Beam Velocity Research Articles

Surface condition, microstructure and microhardness of boronized layers produced on Vanadis-6 steel after modification by diode laser

Abstract The paper presents the study results of surface condition, microstructure and microhardness of Vanadis-6 tool steel after diffusion boriding and laser modification by diode laser. As a result of diffusion boriding the layers consisted of two phases: FeB and Fe2B. A bright area under the continuous boronized layers was visible. This zone was probably rich in boron. As a result of laser surface modification of boronized layers, the microstructure composed of three zones: remelted zone, heat affected zone and the substrate was obtained. The microstructure of remelted zone consisted of boron-martensite eutectic. The depth of laser track (total thickness of remelted zone and heat affected zone) was dependent on laser parameters (laser beam power density and scanning laser beam velocity). The microhardness of laser remelting boronized layer in comparison with diffusion boronized layer was slightly lower. The presence of heat affected zone was advantageous, because it allowed to obtain a mild microhardness gradient between the layer and the substrate.

A theoretical study on laser cooling of silicon monofluoride

The feasibility of direct laser cooling of silicon monofluoride (SiF) is investigated and assessed using the internally contracted multireference configuration interaction method with the Davidson correction and entirely uncontracted aug-cc-pwCV5Z basis sets. As for the A2Σ+(ν′=0)→X2Π transition, the computed radiative lifetime is 0.69μs and the vibrational branching ratio Rν′ν is highly diagonally distributed with the R00 being 0.994, which are desirable for rapid and efficient laser cooling. In addition, good agreement is achieved between our computed spectroscopic properties and the available experimental data for the X2Π and A2Σ+ states of SiF. We propose a kind of laser cooling scheme, in which the wavelengths are located in the visible region. Both our calculated Doppler and recoil temperatures are of the order of μK, and the calculated minimum distance necessary to bring the velocity of a SiF beam to that suitable for trapping is 13cm, indicating that the SiF molecule can be cooled to the ultracold regime through the proposed scheme.

Black hole mass measurement using molecular gas kinematics: what ALMA can do

We study the limits of the spatial and velocity resolution of radio interferometry to infer the mass of supermassive black holes (SMBHs) in galactic centres using the kinematics of circum-nuclear molecular gas, by considering the shapes of the galaxy surface brightness profile, signal-to-noise ratios (S/Ns) of the position-velocity diagram (PVD) and systematic errors due to the spatial and velocity structure of the molecular gas. We argue that for fixed galaxy stellar mass and SMBH mass, the spatial and velocity scale that need to be resolved increase and decrease, respectively, with decreasing \sersic\ index of the galaxy surface brightness profile. We validate our arguments using simulated PVDs for varying beam size and velocity channel width. Furthermore, we consider the systematic effects on the inference of the SMBH mass by simulating PVDs including the spatial and velocity structure of the molecular gas, which demonstrates that their impacts are not significant for a PVD with good S/N unless the spatial and velocity scale associated with the systematic effects are comparable to or larger than the angular resolution and velocity channel width of the PVD from pure circular motion. Also, we caution that a bias in a galaxy surface brightness profile owing to the poor resolution of a galaxy photometric image can largely bias the SMBH mass by an order of magnitude. This study shows the promise and the limit of ALMA observations for measuring SMBH mass using molecular gas kinematics and provides a useful technical justification for an ALMA proposal with the science goal of measuring SMBH mass.

Pre-equilibrium emission to study clustering in nuclei

Clustering structural properties in medium-mass systems have been investigated studying the competition between the evaporation and pre-equilibrium particle emission in central collisions. At variance with light nuclei, in the case of heavier nuclei there are no experimental evidences of such structure effects, since the determination of pre-formed clusters within nuclear matter is less obvious.The two systems 16 O + 65 Cu and 19 F + 62 Ni, leading to the same compound system 81 Rb* , have been studied at the same beam velocity (16 AMeV). The experiments have been performed using the GARFIELD + RCo multi-detection system at the Legnaro National Laboratories.Recent results of the data analysis and of the comparison of the experimental data with different statistical and dynamical model calculations are reported in this contribution.

Application of differential transformation finite element method in aperiodic vibration of non-prismatic beam

The paper presents the combination of multi-step differential transformation method (MsDTM) and finite element method (FEM) in vibration analysis of non-prismatic beam. A new algorithm, named differential transformation finite element method (DTFEM), combines the advantages of both methods. It enables to solve a wide class problems and obtain solutions in the form of piecewise functions that are very useful in further analyses, especially in time-consuming computations of dynamic systems. In contrary to standard DTM, with the proposed method, we can successfully calculate vibrations of non-prismatic structures governed by partial differential equations with variable coefficients. The application of FEM reduces partial differential equation to system of ordinary differential equations depending on time. After applying multi-step DTM the system is converting into a set of recursive algebraic equations which can be solved in a symbolic way. The final approximate solution is composed of a sequence of single solutions obtained in every time interval.The algorithm of DTFEM was described and illustrated with an example of non-prismatic simply supported beam subjected to uniformly distributed load increasing nonlinearly in time. The results in the form of beam displacements, velocities and accelerations were compared with numerical approach based on Newmark method. Two cases of damping model were taken into account: structural damping model and external damping model represented by two viscous dampers. A very good agreement was found in both cases. Presented analyses show that DTFEM is more accurate, with the same time step, than Newmark method. Therefore, in some cases, it may be possible to obtain sufficiently accurate results faster. The main advantage of the proposed method is the solution’s form which is a function of time and not a discrete set of results.

The influence of laser heat treatment on the geometric structure of the surface and condition of the surface layer and selected properties of Waspaloy

In the aviation industry the nickel-based superalloys such as Waspaloy are very often used. Conventional machining of this alloys is difficult and expensive. Therefore a Waspaloy requires the new techniques for machining like e.g. Laser Assisted Machining (LAM). New development directions of mechanical engineering are focusing on this type of hybrid machining, where materials are heated and cut in the single process. LAM enables increasing the material machinability through the increase of its temperature in cutting zone. It is assumed that additional increased temperature in the contact zone between surface of material and cutting tool causes the increase of machinability. This paper presents the results of laser heat treatment process on Waspaloy material. The influence of laser heat treatment parameters on the surface condition and selected properties of Waspaloy were analyzed. Laser heat treatment was carried out using diode laser with nominal power equaled to 3.0 kW. The laser beam power density and its scanning laser beam velocity were analyzed. In the first step the single laser tracks were prepared and analyzed. In the second step the multiple laser tracks were prepared. The special attention was directed on change in microstructure. It was found that the laser heat treatment have significant influence on microstructure. The dendritic microstructure of Waspaloy which is characterized by a lower microhardness, causes better machinability of this material.

Synergetic heating of D-NBI ions in the vicinity of the mode conversion layer in H-D plasmas in JET with the ITER like wall.

This paper discusses the extension of the ‘three-ion’ species ICRF technique for heating mixture plasmas using fast injected NBI ions as resonant ‘third’ species. In this scenario the ICRF power is absorbed by the fast beam ions in the vicinity of the mode conversion layer where the left-hand polarized RF electric field E + is strongly enhanced. The ions in the beam velocity distribution that have a Doppler-shifted resonance close to the mode conversion layer efficiently absorb RF power and undergo acceleration. We show first experimental observations of ICRF heating of D-NBI ions in H-D plasmas in JET with the ITER-like wall. In agreement with theoretical predictions and numerical modelling, acceleration of the D-NBI ions in this D-(DNBI )-H scenario is confirmed by several fast-ion measurements. An extension of the heating scheme discussed here is acceleration of T-NBI and D-NBI ions in D-T plasmas, offering the potential to further boost the Q -value in future D-T campaigns in JET.

Evaluation of an Al-Ce alloy for laser additive manufacturing

This study focuses on the development of a design methodology for alloys in AM, using a newly developed Al-Ce alloy as an initial case study. To evaluate the candidacy of this system for directed energy deposition processes, single-line laser melts were made on cast Al-12Ce plates using three different beam velocities (100, 200, and 300 mm/min). The microstructure was evaluated in the as-melted and heat treated conditions (24 h at 300 °C). An extremely fine microstructure was observed within the melt pools, evolving from eutectic at the outer solid-liquid boundaries to a primary Al FCC dendritic/cellular structure nearer the melt-pool centerline. The observed microstructures were rationalized through the construction of a microstructure selection map for the Al-Ce binary system, which will be used to enable future alloy design. Interestingly, the heat treated samples exhibited no microstructural coarsening.

A novel slithering locomotion mechanism for a snake-like soft robot

A novel mechanism for slithering locomotion of a snake-like soft robot is presented. A rectangular beam with an isotropic coefficient of friction of its contact surface with the flat ground can move forward or backward when actuated by a periodic traveling sinusoidal wave. The Poisson's ratio of the beam plays an important role in the slithering locomotion speed and direction, particularly when it is negative. A theoretical model is proposed to elucidate the slithering locomotion mechanism, which is analogous to the rolling of a wheel on ground. There are two key factors of slithering locomotion: a rotational velocity field and a corresponding local contact region between the beam and ground. During wriggling motion of the rectangular beam, a rotational velocity field is observed near the maximum curvature point of the beam. If the beam has a negative Poisson's ratio, the axial tension will cause a lateral expansion so that the contact region between the beam and ground is located at the outer edge of the maximum curvature (the largest lateral expansion point). The direction of the beam's velocity at this outer edge is usually opposite to the traveling wave direction, so the friction force propels the beam in the direction of the traveling wave. A similar scenario is found for the relatively large amplitude of wriggling motion when the beam's Poisson's ratio is positive. Finite element method (FEM) simulation was conducted to verify the slithering locomotion mechanism, and good agreement was found between the FEM simulation results and theoretical predictions. The insights obtained here present a simple, novel and straightforward mechanism for slithering locomotion and are helpful for future designs of snake-like soft robots.

Modal characteristics of a rotating flexible beam with a concentrated mass based on the absolute nodal coordinate formulation

A new dynamic model of a rotating flexible beam with a concentrated mass located in arbitrary position is derived based on the absolute nodal coordinate formulation, and its modal characteristics are investigated in this paper. To consider the concentrated mass at an arbitrary location of the beam, a Dirac’s delta function is used to express the mass per unit length of the beam. Based on the proposed dynamic model, the frequency analysis is performed. The nonlinear equation is transformed into the linear one via employing the linear perturbation analysis method. The stiffness matrix of static equilibrium of the system under the deformed condition is obtained, in which the effect of coupling between the longitudinal deformation and transversal deformation is included. This means even if only the chordwise bending equation is solved, the longitudinal vibration effect can be still considered. As we know, once the longitudinal deformation is large, it will significantly affect the chordwise bending vibration. So the proposed model in this paper is more accurate than the traditional dynamic models which are usually lack of the coupling terms between the longitudinal deformation and transversal deformation. In fact, the traditional dynamic models for the chordwise vibration analysis in the existing literature are usually linear due to neglecting the coupling terms, and consequently, they are only suitable for the modal characteristic analysis of a beam under small deformations. In order to get some general conclusions of the natural frequencies and mode shapes, the equation which governs the chordwise bending vibration of the rotating beam is transformed into a dimensionless form. The dynamic model presented in this paper is nonlinear and can be conveniently used to analyze the modal characteristics of a rotating flexible beam with large deformations. To demonstrate the power of the new dynamic model presented in this paper, the dynamic simulations involving the comparisons between the different frequencies obtained using the model proposed in this paper and the models in the existing literature and the investigating in frequency veering and mode shift phenomena are given. The simulation results show that the angular velocity of the flexible beam will give rise to the phenomena of the natural frequency loci veering and the associated mode shift which is verified in the previous studies. In addition, the phenomena of the natural frequency loci veering rather than crossing can be observed due to the changing of the magnitude of the concentrated mass or of the location of the concentrated mass which are found for the first time. Furthermore, there is an interesting phenomenon that the natural frequency loci will veer more than once due to different types of mode coupling between the bending and stretching vibrations of the rotating beam. At the same time, the mode shift phenomenon will occur correspondingly. Additionally, the characteristics of the vibration nodes are also investigated in this paper.

Analysis of Selective Laser Melting Process Parameters Effect on Mechanical and Material Properties for Stainless Steel 316L

This paper deals with a testings of the Selective Laser Melting (SLM) process parameters on mechanical properties, material behavior, surface quality and on machinability of austenitic steel 316L. The SLM process conditions were changed to assess their effect on mechanical properties of the sintered material measured in tensile testing. The laser power, the scanning velocity of laser beam, the layer thickness and the laser focus plane were set to find the most appropriate set of process parameters to obtain the mechanical properties of parts.

Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event

We search for indications of waves in the 25-2000 MHz radio spectrum of the 1 August 2010 event (SOL2010-08-01T08:57:00L075C013), where fast propagating waves in the solar corona with the periods of 181, 69, and 40 seconds were detected in UV observations. Using the wavelet technique we construct a new type of map of oscillations for selected periods in the whole domain of the radio spectrum. While the oscillation with the period of 181 seconds was recognized in the whole 25-2000 MHz radio spectrum, oscillations with periods of 69 and 40 seconds were confirmed only in the 250-870 MHz frequency range. In the 800-2000 MHz range we found periods of 50 and 80 seconds. Moreover, in the 250-870 MHz frequency range, the oscillation with the period of about 420 seconds was detected. We also made maps of phases of the 181-second oscillations in order to analyze their frequency drift. At the beginning of the radio event, in the 2000-500 MHz frequency range the phase of the 181-second oscillation drifts towards lower frequencies. On the other hand, at frequencies 25-500 MHz we found that the phase is nearly synchronous. While the phase drift at higher frequencies can be interpreted as being caused by the UV wave, the synchronization of the phase on lower frequencies is explained by the fast-electron beams, whose acceleration is modulated by the UV wave. Owing to this modulation, the electron beams are accelerated with the period of the UV wave (181 seconds). These beams propagate upwards through the solar corona and generate the 25-500 MHz radio emission with the 181-second period. Due to high beam velocity (~c/3, where c is the light speed) the 25-500 MHz radio emission, corresponding to a large interval of heights in the solar corona, is nearly synchronous.

Coherent Cherenkov radiation and laser oscillation in a photonic crystal

We demonstrate that photonic crystals can be used to generate powerful and highly coherent laser radiation when injecting a beam of free electrons. Using theoretical investigations we present the startup dynamics and coherence properties of such laser, in which gain is provided by matching the optical phase velocity in the photonic crystal to the velocity of the electron beam.

Band structure of the growth rate of the two-stream instability of an electron beam propagating in a bounded plasma

This paper presents a study of the two-stream instability of an electron beam propagating in a finite-size plasma placed between two electrodes. It is shown that the growth rate in such a system is much smaller than that of an infinite plasma or a finite size plasma with periodic boundary conditions. Even if the width of the plasma matches the resonance condition for a standing wave, a spatially growing wave is excited instead with the growth rate small compared to that of the standing wave in a periodic system. The approximate expression for this growth rate is γ≈(1/13)ωpe(nb/np)(Lωpe/vb)ln(Lωpe/vb)[1−0.18 cos (Lωpe/vb+π/2)], where ωpe is the electron plasma frequency, nb and np are the beam and the plasma densities, respectively, vb is the beam velocity, and L is the plasma width. The frequency, wave number, and the spatial and temporal growth rates, as functions of the plasma size, exhibit band structure. The amplitude of saturation of the instability depends on the system length, not on the beam current. For short systems, the amplitude may exceed values predicted for infinite plasmas by more than an order of magnitude.

Theoretical derivation and simulation of a versatile electrostatic trap for cold polar molecules**Project supported by the National Nature Science Foundation of China (Grant No. 11504318).

We propose a versatile electrostatic trap scheme using several charged spherical electrodes and a bias electric field. We first give the two-ball scheme and derive the analytical solution of the electric field. In order to make a comparison, we also give the numerical solution calculated by the finite element software (Ansoft Maxwell). Considering the loading of cold polar molecules into the trap, we give the three-ball scheme. We first give the analytical and numerical solutions of the distribution of the electric field. Then we simulate the dynamic process of the loading and trapping cold molecules using the classical Monte Carlo method. We analyze the influence of the velocity of the incident molecular beam and the loading time on the loading efficiency. After that, we give the temperature of the trapped cold molecules. Our study shows that the loading efficiency can reach 82%, and the corresponding temperature of the trapped molecules is about 24.6 mK. At last, we show that the single well divides into two ones by increasing the bias electric field or decreasing the voltages applied to the spherical electrodes.

Nonlinear dynamic characteristic analysis of jointed beam with clearance

The impact and elasticity of discontinuous beams with clearance frequently affect the dynamic response of structures used in space missions. This study investigates the dynamic response of jointed beams which are the periodic units of deployable structures. The vibration process of jointed beams includes free-play and impact stages. A method for the dynamic analysis of jointed beams with clearance is proposed based on mode superposition and instantaneous static deformation. Transfer matrix, which expresses the relationship of the responses before and after the impact of jointed beams, is derived to calculate the response of the jointed beams after a critical position. The dynamic responses of jointed beams are then simulated. The effects of various parameters on the displacement and velocity of beams are investigated.

Laser melt injection of austenitic cast iron Ch16D7GKh with titanium

The results of studying the microstructure and microhardness of Ni-resist cast iron ChN16D7GKh after laser melt injection by means of introducing titanium particles into the melt are presented. The treatment was performed using a fiber laser with a beam focused into a spot 0.2 mm in diameter with a radiation power of 1 kW and the motion velocity of the laser beam of 10–40 mm/s. Titanium is dissolved in the cast-iron melt, and TiC particles are formed in the structure upon cooling. The coefficient of using the titanium powder increases as the fusion zone size increases and reaches 50% in the best case. A modified layer has a composite structure with a metallic matrix and a comparatively uniform distribution of titanium carbide particles. The microhardness of the modified zone is 600–700 HV. Its further growth is suppressed by the partial removal of carbon from the melt zone in the composition of red fume evolved in the process. Therefore, the Laves phase (TiFe2) is formed instead of an increase in the TiC content upon increasing the titanium supply. The experimental data on the regularities of the weight loss caused by the substance removal from the melt zone depending on laser melting parameters are presented.

Development of a beam ion velocity detector for the heavy ion beam probe.

In an axisymmetric plasma, the conservation of canonical angular momentum constrains heavy ion beam probe (HIBP) trajectories such that measurement of the toroidal velocity component of secondary ions provides a localized determination of the poloidal flux at the volume where they originated. We have developed a prototype detector which is designed to determine the beam angle in one dimension through the detection of ion current landing on two parallel planes of detecting elements. A set of apertures creates a pattern of ion current on wires in the first plane and solid metal plates behind them; the relative amounts detected by the wires and plates determine the angle which beam ions enter the detector, which is used to infer the toroidal velocity component. The design evolved from a series of simulations within which we modeled ion beam velocity changes due to equilibrium and fluctuating magnetic fields, along with the ion beam profile and velocity dispersion, and studied how these and characteristics such as the size, cross section, and spacing of the detector elements affect performance.

Vertical beam modal response in a broadband energy harvester

We examined energy harvesting using a vertical composite laminate beam with an additional moving mass subjected to kinematic harmonic excitation. The gravity effect and the moving tip mass applied to the system cause considerable changes in effective spring-mass characteristics of the bending beam. Simultaneously, we observed dynamical beam damping by an additional degree of freedom and non-linear effects including friction between the moving mass and the beam structure. The experiments were performed on the beam excited kinematically by a shaker, while beam velocity measurements were made by a scanning laser vibrometer. We applied modal analysis in the limit of a fairly low excitation level. The selected modal vibrations are illustrated by corresponding output time series.

Beam Velocity and Density Influences on Ion-Beam Pulses Moving in Magnetized Plasmas

The wakefield and stopping power of an ion-beam pulse moving in magnetized plasmas are investigated by particle-in-cell (PIC) simulations. The effects of beam velocity and density on the wake and stopping power are discussed. In the presence of magnetic field, it is found that beside the longitudinal conversed V-shaped wakes, the strong whistler wave are observed when low-density and low-velocity pulses moving in plasmas. The corresponding stopping powers are enhanced due to the drag of these whistler waves. As beam velocities increase, the whistler waves disappear, and only are conversed V-shape wakes observed. The corresponding stopping powers are reduced compared with these in isotropic plasmas. When high-density pulses transport in the magnetized plasmas, the whistler waves are greatly inhibited for low-velocity pulses and disappear for high-velocity pulses. Additionally, the magnetic field reduces the stopping powers for all high-density cases.