9,769 research outputs found
The pentaquark in K-plus-d total cross section data
An analysis of -d total cross section data is undertaken to explore
possible effects of the recently observed resonance in the S=+1 hadronic system
with mass around 1.55 GeV. It is found that a structure corresponding to the
resonance is visible in the data. The width consistent with the observed
deviation from background is found to be MeV and the mass is
GeV/c for spin-parity \h^+ and \
GeV/c for \h^-. The errors are one standard deviation and statistical
only.
\Comment: 10 pages, 5 figures Replaced to correct references, add and correct
text. No change in content. More discussion of errors, increased error on
width, corrected one figur
QCD--Instanton Induced Final States in Deep Inelastic Scattering
We report briefly on a broad and systematic study of possible manifestations
of QCD-instantons at HERA. We concentrate on the high multiplicity final state
structure, reminiscent of an isotropically decaying ``fireball''. First results
of a Monte Carlo simulation are presented, with emphasis on the typical
event-structure and the transverse energy, muon and flows.Comment: 10 pages, latex, epsfig, 9 uuencoded figure
Pion double charge exchange on 4He
The doubly differential cross sections for the He
reaction were calculated using both a two-nucleon sequential single charge
exchange model and an intranuclear cascade code. Final state interactions
between the two final protons which were the initial neutrons were included in
both methods. At incident pion energies of 240 and 270 MeV the low-energy peak
observed experimentally in the energy spectrum of the final pions can be
understood only if the contribution of pion production is included. The
calculated cross sections are compared with data.Comment: 25 pages, 9 figure
Grand potential in thermodynamics of solid bodies and surfaces
Using the chemical potential of a solid in a dissolved state or the
corresponding component of the chemical potential tensor at equilibrium with
the solution, a new concept of grand thermodynamic potential for solids has
been suggested. This allows generalizing the definition of Gibbs' quantity
(surface work often called the solid-fluid interfacial free energy) at
a planar surface as an excess grand thermodynamic potential per unit surface
area that (1) does not depend on the dividing surface location and (2) is
common for fluids and solids.Comment: 6 page
New biostratigraphic, magnetostratigraphic and isotopic insights into the Middle Eocene Climatic Optimum in low latitudes
The Middle Eocene Climatic Optimum (MECO) was a warming event that interrupted the long-term Eocene cooling trend. While this event is well documented at high southern and mid-latitudes, it is poorly known from low latitudes and its timing and duration are not well constrained because of problems of hiati, microfossil preservation and weak magnetic polarity in key sedimentary sections. Here, we report the results of a study designed to improve the bio-, magneto- and chemostratigraphy of the MECO interval using high-resolution records from two low-latitude sections in the Atlantic Ocean, Ocean Drilling Program (ODP) Sites 1051 and 1260. We present the first detailed benthic foraminiferal stable isotope records of the MECO from the low latitudes as well as the biostratigraphic counts of Orbulinoides beckmanni and new magnetostratigraphic results. Our data demonstrate a ~ 750 kyr-long duration for the MECO characterized by increasing δ13C and decreasing δ18O, with minimum δ18O values lasting ~ 40 kyr at 40.1 Ma coincident with a short-lived negative δ13C excursion. Thereafter, δ18O and δ13C values recover rapidly. The shift to minimum δ18O values at 40.1 Ma is coincident with a marked increase in the abundance of the planktonic foraminifera O. beckmanni, consistent with its inferred warm-water preference. O. beckmanni is an important Eocene biostratigraphic marker, defining planktonic foraminiferal Zone E12 with its lowest and highest occurrences (LO and HOs). Our new records reveal that the LO of O. beckmanni is distinctly diachronous, appearing ~ 500 kyr earlier in the equatorial Atlantic than in the subtropics (40.5 versus 41.0 Ma). We also show that, at both sites, the HO of O. beckmanni at 39.5 Ma is younger than the published calibrations, increasing the duration of Zone E12 by at least 400 kyr. In accordance with the tropical origins of O. beckmanni, this range expansion to higher latitudes may have occurred in response to sea surface warming during the MECO and subsequently disappeared with cooling of surface waters
Instantons in the QCD Vacuum and in Deep Inelastic Scattering
We give a brief status report on our on-going investigation of the prospects
to discover QCD instantons in deep inelastic scattering (DIS) at HERA. A recent
high-quality lattice study of the topological structure of the QCD vacuum is
exploited to provide crucial support of our predictions for DIS, based on
instanton perturbation theory.Comment: 6 pages, 5 figures, talk presented at the 7th International Workshop
on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen/Germany, April 19-23,
1999; to be published in the Proceedings (Nuclear Physics B (Proc. Suppl.)
Symbiont 'bleaching' in planktic foraminifera during the Middle Eocene Climatic Optimum
Many genera of modern planktic foraminifera are adapted to nutrient-poor (oligotrophic) surface waters by hosting photosynthetic symbionts, but it is unknown how they will respond to future changes in ocean temperature and acidity. Here we show that ca. 40 Ma, some fossil photosymbiont-bearing planktic foraminifera were temporarily 'bleached' of their symbionts coincident with transient global warming during the Middle Eocene Climatic Optimum (MECO). At Ocean Drilling Program (ODP) Sites 748 and 1051 (Southern Ocean and mid-latitude North Atlantic, respectively), the typically positive relationship between the size of photosymbiont-bearing planktic foraminifer tests and their carbon isotope ratios (δ13C) was temporarily reduced for ∼100 k.y. during the peak of the MECO. At the same time, the typically photosymbiont-bearing planktic foraminifera Acarinina suffered transient reductions in test size and relative abundance, indicating ecological stress. The coincidence of minimum δ18O values and reduction in test size–δ13C gradients suggests a link between increased sea-surface temperatures and bleaching during the MECO, although changes in pH and nutrient availability may also have played a role. Our findings show that host-photosymbiont interactions are not constant through geological time, with implications for both the evolution of trophic strategies in marine plankton and the reliability of geochemical proxy records generated from symbiont-bearing planktic foraminifera
Generalized entropy arising from a distribution of q-indices
It is by now well known that the Boltzmann-Gibbs (BG) entropy
can be usefully generalized into the
entropy (). Microscopic dynamics determines, given classes of initial
conditions, the occupation of the accessible phase space (or of a
symmetry-determined nonzero-measure part of it), which in turn appears to
determine the entropic form to be used. This occupation might be a uniform one
(the usual {\it equal probability hypothesis} of BG statistical mechanics),
which corresponds to ; it might be a free-scale occupancy, which appears
to correspond to . Since occupancies of phase space more complex than
these are surely possible in both natural and artificial systems, the task of
further generalizing the entropy appears as a desirable one, and has in fact
been already undertaken in the literature. To illustrate the approach, we
introduce here a quite general entropy based on a distribution of -indices
thus generalizing . We establish some general mathematical properties for
the new entropic functional and explore some examples. We also exhibit a
procedure for finding, given any entropic functional, the -indices
distribution that produces it. Finally, on the road to establishing a quite
general statistical mechanics, we briefly address possible generalized
constraints under which the present entropy could be extremized, in order to
produce canonical-ensemble-like stationary-state distributions for Hamiltonian
systems.Comment: 14 pages including 3 figure
A content validity approach to creating an end-user computer skill assessment tool
Practical assessment instruments are commonly used in the workplace and educational environments to assess a person's level of digital literacy and end-user computer skill. However, it is often difficult to find statistical evidence of the actual validity of instruments being used. To ensure that the correct factors are being assessed for a particular purpose it is necessary to undertake some type of psychometric testing, and the first step is to study the content relevance of the measure. The purpose of this paper is to report on the rigorous judgment quantification process using panels of experts in order to establish inter-rater reliability and agreement in the development of end-user instruments developed to measure workplace skills using spreadsheet and word-processing applications
Are workplace end-user computing skills at a desirable level? A New Zealand perspective
End-user computing is part of many occupations. The most requested end-user computing skills are experience with word-processing and spreadsheet applications. Often an employee’s skill level may not be
good enough to be deemed effective. Frequently this occurs because employers expect that employees will have the requisite skill level without formally assessing this. This paper presents a study involving the
testing of people who, in their jobs, use word-processing and spreadsheet software. Two instruments were created to assess skill in common work place computing tasks. The results showed that the majority of
participants could only manage very basic spreadsheet tasks, even though the use of spreadsheets was part of their employment. Results for word-processing skill was more positive, with most participants
completing all of the basic and some moderately advanced tasks. These results confirm that end-user computer skill, while required, is not at a level that could be deemed proficient
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