141 research outputs found
Fermion Pairing Dynamics in the Relativistic Scalar Plasma
Using many-body techniques we obtain the time-dependent Gaussian
approximation for interacting fermion-scalar field models. This method is
applied to an uniform system of relativistic spin-1/2 fermion field coupled,
through a Yukawa term, to a scalar field in 3+1 dimensions, the so-called
quantum scalar plasma model. The renormalization for the resulting Gaussian
mean-field equations, both static and dynamical, are examined and initial
conditions discussed. We also investigate solutions for the gap equation and
show that the energy density has a single minimum.Comment: 21 pages, latex, 4 postscript figures, new sections, some literary
changes, notation corrections, accepted for publication in Phys. Rev
Phases of quantum states in completely positive non-unitary evolution
We define an operational notion of phases in interferometry for a quantum
system undergoing a completely positive non-unitary evolution. This definition
is based on the concepts of quantum measurement theory. The suitable
generalization of the Pancharatnan connection allows us to determine the
dynamical and geometrical parts of the total phase between two states linked by
a completely positive map. These results reduce to the knonw expressions of
total, dynamical and geometrical phases for pure and mixed states evolving
unitarily.Comment: 2 figure
Molecular analysis of two novel missense mutations in the GDF5 proregion that reduce protein activity and are associated with brachydactyly type C
Growth and differentiation factor 5 (GDF5) plays a central role in bone and cartilage development by regulating the proliferation and differentiation of chondrogenic tissue. GDF5 is synthesized as a preproprotein. The biological function of the proregion comprising 354 residues is undefined. We identified two families with a heterozygosity for the novel missense mutations p.T201P or p.L263P located in the proregion of GDF5. The patients presented with dominant brachydactyly type C characterized by the shortening of skeletal elements in the distal extremities. Both mutations gave rise to decreased biological activity in in vitro analyses. The variants reduced the GDF5-induced activation of SMAD signaling by the GDF5 receptors BMPR1A and BMPR1B. Ectopic expression in micromass cultures yielded relatively low protein levels of the variants and showed diminished chondrogenic activity as compared to wild-type GDF5. Interestingly, stimulation of micromass cells with recombinant human proGDF5(T201P) and proGDF5(L263P) revealed their reduced chondrogenic potential compared to the wild-type protein. Limited proteolysis of the mutant recombinant proproteins resulted in a fragment pattern profoundly different from wild-type proGDF5. Modeling of a part of the GDF5 proregion into the known three-dimensional structure of TGFbeta1 latency-associated peptide revealed that the homologous positions of both mutations are conserved regions that may be important for the folding of the mature protein or the assembly of dimeric protein complexes. We hypothesize that the missense mutations p.T201P and p.L263P interfere with the protein structure and thereby reduce the amount of fully processed, biologically active GDF5, finally causing the clinical loss of function phenotype
Exact Solution of an Evolutionary Model without Ageing
We introduce an age-structured asexual population model containing all the
relevant features of evolutionary ageing theories. Beneficial as well as
deleterious mutations, heredity and arbitrary fecundity are present and managed
by natural selection. An exact solution without ageing is found. We show that
fertility is associated with generalized forms of the Fibonacci sequence, while
mutations and natural selection are merged into an integral equation which is
solved by Fourier series. Average survival probabilities and Malthusian growth
exponents are calculated indicating that the system may exhibit mutational
meltdown. The relevance of the model in the context of fissile reproduction
groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.
Small oscillations of a chiral Gross-Neveu system
We study the small oscillations regime (RPA approximation) of the
time-dependent mean-field equations, obtained in a previous work, which
describe the time evolution of one-body dynamical variables of a uniform Chiral
Gross-Neveu system. In this approximation we obtain an analytical solution for
the time evolution of the one-body dynamical variables. The two-fermion physics
can be explored through this solution. The condition for the existence of bound
states is examined.Comment: 21pages, Latex, 1postscript figur
Isospin structure of one- and two-phonon GDR excitations
Isospin is included in the description of Coulomb excitation of multiple
giant isovector dipole resonances. In the excitation of even-even nuclei, a
relevant portion of the excitation strength is shown to be associated with 1+
two-phonon states, which tends to be hindered or completely supressed in
calculations in which the isospin degree of freedom is not considered. We find
that the excitation cross sections is strongly dependent on the ground state
isospin.Comment: 8 pages, 2 figure
Preparation and control of a cavity-field state through atom-driven field interaction: towards long-lived mesoscopic states
The preparation of mesoscopic states of the radiation and matter fields
through atom-field interactions has been achieved in recent years and employed
for a range of striking applications in quantum optics. Here we present a
technique for the preparation and control of a cavity mode which, besides
interacting with a two-level atom, is simultaneously submitted to linear and
parametric amplification processes. The role of the amplification-controlling
fields in the achievement of real mesoscopic states, is to produce
highly-squeezed field states and, consequently, to increase both: i) the
distance in phase space between the components of the prepared superpositions
and ii) the mean photon number of such superpositions. When submitting the
squeezed superposition states to the action of similarly squeezed reservoirs,
we demonstrate that under specific conditions the decoherence time of the
states becomes independent of both the distance in phase space between their
components and their mean photon number. An explanation is presented to support
this remarkable result, together with a discussion on the experimental
implementation of our proposal. We also show how to produce number states with
fidelities higher than those derived as circular states
First evidence of multiple beta-delayed neutron emission for isotopes with A > 100
The beta-delayed neutron emission probability, P-n, of very neutron-rich nuclei allows us to achieve a better understanding of the nuclear structure above the neutron separation energy, S-n. The emission of neutrons can become the dominant decay process in neutron-rich astrophysical phenomena such as the rapid neutron capture process (r-process). There are around 600 accessible isotopes for which beta-delayed one-neutron emission (beta 1n) is energetically allowed, but the branching ratio has only been determined for about one third of them. beta 1n decays have been experimentally measured up to the mass A similar to 1 5 0, plus a single measurement of Tl-210. Concerning two-neutron emitters (beta 2n), similar to 3 0 0 isotopes are accessible and only 24 have been measured so far up to the mass A = 100. In this contribution, we report recent experiments which allowed the measurement of beta 1n emitters for masses beyond A > 200 and N > 1 2 6 and identified the heaviest beta 2n emitter measured so far, Sb-136.Peer reviewe
Cumulative Prognostic Score Predicting Mortality in Patients Older Than 80 Years Admitted to the ICU.
OBJECTIVES: To develop a scoring system model that predicts mortality within 30 days of admission of patients older than 80 years admitted to intensive care units (ICUs). DESIGN: Prospective cohort study. SETTING: A total of 306 ICUs from 24 European countries. PARTICIPANTS: Older adults admitted to European ICUs (N = 3730; median age = 84 years [interquartile range = 81-87 y]; 51.8% male). MEASUREMENTS: Overall, 24 variables available during ICU admission were included as potential predictive variables. Multivariable logistic regression was used to identify independent predictors of 30-day mortality. Model sensitivity, specificity, and accuracy were evaluated with receiver operating characteristic curves. RESULTS: The 30-day-mortality was 1562 (41.9%). In multivariable analysis, these variables were selected as independent predictors of mortality: age, sex, ICU admission diagnosis, Clinical Frailty Scale, Sequential Organ Failure Score, invasive mechanical ventilation, and renal replacement therapy. The discrimination, accuracy, and calibration of the model were good: the area under the curve for a score of 10 or higher was .80, and the Brier score was .18. At a cut point of 10 or higher (75% of all patients), the model predicts 30-day mortality in 91.1% of all patients who die. CONCLUSION: A predictive model of cumulative events predicts 30-day mortality in patients older than 80 years admitted to ICUs. Future studies should include other potential predictor variables including functional status, presence of advance care plans, and assessment of each patient's decision-making capacity
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