12,470 research outputs found
Baryon Number Transport in a Cosmic QCD-Phase Transition
We investigate the transport of baryon number across phase boundaries in a
putative first order QCD-phase transition. Two independent phenomenological
models are employed to estimate the baryon penetrability at the phase boundary:
chromoelectric flux tube models; and an analogy to baryon-baryon coalescence in
nuclear physics. Our analysis indicates that baryon transport across phase
boundaries may be order of magnitude more efficient than other work has
suggested. We discuss the substantial uncertainties involved in estimating
baryon penetrability at phase boundaries.Comment: 25 pages, 4 figures (available upon request by mail or fax), plain
tex, UCRL-JC-00000
Sterile Neutrino Hot, Warm, and Cold Dark Matter
We calculate the incoherent resonant and non-resonant scattering production
of sterile neutrinos in the early universe. We find ranges of sterile neutrino
masses, vacuum mixing angles, and initial lepton numbers which allow these
species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM)
candidates which meet observational constraints. The constraints considered
here include energy loss in core collapse supernovae, energy density limits at
big bang nucleosynthesis, and those stemming from sterile neutrino decay:
limits from observed cosmic microwave background anisotropies, diffuse
extragalactic background radiation, and Li-6/D overproduction. Our calculations
explicitly include matter effects, both effective mixing angle suppression and
enhancement (MSW resonance), as well as quantum damping. We for the first time
properly include all finite temperature effects, dilution resulting from the
annihilation or disappearance of relativistic degrees of freedom, and the
scattering-rate-enhancing effects of particle-antiparticle pairs (muons,
tauons, quarks) at high temperature in the early universe.Comment: 24 pages, including 8 figures. v3: to match version in PRD, added
references and numerous minor changes. High resolution color figures
available at http://superbeast.ucsd.edu/~kev/nucd
An evaluation of the utilization of remote sensing in resource and environmental management of the Chesapeake Bay region
A nine-month study was conducted to assess the effectiveness of the NASA Wallops Chesapeake Bay Ecological Program in remote sensing. The study consisted of a follow-up investigation and information analysis of actual cases in which remote sensing was utilized by management and research personnel in the Chesapeake Bay region. The study concludes that the NASA Wallops Chesapeake Bay Ecological Program is effective, both in terms of costs and performance
Absence of a Lower Limit on Omega_b in Inhomogeneous Primordial Nucleosynthesis
We show that a class of inhomogeneous big bang nucleosynthesis models exist
which yield light-element abundances in agreement with observational
constraints for baryon-to-photon ratios significantly smaller than those
inferred from standard homogeneous big bang nucleosynthesis (HBBN). These
inhomogeneous nucleosynthesis models are characterized by a bimodal
distribution of baryons in which some regions have a local baryon-to-photon
ratio eta=3*10e-10, while the remaining regions are baryon-depleted. HBBN
scenarios with primordial (2H+3He)/H<9*10e-5 necessarily require that most
baryons be in a dark or non-luminous form, although new observations of a
possible high deuterium abundance in Lyman-alpha clouds may relax this
requirement somewhat. The models described here present another way to relax
this requirement and can even eliminate any lower bound on the baryon-to-photon
ratio.Comment: 13 pages, 2 figures (available upon request by email), plain te
Presupernova collapse models with improved weak-interaction rates
Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.Comment: 4 pages, 2 figure
Evidence for an Intense Neutrino Flux during -Process Nucleosynthesis?
We investigate the possibility that neutrino capture on heavy nuclei competes
with beta decay in the environment where the -Process elements are
synthesized. We find that such neutrino capture is not excluded by existing
abundance determinations. We show that inclusion of significant neutrino
capture on the (neutron number) N=82 waiting point nuclei can allow the
inferred abundances of these species to provide a good fit to steady weak (beta
decay plus neutrino capture) flow equilibrium. In fact, for particular choices
of neutrino flux conditions, this fit is improved over the case where nuclei
change their charge by beta decay alone. However, this improved fit can be
realized only if neutrino capture plays a negligible role in nuclear decay back
toward stability. We discuss the implications of these considerations for
current proposed sites and models for -Process nucleosynthesis.Comment: 10 pages, plain tex, submitted to ApJ
The art of being human : a project for general philosophy of science
Throughout the medieval and modern periods, in various sacred and secular guises, the unification of all forms of knowledge under the rubric of âscienceâ has been taken as the prerogative of humanity as a species. However, as our sense of species privilege has been called increasingly into question, so too has the very salience of âhumanityâ and âscienceâ as general categories, let alone ones that might bear some essential relationship to each other. After showing how the ascendant Stanford School in the philosophy of science has contributed to this joint demystification of âhumanityâ and âscienceâ, I proceed on a more positive note to a conceptual framework for making sense of science as the art of being human. My understanding of âscienceâ is indebted to the red thread that runs from Christian theology through the Scientific Revolution and Enlightenment to the Humboldtian revival of the university as the site for the synthesis of knowledge as the culmination of self-development. Especially salient to this idea is scienceâs epistemic capacity to manage modality (i.e. to determine the conditions under which possibilities can be actualised) and its political capacity to organize humanity into projects of universal concern. However, the challenge facing such an ideal in the twentyfirst century is that the predicate âhumanâ may be projected in three quite distinct ways, governed by what I call âecologicalâ, âbiomedicalâ and âcyberneticâ interests. Which one of these future humanities would claim todayâs humans as proper ancestors and could these futures co-habit the same world thus become two important questions that general philosophy of science will need to address in the coming years
Enhanced Heavy-Element Formation in Baryon-Inhomogeneous Big-Bang Models
We show that primordial nucleosynthesis in baryon inhomogeneous big-bang
models can lead to significant heavy-element production while still satisfying
all the light-element abundance constraints including the low lithium abundance
observed in population II stars. The parameters which admit this solution arise
naturally from the process of neutrino induced inflation of baryon
inhomogeneities prior to the epoch of nucleosynthesis. These solutions entail a
small fraction of baryons (\le 2\%) in very high density regions with local
baryon-to-photon ratio , while most baryons are at a
baryon-to-photon ratio which optimizes the agreement with light-element
abundances. The model would imply a unique signature of baryon inhomogeneities
in the early universe, evidenced by the existence of primordial material
containing heavy-element products of proton and alpha- burning reactions with
an abundance of .Comment: 19 pages in plain Tex, 5 figures (not included) available by fax or
mail upon request, ApJ in press, L
Light Element Synthesis in High Entropy Relativistic Flows Associated with Gamma Ray Bursts
We calculate and discuss the light element freeze-out nucleosynthesis in high
entropy winds and fireballs for broad ranges of entropy-per-baryon, dynamic
timescales characterizing relativistic expansion, and neutron-to-proton ratios.
With conditions characteristic of Gamma Ray Bursts (GRBs) we find that
deuterium production can be prodigious, with final abundance values 2H/H
approximately 2%, depending on the fireball isospin, late time dynamics, and
the effects of neutron decoupling- induced high energy non-thermal nuclear
reactions. This implies that there potentially could be detectable local
enhancements in the deuterium abundance associated with GRB events.Comment: 14 pages 3 figure
Deer reduce habitat quality for a woodland songbird: evidence from settlement patterns, demographic parameters, and body condition.
Understanding avian responses to ungulate-induced habitat modification is important because deer populations are increasing across much of temperate Europe and North America. Our experimental study examined whether habitat quality for Blackcaps (Sylvia atricapilla) in young woodland in eastern England was affected by deer, by comparing Blackcap behavior, abundance, and condition between paired plots (half of each pair protected from deer). The vegetation in each pair of plots was the same age. The Blackcap is an ideal model species for testing effects of deer on avian habitat quality because it is dependent on dense understory vegetation and is abundant throughout much of Europe. We compared timing of settlement, abundance, age structure (second-year vs. after-second-year), and phenotypic quality (measured as a body condition index, body mass divided by tarsus length) between experimental and control plots. We used point counts to examine Blackcap distribution, and standardized mist netting to collect demographic and biometric data. Incidence of singing Blackcaps was higher in nonbrowsed than in browsed plots, and singing males were recorded in nonbrowsed plots earlier in the season, indicating earlier and preferential territory establishment. Most Blackcaps, both males and females, were captured in vegetation prior to canopy closure (2â4 years of regrowth). Body condition was superior for male Blackcaps captured in nonbrowsed plots; for second-year males this was most marked in vegetation prior to canopy closure. We conclude that deer browsing in young woodland can alter habitat quality for understory-dependent species, with potential consequences for individual fitness and population productivity beyond the more obvious effects on population density
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