应用于汽车头灯的LED功率转换器

近年来LED在很多产品应用上正逐步取代传统的白炽光源,由于具备非常优异的节能效率,因此LED已被视为照明技术未来的发展重点。在过往LED主要使用在汽车仪表板上警示灯号或是类似的应用。随着高亮度LED技术的发展,不仅使这些光源能够扩大到汽车的内部照明,而且还包括方向灯、尾灯及煞车灯。由于LED具备省电,维修需求低及更高的设计灵活性等特色,预计大多数的汽车制造商将会转而使用LED技术来提供各项头灯功能。     

Re-investigation of optically pumped hydrazine far-infrared laser around 11 /spl mu/m from the 10HP and 10P bands of a pulsed CO/sub 2/ laser: new lines and assignments

A high-peak-power (several hundreds of watts) pulsed CO/sub 2/ laser, recently developed in our laboratory, has been used for exciting optically pumped far-infrared laser transitions of N/sub 2/H/sub 4/. A systematic search for N/sub 2/H/sub 4/ absorption coincidences with 10P and 10HP CO/sub 2/ laser emissions has led to the observation of 27 new far-infrared laser lines, excited by 18 different absorption transitions. All of these new lines have been characterized in wavelength, offset, relative polarization, optimum operation pressure and intensity. Using the LaseRitz program, ten of these lines were assigned, corresponding to five laser systems. For other two laser systems possible J and K quantum numbers of the energy levels involved in the laser transitions were given.     

Fiber-optic confocal reflectance microscope with miniature objective for in vivo imaging of human tissues

We have built a fiber-optic confocal reflectance microscope capable of imaging human tissues in near real time. Miniaturization of the objective lens and the mechanical components for positioning and axially scanning the objective enables the device to be used in inner organs of the human body. The lateral resolution is 2 micrometers and axial resolution is 10 micrometers. Confocal images of fixed tissue biopsies and the human lip in vivo have been obtained at 15 frames/s without any fluorescent stains. Both cell morphology and tissue architecture can be appreciated from images obtained with this microscope.     

An Investigation of the Electrical Degradation of GaN High-Electron-Mobility Transistors by Numerical Simulations of DC Characteristics and Scattering Parameters

The effects of direct-current (DC) stress on GaN high-electron-mobility transistors (HEMTs) are investigated by means of numerical simulations, by which the creation of an acceptor trap in the AlGaN barrier layer was correlated to the observed experimental degradation. An increase in the trap concentration induces a worsening of the saturated current I _DSS, transconductance g _m, and output conductance g _O. An increase in the length of the trapping region induces a degradation of I _DSS and g _m, but can reduce g _O. Analysis of scattering parameters in the saturation region shows that the cutoff frequency f _T matches the trend of g _m.     

On the impact of physical layer awareness on scheduling and resource allocation in broadband multicellular IEEE 802.16 systems [Radio Resource Management and Protocol Engineering for IEEE 802.16]

Multicellular networks based on the IEEE 802.16 standard appear to be very promising candidates to provide end users with broadband wireless access. However, they also pose interesting challenges in terms of radio resource management, where several design choices are not specified in the standard, intentionally left open to implementors. For this reason, we focus in this article on scheduling and resource allocation, and investigate how they could operate in a cross-layer fashion. In particular, we describe the principles of joint scheduling and resource allocation for IEEE 802.16 operating in AMC mode, and discuss the critical role played by physical layer considerations, especially intercell interference estimation and channel state awareness, in the obtained performance. This leads to identifying key open issues and possible general solutions     

Zr‐Doped Indium Oxide (IZRO) Transparent Electrodes for Perovskite‐Based Tandem Solar Cells

Parasitic absorption in transparent electrodes is one of the main roadblocks to enabling power conversion efficiencies (PCEs) for perovskite‐based tandem solar cells beyond 30%. To reduce such losses and maximize light coupling, the broadband transparency of such electrodes should be improved, especially at the front of the device. Here, the excellent properties of Zr‐doped indium oxide (IZRO) transparent electrodes for such applications, with improved near‐infrared (NIR) response, compared to conventional tin‐doped indium oxide (ITO) electrodes, are shown. Optimized IZRO films feature a very high electron mobility (up to ≈77 cm² V^?1 s^?1), enabling highly infrared transparent films with a very low sheet resistance (≈18 Ω □^?1 for annealed 100 nm films). For devices, this translates in a parasitic absorption of only ≈5% for IZRO within the solar spectrum (250–2500 nm range), to be compared with ≈10% for commercial ITO. Fundamentally, it is found that the high conductivity of annealed IZRO films is directly linked to promoted crystallinity of the indium oxide (In₂O₃) films due to Zr‐doping. Overall, on a four‐terminal perovskite/silicon tandem device level, an absolute 3.5 mA cm^?2 short‐circuit current improvement in silicon bottom cells is obtained by replacing commercial ITO electrodes with IZRO, resulting in improving the PCE from 23.3% to 26.2%.     

Slotted ALOHA and CDPA: A comparison of channel accessperformance in cellular systems

The paper compares the performance of two channel-access schemes suitable for the cellular environment, which, in particular, allow the packet capture and can deal with inter-cell interference. The first scheme is the well known S-ALOHA while the second one is the Capture Division Packet Access, recently proposed. The comparison is analytically performed over a common system with a common analytical model. Despite the many analyses appeared on S-ALOHA, the one we develop is new because a throughput density uniformly distributed on the plane is considered in a multiple cell environment. The analysis clearly shows the effect of intra-cell and inter-cell interference on the ALOHA system and quantifies the throughput gain achieved by CDPA, which completely avoids intra-cell interference. Our analysis also provides insight about the effectiveness of power control on both systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solution‐Processed GaSe Nanoflake‐Based Films for Photoelectrochemical Water Splitting and Photoelectrochemical‐Type Photodetectors

Gallium selenide (GaSe) is a layered compound, which has been exploited in nonlinear optical applications and photodetectors due to its anisotropic structure and pseudodirect optical gap. Theoretical studies predict that its 2D form is a potential photocatalyst for water splitting reactions. Herein, the photoelectrochemical (PEC) characterization of GaSe nanoflakes (single‐/few‐layer flakes), produced via liquid phase exfoliation, for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both acidic and alkaline media is reported. In 0.5 m H₂SO₄, the GaSe photoelectrodes display the best PEC performance, corresponding to a ratiometric power‐saved metric for HER (Φ_saved,HER) of 0.09% and a ratiometric power‐saved metric for OER (Φ_saved,OER) of 0.25%. When used as PEC‐type photodetectors, GaSe photoelectrodes show a responsivity of ≈0.16 A W^?1 upon 455 nm illumination at a light intensity of 63.5 µW cm^?2 and applied potential of ?0.3 V versus reversible hydrogen electrode (RHE). Stability tests of GaSe photodetectors demonstrated a durable operation over tens of cathodic linear sweep voltammetry scans in 0.5 m H₂SO₄ for HER. In contrast, degradation of photoelectrodes occurred in both alkaline and anodic operation due to the highly oxidizing environment and O₂‐induced (photo)oxidation effects. The results provide new insight into the PEC properties of GaSe nanoflakes for their exploitation in photoelectrocatalysis, PEC‐type photodetectors, and (bio)sensors.     

Transition‐Metal Dichalcogenide NiTe2: An Ambient‐Stable Material for Catalysis and Nanoelectronics

By means of theory and experiments, the application capability of nickel ditelluride (NiTe₂) transition‐metal dichalcogenide in catalysis and nanoelectronics is assessed. The Te surface termination forms a TeO₂ skin in an oxygen environment. In ambient atmosphere, passivation is achieved in less than 30 min with the TeO₂ skin having a thickness of about 7 Å. NiTe₂ shows outstanding tolerance to CO exposure and stability in water environment, with subsequent good performance in both hydrogen and oxygen evolution reactions. NiTe₂‐based devices consistently demonstrate superb ambient stability over a timescale as long as one month. Specifically, NiTe₂ has been implemented in a device that exhibits both superior performance and environmental stability at frequencies above 40 GHz, with possible applications as a receiver beyond the cutoff frequency of a nanotransistor.     

Electric‐Field‐Controlled Alignment of Rod‐Shaped Fluorescent Nanocrystals in Smectic Liquid Crystal Defect Arrays

Periodic micro‐arrays of straight linear defects containing nanoparticles can be created over large surface areas at the transition from the nematic to smectic‐A phase in a nanoparticle–liquid crystal (LC) composite material confined under the effect of conflicting anchoring conditions (unidirectional planar vs normal) and electric fields. Anisomeric dichroic dye molecules and rod‐shaped fluorescent semiconductor nanocrystals (dot‐in‐rods) with large permanent electric dipole and high linearly polarized photoluminescence quantum yield align parallel to the local LC molecular director and follow its reorientation under application of the electric field. In the nano‐sized core regions of linear defects, where the director is undefined, anisotropic particles align parallel to the defect whereas spherical quantum dots do not show any particular interaction with the defect. Under application of an electric field, ferroelectric semiconductor nanoparticles in the core region align along the field, perpendicular to the defect direction, whereas dichroic dyes remain parallel to the defect. This study provides useful insights into the complex interaction of anisotropic nanoparticles and anisotropic soft materials such as LCs in the presence of external fields, which may help the development of field‐responsive nanoparticle‐based functional materials.