93 research outputs found
Two-electron photoionization of endohedral atoms
Using as an example, we demonstrate that static potential of the
fullerene core essentially alters the cross section of the two-electron
ionization differential in one-electron energy . We found that at high photon energy prominent oscillations
appear in it due to reflection of the second, slow electron wave on the shell, which "dies out" at relatively high values, of about
23 two-electron ionization potentials. The results were presented for
ratios , where is the two-electron differential
photoionization cross section. We have calculated the ratio , that accounts for
reflection of both photoelectrons by the shell. We have calculated
also the value of two-electron photoionization cross section and found that this value is close to that of an isolated
atom.Comment: 13 pages, 4 figure
Relativistic quasipotential equations with u-channel exchange interactions
Various quasipotential two-body scattering equations are studied at the
one-loop level for the case of - and -channel exchange potentials. We
find that the quasipotential equations devised to satisfy the one-body limit
for the -channel exchange potential can be in large disagreement with the
field-theoretical prediction in the case of -channel exchange interactions.
Within the spectator model, the description of the -channel case improves if
another choice of the spectator particle is made. Since the appropriate choice
of the spectator depends strongly on the type of interaction used, one faces a
problem when both types of interaction are contained in the potential.
Equal-time formulations are presented, which, in the light-heavy particle
system corresponding to the mass situation of the system, approximate
in a reasonable way the field-theoretical result for both types of
interactions.Comment: Revtex, 20 pages, 12 PostScript figures, to appear in Phys. Rev.
Bound q\bar q Systems in the Framework of the Different Versions of the 3-Dimensional Reductions of the Bethe-Salpeter Equation
Bound q\bar q systems are studied in the framework of different 3-dimensional
relativistic equations derived from the Bethe-Salpeter equation with the
instantaneous kernel in the momentum space. Except the Salpeter equation, all
these equations have a correct one-body limit when one of the constituent quark
masses tends to infinity. The spin structure of the confining qq interaction
potential is taken in the form ,
with . At first stage, the one-gluon-exchange potential is
neglected and the confining potential is taken in the oscillator form. For the
systems (u\bar s), (c\bar u), (c\bar s) and (u\bar u), (s\bar s) a comparative
qualitative analysis of these equations is carried out for different values of
the mixing parameter x and the confining potential strength parameter. We
investigate: 1)the existence/nonexistence of stable solutions of these
equations; 2) the parameter dependence of the general structure of the meson
mass spectum and leptonic decay constants of pseudoscalar and vector mesons. It
is demonstrated that none of the 3-dimensional equations considered in the
present paper does simultaneously describe even general qualitative features of
the whole mass spectrum of q\bar q systems. At the same time, these versions
give an acceptable description of the meson leptonic decay characteristics.Comment: 22 pages, 5 postscript figures, LaTeX-file (revtex.sty
Relativistic effects and quasipotential equations
We compare the scattering amplitude resulting from the several quasipotential
equations for scalar particles. We consider the Blankenbecler-Sugar, Spectator,
Thompson, Erkelenz-Holinde and Equal-Time equations, which were solved
numerically without decomposition into partial waves. We analyze both
negative-energy state components of the propagators and retardation effects. We
found that the scattering solutions of the Spectator and the Equal-Time
equations are very close to the nonrelativistic solution even at high energies.
The overall relativistic effect increases with the energy. The width of the
band for the relative uncertainty in the real part of the scattering
matrix, due to different dynamical equations, is largest for
backward-scattering angles where it can be as large as 40%.Comment: Accepted for publication in Phys. Rev.
Cigarette smoking and risk of acoustic neuromas and pituitary tumours in the Million Women Study
BACKGROUND: The relationship between cigarette smoking and incidence of acoustic neuromas and pituitary tumours is uncertain. METHODS: We examined the relation between smoking and risk of acoustic neuromas and pituitary tumours in a prospective study of 1.2 million middle-aged women in the United Kingdom. RESULTS: Over 10.2 million person years of follow-up, 177 women were diagnosed with acoustic neuromas and 174 with pituitary tumours. Current smokers at recruitment were at significantly reduced risk of incident acoustic neuroma compared with never smokers (adjusted relative risk (RR)=0.41, 95% confidence interval (CI)=0.24-0.70, P=0.001). Past smokers did not have significantly different risk of acoustic neuroma than never smokers (RR=0.87, 95% CI=0.62-1.22, P=0.4). Smoking was not associated with incidence of pituitary tumours (RR in current vs never smokers=0.91, 95% CI=0.60-1.40, P=0.7). CONCLUSION: Women who smoke are at a significantly reduced risk of acoustic neuromas, but not of pituitary tumours, compared with never smokers. Acoustic neuromas are much rarer than the cancers that are increased among smokers
Multiple Causes for Delay in Arrival at Hospital in Acute Stroke Patients in Aydin, Turkey
This descriptive, hospital-based study, performed in western Turkey, was designed to assess the level of pre-hospital delay and reasons for such delay in acute stroke patients, taking into consideration certain factors such as socioeconomic status, availability of transport options at onset of symptoms. Data were collected from hospital records, and a questionnaire was administered that included questions about socio-demographics, self-reported risk factors and questions related to hospital arrival. The rate of patients arriving at the hospital more than 3 hours after symptom onset was found to be 31.6% for this study. Approximately 1/3 of patients delayed going to the hospital because they were waiting for symptoms to go away while 1/3 of patients were not aware of the importance of seeking immediate medical help. There was a significant relationship between the use of ambulance transportation and length of time before arrival at the hospitals, though there was no statistically significantly relationship between the existence of stroke risk factors and hospital arrival delay. These results will likely be helpful to health care decision makers as they develop a model for stroke health care and community based training
Relativistic bound-state equations in three dimensions
Firstly, a systematic procedure is derived for obtaining three-dimensional
bound-state equations from four-dimensional ones. Unlike ``quasi-potential
approaches'' this procedure does not involve the use of delta-function
constraints on the relative four-momentum. In the absence of negative-energy
states, the kernels of the three-dimensional equations derived by this
technique may be represented as sums of time-ordered perturbation theory
diagrams. Consequently, such equations have two major advantages over
quasi-potential equations: they may easily be written down in any Lorentz
frame, and they include the meson-retardation effects present in the original
four-dimensional equation. Secondly, a simple four-dimensional equation with
the correct one-body limit is obtained by a reorganization of the generalized
ladder Bethe-Salpeter kernel. Thirdly, our approach to deriving
three-dimensional equations is applied to this four-dimensional equation, thus
yielding a retarded interaction for use in the three-dimensional bound-state
equation of Wallace and Mandelzweig. The resulting three-dimensional equation
has the correct one-body limit and may be systematically improved upon. The
quality of the three-dimensional equation, and our general technique for
deriving such equations, is then tested by calculating bound-state properties
in a scalar field theory using six different bound-state equations. It is found
that equations obtained using the method espoused here approximate the wave
functions obtained from their parent four-dimensional equations significantly
better than the corresponding quasi-potential equations do.Comment: 28 pages, RevTeX, 6 figures attached as postscript files. Accepted
for publication in Phys. Rev. C. Minor changes from original version do not
affect argument or conclusion
Electron-deuteron scattering in a current-conserving description of relativistic bound states: formalism and impulse approximation calculations
The electromagnetic interactions of a relativistic two-body bound state are
formulated in three dimensions using an equal-time (ET) formalism. This
involves a systematic reduction of four-dimensional dynamics to a
three-dimensional form by integrating out the time components of relative
momenta. A conserved electromagnetic current is developed for the ET formalism.
It is shown that consistent truncations of the electromagnetic current and the
interaction kernel may be made, order-by-order in the coupling constants,
such that appropriate Ward-Takahashi identities are satisfied. A meson-exchange
model of the interaction is used to calculate deuteron vertex functions.
Calculations of electromagnetic form factors for elastic scattering of
electrons by deuterium are performed using an impulse-approximation current.
Negative-energy components of the deuteron's vertex function and retardation
effects in the meson-exchange interaction are found to have only minor effects
on the deuteron form factors.Comment: 42 pages, RevTe
The Relativistic N-body Problem in a Separable Two-Body Basis
We use Dirac's constraint dynamics to obtain a Hamiltonian formulation of the
relativistic N-body problem in a separable two-body basis in which the
particles interact pair-wise through scalar and vector interactions. The
resultant N-body Hamiltonian is relativistically covariant. It can be easily
separated in terms of the center-of-mass and the relative motion of any
two-body subsystem. It can also be separated into an unperturbed Hamiltonian
with a residual interaction. In a system of two-body composite particles, the
solutions of the unperturbed Hamiltonian are relativistic two-body internal
states, each of which can be obtained by solving a relativistic
Schr\"odinger-like equation. The resultant two-body wave functions can be used
as basis states to evaluate reaction matrix elements in the general N-body
problem. We prove a relativistic version of the post-prior equivalence which
guarantees a unique evaluation of the reaction matrix element, independent of
the ways of separating the Hamiltonian into unperturbed and residual
interactions. Since an arbitrary reaction matrix element involves composite
particles in motion, we show explicitly how such matrix elements can be
evaluated in terms of the wave functions of the composite particles and the
relevant Lorentz transformations.Comment: 42 pages, 2 figures, in LaTe
Changes in treatment and mortality of acute myocardial infarction in Estonian tertiary and secondary care hospitals in 2001 and 2007
<p>Abstract</p> <p>Background</p> <p>High quality care for acute myocardial infarction (AMI) improves patient outcomes. Still, AMI patients are treated in hospitals with unequal access to percutaneous coronary intervention. The study compares changes in treatment and 30-day and 3-year mortality of AMI patients hospitalized into tertiary and secondary care hospitals in Estonia in 2001 and 2007.</p> <p>Results</p> <p>Final analysis included 423 cases in 2001 (210 from tertiary and 213 from secondary care hospitals) and 687 cases in 2007 (327 from tertiary and 360 from secondary care hospitals). The study sample in 2007 was older and had twice more often diabetes mellitus. The patients in the tertiary care hospitals underwent reperfusion for ST-elevation myocardial infarction, cardiac catheterization and revascularisation up to twice as often in 2007 as in 2001. In the secondary care, patient transfer for further invasive treatment into tertiary care hospitals increased (<it>P </it>< 0.001). Prescription rates of evidence-based medications for in-hospital and for outpatient use were higher in 2007 in both types of hospitals. However, better treatment did not improve significantly the short- and long-term mortality within a hospital type in crude and baseline-adjusted analysis. Still, in 2007 a mortality gap between the two hospital types was observed (<it>P </it>< 0.010).</p> <p>Conclusions</p> <p>AMI treatment improved in both types of hospitals, while the improvement was more pronounced in tertiary care. Still, better treatment did not result in a significantly lower mortality. Higher age and cardiovascular risk are posing a challenge for AMI treatment.</p
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