1,178 research outputs found
Design and manufacturing concepts for thermoplastic structures
Results to date on the application of two manufacturing techniques, fiber placement and single diaphragm/coconsolidation, to produce cost-effective, thermoplastic composite (TPC), primary fuselage structure are presented. Applications relative to fuselage upper cover structure indicate potential cost savings relative to conventional approaches. Progress is also presented on efforts concerned with other design details which take advantage of thermoplastic composites such as fastener less stiffener/frame attachments. In addition, results are presented on the development and verification testing of a composite lug analysis program which incorporates through-the-thickness effects
The Four-Loop Planar Amplitude and Cusp Anomalous Dimension in Maximally Supersymmetric Yang-Mills Theory
We present an expression for the leading-color (planar) four-loop four-point
amplitude of N=4 supersymmetric Yang-Mills theory in 4-2 e dimensions, in terms
of eight separate integrals. The expression is based on consistency of
unitarity cuts and infrared divergences. We expand the integrals around e=0,
and obtain analytic expressions for the poles from 1/e^8 through 1/e^4. We give
numerical results for the coefficients of the 1/e^3 and 1/e^2 poles. These
results all match the known exponentiated structure of the infrared
divergences, at four separate kinematic points. The value of the 1/e^2
coefficient allows us to test a conjecture of Eden and Staudacher for the
four-loop cusp (soft) anomalous dimension. We find that the conjecture is
incorrect, although our numerical results suggest that a simple modification of
the expression, flipping the sign of the term containing zeta_3^2, may yield
the correct answer. Our numerical value can be used, in a scheme proposed by
Kotikov, Lipatov and Velizhanin, to estimate the two constants in the
strong-coupling expansion of the cusp anomalous dimension that are known from
string theory. The estimate works to 2.6% and 5% accuracy, providing
non-trivial evidence in support of the AdS/CFT correspondence. We also use the
known constants in the strong-coupling expansion as additional input to provide
approximations to the cusp anomalous dimension which should be accurate to
under one percent for all values of the coupling. When the evaluations of the
integrals are completed through the finite terms, it will be possible to test
the iterative, exponentiated structure of the finite terms in the four-loop
four-point amplitude, which was uncovered earlier at two and three loops.Comment: 72 pages, 15 figures, v2 minor correction
D = 5 maximally supersymmetric Yang-Mills theory diverges at six loops
The connection of maximally supersymmetric Yang-Mills theory to the (2,0)
theory in six dimensions has raised the possibility that it might be
perturbatively ultraviolet finite in five dimensions. We test this hypothesis
by computing the coefficient of the first potential ultraviolet divergence of
planar (large N_c) maximally supersymmetric Yang-Mills theory in D = 5, which
occurs at six loops. We show that the coefficient is nonvanishing. Furthermore,
the numerical value of the divergence falls very close to an approximate
exponential formula based on the coefficients of the divergences through five
loops. This formula predicts the approximate values of the ultraviolet
divergence at loop orders L > 6 in the critical dimension D = 4 + 6/L. To
obtain the six-loop divergence we first construct the planar six-loop
four-point amplitude integrand using generalized unitarity. The ultraviolet
divergence follows from a set of vacuum integrals, which are obtained by
expanding the integrand in the external momenta. The vacuum integrals are
integrated via sector decomposition, using a modified version of the FIESTA
program.Comment: 31 pages, revtex, 12 figure
The effect of environment and superalloy composition on TBC lifetime
While the water vapor content of the combustion gas in natural gas-fired land based turbines is ~10%, it can be 20-85% with coal-derived (syngas or H2) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO2 contents to facilitate carbon capture and sequestration. Also, for land-based, power-generation turbines, there is industry interest in reducing alloy costs by decreasing the superalloy Re content, either by developing new alloys or employing earlier generation superalloys. To investigate the effects of these variables on thermal barrier coating (TBC) lifetime, furnace cycling tests (1h cycles) were performed in air with 10, 50 and 90 vol.% water vapor, O2-50%H2O and CO2-10%H2O and compared to prior results in dry air or O2. Two types of TBC’s were investigated: (1) diffusion bond coatings (Pt diffusion or simple or Pt-modified aluminide) with commercially vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 (1.5%Re) substrates and (2) high velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air-plasma sprayed YSZ top coatings on superalloy X4, 1483 and 247 substrates. For both types of coatings, a 20-50% decrease in coating lifetime was observed with the addition of water vapor for all but the Pt diffusion coatings which were unaffected by the environment. However, the higher water vapor contents in air did not further decrease the coating lifetime. Initial results for similar diffusion bond coatings in CO2-10%H2O also did not show a decrease in lifetime due to the addition of CO2. Characterization of the failed coating microstructures showed only minor effects of water vapor and CO2 additions that do not appear to account for the changes in lifetimes observed. Reductions in TBC lifetime were observed for 1483 substrates (compared to X4), which were attributed to the lower Al content and possible the higher Ti content. The higher Hf content in N515 (compared to N5) likely explains the higher TBC lifetimes observed for this substrate. More recent work with 247 substrates is in progress as well as furnace testing with 100h cycles to better simulate the base load duty cycle. Future work also is planned to investigate the role of SO2 on TBC lifetime as increased water vapor contents in the exhaust do not explain the current 50°-100°C de-rating of syngas-fired turbines
Oil Prices and the Macroeconomy
Citation: Bachmeier, L. and Plante, M. (2018) Oil Prices and the Macroeconomy. Unpublished manuscript.The combination of high inflation and high unemployment experienced in the 1970s and early 1980s has been perhaps the most important macroeconomic event since the Great Depression. Figure 1 shows that there were two spikes in the price of oil in this time period, and both were followed by large increases in inflation and unemployment. This was widely viewed as evidence that changes in the price of oil have large effects on the economy. Not surprisingly, this episode has been the subject of considerable research
Repair of \u3cem\u3eO\u3c/em\u3e\u3csup\u3e6\u3c/sup\u3e-Methylguanine Adducts in Human Telomeric G-Quadruplex DNA by \u3cem\u3eO\u3c/em\u3e\u3csup\u3e6\u3c/sup\u3e-Alkylguanine-DNA Alkyltransferase
O6-alkylguanine-DNA alkyltransferase (AGT) is a single-cycle DNA repair enzyme that removes pro-mutagenic O6-alkylguanine adducts from DNA. Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood. Here, we examine the functions of this enzyme on O6-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex. On a folded 22-nt G-quadruplex substrate, binding saturated at 2 AGT:DNA, significantly less than the ~ 5 AGT:DNA found with linear single-stranded DNAs of similar length, and less than the value found with the telomere sequence under conditions that inhibit quadruplex formation (4 AGT:DNA). Despite these differences, AGT repaired 6mG adducts located within folded G-quadruplexes, at rates that were comparable to those found for a duplex DNA substrate under analogous conditions. Repair was kinetically biphasic with the amplitudes of rapid and slow phases dependent on the position of the adduct within the G-quadruplex: in general, adducts located in the top or bottom tetrads of a quadruplex stack exhibited more rapid-phase repair than did adducts located in the inner tetrad. This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs
Fipronil metabolism, oxidative sulfone formation and toxicity among organophosphate- and carbamate-resistant and susceptible western corn rootworm populations
Fipronil toxicity and metabolism were studied in two insecticide-resistant, and one susceptible western corn rootworm (Diabrotica virgifera virgifera, LeConte) populations. Toxicity was evaluated by exposure to surface residues and by topical application. Surface residue bioassays indicated no differences in fipronil susceptibility among the three populations. Topical bioassays were used to study the relative toxicity of fipronil, fipronil. the mono-oxygenase inhibitor piperonyl butoxide, and fipronil\u27s oxidative sulfone metabolite in two populations (one resistant with elevated mono-oxygenase activity). Fipronil and fipronil-sulfone exhibited similar toxicity and application of piperonyl butoxide prior to fipronil resulted in marginal effects on toxicity. Metabolism of [14C]fipronil was evaluated in vivo and in vitro in the three rootworm populations. In vivo studies indicated the dominant pathway in all populations to be formation of the oxidative sulfone metabolite. Much lower quantities of polar metabolites were also identified. In vitro studies were performed using sub-cellular protein fractions (microsomal and cytosolic), and glutathione-agarose purified glutathione-Stransferase. Oxidative sulfone formation occurred almost exclusively in in vitro microsomal reactions and was increased in the resistant populations. Highly polar metabolites were formed exclusively in in vitro cytosolic reactions. In vitro reactions performed with purified, cytosolic glutathione-Stransferase (MW=27kDa) did not result in sulfone formation, although three additional polar metabolites not initially detectable in crude cytosolic reactions were detected. Metabolism results indicate both cytochromes P450 and glutathione-S-transferases are important to fipronil metabolism in the western corn rootworm and that toxic sulfone formation by P450 does not affect net toxicity
Fipronil metabolism, oxidative sulfone formation and toxicity among organophosphate- and carbamate-resistant and susceptible western corn rootworm populations
Fipronil toxicity and metabolism were studied in two insecticide-resistant, and one susceptible western corn rootworm (Diabrotica virgifera virgifera, LeConte) populations. Toxicity was evaluated by exposure to surface residues and by topical application. Surface residue bioassays indicated no differences in fipronil susceptibility among the three populations. Topical bioassays were used to study the relative toxicity of fipronil, fipronil. the mono-oxygenase inhibitor piperonyl butoxide, and fipronil\u27s oxidative sulfone metabolite in two populations (one resistant with elevated mono-oxygenase activity). Fipronil and fipronil-sulfone exhibited similar toxicity and application of piperonyl butoxide prior to fipronil resulted in marginal effects on toxicity. Metabolism of [14C]fipronil was evaluated in vivo and in vitro in the three rootworm populations. In vivo studies indicated the dominant pathway in all populations to be formation of the oxidative sulfone metabolite. Much lower quantities of polar metabolites were also identified. In vitro studies were performed using sub-cellular protein fractions (microsomal and cytosolic), and glutathione-agarose purified glutathione-Stransferase. Oxidative sulfone formation occurred almost exclusively in in vitro microsomal reactions and was increased in the resistant populations. Highly polar metabolites were formed exclusively in in vitro cytosolic reactions. In vitro reactions performed with purified, cytosolic glutathione-Stransferase (MW=27kDa) did not result in sulfone formation, although three additional polar metabolites not initially detectable in crude cytosolic reactions were detected. Metabolism results indicate both cytochromes P450 and glutathione-S-transferases are important to fipronil metabolism in the western corn rootworm and that toxic sulfone formation by P450 does not affect net toxicity
Fipronil metabolism, oxidative sulfone formation and toxicity among organophosphate- and carbamate-resistant and susceptible western corn rootworm populations
- …