Shadows and Light

in the evening winter is creme among shadows, belting mysteriously to grass and thinly-clad trees..

Titanium-Oxygen Reactivity Study

A program has been conducted at Astronautics to investigate the likelihood of occurrence of the catastrophic oxidation of titanium alloy sheet under conditions which simulate certain cases of accidental failure of the metal while it is in contact with liquid or gaseous oxygen. Three methods of fracturing the metal were used; they consisted of mechanical puncture, tensile fracture of welded joints, and perforation by very high velocity particles. The results of the tests which have been conducted provide further evidence of the reactivity of titanium with liquid and gaseous oxygen. The evidence indicates that the rapid fracturing of titanium sheet while it is in contact with oxygen initiates the catastrophic oxidation reaction. Initiation occurred when the speed of the fracture was some few feet per second, as in both the drop-weight puncture tests and the static tensile fracture tests of welded joints, as well as when the speed was several thousand feet per second, as in the simulated micrometeoroid penetration tests. The slow propagation of a crack, however, did not initiate the reaction. It may logically be concluded that the localized frictional heat of rapid fracture and/or spontaneous oxidation (exothermic) of minute particles emanating from the fracture cause initiation of the reaction. Under conditions of slow fracture, however, the small heat generated may be adequately dissipated and the reaction is not initiated. A portion of the study conducted consisted of investigating various means by which the reaction might be retarded or prevented. Providing a "barrier" at the titanium-oxygen interface consisting of either aluminum metal or a coating of a petroleum base corrosion inhibitor appeared to be only partially effective in retarding the reaction. The accidental puncturing or similar rupturing of thin-walled pressurized oxygen tanks on missiles and space vehicle will usually constitute loss of function, and may sometimes cause their catastrophic destruction by explosive decompression regardless of the type of material used for their construction. In the case of tanks constructed of titanium alloys the added risk is incurred of catastrophic burning of the tanks. In view of this it is recommended that thin-walled tanks constructed of titanium alloys should not be used to contain liquid or gaseous oxygen

Escape Artist

It was a small place, and smelled of onions thinly veiled by cigarette smoke. Olivia Bernard sat in a corner booth, toying with a half-empty glass of Mateus rose..

Models of Electroweak Interactions in Non-Commutative Geometry: A Comparison

Alain Connes' construction of the standard model is based on a generalized Dirac-Yukawa operator and the K-cycle (\HD ,D), with \HD a fermionic Hilbert space. If this construction is reformulated at the level of the differential algebra then a direct comparison with the alternative approach by the Marseille-Mainz group becomes possible. We do this for the case of the toy model based on the structure group $U(1)\times U(1)$ and for the $SU(2)\times U(1)$ of electroweak interactions. Connes' results are recovered without the somewhat disturbing $\gamma_{5}$-factors in the fermion mass terms and Yukawa couplings. We discuss both constructions in the same framework and, in particular, pinpoint the origin of the difference in the Higgs potential obtained by them.Comment: 9p, MZ-TH/93-2

Supersymmetric Contributions to Weak Decay Correlation Coefficients

We study supersymmetric contributions to correlation coefficients that characterize the spectral shape and angular distribution for polarized muon- and beta-decays. In the minimal supersymmetric Standard Model (MSSM), one-loop box graphs containing superpartners can give rise to non-(V-A)x(V-A) four fermion operators in the presence of left-right or flavor mixing between sfermions. We analyze the present phenomenological constraints on such mixing and determine the range of allowed contributions to the weak decay correlation coefficients. We discuss the prospective implications for future muon- and beta-decay experiments, and argue that they may provide unique probes of left-right mixing in the first generation scalar fermion sector.Comment: Revised version - to appear in Phys.Rev.

Neutrino Mass Implications for Muon Decay Parameters

We use the scale of neutrino mass to derive model-independent naturalness constraints on possible contributions to muon decay Michel parameters from new physics above the electroweak symmetry-breaking scale. Focusing on Dirac neutrinos, we obtain a complete basis of effective dimension four and dimension six operators that are invariant under the gauge symmetry of the Standard Model and that contribute to both muon decay and neutrino mass. We show that -- in the absence of fine tuning -- the most stringent bounds on chirality-changing operators relevant to muon decay arise from one-loop contributions to neutrino mass. The bounds we obtain on their contributions to the Michel parameters are four or more orders of magnitude stronger than bounds previously obtained in the literature. We also show that there exist chirality-changing operators that contribute to muon decay but whose flavor structure allows them to evade neutrino mass naturalness bounds. We discuss the implications of our analysis for the interpretation of muon decay experiments.Comment: 19 pages, 4 figure

Improving the patient experience through patient portals: Insights from experienced portal users

Background: Patient portals have become part of the ecosystem of care as both patients and providers use them for a range of activities both individually and collaboratively. As patients and providers gain greater experience using portals, their use and needs related to portals may evolve. Objective: This study aimed to learn from experienced patient portal users to improve our understanding of their perspectives on portal use for collaboration and engagement as well as explore how using a portal influenced their experiences with primary care providers. Methods: Qualitative study involving 29 semi-structured interviews with family medicine patients from a large Academic Medical Center (AMC). Interviewees were patients with chronic conditions who had been identified by their providers as experienced portal users. Interview transcripts were analyzed using rigorous qualitative methods. Results: Common themes emerged around both logistical and psychological benefits of portal use. Logistical benefits included increased efficiency, improved ability to track their health information, and better documentation of communications and information during and between office visits. Psychological benefits were a greater sense of collaboration in care, increased trust in providers, and enhanced engagement in health care activities. Conclusion: Experienced portal users discussed ways in which patient portals improved both their ability to manage their care and their relationships with providers. Frequent users described a sense of collaboration with their providers and greater trust in the relationship. These findings suggest that portal use may be a mechanism through which patients can increase patient engagement and improve the patient experience