77 research outputs found
Cavity cooling of a nanomechanical resonator by light scattering
We present a novel method for opto-mechanical cooling of sub-wavelength sized
nanomechanical resonators. Our scheme uses a high finesse Fabry-Perot cavity of
small mode volume, within which the nanoresonator is acting as a
position-dependant perturbation by scattering. In return, the back-action
induced by the cavity affects the nanoresonator dynamics and can cool its
fluctuations. We investigate such cavity cooling by scattering for a nanorod
structure and predict that ground-state cooling is within reach.Comment: 4 pages, 3 figure
The Adiabatic Transport of Bose-Einstein Condensates in a Double-Well Trap: Case a Small Nonlinearity
A complete adiabatic transport of Bose-Einstein condensate in a double-well
trap is investigated within the Landau-Zener (LZ) and Gaussian Landau-Zener
(GLZ) schemes for the case of a small nonlinearity, when the atomic interaction
is weaker than the coupling. The schemes use the constant (LZ) and
time-dependent Gaussian (GLZ) couplings. The mean field calculations show that
LZ and GLZ suggest essentially different transport dynamics. Significant
deviations from the case of a strong coupling are discussed.Comment: 6 pages, 3 figures, to be published in Laser Physic
STIRAP transport of Bose-Einstein condensate in triple-well trap
The irreversible transport of multi-component Bose-Einstein condensate (BEC)
is investigated within the Stimulated Adiabatic Raman Passage (STIRAP) scheme.
A general formalism for a single BEC in M-well trap is derived and analogy
between multi-photon and tunneling processes is demonstrated. STIRAP transport
of BEC in a cyclic triple-well trap is explored for various values of detuning
and interaction between BEC atoms. It is shown that STIRAP provides a complete
population transfer at zero detuning and interaction and persists at their
modest values. The detuning is found not to be obligatory. The possibility of
non-adiabatic transport with intuitive order of couplings is demonstrated.
Evolution of the condensate phases and generation of dynamical and geometric
phases are inspected. It is shown that STIRAP allows to generate the
unconventional geometrical phase which is now of a keen interest in quantum
computing.Comment: 9 pages, 6 figures. To be published in Laser Physics (v. 19, n.4,
2009
"Pair" Fermi contour and repulsion-induced superconductivity in cuprates
The pairing of charge carriers with large pair momentum is considered in
connection with high-temperature superconductivity of cuprate compounds. The
possibility of pairing arises due to some essential features of
quasi-two-dimensional electronic structure of cuprates: (i) The Fermi contour
with strong nesting features; (ii) The presence of extended saddle point near
the Fermi level; (iii) The existence of some ordered state (for example,
antiferromagnetic) close to the superconducting one as a reason for an
appearing of "pair" Fermi contour resulting from carrier redistribution in
momentum space. In an extended vicinity of the saddle point, momentum space has
hyperbolic (pseudoeuclidean) metrics, therefore, the principal values of
two-dimensional reciprocal reduced effective mass tensor have unlike signs.
Rearrangement of holes in momentum space results in a rise of "pair" Fermi
contour which may be defined as zero-energy line for relative motion of the
pair. The superconducting gap arises just on this line. Pair Fermi contour
formation inside the region of momentum space with hyperbolic metrics results
in not only superconducting pairing but in a rise of quasi-stationary state in
the relative motion of the pair. Such a state has rather small decay and may be
related to the pseudogap regime of underdoped cuprates. It is concluded that
the pairing in cuprates may be due to screened Coulomb repulsion. In this case,
the superconducting energy gap in hole-doped cuprates exists in the region of
hole concentration which is bounded both above and below. The superconducting
state with positive condensation energy exists in more narrow range of doping
level inside this region. Such hole concentration dependence correlates with
typical phase diagram of cuprates.Comment: 23 pages, 11 figures. Submitted to Phys. Rev.
Bogoliubov approach to superfluidity of atoms in an optical lattice
We use the Bogoliubov theory of atoms in an optical lattice to study the
approach to the Mott-insulator transition. We derive an explicit expression for
the superfluid density based on the rigidity of the system under phase
variations. This enables us to explore the connection between the quantum
depletion of the condensate and the quasi-momentum distribution on the one hand
and the superfluid fraction on the other. The approach to the insulator phase
may be characterized through the filling of the band by quantum depletion,
which should be directly observable via the matter wave interference patterns.
We complement these findings by self-consistent Hartree-Fock-Bogoliubov-Popov
calculations for one-dimensional lattices including the effects of a parabolic
trapping potential.Comment: 25 pages, 8 figure
The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description
On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds
Functional Filaments: Creating and Degrading pH-Indicating PLA Filaments for 3D Printing
With the rapid pace of advancements in additive manufacturing and techniques such as fused filament fabrication (FFF), the feedstocks used in these techniques should advance as well. While available filaments can be used to print highly customizable parts, the creation of the end part is often the only function of a given feedstock. In this study, novel FFF filaments with inherent environmental sensing functionalities were created by melt-blending poly(lactic acid) (PLA), poly(ethylene glycol) (PEG), and pH indicator powders (bromothymol blue, phenolphthalein, and thymol blue). The new PLA-PEG-indicator filaments were universally more crystalline than the PLA-only filaments (33â41% vs. 19% crystallinity), but changes in thermal stability and mechanical characteristics depended upon the indicator used; filaments containing bromothymol blue and thymol blue were more thermally stable, had higher tensile strength, and were less ductile than PLA-only filaments, while filaments containing phenolphthalein were less thermally stable, had lower tensile strength, and were more ductile. When the indicator-filled filaments were exposed to acidic, neutral, and basic solutions, all filaments functioned as effective pH sensors, though the bromothymol blue-containing filament was only successful as a base indicator. The biodegradability of the new filaments was evaluated by characterizing filament samples after aging in soil and soil slurry mixtures; the amount of physical deterioration and changes in filament crystallinity suggested that the bromothymol blue filament degraded faster than PLA-only filaments, while the phenolphthalein and thymol blue filaments saw decreases in degradation rates
Pre-breeding foraging ecology of three tern species nesting in the Gulf of Maine
A variety of seabird species migrate annually from wintering grounds in the Southern Hemisphere to the Gulf of Maine, USA to breed and raise their young. Post-migration, adult seabirds depend on the spatio-temporal match of reliable food resources to replenish energy reserves before breeding. However, the conditions during this critical window of time are becoming increasingly uncertain given the magnitude and pace at which climate change is impacting the Gulf of Maine region. We investigated the pre-breeding foraging ecology of Arctic Terns (Sterna paradisaea), Common Terns (S. hirundo), and the federally endangered Roseate Tern (S. dougallii) by analyzing stable carbon (ÎŽ13C) and nitrogen (ÎŽ15N) isotopes in eggshell tissues collected from seven islands in the Gulf of Maine from 2016 to 2018. Results show at the interspecific level, adult foraging patterns are consistent with expectations based on chick diets. At interisland and interannual scales, variation in isotopic values and niche breadths suggest foraging habits are highly localized. Although uncertainty remains, interannual trends also suggest warmer ocean conditions are either affecting tern foraging behaviors and/or prey resource availability during the late spring and early summer. Overall, results provide new information on adult tern foraging ecology in an important breeding area experiencing rapid environmental change
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