2,268 research outputs found
Are we repeating mistakes of the past? A review of the evidence for esketamine
Esketamine has been licensed for 'treatment-resistant depression' in the USA, UK and Europe. Licensing trials did not establish efficacy: two trials were negative, one showed a statistically significant but clinically uncertain effect, and a flawed discontinuation trial was included, against Food and Drug Administration precedent. Safety signals - deaths, including suicides, and bladder damage - were minimised
The time-dependent relativistic mean-field theory and the random phase approximation
The Relativistic Random Phase Approximation (RRPA) is derived from the
Time-dependent Relativistic Mean Field (TD RMF) theory in the limit of small
amplitude oscillations. In the no-sea approximation of the RMF theory, the RRPA
configuration space includes not only the usual particle-hole states, but also
a-h configurations, i.e. pairs formed from occupied states in the Fermi sea and
empty negative-energy states in the Dirac sea. The contribution of the negative
energy states to the RRPA matrices is examined in a schematic model, and the
large effect of Dirac sea states on isoscalar strength distributions is
illustrated for the giant monopole resonance in 116Sn. It is shown that,
because the matrix elements of the time-like component of the vector meson
fields which couple the a-h configurations with the ph-configurations are
strongly reduced with respect to the corresponding matrix elements of the
isoscalar scalar meson field, the inclusion of states with unperturbed energies
more than 1.2 GeV below the Fermi energy has a pronounced effect on giant
resonances with excitation energies in the MeV region. The influence of nuclear
magnetism, i.e. the effect of the spatial components of the vector fields is
examined, and the difference between the non-relativistic and relativistic RPA
predictions for the nuclear matter compression modulus is explained.Comment: 21 pages,2 figures, Nucl.Phys.A in pres
Asymptotic properties of bridge estimators in sparse high-dimensional regression models
We study the asymptotic properties of bridge estimators in sparse,
high-dimensional, linear regression models when the number of covariates may
increase to infinity with the sample size. We are particularly interested in
the use of bridge estimators to distinguish between covariates whose
coefficients are zero and covariates whose coefficients are nonzero. We show
that under appropriate conditions, bridge estimators correctly select
covariates with nonzero coefficients with probability converging to one and
that the estimators of nonzero coefficients have the same asymptotic
distribution that they would have if the zero coefficients were known in
advance. Thus, bridge estimators have an oracle property in the sense of Fan
and Li [J. Amer. Statist. Assoc. 96 (2001) 1348--1360] and Fan and Peng [Ann.
Statist. 32 (2004) 928--961]. In general, the oracle property holds only if the
number of covariates is smaller than the sample size. However, under a partial
orthogonality condition in which the covariates of the zero coefficients are
uncorrelated or weakly correlated with the covariates of nonzero coefficients,
we show that marginal bridge estimators can correctly distinguish between
covariates with nonzero and zero coefficients with probability converging to
one even when the number of covariates is greater than the sample size.Comment: Published in at http://dx.doi.org/10.1214/009053607000000875 the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Comment on: Chen et al. Utilizing the Second-Meal Effect in Type 2 Diabetes: Practical Use of a Soya-Yogurt Snack. Diabetes Care 2010;33:2552–2554
Corrected by: Erratum: Comment on: Chen et al. Utilizing the second-meal effect in type 2 diabetes: Practical use of a soya-yogurt snack. Diabetes Care 2010;33:2552-2554 (Diabetes Care (2011) 34, (e55)), in Diabetes Care 2011 Aug; 34(8): 1887-1887. http://dx.doi.org/10.2337/dc11-er08c. Due to a production error, the page numbers appeared incorrectly in the PDF versions of the articles listed. The correct page numbers are given, followed in brackets by the numbers that incorrectly appeared in the PDF versions. The online PDF versions have been corrected.Christopher K. Rayner, Jing Ma, Karen L. Jones, and Michael Horowit
Collective multipole excitations in a microscopic relativistic approach
A relativistic mean field description of collective excitations of atomic
nuclei is studied in the framework of a fully self-consistent relativistic
random phase approximation (RRPA). In particular, results of RRPA calculations
of multipole giant resonances and of low-lying collective states in spherical
nuclei are analyzed. By using effective Lagrangians which, in the mean-field
approximation, provide an accurate description of ground-state properties, an
excellent agreement with experimental data is also found for the excitation
energies of low-lying collective states and of giant resonances. Two points are
essential for the successful application of the RRPA in the description of
dynamical properties of finite nuclei: (i) the use of effective Lagrangians
with non-linear terms in the meson sector, and (ii) the fully consistent
treatment of the Dirac sea of negative energy states.Comment: 10 figures, submitted to Nucl.Phys.
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Seasonal variability of ozone mixing ratios and budgets in the tropical southern Pacific: A GCTM perspective
Neutron/proton ratio of nucleon emissions as a probe of neutron skin
The dependence between neutron-to-proton yield ratio () and neutron
skin thickness () in neutron-rich projectile induced reactions is
investigated within the framework of the Isospin-Dependent Quantum Molecular
Dynamics (IQMD) model. The density distribution of the Droplet model is
embedded in the initialization of the neutron and proton densities in the
present IQMD model. By adjusting the diffuseness parameter of neutron density
in the Droplet model for the projectile, the relationship between the neutron
skin thickness and the corresponding in the collisions is obtained.
The results show strong linear correlation between and
for neutron-rich Ca and Ni isotopes. It is suggested that may be used
as an experimental observable to extract for neutron-rich nuclei,
which is very significant to the study of the nuclear structure of exotic
nuclei and the equation of state (EOS) of asymmetric nuclear matter.Comment: 7 pages, 5 figures; accepted by Phys. Lett.
Self-consistent description of nuclear compressional modes
Isoscalar monopole and dipole compressional modes are computed for a variety
of closed-shell nuclei in a relativistic random-phase approximation to three
different parametrizations of the Walecka model with scalar self-interactions.
Particular emphasis is placed on the role of self-consistency which by itself,
and with little else, guarantees the decoupling of the spurious
isoscalar-dipole strength from the physical response and the conservation of
the vector current. A powerful new relation is introduced to quantify the
violation of the vector current in terms of various ground-state form-factors.
For the isoscalar-dipole mode two distinct regions are clearly identified: (i)
a high-energy component that is sensitive to the size of the nucleus and scales
with the compressibility of the model and (ii) a low-energy component that is
insensitivity to the nuclear compressibility. A fairly good description of both
compressional modes is obtained by using a ``soft'' parametrization having a
compression modulus of K=224 MeV.Comment: 28 pages and 10 figures; submitted to PR
Levinson's Theorem for Dirac Particles
Levinson's theorem for Dirac particles constraints the sum of the phase
shifts at threshold by the total number of bound states of the Dirac equation.
Recently, a stronger version of Levinson's theorem has been proven in which the
value of the positive- and negative-energy phase shifts are separately
constrained by the number of bound states of an appropriate set of
Schr\"odinger-like equations. In this work we elaborate on these ideas and show
that the stronger form of Levinson's theorem relates the individual phase
shifts directly to the number of bound states of the Dirac equation having an
even or odd number of nodes. We use a mean-field approximation to Walecka's
scalar-vector model to illustrate this stronger form of Levinson's theorem. We
show that the assignment of bound states to a particular phase shift should be
done, not on the basis of the sign of the bound-state energy, but rather, in
terms of the nodal structure (even/odd number of nodes) of the bound state.Comment: Latex with Revtex, 7 postscript figures (available from the author),
SCRI-06109
Relativistic analysis of the 208Pb(e,e'p)207Tl reaction at high momentum
The recent 208Pb(e,e'p)207Tl data from NIKHEF-K at high missing momentum
(p_m>300 MeV/c) are compared to theoretical results obtained with a fully
relativistic formalism previously applied to analyze data on the low missing
momentum (p_m < 300 MeV/c) region. The same relativistic optical potential and
mean field wave functions are used in the two p_m-regions. The spectroscopic
factors of the various shells are extracted from the analysis of the low-p_m
data and then used in the high-p_m region. In contrast to previous analyses
using a nonrelativistic mean field formalism, we do not find a substantial
deviation from the mean field predictions other than that of the spectroscopic
factors, which appear to be consistent with both low- and high-p_m data. We
find that the difference between results of relativistic and nonrelativistic
formalisms is enhanced in the p_m<0 region that will be interesting to explore
experimentally.Comment: 12 pages, LaTeX+Revtex, included 3 postscript figures. To appear in
the Physical Review C (Rapid Communications
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