Thermal Decomposition of Condensed-Phase Nitromethane from Molecular Dynamics from ReaxFF Reactive Dynamics

We studied the thermal decomposition and subsequent reaction of the energetic material nitromethane (CH_3NO_2) using molecular dynamics with ReaxFF, a first principles-based reactive force field. We characterize the chemistry of liquid and solid nitromethane at high temperatures (2000−3000 K) and density 1.97 g/cm^3 for times up to 200 ps. At T = 3000 K the first reaction in the decomposition of nitromethane is an intermolecular proton transfer leading to CH_3NOOH and CH_2NO_2. For lower temperatures (T = 2500 and 2000 K) the first reaction during decomposition is often an isomerization reaction involving the scission of the C−N bond the formation of a C−O bond to form methyl nitrate (CH_3ONO). Also at very early times we observe intramolecular proton transfer events. The main product of these reactions is H_2O which starts forming following those initiation steps. The appearance of H_2O marks the beginning of the exothermic chemistry. Recent quantum-mechanics-based molecular dynamics simulations on the chemical reactions and time scales for decomposition of a crystalline sample heated to T = 3000 K for a few picoseconds are in excellent agreement with our results, providing an important, direct validation of ReaxFF

Quantum delayed-choice experiment with a beam splitter in a quantum superposition

A quantum system can behave as a wave or as a particle, depending on the experimental arrangement. When for example measuring a photon using a Mach-Zehnder interferometer, the photon acts as a wave if the second beam-splitter is inserted, but as a particle if this beam-splitter is omitted. The decision of whether or not to insert this beam-splitter can be made after the photon has entered the interferometer, as in Wheeler's famous delayed-choice thought experiment. In recent quantum versions of this experiment, this decision is controlled by a quantum ancilla, while the beam splitter is itself still a classical object. Here we propose and realize a variant of the quantum delayed-choice experiment. We configure a superconducting quantum circuit as a Ramsey interferometer, where the element that acts as the first beam-splitter can be put in a quantum superposition of its active and inactive states, as verified by the negative values of its Wigner function. We show that this enables the wave and particle aspects of the system to be observed with a single setup, without involving an ancilla that is not itself a part of the interferometer. We also study the transition of this quantum beam-splitter from a quantum to a classical object due to decoherence, as observed by monitoring the interferometer output.Comment: 9 pages, 7 figures, Accepted by Physical Review Letter

Self-assembly of carbon nanotubes into two-dimensional geometries using DNA origami templates

A central challenge in nanotechnology is the parallel fabrication of complex geometries for nanodevices. Here we report a general method for arranging single-walled carbon nanotubes in two dimensions using DNA origami—a technique in which a long single strand of DNA is folded into a predetermined shape. We synthesize rectangular origami templates (~75 nm × 95 nm) that display two lines of single-stranded DNA ‘hooks’ in a cross pattern with ~6 nm resolution. The perpendicular lines of hooks serve as sequence-specific binding sites for two types of nanotubes, each functionalized non-covalently with a distinct DNA linker molecule. The hook-binding domain of each linker is protected to ensure efficient hybridization. When origami templates and DNA-functionalized nanotubes are mixed, strand displacement-mediated deprotection and binding aligns the nanotubes into cross-junctions. Of several cross-junctions synthesized by this method, one demonstrated stable field-effect transistor-like behaviour. In such organizations of electronic components, DNA origami serves as a programmable nanobreadboard; thus, DNA origami may allow the rapid prototyping of complex nanotube-based structures

The linear and nonlinear Jaynes-Cummings model for the multiphoton transition

With the Jaynes-Cummings model, we have studied the atom and light field quantum entanglement of multiphoton transition, and researched the effect of initial state superposition coefficient $C_{1}$, the transition photon number $N$, the quantum discord $\delta$ and the nonlinear coefficient $\chi$ on the quantum entanglement degrees. We have given the quantum entanglement degrees curves with time evolution, and obtained some results, which should have been used in quantum computing and quantum information.Comment: arXiv admin note: text overlap with arXiv:1404.0821, arXiv:1205.0979 by other author

Multiplex PCR System for Rapid Detection of Pathogens in Patients with Presumed Sepsis – A Systemic Review and Meta-Analysis

Background: Blood culture is viewed as the golden standard for the diagnosis of sepsis but suffers from low sensitivity and long turnaround time. LightCycler SeptiFast (LC-SF) is a real-time multiplex polymerase chain reaction test able to detect 25 common pathogens responsible for bloodstream infections within hours. We aim to assess the accuracy of LC-SF by systematically reviewing the published studies. Method Related literature on Medline, Embase, and Cochrane databases was searched up to October 2012 for studies utilizing LC-SF to diagnose suspected sepsis and that provided sufficient data to construct two-by-two tables. Results: A total of 34 studies enrolling 6012 patients of suspected sepsis were included. The overall sensitivity and specificity for LC-SF to detect bacteremia or fungemia was 0·75 (95% CI: 0·65–0·83) and 0·92 (95%CI:0·90–0·95), respectively. LC-SF had a high positive likelihood ratio (10·10) and a moderate negative likelihood ratio (0·27). Specifically, LC-SF had a sensitivity of 0·80 (95%CI: 0·70–0·88) and a specificity of 0·95(95%CI: 0·93–0·97) for the bacteremia outcome, and a sensitivity of 0·61 (95%CI: 0·48–0·72) and a specificity of 0·99 (95%CI: 0·99–0·99) for the fungemia outcome. High heterogeneity was found in the bacteremia outcome subgroup but not in the fungemia outcome subgroup. Conclusion: LC-SF is of high rule-in value for early detection of septic patients. In a population with low pretest probability, LC-SF test can still provide valuable information for ruling out bacteremia or fungemia

Homologous recombination is unlikely to play a major role in influenza B virus evolution

Influenza B viruses cause a significant amount of morbidity and mortality. The occurrence of homologous recombination in influenza viruses is controversial. To determine the extent of homologous recombination in influenza B viruses, recombination analyses of 2,650 sequences representing all eight segments of the influenza B viruses were carried out. Only four sequences were indentified as putative recombinants, which were verified using phylogenetic methods. However, the mosaics detected here were much likely to represent cases of laboratory-generated artificial recombinants. As in other myxoviruses, it is unlikely that homologous recombination plays a major role in influenza B virus evolution

Research Capacity at Traditional Chinese Medicine (TCM) Centers in China: A Survey of Clinical Investigators

Background. The development of an evidence-based approach to traditional Chinese medicine (TCM), which depends on the generation of good quality evidence, requires an adequate workforce. However, the research capacity of TCM investigators is not known. Study Design. This cross-sectional study was conducted to describe the research capacity of TCM clinical investigators in China. Participants. A total of 584 participants from TCM hospitals and research centers were included. They were asked about the academic and research characteristics, needs for research capacity building, and barriers to clinical research. Results. The majority (80.82%) were qualified to at least a Master’s degree, whilst a smaller proportion (40.24%) held a senior professional title. We found that academic outputs were low with the majority (62.16%) authoring less than five publications in total. The most pressing needs for building research capacity identified were training in research methodology (97.43%) and identification of research questions (86.81%), whilst the highest ranking barriers to conducting research were limited motivation, funding (40.72%), and time (37.15%). Conclusion. The methodology training, along with investment in the research workforce, needs to be urgently addressed to improve investigators’ research capacity and the development of an evidence-based approach of TCM

DNA-Linker-Induced Surface Assembly of Ultra Dense Parallel Single Walled Carbon Nanotube Arrays

Ultrathin film preparations of single-walled carbon nanotube (SWNT) allow economical utilization of nanotube properties in electronics applications. Recent advances have enabled production of micrometer scale SWNT transistors and sensors but scaling these devices down to the nanoscale, and improving the coupling of SWNTs to other nanoscale components, may require techniques that can generate a greater degree of nanoscale geometric order than has thus far been achieved. Here, we introduce linker-induced surface assembly, a new technique that uses small structured DNA linkers to assemble solution dispersed nanotubes into parallel arrays on charged surfaces. Parts of our linkers act as spacers to precisely control the internanotube separation distance down to <3 nm and can serve as scaffolds to position components such as proteins between adjacent parallel nanotubes. The resulting arrays can then be stamped onto other substrates. Our results demonstrate a new paradigm for the self-assembly of anisotropic colloidal nanomaterials into ordered structures and provide a potentially simple, low cost, and scalable route for preparation of exquisitely structured parallel SWNT films with applications in high-performance nanoscale switches, sensors, and meta-materials

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Lead contamination alters enzyme activities and microbial composition in the rhizosphere soil of the hyperaccumulator Pogonatherum crinitum

Pogonatherum crinitum is a promising lead (Pb) hyperaccumulator; however, the effects of Pb contamination on P. crinitum rhizosphere soil enzymatic activities and microbial composition remain largely unexplored. Thus, an indoor experiment was conducted by cultivating P. crinitum seedlings and exposing them to four Pb concentrations (0, 1,000, 2000 and 3000 mg/kg Pb). Protease, urease, acid phosphatase and invertase activities were determined using standard methods while soil bacterial composition was determined by 16 S rDNA sequencing. The results showed that rhizosphere soil acid phosphatase activity significantly increased with increasing Pb concentration, while urease activity was significantly greater in rhizosphere soil contaminated with 1000 and 2000 mg/kg than in the control. There was a clear shift in bacterial composition during phytoremediation by P. crinitum. Compared to the control, Bacteroidetes was more abundant in all Pb-contaminated soils, Actinobacteria was more abundant in 1000 mg/kg Pb-treated soil, and Firmicutes was more abundant in 3000 mg/kg Pb-treated soil. Positive correlations were observed between dominant bacterial phyla and soil enzyme activities. Metabolic pathways, such as ABC transporter, quinine reductase, and ATP-binding protein were significantly increased in rhizosphere soil bacteria with Pb contamination. In conclusion, Pb contamination differentially influenced the activities of rhizosphere soil enzymes, specifically increasing acid phosphatase and urease activities, and alters the dominance of soil bacteria through up-regulation of genes related to some metabolic pathways. The strong correlations between dominant bacterial phyla and enzymatic activities suggest synergetic effects on the growth of P. crinitum during Pb contamination