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

Multiple magnetic transitions and magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds

Magnetic and magnetocaloric properties of polycrystalline samples of Gd1-xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in these compounds are explained on the basis of the temperature dependences of the exchange strengths of the rare earth and Mn sublattices. Magnetocaloric effect is found to be positive at the re-entrant ferromagnetic transition, whereas it is negative at the antiferro-ferromagnetic transition. In SmMn2Ge2, the magnetic entropy change associated with the re-entrant transition is found to decrease with field, which is attributed to the admixture effect of the crystal field levels. The isothermal magnetic entropy change is found to decrease with increase in Sm concentration.Comment:

Heat capacity and magnetocaloric effect in polycrystalline Gd1-xSmxMn2Si2

We report the magnetocaloric effect in terms of isothermal magnetic entropy change as well as adiabatic temperature change, calculated using the heat capacity data. Using the zero field heat capacity data, the magnetic contribution to the heat capacity has been estimated. The variations in the magnetocaloric behavior have been explained on the basis of the magnetic structure of these compounds. The refrigerant capacities have also been calculated for these compounds

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

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

Deep Blue Light Emission of (4,3-Oxo?HCMM) Coumarin Derivative for Organic Led Display Application

In the present technological world huge demand of white light emitting diodes has received much importance due to their vast applications in various sensors, lightning devices and display etc. The white light can be produced by mixing exact amount of green, blue and red light. Therefore, we made an attempt to produce a LED application making use of organic compounds. Hence, we synthesized 4-Hydroxy-3-[(4-Hydroxy-2-Oxo-2H-Chromen-3-yl) (4-Methoxyphenyl) Methyl]-2H-Chromen-2-One (4,3-OxoHCMM). In this present work we report, the 4,3-OxoHCMM possesses high color purity, good CIE chromaticity coordinate, and they would have potential organic light emitting devices (LED) application, this simple method to produce the blue light as blue component can play important role in WLED. Uv-Vis absorption spectra is used to determine the optical energy bandgap Eg, andfrom the photoluminescence spectra duality nature of wavelengths for 4,3-OxoHCMM molecule in different solvents is obtained due to solvation effect, this result shows a simple extraction of dye in different solvents which can be used to produce the desired wavelength

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 $\theta_{\mu\nu}$ 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 $\theta_{\mu\nu}$. 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

Entanglement Capacity of Nonlocal Hamiltonians : A Geometric Approach

We develop a geometric approach to quantify the capability of creating entanglement for a general physical interaction acting on two qubits. We use the entanglement measure proposed by us for $N$-qubit pure states (PRA \textbf{77}, 062334 (2008)). Our procedure reproduces the earlier results (PRL \textbf{87}, 137901 (2001)). The geometric method has the distinct advantage that it gives an experimental way to monitor the process of optimizing entanglement production.Comment: 8 pages, 1 figure