On separating a fixed point from zero by invariants

Assume a fixed point v∈V^G can be separated from zero by a homogeneous invariant f∈𝕜[V]^G of degree p^rd, where p>0 is the characteristic of the ground field 𝕜 and p,d are coprime. We show that then v can also be separated from zero by an invariant of degree p^r, which we obtain explicitly from f. It follows that the minimal degree of a homogeneous invariant separating v from zero is a p-power.     

Silyl trifluoromethanesulfonate-activated para-methoxybenzyl methyl ether as an alkylating agent for thiols and aryl ketones

para-Methoxybenzyl methyl ether acts as an alkylating agent for thiols in the presence of trimethylsilyl trifluoromethanesulfonate and trialkylamine base in good yields (58–96%). Aryl ketones are alkylated under similar conditions, probably through an enol silane intermediate, also in high yields (67–95%). The active alkylating species is likely a p-methoxybenzyl cation.     

The structure of poly-2,5-benzoxazole (ABPBO) and poly-2,6-benzothiazole (ABPBT) fibers by X-ray diffraction

The determination of the crystalline structure of oriented fibers of poly-2,5-benzoxazole (ABPBO) and poly-2,6-ben-zothiazole (ABPBT) is described. Both unit cells are metrically orthorhombic, with the parameters: a = 6.061 (17), b = 3.384 (13), c (fiber axis) = 11.575 (6) Å for ABPBO; and a = 6.044 (6), b = 3.417 (7), c (fiber axis) = 12.194 (18) Å for ABPBT. The fiber repeat consists in each structure of two fused ring groups arranged in a planar, zigzag conformation. The conformational torsion angle and orientation of chains within the unit cells are derived from a linked-atom least squares refinement technique. Polymer chains pack laterally through van der Waals interactions. A plausible disorder model which involves defects in chain direction is presented. Refinement of a static disorder model for ABPBO in which 50% of the chains have their chain directions reversed leads to a lower R residual and sum of constraints.     

Synthesis and characterization of novel elastomeric poly(D,L-lactide urethane) maleate composites for bone tissue engineering

Here, we report the synthesis and characterization of a novel 4-arm poly(lactic acid urethane)-maleate (4PLAUMA) elastomer and its composites with nano-hydroxyapatite (nHA) as potential weight-bearing composite. The 4PLAUMA/nHA ratios of the composites were 1:3, 2:5, 1:2 and 1:1. FTIR and NMR characterization showed urethane and maleate units integrated into the PLA matrix. Energy dispersion and Auger electron spectroscopy confirmed homogeneous distribution of nHA in the polymer matrix. Maximum moduli and strength of the composites of 4PLAUMA/nHA, respectively, are 1973.31 ± 298.53 MPa and 78.10 ± 3.82 MPa for compression, 3630.46 ± 528.32 MPa and 6.23 ± 1.44 MPa for tension, 1810.42 ± 86.10 MPa and 13.00 ± 0.72 for bending, and 282.46 ± 24.91 MPa and 5.20 ± 0.85 MPa for torsion. The maximum tensile strains of the polymer and composites are in the range of 5–93%, and their maximum torsional strains vary from 0.26 to 0.90. The composites exhibited very slow degradation rates in aqueous solution, from approximately 50% mass remaining for the pure polymer to 75% mass remaining for composites with high nHA contents, after a period of 8 weeks. Increase in ceramic content increased mechanical properties, but decreased maximum strain, degradation rate, and swelling of the composites. Human bone marrow stem cells and human endothelial cells adhered and proliferated on 4PLAUMA films and degradation products of the composites showed little-to-no toxicity. These results demonstrate that novel 4-arm poly(lactic acid urethane)-maleate (4PLAUMA) elastomer and its nHA composites may have potential applications in regenerative medicine.     

An Ancestral Member of the Polysaccharide Lyase Family 2 Displays Endolytic Activity and Magnesium Dependence

Polysaccharide lyases (PLs) are enzymes that cleave glycosidic linkages in hexuronate polysaccharides, such as homogalacturonan (HG), using a β-elimination mechanism. Traditionally, PL activities on HG have been associated with catalytic calcium cofactors, unusually high pH optima, and arginine Brønstead bases. Recently, however, PL families that harness transition metal cofactors, utilize lysine and histidine Brønstead bases, and display more neutral pH optima have been described. One such family is PL2, which has members found primarily in phytopathogenic (e.g., Dickeya spp. and Pectobacterium spp.) or enteropathogenic (e.g., Yersinia spp.) bacterial species. PL2 is divided into two major subfamilies that are correlated with either an endolytic or exolytic activity. This study has focused on the activity of a PL2 member, which is not classified within either subfamily and helps to illuminate the origin of enzyme activities within the family. In addition, the role of Mg²⁺ as a preferential catalytic metal for an intracellular PL2 (PaePL2) is described. The implications for the relationship between catalytic metal selectivity and the cellular location of pectate lyase-mediated catalysis are discussed.     

Use of ETAAS,FAAS and ICP-OES for production and post-certification monitoring of a multielemental certified reference material according to national regulation limits for elements in drinking water

Accreditation and Quality Assurance - This paper describes the development of a certified reference material (CRM), produced in the National Institute of Quality from Peru (INACAL) in order to...     

Best cooperative partner selection and input resource reallocation using DEA

Reallocation of input resources (RIR) is a process by which certain decision making units (DMUs) reallocate resources among themselves; a process that occurs frequently in many enterprises. In this paper, a new data envelopment analysis (DEA) approach is developed to select the best cooperative partner DMU. Context-dependent DEA is used to identify the different levels of best-practice frontiers. Two DEA-based models are established for two cooperative scenarios, namely, resources pooling only and best-practice sharing. A cooperative method is applied to determine how to reallocate the input resources, and Shapley value is used to estimate the revenue changes that the various DMUs should expect after RIR. Two different situations with different objectives are considered. One objective is to maximize total revenue for the partnership, while the other is to maximize the Shapley value. The proposed approaches are illustrated with two examples.     

A bargaining game model for measuring performance of two-stage network structures

Data envelopment analysis (DEA) is a method for measuring the efficiency of peer decision making units (DMUs), where the internal structures of DMUs are treated as a black-box. Recently DEA has been extended to examine the efficiency of DMUs that have two-stage network structures or processes, where all the outputs from the first stage are intermediate measures that make up the inputs to the second stage. The resulting two-stage DEA model not only provides an overall efficiency score for the entire process, but also yields an efficiency score for each of the individual stages. The current paper develops a Nash bargaining game model to measure the performance of DMUs that have a two-stage structure. Under Nash bargaining theory, the two stages are viewed as players and the DEA efficiency model is a cooperative game model. It is shown that when only one intermediate measure exists between the two stages, our newly developed Nash bargaining game approach yields the same results as applying the standard DEA approach to each stage separately. Two real world data sets are used to demonstrate our bargaining game model.     

Silyl triflate-accelerated additions of catalytically generated zinc acetylides to N-phenyl nitrones

Terminal alkynes readily form zinc acetylides in the presence of iPr₂NEt and 20 mol % ZnBr₂, then attack N-phenyl nitrones activated by trimethylsilyl trifluoromethanesulfonate. Deprotection with aqueous acid yields N-hydroxyl propargylamine. Yields are generally high for nitrones derived from aromatic aldehydes. Control experiments suggest that silyl triflate has a significant accelerating effect upon the reaction.