Department of Physics

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IIT Jodhpur

The design of an all-solid, soft glass-based, large mode area Bragg fiber for effective single mode operation with mode effective area exceeding 1100 μm2 across the wavelength range of 2-4 μm is reported. The design adopts a new strategy to induce large differential loss between the fundamental and higher order modes for effective single-mode operation within few tens of centimetres length of an otherwise multimode fiber. In addition to having the potential for the targeted application in high power laser delivery systems; complemented by a zero dispersion wavelength at 2.04 μm and rapidly developing mid-IR optical sources, the proposed fiber should also be attractive for generation of high power, single mode and less divergent supercontinuum light over this mid-IR window. © 2011 Optical Society of America.

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Optics Express

Design of a Bragg fiber with large mode area for mid-infrared applications

In the scenario with four quark generations, we perform a fit using flavor-physics data and determine the allowed values-preferred central values and errors-of all of the elements of the 4×4 quark-mixing matrix. In addition to the direct measurements of some of the elements, we include in the fit the present measurements of several flavor-changing observables in the K and B systems that have small hadronic uncertainties, and also consider the constraints from the vertex corrections to Z→bb̄. The values taken for the masses of the fourth-generation quarks are consistent with the measurements of the oblique parameters and perturbativity of the Yukawa couplings. We find that |Vtb|0.98 at 3σ, so that a fourth generation cannot account for any large deviation of |Vtb| from unity. The fit also indicates that all the new-physics parameters are consistent with zero, and the mixing of the fourth generation with the other three is constrained to be small: we obtain |Vub′|&lt;0.06, |Vcb′|&lt;0.027, and |Vtb′|&lt;0.31 at 3σ. Still, this does allow for the possibility of new-physics signals in Bd, Bs and rare K decays. © 2011 American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Constraints on the four-generation quark mixing matrix from a fit to flavor-physics data

Recently, the DØ Collaboration measured the CP-violating like-sign dimuon charge asymmetry in neutral B decays, finding a 3.2ν difference from the standard-model (SM) prediction. A non-SMcharge asymmetry as s1 suggests a new-physics (NP) contribution to Bs-Bs mixing. In this case, in order to explain the measured value of as s1 within its 1s range, NP must be present in Γss 12, the absorptive part of the mixing. In this paper, we examine whether such an explanation is possible in models with flavor-changing Z″ (ZFCNC) or Z″ (Z″FCNC) gauge bosons. The models must also reproduce the measured values of the indirect CP asymmetry Sψφ in Bs → J/ψφ, and δΓs, the Bs-Bs width difference. We find that the ZFCNC model cannot reproduce the present measured values of Sψφ and as s1 within their 1s ranges. On the other hand, in the Z″FCNC model, the values of all three observables can be simultaneously reproduced. © SISSA 2011.

Journal of High Energy Physics

Neutral gauge boson contributions to the dimuon charge asymmetry in B decays

Monthly Notices of the Royal Astronomical Society

Erratum: Possible conversion of a neutron star to a quark star in the presence of high magnetic field

A series of Mn-substituted BaMgF4 samples have been synthesized by a hydrothermal route. X-ray diffraction study reveals that the products are monophasic in nature. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) studies were carried out to investigate the morphology and stoichiometry for these compounds. X-ray photoelectron spectroscoy (XPS) and electron spin resonance (ESR) studies were done to confirm the oxidation state of dopant ion. Room temperature ferromagnetism was observed on Mn substitution at the Mg site in BaMgF4 samples. The saturation magnetization increases initially, shows a peaking effect, and then decreases with further increase in Mn concentration in BaMg1-xMnxF4 (0.0 ≥ x ≥ 0.15). However, ferroelectricity was found to decrease with an increase in Mn concentration in the series of investigated BaMg 1-xMnxF4 (0.0 ≥ x ≥ 0.15) samples. First-principle calculations, using the projector augmented wave potentials on Mn-substituted BaMgF4, confirmed the decrease in magnetic moment with an increase in Mn content beyond certain concentration. These samples exhibit very weak magnetocapacitive coupling, which can be attributed to the very small magnetic signal observed in these samples. © 2011 American Chemical Society.

Inorganic Chemistry

Rare examples of fluoride-based multiferroic materials in Mn-substituted BaMgF4 systems: Experimental and theoretical studies

Crossover motifs are integral components for designing DNA-based nanostructures and nanomechanical devices due to their enhanced rigidity compared to the normal B-DNA. Although the structural rigidity of the double helix B-DNA has been investigated extensively using both experimental and theoretical tools, to date there is no quantitative information about structural rigidity and the mechanical strength of parallel crossover DNA motifs. We have used fully atomistic molecular dynamics simulations in explicit solvent to get the force-extension curve of parallel DNA nanostructures to characterize their mechanical rigidity. In the presence of monovalent Na + ions, we find that the stretch modulus (γ 1) of the paranemic crossover and its topoisomer JX DNA structure is significantly higher (∼30%) compared to normal B-DNA of the same sequence and length. However, this is in contrast to the original expectation that these motifs are almost twice as rigid compared to the double-stranded B-DNA. When the DNA motif is surrounded by a solvent with Mg 2+ counterions, we find an enhanced rigidity compared to Na + environment due to the electrostatic screening effects arising from the divalent nature of Mg 2+ ions. To our knowledge, this is the first direct determination of the mechanical strength of these crossover motifs, which can be useful for the design of suitable DNA for DNA-based nanostructures and nanomechanical devices with improved structural rigidity. © 2011 Biophysical Society.

Biophysical Journal

Structural rigidity of paranemic crossover and juxtapose DNA nanostructures

In the internal shock model of gamma ray bursts ultrahigh energy pions, kaons and neutrons are likely to be produced in the interactions of shock accelerated relativistic protons with low energy photons (KeV-MeV). The ultrahigh energy mesons and neutrons subsequently decay to high energy neutrinos/antineutrinos and other secondary particles. In the high internal magnetic fields of gamma ray bursts, the ultrahigh energy charged particles (φ+, K+ and μ+) lose energy significantly due to synchrotron radiations before decaying into secondary high energy neutrinos. However, the relativistic neutrons remain unaffected and decay to high energy antineutrinos, protons and electrons. We have calculated the total neutrino flux (neutrino and antineutrino) considering the decay channels of pions, muons, kaons and neutrons. We show that depending on the values of the parameters of a gamma ray burst the antineutrino flux generated in neutron decay can exceed the total neutrino flux produced from φ+ decay. Moreover, the charged kaons being heavier than pions, lose energy slowly and their secondary neutrino flux is more than that from pions at very high energy. We also discuss that the neutron decay and kaon decay antineutrino/neutrino fluxes may show distinct peaks in the total neutrino spectrum at different energies depending on the values of the parameters (luminosity, Lorentz factor, variability time) of a gamma ray burst.

Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011

High energy neutrinos from gamma ray bursts

Undoubtedly, certain aspects of massively parallel non-central distributive computing have made biological computing far superior than the conventional sequential algorithm based computation. The hardware architecture of a single cell or human brain components has been explored considerably well. However, it is not very well understood how massively parallel computation originates from the individual components of our brain. The failure to establish a logical correlation between an intelligent decision and the hardware components in parametric terms has generated several myths and mysteries related to the biological computation. Since microtubules (MT) abundant in living cells are found to reorganize themselves during cellular functions, a considerable number of attempts have been made to construct computational models based on MT. The correlation between the neuro-physiological studies of our brain and computational models demands a strict protocol to be followed to marginalize the fictional myths and establish factual conclusions based on direct experimental evidences related to MT. In this paper, we point out remarkable predictions and fundamental problems to verify these predictions experimentally. Copyright © 2011 American Scientific Publishers.

Journal of Computational and Theoretical Nanoscience

Computational myths and mysteries that have grown around microtubule in the last half a century and their possible verification

The nonlinear optical (NLO) properties of covalently linked Graphene-(Sn, OH) porphyrin composite materials were investigated using Z-scan technique at 532 nm with picosecond laser pulses. We have observed enhanced figure of merit values for composites in comparison with individual graphene, copper and zinc porphyrin. The enhanced figure of merit values for graphene-porphyrin composite material should be attributed to two-photon absorption and excited state absorption. We also observed different behavior, reverse saturable absorption to saturable absorption and back to reverse saturable absorption in composite molecules leading to better ultrafast nonlinear optical switching applications. © 2011 American Institute of Physics.

AIP Conference Proceedings

Nonlinear optical properties of graphene- (OH, Sn) porphyrin composites in picosecond regime

In this paper, we have proposed a simple method to covalently conjugate biotin to magnetic nanoparticles, which can be targeted to the tumour sites by using pretargeting approach with avidin or streptavidin. Magnetic nanoparticles of manganese ferrite were synthesized by alkaline coprecipitation of ferric chloride hexahydrate, ferrous sulphate heptahydrate and manganese sulphate monohydrate using ammonium hydroxide. The synthesized magnetic nanoparticles were then successfully surface modified by using 3-aminopropyl trimethoxysilane, and the amount of aminopropylsilane bound to the surface of magnetic nanoparticles was quantified by measuring the absorbance of a purple-coloured complex (Ruhemann's purple) formed between amine group and ninhydrin at 576 nm. The aminated magnetic nanoparticles were then conjugated to biotin by reacting them with N-hydroxysuccinimide-biotin in dimethylsulphoxide. The successful conjugation of biotin to magnetic nanoparticles was confirmed by Fourier transform infrared spectroscopy. The size, phase and magnetic nature of the synthesized nanoparticles were analysed by using various techniques like transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and vibrating sample magnetometry. © 2011 Springer-Verlag.