36 research outputs found
Movies, measurement, and modeling: the three Ms of mechanistic immunology
Immunological phenomena that were once deduced from genetic, biochemical, and in situ approaches are now being witnessed in living color, in three dimensions, and in real time. The information in time-lapse imaging can provide valuable mechanistic insight into a host of processes, from cell migration to signal transduction. What we need now are methods to quantitate these new visual data and to exploit computational resources and statistical mechanical methods to develop mechanistic models
An Effective Membrane Model of the Immunological Synapse
The immunological synapse is a patterned collection of different types of
receptors and ligands that forms in the intercellular junction between T Cells
and antigen presenting cells (APCs) during recognition. The synapse is
implicated in information transfer between cells, and is characterized by
different spatial patterns of receptors at different stages in the life cycle
of T cells. We obtain a minimalist model that captures this experimentally
observed phenomenology. A functional RG analysis provides further insights.Comment: 6 pages, 3 figures, submitted for publicatio
Inter-Landau-level Andreev Reflection at the Dirac Point in a Graphene Quantum Hall State Coupled to a NbSe2 Superconductor
Superconductivity and quantum Hall effect are distinct states of matter
occurring in apparently incompatible physical conditions. Recent theoretical
developments suggest that the coupling of quantum Hall effect with a
superconductor can provide a fertile ground for realizing exotic topological
excitations such as non-abelian Majorana fermions or Fibonacci particles. As a
step toward that goal, we report observation of Andreev reflection at the
junction of a quantum Hall edge state in a single layer graphene and a
quasi-two dimensional niobium diselenide (NbSe2) superconductor. Our principal
finding is the observation of an anomalous finite-temperature conductance peak
located precisely at the Dirac point, providing a definitive evidence for
inter-Landau level Andreev reflection in a quantum Hall system. Our
observations are well supported by detailed numerical simulations, which offer
additional insight into the role of the edge states in Andreev physics. This
study paves the way for investigating analogous Andreev reflection in a
fractional quantum Hall system coupled to a superconductor to realize exotic
quasiparticles.Comment: published verio
Properties of a mixed-valent iron compound with the kagomélattice
An organically templated iron sulfate of the formula [HN(CH2)6NH][FeIIIFe2IIF6(SO4)2]·[H3O] possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T2 behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound
Spectroscopic comprehension of Mott-Hubbard insulator to negative charge transfer metal transition in LaNi_{x}V_{1-x}O_{3} thin films
The room temperature (300 K) electronic structure of pulsed laser deposited
LaNi_{x}V_{1-x}O_{3} thin films have been demonstrated. The substitution of
early-transition metal (TM) V in LaVO_{3} thin films with late-TM Ni leads to
the decreasing in out-of-plane lattice parameter. Doping of Ni does not alter
the formal valence state of Ni and V in LaNi_{x}V_{1-x}O_{3} thin films,
divulging the absence of carrier doping into the system. The valence band
spectrum is observed to comprise of incoherent structure owing to the localized
V 3d band along with the coherent structure at Fermi level. With increase in Ni
concentration, the weight of the coherent feature increases, which divulges its
origin to the Ni 3d-O 2p hybridized band. The shift of Ni 3d-O 2p hybridized
band towards higher energy in Ni doped LaVO_{3} films compared to the LaNiO_{3}
film endorses the modification in ligand to metal charge transfer (CT) energy.
The Ni doping in Mott-Hubbard insulator LaVO_{3} leads to the closure of
Mott-Hubbard gap by building of spectral weight that provides the delocalized
electrons for conduction. A transition from bandwidth control Mott-Hubbard
insulator LaVO_{3} to negative CT metallicity character in LaNiO_{3} film is
observed. The study reveals that unlike in Mott-Hubbard insulators where the
strong Coulomb interaction between the 3d electrons decides the electronic
structure of the system, CT energy can deliver an additional degree of freedom
to optimize material properties in Ni doped LaVO_{3} films.Comment: 30 pages, 8 figure
Properties of a mixed-valent iron compound with the kagomé lattice
An organically templated iron sulfate of the formula ͓HN(CH 2 ) 6 NH͔͓Fe III Fe 2 II F 6 (SO 4 ) 2 ͔•͓H 3 O͔ possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T 2 behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound
Origin of the plateau in the low-temperature thermal conductivity of silica
Thermal conductivities of glasses at low temperatures show strikingly similar behavior irrespective of their chemical composition. While for T<1 K the thermal conductivity can be understood in the phenomenological tunneling model; the "universal plateau" in the temperature interval 15>T>2 K is totally unexplained. While Rayleigh scattering of phonons by structural disorder should be the natural cause for limiting the mean free path of phonons in this temperature range, it has been concluded before that in glasses a strong enough source of such scattering does not exist. In this study we show by a proper structural analysis in at least one material (namely, silica) that a strong enough source of Rayleigh scattering of phonons in glasses does exist so that the "universal plateau" can be explained without invoking any new mechanism. This may be for the first time that the low-temperature property of a structural glass has been correlated to its structure
Origin of the plateau in the low-temperature thermal conductivity of silica
Thermal conductivities of glasses at low temperatures show strikingly similar behavior irrespective of their chemical composition. While for T<1 K the thermal conductivity can be understood in the phenomenological tunneling model; the ‘‘universal plateau’’ in the temperature interval 15>T>2 K is totally unexplained. While Rayleigh scattering of phonons by structural disorder should be the natural cause for limiting the mean free path of phonons in this temperature range, it has been concluded before that in glasses a strong enough source of such scattering does not exist. In this study we show by a proper structural analysis in at least one material (namely, silica) that a strong enough source of Rayleigh scattering of phonons in glasses does exist so that the ‘‘universal plateau’’ can be explained without invoking any new mechanism. This may be for the first time that the low-temperature property of a structural glass has been correlated to its structure