5,069 research outputs found
Behavioral indicators of pilot workload
Using a technique that requires a subject to consult an imagined or remembered spatial array while performing a visual task, a reliable reduction in the number of directed eye movements that are available for the acquisition of visual information is shown
Representing Structural Information of Helical Charge Distributions in Cylindrical Coordinates
Structural information in the local electric field produced by helical charge
distributions, such as dissolved DNA, is revealed in a straightforward manner
employing cylindrical coordinates. Comparison of structure factors derived in
terms of cylindrical and helical coordinates is made. A simple coordinate
transformation serves to relate the Green function in cylindrical and helical
coordinates. We also compare the electric field on the central axis of a single
helix as calculated in both systems.Comment: 11 pages in plain LaTex, no figures. Accepted for publication in PRE
March, 199
Low-energy electron beam focusing in self-organized porous alumina vacuum windows
Micromachined, micron-thick porous alumina membranes with closed pore endings show high electron transparency above an energy of 5 keV. This is due to the channeling of electrons along the negatively charged insulating pores after surmounting the thin entrance layer. We also find a sharp hightransparency energy window at energies as low as 2 keV which may be the result of a local maximum of channeling, as predicted by simulations, and positive charge up of the entrance layer causing electron electrostatic focusing. Applications for these membranes range from atmospheric electron spectroscopy to self-assembled, nanoscale, large-area electron collimators
Patent collateral, investor commitment, and the market for venture lending
This paper investigates the market for lending to technology startups (i.e., venture lending) and examines two mechanisms that may facilitate trade within it: (1) the ‘salability’ of patent collateral; and (2) the credible commitment of existing equity investors. We find that intensified trading in the secondary patent market is strongly related to the annual rate of startup lending, particularly for startups with more redeployable patent assets. Moreover, we show that the credibility of venture capitalist commitments to reinvest in their startups’ next round of financing can be critical for startup debt provision. Utilizing the crash of 2000 as a severe and unexpected capital supply shock for VCs, we show that lenders continue to finance startups with recently funded investors better able to credibly commit to refinance their portfolio companies, but withdraw from otherwise-promising projects that may have needed their funds the most. The findings are consistent with predictions of incomplete contracting and financial intermediation theory.Accepted manuscrip
Boulware state and semiclassical thermodynamics of black holes in a cavity
A black hole, surrounded by a reflecting shell, acts as an effective
star-like object with respect to the outer region that leads to vacuum
polarization outside, where the quantum fields are in the Boulware state. We
find the quantum correction to the Hawking temperature, taking into account
this circumstance. It is proportional to the integral of the trace of the total
quantum stress-energy tensor over the whole space from the horizon to infinity.
For the shell, sufficiently close to the horizon, the leading term comes from
the boundary contribution of the Boulware state.Comment: 7 pages. To appear in Phys. Rev.
Dynamic wormholes
A new framework is proposed for general dynamic wormholes, unifying them with
black holes. Both are generically defined locally by outer trapping horizons,
temporal for wormholes and spatial or null for black and white holes. Thus
wormhole horizons are two-way traversible, while black-hole and white-hole
horizons are only one-way traversible. It follows from the Einstein equation
that the null energy condition is violated everywhere on a generic wormhole
horizon. It is suggested that quantum inequalities constraining negative energy
break down at such horizons. Wormhole dynamics can be developed as for
black-hole dynamics, including a reversed second law and a first law involving
a definition of wormhole surface gravity. Since the causal nature of a horizon
can change, being spatial under positive energy and temporal under sufficient
negative energy, black holes and wormholes are interconvertible. In particular,
if a wormhole's negative-energy source fails, it may collapse into a black
hole. Conversely, irradiating a black-hole horizon with negative energy could
convert it into a wormhole horizon. This also suggests a possible final state
of black-hole evaporation: a stationary wormhole. The new framework allows a
fully dynamical description of the operation of a wormhole for practical
transport, including the back-reaction of the transported matter on the
wormhole. As an example of a matter model, a Klein-Gordon field with negative
gravitational coupling is a source for a static wormhole of Morris & Thorne.Comment: 5 revtex pages, 4 eps figures. Minor change which did not reach
publisher
Energy Density of Non-Minimally Coupled Scalar Field Cosmologies
Scalar fields coupled to gravity via in arbitrary
Friedmann-Robertson-Walker backgrounds can be represented by an effective flat
space field theory. We derive an expression for the scalar energy density where
the effective scalar mass becomes an explicit function of and the scale
factor. The scalar quartic self-coupling gets shifted and can vanish for a
particular choice of . Gravitationally induced symmetry breaking and
de-stabilization are possible in this theory.Comment: 18 pages in standard Late
Vacuum polarization in the spacetime of charged nonlinear black hole
Building on general formulas obtained from the approximate renormalized
effective action, the approximate stress-energy tensor of the quantized massive
scalar field with arbitrary curvature coupling in the spacetime of charged
black hole being a solution of coupled equations of nonlinear electrodynamics
and general relativity is constructed and analysed. It is shown that in a few
limiting cases, the analytical expressions relating obtained tensor to the
general renormalized stress-energy tensor evaluated in the geometry of the
Reissner-Nordstr\"{o}m black hole could be derived. A detailed numerical
analysis with special emphasis put on the minimal coupling is presented and the
results are compared with those obtained earlier for the conformally coupled
field. Some novel features of the renormalized stress-energy tensor are
discussed
Galilean invariance and homogeneous anisotropic randomly stirred flows
The Ward-Takahashi (WT) identities for incompressible flow implied by
Galilean invariance are derived for the randomly forced Navier-Stokes equation
(NSE), in which both the mean and fluctuating velocity components are
explicitly present. The consequences of Galilean invariance for the vertex
renormalization are drawn from this identity.Comment: REVTeX 4, 4 pages, no figures. To appear as a Brief Report in the
Physical Review
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