Outgoing Directions Research Articles

Analyzing sharing strategies for finite buffer memory in a router among outgoing channels

We propose a model for a transit node in a data transmission network that distributes the incoming flow over several outgoing directions. We study the influence of the quality of communication channels, distribution of the shares of incoming traffic over outgoing directions, and strategies for dividing a limited buffer memory in the transit node among queues to outgoing communication channels on the throughput of the network fragment with incoming and outgoing interfaces of varying performance.

Directional wavefield decomposition

We bring an alternative view to the computation of the upgoing wavefield and generalize it to directional wavefield decomposition. We start by comparing the integral representation of the upgoing wavefield to the dispersion relation of the wave equation. Developing the relationship between the two, we write a Fourier transform representation that allows to generalize wavefield decomposition to an arbitrary direction. Decomposing the wavefield for arbitrary incoming and outgoing directions at the source and the receiver allows a complete decomposition of the data that can be used for many purposes, such as selecting or enhancing illumination directions for imaging and inversion.

Design of Engineered Reflectors for Radar Cross Section Modification

A technique is proposed for the design of engineered reflectors consisting of doubly periodic arrays printed on thin grounded dielectric substrates that reflect an incoming wave from a given incoming direction to a predetermined outgoing direction. The proposed technique is based on a combination of Floquet theory for propagation in periodic structures and reflect-array principles. A flat surface designed to reflect a TE polarized wave incident at 45° back in the direction of the impinging signal at 14.7 GHz is employed as an example. By means of full-wave simulations, it is demonstrated that the monostatic RCS of a finite reflector is comparable with the specular RCS of a metallic mirror of the same dimensions. It is further shown that comparably high monostatic RCS values are obtained for angles of incidence in the 30°-60° range, which are frequency dependent and thus open opportunities for target localization. A prototype array is fabricated and experimentally tested for validation. The proposed solution can be used to modify the radar cross section of a target. Other potential applications are also discussed.

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Efficient acoustic radiance transfer method with time‐dependent reflections.

Modern desktop computers are equipped with graphics cards that provide massive parallel computation power that was previously available only in supercomputers. On the other hand, there are several room acoustics modeling methods, but only some of them scale well to hundreds or thousands of parallel processors. The scalability of the acoustic radiance transfer method is examined. It is shown that it can almost fully utilize the available computing power. In simple cases, this technique achieves real‐time performance. While taking into account the limitations of the energy‐based acoustic modeling approach, the presented system can model arbitrary reflections. The reflections are presented as bi‐directional reflectance distribution functions, which depend on the incoming and outgoing directions of acoustic energy. It is also possible to add time‐dimension to such a reflection model. Some measurements are presented to show that spreading in time dimension occurs at reflections. Most of the previous room acoustics modeling techniques have ignored that phenomenon, but the acoustic radiance transfer technique can be easily modified to take this spreading effect into account.

Electron energy loss and diffraction of backscattered electrons from silicon

Electrons backscattered from crystals can show Kikuchi patterns: variations in intensity for different outgoing directions due to diffraction by the lattice. Here, we measure these effects as a function of their energy loss for 30 keV electrons backscattered from silicon. The change in diffraction contrast with energy loss depends strongly on the scattering geometry. At steep incidence on the sample, diffraction contrast in the observed Kikuchi bands decreases rapidly with energy loss. For an energy loss larger than about 150 eV the contrast is more than 5 times less than the contrast due to electrons near zero energy loss. However, for grazing incidence angles, maximum Kikuchi band contrast is observed for electrons with an energy loss near 60 eV, where the contrast is more than 2.5× larger than near zero energy loss. In addition, in this grazing incidence geometry, the Kikuchi diffraction effects stay significant even for electrons that have lost hundreds of electron volts. For the maximum measured energy loss of 440 eV, the electrons still show a contrast that is 1.5 × larger than that of the electrons near zero energy loss. These geometry-dependent observations of Kikuchi band diffraction contrast are interpreted based on the elastic and inelastic scattering properties of electrons and dynamical diffraction simulations.

The causal structure of dynamical charged black holes

We study the causal structure of dynamical charged black holes, with a sufficient number of massless fields, using numerical simulations. Neglecting Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature singularity due to mass inflation. When we include Hawking radiation, the inner horizon becomes space-like and is separated from the Cauchy horizon, which is parallel to the out-going null direction. Since a charged black hole must eventually transit to a neutral black hole, we studied the neutralization of the black hole and observed that the inner horizon evolves into a space-like singularity, generating a Cauchy horizon which is parallel to the in-going null direction. Since the mass function is finite around the inner horizon, the inner horizon is regular and penetrable in a general relativistic sense. However, since the curvature functions become trans-Planckian, we cannot say more about the region beyond the inner horizon, and it is natural to say that there is a ‘physical’ space-like singularity. However, if we assume an exponentially large number of massless scalar fields, our results can be extended beyond the inner horizon. In this case, strong cosmic censorship and black hole complementarity can be violated.

Vibrational modes inZnGeN2: Raman study and theory

Polarized Raman spectra were measured for single crystals and polycrystalline ${\text{ZnGeN}}_{2}$ grown by a vapor-liquid-solid method. A group-theoretical analysis of the selection rules governing the predicted dependence of the spectra on incoming and outgoing wave polarizations and propagation direction is presented. First-order Raman spectra corresponding to the zone center phonons are calculated from first principles using density functional perturbation theory. The Brillouin zone integrated density of phonon states is also calculated. Comparison of theory and experiment allows us to identify the ${a}_{1t}$ symmetry modes. However, vibrational density of states features deviating from the pure ${a}_{1t}$ spectrum are also visible in the experimental spectra and indicate some relaxation of momentum conservation rules. Differences in the experimental spectra under different polarization conditions are compared to the calculations. These differences allow us to identify different ${a}_{1t}$ Raman tensor components as well as to obtain at least partial information on the ${b}_{2t}$ modes. The much weaker polarization dependence in experiment than in theory, however, can at least in part be explained by using wurtzite-type selection rules. The observation of features explainable with wurtzite together with orthorhombic selection rules suggest that there is only partial ordering of the cations on their sublattice.

Anisotropy and Interference in Wave Transport: An Analytic Theory

A theory is presented which incorporates the effect of dielectric anisotropy in random multiple scattering media. It predicts anisotropic diffusion, and a deflection of the diffuse energy flow in anisotropic slabs in the direction parallel to the slab. The transmittance integrated over all incoming and outgoing directions scales with the transport mean free path along the surface normal. The escape function in anisotropic dielectrics is no longer bell shaped. In this model anisotropy facilitates Anderson localization.

Linear approximation of Bidirectional Reflectance Distribution Functions

Various empirical and theoretical models of the surface reflectance have been introduced so far. Most of these models are based on functions with non-linear parameters and therefore faces some computational difficulties involved in non-linear optimization processes. In this paper, we introduce a new approach for approximating Bidirectional Reflectance Distribution Functions (BRDF) by employing response surface methodology. The proposed model employs principal component transformations of the explanatory variables which are essentially functions of incoming and outgoing light directions. The resulting model is linear and can be used to represent both isotropic and anisotropic reflectance for diffuse and glossy materials. Considering some widely used reflection models including the Ward model, the Ashikhmin-Shirley model and the Lafortune model, we demonstrate empirically that satisfactory approximations can be made by means of the proposed general, simple and computationally efficient linear model.

Optimal ranking in networks with community structure

The World-Wide Web (WWW) is characterized by a strong community structure in which groups of webpages (e.g. those devoted to a common topic or belonging to the same organization) are densely interconnected by hyperlinks. We study how such network architecture affects the average Google rank of individual communities. Using a mean-field approximation, we quantify how the average Google rank of community webpages depend on the degree to which it is isolated from the rest of the world in both incoming and outgoing directions, and α the only intrinsic parameter of Google's PageRank algorithm. Based on this expression we introduce a concept of a web-community being decoupled or conversely coupled to the rest of the network. We proceed with empirical study of several internal web-communities within two US universities. The predictions of our mean-field treatment were qualitatively verified in those real-life networks. Furthermore, the value α = 0.15 used by Google seems to be optimized for the degree of isolation of communities as they exist in the actual WWW.

Evaluation of effects of irregular shape on quantitative XRF analysis of metal objects

Quantitative XRF analysis of metal alloys can be obtained by using the general fundamental parameter method based on the comparison of x-ray line fluorescence intensities with those obtained from reference standard pellets in identical experimental conditions. Corrections for auto absorption and secondary excitation effects are fundamental to obtaining quantitative results. When analyzing a real object with irregular, or at least nonpellet-shaped, geometry and/or of incorrect positioning, an additional correction factor for x-ray fluorescence line intensities must be entered. In this paper we review the problem of the contributions to the error specific to an irregular surface or incorrect positioning intrinsic to the fundamental parameter method, in the more enlarged context of considering a real experimental setup in which irradiation and detection angles are not exactly constant, as assumed in the fundamental parameter method. They are accounted for by the corrective irregular shape factors. In principle, these factors must be separately calculated for each value of excitation and characteristic x-ray energies, and the relative precision in the quantitative determination of elemental concentrations with the fundamental parameter method can be estimated from the relative amplitude of the variation of shape factor values depending on the exciting energy spectrum. One obtains the result that the correction due to irregular shape or incorrect positioning of the object under examination tends to the limit 1, or, more generally, to a constant value independent of the excitation and emission x-ray energies in the limiting case where the direction of the exciting radiation coincides with that of the detected fluorescence x-rays. The results of calculations of the relative precision of XRF quantitative analysis are shown for gold-based alloy objects in some specific cases of surface roughness and positioning of the object. Dispersion around the nominal values for the angles of incoming and outgoing x-ray directions is assumed as determined by the geometric conditions in two selected instrumental setups. A nominal value of 45° was assumed for both the angles in the first case. In the second case, we considered an irradiation setup where the condition of coincidence for incoming and outgoing x-ray directions is nearly achieved by employing an annular silicon drift detector (SDD) with a central hole, which allows the passage of the exciting x-rays. An interesting result obtained in the latter case is that, looking only at the dependence on the irregular shape, an attainable precision on the order of <1‰ can be achieved. In view of the possible applications of quantitative XRF analysis to jewellery, employing SDD detectors capable of very high counting rates should allow a statistical error under the above-mentioned limit in a reasonably short measuring time. However, concerning the error deriving from intrinsic x-ray tube instability, an investigation aimed at achieving a stable enough system is still needed. Copyright © 2006 John Wiley & Sons, Ltd.

Robustness of the in-degree exponent for the World-Wide Web.

We consider a stochastic model for directed scale-free networks following power laws in the degree distributions in both incoming and outgoing directions. In our model, the number of vertices grow geometrically with time with a growth rate p. At each time step, (i) each newly introduced vertex is connected to a constant number of already existing vertices with the probability linearly proportional to in-degree distribution of a selected vertex, and (ii) each existing vertex updates its outgoing edges through a stochastic multiplicative process with mean growth rate of outgoing edges g and its variance sigma(2). Using both analytic treatment and numerical simulations, we show that while the out-degree exponent gamma(out) depends on the parameters, the in-degree exponent gamma(in) has two distinct values, gamma(in)=2 for p>g and 1 for p<g, independent of different parameters values. The latter case has logarithmic correction to the power law. Since the vertex growth rate p is larger than the degree growth rate g for the World-Wide Web (WWW) nowadays, the in-degree exponent appears robust as gamma(in)=2 for the WWW.

Reciprocity principle for radiative transfer models that use periodic boundary conditions

Many numerical models use periodic boundary conditions in solving the radiative transfer through heterogeneous media specified over a fixed domain. A reciprocity principle applicable to solutions from these models is derived for the common situation of a scattering and absorbing heterogeneous medium that is illuminated over the entire domain from a single direction. The derived reciprocity principle states that the domain-averaged bidirectional reflectance distribution function remains invariant when incoming and outgoing directions are interchanged, regardless of the heterogeneity of the medium and the size of the domain. This reciprocity principle provides a simple and useful benchmark test for radiative transfer models that use periodic boundary conditions.

Monochromator development at 4W1B beamline of BSRF

The 4W1B is a X-ray monochromator beamline for XAFS at BSRF. During the upgrading phase, we have redesigned the monochromator to improve the performance of the beamline. It is a goniometer based, fixed exit double crystal monochromator. A mechanical linkage is employed to adjust the distance between the surfaces of the two crystals as the Bragg angle is changed to keep the outgoing beam direction constant. The whole mechanism is driven by only one stepping motor. The testing result shows that over the scanning range of 5–30°, the shift of outgoing beam position is less then 70 μm in the vertical direction. The basic principle, the mechanical realization, and the error analysis are discussed in detail. The performance and the testing results are also presented in this paper.

Polarimetric neutron spin echo

Neutron spin echo (NSE) spectroscopy inherently involves polarization analysis features. Thus, the very principle of paramagnetic NSE used for the study of magnetically isotropic systems is based on the vector properties of the neutron polarization change in the scattering, which implies that the incoming and outgoing neutron spin directions are not parallel. Another, conventional polarization analysis feature is the opposite sign of the NSE signal for nuclear and nuclear-spin incoherent scattering, or the signal parallel and perpendicular magnetic fluctuations in the presence of a strong magnetizing field. In these cases the measured NSE spectra are the algebraic sums of two components. In its actual form, however, NSE does not allow one to investigate spin-flip and non-spin-flip scattering channels independently from each other. At the expense of rather moderate loss of signal it is, however, possible to generalize the NSE technique for the study of a given channel of spin-dependent scattering processes in the most general sense of neutron polarimetry. This means to perform inelastic NSE analysis on the partial scattering cross-section corresponding to the transition from any incoming spin direction P to any outgoing spin direction P′ . A method of combining NSE with neutron polarimetry will be described together with a simple example of experimental realization.

Asymptotic Properties of the Electromagnetic Field in the External Schwarzschild Spacetime

We study the asymptotic behaviour of the solutions to the vacuum Maxwell equations in the external Schwarzschild spacetime. The results are based on the extensive use of geometric considerations and the introduction of generalized energy estimates. We obtain the asymptotic behaviour along the null outgoing directions and we prove also some partial results concerning the behaviour along the timelike curves. Our techniques can be also used to control the asymptotic behaviour of the various derivatives of the Maxwell field and to obtain the asymptotic behaviour of the Weyl tensor fields, solutions of the spin 2 equations.

A Comparison of Angular Difference Schemes for One-Dimensional Spherical Geometry SN Equations

To investigate errors caused by angular differencing in approximating the streaming terms of the transport equation, five different approximations are evaluated for three test problems in one-dimensional spherical geometry. The following schemes are compared: diamond, special truncation error minimizing weighted diamond, linear continuous (the original SN scheme), linear discontinuous, and new quadratic continuous. To isolate errors caused by angular differencing, the approximations are derived from the transport equation without spatial differencing, and the resulting coupled ordinary differential equations (ODEs) are solved with an ODE solver. Results from the approximations are compared with analytic solutions derived for two-region purely absorbing spheres. Most of the approximations are derived by taking moments of the conservation form of the transport equation. The quadratic continuous approximation is derived taking the zeroth moment of both the transport equation and the first angular derivative of the transport equation. The advantages of this approach are described. In all of the approximations, the desirability is shown of using an initializing computation of the μ = -1 angular flux to correctly compute the central flux and of having a difference approximation that ensures this central flux is the same for all directions. The behavior of the standard discrete ordinates equations in the diffusion limit is reviewed, and the linear and quadratic continuous approximations are shown to have the correct diffusion limit if an equal interval discrete quadrature is used.In all three test problems, the weighted diamond difference approximation has smaller maximum and average relative flux errors than the diamond or the linear continuous difference approximations. The quadratic continuous approximation and the linear discontinuous approximation are both more accurate than the other approximations, and the quadratic continuous approximation has a decided edge over the linear discontinuous approximation in relative flux errors. The diamond, weighted diamond, and linear continuous approximations show quadratic system absorption and system leakage error reduction behavior with increasing N. The linear discontinuous and quadratic continuous approximations show fourth-order error reduction in these quantities. In one of the two-region test problems, the slope of the exact angular flux changes from nearly vertical to nearly horizontal at those points in the exterior region at which the interior region source just becomes visible. At these spatial points, errors in the continuous approximations propagate to each successive outgoing direction, leading to an oscillatory spatial error. The discontinuous approximation does not propagate these errors, although errors near the point of rapid slope change are larger than in the quadratic continuous approximation.

Triply differential cross section for ionization of multielectronic targets

The Continuum Distorted Wave-Eikonal Initial State (CDW-EIS) approach is used to calculate the Triply Differential Cross Section (TDCS) for ionization of multielectronic atomic targets in coincidence with the outgoing projectile direction and recoil momentum of the target. A generatrix state method is used to evaluate the transition amplitudes for a general initial atomic state. The structures presented in both TDCSs are compared standing out the double collision mechanisms. The results obtained in CDW-EIS approximation are compared with previous classical trajectories Monte Carlo (CTMC) calculations.

Generating Reflected Directions from BRDF Data

Monte‐Carlo path tracing algorithms for computer graphics require that given an incident light ray at a surface an outgoing direction can be computed with a distribution given by the magnitude of the bidirectional reflectance distribution function (BRDF). For analytic reflectance functions this can be done using various techniques including inverting the function, or tabulating some representation of the inverse. However, measured BRDF data sets are too large for this to be practical.We present a method to generate reflection rays distributed according to the magnitude of the BRDF. The method relies on a wavelet‐based representation of the BRDF. This representation is efficient and compact, allowing large, anisotropic measured BRDF data sets to be represented with a few thousand coefficients. In particular, we exploit the wavelet representation to quickly compute integrals over ranges of the BRDF.