4,158 research outputs found
Anisotropic Thermal Conduction in Supernova Remnants: Relevance to Hot Gas Filling Factors in the Magnetized ISM
We explore the importance of anisotropic thermal conduction in the evolution
of supernova remnants via numerical simulations. The mean temperature of the
bubble of hot gas is decreased by a factor of ~3 compared to simulations
without thermal conduction, together with an increase in the mean density of
hot gas by a similar factor. Thus, thermal conduction greatly reduces the
volume of hot gas produced over the life of the remnant. This underscores the
importance of thermal conduction in estimating the hot gas filling fraction and
emissivities in high-stage ions in Galactic and proto-galactic ISMs.Comment: Submitted to Astrophysical Journal Letters. 4 pages, 3 figure
Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties
Ferroelectric and dielectric properties of polydomain (twinned)
single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a
nonlinear thermodynamic theory, which has been developed recently for epitaxial
ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3
(PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit
strain-temperature" phase diagrams are calculated and compared with each other.
It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar
to the diagram of PbTiO3 films. They consist of only four different stability
ranges, which correspond to the paraelectric phase, single-domain tetragonal
ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at
x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of
stable polarization states, involving at least one monoclinic polydomain state.
Using the developed phase diagrams, the mean out-of-plane polarization of a
poled PZT film is calculated as a function of the misfit strain and
composition. Theoretical results are compared with the measured remanent
polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane
dielectric response of PZT films on the misfit strain in the heterostructure is
also reported.Comment: 23 pages, 4 figure
Philosophies and pedagogies that shape an integrated engineering programme
Accredited engineering degrees call upon students to develop a wide range of knowledge and skills. These range from technical, scientific and mathematical knowledge, through to transferable skills such as communications, teamwork, business acumen and critical analysis. Through a faculty-wide curriculum development programme we have sought to implement cross-department teaching framework whereby a range of pedagogies are employed to deliver against core philosophies for a new way of teaching aimed at developing students’ knowledge, skills and attitudes while meeting a diverse range of learning outcomes. We argue that is it vital that learning takes place in the context of authentic engineering problems and processes. In this paper, we look at the philosophies, pedagogies and outcomes of an educational-based project which creates a connected curriculum that joins distinct disciplines at key points during the students’ education to provide preparation for, and experience of, professional engineering. It describes the motivation for change and described the implementation and impact of these approaches
Fitness for purpose? project-based, collaborative learning in engineering undergraduate education
In response to evolving work practices in engineering (Royal Academy of Engineering 2010) and the ever-changing nature of vocational and professional knowledge (Broad, 2016), attention has rightly turned to the development of innovative pedagogies to facilitate the entry of graduates to the employment market. Project-based Learning (PjBL) is an example of such an innovative pedagogy and has been developed in some HE contexts to provide students with authentic learning experiences which are designed to embed team working and collaboration; problem solving and solution-finding alongside the development of technical knowledge and skills (Mills and Treagust, 2003). Yet despite the introduction of collaborative inquiry-based curricula in engineering, comprehensive understanding of the pedagogical practices that these innovative practices require has not yet emerged (Damşa & Nerland, 2016). At UCL Engineering, PjBL has been an integral feature of the Integrated Engineering Programme (IEP) undergraduate curriculum since 2014. Drawing upon an on-going collaborative Institute of Education/UCL ‘seed corn’ funded project, this paper will present data collected through observation of project-based learning scenarios and discussion with engineering undergraduates in situ. It will identify and discuss the nature of student learning and engagement in project-based learning activities, with particular attention to disciplinary issues and the development of student disciplinary knowledge. In so doing, it will assess whether PjBL is, indeed, ‘fit for purpose’
Exact Perturbations for inflation with smooth exit
Toy models for the Hubble rate or the scalar field potential have been used
to analyze the amplification of scalar perturbations through a smooth
transition from inflation to the radiation era. We use a Hubble rate that
arises consistently from a decaying vacuum cosmology, which evolves smoothly
from nearly de Sitter inflation to radiation domination. We find exact
solutions for super-horizon perturbations (scalar and tensor), and for
sub-horizon perturbations in the vacuum- and radiation-dominated eras. The
standard conserved quantity for super-horizon scalar perturbations is exactly
constant for growing modes, and zero for the decaying modes.Comment: Minor errors correcte
Highlighting the learning in project-based undergraduate engineering education: pedagogical and methodological considerations
This paper presents a discussion of findings in relation to the pedagogy of Project Based Learning (PjBL) from a collaborative learning and teaching research project at UCL Engineering. It highlights the importance of adopting a) an understanding learning as a social practice in PjBL, and b) developing valid methodological approaches when capturing student learning experiences
The high-lying Li levels at excitation energy around 21 MeV
The H+He cluster structure in Li was investigated by the
H(,H He)n kinematically complete experiment at the incident
energy = 67.2 MeV. We have observed two resonances at =
21.30 and 21.90 MeV which are consistent with the He(H, )Li
analysis in the Ajzenberg-Selove compilation. Our data are compared with the
previous experimental data and the RGM and CSRGM calculations.Comment: 12 pages, 6 figures. Accepted for publication in J. Phys. Soc. Jp
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