4,727 research outputs found
A geometric basis for the standard-model gauge group
A geometric approach to the standard model in terms of the Clifford algebra
Cl_7 is advanced. A key feature of the model is its use of an algebraic spinor
for one generation of leptons and quarks. Spinor transformations separate into
left-sided ("exterior") and right-sided ("interior") types. By definition,
Poincare transformations are exterior ones. We consider all rotations in the
seven-dimensional space that (1) conserve the spacetime components of the
particle and antiparticle currents and (2) do not couple the right-chiral
neutrino. These rotations comprise additional exterior transformations that
commute with the Poincare group and form the group SU(2)_L, interior ones that
constitute SU(3)_C, and a unique group of coupled double-sided rotations with
U(1)_Y symmetry. The spinor mediates a physical coupling of Poincare and
isotopic symmetries within the restrictions of the Coleman--Mandula theorem.
The four extra spacelike dimensions in the model form a basis for the Higgs
isodoublet field, whose symmetry requires the chirality of SU(2). The charge
assignments of both the fundamental fermions and the Higgs boson are produced
exactly.Comment: 17 pages, LaTeX requires iopart. Accepted for publication in J. Phys.
A: Math. Gen. 9 Mar 2001. Typos correcte
On the Change in Archivability of Websites Over Time
As web technologies evolve, web archivists work to keep up so that our
digital history is preserved. Recent advances in web technologies have
introduced client-side executed scripts that load data without a referential
identifier or that require user interaction (e.g., content loading when the
page has scrolled). These advances have made automating methods for capturing
web pages more difficult. Because of the evolving schemes of publishing web
pages along with the progressive capability of web preservation tools, the
archivability of pages on the web has varied over time. In this paper we show
that the archivability of a web page can be deduced from the type of page being
archived, which aligns with that page's accessibility in respect to dynamic
content. We show concrete examples of when these technologies were introduced
by referencing mementos of pages that have persisted through a long evolution
of available technologies. Identifying these reasons for the inability of these
web pages to be archived in the past in respect to accessibility serves as a
guide for ensuring that content that has longevity is published using good
practice methods that make it available for preservation.Comment: 12 pages, 8 figures, Theory and Practice of Digital Libraries (TPDL)
2013, Valletta, Malt
Anthropogenic lead isotopes in Antarctica
We report the first measurements of Pb isotopes in Antarctic snow, which show that even recent snow containing 2.3 pg/g is highly polluted with anthropogenic Pb. This follows from a comparison of isotope abundances of Pb in surface snow and terrestrial dust extracted from ancient Antarctic ice (Dome C, depth 308 m, approximate age 7,500 a BP), the latter being distinctly more radiogenic. This result is independent of geochemical arguments based on measurements of Al, Na and SO_4. South America is suggested as a likely source of this anthropogenic Pb. The presence of significantly less radiogenic Pb in the snow adjacent to two Antarctic base stations indicates that there is contamination from station emissions, although emission from Australia is an alternative explanation for a site 33 km from Dumont d'Urville
Clustering of Primordial Black Holes. II. Evolution of Bound Systems
Primordial Black Holes (PBHs) that form from the collapse of density
perturbations are more clustered than the underlying density field. In a
previous paper, we showed the constraints that this has on the prospects of PBH
dark matter. In this paper we examine another consequence of this clustering:
the formation of bound systems of PBHs in the early universe. These would
hypothetically be the earliest gravitationally collapsed structures, forming
when the universe is still radiation dominated. Depending upon the size and
occupation of the clusters, PBH merging occurs before they would have otherwise
evaporated due to Hawking evaporation.Comment: 23 pages, 1 figure. Submitted to PR
Final Report of the Phase III Archaeological Investigations at the Dr. Upton Scott House (18AP18), Annapolis, Anne Arundel County, Maryland, 1998-1999
In the summers of 1998 and 1999, the Archaeology in Annapolis project carried out archaeological investigation at the eighteenth century Dr. Upton Scott House site (18AP18)located at 4 Shipwright Street in the historic district of Annapolis, Anne Arundel County, Maryland. The Upton Scott House is significant as one of only a few Georgian houses with remnants of its original plantation-inspired landscape still visible (Graham 1998:147). Investigation was completed in agreement with the owners of the historic property, Mr. and Mrs. Paul Christian, who were interested in determining the condition and arrangement of Dr. Upton Scott’s well-documented pleasure gardens. Betty Cosans’ 1972 Archaeological Feasibility Report, the first real archaeological study of the Upton Scott House site, guided the research design and recovery efforts. Cosans determined that testing and survey in the back and side yards of the Scott property would yield important information on the use and history of the property, including that of Scott’s famous gardens. Excavation units and trenches were placed within three separate areas of backyard activity on the site which included Area One: extant brick stables in the southwest of the property; Area Two: the brick foundations of a small outbuilding located in the northwest area of the site; and Area Three: the area of Scott’s formal gardens. The research design included an interest in recovering evidence of African-American spiritual practice and domestic life at the site. Also of significant importance was an analysis of Scott’s garden beds, concerning the order and layout. Also sought was an understanding of the change in perception and use of the backyard by the various owners of the property
A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint Galaxies
Spitzer/IRAC imaging has revealed that the brightest galaxies
often exhibit young ages and strong nebular line emission, hinting at high
ionizing efficiency among early galaxies. However, IRAC's limited sensitivity
has long hindered efforts to study the fainter, more numerous population often
thought largely responsible for reionization. Here we use CEERS JWST/NIRCam
data to characterize 116 UV-faint (median M)
galaxies. The SEDs are typically dominated by young (10-50 Myr), low-mass
() stellar populations, and we find no need for
extremely high stellar masses (). Considering previous
studies of UV-bright (M) galaxies, we find evidence
for a strong (5-10) increase in specific star formation rate toward
lower luminosities (median sSFR=103 Gyr in CEERS). The larger sSFRs
imply a more dominant contribution from OB stars in the relatively numerous
UV-faint population, perhaps suggesting that these galaxies are very efficient
ionizing agents (median erg Hz). In spite of their
much larger sSFRs, we find no significant increase in [OIII]H EWs
towards fainter M (median 780 ). If confirmed,
this may indicate that a substantial fraction of our CEERS galaxies possess
extremely low metallicities (3% ) where [OIII] emission is
suppressed. Alternatively, high ionizing photon escape fractions or bursty star
formation histories can also weaken the nebular lines in a subset of our CEERS
galaxies. While the majority of our objects are very blue (median
), we identify a significant tail of very dusty galaxies
() at 0.5 which may contribute significantly
to the star formation rate density.Comment: Accepted in MNRAS. Updated to use the most recent NIRCam zeropoints.
There are no significant changes to the conclusions relative to v
dictyBase update 2011: web 2.0 functionality and the initial steps towards a genome portal for the Amoebozoa
dictyBase (http://www.dictybase.org), the model organism database for Dictyostelium, aims to provide the broad biomedical research community with well integrated, high quality data and tools for Dictyostelium discoideum and related species. dictyBase houses the complete genome sequence, ESTs, and the entire body of literature relevant to Dictyostelium. This information is curated to provide accurate gene models and functional annotations, with the goal of fully annotating the genome to provide a ‘reference genome’ in the Amoebozoa clade. We highlight several new features in the present update: (i) new annotations; (ii) improved interface with web 2.0 functionality; (iii) the initial steps towards a genome portal for the Amoebozoa; (iv) ortholog display; and (v) the complete integration of the Dicty Stock Center with dictyBase
Kelvin mode of a vortex in a nonuniform Bose-Einstein condensate
In a uniform fluid, a quantized vortex line with circulation h/M can support
long-wavelength helical traveling waves proportional to e^{i(kz-\omega_k t)}
with the well-known Kelvin dispersion relation \omega_k \approx (\hbar k^2/2M)
\ln(1/|k|\xi), where \xi is the vortex-core radius. This result is extended to
include the effect of a nonuniform harmonic trap potential, using a quantum
generalization of the Biot-Savart law that determines the local velocity V of
each element of the vortex line. The normal-mode eigenfunctions form an
orthogonal Sturm-Liouville set. Although the line's curvature dominates the
dynamics, the transverse and axial trapping potential also affect the normal
modes of a straight vortex on the symmetry axis of an axisymmetric Thomas-Fermi
condensate. The leading effect of the nonuniform condensate density is to
increase the amplitude along the axis away from the trap center. Near the ends,
however, a boundary layer forms to satisfy the natural Sturm-Liouville boundary
conditions. For a given applied frequency, the next-order correction
renormalizes the local wavenumber k(z) upward near the trap center, and k(z)
then increases still more toward the ends.Comment: 9 pages, 1 figur
Describing interruptions, multi-tasking and task-switching in the community pharmacy: A qualitative study in England
Background: There is growing evidence base around interruptions and distractions in the community pharmacy setting. There is also evidence to suggest these practices may be associated with dispensing errors. Up to date, qualitative research on this subject is limited.
Objective: To explore interruptions and distractions in the community setting; utilising an ethnographic approach to be able to provide a detailed description of the circumstances surrounding such practices.
Setting: Community pharmacies in England, July to October 2011.
Method: An ethnographic approach was taken. Non participant, unstructured observations were utilised to make records of pharmacists’ every activities. Case studies were formed by combining field notes with detailed information on pharmacists and their respective pharmacy businesses. Content analysis was undertaken both manually and electronically, utilising NVivo 10.
Results: Response rate was 12% (n=11). Over fifteen days, a total of 123 hours and 58 minutes of observations were recorded in 11 separate pharmacies of 11 individual pharmacists. The sample was evenly split by gender (female n=6; male n=5) and pharmacy ownership (independent n=5; multiple n=6). Employment statuses included employee pharmacists (n=6), owners (n=4) and a locum (n=1). Average period of registration as a pharmacist was 19 years (range 5-39 years). Average prescriptions busyness of pharmacies ranged from 2,600 – 24,000 items dispensed per month. Two key themes were: “Interruptions and task-switching” and “distractions and multi-tasking.” All observed pharmacists’ work was dominated by interruptions, task-switches, distractions and multi-tasking, often to manage a barrage of conflicting demands. These practices were observed to be part of a deep-rooted culture in the community setting. Directional work maps illustrated the extent and direction of task switching employed by pharmacists.
Conclusions: In this study pharmacists’ working practices were permeated by interruptions and multi-tasking. These practices are inefficient and potentially reduce patient safety in terms of dispensing accuracy
Primordial Black Hole Minimum Mass
In this paper we revisit thermodynamic constraints on primordial black hole
(PBH) formation in the early universe. Under the assumption that PBH mass is
equal to the cosmological horizon mass, one can use the 2nd Law of
Thermodynamics to put a lower limit on the PBH mass. In models of PBH
formation, however, PBHs are created at some fraction of the horizon mass. We
show that this thermodynamic constraint still holds for sub-horizon PBH
formation.Comment: 9 pages, no figures, replaced with version published in PR
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