Biomedical subjects

M Nobes

Publications and source records attributed to M Nobes.

6 recordsLinked to original sources

PubMed2005

Charmed-meson decay constants in three-flavor lattice QCD.

We present the first lattice QCD calculation with realistic sea quark content of the D+-meson decay constant f(D+). We use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain f(D+)=201+/-3+/-17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain f(Ds)=249+/-3+/-16 MeV for the Ds meson.

Journal Article↗

PubMed2005

Accurate determinations of alpha(s) from realistic lattice QCD.

We obtain a new value for the QCD coupling constant by combining lattice QCD simulations with experimental data for hadron masses. Our lattice analysis is the first to (1) include vacuum polarization effects from all three light-quark flavors (using MILC configurations), (2) include third-order terms in perturbation theory, (3) systematically estimate fourth and higher-order terms, (4) use an unambiguous lattice spacing, and (5) use an [symbol: see text](a2)-accurate QCD action. We use 28 different (but related) short-distance quantities to obtain alpha((5)/(MS))(M(Z)) = 0.1170(12).

Journal Article↗

PubMed2005

Semileptonic decays of d mesons in three-flavor lattice QCD.

We present the first three-flavor lattice QCD calculations for D-->pilnu and D-->Klnu semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC Collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1/8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at q(2)=0 are f(D-->pi)(+)(0)=0.64(3)(6) and f(D-->K)(+)(0)=0.73(3)(7), where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the Cabibbo-Kobayashi-Maskawa matrix elements |V(cd)|=0.239(10)(24)(20) and |V(cs)|=0.969(39)(94)(24), where the last errors are from experimental uncertainties.

Journal Article↗

PubMed2004

High-precision lattice QCD confronts experiment.

The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of "gold-plated" quantities. We find agreement to within statistical and systematic errors of 3% or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics.

Journal Article↗

PubMed1998

Amylin as a growth factor during fetal and postnatal development of the rat kidney.

We have previously reported that amylin has mitogenic actions on tubular epithelial cells isolated from mature rat kidney and cultured in vitro. In experiments using in situ hybridization, we have demonstrated that amylin mRNA can be detected transiently in rat metanephros from embryo day 17 (E17) to postnatal day 3 (PN3). These transcripts are localized in the sub-nephrogenic zone. RT-PCR was performed using oligonucleotide primers for rat amylin and mRNA extracted from fetal body (E19), PN1 and PN5 metanephroi, and adult rat kidney. These results corroborate the finding, using in situ hybridization, that there is a window of expression of rat amylin in the developing kidney in the perinatal period. During this period tubular elongation is evident and amylin peptide, detected by immunohistochemical staining, is found associated with developing tubules. Some of these tubules also express a brush border glycoprotein, detected by immunohistochemical staining. Amylin acts as a mitogen with primary cultures of proximal tubular epithelial cells from PN4 renal cortex. An amylin antagonist inhibited this mitogenic action suggesting that this was mediated by amylin receptors as previously described. We suggest that amylin peptide is biosynthesized in the developing proximal tubules, acts in an autocrine fashion to promote the proliferation and differentiation of brush border epithelial cells and hence plays an important role as a growth factor in the development of the kidney.

Amino Acid Sequence↗

PubMed1997

Amylin stimulates proximal tubular sodium transport and cell proliferation in the rat kidney.

In autoradiographic studies in anesthetized rats, 125I-labeled amylin binding was associated with proximal convoluted tubules but not distal tubules, interstitium, or glomeruli in the renal cortex. Split-drop micropuncture experiments showed that perfusion of the peritubular capillaries with amylin (10(-9) M) stimulated proximal tubular fluid absorption by 28%. This effect was inhibited by luminal addition of ethylisopropylamiloride, indicating mediation by a brush-border Na+/H+ exchanger. Intravenous infusion of an amylin binding antagonist, AC-187, reduced proximal fluid reabsorption (22%) in anesthetized rats, indicating a role for endogenous amylin in salt homeostasis. In primary cultures of rat proximal tubule cells, amylin (10(-7) M) stimulated proliferation with a potency equal to epidermal growth factor. Peptide antagonists (AC-187, AC-413, and AC-512) of the amylin binding sites in the renal cortex blocked the mitogenic action of amylin. We conclude that amylin acts on renal proximal tubules to promote sodium and water reabsorption and cell proliferation. These novel actions may have implications for the development of hypertension for example in non-insulin-dependent diabetes mellitus and obesity in which hyperamylinemia has been observed.

Absorption↗