375 research outputs found
Projection operator approach to transport in complex single-particle quantum systems
We discuss the time-convolutionless (TCL) projection operator approach to
transport in closed quantum systems. The projection onto local densities of
quantities such as energy, magnetization, particle number, etc. yields the
reduced dynamics of the respective quantities in terms of a systematic
perturbation expansion. In particular, the lowest order contribution of this
expansion is used as a strategy for the analysis of transport in "modular"
quantum systems corresponding to quasi one-dimensional structures which consist
of identical or similar many-level subunits. Such modular quantum systems are
demonstrated to represent many physical situations and several examples of
complex single-particle models are analyzed in detail. For these quantum
systems lowest order TCL is shown to represent an efficient tool which also
allows to investigate the dependence of transport on the considered length
scale. To estimate the range of validity of the obtained equations of motion we
extend the standard projection to include additional degrees of freedom which
model non-Markovian effects of higher orders.Comment: 13 pages, 11 figures, accepted for publication in Eur. Phys. J.
About perfection of circular mixed hypergraphs
A mixed hypergraph is a triple H = (X,C,D), where X is the vertex set and each of C and D is a family of subsets of X, the C-edges and D-edges, respectively. A proper k-coloring of H is a mapping c : X → {1,...,k} such that each C-edge has two vertices with a common color and each D-edge has two vertices with different colors. Maximum number of colors in a coloring using all the colors is called upper chromatic number χ ̄(H). Maximum cardinality of subset of vertices which contains no C-edge is C-stability number αC (H). A mixed hypergraph is called C-perfect if χ ̄ (H') = αC (H') for any induced subhypergraph H'. A mixed hyper- graph H is called circular if there exists a host cycle on the vertex set X such that every edge (C- or D-) induces a connected subgraph on the host cycle. We give a characterization of C-perfect circular mixed hypergraphs
Alburnite, Ag₈GeTe₂S₄, a new mineral species from the Roşia Montana Au-Ag epithermal deposit, Apuseni Mountains, Romania
Alburnite, ideally Ag₈GeTe₂S₄, was discovered in the Cârnicel vein from the Roşia Montana epithermal Au-Ag ore deposit, Apuseni Mountains, Romania. The new mineral is associated with tetrahedrite, galena, pyrite, sphalerite, chalcopyrite, and tellurides (hessite, altaite, and sylvanite). Associated gangue minerals are rhodochrosite, quartz, calcite, and rhodonite. Alburnite was observed only at the microscopic scale as rounded to sub-rounded grains, veinlets or irregular inclusions hosted mainly by tetrahedrite, hessite, and rhodochrosite. Due to the small size of alburnite grains observed so far it was not possible to determine some macroscopic properties; reported properties are based on microscopic observations. The mineral has a metallic luster and is opaque. It is non-fluorescent and has an estimated Mohs hardness of 4. The mineral shows no cleavage. Density could not be measured because of the small grain size, but calculated density based on the empirical formula is 7.828 g/cm³. In plane-polarized light in air, alburnite is gray-blue with a bluish tint. It shows no pleochroism or bireflectance in air. Between crossed polars alburnite is isotropic and internal reflections have not been observed in air. The mineral decomposes in intense light. Reflectance minimum values in air (in percents) are: 470 nm 29.70; 546 nm 28.00; 589 nm 27.35; 650 nm 26.95. The average chemical composition based on 18 electron microprobe analyses from 9 different grains in one polished section is (in wt%): Ag 65.49, Ge 4.82, Te 20.16, S 9.66, total 100.13. The ideal formula of alburnite, Ag₈GeTe₂S₄, based on 15 apfu requires Ag 65.43, Ge 5.50, Te 19.35, S 9.72, total 100.00 wt%. Features of the crystal structure of alburnite were determined based on electron backscattered diffraction and transmission electron microscopy. Alburnite is cubic, space group F43m, with unit- cell parameters a = 10.4(1) Å, V = 1125(30) ų, Z = 4. The strongest eight calculated XRD lines [d in Å(I) (hkl)] are: 6.004(67)(111), 3.136(48)(113), 3.002(100)(222), 2.600(26) (004), 2.123(33)(224), 2.002(61)(115), 1.838(76)(044), and 1.644(12)(026). The name of the new mineral alburnite is derived from the Latin name of the locality. Roşia Montana Au-Ag deposit was known during the Roman period as Alburnus Maior. The mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA 2012-073
Development of a two-dimensional virtual pixel X-ray imaging detector for time-resolved structure research
An interpolating two-dimensional X-ray imaging detector based on a single
photon counter with gas amplification by GEM (gas electron multiplier)
structures is presented. The detector system can be used for time-resolved
structure research down to the microsecond-time domain. The prototype detector
has been tested at the SAXS beamline at ELETTRA synchrotron light source with a
beam energy of 8 keV to test its capabilities in the rough beamline
environment. The imaging performance is examined with apertures and standard
diffraction targets. Finally, the application in a time-resolved lipid
temperature jump experiment is presented.Comment: 10 pages, 14 figures, accepted for publication in J. Synchrotron Rad,
revised version, paper shortened, minor change
Imaging with high Dynamic using an Ionization Chamber
In this work a combination of an ionization chamber with one-dimensional
spatial resolution and a MicroCAT structure will be presented. The combination
between gas gain operations and integrating front-end electronics yields a
dynamic range as high as eight to nine orders of magnitude. Therefore this
device is well suitable for medical imaging or applications such as small angle
x-ray scattering, where the requirements on the dynamic of the detector are
exceptional high. Basically the described detector is an ionization chamber
adapted to fan beam geometry with an active area of 192 cm and a pitch of the
anode strips of 150 micrometer. In the vertical direction beams as high as 10
mm can be accepted. Every read-out strip is connected to an analogue
integrating electronics channel realized in a custom made VLSI chip. A MicroCAT
structure utilized as a shielding grid enables frame rates as high as 10kHz.
The high dynamic range observed stems from the fact that the MicroCAT enables
active electron amplification in the gas. Thus a single photon resolution can
be obtained for low photon fluxes even with the integrating electronics. The
specialty of this device is that for each photon flux the gas amplification can
be adjusted in such a fashion that the maximum DQE value is achieved.Comment: 7 pages, 12 figures, distilled by OpenOffice.org 3.
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