Light sensor platform based on the integration of Bacteriorhodopsin with a single electron transistor

This paper reports on the integration of an optical protein with single electron transistors to form a nano-bio-hybrid device for sensing. Bacteriorhodopsin (bR) is an optoelectric protein that translocates a proton across a distance of several nanometers in response to an absorbed photon of incident light. This charge gradient results in a measurable voltage in the dried state. Single electron transistors (SETs) have active regions consisting of one or more quantum islands with a size typically 10 nanometers or less. Integrating bacteriorhodopsin with the gate of a SET provides a device capable of a modulated electrical output in response to optical modulation at the device gate. Modulation of the optoelectric activity of the bR by chemical binding with a targeted environmental antigen can form a direct chemical-to-electrical sensor reducing the size and complexity of fluorescence-based systems. The work resulted in electrical resistance and capacitance characterization of purple membrane containing bR under variable illumination to ensure minimal impact on SET operation. Purple membrane containing bacteriorhodopsin was electrodeposited on the SET gates, and current throughput was well correlated with variable and cyclic illumination. It was confirmed that bR optoelectric activity is capable of driving SETs

From density-matrix renormalization group to matrix product states

In this paper we give an introduction to the numerical density matrix renormalization group (DMRG) algorithm, from the perspective of the more general matrix product state (MPS) formulation. We cover in detail the differences between the original DMRG formulation and the MPS approach, demonstrating the additional flexibility that arises from constructing both the wavefunction and the Hamiltonian in MPS form. We also show how to make use of global symmetries, for both the Abelian and non-Abelian cases.Comment: Numerous small changes and clarifications, added a figur

Emerging assessment trends in higher education

This article discusses the emerging trends in the assessment of learners supported by the Outcomes-based Education and Training (OBET) approach in Health Sciences in response to the challenge to equip learners for professional vocational employment. Information about assessment was obtained from participants from the Technikon Free State and the University of the Free State by using structured interviews. The results of the study indicated that the use of performance assessment methods should receive more attention. Abandoning the traditional paradigm and adopting the principles and ideas of assessment with a new approach with success will require time, energy, effort and patience from educators, faculty and learners. (South African Journal of Higher Education: 2003 17 (3): 49-65

The timing and extent of 'juvenile ovary' phase are highly variable during zebrafish testis differentiation

Gonad differentiation in male zebrafish involves a transformation from a ‘juvenile ovary’ to testis. In our study, this phenomenon was analysed using a stable transgenic line (vas::egfp) created by Krovel & Olsen (Mechanisms of Development, 116: 141–150, 2002). Our data obtained by histological and immunohistochemical methods show that the onset of enhanced green fluorescent protein (EGFP) expression marks the conversion of the bipotential gonad into a ‘juvenile ovary’, and its subsequent decrease in the males indicates transformation into a testis. Furthermore, during the ‘juvenile ovary’ stage, a high level of variation was observed among individuals not only in the starting point and duration of EGFP expression but also in its intensity. The intensity of reporter expression in the males ranged from a high level of expression – similar to that observed in females – to invisible expression and correlated with the number of oocytes, the shape of ‘juvenile ovary’ and its lumen. Therefore, the authors conclude that although all males develop ‘juvenile ovaries’, they differ vastly in the extent of their commitment toward femaleness during this stage before testis differentiation. The differentiating zebrafish testis shows morphological features similar to those of the transforming gonad of protogynous hermaphrodites, and therefore, it could be a good model for the study of the process of female-to-male sex change in adult teleosts

Visualization of stochastic Ca2+ signals in the formed somites during the early segmentation period in intact, normally developing zebrafish embryos

Localized Ca2+ signals were consistently visualized in the formed somites of intact zebrafish embryos during the early segmentation period. Unlike the regular process of somitogenesis, these signals were stochastic in nature with respect to time and location. They did, however, occur predominantly at the medial and lateral boundaries within the formed somites. Embryos were treated with modulators of [Ca2+](i) to explore the signal generation mechanism and possible developmental function of the stochastic transients. Blocking elements in the phosphoinositol pathway eliminated the stochastic signals but had no obvious effect, stochastic or otherwise, on the formed somites. Such treatments did, however, result in the subsequently formed somites being longer in the mediolateral dimension. Targeted uncaging of buffer (diazo-2) or Ca2+ (NP-ethyleneglycoltetraacetic acid [EGTA]) in the presomitic mesoderm, resulted in a regular mediolateral lengthening and shortening, respectively, of subsequently formed somites. These data suggest a requirement for IP3 receptor-mediated Ca2+ release during convergence cell movements in the presomitic mesoderm, which appears to have a distinct function from that of the IP3 receptor-mediated stochastic Ca2+ signaling in the formed somites