Local Structure of Alkaline-Earth Boroaluminate Crystals and Glasses: I, Crystal Chemical Concepts—Structural Predictions and Comparisons to Known Crystal Structures

This paper presents a model which predicts glass structures based on local charge balance considerations. The model is shown to be consistent with known structures of borate, aluminate, and boroaluminate crystals and predicts that boroaluminate glasses should contain 3- and 4-coordinate boron, 4-, 5-, and 6-coordinate aluminum, and oxygens coordinated to one, two, three, and perhaps even four network-forming cations. The predicted glass structures are more complex than previous models for boroaluminate glasses, explaining the solid-state NMR data for the boroaluminate glasses discussed in Part II.     

Using 15N‐Ammonium to Characterise and Map Potassium Binding Sites in Proteins by NMR Spectroscopy

A variety of enzymes are activated by the binding of potassium ions. The potassium binding sites of these enzymes are very specific, but ammonium ions can often replace potassium ions in vitro because of their similar ionic radii. In these cases, ammonium can be used as a proxy for potassium to characterise potassium binding sites in enzymes: the ¹H,¹⁵N spin‐pair of enzyme‐bound ¹⁵NH₄⁺ can be probed by ¹⁵N‐edited heteronuclear NMR experiments. Here, we demonstrate the use of NMR spectroscopy to characterise binding of ammonium ions to two different enzymes: human histone deacetylase 8 (HDAC8), which is activated allosterically by potassium, and the bacterial Hsp70 homologue DnaK, for which potassium is an integral part of the active site. Ammonium activates both enzymes in a similar way to potassium, thus supporting this non‐invasive approach. Furthermore, we present an approach to map the observed binding site onto the structure of HDAC8. Our method for mapping the binding site is general and does not require chemical shift assignment of the enzyme resonances.     

Using the local approach to evaluate scaling effects in ductile fracture

This paper uses a local model to predict ductile fracture in geometrically similar structures of different sizes containing either sharp cracks or blunt stress concentrators. Simple theoretical considerations suggest that when fracture occurs by quasi-isotropic void growth, fracture initiation at blunt notches follows replica scaling, whereas fracture initiation at sharp cracks does not. Simulations with a local fracture model of fracture events in (1) fatigue precracked compact specimens and (2) three-point-bend bars containing blunt notches confirm these conclusions. However, a comparison of simulations with actual experimental results with HY-130 steel specimens leads to mixed conclusions. Predicted and observed behaviors for fracture at sharp cracks agree well, but the discrepancy is considerable for fracture initiating at blunt notches loaded in bending. Significant scaling effects are observed in the experiments for the conditions of fracture initiation at blunt notches. Fractographic analysis reveals that the reason for this discrepancy is a difference in the micromechanisms controlling fracture at sharp cracks as opposed to blunt notches. At sharp cracks, quasi-isotropic void growth dominates, whereas fracture initiates at blunt notches by a shear localization process and the nucleation, growth, and coalescence of voids in a mixed shear and tensile deformation field. The transition from one mode to the other may be governed by the hardening rate and, if so, is material dependent. Therefore, when using local fracture models for predicting fracture under generalized geometric and loading conditions, care must be taken, that the micromechanisms of ductile fracture invoked in the actual material match those assumed by the local fracture model. If this correspondence is verified, local fracture models can be used to predict fracture conditions and associated scaling effects for situations not amenable to treatment by classical elasto-plastic fracture mechanics. However, new or expanded models that can treat ductile fracture in localized shear zones should be developed to realize the full potential of these local fracture methodologies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Romantic jealousy and adult romantic attachment

Research on romantic jealousy is consistent with the idea that jealousy is, at least in part, the product of threats to attachment relationships. Attachment theory was used as a framework for examining individual differences in the ways in which people experience and express jealousy. Emotional, behavioral, and cognitive concomitants of romantic jealousy were related to differences in attachment style in ways consistent with attachment theory. For example, anxious participants were relatively more likely than others to resist expressing their anger, avoidant participants were especially likely to turn their anger and blame against the interloper, and securely attached participants were especially likely to express anger toward the partner and to maintain their relationship. Differences in attachment style, not just differences in level of security, are predictive of qualitative individual differences in jealousy experiences.     

Detection of Candida dubliniensis in oropharyngeal samples from human immunodeficiency virus-infected patients in North America by primary CHROMagar candida screening and susceptibility testing of isolates

Candida dubliniensis has been associated with oropharyngeal candidiasis in patients infected with human immunodeficiency virus (HIV). C. dubliniensis isolates may have been improperly characterized as atypical Candida albicans due to the phenotypic similarity between the two species. Prospective screening of oral rinses from 63 HIV-infected patients detected atypical dark green isolates on CHROMagar Candida compared to typical C. albicans isolates, which are light green. Forty-eight atypical isolates and three control strains were characterized by germ tube formation, differential growth at 37, 42, and 45 degreesC, identification by API 20C, fluorescence, chlamydoconidium production, and fingerprinting by Ca3 probe DNA hybridization patterns. All isolates were germ tube positive. Very poor or no growth occurred at 42 degreesC with 22 of 51 isolates. All 22 poorly growing isolates at 42 degreesC and one isolate with growth at 42 degreesC showed weak hybridization of the Ca3 probe with genomic DNA, consistent with C. dubliniensis identification. No C. dubliniensis isolate but only 18 of 28 C. albicans isolates grew at 45 degreesC. Other phenotypic or morphologic tests were less reliable in differentiating C. dubliniensis from C. albicans. Antifungal susceptibility testing showed fluconazole MICs ranging from 相似文献   

Effects of total replacement of atrial myosin light chain-2 with the ventricular isoform in atrial myocytes of transgenic mice

BACKGROUND: In contrast to their well-known and critical role in excitation-contraction coupling of vascular smooth muscle, the effects of the myosin light chains on cardiomyocyte mechanics are poorly understood. Accordingly, we designed the present experiment to define the cardiac chamber-specific functional effects of the ventricular isoform of the regulatory myosin light chain (MLC2v). METHODS AND RESULTS: Postnatal transgenic cardiac-specific overexpression of MLC2v was achieved by use of the alpha-myosin heavy chain promoter. Enzymatically disaggregated atrial and ventricular mouse myocytes were field-stimulated at multiple frequencies, and mechanical properties and calcium kinetics were studied by use of video edge detection and FURA 2-AM, respectively. MLC2v overexpression resulted in complete replacement of the atrial with the ventricular isoform of the regulatory myosin light chain at the steady-state mRNA and protein levels in the atria of transgenic mice. Mechanical properties of transgenic atrial myocytes were enhanced to the level of ventricular myocytes of control animals in association with modest decreases in the amplitude of the calcium transient. CONCLUSIONS: MLC2v modulates chamber-specific contractility by enhanced calcium sensitivity and/or improved cross-bridge cycling of the thin and thick filaments of the cardiomyocyte.     

Hydration of Calcium Aluminate Cements: A Solid-State 27 Al NMR Study

This paper presents the results of a study of the hydration of calcium monoaluminate (CA) and Lafarge Secar 71 (CA + CA₂) using ²⁷Al MAS and ¹H-²⁷ Al CPMAS NMR spectroscopy. CPMAS, high H ₀ magnetic field strengths (11.7 T), and high MAS spinning speeds (13–14 kHz) provide significant new information about the Al structural environments present during hydration and about the mechanisms of hydration. Important results include the following: (1) Hydrated Al(4) and Al(6) environments are present during the incubation period. This observation is consistent with previously published hydration models. (2) The overall conversion of Al(4) in unhydrated phases to Al(6) in hydrated phases and the crystalline phases detected by XRD are similar to the results of previous studies. (3) There are previously undetected hydrated reaction intermediates present during the main reaction stage. At temperatures above 25°C this phase contains Al(4), and at 4°C it contains Al(4) and possibly Al(5). The incubation period observed for this reaction may be related to the nucleation of this phase.