Numerical conditioning and asymptotic variance of subspace estimates

New formulas for the asymptotic variance of the parameter estimates in subspace identification, show that the accuracy of the parameter estimates depends on certain indices of ‘near collinearity’ of the state and future input subspaces of the system to be identified. This complements the numerical conditioning analysis of subspace methods presented in the companion paper (On the ill-conditioning of subspace identification with inputs, Automatica, doi:10.1016/j.automatica.2003.11.009).     

Nanoindentation Measurements of the Mechanical Properties of Ni Thin Films: Effects of Film Microstructure and Substrate Modulus

This paper presents the results of nanoindentation measurements of the hardness and moduli of normally and obliquely deposited nanocrystalline Ni films on substrates of SiO₂, Si, and bulk Ni. Following an initial characterization of film microstructure and surface topography with atomic force microscopy (AFM), the paper examines the effects of film microstructure, film thickness, and substrate modulus on the measured film mechanical properties. Obliquely deposited films are shown to have lower hardness values than normally deposited films. The measured hardness values and material pile-up are also shown to depend significantly on the mismatch between the film modulus and substrate modulus. A framework is presented for quantifying the effects of substrate modulus mismatch on basic film mechanical properties.     

扁环填料成型模具设计

通过对扁环填料的成型工艺的分析，设计了一种利用多组斜楔机构来实现工件一次成型的模具，不仅提高了生产效率，也为提高产品的质量提供了技术保证。     

Oblique hypervelocity impacts: Implication for the analysis of material retrieved after exposure to space

In the past few years, a wide variety of surfaces have been brought back to Earth after being exposed to the space particulate environment. The impact features found on this material can give clues to the characteristics of the impacting man-made debris and meteoroids. Many investigations have been carried out to deduce projectile parameters (size, shape, and velocity vector) from the morphology of impact features and their origin from the analysis of projectile remnants inside craters formed. However, there are still ambiguities in the interpretation of these results. Recently, the post-flight analysis of solar arrays retrieved from the hubble space telescope (HST) showed the lack of data concerning the interpretation of many impact features. In the present study, we have examined especially the distinctive features of craters caused by particles at oblique incidence. These craters represent more than one third of impacts with a size between 5 μm and 1 mm observed on the European Retrievable Carrier (EuReCa) and HST solar arrays. Interpretation difficulties of this kind of impacts on solar cells led to hypervelocity impacts test onto pure silica targets performed with iron projectiles at different incidence angles and different velocity ranges. They were made in order to find a possible link between the incidence angle of a projectile, the impact velocity, and the parameters, which could be deduced from the analysis of the crater and projectile remnants. A detailed survey of impacts features formed was done for each couple angle velocity. High-resolution observations show an evolution of the crater morphology and circularity with the increasing angles of incidence and velocity, and some changes in the projectile remnants amount, appearance, and position are also noted.     

Dynamic Force Modelling for a Ball-End Milling Cutter Based on the Merchant Oblique Cutting Theory

A new dynamic force model for a ball-end milling cutter is presented in this paper. Based on the principle of the power remaining constant in cuts, the Merchant oblique cutting theory has been successfully used for the differential cutting edge segment of a ball-end milling cutter. A concise method for characterising the relationship of the complex geometry of a ball-end milling cutter and the milling process variables is determined, so that the force coefficients can be decomposed. The geometric property of a ball-end milling cutter and the dynamics of the milling process are integrated into the general model to eliminate the need for the experimental calibration of each cutter geometry and milling process variable. The milling experiments prove that this model can predict accurately the cutting forces in three Cartesian directions.     

Thermoviscoplastic modelling of oblique cutting: forces and chip flow predictions

A modelling of oblique cutting for viscoplastic materials is presented. The thermomechanical properties and the inertia effects are accounted for to describe the material flow in the primary shear zone. At the tool–chip interface, a temperature-dependent friction law is introduced to take account of the extreme conditions of pressure, velocities and temperature encountered during machining. The chip flow angle is calculated by assuming that the friction force is collinear to the chip flow direction on the tool rake face. Due to the temperature dependence of the friction law at the tool–chip interface, the chip flow angle predicted by the model, is affected by the cutting speed, the undeformed chip thickness, the normal rake angle, the edge inclination angle and the thermomechanical behavior of the work material. This dependence and the trends predicted by the present approach are confirmed by experimental observations. Effects of cutting conditions on the cutting forces are also presented and compared to experiments.     

Implementation of the iterative finite-difference time-domain technique for simulation of periodic structures at oblique incidence

In this paper we review a recently developed finite-difference time-domain (FDTD) iterative technique for the analysis of periodic structures at oblique incidence. We show how it can be implemented in FDTD code and estimate required computer memory and time resources. To illustrate performance of our technique we demonstrate the plasmon formation in a thin gold film placed at air/glass interface and calculate reflectance from silicon textured coating at oblique incidence.     

Experiments to study turbulence and flow past a low-rise building at oblique incidence

It is now well-known that high suction pressures develop along the leading edges of the building due to the formation of corner vortices when the wind is incident at oblique angles. These high suction pressures can damage the roof surface, which may even result in total failure. This paper gives the results from experiments carried out on 1:100 scale models of the Texas Tech University Test Building in a wind tunnel under different flow conditions. Both sharp-edged models and round-edged models were used to conduct flow and turbulence experiments. The results from flow visualization experiments reveal that there exists a separation and recirculation region on roof top at normal incidence and corner vortices form at oblique incidence with different magnitudes of rounding of roof edges influencing the turbulence levels and flow differently.     

Estimating the uncertainty of discharge coefficient predicted for oblique side weir using Monte Carlo method

Side weir is a hydraulic structure, which is used in irrigation systems to divert some water from main to side channel. It is installed at the entrance of the side channel to control and measure passing water into the side channel. Many studies provided side weir water surface profile and coefficient of discharge to measure water discharge diverted into the side channel. These studies dealt with different side weir shapes (rectangular, trapezoidal, triangular and circular), which were installed perpendicular to the flow direction. Recently, some studies dealt with skew side weir, but these studies still need to more investigation. Here we report to investigate oblique side weir theoretically using statistical method to supported other studies in this case. Measurement uncertainty discharge coefficient C_d was obtained by two methods: analytical according to the ‘Guide to the expression of uncertainty in measurement’ and the Monte Carlo method. The results indicate that all experimental results are consistent with the analytical results. The relative expanded uncertainty of the discharge coefficient C_d does not exceed 2%.     

Controllable growth of aluminum nanorods using physical vapor deposition

This letter proposes and experimentally demonstrates that oxygen, through action as a surfactant, enables the growth of aluminum nanorods using physical vapor deposition. Based on the mechanism through which oxygen acts, the authors show that the diameter of aluminum nanorods can be controlled from 50 to 500 nm by varying the amount of oxygen present, through modulating the vacuum level, and by varying the substrate temperature. When grown under medium vacuum, the nanorods are in the form of an aluminum metal - aluminum oxide core-shell. The thickness of the oxide shell is ~2 nm as grown and is stable when maintained in ambient for 30 days or annealed in air at 475 K for 1 day. As annealing temperature is increased, the nanorod morphology remains stable while the ratio of oxide shell to metallic core increases, resulting in a fully aluminum oxide nanorod at 1,475 K.