Showing papers on "Energy (signal processing) published in 2002"

Symmetry-general least-squares extraction of elastic data for strained materials from ab initio calculations of stress

Abstract: A symmetry-general approach for the least-squares, therefore precise, extraction of elastic coefficients for strained materials is reported. It analyzes stresses calculated ab initio for properly selected strains. The problem, its implementation, and its solution strategy all differ radically from a previous energy-strain approach that we published last year, but the normal equations turn out to be amenable to the same constrainment scheme that makes both approaches symmetry general. The symmetry considerations governing the automated selection of appropriately strained models and their Cartesian systems are detailed. The extension to materials under general stress is discussed and implemented. VASP was used for ab initio calculation of stresses. A comprehensive range of examples includes a triclinic material (kyanite) and simple materials with a range of symmetries at zero pressure, MgO under hydrostatic pressure, ${\mathrm{Ti}}_{4}{\mathrm{As}}_{3}$ under [001] uniaxial strain, and Si under [001] uniaxial stress. The MgO case agrees with recent experimental work including elastic coefficients as well as their first and second derivatives. The curves of elastic coefficients for Si show a gradual increase in the 33 compliance coefficient, leading to a collapse of the material at -11.7 GPa, compared with -12.0 GPa experimentally. Interpretation of results for Be using two approximations [local density (LDA), generalized gradient (GGA)], two approaches (stress strain and energy strain), two potential types (projector augmented wave and ultrasoft), and two quantum engines (VASP and ORESTES) expose the utmost importance of the cell data used for the elastic calculations and the lesser importance of the other factors. For stiffness at relaxed cell data, differences are shown to originate mostly in the considerable overestimation of the residual compressive stresses at x-ray cell data by LDA, resulting in a smaller relaxed cell, thus larger values for diagonal stiffness coefficients. The symmetry generality of the approach described here enabled the creation of a robust user interface going seamlessly from the database search to the printout of the elastic coefficients. With it, even nonspecialist users can reliably produce technologically relevant results like those discussed here in a simple point-and-click fashion from corresponding entries in the CRYSTMET\textregistered{} and ICSD\textregistered{} structure databases, i.e., for all pure-phase nonorganic materials with known crystal structure. The case of ${\mathrm{Ti}}_{4}{\mathrm{As}}_{3}$ exposes, on a first cluster of properties, stiffness, compliance, and the isotropic properties that can be derived from them, the current reality of mining crystal structure databases with ab initio software for technological properties that were never measured before. Further developments in that direction are currently underway.

Can the clustered dark matter and the smooth dark energy arise from the same scalar field

Abstract: Cosmological observations suggest the existence of two different kinds of energy densities dominating at small $(\ensuremath{\lesssim}500\mathrm{Mpc})$ and large $(\ensuremath{\gtrsim}1000\mathrm{Mpc})$ scales. The dark matter component, which dominates at small scales, contributes ${\ensuremath{\Omega}}_{m}\ensuremath{\approx}0.35$ and has an equation of state $p=0,$ while the dark energy component, which dominates at large scales, contributes ${\ensuremath{\Omega}}_{V}\ensuremath{\approx}0.65$ and has an equation of state $p\ensuremath{\simeq}\ensuremath{-}\ensuremath{\rho}.$ It is usual to postulate weakly interacting massive particles (WIMPs) for the first component and some form of scalar field or cosmological constant for the second component. We explore the possibility of a scalar field with a Lagrangian $L=\ensuremath{-}V(\ensuremath{\varphi})\sqrt{1\ensuremath{-}{\ensuremath{\partial}}^{i}\ensuremath{\varphi}{\ensuremath{\partial}}_{i}\ensuremath{\varphi}}$ acting as both clustered dark matter and smoother dark energy and having a scale-dependent equation of state. This model predicts a relation between the ratio $r={\ensuremath{\rho}}_{V}/{\ensuremath{\rho}}_{\mathrm{DM}}$ of the energy densities of the two dark components and an expansion rate n of the universe [with $a(t)\ensuremath{\propto}{t}^{n}]$ in the form $n=(2/3)(1+r).$ For $r\ensuremath{\approx}2,$ we get $n\ensuremath{\approx}2$ which is consistent with observations.

Parallel calculation of electron multiple scattering using Lanczos algorithms

Abstract: Real space multiple scattering calculations of the electronic density of states and x-ray spectra in solids typically scale as the cube of the system and basis set size, and hence are highly demanding computationally. For example, such x-ray absorption near edge structure (XANES) calculations typically require clusters of order ${N}_{R}$ atoms and s, p, and d states for convergence, with ${N}_{R}$ between about ${10}^{2}--{10}^{3};$ for this case about ${10}^{2}$ inversions of ${9N}_{R}\ifmmode\times\else\texttimes\fi{}{9N}_{R}$ matrices are needed, one for each energy point. We discuss here two ways to speed up these calculations: (1) message passing interface (MPI) parallel processing and (2) fast, Lanczos multiple scattering algorithms. Together these algorithms can reduce computation times typically by two orders of magnitude. These are both implemented in a generalization of the ab initio self-consistent FEFF8 code, which thus makes practical XANES calculations in complex systems with of order ${10}^{3}$ atoms. The Lanczos algorithm also yields a natural crossover between full and finite-order multiple scattering with increasing energy, thus differentiating the extended and near-edge regimes.

Energy detection of a signal with random amplitude

Abstract: Urkowitz (1967) has discussed the detection of a deterministic signal of unknown structure in the presence of band-limited Gaussian noise. That analysis is developed to the case of a signal with random (Rayleigh, Rice, Nakagami, and other) amplitude. For such amplitude the distribution of a decision statistic of an energy detector is retrieved and expressions for detection probability are obtained.

Chemical-order-dependent magnetic anisotropy and exchange stiffness constant of FePt (001) epitaxial films

Abstract: Anomalous Hall voltage was measured for FePt ${L1}_{0}$ films having very high magnetic anisotropy. The magnetic anisotropy ${K}_{1}$ and ${K}_{2}$ were determined with high accuracy by analyzing the magnetization curves obtained from the Hall voltage measurement. The saturation magnetization ${M}_{s}$ of the samples with different chemical-order parameter (S) exhibits a different temperature dependence, implying that the Curie temperature weakly depends on S. The first-order anisotropy ${K}_{1}$ gradually increases with S, while the second-order anisotropy ${K}_{2}$ remains almost constant of about $5\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{e}\mathrm{r}\mathrm{g}/\mathrm{c}\mathrm{c}.$ The temperature dependence of ${K}_{1}$ is correlated with S, that is, ${K}_{1}$ with a small S is more temperature dependent than that with a large S. These behaviors are quite similar to the temperature dependence of ${M}_{s}$ with different S, and can be explained by the conventional model based on thermal spin fluctuations. The domain wall energy ${\ensuremath{\sigma}}_{w}$ evaluated by the theoretical analysis of the stripe-domain structure tends to increase linearly with S, in a similar manner as that of ${K}_{1},$ whereas the exchange stiffness constant A of about $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\mathrm{e}\mathrm{r}\mathrm{g}/\mathrm{c}\mathrm{m}$ deduced from ${\ensuremath{\sigma}}_{w}$ and ${K}_{u}{(=K}_{1}{+K}_{2})$ hardly depends on S.

Effect of the minimal length uncertainty relation on the density of states and the cosmological constant problem

Abstract: We investigate the effect of the minimal length uncertainty relation, motivated by perturbative string theory, on the density of states in momentum space. The relation is implemented through the modified commutation relation $[{x}_{i},{p}_{j}]=i\ensuremath{\Elzxh}[(1+\ensuremath{\beta}{p}^{2}){\ensuremath{\delta}}_{\mathrm{ij}}+{\ensuremath{\beta}}^{\ensuremath{'}}{p}_{i}{p}_{j}].$ We point out that this relation, which is an example of a UV/IR relation, implies the finiteness of the cosmological constant. While our result does not solve the cosmological constant problem, it does shed new light on the relation between this outstanding problem and UV/IR correspondence. We also point out that the blackbody radiation spectrum will be modified at higher frequencies, but the effect is too small to be observed in the cosmic microwave background spectrum.

Exact solution of the harmonic oscillator in arbitrary dimensions with minimal length uncertainty relations

Abstract: We determine the energy eigenvalues and eigenfunctions of the harmonic oscillator where the coordinates and momenta are assumed to obey the modified commutation relations $[{x}_{i},{p}_{j}]=i\ensuremath{\Elzxh}[(1+\ensuremath{\beta}{p}^{2}){\ensuremath{\delta}}_{\mathrm{ij}}+{\ensuremath{\beta}}^{\ensuremath{'}}{p}_{i}{p}_{j}].$ These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relations which appear in perturbative string theory. Our solutions illustrate how certain features of string theory may manifest themselves in simple quantum mechanical systems through the modification of the canonical commutation relations. We discuss whether such effects are observable in precision measurements on electrons trapped in strong magnetic fields.

Breaking eight fold degeneracies in neutrino CP violation, mixing, and mass hierarchy

Abstract: We identify three independent twofold parameter degeneracies $(\ensuremath{\delta},{\ensuremath{\theta}}_{13}),$ $\mathrm{sgn}(\ensuremath{\delta}{m}_{31}^{2})$ and $({\ensuremath{\theta}}_{23},\ensuremath{\pi}/2\ensuremath{-}{\ensuremath{\theta}}_{23})$ inherent in the usual three-neutrino analysis of long-baseline neutrino experiments, which can lead to as much as an eightfold degeneracy in the determination of the oscillation parameters. We discuss the implications these degeneracies have for detecting $\mathrm{CP}$ violation and present criteria for breaking them. A superbeam facility with a baseline at least as long as the distance between Fermilab and Homestake (1290 km) and a narrow band beam with energy tuned so that the measurements are performed at the first oscillation peak can resolve all the ambiguities other than the $({\ensuremath{\theta}}_{23},\ensuremath{\pi}/2\ensuremath{-}{\ensuremath{\theta}}_{23})$ ambiguity (which can be resolved at a neutrino factory) and a residual $(\ensuremath{\delta},\ensuremath{\pi}\ensuremath{-}\ensuremath{\delta})$ ambiguity. However, whether or not $\mathrm{CP}$ violation occurs in the neutrino sector can be ascertained independently of the latter two ambiguities. The $(\ensuremath{\delta},\ensuremath{\pi}\ensuremath{-}\ensuremath{\delta})$ ambiguity can be eliminated by performing a second measurement to which only the $\mathrm{cos}\ensuremath{\delta}$ terms contribute. The hierarchy of mass eigenstates can be determined at other oscillation peaks only in the most optimistic conditions, making it necessary to use the first oscillation maximum. We show that the degeneracies may severely compromise the ability of the proposed SuperJHF-HyperKamiokande experiment to establish $\mathrm{CP}$ violation. In our calculations we use approximate analytic expressions for oscillation probabilitites that agree with numerical solutions with a realistic Earth density profile.

Digital Computation of Fractional Fourier Transform

Abstract: Based on the concept of the fractional fourier transform, its digital computation is given through computer simulation. In terms of linear frequency modulation (LFM) signal, the relation between fractional order and modulation slope is analyzed and the performance comparison with matched filter is given. Moreover, the separation of LFM signal and noise is realized in low signal-to-noise ratio through simulation. Simulation results indicate that the energy of LFM signal will be collected effectively when the fractional order is matching with its modulation slope. In weak signals detection of underwater acoustic domain, we can get high anti-Doppler performance using the Fractional fourier transform algorithm.

Short distance versus long distance physics: The classical limit of the minimal length uncertainty relation

Abstract: We continue our investigation of the phenomenological implications of the ``deformed'' commutation relations $[{x}_{i},{p}_{j}]=i\ensuremath{\Elzxh}[(1+\ensuremath{\beta}{p}^{2}){\ensuremath{\delta}}_{\mathrm{ij}}+{\ensuremath{\beta}}^{\ensuremath{'}}{p}_{i}{p}_{j}].$ These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relation which appears in perturbative string theory. In this paper, we consider the effects of the deformation on the classical orbits of particles in a central force potential. Comparison with observation places severe constraints on the value of the minimum length.

On the use of the adiabatic molecular dynamics technique in the calculation of free energy profiles

Abstract: A new molecular dynamics method for calculating free energy profiles for rare events is presented. The new method is based on the creation of an adiabatic separation between a reaction coordinate subspace and the remaining degrees of freedom within a molecular dynamics run. This is achieved by associating with the reaction coordinate(s) a high temperature and large mass, thereby allowing the activated process to occur while permitting the remaining degrees of freedom to respond adiabatically. In this limit, by applying a formal multiple time scale Liouville operator factorization, it can be rigorously shown that the free energy profile is obtained directly from the probability distribution of the reaction coordinate subspace and, therefore, no unbiasing of the configuration space or postprocessing of the output data is required. The new method is applied to a variety of model problems including a two-dimensional free energy surface and its performance tested against free energy calculations using the “blue moon ensemble” approach. The comparison shows that free energy profiles can be calculated with greater ease and efficiency using the new method.

Probing the high density behavior of the nuclear symmetry energy with high energy heavy-ion collisions.

Abstract: High energy heavy-ion collisions are proposed as a novel means to constrain stringently the high density (HD) behavior of nuclear symmetry energy. Within an isospin-dependent hadronic transport model, it is shown for the first time that the isospin asymmetry of the HD nuclear matter formed in high energy heavy-ion collisions is uniquely determined by the HD behavior of the nuclear symmetry energy. Experimental signatures in two sensitive probes, i.e., ${\ensuremath{\pi}}^{\ensuremath{-}}$ to ${\ensuremath{\pi}}^{+}$ ratio and neutron-proton differential collective flow, are also investigated.

Pseudorapidity distributions of charged particles from Au+Au collisions at the maximum RHIC energy

Abstract: We present charged-particle multiplicities as a function of pseudorapidity and collision centrality for the ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ reaction at $\sqrt{{s}_{\mathrm{NN}}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}200\mathrm{GeV}$. For the $5%$ most central events we obtain ${\mathrm{dN}}_{\mathrm{ch}}/d\ensuremath{\eta}{|}_{\ensuremath{\eta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}625\ifmmode\pm\else\textpm\fi{}55$ and ${N}_{\mathrm{ch}}{|}_{\ensuremath{-}4.7\ensuremath{\le}\ensuremath{\eta}\ensuremath{\le}4.7}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4630\ifmmode\pm\else\textpm\fi{}370$, i.e., $14%$ and $21%$ increases, respectively, relative to $\sqrt{{s}_{\mathrm{NN}}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}130\mathrm{GeV}$ collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around midrapidity. These results constrain current models of particle production at the highest RHIC energy.

Energy aware network management

Abstract: A method of managing a network of sensors in an energy aware manner includes the steps of clustering the sensors to minimize energy consumption, routing the network (step 44), modeling the energy available at each sensor (step 45), and re-routing the network (step 47) when the sensor battery level drops to a predetermined value, or when the energy model is adjusted because it deviates from a sensor's actual energy state.

Generation of highly coherent submicrojoule soft x rays by high-order harmonics

Abstract: We demonstrated the energy scaling of high-order harmonics using a self-guided beam under the phase-matched condition. By adjusting the argon gas density and pump laser focusing condition, a total output harmonic energy as high as $0.7 \ensuremath{\mu}\mathrm{J}$ was obtained in the spectral region of 34.8 to 25.8 nm (the corresponding order of the 23rd to 31st harmonic), while the 27th-order harmonic (29.6 nm) energy attained was as high as $0.3 \ensuremath{\mu}\mathrm{J}.$

Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma.

Abstract: A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of $I{\ensuremath{\lambda}}^{2}g{10}^{22}\mathrm{W}\ensuremath{\mu}{\mathrm{m}}^{2}/{\mathrm{cm}}^{2}$ and duration of 20 fs can convert more than $35%$ of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas.

Application of the fractional Fourier transform to moving target detection in airborne SAR

Abstract: As a useful signal processing technique, the fractional Fourier transform (FrFT) is largely unknown to the radar signal processing community. In this correspondence, the FrFT is applied to airborne synthetic aperture radar (SAR) slow-moving target detection. For airborne SAR, the echo from a ground moving target can be regarded approximately as a chirp signal, and the FrFT is a way to concentrate the energy of a chirp signal. Therefore, the FrFT presents a potentially effective technique for ground moving target detection in airborne SAR. Compared with the common Wigner-Ville distribution (WVD) algorithm, the FrFT is a linear operator, and will not be influenced by cross-terms even if multiple moving targets exist. Moreover, to solve the problem whereby weak targets are shadowed by the sidelobes of strong ones, a new implementation of the CLEAN technique is proposed based on filtering in the fractional Fourier domain. In this way strong moving targets and weak ones can be detected iteratively. This combined method is demonstrated by using raw clutter data combined with simulated moving targets.

Complete mapping of the anisotropic free energy of the crystal-melt interface in Al

Abstract: We have calculated the complete anisotropic crystal-melt interfacial free energy of aluminum, using molecular dynamics simulations of the interfaces in equilibrium. The interfacial free energy, $\ensuremath{\gamma}(\mathbf{n}^),$ can be expressed in terms of two anisotropic parameters, $\ensuremath{\epsilon}=1.2$% and $\ensuremath{\delta}=\ensuremath{-}1.2%,$ as well as an average free energy of ${\ensuremath{\gamma}}_{0}=149{\mathrm{m}\mathrm{J}/\mathrm{m}}^{2}$ in reasonable agreement with current experimental results. The expansion of the free energy in terms of these parameters is consistent with six different orientations, including the (111) interfacial plane, which is found to be rough despite its large stiffness.

Processing of interlaced images in 4–10 MeV dual energy customs system for material recognition

Abstract: The aim of this article is to demonstrate the practical value of radioscopic differentiation of materials in the 1--10 MeV energy range to the work of customs services. The proposed method for achieving singling out and identifying four basic groups of materials according to an atomic number is complex. Atomic numbers are identified using high- and low-energy profiles obtained through the irradiation of materials on an alternate pulse-by-pulse basis. This is done using a bremsstrahlung beam with $8\text{ }\mathrm{MeV}/4\text{ }\mathrm{MeV}$ dual boundary energies and by using scintillating crystals coupled with silicon photodiodes as detecting elements. An image segmentation technique is then used to discern the distribution of an atomic number on any given image. The color visualization of integral absorption and a material's atomic composition is carried out according to the intensity hue saturation (IHS) colorization scheme. The experiments were carried out on a full-scale prototype of an 8 MeV customs inspection system developed by the Efremov Research Institute.

Selected new aspects of the calculus of variations in the large

Abstract: We discuss some of the recent developments in variational methods while emphasizing new applications to nonlinear problems We touch on several issues: (i) the formulation of variational set-ups which provide more information on the location of critical points and therefore on the qualitative properties of the solutions of corresponding Euler-Lagrange equations; (ii) the relationships between the energy of variationally generated solutions, their Morse indices, and the Hausdorff measure of their nodal sets; (iii) the gluing of several topological obstructions; (iv) the preservation of critical levels after deformation of functionals; (v) and the various ways to recover compactness in certain borderline variational problems

Composition dependence of optical phonon energies and Raman line broadening in hexagonal Al x Ga 1 − x N alloys

Abstract: Studies of first- and second-order Raman scattering in hexagonal ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloys are reported. The dependences of frequencies of all Raman-allowed optical phonons versus Al content are traced in detail in the entire composition range. The one-mode behavior of LO phonons and the two-mode behavior of the other phonons is established. It is shown that the composition dependences of ${A}_{1}(\mathrm{TO}),$ ${A}_{1}(\mathrm{LO}),$ ${E}_{1}(\mathrm{LO}),$ and ${E}_{2}(\mathrm{low})$ phonon energies are convenient tools for the quantitative characterization of the Al content in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloys. The energy position of the ${B}_{1}(\mathrm{high})$ silent mode is proposed. A narrow gap separating the dispersion regions of transverse and longitudinal optical phonons is revealed in the phonon density-of-state function. The composition dependence of the phonon line broadening is investigated experimentally and theoretically. It is shown that the broadening is due to elastic phonon scattering by the composition fluctuations. A theoretical approach is used where the statistical and dynamical aspects of the phonon scattering are treated separately. The type, size, and number of the fluctuations responsible for the phonon line broadening are estimated. The theory is qualitatively consistent with the observed composition dependences.

Ground-state energies for helium, H − , and Ps −

Abstract: A triple basis set in Hylleraas coordinates is used to obtain improved variational bounds for the nonrelativistic energy and other properties of He, ${\mathrm{H}}^{\ensuremath{-}},$ and ${\mathrm{Ps}}^{\ensuremath{-}}.$ The accuracy, numerical stability, and computational efficiency are compared with recent work based on quasirandom basis sets. The Kato cusp conditions are used to assess the accuracy of the wave functions at short distances.

Quantum chaos and 1/f noise.

Abstract: It is shown that the energy spectrum fluctuations of quantum systems can be formally considered as a discrete time series. The power spectrum behavior of such a signal for different systems suggests the following conjecture: The energy spectra of chaotic quantum systems are characterized by 1/f noise.

Atomic structure of dislocation cores in GaN

Abstract: The atomic structures of a and c dislocation cores in the wurtzite gallium nitride have been studied by atomic computer simulation using an interatomic potential of the Stillinger-Weber type. Initially, the field of displacements is imposed according to the classical linear elasticity theory and then the system is relaxed to the minimum energy. The dislocation cores present multiple structures that can be related to the location of the dislocation line. The shape and extension of the dislocation cores are analyzed by means of the atomic relative displacements map. The core energy ${E}_{c}$ and core radius ${r}_{c}$ are determined by fitting the strain energy stored in the cylinder of radius R, centered on the dislocation line, to the expression ${E}_{s}{(R)=A}_{0}\mathrm{ln}{(R/r}_{c}{)+E}_{c}.$

Icosahedral growth, magnetic behavior, and adsorbate-induced metal-nonmetal transition in palladium clusters

Abstract: Studies of the atomic and electronic structures of Pd clusters with 2-23, 55, and 147 atoms have been carried out using the ultrasoft pseudopotential plane wave method and the spin-polarized generalized gradient approximation for the exchange-correlation energy. We find predominantly an icosahedral growth in these clusters, and size dependent oscillatory magnetic moments that are not confined just to the surface atoms. Atomically closed shell 13-, 55-, and 147-atom clusters have large moments of $0.61{\ensuremath{\mu}}_{B}/\mathrm{atom},$ $0.47{\ensuremath{\mu}}_{B}/\mathrm{atom},$ and $0.41{\ensuremath{\mu}}_{B}/\mathrm{atom},$ respectively. But cubic ${\mathrm{Pd}}_{55}$ isomer has a low moment of $0.18{\ensuremath{\mu}}_{B}/\mathrm{atom}$ only, indicating the importance of the icosahedral structure in the development of magnetism in Pd clusters. The evolutions of the $\mathrm{sp}\ensuremath{-}d$ hybridization, the magnetic moment and the electronic structure are discussed as a function of the cluster size. The magnetic energy is found to be small. Further studies on the adsorption of H and O show that though both an increase as well as a decrease of the moment are possible, often there is a reduction in the magnetic moments of Pd clusters. A hydrogen induced metal to nonmetal transition is predicted in ${\mathrm{Pd}}_{6}{\mathrm{H}}_{8}$ and ${\mathrm{Pd}}_{13}{\mathrm{H}}_{8}$ clusters.

Energy based collaborative source localization using acoustic micro-sensor array

Abstract: A novel sensor network source localization method based on acoustic energy measurements is presented. This method makes use of the characteristics that the acoustic energy decays exponentially with respect to the distance from an omni-directional acoustic source. By comparing energy readings measured at surrounding acoustic sensors during the same time interval can be accurately estimated. We show that the potential target location is restricted to a hyper-sphere in the sensor field given the acoustic energy reading at a pair of sensors. Given multiple sensor acoustic energy readings, the target location is solved as the location that is closest (in the least square sense) to all the corresponding hyper-spheres. We further simplified this nonlinear least square problem to an unconstrained linear least square problem that yields a closed form solution. Experiment results using military vehicle acoustic data show great promise of this novel approach.

First-principles calculations of lithium ordering and phase stability on Li x NiO 2

Abstract: The phase diagram of ${\mathrm{Li}}_{x}{\mathrm{NiO}}_{2}$ $(0lxl1)$ is calculated using a combination of first-principles energy methods and Monte Carlo simulations. The energy dependence of the Li-vacancy configurational disorder is parametrized with a cluster expansion. At room temperature ordered ${\mathrm{Li}}_{x}{\mathrm{NiO}}_{2}$ phases appear in the phase diagram at $x=1/4,$ 1/3, 2/5, 1/2, and 3/4. The predicted lithium-vacancy ordering at $x=1/4$ and 1/3 are in good agreement with experiments, while for the other phases no detailed experimental evidence has been reported. We predict a previously undetected phase at $x=2/5$ to dominate the phase diagram at low lithium content. The stability of ordered ${\mathrm{Li}}_{x}{\mathrm{NiO}}_{2}$ structures is determined by short-ranged repulsive in-plane Li-Li interactions and long-range attractive interplane Li-Li interactions. These attractive interplane Li-Li interactions are due to the Jahn-Teller activity of ${\mathrm{Ni}}^{+3}$ ions. As a result, ${\mathrm{Li}}_{x}{\mathrm{NiO}}_{2}$ behaves fundamentally different from ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2}$ even though their host structures are identical and Co and Ni have similar ionic sizes.

A hybrid approach to musical note onset detection

Abstract: Common problems with current methods of musical note onsetdetection are detection of fast passages of musical audio, detectionof all onsets within a passage with a strong dynamic range anddetection of onsets of varying types, such as multi-instrumentalmusic. We present a method that uses a subband decompositionapproach to onset detection. An energy-based detector is used onthe upper subbands to detect strong transient events. This yieldsprecision in the time resolution of the onsets, but does not detectsofter or weaker onsets. A frequency based distance measure isformulated for use with the lower subbands, improving detectionaccuracy of softer onsets.We also present a method for improving the detection func-tion, by using a smoothed difference metric. Finally, we show thatthe detection threshold may be set automatically from analysis ofthe statistics of the detection function, with results comparable inmost places to manual setting of thresholds. 1. BACKGROUND Note onset detection aims to find the start of musical events fromthe audio signal itself. It is an essential component of many largersystems such as automatic musical transcription schemes, non-linear time scaling [1], and many new audio effects and editingtools, such as ’beat detective’[2] from Digidesign. It is also com-mon for many synthesis applications to require isolation of the at-tack portions of notes.Despite some proposed solutions, it remains an unsolved, andoften over-simplified, problem. Traditional methods such as highfrequency detection rely on theassumption that allnote onsets con-tain high frequency energy [3]. The assumption that, for most in-struments, a note will contain more high frequency energy at itsonset is fair to make. However, in the case of real world audioexamples where there may be high notes with considerable highfrequency energy at their onset in the same region as low noteswith weak high frequency energy, the lower notes become almostimpossible to detect from the detection function. This work ad-dresses this problem directly.If we consider the nature of musical signals, there is a range ofdifferent types of instrument onsets. Figure 1 shows short sectionsof signals from a guitar and a violin. The guitar is a string in-strument that is played percussively, leading to ’hard’ note onsets,appearing as wide-band noise in the spectogram. For this type ofinstrument, high frequency content is a useful detection method.However, the violin in this figure is an example of a bowed stringinstrument, with a ’soft’ onset. The strings are excited because ofthe stick-slip caused by the friction of the bow. In this case, thenotes are being excited constantly, hence there is little, or no, de-cay. Here, the change in frequency content, particularly at lowerfrequencies, is our best guide to note onsets. Most everyday musi-cal signals contain a range of hard and soft onsets.Figure 1:

Improving the energy product of hard magnetic materials

Abstract: A route toward enhancing the energy product $(\mathrm{BH}{)}_{\mathrm{max}}$ of permanent magnetic materials, at room temperature, based on ferromagnetic-(FM-) antiferromagnetic (AFM) exchange interactions has been developed. The exchange coupling, which is induced by ball milling hard magnetic ${\mathrm{SmCo}}_{5}$ with AFM NiO powders, results in an enhancement of coercivity ${H}_{C}$ and squareness ratio ${M}_{R}{/M}_{S}$ (remnant-saturation magnetizations), which depends on the FM:AFM ratio and the processing conditions. However, the presence of the AFM in the composite results also in a competing effect, i.e., reduction of the overall saturation magnetization, which decreases $(\mathrm{BH}{)}_{\mathrm{max}}.$ Nevertheless, it has been found that after an optimization of the FM:AFM ratio and the milling conditions it is possible to achieve an improvement of $(\mathrm{BH}{)}_{\mathrm{max}}.$