Pressure-Induced Electronic Transition in Black Phosphorus

In a semimetal, both electrons and holes contribute to the density of states at the Fermi level. The small band overlaps and multiband effects engender novel electronic properties. We show that a moderate hydrostatic pressure effectively suppresses the band gap in the elemental semiconductor black phosphorus. An electronic topological transition takes place at approximately 1.2 GPa, above which black phosphorus evolves into a semimetal state that is characterized by a colossal positive magnetoresistance and a nonlinear field dependence of Hall resistivity. The Shubnikov-de Haas oscillations detected in magnetic field reveal the complex Fermi surface topology of the semimetallic phase. In particular, we find a nontrivial Berry phase in one Fermi surface that emerges in the semimetal state, as evidence of a Dirac-like dispersion. The observed semimetallic behavior greatly enriches the material property of black phosphorus and sets the stage for the exploration of novel electronic states in this material.

Analysis of the Contrasting Pathogenicities Induced by the D222G Mutation in 1918 and 2009 Pandemic Influenza A Viruses

In 2009, the D222G mutation in the hemagglutinin (HA) glycoprotein of pandemic H1N1 influenza A virus was found to correlate with fatal and severe human infections. Previous static structural analysis suggested that, unlike the H1N1 viruses prevalent in 1918, the mutation did not compromise binding to human α2,6-linked glycan receptors, allowing it to transmit efficiently. Here we investigate the interconversion mechanism between two predicted binding modes in both 2009 and 1918 HAs, introducing a highly parallel intermediate network search scheme to construct kinetically relevant pathways efficiently. Accumulated mutations at positions 183 and 224 that alter the size of the binding pocket are identified with the fitness of the 2009 pandemic virus carrying the D222G mutation. This result suggests that the pandemic H1N1 viruses could gain binding affinity to the α2,3-linked glycan receptors in the lungs, usually associated with highly pathogenic avian influenza, without compromising viability.

Communication: optimal parameters for basin-hopping global optimization based on Tsallis statistics

A fundamental problem associated with global optimization is the large free energy barrier for the corresponding solid-solid phase transitions for systems with multi-funnel energy landscapes. To address this issue we consider the Tsallis weight instead of the Boltzmann weight to define the acceptance ratio for basin-hopping global optimization. Benchmarks for atomic clusters show that using the optimal Tsallis weight can improve the efficiency by roughly a factor of two. We present a theory that connects the optimal parameters for the Tsallis weighting, and demonstrate that the predictions are verified for each of the test cases.

Searching for new TiO₂ crystal phases with better photoactivity

Using the recently developed stochastic surface walking global optimization method, this work explores the potential energy surface of TiO2 crystals aiming to search for likely phases with higher photocatalytic activity. Five new phases of TiO2 are identified and the lowest energy phase transition pathways connecting to the most abundant phases (rutile and anatase) are determined. Theory shows that a high-pressure phase, α-PbO2-like form (TiO2II) acts as the key intermediate in between rutile and anatase. The phase transition of anatase to rutile belongs to the diffusionless Martensitic phase transition, occurring through a set of habit planes, rutile(101)//TiO2II(001), and TiO2II(100)//anatase(112). With regard to the photocatalytic activity, three pure phases (#110, pyrite and fluorite) are found to possess the band gap narrower than rutile, but they are unstable at the low-pressure condition. Instead, a mixed anatase-TiO2II phase is found to have good stability and narrower band gap than both parent phases. Because of the phase separation, the mixed phase is also expected to improve the photocatalytic performance by reducing the probability of the electron-hole pair recombination.

Confined platinum nanoparticle in carbon nanotube: structure and oxidation

Confined metal particles show unexpected structural versatility, leading to higher stability and better catalytic performance, as predicted from first-principles-based global optimization methods.

How to make a porphyrin flip: dynamics of asymmetric porphyrin oligomers

The pathways and energy barriers from computational and experimental methods reveal the dynamics of asymmetric porphyrin oligomers.

The relation between price and daily consumption of cigarettes and bidis: findings from the Tobacco Control Policy Evaluation Wave 1 Survey

CONTEXT

In India, 14% of the population use smoked tobacco products. Increasing prices of these products is one of the measures to curb their consumption.

AIMS

This study analyzes "unit price" and "daily consumption" of cigarettes and bidis and investigates their relation with each other.

SETTINGS AND DESIGN

A cross-sectional survey was conducted in four states of India (Bihar, West Bengal, Madhya Pradesh and Maharashtra) as a part of the International Tobacco Control Policy (TCP) Evaluation Project (the TCP India Project) during 2010-2011.

METHODS

Information was collected from adult (aged ≥ 15) daily exclusive smokers of cigarette/bidi regarding (a) last purchase (purchase in pack/loose, brand and price) and (b) daily consumption. Average unit price and daily consumption was calculated for different brands and states. Regression model was used to assess the impact of price on daily consumption.

RESULTS

Bidis were much less expensive ([symbol in text]0.39) than cigarettes ([symbol in text]3.1). The daily consumption was higher (14) among bidi smokers than cigarette smokers (8). The prices and daily consumption of bidis ([symbol in text]0.33-0.43; 12-15) and cigarettes ([symbol in text]2.9-3.6; 5-9) varied across the four states. The unit prices of bidis and cigarettes did not influence their daily consumption. Smokers purchasing bidis in packs paid substantially less per unit and purchase of bidis and cigarettes in packs influenced their consumption positively.

CONCLUSIONS

Cigarettes although more expensive than bidis, seem very cheap if compared internationally. Hence, prices of both cigarettes and bidis do not influence their consumption.

The relation between price and daily consumption of cigarettes and bidis: findings from the Tobacco Control Policy Evaluation Wave 1 Survey

CONTEXT

In India, 14% of the population use smoked tobacco products. Increasing prices of these products is one of the measures to curb their consumption.

AIMS

This study analyzes "unit price" and "daily consumption" of cigarettes and bidis and investigates their relation with each other.

SETTINGS AND DESIGN

A cross-sectional survey was conducted in four states of India (Bihar, West Bengal, Madhya Pradesh and Maharashtra) as a part of the International Tobacco Control Policy (TCP) Evaluation Project (the TCP India Project) during 2010-2011.

METHODS

Information was collected from adult (aged ≥ 15) daily exclusive smokers of cigarette/bidi regarding (a) last purchase (purchase in pack/loose, brand and price) and (b) daily consumption. Average unit price and daily consumption was calculated for different brands and states. Regression model was used to assess the impact of price on daily consumption.

RESULTS

Bidis were much less expensive ([symbol in text]0.39) than cigarettes ([symbol in text]3.1). The daily consumption was higher (14) among bidi smokers than cigarette smokers (8). The prices and daily consumption of bidis ([symbol in text]0.33-0.43; 12-15) and cigarettes ([symbol in text]2.9-3.6; 5-9) varied across the four states. The unit prices of bidis and cigarettes did not influence their daily consumption. Smokers purchasing bidis in packs paid substantially less per unit and purchase of bidis and cigarettes in packs influenced their consumption positively.

CONCLUSIONS

Cigarettes although more expensive than bidis, seem very cheap if compared internationally. Hence, prices of both cigarettes and bidis do not influence their consumption.

Chiral gold nanowires with Boerdijk-Coxeter-Bernal structure

A Boerdijk-Coxeter-Bernal (BCB) helix is made of linearly stacked regular tetrahedra (tetrahelix). As such, it is chiral without nontrivial translational or rotational symmetries. We demonstrate here an example of the chiral BCB structure made of totally symmetrical gold atoms, created in nanowires by direct chemical synthesis. Detailed study by high-resolution electron microscopy illustrates their elegant chiral structure and the unique one-dimensional "pseudo-periodicity". The BCB-type atomic packing mode is proposed to be a result of the competition and compromise between the lattice and surface energy.

Stochastic surface walking method for crystal structure and phase transition pathway prediction

SSW-crystal method for automated structure search and phase transition pathway sampling of crystals.

From Atoms to Fullerene: Stochastic Surface Walking Solution for Automated Structure Prediction of Complex Material

It is of general concern whether the automated structure prediction of unknown material without recourse to any knowledge from experiment is ever possible considering the daunting complexity of potential energy surface (PES) of material. Here we demonstrate that the stochastic surface walking (SSW) method can be a general and promising solution to this ultimate goal, which is applied to assemble carbon fullerenes containing up to 100 atoms (including 60, 70, 76, 78, 80, 84, 90, 96, and 100 atoms) from randomly distributed atoms, a long-standing challenge in global optimization. Combining the SSW method with a parallel replica exchange algorithm, we can locate the global minima (GM) of these large fullerenes efficiently without being trapped in numerous energy-nearly degenerate isomers. Detailed analyses on the SSW trajectories allow us to rationalize how and why the SSW method is able to explore the highly complex PES, which highlights the abilities of SSW method for surmounting the high barrier and the preference of SSW trajectories to the low energy pathways. The work demonstrates that the parallel SSW method is a practical tool for predicting unknown materials.

Hydrogen sulfide removal from sediment and water in box culverts/storm drains by iron-based granules

A renewable granular iron-based technology for hydrogen sulfide removal from sediment and water in box culverts and storm drains is discussed. Iron granules, including granular ferric hydroxide (GFH), granular ferric oxide (GFO) and rusted waste iron crusts (RWIC) embedded in the sediment phase removed aqueous hydrogen sulfide formed from sedimentary biological sulfate reduction. The exhausted iron granules were exposed to dissolved oxygen and this regeneration process recovered the sulfide removal capacities of the granules. The recovery is likely attributable to the oxidation of the ferrous iron precipitates film and the formation of new reactive ferric iron surface sites on the iron granules and sand particles. GFH and RWIC showed larger sulfide removal capacities in the sediment phase than GFO, likely due to the less ordered crystal structures on their surfaces. This study demonstrates that the iron granules are able to remove hydrogen sulfide from sediment and water in box culverts and storm drains and they have the potential to be regenerated and reused by contacting with dissolved oxygen.

Quantifying phytate in dairy digesta and feces: alkaline extraction and high-performance ion chromatography

Development of an analytical method with appropriate combination of extraction and quantification approaches for undigested phytate in ruminant feces and digesta will advance knowledge of phytate degradation in ruminants and help to reduce phosphorus excretion. Established quantification methods give satisfactory results for feedstuffs and nonruminant manure but recovery of phytate is incomplete for ruminant feces and digesta because of their complex sample matrix and low ratio of phytate to inorganic P. The objective was to develop a robust, accurate, sensitive, and inexpensive method to extract and quantify phytate in feeds, ruminant feces, and digesta. Diets varying in phytate content were fed to dairy heifers, dry cows, and lactating cows to generate digesta and fecal samples of varying composition to challenge extraction and quantification methods. Samples were extracted with 0.5 M HCl or 0.25 M NaOH + 0.05 M EDTA. Acid extracts were mixed with 20% NaCl, alkaline extracts were acidified to final pH < 2, and then both extracts were clarified with C₁₈ cartridges and 0.2-μm filters. High-performance ion chromatography (HPIC) was used to quantify phytate. In feed samples, the measured phytate was comparable in alkaline and acid extracts (2,965 vs. 3,085 μg/g of DM). In digesta and fecal samples, alkaline extraction yielded greater estimates of phytate content than did acid extraction (40.7 vs. 33.6 and 202.9 vs. 144.4 μg/g of DM for digesta and fecal samples, respectively). Analysis of alkaline extracts by HPIC is usually not possible because of sample matrix interferences; acidification and C(18)-cartridge elution of alkaline extracts prevented this interference. Pure phytate added to dry samples before extraction was almost completely recovered (88 to 105%), indicating high extraction efficiency, no adverse effect of extract clean-up procedures, and accurate quantification of phytate. The proposed method is rapid, inexpensive, robust, and combines the extraction power of NaOH-EDTA with the precision and sensitivity of HPIC quantification, allowing accurate quantification of phytate in feeds, ruminant digesta, and fecal samples.

SU-E-J-180: A Characterization of the LAP Aquarius Phantom for External LAP Laser Alignment and MR Geometric Distortion Verification for the use of SRS Patient Simulation

PURPOSE

To explore additional application of the new Aquarius external laser alignment verification Phantom by LAP (Aq-LAP Phantom) examining geometric accuracy of magnetic resonance images (MRI) commonly used for planning intracranial stereotactic radiation surgery (ICSRS) cases.

METHODS

Newly designed external patient alignment lasers were first aligned by the Aq-LAP Phantom at a Siemens Magneton Vario 3T MR unit. The scans were then performed with the T1 Axial 3D MPRAGE protocols with 0.9 mm temporal resolution, which may be used for ICSRS. They also include FLAIR, T2 BLADE and Diffusion Axial TRACE imaging acquisitions with 1 mm temporal resolution. The MRI will be fused to 1 mm cut computerized tomography (CT) images acquired by a Siemens Somatom Sensation Open©. The geometric distortions (GD) were measured against the CT in all axial, sagital, and coronal directions at different levels.

RESULTS

MR images of the Aquarius Phantom indicate a distinct similarity between the nonlinear GD along the z-axis crosshair and typical magnetic field gradient nonlinearity. There is linear correlation between MR divergence datasets of distorted crosshairs (p-values from 0.57 to 0.00), and nonlinear correlation between MR divergence datasets of the distorted crosshair with the CT divergence datasets of the cross plane (p-values from 8.45×10̂-4 to 1.38×10̂-46). The margin of error exceeded no more than 0.29 mm. GDs up to about 2 mm are observed at the distal regions of the longitudinal axis in the SRS treatment planning MR images.

CONCLUSIONS

Using the Aquarius Phantom, one is able to detect GD in ICSRS planning MRI acquisitions, and align the external LAP patient alignment lasers by following the LAP QA. Based on the results, one may recommend using the Aquarius Phantom to determine if margins should be included for SRS treatment planning. The Aquarius Phantom, used for laser alignment and geometric distortion detection, was provided by LAP of America.