1,678 research outputs found
Continuum mechanical modeling of processing induced initial anisotropy in the finite strain deformation of amorphous thermoplastic polymers
Research Article
[Abstract] During sleep, the brain undergoes dynamic and structural changes. In Drosophila, such changes have been observed in the central complex, a brain area important for sleep control and navigation. The connectivity of the central complex raises the question about how navigation, and specifically the head direction system, can operate in the face of sleep related plasticity. To address this question, we develop a model that integrates sleep homeostasis and head direction. We show that by introducing plasticity, the head direction system can function in a stable way by balancing plasticity in connected circuits that encode sleep pressure. With increasing sleep pressure, the head direction system nevertheless becomes unstable and a sleep phase with a different plasticity mechanism is introduced to reset network connectivity. The proposed integration of sleep homeostasis and head direction circuits captures features of their neural dynamics observed in flies and mice.[Author summary] In Drosophila, sleep and navigation are largely disconnected fields, even though the same brain structures and connected neural circuits are important for the two different functionalities. Motivated by experimental results from both fields as well as the connectome, we use theoretical modeling to describe the coupled dynamics of homeostatic sleep and navigation circuits in the central complex of Drosophila. The resulting model can incorporate and explain several experimental findings about sleep and navigation in flies and mice. The model is based on a ring attractor network which is combined with plasticity rules that change between sleep and wake phases and shows autonomous dynamics during sleep, reminiscent of observations in the head direction system of mice
Integration of sleep homeostasis and navigation in Drosophila
During sleep, the brain undergoes dynamic and structural changes. In Drosophila, such changes have been observed in the central complex, a brain area important for sleep control and navigation. For navigation, the structure and function of the central complex suggest a relationship to ring attractors, networks that model head direction. This raises the question about a similar structure-function relationship for sleep control.Motivated by experimental findings, we develop a ring attractor model that maintains activity at a setpoint in the face of plasticity. In this model, an integrator of sleep drive emerges with a functional role in stabilizing the network. Nevertheless, the network becomes unstable over extended wake time. Therefore, a sleep phase is introduced where autonomous attractor dynamics, related to its activity during wakefulness, reset the network. The proposed integration of sleep and head direction circuits captures features of their neural dynamics observed in flies and mice during wakefulness and sleep.Author Summary In Drosophila, the study of sleep and the study of navigation are largely disconnected fields, even though the same brain structures and connected neural circuits are important for the two different functionalities. Motivated by experimental results from both fields, we use theoretical modeling to describe the coupled dynamics of sleep and navigation circuits and propose a rationale for why they interact. The resulting model can incorporate and explain several experimental findings about sleep and navigation in flies and mice. The model is based on a ring attractor network which is combined with plasticity rules that change between sleep and wake phases and shows autonomous dynamics during sleep, reminiscent of observations in the head direction system of mice
Probe-Configuration-Dependent Decoherence in an Aharonov-Bohm Ring
We have measured transport through mesoscopic Aharonov-Bohm (AB) rings with
two different four-terminal configurations. While the amplitude and the phase
of the AB oscillations are well explained within the framework of the
Landaur-B\"uttiker formalism, it is found that the probe configuration strongly
affects the coherence time of the electrons, i.e., the decoherence is much
reduced in the configuration of so-called nonlocal resistance. This result
should provide an important clue in clarifying the mechanism of quantum
decoherence in solids.Comment: 4 pages, 4 figures, RevTe
The electron lifetime in Luttinger liquids
We investigate the decoherence of the electron wavepacket in purely ballistic
one-dimensional systems described through the Luttinger liquid (LL). At a
finite temperature and long times , we show that the electron Green's
function for a fixed wavevector close to one Fermi point decays as
, as opposed to the power-law behavior occurring at short
times, and the emerging electron lifetime obeys for
spinful as well as spinless electrons. For strong interactions, , reflecting that the electron is not a good Landau quasiparticle in LLs. We
justify that fractionalization is the main source of electron decoherence for
spinful as well as spinless electrons clarifying the peculiar electron mass
renormalization close to the Fermi points. For spinless electrons and weak
interactions, our intuition can be enriched through a diagrammatic approach or
Fermi Golden rule and through a Johnson-Nyquist noise picture. We stress that
the electron lifetime (and the fractional quasiparticles) can be revealed from
Aharonov-Bohm experiments or momentum resolved tunneling. We aim to compare the
results with those of spin-incoherent and chiral LLs.Comment: 20 pages, 1 column, 6 figures, 1 Table; expands cond-mat/0110307 and
cond-mat/0503652; final version to appear in PR
Temperature and magnetic-field dependence of the quantum corrections to the conductance of a network of quantum dots
We calculate the magnetic-field and temperature dependence of all quantum
corrections to the ensemble-averaged conductance of a network of quantum dots.
We consider the limit that the dimensionless conductance of the network is
large, so that the quantum corrections are small in comparison to the leading,
classical contribution to the conductance. For a quantum dot network the
conductance and its quantum corrections can be expressed solely in terms of the
conductances and form factors of the contacts and the capacitances of the
quantum dots. In particular, we calculate the temperature dependence of the
weak localization correction and show that it is described by an effective
dephasing rate proportional to temperature.Comment: 24 pages, 14 figure
Assessment of eosinophils in gastrointestinal inflammatory disease of dogs
Background
Accurate identification of eosinophils in the gastrointestinal (GI) tract of dogs with eosinophilic GI disease (EGID) by histological evaluation is challenging. The currently used hematoxylin and eosin (H&E) staining method detects intact eosinophils but does not detect degranulated eosinophils, thus potentially underrepresenting the number of infiltrating eosinophils.
Objective
To develop a more sensitive method for identifying and quantifying both intact and degranulated eosinophils to diagnose EGID more accurately.
Methods
Endoscopically obtained paraffin‐embedded intestinal biopsy specimens from dogs with GI signs were examined. The study groups were dogs with eosinophilic enteritis (EE), lymphoplasmacytic and mixed enteritis, and control dogs with GI signs but no histologic changes on tissue sections. Consecutive sections were immunolabeled with monoclonal antibodies (mAbs) against the eosinophil granule protein eosinophil peroxidase (Epx) and stained by H&E, respectively. The number of eosinophils was manually quantified and classified as intact or degranulated.
Results
The number of intact eosinophils detected in Epx mAb‐labeled duodenal sections was significantly higher compared with that in H&E‐stained sections, with a similar relationship noted in the colon and stomach. The Epx mAb allowed the unique assessment of eosinophil degranulation. The number of intact and degranulated eosinophils was significantly higher in duodenal lamina propria of the EE and mixed group compared to the control group.
Conclusion
Immunohistochemical detection of Epx provides a more precise method to detect GI tract eosinophils compared to H&E staining and could be used as an alternative and reliable diagnostic tool for assessment of biopsy tissues from dogs with EGID
Disease, activity and schoolchildren's health (DASH) in Port Elizabeth, South Africa: a study protocol
BACKGROUND: An in-depth epidemiological investigation on intestinal parasite infections in an impoverished area of Port Elizabeth, South Africa provides a unique opportunity for research on its impact on children's physical fitness, cognitive performance and psychosocial health. Additionally, we will screen risk factors for the development of diabetes and hypertension in adulthood.
METHODS/DESIGN: A 2-year longitudinal cohort study will be conducted, consisting of three cross-sectional surveys (baseline and two follow-ups), in eight historically black and coloured (mixed race) primary schools located in different townships in Port Elizabeth, South Africa. Approximately 1000 Grade 4 primary schoolchildren, aged 8 to 12 years, will be enrolled and followed. At each survey, disease status, anthropometry and levels of physical fitness, cognitive performance and psychosocial health will be assessed. After each survey, individuals diagnosed with parasitic worm infections will be treated with anthelminthic drugs, while children with other infections will be referred to local clinics. Based on baseline results, interventions will be tailored to the local settings, embedded within the study and implemented in half of the schools, while the remaining schools will serve as controls. Implementation of the interventions will take place over two 8-week periods. The effect of interventions will be determined with predefined health parameters.
DISCUSSION: This study will shed new light on the health burden incurred by children in deprived urban settings of South Africa and provide guidance for specific health interventions. Challenges foreseen in the conduct of this study include: (i) difficulty in obtaining written informed consent from parents/guardians; (ii) administration of questionnaires in schools where three languages are spoken (Afrikaans, Xhosa and English); (iii) challenges in grasping concepts of psychosocial health among schoolchildren using a questionnaire; and (iv) loss to follow-up due to the study setting where illiteracy, mobility and violence are common. Finally, designing the health interventions together with local principals and teachers will allow all concerned with the research to bolster a sense of community ownership and sustained use of the interventions after the study has ceased
Current-voltage correlations in interferometers
We investigate correlations of current at contacts and voltage fluctuations
at voltage probes coupled to interferometers. The results are compared with
correlations of current and occupation number fluctuations at dephasing probes.
We use a quantum Langevin approach for the average quantities and their
fluctuations. For higher order correlations we develop a stochastic path
integral approach and find the generating functions of voltage or occupation
number fluctuations. We also derive a generating function for the joint
distribution of voltage or occupation number at the probe and current
fluctuations at a terminal of a conductor. For energy independent scattering we
found earlier that the generating function of current cumulants in
interferometers with a one-channel dephasing or voltage probe are identical.
Nevertheless, the distribution function for voltage and the distribution
function for occupation number fluctuations differ, the latter being broader
than that of former in all examples considered here.Comment: 23 pages, 10 figures, minor changes, additional appendix, added
reference
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