4,951 research outputs found
Decoherence and entropy of primordial fluctuations II. The entropy budget
We calculate the entropy of adiabatic perturbations associated with a
truncation of the hierarchy of Green functions at the first non trivial level,
i.e. in a self-consistent Gaussian approximation. We give the equation
governing the entropy growth and discuss its phenomenology. It is parameterized
by two model-dependent kernels. We then examine two particular inflationary
models, one with isocurvature perturbations, the other with corrections due to
loops of matter fields. In the first model the entropy grows rapidely, while in
the second the state remains pure (at one loop).Comment: 28 page
Downregulation of major histocompatibility complex class I in bovine papillomas
Bovine papillomavirus (BPV) induces papillomas in cattle; in the great majority of cases, these regress due to the host immune response, but they can persist and progress to malignancy. Even in the absence of malignant transformation, BPV infection persists for a significant period of time before activation of the host immune system, suggesting that the host immune system is unaware of, or disabled by, BPV. E5 is the major oncoprotein of BPV, which, in addition to its transforming properties, downregulates the expression and transport to the cell surface of major histocompatibility complex class I (MHC I). Here, it is shown that co-expression of MHC I and E5 in papillomas caused by BPV-4 infection is mutually exclusive, in agreement with the inhibition of surface MHC I expression by E5 that is observed in vitro. The inhibition of MHC expression in E5-expressing papilloma cells could explain the long period that is required for activation of the immune response and has implications for the progression of papillomas to the malignant stage; absence of peptide presentation by MHC I to cytotoxic T lymphocytes would allow the infected cells to evade the host cellular immune response and allow the lesions to persist
Quantum Performance of Thermal Machines over Many Cycles
The performance of quantum heat engines is generally based on the analysis of
a single cycle. We challenge this approach by showing that the total work
performed by a quantum engine need not be proportional to the number of cycles.
Furthermore, optimizing the engine over multiple cycles leads to the
identification of scenarios with a quantum enhancement. We demonstrate our
findings with a quantum Otto engine based on a two-level system as the working
substance that supplies power to an external oscillator.Comment: 5 pages, 3 figures; published in Phys. Rev. Lett. as an Editors'
Suggestio
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
Site Suitability Analysis for an Intermountain Solid Waste Facility: A Study for Cache County, Utah
The goal of this project was to analyze Cache County for potential sanitary landfill sites covering the period 2020 to 2120. The county population and per capita solid waste were estimated. The minimum landfill size was then calculated. A geographic information system (GIS) was used for data storage and vii analysis. Relevant data were gathered. Areas which would not support a landfill were eliminated. Remaining sites were rated as having slight, moderate, or severe restrictions for use as an area method sanitary landfill based on the Natural Resource Conservation Service (NRCS) Sanitary Facility Report, and the NRCS Soil Interpretations Rating Guide. Seventeen sites were designated as sites for further evaluation. A landfill ranking system giving a primary and/or secondary rating to data items was developed. Nine prime sites had one secondary (.,a ting. These sites should be more closely investigated to determine which are the best potential sites. (136 pages
- …