Interstitial defects stability in FeCr alloys vs Cr concentration

Finding adequate materials to withstand the demanding conditions in the future fusion and fission reactors is a real challenge in the development of these technologies. Structural materials need to sustain high irradiation doses and temperatures that will change the microstructure over time. A better understanding of the changes produced by the irradiation will allow for a better choice of materials, ensuring a safer and reliable future power plants. High-Cr ferritic/martensitic steels head the list of structural materials due to their high resistance to swelling and corrosion. However, it is well known that these alloys present a problem of embrittlement, which could be caused by the presence of defects created by irradiation as these defects act as obstacles for dislocation motion. Therefore, the mechanical response of these materials will depend on the type of defects created during irradiation. In this work, we address a study of the effect Cr concentration has on single interstitial defect formation energies in FeCr alloys.

Floating zone stability

The present state of de preparation of an experiment on floating liquid zones to be performed in the first Spacelab flight is presented. In this experiment,a liquid bridge is to be placed between two parallel coaxial disks (in the Fluid Physics Module)and subjected to very precise disturbances in order to check the theoretical predictions about its stability limits and behavior under mechanical inputs: stretching of the zone, filling or removing the liquid,axial vibration, rotation, disalignment, etc. Several aspects of the research are introduced:1) Relevance of the study. 2) Theoretical predictions of the liquid behavior regarding the floating-zone stability limits and the expected response to vibrational and rotational disturbances. 3) Ground support experiments using the Plateau technique or the small scale simulation. 4) Instrumental aspects of the experimentation: the Fluid Physics Module utilization and post-flight data analysis.5)Research program for future flights.

Improvement of compatibility and stability on polyethylene-modified bitumen by use of an aromatic extra as compatibilizer.

Bitumen modification by polyethylene addition usually improves the mechanical properties of the binder and, therefore, the behavior in service of the bituminous mix: thermal susceptibility and rutting can be diminished, whilst the resistance to low temperature cracking may increase. To achieve this improvement it is necessary a good compatibility between the base bitumen and the polyethylene. Low compatibility between bitumen and polyethylene can lead to phase separation: the polymer- asphalt incompatibility translates into a deterioration of ultimate properties. The object of this research project was to determine if these problems can be diminished by using certain compatibilizer agents, e.g. an aromatic extract from the oil refinery. Compatibility and stability of the polyethylene modified bitumen were studied using conventional test methods and dynamic shear reometer (DSR). Blends of bitumen and polyethylene were prepared with neat bitumen (PMB) or bitumen with compatibilizer as component of the binder (PMBC) and then compared. The experimental results show that “colloid instability index”(IC) is a parameter that can be used to control the compatibility between bitumen and polyethylene. From polyethylene point of view, one of the parameters that govern is the “melt flow index” (MFI). Experimental results show that PMBC formulated with low IC bitumen and hi gh MFI lineal polyethylene can be considered as stable binder.

Thermal and mechanical properties of recycled poly(Lactic acid)

Biodegradable polymers have experienced increased attention in recent years because of their wide range of applications in biomedical, packaging and agriculture fields. PLA, poly(lactic acid), is a linear aliphatic biodegradable thermoplastic polyester, with good mechanical properties, thermal stability, processability and low environmental impact, widely used as an alternative to conventional polymers. PLA products can be recycled after use either by remelting and reprocessing the material, or by hydrolysis to basic lactic acid [1]. The object of this communication is the study of the possible variation in physical properties induced by sub sequent reprocessing cycles of PLA.

Altered stability of pulmonary surfactant in SP-C-deficient mice

The surfactant protein C (SP-C) gene encodes an extremely hydrophobic, 4-kDa peptide produced by alveolar epithelial cells in the lung. To discern the role of SP-C in lung function, SP-C-deficient (−/−) mice were produced. The SP-C (−/−) mice were viable at birth and grew normally to adulthood without apparent pulmonary abnormalities. SP-C mRNA was not detected in the lungs of SP-C (−/−) mice, nor was mature SP-C protein detected by Western blot of alveolar lavage from SP-C (−/−) mice. The levels of the other surfactant proteins (A, B, D) in alveolar lavage were comparable to those in wild-type mice. Surfactant pool sizes, surfactant synthesis, and lung morphology were similar in SP-C (−/−) and SP-C (+/+) mice. Lamellar bodies were present in SP-C (−/−) type II cells, and tubular myelin was present in the alveolar lumen. Lung mechanics studies demonstrated abnormalities in lung hysteresivity (a term used to reflect the mechanical coupling between energy dissipative forces and tissue-elastic properties) at low, positive-end, expiratory pressures. The stability of captive bubbles with surfactant from the SP-C (−/−) mice was decreased significantly, indicating that SP-C plays a role in the stabilization of surfactant at low lung volumes, a condition that may accompany respiratory distress syndrome in infants and adults.

Mechanical behavior in living cells consistent with the tensegrity model

Alternative models of cell mechanics depict the living cell as a simple mechanical continuum, porous filament gel, tensed cortical membrane, or tensegrity network that maintains a stabilizing prestress through incorporation of discrete structural elements that bear compression. Real-time microscopic analysis of cells containing GFP-labeled microtubules and associated mitochondria revealed that living cells behave like discrete structures composed of an interconnected network of actin microfilaments and microtubules when mechanical stresses are applied to cell surface integrin receptors. Quantitation of cell tractional forces and cellular prestress by using traction force microscopy confirmed that microtubules bear compression and are responsible for a significant portion of the cytoskeletal prestress that determines cell shape stability under conditions in which myosin light chain phosphorylation and intracellular calcium remained unchanged. Quantitative measurements of both static and dynamic mechanical behaviors in cells also were consistent with specific a priori predictions of the tensegrity model. These findings suggest that tensegrity represents a unified model of cell mechanics that may help to explain how mechanical behaviors emerge through collective interactions among different cytoskeletal filaments and extracellular adhesions in living cells.

Mechanical, thermal and colorimetric properties of LLDPE coloured with a blue nanopigment and conventional blue pigments

Purpose – This research deals with a new kind of nanopigment, obtained from the combination of organic dyes and layered nanoclays, that the authors call nanoclay-colorant pigment (NCP). Whilst they have already been employed in inks and coatings, to date these nanopigments have not been used as pigments for polymers. The existing lack of knowledge surrounding them must be redressed in order to bridge the gap between current academic studies and commercial exploitation. Therefore, the main purpose of this paper is to examine the hitherto unknown aspects of the NCP, which relate specifically to their applicability as a new type of colorant for polymers. Design/methodology/approach – A blue NCP has been prepared at the laboratory according to the patented method of synthesis (patent WO0104216), using methylene blue and montmorillonite nanoclay. It has then been applied to a thermoplastic polymer (linear low-density polyethylene – LLDPE) to obtain a coloured sample. Furthermore, samples with the same polymer but using conventional blue colorants have been prepared under the same processing conditions. The mechanical, thermal and colorimetric properties of these materials have been compared. Findings – The thermal stability of the sample coloured with NCP is reduced to some extent, while the mechanical strength is slightly increased. Moreover, this sample has better colour performance than the conventionally pigmented samples. Originality/value – In this paper, a blue NCP has been synthesised and successfully employed with polyethylene and the obtained sample shows better colour performance than polyethylene with conventional pigments.

Core stability exercise in chronic low back pain

Exercise is commonly used in the management of chronic musculoskeletal conditions, including chronic low back pain (CLBP). The focus of exercise is varied and may include parameters ranging from strength and endurance training, to specific training of muscle coordination and control. The assumption underpinning these approaches is that improved neuromuscular function will restore or augment the control and support of the spine and pelvis. In a biomechanical model of CLBP, which assumes that pain recurrence is caused by repeated mechanical irritation of pain sensitive structures [1], it is proposed that this improved control and stability would reduce mechanical irritation and lead to pain relief [1]. Although this model provides explanation for the chronicity of LBP, perpetuation of pain is more complex, and contemporary neuroscience holds the view that chronic pain is mediated by a range of changes including both peripheral (eg, peripheral sensitization) and central neuroplastic changes [2]. Although this does not exclude the role of improved control of the lumbar spine and pelvis in management of CLBP, particularly when there is peripheral sensitization, it highlights the need to look beyond outdated simplistic models. One factor that this information highlights is that the refinement of control and coordination may be more important than simple strength and endurance training for the trunk muscles. The objective of this article is to discuss the rationale for core stability exercise in the management of CLBP, to consider critical factors for its implementation, and to review evidence for efficacy of the approach.

Microstructure and mechanical properties of high pressure die cast magnesium alloy AE42 with 1% strontium

The addition of 1 wt-%Sr to AE42 results in an improvement in the tensile strength of the alloy at elevated temperatures of 150 and 175degreesC and an improvement in the constant load creep properties at 175degreesC. The improved elevated temperature tensile and creep strength of the alloy can be attributed to the presence of a strontium-containing phase in the microstructure of the alloy along with an increase in the stability of the microstructure of the alloy at high temperatures. (C) 2004 W. S. Maney Son Ltd.

Robust stability of sequential multi-input multi-output quantitative feedback theory designs

This paper re-examines the stability of multi-input multi-output (MIMO) control systems designed using sequential MIMO quantitative feedback theory (QFT). In order to establish the results, recursive design equations for the SISO equivalent plants employed in a sequential MIMO QFT design are established. The equations apply to sequential MIMO QFT designs in both the direct plant domain, which employs the elements of plant in the design, and the inverse plant domain, which employs the elements of the plant inverse in the design. Stability theorems that employ necessary and sufficient conditions for robust closed-loop internal stability are developed for sequential MIMO QFT designs in both domains. The theorems and design equations facilitate less conservative designs and improved design transparency.

Formation and mechanical properties of Mg65Cu25Er10 and Mg65Cu15Ag10Er10 bulk amorphous alloys

Mg65Cu25Er10 and Mg65Cu15Ag10Er10 bulk amorphous alloys were produced by a copper mould casting method. The alloys have high glass-forming ability and good thermal stability. The maximum diameter of glass formation (D-c), glass transition temperature (T-g), crystallization onset temperature (T-x), temperature interval of the supercooled region (Delta T-x), melting temperature (T-m), liquidus temperature (T-1) as well as heats of crystallization (Delta H-x) and melting (Delta H-m) are reported for these alloys. Both alloys exhibit high hardness and high strength at room temperature. (c) 2005 Elsevier B.V. All rights reserved.

On stability in nonsequential MIMO QFT designs

This paper reexamines the stability of uncertain closed-loop systems resulting from the nonsequential (NS) MIMO QFT design methodology. By combining the effect of satisfying both the robust stability and robust performance specifications in a NS MIMO QFT design, a proof for the stability of the uncertain closed-loop system is derived. The stability theorem proves that, subject to the satisfaction of a critical necessary and sufficient condition, the original NS MIMO QFT design methodology will provide a robustly stable closed-loop system. This necessary and sufficient condition provides a useful existence test for a successful NS MIMO QFT design. The results expose the salient features of the NS MIMO QFT design methodology. Two 2 x 2 MIMO design examples are presented to illustrate the key features of the stability, theorem.

Reversible active switching of the mechanical properties of a peptide film at a fluid-fluid interface

Designer peptides have recently been developed as building blocks for novel self-assembled materials with stimuli-responsive properties. To date, such materials have been based on self-assembly in bulk aqueous solution or at solid-fluid interfaces. We have designed a 21-residue peptide, AM1, as a stimuli-responsive surfactant that switches molecular architectures at a fluid-fluid interface in response to changes in bulk aqueous solution composition. In the presence of divalent zinc at neutral pH, the peptide forms a mechanically strong 'film state'. In the absence of metal ions or at acid pH, the peptide adsorbs to form a mobile 'detergent state'. The two interfacial states can be actively and reversibly switched. Switching between the two states by a change in pH or the addition of a chelating agent leads to rapid emulsion coalescence or foam collapse. This work introduces a new class of surfactants that offer an environmentally friendly approach to control the stability of interfaces in foams, emulsions and fluid-fluid interfaces more generally.

EFFECT OF FORMULATION ON PHYSICO-CHEMICAL PROPERTIES, WATER STATUS AND STABILITY OF PASTA, TOMATO SAUCE AND READY TO EAT PASTA MEALS

Ready to eat pasta meals are an important segment of convenience food, but these products are subjected to significant changes in physico-chemical properties during storage, which reduce their acceptability at the time of consumption. A deep understanding of the properties of the single phases, their dependence upon formulation, and the changes they undergo during storage is very important to intelligently intervene on products properties to improve their quality at the time of consumer’s consumption. This work has focused on the effect of formulation on physico-chemical properties of pasta and tomato sauce with a special focus on mechanical/rheological attributes and water status. Variable considered in pasta formulation were gluten, glycerol and moisture content and their effect was studied in both freshly cooked or shelf-stable cooked pasta. The effect of multiple hydrocolloids (at different levels) was considered in the case of tomato sauce. In the case of pasta, it was found that water content was indeed a very important variable in defying pasta mechanical properties and water status. Higher moisture contents in pasta resulted in softer samples and reduced the changes in physico-chemical parameters during storage. Glycerol was found to favor water uptake and to soften the pasta matrix, acting as plasticizer and increasing molecular mobility. The addition of gluten hardened pasta but did not affect the water status. The combination of higher amount of gluten (15%, g gluten / 100 g product) with higher moisture content (59-65%, g water / 100 g product) were found to minimize the physico-chemical changes occurring in RTE pasta meals during storage, improving quality at longer storage times. Hydrocolloids added into tomato sauce modulated its mechanical attributes and water status in very different manner, depending on hydrocolloid type and concentration. This may allow to produce tomato sauce for different applications and that are expected to have different performance if placed in contact with pasta in a RTE meal. Future work should include an investigation of how the interaction between the two phases (pasta and sauce) can be modulated and controlled by controlling the properties of the single phases with the goal of obtaining highly acceptable products also at longer storage times.

Stability studies on pencillin derivatives

Current analytical assay methods for ampicillin sodium and cloxacillin sodium are discussed and compared, High Performance Liquid Chromatography (H.P.L.C.) being chosen as the most accurate, specific and precise. New H.P.L.C. methods for the analysis of benzathine cloxacillin; benzathine penicillin V; procaine penicillin injection B.P.; benethamine penicillin injection; fortified B.P.C.; benzathine penicillin injection; benzathine penicillin injection, fortified B.P.C.; benzathine penicillin suspnsion; ampicillin syrups and penicillin syrups are described. Mechanical or chemical damage to column packings is often associated with H.P.L.C. analysis. One type, that of channel formation, is investigated. The high linear velocity of solvent and solvent pulsing during the pumping cycle were found to be the cause of this damage. The applicability of nonisotherrnal kinetic experiments to penicillin V preparations, including formulated paediatric syrups, is evaluated. A new type of nonisotherrnal analysis, based on slope estimation and using a 64K Random Access Memory (R.A.M.) microcomputer is described. The name of the program written for this analysis is NONISO. The distribution of active penicillin in granules for reconstitution into ampicillin and penicillin V syrups, and its effect on the stability of the reconstituted products, are investigated. Changing the diluent used to reconstitue the syrups was found to affect the stability of the product. Dissolution and stability of benzathine cloxacillin at pH2, pH6 and pH9 is described, with proposed dissolution mechanisms and kinetic analysis to support these mechanisms. Benzathine and cloxacillin were found to react in solution at pH9, producing an insoluble amide.