Showing papers on "Energy (signal processing) published in 2004"

Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks

Abstract: We consider radio applications in sensor networks, where the nodes operate on batteries so that energy consumption must be minimized, while satisfying given throughput and delay requirements. In this context, we analyze the best modulation and transmission strategy to minimize the total energy consumption required to send a given number of bits. The total energy consumption includes both the transmission energy and the circuit energy consumption. We first consider multi-input-multi-output (MIMO) systems based on Alamouti diversity schemes, which have good spectral efficiency but also more circuitry that consumes energy. We then extend our energy-efficiency analysis of MIMO systems to individual single-antenna nodes that cooperate to form multiple-antenna transmitters or receivers. By transmitting and/or receiving information jointly, we show that tremendous energy saving is possible for transmission distances larger than a given threshold, even when we take into account the local energy cost necessary for joint information transmission and reception. We also show that over some distance ranges, cooperative MIMO transmission and reception can simultaneously achieve both energy savings and delay reduction.

Excitonic fine structure and recombination dynamics in single-crystalline ZnO

Abstract: The optical properties of a high quality bulk $\mathrm{ZnO}$, thermally post treated in a forming gas environment are investigated by temperature dependent continuous wave and time-resolved photoluminescence (PL) measurements. Several bound and free exciton transitions along with their first excited states have been observed at low temperatures, with the main neutral-donor-bound exciton peak at $3.3605\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ having a linewidth of $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ and dominating the PL spectrum at $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This bound exciton transition was visible only below $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, whereas the A-free exciton transition at $3.3771\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ persisted up to room temperature. A-free exciton binding energy of $60\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ is obtained from the position of the excited states of the free excitons. Additional intrinsic and extrinsic fine structures such as polariton, two-electron satellites, donor-acceptor pair transitions, and longitudinal optical-phonon replicas have also been observed and investigated in detail. Time-resolved PL measurements at room temperature reveal a biexponential decay behavior with typical decay constants of $\ensuremath{\sim}170$ and $\ensuremath{\sim}864\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ for the as-grown sample. Thermal treatment is observed to increase the carrier lifetimes when performed in a forming gas environment.

Optical Transition Energies for Carbon Nanotubes from Resonant Raman Spectroscopy: Environment and Temperature Effects

Abstract: This Letter reports the laser energy dependence of the Stokes and anti-Stokes Raman spectra of carbon nanotubes dispersed in aqueous solution and within solid bundles, in the energy range 1.52--2.71 eV. The electronic transition energies (${E}_{ii}$) and the radial breathing mode frequencies (${\ensuremath{\omega}}_{\mathrm{R}\mathrm{B}\mathrm{M}}$) are obtained for 46 different (18 metallic and 28 semiconducting) nanotubes, and the $(n,m)$ assignment is discussed based on the observation of geometrical patterns for ${E}_{ii}$ versus ${\ensuremath{\omega}}_{\mathrm{R}\mathrm{B}\mathrm{M}}$ graphs. Only the low energy component of the ${E}_{11}^{M}$ value is observed from each metallic nanotube. For a given nanotube, the resonant window is broadened and down-shifted for single wall carbon nanotube (SWNT) bundles compared to SWNTs in solution, while by increasing the temperature, the ${E}_{22}^{S}$ energies are redshifted for $S1$ [$(2n+m)\text{ }\mathrm{m}\mathrm{o}\mathrm{d}\text{ }3=1$] nanotubes and blueshifted for $S2$ [$(2n+m)\text{ }\mathrm{m}\mathrm{o}\mathrm{d}\text{ }3=2$] nanotubes.

Evidence for an Oscillatory Signature in Atmospheric Neutrino Oscillations

Abstract: Muon neutrino disappearance probability as a function of neutrino flight length $L$ over neutrino energy $E$ was studied. A dip in the $L/E$ distribution was observed in the data, as predicted from the sinusoidal flavor transition probability of neutrino oscillation. The observed $L/E$ distribution constrained ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ neutrino oscillation parameters; $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}l\ensuremath{\Delta}{m}^{2}l3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{e}\mathrm{V}}^{2}$ and ${sin }^{2}2\ensuremath{\theta}g0.90$ at 90% confidence level.

Proton shock acceleration in laser-plasma interactions.

Abstract: The formation of strong, high Mach number (2--3), electrostatic shocks by laser pulses incident on overdense plasma slabs is observed in one- and two-dimensional particle-in-cell simulations, for a wide range of intensities, pulse durations, target thicknesses, and densities. The shocks propagate undisturbed across the plasma, accelerating the ions (protons). For a dimensionless field strength parameter ${a}_{0}=16$ ($I{\ensuremath{\lambda}}^{2}\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }\ensuremath{\mu}{\mathrm{m}}^{2}$, where $I$ is the intensity and $\ensuremath{\lambda}$ the wavelength), and target thicknesses of a few microns, the shock is responsible for the highest energy protons. A plateau in the ion spectrum provides a direct signature for shock acceleration.

First-principles study of Li ion diffusion in LiFePO 4

Abstract: The diffusion mechanism of Li ions in the olivine ${\mathrm{LiFePO}}_{4}$ is investigated from first-principles calculations. The energy barriers for possible spatial hopping pathways are calculated with the adiabatic trajectory method. The calculations show that the energy barriers running along the $c$ axis are about 0.6, 1.2, and 1.5 eV for ${\mathrm{LiFePO}}_{4},$ ${\mathrm{FePO}}_{4},$ and ${\mathrm{Li}}_{0.5}{\mathrm{FePO}}_{4},$ respectively. However, the other migration pathways have much higher energy barriers resulting in very low probability of Li-ion migration. This means that the diffusion in ${\mathrm{LiFePO}}_{4}$ is one dimensional. The one-dimensional diffusion behavior has also been shown with full ab initio molecular dynamics simulation, through which the diffusion behavior is directly observed.

Chemical equilibrium study in nucleus-nucleus collisions at relativistic energies

Abstract: We present a detailed study of chemical freeze-out in nucleus-nucleus collisions at beam energies of $116A$, $30A$, $40A$, $80A$, and $158A\phantom{\rule{03em}{0ex}}\text{GeV}$ By analyzing hadronic multiplicities within the statistical hadronization approach, we have studied the strangeness production as a function of center-of-mass energy and of the parameters of the source We have tested and compared different versions of the statistical model, with special emphasis on possible explanations of the observed strangeness hadronic phase space undersaturation We show that, in this energy range, the use of hadron yields at midrapidity instead of in full phase space artificially enhances strangeness production and could lead to incorrect conclusions as far as the occurrence of full chemical equilibrium is concerned In addition to the basic model with an extra strange quark nonequilibrium parameter, we have tested three more schemes: a two-component model superimposing hadrons coming out of single nucleon-nucleon interactions to those emerging from large fireballs at equilibrium, a model with local strangeness neutrality and a model with strange and light quark nonequilibrium parameters The behavior of the source parameters as a function of colliding system and collision energy is studied The description of strangeness production entails a nonmonotonic energy dependence of strangeness saturation parameter ${\ensuremath{\gamma}}_{S}$ with a maximum around $30A\phantom{\rule{03em}{0ex}}\text{GeV}$ We also present predictions of the production rates of still unmeasured hadrons including the newly discovered ${\ensuremath{\Theta}}^{+}(1540)$ pentaquark baryon

Palatini form of 1/R gravity.

Abstract: It has been suggested that the Universe's recent acceleration is due to a contribution to the gravitational action proportional to the reciprocal of the Ricci scalar. Although the original version of this theory disagrees with solar system observations, a modified Palatini version, in which the metric and connection are treated as independent variables, has been suggested as a viable model of the cosmic acceleration. We show that this theory is equivalent to a scalar-tensor theory in which the scalar field kinetic energy term is absent from the action. Integrating out the scalar field gives rise to additional interactions among the matter fields of the standard model of particle physics at an energy scale of order ${10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{e}\mathrm{V}$ (the geometric mean of the Hubble and the Planck scales), and so the theory is excluded by, for example, electron-electron scattering experiments.

Surface-plasmon dispersion relations in chains of metallic nanoparticles: An exact quasistatic calculation

Abstract: We calculate the surface-plasmon dispersion relations for a periodic chain of spherical metallic nanoparticles in an isotropic host, including all multipole modes, in a generalized tight-binding approach. For sufficiently small particles $(kd\ensuremath{\ll}1,$ where k is the wave vector and d is the interparticle separation), the calculation is exact. The lowest bands differ only slightly from previous point-dipole calculations provided the particle radius $a\ensuremath{\lesssim}d/3,$ but differ substantially at smaller separation. We also calculate the dispersion relations for many higher bands, and estimate the group velocity ${v}_{g}$ and the exponential decay length ${\ensuremath{\xi}}_{D}$ for energy propagation for the lowest two bands due to single-grain damping. For $a/d=0.33,$ the result for ${\ensuremath{\xi}}_{D}$ is in qualitative agreement with experiments on gold nanoparticle chains, while for smaller separation, such as $a/d=0.45,$ ${v}_{g}$ and ${\ensuremath{\xi}}_{D}$ are expected to be strongly k dependent because of the multipole corrections. When the particles touch, we predict percolation effects in the spectrum, and find surprising symmetry in the plasmon band structure. Finally, we reformulate the band-structure equations for a Drude metal in the time domain, and suggest how to include localized driving electric fields in the equations of motion.

Constraining $\Omega_M$ and Dark Energy with Gamma-Ray Bursts

Abstract: An $E_{\gamma,{\rm jet}}\propto {E'_p}^{1.5}$ relationship with a small scatter for current $\gamma$-ray burst (GRB) data was recently reported, where $E_{\gamma,{\rm jet}}$ is the beaming-corrected $\gamma$-ray energy and $E'_p$ is the $ u F_ u$ peak energy in the local observer frame. By considering this relationship for a sample of 12 GRBs with known redshift, peak energy, and break time of afterglow light curves, we constrain the mass density of the universe and the nature of dark energy. We find that the mass density $\Omega_M=0.35\pm^{0.15}_{0.15}$ (at the $1\sigma$ confident level) for a flat universe with a cosmological constant, and the $w$ parameter of an assumed static dark-energy equation of state $w=-0.84\pm^{0.57}_{0.83}$ ($1\sigma$). Our results are consistent with those from type Ia supernovae. A larger sample established by the upcoming {\em Swift} satellite is expected to provide further constraints.

Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations

Abstract: Thin films of ${M}_{n+1}A{X}_{n}$ layered compounds in the $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{C}$ system were deposited on $\mathrm{MgO}(111)$ and ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(0001)$ substrates held at $900\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ using dc magnetron sputtering from elemental targets of $\mathrm{Ti}$, $\mathrm{Si}$, and $\mathrm{C}$. We report on single-crystal and epitaxial deposition of ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ (the previously reported $MAX$ phase in the $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{C}$ system), a previously unknown $MAX$ phase ${\mathrm{Ti}}_{4}{\mathrm{SiC}}_{3}$ and another type of structure having the stoichiometry of ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{2}{\mathrm{C}}_{3}$ and ${\mathrm{Ti}}_{7}{\mathrm{Si}}_{2}{\mathrm{C}}_{5}$. The latter two structures can be viewed as an intergrowth of 2 and 3 or 3 and 4 $M$ layers between each $A$ layer. In addition, epitaxial films of ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{3}{\mathrm{C}}_{\mathrm{x}}$ were deposited and ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{4}$ is also observed. First-principles calculations, based on density functional theory (DFT) of ${\mathrm{Ti}}_{n+1}{\mathrm{SiC}}_{n}$ for $n=1$,2,3,4 and the observed intergrown ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{2}{\mathrm{C}}_{3}$ and ${\mathrm{Ti}}_{7}{\mathrm{Si}}_{2}{\mathrm{C}}_{5}$ structures show that the calculated difference in cohesive energy between the $MAX$ phases reported here and competing phases ($\mathrm{TiC}$, ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$, ${\mathrm{TiSi}}_{2}$, and ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{3}$) are very small. This suggests that the observed ${\mathrm{Ti}}_{5}{\mathrm{Si}}_{2}{\mathrm{C}}_{3}$ and ${\mathrm{Ti}}_{7}{\mathrm{Si}}_{2}{\mathrm{C}}_{5}$ structures at least should be considered as metastable phases. The calculations show that the energy required for insertion of a $\mathrm{Si}$ layer in the $\mathrm{TiC}$ matrix is independent of how close the $\mathrm{Si}$ layers are stacked. Hardness and electrical properties can be related to the number of $\mathrm{Si}$ layers per $\mathrm{Ti}$ layer. This opens up for designed thin film structures the possibility to tune properties.

First-principles extrapolation method for accurate CO adsorption energies on metal surfaces

Abstract: We show that a simple first-principles correction based on the difference between the singlet-triplet CO excitation energy values obtained by density-functional theory (DFT) and high-level quantum chemistry methods yields accurate CO adsorption properties on a variety of metal surfaces. We demonstrate a linear relationship between the CO adsorption energy and the CO singlet-triplet splitting, similar to the linear dependence of CO adsorption energy on the energy of the CO $2\ensuremath{\pi}*$ orbital found recently [Kresse et al., Phys. Rev. B 68, 073401 (2003)]. Converged DFT calculations underestimate the CO singlet-triplet excitation energy $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}},$ whereas coupled-cluster and configuration-interaction (CI) calculations reproduce the experimental $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}.$ The dependence of ${E}_{\mathrm{chem}}$ on $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}$ is used to extrapolate ${E}_{\mathrm{chem}}$ for the top, bridge, and hollow sites for the (100) and (111) surfaces of Pt, Rh, Pd, and Cu to the values that correspond to the coupled cluster and CI $\ensuremath{\Delta}{E}_{\mathrm{S}\ensuremath{-}\mathrm{T}}$ value. The correction reproduces experimental adsorption site preference for all cases and obtains ${E}_{\mathrm{chem}}$ in excellent agreement with experimental results.

Electronic structure of nanostructured ZnO from x-ray absorption and emission spectroscopy and the local density approximation

Abstract: $\mathrm{O}\phantom{\rule{0.3em}{0ex}}1s$ absorption spectroscopy (XAS) and $\mathrm{O}\phantom{\rule{0.3em}{0ex}}K\ensuremath{\alpha}$ emission spectroscopy (XES) were performed to study the electronic structure of nanostructured ZnO. The band gap is determined by the combined absorption-emission spectrum. Resonantly excited XES spectra showing an energy dependence in the spectral shape reveal the selected excitations to the different $\mathrm{Zn}\phantom{\rule{0.3em}{0ex}}3d$, $4s$, and $4p$ states in hybridization with $\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ states. The partial density of state obtained from local density approximation (LDA) and $\mathrm{LDA}+U$ calculations are compared with the experimental results. The $\mathrm{LDA}+U$ approach is suitable to correct LDA self-interaction error of the cation $d$ states. The atomic eigenstates of $3d$ in zinc and $2p$ in oxygen are energetically close, which induces the strong interaction between $\mathrm{Zn}\phantom{\rule{0.3em}{0ex}}3d$ and $\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p$ states. This anomalous valence band cation-$d$--anion-$p$ hybridization is verified by taking into account the strong localization of the $\mathrm{Zn}\phantom{\rule{0.3em}{0ex}}3d$ states.

Compressing historical information in sensor networks

Abstract: We are inevitably moving into a realm where small and inexpensive wireless devices would be seamlessly embedded in the physical world and form a wireless sensor network in order to perform complex monitoring and computational tasks. Such networks pose new challenges in data processing and dissemination because of the limited resources (processing, bandwidth, energy) that such devices possess. In this paper we propose a new technique for compressing multiple streams containing historical data from each sensor. Our method exploits correlation and redundancy among multiple measurements on the same sensor and achieves high degree of data reduction while managing to capture even the smallest details of the recorded measurements. The key to our technique is the base signal, a series of values extracted from the real measurements, used for encoding piece-wise linear correlations among the collected data values. We provide efficient algorithms for extracting the base signal features from the data and for encoding the measurements using these features. Our experiments demonstrate that our method by far outperforms standard approximation techniques like Wavelets. Histograms and the Discrete Cosine Transform, on a variety of error metrics and for real datasets from different domains.

Quantum phase transitions in the itinerant ferromagnet ZrZn2.

Abstract: We report a study of the ferromagnetism of ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_{2}$, the most promising material to exhibit ferromagnetic quantum criticality, at low temperatures $T$ as a function of pressure $p$. We find that the ordered ferromagnetic moment disappears discontinuously at ${p}_{c}=16.5\text{ }\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$. Thus a tricritical point separates a line of first order ferromagnetic transitions from second order (continuous) transitions at higher temperature. We also identify two lines of transitions of the magnetization isotherms up to 12 T in the $p\mathrm{\text{\ensuremath{-}}}T$ plane where the derivative of the magnetization changes rapidly. These quantum phase transitions (QPT) establish a high sensitivity to local minima in the free energy in ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_{2}$, thus strongly suggesting that QPT in itinerant ferromagnets are always first order.

Quantum Monte Carlo calculations of excited states in A =6-8 nuclei

Abstract: A variational Monte Carlo method is used to generate sets of orthogonal trial functions, ${\ensuremath{\Psi}}_{T}({J}^{\ensuremath{\pi}};T)$, for given quantum numbers in various light $p$-shell nuclei. These ${\ensuremath{\Psi}}_{T}$ are then used as input to Green's function Monte Carlo (GFMC) calculations of first, second, and higher excited $({J}^{\ensuremath{\pi}};T)$ states. Realistic two- and three-nucleon interactions are used. We find that if the physical excited state is reasonably narrow, the GFMC energy converges to a stable result. With the combined Argonne ${\mathrm{v}}_{18}$ two-nucleon and Illinois-2 three-nucleon interactions, the results for many second and higher states in $A=6\char21{}8$ nuclei are close to the experimental values.

Complexity of random energy landscapes, glass transition, and absolute value of the spectral determinant of random matrices.

Abstract: Finding the mean of the total number ${N}_{\mathrm{tot}}$ of stationary points for $N$-dimensional random energy landscapes is reduced to averaging the absolute value of the characteristic polynomial of the corresponding Hessian. For any finite $N$ we provide the exact solution to the problem for a class of landscapes corresponding to the ``toy model'' of manifolds in a random environment. For $N\ensuremath{\gg}1$ our asymptotic analysis reveals a phase transition at some critical value ${\ensuremath{\mu}}_{c}$ of a control parameter $\ensuremath{\mu}$ from a phase with a finite landscape complexity: ${N}_{\mathrm{tot}}\ensuremath{\sim}{e}^{N\ensuremath{\Sigma}}$, $\ensuremath{\Sigma}(\ensuremath{\mu}l{\ensuremath{\mu}}_{c})g0$ to the phase with vanishing complexity: $\ensuremath{\Sigma}(\ensuremath{\mu}g{\ensuremath{\mu}}_{c})=0$. Finally, we discuss a method of dealing with the modulus of the spectral determinant applicable to a broad class of problems.

On the use of phase and energy for musical onset detection in the complex domain

Abstract: We present a study on the combined use of energy and phase information for the detection of onsets in musical signals. The resulting method improves upon both energy-based and phase-based approaches. The detection function, generated from the analysis of the signal in the complex frequency domain is sharp at the position of onsets and smooth everywhere else. Results on a database of recordings show high detection rates for low rates of errors. The approach is more robust than its predecessors both theoretically and practically.

Quantum Monte Carlo studies of superfluid Fermi gases

Abstract: We report results of quantum Monte Carlo calculations of the ground state of dilute Fermi gases with attractive short-range two-body interactions. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the $s$-wave scattering length and the Fermi wave vector, $a{k}_{F}$. We report results for the ground-state energy, the pairing gap $\ensuremath{\Delta}$, and the quasiparticle spectrum. In the weak-coupling regime, $1∕a{k}_{F}l\ensuremath{-}1$, we obtain Bardeen-Cooper-Schrieffer (BCS) superfluid and the energy gap $\ensuremath{\Delta}$ is much smaller than the Fermi gas energy ${E}_{\mathrm{FG}}$. When $ag0$, the interaction is strong enough to form bound molecules with energy ${E}_{\mathrm{mol}}$. For $1∕a{k}_{F}\ensuremath{\gtrsim}0.5$, we find that weakly interacting composite bosons are formed in the superfluid gas with $\ensuremath{\Delta}$ and gas energy per particle approaching $\ensuremath{\mid}{E}_{\mathrm{mol}}\ensuremath{\mid}∕2$. In this region, we seem to have Bose-Einstein condensation (BEC) of molecules. The behavior of the energy and the gap in the BCS-to-BEC transition region, $\ensuremath{-}0.5l1∕a{k}_{F}l0.5$, is discussed.

Dynamic stripes and resonance in the superconducting and normal phases of YBa2Cu3O6.5 ortho-II superconductor

Abstract: We describe the relation between spin fluctuations and superconductivity in a highly ordered sample of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$ using both polarized and unpolarized neutron inelastic scattering. The spin susceptibility in the superconducting phase exhibits one-dimensional incommensurate modulations at low energies, consistent with hydrodynamic stripes. With increasing energy the susceptibility curves upward to a commensurate, intense, well-defined, and asymmetric resonance at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we show is gapless, the resonance remains surprisingly strong and persists clearly in Q scans and energy scans. Its similar asymmetric spectral form above ${T}_{c}=59\mathrm{K}$ suggests that incoherent superconducting pairing fluctuations are present in the normal state. On cooling, the resonance and the stripe modulations grow in well above ${T}_{c}$ below a temperature that is comparable to the pseudogap temperature where suppression occurs in local and low-momentum properties. The spectral weight that accrues to the resonance is largely acquired by transfer from suppressed low-energy fluctuations. We find the resonance to be isotropically polarized, consistent with a triplet carrying $\ensuremath{\sim}2.6%$ of the total spectral weight of the Cu spins in the planes.

Medium modification of jet shapes and jet multiplicities.

Abstract: Medium-induced parton energy loss is widely considered to underlie the suppression of high-${p}_{t}$ leading hadron spectra in $\sqrt{{s}_{NN}}=200\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at the Relativistic Heavy Ion Collider (RHIC). Its description implies a characteristic ${k}_{t}$ broadening of the subleading hadronic fragments associated with the hard parton. However, this latter effect is more difficult to measure and has remained elusive so far. Here, we discuss how it affects genuine jet observables, which are accessible at the Large Hadron Collider and possibly at RHIC. We find that the ${k}_{t}$ broadening of jet multiplicity distributions provides a very sensitive probe of the properties of dense QCD matter, whereas the sensitivity of jet energy distributions is much weaker. In particular, the sensitive kinematic range of jet multiplicity distributions is almost unaffected by the high multiplicity background.

Lorentz violation and short-baseline neutrino experiments

Abstract: A general discussion is given of signals for broken Lorentz symmetry in short-baseline neutrino experiments. Among the effects that Lorentz violation can introduce are a dependence on energy differing from that of the usual massive-neutrino solution and a dependence on the direction of neutrino propagation. Using the published result of the Liquid Scintillator Neutrino Detector experiment, analysis of the effects of broken Lorentz symmetry yields an estimated nonzero value $(3\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ for a combination of coefficients for Lorentz violation. This lies in the range expected for effects originating from the Planck scale in an underlying unified theory.

High sensitivity search for nu;e's from the sun and other sources at KamLAND.

Abstract: Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for ${\overline{\ensuremath{ u}}}_{e}$'s in the energy range $8.3l{E}_{{\overline{\ensuremath{ u}}}_{e}}l14.8\text{ }\text{ }\mathrm{M}\mathrm{e}\mathrm{V}$. No candidates were found for an expected background of $1.1\ifmmode\pm\else\textpm\fi{}0.4$ events. This result can be used to obtain a limit on ${\overline{\ensuremath{ u}}}_{e}$ fluxes of any origin. Assuming that all ${\overline{\ensuremath{ u}}}_{e}$ flux has its origin in the Sun and has the characteristic $^{8}\mathrm{B}$ solar ${\ensuremath{ u}}_{e}$ energy spectrum, we obtain an upper limit of $3.7\ifmmode\times\else\texttimes\fi{}{10}^{2}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (90% C.L.) on the ${\overline{\ensuremath{ u}}}_{e}$ flux. We interpret this limit, corresponding to $2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ of the standard solar model $^{8}\mathrm{B}$ ${\ensuremath{ u}}_{e}$ flux, in the framework of spin-flavor precession and neutrino decay models.

Coupled-cluster approach to nuclear physics

Abstract: Using many-body perturbation theory and coupled-cluster theory, we calculate the ground-state energy of $^{4}\mathrm{He}$ and $^{16}\mathrm{O}$. We perform these calculations using a no-core $G$-matrix interaction derived from a realistic nucleon-nucleon potential. Our calculations employ up to two-particle two-hole coupled-cluster amplitudes.

Theorem on the Origin of Phase Transitions

Abstract: For physical systems described by smooth, finite-range, and confining microscopic interaction potentials $V$ with continuously varying coordinates, we announce and outline the proof of a theorem that establishes that, unless the equipotential hypersurfaces of configuration space ${\ensuremath{\Sigma}}_{v}={({q}_{1},\dots{},{q}_{N})\ensuremath{\in}{\mathbb{R}}^{N}|V({q}_{1},\dots{},{q}_{N})=v}$, $v\ensuremath{\in}\mathbb{R}$, change topology at some ${v}_{c}$ in a given interval $[{v}_{0},{v}_{1}]$ of values $v$ of $V$, the Helmoltz free energy must be at least twice differentiable in the corresponding interval of inverse temperature $\mathbf{(}\ensuremath{\beta}({v}_{0}),\ensuremath{\beta}({v}_{1})\mathbf{)}$ also in the $N\ensuremath{\rightarrow}\ensuremath{\infty}$ limit. Thus, the occurrence of a phase transition at some ${\ensuremath{\beta}}_{c}=\ensuremath{\beta}({v}_{c})$ is necessarily the consequence of the loss of diffeomorphicity among the ${{\ensuremath{\Sigma}}_{v}{}}_{vl{v}_{c}}$ and the ${{\ensuremath{\Sigma}}_{v}{}}_{vg{v}_{c}}$, which is the consequence of the existence of critical points of $V$ on ${\ensuremath{\Sigma}}_{v={v}_{c}}$, that is, points where $\ensuremath{ abla}V=0$.

Temperature-dependent photoluminescence from single-walled carbon nanotubes

Abstract: Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of pillar-suspended single-walled carbon nanotubes has been measured for temperatures between 300 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The atmospheric environment strongly affects the low-temperature luminescence. The PL intensity is quenched at temperatures below $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for nanotubes in high vacuum, while nanotubes in helium ambient remain luminescent. The PL peak emission energy is only very weakly dependent on temperature, with a species-dependent blueshift upon cooling corresponding to a relative shift in bandgap of $\ensuremath{-}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ or less. The integrated peak intensities change by only a factor of 2, with linewidths showing a moderate temperature dependence. In PLE, the second absorption peak energy $({E}_{22})$ is also only weakly temperature dependent, with no significant shift and a limited reduction in linewidth upon cooling to $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In addition to the previously assigned nanotube PL peaks seen at room temperature, at least two distinct new classes of PL peaks are observed at cryogenic temperatures.

Signal processing of sensor node data for vehicle detection

Abstract: We describe an algorithm and experimental work for vehicle detection using sensor node data. Both acoustic and magnetic signals are processed for vehicle detection. We propose a real-time vehicle detection algorithm called the adaptive threshold algorithm (ATA). The algorithm first computes the time-domain energy distribution curve and then slices the energy curve using a threshold updated adaptively by some decision states. Finally, the hard decision results from threshold slicing are passed to a finite-state machine, which makes the final vehicle detection decision. Real-time tests and offline simulations both demonstrate that the proposed algorithm is effective.

Variable-range hopping in quasi-one-dimensional electron crystals

Abstract: We study the effect of impurities on the ground state and the low-temperature Ohmic dc transport in a one-dimensional chain and quasi-one-dimensional systems of many parallel chains. We assume that strong interactions impose a short-range periodicity of the electron positions. The long-range order of such an electron crystal (or equivalently, a ${4k}_{F}$ charge-density wave) is destroyed by impurities, which act as strong pinning centers. We show that a three-dimensional array of chains behaves differently at large and at small impurity concentrations N. At large N, impurities divide the chains into metallic rods. Additions or removal of electrons from such rods correspond to charge excitations whose density of states exhibits a quadratic Coulomb gap. At low temperatures the conductivity is due to the variable-range hopping of electrons between the rods. It obeys the Efros-Shklovskii (ES) law, $\ensuremath{-}\mathrm{ln}\ensuremath{\sigma}\ensuremath{\sim}{(T}_{\mathrm{ES}}{/T)}^{1/2}.$ ${T}_{\mathrm{ES}}$ decreases as N decreases, which leads to an exponential growth of $\ensuremath{\sigma}.$ When N is small, the metallic-rod (also known as ``interrupted-strand'') picture of the ground state survives only in the form of rare clusters of atypically short rods. They are the source of low-energy charge excitations. In the bulk of the crystal the charge excitations are gapped and the electron crystal is pinned collectively. A strongly anisotropic screening of the Coulomb potential produces an unconventional linear in energy Coulomb gap and an unusual law of the variable-range hopping conductivity $\ensuremath{-}\mathrm{ln}\ensuremath{\sigma}\ensuremath{\sim}{(T}_{1}{/T)}^{2/5}.$ The parameter ${T}_{1}$ remains constant over a finite range of impurity concentrations. At smaller N the $2/5$ law is replaced by the Mott law, $\ensuremath{-}\mathrm{ln}\ensuremath{\sigma}\ensuremath{\sim}{(T}_{M}{/T)}^{1/4}.$ In the Mott regime the conductivity gets suppressed as N goes down. Thus, the overall dependence of $\ensuremath{\sigma}$ on N is nonmonotonic. In the case of a single chain, the metallic-rod picture applies at all N. The low-temperature conductivity obeys the ES law, with log corrections, and decreases exponentially with N. Our theory provides a qualitative explanation for the transport properties of organic charge-density wave compounds of TCNQ family.

X-ray emission from z pinches at 10 7 A: current scaling, gap closure, and shot-to-shot fluctuations.

Abstract: We have measured the x-ray power and energy radiated by a tungsten-wire-array $z$ pinch as a function of the peak pinch current and the width of the anode-cathode gap at the base of the pinch. The measurements were performed at 13- and 19-MA currents and 1-, 2-, 3-, and 4-mm gaps. The wire material, number of wires, wire-array diameter, wire-array length, wire-array-electrode design, normalized-pinch-current time history, implosion time, and diagnostic package were held constant for the experiments. To keep the implosion time constant, the mass of the array was increased as ${I}^{2}$ (i.e., the diameter of each wire was increased as $I),$ where $I$ is the peak pinch current. At 19 MA, the mass of the 300-wire 20-mm-diam 10-mm-length array was 5.9 mg. For the configuration studied, we find that to eliminate the effects of gap closure on the radiated energy, the width of the gap must be increased approximately as $I.$ For shots unaffected by gap closure, we find that the peak radiated x-ray power ${P}_{r}\ensuremath{\propto}{I}^{1.24\ifmmode\pm\else\textpm\fi{}0.18},$ the total radiated x-ray energy ${E}_{r}\ensuremath{\propto}{I}^{1.73\ifmmode\pm\else\textpm\fi{}0.18},$ the x-ray-power rise time ${\ensuremath{\tau}}_{r}\ensuremath{\propto}{I}^{0.39\ifmmode\pm\else\textpm\fi{}0.34},$ and the x-ray-power pulse width ${\ensuremath{\tau}}_{w}\ensuremath{\propto}{I}^{0.45\ifmmode\pm\else\textpm\fi{}0.17}.$ Calculations performed with a time-dependent model of an optically thick pinch at stagnation demonstrate that the internal energy and radiative opacity of the pinch are not responsible for the observed subquadratic power scaling. Heuristic wire-ablation arguments suggest that quadratic power scaling will be achieved if the implosion time ${\ensuremath{\tau}}_{i}$ is scaled as ${I}^{\ensuremath{-}1/3}.$ The measured 1\ensuremath{\sigma} shot-to-shot fluctuations in ${P}_{r},$ ${E}_{r},$ ${\ensuremath{\tau}}_{r},$ ${\ensuremath{\tau}}_{w},$ and ${\ensuremath{\tau}}_{i}$ are approximately 12%, 9%, 26%, 9%, and 2%, respectively, assuming that the fluctuations are independent of $I.$ These variations are for one-half of the pinch. If the half observed radiates in a manner that is statistically independent of the other half, the variations are a factor of ${2}^{1/2}$ less for the entire pinch. We calculate the effect that shot-to-shot fluctuations of a single pinch would have on the shot-success probability of the double-pinch inertial-confinement-fusion driver proposed by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. We find that on a given shot, the probability that two independent pinches would radiate the same peak power to within a factor of $1\ifmmode\pm\else\textpm\fi{}\ensuremath{\alpha}$ (where $0l~\ensuremath{\alpha}\ensuremath{\ll}1)$ is equal to $\mathrm{erf}(\ensuremath{\alpha}/2\ensuremath{\sigma}),$ where \ensuremath{\sigma} is the 1\ensuremath{\sigma} fractional variation of the peak power radiated by a single pinch. Assuming \ensuremath{\alpha} must be $l~7%$ to achieve adequate odd-Legendre-mode radiation symmetry for thermonuclear-fusion experiments, \ensuremath{\sigma} must be $l3%$ for the shot-success probability to be $g~90%.$ The observed ${(12/2}^{1/2})%=8.5%$ fluctuation in ${P}_{r}$ would provide adequate symmetry on 44% of the shots. We propose that three-dimensional radiative-magnetohydrodynamic simulations be performed to quantify the sensitivity of the x-ray emission to various initial conditions, and to determine whether an imploding $z$ pinch is a spatiotemporal chaotic system.

Optical Bragg accelerators.

Abstract: It is demonstrated that a Bragg waveguide consisting of a series of dielectric layers may form an excellent optical acceleration structure. Confinement of the accelerating fields is achieved, for both planar and cylindrical configurations by adjusting the first dielectric layer width. A typical structure made of silica and zirconia may support gradients of the order of $1\phantom{\rule{0.3em}{0ex}}\text{GV}∕\mathrm{m}$ with an interaction impedance of a few hundreds of ohms and with an energy velocity of less than $0.5\mathrm{c}$. An interaction impedance of about $1000\phantom{\rule{0.3em}{0ex}}\ensuremath{\Omega}$ may be obtained by replacing the Zirconia with a (fictitious) material of $\ensuremath{\epsilon}=25$. Special attention is paid to the wake field developing in such a structure. In the case of a relatively small number of layers, it is shown that the total electromagnetic power emitted is proportional to the square of the number of electrons in the macrobunch and inversely proportional to the number of microbunches; this power is also inversely proportional to the square of the internal radius of the structure for a cylindrical structure, and to the width of the vacuum core in a planar structure. Quantitative results are given for a higher number of dielectric layers, showing that in comparison to a structure bounded by metallic walls, the emitted power is significantly smaller due to propagation bands allowing electromagnetic energy to escape.