The transverse trapping force of an optical trap: Factors affecting its measurement

Abstract

We report new observations that question the validity of using the escape method to deduce optical trapping forces in optical tweezers. The results were obtained by measuring the minimum beam power required to trap a particle subject to fluid flow, created by movement of the sample stage. The power was found to increase by approximately 50% over the range of amplitudes of movement used. This suggests that the measured trapping force is not solely dependent upon the velocity of the fluid past the trapped particle, as commonly assumed. These effects were observed at all fluid velocities and accelerations employed. We consider various causes for the observed effects but an explanation remains an outstanding challenge.     

Harnessing the Influence of Reactive Edges and Defects of Graphene Substrates for Achieving Complete Cycle of Room‐Temperature Molecular Sensing

Molecular doping and detection are at the forefront of graphene research, a topic of great interest in physical and materials science. Molecules adsorb strongly on graphene, leading to a change in electrical conductivity at room temperature. However, a common impediment for practical applications reported by all studies to date is the excessively slow rate of desorption of important reactive gases such as ammonia and nitrogen dioxide. Annealing at high temperatures, or exposure to strong ultraviolet light under vacuum, is employed to facilitate desorption of these gases. In this article, the molecules adsorbed on graphene nanoflakes and on chemically derived graphene‐nanomesh flakes are displaced rapidly at room temperature in air by the use of gaseous polar molecules such as water and ethanol. The mechanism for desorption is proposed to arise from the electrostatic forces exerted by the polar molecules, which decouples the overlap between substrate defect states, molecule states, and graphene states near the Fermi level. Using chemiresistors prepared from water‐based dispersions of single‐layer graphene on mesoporous alumina membranes, the study further shows that the edges of the graphene flakes (showing p‐type responses to NO₂ and NH₃) and the edges of graphene nanomesh structures (showing n‐type responses to NO₂ and NH₃) have enhanced sensitivity. The measured responses towards gases are comparable to or better than those which have been obtained using devices that are more sophisticated. The higher sensitivity and rapid regeneration of the sensor at room temperature provides a clear advancement towards practical molecule detection using graphene‐based materials.     

A comparison of the Driving Anger Scale and the Propensity for Angry Driving Scale

The present study investigated the factor structures of the 14-item version of the DAS (Driving Anger Scale) and the Propensity for Angry Driving Scale (PADS) using a sample of New Zealand drivers drawn from the general population. The two scales were also investigated with regards to their relationships with general trait anger, risky driving behaviour, along with crash involvement and a variety of crash-related conditions. Confirmatory Factor Analysis supported both scales as unidimensional, although the PADS was reduced from a 19-item to an 18-item scale. Both the PADS and DAS were significantly related to trait anger, risky driving behaviour and near-misses. However, once the influence of the demographic variables and trait anger had been partialled out, the addition of the PADS and DAS made a significant contribution to predicting violations, but it was only the PADS which was significant. In contrast, after the demographic variables and trait anger had been partialled out, the addition of the DAS and PADS again made a significant contribution to the prediction of near-misses, but this time it was only the DAS which made a significant contribution. The present study clearly shows that both scales are robust measures, measuring similar, but slightly different aspects of driving anger.     

Condensed Calculations for Evolutionary Operation Programs

Evolutionary Operation is a method for operating plant processes. Since the method is applied by plant personnel themselves as a continuing normal part of process operation it is desirable to reduce the calculations to a simple routine matter. This paper describes calculation procedures which have been found useful in these circumstances.     

Factorial Designs,the |X′X| Criterion,and Some Related Matters

Two of the basic approaches to choosing an n-point experimental design in many industrial situations are (i) to set down a simple factorial or fractional factorial design in the factors being studied, or (ii) to choose a design based on the well-known |X′X| criterion. Experimenters often prefer (i) due to its simplicity; our viewpoint here is that (ii) is much better. We first indicate some situations for which (when all the factors are restricted to a cuboidal region) the factorial approach is optimal, as judged by the |X′X| criterion, but the assumed models are often not sensible ones in practical work. We then examine what (similarly restricted) designs are optimal under the |X′X| criterion for the standard linear models of first and second order; because of the very rapid increase in computational difficulties, we consider only “cube plus star” type designs for k ≥ 3 (except for k = 3, n = 10). In spite of computational requirements, we recommend use of the |X′X| criterion in general rather than the indiscriminate use of factorials and we briefly discuss the reasons why, both for linear and nonlinear model situations.     

Micronisation and hot air roasting of cowpeas as pretreatments to control the development of hard-to-cook phenomenon

BACKGROUND: Cowpeas stored under conditions of high temperature and high relative humidity (HTHH) develop the hard‐to‐cook (HTC) defect. Cowpeas with HTC defect require long cooking times, limiting their utilisation. Heat pretreatments are aimed at inactivating the enzymes responsible for HTC defect development. In this study, two heat pretreatments, micronisation and hot air roasting, were evaluated to assess their effectiveness in controlling the HTC defect development in cowpeas after storage under HTHH conditions. RESULTS: Micronisation and hot air roasting as pretreatments reduced the cooking time of cowpeas after storage under HTHH conditions compared with the control. The differences in the effectiveness of HTC defect control between micronisation and roasting were dependent on the degree of phytase inactivation on day 0. Phytase activity was reduced by 45 and 70% by roasting and micronisation pretreatments respectively. Reduced phytase activity was associated with higher phytate and soluble pectin contents in micronised cowpeas than in roasted cowpeas after HTHH storage. This observation is in agreement with the phytase‐phytate‐pectin theory. CONCLUSION: Micronisation was more effective than hot air roasting in controlling the development of HTC defect. This was due to a higher degree of phytase inactivation in micronisation when compared with roasting. Copyright © 2011 Society of Chemical Industry     

Digestibility and β-carotene release from lipid nanodispersions depend on dispersed phase crystallinity and interfacial properties

The influence of interfacial structure and lipid physical state on colloidal stability and digestibility of solid lipid nanoparticle dispersions (SLN) and canola oil-in-water emulsions (COE) stabilized with the non-ionic surfactants Poloxamer 188 (P188) and Tween 20 (T20) were examined and the release of encapsulated β-carotene (BC) under simulated gastrointestinal conditions determined. While the SLN and COE were all stable during exposure to gastric conditions (mean diameter ～115 nm), more destabilization was observed for the COE than SLN during the duodenal phase. ζ-Potential measurements indicated rapid adsorption of bile salts (BS) and phospholipids (PL) to both solid and liquid interfaces, with greater surfactant displacement observed for the COE. Compared to the SLN, significantly more lipolysis and BC transfer to the aqueous phase was observed for both the COE-P188 and COE-T20 (p < 0.05). The properties of the colloidal structures present in the aqueous phase, which are important in terms of the uptake of lipolytic products and lipophilic bioactives, depended on non-ionic surfactant type, the extent of lipid digestion, as well as the presence of BS and PL.