91 research outputs found
P\'olya number of continuous-time quantum walks
We propose a definition for the P\'olya number of continuous-time quantum
walks to characterize their recurrence properties. The definition involves a
series of measurements on the system, each carried out on a different member
from an ensemble in order to minimize the disturbance caused by it. We examine
various graphs, including the ring, the line, higher dimensional integer
lattices and a number of other graphs and calculate their P\'olya number. For
the timing of the measurements a Poisson process as well as regular timing are
discussed. We find that the speed of decay for the probability at the origin is
the key for recurrence.Comment: 8 pages, no figures. Accepted for publication in Physical Review
Poor sleep quality predicts psychotic‐like symptoms: an experience sampling study in young adults with schizotypal traits
Objective: Psychotic-like experiences (PLEs) are unusual experiences such as perceptual abnormalities and delusional-like thoughts that resemble the symptoms of psychosis at the sub-clinical level. PLEs are
associated with sleep complaints in healthy and clinical samples; however, evidence for day-to-day associations between poor sleep and subsequent PLEs under naturalistic conditions is scarce. We hypothesized that poor sleep quality would predict next days’ PLEs, and vice versa, daytime PLEs would be associated with worse subsequent sleep quality.
Method: Seventy-three university students with moderate to high levels of positive schizotypy participated in an experience sampling study. Participants rated their sleep each morning, as well as PLEs and affective states during the day over 3 weeks.
Results: Multilevel regression models indicated that poor sleep quality predicted increased PLEs the following day. Poor sleep was linked to negative daytime mood that partially mediated the associations between sleep quality and next days’ PLEs. Furthermore, PLEs were enhanced
in the evening as compared to daytime reports. The prediction of poor sleep quality by previous days’ PLEs was negligible.
Conclusions: The results are consistent with the position that sleep related interventions might reduce the risk of psychosis, especially in individuals that tend to experience psychotic-like phenomena and negative affect
Syntactic Markovian Bisimulation for Chemical Reaction Networks
In chemical reaction networks (CRNs) with stochastic semantics based on
continuous-time Markov chains (CTMCs), the typically large populations of
species cause combinatorially large state spaces. This makes the analysis very
difficult in practice and represents the major bottleneck for the applicability
of minimization techniques based, for instance, on lumpability. In this paper
we present syntactic Markovian bisimulation (SMB), a notion of bisimulation
developed in the Larsen-Skou style of probabilistic bisimulation, defined over
the structure of a CRN rather than over its underlying CTMC. SMB identifies a
lumpable partition of the CTMC state space a priori, in the sense that it is an
equivalence relation over species implying that two CTMC states are lumpable
when they are invariant with respect to the total population of species within
the same equivalence class. We develop an efficient partition-refinement
algorithm which computes the largest SMB of a CRN in polynomial time in the
number of species and reactions. We also provide an algorithm for obtaining a
quotient network from an SMB that induces the lumped CTMC directly, thus
avoiding the generation of the state space of the original CRN altogether. In
practice, we show that SMB allows significant reductions in a number of models
from the literature. Finally, we study SMB with respect to the deterministic
semantics of CRNs based on ordinary differential equations (ODEs), where each
equation gives the time-course evolution of the concentration of a species. SMB
implies forward CRN bisimulation, a recently developed behavioral notion of
equivalence for the ODE semantics, in an analogous sense: it yields a smaller
ODE system that keeps track of the sums of the solutions for equivalent
species.Comment: Extended version (with proofs), of the corresponding paper published
at KimFest 2017 (http://kimfest.cs.aau.dk/
Parentage testing and looking for single nucleotide markers associated with antler quality in deer (<i>Cervus elaphus</i>)
To provide a cost-efficient parentage testing kit for red deer (Cervus elaphus), a 63 SNP set has been developed from a high-density Illumina
BovineHD BeadChip containing 777 962 SNPs after filtering of genotypes of 50
stags. The successful genotyping rate was 38.6 % on the chip. The ratio
of polymorphic loci among effectively genotyped loci was 6.5 %. The
selected 63 SNPs have been applied to 960 animals to perform parentage
control. Thirty SNPs out of the 63 had worked on the OpenArray platform. Their
combined value of the probability of identity and exclusion probability was
4.9×10-11 and 0.99803, respectively.
A search for loci linked with antler quality was also performed on the
genotypes of the above-mentioned stags. Association studies revealed 14 SNPs
associated with antler quality, where low-quality antlers with short and
thin main beam antlers had values from 1 to 2, while high-quality antlers
with long and strong main beams had values between 4 and 5. The chance for a
stag to be correctly identified as having high-value antlers is expected to
be over 88 %.</p
Spine neck plasticity regulates compartmentalization of synapses
Dendritic spines have been proposed to transform synaptic signals through chemical and electrical compartmentalization. However, the quantitative contribution of spine morphology to synapse compartmentalization and its dynamic regulation are still poorly understood. We used time-lapse super-resolution stimulated emission depletion (STED) imaging in combination with fluorescence recovery after photobleaching (FRAP) measurements, two-photon glutamate uncaging, electrophysiology and simulations to investigate the dynamic link between nanoscale anatomy and compartmentalization in live spines of CA1 neurons in mouse brain slices. We report a diversity of spine morphologies that argues against common categorization schemes and establish a close link between compartmentalization and spine morphology, wherein spine neck width is the most critical morphological parameter. We demonstrate that spine necks are plastic structures that become wider and shorter after long-term potentiation. These morphological changes are predicted to lead to a substantial drop in spine head excitatory postsynaptic potential (EPSP) while preserving overall biochemical compartmentalization
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