75 research outputs found
Phase diagram of solution of oppositely charged polyelectrolytes
We study a solution of long polyanions (PA) with shorter polycations (PC) and
focus on the role of Coulomb interaction. A good example is solutions of DNA
and PC which are widely studied for gene therapy. In the solution, each PA
attracts many PCs to form a complex. When the ratio of total charges of PA and
PC in the solution, , equals to 1, complexes are neutral and they condense
in a macroscopic drop. When is far away from 1, complexes are strongly
charged. The Coulomb repulsion is large and free complexes are stable. As
approaches to 1, PCs attached to PA disproportionate themselves in two
competing ways. One way is inter-complex disproportionation, in which PCs make
some complexes neutral and therefore condensed in a macroscopic drop while
other complexes become even stronger charged and stay free. The other way is
intra-complex disproportionation, in which PCs make one end of a complex
neutral and condensed in a small droplet while the rest of the complex forms a
strongly charged tail. Thus each complex becomes a "tadpole". These two ways
can also combine together to give even lower free energy. We get a phase
diagram of PA-PC solution in a plane of and inverse screening radius of the
monovalent salt, which includes phases or phase coexistence with both kinds of
disproportionation.Comment: 29 pages, 10 figures. Major change in results and tex
Attractive Interactions Between Rod-like Polyelectrolytes: Polarization, Crystallization, and Packing
We study the attractive interactions between rod-like charged polymers in
solution that appear in the presence of multi-valence counterions. The
counterions condensed to the rods exhibit both a strong transversal
polarization and a longitudinal crystalline arrangement. At short distances
between the rods, the fraction of condensed counterions increases, and the
majority of these occupy the region between the rods, where they minimize their
repulsive interactions by arranging themselves into packing structures. The
attractive interaction is strongest for multivalent counterions. Our model
takes into account the hard-core volume of the condensed counterions and their
angular distribution around the rods. The hard core constraint strongly
suppresses longitudinal charge fluctuations.Comment: 4 figures, uses revtex, psfig and epsf. The new version contains a
different introduction, and the bibliography has been expande
Paecilomyces fumosoroseus blastospore production using liquid culture in a bioreactor
There are many advantages to using liquid cultures for the production of blastospores. These include mainly the processes of scale up which are relatively easy, as well as the control of parameters such astemperature, aeration and pH. In this work, we evaluated the production of Paecilomyces fumosoroseus blastospores using a low-cost liquid culture medium in a fermenter in comparison to a mediumcommonly used for this purpose, with regard to yield and viability of blastospores. The two media contained the same concentration of glucose but differed in N source (M1 containing casamino acidsand M2 provided with collagen peptone and yeast extract). Starting with an inoculum of 1x106 blastospores/ml, M2 medium produced 2x1010 blastospores/ml after incubation for 72 h at 520 rev/minagitation and 1 v/v/m (volume air/volume liquid.min) aeration, while only 2.4 x 108/ml were produced with M1. In addition, the microorganisms in medium M1 grew more slowly during log phase and reached an earlier plateau at 36 h fermentation. The medium containing collagen peptone and yeast extract is an excellent alternative for the production of P. fumosoroseus blastospores, providing lower cost, higher yield and shorter propagation time, but formulation does need to be improved
Onset of DNA Aggregation in Presence of Monovalent and Multivalent Counterions
We address theoretically aggregation of DNA segments by multivalent
polyamines such as spermine and spermidine. In experiments, the aggregation
occurs above a certain threshold concentration of multivalent ions. We
demonstrate that the dependence of this threshold on the concentration of DNA
has a simple form. When the DNA concentration c_DNA is smaller than the
monovalent salt concentration, the threshold multivalent ion concentration
depends linearly on c_DNA, having the form alpha c_DNA + beta. The coefficients
alpha and beta are related to the density profile of multivalent counterions
around isolated DNA chains, at the onset of their aggregation. This analysis
agrees extremely well with recent detailed measurements on DNA aggregation in
the presence of spermine. From the fit to the experimental data, the number of
condensed multivalent counterions per DNA chain can be deduced. A few other
conclusions can then be reached: i) the number of condensed spermine ions at
the onset of aggregation decreases with the addition of monovalent salt; ii)
the Poisson-Boltzmann theory over-estimates the number of condensed multivalent
ions at high monovalent salt concentrations; iii) our analysis of the data
indicates that the DNA charge is not over-compensated by spermine at the onset
of aggregation.Comment: 12 pages, 8 figures. Biophysical Journal 2003, in pres
Conformational Instability of Rodlike Polyelectrolytes due to Counterion Fluctuations
The effective elasticity of highly charged stiff polyelectrolytes is studied
in the presence of counterions, with and without added salt. The rigid polymer
conformations may become unstable due to an effective attraction induced by
counterion density fluctuations. Instabilities at the longest, or intermediate
length scales may signal collapse to globule, or necklace states, respectively.
In the presence of added-salt, a generalized electrostatic persistence length
is obtained, which has a nontrivial dependence on the Debye screening length.
It is also found that the onset of conformational instability is a re-entrant
phenomenon as a function of polyelectrolyte length for the unscreened case, and
the Debye length or salt concentration for the screened case. This may be
relevant in understanding the experimentally observed re-entrant condensation
of DNA.Comment: 8 pages, 4 figure
Collapse of Stiff Polyelectrolytes due to Counterion Fluctuations
The effective elasticity of highly charged stiff polyelectrolytes is studied
in the presence of counterions, with and without added salt. The rigid polymer
conformations may become unstable due to an effective attraction induced by
counterion density fluctuations. Instabilities at the longest, or intermediate
length scales may signal collapse to globule, or necklace states, respectively.
In the presence of added-salt, a generalized electrostatic persistence length
is obtained, which has a nontrivial dependence on the Debye screening length.Comment: 4 pages RevTex, 3 ps figures included using epsf, final version as
appeared in PR
Diets containing sea cucumber (Isostichopus badionotus) meals are hypocholesterolemic in young rats
Peer reviewedPublisher PD
Health financing policies during the COVID-19 pandemic and implications for universal health care: a case study of 15 countries
Background The COVID-19 pandemic was a health emergency requiring rapid scal resource mobilisation to support national responses. The use of e ective health nancing mechanisms and policies, or lack thereof, a ected the impact of the pandemic on the population, particularly vulnerable groups and individuals. We provide an overview and illustrative examples of health nancing policies adopted in 15 countries during the pandemic, develop a framework for resilient health nancing, and use this pandemic to argue a case to move towards universal health coverage (UHC).
Methods In this case study, we examined the national health nancing policy responses of 15 countries, which were purposefully selected countries to represent all WHO regions and have a range of income levels, UHC index scores, and health system typologies. We did a systematic literature review of peer-reviewed articles, policy documents, technical reports, and publicly available data on policy measures undertaken in response to the pandemic and complemented the data obtained with 61 in-depth interviews with health systems and health nancing experts. We did a thematic analysis of our data and organised key themes into a conceptual framework for resilient health nancing.
Findings Resilient health nancing for health emergencies is characterised by two main phases: (1) absorb and recover, where health systems are required to absorb the initial and subsequent shocks brought about by the pandemic and restabilise from them; and (2) sustain, where health systems need to expand and maintain scal space for health to move towards UHC while building on resilient health nancing structures that can better prepare health systems for future health emergencies. We observed that ve key nancing policies were implemented across the countriesâ namely, use of extra-budgetary funds for a swift initial response, repurposing of existing funds, e cient fund disbursement mechanisms to ensure rapid channelisation to the intended personnel and general population, mobilisation of the private sector to mitigate the gaps in public settings, and expansion of service coverage to enhance the protection of vulnerable groups. Accountability and monitoring are needed at every stage to ensure e cient and accountable movement and use of funds, which can be achieved through strong governance and coordination, information technology, and community engagement.
Interpretation Our ndings suggest that health systems need to leverage the COVID-19 pandemic as a window of opportunity to make health nancing policies robust and need to politically commit to public nancing mechanisms that work to prepare for future emergencies and as a lever for UHC.We thank the management team of the Bill & Melinda Gates Foundation and the Saw Swee Hock School of Public Health (National University of Singapore, Singapore) for all the administrative support given. This research was funded by the Bill & Melinda Gates Foundation (Investment ID INV-005598)
Neutral and Charged Polymers at Interfaces
Chain-like macromolecules (polymers) show characteristic adsorption
properties due to their flexibility and internal degrees of freedom, when
attracted to surfaces and interfaces. In this review we discuss concepts and
features that are relevant to the adsorption of neutral and charged polymers at
equilibrium, including the type of polymer/surface interaction, the solvent
quality, the characteristics of the surface, and the polymer structure. We pay
special attention to the case of charged polymers (polyelectrolytes) that have
a special importance due to their water solubility. We present a summary of
recent progress in this rapidly evolving field. Because many experimental
studies are performed with rather stiff biopolymers, we discuss in detail the
case of semi-flexible polymers in addition to flexible ones. We first review
the behavior of neutral and charged chains in solution. Then, the adsorption of
a single polymer chain is considered. Next, the adsorption and depletion
processes in the many-chain case are reviewed. Profiles, changes in the surface
tension and polymer surface excess are presented. Mean-field and corrections
due to fluctuations and lateral correlations are discussed. The force of
interaction between two adsorbed layers, which is important in understanding
colloidal stability, is characterized. The behavior of grafted polymers is also
reviewed, both for neutral and charged polymer brushes.Comment: a review: 130 pages, 30 ps figures; final form, added reference
Genomic Characterization of Haemophilus parasuis SH0165, a Highly Virulent Strain of Serovar 5 Prevalent in China
Haemophilus parasuis can be either a commensal bacterium of the porcine respiratory tract or an opportunistic pathogen causing Glässer's disease, a severe systemic disease that has led to significant economical losses in the pig industry worldwide. We determined the complete genomic sequence of H. parasuis SH0165, a highly virulent strain of serovar 5, which was isolated from a hog pen in North China. The single circular chromosome was 2,269,156 base pairs in length and contained 2,031 protein-coding genes. Together with the full spectrum of genes detected by the analysis of metabolic pathways, we confirmed that H. parasuis generates ATP via both fermentation and respiration, and possesses an intact TCA cycle for anabolism. In addition to possessing the complete pathway essential for the biosynthesis of heme, this pathogen was also found to be well-equipped with different iron acquisition systems, such as the TonB system and ABC-type transport complexes, to overcome iron limitation during infection and persistence. We identified a number of genes encoding potential virulence factors, such as type IV fimbriae and surface polysaccharides. Analysis of the genome confirmed that H. parasuis is naturally competent, as genes related to DNA uptake are present. A nine-mer DNA uptake signal sequence (ACAAGCGGT), identical to that found in Actinobacillus pleuropneumoniae and Mannheimia haemolytica, followed by similar downstream motifs, was identified in the SH0165 genome. Genomic and phylogenetic comparisons with other Pasteurellaceae species further indicated that H. parasuis was closely related to another swine pathogenic bacteria A. pleuropneumoniae. The comprehensive genetic analysis presented here provides a foundation for future research on the metabolism, natural competence and virulence of H. parasuis
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