PbS sub-micrometer structures with anisotropic shape: ribbons, wires, octapods, and hollowed cubes.

The current paper discusses the preparation, characterization, and clarification of the growth mechanism of PbS wires, ribbons, octapods, and hollowed cubes. Those sub-micrometer structures were prepared by a thermal decomposition of a uni-precursor {[Pb(S(2)CNEt(2))(2)](2)}, using either ethylene diamine (en) or ethylene glycol (eg) as an intermediate reagent, as well as surfactants. The growth in eg produced mainly ribbons and square plates, while the growth in en solutions produced wires at the lower temperatures (80 degrees C) and octapods and hollowed cubes at elevated temperatures (117 degrees C). The experimental observations suggest that the obtained morphologies are primarily determined by the nucleation phase and the subsequent growth kinetics. The growth process developed according to the characteristic habit and subsequent branching processes. The characteristic habit was controlled by the surface energy of the facets and their modulation by the solvent molecules. The branching process was determined by a delicate balance between kinetic and thermodynamic processes, and it was controlled by the variation of the temperature and duration of the reactions.

Air-stable PbSe/PbS and PbSe/PbSexS1-x core-shell nanocrystal quantum dots and their applications.

The optical properties and functionality of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystal quantum dots (NQDs) are presented. These NQDs showed chemical robustness over months and years and band-gap tunability in the near infrared spectral regime, with a reliance on the NQD size and composition. Furthermore, these NQDs exhibit high emission quantum efficiencies of up to 65% and an exciton emission band that is narrower than that of the corresponding PbSe NQDs. In addition, the emission bands showed a peculiar energy shift with respect to the relevant absorption band, changing from a Stokes shift to an anti-Stokes shift, with an increase of the NQD diameter. The described core-shell structures and the corresponding PbSe core NQDs were used as passive Q-switches in eye-safe lasers of Er:glass, where they act as saturable absorbers. The absorber saturation investigations revealed a relatively large ground-state cross-section of absorption (sigma gs = 10(-16) - 10(-15) cm2) and a behavior of a "fast" absorber with an effective lifetime of tau eff approximately 4.0 ps is proposed. This lifetime is associated with the formation of multiple excitons at the measured pumping power. The product of sigma gs and tau eff enables sufficient Q-switching performance and tunability in the near infrared spectral regime. The amplified spontaneous emission properties of PbSe NQDs were examined under continuous illumination by a diode laser at room temperature, suitable for standard device conditions. The results revealed a relatively large gain parameter (g = 2.63 - 6.67 cm-1). The conductivity properties of PbSe NQD self-assembled solids, annealed at 200 degrees C, showed an Ohmic behavior at the measured voltages (up to 30 V), which is governed by a variable-range-hopping charge transport mechanism.

Optically detected magnetic resonance studies of colloidal semiconductor nanocrystals.

The review describes the studies of the magneto-optical properties of II-VI and III-V semiconductor nanocrystals (NCs) capped with organic or inorganic epitaxial shells. The investigations focused on the chemical identification of localization sites (core, shell, or interface) of photogenerated carriers in spherical NCs and elucidated the influence of the surface/interface quality on the optical properties of the materials. Optically detected magnetic resonance (ODMR) spectroscopy was used for the study of the proposed physical properties. The ODMR method provides the means to identify the surface/interface sites and correlate them with specific optical transition. In addition, this method reveals information about the spin multiplicity of band edge and trapped states and the electron-hole exchange interaction, determines the spectroscopic g-factors, distinguishes between the radiative and nonradiative characteristic of a trapping site, and evaluates the spin-lattice relaxation times.

Outpatient urine culture: does collection technique matter?

BACKGROUND: Dysuria is one of the most common presenting complaints of young women, and urinalysis is one of the most common laboratory tests performed. Despite the fact that the midstream clean-catch technique is commonly used for urine collection, contaminated urine cultures occur with distressing regularity. The midstream clean-catch technique is time-consuming to explain, frequently not performed correctly by patients, costly for supplies, often embarrassing for patients and staff, and of unproven benefit. Therefore, we designed a study to compare various methods of obtaining specimens for culture from acutely dysuric young women. METHODS: A total of 242 consecutive female patients who presented with symptoms suggestive of a urinary tract infection were randomized into 3 groups. The first group (n = 77) was instructed to urinate into a clean container. No cleansing was done, and the specimen was not obtained midstream. The second group (n = 84) was instructed to collect a midstream urine sample with perineal cleansing and spreading of the labia. In an attempt to decrease contamination from the vagina, the third group (n = 81) was given the same instructions as group 2, with the addition of using a vaginal tampon. Contamination rates were calculated for all 3 groups. RESULTS: Contamination rates for the 3 groups were nearly identical (29%, 32%, and 31%, respectively). Comparing the no-cleansing group with the combined cleansing, midstream groups also showed no difference in contamination rates (28.6% and 31.5%, respectively, with P =.65). CONCLUSIONS: In young, outpatient women with symptoms suggestive of a urinary tract infection, the midstream clean-catch technique does not decrease contamination rates.

Travel trouble: typhoid fever--A case presentation and review.

Endogenously contracted typhoid fever has decreased dramatically in the industrialized world. A practicing physician may not see a case in a lifetime, but health professionals should not allow typhoid to recede from their consciousness. Typhoid is still endemic in much of the developing world, and as travel increases, illnesses can and do skip around the world in a day. College students are at particular risk because they often travel on a low budget for extended periods, mix freely with local populations in endemic regions, and are not aware of the risks of such travel. College health professionals need to be able to recognize typhoid fever, should it present, and give advice to patients on primary prevention. The author includes a case presentation that is not completely classical for typhoid fever, as well as a state-of-the-art review, including description, epidemiology, signs and symptoms, diagnosis, treatment, and prevention. Special attention is given to the question of who should be immunized and which vaccines are effective.