Evolution of Superconducting and Normal-State Properties in C60 “Polymer” Doped with K

Abstract:

Bulk superconductivity was observed in a new iodine-treated aggregated form of solid C₆₀, believed to be a “polymer”, by doping with alkali metal. Evolution of superconducting (T_c = 17.2 K) and normal-state properties, has been studied as a function of doping with K. The normal-state dc susceptibility exhibited a complex behavior with the increasing K uptake, evolving from an enhanced paramagnetism at low doping level, to a weakly temperature-dependent diamagnetism at the optimum doping level for superconductivity, and ending with a strong temperature-independent diamagnetism in over-doped samples. The measured superconductivity parameters, such as T_c, London penetration depth and the Ginzburg-Landau coherence length, are compared with those of the monomer K₃C₆₀. and the main factors determining the differences between the two systems are discussed.     

Effect of underreaming on bearing capacity of bored pile

Conclusions 1. From the data for the full-scale static tests of piles 6–22 m long, it was found that as the ratio /d increases, the load transmitted through a pile underreaming having the same size decreases proportionally.2. The limit strength at the foot of piles over 10 m long cannot be determined by means of analytical strengths depending only on the depth h and the liquidity index I_L but which do not depend on the ratio /d.Scientific-Research Institute of Bases and Underground Structures. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 12–14, November–December, 1986.     

Nonlinear L2-by-3 transform for PAPR reduction in OFDM systems

Orthogonal frequency division multiplexing (OFDM), the multicarrier modulation technique with high bandwidth efficiency and robustness against multipath fading, is used in several high-speed broadband communication systems including digital video broadcasting (DVB), digital audio broadcasting (DAB), asymmetric digital subscriber line (ADSL), wireless local area network (WLAN IEEE 802.11a,g), high performance radio local area network (HIPERLAN 2), and worldwide interoperability for microwave access (WiMAX IEEE 802.16). However, the transmit signal in OFDM system has a high peak-to-average power ratio (PAPR), one of the major drawbacks of multicarrier transmission, and therefore high dynamic range is required in both the digital to analog converter (DAC) and the power amplifier (PA) for proper operation. Otherwise, the nonlinearities of PA cause out-of-band distortion and increase in bit error rate (BER). Therefore, the reduction in PAPR in OFDM system is desirable in order to obtain power efficiency and increase BER performance. In this paper, a new parametric PAPR reduction technique, L₂-by-3 transform from sliding norm transform (SNT) family is proposed. Based on its parameter, a significant PAPR reduction is obtained. This paper presents the analysis of power saving and computational complexity of the proposed method L₂-by-3 and comparison to two other methods; selected mapping and partial transmit sequence.     

Modeling of organism’s adaptive reaction to environmental changes

A multicellular organism is shown to be a community of special self-regulated cells with rigid and flexible regulating links, and a long-term adaptive trend of its system reaction to environmental changes is due to changes in the consumer gradients of groups of cells functioning against the imbalance between synthesis and decay of microstructures. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 136–147, January–February 2008.     

SOA-based regenerative amplification of phase-noise-degraded DPSK signals: dynamic analysis and demonstration

A theoretical analysis and an experimental demonstration of semiconductor optical amplifier (SOA)-based regenerative amplification (SORA) of phase noise (PN)-degraded return-to-zero (RZ) differential phase-shift keying (DPSK) signals are presented. The Q-factor improvement is 1.6 dB in single-channel and about 0.8 dB in two non-demultiplexed-channel regimes. The key physical mechanism that enables regeneration by the SORA is the discriminative gain provided by the SOA for the logical 0s versus the logical 1s when two mutually antisymmetric ON-OFF keying (OOK) data trains, created by the DPSK signal, collide in the SOA. The modeling results agree with the experiment.     

Synthesis and Properties of Zn2TiO4–Zn2SnO4–ZnFe2O4 Solid Solutions

Zn₂TiO₄–Zn₂SnO₄–ZnFe₂O₄ mixed oxides are prepared by low-temperature hydrogen–oxygen plasma synthesis and solid-state reactions. Zn_{2 – x} (Ti _a Sn _b )_{1 – x} Fe_2x O₄ (a+ b = 1, x = 0–1.0) solid solutions are shown to have an inverted cubic spinel structure (sp. gr. Fd3m). The lattice parameter, electrical conductivity, band gap, and molar polarizability of about 100 samples are determined. With increasing Fe content, the lattice parameter, degree of spinel inversion, density, activation energy, and polarizability of the solid solutions decrease, while their conductivity rises.     

The СПРУТ-VI Instrument Complex for the Mir Orbital Station

The basic elements of the instrument package program for orbital stations are presented. The characteristics of the -VI equipment developed for the Mir orbital station within the framework of this program are described. This equipment allows the simultaneous recording of the characteristics of near-earth space (electron, proton, and nucleus fluxes, magnetic fields, and low-frequency electromagnetic waves) and their effect on the elements of spaceborne equipment and systems. The mass of the equipment is 16 kg; the power consumption is no more than 20 W.     

An improved double sampling s chart

Double sampling (DS) s charts are designed to allow quick detection of a small shift in process standard deviations and to provide a quick response in an agile manufacturing environment. However, current developed DS s charts assume that the sample standard deviations follow a normal distribution. Although valid for relatively large sample sizes, this assumption has limited the application of DS s charts to the monitoring of manufacturing processes with relatively small sample sizes. An improved DS s chart is developed without the normality assumption of the sample standard deviations. The design of the improved DS s chart is formulated as a statistical design optimization problem and solved with a genetic algorithm. The efficiency of the improved DS s charts is compared with that of the DS s charts developed in previous research and with that of the traditional s charts.     

Self-Propagating High-Temperature Synthesis of Functionally Graded PVD Targets with a Ceramic Working Layer of TiB2-TiN or Ti5Si3-TiN

Two- and three-layer functionally graded PVD targets with a working layer (sputtering surface) based on TiN-TiB₂ or TiN-Ti₅Si₃ formation via the technology of forced SHS compaction were considered. It was shown that rather wide (up to 1 mm) transition diffusional zones providing firm adhesion of the layers were formed between the working, intermediate, and third layers. The compositions TiN + TiB₂ + 20%Cu and TiB₂ + 50%Cu were found to be optimum for the intermediate (damping) and third layers of the three-layer PVD targets. The specific features of phase and structure formation of the two- and three-layer products with the working layer based on TiN-TiB₂ and TiN-Ti₅Si₃ were elucidated. Variation of the chemical oven mass exerted a noticeable effect of reduction of the residual porosity and enlarging of the grains of the product phases owing to prolongation of the time for secondary structure formation. The relationship of the hardness of the layers in the functionally graded target on the chemical oven mass allow prediction of the properties of the resultant graded material systems.