Ceramic-metal composites for heat exchangers in concentrated solar power plants.

The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heat exchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1-3, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage4-6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin9. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heat exchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost.

Application of radiopaque micro-particle fillers for 3-D imaging of periodontal pocket analogues using cone beam CT.

BACKGROUND: Periodontitis is an infectious/inflammatory disease most often diagnosed by deepening of the gingival sulcus, which leads to periodontal pockets (PPs) conventional manual periodontal probing does not provide detailed information on the three-dimensional (3-D) nature of PPs. OBJECTIVES: To determine whether accurate 3-D analyses of the depths and volumes of calibrated PP analogues (PPAs) can be obtained by conventional cone beam computed tomography (CBCT) coupled with novel radiopaque micro-particle fillers (described in the companion paper) injected into the PPAs. METHODS: Two PPA models were employed: (1) a human skull model with artificial gingiva applied to teeth with alveolar bone loss and calibrated PPAs, and (2) a pig jaw model with alveolar bone loss and surgically-induced PPAs The PPAs were filled with controlled amounts of radiopaque micro-particle filler using volumetric pipetting Inter-method and intra-method agreement tests were then used to compare the PPA depths and volumes obtained from CBCT images with values obtained by masked examiners using calibrated manual methods. RESULTS: Significant inter-method agreement (0.938-0.991) and intra-method agreement (0.94-0.99) were obtained when comparing analog manual data to digital CBCT measurements enabled by the radiopaque filler. SIGNIFICANCE: CBCT imaging with radiopaque micro-particle fillers is a plausible means of visualizing and digitally assessing the depths, volumes, and 3-D shapes of PPs This approach could transform the diagnosis and treatment planning of periodontal disease, with particular initial utility in complex cases Efforts to confirm the clinical practicality of these fillers are currently in progress.

Development of radiopaque, biocompatible, antimicrobial, micro-particle fillers for micro-CT imaging of simulated periodontal pockets.

OBJECTIVES: Approximately 109 bacteria can be harbored within periodontal pockets (PP) along with inflammatory byproducts implicated in the pathophysiology of systemic diseases linked to periodontitis (PD). Calculation of this inflammatory burden has involved estimation of total pocket surface area using analog data from conventional periodontal probing which is unable to determine the three-dimensional (3-D) nature of PP. The goals of this study are to determine the radiopacity, biocompatibility, and antimicrobial activity of transient micro-particle fillers in vitro and demonstrate their capability for 3-D imaging of artificial PP (U.S. Patent publication number: 9814791 B2). METHODS: Relative radiopacity values of various metal oxide fillers were obtained from conventional radiography and micro-computed tomography (µCT) using in vitro models. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to measure the biocompatibility of calcium tungstate (CaWO4) particles by determination of viable keratinocytes percentage (%) after exposure. After introducing an antibacterial compound (K21) to the radiopaque agent, antimicrobial tests were conducted using Porphyromonas gingivalis (P. gingivalis) and Streptococcus gordonii (S. gordonii) strains and blood agar plates. RESULTS: CaWO4 micro-particle-bearing fillers exhibited an X-ray radiopacity distinct from tooth structures that enabled 3-D visualization of an artificial periodontal pocket created around a human tooth. MTT assays indicated that CaWO4 micro-particles are highly biocompatible (increasing the viability of exposed keratinocytes). Radiopaque micro-particle fillers combined with K21 showed significant antimicrobial activity for P. gingivalis and S. gordonii. SIGNIFICANCE: The plausibility of visualizing PP with 3-D radiographic imaging using new radiopaque, biocompatible, transient fillers was demonstrated in vitro. Antibacterial (or other) agents added to this formula could provide beneficial therapeutic features along with the diagnostic utility.

Pumping liquid metal at high temperatures up to 1,673 kelvin.

Heat is fundamental to power generation and many industrial processes, and is most useful at high temperatures because it can be converted more efficiently to other types of energy. However, efficient transportation, storage and conversion of heat at extreme temperatures (more than about 1,300 kelvin) is impractical for many applications. Liquid metals can be very effective media for transferring heat at high temperatures, but liquid-metal pumping has been limited by the corrosion of metal infrastructures. Here we demonstrate a ceramic, mechanical pump that can be used to continuously circulate liquid tin at temperatures of around 1,473-1,673 kelvin. Our approach to liquid-metal pumping is enabled by the use of ceramics for the mechanical and sealing components, but owing to the brittle nature of ceramics their use requires careful engineering. Our set-up enables effective heat transfer using a liquid at previously unattainable temperatures, and could be used for thermal storage and transport, electric power production, and chemical or materials processing.

Structure-based optical filtering by the silica microshell of the centric marine diatom Coscinodiscus wailesii.

Diatoms are a renewable (biologically reproducible) source of three-dimensional (3-D) nanostructured silica that could be attractive for a variety of photonic devices, owing to the wide range of quasi-periodic patterns of nano-to-microscale pores available on the silica microshells (frustules) of various diatom species. We have investigated the optical behavior of the silica frustule of a centric marine diatom, Coscinodiscus wailesii, using a coherent broadband (400-1700 nm) supercontinuum laser focused to a fine (20 µm diameter) spot. The C. wailesii frustule valve, which possessed a quasi-periodic hexagonal pore array, exhibited position-dependent optical diffraction. Changes in such diffraction behavior across the frustule were consistent with observed variations in the quasi-periodic pore pattern.

Formation of nanostructured, nanocrystalline boron nitride microparticles with diatom-derived 3-D shapes.

The first use of diatom frustules as shape-dictating 3-D templates for the syntheses of nanostructured, nanocrystalline micro-particles of a non-oxide ceramic, boron nitride, is demonstrated.

Ceramic nanoparticle assemblies with tailored shapes and tailored chemistries via biosculpting and shape-preserving inorganic conversion.

A novel biosynthetic paradigm is introduced for fabricating three-dimensional (3-D) ceramic nanoparticle assemblies with tailored shapes and tailored chemistries: biosculpting and shape-preserving inorganic conversion (BaSIC). Biosculpting refers to the use of biomolecules that direct the precipitation of ceramic nanoparticles to form a continuous 3-D structure with a tailored shape. We used a peptide derived from a diatom (a type of unicellular algae) to biosculpt silica nanoparticle based assemblies that, in turn, were converted into a new (nonsilica) composition via a shape-preserving gas/silica displacement reaction. Interwoven, microfilamentary silica structures were prepared by exposing a peptide, derived from the silaffin-1A protein of the diatom Cylindrotheca fusiformis, to a tetramethylorthosilicate solution under a linear shear flow condition. Subsequent exposure of the silica microfilaments to magnesium gas at 900 degrees C resulted in conversion into nanocrystalline magnesium oxide microfilaments with a retention of fine (submicrometer) features. Fluid(gas or liquid)/silica displacement reactions leading to a variety of other oxides have also been identified. This hybrid (biogenic/synthetic) approach opens the door to biosculpted ceramic microcomponents with multifarious tailored shapes and compositions for a wide range of environmental, aerospace, biomedical, chemical, telecommunications, automotive, manufacturing, and defense applications.

Cardiac manifestations in patients with HLA B27-associated juvenile arthritis.

Cardiac involvement is common in adult patients with the presence of HLA B27 with or without the HLA B27-associated spondyloarthropathy ankylosing spondylitis. Most patients with juvenile spondyloarthropathy, which begins at age 16 or younger, do not have spinal involvement and there are only few reports of cardiac involvement. This study sought to assess the prevalence of carditis in patients with HLA B27-associated juvenile arthritis (B27-JA). In a controlled study, 40 patients with B27-JA, among them only 1 with ankylosing spondylitis, were examined by electrocardiogram and echocardiography with pulsed and color-flow Doppler at rest and at the termination of a bicycle exercise and compared to an age- and sex-matched control group negative for HLA B27. Four patients with B27-JA, and none in the control group, had inflammatory aortic regurgitation. Late diastolic flow velocity was significantly increased in patients with B27-JA at the termination of exercise. HLA B27 is a risk factor for endo-/myocardial damage in patients with B27-JA, even in the presence of only short and mild articular disease. Patients with B27-JA should be screened for the presence of aortic regurgitation.

Reactive arthritis due to Salmonella enteritidis complicated by carditis.

Reactive arthritis following infection with enteropathogenic bacteria is usually a self-limiting disease that disappears after a few months without sequela. We describe two girls who developed carditis shortly after the onset of reactive arthritis due to infection with Salmonella enteritidis. The carditis presented with fatigue and arrhythmia and involved the aortic valve in both patients leading to definite aortic regurgitation in one. A similar pattern of cardiac involvement is found in other spondyloarthropathies, including Reiter's syndrome and ankylosing spondylitis. We conclude that Salmonella reactive arthritis may be complicated by carditis.

[Granulomatous endocarditis caused by streptococcus]. / Granulomatöse Endokarditis durch Streptokokken.

Two cases of granulomatous endocarditis are reported. The patients developed aortal endocarditis refractory to antibiotics. Therefore, aortal valve replacement was performed. In both cases, Streptococcus viridans was demonstrated in culture and bacterioscopically to be the cause of infection. Histological examination of the valves showed characteristic endocarditis with fibrinoid necrosis and histiocytic granulomas. Streptococci were found in the cytoplasm of macrophages. The possible causes of this special form of infectious endocarditis are discussed.

Intracardiac calcifications in a case of pseudohypoparathyroidism type Ia (PHP-Ia).

In a 10-year-old boy with pseudohypoparathyroidism type Ia (PHP-Ia) echocardiography detected calcifications within the ventricular septum. This is thought to be the first report of intracardiac calcifications in PHP. Echocardiography should be done routinely in all patients with this rare disorder.

[Secondary immunopathogenesis in myocarditis, diseases of the heart muscles and infarct-associated arrhythmia in childhood and adulthood]. / Sekundäre Immunopathogenese bei Myokarditis, Herzmuskelerkrankungen und infarktassoziierten Rhythmusstörungen im Kindes- und Erwachsenenalter.

In histologically proven or clinically diagnosed perimyocarditis in children and adults alterations in cellular and humoral effector mechanisms are demonstrable: OKIaI-positive B- or activated T-lymphocytes are increased in the peripheral blood, whereas natural killer cell activity is reduced. Antibodies are directed to the membranes of isolated human atrial myocytes and, to a lesser extent with lesser specificity, to endothelial cells and to the extracellular matrix. AMLAs are of diagnostic relevance if they belong to the IgM class, indicating a recent humoral immune stimulation and, if they fix complement, indicating a functional property which is complement associated lysis of target cells. Immunohistological studies demonstrate fixation of immunoglobulins to the autologous biopsy specimens, which are diagnostic only if they also belong to the IgM class and fix complement. In acute rhythm disturbances in the context of a recent "common cold", similar humoral immune reactions can be found in children, which are compatible with a secondary immunopathogenesis after viral illness involving the myocardium.

Non-invasive examination of pulmonary stenosis by transcutaneous Doppler technique.

Analysis of the transcutaneous Doppler velocity blood flow curve was performed in a 12 year old girl with pulmonary stenosis. The blood flow indices of the pulmonary artery were compared with those obtained in a control group.

Tachyarrhythmic syncopes in children with structurally normal hearts with and without QT-prolongation in the electrocardiogram.

Forty children with presumed ventricular tachyarrhythmic syncopes in the absence of structural heart disease were studied. Twenty-nine patients, one of whom was deaf, had a prolonged QT-interval in the resting electrocardiogram (Group 1); eleven patients had a normal QT-interval (Group 2). The median QTc-interval vas 0.51 s in Group 1 and 0.40 s in Group 2. Familial occurrence suggesting autosomal dominant inheritance was found in 21 of 28 normally hearing patients in Group 1 and in 2 of 11 patients in Group 2. Syncopes were definitely stress-induced in 22 patients in Group 1 and in all 11 patients in Group 2. Of 23 patients in Group 1 in whom an electrocardiogram was obtained during physical exercise, only one showed severe ventricular dysrhythmia. In contrast, all eleven patients in Group 2 developed severe ventricular dysrhythmia with exercise. Treatment with beta-blocking medication prevented further syncopes in 15 of 19 patients with several previous attacks in Group 1 and in 3 of 5 patients of Group 2. Four of the 29 patients in Group 1 died suddenly and one more remained apallic after an attack. Of the 11 patients in Group 2, four died suddenly and one retains severe cerebral damage after resuscitation from ventricular fibrillation. We conclude that, besides the group of patients with the long QT-syndrome, there may be a distinct group of patients with a consistently normal QT-interval and severe ventricular dysrhythmia with exercise. Patients of both groups are threatened by sudden death and are improved by treatment with beta-blocking medication.