1,621 research outputs found
Single shot three-dimensional imaging of dilute atomic clouds
Light field microscopy methods together with three dimensional (3D)
deconvolution can be used to obtain single shot 3D images of atomic clouds. We
demonstrate the method using a test setup which extracts three dimensional
images from a fluorescent Rb atomic vapor.Comment: 10 pages, 5 figure
Monosynaptic connections between pairs of spiny stellate cells in layer 4 and pyramidal cells in layer 5A indicate that lemniscal and paralemniscal afferent pathways converge in the infragranular somatosensory cortex.
Monosynaptic interlaminar connections between spiny stellate cells in layer 4 (L4), the main cortical recipient layer for thalamic projections, and pyramidal cells in layer 5A (L5A), one of the main cortical output layers, were examined anatomically and functionally by paired recordings in acute brain slices. The somata of pairs forming interlaminar L4-to-L5A connections were located predominantly close to or directly under the barrel-septum wall in layer 4. Superposition of spiny stellate axon arbors and L5A pyramidal cell dendritic arbors suggested an innervation domain underneath an L4 barrel wall. Functionally, the L4-to-L5A connections were of high reliability and relatively low efficacy, with a unitary EPSP amplitude of 0.6 mV, and the connectivity was moderately high (one in seven pairs tested was connected). The EPSP amplitude was weakly depressing (paired-pulse ratio of approximately 0.8) during repetitive presynaptic action potentials at 10 Hz. The existence of Monosynaptic L4-to-L5A connections indicates that the specific 'lemniscal' thalamic input from the ventro-basal nucleus of the thalamus to the cortex and the more unspecific 'paralemniscal' afferent thalamic projections from the posterior medial nucleus of the thalamus merge already at an initial stage of cortical signal processing. These Monosynaptic connections establish a Monosynaptic coupling of the input to the cortex and its output, thereby effectively bypassing the supragranular layers
From single cells and single columns to cortical networks: dendritic excitability, coincidence detection and synaptic transmission in brain slices and brains
Although patch pipettes were initially designed to record extracellularly the elementary current events from muscle and neuron membranes, the whole-cell and loose cell-attached recording configurations proved to be useful tools for examination of signalling within and between nerve cells. In this Paton Prize Lecture, I will initially summarize work on electrical signalling within single neurons, describing communication between the dendritic compartments, soma and nerve terminals via forward- and backward-propagating action potentials. The newly discovered dendritic excitability endows neurons with the capacity for coincidence detection of spatially separated subthreshold inputs. When these are occurring during a time window of tens of milliseconds, this information is broadcast to other cells by the initiation of bursts of action potentials (AP bursts). The occurrence of AP bursts critically impacts signalling between neurons that are controlled by target-cell-specific transmitter release mechanisms at downstream synapses even in different terminals of the same neuron. This can, in turn, induce mechanisms that underly synaptic plasticity when AP bursts occur within a short time window, both presynaptically in terminals and postsynaptically in dendrites. A fundamental question that arises from these findings is: what are the possible functions of active dendritic excitability with respect to network dynamics in the intact cortex of behaving animals?' To answer this question, I highlight in this review the functional and anatomical architectures of an average cortical column in the vibrissal (whisker) field of the somatosensory cortex (vS1), with an emphasis on the functions of layer 5 thick-tufted cells (L5tt) embedded in this structure. Sensory-evoked synaptic and action potential responses of these major cortical output neurons are compared with responses in the afferent pathway, viz. the neurons in primary somatosensory thalamus and in one of their efferent targets, the secondary somatosensory thalamus. Coincidence-detection mechanisms appear to be implemented in vivo as judged from the occurrence of AP bursts. Three-dimensional reconstructions of anatomical projections suggest that inputs of several combinations of thalamocortical projections and intra- and transcolumnar connections, specifically those from infragranular layers, could trigger active dendritic mechanisms that generate AP bursts. Finally, recordings from target cells of a column reveal the importance of AP bursts for signal transfer to these cells. The observations lead to the hypothesis that in vS1 cortex, the sensory afferent sensory code is transformed, at least in part, from a rate to an interval (burst) code that broadcasts the occurrence of whisker touch to different targets of L5tt cells. In addition, the occurrence of pre- and postsynaptic AP bursts may, in the long run, alter touch representation in cortex
Quantum dynamics of attractive versus repulsive bosonic Josephson junctions: Bose-Hubbard and full-Hamiltonian results
The quantum dynamics of one-dimensional bosonic Josephson junctions with
attractive and repulsive interparticle interactions is studied using the
Bose-Hubbard model and by numerically-exact computations of the full many-body
Hamiltonian. A symmetry present in the Bose-Hubbard Hamiltonian dictates an
equivalence between the evolution in time of attractive and repulsive Josephson
junctions with attractive and repulsive interactions of equal magnitude. The
full many-body Hamiltonian does not possess this symmetry and consequently the
dynamics of the attractive and repulsive junctions are different.Comment: 9 pages, 2 figure
Universality of Fragmentation in the Schr\"odinger Dynamics of Bosonic Josephson Junctions
The many-body Schr\"odinger dynamics of a one-dimensional bosonic Josephson
junction is investigated for up to ten thousand bosons and long times. The
initial states are fully condensed and the interaction strength is weak. We
report on a universal fragmentation dynamics on the many-body level: systems
consisting of different numbers of particles fragment to the same value at
constant mean-field interaction strength. The phenomenon manifests itself in
observables such as the correlation functions of the system. We explain this
universal fragmentation dynamics analytically based on the Bose-Hubbard model.
We thereby show that the extent to which many-body effects become important at
later times depends crucially on the initial state. Even for arbitrarily large
particle numbers and arbitrarily weak interaction strength the dynamics is
many-body in nature and the fragmentation universal. There is no weakly
interacting limit where the Gross-Piatevskii mean-field is valid for long
times.Comment: 11 pages, 5 figure
Accurate multi-boson long-time dynamics in triple-well periodic traps
To solve the many-boson Schr\"odinger equation we utilize the
Multiconfigurational time-dependent Hartree method for bosons (MCTDHB). To be
able to attack larger systems and/or to propagate the solution for longer
times, we implement a parallel version of the MCTDHB method thereby realizing
the recently proposed [Streltsov {\it et al.} arXiv:0910.2577v1] novel idea how
to construct efficiently the result of the action of the Hamiltonian on a
bosonic state vector. We study the real-space dynamics of repulsive bosonic
systems made of N=12, 51 and 3003 bosons in triple-well periodic potentials.
The ground state of this system is three-fold fragmented. By suddenly strongly
distorting the trap potential, the system performs complex many-body quantum
dynamics. At long times it reveals a tendency to an oscillatory behavior around
a threefold fragmented state. These oscillations are strongly suppressed and
damped by quantum depletions. In spite of the richness of the observed
dynamics, the three time-adaptive orbitals of MCTDHB(M=3) are capable to
describe the many-boson quantum dynamics of the system for short and
intermediate times. For longer times, however, more self-consistent
time-adaptive orbitals are needed to correctly describe the non-equilibrium
many-body physics. The convergence of the MCTDHB() method with the number
of self-consistent time-dependent orbitals used is demonstrated.Comment: 37 pages, 7 figure
How does an interacting many-body system tunnel through a potential barrier to open space?
The tunneling process in a many-body system is a phenomenon which lies at the
very heart of quantum mechanics. It appears in nature in the form of
alpha-decay, fusion and fission in nuclear physics, photoassociation and
photodissociation in biology and chemistry. A detailed theoretical description
of the decay process in these systems is a very cumbersome problem, either
because of very complicated or even unknown interparticle interactions or due
to a large number of constitutent particles. In this work, we theoretically
study the phenomenon of quantum many-body tunneling in a more transparent and
controllable physical system, in an ultracold atomic gas. We analyze a full,
numerically exact many-body solution of the Schr\"odinger equation of a
one-dimensional system with repulsive interactions tunneling to open space. We
show how the emitted particles dissociate or fragment from the trapped and
coherent source of bosons: the overall many-particle decay process is a quantum
interference of single-particle tunneling processes emerging from sources with
different particle numbers taking place simultaneously. The close relation to
atom lasers and ionization processes allows us to unveil the great relevance of
many-body correlations between the emitted and trapped fractions of the
wavefunction in the respective processes.Comment: 18 pages, 4 figures (7 pages, 2 figures supplementary information
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