Thermal stress analysis of ceramic gas-path seal components for aircraft turbines

Stress and temperature distributions were evaluated numerically for a blade-tip seal system proposed for gas turbine applications. The seal consists of an abradable ceramic layer on metallic backing with intermediate layers between the ceramic layer and metal substrate. The most severe stresses in the seal, as far as failure is concerned, are tensile stresses at the top of the ceramic layer and shear and normal stresses at the layer interfaces. All these stresses reach their maximum values during the deceleration phase of a test engine cycle. A parametric study was carried out to evaluate the influence of various design parameters on these critical stress values. The influences of material properties and geometric parameters of the ceramic, intermediate, and backing layers were investigated. After the parametric study was completed, a seal system was designed which incorporated materials with beneficial elastic and thermal properties in each layer of the seal. An analysis of the proposed seal design shows an appreciable decrease in the magnitude of the maximum critical stresses over those obtained with earlier configurations

Making the small oblique parameters large

We compute the oblique parameters, including the three new parameters $V$, $W$ and $X$ introduced recently by the Montreal group, for the case of one scalar multiplet of arbitrary weak isospin $J$ and weak hypercharge $Y$. We show that, when the masses of the heaviest and lightest components of the multiplet remain constant, but $J$ increases, the oblique parameter $U$ and the three new oblique parameters increase like $J^3$, while $T$ only increases like $J$. For large multiplets with masses not much higher than $m_Z$, the oblique parameters $U$ and $V$ may become much larger than $T$ and $S$.Comment: 9 pages, standard LATEX, 3 figures available from the authors, report CMU-HEP93-17 and DOE-ER/40682-4

Dephasing dynamics of Rydberg atom spin waves

A theory of Rydberg atom interactions is used to derive analytical forms for the spin wave pair correlation function in laser-excited cold-atom vapors. This function controls the quantum statistics of light emission from dense, inhomogeneous clouds of cold atoms of various spatial dimensionalities. The results yield distinctive scaling behaviors on the microsecond timescale, including generalized exponential decay. A detailed comparison is presented with a recent experiment on a cigar-shaped atomic ensemble [Y. Dudin and A. Kuzmich, Science 336, 887 (2012)], in which Rb atoms are excited to a set of Rydberg levels.Comment: 4 pages, Supplemental Material in Appendix, 4 figure

The superconducting phase transition and gauge dependence

The gauge dependence of the renormalization group functions of the Ginzburg-Landau model is investigated. The analysis is done by means of the Ward-Takahashi identities. After defining the local superconducting order parameter, it is shown that its exponent $\beta$ is in fact gauge independent. This happens because in $d=3$ the Landau gauge is the only gauge having a physical meaning, a property not shared by the four-dimensional model where any gauge choice is possible. The analysis is done in both the context of the $\epsilon$-expansion and in the fixed dimension approach. It is pointed out the differences that arise in both of these approaches concerning the gauge dependence.Comment: RevTex, 3 pages, no figures; accepted for publication in PRB; this paper is a short version of cond-mat/990527

Symptomatology under storm conditions in the north atlantic in control subjects and in persons with bilateral labyrinthine defects

Motion sickness under conditions of stress and anxiety - role of vestibular apparatu

Electroweak Theory Without Higgs Bosons

A perturbative SU(2)_L X U(1)_Y electroweak theory containing W, Z, photon, ghost, lepton and quark fields, but no Higgs or other fields, gives masses to W, Z and the non-neutrino fermions by means of an unconventional choice for the unperturbed Lagrangian and a novel method of renormalisation. The renormalisation extends to all orders. The masses emerge on renormalisation to one loop. To one loop the neutrinos are massless, the A -> Z transition drops out of the theory, the d quark is unstable and S-matrix elements are independent of the gauge parameter xi.Comment: 27 pages, LaTex, no figures; revised for publication; accepted by Int. J. Mod. Phys. A; includes biographical note on A. F. Nicholso

Transient Heat Partition Factor for a Sliding Railcar Wheel

During a wheel slide the frictional heat generated at the contact interface causes intense heating of the adjacent wheel material. If this material exceeds the austenitising temperature and then cools quickly enough, it can transform into martensite, which may ultimately crack and cause wheel failure. A knowledge of the distribution of the heat partitioned into the wheel and the rail and the resulting temperature fields is critical to developing designs to minimize these deleterious effects. A number of theoretical solutions have appeared in the literature to model the thermal aspects of this phenomenon. The objective of this investigation was to examine the limitations of these solutions by comparing them to the results of a finite element analysis that does not incorporate many of the simplifying assumptions on which these solutions are based. It was found that these simplified solutions can produce unrealistic results under some circumstances

Daily Eclosion Pattern of the Saratoga Spittlebug, Aphrophora Saratogensis (Fitch) (Homoptera: Cercopidae)

The Saratoga spittlebug, Aphrophora saratogensis (Fitch), is a destructive pest of young planted pines in the Lake States. The adults injure the pines by feeding on the sap of branches. However, nymphs feed on the sap of alternate host plants, which include many herbs and woody plants on the forest floor. Our studies show that the time of the eclosion and shortly thereafter is one of the most vulnerable periods in the insect\u27s life cycle. During this period the nymphs must free themselves from the eggs that are on pine buds, vacate the pines, search out suitable host plants on the forest floor, initiate feeding, and cover themselves with masses of spittle. And they must do this before they desiccate (Ewan, 1961), starve, or are captured by predators. As part of a survival study we wanted to observe the nymphs at eclosion because their emergence and behavior pattern at that time would certainly affect their survival. In the Lake States area eclosion occurs from early April to late May, a period when weather varies greatly from cool and wet to warm and dry. Reported is the nymphal eclosion pattern during the peak of the eclosion periods in 1969 and 1970