1,012 research outputs found
Pair-distribution functions of the two-dimensional electron gas
Based on its known exact properties and a new set of extensive fixed-node
reptation quantum Monte Carlo simulations (both with and without backflow
correlations, which in this case turn out to yield negligible improvements), we
propose a new analytical representation of (i) the spin-summed
pair-distribution function and (ii) the spin-resolved potential energy of the
ideal two-dimensional interacting electron gas for a wide range of electron
densities and spin polarization, plus (iii) the spin-resolved pair-distribution
function of the unpolarized gas. These formulae provide an accurate reference
for quantities previously not available in analytic form, and may be relevant
to semiconductor heterostructures, metal-insulator transitions and quantum dots
both directly, in terms of phase diagram and spin susceptibility, and
indirectly, as key ingredients for the construction of new two-dimensional spin
density functionals, beyond the local approximation.Comment: 12 pages, 10 figures; misprints correcte
Metabolism of profenofos to 4-bromo-2-chlorophenol, a specific and sensitive exposure biomarker.
Profenofos is a direct acting phosphorothioate organophosphorus (OP) pesticide capable of inhibiting ÎČ-esterases such as acetylcholinesterase, butyrylcholinesterase, and carboxylesterase. Profenofos is known to be detoxified to the biologically inactive metabolite, 4-bromo-2-chlorophenol (BCP); however, limited data are available regarding the use of urinary BCP as an exposure biomarker in humans. A pilot study conducted in Egyptian agriculture workers, demonstrated that urinary BCP levels prior to application (3.3-30.0 ÎŒg/g creatinine) were elevated to 34.5-3,566 ÎŒg/g creatinine during the time workers were applying profenofos to cotton fields. Subsequently, the in vitro enzymatic formation of BCP was examined using pooled human liver microsomes and recombinant human cytochrome P-450s (CYPs) incubated with profenofos. Of the nine human CYPs studied, only CYPs 3A4, 2B6, and 2C19 were able to metabolize profenofos to BCP. Kinetic studies indicated that CYP 2C19 has the lowest Km, 0.516 ÎŒM followed by 2B6 (Km=1.02 ÎŒM) and 3A4 (Km=18.9ÎŒM). The Vmax for BCP formation was 47.9, 25.1, and 19.2 nmol/min/nmol CYP for CYP2B6, 2C19, and 3A4, respectively. Intrinsic clearance (Vmax/Km) values of 48.8, 46.9, and 1.02 ml/min/nmol CYP 2C19, 2B6, and 3A4, respectively, indicate that CYP2C19 and CYP2B6 are primarily responsible for the detoxification of profenofos. These findings support the use of urinary BCP as a biomarker of exposure to profenofos in humans and suggest polymorphisms in CYP 2C19 and CYP 2B6 as potential biomarkers of susceptibility
A family of thermostable fungal cellulases created by structure-guided recombination
SCHEMA structure-guided recombination of 3 fungal class II cellobiohydrolases (CBH II cellulases) has yielded a collection of highly thermostable CBH II chimeras. Twenty-three of 48 genes sampled from the 6,561 possible chimeric sequences were secreted by the Saccharomyces cerevisiae heterologous host in catalytically active form. Five of these chimeras have half-lives of thermal inactivation at 63°C that are greater than the most stable parent, CBH II enzyme from the thermophilic fungus Humicola insolens, which suggests that this chimera collection contains hundreds of highly stable cellulases. Twenty-five new sequences were designed based on mathematical modeling of the thermostabilities for the first set of chimeras. Ten of these sequences were expressed in active form; all 10 retained more activity than H. insolens CBH II after incubation at 63°C. The total of 15 validated thermostable CBH II enzymes have high sequence diversity, differing from their closest natural homologs at up to 63 amino acid positions. Selected purified thermostable chimeras hydrolyzed phosphoric acid swollen cellulose at temperatures 7 to 15°C higher than the parent enzymes. These chimeras also hydrolyzed as much or more cellulose than the parent CBH II enzymes in long-time cellulose hydrolysis assays and had pH/activity profiles as broad, or broader than, the parent enzymes. Generating this group of diverse, thermostable fungal CBH II chimeras is the first step in building an inventory of stable cellulases from which optimized enzyme mixtures for biomass conversion can be formulated
Functional identification of an aggression locus in the mouse hypothalamus
Electrical stimulation of certain hypothalamic regions in cats and rodents can elicit attack behaviour, but the exact location of relevant cells within these regions, their requirement for naturally occurring aggression and their relationship to mating circuits have not been clear. Genetic methods for neural circuit manipulation in mice provide a potentially powerful approach to this problem, but brain-stimulation-evoked aggression has never been demonstrated in this species. Here we show that optogenetic, but not electrical, stimulation of neurons in the ventromedial hypothalamus, ventrolateral subdivision (VMHvl) causes male mice to attack both females and inanimate objects, as well as males. Pharmacogenetic silencing of VMHvl reversibly inhibits inter-male aggression. Immediate early gene analysis and single unit recordings from VMHvl during social interactions reveal overlapping but distinct neuronal subpopulations involved in fighting and mating. Neurons activated during attack are inhibited during mating, suggesting a potential neural substrate for competition between these opponent social behaviours
DeepBrain: Functional Representation of Neural In-Situ Hybridization Images for Gene Ontology Classification Using Deep Convolutional Autoencoders
This paper presents a novel deep learning-based method for learning a
functional representation of mammalian neural images. The method uses a deep
convolutional denoising autoencoder (CDAE) for generating an invariant, compact
representation of in situ hybridization (ISH) images. While most existing
methods for bio-imaging analysis were not developed to handle images with
highly complex anatomical structures, the results presented in this paper show
that functional representation extracted by CDAE can help learn features of
functional gene ontology categories for their classification in a highly
accurate manner. Using this CDAE representation, our method outperforms the
previous state-of-the-art classification rate, by improving the average AUC
from 0.92 to 0.98, i.e., achieving 75% reduction in error. The method operates
on input images that were downsampled significantly with respect to the
original ones to make it computationally feasible
Non-sequential triple ionization in strong fields
We consider the final stage of triple ionization of atoms in a strong
linearly polarized laser field. We propose that for intensities below the
saturation value for triple ionization the process is dominated by the
simultaneous escape of three electrons from a highly excited intermediate
complex. We identify within a classical model two pathways to triple
ionization, one with a triangular configuration of electrons and one with a
more linear one. Both are saddles in phase space. A stability analysis
indicates that the triangular configuration has the larger cross sections and
should be the dominant one. Trajectory simulations within the dominant symmetry
subspace reproduce the experimentally observed distribution of ion momenta
parallel to the polarization axis.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Synchronized pulses generated at 20 eV and 90 eV for attosecond pump-probe experiments
The development of attosecond pulses across different photon energies is an essential precursor to performing pumpâprobe attosecond experiments in complex systems, where the potential of attosecond science1 can be further developed2,3. We report the generation and characterization of synchronized extreme ultraviolet (90â
eV) and vacuum ultraviolet (20â
eV) pulses, generated simultaneously via high-harmonic generation. The vacuum ultraviolet pulses are well suited for pumpâprobe experiments that exploit the high photo-ionization cross-sections of many molecules in this spectral region4 as well as the higher photon flux due to the higher conversion efficiency of the high harmonic generation process at these energies5. We temporally characterized all pulses using the attosecond streaking technique6 and the FROG-CRAB retrieval method7. We report 576â±â16â
as pulses at 20â
eV and 257â±â21â
as pulses at 90â
eV. Our demonstration of synchronized attosecond pulses at different photon energies, which are inherently jitter-free due to the common-path geometry implemented, offers unprecedented possibilities for pumpâprobe studies
Initial-state dependence in time-dependent density functional theory
Time-dependent density functionals in principle depend on the initial state
of the system, but this is ignored in functional approximations presently in
use. For one electron it is shown there is no initial-state dependence: for any
density, only one initial state produces a well-behaved potential. For two
non-interacting electrons with the same spin in one-dimension, an initial
potential that makes an alternative initial wavefunction evolve with the same
density and current as a ground state is calculated. This potential is
well-behaved and can be made arbitrarily different from the original potential
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Cyclin D2-knock-out mice with attenuated dentate gyrus neurogenesis have robust deficits in long-term memory formation.
Neurobehavioral studies have produced contradictory findings concerning the function of neurogenesis in the adult dentate gyrus. Previous studies have proved inconsistent across several behavioral endpoints thought to be dependent on dentate neurogenesis, including memory acquisition, short-term and long-term retention of memory, pattern separation, and reversal learning. We hypothesized that the main function of dentate neurogenesis is long-term memory formation because we assumed that a newly formed and integrated neuron would have a long-term impact on the local neural network. We used a cyclin D2-knock-out (cyclin D2-/-) mouse model of endogenously deficient dentate neurogenesis to test this hypothesis. We found that cyclin D2-/- mice had robust and sustained loss of long-term memory in two separate behavioral tasks, Morris water maze (MWM) and touchscreen intermediate pattern separation. Moreover, after adjusting for differences in brain volumes determined by magnetic resonance (MR) imaging, reduced dentate neurogenesis moderately correlated with deficits in memory retention after 24âhours. Importantly, cyclin D2-/- mice did not show deficits in learning acquisition in a touchscreen paradigm of intermediate pattern separation or MWM platform location, indicating intact short-term memory. Further evaluation of cyclin D2-/- mice is necessary to confirm that deficits are specifically linked to dentate gyrus neurogenesis since cyclin D2-/- mice also have a reduced size of the olfactory bulb, hippocampus, cerebellum and cortex besides reduced dentate gyrus neurogenesis
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