Quantum Hall Ferromagnets: Induced Topological term and electromagnetic interactions

The $\nu = 1$ quantum Hall ground state in materials like GaAs is well known to be ferromagnetic in nature. The exchange part of the Coulomb interaction provides the necessary attractive force to align the electron spins spontaneously. The gapless Goldstone modes are the angular deviations of the magnetisation vector from its fixed ground state orientation. Furthermore, the system is known to support electrically charged spin skyrmion configurations. It has been claimed in the literature that these skyrmions are fermionic owing to an induced topological Hopf term in the effective action governing the Goldstone modes. However, objections have been raised against the method by which this term has been obtained from the microscopics of the system. In this article, we use the technique of the derivative expansion to derive, in an unambiguous manner, the effective action of the angular degrees of freedom, including the Hopf term. Furthermore, we have coupled perturbative electromagnetic fields to the microscopic fermionic system in order to study their effect on the spin excitations. We have obtained an elegant expression for the electromagnetic coupling of the angular variables describing these spin excitations.Comment: 23 pages, Plain TeX, no figure

The SONYC survey: Towards a complete census of brown dwarfs in star forming regions

SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey program to provide a census of the substellar population in nearby star forming regions. We have conducted deep optical and near-infrared photometry in five young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3), combined with proper motions, and followed by extensive spectroscopic campaigns with Subaru and VLT, in which we have obtained more than 700 spectra of candidate low-mass objects. We have identified and characterized more than 60 new substellar objects, among them a handful of objects with masses close to, or below the Deuterium burning limit. Through SONYC and surveys by other groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and we find that the ratio of the number of stars with respect to brown dwarfs lies between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to ~5MJup, free-floating objects with planetary masses are 20-50 times less numerous than stars, i.e. their total contribution to the mass budget of the clusters can be neglected.Comment: to appear in the proceedings of the conference 'Brown dwarfs come of age', May 20-24 2013, Memorie della Societa Astronomica Italian

Multiplication of bacteriophage P22 in penicillin-induced spheroplasts of Salmonella typhimurium

The spheroplasts of Salmonella typhimurium (LT2) prepared by treatment with penicillin were capable of adsorbing phage P22 C1. The normal multiplication of the phage took place, although the burst size was reduced to one-fourth of that in intact cells. Rate of incorporation of 14C-thymidine into spheroplasts was increased severalfold on phage infection. Multiplication of C+ also took place, but no lysogeny could be established in spheroplasts. Furthermore, spheroplasts prepared from cells lysogenized with wild-type phage, LT2 (C+), and a temperature-inducible C2 mutant, LT2(tsC2), were not inducible. Unlike normal cells, both mitomycin C and actinomycin D interfered with the phage multiplication in spheroplasts. The spheroplast system offers great advantages in the study of the synthesis of nucleic acids and proteins in phage-infected LT2

Uzbuda autoionizacijskog stanja u Na udarom elektrona

Electron-impact integral cross sections for the excitation of the lowest lying autoionizing level generated by the inner-shell 1s2 2s2 2p6 3s 2S e → 1s2 2s2 2p5 3s2 2P 0 complex transition in sodium (Na) atomic system have been calculated. In the calculation, single-configuration Hartree-Fock (HF) wave functions for both initial and final states involved in the transition matrix element within the asymptotic Green function approximation (AGFA) proposed by Tiwary (1981) were employed. The calculation was done exactly in the same way as in the earlier work in the case of the lightest alkali-metal atom lithium (Tiwary (1985), Tiwary, Macek and Madison (1985)) and the heaviest alkali-metal atom caesium (Tiwary (1983)) in the bombarding energy range from the threshold to 1500 eV. For the first time, Tiwary (1983) predicted the resonance behaviour in near vicinity of the excitation threshold in Cs using AGFA. Feuerstein et al. (1998) performed the experiment and observed resonance behaviour in the neighbourhood of excitation threshold in Na. Comparison has been made with available relevant experimental observations and other theoretical predictions. Our present AGFA theoretical result is qualitatively in accord with the experimental results.Izračunali smo integralne udarne presjeke za uzbudu najnižeg autoionizacijskog stanja koje nastaje udarom elektrona te putem kompleksnog prijelaza 1s2 2s2 2p6 3s 2S e Q 1s2 2s2 2p5 3s2 2P 0 među unutarnjim ljuskama u atomima natrija. U računu smo primijenili jedno-konfiguracijske Hartree-Fockove (HF) valne funkcije za odnosna početna i konačna stanja u matričnom elementu unutar asimptotskog približenja za Greenove funkcije (AGFA), predloženog Tiwary-em (1981). Račun je proveden točno na način kao u ranijem radu za najlakši alkalijski metalni atom litij (Tiwary (1985), Tiwary, Macek and Madison (1985)) i najteži alkalijski metalni atom cezij (Tiwary (1983)), za energije elektrona od praga do 1500 eV. Tiwary (1983) je prvi predvidio rezonanciju blizu iznad uzbudnog praga u Cs primjenom AGFA-e. Feuerstein et al. (1998) izveli su mjerenja i vidjeli rezonanciju u blizini uzbudnog praga u Na. Načinili smo usporedbu poznatih eksperimentalnih podataka i drugih teorijskih predviđanja. Naši su sadašnji teorijski rezultati u skladu s eksperimentalnima

Surface plasmon resonance imaging detection of silver nanoparticle-tagged immunoglobulin

This article is available open access through the publisher’s website at the link below. Copyright @ 2011 The Royal Society.The detection sensitivity of silver nanoparticle (AgNP)-tagged goat immunoglobulin G (gIgG) microarrays was investigated by studying surface plasmon resonance (SPR) images captured in the visible wavelength range with the help of a Kretchmann-configured optical coupling set-up. The functionalization of anti-gIgG molecules on the AgNP surface was studied using transmission electron microscopy, photon correlation measurements and UV–visible absorption spectroscopy. A value of 1.3 × 107 M−1 was obtained for the antibody–antigen binding constant by monitoring the binding events at a particular resonance wavelength. The detection limit of this SPR imaging instrument is 6.66 nM of gIgG achieved through signal enhancement by a factor of larger than 4 owing to nanoparticle tagging with the antibody.The European Commissio

Effect of Trivalent Additions and Processing on Structural and Magnetic Transitions in Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand showed the formation of a similar modulated structure without composition change in alloys containing Al and the alloys containing Al and B. In addition, the former showed a presence of an amorphous phase with latter showing crystalline boron rich phases. The magnetisation of the B containing alloys in both the processing technique was however very low, showing lower magnetic exchange interaction in such alloys.Defence Science Journal, 2012, 62(4), pp.252-260, DOI:http://dx.doi.org/10.14429/dsj.62.127

Transport and bistable kinetics of a Brownian particle in a nonequilibrium environment

A system reservoir model, where the associated reservoir is modulated by an external colored random force, is proposed to study the transport of an overdamped Brownian particle in a periodic potential. We then derive the analytical expression for the average velocity, mobility, and diffusion rate. The bistable kinetics and escape rate from a metastable state in the overdamped region are studied consequently. By numerical simulation we then demonstrate that our analytical escape rate is in good agreement with that of numerical result.Comment: 10 pages, 2 figures, RevTex4, minor correction