1,399 research outputs found
Correlated electron emission in laser-induced nonsequence double ionization of Helium
In this paper, we have investigated the correlated electron emission of the
nonsequence double ionization (NSDI) in an intense linearly polarized field.
The theoretical model we employed is the semiclassical rescattering model, the
model atom we used is the helium. We find a significant correlation between
magnitude and direction of the momentum of two emission electrons, and give a
good explanation for this striking phenomenon by observing the classical
collisional trajectories. We argue that this correlation phenomenon is
universal in NSDI process, as revealed by the recent experiment on the argon.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.
Heavy ion beam measurement of the hydration of cementitious materials
The setting and development of strength of Portland cement concrete depends upon the reaction of water with various phases in the Portland cement. Nuclear resonance reaction analysis (NRRA) involving the 1H(15N,α,γ)12C reaction has been applied to measure the hydrogen depth profile in the few 100 nm thick surface layer that controls the early stage of the reaction. Specific topics that have been investigated include the reactivity of individual cementitious phases and the effects of accelerators and retarders
Homogeneous nucleation of quark-gluon plasma, finite size effects and long-lived metastable objects
The general formalism of homogeneous nucleation theory is applied to study
the hadronization pattern of the ultra-relativistic quark-gluon plasma (QGP)
undergoing a first order phase transition. A coalescence model is proposed to
describe the evolution dynamics of hadronic clusters produced in the nucleation
process. The size distribution of the nucleated clusters is important for the
description of the plasma conversion. The model is most sensitive to the
initial conditions of the QGP thermalization, time evolution of the energy
density, and the interfacial energy of the plasma-hadronic matter interface.
The rapidly expanding QGP is first supercooled by about . Then it reheats again up to the critical temperature T_c. Finally it
breaks up into hadronic clusters and small droplets of plasma. This fast
dynamics occurs within the first . The finite size effects and
fluctuations near the critical temperature are studied. It is shown that a drop
of longitudinally expanding QGP of the transverse radius below 4.5 fm can
display a long-lived metastability. However, both in the rapid and in the
delayed hadronization scenario, the bulk pion yield is emitted by sources as
large as 3-4.5 fm. This may be detected experimentally both by a HBT
interferometry signal and by the analysis of the rapidity distributions of
particles in narrow p_T-intervals at small p_T on an event-by-event basis.Comment: 29 pages, incl. 12 figures and 1 table; to be published in Phys. Rev.
A Step Beyond the Bounce: Bubble Dynamics in Quantum Phase Transitions
We study the dynamical evolution of a phase interface or bubble in the
context of a \lambda \phi^4 + g \phi^6 scalar quantum field theory. We use a
self-consistent mean-field approximation derived from a 2PI effective action to
construct an initial value problem for the expectation value of the quantum
field and two-point function. We solve the equations of motion numerically in
(1+1)-dimensions and compare the results to the purely classical evolution. We
find that the quantum fluctuations dress the classical profile, affecting both
the early time expansion of the bubble and the behavior upon collision with a
neighboring interface.Comment: 12 pages, multiple figure
Characterization of the Si:Se+ Spin-Photon Interface
Silicon is the most-developed electronic and photonic technological platform and hosts some of the highest-performance spin and photonic qubits developed to date. A hybrid quantum technology harnessing an efficient spin-photon interface in silicon would unlock considerable potential by enabling ultralong-lived photonic memories, distributed quantum networks, microwave-to-optical photon converters, and spin-based quantum processors, all linked with integrated silicon photonics. However, the indirect band gap of silicon makes identification of efficient spin-photon interfaces nontrivial. Here we build upon the recent identification of chalcogen donors as a promising spin-photon interface in silicon. We determine that the spin-dependent optical degree of freedom has a transition dipole moment stronger than previously thought [here 1.96(8) D], and the spin T1 lifetime in low magnetic fields is longer than previously thought [here longer than 4.6(1.5) h]. We furthermore determine the optical excited-state lifetime [7.7(4) ns], and therefore the natural radiative efficiency [0.80(9)%], and by measuring the phonon sideband determine the zero-phonon emission fraction [16(1)%]. Taken together, these parameters indicate that an integrated quantum optoelectronic platform based on chalcogen-donor qubits in silicon is well within reach of current capabilities
Polymer-Layered Silicate Nanocomposites for Cryotank Applications
Previous composite cryotank designs have relied on the use of conventional composite materials to reduce microcracking and permeability. However, revolutionary advances in nanotechnology derived materials may enable the production of ultra-lightweight cryotanks with significantly enhanced durability and damage tolerance, as well as reduced propellant permeability. Layered silicate nanocomposites are especially attractive in cryogenic storage tanks based on results that have been reported for epoxy nanocomposite systems. These materials often exhibit an order of magnitude reduction in gas permeability when compared to the base resin. In addition, polymer-silicate nanocomposites have been shown to yield improved dimensional stability, strength, and toughness. The enhancement in material performance of these systems occurs without property trade-offs which are often observed in conventionally filled polymer composites. Research efforts at NASA Glenn Research Center have led to the development of epoxy-clay nanocomposites with 70% lower hydrogen permeability than the base epoxy resin. Filament wound carbon fiber reinforced tanks made with this nanocomposite had a five-fold lower helium leak rate than the corresponding tanks made without clay. The pronounced reduction observed with the tank may be due to flow induced alignment of the clay layers during processing. Additionally, the nanocomposites showed CTE reductions of up to 30%, as well as a 100% increase in toughness
On Low-Energy Effective Actions in N = 2, 4 Superconformal Theories in Four Dimensions
We study some aspects of low-energy effective actions in 4-d superconformal
gauge theories on the Coulomb branch. We describe superconformal invariants
constructed in terms of N=2 abelian vector multiplet which play the role of
building blocks for the N=2,4 supersymmetric low-energy effective actions. We
compute the one-loop effective actions in constant N=2 field strength
background in N=4 SYM theory and in N=2 SU(2) SYM theory with four
hypermultiplets in fundamental representation. Using the classification of
superconformal invariants we then find the manifestly N=2 superconformal form
of these effective actions. While our explicit computations are done in the
one-loop approximation, our conclusions about the structure of the effective
actions in N=2 superconformal theories are general. We comment on some
applications to supergravity - gauge theory duality in the description of
D-brane interactions.Comment: 18 pages, latex, comments/reference adde
Patterns of use of recombinant zoster vaccine among commercially-insured immunocompetent and immunocompromised adults 50–64 years old in the United States
Purpose: The Centers for Disease Control and Prevention (CDC) recommends recombinant zoster vaccination (RZV) for adults ≥ 50 years to prevent herpes zoster (HZ) and its sequelae. Initially, no distinct recommendation was made for immunocompromised adults, who experience higher HZ rates and more severe outcomes. We characterized receipt of first RZV dose (initiation) and both doses (completion) over time, and the impact of immune function on RZV uptake among adults aged 50–64 years in the United States. Methods: We identified RZV claims from the IBM MarketScan database between 1/1/2018 and 12/31/2019. We characterized immunocompromised enrollees as having malignancy, HIV, solid organ transplant, primary immunosuppression, or medication-induced immunosuppression using inpatient, outpatient, and prescription claims in the 6 months prior to study start. We evaluated patterns of vaccine uptake by demographic and healthcare access characteristics and immune status. Results: The cumulative incidence of RZV initiation during the study period was 10.0%. Incidence increased with age and number of medical office visits, and was higher among women, urban residents, high-deductible insurance beneficiaries, and those who were immunocompromised compared to immunocompetent. Among immunocompromised adults, RZV initiation was highest among those with HIV and primary immunodeficiencies. Of those who initiated RZV, 89.5% received both doses. RZV completion was highest among those who received the first dose at a pharmacy. Most enrollees (88.6%) who completed RZV vaccination did so within the recommended dosing schedule. Conclusions: RZV uptake was low in the two years since the CDC recommendation, and differed by demographic, healthcare access, and clinical characteristics. Initiation rates were higher among immunocompromised adults compared to immunocompetent adults, despite no CDC recommendation for vaccination in these groups during the study period. The CDC has since recommended RZV for immunocompromised individuals, and our findings may inform efforts to increase RZV uptake in individuals at higher risk of severe disease
Quasars and their host galaxies
This review attempts to describe developments in the fields of quasar and
quasar host galaxies in the past five. In this time period, the Sloan and 2dF
quasar surveys have added several tens of thousands of quasars, with Sloan
quasars being found to z>6. Obscured, or partially obscured quasars have begun
to be found in significant numbers. Black hole mass estimates for quasars, and
our confidence in them, have improved significantly, allowing a start on
relating quasar properties such as radio jet power to fundamental parameters of
the quasar such as black hole mass and accretion rate. Quasar host galaxy
studies have allowed us to find and characterize the host galaxies of quasars
to z>2. Despite these developments, many questions remain unresolved, in
particular the origin of the close relationship between black hole mass and
galaxy bulge mass/velocity dispersion seen in local galaxies.Comment: Review article, to appear in Astrophysics Update
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