A Self Bit Synchronizer Matched to the Signal Shape

A suboptimum self bit synchronizer is considered that matches the signal shape, i. e., operates making a clever use of the knowledge of the signaling waveform. The noise performance of this system is analyzed for high signal-to-noise ratios, and an expression is obtained for the variance of the timing errors. This variance is compared with that of systems proposed by other authors on the basis of equal closed-loop noise bandwidth and equal signal shape. It is found that the use of this matched synchronizer enables appreciable timing jitter reductions.     

A new application of LBNP to measure orthostatic tolerance before and after 0-g simulation (water immersion)

Lower body negative pressure (LBNP) remains an important device for the generation of orthostatic stress in the space flight environment as well as a tool to measure inflight and postflight changes in orthostatic response.

These applied levels of LBNP have typically not exceeded 50–60 mm Hg negative pressure. Information is incomplete as to the levels of absolute LBNP orthostatic tolerance, and the factors responsible for their variance. A better definition of the tolerance limits for males and females could be expected to aid the evaluation of lower levels of LBNP.

An LBNP device was built to study absolute orthostatic tolerance; additionally, another LBNP device was constructed to permit orthostatic tolerance testing directly after a controlled water immersion period.

Absolute LBNP orthostatic tolerance patterns are analyzed for a group of males and females (series I). A preliminary statement on the variations of LBNP orthostatic tolerance after limited periods of water immersion and bed rest is also provided (series II).     

The importance of spectroscopy in the 80–800 å region for plasma diagnostics in the solar atmosphere

We discuss the importance of the spectral range from about 80 to 800 Å for determining physical conditions in different regions of the solar atmosphere. We give examples of line ratios that may be used to determine electron densities in quiet Sun regions, active regions, and flares. We discuss the possibility of determining electron temperatures from line ratios in the EUV.We show that profiles as well as intensities of spectral lines must be obtained for a proper interpretation of the spectra. We give approximate parameters for a solar grazing incidence spectrograph suitable for the study of the 80–800 Å wavelength region.Given as an invited review paper at the EGAS Meeting in Munich, Germany, 11–14 July 1978.     

Optimization of biased proportional navigation [guided projectiles]

An analytical treatment of the biased proportional navigation (BPN) is carried out with the aim of optimizing the bias parameter. It is shown that optimum biasing can lead to significantly more control-effort-efficient PN guidance in a wide variety of engagement situations, especially those involving higher target maneuvers. The performance of the BPN is compared with the standard (unbiased) PN system for the general case of a maneuvering target, and performance of the BPN is maximised to obtain the optimum bias value. The optimum bias is expressed through a simple algebraic equation, which can be readily solved. For the special (and very useful) case of the effective navigation constant being equal to three, the equation reduces to a quadratic, leading to an explicit expression for the optimum bias. Specific examples are provided to show the benefits of the BPN law. The higher control efficiency of the law is especially useful in extra-atmospheric interception, where the savings in control effort directly translates to a saving of propellent which forms part of the payload     

Comments on "Bounds on Probability of Error in Decision Feedback Equalizers"

In the above paper1 a technique was proposed to derive an upper bound on the error probability of a decision feedback equalizer. It involves decomposition of the probability density function of residual intersymbol interference and derivation of Chebyshev-type bounds on the error functionals over the decomposed functions. In this correspondence, we demonstrate that the technique is not applicable in general. The result is not a bound in many cases.     

Spherule beds 3.47-3.24 billion years old in the Barberton Greenstone Belt,South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approximately 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.     

Remote sensing of the atmospheric from scientific stations “Salyut”

A review of the four-channel teleradiometer “Micron” calibration and data processing techniques has been presented. The sensor validation of the space-borne teleradiometer “Micron” was based on the following: the preflight absolute calibration with the state certificated standard, the secondary onboard standard (miniature filament lamp), the inflight measurements of the Moon's brightness. The procedure of the extinction coefficient determination from the daytime horizon profiles has been developed. The validity of the used techniques was estimated by carring out model calculations. An optimal measuring procedure has been recommended. The proposed simple techniques are used for processing the space measured horizon brightness data. The results have been compared with the earlier published ones.     

Morphology: an ambiguous indicator of biogenicity

This paper deals with the difficulty of decoding the origins of natural structures through the study of their morphological features. We focus on the case of primitive life detection, where it is clear that the principles of comparative anatomy cannot be applied. A range of inorganic processes are described that result in morphologies emulating biological shapes, with particular emphasis on geochemically plausible processes. In particular, the formation of inorganic biomorphs in alkaline silica-rich environments are described in detail.     

A Note on Satellite Dynamics

It is demonstrated here that inertial differentiation of angular momentum-is independent of the choice of the moving reference coordinate system. The results agree with Greensite [1] and contradict Sen's results [2] by indicating a basic error in his derivation. However, Sen's step [2] is correct.