12,726 research outputs found
Reciprocal relativity of noninertial frames: quantum mechanics
Noninertial transformations on time-position-momentum-energy space {t,q,p,e}
with invariant Born-Green metric ds^2=-dt^2+dq^2/c^2+(1/b^2)(dp^2-de^2/c^2) and
the symplectic metric -de/\dt+dp/\dq are studied. This U(1,3) group of
transformations contains the Lorentz group as the inertial special case. In the
limit of small forces and velocities, it reduces to the expected Hamilton
transformations leaving invariant the symplectic metric and the nonrelativistic
line element ds^2=dt^2. The U(1,3) transformations bound relative velocities by
c and relative forces by b. Spacetime is no longer an invariant subspace but is
relative to noninertial observer frames. Born was lead to the metric by a
concept of reciprocity between position and momentum degrees of freedom and for
this reason we call this reciprocal relativity.
For large b, such effects will almost certainly only manifest in a quantum
regime. Wigner showed that special relativistic quantum mechanics follows from
the projective representations of the inhomogeneous Lorentz group. Projective
representations of a Lie group are equivalent to the unitary reprentations of
its central extension. The same method of projective representations of the
inhomogeneous U(1,3) group is used to define the quantum theory in the
noninertial case. The central extension of the inhomogeneous U(1,3) group is
the cover of the quaplectic group Q(1,3)=U(1,3)*s H(4). H(4) is the
Weyl-Heisenberg group. A set of second order wave equations results from the
representations of the Casimir operators
Temperature Fluctuations driven by Magnetorotational Instability in Protoplanetary Disks
The magnetorotational instability (MRI) drives magnetized turbulence in
sufficiently ionized regions of protoplanetary disks, leading to mass
accretion. The dissipation of the potential energy associated with this
accretion determines the thermal structure of accreting regions. Until
recently, the heating from the turbulence has only been treated in an
azimuthally averaged sense, neglecting local fluctuations. However, magnetized
turbulence dissipates its energy intermittently in current sheet structures. We
study this intermittent energy dissipation using high resolution numerical
models including a treatment of radiative thermal diffusion in an optically
thick regime. Our models predict that these turbulent current sheets drive
order unity temperature variations even where the MRI is damped strongly by
Ohmic resistivity. This implies that the current sheet structures where energy
dissipation occurs must be well resolved to correctly capture the flow
structure in numerical models. Higher resolutions are required to resolve
energy dissipation than to resolve the magnetic field strength or accretion
stresses. The temperature variations are large enough to have major
consequences for mineral formation in disks, including melting chondrules,
remelting calcium-aluminum rich inclusions, and annealing silicates; and may
drive hysteresis: current sheets in MRI active regions could be significantly
more conductive than the remainder of the disk.Comment: 16 pages, 13 figures, ApJ In Press, updated to match proof
The Influence of Metallicity on Star Formation in Protogalaxies
In cold dark matter cosmological models, the first stars to form are believed
to do so within small protogalaxies. We wish to understand how the evolution of
these early protogalaxies changes once the gas forming them has been enriched
with small quantities of heavy elements, which are produced and dispersed into
the intergalactic medium by the first supernovae. Our initial conditions
represent protogalaxies forming within a fossil H II region, a previously
ionized region that has not yet had time to cool and recombine. We study the
influence of low levels of metal enrichment on the cooling and collapse of
ionized gas in small protogalactic halos using three-dimensional, smoothed
particle hydrodynamics (SPH) simulations that incorporate the effects of the
appropriate chemical and thermal processes. Our previous simulations
demonstrated that for metallicities Z < 0.001 Z_sun, metal line cooling alters
the density and temperature evolution of the gas by less than 1% compared to
the metal-free case at densities below 1 cm-3) and temperatures above 2000 K.
Here, we present the results of high-resolution simulations using particle
splitting to improve resolution in regions of interest. These simulations allow
us to address the question of whether there is a critical metallicity above
which fine structure cooling from metals allows efficient fragmentation to
occur, producing an initial mass function (IMF) resembling the local Salpeter
IMF, rather than only high-mass stars.Comment: 3 pages, 2 figures, First Stars III conference proceeding
Validity and reliability of the rear foot elevated split squat 5 repetition maximum to determine unilateral leg strength symmetry
The purpose of this study was to examine the validity and reliability of the Rear Foot Elevated Split Squat (RFESS) five repetition maximum (5RM) test as a field method for measuring unilateral leg strength symmetry. As a validated method of testing symmetry, the RFESS 5RM may be used by Strength and Conditioning coaches and sports medicine staff to measure the presence of imbalances with minimal equipment and time. 26 subjects (age = 23.8 ±4.6 years, mass = 88.1 ± 10.7 kg, height = 1.79 ± 0.1 m) with a minimum two years strength and conditioning experience were recruited. Following a familiarization session, subjects performed an incremental five repetition maximum (5RM) protocol on both legs, on two occasions where 3D motion and force data were collected. Moderate reliability of bar load symmetry was found between test and re-test conditions correlation (ICC = 0.73, 0.33-0.91) with no proportional bias between sessions. Validation of the exercise was analyzed using a correlation between asymmetries in mean set vertical ground reaction forces (vGRF) of the lead foot during the concentric phase, with bar load. When all maximal trials, from both test conditions, were analyzed, a most likely large positive correlation (0.57, 0.30 to 0.76) were found for mean set concentric lead foot vGRF. When a threshold level of load symmetry (96.54% - 103.46%) was applied, a most likely large positive correlation (r = 0.59, 0.14-0.84) between symmetry in lead foot vGRF was found in subjects who exceeded this limit. Conversely, analysis of subjects within the threshold produced unclear correlations. Findings of this study suggest the RFESS is a valid and reliable measure of unilateral leg strength symmetry. Practitioners are recommended to use this exercise to investigate the strength symmetry of athletes, but are guided to note that a threshold level of symmetry (96.54% - 103.46%) may be required to have been exceeded to indicate a true difference in vGRF production
The Autistic Experience of Exercising within Nature-Based Environments: An Interpretive Phenomenological Analysis
Background: The psychological impact of exercising in nature has gained considerable research attention in recent years under the heading green exercise (GE). Literature has examined specific benefits of GE, comparison between indoor and outdoor environments and has utilised different theories to understand these benefits and differences. To date no academic literature has examined the impact of GE on autistic people with a diagnoses of Aspergers Syndrome (AS) (a former term to refer to autism without an accompanying intellectual disability), and a condition characterised by hypersensitive and hyposensitive senses, intuitively it has been suggested that the natural environment might not be a compatible setting for autistic people due to its unpredictable and sensory provoking conditions.
Method: A group of four autistic males were interviewed using a semi structured interview schedule. Interviews were transcribed and then analysed using interpretive phenomenological analysis (IPA).
Results/Discussion: Three superordinate themes were identified, positive introductions to nature (this group discussed how important having a good start in this environment was to engaging in this activity), positive association with nature (the participants viewed natural environments where they exercised in a positive way), and purpose and practicalities (participants spoke of viewing GE favourably when there was a purpose to it above and beyond doing it for its own sake) with 5 associated subordinate themes. Results suggest that autistic people appear to get considerable positive psychological outcomes from engaging within GE which relate directly to some of the features of AS e.g. disruptive concerns and that a functional purpose to the GE would be helpful in terms of encouraging uptake of and adherence to GE within an autistic group
NICMOS Observations of the Pre-Main-Sequence Planetary Debris System HD 98800
Spectral energy distributions (SEDs) from 0.4 to 4.7 microns are presented
for the two principal stellar components of HD~98800, A and B. The third major
component, an extensive planetary debris system (PDS), emits > 20% of the
luminosity of star B in a blackbody SED at 164 +/- 5K extending from mid-IR to
millimeter-wavelengths. At 0.95 microns a preliminary upper limit of < 0.06 is
obtained for the ratio of reflected light to the total from star B. This result
limits the albedo of the PDS to < 0.3. Values are presented for the
temperature, luminosity, and radius of each major systemic component.
Remarkable similarities are found between the PDS and the interplanetary debris
system around the Sun as it could have appeared a few million years after its
formation.Comment: LaTeX, 9 pages with 1 encapsulated postscript figure and one
specially formatted Table which is rendered as a postscript file and included
as a figure. Accepted for publication in Astrophysical Journal Letter
Effect of car exhausts on lead contamination in vegetables grown adjacent to Kuala Lumpur - Ceras Highway
It has already been established from studies over a wide area of Kuala Lumpur that lead contamination
in grass adjacent to heavy-traffic roads is hazardous to grazing cattle if local forage grass is the only source
of food (Low, Lee and Arshad, 1979). In Kuala Lumpur, a number of vegetable farms are located near
heavy-traffic roads and contamination of lead caused by car exhausts on these vegetables has not been reported.
This paper reports the levels of lead in leafy vegetables and their supporting soils in two locations. The first was a commercial vegetable farm some 50 m from the Kuala Lumpur - Ceras Highway with heavy tra/fic density. The second was a domestic garden located on the Universiti Pertanian Malaysia campus where the flow of vehicles is generally low. In these areas deposition oflead, if any, on vegetables comes almost exclusively from automobile exhausts. There is no other known source of lead contamination in these areas
Presymmetry beyond the Standard Model
We go beyond the Standard Model guided by presymmetry, the discrete
electroweak quark-lepton symmetry hidden by topological effects which explain
quark fractional charges as in condense matter physics. Partners of the
particles of the Standard Model and the discrete symmetry associated with this
partnership appear as manifestations of a residual presymmetry and its
extension from matter to forces. This duplication of the spectrum of the
Standard Model keeps spin and comes nondegenerated about the TeV scale.Comment: 6 pages, 11 figures. To be published in the proceedings of DPF-2009,
Detroit, MI, July 2009, eConf C09072
A study of wastewater discharge from electroplating factories
There are some fifteen electroplating factories
lIT Kuala Lumpur and Klang area, specializing
in various forms of plating, namely chromium,
zinc, silver and occasionally, cadmium, Almost
all of these electroplating factories do not have
any facilities for wastewater treatment. Wastewater
containing cyanide and metallic ions like
copper, nickel, chromium, lead, zinc, silver and
others is discharged directly into drains. The
presence of these pollutants can pose a health
hazard to the environment if their levels exceed
certain allowable limits. The present study is
an attempt to determine the extent of cyanide
and metal pollution in the wastewater of a typical
electroplating factory without wastewater treatment
and to compare the quality of its wastewater
with another with treatment facilitie
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