4,221 research outputs found
A Noninvasive Method For In situ Determination of Mating Success in Female American Lobsters (Homarus americanus)
Despite being one of the most productive fisheries in the Northwest Atlantic, much remains unknown about the natural reproductive dynamics of American lobsters. Recent work in exploited crustacean populations (crabs and lobsters) suggests that there are circumstances where mature females are unable to achieve their full reproductive potential due to sperm limitation. To examine this possibility in different regions of the American lobster fishery, a reliable and noninvasive method was developed for sampling large numbers of female lobsters at sea. This method involves inserting a blunt-tipped needle into the female\u27s seminal receptacle to determine the presence or absence of a sperm plug and to withdraw a sample that can be examined for the presence of sperm. A series of control studies were conducted at the dock and in the laboratory to test the reliability of this technique. These efforts entailed sampling 294 female lobsters to confirm that the presence of a sperm plug was a reliable indicator of sperm within the receptacle and thus, mating. This paper details the methodology and the results obtained from a subset of the total females sampled. Of the 230 female lobsters sampled from George\u27s Bank and Cape Ann, MA (size range = 71-145 mm in carapace length), 90.3% were positive for sperm. Potential explanations for the absence of sperm in some females include: immaturity (lack of physiological maturity), breakdown of the sperm plug after being used to fertilize a clutch of eggs, and lack of mating activity. The surveys indicate that this technique for examining the mating success of female lobsters is a reliable proxy that can be used in the field to document reproductive activity in natural populations
Chiral Reductions in the Salam-Sezgin Model
Reductions from six to four spacetime dimensions are considered for a class
of supergravity models based on the six-dimensional Salam-Sezgin model, which
is a chiral theory with a gauged U(1) R-symmetry and a positive scalar-field
potential. Reduction on a sphere and monopole background of such models
naturally yields four-dimensional theories without a cosmological constant. The
question of chirality preservation in such a reduction has been a topic of
debate. In this article, it is shown that the possibilities of dimensional
reduction bifurcate into two separate consistent dimensional-reduction schemes.
One of these retains the massless SU(2) vector gauge triplet arising from the
sphere's isometries, but it produces a non-chiral four-dimensional theory. The
other consistent scheme sets to zero the SU(2) gauge fields, but retains the
gauged U(1) from six dimensions and preserves chirality although the U(1) is
spontaneously broken. Extensions of the Salam-Sezgin model to include larger
gauge symmetries produce genuinely chiral models with unbroken gauge
symmetries.Comment: 37 page
A Noninvasive Method For In situ Determination of Mating Success in Female American Lobsters (Homarus americanus)
Despite being one of the most productive fisheries in the Northwest Atlantic, much remains unknown about the natural reproductive dynamics of American lobsters. Recent work in exploited crustacean populations (crabs and lobsters) suggests that there are circumstances where mature females are unable to achieve their full reproductive potential due to sperm limitation. To examine this possibility in different regions of the American lobster fishery, a reliable and noninvasive method was developed for sampling large numbers of female lobsters at sea. This method involves inserting a blunt-tipped needle into the female\u27s seminal receptacle to determine the presence or absence of a sperm plug and to withdraw a sample that can be examined for the presence of sperm. A series of control studies were conducted at the dock and in the laboratory to test the reliability of this technique. These efforts entailed sampling 294 female lobsters to confirm that the presence of a sperm plug was a reliable indicator of sperm within the receptacle and thus, mating. This paper details the methodology and the results obtained from a subset of the total females sampled. Of the 230 female lobsters sampled from George\u27s Bank and Cape Ann, MA (size range = 71-145 mm in carapace length), 90.3% were positive for sperm. Potential explanations for the absence of sperm in some females include: immaturity (lack of physiological maturity), breakdown of the sperm plug after being used to fertilize a clutch of eggs, and lack of mating activity. The surveys indicate that this technique for examining the mating success of female lobsters is a reliable proxy that can be used in the field to document reproductive activity in natural populations
Fouling During the Use of Seawater as Coolant - The Development of a âUser Guideâ
ESDU International of London, UK has recently published a âUser Guideâ on fouling in heat exchange systems using seawater as the coolant. Developed over a period of eighteen months in close collaboration with a team of oil refiners, heat transfer equipment and services suppliers and universities, with valuable input from the power industry, the User Guide is a practical guide to the current state of knowledge relating to fouling in cooling systems using seawater. Its objective is to provide the designer and the operator of both onshore and offshore equipment with a practical source of guidance on the occurrence, the mechanisms and the mitigation of seawater fouling in these systems.
ESDUâs collaborative Oil Industry Fouling Working Party was formed in recognition of the huge economic and environmental importance of heat exchanger fouling and the potential benefits that can accrue from better understanding of mitigation strategies. The seawater fouling User Guide is the second in a group, following the development of the Crude Oil Fouling User Guide issued in 2000. Work is now underway on cooling water fouling,
The development of the User Guide is discussed in this paper and its technical content is summarize
A noninvasive method for in situ determination of mating success in female American lobsters (Homarus americanus)
Despite being one of the most productive fisheries in the Northwest Atlantic, much remains unknown about the natural reproductive dynamics of American lobsters. Recent work in exploited crustacean populations (crabs and lobsters) suggests that there are circumstances where mature females are unable to achieve their full reproductive potential due to sperm limitation. To examine this possibility in different regions of the American lobster fishery, a reliable and noninvasive method was developed for sampling large numbers of female lobsters at sea. This method involves inserting a blunt-tipped needle into the female's seminal receptacle to determine the presence or absence of a sperm plug and to withdraw a sample that can be examined for the presence of sperm. A series of control studies were conducted at the dock and in the laboratory to test the reliability of this technique. These efforts entailed sampling 294 female lobsters to confirm that the presence of a sperm plug was a reliable indicator of sperm within the receptacle and thus, mating. This paper details the methodology and the results obtained from a subset of the total females sampled. Of the 230 female lobsters sampled from George's Bank and Cape Ann, MA (size range = 71-145 mm in carapace length), 90.3% were positive for sperm. Potential explanations for the absence of sperm in some females include: immaturity (lack of physiological maturity), breakdown of the sperm plug after being used to fertilize a clutch of eggs, and lack of mating activity. The surveys indicate that this technique for examining the mating success of female lobsters is a reliable proxy that can be used in the field to document reproductive activity in natural populations
FOULING DURING THE USE OF âFRESHâ WATER AS COOLANT- THE DEVELOPMENT OF A âUSER GUIDEâ
IHS ESDU recently published its latest âUser Guideâ to fouling in heat exchange systems, for systems with fresh water as the coolant. ESDU 07006 [1] is the third in a group, following the development of the Crude Oil Fouling User Guide [2] issued in 2000 and the Seawater Fouling User Guide [3] issued in 2004. ESDU 07006 was developed by IHS ESDU over a period of five years under the guidance of the Oil Industry Fouling Working Party, a collaborative team of oil refiners, heat transfer equipment and services suppliers and Universities. It provides designers and operators of cooling water facilities with a practical source of guidance on the occurrence, the mechanisms and the mitigation of fresh water fouling in these systems. IHS ESDUâs Oil Industry Fouling Working Party was formed in recognition of the huge economic and environmental importance of heat exchanger fouling and the potential benefits that can accrue from better understanding of mitigation strategies. Work is now underway on reboiler and FCCU fouling. The development of the User Guide ESDU 07006 is discussed in this paper and its technical content is summarized
On closing for flows on 2-manifolds
For some full measure subset B of the set of iet's (i.e. interval exchange
transformations) the following is satisfied: Let X be a , , vector field, with finitely many singularities, on a compact
orientable surface M. Given a nontrivial recurrent point of X, the
holonomy map around p is semi-conjugate to an iet If
then there exists a vector field Y, arbitrarily close to X, in
the topology, such that Y has a closed trajectory passing through p.Comment: 7 pages, 1 figur
Antimatter production in proton-proton and heavy-ion collisions at ultrarelativistic energies
One of the striking features of particle production at high beam energies is
the near equal abundance of matter and antimatter in the central rapidity
region. In this paper we study how this symmetry is reached as the beam energy
is increased. In particular, we quantify explicitly the energy dependence of
the approach to matter/antimatter symmetry in proton-proton and in heavy-ion
collisions. Expectations are presented also for the production of more complex
forms of antimatter like antihypernuclei.Comment: 7 pages, 5 figure
High-pressure structural, elastic and electronic properties of the scintillator host material, KMgF_3
The high-pressure structural behaviour of the fluoroperovskite KMgF_3 is
investigated by theory and experiment. Density functional calculations were
performed within the local density approximation and the generalized gradient
approximation for exchange and correlation effects, as implemented within the
full-potential linear muffin-tin orbital method. In situ high-pressure powder
x-ray diffraction experiments were performed up to a maximum pressure of 40 GPa
using synchrotron radiation. We find that the cubic Pm\bar{3}m crystal symmetry
persists throughout the pressure range studied. The calculated ground state
properties -- the equilibrium lattice constant, bulk modulus and elastic
constants -- are in good agreement with experimental results. By analyzing the
ratio between the bulk and shear modulii, we conclude that KMgF_3 is brittle in
nature. Under ambient conditions, KMgF_3 is found to be an indirect gap
insulator with the gap increasing under pressure.Comment: 4 figure
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