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Conventional ambulatory heart rhythm monitoring is limited in its ability to provide rapid diagnosis of arrhythmias in athletes participating in water or high-intensity sports. This case report is of a 17-year-old female competitive swimmer who underwent loop recorder implantation with Confirm Rx™ ICM 3500 (Abbott, Minneapolis, MN) to monitor for arrhythmias during swimming. The purpose of this case report is to describe the utility of implantable loop recorders in arrhythmia diagnosis and symptom evaluation in water sport athletes.
A method is described for the preparation of a vaccine, consisting of a suspension of bacterial cells in a vegetable oil, which retains the antigenic activity of both Vi and O antigens of S. typhi. The ability of such a vaccine to induce active and passive protection in mice is demonstrated.
The observations reported here show that the T Vi antigen is effective in stimulating antibodies when it is attached to the cells. It is also clear that the Vi antigen is readily removed in aqueous solutions, but in such organic solvents as acetone, chloroform, ether, alcohol, carbon tetrachloride and benzene it is retained by the cell. In alcohol-water mixtures the Vi antigen is progressively more soluble in those solutions where the alcohol concentration is less than 70 %. However, its solubility in water is limited, and by making progressively heavier suspensions it was found that a point is reached at which Vi antigen is retained by the cell, the suspending solution apparently being saturated. Such an aqueous suspension is able to stimulate the production of Vi antibody.
The administration of dried organisms in peanut oil resulted in the production of antibodies against both O and Vi antigens. This was in contradistinction to the results obtained when mineral oil, mineral oil + saline, or peanut oil + saline were used: in these cases the O antibody titre was lower and Vi antibodies were produced in low titre or not at all. It seems clear that the presence of water in the vaccine has the effect of removing the antigenicity of the Vi hapten; water-free, vegetable-oil vaccine is suggested by these studies as an effective agent for immunizing against all of the antigens of Salmonella typhi. The use of such a vaccine in producing active and passive immunity in animals is discussed in the paper which follows.
Identifying risk factors for the development of post-traumatic stress disorder (PTSD) is important for understanding and ultimately preventing the disorder. This study assessed pain shortly after traumatic injury (i.e. peritraumatic pain) as a risk factor for PTSD.
Participants (n=115) were patients admitted to a Level 1 Surgical Trauma Center. Admission to this service reflected a severe physical injury requiring specialized, emergent trauma care. Participants completed a pain questionnaire within 48 h of traumatic injury and a PTSD diagnostic module 4 and 8 months later.
Peritraumatic pain was associated with an increased risk of PTSD, even after controlling for a number of other significant risk factors other than acute stress disorder symptoms. An increase of 0.5 s.d. from the mean in a 0–10 pain rating scale 24–48 h after injury was associated with an increased odds of PTSD at 4 months by more than fivefold, and at 8 months by almost sevenfold. A single item regarding amount of pain at the time of hospital admission correctly classified 65% of participants.
If these findings are replicated in other samples, high levels of peritraumatic pain could be used to identify individuals at elevated risk for PTSD following traumatic injury.
Strained-Si based Field Effect Transistors (FETs) have enabled improvement of carrier transport in Metal Oxide Semiconductor (MOS)-based devices, both in the ON state of the device and in the sub-threshold region. This leads to devices with higher ratios of on-to-off current, improvements in the device sub-threshold slope, lower voltage operation, and carrier mobility enhancement. However, in order to understand the fundamental physics of these devices, it is important to address the stress conditions of the strained-Si channel layers after device processing, particularly after the ion-implantation process. In this work, we have studied Si+ self ion-implantation and thermally annealed strained-Si channel layers in n-MOSFETs. It has been observed that the density of defects in the strained-Si layer depends upon implant dose as well as thermal treatment. Using energy dispersive spectroscopy (EDS) spectra, it is found that Ge is present in the strained Si layer when analyzed after Si+ implantation and rapid thermal annealing. The presence of Ge in the strained Si channel layer causes relaxation of strain. This is verified by Convergent Beam Electron Diffraction (CBED) by measuring the lattice constant of the strained channel. It is concluded that electron mobility enhancements can be degraded in n- MOSFETs due to presence of both Ge up-diffusion and defects.
The diffusion behavior of ion implanted arsenic and phosphorus in relaxed-Si0.8Ge0.2 is investigated. Both dopants exhibit enhanced diffusivities in SiGe compared to those in Si under equilibrium conditions. The ratio of the effective diffusivity in SiGe relative to that in Si is found to be approximately seven for arsenic, and roughly two for phosphorus at high concentrations. Under transient diffusion conditions, arsenic diffusion in SiGe is retarded while arsenic diffusion in Si is enhanced by the ion implant damage. The transient retardation of arsenic diffusion in SiGe is observed at temperatures ranging from 900 to 1050°C. These results suggest that using arsenic, it is possible to form n+/p junctions in relaxed-Si0.8Ge0.2 as shallow as those in Si, by optimizing the implant annealing conditions.
A MEMS-based gas turbine engine is being developed for use as a button-sized portable power generator or micro-aircraft propulsion source. Power densities expected for the micro- engine require high combustor exit temperatures (1300-1700K) and very high rotor peripheral speeds (300-600m/s). These harsh operating conditions induce high stress levels in the engine structure, and thus require refractory materials with high strength. Silicon carbide has been chosen as the most promising material for use in the near future due to its high strength and chemical inertness at elevated temperatures. However, techniques for microfabricating single- crystal silicon carbide to the level of high precision needed for the micro-engine are not currently available. To circumvent this limitation and to take advantage of the well-established precise silicon microfabrication technologies, silicon-silicon carbide (SiC) hybrid turbine structures are being developed using chemical vapor deposition of poly-SiC on silicon wafers and wafer bonding processes. Residual stress control of SiC coatings is of critical importance to all the silicon-silicon carbide hybrid structure fabrication steps since a high level of residual stresses causes wafer cracking during the planarization, as well as excessive wafer bow, which is detrimental to the subsequent planarization and bonding processes. The origins of the residual stresses in CVD SiC layers have been studied. SiC layers (as thick as 30µm) with low residual stresses (on the order of several tens of MPa) have been produced by controlling CVD process parameters such as temperature and gas ratio. Wafer-level SiC planarization has been accomplished by mechanical polishing using diamond grit and bonding processes are currently under development using interlayer materials such as silicon dioxide or poly-silicon. These process development efforts will be reviewed in the context of the overall micro-engine development program.
The fabrication of 250 Å thick, undoped, single crystal silicon on insulator by lateral solid phase epitaxial growth from amorphous silicon on oxide patterned (001) silicon substrates is reported. Amorphous silicon was grown by low pressure chemical vapor deposition at 525°C using disilane. Annealing at temperatures between 540 and 570°C is used to accomplish the lateral epitaxial growth. The process makes use of a Si/Si1-xGex/Si stacked structure and selective etching. The thin Si1-xGex etch stop layer (x=0.2) is deposited in the amorphous phase and crystallized simultaneously with the Si layers. The lateral growth distance of the epitaxial region was 2.5 μm from the substrate seed window. This represents a final lateral to vertical aspect ratio of 100:1 for the single crystal silicon over oxide regions after selective etching of the top sacrificial Si layer. The effects of Ge incorporation on the lateral epitaxial growth process are also discussed. The lateral epitaxial growth rate of 20% Ge alloys is enhanced by roughly a factor of three compared to the rate of Si films at an anneal temperature of 555°C. Increased random nucleation rates associated with Ge alloy films are shown to be an important consideration when employing Si1-xGex to enhance lateral growth or as an etch stop layer.
The immunological basis for autoimmune disease is complex, and autoimmune diseases themselves are diverse in character. The pathogenesis of specific autoimmune diseases may well be different, involving both genetic and environmental factors. However, many autoimmune diseases share an association with the HLA locus and, more specifically, the highly polymorphic class I and class II alleles found in this region. Recent advances in the understanding of the structure and function of HLA class I and class II molecules have made it possible to begin to decipher mechanisms by which these genes may be contributing to the development of autoimmunity. In this chapter, we will address the evidence that the HLA locus is associated with autoimmunity, the possible mechanisms by which HLA genes could contribute to disease, and the implication that this information will have on future assessment and treatment of patients with autoimmune diseases.
The HLA locus
The HLA locus is a cluster of genes found on chromosome 6 (6p21.3). This region includes the genes encoding HLA class I and class II proteins, complement and other factors important in the generation of the immune response. Figure 3.1 demonstrates the distribution of genes across this region. The HLA class I genes are located at the telomeric end of the human MHC. The HLA-A, HLA-B and HLA-C loci are referred to as class I genes and encode the principle transplantation antigens, which are expressed in all nucleated cells. The class I genes each encode a single polypeptide, the HLA class I heavy chain. The class I heavy chain forms a complex with β2–microglobulin, a protein encoded outside of the MHC region, to form the functional HLA class I molecule.
A status report is given on a comprehensive modeling project aimed at predicting failure time distributions of interconnect lines. We discuss our novel approach to calculate the evolution of stresses in lines using elastic response functions. It is argued that this approach makes it possible to model the stress and damage evolution in a large ensemble of lines efficiently so that statistically meaningful failure time distributions can be generated.
The elastic response functions enable us also to derive a generalized Korhonen equation which includes the effects of mass transport at remote locations. Basic features of this equation are demonstrated with a one-dimensional implementation and its results are compared with the classical Korhonen [8, 9, 10] model.
The first demonstration of n-MOSFETs fabricated using strained Si1-yCy surface channels is reported. Tensile-strained Si1-yCy layers with substitutional carbon contents up to 0.8 atomic percent were epitaxially grown on <100> Si substrates by rapid thermal chemical vapor deposition, using silane and methylsilane as the silicon and carbon precursors. n-MOSFETS were fabricated using standard MOS processing with reduced thermal exposure to minimize the possibility of strain relaxation. A remote plasma CVD oxide was employed to form the gate oxide. The Si1-yCy devices exhibit electrical characteristics that are typical for Si n-MOSFETs, with good turn-on and subthreshold characteristics. MOS capacitance-voltage analysis demonstrates comparable oxide interface qualities for the Si1-yCy and Si control devices. No carbon-related leakage current is observed in source and drain diode junctions. Characterization of the MOSFET electron inversion layer mobility at room temperature shows comparable mobilities, within the sensitivity of the measurement, for the Si1-yCy and Si control devices. This is in contrast to the mobility enhancement observed in n-MOSFETs fabricated using tensile- strained Si grown on relaxed Si1-xGex layers. At low temperatures, the inversion layer mobility of Si1-yCy devices is lower than that of the Si controls, and appears to be affected by Coulomb and possibly random alloy scattering.
Epitaxial Si1-x-yGexCy and Si1-yCy layers grown on Si are opening up new possibilities for bandstructure engineering of electronic devices. Thin Si1-yCy layers containing a few atomic percent substitutional carbon, grown on Si substrates, experience biaxial tensile strain, which produces a conduction band energy splitting that is expected to be favorable for in-plane electron transport. For other applications, C may be useful as a means of compensating the compressive strain of Ge in ternary Si1-x-yGexCy alloys. Although the understanding of the electronic properties of these materials is still at an early stage, interesting trends are emerging.
A key issue for synthesis of these alloys is the low equilibrium solubility of carbon in silicon. However, a number of non-equilibrium methods have been employed to grow these materials. This work focuses on the properties of Si1-yCy and Si1-x-yGexCy grown by chemical vapor deposition. There is a strong influence of the growth conditions on the fraction of the total carbon concentration which is substitutional on the silicon lattice. Using low temperatures (e.g. 550°C) and very high silane partial pressures for Si1-yCy growth, good agreement is obtained between the carbon contents determined by x-ray diffraction and secondary ion mass spectrometry, for carbon concentrations up to about 1.8 atomic percent. Metal-oxidesemiconductor capacitors fabricated on Si1-x-yGexCy and Si/Si1-yCy epitaxial layers show wellbehaved electrical characteristics. Temperature dependent capacitance-voltage analysis is used to extract the band offsets, and indicates that the conduction band energy is lowered as carbon is added to Si. Complementary to the case of strained Si1-xGex grown on Si, for which most of the energy offset is in the valence band, the band offset appears primarily in the conduction band for Si1-yCy/Si heterojunctions.
We examine the distribution of failure times in a simple and computationally efficient, yet reasonably authentic, model of interconnect reliability that allows consideration of statistically significant samples. The model includes an approximate description of the distribution of grain sizes and texture in narrow interconnects, an effective treatment of stress evolution associated with mass transport along grain boundaries, and local relaxation of stresses due to void formation. Failure time distributions for populations of idealized structures are analyzed to aid in interpretation of model behavior.
The ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering spectroscopy (ToF-MEISS) system. A series of silicon-silicon/germanium (Si/Sil-xGex) hetero-structure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapour deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Sil-xGex can be uniquely identified with a depth resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition and the results compared with conventional Rutherford back-scattering spectrometry (RBS).
We have measured the dielectric functions of three Si1−yCy, alloys layers (y ≤1.4%) grown pseudomorphically on Si (001) substrates using molecular beam epitaxy at low temperatures. From the numerical derivatives of the measured spectra, we determine the critical point energies E′0 and E1 as a function of y (y ≤ 1.4%) using a comparison with analytical line shapes and analyze these energies in terms of the expected shifts and splittings due to negative hydrostatic pressure, shear stress, and alloying. Our data agree well with the calculated shifts for El, but the E′0 energies are lower than expected. We discuss our results in comparison with recent tight-binding molecular dynamics simulations by Demkov and Sankey (Phys. Rev. B 48, 2207, 1993) prediciting a total breakdown of the virtual-crystal approximation for such alloys.