Mullite for Structural, Electronic, and Optical Applications

Mullite (3Al₂O₃·2SiO₂) is becoming increasingly important in electronic, optical, and high-temperature structural applications. This paper reviews the current state of mullite-related research at a fundamental level, within the framework of phase equilibria, crystal structure, synthesis, processing, and properties. Phase equilibria are discussed in terms of the problems associated with the nucleation kinetics of mullite and the large variations observed in the solid-solution range. The incongruent melting behavior of mullite is now widely accepted. Large variations in the solid solubility from 58 to 76 mol% alumina are related to the ordering/disordering of oxygen vacancies and are strongly coupled with the method of synthesis used to form mullite. Similarly, reaction sequences which lead to the formation of mullite upon heating depend on the spatial scale at which the components are mixed. Mixing at the atomic level is useful for low-temperature (<1000°C) synthesis of mullite but not for low-temperature sintering. In contrast, precursors that are segregated are better suited for low-temperature (1250° to 1500°C) densification through viscous deformation. Flexural strength and creep resistance at elevated temperatures are significantly affected by the presence of glassy boundary inclusions; in the absence of glassy inclusions, polycrystalline mullite retains >90% of its room-temperature strength to 1500°C and displays very high creep resistance. Because of its low dielectric constant, mullite has now emerged as a substrate material in high-performance packaging applications. Interest in optical applications mainly centers on its applicability as a window material within the mid-infrared range.     

Fracture mechanics model for subthreshold indentation flaws

A fracture mechanics model for subthreshold indentation flaws is. described. The model describes the initiation and extension of a microcrack from a discrete deformation-induced shear fault (shear crack) within the contact zone. A stress-intensity factor analysis for the microcrack extension in residual-contact and applied-stress fields is used in conjunction with appropriate fracture conditions, equilibrium in Part I and non-equilibrium in Part II, to determine critical instability configurations.In Part I, the K-field relations are used in conjunction with the Griffith requirements for crack equilibrium in essentially inert environments to determine: (i) the critical indentation size (or load) for spontaneous radial crack pop-in from a critical shear fault under the action of residual stresses alone; (ii) the inert strengths of surfaces with subthreshold or postthreshold flaws. The theory is fitted to literature data for silicate glasses. These fits are used to calibrate dimensionless parameters in the fracture mechanics expressions, for later use in Part II. The universality of the analysis in its facility to predict the main features of crack initiation and propagation in residual and applied fields will be demonstrated. Special emphasis is placed on the capacity to account for the significant increase in strength (and associated scatter) observed on passing from the postthreshold to the subthreshold domain.     

Multifunctional and Low-Density Inorganic Nanocomposites

We summarize our recent studies on the use of low-density nanoporous silica structures prepared through templating of a self-assembling disordered liquid-crystalline L ₃ phase, as a matrix for use in numerous applications, including sensing, optical data storage, drug release, and structural. The silica matrix exhibits low density (0.5 g cm⁻³ to 0.8 g cm⁻³ for monoliths, 0.6 g cm⁻³ to 0.99 g cm⁻³ for fibers) coupled with high surface areas (up 1400 m² g⁻¹) and void volumes (65% or higher). High-surface-area coatings are used to increase the sensitivity of mass-detecting quartz crystal microbalances to over 4000 times that of uncoated crystals. Monoliths, films, and fibers are produced using the templated silica gel. Once dried and converted to silica, the nanostructured material exhibits high fracture strength (up to 35 MPa in fibers) and Young’s modulus (30 GPa to 40 GPa in fibers). These values are, respectively, two orders of magnitude and twice those of nanostructured silicas having comparable densities.     

Testosterone and occupational choice: Actors, ministers, and other men.

Occupational differences in testosterone concentrations, focusing on actors and ministers, were explored in 3 studies. The 1st examined salivary testosterone in 7 occupational groups and an unemployed comparison group and found actors and football players higher than ministers but no other significant differences. The 2nd examined salivary testosterone in 2 kinds of actors (stage actors and comedians) and 2 kinds of ministers (pastoral ministers and missionaries) and found actors high and ministers low but no differences between subgroups within each occupation. The 3rd examined serum testosterone in entertainers and ministers in a archival sample of military veterans and found entertainers high and ministers low. The results are interpreted in terms of dominance and antisocial tendencies, with the conclusion that these variables are complex and can affect occupational preference in subtle ways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biliary excretion mechanism of CPT-11 and its metabolites in humans: involvement of primary active transporters

After administration of CTP-11, a camptothecin derivative exhibiting a wide spectrum of antitumor activity, dose-limiting gastrointestinal toxicity with great interpatient variability is observed. Because the biliary excretion is a major elimination pathway for CPT-11 and its metabolites [an active metabolite, 7-ethyl-10-hydroxy-camptothecin (SN-38), and its glucuronide, SN38-Glu], several hypotheses for the toxicity involve biliary excretion. Here, we investigated whether primary active transport is involved in the biliary excretion of anionic forms of CPT-11 and its metabolites in humans using bile canalicular membrane vesicles (cMVs). Uptake of the carboxylate form of CPT-11 and the carboxylate and lactone forms of SN38-Glu by cMVs prepared from five human liver samples was ATP dependent. The concentration dependence of the ATP-dependent uptake of the carboxylate form of CPT-11 and SN38-Glu suggests the involvement of at least two saturable transport components, both with lower affinity and higher capacity than in rats. The ATP-dependent uptake of the carboxylate form of SN-38 showed a single saturable component but was detectable only in one human cMV sample. Both carboxylate and lactone forms of SN38-Glu uptake also showed a large intersample variability, although the variability was less than that observed for the carboxylate form of SN-38. On the other hand, the carboxylate form of CPT-11 exhibited much less variability. The carboxylate forms of SN38-Glu and SN-38 almost completely inhibited the ATP-dependent uptake of leukotriene C4, a well-known substrate of canalicular multispecific organic anion transporter, whereas the inhibition by the carboxylate form of CPT-11 was not as marked. Thus, multiple primary active transport systems are responsible for the biliary excretion of CPT-11 and its metabolites, and the major transport system for CPT-11 differs from that for the other two compounds. A greater degree of inter-cMV variability in the uptake of SN-38 and SN38-Glu may imply that interindividual variability in biliary excretion of these metabolites might contribute to interpatient variability in the toxicity caused by CPT-11.     

Testosterone as a Social Inhibitor: Two Case Studies of the Effect of Testosterone Treatment on Language.

This study aimed to correlate testosterone levels with natural written language in 2 people undergoing testosterone therapy. Two participants, a man receiving treatment for loss of upper-body strength and a female-to-male transgendered individual, supplied records of injections over 1-2 years along with e-mails or journal entries as writing samples. Results showed that higher testosterone levels correlated with reduced use of words related to social connections. Language relating to anger, sexuality, and achievement was unrelated to testosterone levels. It appears that testosterone steers attention away from social connections but not necessarily toward concerns with aggression or sexual activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-esteem, communicator characteristics, and attitude change.

Characteristic defenses were predicted to cause different Ss to resist influence from different kinds of persuasive communications. In a 3-way factorial design, 88 Ss representing high and low self-esteem were exposed to optimistic and pessimistic communications from communicators who were portrayed as "copers" or "noncopers." Optimism-pessimism unexpectedly produced no effect. However, characteristics of the communicator interacted with characteristics of Ss in producing attitude change. High-esteem Ss were influenced more by the coper and low-esteem Ss by the noncoper, even though all Ss evaluated the noncoper unfavorably. Further investigation indicated that Ss high and low in self-esteem were themselves copers and noncopers, respectively. Ss appeared to accept persuasive influence from the communicator more comparable to themselves, regardless of how they consciously felt toward him. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subthreshold flaws and their failure prediction in long-distanceoptical fiber cables

A study of surface defects and static fatigue data is presented to support the view that subthreshold surface defects are responsible for failure in proof-tested optical fibers. For this type of defect, crack initiation, as opposed to crack growth, is the rate-limiting step. Classical crack propagation theory does not describe this process sufficiently well for lifetime production, but semiempirical techniques indicate that this popular treatment may be pessimistic. A more conventional reliability treatment, similar to that used for other system components, appears to offer the best available approach to the task of failure lifetime prediction in proof-tested fibers     

Analytical evaluation and comparison of Dupont aca lactate dehydrogenase-1 (LD1) isoenzyme assay diagnostic efficiency for acute myocardial infarction detection with other LD1 methods and aca CK-MB. A two-site study

The purpose of this study was to examine the analytical characteristics of a rapid new assay for lactate dehydrogenase 1 (LD1) isoenzyme on the Dupont aca analyzer and the diagnostic efficiency of LD1 for detection of acute myocardial infarction (AMI) when used alone and with creatine kinase MB (CKMB). Total aca LD1 assay precision, with percent coefficients of variation (%CVs) of less than 3.2% from 56 U/L to 469 U/L LD1, across fifty assay days was excellent. Linearity was confirmed from 0 to 332 U/L and no detectable calibration drift was noted from 5 to 489 U/L over a ninety-day period. The aca LD1 results compared well with Roche Isomune-LD1, Abbott Spectrum A-Gent, Helena electrophoresis, and Beckman electrophoresis LD1 methods, giving r's from 0.987 to 0.994, slopes from 0.94 to 1.65, and y-intercepts from -2.95 to 6.94 U/L. Examination of 450 ambulatory subjects, about equally distributed by sex, yielded a 43 +/- 14 U/L aca LD1 patient reference interval. Serum samples from 159 consecutive patients at the University of Tennessee Memorial Hospital and 96 patients at Allentown Hospital, submitted for AMI detection assistance, were assayed in a single-blind study for LD1 and ion-exchange CKMB by Dupont aca methods, which provide automated results in ten minutes whenever needed. The aca LD1 assay yielded a clinical sensitivity of 89% and specificity of 95% for AMI with a decision threshold of 120 U/L. The diagnostic efficiency of the aca LD1 assay was 94% at 120 U/L, which equaled or exceeded that of the three comparative LD1 methods. The predictive value of positive (PV+) and negative (PV-) results on the first sample collected were 80% and 85% for aca LD1, 65% and 90% for aca ion-exchange CKMB, and 83% and 90% when both tests were combined. Significantly, the PV+ and PV- results when two or more samples were assayed was improved to 88% and 95% for aca LD1, relatively constant at 65% and 97% for aca ion-exchange CKMB, and dramatically improved to 95% and 100% when both CKMB and LD1 tests were combined. The results from these two medical centers show that the aca LD1 assay provides useful clinical information for AMI diagnosis when employed alone or in combination with aca CKMB. These results also suggest that LD1 should be included in biochemical evaluations for AMI to attain optimal predictive values of results.