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Underlying Role (underlying + role)
Selected AbstractsManaging ecosystem services: what do we need to know about their ecology?ECOLOGY LETTERS, Issue 5 2005Claire Kremen Abstract Human domination of the biosphere has greatly altered ecosystems, often overwhelming their capacity to provide ecosystem services critical to our survival. Yet ecological understanding of ecosystem services is quite limited. Previous work maps the supply and demand for services, assesses threats to them, and estimates economic values, but does not measure the underlying role of biodiversity in providing services. In contrast, experimental studies of biodiversity,function examine communities whose structures often differ markedly from those providing services in real landscapes. A bridge is needed between these two approaches. To develop this research agenda, I discuss critical questions and key approaches in four areas: (1) identifying the important ,ecosystem service providers'; (2) determining the various aspects of community structure that influence function in real landscapes, especially compensatory community responses that stabilize function, or non-random extinction sequences that rapidly erode it; (3) assessing key environmental factors influencing provision of services, and (4) measuring the spatio-temporal scale over which providers and services operate. I show how this research agenda can assist in developing environmental policy and natural resource management plans. [source] Epstein,Barr virus reactivation and multiple sclerosisEUROPEAN JOURNAL OF NEUROLOGY, Issue 1 2008Ø. Torkildsen Infection with Epstein,Barr virus (EBV) is considered one of the possible key environmental factors in the aetiology of multiple sclerosis (MS). Whether EBV plays an underlying role as an activator of MS remains, however, controversial. Sixty-one patients with definite relapsing,remitting multiple sclerosis (RRMS) according to the Poser criteria were followed for 1 year. Blood samples were drawn at baseline, months 3, 6 and 12, and in case of any clinical exacerbation. Twenty-three baseline,paired exacerbation samples in the same set were quantitatively analysed to examine whether exacerbations in MS were associated with a change in anti-diffuse component of the EBV-early antigen (EA-D) IgG ratio. All the 61 patients (100%) were anti-viral capsid antigen (VCA) IgG positive, one (2%) was anti-VCA IgM positive and 60 (98%) were anti-EBV nuclear antigen IgG positive. Mean anti-EA-D IgG at baseline was 0.57 (range 0.12,2.70) and at the time of exacerbations 0.61 (range 0.11,2.70). Wilcoxon signed rank test revealed no differences between the 23 baseline and paired exacerbation samples (P = 0.58). Our findings suggest that reactivation of latent EBV infection does not play a significant role for exacerbations in RRMS. [source] Effects of ouabain on contractions induced by manganese ions in Ca2+ -free, isotonic solutions with varying concentrations of K+ in guinea-pig taenia coliFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 3 2005Tetsuyuki Nasu Abstract The action of ouabain, a cell membrane Na+, K+ -ATPase blocker, on contractions induced by manganese ions (Mn2+) in Ca2+ -free, isotonic solutions with varying concentrations of K+ in the external medium were investigated in order to evaluate the underlying role of external Na+ in Mn2+ -induced contractions in isolated taenia coli of the guinea-pig. Mn2+ at 5 mm induced greater contractions as external isotonic K+ concentrations progressively increased from 10 to 100 mm. Ouabain (2 × 10,4 m) completely inhibited tension development stimulated by 5 mm Mn2+ in isotonic, 30 mm K+ (96 mm Na+) medium. Whereas, the tension inhibitory effects of ouabain became progressively weaker as isotonic, external K+ concentrations increased to 60 mm, which successively decreased external Na+ concentrations. Eventually, ouabain failed to affect contractions stimulated by Mn2+ in isotonic, 126 mm K+, Na+ -deficient medium. Ouabain caused progressively greater increase in cellular Na+ concentrations as the Na+ concentrations increased in the isotonic, K+ medium. While, pyruvate, which penetrates cell independently of external Na+, reversed the inhibition of tension by ouabain in isotonic, 30 mm K+, Na+ -sufficient (96 mm) medium containing 5 mm Mn2+. These results suggested that Mn2+ induced the contraction, which was maintained by glucose transport depending on external Na+, in the case of Na+ -sufficient medium in K+ -depolarized taenia coli. However, it induced the contraction independent of external Na+, in the case of Na+ -deficient, K+ medium. Ouabain might exhibit greater inhibition of the contraction induced by Mn2+ as the decrease in the Na+ gradient across the cell membranes continues. [source] Genetic variants in germline TP53 and MDM2 SNP309 are not associated with early onset colorectal cancer,JOURNAL OF SURGICAL ONCOLOGY, Issue 7 2008Sajid A. Khan MD Abstract Background and Objectives Colorectal cancer (CRC) arising in patients under age 30 is a rare disease, and few cases have been reported within Li-Fraumeni kindreds. To determine how often alterations in the p53 pathway genes contribute to disease susceptibility, we have evaluated patients with early onset CRC for the presence of germline variants in the p53 gene and MDM2 SNP309. Methods Thirty-five patients with CRC diagnosed before age 30 were included in this study-based on tissue availability. DNA samples from peripheral blood leukocytes were analyzed for constitutional mutations and polymorphisms in p53 as well as polymorphisms in MDM2 SNP309. Results No mutations were found in exons 4,10 of the p53 gene. The frequencies of polymorphisms in p53 and in MDM2 SNP309 did not differ from rates previously reported for normal control populations, and no polymorphism in either gene could be associated with early onset CRC. Conclusions Neither germline variants in p53 nor MDM2 SNP309 play an underlying role in the development of very early onset CRC. For the large majority of cases, the genetic basis of this disease remains unknown. J. Surg. Oncol. 2008;97:621,625. © 2008 Wiley-Liss, Inc. [source] Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn,Teller transitions in ABX3 perovskites.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009The structural evolution of selected perovskites containing Jahn,Teller cations has been investigated in the light of a formal analysis of symmetry hierarchies for phase transitions driven by octahedral tilting and Jahn,Teller cooperative distortions. General expressions derived from the strain/order-parameter coupling relationships allowed by symmetry are combined with observed changes in lattice parameters to reveal details of order-parameter evolution and coupling. LuVO3, YbVO3, YVO3 and CeVO3 are representative of systems which develop Jahn,Teller ordering schemes associated with irreducible representations and of the space group . Tilting of their octahedra is associated with and . The Pnma ( tilting) ,P21/a ( tilting, Jahn,Teller order) transition below room temperature is close to second order in character. Shear strains which depend primarily on tilt angles show little variation, implying that there is only weak coupling between the tilting and Jahn,Teller order parameters. The subsequent P21/a,Pnma ( tilting, Jahn,Teller order) is first order in character, and involves either a reduction in the tilt angle or a change in the strength of tilt/Jahn,Teller order-parameter coupling. In LaMnO3, the isosymmetric Pnma ( tilting) ,Pnma ( tilting, Jahn,Teller order) transition can be described in terms of a classical first-order transition conforming to a 246 Landau expansion with negative fourth-order coefficients. Strain evolution in Ba-doped samples suggests that the transition becomes second order in character and reveals a new strain relaxation mechanism in LaMnO3 which might be understood in terms of local strain heterogeneities due to the disordering of distorted MnO6 octahedra. Transitions in PrAlO3 and La0.5Ba0.5CoO3 illustrate the transformation behaviour of systems in which the Jahn,Teller ordering scheme is associated with the irreducible representation . Overall, coupled tilting + Jahn,Teller phase transitions in perovskites conform to mean-field behaviour, consistent with the underlying role of strain in promoting long interaction lengths. [source] | ||||||||||