2,042 research outputs found
Erythromycin for prokinesis: imprudent prescribing?
Problems with antibiotic resistant bacteria are increasing in the hospital and particularly in the intensive care unit. Methicillin-resistant Staphylococcus aureus, Acinetobacter baumanii and extended spectrum beta-lactamase producing Gram-negative bacilli constitute a therapeutic and infection control challenge. Early enteral feeding improves survival in patients in the intensive care unit. Prokinetic agents are routinely used in patients with inappropriate gastrointestinal motility. The use of erythromycin at sub-therapeutic doses as a prokinetic agent is a cause of concern for the following reasons: it can increase the emergence and spread of antibiotic resistance and the likelihood of Clostridium difficile disease. The use of an antibiotic as a prokinetic agent does not constitute prudent antimicrobial prescribing and should be avoided. Alternative agents, whenever possible, should be used
Measures of Model Performance Based On the Log Accuracy Ratio
Quantitative assessment of modeling and forecasting of continuous quantities uses a variety of approaches. We review existing literature describing metrics for forecast accuracy and bias, concentrating on those based on relative errors and percentage errors. Of these accuracy metrics, the mean absolute percentage error (MAPE) is one of the most common across many fields and has been widely applied in recent space science literature and we highlight the benefits and drawbacks of MAPE and proposed alternatives. We then introduce the log accuracy ratio and derive from it two metrics: the median symmetric accuracy and the symmetric signed percentage bias. Robust methods for estimating the spread of a multiplicative linear model using the log accuracy ratio are also presented. The developed metrics are shown to be easy to interpret, robust, and to mitigate the key drawbacks of their more widely used counterparts based on relative errors and percentage errors. Their use is illustrated with radiation belt electron flux modeling examples.Peer reviewe
Testing linear hypotheses in high-dimensional regressions
For a multivariate linear model, Wilk's likelihood ratio test (LRT)
constitutes one of the cornerstone tools. However, the computation of its
quantiles under the null or the alternative requires complex analytic
approximations and more importantly, these distributional approximations are
feasible only for moderate dimension of the dependent variable, say .
On the other hand, assuming that the data dimension as well as the number
of regression variables are fixed while the sample size grows, several
asymptotic approximations are proposed in the literature for Wilk's \bLa
including the widely used chi-square approximation. In this paper, we consider
necessary modifications to Wilk's test in a high-dimensional context,
specifically assuming a high data dimension and a large sample size .
Based on recent random matrix theory, the correction we propose to Wilk's test
is asymptotically Gaussian under the null and simulations demonstrate that the
corrected LRT has very satisfactory size and power, surely in the large and
large context, but also for moderately large data dimensions like or
. As a byproduct, we give a reason explaining why the standard chi-square
approximation fails for high-dimensional data. We also introduce a new
procedure for the classical multiple sample significance test in MANOVA which
is valid for high-dimensional data.Comment: Accepted 02/2012 for publication in "Statistics". 20 pages, 2 pages
and 2 table
Pressure of thermal excitations in superfluid helium
We find the pressure, due to the thermal excitations of superfluid helium, at
the interface with a solid. The separate contributions of phonons, rotons
and rotons are derived. The pressure due to rotons is shown to be
negative and partially compensates the positive contribution of rotons,
so the total roton pressure is positive but several times less than the
separate and roton contributions. The pressure of the quasiparticle
gas is shown to account for the fountain effect in . An experiment is
proposed to observe the negative pressure due to rotons.Comment: 14 pages, 4 figure
Helium mixtures in nanotube bundles
An analogue to Raoult's law is determined for the case of a 3He-4He mixture
adsorbed in the interstitial channels of a bundle of carbon nanotubes. Unlike
the case of He mixtures in other environments, the ratio of the partial
pressures of the coexisting vapor is found to be a simple function of the ratio
of concentrations within the nanotube bundle.Comment: 3 pages, no figures, submitted to Phys. Rev. Let
Correlation effects in Ni 3d states of LaNiPO
The electronic structure of the new superconducting material LaNiPO
experimentally probed by soft X-ray spectroscopy and theoretically calculated
by the combination of local density approximation with Dynamical Mean-Field
Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray
emission (XES) and absorption (XAS) spectra which probe the occupied and
unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are
strongly renormalized by dynamical correlations and shifted about 1.5 eV lower
in the valence band than the corresponding Fe 3d states in LaFeAsO. We further
obtain a lower Hubbard band at -9 eV below the Fermi level in LaNiPO which
bears striking resemblance to the lower Hubbard band in the correlated oxide
NiO, while no such band is observed in LaFeAsO. These results are also
supported by the intensity ratio between the transition metal L2 and L3 bands
measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the
presence of the stronger electron correlations in the Ni 3d states in LaNiPO in
comparison with the Fe 3d states in LaFeAsO. These findings are in accordance
with resonantly excited transition metal L3 X-ray emission spectra which probe
occupied metal 3d-states and show the appearance of the lower Hubbard band in
LaNiPO and NiO and its absence in LaFeAsO.Comment: 6 pages, 5 figure
Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure
The following article appeared in Journal of Applied Physics 111.3 (2012): 034903 and may be found at http://scitation.aip.org/content/aip/journal/jap/111/3/10.1063/1.3679604Na has deliberately been incorporated into Cu(In,Ga)Se2 (CIGSe) chalcopyrite thin-film solar cell absorbers deposited on Mo-coated polyimide flexible substrates by adding differently thick layers of NaF in-between CIGSe absorber and Mo back contact. The impact of Na on the chemical and electronic surface structure of CIGSe absorbers with various Cu-contents deposited at comparatively low temperature (420 C) has been studied using x-ray photoelectron and x-ray excited Auger electron spectroscopy. We observe a higher Na surface content for the Cu-richer CIGSe samples and can distinguish between two different chemical Na environments, best described as selenide-like and oxidized Na species, respectively. Furthermore, we find a Cu-poor surface composition of the CIGSe samples independent of Na content and - for very high Na contents - indications for the formation of a (Cu,Na)-(In,Ga)-Se like compound. With increasing Na surface content, also a shift of the photoemission lines to lower binding energies could be identified, which we interpret as a reduction of the downward band bending toward the CIGSe surface explained by the Na-induced elimination of In Cu defects.X.S., R.F., D.G., R.G.W., and M.B. are grateful to the Helmholtz-Association for financial support (VH-NG-423). R.F. also acknowledges the support by the German Academic Exchange Agency (DAAD; 331 4 04 002)
Scattering of second sound waves by quantum vorticity
A new method of detection and measurement of quantum vorticity by scattering
second sound off quantized vortices in superfluid Helium is suggested.
Theoretical calculations of the relative amplitude of the scattered second
sound waves from a single quantum vortex, a vortex ring, and bulk vorticity are
presented. The relevant estimates show that an experimental verification of the
method is feasible. Moreover, it can even be used for the detection of a single
quantum vortex.Comment: Latex file, 9 page
- …