First order magnetic transition in CeFe2_2 alloys: Phase-coexistence and metastability

First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped-CeFe$_2$ alloys is studied with micro-Hall probe technique. Clear visual evidence of magnetic phase-coexistence on micrometer scales and the evolution of this phase-coexistence as a function of temperature, magnetic field and time across the first order FM-AFM transition is presented. Such phase-coexistence and metastability arise as natural consequence of an intrinsic disorder-influenced first order transition. Generality of this phenomena involving other classes of materials is discussed.Comment: 11 pages of text and 3 figure

Physicochemical Properties of Irradiation Modified Starch Extrudates

Corn starch samples containing 0, 25, 50 and 70% amylose irradiated with -y -radiation dosages of 0 (native) , 5 , 10, 20 (containing 0, 2.5 or 5% potassium persulfate , hydrogen peroxide or eerie ammonium nitrate) or 30 kGy were extrusion cooked using a C. W. Brabender single-screw extruder at a barrel temperature of 140 °C, a screw speed of 140 rpm and 18% moisture content. Increasing irradiation dosages from 0 to 30 kGy gave consistently increased expansion ratios from 2.9 to 7.9 for 25% amylose starches and from 6.5 to 14.5 for 50% amylose starches, while the expansion ra tios consistently decreased from 6.0 to 2.1 for 0% amylose starches. The expansion ratios for 70% amylose starches remained more or less constant at 10 irrespective of irradiation dosage. Expansion ratios of all the 20 kGy irradiated starch samples treated with chemical agents, however, decreased to 5 or below. The patterns of bulk densities and expansion ratios of the products were generally similar. Increasing irradiation dosages caused darkening of the product color. The water solubility increased from \u3c l% for native starches to almost 100% for certain irradiated starches processed with chemical additives. Overall, increasing amylose contents of the starches appeared to be resistant to changes that otherwise occurred due to irradiation modifications and chemical treatments. Molecular weights and iodine binding capacities of starches were significantly reduced with irradiation dosages and chemical treatments

First order magneto-structural transition in functional magnetic materials: phase-coexistence and metastability

First order magneto-structural transition plays an important role in the functionality of various magnetic materials of current interest like manganese oxide systems showing colossal magnetoresistance, Gd5(Ge, Si)4 alloys showing giant magnetocaloric effects and magnetic shape memory alloys. The key features of this magneto-structural transition are phase-coexistence and metastability. This generality is highlighted with experimental results obtained in a particular class of materials. A generalized framework of disorder influenced first order phase transition is introduced to understand the interesting experimental results which have some bearing on the functionality of the concerned materials

Oxide_Oxide Ceramic Matrix Composite (CMC) Exhaust Mixer Development in the NASA Environmentally Responsible Aviation (ERA) Project

Rolls-Royce North American Technologies, Inc. (LibertyWorksLW) began considering the development of CMC exhaust forced mixers in 2008, as a means of obtaining reduced weight and hotter operating temperature capability, while minimizing shape distortion during operation, which would improve mixing efficiency and reduce fuel burn. Increased component durability, enhanced ability to fabricate complex-shaped components, and engine noise reduction are other potential advantages of CMC mixers (compared to metallic mixers). In 2010, NASA was pursuing the reduction of NOx emissions, fuel burn, and noise from turbine engines in Phase I of the Environmentally Responsible Aviation (ERA) Project. ERA subtasks, including those focused on CMC components, were formulated with the goal of maturing technology from proof of concept validation (TRL 3) to a systemsubsystem or prototype demonstration in a relevant environment (TRL 6). In April 2010, the NASA Glenn Research Center (GRC) and LibertyWorks jointly initiated a CMC Exhaust System Validation Program within the ERA Project, teaming on CMC exhaust mixer development for subsonic jet engines capable of operating with increased performance. Our initial focus was on designing, fabricating, and characterizing the thrust and acoustic performance of a roughly quarter-scale 16-lobe oxide oxide CMC mixer and tail cone along with a conventional low bypass exhaust nozzle. Support Services, LLC (Allendale, MI) and ATK COI Ceramics, Inc. (COIC, in San Diego, CA) supported the design of a subscale nozzle assembly that consisted of an oxide oxide CMC mixer and center body, with each component mounted on a metallic attachment ring. That design was based upon the operating conditions a mixer would experience in a turbofan engine. Validation of the aerodynamic and acoustic performance of the subscale mixer via testing and the achievement of TRL 4 encouraged the NASALWCOIC team to move to the next phase where a full scale CMC mixer sized for a RR AE3007 engine and a compatible attachment flange were designed, followed by CMC component fabrication by COIC, and vibration testing at GRC under conditions simulating the structural and dynamic environment encountered during engine operation. AFRL (WPAFB) supported this testing by performing 3D laser vibrometry to identify the mixer mode shapes and modal frequencies. The successful fabrication and testing of such a component has been achieved. The CMC mixer demonstrated good durability during vibration testing at room and elevated temperature (TRL5). This has cleared the article for a ground-based test on a Rolls-Royce AE3007 engine, where the performance and benefits of the component can be further assessed

Properties of Irradiated Starches

Properties of irradiated starches have been outlined in this review . \u27)\u27 -radiation generates free radicals on starch molecules which cause changes in starch properties . The intensity of free radicals is dependent upon starch moisture content , and temperature and duration of storage. Increasing dosages of -y-irradiation creates in creasing intensities of free radicals on carbohydrates. These free radicals are responsible for bringing about molecular changes and fragmentation of starch molec ules. Increasing \u27)\u27 -irradiation dosages cause an in crease in acidity , and decreases in viscosity and water solubility of starches. The granule structure remains visually undamaged at low dosages of irradiation, but may suffer severe damage at higher dosages (100 kGy) . Safety of irradiated foods continues to remain a subject of public concern . Studies have shown that irradiated foods are toxicologically and chemically safe for human consumption. Irradiation of starchy foods can be controlled to bring about required changes beneficial to the industry , and at the same time provide wholesome food to the consumers

Metastability and giant relaxation across the ferromagnetic to antiferromagnetic transition in Ce (Fe<SUB>0.96</SUB>Ru<SUB>0.04</SUB>)<SUB>2</SUB>

Experimental results of magnetization measurements of first-order ferromagnetic-antiferromagnetic transitions in Ce(Fe0.96Ru0.04)2 alloy are presented. The metastability of states in the transition region gives rise to large relaxation and lack of end-point-memory effect in the magnetization. Traditional phenomenological asymmetry between the extent of supercooling and superheating is observed in the temperature and magnetic field variation of the magnetization and is also confirmed in relaxation results. Nonuniform variation of the relaxation rate with magnetic field gives a clear picture of the nucleation and growth of phases

Signatures of phase separation across the disorder broadened first order ferromagnetic to antiferromagnetic transition in doped-CeFe<SUB>2</SUB> alloys

Experimental evidences of phase coexistence and metastability are presented over a substantial field-temperature regime across the ferromagnetic to antiferromagnetic transition in CeFe2 based alloys. The idea of phase separation due to the influence of quenched disorder on a first order transition is used to interpret the results. Certain thermomagnetic history effects raise additional questions concerning the kinetics of such phase transitions