Resonance peak and incommensurability in cuprate perovskites

The magnetic susceptibility of yttrium and lanthanum cuprates is interpreted based on the self-consistent solution of the t-J model of Cu-O planes. To take a proper account of strong electron correlations inherent in cuprates, the calculations were carried out in the formalism of the Hubbard operators and Mori’s projection operator technique. The calculations correctly reproduce the frequency and momentum dependences of the resonance peak in YBa₂Cu₃O_{7 ? y} and its variation with doping and temperature in the normal and superconducting states. In lanthanum cuprates, spin excitations near the antiferromagnetic wave vector Q = (π, π) are overdamped and, therefore, a broad maximum is observed in the susceptibility instead of a sharp peak. For low frequencies, temperatures, and hole concentrations x ≥ 0.02, the susceptibility is peaked at incommensurate wave vectors (π ± 2πδ, π), (π, π ± 2πδ). The incommensurability is connected with the minimum in the magnon damping at Q in the crystal with a short-range antiferromagnetic order. Generally, the incommensurate magnetic response is not accompanied by an inhomogeneity of the charge-carrier density.     

Inaccuracy in Legionella tests of building water systems due to sample holding time

Most Legionella culture tests are performed on building water samples that have been shipped to analytical laboratories for analysis. Significant (≥1 log₁₀ unit) changes in results were observed in 52% of held samples (6 h or longer, ambient temperature) drawn from building water systems in a 42-sample initial survey. It was not practical to use the spread plate protocol for on-site “t = 0” cultures in a larger, more diverse survey of thousands of building water systems. Two thousand four hundred twenty-one (2421) building water samples were split for on-site analysis using a field culture protocol and then also cultured after overnight shipment to the lab for analysis with the standardized spread plate method. Legionella test results from building water system samples are usually interpreted as ≥a numerical detection or action limit. Therefore, binary statistical analyses were calculated by setting t = 0 culture results to “true”. Overall in this survey, 10.4% of water samples sent to the laboratory for analysis returned either false-positive or false-negative results. The overall positive predictive value of results was poor (36%). Most (83%) false-positive results were returned from utility water systems. Most (74%) false-negative results were returned from potable water systems. These inaccuracies have serious implications in regard to interpretation and use of Legionella test results. The overall negative predictive value of results was excellent (99%) and also it was good (92%) for results from a polymerase chain reaction (PCR) assay that can be therefore used as a negative screening method.     

Arsenic in Oregon community water systems: demography matters

Recently, the maximum contaminate level (MCL) for arsenic was lowered to 10 microg/L in community water systems (CWS) throughout the United States. In this study, CWS in Oregon were assessed for the occurrence and magnitude of arsenic >10 microg/L between the effective and compliance dates for the new MCL. Ten CWS, with a combined population of 49,395, met the criteria for this study. Arsenic levels above the new MCL ranged from 11-25 microg/L. The demographic characteristics of these systems were queried and considered in the context of risk, exposure and outreach. A disproportionate percent of residents in affected CWS were of Hispanic origin (35%) compared to the statewide average (8%). Residents in these CWS had a lower median household income (20% less than the statewide average), a lower median age (32.5 vs. 36.3) and a higher percent of a second language spoken in the home besides English (34.6% vs. 12.1%) compared to the statewide census. These community characteristics have implications for exposure, risk and outreach associated with the occurrence of arsenic in drinking water. Consequently, demographic parameters are informative for risk management and communication and ultimately, beneficial to the affected public.     

The natural history of cigarette smoking from adolescence to adulthood in a midwestern community sample: Multiple trajectories and their psychosocial correlates.

Previous research on the natural history of smoking has focused on overall group trajectories without considering the possibility of risk subgroup variation. To address this limitation, the authors of the present study aimed to identify subgroups with varying trajectories of smoking behavior. The authors accomplished this within a cohort-sequential study of a large community sample (N?=?8,556) with measurements spanning ages 11–31. After removing 2 a priori groups (abstainers and erratics), the authors empirically identified 4 trajectory groups—early stable smokers, late stable smokers, experimenters, and quitters—and psychosocial variables from adolescence and young adulthood were significantly distinguished among them. Given recent advances in quantitative methods, it is now feasible to consider subgroups of trajectories within an overall longitudinal design. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Mode I interlaminar fracture toughness of Nylon 66 nanofibrilmat interleaved carbon/epoxy laminates

Carbon/epoxy laminates interleaved with laboratory scale electrospun Nylon 66 nanofibrilmat and spunbonded nonwoven mats were investigated. The effect of the nanoscale fibers on the fracture toughness of the composite under pure Mode I loading was evaluated. It was shown that the nanofibrilmat is responsible for a major interlaminar fracture toughness improvement, as high as 255–322%, compared to a noninterleaved carbon/epoxy reference laminate. We further studied the improvement mechanism of the electrospun nanofibrilmat compared to a commercial spunbonded nonwoven Nylon 66 mat. A combination of two interlayer fracture mechanisms responsible for the toughness improvement is suggested: the first is related to the high energy dissipated by bridged thermoplastic nanofibers and the second is attributed to the generation of a plastic zone near the crack tip. The interlaminar fracture mechanisms of both electrospun nanofibrilmat and the nonwoven mat interleaving was analyzed and discussed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers