Reducing sensing error in cognitive PANs through reduction of the channel set and split sensing

Cognitive radio technology necessitates accurate and timely sensing of the primary users’ activity on the chosen set of channels. If sensing error is unacceptably high, we can reduce the number of working channels so as to improve the channels-vs.-sensing nodes ratio, and undertake differential or split sensing in which subsets of sensing nodes target idle and active channels, respectively. The paper presents a probabilistic analysis of the sensing process, including the split sensing policy, and investigates the range of values in which such, incomplete sensing is capable of maintaining an accurate view of the status of the working channel set.     

Giant pulsar pulses for precision comparison of clocks

The possibility of achieving high-precison comparison of clocks with the use of giant pulsar pulses of enormous peak density of a nanosecond flux is considered. There are practically no constraints on the distance between the synchronized clocks, which may be located either on Earth or in outer space. Radio telescopes of moderate dimensions, low-noise receivers, and high-speed recorders are needed for a such a comparison of clocks. Giant pulsar pulses may be used for space navigation as well as for determining moments (epochs) in the scale of pulsar time.     

Improving the controlled cooling of hot-rolled steel coils

The thermostatting of alloy-steel coils after hot rolling in a continuous broad-strip mill is considered. A technological chart of slow controlled cooling of the coils is developed. Measures are proposed for the production of high-quality and highly profitable steel coils without additional capital expenditures or operating costs.     

Experiments on Dynamic Behavior of Molten Metal and Solid Particles Under Direct Current Passing

At electrodischarge sintering of powder mixtures by electric direct current, some essential displacements of molten metal and solid particles were revealed. Such displacements at conventional sintering were not known to us. The objects were powders (mixtures): Sn–Cu (dispersivity 100–200 µm); Sn–high-temperature alloy on nickel base or electrocorundum; copper alloy-electrocorundum (dispersivity 63–500 µm); Ni (dispersivity 10 µm). The electric direct current was passed in vertical direction parallel with the axis of cylindrical mould or through the series circuit steel-powder nickel layer-hard alloy. If the cylindrical container (mould) did not have the upper punch (a load on top was absent), the sample after solidification had the form of a bullet. This sample became convex on top and concave on bottom. At the application of prepressing (start pressing) on top, the movement of suspension (molten matrix and solid particles) occurred in a similar way. Under the action of electromagnetic forces, a redistribution of solid particles in volume of suspension occurs. Particles with more high conductivity than liquid phase begin to cluster at the center. For the case of lower conductivity, the motion of the particles to the outer side surface of mould prevails. As the current passed through the series of circuit steel-nickel powder layer-hard alloy, three named parts of the circuit were sintered into a single block. After destruction at testing, the interlayer had the form of a ring. This shows the nonuniformity of the passing of electric current through the interlayer. The cause of displacements of solid (nonmolten) particles may be the simultaneous influence of thermic convection and squeezing out by the electromagnetic Lorentz-forces, which are directed radially. The phenomena described may be applied in the production of objects with a gradient (variable in volume) concentration of particles added specially. This refers to products of their interaction with molten matrix as well.     

Gamma-Spectrometric Determination of the 89Sr Half-Life

The half-life T1/2 of ⁸⁹Sr was estimated at 1208±9 h, or 50.34±0.37 days, by semiconductor [Ge(Li) detector] -ray spectrometry with measuring the intensity of the 913-keV -line (⁸⁹Sr) for 6000 h relative to the 661.7-keV -line (¹³⁷Cs) as the internal reference. The inaccuracy is given for the confidence level P = 0.95.     

Embedding Impurities into Liquid Helium

We have introduced guest particles into superfluid helium using a directed helium jet containing traces of species under study. The distinguishing peculiarity of the method consists in that the whole system is sealed from the cryostat main helium bath. This allows: (i) on the account of the absence of evaporating helium upflow to realize a complete capture of the impurities from the jet into liquid helium; (ii) to eliminate the dependence of the process conditions on liquid He level position in the main bath as well as on the amount of liquid He condensed inside a cell; and (iii) this method can be used to introduce impurities into liquid ³He. Two modifications of the technique have been designed—one for an optical cryostat and another for a cryostat with narrow 1 tail typical for use in a very high magnetic field. Optical and X-ray diffraction studies have confirmed the possibility of embedding in superfluid helium samples consisting of submicron D₂ particles with a rate of 10mmoles per hour. Such samples are necessary for the achievement of strong D₂ nuclear spin polarization by the brute force method.     

Grating theory: new equations in Fourier space leading to fast converging results for TM polarization

Using theorems of Fourier factorization, a recent paper [J. Opt. Soc. Am. A 13, 1870 (1996)] has shown that the truncated Fourier series of products of discontinuous functions that were used in the differential theory of gratings during the past 30 years are not converging everywhere in TM polarization. They turn out to be converging everywhere only at the limit of infinitely low modulated gratings. We derive new truncated equations and implement them numerically. The computed efficiencies turn out to converge about as fast as in the TE-polarization case with respect to the number of Fourier harmonics used to represent the field. The fast convergence is observed on both metallic and dielectric gratings with sinusoidal, triangular, and lamellar profiles as well as with cylindrical and rectangular rods, and examples are shown on gratings with 100% modulation. The new formulation opens a new wide range of applications of the method, concerning not only gratings used in TM polarization but also conical diffraction, crossed gratings, three-dimensional problems, nonperiodic objects, rough surfaces, photonic band gaps, nonlinear optics, etc. The formulation also concerns the TE polarization case for a grating ruled on a magnetic material as well as gratings ruled on anisotropic materials. The method developed is applicable to any theory that requires the Fourier analysis of continuous products of discontinuous periodic functions; we propose to call it the fast Fourier factorization method.     

High-accuracy translation-rotation encoder with two gratings in a Littrow mount

A new type of translation-rotation encoder that makes use of two identical transparent dielectric gratings lighted in a -1-order Littrow mount is proposed. The correct choice of the wavelength-to-groove-spacing ratio produces only two transmitted beams, which interfere with the highest possible visibility in a large range of experimental conditions. Thus this mounting permits high-accuracy encoders to be produced by the use of cheap photoresist or plastic gratings and opens the way to industrial applications in high-precision mechanics, information processing, etc.     

Transport and turnover of microtubules in frog neurons depend on the pattern of axonal growth

Empirical analysis of the profitability of moderate grazing are presented based on sample dairy farms in Pennsylvania and New York. Net income per cow was higher for dairy farms that employed moderate intensive grazing than for dairy farms that employed extensive grazing. Income appeared to be adequate for family living expenses, but moderate intensive grazing could not be considered a high profit system. Detailed analyses of dairy farms that employed moderate and extensive grazing in northern Pennsylvania indicated that returns to management and owner equity were higher for pasture enterprises than for corn silage or hay enterprises. Positive dairy profits were related to lower feed costs. Milk production was lower on farms that employed moderate grazing than on farms that employed extensive grazing. Logit regression analysis characterized farms that employed moderate intensive grazing as oriented toward dairy rather than toward crop production; these farms had lower culling rates and a greater dependence on milk sales as a share of total sales. The reduced use of fertilizers and chemicals suggests that moderate grazing had environmentally sustainable features.