Swarm applications use motion capture system or GPS sensors as localization systems. However, motion capture systems provide local solutions, and GPS sensors are not reliable in occluded environments. For reliable and versatile operation in a swarm, robots must sense each other and interact locally. Motivated by this requirement, we propose an onboard localization framework for multi-robot systems. Our framework consists of an anchor robot with three ultrawideband (UWB) sensors and a tag robot with a single UWB sensor. The anchor robot utilizes the three UWB sensors as a localization infrastructure and estimates the tag robot's location by using its on-board sensing and computational capabilities solely, without explicit inter-robot communication. We utilize a dual Monte-Carlo localization approach to capture the agile maneuvers of the tag robot with acceptable precision. We validate the effectiveness of our algorithm with simulations as well as indoor and outdoor experiments on a two-drone setup. The proposed framework with the dual MCL algorithm yields accurate estimates for various speed profiles of the tag robot, outperforms the standard particle filter and extended Kalman filter, and suffice for a relative position maintenance application.

RATIONALE:The compositional and structural information of the soot particles is essential for a better understanding of the chemistry and mechanism during the combustion. The aim of the present study was to develop a method to analyze such soot particulate samples with high complexity and poor solubility. METHODS:The solvent-free sample preparation MALDI technique was combined with the ultrahigh resolution FT ICR mass spectrometry for the characterization of solid soot particulates. Moreover, a modified iso-abundance plot (Carbon Number vs. Hydrogen Number vs. Abundance) was introduced to visualize the distributions of various chemical species, and to examine the agreement between the hydrogen- abstraction- carbon- addition (HACA) mechanism and the polycyclic aromatic hydrocarbon growth in the investigated flame system. RESULTS:This solvent-free MALDI method enabled the effective ionization of the solid soot particulates without any dissolving procedure. With the accurate m/z ratios from FT ICR MS, a unique chemical formula was assigned to each of the recorded mass signals. The combustion products were proven to be mainly large polycyclic aromatic hydrocarbons, together with a small amount (<5%) of oxidized hydrocarbons. CONCLUSIONS:The developed method provides a new approach for the molecular characterization of soot particulates like carbonaceous materials. The investigated soot particulates are mainly polycyclic aromatic hydrocarbons (PAHs) with no or very short aliphatic chains. The PAHs growth mechanism during combustion can be examined against the classic HACA mechanism.

Conductors that can sustain large strains without change in resistance are highly needed for wearable electronic systems. Here, the fabrication of highly stretchable coaxial fiber conductors through self-buckling of conductive polymer ribbons inside thermoplastic elastomer channels, using a “solution stretching–drying–buckling” process, is reported. The unique hierarchically buckled and conductive core in the axial direction makes the resistance of the fiber very stable, with less than 4% change when applying as much as 680% strain. These fibers can then be directly used as stretchable electrical interconnects or wearable heaters.

This article aims to manufacture homogenous dual-matrix Al–Mg/Al2O3 nanocomposite from their raw materials and give insight into the correlation between powder morphology, crystallite structure and their mechanical and tribological properties. Al–Mg dual-matrix reinforced with micro/nano Al2O3 particles was manufactured by a novel double high-energy ball milling process followed by a cold consolidation and sintering. Microstructure and phase composition of the prepared samples were characterized using FE-SEM, EDS and XRD inspections. Mechanical and wear properties were characterized using compression and sliding wear tests. The results showed that a milling of Mg with Al2O3 particles in an initial step before mixing with Al has the beneficial of well dispersion of Al2O3 nanoparticles in Al–Mg dual matrix. The Al–Mg dual matrix reinforced with nano-size Al2O3 showed 3.29-times smaller crystallite size than pure Al. Moreover, the hardness and compressive strength are enhanced by adding nano-size Al2O3 with Al–Mg dual matrix composite while the ductility is maintained relatively high. Additionally, the wear rate of this composite was reduced by a factor of 2.7 compared to pure Al. The reduced crystallite size, the dispersion of Al2O3 nanoparticles and the formation of (Al–Mg)ss were the main improvement factors for mechanical and wear properties.

We report a highly sensitive wide-range resonant pressure sensor. The concept is based on tracking multiple modes of vibration of an electrothermally heated initially curved micro-beam experiencing the veering phenomenon between its first and third vibration modes. For low values of pressure, the third resonance frequency is very sensitive, and thus its variation with pressure is monitored and recorded. As increasing pressure, the resonance frequency of the third mode decreases until reaching the veering phenomenon. At that point, the first mode exchanges role with the third mode, becoming very sensitive, and hence its frequency is tracked afterward as varying pressure. We show that using this concept, the sensitivity of the resonant pressure micro-sensor is significantly enhanced. Finite element method (FEM) simulations and experimental data show that the proposed micro-sensor becomes highly sensitive for wide-range of pressure from 38 mTorr to 200 Torr. The effect of various parameters on the performance of the proposed pressure sensor is investigated including the thickness of the micro-beam, the vacuum chamber size, and the thermal actuation load.

The Richtmyer-Meshkov (RM) instability is numerically investigated on an unperturbed interface subjected to a diffracted convergent shock created by diffracting an initially cylindrical shock over a rigid cylinder. Four gas interfaces are considered with Atwood number ranging from 0.18 to 0.67. Results indicate that the diffracted convergent shock increases its strength gradually and reduces its amplitude quickly when it propagates towards the convergence centre. After the strike of the diffracted convergent shock, the initially unperturbed interface deforms with a bulge structure at the centre and two interface steps at both sides, which can be ascribed to the non-uniformity of the pressure distribution behind the diffracted convergent shock. With the decrease of Atwood number, the bulge structure becomes more pronounced. Quantitatively, the interface amplitude experiences a fast but short growing stage and then enters a linear stage. A good collapse of the dimensionless amplitude is found for all cases, which indicates a weak dependence of the growth rate on Atwood number in the deformed shock-induced RM instability. Then the impulsive theory is modified by eliminating the Atwood number and considering the geometry convergence, which well predicts the amplitude growth for the deformed shock-induced RM instability. Finally, the underlying mechanism is decoupled into three parts, and it is found that both the impulsive pressure perturbation and the geometry convergence promote the growth of interface perturbation while the continuous pressure perturbation inhibits the growth. As the Atwood number decreases, the impulsive perturbation plays an increasingly important role, which suggests that the impulsive perturbation dominates the deformed shock-induced RM instability at the linear stage.

In this paper we study the enstrophy transfers in helical turbulence using direct numerical simulation. We observe that the helicity injection does not have significant effects on the inertial-range energy and helicity spectra (∼k-5/3) and fluxes (constants). We also calculate the separate contributions to enstrophy transfers via velocity-to-vorticity and vorticity-to-vorticity channels. There are four different enstrophy fluxes associated with the former channel or vorticity stretching, and one flux associated with the latter channel or vorticity advection. In the inertial range, the fluxes due to vorticity stretching are larger than that due to advection. These transfers too are insensitive to helicity injection.

Many proposals for fuel rating in spark ignition (SI) engine have been suggested till date and still no consensus on this has been reached. The automobile industry is still using RON and MON tests for rating fuels, and still there exists a need to come up with new fuel rating systems. The fuel's knocking tendency in SI engines is primarily governed by the end-gas autoignition. Another combustion mode, homogeneous charge compression ignition (HCCI), is also driven by autoignition of the complete charge inside the cylinder. Fundamentally, the combustion process in both combustion modes is driven by autoignition, and HCCI combustion mode can be used to understand the knocking behavior in SI engines. The lean combustion environment in HCCI mode provides a good platform to replicate the operating conditions of modern SI engines, which are operating at boosted pressures and low intake temperatures, and understanding of the fuel knocking behavior under such conditions is vital for achieving high-efficient engines. Therefore in this study, HCCI combustion will be used in the standard CFR engine to understand the autoignition behavior of the fuels for SI engines. For this purpose, three fuel blends were selected, which had the research octane number equal to 90. The standard CFR engine was operated with varying intake pressures and temperatures under HCCI combustion mode. The Lund-Chevron HCCI fuel number was used to rate the fuels and this was compared with RON and MON of the blends. It was found that HCCI combustion could be used to rate the fuels with the standard CFR engine with minor modifications to accommodate the boosted conditions without affecting the geometry and the flow inside the CFR engine. Low temperature reactions were observed and were correlated with the Lund-Chevron HCCI fuel numbers.

A 10-kHz one-dimensional Rayleigh–CH4 Raman instrument capable of achieving highly precise measurement of temperature and methane mole fraction is demonstrated. The system uses a pulse-burst laser as the light source and back-illuminated electron-multiplied CCD cameras as the detectors. The cameras are operated in the subframe burst gating mode, to combine a high sampling rate, low noise, and a slow readout. The improved precision of this configuration is demonstrated by measuring temperature and methane mole fractions in ambient temperature gas mixtures and in a non-premixed inverse diffusion flame.

Next-generation stretchable electronics, such as wearable electronics and implantable sensors, require stretchable conductive fibers. Despite their great popularity for wearable electronics, conducting polymers do not sustain deformation very well because of their rigid conjugated backbone. Here, we report the production of stretchable conductive poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS)- conjugated polymer fibers, using optimal wet-spinning, followed by hot drawing. We engineer the fibers by introducing a copolymer, polyethylene-block-poly (ethylene glycol) (PBP), that modifies both the electrical and mechanical properties of the raw PEDOT/PSS. We then systematically investigate the effects of the PBP fraction (fs) on the properties of the PEDOT/PSS by analyzing the changes in the conductivity, morphology, stretchability, and conformation of the PEDOT chains. We find that the conductivity of PEDOT/PSS increases from 311 ± 8 S/cm to 415 ± 12 S/cm (133% increase), when fs = 0.4, and that the strain of the fibers, at failure, is as high as (ε = 36%) for fs = 0.7, eq. 3x the value of as-spun PEDOT/PSS fibers. Raman and XRD analyses show that the conformational changes from benzoid to quinoid structures, in the PEDOT chains, significantly enhance the conductivity of the fibers. This conformational change facilitate the switch from a coil structure of PEDOT/PSS into a linear or an extended-coil conformation that increases interchain interaction.