On the electrical double layer contribution to the interfacial tension of protein crystals

We study the electrical double layer at the interface between a protein crystal and a salt solution or a dilute solution of protein, and estimate the double layer's contribution to the interfacial tension of this interface. This contribution is negative and decreases in magnitude with increasing salt concentration. We also consider briefly the interaction between a pair of protein surfaces.Comment: 6 pages, 3 figures, revtex

Electroneutrality and Phase Behavior of Colloidal Suspensions

Several statistical mechanical theories predict that colloidal suspensions of highly charged macroions and monovalent microions can exhibit unusual thermodynamic phase behavior when strongly deionized. Density-functional, extended Debye-H\"uckel, and response theories, within mean-field and linearization approximations, predict a spinodal phase instability of charged colloids below a critical salt concentration. Poisson-Boltzmann cell model studies of suspensions in Donnan equilibrium with a salt reservoir demonstrate that effective interactions and osmotic pressures predicted by such theories can be sensitive to the choice of reference system, e.g., whether the microion density profiles are expanded about the average potential of the suspension or about the reservoir potential. By unifying Poisson-Boltzmann and response theories within a common perturbative framework, it is shown here that the choice of reference system is dictated by the constraint of global electroneutrality. On this basis, bulk suspensions are best modeled by density-dependent effective interactions derived from a closed reference system in which the counterions are confined to the same volume as the macroions. Linearized theories then predict bulk phase separation of deionized suspensions only when expanded about a physically consistent (closed) reference system. Lower-dimensional systems (e.g., monolayers, small clusters), depending on the strength of macroion-counterion correlations, may be governed instead by density-independent effective interactions tied to an open reference system with counterions dispersed throughout the reservoir, possibly explaining observed structural crossover in colloidal monolayers and anomalous metastability of colloidal crystallites.Comment: 12 pages, 5 figures. Discussion clarified, references adde

Binding effects in multivalent Gibbs-Donnan equilibrium

The classical Gibbs-Donnan equilibrium describes excess osmotic pressure associated with confined colloidal charges embedded in an electrolyte solution. In this work, we extend this approach to describe the influence of multivalent ion binding on the equilibrium force acting on a charged rod translocating between two compartments, thereby mimicking ionic effects on force balance during in vitro DNA ejection from bacteriophage. The subtle interplay between Gibbs-Donnan equilibrium and adsorption equilibrium leads to a non-monotonic variation of the ejection force as multivalent salt concentration is increased, in qualitative agreement with experimental observations

Aging and ultra-slow equilibration in concentrated colloidal hard spheres

We study the dynamic behaviour of concentrated colloidal hard spheres using Time Resolved Correlation, a light scattering technique that can detect the slow evolution of the dynamics in out-of-equilibrium systems. Surprisingly, equilibrium is reached a very long time after sample initialization, the non-stationary regime lasting up to three orders of magnitude more than the relaxation time of the system. Before reaching equilibrium, the system displays unusual aging behaviour. The intermediate scattering function decays faster than exponentially and its relaxation time evolves non-monotonically with sample age.Comment: Submitted to the proceedings of the 6th EPS Liquid Matter Conference, Utrecht 2-6 July 200

Phase behaviour of charged colloidal sphere dispersions with added polymer chains

We study the stability of mixtures of highly screened repulsive charged spheres and non-adsorbing ideal polymer chains in a common solvent using free volume theory. The effective interaction between charged colloids in an aqueous salt solution is described by a screened-Coulomb pair potential, which supplements the pure hard-sphere interaction. The ideal polymer chains are treated as spheres that are excluded from the colloids by a hard-core interaction, whereas the interaction between two ideal chains is set to zero. In addition, we investigate the phase behaviour of charged colloid-polymer mixtures in computer simulations, using the two-body (Asakura-Oosawa pair potential) approximation to the effective one-component Hamiltonian of the charged colloids. Both our results obtained from simulations and from free volume theory show similar trends. We find that the screened-Coulomb repulsion counteracts the effect of the effective polymer-mediated attraction. For mixtures of small polymers and relatively large charged colloidal spheres, the fluid-crystal transition shifts to significantly larger polymer concentrations with increasing range of the screened-Coulomb repulsion. For relatively large polymers, the effect of the screened-Coulomb repulsion is weaker. The resulting fluid-fluid binodal is only slightly shifted towards larger polymer concentrations upon increasing the range of the screened-Coulomb repulsion. In conclusion, our results show that the miscibility of dispersions containing charged colloids and neutral non-adsorbing polymers increases, upon increasing the range of the screened-Coulomb repulsion, or upon lowering the salt concentration, especially when the polymers are small compared to the colloids.Comment: 25 pages,13 figures, accepted for publication on J.Phys.:Condens. Matte

Volume terms for charged colloids: a grand-canonical treatment

We present a study of thermodynamic properties of suspensions of charged colloids on the basis of linear Poisson-Boltzmann theory. We calculate the effective Hamiltonian of the colloids by integrating out the ionic degrees of freedom grand-canonically. This procedure not only yields the well-known pairwise screened-Coulomb interaction between the colloids, but also additional volume terms which affect the phase behavior and the thermodynamic properties such as the osmotic pressure. These calculations are greatly facilitated by the grand-canonical character of our treatment of the ions, and allow for relatively fast computations compared to earlier studies in the canonical ensemble. Moreover, the present derivation of the volume terms are relatively simple, make a direct connection with Donnan equilibrium, yield an explicit expression for the effective screening constant, and allow for extensions to include, for instance, nonlinear effects.Comment: 16 pages, 6 figures, published in Phys.Rev.

Intelligent Liver Function Testing (iLFT):A trial of automated diagnosis and staging of liver disease in Primary Care

Background: Liver function tests (LFTs) are frequently requested blood tests which may indicate liver disease. LFTs are commonly abnormal, the causes of which can be complex and frequently under investigated. This can lead to missed opportunities to diagnose and treat liver disease at an early stage. We developed an automated investigation algorithm, which would maximise early diagnosis of liver related diseases. Our aim was to determine whether this new pathway of care, Intelligent Liver Function testing (iLFT) increased diagnosis of liver disease and was cost-effective. Methods: We developed an automated system that further investigated abnormal LFTs on initial testing samples to generate a probable diagnosis and management plan. We integrated an automated investigation algorithm into the laboratory management system, based on minimal diagnostic criteria, liver fibrosis estimation, and reflex testing for causes of liver disease. This algorithm then generated a diagnosis and/or management plan. A stepped-wedged trial design was utilised to compare LFT outcomes in General Practices in the 6 months before and after introduction of the iLFT system. Diagnostic outcomes were collated and compared. Results: Using iLFT, the diagnosis of liver disease was increased by 43%. It was cost-effective with a low initial incremental cost-effectiveness ratio (ICER) of £284 per correct diagnosis, and a saving to the NHS of £3,216 per patient lifetime. Conclusions: iLFT increases liver diagnosis, improves quality of care, and is highly cost-effective. This can be achieved with minor changes to working practices and exploitation of functionality existing within modern laboratory diagnostics systems. Lay Summary: There is a growing epidemic of advanced liver disease, this could be offset by early detection and management. Checking liver blood tests (LFTs) should be an opportunity diagnose liver problems, but abnormal results are often incompletely investigated. In this study we were able to substantially increase the diagnostic yield of the abnormal LFTs using the automated iLFT system. With the addition of referral recommendations and management plans, this strategy provides optimum investigation and management of LFTs and is cost saving to the NHS

Грунти як об’єкт науки

Висвітлюються деякі аспекти розвитку наших уявлень про ґрунтознавство як науковий напрямок природознавства та про ґрунти як об’єкт науки.Освещаются некоторые аспекты развития наших представлений о почвоведении как научном направлении природоведения и о почвах как объекте науки.The author highlights several aspects of human knowledge about soil research as a field of natural science, and about soils as a research object

Understanding health-care outcomes of older people with cognitive impairment and/or dementia admitted to hospital: a mixed-methods study

BACKGROUND: Cognitive impairment is common in older people admitted to hospital, but previous research has focused on single conditions. OBJECTIVE: This project sits in phase 0/1 of the Medical Research Council Framework for the Development and Evaluation of Complex Interventions. It aims to develop an understanding of current health-care outcomes. This will be used in the future development of a multidomain intervention for people with confusion (dementia and cognitive impairment) in general hospitals. The research was conducted from January 2015 to June 2018 and used data from people admitted between 2012 and 2013. DESIGN: For the review of outcomes, the systematic review identified peer-reviewed quantitative epidemiology measuring prevalence and associations with outcomes. Screening for duplication and relevance was followed by full-text review, quality assessment and a narrative review (141 papers). A survey sought opinion on the key outcomes for people with dementia and/or confusion and their carers in the acute hospital (n = 78). For the analysis of outcomes including cost, the prospective cohort study was in a medical admissions unit in an acute hospital in one Scottish health board covering 10% of the Scottish population. The participants (n = 6724) were older people (aged ≥ 65 years) with or without a cognitive spectrum disorder who were admitted as medical emergencies between January 2012 and December 2013 and who underwent a structured nurse assessment. ‘Cognitive spectrum disorder’ was defined as any combination of delirium, known dementia or an Abbreviated Mental Test score of < 8 out of 10 points. The main outcome measures were living at home 30 days after discharge, mortality within 2 years of admission, length of stay, re-admission within 2 years of admission and cost. DATA SOURCES: Scottish Morbidity Records 01 was linked to the Older Persons Routine Acute Assessment data set. RESULTS: In the systematic review, methodological heterogeneity, especially concerning diagnostic criteria, means that there is significant overlap in conditions of patients presenting to general hospitals with confusion. Patients and their families expect that patients are discharged in the same or a better condition than they were in on admission or, failing that, that they have a satisfactory experience of their admission. Cognitive spectrum disorders were present in more than one-third of patients aged ≥ 65 years, and in over half of those aged ≥ 85 years. Outcomes were worse in those patients with cognitive spectrum disorders than in those without: length of stay 25.0 vs. 11.8 days, 30-day mortality 13.6% vs. 9.0%, 1-year mortality 40.0% vs. 26.0%, 1-year mortality or re-admission 62.4% vs. 51.5%, respectively (all p < 0.01). There was relatively little difference by cognitive spectrum disorder type; for example, the presence of any cognitive spectrum disorder was associated with an increased mortality over the entire period of follow-up, but with different temporal patterns depending on the type of cognitive spectrum disorder. The cost of admission was higher for those with cognitive spectrum disorders, but the average daily cost was lower. LIMITATIONS: A lack of diagnosis and/or standardisation of diagnosis for dementia and/or delirium was a limitation for the systematic review, the quantitative study and the economic study. The economic study was limited to in-hospital costs as data for social or informal care costs were unavailable. The survey was conducted online, limiting its reach to older carers and those people with cognitive spectrum disorders. CONCLUSIONS: Cognitive spectrum disorders are common in older inpatients and are associated with considerably worse health-care outcomes, with significant overlap between individual cognitive spectrum disorders. This suggests the need for health-care systems to systematically identify and develop care pathways for older people with cognitive spectrum disorders, and avoid focusing on only condition-specific pathways. FUTURE WORKS: Development and evaluation of a multidomain intervention for the management of patients with cognitive spectrum disorders in hospital. STUDY REGISTRATION: This study is registered as PROSPERO CRD42015024492. FUNDING: This project was funded by the National Institute for Health Research (NIHR) Health Services and Delivery Research programme and will be published in full in Health Services and Delivery Research; Vol. 9, No. 8. See the NIHR Journals Library website for further project information