Bandwidth considerations in modulated and transient photoconductivity measurements to determine localized state distributions

This work examines the influence of limited instrumental bandwidth on the accuracy of recovery of the density of localized states in semiconductors from transient and modulated photoconductivity data. Paradoxically, knowledge of the short-time transient photoresponse can be vital in the estimation, via a Fourier transform, of the density of deep-lying states. We demonstrate that retention of the natural response of a bandwidth limited system, although subject to distortion at short times, can lead to much improved accuracy in density of states determination than simple truncation of the short-time response. It is shown that this improvement arises simply from the integrating effect of a bandwidth limited system over short time intervals, which makes it possible to access and exploit information originating at times much shorter than the instrumentation rise time. These concepts are exemplified using computer simulated transient photoconductivity for several model systems including one which mimics the expected density of states in amorphous silicon

Effects of bandwidth limitations on the localized state distribution calculated from transient photoconductivity data

The possible effects of experimental bandwidth limitation on the accuracy of the energy distribution of the density of localized states (DOS) calculated from transient photoconductivity data by the Fourier transform method is examined. An argument concerning the size of missing contributions to the numerical Fourier integrals is developed. It is shown that the degree of distortion is not necessarily large even for relatively small experimental bandwidths. The density of states calculated from transient photodecay measurements in amorphous arsenic triselenide is validated by comparing with modulated photocurrent data. It is pointed out that DOS distributions calculated from transient photoconductivity data at a high photoexcitation density are valid under certain conditions. This argument is used to probe the conduction band tail in undoped a-Si:H to energies shallower than 0.1 eV below the mobility edge. It is concluded that there is a deviation in the DOS from exponential at about 0.15 eV below the mobility edge

El Diario de Pontevedra : periódico liberal: Ano XLII Número 12618 - 1927 febreiro 2

Tables S1–S8 and Figures S1–S8. (PDF 1274 kb

The Effect of Inadequate Initial Empiric Antimicrobial Treatment on Mortality in Critically Ill Patients with Bloodstream Infections: A Multi-Centre Retrospective Cohort Study

Hospital mortality rates are elevated in critically ill patients with bloodstream infections. Given that mortality may be even higher if appropriate treatment is delayed, we sought to determine the effect of inadequate initial empiric treatment on mortality in these patients. A retrospective cohort study was conducted across 13 intensive care units in Canada. We defined inadequate initial empiric treatment as not receiving at least one dose of an antimicrobial to which the causative pathogen(s) was susceptible within one day of initial blood culture. We evaluated the association between inadequate initial treatment and hospital mortality using a random effects multivariable logistic regression model. Among 1,190 patients (1,097 had bacteremia and 93 had candidemia), 476 (40%) died and 266 (22%) received inadequate initial treatment. Candidemic patients more often had inadequate initial empiric therapy (64.5% versus 18.8%), as well as longer delays to final culture results (4 vs 3 days) and appropriate therapy (2 vs 0 days). After adjustment, there was no detectable association between inadequate initial treatment and mortality among bacteremic patients (Odds Ratio (OR): 1.02, 95% Confidence Interval (CI) 0.70-1.48); however, candidemic patients receiving inadequate treatment had nearly three times the odds of death (OR: 2.89, 95% CI: 1.05-7.99). Inadequate initial empiric antimicrobial treatment was not associated with increased mortality in bacteremic patients, but was an important risk factor in the subgroup of candidemic patients. Further research is warranted to improve early diagnostic and risk prediction methods in candidemic patients