2,174 research outputs found
Formation and stability of a two-dimensional nickel silicide on Ni (111) an Auger, LEED, STM, and high-resolution photoemission Study
Using low energy electron diffraction (LEED), Auger electron spectroscopy
(AES), scanning tunnelling microscopy (STM) and high resolution photo-electron
spectroscopy (HR-PES) techniques we have studied the annealing effect of one
silicon monolayer deposited at room temperature onto a Ni (111) substrate. The
variations of the Si surface concentration, recorded by AES at 300{\deg}C and
400{\deg}C, show at the beginning a rapid Si decreasing followed by a slowing
down up to a plateau equivalent to about 1/3 silicon monolayer. STM images and
LEED patterns, both recorded at room temperature just after annealing, reveal
the formation of an ordered hexagonal superstructure(rot3xrot3)R30{\deg}-type.
From these observations and from a quantitative analysis of HR-PES data,
recorded before and after annealing, we propose that the (rot3 x
rot3)R30{\deg}superstructure corresponds to a two dimensional (2D) Ni2Si
surface silicide.Comment: Journal Physical Review B (2012
Cross phase modulation in a five--level atomic medium: Semiclassical theory
The interaction of a five-level atomic system involving electromagnetically
induced transparency with four light fields is investigated. Two different
light-atom configurations are considered, and their efficiency in generating
large nonlinear cross-phase shifts compared. The dispersive properties of those
schemes are analyzed in detail, and the conditions leading to group velocity
matching for two of the light fields identified. An analytical treatment based
on amplitude equations is used in order to obtain approximate solutions for the
susceptibilities, ehich are shown to fit well with the numerical simulations of
the full Bloch equations in a large parameter region.Comment: New version: section on pulse propagation added, reference list
expanded; 17 pages, 15 figure
Quantum theory of a polarization phase-gate in an atomic tripod configuration
We present the quantum theory of a polarization phase-gate that can be
realized in a sample of ultracold rubidium atoms driven into a tripod
configuration. The main advantages of this scheme are in its relative
simplicity and inherent symmetry. It is shown that the conditional phase shifts
of order can be attained.Comment: X International Conference on Quantum Optics, Minsk, Belaru
Immune-Neuroendocrine Interactions: Evolution, Ecology, and Susceptibility to Illness
The integration between immune and neuroendocrine systems is crucial for maintaining homeostasis from invertebrates to humans. In the first, the phagocytic cell, i.e., the immunocyte, is the main actor, while in the latter, the principle player is the lymphocyte. Immunocytes are characterized by the presence of pro-opiomelanocortin (POMC) peptides, CRH, and other molecules that display a significant similarity to their mammalian counterparts regarding their functions, as both are mainly involved in fundamental functions such as immune (chemotaxis, phagocytosis, cytotoxicity, etc.) and neuroendocrine (stress) responses. Furthermore, the immune-neuroendocrine system provides vital answers to ecological and immunological demands in terms of economy and efficiency. Finally, susceptibility to disease emerges as the result of a continuous dynamic interaction between the world within and the world outside. New fields such as ecological immunology study the susceptibility to pathogens in an evolutionary perspective while the field of neuro-endocrine-immunology studies the susceptibility from a more immediate perspective
Fundamental limits of repeaterless quantum communications
Quantum communications promises reliable transmission of quantum information, efficient distribution of entanglement and generation of completely secure keys. For all these tasks, we need to determine the optimal point-to-point rates that are achievable by two remote parties at the ends of a quantum channel, without restrictions on their local operations and classical communication, which can be unlimited and two-way. These two-way assisted capacities represent the ultimate rates that are reachable without quantum repeaters. Here, by constructing an upper bound based on the relative entropy of entanglement and devising a dimension-independent technique dubbed ‘teleportation stretching’, we establish these capacities for many fundamental channels, namely bosonic lossy channels, quantum-limited amplifiers, dephasing and erasure channels in arbitrary dimension. In particular, we exactly determine the fundamental rate-loss tradeoff affecting any protocol of quantum key distribution. Our findings set the limits of point-to-point quantum communications and provide precise and general benchmarks for quantum repeaters
Morpho-functional changes of fat body in bacteria fed Drosophila melanogaster strains
We have examined the addition of Escherichia coli to the diet at day 0 of adult life of females from two Oregon R Drosophila melanogaster strains, selected for different longevities: a short-life with an average adult life span of 10 days and a long-life standard R strain with an average adult life span of 50 days. The addition of bacteria to the diet significantly prolonged the fly longevity in both strains and affected the structure and histochemical reactivity of the fat body. The increased survival was characterized by great amount of glycogen accumulated in fat body cells from both strains. In aged control animals, fed with standard diet, lipid droplets were seen to be stored in fat body of short-lived, but not long-lived, flies. On the whole, our data indicate that exogenous bacteria are able to extend the survival of Drosophila females, and suggest that such a beneficial effect can be mediated, at least in part, by the fat body cells that likely play a role in modulating the accumulation and mobilization of reserve stores to ensure lifelong energy homeostasis
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