4,915 research outputs found
Composite Majorana Fermion Wavefunctions in Nanowires
We consider Majorana fermions (MFs) in quasi-one-dimensional nanowire systems
containing normal and superconducting sections where the topological phase
based on Rashba spin orbit interaction can be tuned by magnetic fields. We
derive explicit analytic solutions of the MF wavefunction in the weak and
strong spin orbit interaction regimes. We find that the wavefunction for one
single MF is a composite object formed by superpositions of different MF
wavefunctions which have nearly disjoint supports in momentum space. These
contributions are coming from the extrema of the spectrum, one centered around
zero momentum and the other around the two Fermi points. As a result, the
various MF wavefunctions have different localization lengths in real space and
interference among them leads to pronounced oscillations of the MF probability
density. For a transparent normal-superconducting junction we find that in the
topological phase the MF leaks out from the superconducting into the normal
section of the wire and is delocalized over the entire normal section, in
agreement with recent numerical results by Chevallier et al. (arXiv:1203.2643)
Hierarchy of QM SUSYs on a Bounded Domain
We systematically formulate a hierarchy of isospectral Hamiltonians in
one-dimensional supersymmetric quantum mechanics on an interval and on a
circle, in which two successive Hamiltonians form N=2 supersymmetry. We find
that boundary conditions compatible with supersymmetry are severely restricted.
In the case of an interval, a hierarchy of, at most, three isospectral
Hamiltonians is possible with unique boundary conditions, while in the case of
a circle an infinite tower of isospectral Hamiltonians can be constructed with
two-parameter family of boundary conditions.Comment: 15 pages, 3 figure
A low energy theory for superfluid and solid matter and its application to the neutron star crust
We formulate a low energy effective theory describing phases of matter that
are both solid and superfluid. These systems simultaneously break translational
symmetry and the phase symmetry associated with particle number. The symmetries
restrict the combinations of terms that can appear in the effective action and
the lowest order terms featuring equal number of derivatives and Goldstone
fields are completely specified by the thermodynamic free energy, or
equivalently by the long-wavelength limit of static correlation functions in
the ground state. We show that the underlying interaction between particles
that constitute the lattice and the superfluid gives rise to entrainment, and
mixing between the Goldstone modes. As a concrete example we discuss the low
energy theory for the inner crust of a neutron star, where a lattice of ionized
nuclei coexists with a neutron superfluid.Comment: 21 pages, 1 figur
Flavored Quantum Boltzmann Equations
We derive from first principles, using non-equilibrium field theory, the
quantum Boltzmann equations that describe the dynamics of flavor oscillations,
collisions, and a time-dependent mass matrix in the early universe. Working to
leading non-trivial order in ratios of relevant time scales, we study in detail
a toy model for weak scale baryogenesis: two scalar species that mix through a
slowly varying time-dependent and CP-violating mass matrix, and interact with a
thermal bath. This model clearly illustrates how the CP asymmetry arises
through coherent flavor oscillations in a non-trivial background. We solve the
Boltzmann equations numerically for the density matrices, investigating the
impact of collisions in various regimes.Comment: 41 pages, 7 figures. v2: references added, minor corrections and
clarification
Shear viscosity and chemical equilibration of the QGP
We have investigated, in the frame work of the transport approach, different
aspects of the QGP created in Heavy Ion Collisions at RHIC and LHC energies.
The shear viscosity has been calculated by using the Green-Kubo relation
at the cascade level. We have compared the numerical results for
obtained from the Green-Kubo correlator with the analytical formula in both the
Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE).
From this comparison we show that in the range of temperature explored in a
Heavy Ion collision the RTA underestimates the viscosity by about a factor of
2, while a good agreement is found between the CE approximation and Gree-Kubo
relation already at first order of approximation. The agreement with the CE
approximation supplies an analytical formula that allows to develop kinetic
transport theory at fixed shear viscosity to entropy density ratio, .
We show some results for the build up of anisotropic flows in a
transport approach at fixed shear viscosity to entropy density ratio, .
We study the impact of a T-dependent on the generation of the
elliptic flows at both RHIC and LHC. We show that the transport approach
provides, in a unified way, a tool able to naturally describe the
in a wide range of , including also the description of
the rise and fall and saturation of the observed at LHC.
Finally, we have studied the evolution of the quark-gluon composition employing
a Boltzmann-Vlasov transport approach that include: the mean fields dynamics,
associated to the quasi-particle model, and the elastic and inelastic
collisions for massive quarks and gluons. Following the chemical evolution from
an initial gluon dominated plasma we predict a quark dominance close to
paving the way to an hadronization via quark coalescence.Comment: 15 pages, 10 figures, Invited Talk given by S. Plumari at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Directed Molecular Stacking for Engineered Fluorescent Three-Dimensional Reduced Graphene Oxide and Coronene Frameworks
[EN] Three‐dimensional fluorescent graphene frameworks with controlled porous morphologies are of significant importance for practical applications reliant on controlled structural and electronic properties, such as organic electronics and photochemistry. Here we report a synthetically accessible approach concerning directed aromatic stacking interactions to give rise to new fluorogenic 3D frameworks with tuneable porosities achieved through molecular variations. The binding interactions between the graphene‐like domains present in the in situ‐formed reduced graphene oxide (rGO) with functional porphyrin molecules lead to new hybrids via an unprecedented solvothermal reaction. Functional free‐base porphyrins featuring perfluorinated aryl groups or hexyl chains at their meso‐ and β‐positions were employed in turn to act as directing entities for the assembly of new graphene‐based and foam‐like frameworks and of their corresponding coronene‐based hybrids. Investigations in the dispersed phase and in thin‐film by XPS, SEM and FLIM shed light onto the nature of the aromatic stacking within functional rGO frameworks (denoted rGOFs) which was then modelled semi‐empirically and by DFT calculations. The pore sizes of the new emerging reduced graphene oxide hybrids are tuneable at the molecular level and mediated by the bonding forces with the functional porphyrins acting as the “molecular glue”. Single crystal X‐ray crystallography described the stacking of a perfluorinated porphyrin with coronene, which can be employed as a molecular model for understanding the local aromatic stacking order and charge transfer interactions within these rGOFs for the first time. This opens up a new route to controllable 3D framework morphologies and pore size from the Ångstrom to the micrometre scale. Theoretical modelling showed that the porosity of these materials is mainly due to the controlled inter‐planar distance between the rGO, coronene or graphene sheets. The host‐guest chemistry involves the porphyrins acting as guests held through π‐π stacking, as demonstrated by XPS. The objective of this study is also to shed light into the fundamental localised electronic and energy transfer properties in these new molecularly engineered porous and fluorogenic architectures, aiming in turn to understand how functional porphyrins may exert stacking control over the notoriously disordered local structure present in porous reduced graphene oxide fragments. By tuning the porosity and the distance between the graphene sheets using aromatic stacking with porphyrins, it is also possible to tune the electronic structure of the final nanohybrid material, as indicated by FLIM experiments on thin films. Such nanohybrids with highly controlled pores dimensions and morphologies open the way to new design and assembly of storage devices and applications incorporating π‐conjugated molecules and materials and their π‐stacks may be relevant towards selective separation membranes, water purification and biosensing applications.S.I.P. and S.W.B. thank The Royal Society and STFC for funding. B.Y.M. thanks the University of Bath for a studentship (ORS). D.G.C. thanks the Fundación General CSIC for funding (ComFuturo Program). Dr. Jose A. Ribeiro Martins, Professors Jeremy K. M. Sanders and Paul Raithby are acknowledged for training, helpful discussions and porphyrin supramolecular chemistry. The S.I.P. group thanks the EPSRC for funding to the Centre of Graphene Science (EP/K017160/1) and to the Centre for Doctoral Training in Sustainable Chemical Technologies (EP/L016354/1). The authors thank EPSRC National Service for Mass Spectrometry at Swansea and EPSRC National Service for Crystallography at Southampton for data collection. The authors also acknowledge the ERC for the Consolidator Grant O2SENSE (617107, 2014–2019)
Large transconductance oscillations in a single-well vertical Aharonov-Bohm interferometer
Aharonov-Bohm (AB) interference is reported for the first time in the
conductance of a vertical nanostructure based on a single GaAs/AlGaAs quantum
well (QW). The two lowest subbands of the well are spatially separated by the
Hartree barrier originating from electronic repulsion in the modulation-doped
QW and provide AB two-path geometry. Split-gates control the in-plane
electronic momentum dispersion. In our system, we have clearly demonstrated AB
interference in both electrostatic and magnetic modes. In the latter case the
magnetic field was applied parallel to the QW plane, and perpendicular to the
0.02 um^2 AB loop. In the electrostatic mode of operation the single-QW scheme
adopted led to large transconductance oscillations with relative amplitudes
exceeding 30 %. The relevance of the present design strategy for the
implementation of coherent nanoelectronic devices is underlined.Comment: Accepted for publication on Physical Review B Rapid Communication
Essential Role of Lyn in Fibrosis.
Fibrotic disorders involve replacement of normal parenchyma with myofibroblasts, which deposit connective tissue, leading to obliteration of the function of the underlying organ. The treatment options are inadequate and reflect the fact that signaling targets in myofibroblasts are unknown. Here we identify the hyperactive Lyn signaling in myofibroblasts of patients with chronic pancreatitis-induced fibrosis. Lyn activation coexpress with markers of activated myofibroblasts, and is increased ~11-fold in chronic pancreatitis compared to normal tissue. Inhibition of Lyn with siRNA or INNO-406 leads to the substantial decrease of migration and proliferation of human chronic pancreatitis myofibroblasts in vitro, while leaving migration and proliferation of normal myofibroblasts only slightly affected. Furthermore, inhibition of Lyn prevents synthesis of procollagen and collagen in myofibroblasts in a mouse model of chronic pancreatitis-induced fibrosis. We conclude that Lyn, as a positive regulator of myofibroblast migration, proliferation, and collagen production, is a key target for preventing fibrosis
Universal control of quantum subspaces and subsystems
We describe a broad dynamical-algebraic framework for analyzing the quantum
control properties of a set of naturally available interactions. General
conditions under which universal control is achieved over a set of
subspaces/subsystems are found. All known physical examples of universal
control on subspaces/systems are related to the framework developed here.Comment: 4 Pages RevTeX, Some typos fixed, references adde
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