1,263 research outputs found
A new Tolman test of a cosmic distance duality relation at 21 cm
Under certain general conditions in an expanding universe, the luminosity
distance (d_L) and angular diameter distance (d_A) are connected by the
Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use
of objects of known surface brightness, to test this relation. In this letter,
we propose the use of redshifted 21 cm signal from disk galaxies, where neutral
hydrogen (HI) masses are seen to be almost linearly correlated with surface
area, to conduct a new Tolman test. We construct simulated catalogs of
galaxies, with the observed size-luminosity relation and realistic redshift
evolution of HI mass functions, likely to be detected with the planned Square
Kilometer Array (SKA). We demonstrate that these observations may soon provide
the best implementation of the Tolman test to detect any violation of the
Etherington relation.Comment: 4 pages, 2 figures, 1 table, v2: published versio
Preferences of University Academic Staff for Their Surrounding Environment: Uludag University as a Case Study
As a result of the damage to natural areas, open and green spaces in cities shrink in area and even disappear. This has caused an increase in the number of studies concerned with human-nature relations in urban landscaping. Contrary to the fact that the major part of our lives is spent in our workplaces, there are not many studies that investigate human-nature relations in workspaces. However, workspaces cover big areas of the urban landscape, their arrangement is of major importance in both an ecological and economical sense. The present study aims to shed light on how the academic staffs working at the Uludag University campus perceive the nature that surrounds their workspace and what their expectations concerning their natural surroundings are. Although the employees wish to see arranged landscapes surrounding their workplace, they significantly prefer naturally arranged spaces. It is evident that the staffs are concerned about the surroundings of the buildings they work in and that they make correct assumptions about and descriptions of the surroundings of their buildings
The Effects of Planting Density on the Dry Matter Yield and the Overwintering Ability of the Dwarf and Normal Napiergrasses in Two Years after Planting
The objective of this study is to determine the optimum planting density in napiergrass (Pennisetum purpureum Schumach) among two dwarf varieties introduced from Thailand and two normal ones under three levels of density. Dwarf varieties showed lower plant height and mean tiller weight, and higher leaf area index (LAI) and leaf blade percentage. Crop growth rate was positively correlated with LAI, and net assimilation rate and canopy extinction coefficient (K) were negatively correlated with LAI in the second year, including all dwarf and normal varieties, while K tended to be lower in the dwarf varieties. With the increase in the planting density, dry matter yield tended to increase, the difference between the normal varieties and early-heading dwarf variety was reduced, and the over wintering ability in all varieties was decreased. It was concluded that late-heading dwarf and normal varieties should be planted at the medium density by a desirable combination of productivity and considerable over wintering ability
Bulk phantom fields, increasing warp factors and fermion localisation
A bulk phantom scalar field (with negative kinetic energy) in a sine--Gordon
type potential is used to generate an exact thick brane solution with an
increasing warp factor. It is shown that the growing nature of the warp factor
allows the localisation of massive as well as massless spin-half fermions on
the brane even without any additional non--gravitational interactions. The
exact solutions for the localised massive fermionic modes are presented and
discussed. The inclusion of a fermion--scalar Yukawa coupling appears to change
the mass spectrum and wave functions of the localised fermion though it does
not play the crucial role it did in the case of a decreasing warp factor.Comment: 11 pages, 3 figures, RevTex
Proton-electron mass ratio from HD revisited
We present a new derivation of the proton-electron mass ratio from the
hydrogen molecular ion, HD. The derivation entails the adjustment of the
mass ratio in highly precise theory so as to reproduce accurately measured
ro-vibrational frequencies. This work is motivated by recent improvements of
the theory, as well as the more accurate value of the electron mass in the
recently published CODATA-14 set of fundamental constants, which justifies
using it as input data in the adjustment, rather than the proton mass value as
done in previous works. This leads to significantly different sensitivity
coefficients and, consequently, a different value and larger uncertainty margin
of the proton-electron mass ratio as obtained from HD
Optimization Rules in DLV for the Bridge Crossing Problem
Disjunctive logic programming is a powerful tool in knowledge representation and commonsense reasoning. The first solid implementation of a DLP system is called DLV (Datalog with Vel). In this paper we offer three strategies to produce optimal solutions in DLV for the well-known Bridge Crossing Problem. These strategies are a piggyback strategy, a non-piggyback strategy, and a mixed strategy. An analysis to determine the number of time steps required for an optimal solution using these strategies is provided. We also characterize and prove the conditions under which a particular strategy should be used to obtain an optimal solution. These strategies are implemented in the form of optimization rules in a DLV program for the bridge crossing problem. Preliminary results indicate a drastic reduction in execution time when compared to other DLV programs for bridge crossing which do not incorporate these strategies. Our implementation uses a DLV Java wrapper, allowing us to embed disjunctive logic programs inside an object-oriented environment
Cosmic optical activity from an inhomogeneous Kalb-Ramond field
The effects of introducing a harmonic spatial inhomogeneity into the
Kalb-Ramond field, interacting with the Maxwell field according to a
`string-inspired' proposal made in earlier work are investigated. We examine in
particular the effects on the polarization of synchrotron radiation from
cosmologically distant (i.e. of redshift greater than 2) galaxies, as well as
the relation between the electric and magnetic components of the radiation
field. The rotation of the polarization plane of linearly polarized radiation
is seen to acquire an additional contribution proportional to the square of the
frequency of the dual Kalb-Ramond axion wave, assuming that it is far smaller
compared to the frequency of the radiation field.Comment: 9 pages, Revtex, no figure
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