2,746 research outputs found
Energy loss mechanism for suspended micro- and nanoresonators due to the Casimir force
A so far not considered energy loss mechanism in suspended micro- and
nanoresonators due to noncontact acoustical energy loss is investigated
theoretically. The mechanism consists on the conversion of the mechanical
energy from the vibratory motion of the resonator into acoustic waves on large
nearby structures, such as the substrate, due to the coupling between the
resonator and those structures resulting from the Casimir force acting over the
separation gaps. Analytical expressions for the resulting quality factor Q for
cantilever and bridge micro- and nanoresonators in close proximity to an
underlying substrate are derived and the relevance of the mechanism is
investigated, demonstrating its importance when nanometric gaps are involved
Self-similar impulsive capillary waves on a ligament
We study the short-time dynamics of a liquid ligament, held between two solid
cylinders, when one is impulsively accelerated along its axis. A set of
one-dimensional equations in the slender-slope approximation is used to
describe the dynamics, including surface tension and viscous effects. An exact
self-similar solution to the linearized equations is successfully compared to
experiments made with millimetric ligaments. Another non-linear self-similar
solution of the full set of equations is found numerically. Both the linear and
non-linear solutions show that the axial depth at which the liquid is affected
by the motion of the cylinder scales like . The non-linear solution
presents the peculiar feature that there exists a maximum driving velocity
above which the solution disappears, a phenomenon probably related to
the de-pinning of the contact line observed in experiments for large pulling
velocities
Wannier-Stark ladders in one-dimensional elastic systems
The optical analogues of Bloch oscillations and their associated
Wannier-Stark ladders have been recently analyzed. In this paper we propose an
elastic realization of these ladders, employing for this purpose the torsional
vibrations of specially designed one-dimensional elastic systems. We have
measured, for the first time, the ladder wave amplitudes, which are not
directly accessible either in the quantum mechanical or optical cases. The wave
amplitudes are spatially localized and coincide rather well with theoretically
predicted amplitudes. The rods we analyze can be used to localize different
frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let
Anomalous quantum chaotic behavior in nanoelectromechanical structures
It is predicted that for sufficiently strong electron-phonon coupling an
anomalous quantum chaotic behavior develops in certain types of suspended
electro-mechanical nanostructures, here comprised by a thin cylindrical quantum
dot (billiard) on a suspended rectangular dielectric plate. The deformation
potential and piezoelectric interactions are considered. As a result of the
electron-phonon coupling between the two systems the spectral statistics of the
electro-mechanic eigenenergies exhibit an anomalous behavior. If the center of
the quantum dot is located at one of the symmetry axes of the rectangular
plate, the energy level distributions correspond to the Gaussian Orthogonal
Ensemble (GOE), otherwise they belong to the Gaussian Unitary Ensemble (GUE),
even though the system is time-reversal invariant.Comment: 4 pages, pdf forma
Artemis Curation: Preparing for Sample Return from the Lunar South Pole
Space Policy Directive-1 mandates that the United States will lead the return of humans to the Moon for long-term exploration and utilization, followed by human missions to Mars and other destinations. In addition, the Vice President stated that It is the stated policy of this administration and the United States of America to return American astronauts to the Moon within the next five years, that is, by 2024. These efforts, under the umbrella of the recently formed Artemis Program, include such historic goals as the flight of the first woman to the Moon and the exploration of the lunar south-polar region. Among the top priorities of the Artemis Program is the return of a suite of geologic samples, providing new and significant opportunities for progressing lunar science and human exploration. In particular, successful sample return is necessary for understanding the history of volatiles in the Solar System and the evolution of the Earth-Moon system, fully constraining the hazards of the lunar polar environment for astronauts, and providing the necessary data for constraining the abundance and distribution of resources for in-situ resource utilization (ISRU). Here we summarize the ef-forts of the Astromaterials Acquisition and Curation Office (hereafter referred to as the Curation Office) to ensure the success of Artemis sample return (per NASA Policy Directive (NPD) 7100.10E)
Quantum chaos in nanoelectromechanical systems
We present a theoretical study of the electron-phonon coupling in suspended
nanoelectromechanical systems (NEMS) and investigate the resulting quantum
chaotic behavior. The phonons are associated with the vibrational modes of a
suspended rectangular dielectric plate, with free or clamped boundary
conditions, whereas the electrons are confined to a large quantum dot (QD) on
the plate's surface. The deformation potential and piezoelectric interactions
are considered. By performing standard energy-level statistics we demonstrate
that the spectral fluctuations exhibit the same distributions as those of the
Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE),
therefore evidencing the emergence of quantum chaos. That is verified for a
large range of material and geometry parameters. In particular, the GUE
statistics occurs only in the case of a circular QD. It represents an anomalous
phenomenon, previously reported for just a small number of systems, since the
problem is time-reversal invariant. The obtained results are explained through
a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column
Reconstruction microchirurgicale et prise en charge globale des patients porteurs de cancer ORL : lâimportance dâune approche qualitĂ© et dâun circuit protocolisĂ© [Microsurgical reconstruction and full management of patients with head and neck cancer: Importance of a quality approach and a circuit protocolisation]
Main of study: Management and surgical reconstruction of head and neck cancers remain a challenge. From the first consultation to surgery and radiotherapy, it is necessary to save time to ensure optimum treatment and better survival rates. Objectif: To establish a kind of quality approach to the management of patients with head and neck cancers. 54 patients who had microsurgical reconstruction after head and neck cancer were included in this study between 1997 and 2006. Results : Multiple data were considered: body mass index (BMI), ASA stage, age, existence of a pre-or postoperative radiotherapy, the surgeon's experience and the number of veins drainage. The success rate is superior when more than one draining vein is sutured to the flap for patients with a BMI > 20. Radiotherapy does not seem to affect the survival of the flap. Conclusion: According to current literature, the survival rate of these patients is better when the overall time care is less than 100 days. That period is possible with a perfect organization of the medical and paramedical team. Therefore, we propose to include these patients in a circuit protocolisation care, which saves time, to better inform patients and improve survival rates.
Buts: la prise en charge et la reconstruction chirurgicale des cancers ORL restent un challenge. De la premiĂšre consultation Ă la chirurgie et la radiothĂ©rapie, il est nĂ©cessaire de gagner du temps afin dâassurer une traitement optimum et un meilleur taux de survie. Objectif : Ă©tablir une sorte dâapproche qualitĂ© de la prise en charge des patients porteurs de cancers ORL. 54 patients qui ont bĂ©nĂ©ficiĂ© dâune reconstruction microchirurgicale suite Ă un cancer ORL ont Ă©tĂ© inclus dans cette Ă©tude entre 1997 et 2006. RĂ©sultats : plusieurs donnĂ©es ont Ă©tĂ© Ă©tudiĂ©es : lâindex de masse corporelle (IMC), le stade ASA, lâĂąge, lâexistence dâune radiothĂ©rapie prĂ© ou post opĂ©ratoire, lâexpĂ©rience du chirurgien ainsi que le nombre de veines de drainage. Le taux de succĂšs se rĂ©vĂšle supĂ©rieur lorsque plus dâune veine de drainage est suturĂ©e au lambeau, pour des patients ayant un IMC > 20. La radiothĂ©rapie ne semble pas avoir de rĂ©percussion sur la survie du lambeau. Conclusion : conformĂ©ment Ă la littĂ©rature actuelle, le taux de survie de ces patients est meilleur lorsque le temps global de prise en charge est infĂ©rieur Ă 100 jours. Ce dĂ©lai court nâest possible quâavec une parfaite organisation de lâĂ©quipe mĂ©dicale et paramĂ©dicale. De ce fait, nous proposons dâinclure ces patients dans un circuit de prise en charge protocolisĂ©, ce qui permet de gagner du temps, de mieux informer le patient et dâamĂ©liorer le taux de survie
Gaussian random waves in elastic media
Similar to the Berry conjecture of quantum chaos we consider elastic analogue
which incorporates longitudinal and transverse elastic displacements with
corresponding wave vectors. Based on that we derive the correlation functions
for amplitudes and intensities of elastic displacements. Comparison to numerics
in a quarter Bunimovich stadium demonstrates excellent agreement.Comment: 4 pages, 4 figure
Atomic layer deposition of cobalt phosphide for efficient water splitting
Transitionâmetal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin CoâP films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by selfâlimited layerâbyâlayer growth, and the deposited CoâP films were highly pure and smooth. The CoâP films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar CoâP films prepared by the traditional postâphosphorization method. Moreover, the deposition of ultrathin CoâP films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex threeâdimensional (3D) architectures
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