Effects of sidewall geometry on the installed performance of nonaxisymmetric convergent-divergent exhaust nozzles

The investigation was conducted at static conditions and over a Mach number range from 0.6 to 1.2. Angle of attack was held constant at 0 deg. High pressure air was used to simulate jet exhaust flow at ratios of jet total pressure to free-stream static pressure from 1 (jet off) to approximately 10. Sidewall cutback appears to be a viable way of reducing nozzle weight and cooling requirements without compromising installed performance

Effects of twin-vertical-tail parameters on twin-engine afterbody/nozzle aerodynamic characteristics

The Langley 16-foot transonic tunnel was used to determine the effects of several empennage and afterbody parameters on twin-engine aft-end aerodynamic characteristics. Model variables included twin-vertical-tail cant angle, toe angle, airfoil camber, and root-chord length and afterbody/engine interfairing shape. Tests were conducted over a Mach number range from 0.6 to 1.2 and over an angle-of-attack range from 2 deg to 10 deg. Nozzle pressure ratio was varied from 1.0 (jet off) to approximately 10.0

German mathematics teachers\u27 subject content and pedagogical content knowledge

How required teacher knowledge is obtained is debated in today\u27s educational context. This dichotomy in acquisition of teacher knowledge between university training including content and pedagogy versus classroom experiences combined with strong subject background has become particularly important as the U.S. seeks to find key components to increase student achievement and to improve education. International comparisons indicating the U.S. consistently lags behind top-performing countries have spurred such efforts; Review of existing literature exposed differences in what is considered necessary knowledge for effective teaching, and where such knowledge can be developed. Types of knowledge and where such knowledge is acquired are examined. A gap in the body of knowledge is identified followed by a description to begin to fill it. An examination of international mathematical comparisons, typically resulting in an Asian-U.S. comparison, is included. Justification is provided to analyze Germany to challenge current assumptions concerning teacher knowledge and the role thereof on student achievement. German teachers receive increased content and pedagogy training, yet German students score only average on international mathematics comparisons; To understand better the impact of reforms calling for increased teacher subject content knowledge, further investigation into teachers\u27 understanding of subject content knowledge along with contributions to such knowledge was conducted. To investigate this issue three research questions emerged: Do German mathematics teachers possess the knowledge and skills to solve correctly basic mathematics problems? Can they translate this knowledge into accurate representations? According to them, what is the contribution of teacher education and classroom experiences in building teacher knowledge? A qualitative interview project approach involving surveys and interviews was utilized; Findings indicate that German mathematics teachers possess the knowledge and skills to solve basic mathematical problems correctly implying solid subject content knowledge; however, are not as successful in generating accurate representations and explanations implying a limited pedagogical content knowledge. According to these teachers, teacher preparation courses contributed to pedagogical not content knowledge while classroom experiences were valued as contributing to both types of knowledge. Results can inform educational policies, practices, and reforms in the U.S., and provide a basis for further research, with increased student achievement the ultimate goal

Effects of Head Formation and Heat Treatment on the Mechanical Properties of Connecting Rod Bolts

Oliver Racing Parts (ORP; Charlevoix, Michigan) is looking to optimize their manufacturing process for high-strength connecting rod bolts. A high yield strength is desired for the bolts because deformation would result in catastrophic engine failure. The bolts were made of H11, a chromium hot-work tool steel; and MLX17, a precipitation hardenable stainless steel. Tensile testing was performed to determine the tensile and yield strengths of the bolts. Fracture surfaces were imaged via scanning electron microscopy to characterize the failure modes. To observe the effects of bolt heading on microstructure and bolt strength, two batches of MLX17 were prepared; one batch being headed then aged (Group A); the other batch being headed, solution annealed, and then aged (Group B). These bolts were compared to H11 bolts to determine their viability for use, with the results being in the order of highest to lowest yield strength: H11 (272 ksi), MLX17 Treatment B (250 ksi), and MLX17 Treatment A (235 ksi). In the order of highest to lowest tensile strength: H11 (300 ksi), MLX17 Group B (255 ksi), MLX17 Group A (238 ksi). It is suggested that the bolt heading process is causing some overaging in the MLX17 samples, shown by the increase in strength when strain and aging from the heading process are undone through heat treatment. H11 bolts were the strongest tested. Recommendations are to not replace H11 bolts with MLX17 due to a decrease in strength

RFI mitigation with phase-only adaptive beamforming

Connected radio interferometers are sometimes used in the tied-array mode: signals from antenna elements are coherently added and the sum signal applied to a VLBI backend or pulsar processing machine. Usually there is no computer-controlled amplitude weighting in the existing radio interferometer facilities. Radio frequency interference (RFI) mitigation with phase-only adaptive beamforming is proposed for this mode of observation. Small phase perturbations are introduced in each of the antenna's signal. The values of these perturbations are optimized in such a way that the signal from a radio source of interest is preserved and RFI signals suppressed. An evolutionary programming algorithm is used for this task. Computer simulations, made for both one-dimensional and two-dimensional array set-ups, show considerable suppression of RFI and acceptable changes to the main array beam in the radio source direction.Comment: 7 pages, 11 figure

Kirby-Bauer Disc Diffusion Method Indicates Absence of Antimicrobial Properties in Ariolimax columbianus Mucus

Antibiotic resistance is a rapidly accelerating epidemic demanding novel approaches. Gastropod mucus has been shown to possess antimicrobial properties and could potentially be used as an ingredient in antibiotic development. However, whether the mucus of Ariolimax columbianus, the banana slug, also displays antimicrobial properties is unknown. In this study, we investigated whether the mucus of A. columbianus is resistant to Escherichia coli (E.coli), Streptococcus aureus (S.aureus), and Klebsiella pneumoniae (K.pneumoniae), three medically relevant strains of bacteria. Specimens were collected from a coniferous forest and isolated for downstream mucus extraction. We spread uniform concentrations of our bacteria on Mueller-Hinton agar plates and subjected them to a Kirby-Bauer disc diffusion test by treating them with either discs dipped in mucus or discs dipped in mucus and HBSS. Zones of inhibition did not form on the plates after subjecting the bacteria to either treatment. While this study was limited to a few taxa and one experimental approach, our study suggests that gastropod mucus may not have a generalized scope of antimicrobial activity. Rather, antimicrobial activity of mucus may be more specific to taxa encountered by the slugs in their redwood forest habitat. Our results can be used to refine mucus extraction methods for A. columbianus in future studies that seek to investigate the potential of mucus for biotechnological applications

Addition of H_2O and O_2 to Acetone and Dimethylsulfoxide Ligated Uranyl(V) Dioxocations

Gas-phase complexes of the formula [UO_2(lig)]^+ (lig = acetone (aco) or dimethylsulfoxide (dmso)) were generated by electrospray ionization (ESI) and studied by tandem ion-trap mass spectrometry to determine the general effect of ligand charge donation on the reactivity of UO_2^+ with respect to water and dioxygen. The original hypothesis that addition of O_2 is enhanced by strong σ-donor ligands bound to UO_2^+ is supported by results from competitive collision-induced dissociation (CID) experiments, which show near exclusive loss of H_2O from [UO_2(dmso)(H_2O)(O_2)]^+, whereas both H_2O and O_2 are eliminated from the corresponding [UO_2(aco)(H_2O)(O_2)]^+ species. Ligand-addition reaction rates were investigated by monitoring precursor and product ion intensities as a function of ion storage time in the ion-trap mass spectrometer: these experiments suggest that the association of dioxygen to the UO_2^+ complex is enhanced when the more basic dmso ligand was coordinated to the metal complex. Conversely, addition of H_2O is favored for the analogous complex ion that contains an aco ligand. Experimental rate measurements are supported by density function theory calculations of relative energies, which show stronger bonds between UO_2^+ and O_2 when dmso is the coordinating ligand, whereas bonds to H_2O are stronger for the aco complex