Crystal-controlled multivibrator

Method is described for designing crystal oscillator which has frequency and symmetry stability suitable for system-clock-generators used in spacecraft data systems. Simple multivibrator is used in which timing capacitor is replaced by a crystal

Vibrations and Relaxations in a Soft Sphere Glass: Boson Peak and Structure Factors

The dynamics of a soft sphere model glass, studied by molecular dynamics, is investigated. The vibrational density of states divided by $\omega^2$ shows a pronounced boson peak. Its shape is in agreement with the universal form derived for soft oscillators interacting with sound waves. The excess vibrations forming the boson peak have mainly transverse character. From the dynamic structure factor in the Brillouin regime pseudo dispersion curves are calculated. Whereas the longitudinal phonons are well defined up to the pseudo zone boundary the transverse ones rapidly get over-damped and go through the Ioffe-Regel limit near the boson peak frequency. In the high $q$ regime constant-$\omega$ scans of the dynamic structure factor for frequencies around the boson peak are clearly distinct from those for zone boundary frequencies. Above the Brillouin regime, the scans for the low frequency modes follow closely the static structure factor. This still holds after a deconvolution of the exact harmonic eigenmodes into local and extended m odes. Also the structure factor for local relaxations at finite temperatures resembles the static one. This semblance between the structure factors mirrors the collective motion of chain like structures in both low frequency vibrations and atomic hopping processes, observed in the earlier investigations

Microscopic theory of refractive index applied to metamaterials: Effective current response tensor corresponding to standard relation n2=εeffμeffn^2 = \varepsilon_{\mathrm{eff}} \mu_{\mathrm{eff}}

In this article, we first derive the wavevector- and frequency-dependent, microscopic current response tensor which corresponds to the "macroscopic" ansatz $\vec D = \varepsilon_0 \varepsilon_{\mathrm{eff}} \vec E$ and $\vec B = \mu_0 \mu_{\mathrm{eff}} \vec H$ with wavevector- and frequency-independent, "effective" material constants $\varepsilon_{\mathrm{eff}}$ and $\mu_{\mathrm{eff}}$. We then deduce the electromagnetic and optical properties of this effective material model by employing exact, microscopic response relations. In particular, we argue that for recovering the standard relation $n^2 = \varepsilon_{\mathrm{eff}} \mu_{\mathrm{eff}}$ between the refractive index and the effective material constants, it is imperative to start from the microscopic wave equation in terms of the transverse dielectric function, $\varepsilon_{\mathrm{T}}(\vec k, \omega) = 0$. On the phenomenological side, our result is especially relevant for metamaterials research, which draws directly on the standard relation for the refractive index in terms of effective material constants. Since for a wide class of materials the current response tensor can be calculated from first principles and compared to the model expression derived here, this work also paves the way for a systematic search for new metamaterials.Comment: minor correction

Performance Analysis and Enhancement of Multiband OFDM for UWB Communications

In this paper, we analyze the frequency-hopping orthogonal frequency-division multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless personal area networks (WPANs) based on ultra-wideband (UWB) transmission. Besides considering the standard, we also propose and study system performance enhancements through the application of Turbo and Repeat-Accumulate (RA) codes, as well as OFDM bit-loading. Our methodology consists of (a) a study of the channel model developed under IEEE 802.15 for UWB from a frequency-domain perspective suited for OFDM transmission, (b) development and quantification of appropriate information-theoretic performance measures, (c) comparison of these measures with simulation results for the Multiband OFDM standard proposal as well as our proposed extensions, and (d) the consideration of the influence of practical, imperfect channel estimation on the performance. We find that the current Multiband OFDM standard sufficiently exploits the frequency selectivity of the UWB channel, and that the system performs in the vicinity of the channel cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading algorithm improve the system power efficiency by over 6 dB at a data rate of 480 Mbps.Comment: 32 pages, 10 figures, 1 table. Submitted to the IEEE Transactions on Wireless Communications (Sep. 28, 2005). Minor revisions based on reviewers' comments (June 23, 2006

Error Rate Analysis for Coded Multicarrier Systems over Quasi-Static Fading Channels

This paper presents two methods for approximating the performance of coded multicarrier systems operating over frequency-selective, quasi-static fading channels with non-ideal interleaving. The first method is based on approximating the performance of the system over each realization of the channel, and is suitable for obtaining the outage performance of this type of system. The second method is based on knowledge of the correlation matrix of the frequency-domain channel gains and can be used to directly obtain the average performance. Both of the methods are applicable for convolutionally-coded interleaved systems employing Quadrature Amplitude Modulation (QAM). As examples, both methods are used to study the performance of the Multiband Orthogonal Frequency Division Multiplexing (OFDM) proposal for high data-rate Ultra-Wideband (UWB) communication.Comment: 5 pages, 3 figures, 2 tables. Submitted to Globecom 200

Linear electromagnetic wave equations in materials

After a short review of microscopic electrodynamics in materials, we investigate the relation of the microscopic dielectric tensor to the current response tensor and to the full electromagnetic Green function. Subsequently, we give a systematic overview of microscopic electromagnetic wave equations in materials, which can be formulated in terms of the microscopic dielectric tensor.Comment: consistent with published version in Phot. Nano. Fund. Appl. (2017

Time-Temperature Superposition of Structural Relaxation in a Viscous Metallic Liquid

Bulk metallic glass-forming Pd40Ni10Cu30P20 has been investigated in its equilibrium liquid by quasielastic neutron scattering. The quasielastic signal exhibits a structural relaxation as known from nonmetallic viscous liquids. Even well above the melting point, the structural relaxation is nonexponential and obeys a universal time-temperature superposition. From the mean relaxation times average diffusivities have been determined, resulting in values on a 10^-10 m^2 s^-1 scale, 3 orders of magnitude slower than in simple metallic liquids