4,946 research outputs found
The Solar hep Process in Effective Field Theory
Using effective field theory, we calculate the S-factor for the hep process
in a totally parameter-free formulation. The transition operators are organized
according to chiral counting, and their matrix elements are evaluated using the
realistic nuclear wave functions obtained in the
correlated-hyperspherical-harmonics method. Terms of up to
next-to-next-to-next-to-leading order in heavy-baryon chiral perturbation
theory are considered. Fixing the only parameter in the theory by fitting the
tritium \beta-decay rate, we predict the hep S-factor with accuracy better than
\sim 20 %.Comment: 4 pages, Revtex. Minor revision has been mad
Parameter-Free Calculation of the Solar Proton Fusion Rate in Effective Field Theory
Spurred by the recent complete determination of the weak currents in
two-nucleon systems up to in heavy-baryon chiral perturbation
theory, we carry out a parameter-free calculation of the solar proton fusion
rate in an effective field theory that combines the merits of the standard
nuclear physics method and systematic chiral expansion. Using the tritium
beta-decay rate as an input to fix the only unknown parameter in the effective
Lagrangian, we can evaluate with drastically improved precision the ratio of
the two-body contribution to the well established one-body contribution; the
ratio is determined to be (0.86\pm 0.05) %. This result is essentially
independent of the cutoff parameter for a wide range of its variation (500 MeV
\le \Lambda \le 800 MeV), a feature that substantiates the consistency of the
calculation.Comment: 10 pages. The argument is considerably more sharpened with a reduced
error ba
The Possible z=0.83 Precursors of z=0 M* Early-type Cluster Galaxies
We examine the distribution of stellar masses of galaxies in MS 1054-03 and
RX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellar
mass estimates, from spectral energy distribution fitting, reproduce the
dynamical masses as measured from velocity dispersions and half-light radii
with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict
our sample of members to high stellar masses, > 1e11.1 Msun (M* in the
Schechter mass function for cluster galaxies), we find that the fraction of
early-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for the
Coma cluster, consistent with no evolution. Previous work with
luminosity-selected samples finds that the early-type fraction in rich clusters
declines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in the
early-type fraction from luminosity-selected samples must predominately occur
among sub-M* galaxies. As M* for field and group galaxies, especially
late-types, is below M* for clusters galaxies, infall could explain most of the
recent early-type fraction growth. Future surveys could determine the
morphological distributions of lower mass systems which will confirm or refute
this explanation.Comment: 5 pages in emulate ApJ format with three color figures. Accepted for
publication in ApJ Letters, v642n2. Updated to correct grammatical and
typographic errors found by the journa
Benchmark calculation of n-3H and p-3He scattering
The n-3H and p-3He elastic phase-shifts below the trinucleon disintegration
thresholds are calculated by solving the 4-nucleon problem with three different
realistic nucleon-nucleon interactions (the I-N3LO model by Entem and
Machleidt, the Argonne v18 potential model, and a low-k model derived from the
CD-Bonn potential). Three different methods -- Alt, Grassberger and Sandhas,
Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been used and their
respective results are compared. For both n-3H and p-3He we observe a rather
good agreement between the three different theoretical methods. We also compare
the theoretical predictions with the available experimental data, confirming
the large underprediction of the p-3He analyzing power.Comment: 18 pages, 9 figure
Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0
We examined the morphology-density relations for galaxy samples selected by
luminosity and by mass in each of five massive X-ray clusters from z=0.023 to
0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and
visual morphologies were obtained primarily from Hubble Space Telescope images.
Morphology-density relations (MDR) are derived in each cluster from a complete,
luminosity-selected sample of 452 galaxies with a magnitude limit M_V <
M^{*}_{V} + 1. The change in the early-type fraction with redshift matches
previous work for massive clusters of galaxies. We performed a similar
analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies
with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects,
the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and
encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the
mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar
to those in the luminosity-selected sample but show larger early-type
fractions. However, the trend with redshift in the fraction of elliptical and
S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the
mass- and luminosity-selected samples. The clear trend seen in the early-type
fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The
early-type galaxy fraction changes much less, and is consistent with being
constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 <
\Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than
> 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type
fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to
ApJ. Version updated to reflect published version, includes new references
and a correction to table
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
Side Effects of Human Drug Use: An Overview of the Consequences of Eels’ Exposure to Cocaine
The widespread use of drugs is a global problem which affects not only humans but also
the environment around them, as research is showing the presence of these substances in different
environmental matrices, like air, water, and soil. Above all, due to the remarkable pharmacological
properties of drugs, it is discovered that organisms accidentally exposed to them, as aquatic organisms,
undergo behavioral and physiological changes that can compromise their health, survival, and
reproduction ability. In addition to this, we must consider the ability of some drugs to accumulate
within these organisms, thus entering the food chain, and the possible interactions that drugs in water
can establish with each other and with other possible pollutants, making the final effects on exposed
organisms unpredictable. This article is an overview of the effects of one of these drugs, cocaine, one
of the drugs commonly found in the aquatic environment, on European eel, an endangered species
and known biomonitor of aquatic contaminatio
Total 4He Photoabsorption Cross Section Revisited: Correlated HH versus Effective Interaction HH
Two conceptually different hyperspherical harmonics expansions are used for
the calculation of the total 4He photoabsorption cross section. Besides the
well known method of CHH the recently introduced effective interaction approach
for the hyperspherical formalism is applied. Semi-realistic NN potentials are
employed and final state interaction is fully taken into account via the
Lorentz integral transform method. The results show that the effective
interaction leads to a very good convergence, while the correlation method
exhibits a less rapid convergence in the giant dipole resonance region. The
rather strong discrepancy with the experimental photodisintegration cross
sections is confirmed by the present calculations.Comment: LaTeX, 7 pages, 3 ps figure
Proton-He elastic scattering at low energies
We present new accurate measurements of the differential cross section
and the proton analyzing power for proton-He
elastic scattering at various energies. A supersonic gas jet target has been
employed to obtain these low energy cross section measurements. The
distributions have been measured at = 0.99, 1.59,
2.24, 3.11, and 4.02 MeV. Full angular distributions of have been
measured at = 1.60, 2.25, 3.13, and 4.05 MeV. This set of
high-precision data is compared to four-body variational calculations employing
realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the
unpolarized cross section the agreement between the theoretical calculation and
data is good when a potential is used. The comparison between the
calculated and measured proton analyzing powers reveals discrepancies of
approximately 50% at the maximum of each distribution. This is analogous to the
existing `` Puzzle'' known for the past 20 years in nucleon-deuteron
elastic scattering.Comment: 22 pages, 9 figures, to be published in Physical Review C, corrected
reference 4
Beginning of the End of Cost Competitiveness in CEE Countries - Analysis of Dependence between Labor Costs and Internationalization of the Region
In order to exemplify the above econometric model I carried out empirical analysis of the companies listed on the Warsaw Stock Exchange, identifying the companies for which efficiency-seeking is the main internationalization motive. The analysis of internationalization of 26 companies during the years 1990-2010 clearly shows that a significant part of investments is located outside the territory of Poland, in the countries with lower labor costs. This fact confirms that CEE countries will gradually become less and less attractive in terms of costs not only for MNEs from developed countries but also for the companies originating from transition economies.Głównym celem artykułu jest weryfikacja, czy niski poziom kosztów pracy w Europie Środkowej i Wschodniej będący do tej pory jednym z czynników wpływających na konkurencyjność tego regionu pozostanie nim w dłuższej perspektywie czasowej. W pracy na podstawie próby wszystkich państw UE zbadano zależność pomiędzy poziomem internacjonalizacji (stan odpływu BIZ per capita) a kosztami pracy w sektorze przedsiębiorstw i GNP per capita. Analiza regresji potwierdziła istnienie zależności pomiędzy wyżej wymienionymi czynnikami. Oznacza to, że stopniowy wzrost kosztów pracy w państwach Europy Środkowej i Wschodniej prowadził będzie do stopniowego odpływu BIZ z tego regionu do państw bardziej konkurencyjnych kosztowo. W celu egzemplifikacji powyższych zależności w pracy dodatkowo przedstawiono analizę inwestycji zagranicznych polskich spółek notowanych na GPW, z których to 26 dokonało inwwestycji zagranicznych o wyraźnych motywach związanych z obniżeniem kosztów produkcji. Fakt ten potwierdza powolny spadek konkurencyjności kosztowej polskiej gospodarki, tym samym zmusza do poszukiwania nowych rozwiązań instytucjonalnych mogących utrzymać konkurencyjność polskiej gospodarki w długim okresie
- …