3,611 research outputs found
A new chiral electro-optic effect: Sum-frequency generation from optically active liquids in the presence of a dc electric field
We report the observation of sum-frequency signals that depend linearly on an
applied electrostatic field and that change sign with the handedness of an
optically active solution. This recently predicted chiral electro-optic effect
exists in the electric-dipole approximation. The static electric field gives
rise to an electric-field-induced sum-frequency signal (an achiral third-order
process) that interferes with the chirality-specific sum-frequency at
second-order. The cross-terms linear in the electrostatic field constitute the
effect and may be used to determine the absolute sign of second- and
third-order nonlinear optical susceptibilities in isotropic media.Comment: Submitted to Physical Revie
Actions of Agonists, Fipronil and Ivermectin on the Predominant In Vivo Splice and Edit Variant (RDLbd, I/V) of the Drosophila GABA Receptor Expressed in Xenopus laevis Oocytes
Ionotropic GABA receptors are the targets for several classes of insecticides. One of the most widely-studied insect GABA receptors is RDL (resistance to dieldrin), originally isolated from Drosophila melanogaster. RDL undergoes alternative splicing and RNA editing, which influence the potency of GABA. Most work has focussed on minority isoforms. Here, we report the first characterisation of the predominant native splice variant and RNA edit, combining functional characterisation with molecular modelling of the agonist-binding region. The relative order of agonist potency is GABA> muscimol> TACA> ÎČ-alanine. The I/V edit does not alter the potency of GABA compared to RDLbd. Docking calculations suggest that these agonists bind and activate RDLbdI/V through a similar binding mode. TACA and ÎČ-alanine are predicted to bind with lower affinity than GABA, potentially explaining their lower potency, whereas the lower potency of muscimol and isoguvacine cannot be explained structurally from the docking calculations. The A301S (resistance to dieldrin) mutation reduced the potency of antagonists picrotoxin, fipronil and pyrafluprole but the I/V edit had no measurable effect. Ivermectin suppressed responses to GABA of RDLbdI/V, RDLbd and RDLbdI/VA301S. The dieldrin resistant variant also showed reduced sensitivity to Ivermectin. This study of a highly abundant insect GABA receptor isoform will help the design of new insecticides
Evaluation of specific heat for superfluid helium between 0 - 2.1 K based on nonlinear theory
The specific heat of liquid helium was calculated theoretically in the Landau
theory. The results deviate from experimental data in the temperature region of
1.3 - 2.1 K. Many theorists subsequently improved the results of the Landau
theory by applying temperature dependence of the elementary excitation energy.
As well known, many-body system has a total energy of Galilean covariant form.
Therefore, the total energy of liquid helium has a nonlinear form for the
number distribution function. The function form can be determined using the
excitation energy at zero temperature and the latent heat per helium atom at
zero temperature. The nonlinear form produces new temperature dependence for
the excitation energy from Bose condensate. We evaluate the specific heat using
iteration method. The calculation results of the second iteration show good
agreement with the experimental data in the temperature region of 0 - 2.1 K,
where we have only used the elementary excitation energy at 1.1 K.Comment: 6 pages, 3 figures, submitted to Journal of Physics: Conference
Serie
Evidence-Based Dialogue Maps as a research tool to evaluate the quality of school pupilsâ scientific argumentation
This pilot study focuses on the potential of Evidence-based Dialogue Mapping as a participatory action research tool to investigate young teenagersâ scientific argumentation. Evidence-based Dialogue Mapping is a technique for representing graphically an argumentative dialogue through Questions, Ideas, Pros, Cons and Data. Our research objective is to better understand the usage of Compendium, a Dialogue Mapping software tool, as both (1) a learning strategy to scaffold school pupilsâ argumentation and (2) as a method to investigate the quality of their argumentative essays. The participants were a science teacher-researcher, a knowledge mapping researcher and 20 pupils, 12-13 years old, in a summer science course for âgifted and talentedâ children in the UK. This study draws on multiple data sources: discussion forum, science teacher-researcherâs and pupilsâ Dialogue Maps, pupil essays, and reflective comments about the uses of mapping for writing. Through qualitative analysis of two case studies, we examine the role of Evidence-based Dialogue Maps as a mediating tool in scientific reasoning: as conceptual bridges for linking and making knowledge intelligible; as support for the linearisation task of generating a coherent document outline; as a reflective aid to rethinking reasoning in response to teacher feedback; and as a visual language for making arguments tangible via cartographic conventions
Darcy-BĂ©nard-Bingham convection
The present paper is the first to consider DarcyâBĂ©nardâBingham convection. A Bingham fluid saturates a horizontal porous layer that is subjected to heating from below. It is shown that this simple extension to the classical DarcyâBĂ©nard problem is linearly stable to small-amplitude disturbances but nevertheless admits strongly nonlinear convection. The Pascal model for a Bingham fluid occupying a porous medium is adopted, and this law is regularized in a frame-invariant manner to yield a set of two-dimensional governing equations that are then solved numerically using finite difference approximations. A weakly nonlinear theory of the regularized Pascal model is used to show that the onset of convection is via a fold bifurcation. Some parametric studies are performed to show that this non-linear onset of convection arises at increasing values of the DarcyâRayleigh number as the ReesâBingham number increases and that, for a fixed ReesâBingham number, the wavenumber at which the rate of heat transfer is maximized increases with the DarcyâRayleigh number
Problems and Prospects of Developing Countries in Forestry and Wood-Processing Industries. Report from an IIASA/UNIDO Workshop
This paper reports in a summary form on the discussions during a workshop organized by IIASA and UNIDO in January 1983. The workshop treated problems and prospects relating to developing countries in the sectors of forestry and wood-processing industries. The results of the workshop will be used in IIASA's project "Structural Change in the Forest Sector" and in UNIDO's work on its world-wide study on wood and wood processing industries. The invited participants came mainly from developing countries and from the two institutions mentioned.
The issues raised during the meeting are summarized systematically in Figure 2. The main concern of the meeting related to the sustainability of the wood resources, over-exploitation and depletion and suitable counter-balancing measures, such as afforestation, reforestation, and more efficient use of available resources. Trade patterns were also discussed. A global trade model for forestry industry products was presented
A comparative analysis of the skilled use of automated feedback tools through the lens of teacher feedback literacy
Effective learning depends on effective feedback, which in turn requires a set of skills, dispositions and practices on the part of both students and teachers which have been termed feedback literacy. A previously published teacher feedback literacy competency framework has identified what is needed by teachers to implement feedback well. While this framework refers in broad terms to the potential uses of educational technologies, it does not examine in detail the new possibilities of automated feedback (AF) tools, especially those that are open by offering varying degrees of transparency and control to teachers. Using analytics and artificial intelligence, open AF tools permit automated processing and feedback with a speed, precision and scale that exceeds that of humans. This raises important questions about how human and machine feedback can be combined optimally and what is now required of teachers to use such tools skillfully. The paper addresses two research questions: Which teacher feedback competencies are necessary for the skilled use of open AF tools? and What does the skilled use of open AF tools add to our conceptions of teacher feedback competencies? We conduct an analysis of published evidence concerning teachersâ use of open AF tools through the lens of teacher feedback literacy, which produces summary matrices revealing relative strengths and weaknesses in the literature, and the relevance of the feedback literacy framework. We conclude firstly, that when used effectively, open AF tools exercise a range of teacher feedback competencies. The paper thus offers a detailed account of the nature of teachersâ feedback literacy practices within this context. Secondly, this analysis reveals gaps in the literature, signalling opportunities for future work. Thirdly, we propose several examples of automated feedback literacy, that is, distinctive teacher competencies linked to the skilled use of open AF tools
What do people do with porn? qualitative research into the consumption, use and experience of pornography and other sexually explicit media
This article reviews qualitative research into the consumption of pornography and other sexually explicit media emerging from a range of subject areas. Taking a critique of quantitative methods and a focus on measuring sexual effects and attitudes as a starting point, it considers the proposition that qualitative work is more suited to an examination of the complex social, cultural and political constructions of sexuality. Examining studies into the way men, women and young people see, experience, and use explicit media texts, the article identifies the key findings that have emerged. Qualitative work shows that sexuality explicit media texts are experienced and understood in a variety of ways and evoke strong and often contradictory reactions, not all of which are represented in public debates about pornography. These texts function in a range of different ways, depending on context; as a source of knowledge, a resource for intimate practices, a site for identity construction, and an occasion for performing gender and sexuality. The article reviews these studies and their findings, identifying what they suggest about directions for future research, both in terms of developing methodology and refining approaches to sexuality and media consumption.</p
Lorentz-Lorenz Coefficient, Critical Point Constants, and Coexistence Curve of 1,1-Difluoroethylene
We report measurements of the Lorentz-Lorenz coefficient density dependence,
the critical temperature, and the critical density, of the fluid
1,1-difluoroethylene. Lorentz-Lorenz coefficient data were obtained by
measuring refractive index and density of the same fluid sample independently
of one another. Accurate determination of the Lorentz-Lorenz coefficient is
necessary for transformation of refractive index data into density data from
optics-based experiments on critical phenomena of fluid systems done with
different apparatus, with which independent measurement of the refractive indes
and density is not possible. Measurements were made along the coexistence curve
of the fluid and span the density range 0.01 to 0.80 g/cc. The Lorentz-Lorenz
coefficient results show a stronger density dependence along the coexistence
curve than previously observed in other fluids, with a monotonic decrease from
a density of about 0.2 g/cc onwards, and an overall variation of about 2.5% in
the density range studied. No anomaly in the Lorentz-Lorenz coefficient was
observed near the critical density. The critical temperature is measured at
Tc=(302.964+-0.002) K (29.814 C) and the measured critical density is
(0.4195+-0.0018)g/cc.Comment: 14 pages, 6 figures, MikTeX 2.4, submitted to Physical Review
'Surely the most natural scenario in the worldâ: Representations of âFamilyâ in BBC Pre-school Television
Historically, the majority of work on British childrenâs television has adopted either an institutional or an audience focus, with the texts themselves often overlooked. This neglect has meant that questions of representation in British childrenâs television â including issues such as family, gender, class or ethnicity - have been infrequently analysed in the UK context. In this article, we adopt a primarily qualitative methodology and analyse the various textual manifestations of âfamilyâ, group, or community as represented in a selected number of BBC pre-school programmes. In doing so, we question the (limited amount of) international work that has examined representations of the family in childrenâs television, and argue that nuclear family structures do not predominate in this sphere
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