473 research outputs found
Diffraction-contrast imaging of cold atoms
We consider the inverse problem of in-line holography, applied to
minimally-destructive imaging of cold atom clouds. Absorption imaging
near-resonance provides a simple, but destructive measurement of atom column
density. Imaging off resonance greatly reduces heating, and sequential images
may be taken. Under the conditions required for off-resonant imaging, the
generally-intractable inverse problem may be linearized. A
minimally-destructive, quantitative and high-resolution image of the atom cloud
column density is then retrieved from a single diffraction pattern.Comment: 4 pages, 3 figures v2: minor changes in response to referee reports,
mostly additional experimental detail v3: revisions to figure 3: added trace
and changed image. Minor text and referencing changes. Accepted by Phys Rev A
(Rapid Commun
Plasma Physics
Contains reports on two research projects.United States Atomic Energy Commission (Contract AT(30-1)-1842
Atomic quasi-Bragg diffraction in a magnetic field
We report on a new technique to split an atomic beam coherently with an
easily adjustable splitting angle. In our experiment metastable helium atoms in
the |{1s2s}^3S_1 M=1> state diffract from a polarization gradient light field
formed by counterpropagating \sigma^+ and \sigma^- polarized laser beams in the
presence of a homogeneous magnetic field. In the near-adiabatic regime, energy
conservation allows the resonant exchange between magnetic energy and kinetic
energy. As a consequence, symmetric diffraction of |M=0> or |M=-1> atoms in a
single order is achieved, where the order can be chosen freely by tuning the
magnetic field. We present experimental results up to 6th order diffraction (24
\hbar k momentum splitting, i.e., 2.21 m/s in transverse velocity) and present
a simple theoretical model that stresses the similarity with conventional Bragg
scattering. The resulting device constitutes a flexible, adjustable,
large-angle, three-way coherent atomic beam splitter with many potential
applications in atom optics and atom interferometry.Comment: 4 pages, 5 figure
Plasma Physics
Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(30- 1)- 1842
General public’s privacy concerns regarding drone use in residential and public areas:Empirical research report, May 2017
Chiral shape fluctuations and the origin of chirality in cholesteric phases of DNA origamis
Lyotropic cholesteric liquid crystal phases are ubiquitously observed in
biological and synthetic polymer solutions, characterized by a complex
interplay between thermal fluctuations, entropic and enthalpic forces. The
elucidation of the link between microscopic features and macroscopic chiral
structure, and of the relative roles of these competing contributions on phase
organization, remains a topical issue. Here we provide theoretical evidence of
a novel mechanism of chirality amplification in lyotropic liquid crystals,
whereby phase chirality is governed by fluctuation-stabilized helical
deformations in the conformations of their constituent molecules. Our results
compare favorably to recent experimental studies of DNA origami assemblies and
demonstrate the influence of intra-molecular mechanics on chiral
supra-molecular order, with potential implications for a broad class of
experimentally-relevant colloidal systems
Origin of the overall water splitting activity of Ta3N5 revealed by ultrafast transient absorption spectroscopy
Tantalum nitride (Ta3N5) is one of the few visible light absorbing photocatalysts capable of overall water splitting (OWS), by which the evolution of both H2 and O2 is possible. Despite favourable energetics, realizing the OWS or efficient H2 evolution in Ta3N5 prepared by the nitridation of tantalum oxide (Ta2O5) or Ta foil remains a challenge even after 15 years of intensive research. Recently our group demonstrated OWS in Ta3N5 when prepared by the short time nitridation of potassium tantalate (KTaO3). To obtain a mechanistic insight on the role of Ta precursor and nitridation time in realizing OWS, ultrafast dynamics of electrons (3435 nm probe) and holes (545 nm probe) is investigated using transient absorption spectroscopy. Electrons decay majorly by trapping in Ta3N5 prepared by the nitridation of Ta2O5, which do not show OWS. However, OWS activity in Ta3N5 prepared by 0.25 hour nitridation of KTaO3 is particularly favoured by the virtually absent electron and hole trapping. On further increasing the nitridation time of KTaO3 from 0.25 to 10 hour, trapping of both electron and hole is enhanced which concurrently results in a reduction of the OWS activity. Insights from correlating the synthesis conditions—structural defects—carrier dynamics—photocatalytic activity is of importance in designing novel photocatalysts to enhance solar fuel production
A proposal for curriculum content in transfusion medicine and blood banking education in pathology residency programs
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71606/1/j.1537-2995.2007.01417.x.pd
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