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- J.G., Cohen, et al.
(författare)
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Abundances In Very Metal-Poor Dwarf Stars
- 2004
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Ingår i: Astrophysical Journal. - 0004-637X. ; 603:2, s. 1107-1135
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- We discuss the detailed composition of 28 extremely metal-poor (EMP) dwarfs, 22 of which are from the Hamburg/ESO Survey (HES), based on Keck echelle spectra. Our sample has a median [Fe/H] of -2.7 dex, extends to -3.5 dex, and is somewhat less metal-poor than was expected from [Fe/H](HK, HES) determined from low-resolution spectra. Our analysis supports the existence of a sharp decline in the distribution of halo stars with metallicity below [Fe/H]=-3.0 dex. So far no additional turnoff stars with [Fe/H]<-3.5 have been identified in our follow-up efforts. For the best-observed elements between Mg and Ni, we find that the abundance ratios appear to have reached a plateau, i.e., [X/Fe] is approximately constant as a function of [Fe/H], except for Cr, Mn, and Co, which show trends of abundance ratios varying with [Fe/H]. These abundance ratios at low metallicity correspond approximately to the yield expected from Type II supernovae (SNe) with a narrow range in mass and explosion parameters; high-mass Type II SN progenitors are required. The dispersion of [X/Fe] about this plateau level is surprisingly small and is still dominated by measurement errors rather than intrinsic scatter. These results place strong constraints on the characteristics of the contributing SNe. The dispersion in neutron-capture elements and the abundance trends for Cr, Mn, and Co are consistent with previous studies of evolved EMP stars. We find halo-like enhancements for the α-elements Mg, Ca, and Ti, but solar Si/Fe ratios for these dwarfs. This contrasts with studies of EMP giant stars, which show Si enhancements similar to other α-elements. Sc/Fe is another case where the results from EMP dwarfs and from EMP giants disagree; our Sc/Fe ratios are enhanced compared to the solar value by ~0.2 dex. Although this conflicts with the solar Sc/Fe values seen in EMP giants, we note that α-like Sc/Fe ratios have been claimed for dwarfs at higher metallicity. Two dwarfs in the sample are carbon stars, while two others have significant C enhancements, all with 12C/13C ~7 and with C/N between 10 and 150. Three of these C-rich stars have large enhancements of the heavy neutron capture elements, including lead, which implies a strong s-process contribution, presumably from binary mass transfer; the fourth shows no excess of Sr or Ba.
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| 2. |
- Jamain, Stephane, et al.
(författare)
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Mutations of the X-linked genes encoding neuroligins NLGN3 and NLGN4 are associated with autism
- 2003
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 34:1, s. 27-29
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Tidskriftsartikel (refereegranskat)abstract
- Many studies have supported a genetic etiology for autism. Here we report mutations in two X-linked genes encoding neuroligins NLGN3 and NLGN4 in siblings with autism-spectrum disorders. These mutations affect cell-adhesion molecules localized at the synapse and suggest that a defect of synaptogenesis may predispose to autism.
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| 5. |
- Berlow, E.L., et al.
(författare)
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Interaction strengths in food webs : Issues and opportunities
- 2004
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 73:3, s. 585-598
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Forskningsöversikt (refereegranskat)abstract
- 1. Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2. Much confusion stems from lack of clarity about whether the questions posed relate to community-level patterns or to species dynamics, and to what authors actually mean by the term 'interaction strength'. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field. 3. Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits. 4. Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity. 5. Finally, the prime focus on predator-prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of nontrophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes.
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| 6. |
- Borovok, I, et al.
(författare)
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Streptomyces spp. contain class Ia and class II ribonucleotide reductases: expression analysis of the genes in vegetative growth
- 2002
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Ingår i: Microbiology (Reading, England). - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 148:Pt 2, s. 391-404
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Tidskriftsartikel (refereegranskat)abstract
- Genes encoding two ribonucleotide reductases (RNRs) were identified in members of the genusStreptomyces. One gene,nrdJ, encoded an oligomeric protein comprising four identical subunits each with a molecular mass of ∼108 kDa. The activity of this protein depended on the presence of 5′-deoxyadenosylcobalamine (coenzyme B12), establishing it as a class II RNR. TheStreptomyces clavuligerus nrdJgene was cloned, using internal peptide sequences from the purified protein, and was found to encode a polypeptide of 961 aa. Molecular phylogenetic analysis showed that theS. clavuligerusclass II RNR shares significant similarity with most other bacterial and archaeal class II RNRs. Two other genes,nrdAandnrdB, were initially identified in theStreptomyces coelicolorgenome database in unannotated ORFs as encoding a class Ia RNR. Southern analysis demonstrated that thenrdABgenes were present in differentStreptomycesspp. TheS. coelicolor nrdABgenes were cloned and expressed inEscherichia coli, and the recombinant proteins were shown to represent a class I RNR. It was shown, using quantitative real-time PCR, that theS. clavuligerusclass Ia and class II RNR genes were differentially transcribed during vegetative growth. The copy number of the class IInrdJtranscripts was approximately constant throughout the exponential phase of vegetative growth (3–5×105copies per 400 ng total RNA after reverse transcription). In contrast, the copy number of the class IanrdABtranscripts was some 10- to 20-fold less than that ofnrdJin the early-exponential growth phase (2·8×104copies), and decreased markedly at the mid-exponential (4×103copies) and late-exponential phases (1·1×103copies) of growth. A possible role for the involvement of two RNRs during vegetative growth is discussed.
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| 7. |
- Cleland, J. G., et al.
(författare)
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The EuroHeart Failure survey programme-- a survey on the quality of care among patients with heart failure in Europe. Part 1: patient characteristics and diagnosis
- 2003
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Ingår i: European heart journal. - 0195-668X. ; 24:5, s. 442-63
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Forskningsöversikt (refereegranskat)abstract
- BACKGROUND: The European Society of Cardiology (ESC) has published guidelines for the investigation of patients with suspected heart failure and, if the diagnosis is proven, their subsequent management. Hospitalisation provides a key point of care at which time diagnosis and treatment may be refined to improve outcome for a group of patients with a high morbidity and mortality. However, little international data exists to describe the features and management of such patients. Accordingly, the EuroHeart Failure survey was conducted to ascertain if appropriate tests were being performed with which to confirm or refute a diagnosis of heart failure and how this influenced subsequent management. METHODS: The survey screened consecutive deaths and discharges during 2000-2001 predominantly from medical wards over a 6-week period in 115 hospitals from 24 countries belonging to the ESC, to identify patients with known or suspected heart failure. RESULTS: A total of 46788 deaths and discharges were screened from which 11327 (24%) patients were enrolled with suspected or confirmed heart failure. Forty-seven percent of those enrolled were women. Fifty-one percent of women and 30% of men were aged >75 years. Eighty-three percent of patients had a diagnosis of heart failure made on or prior to the index admission. Heart failure was the principal reason for admission in 40%. The great majority of patients (>90%) had had an ECG, chest X-ray, haemoglobin and electrolytes measured as recommended in ESC guidelines, but only 66% had ever had an echocardiogram. Left ventricular ejection fraction had been measured in 57% of men and 41% of women, usually by echocardiography (84%) and was <40% in 51% of men but only in 28% of women. Forty-five percent of women and 22% of men were reported to have normal left ventricular systolic function by qualitative echocardiographic assessment. A substantial proportion of patients had alternative explanations for heart failure other than left ventricular systolic or diastolic dysfunction, including valve disease. Within 12 weeks of discharge, 24% of patients had been readmitted. A total of 1408 of 10434 (13.5%) patients died between admission and 12 weeks follow-up. CONCLUSIONS: Known or suspected heart failure comprises a large proportion of admissions to medical wards and such patients are at high risk of early readmission and death. Many of the basic investigations recommended by the ESC were usually carried out, although it is not clear whether this was by design or part of a general routine for all patients being admitted regardless of diagnosis. The investigation most specific for patients with suspected heart failure (echocardiography) was performed less frequently, suggesting that the diagnosis of heart failure is still relatively neglected. Most men but a minority of women who underwent investigation of cardiac function had evidence of moderate or severe left ventricular dysfunction, the main target of current advances in the treatment of heart failure. Considerable diagnostic uncertainty remains for many patients with suspected heart failure, even after echocardiography, which must be resolved in order to target existing and new therapies and services effectively.
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| 10. |
- Komajda, M., et al.
(författare)
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The EuroHeart Failure Survey programme--a survey on the quality of care among patients with heart failure in Europe. Part 2: treatment
- 2003
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Ingår i: European heart journal. - 0195-668X. ; 24:5, s. 464-74
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Forskningsöversikt (refereegranskat)abstract
- BACKGROUND: National surveys suggest that treatment of heart failure in daily practice differs from guidelines and is characterized by underuse of recommended medications. Accordingly, the Euro Heart Failure Survey was conducted to ascertain how patients hospitalized for heart failure are managed in Europe and if national variations occur in the treatment of this condition. METHODS: The survey screened discharge summaries of 11304 patients over a 6-week period in 115 hospitals from 24 countries belonging to the ESC to study their medical treatment. RESULTS: Diuretics (mainly loop diuretics) were prescribed in 86.9% followed by ACE inhibitors (61.8%), beta-blockers (36.9%), cardiac glycosides (35.7%), nitrates (32.1%), calcium channel blockers (21.2%) and spironolactone (20.5%). 44.6% of the population used four or more different drugs. Only 17.2% were under the combination of diuretic, ACE inhibitors and beta-blockers. Important local variations were found in the rate of prescription of ACE inhibitors and particularly beta-blockers. Daily dosage of ACE inhibitors and particularly of beta-blockers was on average below the recommended target dose. Modelling-analysis of the prescription of treatments indicated that the aetiology of heart failure, age, co-morbid factors and type of hospital ward influenced the rate of prescription. Age <70 years, male gender and ischaemic aetiology were associated with an increased odds ratio for receiving an ACE inhibitor. Prescription of ACE inhibitors was also greater in diabetic patients and in patients with low ejection fraction (<40%) and lower in patients with renal dysfunction. The odds ratio for receiving a beta-blocker was reduced in patients >70 years, in patients with respiratory disease and increased in cardiology wards, in ischaemic heart failure and in male subjects. Prescription of cardiac glycosides was significantly increased in patients with supraventricular tachycardia/atrial fibrillation. Finally, the rate of prescription of antithrombotic agents was increased in the presence of supraventricular arrhythmia, ischaemic heart disease, male subjects but was decreased in patients over 70. CONCLUSION: Our results suggest that the prescription of recommended medications including ACE inhibitors and beta-blockers remains limited and that the daily dosage remains low, particularly for beta-blockers. The survey also identifies several important factors including age, gender, type of hospital ward, co morbid factors which influence the prescription of heart failure medication at discharge.
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