Non-symmetrical Configuration Research Articles

Propagation of a pulsed nanosecond discharge on a water surface in non-symmetrical configuration, and comparison with the symmetrical configuration

Non-thermal plasmas produced by pulsed nanosecond discharges at atmospheric pressure are of great interest for fundamental as well as technological and environmental applications due to their high reactivity. When generated in air in contact with water, these discharges induce many physical and chemical phenomena at the interface, including pattern formation. Although the patterns generated in symmetrical configuration have been extensively studied, those produced by asymmetrical discharges are not well characterized. In this study, we report the propagation dynamics of a nanosecond discharge produced in air in contact with water using electrodes mounted in parallel direction relative to the water surface (i.e. asymmetric configuration). The influence of the high voltage polarity and water electrical conductivity on the discharge pattern is investigated using fast imaging and electrical diagnostics. The obtained results demonstrate that under positive voltage polarity, plasma dots are produced along the ionization front. These dots have been previously observed in symmetrical configuration; however, their propagation velocity is greater in asymmetrical configuration, particularly in front of the anode. Under negative polarity conditions, a homogeneous emission pattern is observed, except in the area in front of the cathode, where dots are detected in the ionization front. Based on this data, the E-field threshold beyond which plasma dots are formed is estimated to be ∼5 × 108 V m−1. Overall, the results reported herein provide a fundamental understanding of plasma-water interactions.

Effect of Sac Asymmetry, Neck and Iliac Angle on the Hemodynamic Behavior of Idealized Abdominal Aortic Aneurysm Geometries

Abdominal Aortic Aneurysms (AAAs) are currently treated based on the universal maximum diameter criterion, but other geometric variables may play a role in the risk of rupture. The hemodynamic environment inside the AAA sac has been shown to interact with several biologic processes which can affect prognosis. AAA geometric configuration has a significant impact in the hemodynamic conditions that develop, which has only been recently realized, with implications for rupture risk estimations. We aim to perform a parametric study to evaluate the effect of aortic neck angulation, angle between the iliac arteries and sac asymmetry on the hemodynamic variables of AAAs. This study uses idealized AAA models and it is parametrized in terms of three quantities: the neck angle, φ(o), iliac angle, θ(o), and sac asymmetry, SA(%), each of which accepts three different values, specifically φ=(0o,30o,60o),θ=(40o,60o,80o), and SA=(S,SS,OS) where the sac asymmetry can either be on the same side with respect to neck (SS) or on the opposite side (OS). Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), Relative Residence Time (RRT) and the velocity profile are calculated for different geometric configurations while the percentage of the total surface area under thrombogenic conditions, using thresholds previously reported in the literature, is also recorded. In case of an angulated neck and a higher angle between iliac arteries, favorable hemodynamic conditions are predicted with higher TAWSS and lower OSI and RRT values. The area under thrombogenic conditions reduces by 16%-46% as the neck angle increases from 0o to 60o, depending on the hemodynamic variable under consideration. The effect of iliac angulation is present but less pronounced with 2.5%-7.5% change between the lower and the higher angle. The effect of sac asymmetry seems to be significant for OSI with a non-symmetrical configuration being hemodynamically favorable, which in the presence of an angulated neck is more pronounced for the OS outline. Favorable hemodynamic conditions develop inside the sac of idealized AAAs with increasing neck and iliac angles. Regarding the sac asymmetry parameter, asymmetrical configurations most often appear advantageous. Concerning the velocity profile the triplet (φ,θ,SA) may affect outcomes under certain conditions and thus should be taken into account when parametrizing the geometric characteristics of AAAs.

Simple interferometric setup enabling sub-Fourier-scale ultra-short laser pulses

In this work, we describe an interferometric method to generate ultra-short pulses below the Fourier limit. It is done by extending concepts first developed in the spatial domain to achieve sub-diffractive beams through the addition of a spatial chirp in one of the arms of a Michelson interferometer using a spherical mirror. To experimentally synthesize sub-Fourier pulses, we replace the spherical mirror with a water cell, since it produces chirp in the temporal domain. We also present an alternative procedure, based on asymmetrical interference between the widened pulse and the original pulse where the peaks of both pulses exhibit a temporal delay achieving the narrowing of ultra-short pulses with sub-Fourier scales. To characterize the performance of the system, we performed a preliminary assessment considering the percentage of full width at half-maximum shrinking obtained for each scheme. By means of a symmetrical configuration, 7% and 12% pulse reductions were verified, both experimentally and analytically, while for the non-symmetrical configuration, 10% and 24% reductions were achieved corresponding to main lobe to side-lobe ratios of 10% and 30%. The experimental setup scheme is simple, versatile and able to work with high-power laser sources and ultra-short pulses with a broad bandwidth at any central wavelength. The results presented in this work are promising and help to enlighten new routes and strategies in the design of coherent control systems. We envision that they will become broadly useful in different areas from strong field domain to quantum information.

Dynamics-Based Piecewise Constant Control of an Omnivehicle

For the nonsymmetrical vehicle configuration, we propose a numerical procedure of solving boundary-value problems that uses parametric continuation of the solution obtained for the symmetric vehicle. It shows that the proposed type of control can be used for an arbitrary vehicle configuration.

Theoretical and parametric studies of a self-centering modular steel structure connection

A novel modular steel structure (MSS) connection using symmetrical self-centering (SC) haunch braces is proposed to expand the current research limits and create a modular structure with superior seismic resilient performance and functional recoverability after earthquakes. An advanced connection technique of the modules consisting of a cross-shaped plug-in connector, cover plates, and several bolts is used to provide adequate stiffness and ensure structural integrity. A theoretical model of the self-centering MSS (SC-MSS) connection system is established to evaluate the haunch brace effects on the key components, and the model is validated by simulations. The effects of the dimension of the plug-in connector, the location and performance parameters of the SC haunch brace, and the haunch brace configuration on the seismic resilient performance of the connection are analyzed. The SC-MSS connections exhibit satisfactory self-centering capability, and the bearing capacity is substantially higher than that of the MSS connection. A large tenon height in the connector increases the local strength of the column flanges, ensuring the ductile failure mode in areas of concentrated plasticity in the beams. As the installation distance, angle and pre-stressed force of the SC haunch brace increases, the bearing capacity and self-centering capability of the connection are effectively improved. The stable and expected behavior of the connection with the non-symmetrical haunch configuration demonstrates the feasibility of the independent selection of the haunch patterns of each module. The additional strength and stiffness provided by the SC haunch braces result in acceptable energy dissipation of the SC-MSS connection and significant damage reduction.

Characterization of base bleed effects on subsonic trailing edge flows

Trailing edge injection enables control of the detached and unsteady flow within the base region. The interaction of the jet with the base region alters the flow topology causing pressure bifurcations at the trailing edge that affect the aerodynamic performance of the system and modify the vortex patterns downstream the body. The purpose of this work is to fully characterize the physical effects related to the use of base bleed on the trailing edge of an airfoil at subsonic conditions. Defining a non-dimensional base bleed rate Cb=m˙/ρ∞U∞h, a wide range from Cb=0 to Cb=1 is applied to a simplified model of a turbine blade. The influence of the trailing edge geometry shape is also evaluated, showing that rounded geometries have the potential to minimize the undesirable effects of the injection. Vortex shedding is neutralized when the (non-dimensional) ejected mass flow exceeds the value of Cb=0.8 and Cb=0.55 for straight and rounded geometries, respectively. Additionally, neutralization of the shedding also occurs for relatively low base bleed rates, often accompanied by the onset of a non-symmetrical configuration at the trailing edge. This work has particular relevance in aerothermal gas turbine design, where coolant flow may be ejected at the trailing edge to ensure adequate thermal protection of the airfoils.

Contactless Silicon-Based Multi-Dimensional Hall Sensor with Simultaneous Magnetic Sensing and Omni-Rotational Angle Measurement

This experimental research proposes a contactless silicon-based two-dimensional (2D) Hall sensor capable of simultaneous parallel-and perpendicular-directional magnetic sensing, with a 360° angle measurement. The Hall sensor was of non-symmetrical five-ohmic contact configuration (C1 – C5). In the study, experiments were carried out in three stages. In the first-stage experiment, the current (I) and voltage (V) of the 2D Hall sensor were determined under three schemes: schemes A (C1&C2), B (C2&C5), and C (C3&C4). In the second-stage experiment, the parallel and perpendicular absolute sensitivities of the 2D sensor were examined. Considering the discrepancy between the parallel and perpendicular absolute sensitivities, signal conditioning circuitry was incorporated into the sensor system to compensate, and the rotational angles measured in the final-stage experiment. The results revealed that the I-V curves were dominantly linear, corresponding to Ohm’s law. However, the parallel and perpendicular absolute sensitivities were low and unequal. Thus, signal conditioning circuitry was incorporated into the system to address the discrepancy and improve the performance. Importantly, the 2D Hall sensor exhibited a mere ±3odiscrepancy between the measured and reference rotational angles, given the magnetic flux density of 1000 G, with the hysteresis error of 2.8%. In essence, the proposed contactless silicon-based 2D Hall sensor possesses high potential for high-precision industrial applications.

Numerical study of spheres settling in Oldroyd-B fluids

In order to simulate the motion of balls settling in Oldroyd-B fluids, we have generalized to three dimensions the distributed Lagrange multiplier based fictitious domain method we developed in the study by Hao et al. [“A fictitious domain/distributed Lagrange multiplier method for the particulate flow of Oldroyd-B fluids: A positive definiteness preserving approach,” J. Non-Newtonian Fluid Mech. 156, 95 (2009)] for viscoelastic particulate flow in two-dimensional channels. The effect of the fluid elastic number and that of the density ratio of the particle and fluid on the chaining of balls have been studied. For the cases of two balls released side-by-side at high elasticity numbers, the two balls attract each other first and then form a chain, and such a chain settles vertically. But at low elasticity numbers, the two balls either stay separate and interact periodically or attract each other, turn, and separate periodically. At high blockage ratios, a stronger wall effect enhances the formation of two ball chains. For the cases of three balls released side-by-side, the ball interaction is slightly more complicated due to its non-symmetrical initial configuration. At high elasticity numbers, either a three ball chain settles vertically or the leading two balls form a chain which leaves the third ball behind. But at low elasticity numbers considered in this article, only the leading two balls form a chain. For the vertical initial configuration, a three ball chain can be obtained at higher elasticity numbers and also the heavier balls can form a vertical chain easily.

Symmetrical or Non-Symmetrical Debonds at Fiber–Matrix Interfaces: A Study by BEM and Finite Fracture Mechanics on Elastic Interfaces

A recently proposed criterion is used to study the behavior of debonds produced at a fiber–matrix interface. The criterion is based on the Linear Elastic–(Perfectly) Brittle Interface Model (LEBIM) combined with a Finite Fracture Mechanics (FFM) approach, where the stress and energy criteria are suitably coupled. Special attention is given to the discussion about the symmetry of the debond onset and growth in an isolated single fiber specimen under uniaxial transverse tension. A common composite material system, glass fiber–epoxy matrix, is considered. The present methodology uses a two-dimensional (2D) Boundary Element Method (BEM) code to carry out the analysis of interface failure. The present results show that a non-symmetrical interface crack configuration (debonds at one side only) is produced by a lower critical remote load than the symmetrical case (debonds at both sides). Thus, the non-symmetrical solution is the preferred one, which agrees with the experimental evidences found in the literature.

The Wide-Open Three-Legged Parallel Robot for Long-Bone Fracture Reduction

Robotic reduction of long bones is associated with the need for considerable force and high precision. To balance the accuracy, payload, and workspace, we have designed a new six degrees-of-freedom three-legged wide-open robotic system for long-bone fracture reduction. Thanks to the low number of legs and their nonsymmetrical configuration, the mechanism enjoys a unique architecture with a frontally open half-plane. This facilitates positioning the leg inside the mechanism and provides a large workspace for surgical maneuvers, as shown and compared to the well-known Gough–Stewart platform. The experimental tests on a phantom reveal that the mechanism is well capable of applying the desired reduction steps against the large muscular payloads with high accuracy.

TUNABLE ULTRA-LONG RANDOM DISTRIBUTED FEEDBACK FIBER LASER

A 72 km open-ended symmetrical tunable random distributed feedback fiber laser (RDB-FL) with different pumping schemes is presented in this study. The random distributed feedback was contributed by Rayleigh scattering in the single-mode fiber while distributed gain was provided by the effect of stimulated Raman scattering. The pumping schemes tested with the configuration was outward and inward pumping, where these would be backward and forward pumping in a non-symmetrical configuration of a fiber laser, respectively. The tuning range was also varied in conjunction with the different pumping schemes to determine the optimum performance. Random lasing in the RDB-FL was achieved by utilizing multiple scattering in the disordered gain medium to achieve resonance. With pump power limited to 1.5 W, the best threshold was measured as low as 1.4 W while the highest total output power was at 8 mW. In outward pumping configuration, the wavelengths that are within the maximum Raman gain (1555-1565 nm) show the best peak powers and total output power with a narrow linewidth, as low as 0.25 nm.

Digitally tunable holographic lithography using a spatial light modulator as a programmable phase mask

In this paper, we study tunable holographic lithography using an electrically addressable spatial light modulator as a programmable phase mask. We control the phases of interfering beams diffracted from the phase pattern displayed in the spatial light modulator. We present a calculation method for the assignment of phases in the laser beams and validate the phases of the interfering beams in phase-sensitive, dual-lattice, and two-dimensional patterns formed by a rotationally non-symmetrical configuration. A good agreement has been observed between fabricated holographic structures and simulated interference patterns. The presented method can potentially help design a gradient phase mask for the fabrication of graded photonic crystals or metamaterials.

Identification of meaningful coherent structures in the wind-induced pressure on a prismatic body

The concept of coherent structure is often invoked for the qualitative analysis of the wind-induced pressure field acting on bluff bodies. Coherent structures are traditionally extracted from the measured data through the Proper Orthogonal Decomposition (or Principal Component Analysis, PCA), but serious concerns on their meaningfulness have been risen. In an attempt to mitigate these problems, the Independent Component Analysis (ICA) has been introduced and demonstrated some potentials to extract coherent structures that are consistent with the observed phenomenon in term of some features that are defined in this paper. Considering the case of the pressure measured on a square-base prism immersed in a turbulent boundary layer with a non-symmetrical configuration, PCA and ICA are applied to extract coherent structures. The role of the model order, as well as the effect of a non-homogeneous spatial discretization is investigated.

Comparative effects of structural and material parameters variability on Pellet–Cladding Interaction in a PWR fuel rod

In the water pressurised nuclear reactors, the fuel rod cladding is the first barrier against radioactive isotopes release. Its integrity must be demonstrated all along the fuel rod irradiation with increasing strenuous operating conditions. This paper deals with a study made with Electricité de France (EDF) in order to improve the understanding and modelling of the thermomechanical behaviour of fuel rods under these more arduous conditions. The aim of this study is to evaluate the separate influences of structural and material parameters variability on Pellet–Cladding Interaction (PCI). The following parameters have been tested by 3D simulations for a common ramping condition: axial and radial pellet cracks numbers, pellet fragment size, relative fragments displacement, non-symmetrical configuration, pellet–pellet friction and pellet–cladding friction. The second part of the article deals with the development of a model, which gives a better assessment of cladding stress concentration near radial fuel cracks. The implementation in the 1D fuel rod EDF code CYRANO3 and the validation of the model are presented.

On plasma processing of polymers and the stability of the surface properties for enhanced adhesion to metals

This paper deals with the plasma surface treatment of polymers in a low frequency bell jar reactor with non-symmetrical configuration of electrodes. The highly energetic character of this discharge due to its low excitation frequency and electrode configuration, as well as its small discharge volume makes it a very efficient and fast functionalization process. Amongst the different plasma gases used for the adhesion improvement of polypropylene to aluminum, ammonia has shown to be the most suitable one for this application. Since the NH and NH 2 radicals play an important role in the kinetics of nitrogen incorporation in polymers, mixtures of N 2 and H 2 were also used as possible substitutes for ammonia. The former are more environmentally friendly and easier to handle in industry than ammonia. The efficiency of nitrogen rich mixtures in the case of the second application, i.e. adhesion improvement of copper to fluoropolymers has been compared to that of ammonia which still shows faster nitrogen incorporation. The last part of this paper is devoted to the study of the energetic character of plasmas of mixtures of He+NH 3 by OES and electrical measurements in the whole range of composition of the two gases. The results show that an ammonia percentage ranging from 5 to 10% in plasmas of mixtures of He/NH 3 represents a transition between two different discharge regimes. Plasmas of mixtures of He+2% NH 3, characterized by highly energetic electrons, ions and probably metastables of helium give rise to enhanced adhesion of PP to aluminum which remains stable with time.

Analysis of dynamical behaviour of a rotor with deflection limiters

The dynamical behaviour of a rotor running into contact with a non-annular stator is studied by numerical simulations. The rotor is represented by a 2-dof model moving in one plane. The stator models an arbitrary number of discrete stops by superimposing annular stators with large clearances and high offsets. Friction forces are included in the contact description. The strongly nonlinear differential equations are integrated using a fourth-order Runge-Kutta procedure. Time histories for start-up and run-down sequences are simulated in two numerical examples. Different stop configurations have been evaluated. For a configuration with four symmetrically distributed stops an interesting bouncing phenomenon was discovered. This was not found for a non-symmetrical configuration. When the bouncing phenomenon occurred, the radial displacement of the rotor was larger for the stators with stops than for an annular stator.

Study of plasmas in He–O2mixtures and their role on the stability of the surface properties of polymers

The characteristics of a low frequency (70 kHz) discharge with non-symmetrical configuration of electrodes in He–O 2 mixtures were investigated. The Langmuir probe technique, emission spectroscopy, mass spectrometry and absorption spectroscopy were used for plasma diagnostics. The physicochemical properties of PET (polyethylene terephtalate) were analyzed via contact angle measurements and XPS spectroscopy. The presence of the oxygen is shown to modify both the densities of the helium metastable states and also the energetic character of the discharge. The very efficient loss of He excited species and in particularly the metastables, for amounts of O 2 higher than a few percents, affects the surface modification in terms of crosslinking, and therefore the stability. This work has shown that one of the important species responsible for the crosslinking process leading to stable surface properties could be the helium metastables.

Rhenium(V)-Salen Complexes: Configurational Control and Ligand Exchange.

Reactions of ReO(PPh(3))(2)Cl(3) with tetradentate bis(salicylideneamine) ligands, H(2)salpd (1) and H(2)salbd (2), in different alcohols gave the novel mixed-ligand rhenium complexes ReO(sal)OAlk (OAlk = variety of alkoxy ligands). Configurational studies show that the rhenium complexes ReO(salpd)OAlk (1a-f) display either a symmetrical or a nonsymmetrical configuration, depending on the size of the alcohol and its boiling point. The rhenium complexes ReO(salbd)OAlk (2a-d) are all nonsymmetrical due to the number of carbons that bridge the imine nitrogens. In the case of the symmetrical ReO(salpd)OMe (1a) complex the methoxy ligand can be exchanged for a number of ligands of different types (OAlk, OPh, SAlk, OC(O)Alk). In the newly formed complexes the original configuration was retained except for the ReO(salpd)SAlk (1i,j) complexes which were isolated in the nonsymmetrical configuration. Starting from the nonsymmetrical ReO(salpd)OPr (2c) complex, ligand exchange led to a mixture of the symmetrical and nonsymmetrical complexes, with ratios depending on the reaction time. The crystal structures of ReO(salbd)OPr (2c), and ReO(salpd)OPhOMe (1g) have been determined. ReO(salbd)OPr crystallizes in the triclinic space group P&onemacr;, Z = 2, with a = 10.0344(16) Å, b = 10.647(2) Å, c = 11.481(2) Å, alpha = 86.551(15) degrees, beta = 86.998(14) degrees, gamma = 80.112(15) degrees, V = 1205.1(4) Å(3), and final R = 0.0460. Crystals of ReO(salpd)OPhOMe are orthorhombic, space group P2(1)2(1)2(1), Z = 4, with a = 10.6222(15) Å, b = 12.442(3) Å, c = 16.354(3) Å, V = 2161.4(7) Å(3), and final R = 0.0371. Under the influence of traces of water a number of symmetrical complexes react to a "dimeric" structure, consisting of two ReO(salpd) moieties bridged by an oxygen atom with the bridging Re-O-Re angle symmetrically imposed at 180 degrees. [ReO(salpd)](2)O (3) crystallizes in the monoclinic, space group P2(1)/c, Z = 4, with a = 14.860(2) Å, b = 12.545(2) Å, c = 16.5111(17) Å, beta = 95.030(10) degrees, V = 3066.1(7) Å(3), and final R = 0.0439.

Quantitative Analysis of the Symmetry of Artefacts: Lower Paleolithic Handaxes

The ability to perceive and produce symmetrical shapes is usually taken to be a major step in the development of human cognition. Despite the importance of the concept of symmetry to studies of early human development, its current use is usually based on loose qualitative assessment. A more informative approach would be to use a continuous scale of this shape property rather than the strict current language of “more” or “less”. A symmetry measurement tool has been developed, which is based on evaluation of the minimal distances that the vertices of a structure have to move in order to attain the required symmetry. Using this Continuous Symmetry Measure (CSM) method, it is possible to evaluate quantitatively how much symmetry exists in a non-symmetrical configuration and how the nearest symmetrical shape looks. We test and demonstrate the feasibility and versatility of this approach on handaxe samples from three Lower Paleolithic sites in Israel, Ubeidiya, Gesher Benot Ya'aqov and Ma'ayan Barukh, representing various stages in the Acheulian Techno-complex of the Levant. We provide, to the best of our knowledge for the first time, quantitative demonstration that the overall symmetry of handaxes generally increases, and that the variability decreases over time.

Study of the surface properties and stability of polymer films treated by NH3 plasma and its mixtures.

This paper deals with the plasma surface treatment of polymers in a low frequency bell jar reactor with non-symmetrical configuration of electrodes. This special configuration of electrodes simulates the industrial surface treatment of polymers i.e. very short treatment times (milliseconds to a few seconds). The physicochemical properties of different polymers modified in such a reactor using ammonia and its mixtures have been investigated. The industrial aim of such treatments were for adhesion improvement in applications such as metallization and immobilization of proteins for the fabrication of immunosensors. The last part of this paper was devoted to the study of the stability of the plasma modified polymers which is an important issue for the industrial development of plasma processes. A pretreatment in a noble gas such as helium was proposed in order to stabilize the extreme surface layer via crosslinking before the functionalization treatment in ammonia plasma. In order to carry out the crosslinking and functionalization process in a one step process, mixtures of He+NH3 plasmas were studied.