519 research outputs found
Energy Storage and Delivery Systems -An Urgent Requirement for Aerospace Contingencies
A few months ago, a major disaster at sea startled the world. The U.S.S. \u27Thresher\u27 was lost with all hands, in waters which are among the best charted and best known in the whole world and a few miles only from the main base of operations
The role of individual and social variables in task performance.
This paper reports on a data-based study in which we explored - as part of a larger-scale British-Hungarian research project - the effects of a number of affective and social variables on foreign language (L2) learnersâ engagement in oral argumentative tasks. The assumption underlying the investigation was that studentsâ verbal behaviour in oral task situations is partly determined by a number of non-linguistic and non-cognitive factors whose examination may constitute a potentially fruitful extension of existing task-based research paradigms. The independent variables in the study included various aspects of L2 motivation and several factors characterizing the learner groups the participating students were members of (such as group cohesiveness and intermember relations), as well as the learnersâ L2 proficiency and âwillingness to communicateâ in their L1. The dependent variables involved objective measures of the studentsâ language output in two oral argumentative tasks (one in the learnersâ L1, the other in their L2): the quantity of speech and the number of turns produced by the speakers. The results provide insights into the interrelationship of the multiple variables determining the learnersâ task engagement, and suggest a multi-level construct whereby some independent variables only come into force when certain conditions have been met
Strange Decays of Nonstrange Baryons
The strong decays of excited nonstrange baryons into the final states Lambda
K, Sigma K, and for the first time into Lambda(1405) K, Lambda(1520) K,
Sigma(1385) K, Lambda K*, and Sigma K*, are examined in a relativized quark
pair creation model. The wave functions and parameters of the model are fixed
by previous calculations of N pi and N pi pi, etc., decays. Our results show
that it should be possible to discover several new negative parity excited
baryons and confirm the discovery of several others by analyzing these final
states in kaon production experiments. We also establish clear predictions for
the relative strengths of certain states to decay to Lambda(1405) K and
Lambda(1520) K, which can be tested to determine if a three-quark model of the
Lambda(1405) K is valid. Our results compare favorably with the results of
partial wave analyses of the limited existing data for the Lambda K and Sigma K
channels. We do not find large Sigma K decay amplitudes for a substantial group
of predicted and weakly established negative-parity states, in contrast to the
only previous work to consider decays of these states into the strange final
states Lambda K and Sigma K.Comment: 25 pages, 8 figures, RevTe
Zanamivir susceptibility monitoring and characterization of influenza virus clinical isolates obtained during phase II clinical efficacy studies
Zanamivir is a highly selective neuraminidase (NA) inhibitor with
demonstrated clinical efficacy against influenza A and B virus infections.
In phase II clinical efficacy trials (NAIB2005 and NAIB2008), virological
substudies showed mean reductions in virus shedding after 24 h of
treatment of 1.5 to 2.0 log(10) 50% tissue culture infective doses
compared to a placebo, with no reemergence of virus after the completion
of therapy. Paired isolates (n = 41) obtained before and during therapy
with zanamivir demonstrated no shifts in susceptibility to zanamivir when
measured by NA assays, although for a few isolates NA activity was too low
to evaluate. In plaque reduction assays in MDCK cells, the susceptibility
of isolates to zanamivir was extremely variable even at baseline and did
not correlate with the speed of resolution of virus shedding. Isolates
with apparent limited susceptibility to zanamivir by plaque reduction
proved highly susceptible in vivo in the ferret model. Further sequence
analysis of paired isolates revealed no changes in the hemagglutinin and
NA genes in the majority of isolates. The few changes observed were all
natural variants. No amino acid changes that had previously been
identified in vitro as being involved with reduced susceptibility to
zanamivir were observed. These studies highlighted problems associated
with monitoring susceptibility to NA inhibitors in the clinic, in that no
reliable cell-based assay is available. At present the NA assay is the
best available predictor of susceptibility to NA inhibitors in vivo, as
measured in the validated ferret model of infection
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
Search for CP Violation in the Decay Z -> b (b bar) g
About three million hadronic decays of the Z collected by ALEPH in the years
1991-1994 are used to search for anomalous CP violation beyond the Standard
Model in the decay Z -> b \bar{b} g. The study is performed by analyzing
angular correlations between the two quarks and the gluon in three-jet events
and by measuring the differential two-jet rate. No signal of CP violation is
found. For the combinations of anomalous CP violating couplings, and , limits of \hat{h}_b < 0.59h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st
Discriminatory optical force for chiral molecules
We suggest that the force F exerted upon a chiral molecule by light assumes the form F = aâw + bâh under appropriate circumstances, where a and b pertain to the molecule whilst w and h are the local densities of electric energy and helicity in the optical field; the gradients â of these quantities thus governing the moleculeâs centre-of-mass motion. Whereas a is identical for the mirror- image forms or enantiomers of the molecule, b has opposite signs; the associated contribution to F therefore pointing in opposite directions. A simple optical field is presented for which âw vanishes but âh does not, so that F is absolutely discriminatory. We then present two potential applications: a SternâGerlach-type deflector capable of spatially separating the enantiomers of a chiral molecule and a diffraction grating to which chiral molecules alone are sensitive; the resulting diffraction patterns thus encoding information about their chiral geometry
Comparison of Lambda and Sigma(0) Threshold Production in Proton-Proton Collisions
Threshold measurements of the associated strangeness production reactions pp
--> p K(+) Lambda and pp --> p K(+) Sigma(0) are presented. Although slight
differences in the shapes of the excitation functions are observed, the most
remarkable feature of the data is that at the same excess energy the total
cross section for the Sigma(0) production appears to be about a factor of 28
smaller than the one for the Lambda particle. It is concluded that strong
Sigma(0)-p final state interactions, and in particular the Sigma-N --> Lambda-p
conversion reaction, are the likely cause of the depletion for the yield in the
Sigma signal. This hypothesis is in line with other experimental evidence in
the literature.Comment: 13 pages, 3 figures, 1 tabl
Close-to-threshold Meson Production in Hadronic Interactions
Studies of meson production at threshold in the hadron--hadron interaction
began in the fifties when sufficient energies of accelerated protons were
available. A strong interdependence between developments in accelerator
physics, detector performance and theoretical understanding led to a unique
vivid field of physics. Early experiments performed with bubble chambers
revealed already typical ingredients of threshold studies, which were
superseded by more complete meson production investigations at the nucleon beam
facilities TRIUMF, LAMPF, PSI, LEAR and SATURNE. Currently, with the advent of
the new cooler rings as IUCF, CELSIUS and COSY the field is entering a new
domain of precision and the next step of further progress.
The analysis of this new data in the short range limit permits a more
fundamental consideration and a quantitative comparison of the production
processes for different mesons in the few--body final states. The
interpretation of the data take advantage of the fact that production reactions
close-to-threshold are characterized by only a few degrees of freedom between a
well defined combination of initial and exit channels. Deviations from
predictions of phase-space controlled one-meson-exchange models are indications
of new and exciting physics. Precision data on differential cross sections,
isospin and spin observables -- partly but by no means adequately available --
are presently turning up on the horizon. There is work for the next years and
excitement of the physics expected. Here we try to give a brief and at the same
time comprehensive overview of this field of hadronic threshold production
studies.Comment: 100 pages, Review article to be published in Prog. Part. Nucl. Phys.
Vol. 49, issue 1 (2002
- âŠ