Neutral Fluid Research Articles

GENERATING SYNTHETIC MAGNETIC FIELD INTERMITTENCY USING A MINIMAL MULTISCALE LAGRANGIAN MAPPING APPROACH

The Minimal Multiscale Lagrangian Mapping procedure developed in the context of neutral fluid turbulence is a simple method for generating synthetic vector fields. Using a sequence of low-pass filtered fields, fluid particles are displaced at their rms speed for some scale-dependent time interval, and then interpolated back to a regular grid. Fields produced in this way are seen to possess certain properties of real turbulence. This paper extends the technique to plasmas by taking into account the coupling between the velocity and magnetic fields. We examine several possible applications to plasma systems. One use is as initial conditions for simulations, wherein these synthetic fields may efficiently produce a strongly intermittent cascade. The intermittency properties of the synthetic fields are also compared with those of the solar wind. Finally, studies of cosmic ray transport and modulation in the test particle approximation may benefit from improved realism in synthetic fields produced in this way.

Complexation of Zr and Hf monomers in supercritical aqueous solutions: Insights from ab initio molecular dynamics simulations

The enhanced mobilization of high field strength elements (HFSE) by certain geological fluids at high pressures, P, and high temperatures, T, as indicated by field observations and recent solubility measurements is most likely related to the type of complex formation in the fluid phase. However, only a few in situ experimental studies have been performed so far to constrain HFSE speciation in supercritical aqueous fluids. Here, we complement these investigations by ab initio molecular dynamics simulations to explore the complexation of Zr4+ and Hf4+ monomers in aqueous solutions at T=1000K and P∼1GPa. Regardless of the type of fluid (basic, neutral, acidic) both Zr and Hf seem to prefer an octahedral coordination. By systematically changing fluid composition and coordinating anions, the structure of various [(Zr,Hf)Clk(OH)m(H2O)n]4−k−m(k=0–6,m=2–6,n=0–4) complexes is investigated. For each complex that is stable on the time scale of the simulation, theoretical X-ray absorption spectra are calculated and compared to experimental data. From this comparison, the most likely complexes in HCl solutions are [(Zr,Hf)Cl3(Cl,OH)2(H2O)]−. The differences between experimental and theoretical XANES spectra present in the case of NaOH solutions indicate HFSE speciation beyond monomers in this system. Charge-neutral [(Zr,Hf)(OH)4(H2O)1–2] complexes, which may be the dominant species in neutral fluids at very low HFSE concentrations, show the lowest coordination (5.2(1)) of all investigated species. Finally, differences in the complexation of Zr and Hf in aqueous solutions at ambient and supercritical conditions and the possible formation of more complex oligomeric species are discussed.

Investigating high‐latitude ionospheric turbulence using global positioning system data

AbstractStatistical properties of the amplitude and phase of GPS L1 signals sampled at 50 Hz are investigated to understand the turbulent behavior of the polar region ionosphere. Wavelet detrended amplitude and phase data are used to construct the probability distribution function (PDF) of the amplitude and phase fluctuations of the signal. Turbulent behavior of the ionosphere is quantified using the skewness and kurtosis of the PDF. It is found that these two independent moments are related through a parabolic relationship, which was also reported in the case of turbulent neutral fluids and turbulent laboratory plasmas.

A new class of relativistic charged anisotropic super dense star models

In the present article we have obtained a class of analytical solutions for an anisotropic charged fluid distribution. The neutral anisotropic fluid sphere has already been obtained by Maurya and Gupta (Phys. Scr. 86:025009, 2012). The solutions depend upon both the anisotropic and the charge parameter. The anisotropy parameter and the electric intensity is zero at the centre and monotonically increasing towards the pressure free interface. All the physical entities such as energy density, radial pressure, tangential pressure, and velocity of sound are monotonically decreasing towards the surface.

A penalization technique to model plasma facing components in a tokamak with temperature variations

To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modeling of particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.

Developments of large eddy simulation for compressible space plasma turbulence

In this paper, brief review of studies of compressible space plasma turbulence is given. Magnetic fields and compressibility are present that are different from properties of hydrodynamic incompressible turbulence of neutral fluid. This considerably complicates studies of characteristics of compressible magnetohydrodynamic turbulence with direct numerical simulation. Large eddy simulation method developed as alternative of direct modeling is discussed in the review. The method is based on filtrating procedure of governing equations of magnetohydrodynamics and subgrid-scale modeling of universal small-scale turbulence. Descriptions of both the method and different subgrid-scale models for compressible magnetohydrodynamic turbulent flows are present. It is shown that large eddy simulation has good future trends for research of compressible magnetohydrodynamic turbulence.

The impact of fluid intervention on complications and length of hospital stay after pancreaticoduodenectomy (Whipple's procedure).

BackgroundThere is limited information on the impact on perioperative fluid intervention on complications and length of hospital stay following pancreaticoduodenectomy. Therefore, we conducted a detailed analysis of fluid intervention in patients undergoing pancreaticoduodenectomy at a university teaching hospital to test the hypothesis that a restrictive intravenous fluid regime and/or a neutral or negative cumulative fluid balance, would impact on perioperative complications and length of hospital stay.MethodsWe retrospectively obtained demographic, operative details, detailed fluid prescription, complications and outcomes data for 150 consecutive patients undergoing pancreaticoduodenectomy in a university teaching hospital. Prognostic predictors for length of hospital stay and complications were determined.ResultsOne hundred and fifty consecutive patients undergoing pancreaticoduodenectomy were evaluated between 2006 and 2012. The majority of patients were, middle-aged, overweight and ASA class III. Postoperative complications were frequent and occurred in 86 patients (57%). The majority of complications were graded as Clavien-Dindo Class 2 and 3. Postoperative pancreatic fistula occurred in 13 patients (9%), and delayed gastric emptying occurred in 25 patients (17%). Other postoperative surgical complications included sepsis (22%), bile leak (4%), and postoperative bleeding (2%). Serious medical complications included pulmonary edema (6%), myocardial infarction (8%), cardiac arrhythmias (13%), respiratory failure (8%), and renal failure (7%). Patients with complications received a higher median volume of intravenous therapy and had higher cumulative positive fluid balances. Postoperative length of stay was significantly longer in patients with complications (median 25 days vs. 10 days; p < 0.001). After adjustment for covariates, a fluid balance of less than 1 litre on postoperative day 1 and surgeon caseloads were associated with the development of complications.ConclusionsIn the context of pancreaticoduodenectomy, restrictive perioperative fluid intervention and negative cumulative fluid balance were associated with fewer complications and shorter length of hospital stay. These findings provide good opportunities to evaluate strategies aimed at improving perioperative care.

Embedded electromagnetically sensitive particle motion in functionalized fluids

The primary objective of this paper is to characterize the motion of small electromagnetically sensitive particles which are embedded in a flowing neutral fluid. There are a variety of industrial applications for electromagnetic particle-laden fluids, such as fluid-based actuators, coatings and functionalized inks, to name a few. This work compares the relative strengths of the forces induced by electromagnetic fields and fluid drag, and their composite effects on particle motion. Both analytical and numerical investigations are undertaken. After an analysis of a single isolated particle, a three-dimensional model problem comprised of a Representative Volume Element of flowing particle-laden fluid, under the action of external electromagnetic fields, is studied. A computational staggering scheme is developed to solve the coupled system utilizing a fully implicit Finite-Difference discretization of the Navier–Stokes equations for the fluid and a direct particle-dynamics description is used for the particles. For large numbers of embedded particles, because of the extreme computational difficulty of interface-conforming fine-mesh spatial discretizations for the fluid, simplifying assumptions for the coupling are made based on semi-analytical computation of drag-coefficients, allowing for the use of coarser meshes. Even after these simplifications, the particle-fluid system is strongly-coupled. The strongly-coupled system is implicitly solved, iteratively, within each time-step using a recursive staggering scheme, which employs temporal adaptivity to control the coupling error. The approach allows researchers to rapidly compute such systems with moderate laptop/desktop resources. Numerical examples are provided to illustrate the model and the numerical solution scheme, and limitations and extensions of the model are discussed.

Cosmologically inspired Kastor-Traschen solution

Kastor-Traschen (KT) type solution in a cosmological set up is studied in this article. We examine a hybrid of a KT metric and a Friedmann-Robertson-Walker-Lemaitre (FRWL) solution. The problem is treated in a general number of dimensions D>=4 and we include the cosmological constant Lambda parameter into the Einstein-Maxwell equations. The matter source consists of two fluids - charged dust and neutral fluid with non-vanishing pressure. The equations of motion for the fluid and electromagnetic (EM) field are written down and an exact solution generalising extremely charged Reissner-Nordstr\"{o}m black hole to arbitrary spatial curvature parameter is presented. We examine metric and curvature scalars singularities, trapped horizons as well as energy conditions.

Rayleigh-Taylor instability in partially ionized compressible plasmas: One fluid approach

We study the modification of the classical criterion for the linear onset and growth rate of the Rayleigh-Taylor instability (RTI) in a partially ionized (PI) plasma in the one-fluid description, considering a generalized induction equation. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The boundary conditions lead to an equation for the frequencies in which some of them have positive complex parts, marking the appearance of the RTI. We study the ambipolar term alone first, extending the result to the full induction equation later. We find that the configuration is always unstable because of the presence of a neutral species. In the classical stability regime the growth rate is small, since the collisions prevent the neutral fluid to fully develop the RTI. For parameters in the classical instability regime the growth rate is lowered, but for the considered theoretical values of the collision frequencies and diffusion coefficients for solar prominences the differences with the compressible MHD case are small. We conclude that PI modifies some aspects of the linear RTI instability, since it takes into account that neutrals do not feel the stabilizing effect of the magnetic field. For the set of parameters representative for solar prominences, our model gives the resulting timescale comparable with observed lifetimes of RTI plumes.

Numerical study on a canonized Hamiltonian system representing reduced magnetohydrodynamics and its comparison with two-dimensional Euler system

Introducing a Clebsch-like parameterization, we have formulated a canonical Hamiltonian system on a symplectic leaf of reduced magnetohydrodynamics. An interesting structure of the equations is in that the Lorentz-force, which is a quadratic nonlinear term in the conventional formulation, appears as a linear term −ΔQ, just representing the current density (Q is a Clebsch variable, and Δ is the two-dimensional Laplacian); omitting this term reduces the system into the two-dimensional Euler vorticity equation of a neutral fluid. A heuristic estimate shows that current sheets grow exponentially (even in a fully nonlinear regime) together with the action variable P that is conjugate to Q. By numerical simulation, the predicted behavior of the canonical variables, yielding exponential growth of current sheets, has been demonstrated.

A simple and rapid decalcification procedure of skeletal tissues for pathology using an ultrasonic cleaner with D-mannitol and formic acid

Decalcification procedures are required in order to prepare histopathological preparations of hard tissues such as bone and teeth. Decalcification is usually performed by immersing the hard tissue in different decalcification fluids with various properties. These decalcification fluids typically include inorganic and organic acids, a neutral fluid containing a chelating agent, or a mixture of solutions. Unfortunately, there is no universal decalcification fluid that satisfies all the requirements of pathologists such as rapid decalcification, easy handling, and minimal tissue damage. Techniques involving use of microwaves (MW) or ultrasonic apparatus (US) have been shown to be useful for shortening the time for decalcification procedures. In the present study, we investigated a unique decalcification procedure that uses a common commercial ultrasonic cleaner and a decalcification fluid (formic acid) containing a free-radical scavenger (D-mannitol). The time required to complete the procedure is approximately half of that required to complete a standard decalcification procedure. In addition, tissue morphology and antigenicity is fairly well preserved after decalcification. The procedure is quick, easy to perform, and achieves decalcification of hard tissue with minimal tissue damage.

Bisulfite and sulfite as derivatives of sulfur dioxide alters biomechanical behaviors of airway smooth muscle cells in culture

Sulfur dioxide (SO2) is a common air pollutant that triggers asthmatic symptoms, but its toxicological mechanisms are not fully understood. Specifically, it is unclear how SO2 in vivo affects airway smooth muscle (ASM) cells of which the mechanics is known to ultimately mediate airway hyperresponsiveness (AHR) – a hallmark feature of asthma. To this end, we investigated the effects of bisulfite/sulfite (1:3 M/M in neutral fluid to simulate the in vivo derivatives of inhaled SO2 in the airways), on the viability, migration, stiffness and contractility of ASM cells cultured in vitro. The results showed that bisulfite/sulfite consistently increased viability, migration, F-actin intensity and stiffness of ASM cells in similar fashion as concentration increasing from 10−4 to 10−1 mmol/L. However, bisulfite/sulfite increased the ASM cell contractility induced by KCl only at the concentration between 10−4 and 10−3 mmol/L (p < 0.05), while having no consistent effect on that induced by histamine. At the concentration of 100 mmol/L, bisulfite/sulfite became acutely toxic to the ASM cells. Taken together, the data suggest that SO2 derivatives at low levels in vivo may directly increase the mass, stiffness and contractility of ASM cells, which may help understand the mechanism in which specific air pollutants contribute in vivo to the pathogenesis of asthma.

Isospin dependence of entrainment in superfluid neutron stars in a relativistic model

We study the entrainment effect between superfluid neutrons and charge neutral fluid (called the proton fluid) which is made of protons and electrons in a neutron star interior within the two-fluid formalism and using a relativistic model where baryon-baryon interaction is mediated by the exchange of $\ensuremath{\sigma}$, $\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons. This model of strong interaction also includes scalar self-interactions. The entrainment matrix and entrainment parameter are calculated using the parameter sets of Glendenning (GL) and another non-linear (NL3) interaction. The inclusion of $\ensuremath{\rho}$ mesons strongly influences the entrainment parameter (${ϵ}_{\text{mom}}$) in a superfluid neutron star. The entrainment parameter is constant at the core and drops rapidly at the surface. It takes values within the physical range.

Purely helical absolute equilibria and chirality of (magneto)fluid turbulence

AbstractPurely helical absolute equilibria of incompressible neutral fluids and plasmas (electron, single-fluid and two-fluid magnetohydrodynamics) are systematically studied with the help of helical (wave) representation and truncation, for genericities and specificities about helicity. A unique chirality selection and amplification mechanism and relevant insights, such as the one-chiral-sector-dominated states, among others, about (magneto)fluid turbulence follow.

Effect of standard and neutral-pH peritoneal dialysis solutions upon fibroblasts proliferation.

Continuous exposition of the peritoneal membrane to conventional dialysis solutions is an important risk factor for inducing structural and functional alterations. To compare in vitro mouse fibroblast NIH-3T3 cell viability after exposition to a neutral pH dialysis solution in comparison to cells exposed to a standard solution. Experimental study to compare the effects of a conventional standard or a neutral-pH, low-glucose degradation products peritoneal dialysis solution on the viability of exposed fibroblasts in cell culture. Both solutions were tested in all the commercially available glucose concentrations. Cell viability was evaluated with tetrazolium salt colorimetric assay. Fibroblast viability was significantly superior in the neutral pH solution in comparison to control, in all three glucose concentrations (Optical density in nm-means ± SD: 1.5% 0.295 ± 0.047 vs. 0.372 ± 0.042, p < 0.001; 2.3% 0.270 ± 0.036 vs. 0.337 ± 0.051, p < 0.001; 4.25% 0.284 ± 0.037 vs. 0.332 ± 0.032, p < 0.001; control vs. neutral pH respectively, Student t Test). There was no significant difference in cell viability between the three concentrations of glucose when standard solution was used (ANOVA p = 0.218), although cell viability was higher after exposition to neutral pH peritoneal dialysis fluid at 1.5% in comparison to 2.3 and 4.25% glucose concentrations (ANOVA p = 0.008: Bonferroni 1.5% vs. 2.3% p = 0.033, 1.5% vs. 4.25% p = 0.014, 2.3% vs. 4.25% p = 1.00). Cell viability was better in neutral pH dialysis solution, especially in the lower glucose concentration. A more physiological pH and lower glucose degradation products may be responsible for such results.

Biodegradable, pH‐Responsive Carboxymethyl Cellulose/Poly(Acrylic Acid) Hydrogels for Oral Insulin Delivery

Biodegradable and pH-responsive carboxymethyl cellulose/poly(acrylic acid) hybrid hydrogels are synthesized. The hydrogels deswell in acidic artificial gastric fluid (AGF) but rapidly swell in neutral artificial intestinal fluid (AIF), rendering selective enzymatic degradation of the gels as well as accelerated drug release from insulin-loaded hydrogels in AIF. Oral administration of insulin-loaded hydrogels to streptozotocin-induced diabetic rats leads to a continuous decline in the fasting blood glucose level within 6 h post-administration, and the relative pharmacological availability increases more than 10 times compared to oral administration of free insulin solution. The relative bioavailability of hydrogel-encapsulated insulin after oral administration to healthy rabbits is 6.6%.

Kaluza-Klein reduction of relativistic fluids and their gravity duals

We study the hydrodynamics of relativistic fluids with several conserved global charges (i.e., several species of particles) by performing a Kaluza-Klein dimensional reduction of a neutral fluid on a N-torus. Via fluid/gravity correspondence, this allows us to describe the long-wavelength dynamics of black branes with several Kaluza-Klein charges. We obtain the equation of state and transport coefficients of the charged fluid directly from those of the higher-dimensional neutral fluid. We specialize these results for the fluids dual to Kaluza-Klein black branes.

SIMULATING NANOFLUIDS VIA THE WEIGHTED DENSITY LATTICE BOLTZMANN APPROACH

The structure and transport of neutral and charged fluids under nanoscopic confinement are derived from the kinetic and microscopic perspective. As compared to lumped parameter approaches, the strategy is to resolve the collision between particles for hard-core forces and to use a mean field treatment for soft- and long-ranged forces. The numerical strategy adapts the Lattice Boltzmann (LB) scheme to handle interatomic and electrostatic interactions.

A STUDY OF ALFVÉN WAVE PROPAGATION AND HEATING THE CHROMOSPHERE

Alfven wave propagation, reflection, and heating of the chromosphere are studied for a one-dimensional solar atmosphere by self-consistently solving plasma, neutral fluid, and Maxwell's equations with incorporation of the Hall effect and strong electron-neutral, electron-ion, and ion-neutral collisions. We have developed a numerical model based on an implicit backward difference formula of second-order accuracy both in time and space to solve stiff governing equations resulting from strong inter-species collisions. A non-reflecting boundary condition is applied to the top boundary so that the wave reflection within the simulation domain can be unambiguously determined. It is shown that due to the density gradient the Alfven waves are partially reflected throughout the chromosphere and more strongly at higher altitudes with the strongest reflection at the transition region. The waves are damped in the lower chromosphere dominantly through Joule dissipation, producing heating strong enough to balance the radiative loss for the quiet chromosphere without invoking anomalous processes or turbulences. The heating rates are larger for weaker background magnetic fields below ~500 km with higher-frequency waves subject to heavier damping. There is an upper cutoff frequency, depending on the background magnetic field, above which the waves are completely damped. At the frequencies below which the waves are not strongly damped, the interaction of reflected waves with the upward propagating waves produces power at their double frequencies, which leads to more damping. The wave energy flux transmitted to the corona is one order of magnitude smaller than that of the driving source.