Arbitrary Samples Research Articles

Nanoscale nuclear magnetic imaging with chemical contrast.

Scanning probe microscopy is one of the most versatile windows into the nanoworld, providing imaging access to a variety of electronic, dielectric, magnetic and topographic sample properties, depending on the probe used. Here, we demonstrate a scanning probe imaging method that extends the range of accessible quantities to label-free imaging of chemical species while operating on arbitrary samples--including insulating materials--under ambient conditions. Moreover, its sensitivity extends below the surface of a sample, allowing for imaging of subsurface features. We achieve these results by recording NMR signals from a sample surface with a recently introduced scanning probe, a single nitrogen-vacancy centre in diamond. We demonstrate NMR imaging with 10 nm resolution and achieve chemically specific contrast by separating fluorine from hydrogen-rich regions. Our result opens the door to scanning probe imaging of the chemical composition and molecular structure of arbitrary samples. A method with these abilities will find widespread application in materials science, even on biological specimens down to the level of single macromolecules.

The influence of chain defects on the crystallisation behaviour of isotactic polypropylene

The crystallization characteristics of the -, #-and $-phases of isotactic polypropylene were studied for welldefined and fully characterized polymers with varying amounts of stereo- and regio-defects. The specimens enabled us to study separately the influence of the type of chain defect and the concentration of defects on the parameters of interest. A combined defect fraction (CDF) was introduced to describe arbitrary iPP samples with a varying amount of stereo- and regio-defects and a combination thereof. Crystal growth rates were found to decrease linearly with the defect fraction and were substantially stronger influenced by regio-defects as compared with stereo-defects. The deceleration of the growth rate of the #-phase is higher compared to the -phase with increasing defect fraction. We also found a critical defect fraction, (Xcrit) for which the growth rates of the - and #-phases are equal. Analysis of the crystallization was performed using the model of Sanchez and Eby. Results of the analysis are in good agreement with the results found for the samples with a variation in the number of stereo-defects. The excess free energy for incorporating a stereo-defect into the trigonal crystal lattice of the #-phase is lower as compared with the -phase. The theory correctly predicts the critical defect fraction, for which the growth rate of the - and #-phase is equal.

Adaptive variable step algorithm for missing samples recovery in sparse signals

Recovery of arbitrarily positioned samples that are missing in sparse signals recently attracted significant research interest. Sparse signals with heavily corrupted arbitrary positioned samples could be analysed in the same way as compressive sensed signals by omitting the corrupted samples and considering them as unavailable during the recovery process. The reconstruction of the missing samples is done by using one of the well-known reconstruction algorithms. In this study, the authors will propose a very simple and efficient algorithm, applied directly to the concentration measures, without reformulating the reconstruction problem within the standard linear programming form. Direct application of the gradient approach to the non-differentiable forms of measures lead us to introduce a variable step size algorithm. A criterion for changing the adaptive algorithm parameters is presented. The results are illustrated on the examples with sparse signals, including approximately sparse signals and noisy sparse signals.

USO DO PROCEDIMENTO DE MÁSCARA PARA VERIFICAR RELAÇÕES DE CONTROLE DE ESTÍMULOS EM MACACOS-PREGO

Diferenças sutis entre as relações de controle planejadas pelo experimentador e aquelas efetivamente estabelecidas nos treinos discriminativos são frequentemente encontradas em estudos com participantes humanos com desenvolvimento severamente atrasado ou com sujeitos não humanos. Grande parte das vezes, essas diferenças só são identificadas por meio de testes. O presente estudo avaliou a viabilidade do uso do procedimento de máscara para verificar relações de controle em discriminação condicional (emparelhamento ao modelo por identidade) com macacos. Foram utilizados dois macacos da espécie Cebus cf. apella como sujeitos. O procedimento consistiu no treino de emparelhamento ao modelo por identidade e testes de relações de controle, nos quais ora o S+, ora o S– era substituído por uma janela vazia (máscara). Com a remoção desses estímulos em tentativas de sonda, avaliou-se sua participação na determinação de diferentes tipos de relações de controle do comportamento de escolha: Controle pelo S– ou Controle por Rejeição; Controle pelo S+ ou Controle por Seleção; ou ambos, ou seja, Controle Misto. Os dados obtidos mostram que (1) as discriminações estabelecidas não deterioraram com a aplicação dos testes e (2) as escolhas nas tentativas de sonda permitiram inferir com sucesso as relações de controle vigentes. O sujeito M09 apresentou Controle por Rejeição inicialmente em uma das relações condicionais e Controle Misto nas outras relações testadas. O sujeito M16 apresentou Controle Misto em todas as relações testadas. Com esses achados, o procedimento de máscara pode ser considerado adequado para verificação de relações de controle em discriminações condicionais com macacos como sujeitos. Encoraja-se o uso desse procedimento em estudos futuros sobre classes de equivalência com não humanos para verificar se de fato foram estabelecidas relações condicionais arbitrárias modelo-S+ (i.e., Controle por Seleção ou Misto). Palavras-chave: procedimento de máscara, emparelhamento ao modelo por identidade, Cebus cf. apella.

Force sensing with a shaped dielectric micro-tool

We analyse the thermal motion of a holographically trapped non-spherical force probe, capable of interrogating arbitrary samples with nanometer resolution. High speed video stereo-microscopy is used to track the translational and rotational coordinates of the micro-tool in three dimensions, and the complete 6 × 6 stiffness matrix for the system is determined using equipartition theorem. The Brownian motion of the extended structure is described in terms of a continuous distribution of thermal ellipsoids. A centre of optical stress, at which rotational and translational motion is uncoupled, is observed and controlled. Once calibrated, the micro-tool is deployed in two modes of operation: as a force sensor with <150 femto-Newton sensitivity, and in a novel form of photonic force microscopy.

Atomic-scale effects behind structural instabilities in Si lamellae during ion beam thinning

The rise of nanotechnology has created an ever-increasing need to probe structures on the atomic scale, to which transmission electron microscopy has largely been the answer. Currently, the only way to efficiently thin arbitrary bulk samples into thin lamellae in preparation for this technique is to use a focused ion beam (FIB). Unfortunately, the established FIB thinning method is limited to producing samples of thickness above ∼20 nm. Using atomistic simulations alongside experiments, we show that this is due to effects from finite ion beam sharpness at low milling energies combined with atomic-scale effects at high energies which lead to shrinkage of the lamella. Specifically, we show that attaining thickness below 26 nm using a milling energy of 30 keV is fundamentally prevented by atomistic effects at the top edge of the lamella. Our results also explain the success of a recently proposed alternative FIB thinning method, which is free of the limitations of the conventional approach due to the absence of these physical processes.

Symmetric extreme learning machine

Extreme learning machine (ELM) can be considered as a black-box modeling approach that seeks a model representation extracted from the training data. In this paper, a modified ELM algorithm, called symmetric ELM (S-ELM), is proposed by incorporating a priori information of symmetry. S-ELM is realized by transforming the original activation function of hidden neurons into a symmetric one with respect to the input variables of the samples. In theory, S-ELM can approximate N arbitrary distinct samples with zero error. Simulation results show that, in the applications where there exists the prior knowledge of symmetry, S-ELM can obtain better generalization performance, faster learning speed, and more compact network architecture.

Single sine wave parameters estimation method based on four equally spaced samples

This article presents a general method to determine all the parameters of a single wave carrier signal i.e. the frequency, phase, amplitude and DC component, based on four different samples. The analytical formulas are derived for arbitrary samples and finally particularised for equally spaced samples. To check the fairness of our formulas, simulations have been performed in two different scenarios: when the sine-wave that is sampled is affected by white Gaussian noise and when the samples are quantised on a given number of bits. The results show that the relative error of the estimated parameters is decreasing linearly as the signal-to-noise ratio (SNR) increases, with a slope of 0.1/20 dB. When the samples are quantised on a given number of bits, the relative error is decreasing almost linearly with approximately for each extra bit in the sample representation. An increase of the number of bits is more then 15 is no longer useful since the performances are no longer increasing from that point.

Development of Novel Methods for Compensation of Stress-strain Curves

In this study, we analyze in detail the stress variation due to friction between the top surface of a cylindrical sample and the anvil surface by carrying out FEM analysis. We propose pragmatic and simple approaches to compensate the stress-strain curve for both Rastegaev-geometry samples and arbitrary cylindrical samples. By using these equations, the compensation process becomes easy and convenient, and the compensated flow stresses are reliable for the compression process of 5065B aluminum alloy.

Determination of the Metallic/Semiconducting Ratio in Bulk Single-Wall Carbon Nanotube Samples by Cobalt Porphyrin Probe Electron Paramagnetic Resonance Spectroscopy

A simple and quantitative, self-calibrating spectroscopic technique for the determination of the ratio of metallic to semiconducting single-wall carbon nanotubes (SWCNTs) in a bulk sample is presented. The technique is based on the measurement of the electron paramagnetic resonance (EPR) spectrum of the SWCNT sample to which cobalt(II)octaethylporphyrin (CoOEP) probe molecules have been added. This yields signals from both CoOEP molecules on metallic and on semiconducting tubes, which are easily distinguished and accurately characterized in this work. By applying this technique to a variety of SWCNT samples produced by different synthesis methods, it is shown that these signals for metallic and semiconducting tubes are independent of other factors such as tube length, defect density, and diameter, allowing the intensities of both signals for arbitrary samples to be retrieved by a straightforward least-squares regression. The technique is self-calibrating in that the EPR intensity can be directly related to the number of spins (number of CoOEP probe molecules), and as the adsorption of the CoOEP molecules is itself found to be unbiased toward metallic or semiconducting tubes, the measured intensities can be directly related to the mass percentage of metallic and semiconducting tubes in the bulk SWCNT sample. With the use of this method it was found that for some samples the metallic/semiconducting ratios strongly differed from the usual 1:2 ratio.

Inductive conductivity tensor measurement for flowline or material samples

Present-day galvanic-based electrical conductivity measurements are hampered by limitations and necessary corrections, especially in the domain of geological core analysis. Low-accuracy techniques such as crucible, two-electrode, and four-electrode are constricted by current-path requirements, while high-accuracy techniques are time consuming and have limited domains of applicability. We present a novel apparatus capable of electrical conductivity tensor measurements in a noninvasive, noncontact, inductive manner with resolution from 5 mS/m. Inspired by the triaxial induction logging technology appearing in the oil patch today, our apparatus is naturally applicable in a novel way not only to anisotropic geological core analysis but also to arbitrary material samples and flowline systems.

Construction and cross-correlation analysis of the affective physiological response database

Six kinds of emotions, namely joy, surprise, disgust, grief, anger and fear, are elicited from 300 ordinary college students by means of high-rated movie clips. The signals of galvanic skin response (GSR), heart rate (HR), blood volume pulse (BVP), electrocardiogram (ECG), respiration (Rsp.), facial electromyography (EMG) and two channels of electroencephalography (EEG) from the frontal lobe were recorded while the subjects were watching the affective eliciting materials. The samples of each kind of signals are analyzed by using random matrix theory (RMT). From the distribution of the eigenvalues and eigenvectors of the correlation matrices of BVP, facial EMG and two EEGs, we find that the statistical properties of these four kinds of signals coincide with the RMT predictions. However, the largest eigenvalue and the corresponding eigenvector component distribution of the correlation matrices of GSR, HR, ECG and Rsp. have deviated significantly from the RMT predictions. Our experiments also reveal that the correlations between two arbitrary samples of BVP, facial EMG or EEGs does not result from affective response but from random noises, whereas the amplitude variations of GSR, HR, ECG and Rsp. contain the correlated affective physiological response patterns. According to the data analysis results of RMT, 110 features are firstly extracted from the GSR and HR signals, and then a subset of the initial features is selected by using the Backward Selection algorithm. The affective data samples each of which is a vector of the features are classified by using a Fisher classifier, and furthermore, the user-independent emotion recognition systems with good prediction performance are constructed during the model selection process.

Simulation of L X-ray yields induced by He ions

Abstract The PIXE simulation open-source library, LibCPIXE [1] , publicly released, allows the simulation of X-ray yields of PIXE spectra taken from arbitrary samples irradiated with proton beams, including multilayered targets. Nevertheless, IBA analysis of many systems of interest to material sciences and other applications frequently require the quantification of He ions induced X-ray yields. LibCPIXE was thus adapted to this requirement. In this work, simulated intensities of the L lines are compared to the experimental results from W compound samples irradiated with He 2 + ion beams [2] . Problems overcome or faced during this extension to He beams, including fundamental parameters details on the database and approximations used, are discussed.

An efficient algorithm for the stratification and triangulation of an algebraic surface

We present a method to compute the exact topology of a real algebraic surface S, implicitly given by a polynomial f ∈ Q [ x , y , z ] of arbitrary total degree N. Additionally, our analysis provides geometric information as it supports the computation of arbitrary precise samples of S including critical points. We compute a stratification Ω S of S into O ( N 5 ) non-singular cells, including the complete adjacency information between these cells. This is done by a projection approach. We construct a special planar arrangement A S with fewer cells than a cad in the projection plane. Furthermore, our approach applies numerical and combinatorial methods to minimize costly symbolic computations. The algorithm handles all sorts of degeneracies without transforming the surface into a generic position. Based on Ω S we also compute a simplicial complex which is isotopic to S. A complete C++-implementation of the stratification algorithm is presented. It shows good performance for many well-known examples from algebraic geometry.

Sheath Voltage Estimation for Inductively Coupled Plasma Etcher by Impedance Analysis

A thick quartz glass is etched using an inductively coupled plasma device under constant antenna power. Sheath voltage, which is the RF voltage from the plasma edge to the sample surface, is estimated by impedance analysis. Sheath resistance and sheath capacitance are determined from some experimental bias voltage, which is the RF voltage applied to the sample bed electrode. Once they are determined, the bias and sheath voltages for arbitrary thick samples and bias power can be calculated. The calculated bias voltages agree with the experimental ones within 5%. Etching rate is proportional to sheath voltage for various etching conditions. A quartz sample 5-mm-thick can be etched at the same etch rate as a thin quartz sample using a thick quartz sample bed with a hole where the quartz sample is placed.

Spatial Localization with Single-Sided NMR Sensors

In the last years, special effort has been made to achieve spatial localization with single-sided nuclear magnetic resonance systems. The implementation of three-dimensional imaging techniques on such sensors converted the tool in a truly noninvasive open tomograph useful to resolve the structure of arbitrary large samples. This paper summarizes the strategy developed to incorporate spatial resolution on open sensors, and presents a number of applications that illustrate the performance of the technique in fields like quality control, medicine, and materials science. In some cases the structure of the sample under study changes only along the depth direction. To resolve the depth structure with high resolution, a sensor generating strong and highly uniform static gradient has been presented. This profiling tool quickly found important applications in resolving multilayer structures, where even dynamic processes happening at the surface of the sample can be followed in real time. In this work the method is used to study the efficiency of barrier layers included to stop the diffusion of solvents penetrating into the sample and to study aging processes that degrade the material structure. These examples demonstrate the potential of single-sided sensors to assist in the design of materials with improved properties.

Simultaneous PIXE and RBS data analysis using Bayesian inference with the DataFurnace code

The Rutherford backscattering spectroscopy (RBS) and particle induced X-ray emission (PIXE) techniques can be used to obtain complementary information about the characteristics of a sample but, traditionally, a gap has separated the available computer codes for analyzing data from each technique, being hard to simultaneously analyze data from the same sample. The recent development of a free and open source library, LibCPIXE, for PIXE simulation and analysis of arbitrary multilayered samples, has permitted to integrate this technique into the DataFurnace code which already handles many other IBA techniques such as Rutherford and non-Rutherford backscattering, elastic recoil detection and non-resonant nuclear reaction analysis. The fitting capabilities of DataFurnace can therefore now be applied to PIXE spectra as well, including the Bayesian inference analysis and the simultaneous and coherent fitting of multiple spectra from different techniques. Various examples are presented in which the simultaneous RBS and PIXE analysis allows us to obtain consistent results that cannot be obtained by independent analysis of the data from each technique.

LibCPIXE: A PIXE simulation open-source library for multilayered samples

Most particle induced X-ray emission (PIXE) data analysis codes are not focused on handling multilayered samples. We have developed an open-source library called “LibCPIXE”, for PIXE data analysis. It is written in standard C and implements functions for simulating X-ray yields of PIXE spectra taken from arbitrary samples, including multilayered targets. The library is designed to be fast, portable, modular and scalable, as well as to facilitate its incorporation into any existing program. In order to demonstrate the capabilities of the library, a program called CPIXE was developed and used to analyze various real samples involving both bulk and layered samples. Just as the library, the CPIXE source code is freely available under the General Public License. We demonstrate that it runs both under GNU/Linux systems as well as under MS Windows. There is in principle no limitation to port it to other platforms.

AB‐plot assisted determination of fluorophore mixtures in a fluorescence lifetime microscope using spectra or quenchers

Most treatments of frequency domain lifetime measurements indicate that a set of measurements must be made at multiple frequencies in order to determine the lifetimes of the components in a mixture. Although this is the case in general, under special conditions, single-frequency data can resolve multiple lifetimes. Here, data are presented showing several approaches to determining fluorescence lifetimes in two-component mixtures using single-frequency data. Common to all of the procedures presented is exploitation of variations in the relative contributions of a particular fluorophore to the total fluorescence from a mixture of fluorophores. This variation can be produced intentionally by observing a number of samples which contain different relative amounts of the fluorophores. It can be produced fortuitously by observing spatial variations in a mixture of fluorophores in a specimen or set of specimens observed with a lifetime imaging system. It can also be produced by examination of the lifetime spectrum obtained from a fluorophore mixture or by varying the concentration of a quencher in a fluorophore mixture, in which the two fluorophores have different rate constants for quenching. In many instances, the set of approaches presented here will be unsuitable for examination of arbitrary samples of unknown composition for which the multifrequency approach should be used. However, measurements produced using single-frequency methods may be applied to good effect for controlled experiments having defined fluorophores or sets of fluorophores, particularly in the case of biological lifetime imaging studies.

Comparison of Analytical Techniques for Purity Evaluation of Single-Walled Carbon Nanotubes

We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of this paper is to provide the chemical community with a realistic evaluation of current analytical tools for the purity evaluation of a bulk sample of SWNTs. The secondary goal is to draw attention to the growing crisis in the SWNT industry as a result of the lack of quality control and the misleading advertising by suppliers of this material.