Formation of PbSe Nanocrystals: A Growth toward Nanocubes

In this paper we report an electron microscopic observation of crystal shape development when PbSe nanocrystals were synthesized using a dynamic injection technique at different temperatures in the presence of oleic acid. A two-step evolution mechanism was proposed, indicating that the shape evolution of PbSe nanocrystals is dependent on the growth time, whereas the crystalline size can be tuned by varying the growth temperature under the studied conditions. It also implies that a higher growth rate in the 〈111 〉 direction compared to that in the 〈100 〉 direction results in the formation of nanocubes. Lead chalcogenides are inspiring semiconductors with a narrow band gap. Size- and shape-controlled nanocrystals (NCs) of this family have demonstrated unique properties1-5 and can potentially be employed in numerous applications, such as near-IR luminescence6 and thermoelectric devices.7,8 To produce monodisperse NCs of lead chalcogenides with high quality and tunable size and shape, it is significant to understand their NC formation process. Since the growth of PbS9,10 and PbTe NCs11 has been investigated previously, similar exploration on PbS

Comparison of radiation dose calculation differences between uRT-TPS and Monaco-TPS for the same linear accelerator in multiple cancers

Background and Purpose: In recent years, domestic radiotherapy equipment and related software have made great progress, and testing the functionality and stability of the equipment and software is an essential step. This paper focused on comparing the differences in intensity-modulated radiation therapy (IMRT) plans dosimetry and organ at risk (OAR) volume calculations for common cancers between uRT-treatment planning system (TPS) and Monaco-TPS, and to evaluate the feasibility of dose calculation for Infinity linac (linear accelerator, Elekta, Sweden) using uRT-TPS. Methods: Twenty cases of rectal cancer, lung cancer, breast cancer and nasopharyngeal carcinoma were selected. The IMRT plans were completed in uRT-TPS and Monaco-TPS. The dose uniformity and conformity, mean dose, maximum dose of planning target volume (PTV) and OAR between two plans under the same prescribed dose of PTV were compared. And the pass rates of two TPS plans validated at the same linear accelerator were compared. Meanwhile, monitor units (MU), source skin distance (SSD) and the volume of OAR in uRT-TPS and Monaco-TPS were compared. Results: Wonderful plans that met the clinical requirements were obtained in uRT-TPS and Monaco-TPS. Comparable uniformity and conformability was received in PTV, and the maximum dose of PTV was reduced by 1.1 Gy for uRT-TPS (P = 0.006). For breast cancer and lung cancer, the dose in lung was lower for Monaco-TPS (P<0.05). For nasopharyngeal carcinoma, the dose indicators that oral cavity and throat in the uRT-TPS was reduced by 9.2% and 5.1%, respectively. The verification results of absolute point dose (<3%) and three-dimensional surface dose (>95%) for both plans met the clinical requirements. The region of interest in uRT-TPS was smaller compared with Monaco-TPS (P<0.05). Conclusion: A comparable IMRT plan was obtained for common tumors in uRT-TPS and Monaco-TPS. It is feasible to calculate the dose of Infinity linac using uRT-TPS

Remarkable nucleation and growth of ultrafine particles from vehicular exhaust

High levels of ultrafine particles (UFPs; diameter of less than 50 nm) are frequently produced from new particle formation under urban conditions, with profound implications on human health, weather, and climate. However, the fundamental mechanisms of new particle formation remain elusive, and few experimental studies have realistically replicated the relevant atmospheric conditions. Previous experimental studies simulated oxidation of one compound or a mixture of a few compounds, and extrapolation of the laboratory results to chemically complex air was uncertain. Here, we show striking formation of UFPs in urban air from combining ambient and chamber measurements. By capturing the ambient conditions (i.e., temperature, relative humidity, sunlight, and the types and abundances of chemical species), we elucidate the roles of existing particles, photochemistry, and synergy of multipollutants in new particle formation. Aerosol nucleation in urban air is limited by existing particles but negligibly by nitrogen oxides. Photooxidation of vehicular exhaust yields abundant precursors, and organics, rather than sulfuric acid or base species, dominate formation of UFPs under urban conditions. Recognition of this source of UFPs is essential to assessing their impacts and developing mitigation policies. Our results imply that reduction of primary particles or removal of existing particles without simultaneously limiting organics from automobile emissions is ineffective and can even exacerbate this problem

Remarkable nucleation and growth of ultrafine particles from vehicular exhaust

High levels of ultrafine particles (UFPs; diameter of less than 50 nm) are frequently produced from new particle formation under urban conditions, with profound implications on human health, weather, and climate. However, the fundamental mechanisms of new particle formation remain elusive, and few experimental studies have realistically replicated the relevant atmospheric conditions. Previous experimental studies simulated oxidation of one compound or a mixture of a few compounds, and extrapolation of the laboratory results to chemically complex air was uncertain. Here, we show striking formation of UFPs in urban air from combining ambient and chamber measurements. By capturing the ambient conditions (i.e., temperature, relative humidity, sunlight, and the types and abundances of chemical species), we elucidate the roles of existing particles, photochemistry, and synergy of multipollutants in new particle formation. Aerosol nucleation in urban air is limited by existing particles but negligibly by nitrogen oxides. Photooxidation of vehicular exhaust yields abundant precursors, and organics, rather than sulfuric acid or base species, dominate formation of UFPs under urban conditions. Recognition of this source of UFPs is essential to assessing their impacts and developing mitigation policies. Our results imply that reduction of primary particles or removal of existing particles without simultaneously limiting organics from automobile emissions is ineffective and can even exacerbate this problem

Insights into vertical differences of particle number size distributions in winter in Beijing, China

Particle number size distribution (PNSD) is of importance for understanding the mechanisms of particle growth, haze formation and climate impacts. However, the measurements of PNSD aloft in megacities are very limited. Here we report the first simultaneous winter measurements of size-resolved particle number concentrations along with collocated gaseous species and aerosol composition at ground level and 260 m in Beijing. Our study showed that the vertical differences of particle number concentrations between ground level and aloft varied significantly as a function of particle size throughout the study. Further analysis illustrated the impacts of boundary dynamics and meteorological conditions on the vertical differences of PNSD. In particular, the temperature and relative humidity inversions were one of the most important factors by decoupling the boundary layer into different sources and processes. Positive matrix factorization analysis identified six sources of PNSD at both ground level and city aloft. The local source emissions dominantly contributed to Aitken-mode particles, and showed the largest vertical gradients in the city. Comparatively, the regional particles were highly correlated between ground level and city aloft, and the vertical differences were relatively stable throughout the day. Our results point to-wards a complex vertical evolution of PNSD due to the changes in boundary layer dynamics, meteorological con-ditions, sources, and processes in megacities. (c) 2021 Elsevier B.V. All rights reserved.Peer reviewe

Multiple organ infection and the pathogenesis of SARS

After >8,000 infections and >700 deaths worldwide, the pathogenesis of the new infectious disease, severe acute respiratory syndrome (SARS), remains poorly understood. We investigated 18 autopsies of patients who had suspected SARS; 8 cases were confirmed as SARS. We evaluated white blood cells from 22 confirmed SARS patients at various stages of the disease. T lymphocyte counts in 65 confirmed and 35 misdiagnosed SARS cases also were analyzed retrospectively. SARS viral particles and genomic sequence were detected in a large number of circulating lymphocytes, monocytes, and lymphoid tissues, as well as in the epithelial cells of the respiratory tract, the mucosa of the intestine, the epithelium of the renal distal tubules, the neurons of the brain, and macrophages in different organs. SARS virus seemed to be capable of infecting multiple cell types in several organs; immune cells and pulmonary epithelium were identified as the main sites of injury. A comprehensive theory of pathogenesis is proposed for SARS with immune and lung damage as key features

Persistent sulfate formation from London Fog to Chinese haze

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO2 by NO2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH3 neutralization or under cloud conditions. Under polluted environments, this SO2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH3 and NO2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world

Hyperporous Carbons from Hypercrosslinked Polymers.

Porous carbons with extremely high surface areas are produced through the carbonization of hypercrosslinked benzene, pyrrole, and thiophene. Such carbons show largely microporous and mesoporous domains and exhibit Brunaeur-Emmett-Teller surface areas up to 4300 m(2) g(-1) . The best performing material also displays exceptionally high CO2 and H2 uptakes

Characterization of synthesized titanium oxide nanoclusters by MALDI-TOF mass spectrometry

Titania represents an important material that has wide applications. The bactericidal efficiency of TiO 2 has been shown to be dependent on the size of the nanoparticles, so it is important to be able to reliably estimate their dimensions. In this study, a stable TiO 2 cluster suspension is produced by the thermal solvent process, and ultrasmall clusters (Ͻ1 nm) with different sizes are obtained by size-selection treatment. MALDI-TOF-MS and LDI-TOF-MS are shown to be useful for characterization of these ultrasmall nanoparticles. Peak maxima are found to correlate with nanoparticle size, and the possibility of using these mass spectrometry-based approaches to estimate nanoparticle size is affirmed. The size distributions of TiO 2 nanoparticles obtained from MALDI-and LDI-TOF-MS are in good agreement with parallel TEM observations. Finally, PSD analysis of inorganic nanomaterials is performed and valuable information about the structure of analytes has been obtained. (J Am Soc Mass Spectrom 2007, 18, 517-524

Non-limit passive soil pressure on rigid retaining walls

This paper aims to reveal the depth distribution law of non-limit passive soil pressure on rigid retaining wall that rotates about the top of the wall (rotation around the top (RT) model). Based on Coulomb theory, the disturbance degree theory, as well as the spring-element model, by setting the rotation angle of the wall as the disturbance parameter, we establish both a depth distribution function for sand and a nonlinear depth distribution calculation method for the non-limit passive soil pressure on a rigid retaining wall under the RT model, which is then compared with experiment. The results suggest that under the RT model: the non-limit soil pressure has a nonlinear distribution; the backfill disturbance degree and the lateral soil pressure increase with an increase in the wall rotation angle; and, the points where the resultant lateral soil pressure acts on the retaining wall are less than 2/3 of the height of the wall. The soil pressure predicted by the theoretical calculation put forward in this paper are quite similar to those obtained by the model experiment, which verifies the theoretical value, and the engineering guidance provided by the calculations are of significance. Keywords: RT model, Rigid wall, Non-limit passive soil pressure, Spring element, Genetic algorith