5,553 research outputs found
Concept of multiple-cell cavity for axion dark matter search
In cavity-based axion dark matter search experiments exploring high mass
regions, multiple-cavity design is considered to increase the detection volume
within a given magnet bore. We introduce a new idea, referred to as
multiple-cell cavity, which provides various benefits including a larger
detection volume, simpler experimental setup, and easier phase-matching
mechanism. We present the characteristics of this concept and demonstrate the
experimental feasibility with an example of a double-cell cavity.Comment: 8 pages, 11 figure
DOF phase separation of the Lennard-Jones fcc(111) surface
Recent lattice model calculations have suggested that a full-layered crystal
surface may undergo, under canonical (particle-conserving) conditions, a
preroughening-driven two-dimensional phase separation into two disordered flat
(DOF) regions, of opposite order parameter. We have carried out extensive
classical molecular dynamics (MD) simulations of the Lennard-Jones fcc(111)
surface, to check whether these predictions are relevant or not for a realistic
continuous system. Very long simulation times, a grid of temperatures from
(2/3)Tm to Tm, and unusually large system sizes are employed to ensure full
equilibrium and good statistics. By examining layer-by-layer occupancies,
height fluctuations, sublattice order parameter and X-ray structure factors, we
find a clear anomaly at ~0.83Tm. The anomaly is distinct from roughening (whose
incipiency is also detected at ~0.94Tm), and is seen to be consistent with the
preroughening plus phase separation scenario.Comment: REVTeX, 8 pages, 4 figures; new figure showing simulation snapshots
added; reference updated and other minor change
Assessing Faculty Shortages in Comprehensive Colleges and Universities
In the last two years, the national media and higher education publications have begun warning of faculty shortages. In the fall of 1989 Edward Fiske and Elizabeth Fowler wrote in the New York Times that colleges and universities would be facing major faculty shortages in the humanities and social sciences (Fiske 1989; Fowler 1989). A few months earlier, Joseph Berger (1989) warned in the New York Times that the Slowing Pace to Doctorates Spurs Worry on Filling Jobs. The Chronicle of Higher Education has been running a series of articles on various aspects of the faculty labor market --concerning the extent of anticipated shortages and how colleges and universities are coping with them (Mooney 1989a; Mooney 1989b; Blum 1989), the pros and cons of academic careers ( The Pros and Cons... 1989), and the lost generation of scholars (Heller 1990).
These articles present the overall picture, with some attention to differences among the disciplines. None identifies how different types of institutions will experience changes in the supply and demand for faculty. This paper focuses especially on the implications of changes in the faculty labor market for comprehensive universities, four-year primarily undergraduate universities that are neither research universities nor liberal arts colleges (Harcleroad and Ostar 1987; Youn, Finnegan, and Gamson forthcoming). It draws on several national studies to present statistics on anticipated faculty supply and demand for higher education as a whole and then disaggregates these statistics for comprehensive institutions. Next, the paper presents preliminary results from a field study of how several comprehensive universities in New England have been handling faculty recruitment and retention. It concludes with a number of implications of these findings for future institutional responses to changes in the faculty labor market
Spatial and temporal characterization of a Bessel beam produced using a conical mirror
We experimentally analyze a Bessel beam produced with a conical mirror,
paying particular attention to its superluminal and diffraction-free
properties. We spatially characterized the beam in the radial and on-axis
dimensions, and verified that the central peak does not spread over a
propagation distance of 73 cm. In addition, we measured the superluminal phase
and group velocities of the beam in free space. Both spatial and temporal
measurements show good agreement with the theoretical predictions.Comment: 5 pages, 6 figure
Symmetry-Breaking Motility
Locomotion of bacteria by actin polymerization, and in vitro motion of
spherical beads coated with a protein catalyzing polymerization, are examples
of active motility. Starting from a simple model of forces locally normal to
the surface of a bead, we construct a phenomenological equation for its motion.
The singularities at a continuous transition between moving and stationary
beads are shown to be related to the symmetries of its shape. Universal
features of the phase behavior are calculated analytically and confirmed by
simulations. Fluctuations in velocity are shown to be generically
non-Maxwellian and correlated to the shape of the bead.Comment: 4 pages, 2 figures, REVTeX; formatting of references correcte
Noise temperature measurements for axion haloscope experiments at IBS/CAPP
The axion was first introduced as a consequence of the Peccei-Quinn mechanism
to solve the CP problem in strong interactions of particle physics and is a
well motivated cold dark matter candidate. This particle is expected to
interact extremely weakly with matter and its mass is expected to lie in
eV range with the corresponding frequency roughly in GHz range. In 1983 P.
Sikivie proposed a detection scheme, so called axion haloscope, where axions
resonantly convert to photons in a tunable microwave cavity permeated by a
strong magnetic field. A major source of the experimental noise is attributed
to added noise by RF amplifiers, and thus precise understandings of amplifiers'
noise is of importance. We present the measurements of noise temperatures of
various low noise amplifiers broadly used for axion dark matter searches.Comment: 7 pages, 3 figure
Modelling stochastic bivariate mortality
Stochastic mortality, i.e. modelling death arrival via a jump process with stochastic intensity, is gaining increasing reputation as a way to represent mortality risk. This paper represents a first attempt to model the mortality risk of couples of individuals, according to the stochastic intensity approach.
On the theoretical side, we extend to couples the Cox processes set up, i.e. the idea that mortality is driven by a jump process whose intensity is itself a stochastic process, proper of a particular generation within each gender. Dependence between the survival times of the members of a couple is captured by an Archimedean copula.
On the calibration side, we fit the joint survival function by calibrating separately the (analytical) copula and the (analytical) margins. First, we select the best fit copula according to the methodology of Wang and Wells (2000) for censored data. Then, we provide a sample-based calibration for the intensity, using a time-homogeneous, non mean-reverting, affine process: this gives the analytical marginal survival functions. Coupling the best fit copula with the calibrated margins we obtain, on a sample generation, a joint survival function which incorporates the stochastic nature of mortality improvements and is far from representing independency.On the contrary, since the best fit copula turns out to be a Nelsen one, dependency is increasing with age and long-term dependence exists
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