22,600 research outputs found
Configurational factors in the perception of unfamiliar faces
Young et al (1987) have demonstrated that the juxtaposition of top and bottom halves of different faces produces a powerful impression of a novel face. It is difficult to isolate perceptually either half of the 'new' face. Inversion of the stimulus, however, makes this task easier. Upright chimeric faces appear to evoke strong and automatic configurational processing mechanisms which interfere with selective piecemeal processing. In this paper three experiments are described in which a matching paradigm was used to show that Young et al's findings apply to unfamiliar as well as to familiar faces. The results highlight the way in which minor procedural differences may alter the way in which subjects perform face-recognition tasks
Hypersonic Navier-Stokes Comparisons to Orbiter Flight Data
During the STS-119 flight of Space Shuttle Discovery, two sets of surface temperature measurements were made. Under the HYTHIRM program3 quantitative thermal images of the windward side of the Orbiter with a were taken. In addition, the Boundary Layer Transition Flight Experiment 4 made thermocouple measurements at discrete locations on the Orbiter wind side. Most of these measurements were made downstream of a surface protuberance designed to trip the boundary layer to turbulent flow. In this paper, we use the US3D computational fluid dynamics code to simulate the Orbiter flow field at conditions corresponding to the STS-119 re-entry. We employ a standard two-temperature, five-species finite-rate model for high-temperature air, and the surface catalysis model of Stewart.1 This work is similar to the analysis of Wood et al . 2 except that we use a different approach for modeling turbulent flow. We use the one-equation Spalart-Allmaras turbulence model8 with compressibility corrections 9 and an approach for tripping the boundary layer at discrete locations. In general, the comparison between the simulations and flight data is remarkably goo
Quantum QED Flux Tubes in 2+1 and 3+1 Dimensions
We compute energies and energy densities of static electromagnetic flux tubes
in three and four spacetime dimensions. Our calculation uses scattering data
from the potential induced by the flux tube and imposes standard perturbative
renormalization conditions. The calculation is exact to one-loop order, with no
additional approximation adopted. We embed the flux tube in a configuration
with zero total flux so that we can fully apply standard results from
scattering theory. We find that upon choosing the same on-shell renormalization
conditions, the functional dependence of the energy and energy density on the
parameters of the flux tube is very similar for three and four spacetime
dimensions. We compare our exact results to those obtained from the derivative
and perturbation expansion approximations, and find good agreement for
appropriate parameters of the flux tube. This remedies some puzzles in the
prior literature.Comment: 49 pages, 13 figures, minor changes in wording, accepted for
publication in Nucl. Phys.
Energies of Quantum QED Flux Tubes
In this talk I present recent studies on vacuum polarization energies and
energy densities induced by QED flux tubes. I focus on comparing three and four
dimensional scenarios and the discussion of various approximation schemes in
view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona,
Sept. 2005. To appear in the proceeding
Exact solutions for the spatial de Vaucouleurs and Sersic laws and related quantities
Using the Mathematica package, we find exact analytical expressions for the
so-called de-projected De Vaucouleurs and Sersic laws as well as for related
spatial (3D) quantities, such the mass, gravitational potential, the total
energy and the central velocity dispersion, generally involved in astronomical
calculations expressed in terms of the Meijer G functions.Comment: 11 pages, accepted in A
Human papillomavirus E2 regulates SRSF3 (SRp20) to promote capsid protein expression in infected differentiated keratinocytes
The human papillomavirus (HPV) life cycle is tightly linked to differentiation of the infected epithelial cell suggesting a sophisticated interplay between host cell metabolism and virus replication. Previously we demonstrated in differentiated keratinocytes in vitro and in vivo that HPV16 infection caused increased levels of the cellular SR splicing factors (SRSFs) SRSF1 (ASF/SF2), SRSF2 (SC35) and SRSF3 (SRp20). Moreover, the viral E2 transcription and replication factor that is expressed at high levels in differentiating keratinocytes could bind and control activity of the SRSF1 gene promoter. Here we reveal that E2 proteins of HPV16 and HPV31 control expression of SRSFs 1, 2 and 3 in a differentiation-dependent manner. E2 has the greatest trans-activation effect on expression of SRSF3. siRNA depletion experiments in two different models of the HPV16 life cycle (W12E and NIKS16) and one model of the HPV31 life cycle (CIN612-9E) revealed that only SRSF3 contributed significantly to regulation of late events in the virus life cycle. Increased levels of SRSF3 are required for L1 mRNA and capsid protein expression. Capsid protein expression was regulated specifically by SRSF3 and appeared independent of other SRSFs. Taken together these data suggest a significant role of the HPV E2 protein in regulating late events in the HPV life cycle through transcriptional regulation of SRSF3 expression.
IMPORTANCE Human papillomavirus replication is accomplished in concert with differentiation of the infected epithelium. Virus capsid protein expression is confined to the upper epithelial layers so as to avoid immune detection. In this study we demonstrate that the viral E2 transcription factor activates the promoter of the cellular SRSF3 RNA processing factor. SRSF3 is required for expression of the E4Ě‚L1 mRNA and so controls expression of the HPV L1 capsid protein. Thus we reveal a new dimension of virus-host interaction crucial for production of infectious virus. SRSF proteins are known drug targets. Therefore, this study provides an excellent basis for developing strategies to regulate capsid protein production in the infected epithelium and production of new virions
Calculating Vacuum Energies in Renormalizable Quantum Field Theories: A New Approach to the Casimir Problem
The Casimir problem is usually posed as the response of a fluctuating quantum
field to externally imposed boundary conditions. In reality, however, no
interaction is strong enough to enforce a boundary condition on all frequencies
of a fluctuating field. We construct a more physical model of the situation by
coupling the fluctuating field to a smooth background potential that implements
the boundary condition in a certain limit. To study this problem, we develop
general new methods to compute renormalized one--loop quantum energies and
energy densities. We use analytic properties of scattering data to compute
Green's functions in time--independent background fields at imaginary momenta.
Our calculational method is particularly useful for numerical studies of
singular limits because it avoids terms that oscillate or require cancellation
of exponentially growing and decaying factors. To renormalize, we identify
potentially divergent contributions to the Casimir energy with low orders in
the Born series to the Green's function. We subtract these contributions and
add back the corresponding Feynman diagrams, which we combine with counterterms
fixed by imposing standard renormalization conditions on low--order Green's
functions. The resulting Casimir energy and energy density are finite
functionals for smooth background potentials. In general, however, the Casimir
energy diverges in the boundary condition limit. This divergence is real and
reflects the infinite energy needed to constrain a fluctuating field on all
energy scales; renormalizable quantum field theories have no place for ad hoc
surface counterterms. We apply our methods to simple examples to illustrate
cases where these subtleties invalidate the conclusions of the boundary
condition approach.Comment: 36pages, Latex, 20 eps files. included via epsfi
Reduction in jejunal fluid absorption in vivo through distension and cholinergic stimulation not attributable to enterocyte secretion
Jejunal fluid absorption in vivo was reduced by distension and by hydrostatic pressure and further declined on adding E. coli STa enterotoxin but no net fluid secretion was detected. Luminal atropine reduced pressure mediated reductions in fluid absorption to normal values but intravenous hexamethonium was without effect. A neural component to inhibition of absorption by pressure (though not stretch) may be mediated by axon reflexes within cholinergic neurons.Perfusion of cholinergic compounds also reduced net fluid absorption but did not cause secretion. In order to show that these actions were not secretory processes stimulated by cholinergic compounds that offset normal rates of absorption, these compounds were tested for their ability to cause net secretion in loops that were perfused with solutions in which choline substituted for sodium ion. In addition, these perfusates additionally contained E. coli STa enterotoxin or EIPA (ethyl-isopropyl-amiloride) to minimize absorption.In these circumstances, where it might be expected to do so if it were acting through a secretory rather than an absorptive mechanism, carbachol did not cause net fluid secretion. Cholinergic stimulation and pressure induced distension are thought to reduce net fluid absorption through inducing secretion but are found only to reduce fluid absorption.In conclusion, distension and cholinergic stimulation of the small intestine are two further circumstances in which fluid secretion is assumed to explain their action on fluid movement, as required by the enterocyte secretion model of secretion but, which like STa enterotoxin, instead are only able to reduce fluid absorption. This casts further doubt on the widespread validity of the enterocyte secretion model for fluid appearance in the lumen in diarrhoeal diseases
Heavy Fermion Quantum Effects in SU(2)_L Gauge Theory
We explore the effects of a heavy fermion doublet in a simplified version of
the standard electroweak theory. We integrate out the doublet and compute the
exact effective energy functional of spatially varying gauge and Higgs fields.
We perform a variational search for a local minimum of the effective energy and
do not find evidence for a soliton carrying the quantum numbers of the
decoupled fermion doublet. The fermion vacuum polarization energy offsets the
gain in binding energy previously argued to be sufficient to stabilize a
fermionic soliton. The existence of such a soliton would have been a natural
way to maintain anomaly cancellation at the level of the states. We also see
that the sphaleron energy is significantly increased due to the quantum
corrections of the heavy doublet. We find that when the doublet is slightly
heavier than the quantum--corrected sphaleron, its decay is exponentially
suppressed owing to a new barrier. This barrier exists only for an intermediate
range of fermion masses, and a heavy enough doublet is indeed unstable.Comment: 30 pages LaTeX, 3 eps-figure
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