New directions in InP solar cell research

Recent research efforts representing new directions in InP solar cell research are reviewed. These include heteroepitaxial growth on silicon and gallium arsenide substrates, V-grooved cells, large area high efficiency cells, and surface passivation. Improvements in heteroepitaxial cell efficiency are described together with processing of 19.1 percent, 4 sq cm cells. Recommendations are made for improvements in processing leading to increased efficiencies

Neutrino Anomalies in an Extended Zee Model

We discuss an extended $SU(2)\times U(1)$ model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies. No right-handed neutrinos are introduced in the model.The model uses a softly broken $L_e-L_{\mu}-L_{\tau}$ symmetry. Neutrino masses arise only at the loop level. The one-loop neutrino masses which arise as in the Zee model solve the atmospheric neutrino anomaly while breaking of $L_e-L_{\mu}-L_{\tau}$ generates at two-loop order a mass splitting needed for the vacuum solution of the solar neutrino problem. A somewhat different model is possible which accommodates the large-angle MSW resolution of the solar neutrino problem.Comment: 11 pages including 2 figures; a reference added and text changed accordingl

Type-Constrained Representation Learning in Knowledge Graphs

Large knowledge graphs increasingly add value to various applications that require machines to recognize and understand queries and their semantics, as in search or question answering systems. Latent variable models have increasingly gained attention for the statistical modeling of knowledge graphs, showing promising results in tasks related to knowledge graph completion and cleaning. Besides storing facts about the world, schema-based knowledge graphs are backed by rich semantic descriptions of entities and relation-types that allow machines to understand the notion of things and their semantic relationships. In this work, we study how type-constraints can generally support the statistical modeling with latent variable models. More precisely, we integrated prior knowledge in form of type-constraints in various state of the art latent variable approaches. Our experimental results show that prior knowledge on relation-types significantly improves these models up to 77% in link-prediction tasks. The achieved improvements are especially prominent when a low model complexity is enforced, a crucial requirement when these models are applied to very large datasets. Unfortunately, type-constraints are neither always available nor always complete e.g., they can become fuzzy when entities lack proper typing. We show that in these cases, it can be beneficial to apply a local closed-world assumption that approximates the semantics of relation-types based on observations made in the data

A double junction model of irradiated silicon pixel sensors for LHC

In this paper we discuss the measurement of charge collection in irradiated silicon pixel sensors and the comparison with a detailed simulation. The simulation implements a model of radiation damage by including two defect levels with opposite charge states and trapping of charge carriers. The modeling proves that a doubly peaked electric field generated by the two defect levels is necessary to describe the data and excludes a description based on acceptor defects uniformly distributed across the sensor bulk. In addition, the dependence of trap concentrations upon fluence is established by comparing the measured and simulated profiles at several fluences and bias voltages.Comment: Talk presented at the 10th European Symposium on Semiconductor Detectors, June 12-16 2005, Wildbad Kreuth, Germany. 9 pages, 4 figure

The Move toward a Cashless Society: A Closer Look at Payment Instrument Economics

Ever since the first general-purpose charge card debuted in the early 1950s, pundits have been predicting the "cashless society." Over fifty years later, we may finally be getting close to that vision. This study is the first to examine empirically the move toward a cashless society using a cost-benefit framework. We find that when all key parties to a transaction are considered and benefits are added, cash and checks are more costly than many earlier studies suggest. In general, the shift toward a cashless society appears to be a beneficial one.

GaAs homojunction solar cell development

The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells

Magnetic Moment Formation in Graphene Detected by Scattering of Pure Spin Currents

Hydrogen adatoms are shown to generate magnetic moments inside single layer graphene. Spin transport measurements on graphene spin valves exhibit a dip in the non-local spin signal as a function of applied magnetic field, which is due to scattering (relaxation) of pure spin currents by exchange coupling to the magnetic moments. Furthermore, Hanle spin precession measurements indicate the presence of an exchange field generated by the magnetic moments. The entire experiment including spin transport is performed in an ultrahigh vacuum chamber, and the characteristic signatures of magnetic moment formation appear only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate similar behavior indicating that the magnetic moment formation originates from pz-orbital defects.Comment: accepted to Phys. Rev. Let