Superconductivity in irradiated A-15 compounds at low fluences. I. Neutron-irradiated V3Si

The behavior of the superconducting transition temperature T _c of singlecrystal and polycrystalline V₃Si was investigated as a function of low-fluence neutron irradiation. It is found that the initial degradation of T _c is sample-dependent, some specimens showing no degradation in T _c up to a fluence of 2 × 10¹⁸ n/cm². This and many other earlier observations on low-fluence behavior are explained in terms of a recently proposed model of radiation damage in A-15 compounds.Work performed under the auspices of the U.S. Energy Research and Development Administration.     

Synthesis, kinetic observations and characteristics of polyarylene ether sulphones prepared via a potassium carbonate DMAC process

The classical route for the synthesis of this family of macromolecules is via nucleophilic aromatic substitution of 4,4′-dichlorodiphenyl sulphone with bisphenates using dimethylsulphoxide (DMSO) and aqueous sodium hydroxide. High molecular weight homopolymers can be synthesized in a relatively short time. However, hydrolytic side reactions can limit its scope for the synthesis of both homopolymers derived from insoluble bisphenates and for copolymers. An alternate route is discussed herein that uses potassium carbonate/dimethylacetamide as base and aprotic dipolar solvent, respectively, for the synthesis of several homopolymers and copolymers derived from various bisphenols. In this system, excess potassium carbonate, unlike aqueous caustic, does not prevent the synthesis of high molecular weight macromolecules. Investigations of the kinetics and mechanism of this process were conducted. These studies demonstrated that this route deviates from the relatively simple second order kinetics previously observed for the aqueous sodium hydroxide/DMSO system. This deviation has been rationalized as resulting from the partially heterogeneous nature of the potassium carbonate.     

Fatty acid metabolism in hypoxic rat liver

Fatty acid metabolism was investigated in adult male albino rats exposed to hypobaric hypoxia at 25,000 ft simulated altitude for 6 h at 32 degrees C. Oxidation and esterification of palmitic acid-1-14C and de novo lipogenesis from acetate-1-14C were studied. Palmitic acid-1-14C oxidation in liver slices was normal while acetoacetate formation was increased. In vivo esterification of palmitic acid-1-14C to form triglycerides was increased while formation of phosphatidylcholine and phosphatidylethanolamine was observed to decrease. Decreased incorporation into plasma phosphatidylcholine with unaltered total activity in plasma triglycerides was observed. The incorporation of acetate-1-14C was observed to remain unaltered in triglycerides and phospholipids of liver with a similar pattern in the plasma indicating unaltered de novo lipogenesis. There appears to be increased esterification of fatty acids with probably impaired release of triglycerides into plasma while fatty acid biosynthesis remains unaffected.     

Persistency of excitation for nonminimal models of systems having purely deterministic disturbances

All results to date on the question of persistency of excitation depend on the model being minimal. Thus the results do not apply to systems having purely deterministic disturbances since these automatically give rise to uncontrollable modes on the unil circle. This note presents new results on persistency of excitation applicable to nonminimal models of systems having purely deterministic disturbances.     

A three-dimensional approach to the electrolytic degradation of solid electrolytes

A semiquantitative three-dimensional analysis of the electrolytic degradation of solid electrolytes is presented. This analysis leads to critical current densities that are in accord with experimental observations in contrast with the two-dimensional models which lead to a discrepancy of three orders of magnitude. The effect of microstructure has also been incorporated into the analysis.     

The effect of impurities and strength level on hydrogen induced cracking in a low alloy turbine steel

The effect of impurities on the threshold stress intensity for cracking in H₂S (K{ISCC}) has been investigated at various yield strength levels for a low alloy steel. Results show that the effect of impurities on K_ISCC is a function of the yield strength level. At low yield strength levels the K_ISCC of the steel is lowered markedly due to additions of impurities. However, at higher yield strength levels the K_ISCC data for pure and impure steels converge to a single value. In addition, the effect of yield strength level on Xiscc is a function of the degree of temper embrittlement caused by impurity segregation. For small degrees of temper embrittlement, increasing the yield strength decreases the -Kiscc appreciably, while for large degrees of temper embrittlement,K _ISCC is relatively insensitive to the yield strength. At K_ISCCvalues below about 50 MPa Vm, the percentage of intergranular fracture in H₂S is found to be uniquely related to K_ISCC regardless of the yield strength-impurity combination by which a givenK _ISCC is obtained. Results of the study indicate that the K_ISCC OF steels is affected by impurities, yield strength and H2S both directly and indirectly via interactive mechanisms.     

Martensitic transformations in V3Ga and Nb3Al

It is shown by low-temperature heat capacity measurements using ac technique that martensitic transformation in small samples of V₃Ga and Nb₃A1 can be prevented by covering them nearly completely with copper plating.     

ON THE CONCEPT OF THE STEADY STATE IN CHEMICAL REACTOR ANALYSIS

The inlet and outlet streams of a chemical reactor may reach a steady state before the internal distributions of concentration, etc. have come to the steady state. Such a steady state, in which the reactor is viewed only as a system with certain inputs and outputs, may be called the black-box steady state (BBSS). The existence of a BBSS does not always imply that of a true SS, and the BBSS may be attained in a finite time even though the SS is only attained asymptotically. Indeed under some circumstances the BBSS can be achieved immediately upon start-up. Provided that the internal transients are not catastrophic, the practical, or operator's, concept of a steady state is really that of a BBSS.     

Compressive buckling analysis and design of stiffened flat plates with multilayered composite reinforcement

This paper describes an analysis and its application in design for compressive buckling of flat stiffened plates considered as an assemblage of linked orthotropic flat plate and beam elements. Plates can be multilayered, with possible coupling between bending and stretching. Structural lips and beads are idealized as beams. The plate and the beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Buckling loads are found as the lowest of all possible general and local failure modes. The mode shape is used to determine whether buckling is a local or general instability and is particularly useful to the designer in identifying the weak elements for redesign purposes. Typical design curves are presented for the initial buckling of a hat stiffened plate locally reinforced with boron fiber composite.