Chemical vapour deposited (CVD) diamond is finding increased application and it is important to study its strength and fatigue properties. The present paper describes research on a batch of ...di-electric (optical) grade CVD material. The procedure in the experiments was to use some samples from a batch to obtain an average failure load. Other samples were then stress cycled to a chosen fraction of this average load. If they survived 10
7 cycles, they were considered to be immune to fatigue at that load, and their strengths were measured using a three-point bend test. Some samples survived at least 95% of their critical fracture stress for 10
7 cycles without fatiguing. In other experiments, a 4-point (double torsion) rig was used to stress samples with macro-flaws in different environments. The observation that fatigue does not reduce the strength of CVD diamond in normal environments adds to its attractiveness for various applications.
Context.
Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which ...source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are the most important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a direct comparison with observational data.
Aims.
We present the SYnthetic Measurement creator for long Baseline Arrays (
SYMBA
), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations.
SYMBA
takes into account several realistic atmospheric, instrumental, and calibration effects.
Methods.
We used
SYMBA
to create synthetic observations for the Event Horizon Telescope (EHT), a millimetre VLBI array, which has recently captured the first image of a black hole shadow. After testing
SYMBA
with simple source and corruption models, we study the importance of including all corruption and calibration effects, compared to the addition of thermal noise only. Using synthetic data based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M 87, we performed case studies to assess the image quality that can be obtained with the current and future EHT array for different weather conditions.
Results.
Our synthetic observations show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of our GRMHD source models can be recovered robustly with the EHT2017 array after performing calibration steps, which include fringe fitting, a priori amplitude and network calibration, and self-calibration. With the planned addition of new stations to the EHT array in the coming years, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images.
The mechanisms producing fast variability of the γ-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E > 100 GeV) γ-ray ...flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5 ± 0.3) × 10−10 photons cm−2 s−1 and halving time of 26 ± 8 min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E > 100 MeV) γ-ray bands. In this paper we present the MAGIC VHE γ-ray data together with multi-wavelength data from radio, optical, X-rays, and HE γ rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE γ-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE γ-rays is very similar to two other observed VHE γ-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43 GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the γ-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE γ-ray flare, but all have some tension with the multi-wavelength observations.
In the present work, an attempt has been made to study the mechanical properties of bamboo so as to explore the possibility of its’ usage as structural material in place of wood. Dry bamboo culms of ...Dendrocalamus strictus were processed into thin laminae and cold pressed using epoxy resin to produce LBCs. Mechanical properties of bamboo laminae and their LBCs have been evaluated under different loading conditions. Similar to wood, there is better correlation for stiffness than strength of bamboo laminae under tensile, compressive and flexural loading but there are fewer correlations in mechanical properties of LBCs owing to random selection of laminae from different locations and also because of addition of epoxy during preparation of LBCs. Comparisons with woods indicate that average strength of bamboo laminae obtained under different loading conditions is better than softwoods and comparable with hard woods. It is inferred from the results that bamboo can be utilized for fabrication of LBCs. Furthermore, tests results and comparisons clearly show that LBCs can be used as an alternative to wood and wood based composites for structural purposes.
It is difficult to find the optimum machining conditions in wire electrical discharge machining (wire-EDM), because discharge current is influenced by the impedances of the wire and workpiece ...electrodes which may vary depending on the diameter of the wire, height of the workpiece and materials of wire and workpiece even if the pulse conditions are the same. Hence, this study aims to develop a simulator to analyze the distribution of the current density, and magnetic flux density in and around the wire t o obtain the impedances of the wire and workpiece electrodes using the electromagnetic field analysis by finite element method (FEM). With this method, the dependences of the impedances on the electromagnetic properties of the electrodes were investigated. The impedances measured using an LCR meter coincided with the analysis results. Thus it was confirmed that this analysis is useful to obtain the discharge current waveform which may change depending on the dimensions and material properties of the electrodes, serving a tool to optimize the machining conditions.
A four-point bend test was used to determine the fracture toughness of mechanical grade and di-electric (optical) grade chemical vapour deposited (CVD) diamond. The validity of the test was first ...confirmed by measuring the toughness of alumina and confirming the results with literature values. The toughnesses of both types of CVD were similar; 8.5 ± 1.0 and 8.3 ± 0.4 MPa respectively. This is higher than the value of 3 4 ± 0 5 MPa measured for good quality natural diamond by Field and Freeman, 1 using an indentation technique. It is suggested that this is primarily due to differences in surface roughness. There were enough samples to make a preliminary study of the effect of temperature and these data are reported.
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