2,928 research outputs found
Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films
Building usefully coherent superconducting quantum processors depends on
reducing losses in their constituent materials. Tantalum, like niobium, has
proven utility as the primary superconducting layer within highly coherent
qubits. But, unlike Nb, high temperatures are typically used to stabilize the
desirable body-centered-cubic phase, alpha-Ta, during thin film deposition. It
has long been known that a thin Nb layer permits the room-temperature
nucleation of alpha-Ta, although neither an epitaxial process nor few-photon
microwave loss measurements have been reported for Nb-nucleated Ta films prior
to this study. We compare resonators patterned from Ta films grown at high
temperature (500 {\deg}C) and films nucleated at room temperature, in order to
understand the impact of crystalline order on quantum coherence. In both cases,
films grew with Al2O3 (001) || Ta (110) indicating that the epitaxial
orientation is independent of temperature and is preserved across the Nb/Ta
interface. We use conventional low-power spectroscopy to measure two level
system (TLS) loss, as well as an electric-field bias technique to measure the
effective dipole moments of TLS in the surfaces of resonators. In our
measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 +/- 0.1
x 10^-5) than non-nucleated (5 +/- 1 x 10^-6) in approximate proportion to
defect densities as characterized by X-ray diffraction (0.27 {\deg} vs 0.18
{\deg} [110] reflection width) and electron microscopy (30 nm vs 70 nm domain
size). The dependence of the loss tangent on domain size indicates that the
development of more ordered Ta films is likely to lead to improvements in qubit
coherence times. Moreover, low-temperature alpha-Ta epitaxy may enable the
growth of new, microstate-free heterostructures which would not withstand high
temperature processing
Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study
The Field Induced Spin Density Wave phases observed in quasi-one-dimensional
conductors of the Bechgaard salts family under magnetic field exhibit both Spin
Density Wave order and a Quantized Hall Effect, which may exhibit sign
reversals. The original nature of the condensed phases is evidenced by the
collective mode spectrum. Besides the Goldstone modes, a quasi periodic
structure of Magneto-Roton modes, predicted to exist for a monotonic sequence
of Hall Quantum numbers, is confirmed, and a second mode is shown to exist
within the single particle gap. We present numerical estimates of the
Magneto-Roton mode energies in a generic case of the monotonic sequence. The
mass anisotropy of the collective mode is calculated. We show how differently
the MR spectrum evolves with magnetic field at low and high fields. The
collective mode spectrum should have specific features, in the sign reversed
"Ribault Phase", as compared to modes of the majority sign phases. We
investigate numerically the collective mode in the Ribault Phase.Comment: this paper incorporates material contained in a previous cond-mat
preprint cond-mat/9709210, but cannot be described as a replaced version,
because it contains a significant amount of new material dealing with the
instability line and with the topic of Ribault Phases. It contains 13 figures
(.ps files
HI in NGC 5433 and its Environment: High-Latitude Emission in a Small Galaxy Group
We present HI synthesis maps of the edge-on starburst NGC 5433 and its
environment, obtained with the VLA in its C and D configurations. The
observations and spectral model residuals of the main disc emission in NGC 5433
reveal 3 extraplanar features. We associate 2 of these features with coherent
extraplanar extensions across multiple spectral channels in our data, including
a complete loop in position-velocity space. Interpreting the latter as an
expanding shell we derive a corresponding input energy of 2 x 10^54 ergs,
comparable to that for the largest supershells found in the Galaxy and those in
other edge-on systems. NGC 5433 is in a richer environment than previously
thought. We confirm that KUG 1359+326 is a physical companion to NGC 5433 and
find two new faint companions, both with Minnesota Automated Plate Scanner
identifications, that we label SIS-1 and SIS-2. Including the more distant IC
4357, NGC 5433 is the dominant member of a group of at least 5 galaxies,
spanning over 750 kpc in a filamentary structure. A variety of evidence
suggests that interactions are occurring in this group. While a number of
underlying mechanisms are consistent with the morphology of the high-latitude
features in NGC 5433, we argue that environmental effects may play a role in
their generation.Comment: 18 pages including 10 figures. Accepted for publication in MNRAS. For
higher resolution Fig. 1, see http://www.astro.cornell.edu/~spekkens/papers/
v2: Proof-corrected cop
RNA-Seq identifies SPGs as a ventral skeletal patterning cue in sea urchins
The sea urchin larval skeleton offers a simple model for formation of developmental patterns. The calcium carbonate skeleton is secreted by primary mesenchyme cells (PMCs) in response to largely unknown patterning cues expressed by the ectoderm. To discover novel ectodermal cues, we performed an unbiased RNA-Seq-based screen and functionally tested candidates; we thereby identified several novel skeletal patterning cues. Among these, we show that SLC26a2/7 is a ventrally expressed sulfate transporter that promotes a ventral accumulation of sulfated proteoglycans, which is required for ventral PMC positioning and skeletal patterning. We show that the effects of SLC perturbation are mimicked by manipulation of either external sulfate levels or proteoglycan sulfation. These results identify novel skeletal patterning genes and demonstrate that ventral proteoglycan sulfation serves as a positional cue for sea urchin skeletal patterning
Braneworlds in six dimensions: new models with bulk scalars
Six dimensional bulk spacetimes with 3-- and 4--branes are constructed using
certain non--conventional bulk scalars as sources. In particular, we
investigate the consequences of having the phantom (negative kinetic energy)
and the Brans--Dicke scalar in the bulk while obtaining such solutions. We find
geometries with 4--branes with a compact on--brane dimension (hybrid
compactification) which may be assumed to be small in order to realize a
3--brane world. On the other hand, we also construct, with similar sources,
bulk spacetimes where a 3--brane is located at a conical singularity.
Furthermore, we investigate the issue of localization of matter fields (scalar,
fermion, graviton, vector) on these 3-- and 4--branes and conclude with
comments on our six dimensional models.Comment: 24 pages, 1 figure, Replaced to match version published in Class.
Quant. Gra
Hidden heterochromatin: Characterization in the Rodentia species Cricetus cricetus, Peromyscus eremicus (Cricetidae) and Praomys tullbergi (Muridae)
The use of in situ restriction endonuclease (RE) (which cleaves DNA at specific sequences) digestion has proven to be a useful technique in improving the dissection of constitutive heterochromatin (CH), and in the understanding of the CH evolution in different genomes. In the present work we describe in detail the CH of the three Rodentia species, Cricetus cricetus, Peromyscus eremicus (family Cricetidae) and Praomys tullbergi (family Muridae) using a panel of seven REs followed by C-banding. Comparison of the amount, distribution and molecular nature of C-positive heterochromatin revealed molecular heterogeneity in the heterochromatin of the three species. The large number of subclasses of CH identified in Praomys tullbergi chromosomes indicated that the karyotype of this species is the more derived when compared with the other two genomes analyzed, probably originated by a great number of complex chromosomal rearrangements. The high level of sequence heterogeneity identified in the CH of the three genomes suggests the coexistence of different satellite DNA families, or variants of these families in these genomes
GMRT Observations of NGC 3079
We present new observations at three frequencies (326 MHz, 615 MHz, and 1281
MHz) of the radio lobe spiral galaxy, NGC 3079, using the Giant Metrewave Radio
Telescope. These observations are consistent with previous data obtained at
other telescopes and reveal the structure of the nuclear radio lobes in
exquisite detail. In addition, new features are observed, some with HI
counterparts, showing broad scale radio continuum emission and extensions. The
galaxy is surrounded by a radio halo that is at least 4.8 kpc in height. Two
giant radio extensions/loops are seen on either side of the galaxy out to
11 kpc from the major axis, only slightly offset from the direction of
the smaller nuclear radio lobes. If these are associated with the nuclear
outflow, then the galaxy has experienced episodic nuclear activity. Emission
along the southern major axis suggests motion through a local IGM (not yet
detected) and it may be that NGC 3079 is itself creating this local
intergalactic gas via outflows. We also present maps of the minimum energy
parameters for this galaxy, including cosmic ray energy density, electron
diffusion length, magnetic field strength, particle lifetime, and power.Comment: 11 pages, 8 figures, 4 tables, accepted for publication in MNRA
First Measurement of the Total Neutron Cross Section on Argon between 100 and 800 MeV
We report the first measurement of the neutron cross section on argon in the energy range of 100-800 MeV. The measurement was obtained with a 4.3-h exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. The total cross section is measured from the attenuation coefficient of the neutron flux as it traverses the liquid argon volume. A set of 2631 candidate interactions is divided in bins of the neutron kinetic energy calculated from time-of-flight measurements. These interactions are reconstructed with custom-made algorithms specifically designed for the data in a time projection chamber the size of the Mini-CAPTAIN detector. The energy averaged cross section is 0.91±0.10(stat)±0.09(syst) b. A comparison of the measured cross section is made to the GEANT4 and FLUKA event generator packages, where the energy averaged cross sections in this range are 0.60 and 0.68 b, respectively
Cold gas accretion in galaxies
Evidence for the accretion of cold gas in galaxies has been rapidly
accumulating in the past years. HI observations of galaxies and their
environment have brought to light new facts and phenomena which are evidence of
ongoing or recent accretion:
1) A large number of galaxies are accompanied by gas-rich dwarfs or are
surrounded by HI cloud complexes, tails and filaments. It may be regarded as
direct evidence of cold gas accretion in the local universe. It is probably the
same kind of phenomenon of material infall as the stellar streams observed in
the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI
have been found in nearby spiral galaxies. While a large fraction of this gas
is produced by galactic fountains, it is likely that a part of it is of
extragalactic origin. 3) Spirals are known to have extended and warped outer
layers of HI. It is not clear how these have formed, and how and for how long
the warps can be sustained. Gas infall has been proposed as the origin. 4) The
majority of galactic disks are lopsided in their morphology as well as in their
kinematics. Also here recent accretion has been advocated as a possible cause.
In our view, accretion takes place both through the arrival and merging of
gas-rich satellites and through gas infall from the intergalactic medium (IGM).
The infall may have observable effects on the disk such as bursts of star
formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold
gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates
needed to sustain the observed star formation (~1 Msol/yr), additional infall
of large amounts of gas from the IGM seems to be required.Comment: To appear in Astronomy & Astrophysics Reviews. 34 pages.
Full-resolution version available at
http://www.astron.nl/~oosterlo/accretionRevie
QSAR-Driven Discovery of Novel Chemical Scaffolds Active against Schistosoma mansoni.
Schistosomiasis is a neglected tropical disease that affects millions of people worldwide. Thioredoxin glutathione reductase of Schistosoma mansoni (SmTGR) is a validated drug target that plays a crucial role in the redox homeostasis of the parasite. We report the discovery of new chemical scaffolds against S. mansoni using a combi-QSAR approach followed by virtual screening of a commercial database and confirmation of top ranking compounds by in vitro experimental evaluation with automated imaging of schistosomula and adult worms. We constructed 2D and 3D quantitative structure-activity relationship (QSAR) models using a series of oxadiazoles-2-oxides reported in the literature as SmTGR inhibitors and combined the best models in a consensus QSAR model. This model was used for a virtual screening of Hit2Lead set of ChemBridge database and allowed the identification of ten new potential SmTGR inhibitors. Further experimental testing on both shistosomula and adult worms showed that 4-nitro-3,5-bis(1-nitro-1H-pyrazol-4-yl)-1H-pyrazole (LabMol-17) and 3-nitro-4-{[(4-nitro-1,2,5-oxadiazol-3-yl)oxy]methyl}-1,2,5-oxadiazole (LabMol-19), two compounds representing new chemical scaffolds, have high activity in both systems. These compounds will be the subjects for additional testing and, if necessary, modification to serve as new schistosomicidal agents
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