2,425 research outputs found
Empirical distributions of galactic spin parameters from the SDSS
Using simple dimensional arguments for both spiral and elliptical galaxies,
we present formulas to derive an estimate of the halo spin parameter
for any real galaxy, in terms of common observational parameters. This allows a
rough estimate of , which we apply to a large volume limited sample of
galaxies taken from the SDSS data base. The large numbers involved (11,597)
allow the derivation of reliable distributions, as signal adds up
significantly in spite of the errors in the inferences for particular galaxies.
We find that if the observed distribution of is modeled with a
log-normal function, as often done for this distribution in dark matter halos
that appear in cosmological simulations, we obtain parameters and , interestingly consistent with
values derived from simulations. For spirals, we find a good correlation
between empirical values of and visually assigned Hubble types,
highlighting the potential of this physical parameter as an objective
classification tool.Comment: 8 pages, 6 figures, expanded final version, MNRAS (in press
Simple Pendulum Revisited
We describe a 8085 microprocessor interface developed to make reliable time
period measurements. The time period of each oscillation of a simple pendulum
was measured using this interface. The variation of the time period with
increasing oscillation was studied for the simple harmonic motion (SHM) and for
large angle initial displacements (non-SHM). The results underlines the
importance of the precautions which the students are asked to take while
performing the pendulum experiment.Comment: 17 pages with 10 figure
Bundle Theory of Improper Spin Transformations
{\it We first give a geometrical description of the action of the parity
operator () on non relativistic spin Pauli spinors in
terms of bundle theory. The relevant bundle, , is a
non trivial extension of the universal covering group .
is the non relativistic limit of the corresponding Dirac matrix
operator and obeys . Then, from the direct
product of O(3) by , naturally induced by the structure of the galilean
group, we identify, in its double cover, the time reversal operator ()
acting on spinors, and its product with . Both, and
, generate the group . As in the case of parity,
is the non relativistic limit of the corresponding Dirac matrix
operator , and obeys .}Comment: 8 pages, Plaintex; titled changed, minor text modifications, one
reference complete
Conformal Couplings in Induced Gravity
It is found that the induced gravity with conformal couplings requires the
conformal invariance in both classical and quantum levels for consistency. This
is also true for the induced gravity with an extended conformal coupling
interacting with torsion.Comment: 10 pages, Revtex3.0, to appear in General Relativity and Gravitatio
Non-L\'evy mobility patterns of Mexican Me'Phaa peasants searching for fuelwood
We measured mobility patterns that describe walking trajectories of
individual Me'Phaa peasants searching and collecting fuelwood in the forests of
"La Monta\~na de Guerrero" in Mexico. These one-day excursions typically follow
a mixed pattern of nearly-constant steps when individuals displace from their
homes towards potential collecting sites and a mixed pattern of steps of
different lengths when actually searching for fallen wood in the forest.
Displacements in the searching phase seem not to be compatible with L\'evy
flights described by power-laws with optimal scaling exponents. These findings
however can be interpreted in the light of deterministic searching on heavily
degraded landscapes where the interaction of the individuals with their scarce
environment produces alternative searching strategies than the expected L\'evy
flights. These results have important implications for future management and
restoration of degraded forests and the improvement of the ecological services
they may provide to their inhabitants.Comment: 15 pages, 4 figures. First version submitted to Human Ecology. The
final publication will be available at http://www.springerlink.co
Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB
We present results of a dark matter search performed with a 0.6 kg day
exposure of the DAMIC experiment at the SNOLAB underground laboratory. We
measure the energy spectrum of ionization events in the bulk silicon of
charge-coupled devices down to a signal of 60 eV electron equivalent. The data
are consistent with radiogenic backgrounds, and constraints on the
spin-independent WIMP-nucleon elastic-scattering cross section are accordingly
placed. A region of parameter space relevant to the potential signal from the
CDMS-II Si experiment is excluded using the same target for the first time.
This result obtained with a limited exposure demonstrates the potential to
explore the low-mass WIMP region (<10 GeV/) of the upcoming DAMIC100, a
100 g detector currently being installed in SNOLAB.Comment: 11 pages, 11 figure
Development of a Monitoring and Verification (M&V) Plan and Baseline for the Fort Hood ESPC Project
Fort Hood has selected an Energy Services
Performance Contract (ESPC) contractor to help
achieve its energy reduction goals as mandated by
Executive Order. This ESPC is expected to be a $3.8
million, 20 year contract, which includes five primary
types of Energy Conservation Measures (ECMs) in
56 buildings, and includes boiler insulation, control
system upgrades, vending machine controls, cooling
tower variable frequency drives (VFDs), and lighting
retrofits. The plan of action for the ESPC includes
cost effective M&V, using IPMVP Options B and C
for the first two years after the retrofits are installed,
and Option A combined with annual performance
verification for the remainder of the contract. This
paper discusses the development the Measurement
and Verification (M&V) Plan for the Fort Hood
Energy Services Performance Contract, and includes
results of the baseline calculations (Haberl et al.
2002, 2003b)
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