1,481 research outputs found
CRUDE OIL FOULING IN A PILOT-SCALE PARALLEL TUBE APPARATUS
Maya crude oil fouling reveals a seemingly straightforward dependency of initial fouling rate on surface temperature but a maximum is found in the initial fouling rate – velocity relationship which mirrors that found in a model chemical system of styrene polymerization. The linear dependency of the logarithm of the pre-exponential factor on apparent activation energy for the crude oil is also found in the styrene system. The apparent activation energy for the crude oil ranged from 26.4 kJ/mol at 1.0 m/s to 245 kJ/mol at 4.0 m/s. Such strong dependencies of apparent activation energy on velocity, even at high velocity, are consistent with Epstein’s mass transfer-reaction-attachment model. Surface temperatures at which the fouling rate becomes velocity-independent are 274°C and 77°C for Maya crude oil and styrene, respectively. For surface temperatures in excess of this isokinetic temperature, an increase in velocity would lead to an increase in the rate of fouling
Probing Dark Energy with the Kunlun Dark Universe Survey Telescope
Dark energy is an important science driver of many upcoming large-scale
surveys. With small, stable seeing and low thermal infrared background, Dome A,
Antarctica, offers a unique opportunity for shedding light on fundamental
questions about the universe. We show that a deep, high-resolution imaging
survey of 10,000 square degrees in \emph{ugrizyJH} bands can provide
competitive constraints on dark energy equation of state parameters using type
Ia supernovae, baryon acoustic oscillations, and weak lensing techniques. Such
a survey may be partially achieved with a coordinated effort of the Kunlun Dark
Universe Survey Telescope (KDUST) in \emph{yJH} bands over 5000--10,000 deg
and the Large Synoptic Survey Telescope in \emph{ugrizy} bands over the same
area. Moreover, the joint survey can take advantage of the high-resolution
imaging at Dome A to further tighten the constraints on dark energy and to
measure dark matter properties with strong lensing as well as galaxy--galaxy
weak lensing.Comment: 9 pages, 6 figure
CMB Anisotropy Induced by Cosmic Strings on Angular Scales
We have computed an estimate of the angular power spectrum of the Cosmic
Microwave Background (CMB) induced by cosmic strings on angular scales , using a numerical simulation of a cosmic string network; and decomposed
this pattern into scalar, vector, and tensor parts. We find no evidence for
strong acoustic oscillations in the scalar anisotropy but rather a broad peak.
The anisotropies from vector modes dominate except on very small angular scales
while the tensor anisotropies are sub-dominant on all angular scales. The
anisotropies generated after recombination are even more important than in
adiabatic models. We expect that these qualitative features are robust to the
varying of cosmological parameters, a study which has not yet been done.Comment: 4 pages, 2 figure
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Interference in Exclusive Vector Meson Production in Heavy Ion Collisions
Photons emitted from the electromagnetic fields of relativistic heavy ions
can fluctuate into quark anti-quark pairs and scatter from a target nucleus,
emerging as vector mesons. These coherent interactions are identifiable by
final states consisting of the two nuclei and a vector meson with a small
transverse momentum. The emitters and targets can switch roles, and the two
possibilities are indistinguishable, so interference may occur. Vector mesons
are negative parity so the amplitudes have opposite signs. When the meson
transverse wavelength is larger than the impact parameter, the interference is
large and destructive.
The short-lived vector mesons decay before amplitudes from the two sources
can overlap, and so cannot interfere directly. However, the decay products are
emitted in an entangled state, and the interference depends on observing the
complete final state. The non-local wave function is an example of the
Einstein-Podolsky-Rosen paradox.Comment: 13 pages with 3 figures; submitted to Physical Review Letter
Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps
Supermassive black hole binary systems (SMBHB) are standard sirens -- the
gravitational wave analogue of standard candles -- and if discovered by
gravitational wave detectors, they could be used as precise distance
indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB
signals, seriously degrading any distance measurements. Using a weak lensing
map of the SMBHB line of sight, we can estimate its magnification and thereby
remove some uncertainty in its distance, a procedure we call "delensing." We
find that delensing is significantly improved when galaxy shears are combined
with flexion measurements, which reduce small-scale noise in reconstructed
magnification maps. Under a Gaussian approximation, we estimate that delensing
with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce
distance errors by about 30-40% for a SMBHB at z=2. Including an additional
wide shear map from a space survey telescope could reduce distance errors by
50%. Such improvement would make SMBHBs considerably more valuable as
cosmological distance probes or as a fully independent check on existing
probes.Comment: 9 pages, 4 figures, submitted to MNRA
Direct Signature of Evolving Gravitational Potential from Cosmic Microwave Background
We show that time dependent gravitational potential can be directly detected
from the cosmic microwave background (CMB) anisotropies. The signature can be
measured by cross-correlating the CMB with the projected density field
reconstructed from the weak lensing distortions of the CMB itself. The
cross-correlation gives a signal whenever there is a time dependent
gravitational potential. This method traces dark matter directly and has a well
defined redshift distribution of the window projecting over the density
perturbations, thereby avoiding the problems plaguing other proposed
cross-correlations. We show that both MAP and Planck will be able to probe this
effect for observationally relevant curvature and cosmological constant models,
which will provide additional constraints on the cosmological parameters.Comment: 4 pages, 2 figures. Submitted to PR
Radio Weak Gravitational Lensing with VLA and MERLIN
We carry out an exploratory weak gravitational lensing analysis on a combined
VLA and MERLIN radio data set: a deep (3.3 micro-Jy beam^-1 rms noise) 1.4 GHz
image of the Hubble Deep Field North. We measure the shear estimator
distribution at this radio sensitivity for the first time, finding a similar
distribution to that of optical shear estimators for HST ACS data in this
field. We examine the residual systematics in shear estimation for the radio
data, and give cosmological constraints from radio-optical shear
cross-correlation functions. We emphasize the utility of cross-correlating
shear estimators from radio and optical data in order to reduce the impact of
systematics. Unexpectedly we find no evidence of correlation between optical
and radio intrinsic ellipticities of matched objects; this result improves the
properties of optical-radio lensing cross-correlations. We explore the
ellipticity distribution of the radio counterparts to optical sources
statistically, confirming the lack of correlation; as a result we suggest a
connected statistical approach to radio shear measurements.Comment: 16 pages with 19 figures, accepted for publication in MNRAS; Minor
corrections to section 6.3; 2 references adde
Extended Inflation with a Curvature-Coupled Inflaton
We examine extended inflation models enhanced by the addition of a coupling
between the inflaton field and the space-time curvature. We examine two types
of model, where the underlying inflaton potential takes on second-order and
first-order form respectively. One aim is to provide models which satisfy the
solar system constraints on the Brans--Dicke parameter . This
constraint has proven very problematic in previous extended inflation models,
and we find circumstances where it can be successfully evaded, though the
constraint must be carefully assessed in our model and can be much stronger
than the usual . In the simplest versions of the model, one may
avoid the need to introduce a mass for the Brans--Dicke field in order to
ensure that it takes on the correct value at the present epoch, as seems to be
required in hyperextended inflation. We also briefly discuss aspects of the
formation of topological defects in the inflaton field itself.Comment: 24 pages, LaTeX (no figures), to appear, Physical Review D,
mishandling of the solar system constraint on extended gravity theories
corrected, SUSSEX-AST 93/6-
Can the Gravitational Wave Background from Inflation be Detected Locally?
The Cosmic Background Explorer (COBE) detection of microwave background
anisotropies may contain a component due to gravitational waves generated by
inflation. It is shown that the gravitational waves from inflation might be
seen using `beam-in-space' detectors, but not the Laser Interferometer Gravity
Wave Observatory (LIGO). The central conclusion, dependent only on weak
assumptions regarding the physics of inflation, is a surprising one. The larger
the component of the COBE signal due to gravitational waves, the {\em smaller}
the expected local gravitational wave signal.Comment: 8 pages, standard LaTeX (no figures), SUSSEX-AST 93/7-
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