Observation of an adiabatic shear band in AISI 4340 steel by high-voltage transmission electron microscopy

Adiabatic shear bands, formed in a hollow AISI 4340 steel cylinder subjected to dynamic expansion by means of an explosive charge placed in its longitudinal axis, were characterized. The adiabatic shear bands formed in this quenched and tempered steel were of the classical “transformed” type. Scanning electron microscopy (SEM) of etched surfaces revealed that alignment of the lamellae along the direction of shear seems to be the event that precedes shear localization. The transmission electron microscopy of a “white”-etching shear band having undergone a shear strain of approximately 4 revealed that it containedX (Fe₅C₂) carbides in a martensitic structure. These carbides were observed to form on (112) internal microtwins. Grains could not be resolved inside of the shear band, but they could be observed in the surrounding matrix material. A traverse of the shear band was made, and there existed no definite boundary between the matrix and the shear band. No evidence of a transformation to austenite was observed. Heat transfer calculations were conducted to help explain the features observed inside of the shear band. It is concluded that the “white”-etching bands, commonly referred to in the literature as “transformed” bands, do not exhibit a transformation at values of shear strain of up to 4. The enhanced reflectivity is an etching artifact and is possibly due to microstructural changes, a very small grain size, and carbide redissolution in the bands. Formerly with the Department of Metallurgical and Materials Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801.     

Penetration of aluminum alloys by projectiles

Bands of intense shear may be formed during the penetration of aluminum alloys by projectiles. It is shown that the formation of these bands lowers the ability of the material to withstand further projectile penetration. The structure of these bands has been investigated by electron microscopy and the results obtained indicate that melting occurs within the bands. A simple model of a propagating shear band predicts that the material within the band will melt.     

Prediction and uncertainty in human Pavlovian to instrumental transfer.

Attentional capture and behavioral control by conditioned stimuli have been dissociated in animals. The current study assessed this dissociation in humans. Participants were trained on a Pavlovian schedule in which 3 visual stimuli, A, B, and C, predicted the occurrence of an aversive noise with 90%, 50%, or 10% probability, respectively. Participants then went on to separate instrumental training in which a key-press response canceled the aversive noise with a .5 probability on a variable interval schedule. Finally, in the transfer phase, the 3 Pavlovian stimuli were presented in this instrumental schedule and were no longer differentially predictive of the outcome. Observing times and gaze dwell time indexed attention to these stimuli in both training and transfer. Aware participants acquired veridical outcome expectancies in training—that is, A > B > C, and these expectancies persisted into transfer. Most important, the transfer effect accorded with these expectancies, A > B > C. By contrast, observing times accorded with uncertainty—that is, they showed B > A = C during training, and B     

A New Learning Paradigm Elicits Fast Visual Discrimination in Pigeons.

The authors describe a novel multistimulus, multiple-matching learning paradigm for pigeons, which they believe not only simulates pigeons' natural foraging behavior but also more realistically shows their visual discrimination ability. A touch screen thin film transistor panel shows a stimulus configuration consisting of a 2-dimensional array of bitmap images that changes from trial to trial. The pigeon's task during each trial is to peck at images that are defined as positive by the experimenter. An experiment exploring the ability of pigeons to discriminate between achromatic male and female human faces demonstrated the effectiveness of the procedure. In contrast to 12 pigeons that show little improvement over 60 hr of go/no-go discrimination training, 14 multiple-matching pigeons mastered the problem within a few hours. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mineralocorticoid hormone receptor and the epithelial sodium channel in a human leukemic cell line

A Cell extract from the HEL (human erythroblastic leukemia) cell line was positive for both the epithelial sodium channel (ENaC) and the mineralocorticoid receptor (MCR) as glycosylated 82-84 kDa bands, and a single 102 kDa band, respectively, in Western blots using polyclonal antibodies raised against these proteins. The immunofluorescent labeling of the MCR in all cell lines showed a nucleocytoplasmic localization of the receptor whereas the ENaC was exclusively membrane-bound. These results were confirmed by confocal microscopy. The expression of the MCR in HEL cells was evident as a predicted band of 843 bp (234 amino acids) after total RNA from HEL cells had been reverse transcribed and then amplified by PCR; the ENaC was similarly evident as a predicted band of 520 bp. In both cases, near 100% identity was observed between the deduced amino acid sequences of the PCR products and those from known human sources. The multiplication of HEL cells was influenced by antagonists (RU 26752, ZK 91587) targeted for specificity to the MCR and this was reversed by the natural hormone aldosterone. These steroids also provoked chromatin condensation in the HEL population.     

Inhomogeneous deformation in INCONEL 718 during monotonic and cyclic loadings

The deformation microstructures produced by room-temperature monotonie tensile and uniaxial low-cycle fatigue tests in aged (precipitate-hardened) INCONEL 718 were examined by transmission electron microscopy (TEM). Regularly spaced arrays of deformation bands on {111} slip planes were observed. Under monotonie loading, the dislocation structure within a deformation band formed an inverse pileup at a grain boundary, indicating that the boundary was the probable dislocation source. Under fatigue loading, the bands contained a high density of dislocations in a complex arrangement, which was attained after relatively few cycles. Samples of homogenized (precipitate-free) material were deformed monotonically in tension for comparison with the aged material. Early in the deformation, there was only one deformation band per grain and little evidence of work hardening; that is, there was a region of constant flow stress. With increased deformation, work hardening began, more bands nucleated, and their spacing became similar to that in the aged material. This result demonstrates that the degree of coarseness of inhomogeneous deformation in this material was not necessarily a result of a softening process within the bands because of precipitate shearing, but rather, it was primarily a function of the amount of work hardening within the bands. The regularity of the bands and the dislocation structure can be rationalized in terms of a periodic resistance to glide of the dislocations due to the presence of the precipitates and a distribution of dislocation sources along the grain boundaries. D.W. WORTHEM, formerly Graduate Student, Department of Theoretical and Applied Mechanics and Materials Research Laboratory, University of Illinois F.A. LECKIE, formerly Professor, Department of Theoretical and Applied Mechanics and Materials Research Laboratory, University of Illinois     

Abstract-concept learning carryover effects from the initial training set in pigeons (Columba livia).

Three groups of pigeons were trained in a same/different task with 32, 64, or 1,024 color-picture stimuli. They were tested with novel transfer pictures. The training-testing cycle was repeated with training-set doublings. The 32-item group learned the same/different task as rapidly as a previous 8-item group and transferred better than the 8-item group at the 32-item training set. The 64- and 1,024-item groups learned the task only somewhat slower than other groups, but their transfer was better and equivalent to baseline performances. These results show that pigeons trained with small sets (e.g., 8 items) have carryover effects that hamper transfer when the training set is expanded. Without carryover effects (i.e., initial transfer from the 32- and 64-item groups), pigeons show the same degree of transfer as rhesus and capuchin monkeys at these same set sizes. This finding has implications for the general ability of abstract-concept learning across species with different neural architectures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-Dimensional Reconstruction of Planar Deformation Features from Single Electron Micrographs

Dislocations are crystal defects responsible for plastic deformation, and understanding their behavior is key to the design of materials with better properties. Electron microscopy has been widely used to characterize dislocations, but the resulting images are only two-dimensional projections of the real defects. The current work introduces a framework to determine the sample and crystal orientations from micrographs with planar deformation features (twins, stacking faults, and slip bands) in three or four non-coplanar slip systems of an fcc material. This is then extended into a methodology for the three-dimensional reconstruction of dislocations lying on planes with a known orientation that can be easily coupled with a standard Burgers vector analysis, as proved here in a nickel-based superalloy. This technique can only be used in materials that show specific deformation conditions, but it is faster than other alternatives as it relies on the manual tracing of dislocations in a single micrograph.     

Relations Between Pavlovian-Instrumental Transfer and Reinforcer Devaluation.

Relations between posttraining reinforcer devaluation and Pavlovian-instrumental transfer were examined in 2 experiments. When a single reinforcer was used, extended training of the instrumental response increased transfer but reduced devaluation effects. When multiple instrumental reinforcers were used, both reinforcer-specific transfer and devaluation effects were less influenced by the amount of instrumental training. Finally, although reinforcer devaluation decreased both Pavlovian conditioned responses and baseline instrumental responding, it had no effect on either single-reinforcer or reinforcer-specific transfer. These results indicate that transfer and reinforcer devaluation can reflect different aspects of associative learning and that the nature of associative learning can be influenced by parameters such as the amount of training and the use of multiple reinforcers. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Biochemical maturation of Spam1 (PH-20) during epididymal transit of mouse sperm involves modifications of N-linked oligosaccharides

Indirect immunofluorescence of mouse caput and caudal sperm shows distinctly different distributions of Spaml protein, which is associated with structural and functional differences of the molecule. Spam1 is uniformly distributed over the surface of the head of caput sperm while in caudal sperm, light and confocal microscopy demonstrate that it is localized to the anterior and posterior regions. The hyaluronidase activity of Spaml in acrosome-intact caput sperm was significantly lower (4.3-fold; P < 0.0001) than that of caudal sperm. The increase in enzymatic activity in caudal sperm is accompanied by a reduction in the molecular weight (MW): in extracts from caput sperm there was a major band at approximately 74 kDa and a minor band at approximately 67 kDa; while for the cauda there was a major band at approximately 67 kDa and minor bands at approximately 70 and -56 kDa. Additionally, the bands from caput sperm were 4.9 to 7.7-fold less intense than those from caudal sperm. This decreased affinity for the polyclonal anti-Spaml suggests the presence of different surface characteristics of the molecule from the two epididymal regions. Computer analysis of the protein structure from Spam1 cDNA sequence reveals four putative N-linked glycosylation sites, and enzymatic deglycosylation suggests that all sites are functional. After endoglycosidase activity of extracts from caput and caudal sperm, both show a major band with a MW of approximately 56 kDa, the size of the membrane-anchored polypeptide backbone. Based on the difference in size and intensity of the Spaml bands and hyaluronidase activities from caput and caudal sperm, the data suggest that the activation of Spaml during epididymal maturation is regulated by deglycosylation.     

TEM and SANS investigation of age hardened nimonic PE16 after cyclic loading at room temperature

A nickelbase superalloy Nimonic PE16 shows softening when subjected to low cycle fatigue (LCF) at room temperature. Controversy exists in literature over the mechanisms of such softening observed in many precipitation hardened alloys. Small angle neutron scattering (SANS) and transmission electron microscopy (TEM) have been used to study the morphology of γ′-precipitates in the Nimonic PE16 after LCF at room temperature. In TEM dark field images using superlattice reflections, deformation bands free of γ′-precipitates are observed. SANS measurements allowed the characterization of the disappeared precipitates with regard to their average size, size distribution and volume fraction by comparing the scattered intensities of loaded and unloaded specimens. An analysis of the results shows that the γ′-precipitates within the deformation bands have completely dissolved and not just disordered or cut to sizes smaller than the TEM resolution limit.     

Luders deformation of low-carbon steel

The development of Chernov–Luders bands on elastoplastic transition in low-carbon steel is investigated. The main factors responsible for the creation and development of the bands are identified. The kinetics of the mobile band boundaries (fronts) is of particular interest. The characteristic speeds are determined. The nucleation rate of Chernov–Luders bands exceeds their expansion rate by more than an order of magnitude. The simultaneous development of more than one band, with the appearance of several moving fronts, is considered. In all cases, the fronts of the Chernov–Luders bands move at matched speeds, so that, at any time, the generalized expansion rate of the deformation zone is constant. The influence of the strain rate on the kinetics of the band fronts is analyzed. Both the generalized expansion rate of the deformed zone and the speeds of individual fronts increase with increase in the loading rate. This is a nonlinear dependence (a power law). The fronts of the Chernov–Luders bands are complex in structure. Different sections of the front may move at nonuniform speeds, so that the front is locally distorted and split. Ahead of the front, in the undeformed sample, precursors whose configuration resembles that of the incipient Chernov–Luders bands may be observed. When they meet, the fronts of adjacent bands cancel out. Annihilation of the band fronts is a complex process, characterized by the formation of precursors and secondary diffuse Chernov–Luders bands. These findings indicate that the simplified concept of the Chernov–Luders bands as a deformed region in a loaded sample, as the front of a band, or as the boundary between deformed and undeformed zones must be revised. A microscopic theory of Luders deformation is based on the cascade growth in density of mobile dislocations on account of their breakaway from the points of attachment and their subsequent multiplication, which occurs instantaneously at the upper yield point within the crystallite (grain). At the same time, the formation of a mobile macroscopic strain front calls for the transfer of plastic deformation by adjacent grains, without strengthening. In other words, grain-boundary accommodation is required. The results obtained suggest that the Chernov–Luders band is such an accommodation zone, and so it has a complex structure.     

Etiopathogenesis of acute myocardial infarction: role of early leukocytosis]

Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.     

Hyperspecificity in Visual Implicit Learning: Learning of Spatial Layout Is Contingent on Item Identity.

Humans conduct visual search faster when the same display is presented for a 2nd time, showing implicit learning of repeated displays. This study examines whether learning of a spatial layout transfers to other layouts that are occupied by items of new shapes or colors. The authors show that spatial context learning is sometimes contingent on item identity. For example, when the training session included some trials with black items and other trials with white items, learning of the spatial layout became specific to the trained color--no transfer was seen when items were in a new color during testing. However, when the training session included only trials in black (or white), learning transferred to displays with a new color. Similar results held when items changed shapes after training. The authors conclude that implicit visual learning is sensitive to trial context and that spatial context learning can be identity contingent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in visual functions in myopia 6 months after photorefractive keratectomy

Clubfoot deformity associated with congenital constriction band syndrome (CCBS) has different characteristics than classic idiopathic clubfoot, and is more difficult to treat. We describe the manifestations, treatment, and outcomes of nine patients treated for 11 CCBS-associated clubfoot deformities between 1980 and 1993. All but one of these children had an abnormal gestational or neonatal history. From an assessment of the correctability of the deformity and the associated secondary changes, the clubfoot severities were all classified as grade B (intermediate). The constriction bands in eight clubfeet were classified as type 0 (5 feet), II (2), or III (1), according to the location and depth of the band. Band types in three feet were unclassified because the band release was performed at other hospitals. We released the bands before correcting the clubfeet in the two patients with type II bands. The five patients with type 0 bands received casting first but with poor response. All clubfeet were corrected surgically; the procedures were posteromedial release in 10 feet, split tibialis anterior tendon transfer in five, and lengthening of the Achilles tendon in three. At an average follow-up of 3.8 years, seven of the 11 clubfeet were classified as having good results and four as fair. Among the six clubfeet with constriction bands on the ipsilateral leg, five were classified as having good results and one as fair. Two of the five clubfeet without constriction bands on the ipsilateral leg had good results and three had fair results. The presence of a band did not influence the final outcome of the clubfoot deformity (p > 0.05). In the five patients with forefoot varus deformity due to peroneal weakness, tibialis anterior tendon transfer successfully corrected the deformity. All the clubfeet treated in this series were plantigrade after treatment and had satisfactory results.     

Correction to Holland (2004).

Reports an error in the original article "Relations Between Pavlovian-Instrumental Transfer and Reinforcer Devaluation," by Peter C. Holland (Journal of Experimental Psychology: Animal Behavior Processes, 2004, Vol. 30, No. 2, pp. 104-117). On page 113, there were two errors in Panel D of Figure 4. First, the three bars labeled O1 were exchanged with those labeled O2. Second, the error bars (±SEMs) were omitted for baseline responding. The correct panel is provided. (The following abstract of this article originally appeared in record 2004-12429-003.) Relations between posttraining reinforcer devaluation and Pavlovian-instrumental transfer were examined in 2 experiments. When a single reinforcer was used, extended training of the instrumental response increased transfer but reduced devaluation effects. When multiple instrumental reinforcers were used, both reinforcer-specific transfer and devaluation effects were less influenced by the amount of instrumental training. Finally, although reinforcer devaluation decreased both Pavlovian conditioned responses and baseline instrumental responding, it had no effect on either single-reinforcer or reinforcer-specific transfer. These results indicate that transfer and reinforcer devaluation can reflect different aspects of associative learning and that the nature of associative learning can be influenced by parameters such as the amount of training and the use of multiple reinforcers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shear band formation in plane strain compression

Shear band formation during plane strain compression of single crystals and polycrystals of an Al-3 wt% Cu alloy was studied. X-ray and electron diffraction, optical microscopy, and electron (TEM/STEM) microscopy were used to document the structure and micromechanisms of the localization process. Complementary finite element studies were performed using the measured single crystals' single slip system strain hardening data. The experimental observations and the computed deformation response are in very close agreement, and indicate that localization, through macroscopic shear band formation, occurs in continuously strain hardening, damage-free material. Shear band formation was preceeded by the development of very coarse slip which, like the shear bands, propagated across entire grains and, in single crystals, across the entire crystal. The computations and experiments showed that geometrical softening, caused by nonuniform lattice reorientation, is an important micromechanical influence on the localization process in both single crystals and polycrystals. Also, the propagation of shear bands across grain boundaries in polycrystals was looked at experimentally and computationally. Particular attention was paid to the crystallography of shear band transmission through grain boundaries.     

Biosynthesis of chondroitin sulfate. Purification of glucuronosyl transferase II and use of photoaffinity labeling for characterization of the enzyme as an 80-kDa protein

A photoaffinity analogue, [beta-32P]5-azido-UDP-GlcA, was used to photolabel the enzymes that utilize UDP-GlcA in cartilage microsomes and rat liver microsomes. SDS-polyacrylamide gel electrophoresis analysis of photolabeled cartilage microsomes, which are specialized in chondroitin sulfate synthesis, showed a major radiolabeled band at 80 kDa and other minor radiolabeled bands near 40 and 60 kDa. Rat liver microsomes, which are enriched for enzymes of detoxification by glucuronidation, had a different pattern with multiple major labeled bands near 50-60 and 35 kDa. To determine that the photolabeled 80-kDa protein is the GlcA transferase II, we have purified the enzyme from cartilage microsomes. This membrane-bound enzyme, involved in the transfer of GlcA residues to non-reducing terminal GalNAc residues of the chondroitin polymer, has now been solubilized, stabilized, and then purified greater than 1350-fold by sequential chromatography on Q-Sepharose, heparin-Sepharose, and WGA-agarose. The purified enzyme exhibited a conspicuous silver-stained protein band on SDS-polyacrylamide gel electrophoresis that coincided with the major radiolabeled band of 80 kDa. SDS-polyacrylamide gel analysis of photoaffinity-labeled active fractions from the Q-Sepharose, heparin-Sepharose, and WGA-agarose also indicated only the single radiolabeled band at 80 kDa. Intensity of photolabeling in each of the fractions examined coincided with enzyme activity. The photolabeling of this 80-kDa protein was saturable with the photoprobe and could be inhibited by the addition of UDP-GlcA prior to the addition of the photoprobe. Thus, the photolabeling with [beta-32P]5-azido-UDP-GlcA has identified the GlcA transferase II as an 80-kDa protein. The purified enzyme was capable of transferring good amounts of GlcA residues to chondroitin-derived pentasaccharide with negligible transfer to pentasaccharides derived from hyaluronan or heparan.