We provide a review of the alignment literature in IT, addressing questions such as: What have we learned? What is disputed? Who are contributors to the debate? The article is intended to be useful to faculty and graduate students considering conducting research on alignment, instructors preparing lectures, and practitioners seeking to assess the ‘state-of-play’. It is both informational and provocative. Challenges to the value of alignment research, divergent views, and new perspectives on alignment are presented. It is hoped that the article will spark helpful conversation on the merits of continued investigation of IT alignment.

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IT alignment: what have we learned?

A hierarchical approach to defining marine heatwaves

A chemical description of the action of phospholipase A2 (PLA2) can now be inferred with confidence from three high-resolution x-ray crystal structures. The first is the structure of the PLA2 from the venom of the Chinese cobra (Naja naja atra) in a complex with a phosphonate transition-state analogue. This enzyme is typical of a large, well-studied homologous family of PLA2S. The second is a similar complex with the evolutionarily distant bee-venom PLA2. The third structure is the uninhibited PLA2 from Chinese cobra venom. Despite the different molecular architectures of the cobra and bee-venom PLA2s, the transition-state analogue interacts in a nearly identical way with the catalytic machinery of both enzymes. The disposition of the fatty-acid side chains suggests a common access route of the substrate from its position in the lipid aggregate to its productive interaction with the active site. Comparison of the cobra-venom complex with the uninhibited enzyme indicates that optimal binding and catalysis at the lipid-water interface is due to facilitated substrate diffusion from the interfacial binding surface to the catalytic site rather than an allosteric change in the enzyme9s structure. However, a second bound calcium ion changes its position upon the binding of the transition-state analogue, suggesting a mechanism for augmenting the critical electrophile.

/pdf/interfacial-catalysis-the-mechanism-of-phospholipase-a2-4gx13xg0nq.pdf

Interfacial catalysis: the mechanism of phospholipase A2

Social capital has many faces in the geography of urban opportunity, and as such, particular housing policies might have positive effects on some forms of social capital and negative effects on others. The author defines social support and social leverage as two key dimensions of social capital that can be accessed by individuals. A sample of 132 low‐income African‐American and Latino adolescents is used to examine the early impacts of a Yonkers, NY, housing mobility program on social capital.1 Overall, program participants (‘’movers‘’) appear to be no more cut off from social support than a control group of “stayer” youth. On the other hand, movers are also no more likely to report access to good sources of job information or school advice— to leverage that might enhance opportunity. Adding just one steadily employed adult to an adolescent's circle of significant ties has dramatic effects on perceived access to such leverage.

https://dusp.mit.edu/sites/dusp.mit.edu/files/attachments/publication/br%20kids%20HPD%2098.pdf

Brown kids in white suburbs: Housing mobility and the many faces of social capital

Determinants of capital structure: new evidence from Spanish panel data

This study investigates the applicability of the J-integral test procedure to test short crack specimens in the temperature region below the initiation of ductile tearing where J 1 c cannot be measured. The current J-integral test procedure is restricted to determining the initiation of ductile tearing and requires that no specimen demonstrates brittle cleavage fracture. The J 1 c test specimen is also limited to crack-depth to specimen-width ratios (a/W) between 0.50 and 0.75. In contrast, the crack tip opening displacement (CTOD) test procedure can be used for testing throughout the entire temperature-toughness transition region from brittle to fully ductile behavior. Also, extensive research is being conducted to extend the CTOD test procedure to the testing of short crack specimens (alW ratios of approximately 0.15). The CTOD and J-integral fracture parameters are compared both analytically and experimentally using square (cross-section) three-point bend specimens of A36 steel with a/W ratios of 0.50 (deep crack) and 0.15 (short crack). Three-dimensional elastic-plastic finite element analyses are conducted on both the deep crack and the short crack specimens. The measured J-integral and CTOD results are compared at various levels of linear-elastic and elastic-plastic behavior. Experimental testing is conducted throughout the lower shelf and lower transition regions where stable crack growth does not occur. Very good agreement exists between the analytical and experimental results for both the short crack and deep crack specimens. Results of this study show that both the J-integral and the CTOD fracture parameters work well for testing in the lower shelf and lower transition regions where stable crack growth does not occur. A linear relationship is shown to exist between J-integral and CTOD throughout these regions for both the short and the deep crack specimens. These observations support the consideration to extend the J-integral test procedure into the temperature region of brittle fracture rather than limiting it to J 1 c at the initiation of ductile tearing. Also, analyzing short crack three-point bend specimen (a/W < 0.15) records using the load versus load-line displacement (LLD) record has great potential as an experimental technique. The problems of accurately measuring the CMOD of short crack specimens in the laboratory without affecting the crack tip behavior may be eliminated using the J-integral test procedure.

A Comparison of the J -lntegral and CTOD Parameters for Short Crack Specimen Testing

Short crack test specimens (a/W ≪ 0.50) are frequently employed when conventional deep crack specimens are either inappropriate or impossible to obtain, for example, in testing of particular microstructures in weldments and in-service structures containing shallow surface flaws. Values of elastic-plastic fracture toughness, here characterized by the crack tip opening displacement (CTOD), are presented for square (cross-section) three-point bend specimens with a/W ratios of 0.15 and 0.50 throughout the lower-shelf and lower-transition regions. Three dimensional, finite-element analyses are employed to correlate the measured load and crack mouth opening displacement (CMOD) values to the corresponding CTOD values, thus eliminating a major source of experimental difficulty in previous studies of shallow crack specimens. In the lower-transition region, where extensive plasticity (but no ductile crack growth) precedes brittle fracture, critical CTOD values for short crack specimens are significantly larger (factor of 2–3) than the CTOD values for deep crack specimens at identical temperatures. Short crack specimens are shown to exhibit increased toughness at the initiation of ductile tearing and decreased brittle-to-ductile transition temperatures. Numerical analyses for the two a/W ratios reveal large differences in stress fields ahead of the crack tip at identical CTOD levels which verify the experimentally observed differences in critical CTOD values. Correlations of the predicted stresses with measured critical CTOD values demonstrate the limitations of single-parameter fracture mechanics (as currently developed) to characterize the response.

Effects of crack depth on elastic-plastic fracture toughness

Numerical evaluation of a 3-D J-integral and comparison with experimental results for a 3-Point bend specimen

The effect of crack-depth to specimen-width ratio on crack tip opening displacement (CTOD) fracture toughness is an important consideration in relating the results of laboratory tests to the behavior of actual structures.Deeply cracked three-point bend specimens with crack-depth to specimen-width ratios (a/W) of 0.50 are most often used in laboratory tests. However, to evaluate specific weld microstructures or the behavior of structures with shallow surface cracks, specimens with a/W ratios much less than 0.50 often are required. Laboratory tests reveal that three-point bend specimens with short cracks (a/W = 0.15) exhibit significantly larger critical CTOD values than specimens with deep cracks (a/W = 0.5) up to the point of ductile initiation. In this study, finite element analyses are employed to compare the elastic-plastic behavior of square (cross-section) three-point bend specimens with crack-depth to specimen-width ratios (a/W) ranging between 0.50 and 0.05. The two-dimensional analysis of the specimen with an a/W ratio of 0.15 reveals a fundamental change in the deformation pattern from the deep crack deformation pattern. The plastic zone extends to the free surface behind the crack concurrent with the development of a plastic hinge. For shorter cracks (a/W = 0.10 and 0.05), the plastic zone extends to the free surface behind the crack prior to the development of a plastic hinge. For longer cracks (a/W > 0.20), a plastic hinge develops before the plastic zone extends to the free surface behind the crack. These results prompted further study of specimens with an a/W ratio of 0.15 using three-dimensional, elastic-plastic finite element analyses. Results of the short crack (a/W = 0.15) analysis are compared to the results of the deep crack (a/W = 0.50) analysis reported previously by the authors. In the linear-elastic regime (characterized by small-scale plastic deformation) the relationship of stress ahead of the crack tip to CTOD is identical for the short crack and the deep crack specimens. At identical CTOD levels in the elastic-plastic regime (large-scale plasticity, hinge formation), the crack tip stress is significantly lower for specimens with a/W = 0.15 than for specimens with a/W = 0.50. Correspondingly, at equivalent stress levels, the CTOD for the short crack is approximately 2.5 times the CTOD for the deep crack. This observation has considerable significance in the application of CTOD results to failure analysis or specification development where the fracture mechanism is cleavage preceded by significant crack tip plasticity.

An Analytical Comparison of Short Crack and Deep Crack CTOD Fracture Specimens of an A36 Steel

This paper describes the results of an experimental and analytical study of the effect of specimen size on the fracture-toughness behavior of A36 steel, primarily in the lower-transition region. This region is beyond the limits of plane-strain as defined by ASTM E-399, but in the region where failure occurs prior to any macroscopic fibrous tearing. Experimental results were obtained using Crack-Tip Opening Displacement (CTOD) three-point bend specimens and analytical results were obtained using a 3-D elastic-plastic finite-element analysis. Two specimen sizes, full thickness (31.8 mm (1.25'') thick) and reduced thickness (12.7 mm (0.50'') thick), were investigated using the preferred t x 2t x 8t specimen size.

William A. Sorem

Papers

A Comparison of the J -lntegral and CTOD Parameters for Short Crack Specimen Testing

Effects of crack depth on elastic-plastic fracture toughness

Numerical evaluation of a 3-D J-integral and comparison with experimental results for a 3-Point bend specimen

An Analytical Comparison of Short Crack and Deep Crack CTOD Fracture Specimens of an A36 Steel

Specimen Thickness Effects for Elastic-Plastic CTOD Toughness of an A36 Steel