Droplet pinning by PEM fuel cell GDL surfaces

In this work, side view images of liquid–gas–solid interfaces are observed during the evaporation of liquid water droplets on various commercially available untreated gas diffusion layers (GDLs). The change in contact diameter as a function of evaporative volume loss is measured to quantify the unpinning rates of micro-sized droplets. This contact diameter pinning behaviour during evaporation is correlated to the material topography, which is quantified through profilometry measurements. The carbon fibre paper with the smallest average roughness (15 μm) exhibits the strongest degree of pinning (unpinning at a rate of 0.13 mm/μL). Higher average surface roughnesses for felt (30 μm) and cloth yarn (32 μm) result in higher unpinning rates, 0.21 mm/μL and 0.19 mm/μL, respectively. These results indicate that common GDL materials exhibit Cassie–Baxter wetting behaviour, and reduced GDL roughness promotes droplet pinning. The material-specific droplet contact diameter progression should be considered during GDL selection for polymer electrolyte membrane (PEM) fuel cells. This work provides insight into the effect of GDL material properties on gas channel water management, as water droplets are expected to experience similar pinning to that observed in this work within the cathode gas channels of a PEM fuel cell.     

Neural stimulation with a carbon nanotube microelectrode array

We present a novel prototype neural interface using vertically aligned multiwalled carbon nanotube (CNT) pillars as microelectrodes. Functionalized hydrophilic CNT microelectrodes offer a high charge injection limit (1-1.6 mC/cm2) without faradic reactions. The first repeated in vitro stimulation of hippocampal neurons with CNT electrodes is demonstrated. These results suggest that CNTs are capable of providing far safer and more efficacious solutions for neural prostheses than previous metal electrode approaches.     

Features of shear failure of brittle materials and concrete structures on rock foundations

The failure of brittle materials under compressive shear loading is described mainly on the basis of experimental investigations. The failure is accompanied by the formation of a combined fracture of a curvilinear or broken line shape, developing along the trajectories of the principal planes. A primary tensile crack is formed along the principal tensile stress planes. A thin streak or tight crack named a compressive crack develops along the principal compressive stress planes. Formation of the compressive crack coincides with a limiting condition, the peak shear strength τ_p. Reasons for the discordance of conventional shear theories as applied to brittle materials are discussed. The criterion of a material strength parameter, crushing resistance R_cr, is proposed and corrections are introduced into traditional methods of analysis of concrete dam stability. Examples of engineering applications of the failure features obtained are given.     

Designing efficiencies: The parallel narratives of distance education and composition studies

Distance education (DE) programs at many universities have been initiated to generate new efficiencies for the academic process, particularly cost efficiency and pedagogical efficiency. In writing studies, this move toward digitally mediated instruction has, in some classrooms, recreated practices that resonate with the pedagogy that resulted from Current-Traditional Rhetoric (CTR). Thus, a trace of distance education's and composition studies’ parallel narratives demonstrates that writing studies has already addressed some of the questions (and concerns) that online writing instruction raises. By specifically focusing on the tensions created by negotiating cost efficiencies and pedagogical efficiencies with communication efficiencies and medium efficiencies, we interrogate current administrative decisions as well their pedagogical outcomes. We conclude by proposing strategies for rearticulating future narratives about online writing instruction in potentially productive ways.     

Patterns of visual field progression in patients with retinitis pigmentosa

OBJECTIVE: The purpose of the study was to determine whether distinct patterns of visual field progression are present in patients with retinitis pigmentosa (RP) and to evaluate the correlation between these patterns, if present, and different genetic subtypes of RP. DESIGN: A retrospective analysis of patterns of visual field progression in RP was performed. PARTICIPANTS: Visual fields of 162 patients with RP, including 55 with type 2 Usher syndrome, who had at least 3 Goldmann visual field examinations during a period of at least 3 years were reviewed. MAIN OUTCOME MEASURES: Goldmann visual fields. RESULTS: Visual fields of 86 patients could be classified into one of three specific patterns of visual field progression. Pattern I included those patients with a progressive concentric loss of visual fields; pattern II included those with visual field loss that began superiorly and subsequently developed an arcuate scotoma that progressed either from the nasal (IIA) or the temporal (IIB and IIC) side; and pattern III included patients whose visual field loss was characterized initially by a complete or incomplete midperipheral "ring scotoma" that broke through into the periphery. The end stage of all these patterns was a residual central visual field, sometimes also associated with a small peripheral island. In 53 of the 162 patients, the pattern of visual field loss could not be categorized because of an advanced stage of field loss at the time of the initial examination. CONCLUSIONS: Distinctive patterns of visual field progression can be observed in patients with retinitis pigmentosa and type 2 Usher syndrome. There were no intrafamilial variations in the pattern of visual field loss in our data on 24 patients from 11 families. Within certain genetic subtypes, there was a predilection for a preponderance of a specific pattern of visual field progression. Future studies may be able to correlate these patterns of visual field loss with different genetic mutations. A greater understanding as to why certain patterns of field loss exist could potentially provide greater insight into the various pathogenetic mechanism(s) by which photoreceptor cells degenerate in this group of patients.     

Effect of mechanical activation on the morphology and structure of hydroxyapatite

We have studied the effect of grinding in planetary mills on the phase composition, morphology, and water content of hydroxyapatite powder. The results indicate that milling for even relatively short times, which reduces the average particle size by a factor of 2, causes the monetite present in the unmilled powder to disappear and reduces the crystallite size of the hydroxyapatite. The fraction of nanoparticles in the powder is then 98% and remains constant during further milling. Milling for longer times leads to hydroxyapatite amorphization. For an average size of large particles R ≥ 1 μm, the surface area of the particles per unit volume, E (cm⁻¹), is determined only by R (E ∼ 1/R).     

Stability of concrete retaining structures and their interface with rock foundations

Three failure mechanisms of concrete retaining structures situated on rock foundations: sliding, overturning and limit turning, are discussed. Investigations have shown that sliding is possible only in specific cases when weakened subhorizontal surfaces with low shear parameters are present near the interface between the structure and foundation. If these conditions are not present, then failure due to sliding does not occur. The classical overturning mode, which involves turning of the structure relative to the downstream toe, is not possible, as it requires unrealistic conditions of infinitely strong rock or concrete. The limit turning mode, which seems to be the most likely of the three, involves partial turning of the structure and is accompanied by downstream crushing and upstream rupture of the foundation. Finally, a practical method to analyze a structure's resistance to limit turning is presented, and preparation of the interface between a concrete retaining structure and its rock foundations, taking into account the specific characteristics of limit turning failure is discussed.     

Group therapy and the somatoform patient: An integration.

Recent reports and literature reviews suggest that psychotherapeutic interventions with somatoform patients have efficacy. From their clinical experience with somatoform patients, the authors identify helplessness as the central psychotherapeutic issue for these patients. They propose that effective group therapy interventions have their impact through the addressing and working through of this affect. They discuss paradigmatic stages in the group therapeutic process of addressing helplessness in somatoform patients. Technical issues regarding membership selection and leadership style with this intervention are proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigment inhomogeneity and void formation in organic coatings

The conventional theory of organic coatings assumes that the volume density of pigment particles is uniform throughout the sample. The coating is then described in terms of the pigment volume concentration Π, which equals the volume of pigment divided by the volume of pigment and polymer. Voids form in the coating when the pigment particles are randomly dense-packed, which implies that Π exceeds the critical pigment volume concentration (Φ_c or that Λ=Π/Φ_c > 1. Due to fluctuations in the local density of pigment however, some regions in the coating may become randomly dense-packed even below Φ_c. Hence, voids may form in the densely-packed islands even when Λ<1. Our model for void formation contains two fitting parameters: N_o is the smallest number of pigment particles in a densely-packed cluster that may contain a void; C_q is the coarseness of the polymer space-filling in the volume of the sample not occupied by pigment. When C_q=0 and Π > 1, the polymer completely fills the interstitial volume and the void concentration vanishes. But when C_q > 0, voids may form in the densely-packed regions of the coating even below Φ_c. The coarseness parameter C_q, depends on the sample preparation, on the properties of the pigment and polymer, and on the pigment volume concentration Π. For any nonzero C_q we conclude that optical measurements will systematically underestimate Φ_c. On the other hand, since the density of polymer is less than half the density of pigment, the peak in the mass density p(Π) of the coating will overestimate Φ_c. Unless C_q is abnormally large, the void percolation threshold value Φ_v is larger than Φ_c and is a decreasing function of the coarseness C_q. The predictions of this simple model are in good agreement with experiment, and are relevant to the general class of random concentrated composites which include organic coatings, ceramic polymer slips, composite solid polymer electrodes and some forms of battery separators.