44,248 research outputs found
The relationship between grade 12 learners’ understandings about scientific inquiry and achievement in physical sciences
Abstract: Inquiry Based Learning (IBL) has driven curriculum reforms in science education globally, with many educators teaching science as inquiry, in the hope of improving learners’ understandings of scientific concepts and improving achievements in standardised tests. The curiosity of whether learners’ engagements and understandings of the Nature of Scientific Inquiry (NOSI) is capable of improving achievement in standardised Physical Sciences tests is important in validating the global emphasis on Inquiry Based Science Education (IBSE). The main aim of this study was to assess grade twelve Physical Sciences learners’ understandings about the NOSI using the Views About Scientific Inquiry (VASI) questionnaire and then compare VASI scores with achievement scores obtained from the National Senior Certificate (NSC) preparatory Physical Sciences examination, a standardised provincial test used in preparing matriculants for the final NSC grade twelve examinations. The study followed a cross-sectional survey design, and involved one hundred and seven (107) grade twelve learners from three Johannesburg high schools. Data were collected using the adopted VASI questionnaire. Responses from the VASI questionnaire were coded and scored with the aid of a rubric. VASI scores were compared against the NSC preparatory test scores using descriptive and inferential statistics..
Maximally Symmetric Minimal Unification Model SO(32) with Three Families in Ten Dimensional Space-time
Based on a maximally symmetric minimal unification hypothesis and a quantum
charge-dimension correspondence principle, it is demonstrated that each family
of quarks and leptons belongs to the Majorana-Weyl spinor representation of
14-dimensions that relate to quantum spin-isospin-color charges. Families of
quarks and leptons attribute to a spinor structure of extra 6-dimensions that
relate to quantum family charges. Of particular, it is shown that 10-dimensions
relating to quantum spin-family charges form a motional 10-dimensional quantum
space-time with a generalized Lorentz symmetry SO(1,9), and 10-dimensions
relating to quantum isospin-color charges become a motionless 10-dimensional
quantum intrinsic space. Its corresponding 32-component fermions in the spinor
representation possess a maximal gauge symmetry SO(32). As a consequence, a
maximally symmetric minimal unification model SO(32) containing three families
in ten dimensional quantum space-time is naturally obtained by choosing a
suitable Majorana-Weyl spinor structure into which quarks and leptons are
directly embedded. Both resulting symmetry and dimensions coincide with the
ones of type I string and heterotic string SO(32) in string theory.Comment: 17 pages, RevTex, published version with minor typos correcte
Comments on Sweeny and Gliozzi dynamics for simulations of Potts models in the Fortuin-Kasteleyn representation
We compare the correlation times of the Sweeny and Gliozzi dynamics for
two-dimensional Ising and three-state Potts models, and the three-dimensional
Ising model for the simulations in the percolation prepresentation. The results
are also compared with Swendsen-Wang and Wolff cluster dynamics. It is found
that Sweeny and Gliozzi dynamics have essentially the same dynamical critical
behavior. Contrary to Gliozzi's claim (cond-mat/0201285), the Gliozzi dynamics
has critical slowing down comparable to that of other cluster methods. For the
two-dimensional Ising model, both Sweeny and Gliozzi dynamics give good fits to
logarithmic size dependences; for two-dimensional three-state Potts model,
their dynamical critical exponent z is 0.49(1); the three-dimensional Ising
model has z = 0.37(2).Comment: RevTeX, 4 pages, 5 figure
Cloaking and imaging at the same time
In this letter, we propose a conceptual device to perform subwavelength
imaging with positive refraction. The key to this proposal is that a drain is
no longer a must for some cases. What's more, this device is an isotropic
omnidirectional cloak with a perfect electric conductor hiding region and shows
versatile illusion optical effects. Numerical simulations are performed to
verify the functionalities.Comment: 15 pages, 4 figure
Pilot Study: Unique Response of Bone Tissue During an Investigation of Radio-Adaptive Effects in Mice
PURPOSE: We obtained bone tissue to evaluate the collateral effects of experiments designed to investigate molecular mechanisms of radio-adaptation in a mouse model. Radio-adaptation describes a process by which the prior exposure to low dose radiation can protect against the toxic effect of a subsequent high dose exposure. In the radio-adaptation experiments, C57Bl/6 mice were exposed to either a Sham or a priming Low Dose (5 cGy) of Cs-137 gamma rays before being exposed to either a Sham or High Dose (6 Gy) 24 hours later. ANALYSIS: Bone tissue were obtained from two experiments where mice were sacrificed at 3 days (n=3/group, 12 total) and at 14 days (n=6/group, 24 total) following high dose exposure. Tissues were analyzed to 1) evaluate a radio-adaptive response in bone tissue and 2) describe cellular and microstructural effects for two skeletal sites with different rates of bone turnover. One tibia and one lumbar vertebrae (LV2), collected at the 3-day time-point, were analyzed by bone histomorphometry and micro-CT to evaluate the cellular response and any evidence of microarchitectural impact. Likewise, tibia and LV2, collected at the 14-day time-point, were analyzed by micro-CT alone to evaluate resulting changes to bone structure and microarchitecture. The data were analyzed by 2-way ANOVA to evaluate the effects of the priming low dose radiation, of the high dose radiation, and of any interaction between the priming low and high doses of radiation. Bone histomorphometry was performed in the cancellous bone (aka trabecular bone) compartments of the proximal tibial metaphysis and of LV2. RESULTS: Cellular Response @ 3 Days The priming Low Dose radiation decreased osteoblast-covered bone perimeter in the proximal tibia and the total cell density in the bone marrow in the LV2. High Dose radiation, regardless of prior exposure to priming dose, dramatically reduced total cell density in bone marrow of both the long bone and vertebra. However, in the proximal tibia, High Dose radiation increased the osteoclast-covered bone perimeters, the density of adipocytes in bone marrow, and the area of bone marrow occupied by fat cells -- while in the LV2, adipocytes were rare and not stimulated by High Dose radiation. In an unexpected response, High Dose radiation dramatically increased (10-fold) osteoblast-covered bone perimeter in the LV2
A spectroscopic cell for fast pressure jumps across the glass transition line
We present a new experimental protocol for the spectroscopic study of the
dynamics of glasses in the aging regime induced by sudden pressure jumps
(crunches) across the glass transition line. The sample, initially in the
liquid state, is suddenly brought in the glassy state, and therefore out of
equilibrium, in a four-window optical crunch cell which is able to perform
pressure jumps of 3 kbar in a time interval of ~10 ms. The main advantages of
this setup with respect to previous pressure-jump systems is that the pressure
jump is induced through a pressure transmitting fluid mechanically coupled to
the sample stage through a deformable membrane, thus avoiding any flow of the
sample itself in the pressure network and allowing to deal with highly viscous
materials. The dynamics of the sample during the aging regime is investigated
by Brillouin Light Scattering (BLS). For this purpose the crunch cell is used
in conjunction with a high resolution double monochromator equipped with a CCD
detector. This system is able to record a full spectrum of a typical glass
forming material in a single 1 s shot. As an example we present the study of
the evolution toward equilibrium of the infinite frequency longitudinal elastic
modulus (M_infinity) of a low molecular weight polymer (Poly(bisphenol
A-co-epichlorohydrin), glycidyl end capped). The observed time evolution of
M_infinity, well represented by a single stretched exponential, is interpreted
within the framework of the Tool-Narayanaswamy theory.Comment: 9 pages, 11 figure
Phasing diffuse scattering. Application of the SIR2002 algorithm to the non-crystallographic phase problem
A new phasing algorithm has been used to determine the phases of diffuse
elastic X-ray scattering from a non-periodic array of gold balls of 50 nm
diameter. Two-dimensional real-space images, showing the charge-density
distribution of the balls, have been reconstructed at 50 nm resolution from
transmission diffraction patterns recorded at 550 eV energy. The reconstructed
image fits well with scanning electron microscope (SEM) image of the same
sample. The algorithm, which uses only the density modification portion of the
SIR2002 program, is compared with the results obtained via the
Gerchberg-Saxton-Fienup HIO algorithm. In this way the relationship between
density modification in crystallography and the HiO algorithm used in signal
and image processing is elucidated.Comment: 7 pages, 12 figure
Step by step capping and strain state of GaN/AlN quantum dots studied by grazing incidence diffraction anomalous fine structure
The investigation of small size embedded nanostructures, by a combination of
complementary anomalous diffraction techniques, is reported. GaN Quantum Dots
(QDs), grown by molecular beam epitaxy in a modified Stranski-Krastanow mode,
are studied in terms of strain and local environment, as a function of the AlN
cap layer thickness, by means of grazing incidence anomalous diffraction. That
is, the X-ray photons energy is tuned across the Ga absorption K-edge which
makes diffraction chemically selective. Measurement of \textit{hkl}-scans,
close to the AlN (30-30) Bragg reflection, at several energies across the Ga
K-edge, allows the extraction of the Ga partial structure factor, from which
the in-plane strain of GaN QDs is deduced. From the fixed-Q energy-dependent
diffracted intensity spectra, measured for diffraction-selected iso-strain
regions corresponding to the average in-plane strain state of the QDs,
quantitative information regarding composition and the out-of-plane strain has
been obtained. We recover the in-plane and out-of-plane strains in the dots.
The comparison to the biaxial elastic strain in a pseudomorphic layer indicates
a tendency to an over-strained regime.Comment: submitted to PR
Effects of dissipation on disordered quantum spin models
We study the effects of the coupling to an Ohmic quantum reservoir on the
static and dynamical properties of a family of disordered SU(2) spin models in
a transverse magnetic field using a method of direct spin summation. The
tendency to form a glassy phase increases with the strength of the coupling of
the system to the environment. We study the influence of the environment on the
features of the phase diagram of the various models as well as the stability of
the possible phases.Comment: 24 pages, 8 fig
Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned
The complex resistivity of the vortex lattice in an
untwinned crystal of 93-K has been measured at frequencies
from 100 kHz to 20 MHz in a 2-Tesla field ,
using a 4-probe RF transmission technique that enables continuous measurements
versus and temperature . As is increased, the inductance increases steeply to a cusp
at the melting temperature , and then undergoes a steep collapse
consistent with vanishing of the shear modulus . We discuss in detail
the separation of the vortex-lattice inductance from the `volume' inductance,
and other skin-depth effects. To analyze the spectra, we consider a weakly
disordered lattice with a low pin density. Close fits are obtained to
over 2 decades in . Values of the pinning parameter
and shear modulus obtained show that collapses by
over 4 decades at , whereas remains finite.Comment: 11 pages, 8 figures, Phys. Rev. B, in pres
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