1,422 research outputs found
Non-Pauli Transitions From Spacetime Noncommutativity
There are good reasons to suspect that spacetime at Planck scales is
noncommutative. Typically this noncommutativity is controlled by fixed
"vectors" or "tensors" with numerical entries. For the Moyal spacetime, it is
the antisymmetric matrix . In approaches enforcing Poincar\'e
invariance, these deform or twist the method of (anti-)symmetrization of
identical particle state vectors. We argue that the earth's rotation and
movements in the cosmos are "sudden" events to Pauli-forbidden processes. They
induce (twisted) bosonic components in state vectors of identical spinorial
particles in the presence of a twist. These components induce non-Pauli
transitions. From known limits on such transitions, we infer that the energy
scale for noncommutativity is . This suggests a
new energy scale beyond Planck scale.Comment: 11 pages, 1 table, Slightly revised for clarity
Computational Modeling of Channelrhodopsin-2 Photocurrent Characteristics in Relation to Neural Signaling
Channelrhodopsins-2 (ChR2) are a class of light sensitive proteins that offer
the ability to use light stimulation to regulate neural activity with
millisecond precision. In order to address the limitations in the efficacy of
the wild-type ChR2 (ChRwt) to achieve this objective, new variants of ChR2 that
exhibit fast mono-exponential photocurrent decay characteristics have been
recently developed and validated. In this paper, we investigate whether the
framework of transition rate model with 4 states, primarily developed to mimic
the bi-exponential photocurrent decay kinetics of ChRwt, as opposed to the low
complexity 3 state model, is warranted to mimic the mono-exponential
photocurrent decay kinetics of the newly developed fast ChR2 variants: ChETA
(Gunaydin et al., Nature Neurosci, 13:387-392, 2010) and ChRET/TC (Berndt et
al., PNAS, 108:7595-7600, 2011). We begin by estimating the parameters for the
3-state and 4-state models from experimental data on the photocurrent kinetics
of ChRwt, ChETA and ChRET/TC. We then incorporate these models into a
fast-spiking interneuron model (Wang and Buzsaki., J Neurosci,
16:6402-6413,1996) and a hippocampal pyramidal cell model (Golomb et al., J
Neurophysiol, 96:1912-1926, 2006) and investigate the extent to which the
experimentally observed neural response to various optostimulation protocols
can be captured by these models. We demonstrate that for all ChR2 variants
investigated, the 4 state model implementation is better able to capture neural
response consistent with experiments across wide range of optostimulation
protocol. We conclude by analytically investigating the conditions under which
the characteristic specific to the 3-state model, namely the mono-exponential
photocurrent decay of the newly developed variants of ChR2, can occurs in the
framework of the 4-state model.Comment: 10 figure
A novel modulated phase of liquid crystals: Covariant elasticity in the context of soft, achiral smectic-C materials
Ginzburg-Landau-de Gennes -type covariant theories are extensively used in
connection with twist grain boundary (TGB) phases of chiral smectogens. We
analyze the stability conditions for the linear, covariant elasticity theory of
smectic-C liquid crystals in the context of achiral materials, and predict an
equilibrium modulated structure with an oblique wavevector. We suggest that a
previous experimental observation of stripes in smectic-C is consistent with
the predicted structure.Comment: 4 pages, 3 figure
Self-assembly of like-charged nanoparticles into microscopic crystals
Like-charged nanoparticles, NPs, can assemble in water into large, faceted crystals, each made of several million particles. These NPs are functionalized with mixed monolayers comprising ligands terminating in carboxylic acid group ligands as well as positively charged quaternary ammonium ligands. The latter groups give rise to electrostatic interparticle repulsions which partly offset the hydrogen bonding between the carboxylic acids. It is the balance between these two interactions that ultimately enables self-assembly. Depending on the pH, the particles can crystallize, form aggregates, remain unaggregated or even-in mixtures of two particle types-can choose whether to crystallize with like-charged or oppositely charged particles.open
Self-assembly of like-charged nanoparticles into microscopic crystals
Like-charged nanoparticles, NPs, can assemble in water into large, faceted crystals, each made of several million particles. These NPs are functionalized with mixed monolayers comprising ligands terminating in carboxylic acid group ligands as well as positively charged quaternary ammonium ligands. The latter groups give rise to electrostatic interparticle repulsions which partly offset the hydrogen bonding between the carboxylic acids. It is the balance between these two interactions that ultimately enables self-assembly. Depending on the pH, the particles can crystallize, form aggregates, remain unaggregated or even-in mixtures of two particle types-can choose whether to crystallize with like-charged or oppositely charged particles.open
Multipartite entanglement in fermionic systems via a geometric measure
We study multipartite entanglement in a system consisting of
indistinguishable fermions. Specifically, we have proposed a geometric
entanglement measure for N spin-1/2 fermions distributed over 2L modes (single
particle states). The measure is defined on the 2L qubit space isomorphic to
the Fock space for 2L single particle states. This entanglement measure is
defined for a given partition of 2L modes containing m >= 2 subsets. Thus this
measure applies to m <= 2L partite fermionic system where L is any finite
number, giving the number of sites. The Hilbert spaces associated with these
subsets may have different dimensions. Further, we have defined the local
quantum operations with respect to a given partition of modes. This definition
is generic and unifies different ways of dividing a fermionic system into
subsystems. We have shown, using a representative case, that the geometric
measure is invariant under local unitaries corresponding to a given partition.
We explicitly demonstrate the use of the measure to calculate multipartite
entanglement in some correlated electron systems. To the best of our knowledge,
there is no usable entanglement measure of m > 3 partite fermionic systems in
the literature, so that this is the first measure of multipartite entanglement
for fermionic systems going beyond the bipartite and tripartite cases.Comment: 25 pages, 8 figure
Chiral symmetry breaking in three-dimensional smectic-C liquid-crystal domains
We report an observation of a unique type of spontaneous chiral symmetry breaking in three-dimensional domains of a smectic-C material consisting of achiral molecules. The observed helical structure clearly demonstrates the effect of an elastic coupling between the bend and the twist distortions in the c field. The sign and the magnitude of the coupling coefficient are determined experimentally. We also demonstrate that an external chiral bias field favors domains of one handedness
Lehmann-Symanzik-Zimmermann S-Matrix elements on the Moyal Plane
Field theories on the Groenewold-Moyal(GM) plane are studied using the
Lehmann-Symanzik-Zimmermann(LSZ) formalism. The example of real scalar fields
is treated in detail. The S-matrix elements in this non-perturbative approach
are shown to be equal to the interaction representation S-matrix elements. This
is a new non-trivial result: in both cases, the S-operator is independent of
the noncommutative deformation parameter and the change in
scattering amplitudes due to noncommutativity is just a time delay. This result
is verified in two different ways. But the off-shell Green's functions do
depend on . In the course of this analysis, unitarity of the
non-perturbative S-matrix is proved as well.Comment: 18 pages, minor corrections, To appear in Phys. Rev. D, 201
Disorder-free localisation in permutation symmetric fermionic quantum walks
We investigate the phenomenon of disorder-free localisation in a quantum
system with a global permutation symmetry and the exchange symmetry for
identical particles. We start with a systematic construction of many-fermion
Hamiltonians with a global permutation symmetry using the conjugacy classes of
the permutation group , with being the total number of fermions. The
resulting Hamiltonians are interpreted as generators of continuous-time quantum
walk of indistinguishable fermions. In this setup we analytically solve the
simplest example and show that for large all the states are localised
without the introduction of any disorder coefficients. The localisation is also
time-independent and is not the result of any emergent disorder. This seems to
be an important distinction from other mechanisms of disorder-free
localisation. Furthermore, we show that the localisation is stable to
interactions that preserve the global symmetry making these systems
potential candidates for a quantum memory. By marking sites and reducing the
symmetry to subgroups of , the localisation can be obtained for any by
tuning the symmetry-reducing parameters in the Hamiltonian. Finally we show
that similar localisation also occurs for spin systems governed by a
-symmetric Heisenberg chain and we make a few comments about
-symmetric bosonic systems. The models we propose feature all-to-all
connectivity and can be realised on superconducting quantum circuits and
trapped ion systems.Comment: 24 pages, 2 figures ; v2- 27 pages, 2 figures, slight modifications
in the abstract and introductio
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