6,195 research outputs found
Improved limit on the permanent electric dipole moment of 199Hg
We report the results of a new experimental search for a permanent electric
dipole moment of 199Hg utilizing a stack of four vapor cells. We find d(199Hg)
= (0.49 \pm 1.29_stat \pm 0.76_syst) x 10^{-29} e cm, and interpret this as a
new upper bound, |d(199Hg)| < 3.1 x 10^{-29} e cm (95% C.L.). This result
improves our previous 199Hg limit by a factor of 7, and can be used to set new
constraints on CP violation in physics beyond the standard model.Comment: 4 pages, 4 figures. additional reference, minor edits in response to
reviewer comment
Mid-infrared Variability from the Spitzer Deep Wide-field Survey
We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg^2 of the NOAO Deep Wide Field Survey Boötes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 μm bands. Out of 474, 179 analyzed sources, 1.1% meet our standard variability selection criteria that the two light curves are strongly correlated (r > 0.8) and that their joint variance (σ_(12)) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 μm selected active galactic nucleus (AGN) candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects, although most of the stellar, galaxy, and unclassified sources are false positives. For our standard selection criteria, 11%-12% of the mid-IR counterparts to X-ray sources, 24 μm AGN candidates, and spectroscopically identified AGNs show variability. The exact fractions depend on both the search depth and the selection criteria. For example, 12% of the 1131 known z>1 AGNs in the field and 14%-17% of the known AGNs with well-measured fluxes in all four Infrared Array Camera bands meet our standard selection criteria. The mid-IR AGN variability can be well described by a single power-law structure function with an index of γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S _0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities
Measurement of Linear Stark Interference in 199Hg
We present measurements of Stark interference in the 6
6 transition in Hg, a process whereby a static electric field
mixes magnetic dipole and electric quadrupole couplings into an electric
dipole transition, leading to -linear energy shifts similar to those
produced by a permanent atomic electric dipole moment (EDM). The measured
interference amplitude, = = (5.8 1.5) (kV/cm), agrees with relativistic, many-body predictions and
confirms that earlier central-field estimates are a factor of 10 too large.
More importantly, this study validates the capability of the Hg EDM
search apparatus to resolve non-trivial, controlled, and sub-nHz Larmor
frequency shifts with EDM-like characteristics.Comment: 4 pages, 4 figures, 1 table; revised in response to reviewer comment
Heterotic Compactification, An Algorithmic Approach
We approach string phenomenology from the perspective of computational
algebraic geometry, by providing new and efficient techniques for proving
stability and calculating particle spectra in heterotic compactifications. This
is done in the context of complete intersection Calabi-Yau manifolds in a
single projective space where we classify positive monad bundles. Using a
combination of analytic methods and computer algebra we prove stability for all
such bundles and compute the complete particle spectrum, including gauge
singlets. In particular, we find that the number of anti-generations vanishes
for all our bundles and that the spectrum is manifestly moduli-dependent.Comment: 36 pages, Late
Radio Observations of the Supernova Remnant Candidate G312.5-3.0
The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850
MHz have revealed a number of previously unknown radio sources. One such
source, G312.5-3.0 (PMN J1421-6415), has been observed using the
multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at
frequencies of 1380 MHz and 2378 MHz. Further observations of the source were
made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency
of 843 MHz. The source has an angular size of 18 arcmin and has a distinct
shell structure. We present the reduced multi-frequency observations of this
source and provide a brief argument for its possible identification as a
supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA
The characteristics and experiences of anticipatory mourning in caregivers of teenagers and young adults
This article reports a systematic review of literature undertaken to identify characteristics and experiences of anticipatory mourning in caregivers of teenagers and young adults with life-limiting or life-threatening conditions. A comprehensive literature search was conducted using the key words ‘anticipatory’, ‘mourning’, ‘grief’, and synonyms. This review focused on six studies that met inclusion criteria and reported characteristics of anticipatory mourning in caregivers of teenagers and young adults. Characteristics and experiences were sorted into four main themes: symptoms; a sense of loss; caregiver behaviour; and the unique experience of caring for, or losing, a teenager or young adult. The review suggests that there are characteristics and experiences of anticipatory mourning that are unique to caregivers of this age group. The review also suggests that consideration of anticipatory mourning is important in offering holistic care to young adults and their caregivers, and points to the need for further research in this area
Kirchhoff's Rule for Quantum Wires
In this article we formulate and discuss one particle quantum scattering
theory on an arbitrary finite graph with open ends and where we define the
Hamiltonian to be (minus) the Laplace operator with general boundary conditions
at the vertices. This results in a scattering theory with channels. The
corresponding on-shell S-matrix formed by the reflection and transmission
amplitudes for incoming plane waves of energy is explicitly given in
terms of the boundary conditions and the lengths of the internal lines. It is
shown to be unitary, which may be viewed as the quantum version of Kirchhoff's
law. We exhibit covariance and symmetry properties. It is symmetric if the
boundary conditions are real. Also there is a duality transformation on the set
of boundary conditions and the lengths of the internal lines such that the low
energy behaviour of one theory gives the high energy behaviour of the
transformed theory. Finally we provide a composition rule by which the on-shell
S-matrix of a graph is factorizable in terms of the S-matrices of its
subgraphs. All proofs only use known facts from the theory of self-adjoint
extensions, standard linear algebra, complex function theory and elementary
arguments from the theory of Hermitean symplectic forms.Comment: 40 page
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
Fracture toughness in some hetero-modulus composite carbides: carbon inclusions and voids. Advances in Applied Ceramics
Fracture toughness of ceramics in some cases can be significantly improved by the inclusion of low-modulus phase and even voids. Structure and mechanical characteristics of dense ceramic composites synthesised by reactive hot pressing of TiC-B4C powder mixtures at 1800 - 1950°С under 30MPa during 16 minutes are investigated. X-Ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM and EDX) have shown that during hot pressing solid phase chemical interaction 2TiС + B4C = 2TiВ2 + 3С has occurred resulting in TiB2-TiC-C, TiB2-C or TiB2-B4C-C hetero-modulus composite formation with approximately 1μm carbon precipitates. The volume of such precipitated carbon can reach 35 vol. %. The fracture toughness depends on the precipitate size and amount of graphite precipitation and has a distinct maximum K1C = 10MPa∙m1/2 at nearly 7 vol. % . Such fracture toughness behaviour is explained by the proposed model of crack propagation and the model-based assessment of hetero-modulus ceramic fracture toughness. It is shown that voids and low modulus carbon inclusions blunt the cracks and can increase ceramic toughness. The later has been demonstrated in the another carbon containing ceramic Cr2AlC, so named MAX phase material, when thin film fracture resistance increases as the ceramic was deposited to be porous
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