Ion chromatographic determination of acidity

The practice of determining acid concentrations by titrations has remained unchanged for more than a century. We introduce a new approach to the determination of acid concentrations based on cation exchange chromatography. We demonstrate the ability of sulfonated styrene-divinylbenzene based stationary phases to separate the hydrogen ion from other monovalent cations. The eluent is a dilute solution of a neutral salt, sometimes containing a small concentration of the corresponding acid, e.g., sodium ethanesulfonate, pH adjusted with ethanesulfonic acid. The high equivalent conductance (approximately 350 S.cm2/equiv) of H+ and relatively low eluent concentration allows sensitive conductometric detection of H+, down to the 50 microM level under favorable conditions. The conductometric response to H+ can be linear over a wide range of H+ concentrations, from sub-millimolar to several molar concentrations. The system allows the rapid quantitation of strong acids; weak acids can also be determined depending on pKa and injected concentration. The determinations of several strong and weak acids are presented along with factors that govern their chromatographic analysis.     

Fracture mechanisms of sapphire under bending

The fracture mechanisms of a rapidly advancing crack in a single crystal are under investigation. Thin sapphire plates parallel to the basal plane were used as a model material for this purpose. Tests in three point bending (3PB) were carried out with smooth and with notched thin strip-shaped specimens having three different orientations with respect to the (1010) plane. The effect of the orientation on the fracture mechanisms is discussed and explained. Unique behavior was observed in the 3PB loading configuration, resulted from the typical state of stress in bending, i.e., tension in the lower, and compression in the upper region of the beam, which affected the fracture mechanisms. The continual changes of the crack direction and energy revealed a large spectrum of fracture phenomena. The major phenomena are explained. The effect of the mechanical energy on fracture mechanisms and topology is discussed.     

Gradient maintenance using discrete brine injections in a salt gradient solar pond

A method for the maintenance of the stratification in the gradient zone of a salt gradient solar pond is presented. The method is unique for solar ponds in that it involves the injection of highly turbulent colummar jets into homogeneous convective zones. This contrasts with the more common practice of traversing the gradient zone with a disk-shaped diffuser while injecting fluid at low exit Froude numbers. Using turbulent jet theory which is well understood for columnar buoyant jets, the method allows a priori determination of the resulting salinity gradient with a reasonable level of confidence. The simple injector is easily constructed and deployed. Field data collected at the Alice Springs solar pond show that the technique can quickly remove internal convective zones as well as extend the top of the gradient into the surface layer, providing a valuable tool for the operators of solar ponds.     

Relation between self-reported affect and drug urges and cravings in continuing and withdrawing smokers.

Investigated, in 2 experiments, the effects of withdrawal and stress on the affective correlates of urges to smoke. In both, habitual cigarette smokers were divided into continuing and withdrawing smoker groups. In the 1st study, 44 adults reported current mood, urge, and expectations over a 24-hr period. In the 2nd, a controlled laboratory study, urge, affect, and physiological data were obtained from continuing and withdrawing groups (N?=?64) exposed to high- or low-stress conditions. Urges among withdrawing smokers were positively associated with negative affect and negatively associated with positive affect; continuing smokers reported urges that were directly associated with positive affect and unrelated to negative affect. Stress and withdrawal produced urge and self-reports that were related to negative affect. Moreover, Ss who smoked after exposure to withdrawal and stress reported greater pleasure and arousal than did other Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning patterns in terms of other patterns

This paper investigates the learning of patterns in terms of previously learned patterns. The main problem is to efficiently select from the set of all previously learned patterns a few in terms of which the pattern to be learned can be described. A computer program for doing this is described and the importance of its memory organization is discussed.     

Bioinspired Golden Spiral Shapes on Crushing Protection Behaviors of Tubular Structures

Advanced structure design for energy absorption is a long-lasting pursuit due to its fascinating scientific merit in mechanics and important engineering application. Curves, a type of mathematical variation in geometry, are widely adopted in the biological system and biomaterial structures after long-time nature evolution toward optimization and adaption. Inspired by nature, a novel type of tubular structure is designed with golden spiral curvature. With the variations in the hierarchy of the supporting spirals and the number of arms, a maximum of 38.8% increase is demonstrated in performance over an uncurved counterpart structure. The computational modeling reveals that the additional added golden spiral arms within the tube enhance the rigidity and increase the energy dissipation via progress buckling involved by additional materials such that the energy absorption upon crushing is significantly improved. Theoretical models then provide intrinsic underlying mechanics analysis with more intuitive design guidance for such structures. Results develop an efficient yet simple design based on widely accepted tubular structure design for impact protection, enrich the mechanistic understanding of the nonlinear buckling behaviors, and provide applicable design guidance for engineering structures.     

Chemoenzymatic Synthesis of Glycosylated Macrolactam Analogues of the Macrolide Antibiotic YC‐17

YC‐17 is a 12‐membered ring macrolide antibiotic produced from Streptomyces venezuelae ATCC 15439 and is composed of the polyketide macrolactone 10‐deoxymethynolide appended with D ‐desosamine. In order to develop structurally diverse macrolactam analogues of YC‐17 with improved therapeutic potential, a combined approach involving chemical synthesis and engineered cell‐based biotransformation was employed. Eight new antibacterial macrolactam analogues of YC‐17 were generated by supplying a novel chemically synthesized macrolactam aglycone to S. venezuelae mutants harboring plasmids capable of synthesizing several unnatural sugars for subsequent glycosylation. Some YC‐17 macrolactam analogues were active against erythromycin‐resistant bacterial pathogens and displayed improved metabolic stability in vitro. The enhanced therapeutic potential demonstrated by these glycosylated macrolactam analogues reveals the unique potential of chemoenzymatic synthesis in antibiotic drug discovery and development.

     

Guest Entrapment in Metal-Organic Nanosheets for Quantifiably Tuneable Luminescence

Luminescent metal-organic frameworks (LMOFs) are promising materials for nanophotonic applications due to their tuneable structure and programmability. Yet, the 3D nature of LMOFs creates challenges for stability, optical transparency, and device integration. Metal-organic nanosheets (MONs) potentially overcome these limitations by combining the benefits of metal-organic frameworks (MOFs) with an atomically thin morphology of large planar dimensions. Herein, the bottom-up synthesis of few-layer thin ZIF-7-III MONs via facile low-energy salt-templating is reported. Employing guest@MOF design, the fluorophores Rhodamine B and Fluorescein are intercalated into ZIF-7 nanosheets (Z7-NS) to form light emissive systems exhibiting intense and highly photostable fluorescence. Aggregation and Förster resonance energy transfer, enabled by the MON framework, are revealed as the mechanisms behind fluorescence. By varying guest concentration, these mechanisms provide predictable quantified control over emission chromaticity of a dual-guest Z7-NS material and the definition of an “emission chromaticity fingerprint” – a unique subset of the visible spectrum that a material can emit by fluorescence.     

Model-based systems engineering approaches to chemicals and materials manufacturing

Model-based systems engineering (MBSE) is part of a long-term trend toward model-centric approaches adopted by many engineering disciplines. We establish the need of an MBSE approach by reviewing the importance, complexity, and vulnerability of the U.S. chemical supply chains. We discuss the origins, work processes, modeling approaches, and supporting tools of the systems engineering discipline (SE) and discuss limitations of the Process Systems Engineering (PSE) framework. We make the case for MBSE as a more generalizable approach. We introduce systems modeling strategies for MBSE, and a novel MBSE method that supports the automation tailored and extended to support the analysis of chemical supply chains. We demonstrate a specific use case of this method by creating a systems model for the manufacturing of an active pharmaceutical ingredient, Atropine. We conclude with a prospectus on developmental opportunities for extracting greater benefit from MBSE in the design and management of chemical supply chains.