5,391 research outputs found
Nuclear-spin-dependent corrections to the transition polarizability in cesium
The Stark-interference technique is commonly used to amplify the feeble
parity-violating signal in atomic experiments. As a result, interpretation of
these experiments in terms of electroweak observables requires knowledge of the
Stark-induced transition amplitudes or, equivalently, transition
polarizabilities. While the literature assumes that these transition
polarizabilities do not depend on the nuclear spin, here we prove the contrary.
The nuclear spin dependence arises due to hyperfine mixing of atomic states and
requires a third-order perturbation theory (one hyperfine interaction and two
electric-dipole interactions) treatment. We demonstrate that the so far
neglected {\em tensor} contribution appears in the transition polarizability
and present numerical results for the nuclear-spin-dependent corrections to the
transition polarizability in Cs. We
investigate the effect of these corrections to transition polarizabilities on
the extraction of the Cs anapole moment from the Boulder experiment
[Science 275, 1759 (1997)]. We also consider their effect on the extraction of
the ratio between the scalar and vector transition polarizabilities from the
measurements [Phys. Rev. A 55, 2 (1997)]. While the corrections are minor at
the current level of experimental accuracy, our analysis provides a framework
for future experiments.Comment: 11 pages, 1 figur
Reevaluation of Stark-induced transition polarizabilities in cesium
Extracting electroweak observables from experiments on atomic parity
violation (APV) using the Stark interference technique requires accurate
knowledge of transition polarizabilities. In cesium, the focus of our paper,
the APV amplitude is deduced from the measured
ratio of the APV amplitude to the vector transition polarizability, .
This ratio was measured with a uncertainty by the Boulder group
[Science 275, 1759 (1997)]. Currently, there is a sizable discrepancy in
different determinations of critically limiting the interpretation of
the APV measurement. The most recent value [Phys. Rev. Lett. 123, 073002
(2019)] of was deduced from a semi-empirical
sum-over-state determination of the scalar transition polarizability
and the measured ratio [Phys. Rev. A 55, 1007 (1997)]. This
value of , however, differs by or from the
previous determination of by [Phys. Rev. A 62, 052101
(2000)] based on the measured ratio of the magnetic-dipole
matrix element to . Here, we revise the
determination of by [Phys. Rev. Lett. 123, 073002 (2019)], using a more
consistent and more theoretically complete treatment of contributions from the
excited intermediate states in the sum-over-state method. Our
result of resolves the tension between the
and approaches. We recommend the value of
obtained by averaging our result and that of [Phys. Rev. A
62, 052101 (2000)].Comment: 9 pages, 2 figures v2: Reference added, small cosmetic changes to the
tex
Linear Query Approximation Algorithms for Non-monotone Submodular Maximization under Knapsack Constraint
This work, for the first time, introduces two constant factor approximation
algorithms with linear query complexity for non-monotone submodular
maximization over a ground set of size subject to a knapsack constraint,
and . is a deterministic algorithm
that provides an approximation factor of while is a
randomized algorithm with an approximation factor of . Both run in
query complexity. The key idea to obtain a
constant approximation ratio with linear query lies in: (1) dividing the ground
set into two appropriate subsets to find the near-optimal solution over these
subsets with linear queries, and (2) combining a threshold greedy with
properties of two disjoint sets or a random selection process to improve
solution quality. In addition to the theoretical analysis, we have evaluated
our proposed solutions with three applications: Revenue Maximization, Image
Summarization, and Maximum Weighted Cut, showing that our algorithms not only
return comparative results to state-of-the-art algorithms but also require
significantly fewer queries
A real-time RT-PCR for detection of clade 1 and 2 H5N1 Influenza A virus using Locked Nucleic Acid (LNA) TaqMan probes
<p>Abstract</p> <p>Background</p> <p>The emergence and co-circulation of two different clades (clade 1 and 2) of H5N1 influenza viruses in Vietnam necessitates the availability of a diagnostic assay that can detect both variants.</p> <p>Results</p> <p>We developed a single real-time RT-PCR assay for detection of both clades of H5N1 viruses, directly from clinical specimens, using locked nucleic acid TaqMan probes. Primers and probe used in this assay were designed based on a highly conserved region in the <it>HA </it>gene of H5N1 viruses. The analytical sensitivity of the assay was < 0.5 PFU and 10 - 100 ssDNA plasmid copies. A total of 106 clinical samples (58 from patients infected with clade 1, 2.1 or 2.3 H5N1 viruses and 48 from uninfected or seasonal influenza A virus-infected individuals) were tested by the assay. The assay showed 97% concordance with initial diagnostics for H5 influenza virus infection with a specificity of 100%.</p> <p>Conclusions</p> <p>This assay is a useful tool for diagnosis of H5N1 virus infections in regions where different genetic clades are co-circulating.</p
Building the hospital event-based surveillance system in Viet Nam: a qualitative study to identify potential facilitators and barriers for event reporting
Introduction: Hospitals are a key source of information for the early identification of emerging disease outbreaks and acute public health events for risk assessment, decision-making, and public health response. The objectives of this study were to identify potential facilitators and barriers for reporting of unusual events from the curative sector to the preventive medicine system in Viet Nam.
Methods: In 2016, we conducted 18 semi-structured in-depth interviews and 9 focus group discussions with representatives from the curative and preventive medicine sectors in four provinces. We transcribed the interviews and focus group discussions and conducted a thematic analysis of the factors that appeared to affect public health event reporting.
Results: We identified five major themes. Firstly, the lack of a legal framework to guide reporting meant there was an over-reliance on internal procedures. Secondly, participants reported the importance of an enabling environment to facilitate reporting such as leadership support and having focal points for reporting. Thirdly, potential benefits for reporting were seen such as support during outbreaks and receiving feedback. Fourthly, some challenges prohibited timely reporting such as not perceiving reporting to be the task of the curative sector and hesitancy to report without laboratory confirmation. Finally, the limited resources and specialist capacities in remote areas hindered timely detection and reporting of unusual events.
Discussion: This study identified potential opportunities to promote the detection and reporting of unusual events from health care workers to the public health sector, and thus improving the overall health security system in Viet Nam and beyond
Immunolocalization of NLRP3 Inflammasome in Normal Murine Airway Epithelium and Changes following Induction of Ovalbumin-Induced Airway Inflammation
Little is known about innate immunity and components of inflammasomes in airway epithelium. This study evaluated immunohistological evidence for NLRP3 inflammasomes in normal and inflamed murine (Balb/c) airway epithelium in a model of ovalbumin (OVA) induced allergic airway inflammation. The airway epithelium of control mice exhibited strong cytoplasmic staining for total caspase-1, ASC, and NLRP3, whereas the OVA mice exhibited strong staining for active caspase-1, with redistribution of caspase-1, IL-1β and IL-18, indicating possible activation of the NLRP3 inflammasome. Active caspase-1, NLRP3, and other inflammasome components were also detected in tissue eosinophils from OVA mice, and may potentially contribute to IL-1β and IL-18 production. In whole lung, inRNA expression of NAIP and procaspase-1 was increased in OVA mice, whereas NLRP3, IL-1β and IL-18 decreased. Some OVA-treated mice also had significantly elevated and tightly correlated serum levels of IL-1β and TNFα. In cultured normal human bronchial epithelial cells, LPS priming resulted in a significant increase in NLRP3 and II-lp protein expression. This study is the first to demonstrate NLRP3 inflammasome components in normal airway epithelium and changes with inflammation. We propose activation and/or luminal release of the inflammasome is a feature of allergic airway inflammation which may contribute to disease pathogenesis
A Model for the Prediction of Fiber Elasticity
A model is presented that enables the elastic properties of wood fibers to be estimated from the properties of its polymeric constituents, cellulose, hemicellulose, and lignin. The influence of the value of the axial stiffness of the cellulose crystal is demonstrated, its proper value being discussed in comparison with experimental data on fibers. The effects on fiber stiffness of the S2 fibril angle, the fibril angles of other layers, the crystallinity, and layer thicknesses are analyzed. The manner in which the effect of a variation in yield can be simulated by a change in shape factor of the reinforcing cellulose crystals is demonstrated, the cell wall thus being considered to be a discontinuous reinforced composite
Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes
Two-dimensional materials offer new opportunities for both fundamental
science and technological applications, by exploiting the electron spin. While
graphene is very promising for spin communication due to its extraordinary
electron mobility, the lack of a band gap restricts its prospects for
semiconducting spin devices such as spin diodes and bipolar spin transistors.
The recent emergence of 2D semiconductors could help overcome this basic
challenge. In this letter we report the first important step towards making 2D
semiconductor spin devices. We have fabricated a spin valve based on ultra-thin
(5 nm) semiconducting black phosphorus (bP), and established fundamental spin
properties of this spin channel material which supports all electrical spin
injection, transport, precession and detection up to room temperature (RT).
Inserting a few layers of boron nitride between the ferromagnetic electrodes
and bP alleviates the notorious conductivity mismatch problem and allows
efficient electrical spin injection into an n-type bP. In the non-local spin
valve geometry we measure Hanle spin precession and observe spin relaxation
times as high as 4 ns, with spin relaxation lengths exceeding 6 um. Our
experimental results are in a very good agreement with first-principles
calculations and demonstrate that Elliott-Yafet spin relaxation mechanism is
dominant. We also demonstrate that spin transport in ultra-thin bP depends
strongly on the charge carrier concentration, and can be manipulated by the
electric field effect
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