1,459 research outputs found
Capabilities and limitations of a new thermal finite volume model for the evaluation of laser-induced thermo-mechanical retinal damage
Many experimental studies focus on the physical damage mechanisms of short-term exposure to laser radiation. In the nanosecond (ns) pulse range, damage
in the Retinal Pigment Epithelium (RPE) will most likely occur at threshold levels due to bubble formation at the surface of the absorbing melanosome. The
energy uptake of the melanosomes is one key aspect in modeling the bubble formation and damage thresholds. This work presents a thermal finite volume model
for the investigation of rising temperatures and the temperature distribution of irradiated melanosomes. The model takes the different geometries and thermal
properties of melanosomes into account, such as the heat capacity and thermal conductivity of the heterogeneous absorbing melanosomes and the surrounding
tissue. This is the first time the size and shape variations on the melanosomes‘ thermal behavior are considered. The calculations illustrate the effect of the
geometry on the maximum surface temperature of the irradiated melanosome and the impact on the bubble formation threshold. A comparison between the
calculated bubble formation thresholds and the RPE cell damage thresholds within a pulse range of 3 to 5000 ns leads to a mean deviation of = 22 mJ ∕ cm2
with a standard deviation of = 21 mJ ∕ cm2. The best results are achieved between the simulation and RPE cell damage thresholds for pulse durations close to
the thermal confinement time of individual melanosomes
Extensive collection of femtoliter pad secretion droplets in beetle Leptinotarsa decemlineata allows nanoliter microrheology
Pads of beetles are covered with long, deformable setae, each ending in a
micrometric terminal plate coated with secretory fluid. It was recently shown
that the layer of the pad secretion covering the terminal plates is responsible
for the generation of strong attractive forces. However, less is known about
the fluid itself because it is produced in extremely small quantity. We here
present a first experimental investigation of the rheological properties of the
pad secretion in the Colorado potato beetle {\it Leptinotarsa decemlineata}.
Because the secretion is produced in an extremely small amount at the level of
the terminal plate, we first develop a procedure based on capillary effects to
collect the secretion. We then manage to incorporate micrometric beads,
initially in the form of a dry powder, and record their thermal motion to
determine the mechanical properties of the surrounding medium. We achieve such
a quantitative measurement within the collected volume, much smaller than the
l sample volume usually required for this technique. Surprisingly,
the beetle secretion was found to behave as a purely viscous liquid, of high
viscosity. This suggests that no specific complex fluid behaviour is needed
during beetle locomotion. We build a scenario for the contact formation between
the spatula at the setal tip and a substrate, during the insect walk. We show
that the attachment dynamics of the insect pad computed from the high measured
viscosity is in good agreement with observed insect pace. We finally discuss
the consequences of the secretion viscosity on the insect adhesion
Complete physical simulation of the entangling-probe attack on the BB84 protocol
We have used deterministic single-photon two qubit (SPTQ) quantum logic to
implement the most powerful individual-photon attack against the
Bennett-Brassard 1984 (BB84) quantum key distribution protocol. Our measurement
results, including physical source and gate errors, are in good agreement with
theoretical predictions for the Renyi information obtained by Eve as a function
of the errors she imparts to Alice and Bob's sifted key bits. The current
experiment is a physical simulation of a true attack, because Eve has access to
Bob's physical receiver module. This experiment illustrates the utility of an
efficient deterministic quantum logic for performing realistic physical
simulations of quantum information processing functions.Comment: 4 pages, 5 figure
Bodies, technologies and action possibilities: when is an affordance?
Borrowed from ecological psychology, the concept of affordances is often said to offer the social study of technology a means of re-framing the question of what is, and what is not, ‘social’ about technological artefacts. The concept, many argue, enables us to chart a safe course between the perils of technological determinism and social constructivism. This article questions the sociological adequacy of the concept as conventionally deployed. Drawing on ethnographic work on the ways technological artefacts engage, and are engaged by, disabled bodies, we propose that the ‘affordances’ of technological objects are not reducible to their material constitution but are inextricably bound up with specific, historically situated modes of engagement and ways of life
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