206 research outputs found
Developing an Orthography for Onya Darat (Western Borneo) Practical and Theoretical Considerations
Onya Darat is a language spoken, with great dialectal variation, in the interiorof western Borneo. It is the southernmost member of Land Dayak, a branchof the Austronesian language family. This article reports on the developmentof a writing system for Onya Darat. In addition to five vowels and 19 simpleconsonants, Onya Darat also exhibits three series of complex oral-nasalsegments: prenasalized oral stops, preoralized nasals, and postoralized nasals.An analysis of the Onya Darat sound system reveals that of these three seriesonly postoralized nasals are distinctive and therefore need to be representedin the writing system. The proposed orthography, developed with the aid ofnative speakers, represents all and only the phonemes of Onya Darat withoutresorting to diacritics or special characters
Structure and Strength of Dislocation Junctions: An Atomic Level Analysis
The quasicontinuum method is used to simulate three-dimensional
Lomer-Cottrell junctions both in the absence and in the presence of an applied
stress. The simulations show that this type of junction is destroyed by an
unzipping mechanism in which the dislocations that form the junction are
gradually pulled apart along the junction segment. The calculated critical
stress needed for breaking the junction is comparable to that predicted by line
tension models. The simulations also demonstrate a strong influence of the
initial dislocation line directions on the breaking mechanism, an effect that
is neglected in the macroscopic treatment of the hardening effect of junctions.Comment: 4 pages, 3 figure
Effective pair potentials for spherical nanoparticles
An effective description for spherical nanoparticles in a fluid of point
particles is presented. The points inside the nanoparticles and the point
particles are assumed to interact via spherically symmetric additive pair
potentials, while the distribution of points inside the nanoparticles is taken
to be spherically symmetric and smooth. The resulting effective pair
interactions between a nanoparticle and a point particle, as well as between
two nanoparticles, are then given by spherically symmetric potentials. If
overlap between particles is allowed, the effective potential generally has
non-analytic points, but for each effective potential the expressions for
different overlapping cases can be written in terms of one analytic auxiliary
potential. Effective potentials for hollow nanoparticles (appropriate e.g. for
buckyballs) are also considered, and shown to be related to those for solid
nanoparticles. Finally, explicit expressions are given for the effective
potentials derived from basic pair potentials of power law and exponential
form, as well as from the commonly used London-Van der Waals, Morse,
Buckingham, and Lennard-Jones potential. The applicability of the latter is
demonstrated by comparison with an atomic description of nanoparticles with an
internal face centered cubic structure.Comment: 27 pages, 12 figures. Unified description of overlapping and
nonoverlapping particles added, as well as a comparison with an idealized
atomic descriptio
Dislocation Emission around Nanoindentations on a (001) fcc Metal Surface Studied by STM and Atomistic Simulations
We present a combined study by Scanning Tunneling Microscopy and atomistic
simulations of the emission of dissociated dislocation loops by nanoindentation
on a (001) fcc surface. The latter consist of two stacking-fault ribbons
bounded by Shockley partials and a stair-rod dislocation. These dissociated
loops, which intersect the surface, are shown to originate from loops of
interstitial character emitted along the directions and are usually
located at hundreds of angstroms away from the indentation point. Simulations
reproduce the nucleation and glide of these dislocation loops.Comment: 10 pages, 4 figure
Coupled surface polaritons and the Casimir force
The Casimir force between metallic plates made of realistic materials is
evaluated for distances in the nanometer range. A spectrum over real
frequencies is introduced and shows narrow peaks due to surface resonances
(plasmon polaritons or phonon polaritons) that are coupled across the vacuum
gap. We demonstrate that the Casimir force originates from the attraction
(repulsion) due to the corresponding symmetric (antisymmetric) eigenmodes,
respectively. This picture is used to derive a simple analytical estimate of
the Casimir force at short distances. We recover the result known for Drude
metals without absorption and compute the correction for weakly absorbing
materials.Comment: revised version submitted to Phys. Rev. A, 06 November 200
Entropy Stable Numerical Schemes for Two-Fluid Plasma Equations
Two-fluid ideal plasma equations are a generalized form of the ideal MHD
equations in which electrons and ions are considered as separate species. The
design of efficient numerical schemes for the these equations is complicated on
account of their non-linear nature and the presence of stiff source terms,
especially for high charge to mass ratios and for low Larmor radii. In this
article, we design entropy stable finite difference schemes for the two-fluid
equations by combining entropy conservative fluxes and suitable numerical
diffusion operators. Furthermore, to overcome the time step restrictions
imposed by the stiff source terms, we devise time-stepping routines based on
implicit-explicit (IMEX)-Runge Kutta (RK) schemes. The special structure of the
two-fluid plasma equations is exploited by us to design IMEX schemes in which
only local (in each cell) linear equations need to be solved at each time step.
Benchmark numerical experiments are presented to illustrate the robustness and
accuracy of these schemes.Comment: Accepted in Journal of Scientific Computin
Melting of polymer blends in single-screw extrusion : an experimental study
Melting is a major step in plasticating single screw extrusion, but most of the existing phenomenological
know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread
industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply,
or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP
blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical
Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed.The authors are grateful to Portuguese Fundacao para a Ciencia e Tecnologia for supporting this work under grant SFRH/BD/19997/2004 and to DSM, the Netherlands, for supplying PA6
The Simple View of Reading Made Complex by Morphological Decoding Fluency in Bilingual Fourth-Grade Readers of English
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordThis study examined the complexity of the Simple View of Reading focusing on morphological
decoding fluency in fourth-grade readers of English in Singapore. The participants were three
groups of students who all learned to become bilingual and biliterate in the English language
(EL) and their respective ethnic language in school but differed in the home language they used.
The first group was ethnic Chinese students who used English as the dominant home language
(Chinese EL1); the other two groups were ethnic Chinese and Malay students whose dominant
home language was not English but Chinese (Chinese EL2) and Malay (Malay EL2),
respectively. The measures included pseudo word decoding (phonemic decoding), timed
decoding of derivational words (morphological decoding fluency), oral vocabulary, and passage
comprehension. Path analysis showed that oral vocabulary significantly predicted reading
comprehension across all three groups; yet a significant effect of morphological decoding
fluency surfaced in the Chinese EL1 and Malay EL2 groups but not the Chinese EL2 group.
Multi-group path analysis and commonality analysis further confirmed that morphological
decoding played a larger role in the in the Chinese EL1 and Malay EL2 groups. These findings
are discussed in light of the joint influence of target language experience and cross-linguistic
influence on second language or bilingual reading development.Office of Education Research, National Institute of Education, Nanyang Technological Universit
Merkel cell carcinoma of skin-current controversies and recommendations
The review covers the current recommendations for Merkel cell carcinoma (MCC), with detailed discussion of many controversies. The 2010 AJCC staging system is more in-line with other skin malignancies although more complicated to use. The changes in staging system over time make comparison of studies difficult. A wide excision with margins of 2.5â3 cm is generally recommended. Even for primary </= 1 cm, there is a significant risk of nodal and distant metastases and hence sentinel node biopsy should be done if possible; otherwise adjuvant radiotherapy to the primary and nodal region should be given. Difficulties of setting up trials owing to the rarity of the disease and the mean age of the patient population result in infrequent reports of adjuvant or concurrent chemotherapy in the literature. The benefit, if any, is not great from published studies so far. However, there may be a subgroup of patients with high-risk features, e.g. node-positive and excellent performance status, for whom adjuvant or concurrent chemotherapy may be considered. Since local recurrence and metastases generally occur within 2 years of the initial diagnosis, patients should be followed more frequently in the first 2 years. However delayed recurrence can still occur in a small proportion of patients and long-term follow-up by a specialist is recommended provided that the general condition of the patient allows it. In summary, physician judgment in individual cases of MCC is advisable, to balance the risk of recurrence versus the complications of treatment
The only African wild tobacco, Nicotiana africana: Alkaloid content and the effect of herbivory
Herbivory in some Nicotiana species is known to induce alkaloid production. This study examined herbivore-induced defenses in the nornicotine-rich African tobacco N. africana, the only Nicotiana species indigenous to Africa. We tested the predictions that: 1) N. africana will have high constitutive levels of leaf, flower and nectar alkaloids; 2) leaf herbivory by the African bollworm Helicoverpa armigera will induce increased alkaloid levels in leaves, flowers and nectar; and 3) increased alkaloid concentrations in herbivore-damaged plants will negatively affect larval growth. We grew N. africana in large pots in a greenhouse and exposed flowering plants to densities of one, three and six fourth-instar larvae of H. armigera, for four days. Leaves, flowers and nectar were analyzed for nicotine, nornicotine and anabasine. The principal leaf alkaloid was nornicotine (mean: 28 ”g/g dry mass) followed by anabasine (4.9 ”g/g) and nicotine (0.6 ”g/g). Nornicotine was found in low quantities in the flowers, but no nicotine or anabasine were recorded. The nectar contained none of the alkaloids measured. Larval growth was reduced when leaves of flowering plants were exposed to six larvae. As predicted by the optimal defense theory, herbivory had a localized effect and caused an increase in nornicotine concentrations in both undamaged top leaves of herbivore damaged plants and herbivore damaged leaves exposed to one and three larvae. The nicotine concentration increased in damaged compared to undamaged middle leaves. The nornicotine concentration was lower in damaged leaves of plants exposed to six compared to three larvae, suggesting that N. africana rather invests in new growth as opposed to protecting older leaves under severe attack. The results indicate that the nornicotine-rich N. africana will be unattractive to herbivores and more so when damaged, but that potential pollinators will be unaffected because the nectar remains alkaloid-free even after herbivory
- âŠ