27,917 research outputs found
The effects of spacecraft environments on some hydrolytic enzyme patterns in bacteria
The effects of space flight on the production and characteristics of proteolytic enzymes are studied for a number of bacterial species isolated from crew members and spacecraft. Enzymatic make-up and cultural characteristics of bacteria isolated from spacecraft crew members are determined. The organism Aeromonas proteolytica and the proteolytic enzymes which it produces are used as models for future spacecraft experiments
Water resource records of the Econfina Creek Basin area, Florida
The Econfina Creek basin area in northwestern Florida, which includes Bay
County, southeastern Washiigton County, and parts of Calhoun, Gulf, and
Jackson counties is shown in figure 1. The basin has an abundant supply of
ground water and surface water of good quality. This determination is based on
a three-year investigation of the water resources of the basin by the U. S.
Geological Survey in cooperation with the Division of Geology, Florida Board of
Conservation, during the period from October 1961 through June 1964. The
purpose of this report is to assemble the basic data collected during this
investigation for those persons interested in water development or management
in this basin.
(Document has 131 pages.
Water-resource records of Brevard County, Florida
The U. S. Geological Survey made a comprehensive
investigation of the water resources of Brevard County
from 1954 to 1958. The purposes of this investigation were:
(1) to determine the occurrence and chemical quality of
water in the streams and lakes, (2) to determine the location
and the thickness of aquifers, and (3) to determine the
occurrence and chemical quality of the ground water. During
the period from 1933 to 1954, water records were collected
from a few stream-gaging stations and a few observation
wells. The purpose of this report is to present basic data
collected during these investigations. (Document has 188 pages.
Determination of Frequency and Distribution of Hessian Fly (Diptera: Cecidomyiidae) Biotypes in the Northeastern Soft Wheat Region
Fifteen collections of Hessian flies from the northern soft winter wheat region of the United States were used to determine the composition and frequency of biotypes. The wheat cultivars \u27Seneca\u27 (H7Hs), \u27Monon\u27 (H3), \u27Knox 62\u27 (~, H7Hg), and \u27Abe\u27 (Hs) were used as differentials. Biotypes J and L replaced biotype B as the prevalent biotype in Indiana, since wheat cultivars having the Hs and the H6 genes have been grown. Biotype GP, the least virulent of any Hessian fly biotypes, was still present in New York indicating that wheat cuItivars with no genes for resistance are still being grown there. The genetic variability of Hessian fly biotypes that enables them to overcome the resistance in wheat cultivars is discussed
Systematic derivation of a surface polarization model for planar perovskite solar cells
Increasing evidence suggests that the presence of mobile ions in perovskite
solar cells can cause a current-voltage curve hysteresis. Steady state and
transient current-voltage characteristics of a planar metal halide
CHNHPbI perovskite solar cell are analysed with a drift-diffusion
model that accounts for both charge transport and ion vacancy motion. The high
ion vacancy density within the perovskite layer gives rise to narrow Debye
layers (typical width 2nm), adjacent to the interfaces with the transport
layers, over which large drops in the electric potential occur and in which
significant charge is stored. Large disparities between (I) the width of the
Debye layers and that of the perovskite layer (600nm) and (II) the ion
vacancy density and the charge carrier densities motivate an asymptotic
approach to solving the model, while the stiffness of the equations renders
standard solution methods unreliable. We derive a simplified surface
polarisation model in which the slow ion dynamic are replaced by interfacial
(nonlinear) capacitances at the perovskite interfaces. Favourable comparison is
made between the results of the asymptotic approach and numerical solutions for
a realistic cell over a wide range of operating conditions of practical
interest.Comment: 32 pages, 7 figure
Drugs for neglected diseases: a failure of the market and a public health failure?
Infectious diseases cause the suffering of hundreds of millions of people, especially in tropical and subtropical areas. Effective, affordable and easy-to-use medicines to fight these diseases are nearly absent. Although science and technology are sufficiently advanced to provide the necessary medicines, very few new drugs are being developed. However, drug discovery is not the major bottleneck. Today's R&D-based pharmaceutical industry is reluctant to invest in the development of drugs to treat the major diseases of the poor, because return on investment cannot be guaranteed. With national and international politics supporting a free market-based world order, financial opportunities rather than global health needs guide the direction of new drug development. Can we accept that the dearth of effective drugs for diseases that mainly affect the poor is simply the sad but inevitable consequence of a global market economy? Or is it a massive public health failure, and a failure to direct economic development for the benefit of society? An urgent reorientation of priorities in drug development and health policy is needed. The pharmaceutical industry must contribute to this effort, but national and international policies need to direct the global economy to address the true health needs of society. This requires political will, a strong commitment to prioritize health considerations over economic interests, and the enforcement of regulations and other mechanisms to stimulate essential drug development. New and creative strategies involving both the public and the private sector are needed to ensure that affordable medicines for today's neglected diseases are developed. Priority action areas include advocating an essential medicines R&D agenda, capacity-building in and technology transfer to developing countries, elaborating an adapted legal and regulatory framework, prioritizing funding for essential drug development and securing availability, accessibility, distribution and rational use of these drugs
Link and subgraph likelihoods in random undirected networks with fixed and partially fixed degree sequence
The simplest null models for networks, used to distinguish significant
features of a particular network from {\it a priori} expected features, are
random ensembles with the degree sequence fixed by the specific network of
interest. These "fixed degree sequence" (FDS) ensembles are, however, famously
resistant to analytic attack. In this paper we introduce ensembles with
partially-fixed degree sequences (PFDS) and compare analytic results obtained
for them with Monte Carlo results for the FDS ensemble. These results include
link likelihoods, subgraph likelihoods, and degree correlations. We find that
local structural features in the FDS ensemble can be reasonably well estimated
by simultaneously fixing only the degrees of few nodes, in addition to the
total number of nodes and links. As test cases we use a food web, two protein
interaction networks (\textit{E. coli, S. cerevisiae}), the internet on the
autonomous system (AS) level, and the World Wide Web. Fixing just the degrees
of two nodes gives the mean neighbor degree as a function of node degree,
, in agreement with results explicitly obtained from rewiring. For
power law degree distributions, we derive the disassortativity analytically. In
the PFDS ensemble the partition function can be expanded diagrammatically. We
obtain an explicit expression for the link likelihood to lowest order, which
reduces in the limit of large, sparse undirected networks with links and
with to the simple formula . In a
similar limit, the probability for three nodes to be linked into a triangle
reduces to the factorized expression .Comment: 17 pages, includes 11 figures; first revision: shortened to 14 pages
(7 figures), added discussion of subgraph counts, deleted discussion of
directed network
The Y-Band at 1.035 um: Photometric Calibration and the Dwarf Stellar/Sub-Stellar Color Sequence
We define and characterize a photometric bandpass (called "Y") that is
centered at 1.035 um, in between the traditionally classified ``optical'' and
``infrared'' spectral regimes. We present Y magnitudes and Y-H and Y-K colors
for a sample consisting mostly of photometric and spectral standards, spanning
the spectral type range sdO to T5V. Deep molecular absorption features in the
near-infrared spectra of extremely cool objects are such that the Y-H and Y-K
colors grow rapidly with advancing spectral type especially from late M through
mid L, substantially more rapidly than J-H or H-K which span a smaller total
dynamic range. Consistent with other near-infrared colors, however, Y-H and Y-K
colors turn blueward in the L6-L8 temperature range with later T-type objects
having colors similar to those of warmer M and L stars. Use of the Y-band
filter is nonetheless promising for easy identification of low-mass stars and
brown dwarfs, especially at young ages. The slope of the interstellar reddening
vector within this filter is A_Y = 0.38 x A_V. Reddening moves stars nearly
along the YHK dwarf color sequence making it more difficult to distinguish
unambiguously very low mass candidate brown dwarf objects from higher mass
stars seen, e.g. through the galactic plane or towards star-forming regions.
Other diagrams involving the Y-band may be somewhat more discriminating.Comment: accepted at PAS
Network growth models and genetic regulatory networks
We study a class of growth algorithms for directed graphs that are candidate
models for the evolution of genetic regulatory networks. The algorithms involve
partial duplication of nodes and their links, together with innovation of new
links, allowing for the possibility that input and output links from a newly
created node may have different probabilities of survival. We find some
counterintuitive trends as parameters are varied, including the broadening of
indegree distribution when the probability for retaining input links is
decreased. We also find that both the scaling of transcription factors with
genome size and the measured degree distributions for genes in yeast can be
reproduced by the growth algorithm if and only if a special seed is used to
initiate the process.Comment: 8 pages with 7 eps figures; uses revtex4. Added references, cleaner
figure
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