580 research outputs found
The short-time self-diffusion coefficient of a sphere in a suspension of rigid rods
The short--time self diffusion coefficient of a sphere in a suspension of
rigid rods is calculated in first order in the rod volume fraction. For low rod
concentrations the correction to the Einstein diffusion constant of the sphere
is a linear function of the rod volume fraction with the slope proportional to
the equilibrium averaged mobility diminution trace of the sphere interacting
with a single freely translating and rotating rod. The two--body hydrodynamic
interactions are calculated using the so--called bead model in which the rod is
replaced by a stiff linear chain of touching spheres. The interactions between
spheres are calculated numerically using the multipole method. Also an
analytical expression for the diffusion coefficient as a function of the rod
aspect ratio is derived in the limit of very long rods. We show that in this
limit the correction to the Einstein diffusion constant does not depend on the
size of the tracer sphere. The higher order corrections depending on the
applied model are computed numerically. An approximate expression is provided,
valid for a wide range of aspect ratios.Comment: 11 pages, 6 figure
Anthropocene history of rich fen acidification in W Poland: causes and indicators of change
In the time of the global climate crisis, it is vital to protect and restore peatlands to maintain their functioning as carbon sinks. Otherwise, their transformations may trigger a shift to a carbon source state and further contribute to global warming. In this study, we focused on eutrophication, which resulted in its transition from rich fen to poor fen conditions. The prior aim was to decipher how i) climate, ii) human, and iii) autogenic processes influenced the pathway of peatland changes in the last ca. 250 years. We applied a high-resolution palaeoecological analysis, based mainly on testate amoebae (TA) and plant macroremains. Our results imply that before ca. 1950 CE, dry shifts on the Kazanie fen were generally climate-induced. Later, autogenic processes, human pressure and climate warming synergistically affected the fen, contributing to its transition to poor fen within ca. 30 years. Its establishment not only caused changes in vegetation but also altered TA taxonomic content and resulted in a lower diversity of TA. According to our research M. patella is an incredibly sensitive testate amoeba that after ca. 200 years of presence, disappeared within 2 years due to changes in water and nutrient conditions. As a whole, our study provides a long-term background that is desired in modern conservation studies and might be used to define future restoration targets. It also confirms the already described negative consequences connected with the Anthropocene and not sustainable exploitation of nature.1. Introduction 2. Material and methods 2.1. State of art 2.1.1. Study site 2.1.2. Core retrieval and chronology 2.1.3. Plant macrofossils 2.2. Testate amoebae (TA) 2.3. Statistical analyses and visualization 3. Results and interpretation 3.1. Mire succession: plant macrofossils, testate amoebae, water table and conductivity 3.1.1. Phase I – rich fen; 91–35.5 cm; ca. 1767±45–1982±3 CE 3.1.2. Phase II – poor fen; 35.5–0 cm; ca. 1982±3–2017 CE 3.2. Non-Metric Multidimensional Scaling (NMDS) 4. Discussion 4.1. An abrupt rich to poor fen transition – causes of change 4.2. Quality of testate amoebae indicators of the rich-poor fen transformatio
Capillary interactions in Pickering emulsions
The effective capillary interaction potentials for small colloidal particles
trapped at the surface of liquid droplets are calculated analytically. Pair
potentials between capillary monopoles and dipoles, corresponding to particles
floating on a droplet with a fixed center of mass and subjected to external
forces and torques, respectively, exhibit a repulsion at large angular
separations and an attraction at smaller separations, with the latter
resembling the typical behavior for flat interfaces. This change of character
is not observed for quadrupoles, corresponding to free particles on a
mechanically isolated droplet. The analytical results for quadrupoles are
compared with the numerical minimization of the surface free energy of the
droplet in the presence of ellipsoidal particles.Comment: twocolumn, 8 pages, 3 figures, submitted to Phys. Rev.
Anthropocene history of rich fen acidification in W Poland: Causes and indicators of change
In the time of the global climate crisis, it is vital to protect and restore peatlands to maintain their functioning as carbon sinks. Otherwise, their transformations may trigger a shift to a carbon source state and further contribute to global warming. In this study, we focused on eutrophication, which resulted in its transition from rich fen to poor fen conditions. The prior aim was to decipher how i) climate, ii) human, and iii) autogenic processes influenced the pathway of peatland changes in the last ca. 250 years. We applied a high-resolution palaeoecological analysis, based mainly on testate amoebae (TA) and plant macroremains. Our results imply that before ca. 1950 CE, dry shifts on the Kazanie fen were generally climate-induced. Later, autogenic processes, human pressure and climate warming synergistically affected the fen, contributing to its transition to poor fen within ca. 30 years. Its establishment not only caused changes in vegetation but also altered TA taxonomic content and resulted in a lower diversity of TA. According to our research M. patella is an incredibly sensitive testate amoeba that after ca. 200 years of presence, disappeared within 2 years due to changes in water and nutrient conditions. As a whole, our study provides a long-term background that is desired in modern conservation studies and might be used to define future restoration targets. It also confirms the already described negative consequences connected with the Anthropocene and not sustainable exploitation of nature.1. Introduction 2. Material and methods 2.1. State of art 2.1.1. Study site 2.1.2. Core retrieval and chronology 2.1.3. Plant macrofossils 2.2. Testate amoebae (TA) 2.3. Statistical analyses and visualization 3. Results and interpretation 3.1. Mire succession: plant macrofossils, testate amoebae, water table and conductivity 3.1.1. Phase I – rich fen; 91–35.5 cm; ca. 1767±45–1982±3 CE 3.1.2. Phase II – poor fen; 35.5–0 cm; ca. 1982±3–2017 CE 3.2. Non-Metric Multidimensional Scaling (NMDS) 4. Discussion 4.1. An abrupt rich to poor fen transition – causes of change 4.2. Quality of testate amoebae indicators of the rich-poor fen transformatio
Direct comparison of sterile neutrino constraints from cosmological data, <i>ν</i><sub><i>e</i></sub> disappearance data and <i>ν</i><sub><i>μ</i></sub>→ <i>ν</i><sub><i>e</i></sub> appearance data in a 3+1 model
Reply to ‘Reduction in grain pollen indicates population decline, but not necessarily Black Death mortality’
Free energy of colloidal particles at the surface of sessile drops
The influence of finite system size on the free energy of a spherical
particle floating at the surface of a sessile droplet is studied both
analytically and numerically. In the special case that the contact angle at the
substrate equals a capillary analogue of the method of images is
applied in order to calculate small deformations of the droplet shape if an
external force is applied to the particle. The type of boundary conditions for
the droplet shape at the substrate determines the sign of the capillary
monopole associated with the image particle. Therefore, the free energy of the
particle, which is proportional to the interaction energy of the original
particle with its image, can be of either sign, too. The analytic solutions,
given by the Green's function of the capillary equation, are constructed such
that the condition of the forces acting on the droplet being balanced and of
the volume constraint are fulfilled. Besides the known phenomena of attraction
of a particle to a free contact line and repulsion from a pinned one, we
observe a local free energy minimum for the particle being located at the drop
apex or at an intermediate angle, respectively. This peculiarity can be traced
back to a non-monotonic behavior of the Green's function, which reflects the
interplay between the deformations of the droplet shape and the volume
constraint.Comment: 24 pages, 19 figure
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