Showing papers by "University of New South Wales published in 1999"

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

Abstract: We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

Evolutionary programming made faster

Abstract: Evolutionary programming (EP) has been applied with success to many numerical and combinatorial optimization problems in recent years. EP has rather slow convergence rates, however, on some function optimization problems. In the paper, a "fast EP" (FEP) is proposed which uses a Cauchy instead of Gaussian mutation as the primary search operator. The relationship between FEP and classical EP (CEP) is similar to that between fast simulated annealing and the classical version. Both analytical and empirical studies have been carried out to evaluate the performance of FEP and CEP for different function optimization problems. The paper shows that FEP is very good at search in a large neighborhood while CEP is better at search in a small local neighborhood. For a suite of 23 benchmark problems, FEP performs much better than CEP for multimodal functions with many local minima while being comparable to CEP in performance for unimodal and multimodal functions with only a few local minima. The paper also shows the relationship between the search step size and the probability of finding a global optimum and thus explains why FEP performs better than CEP on some functions but not on others. In addition, the importance of the neighborhood size and its relationship to the probability of finding a near-optimum is investigated. Based on these analyses, an improved FEP (IFEP) is proposed and tested empirically. This technique mixes different search operators (mutations). The experimental results show that IFEP performs better than or as well as the better of FEP and CEP for most benchmark problems tested.

High performance scalable image compression with EBCOT

Abstract: A new image compression algorithm is proposed, based on independent embedded block coding with optimized truncation of the embedded bit-streams (EBCOT). The algorithm exhibits state-of-the-art compression performance while producing a bit-stream with a rich feature set, including resolution and SNR scalability together with a random access property. The algorithm has modest complexity and is extremely well suited to applications involving remote browsing of large compressed images. The algorithm lends itself to explicit optimization with respect to MSE as well as more realistic psychovisual metrics, capable of modeling the spatially varying visual masking phenomenon.

Commonality in Liquidity

Abstract: Traditionally and understandably, the microscope of market microstructure has focused on attributes of single assets. Little theoretical attention and virtually no empirical work has been devoted to common determinants of liquidity nor to their empirical manifestation, correlated movements in liquidity. But a wider-angle lens exposes an imposing image of commonality. Quoted spreads, quoted depth, and effective spreads co-move with market- and industry-wide liquidity. After controlling for well-known individual liquidity determinants such as volatility, volume, and price, common influences remain significant and material. Recognizing the existence of commonality is a key to uncovering some suggestive evidence that inventory risks and asymmetric information both affect intertemporal changes in liquidity.

Managing split-attention and redundancy in multimedia instruction

Abstract: Two experiments investigated alternatives to split-attention instructional designs. It was assumed that because a learner has a limited working memory capacity, any increase in cognitive resources required to process split-attention materials decreases resources available for learning. Using computer-based instructional material consisting of diagrams and text, Experiment 1 attempted to ameliorate split-attention effects by increasing effective working memory size by presenting the text in auditory form. Auditory presentation of text proved superior to visual-only presentation but not when the text was presented in both auditory and visual forms. In that case, the visual form was redundant and imposed a cognitive load that interfered with learning. Experiment 2 ameliorated split-attention effects by using colour coding to reduce cognitive load inducing search for diagrammatic referents in the text. Mental load rating scales provided evidence in both experiments that alternatives to split-attention instructional designs were effective due to reductions in cognitive load. Copyright © 1999 John Wiley & Sons, Ltd.

What the Student Does: teaching for enhanced learning

Abstract: Many teachers see major difficulties in maintaining academic standards in today's larger and more diversified classes. The problem becomes more tractable if learning outcomes are seen as more a function of students' activities than of their fixed characteristics. The teacher's job is then to organise the teaching/learning context so that all students are more likely to use the higher order learning processes which “academic” students use spontaneously. This may be achieved when all components are aligned, so that objectives express the kinds of understanding that we want from students, the teaching context encourages students to undertake the learning activities likely to achieve those understandings, and the assessment tasks tell students what activities are required of them, and tell us how well the objectives have been met. Two examples of aligned teaching systems are described: problem-based learning and the learning portfolio.

The Star Formation Histories of Galaxies in Distant Clusters

Abstract: We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressler et al. We investigate the nature of the different spectral classes defined by Dressler et al., including star-forming, poststarburst, and passive galaxy populations, and reproduce their basic properties using our spectral synthesis model. We attempt to identify the evolutionary pathways between the various spectral classes in order to search for the progenitors of the numerous poststarburst galaxies. The comparison of the spectra of the distant galaxy populations with samples drawn from the local universe leads us to identify a significant population of dust-enshrouded starburst galaxies, showing both strong Balmer absorption and relatively modest [O II] emission, that we believe are the most likely progenitors of the poststarburst population. We present the differences between the field and cluster galaxies at z=0.4-0.5. We then compare the spectral and morphological properties of the distant cluster galaxies, exploring the connection between the quenching of star formation inferred from the spectra and the strong evolution of the S0 population discussed by Dressler et al. We conclude that either two different timescales and/or two different physical processes are responsible for the spectral and morphological transformation.

24·5% Efficiency silicon PERT cells on MCZ substrates and 24·7% efficiency PERL cells on FZ substrates

Abstract: This paper reports the recent improvements in the energy conversion efficiencies of solar cells on magnetically-confined Czochralski grown (MCZ) and float zone (FZ) silicon substrates at the University of New South Wales. A PERT (passivated emitter, rear totally-diffused) cell structure has been used to reduce the cell series resistance from higher resistivity substrates. The total rear boron diffusion in this PERT structure appears to improve the surface passivation quality of MCZ and some FZ substrates. Hence, higher open-circuit voltages were observed for some PERT cells. One of these cells on MCZ substrates demonstrated 24·5% energy conversion efficiency at Sandia National Laboratories under the standard global spectrum (100 mW/cm2) at 25°C. This is the highest efficiency ever reported for a MCZ silicon solar cell. The cells made on MCZ substrates also showed stable cell performance rather than the usually reported unstable performance for boron-doped CZ substrates. Also reported is a PERL (passivated emitter, rear locally-diffused) cell on a FZ substrate of 24·7% efficiency, which is the highest efficiency ever reported for any silicon solar cell. Copyright © 1999 John Wiley & Sons, Ltd.

Search for Time Variation of the Fine Structure Constant

Abstract: An order of magnitude sensitivity gain is described for using quasar spectra to investigate possible time or space variation in the fine structure constant $\ensuremath{\alpha}$. Applied to a sample of 30 absorption systems, spanning redshifts $0.5lzl1.6$, we derive limits on variations in $\ensuremath{\alpha}$ over a wide range of epochs. For the whole sample, $\ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}1.1\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. This deviation is dominated by measurements at $zg1$, where $\ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}1.9\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. For $zl1$, $\ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}0.2\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. While this is consistent with a time-varying $\ensuremath{\alpha}$, further work is required to explore possible systematic errors in the data, although careful searches have so far revealed none.

The impact of communication effectiveness and service quality on relationship commitment in consumer, professional services

Abstract: Most previous research in the domain of relationship marketing has focused on the antecedents of loyalty and commitment in industrial markets, distribution channels or consumer goods. This study, however, models the antecedents of clients’ relationship commitment in the context of a professional service, high in credence qualities (where customers have difficulty in confidently evaluating service quality, even purchase and consumption) ‐ i.e. personal financial planning services. The impact of four key explanatory variables (communication effectiveness, technical quality, functional quality and trust) are examined. The results support the hypothesized model and show communication effectiveness to be a key driver of all antecedent variables, and the single most powerful determinant of relationship commitment.

Evidence that halogenated furanones from Delisea pulchra inhibit acylated homoserine lactone (AHL)-mediated gene expression by displacing the AHL signal from its receptor protein.

Abstract: Summary: Acylated homoserine lactone (AHL)-mediated gene expression controls phenotypes involved in colonization, often specifically of higher organisms, in both marine and terrestrial environments. The marine red alga Delisea pulchra produces halogenated furanones which resemble AHLs structurally and show inhibitory activity at ecologically realistic concentrations in AHL bioassays. Evidence is presented that halogenated furanones displace tritiated OHHL [N-3- (oxohexanoy1)-L-homoserine lactone] from Escherichia coli cells overproducing LuxR with potencies corresponding to their respective inhibitory activities in an AHL-regulated bioluminescence assay, indicating that this is the mechanism by which furanones inhibit AHL-dependent phenotypes. Alternative mechanisms for this phenomenon are also addressed. General metabolic disruption was assessed with two-dimensional PAGE, revealing limited non- AHL-related effects. A direct chemical interaction between the algal compounds and AHLs, as monitored by 1H NMR spectroscopy, was shown not to occur in vitro. These results support the contention that furanones, at the concentrations produced by the alga, can control bacterial colonization of surfaces by specifically interfering with AHL-mediated gene expression at the level of the LuxR protein.

Role of Nanoparticles in Photocatalysis

Abstract: The aim of this review paper is to give an overview of the development and implications of nanotechnology in photocatalysis. The topics covered include a detailed look at the unique properties of nanoparticles and their relation to photocatalytic properties. Current applications of and research into the use of nanoparticles as photocatalysts has also been reviewed. Also covered is the utilization of nanoparticles in doped, coupled, capped, sensitized and organic–inorganic nanocomposite semiconductor systems, with an effort to enhance photocatalytic and/or optical properties of commonly used semiconductor materials. The use of nanocrystalline thin films in electrochemically assisted photocatalytic processes has been included. Finally, the use of nanoparticles has made a significant contribution in providing definitive mechanistic information regarding the photocatalytic process.

A Spectroscopic catalog of 10 distant rich clusters of galaxies

Abstract: We present spectroscopic observations of galaxies in the fields of 10 distant clusters for which we have previously presented deep imaging with WFPC2 on board the Hubble Space Telescope. The clusters span the redshift range z=0.37-0.56 and are the subject of a detailed ground- and space-based study to investigate the evolution of galaxies as a function of environment and epoch. The data presented here include positions, photometry, redshifts, spectral line strengths, and classifications for 657 galaxies in the fields of the 10 clusters. The catalog is composed of 424 cluster members across the 10 clusters and 233 field galaxies, with detailed morphological information from our WFPC2 images for 204 of the cluster galaxies and 71 in the field. We illustrate some basic properties of the catalog, including correlations between the morphological and spectral properties of our large sample of cluster galaxies. A direct comparison of the spectral properties of the high-redshift cluster and field populations suggests that the phenomenon of strong Balmer lines in otherwise passive galaxies (commonly called E + A but renamed here as the k + a class) shows an order-of-magnitude increase in the rich cluster environment compared with a more modest increase in the field population. This suggests that the process or processes involved in producing k + a galaxies are either substantially more effective in the cluster environment or that this environment prolongs the visibility of this phase. A more detailed analysis and modeling of these data is presented in Poggianti et al.

Rolling friction in the dynamic simulation of sandpile formation

Abstract: The contact between spheres results in a rolling resistance due to elastic hysteresis losses or viscous dissipation. This resistance is shown to be important in the three-dimensional dynamic simulation of the formation of a heap of spheres. The implementation of a rolling friction model can avoid arbitrary treatments or unnecessary assumptions, and its validity is confirmed by the good agreement between the simulated and experimental results under comparable conditions. Numerical results suggest that the angle of repose increases significantly with the rolling friction coefficient and decreases with particle size.

The psychosocial effects of torture, mass human rights violations, and refugee trauma : Toward an integrated conceptual framework

Abstract: Torture is a complex trauma that often occurs within the context of widespread persecution and human rights violations. In addition, the nature of modern warfare is such that whole populations are at risk of suffering extensive trauma, injustices, loss, and displacement. Refugees, in particular, experience sequential stresses that may compound each other over prolonged periods of time. The present overview examines whether contemporary notions of trauma, and especially a focus on the category of posttraumatic stress disorder (PTSD), are adequate in assessing the multiple effects of such experiences. Recent studies are reviewed to indicate the strengths and limitations of current research approaches. Rates of PTSD in such studies have varied with relatively low rates being found in recent epidemiologic studies undertaken on refugee populations. It is suggested that a focus on intervening psychosocial adaptive systems may assist in delineating more clearly the pathways that determine whether traumatized persons achieve psychosocial restitution or are at risk of ongoing psychiatric disability. A model is proposed which suggests that torture and related abuses may challenge five core adaptive systems subserving the functions of "safety," "attachment," "justice," "identity-role," and "existential-meaning." It is argued that a clearer delineation of such adaptive systems may provide a point of convergence that may link research endeavors more closely to the subjective experience of survivors and to the types of clinical interventions offered by trauma treatment services.

Pancreatic stellate cells are activated by proinflammatory cytokines: implications for pancreatic fibrogenesis

Abstract: BACKGROUND—The pathogenesis of pancreatic fibrosis is unknown. In the liver, stellate cells play a major role in fibrogenesis by synthesising increased amounts of collagen and other extracellular matrix (ECM) proteins when activated by profibrogenic mediators such as cytokines and oxidant stress. AIMS—To determine whether cultured rat pancreatic stellate cells produce collagen and other ECM proteins, and exhibit signs of activation when exposed to the cytokines platelet derived growth factor (PDGF) or transforming growth factor β (TGF-β). METHODS—Cultured pancreatic stellate cells were immunostained for the ECM proteins procollagen III, collagen I, laminin, and fibronectin using specific polyclonal antibodies. For cytokine studies, triplicate wells of cells were incubated with increasing concentrations of PDGF or TGF-β. RESULTS—Cultured pancreatic stellate cells stained strongly positive for all ECM proteins tested. Incubation of cells with 1, 5, and 10 ng/ml PDGF led to a significant dose related increase in cell counts as well as in the incorporation of 3H-thymidine into DNA. Stellate cells exposed to 0.25, 0.5, and 1 ng/ml TGF-β showed a dose dependent increase in α smooth muscle actin expression and increased collagen synthesis. In addition, TGF-β increased the expression of PDGF receptors on stellate cells. CONCLUSIONS—Pancreatic stellate cells produce collagen and other extracellular matrix proteins, and respond to the cytokines PDGF and TGF-β by increased proliferation and increased collagen synthesis. These results suggest an important role for stellate cells in pancreatic fibrogenesis. Keywords: pancreatic fibrosis; stellate cell activation; cytokines

The relationship between commitment and organizational culture, subculture, leadership style and job satisfaction in organizational change and development

Abstract: The concept of organizational commitment has been examined extensively in organizational literature, yet the relationships between organizational culture, subculture and commitment have received little attention so far. Acknowledging the complexity and the multifaceted nature of antecedents involved in organizational commitment, it is still necessary to understand the dynamics of relationships between these variables. It was found that organizational subculture was more strongly related to commitment than was organizational culture. Satisfaction with the level of control over working environment had the highest correlation with the level of commitment. The leadership style variable, consideration, was also relatively strongly related to commitment when compared with other variables. There was a small positive association between age and commitment. However, participants’ level of education, years in position and years of experience failed to show any relationship with commitment.

Skeletal muscle hypertrophy is mediated by a Ca2+-dependent calcineurin signalling pathway.

Abstract: Skeletal muscle hypertrophy and regeneration are important adaptive responses to both physical activity and pathological stimuli1 Failure to maintain these processes underlies the loss of skeletal muscle mass and strength that occurs with ageing and in myopathies2 Here we show that stable expression of a gene encoding insulin-like growth factor 1 (IGF-1) in C2C12 skeletal muscle cells, or treatment of these cells with recombinant IGF-1 or with insulin and dexamethasone, results in hypertrophy of differentiated myotubes and a switch to glycolytic metabolism Treatment with IGF-1 or insulin and dexamethasone mobilizes intracellular calcium, activates the Ca2+/calmodulin-dependent phosphatase calcineurin, and induces the nuclear translocation of the transcription factor NF-ATc1 Hypertrophy is suppressed by the calcineurin inhibitors cyclosporin A or FK506, but not by inhibitors of the MAP-kinase or phosphatidylinositol-3-OH kinase pathways Injecting rat latissimus dorsi muscle with a plasmid encoding IGF-1 also activates calcineurin, mobilizes satellite cells and causes a switch to glycolytic metabolism We propose that growth-factor-induced skeletal-muscle hypertrophy and changes in myofibre phenotype are mediated by calcium mobilization and are critically regulated by the calcineurin/NF-ATc1 signalling pathway

Bullying behaviour and psychosocial health among school students in New South Wales, Australia: cross sectional survey

Abstract: Objectives: To examine the prevalence of bullying behaviours in schoolchildren and the association of bullying with psychological and psychosomatic health. Design: Cross sectional survey. Setting: Government and non-government schools in New South Wales, Australia. Participants: 3918 schoolchildren attending year 6 (mean age 11.88 years), year 8 (13.96), and year 10 (15.97) classes from 115 schools. Main outcome measures: Self reported bullying behaviours and psychological and psychosomatic symptoms. Results: Almost a quarter of students (23.7%) bullied other students, 12.7% were bullied, 21.5% were both bullied and bullied others on one or more occasions in the last term of school, and 42.4% were neither bullied nor bullied others. More boys than girls reported bullying others and being victims of bullying. Bullying behaviour was associated with increased psychosomatic symptoms Bullies tended to be unhappy with school; students who were bullied tended to like school and to feel alone. Students who both bullied and were bullied had the greatest number of psychological and psychosomatic symptoms. Conclusions: Being bullied seems to be widespread in schools in New South Wales and is associated with increased psychosomatic symptoms and poor mental health. Health practitioners evaluating students with common psychological and psychosomatic symptoms should consider bullying and the student9s school environment as potential causes. Key messages Bullying behaviour occurs in schools worldwide and is likely to be associated with poor health in schoolchildren Research into bullying has been mainly focused on victims but there are other categories of bullying that deserve attention At least three out of five students experienced or participated in bullying in schools in New South Wales, Australia The psychosocial and psychosomatic health of the students varied according to their bullying status

States, Markets, Families: Gender, Liberalism and Social Policy in Australia, Canada, Great Britain and the United States

Abstract: The 1990s have seen dramatic restructuring of state social provision in the US, the UK, Canada and Australia. This has occurred largely because of the rise of market liberalism, which challenges the role of the state. This important book examines the impact of changes in social policy regimes on gender roles and relations. Structured thematically and systematically comparative, it analyses three key policy areas: labor markets, income maintenance and reproductive rights. Largely driven by issues of equality, it considers the role of the state as a site for gender and sexual politics at a time when primacy is given to the market, developing an argument about social citizenship in the process. Eminent scholars in the field, Julia O'Connor, Ann Orloff and Sheila Shaver make a landmark contribution to debates about social policy and gender relations in this era of economic restructuring and deregulation.

A New Catalog of Photometric Redshifts in the Hubble Deep Field

Abstract: Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects [AB(8140)<26.0]. From a study of the distribution of residuals [Δzrms/(1+z)≈0.1 at all redshifts], we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and we finish by presenting a list of bright high-redshift (z≈5) candidates extracted from our catalog together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.

Changes to AIDS dementia complex in the era of highly active antiretroviral therapy

Abstract: Objectives: To determine the protective efficacy of highly active antiretroviral therapy (HAART) against AIDS dementia complex (ADC) relative to other initial AIDS-defining illnesses (ADls), Australian AIDS notification data over recent years were examined. Methods: All initial ADls in Australia over the period 1992-1997 were included. Three initial ADI groups were established: ADC; other predominantly central nervous system (CNS) ADls (toxoplasmosis and cryptococcosis); and non-CNS ADls. For each ADI grouping, the proportion of total ADls, and median CD4 cell count in the pre-HAART era (1992-1995) were compared with the HAART era (1996 and 1997). Results: Initial ADls peaked in Australia in 1994 (n = 1049), with a gradual decline to 1996 (n = 722), and a marked decline in 1997 (n = 367). ADC constituted 4.4% of initial ADls over the period 1992-1995, but increased after the introduction of HAART to 6.0% in 1996 and 6.5% in 1997 (P = 0.02). In contrast, the proportion of other CNS ADls (1992-1995, 8.1%; 1996, 6.0%; 1997, 8.2%; P = 0.41) was stable over the period 1992-1997. The median CD4 cell count at ADC diagnosis increased from 70/mm 3 in 1992-1995 to 120/mm 3 in 1996 and 170/mm 3 in 1997 (P = 0.04). Although the median CD4 cell count also increased significantly over this period for both other CNS ADls (40-60/mm 3 P = 0.02), and non-CNS ADls (60-70/mm 3 ; P = 0.02), the increase was small. Conclusion: A proportional increase in ADC compared with other ADls and a marked increase in the median CD4 cell count at ADC diagnosis have occurred since the introduction of HAART in Australia. These changes suggest that HAART has a lesser impact on ADC than on other ADls, with the poor CNS penetration of many antiretroviral agents a possible explanation.

Segmented principal components transformation for efficient hyperspectral remote-sensing image display and classification

Abstract: A segmented, and possibly multistage, principal components transformation (PCT) is proposed for efficient hyperspectral remote-sensing image classification and display. The scheme requires, initially, partitioning the complete set of bands into several highly correlated subgroups. After separate transformation of each subgroup, the single-band separabilities are used as a guide to carry out feature selection. The selected features can then be transformed again to achieve a satisfactory data reduction ratio and generate the three most significant components for color display. The scheme reduces the computational load significantly for feature extraction, compared with the conventional PCT. A reduced number of features will also accelerate the maximum likelihood classification process significantly, and the process will not suffer the limitations encountered by trying to use the full set of hyperspectral data when training samples are limited. Encouraging results have been obtained in terms of classification accuracy, speed, and quality of color image display using two airborne visible/infrared imaging spectrometer (AVIRIS) data sets.

A comparison of algorithms for stream flow recession and baseflow separation

Abstract: Simple hydraulic models for outflow of groundwater into a stream suggest that the form of the storage–discharge relationship for groundwater changes from linear, for a confined aquifer, to quadratic, for an unconfined flow. Tests of the form of stream flow recessions in 11 streams, during periods of no recharge, show that for most catchments the storage–discharge relationship is more strongly non-linear than the quadratic form. However, for the commonly occurring case of recessions of duration up to about 10 days, the linear model remains a very good approximation, using a biased value of the groundwater turnover time. In contrast, estimates, from the stream hydrograph, of recharge during a storm event are very sensitive to the form of the storage–discharge relationship. The results of this study also show great variability in the parameters of the recession algorithm from one recession to another, attributable to spatial variability in groundwater recharge. An extension of the linear model to ‘leaky’ catchments, where the recession reaches zero flow, has been tested on two data sets. The second part of the paper deals with algorithms for baseflow during surface runoff events—the problem of hydrograph separation. Algorithms with one, two and three parameters have been compared, using data for the same 11 streams, and the results show significant differences in the baseflow index (BFI) predicted for some catchments. The two-parameter algorithm, which is fitted subjectively, is more consistent in providing plausible results than either the one- or three-parameter algorithms, both of which can be fitted objectively. Copyright © 1999 John Wiley & Sons, Ltd.

Activation of Pancreatic Stellate Cells in Human and Experimental Pancreatic Fibrosis

Abstract: The mechanisms of pancreatic fibrosis are poorly understood. In the liver, stellate cells play an important role in fibrogenesis. Similar cells have recently been isolated from the pancreas and are termed pancreatic stellate cells. The aim of this study was to determine whether pancreatic stellate cell activation occurs during experimental and human pancreatic fibrosis. Pancreatic fibrosis was induced in rats (n = 24) by infusion of trinitrobenzene sulfonic acid (TNBS) into the pancreatic duct. Surgical specimens were obtained from patients with chronic pancreatitis (n = 6). Pancreatic fibrosis was assessed using the Sirius Red stain and immunohistochemistry for collagen type I. Pancreatic stellate cell activation was assessed by staining for α-smooth muscle actin (αSMA), desmin, and platelet-derived growth factor receptor type β (PDGFRβ). The relationship of fibrosis to stellate cell activation was studied by staining of serial sections for αSMA, desmin, PDGFRβ, and collagen, and by dual-staining for αSMA plus either Sirius Red or in situ hybridization for procollagen α1 (I) mRNA. The cellular source of TGFβ was examined by immunohistochemistry. The histological appearances in the TNBS model resembled those found in human chronic pancreatitis. Areas of pancreatic fibrosis stained positively for Sirius Red and collagen type I. Sirius Red staining was associated with αSMA-positive cells. αSMA staining colocalized with procollagen α1 (I) mRNA expression. In the rat model, desmin staining was associated with PDGFRβ in areas of fibrosis. TGFβ was maximal in acinar cells adjacent to areas of fibrosis and spindle cells within fibrotic bands. Pancreatic stellate cell activation is associated with fibrosis in both human pancreas and in an animal model. These cells appear to play an important role in pancreatic fibrogenesis.

A comparison of cognitive load associated with discovery learning and worked examples

Abstract: This article reports experimental work comparing exploration and worked-examples practice in learning to use a database program. Exploration practice is based on discovery learning principles, whereas worked-examples practice arose from the development of cognitive load theory. Exploration practice was expected to place a considerable load on working memory, whereas a heavy use of worked examples was hypothesized to lead to more effective processing by reducing extraneous mental load. Students with no previous domain familiarity with databases were found to substantially benefit from worked examples in comparison to exploration. However, if students had previous familiarity with the database domain, the type of practice made no significant difference to their learning because the exploration students were able to draw on existing, well-developed domain schemas to guide their exploration.