固体激光用Nd:Lu2O3透明陶瓷的制备和光学性能研究

Nd:Lu₂O₃材料由于具有高热导率、低声子能量和优异的光学特性而成为非常有前景的高功率固体激光器用的增益介质。但Lu₂O₃单晶的熔点超过2400 ℃, 难以生长, 而Lu₂O₃陶瓷既能在低温下制备, 又具有与晶体相当的光学性质和激光性能从而备受关注。本研究制备了高透明的Nd:Lu₂O₃陶瓷并对其光学性质和激光性能进行探究。以共沉淀法制备的纳米粉体为原料, 采用真空烧结结合热等静压(HIP)两步烧结法制备了1.0at%Nd:Lu₂O₃透明陶瓷。对制备的粉体、素坯和陶瓷的微结构进行了表征: HIP后处理的陶瓷平均晶粒尺寸是724.2 nm。厚度为1.0 mm的1.0at%Nd:Lu₂O₃透明陶瓷在1100 nm处的直线透过率是82.4%, 样品在806 nm处的吸收截面为1.50′10^-20 cm², 而根据荧光光谱计算得到的发射截面为6.5′10^-20 cm²。分别在878.8 和895.6 nm波长激发下, 1.0at%Nd:Lu₂O₃透明陶瓷⁴F_3/2·⁴I_11/2跃迁的平均荧光寿命均为169 ms。当输出耦合镜的透过率T_OC=2.0%时, 退火后的1.0at% Nd:Lu₂O₃透明陶瓷获得了最大输出功率为0.47 W的准连续(QCW)激光输出, 斜率效率为8.7%。本研究成功制备了显微结构均匀、高透明度的1.0at%Nd:Lu₂O₃陶瓷, 并展示了其在固体激光增益介质领域的广阔应用潜力。     

Anisotropies of the g-factor tensor and diamagnetic coefficient in crystal-phase quantum dots in InP nanowires

Nano Research - Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing. In this context, unveiling...     

Mobile robot programming using natural language

How will naive users program domestic robots? This paper describes the design of a practical system that uses natural language to teach a vision-based robot how to navigate in a miniature town. To enable unconstrained speech the robot is provided with a set of primitive procedures derived from a corpus of route instructions. When the user refers to a route that is not known to the robot, the system will learn it by combining primitives as instructed by the user. This paper describes the components of the Instruction-Based Learning architecture and discusses issues of knowledge representation, the selection of primitives and the conversion of natural language into robot-understandable procedures.     

Design of Supervisors to Avoid Deadlock in Flexible Assembly Systems

Modern production systems exhibit a high degree of resource sharing that can lead to deadlock conditions. Deadlock arises when some parts remain indefinitely blocked because each of them requests access to a resource held by some other parts. One of the tasks of the control system lies in preventing such situations from occurring by proper resource management.This article addresses the deadlock problem for an important class of production facilities, that is, flexible assembly systems, that can perform both manufacturing or assembly operations. In particular, we develop an approach to deadlock avoidance based on a supervisory control that works by inhibiting or enabling the events involving resource allocation. The article proposes two supervisors characterized by easy implementation, efficiency, and flexibility in resource management. The analysis of some case studies, performed by discrete event simulation, confirms the effectiveness of the approach.     

Low Cost Microwave Sensor for Moisture Content Measurement in Paper Milling Industry

The interest about RF and microwave sensors for the measurement of dielectric properties of materials during industrial processes has been growing recently. Microwave sensors are particularly attractive for their ability of performing non-invasive measurements. An interesting field of application is the real-time moisture measurement during industrial processes. A smart active sensor for measuring the moisture content of felts used in the paper milling industry and more generally of sheet-like materials, is here proposed. The sensor consists of a cavity backed slot resonator interacting with the material under test through near fields. The design aspects of the sensor and the related measuring front-end are discussed with respect to the dielectric properties of the material, and to the resonator response. The parametric sensitivity of the measuring method with the distance between the sample and the sensor surface and the sample thickness is also analyzed. An inversion procedure based on an Artificial Neural Network (ANN) approach is proposed in order to determine the moisture content of the felts. Measurements on several reference felts, with different density, thickness, and moisture content levels, ranging from dry to waterlogged state, proved the effectiveness of the proposed sensor architecture and the ANN-based inversion procedure.     

Comparison of hardmetal and hard chromium coatings under different tribological conditions

Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of applications for wear protection of component surfaces. The two protective coating types are tested in direct comparison for tribological conditions of dry abrasive wear (Taber Abraser test) and dry oscillating wear load. Oscillating wear tests are carried out both with hardened 100Cr6 steel and alumina balls as counterbody. Different types of hardmetal coatings are imparted. Besides HVOF sprayed coatings also coatings sprayed by an APS gun with axial powder feed are tested. For HVOF spraying besides standard WC/Co(Cr) feedstock also coarse (d₅₀ = 5 μm) and fine carbide feedstock (d₅₀ = 0.8 μm) and ultrafine powders, i.e. 2 μm < d < 12 μm, are considered. Use of ultrafine powders is particularly interesting from the economical point of view, as belt grinding can be sufficient for finishing in many cases. The optimum coating solution for wear protection depends on the specific tribosystem. The choice of feedstock, spraying process, equipment and processing conditions does not only depend on the resultant tribological properties. Therefore simultaneous influence on corrosion protection capability and thermal conductivity might have to be considered.     

Modelling defeasible and prioritized support in bipolar argumentation

Cayrol and Lagasquie-Schiex introduce bipolar argumentation frameworks by introducing a second relation on the arguments for representing the support among them. The main drawback of their approach is that they cannot encode defeasible support, for instance they cannot model an attack towards a support relation. In this paper, we introduce a way to model defeasible support in bipolar argumentation frameworks. We use the methodology of meta-argumentation in which Dung??s theory is used to reason about itself. Dung??s well-known admissibility semantics can be used on this meta-argumentation framework to compute the acceptable arguments, and all properties of Dung??s classical theory are preserved. Moreover, we show how different contexts can lead to the alternative strengthening of the support relation over the attack relation, and converse. Finally, we present two applications of our methodology for modeling support, the case of arguments provided with an internal structure and the case of abstract dialectical frameworks.     

Extended-order algebras and fuzzy implicators

In this work we reconsider the notion of implicator in a complete lattice L and discuss its properties, taking into account the viewpoint of the implication operation of classes of (weak) extended-order algebras, introduced by C. Guido and P. Toto and included in the class of implicative algebras considered by E. Rasiowa. In fact, such an implication, that is an extension of an order relation, can be viewed as an implicator in L, whose properties depend on those characterizing the structure of the algebra. We also propose in a (weak) right-distributive complete extended-order algebra $(L,\rightarrow,\top)$ with adjoint product ? a relative implication as a further implicator beyond ${\rightarrow}{.}$ The relative implication allows an extension of the inclusion relation between L-sets A and B, different from the subsethood degree, that consists in seeing to which extent A is included in its conjunction with B. Moreover, we introduce in $(L,\rightarrow,\top)$ a further binary operation that we call conditional conjunction that can be read as “a” and “b, given a”, which motivates the term we have chosen to denote it. This operation, strictly related to the divisibility condition of BL-algebras, satisfies most conditions usually asked to a conjunction and it is well behaved with the adjoint product ? and the meet operation ∧.     

Transmission control of Variable-Bit-Rate video streaming in UMTS networks

Variable-Bit-Rate (VBR) video transmission over UMTS networks is assuming an ever growing importance, then scheduling VBR data over wireless channels attracts great interest today. This paper proposes an on-line PI control algorithm for easily and suitably scheduling interactive multimedia transmission of VBR video streams. It dynamically adapts the transmitted bit rate to the user's actions that can suddenly and highly modify the client buffer level. The Real-time Transport Control Protocol (RTCP) packets periodically feed back the buffer level to the server for keeping the free buffer space at 50% of its capacity, so as to prevent both buffer overflow and underflow. Numerical results of different simulated scenarios show the effectiveness of the proposed controller in comparison with two well-established algorithms, enhanced with RTCP information.     

Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers

We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO interferometers, designed to run with 30 W input power. At four times the power of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift, minimal thermal lensing, and higher optical efficiency. The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO.