Microstructures and fracture toughness of directionally solidified Mo-ZrC eutectic composites

Microstructures and fracture toughness of arc-melted and directionally solidified Mo–ZrC eutectic composites were investigated in this study. Two kinds of directionally solidified composites were prepared by spot-melting and floating zone-melting. Microstructure of the arc-melted composite (AMC) consists of equiaxed eutectic colonies, in which ZrC particles are dispersed. The spot-melted composite (SMC) exhibits spheroidal colony structure, which is rather inhomogeneous in size and morphology. ZrC fibers in the eutectic colonies are aligned almost parallel to the growth direction. Well aligned, homogeneous columnar structure with thin ZrC fibers evolves in the floating zone-melted composite (FZC). Texture measurement by X-ray diffractometry revealed that the growth direction of Mo solid solution (Mo_SS) in FZC is preferentially 〈100〉, while that of SMC is scattered. Fracture toughness K_q evaluated by three point bending test using the single edge notched beam method is >13 MPa m^1/2 for AMC, 20 MPa m^1/2 for SMC and 9 MPa m^1/2 for FZC. Intergranular fracture along colony boundaries is often observed in AMC. In contrast, transgranular fracture is dominant in SMC and FZC, although significant gaps caused by intergranular fracture are occasionally observed in SEM micrographs of SMC. Fracture surface in FZC is wholly flat. Pull-out of ZrC occurs owing to Mo/ZrC interfacial debonding in intergranularly fractured regions of AMC and SMC.

Coarse elongated colonies in SMC and FZC induce transgranular fracture instead of intergranular fracture. Intergranular fracture and interfacial debonding in AMC and SMC causes frequent crack deflection accompanied by ligament formation and crack branching, which is responsible for the high fracture toughness of the composites. Preferred 〈100〉 growth of Mo_SS phase in FZC leads to brittle 〈100〉 cleavage fracture associated with low fracture toughness.     

Investigation and comparison between new satellite impact test results and NASA standard breakup model

This paper summarizes two new satellite impact tests conducted in order to investigate on the outcome of low- and hypervelocity impacts on two identical target satellites. The first experiment was performed at a low velocity of 1.5 km/s using a 40-g aluminum alloy sphere, whereas the second experiment was performed at a hypervelocity of 4.4 km/s using a 4-g aluminum alloy sphere, by a two-stage light gas gun. To date, approximately 1500 fragments from each impact test have been collected for detailed analysis. Each piece was analyzed based on the method used in the NASA standard breakup model 2000 revision. The detailed analysis will conclude (1) the similarity in mass distribution of fragments between low- and hypervelocity impacts encourages the development of a general-purpose mass-based distribution model applicable for a wide impact velocity range, and (2) the difference in area-to-mass ratio distribution between the impact experiments and the NASA standard breakup model suggests to describe the area-to-mass ratio by a bi-normal distribution.     

S19159, a modulator of neurite outgrowth produced by the ascomycete Preussia aemulans. II. Structure elucidation

A trend can be observed for multinational research-based drug companies shifting their resources away from Germany (and partly also from Europe) and expanding their preclinical and clinical drug research and development programmes and organizations in the USA. The main reasons, which are presently under discussion in Germany, are the image and public acceptance of clinical drug research, professionalism of clinical studies (i.e. availability of an adequate infrastructure), the process of ethics committees votes, the citation impact of publications, the legal obstacles, the implementation of Good Clinical Practice (GCP), the regulatory and institutional situation and the political environment. These problems have been recognised and appraised recently by the pharmaceutical industry, universities, scientific associations, and governmental institutions. Prerequisites to improve the basic conditions of clinical research in Germany to make it internationally competitive are proposed in this paper.     

Spontaneous regression of localized neuroblastoma detected by mass screening

PURPOSE: A retroperitoneal access is commonly used for open urological procedures. Since the introduction of the balloon dissecting technique by Gaur this anatomical route has also been used for laparoscopic surgery. We present our experience with retroperitoneoscopy in 200 cases. MATERIALS AND METHODS: From December 1992 to October 1997 a total of 200 retroperitoneoscopic procedures were performed in 197 patients 4 to 82 years old, comprising 78 nephrectomies, 50 renal cyst resections, 14 nephropexies, 11 ureterolyses, 8 retroperitoneal lymph node dissections, 8 renal biopsies, 6 adrenalectomies, 6 heminephrectomies, 6 pyeloplasties, 5 ureterolithotomies, 6 ureterocutaneostomies and 2 others. Of the patients 38 (19%) and 22 (11%) had undergone previous abdominal surgery, and kidney and ureter operations, respectively. Dissection of the retroperitoneal space was enabled by the use of a balloon catheter in 14, balloon trocar system in 93 and finger dissection technique in 93 cases. RESULTS: We classified 76 procedures (38%) as simple (renal biopsy, renal cyst resections, ureterocutaneostomy), 102 (51%) as difficult (adrenalectomy, nephrectomy, nephropexy) and 22 (11%) as very difficult (pyeloplasty, heminephrectomy, lymphadenectomy). There was a significant learning curve during the first 50 cases reflected by longer operating time, and higher complication, conversion to open surgery and open reintervention rates (14, 10 and 6%, respectively). In addition to the learning curve, mean operating time depended on the difficulty of the procedure, averaging 45 to 100 minutes for a simple, 95 to 185 for a difficult and 185 to 240 for a very difficult retroperitoneoscopy. In the last 50 cases the complication, conversion and reintervention rates (2, 4 and 2%, respectively) were acceptable for routine clinical application. CONCLUSIONS: After experience with more than 200 cases of retroperitoneoscopy the access technique has been significantly simplified. The procedure is standardized, safe and reproducible.     

A brimmed valved conduit in repair of fibrous skeleton abscess

Aortomitral common annular involvement, which is not uncommon in infective endocarditis, necessitates deliberate surgical procedures. To repair fibrous skeleton abscess accompanied with annuloaortic ectasia, we used a brimmed valved conduit. Tension-free reconstruction of the aortic root and aortomitral common annulus was easily performed with this method.     

Correlation between voltage holding capability and light emission in a 500 keV electrostatic accelerator utilized for fusion application

Voltage holding capability in a 500 keV electrostatic accelerator with large FRP insulators was examined without the beam acceleration. When high voltage was applied, the light with a broad peak at a wavelength of 420 nm was mostly emitted inside the accelerator even though breakdown did not occur. The voltage holding capability has a strong correlation with the light intensity. Stable voltage holding was realized under the conditions in which light emission was well suppressed.     

Phase field and room-temperature mechanical properties of the C15 laves phase in the Zr-Ta-Cr alloy system

The phase field of the C15 Laves phase in the Zr-Ta-Cr alloy system at 1273 K exhibited a continuous solid solution along the ZrCr₂-TaCr₂ pseudobinary line and also a broad off-stoichiometric range on the (Zr,Ta)-rich side. The defect structures in the C15 Laves phase were evaluated by lattice parameter and density measurements. The room-temperature fracture toughness was assessed by Vickers indentation testing. Alloying, off-stoichiometry, and the related defect structures were shown to be beneficial for improving the room-temperature deformability of the C15 Laves phase in the Zr-Ta-Cr alloy system. The results are discussed in terms of the constituent atomic sizes on the most closely packed planes in the C15 Laves phase where shear deformation takes place. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

Functional disabilities of disabled workers in vocational aid facilities and a social welfare factory

Detection of nucleic acid sequence at the ultrastructural level has allowed us to better understand the expression of genes in some fields of application in cell biology. In situ hybridization at the ultrastructural level can be carried out using three different methods: on vibratome sections before embedding in epoxy resin, on ultrathin frozen section, or on ultrathin section of tissue embedded in hydrophilic resin such as Lowicryl. Before starting the detection of nucleic acid sequences at the electron microscope level, the experimenter has to choose various parameters; the type of tissue fixation, the probe and its label, and the in situ hybridization method, depending on the sensitivity, the resolution and the ultrastructural preservation required. This review of technical aspects, by describing the different methods of ultrastructural in situ hybridization, will help the experimenter to optimize each step of the hybridization procedure.