24,161 research outputs found
Larval Ecology of Some Lower Michigan Black Flies (Diptera: Simuliidae) With Keys to the Immature Stages
The species composition, succession, and seasonal abundance of -immature simuliids ocmrrhg in the Rose Lake Wildlife Research Area in lower Michigan are presented. Selected physical and chemical characteristics of streams in the above area were examined and compared in relation to faunal distributions. Comparisons of species differences between permanent and temporary streams were made utilizing the functional group concept based on feeding mechanisms.
Keys and illustrations are presented for the identiiication of larvae and pupae of four genera (Prosimulium, Simulium, Stegopterna, Cnephia) and 19 species of Simuliidae known to occur in lower Michigan. Two species, Cnephia ornithophilia and Simulium vemum, were recorded for the first time in Michigan
Bequests as a Means of Payment
Although recent research suggests that intergenerational transfers play an important role in aggregate capital accumulation, our understanding of bequest motives remains incomplete. We develop a simple model of"exchange-motivated" bequests, in which a testator influences the decisions ofhis beneficiaries by holding wealth in bequeathable forms and by conditioning the division of bequests on the beneficiaries' actions. The model generates falsifiable empirical predictions which are inconsistent with other theories of intergenerational transfers. We present econometric and other evidence which strongly suggests that bequests are often used as a means of payment for services rendered by beneficiaries.
Unconditional convergence and optimal error estimates of a Galerkin-mixed FEM for incompressible miscible flow in porous media
In this paper, we study the unconditional convergence and error estimates of
a Galerkin-mixed FEM with the linearized semi-implicit Euler time-discrete
scheme for the equations of incompressible miscible flow in porous media. We
prove that the optimal error estimates hold without any time-step
(convergence) condition, while all previous works require certain time-step
condition. Our theoretical results provide a new understanding on commonly-used
linearized schemes for nonlinear parabolic equations. The proof is based on a
splitting of the error function into two parts: the error from the time
discretization of the PDEs and the error from the finite element discretization
of corresponding time-discrete PDEs. The approach used in this paper is
applicable for more general nonlinear parabolic systems and many other
linearized (semi)-implicit time discretizations
We haven't got a seat on the bus for you or All the seats are mine: Narratives and career transitions in professional golf
In this article we explore how the stories an athlete tells throughout life in sport affect her career transition experiences. We base our enquiry on a social constructionist conception of narrative theory which holds that storytelling is integral to the creation and maintenance of identity and sense of self. Life stories were gathered through interviews with two professional women golfers (Christiana and Kandy) over a six‐year period. Through a narrative analysis of structure and form we explored each participant’s stories of living in and withdrawing from professional golf. We suggest Christiana told monological performance‐oriented stories which, while aligning with the culture of elite sport, resulted in an exclusive athletic identity and foreclosure of alternative selves and roles. On withdrawal, Christiana experienced narrative wreckage, identity collapse, mental health difficulties and considerable psychological trauma. In contrast, Kandy told dialogical discovery‐oriented stories which, while being in tension with the dominant performance narrative, created and sustained a multidimensional identity and self. Her stories and identity remained intact, authentic and continuous on withdrawal from tournament golf and she experienced few psychological problems
Casimir interactions in Ising strips with boundary fields: exact results
An exact statistical mechanical derivation is given of the critical Casimir
forces for Ising strips with arbitrary surface fields applied to edges. Our
results show that the strength as well as the sign of the force can be
controled by varying the temperature or the fields. An interpretation of the
results is given in terms of a linked cluster expansion. This suggests a
systematic approach for deriving the critical Casimir force which can be used
in more general models.Comment: 10 pages, 4 figure
MODELLING THE ELECTRON WITH COSSERAT ELASTICITY
Interactions between a finite number of bodies and the surrounding fluid, in a channel for instance, are investigated theoretically. In the planar model here the bodies or modelled grains are thin solid bodies free to move in a nearly parallel formation within a quasi-inviscid fluid. The investigation involves numerical and analytical studies and comparisons. The three main features that appear are a linear instability about a state of uniform motion, a clashing of the bodies (or of a body with a side wall) within a finite scaled time when nonlinear interaction takes effect, and a continuum-limit description of the body–fluid interaction holding for the case of many bodies
Reverse geometric engineering of singularities
One can geometrically engineer supersymmetric field theories theories by
placing D-branes at or near singularities. The opposite process is described,
where one can reconstruct the singularities from quiver theories. The
description is in terms of a noncommutative quiver algebra which is constructed
from the quiver diagram and the superpotential. The center of this
noncommutative algebra is a commutative algebra, which is the ring of
holomorphic functions on a variety V. If certain algebraic conditions are met,
then the reverse geometric engineering produces V as the geometry that D-branes
probe. It is also argued that the identification of V is invariant under
Seiberg dualities.Comment: 17 pages, Latex. v2: updates reference
Interfaces in driven Ising models: shear enhances confinement
We use a phase-separated driven two-dimensional Ising lattice gas to study
fluid interfaces exposed to shear flow parallel to the interface. The interface
is stabilized by two parallel walls with opposing surface fields and a driving
field parallel to the walls is applied which (i) either acts locally at the
walls or (ii) varies linearly with distance across the strip. Using computer
simulations with Kawasaki dynamics, we find that the system reaches a steady
state in which the magnetisation profile is the same as that in equilibrium,
but with a rescaled length implying a reduction of the interfacial width. An
analogous effect was recently observed in sheared phase-separated colloidal
dispersions. Pair correlation functions along the interface decay more rapidly
with distance under drive than in equilibrium and for cases of weak drive can
be rescaled to the equilibrium result.Comment: 4 pages, 3 figures Text modified, added Fig. 3b. To appear in Phys.
Rev. Letter
Neuromuscular control of wingbeat kinematics in Anna's hummingbirds (Calypte anna)
Hummingbirds can maintain the highest wingbeat frequencies of any flying vertebrate – a feat accomplished by the large pectoral muscles that power the wing strokes. An unusual feature of these muscles is that they are activated by one or a few spikes per cycle as revealed by electromyogram recordings (EMGs). The relatively simple nature of this activation pattern provides an opportunity to understand how motor units are recruited to modulate limb kinematics. Hummingbirds made to fly in low-density air responded by moderately increasing wingbeat frequency and substantially increasing the wing stroke amplitude as compared with flight in normal air. There was little change in the number of spikes per EMG burst in the pectoralis major muscle between flight in normal and low-density heliox (mean=1.4 spikes cycle^(–1)). However the spike amplitude, which we take to be an indication of the number of active motor units, increased in concert with the wing stroke amplitude, 1.7 times the value in air. We also challenged the hummingbirds using transient load lifting to elicit maximum burst performance. During maximum load lifting, both wing stroke amplitude and wingbeat frequency increased substantially above those values during hovering flight. The number of spikes per EMG burst increased to a mean of 3.3 per cycle, and the maximum spike amplitude increased to approximately 1.6 times those values during flight in heliox. These results suggest that hummingbirds recruit additional motor units (spatial recruitment) to regulate wing stroke amplitude but that temporal recruitment is also required to maintain maximum stroke amplitude at the highest wingbeat frequencies
Standing gravitational waves from domain walls
We construct a plane symmetric, standing gravitational wave for a domain wall
plus a massless scalar field. The scalar field can be associated with a fluid
which has the properties of `stiff' matter, i.e. matter in which the speed of
sound equals the speed of light. Although domain walls are observationally
ruled out in the present era the solution has interesting features which might
shed light on the character of exact non-linear wave solutions to Einstein's
equations. Additionally this solution may act as a template for higher
dimensional 'brane-world' model standing waves.Comment: 4 pages two-column format, no figures, added discussion of physical
meaning of solution, added refernces, to be published PR
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