21,667 research outputs found
A assessment of an audio-visual French reading course for use in the primary school
Prior to the work carried out in 1968 by the author of this thesis, a French reading course for use in the primary school had been designed in the Department of Education at Durham University and given a small-scale trial. This thesis describes the work carried out in assessing the use of the course in a larger number of primary classes under as near as possible normal conditions. Part I of the thesis describes the background to the experiment: the rapid growth of primary French teaching in the sixties, the basic need for oral competence, and the problems expected in introducing reading. In Part II of the thesis the designing and initial trial of the reading course is described. After it had been established that the introduction of French reading did cause problems, an audio-visual reading course was designed which used a partly look-and-say, partly phonetic method. At the same time tests were designed which were to indicate how successful the course was. The course was taught to two primary classes in 1967 by a research student and the results, compared to a grammar school control group, were promising. Part III of the thesis describes the preparations made for a larger-scale assessment of the material using firstly a group of eight primary school classes taught by their usual teachers, and then in the following year a smaller group of five similar classes. The make-up of the sample and the running of the assessment programme are described. In Part IV the results of the experiment are given, and reasons suggested for the lower level of success achieved. The results of the five-class group are examined separately. Part IV concludes with a consideration of some of the linguistic problems brought to light
Convex Rank Tests and Semigraphoids
Convex rank tests are partitions of the symmetric group which have desirable
geometric properties. The statistical tests defined by such partitions involve
counting all permutations in the equivalence classes. Each class consists of
the linear extensions of a partially ordered set specified by data. Our methods
refine existing rank tests of non-parametric statistics, such as the sign test
and the runs test, and are useful for exploratory analysis of ordinal data. We
establish a bijection between convex rank tests and probabilistic conditional
independence structures known as semigraphoids. The subclass of submodular rank
tests is derived from faces of the cone of submodular functions, or from
Minkowski summands of the permutohedron. We enumerate all small instances of
such rank tests. Of particular interest are graphical tests, which correspond
to both graphical models and to graph associahedra
C-Cl Bond Fission, Hcl Elimination, And Secondary Radical Decomposition In The 193 Nm Photodissociation Of Allyl Chloride
The primary photodissociation dynamics of allyl chloride upon excitation at 193 nm is investigated in a crossed laser-molecular beam scattering apparatus. Tunable vacuum ultraviolet (VUV) photoionization of the products provides a unique ability to learn about the secondary reaction products of the nascent photoproducts formed. The data show evidence for four significant primary reaction channels: a previously unidentified low kinetic energy C-Cl bond fission channel producing unstable allyl radicals, an excited state C-Cl bond fission channel producing Cl atoms with high translational energy, an HCl elimination pathway releasing significant energy to product translation to HCl and its momentum-matched mass 40 partner, and an HCl elimination channel producing low kinetic energy HCl products and predominantly unstable mass 40 products. The measured branching of these primary reaction channels of [all C-Cl] : [fast C-Cl] : [slow C-Cl] : [fast HCl] : [slow HCl] : [all HCl] is 1.00: 0.971: 0.029: 0.291: 0.167: 0.458 (where fast refers to the high recoil kinetic energy channels). The high internal energy allyl radicals formed in the slow C-Cl fission pathway of allyl chloride further dissociate/isomerize, as do the unstable mass 40 products formed in the HCl elimination pathways, and these products are investigated. Photoionization efficiency (PIE) curves of the HCl product suggest that a three-centered elimination mechanism contributes significantly to an observed HCl elimination reaction. (C) 2002 American Institute of Physics
Non-axisymmetric oscillations of stratified coronal magnetic loops with elliptical cross-sections
We study non-axisymmetric oscillations of a straight magnetic tube with an
elliptic cross-section and density varying along the tube. The governing
equations for kink and fluting modes in the thin tube approximation are
derived. We found that there are two kink modes, polarised along the large and
small axes of the elliptic cross-section. We have shown that the ratio of
frequencies of the first overtone and fundamental harmonic is the same for both
kink modes and independent of the ratio of the ellipse axes. On the basis of
this result we concluded that the estimates of the atmospheric scale height
obtained using simultaneous observations of the fundamental harmonic and first
overtone of the coronal loop kink oscillations are independent of the
ellipticity of the loop cross-section
Numerical analysis of the Iosipescu specimen for composite materials
A finite element analysis of the Iosipescu shear tests for unidirectional and cross-ply composites is presented. It is shown that an iterative analysis procedure must be used to model the fixture-specimen kinematics. The correction factors which are needed to compensate for the nonuniformity of stress distribution in calculating shear modulus are shown to be dependent on the material orthotropic ratio and the finite element loading models. Test section strain distributions representative of typical graphite-epoxy specimens are also presented
Spin Amplification for Magnetic Sensors Employing Crystal Defects
Recently there have been several theoretical and experimental studies of the
prospects for magnetic field sensors based on crystal defects, especially
nitrogen vacancy (NV) centres in diamond. Such systems could potentially be
incorporated into an AFM-like apparatus in order to map the magnetic properties
of a surface at the single spin level. In this Letter we propose an augmented
sensor consisting of an NV centre for readout and an `amplifier' spin system
that directly senses the local magnetic field. Our calculations show that this
hybrid structure has the potential to detect magnetic moments with a
sensitivity and spatial resolution far beyond that of a simple NV centre, and
indeed this may be the physical limit for sensors of this class
The interaction of unidirectional winds with an isolated barchan sand dune
Velocity profile measurements are determined on and around a barchan dune model inserted in the roughness layer on the tunnel floor. A theoretical investigation is made into the factors influencing the rate of sand flow around the dune. Flow visualization techniques are employed in the mapping of streamlines of flow on the dune's surface. Maps of erosion and deposition of sand are constructed for the barchan model, utilizing both flow visualization techniques and friction velocities calculated from the measured velocity profiles. The sediment budget found experimentally for the model is compared to predicted and observed results reported. The comparison shows fairly good agreement between the experimentally determined and predicted sediment budgets
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