Misfit of rigid tools and interferometer subapertures on off-axis aspheric mirror segments

Rigid tools can confer advantages at certain stages of manufacturing off-axis mirror segments, but the misfit due to surface asphericity and asymmetry poses constraints on their application. Types of misfit are classified and, using least squares, the best-fit tool forms with different distances from the pole of the parent asphere are calculated. The outer mirror segment for the European extremely large telescope is taken as a case-study, assuming a rigid tool size of 150 mm. A simple independent approximation validates the calculation. A close parallel is wavefront misfit in subaperture interferometry, which is also considered

Coordinate transformation of an industrial robot and its application in deterministic optical polishing

An IRB6620 industrial robot from ABB Co. Ltd. (Zurich, Switzerland) is used as a processing platform for optical processing, and computer-controlled optical surfacing is applied as a key technology. The function of each coordinate system of the robot in processing is reviewed, as well as the relationship of each coordinate system and coordinate transformation. An algorithm governing coordinate transformations is provided. In order to assess the functionality of the robot as a polishing instrument, experiments have been designed so that the removal rate and surface form error correction of the robot facility have been compared with those from established computer numerical control polishing. The importance for the application of industrial robot in optical processing is also presented

Development of swinging part profilometer for optics

A new surface metrology instrument, the ‘Swinging Part Profilometer’ (SPP), has been developed for in-situ measurement of optics undergoing robot-processing in the ground (non-specular) state. In this paper, we present the hardware-design of the SPP, together with software for hardware-control, data-acquisition and surface-reconstruction. First results on a sample part are presented, compared with interferometric metrology, and error-contributions considered. Notably, during each individual scan of a measurement-cycle, the probe remains fixed. This lends itself to automated probe-deployment by the same robot as performs surface-processing, as probe stability is required on only the time-scale for a single scan

Synergistic Influence of Local Climate Zones and Wind Speeds on the Urban Heat Island and Heat Waves in the Megacity of Beijing, China

Large-scale modifications to urban underlying surfaces owing to rapid urbanization have led to stronger urban heat island (UHI) effects and more frequent urban heat wave (HW) events. Based on observations of automatic weather stations in Beijing during the summers of 2014–2020, we studied the interaction between HW events and the UHI effect. Results showed that the UHI intensity (UHII) was significantly aggravated (by 0.55°C) during HW periods compared to non-heat wave (NHW) periods. Considering the strong impact of unfavorable weather conditions and altered land use on the urban thermal environment, we evaluated the modulation of HW events and the UHI effect by wind speed and local climatic zones (LCZs). Wind speeds in urban areas were weakened due to the obstruction of dense high-rise buildings, which favored the occurrence of HW events. In detail, 35 HW events occurred over the LCZ1 of a dense high-rise building area under low wind speed conditions, which was much higher than that in other LCZ types and under high wind speed conditions (< 30 HW events). The latent heat flux in rural areas has increased more due to the presence of sufficient water availability and more vegetation, while the increase in heat flux in urban areas is mainly in the form of sensible heat flux, resulting in stronger UHI effect during HW periods. Compared to NHW periods, lower boundary layer and wind speed in the HW events weakened the convective mixing of air, further expanding the temperature gap between urban and rural areas. Note that LCZP type with its high-density vegetation and water bodies in the urban park area generally exhibited, was found to have a mitigating effect on the UHI, whilst at the same time increasing the frequency and duration of HW events during HW periods. Synergies between HWs and the UHI amplify both the spatial and temporal coverage of high-temperature events, which in turn exposes urban residents to additional heat stress and seriously threatens their health. The findings have important implications for HWs and UHII forecasts, as well as for scientific guidance on decision-making to improve the thermal environment and to adjust the energy structure

Analysis of tool-mass-acceleration effects onto sub-aperture computer controlled polishing (CCP)

Although computer controlled polishing (CCP) of aspheres and freeforms is one of the best understood state-of-the-art fab processes today, there are yet some unsolved issues: e.g. compared to bonnet polishing, fluid jet polishing is taking less iteration steps reaching the same form accuracy and ion beam figuring eventually is reaching much higher shape accuracies. This paper is a first move into solving this matter by introducing a novel footprint recording approach for CCP. To that aim, a new method for measuring the impact of a single tool mass acceleration value onto footprint shape is presented, the second derivative footprint recording (SECondo) method. First experimental evidence of the SECondo effect is presented, demonstrating that for bonnet polishing, acceleration of tool mass significantly alters the pressure distribution within the footprint and consequently affects its cross sectio

Optimisation of grolishing freeform surfaces with rigid and semi-rigid tools

After the formal acceptance of our fabrication of E-ELT segments, we aim to further accelerate the mass production by introducing an intermediate grolishing procedure using industrial robots, reducing the total process time by this much faster and parallel link. In this paper, we have presented research outputs on tool design, tool path generation, study of mismatch between rigid, semi-rigid tool and aspheric surface. It is indicated that the generation of mid-spatial frequency is proportional to the grit size and misfit between work piece and tool surfaces. Using a Non-Newtonian material tool with a spindle speed of 30 rpm has successfully reduce the mid-spatial error. The optimization of process parameters involve the study the combination effects of the above factors. These optimized parameters will result in a lookup table for reference of given input surface quality. Future work may include the higher spindle speed for grolishing with non- Newtonian tool looking for potential applications regarding to form correction, higher removal rate and edge contro

Adversarial behaviours in mixing coins under incomplete information

Criminals can launder crypto-currencies through mixing coins, whose original purpose is preservation of privacy in the presence of traceability. Therefore, it is essential to elaborately design mixing polices to achieve both privacy and anti-money laundering. Existing work on mixing policies relies on the knowledge of a blacklist. However, these policies are paralysed under the scenario where the blacklist is unknown or evolving. In this paper, we regard the above scenario as games under incomplete information where parties put down a deposit for the quality of coins, which is suitably managed by a smart contract in case of mixing bad coins. We extend the poison and haircut policies to incomplete information games, where the blacklist is updated after mixing. We prove the existence of equilibria for the improved polices, while it is known that there is no equilibria in the original poison and haircut policies, where blacklist is public known. Furthermore, we propose a seminal suicide policy: the one who mixes more bad coins will be punished by not having the deposit refunded. Thus, parties have no incentives to launder money by leveraging mixing coins. In effect, all three policies contrast money laundering while preserving privacy under incomplete information. Finally, we simulate and verify the validity of these policies

Research on edge-control methods in CNC polishing

Background: We have developed edge-control for the Precessions TM process suitable for fast fabrication of large mirror segments, and other applications sensitive to edge mis-figure. This has been applied to processing of European extremely large telescope (E-ELT) prototype mirror-segments, meeting the specification on maximum edge mis-figure. However we have observed residuals that have proved impossible to correct with this approach, being in part the legacy of asymmetries in the input edge-profiles. Methods: We have therefore compared different proposed methods experimentally and theoretically and report here on a new edge-rectification step, which operates locally on edges, does not disturb the completed bulk area. Results: A new toolpath has been developed and experiments have been carried out to demonstrate that local edge rectification can be carried out. Conclusions: With this method, the residue error on edges can be removed separately and has potential to reduce total process time

Impact of Brain Injury on Processing of Emotional Prosodies in Neonates

Being able to appropriately process different emotional prosodies is an important cognitive ability normally present at birth. In this study, we used event-related potential (ERP) to assess whether brain injury impacts the ability to process different emotional prosodies (happy, fear, and neutral) in neonates; whether the ERP measure has potential value for the evaluation of neurodevelopmental outcome in later childhood. A total of 42 full-term neonates were recruited from the neonatology department of Peking University First Hospital from June 2014 to January 2015. They were assigned to the brain injury group (n = 20) or control group (n = 22) according to their clinical manifestations, physical examinations, cranial images and routine EEG outcomes. Using an oddball paradigm, ERP data were recorded while subjects listened to happy (20%, deviation stimulus), fearful (20%, deviation stimulus) and neutral (80%, standard stimulus) prosodies to evaluate the potential prognostic value of ERP indexes for neurodevelopment at 30 months of age. Results showed that while the mismatch responses (MMRs) at the frontal lobe were larger for fearful than happy prosody in control neonates, this difference was not observed in neonates with brain injuries. This finding suggests that perinatal brain injury may influence the cognitive ability to process different emotional prosodies in neonatal brain; this deficit could be reflected by decreased MMR amplitudes in response to fearful prosody. Moreover, the decreased MMRs at the frontal lobe was associated with impaired neurodevelopment at 30 months old

Incentive compatible and anti-compounding of wealth in proof-of-stake

Geometric reward function is proposed as an alternative choice to circumvent the problem of compounding. However, it’s not so desirable since no parties have incentives to participate in the consensus mechanism. In this paper, we tailor a new bonus reward function by adding random salts to the geometric reward function. The new reward function is a tradeoff between equitablity and incentive compatibility. We conclude that the quitability of the new reward function is optimal compared with others. Beyond that, we present Gini coefficients to fine-evaluate euqitability of reward functions. We propose a new metric (aka. reward ratio) to quantify the level of incentive compatibility. Our simulation results show that the new reward function performs better than others in both incentive compatibility and anti-compounding