196,245 research outputs found
-diagram technique for , superfields
No full textWe describe a diagrammatic procedure to carry out the Grassmann integration in super-Feynman diagrams of 4d theories expressed in terms of superfields. This method is alternative to the well known D-algebra approach. We develop it in detail for theories containing vector, chiral and anti-chiral superfields, with the type of interactions which occur in SYM theories with massless matter, but it would be possible to extend it to other cases. The main advantage is that this method is algorithmic; we implemented it as a Mathematica program that, given the description of a super Feynman diagram in momentum space, returns directly the polynomial in the momenta produced by the Grassmann integration
The Extracellular Matrix, Growth Factors and Morphogens in Biomaterial Design and Tissue Engineering
No full textCells, morphogens, growth factors, and custom scaffolds are the critical ingredients for successful tissue regeneration in which morphogens and growth factors function sequentially. Extensive studies, in vitro and in vivo, have been made to explore the mechanisms and the roles played by these molecules. As a consequence, precise, localized control over the signaling of these factors and appropriate strategy selection, depending on the tissue or organ to be repaired or regenerated, is known to permit specific management of regenerative processes. The first part of the chapter examines natural ECMs which are a set of molecules secreted by cells that provide structural and biochemical support to the surrounding cells. ECMs also perform many other functions, such as actively regulating cell function through the control of biochemical gradients, cell density, spatial organization, and ligand attachment, thus influencing various types of cell processes. Subsequently, growth factors and morphogens are examined in greater depth to clarify to what degree progress has been made into improving methodologies and functionality and, perhaps, to hint at what remains to be done for the future of tissue engineering
Rydberg spectroscopy of a Rb MOT in the presence of applied or ion created electric fields
No full textRydberg spectroscopy of rubidium cold atoms trapped in a magneto-optical
trap (MOT) was performed in a quartz cell. When electric fields acting
on the atoms generated by a plate external to the cell were continuously
applied, electric charges on the cell walls were created, as monitored
on the Rydberg spectra. Avoiding accumulation of the charges and
realizing good control over the applied electric field was instead
obtained when the fields were applied only for a short time, typically a
few microseconds. In a two-photon excitation via the 6(2)P state to the
Rydberg state, the laser resonant with the 5(2)S-6(2)P transition
photoionizes the excited state. The photoionization-created ions produce
an internal electric field which deforms the excitation spectra, as
monitored on the Autler-Townes absorption spectra
Rydberg excitations in Bose-Einstein condensates in quasi-one-dimensional potentials and optical lattices
No full textWe experimentally realize Rydberg excitations in Bose-Einstein
condensates of rubidium atoms loaded into quasi-one-dimensional traps
and in optical lattices. Our results for condensates expanded to
different sizes in the one-dimensional trap agree well with the
intuitive picture of a chain of Rydberg excitations. We also find that
the Rydberg excitations in the optical lattice do not destroy the phase
coherence of the condensate, and our results in that system agree with
the picture of localized collective Rydberg excitations including
nearest-neighbor blockade
Rydberg excitation of a Bose-Einstein condensate
No full textWe have performed two-photon excitation via the 6P3/2 state to n=50-80 S or D
Rydberg state in Bose-Einstein condensates of rubidium atoms. The Rydberg
excitation was performed in a quartz cell, where electric fields generated by
plates external to the cell created electric charges on the cell walls.
Avoiding accumulation of the charges and realizing good control over the
applied electric field was obtained when the fields were applied only for a
short time, typically a few microseconds. Rydberg excitations of the
Bose-Einstein condensates loaded into quasi one-dimensional traps and in
optical lattices have been investigated. The results for condensates expanded
to different sizes in the one-dimensional trap agree well with the intuitive
picture of a chain of Rydberg excitations controlled by the dipole-dipole
interaction. The optical lattice applied along the one-dimensional geometry
produces localized, collective Rydberg excitations controlled by the
nearest-neighbour blockade
Quantum driving of a two level system: Quantum speed limit and superadiabatic protocols - An experimental investigation
No full textA fundamental requirement in quantum information processing and in many other areas of science is the capability of precisely controlling a quantum system by preparing a quantum state with the highest fidelity and/or in the fastest possible way. Here we present an experimental investigation of a two level system, characterized by a time-dependent Landau-Zener Hamiltonian, aiming to test general and optimal high-fidelity control protocols. The experiment is based on a Bose-Einstein condensate (BEC) loaded into an optical lattice, then accelerated, which provides a high degree of control over the experimental parameters. We implement generalized Landau-Zener sweeps, comparing them with the well-known linear Landau-Zener sweep. We drive the system from an initial state to a final state with fidelity close to unity in the shortest possible time (quantum brachistochrone), thus reaching the ultimate speed limit imposed by quantum mechanics. On the opposite extreme of the quantum control spectrum, the aim is not to minimize the total transition time but to maximize the adiabaticity during the time-evolution, the system being constrained to the adiabatic ground state at any time. We implement such transitionless superadiabatic protocols by an appropriate transformation of the Hamiltonian parameters. This transformation is general and independent of the physical system
Rydberg excitation in one dimensional system and optical lattices
No full textHighly excited atoms exhibit large long range dipole-dipole interaction, making them a perfect tool for studying strongly correlated quantum gases and for implementing basic elements for quantum computation with cold neutral atoms [1,2]. Here we present an experimental study of Rydberg excitations of rubidium Bose Einstein condensates loaded in a quasi-one dimensional potential (dipole trap) and in periodic potentials (optical lattices). The excitation of Rydberg atoms in periodic potentials is one of the possible paths towards reaching the scalability requirements in quantum computation devices, with quantum gates based on the dipole blockade effect [3,4]
Rydberg excitation in Bose-Einstein Condensates and optical lattices”, International Workshop on Ultracold Rydberg Physics
No full textHuman parvovirus B19 infection and autoimmunity.
No full textHuman parvovirus B19 infection is responsible for a wide range of human diseases ranging from mild erythema infectiosum in immunocompetent children to fetal loss in primary infected pregnant women and aplastic anemia or lethal cytopenias in adult immunocompromised patients. Since persistent viral infection is responsible for an autoimmune response and clinical symptoms can mimic autoimmune inflammatory disorders, parvovirus B19 is the object of intense efforts to clarify whether it is also able to trigger autoimmune diseases. Indeed the virus has been implicated as the causative or the precipitating agent of several autoimmune disorders including rheumatoid arthritis, systemic lupus, antiphospholipid syndrome, systemic sclerosis and vasculitides. Molecular mimicry between host and viral proteins seems to be the main mechanism involved in the induction of autoimmunity. By means of a random peptide library approach, we have identified a peptide that shares homology with parvovirus VP1 protein and with human cytokeratin. Moreover the VP peptide shares similarity with the transcription factor GATA1 that plays an essential role in megakaryopoiesis and in erythropoiesis. These new data sustain the role played by molecular mimicry in the induction of cross-reactive (auto)antibodies by parvovirus B19 infection
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