Simulations of nanoscale Ni/Al multilayer foils with intermediate Ni2Al3 growth

Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit self-propagating exothermic reactions due to the high formation enthalpy of the intermetallic compounds. Most of the previous modelingapproaches on the reactions of this system rely on the use of mass diffusionwith a phenomenological derived diffusion coefficient representing single-phase (NiAl) growth, coupled with heat transport. We show that the reaction kinetics, temperatures, and thermal front width can be reproduced more satisfactorily with the sequential growth of Ni2Al3 followed by NiAl, utilizing independently obtained interdiffusivities. The computational domain was meshed with a dynamically generated bi-modal grid consisting of fine and coarse zones corresponding to rapid and slower reacting regions to improve computational efficiency. The PDEPE function in MATLAB was used as a basis for an alternating direction scheme. A modified parabolic growth law was employed to model intermetallic growth in the thickness direction. A multiphase enthalpy function was formulated to solve for temperatures after discrete phase growth and transformations at each time step. The results show that the Ni2Al3formation yields a preheating zone to facilitate the slower growth of NiAl. At bilayer thicknesses lower than 12 nm, the intermixing layer induces oscillating thermal fronts, sharply reducing the average velocities

The Impact Of Crystal Morphology On The Thermal Responses Of Ultrasonically-Excited Energetic Materials

The ability to detect explosive materials may be significantly enhanced with local increases in vapor pressure caused by an elevation of the materials\u27temperature. Recently, ultrasonic excitation has been shown to generate heat within plastic-bonded energetic materials. To investigate the impact of crystal morphology on this heating, samples of elastic binder are implanted with single ammonium perchlorate crystals of two distinct shape groups. Contact piezoelectric transducers are then used to excite the samples at ultrasonicfrequencies. The thermal responses of the crystals are recorded using infrared thermography, and the rate of heating is estimated. Surface temperature increases up to 15 °C are found to arise after 2 s of excitation, with much higher heating levels expected near the inclusions themselves as demonstrated by the chemical decomposition of some crystals under favorable excitation conditions. The rates of heat generation are compared to various crystal morphology features through 2D estimates of length scale, perimeter and irregularity. It is observed that crystals grown in the lab, featuring sharp geometric facets, exhibit a higher probability of significant heat generation than inclusions with more spherical shapes. However, no statistical link is found between the rates of heat generation and the crystal morphology in those samples that do generate significant heating, likely because variations in surface roughness cannot be entirely eliminated during experimentation. It is hoped that this study will lead to a better understanding of the nature of heat generation in energetic materialsfrom ultrasonic sources

Heat generation in an elastic binder system with embedded discrete energetic particles due to high-frequency, periodic mechanical excitation

High-frequency mechanical excitation can induce heating within energetic materials and may lead to advances in explosives detection and defeat. In order to examine the nature of this mechanically induced heating, samples of an elastic binder (Sylgard 184) were embedded with inert and energetic particles placed in a fixed spatial pattern and were subsequently excited with an ultrasonic transducer at discrete frequencies from 100 kHz to 20 MHz. The temperature and velocity responses of the sample surfaces suggest that heating due to frictional effects occurred near the particles at excitation frequencies near the transducer resonance of 215 kHz. An analytical solution involving a heat point source was used to estimate heating rates and temperatures at the particle locations in this frequency region. Heating located near the sample surface at frequencies near and above 1 MHz was attributed to viscoelastic effects related to the surface motion of the samples. At elevated excitation parameters near the transducer resonance frequency, embedded particles of ammonium perchlorate and cyclotetramethylene-tetranitramine were driven to chemical decomposition

The Influence of the effect of solute on the thermodynamic driving force on grain refinement of Al alloys

Grain refinement is known to be strongly affected by the solute in cast alloys. Addition of some solute can reduce grain size considerably while others have a limited effect. This is usually attributed to the constitutional supercooling which is quantified by the growth restriction factor, Q. However, one factor that has not been considered is whether different solutes have differing effects on the thermodynamic driving force for solidification. This paper reveals that addition of solute reduces the driving force for solidification for a given undercooling, and that for a particular Q value, it is reduced more substantially when adding eutectic-forming solutes than peritectic-forming elements. Therefore, compared with the eutectic-forming solutes, addition of peritectic-forming solutes into Al alloys not only possesses a higher initial nucleation rate resulted from the larger thermodynamic driving force for solidification, but also promotes nucleation within the constitutionally supercooled zone during growth. As subsequent nucleation can occur at smaller constitutional supercoolings for peritectic-forming elements, a smaller grain size is thus produced. The very small constitutional supercooling required to trigger subsequent nucleation in alloys containing Ti is considered as a major contributor to its extraordinary grain refining efficiency in cast Al alloys even without the deliberate addition of inoculants.The Australian Research Council (ARC DP10955737)

The Inhibitor of Growth Protein 5 (ING5) Depends on INCA1 as a Co-Factor for Its Antiproliferative Effects

The proteins of the Inhibitor of Growth (ING) family are involved in multiple cellular functions such as cell cycle regulation, apoptosis, and chromatin remodeling. For ING5, its actual role in growth suppression and the necessary partners are not known. In a yeast-two-hybrid approach with human bone marrow derived cDNA, we identified ING5 as well as several other proteins as interaction partners of Inhibitor of cyclin A1 (INCA1) that we previously characterized as a novel interaction partner of cyclin A1/CDK2. ING5 expression in leukemic AML blasts was severely reduced compared to normal bone marrow. In line, ING5 inhibited bone marrow colony formation upon retroviral transduction. However, Inca1−/− bone marrow colony formation was not suppressed by ING5. In murine embryonic fibroblast (MEF) cells from Inca1+/+ and Inca1−/− mice, overexpression of ING5 suppressed cell proliferation only in the presence of INCA1, while ING5 had no effect in Inca1−/− MEFs. ING5 overexpression induced a delay in S-phase progression, which required INCA1. Finally, ING5 overexpression enhanced Fas-induced apoptosis in Inca1+/+ MEFs, while Inca1−/− MEFs were protected from Fas antibody-induced apoptosis. Taken together, these results indicate that ING5 is a growth suppressor with suppressed expression in AML whose functions depend on its interaction with INCA1

Nucleation of the electroactive γ phase and enhancement of the optical transparency in low filler content poly(vinylidene)/clay nanocomposites

Poly(vinylidene fluoride), PVDF, based nanocomposites with different clays structures have been processed by solvent casting and melt crystallisation. Depending on the melting temperature of the polymer, the nanocomposite recrystalises in the electroactive or non electroactive β-phase of the polymer. This fact is related to the thermal behaviour of the clay. For montmorillonite clay, the full crystallisation of the electroactiveγ-phase occurs for clay contents lower than 0.5 wt%, allowing the nanocomposites to maintain the mechanical properties of the polymer matrix. The electroactivity of the material has been proven by measuring the piezoelectric d33 response of the material. The obtained value of d33 is -7 pC/N, lower than in β-PVDF obtained by mechanical stretching, but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. Finally, it is demonstrated that the nucleation of the β-phase can be also obtained in other clays, such as in kaolinite and laponite.Fundação para a Ciência e a Tecnologia (FCT) - NANO/NMed-SD/0156/2007, PTDC/CTM/69316/2006, PTDC/CTM-NAN/112574/2009, SFRH/BD/62507/2009.FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETECOST Action MP1003, the ‘European Scientific Network for Artificial Muscles’ (ESNAM)

Total and corrected antioxidant capacity in hemodialyzed patients

BACKGROUND: Oxidative stress may play a critical role in the vascular disease of end stage renal failure and hemodialysis patients. Studies, analyzing either discrete analytes and antioxidant substances, or the integrated total antioxidant activity of human plasma during hemodialysis, give contradictory results. METHODS: Recently, we have introduced a new automated method for the determination of Total Antioxidant Capacity (TAC) of human plasma. We have serially measured TAC and corrected TAC (cTAC: after subtraction of the interactions due to endogenous uric acid, bilirubin and albumin) in 10 patients before the onset of the dialysis session, 10 min, 30 min, 1 h, 2 h and 3 h into the procedure and after completion of the session. RESULTS: Our results indicate that TAC decreases, reaching minimum levels at 2 h. However, corrected TAC increases with t(1/2 )of about 30 min. We then repeated the measurements in 65 patients undergoing dialysis with different filters (36 patients with ethylene vinyl alcohol copolymer resin filter -Eval-, 23 patients with two polysulfone filters -10 with F6 and 13 with PSN140-, and 6 patients with hemophan filters). Three specimens were collected (0, 30, 240 min). The results of this second group confirm our initial results, while no significant difference was observed using either filter. CONCLUSIONS: Our results are discussed under the point of view of possible mechanisms of modification of endogenous antioxidants, and the interaction of lipid- and water-soluble antioxidants