Kinetic and vibration analysis of off-road bicycle suspension systems

The aim of the present project was to quantify and compare differences in impact performance and damping effectiveness among various off-road bicycle suspension systems. Two experiments were conducted to compare suspensions. Fork impact performance was tested by measuring peak antero-posterior braking forces and impulses during impact with bumps of 6- and 10-cm height for five mountain bike suspension systems. These results were compared to a rigid fork condition. Comparisons among suspension systems showed small but significant differences in performance. While only marginal differences in peak force were found for the suspension conditions, more substantial differences in braking impulse were observed. Air-Oil design forks had the lowest braking impulse for the range of speeds and impact characteristics of this experiment. In another setting, an analysis of acceleration signals over a range of frequencies on two surface conditions (gravel and trail) was conducted to assess the damping effectiveness of the five suspension systems. The mountain bike was equipped with accelerometers mounted at the axle and frame. A spectral analysis of the signal was performed for each signal to provide a measure of fork effectiveness. Results showed that accelerations ranged from -33 to +40 g at the axle and from -13 to +13 g at the frame, while spectral analyses of the acceleration signals revealed two distinct frequency regions from 0 to 100 Hz and from 300 to 400 Hz. The various suspension systems were all effective in attenuating vibration over the first region. Vibration amplitudes at the frame were considerably less than at the axle for the suspension conditions while similar axle-frame vibrations were observed with the rigid fork. Lower frequency vibration amplitudes were typically greater on the trail than on gravel. In the frequency region between 300-400 Hz, the signal was attenuated at the frame for all conditions including the rigid fork. The quantification and comparison process of the various suspension forks using impulse provided an objective marker for performance, and allowed differentiation between various suspension conditions. Moreover, the effectiveness analysis through the use of accelerometers provided insight into the range of frequencies dampened by a suspension. The lower frequency range dampening suggested that effectiveness of a suspension fork can be quantified even though the experiment did not conclusively differentiate between the forks

Exclusión de linajes como estrategia para la obtención de resistencia durable en el arroz a Pyricularia grisea Sacc. en Colombia

Rice blast has challenged plant breeders when they were searching for durable resistance in Colombia. Rapid resistance breakdowns were commonly observed in newly bred cultivars and they are attributed to frequent appearance of new pathotypes. Recent population studies of the rice blast pathosystem have shown that Pyricularia grisea in a given region, typically expresses a phylogenetic organization of distinct lineages (‘genetic families’ as defined by MGR-DNA  fingerprinting). Each lineage exhibits a definable virulence  spectrum, and the potential for developing new pathotypes appears to be constrained by lineage-specific avirulences. Lineageexclusion is a breeding strategy aimed to enlighten the choosing of genes to obtain more durable resistance in the field. Combining genes that complementary exclude fragments of virulence, will provide complete resistance to known lineages. The resistance of pyramids bearing the major resistance genes Pi-1 (t) and Pi-2 (t) was determined at three sites in a primary rice growing region in Colombia, from 1996 to 1998.The chosen R-genes are individually defeated by common lineages in Colombia, but combined, provide resistance to the complementary spectra of virulence. The pyramids were selected by screening the progeny of a cross of nearisogenic lines with the representative.The presence and homozygosity of both genes were confirmed through molecular markers. Neither single Colombian isolate, nor mixture of isolates infected the pyramids. The pyramids proved to be highly resistant in the field, and no major changes in lineage composition or virulence spectrum were observed. However, some moderately compatible isolates of lineage SRL-6 were transiently observed in the area of Santa Rosa. Resistance breakdown (vulnerability) may depend on within lineage rather than between lineage distributions of virulence.La durabilidad de la resistencia genética del arroz a Pyricularia grisea Sacc. había estado comprometida en Colombia, por una rápida adaptación aparente del patógeno a los genes dispuestos para contrarrestar su incidencia. Las variedades mejoradas se veían afectadas por la enfermedad en el curso de pocos años y, en ocasiones, a sólo meses de haber sido liberadas. La exclusión de linajes es una estrategia de mejoramiento que propone la identificación y posterior ‘piramidación’ de genes con habilidad para reconocer de manera complementaria las avirulencias de las familias genéticas (linajes) del patógeno. Poblaciones ecológicamente distintitas, caracterizadas molecularmente mediante la sonda MGR-586, exhiben una estructura clonal en la que cada aislamiento del linaje comparte históricamente el mismo espectro de virulencia. La resistencia obtenida con la piramidación de genes complementarios funciona como factor de exclusión hacia la totalidad de la virulencia en la población del patógeno en un ecosistema determinado. Así, en Colombia, los genes Pi-1 (t) y Pi-2 (t) son diferencial y complementariamente excluyentes de la virulencia de las poblaciones de P. grisea. Fueron obtenidas líneas con estos genes piramidados mediante el cruzamiento de dos líneas isogénicas; la presencia y condición homocigota de los genes de resistencia en las nuevas líneas fue establecida a través de marcadores moleculares. El comportamiento de las pirámides fue evaluado en el laboratorio, en cámaras de crecimiento con aislamientos representativos de los linajes colombianos y, en el campo, en una región dedicada tradicionalmente a la producción de arroz donde las epidemias de piricularia son frecuentes.Tanto en las inoculaciones artificiales, como en las áreas de cultivo, las pirámides conservaron la resistencia. La estructura de virulencia entre la población del patógeno en el campo permaneció estable durante tres años, aunque estacional y transitoriamente se identificaron algunos aislamientos virulentos a las pirámides en la estación experimental.   &nbsp

Anarchism, individualism and communism: William Morris's critique of anarcho-communism

This collection of essays, showing how the boundaries between Marxism and anarchism have been more porous and fruitful than is conventionally recognised, charts a history of radical socialist collaborations from the late 19th ..

β\beta-NMR of Isolated 8^{8}Li+^{+} Implanted into a Thin Copper Film

Depth-controlled $\beta$-NMR was used to study highly spin-polarized $^8$Li in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight Shifts and spin relaxation data show that $^8$Li occupies two sites at low temperatures, assigned to be the substitutional ($S$) and octahedral ($O$) interstitial sites. Between 50 to 100 K, there is a site change from $O$ to $S$. The temperature dependence of the Knight shifts and spin-lattice relaxation rates at high temperatures, i.e. when all the Li are in the $S$ site, is consistent with the Korringa Law for a simple metal.Comment: Accepted for publication in Phys. Rev.

Newly diagnosed heart failure: change in quality of life, mood, and illness beliefs in the first 6 months after diagnosis

Objectives. This study sought to examine how patients’ mood and quality of life (QoL) change during the early high-risk period after a diagnosis of heart failure (HF) and to identify factors that may influence change. Design. A within-subjects, repeated-measures design was used. Assessments took place within 4 weeks of diagnosis and 6 months later. Methods. One hundred and sixty six patients with HF completed assessments of their mood, QoL, and beliefs about HF and its treatment. Correlation analysis was conducted between the variables and analysis of variance and t-tests were used to assess differences in categorical variables. To examine which variables predicted mood and QoL, hierarchical multiple regressions were conducted. Results. At follow-up, patients’ beliefs indicated a realization of the chronicity of their HF, however their beliefs about the consequences of having HF did not change and their satisfaction with their treatment remained high. QoL and anxiety improved significantly over time but there was no significant change in depressed mood. As would be expected, improvement in symptoms was a key factor in improved mood and QoL. Other significant explanatory variables included age, comorbid chronic obstructive pulmonary disease, depressed mood, patients’ beliefs about the consequences of their HF and their concerns about treatment. Conclusions. This study suggests that addressing patients’ mood and beliefs about their illness and its treatment may be additional ways of improving patient QoL in the early period after the diagnosis of HF

Cooling of Dense Gas by H2O Line Emission and an Assessment of its Effects in Chondrule-Forming Shocks

We consider gas at densities appropriate to protoplanetary disks and calculate its ability to cool due to line radiation emitted by H2O molecules within the gas. Our work follows that of Neufeld & Kaufman (1993; ApJ, 418, 263), expanding on their work in several key aspects, including use of a much expanded line database, an improved escape probability formulism, and the inclusion of dust grains, which can absorb line photons. Although the escape probabilities formally depend on a complicated combination of optical depth in the lines and in the dust grains, we show that the cooling rate including dust is well approximated by the dust-free cooling rate multiplied by a simple function of the dust optical depth. We apply the resultant cooling rate of a dust-gas mixture to the case of a solar nebula shock pertinent to the formation of chondrules, millimeter-sized melt droplets found in meteorites. Our aim is to assess whether line cooling can be neglected in chondrule-forming shocks or if it must be included. We find that for typical parameters, H2O line cooling shuts off a few minutes past the shock front; line photons that might otherwise escape the shocked region and cool the gas will be absorbed by dust grains. During the first minute or so past the shock, however, line photons will cool the gas at rates ~ 10,000 K/hr, dropping the temperature of the gas (and most likely the chondrules within the gas) by several hundred K. Inclusion of H2O line cooling therefore must be included in models of chondrule formation by nebular shocks.Comment: Accepted for publication in The Astrophysical Journa

Debye representation of dispersive focused waves

We report on a matrix-based diffraction integral that evaluates the focal field of any diffraction-limited axisymmetric complex system. This diffraction formula is a generalization of the Debye integral applied to apertured focused beams, which may be accommodated to broadband problems. Longitudinal chromatic aberration may limit the convenience of the Debye formulation and, additionally, spatial boundaries of validity around the focal point are provided. Fresnel number is reformulated in order to guarantee that the focal region is entirely into the region of validity of the Debye approximation when the Fresnel number of the focusing geometry largely exceeds unity. We have applied the matrix-based Debye integral to several examples. Concretely, we present an optical system for beam focusing with strong angular dispersion and free of longitudinal chromatic aberration. This simple formalism leaves an open door for analysis and design of focused beams with arbitrary angular dispersion. Our results are valid for ultrashort pulsed and polychromatic incoherent sources