Hollow Density Research Articles

Analysis of moisture management properties of cotton/milkweed blended rotor yarn fabrics

PurposeClothing must also assist the body’s thermal control function under changing physical loads in such a way that the body’s thermal and moisture management is balanced, and a microclimate is created next to the skin. One of the factors which affect moisture transport in a fabric is a fibre type. Hence, the purpose of this paper is to blend the natural hollow and low density fibre, milkweed, with cotton fibre at different proportions and to analyse and compare the influence of milkweed blend proportion on moisture management properties of rotor yarn fabrics with 100 per cent cotton fabric.Design/methodology/approachIn the present study, cotton/milkweed blended rotor yarns were produced by using S-4 cotton variety and milkweed fibres in three different blend proportions such as cotton/milkweed 80/20, 60/40 and 40/60 along with 100 per cent cotton yarn with yarn count of 20 Ne. The single jersey knitted fabrics were produced with similar constructional parameters and then the fabrics were then scoured, bleached and neutralised as per the standard procedure. The fabrics have been analysed for its various moisture management properties using moisture management tester (MMT) and are statistically analysed.FindingsThe results indicate that, all the C/M blended fabrics have been classified as “moisture management fabric” and 100 per cent cotton fabric has been classified as “Fast absorbing and Quick Drying Fabric”. The overall moisture management capacity of C/M 40/60 fabric is excellent and could be used for summer, active and summer wear applications. One-way ANOVA analysis carried out at 95 per cent confidence level showed that the results are statistically significant. The pair-wise strength and association between various moisture management indices was analysed using Pearson correlation coefficient and observed that OWTC and OMMC was found to be positively and linearly related to each other.Originality/valueThe authors are confident that the cotton/milkweed blended yarns can be used as an inner wear and sportswear applications owing to the higher moisture regain and hollowness of milkweed fibre combined with the low packing density of C/M blended yarns which leads to overall improvement in moisture management properties of fabrics.

Impurity density gradient influence on trapped particle modes

The effect of the presence of an impurity species on the trapped particle turbulence is studied using the gyro-bounce kinetic code TERESA, which allows the study of Trapped Electron Modes and Trapped Ion Modes. The impurity species is treated self-consistently and its influence on the nature of the turbulence, ion driven or electron driven, is investigated. It is found that the presence of heavy impurities with a flat density profile tends to stabilize the both electron and ion modes, whereas a peaked or hollow impurity density profile can change the turbulence from an electron driven turbulence to an ion driven turbulence. The effect of the turbulence regime on impurity transport is studied.

Role of ion magnetization in formation of radial density profile in magnetically expanding plasma produced by helicon antenna

Experimentally, the density profile in the magnetic nozzle of a helicon antenna based plasma device is seen to be modified from being centrally peaked to that of hollow nature as the external magnetic field is increased. It occurs above a characteristic field value when the ions become magnetized in the expansion chamber. The density profile in the source chamber behind the nozzle, however, remains peaked on-axis irrespective of the magnetic field. The electron temperature there is observed to be hollow and this nature is carried to the expansion chamber along the field line. In the electron energy distribution near the off axis peak location, a high energy tail exists. Rotation of these tail electrons in the azimuthal direction due to the gradient-B drift in the expansion chamber leads to an additional off-axis ionization and forms the hollow density profile. It seems that if the ions are not magnetized, then the off-axially produced additional plasma is not confined and the density profile retains the on-axis peak nature. The present experiment successfully demonstrates how the knowledge of the ion magnetization together with tail electrons significantly contributes to the design of an efficient helicon plasma based thruster.

Non-inductively driven tokamak plasmas at near-unity βt in the Pegasus toroidal experiment

A major goal of the spherical tokamak (ST) research program is accessing a state of low internal inductance ℓi, high elongation κ, and high toroidal and normalized beta (βt and βN) without solenoidal current drive. Local helicity injection (LHI) in the Pegasus ST [Garstka et al., Nucl. Fusion 46, S603 (2006)] provides non-solenoidally driven plasmas that exhibit these characteristics. LHI utilizes compact, edge-localized current sources for plasma startup and sustainment. It results in hollow current density profiles with low ℓi. The low aspect ratio (R0/a∼1.2) of Pegasus allows access to high κ and high normalized plasma currents (IN=Ip/aBT>14). Magnetic reconnection during LHI provides auxiliary ion heating. Together, these features provide access to very high βt plasmas. Equilibrium analyses indicate that βt up to ∼100% is achieved. These high βt discharges disrupt at the ideal no-wall β limit at βN∼7.

Effects of hollow glass microsphere density and surface modification on the mechanical and thermal properties of poly(methyl methacrylate) syntactic foams

Syntactic foams offer low density polymers for insulation and transportation applications with the advantage of having high mechanical properties. In this study, poly(methyl methacrylate) (PMMA) syntactic foams were produced with three different types of hollow glass microspheres (HGMs) as low, medium and high density. It was observed that the density of the syntactic foams was in inverse ratio to the strength properties of the syntactic foams. The lowest measured syntactic foam density was obtained with the addition of high density HGMs into the PMMA matrix without compromising the mechanical properties. Surface coating of HGMs allowed increase in the flexural strength and the impact strength of PMMA syntactic foam by 12% and 17%, respectively, when they were compared with their counterparts with the uncoated HGMs. Addition of HGMs with modified surfaces into PMMA matrix reduced the composite density by 10% with respect to the neat PMMA while had no significant effect on its thermal characteristics.

Transport modeling of convection dominated helicon discharges in Proto-MPEX with the B2.5-Eirene code

Data-constrained interpretative analyses of plasma transport in convection dominated helicon discharges in the Proto-MPEX linear device, and predictive calculations with additional Electron Cyclotron Heating/Electron Bernstein Wave (ECH/EBW) heating, are reported. The B2.5-Eirene code, in which the multi-fluid plasma code B2.5 is coupled to the kinetic Monte Carlo neutrals code Eirene, is used to fit double Langmuir probe measurements and fast camera data in front of a stainless-steel target. The absorbed helicon and ECH power (11 kW) and spatially constant anomalous transport coefficients that are deduced from fitting of the probe and optical data are additionally used for predictive simulations of complete axial distributions of the densities, temperatures, plasma flow velocities, particle and energy fluxes, and possible effects of alternate fueling and pumping scenarios. The somewhat hollow electron density and temperature radial profiles from the probe data suggest that Trivelpiece-Gould wave absorption is the dominant helicon electron heating source in the discharges analyzed here. There is no external ion heating, but the corresponding calculated ion temperature radial profile is not hollow. Rather it reflects ion heating by the electron-ion equilibration terms in the energy balance equations and ion radial transport resulting from the hollow density profile. With the absorbed power and the transport model deduced from fitting the sheath limited discharge data, calculated conduction limited higher recycling conditions were produced by reducing the pumping and increasing the gas fueling rate, resulting in an approximate doubling of the target ion flux and reduction of the target heat flux.

Plasma confinement during ECR heating with a volume power density of 3 mW/m3 at the L-2M stellarator

The experiments on ECR plasma heating were carried out at the L-2M stellarator at very high volume power density (up to 3.0 MW/m3). Under these conditions, non-monotonous hollow density profiles were measured. At the maximum heating power of P = 0.75 MW, the concavity in the axial region becomes drastic ne(0)/nemax = 0.5. In these experiments, plasma temperature profiles measured in the axial plasma region r/ap < 0.4 occur to be rather flat. We have also measured two-slope SXR spectra in the range from 2 to 12 keV. The possible reasons for these observed phenomena were discussed. However, with growing ECRH power up to PECRH = 0.75 MW, we have not observed dramatic deterioration of plasma confinement at the L-2M stellarator. The measured energy lifetime is generally consistent with that determined from the international LHD scaling.

Density gradient driven microinstabilities and turbulence in ASDEX Upgrade pellet fuelled plasmas

ASDEX Upgrade plasmas fuelled by pellets in the H-mode confinement regime are analyzed. The gyrokinetic code GKW is applied to calculate the microinstabilities which are predicted to be unstable in these plasmas. Two types of density gradient driven modes are found, outside and inside the pellet deposition location. The first mode is driven by a negative radial density gradient, and corresponds to the usual density gradient driven trapped electron mode instability, producing a large diffusive particle flux directed outwards, and becomes more unstable with increasing trapped particle fraction and with decreasing collisionality. The second is driven by a positive radial density gradient (that is, a locally hollow density profile) and is identified for the first time in this work. The instability is located in the proximity of the high field side of the poloidal cross section, and drives a diffusive particle flux directed inward. It is mainly produced by the non-adiabatic response of passing particles with low parallel velocities at high collisionality and it becomes more unstable with increasing passing particle fraction and increasing collision frequency. Nonlinear gyrokinetic turbulence simulations show that these instabilities can lead to saturated turbulence and produce particle diffusion at experimentally relevant levels. In contrast to the usual behavior of the turbulent fields in tokamak plasmas, which have largest fluctuations on the low field side, locally hollow density profiles are prediced to lead to turbulent electrostatic potential and density fluctuations which are maximum on the high field side of the torus.

Analytic axisymmetric equilibria with pressure anisotropy and non-parallel flow

We extend previous work by two of the authors [Evangelias and Throumoulopoulos 2016 Plasma Phys. Control. Fusion 58 045022] and find analytic solutions to a generalized Grad–Shafranov equation (GGSE) with pressure anisotropy, hollow toroidal current density and incompressible flow of arbitrary direction. By specifying the surface-function terms involved in the GGSE as quadratic functions of the poloidal magnetic flux function, we derive analytic tokamak pertinent equilibria. It turns out that, irrespective of the shape of the toroidal current density profile, which is noticeably affected by the pressure anisotropy, this anisotropy has a paramagnetic effect for and a diamagnetic one for . In addition, the parallel flow induces paramagnetism, while the residual toroidal flow associated with the electric field induces diamagnetism. The analytic results obtained here contribute to the physics understanding of axisymmetric equilibria with pressure anisotropy and flow, and can be employed for validating equilibrium codes.

Gyrokinetic simulations of particle transport in pellet fuelled JET discharges

Pellet injection is a likely fuelling method of reactor grade plasmas. When the pellet ablates, it will transiently perturb the density and temperature profiles of the plasma. This will in turn change dimensionless parameters such as and plasma β. The microstability properties of the plasma then changes which influences the transport of heat and particles. In this paper, gyrokinetic simulations of a JET L-mode pellet fuelled discharge are performed. The ion temperature gradient/trapped electron mode turbulence is compared at the time point when the effect from the pellet is the most pronounced with a hollow density profile and when the profiles have relaxed again. Linear and nonlinear simulations are performed using the gyrokinetic code GENE including electromagnetic effects and collisions in a realistic geometry in local mode. Furthermore, global nonlinear simulations are performed in order to assess any nonlocal effects. It is found that the positive density gradient has a stabilizing effect that is partly counteracted by the increased temperature gradient in the this region. The effective diffusion coefficients are reduced in the positive density region region compared to the intra pellet time point. No major effect on the turbulent transport due to nonlocal effects are observed.

Formation of impurity transport barrier in LHD plasmas with hollow density profile

The iron impurity density in the central column of Large Helical Device (LHD) plasmas with a hollow electron density profile is found to be much smaller than those with a peaked density profile based on the radial density profile measurement of iron ions in several ionization stages. The iron impurity transport has been studied with the help of a 1D simulation code. The radial structure of the convective velocity suggests that an impurity transport barrier is formed by a strong density gradient effect on the impurity convection near the edge region of LHD plasmas with a hollow electron density profile.

Impact of a hollow density profile on turbulent particle fluxes: Gyrokinetic and fluid simulations

Hollow density profiles may occur in connection with pellet fuelling and L to H transitions. A positive density gradient could potentially stabilize the turbulence or change the relation between convective and diffusive fluxes, thereby reducing the turbulent transport of particles towards the center, making the pellet fuelling scheme inefficient. In the present work, the particle transport driven by Ion Temperature Gradient/Trapped Electron (ITG/TE) mode turbulence in hollow density profiles is studied by fluid as well as gyrokinetic simulations. The fluid model used, an extended version of the Weiland transport model, Extended Drift Wave Model (EDWM), incorporates an arbitrary number of ion species in a multi-fluid description and an extended wavelength spectrum. The fluid model, which is fast and hence suitable for use in predictive simulations, is compared to gyrokinetic simulations using the code GENE. Typical tokamak parameters are used based on the Cyclone Base Case. Parameter scans in key plasma parameters like plasma β, R/LT, and magnetic shear are investigated. In addition, the effects of a fast species are studied and global ITG simulations in a simplified physics description are performed in order to investigate nonlocal effects. It is found that β in particular, has a stabilizing effect in the negative R/Ln region. Both nonlinear GENE and EDWM simulations show a decrease in inward flux for negative R/Ln and a change in the direction from inward to outward for positive R/Ln. Moreover, the addition of fast particles was shown to decrease the inward main ion particle flux in the positive gradient region further. This might have serious consequences for pellet fuelling of high β plasmas. Additionally, the heat flux in global ITG turbulence simulations indicates that nonlocal effects can play a different role from usual in connection with pellet fuelling.

Gyrokinetic modeling of impurity peaking in JET H-mode plasmas

Quantitative comparisons are presented between gyrokinetic simulations and experimental values of the carbon impurity peaking factor in a database of JET H-modes during the carbon wall era. These plasmas feature strong NBI heating and hence high values of toroidal rotation and corresponding gradient. Furthermore, the carbon profiles present particularly interesting shapes for fusion devices, i.e., hollow in the core and peaked near the edge. Dependencies of the experimental carbon peaking factor (R/LnC) on plasma parameters are investigated via multilinear regressions. A marked correlation between R/LnC and the normalised toroidal rotation gradient is observed in the core, which suggests an important role of the rotation in establishing hollow carbon profiles. The carbon peaking factor is then computed with the gyrokinetic code GKW, using a quasi-linear approach, supported by a few non-linear simulations. The comparison of the quasi-linear predictions to the experimental values at mid-radius reveals two main regimes. At low normalised collisionality, ν*, and Te/Ti&amp;lt;1, the gyrokinetic simulations quantitatively recover experimental carbon density profiles, provided that rotodiffusion is taken into account. In contrast, at higher ν* and Te/Ti&amp;gt;1, the very hollow experimental carbon density profiles are never predicted by the simulations and the carbon density peaking is systematically over estimated. This points to a possible missing ingredient in this regime.

Fluid and gyrokinetic modelling of particle transport in plasmas with hollow density profiles

Hollow density profiles occur in connection with pellet fuelling and L to H transitions. A positive density gradient could potentially stabilize the turbulence or change the relation between convective and diffusive fluxes, thereby reducing the turbulent transport of particles towards the center, making the fuelling scheme inefficient. In the present work, the particle transport driven by ITG/TE mode turbulence in regions of hollow density profiles is studied by fluid as well as gyrokinetic simulations. The fluid model used, an extended version of the Weiland transport model, Extended Drift Wave Model (EDWM), incorporates an arbitrary number of ion species in a multi-fluid description, and an extended wavelength spectrum. The fluid model, which is fast and hence suitable for use in predictive simulations, is compared to gyrokinetic simulations using the code GENE. Typical tokamak parameters are used based on the Cyclone Base Case. Parameter scans in key plasma parameters like plasma β, R/LT, and magnetic shear are investigated. It is found that β in particular has a stabilizing effect in the negative R/Ln region, both nonlinear GENE and EDWM show a decrease in inward flux for negative R/Ln and a change of direction from inward to outward for positive R/Ln. This might have serious consequences for pellet fuelling of high β plasmas.

Structure and Compressive Properties of Invar-Cenosphere Syntactic Foams

The present study investigates the mechanical performance of syntactic foams produced by means of the metal powder injection molding process having an Invar (FeNi36) matrix and including cenospheres as hollow particles at weight fractions (wt.%) of 5 and 10, respectively, corresponding to approximately 41.6 and 60.0 vol.% in relation to the metal content and at 0.6 g/cm3 hollow particle density. The synthesis process results in survival of cenospheres and provides low density syntactic foams. The microstructure of the materials is investigated as well as the mechanical performance under quasi-static and high strain rate compressive loads. The compressive stress-strain curves of syntactic foams reveal a continuous strain hardening behavior in the plastic region, followed by a densification region. The results reveal a strain rate sensitivity in cenosphere-based Invar matrix syntactic foams. Differences in properties between cenosphere- and glass microsphere-based materials are discussed in relation to the findings of microstructural investigations. Cenospheres present a viable choice as filler material in iron-based syntactic foams due to their higher thermal stability compared to glass microspheres.

中空糸膜状浸漬型MBRにおいて膜密度がモジュール内部の流動特性に及ぼす影響

中空糸膜状浸漬型MBRにおいて膜密度がモジュール内部の流動特性に及ぼす影響

Simulation and experimental study on the effect of channeling flows on the transport of toxins in hemodialyzers

Channeling flows are common phenomena that exist on the dialysate side in hemodialyzers, and they significantly affect the performance of hemodialyzers. Today, the effect of channeling flows on the clearance of uremic toxins has been studied only experimentally and not theoretically because of its complexity. In this paper, we for the first time introduced a method to mimic channeling flows and, thus, quantitatively investigated the impact of channeling flows on the transport of toxins. The experimental results show that the effect of channeling flows is more significant when the dialysate flow rate is low. The theoretical results show that the flow velocity and toxin concentration fields under channeling flows are qualitatively consistent with the ones published in the literature. Channeling flows induced by the non-uniformity in the hollow fiber packing density can significantly affect the toxin concentration profiles on both dialysate and blood sides and, thus, decrease the clearance of toxins. The effect of channeling flows on the toxin transport is more significant when the fiber packing density is low. The method developed here can be embedded into various theoretical models to match more closely the calculated toxin clearance to reality or to optimize the dialysate flow profiles in hemodialyzers.

Comparison of current density profiles based on particle orbit-driven current in steady-state plasma on QUEST

In the present RF-driven divertor plasma of QUEST, it has been observed that orbit-driven current flows in the open magnetic surfaces outside of the closed magnetic surfaces. To observe this phenomenon and the characteristics of the orbit-driven current, current density profiles have been calculated on two different equilibrium conditions. We calculated current density profiles from particle guiding center orbits both for the fundamental and the second harmonic resonances for the 8.2GHz electron cyclotron current drive. From this calculation, hollow current density profiles have been obtained with significant characteristics on both conditions. Only positive current distribution has been observed in the open magnetic surfaces outside of the closed magnetic surfaces.

Transport analysis and modelling of the evolution of hollow density profiles plasmas in JET and implication for ITER

The density evolution during the transient phase just after the L–H transition is investigated using theoretical transport models. Cases characterized by core densities which evolve in longer timescales than the edge densities, leading to hollow density profiles () are modelled. This density evolution is particularly interesting because it has been shown to be beneficial in the view of the access to burning plasma conditions in ITER (Loarte et al 2013 Nucl. Fusion 53 083031). Self-consistent simulations of the JET discharge 79676 of the density-only, and of the density and the temperatures are carried out using a quasilinear gyrokinetic code, QuaLiKiz (Bourdelle et al 2007 Phys. Plasmas 14 112501), coupled with a transport code CRONOS (Artaud et al 2010 Nucl. Fusion 50 043001). The slow evolution of the hollow density, associated with the self-consistently calculated hollow NBI particle deposition, is well reproduced in the plasma core. Indeed, QuaLiKiz is shown to reproduce nonlinear gyrokinetic heat and particle fluxes well for both positive and negative . That gives a theoretical and general basis for the persistence of the hollowness, laying the groundwork for the extrapolation to ITER.

Tree hollows and forest stand structure in Australian warm temperate Eucalyptus forests are adversely affected by logging more than wildfire

Ecologically sustainable forest management aims to maintain biodiversity values within managed forest ecosystems. A key habitat component within Australian forest ecosystems are hollow-bearing trees which are crucially important for fauna species requiring tree hollows for diurnal shelter and nesting. The effect of disturbance regimes, in particular logging and fire, on hollow dynamics is poorly understood. The aim of this study was to determine the relationships between logging intensity and fire frequency on hollow abundance and forest stand structural attributes in two different eastern Australian Eucalyptus forest types.We found that average stand tree diameter at breast height was negatively correlated to logging intensity. Logging intensity was negatively correlated with tree diameter at breast height (DBH), and the density of both hollow-bearing trees and hollows. Losses of hollow-bearing trees and hollows occurred through an interaction between logging intensity and fire frequency, resulting in an absence of recruitment of hollow trees. However in unlogged forest, fire was positively correlated to the density of hollows. Under a regime of frequent fire, in areas that have had some degree of logging activity, a net loss of hollows may occur. We recommend additional hollow recruitment trees be retained on logged sites in the future if no net losses of hollows are to occur in the future, or for wider unlogged buffers to be established adjacent to the cutting area.