11,222 research outputs found
Dynamical properties of a nonequilibrium quantum dot close to localized-delocalized quantum phase transitions
We calculate the dynamical decoherence rate and susceptibility of a
nonequilibrium quantum dot close to the delocalized-to-localized quantum phase
transitions. The setup concerns a resonance-level coupled to two spinless
fermionic baths with a finite bias voltage and an Ohmic bosonic bath
representing the dissipative environment. The system is equivalent to an
anisotropic Kondo model.
As the dissipation strength increases, the system at zero temperature and
zero bias show quantum phase transition between a conducting delocalized phase
to an insulating localized phase. Within the nonequilibrium functional
Renormalization Group (FRG) approach, we address the finite bias crossover in
dynamical decoherence rate and charge susceptibility close to the phase
transition. We find the dynamical decoherence rate increases with increasing
frequency. In the delocalized phase, it shows a singularity at frequencies
equal to positive or negative bias voltage. As the system crossovers to the
localized phase, the decoherence rate at low frequencies get progressively
smaller and this sharp feature is gradually smeared out, leading to a single
linear frequency dependence. The dynamical charge susceptibility shows a
dip-to-peak crossover across the delocalized-to-localized transition. Relevance
of our results to the experiments is discussed.Comment: 7 pages, 7 figure
A search for evidence of large body Earth impacts associated with biological crisis zones in the fossil record
The natural history of the Earth, how the present plant and animal species developed, how others completely died out, etc., was studied. The rock strata sampled and studied were at the time of deposition at sea bottom. It was found that, exactly at the stratigraphic level corresponding to the extinction, a thin clay layer was greatly enriched in the the rare element iridium. It was hypothesized that the excess irridium at the boundary came from a large steroid like object that hit the earth, and that the impact of this object threw up a dust cloud dense enough and long lasting enough to bring about the extinction of a wide variety of plants and animals, producing the unique break in in the fossil record, the cretaceous-tertiary boundary. The same iridium and platinum metals enrichement are found in a thin clay layer that corresponds with the boundary as difined by sudden radical changes in plant populations. The irridium enrichement is confirmed at other fresh water origin rites in the Raton Basin
Technology transfer - A selected bibliography
Selected bibliography on technology transfe
Generalized coherent states are unique Bell states of quantum systems with Lie group symmetries
We consider quantum systems, whose dynamical symmetry groups are semisimple
Lie groups, which can be split or decay into two subsystems of the same
symmetry. We prove that the only states of such a system that factorize upon
splitting are the generalized coherent states. Since Bell's inequality is never
violated by the direct product state, when the system prepared in the
generalized coherent state is split, no quantum correlations are created.
Therefore, the generalized coherent states are the unique Bell states, i.e.,
the pure quantum states preserving the fundamental classical property of
satisfying Bell's inequality upon splitting.Comment: 4 pages, REVTeX, amssymb style. More information on
http://www.technion.ac.il/~brif/science.htm
Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations
We investigate electron transfer processes in donor-acceptor systems with a
coupling of the electronic degrees of freedom to a common bosonic bath. The
model allows to study many-particle effects and the influence of the local
Coulomb interaction U between electrons on donor and acceptor sites. Using the
non-perturbative numerical renormalization group approach we find distinct
differences between the electron transfer characteristics in the single- and
two-particle subspaces. We calculate the critical electron-boson coupling
alpha_c as a function of and show results for density-density correlation
functions in the whole parameter space. The possibility of many-particle
(bipolaronic) and Coulomb-assisted transfer is discussed.Comment: 4 pages, 4 figure
The Absence of Extra-Tidal Structure in the Sculptor Dwarf Spheroidal Galaxy
The results of a wide-field survey of the Sculptor dwarf spheroidal galaxy
are presented. Our aims were to obtain an accurate map of the outer structure
of Sculptor, and to determine the level of interaction between this system and
the Galaxy. Photometry was obtained in two colours down to the magnitude limits
of V=20 and I=19, covering a 3.1 times 3.1 square deg area centred on Sculptor.
The resulting colour-magnitude data were used as a mask to select candidate
horizontal branch and red giant branch stars for this system. Previous work has
shown that the red horizontal branch (HB) stars are more concentrated than the
blue HB stars. We have determined the radial distributions of these two
populations and show that the overall Sculptor density profile is well
described by a two component model based on a combination of these radial
distributions. Additionally, spectra of the Ca ii triplet region were obtained
for over 700 candidate red giant stars over the 10 square deg region using the
2dF instrument on the Anglo-Australian Telescope. These spectra were used to
remove foreground Galactic stars based on radial velocity and Ca ii triplet
strength. The final list of Sculptor members contained 148 stars, seven of
which are located beyond the nominal tidal radius. Both the photometric and
spectroscopic datasets indicate no significant extra-tidal structure. These
results support at most a mild level of interaction between this system and the
Galaxy, and we have measured an upper mass limit for extra-tidal material to be
2.3 +/- 0.6% of the Sculptor luminous mass. This lack of tidal interaction
indicates that previous velocity dispersion measurements (and hence the amount
of dark matter detected) in this system are not strongly influenced by the
Galactic tidal field.Comment: 53 pages, 23 figures. Accepted for publication in the Astronomical
Journal. Some figures are reduced in size, and a full version is available
at: ftp://ftp.mso.anu.edu.au/pub/coleman/sculptor.pd
The Physical Basis for Long-lived Electronic Coherence in Photosynthetic Light Harvesting Systems
The physical basis for observed long-lived electronic coherence in
photosynthetic light-harvesting systems is identified using an analytically
soluble model. Three physical features are found to be responsible for their
long coherence lifetimes: i) the small energy gap between excitonic states, ii)
the small ratio of the energy gap to the coupling between excitonic states, and
iii) the fact that the molecular characteristics place the system in an
effective low temperature regime, even at ambient conditions. Using this
approach, we obtain decoherence times for a dimer model with FMO parameters of
160 fs at 77 K and 80 fs at 277 K. As such, significant
oscillations are found to persist for 600 fs and 300 fs, respectively, in
accord with the experiment and with previous computations. Similar good
agreement is found for PC645 at room temperature, with oscillations persisting
for 400 fs. The analytic expressions obtained provide direct insight into the
parameter dependence of the decoherence time scales.Comment: 5 figures; J. Phys. Chem. Lett. (2011
Becoming the leader: Leadership as material presence
This paper seeks to understand leaders as material presences. Leadership theory has traditionally explored leaders as sites of disembodied traits, characteristics and abilities. Our qualitative, mixed method study suggests that managers charged with the tasks of leadership operate within a very different understanding. Their endogenous or lay theory understands leadership as physical, corporeal and visible, and as something made manifest through leaders’ material presence. This theory-in-practice holds that leadership qualities are signified by the leader’s physical appearance: the good leader must look the part. Actors consequently work on their own appearance to present an image of themselves as leader. They thus offer a fundamental challenge to dominant exogenous, or academic, theories of leadership. To understand the unspoken assumptions that underpin the lay theory of leadership as material presence, we interrogate it using the new materialist theory of Karen Barad and the object relations theory of Christopher Bollas. This illuminates the lay theory’s complexities and sophisticated insights. In academic terms it offers a theory of how sentient and non-sentient actors intra-act and performatively constitute leadership through complex entanglements that enact and circulate organizational and leadership norms. The paper’s contribution is thus a theory of leadership micro-dynamics in which the leader is materialized through practices of working on a corporeal self for presentation to both self and others
Fabrication of minority-carrier-limited n-Si/insulator/metal diodes
A photoelectrochemical anodization technique has been used to fabricate n-Si/insulator/metal (MIS) diodes with improved electrical properties. MIS structures fabricated with Au have provided the first experimental observation of a solid-state n-Si surface barrier device whose open circuit voltage Voc is controlled by minority-carrier bulk diffusion/recombination processes. For these diodes, variation of the minority-carrier diffusion length and majority-carrier dopant density produced changes in Voc that were in accord with bulk diffusion/recombination theory. Additionally, the variation in Voc in response to changes in the work function of the metal overlayer indicated that these MIS devices were not subject to the Fermi level pinning restrictions observed for n-Si Schottky structures. X-ray photoelectron spectroscopic characterization of the anodically grown insulator indicated 8.2±0.9 Å of a strained SiO2 layer as the interfacial insulator resulting from the photoanodization process
The channels of technology acquisition in commercial firms, and the NASA dissemination program
Technology acquisition in commercial firms, and NASA dissemination progra
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