Pulsed Laser Beam Welding of Pd\u3csub\u3e43\u3c/sub\u3eCu\u3csub\u3e27\u3c/sub\u3eNi\u3csub\u3e10\u3c/sub\u3eP\u3csub\u3e20\u3c/sub\u3e Bulk Metallic Glass

We used pulsed laser beam welding method to join Pd43Cu27Ni10P20 (at.%) bulk metallic glass and characterized the properties of the joint. Fusion zone and heat-affected zone in the weld joint can be maintained completely amorphous as confirmed by X-ray diffraction and differential scanning calorimetry. No visible defects were observed in the weld joint. Nanoindentation and bend tests were carried out to determine the mechanical properties of the weld joint. Fusion zone and heat-affected zone exhibit very similar elastic moduli and hardness when compared to the base material, and the weld joint shows high ductility in bending which is accomplished through the operation of multiple shear bands. Our results reveal that pulsed laser beam welding under appropriate processing parameters provides a practical viable method to join bulk metallic glasses

Covariant transport equation and gravito-conductivity in generic stationary spacetimes

We find a near detailed balance solution to the relativistic Boltzmann equation under the relaxation time approximation with a collision term which differs from the Anderson–Witting model and is dependent on the stationary observer. Using this new solution, we construct an explicit covariant transport equation for the particle flux in response to the generalized temperature and chemical potential gradients in generic stationary spacetimes, with the transport tensors characterized by some integral functions in the chemical potential and the relativistic coldness. To illustrate the application of the transport equation, we study probe systems in Rindler and Kerr spacetimes and analyze the asymptotic properties of the gravito-conductivity tensor in the near horizon limit. It turns out that both the longitudinal and lateral parts (if present) of the gravito-conductivity tend to be divergent in the near horizon limit. In the weak field limit, our results coincide with the non-relativistic gravitational transport equation which follows from the direct application of the Drude model

Microstructure, phase stability and mechanical properties of Nb–Ni–Ti–Co–Zr and Nb–Ni–Ti–Co–Zr–Hf high entropy alloys

Owning to their excellent thermal stability and high strength at elevated temperature, high entropy alloys (HEAs) possess great potential for the application in aviation and aerospace fields. In present work, two novel Nb–Ni–Ti–Co–Zr and Nb–Ni–Ti–Co–Zr–Hf HEAs were prepared by arc melting and copper mold suction-casting method. The microstructure, phase stability, mechanical properties at room temperature and elevated temperature of the two HEAs were studied. Both of the HEAs possess high yield stress at room temperature, especially for the Nb–Ni–Ti–Co–Zr (with 2331 Mpa). In addition, the Nb–Ni–Ti–Co–Zr HEA exhibited high yield stress of 564 Mpa at elevated temperature of 800 °C and large compressive plastic strain (more than 50% at 800 °C). Nb–Ni–Ti–Co–Zr–Hf alloy showed new phase precipitation at 800 °C, whereas the structure of Nb–Ni–Ti–Co–Zr was more stable, which is one of the reason why it possesses high strength at room temperature and elevated temperature. The high temperature properties of the Nb–Ni–Ti–Co–Zr HEA make it promising for high temperature application

Competition and Cooperation for Multiple Solar Powered Unmanned Aerial Vehicles under Static Soaring

This work examines the competition and allocation of multiple solar-powered unmanned aerial vehicles (SUAVs) to a single thermal since multiple SUAVs often demonstrate superior mission performance compared to a single SUAV. Additionally, they can harvest extra energy from thermal updrafts. This work considers two conditions, a non-cooperative competition and a cooperative allocation of thermal. In each case, corresponding objective functions and constraints are established, and assignment schemes are derived by solving these objective functions. The allocation results are simulated and integrated with the dynamics and solar energy model. The numerical results show that, in the non-cooperative mode, the first vehicle to reach the thermal can occupy it for soaring, while the remaining SUAVs will fly towards the destination directly. But in the cooperative mode, the multiple SUAVs will allocate the thermal to the SUAV with the highest energy gain through soaring, to maximize the overall electric energy storage of the SUAV group

Durable Microstructured Surfaces: Combining Electrical Conductivity with Superoleophobicity

In this study, electrically conductive and superoleophobic polydimethylsiloxane (PDMS) has been fabricated through embedding Ag flakes (SFs) and Ag nanowires (SNWs) into microstructures of the trichloroperfluorooctyl­silane (FDTS)-blended PDMS elastomer. Microstructured PDMS surfaces became conductive at the percolation surface coverage of 3.0 × 10^–2 mg/mm² for SFs; the highest conductivity was 1.12 × 10⁵ S/m at the SFs surface coverage of 6.0 × 10^–2 mg/mm². A significant improvement of the conductivity (increased 3 times at the SNWs fraction of 11%) was achieved by using SNWs to replace some SFs because of the conductive pathways from the formed SNWs networks and its connections with SFs. These conductive fillers bonded strongly with microstructured FDTS-blended PDMS and retained surface properties under the sliding preload of 8.0 N. Stretching tests indicated that the resistance increased with the increasing strains and returned to its original state when the strain was released, showing highly stretchable and reversible electrical properties. Compared with SFs embedded surfaces, the resistances of SFs/SNWs embedded surfaces were less dependent on the strain because of bridging effect of SNWs. The superoleophobicity was achieved by the synergetic effect of surface modification through blending FDTS and the microstructures transferred from sand papers. The research findings demonstrate a simple approach to make the insulating elastomer to have the desired surface oleophobicity and electrical conductivity and help meet the needs for the development of conductive devices with microstructures and multifunctional properties

Geostationary Full-Spectrum Wide-Swath High-Fidelity Imaging Spectrometer: Optical Design and Prototype Development

The optical system of an imaging spectrometer working on a geostationary earth orbit (GEO) covering a full optical spectrum of 0.3–12.5 μm is analyzed and designed. It enables a ground coverage of 400 × 400 km by internal scanning and achieves a high spatial resolution of 25 m. The full spectrum is divided into five sub-bands, and each band adopts four spectrometers to splice in the field of view to achieve the ultra-long slit required by the wide swath. The total length of the slit is up to 241.3 mm. This paper focuses on compact spectrometers with long slits that can meet the splicing requirements and points out that low spectral distortions, low stray light, high signal-to-noise ratio, and uniform spectral response are necessary for high-fidelity performance. The Offner and Wynne–Offner high-fidelity spectrometers based on convex blazed gratings are designed, and prototypes of each band are developed as well. The properties of long slits and convex blazed gratings are presented. The maximum length of a single slit is 61.44 mm. The groove density of gratings for five bands ranges from 8.8 lp/mm to 312.1 lp/mm, and the peak efficiency is up to 86.4%. The alignment and test of the spectrometers are introduced. Results show that the developed spectrometers have high fidelity and fulfill all requirements

Collision Risk Assessment and Operation Assistant Strategy for Teleoperation System

Teleoperation robots remain superior to fully automated robots in complicated and unstructured environments (e.g., in-orbit assembly). However, the collision risk is also greatly increased in these environments. Therefore, the teleoperation robot should possess the capability of collision risk perception and be configured with security assistance strategy to improve safety and efficiency. With this objective in mind, this paper proposes a collision risk assessment system based on fuzzy theory, which comprehensively considers the effects of shortest distance, operation speed, and delay time. The introduction of fuzzy theory makes the risk assessment results more accurate. Furthermore, this paper also proposes a creative discrete expandable bounding box method to make the calculation of the nearest distance between complicated obstacles and the robot more efficient and faster. Secondly, to improve the safety and efficiency of teleoperation, this paper proposes a set of teleoperation assistance strategies for teleoperation robots based on collision risk. The strategies include partial view highlighting, variation in the motion mapping ratio, and haptic risk warning, all of which are achieved in the graphical interactive interface. Finally, this paper verifies the proposed collision risk model and the operation assistant strategy through experiments. The results show that the proposed fuzzy collision risk model has a correct trend with risk factors, and the proposed operation assistance strategies can effectively reduce the robot collision risk and improve the safety of teleoperation robots. In conclusion, this research contributes to the collision risk assessment and obstacle avoidance assistance strategy of teleoperation robots

How Many Bulk Metallic Glasses Are There?

Quantitative prediction of glass forming ability using a priori known parameters is highly desired in metallic glass development; however proven to be challenging because of the complexity of glass formation. Here, we estimate the number of potential metallic glasses (MGs) and bulk metallic glasses (BMGs) forming systems and alloys, from empirically determined alloy design rules based on a priori known parameters. Specifically, we take into account atomic size ratio, heat of mixing, and liquidus temperature, which we quantify on binary glasses and centimeter-sized BMGs. When expanding into higher order systems that can be formed among 32 practical elements, we reduce the composition space for BMG formation using developed criteria by 10⁶ times and estimate ∼3 million binary, ternary, quaternary, and quinary BMGs alloys

Characteristics of a Magnetic Bulk Thermostat for Granular Gas Investigations in Microgravity

A magnetic thermostat employing soft-ferromagnetic particles and a varying magnetic field has been developed to investigate a homogeneous granular gas system in microgravity. While the thermostat's mechanism of creating homogeneous distribution of the particles was shown earlier, its characteristics have not been understood well due to limited access to a microgravity environment. Therefore, a parametric study by numerical simulation based on the discrete element method is carried out in this paper to evaluate effects of tunable parameters in the thermostat. The result shows the capability of the system and provides a wide range of options and improvements for future experiments. Moreover, it predicts that the thermostat allows variation of homogeneity and excitation level of the granular gas just by changing the magnetic parameters without using any mechanical means. In addition, the suggested improvement is experimentally implemented and evaluated in a drop tower test