2,663 research outputs found
Solving the Bethe-Salpeter equation for bound states of scalar theories in Minkowski space
We apply the perturbation theory integral representation (PTIR) to solve for
the bound state Bethe-Salpeter (BS) vertex for an arbitrary scattering kernel,
without the need for any Wick rotation. The results derived are applicable to
any scalar field theory (without derivative coupling). It is shown that solving
directly for the BS vertex, rather than the BS amplitude, has several major
advantages, notably its relative simplicity and superior numerical accuracy. In
order to illustrate the generality of the approach we obtain numerical
solutions using this formalism for a number of scattering kernels, including
cases where the Wick rotation is not possible.Comment: 28 pages of LaTeX, uses psfig.sty with 5 figures. Also available via
WWW at
http://www.physics.adelaide.edu.au/theory/papers/ADP-97-10.T248-abs.html or
via anonymous ftp at
ftp://bragg.physics.adelaide.edu.au/pub/theory/ADP-97-10.T248.ps A number of
(crucial) typographical errors in Appendix C corrected. To be published in
Phys. Rev. D, October 199
Cucurbit[n]uril binding of platinum anticancer complexes
The encapsulation of cisplatin by cucurbit[7]uril (Q[7]) and multinuclear platinum complexes linked via a 4,4âČ-dipyrazolylmethane (dpzm) ligand by Q[7] and cucurbit[8]uril (Q[8]) has been studied by NMR spectroscopy and molecular modelling. The NMR studies suggest that some cisplatin binds in the cucurbituril cavity, while cis-[PtCl(NH3)2(H2O)]+ only binds at the portals. Alternatively, the dpzm-linked multinuclear platinum complexes are quantitatively encapsulated within the cavities of both Q[7] and Q[8]. Upon encapsulation, the non-exchangeable proton resonances of the multinuclear platinum complexes show significant upfield shifts in 1H NMR spectra. The H3/H3* resonances shift upfield by 0.08 to 0.55 ppm, the H5/H5* shift by 0.9 to 1.6 ppm, while the methylene resonances shift by 0.74 to 0.88 ppm. The size of the resonance shift is dependent on the cavity size of the encapsulating cucurbituril, with Q[7] encapsulation producing larger shifts than Q[8]. The upfield shifts of the dpzm resonances observed upon cucurbituril encapsulation indicate that the Q[7] or Q[8] is positioned directly over the dpzm linking ligand. The terminal platinum groups of trans-[{PtCl(NH3)2}2ÎŒ-dpzm]2+ (di-Pt) and trans-[trans-{PtCl(NH3)2}2-trans-{Pt(dpzm)2(NH3)2}]4+ (tri-Pt) provide a barrier to the on and off movement of cucurbituril, resulting in binding kinetics that are slow on the NMR timescale for the metal complex. Although the dpzm ligand has relatively few rotamers, encapsulation by the larger Q[8] resulted in a more compact di-Pt conformation with each platinum centre retracted further into each Q[8] portal. Encapsulation of the hydrolysed forms of di-Pt and tri-Pt is considerably slower than for the corresponding Cl forms, presumably due to the high-energy cost of passing the +2 platinum centres through the cucurbituril portals. The results of this study suggest that cucurbiturils could be suitable hosts for the pharmacological delivery of multinuclear platinum complexe
Regularization-independent study of renormalized non-perturbative quenched QED
A recently proposed regularization-independent method is used for the first
time to solve the renormalized fermion Schwinger-Dyson equation numerically in
quenched QED. The Curtis-Pennington vertex is used to illustrate the
technique and to facilitate comparison with previous calculations which used
the alternative regularization schemes of modified ultraviolet cut-off and
dimensional regularization. Our new results are in excellent numerical
agreement with these, and so we can now conclude with confidence that there is
no residual regularization dependence in these results. Moreover, from a
computational point of view the regularization independent method has enormous
advantages, since all integrals are absolutely convergent by construction, and
so do not mix small and arbitrarily large momentum scales. We analytically
predict power law behaviour in the asymptotic region, which is confirmed
numerically with high precision. The successful demonstration of this efficient
new technique opens the way for studies of unquenched QED to be undertaken in
the near future.Comment: 20 pages,5 figure
Geographic Variation in Influenza Vaccination Disparities Between Hispanic and Non-Hispanic White US Nursing Home Residents
BACKGROUND: Disparities in influenza vaccination exist between Hispanic and non-Hispanic White US nursing home (NH) residents, but the geographic areas with the largest disparities remain unknown. We examined how these racial/ethnic disparities differ across states and hospital referral regions (HRRs). METHODS: This retrospective cohort study included >14 million short-stay and long-stay US NH resident-seasons over 7 influenza seasons from October 1, 2011, to March 31, 2018, where residents could contribute to 1 or more seasons. Residents were aged â„65â
years and enrolled in Medicare fee-for-service. We used the Medicare Beneficiary Summary File to ascertain race/ethnicity and Minimum Data Set assessments for influenza vaccination. We calculated age- and sex-standardized percentage point (pp) differences in the proportions vaccinated between non-Hispanic White and Hispanic (any race) resident-seasons. Positive pp differences were considered disparities, where the proportion of non-Hispanic White residents vaccinated was greater than the proportion of Hispanic residents vaccinated. States and HRRs with â„100 resident-seasons per ageâsex stratum per racial/ethnic group were included in analyses. RESULTS: Among 7 442 241 short-stay resident-seasons (94.1% non-Hispanic White, 5.9% Hispanic), the median standardized disparities in influenza vaccination were 4.3 pp (minimum, maximum: 0.3, 19.2; n = 22 states) and 2.8 pp (minimum, maximum: â3.6, 10.3; n = 49 HRRs). Among 6 758 616 long-stay resident-seasons (93.7% non-Hispanic White, 6.5% Hispanic), the median standardized differences were â0.1 pp (minimum, maximum: â4.1, 11.4; n = 18 states) and â1.8 pp (minimum, maximum: â6.5, 7.6; n = 34 HRRs). CONCLUSIONS: Wide geographic variation in influenza vaccination disparities existed across US states and HRRs. Localized interventions targeted toward areas with high disparities may be a more effective strategy to promote health equity than one-size-fits-all national interventions
Nonperturbative improvement and tree-level correction of the quark propagator
We extend an earlier study of the Landau gauge quark propagator in quenched
QCD where we used two forms of the O(a)-improved propagator with the
Sheikholeslami-Wohlert quark action. In the present study we use the
nonperturbative value for the clover coefficient c_sw and mean-field
improvement coefficients in our improved quark propagators. We compare this to
our earlier results which used the mean-field c_sw and tree-level improvement
coefficients for the propagator. We also compare three different
implementations of tree-level correction: additive, multiplicative, and hybrid.
We show that the hybrid approach is the most robust and reliable and can
successfully deal even with strong ultraviolet behavior and zero-crossing of
the lattice tree-level expression. We find good agreement between our improved
quark propagators when using the appropriate nonperturbative improvement
coefficients and hybrid tree-level correction. We also present a simple
extrapolation of the quark mass function to the chiral limit.Comment: 12 pages, 18 figures, RevTeX4. Some clarifications and corrections.
Final version, to appear in Phys.Rev.
Radiative equilibrium in Monte Carlo radiative transfer using frequency distribution adjustment
The Monte Carlo method is a powerful tool for performing radiative
equilibrium calculations, even in complex geometries. The main drawback of the
standard Monte Carlo radiative equilibrium methods is that they require
iteration, which makes them numerically very demanding. Bjorkman & Wood
recently proposed a frequency distribution adjustment scheme, which allows
radiative equilibrium Monte Carlo calculations to be performed without
iteration, by choosing the frequency of each re-emitted photon such that it
corrects for the incorrect spectrum of the previously re-emitted photons.
Although the method appears to yield correct results, we argue that its
theoretical basis is not completely transparent, and that it is not completely
clear whether this technique is an exact rigorous method, or whether it is just
a good and convenient approximation. We critically study the general problem of
how an already sampled distribution can be adjusted to a new distribution by
adding data points sampled from an adjustment distribution. We show that this
adjustment is not always possible, and that it depends on the shape of the
original and desired distributions, as well as on the relative number of data
points that can be added. Applying this theorem to radiative equilibrium Monte
Carlo calculations, we provide a firm theoretical basis for the frequency
distribution adjustment method of Bjorkman & Wood, and we demonstrate that this
method provides the correct frequency distribution through the additional
requirement of radiative equilibrium. We discuss the advantages and limitations
of this approach, and show that it can easily be combined with the presence of
additional heating sources and the concept of photon weighting. However, the
method may fail if small dust grains are included... (abridged)Comment: 17 pages, 2 figures, accepted for publication in New Astronom
Psychometric properties of the PTSD Checklist for DSM-5 in a sample of trauma exposed mental health service users
Background: PTSD self-report measures are frequently used in mental health services but very few have been evaluated in clinical samples that include civilians. The PCL-5 was developed to assess for DSM-5 PTSD.
Objective: The aim of this study was to evaluate the psychometric properties of the PCL-5 in a sample of trauma-exposed mental health service users who were evidencing symptoms of PTSD.
Method: Reliability and validity of the PCL-5 were investigated in a sample of 273 participants who reported past diagnosis for PTSD or who had screened positively for traumatic stress symptoms. Diagnostic utility was evaluated in comparison to the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5).
Results: The PCL-5 demonstrated high internal consistency, good convergent and divergent validity, acceptable stability and good diagnostic utility. However, operating characteristics differed from those found in other samples. Scores of 43â44 provided optimal efficiency for diagnosing PTSD. A post hoc regression analysis showed that depression explained more of the variance in PCL-5 total score than the CAPS-5.
Conclusion: Whilst the PCL-5 is psychometrically sound it appears to have difficulty differentiating self-reported depression and anxiety symptoms from PTSD in trauma-exposed mental health service users and clinicians should take care to assess full symptomatology when individuals screen positively on the PCL-5. Clinicians and researchers should also take care not to assume that operating characteristics of self-report PTSD measures are valid for mental health service users, when these have been established in other populations
Dynamical chiral symmetry breaking and confinement with an infrared-vanishing gluon propagator?
We study a model Dyson-Schwinger equation for the quark propagator closed
using an {\it Ansatz} for the gluon propagator of the form \mbox{} and two {\it Ans\"{a}tze} for the quark-gluon vertex: the
minimal Ball-Chiu and the modified form suggested by Curtis and Pennington.
Using the quark condensate as an order parameter, we find that there is a
critical value of such that the model does not support dynamical chiral
symmetry breaking for . We discuss and apply a confinement test which
suggests that, for all values of , the quark propagator in the model {\bf is
not} confining. Together these results suggest that this Ansatz for the gluon
propagator is inadequate as a model since it does not yield the expected
behaviour of QCD.Comment: 21 Pages including 4 PostScript figures uuencoded at the end of the
file. Replacement: slight changes of wording and emphasis. ADP-93-215/T133,
ANL-PHY-7599-TH-93, FSU-SCRI-93-108, REVTEX 3.
Infinite Volume and Continuum Limits of the Landau-Gauge Gluon Propagator
We extend a previous improved action study of the Landau gauge gluon
propagator, by using a variety of lattices with spacings from to
0.41 fm, to more fully explore finite volume and discretization effects. We
also extend a previously used technique for minimizing lattice artifacts, the
appropriate choice of momentum variable or ``kinematic correction'', by
considering it more generally as a ``tree-level correction''. We demonstrate
that by using tree-level correction, determined by the tree-level behavior of
the action being considered, it is possible to obtain scaling behavior over a
very wide range of momenta and lattice spacings. This makes it possible to
explore the infinite volume and continuum limits of the Landau-gauge gluon
propagator.Comment: 24 pages RevTex, 18 figures; Responses to referee comments, minor
change
Parton-Hadron Duality in Unpolarised and Polarised Structure Functions
We study the phenomenon of parton-hadron duality in both polarised and
unpolarised electron proton scattering using the HERMES and the Jefferson Lab
data, respectively. In both cases we extend a systematic perturbative QCD based
analysis to the integrals of the structure functions in the resonance region.
After subtracting target mass corrections and large x resummation effects, we
extract the remaining power corrections up to order 1/Q^2. We find a sizeable
suppression of these terms with respect to analyses using deep inelastic
scattering data. The suppression appears consistently in both polarised and
unpolarised data, except for the low Q^2 polarised data, where a large negative
higher twist contribution remains. Possible scenarios generating this behavior
are discussed.Comment: 17 pages, 9 figure
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