66,634 research outputs found
Closed-shell properties of O with {\em ab initio} coupled-cluster theory
We present an \emph{ab initio} calculation of spectroscopic factors for
neutron and proton removal from O using the coupled-cluster method and a
state-of-the-art chiral nucleon-nucleon interaction at
next-to-next-to-next-to-leading order. In order to account for the coupling to
the scattering continuum we use a Berggren single-particle basis that treats
bound, resonant, and continuum states on an equal footing. We report neutron
removal spectroscopic factors for the O states ,
, and , and proton removal spectroscopic factors for the
N states and . Our calculations support the accumulated
experimental evidence that O is a closed-shell nucleus.Comment: 5 pages, 2 figures, 1 tabl
Quantum spin configurations in Tb2Ti2O7
Low energy collective angular momentum states of the Tb3+ ions in Tb2Ti2O7
are classified according to the irreducible representations of the octahedral
point group. Degeneracy lifting due to the exchange interaction is discussed.
Diffuse neutron scattering intensity patterns are calculated for each
collective angular momentum state and the ground state is inferred by comparing
to experiment.Comment: 5 pages, 1 colour figure. Slight corrections and additions to text
and figur
Generalized contour deformation method in momentum space: two-body spectral structures and scattering amplitudes
A generalized contour deformation method (GCDM) which combines complex
rotation and translation in momentum space, is discussed. GCDM gives accurate
results for bound, virtual (antibound), resonant and scattering states starting
with a realistic nucleon-nucleon interaction. It provides a basis for full
off-shell -matrix calculations both for real and complex input energies.
Results for both spectral structures and scattering amplitudes compare
perfectly well with exact values for the separable Yamaguchi potential.
Accurate calculation of virtual states in the Malfliet-Tjon and the realistic
CD-Bonn nucleon-nucleon interactions are presented.
GCDM is also a promising method for the computation of in-medium properties
such as the resummation of particle-particle and particle-hole diagrams in
infinite nuclear matter. Implications for in-medium scattering are discussed.Comment: 15 pages, revte
Oscillations and temporal signalling in cells
The development of new techniques to quantitatively measure gene expression
in cells has shed light on a number of systems that display oscillations in
protein concentration. Here we review the different mechanisms which can
produce oscillations in gene expression or protein concentration, using a
framework of simple mathematical models. We focus on three eukaryotic genetic
regulatory networks which show "ultradian" oscillations, with time period of
the order of hours, and involve, respectively, proteins important for
development (Hes1), apoptosis (p53) and immune response (NFkB). We argue that
underlying all three is a common design consisting of a negative feedback loop
with time delay which is responsible for the oscillatory behaviour
Use of recurrence quantification analysis to examine associations between changes in text structure across an expressive writing intervention and reductions in distress symptoms in women wth breast cancer
The current study presents an exploratory analysis of using Recurrence Quantification Analysis (RQA) to analyze text data from an Expressive Writing Intervention (EWI) for Danish women treated for Breast Cancer. The analyses are based on the analysis of essays from a subsample with the average age 54.6 years (SD = 9.0), who completed questionnaires for cancer-related distress (IES) and depression symptoms (BDI-SF). The results show a significant association between an increase in recurrent patterns of text structure from first to last writing session and a decrease in cancer-related distress at 3 months post-intervention. Furthermore, the change in structure from first to last essay displayed a moderate, but significant correlation with change in cancer-related distress from baseline to 9 months post-intervention. The results suggest that changes in recurrence patterns of text structure might be an indicator of cognitive restructuring that leads to amelioration of cancer-specific distress
Loci Controlling Resistance to High Plains Virus and Wheat Streak Mosaic Virus in a B73 × Mo17 Population of Maize
High Plains disease has the potential to cause significant yield loss in susceptible corn (Zea mays L.) and wheat (Triticum aestivum L.) genotypes, especially in the central and western USA. The primary causal agent, High Plains virus (HPV), is vectored by wheat curl mite (WCM; Aceria tossicheila Keifer), which is also the vector of wheat streak mosaic virus (WSMV). In general, the two diseases occur together as a mixed infection in the field. The objective of this research was to characterize the inheritance of HPV and WSMV resistance using B73 (resistant to HPV and WSMV) × Mo17 (moderately susceptible to HPV and WSMV) recombinant inbred lines. A population of 129 recombinant inbred lines scored for 167 molecular markers was used to evaluate resistance to WSMV and to a mixed infection of WSMV and HPV. Loci conferring resistance to systemic movement of WSMV in plants mapped to chromosomes 3, 6, and 10, consistent with the map position of wsm2, wsm1, and wsm3, respectively. Major genes for resistance to systemic spread of HPV in doubly infected plants mapped to chromosomes 3 and 6, coincident or tightly linked with the WSMV resistance loci. Analysis of doubly infected plants revealed that chromosome 6 had a major effect on HPV resistance, consistent with our previous analysis of B73 × W64A and B73 × Wf9 populations. Quantitative trait loci (QTL) affecting resistance to localized symptom development mapped to chromosomes 4 (umc66), 5 (bnl5.40), and 6 (umc85), and accounted for 24% of the phenotypic variation. Localized symptoms may reflect the amount of mite feeding or the extent of virus spread at the point of infection. Identification of cosegregating markers may facilitate selection for HPV and WSMV resistance in corn breeding programs
Self-organisation to criticality in a system without conservation law
We numerically investigate the approach to the stationary state in the
nonconservative Olami-Feder-Christensen (OFC) model for earthquakes. Starting
from initially random configurations, we monitor the average earthquake size in
different portions of the system as a function of time (the time is defined as
the input energy per site in the system). We find that the process of
self-organisation develops from the boundaries of the system and it is
controlled by a dynamical critical exponent z~1.3 that appears to be universal
over a range of dissipation levels of the local dynamics. We show moreover that
the transient time of the system scales with system size L as . We argue that the (non-trivial) scaling of the transient time in the
OFC model is associated to the establishment of long-range spatial correlations
in the steady state.Comment: 10 pages, 6 figures; accepted for publication in Journal of Physics
Oscillation patterns in negative feedback loops
Organisms are equipped with regulatory systems that display a variety of
dynamical behaviours ranging from simple stable steady states, to switching and
multistability, to oscillations. Earlier work has shown that oscillations in
protein concentrations or gene expression levels are related to the presence of
at least one negative feedback loop in the regulatory network. Here we study
the dynamics of a very general class of negative feedback loops. Our main
result is that in these systems the sequence of maxima and minima of the
concentrations is uniquely determined by the topology of the loop and the
activating/repressing nature of the interaction between pairs of variables.
This allows us to devise an algorithm to reconstruct the topology of
oscillating negative feedback loops from their time series; this method applies
even when some variables are missing from the data set, or if the time series
shows transients, like damped oscillations. We illustrate the relevance and the
limits of validity of our method with three examples: p53-Mdm2 oscillations,
circadian gene expression in cyanobacteria, and cyclic binding of cofactors at
the estrogen-sensitive pS2 promoter.Comment: 10 pages, 8 figure
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