11,021 research outputs found
Geometric phase in open systems: beyond the Markov approximation and weak coupling limit
Beyond the quantum Markov approximation and the weak coupling limit, we
present a general theory to calculate the geometric phase for open systems with
and without conserved energy. As an example, the geometric phase for a
two-level system coupling both dephasingly and dissipatively to its environment
is calculated. Comparison with the results from quantum trajectory analysis is
presented and discussed
Berry phase in a composite system
The Berry phase in a composite system with only one subsystem being driven
has been studied in this Letter. We choose two spin- systems with
spin-spin couplings as the composite system, one of the subsystems is driven by
a time-dependent magnetic field. We show how the Berry phases depend on the
coupling between the two subsystems, and what is the relation between these
Berry phases of the whole system and those of the subsystems.Comment: 4 pages, 6 figure
Nitric oxide stress and activation of AMP-activated protein kinase impair β-cell sarcoendoplasmic reticulum calcium ATPase 2b activity and protein stability
The sarcoendoplasmic reticulum Ca(2+) ATPase 2b (SERCA2b) pump maintains a steep Ca(2+) concentration gradient between the cytosol and ER lumen in the pancreatic β-cell, and the integrity of this gradient has a central role in regulated insulin production and secretion, maintenance of ER function and β-cell survival. We have previously demonstrated loss of β-cell SERCA2b expression under diabetic conditions. To define the mechanisms underlying this, INS-1 cells and rat islets were treated with the proinflammatory cytokine interleukin-1β (IL-1β) combined with or without cycloheximide or actinomycin D. IL-1β treatment led to increased inducible nitric oxide synthase (iNOS) gene and protein expression, which occurred concurrently with the activation of AMP-activated protein kinase (AMPK). IL-1β led to decreased SERCA2b mRNA and protein expression, whereas time-course experiments revealed a reduction in protein half-life with no change in mRNA stability. Moreover, SERCA2b protein but not mRNA levels were rescued by treatment with the NOS inhibitor l-NMMA (NG-monomethyl L-arginine), whereas the NO donor SNAP (S-nitroso-N-acetyl-D,L-penicillamine) and the AMPK activator AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) recapitulated the effects of IL-1β on SERCA2b protein stability. Similarly, IL-1β-induced reductions in SERCA2b expression were rescued by pharmacological inhibition of AMPK with compound C or by transduction of a dominant-negative form of AMPK, whereas β-cell death was prevented in parallel. Finally, to determine a functional relationship between NO and AMPK signaling and SERCA2b activity, fura-2/AM (fura-2-acetoxymethylester) Ca(2+) imaging experiments were performed in INS-1 cells. Consistent with observed changes in SERCA2b expression, IL-1β, SNAP and AICAR increased cytosolic Ca(2+) and decreased ER Ca(2+) levels, suggesting congruent modulation of SERCA activity under these conditions. In aggregate, these results show that SERCA2b protein stability is decreased under inflammatory conditions through NO- and AMPK-dependent pathways and provide novel insight into pathways leading to altered β-cell calcium homeostasis and reduced β-cell survival in diabetes
Temporal and Spatial Changing Trends on the Fluvial Sedimentation in the Three Gorges Reservoir, Yangtze River in China
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive
A smoothing projected Newton-type algorithm for semi-infinite programming
2008-2009 > Academic research: refereed > Publication in refereed journa
Effective Hamiltonian approach to adiabatic approximation in open systems
The adiabatic approximation in open systems is formulated through the
effective Hamiltonian approach. By introducing an ancilla, we embed the open
system dynamics into a non-Hermitian quantum dynamics of a composite system,
the adiabatic evolution of the open system is then defined as the adiabatic
dynamics of the composite system. Validity and invalidity conditions for this
approximation are established and discussed. A High-order adiabatic
approximation for open systems is introduced. As an example, the adiabatic
condition for an open spin- particle in time-dependent magnetic
fields is analyzed.Comment: 6 pages, 2 figure
Fabrication of in situ TiC reinforced aluminum matrix composites Part I: Microstructural characterization
In the present work traditional ingot metallurgy plus rapid solidification techniques were used to in situ produce Al-TiC composites with refined microstructures and enhanced dispersion hardening of the reinforcing phases. Microstructural characterization of the experimental materials were comprehensively done by optical, electron microscopy and X-ray diffraction. The results show that the in situ synthesized TiC particles possess a metastable fcc crystal structure with an atomic composition of TiC08 and a lattice parameter of 0.431 nm. The typical ingot metallurgy microstructures exhibit aggregates of TiC particle phase segregated generally at the α-Al subgrain or grain boundaries and consisted of fine particles of 0.2–1.0 μm. After re-melting of the ingots and hence rapid solidification, the microstructures formed under certain thermal history conditions contained uniform fine-scale dispersion of TiC phase particles with a size range of 40–80 nm in an Al supersaturated matrix of 0.30–0.85 μm grain size. In the most case these dispersed TiC particles have a semi-coherent relationship with the α-Al matrix.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44752/1/10853_2004_Article_202786.pd
Relationship of uncertainty between polygon segment and line segment for spatial data in GIS
Version of RecordPublishe
- …