1,560 research outputs found
Surface Waves on Byrd Glacier, Antarctica
Byrd Glacier has one of the largest ice catchment areas in Antarctica, delivers more ice to the Ross Ice Shelf than any other ice stream, and is the fastest of these ice streams. A force balance, combined with a mass balance, demonstrates that stream flow in Byrd Glacier is transitional from sheet flow in East Antarctica to shelf flow in the Ross Ice Shelf. The longitudinal pulling stress, calculated along an ice flowband from the force balance, is linked to variations of ice thickness, to the ratio of the basal water pressure to the ice overburden pressure where Byrd Glacier is grounded, and is reduced by an ice-shelf buttressing stress where Byrd Glacier is floating. Longitudinal tension peaks at pressure-ratio maxima in grounded ice and close to minima in the ratio of the pulling stress to the buttressing stress in floating ice. The longitudinal spacing of these tension peaks is rather uniform and, for grounded ice, the peaks occur at maxima in surface slope that have no clear relation to the bed slope. This implies that the maxima in surface slope constitute a wave train that is related to regular variations in ice-bed coupling, not primarily to bed topography. It is unclear whether these surface waves are standing waves or are migrating either upslope or downslope, possibly causing the grounding line to either retreat or advance. Deciding which is the case will require obtaining bed topography in the map plane, a new map of surface topography, and more sophisticated modeling that includes ice flow linked to subglacial hydrology in the map plane
High resolution charge-exchange spectroscopic measurements of aluminum impurity ions in a high temperature plasma
Charge-exchange recombination spectroscopy, which is generally used to measure low-Z impurities in fusion devices, has been used for measuring Al+11 and Al+13 impurities in the Madison Symmetric Torus reversed field pinch. To obtain the impurity ion temperature, the experimental emission spectrum is fitted with a model which includes fine structure in the atomic transition. Densities of these two ionization states, calculated from charge-exchange emission brightness, are used in combination with a collisional radiative model to estimate the abundance of all other charge states of aluminum in the plasma and the contribution of aluminum to the effective ionic charge of the plasma
Exact broken-symmetry states and Hartree-Fock solutions for quantum dots at high magnetic fields
Wigner molecules formed at high magnetic fields in circular and elliptic
quantum dots are studied by exact diagonalization (ED) and unrestricted
Hartree-Fock (UHF) methods with multicenter basis of displaced lowest Landau
level wave functions. The broken symmetry states with semi-classical charge
density constructed from superpositions of the ED solutions are compared to the
UHF results. UHF overlooks the dependence of the few-electron wave function on
the actual relative positions of electrons localized in different charge
puddles and partially compensates for this neglect by an exaggerated separation
of charge islands which are more strongly localized than in the exact
broken-symmetry states.Comment: QD2004 proceedings under press in Physica
Effect of grazing and mowing on the clonal structure of Elytrigia atherica: a long-term study of abandoned and managed sites
Physical disturbance by large herbivores can affect species diversity at the community level and concurrently
genetic diversity at the species level. As seedling establishment is rarely observed in clonal
plants, short-term experiments and demographic studies are unlikely to reveal the response of clonal
plants to disturbances. A long-term (30-year) field experiment and the availability of molecularmarkers
allowed us to investigate the clonal structure of populations of Elytrigia atherica subjected to different
management regimes. The long-term field study provided us with five replicated blocks that had
been subjected to three different management regimes, grazing by cattle, mowing and abandonment.
In this study we examined the effects of herbivore grazing andmowing on clonal richness and genetic
diversity of populations in salt marshes using multilocus microsatellite genotypes. In addition,
phenotypic traits and spatial positions of E. atherica ramets were determined for 20 samples in a 5 Ă— 10m
plot in each of the blocks. Abundance and phenotypic traits were affected by the management
regimes, resulting in a higher abundance in abandoned fields and plants having shorter and narrower
leaves in managed fields. Biomass removal did affect the clonal structure of populations and increased
the genetic diversity compared to that in abandoned fields. However, no distinct difference was found
between the two management regimes, mowing and grazing. Although seedling recruitment has
rarely been observed, the present study shows that such rare events have occurred within the populations
studied. Thus, molecular tools can greatly increase our understanding of vegetation dynamics
and processes within populations growing under different conditions
Ground state energies of quantum dots in high magnetic fields: A new approach
We present a new method for calculating ground state properties of quantum
dots in high magnetic fields. It takes into account the equilibrium positions
of electrons in a Wigner cluster to minimize the interaction energy in the high
field limit. Assuming perfect spin alignment the many-body trial function is a
single Slater determinant of overlapping oscillator functions from the lowest
Landau level centered at and near the classical equilibrium positions. We
obtain an analytic expression for the ground state energy and present numerical
results for up to N=40.Comment: 4 pages, including 2 figures, contribution to the Proceedings of
EP2DS-14, submitted to Physica
Light-chain-induced renal tubular acidosis: effect of sodium bicarbonate on sodium-proton exchange
We measured sodium-proton (Na+/H+) exchange in lymphocytes and platelets of a 46-year-old woman with the adult Fanconi syndrome before, during, and after treatment with NaHCO3. Kappa light chains in her urine and unique but rarely observed crystalline structures confirmed the presence of light-chain nephropathy. Her glomerular filtration rate was only moderately impaired at 72 ml/min. NaHCO3 at 1, 3, and 5 mmol/kg/day for 5 days increased her serum HCO3 and pH from 17 to 21 mmol/l and 7.28 to 7.39 respectively. Plasma renin and aldosterone values were decreased by NaHCO3. Na+/H+ exchange (δHi/min) was measured with the fluorescent marker BCECF after acidification of lymphocytes and platelets with sodium propionate at five (10-50mM) doses. Na+/H+ exchange was accelerated in this patient compared to normal controls. NaHCO3 treatment significantly decreased Na+/H+ exchange in lymphocytes, but not in platelets. These findings suggest that Na+/H+ exchange can be influenced by NaHCO3 ingestion at doses that only modestly affect systemic pH. Since Na+/H+ exchange is involved in stimulus response coupling, cell growth regulation, cell differentiation, and perhaps the progression of nephrosclerosis, these observations may have clinical relevanc
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