278 research outputs found
Measuring Space-Time Geometry over the Ages
Theorists are often told to express things in the "observational plane". One
can do this for space-time geometry, considering "visual" observations of
matter in our universe by a single observer over time, with no assumptions
about isometries, initial conditions, nor any particular relation between
matter and geometry, such as Einstein's equations. Using observables as
coordinates naturally leads to a parametrization of space-time geometry in
terms of other observables, which in turn prescribes an observational program
to measure the geometry. Under the assumption of vorticity-free matter flow we
describe this observational program, which includes measurements of
gravitational lensing, proper motion, and redshift drift. Only 15% of the
curvature information can be extracted without long time baseline observations,
and this increases to 35% with observations that will take decades. The rest
would likely require centuries of observations. The formalism developed is
exact, non-perturbative, and more general than the usual cosmological analysis.Comment: Originally written for the Gravity Research Foundation 2012 Awards
for Essays on Gravitation and received Honorable Mentio
Simplified Cost Models For Underground Mine Evaluation: A Handbook for Quick Prefeasibility Cost Estimates
This handbook provides simplified cost models for evaluating underground mines. Regression analysis is used to generate capital and operating cost equations for each model in the form Y = AXB, where Y is the cost estimated and X is the assumed production capacity in tonnes per day. A and B are constants determined by the regression analysis. Equations are developed for operating costs in five subcategories: equipment operation, supplies, hourly labor, administration, and sundries. Subcategories for capital costs are: equipment purchase, preproduction underground excavation, surface facilities, engineering & management, contingency, and working capital. Cost models are developed for eight underground mining methods
A Geometrical Test of the Cosmological Energy Contents Using the Lyman-alpha Forest
In this Letter we explore a version of the test of cosmological geometry
proposed by Alcock and Paczynski (1979), using observations of the Lyman-alpha
forest in the spectra of close quasar pairs. By comparing the correlations in
absorption in one quasar spectrum with correlations between the spectra of
neighboring quasars one can determine the relation of the redshift distance
scale to the angle distance scale at the redshift of the absorbers, . Since this relationship depends on the parameters of the cosmological
model, these parameters may be determined using the Lyman-alpha forest. While
this test is relatively insensitive to the density parameter in a
dust-dominated universe, it is more sensitive to the presence of a matter
component with large negative pressure (such as a cosmological constant
) and its equation of state. With only 25 pairs of quasar spectra at
angular separations , one can discriminate between an open universe () and an flat
(-dominated) universe at the level. The S/N can be enhanced
by considering quasar pairs at smaller angular separations, but requires proper
modeling of nonlinear redshift space distortions. Here the correlations and
redshift space distortions are modeled using linear theory.Comment: 13 pages, 2 ps figures, submitted to ApJ
Primordial Gravity Waves and Weak Lensing
Inflation produces a primordial spectrum of gravity waves in addition to the
density perturbations which seed structure formation. We compute the signature
of these gravity waves in the large scale shear field. In particular, the shear
can be divided into a gradient mode (G or E) and a curl mode (C or B). The
former is produced by both density perturbations and gravity waves, while the
latter is produced only by gravity waves, so the observations of a non-zero
curl mode could be seen as evidence for inflation. We find that the expected
signal from inflation is small, peaking on the largest scales at
at and falling rapidly there after. Even for
an all-sky deep survey, this signal would be below noise at all multipoles.
Part of the reason for the smallness of the signal is a cancellation on large
scales of the standard line-of-sight effect and the effect of ``metric shear.''Comment: 4 pages, 1 figur
CARMA CO(J = 2 - 1) Observations of the Circumstellar Envelope of Betelgeuse
We report radio interferometric observations of the 12C16O 1.3 mm J = 2-1
emission line in the circumstellar envelope of the M supergiant Alpha Ori and
have detected and separated both the S1 and S2 flow components for the first
time. Observations were made with the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) interferometer in the C, D, and E antenna
configurations. We obtain good u-v coverage (5-280 klambda) by combining data
from all three configurations allowing us to trace spatial scales as small as
0.9\arcsec over a 32\arcsec field of view. The high spectral and spatial
resolution C configuration line profile shows that the inner S1 flow has
slightly asymmetric outflow velocities ranging from -9.0 km s-1 to +10.6 km s-1
with respect to the stellar rest frame. We find little evidence for the outer
S2 flow in this configuration because the majority of this emission has been
spatially-filtered (resolved out) by the array. We also report a SOFIA-GREAT
CO(J= 12-11) emission line profile which we associate with this inner higher
excitation S1 flow. The outer S2 flow appears in the D and E configuration maps
and its outflow velocity is found to be in good agreement with high resolution
optical spectroscopy of K I obtained at the McDonald Observatory. We image both
S1 and S2 in the multi-configuration maps and see a gradual change in the
angular size of the emission in the high absolute velocity maps. We assign an
outer radius of 4\arcsec to S1 and propose that S2 extends beyond CARMA's field
of view (32\arcsec at 1.3 mm) out to a radius of 17\arcsec which is larger than
recent single-dish observations have indicated. When azimuthally averaged, the
intensity fall-off for both flows is found to be proportional to R^{-1}, where
R is the projected radius, indicating optically thin winds with \rho \propto
R^{-2}.Comment: 11 pages, 8 figures To be published in the Astronomical Journal
(Received 2012 February 10; accepted 2012 May 25
Introduction: looking beyond the walls
In its consideration of the remarkable extent and variety of non-university researchers, this book takes a broader view of ‘knowledge’ and ‘research’ than in the many hot debates about today’s knowledge society, ‘learning age’, or organisation of research. It goes beyond the commonly held image of ‘knowledge’ as something produced and owned by the full-time experts to take a look at those engaged in active knowledge building outside the university walls
Searching for Long Strings in CMB Maps
Using analytical methods and Monte Carlo simulations, we analyze new
statistics designed to detect isolated step-like discontinuities which are
coherent over large areas of Cosmic Microwave Background (CMB) pixel maps. Such
coherent temperature discontinuities are predicted by the Kaiser-Stebbins
effect to form due to long cosmic strings present in our present horizon. The
background of the coherent step-like seed is assumed to be a scale invariant
Gaussian random field which could have been produced by a superposition of
seeds on smaller scales and/or by inflationary quantum fluctuations. We find
that the proposed statistics can detect the presense of a coherent
discontinuity at a sensitivity level almost an order of magnitude better
compared to more conventional statistics like the skewness or the kurtosis.Comment: 10 pages, 3 Figures, Use RevTe
Galaxy Clustering in Early SDSS Redshift Data
We present the first measurements of clustering in the Sloan Digital Sky
Survey (SDSS) galaxy redshift survey. Our sample consists of 29,300 galaxies
with redshifts 5,700 km/s < cz < 39,000 km/s, distributed in several long but
narrow (2.5-5 degree) segments, covering 690 square degrees. For the full,
flux-limited sample, the redshift-space correlation length is approximately 8
Mpc/h. The two-dimensional correlation function \xi(r_p,\pi) shows clear
signatures of both the small-scale, ``fingers-of-God'' distortion caused by
velocity dispersions in collapsed objects and the large-scale compression
caused by coherent flows, though the latter cannot be measured with high
precision in the present sample. The inferred real-space correlation function
is well described by a power law, \xi(r)=(r/6.1+/-0.2 Mpc/h)^{-1.75+/-0.03},
for 0.1 Mpc/h < r < 16 Mpc/h. The galaxy pairwise velocity dispersion is
\sigma_{12} ~ 600+/-100 km/s for projected separations 0.15 Mpc/h < r_p < 5
Mpc/h. When we divide the sample by color, the red galaxies exhibit a stronger
and steeper real-space correlation function and a higher pairwise velocity
dispersion than do the blue galaxies. The relative behavior of subsamples
defined by high/low profile concentration or high/low surface brightness is
qualitatively similar to that of the red/blue subsamples. Our most striking
result is a clear measurement of scale-independent luminosity bias at r < 10
Mpc/h: subsamples with absolute magnitude ranges centered on M_*-1.5, M_*, and
M_*+1.5 have real-space correlation functions that are parallel power laws of
slope ~ -1.8 with correlation lengths of approximately 7.4 Mpc/h, 6.3 Mpc/h,
and 4.7 Mpc/h, respectively.Comment: 51 pages, 18 figures. Replaced to match accepted ApJ versio
Lifestyle travellers: Backpacking as a way of life
Scholarship on backpackers speculates some individuals may extend backpacking to a way of life. This article empirically explores this proposition using lifestyle consumption as its framing concept and conceptualises individuals who style their lives around the enduring
practice of backpacking as ‘lifestyle travellers’. Ethnographic interviews with lifestyle travellers in India and Thailand offer an emic account of the practices, ideologies and social identity that characterise lifestyle travel as a distinctive subtype within backpacking.
Departing from the drifter construct, which (re)constitutes this identity as socially deviant, the concept of lifestyle allows for a contemporary appraisal of these individuals’ patterns of meaningful consumption and wider insights into how ongoing mobility can lead to different ways of understanding identities and relating to place.
Keywords: lifestyle consumption; backpacker; mobility; drifter; identit
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