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Nonlinear and magneto-optical transmission studies on magnetic nanofluids of non-interacting metallic nickel nanoparticles
No full textOpen AccessOxide free stable metallic nanofluids have the potential for various applications such as in
thermal management and inkjet printing apart from being a candidate system for fundamental
studies. A stable suspension of nickel nanoparticles of ∼5 nm size has been realized by a
modified two-step synthesis route. Structural characterization by x-ray diffraction and
transmission electron microscopy shows that the nanoparticles are metallic and are phase pure.
The nanoparticles exhibited superparamagnetic properties. The magneto-optical transmission
properties of the nickel nanofluid (Ni-F) were investigated by linear optical dichroism
measurements. The magnetic field dependent light transmission studies exhibited a polarization
dependent optical absorption, known as optical dichroism, indicating that the nanoparticles
suspended in the fluid are non-interacting and superparamagnetic in nature. The nonlinear
optical limiting properties of Ni-F under high input optical fluence were then analyzed by an
open aperture z-scan technique. The Ni-F exhibits a saturable absorption at moderate laser
intensities while effective two-photon absorption is evident at higher intensities. The Ni-F
appears to be a unique material for various optical devices such as field modulated gratings and
optical switches which can be controlled by an external magnetic field
Improved optical limiting in dispersible carbon nanotubes and their metal oxide hybrids
No full textRestricted Access.The mechanism and performance of optical limiting in carbon nanotubes (CNTs) and their metal oxide hybrids are presented. The mechanism of nonlinear absorption (NLA) in dispersed CNTs was an "effective" three-photon absorption arising due to sequential transitions between the real excited states. The effect of nonlinear scattering was minimal, and it was found that the metal oxide immobilization on the CNT surface does not alter either the mechanism of NLA, or the optical limiting threshold. With limiting thresholds in the range of 0.37-0.46 J/cm(2), these highly dispersible MWCNTs and their hybrids are excellent optical liming nanocarbons. (C) 2011 Elsevier Ltd. All rights reserved
Electro-optical investigations and effect of asymmetry in bent-core liquid crystals
No full textRestricted Access.We report the synthesis and mesomorphic properties of a homologous series (10a–10g) of bent-core molecules
constructed through covalent linkage of structurally non-symmetrical rod-like mesogens connected with a 1,
3-phenylene unit. The study of homologous series underlines the importance of length and nature of terminal
chains. The homologues of shorter chains show a typical non-switchable rectangular columnar B1 phase, while the
switchable lamellar (B2) phase is induced on moving to higher homologues. X-ray diffraction patterns indicate the
presence of B1 and B2 mesophases. Polarised optical microscopy investigations under electric field in the B2 phases
revealed the existence of anticlinic antiferroelectric texture. The measured spontaneous polarisation value in one
of the compounds is 936 nC cm−2, a high polarisation value in bent-core liquid crystals
Multispecies model with interconversion, chipping, and injection
No full textOpen AccessMotivated by the phenomenology of transport through the Golgi apparatus of cells, we study a multispecies model with boundary injection of one species of particle, interconversion between the different species of particle, and driven diffusive movement of particles through the system by chipping of a single particle from a site. The model is analyzed in one dimension using equations for particle currents. It is found that, depending on the rates of various processes and the asymmetry in the hopping, the system may exist either in a steady phase, in which the average mass at each site attains a time-independent value, or in a “growing” phase, in which the total mass grows indefinitely in time, even in a finite system. The growing phases have interesting spatial structure. In particular, we find phases in which some spatial regions of the system have a constant average mass, while other regions show unbounded growth
Studies of quasi-periodic oscillations in the black hole transient XTE J1817-330
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We have used archival Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data to investigate the timing and spectral characteristics of the transient XTE J1817-330. The data pertain to 160 PCA pointed observations made during the outburst period 2006 January 27 to August 2. A detailed analysis of quasi-periodic oscillations (QPOs) in this black hole X-ray binary is carried out. Power density spectra were obtained using the light curves of the source. QPOs have been detected in the 2-8 keV band in 10 of the observations. In eight of these observations, QPOs are present in the 8-14 keV and in five observations in the 15-25 keV band. XTE J1817-330 is the third black hole source from which low-frequency QPOs are clearly detected in hard X-rays. The QPO frequency lies in approximate to 4-9 Hz and the rms amplitude in the 1.7-13.3 per cent range, the amplitude being higher at higher energies. We have fitted the power density spectra of the observations with Lorentzian and power-law models. Energy spectra are derived for those observations in which the QPOs are detected, in order to investigate any dependence of the QPO characteristic on the spectral parameters. These spectra are well fitted with a two-component model, which includes the disc blackbody component and a power-law component. The QPO characteristics and their variations are discussed and the implications on the origin of QPOs are examined
Interplay of energy dependent astrophysical neutrino flavor ratios and new physics effects
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We discuss the importance of flavor ratio measurements in neutrino telescopes, such as by measuring the ratio between muon tracks to cascades, for the purpose of extracting new physics signals encountered by astrophysical neutrinos during propagation from the source to the detector. The detected flavor ratios not only carry the energy information of specific new physics scenarios which alter the transition probabilities in distinctive ways, but also the energy dependent flavor composition at the source. In the present work, we discuss the interplay of these two energy dependent effects and identify which new physics scenarios can be distinguished from the detected flavor ratios as a function of astrophysical parameters. We use a recently developed self-consistent neutrino production model as our toy model to generate energy dependent source flavor ratios and discuss (invisible) neutrino decay and quantum decoherence as specific new physics examples. Furthermore, we identify potentially interesting classes of sources on the Hillas plot for the purpose of new physics searches. We find that sources with substantial magnetic fields 103 GausslesssimBlesssim106 Gauss, such as Active Galactic Nuclei (AGN) cores, white dwarfs, or maybe gamma-ray bursts, have, in principle, the best discrimination power for the considered new physics scenarios, whereas AGN jets, which typically perform as pion beam sources, can only discriminate few sub cases in the new physics effects. The optimal parameter region somewhat depends on the class of new physics effect considered
The Japanese space gravitational wave antenna - DECIGO
No full textRestricted Access.Gravitational Waves: Proceedings of the Seventh Edoardo Amaldi Conference,2008The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window of observation for gravitational wave astronomy and to obtain insight into significant areas of science, such as verifying and characterizing inflation, determining the thermal history of the universe, characterizing dark energy, describing the formation mechanism of supermassive black holes in the center of galaxies, testing alternative theories of gravity, seeking black hole dark matter, understanding the physics of neutron stars and searching for planets around double neutron stars. DECIGO consists of four clusters of spacecraft in heliocentric orbits; each cluster employs three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by three pairs of differential Fabry–Perot Michelson interferometers. Two milestone missions, DECIGO pathfinder and Pre-DECIGO, will be launched to demonstrate required technologies and possibly to detect gravitational waves
Hamiltonian constraint in polymer parametrized field theory
No full textOpen AccessRecently, a generally covariant reformulation of two-dimensional flat spacetime free scalar field theory known as parametrized field theory was quantized using loop quantum gravity (LQG) type “polymer” representations. Physical states were constructed, without intermediate regularization structures, by averaging over the group of gauge transformations generated by the constraints, the constraint algebra being a Lie algebra. We consider classically equivalent combinations of these constraints corresponding to a diffeomorphism and a Hamiltonian constraint, which, as in gravity, define a Dirac algebra. Our treatment of the quantum constraints parallels that of LQG and obtains the following results, expected to be of use in the construction of the quantum dynamics of LQG: (i) the (triangulated) Hamiltonian constraint acts only on vertices, its construction involves some of the same ambiguities as in LQG and its action on diffeomorphism invariant states admits a continuum limit, (ii) if the regulating holonomies are in representations tailored to the edge labels of the state, all previously obtained physical states lie in the kernel of the Hamiltonian constraint, (iii) the commutator of two (density weight 1) Hamiltonian constraints as well as the operator correspondent of their classical Poisson bracket converge to zero in the continuum limit defined by diffeomorphism invariant states, and vanish on the Lewandowski-Marolf habitat, (iv) the rescaled density 2 Hamiltonian constraints and their commutator are ill-defined on the Lewandowski-Marolf habitat despite the well-definedness of the operator correspondent of their classical Poisson bracket there, (v) there is a new habitat which supports a nontrivial representation of the Poisson-Lie algebra of density 2 constraints
Rheological properties of a chiral liquid crystal exhibiting type-II character
No full textRestricted Access.We measured rheological properties of cholesteryl nonanoate and its mixture with
40-octyloxy-4-cyanobiphenyl. In both systems, wider temperature range of blue
phase under shear with anomalous increase in viscosity associated with non- Newtonian
flow behavior has been observed. Shear thinning followed by Newtonian flow is
found in cholesteric phase and non-Newtonian flow behavior at high shear rates is
seen in smectic-A phase. In cholesteryl nonanoate a small peak in the viscosity at
cholesteric to smectic-A transition along with a shear rate dependent viscosity at
higher shear rate is attributed to the type-II character of the compound. We find that
the type-II character of the compound is further enhanced by mixing a small amount
(20 wt%) of 40-octyloxy-4-cyanobiphenyl in cholesteryl nonanoate. No significant
change in the temperature dependent rheological behavior is observed at the twistgrain-
boundary-A to smectic-A transition. It is suggested that the small anomalous
peak in the viscosity just above the twist-grain-boundary-A phase is due the existence
of chiral line liquid phase
Transport coefficients for the shear dynamo problem at small Reynolds numbers
No full textOpen Access.We build on the formulation developed in S. Sridhar and N. K. Singh [J. Fluid Mech. 664, 265 (2010)] and present a theory of the shear dynamo problem for small magnetic and fluid Reynolds numbers, but for arbitrary
values of the shear parameter. Specializing to the case of a mean magnetic field that is slowly varying in time,
explicit expressions for the transport coefficients αil and ηiml are derived. We prove that when the velocity
field is nonhelical, the transport coefficient αil vanishes. We then consider forced, stochastic dynamics for the
incompressible velocity field at low Reynolds number. An exact, explicit solution for the velocity field is derived,
and the velocity spectrum tensor is calculated in terms of the Galilean-invariant forcing statistics. We consider
forcing statistics that are nonhelical, isotropic, and delta correlated in time, and specialize to the case when the
mean field is a function only of the spatial coordinate X3 and time τ ; this reduction is necessary for comparison
with the numerical experiments of A. Brandenburg, K. H. R¨adler, M. Rheinhardt, and P. J. K¨apyl¨a [Astrophys.
J. 676, 740 (2008)]. Explicit expressions are derived for all four components of the magnetic diffusivity tensor
ηij (τ ). These are used to prove that the shear-current effect cannot be responsible for dynamo action at small Re
and Rm, but for all values of the shear parameter