Selective Laser Melting of Ti-6Al-4V Alloy: Correlation Between Processing Parameters, Microstructure and Corrosion Properties

Additive Manufacturing technology has continually advanced, allowing microstructure and property optimization. In recent years, several studies have been carried out with the aim of understanding mechanisms of formation and evolution of the microstructure and, consequently, their influence on mechanical properties. However, correlations between microstructure and corrosion properties are not completely understood, making more systematic investigations necessary. In this work, samples of the Ti-6Al-4V alloy were produced by combining different laser powers and scanning speeds in order to generate different energy density values (VED) with subsequent microstructures and properties. The samples were characterized by optical and scanning electron microscopy, hardness and relative density. Complementarily, corrosion tests were carried out. For the entire set of parameters used, the processed samples showed the formation of acicular martensite α´, followed by different levels of porosity depending on the applied energy density. VED proved to be an important control parameter, and the best combinations of hardness and corrosion resistance were obtained for the parameter ratio that generated energy densities greater than 100 J/mm3

A proposed measurement of the ß asymmetry in neutron decay with the Los Alamos Ultra-Cold Neutron Source

This article reviews the status of an experiment to study the neutron spin-electron angular correlation with the Los Alamos Ultra-Cold Neutron (UCN) source. The experiment will generate UCNs from a novel solid deuterium, spallation source, and polarize them in a solenoid magnetic field. The experiment spectrometer will consist of a neutron decay region in a solenoid magnetic field combined with several different detector possibilities. An electron beam and a magnetic spectrometer will provide a precise, absolute calibration for these detectors. An A-correlation measurement with a relative precision of 0.2% is expected by the end of 2002

Search for Λ6^6_\LambdaH hypernucleus by the 6^6Li(π−,K+)(\pi^-,K^+) reaction at pπ−p_{\pi^-} = 1.2 GeV/cc

We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_{\Lambda}$H, by the $^6$Li($\pi^-,K^+$) reaction at $p_{\pi^-}$ =1.2 GeV/$c$. The obtained missing mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the $^6_{\Lambda}$H hypernucleus neither below nor above the $^4_{\Lambda}$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_{\Lambda}$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.Comment: 6 pages, 5 figures, published versio

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging

Hydrodynamic cavitation is useful in many processing applications, for example, in chemical reactors, water treatment and biochemical engineering. An important type of hydrodynamic cavitation that occurs in a Venturi tube is vortex cavitation known to cause luminescence whose intensity is closely related to the size and number of cavitation events. However, the mechanistic origins of bubbles constituting vortex cavitation remains unclear, although it has been concluded that the pressure fields generated by the cavitation collapse strongly depends on the bubble geometry. The common view is that vortex cavitation consists of numerous small spherical bubbles. In the present paper, aspects of vortex cavitation arising in a Venturi tube were visualized using high-speed X-ray imaging at SPring-8 and European XFEL. It was discovered that vortex cavitation in a Venturi tube consisted of angulated rather than spherical bubbles. The tangential velocity of the surface of vortex cavitation was assessed considering the Rankine vortex model

Characterization of the L-Lactate Dehydrogenase from Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a Gram-negative opportunistic pathogen and the proposed causative agent of localized aggressive periodontitis. A. actinomycetemcomitans is found exclusively in the mammalian oral cavity in the space between the gums and the teeth known as the gingival crevice. Many bacterial species reside in this environment where competition for carbon is high. A. actinomycetemcomitans utilizes a unique carbon resource partitioning system whereby the presence of L-lactate inhibits uptake of glucose, thus allowing preferential catabolism of L-lactate. Although the mechanism for this process is not fully elucidated, we previously demonstrated that high levels of intracellular pyruvate are critical for L-lactate preference. As the first step in L-lactate catabolism is conversion of L-lactate to pyruvate by lactate dehydrogenase, we proposed a model in which the A. actinomycetemcomitans L-lactate dehydrogenase, unlike homologous enzymes, is not feedback inhibited by pyruvate. This lack of feedback inhibition allows intracellular pyruvate to rise to levels sufficient to inhibit glucose uptake in other bacteria. In the present study, the A. actinomycetemcomitans L-lactate dehydrogenase was purified and shown to convert L-lactate, but not D-lactate, to pyruvate with a Km of approximately 150 µM. Inhibition studies reveal that pyruvate is a poor inhibitor of L-lactate dehydrogenase activity, providing mechanistic insight into L-lactate preference in A. actinomycetemcomitans

A hybrid method of laparoscopic-assisted open liver resection through a short upper midline laparotomy can be applied for all types of hepatectomies

Background Although hepatectomy procedures should be designed to provide both curability and safety, minimal invasiveness also should be pursued. Methods We analyzed the data related to our method for laparoscopy-assisted open resections (hybrid method) through a short upper midline incision for various types of hepatectomies. Of 215 hepatectomies performed at Nagasaki University Hospital between November 2009 and June 2012, 102 hepatectomies were performed using hybrid methods. Results A hybrid method was applicable for right trisectionectomy in 1, right hemihepatectomy in 32, left hemihepatectomy in 29, right posterior sectionectomy in 7, right anterior sectionectomy in 1, left lateral sectionectomy in 2, and segmentectomy in 7 patients, and for a minor liver resection in 35 patients (12 combined resections). The median duration of surgery was 366.5 min (range 149-709) min, and the median duration of the laparoscopic procedure was 32 min (range 18-77) min. The median blood loss was 645 g (range 50-5,370) g. Twelve patients (12 %) developed postoperative complications, including bile leakage in three patients, wound infections in two patients, ileus in two patients, and portal venous thrombus, persistent hyperbilirubinemia, incisional hernia, local liver infarction each in one patient. There were no perioperative deaths. Conclusions Our method of hybrid hepatectomy through a short upper midline incision is considered to be applicable for all types of hepatectomy and is a reasonable approach with no abdominal muscle disruption, which provides safe management of the hepatic vein and parenchymal resection even for patients with bilobular disease

Human Fibroblast Sheet Promotes Human Pancreatic Islet Survival and Function In Vitro

In previous work, we engineered functional cell sheets using bone marrow-derived mesenchymal stem cells (BM-MSCs) to promote islet graft survival. In the present study, we hypothesized that a cell sheet using dermal fibroblasts could be an alternative to MSCs, and then we aimed to evaluate the effects of this cell sheet on the functional viability of human islets. Fibroblast sheets were fabricated using temperature-responsive culture dishes. Human islets were seeded onto fibroblast sheets. The efficacy of the fibroblast sheets was evaluated by dividing islets into three groups: the islets-alone group, the coculture with fibroblasts group, and the islet culture on fibroblast sheet group. The ultrastructure of the islets cultured on each fibroblast sheet was examined by electron microscopy. The fibroblast sheet expression of fibronectin (as a component of the extracellular matrix) was quantified by Western blotting. After 3 days of culture, islet viabilities were 70.2 ± 9.8%, 87.4 ± 5.8%, and 88.6 ± 4.5%, and survival rates were 60.3 ± 6.8%, 65.3 ± 3.0%, and 75.8 ± 5.6%, respectively. Insulin secretions in response to high-glucose stimulation were 5.1 ± 1.6, 9.4 ± 3.8, and 23.5 ± 12.4 μIU/islet, and interleukin-6 (IL-6) secretions were 3.0 ± 0.7, 5.1 ± 1.2, and 7.3 ± 1.0 ng/day, respectively. Islets were found to incorporate into the fibroblast sheets while maintaining a three-dimensional structure and well-preserved extracellular matrix. The fibroblast sheets exhibited a higher expression of fibronectin compared to fibroblasts alone. In conclusion, human dermal fibroblast sheets fabricated by tissue-engineering techniques could provide an optimal substrate for human islets, as a source of cytokines and extracellular matrix