Polysulphides and extreme-pressure lubrication

Imperial Users onl

Empirical relation between induced velocity, thrust, and rate of descent of a helicopter rotor as determined by wind-tunnel tests on four model rotors

The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests

Réflexion critique sur l'hétérogène

Les deux auteurs proposent une réflexion critique qui fait retour sur les articles réunis dans ce recueil. Si l'envergure interdisciplinaire et historique de l'objet «hétérogène» paraît illimitée, l'apparition en force de cet objet aujourd'hui est néanmoins liée à un intérêt de connaissance qui émane d'une conjoncture précise: le passage du modernisme au postmodernisme. Dans cette conjoncture, il s'agit d'expliciter clairement les enjeux épistémiques de la connaissance de l'hétérogèneThe two authors engage in a critical reflexion on the essays gathered in this collection. While the interdisciplinary as well as historical range of the heterogeneous object seems illimited, its strong emergence today is clearly linked with an interest of knowledge rooted in a precise historical situation: the transition from modernism to postmodernism. In this situation it is important to spell out the epistemic issues involved in the process of aquiring knowledge about heterogeneous objects

Empirical Relation Between Induced Velocity, Thrust, and Rate of Descent of a Helicopter Rotor as Determined by Wind-tunnel Tests on Four Model Rotors

The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests

Meta-Analysis of Anger and Persuasion: An Empirical Integration of Four Models

Despite the increasing use of anger in persuasive messaging, such as political ads and health campaigns, very little is known about when and how anger affects persuasion. Building on theoretical propositions derived from four theoretical models that have addressed the link between anger and persuasion, the current meta-analysis (k = 55, N = 6,805) finds a weak impact of anger on behavior (r = .15, p = .04) and nonsignificant effects on attitudes (r = −.03, p = .30) and intent (r = .06, p = .13). Yet a closer look reveals a more complicated reality, where positive effects are identified with the presence of strong arguments, relevant anger, and the inclusion of efficacy appeals. Further, the study identifies an interplay between emotional intensity and argument strength, such that argument strength plays an important role only at lower levels of anger. The study concludes by integrating the results and proposing three promising areas for future research into anger and persuasion

Comprehensive mean-field analysis of magnetic and charge orders in the two-dimensional Hubbard model

We present an unbiased mean-field analysis of magnetic and charge orders in the two-dimensional Hubbard model on a square lattice, both at zero and finite temperatures. Unrestricted Hartree-Fock calculations on large finite lattices are complemented by solutions restricted to N\'eel and circular spiral order in the thermodynamic limit. The magnetic states are classified by a systematic scheme based on the dominant Fourier components of the spin texture. On finite lattices a whole zoo of ordering patterns appears. We show that many of these states are finite size artifacts related to the limited choice of ordering wave vectors on a finite lattice. In the thermodynamic limit only three classes of states with a relatively simple structure survive: N\'eel, circular spiral, and stripe states. Stripes involve also charge order and can be unidirectional or bidirectional, with horizontal and/or vertical orientation. We present complete phase diagrams in the plane spanned by electron density and temperature, for a moderate Hubbard interaction and various choices of the next-nearest neighbor hopping amplitude.Comment: 15 pages, 14 figure

Patterns and sources of anthropogenic contaminants in the Otter Creek watershed, Madison County, Kentucky

Stream systems are often affected by anthropogenic contaminants that affect water quality and stream ecosystems. Land use determines the type and quantity of contaminants present in natural waters. The Otter Creek watershed (170 km2; Madison County, Kentucky) consists predominantly of pasture and rural housing, with some cropland. The basin also receives runoff from the town of Richmond and a sewage treatment plant operates within the watershed. We measured concentrations of nutrients (phosphate, ammonium, nitrate) and fecal microbes to discover levels of anthropogenic contaminants affecting water quality and to identify contaminant sources. We sampled 4 times in the summer field season of 2015 over a variety of conditions. Water samples for nutrient analysis were pressed through a 0.45 µm filter, placed in pre-acidified vials, and measured one or two days after collection. Nutrients were measured colorimetrically using established methods. Microbial samples were collected in sterile containers, placed on ice in the field, and then transported to the lab where they were spiked with Colilert-18 media. Samples incubated overnight at 35oC, and Escherichia coli were quantified using IDEXX rapid-assay techniques. Phosphate (0 – 0.5 mg/L) and ammonium (\u3c0.1 mg/L) concentrations were low for all sampling days, whereas nitrate was the dominant anthropogenic nutrient contaminant showing concentrations of 1 – 3 mg/L. Consistently higher levels of phosphate and nitrate were found in the waters of Dreaming Creek, which drains urban Richmond. High ammonium levels were sporadic and associated with pasture. High E. coli counts occurred in Dreaming Creek, the upper reaches of Otter Creek, and proximal to pastures. Both point- and non-point sources exist for contaminants. The sewage treatment plant is a definite point source for nitrate and less so for phosphate and ammonium. High concentrations of nitrate, phosphate, and fecal microbes occur along Dreaming Creek, likely due to leaky sewage distribution pipes. Spikes in ammonium concentration are sourced from cattle pasture. We also tested contaminant levels immediately before and after a rainfall event associated with tropical storm Bill. Phosphate and ammonium levels decreased, whereas nitrate increased significantly. E. coli counts also increased dramatically

Patterns of anthropogenic nutrient contaminants in the Otter Creek watershed, Madison County, Kentucky

We measured nutrient concentrations within the Otter Creek watershed (Madison County, Kentucky) to: (1) discover levels of anthropogenic contaminants affecting the water quality; (2) compare these measurements to a national data set; and (3) identify nutrient sources. The watershed mainly drains rural land characterized by cattle grazing, but also drains the town of Richmond. We sampled throughout the watershed to gain a representative perspective of nutrient levels and specifically targeted localities of suspected anthropogenic nutrient sources. Water samples were passed through a 0.45 mm filter, placed in pre-acidified vials, and measured one to two days after collection. Nutrients – ammonium, nitrate, and phosphate – were measured colorimetrically using the sodium hypochlorite, cadmium reduction, and ascorbic acid methods, respectively. Nutrients within the watershed show distinctively different concentration patterns. Ammonium and phosphate levels remain low for all sampling days. Higher ammonium concentrations are sporadic, but higher phosphate levels persist along Dreaming Creek, which drains Richmond. Nitrate consistently shows higher concentration levels of 4 to 7 mg/L and generally falls with the 25 to 50 percentile range as compared to impacted streams nationally. We sampled the watershed before and after a significant rain event. Ammonium and phosphate values changed little, but much larger amounts of nitrate entered Otter Creek afterward. We attribute higher nutrient values to several sources. A sewage treatment plant is a definite point source for nitrate and to lesser extent for phosphate. High nutrient values in Dreaming Creek are likely due leaky sewage pipes. The major non-point source is from cattle pasture

Extreme suction attachment performance from specialised insects living in mountain streams (Diptera: Blephariceridae).

Suction is widely used by animals for strong controllable underwater adhesion but is less well understood than adhesion of terrestrial climbing animals. Here we investigate the attachment of aquatic insect larvae (Blephariceridae), which cling to rocks in torrential streams using the only known muscle-actuated suction organs in insects. We measured their attachment forces on well-defined rough substrates and found that their adhesion was less reduced by micro-roughness than that of terrestrial climbing insects. In vivo visualisation of the suction organs in contact with microstructured substrates revealed that they can mould around large asperities to form a seal. We have shown that the ventral surface of the suction disc is covered by dense arrays of microtrichia, which are stiff spine-like cuticular structures that only make tip contact. Our results demonstrate the impressive performance and versatility of blepharicerid suction organs and highlight their potential as a study system to explore biological suction mechanisms