12,768 research outputs found
Thermoplasmonics: Quantifying plasmonic heating in single nanowires
Plasmonic absorption of light can lead to significant local heating in
metallic nanostructures, an effect that defines the sub-field of
thermoplasmonics and has been leveraged in diverse applications from biomedical
technology to optoelectronics. Quantitatively characterizing the resulting
local temperature increase can be very challenging in isolated nanostructures.
By measuring the optically-induced change in resistance of metal nanowires with
a transverse plasmon mode, we quantitatively determine the temperature increase
in single nanostructures, with the dependence on incident polarization clearly
revealing the plasmonic heating mechanism. Computational modeling explains the
resonant and nonresonant contributions to the optical heating and the dominant
pathways for thermal transport. These results, obtained by combining electronic
and optical measurements, place a bound on the role of optical heating in prior
experiments, and suggest design guidelines for engineered structures meant to
leverage such effects.Comment: 17 pages, 4 figures + 3 pages supporting materia
Realistic lower bounds for the factorization time of large numbers on a quantum computer.
Published versio
Hot entanglement in a simple dynamical model
How mixed can one component of a bi-partite system be initially and still
become entangled through interaction with a thermalized partner? We address
this question here. In particular, we consider the question of how mixed a
two-level system and a field mode may be such that free entanglement arises in
the course of the time evolution according to a Jaynes-Cummings type
interaction. We investigate the situation for which the two-level system is
initially in mixed state taken from a one-parameter set, whereas the field has
been prepared in an arbitrary thermal state. Depending on the particular choice
for the initial state and the initial temperature of the quantised field mode,
three cases can be distinguished: (i) free entanglement will be created
immediately, (ii) free entanglement will be generated, but only at a later time
different from zero, (iii) the partial transpose of the joint state remains
positive at all times. It will be demonstrated that increasing the initial
temperature of the field mode may cause the joint state to become distillable
during the time evolution, in contrast to a non-distillable state at lower
initial temperatures. We further assess the generated entanglement
quantitatively, by evaluating the logarithmic negativity numerically, and by
providing an analytical upper bound.Comment: 5 pages, 2 figures. Contribution to the proceedings of the
'International Conference on Quantum Information', Oviedo, July 13-18, 2002.
Discusses sudden changes of entanglement properties in a dynamical quantum
mode
On the Preparation of Pure States in Resonant Microcavities
We consider the time evolution of the radiation field (R) and a two-level
atom (A) in a resonant microcavity in terms of the Jaynes-Cummings model with
an initial general pure quantum state for the radiation field. It is then
shown, using the Cauchy-Schwarz inequality and also a Poisson resummation
technique, that {\it perfect} coherence of the atom can in general never be
achieved. The atom and the radiation field are, however, to a good
approximation in a pure state in the middle of what
has been traditionally called the ``collapse region'', independent of the
initial state of the atoms, provided that the initial pure state of the
radiation field has a photon number probability distribution which is
sufficiently peaked and phase differences that do not vary significantly around
this peak. An approximative analytic expression for the quantity
\Tr[\rho^2_{A}(t)], where is the reduced density matrix for the
atom, is derived. We also show that under quite general circumstances an
initial entangled pure state will be disentangled to the pure state .Comment: 14 pages and 3 figure
Depth-averaged simulation of flows in asymmetric compound channels with smooth and rough narrow floodplains
Depth-averaged hydrodynamic models are predominantly used in numerical simulations of
compound channel flows. One of the most popular methods for the depth-averaged simulation
is Shiono and Knight method (SKM). This method accounts for the effects of bed friction, lateral
turbulence and secondary flows, via three key parameters f, λ and Γ, respectively. The conventional
expressions that are developed to calibrate these parameters are generally based on
experiments in compound channels with wide floodplains. In this study, the application of SKM
to an asymmetric compound channel with a narrow floodplain is examined in terms of the
calibration requirements. Two sets of experiments that have smooth and rough floodplains are
conducted and then simulated by SKM. In smooth floodplain cases, the results reveal that SKM
model with the conventional calibration expressions of f, λ and Г is reasonably capable of
predicting the distributions of depth-averaged velocity and boundary shear stress in the main
channel. However, in the floodplain region, the expressions recommended for calibrating Г
need to be modified to improve the predicted results in that region. In cases of the rough
floodplain, the results indicate that only the values of λ in the main channel need to be
changed from its conventional values to improve the predictions
A Research-Based Curriculum for Teaching the Photoelectric Effect
Physics faculty consider the photoelectric effect important, but many
erroneously believe it is easy for students to understand. We have developed
curriculum on this topic including an interactive computer simulation,
interactive lectures with peer instruction, and conceptual and mathematical
homework problems. Our curriculum addresses established student difficulties
and is designed to achieve two learning goals, for students to be able to (1)
correctly predict the results of photoelectric effect experiments, and (2)
describe how these results lead to the photon model of light. We designed two
exam questions to test these learning goals. Our instruction leads to better
student mastery of the first goal than either traditional instruction or
previous reformed instruction, with approximately 85% of students correctly
predicting the results of changes to the experimental conditions. On the
question designed to test the second goal, most students are able to correctly
state both the observations made in the photoelectric effect experiment and the
inferences that can be made from these observations, but are less successful in
drawing a clear logical connection between the observations and inferences.
This is likely a symptom of a more general lack of the reasoning skills to
logically draw inferences from observations.Comment: submitted to American Journal of Physic
Mountain Pine Beetle Outbreaks in the Rocky Mountains: Regulators of Primary Productivity?
We consider the hypothesis that mountain pine beetles function as cybernetic regulators of primary productivity in ecosystems of lodgepole pine forest through their selective killing of dominant trees and the subsequent redistribution of resources. Following a recent major beetle outbreak in Yellowstone and Grand Teton national parks, surviving trees did grow significantly faster (P \u3c .1); wood production was redistributed among canopy, subcanopy, and understory trees; and annual wood production per hectare usually returned to pre-attack levels or exceeded them within 10-15 yr. However, reconstructions of annual wood production over the last 70-80 yr indicate that the beetle outbreak did not reduce the variation in productivity; rather, the beetles introduced more variation than would have existed in their absence. Hence, our results do not support the hypothesis that the beetles function as cybernetic regulators (in the strict sense). Nevertheless, the beetle-pine system that we studied shows great resilience, and the effects of beetles on primary productivity do not appear to be as severe as conventional wisdom maintains. Annual wood production per hectare returned quickly to previous levels in the stands we studied, and associated ecological changes can be considered generally benign or even beneficial
The Effects of Thawing Procedure and Supplementation on the Motility and Viability of Frozen-thawed Boar Semen
The effect of two thawing procedures on frozen boar semen and supplementations to the fertilization media were studied. Frozen boar semen was thawed using either Percoll gradient or phosphate buffered saline (PBS)procedure. Supplementations were 1.0 mM L-glutamate, 1.0 mM N-acetylcysteine (NAC) , and 1.0 mM NAC-amide (NACA). Spermatozoa were analyzed for forward progressive motility (FPM) and viability every 0.5 h for 3 .0 h post-thawing. There were significantly (P \u3c 0.05) higher numbers of viable (76.0 ± 5.1 %) and FPM (30 .0 ± 2.4%) spermatozoa at 3.0 h post thawing using the PBS procedure compared to the Percoll gradient thawed spermatozoa (65.0 ± 3.9%; 10.0 ± 4.5 %, respectively). Supplementation of 1.0 mM L-glutamate, 1.0 mM NAC, or 1.0 mM NACA had no significant effect on spermatozoa viability regardless of the time post-thaw.Supplementation of 1.0 mM L-glutamate, 1.0 mM NAC , or 1.0 mM NACA had no significant effect on FPM up to 1.0 h post-thaw. Spermatozoa with no supplementation or 1.0 mM L-glutamate had significantly higher (P \u3c 0.05) FPM compared to the 1.0 mM NAC and 1.0 mM NACA supplemented groups at 1.5, 2.0, 2 .5, and 3.0 h post-thaw. There was no significant difference between no supplementation or 1.0 mM L-glutamate on FPM regardless of the time post-thaw. There was no significant difference between 1.0 mM NAC or 1.0 mM NACA on FPM regardless of the time post-thaw. These results indicate that thawing procedure has an effect on spermatozoa viability and FPM but supplementation does not have an effect on the overall viability of spermatozoa during thawing, but may reduce FPM
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