Small Samples Of Material Research Articles

Use of the Master Curve methodology for real three dimensional cracks

At VTT, development work has been in progress for 15 years to develop and validate testing and analysis methods applicable for fracture resistance determination from small material samples. The VTT approach is a holistic approach by which to determine static, dynamic and crack arrest fracture toughness properties either directly or by correlations from small material samples. The development work has evolved a testing standard for fracture toughness testing in the transition region. The standard, known as the Master Curve standard is in a way “first of a kind”, since it includes guidelines on how to properly treat the test data for use in structural integrity assessment. No standard, so far, has done this. The standard is based on the VTT approach, but presently, the VTT approach goes beyond the standard. Key components in the standard are statistical expressions for describing the data scatter, and for predicting a specimens size (crack front length) effect and an expression (Master Curve) for the fracture toughness temperature dependence. The standard and the approach, it is based upon, can be considered to represent the state of the art of small specimen fracture toughness characterization. Normally, the Master Curve parameters are determined using test specimens with “straight” crack fronts and comparatively uniform stress state along the crack front. This enables the use of a single K I value and single constraint value to describe the whole specimen. For a real crack in a structure, this is usually not the case. Normally, both K I and constraint vary along the crack front and in the case of a thermal shock, even the temperature will vary along the crack front. A proper means of applying the Master Curve methodology for such cases is presented here.

Cardenolide Genin Pattern in Isoplexis Plants and Shoot Cultures

An HPLC method for the quantitative analysis of cardenolides was developed and applied. The procedure was optimised for analysing small samples (40 mg dw) of plant and tissue culture material. ISOPLEXIS CANARIENSIS plants obtained from seeds accumulated cardenolides to about 20 - 40 micromol g (-1) dw as calculated from the levels of cardenolide genins released after acidic hydrolysis of methanolic extracts. The relative contents of xysmalogenin, digitoxigenin, uzarigenin and canarigenin were 5 - 15 %, 0 - 5 %, 10 - 15 % and 70 - 90 %, respectively. Shoot cultures were initiated from seeds, established as permanent cultures and cultivated on agar-solidified or in liquid medium. Shoot cultures maintained on solid medium contained an average of about 6 micromol cardenolides g (-1) dw. A relatively high proportion of digitoxigenin was found in two-thirds of the shoot cultures examined. The cardenolide content of amphibian shoot cultures averaged to about 1 micromol g (-1) dw. Plants regenerated from shoot cultures and maintained under hydroponic conditions accumulated the same amount of cardenolides as plants collected in the field. No cardenolides could be detected in callus cultures.

A drop tower for controlled impact testing of biological tissues

Impact damage, in particular to tissues such as articular cartilage, is a recognised source of morbidity. To understand better the clinical outcomes, it is important to know the mechanics of the damage sustained and the biological response of cells to rapidly applied forces and subsequent tissue disruption. An instrumented drop tower has been designed to enable controlled impact loads to be applied to small samples of biological materials. Impact severity can be controlled by using impactors of different masses and various drop heights. Force and deceleration at impact are recorded at 50,000 samples s −1 by a force transducer under the sample and an accelerometer on the impactor. Repeatability was tested on rubber washers and coefficients of variation were found to be better than 8% for dynamic stiffness, 3.4% for stress and 4.3% for strain. Initial tests on isolated biopsies of articular cartilage showed that at an initial strain rate of 916 s −1, the peak dynamic modulus of human femoral head cartilage was 59 MPa, and for a bovine biopsy the initial strain rate and corresponding peak dynamic modulus were 3380 s −1 and 130 MPa, respectively. The equipment described is capable of applying an impact load to small biopsies of tissue with a defined energy and velocity and measuring deformation and load at high rates of loading.

Multimicrophone method for measurement of acoustic absorption

A multimicrophone method for measurement of the acoustic absorption of small material samples using impedance tubes is presented. The multimicrophone method may be implemented with actual or synthetic microphone arrays, the latter involving successive measurements and a roving microphone, and is an alternative to the two-microphone method of ASTM E 1050. The effects of absorption measurement inaccuracy due to microphone response (magnitude and phase) bias and measurement noise are determined by simulation. Simulation results indicate that the multimicrophone method is more robust against microphone bias and noise and is therefore more accurate than the standard method, especially as microphone counts increase, while requiring minimal additional effort and cost.

High-resolution respirometry–a modern tool in aging research

Alterations in mitochondrial function are believed to play a major role in aging processes in many species, including fungi and animals, and increased oxidative stress is considered a major consequence of altered mitochondrial function. In support of this theory, a lot of correlative evidence has been collected, suggesting that changes in mitochondrial DNA accumulate with age in certain tissues. Furthermore, genetic experiments from lower eukaryotic model organisms, indicate a strong correlative link between increased resistance to oxidative stress and an extended lifespan; in addition, limited experimental evidence suggests that the inhibition of mitochondrial function by selected pharmacologically active compounds can extend lifespan in certain species. However, changes in mitochondrial function may affect aging in a different way in various tissues, and a clear statement about the role of mitochondrial deterioration during physiological aging is missing for most if not all species. At this point, respirometric analyses of mitochondrial function provide a tool to study age-associated changes in mitochondrial respiratory chain function and mitochondrial ATP production within living cells and isolated mitochondria. In the recent years, new instruments have been developed, which allow for an unprecedented high-resolution respirometry, which enables us to determine many parameters of mitochondrial function in routine assays using small samples of biological material. It is conceivable that this technology will become an important tool for all those, who are interested in experimentally addressing the mitochondrial theory of aging. In this article, we provide a synopsis of traditional respirometry and the advances of modern high-resolution respirometry, and discuss how future applications of this technology to recently established experimental models in aging research may provide exciting new insights into the role of mitochondria in the aging process.

Soft-materials elastic and shear moduli measurement using piezoelectric cantilevers

We have developed a soft-material elastic modulus and shear modulus sensor using piezoelectric cantilevers. A piezoelectric cantilever is consisted of a highly piezoelectric layer, e.g., lead–zirconate–titanate bonded to a nonpiezoelectric layer, e.g., stainless steel. Applying an electric field in the thickness direction causes a piezoelectric cantilever to bend, generating an axial displacement or force. When a piezoelectric cantilever is in contact with an object, this electric field-generated axial displacement is reduced due to the resistance by the object. With a proper design of the piezoelectric cantilever’s geometry, its axial displacements with and without contacting the object could be accurately measured. From these measurements the elastic modulus of the object can be deduced. In this study, we tailored the piezoelectric cantilevers for measuring the elastic and shear moduli of tissue-like soft materials with forces in the submilli Newton to milliNewton range. Elastic moduli and shear moduli of soft materials were measured using piezoelectric cantilevers with a straight tip and an L-shaped tip, respectively. Using gelatin and commercial rubber material as model soft tissues, we showed that a piezoelectric cantilever 1.5–2cm long could measure the elastic modulus and the shear modulus of a small soft material sample (1–3mm wide) in the small strain range (<1%). For samples 5mm high, the resultant compressive (shear) strains were less than 0.5% (1%). The measurements were validated by (1) comparing the measured Young’s modulus of the commercial rubber sample with its known value and (2) by measuring both the Young’s modulus and shear modulus on the samples and confirming the thus deduced Poisson’s ratios with the separately measured Poisson’s ratios.

High-energy proton irradiation and induced radioactivity analysis for some construction materials for the CERN LHC

The dose rate to personnel due to remnant radioactivity during maintenance periods will be an important issue at the forthcoming Large Hadron Collider (LHC). Among the most abundant construction materials are aluminum, steel, copper and lead. In order to obtain more reliable estimates on the radioisotope production in a high-energy hadron environment, we irradiated small samples of these materials behind the beam-stop of the CERN 24 GeV/c proton synchrotron. This environment is characterized by high spallation neutron flux and a non-negligible contribution of protons and pions up to the total beam momentum. Gamma-ray spectra of the samples were measured and analyzed with the SAMPO program and detailed nuclide identification was carried out with the SHAMAN program. The total energy emission and results of the spectrum analyses were compared to predictions of the FLUKA hadron cascade simulation package.

Use of Rigid Spherical Inclusions in Young’s Moduli Determination: Application to DNA-Crosslinked Gels

Current techniques for measuring the bulk shear or elastic (E) modulus of small samples of soft materials are usually limited by materials handling issues. This paper describes a nondestructive testing method based on embedded spherical inclusions. The technique simplifies materials preparation and handling requirements and is capable of continuously monitoring changes in stiffness. Exact closed form derivations of E as functions of the inclusion force-displacement relationship are presented. Analytical and numerical analyses showed that size effects are significant for medium dimensions up to several times those of the inclusion. Application of the method to DNA-crosslinked gels showed good agreement with direct compression tests.

A New Simple Gas Permeameter for Permeability Measurement of Small Samples of Volcanic Eruptive Materials and Experimental Run Products

A New Simple Gas Permeameter for Permeability Measurement of Small Samples of Volcanic Eruptive Materials and Experimental Run Products

Expression profile analysis of neurodegenerative disease: advances in specificity and resolution.

Microarray technology has become a common tool for developing expression profiles. Initially used in the analysis of cells lines and homogeneous tissues, this platform has been applied to more diverse tissues, such as the brain. Several neural disorders have already been profiled by microarrays using relatively large amounts of tissue. This data has unveiled many genes with differential expression between normal and diseased tissue that could potentially be used as gene markers for these afflictions. Because of the heterogeneity of the CNS, it is likely that small differences between gene expression in these studies would be enhanced by the sampling of a subset of cells based on these newly characterized gene markers. Subtraction of normal, unaffected cells from the sample may also result in a more accurate profile of a diseased cell. Expression profile studies from several neuropathological states are presented, with emphasis placed on those studies using small samples of cellular material and those using specialized methods of cell isolation and RNA amplification.

An improved scintillation cell for radon measurements

Scintillation cells like “Modified Lucas cells” are widely used for grab-sample measurements of radon in the environment including those developed in the laboratory for evaluation of radon diffusion coefficients of radon barriers, radon emanation powers in small samples of porous materials and radon concentrations in small chambers used for different research studies. In this paper we describe the main characteristics of an improved and practical scintillation cell developed in our laboratory. Experimental efficiency values obtained for different cell volumes ranged between 0.038 and 0.123 cpm/Bq/m 3. The effects of atmospheric pressure on the detection efficiency as a function of the diameter of the cell were also studied. In general, a decrease of 15% was observed when increasing the pressure from 827 to 1013 hPa.

Test of Four Different Experimental Methods to Determine Sorption Isotherms

One important property of materials is their moisture fixation capacity, i.e., their ability to hold moisture at different relative humidities. The sorption isotherm is one of the main input data in moisture diffusion models, and it can also be used to evaluate properties of the microstructure. We have used four different methods to measure the sorption isotherm of sandstone and porous glass. The first method was to equilibrate samples over saturated salt solutions. The second was a sorption balance in which small material samples were weighed as they were exposed to different relative humidities. The third method was the pressure plate extractor, in which a totally wet sample was equilibrated at various overpressures, corresponding to certain relative humidities. The fourth method was a newly developed microcalorimetric technique to measure sorption isotherms. Despite the different natures of the methods, a satisfying agreement was found.

The X Chromosome and the Female Survival Advantage

Despite differences in research traditions, the disciplines of genetics, epidemiology, and demography are becoming increasingly integrated in health-related research. The enormous development within genetic technology, with the possibility of genotyping thousands of variants from small samples of biological material obtained by non-invasive methods, now makes it feasible to include genetic information in epidemiologic and demographic studies. Simultaneously, new insight can be obtained from hybrids of methods and data from the three disciplines. This paper illustrates how a genetic observation combined with demographic insight and a modified genetic-epidemiologic design (a twin study) provides evidence that part of the sex difference in survival can be attributed to the fact that females have two X chromosomes and males have only one, a result that is of potential interest for genetics, epidemiology, and demography.

A transient technique for measuring the thermal conductivity of non-metals

Abstract A transient technique for the measurement of the thermal conductivity of non-metals is described. A small sample of material is held between a hot copper block and a cold base, and the thermal conductivity of the material is deduced from the exponential decay in the temperature difference between the copper block and the base. The influences of heat losses from the block and contact resistance are established by calibration. Very rapid measurements may be made to an accuracy of about ±5% over the thermal conductivity range 0.1–1 W/m K, although thermal conductivities outside this range may also be measured with careful operation using samples of an appropriate size. The accuracy and repeatability of the results are demonstrated by the results of tests on small resin samples.

APPLICATION OF RADIOANALYSIS TO THE TRANSPORT OF MICRO-CONSTITUENTS BY DIFFUSION

Predictions on the leaching behaviour of microconstituents from dumped, stored, or immobilised wastes are based on estimates of the effective diffusion coefficients involved, which usually range from ∼10−6 to ∼10−12 cm2·s−1. Radioanalysis, especially radiotracer procedures, can be applied to determine these parameters on small (field) samples of granular material and test specimens of immobilised wastes. A summary of standard experiments for both types of material under non-steady state and steady state conditions is submitted.

Method for the measurement of antioxidant activity in human fluids

Aim—To develop a new, simple, and cheap method for estimating antioxidant activity in human fluids. Methods—The assay measured the capacity of the biological fluids to inhibit the production of thiobarbituric...

High-sensitivity quadrupole mass spectometry system for the determination of hydrogen in irradiated materials

High levels of helium and hydrogen are generated in metals in fusion reactors, and fusion simulations in mixed-spectrum fission reactors, spallation neutron sources, and high-energy charged particle environments. Although hydrogen generation rates are generally higher than those of helium, hydrogen is thought to quickly diffuse out of metals, especially at elevated temperatures. There appear to be some conditions, however, where significant hydrogen retention can occur. To assess this potential, a high-sensitivity analysis system has been developed for the measurement of hydrogen in small samples of irradiated materials. The system is based on a low-volume extraction furnace in combination with a quadrupole mass spectrometer, and has a detection limit of ∼1 appm for steel. Hydrogen levels have been measured in high-energy proton-irradiated tungsten and Inconel 718, in iron-based alloys and vanadium alloys from fusion materials programs, and in stainless steels and pure metals irradiated in light water reactors. Details of the system and typical results are presented.

Noncontact technique for measuring surface tension and viscosity of molten materials using high temperature electrostatic levitation

A new, noncontact technique is described which entails simultaneous measurements of the surface tension and the dynamic viscosity of molten materials. In this technique, four steps were performed to achieve the results: (1) a small sample of material was levitated and melted in a high vacuum using a high temperature electrostatic levitator, (2) the resonant oscillation of the drop was induced by applying a low level ac electric field pulse at the drop of resonance frequency, (3) the transient signals which followed the pulses were recorded, and (4) both the surface tension and the viscosity were extracted from the signal. The validity of this technique was demonstrated using a molten tin and a zirconium sample. In zirconium, the measurements could be extended to undercooled states by as much as 300 K. This technique may be used for both molten metallic alloys and semiconductors.

MCNP modelling of a combined neutron/gamma counter

A series of Monte Carlo neutron calculations for a combined gamma/passive neutron coincidence counter has been performed. This type of device, part of a suite of non-destructive assay instruments utilised for the enforcement of the Euratom nuclear safeguards within the European Union, is to be used for high accuracy measurements of the plutonium content of small samples of nuclear materials. The multi-purpose Monte Carlo N-particle (MCNP) code version 4B has been used to model in detail the neutron coincidence detector and to investigate the leakage self-multiplication of PuO 2 and mixed U-Pu oxide (MOX) reference samples used to calibrate the instrument. The MCNP calculations have been used together with a neutron coincidence counting interpretative model to determine characteristic parameters of the detector. A comparative study to both experimental and previous numerical results has been performed. Sensitivity curves of the variation of the detector's efficiency, ε, to, α, the ratio of (α,n) to spontaneous fission neutron emission rate and to f R, the reals coincidence gate utilisation factor, are presented. Sources of the inaccuracy in the calculations have not yet been fully investigated, because of the vast parameter space to be considered, but values of the coincidence gate utilisation factor derived directly from the MCNP data have been found to be overestimated by about 8.2%. Once bias-corrected, the trends of the real coincidence counts rate as a function of sample mass for three types of sample could be matched to experimental results within 0.33%. This result confirms the possible use of MCNP to calculate response trends accurately for a wide variety of source materials, given a limited experimental calibration set.

Optical measurements of high temperatures for material investigations in nuclear reactor environments

An optical method for high-temperature thermometry in heavy radiation fields has been demonstrated. The measurement system consisted of signal generator, transmitting optical fiber and optical detector. The signal generator was a small blackbody cavity and the radiance from the cavity was used to determine the temperature. The method is applicable to high temperature measurements of small material samples in reactor environments also in strong electromagnetic fields. The theory of operation was confirmed in an experiment at Japan Materials Testing Reactor where the tip of the transmitting pure-silica-core fiber itself served as blackbody cavity and the temperature of a small alumina sample was determined by optical means. It was shown that thermally powered infrared emissive sensors have the ability to be used for the full lifetime of the transmitting optical fibers as temperature data could be obtained for 2 full-power (50 MW) weeks. In the performed experiments the heating was induced mainly by γ -radiation and optically measured temperatures ranged from 250 to 800°C. The demonstrated method relies on simple and compact sensors that require no electro-optical sources and can be used in environments where both nuclear radiation and electromagnetic fields are prevalent for extended periods of time.