235 research outputs found
Potential Harmonics Expansion Method for Trapped Interacting Bosons : Inclusion of Two-Body Correlation
We study a system of identical interacting bosons trapped by an external
field by solving ab initio the many-body Schroedinger equation. A complete
solution by using, for example, the traditional hyperspherical harmonics (HH)
basis develops serious problems due to the large degeneracy of HH basis,
symmetrization of the wave function, calculation of the matrix elements, etc.
for large . Instead of the HH basis, here we use the "potential harmonics"
(PH) basis, which is a subset of HH basis. We assume that the contribution to
the orbital and grand orbital [in -dimensional space of the reduced
motion] quantum numbers comes only from the interacting pair. This implies
inclusion of two-body correlations only and disregard of all higher-body
correlations. Such an assumption is ideally suited for the Bose-Einstein
condensate (BEC), which is extremely dilute. Unlike the hyperspherical
variables in HH basis, the PH basis involves only three {\it{active}}
variables. It drastically reduces the number of coupled equations and
calculation of the potential matrix becomes tremendously simplified, as it
involves integrals over only three variables for any . One can easily
incorporate realistic atom-atom interactions in a straight forward manner. We
study the ground and excited state properties of the condensate for both
attractive and repulsive interactions for various particle number.Comment: 36 pages, 7 included figures, plain late
Condenser-free contrast methods for transmitted-light microscopy
Phase contrast microscopy allows the study of highly transparent yet detail-rich specimens by producing intensity contrast from phase objects within the sample. Presented here is a generalized phase contrast illumination schema in which condenser optics are entirely abrogated, yielding a condenser- free yet highly effective method of obtaining phase contrast in transmitted-light microscopy. A ring of light emitting diodes (LEDs) is positioned within the light-path such that observation of the objective back focal plane places the il- luminating ring in appropriate conjunction with the phase ring. It is demonstrated that true Zernike phase contrast is obtained, whose geometry can be flexibly manipulated to provide an arbitrary working distance between illuminator and sample. Condenser-free phase contrast is demonstrated across a range of magnifications (4–100×), numerical apertures (0.13–1.65NA) and conventional phase positions. Also demonstrated is condenser-free darkfield microscopy as well as combinatorial contrast including Rheinberg illumination and simultaneous, colour-contrasted, brightfield, darkfield and Zernike phase contrast. By providing enhanced and arbitrary working space above the preparation, a range of concurrent imaging and electrophysiological techniques will be technically facilitated. Condenser-free phase contrast is demonstrated in conjunction with scanning ion conductance microscopy (SICM), using a notched ring to admit the scanned probe. The compact, versatile LED illumination schema will further lend itself to novel next-generation transmitted-light microscopy designs. The condenser-free illumination method, using rings of independent or radially-scanned emitters, may be exploited in future in other electromagnetic wavebands, including X-rays or the infrared
A comparative evaluation of interest point detectors and local descriptors for visual SLAM
Abstract In this paper we compare the behavior of different interest points detectors and descriptors under the
conditions needed to be used as landmarks in vision-based simultaneous localization and mapping (SLAM).
We evaluate the repeatability of the detectors, as well as the invariance and distinctiveness of the descriptors,
under different perceptual conditions using sequences of images representing planar objects as well as 3D scenes.
We believe that this information will be useful when selecting an appropriat
Remarkable enhancement in crystalline perfection, second harmonic generation efficiency, optical transparency, and laser damage threshold in potassium dihydrogen phosphate crystals by L-threonine doping
Effect of L-threonine (LT) doping on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency, and laser damage threshold (LDT) in potassium dihydrogen phosphate (KDP) crystals grown by slow evaporation solution technique (SEST) has been investigated. The influence of doping on growth rate and morphology of the grown crystals has also been studied. Powder x-ray diffraction data confirms the crystal structure of KDP and shows a systematic variation in intensity of diffraction peaks in correlation with morphology due to varying LT concentration. No extra phase formation was observed which is further confirmed by Fourier transform Raman (FT-Raman) studies. High-resolution x-ray diffraction curves indicate that crystalline perfection has been improved to a great extent at low concentrations with a maximum perfection at 1 mol % doping. At higher concentrations (5 to 10 mol %), it is slightly reduced due to excess incorporation of dopants at the interstitial sites of the crystalline matrix. LDT has been increased considerably with increase in doping concentration, whereas SHG efficiency was found to be maximum at 1 mol % in correlation with crystalline. The optical transparency for doped crystals has been increased as compared to that of pure KDP with a maximum value at 1 mol % doping
Effect of a Physical Phase Plate on Contrast Transfer in an Aberration-Corrected Transmission Electron Microscope
In this theoretical study we analyze contrast transfer of weak-phase objects
in a transmission electron microscope, which is equipped with an aberration
corrector (Cs-corrector) in the imaging lens system and a physical phase plate
in the back focal plane of the objective lens. For a phase shift of pi/2
between scattered and unscattered electrons induced by a physical phase plate,
the sine-type phase contrast transfer function is converted into a cosine-type
function. Optimal imaging conditions could theoretically be achieved if the
phase shifts caused by the objective lens defocus and lens aberrations would be
equal zero. In reality this situation is difficult to realize because of
residual aberrations and varying, non-zero local defocus values, which in
general result from an uneven sample surface topography. We explore the
conditions - i.e. range of Cs-values and defocus - for most favourable contrast
transfer as a function of the information limit, which is only limited by the
effect of partial coherence of the electron wave in Cs-corrected transmission
electron microscopes. Under high-resolution operation conditions we find that a
physical phase plate improves strongly low- and medium-resolution object
contrast, while improving tolerance to defocus and Cs-variations, compared to a
microscope without a phase plate
Proton-He elastic scattering at low energies
We present new accurate measurements of the differential cross section
and the proton analyzing power for proton-He
elastic scattering at various energies. A supersonic gas jet target has been
employed to obtain these low energy cross section measurements. The
distributions have been measured at = 0.99, 1.59,
2.24, 3.11, and 4.02 MeV. Full angular distributions of have been
measured at = 1.60, 2.25, 3.13, and 4.05 MeV. This set of
high-precision data is compared to four-body variational calculations employing
realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the
unpolarized cross section the agreement between the theoretical calculation and
data is good when a potential is used. The comparison between the
calculated and measured proton analyzing powers reveals discrepancies of
approximately 50% at the maximum of each distribution. This is analogous to the
existing `` Puzzle'' known for the past 20 years in nucleon-deuteron
elastic scattering.Comment: 22 pages, 9 figures, to be published in Physical Review C, corrected
reference 4
Wideband THz time domain spectroscopy based on optical rectification and electro-optic sampling
We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement
Watching a superfluid untwist itself: Recurrence of Rabi oscillations in a Bose-Einstein condensate
The order parameter of a condensate with two internal states can continuously
distort in such a way as to remove twists that have been imposed along its
length. We observe this effect experimentally in the collapse and recurrence of
Rabi oscillations in a magnetically trapped, two-component Bose-Einstein
condensate of ^87Rb
Soft X-Ray Projection Lithography Using a 1-1 Ring Field Optical-System
An iridium-coated Offner 1:1 ring field camera has been used to carry out projection lithography using 42 nm light from an undulator in the vacuum ultra violet storage ring at Brookhaven National Laboratory. Near-diffraction-limited resolution has been obtained showing features as small as 0.2-mu-m within a 2 mm x 0.25 mm image field. Images of both transmission and reflection masks have been obtained. The impact of source coherence on imagery has been investigated. Hydrocarbon contamination problems experienced in this photon energy range have been investigated and possible solutions are suggested
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