The molecular mechanism for destabilization of foams by organic ions

The effect of tetraalkylammonium ions on the destabilization of foam has been studied by measuring the half-life of foam (τ_1/2), area/molecule at the air/water interface, surface viscosity and critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS). The area/molecule of SDS in organic salt solutions, calculated from the Gibbs isotherm, increases as the size of organic ion increases, and surface viscosity of the film decreases with the size of organic ions. The interaction of tetraalkylammonium ions with SDS decreases the CMC of the solution, and hence the concentration of SDS monomers decreases. The CMC of SDS decreases with the increase in the size and concentration of organic ions. The decrease in the CMC, increase in the area/molecule of SDS at the air/water interface and the decrease in surface viscosity by tetraalkylammonium ions all work to decrease the foam stability. The results indicate that the change in intermolecular distance between surfactant molecules in the adsorbed film by organic ions can significantly influence the surface viscosity and foam stability. The foam destabilizing efficiency of tetra-alkylammonium ions was superior or equivalent to that of tributyl phosphate and 2-ethyl hexanol, which are used in many antifoaming formulations.     

Selecting high-temperature structural intermetallic compounds: The engineering approach

While there are nearly 300 high-melting-temperature intermetallic compounds, numerous factors limit the commercial viability of these materials for structural applications. Once the desirability of a material’s crystal structure has been determined, the engineer must then focus on the compound’s oxidation and corrosion resistance, its cost and any associated environmental hazards that may diminish its practical value. The final engineering limitations are imposed by process capabilities, which must be improved if high-temperature intermetallics are to one day emerge from the laboratory.     

The formation and persistence of various aluminum oxy-hydroxy-sulfate solid phases under different experimental conditions

The nature and type of interlayered Al formed in Wyoming bentonite clay in the presence of Cl and SO₄ anions is discussed. The ion activity product (Al) (OH)³, the exchange characteristics and solid phases formed in Cl and SO₄ systems were quite different. The cation exchange capacity (C.E.C.) of the Wyoming bentonite clay was permanently reduced in the Cl system when the aluminum precipitated was less than 800 meq./100 g clay. In the SO₄ system, however, such permanent reduction of C.E.C. did not occur irrespective of the amount of Al precipitated. The aluminum hydroxy sulfate solid phase formed in the presence or in the absence of Wyoming bentonite clay is metastable with respect to gibbsite. However, this aluminum hydroxy sulfate solid phase is stable with respect to the aluminum interlayered Wyoming bentonite formed in the presence of Cl when the precipitated Al is less than 800 meq./100 g of Wyoming bentonite. This information has been employed in removing the interlayered aluminum from Wyoming bentonite by changing the chemical environment of the system which resulted in the regaining of the blocked cation exchange capacity.     

Directional solidification of lead-copper immiscible alloys in a cyclic gravity environment

Hypermonotectic copper-lead alloys were directionally solidified at unit gravity on earth and also in the cyclic gravitational environment attainable during flight of NASA's KC-135 aircraft. In both cases macrosegregation developed that consisted of an initial lead-rich phase above which an aligned composite structure of apparent monotectic composition grew. Differences within these regions are examined, and the suitability of the KC-135 environment for directional solidification of monotectic alloys is discussed. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25–229, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee.     

Effect of modifier concentration on the fracture behaviour of rubber-modified PMMA

Izod fracture surfaces of blends of PMMA with various amounts of a rubber modifier were studied using scanning electron microscopy. Attention was focused on modes of crack initiation and propagation and on the role of the modifier in the fracture process. It was found that the impact strength of this class of materials increased monotonically with an increase in modifier concentration, at least up to 40 wt% modifier. Unmodified PMMA was studied to provide a basis for understanding the morphological features on the fracture surfaces of the rubber-modified blends. It was confirmed that PMMA fractures through the formation and rupture of crazes. This phenomenon was also found to occur in blends containing 10 wt% modifier. However, blends with 20 wt% modifier crazed only in the later stages of the fracture process, when the crack speed had exceeded some critical value. No evidence of crazing was found in blends with 30 and 40 wt% modifier loadings, although extensive plastic deformation was observed on the fracture surfaces.     

Preoperative evaluation of the chemosensitivity of breast cancer by means of double phase 99mTc-MIBI scintimammography

The chemosensitivity of breast cancer is important for its management, but it is difficult to evaluate preoperatively. Tc-99m hexakis-2-methoxyisobutylisonitrile (MIBI) scintimammography has been reported to indicate the expression of P-glycoprotein, which is one factor concerned with multidrug resistance. We developed a chemosensitivity assay by using surgical specimens to investigate whether 99mTc-MIBI scintimammography findings before the operation are related to chemosensitivity according to our assay. Fifteen patients with primary breast cancer were enrolled into the study. Early and delayed images were obtained at 10 and 120 minutes after intravenous injection of 99mTc-MIBI, respectively. Regions of interest were placed on the tumors and the contralateral healthy breasts in each patient to estimate 99mTc-MIBI uptake in the tumor, and retention indices were then calculated to assess the washout of 99mTc-MIBI. Chemosensitivity assay was performed by incubating surgical specimens with anticancer agents such as doxorubicin, epirubicin, pinorubicin, mitomycin C, cisplatin and 5-fluorouracil. 99mTc-MIBI washout on scintimammography was successfully related to inhibition ratios on chemosensitivity tests when compared with 99mTc-MIBI uptake by the tumor. In particular, high correlation coefficients were obtained between the retention index of 99mTc-MIBI and the inhibition ratios of doxorubicin (r = 0.75), epirubicin (r = 0.60) and pinorubicin (r = 0.62), but poor correlation was found for mitomycin C (r = 0.44) and cisplatin (r = 0.31). Our results indicate that the retention index of 99mTc-MIBI is closely correlated to chemosensitivity to anthracyclines, suggesting that double-phase scintimammography allows preoperative prediction of chemosensitivity of breast cancer.     

Exophthalmos and iatrogenic Cushing's syndrome

A 38-year-old physician presented with a 9-month history of progressive self-administration of oral prednisone < or = 160 mg per day for Addison's disease. Examination demonstrated typical Cushingoid features and bilateral proptosis with elevated intraocular pressure. Computed tomography disclosed increased intraorbital adipose tissue. We hypothesize that the increased intraorbital adipose deposition was due to the differential binding of glucocorticoids to adipose tissue receptors and an enhancement of lipoprotein lipase activity. We conclude that the findings in this case may be related to glucocorticoid-induced changes in the ocular and periorbital structures. Cushing's syndrome should be considered in the differential diagnosis of acquired exophthalmos and elevated intraocular pressure and findings of increased orbital fat on orbital imaging.     

Fuzzy logic techniques in multineuron studies

The following topics are discussed: parallel analyses; digital spike representation; stochastic spike representation; neural-fuzzy connection; fuzzy spike representation; artificial neural network (ANN) model; functional lesioning technique; multi-unit data; fuzzy spike trains; ANN performance; network analyses; effective connectivity