Roughness-Induced Crack Closure: An Explanation for Microstructurally Sensitive Fatigue Crack Growth

The concept of roughness-induced crack closure is utilized to explain the role of prior austenite grain size and pearlite interlamellar spacing on near-threshold fatigue crack propagation in fully pearlitic eutectoid steel tested at low and high stress ratio in lab air and purified helium. It is shown that at low load ratios, near-threshold growth rates are significantly reduced for coarse-grained microstructures, compared to fine-grained at constant yield strength, due to roughness-induced crack closure. Using roughness-profile microscopy, it was found that fracture surface roughness near threshold scaled with grain size and inversely with yield strength, macroscopic roughnesses at threshold being considerably larger than the conventionally calculated cyclic crack tip opening displacement. Auger analysis of near-threshold corrosion products showed it to be iron oxide; the oxide thickness was seen to be decreased by increased stress ratio. The significance of this model to near-threshold fatigue crack growth behavior, in terms of load ratio, microstructure, and environment is discussed. Formerly with Carnegie-Mellon University.     

A STEM/X-ray microanalytical study of the equilibrium segregation of bismuth in copper

Combined scanning transmission electron microscopy (STEM) and X-ray microanalysis have been used to detect the equilibrium segregation of bismuth to grain boundaries in copper. Quantification of the X-ray data gives grain boundary bismuth concentrations close to those reported previously by Auger electron spectroscopy (AES). Samples tempered at low temperatures (773,873 K) had detectable bismuth concentrations at more boundaries than those samples tempered at high temperature (1073 K). There is evidence that the degree of segregation varies strongly from boundary to boundary.     

Excess-noise and receiver sensitivity measurements of In0.53Ga0.47As/InP avalanche photodiodes

We report the results of excess-noise and normalised receiver sensitivity measurements for In0.53Ga0.47As/InP avalanche photodiodes for use in the ?=0.95 ?m to 1.65 ?m spectral region. The excess-noise measurements are consistent with a hole-to-electron ionisation rate ratio in InP of ~ 0.4. The receiver sensitivity, measured at 45 Mbit/s and 10?9 bit-error-rate, was ?53.2 dBm at a gain of 20 assuming unity quantum efficiency for the detector. This sensitivity is the highest reported at ?=1.3 ?m and represents an improvement over a PIN detector using the same amplifier.     

Long/short address optimization in assemblers

In a number of computer systems an instruction in symbolic assembly language may be translated as either a long form or a short form instruction in machine code depending on certain conditions. Assemblers which optimize the size of a program by using short form instructions wherever possible, sometimes require three or more passes to achieve this. This paper describes an approach to solving this type of problem which can be implemented in a two-pass or even a one-pass assembler.     

Adrenergic receptors mediating depolarization in brown adipose tissue

Adrenergic receptors mediating depolarization in in vitro neonatal rat brown adipose tissue (BAT) have been characterized by use of adrenergic agonists and antagonists. Releasable endogenous catecholamine was present in BAT as demonstrated by tyramine- and 1,1-dimethyl-4-phenylpiperazinium iodide- (DMPP) induced depolarization in BAT from normal rats and its absence when BAT from reserpinized rats was used. In BAT from reserpinized rats l-norepinephrine, l-phenylephrine, and l-isoproterenol all similarly depolarized the bronw adipocytes over the concentration range of 10(-8) to 10(-6) M with a maximal depolarization of about 25 mV. Dopamine and d-norepinephrine were more than 100 times less potent. The beta-adrenergic blocker propranolol competitively inhibited isoproterenol-induced depolarization, whereas the alpha-adrenergic blackers, phentolamine and phenoxybenzamine, inhibited the phenylephrine-induced depolarization with much smaller inhibitory effects on the isoproterenol-induced depolarization. Both phenylephrine and isoproterenol elicited transient depolarizations when briefly added to the bathing medium while continuously recording from the same cell. Both the agonist and antagonist studies are interpreted as indicating the presence of both alpha- and beta-adrenergic receptors on BAT cells which mediate catecholamine-induced depolarization.     

Human thyroid adenyl cyclase-stimulating activity in immunoglobulin G of patients with Graves' disease

We have studied the characteristics of the stimulation of adenyl cyclase (AC) activity in human thyroid plasma membranes by thyroid-stimulating hormone (TSH) and by immunoglobulin G (IgG) from the sera of patients with Graves' disease. AC activity was measured as adenosine 3',5'-cyclic monophosphate (cAMP) generated by membranes in a 10 minute incubation. IgG from two patients with Graves' disease possessed particularly potent human thyroid AC-stimulating activity; the dose-response curves with these IgGs were essentially parallel to those obtained with TSH. As little as 30 mug of the IgG of one patient with Graves' disease or 8 muU of TSH caused significant AC stimulation. A Lineweaver-Burk plot of the data suggested similarity in the site of action of both TSH and human thyroid adenyl cyclase stimulator (HTACS) in Graves' IgG. Submaximal doses of HTACS and TSH had additive effects on AC stimulation, but a large dose of a Graves' IgG with potent AC stimulating activity did not enhance AC stimulation by a maximal dose of TSH. The effect of HTACS on AC was slower in onset and longer in duration than an equipotent dose of TSH. HTACS was detectable in IgGs of 9 of 15 untreated hyperthyroid Graves' disease patients; its concentration, however, did not correlate significantly with tests of thyroid function, nor with long-acting thyroid stimulator (LATS) activity. In another 11 treated patients with Graves' disease, selected for the presence of LATS, HTACS and LATS were significantly correlated. We observed no inhibition of LATS activity in a Graves' IgG chosen for such testing because of its high titer of HTACS and no detectable LATS. However, an inhibitor of HTACS was detected in 2 of 4 IgGs; one of these two IgGs also inhibited AC stimulation by TSH. Conclusions: 1) Some Graves' disease IgGs contain a human thyroid AC stimulator (HTACS), probably different from LATS. 2) HTACS may act via a common pathway with TSH; it differs from TSH, however, in having a slower onset and a greater effect during more prolonged incubation with plasma membranes. 3) There is also an inhibitor of HTACS activity in some Graves' disease IgGs.     

Advances in Solar Energy: K. W. Boer and J. Duffie (Editors), American Solar Energy Society,Inc., 110 W. 34th St. New York,N.Y. 10001, 1982. Cost $95.00

Thermodynamic and physical property data equations are presented for the NH₃?LiNO₃ and NH₃?NaSCN absorption refrigeration systems. These equations are presented in a form readily adaptable to a computer program for use by other investigators when thermodynamic and economic cycle calculations for NH₃?LiNO₃ and NH₃?NaSCN absorption systems are to be performed.     

Competition between stimulus-reinforcer contingencies and anticipatory contrast

Procedures used to study anticipatory contrast are conceptually similar to those used to study autoshaping, in that two target stimuli signal either higher or lower rates of reinforcement in the following components of the schedule. Despite this signal contingency, anticipatory contrast entails response rates that are higher to the target stimulus followed by the lower rate of reinforcement. To determine the relation between such effects and autoshaping, different variations of the procedure were used in which the signal contingency was presented in the absence of reinforcement in the target components themselves and in which the reinforcement schedules in the different following components were signaled by the same stimulus. Autoshaping effects of this signal contingency were demonstrated when no reinforcement was available during the target-component signals themselves. Intermediate patterns of behavior occurred when reinforcement was available during the target-component signals and when their different following schedules were correlated with the same stimulus. Attempts to isolate these signal and contrast effects functionally by using the signal-key procedure were unsuccessful. The results demonstrate that Pavlovian stimulus contingencies are in competition with the dynamics of anticipatory contrast, thus reducing its occurrence under some circumstances.