A Novel Hybrid Gradient-Based Optimizer and Grey Wolf Optimizer Feature Selection Method for Human Activity Recognition Using Smartphone Sensors

Human activity recognition (HAR) plays a vital role in different real-world applications such as in tracking elderly activities for elderly care services, in assisted living environments, smart home interactions, healthcare monitoring applications, electronic games, and various human–computer interaction (HCI) applications, and is an essential part of the Internet of Healthcare Things (IoHT) services. However, the high dimensionality of the collected data from these applications has the largest influence on the quality of the HAR model. Therefore, in this paper, we propose an efficient HAR system using a lightweight feature selection (FS) method to enhance the HAR classification process. The developed FS method, called GBOGWO, aims to improve the performance of the Gradient-based optimizer (GBO) algorithm by using the operators of the grey wolf optimizer (GWO). First, GBOGWO is used to select the appropriate features; then, the support vector machine (SVM) is used to classify the activities. To assess the performance of GBOGWO, extensive experiments using well-known UCI-HAR and WISDM datasets were conducted. Overall outcomes show that GBOGWO improved the classification accuracy with an average accuracy of 98%.     

Exponentially Weighted Multivariate HAR Model with Applications in the Stock Market

This paper considers a multivariate time series model for stock prices in the stock market. A multivariate heterogeneous autoregressive (HAR) model is adopted with exponentially decaying coefficients. This model is not only suitable for multivariate data with strong cross-correlation and long memory, but also represents a common structure of the joint data in terms of decay rates. Tests are proposed to identify the existence of the decay rates in the multivariate HAR model. The null limiting distributions are established as the standard Brownian bridge and are proven by means of a modified martingale central limit theorem. Simulation studies are conducted to assess the performance of tests and estimates. Empirical analysis with joint datasets of U.S. stock prices illustrates that the proposed model outperforms the conventional HAR models via OLSE and LASSO with respect to residual errors.     

Application of a portable nuclear magnetic resonance surface probe to porous media

A portable nuclear magnetic resonance (NMR) surface probe was used to determine the time-dependent self-diffusion coefficient D(t) of water molecules in two fluid-filled porous media. The measuring equipment and the inhomogeneous magnetic fields in the sensitive volume of the probe are described. It is discussed how to evaluate D(t) using a surface probe from the primary and stimulated echoes generated in three-pulse experiments. Furthermore, the evaluation of D(t) allows one to determine the geometrical structure of porous materials.     

Near-field scanning optical microscopy based on surface-enhanced Raman scattering

We describe a near-field optical microscopy technique based on the interaction of a probe molecule with the sample surface (e.g., with a flat metal surface) in the field of external optical radiation and consider the spontaneous Raman scattering characterized, in the presence of a metal surface, by the effective polarizability of the probe molecule, depending on the frequency and the distance to the sample surface. At certain distances from the probe molecule to the surface, the effective polarizability of this molecule (determined with allowance for the polarizing influence of the surface of a semi-infinite medium) at the Stokes frequency sharply increases in comparison to the quantum polarizability of an isolated molecule, which is indicative of the formation of optical near-field resonances. It is shown that the proposed method of near-field optical microscopy is characterized by high sensitivity and high spatial resolution (on the order of 1 Å).     

纳米表面相互作用及振动测头模型

如何实现高精度的测量是现代制造业及微电子技术领域的热点问题之一. 基于微纳米测头的三坐标测量机是当前实现高精度测量的重要手段. 随着测量尺寸的减小, 常用的纳米/微纳尺度的测头与待测表面之间形成静态接触, 其表面相互作用成为了影响其测量精度和可靠性的关键因素之一. 本文基于一种触发式振动测头, 研究了其动力学模型, 并通过对测头纳米尺度表面相互作用的理论分析及数值模拟, 确立了测头振动参数与表面相互作用之间的关联. 实验研究表明, 参数优化后的谐振微纳测头能有效抑制表面作用带来的干扰, 提高测量精度.     

First-principles study on exchange force image of NiO(0 0 1) surface using a ferromagnetic Fe probe

Exchange force of a ferromagnetic Fe probe on antiferromagnetic NiO(0 0 1) surface has been investigated by means of a first-principles calculation. Calculated exchange force images show a clear spin image when the probe is located within 1 Å above the contact point. We can see antiferromagnetic pattern of the surface Ni atoms along the [1 1 0] direction, and asymmetric feature around surface O sites. The main contrast of Ni comes from the direct exchange interaction between the Fe probe and the surface Ni atom, while the asymmetric image possibly comes from the super exchange interaction between the Fe probe and the second layer Ni atom via the surface O. Such asymmetric feature is a key proof of the exchange force microscope image on observation.     

Misalignment error calibration of faro retro probe for laser tracker system

A technique to calibrate faro retro probe using laser tracker system (LTS) is presented. The deep-access retro probe enables LTS to perform three-dimensional (3D) measurements of surface hidden features. It has been shown that misalignment errors are the key contributor to measuring errors of retro probe. A device for measuring misalignment errors of retro probe is invented. Theoretical analysis and experiment show that using this technique to calibrate retro probe, the misalignment errors of retro probe can be eliminated effectively and quickly.     

Enhanced optical sensitivity to adsorption due to depolarization of anisotropic surface states

Reflectance difference spectroscopy is used to probe the optical transitions between surface states on the Cu(110) surface. Upon deposition of smallest amounts of carbon monoxide (CO) the signal is strongly quenched, which translates into a huge cross section of the order of 1000 A(2) for a single adsorbed CO molecule. This strongly enhanced surface sensitivity is interpreted as the loss in anisotropy (depolarization) of the surface states due to scattering from the adsorbed CO molecules. This feature renders RDS an extremely sensitive tool to probe the adsorption kinetics on anisotropic metal surfaces.     

Characterization of photovoltage evolution of ZnO films using a scanning Kelvin probe system

Work function (WF) and surface photovoltage evolution of films can be measured using the Kelvin probe technique, and further analysis of the photoelectronic behavior can provide information on the energy level structure. In this paper, a theoretical analysis to measure surface photovoltage using Kelvin probe technique is presented. Based on this analysis, the surface photovoltage and its time-resolved evolution process as well as the energy level structure of ZnO films are determined using a scanning Kelvin probe. The present study therefore provides a simple and practical methodology for the characterization of the electronic behavior of films.     

Molecular dynamics simulation study of the nano-wear characteristics of alkanethiol self-assembled monolayers

A molecular dynamics (MD) simulation study of the probe-based nano-lithography of an alkanethiol self-assembled monolayer (SAM) on a metal surface was performed. The motivation of this work was to understand the nano-tribological phenomena of the nano-metric scribing process of alkanethiol molecules and gain insight into the interaction between the probe tip and the SAM-coated surface during the scribing process. The simulation results revealed that the organothiol molecules were displaced and dragged by the probe tip during scribing due to the strong interchain interactions. It was also found that the scribed pattern width was largely dependent on the tip–surface interaction induced by the probe shape rather than the tip–surface contact size. Also, the minimum load for tip–substrate contact changed with the number of molecules that interact with the probe tip. Furthermore, from the investigation of the effect of the scribing speed on the surface-damage characteristics of the chain molecules, it was found that relatively high-speed scribing could induce excessive removal of the SAM molecules from the surface. PACS 02.70.Ns; 31.15.Qg; 81.16.Nd; 68.35.Af     

扰动角关联在表面研究中的应用

扰动角关联方法,作为一种超精细相互作用技术,具有高的微观灵敏度,可研究局部范围的表面性质.其在表面研究中的应用已涉及表面现象的各个方面,揭示了一系列感兴趣的现象.通过测量作用在探核上的电场梯度,可辨认探针在表面的不同位置,研究杂质与探针相互作用及扩散过程.利用扰动角关联技术已经观察到探核从表面吸附位置经与台阶有关的位置到达表面最上层晶格点阵替位的微扩散过程.本文综述扰动角关联在表面物理研究中的应用以及Ni 单晶表面和超薄Ni 膜磁性质研究的最新结果. Recently,the perturbed angular correlation (PAC) technique with the microscopicsensitivity to study local surface properties has been applied to study surface phenomena.The electricfield gradient acting at the probe nuclei can serve as a fingerprint to elucidate different probe sites atthe surface,impurity-probe configurations and diffusion of impurities.The microscopic diffusion ofPAC-probes from adatomic sites via step sites to substitutional terrace sites has been observed withPAC...     

Fabrication of high-aspect-ratio silicon nanostructures using near-field scanning optical lithography and silicon anisotropic wet-etching process

A new process in which near-field scanning optical lithography (NSOL) is combined with anisotropic wet-etching of (110) silicon is developed for the fabrication of high-aspect-ratio (HAR) nanochannels. In the proposed process, NSOL is applied to produce nanopatterns on a commercial positive photoresist as in an optical lithography. The use of a commercial photoresist is an advantage of this process because it allows the direct application of many photoresists currently available without pretreatment, saving cost and time. A bare (110) silicon wafer coated with a thin Si₃N₄ layer, of approximately 10 nm thickness, is used as the sample and the photoresist is spincoated on the Si₃N₄ layer to a thickness of about 50–80 nm. Nanopatterning of the photoresist using a contact mode NSOL, transfer of the photoresist pattern onto the Si₃N₄ layer by reactive ion etching, and anisotropic wet etching of the silicon wafer using the patterned Si₃N₄ layer as an etch mask, lead to the intended HAR nanostructures. Fabrication of silicon nanochannels with a channel width below 150 nm and an aspect ratio greater than 3 is demonstrated. PACS 81.16.Nd; 81.16.Rf; 85.40.Hp     

Electrostatic Probes for Studying Transport Properties in Tokamak Plasmas

Electrostatic probes for measuring the boundary plasma in tokamaks are reviewed and presented. Transport properties in JFT‐2, the ion temperature and the magnetic surface in JFT‐2M and floating potential fluctuations during the strong additional heating in JT‐60 are measured by several types of electrostatic probe the above‐mentioned purposes. The Langmuir probe including the double probe is applied to measure the spatial profile of boundary plasma in JFT‐2. The ion sensitive probe, the rotating cylindrical double probe, the asymmetric double probe and the differential double probe are applied to measure the ion temperature and magnetic surface in JFT‐2M. The reciprocating Langmuir probe applied to JFT‐2M observes the potential and density fluctuations and a new type probe is proposed for the quick diagnostic of core hot plasmas as a development of this probe. The fluctuation observed in JT‐60 is identified to be the ion cyclotron instability of the hot plasma caused by the strong anisotropy of the ion distribution function (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Au表面等离子体激元激发的扫描探针电子能谱

结合扫描隧道显微镜（STM）与电子能谱仪是实现表面微区元素分析的途径之一．我们将环形电子能量分析器和三维扫描探针系统相结合,建立了一台扫描探针电子能谱仪(SPEES)．通过测量针尖近场发射束流激发的Au表面能量损失谱,我们用研究了Au原子的等离子体激元激发现象．进一步通过改变针尖－样品距离,我们研究了Au等离子体激元峰与弹性散射峰的强度比随针尖－样品距离变化的关系．研究结果发现该强度比与针尖－样品距离的关系并不是单调变化,而是在一个特定位置存在极大．     

Tribological behavior of micro/nano-patterned surfaces in contact with AFM colloidal probe

In effort to investigate the influence of the micro/nano-patterning or surface texturing on the nanotribological properties of patterned surfaces, the patterned polydimethylsiloxane (PDMS) surfaces with pillars were fabricated by replica molding technique. The surface morphologies of patterned PDMS surfaces with varying pillar sizes and spacing between pillars were characterized by atomic force microscope (AFM) and scanning electron microscope (SEM). The AFM/FFM was used to acquire the friction force images of micro/nano-patterned surfaces using a colloidal probe. A difference in friction force produced a contrast on the friction force images when the colloidal probe slid over different regions of the patterned polymer surfaces. The average friction force of patterned surface was related to the spacing between the pillars and their size. It decreased with the decreasing of spacing between the pillars and the increasing of pillar size. A reduction in friction force was attributed to the reduced area of contact between patterned surface and colloidal probe. Additionally, the average friction force increased with increasing applied load and sliding velocity.     

Electric-potential-measurement-based methodology for estimation of electric charge density at the surface of tribocharged insulating slabs

The auto-compensated electrostatic induction probe (ACEIP) is widely used for measuring the electric potential at the surface of conductive or insulating bodies. The aim of this paper is to elaborate a methodology for using this probe in view of performing the estimation of electric charge density at the surface of tribocharged insulating slabs. In such cases, the electric potential is not uniformly distributed on the surface under investigation. Metallic plates trimmed with different shapes were used to characterize the probe. Thus, a first series of experiments enabled a crude evaluation of the shape and size of the area “seen by the probe”: a 10-mm-diameter circle. Other experiments served to determine the transfer function that relates the value measured by the probe to the potential of a small area of constant electric potential located at a well-defined distance from it. By dividing the surface under investigation into a large number of small elementary areas, it was possible to use this transfer function to express the potential measured by the ACEIP as the sum of the contributions of each such element. An inverse matrix computation method enabled the estimation of the actual surface electric potential. Based on the results of a final set of experiments, the distribution of the electric charge density was estimated for slabs charged by corona-respectively triboelectric-effect.     

Surface physics with radioactive ion beams

Nuclear methods using radiation detection are very well suited for surface and interface investigations, since they generally require only a small number of radioactive probe nuclei. Virtually isolated probe atoms can be investigated. The use of an isotope separator to solve the central problem in the application of radioactive atoms for the study of surfaces, the clean deposition of the probe nuclei, is described. First physics experiments include studies of desorption isochrones and characterization of adatom sites on flat and vicinal surfaces by PAC. A particularly complete picture could be obtained for Cd and In on the Pd(111) surface, where five different sites successively populated in the surface diffusion process were observed. Other nuclear methods suitable for a future extension of the surface investigations, such as Mössbauer spectroscopy, decay recoil angular distribution and emission channeling, are briefly discussed.     

Near-Field Birefringence Response of Liquid Crystal Molecules in Thickness Direction of Liquid Crystal Thin Film Orientated by Shear Force

Information of molecular orientation in nematic liquid crystal （LC） is attractive and important for applications in the field of display devices. We demonstrate a novel method using a birefringence scanning near-field optical microscope （Bi-SNOM） with a probe which is inserted into the LC thin film to detect the molecular orientation from its birefringence responses in the thickness direction of the LC thin film. The probe is laterally vibrated when going forward into the LC thin film, and the retardation and azimuth angle are recorded as the probe going down. Firstly, the thickness of the LC thin film is measured by the shear force detection. Since the shear force acts as a stimulation to reorientate the LC molecules above the substrate surface, we can detect the molecular orientation caused by a polyimide alignment substrate and the effect to molecular orientation caused by vibration of fibre probe. As a result, the orientation profiling of the LC film in depth direction is obtained in both the cases that the direction of probe vibrating is vertical/parallel to the rubbing direction of the alignment film. Furthermore, the thickness of completely orientated layers just above the substrate surface can also be obtained by either vibrating probe or no-vibrating probe. Ultimately, the LC thin film can be modelled in thickness direction from all the results using this method.     

Field enhancement effect of metal probe in evanescent field

Field enhancement effect of metal probe in evanescent field, induced by using a multi-layers structure for exciting surface plasmon resonance （SPR）, is analyzed numerically by utilizing two-dimensional （2D） TM- wave finite difference time-domain （FDTD） method. In this letter, we used a flmdamental mode Gaussian beam to induce evanescent field, and calculated the electric intensity. The results show that compared with the nonmetal probe, the metal probe has a larger field enhancement effect, and its scattering wave induced by field enhancement has a bigger decay coefficient. The field enhancement effect should conclude that the metal probe has an important application in nanolithography.     

Electroless nickel plating on optical fiber probe

As a component of near-field scanning optical microscope （NSOM）, optical fiber probe is an important factor influncing the equipment resolution. Electroless nickel plating is introduced to metallize the optical fiber probe. The optical fibers are etched by 40% HF with Turner etching method. Through pretreatment, the optical fiber probe is coated with Ni-P film by electroless plating in a constant temperature water tank. Atomic absorption spectrometry （AAS）, scanning electron microscopy （SEM）, and energy dispersive X-ray spectrometry （EDXS） are carried out to characterize the deposition on fiber probe. We have reproducibly fabricated two kinds of fiber probes with a Ni-P film： aperture probe and apertureless probe. In addition, reductive particle transportation on the surface of fiber probe is proposed to explain the cause of these probes.