106,264 research outputs found
On the Measure in Simplicial Gravity
Functional measures for lattice quantum gravity should agree with their
continuum counterparts in the weak field, low momentum limit. After showing
that the standard simplicial measure satisfies the above requirement, we prove
that a class of recently proposed non-local measures for lattice gravity do not
satisfy such a criterion, already to lowest order in the weak field expansion.
We argue therefore that the latter cannot represent acceptable discrete
functional measures for simplicial geometries.Comment: LaTeX, 15 pages, 2 figure
Non-parametric Reconstruction of Cluster Mass Distribution from Strong Lensing: Modelling Abell 370
We describe a new non-parametric technique for reconstructing the mass
distribution in galaxy clusters with strong lensing, i.e., from multiple images
of background galaxies. The observed positions and redshifts of the images are
considered as rigid constraints and through the lens (ray-trace) equation they
provide us with linear constraint equations. These constraints confine the mass
distribution to some allowed region, which is then found by linear programming.
Within this allowed region we study in detail the mass distribution with
minimum mass-to-light variation; also some others, such as the smoothest mass
distribution. The method is applied to the extensively studied cluster Abell
370, which hosts a giant luminous arc and several other multiply imaged
background galaxies. Our mass maps are constrained by the observed positions
and redshifts (spectroscopic or model-inferred by previous authors) of the
giant arc and multiple image systems. The reconstructed maps obtained for \a370
reveal a detailed mass distribution, with substructure quite different from the
light distribution. The method predicts the bimodal nature of the cluster and
that the projected mass distribution is indeed elongated along the axis defined
by the two dominant cD galaxies. But the peaks in the mass distribution appear
to be offset from the centres of the cDs. We also present an estimate for the
total mass of the central region of the cluster. This is in good agreement with
previous mass determinations. The total mass of the central region is
M=(2.0-2.7) 10^14 Msun/h50, depending on the solution chosen.Comment: 14 pages(19 postscript figures), minor corrections, MNRAS in pres
Three-body recombination in a three-state Fermi gas with widely tunable interactions
We investigate the stability of a three spin state mixture of ultracold
fermionic Li atoms over a range of magnetic fields encompassing three
Feshbach resonances. For most field values, we attribute decay of the atomic
population to three-body processes involving one atom from each spin state and
find that the three-body loss coefficient varies by over four orders of
magnitude. We observe high stability when at least two of the three scattering
lengths are small, rapid loss near the Feshbach resonances, and two unexpected
resonant loss features. At our highest fields, where all pairwise scattering
lengths are approaching , we measure a three-body loss
coefficient and a trend
toward lower decay rates for higher fields indicating that future studies of
color superfluidity and trion formation in a SU(3) symmetric Fermi gas may be
feasible
Groups of Fibonacci type revisited
This article concerns a class of groups of Fibonacci type introduced by Johnson and Mawdesley that includes Conway?s Fibonacci groups, the Sieradski groups, and the Gilbert-Howie groups. This class of groups provides an interesting focus for developing the theory of cyclically presented groups and, following questions by Bardakov and Vesnin and by Cavicchioli, Hegenbarth, and Repov?s, they have enjoyed renewed interest in recent years. We survey results concerning their algebraic properties, such as isomorphisms within the class, the classification of the finite groups, small cancellation properties, abelianizations, asphericity, connections with Labelled Oriented Graph groups, and the semigroups of Fibonacci type. Further, we present a new method of proving the classification of the finite groups that deals with all but three groups
Flow instabilities in transonic small disturbance theory
The dynamics of unsteady transonic small disturbance flows about two-dimensional airfoils is examined, with emphasis on the behavior in the region where the steady state flow is nonunique. It is shown that nonuniqueness results from an extremely long time scale instability which occurs in a finite Mach number and angle of attack range. The similarity scaling rules for the instability are presented and the possibility of similar behavior in the Euler equations is discussed
Low-speed aerodynamic performance of 50.8-centimeter-diameter noise-suppressing inlets for the Quiet, Clean, Short-haul Experimental Engine (QCSEE)
Two basic inlet concepts, a high throat Mach number (0.79) design and a low throat Mach number (0.60) design, were tested with four diffuser acoustical treatment designs that had face sheet porosity ranging from 0 to 24 percent for the high Mach number inlet and 0 to 28 percent for the low Mach number inlet. The tests were conducted in a low speed wind tunnel at free stream velocities of 0, 41, and 62 m/sec and angles of attack to 50 deg. Inlet throat Mach number was varied about the design value. Increasing the inlet diffuser face sheet porosity resulted in an increase in total pressure loss in the boundary layer for both the high and low Mach number inlet designs, however, the overall effect on inlet total pressure recovery of 0.991 at the design throat Mach number, a free stream velocity of 41 m/sec, and an angle of attack of 50 deg; Inlet flow separation at an angle of attack of 50 deg was encountered with only one inlet configuration the high Mach number design with the highest diffuser face sheet porosity (24 percent)
Inhibition Of Adventitious Rooting In Backhousia Citriodora F. Muell. Cuttings Correlate With The Concentration Of Essential Oil
Backhousia citriodora is typical of the many commercially valuable woody Australian Myrtaceae species that are recalcitrant in forming adventitious roots from cuttings after maturation. A series of experiments were conducted to identify an endogenous rooting inhibitor in line with established criteria. Endogenous levels of citral were correlated with the rooting capacities of juvenile versus mature, and easy- versus difficult-to-root genotypes of B. citriodora, in both winter and summer. The biological activity of citral was confirmed in bioassays on mung beans and easy-to-root B. citriodora seedlings. Evidence of a common mechanism of root inhibition with other species in the family Myrtaceae and the role of action of citral are discussed
Adventitious Root Formation In Cuttings Of Backhousia citriodora F. Muell: 1 Plant Genotype, Juvenility And Characteristics Of Cuttings
Backhousia citriodora is a commercially valuable Australian woody species that has a reputation for being recalcitrant in forming adventitious roots from cuttings. A study was carried out to determine whether maturation and plant genotype influenced rooting. It also tried to establish whether genotypic differences in rooting ability were related to characteristics of the cutting material. The rooting of cuttings in B. citriodora declines after maturation and is strongly influenced by genotype. The cutting characteristics of actively growing axillary buds, wide stems and mature leaves are associated with rooting and survival but not related to genotype. Furthermore, the 8 to 24 weeks required by B. citriodora to form roots from cuttings makes it difficult to distinguish between the characteristics that increase rooting and those characteristics that enhance survival. A subsequent disbudding experiment demonstrated that axillary buds per se have an inhibitory effect on rooting. This suggests that the presence of actively growing axillary buds are an indication of overall growth and condition of the stock plant unrelated to the formation of adventitious rooting. The effects of other cutting characteristics on rooting are also discussed
Angular separations of the lensed QSO images
We have analyzed the observed image separations of the gravitationally lensed
images of QSOs for a possible correlation with the source redshift. Contrary to
the previously noted anti-correlation based on a smaller data set, no
correlation is found for the currently available data. We have calculated the
average image separations of the lensed QSOs as a function of source redshifts,
for isothermal spheres with cores in a flat universe, taking into account the
amplification bias caused by lensing. The shape of the distribution of average
image separation as a function of redshift is very robust and is insensitive to
most model parameters. Observations are found to be roughly consistent with the
theoretical results for models which assume the lens distribution to be (i)
Schechter luminosity function which, however, can not produce images with large
separation and (ii) the mass condensations in a cold dark matter universe, as
given by the Press-Schechter theory if an upper limit of 1-7
M is assumed on the mass of the condensations.Comment: 20 pages, 7 postscript figures, accepted for publication in The
Astrophysical Journa
- …