2,371 research outputs found
How Well Do We Know the Beta-Decay of 16N and Oxygen Formation in Helium Burning
We review the status of the 12C(a,g)16O reaction rate, of importance for
stellar processes in a progenitor star prior to a super-nova collapse. Several
attempts to constrain the p-wave S-factor of the 12C(a,g)16O reaction at Helium
burning temperatures (200 MK) using the beta-delayed alpha-particle emission of
16N have been made, and it is claimed that this S-factor is known, as quoted by
the TRIUMF collaboration. In contrast reanalyses (by G.M. hale) of all thus far
available data (including the 16N data) does not rule out a small S-factor
solution. Furthermore, we improved our previous Yale-UConn study of the beta-
delayed alpha-particle emission of \n16 by improving our statistical sample (by
more than a factor of 5), improving the energy resolution of the experiment (by
20%), and in understanding our line shape, deduced from measured quantities.
Our newly measured spectrum of the beta-delayed alpha-particle emission of 16N
is not consistent with the TRIUMF('94) data, but is consistent with the
Seattle('95) data, as well as the earlier (unaltered !) data of Mainz('71). The
implication of this discrepancies for the extracted astrophysical p-wave
s-factor is briefly discussed.Comment: 6 pages, 4 figures, Invited Talk, Physics With Radioactive Beams,
Puri, India, Jan. 12-17, 1998, Work Supported by USDOE Grant No.
DE-FG02-94ER4087
The Study on Cracking Strength of AIJs to Release the Early-Age Stress of Mass Concrete
This paper aims to theoretically and numerically assess the effect of setting artificial-induced joints (AIJs) during construction period of amass concrete structure to release the early-stage thermal stress. With respect to the coupling influences of various factors such as size and boundary of AIJs, an analytical model for its cracking strength on the setting section of mass concrete is proposed based on double-parameter fracture theory. A kind of hyper-finite element analysis (FEA) for many array AIJs in simplified plane pate is also presented by using bilinear cohesive force distribution. The results from the present model and numerical simulation were compared to those of experimental data to prove the efficiency and accuracy of the analytical model and FEA. The model presented in this study for the cracking strength of AIJs provides a simple useful tool to accurately evaluate how many early stress AIJs reduced. The theoretical solution and FEA results could also be significantly contributed to find the "just" and "perfect" release of the temperature stress and to improve the design level of AIJs in mass concrete structure
Influence of steps on the tilting and adsorption dynamics of ordered Pn films on vicinal Ag(111) surfaces
Here we present a structural study of pentacene (Pn) thin films on vicinal
Ag(111) surfaces by He atom diffraction measurements and density functional
theory (DFT) calculations supplemented with van der Waals (vdW) interactions.
Our He atom diffraction results suggest initial adsorption at the step edges
evidenced by initial slow specular reflection intensity decay rate as a
function of Pn deposition time. In parallel with the experimental findings, our
DFT+vdW calculations predict the step edges as the most stable adsorption site
on the surface. An isolated molecule adsorbs as tilted on the step edge with a
binding energy of 1.4 eV. In addition, a complete monolayer (ML) with
pentacenes flat on the terraces and tilted only at the step edges is found to
be more stable than one with all lying flat or tilted molecules, which in turn
influences multilayers. Hence our results suggest that step edges can trap Pn
molecules and act as nucleation sites for the growth of ordered thin films with
a crystal structure similar to that of bulk Pn.Comment: 4 pages, 4 figures, 1 tabl
Identification of new transitions and mass assignments of levels in Pr
The previously reported levels assigned to 151,152,153Pr have recently been
called into question regarding their mass assignment. The above questioned
level assignments are clarified by measuring g-transitions tagged with A and Z
in an in-beam experiment in addition to the measurements from 252Cf spontaneous
fission (SF) and establish new spectroscopic information from to
in the Pr isotopic chain. The isotopic chain 143-153Pr has been studied from
the spontaneous fission of 252Cf by using Gammasphere and also from the
measurement of the prompt g-rays in coincidence with isotopically-identified
fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced
using 238U beams on a 9Be target at energies around the Coulomb barrier. The
g-g-g-g data from 252Cf (SF) and those from the GANIL in-beam A- and Z-gated
spectra were combined to unambiguously assign the various transitions and
levels in 151,152,153Pr and other isotopes. New transitions and bands in
145,147,148,149,150Pr were identified by using g-g-g and g-g-g-g coincidences
and A and Z gated g-g spectra. The transitions and levels previously assigned
to 151,153Pr have been confirmed by the (A,Z) gated spectra. The transitions
previously assigned to 152Pr are now assigned to 151Pr on the basis of the
(A,Z) gated spectra. Two new bands with 20 new transitions in 152Pr and one new
band with 7 new transitions in 153Pr are identified from the g-g-g-g
coincidence spectra and the (A,Z) gated spectrum. In addition, new g-rays are
also reported in 143-146Pr. New levels of 145,147-153Pr have been established,
reliable mass assignments of the levels in 151,152,153Pr have been reported and
new transitions have been identified in 143-146Pr showing the new avenues that
are opened by combining the two experimental approaches.Comment: Accepted in Phys. Rev.
The historical vanishing of the Blazhko effect of RR Lyr from GEOS and Kepler surveys
RR Lyr is one of the most studied variable stars. Its light curve has been
regularly monitored since the discovery of the periodic variability in 1899.
Analysis of all observed maxima allows us to identify two primary pulsation
states defined as pulsation over a long (P0 longer than 0.56684 d) and a short
(P0 shorter than 0.56682 d) primary pulsation period. These states alternate
with intervals of 13-16 yr, and are well defined after 1943. The 40.8 d
periodical modulations of the amplitude and the period (i.e. Blazhko effect)
were noticed in 1916. We provide homogeneous determinations of the Blazhko
period in the different primary pulsation states. The Blazhko period does not
follow the variations of P0 and suddenly diminished from 40.8 d to around 39.0
d in 1975. The monitoring of these periodicities deserved and deserves a
continuous and intensive observational effort. For this purpose we have built
dedicated, transportable and autonomous small instruments, Very Tiny Telescopes
(VTTs), to observe the times of maximum brightness of RR Lyr. As immediate
results the VTTs recorded the last change of P0 state in mid-2009 and extended
the time coverage of the Kepler observations, thus recording a maximum O-C
amplitude of the Blazhko effect at the end of 2008, followed by the
historically smallest O-C amplitude in late 2013. This decrease is still
ongoing and VTT instruments are ready to monitor the expected increase in the
next few years.Comment: 10 pages, 6 figures. Accepted for publication in MNRAS. Contents of
appendix B may be requested to first autho
Probing UV-Sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in
surface layers of disks around young stars. In an effort to understand the
relationship between photocatalyzing UV radiation fields and gas emission
observed at infrared and sub-mm wavelengths, we present an analysis of new and
archival HST, Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus
cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to
measure LyA and FUV continuum fluxes reaching the disk surface, which are
responsible for dissociating relevant molecular species (e.g. HCN, N2).
Semi-forbidden C II] 2325 and UV-fluorescent H2 emission were also measured to
constrain inner disk populations of C+ and vibrationally excited H2. We find a
significant positive correlation between 14 micron HCN emission and fluxes from
the FUV continuum and C II] 2325, consistent with model predictions requiring
N2 photodissociation and carbon ionization to trigger the main CN/HCN formation
pathways. We also report significant negative correlations between sub-mm CN
emission and both C II] and FUV continuum fluxes, implying that CN is also more
readily dissociated in disks with stronger FUV irradiation. No clear
relationships are detected between either CN or HCN and LyA or UV-H2 emission.
This is attributed to the spatial stratification of the various molecular
species, which span several vertical layers and radii across the inner and
outer disk. We expect that future observations with JWST will build on this
work by enabling more sensitive IR surveys than were possible with Spitzer.Comment: Accepted for publication in A
TB STIGMA – MEASUREMENT GUIDANCE
TB is the most deadly infectious disease in the world, and stigma continues to play a significant role in worsening the epidemic. Stigma and discrimination not only stop people from seeking care but also make it more difficult for those on treatment to continue, both of which make the disease more difficult to treat in the long-term and mean those infected are more likely to transmit the disease to those around them. TB Stigma – Measurement Guidance is a manual to help generate enough information about stigma issues to design and monitor and evaluate efforts to reduce TB stigma. It can help in planning TB stigma baseline measurements and monitoring trends to capture the outcomes of TB stigma reduction efforts. This manual is designed for health workers, professional or management staff, people who advocate for those with TB, and all who need to understand and respond to TB stigma
Fluorescent Molecular Hydrogen Emission in IC 63: FUSE, HUT, and Rocket Observations
We present far-ultraviolet observations of IC 63, an emission/reflection
nebula illuminated by the B0.5IV star gamma Cassiopeia, located 1.3 pc from the
nebula. Molecular hydrogen fluorescence was detected first in IC 63 by IUE and
later at shorter wavelengths by ORFEUS. Here we present Far Ultraviolet
Spectroscopic Explorer (FUSE) observations towards three locations in the
nebula, complemented by Hopkins Ultraviolet Telescope (HUT) data on the central
nebular position. In addition, we present a sounding rocket calibration of a
FUSE spectrum of gamma Cas. Molecular hydrogen fluorescence is detected in all
three FUSE pointings. The intensity of this emission as well as the
contributions from other species are seen to vary with position. The absolute
flux calibration of the sounding rocket data allows us to reliably predict the
radiation field incident on IC 63. We use these data to test models of the
fluorescent process. Our modeling resolves the perceived discrepancy between
the existing ultraviolet observations and achieves a satisfactory agreement
with the H_2 rotational structure observed with FUSE.Comment: 7 pages, 6 figures, using emulateapj. Accepted by Ap
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