Papers by Yashar Hormozan
Worldwide , there has been a large increase in tertiary student numbers, not entirely matched by ... more Worldwide , there has been a large increase in tertiary student numbers, not entirely matched by funding increases. Consequently, instructors are faced with large, diverse classes, and find themselves struggling to provide adequate assessment and prompt feedback, two quantities critical in an effective learning environment. Personal computers and the Internet can help solve this problem. The aim of this study was to develop, implement and validate a Web-based software package that, through providing practice and assessment opportunities, improved student learning and reduced marking and related mundane aspects of instructor workload. At the start of the study, such a package already existed in prototype form: OASIS (Online Assessment System with Integrated Study). As the study progressed, this software package was first fully rewritten and then repeatedly modified. OASIS delivers individualised tasks, marks student responses, supplies prompt feedback, and logs student activity. Staff can deliver sets of practice questions and assessments to students: assessments may involve different questions for different students, not just numerically different versions of the same questions. Given my role as teacher, the traditional research ideal of observing without affecting the research environment was both impossible and unconscionable. In particular, since preliminary evidence suggested that OASIS did enhance student learning, I could not adopt a 'two groups' approach to the research, with one group using OASIS while the other did not. Instead, an action research methodology was seen as most appropriate for my double role of teacher and researcher. This methodology enabled me, in the light of my findings, to continuously modify the learning environment and enhance student learning. The action research proceeded through a spiral of one-semester cycles of planning, acting, observing and reflecting. To maximize rigour, the research ran through eight cycles over four years and involved considerable triangulation. OASIS itself collected much quantitative data. Further data were collected via interview, survey, email and informal discussion from three groups: current students, postgraduates and academics. My colleagues I gratefully acknowledge the undergraduates, postgraduates and fellow staff of the Department of Electrical and Computer Engineering at the University of Auckland who were so willing to make time to share their thoughts and experiences with me. I appreciate their input to my study and to the development and implementation of OASIS. In particular, I acknowledge the huge contribution made by Colin Coghill, the OASIS programmer, and also the sterling work of the other members of the OASIS Committee: Mark Andrews, Abbas Bigdeli, John Boys and Gerard Rowe. Their wisdom and experience has been much appreciated and I have enjoyed working with them. I thank my wife Gail, my parents Joan and Graham, and my children Francis and Simon for their wholehearted understanding and support throughout my odyssey of part-time study. I also thank Professor David Treagust, my supervisor, who guided me well on my journey. In spite of many demands on his time, his advice and analysis was always expert and unstinted. v
physica status solidi (a), 2015
Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs)... more Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs) embedded in oxide is usually attributed to trapping/de-trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X-rays. In this work, we present a study of the effect of Xray irradiation (up to 65 kGy in SiO 2) on the blinking of single Si-NCs embedded in oxide nanowalls. We show that the lu-minescence characteristics, such as spectrum and lifetime , are unaffected by X-rays. However, substantial changes in ON-state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON-and OFF-time distributions remain of mono-exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si-NCs could be blinking-engineered via X-ray irradiation.
Key Engineering Materials, 2007
Mn-Zn ferrites with chemical formula (Mn-Zn) Fe2O4 have widespread applications in the electrical... more Mn-Zn ferrites with chemical formula (Mn-Zn) Fe2O4 have widespread applications in the electrical and electronics industries. These ferrites are synthesized generally by conventional method. This method, which contains calcination of raw materials, is affected by several parameters such as composition and purity of the raw materials and temperature, time and atmosphere of the process. Optimization of these parameters is very important because these parameters affect the magnetic and electrical properties of the material. In this work, the ratio of the different Iranian routs of the raw materials for production of high Ms ferrite powder has been optimized and the effects of calcination conditions have been investigated using XRD, DTA/TGA techniques. The magnetic properties have also been measured.
Plant Growth Regulation, 1995
Two synthetic brassinosteroids, 24-epibrassinolide (24-epiBR) and 2o,3a,l7P-trihydroxy-5cu-andros... more Two synthetic brassinosteroids, 24-epibrassinolide (24-epiBR) and 2o,3a,l7P-trihydroxy-5cu-androstan-6-one (THA-BR), exhibit different effects on growth of tobacco callus tissue. When added to a culture medium containing growth-limiting amounts of auxin, 24-epiBR reduced and THA-BR increased the fresh weight yield of tissue up to 53% and 207%, respectively, after 6 weeks of cultivation. The stimulatory and inhibitory effects of the two brassinosteroids on tissue growth occurred over a broad range of concentrations without a pronounced maximum corresponding to the 'yes or no' type of response. Different effects of 24-epiBR and THA-BR on tissue growth were inversely proportional to the content of endogenous cytokinins. Maximum contents of predominant cytokinins N6-(A=-isopentenyl)adenine (iP) and trans-zeatin (Z) in tissues supplied with 24-epiBR in growth-inhibiting concentrations were up to 3.7 fold and 3.4 fold higher, respectively, as compared to tissues grown on media containing growth-stimulating concentrations of THA-BR. Stimulation of tissue growth by THA-BR correlated with content of endogenous IAA and an inverse correlation was found between the content of endogenous IAA and cytokinins in tissues supplied with 24-epiBR. THA-BR exhibited weak cytokinin-like activity in a bioassay based on stimulation of growth of lateral buds of pea while 24-epiBR was inactive. Results indicate that the qualitatively different effects of the two brassinosteroids on growth of tobacco tissue may reflect their different influence on content of endogenous cytokinin.
Langmuir, 2012
The surface structure is known to significantly affect the long-range capillary forces between hy... more The surface structure is known to significantly affect the long-range capillary forces between hydrophobic surfaces in aqueous solutions. It is, however, not clear how small depressions in the surface will affect the interaction. To clarify this, we have used the AFM colloidal probe technique to measure interactions between hydrophobic microstructured pore array surfaces and a hydrophobic colloidal probe. The pore array surfaces were designed to display two different pore spacings, 1.4 and 4.0 μm, each with four different pore depths ranging from 0.2 to 12.0 μm. Water contact angles measured on the pore array surfaces are lower than expected from the Cassie-Baxter and Wenzel models and not affected by the pore depth. This suggests that the position of the three-phase contact line, and not the interactions underneath the droplet, determines the contact angle. Confocal Raman microscopy was used to investigate whether water penetrates into the pores. This is of importance for capillary forces where both the movement of the three-phase contact line and the situation at the solid/liquid interface influence the stability of bridging cavities. By analyzing the shape of the force curves, we distinguish whether the cavity between the probe and the surfaces was formed on a flat part of the surface or in close proximity to a pore. The pore depth and pore spacing were both found to statistically influence the distance at which cavities form as surfaces approach each other and the distance at which cavities rupture during retraction.
Journal of Experimental Botany, 2006
Changes in the contents of polyamines (PAs) in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin... more Changes in the contents of polyamines (PAs) in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin 38) grown under 16 h photoperiod were correlated with arginine and ornithine decarboxylase (EC 4.1.1.19 and EC 4.1.1.17) and diamine oxidase (EC 1.4.3.6) activities. The maximum of free and soluble conjugated forms of PAs occurred 1-2 h after the middle of the light period and was followed by two distinct peaks at the end of the light and at the beginning of the dark phase. Putrescine was the most abundant and cadaverine the least abundant PA in both free and PCA-soluble forms. However, cadaverine was predominant in PCAinsoluble conjugates, followed by putrescine, spermidine, and spermine. Both arginine and ornithine decarboxylases are involved in putrescine biosynthesis in tobacco leaves. Light dramatically stimulated the activity of ornithine decarboxylase, while no photoinduction of arginine decarboxylase activity was observed. Ornithine decarboxylase was found mainly in the particulate fraction. Only one peak, just after light induction, occurred in the cytosolic fraction, with 35% of the total ornithine decarboxylase activity. By contrast, the total arginine decarboxylase activity was equally divided between the soluble and pellet fractions. A sharp increase in diamine oxidase activity occurred 1 h after exposure to light, concomitant with the light-induced increase in ornithine decarboxylase activity. After a decline, diamine oxidase activity increased again, together with the rise in the amount of free Put. The roles of both conjugation of PAs with hydroxycinnamic acids and oxidative degradation of putrescine in maintaining free PA levels during the 24 h light/dark cycle are discussed. The presented results have shown that the parameters studied here followed rhythmical changes and were not only affected by light.
Journal of Colloid and Interface Science, 2013
Interactions between and wetting behavior of structured hydrophobic surfaces using different conc... more Interactions between and wetting behavior of structured hydrophobic surfaces using different concentrations of water/ethanol mixtures have been investigated. Silica surfaces consisting of pore arrays with different pore spacings and pore depths were made hydrophobic by silanization. Their static and dynamic contact angles were found to be independent of the pore depth while fewer pores on the surface, i.e. a closer resemblance to a flat surface, gave a lower contact angle. As expected, a higher amount of ethanol facilitated wetting on all the surfaces tested. Confocal Raman microscopy measurements proved both water and ethanol to penetrate into the pores. AFM colloidal probe force measurements clearly showed that formation of air cavitation was hindered between the hydrophobic surfaces in presence of ethanol, and an increase in ethanol concentration was followed by a smaller jump-in distance and a weaker adhesion force. On separation, an immediate jump-out of contact occurred. The measured forces were interpreted as being due to capillary condensation of ethanol between the surfaces giving rise to very unstable cavities immediately rupturing on surface separation.
IEEE Transactions on Nuclear Science, 2012
Biologia Plantarum, 1994
A small protein, NP-PI-II, with an N terminus identical to a part of a NJcotiana alata proteinase... more A small protein, NP-PI-II, with an N terminus identical to a part of a NJcotiana alata proteinase inhibitor (PI) II, and an inhibitory activity towards trypsin, has been isolated from flowers of Nicotiana plumbaginifolia. A larger protein was also present from which the smaller protein is likely derived. In N. plumbaginifolia the inhibitor is expressed at very early stages of floral development, this differs from the accumulation pattern during the development of N. tabacum flowers. In mature flowers of both species the inhibitor is constituvely expressed at high level in all floral organs. No inhibitor is present in the vegetative meristems and only a low level of inhibitory activity could be induced by wounding leaves. The inhibitory activity rem~ains high throughout the flower maturation and rapidly declines in the ovary after pollination, in fully developed, green, fruit no inhibitory activity could be detected. In mature N. tabacum flowers trypsin inhibitory activity is detected extraeelhilarly in the stigma exudate. PI activity is not a regular feature in the stigmas of several Solanaceous genera, this could be related to different strategies concerning fruit-function and subsequent dispersal of seeds. In Nicotiana the processing and localization of PI-II appear to be very conserved and PI-II possibly also has a protective function in the flower organs.
Biologia Plantarum, 1994
Second-order rate constants (kN) have been measured spectrophotometrically for reactions of 2,4-d... more Second-order rate constants (kN) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-NO2) with a series of Z-substituted pyridines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 o C. The Brønsted-type plots exhibit downward curvature (e.g., β2 = 0.89 ~ 0.96 when pKa < 9.5 while β1 = 0.38 ~ 0.46 when pKa > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The pKa o , defined as the pKa at the center of Brønsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of kN into the microscopic rate constants k1 and k2/k-1 ratio has revealed that k1 is governed by the electronic nature of the substituent X but the k2/k-1 ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the k2/k-1 ratio.
Acta Physiologiae Plantarum, 2009
The responses of plants to exogenous treatment with new synthetic brassinosteroids (BRs) were ass... more The responses of plants to exogenous treatment with new synthetic brassinosteroids (BRs) were assessed and compared with the activity of natural 24-epibrassinolide (24-EPI). Morphological experiments on plants of pea and flax showed that the boundary between stimulatory and inhibitory concentrations of individual BRs and 24-EPI used is very narrow and differs also with the plant species. Moreover brassinosteroids can exhibit effects similar to various other plant hormones. This was proven also in our experiments, where auxin, anti-auxin and cytokinin like effects were achieved by BRs application. One of the explanations of the different morphological effects could be the influence of brassinosteroid application on the level of endogenous hormones. There are changes in the levels of indole-3-acetic acid, 6-benzylaminopurine, trans-zeatin and dihydrozeatin in rape and wheat plants caused by BR 4 and 24-EPI application, but there is no general trend explaining unequivocally their influence. The fact that all tested BRs significantly increased the dry weight accumulation in comparison with non-treated reference rape plants can be accounted for the known BRs characteristics to avoid biotic stresses.
Medical Physics, 2016
In this study, the authors introduce a new generation of finely structured scintillators with a v... more In this study, the authors introduce a new generation of finely structured scintillators with a very high spatial resolution (a few micrometers) compared to conventional scintillators, yet maintaining a thick absorbing layer for improved detectivity. Methods: Their concept is based on a 2D array of high aspect ratio pores which are fabricated by ICP etching, with spacings (pitches) of a few micrometers, on silicon and oxidation of the pore walls. The pores were subsequently filled by melting of powdered CsI(Tl), as the scintillating agent. In order to couple the secondary emitted photons of the back of the scintillator array to a CCD device, having a larger pixel size than the pore pitch, an open optical microscope with adjustable magnification was designed and implemented. By imaging a sharp edge, the authors were able to calculate the modulation transfer function (MTF) of this finely structured scintillator. Results: The x-ray images of individually resolved pores suggest that they have been almost uniformly filled, and the MTF measurements show the feasibility of a few microns spatial resolution imaging, as set by the scintillator pore size. Compared to existing techniques utilizing CsI needles as a structured scintillator, their results imply an almost sevenfold improvement in resolution. Finally, high resolution images, taken by their detector, are presented. Conclusions: The presented work successfully shows the functionality of their detector concept for high resolution imaging and further fabrication developments are most likely to result in higher quantum efficiencies.
Langmuir, 2012
The surface structure is known to significantly affect the long-range capillary forces between hy... more The surface structure is known to significantly affect the long-range capillary forces between hydrophobic surfaces in aqueous solutions. It is, however, not clear how small depressions in the surface will affect the interaction. To clarify this, we have used the AFM colloidal probe technique to measure interactions between hydrophobic microstructured pore array surfaces and a hydrophobic colloidal probe. The pore array surfaces were designed to display two different pore spacings, 1.4 and 4.0 μm, each with four different pore depths ranging from 0.2 to 12.0 μm. Water contact angles measured on the pore array surfaces are lower than expected from the Cassie−Baxter and Wenzel models and not affected by the pore depth. This suggests that the position of the three-phase contact line, and not the interactions underneath the droplet, determines the contact angle. Confocal Raman microscopy was used to investigate whether water penetrates into the pores. This is of importance for capillary forces where both the movement of the three-phase contact line and the situation at the solid/liquid interface influence the stability of bridging cavities. By analyzing the shape of the force curves, we distinguish whether the cavity between the probe and the surfaces was formed on a flat part of the surface or in close proximity to a pore. The pore depth and pore spacing were both found to statistically influence the distance at which cavities form as surfaces approach each other and the distance at which cavities rupture during retraction.
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Papers by Yashar Hormozan