19,762 research outputs found
Impurity and edge roughness scattering in armchair graphene nanoribbons: Boltzmann approach
The conductivity of armchair graphene nanoribbons in the presence of
short-range impurities and edge roughness is studied theoretically using the
Boltzmann transport equation for quasi-one-dimensional systems. As the number
of occupied subbands increases, the conductivity due to short-range impurities
converges towards the two-dimensional case. Calculations of the
magnetoconductivity confirm the edge-roughness-induced dips at cyclotron radii
close to the ribbon width suggested by the recent quantum simulations
Pseudoscalar mixing in J/psi and psi(2S) decay
Based on the branching fractions of J/psi(psi(2S))-> VP from different
collaborations, the pseudoscalar mixing is extensively discussed with a well
established phenomenological model. The mixing angle is determined to be -14
degree by fitting to the new world average if only quark content is considered.
After taking into account the gluonic content in eta and eta prime
simultaneously, the investigation shows that eta favors only consisting of
light quarks, while the gluonic content of eta prime is Z_{eta
prime}^2=0.30\pm0.24.Comment: 8 page
Plasmonic resonators for enhanced diamond NV- center single photon sources
We propose a novel source of non-classical light consisting of plasmonic
aperture with single-crystal diamond containing a single Nitrogen-Vacancy (NV)
color center. Theoretical calculations of optimal structures show that these
devices can simultaneously enhance optical pumping by a factor of 7,
spontaneous emission rates by Fp ~ 50 (Purcell factor), and offer collection
efficiencies up to 40%. These excitation and collection enhancements occur over
a broad range of wavelengths (~30nm), and are independently tunable with device
geometry, across the excitation (~530nm) and emission (~600-800nm) spectrum of
the NV center. Implementing this system with top-down techniques in bulk
diamond crystals will provide a scalable architecture for a myriad of diamond
NV center applications.Comment: 9 pages, 7 figure
Can simulations reproduce the observed temperature-mass relation for clusters of galaxies?
It has become increasingly apparent that traditional hydrodynamical
simulations of galaxy clusters are unable to reproduce the observed properties
of galaxy clusters, in particular overpredicting the mass corresponding to a
given cluster temperature. Such overestimation may lead to systematic errors in
results using galaxy clusters as cosmological probes, such as constraints on
the density perturbation normalization sigma_8. In this paper we demonstrate
that inclusion of additional gas physics, namely radiative cooling and a
possible preheating of gas prior to cluster formation, is able to bring the
temperature-mass relation in the innermost parts of clusters into good
agreement with recent determinations by Allen, Schmidt & Fabian using Chandra
data.Comment: 5 pages, submitted to MNRA
Infrared Variability of Two Dusty White Dwarfs
The most heavily polluted white dwarfs often show excess infrared radiation
from circumstellar dust disks, which are modeled as a result of tidal
disruption of extrasolar minor planets. Interaction of dust, gas, and
disintegrating objects can all contribute to the dynamical evolution of these
dust disks. Here, we report on two infrared variable dusty white dwarfs, SDSS
J1228+1040 and G29-38. For SDSS J1228+1040, compared to the first measurements
in 2007, the IRAC [3.6] and [4.5] fluxes decreased by 20% by 2014 to a level
also seen in the recent 2018 observations. For G29-38, the infrared flux of the
10 m silicate emission feature became 10% stronger between 2004 and 2007,
We explore several scenarios that could account for these changes, including
tidal disruption events, perturbation from a companion, and runaway accretion.
No satisfactory causes are found for the flux drop in SDSS J1228+1040 due to
the limited time coverage. Continuous tidal disruption of small planetesimals
could increase the mass of small grains and concurrently change the strength of
the 10 m feature of G29-38. Dust disks around white dwarfs are actively
evolving and we speculate that there could be different mechanisms responsible
for the temporal changes of these disks.Comment: ApJ, in pres
Ocean acidification increases iodine accumulation in kelp-based coastal food webs
Kelp are main iodine accumulators in the ocean, and their growth and photosynthesis are likely to benefit from elevated seawater CO2 levels due to ocean acidification. However, there are currently no data on the effects of ocean acidification on iodine metabolism in kelp. As key primary producers in coastal ecosystems worldwide, any change in their iodine metabolism caused by climate change will potentially have important consequences for global geochemical cycles of iodine, including iodine levels of coastal food webs that underpin the nutrition of billions of humans around the world. Here, we found that elevated pCO2 enhanced growth and increased iodine accumulation not only in the model kelp Saccharina japonica using both short‐term laboratory experiment and long‐term in situ mesocosms, but also in several other edible and ecologically significant seaweeds using long‐term in situ mesocosms. Transcriptomic and proteomic analysis of S. japonica revealed that most vanadium‐dependent haloperoxidase genes involved in iodine efflux during oxidative stress are down‐regulated under increasing pCO2, suggesting that ocean acidification alleviates oxidative stress in kelp, which might contribute to their enhanced growth. When consumed by abalone (Haliotis discus), elevated iodine concentrations in S. japonica caused increased iodine accumulation in abalone, accompanied by reduced synthesis of thyroid hormones. Thus, our results suggest that kelp will benefit from ocean acidification by a reduction in environmental stress however, iodine levels in kelp‐based coastal food webs will increase, with potential impacts on biogeochemical cycles of iodine in coastal ecosystems
Discovery of the Central Excess Brightness in Hard X-rays in the Cluster of Galaxies Abell 1795
Using the X-ray data from \ASCA, spectral and spatial properties of the
intra-cluster medium (ICM) of the cD cluster Abell 1795 are studied, up to a
radial distance of ( kpc). The ICM
temperature and abundance are spatially rather constant, although the cool
emission component is reconfirmed in the central region. The azimuthally-
averaged radial X-ray surface brightness profiles are very similar between soft
(0.7--3 keV) and hard (3--10 keV) energy bands, and neither can be fitted with
a single- model due to a strong data excess within of the
cluster center. In contrast, double- models can successfully reproduce
the overall brightness profiles both in the soft and hard energy bands, as well
as that derived with the \ROSAT PSPC. Properties of the central excess
brightness are very similar over the 0.2--10 keV energy range spanned by \ROSAT
and \ASCA. Thus, the excess X-ray emission from the core region of this cluster
is confirmed for the first time in hard X-rays above 3 keV. This indicates that
the shape of the gravitational potential becomes deeper than the King-type one
towards the cluster center. Radial profiles of the total gravitating matter,
calculated using the double- model, reveal an excess mass of within kpc of the cluster
center. This suggests a hierarchy in the gravitational potential corresponding
to the cD galaxy and the entire cluster.Comment: 27 pages, 8 figures; to appear ApJ 500 (June 20, 1998
Supplements to article: A novel transcription complex that selectively modulates apoptosis of breast cancer cells through regulation of FASTKD2
The materials provided here are supplemental tables and figures to an
article to be published in 'Molecular and Cellular Biology.'(This refers to the article.) We previously reported that expression of
NRIF3 (Nuclear Receptor Interacting Factor-3) rapidly and selectively
leads to apoptosis of breast cancer cells. DIF-1 (a.k.a IRF-2BP2), the
cellular target of NRIF3, was identified as a transcriptional repressor
and DIF-1 knockdown leads to apoptosis of breast cancer cells but not
other cell types. Here, we identify IRF2BP1 (Interferon Regulatory
Factor-2 Binding Protein 1) and EAP1 (Enhanced At Puberty 1) as
important components of the DIF-1 complex mediating both complex
stability and transcriptional repression. This interaction of DIF-1,
IRF2BP1, and EAP1 occurs through the conserved C4 zinc-fingers of these
proteins. Microarray studies were carried out in breast cancer cell
lines engineered to conditionally and rapidly increase the levels of the
Death Domain region of NRIF3 (DD1). The DIF-1 complex was found to
repress FASTKD2, a putative pro-apoptotic gene, in breast cancer cells
and to bind to the FASTKD2 gene by chromatin immunoprecipitation.
FASTKD2 knockdown prevents apoptosis of breast cancer cells from NRIF3
expression or DIF-1 knockdown while expression of FASTKD2 leads to
apoptosis of both breast and non-breast cancer cells. Thus, regulation
of FASTKD2 by NRIF3 and the DIF-1 complex acts as a novel death switch
that selectively modulates apoptosis in breast cancer
Consistency and diversity of spike dynamics in the neurons of bed nucleus of Stria Terminalis of the rat: a dynamic clamp study
Neurons display a high degree of variability and diversity in the expression and regulation of their voltage-dependent ionic channels. Under low level of synaptic background a number of physiologically distinct cell types can be identified in most brain areas that display different responses to standard forms of intracellular current stimulation. Nevertheless, it is not well understood how biophysically different neurons process synaptic inputs in natural conditions, i.e., when experiencing intense synaptic bombardment in vivo. While distinct cell types might process synaptic inputs into different patterns of action potentials representing specific "motifs'' of network activity, standard methods of electrophysiology are not well suited to resolve such questions. In the current paper we performed dynamic clamp experiments with simulated synaptic inputs that were presented to three types of neurons in the juxtacapsular bed nucleus of stria terminalis (jcBNST) of the rat. Our analysis on the temporal structure of firing showed that the three types of jcBNST neurons did not produce qualitatively different spike responses under identical patterns of input. However, we observed consistent, cell type dependent variations in the fine structure of firing, at the level of single spikes. At the millisecond resolution structure of firing we found high degree of diversity across the entire spectrum of neurons irrespective of their type. Additionally, we identified a new cell type with intrinsic oscillatory properties that produced a rhythmic and regular firing under synaptic stimulation that distinguishes it from the previously described jcBNST cell types. Our findings suggest a sophisticated, cell type dependent regulation of spike dynamics of neurons when experiencing a complex synaptic background. The high degree of their dynamical diversity has implications to their cooperative dynamics and synchronization
Silicon-Based Antenna-Coupled Polarization-Sensitive Millimeter-Wave Bolometer Arrays for Cosmic Microwave Background Instruments
We describe feedhorn-coupled polarization-sensitive detector arrays that
utilize monocrystalline silicon as the dielectric substrate material.
Monocrystalline silicon has a low-loss tangent and repeatable dielectric
constant, characteristics that are critical for realizing efficient and uniform
superconducting microwave circuits. An additional advantage of this material is
its low specific heat. In a detector pixel, two Transition-Edge Sensor (TES)
bolometers are antenna-coupled to in-band radiation via a symmetric planar
orthomode transducer (OMT). Each orthogonal linear polarization is coupled to a
separate superconducting microstrip transmission line circuit. On-chip
filtering is employed to both reject out-of-band radiation from the upper band
edge to the gap frequency of the niobium superconductor, and to flexibly define
the bandwidth for each TES to meet the requirements of the application. The
microwave circuit is compatible with multi-chroic operation. Metalized silicon
platelets are used to define the backshort for the waveguide probes. This
micro-machined structure is also used to mitigate the coupling of out-of-band
radiation to the microwave circuit. At 40 GHz, the detectors have a measured
efficiency of 90%. In this paper, we describe the development of the 90 GHz
detector arrays that will be demonstrated using the Cosmology Large Angular
Scale Surveyor (CLASS) ground-based telescope
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