12,258 research outputs found
Harmonic sets and the harmonic prime number theorem
We restrict primes and prime powers to sets H(x)= U∞n=1 (x/2n, x/(2n-1)). Let θH(x)= ∑ pεH(x)log p. Then the error in θH(x) has, unconditionally, the expected order of magnitude θH (x)= xlog2 + O(√x). However, if ψH(x)= ∑pmε H(x) log p then ψH(x)= xlog2+ O(log x). Some reasons for and consequences of these sharp results are explored. A proof is given of the “harmonic prime number theorem” π H(x)/ π(x) → log2
Toxicity of materials in fire situations: Laboratory data obtained at the University of San Francisco
Approximately 300 materials were evaluated using a specific set of test conditions. Materials tested included wood, fibers, fabrics and synthetic polymers. Data obtained using 10 different sets of test conditions are presented
Optimising sward structure and herbage yield for the performance of dairy cows at pasture.
End of Project ReportsThe basic unit of intake is the bite. The total daily intake of grazed
grass is determined by the number of bites taken and the weight of the
average bite. In this project the focus was on sward structure (architecture)
and its effects on bite volume and weight. There were two objectives. The
first was to determine the plant growth mechanism responsible for variations
in sward structure. The investigation was carried out at The Queen’s
University in Belfast and involved microscopic study of leaves from plants
grown under controlled conditions. The second objective, to determine how
bite volume and mass was affected by differences in sward structure was a
field study using fistulated cows and was done at Moorepark.EU Structural Funds
(EAGGF
Active Carbon and Oxygen Shell Burning Hydrodynamics
We have simulated 2.5 s of the late evolution of a star with full hydrodynamic behavior. We present the first simulations
of a multiple-shell burning epoch, including the concurrent evolution and
interaction of an oxygen and carbon burning shell. In addition, we have evolved
a 3D model of the oxygen burning shell to sufficiently long times (300 s) to
begin to assess the adequacy of the 2D approximation. We summarize striking new
results: (1) strong interactions occur between active carbon and oxygen burning
shells, (2) hydrodynamic wave motions in nonconvective regions, generated at
the convective-radiative boundaries, are energetically important in both 2D and
3D with important consequences for compositional mixing, and (3) a spectrum of
mixed p- and g-modes are unambiguously identified with corresponding adiabatic
waves in these computational domains. We find that 2D convective motions are
exaggerated relative to 3D because of vortex instability in 3D. We discuss the
implications for supernova progenitor evolution and symmetry breaking in core
collapse.Comment: 5 pages, 4 figures in emulateapj format. Accepted for publication in
ApJ Letters. High resolution figure version available at
http://spinach.as.arizona.ed
Constraint algebra in LQG reloaded : Toy model of a U(1)^{3} Gauge Theory I
We analyze the issue of anomaly-free representations of the constraint
algebra in Loop Quantum Gravity (LQG) in the context of a
diffeomorphism-invariant gauge theory in three spacetime dimensions. We
construct a Hamiltonian constraint operator whose commutator matches with a
quantization of the classical Poisson bracket involving structure functions.
Our quantization scheme is based on a geometric interpretation of the
Hamiltonian constraint as a generator of phase space-dependent diffeomorphisms.
The resulting Hamiltonian constraint at finite triangulation has a conceptual
similarity with the "mu-bar"-scheme in loop quantum cosmology and highly
intricate action on the spin-network states of the theory. We construct a
subspace of non-normalizable states (distributions) on which the continuum
Hamiltonian constraint is defined which leads to an anomaly-free representation
of the Poisson bracket of two Hamiltonian constraints in loop quantized
framework.Comment: 60 pages, 6 figure
Analysis of the kinetic mechanism of recombinant human isoprenylcysteine carboxylmethyltransferase (Icmt)
BACKGROUND: Isoprenylcysteine carboxyl methyltransferase (Icmt) is the third of three enzymes that posttranslationally modify proteins that contain C-terminal CaaX motifs. The processing of CaaX proteins through this so-called prenylation pathway via a route initiated by addition of an isoprenoid lipid is required for both membrane targeting and function of the proteins. The involvement of many CaaX proteins such as Ras GTPases in oncogenesis and other aberrant proliferative disorders has led to the targeting of the enzymes involved in their processing for therapeutic development, necessitating a detailed understanding of the mechanisms of the enzymes. RESULTS: In this study, we have investigated the kinetic mechanism of recombinant human Icmt. In the reaction catalyzed by Icmt, S-adenosyl-L-methionine (AdoMet) provides the methyl group that is transferred to the second substrate, the C-terminal isoprenylated cysteine residue of a CaaX protein, thereby generating a C-terminal prenylcysteine methyl ester on the protein. To facilitate the kinetic analysis of Icmt, we synthesized a new small molecule substrate of the enzyme, biotin-S-farnesyl-L-cysteine (BFC). Initial kinetic analysis of Icmt suggested a sequential mechanism for the enzyme that was further analyzed using a dead end competitive inhibitor, S-farnesylthioacetic acid (FTA). Inhibition by FTA was competitive with respect to BFC and uncompetitive with respect to AdoMet, indicating an ordered mechanism with SAM binding first. To investigate the order of product dissociation, product inhibition studies were undertaken with S-adenosyl-L-homocysteine (AdoHcy) and the N-acetyl-S-farnesyl-L-cysteine methylester (AFCME). This analysis indicated that AdoHcy is a competitive inhibitor with respect to AdoMet, while AFCME shows a noncompetitive inhibition with respect to BFC and a mixed-type inhibition with respect to AdoMet. These studies established that AdoHcy is the final product released, and that BFC and AFCME bind to different forms of the enzyme. CONCLUSIONS: These studies establish that catalysis by human Icmt proceeds through an ordered sequential mechanism and provide a kinetic framework for analysis of specific inhibitors of this key enzyme
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