1,916 research outputs found
On a problem of Andersson and Perlman
We present a simple solution to a problem posed recently by Andersson and Perlman. This solution allows us to find the conditional independence assumptions necessary
to permit maximum likelihood estimation of the parameters of a multivariate normal
distribution, when certain observations are missing
Factors enhancing mobile technology acceptance: A case study of 15 teachers in a Pretoria secondary school
While a considerable body of research has focused on learners’ acceptance of or resistance to mobile technologies, fewer studies have focused on teachers. This research study aimed to understand the factors influencing South African teachers’ acceptance of or resistance to using mobile technologies in their classroom practice. The Technology Acceptance Model (TAM) was used as a lens to explore factors that enhance mobile technology acceptance. The study consisted of a sequential mixed method, action research approach. Fifteen participants received training at a Mobile Technology workshop, aiming to provide professional development and enhance technological literacy knowledge and skills for teachers. The participants were then tasked to teach with technology and to share and reflect on their experiences and perceptions during the community of practice meetings. Content analysis was used to analyse the transcripts of these meetings and this led to the identification of 2 key factors, which enhanced the teachers’ acceptance of mobile technology, namely, perceived usefulness and perceived ease of use. Six sub-factors affecting acceptance were also identified: anxiety, ability, attitude, facilitating conditions, subjective norm and voluntariness. The factors that were identified suggest that additional professional development, infrastructure and resources need to be provided for teachers. We argue that by providing these necessities and eliminating or significantly reducing these factors, the use of mobile technology will be a success.
Keywords: improving classroom teaching; interactive learning environments; learning communities; mobile technology acceptance; secondary education; teaching/learning strategie
Constraints on discrete symmetries from anomaly cancellation in compactified superstring theories
Compactified string theories give rise to discrete symmetries which are
essential if they are to provide a realistic low energy theory. We find that in
a class of four dimensional string theories these symmetries are constrained by
similar conditions to those discrete anomaly cancellation conditions found in
the case the discrete symmetry is a residue of a spontaneously broken gauge
symmetry. Such conditions strongly constrain the allowed form of the low energy
effective theory.Comment: 8 pages, OUTP-93-14
Racial and Ethnic Variations in Knowledge and Attitudes about Genetic Testing
This study was designed to shed light on whether differences in utilization of genetic testing by African-Americans, Latinos, and non-Hispanic Whites are due primarily to different preferences, or whether they instead reflect other values and beliefs or differential access. It explores the values, attitudes, and beliefs of African-Americans, Latinos, and non-Hispanic Whites with respect to genetic testing by means of a telephone survey of representative samples of these three groups. The study finds clear evidence that Latinos and African-Americans are, if anything, more likely to express preferences for both prenatal and adult genetic testing than White respondents. At the same time, they hold other beliefs and attitudes that may conflict with, and override, these preferences in specific situations. African-Americans and Latinos are also less knowledgeable about genetic testing than non-Hispanic Whites, and they are less likely to have the financial resources or insurance coverage that would facilitate access to testing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63127/1/109065704323016012.pd
Gene-flow between populations of cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is highly variable between years
Both large and small scale migrations of Helicoverpa armigera Hübner in Australia were investigated using AMOVA analysis and genetic assignment tests. Five microsatellite loci were screened across 3142 individuals from 16 localities in eight major cotton and grain growing regions within Australia, over a 38-month period (November 1999 to January 2003). From November 1999 to March 2001 relatively low levels of migration were characterized between growing regions. Substantially higher than average gene-flow rates and limited differentiation between cropping regions characterized the period from April 2001 to March 2002. A reduced migration rate in the year from April 2002 to March 2003 resulted in significant genetic structuring between cropping regions. This differentiation was established within two or three generations. Genetic drift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Helicoverpa armigera in Australia demonstrated isolation by distance, so immigration into cropping regions is more likely to come from nearby regions than from afar. This effect was most pronounced in years with limited migration. However, there is evidence of long distance dispersal events in periods of high migration (April 2001–March 2002). The implications of highly variable migration patterns for resistance management are considered.K.D. Scott, K.S. Wilkinson, N. Lawrence, C.L. Lange, L.J. Scott, M.A. Merritt, A.J. Lowe and G.C Graha
Radiative Correction to the Dirichlet Casimir Energy for Theory in Two Spatial Dimensions
In this paper, we calculate the next to the leading order Casimir energy for
real massive and massless scalar fields within theory,
confined between two parallel plates with the Dirichlet boundary condition in
two spatial dimensions. Our results are finite in both cases, in sharp contrast
to the infinite result reported previously for the massless case. In this paper
we use a renormalization procedure introduced earlier, which naturally
incorporates the boundary conditions. As a result our radiative correction term
is different from the previously calculated value. We further use a
regularization procedure which help us to obtain the finite results without
resorting to any analytic continuation techniques.Comment: 8 pages, 3 figure
Nigrosine staining of wheat endosperm proteolipid patterns on starch gels
We have previously characterized a group of proteolipids from wheat endosperm, designated CM proteins, which are soluble in chloroformmethanol (2:1, v/v) and have a molecular weight lower than 25,000 daltons (1-3). These have been also studied by Redman and Ewart (4). The CM proteins are suitably fractionated into several components by starch gel electrophoresis at pH 3.2 (1). A sensitive staining procedure was required in connection with genetic studies of these proteins because phenotypes had to be ascertained in small endosperm fractions dissected without impairing normal germination and plant development. We report here on Nigrosine staining conditions for CM proteins under which high sensitivity and selectivity are achieve
Akt regulates centrosome migration and spindle orientation in the early Drosophila melanogaster embryo
Correct positioning and morphology of the mitotic spindle is achieved through regulating the interaction between microtubules (MTs) and cortical actin. Here we find that, in the Drosophila melanogaster early embryo, reduced levels of the protein kinase Akt result in incomplete centrosome migration around cortical nuclei, bent mitotic spindles, and loss of nuclei into the interior of the embryo. We show that Akt is enriched at the embryonic cortex and is required for phosphorylation of the glycogen synthase kinase-3β homologue Zeste-white 3 kinase (Zw3) and for the cortical localizations of the adenomatosis polyposis coli (APC)–related protein APC2/E-APC and the MT + Tip protein EB1. We also show that reduced levels of Akt result in mislocalization of APC2 in postcellularized embryonic mitoses and misorientation of epithelial mitotic spindles. Together, our results suggest that Akt regulates a complex containing Zw3, Armadillo, APC2, and EB1 and that this complex has a role in stabilizing MT–cortex interactions, facilitating both centrosome separation and mitotic spindle orientation
Generalized Farey trees, transfer Operators and phase transitions
We consider a family of Markov maps on the unit interval, interpolating
between the tent map and the Farey map. The latter map is not uniformly
expanding. Each map being composed of two fractional linear transformations,
the family generalizes many particular properties which for the case of the
Farey map have been successfully exploited in number theory. We analyze the
dynamics through the spectral analysis of generalized transfer operators.
Application of the thermodynamic formalism to the family reveals first and
second order phase transitions and unusual properties like positivity of the
interaction function.Comment: 39 pages, 10 figure
Nonequilibrium wetting
When a nonequilibrium growing interface in the presence of a wall is
considered a nonequilibrium wetting transition may take place. This transition
can be studied trough Langevin equations or discrete growth models. In the
first case, the Kardar-Parisi-Zhang equation, which defines a very robust
universality class for nonequilibrium moving interfaces, with a soft-wall
potential is considered. While in the second, microscopic models, in the
corresponding universality class, with evaporation and deposition of particles
in the presence of hard-wall are studied. Equilibrium wetting is related to a
particular case of the problem, it corresponds to the Edwards-Wilkinson
equation with a potential in the continuum approach or to the fulfillment of
detailed balance in the microscopic models. In this review we present the
analytical and numerical methods used to investigate the problem and the very
rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure
- …