668 research outputs found
Processing Issues in Top-Down Approaches to Quantum Computer Development in Silicon
We describe critical processing issues in our development of single atom
devices for solid-state quantum information processing. Integration of single
31P atoms with control gates and single electron transistor (SET) readout
structures is addressed in a silicon-based approach. Results on electrical
activation of low energy (15 keV) P implants in silicon show a strong dose
effect on the electrical activation fractions. We identify dopant segregation
to the SiO2/Si interface during rapid thermal annealing as a dopant loss
channel and discuss measures of minimizing it. Silicon nanowire SET pairs with
nanowire width of 10 to 20 nm are formed by electron beam lithography in SOI.
We present first results from Coulomb blockade experiments and discuss issues
of control gate integration for sub-40nm gate pitch levels
QFT on homothetic Killing twist deformed curved spacetimes
We study the quantum field theory (QFT) of a free, real, massless and
curvature coupled scalar field on self-similar symmetric spacetimes, which are
deformed by an abelian Drinfel'd twist constructed from a Killing and a
homothetic Killing vector field. In contrast to deformations solely by Killing
vector fields, such as the Moyal-Weyl Minkowski spacetime, the equation of
motion and Green's operators are deformed. We show that there is a *-algebra
isomorphism between the QFT on the deformed and the formal power series
extension of the QFT on the undeformed spacetime. We study the convergent
implementation of our deformations for toy-models. For these models it is found
that there is a *-isomorphism between the deformed Weyl algebra and a reduced
undeformed Weyl algebra, where certain strongly localized observables are
excluded. Thus, our models realize the intuitive physical picture that
noncommutative geometry prevents arbitrary localization in spacetime.Comment: 23 pages, no figures; v2: extended discussion of physical
consequences, compatible with version to be published in General Relativity
and Gravitatio
Risk factors of visceral leishmaniasis in East Africa: a case-control study in Pokot territory of Kenya and Uganda
BACKGROUND: In East Africa, visceral leishmaniasis (VL) is endemic in parts of Sudan, Ethiopia, Somalia, Kenya and Uganda. It is caused by Leishmania donovani and transmitted by the sandfly vector Phlebotomus martini. In the Pokot focus, reaching from western Kenya into eastern Uganda, formulation of a prevention strategy has been hindered by the lack of knowledge on VL risk factors as well as by lack of support from health sector donors. The present study was conducted to establish the necessary evidence-base and to stimulate interest in supporting the control of this neglected tropical disease in Uganda and Kenya. METHODS: A case-control study was carried out from June to December 2006. Cases were recruited at Amudat hospital, Nakapiripirit district, Uganda, after clinical and parasitological confirmation of symptomatic VL infection. Controls were individuals that tested negative using a rK39 antigen-based dipstick, which were recruited at random from the same communities as the cases. Data were analysed using conditional logistic regression. RESULTS: Ninety-three cases and 226 controls were recruited into the study. Multivariate analysis identified low socio-economic status and treating livestock with insecticide as risk factors for VL. Sleeping near animals, owning a mosquito net and knowing about VL symptoms were associated with a reduced risk of VL. CONCLUSIONS: VL affects the poorest of the poor of the Pokot tribe. Distribution of insecticide-treated mosquito nets combined with dissemination of culturally appropriate behaviour-change education is likely to be an effective prevention strategy
Factors determining microbial colonization of liquid nitrogen storage tanks used for archiving biological samples
The availability of bioresources is a precondition for life science research, medical applications, and diagnostics, but requires a dedicated quality management to guarantee reliable and safe storage. Anecdotal reports of bacterial isolates and sample contamination indicate that organisms may persist in liquid nitrogen (LN) storage tanks. To evaluate the safety status of cryocollections, we systematically screened organisms in the LN phase and in ice layers covering inner surfaces of storage tanks maintained in different biobanking facilities. We applied a culture-independent approach combining cell detection by epifluorescence microscopy with the amplification of group-specific marker genes and high-throughput sequencing of bacterial ribosomal genes. In the LN phase, neither cells nor bacterial 16S rRNA gene copy numbers were detectable (detection limit, 102 cells per ml, 103 gene copies per ml). In several cases, small numbers of bacteria of up to 104 cells per ml and up to 106 gene copies per ml, as well as Mycoplasma, or fungi were detected in the ice phase formed underneath the lids or accumulated at the bottom. The bacteria most likely originated from the stored materials themselves (Elizabethingia, Janthibacterium), the technical environment (Pseudomonas, Acinetobacter, Methylobacterium), or the human microbiome (Bacteroides, Streptococcus, Staphylococcus). In single cases, bacteria, Mycoplasma, fungi, and human cells were detected in the debris at the bottom of the storage tanks. In conclusion, the limited microbial load of the ice phase and in the debris of storage tanks can be effectively avoided by minimizing ice formation and by employing hermetically sealed sample containers
Asymptotic expansion for reversible A + B <-> C reaction-diffusion process
We study long-time properties of reversible reaction-diffusion systems of
type A + B C by means of perturbation expansion in powers of 1/t (inverse
of time). For the case of equal diffusion coefficients we present exact
formulas for the asymptotic forms of reactant concentrations and a complete,
recursive expression for an arbitrary term of the expansions. Taking an
appropriate limit we show that by studying reversible reactions one can obtain
"singular" solutions typical of irreversible reactions.Comment: 6 pages, no figures, to appear in PR
Noncommutative Solitons of Gravity
We investigate a three-dimensional gravitational theory on a noncommutative
space which has a cosmological constant term only. We found various kinds of
nontrivial solutions, by applying a similar technique which was used to seek
noncommutative solitons in noncommutative scalar field theories. Some of those
solutions correspond to bubbles of spacetimes, or represent dimensional
reduction. The solution which interpolates and Minkowski metric
is also found. All solutions we obtained are non-perturbative in the
noncommutative parameter , therefore they are different from solutions
found in other contexts of noncommutative theory of gravity and would have a
close relation to quantum gravity.Comment: 29 pages, 5 figures. v2: minor corrections done in Section 3.1 and
Appendix, references added. v3, v4: typos correcte
Algebraic approach to quantum field theory on a class of noncommutative curved spacetimes
In this article we study the quantization of a free real scalar field on a
class of noncommutative manifolds, obtained via formal deformation quantization
using triangular Drinfel'd twists. We construct deformed quadratic action
functionals and compute the corresponding equation of motion operators. The
Green's operators and the fundamental solution of the deformed equation of
motion are obtained in terms of formal power series. It is shown that, using
the deformed fundamental solution, we can define deformed *-algebras of field
observables, which in general depend on the spacetime deformation parameter.
This dependence is absent in the special case of Killing deformations, which
include in particular the Moyal-Weyl deformation of the Minkowski spacetime.Comment: LaTeX 14 pages, no figures, svjour3.cls style; v2: clarifications and
references added, compatible with published versio
Four Lessons in Versatility or How Query Languages Adapt to the Web
Exposing not only human-centered information, but machine-processable data on the Web is one of the commonalities of recent Web trends. It has enabled a new kind of applications and businesses where the data is used in ways not foreseen by the data providers. Yet this exposition has fractured the Web into islands of data, each in different Web formats: Some providers choose XML, others RDF, again others JSON or OWL, for their data, even in similar domains. This fracturing stifles innovation as application builders have to cope not only with one Web stack (e.g., XML technology) but with several ones, each of considerable complexity. With Xcerpt we have developed a rule- and pattern based query language that aims to give shield application builders from much of this complexity: In a single query language XML and RDF data can be accessed, processed, combined, and re-published. Though the need for combined access to XML and RDF data has been recognized in previous work (including the W3C’s GRDDL), our approach differs in four main aspects: (1) We provide a single language (rather than two separate or embedded languages), thus minimizing the conceptual overhead of dealing with disparate data formats. (2) Both the declarative (logic-based) and the operational semantics are unified in that they apply for querying XML and RDF in the same way. (3) We show that the resulting query language can be implemented reusing traditional database technology, if desirable. Nevertheless, we also give a unified evaluation approach based on interval labelings of graphs that is at least as fast as existing approaches for tree-shaped XML data, yet provides linear time and space querying also for many RDF graphs. We believe that Web query languages are the right tool for declarative data access in Web applications and that Xcerpt is a significant step towards a more convenient, yet highly efficient data access in a “Web of Data”
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