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Assessing time knowledge in children aged 10 to 11 years
The acquisition of time knowledge involves learning how to read clocks, estimate time, read dates and learn about temporal sequences. Evidence suggests that many of these competencies are acquired by 10 years of age although not all children may follow this developmental path. The main purpose of this study was to collect normative data for a screening tool that assesses time knowledge. These data identify the prevalence and pattern of difficulties with time knowledge among a UK sample of Year 6 pupils (aged 10 to 11 years). The Time Screening Assessment tool (Doran, Dutt & Pembery, 2015), designed to assess time knowledge, was administered individually to a sample of 79 children. Findings revealed a median overall score of 32 out of a maximum score of 36. 25% of children performed at or close to ceiling, however seven children scored more than -1.5 standard deviations below the mean. The value of these findings to practitioners working with children in schools is discussed
The boundary between the middle Eocene Brussel sand and the Lede sand formations in the Zaventem-Nederokkerzeel area (northeast of Brussels, Belgium)
In the Zaventem airport railway cutting, to the north-east of Brussels, the upper part of the Brussel Sand Formation consists of two major units, both attributable to calcareous nannofossil zone NP14a. The lower predominantly sandy unit ZB1 (including subunits A, B and C, belonging to NP14al) is built up of sparsely glauconitic, relatively coarse tidal current deposits with nodule levels cemented by carbonate and silica, of which one shows slumping structures and is interpreted as a seismite. The uppermost unit ZB2 (also labelled D, belonging to NP14a2), composed of alternating thin fine sandstone bands and silty marls, represents the fill of a large channel. In the Berg-Nederokkerzeel sandpit the carbonate-rich Brussel Sand Formation is finer grained and more homogeneous. Here, the basal sand (unit A) is attributable to NP14a3 and consequently, younger than the section exposed at Zaventem. It is incised at its the top by a rather narrow erosive gully, filled in with well-sorted fine sand rich in washed-in molluscs (unit B), some of which seem to point to a brackish influence. The extreme top is made up of half a meter of sand with abundant Callianassa burrows and echinid fragments (unit C). From the nannofossil data it appears that, east of Brussels, at least two generations of tidal channel systems seem to have occurred within the Brussel Sand Formation, followed by a partial emersion at the end of the filling of the uppermost channel (Nederokkerzeel B). This was succeeded by a relative sea-level rise, as shown by unit C and the remains of a completely eroded fully marine deposit, reworked in the base of the overlying Lede Sand Formation. The lowest relative sea level, with at least partial emergence of the Brussels area, occurred during middle to late Biochron NP14b. In both outcrops the Lede Sand Formation displays its characteristic pale grey relatively fine-grained homogeneous nature with a stone layer near its base. It can be concluded that, at the beginning of the "Lede transgression", an erosion of older deposits, containing already lifhified stone layers, occurred. This was, apparently, at least locally, caused by storms, which could redistribute, imbricate and turn over the stones, explaining their bio-perforation on both sides. Afterwards the stones have been above water for a relatively long time, enough to allow the dissolution of the perforating organisms and consequently an important oxidation of their surfaces. These stones have subsequently been colonised by a new marine fauna. Part of the shark teeth and calcareous nannofossil assemblages found in the coarse base of the Lede Sand is definitely older than the taxa normally found in the Lede Sand Formation. These fossils are the remains of a sediment package, believed to represent the formerly "Laekenian" stage
Measuring the mixing efficiency in a simple model of stirring:some analytical results and a quantitative study via Frequency Map Analysis
We prove the existence of invariant curves for a --periodic Hamiltonian
system which models a fluid stirring in a cylindrical tank, when is small
and the assigned stirring protocol is piecewise constant. Furthermore, using
the Numerical Analysis of the Fundamental Frequency of Laskar, we investigate
numerically the break down of invariant curves as increases and we give a
quantitative estimate of the efficiency of the mixing.Comment: 10 figure
Impact of ultrafast electronic damage in single particle x-ray imaging experiments
In single particle coherent x-ray diffraction imaging experiments, performed
at x-ray free-electron lasers (XFELs), samples are exposed to intense x-ray
pulses to obtain single-shot diffraction patterns. The high intensity induces
electronic dynamics on the femtosecond time scale in the system, which can
reduce the contrast of the obtained diffraction patterns and adds an isotropic
background. We quantify the degradation of the diffraction pattern from
ultrafast electronic damage by performing simulations on a biological sample
exposed to x-ray pulses with different parameters. We find that the contrast is
substantially reduced and the background is considerably strong only if almost
all electrons are removed from their parent atoms. This happens at fluences of
at least one order of magnitude larger than provided at currently available
XFEL sources.Comment: 15 pages, 3 figures submitted to PR
Observation of Pure Spin Transport in a Diamond Spin Wire
Spin transport electronics - spintronics - focuses on utilizing electron spin
as a state variable for quantum and classical information processing and
storage. Some insulating materials, such as diamond, offer defect centers whose
associated spins are well-isolated from their environment giving them long
coherence times; however, spin interactions are important for transport,
entanglement, and read-out. Here, we report direct measurement of pure spin
transport - free of any charge motion - within a nanoscale quasi 1D 'spin
wire', and find a spin diffusion length ~ 700 nm. We exploit the statistical
fluctuations of a small number of spins ( < 100 net spins) which are
in thermal equilibrium and have no imposed polarization gradient. The spin
transport proceeds by means of magnetic dipole interactions that induce
flip-flop transitions, a mechanism that can enable highly efficient, even
reversible, pure spin currents. To further study the dynamics within the spin
wire, we implement a magnetic resonance protocol that improves spatial
resolution and provides nanoscale spectroscopic information which confirms the
observed spin transport. This spectroscopic tool opens a potential route for
spatially encoding spin information in long-lived nuclear spin states. Our
measurements probe intrinsic spin dynamics at the nanometre scale, providing
detailed insight needed for practical devices which seek to control spin.Comment: 7 pages, 2 figures, under consideration at Nature Nanotechnolog
Surface scattering velocities in III-nitride quantum well laser structures via the emission of hybrid phonons
We have theoretically and numerically studied nitride-based quantum well (QW)
laser structures. More specifically, we have used a QW made with III-nitride
where the width of the barrier region is large relative to the electron mean
free path, and we have calculated the electron surface capture velocities by
considering an electron flux which is captured into the well region. The
process is assisted by the emission of the longitudinal optical phonons as
predicted by the hybrid (HB) model. The results of surface capture velocities
via the emission of HB phonons are compared to the emission of the dielectric
continuum phonons (Zakhleniuk et al 1999 Phys. Status Solidi a 176 79). Our
investigation shows that the two different phonon models predict almost the
same results for the non-retarded limit. Furthermore, the surface capture
velocities strongly depend on the size of the structure and the heterostructure
materials. Lastly, a comparison to the recent experimental values shows that
our model could accurately describe the experimentally measured parameters of
the quantum capture processes
2-Thiabicyclo[3.2.0]hepta-3,6-Dienes. 1. Aluminum Chloride Catalyzed Thermal [2 + 2] Cycloaddition of 2-Butynedinitrile with Alkyl-Substituted Thiophenes
Tetra- and Trialkylthiophenes 4–6 React with 2-Butynedinitrile in the Presence of 1 Equiv of Aluminum Chloride in Dichloromethane at 0 °C Via [2 + 2] Cycloaddition to 2-3.2.0] hepta-3,6-Diene-6,7-Dicarbonitriles 7–10 as the Major Products. Reaction of 4 and 5 Also Gave Small Amounts (4% and 6%) of 1,2-Benzenedicarbonitriles 11 and 12 Which Result from [4 + 2] Cycloaddition and Subsequent Extrusion of Sulfur. 4,5,6,7-Tetrahydro-1,3-Dimethylbenzo[C]thiophene (6) Reacts with 2-Butynedinitrile under the Same Conditions to Give an Ene Adduct (13) in Addition to the [2 + 2] Cycloadduct 10. 2,5-Dimethylthiophene (3) Gave a 2:1 Reaction Product 14, the Formation of Which Can Be Explained Via Friedel-Crafts Alkylation of 3 by the Initially Formed [2 + 2] Cycloadduct. the 2-3.2.0] hepta-3,6-Dienes 7–10 and the Ene Adduct 13 Show Intramolecular Charge-Transfer Absorptions in the UV Spectra. © 1982, American Chemical Society. All Rights Reserved
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