565 research outputs found
Radiative proton-antiproton annihilation and isospin mixing in protonium
A detailed analysis of the radiative annihilation is made in the
framework of a two-step formalism, the annihilates into meson
channels containing a vector meson with a subsequent conversion into a photon
via the vector dominance model (VDM). Both steps are derived from the
underlying quark model. First, branching ratios for radiative protonium
annihilation are calculated and compared with data. Then, details of the
isospin interference are studied for different models of the initial protonium
state and also for different kinematical form factors. The isospin interference
is shown to be uniquely connected to the mixing in the
protonium state. Values of the interference terms directly deduced from data
are consistent with theoretical expectations, indicating a dominant
component for the and a sizable component for the
protonium state. The analysis is extended to the
transition, where the large observed branching ratio remains unexplained in the
VDM approach.Comment: 34 pages, RevTeX, 2 figures, to appear in Phys. Rev. C; typos
correcte
Potential methodological influences on the determination of particle retention efficiency by suspension feeders: Mytilus edulis and Ciona intestinalis
The retention efficiency (RE) of suspension-feeding bivalve molluscs depends on particle size and is generally assumed to decline below a maximum retention of particles larger than 3 to 7 µm. Previous suggestions that the RE spectrum of mussels Mytilus edulis can exhibit variability, possibly as a result of physiological regulation, have been attributed to artifacts associated with the indirect method. The possibility that variable physical properties of seston particles and/or miscalculations can result in inaccurate RE measurements was examined using 3 methodologies (static, flow-through and a new approach based on the static method) and 3 particle sources (natural seston, algal cell monocultures and clay). Measurements obtained with the static method varied depending on the selected sampling interval. However, this artifact can be removed using frequent sampling and a regression analysis approach. Accurate RE measurements can be obtained with the flow-through method when feeding behaviour is flow independent. For all particle suspensions and methods, mussels from the study site in Lysefjord, Norway, had a maximum RE for particles >8–11 µm (1 to 5 September 2015). The RE for smaller particles declined gradually, with 50–60% retention of 4 µm particles and 30–40% retention of 2 µm particles. Differences in the RE size spectra of mussels and tunicates Ciona intestinalis, collected and measured at the same site, further indicated that RE was not influenced by potentially confounding methodological factors. Assumptions regarding the RE spectrum of bivalves have contributed to many conclusions on their ecosystem interactions. The reliability of clearance rate measurements obtained using the indirect method can only be assured if the effective retention of tracer particles is confirmed and not assumed.publishedVersio
ASAS Light Curves of Intermediate Mass Eclipsing Binaries and the Parameters of HI Mon
We present a catalog of 56 candidate intermediate mass eclipsing binary
systems extracted from the 3rd data release of the All Sky Automated Survey. We
gather pertinent observational data and derive orbital properties, including
ephemerides, for these systems as a prelude to anticipated spectroscopic
observations. We find that 37 of the 56, or ~66% of the systems are not
identified in the Simbad Astronomical Database as known binaries. As a specific
example, we show spectroscopic data obtained for the system HI Mon (B0 V + B0.5
V) observed at key orbital phases based on the computed ephemeris, and we
present a combined spectroscopic and photometric solution for the system and
give stellar parameters for each component.Comment: 83 pages, 63 figure
Reanalysis of two eclipsing binaries: EE Aqr and Z Vul
We study the radial-velocity and light curves of the two eclipsing binaries
EE Aqr and Z Vul. Using the latest version of the Wilson & Van Hamme (2003)
model, absolute parameters for the systems are determined. We find that EE Aqr
and Z Vul are near-contact and semi-detached systems, respectively. The primary
component of EE Aqr fills about 96% of its 'Roche lobe', while its secondary
one appears close to completely filling this limiting volume. In a similar way,
we find fill-out proportions of about 72 and 100% of these volumes for the
primary and secondary components of Z Vul respectively. We compare our results
with those of previous authors.Comment: 13 pages, 8 figures, 10 table
Charge transfer dynamical processes at graphene-transition metal oxides/electrolyte interface for energy storage: Insights from in-situ Raman spectroelectrochemistry
Hybrids consisting of supercapacitive functionalized graphene (graphene oxide; GO reduced graphene oxide; rGO multilayer graphene; MLG, electrochemically reduced GO; ErGO) and three-dimensional graphene scaffold (rGO HT ; hydrothermally prepared) decorated with cobalt nanoparticles (CoNP), nanostructured cobalt (CoO and Co 3 O 4 ) and manganese (MnO 2 ) oxide polymorphs, assembled electrochemically facilitate chemically bridged interfaces with tunable properties. Since Raman spectroscopy can capture variations in structural and chemical bonding, Raman spectro-electrochemistry in operando i.e. under electrochemical environment with applied bias is employed to 1) probe graphene/metal bonding and dynamic processes, 2) monitor the spectral changes with successive redox interfacial reactions, and 3) quantify the associated parameters including type and fraction of charge transfer. The transverse optical (TO) and longitudinal optical (LO) phonons above 500 cm -1 belonging to Co 3 O 4 , CoO, MnO 2 and carbon-carbon bonding occurring at 1340 cm -1 , 1590 cm -1 and 2670 cm -1 belonging to D, G, and 2D bands, respectively, are analyzed with applied potential. Consistent variation in Raman band position and intensity ratio reveal structural modification, combined charge transfer due to localized orbital re-hybridization and mechanical strain, all resulting in finely tuned electronic properties. Moreover, the heterogeneous basal and edge plane sites of graphene nanosheets in conjunction with transition metal oxide \u27hybrids\u27 reinforce efficient surface/interfacial electron transfer and available electronic density of states near Fermi level for enhanced performance. We estimated the extent and nature (n- or p-) of charge transfer complemented with Density Functional Theory calculations affected by hydration and demonstrate the synergistic coupling between graphene nanosheets and nanoscale cobalt (and manganese) oxides for applied electrochemical applications
Broadband laser cooling of trapped atoms with ultrafast pulses
We demonstrate broadband laser cooling of atomic ions in an rf trap using
ultrafast pulses from a modelocked laser. The temperature of a single ion is
measured by observing the size of a time-averaged image of the ion in the known
harmonic trap potential. While the lowest observed temperature was only about 1
K, this method efficiently cools very hot atoms and can sufficiently localize
trapped atoms to produce near diffraction-limited atomic images
A Search for Hierarchical Triples using Kepler Eclipse Timing
We present the first results of a Kepler survey of 41 eclipsing binaries that
we undertook to search for third star companions. Such tertiaries will
periodically alter the eclipse timings through light travel time and dynamical
effects. We discuss the prevalence of starspots and pulsation among these
binaries and how these phenomena influence the eclipse times. There is no
evidence of short period companions (P < 700 d) among this sample, but we do
find evidence for long term timing variations in 14 targets (34%). We argue
that this finding is consistent with the presence of tertiary companions among
a significant fraction of the targets, especially if many have orbits measured
in decades. This result supports the idea that the formation of close binaries
involves the deposition of angular momentum into the orbital motion of a third
star.Comment: AJ, in press, 104 pages, 2 figure sets plus 1 regular figur
Radial Velocity Studies of Close Binary Stars.XIII
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: EG Cep,V1191
Cyg, V1003 Her, BD+7_3142, V357 Peg, V407 Peg, V1123 Tau, V1128 Tau, HH UMa,
and PY Vir. While most of the studied eclipsing systems are contact binaries,
EG Cep is a detached or a semi-detached double-lined binary and V1003 Her is a
close binary of an uncertain type seen at a very low inclination angle. We
discovered two previously unknown triple systems, BD+7_3142 and PY Vir, both
with late spectral-type (K2V) binaries. Of interest is the low-mass ratio (q =
0.106) close binary V1191 Cyg showing an extremely fast period increase; the
system has a very short period for its spectral type and shows a W-type light
curve, a feature rather unexpected for such a low mass-ratio system.Comment: Accepted by AJ. 19 pages including 5 figure
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