UNSTEADY NATURAL CONVECTION OF AIR IN A TALL AXISYMMETRIC,NONISOTHERMAL ANNULUS

This article presents numerical predictions of axisymmetric natural convection within a tall annular cavity with an aspect ratio of 10 and a radius ratio of 0.6. The temperature of the bounding inner vertical cylinder is hot at its base and decreases linearly with height, while the outer cylinder is cold at its base and its temperature increases linearly with height. These boundary conditions promote a steady bi-cellular flow at low Rayleigh numbers. As the Rayleigh number is increased, the flow transitions to a time-varying state in which the interface between the two natural-convection cells starts to oscillate. If the Rayleigh number is further increased, hysteresis, subharmonics, multiple solutions, and a reverse transition back to a steady state are all predicted. Results predicting the onset of unsteady flow for the Cartesian case are also presented.     

Molecular Details of the Frataxin–Scaffold Interaction during Mitochondrial Fe–S Cluster Assembly

Iron–sulfur clusters are essential to almost every life form and utilized for their unique structural and redox-targeted activities within cells during many cellular pathways. Although there are three different Fe–S cluster assembly pathways in prokaryotes (the NIF, SUF and ISC pathways) and two in eukaryotes (CIA and ISC pathways), the iron–sulfur cluster (ISC) pathway serves as the central mechanism for providing 2Fe–2S clusters, directly and indirectly, throughout the entire cell in eukaryotes. Proteins central to the eukaryotic ISC cluster assembly complex include the cysteine desulfurase, a cysteine desulfurase accessory protein, the acyl carrier protein, the scaffold protein and frataxin (in humans, NFS1, ISD11, ACP, ISCU and FXN, respectively). Recent molecular details of this complex (labeled NIAUF from the first letter from each ISC protein outlined earlier), which exists as a dimeric pentamer, have provided real structural insight into how these partner proteins arrange themselves around the cysteine desulfurase, the core dimer of the (NIAUF)₂ complex. In this review, we focus on both frataxin and the scaffold within the human, fly and yeast model systems to provide a better understanding of the biophysical characteristics of each protein alone and within the FXN/ISCU complex as it exists within the larger NIAUF construct. These details support a complex dynamic interaction between the FXN and ISCU proteins when both are part of the NIAUF complex and this provides additional insight into the coordinated mechanism of Fe–S cluster assembly.     

Is Disney the Nicest Place on Earth? A Content Analysis of Prosocial Behavior in Animated Disney Films

The purpose of this study was to examine the multidimensionality of prosocial behavior in Disney animated films. Characteristics of the target and initiator and context of each prosocial act were also examined. Prosocial behavior was portrayed at a rate of approximately 1 act per minute, rarely occurred in combination with aggression, targets were most prosocial toward friends, and tended to help those similar to themselves. This study views Disney in a more positive light than past studies by highlighting high levels of prosocial behavior, as well as portrayal that may facilitate imitation. This study also used a broad definition of prosocial behavior that provides a more nuanced picture of the nature of prosocial behavior in children's programming.     

An anthropologically based model of the impact of asymptomatic cases on the spread of Neisseria gonorrhoeae

Neisseria gonorrhoeae (GC) remains a serious burden in many high-sexual-activity, undertreated populations. Using empirical data from a 2009 study of GC burden among pastoralists in Kaokoveld, Namibia, we expand the standard gonorrhoea transmission model by using locally derived sexual contact data to explore transmission dynamics in a population with high rates of partner exchange and low treatment-seeking behaviour. We use the model to generate ball-park estimates for transmission probabilities and other parameter values for low-level (i.e. less than approx. 1200 copies/20 µl PCR reaction) asymptomatic infections, which account for 74% of all GC infections found in Kaokoveld in 2009, and to describe the impact of asymptomatic, low-level infections on overall prevalence patterns. Our results suggest that GC transmission probabilities are higher than previously estimated, that untreated infections take longer to clear than previously estimated and that a high prevalence of low-level infections is partially due to larger numbers of untreated, asymptomatic infections. These results provide new insights into the natural history of GC and the challenge of syndromic management programmes for the eradication of endemic gonorrhoea.     

Reduction of volatile organic compound emission. II. Use of alkoxy‐modified silsesquioxane for compounding silica‐filled rubbers

A class of alkoxy‐modified silsesquioxane (AMS) containing less than 5 wt % of latent alcohol that can be used for compounding silica‐filled rubbers is described. The AMS derived from octyl‐triethoxysilane (OTES) behaves as a good shielding agent in silica‐filled rubber to significantly reduce the compound Mooney viscosity and filler flocculation. The co‐AMS prepared from OTES and 3‐mercaptopropyl‐trimethoxysilane yielded an effective shielding and coupling agent for reinforcing the silica‐filled vulcanizates. The alcohols released as volatile organic compounds (VOC) are quantified during compounding and processing along with the compound properties of silica‐filled vulcanizates containing various silicon compounds such as bis‐(triethoxysilyl propyl) disulfide (TESPD), a polyhedral oligomeric silsesquioxanes (POSS), OTES, AMS, or co‐AMS. Dynamic mechanical properties such as dependences of hysteresis on temperature (HTD) and storage modulus on strain (MSD) are discussed. Stronger HTD and weaker MSD were found in stocks containing co‐AMS or a combination of AMS and a coupling agent when compared with that with TESPD. Stronger HTD and weaker MSD may benefit a tire compound with lower rolling resistance, more stable handling performance, as well as better wet traction. More importantly, the VOC released during the manufacture of rubber articles are significantly reduced in stocks containing AMS (or co‐AMS) when compared with those with a silane. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Design and Demonstration of Polarizing Polymer Waveguides Using Birefringent Polymers

TE-pass and TM-pass polarizing waveguides were fabricated by adjusting the birefringence properties of multi-layer stacks. The desired values of indices of refraction and birefringence were obtained by the proper selection and customization of core and cladding materials. The technique developed was used in the fabrication of waveguides in various design configurations such as etched ribs, backfilled trenches and photobleached channels. Both passive and active (electro-optic) core materials were successfully used in demonstrating the polarization extinction ratios as high as 61 dB. To our knowledge, this is the highest extinction ratio reported with polarizing polymer waveguides. In the case of electro-optic polymer waveguides, the designs were modified to enhance the electric field strength in the core without compromising the polarizing extinction ratios of the waveguides.     

Atomic force microscope cantilever calibration using a focused ion beam

A calibration method is presented for determining the spring constant of atomic force microscope (AFM) cantilevers, which is a modification of the established Cleveland added mass technique. A focused ion beam (FIB) is used to remove a well-defined volume from a cantilever with known density, substantially reducing the uncertainty usually present in the added mass method. The technique can be applied to any type of AFM cantilever; but for the lowest uncertainty it is best applied to silicon cantilevers with spring constants above 0.7?N?m(-1), where uncertainty is demonstrated to be typically between 7 and 10%. Despite the removal of mass from the cantilever, the calibration method presented does not impair the probes' ability to acquire data. The technique has been extensively tested in order to verify the underlying assumptions in the method. This method was compared to a number of other calibration methods and practical improvements to some of these techniques were developed, as well as important insights into the behavior of FIB modified cantilevers. These results will prove useful to research groups concerned with the application of microcantilevers to nanoscience, in particular for cases where maintaining pristine AFM tip condition is critical.     

Interfacial recognition of human prostate-specific antigen by immobilized monoclonal antibody: effects of solution conditions and surface chemistry

The specific recognition between monoclonal antibody (anti-human prostate-specific antigen, anti-hPSA) and its antigen (human prostate-specific antigen, hPSA) has promising applications in prostate cancer diagnostics and other biosensor applications. However, because of steric constraints associated with interfacial packing and molecular orientations, the binding efficiency is often very low. In this study, spectroscopic ellipsometry and neutron reflection have been used to investigate how solution pH, salt concentration and surface chemistry affect antibody adsorption and subsequent antigen binding. The adsorbed amount of antibody was found to vary with pH and the maximum adsorption occurred between pH 5 and 6, close to the isoelectric point of the antibody. By contrast, the highest antigen binding efficiency occurred close to the neutral pH. Increasing the ionic strength reduced antibody adsorbed amount at the silica–water interface but had little effect on antigen binding. Further studies of antibody adsorption on hydrophobic C8 (octyltrimethoxysilane) surface and chemical attachment of antibody on (3-mercaptopropyl)trimethoxysilane/4-maleimidobutyric acid N-hydroxysuccinimide ester-modified surface have also been undertaken. It was found that on all surfaces studied, the antibody predominantly adopted the ‘flat on’ orientation, and antigen-binding capabilities were comparable. The results indicate that antibody immobilization via appropriate physical adsorption can replace elaborate interfacial molecular engineering involving complex covalent attachments.     

Recovery of Rotorua geothermal field, New Zealand: Progress, issues and consequences

Recovery of most surface features in many parts of the Rotorua geothermal field (RGF) has continued as water levels rose and pressures increased following bore closures that began in 1986. However, the pattern of recovery of features is very variable, even within a relatively small area, with no apparent consistency as to location or type of feature. Most features in the Whakarewarewa Thermal Area that were affected by the pre-1986 pressure drawdown have recovered, but some have not. More puzzling is the behaviour of a few features (such as Waikorohihi and Mahanga geysers) that initially showed recovery, but later ceased activity. Chemical data indicate that for some features there has been an increase in the amounts of deep fluid reaching the surface, but in others there has been no change. Examination of seismic records suggests that the unusual behaviour is not related to local seismic activity. The recovery of many thermal features has been beneficial from a tourist and environmental viewpoint. However, there have been some detrimental occurrences. Following the decline and disappearance of thermal features before the bore closures, the vents of some features were inadvertently filled in and the land around them reclaimed and used for buildings or services. As water levels recovered after the closures, discharge to the surface recommenced, causing damage to buildings and associated services, resulting in several houses being damaged or forced to be relocated. In all cases, however, the discharges were from historically active vents. The data suggest that while most natural thermal features may recover from the effects of geothermal exploitation some may not, and in the case of Rotorua there does not appear to be any pattern or explanation for such non-recovery.