Screening of a macroion by multivalent ions: A new boundary condition for Poisson-Boltzmann equation and charge inversion

Screening of a macroion by multivalent counterions is considered. It is shown that ions form strongly correlated liquid at the macroion surface. Cohesive energy of this liquid leads to strong additional attraction of counterions to the surface. Away from the surface this attraction is taken into account by a new boundary condition for the Poisson-Boltzmann equation. This equation is solved with the new boundary condition for a charged flat surface and a long cylinder. For a cylinder Onsager-Manning theory looses its universality so that apparent charge of the cylinder is smaller than their theory predicts and depends on its bare charge. It can also vanish or change sign.Comment: 4 pages, no figure

Habitat Selection and Risk of Predation: Re-colonization by Lynx had Limited Impact on Habitat Selection by Roe Deer

Risk of predation is an evolutionary force that affects behaviors of virtually all animals. In this study, we examined how habitat selection by roe deer was affected by risk of predation by Eurasian lynx - the main predator of roe deer in Scandinavia. Specifically, we compared how habitat selection by roe deer varied (1) before and after lynx re-established in the study area and (2) in relation to habitat-specific risk of predation by lynx. All analyses were conducted at the spatial and temporal scales of home ranges and seasons. We did not find any evidence that roe deer avoided habitats in which the risk of predation by lynx was greatest and information-theoretic model selection showed that re-colonization by lynx had limited impact on habitat selection by roe deer despite lynx predation causing 65% of known mortalities after lynx re-colonized the area. Instead we found that habitat selection decreased when habitat availability increased for 2 of 5 habitat types (a pattern referred to as functional response in habitat selection). Limited impact of re-colonization by lynx on habitat selection by roe deer in this study differs from elk in North America altering both daily and seasonal patterns in habitat selection at the spatial scales of habitat patches and home ranges when wolves were reintroduced to Yellowstone National Park. Our study thus provides further evidence of the complexity by which animals respond to risk of predation and suggest that it may vary between ecosystems and predator-prey constellations

Bloodstream infections in patients with hematological malignancies

Patients with hematological malignancies have an increased risk of infectious complications. These complications can be caused by disease-specific factors or be treatment-related. Bloodstream infections increase the risk of morbidity, mortality, have a negative impact on quality of life, and may lead to reductions in treatment intensity. Surveillance studies on infectious complications and new technologies in diagnosing bloodstream infections are two important fields in improving management of patients with hematological malignancies. Paper I: This is a retrospective study of positive blood cultures from patients mainly treated with dose-intensive antitumoural treatment between 2002 and 2008. Bacterial distribution, bacterial resistance and mortality from 667 fever episodes are presented. Results are compared with historical, previous published, material from the same institution and setting. Subsequently, temporal trends from 1980 to 2008 could be analysed. In a setting with very low use of fluoroquinolone-prophylaxis it can be concluded that; the distribution of Gram-positive bacteremia is stable, the crude mortality remains low in an international perspective and acquired resistance is uncommon but a significant increase in ciprofloxacin resistance in Escherichia coli is observed. The five most common bacteria in the study are; E. coli, coagulase-negative staphylococci, viridans streptococci, Klebsiella spp., and Staphylococcus aureus. Paper II: This is a retrospective study that investigated temporal trends in bloodstream infections in patients with chronic lymphocytic leukemia between 1988-2008. We find a decrease in positive blood cultures over time and speculate if this could be due to more effective antitumoural treatment in recent years. Moreover a bloodstream infection is, as intuitively foreseen, associated with worse prognosis. Dominating pathogens in the study are; E. coli, Streptococcus pneumoniae, P. aeruginosa, S. aureus, and viridans streptococci. Coagulase-negative staphylococcus, a common skin contaminant, is the most frequently detected bacteria. Paper III: This is a prospective study of 33 patients with aggressive hematological malignancies in need of dose-intensive chemotherapy. One hundred thirty blood samples were collected at different time points during episodes with neutropenia and fever between 2013 and 2014. Conventional blood culture findings were compared with a method applicable also for unculturable bacteria, 16S rRNA amplicon sequencing. Sequencing yielded reads belonging to Proteobacteria (55.2%), Firmicutes (33.4%), Actinobacteria (8.6%), Fusobacteria (0.4%), and Bacteroidetes (0.1%). The results display a much broader diversity of bacteria in bloodstream infections than expected. Changes in the relative abundance in the sequence data after commencement of antibiotics could be suggestive for a new method for estimating antibiotic efficacy. Lastly, the results are indicative for translocation, especially of gut microbiota, playing an important etiological factor in fever episodes in the neutropenic host. Paper IV: This is a prospective study of 9 patients with acute leukemia in which we applied shotgun metagenomics for 27 blood samples collected during episodes of neutropenia and fever between 2013 and 2014. Shotgun metagenomics can characterize DNAemia and reconstruct unculturable microbial communities, resistance markers and gene ontology. The study confirms the method’s applicability in bloodstream infections demonstrating bacteria, viruses and fungi. Furthermore, the observed dynamics of microbe sequences during fever episodes as well as gene ontology makes this diagnostic approach appealing for exploring the fever episodes in this patient category

Non-monotonic swelling of a macroion due to correlation-induced charge inversion

It is known that a large, charged body immersed in a solution of multivalent counterions may undergo charge inversion as the counterions adsorb to its surface. We use the theory of charge inversion to examine the case of a deformable, porous macroion which may adsorb multivalent ions into its bulk to form a three-dimensional strongly-correlated liquid. This adsorption may lead to non-monotonic changes in the size of the macroion as multivalent ions are added to the solution. The macroion first shrinks as its bare charge is screened and then reswells as the adsorbed ions invert the sign of the net charge. We derive a value for the outward pressure experienced by such a macroion as a function of the ion concentration in solution. We find that for small deviations in the concentration of multivalent ions away from the neutral point (where the net charge of the body is zero), the swollen size grows parabolically with the logarithm of the ratio of multivalent ion concentration to the concentration at the neutral point.Comment: 7 pages, 4 figures; typos fixed; final published versio

Efficient Modeling of a Flexible Beam in Dymola using Coupled Substructures in a Floating Frame of Reference Formulation

In this Master Thesis a three dimensional Euler-Bernoulli beam model was implemented in the simulation software Dymola. The beam model is based on the Floating Frame of Reference formulation combined with the Craig-Bampton method. The theory is developed with the scope to capture the dynamic and static responses of a beam model in a compact and computer efficient implementation. The Thesis includes derivation of kinematic description, mass matrix, stiffness matrix and force vectors of an Euler-Bernoulli beam in three-dimensional space. Two one-dimensional models have been derived as well. The implementation in Dymola is described together with validation of the model, discussion and conclusions. The validation of the model shows great accuracy in static loading both in elongation, torsion and bending. Excitation of eigenfrequencies is possible but the results slightly differs from the analytical solutions. Dynamic tests of the beam model shows realistic responses but further testing on this subject is recommended. Compatibility with other components in Dymola works fine. However there are some minor issues that should be solved to enhance the efficiency. Overall the static and dynamic responses of the beam model works sufficiently well

Activation of Retinoid X Receptor increases dopamine cell survival in models for Parkinson's disease

<p>Abstract</p> <p>Background</p> <p>Parkinson's disease (PD) is caused by degeneration of dopamine (DA) neurons in the ventral midbrain (vMB) and results in severely disturbed regulation of movement. The disease inflicts considerable suffering for the affected and their families. Today, the opportunities for pharmacological treatment are meager and new technologies are needed. Previous studies have indicated that activation of the nuclear receptor Retinoid X Receptor (RXR) provides trophic support for DA neurons. Detailed investigations of these neurotrophic effects have been hampered by the lack of readily available DA neurons <it>in vitro</it>. The aim of this study was to further describe the potential neurotrophic actions of RXR ligands and, for this and future purposes, develop a suitable <it>in vitro</it>-platform using mouse embryonic stem cells (mESCs).</p> <p>Results</p> <p>We studied the potential neurotrophic effects of the RXR ligand LG100268 (LG268) and the RXR-Nurr1 ligand XCT0139508 (XCT) in neuronal cultures derived from rat primary vMB and mESCs. RXR ligands protect DA neurons from stress, such as that induced by the PD-modeling toxin 6-hydroxy dopamine (6-OHDA) and hypoxia, but not from stress induced by oxidative hydrogen peroxide (H₂O₂) or the excitotoxic agent kainic acid (KA). The neurotrophic effect is selective for DA neurons. DA neurons from rat primary vMB and mESCs behaved similarly, but the mESC-derived cultures contained a much higher fraction of DA cells and thus provided more accessible experimental conditions.</p> <p>Conclusions</p> <p>RXR ligands rescue DA neurons from degeneration caused by the PD simulating 6-OHDA as well as hypoxia. Thus, RXR is a novel promising target for PD research. mESC-derived DA cells provide a valid and accessible <it>in vitro</it>-platform for studying PD inducing toxins and potential trophic agents.</p

McMillan–Mayer theory for solvent effects in inhomogeneous systems: Calculation of interaction pressure in aqueous electrical double layers

We demonstrate how to use the McMillan–Mayer theory to include solvent effects in effective solute–solute interactions for inhomogeneous systems, extending a recent derivation [S. Marčelja, Langmuir 16, 6081 (2000)] for symmetric planar double layers to the general case. In the exact treatment, the many-body potential of mean force between the solute molecules can be evaluated for an inhomogeneous reference system in equilibrium with pure bulk solvent. The reference system contains only solvent and a finite number, n, of fixed solute molecules and it has an external potential that in some cases is different from that of the original system. It is discussed how the n-body potential of mean force between the ions for the relevant cases of large n values can be approximated by a sum of effective singlet and pair interactions evaluated in the presence of, on average, all n ions, i.e., at finite concentration. In examples considered in this work we use effective interionic pair potentials evaluated from bulk electrolyte calculations at finite electrolyte concentrations. We calculate the contribution to the double layer interaction pressure arising from the interaction between ions dissolved in aqueous electrolyte. In cases of moderate or high surface charge, calculations show several new effects. At small surface separations one finds attractive and then strongly repulsive contributions. For surface charge density around one negative charge per 70 Å2 the full results for pressures resemble “secondary hydration force” measured in classical experiments in 1980s. When there is a tendency for ions to adsorb at the surfaces there is a marked change in behavior. The force is then oscillatory, reminiscent of results obtained with the surface force apparatus at low electrolyte concentration