927 resultados para Nucleophilic attack
Resumo:
The acorn barnacle Chthamalus montagui can present strong variation in shell morphology, ranging from flat conic to a highly bent form, caused by a substantial overgrowth of the rostrum plate. Shell shape distribution was investigated between January and May 2004 from geographical to microhabitat spatial scales along the western coast of Britain. Populations studied in the north (Scotland and Isle of Man) showed a higher degree of shell variation compared to those in the south (Wales and south-west England). In the north, C. montagui living at lower tidal levels and in proximity to the predatory dogwhelk, Nucella lapillus, were more bent in profile. Laboratory experiments were conducted to examine behavioural responses, and vulnerability of bent and conic barnacles to predation by N. lapillus. Dogwhelks did not attack one morphotype more than the other, but only 15 % of attacks on bent forms were successful compared to 75 % in conic forms. Dogwhelk effluent reduced the time spent feeding by C. montagui (11 %), but there was no significant difference between conic and bent forms. Examination of barnacle morphology indicated a trade-off in investment in shell structure and feeding appendages associated with being bent, but none with egg or somatic tissue mass. These results are consistent with C. montagui showing an induced defence comparable to that found in its congeners Chthamalus anisopoma and Chthamalus fissus on the Pacific coast of North America, but further work to demonstrate inducibility is required.
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It is almost a tradition that celluloid (or digital) villains are represented with some characteristics that remind us the real political enemies of the producer country of the film, or even enemies within the country according to the particular ideology that sustains the film. The case of Christopher Nolan The Dark Knight trilogy, analyzed here, is representative of this trend for two reasons. First, because it gets marked by political radicalization conducted by the US government after the attack of September 11, 2001. Secondly, because it offers a profuse gallery of villains who are outside the circle of friends as the new doctrine “either with us or against us” opened by George Bush for the XXI century. This gallery includes from the very terrorists who justify the War on Terror (Ra's al Ghul, the Joker), to the “radical left” (Bane, Talia al Ghul) including liberal politicians (Harvey Dent), and corrupt that take advantage of the softness of the law to commit crimes with impunity (Dr. Crane, the Scarecrow).
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Objective: To determine the epidemiology of out of hospital sudden cardiac death (OHSCD) in Belfast from 1 August 2003 to 31 July 2004.
Design: Prospective examination of out of hospital cardiac arrests by using the Utstein style and necropsy reports. World Health Organization criteria were applied to determine the number of sudden cardiac deaths.
Results: Of 300 OHSCDs, 197 (66%) in men, mean age (SD) 68 (14) years, 234 (78%) occurred at home. The emergency medical services (EMS) attended 279 (93%). Rhythm on EMS arrival was ventricular fibrillation (VF) in 75 (27%). The call to response interval (CRI) was mean (SD) 8 (3) minutes. Among patients attended by the EMS, 9.7% were resuscitated and 7.2% survived to leave hospital alive. The CRI for survivors was mean (SD) 5 (2) minutes and for non-survivors, 8 (3) minutes (p < 0.001). Ninety one (30%) OHSCDs were witnessed; of these 91 patients 48 (53%) had VF on EMS arrival. The survival rate for witnessed VF arrests was 20 of 48 (41.7%): all 20 survivors had VF as the presenting rhythm and CRI ? 7 minutes. The European age standardised incidence for OHSCD was 122/100 000 (95% confidence interval 111 to 133) for men and 41/100 000 (95% confidence interval 36 to 46) for women.
Conclusion: Despite a 37% reduction in heart attack mortality in Ireland over the past 20 years, the incidence of OHSCD in Belfast has not fallen. In this study, 78% of OHSCDs occurred at home.
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This paper presents a study of the residual strength of Pinus sylvestris, which has been subject to attack by the furniture beetle (Anobium punctatum). It is relatively easy to stop the infestation, but difficult to assess the structural soundness of the remaining timber. Removal and replacement of affected structural elements is usually difficult and expensive, particularly in buildings of historic interest. Current on-site assessment procedures are limited. The main object of the study was to develop an on-site test of timber quality: a test which can be carried out on the surface and also at varying depths into the timber. It is based on a probe pull-out technique using a portable load-measuring device. Pull-out force values have been correlated with both strength and energy absorbed as measured by compression testing on laboratory samples of both sound and infested timber. These two relationships are significant and could be used to assess whether remedial work is needed. In addition, work on the use of artificial borings to simulate the natural worming of timber is presented and the findings discussed.
Resumo:
Density functional calculations of the structure, potential energy surface and reactivity for organic systems closely related to bisphenol-A-polycarbonate (BPA-PC) provide the basis for a model describing the ring-opening polymerization of its cyclic oligomers by nucleophilic molecules. Monte Carlo simulations using this model show a strong tendency to polymerize that is increased by increasing density and temperature, and is greater in 3D than in 2D. Entropy in the distribution of inter-particle bonds is the driving force for chain formation. (C) 2002 Elsevier Science B.V. All rights reserved.
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This paper explores the school experiences of seven 11–14 year old disabled children, and focuses on their agency as they negotiated a complex, changing, and often challenging social world at school where “difference” was experienced in negative ways. The paper draws on ethnographic data from a wider three-year study that explores the influence of school experiences on both disabled and non-disabled children’s identity as they make the transition from primary to secondary school in regular New Zealand schools (although the focus of the present paper is only on the experiences of disabled children). The wider study considers how Maori (indigenous people of Aotearoa/New Zealand) and Pakeha (New Zealanders of NZ European descent) disabled children and their non- disabled matched peers (matched for age, gender and classroom) understand their personal identity, and how factors relating to transition (from primary to secondary school); culture; impairment (in the case of disabled children); social relationships; and school experience impact on children’s identities. Data on Maori children’s school experiences is currently being collected, and is not yet available for inclusion in this paper. On the basis of our observations in schools we will illustrate how disabled children felt and were made to feel different through an array of structural barriers such as separate provision for disabled students, and peer and teacher attitudes to diversity. However, we agree with Davis, Watson, Shakespeare and Corker’s (2003) interpretation that disabled children’s rights and participation at school are also under attack from a “deeper cultural division” (p. 205) in schools based on discourses of difference and normality. While disabled students in our study were trying to actively construct and shape their social and educational worlds, our data also show that teachers and peers have the capacity to either support or supplant these attempts to be part of the group of “all children”. We suggest that finding solutions that support disabled children’s full inclusion and participation at school requires a multi-faceted and systemic approach focused on a pedagogy for diverse learners, and on a consistent and explicitly inclusive policy framework centred on children’s rights.
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Human-induced selection on animals and plants has been highly influential throughout our history and resulted in both intentional benefits and unintended detriments. Fisheries-induced evolution (FIE) describes the unintended selection on wild fish populations by fishing that has resulted in the evolution of exploited populations. While the use of aquatic protected areas that exclude angling might be considered an evolutionarily-enlightened management approach to dealing with issues arising from FIE little is known about the effectiveness of this approach for maintaining the phenotypic diversity of traits in protected areas versus those outside of their boundaries. In species that exhibit parental care, including the largemouth bass (Micropterus salmoides), active nest guarding and aggression towards potential brood predators by males increases the survival of offspring. This aggression may render these individuals particularly vulnerable to capture via angling as a result of increased propensity to attack fishing lures near their nests. Relative levels of aggression by these males during the parental care period correlate with their vulnerability to angling year round. Inasmuch as this parental behavior is heritable, this selective removal of more aggressive individuals by anglers should drive population-average phenotypes towards lower levels of aggression. To assess the effectiveness of protected areas at mitigating FIE, I compared the nest guarding behaviours of wild, free-swimming male bass during the early nesting period for bass within and outside protected areas. I found that nesting males within long-standing fishing sanctuaries (>70 yrs) were more aggressive towards captive bluegill sunfish (Lepomis macrochirus) placed directly on their nests, and patrolled larger areas around their nests compared to bass outside of sanctuaries. Males within protected areas were more likely to strike at artificial fishing lures and more prone to capture during experimental angling events. Collectively, my findings suggest that recreational angling selects for individual bass with lower levels of parental care and aggression, and that the establishment of protected areas may mitigate potential FIE. The extent to which this phenomenon occurs in other species and systems likely depends on the reproductive strategies of the fishes being considered, their spatial ecology relative to sanctuary boundaries, and habitat quality within protected areas.
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Odorous frogs of the sub-genus Odorrana are of oriental distribution, and are so called due to the foul smell of their defensive skin secretions released from specialized skin glands following stress or predator attack. Here we report the application of a “shotgun” skin secretion cDNA library cloning technique which can rapidly expedite identification of secretion bioactive peptides. From a library constructed from the skin secretion of the Large Chinese Odorous frog, Rana (Odorrana) livida, we have identified four novel peptides whose primary structures were deduced initially from cloned precursors. Subsequently, mature peptides were located in and structurally characterized from reverse phase HPLC fractions of skin secretion. Named lividins 1–4, these were found to be structural homologs of known antimicrobial peptide families from Rana frogs. Rapid identification of novel peptides can thus be rapidly achieved using this non-invasive, non-destructive technology and the extensive similarities revealed between antimicrobial peptide precursor organization and nucleic acid sequences would lend support to the hypothesis that they have a common ancestral origin.
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The defensive strategy of amphibians against predator attack relies heavily on the secretion of noxious/toxic chemical cocktails from specialized skin granular glands. Bioactive peptides constitute a major component of secretions in many species and the most complex are produced by neotropical leaf frogs of the sub-family Phyllomedusinae. We recently reported that these skin secretions contain elements of both the granular gland peptidome and transcriptome and that polyadenylated mRNAs constituting the latter are protected from degradation by interactions with endogenous amphipathic peptides. This thus permits parallel amino acid sequencing of peptides and nucleic acid sequencing of cloned precursor transcripts from single lyophilized samples of secretion. Here we report that the protection afforded is sufficiently robust to permit transcriptome studies by cloning of full-length polyadenylated peptide precursor encoding mRNAs from libraries constructed using ambient temperature air-dried skin from recently deceased specimens as source material. The technique was sufficiently sensitive to permit the identification of cDNAs encoding antimicrobial peptides constituted by six different isoforms of phylloseptin and two dermaseptins. Also, for the first time, establishment of the nucleic acid and amino acid sequence of the precursor encoding the phyllomedusine frog skin bradykinin-related peptide, phyllokinin, from cloned cDNA, was achieved. These data unequivocally demonstrate that the granular gland transcriptome persists in air-dried amphibian skin—a finding that may have fundamental implications in the study of archived materials but also in the wider field of molecular biology.
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OBJECTIVES: This study reports the development, characterisation and microbiological testing of surface-modified polyvinylchloride (PVC) films for the purpose of reducing bacterial adherence.
METHODS: Irreversible covalent surface modification was achieved via nucleophilic substitution of fluorinated thiol-terminated compounds onto the polymer backbone. Four fluorinated modifiers, 2,3,5,6-tetrafluorothiophenol (TFTP), 4-(trifluoromethyl)thiophenol (TFMTP), 3,5-bis(trifluoromethyl)benzenethiol (BTFMBT) and 3,3,4,4,5,5,6,6,7, 7,8,8,9,9,10,10,10-heptadecafluoro-decane-1-thiol (HDFDT), were investigated. Modification was confirmed using attenuated total reflectance infrared spectroscopy; Raman mapping demonstrated that modification was homogenous on the macroscopic scale. The influence of fluorination on surface hydrophobicity was studied by contact angle analysis. The effect on microbial adherence was examined using Pseudomonas aeruginosa and Staphylococcus aureus.
KEY FINDINGS: The resultant changes in contact angle relative to control PVC ranged from -4 degrees to +14 degrees . In all cases, adherence of P. aeruginosa and S. aureus was significantly reduced relative to control PVC, with adherence levels ranging from 62% and 51% for TFTP-modified PVC to 32% and 7% for TFMTP-modified PVC.
CONCLUSIONS: These results demonstrate an important method in reducing the incidence of bacterial infection in PVC medical devices without compromising mechanical properties.
Resumo:
Because of the different mix design in comparison with traditional concrete and the absence of vibration, different durability characteristics might be expected for self-compacting concrete. The stateof- the-art report, prepared by RILEM Technical Committee TC 205-DSC focuses on the Durability of SCC, by first gathering the available information concerning pore structure, air-void system and transport mechanisms. The available durability results are studied and summarised keeping in mind the fundamental mechanisms and driving forces. All relevant durability issues are considered, like carbonation, chloride penetration, frost resistance, ASR, sulphate attack, thaumasite formation, fire resistance, etc... It is not the intention to give a review on these durability aspects for concrete in general. The aim however is to point at the specifics related to the use of SCC, e.g. due to the addition of a large amount of limestone filler, etc... This paper summarizes the main conclusions of the State-of-the-Art Report.
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Ettringite and thaumasite can be found among the deterioration products of cementitious materials exposed to sulfate and hydrochloric attack. The results of a test program to investigate the acid resistance of self-compacting concrete (SCC) and conventional concrete (CC), immersed up to 18 weeks at 20°C in sulfuric and hydrochloric acid solutions, are described. The SCC was prepared with 47% carboniferous limestone powder, as a replacement for cement, and an ordinary portland cement. The CC was prepared with portland cement only. The water-binder ratios of the SCC and CC were 0.36 and 0.46, respectively. The parameter investigated was the time, in weeks, taken to cause 10% mass loss of fully immersed concrete specimens in a 1% solution of sulfuric acid and the same amount of loss in a 1% solution of hydrochloric acid. The investigation indicated that the SCC performed better than the CC in sulfuric solution but was slightly more vulnerable to hydrochloric acid attack compared to CC. The mode of attack between the two solutions was different.
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A new class of low-melting N,N'-dialkylimidazolium salts has been prepared with carborane counterions, some of the most inert and least nucleophilic anions presently known. The cations and anions have been systematically varied with combinations of 1-ethyl-3-methyl-(EMIM+), 1-octyl-3-methyl-(OMIM+), 1-ethyl-2,3-dimethyl- (EDMIM+), and 1-butyl-2,3-dimethyl- (BDMIM+) imidazolium cations and CB11H12-CB11H6Cl6-, and CB11H6Br6- carborane anions to elucidate the factors which affect their melting points. From trends in melting points, which range from 156 degrees C down to 45 degrees C, it is clear that the alkylation pattern on the imidazolium cation is the main determinant of melting point and that packing inefficiency of the cation is the intrinsic cause of low melting points. C-Alkylation of the anion can also contribute to low melting points by the introduction of a further packing inefficiency. Nine of the thirteen salts have been the subject of X-ray crystal structural determination. Notably, crystallographic disorder of the cation is observed in all but one of these salts. It is the most direct evidence to date that packing inefficiency is the major reason unsymmetrical N,N'-dialkylimidazolium salts can be liquids at room temperature.
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This article is a response to an article by Ray Mackay (1996) which constitutes an attack on stylistic analysis in general, and the writings of the above authors and Ron Carter in particular. Mackay's article (in Language and Communication) accuses stylistics of 'scientificness' and claims that its attempt to provide objective analyses of literary texts is futile.1 We suggest that Mackay has misrepresented what stylisticians have said about objectivity, and that his understanding of objectivity, science and the nature of text-interpretative argument is seriously flawed.
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The design, fabrication, and characterization of single-screen perturbed frequency-selective surfaces (FSS) at infrared frequencies for single and multiband applications are reported. Single-band FSS based on parallel strips have been perturbed by decreasing the length of every second strip within the array in order to achieve dual band-stop responses. The same principle has been extended to design FSS exhibiting tri- and quadreflection bands. In addition, strip FSSs have been perturbed by replacing every second strip for a metallic ring, resulting in dual-band filters with different polarization responses of the bands. These designs have been fabricated on large thin polyimide membranes using sacrificial silicon wafers. An oxide interlayer between the sacrificial silicon wafer and the polyimide membrane is employed to stop the silicon etching and is wet etched subsequently by a solution of ammonium fluoride and acetic acid that does not attack either the polyimide membrane or the aluminium FSS elements. Fourier transform infrared spectroscopy measurements are presented to validate the predicted responses of the fabricated prototypes.