1,654 research outputs found
Unipolar potentiation and depression in memristive devices utilising the subthreshold regime
We present a resistance switching device that exhibits analogue potentiation and depression of conductance under the same voltage polarity. This contrasts with previously studied devices that potentiate and depress under opposite polarities. We refer to this mode of operation as the subthreshold regime due to it occurring at voltage or current biases that are insufficient to produce discrete or non-volatile switching. This behaviour has the potential to reduce the complexity of neuronal and synaptic circuitry in neuromorphic computing by removing the need for voltage pulses of both positive and negative polarities. The characteristically long timescales may also help replicate bio-realistic timings. In this paper, we detail how to induce this unique behaviour, how to tune its properties to a desired response, and finally, we demonstrate one potential application
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Global Modeling of Secondary Organic Aerosol Formation from Aromatic Hydrocarbons: High- vs. Low-Yield Pathways
Formation of SOA from the aromatic species toluene, xylene, and, for the first time, benzene, is added to a global chemical transport model. A simple mechanism is presented that accounts for competition between low and high-yield pathways of SOA formation, wherein secondary gas-phase products react further with either nitric oxide (NO) or hydroperoxy radical to yield semi- or non-volatile products, respectively. Aromatic species yield more SOA when they react with OH in regions where the ratios are lower. The SOA yield thus depends upon the distribution of aromatic emissions, with biomass burning emissions being in areas with lower ratios, and the reactivity of the aromatic with respect to OH, as a lower initial reactivity allows transport away from industrial source regions, where ratios are higher, to more remote regions, where this ratio is lower and, hence, the ultimate yield of SOA is higher. As a result, benzene is estimated to be the most important aromatic species with regards to global formation of SOA, with a total production nearly equal that of toluene and xylene combined. Global production of SOA from aromatic sources via the mechanisms identified here is estimated at 3.5 Tg/yr, resulting in a global burden of 0.08 Tg, twice as large as previous estimates. The contribution of these largely anthropogenic sources to global SOA is still small relative to biogenic sources, which are estimated to comprise 90% of the global SOA burden, about half of which comes from isoprene. Uncertainty in these estimates owing to factors ranging from the atmospheric relevance of chamber conditions to model deficiencies result in an estimated range of SOA production from aromatics of 2â12 Tg/yr. Though this uncertainty range affords a significant anthropogenic contribution to global SOA, it is evident from comparisons to recent observations that additional pathways for production of anthropogenic SOA still exist beyond those accounted for here. Nevertheless, owing to differences in spatial distributions of sources and seasons of peak production, regions exist in which aromatic SOA produced via the mechanisms identified here are predicted to contribute substantially to, and even dominate, the local SOA concentrations, such as outflow regions from North America and South East Asia during the wintertime, though total modeled SOA concentrations there are small .Chemistry and Chemical BiologyEngineering and Applied Science
Search for Heavy Leptons at Hadron Colliders
Four models are considered which contain heavy leptons beyond the three
families of the standard model. Two are fourth-generation extensions of the
standard model in which the right-handed heavy leptons are either isosinglets
or in an isodoublet; the other two are motivated by the aspon model of CP
violation. In all these models, the heavy neutrino can either be heavier than,
or comparable in mass to, the charged lepton leading to the possibility that
the charged lepton is very long-lived. Production cross section and signatures
for the heavy leptons are computed for the SSC and LHC.Comment: 17 pages(8 figures are not included),TRI-PP-92-9
The 331 model with right-handed neutrinos
We explore some more consequences of the electroweak
model with right-handed neutrinos. By introducing the mixing angle
, the {\it exact} physical eigenstates for neutral gauge bosons are
obtained. Because of the mixing, there is a modification to the coupling
proportional to . The data from the -decay allows us to fix the
limit for as . >From the neutrino
neutral current scatterings, we estimate a bound for the new neutral gauge
boson mass in the range 300 GeV, and from symmetry-breaking hierarchy a
bound for the new charged and neutral (non-Hermitian) gauge bosons are obtained.Comment: Slight changes in section 5, Latex, 16 page
Interference and interaction effects in multi-level quantum dots
Using renormalization group techniques, we study spectral and transport
properties of a spinless interacting quantum dot consisting of two levels
coupled to metallic reservoirs. For strong Coulomb repulsion and an applied
Aharonov-Bohm phase , we find a large direct tunnel splitting
between the levels of
the order of the level broadening . As a consequence we discover a
many-body resonance in the spectral density that can be measured via the
absorption power. Furthermore, for , we show that the system can be
tuned into an effective Anderson model with spin-dependent tunneling.Comment: 5 pages, 4 figures included, typos correcte
All-sky convolution for polarimetry experiments
We discuss all-sky convolution of the instrument beam with the sky signal in
polarimetry experiments, such as the Planck mission which will map the
temperature anisotropy and polarization of the cosmic microwave background
(CMB). To account properly for stray light (from e.g. the galaxy, sun, and
planets) in the far side-lobes of such an experiment, it is necessary to
perform the beam convolution over the full sky. We discuss this process in
multipole space for an arbitrary beam response, fully including the effects of
beam asymmetry and cross-polarization. The form of the convolution in multipole
space is such that the Wandelt-Gorski fast technique for all-sky convolution of
scalar signals (e.g. temperature) can be applied with little modification. We
further show that for the special case of a pure co-polarized, axisymmetric
beam the effect of the convolution can be described by spin-weighted window
functions. In the limits of a small angle beam and large Legendre multipoles,
the spin-weight 2 window function for the linear polarization reduces to the
usual scalar window function used in previous analyses of beam effects in CMB
polarimetry experiments. While we focus on the example of polarimetry
experiments in the context of CMB studies, we emphasise that the formalism we
develop is applicable to anisotropic filtering of arbitrary tensor fields on
the sphere.Comment: 8 pages, 1 figure; Minor changes to match version accepted by Phys.
Rev.
Regulation of Brain-Derived Neurotrophic Factor Exocytosis and Gamma-Aminobutyric Acidergic Interneuron Synapse by the Schizophrenia Susceptibility Gene Dysbindin-1
AbstractBackgroundGenetic variations in dystrobrevin binding protein 1 (DTNBP1 or dysbindin-1) have been implicated as risk factors in the pathogenesis of schizophrenia. The encoded protein dysbindin-1 functions in the regulation of synaptic activity and synapse development. Intriguingly, a loss of function mutation in Dtnbp1 in mice disrupted both glutamatergic and gamma-aminobutyric acidergic transmission in the cerebral cortex; pyramidal neurons displayed enhanced excitability due to reductions in inhibitory synaptic inputs. However, the mechanism by which reduced dysbindin-1 activity causes inhibitory synaptic deficits remains unknown.MethodsWe investigated the role of dysbindin-1 in the exocytosis of brain-derived neurotrophic factor (BDNF) from cortical excitatory neurons, organotypic brain slices, and acute slices from dysbindin-1 mutant mice and determined how this change in BDNF exocytosis transsynaptically affected the number of inhibitory synapses formed on excitatory neurons via whole-cell recordings, immunohistochemistry, and live-cell imaging using total internal reflection fluorescence microscopy.ResultsA decrease in dysbindin-1 reduces the exocytosis of BDNF from cortical excitatory neurons, and this reduction in BDNF exocytosis transsynaptically resulted in reduced inhibitory synapse numbers formed on excitatory neurons. Furthermore, application of exogenous BDNF rescued the inhibitory synaptic deficits caused by the reduced dysbindin-1 level in both cultured cortical neurons and slice cultures.ConclusionsTaken together, our results demonstrate that these two genes linked to risk for schizophrenia (BDNF and dysbindin-1) function together to regulate interneuron development and cortical network activity. This evidence supports the investigation of the association between dysbindin-1 and BDNF in humans with schizophrenia
Wnt-modified materials mediate asymmetric stem cell division to direct human osteogenic tissue formation for bone repair
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
Status of Muon Collider Research and Development and Future Plans
The status of the research on muon colliders is discussed and plans are
outlined for future theoretical and experimental studies. Besides continued
work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy
collider, many studies are now concentrating on a machine near 0.1 TeV (CoM)
that could be a factory for the s-channel production of Higgs particles. We
discuss the research on the various components in such muon colliders, starting
from the proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay ()
channel, muon cooling, acceleration, storage in a collider ring and the
collider detector. We also present theoretical and experimental R & D plans for
the next several years that should lead to a better understanding of the design
and feasibility issues for all of the components. This report is an update of
the progress on the R & D since the Feasibility Study of Muon Colliders
presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A.
Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics
(Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics,
Accelerators and Beam
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