To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Additive manufacturing (AM) has made long strides in the recent past and rapidly evolved into a promising alternative in specific applications. The aircraft industry is not an exception to this. The true just-intime production possibility is critical for the aircraft maintenance industries, though the lack of material freedom is a major hurdle. Several fire-retardant materials were investigated for AM in the aerospace context, but mainly for fused deposition modeling (FDM). The material consolidation constraints in FDM led to the expansion to the use of selective laser sintering (SLS) to some extent. Nevertheless, the material options are still limited, proprietary, and lack scientific insights into the material consolidation mechanics. Attempts are made in this paper to fill this gap, evaluating a new fire-retardant material for processing by SLS. Experiments conducted to ascertain the material, process, structure, and consolidation relationships indicated energy density levels 0.062–0.070 J/mm2 with laser power 13 W and scan speed varied slightly around 390 mm/s to give the best laser sintering and mechanical property results in polyetherimide powders.
Nickel-coated carbon nanotubes (Ni-CNTs) were achieved by electroless plating. Laser cladded IN718 and IN718 with 10, 30, and 50 wt% additions of Ni-CNTs were fabricated. The structural evolution of CNTs in the laser-deposited layers was studied; the microstructure, tensile, and wear properties of the laser-cladded alloys were characterized. The results show that CNTs in the laser-deposited layers are mostly transformed to carbon nanoproducts (CNPs) in the forms of graphene nanosheets, graphene fragments, carbon nanoribbons, and diamond-like nanoparticles by unzipping, interbonding, collapsing, and curvature of CNTs. The interdendritic Laves phase formation is dramatically depressed due to the addition of Ni-CNTs, but the excess addition of the Ni-CNTs can undesirably increase the formation of NbC. The addition of Ni-CNTs effectively improves the tensile and wear properties. The most superior tensile and wear properties are achieved in the layers with 30 and 50 wt% additions of Ni-CNTs, respectively. The generation of intermetallic phase and CNPs are revealed to be two dominant effects both on the tensile and wear properties of the laser-cladded alloys.
Additively manufactured parts produced via laser powder bed fusion (LPBF) have limitations in their applications due to post-processing requirements caused by high surface roughness. The characteristics of side-skin surfaces are generally assumed to be dominated by adhered powder particles. This work aims to analyze and interpret the effects of LPBF processing parameters on side-skin surfaces. As such, this work has two sections to investigate the effect of (i) core and (ii) border LPBF parameters on side-skin surface roughness for Ti–6Al–4V. The findings show that there is a robust correlation between both core and border LPBF parameters on side-skin surface morphologies. In terms of core LPBF parameters, an interaction between laser power and beam velocity is shown to influence side-skin surface roughness, resulting in Sa values in the range of 11–26 μm. Additionally, a preliminary investigation into the effect of melting mode phenomena at the border leads to a possibility of obtaining Sa values of <10 μm, with reduced effects of adhered and partially fused powder.
We observe experimentally periodic proton beam filamentation in laser-produced dense plasma using multilayered (CH–Al–CH) sandwich targets. The accelerated MeV proton beams from these targets exhibit periodic frozen filaments up to 5–10 µm as a result of resistive Weibel instabilities in the expanding plasma. The evolution of strong self-generated resistive magnetic fields at the targets interface is attributed to such plasma effects, which are supported, by our theory and simulations. We suggest that the resistive Weibel instability could be effectively employed to understand the evolution of magnetic fields in laser-generated plasma in the astrophysics scenario or the advanced fast igniter approach of the inertial confinement fusion.
In this research, a novel titanium metallic composite, Ti6Al4V powder mixed with 5 at.% Nb powder, was fabricated by selective laser melting (SLM). The effect of Nb addition on their phase transformation, microstructure evolution, mechanical properties, and corrosion behavior were studied. Interestingly, the novel alloy shows a combination of superior plastic deformation (εp= 18.9 ± 1.8%) and high compressive strength (σc= 1593 ± 38 MPa), which is 60.2 and 3.2% higher than that of the SLM-processed Ti6Al4V alloy under optimum printing parameters, respectively. However, the yield strength of Ti6Al4V + 5Nb (973 ± 45 MPa) is lower than that of the Ti6Al4V alloy (1066 ± 12 MPa). The solidification mechanism changes from planar to cellular mode with Nb addition. The ultrafine microstructure β grains are observed, which show a columnar shape and cellular shape. More importantly, the volume fraction of the β phase is significantly increased from 3.7% to 20.4% because of the Nb addition. In addition, the Ti6Al4V + 5Nb alloy possesses better corrosion resistance than the Ti6Al4V alloy. The research highlights that the addition of Nb powder in Ti6Al4V processed by SLM can improve the mechanical properties and corrosion resistance of the material.
Laser surface treatment is widely used as an engineering technique due to its special characteristics and several advantages over other surface modification techniques. In the present study, elemental mechanically pre-alloyed powder consisting of Niobium, Titanium and Nickel was deposited onto a grade 5 Titanium alloy substrates to form a high wear resistance coating. This was such that the surface mechanical properties of the base metal can be improved. The fabricated samples were characterised using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Differential Scanning Calorimeter (DSC), micro hardness tester and wear machine. The deposited coatings were well bonded and consisted of various phases. Hardness was seen decrease with increase in Nb content while wear resistance increasing with increase in niobium content.
Pairs of conjugate donor-acceptor fluorescent probes have proven themselves useful in stimulated emission depletion (STED) microscopy in recent years. For instance, it has been shown that the lifetime of said probes directly correlates to the resolution of the microscope. However, once the lifetimes of the probes have been optimized, it is desirable to control their fluorescence in order to improve the resolution further. Here, we propose combining model-free control with sliding mode control to track nanosecond pulses of red-shifted acceptor fluorescence in order to inhibit visible light emitted from the image plane, shrink the point spread function, and subsequently improve the resolution of the microscope. This is achieved by automatic adjustment of the STED laser beam pump power. This controller is numerically simulated against a generic model created from Förster resonance energy transfer (FRET) theory. However, since it is data-driven, it can be easily applied to various physical systems with drastically different dynamics. This work provides a reliable theoretic control solution to modern super resolution microscopy for biological imaging.
A hollow γ-TNB turbine blade was 3D printed in this studying using the –R Optomec LENS machine from the elemental powders of aluminium, niobium and titanium making use of the laser “in situ” alloying approaching. The printed blade was characterised of a nearly lamellar β microstructure in the As-built state. The microstructure of the blade post heat treated was characterised of grain growth and coarsening and the formation of the γ phase which was of the result of the transformation of β. This transformation was also observed in the As-built state and is reported here for the first time. A massive crack that was observed half-way through in the built was attributed to the thermal shocks that are experienced by the almost immediately after manufacturing. The EDS and Map taken on the As-built and heat treated samples conclude that there was no segregation in the alloying element during manufacturing and that the blade was of the dual phase. Hardness results indicated the heat treated sample was 91 HV0.5 lower in hardness when compared to the As-built component. The successful print of this hollow blade indicate that γ-TNB and other Ti-Al alloys can be printed with the LENS but if a crack free sample was to be achieved the set-up had to be manipulated or addition resources must be added to adapt the set-up. Meanwhile the successes of this study show that LENS is going to be considered as a cost-effective manufacturing tool in the future for 3D printing Ti-Al and other metallic structure that would have improved properties when compared to traditional manufacturing technique such as casting and the powder bed systems.
Ignition with the help of a shock wave is performed by the interaction of accelerated plasma block by a petawatt-picosecond (PW-ps) laser, with a solid-state density fuel that it is a new possibility for achieving controlled fusion by inertial confinement. The unexpected production of plasma blocks provides new access to the ignition of solid-state density fuel according to the Chu hydrodynamic model. When the produced plasma block by the PW-ps laser hits the main fuel due to the density differences between the plasma block and the main fuel of the shock wave, this progressive wave increases the density of solidified fuels and reduces the energy of the ignition threshold and increases the flammability. In this study, a new discovery of shock waves has been observed leading to the resonance phenomenon. Nuclear heat shock waves resonance in the side-on ignition of fuel in the internal layer of fuel at x ≠ 0 appears from the exact solution of the hydrodynamic equations with respect to the density profile. This important finding achieves the required ignition temperature for solid-state fuel deuterium–tritium (D–T) in certain energies, with a significant increase due to the resonance of thermonuclear waves. This discovery will facilitate practical experiments on the ignition of advanced solid-state fuels with the accelerated plasma blocks by a PW-ps laser at certain energies.
Advances in technology have seen mobile robots becoming a viable solution to many global challenges. A key limitation for tetherless operation, however, is the energy density of batteries. Whilst significant research is being undertaken into new battery technologies, wireless power transfer may be an alternative solution. The majority of the available technologies are not targeted toward the medium power requirements of mobile robots; they are either for low powers (a few Watts) or very large powers (kW). This paper reviews existing wireless power transfer technologies and their applications on mobile robots. The challenges of using these technologies on mobile robots include delivering the power required, system efficiency, human safety, transmission medium, and distance, all of which are analyzed for robots operating in a hazardous environment. The limitations of current wireless power technologies to meet the challenges for mobile robots are discussed and scenarios which current wireless power technologies can be used on mobile robots are presented.
A comparative study of properties of the films based on polyimide powders synthesized by chemical or thermal imidization is presented. It is shown that the imidization method affects the shape, size, bulk density, and size distribution of the synthesized polyimide powder particles, which influences the properties of the films obtained. The method of chemical modification allows to obtain denser powders comparing to the thermally imidized powder. The films were obtained with the help of selective laser sintering (SLS) for the first time. It is shown that the films produced by SLS from chemically imidized polyimide powder are more dense and monolithic as compared to those made from thermally imidized polyimide, which provides, obviously, higher mechanical characteristics of the former. They have the strength higher in 2.5 times and the elastic modulus twice as high than latter one. The optimal laser power is 65 W.
Considering that traditional visual navigation cannot be utilised in low illumination and sparse feature environments, a novel visual-inertial integrated navigation method using a Structured Light Visual (SLV) sensor for Micro Aerial Vehicles (MAVs) is proposed in this paper. First, the measurement model based on an SLV sensor is studied and built. Then, using the state model based on error equations of an Inertial Navigation System (INS), the measurement model based on the error of the relative motion measured by INS and SLV is built. Considering that the measurements in this paper are mainly related to the position and attitude information of the present moment, the state error accumulation in traditional visual-inertial navigation can be avoided. An Adaptive Sage-Husa Kalman Filter (ASHKF) based on multiple weighting factors is proposed and designed to make full use of the SLV measurements. The results of the simulation and the experiment based on real flight data indicate that high accuracy position and attitude estimations can be obtained with the help of the algorithm proposed in this paper.
Laser-induced acoustic desorption (LIAD) enables the desorption of nonvolatile and/or thermally labile neutral compounds, such as asphaltenes, saturated hydrocarbons in base-oil fractions and biomolecules, from a metal surface into a mass spectrometer. This is a “gentle” evaporation technique and causes minimal fragmentation to the desorbed neutral molecules, including oligonucleotides and polypeptides. LIAD can be coupled with a wide range of ionization methods to facilitate analysis of the desorbed analytes by using many different types of mass spectrometers, including Fourier transform ion cyclotron resonance, linear quadrupole ion trap and quadrupole time-of-flight instruments. The development and improvement of LIAD remains an active research area with diverse goals such as better desorption efficiencies, minimized analyte fragmentation and greater versatility. This article details the theory, experimental methods, applications, and future directions of LIAD in combination with mass spectrometry.
Over the past three years, my colleagues and I have embarked on an exciting journey into electric-field control of magnetism, parts of which we describe in this article. What we present to you is something that we believe is extremely exciting from both a fundamental science and applications perspective, and has the potential to revolutionize our world. Needless to say, this will require a lot of new innovations, both in the fundamental science arena as well as translating scientific discoveries into real applications. We hope this article will help spur more research in electric-field control of magnetism within the broad materials community.
The realization of an electrically driven organic solid-state laser is an ambitious but highly desirable goal. Many obstacles need to be solved before a working device can be realized. One of the most challenging tasks is an incorporation of intracavity metal contacts, which, on the one hand, would not substantially degrade optical properties of the whole device and, on the other hand, would ensure sufficient current density to reach lasing. In this paper, we present different contact compositions aiming to realize high-quality intracavity metal contacts. We build a top contact consisting of 0.5 nm of aluminum and 4 nm of silver which has a conductivity of 1.9 × 107 (Ω/m) and is not increasing the optical lasing threshold of an organic microcavity. To get a better understanding of charge carriers influencing the device performance, we have performed a set of measurements, where a hybrid OLED–MC device was excited both optically and electrically at the same time. These experiments suggest that the charge carriers do not degrade electrical performance, at least for current densities in the range of A/cm2. Moreover, our observations suggest that, in some cases, simultaneous optical excitation can contribute to more efficient electrical pumping of the OLED-MC device.
The present work aims to explore the tribological behavior of the laser texturing process with different patterns on a Co based alloy using a pulsed Nd: YAG laser. Different parameters such as peak power, speed and spot diameter of the laser were explored for the experimental setting. The microstructural analysis was performed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nanoindentation tests. The influence of the different textured patterns of the tribological performance tested with a pin-on-disc tribometer under lubricated sliding condition was evaluated. The results showed that typical interdendritic structures in the as-cast CoCr alloy condition were refined due to the heat input and fast cooling rate during the laser treatment. The refined microstructure showed less volumetric loss resulting in a increment of wear resistance and a better tribological performance than as-cast alloy. The correlation among laser parameters, microstructural effect and their influence in wear resistance is discussed.
We propose a method for precision control of the temporal pulse shape in 808 nm emission from Er-doped fluoroindate glasses. Previously, authors have reported the model based controller design, in which the controller varies and controls the pump rate in real time through the pump power. In model-based design, the performance of the resultant controller depends on the accuracy of the mathematical model used to represent the device in the design process. In this paper a more robust control scheme using model-free approach is presented. Specifically, the controller design is independent of the mathematical model and hence any modeling error has no effect on the device performance. This robustness against modeling error is critical for control purposes in optical materials where various up-conversion parameters are unknown or hard to determine with certainty.
Recent progress in semiconductor materials with minor nonradiative recombination has stimulated investigations of novel photovoltaic (PV) converters with optical control of radiative emission. Angle restricted emission was experimentally demonstrated in PV devices with external photon recycling due to specific photonic crystals or mirrors. In this work we investigate the power beam conversion by the cell with front “greenhouse” filter, which transmits the laser light, but recycles the low energy bandgap quanta emitted by the semiconductor cell. We calculate the limiting characteristics of the greenhouse PV converters and optimize design of the converter taking into account the nonradiative recombination processes. In optimized devices addition of the greenhouse filter can increase power beam conversion efficiency by several percent.
Different materials have been welded by laser beam. This process allows to obtain high quality welds with lower thermal effect. Laser beam welding produces narrow and high penetration welds without filler material. However, this process modifies the mechanical and microstructural properties of the welded joints. Therefore, this is currently a research topic, mainly using Advanced High Strength Steel (AHSS). These materials are used in the automotive industry. As a result, it is important to study the thermometallurgical and mechanical behavior of welded steels. In addition, a tool used to approximate the thermal effect in the fusion zone (FZ) and heat affected zone (HAZ) has been the computational numerical simulation. In this work, two butt joints of DP600 steel plates of 200 mm x 150 mm and 2 mm thickness with different welding sequences were simulated using the SYSWELD finite element software. The results of both coupons were compared and it was determined that the distortion and residual stresses decreased in the second coupon by applying a different welding sequence with equal heat input.
Substantial increase of output current, and Ion / Ioff ratio for sub-7nm low power CMOS transistors, can be accomplished using a novel optoelectronic technology, which is 100% compatible with existing CMOS process flow. For RF or mixed signal ASICs, adding photonic components may improve the cut-off frequency, and reduce series resistance. Products that utilize power regulating devices, such as power MOSFETs, will benefit from the optoelectronic configuration to achieve much lower Rdson and high voltage at the same time. For semiconductor memories, such as DRAM or FLASH, the photonic technique may reduce the ERASE / WRITE / access time and improve the reliability.