Temperature Gradient Mode Research Articles

Effects of temperature on modal characteristics of non-uniform rigid-frame bridges

The effect of temperature on structural modal characteristics plays an important role in structural health monitoring and evaluation. Herein, the free vibration analysis of rigid-frame bridge is conducted by taking into account the effect of temperature. Firstly, the non-uniform rigid-frame bridge is divided into several members to develop the flexural and axial vibration equations for members under the effect of temperature in accordance with Hamilton’s principle. Secondly, each member is further divided into several segments, and the transfer relationship between segments is established to obtain the generalized dynamic stiffness matrix of the member. Then, the generalized dynamic stiffness matrix of each member is constructed by using the numerical assembly method similar to the finite element method so as to obtain the characteristic equation of rigid-frame bridge. Furthermore, the natural frequency and mode shape of the whole rigid-frame bridge are calculated by using the algorithm of Wittrick-Williams. Finally, the dynamic characteristic test of Yong-an bridge and the numerical calculation of the rigid-frame bridge are carried out to verify the generality and accuracy of the proposed method. The results indicate that the change of temperature will lead to the secondary internal force and the change of Young’s modulus, which together affect the modal characteristics of the structure, and the change of natural frequency caused by the change of Young’s modulus is greater than that caused by the secondary internal forces. In addition, there is a negative correlation between temperature and natural frequency of the rigid-frame bridge, and different temperature gradient modes also have certain influence on the mode shape of rigid-frame bridge.

Determination of five 3-alkyl-2-methoxypyrazines employing HS-SPME-GC-NPD: Application in evaluation of off-flavor of South American wines

High concentrations of 3-alkyl-2-methoxypyrazines (MPs) in wines can affect the quality and contribute to the rejection of consumers. This work proposes the determination of five MPs in nine wine samples from South America using headspace solid phase microextraction with gas chromatography coupled to nitrogen-phosphorus detector. The separation of the analytes was performed with a HP 5 capillary column in temperature gradient mode and injection in splitless mode. The optimization of the main parameters gives the optimal extraction conditions: Divinylbenzene-Carboxen-Polydimethylsiloxane fiber, sample dilution ratio of 1:3 with water, salt addition of 30 % (w/v) sodium chloride, extraction time of 30 min and extraction temperature of 35 °C. The main parameters of merit of the method were evaluated, showing coefficients of determination greater than 0.995, limits of detection ranging from 6.10–31.2 ng L−1, recovery from 75.2–118% and precisions with values less than 20 %. The validation parameters obtained and the concentration levels of ng L−1 achieved characterize this method as efficient for the determination of these off-flavors in wine. From the nine analysed wines, 3-ethyl-2-methoxypyrazine and 3-isobutyl-2-methoxypyrazine were identified and quantified. The levels are well above the odor detection threshold, thus contributing to generation of off-flavor in the aroma and flavor of these wines.

Fractionation of chain walking polyethylene and elucidation of branching, conformation and molar mass distributions

State-of-the-art liquid interaction chromatography (IC) allows separation of macromolecules according to chemical composition (CC), functionality or molecular topology in contrast to size-based approaches such as size exclusion chromatography (SEC), which has its limitations in distinguishing chemical structures. Yet, for macromolecules with multivariate molecular distributions, online identification and characterization of distinct components in bulk samples is a considerable challenge. A useful approach to narrow down the complexity of a given sample is preparative molar mass fractionation (pMMF) that provides fractions in mg or g scale, which can be subjected to further advanced analysis to elucidate the physical and structural properties of the sample. In this study, novel chain-walking polyethylenes (CWPE), which differ substantially in macromolecular architecture, are fractionated using pMMF. Using IC in temperature and solvent gradient modes (TGIC, SGIC), the pMMF fractions are separated according to branching topology. Quadruple-detector high temperature SEC is carried out to determine the physical properties and study the MM-dependent structural transformation of CWPE. A detailed branching analysis was carried out by means of nuclear magnetic resonance. Two-dimensional liquid chromatography (LC) hyphenating IC and SEC provides comprehensive bivariate correlations between MM and molecular topology.

ASPECTS OF DETERMINATION OF THIODIACETIC ACID IN URINE AS BIOMARKERS FOR INDUSTRIAL EXPOSURE TO VINYL CHLORIDE AND 1,2 -DICHLOROETHANE

There was developed and certified the analytical method for the determination of thiodiacetic acid in the urine in the range of from 0.1 to 10µg/cm3. The sample preparation is based on the execution of derivatization of methanol in the presence of boron trifluoride (10 wt%) followed by liquid-liquid microextraction with dimethyl ester the acid. Derivatization reaction was carried out for 15 min at 80°C. Gas chromatographic analysis was performed on a capillary column HP-5ms under the temperature gradient and splitless modes. Mass spectrometric detection occurred during the registration of selective ions (SIM). Identification of derivatives of thiodiacetic acid on the mass chromatograms was carried out by the absolute retention time (10.36 min) and the ratio of peak intensities of detected ions. The random error in the determination of component and the accuracy of the expanded uncertainty does not exceed 2 and 25%, respectively. There was made a comparative evaluation of the content of thiodiacetic acid in the urine of workers of main shops production of PVC with persons of the control group, not involved in the production. The results can be used for the identification of the fact of the exposure to toxic substances and assessment of the level of exposure and biomonitoring, as a component of health interventions for the prevention of occupational and production-related diseases.

Temperature Gradient Elution and Superheated Eluents in Chip-HPLC

Utilizing temperature as an active parameter for optimization in chip-based liquid chromatography is an important step toward high-speed and high-efficiency separations on the microscale. A device including a low thermal mass micro thermostat and a microfluidic glass chip as central elements were designed and evaluated for maximal heating performance of up to 4.7 °C s-1 at up to 200 °C. With this enabling technology, high-speed separations in temperature gradient mode were performed both in common reversed-phase eluents and environmental friendly ethanol-based alternatives.

Role of substituents in cyclodextrin derivatives for enantioselective gas chromatographic separation of chiral terpenoids in the essential oils of Mentha spicata.

Enantioselective GC-FID and enantioselective GC-MS have been utilized under temperature gradient mode with differently substituted heptakis- and octakis-cyclodextrins to achieve the resolution of chiral terpenoids in the essential oil of indigenously grown cultivars of Mentha spicata. Modified cyclodextrins were derivatized in GC column for the separation of chiral terpenoids. A 2,3-diethyl-6-tert-butyldimethylsilyl-β-cyclodextrin doped into 14% cyanopropylphenyl/86%dimethylpolysiloxane (TBDE-β-CD) showed good enantioselectivity for all the studied chiral compounds excluding carvone. Carvone enantiomers were well resolved in 2,3-diacetoxy-6-tert-butyldimethylsilyl-β-cyclodextrin column (TBDA-β-CD) with enantioseparation (Es) of 1.006. A TBDE-β-CD provides maximum enantiomeric separation for β-pinene (Es 1.038), sabinene (Es 1.051), limonene (Es 1.045), isomenthone (Es 1.029) and α-terpineol (Es 1.014). Furthermore, enantiomer elution order reversal was observed for sabinene, menthone, terpinen-4-ol and menthol while changing from β- to γ-cyclodextrin phase. Carvone exhibits enantiomer elution order reversal by changing substituents i.e., methyl to acetyl at 2- & 3- position of the cyclodextrin derivative. Chiral constituents such as (+)-isomenthone, (-)-menthone, (1R,2S,5R)-(-)-menthol and (4S)-(+)-piperitone exist as a single enantiomer with >99% excess. Existence of (R)-(+)-limonene and (S)-(+)-carvone enantiomers has been proven first time in M. spicata essential oils and can be used as the marker for Indian origin.

Determination of Henry Constants of Azelnidipine Enantiomers on Chiralpak AD Column at Different Temperatures

Simulated moving bed (SMB) chromatographic separation has become a highly promising method for chiral separation due to the less solvent consumption and efficient utilization of stationary phase. As reported, Azelnidipine exists two isomeric forms, it is necessary to product azelnidipine single enantiomer for medical safety and drug developmen. However, the separation of azelnidipine enantiomers on SMB is complex, requiring many operating parameters. And the SMB processes with temperature gradient (non-isotherm) mode may have significant advantages over the traditional isothermal mode. In this article, the Henry constants of azelnidipine enantiomers were determined with pulse experiments on Chiralpak AD column at different temperatures. It provided important references for the production of azelnidipine single enantiomer with non-isotherm SMB.

Numerical Simulation of Toroidal Momentum Transport with Neutral Beam Injection on Tokamak

In modern tokamaks, the toroidal plasma rotation has been demonstrated to play a beneficial role in the fusion plasmas. In this paper, the simulation of the toroidal momentum sources, momentum diffusivity χϕ and plasma rotation with neutral beam injection (NBI) on EAST tokamak have been carried out by using MMM95 and GLF23 anomalous transport models in ONETWO and NUBEAM codes. The physical characteristics of the toroidal momentum transport for the different plasma density and temperature are analyzed. According to the simulation results, the main momentum sources for NBI are from the collision and \(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {J} \times \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B}\) (\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {J}\) is the plasma current and \(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B}\) is the magnetic field). The former is most in the center and the latter is primary in the middle of the plasma. Also, for EAST, χϕ is about twice of the thermal diffusivity χi according to the MMM95 model in the like H-mode. Moreover, because of the enhancement of collision and deposition, the density tends to improve the total beam torque. Nevertheless, to keep the neutrality of the plasma, the density reduces the plasma rotation by increasing the ion density and the momentum diffusivity according to the MMM95 and GLF23 anomalous transport models. In addition, in the L-mode plasma, although the increasing temperature displays little influence on the beam torque, it improves the momentum diffusivity because of the ion temperature gradient (ITG) mode in the anomalous transport and reduces the plasma rotation. The results will be valuable for the experimental research of the momentum transport on EAST or ITER.

A Multi Water Bag model of drift kinetic electron plasma

A Multi Water Bag model is proposed for describing drift kinetic plasmas in a magnetized cylindrical geometry, relevant for various experimental devices, solar wind modeling... The Multi Water Bag (MWB) model is adapted to the description of a plasma with kinetic electrons as well as an arbitrary number of kinetic ions. This allows to describe the kinetic dynamics of the electrons, making possible the study of electron temperature gradient (ETG) modes, in addition to the effects of non adiabatic electrons on the ion temperature gradient (ITG) modes, that are of prime importance in the magnetized plasmas micro-turbulence [X. Garbet, Y. Idomura, L. Villard, T.H. Watanabe, Nucl. Fusion 50, 043002 (2010); J.A. Krommes, Ann. Rev. Fluid Mech. 44, 175 (2012)]. The MWB model is shown to link kinetic and fluid descriptions, depending on the number of bags considered. Linear stability of the ETG modes is presented and compared to the existing results regarding cylindrical ITG modes [P. Morel, E. Gravier, N. Besse, R. Klein, A. Ghizzo, P. Bertrand, W. Garbet, Ph. Ghendrih, V. Grandgirard, Y. Sarazin, Phys. Plasmas 14, 112109 (2007)].

Fractionation of Ethylene/1-Octene Copolymers by High-Temperature Thermal Gradient Interaction Chromatography

High-temperature thermal gradient interaction chromatography (HT-TGIC) was recently introduced into the area of polyolefin analysis. This new technique uses commercially available Hybercarb columns to separate polyolefin chains based on their interaction with the porous graphitic carbon stationary phase in a temperature gradient mode. In this paper, a systematic study of HT-TGIC operation conditions is presented for ethylene/1-octene copolymers and their blends. One of the objectives of this investigation is to identify the best set of conditions that maximize peak separation of copolymers in a binary blend. Although the chromatograms of individual resins and their blends are independent of the cooling rate, it will be shown that sample volume (column loading) and heating rate during the elution cycle affect the peak separation of the components in binary blends.

Inward particle transport at high collisionality in the Experimental Advanced Superconducting Tokamak

We have made the first drift wave study of particle transport in the Experimental Advanced Superconducting Tokamak (Wan et al., Nucl. Fusion 49, 104011 (2009)). The results reveal that collisions make the particle flux more inward in the high collisionality regime. This can be traced back to effects that are quadratic in the collision frequency. The particle pinch is due to electron trapping which is not very efficient in the high collisionality regime so the approach to equilibrium is slow. We have included also the electron temperature gradient (ETG) mode to give the right electron temperature gradient, since the Trapped Electron Mode (TE mode) is weak in this regime. However, at the ETG mode number ions are Boltzmann distributed so the ETG mode does not give particle transport.

Turbulent impurity transport modeling for Alcator C-Mod

AbstractTurbulent particle transport is investigated with a quasilinear theory that is motivated by the boron impurity transport experiments in the Alcator C-Mod. Eigenvalue problems for sets of reduced fluid equations for multi-component plasmas are solved for the self-consistent fluctuating field vectors composed of the electric potential φ, the main ion density δni, the impurity density δnz and the ion temperature fluctuation δTi. For Alcator C-Mod parameters, we investigate two drift wave models: (1) the density-gradient-driven impurity drift wave and (2) the ion-temperature-gradient-driven ion temperature gradient (ITG) mode. Analytic and numerical results for particle transport coefficients are derived and compared with the transport data and the neoclassical theory. We explore the ability of the model to explain impurity density profiles in three confinement regimes: H-mode, I-mode and internal transport barrier (ITB) regime in C-Mod. Related experiments reported on the Large Helical Device are briefly discussed.

Claudin-11 expression increased in spermatogenic defect in human testes

Expression of claudin-11, which builds up blood-testis barrier (BTB), was increased in decreased spermatogenesis, including in hypospermatogenesis, spermatocytic and maturation arrest, and Sertoli cell only (SCO) testes. Increased claudin-11 immunoreactivity was observed at the inter-Sertoli tight junctions in maturation arrest and in the cytoplasm of Sertoli cells in SCO. The late spermatogenic wave may negatively regulate claudin-11 gene activation and the subcellular localization of claudin-11 in Sertoli cells, thus altering the BTB in the human testis.

A Novel Method Of Transport Barrier Formation

A novel technique is proposed for creating transport barriers by the rf waves. This is that the transport barriers can be created by the rf induced ponderomotive force itself and no rf induced flow shear generation is necessary. It is demonstrated that the ponderomotive force of the rf waves can stabilize the ion temperature gradient (ITG) mode, considered nowadays as the dominant source of anomalous energy losses in the low confinement (L) mode. It is also shown that this stabilization can be achieved for rather modest values of the rf power and hence should be easily obtained in actual experiments.

Ion temperature gradient-driven dipolar vortices in dusty plasmas

The nonlinear dynamics of the ion temperature gradient (ITG) mode is investigated in a dusty plasma assuming the dust grains to be tiny and highly charged. The electrostatic drift waves cannot be ignored in the linear dispersion relation if polarization drifts of ions and dust are taken into account. The dipolar vortices are predicted to be formed in the nonlinear regime. The relevance of this study to space and astrophysical plasmas is pointed out.

A Spectral Global Gyrokinetic Approach to Plasma Linear Microinstability Analysis

With the term microinstabilities, we indicate a class of plasma drift waves such as the ion temperature gradient (ITG) mode, the trapped electron mode (TEM), and the electromagnetic Alfvénic ion temperature gradient (AITG) mode. They are usually driven by spatial gradients in the plasma and they are held responsible for anomalous transport and enhanced heat flux in tokamaks. Their understanding is therefore crucial for the development of magnetically confined plasma fusion devices. Our approach is based on the gyrokinetic model (Hahm 1988) for particle dynamics. The gyrokinetic nonlinear Vlasov equation, in the presence of an electromagnetic perturbation (Brizard 1989, 1995), is derived using Lie perturbation theory (Cary and Littlejohn 1983) to average out the fast particle motion around the gyrocenter. We have linearized the gyrokinetic Vlasov equation and added the quasi‐neutrality equation and Ampère's law, providing closure to the system. A temporal spectral formulation is used, ensuring the absence of numerical instabilities due to high frequency modes. The equations are simplified with a large aspect ratio approximation for an axisymmetric toroidal configuration. The fields are expanded in a Fourier series in the three spatial directions (radial, poloidal, and toroidal) reducing the problem in a matrix form. The code EM‐GLOGYSTO (Brunner et al. 1998; Falchetto et al. 2003; Joint Varenna‐Lausanne International Workshop 2002) has been developed to look at its solutions. Recently, we have included in the model an electrostatic equilibrium potential in order to provide E×B sheared flow. The code has been optimized for running in a parallel environment using MPI routines, and it allows us to study frequencies, growth rates, and mode structures of electromagnetic microinstabilities. Results on an AITG mode are shown to illustrate these features.

A full radius gyrokinetic stability analysis for large aspect ratio finite-β tokamaks

Linear, fully gyrokinetic, full radius (global), large aspect ratio studies of Alfvén-ion temperature gradient mode (AITG) or kinetic ballooning modes or beta-induced Alfvén eigenmodes considering only “passing” species is presented. Effects hitherto completely neglected in a full radius approach such as B∥-fluctuations and the ones which have been treated partly [Phys. Plasmas 10, 1424 (2003)] such as Shafranov shifts are included. To this end, an existing code EM-GLOGYSTO has been upgraded to incorporate these effects. Among others, the most interesting results include: (i) For relatively large positive magnetic shear ŝ [1.25<ŝ<4.25, ŝ=d ln qs/d ln ρ, where qs(ρ) is safety factor and ρ minor radius], B∥ fluctuations have a benign effect on AITG growth rates and for positive but small shear (0.0<ŝ<2.7), B∥ fluctuations are too weak to play any crucial role. (ii) In the later case, inclusion of Shafranov shift leads to the following: (a) Growth rates without Shafranov shift effects are in general larger than those including Shafranov shift; (b) nonmonotonous dependence of growth rates and frequencies on β=2μ0NTi/B02; (c) the presence of multiple eigenmodes with competing growth rates for same values of β; (d) no sign of complete stabilization with increasing β. Finally eigenmode structures [φ,A∥,Aθ] with and without Shafranov shift are reported. The growth rates and frequencies thus obtained may serve as estimates of transport coefficients and for future bench marking of the (then) global electromagnetic, gyrokinetic, time evolution codes (particle-in-cell or otherwise).

Burning Plasma Confinement Projections and Renormalization of the GLF23 Drift-Wave Transport Model

Fusion power predictions are presented using the GLF23 drift-wave transport model for several next-step tokamak designs including ITER, FIRE, and IGNITOR. The GLF23 model has been renormalized using recent gyrokinetic simulations and a database of nearly 50 H-mode discharges from three different tokamaks. The renormalization reduces the ion temperature gradient/trapped electron mode (ITG/TEM)-driven transport by a factor of 3.7 while electron temperature gradient (ETG) mode transport is increased by a factor of 4.8 with respect to the original model. Using the renormed model, the fusion power performance is uniformly assessed, and the pedestal requirements are summarized for each device. The renormed model is still quite stiff and yields somewhat more optimistic predictions for next-step burning plasma experiments. The consequences of stiff transport in the plasma core are discussed. A fusion fit formula is derived whereby the GLF23 results follow a universal stiff model curve for the normalized fusion power versus pedestal temperature.

Characterization of complex mixtures of polyglycerol fatty acid esters using temperature and solvent gradients in packed capillary LC

AbstractA highly complex sample of polyglycerol fatty acid esters has been characterized using both temperature gradient and solvent gradient reversed‐phase packed capillary LC coupled to ELSD and ESI‐TOF‐MS. The techniques showed fairly similar performance in terms of selectivity and efficiency, providing a nice separation of not only the polyglycerol mono‐, di‐, tri‐ and tetra‐fatty acid esters, but also the non‐reacted polyglycerols. The different groups were identified by coupling the packed capillary LC system to a TOF‐MS using an electrospray interface, although the identification of the latest eluting groups in the temperature gradient separation was hampered due to significant column bleeding at elevated column temperatures. By calculating the peak areas in the ELSD chromatograms, the PGE sample was estimated to contain 20.2 ± 0.4 and 22.6 ± 0.5% non‐reacted polyglycerols, 44.4 ± 1.9 and 34.1 ± 1.4% mono‐fatty acid esters, 26.2 ± 1.5 and 27.9 ± 1.7% di‐fatty acid esters, 7.7 ± 0.7 and 12.6 ± 1.0% tri‐fatty acid esters, and 1.4 ± 0.2 and 2.8 ± 0.3% tetra‐fatty acid esters in temperature and solvent gradient mode (n = 3), respectively. The intra‐day precision of the retention times was 0.5–1.4% (n = 3) in the temperature gradient mode, while it was 0.3–1.7% (n = 3) in the solvent gradient mode.

Novel column oven concept for cold spot large volume sample enrichment in high throughput temperature gradient capillary liquid chromatography

AbstractA novel column oven concept with an incorporated cold spot has been tailored for use in capillary liquid chromatography, allowing efficient injection of increased sample volumes by sub‐ambient temperature‐promoted solute enrichment. The column oven system consists of two horizontally connected temperature zones surrounding the packed capillary column. The oven is designed to allow horizontal sliding of the capillary column inside the column oven housing, enabling rapid transportation of the column inlet between the two temperature zones. This design eliminates the time consuming process of re‐cooling the oven after a temperature gradient, which is associated with other column ovens, providing the possibility of high throughput analyses. The cold inlet zone of the oven was operated at sub‐ambient temperatures where elution is suppressed to allow enrichment of large volumes of solutes dissolved in solvents usually associated with high eluting properties. The hot column oven zone allowed temperature‐programmed gradient action, but could also be operated isothermally resulting in a temperature step gradient. The oven was evaluated using the antioxidants Irgafos 168, Irgafos 168‐phosphate, and Irganox 1076 as model compounds using UV‐detection. A 3.5 μm Kromasil C18 0.25 mm ID×20 cm capillary column was used, while the mobile phase and the sample solvent was neat acetonitrile. The flow rate was 5 μL/min. Within‐assay precision and between‐assay precision of peak areas were in the range of 4.3–8.2% relative standard deviation (RSD). The retention time RSD in temperature gradient mode was 2%. The method was linear in the investigated range of 5–100 ng, displaying a correlation coefficient of 0.9995.