39,982 research outputs found
The Mayflies (Ephemeroptera) of Tennessee, With a Review of the Possibly Threatened Species Occurring Within the State
One hundred and forty-three species of mayflies are reported from the state of Tennessee. Sixteen species (Ameletus cryptostimulus, Choroterpes basalis, Baetis virile, Ephemera blanda, E. simulans, Ephemerella berneri, Heterocloeon curiosum, H. petersi, Labiobaetis ephippiatus, Leptophlebia bradleyi, Macdunnoa brunnea, Paraleptophlebia assimilis, P. debilis, P. mollis, Rhithrogenia pellucida and Siphlonurus mirus) are reported for the first time. Rare and vulnerable species occurring in the state are also discussed. This represents the first comprehensive statewide list of mayflies for Tennessee
Investment Patterns and Financial Leverage
This study Investigates the influence of the type of investment opportunities facing a firm on its choice of capital structure. It is shown that the more discretionary investment opportunities a firm faces,the lower its financial leverage. Inclusion of other possible determinants of capital structure, such as availability of internal funds, tax effects and risk, while significant, do not affect the importance of discretionary investment. The evidence supports (1) the existence of a moral bazzard problem which inversely relates risky debt and discretionary investment choice, and (2) a desire by most firms to use sources of internal funds prior to entering the capital market.
Uncoupling of p97 ATPase activity has a dominant negative effect on protein extraction
p97 is a highly abundant, homohexameric AAA+ ATPase that performs a variety of essential cellular functions. Characterized as a ubiquitin-selective chaperone, p97 recognizes proteins conjugated to K48-linked polyubiquitin chains and promotes their removal from chromatin and other molecular complexes. Changes in p97 expression or activity are associated with the development of cancer and several related neurodegenerative disorders. Although pathogenic p97 mutations cluster in and around p97's ATPase domains, mutant proteins display normal or elevated ATPase activity. Here, we show that one of the most common p97 mutations (R155C) retains ATPase activity, but is functionally defective. p97-R155C can be recruited to ubiquitinated substrates on chromatin, but is unable to promote substrate removal. As a result, p97-R155C acts as a dominant negative, blocking protein extraction by a similar mechanism to that observed when p97's ATPase activity is inhibited or inactivated. However, unlike ATPase-deficient proteins, p97-R155C consumes excess ATP, which can hinder high-energy processes. Together, our results shed new insight into how pathogenic mutations in p97 alter its cellular function, with implications for understanding the etiology and treatment of p97-associated diseases
Macromolecular separation through a porous surface
A new technique for the separation of macromolecules is proposed and
investigated. A thin mesh with pores comparable to the radius of gyration of a
free chain is used to filter chains according to their length. Without a field
it has previously been shown that the permeability decays as a power law with
chain length. However by applying particular configurations of pulsed fields,
it is possible to have a permeability that decays as an exponential. This
faster decay gives much higher resolution of separation. We also propose a
modified screen containing an array of holes with barb-like protrusions running
parallel to the surface. When static friction is present between the
macromolecule and the protrusion, some of the chains get trapped for long
durations of time. By using this and a periodic modulation of an applied
electric field, high resolution can be attained.Comment: 18 pages latex, 6 postscript figures, using psfi
The interpretation of the field angle dependence of the critical current in defect-engineered superconductors
We apply the vortex path model of critical currents to a comprehensive
analysis of contemporary data on defect-engineered superconductors, showing
that it provides a consistent and detailed interpretation of the experimental
data for a diverse range of materials. We address the question of whether
electron mass anisotropy plays a role of any consequence in determining the
form of this data and conclude that it does not. By abandoning this false
interpretation of the data, we are able to make significant progress in
understanding the real origin of the observed behavior. In particular, we are
able to explain a number of common features in the data including shoulders at
intermediate angles, a uniform response over a wide angular range and the
greater discrimination between individual defect populations at higher fields.
We also correct several misconceptions including the idea that a peak in the
angular dependence of the critical current is a necessary signature of strong
correlated pinning, and conversely that the existence of such a peak implies
the existence of correlated pinning aligned to the particular direction. The
consistency of the vortex path model with the principle of maximum entropy is
introduced.Comment: 14 pages, 7 figure
Catching VY Sculptoris in a low state
Context. In the context of a large campaign to determine the system
parameters of high mass transfer cataclysmic variables, we found VY Scl in a
low state in 2008. Aims. Making use of this low state, we study the stellar
components of the binary with little influence of the normally dominating
accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl
taken during the low state are presented. We analysed the light-curve and
radial velocity curve and use time-resolved spectroscopy to calculate Doppler
maps of the dominant emission lines. Results. The spectra show narrow emission
lines of Halpha, Hbeta, HeI, NaID, and FeII, as well as faint TiO absorption
bands that trace the motion of the irradiated secondary star, and Halpha and
HeI emission line wings that trace the motion of the white dwarf. From these
radial velocities, we find an orbital period of 3.84 h, and put constraints on
binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of
15 deg. With a secondary's mass between 0.3 and 0.35 Msol, we derive the mass
for the white dwarf as M1 = 0.6-0.1 Msol.Comment: 8 pages, 9 figures, accepted for publication in A&
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