30,302 research outputs found
On the Algebraic Structure of Gravitational Descendants in CP(n-1) Coset Models
We investigate how specific free-field realizations of twisted N=2
supersymmetric coset models give rise to natural extensions of the ``matter''
Hilbert spaces in such a manner as to incorporate the various gravitational
excitations. In particular, we show that adopting a particular screening
prescription is equivalent to imposing the requisite equivariance condition on
cohomology. We find a simple algebraic characterization of the
-gravitational ground ring spectra of these theories in terms of
affine- highest weights..Comment: 12p, harvmac/lanlmac with hyperlinks, 1 uuencoded PostScript figure,
CERN-TH.7442/94, USC-94/01
Free Field Realization of Super Algebra
We study the quantum super- algebra using the free field
realization, which is obtained from the supersymmetric Miura transformation
associated with the Lie superalgebra . We compute the full operator
product expansions of the algebra explicitly. It is found that the results
agree with those obtained by the OPE method.Comment: 10 pages, latex, NBI-HE-93-0
Food-chain competition influences gene's size
We have analysed an effect of the Bak-Sneppen predator-prey food-chain
self-organization on nucleotide content of evolving species. In our model,
genomes of the species under consideration have been represented by their
nucleotide genomic fraction and we have applied two-parameter Kimura model of
substitutions to include the changes of the fraction in time. The initial
nucleotide fraction and substitution rates were decided with the help of random
number generator. Deviation of the genomic nucleotide fraction from its
equilibrium value was playing the role of the fitness parameter, , in
Bak-Sneppen model. Our finding is, that the higher is the value of the
threshold fitness, during the evolution course, the more frequent are large
fluctuations in number of species with strongly differentiated nucleotide
content; and it is more often the case that the oldest species, which survive
the food-chain competition, might have specific nucleotide fraction making
possible generating long genesComment: 11 pages including 7 figure
Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Rr: C-H and N-H activation and catalytic transfer hydrogenation
Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine–NHC and amido–NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [( p -cymene)RuCl 2 ] 2 and [Cp*MCl 2 ] 2 (M = Rh, Ir). Treating 2a with [Cp*MCl 2 ] 2 and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3 ;M = Ir, 4 ), resulting from aromatic C–H activation. In contrast, treating 2b with [( p -cymene)RuCl 2 ] 2 ,Ag 2 O and KI gave the amine–NHC complex [( p -cymene)Ru(C,NH 2 )I]I ( 5 ). The reaction of 2b with [Cp*MCl 2 ] 2 (M = Rh, Ir), NaO t Bu and KI gave the amine–NHC complex [Cp*Rh(NH 2 )I]I ( 6 ) or the amido–NHC complex Cp*Ir(C,NH)I ( 7 ); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine–NHC complex [Cp*Ir(C,NH 2 )I][CF 3 CO 2 ]( 8 ). These are the first primary amine– or amido–NHC complexes of Rh and Ir. Solid-state structures of the complexes 3–8 have been determined by single crystal X-ray diffraction. Complexes 5 , 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity
Non-catalytic Roles of Tet2 Are Essential to Regulate Hematopoietic Stem and Progenitor Cell Homeostasis
The Ten-eleven translocation (TET) enzymes regulate gene expression by promoting DNA demethylation and partnering with chromatin modifiers. TET2, a member of this family, is frequently mutated in hematological disorders. The contributions of TET2 in hematopoiesis have been attributed to its DNA demethylase activity, and the significance of its nonenzymatic functions has remained undefined. To dissect the catalytic and non-catalytic requirements of Tet2, we engineered catalytically inactive Tet2 mutant mice and conducted comparative analyses of Tet2 mutant and Tet2 knockout animals. Tet2 knockout mice exhibited expansion of hematopoietic stem and progenitor cells (HSPCs) and developed myeloid and lymphoid disorders, while Tet2 mutant mice predominantly developed myeloid malignancies reminiscent of human myelodysplastic syndromes. HSPCs from Tet2 knockout mice exhibited distinct gene expression profiles, including downregulation of Gata2. Overexpression of Gata2 in Tet2 knockout bone marrow cells ameliorated disease phenotypes. Our results reveal the non-catalytic roles of TET2 in HSPC homeostasis
A Neumann interface optimal control problem with elliptic PDE constraints and its discretization and numerical analysis
We study an optimal control problem governed by elliptic PDEs with interface,
which the control acts on the interface. Due to the jump of the coefficient
across the interface and the control acting on the interface, the regularity of
solution of the control problem is limited on the whole domain, but smoother on
subdomains. The control function with pointwise inequality constraints is
served as the flux jump condition which we called Neumann interface control. We
use a simple uniform mesh that is independent of the interface. The standard
linear finite element method can not achieve optimal convergence when the
uniform mesh is used. Therefore the state and adjoint state equations are
discretized by piecewise linear immersed finite element method (IFEM). While
the accuracy of the piecewise constant approximation of the optimal control on
the interface is improved by a postprocessing step which possesses
superconvergence properties; as well as the variational discretization concept
for the optimal control is used to improve the error estimates. Optimal error
estimates for the control, suboptimal error estimates for state and adjoint
state are derived. Numerical examples with and without constraints are provided
to illustrate the effectiveness of the proposed scheme and correctness of the
theoretical analysis.Comment: 31pages, 12 figures, 4 table
Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors
Upon introducing charge carriers into the copper-oxygen sheets of the
enigmatic lamellar cuprates the ground state evolves from an insulator into a
superconductor, and eventually into a seemingly conventional metal (a Fermi
liquid). Much has remained elusive about the nature of this evolution and about
the peculiar metallic state at intermediate hole-carrier concentrations (p).
The planar resistivity of this unconventional metal exhibits a linear
temperature dependence (\rho T) that is disrupted upon cooling toward
the superconducting state by the opening of a partial gap (the pseudogap) on
the Fermi surface. Here we first demonstrate for the quintessential compound
HgBaCuO a dramatic switch from linear to purely quadratic
(Fermi-liquid-like, \rho T) resistive behavior in the pseudogap
regime. Despite the considerable variation in crystal structures and disorder
among different compounds, our result together with prior work gives new
insight into the p-T phase diagram and reveals the fundamental resistance per
copper-oxygen sheet in both linear (\rho_S = A_{1S} T) and quadratic (\rho_S =
A_{2S} T) regimes, with A_{1S} A_{2S} 1/p. Theoretical
models can now be benchmarked against this remarkably simple universal
behavior. Deviations from this underlying behavior can be expected to lead to
new insights into the non-universal features exhibited by certain compounds
An Empirical Explanation of the Anomalous Increases in the Astronomical Unit and the Lunar Eccentricity
Both the recently reported anomalous secular increase of the astronomical
unit, of the order of a few cm yr^-1, and of the eccentricity of the lunar
orbit e_ = (9+/-3) 10^-12 yr^-1 can be phenomenologically explained by
postulating that the acceleration of a test particle orbiting a central body,
in addition to usual Newtonian component, contains a small additional radial
term proportional to the radial projection vr of the velocity of the particle's
orbital motion. Indeed, it induces secular variations of both the semi-major
axis a and the eccentricity e of the test particle's orbit. In the case of the
Earth and the Moon, they numerically agree rather well with the measured
anomalies if one takes the numerical value of the coefficient of
proportionality of the extra-acceleration approximately equal to that of the
Hubble parameter H0 = 7.3 10^-11 yr^-1.Comment: Latex2e, no figures, no tables, 9 pages, 51 references. Published in
The Astronomical Journal (AJ
Functional Analysis of a Juvenile Hormone Inducible Transcription Factor, Krüppel homolog 1, in the Bean Bug, Riptortus pedestris
Juvenile hormone (JH) has two major functions in insects, i.e., suppression of metamorphosis in the larval or nymphal stage and promotion of reproduction in the adult stage. Krüppel homolog 1 (Kr-h1), a C2H2 zinc-finger type transcription factor, is reported to act downstream of the JH receptor complex. In the present study, the function of Kr-h1 was examined in adults and nymphs of Riptortus pedestris by RNA interference (RNAi). After injection of adults with dsRNA of Kr-h1, the expression level of Kr-h1 was significantly decreased in the abdomen. Kr-h1 dsRNA-injection resulted in a lower proportion of individuals with developed ovaries, but the difference was not statistically significant. The transcript levels of cyanoprotein-α and vitellogenin-1, which are JH-inducible genes encoding yolk proteins, were not affected in the abdomen by Kr-h1 knockdown. Kr-h1 dsRNA-injection was effective for suppression of Kr-h1 expression in nymphs. Some Kr-h1 dsRNA-injected fifth (final) instar nymphs had morphological defects in the wing bud. Moreover, they had several adult morphological features, including ocelli in the head, connexivum in the abdomen, coloring of the dorsal abdomen, and genitals. The nymphs possessing adult features did not emerge as adults during 1 month. These results demonstrated that Kr-h1 is necessary for maintaining nymphal characters in R. pedestris. The function of Kr-h1 in ovarian development remains unclear in R. pedestris
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