To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The resistive tearing mode instability is a mechanism that in some cases will render unstable a magnetohydrodynamic equilibrium of a plasma that is ideally stable, i.e. stable if no dissipative oiesses are taken into account. There is much experimental evidence that this instability is the cause of the current disruptions observed in laboratory plasma devices (von Goeler et al. 1974). In the astrophysical context, the instability has been invoked in connection with the solar flare energy release mechanism (Coppi and Friedland 1971) and the problem of the disconnection of the protostar matter from the interstellar magnetic field during star formation (Mestel 1966). In the latter problem the tearing instability gives rise to a much smaller timescale for magnetic reconnection than does ordinary resistive diffusion.
In theories of the heating of the solar corona a number of authors have recently considered the propagation and damping of fast and slow magnetohydrodynamic waves, in the form of surface waves localized on the interfaces of coronal flux tubes (Ionson 1978, Wentzel 1979, Roberts 1981, Cramer and Donnelly 1983). The damping of these waves occurs, in addition to a rather weak global damping due to viscous or resistive dissipation, by means of a localized absorption at a so-called ‘resonance’ in the density or magnetic field profile forming the flux tube. At such a resonance, the wave frequency is equal to the local value of the Alfven wave frequency, in the case of Alfven resonance absorption, or at the local slow mhd wave frequency, in the case of the ‘cusp’ or ‘compressive singularity’ resonance in a finite pressure plasma.
A common form of wave propagation in the highly structured magnetic fields and density profiles of the solar atmosphere should be magnetohydrodynamic surface waves, i.e. waves with magnetic and velocity fields concentrated at an interface of two regions of plasma of differing properties. For example, local concentrations of equilibrium magnetic fields forming flux tubes will support these waves on their surfaces, in addition to the more commonly considered ‘body waves’ that are supported by an isolated flux tube, waves with an oscillatory radial dependence inside the tube. Mhd surface waves have recently been identified in a laboratory plasma at Sydney University (Collins, Cramer and Donnelly 1983).
This study aimed (1) to report the long-term effects of infliximab, a murine monoclonal antibody directed against tumour necrosis factor-α, on autoimmune inner ear disease, and (2) to discuss dilemmas surrounding the long-term management of autoimmune inner ear disease.
A 49-year-old man presented with sudden-onset, left-sided, sensorineural hearing loss, tinnitus and vertigo. He was prescribed oral prednisolone, with benefit. Over several subsequent months, he experienced frequent relapses and progressive deterioration of high-frequency hearing bilaterally. Multiple agents failed to stabilise his condition. Following infliximab treatment, there was a documented and sustained improvement in his hearing and tinnitus. He stopped the treatment after 46 weeks, with rapid relapse of his condition. His hearing recovered quickly again after recommencing infliximab.
The benefits of prolonged infliximab use and potential side effects must be balanced against allowing the disease to take its course, with progressive deafness. Randomised controlled trials are required to assess infliximab's optimal duration of use, long-term efficacy and safety in the treatment of autoimmune inner ear disease.
This study aimed to determine whether there was a difference in skin permeability to methylene blue dye or skin morphology between dairy cows that differed in their susceptibility to digital dermatitis (DD) and to assess the effect of contact with slurry on skin permeability. Twenty nine dairy cows were monitored for DD during the winter housing period and classed as DD+ (previous DD infection, n = 17), or DD− (no recorded infection, n = 12). The animals were culled and a skin sample was taken from above the heel of each hind foot and frozen. Samples were later defrosted and one sample from each cow was tested for permeability, whereas the other was treated with slurry for 24 h before permeability testing. To test permeability, methylene blue dye was applied to the skin surface in a Franz diffusion cell. After 48 h, the amount of dye that had passed through the skin was estimated. The stratum corneum thickness and the density of hair follicles were determined from additional heel skin samples. Skin permeability to methylene blue dye was significantly greater for samples that had been treated with slurry but did not differ between DD+ and DD− animals. No difference was found in the stratum corneum thickness or density of hair follicles between DD+ and DD− animals. These findings imply that individual differences in general skin permeability are not a major factor in determining DD susceptibility and suggest that contact with slurry could contribute to DD infection by increasing the permeability of the skin, which may facilitate pathogen entry. Further work is required to clarify the role played by slurry in the pathogenesis of DD.
One of the central results in Einstein’s theory of Brownian motion is that the mean
square displacement of a randomly moving Brownian particle scales linearly with time. Over
the past few decades sophisticated experiments and data collection in numerous biological,
physical and financial systems have revealed anomalous sub-diffusion in which the mean
square displacement grows slower than linearly with time. A major theoretical challenge
has been to derive the appropriate evolution equation for the probability density function
of sub-diffusion taking into account further complications from force fields and
reactions. Here we present a derivation of the generalised master equation for an ensemble
of particles undergoing reactions whilst being subject to an external force field. From
this general equation we show reductions to a range of well known special cases, including
the fractional reaction diffusion equation and the fractional Fokker-Planck equation.
A spontaneous cerebrospinal fluid leak can sometimes only become apparent following grommet insertion and usually represents dehiscence of the tegmen tympani, which is an uncommon condition.
This report aimed to reaffirm the importance of recognising this unusual presentation and outline management options.
A 63-year-old man with conductive hearing loss and type B (flat) tympanometry underwent grommet insertion into his left ear, which resulted in cerebrospinal fluid otorrhoea. A defect of the tegmen tympani was found. This was successfully repaired via a transmastoid approach using a multi-layered grafting technique.
Dehiscence of the tegmen tympani is uncommon and may only come to light following grommet insertion, which may be problematic for the uninformed otolaryngologist. Education is important to ensure early recognition and appropriate management.
The interaction of a Cl2 plasma with a Si(100) surface has been investigated by angle resolved x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. From XPS, it was found that the amount of chlorine incorporated at the Si surface increases with ion energy. Chlorine is present as SiClx (x = 1-3) with average relative coverages (integrated over depth) of [SiCl]:[SiCl2]:[SiCl3] ≅ 1:0.33:0.1. These relative coverages don’t depend strongly on ion energy between 40 and 280 eV. Real-time spectroscopic ellipsometry measurements showed that the layer present during etching is stable when the plasma is extinguished and the gas pumped away. In addition, the equivalent thickness of damaged silicon and silicon-chloride within the surface layer increases with ion energy.
To review our experience of cochlear implant failure and subsequent revision surgery, and to illustrate the experience we have gained by presenting a series of lessons learned.
A combined retrospective and prospective study of revision surgery in a UK regional cochlear implant centre.
Of the 746 cochlear implantations undertaken, 33 (4.7 per cent of adults and 4.1 per cent of children) had a registered failure requiring re-implantation. The mean time to device failure was 60 months in adults and 35 months in children. Causes of cochlear implant failure were medical (n = 11), electrode displacement (n = 2), ‘hard device failure’ (n = 15) and ‘soft device failure’ (n = 5). Chronic suppurative otitis media and post-auricular mastoid abscess were the commonest causes of medical failure. There was one case of electrode array displacement as a direct result of skin flap revision surgery. In 80 per cent of cases, audiological performances were stable or improved following re-implantation.
As the number of cochlear implants increase and patients outlive the lifespan of their devices, we will face a growing number of revision procedures. Audiologists and otologists should be competent in diagnosing and managing device failure and medical complications requiring cochlear re-implantation.
Long-term sediment and ground-penetrating radar data from Davis Pond, a small lake near the Hudson River valley, reveal past droughts in a historically humid region that presently supplies water to millions of people in and around New York City. A minimum of eleven sandy paleoshoreline deposits in the lake date from 13.4 to 0.6 cal ka BP. The deposits span 1500 to 200 yr between bracketing radiocarbon ages, and intrude into lacustrine silts up to 9.0 m below the modern lake surface in a transect of six sediment cores. Three low stands, ca. 13.4–10.9, 9.2 and 8.2 cal ka BP indicate low regional moisture balance when low temperatures affected the North Atlantic region. Consistent with insolation trends, water levels rose from ca. 8.0 cal ka BP to present, but five low stands interrupted the rise and are likely associated with ocean–atmosphere interactions. Similar to evidence from other studies, the data from Davis Pond indicate repeated multi-century periods of prolonged or frequent droughts super-imposed on long-term regional trends toward high water levels. The patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern United States are more prone to severe drought than historically expected.
The deep ultraviolet (250 nm) photopatterning of spin-on films of polymeric Au mercaptide results in formation of adherent Au patterns. Fxcimer laser projection patterning and standard contact printing techniques give excellent pattern resolution on the micron scale. Laser direct write produces lines at very fast writing speeds. Exposed areas are less soluble than unexposed areas, i.e. the film behaves as a negative photoresist. Bakeout of developed patterns at 250°C yields good purity Au micropatterns up to 500 Å thick. Mechanistic information about pattern formation is gained from uv-visible, infrared, and mass spectrometric monitoring of the photolysis process, and from Auger analysis of films. Adherent patterns are apparently formed by photochemical cleavage of Au-S bonds followed by evaporation of a small amount of free mercaptide. The loss of ligand in the exposed areas renders them less soluble than unexposed film. Thermal decomposition of both photolyzed and unphotolyzed films has the same result of volatilizing all film material except Au.
Hard carbon films have been deposited onto room-temperature silicon substrates in a de plasma of methane and hydrogen. The substrates are placed on the cathode. A stainless mesh is held at the same potential as the cathode and is set above the substrates. Although the deposited films are amorphous and contain 24.4 atomic percent hydrogen, they have the following diamondlike properties: hardness is almost equivalent to that of natural diamond; electrical resistivity is on the order of 1013Ωcm; chemical inertness is excellent to acids; thermal diffusivity is 5.2 cm2 /sec. However, the films have a large compressive stress of 1.3×1010 dyn/cm2.
Annealed films exhibit dehydrogenation, graphitization, an increase in chemical reactivity, volume expansion and stress relaxation above 400°C. The activation energy for the transformation from the diamondlikephase to the graphitic phase is 18 kcal/mole.
The dependence of the thermal diffusivity and hydrogen content on both the CH4/H2 gas mix ratio and the total pressure have been measured for the films deposited in a dc plasma without the mesh.
Chlorine-enhanced GaAs maskless etching using a novel focused-ion-beametching (FIBE) system has been examined for establishing high-rate and smooth FIBE. The system is composed of an air-locked ultrahigh-vacuum chamber, a 30 KeV Ga+ FIB column and two kinds of chlorine-irradiation nozzles. A fine nozzle enabled us to irradiate a high-density Cl2 flux on a desired, small area of the sample while retaining a sufficiently low surrounding-gas pressure for stable Ga+ FIB emission. Highly chemically-enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained. At the maximum yield, line-scanned deep-groove (6.5 um) etching with a smooth surface, capable of fabricating a laser-cavity optical mirror, was demonstrated. The chemical-enhancement effect showed high FIB-scanning-time dependence. This effect was also observed by irradiating with a plasma-dissociated Cl radicals using a novel radical beam gun. An analytical model, based on the Ga+-ion bombardment on the chlorine-adsorbed substrate surface, suggested that the maximum chemical enhancement is obtained when the Ga+-FIB scanning time is adjusted to the chlorine-coverage time, given by the Cl2-molecule or Cl-radical flux density.
The technique of ion beam deposition (IBD) is utilized to investigate low-energy, ion-induced damage on Si and Ge; to study reactive ion cleaning of Si and Ge; to fabricate amorphous isotopic heterostructures; and to fabricate and study the low-temperature epitaxial deposition of 74Ge on Ge(100), 30Si on Si(100), and 74Ge on Si(100). The techniques of ion scattering/channeling and cross-sectional TEM are combined to characterize the deposits.
Synthesis of diamond thin-films has been tried by an ArF excimer laser-induced chemical vapor deposition (LCVD) technique, using acetylene diluted with hydrogen as a source gas and a silicon wafer as a substrate. In these experiments, irradiation geometry, substrate temperature and laser power density were varied. Upon irradiation by a focused laser beam, deposition of diamond on substrates heated above 400°Cwas observed, and was confirmed by reflection electron diffraction (RED) photographs. Homogeneity of the diamond films was improved by irradiation parallel to the substrate. These facts suggest that the formation of diamond proceeds through multiple photon decomposition of the reactant gas, and that electronic excitation of gas phase rather than that of substrate or adsorbate layer is essential to form diamond.
Laser-assisted etching techniques have been developed for alloyselective patterning of GaAs/AlGaAs layered structures. Such techniques are potentially very important for the fabrication of a large variety of heterostructure devices. Studies have been carried out with several liquid etchants and have utilized a CW dye laser tuned to a wavelength above the band edge of GaAs, but below that of the AlGaAs layer (e.g., λ = 0.85 μm) to etch GaAs. Using the laser focal spot to spatially define the etched area, features exhibiting very smooth interface surfaces were produced in MBE-grown epitaxial layers. A high degree of selectivity for GaAs over A1(0.4)Ga(0.6)As, low background etch rates, and high feature etch rates (> 2 μm/min) were demonstrated. Patterned etching with AZ 1350J photoresist exhibited good pattern resolution and nearly vertical sidewall profiles. Etchant mixtures of dilute H2S04:H202:H20 and HNO3:H20 produced qualitatively different results, with the HNO3:H20 mixture exhibiting a tendency to leave a residual GaAs layer at the interface, even for long etch times. Surface analysis techniques, including Auger spectroscopy, profilometry, and interference contrast microscopy have been used to characterize the etched structures, and a simplified analytical model has been used to predict the qualitative dependence of etch rate on layer thickness.
Etching of silicon by molecular fluorine is accelerated when trace quantities of copper are present on the surface. Copper is a residue formed when sputter-deposited aluminum (containing 0.5 % copper) is selectively removed by HF from the silicon surface. The temperature dependence of the etching rate was studied in the range 60–290°C. At temperatures higher than 80°C copper causes a ˜100-fold increase in the rate of etching of the underlying silicon (100), compared to unmetallized samples. Above 180°C, F2 exhibits a higher absolute etch rate than equivalent concentrations of fluorine atoms. Preliminary results for other metal contaminants and etchant gases indicate that silver also accelerates F2 etching, and copper enhances etching by NF3. The results are interpreted in terms of a catalytic mechanism.
An Ar+ ion laser has been used for direct writing of GaAs and GaAsP single crystal films on thermally biased GaAs substrates. Multiple scanning of the laser beam at speeds in the range 100–200 μm/s at carefully selected growth conditions resulted in single crystalline selectively deposited films. Photoluminescence indicates that these deposited films have optical properties that are comparable with the conventionally (MOCVD) grown material.
Laser beam irradiation has been used to form a superlattice (SL) structure which has been demonstrated in the GaAsP-GaAs system. When a GaAs substrate is exposed to fluxes of AsH3, PH3 and TMG at 500°C, only GaAs will be deposited because of the insufficient cracking of PH3. However, localized laser heating results in GaAsP deposition. A GaAsP-GaAs superlattice with a period of about 400 Å has been synthesized. This laser induced technique can thus have potential applications in the generation of abrupt interfaces without the use of shutters as in MBE or gas switching as in MOCVD.
TiSi2 formation on various substrates has been widely investigated in the past and one of the critical parameters has been found to be the quality of the interface before deposition. In this paper the quality of the suicide formed on a range of oxides, from lnm to 15nm, has been systematically studied using sheet resistance measurements, Scanning Electron Microscopy, Atomic Force Microscopy and Auger Electron Microscopy. The critical thickness, above which the quality of the suicide formed is affected, was found to be 2.2nm and no suicide was detected > 13.0nm. A notable difference in the suicide formation occured in a narrow band around 5.0nm. It is proposed that this is the transition region in which the oxide becomes the main source of Si for TiSi2 formation rather than the substrate.
The Focused Ion Beam Microscope (FIB) has been used to fabricate capacitors from single crystals of BaTiO3 and SrTiO3 with electrode areas ∼200μm2, and thickness of single crystal dielectric between 2μm and 500nm. Cross-sectional transmission electron microscopy revealed that during capacitor fabrication, the FIB rendered around 20nm of dielectric at the electrode-dielectric interface amorphous, associated with local gallium impregnation. Such a region would act electrically in series with the single crystal and would presumably have a considerable negative influence on dielectric properties. However, annealing prior to electrode deposition was found to fully recover the single crystal, and homogenise the gallium profile. Some subsequent dielectric testing of SrTiO3 was performed yielding a room temperature dielectric constant of ∼150 and loss tangent of 0.015 at 100kHz. A technique has therefore been demonstrated which allows fabrication of capacitors in which size-effects in ‘thin-films’ can be studied, without the influence of grain boundaries, and other issues associated with conventional thin film growth.