499 research outputs found
Teaching powerful geographical knowledge : a matter of social justice : initial findings from the GeoCapabilities 3 project
GeoCapabilities offers an approach for unlocking powerful disciplinary knowledge (PDK) for children. In phase three of the project, we are exploring how far GeoCapabilities ‘works’ for teachers serving communities in challenging socio-economic circumstances. We connect GeoCapabilities to social justice in education, theoretically. Then, using the topic of migration, we discuss initial empirical findings of how teachers understand PDK and their challenges for teaching PDK. Collaborative work between teachers and academics suggests that the social justice dimension of GeoCapabilities could be realised, with appropriate support for teachers. We conclude with a set of principles to inform the future work of GeoCapabilities
Near-Earth asteroid (3200) Phaethon. Characterization of its orbit, spin state, and thermophysical parameters
The near-Earth asteroid (3200) Phaethon is an intriguing object: its
perihelion is at only 0.14 au and is associated with the Geminid meteor stream.
We aim to use all available disk-integrated optical data to derive a reliable
convex shape model of Phaethon. By interpreting the available space- and
ground-based thermal infrared data and Spitzer spectra using a thermophysical
model, we also aim to further constrain its size, thermal inertia, and visible
geometric albedo. We applied the convex inversion method to the new optical
data obtained by six instruments and to previous observations. The convex shape
model was then used as input for the thermophysical modeling. We also studied
the long-term stability of Phaethon's orbit and spin axis with a numerical
orbital and rotation-state integrator. We present a new convex shape model and
rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and
ecliptic coordinates of the preferred pole orientation of (319,
39) with a 5 uncertainty. Moreover, we derive its size
(=5.10.2 km), thermal inertia (=600200 J m
s K), geometric visible albedo
(=0.1220.008), and estimate the macroscopic surface
roughness. We also find that the Sun illumination at the perihelion passage
during the past several thousand years is not connected to a specific area on
the surface, which implies non-preferential heating.Comment: Astronomy and Astrophysics. In pres
Homeomorphic Embedding for Online Termination of Symbolic Methods
Well-quasi orders in general, and homeomorphic embedding in particular, have gained popularity to ensure the termination of techniques for program analysis, specialisation, transformation, and verification. In this paper we survey and discuss this use of homeomorphic embedding and clarify the advantages of such an approach over one using well-founded orders. We also discuss various extensions of the homeomorphic embedding relation. We conclude with a study of homeomorphic embedding in the context of metaprogramming, presenting some new (positive and negative) results and open problems
YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus
The rotation states of small asteroids are affected by a net torque arising
from an anisotropic sunlight reflection and thermal radiation from the
asteroids' surfaces. On long timescales, this so-called YORP effect can change
asteroid spin directions and their rotation periods. We analyzed lightcurves of
four selected near-Earth asteroids with the aim of detecting secular changes in
their rotation rates that are caused by YORP. We use the lightcurve inversion
method to model the observed lightcurves and include the change in the rotation
rate as a free parameter of optimization. We
collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used
thermal infrared data from the WISE spacecraft and estimated their size and
thermal inertia. We also used the currently available optical and radar
astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We
detected a YORP acceleration of for asteroid Cacus. For
Toro, we have a tentative () detection of YORP from a significant
improvement of the lightcurve fit for a nonzero value of . For asteroid
Eger, we confirmed the previously published YORP detection with more data and
updated the YORP value to . We also updated the shape model of
asteroid Ra-Shalom and put an upper limit for the change of the rotation rate
to . Ra-Shalom has a greater than
Yarkovsky detection with a theoretical value consistent with observations
assuming its size and/or density is slightly larger than the nominally expected
values
The non-convex shape of (234) Barbara, the first Barbarian
Asteroid (234) Barbara is the prototype of a category of asteroids that has
been shown to be extremely rich in refractory inclusions, the oldest material
ever found in the Solar System. It exhibits several peculiar features, most
notably its polarimetric behavior. In recent years other objects sharing the
same property (collectively known as "Barbarians") have been discovered.
Interferometric observations in the mid-infrared with the ESO VLTI suggested
that (234) Barbara might have a bi-lobated shape or even a large companion
satellite. We use a large set of 57 optical lightcurves acquired between 1979
and 2014, together with the timings of two stellar occultations in 2009, to
determine the rotation period, spin-vector coordinates, and 3-D shape of (234)
Barbara, using two different shape reconstruction algorithms. By using the
lightcurves combined to the results obtained from stellar occultations, we are
able to show that the shape of (234) Barbara exhibits large concave areas.
Possible links of the shape to the polarimetric properties and the object
evolution are discussed. We also show that VLTI data can be modeled without the
presence of a satellite.Comment: 10 pages, 6 figure
Microscopic observation of magnon bound states and their dynamics
More than eighty years ago, H. Bethe pointed out the existence of bound
states of elementary spin waves in one-dimensional quantum magnets. To date,
identifying signatures of such magnon bound states has remained a subject of
intense theoretical research while their detection has proved challenging for
experiments. Ultracold atoms offer an ideal setting to reveal such bound states
by tracking the spin dynamics after a local quantum quench with single-spin and
single-site resolution. Here we report on the direct observation of two-magnon
bound states using in-situ correlation measurements in a one-dimensional
Heisenberg spin chain realized with ultracold bosonic atoms in an optical
lattice. We observe the quantum walk of free and bound magnon states through
time-resolved measurements of the two spin impurities. The increased effective
mass of the compound magnon state results in slower spin dynamics as compared
to single magnon excitations. In our measurements, we also determine the decay
time of bound magnons, which is most likely limited by scattering on thermal
fluctuations in the system. Our results open a new pathway for studying
fundamental properties of quantum magnets and, more generally, properties of
interacting impurities in quantum many-body systems.Comment: 8 pages, 7 figure
Constraint solving in non-permutative nominal abstract syntax
Nominal abstract syntax is a popular first-order technique for encoding, and
reasoning about, abstract syntax involving binders. Many of its applications
involve constraint solving. The most commonly used constraint solving algorithm
over nominal abstract syntax is the Urban-Pitts-Gabbay nominal unification
algorithm, which is well-behaved, has a well-developed theory and is applicable
in many cases. However, certain problems require a constraint solver which
respects the equivariance property of nominal logic, such as Cheney's
equivariant unification algorithm. This is more powerful but is more
complicated and computationally hard. In this paper we present a novel
algorithm for solving constraints over a simple variant of nominal abstract
syntax which we call non-permutative. This constraint problem has similar
complexity to equivariant unification but without many of the additional
complications of the equivariant unification term language. We prove our
algorithm correct, paying particular attention to issues of termination, and
present an explicit translation of name-name equivariant unification problems
into non-permutative constraints
Intercomparison Exercise for Heavy Metals in PM10
The Joint Research Centre (JRC) has carried out an Intercomparison Exercise (IE) for the determination of heavy metals in particulate matter (PM10). The IE focussed on Lead (Pb), Arsenic (As), Nickel (Ni) and Cadmium (Cd), the heavy metals regulated by the 1st and 4th Daughter Directives for Air Pollution. Copper (Cu), Chromium (Cr) and Zinc (Zn), the elements included in the EMEP programme together with Aluminium (Al), Cobalt (Co), Iron (Fe), Manganese (Mn) and Vanadium (V) were also tested. Fourteen Laboratories, generally members of the Network of Air Quality Reference Laboratories (AQUILA), participated in the IE. The participants mainly used microwave digestion with nitric acid and hydrogen peroxide and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) or Graphite Furnace Atomic Absorption Spectrometry (GF-AAS) for analysis as recommended in the reference method (EN 14902). However, a few participants used other methods: Energy Dispersive X-ray Fluorescence (EDXRF), Atomic Emission Spectrometry (ICP-AES) and Voltammetry for analysis and vaporisation on hot plate before microwave digestion, Soxhlet extraction, high pressure or cold Hydrogen Fluoride methods for digestion.
Each participant received 5 samples to be analysed: a liquid sample prepared by dilution of a Certified Reference Material (CRM), a solution of a dust CRM sample digested by the JRC13F, a sub-sample of a dust CRM that each participating laboratory had to digest and analyse, a solution prepared by JRC after digestion of an exposed filter and a pair of filters (one blank filter and one exposed filter) to be digested and analysed by each participant.
For 89 % of all types of samples, the DQOs of the 1st and 4th European Directives (uncertainty of 25 % for Pb and 40 % for As, Cd and Ni) were met. All together, this is a very good score. The best results were obtained for the liquid CRM, dust CRM digested by JRC, dust CRM and filter digested by JRC with 92, 90, 96 and 93 % of DQOs being met, respectively. It was found that the DQOs were not met if the difference of acidity between test samples and participant calibration standards was high.
Conversely, only 76 % of DQOs were met for the filter to be digested by each participant with (about 85 % for Cd and Ni, 73/64 % for Pb and As, the most difficult element to determine). The worst results were associated with special events: explosion in microwave oven during digestion for two participants, a wrong dilution factor used by one participant and a huge contamination in the blank filter for another participant. Among the two explosions, one of them was probably the effect of a lack of temperature control in the digestion vessel. For the other explosion, the microwave digestion and the digestion program advised by EN 14902 is to be questioned. Moreover, satisfactory results were obtained using Soxhlet extraction, high pressure method and cold Hydrogen Fluoride digestion methods which are not presented in EN 14902. The DQOs of As and Cd could not be met with EDXRF whose limit of detection was too high for these two elements and for Cd using Voltammetry which suffered a strong interference for this element.
Regarding the methods of analysis, apart the points mentioned just before about EDXRF and Voltammetry, good results were observed using ICP-OES for Cd, Ni and Pb. A few discrepancies were also registered for GF-AAS and ICP-MS but they were created by the special events or acidity problem mentioned before. This shows that even though GF-AAS and ICP-MS are found suitable, the implementation by each participant may be responsible for important mistakes.JRC.H.4-Transport and air qualit
Structure of the two-component S-layer of the archaeon Sulfolobus acidocaldarius
This is the author accepted manuscript. The final version is available from eLife Sciences Publications via the DOI in this recordData availability:
The atomic coordinates of SlaA were deposited in the Protein Data Bank (https://www.rcsb.org/) with accession numbers PDB-7ZCX, PDDB-8AN3, and PDB-8AN3 for pH 4, 7 and 10, respectively. The electron density maps were deposited in the EM DataResource (https://www.emdataresource.org/) with accession numbers EMD-14635, EMD-15531 and EMD-15531 for pH 4, 7 and 10, respectively. Sub-tomogram averaging map of the S-layer has been deposited in the EMDB (EMD-18127) and models of the hexameric and trimeric pores in the Protein Databank under accession codes PDB-8QP0 and PDB-8QOX, respectivelyOther structural data used in this study are: H. volcanii csg (PDB ID: 7PTR, http://dx.doi.org/10.2210/pdb7ptr/pdb), and C. crescentus RsaA ((N-terminus PDB ID: 6T72, http://dx.doi.org/10.2210/pdb6t72/pdb, C-terminus PDB ID: 5N8P, http://dx.doi.org/10.2210/pdb5n8p/pdb).Surface layers (S-layers) are resilient two-dimensional protein lattices that encapsulate many bacteria and most archaea. In archaea, S-layers usually form the only structural component of the cell wall and thus act as the final frontier between the cell and its environment. Therefore, S-layers are crucial for supporting microbial life. Notwithstanding their importance, little is known about archaeal S-layers at the atomic level. Here, we combined single particle cryo electron microscopy (cryoEM), cryo electron tomography (cryoET) and Alphafold2 predictions to generate an atomic model of the two-component S-layer of Sulfolobus acidocaldarius. The outer component of this S-layer (SlaA) is a flexible, highly glycosylated, and stable protein. Together with the inner and membrane-bound component (SlaB), they assemble into a porous and interwoven lattice. We hypothesise that jackknife-like conformational changes, changes play important roles in S-layer assembly.European Research CouncilWellcome TrustWellcome TrustAgence Nationale de la RechercheAgence Nationale de la RechercheLeverhulme TrustBiotechnology and Biological Sciences Research Council (BBSRC
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