1,065 research outputs found
Math and Coding Connections in Elementary
In this session, participants learn ways to use coding tools in elementary classrooms to provide engaging and motivating contexts for students to develop and use mathematical and computational reasoning. Integrating technology to support mathematics learning in meaningful ways is often challenging, and discussions in this session will emphasize the synergies among technology, coding, and mathematics for supporting skills with coding tools
Optical absorption spectra in fullerenes C60 and C70: Effects of Coulomb interactions, lattice fluctuations, and anisotropy
Effects of Coulomb interactions and lattice fluctuations in the optical
absorption spectra of C60 and C70 are theoretically investigated by using a
tight binding model with long-range Coulomb interaction and bond disorder.
Anisotropy effects in C70 are also considered. Optical spectra are calculated
by using the Hartree-Fock approximation followed by the configuration
interaction method. The main conclusions are as follows: (1) The broad peaks at
excitation energies, 3.7eV, 4.7eV, and 5.7eV, observed in experiments of C60
molecules in a solution are reasonably described by the present theory. Peak
positions and relative oscillator strengths are in overall agreement with the
experiments. The broadening of peaks by lattice fluctuations is well simulated
by the bond disorder model. (2) The optical gap of C70 is larger when the
electric field of light is parallel to the long axis of the molecule. The shape
of the frequency dispersion also depends on the orientation of the molecule.
These properties are common in the free electron model and the model with
Coulomb interactions. (3) The spectrum of C70 averaged over bond disorder and
random orientations is compared with experiments in a solution. There is an
overall agreement about the spectral shape. Differences in the spectra of C60
and C70 are discussed in connection with the symmetry reduction from a
soccerball to a rugbyball.Comment: PACS numbers: 78.66.Qn, 78.20.Dj, 71.35.+z, 31.20.Tz; LaTeX, 15
pages, 5 figures (Physical Review B); Note: Please request figures to
Authors. They will be sent via snail mai
Persistent Transport Barrier on the West Florida Shelf
Analysis of drifter trajectories in the Gulf of Mexico has revealed the
existence of a region on the southern portion of the West Florida Shelf (WFS)
that is not visited by drifters that are released outside of the region. This
so-called ``forbidden zone'' (FZ) suggests the existence of a persistent
cross-shelf transport barrier on the southern portion of the WFS. In this
letter a year-long record of surface currents produced by a Hybrid-Coordinate
Ocean Model simulation of the WFS is used to identify Lagrangian coherent
structures (LCSs), which reveal the presence of a robust and persistent
cross-shelf transport barrier in approximately the same location as the
boundary of the FZ. The location of the cross-shelf transport barrier undergoes
a seasonal oscillation, being closer to the coast in the summer than in the
winter. A month-long record of surface currents inferred from high-frequency
(HF) radar measurements in a roughly 60 km 80 km region on the WFS off
Tampa Bay is also used to identify LCSs, which reveal the presence of robust
transient transport barriers. While the HF-radar-derived transport barriers
cannot be unambiguously linked to the boundary of the FZ, this analysis does
demonstrate the feasibility of monitoring transport barriers on the WFS using a
HF-radar-based measurement system. The implications of a persistent cross-shelf
transport barrier on the WFS for the development of harmful algal blooms on the
shoreward side of the barrier are considered.Comment: Submitted to Geophysical Research Letter
Reliability of upright posture measurements in primary school children
BACKGROUND: Correct upright posture is considered to be a measure of good musculoskeletal health. Little is known about the usual variability of children's upright standing posture. The aim of this study was to assess differences between repeated measures of upright posture in a group of primary school children. METHODS: Sagittal plane photographs of usual, relaxed upright standing posture of 38 boys and girls aged 5–12 years were taken twice within an hour. Reflective markers were placed over the canthus, tragus, C7 spinous process, greater trochanter and lateral malleolus. Digitising software was used to calculate the x,y plane coordinates, from which five postural angles were calculated (trunk, neck, gaze, head on neck, lower limb). Height, weight, motor control estimates (as measured by the Brace Tests) and presence of recent pain were recorded for each child, and the association between the first test measure of posture angles and these factors was assessed using linear regression and ANOVA models. Multiple ANOVA models were applied to analyse the effect of repeated testing, and significant predictors on the angles. RESULTS: Four of the five postural angles (trunk, neck, head on neck, lower limb) were significantly influenced by age. As age was strongly associated with height (r(2 )= 0.84) and moderately associated with weight and motor control (r(2 )= 0.67, 0.56 respectively), these developmental parameters may well explain the age effect on angles. There was no relationship between age and pain reported on either the testing day, or recently, and there was no gender influence on any angle. There was no significant effect of repeated testing on any angle (ICC>0.93). None of the hypothesized predictors were associated with differences in angles from repeated testing. CONCLUSION: This study outlined the variability of relaxed upright standing posture of children aged 5–12 years, when measured twice in an hour. Age influenced the size of the angles but not the variability. While the subject numbers in this study are small, the findings provide useful information on which further studies in posture and its development in pre-adolescent children can be based
Multiexcitons confined within a sub-excitonic volume: Spectroscopic and dynamical signatures of neutral and charged biexcitons in ultrasmall semiconductor nanocrystals
The use of ultrafast gating techniques allows us to resolve both spectrally
and temporally the emission from short-lived neutral and negatively charged
biexcitons in ultrasmall (sub-10 nm) CdSe nanocrystals (nanocrystal quantum
dots). Because of forced overlap of electronic wave functions and reduced
dielectric screening, these states are characterized by giant interaction
energies of tens (neutral biexcitons) to hundreds (charged biexcitons) of meV.
Both types of biexcitons show extremely short lifetimes (from sub-100
picoseconds to sub-picosecond time scales) that rapidly shorten with decreasing
nanocrystal size. These ultrafast relaxation dynamics are explained in terms of
highly efficient nonradiative Auger recombination.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Correlation property of length sequences based on global structure of complete genome
This paper considers three kinds of length sequences of the complete genome.
Detrended fluctuation analysis, spectral analysis, and the mean distance
spanned within time are used to discuss the correlation property of these
sequences. The values of the exponents from these methods of these three kinds
of length sequences of bacteria indicate that the long-range correlations exist
in most of these sequences. The correlation have a rich variety of behaviours
including the presence of anti-correlations. Further more, using the exponent
, it is found that these correlations are all linear (). It is also found that these sequences exhibit noise in some
interval of frequency (). The length of this interval of frequency depends
on the length of the sequence. The shape of the periodogram in exhibits
some periodicity. The period seems to depend on the length and the complexity
of the length sequence.Comment: RevTex, 9 pages with 5 figures and 3 tables. Phys. Rev. E Jan. 1,2001
(to appear
Waveforms and Sonic Boom Perception and Response (WSPR): Low-Boom Community Response Program Pilot Test Design, Execution, and Analysis
The Waveforms and Sonic boom Perception and Response (WSPR) Program was designed to test and demonstrate the applicability and effectiveness of techniques to gather data relating human subjective response to multiple low-amplitude sonic booms. It was in essence a practice session for future wider scale testing on naive communities, using a purpose built low-boom demonstrator aircraft. The low-boom community response pilot experiment was conducted in California in November 2011. The WSPR team acquired sufficient data to assess and evaluate the effectiveness of the various physical and psychological data gathering techniques and analysis methods
Characteristics of outdoor falls among older people: A qualitative study
Background Falls are a major threat to older people’s health and wellbeing. Approximately half of falls occur in outdoor environments but little is known about the circumstances in which they occur. We conducted a qualitative study to explore older people’s experiences of outdoor falls to develop understanding of how they may be prevented. Methods We conducted nine focus groups across the UK (England, Wales, and Scotland). Our sample was from urban and rural settings and different environmental landscapes. Participants were aged 65+ and had at least one outdoor fall in the past year. We analysed the data using framework and content analyses. Results Forty-four adults aged 65 – 92 took part and reported their experience of 88 outdoor falls. Outdoor falls occurred in a variety of contexts, though reports suggested the following scenarios may have been more frequent: when crossing a road, in a familiar area, when bystanders were around, and with an unreported or unknown attribution. Most frequently, falls resulted in either minor or moderate injury, feeling embarrassed at the time of the fall, and anxiety about falling again. Ten falls resulted in fracture, but no strong pattern emerged in regard to the contexts of these falls. Anxiety about falling again appeared more prevalent among those that fell in urban settings and who made more visits into their neighbourhood in a typical week. Conclusions This exploratory study has highlighted several aspects of the outdoor environment that may represent risk factors for outdoor falls and associated fear of falling. Health professionals are recommended to consider outdoor environments as well as the home setting when working to prevent falls and increase mobility among older people
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