Revisiting the Poisson-Boltzmann theory: charge surfaces, multivalent ions and inter-plate forces

The Poisson-Boltzmann (PB) theory is extensively used to gain insight on charged colloids and biological systems as well as to elucidate fundamental properties of intermolecular forces. Many works were devoted in the past to study PB related features and to confirm them experimentally. In this work we explore the properties of inter-plate forces in terms of different boundary conditions. We treat the cases of constant surface charge, constant surface potential and mixed boundaries. The interplay between electrostatic interactions, attractive counter-ions release, and repulsive van 't Hoff contribution are discussed separately for each case. Finally, we discuss how the crossover between attractive and repulsive interactions for constant surface charge case is influenced by the presence of multivalent counter-ions, where it is shown that the range of the attractive interaction grows with the valency

Novel perspectives for the application of total internal reflection microscopy

Total Internal Reflection Microscopy (TIRM) is a sensitive non-invasive technique to measure the interaction potentials between a colloidal particle and a wall with femtonewton resolution. The equilibrium distribution of the particle-wall separation distance z is sampled monitoring the intensity I scattered by the Brownian particle under evanescent illumination. Central to the data analysis is the knowledge of the relation between I and the corresponding z, which typically must be known a priori. This poses considerable constraints to the experimental conditions where TIRM can be applied (short penetration depth of the evanescent wave, transparent surfaces). Here, we introduce a method to experimentally determine I(z) by relying only on the distance-dependent particle-wall hydrodynamic interactions. We demonstrate that this method largely extends the range of conditions accessible with TIRM, and even allows measurements on highly reflecting gold surfaces where multiple reflections lead to a complex I(z).Comment: 11 pages, 7 figure

Salt-induced changes of colloidal interactions in critical mixtures

We report on salt-dependent interaction potentials of a single charged particle suspended in a binary liquid mixture above a charged wall. For symmetric boundary conditions (BC) we observe attractive particle-wall interaction forces which are similar to critical Casimir forces previously observed in salt-free mixtures. However, in case of antisymmetric BC we find a temperature-dependent crossover from attractive to repulsive forces which is in strong contrast to salt-free conditions. Additionally performed small-angle x-ray scattering experiments demonstrate that the bulk critical fluctuations are not affected by the addition of salt. This suggests that the observed crossover can not be attributed alone to critical Casimir forces. Instead our experiments point towards a possible coupling between the ionic distributions and the concentration profiles in the binary mixture which then affects the interaction potentials in such systems.Comment: 5 pages, 4 Figure

Understanding depletion forces beyond entropy

The effective interaction energy of a colloidal sphere in a suspension containing small amounts of non-ionic polymers and a flat glass surface has been measured and calculated using total internal reflection microscopy (TIRM) and a novel approach within density functional theory (DFT), respectively. Quantitative agreement between experiment and theory demonstrates that the resulting repulsive part of the depletion forces cannot be interpreted entirely in terms of entropic arguments but that particularly at small distances ($\lesssim$ 100 nm) attractive dispersion forces have to be taken into account

Many-particle hydrodynamic interactions in parallel-wall geometry: Cartesian-representation method

This paper describes the results of our theoretical and numerical studies of hydrodynamic interactions in a suspension of spherical particles confined between two parallel planar walls, under creeping-flow conditions. We propose a novel algorithm for accurate evaluation of the many-particle friction matrix in this system--no such algorithm has been available so far. Our approach involves expanding the fluid velocity field into spherical and Cartesian fundamental sets of Stokes flows. The interaction of the fluid with the particles is described using the spherical basis fields; the flow scattered with the walls is expressed in terms of the Cartesian fundamental solutions. At the core of our method are transformation relations between the spherical and Cartesian basis sets. These transformations allow us to describe the flow field in a system that involves both the walls and particles. We used our accurate numerical results to test the single-wall superposition approximation for the hydrodynamic friction matrix. The approximation yields fair results for quantities dominated by single particle contributions, but it fails to describe collective phenomena, such as a large transverse resistance coefficient for linear arrays of spheres

Evaluating Water Quality Upstream and Downstream from a Proposed Restoration Project on the Pomme de Terre River in Morris, MN

The recent push to restore natural river conditions provides opportunities to investigate the effects of dam removal and channel modification, particularly if data are collected before such projects are initiated. The MN DNR plans to modify the Pomme de Terre River channel at the Crissy Lake dam (Morris, MN) by constructing and directing water flow over stone arch rapids to remove the barrier to fish, restore flow, and enhance river conditions. We aim to characterize the Pomme de Terre River upstream and downstream from the project site before construction to provide data to compare with river conditions after the project is completed. We collected data bi-weekly from September–November at 3 sites upstream and 3 downstream from the Crissy Lake dam. We measured dissolved oxygen (DO), total dissolved solids (TDS), and Turbidity at each site. Average (range) values downstream were: DO 11.70 (7.36-17.53) mg/L, TDS 509.78 (469.20-:605.70) ppm, and Turbidity 2.70 (1.10-5.75) ntu. Average values upstream were: DO 12.54 (7.23-21.58) mg/L TDS of 476.79 (424.40-666.4) ppm, and Turbidity of 1.61 (0.55-4.00) ntu. DO levels suggest high levels of primary productivity and the capability of supporting aquatic life. TDS would be considered on the high-acceptable side of drinking water. Low turbidity levels show no indication of water quality impairment and reflect base flow conditions and lack of erosion in the absence of significant precipitation during the study period.https://digitalcommons.morris.umn.edu/urs_2025/1010/thumbnail.jp

Religious Land Use Jurisprudence: The Negative Ramifications for Religious Activities in Washington After \u3cem\u3eOpen Door Baptist Church v. Clark County\u3c/em\u3e

Part II of this Note provides a history of religious land use jurisprudence in Washington. This part addresses growth management laws generally, and where these laws cross paths with constitutional guarantees of the free exercise of religion. Part III focuses on the Washington Supreme Court\u27s Open Door decision, separately addressing both the majority opinion and the dissent. Part IV illustrates how the Washington Supreme Court misapplied Washington\u27s religious freedom test in Open Door and significantly shifted religious land use jurisprudence. Part IV further discusses how this shift may include Washington\u27s adoption of the lower federal standard and elaborates upon the negative ramifications this shift would have on churches throughout the state. Part V concludes this Note, discussing how the free exercise of religion has historically been afforded great protection in Washington, and how the Washington Supreme Court is seemingly moving in a different direction

Women, Shame, and Mental Health: A Systematic Review of Approaches in Psychotherapy

Shame is a self-conscious emotion that affects self-esteem, self-concept and evaluation of the self. Shame is seen more often in women than men; in part due to societal and cultural standards placed upon women that create negative self-evaluations in women when those standards are not met. Shame is seen in mental health diagnoses such as depression, anxiety, substance use disorders and eating disorders. When a woman presents for therapy or counseling, shame may be apparent and necessary to work on during therapy. This systematic review was designed to answer the research question: what therapeutic approaches are used in psychotherapy targeting shame in women with a mental health diagnosis? The review was set up using peer-reviewed articles published between 2000 and 2016. Using the database of PsycINFO, 11 peer-reviewed articles met the search criteria and were read and analyzed, which resulted in four themes being identified. These themes include: 1) the format of treatment, 2) increasing compassion, 3) mindfulness, and 4) acceptance. The research suggests using compassion focused therapies, mindfulness and acceptance skills to target shame in women with mental health diagnoses. Shame research is relatively new and more research is needed to replicate studies to ensure accuracy and validity of the results. Further research is also needed to understand the therapists\u27 feelings about addressing shame in psychotherapy

Interaction and flocculation of spherical colloids wetted by a surface-induced corona of paranematic order

Particles dispersed in a liquid crystal above the nematic-isotropic phase transition are wetted by a surface-induced corona of paranematic order. Such coronas give rise to pronounced two-particle interactions. In this article, we report details on the analytical and numerical study of these interactions published recently [Phys. Rev. Lett. 86, 3915 (2001)]. We especially demonstrate how for large particle separations the asymptotic form of a Yukawa potential arises. We show that the Yukawa potential is a surprisingly good description for the two-particle interactions down to distances of the order of the nematic coherence length. Based on this fact, we extend earlier studies on a temperature induced flocculation transition in electrostatically stabilized colloidal dispersions [Phys. Rev. E 61, 2831 (2000)]. We employ the Yukawa potential to establish a flocculation diagram for a much larger range of the electrostatic parameters, namely the surface charge density and the Debye screening length. As a new feature, a kinetically stabilized dispersion close to the nematic-isotropic phase transition is found.Comment: Revtex v4.0, 16 pages, 12 Postscript figures. Accepted for publication in Phys. Rev.

Women, Shame, and Mental Health: A Systematic Review of Approaches in Psychotherapy

Shame is a self-conscious emotion that affects self-esteem, self-concept and evaluation of the self. Shame is seen more often in women than men; in part due to societal and cultural standards placed upon women that create negative self-evaluations in women when those standards are not met. Shame is seen in mental health diagnoses such as depression, anxiety, substance use disorders and eating disorders. When a woman presents for therapy or counseling, shame may be apparent and necessary to work on during therapy. This systematic review was designed to answer the research question: what therapeutic approaches are used in psychotherapy targeting shame in women with a mental health diagnosis? The review was set up using peer-reviewed articles published between 2000 and 2016. Using the database of PsycINFO, 11 peer-reviewed articles met the search criteria and were read and analyzed, which resulted in four themes being identified. These themes include: 1) the format of treatment, 2) increasing compassion, 3) mindfulness, and 4) acceptance. The research suggests using compassion focused therapies, mindfulness and acceptance skills to target shame in women with mental health diagnoses. Shame research is relatively new and more research is needed to replicate studies to ensure accuracy and validity of the results. Further research is also needed to understand the therapists’ feelings about addressing shame in psychotherapy