Advanced Computational Analysis of Cobalt-Based Superalloys through Crystal Plasticity

This study introduces an advanced computational method aimed at accelerating continuum-scale processes using crystal plasticity approaches to predict mechanical responses in cobalt-based superalloys. The framework integrates two levels, namely, sub-grain and homogenized, at the meso-scale through crystal plasticity finite element (CPFE) platforms. The model is applicable across a temperature range from room temperature up to 900 °C, accommodating various dislocation mechanisms in the microstructure. The sub-grain level explicitly incorporates precipitates and employs a dislocation density-based constitutive model that is size-dependent. In contrast, the homogenized level utilizes an activation energy-based constitutive model, implicitly representing the γ' phase for efficiency in computations. This level considers the effects of composition and morphology on mechanical properties, demonstrating the potential for cobalt-based superalloys to rival nickel-based superalloys. The study aims to investigate the impacts of elements including tungsten, tantalum, titanium, and chromium through the homogenized constitutive model. The model accounts for the locking mechanism to address the cross-slip of screw dislocations at lower temperatures as well as the glide and climb mechanism to simulate diffusions at higher temperatures. The model's validity is established across diverse compositions and morphologies, as well as various temperatures, through comparison with experimental data. This advanced computational framework not only enables accurate predictions of mechanical responses in cobalt-based superalloys across a wide temperature range, but also provides valuable insights into the design and optimization of these materials for high-temperature applications.

Multi-Scale Crystal Plasticity Model of Creep Responses in Nickel-Based Superalloys

The current study focuses on the modeling of two-phase γ-γ′ nickel-based superalloys, utilizing multi-scale approaches to simulate and predict the creep behaviors through crystal plasticity finite element (CPFE) platforms. The multi-scale framework links two distinct levels of the spatial spectrum, namely, sub-grain and homogenized scales, capturing the complexity of the system responses as a function of a tractable set of geometric and physical parameters. The model considers two dominant features of γ′ morphology and composition. The γ′ morphology is simulated using three parameters describing the average size, volume fraction, and shape. The sub-grain level is expressed by a size-dependent, dislocation density-based constitutive model in the CPFE framework with the explicit depiction of γ-γ′ morphology as the building block of the homogenized scale. The homogenized scale is developed as an activation energy-based crystal plasticity model reflecting intrinsic composition and morphology effects. The model incorporates the functional configuration of the constitutive parameters characterized over the sub-grain γ-γ′ microstructural morphology. The developed homogenized model significantly expedites the computational processes due to the nature of the parameterized representation of the dominant factors while retains reliable accuracy. Anti-Phase Boundary (APB) shearing and, glide-climb dislocation mechanisms are incorporated in the constitutive model which will become active based on the energies associated with the dislocations. The homogenized constitutive model addresses the thermo-mechanical behavior of nickel-based superalloys for an extensive temperature domain and encompasses orientation dependence as well as the loading condition of tension-compression asymmetry aspects. The model is validated for diverse compositions, temperatures, and orientations based on previously reported data of single crystalline nickel-based superalloy.

Nitrogen Effects in Additively Manufactured Martensitic Stainless Steels: Conventional Thermal Processing and Comparison with Wrought

The microstructures of additively manufactured (AM) precipitation-hardenable stainless steels 17-4 and 15-5 were investigated and compared to those of conventionally produced materials. The residual N found in N₂-atomized 17-4 powder feedstock is inherited by the additively produced material, and has dramatic effects on phase stability, microstructure, and microstructural evolution. Nitrogen is a known austenite stabilizing element, and the as-built microstructure of AM 17-4 can contain up to 90 pct or more retained austenite, compared to the nearly 100 pct martensite structure of wrought 17-4. Even after homogenization and solutionization heat treatments, AM 17-4 contains 5 to 20 pct retained austenite. In contrast, AM 15-5 and Ar-atomized AM 17-4 contain<5 pct retained austenite in the as-built condition, and this level is further decreased following post-build thermal processing. Computational thermodynamics-based calculations qualitatively describe the observed depression in the martensite start temperature and martensite stability as a function of N-content, but require further refinements to become quantitative. A significant increase in the volume fraction of fine-scale carbide precipitates attributed to the high N-content of AM 17-4 is also hypothesized to give rise to additional activation barriers for the dislocation motion required for martensite nucleation and subsequent growth. An increase in the volume fraction of carbide/nitride precipitates is observed in AM 15-5, although they do not inhibit martensite formation to the extent observed in AM 17-4.

Simulation of TTT Curves for Additively Manufactured Inconel 625

The ability to use common computational thermodynamic and kinetic tools to study the microstructure evolution in Inconel 625 (IN625) manufactured using the additive manufacturing (AM) technique of laser powder-bed fusion is evaluated. Solidification simulations indicate that laser melting and re-melting during printing produce highly segregated interdendritic regions. Precipitation simulations for different degrees of segregation show that the larger the segregation, i.e., the richer the interdendritic regions are in Nb and Mo, the faster the δ-phase (Ni₃Nb) precipitation. This is in accordance with the accelerated d precipitation observed experimentally during post-build heat treatments of AM IN625 compared to wrought IN625. The δ-phase may be undesirable since it can lead to detrimental effects on the mechanical properties. The results are presented in the form of a TTT diagram and agreement between the simulated diagram and the experimental TTT diagram demonstrate how these computational tools can be used to guide and optimize post-build treatments of AM materials.

The Effect of Oxygen on Phase Equilibria in the Ti-V System: Impacts on the AM Processing of Ti Alloys

Oxygen is always a constituent in "real" titanium alloys including titanium alloy powders used for powder-based additive manufacturing (AM). In addition, oxygen uptake during powder handling and printing is hard to control and, hence, it is important to understand and predict how oxygen is affecting the microstructure. Therefore, oxygen is included in the evaluation of the thermodynamic properties of the titanium-vanadium system employing the CALculation of PHAse Diagrams method and a complete model of the O-Ti-V system is presented. The β-transus temperature is calculated to increase with increasing oxygen content whereas the extension of the α-Ti phase field into the binary is calculated to decrease, which explains the low vanadium solubilities measured in some experimental works. In addition, the critical temperature of the metastable miscibility gap of the β-phase is calculated to increase to above room temperature when oxygen is added. The effects of oxygen additions on phase fractions, martensite and ω formation temperatures are discussed, along with the impacts these changes may have on AM of titanium alloys.

Systems Design Approach to Low-Cost Coinage Materials

A systems approach within an Integrated Computational Materials Engineering framework was used to design three new low-cost seamless replacement coinage alloys to reduce the raw material of the current US coinage alloys. Maintaining compatibility with current coinage materials required matching the currently used alloy properties of yield strength, work-hardening behavior, electrical conductivity, color, corrosion resistance and wear resistance. In addition, the design alloys were required to use current production processes. CALPHAD-based models for electrical conductivity and color were developed to integrate into the system design. Three prototype alloys were designed, produced and characterized. The design process highlighted the trade-off between minimizing the raw material costs and achieving the desired color properties. Characterization of the three prototype alloys showed good agreement with the design goals.

Generating Domain Terminologies using Root- and Rule-Based Terms

Motivated by the need for flexible, intuitive, reusable, and normalized terminology for guiding search and building ontologies, we present a general approach for generating sets of such terminologies from natural language documents. The terms that this approach generates are root- and rule-based terms, generated by a series of rules designed to be flexible, to evolve, and, perhaps most important, to protect against ambiguity and standardize semantically similar but syntactically distinct phrases to a normal form. This approach combines several linguistic and computational methods that can be automated with the help of training sets to quickly and consistently extract normalized terms. We discuss how this can be extended as natural language technologies improve and how the strategy applies to common use-cases such as search, document entry and archiving, and identifying, tracking, and predicting scientific and technological trends.

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion

Elemental segregation is a ubiquitous phenomenon in additive-manufactured (AM) parts due to solute rejection and redistribution during the solidification process. Using electron microscopy, in situ synchrotron X-ray scattering and diffraction, and thermodynamic modeling, we reveal that in an AM nickel-based superalloy, Inconel 625, stress-relief heat treatment leads to the growth of unwanted δ-phase precipitates on a time scale much faster than that in wrought alloys (minutes versus tens to hundreds of hours). The root cause for this behavior is the elemental segregation that results in local compositions of AM alloys outside the bounds of the allowable range set for wrought alloys. In situ small angle scattering experiments reveal that platelet-shaped δ phase precipitates grow continuously and preferentially along their lateral dimensions during stress-relief heat treatment, while the thickness dimension reaches a plateau very quickly. In situ XRD experiments reveal that nucleation and growth of δ-phase precipitates occur within 5 min during stress-relief heat treatment, indicating a low nucleation barrier and a short incubation time. An activation energy for the growth of δ phase was found to be (131.04 ± 0.69) kJ mol^-1. We further demonstrate that a subsequent homogenization heat treatment can effectively homogenize the AM alloy and remove the deleterious δ phase. The combined experimental and modeling methodology in this work can be extended to elucidate the phase evolution during heat treatments in a broad range of AM materials.

The Influence of Annealing Temperature and Time on the Formation of δ-Phase in Additively-Manufactured Inconel 625

This research evaluated the kinetics of δ-phase growth in laser powder bed additively-manufactured (AM) Inconel 625 during post-build stress-relief heat treatments. The temperatures ranged between 650°C and 1050°C, and the times from 0.25 to 168 hours. The presence of δ-phase was verified for each temperature/time combination through multiple techniques. A conventional time-temperature-transformation diagram was constructed from the time-temperature data. Comparison to the growth in wrought IN625 with a similar nominal composition revealed that δ-phase formation occurred at least two orders of magnitude faster in the AM IN625. The results of this study also revealed that the segregated microstructure in the as-built condition has a strong influence on the kinetics of δ-phase formation in AM IN625 as compared to a homogenized material. Since control of the δ-phase growth is essential for reliable prediction of the performance of IN625 components in service, avoiding heat treatments that promote the formation of δ-phase in AM components that are not homogenized is highly recommended. This will be particularly true at elevated temperatures where the microstructural stability and the consistency of mechanical properties are more likely to be affected by the presence of δ-phase.

A Computational Framework for Material Design

A computational framework is proposed that enables the integration of experimental and computational data, a variety of user-selected models, and a computer algorithm to direct a design optimization. To demonstrate this framework, a sample design of a ternary Ni-Al-Cr alloy with a high work-to-necking ratio is presented. This design example illustrates how CALPHAD phase-based, composition and temperature-dependent phase equilibria calculations and precipitation models are coupled with models for elastic and plastic deformation to calculate the stress-strain curves. A genetic algorithm then directs the search within a specific set of composition and processing constraints for the ideal composition and processing profile to optimize the mechanical properties. The initial demonstration of the framework provides a potential solution to initiate the material design process in a large space of composition and processing conditions. This framework can also be used in similar material systems or adapted for other material classes.

Homogenization Kinetics of a Nickel-based Superalloy Produced by Powder Bed Fusion Laser Sintering

Additively manufactured (AM) metal components often exhibit fine dendritic microstructures and elemental segregation due to the initial rapid solidification and subsequent melting and cooling during the build process, which without homogenization would adversely affect materials performance. In this letter, we report in situ observation of the homogenization kinetics of an AM nickel-based superalloy using synchrotron small angle X-ray scattering. The identified kinetic time scale is in good agreement with thermodynamic diffusion simulation predictions using microstructural dimensions acquired by ex situ scanning electron microscopy. These findings could serve as a recipe for predicting, observing, and validating homogenization treatments in AM materials.

In Situ Structural Characterization of Ageing Kinetics in Aluminum Alloy 2024 across Angstrom-to-Micrometer Length Scales

The precipitate structure and precipitation kinetics in an Al-Cu-Mg alloy (AA2024) aged at 190 °C, 208 °C, and 226 °C have been studied using ex situ Transmission Electron Microscopy (TEM) and in situ synchrotron-based, combined ultra-small angle X-ray scattering, small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS) across a length scale from sub-Angstrom to several micrometers. TEM brings information concerning the nature, morphology, and size of the precipitates while SAXS and WAXS provide qualitative and quantitative information concerning the time-dependent size and volume fraction evolution of the precipitates at different stages of the precipitation sequence. Within the experimental time resolution, precipitation at these ageing temperatures involves dissolution of nanometer-sized small clusters and formation of the planar S phase precipitates. Using a three-parameter scattering model constructed on the basis of TEM results, we established the temperature-dependent kinetics for the cluster-dissolution and S-phase formation processes simultaneously. These two processes are shown to have different kinetic rates, with the cluster-dissolution rate approximately double the S-phase formation rate. We identified a dissolution activation energy at (149.5 ± 14.6) kJ mol^-1, which translates to (1.55 ± 0.15) eV/atom, as well as an activation energy for the formation of S precipitates at (129.2 ± 5.4) kJ mol^-1, i.e. (1.33 ± 0.06) eV/atom. Importantly, the SAXS/WAXS results show the absence of an intermediate Guinier-Preston Bagaryatsky 2 (GPB2)/S″ phase in the samples under the experimental ageing conditions. These results are further validated by precipitation simulations that are based on Langer-Schwartz theory and a Kampmann-Wagner numerical method.

Valence-bond crystalline order in the s = 1/2 J1-J2 model on the honeycomb lattice

Using the coupled cluster method we study the phase diagram of the spin-1/2 Heisenberg antiferromagnet on a honeycomb lattice with nearest-neighbour exchange coupling J1 > 0 and frustrating next-nearest-neighbour coupling J2 ≡ xJ1 > 0. In the range 0 < x < 1 we find four phases exhibiting respectively Néel, 6-spin plaquette, staggered dimer and Néel-II orderings, with quantum critical points at xc1 ≈ 0.207(3), xc2 ≈ 0.385(10) and xc3 ≈ 0.65(5). The transitions at xc1 and xc3 appear to be continuous (and hence deconfined) ones, while that at xc2 appears to be a direct first-order one.

The frustrated Heisenberg antiferromagnet on the honeycomb lattice: J1-J2 model

We study the ground-state phase diagram of the frustrated spin-[Formula: see text] antiferromagnet with J(2) = xJ(1) > 0 (J(1) > 0) on the honeycomb lattice, using the coupled-cluster method. We present results for the ground-state energy, magnetic order parameter and plaquette valence-bond crystal (PVBC) susceptibility. We find a paramagnetic PVBC phase for x(c(1)) < x < x(c(2)), where x(c(1)) ≈ 0.207 ± 0.003 and x(c(2)) ≈ 0.385 ± 0.010. The transition at x(c(1)) to the Néel phase seems to be a continuous deconfined transition (although we cannot exclude a very narrow intermediate phase in the range 0.21 ≲ x ≲ 0.24), while that at x(c(2)) is of first-order type to another quasiclassical antiferromagnetic phase that occurs in the classical version of the model only at the isolated and highly degenerate critical point [Formula: see text]. The spiral phases that are present classically for all values x > 1/6 are absent for all x ≲ 1.

A virus-like agent associated with neurofibromatosis in damselfish

Damselfish neurofibromatosis (DNF) is a transmissible disease involving neurofibromas and chromatophoromas affecting bicolor damselfish Stegastes partitus on Florida reefs. Analysis of genomic DNA by Southern blotting techniques demonstrated the presence of a group of extrachromosomal DNAs in tumors from fish affected with DNF but not in healthy individuals. Cell lines obtained from tumors contained identical DNAs and were shown to be tumorigenic in vivo, while lines established from healthy fish did not contain such DNA and were not tumorigenic. These DNA patterns were also observed in experimentally induced tumors. A DNase resistant component of this DNA was isolated from both tumor cells and conditioned media of tumor cell lines suggesting that these sequences were encapsulated in viral particles. These data support the hypothesis that one or more of these extrachromosomal DNA forms is the genome of an unusual virus and that this virus is the etiologic agent of DNF. We have tentatively termed this agent the damselfish virus-like agent (DVLA).

A dominant repression domain in Tbx3 mediates transcriptional repression and cell immortalization: relevance to mutations in Tbx3 that cause ulnar-mammary syndrome

Mutations in Tbx3 are responsible for ulnar-mammary syndrome (UMS), an autosomal dominant disorder affecting limb, tooth, hair, apocrine gland and genital development. Tbx3 is a member of a family of transcription factors that share a highly conserved DNA-binding domain known as the T-domain. UMS-causing mutations in Tbx3 have been found at numerous sites within the TBX3 gene, with many occurring downstream from the N-terminally located T-domain. The occurrence of mutations downstream of the DNA-binding domain raises the possibility that there exist important functional domains in C-terminal portions of the Tbx3 protein that affect its behavior as a transcription factor. To determine if and how such C-terminal mutations affect transcription we have mapped regions that confer transcriptional activity and nuclear localization and characterized the DNA binding properties of Tbx3. We find that Tbx3 binds the canonical Brachyury binding site as a monomer and represses transcription. We show that a key repression domain (RD1) resides in the Tbx3 C-terminus that can function as a portable repression domain. Most UMS-associated C-terminal mutants lack the RD1 and exhibit decreased or loss of transcriptional repression activity. In addition, we identify a domain responsible for nuclear localization of Tbx3 and show that two C-terminal mutants of Tbx3 have increased rates of protein decay. Finally, we show that Tbx3 can immortalize primary embryo fibroblasts and that the RD1 repression domain is required for this activity. Our results identify critical functional domains within the Tbx3 protein and facilitate interpretation of the functional consequences of present and future UMS mutations.

Progression of infection and tumor development in damselfish

The bicolor damselfish (Stegastes partitus) is a tropical marine teleost naturally affected by multiple neurofibromas and chromatophoromas on South Florida reefs. Damselfish neurofibromatosis is a transmissible disease caused by a subcellular agent. Development of tumors is associated with the appearance of a series of extrachromosomal DNAs ranging in size from 1.2 to 7 kb that appear to be the genome of a small virus-like agent which we termed the damselfish virus-like agent (DVLA). This DNA was found at high copy number in most spontaneous and experimentally induced tumors. An essentially identical pattern of DNA, but with lower copy numbers, was observed in non-tumor-bearing tissue from diseased fish. Copy numbers of DVLA DNA in tumors and nontumorous tissues increased as the disease progressed from early to late stages. In healthy fish in which DVLA DNA was detected, the quantities were much lower than those in diseased fish. Healthy fish from populations with a high prevalence of disease exhibited more infected tissues than fish from populations with low levels.

A biomechanical evaluation of the Christensen temporomandibular joint implant

The Christensen TMJ implant is often used clinically as a total joint replacement of the temporomandibular joint. The system consists of a thin fossa component and a condylar component with a polished articular head. In this study, we analyzed the surface finish and the metal structure of the components. We also measured the contact areas between the two components for different load levels. Such information may be useful in evaluating clinical performance as well as in making future improvements in the design of these implants.

Differential DNA binding and transcription modulation by three T-box proteins, T, TBX1 and TBX2

T-box genes encode a family of phylogenetically conserved DNA-binding proteins that regulate gene expression during embryogenesis. While the developmental importance of many T-box genes has been well documented, little is known about how family members differ in their DNA binding properties and ability to modulate transcription. Here we show that although TBX1, TBX2 and the Xenopus T protein (Xbra) share only 50-60% identity within their DNA-binding domains they can bind the same DNA sequence in vitro. However, the proteins differ in three important respects. While TBX1 protein binds a palindromic T oligonucleotide as a dimer, as had been previously reported for Xbra, TBX2 appears to bind the same DNA sequence as a monomer. Also, T protein/DNA complexes are stabilized in vitro by the addition of specific antibodies, whereas TBX2/DNA complexes are not stabilized by antibodies. Most importantly, TBX2 represses while Xbra activates transcription of the same chimeric reporter plasmid. TBX1, although capable of binding to the chimeric promoter, has no effect on transcription. Thus, while the DNA binding domains of T-box proteins share substantial homology, these proteins differ in both their DNA binding and transcriptional modulation properties. These results suggest that the various T-box proteins, while highly conserved, likely use different mechanisms to modulate transcription and may have different targets in vivo.

Different brain networks mediate task performance in normal aging and AD: defining compensation

OBJECTIVE

To determine whether the pathologic mechanisms of AD alter the brain networks subserving performance of a verbal recognition task.

BACKGROUND

Functional imaging studies comparing task-related activation in AD patients and controls generally have not used network analysis and have not controlled for task difficulty.

METHODS

H2 15O PET was used to measure regional cerebral blood flow in 14 patients and 11 healthy elders during the performance of a serial verbal recognition task under two conditions: low demand, with study list size (SLS) equal to one; and titrated demand, with SLS adjusted so that each subject recognized words at 75% accuracy. The Scaled Subprofile Model was used to identify networks of regionally covarying activity across these task conditions.

RESULTS

In the elders, higher SLS was associated with the recruitment of a network of brain areas involving left anterior cingulate and anterior insula (R2 = 0.94; p < 0.0001). Three patients also expressed this network. In the remaining patients, higher SLS was associated with the recruitment of an alternate network consisting of left posterior temporal cortex, calcarine cortex, posterior cingulate, and the vermis (R2 = 0.81, p < 0.001). Expression of this network was unrelated to SLS in the elders and more intact AD patients.

CONCLUSIONS

The patients' use of the alternate network may indicate compensation for processing deficits. The transition from the normal to the alternate network may indicate a point where brain disease has irreversibly altered brain function and thus may have important implications for therapeutic intervention.

Molecular characterization of a urea transporter in the gill of the gulf toadfish (Opsanus beta)

Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first teleostean urea transporter cloned, has high homology with UTs (facilitated urea transporters) cloned from mammals, an amphibian and a shark, and most closely resembles the UT-A subfamily. When expressed in Xenopus laevis oocytes, tUT increased urea permeability (as measured by [(14)C]urea uptake) five- to sevenfold, and this permeability increase was abolished by phloretin, a common inhibitor of other UTs. Northern analysis using the 1.8 kb clone was performed to determine the tissue distribution and dynamics of tUT mRNA expression. Of six tissues examined (gill, liver, red blood cells, kidney, skin and intestine), only gill showed expression of tUT mRNA, with a predominant band at 1.8 kb and a minor band at 3.5 kb. During several points in the urea pulse cycle of toadfish (0, 4, 6, 12 and 18 h post-pulse), measured by excretion of [(14)C]urea into the water, gill mRNA samples were obtained. Expression of tUT mRNA was found to be largely invariant relative to expression of beta-actin mRNA over the pulse cycle. These results further confirm the gill localization of urea transport in the toadfish and suggest that tUT regulation (and the regulation of pulsatile urea excretion) is probably not at the level of mRNA control. The results are discussed in the context of the mechanisms of vasopressin-regulated UT-A in mammalian kidney and morphological data for the toadfish gill.

Reproducibility of alternative probe synthesis approaches for gene expression profiling with arrays

Before gene expression profiling with microarray technology can be transferred to the diagnostic setting, we must have alternative approaches for synthesizing probe from limited RNA samples, and we must understand the limits of reproducibility in interpreting gene expression results. The current gold standard of probes for use with both microarrays and high-density filter arrays are synthesized from 1 microg of purified poly(A)+ RNA. We evaluated two approaches for synthesizing cDNA probes from total RNA with subsequent hybridization to high-density filter arrays: 1) reverse transcription (RT) of 5 microg total RNA and 2) RT-polymerase chain reaction (RT-PCR) of 1 microg total RNA, using the SMART system. The reproducibility of these two approaches was compared to the current gold standard. All three methods were highly reproducible. Triplicate experiments resulted in the following concordance correlation coefficients to evaluate reproducibility: 0.88 for the gold standard, 0.86 for cDNA probe synthesized by RT from total RNA, and 0.96 for the SMART cDNA probe synthesized from total RNA. We also compared the expression profile of 588 genes for the total RNA methods to that obtained with the gold standard. Of 150 positive genes detected by the gold standard, 97 (65%) were detected by cDNA probe synthesized by RT of total RNA, and 122 (81%) were detected by the SMART cDNA probe. We conclude that SMART cDNA probe produces highly reproducible results and yields gene expression profiles that represent the majority of transcripts detected with the gold standard.

Disruption of the murine nuclear factor I-A gene (Nfia) results in perinatal lethality, hydrocephalus, and agenesis of the corpus callosum

The phylogenetically conserved nuclear factor I (NFI) family of transcription/replication proteins is essential both for adenoviral DNA replication and for the transcription of many cellular genes. We showed previously that the four murine NFI genes (Nfia, Nfib, Nfic, and Nfix) are expressed in unique but overlapping patterns during mouse development and in adult tissues. Here we show that disruption of the Nfia gene causes perinatal lethality, with >95% of homozygous Nfia(-/-) animals dying within 2 weeks after birth. Newborn Nfia(-/-) animals lack a corpus callosum and show ventricular dilation indicating early hydrocephalus. Rare surviving homozygous Nfia(-/-) mice lack a corpus callosum, show severe communicating hydrocephalus, a full-axial tremor indicative of neurological defects, male-sterility, low female fertility, but near normal life spans. These findings indicate that while the Nfia gene appears nonessential for cell viability and DNA replication in embryonic stem cells and fibroblasts, loss of Nfia function causes severe developmental defects. This finding of an NFI gene required for a developmental process suggests that the four NFI genes may have distinct roles in vertebrate development.

Transcription repression by Xenopus ET and its human ortholog TBX3, a gene involved in ulnar-mammary syndrome

T box (Tbx) genes are a family of developmental regulators with more than 20 members recently identified in invertebrates and vertebrates. Mutations in Tbx genes have been found to cause several human diseases. Our understanding of functional mechanisms of Tbx products has come mainly from the prototypical T/Brachyury, which is a transcription activator. We previously discovered ET, a Tbx gene expressed in Xenopus embryos. We report here that ET is an ortholog of the human Tbx3 and that ET is a repressor of basal and activated transcription. Functional dissection of the ET protein reveals a novel transcription-repression domain highly conserved among ET, human TBX3, and TBX2. These results reveal a new transcription repressor domain, show the existence of a subfamily of transcription repressors in the Tbx superfamily, and provide a basis for understanding etiology of diseases caused by Tbx3 mutations.

The spectrum of mutations in TBX3: Genotype/Phenotype relationship in ulnar-mammary syndrome

Ulnar-mammary syndrome (UMS) is a pleiotropic disorder affecting limb, apocrine-gland, tooth, hair, and genital development. Mutations that disrupt the DNA-binding domain of the T-box gene, TBX3, have been demonstrated to cause UMS. However, the 3' terminus of the open reading frame (ORF) of TBX3 was not identified, and mutations were detected in only two families with UMS. Furthermore, no substantial homology outside the T-box was found among TBX3 and its orthologues. The subsequent cloning of new TBX3 cDNAs allowed us to complete the characterization of TBX3 and to identify alternatively transcribed TBX3 transcripts, including one that interrupts the T-box. The complete ORF of TBX3 is predicted to encode a 723-residue protein, of which 255 amino acids are encoded by newly identified exons. Comparison of other T-box genes to TBX3 indicates regions of substantial homology outside the DNA-binding domain. Novel mutations have been found in all of eight newly reported families with UMS, including five mutations downstream of the region encoding the T-box. This suggests that a domain(s) outside the T-box is highly conserved and important for the function of TBX3. We found no obvious phenotypic differences between those who have missense mutations and those who have deletions or frameshifts.

Constitutive expression of the Wilms tumor suppressor gene (WT1) in renal cell carcinoma

The expression of the Wilms tumor suppressor gene WT1 is largely restricted to elements of the developing urogenital system. In the fetal kidney, WT1 transcripts are present at low levels in the condensing mesenchyme and at much higher levels in differentiating glomerular epithelium and are not detected in other mesenchymal-derived epithelial structures such as the proximal and distal tubules. However, WT1 expression is observed in tubule-like elements found in some Wilms tumors. As renal cell carcinoma (RCC) of the clear cell type is one of the most prevalent adult tumors of the kidney, and is thought to originate from the epithelial cells of the proximal tubules, we studied WT1 expression in RCCs. Despite the absence of WT1 in normal primary epithelial cells derived from proximal tubules, RCC tumors and tumor-derived cell lines expressed WT1 RNA. Immunocytochemical analyses of tumor cryosections showed widespread expression throughout the poorly differentiated epithelial components of the tumor. Immunoblots of RCC samples detected a normal size WT I protein and reciprocal antibody immunoprecipitations of RCC cell extracts indicated that WT I interacts with p53 as has been demonstrated for normal human fetal kidney. The aberrant expression of functional WT1 in RCC may represent a reversion to a more de-differentiated phenotype and may contribute to the tumorigenic phenotype by inappropriately activating or repressing genes involved in growth regulation.

Genomic structure of TBX2 indicates conservation with distantly related T-box genes

TBX2 is a member of a recently discovered gene family of transcription factors, named T-box genes after the Brachyury or T gene. Mutations in two of these family members, TBX5 and TBX3, have recently been shown to be responsible for the congenital abnormalities associated with Holt Oram syndrome and ulnar-mammary syndrome respectively, while mutations in T-box genes in other species also result in developmental abnormalities in the tissues where the gene is normally expressed. Thus, it likely that other T-box genes are responsible for additional human developmental anomalies. Here we report the exon/intron boundaries of TBX2 and a polymorphism within intron 2 of TBX2 that should be useful for exploring the involvement of this gene in human genetic disease. We further note that the exon/intron boundaries of TBX2 are highly conserved within the T-box domain with those of both T and TBX5, as well as with a new human T-box gene and more distantly related genes from Caenorhabditis elegans and Drosophila. This observation should facilitate the analysis of the genomic structure of other members of this gene family. It is also of interest that several members of this gene family have an additional intron that is variably present within members of at least two different lineages of the T-box family. This observation has implications regarding the evolution of T-box genes.

Tissue-specific regulation of the WT1 locus

The 11p13 Wilms' tumor locus consists of two coordinately regulated transcripts, WT1 and WIT-1. These genes are highly expressed in the developing urogenital system, beginning with the urogenital ridge at day 10.5, the metanephric blastema at day 11.5, and during glomerular formation at day 13.5, becoming ultimately restricted to the podocytes. Stromal cells of the gonad also show abundant expression. WT1 is expressed at lower levels in spleen, uterus, mesothelial linings of organs in the abdominal and thoracic cavities, and the ependymal layer of the ventral aspect of the spinal cord. WIT-1 mRNA is about 10-fold less abundant than WT1, but appears to be expressed in the same tissue-restricted manner. Expression of the WT1 protein is required for kidney development, although its physiological function remains to be determined. The function of WIT-1 is similarly unknown but one intriguing possibility is that it is an antisense regulator of WT1. An understanding of events controlling spatial and temporal regulation of these genes will greatly improve our ability to study the role of WT1 and WIT-1 in urogenital development. We have found that while chimeric reporter constructs containing 0.6-2.5 kb of the 5' region of the WT1 gene direct transcription in many different cell lines, we were unable to detect expression in 13.5-day mouse embryos. However, a cosmid containing about 42 kb encompassing this region was able to direct the expression of abundant levels of mRNA from the appropriate transcription initiation sites in both stable transfectants of mouse Leydig cells (TM3) or in transgenic embryos. We are currently localizing the DNA elements required for this expression.

Regulation of WT1 by phosphorylation: inhibition of DNA binding, alteration of transcriptional activity and cellular translocation

Phosphorylation is one of the major post-translational mechanisms by which the activity of transcription factors is regulated. We have investigated the role of phosphorylation in the regulation of nucleic acid binding activity and the nuclear translocation of WT1. Two recombinant WT1 proteins containing the DNA binding domain with or without a three amino acid (KTS) insertion (WT1ZF + KTS and WT1ZF - KTS) were strongly phosphorylated by protein kinase A (PKA) and protein kinase C (PKC) in vitro. Both PKA and PKC phosphorylation inhibited the ability of WT1ZF + KTS or WT1ZF - KTS to bind to a sequence derived from the WT1 promoter region in gel mobility shift assays. The binding of WT1ZF - KTS to an EGR1 consensus binding site was also inhibited by prior PKA and PKC phosphorylation. We also demonstrate the RNA binding activity of WT1, but this was not altered by phosphorylation. PKA activation by dibutyryl cAMP in WT1-transfected cells resulted in the reversal of WT1 suppression of a reporter construct. Although WT1 protein is predominantly localized to the nucleus, this expression pattern is altered upon PKA activation, resulting in the cytoplasmic retention of WT1. Accordingly, phosphorylation may play a role in modulating the transcriptional regulatory activity of WT1 through interference with nuclear translocation, as well as by inhibition of WT1 DNA binding.

Is there implicit memory after propofol sedation?

Recent evidence indicates that implicit memory may be preserved during general anaesthesia. We tested for the presence of explicit and implicit memory in patients undergoing surgical procedures with local or regional anaesthesia and sedation with propofol. Initial i.v. boluses of propofol 0.5 mg kg-1 and fentanyl 1 microgram kg-1 were administered, followed by an infusion of propofol 50 micrograms kg-1 min-1. Administration of one or more doses of propofol 30 mg i.v. during operation was controlled either by the patient or the anaesthetist. At the start of the last skin stitch, patients were presented with a list of 15 stimulus words and the most frequently associated response. The infusion was then discontinued. After 1 h in the recovery area, all patients were tested for free recall, free association, cued recall and recognition on the list presented during surgery (critical list) and a matched list not presented (neutral list). Data of all patients without free recall (explicit memory) were analysed with repeated-measures analysis of variance. Of 36 patients, five demonstrated free recall. For the remaining 31 patients, cued recall and recognition showed no evidence of explicit memory. However, the free association tests demonstrated significant priming. The mean number of critical free associations was 6.6 (SEM 0.4) compared with 5.5 (0.4) neutral free association (P < 0.05). In the absence of explicit memory, implicit memory persists after intraoperative sedation with propofol.

Synergistic transcriptional activation of the tissue inhibitor of metalloproteinases-1 promoter via functional interaction of AP-1 and Ets-1 transcription factors

The tissue inhibitor of metalloproteinases-1 (TIMP-1) is an inhibitor of the extracellular matrix-degrading metalloproteinases. We characterized response elements that control TIMP-1 gene expression. One contains a binding site that selectively binds c-Fos and c-Jun in vitro and confers a response to multiple AP-1 family members in vivo. Adjacent to this is a binding site for Ets domain proteins. Although c-Ets-1 alone did not activate transcription from this element, it enhanced transcription synergistically with AP-1 either in the context of the natural promoter or when the sequence was linked upstream of a heterologous promoter. Furthermore, a complex of c-Jun and c-Fos interacted with c-Ets-1 in vitro. These results suggest that AP-1 tethers c-Ets-1 to the TIMP-1 promoter via protein-protein interaction to achieve Ets-dependent transcriptional regulation. Collectively, our results indicate that TIMP-1 expression is controlled by several DNA response elements that respond to variations in the level and activity of AP-1 and Ets transcriptional regulatory proteins.

A constant cathodic potential device for faradic stimulation of osteogenesis

The purpose of this study was to design, develop, and test a device that continuously maintains a constant potential at a cathode with respect to a reference electrode by automatically varying the potential between the cathode and an anode. The ability of the device to maintain a constant cathodic potential with respect to a silver/silver chloride reference electrode is demonstrated in acute testing with a variety of electrodes as well as in chronic testing conducted until battery failure. This constant cathodic potential device permits delivery of current at an optimal cathodic potential for faradic stimulation of osteogenesis which involves a net transfer of charge through biological tissue between, typically, an implanted cathode, the negative electrode where osteogenesis occurs, and either an implanted or a topical anode, the positive electrode required only to complete the electrical circuit. Unlike present devices that maintain a constant direct current between a cathode and an anode but permit potential between said electrodes to vary, this device presents the possible detrimental effects of an undesired electrochemical reaction due to an excessive cathodic potential.

Asymptomatic undetected mediastinal mass: a death during ambulatory anesthesia

T-cell lymphoma is the fastest growing non-Hodgkin's lymphoma occurring in children. Its clinical presentation is frequently abrupt, and total tumor mass can double every few days. At the same time, the number of ambulatory anesthesia procedures for children is increasing at a rapid rate. Anesthesiologists are constantly faced with decisions regarding the adequacy of available preoperative information. What information do we need, and how recent should it be? This case shows that recent diagnostic imaging studies not showing the presence of a mediastinal lymphoma can be misleading. It provides a strong warning to all anesthesiogists involved in ambulatory anesthesia.

Antisense transcripts and protein binding motifs within the Wilms tumour (WT1) locus

Transcription of the WT1 locus is restricted, both temporally and spatially, to a subset of epithelial cells in mammalian kidneys and gonads. WT1, one of the two divergent transcripts mapping to this locus encodes a zinc finger protein that is likely a transcriptional regulator. The other transcript, WIT1, encodes a product of unknown function that is subject to alternate splicing in the region immediately 5' of the WT1 gene. Analysis of the 5' end of this locus further revealed the presence of multiple transcriptional start sites for both genes, such that some of the WIT1 transcripts are encoded by the antisense strand of the first exon of WT1. The genomic region surrounding the transcriptional start sites appears to constitute part of a bi-directional promoter based on the ability of a DNA fragment derived from this region to direct expression of a chimeric CAT gene construct in transient transfection assays. Discrete sequences within the region are capable of interaction in vitro with nuclear extracts derived from a variety of rat and mouse tissues. Interestingly, recombinant WT1, representing the product of zinc finger region of the most abundant of the four alternatively spliced transcripts, is also capable of binding to sequences within this region.

The role of WT1 in Wilms tumorigenesis

Genetic alterations in tumor suppressor genes are believed to play an important role in the initiation of childhood and adult malignancies. Tumor-specific loss of heterozygosity for particular chromosomal regions has provided the starting point for the cloning of different tumor suppressor genes, including the Wilms tumor predisposing gene, WT1, at chromosome 11p13. This article reviews the pathology and genetics of Wilms tumor, the cloning of WT1, and the WT1 mutations reported thus far in 15 hereditary and nonhereditary Wilms tumors. The presence of constitutional WT1 mutations in 35 patients with the Denys-Drash syndrome (a syndrome consisting of nephropathy, intersex disorders, and Wilms tumor) is also described. To date, mutations in the WT1 gene have been found in less than 10% of Wilms tumors specimens examined and in greater than 95% of Denys-Drash patients. The possible significance of this observation with regard to both the cellular function of the WT1 protein and the involvement of alternative loci in the development of Wilms tumor is discussed.

Review of respirator performance testing in the workplace: issues and concerns

Performance capability of respirators has traditionally been evaluated by testing components of the respirator (e.g., filter efficiency), facepiece fit, total inward leakage, or some other measure of performance evaluated under laboratory conditions. In recent years, increased emphasis has been placed on development of test methods suitable for evaluating respirator performance in the workplace. The goal of such testing is to evaluate the level of protection provided by respirators in the work environment. The AIHA Respiratory Protection Committee believes that workplace testing of respirators has the potential to be an excellent tool for increasing knowledge about the effectiveness of respiratory protection. However, a number of technical issues remain to be addressed before optimal test protocols and data analysis methods can be defined. The progress made to date in workplace testing will be reviewed, and broader discussion about key elements that must be considered when developing guidelines for testing respirators in the workplace will be initiated.

Loss of heterozygosity mapping in Wilms tumor indicates the involvement of three distinct regions and a limited role for nondisjunction or mitotic recombination

Loss of heterozygosity (LOH) for polymorphic markers is a frequently occurring event in some tumors, reflecting the role of allele loss in the development of these tumors. We have determined LOH in 38 cases of Wilms tumor for the 2 known loci on chromosome arm 11p and for a newly detected locus on chromosome arm 16q. Only 7 of the 38 tumors studied showed reduction to homozygosity of 11p13 markers. In 4 of these tumors, reduced expression of WT1 and WIT1, genes located at 11p13 and implicated in Wilms tumorigenesis, was noted. However, this was also found in 2 of 7 tumors showing LOH exclusively of 11p15 markers and in 15 of the remaining 24 tumors in which there was no LOH for 11p markers. This suggests that events not involving mitotic recombination or chromosome nondisjunction are the most common mechanisms for mutations at the 11p Wilms tumor locus. We also noted that mitotic recombination involving 11p15 loci occurred in addition to reduced expression of the 11p13 locus genes in 2 tumors, suggesting a possible interaction between these 2 loci. In addition, LOH for 16q markers was observed in 6 tumors. In one case this was coincident with reduction of WT1 and WIT1 gene expression, and in 3 other cases it occurred in addition to 11p LOH. This indicates that an additional locus on 16q is likely to be involved in Wilms tumorigenesis.

Intravenous nitroglycerin for uterine inversion

Uterine inversion following vaginal delivery or during Cesarean section is rare. Cardiovascular instability resulting from blood loss is possible. This article describes the use of intravenous nitroglycerin as an alternative to the induction of general anesthesia and administration of volatile anesthetics to provide uterine relaxation.

Identification of a serum- and phorbol ester-responsive element in the murine tissue inhibitor of metalloproteinase gene

Tissue inhibitor of metalloproteinase (TIMP) is one of a family of metalloproteinase inhibitors and a major interstitial inhibitor of collagenase. Transcription of the TIMP gene is induced by such diverse agents as viruses, phorbol esters, serum, and growth factors. We have previously assigned the regulatory elements responsible for induction of transcription in response to viruses to the first intron of the murine TIMP gene. Here we have identified a promoter and an enhancer element responsive to serum and the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate. Based on a comparative sequence analysis of the murine and human genes, the enhancer element is part of a 38-base pair conserved sequence. Gel mobility shift assays indicate that this enhancer is a phorbol ester-responsive-like element that likely binds one of a family of AP-1 proteins. Interestingly, the region containing the phorbol ester-responsive-like element is also sufficient to direct a response to transforming growth factor beta 1 in the presence of serum.

Tissue, developmental, and tumor-specific expression of divergent transcripts in Wilms tumor

The Wilms tumor locus on chromosome 11p13 has been mapped to a region defined by overlapping, tumor-specific deletions. Complementary DNA clones representing transcripts of 2.5 (WIT-1) and 3.5 kb (WIT-2) mapping to this region were isolated from a kidney complementary DNA library. Expression of WIT-1 and WIT-2 was restricted to kidney and spleen. RNase protection revealed divergent transcription of WIT-1 and WIT-2, originating from a DNA region of less than 600 bp. Both transcripts were present at high concentrations in fetal kidney and at much reduced amounts in 5-year-old and adult kidneys. Eleven of 12 Wilms tumors classified as histopathologically heterogeneous exhibited absent or reduced expression of WIT-2, whereas only 4 of 14 histopathologically homogeneous tumors showed reduced expression. These data demonstrate a molecular basis for the pathogenetic heterogeneity in Wilms tumorigenesis.