1-D constitutive model for evolution of stress-induced R-phase and localized Lüders-like stress-induced martensitic transformation of super-elastic NiTi wires

NiTi alloys have been widely used in the applications for micro-electro-mechanical-systems (MEMS), which often involve some precise and complex motion control. However, when using the NiTi alloys in MEMS application, the main problem to be considered is the degradation of functional property during cycling loading. This also stresses the importance of accurate prediction of the functional behavior of NiTi alloys. In the last two decades, a large number of constitutive models have been proposed to achieve the task. A portion of them focused on the deformation behavior of NiTi alloys under cyclic loading, which is a practical and non-negligible situation. Despite of the scale of modeling studies of the field in NiTi alloys, two experimental observations under uniaxial tension loading have not received proper attentions. First, a deviation from linearity well before the stress-induced martensitic transformation (SIMT) has not been modeled. Recent experiments confirmed that it is caused by the formation of stress-induced R phase. Second, the influence of the well-known localized Lüders-like SIMT on the macroscopic behavior of NiTi alloys, in particular the residual strain during cyclic loading, has not been addressed. In response, we develop a 1-D phenomenological constitutive model for NiTi alloys with two novel features: the formation of stress-induced R phase and the explicit modeling of the localized Lüders-like SIMT. The derived constitutive relations are simple and at the same time sufficient to describe the behavior of NiTi alloys. The accumulation of residual strain caused by R phase under different loading schemes is accurately described by the proposed model. Also, the residual strain caused by irreversible SIMT at different maximum loading strain under cyclic tension loading in individual samples can be explained by and fitted into a single equation in the proposed model. These results show that the proposed model successfully captures the behavior of R phase and the essence of localized SIMT.

Biphenyl dioxygenase-catalysed cis-dihydroxylation of tricyclic azaarenes: chemoenzymatic synthesis of arene oxide metabolites and furoquinoline alkaloids

Biotransformation of acridine, dictamnine and 4-chlorofuro[2,3-b]quinolone, using whole cells of Sphingomonas yanoikuyae B8/36, yielded five enantiopure cyclic cis-dihydrodiols, from biphenyl dioxygenase-catalysed dihydroxylation of the carbocyclic rings. cis-Dihydroxylation of the furan ring in dictamnine and 4-chlorofuro[2,3-b] quinoline, followed by ring opening and reduction, yielded two exocyclic diols. The structures and absolute configurations of metabolites have been determined by spectroscopy and stereochemical correlation methods. Enantiopure arene oxide metabolites of acridine and dictamnine have been synthesised, from the corresponding cis-dihydrodiols. The achiral furoquinoline alkaloids robustine, gamma-fagarine, haplopine, isohaplopine-3,3'-dimethylallylether and pteleine have been obtained, from either cis-dihydrodiol, catechol or arene oxide metabolites of dictamnine.

Constitutive expression of human keratin 14 gene in mouse lung induces premalignant lesions and squamous differentiation

Squamous cell carcinoma accounts for 20% of all human lung cancers and is strongly linked to cigarette smoking. It develops through premalignant changes that are characterized by high levels of keratin 14 (K14) expression in the airway epithelium and evolve through basal cell hyperplasia, squamous metaplasia and dysplasia to carcinoma in situ and invasive carcinoma. In order to explore the impact of K14 in the pulmonary epithelium that normally lacks both squamous differentiation and K14 expression, human keratin 14 gene hK14 was constitutively expressed in mouse airway progenitor cells using a mouse Clara cell specific 10 kDa protein (CC10) promoter. While the lungs of CC10-hK14 transgenic mice developed normally, we detected increased expression of K14 and the molecular markers of squamous differentiation program such as involucrin, loricrin, small proline-rich protein 1A, transglutaminase 1 and cholesterol sulfotransferase 2B1. In contrast, wild-type lungs were negative. Aging CC10-hK14 mice revealed multifocal airway cell hyperplasia, occasional squamous metaplasia and their lung tumors displayed evidence for multidirectional differentiation. We conclude that constitutive expression of hK14 initiates squamous differentiation program in the mouse lung, but fails to promote squamous maturation. Our study provides a novel model for assessing the mechanisms of premalignant lesions in vivo by modifying differentiation and proliferation of airway progenitor cells. © The Author 2008. Published by Oxford University Press. All rights reserved.

Review of constitutive models for describing the time dependent behaviour of soft clays

Different classes of constitutive models have been proposed to capture the time-dependent behaviour of soft soil (creep, stress relaxation, rate dependency). This paper critically reviews many of the models developed based on understanding of the time dependent stress-strain-stress rate-strain rate behaviour of soils and viscoplasticity in terms of their strengths and weaknesses. Some discussion is also made on the numerical implementation aspects of these models. Typical findings from numerical analyses of geotechnical structures constructed on soft soils are also discussed. The general elastic viscoplastic (EVP) models can roughly be divided into two categories: models based on the concept of overstress and models based on non-stationary flow surface theory. Although general in structure, both categories have their own strengths and shortcomings. This review indicates that EVP analysis is yet to be vastly used by the geotechnical engineers, apparently due to the mathematical complication involved in the formulation of the constitutive models, unconvincing benefit in terms of the accuracy of performance prediction, requirement of additional soil parameter(s), difficulties in determining them, and the necessity of excessive computing resources and time. © 2013 Taylor & Francis.

Constitutive modeling, microstructure evolution, and processing map for a nitride-strengthened heat-resistant steel

A constitutive equation was established to describe the deformation behavior of a nitride-strengthened (NS) steel through isothermal compression simulation test. All the parameters in the constitutive equation including the constant and the activation energy were precisely calculated for the NS steel. The result also showed that from the stress-strain curves, there existed two different linear relationships between critical stress and critical strain in the NS steel due to the augmentation of auxiliary softening effect of the dynamic strain-induced transformation. In the calculation of processing maps, with the change of Zener-Hollomon value, three domains of different levels of workability were found, namely excellent workability region with equiaxed-grain microstructure, good workability region with “stripe” microstructure, and the poor workability region with martensitic-ferritic blend microstructure. With the increase of strain, the poor workability region first expanded, then shrank to barely existing, but appeared again at the strain of 0.6.

Towards an understanding of bacterial metabolites prodigiosin and violacein and their potential for use in commercial sunscreens

Synopsis
Objectives

To exploit the microbial ecology of bacterial metabolite production and, specifically, to: (i) evaluate the potential use of the pigments prodigiosin and violacein as additives to commercial sunscreens for protection of human skin, and (ii) determine antioxidant and antimicrobial activities (against pathogenic bacteria) for these two pigments.

Methods
Prodigiosin and violacein were used to supplement extracts of Aloe vera leaf and Cucumis sativus (cucumber) fruit which are known to have photoprotective activity, as well as some commercial sunscreen preparations. For each, sunscreen protection factors (SPFs) were determined spectrophotometrically. Assays for antimicrobial activity were carried out using 96-well plates to quantify growth inhibition of Staphylococcus aureus and Escherichia coli.
Results
For the plant extracts, SPFs were increased by an order of magnitude (i.e. up to ~3.5) and those for the commercial sunscreens increased by 10–22% (for 4% w/w violacein) and 20–65% (for 4% w/w prodigiosin). The antioxidant activities of prodigiosin and violacein were approximately 30% and 20% those of ascorbic acid (a well-characterized, potent antioxidant). Violacein inhibited S. aureus (IC_{506.99 ± 0.146 μM) but not E. coli, whereas prodigiosin was effective against both of these bacteria (IC50 values were 0.68 ± 0.06 μM and 0.53 ± 0.03 μM, respectively).}

Conclusion
The bacterial pigments prodigiosin and violacein exhibited antioxidant and antimicrobial activities and were able to increase the SPF of commercial sunscreens as well as the extracts of the two plant species tested. These pigments have potential as ingredients for a new product range of and, indeed, represent a new paradigm for sunscreens that utilize substances of biological origin. We discussed the biotechnological potential of these bacterial metabolites for use in commercial sunscreens, and the need for studies of mammalian cells to determine safety.

Biotransformation of zearalenone and zearalenols to their major glucuronide metabolites reduces estrogenic activity

Zearalenone (ZEN) is a mycotoxin produced by Fusarium fungi. Once ingested, ZEN may be absorbed andmetabolised to a- and b-zearalenol (a-ZOL, b-ZOL), and to a lesser extent a- and b-zearalanol (a-ZAL,b-ZAL). Further biotransformation to glucuronide conjugates also occurs to facilitate the elimination ofthese toxins from the body. Unlike ZEN and its metabolites, information regarding the estrogenic activityof these glucuronide conjugates in various tissues is lacking. ZEN-14-O-glucuronide, a-ZOL-14-O-glucuronide,a-ZOL-7-O-glucuronide, b-ZOL-14-O-glucuronide and b-ZOL-16-O-glucuronide, previouslyobtained as the major products from preparative enzymatic synthesis, were investigated for their potentialto cause endocrine disruption through interference with estrogen receptor transcriptional activity.All five glucuronide conjugates showed a very weak agonist response in an estrogen responsive reportergene assay (RGA), with activity ranging from 0.0001% to 0.01% of that of 17b-estradiol, and also lessthan that of ZEN, a-ZOL and b-ZOL which have previously shown estrogenic potencies of the order 17bestradiol> a-ZOL > ZEN > b-ZOL. Confirmatory mass spectrometry revealed that any activity observedwas likely a result of minor deconjugation of the glucuronide moiety. This study confirms that formationof ZEN and ZOL glucuronides is a detoxification reaction with regard to estrogenicity, serving as a potentialhost defence mechanism against ZEN-induced estrogenic activity.

Removal of microorganisms and their chemical metabolites from water using semiconductor photocatalysis

Semiconductor photocatalysis has been applied to the remediation of an extensive range of chemical pollutants in water over the past 30 years. The application of this versatile technology for removal of micro-organisms and cyanotoxins has recently become an area that has also been the subject of extensive research particularly over the past decade. This paper considers recent research in the application of semiconductor photocatalysis for the treatment of water contaminated with pathogenic micro-organisms and cyanotoxins. The basic processes involved in photocatalysis are described and examples of recent research into the use of photocatalysis for the removal of a range of microorganisms are detailed. The paper concludes with a review of the key research on the application of this process for the removal of chemical metabolites generated from cyanobacteria.

Toluene Dioxygenase Catalysed synthesis and reactions of cis-diol metabolites derived from 2 and 3-methoxy phenols

Using toluene dioxygenase as biocatalyst, enantiopure cisdihydrodiol and cis-tetrahydrodiol metabolites, isolated as their ketone tautomers, were obtained from meta and ortho methoxyphenols. Although these isomeric phenol substrates are structurally similar, the major bioproducts from each of these biotransformations were found at different oxidation levels. The relatively stable cyclohexenone cis-diol metabolite from meta methoxyphenol was isolated, while the corresponding metabolite from ortho methoxyphenol was rapidly bioreduced to a cyclohexanone cis-diol. The chemistry of the 3-methoxycyclohexenone cis-diol product was investigated and elimination, aromatization, hydrogenation, regioselective O-exchange, Stork−Danheiser transposition and O-methylation reactions were observed. An offshoot of this technology provided a two-step chemoenzymatic synthesis, from meta methoxyphenol, of a recently reported chiral fungal metabolite; this synthesis also established the previously unassigned absolute configuration.

BACTERIAL OXIDATION OF BENZOCYCLOALKENES TO YIELD MONOL, DIOL AND TRIOL METABOLITES

Benzylic monooxygenation of benzocycloalkenes, 2-4, by enzymes in intact cultures of Pseudomonas putida UV4 yielded exclusively the [R] enantiomers, 6-8, and the derived ketones 10-12; by contrast, biotransformation of benzocyclobutene, 1, yielded both monooxygenation (5 and 9), dioxygenation (13, 14 and 15), and trioxygenation (16) products.

Does chemical composition of individual Scots pine trees determine the biodiversity of their associated ground vegetation?

Despite plant secondary metabolites being major determinants of species interactions and ecosystem processes, their role in the maintenance of biodiversity has received little attention. In order to investigate the relationship between chemical and biological diversity in a natural ecosystem, we considered the impact of chemical diversity in individual Scots pine trees (Pinus sylvestris) on species richness of associated ground vegetation. Scots pine trees show substantial genetically determined constitutive variation between individuals in concentrations of a group of secondary metabolites, the monoterpenes. When the monoterpenes of particular trees were assessed individually, there was no relationship with species richness of associated ground flora. However, the chemical diversity of monoterpenes of individual trees was significantly positively associated with the species richness of the ground vegetation beneath each tree, mainly the result of an effect among the non-woody vascular plants. This correlation suggests that the chemical diversity of the ecosystem dominant species has an important role in shaping the biodiversity of the associated plant community. The extent and significance of this effect, and its underlying processes require further investigation.

Enzyme-catalysed oxidation of 1,2-disulfides to yield chiral thiosulfinate, sulfoxide and cis-dihydrodiol metabolites

Enantioenriched and enantiopure thiosulfinates were obtained by asymmetric sulfoxidation of cyclic 1,2-disulfides, using chemical and enzymatic (peroxidase, monooxygenase, dioxygenase) oxidation methods and chiral stationary phase HPLC resolution of racemic thiosulfinates. Enantiomeric excess values, absolute configurations and configurational stabilities of chiral thiosulfinates were determined. Methyl phenyl sulfoxide, benzo[c]thiophene cis-4,5-dihydrodiol and 1,3-dihydrobenzo[c]thiophene derivatives were among unexpected types of metabolites isolated, when acyclic and cyclic 1,2-disulfide were used as substrates for Pseudomonas putida strains. Possible biosynthetic pathways are presented for the production of metabolites from 1,4-dihydrobenzo-2,3-dithiane, including a novel cis-dihydrodiol metabolite that was also derived from benzo[c]thiophene and 1,3-dihydrobenzo[c]thiophene.

Constitutive OGG1 variant together with BRCA mutations display accelerated telomere shortening

Dissertação de mestrado, Oncobiologia, Departamento de Ciências Biomédicas e Medicina, Universidade do Algarve, 2015