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The relationships between different levels of severity of ambulatory cerebral palsy, defined by the Gross Motor Function Classification System (GMFCS), and several pediatric outcome instruments were examined. Data from the Gross Motor Function Measure (GMFM), Pediatric Orthopaedic Data Collection Instrument (PODCI), temporal–spatial gait parameters, and oxygen cost were collected from six sites. The sample size for each assessment tool ranged from 226 to 1047 participants. There were significant differences among GMFCS levels I, II, and III for many of the outcome tools assessed in this study. Strong correlations were seen between GMFCS level and each of the GMFM sections D and E scores, the PODCI measures of Transfer and Mobility, and Sports and Physical Function, Gait Velocity, and Oxygen Cost. Correlations among tools demonstrated that the GMFM sections D and E scores correlated with the largest number of other tools. Logistic regression showed GMFM section E score to be a significant predictor of GMFCS level. GMFM section E score can be used to predict GMFCS level relatively accurately (76.6%). Study data indicate that the assessed outcome tools can distinguish between children with different GMFCS levels. This study establishes justification for using the GMFCS as a classification system in clinical studies.
The retinal vasculature of postmortem normal human and diabetic
eyes was studied using an
immunohistochemical technique in conjunction with confocal laser scanning
microscopy. The technique,
which stained for von Willebrand factor, allowed both large areas of the
retinal vasculature to be visualised
and abnormalities to be studied in detail without disturbing the tissue
architecture. Only one
microaneurysm, defined as any focal capillary dilation, was observed in
10 normal eyes but numerous
microaneurysms were seen in 4 out of 5 diabetic retinas; counts varied
between 0 and 26 per 0.41 mm2
sample area. Microaneurysms were classified into 3 categories according
to morphology: saccular, fusiform
and focal bulges. Most were saccular, these having no preferred orientation.
The majority of
microaneurysms were associated with just 2 vessels suggesting they were
unlikely to develop at vascular
junctions. The majority were observed to originate from the inner nuclear
layer and were therefore in the
deeper part of the inner retinal capillary plexus. Variation in the staining
of microaneurysms may correlate
with endothelial dysfunction seen clinically as dye leakage during fluorescein
Silicon nitride films deposited from silane-nitrogen and silane-ammonia mixtures by PECVD contain large amounts of hydrogen. We have determined that adding argon to the gas mixture reduces the amount of hydrogen in the resulting films. Differences in film composition are obviously due to changes in the chemistry of the discharge which was characterized by line-of-sight mass spectrometry, optical emission spectroscopy and plasma double probe measurements. Substrate temperature was fixed at 325°C, pressure was 500 mtorr, the RF power was 0.25 watts cm−2, the silane to nitrogen ratio was varied from 0.003 to 0.02, the silane to ammonia ratio was varied from 0.01 to 0.5, and the argon additions were 10% of the total gas flow. Argon additions to the discharge increased the plasma density in both nitrogen and ammonia plasmas. Optical emission from N2 and Si-H species increased upon the addition of 10% argon to the silane-nitrogen discharge, whereas the N-H emission decreased upon addition of argon to the silane-ammonia discharge. Infrared transmission spectra of films deposited with and without argon show no change in peak position or intensity of Si-H and N-H absorption bands in the spectral range studied, despite a large (over 20%) reduction in hydrogen content, as determined by nuclear profiling, upon the addition of argon. These results suggest that a substantial fraction of the hydrogen in the films is not infrared active. We propose that the reduction in hydrogen content is due to bombardment of the growing film by argon ions, which sputter the adsorbed hydrogen molecules.
Oxide compounds have been extensively studied through the years because they exhibit a broad spectrum of electrical, magnetic, and optical properties providing both scientific and technological interest. Most oxides are insulators, but a few of them (e.g., LiTi2O4 or BaPb1−x BixO3 show metallic conductivity and even superconductivity at low temperatures. The discovery of superconductivity at 35 K by Bednorz and Müller in the cuprate La-Ba-Cu-O system prompted the search for other high Tc compounds among this oxide family. Superconductivity above liquid nitrogen was then rapidly achieved with the Y-Ba-Cu-O system (Tc=90 K) and subsequently, with the Bi-Sr-Ca-Bu-O and Tl-Ba-Ca-Cu-O systems, Tc was raised to 110 K and then 125 K.
A common feature of these new high Tc cuprates is that they belong to the large family of materials, termed perovskites, which have been studied over the years because of their ability to absorb or lose oxygen reversibly (i.e., for their nonstoichiometry in oxygen). It had been previously established in the field of superconductivity that Tc is extremely sensitive to compositional stoichiometry.
Superconducting thin films of YBa2Cu3O7 are prepared in-situ by on-axis, sputter deposition from a single, composite target. Our planar magnetron target composition of Y:Ba:Cu = 1.08:1.76:4.5 sputtered onto MgO at T~750°C in a 600mTorr Ar-O2 atmosphere yields reproducible superconducting films having Tc(R = 0)>80K and stoichiometry 1:2:3, that are shiny and of near epitaxial, crystalline quality. In order to ensure clean interfaces, YBa2Cu3O7/normal metal bilayers (to form SNS' Josephson junctions) and YBa2Cu3O7/normal metal/insulating barrier trilayers (to form SNIS' proximity tunnel junctions) are grown completely in-situ. (The S' = Pb counter electrode is evaporated ex-situ.) A supercurrent and Shapiro steps are observed in microwave irradiated SNS' (N = Ag) small area (5x10-5cm2) junctions. In SNIS' tunnel junctions, high-quality Pb tunneling is observed.
A substitution for Cu by a 3d-metal (Fe, Co, Mn) in the superconducting Bi phases (Bi2Sr2Can−1CunOy; n = 1,2 and 3) has led to the discovery of new phases. These 3d-metal substituted phases are non-superconducting and, in contrast to the Cu-based phases, they exhibit a structural modulation that is commensurate. Single crystal x-ray studies were performed on the Bi2Sr3Fe2Oy, Bi2Sr2CoOy and Bi2Sr2MnOy compounds. A result, in common, is that the modulation is caused by the periodic insertion of a row of oxygen atoms in the Bi layers and this results in a corrugated-like slab structure. The Bi-O layers can be described as composed of alternating rocksalt-type and oxygen deficient perovskite-type blocks. For the Fe (n=2) phase the Bi atoms form ribbons (chains) in the ab plane. This is in contrast to the n=1 Co or Mn phases for which a disorder at the oxygen position is observed. Although the extra oxygen in the Bi-O layer could account for the doping mechanism in the high Tc Bi-phases, cation non-stoichiometry may also beimportant.
Since the discovery of superconductivity in certain classes of cuprates, there has been much research activity aimed at understanding the structure, microstructure, electrical and other physical properties of these materials. In this paper, we present a summary of the current status of on-going research on structural and microstructural characterization of the Bi cuprates and cationically substituted derivatives of these superconducting compounds. High resolution structural imaging together with conventional and analytical electron microscopy is used to examine the structure[l]. The overall aim of these studies is to characterize the structural and microstructural evolution and ultimately to determine the effect on the superconducting properties.
If G is a locally compact group such that G/G0 contains a uniform compactly generated nilpotent subgroup, then G has a maximal compact normal subgroup K such that G/G is a Lie group. A topological group G is an N-group if, for each neighbourhood U of the identity and each compact set C ⊂G, there is a neighbourhood V of the identity such that for each g∈G. Several results on N-groups are obtained and it is shown that a related weaker condition is equivalent to local finiteness for certain totally disconnected groups.
The structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xMxO7-y (M = Ni,Zn,Fe and Co) are reported. Values of y, determined by titration, are found to be dependent on the nature and amount of the doping. The range of solubility is greater for the Fe and Co compounds (x = 1) than for those with Ni or Zn (x = 0.3). The undoped material is orthorhombic and remains orthorhombic after substitution for Cu by Ni or Zn, whereas a tetragonal phase is observed when Fe, Co are substituted for Cu. DC resistance and AC susceptibility measurements show that Tc is depressed from 90K (x = 0) to 45K (x = 0.2) for both the Ni and Zn doped compounds and Tc is destroyed in the Fe and Co doped compounds when x reaches 0.4. We suggest that a valence of 2 be assigned to the Ni and Zn and 3 to the Fe and Co ions.
We have synthesized the high Tc superconducting oxide YBa2Cu3O7-y using a solution technique and compare the resultant properties to materials synthesized by solid state reactions. Because the cations are mixed at the microscopic level, we observe that this solution technique allows lower reaction temperatures and shorter reaction times to obtain the superconducting material. They yield materials with particle sizes of about 1 μm and having a narrow size dispersion (as compared to the typically 50 μm particle sizes obtained by solid state reactions). The smaller, uniform particle sizes yield denser compacts upon sintering. Densities of 90% have been achieved and metallic-like behavior improves and is correlated with increasing density. The solution derived materials superconduct at 91 K and have narrow transition temperatures (0.6K width) which we attribute to sample compositional and structural homogeneity. Because we are able to produce stable, viscous gels, we have investigated the preparation of large area thick films on various substrates of technological interest (e.g. alumina, zirconia.strontium titanate).
An almost sure convergence result for the normed population size of a bisexual population model is proved. Properties of the limit random variable are deduced. The derivation of similar results for a general class of such processes is discussed.
The pyrolytic conversion of an organosilsesquioxane (Owens-Illinois resin GR650) to SiO2 is characterized by ir spectroscopy, thermogravimetry and evolved gas analysis (line-of-sight mass spectroscopy). Scanning calorimetry, ramping at 10°C/min, on the as-received (room temperature annealed) resin indicates a glass transition temperature of 67°C which decreases to 58°C for an unrelaxed sample. The ir spectra have bands which can be assigned to Si-CH3 and Si-O-Si modes. For 30 minute isothermal anneals at temperatures above 420°C there is a continuous decrease in the bands associated with the Si-CH3 groups such that after 30 minutes at 650°C the ir spectrum has evolved to that for SiO2. Evolved gas analysis indicates that there are four major components evolving. Over the temperature range (ramping at 10°C/min) ∼180 to ∼500°C we observe C2H5OH and H2O, both of which are condensation reaction products from the curing reaction. Methane is a major evolving species over the temperature range ∼500 to ∼800°C and the thermal spectrum is double peaked which we attribute to CH3+ bound to the inside and outside of the polymer cage structures. The final major component detected was H2, over the temperature range ∼600 to ∼1100°C, which was attributed to pyrolysis of the organic components, both trapped and evolving. The features of the weight loss curve can be accounted for by the measured evolving species spectra.
Let H and K be topological groups, and let HⓈ K denote the semidirect product determined by a homomorphism (η): H → A(K), where A(K) is the automorphism group of K. In this paper we consider two restricted types of semidirect products. We say that HⓈ K is a semidirect product of type I if η(h) is the identity on Z(K), the centre of K, for each hє H, and of type II if η(H) є I(K), where I(K) is the group of inner automorphisms of K. We obtain conditions under which a type II semidirect product of two groups with equal uniformities has equal uniformities, and conditions under which a type I (hence type II) product of two central groups is central. A group G is central if G/Z(G) is compact, where Z(G) is the centre of G.