55,585 research outputs found
Many-body processes in black and grey matter-wave solitons
We perform a comparative beyond mean-field study of black and grey solitonic
excitations in a finite ensemble of ultracold bosons confined to a
one-dimensional box. An optimized density-engineering potential is developed
and employed together with phase-imprinting to cleanly initialize grey
solitons. Based on our recently developed Multi-Layer Multi-Configuration
Time-Dependent Hartree Method for Bosons, we demonstrate an enhancement of the
quantum fluctuations limited lifetime of the soliton contrast with increasing
soliton velocity. A natural orbital analysis reveals a two-stage process
underlying the decay of the soliton contrast. The broken parity symmetry of
grey solitons results in a local asymmetry of the orbital mainly responsible
for the decay, which leads to a characteristic asymmetry of remarkably
localized two-body correlations. The emergence and decay of these correlations
as well as their displacement from the instantaneous soliton position are
analysed in detail. Finally, the role of phase-imprinting for the many-body
dynamics is illuminated and additional non-local correlations in pairs of
counter-propagating grey solitons are unravelled
Emergence of a stable cortical map for neuroprosthetic control.
Cortical control of neuroprosthetic devices is known to require neuronal adaptations. It remains unclear whether a stable cortical representation for prosthetic function can be stored and recalled in a manner that mimics our natural recall of motor skills. Especially in light of the mixed evidence for a stationary neuron-behavior relationship in cortical motor areas, understanding this relationship during long-term neuroprosthetic control can elucidate principles of neural plasticity as well as improve prosthetic function. Here, we paired stable recordings from ensembles of primary motor cortex neurons in macaque monkeys with a constant decoder that transforms neural activity to prosthetic movements. Proficient control was closely linked to the emergence of a surprisingly stable pattern of ensemble activity, indicating that the motor cortex can consolidate a neural representation for prosthetic control in the presence of a constant decoder. The importance of such a cortical map was evident in that small perturbations to either the size of the neural ensemble or to the decoder could reversibly disrupt function. Moreover, once a cortical map became consolidated, a second map could be learned and stored. Thus, long-term use of a neuroprosthetic device is associated with the formation of a cortical map for prosthetic function that is stable across time, readily recalled, resistant to interference, and resembles a putative memory engram
Statistical Thermodynamics of Clustered Populations
We present a thermodynamic theory for a generic population of individuals
distributed into groups (clusters). We construct the ensemble of all
distributions with fixed and , introduce a selection functional that
embodies the physics that governs the population, and obtain the distribution
that emerges in the scaling limit as the most probable among all distributions
consistent with the given physics. We develop the thermodynamics of the
ensemble and establish a rigorous mapping to thermodynamics. We treat the
emergence of a so-called "giant component" as a formal phase transition and
show that the criteria for its emergence are entirely analogous to the
equilibrium conditions in molecular systems. We demonstrate the theory by an
analytic model and confirm the predictions by Monte Carlo simulation.Comment: Minor edits to tex
Epistemic and Ontic Quantum Realities
Quantum theory has provoked intense discussions about its interpretation since its pioneer days. One of the few scientists who have been continuously engaged in this development from both physical and philosophical perspectives is Carl Friedrich von Weizsaecker. The questions he posed were and are inspiring for many, including the authors of this contribution. Weizsaecker developed Bohr's view of quantum theory as a theory of knowledge. We show that such an epistemic perspective can be consistently complemented by Einstein's ontically oriented position
- …