153 research outputs found
Em que medida o conteúdo sobre genética nos manuais escolares contribuipara a literacia cientifíca? Análise dos temas ciência-tecnologia-sociedade-ambiente em manuais escolares
Our article analyses science-technology- society-environment (STSE) issues in the genetics-related chapters of Portuguese natural sciences and biology textbooks and considers how they contribute to students’ scientific literacy. We inspected manner of imparting of the decontextualized and socially neutral view of science and technology (S&T) as an obstacle for achieving scientific literacy. Our sample comprised four textbooks, two for the 9th and two the 12th grades. We identified and content-analytically analyzed 1019 STSE statements with regard to their compliance with previously proposed criteria. We quantitatively analyzed the statements’ frequencies. We noted an attempt to approach STSE issues, but we found important deficiencies in all the textbooks, as well as indicators of a distorted view of science. We discuss possible influences of the socio-cultural context in the selection of STSE contents, in the terms being applied, as well as in the S&T conceptions displayed by the textbooks.O nosso artigo analisa o tema das relações entre a ciência, a tecnologia, a sociedade e o ambiente (conhecidos na língua inglesa como STSE issues), nos capítulos relacionados com a genética, em manuais de ciências naturais e de biologia, e considera em que medida eles contribuem para a literacia científica dos alunos. Adicionalmente, foi averiguada a transmissão da visão descontextualizada e socialmente neutra da ciência e da tecnologia, enquanto obstáculo à literacia científica. A amostra compreende quatro manuais portugueses de Biologia e de Ciências Naturais, nomeadamente, dois para o 9.º ano e dois para o 12.º. Identificámos e analisámos 1019 expressões com conteúdo STSE, conformes com critérios previamente propostos, e procedemos à análise de frequências. Verificou-se uma tentativa de abordagem de conteúdos STSE, tendo sido também detetadas deficiências importantes em todos os manuais, assim como indicadores daquela visão distorcida da ciência e da tecnologia. Discutem-se ainda possíveis influências do contexto sociocultural na seleção dos conteúdos STSE, nos termos utilizados, bem como na conceção sobre ciência e tecnologia refletidas nos manuais
Probing the mechanical properties of graphene using a corrugated elastic substrate
The exceptional mechanical properties of graphene have made it attractive for
nano-mechanical devices and functional composite materials. Two key aspects of
graphene's mechanical behavior are its elastic and adhesive properties. These
are generally determined in separate experiments, and it is moreover typically
difficult to extract parameters for adhesion. In addition, the mechanical
interplay between graphene and other elastic materials has not been well
studied. Here, we demonstrate a technique for studying both the elastic and
adhesive properties of few-layer graphene (FLG) by placing it on deformable,
micro-corrugated substrates. By measuring deformations of the composite
graphene-substrate structures, and developing a related linear elasticity
theory, we are able to extract information about graphene's bending rigidity,
adhesion, critical stress for interlayer sliding, and sample-dependent tension.
The results are relevant to graphene-based mechanical and electronic devices,
and to the use of graphene in composite, flexible, and strain-engineered
materials.Comment: 5 pages, 4 figure
New Perspectives on Glacial Geomorphology in Earth's Deep Time Record
International audienceThe deep time (pre-Quaternary) glacial record is an important means to understand the growth, development, and recession of the global cryosphere on very long timescales (10 6-10 8 Myr). Sedimentological description and interpretation of outcrops has traditionally played an important role. Whilst such data remain vital, new insights are now possible thanks to freely accessible aerial and satellite imagery, the widespread availability and affordability of Uncrewed Aerial Vehicles, and accessibility to 3D rendering software. In this paper, we showcase examples of glaciated landscapes from the Cryogenian, Ediacaran, Late Ordovician and Late Carboniferous where this approach is revolutionizing our understanding of deep time glaciation. Although some problems cannot be overcome (erosion or dissolution of the evidence), robust interpretations in terms of the evolving subglacial environment can be made. Citing examples from Australia (Cryogenian), China (Ediacaran), North and South Africa (Late Ordovician, Late Carboniferous), and Namibia (Late Carboniferous), we illustrate how the power of glacial geomorphology can be harnessed to interpret Earth's ancient glacial record
Arabidopsis CURVATURE THYLAKOID1 Proteins Modify Thylakoid Architecture by Inducing Membrane Curvature
Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme curvature at margins is generated and maintained. We report the identification of the CURVATURE THYLAKOID1 (CURT1) protein family, conserved in plants and cyanobacteria. The four Arabidopsis thaliana CURT1 proteins (CURT1A, B, C, and D) oligomerize and are highly enriched at grana margins. Grana architecture is correlated with the CURT1 protein level, ranging from flat lobe-like thylakoids with considerably fewer grana margins in plants without CURT1 proteins to an increased number of membrane layers (and margins) in grana at the expense of grana diameter in overexpressors of CURT1A. The endogenous CURT1 protein in the cyanobacterium Synechocystis sp PCC6803 can be partially replaced by its Arabidopsis counterpart, indicating that the function of CURT1 proteins is evolutionary conserved. In vitro, Arabidopsis CURT1A proteins oligomerize and induce tubulation of liposomes, implying that CURT1 proteins suffice to induce membrane curvature. We therefore propose that CURT1 proteins modify thylakoid architecture by inducing membrane curvature at grana margins
Stark deceleration of CaF molecules in strong- and weak-field seeking states
We report the Stark deceleration of CaF molecules in the strong-field seeking
ground state and in a weak-field seeking component of a rotationally-excited
state. We use two types of decelerator, a conventional Stark decelerator for
the weak-field seekers, and an alternating gradient decelerator for the
strong-field seekers, and we compare their relative merits. We also consider
the application of laser cooling to increase the phase-space density of
decelerated molecules.Comment: 10 pages, 8 figure
Cold heteromolecular dipolar collisions
We present the first experimental observation of cold collisions between two
different species of neutral polar molecules, each prepared in a single
internal quantum state. Combining for the first time the techniques of Stark
deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the
enhancement of molecular interaction time by 10. This has enabled an
absolute measurement of the total trap loss cross sections between OH and
ND at a mean collision energy of 3.6 cm (5 K). Due to the dipolar
interaction, the total cross section increases upon application of an external
polarizing electric field. Cross sections computed from \emph{ab initio}
potential energy surfaces are in excellent agreement with the measured value at
zero external electric field. The theory presented here represents the first
such analysis of collisions between a radical and a closed-shell
polyatomic molecule.Comment: 7 pages, 5 figure
Scattering of Stark-decelerated OH radicals with rare-gas atoms
We present a combined experimental and theoretical study on the rotationally
inelastic scattering of OH (X\,^2\Pi_{3/2}, J=3/2, f) radicals with the
collision partners He, Ne, Ar, Kr, Xe, and D as a function of the collision
energy between cm and 400~cm. The OH radicals are state
selected and velocity tuned prior to the collision using a Stark decelerator,
and field-free parity-resolved state-to-state inelastic relative scattering
cross sections are measured in a crossed molecular beam configuration. For all
OH-rare gas atom systems excellent agreement is obtained with the cross
sections predicted by close-coupling scattering calculations based on accurate
\emph{ab initio} potential energy surfaces. This series of experiments
complements recent studies on the scattering of OH radicals with Xe [Gilijamse
\emph{et al.}, Science {\bf 313}, 1617 (2006)], Ar [Scharfenberg \emph{et al.},
Phys. Chem. Chem. Phys. {\bf 12}, 10660 (2010)], He, and D [Kirste \emph{et
al.}, Phys. Rev. A {\bf 82}, 042717 (2010)]. A comparison of the relative
scattering cross sections for this set of collision partners reveals
interesting trends in the scattering behavior.Comment: 10 pages, 5 figure
Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes
The small mass and atomic-scale thickness of graphene membranes make them
highly suitable for nanoelectromechanical devices such as e.g. mass sensors,
high frequency resonators or memory elements. Although only atomically thick,
many of the mechanical properties of graphene membranes can be described by
classical continuum mechanics. An important parameter for predicting the
performance and linearity of graphene nanoelectromechanical devices as well as
for describing ripple formation and other properties such as electron
scattering mechanisms, is the bending rigidity, {\kappa}. In spite of the
importance of this parameter it has so far only been estimated indirectly for
monolayer graphene from the phonon spectrum of graphite, estimated from AFM
measurements or predicted from ab initio calculations or bond-order potential
models. Here, we employ a new approach to the experimental determination of
{\kappa} by exploiting the snap-through instability in pre-buckled graphene
membranes. We demonstrate the reproducible fabrication of convex buckled
graphene membranes by controlling the thermal stress during the fabrication
procedure and show the abrupt switching from convex to concave geometry that
occurs when electrostatic pressure is applied via an underlying gate electrode.
The bending rigidity of bilayer graphene membranes under ambient conditions was
determined to be eV. Monolayers have significantly lower
{\kappa} than bilayers
On the role of the magnetic dipolar interaction in cold and ultracold collisions: Numerical and analytical results for NH() + NH()
We present a detailed analysis of the role of the magnetic dipole-dipole
interaction in cold and ultracold collisions. We focus on collisions between
magnetically trapped NH molecules, but the theory is general for any two
paramagnetic species for which the electronic spin and its space-fixed
projection are (approximately) good quantum numbers. It is shown that dipolar
spin relaxation is directly associated with magnetic-dipole induced avoided
crossings that occur between different adiabatic potential curves. For a given
collision energy and magnetic field strength, the cross-section contributions
from different scattering channels depend strongly on whether or not the
corresponding avoided crossings are energetically accessible. We find that the
crossings become lower in energy as the magnetic field decreases, so that
higher partial-wave scattering becomes increasingly important \textit{below} a
certain magnetic field strength. In addition, we derive analytical
cross-section expressions for dipolar spin relaxation based on the Born
approximation and distorted-wave Born approximation. The validity regions of
these analytical expressions are determined by comparison with the NH + NH
cross sections obtained from full coupled-channel calculations. We find that
the Born approximation is accurate over a wide range of energies and field
strengths, but breaks down at high energies and high magnetic fields. The
analytical distorted-wave Born approximation gives more accurate results in the
case of s-wave scattering, but shows some significant discrepancies for the
higher partial-wave channels. We thus conclude that the Born approximation
gives generally more meaningful results than the distorted-wave Born
approximation at the collision energies and fields considered in this work.Comment: Accepted by Eur. Phys. J. D for publication in Special Issue on Cold
Quantum Matter - Achievements and Prospects (2011
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