6,510 research outputs found
Study of boundary-layer transition using transonic-cone preston tube data
The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones
Designable buried waveguides in sapphire by proton implantation
Buried and stacked planar as well as buried single and parallel channel waveguides are fabricated in sapphire by proton implantation. Good control of the implantation parameters provides excellent confinement of the guided light in each structure. Low propagation losses are obtained in fundamental-mode, buried channel waveguides without postimplantation annealing. Choice of the implantation parameters allows one to design mode shapes with different ellipticity and/or mode asymmetry in each orthogonal direction, thus demonstrating the versatility of the fabrication method. Horizontal and vertical parallelization is demonstrated for the design of one- or two-dimensional waveguide arrays in hard crystalline materials
Sapphire planar waveguides fabricated by H+ ion beam implantation
1.1-MeV proton-implanted sapphire waveguides are investigated for the first time. Optical measurements show that the planar waveguides support low-order transverse-mode propagation with good guiding properties without the need to anneal the samples
Proton implanted sapphire planar and channel waveguides
We report low-order transverse-mode planar waveguides in sapphire fabricated for the first time by proton implantation. The waveguides show good guiding properties without post-implantation annealing. Channel waveguiding was achieved by polyimide strip-loading
Irreversible flow of vortex matter: polycrystal and amorphous phases
We investigate the microscopic mechanisms giving rise to plastic depinning
and irreversible flow in vortex matter. The topology of the vortex array
crucially determines the flow response of this system. To illustrate this
claim, two limiting cases are considered: weak and strong pinning interactions.
In the first case disorder is strong enough to introduce plastic effects in the
vortex lattice. Diffraction patterns unveil polycrystalline lattice topology
with dislocations and grain boundaries determining the electromagnetic response
of the system. Filamentary flow is found to arise as a consequence of
dislocation dynamics. We analize the stability of vortex lattices against the
formation of grain boundaries, as well as the steady state dynamics for
currents approaching the depinning critical current from above, when vortex
motion is mainly localized at the grain boundaries. On the contrary, a
dislocation description proves no longer adequate in the second limiting case
examined. For strong pinning interactions, the vortex array appears completely
amorphous and no remnant of the Abrikosov lattice order is left. Here we obtain
the critical current as a function of impurity density, its scaling properties,
and characterize the steady state dynamics above depinning. The plastic
depinning observed in the amorphous phase is tightly connected with the
emergence of channel-like flow. Our results suggest the possibility of
establishing a clear distinction between two topologically disordered vortex
phases: the vortex polycrystal and the amorphous vortex matter.Comment: 13 pages, 16 figure
Fabrication of optical planar waveguides in by He-ion implantation
In this paper, planar waveguides produced by He-ion implantation have been demonstrated in undoped and Yb-doped KY(WO/sub 4/)/sub 2/ crystals. The effective refractive indices of guided modes in surface planar waveguides were measured by dark m-line spectroscopy and the refractive index profiles were reconstructed by calculations based on the inverse WKB method. The end-faces of implanted crystals were polished and the waveguiding properties of the obtained planar structures were investigated using a laser diode at 980 nm and a CCD camera
Multiple tidal disruption flares in the active galaxy IC 3599
Tidal disruption events occur when a star passes too close to a massive black
hole and it is totally ripped apart by tidal forces. It may also happen that
the star is not close enough to the black hole to be totally disrupted and a
less dramatic event might happen. If the stellar orbit is bound and highly
eccentric, just like some stars in the centre of our own Galaxy, repeated
flares should occur. When the star approaches the black hole tidal radius at
periastron, matter might be stripped resulting in lower intensity outbursts
recurring once every orbital period. We report on Swift observations of a
recent bright flare from the galaxy IC 3599 hosting a middle-weight black hole,
where a possible tidal disruption event was observed in the early 1990s. By
light curve modelling and spectral fitting we can consistently account for the
events as the non-disruptive tidal stripping of a star into a highly eccentric
orbit. The recurrence time is 9.5 yr. IC 3599 is also known to host a
low-luminosity active galactic nucleus. Tidal stripping from this star over
several orbital passages might be able to spoon-feed also this activity.Comment: Accepted for publication to Astronomy & Astrophysic
Symptoms of posttraumatic stress disorder in adolescents with conduct disorder: Sex differences and onset Patterns
Examined sex differences in the rate and symptoms of posttraumatic stress disorder (PTSD), trauma exposure, and onset patterns in youth with conduct disorder (CD). 45 male and 31 female 10–17 yr olds admitted to a clinical facility for severe behavior problems completed the Diagnostic Interview for Children and Adolescents—Revised (DICA-R) to assess the presence of CD and PTSD. Over one-half of CD youth reported exposure to trauma, yet only 17% met criteria for PTSD. PTSD was more frequent in CD girls (28%) than in boys (10%), and girls experienced greater symptom intensity and anhedonia, difficulty feeling love or affection, and disturbance of s1eep and concentration. Girls more frequently reported sexual assault, while boys were more likely to report accidents, physical assaults, and witnessing the death of a loved one. Retrospective reports indicated that PTSD tended to develop subsequent to CD
The Brera Multi-scale Wavelet Chandra Survey. I. Serendipitous source catalogue
We present the BMW-Chandra source catalogue drawn from essentially all
Chandra ACIS-I pointed observations with an exposure time in excess of 10ks
public as of March 2003 (136 observations). Using the wavelet detection
algorithm developed by Lazzati et al. (1999) and Campana et al. (1999), which
can characterise both point-like and extended sources, we identified 21325
sources. Among them, 16758 are serendipitous, i.e. not associated with the
targets of the pointings, and do not require a non-automated analysis. This
makes our catalogue the largest compilation of Chandra sources to date. The
0.5--10 keV absorption corrected fluxes of these sources range from ~3E-16 to
9E-12 erg cm^-2 s^-1 with a median of 7E-15 erg cm^-2 s^-1. The catalogue
consists of count rates and relative errors in three energy bands (total,
0.5-7keV; soft, 0.5-2keV; and hard, 2-7keV), and source positions relative to
the highest signal-to-noise detection among the three bands. The wavelet
algorithm also provides an estimate of the extension of the source. We include
information drawn from the headers of the original files, as well, and
extracted source counts in four additional energy bands, SB1 (0.5-1keV), SB2
(1-2keV), HB1 (2-4keV), and HB2 (4-7keV). We computed the sky coverage for the
full catalogue and for a subset at high Galactic latitude (|b|> 20deg). The
complete catalogue provides a sky coverage in the soft band (0.5-2keV, S/N =3)
of ~8 deg^2 at a limiting flux of 1E-13 erg cm^-2 s^-1, and ~2 deg^2 at a
limiting flux of ~1E-15 erg cm^-2 s^-1.Comment: Accepted by A&A, Higher res. Figs 4 and 5 at
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f4.eps
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f5.eps, Catalog Web
pages: http://www.brera.inaf.it/BMC/bmc_home.html
http://www.ifc.inaf.it/~romano/BMC/bmc_home.html (Mirror
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