4,735 research outputs found
Evaluation of the CNS and cardiovascular effects of prolonged exposure to bromotrifluromethane (CBrF3)
The proposed use of bromotrifluoromethane (CBrF3) as a fire extinguishant in aircraft, spacecraft and submarines has stimulated increasing interest and research in the toxicological properties of this compound. In a spacecraft, because of its unique recirculating life support system, the introduction of CBrF3 by leakage or intentional discharge, will result in continuous exposure of crewman to low concentrations of this compound for periods of up to 7 days, or possibly even longer. The effects of low concentrations of CBrF3, under continuous exposure conditions, on the CNS and cardiovascular systems of animals to enable an assessment of these risks were investigated
Gravitational intraction on quantum level and consequences thereof
The notion of gravitational emission as an emission of the same level with
electromagnetic emission is based on the proven fact of existence of electrons
stationary states in its own gravitational field, characterized by
gravitational constantComment: 22 pages, 9 figure
Auto-calibration of ultrasonic lubricant-film thickness measurements
The measurement of oil film thickness in a lubricated component is essential information for performance monitoring and design. It is well established that such measurements can be made ultrasonically if the lubricant film is modelled as a collection of small springs. The ultrasonic method requires that component faces are separated and a reference reflection recorded in order to obtain a reflection coefficient value from which film thickness is calculated. The novel and practically useful approach put forward in this paper and validated experimentally allows reflection coefficient measurement without the requirement for a reference. This involves simultaneously measuring the amplitude and phase of an ultrasonic pulse reflected from a layer. Provided that the acoustic properties of the substrate are known, the theoretical relationship between the two can be fitted to the data in order to yield reflection coefficient amplitude and phase for an infinitely thick layer. This is equivalent to measuring a reference signal directly, but importantly does not require the materials to be separated. The further valuable aspect of this approach, which is demonstrated experimentally, is its ability to be used as a self-calibrating routine, inherently compensating for temperature effects. This is due to the relationship between the amplitude and phase being unaffected by changes in temperature which cause unwanted changes to the incident pulse. Finally, error analysis is performed showing how the accuracy of the results can be optimized. A finding of particular significance is the strong dependence of the accuracy of the technique on the amplitude of reflection coefficient input data used. This places some limitations on the applicability of the technique. © 2008 IOP Publishing Ltd
Effective Viscosity of Dilute Bacterial Suspensions: A Two-Dimensional Model
Suspensions of self-propelled particles are studied in the framework of
two-dimensional (2D) Stokesean hydrodynamics. A formula is obtained for the
effective viscosity of such suspensions in the limit of small concentrations.
This formula includes the two terms that are found in the 2D version of
Einstein's classical result for passive suspensions. To this, the main result
of the paper is added, an additional term due to self-propulsion which depends
on the physical and geometric properties of the active suspension. This term
explains the experimental observation of a decrease in effective viscosity in
active suspensions.Comment: 15 pages, 3 figures, submitted to Physical Biolog
Semiclassical energy formulas for power-law and log potentials in quantum mechanics
We study a single particle which obeys non-relativistic quantum mechanics in
R^N and has Hamiltonian H = -Delta + V(r), where V(r) = sgn(q)r^q. If N \geq 2,
then q > -2, and if N = 1, then q > -1. The discrete eigenvalues E_{n\ell} may
be represented exactly by the semiclassical expression E_{n\ell}(q) =
min_{r>0}\{P_{n\ell}(q)^2/r^2+ V(r)}. The case q = 0 corresponds to V(r) =
ln(r). By writing one power as a smooth transformation of another, and using
envelope theory, it has earlier been proved that the P_{n\ell}(q) functions are
monotone increasing. Recent refinements to the comparison theorem of QM in
which comparison potentials can cross over, allow us to prove for n = 1 that
Q(q)=Z(q)P(q) is monotone increasing, even though the factor Z(q)=(1+q/N)^{1/q}
is monotone decreasing. Thus P(q) cannot increase too slowly. This result
yields some sharper estimates for power-potential eigenvlaues at the bottom of
each angular-momentum subspace.Comment: 20 pages, 5 figure
Magnetoelastic coupling behavior at the ferromagnetic transition in the partially disordered double perovskite La2NiMnO6
The magnetocapacitance and magnetoresistance properties near room temperature of partially disordered double perovskite
L
a
2
NiMn
O
6
are related, at least in part, to coupled ferroelastic and magnetic instabilities that are responsible for a ferromagnetic phase transition near 280 K. A systematic analysis of this coupling from the perspectives of strain and elasticity has revealed a system with biquadratic coupling among three order parameters belonging to irreducible representations of
X
+
3
,
Γ
+
4
and
m
Γ
+
4
of the parent space group
F
m
¯
3
m
. Classical octahedral tilting drives the structural transitions at high temperatures and strong acoustic attenuation through the temperature interval ∼300–500 K, observed by resonant ultrasound spectroscopy from a polycrystalline sample, is consistent with pinning of ferroelastic twin walls by point defects. Below room temperature, stiffening of the shear modulus by up to ∼40% can be understood in terms of biquadratic coupling of the ferromagnetic order parameter with strain. Acoustic attenuation with Debye-like patterns of loss in the temperature interval ∼150–280 K yielded activation energies and relaxation times which match up with AC magnetic and dielectric spectroscopy data reported previously in the literature. The dynamic loss mechanism, perhaps related to hopping of electrons between
N
i
2
+
and
M
n
4
+
, is potentially multiferroic, therefore. In addition to the possibilities for tailoring the intrinsic properties of
L
a
2
NiMn
O
6
by controlling oxygen content,
B
-site order or by choice of substrate for imposing a strain on thin films, it should be possible also to engineer extrinsic properties which would respond to applied electric, magnetic, and stress fields
The Commensal Real-time ASKAP Fast Transients (CRAFT) survey
We are developing a purely commensal survey experiment for fast (<5s)
transient radio sources. Short-timescale transients are associated with the
most energetic and brightest single events in the Universe. Our objective is to
cover the enormous volume of transients parameter space made available by
ASKAP, with an unprecedented combination of sensitivity and field of view. Fast
timescale transients open new vistas on the physics of high brightness
temperature emission, extreme states of matter and the physics of strong
gravitational fields. In addition, the detection of extragalactic objects
affords us an entirely new and extremely sensitive probe on the huge reservoir
of baryons present in the IGM. We outline here our approach to the considerable
challenge involved in detecting fast transients, particularly the development
of hardware fast enough to dedisperse and search the ASKAP data stream at or
near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of
the key technologies and survey modes proposed for high time resolution science
with the SKA.Comment: accepted for publication in PAS
Homogeneous bubble nucleation limit of mercury under the normal working conditions of the planned European Spallation Source
In spallation neutron sources, liquid mercury is the subject of big thermal
and pressure shocks, upon adsorbing the proton beam. These changes can cause
unstable bubbles in the liquid, which can damage the structural material. While
there are methods to deal with the pressure shock, the local temperature shock
cannot be avoided. In our paper we calculated the work of the critical cluster
formation (i.e. for mercury micro-bubbles) together with the rate of their
formation (nucleation rate). It is shown that the homogeneous nucleation rates
are very low even after adsorbing several proton pulses, therefore the
probability of temperature induced homogeneous bubble nucleation is negligible.Comment: 22 Pages, 11 figures, one of them is colour, we plan to publish it in
Eur. Phys. J.
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