Evershed and Counter-Evershed Flows in Sunspot MHD Simulations

Siu-Tapia, A. L.,Rempel, M.,Lagg, A.,Solanki, S. K. American Astronomical Society 2018 The Astrophysical journal Vol.852 No.2

<P>There have been a few reports in the literature of counter-Evershed flows observed in well-developed sunspot penumbrae, i.e., flows directed toward the umbra along penumbral filaments. Here, we investigate the driving forces of such counter-Evershed flows in a radiative magnetohydrodynamic simulation of a sunspot, and compare them to the forces acting on the normal Evershed flow. The simulation covers a timespan of 100 solar hours and generates an Evershed outflow exceeding 8 km s(-1) in the penumbra along radially aligned filaments where the magnetic field is almost horizontal. Additionally, the simulation produces a fast counter-Evershed flow (i.e., an inflow near tau = 1) in some regions within the penumbra, reaching peak flow speeds of similar to 12 km s(-1). The counter-Evershed flows are transient and typically last a few hours before they turn into outflows again. By using the kinetic energy equation and evaluating its various terms in the simulation box, we found that the Evershed flow occurs due to overturning convection in a strongly inclined magnetic field, while the counter-Evershed flows can be well-described as siphon flows.</P>

Organic solvent-free catalytic hydrogenation of diene-based polymer nanoparticles in latex form: Mass transfer of hydrogen in a semibatch process

Hui Wang,Garry L. Rempel 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.25 No.-

The mass transfer process of hydrogen during hydrogenation of diene-based latex nanoparticles remains as one of the most discussed and sought-after research topics particularly for potential commercial processes carried out in a semibatch reaction mode. In this research, in-house prepared nitrile butadiene rubber (NBR) nanoparticle latices were prepared as the substrate for the subsequent hydrogenation experiments. The mass transfer pathway of hydrogen molecules in a gas (hydrogen)–liquid (water)– solid (polymer) three phase hydrogenation system under semibatch operation was examined, wherein the hydrogen transports from the bulk gas phase to an intermediate liquid phase, and then to the solid polymer phase. The mass transfer of hydrogen across the interfacial surfactant layer at the water/ polymer interface was studied. A one-dimensional, moving boundary model was developed to describe the diffusion of hydrogen into the polymer nanoparticles by incorporating the level of bound hydrogen in the aqueous phase and the mass diffusivity of hydrogen in the polymer phase. Our results show that the mass transfer of hydrogen cannot account for the rate-determining step of NBR latex hydrogenation. This research report provides some further insight into the mass transfer of hydrogen during catalytic latex hydrogenation.

WAVES AS THE SOURCE OF APPARENT TWISTING MOTIONS IN SUNSPOT PENUMBRAE

Bharti, L.,Cameron, R. H.,Rempel, M.,Hirzberger, J.,Solanki, S. K. IOP Publishing 2012 The Astrophysical journal Vol.752 No.2

<P>The motion of dark striations across bright filaments in a sunspot penumbra has become an important new diagnostic of convective gas flows in penumbral filaments. The nature of these striations has, however, remained unclear. Here, we present an analysis of small-scale motions in penumbral filaments in both simulations and observations. The simulations, when viewed from above, show fine structure with dark lanes running outward from the dark core of the penumbral filaments. The dark lanes either occur preferentially on one side or alternate between both sides of the filament. We identify this fine structure with transverse (kink) oscillations of the filament, corresponding to a sideways swaying of the filament. These oscillations have periods in the range of 5-7 minutes and propagate outward and downward along the filament. Similar features are found in observed G-band intensity time series of penumbral filaments in a sunspot located near disk center obtained by the Broadband Filter Imager on board the Hinode. We also find that some filaments show dark striations moving to both sides of the filaments. Based on the agreement between simulations and observations we conclude that the motions of these striations are caused by transverse oscillations of the underlying bright filaments.</P>

Meta-Analysis: Association Between Wrist Posture and Carpal Tunnel Syndrome Among Workers

유동희,Allan H. Smith,David Rempel 한국산업안전보건공단 산업안전보건연구원 2014 Safety and health at work Vol.5 No.1

BackgroundCarpal tunnel syndrome (CTS) is a common work-related peripheral neuropathy. In addition to grip force and repetitive hand exertions, wrist posture (hyperextension and hyperflexion) may be a risk factor for CTS among workers. However, findings of studies evaluating the relationship between wrist posture and CTS are inconsistent. The purpose of this paper was to conduct a meta-analysis of existing studies to evaluate the evidence of the relationship between wrist posture at work and risk of CTS. MethodsPubMed and Google Scholar were searched to identify relevant studies published between 1980 and 2012. The following search terms were used: “work related”, “carpal tunnel syndrome”, “wrist posture”, and “epidemiology”. The studies defined wrist posture as the deviation of the wrist in extension or flexion from a neutral wrist posture. Relative risk (RR) of individual studies for postural risk was pooled to evaluate the overall risk of wrist posture on CTS. ResultsNine studies met the inclusion criteria. All were cross-sectional or case–control designs and relied on self-report or observer's estimates for wrist posture assessment. The pooled RR of work-related CTS increased with increasing hours of exposure to wrist deviation or extension/flexion [RR = 2.01; 95% confidence interval (CI): 1.646–2.43; p < 0.01: Shore-adjusted 95% CI: 1.32–2.97]. ConclusionWe found evidence that prolonged exposure to non-neutral wrist postures is associated with a twofold increased risk for CTS compared with low hours of exposure to non-neutral wrist postures. Workplace interventions to prevent CTS should incorporate training and engineering interventions that reduce sustained non-neutral wrist postures.

Synthesis and Properties of UV Curable Waterborne Polyurethane Acrylate Nanocomposite Films Based on the Surface Modification of γ-Al₂O₃

Wen Ran,Shaohui Lin,Garry L. Rempel,Qinmin Pan 한국고분자학회 2017 폴리머 Vol.41 No.3

Waterborne polyurethane acrylate/surface-modified γ-Al₂O₃ (WPUA/SAl₂O₃) nanocomposite films were prepared via a UV-initiated free radical photopolymerization system composed of nanocomposite emulsion, reactive diluents and a photoinitiator. To improve the compatibility of inorganic and organic phases, γ-Al₂O₃ nanoparticles were surface-modified by γ-methacryloxypropyl trimethoxysilane and combined with a WPUA matrix. The WPUA oligomer was initially prepared by step-growth polymerization, and the content of hydrophilic chain extender, dimethylolpropionic acid (DMPA) was varied to investigate its effect on the properties of the oligomer emulsion. Performance of nanocomposite films with various loadings of SAl₂O₃ was evaluated by TGA and DSC, water uptake/swelling degree, surface wettability, tensile strength and elongation at break, etc. The results revealed that thermostability of the nanocomposite film was reinforced compared with the WPUA matrix. Swelling capacity and mechanical strength were also improved due to the increase of crosslinking density. Moreover, the optimum content of DMPA for oligomer synthesis was 5%.

Fabrication of Poly(styrene-co-acrylic acid)/Polystyrene Anisotropic Nanoparticles via Seeded Emulsion Polymerization

Feng Zhou,Shaohui Lin,Garry L. Rempel,Qinmin Pan 한국고분자학회 2017 폴리머 Vol.41 No.6

Anisotropic nanoparticles have potentially various important applications, especially in 3D printing materials, binders and phase compatible agents, for which it is essential that the components and the structures are well designed and controlled. This paper investigated nanoparticles consisting of two lobes with opposite properties. As a model system, synthesis of poly(styrene-co-acrylic acid)/polystyrene anisotropic nanoparticles was studied and the effects of temperature, surfactant amount, inhibitors, and initiators for the involved polymerization procedures, and the swelling temperature, and swelling ratio for making the second lobe, on the morphology and size of the produced particles , were investigated. As a result, the anisotropic nanoparticles with uniform asymmetry, one lobe with hydrophilicity and the other with hydrophobicity, were successfully realized. The apparent size of the nanoparticles was below 200 nm, and the strategies for achieving various morphologies, such as snowman-like, potato-like and dumbbell-like, were established. The anisotropic nanoparticles achieved in this study are very useful in the 3D material development that is involved in our another research.

Meta-Analysis: Association Between Wrist Posture and Carpal Tunnel Syndrome Among Workers

You, Doohee,Smith, Allan H.,Rempel, David Occupational Safety and Health Research Institute 2014 Safety and health at work Vol.5 No.1

Background: Carpal tunnel syndrome (CTS) is a common work-related peripheral neuropathy. In addition to grip force and repetitive hand exertions, wrist posture (hyperextension and hyperflexion) may be a risk factor for CTS among workers. However, findings of studies evaluating the relationship between wrist posture and CTS are inconsistent. The purpose of this paper was to conduct a meta-analysis of existing studies to evaluate the evidence of the relationship between wrist posture at work and risk of CTS. Methods: PubMed and Google Scholar were searched to identify relevant studies published between 1980 and 2012. The following search terms were used: "work related", "carpal tunnel syndrome", "wrist posture", and "epidemiology". The studies defined wrist posture as the deviation of the wrist in extension or flexion from a neutral wrist posture. Relative risk (RR) of individual studies for postural risk was pooled to evaluate the overall risk of wrist posture on CTS. Results: Nine studies met the inclusion criteria. All were cross-sectional or case-control designs and relied on self-report or observer's estimates for wrist posture assessment. The pooled RR of work-related CTS increased with increasing hours of exposure to wrist deviation or extension/flexion [RR = 2.01; 95% confidence interval (CI): 1.646-2.43; p < 0.01: Shore-adjusted 95% CI: 1.32-2.97]. Conclusion: We found evidence that prolonged exposure to non-neutral wrist postures is associated with a twofold increased risk for CTS compared with low hours of exposure to non-neutral wrist postures. Workplace interventions to prevent CTS should incorporate training and engineering interventions that reduce sustained non-neutral wrist postures.

Kinetics and modeling of methyl methacrylate graft copolymerization in the presence of natural rubber latex

Tanita Sirirat,Terdthai Vatanatham,Nanthiya Hansupalak,Garry Llewellyn Rempel,Wanvimon Arayapranee 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.5

A graft copolymerization model for using cumene hydroperoxide/tetraethylenepentamine (CHPO/TEPA) as a redox initiator was developed to describe the grafting of methyl methacrylate onto natural rubber latex as a coreshell particle. The model allows estimating the effects of the initiator concentration, monomer-rubber weight ratio, and temperature on the properties of graft product, e.g., % grafting efficiency and the % monomer composition in the graft copolymer and free polymer. The rate expressions of polymer chain formation are developed by taking into account a reduction of CHPO by TEPA and a population event of radicals between core/shell phases. The parameter estimation is performed to find the kinetic parameters. Validation with experimental results demonstrates a good applicability of the proposed model. The model results reveal that the formation of grafted polymer chains rather form by the chain transfer reaction to rubber chains from homopolymer radicals and the initiation reaction of cumyloxy radicals to rubber chains.

Adsorption Behaviors and Mechanism of Single/Multi-Metals by Ion Exchange Resins

Xinping Qian,Shaohui Lin,Xianshe Feng,Garry L. Rempel,Henry Grace,Qinmin Pan 한국고분자학회 2019 폴리머 Vol.43 No.6

Adsorption of Fe(Ш), Co(II), Cu(II), Zn(II) and K(I) by strong acid resins, Dowex 50WX2 200-400 (H) and Amberlite IRP-69, was studied to investigate the adsorption behaviors and mechanism in single-metal and multi-metal systems. The results showed that 99.9% Fe(III) can be removed by Dowex 50WX2 200-400 (H) in 100 min ([Fe(Ш)] < 40 mg/L, resin amount = 50 mg, pH = 3.0, 60 ºC). Mechanism studies revealed that Langmuir model and pseudo-second- order kinetic equation illustrate better fit for the adsorption of Fe(Ш). Furthermore, the investigations on multi-metal adsorption indicated that resins display a similar adsorption ratio for the same-valence metal ions (Co(II) = Cu(II) = Zn(II)), and a more selective adsorption for high-valence metal ions than low-valence metal ions (Fe(III) > Co(II) > K(I)). The above results can be used for the treatment of wastewater and the recovery of metals from the spent catalysts.

Reassessing Alberta Stroke Program Early CT Score on Non-Contrast CT Based on Degree and Extent of Ischemia

Johanna M. Ospel,Bijoy K. Menon,Martha Marko,Arnuv Mayank,Aravind Ganesh,Raul G. Nogueira,Ryan A. McTaggart,Andrew M. Demchuk,Alexandre Y. Poppe,Jeremy L. Rempel,Manish Joshi,Mohammed A. Almekhlafi,Ch 대한뇌졸중학회 2021 Journal of stroke Vol.23 No.3

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