Ll-CFAR: a flexible and robust alternative

A new family of constant false alarm rate (CFAR) processors is introduced. An Ll-CFAR forms its noise power estimate by linearly filtering ranked samples from the reference set; the weights of this combination, however, depend not only on the rank, but also on the relative proximity of the sample to the cell under test. From the class of Ll-CFARs may be chosen members which effectively censor spurious targets; members which exhibit impressive control of false alarm in the presence of a clutter edge; and members which are robust against both such inhomogeneities. While the design of such schemes is involved, their implementation is not significantly more burdensome than that of plain ordered statistic CFAR (OS-CFAR). After a discussion of the stochastic training of Ll-CFAR, the performance is thoroughly assessed under the most commonly encountered instances of environmental conditions, and compared with those of classical CFAR techniques     

Investigation of corona initiation voltage at reduced pressures

The results of an experimental study of the 60 Hz ac corona inception voltage at reduced pressures for a cylindrical conductor and a parallel ground plane are presented. Several spacings and bare and insulated conductors of several diameters are considered. Empirical expressions from which a reasonably accurate prediction of the corona inception voltage (CIV) may be made have been inferred from experimental data     

Speech Data Rate Reduction Part II: Applicability of Sensitivity and Error Analysis

This paper deals with the application of modern estimation techniques to the problem of speech data rate reduction. It is desirable to adaptively identify and quantitize the parameters of the speech model. These paramaters cannot be identified and quantized exactly; the performance of the predictor is thereby degraded and this could prevent data reduction. In many cases it is desirable to emply a suboptimal predictor in order to simplify the algorithms, and predictor performance is again degraded. This paper develops sensitivity and error analysis as a potential method for determining quantitatively how speech data reduction system performance is degraded by imprecise parameter knowledge or suboptimal filtering. An intended use of the sensitivity and error analysis algorithms is to determine parameter identification and model structure requirements of configuration concepts for adaptive speech digitizers. First, sensitivity and error analysis algorithms are presented that form the basis for the remainder of the work. The algorithms are then used to determine how imprecise knowledge of vocal tract parameters degrades predictor performance in speech. Transversal filters have previously been proposed for this application. The sensitivity analysis algorithms are then used to determine when and by how much the transverse filter is suboptimal to the Kalman filter. In particular, the question of how effectively a higher order of all-pole model approximates a system with zeros is answered, as this question is of considerable importance in speech. Finally, the physical significance of the innovations process in speech data rate reduction is studied.     

Long-term survival of bacterial spores in space.

On board of the NASA Long Duration Exposure Facility (LDEF), spores of Bacillus subtilis in monolayers (10(6)/sample) or multilayers (10(8)/sample) were exposed to the space environment for nearly six years and their survival was analyzed after retrieval. The response to space parameters, such as vacuum (10(-6) Pa), solar electromagnetic radiation up to the highly energetic vacuum-ultraviolet range (10(9) J/m2) and/or cosmic radiation (4.8 Gy), was studied and compared to the results of a simultaneously running ground control experiment. If shielded against solar ultraviolet (UV)-radiation, up to 80 % of spores in multilayers survive in space. Solar UV-radiation, being the most deleterious parameter of space, reduces survival by 4 orders of magnitude or more. However, up to 10(4) viable spores were still recovered, even in completely unprotected samples. Substances, such as glucose or buffer salts serve as chemical protectants. With this 6 year study in space, experimental data are provided to the discussion on the likelihood of "Panspermia".     

Peculiarities of biological processes under conditions of microgravity.

The results of experiments aboard spacecraft demonstrated the dependence of the pattern of biological processes on microgravity and on the ability of biological objects to adapt themselves to new environmental conditions. This is of fundamental importance for solving theoretical and practical problems of space biology, or elaborating the theory of organism's behavior in weightlessness, and for elucidating the global mechanisms of the action of microgravity on living systems.     

The human cardiovascular system during space flight

Purpose of the work is to analyze and to summarize the data of investigations into human hemodynamics performed over 20 years aboard orbital stations Salyut-7 and Mir with participation of 26 cosmonauts on space flights (SF) from 8 to 438 days in duration. The ultrasonic techniques and occlusive plethysmography demonstrated dynamics of changes in the cardiovascular system during SF of various durations. The parameters of general hemodynamics, the pumping function of the heart and arterial circulation in the brain remained stable in all the space flights; however, there were alterations in peripheral circulation associated with blood redistribution and hypovolemie in microgravity. The anti-gravity distribution of the vascular tone decayed gradually as unneeded. The most considerable changes were observed in leg vessels, equally in arteries (decrease in resistance) and veins (increase in maximum capacity). The lower body negative pressure test (LBNP) revealed deterioration of the gravity-dependent reactions that changed for the worse as SF duration extended. The cardiovascular deconditioning showed itself as loss of descent acceleration tolerance and orthostatic instability in the postflight period.     

Does mental arithmetic before head up tilt have an effect on the orthostatic cardiovascular and hormonal responses?

Passive head up tilt (HUT) and mental arithmetic (MA) are commonly used for providing mental and orthostatic challenges, respectively. In animal experiments, even a single exposure to a stressor has been shown to modify the response to subsequent stress stimulus. We investigated whether MA applied before HUT elicits synergistic responses in orthostatic heart rate (HR), cardiac output (CO), heart rate variability and arterial blood pressure. The 15 healthy young males were subjected to two randomized protocols: (a) HUT and (b) HUT preceded by MA, with sessions randomized and ≥2 weeks apart. Beat to beat continuous hemodynamic variables were measured and saliva samples taken for hormonal assay. HUT alone increased HR from 59±7 (baseline) to 80±10 bpm (mean±SD) and mean blood pressure (MBP) from 88±10 to 91±14 mmHg. HUT results after MA were not different from those with HUT alone. The activity of alpha amylase showed differences during the experiments irrespective of the protocols. We conclude that mental challenge does not affect orthostatic cardiovascular responses when applied before; the timing of mental loading seems to be critical if it is intended to alter cardiovascular responses to upright standing.     

Further Results on Multipath Angle Error Reduction Using Multiple-Target Methods

The two-target technique proposed by the author in an earlier paper [1] for reducing radar multipath angle tracking errors has been simulated on a digital computer assuming an actual closed-loop system. When tracking with noise, the technique provides angle error performance which compares quite favorably with the expected performance given in [1] Furthermore, the large bias errors usually encountered in normal monopulse systems at low elevation angles are removed. Results of typical tracks are given, both for the method of [1], and for a modified version of the method which applies primarily to shipboard radar systems. Some results on loss of lock are also presented.