6,753 research outputs found
Vehicle for civil helicopter ride quality research
A research aircraft for investigating the factors involved in civil helicopter operations was developed for NASA Langley Research Center. The aircraft is a reconfigured 17000 kg (36000 lb) military transport helicopter. The basic aircraft was reconfigured with advanced acoustic treatment, air-conditioning, and a 16-seat airline cabin. During the spring of 1975, the aircraft was flight tested to measure interior environment characteristics - noise and vibration - and was flown on 60 subjective flight missions with over 600 different subjects. Data flights established noise levels somewhat higher than expected, with a pure tone at 1400 Hz and vertical vibration levels between 0.07g and 0.17g. The noise and vibration levels were documented during subjective flight evaluations as being the primary source of discomfort. The aircraft will be utilized to document in detail the impact of various noise and vibration levels on passenger comfort during typical short-haul missions
Proper definition and evolution of generalized transverse momentum distributions
We consider one of the most fundamental sets of hadronic matrix elements,
namely the generalized transverse momentum distributions (GTMDs), and argue
that their existing definitions lack proper evolution properties. By exploiting
the similarity of GTMDs with the much better understood transverse momentum
distributions, we argue that the existing definitions of GTMDs have to include
an additional dependence on soft gluon radiation in order to render them
properly defined. With this, we manage to obtain the evolution kernel of all
(un)polarized quark and gluon GTMDs, which turns out to be spin independent. As
a byproduct, all large logarithms can be resummed up to
next-to-next-to-leading-logarithmic accuracy with the currently known
perturbative ingredients.Comment: v2: typo in eq.(19) corrected. Matches published version in PLB. v1:
9 pages, 2 figure
CMB dipoles and other low-order multipoles in the quasispherical Szekeres model
Several authors have previously shown that a Gpc-scale void based on the spherically symmetric Lemaıˆtre-Tolman-Bondi (LTB) model can provide a good fit to certain cosmological data, including the SNIa data, but it is only consistent with the observed CMB dipole if we are located very close to the center, in violation of the Copernican principle. In this work we investigate the more general quasispherical Szekeres model, which does not include spherical symmetry, in order to determine whether this option may be less constricting. We find that the observer is still constrained to a small region, but it is not as geometrically ''special'' as the center of a LTB void. Furthermore, whereas the quadrupole and octupole near the center of a LTB void are necessarily small, certain Szekeres models can include a significant quadrupole while still being consistent with the observed dipole, hinting that Szekeres models may be able to give an explanation for the observed quadrupole/octupole anomalies
Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321
We report on the X-ray observation of the radio selected supernova SN1979C
carried out with ASCA in 1997 December and serendipitously available from a
Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN
II-Linear (SN IIL), was first observed in the optical and occurred in the
weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a
member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at
least three other supernovae discovered in this century. The useful exposure
time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the
Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's
Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the
radio position of SN1979C in a 3' diameter half power response circle in the
ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper
limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band
(0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10
keV band. In the Chandra data, a source at the position of SN1979C is
marginally detected at energies below 2 keV at a flux consistent with the ROSAT
HRI detection in 1995. At energies above 2 keV, no source is detected with an
upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever
x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic
of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A
Extrapolation of Galactic Dust Emission at 100 Microns to CMBR Frequencies Using FIRAS
We present predicted full-sky maps of submillimeter and microwave emission
from the diffuse interstellar dust in the Galaxy. These maps are extrapolated
from the 100 micron emission and 100/240 micron flux ratio maps that Schlegel,
Finkbeiner, & Davis (1998; SFD98) generated from IRAS and COBE/DIRBE data.
Results are presented for a number of physically plausible emissivity models.
We find that no power law emissivity function fits the FIRAS data from 200 -
2100 GHz. In this paper we provide a formalism for a multi-component model for
the dust emission. A two-component model with a mixture of silicate and
carbon-dominated grains (motivated by Pollack et al., 1994}) provides a fit to
an accuracy of about 15% to all the FIRAS data over the entire high-latitude
sky. Small systematic differences are found between the atomic and molecular
phases of the ISM.
Our predictions for the thermal (vibrational) emission from Galactic dust at
\nu < 3000 GHz are available for general use. These full-sky predictions can be
made at the DIRBE resolution of 40' or at the higher resolution of 6.1 arcmin
from the SFD98 DIRBE-corrected IRAS maps.Comment: 48 pages, AAS LaTeX, 6 figures, ApJ (accepted). Data described in the
text, as well as 4 additional figures, are available at
http://astro.berkeley.edu/dus
Distances between two chromosomes in interphase nuclei as determined with digitized image analysis
- …