Magnetic soft X-ray transmission microscopy

Recent advances in imaging magnetic microstructures on a nanometer length-scale and their temporal evolution on a sub-nanosecond time-scale have been achieved with magnetic transmission X-ray microscopy. With a lateral resolution down to 20 nm, element-specificity, recording in external magnetic fields and stroboscopic pump-and-probe imaging, insights into fundamental mechanisms of the magnetism in thin films and nanopatterned elements are provided which are also relevant in magnetic storage and sensor technologies.     

Microstructural designing of silicon nitride related to toughness

Two ways of microstructural control were investigated with the intention to improve fracture toughness of gas pressure sintered silicon nitride : seeding and optimisation of sintering time. In order to study the effect of seeding, different amounts of large β-Si₃N₄ whiskers were added to different silicon nitride powders. Seeding can lead to a low toughening improvement, providing that the initial powder is free from large pre-existing β nuclei. If not, seeding has a negligible effect on the microstructure because of nuclei interaction and an unfavourable effect on densification, hence on toughness. The effect of the sintering time was studied in a case of abnormal nuclei growth. Toughness can be improved by increasing the sintering time, providing that the composition of the intergranular phase remains stable. Correlations between microstructural parameters and toughness are consistent with the reinforcing mechanisms in composites (crack bridging and crack deviation): toughness is proportional to the grain diameter square root and increases as the fraction of the large grains increases.     

Processes in silicon deposition by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition is a rapidly developing CVD technique for the deposition of silicon thin films and silicon alloys and may become a competitor of the plasma-enhanced (PE) CVD method due to significant advantages such as high deposition rate, efficient source gas utilization, lack of ion bombardment, and low equipment cost. Little is known, however, about the mechanisms for catalytic decomposition of the source gases, gas phase reactions at commonly used pressures, and the growth reactions. In this article, the differences in the reactions at various filament materials are discussed and it is shown that the subsequent reactions in the gas phase and reactions contributing to film growth can be substantially different from those in PE-CVD, due to the lack of energetic electrons and ions. Further work is necessary to identify the role of each precursor for the deposition of amorphous and microcrystalline films.     

A novel fiber-reinforced polyethylene composite with added silicon nitride particles for enhanced thermal conductivity

A novel thermally conductive plastic composite was prepared from a mixture of silicon nitride (Si₃N₄) filler particles and an ultrahigh molecular weight polyethylene–linear low density polyethylene blend. The effects of Si₃N₄ particle sizes, concentration, and dispersion on the thermal conductivity and relevant dielectric properties were investigated. With proper fabrication the Si₃N₄ particles could form a continuously connected dispersion that acted as the dominant thermally conductive pathway through the plastic matrix. By adding 0–20% Si₃N₄ filler particles, the composite thermal conductivity was increased from 0.2 to ～1.0 W m^?1 K^?1. Also, the composite thermal conductivity was further enhanced to 1.8 W m^?1 K^?1 by decreasing the Si₃N₄ particle sizes from 35, 3 and 0.2 μm, and using coupling agent, for the composites with higher filler content. Alumina short fibers were then added to improve the overall composite toughness and strength. Optimum thermal, dielectric and mechanical properties were obtained for a fiber-reinforced polyethylene composite with 20% total alumina–Si₃N₄ (0.2 μm size) filler particles.     

Robot control systems: A survey

Robot manipulators have attracted considerable interest from researchers both in universities and industry during recent years. This interest covers a broad spectrum from task planning, robot language and artificial intelligence to mechanics, sensing and control. This survey paper addresses the area of robot position control and attempts to give an overview of the basic problems involved and some existing solutions.     

An SLA-based cloud computing that facilitates resource allocation in the distributed data centers of a cloud provider

The number of cloud service users has increased worldwide, and cloud service providers have been deploying and operating data centers to serve the globally distributed cloud users. The resource capacity of a data center is limited, so distributing the load to global data centers will be effective in providing stable services. Another issue in cloud computing is the need for providers to guarantee the service level agreements (SLAs) established with consumers. Whereas various load balancing algorithms have been developed, it is necessary to avoid SLA violations (e.g., service response time) when a cloud provider allocates the load to data centers geographically distributed across the world. Considering load balancing and guaranteed SLA, therefore, this paper proposes an SLA-based cloud computing framework to facilitate resource allocation that takes into account the workload and geographical location of distributed data centers. The contributions of this paper include: (1) the design of a cloud computing framework that includes an automated SLA negotiation mechanism and a workload- and location-aware resource allocation scheme (WLARA), and (2) the implementation of an agent-based cloud testbed of the proposed framework. Using the testbed, experiments were conducted to compare the proposed schemes with related approaches. Empirical results show that the proposed WLARA performs better than other related approaches (e.g., round robin, greedy, and manual allocation) in terms of SLA violations and the provider’s profits. We also show that using the automated SLA negotiation mechanism supports providers in earning higher profits.     

Numerical study of surface charge effects on a p-n junction model system: Modulation of junction potential,band diagrams,and recombinations

We theoretically investigate the surface charge effects on a p-n junction model system. It is calculated that the polarity of the surface charges around the junction interface induces different variations in the built-in potential, which has been demonstrated to affect the band diagrams of p-n junction systems. That is, the more negative the surface charge is, the more the built-in potential decreases, and vice versa for positive surface charges in the system. These surface charges affect the modulation of three recombination processes, i.e. the Shockley-Read-Hall, band-to-band, and Auger recombination processes, and are numerically investigated with different surface charge densities imposed at the junction interface. As a result, it is calculated that the three recombination rates are reduced with increasing magnitudes of surface charge density due to the free carrier depletion that occurs around the p-n junction regions.     

Electronic transfer from aluminum into the core of gold nanoparticles capped with conjugated 2-naphthalenethiol

The electronic contact between a bulk metal and metal nanoparticles can be significantly different from that between two bulk metals due to the unique electronic structure in the nanometer size. In this work, the electronic contact between Au nanoparticles and Al is studied by X-ray photoelectron spectroscopy. Al is deposited on a layer of Au nanoparticles capped with conjugated 2-naphthalenethiol (Au-2NT NPs) in high vacuum by e-beam deposition at room temperature. The Au 4f X-ray photoelectron spectrum (XPS) significantly changes after the Al deposition. New XPS bands with higher binding energy appear. The angle dependence of the Au 4f XPS bands indicates that the electron transfer takes place at the contact between Al and Au-2NT NPs. In contrast, the Al deposition hardly changes the Au 4f XPS spectrum for Au nanoparticles capped with saturated 1-dodecanethiol. The effect of the Al deposition on the Au 4f XPS spectrum of Au nanoparticles capped with 2-naphthalenethiol is attributed to the electron transfer from Al through the conjugated 2-naphthalenehiol into the core of Au nanoparticles, as the Fermi energy of Al is higher than Au. This understanding on the contact between metal and metal nanoparticles provides guidance for the development of novel electronic devices.     

An online Bayesian filtering framework for Gaussian process regression: Application to global surface temperature analysis

Over the past centuries, global warming has gradually become one of the most significant issues in our life. Hence, it is crucial to analyze global surface temperature with an efficient and accurate model. Gaussian process (GP) is a popular nonparametric model, due to the power of Bayesian inference framework. However, the performance of GP is often deteriorated for large-scale data sets such as global surface temperature. In this work, we propose a novel online Bayesian filtering framework for large-scale GP regression. There are three contributions. Firstly, we develop a novel GP-based state space model to efficiently process data in a sequential manner. Secondly, based on our state space model, we design a marginalized particle filter to infer the latent function values and learn the model parameters online. It can efficiently reduce the computation burden of GP while improving the estimation accuracy in a recursive Bayesian inference framework. Finally, we successfully apply our approach to a number of synthetic data sets and the large-scale global surface temperature data set. The results show that our approach outperforms related GP variants, and it is an efficient and accurate expert system for global surface temperature analysis.     

An eye detection method robust to eyeglasses for mobile iris recognition

Finding the accurate position of an eye is crucial for mobile iris recognition system in order to extract the iris region quickly and correctly. Unfortunately, this is very difficult to accomplish when a person is wearing eyeglasses because of the interference from the eyeglasses. This paper proposes an eye detection method that is robust to eyeglass interference in mobile environment. The proposed method comprises two stages: eye candidate generation and eye validation. In the eye candidate generation stage, multi-scale window masks consisting of 2 × 3 subblocks are used to generate all image blocks possibly containing an eye image. In the ensuing eye validation stage, two methods are employed to determine which blocks actually contain true eye images and locate their precise positions as well: the first method searches for the glint of an NIR illuminator on the pupil region. If this first method fails, the next method computes the intensity difference between the assumed pupil and its surrounding region using multi-scale 3 × 3 window masks. Experimental results show that the proposed method detects the eye position more accurately and quickly than competing methods in the presence of interference from eyeglass frames.