The development of a superconductive detector for simultaneous measurement of energy and arrival time is reported. The detector consists of two superconducting tunnel junctions coupled through a passive network. The first junction operates in the quasi-particle regime and measures the energy absorbed by counting the total charge that tunnels. The second junction uses the DC Josephson effect to act as a fast discriminator for the onset of surplus current in the first junction. The feasibility of the detector is demonstrated through simultaneous time and energy measurements of 6 keV X-rays. A model of the detector is presented and numerical simulations show good correspondence with experimental data. 相似文献
We investigate the effects of pilot assignment in multi-cell massive multiple-input multiple-output systems. When deploying a large number of antennas at base station (BS), and linear detection/precoding algorithms, the system performance in both uplink (UL) and downlink (DL) is mainly limited by pilot contamination. This interference is proper of each pilot, and thus system performance can be improved by suitably assigning the pilot sequences to the users within the cell, according to the desired metric. We show in this paper that UL and DL performances constitute conflicting metrics, in such a way that one cannot achieve the best performance in UL and DL with a single pilot assignment configuration. Thus, we propose an alternative metric, namely total capacity, aiming to simultaneously achieve a suitable performance in both links. Since the PA problem is combinatorial, and the search space grows with the number of pilots in a factorial fashion, we also propose a low complexity suboptimal algorithm that achieves promising capacity performance avoiding the exhaustive search. Besides, the combination of our proposed PA schemes with an efficient power control algorithm unveils the great potential of the proposed techniques in providing improved performance for a higher number of users. Our numerical results demonstrate that with 64 BS antennas serving 10 users, our proposed method can assure a 95%-likely rate of 4.2 Mbps for both DL and UL, and a symmetric 95%-likely rate of 1.4 Mbps when serving 32 users. 相似文献
The current application of virtual reality (VR) systems in the design process is limited mostly to design review. The reason for this limitation is the different data formats used for CAD and VR visualization. To use the benefits of VR during the design process, solutions for immersive design - the model manipulation inside the VE based on CAD data - are required. There are different approaches allowing VR systems to work as an active development platform. Three examples introduce the realization of the integration of CAD and VR software at different levels by the online coupling of complete applications or by integration of CAD core functionalities in VR systems. 相似文献
The contribution to the tunneling current of a Josephson junction from the Two-particle tunneling, to the 2nd order approximation in the barrier transparency, is investigated. Expressions for the current onset amplitudes corresponding to eV = 1,2 are given together with the full expressions for the voltage and the temperature dependencies of the two-particles current. The theory has ben developed to take also into account corrections due to depairing mechanisms, which lead to the smearing of the current singularities. Introducing a depairing parameter , which accounts for the probability of these processes, I–V curves in the voltage region of the onset of single and two particle current are obtained. It is shown that, though having the same functional dependence, spreading occurs over a voltage range of different widths. In particular, it is shown that the width of the single-particle structure is twice larger the one for the two-particle. A careful investigation of the I–V curves in the region 2 -eV is presented and some aspects of the interesting voltage region near ¦1-2¦ is discussed. 相似文献
This paper is devoted to the problem of computing control laws for the stabilization of continuous‐time linear time‐varying systems. First, a necessary and sufficient condition to assess the stability of a linear time‐varying system based on the norm of the transition matrix computed over a sequence of successive finite‐time intervals is proposed. A link with a stability condition for an equivalent discrete‐time model is also established. Then, 3 approaches for the computation of stabilizing state‐feedback gains are proposed: a continuous‐time technique, ie, directly derived from the stability condition, not suitable for numerical implementation; a method based on the stabilization of the discrete‐time equivalent model along with a transformation to generate the desired continuous‐time gain; and the computation of stabilizing gains for a set of periodic discrete‐time systems. Finally, by adapting one of the existing methods for the stabilization of periodic discrete‐time systems, an algorithm for the computation of a stabilizing state‐feedback continuous‐time gain is proposed. A numerical example illustrates the validity of the technique. 相似文献
Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.
The influence of plasma functionalization of multilayer graphene (MG) as an additive for low-viscosity polyolester (POE) oil in terms of dispersion stability and tribological behaviour was investigated. Pure MG and MG functionalized via N2 and NH3 plasma were analysed. The plasma functionalization significantly improved the substrate wettability and the dispersion stability of the nanofluids. The tribological behaviour of the nanofluids was investigated using a reciprocating cylinder on plane configuration. 0.05 wt% of the functionalized nanoparticles dramatically increased the scuffing resistance and significantly improved the anti-wear properties of the POE oil (over 60% wear reduction). Optical microscopy, white light interferometry, scanning electron microscopy and micro-Raman spectroscopy were used to identify the wear mechanisms. The functionalization provides a well-dispersed suspension, which contributes to the formation of a continuous and homogeneous anti-wear tribofilm. Once between the sliding surfaces, the MG improves the load-carrying capacity of the oil, avoiding the seizure of the tribolayer. 相似文献