Intermediate-scale theory for electrons coupled to frustrated local-moments

A classic route for destroying long-lived electronic quasiparticles in a weakly interacting Fermi liquid is to couple them to other low-energy degrees of freedom that effectively act as a bath. We consider here the problem of electrons scattering off the spin fluctuations of a geometrically frustrated antiferromagnet, whose non-linear Landau-Lifshitz dynamics, which remains non-trivial at all temperatures, we model in detail. At intermediate temperatures and in the absence of any magnetic ordering, the fluctuating local-moments lead to a non-trivial angular anisotropy of the scattering-rate along the Fermi surface, which disappears with increasing temperature, elucidating the role of "hot-spots". Over a remarkably broad window of intermediate and high temperatures, the electronic properties can be described by employing a local approximation for the dynamical spin-response. This we contrast with the more familiar setup of electrons scattering off classical phonons, whose high-temperature limit differs fundamentally on account of their unbounded Hilbert space. We place our results in the context of layered magnetic delafossite compounds.Comment: 4.5 pages, 3 figures. Supplementary material: 6 pages, 4 figure

Scaling of dynamical susceptibility at the onset of rigidity for disordered viscoelastic matter

The onset of rigidity in interacting liquids, as they undergo a transition to a disordered solid, is associated with a dramatic rearrangement of the low-frequency vibrational spectrum. In this letter, we derive scaling forms for the singular dynamical response of disordered viscoelastic networks near both jamming and rigidity percolation. Using effective-medium theory, we extract critical exponents, invariant scaling combinations and analytical formulas for universal scaling functions near these transitions. Our scaling forms describe the behavior in space and time near the various onsets of rigidity, for rigid and floppy phases and the crossover region, including diverging length and time scales at the transitions. We expect that these behaviors can be measured in systems ranging from colloidal suspensions to anomalous charge-density fluctuations of "strange" metals.Comment: 6 pages, 3 figure

T−T-linear resistivity from magneto-elastic scattering: application to PdCrO2_2

An electronic solid with itinerant carriers and localized magnetic moments represents a paradigmatic strongly correlated system. The electrical transport properties associated with the itinerant carriers, as they scatter off these local moments, has been scrutinized across a number of materials. Here we analyze the transport characteristics associated with ultra-clean PdCrO$_2$ -- a quasi two-dimensional material consisting of alternating layers of itinerant Pd-electrons and Mott-insulating CrO$_2$ layers -- which shows a pronounced regime of $T-$linear resistivity over a wide-range of intermediate temperatures. By contrasting these observations to the transport properties in a closely related material PdCoO$_2$, where the CoO$_2$ layers are band-insulators, we can rule out the traditional electron-phonon interactions as being responsible for this interesting regime. We propose a previously ignored electron-magnetoelastic interaction between the Pd-electrons, the Cr local-moments and an out-of-plane phonon as the main scattering mechanism that leads to the significant enhancement of resistivity and a $T-$linear regime in PdCrO$_2$ at temperatures far in excess of the magnetic ordering temperature. We suggest a number of future experiments to confirm this picture in PdCrO$_2$, as well as other layered metallic/Mott-insulating materials.Comment: 7 pages, 3 figures. Supplementary material: 10 pages, 3 figure

LTP Requires a Unique Postsynaptic SNARE Fusion Machinery

SummaryMembrane fusion during exocytosis is mediated by assemblies of SNARE (soluble NSF-attachment protein receptor) and SM (Sec1/Munc18-like) proteins. The SNARE/SM proteins involved in vesicle fusion during neurotransmitter release are well understood, whereas little is known about the protein machinery that mediates activity-dependent AMPA receptor (AMPAR) exocytosis during long-term potentiation (LTP). Using direct measurements of LTP in acute hippocampal slices and an in vitro LTP model of stimulated AMPAR exocytosis, we demonstrate that the Q-SNARE proteins syntaxin-3 and SNAP-47 are required for regulated AMPAR exocytosis during LTP but not for constitutive basal AMPAR exocytosis. In contrast, the R-SNARE protein synaptobrevin-2/VAMP2 contributes to both regulated and constitutive AMPAR exocytosis. Both the central complexin-binding and the N-terminal Munc18-binding sites of syntaxin-3 are essential for its postsynaptic role in LTP. Thus, postsynaptic exocytosis of AMPARs during LTP is mediated by a unique fusion machinery that is distinct from that used during presynaptic neurotransmitter release

Phase transition beneath the superconducting dome in BaFe2(As1-xPx)2

We present a theory for the large suppression of the superfluid density ρs in BaFe2(As1−xPx)2 in the vicinity of a putative spin-density wave quantum critical point at a P doping, x=xc. We argue that the transition becomes weakly first order in the vicinity of xc, and disorder induces puddles of superconducting and antiferromagnetic regions at short length scales; thus, the system becomes an electronic microemulsion. We propose that frustrated Josephson couplings between the superconducting grains suppress ρs. In addition, the presence of “normal” quasiparticles at the interface of the frustrated Josephson junctions will give rise to a highly nontrivial feature in the low-frequency response in a narrow vicinity around xc. We propose a number of experiments to test our theory.Physic

Simultaneous multi-wavelength observations of the TeV Blazar Mrk 421 during February - March 2003: X-ray and NIR correlated variability

In the present paper, we have reported the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February $-$ March 2003. In this period, we have observed Mrk 421 using Pachmarhi Array of \v{C}erenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the published literature and public data archives. We have analyzed the high quality X-ray (2-20 keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We have seen a possible correlated variability between X-ray and J band (1.25 $\mu$) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here is indicating a similar origin for NIR and X-ray emission. The emission is not affected much by the environment of the surrounding medium around the central engine of the Mrk 421. The observations are consistent with the shock-in-jet model for the emission of radiations.Comment: 11 pages, 5 figures, Accepted for Publication in ChJA

Planned Marketing Adaptation and Multinationals' Choices Between Acquisitions and Greenfields

International marketing studies have extensively examined the antecedents of firms' marketing standardization/ adaptation decisions. However, it is unclear whether such decisions, once planned, codetermine the choice between buying and building foreign subsidiaries. Analyzing a sample of 150 foreign entries by Dutch firms, the authors find that the level of marketing adaptation planned for a wholly owned subsidiary is positively related to the likelihood that the subsidiary will be established through an acquisition rather than through a greenfield investment. Moreover, the authors find substantial evidence that this positive relationship is stronger for firms that (1) are establishing relatively larger subsidiaries, (2) have less experience with the industry entered, or (3) are entering less developed countries. The findings show that firms pursuing higher levels of marketing adaptation assign more value to the marketing adaptation advantages of acquisitions over greenfields, especially if the risks associated with implementing the planned adaptation level are high. In addition, firms typically strive for a fit between their international marketing strategy and their mode of foreign establishment. (authors' abstract

Cell-surface sensors for real-time probing of cellular environments

Author Manuscript 2012 August 1.The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a signal. The sensor, which is covalently attached to the membranes of mesenchymal stem cells, can quantitatively detect with high spatial and temporal resolution PDGF that is added in cell culture medium or secreted by neighbouring cells. The engineered stem cells retain their ability to find their way to the bone marrow and can be monitored in vivo at the single-cell level using intravital microscopy.National Institutes of Health (U.S.) (Grant HL097172)National Institutes of Health (U.S.) (Grant HL095722)National Institutes of Health (U.S.) (Grant DE019191)National Institutes of Health (U.S.) (Grant NIAID 5RC1AI086152)Charles A. Dana FoundationAmerican Heart Association (Grant 0970178N)National Science Foundation (U.S.) (Graduate Fellowship