6,311 research outputs found
Charge and Spin Response of the Spin--Polarized Electron Gas
The charge and spin response of a spin--polarized electron gas is
investigated including terms beyond the random phase approximation. We evaluate
the charge response, the longitudinal and transverse spin response, and the
mixed spin--charge response self--consistently in terms of the susceptibility
functions of a non--interacting system. Exchange--correlation effects between
electrons of spin and are included following Kukkonen and
Overhauser, by using spin--polarization dependent generalized Hubbard local
field factors and . The general
condition for charge--density and spin--density--wave excitations of the system
is discussed.Comment: 4 pages, latex, no figure
Self-force of a scalar field for circular orbits about a Schwarzschild black hole
The foundations are laid for the numerical computation of the actual
worldline for a particle orbiting a black hole and emitting gravitational
waves. The essential practicalities of this computation are here illustrated
for a scalar particle of infinitesimal size and small but finite scalar charge.
This particle deviates from a geodesic because it interacts with its own
retarded field \psi^\ret. A recently introduced Green's function G^\SS
precisely determines the singular part, \psi^\SS, of the retarded field. This
part exerts no force on the particle. The remainder of the field \psi^\R =
\psi^\ret - \psi^\SS is a vacuum solution of the field equation and is
entirely responsible for the self-force. A particular, locally inertial
coordinate system is used to determine an expansion of \psi^\SS in the
vicinity of the particle. For a particle in a circular orbit in the
Schwarzschild geometry, the mode-sum decomposition of the difference between
\psi^\ret and the dominant terms in the expansion of \psi^\SS provide a
mode-sum decomposition of an approximation for from which the
self-force is obtained. When more terms are included in the expansion, the
approximation for is increasingly differentiable, and the mode-sum
for the self-force converges more rapidly.Comment: RevTex, 31 pages, 1 figure, modified abstract, more details of
numerical method
Assistive tool for collaborative learning of conceptual structures
The final publication is available at link.springer.comThere is a demand for computational methods assisting learners to generate relevantassociations for current context. Many concepts in natural language have ambiguous meaningsimplying alternative ways to define associations for them. It is crucial to develop collaborativemethods that support free experiments with promising conceptual structures in learning.Methods for evaluating these structures in respect to the person’s needs are also required. Wepropose a new collaborative ideation scheme and based on that we have implemented anassistive tool for learning conceptual structures in a collaborative Web environment.Peer reviewe
Efficacy of entomopathogenic nematodes for control of large pine weevil, Hylobius abietis: effects of soil type, pest density and spatial distribution
The large pine weevil Hylobius abietis (L.), LPW, is a major pest of trees in replanted coniferous forests in northern Europe. The use of entomopathogenic nematodes (EPNs) applied against developing stages for population suppression is increasingly recognized as an effective alternative to plant protection using chemical pesticides. Here, we report results from a series of trials we conducted over 2 years using two species of EPN, Steinernema carpocapsae (Weiser) and Heterorhabitis downesi (Stock, Griffin, and Burnell) with different foraging strategies. Trials were conducted at lodgepole pine sites in Ireland on both mineral and peat soil type. EPN suspension was applied to the stumps of felled pine trees, and EPN efficacy was determined afterwards by directly assessing parasitism rates after debarking one quarter of the stumps and by collecting emerging adult weevils from traps erected over other treated and control stumps. Our results suggest that both species of EPN are equally effective in suppressing LPW populations to below the current, informal thresholds of economic damage. EPN were equally efficient in controlling LPW in peat and in mineral (lithosols/regosols and acid brown earth/brown podzolics) soils. Weevil density and distribution within pine stumps in peat versus mineral sites can explain patterns of LPW parasitism and suppression. Our results also suggest that infestation level (number of weevils per stump) can be an important factor in forecasting EPN application success as there is evidence of negative density-dependent parasitism when weevil densities were high. © 2016 Springer-Verlag Berlin Heidelber
Neural Circuitry of Novelty Salience Processing in Psychosis Risk: Association With Clinical Outcome
Psychosis has been proposed to develop from dysfunction in a hippocampal-striatal-midbrain circuit, leading to aberrant salience processing. Here, we used functional magnetic resonance imaging (fMRI) during novelty salience processing to investigate this model in people at clinical high risk (CHR) for psychosis according to their subsequent clinical outcomes. Seventy-six CHR participants as defined using the Comprehensive Assessment of At-Risk Mental States (CAARMS) and 31 healthy controls (HC) were studied while performing a novelty salience fMRI task that engaged an a priori hippocampal-striatal-midbrain circuit of interest. The CHR sample was then followed clinically for a mean of 59.7 months (~5 y), when clinical outcomes were assessed in terms of transition (CHR-T) or non-transition (CHR-NT) to psychosis (CAARMS criteria): during this period, 13 individuals (17%) developed a psychotic disorder (CHR-T) and 63 did not. Functional activation and effective connectivity within a hippocampal-striatal-midbrain circuit were compared between groups. In CHR individuals compared to HC, hippocampal response to novel stimuli was significantly attenuated (P = .041 family-wise error corrected). Dynamic Causal Modelling revealed that stimulus novelty modulated effective connectivity from the hippocampus to the striatum, and from the midbrain to the hippocampus, significantly more in CHR participants than in HC. Conversely, stimulus novelty modulated connectivity from the midbrain to the striatum significantly less in CHR participants than in HC, and less in CHR participants who subsequently developed psychosis than in CHR individuals who did not become psychotic. Our findings are consistent with preclinical evidence implicating hippocampal-striatal-midbrain circuit dysfunction in altered salience processing and the onset of psychosis
YAP and β-catenin co-operate to drive oncogenesis in basal breast cancer
Targeting cancer stem cells (CSCs) can serve as an effective approach toward limiting resistance to therapies and the development of metastases in many forms of cancer. While basal breast cancers encompass cells with CSC features, rational therapies remain poorly established. Here, we show that receptor tyrosine kinase Met signalling promotes the activity of the Hippo component YAP in basal breast cancer. Further analysis revealed enhanced YAP activity within the CSC population. Using both genetic and pharmaceutical approaches, we show that interfering with YAP activity delays basal cancer formation, prevents luminal to basal trans-differentiation and reduces CSC survival. Gene expression analysis of YAP knock-out mammary glands revealed a strong decrease in β-catenin target genes in basal breast cancer, suggesting that YAP is required for nuclear β-catenin activity. Mechanistically, we find that nuclear YAP interacts and overlaps with β-catenin and TEAD4 at common gene regulatory elements. Analysis of proteomic data from primary breast cancer patients identified a significant upregulation of the YAP activity signature in basal compared to other breast cancers, suggesting that YAP activity is limited to basal types. Our findings demonstrate that in basal breast cancers, β-catenin activity is dependent on YAP signalling and controls the CSC program. These findings suggest that targeting the YAP/TEAD4/β-catenin complex offers a potential therapeutic strategy for eradicating CSCs in basal (triple-negative) breast cancers
Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation
In this paper we consider the problem of tracking the state of a quantum
system via a continuous measurement. If the system Hamiltonian is known
precisely, this merely requires integrating the appropriate stochastic master
equation. However, even a small error in the assumed Hamiltonian can render
this approach useless. The natural answer to this problem is to include the
parameters of the Hamiltonian as part of the estimation problem, and the full
Bayesian solution to this task provides a state-estimate that is robust against
uncertainties. However, this approach requires considerable computational
overhead. Here we consider a single qubit in which the Hamiltonian contains a
single unknown parameter. We show that classical frequency estimation
techniques greatly reduce the computational overhead associated with Bayesian
estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page
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