Return to return point memory

We describe a new class of systems exhibiting return point memory (RPM), different from those discussed before in the context of ferromagnets. We show numerically that one-dimensional random Ising antiferromagnets have exact RPM when evolving from a large field, but not when started at finite field, unlike the ferromagnetic case. This implies that the standard approach to understanding ferromagnetic RPM will fail for this case. We also demonstrate RPM with a set of variables that keeps track of spin flips at each site. Conventional RPM for the spins is a projection of this result, suggesting that spin flip variables might be a more fundamental representation of the dynamics. We also present a mapping that embeds the antiferromagnetic chain in a two-dimensional ferromagnet, and prove RPM for spin-exchange dynamics in the interior of the chain with this mapping.     

Multiple internal reflections in the cochlea and their effect on DPOAE fine structure

In recent years, evidence has accumulated in support of a two-source model of distortion product otoacoustic emissions (DPOAEs). According to such models DPOAEs recorded in the ear canal are associated with two separate sources of cochlear origin. It is the interference between the contributions from the two sources that gives rise to the DPOAE fine structure (a pseudoperiodic change in DPOAE level or group delay with frequency). Multiple internal reflections between the base of the cochlea (oval window) and the DP tonotopic place can add additional significant components for certain stimulus conditions and thus modify the DPOAE fine structure. DPOAEs, at frequency increments between 4 and 8 Hz, were recorded at fixed f2/f1 ratios of 1.053, 1.065, 1.08, 1.11, 1.14, 1.18, 1.22, 1.26, 1.30, 1.32, 1.34, and 1.36 from four subjects. The resulting patterns of DPOAE amplitude and group delay (the negative of the slope of phase) revealed several previously unreported patterns in addition to the commonly reported log sine variation with frequency. These observed "exotic" patterns are predicted in computational simulations when multiple internal reflections are included. An inverse FFT algorithm was used to convert DPOAE data from the frequency to the "time" domain. Comparison of data in the time and frequency domains confirmed the occurrence of these "exotic" patterns in conjunction with the presence of multiple internal reflections. Multiple internal reflections were observed more commonly for high primary ratios (f2/f1 > or = 1.3). These results indicate that a full interpretation of the DPOAE level and phase (group delay) must include not only the two generation sources, but also multiple internal reflections.     

A modified approach to 2-(N-aryl)-1,3-oxazoles: application to the synthesis of the IMPDH inhibitor BMS-337197 and analogues

[structure: see text] A modified approach to the synthesis of 2-(N-aryl)-1,3-oxazoles, employing an optimized iminophosphorane/heterocumulene-mediated methodology, and its application to the synthesis of BMS-337197, a potent inhibitor of IMPDH, are described.     

Enhancing robustness of multiparty quantum correlations using weak measurement

Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger–Horne–Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources.     

Investigation of nonlinear optical parameters of zinc based amorphous chalcogenide films

Third order nonlinear optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films have been investigated using single beam transmission z-scan technique at 1064 nm of Nd:YAG laser. Measurement of optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films prepared by thermal evaporation technique has been made. X-ray diffraction patterns of chalcogenide films confirm the amorphous nature. Optical band gap (E_g) has been estimated using Tauc's plot method from transmission spectra that is found to decrease with increase in content due to valence band broadening and band tailing the system. Nonlinear refractive index (n₂), nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ³) of chalcogenide films have been estimated. Self-focusing effect has been observed in closed aperture and reverse saturable absorption in open aperture scheme. Limiting threshold and dynamic range have been calculated from optical limiting studies. The increase in nonlinearity with increase in Zn content has been observed that is understood to be due to decrease in band gap on Zn doping. High nonlinearity makes these films a potential candidate for waveguides, fibers and two photon absorption in optical limiters.     

Dielectric and electro-optical response of a room temperature tri-component antiferroelectric mixture

Frequency- and temperature-dependent dielectric and switching parameters of a room temperature tri-component antiferroelectric liquid crystal mixture W-287 have been determined. Dielectric, optical texture and thermodynamic studies show wide room temperature range antiferroelectric SmC*_a (?91.1°C to <–25°C) phase in addition to high temperature paraelectric SmA* (?2.6°C) and ferroelectric SmC* (?4.4°C) phases. The dielectric studies carried out in the frequency range of 1–35 MHz under planar anchoring condition of the molecules show five different relaxation modes appearing in the SmA*, SmC* and SmC*_a phases. Using Curie–Weiss law fit, ferroelectric SmC* to paraelectric SmA* transition temperature has been found to be 91.8°C. The dielectric response of SmC*_a phase exhibits unusually three relaxation modes due to collective as well as individual molecular processes in addition to phason mode in the SmC* phase and amplitudon mode in the SmA* phase. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of P_S is ?300 nC/cm², whereas viscosity is moderate. Switching time is of the order of few milli seconds.     

Phase diagrams and morphology of polymer-dispersed liquid crystals: An analysis

Thermal and morphological studies of polymer-dispersed liquid crystals (PDLCs) for various compositions of liquid crystalline material 4-undecyloxybenzoic acid (UDBA) in two polymer matrices, polyvinylidenefluoride-co-hexafluoropropylene P(VdF–HFP) or polyethylene oxide (PEO), have been carried out using differential scanning calorimetry (DSC) and polarising optical microscopy (POM). Phase diagrams for different series of PDLCs have been analysed using the Flory–Huggins theory of isotropic mixing and the Maier–Saupe–McMillan theory, to include the anisotropic contributions. Mesogenic transitions of UDBA are observed to be greatly influenced when dispersed in these polymers. The morphologies and miscibility studies of these PDLCs suggest that UDBA is highly miscible in PEO, only partially miscible in poly(methyl methacrylate) (PMMA), but almost immiscible in P(VdF–HFP).     

Dye-sensitised solar cells with iodine-free discotic electrolytes

Discotic mesogenic molecules viz., hexahexylthiotriphenylene (HHTT) and hexahexyloxytriphenylene were applied, for the first time, as iodine-free redox electrolyte in dye-sensitised solar cells (DSSCs). The cell shows open circuit voltage (V_oc) of 0.95 V, short circuit current density (J_sc) of 0.534 mA/cm², fill factor 88.24% and overall power conversion efficiency (η) 0.45% in a typical fluorine doped tin oxide/TiO₂/N719/HHTT/Pt DSSC configuration. Scanning electron microscopy was used to study surface profile of electrolytes while electrochemical impedance spectroscopy was used to understand the electrochemical behaviour of electrolytes. The photovoltaic parameters were measured under standard conditions using Oriel solar simulator class AAA. These first results demonstrate the potential of the discotic molecules as charge transporter and mediator and show promise to be used in iodine-free DSSCs.