Streaming Current for Surfaces Covered by Square and Hexagonal Monolayers of Spherical Particles.

The interface and particle contributions to the streaming current of flat substrates covered with ordered square or hexagonal monolayers of spherical particles were theoretically evaluated for particle coverage up to close packing. The exact numerical results were approximated using fitting functions that contain exponential and linear terms to account for hydrodynamic screening and charge convection from the particle surfaces exposed to external flow. According to our calculations, the streaming currents for the ordered and random particle arrangements differ within a typical experimental error. Thus, streaming-current measurements, supplemented with our fitting functions, can be conveniently used to evaluate the particle coverage without detailed knowledge of the particle distribution. Our results for equal interface and particle ζ-potentials indicate that roughness can reduce the streaming current by more than 30%, even in the limit of the small size of spherical roughness asperities.

The psychosocial burden and stress coping strategies among seafarers.

BACKGROUND: The seafarers' professional group is one of the most numerous in the world. According to the statistics of the European Maritime Safety Agency (2020), there are approximately 280,000 people employed at sea in the European Union. The specific work environment on the ship (climatic, physical, chemical, psychological factors, etc.) is related to experiencing long-term stress. The World Health Organization considers work-related stressors to be very important determinants of health and disease. One of the basic psychological resources related to adaptation to demanding working conditions are strategies for coping with stress. The aim of the study is to assess the occurrence of harmful psychosocial factors in the work of seafarers and the stress coping strategies and their relationship with somatic diseases. MATERIALS AND METHODS: One hundred and fifteen seafarers who received a maritime health certificate participated in the study at the Occupational Medicine Clinic. The study was part of a larger project looking at the prevalence of cardiovascular risk factors among seafarers. The study used the Coping Questionnaire in Stressful Situations (CISS) (Endler and Parker) and a general questionnaire created for the purposes of the study. RESULTS: Thirty six per cent respondents were exposed to traumatic event and to having nightmares, 13% had been discriminated at least once in the workplace. A positive correlation was found between discrimination and depression, nightmares and trauma. In addition, people who admitted having experienced trauma slept shorter (also while at home) and experienced nightmares more often. The most common style of coping was task oriented (29; 28.5%), and avoidance oriented (15%). The study also found a positive correlation between depression and the style of emotion-oriented coping and avoidance-oriented coping. CONCLUSIONS: The specific working conditions and exposure to traumatic events have a negative impact on the health of seafarers by increasing the risk of depression and cardiovascular diseases. The coping styles with stress depend on the position in the ship hierarchy.

Dynamics of ball chains and highly elastic fibres settling under gravity in a viscous fluid.

We study experimentally the dynamics of one and two ball chains settling under gravity in a highly viscous silicon oil at a Reynolds number much smaller than unity. We record the motion and shape deformation using two cameras. We demonstrate that single ball chains in most cases do not tend to be planar and often rotate, not keeping the ends at the same horizontal level. Shorter ball chains usually form shapes resembling distorted U. Longer ones in the early stage of the evolution form a shape resembling distorted W, and later deform non-symmetrically and significantly out of a plane. The typical evolution of shapes observed in our experiments with single ball chains is reproduced in our numerical simulations of a single elastic filament. In the computations, the filament is modelled as a chain of beads. Consecutive beads are connected by springs. Additional springs link consecutive pairs of beads. Elastic forces are assumed to be much smaller than gravity. As a result, the fibre is very flexible. We assume that the fluid sticks to the surfaces of the beads. We perform multipole expansion of the Stokes equations, with a lubrication correction. This method is implemented in the precise HYDROMULTIPOLE numerical codes. In our experiments, two ball chains, initially one above the other, later move away or approach each other, for a larger or smaller initial distance, respectively.

DNA supercoiling-induced shapes alter minicircle hydrodynamic properties.

DNA in cells is organized in negatively supercoiled loops. The resulting torsional and bending strain allows DNA to adopt a surprisingly wide variety of 3-D shapes. This interplay between negative supercoiling, looping, and shape influences how DNA is stored, replicated, transcribed, repaired, and likely every other aspect of DNA activity. To understand the consequences of negative supercoiling and curvature on the hydrodynamic properties of DNA, we submitted 336 bp and 672 bp DNA minicircles to analytical ultracentrifugation (AUC). We found that the diffusion coefficient, sedimentation coefficient, and the DNA hydrodynamic radius strongly depended on circularity, loop length, and degree of negative supercoiling. Because AUC cannot ascertain shape beyond degree of non-globularity, we applied linear elasticity theory to predict DNA shapes, and combined these with hydrodynamic calculations to interpret the AUC data, with reasonable agreement between theory and experiment. These complementary approaches, together with earlier electron cryotomography data, provide a framework for understanding and predicting the effects of supercoiling on the shape and hydrodynamic properties of DNA.

DNA supercoiling-induced shapes alter minicircle hydrodynamic properties.

DNA in cells is organized in negatively supercoiled loops. The resulting torsional and bending strain allows DNA to adopt a surprisingly wide variety of 3-D shapes. This interplay between negative supercoiling, looping, and shape influences how DNA is stored, replicated, transcribed, repaired, and likely every other aspect of DNA activity. To understand the consequences of negative supercoiling and curvature on the hydrodynamic properties of DNA, we submitted 336 bp and 672 bp DNA minicircles to analytical ultracentrifugation (AUC). We found that the diffusion coefficient, sedimentation coefficient, and the DNA hydrodynamic radius strongly depended on circularity, loop length, and degree of negative supercoiling. Because AUC cannot ascertain shape beyond degree of non-globularity, we applied linear elasticity theory to predict DNA shapes, and combined these with hydrodynamic calculations to interpret the AUC data, with reasonable agreement between theory and experiment. These complementary approaches, together with earlier electron cryotomography data, provide a framework for understanding and predicting the effects of supercoiling on the shape and hydrodynamic properties of DNA.

Correction: Stokesian dynamics of sedimenting elastic rings.

Correction for 'Stokesian dynamics of sedimenting elastic rings' by Magdalena Gruziel-Slomka et al., Soft Matter, 2019, 15, 7262-7274, https://doi.org/10.1039/C9SM00598F.

Occupational Activity After Renal Transplantation vs Quality of Life, Personality Profile, and Stress Coping Styles.

INTRODUCTION: Kidney transplantation (KT) increases the quality of life (QoL) of patients with chronic kidney disease. Employment is one the objective indicators of KT success. The aim of the presented study was to assess the psychological predispositions of KT and hemodialysis (HD) patients, such as stress coping styles, chosen personality features, and their relationship with employment and QoL. MATERIAL AND METHODS: One hundred and sixty-one persons were examined, 101 after KT, and 60 HD patients. The following methods were applied: NEO-FFI Personality Inventory; Coping Inventory for Stressful Situations (CISS); WHOQoL-BREF; and general survey, measuring sociodemographic data and work experience. RESULTS: In the KT group, 58 persons were employed and 43 were unemployed. HD patients were mostly unemployed, with only 15 persons working. Significant differences were identified between the results of the following variables: WHOQoL environmental scale (employed m= 16.8, standard deviation [SD] = 3; unemployed m= 15, SD = 2.8); extraversion (employed m = 6.7, SD = 2; unemployed m = 5.6, SD = 2); somatic WHOQoL scale (HD m = 12.2, SD = 2.7; KT m = 14.2, SD = 3.5). In the KT group, the following correlations were identified: extraversion with contact seeking strategy (r = 0.553), agreeableness (r = 0.245), and conscientiousness (r = 0.384); agreeableness with conscientiousness (r = 0.336). In the HD group, the following correlations were identified: task-oriented style with conscientiousness (r = 0.474); avoidance-oriented style with conscientiousness (r = -0.466); contact seeking with extraversion (r = 0.402) and agreeableness (r = 0.469). CONCLUSIONS: The following conclusions were reached: Social competence, such as seeking and maintaining contacts, positively translates to features connected with occupational activity. Social skills strengthen the organization of healthier environment and increase QoL. Employed patients have higher social skills and QoL.

Flexible fibers in shear flow approach attracting periodic solutions.

The three-dimensional dynamics of a single non-Brownian flexible fiber in shear flow is evaluated numerically, in the absence of inertia. A wide range of ratios A of bending to hydrodynamic forces and hundreds of initial configurations are considered. We demonstrate that flexible fibers in shear flow exhibit much more complicated evolution patterns than in the case of extensional flow, where transitions to higher-order modes of characteristic shapes are observed when A exceeds consecutive threshold values. In shear flow, we identify the existence of an attracting steady configuration and different attracting periodic motions that are approached by long-lasting rolling, tumbling, and meandering dynamical modes, respectively. We demonstrate that the final stages of the rolling and tumbling modes are effective Jeffery orbits, with the constant parameter C replaced by an exponential function that either decays or increases in time, respectively, corresponding to a systematic drift of the trajectories. In the limit of C→0, the fiber aligns with the vorticity direction and in the limit of C→∞, the fiber periodically tumbles within the shear plane. For moderate values of A, a three-dimensional meandering periodic motion exists, which corresponds to intermediate values of C. Transient, close to periodic oscillations are also detected in the early stages of the modes.

Sedimenting pairs of elastic microfilaments.

The dynamics of two identical elastic filaments settling under gravity in a viscous fluid in the low Reynolds number regime is investigated numerically. A large family of initial configurations symmetric with respect to a vertical plane is considered, as well as their non-symmetric perturbations. The behaviour of the filaments is primarily governed by the elasto-gravitational number, which depends on the filament's length and flexibility, and the strength of the external force. Flexible filaments usually converge toward horizontal and parallel orientation. We explain this phenomenon and show that it occurs also for curved rigid particles of similar shapes. Once aligned, the two fibres either converge toward a stationary, flexibility-dependent distance, or tend to collide or continuously repel each other. Rigid and straight rods perform periodic motions while settling down. Apart from very stiff particles, the dynamics is robust to non-symmetric perturbations.

Stokesian dynamics of sedimenting elastic rings.

We consider elastic microfilaments which form closed loops. We investigate how the loops change shape and orientation while settling under gravity in a viscous fluid. Loops are circular at the equilibrium. Their dynamics are investigated numerically based on the Stokes equations for the fluid motion and the bead-spring model of the microfilament. The Rotne-Prager approximation for the bead mobility is used. We demonstrate that the relevant dimensionless parameter is the ratio of the bending resistance of the filament to the gravitation force corrected for buoyancy. The inverse of this ratio, called the elasto-gravitation number B, is widely used in the literature for sedimenting elastic linear filaments. We assume that B is of the order of 104-106, which corresponds to easily deformable loops. We find out that initially tilted circles evolve towards different sedimentation modes, depending on B. Very stiff or stiff rings attain almost planar, oval shapes, which are vertical or tilted, respectively. More flexible loops deform significantly and converge towards one of several characteristic periodic motions. These sedimentation modes are also detected when starting from various shapes, and for different loop lengths. In general, multi-stability is observed: an elastic ring converges to one of several sedimentation modes, depending on the initial conditions. This effect is pronounced for very elastic loops. The surprising diversity of long-lasting periodic motions and shapes of elastic rings found in this work gives a new perspective for the dynamics of more complex deformable objects at micrometer and nanometer scales, sedimenting under gravity or rotating in a centrifuge, such as red blood cells, ring polymers or circular DNA.

Is it worth to continue to analyse the factors of cardiovascular risk among the sailors? Review of literature.

BACKGROUND: Cardiovascular diseases are still the most common cause of death from natural causes among seafarers. The aim of the study was to determine which of the cardiovascular risk factors listed in the current recommendations of the European Society of Cardiology occur among seafarers. MATERIALS AND METHODS: The paper is a review of literature from PubMed Database. RESULTS: Based on conducted analysis of over 31 papers high prevalence of classic and other cardiovascular risk factors among seafarers was proven. The most common risk factors among off-shore workers are overweight and obesity (over 64%); moreover, these factors occur more often among seafarers than in the general popula- tion. Also hypertension, smoking, type 2 diabetes and unfavourable lipid profile were present more often in this occupational group. In the analysed studies attention was also paid to factors often overlooked in risk assess- ment such as mental and inflammatory illnesses, unfavourable working conditions and psychological burden. CONCLUSIONS: Seafarers have a higher cardiovascular risk because, among other things, the prevalence of "old and new" risk factors among them is higher than in general population.

Stokes velocity generated by a point force in various geometries.

In this short review, we visualize the fluid velocity generated by a point force close to a plane free surface or a plane rigid wall. We present separately contributions from all the multipoles which form the corresponding classical systems of images. Such graphical images might be useful in the theoretical and numerical modeling of the dynamics of micro-objects moving close to an interface.

Establishment of the International Maritime Health Foundation: the next step in scientific publishing in maritime health.

The Bulletin of the Institute of Maritime and Tropical Medicine (IMTM) was published first time in 1948 as a preliminary publication. Since then it has developed and from 1999 it is known as International Maritime Health (IMH). Initially it was published by the Institute of Maritime and Tropical Medicine (IMTM) in Gdynia. From 2009 it was published by the Polish Society of Maritime, Tropical and Travel Medicine (PSMTTM) in cooperation with the International Maritime Health Association (IMHA) and the Norwegian Centre for Maritime Medicine (NCMM), later the Norwegian Centre for Maritime and Diving Medicine (NCMDM) at the Department of Occupational Medicine, Haukeland University Hospital, Bergen. After a couple of years of planning and discussions on how to take the journal forward, the International Maritime Health Foundation (IMHF) was established under Polish Law, 21st June 2018. This article discusses the process from the very beginning of the journal, until the establishment of the IMHF as well as the foundation's objectives and way forward.

Periodic Motion of Sedimenting Flexible Knots.

We study the dynamics of knotted deformable closed chains sedimenting in a viscous fluid. We show experimentally that trefoil and other torus knots often attain a remarkably regular horizontal toroidal structure while sedimenting, with a number of intertwined loops, oscillating periodically around each other. We then recover this motion numerically and find out that it is accompanied by a very slow rotation around the vertical symmetry axis. We analyze the dependence of the characteristic timescales on the chain flexibility and aspect ratio. It is observed in the experiments that this oscillating mode of the dynamics can spontaneously form even when starting from a qualitatively different initial configuration. In numerical simulations, the oscillating modes are usually present as transients or final stages of the evolution, depending on chain aspect ratio and flexibility, and the number of loops.

Different bending models predict different dynamics of sedimenting elastic trumbbells.

The main goal of this paper is to examine theoretically and numerically the impact of a chosen bending model on the dynamics of elastic filaments settling in a viscous fluid under gravity at low-Reynolds-number. We use the bead-spring approximation of a filament and the Rotne-Prager mobility matrix to describe hydrodynamic interactions between the beads. We analyze the dynamics of trumbbells, for which bending angles are typically larger than for thin and long filaments. Each trumbbell is made of three beads connected by springs and it exhibits a bending resistance, described by the harmonic or - alternatively - by the 'cosine' (also called the Kratky-Porod) bending models, both often used in the literature. Using the harmonic bending potential, and coupling it to the spring potential by the Young's modulus, we find simple benchmark solutions: stable stationary configurations of a single elastic trumbbell and attraction of two elastic trumbbells towards a periodic long-lasting orbit. As the most significant result of this paper, we show that for very elastic trumbbells at the same initial conditions, the Kratky-Porod bending potential can lead to qualitatively and quantitatively different spurious dynamics, with artificially large bending angles and unrealistic shapes. We point out that for the bead models of an elastic filament, the range of applicability of the Kratky-Porod model might not go beyond bending angles smaller than π/2 for touching beads and beyond an even much lower value for beads well-separated from each other. The existence of stable stationary configurations of elastic trumbbells and a family of periodic oscillations of two elastic trumbbells are very important findings on their own.

Signal and binding. II. Converting physico-chemical responses to macromolecule-ligand interactions into thermodynamic binding isotherms.

Physico-chemical titration techniques are the most commonly used methods in characterizing molecular interactions. These methods are mainly based on spectroscopic, calorimetric, hydrodynamic, etc., measurements. However, truly quantitative physico-chemical methods are absolutely based on the determination of the relationship between the measured signal and the total average degree of binding in order to obtain meaningful interaction parameters. The relationship between the observed physico-chemical signal of whatever nature and the degree of binding must be determined and not assumed, based on some ad hoc intuitive relationship/model, leading to determination of the true binding isotherm. The quantitative methods reviewed and discussed here allow an experimenter to rigorously determine the degree of binding and the free ligand concentration, i.e., they lead to the construction of the thermodynamic binding isotherm in a model-independent fashion from physico-chemical titration curves.

Signal and binding. I. Physico-chemical response to macromolecule-ligand interactions.

Obtaining a detailed knowledge about energetics of ligand-macromolecule interactions is a prerequisite for elucidation of the nature, behavior, and activities of the formed complexes. The most commonly used methods in characterizing molecular interactions are physico-chemical techniques based mainly on spectroscopic, calorimetric, hydrodynamic, etc., measurements. The major advantage of the physico-chemical methods is that they do not require large quantities of material and, if performed carefully, do not perturb examined reactions. Applications of several different physico-chemical approaches, commonly encountered in analyses of biochemical interactions, are here reviewed and discussed, using examples of simple binding reactions. It is stressed that without determination of the relationship between the measured signal and the total average degree of binding, the performed analysis of a single physico-chemical titration curve may provide only fitting parameters, instead of meaningful interaction parameters, already for the binding systems with only two ligand molecules. Some possible pitfalls in the analyses of single titration curves are discussed.

Dynamics of flexible fibers and vesicles in Poiseuille flow at low Reynolds number.

The dynamics of flexible fibers and vesicles in unbounded planar Poiseuille flow at low Reynolds number is shown to exhibit similar basic features, when their equilibrium (moderate) aspect ratio is the same and vesicle viscosity contrast is relatively high. Tumbling, lateral migration, accumulation and shape evolution of these two types of flexible objects are analyzed numerically. The linear dependence of the accumulation position on relative bending rigidity, and other universal scalings are derived from the local shear flow approximation.

Assessment of selected psychological factors in patients with inflammatory bowel disease.

INTRODUCTION: In the majority of patients with inflammatory bowel diseases (IBD) mental health problems are demonstrated in the form of excessive anxiety and unstable emotional reactions. Emotional instability affects the wellbeing of these patients, and also their attitude towards the disease and the course of treatment. AIM: The objective of the study is to evaluate psychological factors in patients with IBD, and to compare patients with ulcerative colitis (UC) and patients suffering from Crohn's disease (CD) with respect to intensity of these factors. MATERIAL AND METHODS: The study included 108 patients with IBD. NEO-FFI and type-D Scale were used to evaluate personality traits. Anxiety level was measured with STAI. CECS was used to measure the patients' tendency to suppress negative emotions. RESULTS: In the patients with CD 45% of subjects presented type D personality. In the group of patients with UC, type D personality was found in 38%. The higher levels of neuroticism and extraversion were observed in patients with UC, whereas the patients with CD exhibited a higher level of openness to experience and agreeableness. In patients with CD the levels of state anxiety were elevated, whereas in patients with UC higher scores were both for state and trait anxiety. CONCLUSIONS: There were no statistically significant differences in terms of personality factors in a group of patients with CD and UC. It was found that the majority of patients with IBD suffer elevated or high sense of anxiety.