1,543 research outputs found
The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy
High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer (GRIS) is one of the experiments selected as part of this program. The instrument contains a number of new and innovative features that are expected to produce a significant improvement in source location accuracy and sensitivity over previous balloon and satellite experiments
A coded aperture imaging system optimized for hard X-ray and gamma ray astronomy
A coded aperture imaging system was designed for the Gamma-Ray imaging spectrometer (GRIS). The system is optimized for imaging 511 keV positron-annihilation photons. For a galactic center 511-keV source strength of 0.001 sq/s, the source location accuracy is expected to be + or - 0.2 deg
Interdigitated back contact silicon heterojunction solar cells Towards an industrially applicable structuring method
We report on the investigation and comparison of two different processing approaches for interdigitated back contacted silicon heterojunction solar cells our photolithography based reference procedure and our newly developed shadow mask process. To this end, we analyse fill factor losses in different stages of the fabrication process. We find that although comparably high minority carrier lifetimes of about 4 ms can be observed for both concepts, the shadow masked solar cells suffer yet from poorly passivated emitter regions and significantly higher series resistance. Approaches for addressing the observed issues are outlined and first solar cell results with efficiencies of about 17 and 23 for shadow masked and photolithographically structured solar cells, respectively, are presente
Computing the lower and upper bounds of Laplace eigenvalue problem: by combining conforming and nonconforming finite element methods
This article is devoted to computing the lower and upper bounds of the
Laplace eigenvalue problem. By using the special nonconforming finite elements,
i.e., enriched Crouzeix-Raviart element and extension , we get
the lower bound of the eigenvalue. Additionally, we also use conforming finite
elements to do the postprocessing to get the upper bound of the eigenvalue. The
postprocessing method need only to solve the corresponding source problems and
a small eigenvalue problem if higher order postprocessing method is
implemented. Thus, we can obtain the lower and upper bounds of the eigenvalues
simultaneously by solving eigenvalue problem only once. Some numerical results
are also presented to validate our theoretical analysis.Comment: 19 pages, 4 figure
Hybrid fiber reinforcement and crack formation in cementitious composite materials
The use of different types of fibers simultaneously for reinforcing cementitious
matrices is motivated by the concept of a multi-scale nature of the
crack propagation process. Fibers with different geometrical and mechanical properties
are used to bridge cracks of different sizes from the micro- to the macroscale.
In this study, the performance of different fiber reinforced cementitious
composites is assessed in terms of their tensile stress-crack opening behavior. The
results obtained from this investigation allow a direct quantitative comparison of
the behavior obtained from the different fiber reinforcement systems. The research
described in this paper shows that the multi-scale conception of cracking and the
use of hybrid fiber reinforcements do not necessarily result in an improved tensile
behavior of the composite. Particular material design requirements may nevertheless
justify the use of hybrid fiber reinforcements.Fundação para a Ciência e a Tecnologia (FCT) - SFRH / BD / 36515 / 200
Pseudo-Hermitian continuous-time quantum walks
In this paper we present a model exhibiting a new type of continuous-time
quantum walk (as a quantum mechanical transport process) on networks, which is
described by a non-Hermitian Hamiltonian possessing a real spectrum. We call it
pseudo-Hermitian continuous-time quantum walk. We introduce a method to obtain
the probability distribution of walk on any vertex and then study a specific
system. We observe that the probability distribution on certain vertices
increases compared to that of the Hermitian case. This formalism makes the
transport process faster and can be useful for search algorithms.Comment: 13 page, 7 figure
Medication-Wide Association Studies
Undiscovered side effects of drugs can have a profound effect on the health of the nation, and electronic health-care databases offer opportunities to speed up the discovery of these side effects. We applied a “medication-wide association study” approach that combined multivariate analysis with exploratory visualization to study four health outcomes of interest in an administrative claims database of 46 million patients and a clinical database of 11 million patients. The technique had good predictive value, but there was no threshold high enough to eliminate false-positive findings. The visualization not only highlighted the class effects that strengthened the review of specific products but also underscored the challenges in confounding. These findings suggest that observational databases are useful for identifying potential associations that warrant further consideration but are unlikely to provide definitive evidence of causal effects
Three Terminal Perovskite Silicon Tandem Solar Cells with Top and Interdigitated Rear Contacts
We present a three terminal 3T tandem approachfor the interconnection of a perovskite top cell with aninterdigitated back contact IBC silicon heterojunction SHJ bottom cell. The general viability of our cell design is verified withdrift diffusion simulations indicating efficient charge carriertransport throughout the whole device and an efficiency potentialof amp; 8776;27 by using readily available absorber and contact materials.Our experimental proof of concept device reaches a combinedPCE of 17.1 when both subcells are operating at their individualmaximum power point. To emulate different operation conditions,the current amp; 8722;voltage characteristics of both cells were obtained bymeasuring one subcell while the other cell was set to afixed biasvoltage. Only a slight mutual dependence of both subcells wasfound. As determined by electrical simulations, this dependence likely stems from the resistance of the electron contact on the cell srear side, which is shared by both subcells. The optimization of this contact turns out to be a major design criterion for IBC 3Ttandems. We demonstrate that our current proof of concept cells are limited by this series resistance as well as by optical losses, andwe discuss pathways to approach the simulated efficiency potential by an optimized device desig
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