25,600 research outputs found
Sequence motifs that distinguish ATP(CTP) : tRNA nucleotidyl transferases from eubacterial poly(A) polymerases
ATP(CTP):tRNA nucleotidyl transferases, tRNA maturing enzymes found in all organisms, and eubacterial poly(A) polymerases, enzymes involved in mRNA degradation, are so similar that until now their biochemical functions could not be distinguished by their amino acid sequence. BLAST searches and analysis with the program "Sequence Space" for the prediction of functional residues revealed sequence motifs which define these two protein families. One of the poly(A) polymerase defining motifs specifies a structure that we propose to function in binding the 3' terminus of the RNA substrate. Similar motifs are found in other homopolyribonucleotidyl transferases. Phylogenetic classification of nucleotidyl tranferases from sequenced genomes reveals that eubacterial poly(A) polymerases have evolved relatively recently and are found only in a small group of bacteria and surprisingly also in plants, where they may function in organelles
Dynamical mean-field theory for the normal phase of the attractive Hubbard model
We analyze the normal phase of the attractive Hubbard model within dynamical
mean-field-theory. We present results for the pair-density, the
spin-susceptibility, the specific heat, the momentum distribution, and for the
quasiparticle weight. At weak coupling the low-temperature behavior of all
quantities is consistent with Fermi liquid theory. At strong coupling all
electrons are bound pairs, which leads to a spin gap and removes fermionic
quasi-particle excitations. The transition between the Fermi liquid phase and
the pair phase takes place at a critical coupling of the order of the
band-width and is generally discontinuous at sufficiently low temperatures
Economic method for measuring ultra-low flow rates of fluids
Capillary tube flowmeter measures ultra-low flows of very corrosive fluids /such as chlorine trifluoride and liquid fluorine/ and other liquids with reasonable accuracy. Flowmeter utilizes differential pressure transducer and operates on the principle that for laminar flow in the tube, pressure drop is proportional to flow rate
Non trivial examples of coupled equations for K\"ahler metrics and Yang-Mills connections
We provide non trivial examples of solutions to the system of coupled
equations introduced by M. Garc\'ia-Fern\'andez for the uniformization problem
of a triple where is a holomorphic vector bundle over a polarized
complex manifold , generalizing the notions of both constant scalar
curvature K\"ahler metric and Hermitian-Einstein metric.Comment: 17 page
An error accounting algorithm for electron counting experiments
Electron counting experiments attempt to provide a current of a known number
of electrons per unit time. We propose architectures utilizing a few readily
available electron-pumps or turnstiles with modest error rates of 1 part per
with common sensitive electrometers to achieve the desirable accuracy of
1 part in . This is achieved not by counting all transferred electrons
but by counting only the errors of individual devices; these are less frequent
and therefore readily recognized and accounted for. Our proposal thereby eases
the route towards quantum based standards for current and capacitance.Comment: 5 pages, 3 figures. Builds on and extends white paper arXiv:0811.392
Pressure regulating system Patent
Pressure regulating system with high pressure fluid source, adapted to maintain constant downstream pressur
W Plus Heavy Quark Production at the Tevatron
We summarize the motivations for and the status of the calculation of the heavy quark production process in colliders to Next-to-Leading
Order in QCD. This process can be used to constrain the strange quark
distribution function at high at the Tevatron, and also to study the
bottom content of ~jet events. In addition, when crossed, the calculation
essentially describes the single top quark production process to
Next-to-Leading Order in QCD.Comment: Presented by S. Keller at DPF94 Meeting, Albuquerque, New Mexico,
August 1-6,1994. 4 pages, no macros, no figures. Fermilab-Conf-94/260-T,
FSU--HEP--940817. A postscript file is available via anonymous ftp at
hepsg1.physics.fsu.edu, file is /pub/keller/fsu-hep-940817.p
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