842 research outputs found
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
Transport properties of quantum dots in the Wigner molecule regime
The transport properties of quantum dots with up to N=7 electrons ranging
from the weak to the strong interacting regime are investigated via the
projected Hartree-Fock technique. As interactions increase radial order
develops in the dot, with the formation of ring and centered-ring structures.
Subsequently, angular correlations appear, signalling the formation of a Wigner
molecule state. We show striking signatures of the emergence of Wigner
molecules, detected in transport. In the linear regime, conductance is
exponentially suppressed as the interaction strength grows. A further
suppression is observed when centered-ring structures develop, or peculiar spin
textures appear. In the nonlinear regime, the formation of molecular states may
even lead to a conductance enhancement.Comment: 26 pages, 14 figures, Accepted for publication on New Journal of
Physic
Two different epigenetic information channels in wild three-spined sticklebacks are involved in salinity adaptation
Epigenetic inheritance has been proposed to contribute to adaptation and acclimation via two information channels: (i) inducible epigenetic marks that enable transgenerational plasticity and (ii) noninducible epigenetic marks resulting from random epimutations shaped by selection. We studied both postulated channels by sequencing methylomes and genomes of Baltic three-spined sticklebacks ( Gasterosteus aculeatus ) along a salinity cline. Wild populations differing in salinity tolerance revealed differential methylation (pop-DMS) at genes enriched for osmoregulatory processes. A two-generation experiment demonstrated that 62% of these pop-DMS were noninducible by salinity manipulation, suggesting that they are the result of either direct selection or associated genomic divergence at cis- or trans-regulatory sites. Two-thirds of the remaining inducible pop-DMS increased in similarity to patterns detected in wild populations from corresponding salinities. The level of similarity accentuated over consecutive generations, indicating a mechanism of transgenerational plasticity. While we can attribute natural DNA methylation patterns to the two information channels, their interplay with genomic variation in salinity adaptation is still unresolved
Spatial structure of an individual Mn acceptor in GaAs
The wave function of a hole bound to an individual Mn acceptor in GaAs is
spatially mapped by scanning tunneling microscopy at room temperature and an
anisotropic, cross-like shape is observed. The spatial structure is compared
with that from an envelope-function, effective mass model, and from a
tight-binding model. This demonstrates that anisotropy arising from the cubic
symmetry of the GaAs crystal produces the cross-like shape for the hole
wave-function. Thus the coupling between Mn dopants in GaMnAs mediated by such
holes will be highly anisotropic.Comment: 3 figures, submitted to PR
Electron correlation in metal clusters, quantum dots and quantum rings
This short review presents a few case studies of finite electron systems for
which strong correlations play a dominant role. In simple metal clusters, the
valence electrons determine stability and shape of the clusters. The ionic
skeleton of alkali metals is soft, and cluster geometries are often solely
determined by electron correlations. In quantum dots and rings, the electrons
may be confined by an external electrostatic potential, formed by a gated
heterostructure. In the low density limit, the electrons may form so-called
Wigner molecules, for which the many-body quantum spectra reveal the classical
vibration modes. High rotational states increase the tendency for the electrons
to localize. At low angular momenta, the electrons may form a quantum Hall
liquid with vortices. In this case, the vortices act as quasi-particles with
long-range effective interactions that localize in a vortex molecule, in much
analogy to the electron localization at strong rotation.Comment: Review presented in the Conference on Strongly Coupled Coulomb
Systems (SCCS), Camerino, July 200
Quantum-dot lithium in zero magnetic field: Electronic properties, thermodynamics, and a liquid-solid transition in the ground state
Energy spectra, electron densities, pair correlation functions and heat
capacity of a quantum-dot lithium in zero external magnetic field (a system of
three interacting two-dimensional electrons in a parabolic confinement
potential) are studied using the exact diagonalization approach. A particular
attention is given to a Fermi-liquid -- Wigner-solid transition in the ground
state of the dot, induced by the intra-dot Coulomb interaction.Comment: 12 pages, incl. 16 figure
Reaction paths of phosphine dissociation on silicon (001)
Using density functional theory and guided by extensive scanning tunneling microscopy (STM) image data, we formulate a detailed mechanism for the dissociation of phosphine (PH3) molecules on the Si(001) surface at room temperature. We distinguish between a main sequence of dissociation that involves PH2+H, PH+2H, and P+3H as observable intermediates, and a secondary sequence that gives rise to PH+H, P+2H, and isolated phosphorus adatoms. The latter sequence arises because PH2 fragments are surprisingly mobile on Si(001) and can diffuse away from the third hydrogen atom that makes up the PH3 stoichiometry. Our calculated activation energies describe the competition between diffusion and dissociation pathways and hence provide a comprehensive model for the numerous adsorbate species observed in STM experiments
Genotyping an Emiliania huxleyi (prymnesiophyceae) bloom event in the North Sea reveals evidence of asexual reproduction
Due to the unprecedented rate at which our climate is changing, the ultimate consequence for many species is likely to be either extinction or migration to an alternate habitat. Certain species might, however, evolve at a rate that could make them resilient to the effects of a rapidly changing environment. This scenario is most likely to apply to species that have large population sizes and rapid generation times, such that the genetic variation required for adaptive evolution can be readily supplied. Emiliania huxleyi (Lohm.) Hay and Mohler (Prymnesiophyceae) is likely to be such a species, as it is the most conspicuous extant calcareous phytoplankton species in our oceans with growth rates of 1 day−1. Here we report on a validated set of microsatellites, in conjunction with the coccolithophore morphology motif genetic marker, to genotype 93 clonal isolates collected from across the world. Of these, 52 came from a single bloom event in the North Sea collected on the D366 United Kingdom Ocean Acidification cruise in June–July 2011. There were 26 multilocus genotypes (MLGs) encountered only once in the North Sea bloom and 8 MLGs encountered twice or up to six times. Each of these repeated MLGs exhibited Psex values of less than 0.05, indicating each repeated MLG was the product of asexual reproduction and not separate meiotic events. In addition, we show that the two most polymorphic microsatellite loci, EHMS37 and P01E05, are reporting on regions likely undergoing rapid genetic drift during asexual reproduction. Despite the small sample size, there were many more repeated genotypes than previously reported for other bloom-forming phytoplankton species, including a previously genotyped E. huxleyi bloom event. This study challenges the current assumption that sexual reproduction predominates during bloom events. Whilst genetic diversity is high amongst extant populations of E. huxleyi, the root cause for this diversity and ultimate fate of these populations still requires further examination. Nonetheless, we show that certain CMM genotypes are found everywhere, while others appear to have a regional bias
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