553 research outputs found
Strict extensions in pointfree topology
Extensions of spaces have been constructed and used since the 19th century, for example, to form the complex sphere from the complex plane by adding a point at in nity. Once topological spaces were invented in the 20th century, completions and compactications became important examples of extensions. Banaschewski wrote that extension problems have a """"philosophical charm"""" in that they seem to ask the question: """"What possibilities in the unknown are determined by the known?"""" Strict extensions were first defined for topological spaces by Stone. The idea was initially translated into the pointfree setting by Hong, and has since been extensively studied. Just recently, interest has been shown in studying strict extensions in the asymmetric setting of biframes, for example, by Frith and Schauerte. The intention of this dissertation is to provide a systematic and detailed exposition of strict extensions of frames and nearness frames, which can be used as a reference on this topic. For instance, someone interested in pursuing strict extensions of biframes might obtain the relevant background from reading this text, although the topic of strict extensions of biframes itself will not be discussed here
How high the temperature of a liquid be raised without boiling?
How high the temperature of a liquid be raised beyond its boiling point
without vaporizing (known as the limit of superheat) is an interesting subject
of investigation. A new method of finding the limit of superheat of liquids is
presented here. The superheated liquids are taken in the form of drops
suspended in visco elastic gel. The nucleation is detected acoustically by a
sensitive piezo-electric transducer, coupled to a multi channel scaler and the
nucleation is observed as a funtion of time and with increase of temperature.
The limit of superheat measured by the present method supersedes all other
measurements and theoretical predictions in reaching closest to the critical
temperature and warrants improved theoretical predictions.Comment: 10 pages, 1 fig. Phys, Rev. E. (2000) in pres
Low-frequency noise reduction of spacecraft structures
Low frequency noise reduction of spacecraft structure
Electrophysiological effects of progesterone on hepatocytes
AbstractThe addition of progesterone (1â100 ÎŒmol/l) to the extracellular fluid bathing rat hepatocytes led to a rapid and fully reversible depolarization of the cell membrane. The progesterone-induced depolarization was paralleled by a decrease of potassium selectivity and an increase of cell membrane resistance and was abolished in the presence of the potassium channel blocker barium. Accordingly, in whole cell recordings, progesterone led to a decrease of the cell membrane conductance. 17 α-Hydroxyprogesterone and ÎČ-estradiol were less effective by a factor of 10, whereas cholesterol, corticosterone and hydrocortisone did not significantly alter the potential difference across the cell membrane. In conclusion, acute administration of progesterone depolarized rat hepatocytes by decreasing the potassium conductance of the cell membrane
Superheated Microdrops as Cold Dark Matter Detectors
It is shown that under realistic background considerations, an improvement in
Cold Dark Matter sensitivity of several orders of magnitude is expected from a
detector based on superheated liquid droplets. Such devices are totally
insensitive to minimum ionizing radiation while responsive to nuclear recoils
of energies ~ few keV. They operate on the same principle as the bubble
chamber, but offer unattended, continuous, and safe operation at room
temperature and atmospheric pressure.Comment: 15 pgs, 4 figures include
First Dark Matter Limits from a Large-Mass, Low-Background Superheated Droplet Detector
We report on the fabrication aspects and calibration of the first large
active mass ( g) modules of SIMPLE, a search for particle dark matter
using Superheated Droplet Detectors (SDDs). While still limited by the
statistical uncertainty of the small data sample on hand, the first weeks of
operation in the new underground laboratory of Rustrel-Pays d'Apt already
provide a sensitivity to axially-coupled Weakly Interacting Massive Particles
(WIMPs) competitive with leading experiments, confirming SDDs as a convenient,
low-cost alternative for WIMP detection.Comment: Final version, Phys. Rev. Lett. (in press
Nonlinear Modes of Liquid Drops as Solitary Waves
The nolinear hydrodynamic equations of the surface of a liquid drop are shown
to be directly connected to Korteweg de Vries (KdV, MKdV) systems, giving
traveling solutions that are cnoidal waves. They generate multiscale patterns
ranging from small harmonic oscillations (linearized model), to nonlinear
oscillations, up through solitary waves. These non-axis-symmetric localized
shapes are also described by a KdV Hamiltonian system. Recently such ``rotons''
were observed experimentally when the shape oscillations of a droplet became
nonlinear. The results apply to drop-like systems from cluster formation to
stellar models, including hyperdeformed nuclei and fission.Comment: 11 pages RevTex, 1 figure p
Evidence of Sulfur Non-Innocence in [CoII(dithiacyclam)]2+-Mediated Catalytic Oxygen Reduction Reactions
In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2N2-cyclam)]2+ (2; S2N2-cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2
Prospects for SIMPLE 2000: A large-mass, low-background Superheated Droplet Detector for WIMP searches
SIMPLE 2000 (Superheated Instrument for Massive ParticLE searches) will
consist of an array of eight to sixteen large active mass ( g)
Superheated Droplet Detectors(SDDs) to be installed in the new underground
laboratory of Rustrel-Pays d'Apt. Several factors make of SDDs an attractive
approach for the detection of Weakly Interacting Massive Particles (WIMPs),
namely their intrinsic insensitivity to minimum ionizing particles, high
fluorine content, low cost and operation near ambient pressure and temperature.
We comment here on the fabrication, calibration and already-competitive first
limits from SIMPLE prototype SDDs, as well as on the expected immediate
increase in sensitivity of the program, which aims at an exposure of 25
kg-day during the year 2000. The ability of modest-mass fluorine-rich detectors
to explore regions of neutralino parameter space beyond the reach of the most
ambitious cryogenic projects is pointed out.Comment: 19 pages, 10 figures included. New Journal of Physics, in pres
Independent Ion Migration in Suspensions of Strongly Interacting Charged Colloidal Spheres
We report on sytematic measurements of the low frequency conductivity in
aequous supensions of highly charged colloidal spheres. System preparation in a
closed tubing system results in precisely controlled number densities between
1E16/m3 and 1E19/m^3 (packing fractions between 1E-7 and 1E-2) and electrolyte
concentrations between 1E-7 and 1E-3 mol/l. Due to long ranged Coulomb
repulsion some of the systems show a pronounced fluid or crystalline order.
Under deionized conditions we find s to depend linearily on the packing
fraction with no detectable influence of the phase transitions. Further at
constant packing fraction s increases sublinearily with increasing number of
dissociable surface groups N. As a function of c the conductivity shows
pronounced differences depending on the kind of electrolyte used. We propose a
simple yet powerful model based on independent migration of all species present
and additivity of the respective conductivity contributions. It takes account
of small ion macro-ion interactions in terms of an effectivly transported
charge. The model successfully describes our qualitatively complex experimental
observations. It further facilitates quantitative estimates of conductivity
over a wide range of particle and experimental parameters.Comment: 32 pages, 17 figures, 2 tables, Accepted by Physical Review
- âŠ