InP/InGaAsP double-heterostructure optoelectronic switch

The double-heterostructure optoelectronic switch (DOES), fabricated in the InP/InGaAsP material system, is demonstrated. The functional characteristics and operational parameters exhibit a lower switching voltage (≈1.8 V) and a higher on-state holding current (≈20 mA) than found in either the Si/SiGe- or GaAs/AlGaAs-based DOES of comparable structures and doping levels. In the on-state, optical emission is observed in a manner analogous to a light emitting diode. However, enhanced optical emission is observed when the device is biased in the regime of negative differential resistance     

Time to clinical stability in patients hospitalized with community-acquired pneumonia: implications for practice guidelines

CONTEXT: Many groups have developed guidelines to shorten hospital length of stay in pneumonia in order to decrease costs, but the length of time until a patient hospitalized with pneumonia becomes clinically stable has not been established. OBJECTIVE: To describe the time to resolution of abnormalities in vital signs, ability to eat, and mental status in patients with community-acquired pneumonia and assess clinical outcomes after achieving stability. DESIGN: Prospective, multicenter, observational cohort study. SETTING: Three university and 1 community teaching hospital in Boston, Mass, Pittsburgh, Pa, and Halifax, Nova Scotia. PATIENTS: Six hundred eighty-six adults hospitalized with community-acquired pneumonia. MAIN OUTCOME MEASURES: Time to resolution of vital signs, ability to eat, mental status, hospital length of stay, and admission to an intensive care, coronary care, or telemetry unit. RESULTS: The median time to stability was 2 days for heart rate (< or =100 beats/min) and systolic blood pressure (> or =90 mm Hg), and 3 days for respiratory rate (< or =24 breaths/min), oxygen saturation (> or =90%), and temperature (< or =37.2 degrees C [99 degrees F]). The median time to overall clinical stability was 3 days for the most lenient definition of stability and 7 days for the most conservative definition. Patients with more severe cases of pneumonia at presentation took longer to reach stability. Once stability was achieved, clinical deterioration requiring intensive care, coronary care, or telemetry monitoring occurred in 1% of cases or fewer. Between 65% to 86% of patients stayed in the hospital more than 1 day after reaching stability, and fewer than 29% to 46% were converted to oral antibiotics within 1 day of stability, depending on the definition of stability. CONCLUSIONS: Our estimates of time to stability in pneumonia and explicit criteria for defining stability can provide an evidence-based estimate of optimal length of stay, and outline a clinically sensible approach to improving the efficiency of inpatient management.     

Extreme field-induced cyclotron mass variations in coupled double quantum wells

We observe deviations in the cyclotron effective mass m_c near the partial energy gap formed in strongly coupled GaAs double quantum wells (QWs) subject to in-plane magnetic fields B. In k-space, B shifts the two QW dispersion curves relative to one another, resulting in an anticrossing and opening the energy gap. This gives rise to large B-tunable distortions in the Fermi surface and density of states. This system is thus unique in that the Fermi surface and energy position of the gap can be controlled by sweeping B. Recently, Lyo has predicted that m_c undergoes large variations as the partial energy gap is moved through the Fermi level by B. By tilting our sample by a small angle θ, we introduce a small perpendicular magnetic field B, in addition to B, and analyze the temperature dependence of the resulting Shubnikov-de Haas oscillations to obtain m_c(B). Due to the strongly distorted dispersion near the gap, m_c is suppressed by more than a factor of 3 near the upper gap edge, and enhanced by 50% near the lower gap edge, in excellent agreement with the theory of Lyo. We also observe the quantum Hall effect in a double QW at a high, constant B.     

The functional anatomy of imagining and perceiving colour

OBJECTIVE: To determine whether the progression of urinary albumin excretion rate (AER) is higher during puberty than before or after this period. RESEARCH DESIGN AND METHODS: A prospective study was conducted in which normoalbuminuric prepubertal (n = 20), pubertal (n = 28), and postpubertal (n = 26) IDDM groups matched for diabetes duration and long-term metabolic control were followed for 3 years. At 6-month intervals, 24-h urine collection was used to determine AER. RESULTS: AER increased significantly over a period of 3 years in the pubertal (P = 0.001) and postpubertal (P = 0.003) subjects but not in prepubertal subjects. The annual progression of AER was significantly higher in the pubertal group than in the prepubertal (P = 0.001) or postpubertal (P = 0.001) groups. Six pubertal, two postpubertal, and none of the prepubertal subjects developed microalbuminuria (AER > or = 20 micrograms/min on two consecutive occasions) over a 3-year period (P = 0.047). Multiple logistic regression analysis showed that the risk of development of microalbuminuria was increased in pubertal subjects compared with the prepubertal and postpubertal subjects (adjusted relative risk [95% CI]: 4.3 [1.5-9.3], P = 0.012, and 2.1 [1.1-5.0], P = 0.023, respectively). CONCLUSIONS: Puberty represents an independent risk of the development of microalbuminuria in diabetes. This findings suggests that the endocrine changes of puberty lead to an accelerated process of early kidney damage in diabetes. In pediatric diabetes care, screening for microalbuminuria is needed soon after the onset of puberty.     

Comparison of factor VIII-related antigen and erythrocyte sedimentation rate in outpatient management of vasculitis

Electroimmunodiffusion (Laurell rocket) determinations of factor VIII-related antigen in plasma were ordered to determine the cost/benefit ratio for factor VIII-related antigen as a putative test for endothelial damage in suspected vasculitis. Twenty-seven consecutive patients referred for vasculitis or suspected vasculitis were identified and followed up for an average of 9.1 +/- months (range: one to thirty-three months) in a prospective, unblinded study performed in a clinic, associated with a 1054-bed inner-city university hospital. There was no difference in Westergren erythrocyte sedimentation rate (WESR) in patients with final diagnosis of systemic vasculitis (SV) (38 +/- 12 mm/hour) compared to those without vasculitis (NV) (27 +/- 7) as the final diagnosis. The mean plasma concentration of factor VIII-related antigen was significantly elevated in SV (344 +/- 100%) when compared with NV (147 +/- 39%) (P < 0.016). The factor VIII-related antigen test in this study was 2.56 times more likely (crude odds ratio) than the WESR to contribute to a change in diagnosis or therapy (P = 0.016). Positive and negative predictive values (PPV and NPV) for factor VIII-related antigen (abnormal at greater than 220% of the normal value) were both 70%. PPV and NPV for WESR were 56% and 86%, respectively. The factor VIII-related test was less cost-effective than the WESR in the follow-up period unless it was important to define complete remission or differentiate vasculitis flare from infection. The authors conclude that factor VIII-related antigen is a useful test in the initial diagnosis of vasculitis.     

NT-3, but not BDNF, prevents atrophy and death of axotomized spinal cord projection neurons

Following spinal cord injury, projection neurons are frequently axotomized and many of the cells subsequently die. One goal in spinal injury research is to preserve damaged neurons so that ultimately they are accessible to regeneration-promoting strategies. Here we ask if neurotrophin treatment can prevent atrophy and death of axotomized sensory projection neurons. In adult rats, a hemisection was made in the thoracic spinal cord and axotomized neurons were retrogradely labelled with Fluoro-Gold. Four distinct populations of cells were identified in the lumbar spinal cord, and both numbers and sizes of labelled cells were assessed at different time points postlesion. A progressive and significant degeneration was observed over time with severe atrophy apparent in all cell populations and significant cell loss evident by 4 weeks postlesion. This time point was used to assess neurotrophin effects. Hemisected rats were treated with either neurotrophin 3 (NT-3) or brain-derived neurotrophic factor (BDNF, 12 microg/day for each), or a vehicle solution, delivered continuously to the lesion site via an osmotic minipump. Treatment with NT-3, but not BDNF, completely reversed cell atrophy in three of the four cell populations and also induced a significant increase in the number of surviving cells. In situ hybridization experiments showed trkB and trkC mRNA to be expressed in the majority of ascending spinal projection neurons, suggesting that these cells should be responsive to both BDNF and NT-3. However, only NT-3 treatment was neuroprotective, indicating that BDNF may not have reached the cell bodies of injured neurons. These results demonstrate that NT-3 may be of benefit in preventing the secondary cell loss that occurs following spinal injury.     

Assessing the effect of HIV vaccination on infectiousness

Traditionally, measures of vaccine efficacy have focused on a vaccine's ability to prevent infection or disease. HIV vaccination, however, may have important indirect effects by reducing the level of infectiousness of vaccinees who become infected. This latter effect is not captured by the usual estimators of vaccine efficacy. To obtain an estimate of a vaccine's effect on infectiousness, Koopman and Little have proposed a trial design in which HIV-uninfected couples are randomized to the vaccine or control arm of the study. At least one member is assumed to be at risk of HIV infection from outside the partnership. Using this design, we formulate martingales from counting processes which record the number of infected participants over the course of the trial. An alternative estimator of a vaccine's effect on infectiousness along with an estimate of its variance is derived from these martingales. The precision of the estimate is shown to depend on the secondary attack rate within the couple. High secondary attack rates are required for narrow confidence intervals unless very large studies are contemplated.