545 research outputs found
Imaging Molecules from Within: Ultra-fast, {\AA}ngstr\"om Scale Structure Determination of Molecules via Photoelectron Holography using Free Electron Lasers
A new scheme based on (i) upcoming brilliant X-ray Free Electron Laser (FEL)
sources, (ii) novel energy and angular dispersive, large-area electron imagers
and (iii) the well-known photoelectron holography is elaborated that provides
time-dependent three-dimensional structure determination of small to medium
sized molecules with {\AA}ngstr\"om spatial and femtosecond time resolution.
Inducing molecular dynamics, wave-packet motion, dissociation, passage through
conical intersections or isomerization by a pump pulse this motion is
visualized by the X-ray FEL probe pulse launching keV photoelectrons within few
femtoseconds from specific and well-defined sites, deep core levels of
individual atoms, inside the molecule. On their way out the photoelectrons are
diffracted generating a hologram on the detector that encodes the molecular
structure at the instant of photoionization, thus providing 'femtosecond
snapshot images of the molecule from within'. Detailed calculations in various
approximations of increasing sophistication are presented and three-dimensional
retrieval of the spatial structure of the molecule with {\AA}ngstr\"om spatial
resolution is demonstrated. Due to the large photo-absorption cross sections
the method extends X-ray diffraction based, time-dependent structure
investigations envisioned at FELs to new classes of samples that are not
accessible by any other method. Among them are dilute samples in the gas phase
such as aligned, oriented or conformer selected molecules, ultra-cold ensembles
and/or molecular or cluster objects containing mainly light atoms that do not
scatter X-rays efficiently.Comment: 18 pages, 11 figure
Spectrophotometric experiment on the Verera-11 and Venera-12 descent vehicles: Some results of the analysis of the spectrum of the daytime sky of Venus
The spectra of the daytime sky of Venus were recorded on the Venera-11 and Venera-12 descent vehicles at various altitudes above the planet's surface, within the interval of 4500 to 12,000 Angstroms. The angular distribution of the brightness of the scattered radiation was recorded and the ratio of water and carbon dioxide were studied, with respect to the cloud cover boundaries
Results and interpretation of measurements of the light flux in the near-surface layer of the Venusian atmosphere
The characteristics of the field of radiation in the near surface layer of the atmosphere and on the surface of Venus are reported. Optical measurements made during the landing of the descent vehicles are described. The relief of the surface and the amount of dust on it are examined. The spectral relationship of the albedo of the soil and the light flux incident on the surface is discussed
Scintillation counter with MRS APD light readout
START, a high-efficiency and low-noise scintillation detector for ionizing
particles, was developed for the purpose of creating a high-granular system for
triggering cosmic muons. Scintillation light in START is detected by MRS APDs
(Avalanche Photo-Diodes with Metal-Resistance-Semiconductor structure),
operated in the Geiger mode, which have 1 mm^2 sensitive areas. START is
assembled from a 15 x 15 x 1 cm^3 scintillating plastic plate, two MRS APDs and
two pieces of wavelength-shifting optical fiber stacked in circular coils
inside the plastic. The front-end electronic card is mounted directly on the
detector. Tests with START have confirmed its operational consistency, over 99%
efficiency of MIP registration and good homogeneity. START demonstrates a low
intrinsic noise of about 10^{-2} Hz. If these detectors are to be
mass-produced, the cost of a mosaic array of STARTs is estimated at a moderate
level of 2-3 kUSD/m^2.Comment: 6 pages, 5 figure
Exact Solutions for Domain Walls in Coupled Complex Ginzburg - Landau Equations
The complex Ginzburg Landau equation (CGLE) is a ubiquitous model for the
evolution of slowly varying wave packets in nonlinear dissipative media. A
front (shock) is a transient layer between a plane-wave state and a zero
background. We report exact solutions for domain walls, i.e., pairs of fronts
with opposite polarities, in a system of two coupled CGLEs, which describe
transient layers between semi-infinite domains occupied by each component in
the absence of the other one. For this purpose, a modified Hirota bilinear
operator, first proposed by Bekki and Nozaki, is employed. A novel
factorization procedure is applied to reduce the intermediate calculations
considerably. The ensuing system of equations for the amplitudes and
frequencies is solved by means of computer-assisted algebra. Exact solutions
for mutually-locked front pairs of opposite polarities, with one or several
free parameters, are thus generated. The signs of the cubic gain/loss, linear
amplification/attenuation, and velocity of the coupled-front complex can be
adjusted in a variety of configurations. Numerical simulations are performed to
study the stability properties of such fronts.Comment: Journal of the Physical Society of Japan, in pres
Magnetostimulated Chandges of Microhardness in Potassium Acid Phthalate Crystals
A decrease in microhardness along the (010) cleavage in potassium acid
phthalate single crystals by 15--18% after the application of a permanent
magnetic field was revealed for the first time. It is shown that the effect
revealed is of the volume character. The role of interlayer water in the
processes stimulated by a magnetic field is studied., Interlayer water plays
does not cause the observed changes it only plays the part of an indicator of
these changes in potassium acid phthalate crystals in a magnetic field. It is
established that microhardness in the (100) plane of the crystal in an applied
a magnetic field first increases by 12--15% and then remains constant in time
within the accuracy of the experiment. The possibility of varying the crystal
structure of potassium acid phthalate crystals by applying magnetic fields
inducing rearrangement in the system of hydrogen bonds or in the defect
structure is discussed.Comment: 6 pages, 7 figure
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