487 research outputs found
Where the linearized Poisson-Boltzmann cell model fails: (I) spurious phase separation in charged colloidal suspensions
We perform a linearization of the Poisson-Boltzmann (PB) density functional
for spherical Wigner-Seitz cells that yields Debye-H\"uckel-like equations
agreeing asymptotically with the PB results in the weak-coupling
(high-temperature) limit. Both the canonical (fixed number of microions) as
well as the semi-grand-canonical (in contact with an infinite salt reservoir)
cases are considered and discussed in a unified linearized framework. In the
canonical case, for sufficiently large colloidal charges the linearized theory
predicts the occurrence of a thermodynamical instability with an associated
phase separation of the homogeneous suspension into dilute (gas) and dense
(liquid) phases. In the semi-grand-canonical case it is predicted that the
isothermal compressibility and the osmotic-pressure difference between the
colloidal suspension and the salt reservoir become negative in the
low-temperature, high-surface charge or infinite-dilution (of polyions) limits.
As already pointed out in the literature for the latter case, these features
are in disagreement with the exact nonlinear PB solution inside a Wigner-Seitz
cell and are thus artifacts of the linearization. By using explicitly
gauge-invariant forms of the electrostatic potential we show that these
artifacts, although thermodynamically consistent with quadratic expansions of
the nonlinear functional and osmotic pressure, may be traced back to the
non-fulfillment of the underlying assumptions of the linearization.Comment: 32 pages, 3 PostScript figures, submitted to J. Chem. Phy
Increased incidence of entanglements and ingested marine debris in Dutch seals from 2010 to 2020
In recent decades, the amount of marine debris has increased in our oceans. As wildlife interactions with debris increase, so does the number of entangled animals, impairing normal behavior and potentially affecting the survival of these individuals. The current study summarizes data on two phocid species, harbor (Phoca vitulina) and gray seals (Halichoerus grypus), affected by marine debris in Dutch waters from 2010 to 2020. The findings indicate that the annual entanglement rate (13.2 entanglements/year) has quadrupled compared with previous studies. Young seals, particularly gray seals, are the most affected individuals, with most animals found or sighted with fishing nets wrapped around their necks. Interestingly, harbor seals showed a higher incidence of ingested debris. Species differences with regard to behavior, foraging strategies, and habitat preferences may explain these findings. The lack of consistency across reports suggests that it is important to standardize data collection from now on. Despite increased public awareness about the adverse environmental effects of marine debris, more initiatives and policies are needed to ensure the protection of the marine environment in the Netherlands
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Predicting visual function from the measurements of retinal nerve fiber layer structure
Purpose: To develop and validate a method for predicting visual function from retinal nerve fibre layer (RNFL) structure in glaucoma.
Methods: RNFL thickness (RNFLT) measurements from GDxVCC scanning laser polarimetry (SLP) and visual field (VF) sensitivity from standard automated perimetry were made available from 535 eyes from three centres. In a training dataset, structure-function relationships were characterized using linear regression and a type of neural network: Radial Basis Function customised under a Bayesian framework (BRBF). These two models were used in a test dataset to 1) predict sensitivity values at individual VF locations from RNFLT measurements and 2) predict the spatial relationship between VF locations and positions at a peripapillary RNFLT measurement annulus. Predicted spatial relationships were compared with a published anatomical structure-function map.
Results: Compared with linear regression, BRBF yielded a nearly two-fold improvement (P<0.001; paired t-test) in performance of predicting VF sensitivity in the test dataset (mean absolute prediction error of 2.9dB (standard deviation (SD) 3.7dB) versus 4.9dB (SD 4.0dB)). The predicted spatial structure-function relationship accorded better (P<0.001; paired t-test) with anatomical prior knowledge when the BRBF was compared with the linear regression (median absolute angular difference of 15° versus 62°).
Conclusions: The BRBF generates clinically useful relationships that relate topographical maps of RNFL measurement to VF locations and allows the VF sensitivity to be predicted from structural measurements. This method may allow clinicians to evaluate structural and functional measures in the same domain. It could also be generalized to use other structural measures
Effective Interactions and Volume Energies in Charged Colloids: Linear Response Theory
Interparticle interactions in charge-stabilized colloidal suspensions, of
arbitrary salt concentration, are described at the level of effective
interactions in an equivalent one-component system. Integrating out from the
partition function the degrees of freedom of all microions, and assuming linear
response to the macroion charges, general expressions are obtained for both an
effective electrostatic pair interaction and an associated microion volume
energy. For macroions with hard-sphere cores, the effective interaction is of
the DLVO screened-Coulomb form, but with a modified screening constant that
incorporates excluded volume effects. The volume energy -- a natural
consequence of the one-component reduction -- contributes to the total free
energy and can significantly influence thermodynamic properties in the limit of
low-salt concentration. As illustrations, the osmotic pressure and bulk modulus
are computed and compared with recent experimental measurements for deionized
suspensions. For macroions of sufficient charge and concentration, it is shown
that the counterions can act to soften or destabilize colloidal crystals.Comment: 14 pages, including 3 figure
Progression Detection of Glaucoma from Polarimetric Images
Detecting glaucoma progression is crucial for assessing the effectivity of the treatment. This paper describes three methods for detecting progression related changes in polarimetric images of the retinal nerve fiber layer (NFL), both on a global and on a local scale. Detecting global changes proved not to be feasible due to poor reproducibility of the measurements at the pixel level. Local progression on the other hand could be detected. A distribution based approach did not work, but locating specific areas with minimum size and minimum NFL decrease did give relevant results. The described algorithm yielded a TPR of 0.42 and an FPR of 0.095 on our datasets. It proved to be able to outline suspect areas that show NFL reductio
On the fluid-fluid phase separation in charged-stabilized colloidal suspensions
We develop a thermodynamic description of particles held at a fixed surface
potential. This system is of particular interest in view of the continuing
controversy over the possibility of a fluid-fluid phase separation in aqueous
colloidal suspensions with monovalent counterions. The condition of fixed
surface potential allows in a natural way to account for the colloidal charge
renormalization. In a first approach, we assess the importance of the so called
``volume terms'', and find that in the absence of salt, charge renormalization
is sufficient to stabilize suspension against a fluid-fluid phase separation.
Presence of salt, on the other hand, is found to lead to an instability. A very
strong dependence on the approximations used, however, puts the reality of this
phase transition in a serious doubt. To further understand the nature of the
instability we next study a Jellium-like approximation, which does not lead to
a phase separation and produces a relatively accurate analytical equation of
state for a deionized suspensions of highly charged colloidal spheres. A
critical analysis of various theories of strongly asymmetric electrolytes is
presented to asses their reliability as compared to the Monte Carlo
simulations
Engineering <i>Saccharomyces cerevisiae</i> for co-utilization of D-galacturonic acid and D-glucose from citrus peel waste
Pectin-rich agricultural byproducts are ideal feedstocks for biobased chemicals production. Here, the authors engineer the yeast, S. cerevisiae, in several steps to co-utilize d-galacturonic acid and d-glucose and demonstrate the potential of producing meso-galactaric acid from industrial orange peel
The osmotic pressure of charged colloidal suspensions: A unified approach to linearized Poisson-Boltzmann theory
We study theoretically the osmotic pressure of a suspension of charged
objects (e.g., colloids, polyelectrolytes, clay platelets, etc.) dialyzed
against an electrolyte solution using the cell model and linear
Poisson-Boltzmann (PB) theory. From the volume derivative of the grand
potential functional of linear theory we obtain two novel expressions for the
osmotic pressure in terms of the potential- or ion-profiles, neither of which
coincides with the expression known from nonlinear PB theory, namely, the
density of microions at the cell boundary. We show that the range of validity
of linearization depends strongly on the linearization point and proof that
expansion about the selfconsistently determined average potential is optimal in
several respects. For instance, screening inside the suspension is
automatically described by the actual ionic strength, resulting in the correct
asymptotics at high colloid concentration. Together with the analytical
solution of the linear PB equation for cell models of arbitrary dimension and
electrolyte composition explicit and very general formulas for the osmotic
pressure ensue. A comparison with nonlinear PB theory is provided. Our analysis
also shows that whether or not linear theory predicts a phase separation
depends crucially on the precise definition of the pressure, showing that an
improper choice could predict an artificial phase separation in systems as
important as DNA in physiological salt solution.Comment: 16 pages, 5 figures, REVTeX4 styl
Theory of Mind and social functioning among neuropsychiatric disorders:A transdiagnostic study
Social dysfunction is commonly present in neuropsychiatric disorders of schizophrenia (SZ) and Alzheimer's disease (AD). Theory of Mind (ToM) deficits have been linked to social dysfunction in disease-specific studies. Nevertheless, it remains unclear how ToM is related to social functioning across these disorders, and which factors contribute to this relationship. We investigated transdiagnostic associations between ToM and social functioning among SZ/AD patients and healthy controls, and explored to what extent these associations relate to information processing speed or facial emotion recognition capacity. A total of 163 participants were included (SZ: n=56, AD: n=50 and age-matched controls: n=57). Social functioning was assessed with the Social Functioning Scale (SFS) and the De Jong-Gierveld Loneliness Scale (LON). ToM was measured with the Hinting Task. Information processing speed was measured by the Digit Symbol Substitution Test (DSST) and facial emotion recognition capacity by the facial emotion recognition task (FERT). Case-control deficits in Hinting Task performance were larger in AD (rrb = -0.57) compared to SZ (rrb = -0.35). Poorer Hinting Task performance was transdiagnostically associated with the SFS (βHinting-Task = 1.20, p<0.01) and LON (βHinting-Task = -0.27, p<0.05). DSST, but not FERT, reduced the association between the SFS and Hinting Task performance, however the association remained significant (βHinting-Task = 0.95, p<0.05). DSST and FERT performances did not change the association between LON and Hinting Task performance. Taken together, ToM deficits are transdiagnostically associated with social dysfunction and this is partly related to reduced information processing speed
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