4,202 research outputs found
Columbia/Einstein observations of extragalactic X-ray sources
Results are presented of the analysis of data from observations of extragalactic objects with the imaging proportional counter on board the Einstein Observatory. Surveys of normal galaxies, radio galaxies, active galaxies, quasars and BL Lacs, and clusters of galaxies were studied in order to improve the understanding of the origin of the Milky Way Galaxy
An imaging gas scintillation proportional counter for the detection of subkiloelectron-volt X-rays
A large area imaging gas scintillation proportional counter (IGSPC) was constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counted (GSPC) with a micron polyprotylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. Over a sensitive area of 21 cu cm the instrument has a measured energy resolution of 17.5% (FWHM) and 1.9 mm (FWHM) spatial resolution at 1.5 keV
Thermal analysis comparison between two random glass fibre reinforced thermoplastic matrix composites bonded by adhesives using microwaves: preliminary results
[Abstract]: This paper compares the thermal analysis of two types of random glass fibre reinforced thermoplastic matrix composites joined by adhesives using microwave energy. Fixed frequency, 2.45 GHz, microwave facility is used to join thirty three percent by weight random glass fibre reinforced polystyrene composite [PS/GF (33%)] and thirty three percent by weight random glass fibre reinforced low density polyethylene composite [LDPE/GF (33%)]. The facility used is shown in Figure 1. With a given power level, the composites were exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive. The heat distribution of the samples of the two types of composites was analysed and compared. The relationship between the heat distribution and the lap shear strength of the samples was also compared and discussed
Evolution of Fermion Pairing from Three to Two Dimensions
We follow the evolution of fermion pairing in the dimensional crossover from
3D to 2D as a strongly interacting Fermi gas of Li atoms becomes confined
to a stack of two-dimensional layers formed by a one-dimensional optical
lattice. Decreasing the dimensionality leads to the opening of a gap in
radio-frequency spectra, even on the BCS-side of a Feshbach resonance. The
measured binding energy of fermion pairs closely follows the theoretical
two-body binding energy and, in the 2D limit, the zero-temperature mean-field
BEC-BCS theory.Comment: 5 pages, 4 figure
Unusual photoemission resonances of oxygen-dopant induced states in BiSrCaCuO
We have performed an angular-resolved photoemission study of underdoped,
optimally doped and overdoped BiSrCaCuO samples using a
wide photon energy range (15 - 100 eV). We report a small and broad
non-dispersive A peak in the energy distribution curves whose intensity
scales with doping. We attribute it to a local impurity state similar to the
one observed recently by scanning tunneling spectroscopy and identified as the
oxygen dopants. Detailed analysis of the resonance profile and comparison with
the single-layered BiSrCuO suggest a mixing of this local
state with Cu via the apical oxygens.Comment: 4 pages, 4 figure
Fabrication and Characterization of Modulation-Doped ZnSe/(Zn,Cd)Se (110) Quantum Wells: A New System for Spin Coherence Studies
We describe the growth of modulation-doped ZnSe/(Zn,Cd)Se quantum wells on
(110) GaAs substrates. Unlike the well-known protocol for the epitaxy of
ZnSe-based quantum structures on (001) GaAs, we find that the fabrication of
quantum well structures on (110) GaAs requires significantly different growth
conditions and sample architecture. We use magnetotransport measurements to
confirm the formation of a two-dimensional electron gas in these samples, and
then measure transverse electron spin relaxation times using time-resolved
Faraday rotation. In contrast to expectations based upon known spin relaxation
mechanisms, we find surprisingly little difference between the spin lifetimes
in these (110)-oriented samples in comparison with (100)-oriented control
samples.Comment: To appear in Journal of Superconductivity (Proceedings of 3rd
Conference on Physics and Applications of Spin-dependent Phenomena in
Semiconductors
Revealing the Superfluid Lambda Transition in the Universal Thermodynamics of a Unitary Fermi Gas
We have observed the superfluid phase transition in a strongly interacting
Fermi gas via high-precision measurements of the local compressibility, density
and pressure down to near-zero entropy. Our data completely determine the
universal thermodynamics of strongly interacting fermions without any fit or
external thermometer. The onset of superfluidity is observed in the
compressibility, the chemical potential, the entropy, and the heat capacity. In
particular, the heat capacity displays a characteristic lambda-like feature at
the critical temperature of . This is the first clear
thermodynamic signature of the superfluid transition in a spin-balanced atomic
Fermi gas. Our measurements provide a benchmark for many-body theories on
strongly interacting fermions, relevant for problems ranging from
high-temperature superconductivity to the equation of state of neutron stars.Comment: 11 pages, 8 figure
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