Dynamic Viscosity-Temperature Characteristics and Models of Various Lubricating Oils

Measuring of fluid properties such as dynamic viscosity and density has tremendous potential for various applications from physical to biological to chemical sensing. However, it is almost impossible to affect only one of these properties, as dynamic viscosity and density are coupled. Hence, this paper proposes kinematic viscosity as a comprehensive parameter which can be used to study the effect of fluid properties applicable to various fluids from Newtonian fluids, such as water, to non-Newtonian fluids, such as blood. This paper also proposes an ideal microplatform, namely polymeric suspended microfluidics (SPMF3), with flow plane orthogonal to the bending plane of the structure, along with tested results of various fluids covering a wide range of engineering applications. Kinematic viscosity, also called momentum diffusivity, considers changes in both fluid intermolecular forces and molecular inertia that define dynamic viscosity and fluid density, respectively. In this study a 3D suspended polymeric microfluidic system (SPMF3) was employed to detect changes in fluid parameters such as dynamic viscosity and density during fluid processes. Using this innovative design along with theoretical and experimental results, it is shown that, in fluids, the variations of fluid density and dynamic viscosity are not easily comprehensible due to their interconnectivity. Since any change in a fluid will affect both density and dynamic viscosity, measuring both of them is necessary to identify the fluid or process status. Finally, changes in fluid properties were analyzed using simulation and experiments. The experimental results with salt-DI water solution and milk with different fat concentrations as a colloidal fluid show that kinematic viscosity is a comprehensive parameter that can identify the fluids in a unique way using the proposed microplatform.

Hydrogels are made from natural or synthetic polymers and, currently, they have many biomedical applications. In this work, the conditions for obtaining a hydrogel with similar physicochemical characteristics to the vitreous humor were defined using polyvinyl alcohol (PVA) and glutaraldehyde (GLUT) as cross-linker. The concentration of PVA and GLUT were modified, and their effect was analyzed in terms of the refractive index, density, and dynamic viscosity. The hydrogel which was obtained using 3.98% (w/V) of PVA, 3.13 mL (1.57 g) of GLUT in 100 mL, and the initial pH of 7.2 showed similar characteristics to the vitreous humor (density = 1.0174 ± 0.0050 g mL-1 , dynamic viscosity = 3.7425 ± 0.1800 mPa s and refractive index = 1.3410 ± 0.0010). The hydrogels were further investigated by rheological measurements, infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and determination of swelling degree. The reticulation with GLUT promoted an increase in viscosity and glass transition temperature. On the other hand, it stimulated a decrease in the swelling degree, crystallinity, melting temperature, and intensity of the band related to the -OH bond, compared with the PVA without reticulation. The reticulated hydrogel displayed Newtonian behavior and a higher apparent viscosity than the PVA. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1558-1566, 2018.

Twelve different crude oil samples were collected from four oil fields in the Niger Delta Nigeria. The bulk properties of these crude oils which include API gravity, specific gravity, reid vapour pressure, kinematic viscosity, dynamic viscosity, moisture, cloud point, pour point, gum content and Sulphur content were analyzed, using standard procedures of American Society for Testing and Materials (ASTM). The results show API gravity values ranged from 30.540 ± 0.100 - 42.460 ± 0.100, Specific gravity 0.813 ± 0.001 – 0.873 ± 0.001, Kinematic viscosities 2.001 ± 0.001 - 5.547±0.010cSt, Dynamic viscosities 1.631±0.000 - 5.057±0.010 cP at 0°C, Gum content 4.676±0.010 - 87.350±0.100 ml, flash point 15.000±0.200 °C - 27.000±0.200 °C, Pour point –16.000±0.200°C - +14.000±0.200°C. The correlation analysis of kinematic viscosity (Kv) and gum content r =0.965 was strongest, indicating increased viscosity with respect to high gum content. These physicochemical properties play a crucial role in determining the crude oil's suitability for refining, transportation, and its environmental impact. The data highlights the need for tailored handling and processing strategies based on the specific characteristics of each crude oil sample.

Gasoline fuel is the baseline fuel in this research, to which bioethanol, biodiesel and diesel are additives. The fuel blends were prepared based on different volumes and following which, ASTM (American Society for Testing and Materials) test methods analysed some of the important properties of the blends, such as: density, dynamic viscosity, kinematic viscosity and water and sediment. Experimental data were analysed by means of Matlab software. The results obtained from artificial neural network analysis of the data showed that the network with feed forward back propagation of the Levenberg-Marquardt train LM function with 10 neurons in the hidden layer was the best for predicting the parameters, including: Water and sediment (W), dynamic viscosity (DV), kinematic viscosity (KV) and density (De). The experimental data had a good correlation with ANN-predicted values according to 0.96448 for regression.

Preliminary hydrocarbon analysis of crude oils from Umutu/Bomu fields, south west Niger Delta Nigeria

Preparation and Physicochemical Properties of Imidazolium Acetates and the Conductivities of Their Aqueous and Ethanol Solutions

This study introduces phthalic anhydride (P) and glycerol (G)‐based polyester as an additive for upgrading lower‐grade bitumen to higher‐grade bitumen. The different colorless polyesters were synthesized using polycondensation of P and G as a monomer in the ratio of 1:1 and polymerization time of 1, 3, 5, and 7 h. A rheological analysis was performed on all the synthesized polyesters to check their performance with respect to their use in bitumen modification. The polyesters were blended with base bitumens (VG10) to obtain the modified bitumens that were tested for the rheological and physicochemical properties and to assess the performance based on the grade quality test. The quality test of the modified bitumens includes softening point (SP), penetration (PEN), kinematic viscosity (KV), dynamic viscosity (DV), and rheological properties as per standard ASTM test methods. Based on the performance evaluation, P1G1H3 polyester was found suitable for blending with bitumen, and further study was carried out with blending of P1G1H3 with 3, 6, 10, and 15 wt%. The finding illustrates that 6.0 wt% of polyester‐modified bitumen show an enhanced SP, KV, and DV by 23.6, 86, and 30%, respectively, while decreasing the PEN by 49% with respect to VG10. Polyester blending also improved the rheological parameters in terms of deformation resistance, load‐bearing capacity, and the viscoelastic nature of bitumen. The investigation concluded that 6 wt% P1G1H3 polyester on blending in VG10 meets VG30 bitumen specification as per IS:73:2013.

<div class="htmlview paragraph">The dilution of crankcase oils with the heavy ends of gasoline constitutes the outstanding present-day problem in the lubrication of automobile engines. This paper first presents the results of extensive tests designed to determine the rate and extent of dilution for various types of car under various operating-conditions. From these results it appears that, in the average car in winter service in the northern half of the Country, the viscosity of the original oil drops to about one-third of its original value in the first 150 to 180 miles of intermittent operation. Beyond this the viscosity, contrary to general opinion, remains fairly constant at an equilibrium value corresponding to about 15 per cent dilution, where, on the average, the rate at which fresh diluent enters the oil is practically balanced by the rate at which it is eliminated therefrom. Individual cars, of course, vary rather widely from this average figure, depending partly upon the design and condition of the car, but to a greater extent upon the operating conditions. Certain theoretical equations with empirical constants are shown to correspond closely to the observed curves giving the change in dilution with mileage.</div> <div class="htmlview paragraph">With the average oil losing one-third of its viscosity in the first 150 miles of winter operation, to prescribe any ordinary type of oil which will have a really proper viscosity throughout any reasonable period of service is obviously impossible. In general, the widely used medium grades of oil, having around 325-sec. viscosity, are probably the best compromise available; but, for the first 50 miles of operation, their viscosity is considerably too high for easy starting when cold or for effective cold-lubrication in most cars. After 150 miles, the amount of dilution is, in general, so great as to reduce the viscosity to a point too low for safety, especially as road dust and grit accumulate. The use of a heavier oil accentuates the first set of difficulties and undoubtedly causes much of the scoring and wear of cylinders and rings, while the use of a much lighter oil gives an average viscosity after about 150 miles, which is far too low for safety.</div> <div class="htmlview paragraph">As a remedy, this paper suggests the use of a fairly heavy oil, of from 500 to 575-sec. viscosity at 100 deg. fahr., blended with from 10 to 12 per cent of a distillate having a boiling range <i>substantially identical</i> with that found in the average crankcase oil at equilibrium. By this means it is possible to produce an oil with an initial viscosity around 220 sec, which, being thin enough, gives easy starting and good cold-lubrication and yet is so near the average equilibrium-dilution that, in general, it maintains a viscosity in this optimum range throughout its entire period of service. In warm weather, or in cars in which the average running-temperature is high, some of this diluent will shortly be driven-off to give a somewhat higher viscosity, which is desirable for such vehicles, while cars kept in cold garages and frequently started and stopped will have a somewhat lower equilibrium-viscosity, as is desirable for such vehicles.</div> <div class="htmlview paragraph">These theoretical considerations have been fully confirmed by extensive comparative tests in two fleets of cars and trucks operated both summer and winter on the old and new types of oil. Changes in dilution and viscosity were followed closely, and the results for different types of car are presented graphically. If a car dilutes its oil to more than 20 or 25 per cent, the viscosity of even the new type of oil enters a range where the factor of safety is low but, in any case, the new oil is better than the old. If car builders can, by design and by education, keep dilution below 20 or 25 per cent, this oil should solve the remaining dilution problem in a very satisfactory manner. The factors and limitations that determine the optimum composition of the new type of oil are also discussed. Present specifications are, of course, not applicable to these oils.</div>

The kinematic and dynamic viscosities for binary systems of hexan-1-ol with the ortho-, meta-, and para-isomers of dimethylbenzenes have been determined at T = (303.15, 308.15, 313.15, 318.15, and 323.15) K and at atmospheric pressure, and are compared with those calculated by predictive and correlative models. The UNIFAC–VISCO and ASOG–VISCO models were used for the predictive calculations, while the McAllister, Andrade/DIPPR, Grunberg–Nissan and Teja–Rice models were used for the correlative approach. The calculated kinematic viscosities from the ASOG–VISCO model have better compatibility with the experimental values than those obtained from the UNIFAC–VISCO model. The individual contributions of constituent groups in the binary mixtures to the kinematic viscosity were underestimated in the UNIFAC–VISCO model, while they are predicted fairly well in the ASOG–VISCO model. The calculated kinematic viscosities with the McAllister model are in excellent agreement with experimental ones. The root-mean-square deviations from the experimental dynamic viscosity values with those calculated using the Andrade/DIPPR and Grunberg–Nissan models are comparable, while those for the Teja–Rice model are larger, which reflects the differences in the number of fitting parameters among those correlative models.

The study on the influence of glycols on the vapor pressure, density and dynamic viscosity of lithium bromide aqueous solution

The physicochemical and thermophysical properties of sodium dodecyl sulfate: The influence of p-toluene sulfonyl chloride and temperature

Temperature-dependent R-curve and traction-separation relation in mode-I fracture of GFRP laminates

In the practical application of multi-link mechanism, lubricating oil has been widely used in kinematic pairs to reduce the influence of clearance on the accuracy and stability of the mechanism. However, the operation of the press is still inevitably affected by the impact loads. Impact loads will also reduce dynamic response characteristics of the mechanism and affect its accuracy and reliability. At present, the research on dynamic response characteristics of mechanisms mainly focuses on the effect of lubrication clearances. Theoretical research on dynamic of mechanisms with lubrication clearances under impact loads is rare. Experimental studies involving impact loads are uncommon. Therefore, an effective approach for dynamic characteristics of multi-link mechanism with lubrication clearances under impact loads was proposed, and the dynamic response of multi-link presses with lubrication clearances under impact loads was studied in the article. Taking a seven-link press mechanism as an example, a dynamic equation of the mechanism with lubricating clearance was derived based on the Lagrange multiplier method. The dynamic model of the seven-link press mechanism with lubrication clearance under impact load was developed. Then the effects of lubrication conditions, dynamic viscosity, driving speeds, and impact loads on dynamic characteristics of press mechanisms were analyzed, respectively. Finally, an experimental platform consistent with the theoretical model was built. Through the experimental research and the analysis of experimental results, the rationality of models and the validity of theoretical analysis were verified. The study provides a method for understanding dynamic characteristics of presses during impact loads, and provides an important reference for dynamic optimization design of multi-link press mechanism.

In this contribution we have determined densities and kinematic viscosities at atmospheric pressure and four temperatures, T = (293.15, 303.15, 313.15 and 323.15) K for six binary systems formed by three pyridinium-based ionic liquids (1-butylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, or 1-butyl-4-methylpyridinium tetrafluoroborate) and two alkanols (methanol or ethanol). Kinematic viscosities were fitted using a four-body McAllister equation. From experimental densities and kinematic viscosities, absolute viscosities and viscosity deviations were calculated. The viscosity deviations for all systems are negative over the entire composition and temperature ranges. This behavior can be justified by the weakening of the interactions in the pure components during the mixing process.

The descriptions of the new products listed in this section are based on information supplied to us by the manufacturers. Physics Today can assume no responsibility for their accuracy. For more information about a particular product, visit the website at the end of the product description.Plain bearingsSection:ChooseTop of pagePlain bearings <<Carbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometerThe LM76 plain bearings produced by LM-Tarbell employ advanced polytetrafluoroethylene polymers, ceramic, and specialty composites for linear and rotary applications to meet the requirements of motion-system designers. The bearings are chemically and mechanically resistant under harsh conditions. They are compliant with government standards and are suited for food processing and packaging, medical products, pharmaceuticals manufacturing, robotics, assembly and construction equipment, and marine applications. The company provides RC60, 300 series stainless steel, and ceramic-coated shafting and offers pillow blocks and flange blocks in aluminum, ceramic-coated aluminum, and stainless steel. The ceramic-coated series of plain bearings handles high-speed applications and loads up to 10 times faster than linear ball bushing bearings. Also available are custom-blended polymer bearings for extreme applications such as high heat. LM-Tarbell, 140 Industrial Drive, East Longmeadow, MA 01028, http://www.lm-tarbell.com Carbon nanotubes for AFM probesSection:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ... <<Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometer Carbon Design Innovations (CDI) makes atomic force microscope probes from carbon nanotubes. The CNTs offer a method of expanding the depth of profiling from the surface of the probe by several nm to µm. They feature higher resolution, a higher-aspect ratio, and longer lifetimes than typical AFM probes. The result can be a high-resolution image at a molecular and submolecular scale of structures which are several hundred nm to 1 µm deep. CDI’s carbon core high-resolution (CCHR) probes are used for general high-resolution imaging purposes. They are a bit shorter than high-aspect ratio probes, but they are reinforced at the base so they can extend down to about 200 nm. That enables the high-resolution imaging aspects of AFM to be applied to structures of more complicated materials. The CCHR probes’ primary focus application is on material characterization and metrology. Carbon Design Innovations, 1745 Adrian Road, Unit 20, Burlingame, CA 94010, http://www.carbondesigninnovations.com Aluminum coating for excimer lasers Section:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci... <<Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometer Excimer lasers operate only in the pulsed mode, so each exposure consists of numerous pulses. The projection optics typically experience fluences in the range of 0.1 mJ/cm2 to 1 mJ/cm2 per pulse. Some of the other optics in the system are subjected to fluences in the range of 1 mJ/cm2 to several mJ/cm2 per pulse. Since a production-line system might involve several million pulses per day, the optics must be able to withstand several billion pulses over their lifetimes. Saint-Gobain Crystals has introduced a high-reflectance aluminum coating for excimer laser-based scanning applications. The Alpine Research Optics–brand thin film is UV enhanced and delivers more than 95% reflectivity at 193 nm and an average reflectivity of more than 85% from 400 to 1000 nm. The metal/dielectric coating also delivers better than 90% reflectivity at 193 nm over an angle-of-incidence range of ±10°. The coating is supplied on various substrates suitable for galvanometer scanners, including rectangular fused silica with chamfered edges. Saint-Gobain Crystals, 6810 Winchester Circle, Boulder, CO 80301, http://www.saint-gobain-northamerica.com Barrier properties of PLA filmsSection:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA... <<Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometerSono-Tek offers a system to enhance barrier properties of polylactic acid films based on the company’s ultrasonic atomization spray coating line. The system applies an ultrathin layer of clay nanoparticles to compostable films and significantly enhances their barrier properties. It offers the packaging industry an efficient and cost-effective way to prolong the shelf life of compostable packaging films. Nano-particles have a tendency to agglomerate while being dispensed, which results in an uneven coating-layer thickness. Sono-Tek’s ultrasonic nozzles disperse those suspensions with high uniformity by imparting vibrations into the liquid suspension, thereby providing an agglomerate-free, uniform coating. The unpressurized spray cuts down on the amount of overspray, since droplets settle on the substrate rather than bouncing off; the technology reduces waste and generates 30%–60% cost savings. Sono-Tek Corporation, 2012 Route 9W, Milton, NY 12547, http://www.sono-tek.com Carbon nanotubes of improved puritySection:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro... <<Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometerGoodfellow Corp has made available economical, high-purity nanomaterials employing a technique used for carbon nanotube manufacture. The CNTs are developed by Sustainable Carbon NanoTechnology and Engineering in Ohio. Conventionally produced nano-materials include electrochemically active impurities from the catalysts used in their production. The manufacturing technique developed by SCNTE does not involve such catalysts, so the carbon nanomaterials are free from contaminants found in electrochemically active metals such as nickel and iron. The high purity of the materials, which makes inhouse preuse purification unnecessary, can help researchers use carbon nano-materials in their applications at competitive cost. Standard carbon nano-materials in the Goodfellow catalog include 50–100-nm nanoclusters, 1- and 2-µm clusters, whiskers with nominal dimensions of 200 nm by 20 µm, and Carbon Nanokit. Goodfellow Corporation, 305 High Tech Drive, Oakdale, PA 15071-3911, http://www.goodfellow.com Gas plasma system for powder treatment Section:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow... <<Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometerPlasmatech has added to its line of low pressure gas plasma systems the AL200-D for treating powder, pellet, and crystalline materials. A specially designed 5-L rotating chamber ensures treatment consistency, even when processing very fine powders and compounds. Production systems with larger chambers are available to accommodate higher-volume requirements.The AL200-D, which is clean room compatible, is available in a tabletop version or with a freestanding enclosure so users can incorporate a vacuum pump in the system cabinetry. To ensure process repeatability, the system is equipped with programmable logic control, recipe storage, error monitoring, and mass-flow controllers for precise gas measurement. Plasma generation via microwave frequency results in very low chamber temperatures, which eliminates the need for cumbersome, leak-prone liquid electrode cooling. Plasmatech Inc, 1895 Airport Exchange Boulevard, Suite 190, Erlanger, KY 41018, http://www.plasmatechnology.com Heated glass for outdoor cameras Section:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ... <<Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometerAbrisa has announced its new LuxVu heated optical windows for cameras and displays operating in rugged, wet, or cold outdoor environments; for imaging and sensing devices in the field, such as traffic, ground security, and unmanned aerial vehicle cameras; and for optical instrumentation panels on air and ground vehicles. The windows are made of transparent conductive coatings designed to keep the optical glass free from moisture and fog. The heated windows also aid in deicing in extreme weather conditions. They may be combined with various custom display enhancements and coatings. For example, antireflection coatings help protect the display while providing higher performance and improved transmission. Abrisa also offers additional glass fabrication and optical coating services for the heated optical windows. Customized solutions include screen printing, busbar, epoxy, glass strengthening, etching, and special masking. Abrisa, 200 South Hallock Drive, Santa Paula, CA 93060, http://www.abrisa.com Optical coatings on plasticsSection:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast... <<Laser drilling of wafer-b...Portable microviscometerDeposition Sciences Inc (DSI) has introduced optical thin-film coatings for plastic materials and substrates such as Ultem, Zeonex, and various polycarbonate plastics. The rugged, reliable coatings for plastic optics operate from the visible through the IR spectral wavelengths. Thin-film plastic coatings are suitable for applications for which lightweight and low-cost optics are specified, such as LED lighting, medical devices, unmanned aerial vehicle optics, and photovoltaic solar systems. The company’s optical thin-film coatings include bandpass filters, dichroic coatings, and high reflectors. DSI’s sputter deposition technology generates coatings on plastics, metals, and other thin-film materials and creates multilayer thin-film coatings for optics, MEMS, and other nanotechnologies. The company says its coatings will pass the stringent 24-hour humidity, adhesion, and moderate abrasion environmental tests. Deposition Sciences Inc, 3300 Coffey Lane, Santa Rosa, CA 95403, http://www.depsci.com Laser drilling of wafer-based solar cells Section:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b... <<Portable microviscometerThe Jenoptik lasers and material processing division has developed a laser processing technology for drilling minute through holes in wafers for solar cells. One of the crucial factors in the photovoltaic industry is the so-called grid parity, a comparison of the costs of generating electricity via solar energy versus conventional methods. Achieving grid parity requires either an increased level of efficiency or a reduction in production costs. The Jenoptik-Votan Solas 1800 laser system improves solar-cell electrical efficiency through the use of metal wrap through and emitter wrap through technologies. To increase the active surface area of the cells, in both technologies the contacts are laid from the front side to the rear side of the cell. Therefore, users can dispense with the contact fingers, currently used as standard, that cover parts of the active surface area. Lasers & Material Processing Division, Jenoptik Laser-diode GmbH, Goeschwitzer Strasse 29, D-07745 Jena, Germany, http://www.jenoptik.com Portable microviscometerSection:ChooseTop of pagePlain bearingsCarbon nanotubes for AFM ...Aluminum coating for exci...Barrier properties of PLA...Carbon nanotubes of impro...Gas plasma system for pow...Heated glass for outdoor ...Optical coatings on plast...Laser drilling of wafer-b...Portable microviscometer <<Petrolab’s MiniVis 445 can precisely determine dynamic and kinematic viscosity over a wide temperature range. Reflection sensors provide coverage for a wide range of applications; even samples as dark as used or heavy oil can be measured with high accuracy and repeatability. The viscometer includes a small sample volume and automatic sample feeding. The measuring chamber is a rugged glass tube that contains a metal ball. The sample is fed into the tube by the automated system or manually with a syringe. The temperature of the whole sample cell and of the sample introduction system is controlled by a thermoelectric (Peltier) system, which allows for quick determination of viscosity indices. After the ball accelerates to a constant velocity, its time of descent is measured with two reflection sensors. The MiniVis 445 repeats the procedure by rotating the sample cell and measuring in the opposite direction. Ametek Petrolab, 2001 North Indianwood Avenue, Broken Arrow, OK 74012, http://www.petrolab.com © 2009 American Institute of Physics.