461 research outputs found
Local structure of Liquid-Vapour Interfaces
The structure of a simple liquid may be characterised in terms of ground
state clusters of small numbers of atoms of that same liquid. Here we use this
sensitive structural probe to consider the effect of a liquid-vapour interface
upon the liquid structure. At higher temperatures (above around half the
critical temperature) we find that the predominant effect of the interface is
to reduce the local density, which significantly suppresses the local cluster
populations. At lower temperatures, however, pronounced interfacial layering is
found. This appears to be connected with significant orientational ordering of
clusters based on 3- and 5-membered rings, with the rings aligning
perpendicular and parallel to the interface respectively. At all temperatures,
we find that the population of five-fold symmetric structures is suppressed,
rather than enhanced, close to the interface.Comment: 10 pages, 8 figures, accepted for publication by Molecular Physic
Ultrafast electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3 mu m
The authors report a direct measurement of the absorption dynamics in an InAs p-i-n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28 mu m. The absorption change recovers with characteristic times ranging from 62 ps (0 V) to similar to 700 fs (-10 V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism. (c) 2006 American Institute of Physics.</p
The effect of attractions on the local structure of liquids and colloidal fluids
We revisit the role of attractions in liquids and apply these concepts to
colloidal suspensions. Two means are used to investigate the structure; the
pair correlation function and a recently developed topological method. The
latter identifies structures topologically equivalent to ground state clusters
formed by isolated groups of 5 < m < 13 particles, which are specific to the
system under consideration. Our topological methodology shows that, in the case
of Lennard-Jones, the addition of attractions increases the system's ability to
form larger (m>8) clusters, although pair-correlation functions are almost
identical. Conversely, in the case of short-ranged attractions, pair
correlation functions show a significant response to adding attraction, while
the liquid structure exhibits a strong decrease in clustering upon adding
attractions. Finally, a compressed, weakly interacting system shows a similar
pair structure and topology.Comment: 22 page
ERPs reveal the temporal dynamics of auditory word recognition in specific language impairment.
We used event-related potentials (ERPs) to compare auditory word recognition in children with specific language impairment (SLI group; N=14) to a group of typically developing children (TD group; N=14). Subjects were presented with pictures of items and heard auditory words that either matched or mismatched the pictures. Mismatches overlapped expected words in word-onset (cohort mismatches; see: DOLL, hear: dog), rhyme (CONE -bone), or were unrelated (SHELL -mug). In match trials, the SLI group showed a different pattern of N100 responses to auditory stimuli compared to the TD group, indicative of early auditory processing differences in SLI. However, the phonological mapping negativity (PMN) response to mismatching items was comparable across groups, suggesting that just like TD children, children with SLI are capable of establishing phonological expectations and detecting violations of these expectations in an online fashion. Perhaps most importantly, we observed a lack of attenuation of the N400 for rhyming words in the SLI group, which suggests that either these children were not as sensitive to rhyme similarity as their typically developing peers, or did not suppress lexical alternatives to the same extent. These findings help shed light on the underlying deficits responsible for SLI
Photoelectron spectroscopy of manganese-based Heusler alloys
Ultraviolet-photoemission spectroscopy has been employed to investigate the valence-band electronic structures of the magnetic alloys Co2MnSn, Cu2MnAl, and Pd2MnSn.The valence band of Co2MnSn extends to approximately 5 eV below the Fermi level with a high density of states immediately below the Fermi edge. Cu2MnAl and Pd2MnSn have valence-band widths of 6 and 7 eV, respectively, with the highest density of states lying some 3 eV below the Fermi level in each case. Photoemission measurements in the region of the Mn 3p threshold indicate that Mn 3d character extends across the full width of the valence band for all three alloys. For Pd2MnSn, additional photoemission measurements in the region of the Pd 4d Cooper minimum confirm this conclusion. Modulations in photocurrent resulting from Mn 3p-to-3d resonances across the valence band of Co2MnSn are most intense towards the bottom of the band. This is discussed in terms of possible variations in initial-state hybridization. The experimental photoemission spectra are compared with calculated spectra derived from theoretical band structures. Although there are some differences in shape, the bandwidths of the calculated spectra agree very well with the experimental results
Travelling and sticky affects: : Exploring teens and sexualized cyberbullying through a Butlerian-Deleuzian- Guattarian lens
In this paper we combine the thinking of Deleuze and Guattari (1984, 1987) with Judith Butler’s (1990, 1993, 2004, 2009) work to follow the rhizomatic becomings of young people’s affective relations in a range of on- and off-line school spaces. In particular we explore how events that may be designated as sexual cyberbullying are constituted and how they are mediated by technology (such as texting or in/through social networking sites). Drawing on findings from two different studies looking at teens’ uses of and experiences with social networking sites, Arto in Denmark, and Bebo in the UK, we use this approach to think about how affects flow, are distributed, and become fixed in assemblages. We map how affects are manoeuvred and potentially disrupted by young people, suggesting that in the incidences discussed affects travel as well as stick in points of fixation. We argue that we need to grasp both affective flow and fixity in order to gain knowledge of how subjectification of the gendered/classed/racialised/sexualised body emerges. A Butlerian-Deleuzian-Guattarian frame helps us to map some of these affective complexities that shape sexualized cyberbully events; and to recognize technologically mediated lines of flight when subjectifications are at least temporarily disrupted and new terms of recognition and intelligibility staked out. Keywords
Assessment of the potential in vivo ecotoxicity of Double-Walled Carbon Nanotubes (DWNTs) in water, using the amphibian Ambystoma mexicanum
Because of their specific properties (mechanical, electrical, etc), carbon nanotubes (CNTs) are being assessed for inclusion in many manufactured products. Due to their massive production and number of potential applications, the impact of CNTs on the environment must be taken into consideration. The present investigation evaluates the ecotoxic potential of CNTs in the amphibian larvae (Ambystoma mexicanum). Acute toxicity and genotoxicity were analysed after 12 days of exposure in laboratory conditions. The genotoxic effects were analysed by scoring the micronucleated erythrocytes in the
circulating blood of the larvae according to the French standard micronucleus assay. The results obtained in the present study demonstrated that CNTs are neither acutely toxic nor genotoxic to larvae whatever the CNTs concentration in the water, although black masses of CNTs were observed inside the gut. In the increasing economical context of CNTs, complementary studies must be undertaken, especially including mechanistic and environmental investigations
Geometric frustration in small colloidal clusters
We study the structure of clusters in a model colloidal system with competing
interactions using Brownian dynamics simulations. A short-ranged attraction
drives clustering, while a weak, long-ranged repulsion is used to model
electrostatic charging in experimental systems. The former is treated with a
short-ranged Morse attractive interaction, the latter with a repulsive Yukawa
interaction. We consider the yield of clusters of specific structure as a
function of the strength of the interactions, for clusters with m=3,4,5,6,7,10
and 13 colloids. At sufficient strengths of the attractive interaction (around
10 kT), the average bond lifetime approaches the simulation timescale and the
system becomes nonergodic. For small clusters m<=5 where geometric frustration
is not relevant, despite nonergodicity, for sufficient strengths of the
attractive interaction the yield of clusters which maximise the number of bonds
approaches 100%. However for and higher, in the nonergodic regime we find
a lower yield of these structures where we argue geometric frustration plays a
significant role. is a special case, where two structures, of octahedral
and C2v symmetry compete, with the latter being favoured by entropic
contributions in the ergodic regime and by kinetic trapping in the nonergodic
regime. We believe that our results should be valid as far as the one-component
description of the interaction potential is valid. A system with competing
electrostatic repulsions and van der Waals attractions may be such an example.
However, in some cases, the one-component description of the interaction
potential may not be appropriate.Comment: 21 pages, accepted for publication by J. Phys. Condens. Matte
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