3,647 research outputs found
Lack of an Interchromosomal Effect Associated with Spontaneous Recombination in Males of Drosophila Melanogaster
Author Institution: Department of Biological Sciences, Bowling Green State UniversityIt is shown that the frequency of spontaneous male recombination in two different lines of Drosophila melanogaster (OKI and T-007) are not subject to an interchromosomal effect. Second-chromosome male recombination in these lines was not affected by heterozygosity for the multiple third-chromosome inversions In(3LR)TM3 or In(3LR)Ubxm, which do affect recombination in females. It seems, therefore, that a large fraction of spontaneous recombination in males of D. melanogaster occurs by some mechanism other than that in females. We discuss the possibility that the mechanism is chromosome breakage and reunion, and that these breakage events may be caused by a microorganism
Greenstone belts: Their components and structure
Greenstone sucessions are defined as the nongranitoid component of granitoid-greenstone terrain and are linear to irregular in shape and where linear are termed belts. The chemical composition of greenstones is described. Also discussed are the continental environments of greenstone successions. The effects of contact with granitoids, geophysical properties, recumbent folds and late formation structures upon greenstones are examined. Large stratigraphy thicknesses are explained
Tidally-Triggered Star Formation in Close Pairs of Galaxies
We analyze new optical spectra of a sample of 502 galaxies in close pairs and
n-tuples, separated by <= 50/h kpc. We extracted the sample objectively from
the CfA2 redshift survey, without regard to the surroundings of the tight
systems. We probe the relationship between star formation and the dynamics of
the systems of galaxies. The equivalent widths of H\alpha (EW(H\alpha) and
other emission lines anti-correlate strongly with pair spatial separation
(\Delta D) and velocity separation. We use the measured EW(H\alpha) and the
starburst models of Leitherer et al. to estimate the time since the most recent
burst of star for- mation began for each galaxy. In the absence of a large
contribution from an old stellar population to the continuum around H\alpha,
the observed \Delta D -- EW(H\alpha) correlation signifies that starbursts with
larger separations on the sky are, on average, older. By matching the dynamical
timescale to the burst timescale, we show that the data support a simple
picture in which a close pass initiates a starburst; EW(H\alpha) decreases with
time as the pair separation increases, accounting for the anti-correlation.
This picture leads to a method for measuring the duration and the initial mass
function of interaction-induced starbursts: our data are compatible with the
starburst and orbit models in many respects, as long as the starburst lasts
longer than \sim10^8 years and the delay between the close pass and the
initiation of the starburst is less than a few \times 10^7 years. If there is
no large contribution from an old stellar population to the continuum around
H\alpha the Miller-Scalo and cutoff (M <= 30 M_\sun) Salpeter initial mass
functions fit the data much better than a standard Salpeter IMF. (Abridged.)Comment: 43 pages, 22 figures, to appear in the ApJ; we correct an error which
had minor effects on numerical values in the pape
Chemical and Statistical Analysis of a Sampled Interval in the Camp Nelson Limestone (Upper Ordovician) Madison County, Central Kentucky
The Camp Nelson Limestone of the High Bridge Group (Upper Ordovician) is mined at seven sites in central and north-central Kentucky for industrial, construction, and agricultural uses. As part of a regional investigation of its chemical characteristics, a 67-foot section in the upper Camp Nelson, which is being mined at Boonesborough, Madison County, was sampled for major-element analysis.
The upper Camp Nelson in the Boonesborough Mine consists of two zones (23 and 30 feet thick) of low-silica stone (4 percent or less total SiO2) separated by a 14-foot section of slightly argillaceous limestone with an average silica content of 5.19 percent. The lower 23-foot zone has an average silica content of 1.75 percent and an average total carbonate (CaCO3 + MgCO3) content of 96.03 percent. The upper 30-foot zone has an average silica content of 2.48 percent and an average total carbonate content of 93.17 percent.
A statistical study showed a relationship between the sampling interval and the reliability of the mean carbonate (or contaminant) value for a limestone ledge. Moderately high reliability (0.80 to 0.85) can be obtained by taking three to four samples per ledge. If only high reliability (0.90) of the mean value is acceptable, samples should be taken at 1-foot intervals. Very high reliability would require sampling at 1/2-foot intervals
Climate Change Challenges for Land Conservation: Rethinking Conservation Easements, Strategies, and Tools
Climate change has significant consequences for land conservation. Government agencies and nonprofit land trusts heavily rely on perpetual conservation easements. However, climate change and other dynamic landscape changes raise questions about the effectiveness and adaptability of permanent conservation instruments like conservation easements. Building upon a study of 269 conservation easements and interviews with seventy conservation-easement professionals in six different states, we examine the adaptability of conservation easements to climate change. We outline four potential approaches to enhance conservation outcomes under climate change: (1) shift land-acquisition priorities to account for potential climate change impacts; (2) consider conservation tools other than perpetual conservation easements; (3) ensure that the terms of conservation easements permit the holder to adapt to climate change successfully; and (4) provide for more active stewardship of conservation lands. There is still a good deal of uncertainty as to the legal fate of a conservation easement that no longer meets its original purposes. Many state laws provide that conservation easements can be modified or terminated in the same manner as traditional easements. Yet conservation easements are in many ways unlike other easements. The beneficiary is usually the public, not merely a neighboring landowner, and the holder is always a nonprofit conservation organization or a government agency. Thus, there is a case to be made for adaptive protection. An overly narrow focus on perpetual property rights could actually thwart efforts to meet adaptation needs over the long term. We call for careful attention to ensuring conservation outcomes in dynamic landscapes over time
Thermal Decays in a Hot Fermi Gas
We present a study of the decay of metastable states of a scalar field via
thermal activation, in the presence of a finite density of fermions. The
process we consider is the nucleation of ``{\it droplets}'' of true vacuum
inside the false one. We analyze a one-dimensional system of interacting bosons
and fermions, considering the latter at finite temperature and with a given
chemical potential. As a consequence of a non-equilibrium formalism previously
developed, we obtain time-dependent decay rates.Comment: 18 pages, REVTEX, 9 figures available upon reques
Casimir energy of a compact cylinder under the condition
The Casimir energy of an infinite compact cylinder placed in a uniform
unbounded medium is investigated under the continuity condition for the light
velocity when crossing the interface. As a characteristic parameter in the
problem the ratio is used, where and
are, respectively, the permittivity and permeability of the material
making up the cylinder and and are those for the
surrounding medium. It is shown that the expansion of the Casimir energy in
powers of this parameter begins with the term proportional to . The
explicit formulas permitting us to find numerically the Casimir energy for any
fixed value of are obtained. Unlike a compact ball with the same
properties of the materials, the Casimir forces in the problem under
consideration are attractive. The implication of the calculated Casimir energy
in the flux tube model of confinement is briefly discussed.Comment: REVTeX, 12 pages, 1 figure in a separate fig1.eps file, 1 table;
minor corrections in English and misprints; version to be published in Phys.
Rev. D1
- …