Results 1 - 10 of 567
Results 1 - 10 of 567. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] Highlights: • A new analytical model for multi-material composites subject to rotary wear is developed for efficient wear predictions. • Numerical predictions of key wear characteristics for Aluminum/Epoxy composites agree well with the experimental findings. • Potential applications of the wear model for the design of composites subject to dry abrasive rotary wear are discussed. Due to the prevalence of sliding interfaces in mechanical assemblies, fast and reliable wear prediction capabilities are imperative for system design and analysis. This study investigates the rotary wear of multi-material composite systems that have thrust washer geometries. An analytical rotary wear model is developed to predict the rotary wear performance based on Archard's wear law and a Pasternak elastic foundation model. Numerical methods are used to track the evolution of key wear parameters including surface profile, contact pressure distribution, volume loss and composite wear rate during both run-in and steady-state wear regimes. A direct method is also developed to determine the steady-state characteristics from just the initial conditions and configurations of a given composite system. Optimal designs and design guidelines for several wear objectives are identified. Initial optimal material distributions for target steady-state surface profiles are determined. In addition, the steady-state composite wear rate is minimized to reduce material loss for bi-material systems with prescribed volume fractions. It is found that the optimal material configuration for this objective is counterintuitive. Wear tests are conducted to evaluate the proposed models and optimal design solutions. Results obtained from the wear models agree well with the experimental measurements.
[en] Highlights: • Gold triangular nanoprisms were synthesized with structurally diverse ‘seeds’. • A nanoparticle-mediated homogeneous nucleation mechanism is proposed. • For some reactions, nanoparticle precursors act as catalysts rather than templates. Several seed-mediated syntheses of low symmetry anisotropic nanoparticles yield broad product distributions with multiple defect structures. This observation challenges the role of the nanoparticle precursor as a seed for certain syntheses and suggests the possibility of alternate nucleation pathways. Herein, we report a method to probe the role of the nanoparticle precursor in anisotropic nanoparticle nucleation with compositional and structural ‘labels’ to track their fate. We use the synthesis of gold triangular nanoprisms (Au TPs) as a model system. We propose a mechanism in which, rather than acting as a template, the nanoparticle precursor catalyzes homogenous nucleation of Au TPs.
[en] The high luminosity upgrade of the LHC is targeted to deliver 3000 fb−1 at a luminosity of 5×1034 cm−2 s−1. Higher granularity, 140 collisions per bunch crossing and existing bandwidth limitations require a reduction of the amount of data at module level. New modules have binary readout, on-chip discrimination and capabilities to provide track finding data at 40 MHz to the L1-trigger. The CMS collaboration has undertaken R&D effort to develop new planar sensors for the pixel-strip (PS) module, which has to withstand 1×1015 cm−2 1 MeV neutron equivalent fluence in the innermost layer of the tracker. The module is composed of a strip sensor and a macro pixel sensor with 100 μm×1.5 mm pixel size. Sensors were characterized in the laboratory and the effects of different process parameters and sensor concepts were studied. This contribution presents a new sensor prototype with n-pixels in p-bulk material in planar technology for the PS module. A new inverted module concept is presented, which has advantages with respect to the baseline concept. Electrical characterization of sensors and SEM-images are presented.
[en] The LHC machine is planning an upgrade program which will smoothly bring the luminosity to about around 2028, to possibly reach an integrated luminosity of 3000 fb−1 in the following decade. This High Luminosity LHC scenario, HL-LHC, will require a preparation program of the LHC detectors known as Phase-2 upgrade. The current CMS Outer Tracker, already running close to its design limits, will not be able to survive HL-LHC radiation conditions and CMS will need a completely new device, in order to fully exploit the highly demanding operating conditions and the delivered luminosity. The new Tracker should have also L1 trigger capabilities. To achieve such goals, R&D activities are ongoing to explore options and develop solutions that would allow including tracking information at Level-1. The design choices for the CMS Outer Tracker upgrades are discussed along with some highlights of the R&D activities.
[en] Hawking radiation, originally derived in the ray optics limit, exhibits the unfortunate trans-Planckian problem—a Hawking photon near spatial infinity, if back-tracked to the immediate vicinity of the horizon is hugely blue-shifted and found to have had trans-Planckian energy. (And if back-tracked all the way to the horizon, the photon is formally infinitely blue-shifted, and formally acquires infinite energy.) Unruh has forcefully argued that this implies that the Hawking flux represents a vacuum instability in the presence of a horizon, and that the Hawking photons are actually emitted from some region exterior to the horizon. We seek to make this idea more precise and somewhat explicit by building a purely kinematical model for Hawking evaporation based on two Vaidya spacetimes (outer and inner) joined across a thin time-like boundary layer. The kinematics of this model is already quite rich, and we shall defer consideration of the dynamics for subsequent work. In particular we shall present an explicit calculation of the 4-acceleration of the shell (including the effects of gravity, motion, and the outgoing null flux) and relate this 4-acceleration to the Unruh temperature.
[en] Highlights: • Transparent SETEG based on commercial glass has been developed. • The glass based SETEG shows high electric performance and stability. • An automatic measure and real-time display system is developed to track the motion of the stylus. A glass-based single electrode triboelectric generator (SETEG) is developed with polydimethylsiloxane (PDMS) as the negative material. Its performance under different contact forces, frequencies and spacers is investigated in detail. The SETEGs have higher electric output under higher contact force, frequency and larger spacer, and show better performance with a thinner glass layer at lower humidity condition. An open circuit voltage, short circuit current and power up to 318 V, 8.3 μA and 427 μW are obtained for a SETEG of 5×5 cm2 size. Based on the study, a tracking sensor array consisting of nine 5×5 mm2 SETEGs is proposed and developed. A LabVIEW-based automatic measurement system is also developed to record, process and display the real-time output voltages of the sensing array. Results show that an output voltage up to 4 V can be easily generated when a PDMS-covered stylus touches/slides the sensor array, and the output voltages from different sensors are independent from each other. This work demonstrates the great application potential of the SETEGs sensor array for self-powered detection, tracking or monitoring motion or a touch of a stylus or some objects, thus would be very useful for touch screen display, handheld tracking device, domestic security, traffic monitoring etc.
[en] The use of CMOS Pixel Sensors (CPS) for high resolution and low material vertex detectors has been validated with the 2014 and 2015 physics runs of the STAR-PXL detector at RHIC/BNL. This opens the door to the use of CPS for inner tracking devices, with 10-100 times larger sensitive area, which require therefore a sensor design privileging power saving, response uniformity and robustness. The CMOS technology used for the STAR-PXL sensors was considered as too poorly suited to upcoming applications like the upgraded ALICE Inner Tracking System (ITS), which requires sensors with one order of magnitude improvement on readout speed and improved radiation tolerance. This triggered the exploration of a deeper sub-micron CMOS technology, Tower-Jazz , for the design of a CPS well adapted for the new ALICE-ITS running conditions. This paper reports the R & D results for the conception of a CPS well adapted for the ALICE-ITS.
[en] The TOF-tracker concept, the simultaneous measurement of accurate time and bi-dimensional space coordinates in a single gaseous detector, has been previously demonstrated based on Resistive Plate Chamber (RPC) technology. Recently, a larger area, 1550 × 1250 mm2, RPC detector has been built. Signals are induced on metallic strips located in each side of the RPC active volume and coupled to both charge-sensitive and timing circuits, that can be used to generate a coincidence trigger. In this work, the architecture and performance of the trigger system of the detector is reported. The system is based on off-the-shelf inexpensive modules and in a custom program written in VHDL running in a Xilinx Spartan-6 FPGA. It is fast, fully parameterized and supports several trigger strategies, allowing at the same time the collection of data referring to the operating condition of the detector, relevant for tests and detector maintenance.
[en] This work aims at predicting the micro-hardness of XC38 steel using the experiments plans as well as study of tribological behavior of this steel. The heat treatments were considered by adopting the factorial plans 22 methodology at two factors (temperature ‘T’ and holding time ‘t’), each at two levels (−1, +1). The results obtained allowed lead to a mathematical model predicting the micro-hardness ‘Hv’ in every point of the study field. Moreover, the curves of the responses surfaces clearly show the influence of two factors studied (T, t) on ‘Hv’. Mechanical characterization of treated samples showed a significant increase in the micro-hardness, which achieve to 76% for the treated sample at 850 °C during 2 h compared to untreated state. An investigation of wear tracks morphology shows that friction under a load of 10 N results in predominant adhesive wear, while a load of 2 N favor abrasive wear. (paper)
[en] Calculating wake potentials in accelerators are necessary in order to optimize the accelerator performance in terms of stored current and emittance. Wake potentials due to pick-ups can be an important source for current and emittance degradation. In this paper, we present theoretical analysis and computer simulations of the wake potentials for the beam pipe with and without mounted pick-ups. We introduce generalized wake potential to calculate the transverse wake-field and analyze the effect of pick-ups on these potentials. In addition, the effects of wake potentials due to pick-ups on the bunch length and emittance are studied using ELEGANT particle tracking code.