Molecular theory of the static dielectric constant of dipolar fluids

The link between the static dielectric constant and the microscopic intermolecular interactions is the Kirkwood g₁ factor, which depends on the orientational structure of the fluid. Over the years, there have been several attempts to provide an accurate description of the orientational structure of dipolar fluids using molecular theories. However, these approaches were either limited to mean-field approximations for the pair correlation function or, more recently, limited to adjusting the orientational dependence to simulation data. Here, we derive a theory for the dielectric constant of dipolar hard-sphere fluids using the augmented modified mean-field approximation. Qualitative agreement is achieved throughout all relevant thermodynamic states, as demonstrated by a comparison with simulation data from the literature. Excellent quantitative agreement can be obtained using a single empirical scaling factor, the physical origin of which is analyzed and accounted for. In order to predict the dielectric constant of the Stockmayer fluid (Lennard-Jones plus dipole potential), we use an adjusted version of the expression for the dipolar hard-sphere fluid. Comparing theoretical predictions with newly generated simulation data, we show that it is possible to obtain excellent agreement with simulation by performing the calculations at a corresponding state using the same scaling factor. Finally, we compare the theoretical orientational structure of the Stockmayer fluid with that obtained from simulations. The simulated structure is calculated following a post-processing methodology that we introduce by deriving an original expression that relates the proposed theory to the histogram of relative dipole angles.

Corrigendum to "Improving contrast enhancement in pulmonary CTA: The value of breathing maneuvers" [Eur J Radiol Open 7 (2020) 100280]

[This corrects the article DOI: 10.1016/j.ejro.2020.100280.].

Improving Contrast Enhancement in Pulmonary CTA: The value of breathing maneuvers

Purpose

To investigate contrast dynamics and artifacts associated with different breathing maneuvers during pulmonary computed tomography angiography (pCTA) in a prospective randomized clinical trial.

Method

Three different breathing maneuvers (inspiration, expiration, Mueller) were randomly assigned to 146 patients receiving pCTA for suspected pulmonary embolism (PE). Contrast enhancement of central and peripheral arteries and imaging quality of lung parenchyma were compared and analyzed. Results were compared by using the analysis of variances (ANOVA) and Kruskal-Wallis-Test.

Results

Mean enhancement in the pulmonary trunk was highest during breath-hold in inspiration (293 HU, range 195-460 HU) compared to Mueller (259 HU, range 136-429 HU, p = 0022) and expiration (267 HU, range 115-376 HU). This was similar for the right pulmonary artery (inspiration 289 HU, range 173-454 HU; Mueller 250 HU, range 119-378 HU; p = 0.007; expiration 257 HU, range 114-366 HU; p = 0.032) and left pulmonary artery (inspiration 280.3 HU, range 170-462 HU; Mueller 245 HU, range 111-371 HU; p = 0.016; expiration 252 HU, range 110-371 HU).Delineation of peripheral arteries was significantly better in inspiration vs Mueller (p = 0.006) and expiration (p = 0.049). Assessment of the lung parenchyma was significantly better in inspiration vs Mueller (p = 0.013) or expiration (p < 0.001).

Conclusions

Resting inspiratory position achieved the highest enhancement levels in central and peripheral pulmonary arteries and best image quality of the pulmonary parenchyma in comparison to other breathing maneuvers. It is necessary to train the maneuver prior to the examination in order to avoid deep inspiration with the risk of suboptimal opacification of the pulmonary arteries.

Secondary technical resectability of colorectal cancer liver metastases after chemotherapy with or without selective internal radiotherapy in the randomized SIRFLOX trial

Background

Secondary resection of initially unresectable colorectal cancer liver metastases (CRLM) can prolong survival. The added value of selective internal radiotherapy (SIRT) to downsize lesions for resection is not known. This study evaluated the change in technical resectability of CRLM with the addition of SIRT to FOLFOX‐based chemotherapy.

Methods

Baseline and follow‐up hepatic imaging of patients who received modified FOLFOX (mFOLFOX6: fluorouracil, leucovorin, oxaliplatin) chemotherapy with or without bevacizumab (control arm) versus mFOLFOX6 (with or without bevacizumab) plus SIRT using yttrium‐90 resin microspheres (SIRT arm) in the phase III SIRFLOX trial were reviewed by three or five (of 14) expert hepatopancreatobiliary surgeons for resectability. Reviewers were blinded to one another, treatment assignment, extrahepatic disease status, and information on clinical and scanning time points. Technical resectability was defined as at least 60 per cent of reviewers (3 of 5, or 2 of 3) assessing a patient's liver metastases as surgically removable.

Results

Some 472 patients were evaluable (SIRT, 244; control, 228). There was no significant baseline difference in the proportion of technically resectable liver metastases between SIRT (29, 11·9 per cent) and control (25, 11·0 per cent) arms (P = 0·775). At follow‐up, significantly more patients in both arms were deemed technically resectable compared with baseline: 159 of 472 (33·7 per cent) versus 54 of 472 (11·4 per cent) respectively (P = 0·001). More patients were resectable in the SIRT than in the control arm: 93 of 244 (38·1 per cent) versus 66 of 228 (28·9 per cent) respectively (P < 0·001).

Conclusion

Adding SIRT to chemotherapy may improve the resectability of unresectable CRLM.

Identification and functional characterization of rare SHANK2 variants in schizophrenia

Recent genetic data on schizophrenia (SCZ) have suggested that proteins of the postsynaptic density of excitatory synapses have a role in its etiology. Mutations in the three SHANK genes encoding for postsynaptic scaffolding proteins have been shown to represent risk factors for autism spectrum disorders and other neurodevelopmental disorders. To address if SHANK2 variants are associated with SCZ, we sequenced SHANK2 in 481 patients and 659 unaffected individuals. We identified a significant increase in the number of rare (minor allele frequency<1%) SHANK2 missense variants in SCZ individuals (6.9%) compared with controls (3.9%, P=0.039). Four out of fifteen non-synonymous variants identified in the SCZ cohort (S610Y, R958S, P1119T and A1731S) were selected for functional analysis. Overexpression and knockdown-rescue experiments were carried out in cultured primary hippocampal neurons with a major focus on the analysis of morphological changes. Furthermore, the effect on actin polymerization in fibroblast cell lines was investigated. All four variants revealed functional impairment to various degrees, as a consequence of alterations in spine volume and clustering at synapses and an overall loss of presynaptic contacts. The A1731S variant was identified in four unrelated SCZ patients (0.83%) but not in any of the sequenced controls and public databases (P=4.6 × 10(-5)). Patients with the A1731S variant share an early prodromal phase with an insidious onset of psychiatric symptoms. A1731S overexpression strongly decreased the SHANK2-Bassoon-positive synapse number and diminished the F/G-actin ratio. Our results strongly suggest a causative role of rare SHANK2 variants in SCZ and underline the contribution of SHANK2 gene mutations in a variety of neuropsychiatric disorders.

Ileo-ileal invagination--a cause of recurrent mid-gastrointestinal bleeding: diagnostic and endoscopic therapy by means of push-and-pull enteroscopy

The types of lesions that cause bleeding in the small bowel are similar to those found in other areas in the gastrointestinal tract, such as vascular malformations, ulcers and inflammatory lesions, neoplasms and other less common lesions like Meckel's diverticulum. This report describes three patients with suspected mid-gastrointestinal bleeding with no significant past medical history. Before presenting to our unit the diagnostic work-up such as oesophagogastroduodenoscopy, colonoscopy and radiological small bowel imaging such as conventional enteroclysis or magnet resonance imaging enteroclysis had been performed without detecting any bleeding source. Capsule endoscopy suspected an angiodysplasia in the terminal ileum in one patient, in the other two patients a polyp in the region of the ileum as the potential bleeding source was diagnosed. In all three patients, a polyp with an ulcerated tip was found with the anal push-and-pull enteroscopy. An endosocpic resection was performed in all three cases without complication with the exception of one. In this patient a perforation occured 3 days after resection and was treated surgically without further complications. Histology revealed in all three cases, a polypoid diaphragmatic invagination of the small bowel with a vast area of chronic ulceration on the tip of this pseudopolyp with infiltration of the muscularis propria. In summary, the present paper describes the rare cases of erosive pseudopolyps after ileo-ileal invagination treated with endoscopic resection by means of push-and-pull enteroscopy.

Intrusion of fluids into nanogrooves: how geometry determines the shape of the gas-liquid interface

We study the shape of gas-liquid interfaces forming inside rectangular nanogrooves (i.e., slit-pores capped on one end). On account of purely repulsive fluid-substrate interactions the confining walls are dry (i.e., wet by vapor) and a liquid-vapor interface intrudes into the nanogrooves to a distance determined by the pressure (i.e., chemical potential). By means of Monte Carlo simulations in the grand-canonical ensemble (GCEMC) we obtain the density rho(z) along the midline (x = 0) of the nanogroove for various geometries (i.e., depths D and widths L) of the nanogroove. We analyze the density profiles with the aid of an analytic expression which we obtain through a transfer-matrix treatment of a one-dimensional effective interface Hamiltonian. Besides geometrical parameters such as D and L , the resulting analytic expression depends on temperature T , densities of coexisting gas and liquid phases in the bulk rho g,l(x) and the interfacial tension gamma. The latter three quantities are determined in independent molecular dynamics simulations of planar gas-liquid interfaces. Our results indicate that the analytic formula provides an excellent representation of rho(z) as long as L is sufficiently small. At larger L the meniscus of the intruding liquid flattens. Under these conditions the transfer-matrix analysis is no longer adequate and the agreement between GCEMC data and the analytic treatment is less satisfactory.

A lumped-parameter model to investigate the effect of plantar pressure on arterial blood flow in a diabetic foot

This paper presents a lumped-parameter model for the big-toe region that investigates the effect of plantar pressure on the diameter of the blood vessels, specifically the arteries, in the presence of arterial and/or tissue changes. The model developed in this paper uses a multi-domain energy system approach to develop the lumped-parameter differential equations. Blood flow is modelled as fluidic flow through compliant pipes that have inertia, stiffness, and damping. The tissue material is treated as a soft compliant material that transmits the external force to the blood vessels. Conclusions have been drawn to show the effect of plantar pressure, tissue damage, and their combination on the diameter of the blood vessels. The principles used here can be used to model the entire foot and the model used to investigate the effect of plantar pressure, tissue damage, and arterial changes on different parts of the foot. The work presented here may also have applications in other vascular diseases.

Model-based design of an agricultural biogas plant: application of anaerobic digestion model no.1 for an improved four chamber scheme

Different digestion technologies for various substrates are addressed by the generic process description of Anaerobic Digestion Model No. 1. In the case of manure or agricultural wastes a priori knowledge about the substrate in terms of ADM1 compounds is lacking and influent characterisation becomes a major issue. The actual project has been initiated for promotion of biogas technology in agriculture and for expansion of profitability also to rather small capacity systems. In order to avoid costly individual planning and installation of each facility a standardised design approach needs to be elaborated. This intention pleads for bio kinetic modelling as a systematic tool for process design and optimisation. Cofermentation under field conditions was observed, quality data and flow data were recorded and mass flow balances were calculated. In the laboratory different substrates have been digested separately in parallel under specified conditions. A configuration of four ADM1 model reactors was set up. Model calibration identified disintegration rate, decay rates for sugar degraders and half saturation constant for sugar as the three most sensitive parameters showing values (except the latter) about one order of magnitude higher than default parameters. Finally, the model is applied to the comparison of different reactor configurations and volume partitions. Another optimisation objective is robustness and load flexibility, i.e. the same configuration should be adaptive to different load situations only by a simple recycle control in order to establish a standardised design.

Collective dynamics near a phase transition in confined fluids

We performed molecular dynamics simulations in the microcanonical ensemble (MEMD) for a "simple" fluid confined between two solid substrates. From the calculation of the intermediate scattering function F(k( parallel ),t) and through the memory function formalism, we extract material ( i.e. transport and thermodynamics) coefficients in the vicinity of the liquid-gas phase transition. Our results show that approaching the limit of stability ( i.e. the spinodal), the dynamics of the system changes markedly.

Role of nanoscopic liquid bridges in static friction

Interpretations of recent experiments on the effects of humidity on friction hypothesize that liquid-water bridges can span nanoscopic gaps at the interface between the sliding surfaces. By means of a lattice-gas model the mechanisms by which such bridges may engender static friction at a single ideal nanoscopic contact were studied. The model contact consists of a simple (spherically symmetric) fluid constrained between two plane-parallel substrates decorated with weakly and strongly attractive stripes that alternate periodically in one transverse direction. In analogy with the experiments the shear yield stress (yield strength) tau(s) of the contact was computed as a function of the chemical potential mu of the fluid (the analog of humidity). The influence of other thermodynamic state variables, such as temperature and distance between the substrates, and of the relative strength of the stripes on the yield-strength curves (i.e., tau(s) versus mu) was explored. Some intriguing correlations between experiment and theory are observed.

Correlation of stress and structure in a simple fluid confined to a pore with furrowed walls

A Lennard-Jones (12,6) film confined between two furrowed walls was simulated by the grand canonical ensemble Monte Carlo method. The walls are constructed by gouging triangular grooves in planar substrates that are structureless on the molecular scale. The furrows are infinitely long in one transverse direction (y) and of nanoscopic width (s(x)) and depth (D). The furrows in the two walls are maintained parallel and in register. The diagonal components of the stress tensor (T(alphaalpha), alpha=x,y,z) are computed as functions of D and the separation between the substrates (s(z)) at fixed temperature, chemical potential, and s(x). The T(alphaalpha) for the film between the furrowed walls are strongly shifted from their counterparts for the film between flat (i.e., planar) walls. The shifts are rationalized in terms of the structure of the film, which becomes more ordered as the furrows deepen and the packing of film molecules becomes more restricted in the two dimensions normal to the y direction. The results demonstrate the profound impact of the coupling between molecular and nanoscopic scales on the properties of geometrically constrained fluids.

Absence of simulation evidence for critical depletion in slit pores

Recent Monte Carlo simulation studies of a Lennard-Jones fluid confined to a mesoscopic slit pore have reported evidence of "critical depletion" in the pore local number density near the liquid-vapor critical point. In this Brief Report we demonstrate that the observed depletion effect is in fact a simulation artifact arising from small systematic errors associated with the use of long range corrections for the potential truncation. Owing to the large near-critical compressibility, these errors lead to significant changes in the pore local number density. We suggest ways of avoiding similar problems in future studies of confined fluids.

Socially inhibited individuals show heightened DTH response during intense social engagement

To determine whether altered cellular immune response might mediate the increased health risks associated with social inhibition, we examined delayed type hypersensitivity (DTH) responses in 36 adults under conditions of low and high intensity social engagement. Participants come from a study of psychological factors in functional bowel disease and fibromyalgia. Under high engagement conditions, socially inhibited individuals showed significantly increased induration in response to intradermal tetanus toxoid. Under low engagement conditions, these individuals showed less pronounced DTH responses that did not differ in magnitude from those of uninhibited individuals. This pattern of results was found using two different measures of social inhibition and was independent of social inhibition's definition as a continuously distributed trait vs a discrete category. These data are consistent with the general hypothesis that social inhibition represents a predisposition to physiologic hyperresponsiveness that requires an exogenous social trigger for expression.

On the Thermodynamic Stability of Confined Thin Films Under Shear

Thin films of monatomic fluid constrained between two plane-parallel structured solid walls have been modeled by Monte Carlo simulation under conditions (fixed temperature, chemical potential, and normal stress or load) prevailing in high-precision measurements of surface forces. Several states of the film, corresponding to different numbers of layers of fluid parallel with the walls, are generally consistent with these conditions, but only one is thermodynamically stable; the others are metastable. When the walls are properly aligned, epitaxial solid phases are stable. These melt under shear, eventually becoming metastable, whereupon a drainage (or imbibition) transition occurs, leading to a stable phase with fewer (or more) layers.

Resistance to health: when the mind interferes with the desire to become well

Secondary gain has long been viewed as a variable that can significantly affect a patient's recovery from such conditions as chronic pain disorders, factitious and somatoform disorders, and other psychological disorders. Secondary gain has not been evaluated in terms of its impact on major illnesses such as cancer or autoimmune disorders. In this paper I discuss how secondary gain can be present in such illnesses and how it results in a resistance to health. This resistance to health can lead not only to medical noncompliance, but can also ultimately affect the progression and recovery from the illness. I describe how hypnosis can be used to ferret out this resistance to health and how patients in a hypnotic state will indicate or express their resistance to becoming healthy. The advantage of this approach is that it enables the clinician to deal directly with the patient's unconscious resistance to health.

Shear Forces in Molecularly Thin Films

Monte Carlo and molecular dynamics methods have been used to study the shearing behavior of an atomic fluid between two plane-parallel solid surfaces having the face-centered cubic (100) structure. A distorted, face-centered cubic solid can form epitaxially between surfaces that are separated by distances of one to five atomic diameters. Under these conditions a critical stress must be overcome to initiate sliding of the surfaces over one another at fixed separation, temperature, and chemical potential. As sliding begins, a layer of solid exits the space between the surfaces and the remaining layers become fluid.

Acardiac fetus in a triplet pregnancy

The acardiac monster represents one of the most severe but rare congenital anomalies. It occurs only in multiple gestations associated with vascular anastomoses between the affected fetus and its co-twin. The prenatal diagnosis of an acardiac fetus must be suspected in any multiple gestation in which cardiac activity cannot be documented sonographically in a growing fetus. We report an acardiac fetus occurring in a spontaneously conceived triplet pregnancy. A review of the literature, including pathogenetic theories and sonographic reports, is discussed.

A conceptual framework and treatment strategy for the alcoholic urge to drink utilizing hypnosis

The present paper proposes a theoretical framework and a treatment strategy for dealing with the urges to drink that alcoholics experience during recovery. Two models are proposed: the Defense Model and the Conditioning Model. Each model covers a specific period of time during recovery in which the urges to drink occur. The Defense Model describes the urges that result in the initial recovery period, while the Conditioning Model is invoked to explain urges that materialize in the later phases of recovery. Next, a treatment strategy is delineated that incorporates these models and employs the use of hypnosis. The treatment strategy is divided into three phases, with the first and second phases dealing with the alcoholic's unconscious and the third phase being directed at the alcoholic's conscious.