6,800 research outputs found
GCM study of hexadecapole correlations in superdeformed Hg
The role of hexadecapole correlations in the lowest superdeformed band of
Hg is studied by self consistent mean field methods. The generator
coordinate method with particle number projection has been applied using
Hartree-Fock wave functions defined along three different hexadecapole paths.
In all cases, the ground state is not significantly affected by hexadecapole
correlations and the energies of the corresponding first excited hexadecapole
vibrational states lie high in energy. The effect of rotation is investigated
with the Skyrme-Hartree-Fock-Bogolyubov method and a zero range
density-dependent pairing interaction.Comment: REVTeX file, 10 pages, 3 figures (available as postscript files upon
request to [email protected]), submitted to Phys. Rev.
Propfan Test Assessment (PTA)
The objectives of the Propfan Test Assessment (PTA) Program were to validate in flight the structural integrity of large-scale propfan blades and to measure noise characteristics of the propfan in both near and far fields. All program objectives were met or exceeded, on schedule and under budget. A Gulfstream Aerospace Corporation GII aircraft was modified to provide a testbed for the 2.74m (9 ft) diameter Hamilton Standard SR-7 propfan which was driven by a 4475 kw (600 shp) turboshaft engine mounted on the left-hand wing of the aircraft. Flight research tests were performed for 20 combinations of speed and altitude within a flight envelope that extended to Mach numbers of 0.85 and altitudes of 12,192m (40,000 ft). Propfan blade stress, near-field noise on aircraft surfaces, and cabin noise were recorded. Primary variables were propfan power and tip speed, and the nacelle tilt angle. Extensive low altitude far-field noise tests were made to measure flyover and sideline noise and the lateral attenuation of noise. In coopertion with the FAA, tests were also made of flyover noise for the aircraft at 6100m (20,000 ft) and 10,668m (35,000 ft). A final series of tests were flown to evaluate an advanced cabin wall noise treatment that was produced under a separate program by NASA-Langley Research Center
Propfan Test Assessment (PTA): Flight test report
The Propfan Test Assessment (PTA) aircraft was flown to obtain glade stress and noise data for a 2.74m (9 ft.) diameter single rotation propfan. Tests were performed at Mach numbers to 0.85 and altitudes to 12,192m (40,000 ft.). The propfan was well-behaved structurally over the entire flight envelope, demonstrating that the blade design technology was completely adequate. Noise data were characterized by strong signals at blade passage frequency and up to 10 harmonics. Cabin noise was not so high as to preclude attainment of comfortable levels with suitable wall treatment. Community noise was not excessive
The Location of the Core in M81
We report on VLBI observations of M81*, the northwest-southeast oriented
nuclear core-jet source of the spiral galaxy M81, at five different frequencies
between 1.7 and 14.8 GHz. By phase referencing to supernova 1993J we can
accurately locate the emission region of M81* in the galaxy's reference frame.
Although the emission region's size decreases with increasing frequency while
the brightness peak moves to the southwest, the emission region seems sharply
bounded to the southwest at all frequencies. We argue that the core must be
located between the brightness peak at our highest frequency (14.8 GHz) and the
sharp bound to the southwest. This narrowly constrains the location of the
core, or the purported black hole in the center of the galaxy, to be within a
region of +/-0.2 mas or +/-800 AU (at a distance of ~4 Mpc). This range
includes the core position that we determined earlier by finding the most
stationary point in the brightness distribution of M81* at only a single
frequency. This independent constraint therefore strongly confirms our earlier
core position. Our observations also confirm that M81* is a core-jet source,
with a one-sided jet that extends to the northeast from the core, on average
curved somewhat to the east, with a radio spectrum that is flat or inverted
near the core and steep at the distant end. The brightness peak is
unambiguously identified with the variable jet rather than the core, which
indicates limitations in determining the proper motion of nearby galaxies and
in refining the extragalactic reference frame.Comment: LaTeX, 10 pages with 3 figures. Typos fixed and slight rewording for
clarity from previous version. Accepted for publication in the Astrophysical
Journa
The \u3cem\u3elet-7\u3c/em\u3e MicroRNA Family Members \u3cem\u3emir\u3c/em\u3e-48, \u3cem\u3emir\u3c/em\u3e-84, and mir-241 Function Together to Regulate Developmental Timing in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e
The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the hbl-1 3′ UTR and downregulating hbl-1 activity. Genetic analysis indicates that mir-48, mir-84, and mir-241 specify the timing of the L2-to-L3 transition in parallel to the heterochronic genes lin-28 and lin-46. These results indicate that let-7 family microRNAs function in combination to affect both early and late developmental timing decisions
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
Nucleon electromagnetic form factor data (including recent data) is fitted
with models that respect the confinement and asymptotic freedom properties of
QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson
pole contributions and at high momentum transfer conform to the predictions of
perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also
include the width of the rho meson and the addition of higher mass vector meson
exchanges, but do not evolve into the explicit form of PQCD at high momentum
transfer. Different parameterizations of the GK model's hadronic form factors,
the effect of including the width of the rho meson and the addition of the next
(in mass) isospin 1 vector meson are considered. The quality of fit and the
consistency of the parameters select three of the combined HP/GK type models.
Projections are made to the higher momentum transfers which are relevant to
electron-deuteron experiments. The projections vary little for the preferred
models, removing much of the ambiguity in electron-nucleus scattering
predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure,
minor textual changes; email correspondence to [email protected]
Konventionalisierungsfalle? was tun?
Der Öko-Landbau schrieb in den letzten Jahren Erfolgsgeschichte: Der Biosektor und seine Akteure scheinen in ihren Strukturen, Funktions- und Handlungsweisen der konventionellen Landwirtschaft immer ähnlicher zu werden. Während die einen Werte- und Sinnverlust beklagen, begrüßen die anderen Wachstum und öffentliche Anerkennung. Maßnahmen zur Überwindung dieses Spannungsfeldes wurden im März 2005 auf der Wissenschaftstagung zum Ökologischen Landbau im Rahmen eines Symposiums erörtert
Statistical fluctuations for the fission process on its decent from saddle to scission
We reconsider the importance of statistical fluctuations for fission dynamics
beyond the saddle in the light of recent evaluations of transport coefficients
for average motion. The size of these fluctuations are estimated by means of
the Kramers-Ingold solution for the inverted oscillator, which allows for an
inclusion of quantum effects.Comment: 12 pages, Latex, 5 Postscript figures; submitted to PRC e-mail:
[email protected] www home page:
http://www.physik.tu-muenchen.de/tumphy/e/T36/hofmann.htm
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