MAGNETOCALORIC RESPONSE OF NON-STOICHIOMETRIC Ni2MnGa ALLOYS AND THE INFLUENCE OF CRYSTALLOGRAPHIC TEXTURE.

Currently, there is significant interest in magnetocaloric materials for solid state refrigeration. In this work, polycrystalline Heusler alloys belonging to the Ni2+xMn1-xGa family, with x between 0.08 and 0.24, were evaluated for the purpose of finding composition(s) with an enhanced magnetocaloric effect (MCE) close to room temperature. Differential scanning calorimetry (DSC) was successfully used to screen alloy composition for simultaneous magnetic and structural phase transformations; this coupling needed for a giant MCE. The alloy with x = 0.16 showed an excellent match of transformation temperatures and exhibited the highest magnetic entropy change, ΔSM, in the as-annealed state. Furthermore, the MCE increased by up to 84 % with a 2 Tesla (T) field change when the samples were thermally cycled through the martensite to austenite transformation temperature while held under a constant mechanical load. The highest ΔSM measured for our x = 0.16 alloy for a 2 T magnetic field change was -18 J/kg-K. Texture measurements suggest that preferential orientation of martensite variants contributed to the enhanced MCE in the stress-assisted thermally cycled state.

Extremely high strength and work hardening ability in a metastable high entropy alloy.

Design of multi-phase high entropy alloys uses metastability of phases to tune the strain accommodation by favoring transformation and/or twinning during deformation. Inspired by this, here we present Si containing dual phase Fe42Mn28Co10Cr15Si5 high entropy alloy (DP-5Si-HEA) exhibiting very high strength (1.15 GPa) and work hardening (WH) ability. The addition of Si in DP-5Si-HEA decreased the stability of f.c.c. (γ) matrix thereby promoting pronounced transformation induced plastic deformation in both as-cast and grain refined DP-5Si-HEAs. Higher yet sustained WH ability in fine grained DP-5Si-HEA is associated with the uniform strain partitioning among the metastable γ phase and resultant h.c.p. (ε) phase thereby resulting in total elongation of 12%. Hence, design of dual phase HEAs for improved strength and work hardenability can be attained by tuning the metastability of γ matrix through proper choice of alloy chemistry from the abundant compositional space of HEAs.

Enhanced strength and ductility in a friction stir processing engineered dual phase high entropy alloy.

The potential of high-entropy alloys (HEAs) to exhibit an extraordinary combination of properties by shifting the compositional regime from the corners towards the centers of phase diagrams has led to worldwide attention by material scientists. Here we present a strong and ductile non-equiatomic HEA obtained after friction stir processing (FSP). A transformation-induced plasticity (TRIP) assisted HEA with composition Fe50Mn30Co10Cr10 (at.%) was severely deformed by FSP and evaluated for its microstructure-mechanical property relationship. The FSP-engineered microstructure of the TRIP HEA exhibited a substantially smaller grain size, and optimized fractions of face-centered cubic (f.c.c., γ) and hexagonal close-packed (h.c.p., ε) phases, as compared to the as-homogenized reference material. This results in synergistic strengthening via TRIP, grain boundary strengthening, and effective strain partitioning between the γ and ε phases during deformation, thus leading to enhanced strength and ductility of the TRIP-assisted dual-phase HEA engineered via FSP.

Thermal stability of hemoglobin and myoglobin: effect of spin states.

The thermal stability of various methemoglobin and metmyoglobin derivatives at different ligand concentrations and pH were studied by the method of differential scanning calorimetry. Comparing to water as a ligand, cyanide and azide are most effective in protecting the protein; fluoride stabilizes the protein slightly whereas imidazole and thiocyanate have little effect. Assuming thermal denaturation can be described by an activated two-state process, the activation parameters of all the derivatives were determined. We have also found that the stability of hemoglobin and myoglobin does not correlate with the iron atom spin state but depends instead on steric interactions with the ligands. On the reasonable assumption that structure and stability are related, this implies a definite dependence of structure on steric interactions.

Kinetics of cold-induced denaturation of metmyoglobin.

Using a slow temperature-jump spectrophotometer, we have studied the kinetics of cold-induced denaturation of metmyoglobin between 0 degrees C and 20 degrees C at acidic pH. The time-scale of the transition is slow and is of the order of minutes. The results are consistent with the transition's involving a total of three states, native (N), transient intermediate (I) and denatured (D), which are converted from one to the other in that order.

Kinetics of the pretransition of synthetic phospholipids. A calorimetric study.

The pretransition in aqueous dispersions of two synthetic phospholipids (dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine) has been examined in detail by differential scanning calorimetry. The transition from the high-temperature state (state above pretransition) to the low-temperature state (state below pretransition) is complex and appears to occur via some metastable states. In contrast, the kinetics of the transition from the low- to the high-temperature state is consistent with an activated two-state model. The observed hysteresis is shown to arise mainly from the kinetic nature of the pretransition.

Ultrasonic absorption in myoglobin and other globular proteins.

The ultrasonic absorption of myoglobin has been measured by the resonance and pulse-echo techniques as a function of pH. The absorption at a given frequency can be separated into pH-dependent and pH-independent contributions. Like other proteins, two peaks at pH 3 and 11.5 are observed which can be accounted for a proton-transfer reactions of the side-groups. In addition, the absorption undergoes a large increase within a small range of 0.2 pH unit at pH around 4, when denaturation of myoglobin occurs, indicating that the absorption is sensitive to the overall protein conformation. To elucidate the origin of the pH-independent component, the absorptions of several other globular proteins at neutral pH are also measured. The absorptions of these proteins exhibit a linear correlation with their isothermal compressibilities, suggesting that the pH-independent component is related to volume fluctuations of protein molecules. The activation energy of 4 kcal/mol found for this relaxation is consistent with such an interpretation.

Resonance Raman studies of methemoglobin derivatives at room temperature and 77 K.

Raman spectra in preresonance with the Soret absorption band are reported for the following methemoglobin derivatives: cyanide, cyanate, thiocyanate, hydroxy-, azide, and fluoride methemoglobin at 285 K and 77 K. For the mixed-spin derivatives, Raman intensity is observed to shift from the high-spin marker band (approx. 1480 cm-1) to the low-spin marker band (approx. 1505 cm-1) upon cooling to 77 K. In addition, Raman spectra of cyanate methemoglobin were taken as a function of temperature, and the log of the intensity ratio I1480/I1505 was found to be a linear function of 1/T, indicating a thermally activated process. We interpret these results as observations of temperature-induced spin transitions. In the case of cyanate methemoglobin we find the enthalpy and entropy differences between the high-spin and low-spin states to be deltaH = 600 +/- 40 cal x mol-1 and deltaS = 4.7 +/- 0.7 cal x mol-1 x K-1. The high-spin to low-spin ratio for cyanate methemoglobin determined by our experiment disagrees with the value reported for magnetic susceptibility measurements.

The thermodynamics of myoglobin stability. Effects of axial ligand.

The reversible thermal denaturation of four metmyoglobin derivatives, aquomet, cyanomet, azidomet and fluoromet in both the alkaline pH and acidic pH region, has been examined by optical spectrophotometry. The data are analyzed in terms of a two-state model to extract the thermodynamic parameters delta G, delta H, delta S and delta Cp characterizing the transition. The results are consistent with Brandts' phenomenological model of protein denaturation. Among the derivatives examined, cyanomet, azidomet and fluoromet are about 3 kcal/mol, 2 kcal/mol and 0.2 kcal/mol, respectively, more stable than aquometmyoglobin. The observed differences are found to be inconsistent with the hypothesis that the stability is mainly governed by the spin state of the iron atom. In addition, the enthalpic and entropic contributions in delta G are extracted and the differences in delta G for the various derivatives are found to arise from minor changes in delta H and T delta S. Assuming the final denaturated state to be universal, these changes reflect the effect of ligands on the conformational energy of the native protein.

Adiabatic compressibility of myoglobin. Effect of axial ligand and denaturation.

An ultrasonic technique has been employed to study the adiabatic compressibility of three metmyoglobin derivatives (aquomet-, fluoromet- and azidometmyoglobin) at neutral pH, and aquometmyoglobin as a function of pH in the frequency range of 1-10 MHz at 20 degrees C. No difference was observed in the adiabatic compressibility of the various derivatives. This indicates that the binding of different axial ligands to myoglobin does not affect significantly the conformational fluctuations of the protein. The finding is consistent with the results of the hydrogen exchange rate experiment, indicating that both types of measurements are useful for the study of protein dynamics. Upon acid-induced denaturation, the adiabatic compressibility of myoglobin drops from 5.3 X 10(-12) cm2/dyn to 0.5 X 10(-12) cm2/dyn. Plausible reasons for such a decrease are discussed.

Kinetics of electron transfer between cytochrome c and iron hexacyanides. Evidence for two electron-transfer sites.

The electron-transfer reaction between ferrocytochrome c and ferricyanide has been studied by the method of photoexcitation. The observed transfer rate shows saturation behaviour at high ferricyanide concentration. Data analysis indicates that there are two binding sites of vastly different affinities at which electron transfer occurs. The binding constant for the strong binding site decreases from 1600 M-1 to 80 M-1 as the ionic strength increases from 15 mM to 140 mM. At 20 degrees C, the intramolecular electron-transfer rate for this site is 4.65 X 10(4) s-1, which gives an electron-transfer distance of approx. 9.7 A according to Hopfield's model.

Electron transfer between cytochrome c and metal hexacyanide complexes. Effect of thermodynamic driving force on the electron transfer rate.

The electron transfer reactions between ferrocytochrome c and three isomorphic hexacyanide complexes, [Fe(CN)6]3-, [Os(CN)6]3- and [Ru(CN)6]3-, have been studied using the method of photoexcitation. The transfer rates for [Os(CN)6]3- and [Ru(CN)6]3- are, respectively, about 45- and 200-times higher than that of [Fe(CN)6]3-. A reorganization energy of approx. 0.8 eV was found for the cytochrome c-hexacyanide system when the data were analyzed according to the theory of Marcus.

Extraluminal air. Diagnosis and significance.

This article reviews the more common causes of extraluminal gas collections and their manifestations both on plain films and other imaging studies when appropriate.

Chyloperitoneum: CT diagnosis.

We describe a patient with ovarian cancer in whom computed tomography revealed a fat-fluid level within ascites, indicating chyloperitoneum. The significance of this finding is discussed, and a mechanism underlying the unusual radiological appearance is suggested.

Mortality after acute renal failure: models for prognostic stratification and risk adjustment.

To adjust adequately for comorbidity and severity of illness in quality improvement efforts and prospective clinical trials, predictors of death after acute renal failure (ARF) must be accurately identified. Most epidemiological studies of ARF in the critically ill have been based at single centers, or have examined exposures at single time points using discrete outcomes (e.g., in-hospital mortality). We analyzed data from the Program to Improve Care in Acute Renal Disease (PICARD), a multi-center observational study of ARF. We determined correlates of mortality in 618 patients with ARF in intensive care units using three distinct analytic approaches. The predictive power of models using information obtained on the day of ARF diagnosis was extremely low. At the time of consultation, advanced age, oliguria, hepatic failure, respiratory failure, sepsis, and thrombocytopenia were associated with mortality. Upon initiation of dialysis for ARF, advanced age, hepatic failure, respiratory failure, sepsis, and thrombocytopenia were associated with mortality; higher blood urea nitrogen and lower serum creatinine were also associated with mortality in logistic regression models. Models incorporating time-varying covariates enhanced predictive power by reducing misclassification and incorporating day-to-day changes in extra-renal organ system failure and the provision of dialysis during the course of ARF. Using data from the PICARD multi-center cohort study of ARF in critically ill patients, we developed several predictive models for prognostic stratification and risk-adjustment. By incorporating exposures over time, the discriminatory power of predictive models in ARF can be significantly improved.

Spin equilibrium and quaternary structure change in hemoglobin A. Experiments on a quantitative probe of the stereochemical mechanism of hemoglobin cooperativity.

The molecular mechanism of hemoglobin cooperativity was studied kinetically by flash photolysis on mixed-state hemoglobins which consist of three ferrous carboxy subunits and one hybrid ferric subunit including fluoromet, azidomet, cyanatomet, and thiocyanatomet. The effects of conformational transitions on the hybrid subunit were detected by kinetic absorption spectroscopy after the CO was fully photodissociated from the binding sites by a large pulse of light from a tunable dye laser. The hemoglobin conformational transition rate was observed to depend on its state of ligation. At 22 degrees C, pH 7, and 0.1 M phosphate, the deoxy R yields T conformational change rate is 4 x 10(4)s-1. The rate decreases to 1.4 x 10(4)s-1 for singly ligated hemoglobin. The R yields T conformation change alters the energy separation between high- and low-spin states for azidomet, cyanatomet, and thiocyanatomet subunits by about 700, 300, and 300 cal/mol, respectively. There are two possible implications of this result: (1) the iron atom spin state is not the only major factor in the determination of its position with respect to the heme plane or (2) the change with conformation of the protein force exerted by the proximal histidine on the iron atom (for an iron to heme-plane displacement of less than 0.3 A) is less than 50% of that expected from simple models in which this motion is responsible for cooperativity.

Multiple leiomyosarcoma of the transverse colon: report of a case and discussion.

A case is described of a patient found, at operation, to have two infiltrating leiomyosarcomas in the transverse colon. Study indicated them to be two separate primary lesions. Literature on leiomyosarcoma is reviewed.

Small intestine amyloidosis producing a stippled punctate mucosal pattern: radiological-pathological correlation.

A case of small intestinal amyloidosis that has a myriad punctate mucosal relief pattern of minute filling defects and barium flecks is presented with pathological correlation. Amyloidosis is added to the differential diagnosis of this radiographic small bowel appearance.

Air in the fissure for the ligamentum teres: new sign of intraperitoneal air on plain radiographs.

In each of four patients in whom an acute spontaneous pneumoperitoneum developed, a vertically directed area of hyperlucency in the right upper quadrant was seen on radiographs of the abdomen obtained with the patient supine. This finding, which appeared in the absence of other characteristic signs of free air on plain radiographs and which, to the authors' knowledge, has not been previously recognized, represented intraperitoneal gas confined to the fissure for the ligamentum teres (FLT). The location of the hyperlucent area was confirmed with computed tomography or laparotomy in each patient. The distinctive configuration of air in the FLT is a subtle but reliable indicator of pneumoperitoneum.