We report on the synthesis of the newly discovered cubic phase of tin sulfide π-SnS and compare its properties to the well-known phase of tin sulfide, α-SnS. Shape control was achieved by the ...variation of synthesis parameters, resulting in cubic, rhombic dodecahedral and tetrahedral shapes of the π-SnS nanoparticles. X-ray diffraction provided authentication of the proposed model and refined determination of the lattice parameter
a
= 11.595 Å. Raman spectroscopy showed a substantial shift towards higher energies and peak splitting for π-SnS. Optical absorption spectroscopy indicated an indirect band gap of 1.53 eV, in good agreement with density functional theory (DFT) calculations indicating a band gap greater than that of α-SnS. DFT total energy calculations show that the π-SnS phase is energetically similar to α-SnS, and is significantly more stable than the hypothetical ideal rocksalt structure of SnS.
One of the important factors limiting solar-cell efficiency is that incident photons generate one electron-hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The ...possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells. Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions. Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carrier-multiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.
Background. Patients colonized with vancomycin-resistant enterococci (VRE) frequently contaminate their environment, but the environmental role of VRE transmission remains controversial. Methods. ...During a 14-month study in 2 intensive care units, weekly environmental and twice-weekly patient surveillance cultures were obtained. VRE acquisition was defined as a positive culture result >48 h after admission. To determine risk factors for VRE acquisition, Cox proportional hazards models using time-dependent covariates for colonization pressure and antibiotic exposure were examined. Results. Of 1330 intensive care unit admissions, 638 patients were at risk for acquisition, and 50 patients (8%) acquired VRE. Factors associated with VRE acquisition included average colonization pressure (hazard ratio HR, 1.4 per 10% increase; 95% confidence interval CI, 1.2–1.8), mean number of antibiotics (HR, 1.7 per additional antibiotic; 95% CI, 1.2–2.5), leukemia (HR, 3.1; 95% CI, 1.2–7.8), a VRE-colonized prior room occupant (HR, 3.1; 95% CI, 1.6–5.8), any VRE-colonized room occupants within the previous 2 weeks (HR, 2.5; 95% CI, 1.3–4.8), and previous positive room culture results (HR, 3.4; 95% CI, 1.2–9.6). In separate multivariable analyses, a VRE-colonized prior room occupant (HR, 3.8; 95% CI, 2.0–7.4), any VRE-colonized room occupants within the previous 2 weeks (HR, 2.7; 95% CI, 1.4–5.3), and previous positive room culture results (HR, 4.4; 95% CI, 1.5–12.8) remained independent predictors of VRE acquisition, adjusted for colonization pressure and antibiotic exposure. Conclusions. We found that prior room contamination, whether measured via environmental cultures or prior room occupancy by VRE-colonized patients, was highly predictive of VRE acquisition. Increased attention to environmental disinfection is warranted.
Large‐scale 3D assembly of 1D ZnSe nanorods into microstrings (see figure) by simple application of a dc electric field is reported. The ordered rods exhibit polarization perpendicular to their long ...axis in fluorescence emission, contrary to the randomly ordered rods. The switchable assembly into long‐range microstructures with unique polarization behavior holds great promise for novel applications.
Sol-gel transition of carboxylated cellulose nanocrystals has been investigated using rheology, SAXS, NMR and optical spectroscopies to unveil the distinctive roles of ultrasound treatments and ...addition of various cations. Besides cellulose fiber fragmentation, sonication treatment induces fast gelling of the solution. The gelation is independent of the addition of cations, while the final rheological properties are highly influenced by the type, concentration and sequence of the operations since the cations must be added prior to sonication to produce stiff gels. The gel elastic modulus was found to increase proportionally to the ionic charge rather than the cationic size. In cases where ions were added after sonication, SAXS analysis of the Na
hydrogel and Ca
hydrogel indicated the presence of structurally ordered domains in which water is confined, and 1H-NMR investigation showed the dynamics of water exchange within the hydrogels. Conversely, separated phases containing essentially free water were characteristic of the hydrogels obtained by sonication after Ca
addition, confirming that this ion induces irreversible fiber aggregation. The rheological properties of the hydrogels depend on the duration of the ultrasound treatments, enabling the design of programmed materials with tailored energy dissipation response.
To describe a newly observed frontal sinus anatomical variant, the fronto-septal rostrum.
Consecutive sinus computed tomography scans performed during 2013 were reviewed. The fronto-septal rostrum ...was defined as a mucosa-lined air space formed in the attachment of the most upper bony nasal septum and the central floor of the frontal sinuses.
The study included 400 computed tomography scans from 189 women (47.3 per cent) and 211 men (52.8 per cent), with a mean age of 46.8 years. A fronto-septal rostrum was observed in 122 patients (30.5 per cent), with a mean length of 10.63 mm, width of 4.52 mm, height of 2.18 mm and volume of 63.52 mm3. There was no statistically significant difference related to gender (p = 0.343), and no association between the side of the fronto-septal rostrum and age (p = 0.811) or volume (p = 0.203).
The newly described fronto-septal rostrum has possible clinical and surgical implications. It is suggested that this aerated space is used in specific surgical indications and its presence evaluated in cases of septal infection.
The assembly of ultrathin ZnSe nanowires over large areas (see Figure) is achieved by a Langmuir–Blodgett technique in a single step with uniform registry, and without any further secondary technique ...for alignment. Ultrahigh packing density of junctions, exceeding over 60 × 103 μm–2, is achieved by subsequent deposition of a second two‐dimensional nanowire assembly with a controlled angle between the two layers. The resulting network notably surpasses the limit of conventional fabrication techniques.
We report an 119Sn nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of cubic π-phase SnS semiconductor nanoparticles. The data are compared with orthorhombic α-SnS. ...The NMR spectrum of cubic SnS reveals two inequivalent tin atoms in its crystal structure. The spin-lattice relaxation time of 119Sn nuclei in the cubic phase is much longer than that in the orthorhombic phase, indicating that the former is mainly governed by Raman scattering, while the latter is dominated by interaction of nuclear spins with unpaired electron spins of paramagnetic defects. This is supported by EPR measurements showing much larger content of paramagnetic defects in the orthorhombic phase compared with the cubic phase. The study provides novel research findings on the physical properties of the newly discovered cubic π-SnS, which is an emerging semiconducting material system for various applications.
•119Sn NMR and EPR study of cubic π-phase SnS semiconductor nanoparticles.•Data on cubic phase are compared with those of orthorhombic α-SnS.•NMR spectrum of cubic SnS reveals two inequivalent tin atoms in crystal structure.•Spin-lattice relaxation in cubic phase is longer than that in orthorhombic phase.•Smaller density of paramagnetic defects in cubic phase than in orthorhombic phase.
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