42,450 research outputs found
Participatory variety selection and scaling: Small grain cereals
United States Agency for International Developmen
Decoherence and Quantum Interference assisted electron trapping in a quantum dot
We present a theoretical model for the dynamics of an electron that gets
trapped by means of decoherence and quantum interference in the central quantum
dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 K and
300 K. The electron's dynamics is described by a master equation with a
Hamiltonian based on the tight-binding model, taking into account electron-LO
phonon interaction (ELOPI). Based on this configuration, the probability to
trap an electron with no decoherence is almost 27%. In contrast, the
probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K
and 58% at 300 K. Our model provides a novel method of trapping an electron at
room temperature.Comment: Revtex 4, 11 pages, 13 figure
Physical Multi-Layer Phantoms for Intra-Body Communications
This paper presents approaches to creating tissue mimicking materials that
can be used as phantoms for evaluating the performance of Body Area Networks
(BAN). The main goal of the paper is to describe a methodology to create a
repeatable experimental BAN platform that can be customized depending on the
BAN scenario under test. Comparisons between different material compositions
and percentages are shown, along with the resulting electrical properties of
each mixture over the frequency range of interest for intra-body
communications; 100 KHz to 100 MHz. Test results on a composite multi-layer
sample are presented confirming the efficacy of the proposed methodology. To
date, this is the first paper that provides guidance on how to decide on
concentration levels of ingredients, depending on the exact frequency range of
operation, and the desired matched electrical characteristics (conductivity vs.
permittivity), to create multi-layer phantoms for intra-body communication
applications
Multi-scale modelling of macromolecular conformational changes
Modelling protein flexibility and plasticity is computationally challenging but important for understanding the function of biological systems. Furthermore, it has great implications for the prediction of (macro) molecular complex formation. Recently, coarse-grained normal mode approaches have emerged as efficient alternatives for investigating large-scale conformational changes for which more accurate methods like MD simulation are limited due to their computational burden. We have developed a Normal Mode based Simulation (NMSim) approach for efficient conformation generation of macromolecules. Combinations of low energy normal modes are used to guide a simulation pathway, whereas an efficient constraints correction approach is applied to generate stereochemically allowed conformations. Non-covalent bonds like hydrogen bonds and hydrophobic tethers and phi-psi favourable regions are also modelled as constraints. Conformations from our approach were compared with a 10 ns MD trajectory of lysozyme. A 2-D RMSD plot shows a good overlap of conformational space, and rms fluctuations of residues show a correlation coefficient of 0.78 between the two sets of conformations. Furthermore, a comparison of NMSim simulations starting from apo structures of different proteins show that ligand-bound conformations can be sampled for those cases where conformational changes are mainly correlated, e.g., domain-like motion in adenylate kinase. Efforts are currently being made to also model localized but functionally important motions for protein binding pockets and protein-protein interfaces using relevant normal mode selection criteria and implicit rotamer basin creation
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Detection of Aliphatically Bridged Multi-Core Polycyclic Aromatic Hydrocarbons in Sooting Flames with Atmospheric-Sampling High-Resolution Tandem Mass Spectrometry.
This paper provides experimental evidence for the chemical structures of aliphatically substituted and bridged polycyclic aromatic hydrocarbon (PAH) species in gas-physe combustion environments. The identification of these single- and multicore aromatic species, which have been hypothesized to be important in PAH growth and soot nucleation, was made possible through a combination of sampling gaseous constituents from an atmospheric pressure inverse coflow diffusion flame of ethylene and high-resolution tandem mass spectrometry (MS-MS). In these experiments, the flame-sampled components were ionized using a continuous VUV lamp at 10.0 eV and the ions were subsequently fragmented through collisions with Ar atoms in a collision-induced dissociation (CID) process. The resulting fragment ions, which were separated using a reflectron time-of-flight mass spectrometer, were used to extract structural information about the sampled aromatic compounds. The high-resolution mass spectra revealed the presence of alkylated single-core aromatic compounds and the fragment ions that were observed correspond to the loss of saturated and unsaturated units containing up to a total of 6 carbon atoms. Furthermore, the aromatic structures that form the foundational building blocks of the larger PAHs were identified to be smaller single-ring and pericondensed aromatic species with repetitive structural features. For demonstrative purposes, details are provided for the CID of molecular ions at masses 202 and 434. Insights into the role of the aliphatically substituted and bridged aromatics in the reaction network of PAH growth chemistry were obtained from spatially resolved measurements of the flame. The experimental results are consistent with a growth mechanism in which alkylated aromatics are oxidized to form pericondensed ring structures or react and recombine with other aromatics to form larger, potentially three-dimensional, aliphatically bridged multicore aromatic hydrocarbons
ExoCross: a general program for generating spectra from molecular line lists
ExoCross is a Fortran code for generating spectra (emission, absorption) and
thermodynamic properties (partition function, specific heat etc.) from
molecular line lists. Input is taken in several formats, including ExoMol and
HITRAN formats. ExoCross is efficiently parallelized showing also a high degree
of vectorization. It can work with several line profiles such as Doppler,
Lorentzian and Voigt and support several broadening schemes. Voigt profiles are
handled by several methods allowing fast and accurate simulations. Two of these
methods are new. ExoCross is also capable of working with the recently proposed
method of super-lines. It supports calculations of lifetimes, cooling
functions, specific heats and other properties. ExoCross can be used to convert
between different formats, such as HITRAN, ExoMol and Phoenix. It is capable of
simulating non-LTE spectra using a simple two-temperature approach. Different
electronic, vibronic or vibrational bands can be simulated separately using an
efficient filtering scheme based on the quantum numbers
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