100,856 research outputs found
Multilayer gas cells for sub-Doppler spectroscopy
We have carried out theoretical research on ultra-high resolution
spectroscopy of atoms (or molecules) in the suggested cell with a series of
plane-parallel thin gas layers between spatially separated gas regions of this
cell for optical pumping and probing. It is shown the effective velocity
selection of optically pumped atoms because of their specific transit time and
collisional relaxation in such a cell, which lead to narrow sub-Doppler
resonances in absorption of the probe monochromatic light beam. Resolution of
this spectroscopic method is analyzed in cases of stationary and definite
nonstationary optical pumping of atoms by the broadband radiation versus
geometrical parameters of given cells and pumping intensity. The suggested
multilayer gas cell is the compact analog of many parallel atomic (molecular)
beams and may be used also as the basis of new compact optical frequency
standards of high accuracy.Comment: 12 pages, 4 figure
Saturation effects in the sub-Doppler spectroscopy of Cesium vapor confined in an Extremely Thin Cell
Saturation effects affecting absorption and fluorescence spectra of an atomic
vapor confined in an Extremely Thin Cell (cell thickness ) are
investigated experimentally and theoretically. The study is performed on the
line ( of and concentrates on the two
situations and , the most contrasted ones with
respect to the length dependence of the coherent Dicke narrowing. For , the Dicke-narrowed absorption profile simply broadens and
saturates in amplitude when increasing the light intensity, while for , sub-Doppler dips of reduced absorption at line-center appear on the
broad absorption profile. For a fluorescence detection at ,
saturation induces narrow dips, but only for hyperfine components undergoing a
population loss through optical pumping. These experimental results are
interpreted with the help of the various existing models, and are compared with
numerical calculations based upon a two-level modelling that considers both a
closed and an open system.Comment: 11 pages, 12 figure
Full-scale crash test of a CH-47C helicopter
A full-scale crash test of a large troop/cargo carrying CH-47C helicopter was conducted at the Langley impact dynamics research facility. The crash test of this large helicopter was performed as part of a joint U.S. Army-NASA helicopter test program to provide dynamic structural and seat response data. The test, the procedures employed, the instrumentation, a general assessment of the resulting damage, and typical levels of accelerations experienced during the crash are reported. Various energy-absorbing seating systems for crew and troops were installed and instrumented to provide data for use in the development of design criteria for future aircraft. The crash conditions were selected to simulate known crash conditions and are representative of the 95th percentile accident environment for an autorotating helicopter. Visual examination of the crashed test specimen indicated irreparable damage to many of the structural components. The highest accelerations were recorded by the accelerometers located on the cabin floor in the aft section of the helicopter, directly above the primary impact location and on the floor of the cockpit above the secondary impact location(s)
An Extension of the Character Ring of sl(3) and Its Quantisation
We construct a commutative ring with identity which extends the ring of
characters of finite dimensional representations of sl(3). It is generated by
characters with values in the group ring of the extended affine
Weyl group of at . The `quantised' version at
rational level realises the fusion rules of a WZW conformal field
theory based on admissible representations of .Comment: contains two TeX files: main file using harvmac.tex, amssym.def,
amssym.tex, 35p.; file with figures using XY-pic package, 4p; v2: minor
corrections, Note adde
S_4-symmetry of 6j-symbols and Frobenius-Schur indicators in rigid monoidal C^*-categories
We show that a left-rigid monoidal C^*-category with irreducible monoidal
unit is also a sovereign and spherical category. Defining a Frobenius-Schur
type indicator we obtain selection rules for the fusion coefficients of
irreducible objects. As a main result we prove S_4-invariance of 6j-symbols in
such a category.Comment: 21 pages + 16 pages with figures; LaTeX2e plus macro package XYpic;
file with included pictures available as
http://www.desy.de/~jfuchs/s4/s4.ps.g
Charge control experiments on a CH-53E helicopter in a dusty environment
Charge control tests were carried out on a ground based, Marine Corps helicopter to determine if control of the electric fields acting on the engine exhaust gases could be used to reduce the electrification of the helicopter when it operated in a dusty atmosphere. The test aircraft was flown to a dusty, unpaved area and was then isolated electrically from the earth. When the helicopter engines were operated at ground idle with the rotor locked, the isolated aircraft charged positively, as had been observed previously. However, when the rotor brake was released and the turning rotor created a downdraft that raised dust clouds, the aircraft always became charged more positively, to potentials ranging form +30 to +45 kV. The dust clouds raised by the rotor downwash invariably carried negative space charges with concentrations of up to -100 nC/cu m and caused surface electric fields with strengths of up to 10 kV/m immediately down wind of the aircraft. The natural charging of the helicopter operating in these dust clouds was successfully opposed by control of the electric fields acting on the hot, electrically conductive exhaust gases. The control was achieved by placing electrostatic shield around the exhausts
Entanglement swapping using continuous variables
We investigate the efficacy with which entanglement can be teleported using a
continuous measurement scheme. We show that by using the correct gain for the
classical channel the degree of violation of locality that can be demonstrated
(using a CH type inequality) is {\it not} a function of the level of
entanglement squeezing used in the teleportation. This is possible because a
gain condition can always be choosen such that passage through the teleporter
is equivalent to pure attenuation of the input field.Comment: 8 pages, 4 figure
Is it more difficult to write or to cite a paper?
The structure of various indices that are used to evaluate the research output of a scientist is discussed on a moral base.Indices should be used with caution. Albeit scientists who work in the field of infometrics are aware on this, other scientistsof other disciplines may not be fully aware. Measuring quality in science is only the half story. Some verbal description isrequired too
- …