Sample Size Dependence Research Articles

Frictional behaviour of sandstone: A sample-size dependent triaxial investigation

Frictional behaviour of rocks from the initial stage of loading to final shear displacement along the formed shear plane has been widely investigated in the past. However the effect of sample size on such frictional behaviour has not attracted much attention. This is mainly related to the limitations in rock testing facilities as well as the complex mechanisms involved in sample-size dependent frictional behaviour of rocks.In this study, a suite of advanced triaxial experiments was performed on Gosford sandstone samples at different sizes and confining pressures. The post-peak response of the rock along the formed shear plane has been captured for the analysis with particular interest in sample-size dependency. Several important phenomena have been observed from the results of this study: a) the rate of transition from brittleness to ductility in rock is sample-size dependent where the relatively smaller samples showed faster transition toward ductility at any confining pressure; b) the sample size influences the angle of formed shear band and c) the friction coefficient of the formed shear plane is sample-size dependent where the relatively smaller sample exhibits lower friction coefficient compared to larger samples.We interpret our results in terms of a thermodynamics approach in which the frictional properties for finite deformation are viewed as encompassing a multitude of ephemeral slipping surfaces prior to the formation of the through going fracture. The final fracture itself is seen as a result of the self-organisation of a sufficiently large ensemble of micro-slip surfaces and therefore consistent in terms of the theory of thermodynamics. This assumption vindicates the use of classical rock mechanics experiments to constrain failure of pressure sensitive rocks and the future imaging of these micro-slips opens an exciting path for research in rock failure mechanisms.

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N2O decomposition by microwave discharge

RationaleTriple oxygen and nitrogen isotope ratios in nitrate are powerful tools for assessing atmospheric nitrate formation pathways and their contribution to ecosystems. N2O decomposition using microwave‐induced plasma (MIP) has been used only for measurements of oxygen isotopes to date, but it is also possible to measure nitrogen isotopes during the same analytical run.MethodsThe main improvements to a previous system are (i) an automated distribution system of nitrate to the bacterial medium, (ii) N2O separation by gas chromatography before N2O decomposition using the MIP, (iii) use of a corundum tube for microwave discharge, and (iv) development of an automated system for isotopic measurements. Three nitrate standards with sample sizes of 60, 80, 100, and 120 nmol were measured to investigate the sample size dependence of the isotope measurements.ResultsThe δ17O, δ18O, and Δ17O values increased with increasing sample size, although the δ15N value showed no significant size dependency. Different calibration slopes and intercepts were obtained with different sample amounts. The slopes and intercepts for the regression lines in different sample amounts were dependent on sample size, indicating that the extent of oxygen exchange is also dependent on sample size. The sample‐size‐dependent slopes and intercepts were fitted using natural log (ln) regression curves, and the slopes and intercepts can be estimated to apply to any sample size corrections. When using 100 nmol samples, the standard deviations of residuals from the regression lines for this system were 0.5‰, 0.3‰, and 0.1‰, respectively, for the δ18O, Δ17O, and δ15N values, results that are not inferior to those from other systems using gold tube or gold wire.ConclusionsAn automated system was developed to measure triple oxygen and nitrogen isotopes in nitrate using N2O decomposition by MIP. This system enables us to measure both triple oxygen and nitrogen isotopes in nitrate with comparable precision and sample throughput (23 min per sample on average), and minimal manual treatment. Copyright © 2016 John Wiley & Sons, Ltd.

Size Dependence of Oxygen-Annealing Effects on Superconductivity of Fe1+yTe1−xSx

For the Fe-based superconductor Fe{1+y}Te{1-x}S{x}, superconductivity is induced by annealing treatment in oxygen atmosphere, whereas as-grown samples do not show superconductivity. We have investigated the sample-size dependence of O2-annealing effects in Fe1.01Te0.91S0.09. The annealing conditions are fixed to be 1 atm, 200 C, and 2 hours. We have carried out magnetic susceptibility and specific heat measurements in order to evaluate the superconducting volume fraction. We have found that Fe{1+y}Te{1-x}S{x} has an optimal size for the induction of bulk superconductivity by O2 annealing. Our results indicate that O2 annealing is probably effective near the surface of samples over a length of a few tens of micro meters.

Glassy features of crystal plasticity

Crystal plasticity occurs by deformation bursts due to the avalanche-like motion of dislocations. Here we perform extensive numerical simulations of a three-dimensional dislocation dynamics model under quasistatic stress-controlled loading. Our results show that avalanches are power-law distributed, and display peculiar stress and sample size dependence: The average avalanche size grows exponentially with the applied stress, and the amount of slip increases with the system size. These results suggest that intermittent deformation processes in crystalline materials exhibit an extended critical-like phase in analogy to glassy systems, instead of originating from a non-equilibrium phase transition critical point.

Sample size and orientation effects of single crystal aluminum

The mechanical behavior of single crystal Al sample with different sizes in mini-, micro- and nano-scales and different loading directions along [111] and [110] have been systematically investigated. The sample size and orientation effects are examined. The results are compared with previously reported data on other face-centered cubic Ni, Cu, Au and Ag, establishing an interesting trend for sample size effect with respect to stacking fault energy. With higher stacking fault energy and thus higher dislocation mobility such as Al, the sample size dependence would be lower.

Influence of pH, Temperature and Sample Size on Natural and Enforced Syneresis of Precipitated Silica

The production of silica is performed by mixing an inorganic, silicate-based precursor and an acid. Monomeric silicic acid forms and polymerizes to amorphous silica particles. Both further polymerization and agglomeration of the particles lead to a gel network. Since polymerization continues after gelation, the gel network consolidates. This rather slow process is known as “natural syneresis” and strongly influences the product properties (e.g., agglomerate size, porosity or internal surface). “Enforced syneresis” is the superposition of natural syneresis with a mechanical, external force. Enforced syneresis may be used either for analytical or preparative purposes. Hereby, two open key aspects are of particular interest. On the one hand, the question arises whether natural and enforced syneresis are analogous processes with respect to their dependence on the process parameters: pH, temperature and sample size. On the other hand, a method is desirable that allows for correlating natural and enforced syneresis behavior. We can show that the pH-, temperature- and sample size-dependency of natural and enforced syneresis are indeed analogous. It is possible to predict natural syneresis using a correlative model. We found that our model predicts maximum volume shrinkages between 19% and 30% in comparison to measured values of 20% for natural syneresis.

Comparison of methods to determine triple oxygen isotope composition of N2O

The oxygen isotope anomaly, Δ(17) O, of N2 O and nitrate is useful to elucidate nitrogen oxide dynamics. A comparison of different methods for Δ(17) O measurement was performed. For Δ(17) O measurements, N2 O was converted into O2 and N2 using microwave-induced plasma in a quartz or corundum tube reactor, respectively, or conversion was carried out in a gold wire oven. In each case, isotope ratios were measured by isotope ratio mass spectrometry. All the tested methods showed acceptable precision (coefficient of variation <2.4 % at 160 nmol N2 O) with high sample size but the sample size dependence was lowest when using microwave-induced plasma in a corundum tube reactor. The use of microwave-induced plasma in a corundum tube yields best results for Δ(17) O measurement on N2 O gas samples.

Matrix Powers in Spatial Econometric Models

This paper demonstrates several implications of the Cayley-Hamilton Theorem for specification, estimation, and identification of spatial autoregressive models. First, the minimal polynomial of the spatial weights matrix implies an upper bound on the admissible lag order in spatial autoregressive models when powers of the weights matrix are used to form higher-order spatial lags. Second, knowledge of the minimal polynomial facilitates the derivation of closed-form solutions of the marginal effects. Compared to the common practice of numerically inverting the spatial lag polynomial, the use of closed-form solutions enhances the interpretation of the structural model parameters and can be computationally attractive in large samples. Moreover, I demonstrate that the numerical inversion approach may result in biased finite-sample estimates of the marginal effects due to the sample size dependence of the spatial weights matrix even if all coefficient estimates are unbiased. The closed-form solutions can be used to obtain an exact expression of the bias and to avoid it in the first place. Third, I show that the matrix exponential spatial specification has a restricted spatial autoregressive model representation. Finally, I highlight that the order of the minimal polynomial of the spatial weights (or social interaction) matrix is related to the identification of endogenous and exogenous interaction effects in social networks.

Size Dependence of Individual Vortex Penetration into Intrinsic Josephson Junction Stacks of Bi2Sr2CaCu2O8+y

By c-axis transport measurements in an intrinsic Josephson junctions (IJJs) stack of Bi2Sr2CaCu2O8+y in magnetic fields parallel to c-axis, a penetration of individual vortices can be detected as a sudden jump or drop of c-axis resistance or critical current, which has already been reported in a sample of small in-plane area (<2μm2). We explored the individual vortex penetrations in IJJs stacks with much larger in-plane areas and successfully observed the same phenomenon even in a sample as large as 100μm2. Behavior of the c-axis resistance and critical current caused by the individual vortex penetrations are investigated through the sample-size dependence in various temperatures and magnetic fields.

B2-26 表面張力によるメルトフォームの組織緩和実験 : 試料サイズ依存性(浅部マグマ上昇過程,口頭発表)

B2-26 表面張力によるメルトフォームの組織緩和実験 : 試料サイズ依存性(浅部マグマ上昇過程,口頭発表)

Statistics of crystallization kinetics in nanoscale systems

We investigate the statistics of the crystallization kinetics caused by the finite size of nanoscale samples. We define a characteristic length, L C , as a function of the material properties, in order to describe the sample size dependence of the statistics. We find that the samples smaller than L C undergo single-nucleus crystallization, which yields wide distributions of the half-transition time. Finally, we apply our theory to find a way to improve the data retention statistics of sub-20 nm phase-change memory.

In Surgical Treatment of Non-Small-Cell Lung Cancer a Minimum Number of Resected Mediastinal Lymph Nodes Is Mandatory for Accurate Staging

Objective: Increased numbers of removed lymph nodes (LN) are resulting in more accurate staging of the patient (Will-Rogers-Phenomenon). This study evaluates dependence of lymph node sample size to 1) Will-Rogers-Phenomenom, 2) influence of sample size on overall survival and in terms of 3) morbidity and mortality. Methods: 131 patients after pulmonary resection were retrospectively analysed concerning surgery, number of removed lymph nodes, stage, complications and survival. Patients were stratified according to the median number of lymph nodes in two groups (A <12 lymph nodes and B ≥12 lymph nodes). Results: 5% of the patients had only local lymphadenectomy and in 14% a systematic lymphadenectomy was performed. 17% of the patients showed skip metastasis. Lymph node positivity was correlated to the number of removed lymph nodes (p = 0.003). The approximated median survival for UICC (Union internationale contre le cancer) stage I was 511, stage II 521 and stage III 290 days. Subgroup analysis of survival data showed in group A an approximated median survival at stage I of 495 days, at II 537 days and at III 451.5 days. Group B showed at stage I 675 days, at II 521 days and at III 221 days. There was no difference in complications and mortality. Conclusion: A too low sample size leads to understaging due to skip metastasis. Obligatory mediastinal lymph node sampling would decrease the risk of understaging due to skip metastasis and does not increase morbidity or complications. Lymph node sampling is not inferior concerning morbidity and survival in our patient collective. This study cannot recommend a minimum number of LN to be resected. The evaluated limit of 12 LN proves to be suitable as a guideline.

Effect of size and base-element on the jerky flow dynamics in metallic glass

The jerky flow behavior of metallic glasses (MGs) is systematically investigated in this work for various alloy compositions, ranging from the commonly conceived “ductile” MGs, such as those based on Zr and Cu, to the “brittle” ones, such as those based on Mg and Fe, on the microscopic scale. Through extensive microcompression studies, a clear sample size and base-element dependence of the jerky flow in MGs is revealed, which shows that the stress-drop amplitude, as normalized by the corresponding MG yield strength, reduces with decreasing sample size or increasing elastic modulus. Meanwhile, the temporal discontinuity of the jerky flow, as characterized by the duration of the stress-drop event and the delay between two consecutive events, also displays similar size and base-element dependence. Finally, a unified theory based on stick–slip dynamics is proposed to explain the coupled size and base-element effects.

Fish Passage Behavior for Severe Hydraulic Conditions in Baffled Culverts

AbstractLaboratory tests were conducted with brown trout to evaluate their ability to pass through a small, baffled prototype-scale culvert under a variety of culvert slopes and discharge conditions. The culvert was 18.3 m long and 0.60 m in diameter with 0.15D baffle height and 0.9D spacing, where D is the culvert inside diameter. An inverse relationship was observed between fish passage success and flow rate and/or culvert slope. The influence of the sample fish population and the length of the individual fish on passage rates were investigated; the data showed that the brown trout fish passage sample size evaluated in this study (25 per test) was sufficiently large to minimize sample size dependency. The elapsed time required for fish to traverse the culvert decreased with increasing hydraulic difficulty primarily owing to diminishing resting zones. The behavior of fish traversing the culvert was observed and reported, including resting/staging zone locations.

Transmission Resonance Raman Spectroscopy: Experimental Results versus Theoretical Model Calculations

A laser spectroscopic technique is described that combines transmission and resonance-enhanced Raman inelastic scattering together with low laser power (< 30 mW) and good spatial resolution (< 200 μm) as operational features. The monitoring of the transmitted inelastic scattering provides an increased signal-to-noise ratio because the low fluorescence background and, on the other hand, the resonant character of the laser excitation, leads to enhanced analytical sensitivity. The spectroscopic technique was applied to investigate the carotenoid content (specifically the β-carotene concentration) of distinct samples that included fruits, reaching a detection limit of the order of hundreds of picograms in solid samples, which is below the level needed for typical food control analysis. Additional features of the present development are direct sampling, noninvasive character, and fast analysis that is not time consuming. From a theoretical point of view, a model for the Raman signal dependence on the sample thickness is also presented. Essentially, the model considers the sample to be homogeneous and describes the underlying physics using only three parameters: the Raman cross-section, the laser-radiation attenuation cross-section, and the Raman signal attenuation cross-section. The model was applied successfully to describe the sample-size dependence of the Raman signal in both β-carotene standards and carrot roots. The present technique could be useful for direct, fast, and nondestructive investigations in food quality control and analytical or physiological studies of animal and human tissues.

Cast defects induced sample-size dependency on compressive strength and fracture toughness of Mg–Cu–Ag–Gd bulk metallic glass

In this work, Mg59.5Cu22.9Ag6.6Gd11 bulk metallic glass (BMG) is selected to investigate the specimen-size dependency of the compressive fracture strength and notch toughness. As the diameter of cylindrical sample increases, apparent fracture strength is reduced by 25% from ∼950MPa at 1-mm down to ∼710MPa at 10-mm sample, which is associated with the population and size of as-cast porosity in the BMG rods as indicated by X-ray computed tomography (CT). Meanwhile, it is inappropriate to describe the size dependence of fracture strength using Weibull or Gumbel statistics owing to the inhomogeneous distribution of cast defects in different sized rods. Similar to the compressive fracture strength, cast defects in Mg59.5Cu22.9Ag6.6Gd11 BMG also yield specimen-size dependency of the measured notch toughness, when the plate-specimen thickness varies within the range of 1–8mm. With three-parameter Weibull analysis, threshold toughness Kμ of as-cast Mg59.5Cu22.9Ag6.6Gd11 BMG can be estimated, which represents a minimum toughness value below which the cracks arrest. Using finite element analysis, it is confirmed that the specimen-thickness dependency of notch toughness does not result from the transition from plane-stress to plane-strain in the specimen, but from the extrinsic flaws.

Hierarchical Linear Modeling Meta-Analysis of Single-Subject Design Research

The identification of evidence-based practices continues to provoke issues of disagreement across multiple fields. One area of contention is the role of single-subject design (SSD) research in providing scientific evidence. The debate about SSD’s utility centers on three issues: sample size, effect size, and serial dependence. One potential method for addressing all three issues is hierarchical linear modeling (HLM) meta-analysis. This study explored the utility of HLM meta-analysis of SSD. A total of 206 functional behavior assessment–based intervention outcome graphs were aggregated to assess whether HLM meta-analysis could identify (a) an overall effect size and statistical significance for mean shift, slope, and variability; (b) how the results mapped to two additional effect size calculations; and (c) whether the procedure met SSD synthesis criteria outlined by Wolery, Busick, Reichow, and Barton.

Role of Dislocation Density on the Sample-Size Effect in Nanoscale Plastic Yielding

AbstractThe sample-size dependence of plastic yielding in nanoscale metal pillars is not a purely geometrical fact, explainable just in terms of shape and geometry of the pillar, but depends on the actual content of inner dislocations. The present study discusses the role of the initial density of bulk dislocations ρ on the power-law scaling that describes the strengthening effect in yield stress. This paper reports on in-situ mechanical tests on highly miniaturized focused-ion-beam (FIB)–machined Ni pillars and buttons (i.e., very short pillars) of diameters D∼200–300 nm specifically conducted to highlight the decrease in hardness and the disappearance of the power—law scaling that may accompany a controlled decrease in ρ. From an experimental standpoint, it is further demonstrated that nanoindentation tests on pillars make for a useful companion test to standard microcompression to assess actual hardness increase with reducing sample size.

Case study and proofs of ant colony optimisation improved particle filter algorithm

Particle filters (PF), as a kind of non-linear/non-Gaussian estimation method, are suffering from two problems in large-dimensional cases, namely particle impoverishment and sample size dependency. Previous studies from the authors have proposed a novel PF algorithm that incorporates ant colony optimisation (PFACO), to alleviate these problems. In this paper the authors will provide a theoretical foundation of this new algorithm; two theorems are introduced to validate that the PFACO introduces smaller Kullback–Leibler divergence (K–L divergence) between the proposal distribution and the optimal one compared to those produced by the generic PF. In addition, with the same threshold level, the PFACO has a higher probability than the generic PF to achieve a certain K–L divergence. A mobile robot localisation experiment is applied to examine the performance between various PF schemes.

Evidence for intrinsic superconductivity at Tc1 in PrOs4Sb12

Superconductivity in PrOs4Sb12 shows unusual sample size dependence. Large good quality crystals exhibit two superconducting transitions at Tc1 (∼1.85 K) and Tc2 (∼1.74 K). The upper temperature transition is manifested by the change of slope in C/T. It is shown that this transition is suppressed when the crystal is polished to a thickness smaller than 50 μm. At the same time the polishing enhances the transition at Tc2. This behavior is independent on whether material studied is removed from the interior or contains the original surface of the as-cast crystal. The effect of sample polishing is similar to that of powdering, which clearly induces a large number of defects.