884 research outputs found
Halving the Casimir force with conductive oxides
The possibility to modify the strength of the Casimir effect by tailoring the
dielectric functions of the interacting surfaces is regarded as a unique
opportunity in the development of Micro- and NanoElectroMechanical Systems. In
air, however, one expects that, unless noble metals are used, the electrostatic
force arising from trapped charges overcomes the Casimir attraction, leaving no
room for exploitation of Casimir force engineering at ambient conditions. Here
we show that, in the presence of a conductive oxide, the Casimir force can be
the dominant interaction even in air, and that the use of conductive oxides
allows one to reduce the Casimir force up to a factor of 2 when compared to
noble metals.Comment: modified version, accepted for publication in Phys Rev Let
Structure-stiffness relation of live mouse brain tissue determined by depth-controlled indentation mapping
The mechanical properties of brain tissue play a pivotal role in
neurodevelopment and neurological disorders. Yet, at present, there is no
consensus on how the different structural parts of the tissue contribute to its
stiffness variations. Here, we have gathered depth-controlled indentation
viscoelasticity maps of the hippocampus of isolated horizontal live mouse brain
sections. Our results confirm the highly viscoelestic nature of the material
and clearly show that the mechanical properties correlate with the different
morphological layers of the samples investigated. Interestingly, the relative
cell nuclei area seems to negatively correlate with the stiffness observed
Fiber-top atomic force microscope
We present the implementation of an atomic force microscope (AFM) based on fiber-top design. Our results demonstrate that the performances of fiber-top AFMs in contact mode are comparable to those of similar commercially available instruments. Our device thus represents an interesting\ud
alternative to existing AFMs, particularly for applications outside specialized research laboratories, where a compact, user-friendly, and versatile tool might often be preferred
Precision measurement of the Casimir-Lifshitz force in a fluid
The Casimir force, which results from the confinement of the quantum
mechanical zero-point fluctuations of the electromagnetic fields, has received
significant attention in recent years for its effect on micro- and nano-scale
mechanical systems. With few exceptions, experimental observations have been
limited to conductive bodies interacting separated by vacuum or air. However,
interesting phenomena including repulsive forces are expected to exist in
certain circumstances between metals and dielectrics when the intervening
medium is not vacuum. In order to better understand the effect of the Casimir
force in such situations and to test the robustness of the generalized
Casimir-Lifshitz theory, we have performed the first precision measurements of
the Casimir force between two metals immersed in a fluid. For this situation,
the measured force is attractive and is approximately 80% smaller than the
force predicted by Casimir for ideal metals in vacuum. We present experimental
results and find them to be consistent with Lifshitz's theory.Comment: 6 pages, 3 figures. (version before final publication
A study of the mechanisms of corrosion inhibition of AA2024-T3 by vanadates using the split cell technique
The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied in this work using the split cell technique and polarization curves. The electrochemical behavior of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Injection of metavanadates to the cathode side of the different split cell setups greatly reduced the galvanic current, indicating a potent inhibition of the oxygen reduction kinetics. The galvanic current never exhibited a transient current peak, suggesting that metavanadates inhibit AA2024-T3 corrosion by a mechanism that does not involve electrochemical reduction. Injection of metavanadate to the anode side of the different split cells had no effect on the galvanic current. Injection of orange decavanadate to the cathode side of the AA2024-T3 split cell resulted in a large current peak, associated with the electrochemical reduction of decavanadate. However, decavanadates did not impart significant corrosion protection.This work was partially funded by AFOSR under award F 49620-02-0321, Major J. Gresham, PhD, contract monitor. JK’s travel expenses were paid by NATO under grant PST.CLG.979370
Quantum electrodynamical torques in the presence of Brownian motion
Quantum fluctuations of the electromagnetic field give rise to a zero-point energy that persists even in the absence of electromagnetic sources. One striking consequence of the zero-point energy is manifested in the Casimir force, which causes two electrically neutral metallic plates to attract in order to reduce the zero-point energy. A second, less well-known, effect is a torque that arises between two birefringent materials with in-plane optical anisotropy as a result of the zero-point energy. In this paper, we discuss the influence of Brownian motion on two birefringent plates undergoing quantum electrodynamical (QED) rotation as a result of the system's zero-point energy. Direct calculations for the torque are presented, and preliminary experiments are discussed. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Computation and visualization of Casimir forces in arbitrary geometries: non-monotonic lateral forces and failure of proximity-force approximations
We present a method of computing Casimir forces for arbitrary geometries,
with any desired accuracy, that can directly exploit the efficiency of standard
numerical-electromagnetism techniques. Using the simplest possible
finite-difference implementation of this approach, we obtain both agreement
with past results for cylinder-plate geometries, and also present results for
new geometries. In particular, we examine a piston-like problem involving two
dielectric and metallic squares sliding between two metallic walls, in two and
three dimensions, respectively, and demonstrate non-additive and non-monotonic
changes in the force due to these lateral walls.Comment: Accepted for publication in Physical Review Letters. (Expected
publication: Vol. 99 (8) 2007
Fast evaluation of solid harmonic Gaussian integrals for local resolution-of-the-identity methods and range-separated hybrid functionals
An integral scheme for the efficient evaluation of two-center integrals over contracted solid harmonic Gaussian functions is presented. Integral expressions are derived for local operators that depend on the position vector of one of the two Gaussian centers. These expressions are then used to derive the formula for three-index overlap integrals where two of the three Gaussians are located at the same center. The efficient evaluation of the latter is essential for local resolution-of-the-identity techniques that employ an overlap metric. We compare the performance of our integral scheme to the widely used Cartesian Gaussian-based method of Obara and Saika (OS). Non-local interaction potentials such as standard Coulomb, modified Coulomb, and Gaussian-type operators, which occur in range-separated hybrid functionals, are also included in the performance tests. The speed-up with respect to the OS scheme is up to three orders of magnitude for both integrals and their derivatives. In particular, our method is increasingly efficient for large angular momenta and highly contracted basis sets
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Antegrade common femoral artery closure device use is associated with decreased complications.
ObjectiveAntegrade femoral artery access is often used for ipsilateral infrainguinal peripheral vascular intervention. However, the use of closure devices (CD) for antegrade access (AA) is still considered outside the instructions for use for most devices. We hypothesized that CD use for antegrade femoral access would not be associated with an increased odds of access site complications.MethodsThe Vascular Quality Initiative was queried from 2010 to 2019 for infrainguinal peripheral vascular interventions performed via femoral AA. Patients who had a cutdown or multiple access sites were excluded. Cases were then stratified into whether a CD was used or not. Hierarchical multivariable logistic regressions controlling for hospital-level variation were used to examine the independent association between CD use and access site complications. A sensitivity analysis using coarsened exact matching was performed using factors different between treatment groups to reduce imbalance between the groups.ResultsOverall, 11,562 cases were identified and 5693 (49.2%) used a CD. Patients treated with a CD were less likely to be white (74.1% vs 75.2%), have coronary artery disease (29.7% vs 33.4%), use aspirin (68.7% vs 72.4%), and have heparin reversal with protamine (15.5% vs 25.6%; all P < .05). CD patients were more likely to be obese (31.6% vs 27.0%), have an elective operation (82.6% vs 80.1%), ultrasound-guided access (75.5% vs 60.6%), and a larger access sheath (6.0 ± 1.0 F vs 5.5 ± 1.0 F; P < .05 for all). CD cases were less likely to develop any access site hematoma (2.55% vs 3.53%; P < .01) or a hematoma requiring reintervention (0.63% vs 1.26%; P < .01) and had no difference in access site stenosis or occlusion (0.30% vs 0.22%; P = .47) compared with no CD. On multivariable analysis, CD cases had significantly decreased odds of developing any access site hematoma (odds ratio, 0.75; 95% confidence interval, 0.59-0.95) and a hematoma requiring intervention (odds ratio, 0.56; 95% confidence interval, 0.38-0.81). A sensitivity analysis after coarsened exact matching confirmed these findings.ConclusionsIn this nationally representative sample, CD use for AA was associated with a lower odds of hematoma in selected patients. Extending the instructions for use indications for CDs to include femoral AA may decrease the incidence of access site complications, patient exposure to reintervention, and costs to the health care system
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