Dynamical stability of fluid spheres in spacetimes with a nonzero cosmological constant

The Sturm-Liouville eigenvalue equation for eigenmodes of the radial oscillations is determined for spherically symmetric perfect fluid configurations in spacetimes with a nonzero cosmological constant and applied in the cases of configurations with uniform distribution of energy density and polytropic spheres. It is shown that a repulsive cosmological constant rises the critical adiabatic index and decreases the critical radius under which the dynamical instability occurs.Comment: 3 pages, 1 figure, to appear in "Proceedings of the 11th Marcel Grossmann Meeting on General Relativity", eds H. Kleinert, R. T. Jantzen, R. Ruffin

Plant defense under Arctic light conditions: Can plants withstand invading pests?

Global warming is predicted to change the growth conditions for plants and crops in regions at high latitudes (>60° N), including the Arctic. This will be accompanied by alterations in the composition of natural plant and pest communities, as herbivorous arthropods will invade these regions as well. Interactions between previously non-overlapping species may occur and cause new challenges to herbivore attack. However, plants growing at high latitudes experience less herbivory compared to plants grown at lower latitudes. We hypothesize that this finding is due to a gradient of constitutive chemical defense towards the Northern regions. We further hypothesize that higher level of defensive compounds is mediated by higher level of the defense-related phytohormone jasmonate. Because its biosynthesis is light dependent, Arctic summer day light conditions can promote jasmonate accumulation and, hence, downstream physiological responses. A pilot study with bilberry (Vaccinium myrtillus) plants grown under different light regimes supports the hypothesis

Plant defense under Arctic light conditions: Can plants withstand invading pests?

Global warming is predicted to change the growth conditions for plants and crops in regions at high latitudes (>60° N), including the Arctic. This will be accompanied by alterations in the composition of natural plant and pest communities, as herbivorous arthropods will invade these regions as well. Interactions between previously non-overlapping species may occur and cause new challenges to herbivore attack. However, plants growing at high latitudes experience less herbivory compared to plants grown at lower latitudes. We hypothesize that this finding is due to a gradient of constitutive chemical defense towards the Northern regions. We further hypothesize that higher level of defensive compounds is mediated by higher level of the defense-related phytohormone jasmonate. Because its biosynthesis is light dependent, Arctic summer day light conditions can promote jasmonate accumulation and, hence, downstream physiological responses. A pilot study with bilberry (Vaccinium myrtillus) plants grown under different light regimes supports the hypothesis.publishedVersio

Multi-residue analysis of chiral and achiral trace organic contaminants in soil by accelerated solvent extraction and enantioselective liquid chromatography tandem-mass spectrometry.

Reported here is the first analytical methodology for the enantiomeric determination of chiral trace organic contaminants (TOrCs) in soil. Direct enantioselective separations were achieved on a Chirobiotic V2 column operated in polar ionic mode. Initial screening of vancomycin stationary phases found Chirobiotic V2 better suited for multi-residue separation of chiral TOrCs than Chirobiotic V, due to differences in the ligand linkage chemistry. Simultaneous enantioseparation of beta-blockers, beta-agonists, anti-depressants, anti-histamines and stimulants was achieved for the first time. This included the first separation of chlorpheniramine enantiomers with a method suitable for environmental analysis (i.e. coupled to MS). Investigation of mobile phase composition found that the concentration of liophilic ions had the greatest influence on enantioseparations and were of most importance during method development. The optimized method achieved simultaneous separation of salbutamol, propranolol, atenolol, amphetamine, chlorpheniramine and fluoxetine enantiomers with satisfactory resolution ( > 1.0). For completeness, such methods also need to support analysis of achiral TOrCs. Therefore, three achiral TOrCs (carbamazepine, carbamazepine 10,11 epoxide, and triclocarban) were included to demonstrate the method's suitability. Method recoveries for all analytes ranged from 76% to 122%, with method quantitation limits (MQLs) < 1 ng g-1. Application of the method to soil microcosm studies revealed stereoselective degradation of chiral TOrCs for the first time. For example, S(+)-amphetamine degraded at a faster rate than its corresponding enantiomer, leading to an enrichment of R(-)-amphetamine. Therefore, in order to better understand the risk posed from TOrCs on the terrestrial environment, chiral species need to be profiled at the enantiomeric level. This can now be achieved using the proposed methodology, whilst simultaneously profiling achiral TOrCs. Supplementary data and information are included at the end of the main article

Bacteremias caused by Escherichia coli in cancer patients — analysis of 65 episodes

AbstractObjectives: The aims of this study were to evaluate risk factors, clinical presentation, outcome and antimicrobial susceptibility in patients with Escherichia coli bacteremia occurring over seven years in a single cancer hospital.Methods: Sixty five episodes of bacteremia from E. coli appearing over seven years from 12,301 admissions in a single cancer institution were retrospectively analyzed.Results: The proportion of bacteremia caused by E. coli among Gram-negative bacteremia was 20.8% (the second most common organism after Pseudomonas aeruginosa), and infection-associated mortality was 17%.The incidence in 1989–1995 varied from 14.3 to 24.7%. The most common risk factors were: solid tumors as the underlying disease (70.7%); central venous catheter insertion (32.3%); prior surgery (46.2%), and prior chemotherapy within 48 h (44.4%). Neutropenia and urinary catheters did not place patients at high risk in any of the subgroups. When we compared the two subgroups of 61 cases of bacteremia — monomicrobial and polymicrobial (when E. coli was isolated from blood culture with another microorganism) — we found that acute leukemia and breakthrough (recurrence while receiving antibiotics) bacteremia were more frequently associated with polymicrobial E. coli bacteremia. There was also a difference in infection-associated mortality: monomicrobial bacteremia due to E. coli only had a significantly lower mortality in comparison with polymicrobial E. coli bacteremia (8.9 vs 35.0%, respectively; P<0.03).Conclusion: The susceptibility of 115 E. coli strains isolated from 65 episodes of bacteremia was stable. Only two episodes caused by quinolone-resistant strains occurred, both in 1995, after six years of using ofloxacin for prophylaxis in neutropenic patients in our hospital. We found that 85.2–91.3% of all strains were susceptible to aminoglycosides, 97.8% to quinolones, and 90–100% to third generation cephalosporins and imipenems.The patients most commonly infected had solid tumors and the mortality was only 17%