Experimental investigation on micromilling of oxygen-free, high-conductivity copper using tungsten carbide, chemistry vapour deposition and single-crystal diamond micro tools

Insufficient experimental data from various micro tools limit industrial application of the micromilling process. This paper presents an experimental comparative investigation into micromilling of oxygen-free, high-conductivity copper using tungsten carbide (WC), chemistry vapour deposition (CVD) diamond, and single-crystal diamond micromilling tools at a uniform 0.4mm diameter. The experiments were carried out on an ultra-precision micromilling machine that features high dynamic accurate performance, so that the dynamic effect of the machine tool itself on the cutting process can be reduced to a minimum. Micromachined surface roughness and burr height were characterized using white light interferometry, a scanning electron microscope (SEM), and a precision surface profiler. The influence of variation of cutting parameters, including cutting speeds, feedrate, and axial depth of cut, on surface roughness and burr formation were analysed. The experimental results show that there exists an optimum feedrate at which best surface roughness can be achieved. Optical quality surface roughness can be achieved with CVD and natural diamond tools by carefully selecting machining conditions, and surface roughness, Ra, of the order of 10nm can also be obtained when using micromilling using WC tools on the precision micromilling machine.EU FP6 MASMICRO projec

An investigation of nanoindentation tests on the single crystal copper thin film via an AFM and MD simulation

Nanoindentation tests performed in an atomic force microscope have been utilized to directly measure the mechanical properties of single crystal metal thin films fabricated by the vacuum vapor deposition technique. Nanoindentation tests were conducted at various indentation depths to study the effect of indentation depths on the mechanical properties of thin films. The results were interpreted by using the Oliver-Pharr method with which direct observation and measurement of the contact area are not required. The elastic modulus of the single crystal copper film at various indentation depths was determined as 67.0±6.9GPa on average which is in reasonable agreement with the results reported by others. The indentation hardness constantly increases with decreasing indentation depth, indicating a strong size effect. In addition to the experimental work, a three-dimensional nanoindentation model of molecular dynamics (MD) simulations with embedded atom method (EAM) potential is proposed to elucidate the mechanics and mechanisms of nanoindentation of thin films from the atomistic point of view. MD simulations results also show that due to the size effect the plastic deformation via amorphous transformation is more favorable than via the generation and propagation of dislocations in nanoindentation of single crystal copper thin films

Non-linear vortex dynamics and transient effects in ferromagnetic disks

We report a time resolved imaging and micromagnetic simulation study of the relaxation dynamics of a magnetic vortex in the non-linear regime. We use time-resolved photoemission electron microscopy and micromagnetic calculations to examine the emergence of non-linear vortex dynamics in patterned Ni80Fe20 disks in the limit of long field pulses. We show for core shifts beyond ~20-25% of the disk radius, the initial motion is characterized by distortions of the vortex, a transient cross-tie wall state, and instabilities in the core polarization that influence the core trajectories.Comment: 11 pages, 3 figures, submitted to Phys. Rev. Let

Diverse Temporal Properties of GRB Afterglow

The detection of delayed X-ray, optical and radio emission, "afterglow", associated with $\gamma$-ray bursts (GRBs) is consistent with fireball models, where the emission are produced by relativistic expanding blast wave, driven by expanding fireball at cosmogical distances. The emission mechanisms of GRB afterglow have been discussed by many authors and synchrotron radiation is believed to be the main mechanism. The observations show that the optical light curves of two observed gamma-ray bursts, GRB970228 and GRB GRB970508, can be described by a simple power law, which seems to support the synchrotron radiation explanation. However, here we shall show that under some circumstances, the inverse Compton scattering (ICS) may play an important role in emission spectrum and this may influence the temporal properties of GRB afterglow. We expect that the light curves of GRB afterglow may consist of multi-components, which depends on the fireball parameters.Comment: Latex, no figures, minor correctio

Is GRO J1744-28 a Strange Star?

The unusal hard x-ray burster GRO J1744-28 recently discovered by the Compton Gamma-ray Observatory (GRO) can be modeled as a strange star with a dipolar magnetic field $\le 10^{11}$Gauss. When the accreted mass of the star exceeds some critical mass, its crust may break, resulting in conversion of the accreted matter into strange matter and release of energy. Subsequently, a fireball may form and expand relativistically outward. The expanding fireball may interact with the surrounding interstellar medium, causing its kinetic energy to be radiated in shock waves, producing a burst of x-ray radiation. The burst energy, duration, interval and spectrum derived from such a model are consistent with the observations of GRO J1744-28.Comment: Latex, has been published in SCIENCE, Vol. 280, 40

Investigation on the sampling size optimisation in gear tooth surface measurement using a Co-ordinate Measuring Machine

Co-ordinate Measuring Machines (CMMs) are widely used in gear manufacturing industry. One of the main issues for contact inspection using a CMM is the sampling technique. In this paper the gear tooth surfaces are expressed by series of parameters and inspection error compensation and initial value optimisation method are presented. The minimum number of measurement points for 3D tooth surfaces are derived. If high precision is required, more points need to be inspected. The sampling size optimisation is obtained from the criterion equation. The surface form deviation and initial values are optimised using the minimum zone method and Genetic Algorithms. A feature based inspection system for spur/helical gears is developed and trials and simulations demonstrated the developed method is very effective and suitable

Design and finite element mode analysis of noncircular gear

The noncircular gear transmission is an important branch of the gear transmission, it is characterized by its compact structure, good dynamic equilibration and other advantages, and can be used in the automobile, engineering machine, ship, machine tool, aviation and spaceflight field etc. Studying on the dynamics feature of noncircular gear transmission can improve the ability to carry loads of, reduce the vibration and noise of, increase the life of the noncircular gear transmission machine, provides guidance for the design of the noncircular gear, and has significant theories and practical meanings. In this paper, the gear transmission technique is used to studied the design method of the noncircular gear, which contains distribution of teeth on the pitch curve, designs of the tooth tip curve and the tooth root curve, design of the tooth profile curve, the gear system dynamics principle is introduced to establish dynamics model for the noncircular gear; basic theory of finite element and mode analysis method are applied, finite element model for the noncircular gear is established, natural vibration characteristic of the noncircular gear is studied. And the oval gear is taken as an example, the mathematics software MathCAD, the 3D modeling software UG and the finite element software ABAQUS are used to realize precise 3D model of the oval gear. The finite element method is used, the natural vibration characteristic of the oval gear is studied, the main vibration types and natural frequencies of the oval gear and that of the equivalent cylindrical gears are analyzed and compared, the conclusions received reflect the dynamics performance of the oval gear, and solid foundation is laid for dynamics research and engineering application of the oval gear transmission

The Relationship between Structurally Different Pyrrolizidine Alkaloids and Western Flower Thrips Resistance in F2 Hybrids of Jacobaea vulgaros and Jacobaea aquatica

Segregating plant hybrids often have more ecological and molecular variability compared to parental species, and are therefore useful for studying relationships between different traits, and the adaptive significance of trait variation. Hybrid systems have been used to study the relationship between the expression of plant defense compounds and herbivore susceptibility. We conducted a western flower thrips (WFT) bioassay using a hybrid family and investigated the relationship between WFT resistance and pyrrolizidine alkaloid (PA) variation. The hybrid family consisted of two parental (Jacobaea vulgaris and Jacobaea aquatica) genotypes, two F1 genotypes, and 94 F2 hybrid lines. The J. aquatica genotype was more susceptible to thrips attack than the J. vulgaris genotype, the two F1 hybrids were as susceptible as J. aquatica, and susceptibility to WFT differed among F2 hybrid lines: 69 F2 lines were equally susceptible compared to J. aquatica, 10 F2 lines were more susceptible than J. aquatica and 15 F2 lines were as resistant as J. vulgaris or were intermediate to the two parental genotypes. Among 37 individual PAs that were derived from four structural groups (senecionine-, jacobine-, erucifoline- and otosenine-like PAs), the N-oxides of jacobine, jaconine, and jacoline were negatively correlated with feeding damage caused by WFT, and the tertiary amines of jacobine, jaconine, jacoline, and other PAs did not relate to feeding damage. Total PA concentration was negatively correlated with feeding damage. Among the four PA groups, only the total concentration of the jacobine-like PAs was negatively correlated with feeding damage. Multiple regression tests suggested that jacobine-like PAs play a greater role in WFT resistance than PAs from other structural groups. We found no evidence for synergistic effects of different PAs on WFT resistance. The relationship between PA variation and WFT feeding damage in the Jacobaea hybrids suggests a role for PAs in resistance to generalist insects