12,315 research outputs found
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
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
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
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
The Masers Towards IRAS 20126+4104
We present MERLIN observations of OH, water and methanol masers towards the
young high mass stellar object IRAS 20126+4104. Emission from the 1665-MHz OH,
22-GHz H_2O and 6.7-GHz CH_3OH masers is detected and all originates very close
to the central source. The OH and methanol masers appear to trace part of the
circumstellar disk around the central source. The positions and velocities of
the OH and methanol masers are consistent with Keplerian rotation around a
central mass of ~ 5 Msun. The water masers are offset from the OH and methanol
masers and have significantly changed since they were last observed, but still
appear to be associated to the outflow from the source. All the OH masers
components are circularly polarised, in some cases reaching 100 percent while
some OH components also have linear polarisation. We identify one Zeeman pair
of OH masers and the splitting of this pair indicates a magnetic field of
strength ~ 11 mG within ~ 0.5" (850 AU) of the central source. The OH and
methanol maser emission suggest that the disk material is dense, n > 10^6
cm^-3, and warm, T > 125 K and the high abundance of methanol required by the
maser emission is consistent with the evaporation of the mantles on dust grains
in the disk as a result of heating or shocking of the disk materialComment: 9 pages, 7 figures and 6 table
Applications of Skylab EREP photographs to mapping landforms and environmental geomorphology in the Great Plains and Midwest
The following evaluations of Skylab photographs were undertaken: (1) the 1290 Skylab S190A and S190B photographs of Illinois, Iowa, Kansas, Missouri, Nebraska, and South Dakota were evaluated in detail in terms of coverage, cloud cover, photographic quality, endlap, detectability of roads and stereorelief, and utility for geomorphologic mapping, and (2) the utility of the Skylab photos were tested for interpretive analytic mapping of geomorphologic features over large areas representative of different parts of this region. Photointerpretative maps of analytic geomorphology were obtained for various test areas representative of the varied landscapes in the region. These maps are useful for regional land-use planning, ground-water exploration, and other environmental geomorphologic-geologic applications. Compared with LANDSAT-1 MSS images, Skylab photos afford almost as extensive overviews of large areas but in considerably greater detail, and for many SL photos, moderate stereorelief. However, repetitive multiseasonal, cloud-free coverage by high-quality photos is very limited and many areas have no coverage at all
Heartbeat stars and the ringing of tidal pulsations
With the advent of high precision photometry from satellites such as Kepler and CoRoT, a whole new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are an example of such objects. Heartbeat stars are eccen- tric ellipsoidal variables that undergo strong tidal interactions when the stars are almost in contact at the time of closest approach. These interactions deform of the stars and cause a notable light curve variation in the form of a tidal pulse. A subset of these objects (âŒ20%) show prominent tidally induced pulsations: pulsations forced by the binary orbit. We now have a fully functional code that models binary star features (using phoebe) and stellar pulsations simultaneously, enabling a complete and accurate heartbeat star model to be determined. In this paper we show the results of our new code, which uses emcee, a variant of mcmc, to generate a full set of stellar parameters. We further highlight the interesting features of KIC 8164262, including its tidally induced pulsations and resonantly locked pulsations
CHINESE CONSUMER DEMAND FOR ANIMAL PRODUCTS AND IMPLICATIONS FOR U.S. PORK AND POULTRY EXPORTS
This paper examines Chinese consumer preference for major animal products and assesses the potential impacts of a reduction in China's import tariff on its pork and poultry demand and net import. Our analysis suggests that China's demand for animal products will continue to grow as income increases. Using a trade model, results of our scenario analysis indicate that a reduction in China's import tariffs will significantly increase its net pork and poultry imports and the U.S. will capture most of the increases. Nevertheless, the impact on the market price in China and the U.S. is likely to be very small.Almost Ideal Demand System, China, Consumer demand, Demand elasticity, Food demand, Partial equilibrium model, Two-stage budgeting, U.S. meat export, Demand and Price Analysis, International Relations/Trade,
Women secondary head teachers in England: where are they now?
The underrepresentation of women in secondary school headship in England and elsewhere is an early and longstanding theme in the women and gender in educational leadership literature. The purpose of this article is to report findings from a statistical survey of secondary school head teachers across England. Data available in the public domain on school websites have been collated during a single academic year to present a new picture of where women lead secondary schools in England. Mapping the distribution of women by local authority continues to show considerable unevenness across the country. This article argues that a geographical perspective still has value. It might influence the mobilization of resources to targeted areas and ultimately result in womenâs proportionate representation in school leadership. Alongside this is a need for schools and academy trusts to comply with the Public Sector Equality Duty
Photonic band mixing in linear chains of optically coupled micro-spheres
The paper deals with optical excitations arising in a one-dimensional chain
of identical spheres due optical coupling of whispering gallery modes (WGM).
The band structure of these excitations depends significantly on the
inter-mixing between WGMs characterized by different values of angular quantum
number, . We develop a general theory of the photonic band structure of
these excitations taking these effects into account and applied it to several
cases of recent experimental interest. In the case of bands originating from
WQMs with the angular quantum number of the same parity, the calculated
dispersion laws are in good qualitative agreement with recent experiment
results. Bands resulting from hybridization of excitations resulting from
whispering gallery modes with different parity of exhibits anomalous
dispersion properties characterized by a gap in the allowed values of
\emph{wave numbers} and divergence of group velocity.Comment: RevTex, 28 pages, 7 Figure
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