444 research outputs found
Spaser Action, Loss Compensation, and Stability in Plasmonic Systems with Gain
We demonstrate that the conditions of spaser generation and the full loss
compensation in a resonant plasmonic-gain medium (metamaterial) are identical.
Consequently, attempting the full compensation or overcompensation of losses by
gain will lead to instability and a transition to a spaser state. This will
limit (clamp) the inversion and lead to the limitation on the maximum loss
compensation achievable. The criterion of the loss overcompensation, leading to
the instability and spasing, is given in a analytical and universal
(independent from system's geometry) form.Comment: 4 pages, 1 figur
Reply to "Can gravitational dynamics be obtained by diffeomorphism invariance of action?"
In a previous work we showed that, in a suitable setting, one can use
diffeomorphism invariance in order to derive gravitational field equations from
boundary terms of the gravitational action. Standing by our results we reply
here to a recent comment questioning their validity.Comment: Accepted for publication in PR
Emission of light through thin silver films via near-field coupling to surface plasmon polaritons
Copyright © 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 88 (2006) and may be found at http://link.aip.org/link/?APPLAB/88/051109/1We show that the emission of light from a dye layer through an adjacent thin silver film is maximal for a silver thickness of approximately 50 nm. This effect is explained as the result of competition between enhancement of the electric field at the metal surface due to the excitation of a surface plasmon-polariton mode, the amount of power coupled to the surface plasmon-polariton mode, and the attenuation of the field transmitted through the silver, all three of which vary with metal thickness. We indicate how these findings may be of relevance in the design of some surface plasmon-polariton-based fluorescence biosensing schemes
Broad-band polarization-independent total absorption of electromagnetic waves by an overdense plasma
We have shown both experimentally and theoretically that
polarization-independent broad-band absorption of electromagnetic waves by an
overdense plasma, caused by surface plasmon-polaritons (SPP) excitation, can be
achieved due to combination of two factors: a non-zero angle of incidence and a
two-dimensional circular diffraction grating placed at a properly chosen
distance in front of the plasma boundary. Direct detection of SPP has been
achieved for the first time using a miniature antenna imbedded in the plasma.Comment: considerably broadened versio
How visual information influences dual-task driving and tracking
The study examined the impact of visual predictability on dual-task performance in driving and tracking tasks. Participants (N = 27) performed a simulated driving task and a pursuit tracking task. In either task, visual predictability was manipulated by systematically varying the amount of advance visual information: in the driving task, participants drove at night with low beam, at night with high beam, or in daylight; in the tracking task, participants saw a white line that specified the future target trajectory for 200, 400 or 800 ms. Concurrently with driving or tracking, participants performed an auditory task. They had to discriminate between two sounds and press a pedal upon hearing the higher sound. Results show that in general, visual predictability benefited driving and tracking; however, dual-task driving performance was best with highest visual predictability (daylight), dual-task tracking performance was best with medium visual predictability (400 ms). Braking/reaction times were higher in dual tasks compared to single tasks, but were unaffected by visual predictability, showing that its beneficial effects did not transfer to the auditory task. In both tasks, manual accuracy decreased around the moment the foot pressed the pedal, indicating interference between tasks. We, therefore, conclude that despite a general beneficial impact of predictability, the integration of visual information seems to be rather task specific, and that interference between driving and audiomotor tasks, and tracking and audiomotor tasks, seems comparable
TransverseDiff gravity is to scalar-tensor as unimodular gravity is to General Relativity
Transverse Diffeomorphism (TDiff) theories are well-motivated theories of
gravity from the quantum perspective, which are based upon a gauge symmetry
principle. The main contribution of this work is to firmly establish a
correspondence between TransverseDiff and the better-known scalar-tensor
gravity --- in its more general form ---, a relation which is completely
analogous to that between unimodular gravity and General Relativity. We then
comment on observational aspects of TDiff. In connection with this proof, we
derive a very general rule that determines under what conditions the procedure
of fixing a gauge symmetry can be equivalently applied before the variational
principle leading to the equations of motion, as opposed to the standard
procedure, which takes place afterwards; this rule applies to gauge-fixing
terms without derivatives.Comment: 10 pages; amsart style; v3: version as appeared in JCAP, redaction
improve
Photon losses depending on polarization mixedness
We introduce a quantum channel describing photon losses depending on the
degree of polarization mixedness. This can be regarded as a model of quantum
channel with correlated errors between discrete and continuous degrees of
freedom. We consider classical information over a continuous alphabet encoded
on weak coherent states as well as classical information over a discrete
alphabet encoded on single photons using dual rail representation. In both
cases we study the one-shot capacity of the channel and its behaviour in terms
of correlation between losses and polarization mixedness
Midwest Guardrail System with Round Timber Posts
A modified Midwest Guardrail System (MGS) was developed by using small-diameter round wood posts. The barrier system was configured with three timber species: Douglas fir (DF), ponderosa pine (PP), and southern yellow pine (SYP). Barrier VII computer simulation, combined with cantilever post testing in a rigid sleeve and soil, was used to determine the required post diameter for each species. The recommended nominal sizes were 184 mm (7.25 in.) for DF, 203 mm (8 in.) for PP, and 190 mm (7.5 in.) for SYP. A grading criterion limiting knot size and ring density was established for each species. The recommended knot sizes were limited to 38 mm (1.5 in.) or smaller for DF, 89 mm (3.5 in.) or smaller for PP, and 64 mm (2.5 in.) or smaller for SYP. The minimum ring densities equaled or exceeded 6 rings per inch (rpi) for DF, 6 rpi for PP, and 4 rpi for SYP. Two guardrail systems— one using DF posts and another using PP posts—were crash tested according to the Test Level 3 requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. Crash testing was not conducted on the SYP system because of the adequacy of previous testing on 184-mm (7.25-in.) diameter SYP posts in a standard W-beam guardrail system and post design strength comparable to that in the other two species. Both crash tests showed that the modified MGS functioned adequately for both wood species. Three round wood post alternatives were recommended as an acceptable substitute for the standard W152×13.4 (W6×9) steel post used in the MGS
Real-time phase-shift detection of the surface plasmon resonance
We investigate a method to directly measure the phase of a laser beam
reflected from a metallic film after excitation of surface plasmon polaritons.
This method permits real time access to the phase information, it increases the
possible speed of data acquisition, and it may thus prove useful for increasing
the sensitivity of surface plasmon based sensors
On the Meaning of the Principle of General Covariance
We present a definite formulation of the Principle of General Covariance
(GCP) as a Principle of General Relativity with physical content and thus
susceptible of verification or contradiction. To that end it is useful to
introduce a kind of coordinates, that we call quasi-Minkowskian coordinates
(QMC), as an empirical extension of the Minkowskian coordinates employed by the
inertial observers in flat space-time to general observers in the curved
situations in presence of gravitation. The QMC are operationally defined by
some of the operational protocols through which the inertial observers
determine their Minkowskian coordinates and may be mathematically characterized
in a neighbourhood of the world-line of the corresponding observer. It is taken
care of the fact that the set of all the operational protocols which are
equivalent to measure a quantity in flat space-time split into inequivalent
subsets of operational prescriptions under the presence of a gravitational
field or when the observer is not inertial. We deal with the Hole Argument by
resorting to de idea of the QMC and show how it is the metric field that
supplies the physical meaning of coordinates and individuates point-events in
regions of space-time where no other fields exist. Because of that the GCP has
also value as a guiding principle supporting Einstein's appreciation of its
heuristic worth in his reply to Kretschmann in 1918
- …