Particle sizing in the electrodynamic balance

We report a new technique for sizing particles in the electrodynamic balance. In this technique, the trajectory of a falling particle is followed with a photomultiplier tube. Particle velocities are measured by placing a mask between the particle and the detector. The masked region in the particle trajectory is roughly 0.6 mm wide. Output from the PMT is sampled every millisecond by an A/D converter and stored in a computer. Flight times of several hundred milliseconds are measured and the size is then computed from the particle's terminal velocity. With a modification of the mask, the technique is used to verify the uniformity of the electric field through which the particle is falling. In the present work we use the technique to determine size of polystryrene latex microspheres having nominal diameters of 10 and 20 µ. The technique can be used on any size particle, independent of its charge-to-mass ratio, and provides the size information in a short time

Fourier transform infrared spectrometer for a single aerosol particle

A spectrometer is reported here for obtaining the infrared spectrum of a single aqueous aerosol particle by a Fourier transform technique. The particle is held in an electrodynamic balance and irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The size of the particle is modulated by chopping the IR beam, and the resulting visible scattered light fluctuation is detected at 90° with a photomultiplier tube. The amplitude of the scattered light fluctuation is measured with a lock-in amplifier at each interferometer mirror position. The electronic circuitry for stepping the interferometer mirror is presented and discussed. Inverting the lock-in signal by a discrete fast Fourier transform routine (FFT) yields the particle absorption spectrum. The resulting spectrum for an (NH4)2SO4 droplet is presented

How FOSS Replaced Proprietary Software at a University: An Improvisation Perspective in a Low-income Country

The purpose of this study is to understand the rationale for and the process of replacing an imported proprietary higher education management software with a locally developed free and open source software (FOSS). Information Systems (IS) research on FOSS and higher education in low-income countries has focused more on teaching and learning. Less attention has thus been paid to the area of management and administration. Also, low-income country IS research on technology transfer has focused more on applications from the high-income world. Less research therefore exists on transfers between low-income countries. To address these research gaps, this study employs improvisation theory and interpretive case study methodology to investigate why and how a low-income country university replaced a proprietary higher education management software from another low-income country with a locally developed FOSS. The findings show that the university did so through improvisation to overcome the rigidity of the proprietary software and benefit from the flexibility of the FOSS. The study offers rich insight into how low-income country universities can deploy FOSS through improvisation to address design-actuality gap with imported proprietary software and also presents implications for research and practice

The Influence of Social Capital on Natural Resource Management in Marginal Areas of Kenya

This paper analyzes the influence of social capital on the farmers' perception of the soil erosion problem and the level of investments in soil conservation in marginal areas of Kenya. It uses data from a survey of 321 households in Machakos and Taita-Taveta Districts. A Heckman's two-step model is applied to assess the influence of social capital on investments in soil conservation by farmers. Results show that the education level of the household head, slope of farmers' fields, proportion of off-farm income, and the status of soil erosion are significant determinants of the likelihood of farmers recognizing soil erosion as an important problem. Household size, slope, land tenure security, membership diversity, age of household head, farm size per capita and membership in groups influence investments in soil control measures such as terraces. The effects, however, are location-specific. The policy challenge is to establish and strengthen social capital elements that have a strong influence on communities undertaking soil conservation measures to promote sustainable agriculture, and improve land tenure security.Resource /Energy Economics and Policy,

Cloning, purification and characterization of the 6-phospho-3-hexulose isomerase YckF from Bacillus subtilis

The enzyme 6-phospho-3-hexulose isomerase (YckF) from Bacillus subtilis has been prepared and crystallized in a form suitable for X-ray crystallographic analysis. Crystals were grown by the hanging-drop method at 291 K using polyethylene glycol 2000 monomethylether as precipitant. They diffract beyond 1.7 A using an in-house Cu Kalpha source and belong to either space group P6(5)22 or P6(1)22, with unit-cell parameters a = b = 72.4, c = 241.2 A, and have two molecules of YckF in the asymmetric unit