement more conclusive. Our results also indicate that TRG is a promising approach to numerical study of simplicial quantum gravity.

Influence of coolant multi-jets on heat reduction of nose cone with blunt spike at hypersonic flow

The importance of the cooling system for the design of the forebody of high-speed vehicles is significant due to severe aerodynamic heating at hypersonic flight. In the present study, injection of multi and single-coolant jets on the thermal performance of forebody design of nose cone with the cut spike is thoroughly investigated at hypersonic flow. A three-dimensional model of the blunt cone is presented for computational investigations of proposed jet and spike configurations. Injection of two coolant gasses (Helium and carbon dioxide) into the cooling system of the nose cone with a blunt spike is investigated. Three locations for both opposing and lateral jets are compared to find the efficient jet location. Our results indicate that a single lateral jet injected from the tip of the spike is more efficient for heat reduction. A comparison of the multiple injection system also shows that the heat reduction of the helium gas is about 15% more than CO2 jets.

Hypersonic drag and heat reduction mechanism of a new hybrid method of spike, multi-row discs and opposing jets aerodynamic configuration

In this study, the drag force and aerodynamic heating reduction capacity of a novel combined spike root jet and multi-row disk (SRJ-MRD) model consisting of a blunt body, a spike, four aerodisks, and a counterflow jet was compared with geometric reported proposed in other studies. The proposed geometric model was numerically simulated using Reynolds-Averaged Navier–Stokes (RANS) equations with second-order spatial accuracy and the SST k-ω turbulence model. The flow was steady, compressible, and axisymmetric at Mach number 6. The primary attention of the present study has been focused on investigating the effect of the novel configuration on the flow field, shock-shock interaction, location of reattachment shock wave, and intensity of shock wave at the reattachment point. Besides, the effect of these parameters on the specifications of lift force and aerodynamic heating has been studied. Results showed that the existence of four aerodynamic discs (one conical aero disc and three smooth aerodisks) in the proposed model would guide the shear layer and separation shock wave upward, which causes the reattachment shock wave to occur on the blunt nose near the shoulder. Furthermore, the shock-shock interaction does not occur near the nose wall. In addition, the intensity of reattachment shock wave is reduced by the root opposing jet, and the low-temperature outlet will directly cool the front part of the blunt nose. It was found that the spatial location of maximum heat flux on the conical nose's wall is 68.90˚, denoting the positive effect of the proposed configuration on the reattachment shock wave, separation shock wave, and shock-sock interaction. To evaluate the new proposed configuration, the obtained results were compared with nine designs simulated by other researchers which used the same flow conditions and configuration (i.e., diameter, blunt body type, spike length, aerodisks diameter, location, and pressure ratio) but different control approaches. The results revealed that the drag coefficient and maximum heat flux were 0.2619 and 25.13 kw/m2, respectively. Compared to the results of the best design proposed by other researchers, i.e., spike configuration by applying lateral jet and spike tip, the present configuration shows a reduction in total drag coefficient (Cd,all) and maximum heat flux (Qmax) by 7.9% and 10.05%, respectively.

Experimental analysis of jet flow in an aerospike nozzle

The present experimental study aims at analyzing the pressure characteristics in an aerospike nozzle of 15° half-angle conical plug. The current aerospace research has a keen interest in developing launchers through minimalistic equipment with increased efficiency. This purpose can be served by the aerospike nozzles which can be operated in atmospheric and vacuum conditions. The paper is focused in reduction of potential core length which involves the flow investigation in terms of pressure through experimental setup of jet flow apparatus with the assistance of CFD results. It is also proved that the spike configuration results in improvement of efficiency compared to C-D nozzle.

Thermo-Fluid Analysis of Supersonic Flow Over Ballistic Shaped Bodies with multiple aero-disk spike configurations

The aerodynamics of re-entry vehicles has always been in the forefront among space research. With the increasing interests in space exploration, it is important to understand the aerodynamics of spacecrafts and identify an optimum design to overcome the forces due to the earth's atmosphere. In this paper, Computational Fluid Dynamic (CFD) analysis has been carried out on ballistic bodies with a single, double and triple aero-disk spikes. The study also involves the presence and absence of a blunt tip to aid the analysis of flow behaviour on these bodies under two scenarios namely zero-degree angle of attack and at supersonic speed (Mach 2.0). The aerodynamic drag and surface heat transfer effects of these spikes on three different blunt body configurations has been studied. The shape of the blunt bodies vary based on the nose bluntness factor. The flow patterns of these configurations were three-dimensionally visualized via Schlieren-like, Mach and Pressure contours. It was observed that the usage of aero-disk spike reduced the aerodynamic drag by 45%–60% when compared to the bodies without spikes. The configuration labelled 3221 showed the maximum effect with an average drag reduction of more than 55%. There was a remarkable drop in the stagnation point value of surface heat flux with the addition of all five spike system. An efficient performance of localized peak heat fluxes was also noticed upon the addition of double and triple spike systems. In conclusion, it has been observed that the usage of double and triple spikes on the 3221 blunt body has significantly improved its aerodynamic drag and its surface heat flux.

Reduction of wave drag on parameterized blunt bodies using spikes with varied tip geometries

Aeospike based wave drag reduction is investigated using two-equation turbulence model applied to Faver averaged Navier Stokes solver. Three different blunt bodies are considered in a low supersonic stream of Mach number 2. The considered blunt bodies differ in their degree of bluntness defined in terms of half cone angle, area of flattened front side and radius of bluntness. The zero angle of attack flowfield around these three bodies are computationally analyzed with and without the presence of aft spikes to evaluate the wave drag resulting from the formation of front shock structure. The influence of spike configuration on the wave drag is also investigated. The various considered spike tip geometries include aero-disk, sharp and blunt with the length of all the spikes being equal to the base diameter of the blunt bodies (L/D = 1). It has been found that the 3221 blunt body when coupled with a blunt tipped spike yielded the lowest drag coefficient of 0.3, despite the 3221 having the highest standalone drag coefficient of 0.86, among the blunt bodies when simulated individually without spikes. The physics behind the wave drag reduction associated with each combination of blunt body and spike configuration is presented with clarity. This study portrays the importance of taking bluntness factor, semi-cone angle, fineness ratio and blunt body shape factor into consideration while proposing the generalized optimum spike configuration for minimum drag attainment.

Experimental investigation of heat transfer over double disk spike-blunt body at Mach 5.7

The forefront research in the territory to the regime of hypersonic flow is intended to focus on improving the overall performance of the existing aerospace vehicle. Two major hindrances for the development of an effective high speed vehicle are aerodynamic drag acts against the vehicle and heat transfer rate on the body. In this study, we explore the possibility of addressing this issue by placing an aerospike at the nose portion (i.e., stagnation region) of the high speed vehicle and as a result, wave drag of vehicle is considerably reduced. However, this will lead to the increase in heat transfer at the localized spot of the main body. In an attempt to reduce this localized high heat transfer, the current study evaluates the variation in the heat transfer on the body, by modifying the spike through the addition of a smaller hemisphere on the mid-section of the aerodisk spike. In this regard, shock tunnel experiments and computational studies were carried out on this modified spike configuration, termed as “double-disk spike” or “double spike”. The experimental results indicate that heat transfer near the localized spot of the blunt body with spike decreases for a double spike case in comparison to single disk spike. The decrease in heat transfer varies from 5% to 30% depending on the double spike configuration (i.e. varying cap radius and length of the spike). To supplement these results, 3D Finite Volume simulation, “HiFUN” (High Resolution Flow Solver on Unstructured), showed a good trend in heat transfer compared to that obtained from the experiment; it was found that simulated drag from the double spike is less than single spike case.

Investigating the Development of Localized Neutral Density Increases During the 24 August 2005 Geomagnetic Storm

AbstractWe investigate localized thermospheric neutral density increases (or density spikes) developed during the 24 August 2005 geomagnetic storm and utilize a multi‐instrument database for monitoring the underlying thermospheric, ionospheric, magnetospheric, and solar wind conditions. We study five scenarios occurring under eastward/westward BY dominations and demonstrating the development of density spikes during various events. These scenarios show (1) a northern density spike associated with enhanced antisunward polar flows driven by dayside merging along old‐open field lines during the initial phase, (2) some southern density spikes associated with enhanced sunward auroral flows caused by auroral brightening events during the storm initial phase and main phase, (3) two pairs of southern dayside‐nightside density spike configuration associated with enhanced antisunward polar flows caused by dayside merging and nightside magnetotail reconnections along old‐open field lines during the underlying substorm activity, and (4) a series of enhanced polar sunward flows developed in the polar cap driven by different processes during the recovery phase. We provide a detailed analysis of these events including the specification of underlying field aligned current systems, flow channel types, and auroral forms. Observational results demonstrate the various density spikes and their associated auroral forms and/or flow channels and thus provide a better understanding of their development during this intense geomagnetic storm.

Pressure measurements over a hemisphere-cylinder body attached with a forward facing spike

AbstractThe present paper presents oil flow visualisations and pressure measurements over a hemisphere-cylinder body attached with a forward facing spike at Mach 6 and Reynolds number of 1·38 × 108 at 0° and 5° angle-of-attack. The oil flow pictures depict the separation region in the vicinity of the spike on the hemisphere-cylinder body. The oil flow visualisations will help to locate the reattachment shock wave on the hemisphere-cylinder body and also understand the flow field behavior on the blunt-nosed spike configuration. The pressure measurements over the hemisphere-cylinder body depend on the shape and the length of the spike. The pressure distributions over the blunt-nosed body show significant influence of the angle-of-attack. The maximum pressure coefficient on the hemisphere-cylinder body is a function of the spike length, shape of the aerodisk and angle-of-attack. The windward and leeward sides pressure variations show dependence of the geometrical parameters of the spike and shape of the spike. The hemisphere and the flat-faced aerodisk cause considerable reduction of pressure leading to decrease of aerodynamic drag compared to the conical spike.

Mechanism of Neutralization by the Broadly Neutralizing HIV-1 Monoclonal Antibody VRC01

The structure of VRC01 in complex with the HIV-1 gp120 core reveals that this broadly neutralizing CD4 binding site (CD4bs) antibody partially mimics the interaction of the primary virus receptor, CD4, with gp120. Here, we extended the investigation of the VRC01-gp120 core interaction to the biologically relevant viral spike to better understand the mechanism of VRC01-mediated neutralization and to define viral elements associated with neutralization resistance. In contrast to the interaction of CD4 or the CD4bs monoclonal antibody (MAb) b12 with the HIV-1 envelope glycoprotein (Env), occlusion of the VRC01 epitope by quaternary constraints was not a major factor limiting neutralization. Mutagenesis studies indicated that VRC01 contacts within the gp120 loop D, the CD4 binding loop, and the V5 region were necessary for optimal VRC01 neutralization, as suggested by the crystal structure. In contrast to interactions with the soluble gp120 monomer, VRC01 interaction with the native viral spike did not occur in a CD4-like manner; VRC01 did not induce gp120 shedding from the Env spike or enhance gp41 membrane proximal external region (MPER)-directed antibody binding to the Env spike. Finally, VRC01 did not display significant reactivity with human antigens, boding well for potential in vivo applications. The data indicate that VRC01 interacts with gp120 in the context of the functional spike in a manner distinct from that of CD4. It achieves potent neutralization by precisely targeting the CD4bs without requiring alterations of Env spike configuration and by avoiding steric constraints imposed by the quaternary structure of the functional Env spike.

Thermodynamics of the hot BIon

We investigate the thermodynamics of the recently obtained finite temperature BIon solution of [G. Grignani, T. Harmark, A. Marini, N.A. Obers, M. Orselli, Heating up the BIon, arXiv:1012.1494 [hep-th]], focusing on two aspects. The first concerns comparison of the free energy of the three available phases for the finite-temperature brane–antibrane–wormhole configuration. Based on this we propose a heuristic picture for the dynamics of the phases that involves a critical temperature below which a stable phase exists. This stable phase is the finite temperature analogue of the thin throat branch of the extremal brane–antibrane–wormhole configuration. The second aspect that we consider is the possibility of constructing a finite temperature generalization of the infinite spike configuration of the extremal BIon. To this end we identify a correspondence point at the end of the throat where the thermodynamics of the D3–F1 blackfold configuration can be matched to that of k non-extremal black fundamental strings.

The Local Field Potential Reflects Surplus Spike Synchrony

While oscillations of the local field potential (LFP) are commonly attributed to the synchronization of neuronal firing rate on the same time scale, their relationship to coincident spiking in the millisecond range is unknown. Here, we present experimental evidence to reconcile the notions of synchrony at the level of spiking and at the mesoscopic scale. We demonstrate that only in time intervals of significant spike synchrony that cannot be explained on the basis of firing rates, coincident spikes are better phase locked to the LFP than predicted by the locking of the individual spikes. This effect is enhanced in periods of large LFP amplitudes. A quantitative model explains the LFP dynamics by the orchestrated spiking activity in neuronal groups that contribute the observed surplus synchrony. From the correlation analysis, we infer that neurons participate in different constellations but contribute only a fraction of their spikes to temporally precise spike configurations. This finding provides direct evidence for the hypothesized relation that precise spike synchrony constitutes a major temporally and spatially organized component of the LFP.

Spike-layer solutions to singularly perturbed semilinear systems of coupled Schrödinger equations

Let Ω be a bounded domain in RN(N⩽3), we are concerned with the interaction and the configuration of spikes in a double condensate by analyzing the least energy solutions of the following two couple Schrödinger equations in Ω(Sε){−ε2Δu+u=μ1u3+βuv2,−ε2Δv+v=μ2v3+βu2v,u>0,v>0, where μ1,μ2 are positive constants. We prove that under Neumann or Dirichlet boundary conditions, for any ε>0, when −∞<β<min{μ1,μ2} or β>max{μ1,μ2}, system (Sε) has a least energy solution (uε,vε) and when min{μ1,μ2}<β<max{μ1,μ2}, system (Sε) has no solution. Suppose Pε,Qε are the local maximum points of uε,vε respectively. Then under Neumann boundary conditions, as ε small enough, both of Pε,Qε locate on the boundary of Ω. Furthermore, when β⩾0, |Pε−Qε|ε→0 as ε→0 and for N=2 and N=3, Pε,Qε converge to the same point on the boundary which is the maximum point of mean curvature of the boundary. However, when β<0, |Pε−Qε|ε→∞ as ε→0 and suppose Pε→P and Qε→Q, then for N=2 and N=3, P,Q must be the maximum points of the mean curvature on the boundary and P,Q might be a same point if the mean curvature of the boundary has only one maximum point. Under Dirichlet boundary conditions, we can prove that as long as the least energy solution (Sε) exists, the same asymptotic behavior of the least energy solution (uε,vε) holds as described in Lin and Wei (2005) [10] for β>0 or for β<0, thus our results are an extension of the results in Lin and Wei (2005) [10].

Supervised Learning in Spiking Neural Networks with ReSuMe: Sequence Learning, Classification, and Spike Shifting

Learning from instructions or demonstrations is a fundamental property of our brain necessary to acquire new knowledge and develop novel skills or behavioral patterns. This type of learning is thought to be involved in most of our daily routines. Although the concept of instruction-based learning has been studied for several decades, the exact neural mechanisms implementing this process remain unrevealed. One of the central questions in this regard is, How do neurons learn to reproduce template signals (instructions) encoded in precisely timed sequences of spikes? Here we present a model of supervised learning for biologically plausible neurons that addresses this question. In a set of experiments, we demonstrate that our approach enables us to train spiking neurons to reproduce arbitrary template spike patterns in response to given synaptic stimuli even in the presence of various sources of noise. We show that the learning rule can also be used for decision-making tasks. Neurons can be trained to classify categories of input signals based on only a temporal configuration of spikes. The decision is communicated by emitting precisely timed spike trains associated with given input categories. Trained neurons can perform the classification task correctly even if stimuli and corresponding decision times are temporally separated and the relevant information is consequently highly overlapped by the ongoing neural activity. Finally, we demonstrate that neurons can be trained to reproduce sequences of spikes with a controllable time shift with respect to target templates. A reproduced signal can follow or even precede the targets. This surprising result points out that spiking neurons can potentially be applied to forecast the behavior (firing times) of other reference neurons or networks.

The hydrophobic properties of femtosecond laser fabricated spike structures and their effects on cell proliferation

AbstractSilicon (Si) spikes with an average tip surface of 1.4 μm2, an average depth 5.9 μm and a spike‐to‐spike distance of 4.8 μm have been produced with a commercial laser system which delivers sub‐30‐fs pulses at 800 nm and a repetition rate of 1 kHz. The fabricated spikes can be used for the generation of negative replica in soft material such as silicone elastomer. Since the Si spikes were not destroyed during the replication process, it is possible to reproduce ad libitum soft material with the same spike configuration rendering comparison possible. The analysis of the wettability of the surfaces revealed that the structuring induced an increase in hydrophobic character of Si as well as of silicone elastomer. This effect is related to the presence of air trapped in the microstructured surface. Analysis of the effect of the structuring on the proliferation activity of fibroblasts and SH‐SY5Y neuroblastoma cells showed that the spike structures and its negative replicas in silicone elastomer are able to suppress the proliferation of the fibroblasts for 48 h but did not affect the neuroblastoma cells. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Existence and stability analysis of spiky solutions for the Gierer–Meinhardt system with large reaction rates

We study the Gierer–Meinhardt system in one dimension in the limit of large reaction rates. First we construct three types of solution: (i) an interior spike; (ii) a boundary spike and (iii) two boundary spikes. Second we prove results on their stability. It is found that an interior spike is always unstable; a boundary spike is always stable. The two boundary spike configuration can be either stable or unstable, depending on the parameters. We fully classify the stability in this case. We characterize the destabilizing eigenfunctions in all cases. Numerical simulations are shown which are in full agreement with the analytical results.