Centralized power control and routing policies for multihop wireless networks

This paper investigates joint power control and routing policies for general multihop wireless networks when all the transmitting nodes are subject to a long-term average power constraint. The main contribution of this paper is to propose online power and rate control algorithms and prove that these policies stabilize the entire queuing network whenever the packet arrival rates at each node are in the corresponding region of achievable rates. The online policies are time varying and based on the queue size at each node and the instantaneous channel conditions. The theoretical results are supported by simulations for the illustrative cases of both a multiple-access channel and a relay channel.     

Melatonin receptors mediate contraction of a rat cerebral artery

Melatonin receptors are expressed in the cerebral arteries of the rat which form the circle of Willis. We report here that melatonin induces contraction of in vitro preparations of pressurized rat posterior communicating artery, in a concentration-dependent manner. This action of melatonin is inhibited by S-20928, a specific melatonin receptor antagonist. Our results demonstrate that the contractile action of melatonin is mediated by its receptors in the cerebral artery, and suggest a role for melatonin in the regulation of cerebral circulation.     

Microwave and far-infrared propagation in conductive microstructured composites

In a recent publication [T.E. Huber, L. Luo, Appl. Phys. Lett. 70 (1997) 2502.] we discussed a structural enhancement of the electromagnetic transmission in composites. We showed that densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of 10³, relative to an indium foil of equal thickness for far-infrared (10 cm⁻¹ < k < 80 cm⁻¹) propagating along the wire length. The absorption increases as k^{0.45 ± 0.07} and is explained by the dynamic Maxwell-Gannett model, which includes eddy current dissipation. It is of considerable practical interest to extend the range of application of these composite properties to the microwave domain. Here we will discuss recent measurements of the transmission of microwaves in wire array composites in the 8–12 GHz frequency range.     

Synthesis and characterization of polyestermaleamides

Summary Polyestermaleamides have been synthesized from N,N-bisisomaleimide, p-aminophenol, iso-and tere-phthaloyl chlorides. Through ring-opening addition reaction, a bisphenolamide was first formed; it was then polycondensed with acid chlorides to produce Polyestermaleamides, with an ordered sequence. The polymers were fully characterized by elemental analysis, infrared and electronic spectra, solubility in various solvents as well as inherent viscosity measurements. Thermal behaviour of the polymers were determined by thermogravimetric analysis in nitrogen atmosphere.     

Crystalline character of native and chemically treated Egyptian cottons. I. Computation of crystallinity,disorder parameter,orientation factor,and spiral angle

Computer data processing and electronic monochromatization of x-rays were employed for determining crystallinity, disorder parameter, Hermans' orientation factor, as well as DeLuca and Orr spiral angle of native, mercerized and urea-treated cottons. The results indicate the values for the degree of crystallinity to vary significantly between ecttons. Increase in disorder on mercerization is confirmed. The effect of urea treatment is not so well defined. The differences in Hermans' x-ray orientation factor are significant at the 1% level between cottons and at the 10% level between treatments. Besides, from a critical analysis of the values obtained, it is shown that the spiral angle φt in the method of DeLuca and Orr is probably a direct estimate of the mean inclination of the crystallites to the fiber axis, while Hermans' orientation angle β is a complex function of other parameters as well. The computer programs which could be applied to other polymers are included.     

Low-temperature heat capacity of small Nb3Sn polycrystals by ac calorimetry

It is shown by an ac calorimetry technique that the multiple heat capacity anomalies which occur below the superconducting transition temperature for small polycrystalline Nb₃Sn samples are intrinsic to these samples. The recent suggestions that shear stresses can account for these results are analyzed for their validity. The dependence of the occurrence of these multiple anomalies upon the thermal history of the samples was investigated.Supported in part by U.S. Atomic Energy Commission under the Contract No. USAEC-AT-(04-3)-34 at the Department of APIS, UCSD, La Jolla, California. Present work supported under the auspices of ERDA.Supported by Air Force Office of Scientific Research, Air Force Systems Command USAF, under AFOSR Contract No. AFOSR/F-44620-72-C-0017.     

On the relationship between the electronic density of states and the superconducting critical temperature of disordered V3Si

The available data on the effect of neutron and α-particle irradiation on the superconducting properties and the low-temperature specific heat capacity of single- and polycrystalline V₃Si were analyzed in a unified manner. It was found that the electron-phonon renormalization parameter λ does not vary simply proportionally to the bare density of electron states at the Fermi level as had been earlier conjectured by Dynes and Varma, nor does it vary in exactly the same manner as found by Fradin and Williamson to hold for a variety of vanadium-based A15 structure compounds and pseudobinary alloys. When the behavior of V₃Si is compared with that of Nb₃Sn, Nb₃Al, and Nb₃Ge, it is seen that the response to disorder of parameters of importance in the superconductivity of these compounds does not follow any simple, universal behavior.     

Current-controlled oscillator

A relaxation oscillator whose frequency is linearly related to an input control current is described. The circuit configuration is based on the emitter-coupled astable multivibrator. The linear frequency variation is obtained by incorporating a discriminator circuit and high-transconductance elements into the oscillator circuit. Experimental results obtained from a circuit constructed from monolithic transistor arrays indicate that frequency variation over two decades, with a linearity better than 0.1%, can be obtained.