Reliability and validity of the Korean-language version of the Communication Function Classification System in children with cerebral palsy.

PURPOSE: The Communication Function Classification System (CFCS) and Viking Speech Scale (VSS) are useful systems for describing the broad communication function and speech intelligibility, respectively, of children with cerebral palsy (CP). The aims of this study were to determine the reliability and validity of the Korean version of the CFCS and also to investigate the association between the CFCS and the VSS and other functional classifications for children with CP. MATERIALS AND METHODS: Participants were 50 children with CP (33 males, 17 females; mean age 7.2 years, range 4-16 years) recruited from a rehabilitation hospital. We analysed the interrater and intrarater reliabilities of the Korean version of the CFCS and VSS between parents, a physiatrist, and a speech-language pathologist (SLP). The social function domain of the Paediatric Evaluation of Disability Inventory was assessed to examine the concurrent validity of the CFCS and VSS. RESULTS: The intrarater reliabilities of the CFCS and VSS were excellent in a physiatrist (ƙ = 0.92, ƙ = 0.94, respectively) and an SLP (ƙ = 0.98, ƙ = 0.98) and very good in parents (ƙ = 0.87, ƙ = 0.89). The interrater reliability of the CFCS and VSS was very good between the physiatrist and SLP (ƙ = 0.87, ƙ = 0.89) and good between parents and the SLP (ƙ = 0.63, ƙ = 0.78) and between parents and the physiatrist (ƙ = 0.61, ƙ = 0.76). The CFCS and VSS were strongly related with the social function domain of Paediatric Evaluation of Disability Inventory. In addition, we found very strong associations between the VSS and CFCS. CONCLUSIONS: The Korean version of the CFCS is a valid and reliable tool to classify communication ability and is strongly associated with the VSS, a reliable tool to classify speech intelligibility.

Erratum: Collective modes in multi-Weyl semimetals.

This corrects the article DOI: 10.1038/srep34023.

Collective modes in multi-Weyl semimetals.

We investigate collective modes in three dimensional (3D) gapless multi-Weyl semimetals with anisotropic energy band dispersions (i.e., with a positive integer J). For comparison, we also consider the gapless semimetals with the isotropic band dispersions (i.e. E ~ kJ). We calculate analytically long-wavelength plasma frequencies incorporating interband transitions and chiral properties of carriers. For both the isotropic and anisotropic cases, we find that interband transitions and chirality lead to the depolarization shift of plasma frequencies. For the isotropic parabolic band dispersion the long-wavelength plasmons do not decay via Landau damping, while for the higher-order band dispersions the long-wavelength plasmons experience damping below a critical density. For systems with the anisotropic dispersion the density dependence of the long-wavelength plasma frequency along the direction of non-linear dispersion behaves like that of the isotropic linear band model, while along the direction of linear dispersion it behaves like that of the isotropic non-linear model. Plasmons along both directions remain undamped over a broad range of densities due to the chirality induced depolarization shift. Our results provide a comprehensive picture of how band dispersion and chirality affect plasmon behaviors in 3D gapless chiral systems with the arbitrary band dispersion.

Screening and transport in 2D semiconductor systems at low temperatures.

Low temperature carrier transport properties in 2D semiconductor systems can be theoretically well-understood within RPA-Boltzmann theory as being limited by scattering from screened Coulomb disorder arising from random quenched charged impurities in the environment. In this work, we derive a number of analytical formula, supported by realistic numerical calculations, for the relevant density, mobility, and temperature range where 2D transport should manifest strong intrinsic (i.e., arising purely from electronic effects) metallic temperature dependence in different semiconductor materials arising entirely from the 2D screening properties, thus providing an explanation for why the strong temperature dependence of the 2D resistivity can only be observed in high-quality and low-disorder 2D samples and also why some high-quality 2D materials manifest much weaker metallicity than other materials. We also discuss effects of interaction and disorder on the 2D screening properties in this context as well as compare 2D and 3D screening functions to comment why such a strong intrinsic temperature dependence arising from screening cannot occur in 3D metallic carrier transport. Experimentally verifiable predictions are made about the quantitative magnitude of the maximum possible low-temperature metallicity in 2D systems and the scaling behavior of the temperature scale controlling the quantum to classical crossover.

Strongly Metallic Electron and Hole 2D Transport in an Ambipolar Si-Vacuum Field Effect Transistor.

We report experiment and theory on an ambipolar gate-controlled Si(111)-vacuum field effect transistor where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility (∼18 m2/V s) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using random phase approximation screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.

Thermoelectric detection of chiral heat transport in graphene in the quantum Hall regime.

We report measurements of heat transport along the edge conducting channels in monolayer graphene in the integer quantum Hall regime. Hot charge carriers are injected to the edge channels, and the thermoelectric voltage is measured at a distance along the edge from the heat injection point. We confirm that heat transport in graphene in the quantum Hall regime is chiral and the thermoelectric signal is correlated with the charge conductance of ballistic transport, following the Mott relation. The thermoelectric signal decays with distance from the heater, indicating that carriers are partially thermalized during edge transmission.

Theory of 2D transport in graphene for correlated disorder.

We theoretically revisit graphene transport properties as a function of carrier density, taking into account possible correlations in the spatial distribution of the Coulomb impurity disorder in the environment. We find that the charged impurity correlations give rise to a density-dependent graphene conductivity, which agrees well qualitatively with the existing experimental data. We also find, quite unexpectedly, that the conductivity could increase with increasing impurity density if there is sufficient interimpurity correlation present in the system. In particular, the linearity (sublinearity) of graphene conductivity at lower (higher) gate voltage is naturally explained as arising solely from impurity correlation effects in the Coulomb disorder.

Induction of apoptosis by the ginsenoside Rh2 by internalization of lipid rafts and caveolae and inactivation of Akt.

BACKGROUND AND PURPOSE: Lipid rafts and caveolae are membrane microdomains with important roles in cell survival signalling involving the Akt pathway. Cholesterol is important for the structure and function of these microdomains. The ginsenoside Rh2 exhibits anti-tumour activity. Because Rh2 is structurally similar to cholesterol, we investigated the possibility that Rh2 exerted its anti-tumour effect by modulating rafts and caveolae. EXPERIMENTAL APPROACH: A431 cells (human epidermoid carcinoma cell line) were treated with Rh2 and the effects on cell apoptosis, raft localization and Akt activation measured. We also examined the effects of over-expression of Akt and active-Akt on Rh2-induced cell death. KEY RESULTS: Rh2 induced apoptosis concentration- and time-dependently. Rh2 reduced the levels of rafts and caveolae in the plasma membrane and increased their internalization. Furthermore, Akt activity was decreased and consequently, Akt-dependent phosphorylation of Bad, a pro-survival protein, was decreased whereas the pro-apoptotic proteins, Bim and Bax, were increased upon Rh2 treatment. Unlike microdomain internalization induce by cholesterol depletion, Rh2-mediated internalization of rafts and caveolae was not reversed by cholesterol addition. Also, cholesterol addition did not restore Akt activation or rescue cells from Rh2-induced cell death. Rh2-induced cell death was attenuated in MDA-MB-231 cells over-expressing either wild-type or dominant-active Akt. CONCLUSIONS AND IMPLICATIONS: Rh2 induced internalization of rafts and caveolae, leading to Akt inactivation, and ultimately apoptosis. Because elevated levels of membrane rafts and caveolae, and Akt activation have been correlated with cancer development, internalization of these microdomains by Rh2 could potentially be used as an anti-cancer therapy.

The prevalence, characteristics and correlates of falls in Korean community-dwelling older adults.

BACKGROUND: The risk factors for falls that have been reported in Caucasian older adults may not be the same for Korean older adults. OBJECTIVE: To examine the prevalence, characteristics and correlates of falls among community-dwelling older adults in Korea. METHODS: A stratified random sampling method was conducted to recruit participants, and 335 were eligible to participate from September 2006 to March 2007. Socio-demographic data, history of disease and medications, activities of daily living (ADL), cognitive status, health behaviour and fall incidents were collected. Descriptive statistics were used to describe the sample. The prevalence of falls was obtained. Univariate analyses for risk factors of falls using chi-square and t-test statistics, and multivariate logistic regression analyses for correlates of falls were performed. RESULTS: Of the 335 older adults, 48 (15%) elderly had experienced falls. There was a significant difference between older adults who fell and those who did not fall with regard to ADL and exercise behaviour. Non-fallers had higher ADL scores and showed higher levels of adherence to exercise than fallers. The independent risk factor for falls was ADL. CONCLUSIONS/IMPLICATIONS: In this study, an individual's functional status and exercise engagement were significant factors that differentiated fallers and non-fallers. Therefore, an effective fall prevention programme should be focused on encouraging older adults to participate in regular exercise.

Collective modes of the massless dirac plasma.

We develop a theory for the long-wavelength plasma oscillation of a collection of charged massless Dirac particles in a solid, as occurring, for example, in doped graphene layers, interacting via the long-range Coulomb interaction. We find that the long-wavelength plasmon frequency in such a doped massless Dirac plasma is explicitly nonclassical in all dimensions with the plasma frequency being proportional to 1/sqrt[variant Planck's over 2pi]. We also show that the long-wavelength plasma frequency of the D-dimensional superlattice made from such a plasma does not agree with the corresponding D + 1-dimensional bulk plasmon frequency. We compare and contrast such Dirac plasmons with the well-studied regular palsmons in metals and doped semiconductors which manifest the usual classical long-wavelength plasma oscillation.

Screening, Kohn anomaly, Friedel oscillation, and RKKY interaction in bilayer graphene.

We calculate the screening function in bilayer graphene (BLG) in both the intrinsic (undoped) and the extrinsic (doped) regimes within the random phase approximation, comparing our results with the corresponding single layer graphene and the regular two-dimensional electron gas. We find that the Kohn anomaly is strongly enhanced in BLG. We also discuss the Friedel oscillation and the RKKY interaction, which are associated with the nonanalytic behavior of the screening function at q=2k(F). We find that the Kohn anomaly, the Friedel oscillation, and the RKKY interaction are all qualitatively different in the BLG compared with the single layer graphene and the two-dimensional electron gas.

A self-consistent theory for graphene transport.

We demonstrate theoretically that most of the observed transport properties of graphene sheets at zero magnetic field can be explained by scattering from charged impurities. We find that, contrary to common perception, these properties are not universal but depend on the concentration of charged impurities n(imp). For dirty samples (250 x 10(10) cm(-2) < n(imp) < 400 x 10(10) cm(-2)), the value of the minimum conductivity at low carrier density is indeed 4e(2)/h in agreement with early experiments, with weak dependence on impurity concentration. For cleaner samples, we predict that the minimum conductivity depends strongly on n(imp), increasing to 8e(2)/h for n(imp) approximately 20 x 10(10) cm(-2). A clear strategy to improve graphene mobility is to eliminate charged impurities or use a substrate with a larger dielectric constant.

Carrier transport in two-dimensional graphene layers.

Carrier transport in gated 2D graphene monolayers is considered in the presence of scattering by random charged impurity centers with density n(i). Excellent quantitative agreement is obtained (for carrier density n>10(12) cm(-2)) with existing experimental data. The conductivity scales linearly with n/n(i) in the theory. We explain the experimentally observed asymmetry between electron and hole conductivities, and the high-density saturation of conductivity for the highest mobility samples. We argue that the experimentally observed saturation of conductivity at low density arises from the charged impurity induced inhomogeneity in the graphene carrier density which becomes severe for n less, similarn(i) approximately 10(12) cm(-2).

Density dependent exchange contribution to partial differential mu/ partial differential n and compressibility in graphene.

We calculate partial differentialmu/ partial differentialn (where mu=chemical potential and n=electron density), which is associated with the compressibility, in graphene as a function of n, within the Hartree-Fock approximation. The exchange-driven Dirac-point logarithmic singularity in the quasiparticle velocity of intrinsic graphene disappears in the extrinsic case. The calculated renormalized partial differentialmu/ partial differentialn in extrinsic graphene on SiO2 has the same n;{-(1/2)} density dependence but is 20% larger than the inverse bare density of states, a relatively weak effect compared to the corresponding parabolic-band case. We predict that the renormalization effect can be enhanced to about 50% by changing the graphene substrate.

Transport and percolation in a low-density high-mobility two-dimensional hole system.

We present a study of the temperature and density dependence of the resistivity of an extremely high quality two-dimensional hole system grown on the (100) surface of GaAs. For high densities in the metallic regime (p > or approximately4x10;{9} cm;{-2}), the nonmonotonic temperature dependence ( approximately 50-300 mK) of the resistivity is consistent with temperature dependent screening of residual impurities. At a fixed temperature of T=50 mK, the conductivity versus density data indicate an inhomogeneity driven percolation-type transition to an insulating state at a critical density of 3.8x10;{9} cm;{-2}.

Measurement of scattering rate and minimum conductivity in graphene.

The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of 1-20x10(3) cm2/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from 2-15x10(11) cm(-2). In the low carrier density limit, the conductivity exhibits values in the range of 2-12e2/h, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers.

Mixed infections with Opisthorchis viverrini and intestinal flukes in residents of Vientiane Municipality and Saravane Province in Laos.

Faecal examinations for helminth eggs were performed on 1869 people from two riverside localities, Vientiane Municipality and Saravane Province, along the Mekong River, Laos. To obtain adult flukes, 42 people positive for small trematode eggs (Opisthorchis viverrini, heterophyid, or lecithodendriid eggs) were treated with a 20-30 mg kg(-1) single dose of praziquantel and purged. Diarrhoeic stools were then collected from 36 people (18 in each area) and searched for helminth parasites using stereomicroscopes. Faecal examinations revealed positive rates for small trematode eggs of 53.3% and 70.8% (average 65.2%) in Vientiane and Saravane Province, respectively. Infections with O. viverrini and six species of intestinal flukes were found, namely, Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus caninus, Prosthodendrium molenkampi, and Phaneropsolus bonnei. The total number of flukes collected and the proportion of fluke species recovered were markedly different in the two localities; in Vientiane, 1041 O. viverrini (57.8 per person) and 615 others (34.2 per person), whereas in Saravane, 395 O. viverrini (21.9 per person) and 155207 others (8622.6 per person). Five people from Saravane harboured no O. viverrini but numerous heterophyid and/or lecithodendriid flukes. The results indicate that O. viverrini and several species of heterophyid and lecithodendriid flukes are endemic in these two riverside localities, and suggest that the intensity of infection and the relative proportion of fluke species vary by locality along the Mekong River basin.

Temperature dependent weak field Hall resistance in two-dimensional carrier systems.

Using the Drude-Boltzmann semiclassical transport theory, we calculate the weak-field Hall resistance of a two-dimensional system at low densities and temperatures, assuming carrier scattering by screened random charged impurity centers. The temperature-dependent 2D Hall coefficient shows striking nonmonotonicity in strongly screened systems, and, in particular, we qualitatively explain the recent puzzling experimental observation of a decreasing Hall resistance with increasing temperature in a dilute 2D hole system. We predict that the impurity scattering limited Hall coefficient will eventually increase with temperature at higher temperatures.

Quasi-two-dimensional diluted magnetic semiconductor systems.

We develop a theory for two-dimensional diluted magnetic semiconductor systems (e.g., Ga(1-x)Mn(x)As layers) where the itinerant carriers mediating the ferromagnetic interaction between the impurity local moments, as well as the local moments themselves, are confined in a two-dimensional layer. The theory includes exact spatial disorder effects associated with the random local moment positions within a disordered RKKY lattice field theory description. We predict the ferromagnetic transition temperature (T(c)) as well as the nature of the spontaneous magnetization. The theory includes disorder and finite carrier mean-free path effects as well as the important correction arising from the finite temperature RKKY interaction, finding a strong density dependence of T(c) in contrast to the simple virtual crystal approximation.

Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system.

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high-mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this 2D electron system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of approximately 1.4 approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.