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

Many-body interactions and melting of colloidal crystals

We study the melting behavior of charged colloidal crystals, using a simulation technique that combines a continuous mean-field Poisson-Boltzmann description for the microscopic electrolyte ions with a Brownian-dynamics simulation for the mesoscopic colloids. This technique ensures that many-body interactions between the colloids are fully taken into account, and thus allows us to investigate how many-body interactions affect the solid-liquid phase behavior of charged colloids. Using the Lindemann criterion, we determine the melting line in a phase-diagram spanned by the colloidal charge and the salt concentration. We compare our results to predictions based on the established description of colloidal suspensions in terms of pairwise additive Yukawa potentials, and find good agreement at high-salt, but not at low-salt concentration. Analyzing the effective pair-interaction between two colloids in a crystalline environment, we demonstrate that the difference in the melting behavior observed at low salt is due to many-body interactions

The Incidence of Malignancy and the Preoperative Assessment of Women Undergoing Hysterectomy with Morcellation for Benign Indications

Background: The use of power morcellation in gynecologic surgery has come under scrutiny secondary to concerns for occult malignancy dissemination. The incidence of undiagnosed gynecologic malignancy when hysterectomy performed for benign indications is not definitive but has been quoted as high as 2.7% (1:37). There is not a standard recommended preoperative evaluation, and variation is anticipated by preoperative complaint or diagnosis. Objectives: To quantify the malignancy incidence in women undergoing hysterectomy for benign indications and to compare the preoperative evaluation of patients undergoing hysterectomy with and without morcellation. Methods: Retrospective cohort of women undergoing hysterectomies between October 2007 and June 2014 was identified by procedural codes through the hospital billing system. Exclusions included hysterectomies performed by gynecologic oncologists or non-gynecologic surgeons and surgeries performed outside the UMass healthcare system. Chart abstraction included demographics; pre-hysterectomy evaluation, including current cervical cytology, pathologic endometrial assessment (biopsy, dilation and curettage), and imaging (ultrasound, MRI, CT scan, sonohysterogram, or hysteroscopy); intraoperative factors; and final diagnosis. Results: Analytic cohort included 2,332 women undergoing hysterectomy with 396 (17.0%) including use of morcellation. The malignancy incidence on final pathology was 2.1% and was different between non-morcellated versus morcellated specimens (2.5% vs. 0.3%, p Conclusion: The incidence of malignancy at time ofhysterectomy performed by non­-oncology trained gynecologists was 2.1% overall, and 0.3% in morcellated cases. The pre-operative evaluation of patients undergoing hysterectomy with morcellation is similar to those without morcellation, except for lower rates of pathologic endometrial assessment. An argument could be made that a pathology assessment is indicated in this group due to risk of dissemination in the case of occult malignancy. The risk of occult malignancy is rare, but this should be discussed with patients and taken into account during the pre-operative evaluation

Oxygenated compounds in aged biomass burning plumes over the Eastern Mediterranean: evidence for strong secondary production of methanol and acetone

International audienceAirborne measurements of acetone, methanol, PAN, acetonitrile (by Proton Transfer Reaction Mass Spectrometry), and CO (by Tunable Diode Laser Absorption Spectroscopy) have been performed during the Mediterranean Intensive Oxidants Study (MINOS August 2001). We have identified ten biomass burning plumes from strongly elevated acetonitrile mixing ratios. The characteristic biomass burning signatures obtained from these plumes reveal secondary production of acetone and methanol, while CO photochemically declines in the plumes. Mean excess mixing ratios - normalized to CO - of 1.8%, 0.20%, 3.8%, and 0.65% for acetone, acetonitrile, methanol, and PAN, respectively, were found. By scaling to an assumed global annual source of 663-807Tg CO, biomass burning emissions of 25-31 and 29-35 Tg/yr for acetone and methanol are estimated, respectively. Our measurements suggest that the present biomass burning contributions of acetone and methanol are significantly underestimated due to the neglect of secondary formation within the plume. Median acetonitrile mixing ratios throughout the troposphere were around 150pmol/mol, in accord with current biomass burning inventories and an atmospheric lifetime of ~6 months

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

Metabolómica: una nueva herramienta para el estudio conjunto de la aterosclerosis y la estenosis aórtica degenerativa

Comunicaciones a congreso

Hacia un completo entendimiento de la fisiopatología del síndrome coronario agudo mediante la combinación de estudios proteómicos y metabolómicos

Comunicaciones a congreso