5,136 research outputs found
Culture of urine specimens by use of chromID CPS Elite medium can expedite Escherichia coli identification and reduce hands-on time in the clinical laboratory
Urine is one of the most common specimen types submitted to the clinical microbiology laboratory; the use of chromogenic agar is one method by which the laboratory might expedite culture results and reduce hands-on time and materials required for urine culture analysis. The objective of our study was to compare chromID CPS Elite (bioMérieux), a chromogenic medium, to conventional primary culture medium for evaluation of urine specimens. Remnant urine specimens (n = 200) were inoculated into conventional media and into chromID CPS Elite agar (chromID). The time to identification and consumables used were documented for both methods. Clinically significant pathogen(s) were recovered from 51 cultures using conventional media, with Escherichia coli being the most frequently recovered organism (n = 22). The rate of exact uropathogen agreement between conventional and chromogenic media was 82%, while overall categorical agreement was 83.5% The time interval between plating and final organism identification was decreased with chromID agar versus conventional media for E. coli (mean of 24.4 h versus 27.1 h, P < 0.001). Using chromID, clinically significant cultures required less hands-on time per culture (mean of 1 min and 2 s [1:02 min]) compared to conventional media (mean of 1:31 min). In addition, fewer consumables (2.4 versus 3.3 sticks and swabs) and rapid biochemical tests (1.0 versus 1.9) were necessary using chromID versus conventional media. Notably, antimicrobial susceptibility testing demonstrated good overall agreement (97.4%) between the chromID and conventional media for all antibiotics tested. chromID CPS Elite is accurate for uropathogen identification, reduces consumable usage, and may expedite the identification of E. coli in clinical specimens
A Framework for Inferring Taxonomic Class of Asteroids.
Introduction: Taxonomic classification of asteroids based on their visible / near-infrared spectra or multi band photometry has proven to be a useful tool to infer other properties about asteroids. Meteorite analogs have been identified for several taxonomic classes, permitting detailed inference about asteroid composition. Trends have been identified between taxonomy and measured asteroid density. Thanks to NEOWise (Near-Earth-Object Wide-field Infrared Survey Explorer) and Spitzer (Spitzer Space Telescope), approximately twice as many asteroids have measured albedos than the number with taxonomic classifications. (If one only considers spectroscopically determined classifications, the ratio is greater than 40.) We present a Bayesian framework that provides probabilistic estimates of the taxonomic class of an asteroid based on its albedo. Although probabilistic estimates of taxonomic classes are not a replacement for spectroscopic or photometric determinations, they can be a useful tool for identifying objects for further study or for asteroid threat assessment models. Inputs and Framework: The framework relies upon two inputs: the expected fraction of each taxonomic class in the population and the albedo distribution of each class. Luckily, numerous authors have addressed both of these questions. For example, the taxonomic distribution by number, surface area and mass of the main belt has been estimated and a diameter limited estimate of fractional abundances of the near earth asteroid population was made. Similarly, the albedo distributions for taxonomic classes have been estimated for the combined main belt and NEA (Near Earth Asteroid) populations in different taxonomic systems and for the NEA population specifically. The framework utilizes a Bayesian inference appropriate for categorical data. The population fractions provide the prior while the albedo distributions allow calculation of the likelihood an albedo measurement is consistent with a given taxonomic class. These inputs allows calculation of the probability an asteroid with a specified albedo belongs to any given taxonomic class
Electron Waiting Times in Mesoscopic Conductors
Electron transport in mesoscopic conductors has traditionally involved
investigations of the mean current and the fluctuations of the current. A
complementary view on charge transport is provided by the distribution of
waiting times between charge carriers, but a proper theoretical framework for
coherent electronic systems has so far been lacking. Here we develop a quantum
theory of electron waiting times in mesoscopic conductors expressed by a
compact determinant formula. We illustrate our methodology by calculating the
waiting time distribution for a quantum point contact and find a cross-over
from Wigner-Dyson statistics at full transmission to Poisson statistics close
to pinch-off. Even when the low-frequency transport is noiseless, the electrons
are not equally spaced in time due to their inherent wave nature. We discuss
the implications for renewal theory in mesoscopic systems and point out several
analogies with energy level statistics and random matrix theory.Comment: 4+ pages, 3 figure
Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses
Experiments by several groups during the past decade have shown that a molten
polymer nanofilm subject to a large transverse thermal gradient undergoes
spontaneous formation of periodic nanopillar arrays. The prevailing explanation
is that coherent reflections of acoustic phonons within the film cause a
periodic modulation of the radiation pressure which enhances pillar growth. By
exploring a deformational instability of particular relevance to nanofilms, we
demonstrate that thermocapillary forces play a crucial role in the formation
process. Analytic and numerical predictions show good agreement with the pillar
spacings obtained in experiment. Simulations of the interface equation further
determine the rate of pillar growth of importance to technological
applications.Comment: 5 pages, 4 figure
Collapse of an ecological network in Ancient Egypt
The dynamics of ecosystem collapse are fundamental to determining how and why
biological communities change through time, as well as the potential effects of
extinctions on ecosystems. Here we integrate depictions of mammals from
Egyptian antiquity with direct lines of paleontological and archeological
evidence to infer local extinctions and community dynamics over a 6000-year
span. The unprecedented temporal resolution of this data set enables
examination of how the tandem effects of human population growth and climate
change can disrupt mammalian communities. We show that the extinctions of
mammals in Egypt were nonrandom, and that destabilizing changes in community
composition coincided with abrupt aridification events and the attendant
collapses of some complex societies. We also show that the roles of species in
a community can change over time, and that persistence is predicted by measures
of species sensitivity, a function of local dynamic stability. Our study is the
first high-resolution analysis of the ecological impacts of environmental
change on predator-prey networks over millennial timescales, and sheds light on
the historical events that have shaped modern animal communities
A new method for the spectroscopic identification of stellar non-radial pulsation modes. II. Mode identification of the Delta Scuti star FG Virginis
We present a mode identification based on new high-resolution time-series
spectra of the non-radially pulsating Delta Scuti star FG~Vir (HD 106384, V =
6.57, A5V). From 2002 February to June a global Delta Scuti Network (DSN)
campaign, utilizing high-resolution spectroscopy and simultaneous photometry
has been conducted for FG~Vir in order to provide a theoretical pulsation
model. In this campaign we have acquired 969 Echelle spectra covering 147 hours
at six observatories. The mode identification was carried out by analyzing line
profile variations by means of the Fourier parameter fit method, where the
observational Fourier parameters across the line are fitted with theoretical
values. This method is especially well suited for determining the azimuthal
order m of non-radial pulsation modes and thus complementary with the method of
Daszynska-Daszkiewicz (2002) which does best at identifying the degree l. 15
frequencies between 9.2 and 33.5 c/d were detected spectroscopically. We
determined the azimuthal order m of 12 modes and constrained their harmonic
degree l. Only modes of low degree (l <= 4) were detected, most of them having
axisymmetric character mainly due to the relatively low projected rotational
velocity of FG Vir. The detected non-axisymmetric modes have azimuthal orders
between -2 and 1. We derived an inclination of 19 degrees, which implies an
equatorial rotational rate of 66 km/s.Comment: 14 pages, 26 figure
Considering Deflection Missions for Asteroid Impact Risk
No abstract availabl
Structure and electronic properties of the () SnAu/Au(111) surface alloy
We have investigated the atomic and electronic structure of the
() SnAu/Au(111) surface alloy. Low
energy electron diffraction and scanning tunneling microscopy measurements show
that the native herringbone reconstruction of bare Au(111) surface remains
intact after formation of a long range ordered () SnAu2/Au(111) surface alloy. Angle-resolved
photoemission and two-photon photoemission spectroscopy techniques reveal
Rashba-type spin-split bands in the occupied valence band with comparable
momentum space splitting as observed for the Au(111) surface state, but with a
hole-like parabolic dispersion. Our experimental findings are compared with
density functional theory (DFT) calculation that fully support our experimental
findings. Taking advantage of the good agreement between our DFT calculations
and the experimental results, we are able to extract that the occupied Sn-Au
hybrid band is of (s, d)-orbital character while the unoccupied Sn-Au hybrid
bands are of (p, d)-orbital character. Hence, we can conclude that the
Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is
caused by the significant mixing of Au d- to Sn s-states in conjunction with
the strong atomic spin-orbit coupling of Au, i.e., of the substrate.Comment: Copyright:
https://journals.aps.org/authors/transfer-of-copyright-agreement; All
copyrights by AP
Global and local relaxation of a spin-chain under exact Schroedinger and master-equation dynamics
We solve the Schroedinger equation for an interacting spin-chain locally
coupled to a quantum environment with a specific degeneracy structure. The
reduced dynamics of the whole spin-chain as well as of single spins is
analyzed. We show, that the total spin-chain relaxes to a thermal equilibrium
state independently of the internal interaction strength. In contrast, the
asymptotic states of each individual spin are thermal for weak but non-thermal
for stronger spin-spin coupling. The transition between both scenarios is found
for couplings of the order of , with denoting
the Zeeman-splitting. We compare these results with a master equation
treatment; when time averaged, both approaches lead to the same asymptotic
state and finally with analytical results.Comment: RevTeX, 8 pages, 14 figures, added DOI and forgotten reference
Small-worlds: How and why
We investigate small-world networks from the point of view of their origin.
While the characteristics of small-world networks are now fairly well
understood, there is as yet no work on what drives the emergence of such a
network architecture. In situations such as neural or transportation networks,
where a physical distance between the nodes of the network exists, we study
whether the small-world topology arises as a consequence of a tradeoff between
maximal connectivity and minimal wiring. Using simulated annealing, we study
the properties of a randomly rewired network as the relative tradeoff between
wiring and connectivity is varied. When the network seeks to minimize wiring, a
regular graph results. At the other extreme, when connectivity is maximized, a
near random network is obtained. In the intermediate regime, a small-world
network is formed. However, unlike the model of Watts and Strogatz (Nature {\bf
393}, 440 (1998)), we find an alternate route to small-world behaviour through
the formation of hubs, small clusters where one vertex is connected to a large
number of neighbours.Comment: 20 pages, latex, 9 figure
- …