Properties of components with incrementally formed gears

The process class of sheet-bulk metal forming (SBMF) involves several advantages for the manufacture of functional components. Its incremental variant (iSBMF) enables a very flexible dimensioning of components. To treat the unfavorable manufacturing time of the incremental approach, this investigation is focused on an alternative process route using rotating forming tools, which decrease the process time significantly. After an analysis of the mechanical properties as well as the micro- and macroscopic surface quality, a quasi-static benchmark test was performed. Normalized by the weight of the component, gears manufactured by iSBMF and BS600 steel presented the same load capacity as gears manufactured by blanking with subsequent hardening. Here, using innovative high strength steels with a significant strain hardening behavior like high manganese steels enables for weight-reduced gears

Protection against ultraviolet radiation by commercial summer clothing: need for standardised testing and labelling

BACKGROUND: The use of clothing as a means of sun protection has been recommended in recent education campaigns. Contrary to popular opinion, however, some fabrics provide insufficient ultraviolet (UV) protection. MATERIAL AND METHODS: We investigated 236 apparel textiles of the spring/summer collections 2000 and 2001. In accordance with the forthcoming European standard the UV protection factor (UPF) of the fabrics was determined spectrophotometrically. RESULTS: Seventy-eight (33%) fabrics had UPF < 15, 45 (19%) had UPF = or > 15 and < 30, and 113 (48%) had UPF = or > 30 (30+). More than 70% of the wool, polyester, and fabric blends, and only less than 30% of the cotton, linen, and viscose fabrics had UPF values of 30+. Fabrics with black, navy-blue, white, green, or beige colours provided most frequently UPF values of 30+. CONCLUSIONS: It is difficult for the sun-aware consumer to choose the 'right' garment, with a third of summer clothing providing insufficient UV protection and only half of the fabrics having UPF 30+, the UPF recommended by the European standard. Therefore, apparel summer fabrics should be measured and labelled in accordance with a standard document

Thermal effects in dissimilar magnetic pulse welding

Magnetic pulse welding (MPW) is often categorized as a cold welding technology, whereas latest studies evidence melted and rapidly cooled regions within the joining interface. These phenomena already occur at very low impact velocities, when the heat input due to plastic deformation is comparatively low and where jetting in the kind of a distinct material flow is not initiated. As another heat source, this study investigates the cloud of particles (CoP), which is ejected as a result of the high speed impact. MPW experiments with different collision conditions are carried out in vacuum to suppress the interaction with the surrounding air for an improved process monitoring. Long time exposures and flash measurements indicate a higher temperature in the joining gap for smaller collision angles. Furthermore, the CoP becomes a finely dispersed metal vapor because of the higher degree of compression and the increased temperature. These conditions are beneficial for the surface activation of both joining partners. A numerical temperature model based on the theory of liquid state bonding is developed and considers the heating due to the CoP as well as the enthalpy of fusion and crystallization, respectively. The time offset between the heat input and the contact is identified as an important factor for a successful weld formation. Low values are beneficial to ensure high surface temperatures at the time of contact, which corresponds to the experimental results at small collision angle

MULTIWAVELENGTH OBSERVATIONS OF THE SS 433 JETS

We present observations of the SS 433 jets using the Chandra High Energy Transmission Grating Spectrometer with contemporaneous optical and Very Long Baseline Array observations. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The line Doppler shifts from the optical and X-ray lines match well, indicating that they are less than 3 × 10[superscript 14] cm apart. The jet Doppler shifts show aperiodic variations that could result from shocks in interactions with the local environment. These perturbations are consistent with a change in jet direction but not jet speed. The proper motions of the radio knots match the kinematic model only if the distance to SS 433 is 4.5 ± 0.2 kpc. Observations during eclipse show that the occulted emission is very hard, seen only above 2 keV and rising to comprise >50% of the flux at 8 keV. The soft X-ray emission lines from the jet are not blocked, constraining the jet length to [> over ~]2 × 10[superscript 12] cm. The base jet density is in the range 10[superscript 10-13] cm[superscript –3], in contrast to our previous estimate based on the Si XIII triplet, which is likely to have been affected by UV de-excitation. There is a clear overabundance of Ni by a factor of about 15 relative to the solar value, which may have resulted from an unusual supernova that formed the compact object

Ultracold atoms and the Functional Renormalization Group

We give a self-contained introduction to the physics of ultracold atoms using functional integral techniques. Based on a consideration of the relevant length scales, we derive the universal effective low energy Hamiltonian describing ultracold alkali atoms. We then introduce the concept of the effective action, which generalizes the classical action principle to full quantum status and provides an intuitive and versatile tool for practical calculations. This framework is applied to weakly interacting degenerate bosons and fermions in the spatial continuum. In particular, we discuss the related BEC and BCS quantum condensation mechanisms. We then turn to the BCS-BEC crossover, which interpolates between both phenomena, and which is realized experimentally in the vicinity of a Feshbach resonance. For its description, we introduce the Functional Renormalization Group approach. After a general discussion of the method in the cold atoms context, we present a detailed and pedagogical application to the crossover problem. This not only provides the physical mechanism underlying this phenomenon. More generally, it also reveals how the renormalization group can be used as a tool to capture physics at all scales, from few-body scattering on microscopic scales, through the finite temperature phase diagram governed by many-body length scales, up to critical phenomena dictating long distance physics at the phase transition. The presentation aims to equip students at the beginning PhD level with knowledge on key physical phenomena and flexible tools for their description, and should enable to embark upon practical calculations in this field.Comment: 73 pages, 32 figures. Lecture notes for the 49th Schladming Winter School `Physics at all scales: The Renormalization Group' (to appear in the proceedings

A Realistic Roadmap to Formation Flying Space Interferometry

The ultimate astronomical observatory would be a formation flying space interferometer, combining sensitivity and stability with high angular resolution. The smallSat revolution offers a new and maturing prototyping platform for space interferometry and we put forward a realistic plan for achieving first stellar fringes in space by 2030

Optical Spectroscopy of Functionalized Semiconductor Heterostructures - Investigation of III-N-V/Silicon and III-Sb-V/GaAs Heterostructures for Laser Applications

Semiconductor lasers are widely used in all areas of everyday life. They can be found in personal computers, TVs, CD and DVD players, printers and laser pointers, just to name a few. However, a very important field they are used in is optical communication. This thesis tackles two of the major challenges in this field. First, on short distances, i.e. on-chip or chip-to-chip, data is usually transmitted using electrical wires. However, the interconnects between different parts of the processor are actually the limiting factor for device performance. Additionally, the power dissipated due to the interconnects on a chip is significant. Therefore, it is reasonable to consider other approaches to transfer data on-chip and between chips. One possibility is changing the means of data transfer from electrical to optical providing faster interconnects and a higher energy efficiency. To do so, efficient and stable lasers on silicon substrates are needed. Even though optically driven silicon lasing has been demonstrated in the past, silicon is not the first choice because of its indirect band gap. Using other semiconductor materials such as Ga(N,As,P), which is investigated here, is a reasonable choice for optoelectronic integration for the following reasons. For As contents exceeding 70%, the quaternary Ga(N,As,P) is a direct band gap semiconductor that can be grown lattice matched to silicon using standard MOVPE techniques. Furthermore, laser operation at up 150 K - and at RT on GaP substrates - has already been demonstrated. However, from this it becomes clear that further device improvements are necessary to reach RT lasing. This thesis investigates the interplay of optical properties, alloy disorder and structural changes in Ga(N,As,P)/Si heterostructures to get a better understanding of this material. The influence of several growth and annealing parameters and processes on the optical properties is investigated as well as the influence of different sample structures and heterostructure layouts. To reveal the optical properties photoluminescence spectroscopy experiments are performed. In conjunction with structural investigation by Transmission Electron Microscopy the role of structural changes due to growth and annealing procedures and their influence on the optical properties is revealed and discussed. These results not only yield a better understanding of the complex interplay of growth parameters/structural design and optical response, but also can be used as feedback for subsequent growth of further samples leading to better device performance. Furthermore, the band offset, which is a critical parameter of a heterostructure for laser operation, is determined experimentally for the first time. The second part of this thesis deals with light sources for long-range optical communication, which is usually done using optical fibers. These optical fibers are operated best at 1.3 µm or 1.55 µm where the losses are minimal and the dispersion is closest to zero. Semiconductor lasers operating in this wavelength regime are usually made of (Ga,In)(As,P) or (Al,Ga,In)As on InP substrates. Their efficiency is somewhat poor as much of the pump power is converted to heat due to non-radiative processes. One of the most dominant processes is the Auger recombination, where the recombining electron and hole transfer their energy to another charge carrier as kinetic energy rather than creating a photon, which is emitted. To overcome these issues it is helpful to use type-II devices where the recombining electrons and holes are confined in different materials and spatially separated. In such a device the optical properties can be optimized while the Auger losses can be lowered. Additionally, such systems offer more degrees of freedom for device design as more and different materials can be used. In this thesis are investigated (Ga,In)As/Ga(N,As) heterostructures, which are used as type-II light sources in the range of 1.3 µm to 1.55 µm. Furthermore, (Ga,In)As/Ga(As,Sb) heterostructures serving the same purpose are investigated. Particular attention is paid to the influence of the interface these type-II devices inevitably have. Especially, reports on the influence of interfaces on the optical properties of these materials are lacking in the literature. The type-II PL is used as a non-destructive probe for the optical properties of such systems and their changes upon changing the interfaces. It is aimed to reveal the influence of the internal interfaces on the cw-photoluminescence as well as on the recombination dynamics and charge carrier (re-)distribution in the heterostructures. In particular, the latter ones are scarcely investigated in the literature. The optical properties will be correlated with different interface properties such as thickness and morphology. The influence of the interface on disorder is also investigated. Finally, the measurements are also used to determine the Ga(N,As)/GaAs and Ga(As,Sb)/GaAs band offsets, which are disputed in the literature

Optical Spectroscopy of Functionalized Semiconductor Heterostructures - Investigation of III-N-V/Silicon and III-Sb-V/GaAs Heterostructures for Laser Applications

Semiconductor lasers are widely used in all areas of everyday life. They can be found in personal computers, TVs, CD and DVD players, printers and laser pointers, just to name a few. However, a very important field they are used in is optical communication. This thesis tackles two of the major challenges in this field. First, on short distances, i.e. on-chip or chip-to-chip, data is usually transmitted using electrical wires. However, the interconnects between different parts of the processor are actually the limiting factor for device performance. Additionally, the power dissipated due to the interconnects on a chip is significant. Therefore, it is reasonable to consider other approaches to transfer data on-chip and between chips. One possibility is changing the means of data transfer from electrical to optical providing faster interconnects and a higher energy efficiency. To do so, efficient and stable lasers on silicon substrates are needed. Even though optically driven silicon lasing has been demonstrated in the past, silicon is not the first choice because of its indirect band gap. Using other semiconductor materials such as Ga(N,As,P), which is investigated here, is a reasonable choice for optoelectronic integration for the following reasons. For As contents exceeding 70%, the quaternary Ga(N,As,P) is a direct band gap semiconductor that can be grown lattice matched to silicon using standard MOVPE techniques. Furthermore, laser operation at up 150 K - and at RT on GaP substrates - has already been demonstrated. However, from this it becomes clear that further device improvements are necessary to reach RT lasing. This thesis investigates the interplay of optical properties, alloy disorder and structural changes in Ga(N,As,P)/Si heterostructures to get a better understanding of this material. The influence of several growth and annealing parameters and processes on the optical properties is investigated as well as the influence of different sample structures and heterostructure layouts. To reveal the optical properties photoluminescence spectroscopy experiments are performed. In conjunction with structural investigation by Transmission Electron Microscopy the role of structural changes due to growth and annealing procedures and their influence on the optical properties is revealed and discussed. These results not only yield a better understanding of the complex interplay of growth parameters/structural design and optical response, but also can be used as feedback for subsequent growth of further samples leading to better device performance. Furthermore, the band offset, which is a critical parameter of a heterostructure for laser operation, is determined experimentally for the first time. The second part of this thesis deals with light sources for long-range optical communication, which is usually done using optical fibers. These optical fibers are operated best at 1.3 µm or 1.55 µm where the losses are minimal and the dispersion is closest to zero. Semiconductor lasers operating in this wavelength regime are usually made of (Ga,In)(As,P) or (Al,Ga,In)As on InP substrates. Their efficiency is somewhat poor as much of the pump power is converted to heat due to non-radiative processes. One of the most dominant processes is the Auger recombination, where the recombining electron and hole transfer their energy to another charge carrier as kinetic energy rather than creating a photon, which is emitted. To overcome these issues it is helpful to use type-II devices where the recombining electrons and holes are confined in different materials and spatially separated. In such a device the optical properties can be optimized while the Auger losses can be lowered. Additionally, such systems offer more degrees of freedom for device design as more and different materials can be used. In this thesis are investigated (Ga,In)As/Ga(N,As) heterostructures, which are used as type-II light sources in the range of 1.3 µm to 1.55 µm. Furthermore, (Ga,In)As/Ga(As,Sb) heterostructures serving the same purpose are investigated. Particular attention is paid to the influence of the interface these type-II devices inevitably have. Especially, reports on the influence of interfaces on the optical properties of these materials are lacking in the literature. The type-II PL is used as a non-destructive probe for the optical properties of such systems and their changes upon changing the interfaces. It is aimed to reveal the influence of the internal interfaces on the cw-photoluminescence as well as on the recombination dynamics and charge carrier (re-)distribution in the heterostructures. In particular, the latter ones are scarcely investigated in the literature. The optical properties will be correlated with different interface properties such as thickness and morphology. The influence of the interface on disorder is also investigated. Finally, the measurements are also used to determine the Ga(N,As)/GaAs and Ga(As,Sb)/GaAs band offsets, which are disputed in the literature

A novel low-power high speed accurate and precise DAQ with embedded artificial intelligence for long term biodiversity survey

International audienceAcoustic monitoring is a key feature for studying biodiver-sity. Recent works on very high frequency animal soundsopen new insights and challenges on biodiversity survey.In order to set a scaled monitoring, and to cover mostof the frequencies of the present species, a novel multi-channel ultra high velocity recorder has been designed,called Qualilife HighBlue. This paper presents its archi-tecture and characteristics. One of its most innovative fea-tures is an always-on ultra-low power wake-up, trigger-ing recordings when temporal and/or spectral interestingevents are detected. For this task, shallow neural net-works are embedded for advanced pattern detection, aswell as mixed signal features extractors. Several commu-nications devices are implemented, and the system can becustomised. Multiple deployments of this monitoring sys-tem over the world are presented in this paper to demon-strate its robustness, versatility and efficiency