4,408 research outputs found
The antigenic index: a novel algorithm for predicting antigenic determinants
In this paper, we introduce a computer algorithm which can
be used to predict the topological features of a protein directly
from its primary amino acid sequence. The computer program
generates values for surface accessibility parameters and combines
these values with those obtained for regional backbone
flexibility and predicted secondary structure. The output of this
algorithm, the antigenic index, is used to create a linear surface
contour profile of the protein. Because most, if not all,
antigenic sites are located within surface exposed regions of
a protein, the program offers a reliable means of predicting
potential antigenic determinants. We have tested the ability of
this program to generate accurate surface contour profiles and
predict antigenic sites from the linear amino acid sequences
of well-characterized proteins and found a strong correlation
between the predictions of the antigenic index and known structural
and biological data
Brown dwarf populations in open clusters
We present the results of multiple simulations of open clusters, modelling
the dynamics of a population of brown dwarf members. We consider the effects of
a large range of primordial binary populations, including the possibilities of
having brown dwarf members contained within a binary system. We also examine
the effects of various cluster diameters and masses. Our examination of a
population of wide binary systems containing brown dwarfs, reveals evidence for
exchange reactions whereby the brown dwarf is ejected from the system and
replaced by a heavier main-sequence star. We find that there exists the
possibility of hiding a large fraction of the brown dwarfs contained within the
primordial binary population. We conclude that it is probable that the majority
of brown dwarfs are contained within primordial binary systems which then hides
a large proportion of them from detection.Comment: 16 pages, 8 figures; to appear in MNRA
Synthesis and alkyne-coupling chemistry of cyclomanganated 1- and 3-acetylindoles, 3-formylindole and analogues
The syntheses are reported of new cyclomanganated indole derivatives (1-acetyl-ÎșO-indolyl-ÎșC2)dicarbonylbis(trimethylphosphite)manganese (2), (1-methyl-3-acetyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (4), (3-formyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (5a) and (1-methyl-3-formyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (5b). The unusually complicated crystal structure of 5b has been determined, the first for a cyclomanganated aryl aldehyde.
The preparations of a mitomycin-related pyrrolo-indole and related products by thermally promoted and oxidatively (Me3NO) initiated alkyne-coupling reactions of the previously known complex (1-acetyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (1) are reported for different alkynes and solvents. X-ray crystal structures are reported for the dimethyl acetylenedicarboxylate coupling product of 1 (dimethyl 1-methyl-l-hydroxypyrrolo[1,2a]-indole-2,3-dicarboxylate; 6a), and an unusually-cyclised triple insertion product 8 from the coupling of acetylene with 4, in which a cyclopentadiene moiety is η3-allyl-coordinated to Mn through only one double bond and an exocyclic carbon, but which rearranges on heating to an η5-cyclopentadienyl complex
Harding College Spring Sing Program 1975
Program for the 1975 Spring Sing performance at Harding College.
Hosts and Hostesses: Tim Holder, Stacy Peters, Michele Pullara, Sylvia Rose, Ann Ulreyhttps://scholarworks.harding.edu/spring-sing/1001/thumbnail.jp
Progress report on the ground-water resources of the Las Vegas Artesian Basin, Nevada
Whether the tremendously increased population acquired by Las Vegas in the years 1940 to 1942 will be retained cannot at present be foretold. However, the valley will undoubtedly be expected to support a considerably larger population than it did at any time prior to 1940, and continually increasing demands on the water supply for innumerable pcacetimc activities must be anticipated. Therefore, a sound evaluation of tho ground water resources of Las Vegas Valley is directly in line with the other wisely progressive planning programs which are now operating or are taking shape in the valley as well as in the entire State of Nevada
Mother-toddler interaction patterns associated with maternal depression.
Journal ArticleInteractive coordination was observed in laboratory play interactions of pairs of 29 clinically depressed and 14 nondepressed mothers and their 13-29-month-old children (M = 18.9 months). Nondepressed mothers and their children displayed more interactive coordination than depressed-mother dyads (p < .001). Depressed mothers were less likely to repair interrupted interactions, and their toddlers were less likely to maintain interactions than nondepressed controls. Toddlers matched their nondepressed but not their depressed mothers' negative behavior rates. Results suggested that early interventions focus on training mothers to attend to, maintain, and repair mother-child interactions to more closely approximate normal levels of interactive coordination
Direct observations of coherent backscatter of radar waves in precipitation
In previous work, it was argued that a source of radar coherent scatter occurs in the direction perpendicular to the direction of wave propagation because of the presence of grids of enhanced particle concentrations with spatial periodicities in resonance with the radar wavelength. While convincing, the evidence thus far has been indirect. In this work the authors now present direct observations of radar coherent backscattered signals in precipitation in the direction of wave propagation.
The theory is developed for the cross-correlation function of the complex amplitudes in the direction of propagation calculated for nearest neighbor range bins. Data are analyzed in snow and in rain. The results agree with the earlier conclusions in the previous work, namely that coherent scatter occurs in both rain and snow, that it is larger in snow than it is in rain, and that it can be significant at times
Partially coherent backscatter in radar observations of precipitation
Classical radar theory only considers incoherent backscatter from precipitation. Can precipitation generate coherent scatter as well? Until now, the accepted answer has been no, because hydrometeors are distributed sparsely in space (relative to radar wavelength) so that the continuum assumption used to explain coherent scatter in clear air and clouds does not hold.
In this work, a theory for a different mechanism is presented. The apparent existence of the proposed mechanism is then illustrated in both rain and snow. A new power spectrum Z(âfâ), the Fourier transform of the time series of the radar backscattered reflectivities, reveals statistically significant frequencies f of periodic components that cannot be ascribed to incoherent scatter. It is shown that removing those significant fs from Z(âfâ) at lower frequencies greatly reduces the temporal coherency. These lower frequencies, then, are associated with the increased temporal coherency. It is also shown that these fs are also directly linked to the Doppler spectral peaks through integer multiples of one-half the radar wavelength, characteristic of Bragg scatter. Thus, the enhanced temporal coherency is directly related to the presence of coherent scatter in agreement with theory.
Moreover, the normalized backscattered power spectrum Z(âfâ) permits the estimation of the fractional coherent power contribution to the total power, even for an incoherent radar. Analyses of approximately 26 000 one-second Z(âfâ) in both rain and snow reveal that the coherent scatter is pervasive in these data. These findings present a challenge to the usual assumption that the scatter of radar waves from precipitation is always incoherent and to interpretations of backscattered power based on this assumption
The effect of clustering on the uncertainty of differential reflectivity measurements
One of the most important avenues of recent meteorological radar research is the application of polarization techniques to improve radar rainfall estimation. A keystone in many of these methods is the so-called differential reflectivity ZDR, the ratio of the reflectivity factor ZH at horizontal polarization backscattered from a horizontally polarized transmission to that corresponding to a vertically polarized transmission ZV. For such quantitative applications, it is important to understand the statistical accuracy of observations of ZDR. The underlying assumption of all past estimations of meteorological radar uncertainties is that the signals obey Rayleigh statistics. It is now evident, however, that as a radar scans, the meteorological conditions no longer always satisfy the requirements for Rayleigh statistics. In this work, ZDR is reconsidered, but this time within the new framework of non-Rayleigh signal statistics. Using Monte Carlo experiments, it is found that clustering of the scatterers multiplies the standard deviation of ZDR beyond what is always calculated assuming Rayleigh statistics. The magnitude of this enhancement depends on the magnitudes of the clustering index and of the cross correlation between ZHand ZV. Also, it does not depend upon the number of independent samples in an ensemble estimate. An example using real radar data in convective showers suggests that non-Rayleigh signal statistics should be taken into account in future implementations of polarization radar rainfall estimation techniques using ZDR. At the very least, it is time to begin to document the prevalence and magnitude of the clustering index in a wide variety of meteorological conditions
On the enhanced temporal coherency of radar observations in precipitation
In this work, the authors present observations of enhanced temporal coherency beyond that expected using the observations of the standard deviation of the Doppler velocities and the assumption of a family of exponentially decaying autocorrelation functions. The purpose of this paper is to interpret these observations by developing the complex amplitude autocorrelation function when both incoherent and coherent backscatter are present. Using this expression, it is then shown that when coherent scatter is present, the temporal coherency increases as observed. Data are analyzed in snow and in rain. The results agree with the theoretical expectations, and the authors interpret this agreement as an indication that coherent scatter is the likely explanation for the observed enhanced temporal coherency. This finding does not affect decorrelation times measured using time series. However, when the time series is not available (as in theoretical studies), the times to decorrelation are often computed based upon the assumptions that the autocorrelation function is a member of the family of exponentially decaying autocorrelation functions and that the signal decorrelation is due solely to the Doppler velocity fluctuations associated with incoherent scatter. Such an approach, at times, may significantly underestimate the true required times to decorrelation thus leading to overestimates of statistical reliability of parameters
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