667 research outputs found
Navigation/traffic control satellite mission study. Volume 2 - Systems analyses
Systems analysis of spacecraft network for transoceanic traffic contro
Bipartite Anterior Extraperitoneal Teratoma: Evidence for the Embryological Origins of Teratomas?
Teratomas are thought to arise from totipotent primordial germ cells (PGCs) Dehner (1983) which may miss their target destination Moore and Persaud (1984). Teratomas can occur anywhere from the brain to the coccygeal area but are usually in the midline close to the embryological position of the gonadal ridges Bale (1984), Nguyen and Laberge (2000). We report a case of a bipartite anterior extraperitoneal teratoma. This is an unusual position for a teratoma, but one which may support the âmissed targetâ theory of embryology
Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions
We derive a set of new formulas for various distributions in dilepton
production via virtual photon bremsstrahlung from pseudoscalar mesons and
unpolarized spin-one-half fermions. These formulas correspond to the leading
and sub-leading terms in the Low-Burnett-Kroll expansion for real photon
bremsstrahlung. The relation of our leading-term formulas to previous works is
also shown. Existing formulas are examined in the light of Lorentz covariance
and gauge invariance. Numerical comparison is made in a simple example, where
an "exact" formula and real photon data exist. The results reveal large
discrepancies among different bremsstrahlung formulas. Of all the leading-term
bremsstrahlung formulas, the one derived in this work agrees best with the
exact formula. The issues of M_T-scaling and event generators are also
addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure
Supporting family carers of older people in community pharmacy: a review of guidelines and qualitative study
Parton distribution functions from nonlocal light-cone operators with definite twist
We introduce the chiral-even and chiral-odd quark distributions as forward
matrix elements of related bilocal quark operators with well-defined
(geometric) twist. Thereby, we achieve a Lorentz invariant classification of
these distributions which differ from the conventional ones by explicitly
taking into account the necessary trace terms. The relations between both kinds
of distribution functions are given and the mismatch between their different
definition of twist is discussed. Wandzura-Wilczek--like relations between the
conventional distributions (based on dynamical twist) are derived by means of
geometric twist distribution functions.Comment: 17 pages, REVTEX, Extended version, The Introduction has been
rewritten, Setion V "Wandzura-Wilczek--like relations" and App. B are added;
Sign errors are correcte
Weak gauge principle and electric charge quantization
Starting from a weak gauge principle we give a new and critical revision of
the argument leading to charge quantization on arbitrary spacetimes. The main
differences of our approach with respect to previous works appear on spacetimes
with non trivial torsion elements on its second integral cohomology group. We
show that in these spacetimes there can be topologically non-trivial
configurations of charged fields which do not imply charge quantization.
However, the existence of a non-exact electromagnetic field always implies the
quantization of charges. Another consequence of the theory for spacetimes with
torsion is the fact that it gives rise to two natural quantization units that
could be identified with the electric quantization unit (realized inside the
quarks) and with the electron charge. In this framework the color charge can
have a topological origin, with the number of colors being related to the order
of the torsion subgroup. Finally, we discuss the possibility that the
quantization of charge may be due to a weak non-exact component of the
electromagnetic field extended over cosmological scales.Comment: Latex2e, 24 pages, no figure
Pion and Rho Structure Functions from Lattice QCD
We calculate the lower moments of the deep-inelastic structure functions of
the pion and the rho meson on the lattice. Of particular interest to us are the
spin-dependent structure functions of the rho. The calculations are done with
Wilson fermions and for three values of the quark mass, so that we can perform
an extrapolation to the chiral limit.Comment: 30pp, LaTeX2e with 15 eps figures using epsfig. Postscript file also
available from ftp://ftp.th.physik.uni-frankfurt.de/pub/cbest/pionrho.ps or
http://www.th.physik.uni-frankfurt.de/~cbest/pionrho.p
He Structure and Mechanisms of He Backward Elastic Scattering
The mechanism of He backward elastic scattering is studied.
It is found that the triangle diagrams with the subprocesses He,
He and He, where and
denote the singlet deuteron and diproton pair in the state,
respectively, dominate in the cross section at 0.3-0.8 GeV, and their
contribution is comparable with that for a sequential transfer of a pair
at 1-1.5 GeV.
The contribution of the , estimated on the basis of the spectator
mechanism of the He reaction, increases the HeHe cross section by one order of magnitude as compared to the
contribution of the deuteron alone.
Effects of the initial and final states interaction are taken into account.Comment: 17 pages, Latex, 4 postscript figures, expanded version, accepted by
Physical Review
âDo i care?â young adults' recalled experiences of early adolescent overweight and obesity: a qualitative study
<p>Objective:Â Individual behaviour change to reduce obesity requires awareness of, and concern about, weight. This paper therefore describes how young adults, known to have been overweight or obese during early adolescence, recalled early adolescent weight-related awareness and concerns. Associations between recalled concerns and weight-, health- and peer-related survey responses collected during adolescence are also examined.</p>
<p>Design:Â Qualitative semi-structured interviews with young adults; data compared with responses to self-report questionnaires obtained in adolescence.</p>
<p>Participants:Â A total of 35 participants, purposively sub-sampled at age 24 from a longitudinal study of a school year cohort, previously surveyed at ages 11, 13 and 15. Physical measures during previous surveys allowed identification of participants with a body mass index (BMI) indicative of overweight or obesity (based on British 1990 growth reference) during early adolescence. Overall, 26 had been obese, of whom 11 had BMI99.6th centile, whereas 9 had been overweight (BMI=95thâ97.9th centile).</p>
<p>Measures:Â Qualitative interview responses describing teenage life, with prompts for school-, social- and health-related concerns. Early adolescent self-report questionnaire data on weight-worries, self-esteem, friends and victimisation (closed questions).</p>
<p>Results:Â Most, but not all recalled having been aware of their overweight. None referred to themselves as having been obese. None recalled weight-related health worries. Recollection of early adolescent obesity varied from major concerns impacting on much of an individual's life to almost no concern, with little relation to actual severity of overweight. Recalled concerns were not clearly patterned by gender, but young adult males recalling concerns had previously reported more worries about weight, lower self-esteem, fewer friends and more victimisation in early adolescence; no such pattern was seen among females.
Conclusion:Â The popular image of the unhappy overweight teenager was not borne out. Many obese adolescents, although well aware of their overweight recalled neither major dissatisfaction nor concern. Weight-reduction behaviours are unlikely in such circumstances.</p>
Intermediate mass excess of dilepton production in heavy ion collisions at BEVALAC energies
Dielectron mass spectra are examined for various nuclear reactions recently
measured by the DLS collaboration. A detailed description is given of all
dilepton channels included in the transport model UrQMD 1.0, i.e. Dalitz decays
of mesons and of the resonance, direct
decays of vector mesons and bremsstrahlung. The microscopic calculations
reproduce data for light systems fairly well, but tend to underestimate the
data in at high energies and in at low energies. These conventional
sources, however, cannot explain the recently reported enhancement for
nucleus-nucleus collisions in the mass region 0.15 GeV<<0.6 GeV. Chiral
scaling and meson broadening in the medium are investigated as a
source of this mass excess. They also cannot explain the recent DLS data.Comment: 26 pages, 9 figures, references update
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