Dehydroxylation of Perlite and Vermiculite: Impact on Improving the Knock-Out Properties of Moulding and Core Sand with an Inorganic Binder

The article presents the results of research aimed at examining the type of swelling material introduced into moulding or core sand to improve their knock-out properties. Tests on Slovak perlite ore (three grain sizes), Hungarian perlite ore and ground vermiculite (South Africa) were carried out. For this purpose, thermal and structural analyses (FTIR—Fourier Transform Infrared Spectroscopy), a chemical composition test (XRF-X-Ray Fluorescence), phase analysis (XRD—X-Ray Diffraction), and scanning electron microscopy (SEM—Scanning Electron Microscope) as well as final strength tests of moulding sands with the addition of perlite ore and vermiculite were carried out. The results of thermal studies were related to IR (Infrared Spectroscopy) spectra and XRD diffractograms. It has been shown that the water content in the pearlite ore is almost three times lower than in vermiculite, but the process of its removal is different. Moreover, the chemical composition of the perlite ore, in particular the alkali content and its grain size, may influence its structure. The phenomena of expansion (perlite) and peeling (vermiculite) have a positive effect on the reduction of the final sand strength and eliminate technological inconveniences (poor knocking out) that significantly limit the wide use of moulding sands with inorganic binders.     

The Influence of Mechanical Alloying and Plastic Consolidation on the Resistance to Arc Erosion of the Ag–Re Composite Contact Material

The article presents the influence of mechanical alloying and plastic consolidation on the resistance to arc erosion of the composite Ag–Re material against the selected contact materials. The following composites were selected for the tests: Ag90Re10, Ag95Re5, Ag99Re1 (bulk chemical composition). Ag–Re materials were made using two methods. In the first, the materials were obtained by mixing powders, pressing, sintering, extrusion, drawing, and die forging, whereas, in the second, the process of mechanical alloying was additionally used. The widely available Ag(SnO₂)10 and AgNi10 contact materials were used as reference materials. The reference AgNi10 material was made by powder metallurgy in the process of mixing, pressing, sintering, extrusion, drawing, and die forging, while the Ag(SnO₂)10 composite was obtained by spraying AgSniBi alloy with water, and then the powder was pressed, oxidized internally, sintered, extruded into wire, and drawn and die forged. The tests of electric arc resistance were carried out for loads with direct current (DC) and alternating current (AC). For alternating current (I = 60 A, U = 230 V), 15,000 switching cycles were made, while, for constant current 50,000 (I = 10 A, U = 550 V). A positive effect of the mechanical alloying process and the addition of a small amount of rhenium (1% by mass) on the spark erosion properties of the Ag–Re contact material was found. When DC current of 10 A was used, AgRe1 composite was found to be more resistant than commonly used contact materials (AgNi10 and Ag(SnO₂)10).     

Fly-Ash-Based Geopolymers Reinforced by Melamine Fibers

This paper presents the results of research on geopolymer composites based on fly ash with the addition of melamine fibers in amounts of 0.5%, 1% and 2% by weight and, for comparison, without the addition of fibers. The melamine fibers used in the tests retain their melamine resin properties by 100% and are characterized by excellent acoustic and thermal insulation as well as excellent filtration. In addition, these fibers are nonflammable, resistant to chemicals, resistant to UV radiation, characterized by high temperature resistance and, most importantly, do not show thermal-related shrinking, melting and dripping. This paper presents the results of density measurements, compressive and flexural strength as well as the results of the measurement of thermal radiation changes in samples subjected to a temperature of 600 °C. The results indicate that melamine fibers can be used as geopolymer reinforcement. The best result was achieved for 0.5% by weight amount of reinforcement, approximately 53 MPa, compared to 41 MPa for a pure matrix. In the case of flexural strength, the best results were obtained for the samples made of unreinforced geopolymer and samples with the addition of 0.5% by weight of melamine fibers, which were characterized by bending strength values above 9 MPa, amounting to 10.7 MPa and 9.3 MPa, respectively. The thermal radiation measurements and fire-jet test did not confirm the increasing thermal and fire resistance of the composites reinforced by melamine fiber.     

Influence of Modified Epoxy Resins on Peroxide Curing,Mechanical Properties and Adhesion of SBR,NBR and XNBR to Silver Wires—Part II: Application of Carboxy-Containing Peroxy Oligomer (CPO)

This research was aimed at verifying the effect of carboxy-containing peroxy oligomer (CPO) addition on the possibility of rubber crosslinking and a subsequent adhesion of the modified rubber to silver wires. Three commonly industrially used rubbers were selected for the study: styrene–butadiene rubber (SBR), acrylonitrile–butadiene rubber (NBR) and carboxylated acrylonitrile–butadiene rubber (XNBR), together with carboxy-containing peroxy oligomer (CPO). An improvement in the adhesion of rubbers to silver wires was observed when applying the oligomeric peroxide with functional groups, with no deterioration of mechanical properties of the vulcanizates. Crosslinking synergy between dicumyl peroxide (DCP) and the modifier could hardly be observed. Nevertheless, the studies demonstrated, that to a small extent, even the CPO itself can crosslink NBR and especially XNBR, resulting in a material of notable elasticity and adhesion to silver wires.     

Comparison of the Ottawa Surgical Competency Operating Room Evaluation (O-SCORE) to a Single-Item Performance Score

Construct: We compared a single-item performance score with the Ottawa Surgical Competency Operating Room Evaluation (O-SCORE) for their ability in assessing surgical competency. Background: Surgical programs are adopting competency-based frameworks. The adoption of these frameworks for assessment requires tools that produce accurate and valid assessments of knowledge and technical performance. An assessment tool that is quick to complete could improve feasibility, reduce delays, and result in a higher volume of assessments of learners. Previous work demonstrated that the 9-item O-SCORE can produce valid results; the goal of this study was to determine if a single-item performance rating (Is candidate competent to independently complete procedure: yes or no) completed at a separate viewing would correlate to the O-SCORE, thus increasing feasibility of procedural competence assessment. Approach: Nineteen residents and 2 staff orthopedic surgeons from the University of Ottawa volunteered for a 2-part OSCE-style station including a written questionnaire and videotaped simulated open reduction and internal fixation midshaft radius fracture. Each performance was rated independently by 3 orthopedic surgeons using a single-item performance score (Time 1). The performances were assessed again 6?weeks later by the 3 raters using the O-SCORE (Time 2). Correlation between the single-item performance score and the O-SCORE were evaluated. Results: Three orthopedic surgeons completed 21 ratings each resulting in 63 orthopedic ratings. There was a high level of correlation and agreement between the single-item performance score at Time 1 and Time 2 (κ correlation =0.72–1.00; p?<?.001; percentage agreement =90%–100%). The reliability of the O-SCORE at Time 2 with three raters was 0.83 and the internal consistency was 0.89. There was a tendency for each rater to assign more yes responses to the more senior trainees. Conclusions: A single-item performance score correlated highly with the O-SCORE in an orthopedic setting. A single-item score could be used to supplement a multi-item score with similar results in orthopedics. There is still benefit in completing multi-item scores such as the O-SCORE evaluations to guide specific areas of improvement and direct feedback.     

Influence of insertion-deletion polymorphism of the angiotensin converting enzyme gene on left ventricular hypertrophy in patients with aortic stenosis--differences in men and women

The role of different parameters (including genetic factors) on the timing and extend of left ventricle hypertrophy in patients with aortic stenosis is not defined. In our study we analyze the influence of clinical, echocardiographic parameters and I/D polymorphism of the angiotensin converting enzyme gene on the left ventricle hypertrophy (left ventricle mass index) in this group of patients. The study was done with the group of 302 pts with aortic stenosis--120 women and 182 men; mean age 58 +/- 11 yrs. Stepwise (backward) regression was used to assess the influence of the analyzed parameters (age, gender, history of hypertension, EF, MGA, presence of significant coronary artery disease and I/D ACE polymorphism) on the LVH in the all pts and in the women and the men separately. In the whole group the LVMI depends on EF (t = -6.5; p = 0.0001--higher LVMI in lower EF), MGA (t = 3.9; p = 0.0001--higher LVMI in higher MGA) and gender (t = 2.8; p = 0.005--higher LVMI in men). In women LVMI was related with EF (t = -3.6; p = 0.001--higher LVMI in lower EF), age (t = 2.9; p = 0.004--higher LVMI in older pts) and MGA (t = 2.5; p = 0.013--higher LVMI in higher MGA). In men the LVMI depends on EF (t = -4.8; p = 0.0001--higher LVMI in lower EF) and MGA (t = 1.98; p = 0.049--higher LVMI in higher MGA). Significant relationship between LVMI and results of I/D ACE polymorphism was observed both in women and men. I/D polymorphism relationship with LVMI was divergent in these 2 groups--association of higher LVMI with lack of DD type of polymorphism in women and presence of DD polymorphism in men. CONCLUSIONS: 1. Left ventricle hypertrophy in pts aortic stenosis is higher in men than in women. 2. In women left ventricle hypertrophy is related with ejection fraction, maximal aortic gradient, age and I/D ACE polymorphism; in men it is related to EF, MGA and I/D ACE polymorphism. 3. The influence of I/D ACE polymorphism on the left ventricle hypertrophy is divergent in women and men--in women related to the lack of DD polymorphism, in men related to the presence of DD polymorphism.     

Human LTC-IC can be maintained for at least 5 weeks in vitro when interleukin-3 and a single chemokine are combined with O-sulfated heparan sulfates: requirement for optimal binding interactions of heparan sulfate with early-acting cytokines and matrix proteins

We have shown that stromal O-sulfated heparan sulfate glycosaminoglycans (O-S-GAGs) regulate primitive human hematopoietic progenitor cell (HPC) growth and differentiation by colocalizing heparin-binding cytokines and matrix proteins with HPC in stem cell "niches" in the marrow microenvironment. We now show that long-term culture-initiating cells (LTC-IC) are maintained for 5 weeks in the absence of stroma when O-S-GAGs are added to IL-3 and either MIP-1alpha or PF4 (LTC-IC maintenance without GAGs, 32 +/- 2%; with GAGs, 95 +/- 7%; P <.001). When cultured with 5 additional cytokines, O-S-GAGs, IL-3, and MIP-1alpha, LTC-IC expanded 2- to 4-fold at 2 weeks, and 92 +/- 8% LTC-IC were maintained at 5 weeks. Similar results were seen when PF4 replaced MIP-1alpha. Although O-S-GAG omission did not affect 2-week expansion, only 20% LTC-IC were maintained for 5 weeks. When O-S-heparin was replaced by completely desulfated-, N-sulfated (O-desulfated), or unmodified heparins, LTC-IC maintenance at week 5 was not better than with cytokines alone. Unmodified- and O-S-heparin, but not desulfated- or N-sulfated heparin, bound to MIP-1alpha, IL-3, PF4, VEGF, thrombospondin, and fibronectin. However, the affinity of heparin for thrombospondin and PF4, and the association and dissociation rates of heparin for PF4, were higher than those of O-S-heparin. We conclude that (i) although cytokines may suffice to induce early expansion, adult human LTC-IC maintenance for longer than 1 month requires O-S-GAGs, and (ii) HPC support may depend not only on the ability of GAGs to bind proteins, but also on optimal affinity and kinetics of interactions that affect presentation of proteins in a biologically active manner to progenitors. (Blood. 2000;95:147-155)     

Role ofl-arginine, a substrate for nitric oxide-synthase, in gastroprotection and ulcer healing

Nitric oxide (NO) synthesized froml-arginine interacts with prostaglandins (PG) and sensory neuropeptides in the regulation of mucosal integrity, but the role ofl-arginine, a substrate for NO-synthase, in gastroprotection and healing of chronic gastric ulcers has been little studied. In this study we compared the effects of intragastric (i.g.) and systemic (i.v.) administration ofl-arginine ord-arginine on gastric secretion and acute gastric lesions provoked in rats by i.g. application of 100% ethanol, acidified aspirin (ASA), or the exposure to 3.5h of water immersion and restraint stress (WRS). In addition, the effects ofl-arginine on ulcer healing and the formation of new vessels (angiogenesis) were determined, using monoclonal antibody (MAb E-9).l-arginine (10–200 mg/kg i.g.) failed to significantly affect gastric secretion but dose-dependently reduced the gastric lesions induced by 100% ethanol, ASA, and WRS, the doses inhibiting 50% of these lesions being 65, 94, and 72 mg/kg, respectively. This protection was accompanied by a significant rise in the gastric blood flow (GBF), whereasl-arginine given i.v. failed to affect the ethanol-lesions and the GBF.d-arginine or the NO-related amino acids—l-glutamine,l-citrulline, orl-ornithine—failed to significantly influence these lesions. Suppression of the generation of mucosal PG by indomethacin or capsaicin-denervation attenuated the protection and hyperemia induced byl-arginine. The inhibition of constitutive NO synthase byl-NNA had no significant effect on the protection afforded byl-arginine, but reduced the gastric hyperemia accompanying this protection.l-arginine (150 mg/kg per day, i.g.) accelerated the ulcer healing and increased GBF at the ulcer margin, and angiogenesis, whereas treatment with L-NNA had an opposite effect.l-arginine added to N^G-nitro-l-arginine (L-NNA) restored the ulcer healing, hyperemia, and angiogenesis. We conclude that: (1) the protective activity ofl-arginine involves gastric hyperemia mediated by NO and a mild irritant effect due to enhanced generation of endogenous PG, and (2) the ulcer healing properties ofl-arginine depend upon its hyperemic and angiogenic actions, possibly involving NO.     

A decrease of enlarged left atrium following cardioversion of atrial fibrillation predicts the long-term maintenance of sinus rhythm

BACKGROUND: Although increased left atrial size (LA) has been long regarded as one of the factors negatively influencing the long-term maintenance of sinus rhythm (SR) following cardioversion (CV) of atrial fibrillation (AF), some reports suggested that CV might be effective also in patients with large LA.Aim. We sought to determine the role of LA enlargement in long-term SR maintenance after CV of persistent AF. METHODS: 104 consecutive patients (33 females, 71 males, mean age 60.4+/-7.4 years) were assigned to SR restoration and maintenance with serial antiarrhythmic drugs. Transthoracic echocardiographic (TTE) variables were recorded prior to CV. Generalised additive logistic regression was used to investigate the impact of LA enlargement on the long-term SR maintenance. RESULTS: SR was present in 63.5% of patients after one year of follow-up. Increased LA area >28 cm (RR 1.72; 1.09-2.71; p<0.02) and increased fractional shortening values in ranges between 26-40% (1.2; 1.01-1.44; p<0.05) were significantly associated with SR maintenance after one year. In order to determine the influence of the LA diameter on the probability of SR maintenance, we analysed mean LA(ar) values prior to and after CV. Patients with large LA(ar) (28 cm(2)) presented a significant decrease of LA size (31.45+/-3.07 cm(2) vs 28.94+/-3.81 cm(2); p<0.008) during the first 30 days after SR restoration. In the group of patients with LA(ar) 28 cm(2) we noted decrease in LA size by 2.57+/-3.2 cm(2), whereas in patients with a smaller LA volume this decrease was significantly lower, being 0.47+/-2.9 cm(2) (p<0.004). CONCLUSIONS: LA enlargement does not preclude a favourable outcome after CV of AF. The decrease in LA area occurring during 30 days following CV favours long term SR maintenance.