M551 metals melting experiment

Electron beam welding studies were conducted in the Skylab M551 metals melting experiment, on three different materials; namely 2219-T87 aluminum alloy, 304L stainless steel, and commercially pure tantalum (0.5 wt % columbium). Welds were made in both one gravity and zero gravity (Skylab) environments. Segments from each of the welds were investigated by microhardness, optical microscopy, scanning microscopy, and electron probe techniques. In the 2219-T87 aluminum alloy samples, macroscopic banding and the presence of an eutectic phase in the grain boundaries of the heat affected zone were observed. The stainless steel samples exhibited a sharp weld interface and macroscopic bands. The primary microstructural features found in the tantalum were the presence of either columnar grains (ground base) or equiaxed grains (Skylab). The factors contributing to these effects are discussed and the role of reduced gravity in welding is considered

Singlet oxygen generator for a solar powered chemically pumped iodine laser

The potential of solid phase endoperoxides as a means to produce single-delta oxygen in the gas phase in concentrations useful to chemical oxygen-iodine lasers was investigated. The 1,4 - endoperoxide of ethyl 3- (4-methyl - 1-naphthyl) propanoate was deposited over an indium-oxide layer on a glass plate. Single-delta oxygen was released from the endoperoxide upon heating the organic film by means of an electrical discharge through the conductive indium oxide coating. The evolution of singlet-delta oxygen was determined by measuring the dimol emission signal at 634 nm. Comparison of the measured signal with an analytic model leads to two main conclusions: virtually all the oxygen being evolved is in the singlet-delta state and in the gas phase, and there is no significant quenching other than energy pooling on the time scale of the experiment (approximately 10 msec). The use of solid phase endoperoxide as a singlet-delta oxygen generator for an oxygen-iodine laser appears promising

Coexistence of qubit effects

Two quantum events, represented by positive operators (effects), are coexistent if they can occur as possible outcomes in a single measurement scheme. Equivalently, the corresponding effects are coexistent if and only if they are contained in the ranges of a single (joint) observable. Here we give several equivalent characterizations of coexistent pairs of qubit effects. We also establish the equivalence between our results and those obtained independently by other authors. Our approach makes explicit use of the Minkowski space geometry inherent in the four-dimensional real vector space of selfadjoint operators in a two-dimensional complex Hilbert space

Uncertainty reconciles complementarity with joint measurability

The fundamental principles of complementarity and uncertainty are shown to be related to the possibility of joint unsharp measurements of pairs of noncommuting quantum observables. A new joint measurement scheme for complementary observables is proposed. The measured observables are represented as positive operator valued measures (POVMs), whose intrinsic fuzziness parameters are found to satisfy an intriguing pay-off relation reflecting the complementarity. At the same time, this relation represents an instance of a Heisenberg uncertainty relation for measurement imprecisions. A model-independent consideration show that this uncertainty relation is logically connected with the joint measurability of the POVMs in question.Comment: 4 pages, RevTeX. Title of previous version: "Complementarity and uncertainty - entangled in joint path-interference measurements". This new version focuses on the "measurement uncertainty relation" and its role, disentangling this issue from the special context of path interference duality. See also http://www.vjquantuminfo.org (October 2003

Atomistic approach to alloy scattering in Si1−xGexSi_{1-x}Ge_{x}

SiGe alloy scattering is of significant importance with the introduction of strained layers and SiGe channels into CMOS technology. However, alloy scattering has till now been treated in an empirical fashion with a fitting parameter. We present a theoretical model within the atomistic tight-binding representation for treating alloy scattering in SiGe. This approach puts the scattering model on a solid atomistic footing with physical insights. The approach is shown to inherently capture the bulk alloy scattering potential parameters for both n-type and p-type carriers and matches experimental mobility data.Comment: 3 pg 3 figure

The structure of classical extensions of quantum probability theory

On the basis of a suggestive definition of a classical extension of quantum mechanics in terms of statistical models, we prove that every such classical extension is essentially given by the so-called Misra–Bugajski reduction map. We consider how this map enables one to understand quantum mechanics as a reduced classical statistical theory on the projective Hilbert space as phase space and discuss features of the induced hidden-variable model. Moreover, some relevant technical results on the topology and Borel structure of the projective Hilbert space are reviewed

Unsharp Quantum Reality

The positive operator (valued) measures (POMs) allow one to generalize the notion of observable beyond the traditional one based on projection valued measures (PVMs). Here, we argue that this generalized conception of observable enables a consistent notion of unsharp reality and with it an adequate concept of joint properties. A sharp or unsharp property manifests itself as an element of sharp or unsharp reality by its tendency to become actual or to actualize a specific measurement outcome. This actualization tendency-or potentiality-of a property is quantified by the associated quantum probability. The resulting single-case interpretation of probability as a degree of reality will be explained in detail and its role in addressing the tensions between quantum and classical accounts of the physical world will be elucidated. It will be shown that potentiality can be viewed as a causal agency that evolves in a well-defined way

Protecting subspaces by acting on the outside

Many quantum control tasks aim at manipulating the state of a quantum mechanical system within a finite subspace of states. However, couplings to the outside are often inevitable. Here we discuss strategies which keep the system in the controlled subspace by applying strong interactions onto the outside. This is done by drawing analogies to simple toy models and to the quantum Zeno effect. Special attention is paid to the constructive use of dissipation in the protection of subspaces.Comment: 16 pages, 10 figure

The 50-horsepower solar-powered irrigation facility located near Gila Bend, Arizona

The 50 horsepower solar powered irrigation facility near Gila Bend, Arizona which includes a Rankine cycle demonstrates the technical feasibility of solar powered pumping. The design of a facility specifically for the irrigation farmer using the technology that has been developed over the last four years is proposed

Quantum reservoirs with ion chains

Ion chains are promising platforms for studying and simulating quantum reservoirs. One interesting feature is that their vibrational modes can mediate entanglement between two objects which are coupled through the vibrational modes of the chain. In this work we analyse entanglement between the transverse vibrations of two heavy impurity defects embedded in an ion chain, which is generated by the coupling with the chain vibrations. We verify general scaling properties of the defects dynamics and demonstrate that entanglement between the defects can be a stationary feature of these dynamics. We then analyse entanglement in chains composed of tens of ions and propose a measurement scheme which allows one to verify the existence of the predicted entangled state.Comment: 14 pages, 12 figure