7,496 research outputs found
Sudden To Adiabatic Transition in Beta Decay
We discuss effects in beta decays at very low beta energies, of the order of
the kinetic energies of atomic electrons. As the beta energy is lowered the
atomic response changes from sudden to adiabatic. As a consequence, the beta
decay rate increases slightly and the ejection of atomic electrons (shake off)
and subsequent production of X rays is turned off. We estimate the transition
energy and the change in decay rate. The rate increase is largest in heavy
atoms, which have a small Q value in their decay. The X ray switch-off is
independent of Q value.Comment: 6 pages LaTe
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Update on the ICUD-SIU consultation on multi-parametric magnetic resonance imaging in localised prostate cancer
Introduction: Prostate cancer (PCa) imaging is a rapidly evolving field. Dramatic improvements in prostate MRI during the last decade will probably change the accuracy of diagnosis. This chapter reviews recent current evidence about MRI diagnostic performance and impact on PCa management. Materials and methods: The International Consultation on Urological Diseases nominated a committee to review the literature on prostate MRI. A search of the PubMed database was conducted to identify articles focussed on MP-MRI detection and staging protocols, reporting and scoring systems, the role of MP-MRI in diagnosing PCa prior to biopsy, in active surveillance, in focal therapy and in detecting local recurrence after treatment. Results: Differences in opinion were reported in the use of the strength of magnets [1.5 Tesla (T) vs. 3T] and coils. More agreement was found regarding the choice of pulse sequences; diffusion-weighted MRI (DW-MRI), dynamic contrast-enhanced MRI (DCE MRI), and/or MR spectroscopy imaging (MRSI) are recommended in addition to conventional T2-weighted anatomical sequences. In 2015, the Prostate Imaging Reporting and Data System (PI-RADS version 2) was described to standardize image acquisition and interpretation. MP-MRI improves detection of clinically significant PCa (csPCa) in the repeat biopsy setting or before the confirmatory biopsy in patients considering active surveillance. It is useful to guide focal treatment and to detect local recurrences after treatment. Its role in biopsy-naive patients or during the course of active surveillance remains debated. Conclusion: MP-MRI is increasingly used to improve detection of csPCa and for the selection of a suitable therapeutic approach
QSO hosts and environments at z=0.9 to 4.2: JHK images with adaptive optics
We have observed nine QSOs with redshifts 0.85 to 4.16 at near-IR wavelengths
with the adaptive optics bonnette of the Canada-France-Hawaii telescope.
Exposure times ranged from 1500 to 24000s (mostly near 7000s) in J, H, or K
bands, with pixels 0.035 arcsec on the sky. The FWHM of the co-added images at
the location of the quasars are typically 0.16 arcsec. Including another QSO
published previously, we find associated QSO structure in at least eight of ten
objects, including the QSO at z = 4.16. The structures seen in all cases
include long faint features which appear to be tidal tails. In four cases we
have also resolved the QSO host galaxy, but find them to be smooth and
symmetrical: future PSF removal may expand this result. Including one object
previously reported, of the nine objects with more extended structure, five are
radio-loud, and all but one of these appear to be in a dense small group of
compact galaxy companions. The radio-quiet objects do not occupy the same dense
environments, as seen in the NIR. In this small sample we do not find any
apparent trends of these properties with redshift, over the range 0.8 < z <
2.4. The colors of the host galaxies and companions are consistent with young
stellar populations at the QSO redshift. Our observations suggest that adaptive
optic observations in the visible region will exhibit luminous signatures of
the substantial star-formation activity that must be occurring.Comment: 22 pages including 10 tables, plus 11 figures. To appear in A
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
Computing Aggregate Properties of Preimages for 2D Cellular Automata
Computing properties of the set of precursors of a given configuration is a
common problem underlying many important questions about cellular automata.
Unfortunately, such computations quickly become intractable in dimension
greater than one. This paper presents an algorithm --- incremental aggregation
--- that can compute aggregate properties of the set of precursors
exponentially faster than na{\"i}ve approaches. The incremental aggregation
algorithm is demonstrated on two problems from the two-dimensional binary Game
of Life cellular automaton: precursor count distributions and higher-order mean
field theory coefficients. In both cases, incremental aggregation allows us to
obtain new results that were previously beyond reach
Parametrised Complexity of Model Checking and Satisfiability in Propositional Dependence Logic
In this paper, we initiate a systematic study of the parametrised complexity
in the field of Dependence Logics which finds its origin in the Dependence
Logic of V\"a\"an\"anen from 2007. We study a propositional variant of this
logic (PDL) and investigate a variety of parametrisations with respect to the
central decision problems. The model checking problem (MC) of PDL is
NP-complete. The subject of this research is to identify a list of
parametrisations (formula-size, treewidth, treedepth, team-size, number of
variables) under which MC becomes fixed-parameter tractable. Furthermore, we
show that the number of disjunctions or the arity of dependence atoms
(dep-arity) as a parameter both yield a paraNP-completeness result. Then, we
consider the satisfiability problem (SAT) showing a different picture: under
team-size, or dep-arity SAT is paraNP-complete whereas under all other
mentioned parameters the problem is in FPT. Finally, we introduce a variant of
the satisfiability problem, asking for teams of a given size, and show for this
problem an almost complete picture.Comment: Update includes refined result
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
Diffractive Dissociation and Eikonalization in High Energy pp and p Collisions
We show that eikonal corrections imposed on diffraction dissociation
processes calculated in the triple Regge limit, produce a radical change in the
energy dependence of the predicted cross section. The induced correction is
shown to be in general agreement with the new experimental data measured at the
Tevatron.Comment: 11 pages LATEX, ( two figures not included obtainable from authors)
(TAUP 2066-93 and FERMILAB PUB 93/ T
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