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The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ∼218 to ∼913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25-300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ∼913 nm to ∼218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.

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We describe recent upgrades to a 3D tracking microscope to include simultaneous Nipkow spinning disk imaging and time-gated single-particle tracking (SPT). Simultaneous 3D molecular tracking and spinning disk imaging enable the visualization of cellular structures and proteins around a given fluorescently labeled target molecule. The addition of photon time-gating to the SPT hardware improves signal to noise by discriminating against Raman scattering and short-lived fluorescence. In contrast to camera-based SPT, single-photon arrival times are recorded, enabling time-resolved spectroscopy (e.g., measurement of fluorescence lifetimes and photon correlations) to be performed during single molecule/particle tracking experiments.

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Biexciton photoluminescence (PL) quantum yields (Q(2X)) of individual CdSe/CdS core-shell nanocrystal quantum dots with various shell thicknesses are derived from independent PL saturation and two-photon correlation measurements. We observe a near-unity Q(2X) for some nanocrystals with an ultrathick 19-monolayer shell. High Q(2X)'s are, however, not universal and vary widely among nominally identical nanocrystals indicating a significant dependence of Q(2X) upon subtle structural differences. Interestingly, our measurements indicate that high Q(2X)'s are not required to achieve complete suppression of PL intensity fluctuations in individual nanocrystals.

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A strong electron-hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active ('bright') and optically passive ('dark') excitons. This dark-bright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We show that the dark-bright splitting can be widely tuned by controlling the electron-hole spatial overlap in core-shell CdSe/CdS NCs with a variable shell width. In thick-shell samples, the EI energy reduces to <250 µeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron-hole overlap.

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The development of nanocrystal quantum dots (NQDs) with suppressed nonradiative Auger recombination has been an important goal in colloidal nanostructure research motivated by the needs of prospective applications in lasing devices, light-emitting diodes, and photovoltaic cells. Here, we conduct single-nanocrystal spectroscopic studies of recently developed core-shell NQDs (so-called "giant" NQDs) that comprise a small CdSe core surrounded by a 16-monolayer-thick CdS shell. Using both continuous-wave and pulsed excitation, we observe strong emission features due both to neutral and charged biexcitons, as well as multiexcitons of higher order. The development of pronounced multiexcitonic peaks in steady-state photoluminescence of individual nanocrystals, as well as continuous growth of the emission intensity in the range of high pump levels, point toward a significant suppression of nonradiative Auger decay that normally renders multiexcitons nonemissive. The unusually high multiexciton emission efficiencies in these systems open interesting opportunities for studies of multiexciton phenomena using well-established methods of single-dot spectroscopy, as well as new exciting prospects for applications, that have previously been hampered by nonradiative Auger decay.

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We study the effect of the zero- to one-dimensional (1D) transformation on multiparticle Auger recombination using a series of elongated semiconductor nanocrystals (quantum rods). We observe a transition from the three- to two-particle recombination process as the nanocrystal aspect ratio is increased. This transition indicates that in the 1D confinement limit, Auger decay is dominated by Coulomb interactions between 1D excitons that recombine in a bimolecular fashion. One consequence of this effect is strongly reduced decay rates of higher multiparticle states that lead to increased optical-gain lifetimes and efficient light amplification due to involvement of excited electronic states.

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We report on the dynamics of resonant energy transfer in monodisperse, mixed-size, and energy-gradient (layered) assemblies of CdSe nanocrystal quantum dots. Time-resolved and spectrally resolved photoluminescence directly reveals the energy-dependent transfer rate of excitons from smaller to larger dots via electrostatic coupling. The data show a rapid (0.7-1.9 ns) energy transfer directly across a large tens-of-meV energy gap (i.e., between dots of disparate size), and suggest that interdot energy transfer can approach picosecond time scales in structurally optimized systems.

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The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. We examined the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids of these dots. Narrowband stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was observed, as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers.

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BACKGROUND: Heparin administration by physicians can vary greatly, and this variance can result in ineffective anticoagulation and reduced effectiveness of treatment. OBJECTIVE: To examine the use of a heparin nomogram in two community hospitals to validate its effect on anticoagulation parameters and to determine its influence on length of hospital stay. METHODS: Prenomogram and postnomogram intervention in two community hospitals in Sudbury, Ontario. All patients who presented and were admitted to the hospitals between 1991 and 1994 with a confirmed primary diagnosis of deep vein thrombosis and/or pulmonary embolism were eligible for the study. A heparin nomogram was instituted in April 1993 for treatment of deep vein thrombophlebitis and pulmonary embolism in hospitalized patients. The study patients were designated as prenomogram or postnomogram. Anticoagulation parameters (time to therapeutic activated partial thromboplastin time), number of diagnostic tests, percentage of times within the therapeutic range, and length of hospital stay were recorded for both groups. RESULTS: A total of 326 patients were identified from the database; 163 (50%) met the inclusion criteria. Patients in both groups appeared to be similar. Adequate anticoagulation was achieved faster (17.9 hours postnomogram vs 48.8 hours prenomogram; P < .001) and remained subtherapeutic less frequently in the postnomogram group (number of activated partial thromboplastin time tests below the therapeutic window; 56% prenomogram vs 28% postnomogram; P < .001). There were no differences between the groups with respect to length of stay (11.3 days prenomogram vs 10.9 days postnomogram; P = .60). More activated partial thromboplastin time tests were ordered in the postnomogram group (15.6 postnomogram vs 12.7 prenomogram; P = .001); however, fewer prothrombin time tests were ordered in the postnomogram group. CONCLUSIONS: A heparin nomogram was successfully used in a community hospital without a structured hematology-thrombosis service. Therapeutic anticoagulation was achieved faster and maintained more frequently, with less logistical problems, with this protocol. However, additional measures may be required to reduce the length of hospital stay.

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Twenty patients with severe infection, 10 of the urinary tract and the other 10 of the respiratory tract, were enrolled in a clinical trial of aztreonam, a new monobactam antimicrobial agent. For the urinary tract infections, the mean duration of treatment was 7 days, with doses ranging from 0.25 to 1.0 g aztreonam intravenously twice daily. Sustained clinical and microbiological cure was achieved in 9 of the 10 patients. In the group with respiratory infections, the mean duration of treatment was 9.3 days, patients receiving 1 g aztreonam intravenously 3-times daily. Initial clinical cure was achieved in 9 of the patients, the tenth showing an incomplete response. However, bacteriological recurrence, related to the persistent nature of the underlying disease, occurred in 6 of the 10 patients during the 1-month follow-up period. The only side-effects were mild, transient biochemical abnormalities which did not require drug withdrawal in any patient.

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