173,314 research outputs found
Discrete Logarithms in Generalized Jacobians
D\'ech\`ene has proposed generalized Jacobians as a source of groups for
public-key cryptosystems based on the hardness of the Discrete Logarithm
Problem (DLP). Her specific proposal gives rise to a group isomorphic to the
semidirect product of an elliptic curve and a multiplicative group of a finite
field. We explain why her proposal has no advantages over simply taking the
direct product of groups. We then argue that generalized Jacobians offer poorer
security and efficiency than standard Jacobians
Analytical study of catalytic reactors for hydrazine decomposition. One and two dimensional steady-state programs, computer programs manual
Programs manual for one-dimensional and two- dimensional steady state models of catalyzed hydrazine decomposition reaction chamber
Properties of perturbative multi-particle amplitudes in and theories
Threshold amplitudes are considered for multi-particle production in
and theories. It is found that the disappearance of tree-level
threshold amplitudes of on-shell particles producing a large number of
particles occurs in theory only for and . The one-loop
correction to the threshold amplitude for a highly virtual scalar particle
decaying into particles in an model is derived.Comment: 7 pages, LaTex, TPI-MINN-92/60-
Simultaneous rocket and MST radar observation of an internal gravity wave breaking in the mesosphere
In June, 1983, the Structure and Atmospheric Turbulence Environment (STATE) rocket and Poker Flat Mesophere-Stratosphere-Troposphere radar campaign was conducted to measure the interaction between turbulence, electron density and electron density gradient that has produced unusually strong MST radar echoes from the summer mesosphere over Poker Flat, Alaska. Analysis or radar wind measurements and a concurrent wind and temperature profile obtained from a rocket probe carrying a three-axis accelerometer are given. The two data sets provide a fairly complete (and in some cases, redundant) picture of the breaking (or more correctly, the saturation) of a large-amplitude, low-frequency, long-wavelength internal gravity wave. The data show that small-scale turbulence and small-scale wave intensity is greatest at those altitudes where the large-scale wave-induced temperature lapse rate is most negative or most nearly unstable, but the wind shear due to the large-scale wave is a minimum. A brief review of linear gravity-wave theory is presented as an aid to the identification of the gravity-wave signature in the radar and rocket data. Analysis of the time and height cross sections of wind speed and turbulence intensity observed by the Poker Flat MST radar follows. Then, the vertical profile of temperature and winds measured by a rocket probe examined. Finally, the use of the independent data sets provided by the rocket and the radar are discussed and implications for theories of wave saturation are presented
Failure of non-vacuum steam sterilization processes for dental handpieces
Background:
Dental handpieces are used in critical and semi-critical operative interventions. Although a number of dental professional bodies recommend that dental handpieces are sterilized between patient use there is a lack of clarity and understanding of the effectiveness of different steam sterilization processes. The internal mechanisms of dental handpieces contain narrow lumens (0·8-2·3mm) which can impede the removal of air and ingress of saturated steam required to achieve sterilization conditions.
Aim:
To identify the extent of sterilization failure in dental handpieces using a non-vacuum process.
Methods:
In-vitro and in-vivo investigations were conducted on commonly used UK benchtop steam sterilizers and three different types of dental handpieces. The sterilization process was monitored inside the lumens of dental handpieces using thermometric (TM) methods (dataloggers), chemical indicators (CI) and biological indicators (BI).
Findings:
All three methods of assessing achievement of sterility within dental handpieces that had been exposed to non-vacuum sterilization conditions demonstrated a significant number of failures (CI=8/3,024(fails/n tests); BI=15/3,024; TM=56/56) compared to vacuum sterilization conditions (CI=2/1,944; BI=0/1,944; TM=0/36). The dental handpiece most likely to fail sterilization in the non-vacuum process was the surgical handpiece. Non-vacuum sterilizers located in general dental practice had a higher rate of sterilization failure (CI=25/1,620; BI=32/1,620; TM=56/56) with no failures in vacuum process.
Conclusion:
Non-vacuum downward/gravity displacement, type-N steam sterilizers are an unreliable method for sterilization of dental handpieces in general dental practice. The handpiece most likely to fail sterilization is the type most frequently used for surgical interventions
Macromolecular separation through a porous surface
A new technique for the separation of macromolecules is proposed and
investigated. A thin mesh with pores comparable to the radius of gyration of a
free chain is used to filter chains according to their length. Without a field
it has previously been shown that the permeability decays as a power law with
chain length. However by applying particular configurations of pulsed fields,
it is possible to have a permeability that decays as an exponential. This
faster decay gives much higher resolution of separation. We also propose a
modified screen containing an array of holes with barb-like protrusions running
parallel to the surface. When static friction is present between the
macromolecule and the protrusion, some of the chains get trapped for long
durations of time. By using this and a periodic modulation of an applied
electric field, high resolution can be attained.Comment: 18 pages latex, 6 postscript figures, using psfi
Constraints on Stirring and Dissipation of MHD Turbulence in Molecular Clouds
We discuss constraints on the rates of stirring and dissipation of MHD
turbulence in molecular clouds. Recent MHD simulations suggest that turbulence
in clouds decays rapidly, thus providing a significant source of energy input,
particularly if driven at small scales by, for example, bipolar outflows. We
quantify the heating rates by combining the linewidth-size relations, which
describe global cloud properties, with numerically determined dissipation
rates. We argue that, if cloud turbulence is driven on small internal scales,
the CO flux (enhanced by emission from weakly supersonic shocks) will be
much larger than observed; this, in turn, would imply excitation temperatures
significantly above observed values. We reach two conclusions: (1) small-scale
driving by bipolar outflows cannot possibly account for cloud support and yield
long-lived clouds, unless the published MHD dissipation rates are seriously
overestimated; (2) driving on large scales (comparable to the cloud size) is
much more viable from an energetic standpoint, and if the actual net
dissipation rate is only slightly lower than what current MHD simulations
estimate, then the observationally inferred lifetimes and apparent virial
equilibrium of molecular clouds can be explained.Comment: 5 pages, 1 figure. To appear in ApJ (2001 April 10
Investigating steam penetration using thermometric methods in dental handpieces with narrow internal lumens during sterilizing processes with non-vacuum or vacuum processes
Background:
Dental handpieces are required to be sterilized between patient use. Vacuum steam sterilization processes with fractionated pre/post-vacuum phases or unique cycles for specified medical devices, are required for hollow instruments with internal lumens to assure successful air removal. Entrapped air will compromise achievement of required sterilization conditions. Many countries and professional organisations still advocate non-vacuum sterilization processes for these devices.
Aim:
To investigate non-vacuum downward/gravity displacement, type-N steam sterilization of dental handpieces, using thermometric methods to measure time to achieve sterilization temperature at different handpiece locations.
Methods:
Measurements at different positions within air turbines were undertaken with thermocouples and dataloggers. Two examples of commonly used UK benchtop steam sterilizers were tested; a non-vacuum benchtop sterilizer (Little Sister 3, Eschmann, UK) and a vacuum benchtop sterilizer (Lisa, W&H, Austria). Each sterilizer cycle was completed with three handpieces and each cycle in triplicate.
Findings:
A total of 140 measurements inside dental handpiece lumens were recorded. We demonstrate that the non-vacuum process fails (time range 0-150 seconds) to reliably achieve sterilization temperatures within the time limit specified by the International standard (15 seconds equilibration time). The measurement point at the base of the handpiece failed in all test runs (n=9) to meet the standard. No failures were detected with the vacuum steam sterilization type B process with fractionated pre-vacuum and post-vacuum phases.
Conclusion:
Non-vacuum downward/gravity displacement, type-N steam sterilization processes are unreliable in achieving sterilization conditions inside dental handpieces and the base of the handpiece is the site most likely to fail
Summary of solid rocket motor plume flow field and radiation analyses
The inclusion of solid propellant plume flow field effects in analyses and design of the space vehicle was investigated. Results of these analyses are summarized
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