419 research outputs found
Stomatal Opening, Transpiration, and Need/e Moisture in Loblolly Pine Seedlings From Two Texas Seed Sources
Relationships among percentage of open stomates, transpiration, and needle moisture content in seedlings of loblolly pine of two Texas provenances were studied under changing soil moisture conditions. Needle moisture content correlated very well with transpiration under favorable moisture conditions, and with percentage of open stomates under soil moisture stress. Transpiration and percentage of open stomates were correlated under a wide range of moisture conditions. Foliage moisture content was still relatively high in both ecotypes when stomates closed and transpiration drastically declined. The Lost Pines seed source appeared to have superior ability to conserve moisture under droughty conditions by closure of stomares and reduction of transpiration. FOREST SCI. 23: 457-462
Separability of Rotational Effects on a Gravitational Lens
We derive the deflection angle up to due to a Kerr gravitational
lens with mass and specific angular momentum . It is known that at the
linear order in and the Kerr lens is observationally equivalent to the
Schwarzschild one because of the invariance under the global translation of the
center of the lens mass. We show, however, nonlinear couplings break the
degeneracy so that the rotational effect becomes in principle separable for
multiple images of a single source. Furthermore, it is distinguishable also for
each image of an extended source and/or a point source in orbital motion. In
practice, the correction at becomes for the
supermassive black hole in our galactic center. Hence, these nonlinear
gravitational lensing effects are too small to detect by near-future
observations.Comment: 12 pages (RevTeX); accepted for publication in Phys. Rev.
Equation of state of cosmic strings with fermionic current-carriers
The relevant characteristic features, including energy per unit length and
tension, of a cosmic string carrying massless fermionic currents in the
framework of the Witten model in the neutral limit are derived through
quantization of the spinor fields along the string. The construction of a Fock
space is performed by means of a separation between longitudinal modes and the
so-called transverse zero energy solutions of the Dirac equation in the vortex.
As a result, quantization leads to a set of naturally defined state parameters
which are the number densities of particles and anti-particles trapped in the
cosmic string. It is seen that the usual one-parameter formalism for describing
the macroscopic dynamics of current-carrying vortices is not sufficient in the
case of fermionic carriers.Comment: 30 pages, 15 figures, uses ReVTeX, equation of state corrected,
comments and references added. Accepted for publication in Phys. Rev.
Fermionic massive modes along cosmic strings
The influence on cosmic string dynamics of fermionic massive bound states
propagating in the vortex, and getting their mass only from coupling to the
string forming Higgs field, is studied. Such massive fermionic currents are
numerically found to exist for a wide range of model parameters and seen to
modify drastically the usual string dynamics coming from the zero mode currents
alone. In particular, by means of a quantization procedure, a new equation of
state describing cosmic strings with any kind of fermionic current, massive or
massless, is derived and found to involve, at least, one state parameter per
trapped fermion species. This equation of state exhibits transitions from
subsonic to supersonic regimes while the massive modes are filled.Comment: 27 pages, 15 figures, uses ReVTeX. Shortened version, accepted for
publication in Phys. Rev.
Quantum tunneling of superconducting string currents
We investigate the decay of current on a superconducting cosmic string
through quantum tunneling. We construct the instanton describing tunneling in a
simple bosonic string model, and estimate the decay rate. The tunneling rate
vanishes in the limit of a chiral current. This conclusion, which is supported
by a symmetry argument, is expected to apply in general. It has important
implications for the stability of chiral vortons.Comment: 16 pages, 2 figure
Soap Bubbles in Outer Space: Interaction of a Domain Wall with a Black Hole
We discuss the generalized Plateau problem in the 3+1 dimensional
Schwarzschild background. This represents the physical situation, which could
for instance have appeared in the early universe, where a cosmic membrane (thin
domain wall) is located near a black hole. Considering stationary axially
symmetric membranes, three different membrane-topologies are possible depending
on the boundary conditions at infinity: 2+1 Minkowski topology, 2+1 wormhole
topology and 2+1 black hole topology.
Interestingly, we find that the different membrane-topologies are connected
via phase transitions of the form first discussed by Choptuik in investigations
of scalar field collapse. More precisely, we find a first order phase
transition (finite mass gap) between wormhole topology and black hole topology;
the intermediate membrane being an unstable wormhole collapsing to a black
hole. Moreover, we find a second order phase transition (no mass gap) between
Minkowski topology and black hole topology; the intermediate membrane being a
naked singularity.
For the membranes of black hole topology, we find a mass scaling relation
analogous to that originally found by Choptuik. However, in our case the
parameter is replaced by a 2-vector parametrizing the solutions.
We find that where . We also find a periodic wiggle in the scaling relation.
Our results show that black hole formation as a critical phenomenon is far
more general than expected.Comment: 15 pages, Latex, 4 figures include
Profiles of emission lines generated by rings orbiting braneworld Kerr black holes
In the framework of the braneworld models, rotating black holes can be
described by the Kerr metric with a tidal charge representing the influence of
the non-local gravitational (tidal) effects of the bulk space Weyl tensor onto
the black hole spacetime. We study the influence of the tidal charge onto
profiled spectral lines generated by radiating tori orbiting in vicinity of a
rotating black hole. We show that with lowering the negative tidal charge of
the black hole, the profiled line becomes to be flatter and wider keeping their
standard character with flux stronger at the blue edge of the profiled line.
The extension of the line grows with radius falling and inclination angle
growing. With growing inclination angle a small hump appears in the profiled
lines due to the strong lensing effect of photons coming from regions behind
the black hole. For positive tidal charge () and high inclination angles
two small humps appear in the profiled lines close to the red and blue edge of
the lines due to the strong lensing effect. We can conclude that for all values
of , the strongest effect on the profiled lines shape (extension) is caused
by the changes of the inclination angle.Comment: Accepted by General Relativity and Gravitatio
Biological Variation of Plasma and Urinary Markers of Acute Kidney Injury in Patients with Chronic Kidney Disease
BACKGROUND: Identification of acute kidney injury (AKI) is predominantly based on changes in plasma creatinine concentration, an insensitive marker. Alternative biomarkers have been proposed. The reference change value (RCV), the point at which biomarker change can be inferred to have occurred with statistical certainty, provides an objective assessment of change in serial tests results in an individual. METHODS: In 80 patients with chronic kidney disease, weekly measurements of blood and urinary biomarker concentrations were undertaken over 6 weeks. Variability was determined and compared before and after adjustment for urinary creatinine and across subgroups stratified by level of kidney function, proteinuria, and presence or absence of diabetes. RESULTS: RCVs were determined for whole blood, plasma, and urinary neutrophil gelatinase-associated lipocalin (111%, 59%, and 693%, respectively), plasma cystatin C (14%), creatinine (17%), and urinary kidney injury molecule 1 (497%), tissue inhibitor of metalloproteinases 2 (454%), N-acetyl-?-d-glucosaminidase (361%), interleukin-18 (819%), albumin (430%), and ?1-microglobulin (216%). Blood biomarkers exhibited lower variability than urinary biomarkers. Generally, adjusting urinary biomarker concentrations for creatinine reduced (P < 0.05) within-individual biological variability (CVI). For some markers, variation differed (P < 0.05) between subgroups. CONCLUSIONS: These data can form a basis for application of these tests in clinical practice and research studies and are applicable across different levels of kidney function and proteinuria and in the presence or absence of diabetes. Most of the studied biomarkers have relatively high CVI (noise) but also have reported large concentration changes in response to renal insult (signal); thus progressive change should be detectable (high signal-to-noise ratio) when baseline data are available
Transcendence over Diversity: black women in the academy
Universities, like many major public institutions have embraced the notion of ‘diversity’ virtually uncritically- it is seen as a moral ‘good in itself’. But what happens to those who come to represent ‘diversity’- the black and minority ethnic groups targeted to increase the institutions thirst for global markets and aversion to accusations of institutional racism? Drawing on existing literature which analyses the process of marginalization in higher education, this paper explores the individual costs to black and female academic staff regardless of the discourse on diversity. However despite the exclusion of staff, black and minority ethnic women are also entering higher education in relatively large numbers as students. Such ‘grassroots’ educational urgency transcends the dominant discourse on diversity and challenges presumptions inherent in top down initiatives such as ‘widening participation’. Such a collective movement from the bottom up shows the importance of understanding black female agency when unpacking the complex dynamics of gendered and racialised exclusion. Black women’s desire for education and learning makes possible a reclaiming of higher education from creeping instrumentalism and reinstates it as a radical site of resistance and refutation
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
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