5,999 research outputs found
A semi-Markov model for stroke with piecewise-constant hazards in the presence of left, right and interval censoring.
This paper presents a parametric method of fitting semi-Markov models with piecewise-constant hazards in the presence of left, right and interval censoring. We investigate transition intensities in a three-state illness-death model with no recovery. We relax the Markov assumption by adjusting the intensity for the transition from state 2 (illness) to state 3 (death) for the time spent in state 2 through a time-varying covariate. This involves the exact time of the transition from state 1 (healthy) to state 2. When the data are subject to left or interval censoring, this time is unknown. In the estimation of the likelihood, we take into account interval censoring by integrating out all possible times for the transition from state 1 to state 2. For left censoring, we use an Expectation-Maximisation inspired algorithm. A simulation study reflects the performance of the method. The proposed combination of statistical procedures provides great flexibility. We illustrate the method in an application by using data on stroke onset for the older population from the UK Medical Research Council Cognitive Function and Ageing Study
Dopamine in nucleus accumbens: salience modulation in latent inhibition and overshadowing
Latent inhibition (LI) is demonstrated when non-reinforced pre-exposure to a
to-be-conditioned stimulus retards later learning. Learning is similarly
retarded in overshadowing, in this case using the relative intensity of
competing cues to manipulate associability. Electrolytic/excitotoxic lesions to
shell accumbens (NAc) and systemic amphetamine both reliably abolish LI. Here a
conditioned emotional response procedure was used to demonstrate LI and
overshadowing and to examine the role of dopamine (DA) within NAc. Experiment 1
showed that LI but not overshadowing was abolished by systemic amphetamine
(1.0 mg/kg i.p.). In Experiment 2, 6-hydroxydopamine (6-OHDA) was used
to lesion DA terminals within NAc: both shell- and core- (plus shell-)lesioned
rats showed normal LI and overshadowing. Experiment 3 compared the effects of
amphetamine microinjected at shell and core coordinates prior to conditioning:
LI, but not overshadowing, was abolished by 10.0 but not
5.0 µg/side amphetamine injected in core but not shell NAc.
These results suggest that the abolition of LI produced by NAc shell lesions is
not readily reproduced by regionally restricted DA depletion within NAc; core
rather than shell NAc mediates amphetamine-induced abolition of LI;
overshadowing is modulated by different neural substrates
Observation of second sound in graphite at temperatures above 100 K
Wavelike thermal transport in solids, referred to as second sound, has until
now been an exotic phenomenon limited to a handful of materials at low
temperatures. This has restricted interest in its occurrence and in its
potential applications. Through time-resolved optical measurements of thermal
transport on 5-20 {\mu}m length scales in graphite, we have made direct
observations of second sound at temperatures above 100 K. The results are in
qualitative agreement with ab initio calculations that predict wavelike phonon
hydrodynamics on ~ 1-{\mu}m length scale up to almost room temperature. The
results suggest an important role of second sound in microscale transient heat
transport in two-dimensional and layered materials in a wide temperature range
Convincing the crowd: entrepreneurial storytelling in crowdfunding campaigns
This study examines the structure of entrepreneurial stories in pursuit of mobilizing resources from crowds. Based on a comparative analysis of Kickstarter crowdfunding campaigns, we examine in particular how, across different project types, project histories and potential futures are framed and interlinked in narratives to appeal to funders. We find that projects are narrated in different styles—as ongoing journeys” or “results-inprogress”— to convey project value. The former style narrates projects as longer-term endeavors powered by creative initial ideas and a bold vision, inviting audiences to “join the journey”; the latter narrates projects more narrowly as a progression of accomplishments, engaging the audience instrumentally to support next steps. We find that styles are used and combined in different ways, reflecting the tangibility of project outcomes, the sophistication of technology, and the social orientation of projects. Also, successful differ from unsuccessful campaigns in using narratives more coherently. Findings inform research on narrative processes in entrepreneurship and innovation, and research on the mobilization of crowds
The Conformal Sector of F-theory GUTs
D3-brane probes of exceptional Yukawa points in F-theory GUTs are natural
hidden sectors for particle phenomenology. We find that coupling the probe to
the MSSM yields a new class of N = 1 conformal fixed points with computable
infrared R-charges. Quite surprisingly, we find that the MSSM only weakly mixes
with the strongly coupled sector in the sense that the MSSM fields pick up
small exactly computable anomalous dimensions. Additionally, we find that
although the states of the probe sector transform as complete GUT multiplets,
their coupling to Standard Model fields leads to a calculable threshold
correction to the running of the visible sector gauge couplings which improves
precision unification. We also briefly consider scenarios in which SUSY is
broken in the hidden sector. This leads to a gauge mediated spectrum for the
gauginos and first two superpartner generations, with additional contributions
to the third generation superpartners and Higgs sector.Comment: v2: 51 pages, 2 figures, remark added, typos correcte
Catecholaminergic depletion in nucleus accumbens enhances trace conditioning
Purpose: To examine the effect of dopamine depletion in nucleus accumbens on trace conditioning; to distinguish the role of core and shell sub-regions, as far as possible. Material/Methods: 6-hydroxydopamine was used to lesion dopamine terminals within the core and shell accumbens. Experiment 1 assessed conditioning to a tone conditioned stimulus that had previously been paired with footshock (unconditioned stimulus) at a 30s trace interval. Experiment 2 subsequently assessed contiguous conditioning (at 0s trace) using a light conditioned stimulus directly followed by the unconditioned stimulus.
Results: Both sham and shell-lesioned animals showed the normal trace effect of reduced conditioning to the trace conditioned stimulus but 6-hydroxydopamine injections targeted on the core subregion of the nucleus accumbens abolished this effect and enhanced conditioning to the trace conditioned stimulus. However, the depletion produced by this lesion placement extended to the shell. In Experiment 2 (at 0s trace), there was no effect of either lesion placement as all animals showed comparable levels of conditioning to the light conditioned stimulus. Neurochemical analysis across core, shell and comparison regions showed some effects on noradrenalin as well as dopamine.
Conclusions: The pattern of changes in noradrenalin did not systematically relate to the observed behavioural changes after core injections. The pattern of changes in dopamine suggested that depletion in core mediated the increased conditioning to the trace conditioned stimulus seen in the present study. However, the comparison depletion restricted to the shell subregion was less substantial, and a role for secondarily affected brain regions cannot be excluded
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