Magnetic Mixer Research Articles

Study of concentric, eccentric and split type magnetic membrane micro-mixers

Electromagnetically driven elastic magnetic microfluidic mixers were investigated for their performance in air, water and glycerol filled chambers. They were fabricated by embedding flexible magnets in polydimethylsiloxane (PDMS) membrane. At a driving frequency of 100 Hz, oscillating fluid flow was induced and mixing was achieved. Three designs were fabricated and studied: a) concentric type with the magnetic material in the center of the membrane, b) eccentric type with the magnetic material offset from the center of the membrane and c) split type with two regions of magnetic materials with opposing polarities. The split configuration provides additional fluid folding, facilitating mixing of the 20 μL fluorescent dye in 60 μL of solvent. Simulation and experimental results show that the eccentric and split designs were able to achieve a 20–30% reduction in mixing time compared to the concentric design. At the same magnetic flux density, the eccentric type design exhibited the greatest deflection, explaining the better mixing achieved over the concentric type design. The split type design, having the lowest deflection, was able to perform better and more consistently than the eccentric type design by creating a “micro rocker mixer” effect. We postulated that the shapes of the deflection profiles in the eccentric and split designs contributed to the mixing efficiency by promoting better chaotic advection than the concentric design.

Investigation of Electrical Conductivity of Polyacrylonitrile (PAN) Nanofibers/Nano Particul (Ag,Cu, CNT and GNR)

In this study 1% Ag (silver), Cu (copper), CNT (carbon nanotube) and graphene nanoribbon (GNR) nanoparticle reinforced PAN fibers were prepared and the effects of nanoparticle reinforcements upon electrical conductivity were investigated. In experimental study, graphene nanoribbon powders were produced from multiwalled carbon nanotube (MWCNT) through using the chemical approach of Hummers method. Fiber layer was dissolved at room temperature in magnetic mixer with Polyacrylonitrile (PAN) and Dimethil Formamide (DMF) which was at the rate of 10 % by mass. Thus, a viscou gel solution was obtained then nanoparticles were added to the PAN/DMF solution and the solution was vigorously stirred for one hour at room temperature. After stirring that solution was continued for 15 m in ultrasonic bath. The polymeric solution was first transferred to a 5 mL syringe, which was connected to a capillary needle with an inside diameter of 0,8 mm. A copper electrode was attached to the needle, a DC power supply produces 25 kV against a grounded collector screen distant 15cm. With the syringe pump set at 2 mL/h, the electric force overcomes the surface tension of the solution at the capillary tip, and a jet emerges. Produced fibers were collected on the rotary collector which spins at 250 rpm. Nanofiber was dried at 60 °C for 12 h in vacuum oven. Eventually, nanofiber of polyacrylonitrile (PAN) reinforced by metallic nanoparticles and graphene nanoribbon (GNR) were prepared by electro spinning process. Electrical conductivity of the obtained nanofiber were studied by measuring the electrical resistance thanks to home-made plate electrodes.

Change of the Diffusion Reflection Spectra of Coatings Based on Modified Photoluminophore Nanoparticles and Intended for Light-Emitting Diodes of the Visible Range After Irradiation in Vacuum by Ultraviolet Light or Electrons

Photoluminophores intended for light-emitting diodes of visible range while in service can be subjected to the action of radiation of various types. In this case, their optical properties will be deteriorated as a result of formation of defects and color centers. One of the methods of increasing the radiation stability of various powders to the action of radiation of different types is their modification by nanoparticles that being deposited on the surface of grains and granules, form relaxation centers for these defects [1, 2]. Therefore, the application of the given method can be useful for the development of photoand radiation stable luminophores. In the present work, the influence of the modification by ZrO2 and Al2O3 nanoparticles of the FLZh-7 photoluminophore representing gallium-gadolinium garnet (Gd3Ga5O12) activated by cerium (Сe) in the ratio 96.7:2.3 [3, 4] intended for light-emitting diodes of the visible range on the change of the diffusion reflection spectra after irradiation in vacuum by quanta of the solar spectrum or by accelerated electrons is investigated. The luminophore was modified by 0.5 mass% of ZrO2 or Al2O3 nanoparticles. Then the KO-859 varnish was added to the luminophore in the ratio 30:70 and was mixed for 2 h in a magnetic mixer with addition of a solvent. Test samples were prepared by deposition of the paste so obtained on aluminum substrates 28 mm in diameter and drying at room temperature. The diffusion reflection spectra were recorded in vacuum of 10 Torr; then the samples were irradiated by quanta of the solar spectrum (a DKSR-3000M xenon arc lamp) or by electrons with energy of 30 keV and after each irradiation period, the spectra were registered in situ in vacuum [5]. The difference spectra (Δρλ) obtained by subtraction of the spectra after irradiation (ρλt) from the spectra before irradiation (ρλ0) and equated to the absorption spectra induced by irradiation were then registered. In the absorption spectra of the unmodified luminophore, bands at 400–440 and 520 nm were registered. The intensities of these bands increased with time of irradiation by quanta of the solar spectrum or with electron fluence (Fig. 1). A comparison of absolute values Δρ in the absorption band maximum at 400 nm demonstrated that they were large for all three samples. The modification leads to a decrease in the intensity of these bands. To estimate the photoand radiation stability, we have introduced the coefficient (η) characterizing the efficiency of modification by nanoparticles defined by the ratio of the Δρ value for coatings based on unmodified luminophore (Δρi) to the Δρ value for coatings based on modified luminophores (ΔρZr and ΔρAl): ηZr =Δρi/ΔρZr and ηAl = Δρi/ΔρAl (Table 1).

English

The novel device for measuring characteristics of the process that takes place when hydrocarbon liquids are subjected to elevated temperatures is described. The measuring cell has the form of a loop in which circulation is induced by a turbine stirrer. The stirrer contains magnets built into its blades, enabling mixing by a magnetic mixer positioned below the cell. No moving part protrudes from the cell. The fouling process takes place at the hot-wire probe positioned at the centre of the liquid stream. Thermo-graphic images of the cell with circulating liquid are used to establish the type of the flow within the cell. The tests were performed with various types of liquids and versatility of the device demonstrated.

The characterization of the residence time distribution in a magnetic mixer by means of the information entropy

Mixing behavior in a magnetic mixer is investigated using an experimental approach. The concept of the residence time distribution (RTD) was applied to characterize a mixing process under the action of a rotating magnetic field (RMF). The main idea of the proposed approach is the utilization of experimental RTD measurements to determine the information entropy. This paper discusses a method to compute an information degree of mixing as a measure of mixing performance for a continuous flow system. The quality of mixing in the tested equipment is analyzed by means of a proposed mixing capacity. Different operating conditions with respect to liquid flow rates and a magnetic field strength are used to study corresponding effects on a recommended parameter. It is observed that mixing capacity increases with increasing magnetic field strength. This mixing parameter is analytically described as a function of operating flow rates and the applied magnetic field.

Experimental study and mathematical modeling of the residence time distribution in magnetic mixer

This study reports on research results in the field of a mixing process under the action of a transverse rotating magnetic field (TRMF). The main objective of this paper is to present the effect of this type of a magnetic field on residence time distribution (RTD) measurements. This paper evaluates the performance of a magnetic mixer by comparing the results of an experimental investigations in a pilot set-up and theoretical values obtained from mathematical model. This model consisting of the set of ideal continuous stirred tank reactors (CSTR) fitted well the experimental data.

Water Treatment by Coagulation-Flocculation Using Ferric Sulphate as Coagulant

Coagulation and flocculation are two essential processes in water treatment. Their improvement on effectiveness and efficiency will give a significant influence for the overall process. The coagulation and flocculation processes involve a coagulant subsequently used to form flocks that can sink precipitate easily. In this research, the sample taken from Sermo Reservoir located in Kulon Progo Regency. The water was containing 320 ppm of colloid and suspended solids. Here, using a magnetic mixer stirrer, 500ml of raw water was mixed with a certain dosage of ferric sulfate in that used as the coagulant at a certain pH in a beaker glass through a high-speed mixing (240 rpm) for five minutes and low-speed mixing (60 ppm) for 10 minutes, respectively. Subsequently, the absorption was measured using UV/Visible. The result then shows 100 ppm for the optimum dosage of ferric sulfate and 9 for the optimum pH. The results indicate that a higher precipitation constant (kd) has resulted in a higher flock diameter. The correlation between the precipitation constant (kd) and the Reynolds number can be expressed as the following equation, kd = 51.98 Re0.3735 with an average relative error of 9.8%.

Numerical analysis of a rapid magnetic microfluidic mixer

This paper presents a detailed numerical investigation of the novel active microfluidic mixer proposed by Wen et al. (Electrophoresis 2009, 30, 4179-4186). This mixer uses an electromagnet driven by DC or AC power to induce transient interactive flows between a water-based ferrofluid and DI water. Experimental results clearly demonstrate the mixing mechanism. In the presence of the electromagnet's magnetic field, the magnetic nanoparticles create a body force vector that acts on the mixed fluid. Numerical simulations show that this magnetic body force causes the ferrofluid to expand significantly and uniformly toward miscible water. The magnetic force also produces many extremely fine finger structures along the direction of local magnetic field lines at the interface in both upstream and downstream regions of the microchannel when the external steady magnetic strength (DC power actuation) exceeds 30 Oe (critical magnetic Peclet number Pe(m),cr = 2870). This study is the first to analyze these pronounced finger patterns numerically, and the results are in good agreement with the experimental visualization of Wen et al. (Electrophoresis 2009, 30, 4179-4186). The large interfacial area that accompanies these fine finger structures and the dominant diffusion effects occurring around the circumferential regions of fingers significantly enhance the mixing performance. The mixing ratio can be as high as 95% within 2.0 s. at a distance of 3.0 mm from the mixing channel inlet when the applied peak magnetic field supplied by the DC power source exceeds 60 Oe. This study also presents a sample implementation of AC power actuation in a numerical simulation, an experimental benchmark, and a simulation of DC power actuation with the same peak magnetic strength. The simulated flow structures of the AC power actuation agree well with the experimental visualization, and are similar to those produced by DC power. The AC and DC power actuated flow fields exhibited no significant differences. This numerical study suggests approaches to maximize the performance of the proposed rapid magnetic microfluidic mixer, and confirms its exciting potential for use in lab-on-a-chip systems.

Magnetic micropillars as a tool to govern substrate deformations

Magnetic actuated microdevices can be used to achieve several complex functions in microfluidics and microfabricated devices. For example, magnetic mixers and magnetic actuators have been proposed to help handling fluids at a small scale. Here, we present a strategy to create magnetically actuated micropillar arrays. We combined microfabrication techniques and the dispersion of magnetic aggregates embedded inside polymeric matrices to design micrometre scale magnetic features. By creating a magnetic field gradient in the vicinity of the substrate, well-defined forces were applied on these magnetic aggregates which in turn induced a deflection of the micropillars. By dispersing either spherical aggregates or magnetic nanowires into the gels, we can induce synchronized motions of a group of pillars or the movement of isolated pillars under a magnetic field gradient. When combined with microfabrication processes, this versatile tool leads to local as well as global substrate actuations within a range of dimensions that are relevant for microfluidics and biological applications.

Acute toxicity study of three type of Nerium.oleander leaves of hexane extract in mice

Three types of Nerium.oleander leaves of hexane extract were prepared according the color of their flower, red flower group (RFG), pink flower group (PFG) and white flower group (WFG).After drying in the sunlight, grinding by electrical grinder. Extraction with hexane was done by a soxhlet apparatus for each type the extract of each type was dissolved in propylene glycol which was used to dissolve the extract with the aid of magnetic stirrer mixer for ten minutes. The median lethal dose (LD50) experiment for each type, fifty adult mice of mixed sex were used. They were divided into 5 equal number groups and were given different oral doses as following:-The red flower groups (RFG) received oral doses ranging from 225-425mg⁄Kg ,the pink flower group(PFG) received oral doses ranging from 200-400 mg ⁄Kg while the white flower groups (WFG) received doses ranging from 250- 450 mg⁄ Kg of body weight. The LD50 was calculated by employing probit method and found to be 325mg/kg for the RFG, 300mg/kg for the PFG and 350mg/kg for the WFG respectively. These results indicate that the toxic constituents of the leaves nearly same since there were no significance differences between LD50 of the three types.

Solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides

Experimental data on the solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides in the temperature range 66‐90°C and fluorine partial pressure 226‐1066 kPa are presented. Computed values of Henry’s constant for these systems and constants in the equation expressing the linear approximation of the temperature dependence of Henry’s constant are given. Uranium hexafluoride exists as a liquid only at temperature and pressure above the triple point, i.e., 64.05°C and 0.155 MPa. Since it is obtained for commercial purposes by means of the interaction of uranium tetrafluoride with excess fluorine gas [1], liquefaction from commercial gas from fluoridation apparatus can be done only at high pressure and in the process fluorine becomes dissolved in the liquid uranium hexafluoride. For this reason, the solubility of fluorine in liquid uranium hexafluoride affects the choice of the technological arrangement of any facility that is used to liquefy uranium hexafluoride from commercial gases containing fluorine. The objective of the present work is to determine the solubility of gaseous molecular fluorine in liquid metal hexafluorides. The solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides was determined using the apparatus shown schematically in Fig. 1. The nickel vessel 13 with a copper cover 4 had a magnetic mixer 10, placed in plain Teflon bearings 6 and finished on top by a bar made of a ferromagnetic material in aluminum casing 7. The mixer was put into motion by a permanent magnet 3, placed outside and rotated by an electric motor 1 with frequency ranging from 3 to 15 rpm. Three thermocouple pockets 9, made of nickel tubing with 0.2 mm thick wall were uniformly arranged over the height of the vessel. Two couplings with small, nickel, packed gland valves were present on the vessel wall. The initial components were loaded through one of them 5. First, the setup was evacuated, checked for vacuum, and passivated with fluorine gas at 100°C. Metal hexafluorides were loaded by means of condensation into a nickel vessel at liquid-nitrogen temperature. A standard manometer 2 was used to monitor the progress of the loading. The amount of condensed metal hexafluoride permitted the existence of at least 1 cm 3 of vapor above the liquid at the temperature of the experiment. When condensation was completed, fluorine was introduced into the vessel. Next, the vessel 13 with a differential manometer 8 was placed into a water thermostat 14 ,w here the temperature was maintained to within ±0.2°. The total pressure in the vessel was measured with a differential manometer 8. Samples of the liquid metal hexafluoride were extracted every 20 min into the space between the valves 11, whence the liquid sample was completely evaporated into the vessel 12 and delivered in the gas phase to a chromatograph for analysis. Equilibrium was considered to be attained when the solubility with decreasing gas pressure was the same as with increasing gas pressure. Methods for purifying the initial substances and checking their purity as well as the technique for performing chromatographic analysis of extracted samples are described in [2]. The computed error in determining the fluorine concentration did not exceed 0.1%.

Heat-regulating coatings based on BaTi(1-y)Sn y O3 powders

Only one of the three mechanisms of heat transfer (heat conductivity, convection, and radiation), namely, radiation is possible for space vehicles (SV), since they have contact neither with a solid body (there is no contact with other objects), nor with a gas (they operate in deep vacuum). To maintain the thermal mode, active and passive heatregulating systems are used. Passive systems are heat-regulating coatings (HRC) put on heat-regulating radiators or separate units and devices. According to the law of heat emission, the SV temperature is determined by the fourth root of the ratio of the integral solar radiation absorption coefficient (аs) to the emissivity (e): Т ~ (аs /e). During orbital flights, the absorption coefficient аs of the reflecting HRC increases due to the formation of photo-induced and radiative defects that absorb light in the solar range of the spectrum [1–3]. Since the emissivity of all known HRC either remains unchanged or decreases insignificantly (by 5%), the SV temperature increases in flight, which can cause overheating of the equipment and even its failure. This calls for the development of methods of temperature stabilization, one of which can be based on the emissivity increase with the absorption coefficient аs. Another situation in which the emissivity must be changed during an orbital flight is observed for the absorbing coatings. When the SV are in the Earth’s shadow zone or are rotated about their axes even in the zone illuminated by the sun, a fragment of their surface is screened by the airframe and is in the shadow zone, and the surface temperature here decreases because of the lack of the heat source – electromagnetic solar radiation. One of the methods of temperature stabilization at a preset level can be the emissivity decrease with the absorption coefficient аs remaining unchanged. To solve these problems of space materials science, compounds with phase transitions (PT) and general formula A(1-x)BxC(1-y)DyOz in which cations A and (or) C are partly substituted by ions B and D can be used as pigments of reflecting and absorbing coatings. These compounds without substitutes have phase transitions in the temperature dependences of the electric, dielectric, thermophysical, and other properties; after incorporation of substitutes, the phase transitions are displaced along the temperature scale. The displacement magnitude and rate, as well as some other PT characteristics, are determined by the type and concentration of substituting ions and conditions of their incorporation. Works studying the phase transitions in the temperature dependence of the emissivity are few in number, though the importance and practical necessity of such results are obvious. Works with ceramic samples [4] and powders of manganites of rare earth elements [5] should be mentioned here. The present work studies phase transitions in the temperature dependence of the emissivity of synthesized BaTi(1-y)SnyO3 powders to estimate the possibility of their application as pigments of heat-regulating coatings of space vehicles and household and technological enamels. To prepare solid solutions of barium titanate, BaCO3, SnO2, and TiO2 compounds were mixed by a magnetic mixer in bidistilled water; the mixture was evaporated for 1 h at a temperature of 100°C and put in a heat-treatment furnace for synthesis. The compounds with stannum cation concentrations of 10, 15, and 20 mass% were synthesized. The powder so obtained was then mixed with KO-596 lacquer in the 0.4 : 0.6 ratio, and the mixture was put on metal substrates. The

Magnetic microsphere-based mixers for microdroplets

While droplet-based microfluidic systems have several advantages over traditional flow-through devices, achieving adequate mixing between reagents inside droplet-based reactors remains challenging. We describe an active mixing approach based on the magnetic stirring of self-assembled chains of magnetic microspheres within the droplet as these stirrers experience a rotating magnetic field. We measure the mixing of a water-soluble dye in the droplet in terms of a dimensional mixing parameter as the field-rpm, fluid viscosity, and microsphere loading are parametrically varied. These show that the mixing rate has a maximum value at a critical Mason number that depends upon the operating conditions.

Optimisation of Manufacturing Parameters for an Ni–Ag Fuel Cell Electrode

AbstractThe aim of this research is to optimise manufacturing parameters for a fuel cell electrode. The combination of nickel oxide, silver oxide and ammonium bicarbonate powders is used to produce the electrode. The main role of silver element is to increase the activity in the electrode. Ni–Ag electrode can be used in fuel cells as positive and negative electrodes. All powders are mixed in the benzene solution by a magnetic mixer and then compressed to form green electrode. The range of pressure in this step is between 40 and 160 MPa. The green electrode is sintered in hydrogen atmosphere through a tube furnace and then cooled to 200 °C under argon atmosphere. The range of sintering temperature and time is 500–800 °C and 10–60 min, respectively. Also, silver oxide and ammonium bicarbonate percentages are varied from 20 to 65 and 15 to 35%, respectively. All parameters including composition, pressure, sintering temperature and time are changed during electrode fabrication to achieve optimised properties in the electrode. So, it is necessary to perform several tests measuring porosity, surface area, density, weight loss, mechanical strength, shrinkage, exchange current density and metallographic photos.The optimum conditions of the electrode production resulting from this investigation include compacting pressure 60 MPa, sintering temperature 560 °C, sintering time 15 min, silver oxide percentage 50% and ammonium bicarbonate percentage 27%.

Magnetically Actuated Micromixing on an Array-Pattern Microfluidic Chip for Immunoassay of Human Thyrotropin

A novel array-pattern ring microfluidic chip has been designed and fabricated with ITO glass, and a low-cost, easy-to-use active magnetic mixer is developed. The mixer consists of externally driven magnetic stir plates and ferromagnetic microneedles as active mobile stirrers in the microchannel. Mixing performance in the microfluidic chip has been experimentally characterized by chemiluminescence immunoassay of human thyrotropin (TSH) and compared with tube-based chemiluminescence immunoassay. The mixing method proposed in this study can be readily applied to integrated microfluidic systems, such as micro-total-analysis systems, lab-on-a-chip, and so on.

Micro magnetic stir-bar mixer integrated with parylene microfluidic channels

Previously, we reported a micro magnetic stir-bar mixer driven by an external rotating magnetic field and its rapid mixing performance in polydimethyl-siloxane (PDMS) channels. The PDMS piece with embedded fluid channels were manually aligned to a glass substrate and assembled. In this paper, we report the fabrication and testing results of a micro magnetic stir-bar monolithically integrated in parylene surface-micromachined channels with improved design features, including small tolerance of the stir-bar to channel wall (10 microm). Using of parylene based microchannels with improved design not only provides improved mixing, but also eliminates certain problems associated with PDMS-based channels. For example, porosity of PDMS causes evaporation and absorption of chemicals and thus channels made of PDMS are prone to cross-contamination. We have also demonstrated that the magnetic stir-bar can be used to pump liquid in micro channels.

The cellular immune reaction in synovial fluid lymphocytes to Ureaplasma antigens in patients with Reiter's syndrome

Reiter's syndrome (RS) is an seronegative arthritis that occurs after urogenital or enteric infection which in addition with occular and/or mucocutaneous manifestations presents complete form of disease. According to previous understanding arthritis in the RS is the reactive one, which means that it is impossible to isolate its causative agent. However, there are the more and more authors suggesting that arthritis in the urogenital form of disease is caused by the infective agent in the affected joint. This suggestion is based on numerous studies on the presence of Chlamydia trachomatis and Ureaplasma urealyticum in the inflamed joint by using new diagnostic methods in molecular biology published in the recent literature [1-3]. Besides, numerous studies of the humoral and cell-mediated immune response to "triggering" bacteria in the affected joint have supported previous suggestions [4-7]. Aim of the study was to determine whether synovial fluid T-cells specifically recognize the "triggering" bacteria presumably responsible for the Reiter's syndrome. The 3H-thymidine uptake procedure for measuring lymphocyte responses was applied to lymphocytes derived concurrently from synovial fluid (SF) and from peripheral blood (PB) [8]. Ureaplasma antigen and mitogen PHA stimulated lymphocytes in 24 RS patients (24 PB samples, 9 SF samples) and the results were compared with those found in 10 patients with rheumatoid arthritis (RA) (10 PB samples, 5 SF samples). Preparation of ureaplasma antigen. Ureaplasma was cultured on cell-free liquid medium [9]. Sample of 8 ml was heat-inactivated for 15 minutes at 601C and permanently stirred with magnetic mixer. The sample was centrifuged at 2000 x g for 40 minutes and than deposits carefully carried to other sterile glass tubes (Corex) and recentrifuged at 9000 x g for 30 minutes. The deposit was washed 3 times in sterile 0.9% NaCl, and final sediment was resuspended in 1.2 ml sterile 0.9% NaCl. BACTERIOLOGY: Chlamydia trachomatis was isolated by cell culture using cycloheximide-treated McCoy cells [10], while Ureaplasma urealyticum was identified according to its biochemical properties grown on cell-free liquid medium [9]. Proliferative response of the PB lymphocytes to stimulation by mitogen and ureaplasma antigen did not differ between RS and RA patients. Also, there was no difference in proliferative response of SF lymphocytes to mitogen stimulation between RS and RA patients (Figure 1). However, proliferation of SF lymphocytes stimulated by ureaplasma antigen was significantly elevated in RS patients compared with the control group. This difference is statistically significant (p < 0.05) (Figure 2). Difference in proliferative response of the PB and SF lymphocytes stimulated by the ureaplasma antigen was not found in RS patients. It was found that SF lymphocytes of RS patients showed significantly elevated proliferative response to stimulation by the ureaplasma antigen compared with SF lymphocytes of the control group. There was no difference when the lymphocytes were stimulated by the mitogen. Our findings suggest that elevated proliferative response of lymphocytes is the sign of stimulation cell-mediated immunity to antigen present in inflamed joint. Hence, the main immune response to Ureaplasma is on the cell-mediated level in the affected joint. This confirms the earlier finding reported by Ford et al. who concluded that synovial rather than peripheral blood lymphocytes indicate the microbiological cause of arthritis [11, 12]. Horowitz et al. demonstrated the correlation between clinical remission after antibiotic therapy and eradication of Ureaplasma, together with a decrease in cellular immune response synovial fluid lymphocytes to ureaplasma antigen stimulation [13]. In that study Horowitz did not find statistically significant difference of ureaplasma proliferative response between PB and SF lymphocytes in patients with RS. We obtained the same results. Than we concluded that sensibilization of immune system exist in the presence of foreign antigen in RS patients. The other authors demonstrated higher stimulation indices than the ones we found in our patients [11-15]. This difference may be the result of different preparation of antigens, in other words selection of serotype of Ureaplasma for antigen preparation different conditions of lymphocyte cultivation. We concluded that the presence of antigen, antigen-specific T cells and efficient antigen-presenting cells (CD4+ T cells) in the joint of RS patients strongly suggests that a T-cell-mediated response to bacteria has the central role in the pathogenesis of Reiter's syndrome.

A magnetic microstirrer and array for microfluidic mixing

We report the development of a micromachined magnetic-bar micromixer for microscale fluid mixing in biological laboratory-on-a-chip applications. The mixer design is inspired by large scale magnetic bar mixers. A rotating magnetic field causes a single magnetic bar or an array of them to rotate rapidly within a fluid environment. A fabrication process of the magnetic bar mixer is developed. Results of fluid mixing in micro channels and chambers are investigated using experimental means and computer-aided fluid simulation.

Vapor entraining magnetic mixer for reaction and equilibrium applications

Mixing of fluids is a central component to innumerable operations in chemical processing on the plant floor and also in many laboratory operations. Most mixing applications simply require the efficient blending of fluids present in a single phase, such as the mixing of the individual components of a liquid. For these applications, magnetic stirrers often provide a convenient and efficient blending without creating ambient air entertainment into the liquid. This is especially true of fluid mixing operations done in the laboratory. There are many other applications, however, in which the entertainment of a vapor phase with a liquid is specifically desired. Examples of these applications include mixing in two-phase reaction vessels and in apparatus to measure vapor–liquid equilibrium. These mixing operations are difficult to accommodate with magnetic stirrers because the vast majority of such stirrers are designed not to entrain vapor. In this brief paper, we present a novel design of a mixing rotor that efficiently mixes the liquid phase and also achieves entrainment of vapor in the liquid.

Emulsion-derived lithium manganese oxide powder for positive electrodes in lithium-ion batteries

Lithium manganese oxide (LiMn 2O 4) used as a positive-electrode material in lithium-ion batteries is prepared by a new water-in-oil emulsion process. An aqueous solution containing lithium and manganese cations is emulsified in kerosene by adding sorbitan monooleate as the surfactant. When the precursor solution is agitated by a magnetic mixer, impure products are obtained. LiMn 2O 4 is formed along with residual Mn 2O 3 at elevated temperatures because of insufficient dispersion and mixing of the reactive cations. When a homogenizer with a greater agitation speed is used, however, a well-mixed precursor solution is prepared, and pure LiMn 2O 4 with a Fd 3 m structure is synthesized after calcination at 800°C for 1 h. LiMn 2O 4 powder prepared by the homogenizer has higher crystallinity, smaller particle size, and narrower size distribution than that prepared by the magnetic stirrer. Compared with powder prepared by the solid-state method, the LiMn 2O 4 powder exhibits smaller particle size and less agglomeration. Moreover, the emulsion process significantly shortens the heating time required. The prepared LiMn 2O 4 powder has a high discharge capacity (120.4 mA h g −1) on the first cycle and good cycleability.