Manculus and M. quadridigitatus

Number of Pages: 2Integrative BiologyGeological Science

Ultrasonic scattering from decorated grain boundaries

The microstructure of polycrystalline materials is manipulated in many ways to create materials with superior engineering properties. Alloying pure materials, for example, can alter crystallographic structure to strengthen or stiffen the material, but when impurities collect along grain boundaries, the material may become embrittled. This undesirable condition is generally associated with improper heat treatment during fabrication, but it may also occur during the service life of alloys exposed to penetrating radiation or severe thermal conditions. This dissertation studies scattering from decorated grain boundaries theoretically and experimentally, and ties results for isolated scatterers to grain noise measurements on materials composed entirely of scattering structures. The theoretical analysis begins with a treatment of a grain with decorated boundaries. This is modelled as an isolated isotropic spherical scatterer with a shell of spherically orthotropic material surrounding the core. This composite scatterer is embedded in a homogeneous isotropic host, and exact equations for scattering of an incident plane longitudinal wave are developed. Approximate and exact solutions for these equations are derived, and compared to prior solutions in the limiting case of an isotropic shell. The solution is then extended to focused incident fields, using a generalized Fourier series to represent the incident field in a form compatible with the separation of variables method of solving the spherical scatterer problem. Good agreement for scattering from isolated spherical scatterers, without and with a shell, and in a focused field, is obtained when theoretical results are compared with observations on microspheres of titanium - 6 aluminum - 4 vanadium (Ti64) and similar microspheres having a shell of nitrided Ti64. Finally, isolated scatterer theory is incorporated into backscattering models which allow multiple independent scatterers, scattering due to crystallographic anisotropy, and scattering from phase contrast in multiphase materials. Calculations based on these backscattering theories compare favorably with ultrasonic grain noise measurements on solid samples compacted from the Ti64 and nitrided Ti64 microspheres

The theological-political predicament of American Jewry

"Leo Strauss, in an autobiographical aside, spoke of being in the grip of a “theological political predicament” as a young man. He meant by this something like the following. For modern Jews the constellation of religious beliefs that seems to them reasonable and compelling—the theological horizon, so to speak—is constrained by the political horizon. They are spiritually indebted, to the point of dependency, on the values of the political system, which, for the lucky ones at least, derive from the Enlightenment. Judaism therefore depends on the Enlightenment. But what happens when confidence in the Enlightenment begins to wobble and Judaism, now weakened by its dependency, lacks the strength to make up the difference?"(...

Past electron-positron g-2 experiments yielded sharpest bound on CPT violation for point particles

In our past experiments on a single electron and positron we measured the cyclotron and spin-cyclotron difference frequencies omega_c and omega_a and the ratios a = omega_a/ omega_c at omega_c = 141 Ghz for e^- and e^+ and later, only for e^-, also at 164 Ghz. Here, we do extract from these data, as had not done before, a new and very different figure of merit for violation of CPT symmetry, one similar to the widely recognized impressive limit |m_Kaon - m_Antikaon|/m_Kaon < 10^-18 for the K-mesons composed of two quarks. That expression may be seen as comparing experimental relativistic masses of particle states before and after the C, P, T operations had transformed particle into antiparticle. Such a similar figure of merit for a non-composite and quite different lepton, found by us from our Delta a = a^- - a^+ data, was even smaller, h_bar |omega_a^- - omega_a^+|/2m_0 c^2 = |Delta a| h_bar omega_c/2m_0 c^2) < 3(12) 10^-22.Comment: Improved content, Editorially approved for publication in PRL, LATEX file, 5 pages, no figures, 16

Planning and Design Considerations for Computer Supported Collaboration Spaces

Architects have long been aware of the need to design for the behaviors a space is meant to support. However, neither the seminal works on architectural programming or collaborative engineering address the linkages between physical environment design and collaborative work practice. This paper posits that the design of collaboration environments should stand as a third pillar of collaboration engineering, suggests four ways in which physical environment design and collaboration engineering might mutually inform the other, and specifies several dimensions of physical environment affordance collaboration engineers might consider when developing requirements for collaboration space

The Cerebellum and SIDS: Disordered Breathing in a Mouse Model of Developmental Cerebellar Purkinje Cell Loss during Recovery from Hypercarbia.

The cerebellum assists coordination of somatomotor, respiratory, and autonomic actions. Purkinje cell alterations or loss appear in sudden infant death and sudden death in epilepsy victims, possibly contributing to the fatal event. We evaluated breathing patterns in 12 wild-type (WT) and Lurcher mutant mice with 100% developmental cerebellar Purkinje cell loss under baseline (room air), and recovery from hypercapnia, a concern in sudden death events. Six mutant and six WT mice were exposed to 4-min blocks of increasing CO2 (2, 4, 6, and 8%), separated by 4-min recovery intervals in room air. Breath-by-breath patterns, including depth of breathing and end-expiratory pause (EEP) durations during recovery, were recorded. No baseline genotypic differences emerged. However, during recovery, EEP durations significantly lengthened in mutants, compared to WT mice, following the relatively low levels of CO2 exposure. Additionally, mutant mice exhibited signs of post-sigh disordered breathing during recovery following each exposure. Developmental cerebellar Purkinje cell loss significantly affects compensatory breathing patterns following mild CO2 exposure, possibly by inhibiting recovery from elevated CO2. These data implicate cerebellar Purkinje cells in the ability to recover from hypercarbia, suggesting that neuropathologic changes or loss of these cells contribute to inadequate ventilatory recovery to increased environmental CO2. Multiple disorders, including sudden infant death syndrome (SIDS) and sudden unexpected death in epilepsy (SUDEP), appear to involve both cardiorespiratory failure and loss or injury to cerebellar Purkinje cells; the findings support the concept that such neuropathology may precede and exert a prominent role in these fatal events

Motion about the stable libration points in the linearized, restricted three-body problem

The motion of a point particle in the neighborhood of a triangular libration point (L sub 4 or L sub 5) in the linearized, restricted problem of three bodies in the plane is described. The derivation of the equations of motion is standard. From these equations, three invariants of the motion are obtained; the Jacobi integral is expressed linearly in terms of two of these. The trajectories for varied initial conditions are drawn, and a complete geometric description of the particle motion is given in elementary terms. Each trajectory has an exterior boundary curve; its equation is found. An approximation to this boundary curve was known; the two curves are compared graphically. For certain initial conditions, there is an interior region from which the trajectory is excluded; the equation of the boundary of this region is given