Exciton storage by Mn(2+) in colloidal Mn(2+)-doped CdSe quantum dots

Colloidal Mn (2+)-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to tau exc = 15 mus at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by approximately 10 (3) and are shown to arise from the creation of excitons by back energy transfer from excited Mn (2+) dopant ions. A kinetic model describing thermal equilibrium between Mn (2+ 4)T 1 and CdSe excitonic excited states reproduces the experimental observations and reveals that, for some quantum dots, excitons can emit with near unity probability despite being approximately 100 meV above the Mn (2+ 4)T 1 state. The effect of Mn (2+) doping on CdSe quantum dot luminescence at high temperatures is thus completely opposite from that at low temperatures described previously.     

Specifying and proving properties of timed I/O automata using Tempo

Timed I/O automata (TIOA) is a mathematical framework for modeling and verification of distributed systems that involve discrete and continuous dynamics. TIOA can be used for example, to model a real-time software component controlling a physical process. The TIOA model is sufficiently general to subsume other models in use for timed systems. The Tempo Toolset, currently under development, is aimed at supporting system development based on TIOA specifications. The Tempo Toolset is an extension of the IOA toolkit, which provides a specification simulator, a code generator, and both model checking and theorem proving support for analyzing specifications. This paper focuses on the modeling of timed systems and their properties with TIOA and on the use of TAME4TIOA, the TAME (Timed Automata Modeling Environment) based theorem proving support provided in Tempo, for proving system properties, including timing properties. Several examples are provided by way of illustration.     

Growth method,composition, and defect structure dependence of mercury diffusion in CdxHg1–xTe

Mercury radiotracer diffusion results are presented, in the range 254 to 452°C, for bulk and epitaxial Cd_xHg_1–xTe, and we believe this to be the first report for metalorganic vapor phase epitaxy (MOVPE) grown Cd_xHg_1–xTe. For all growth types studied, with compositions of x_Cd=0.2±0.04, the variation of the lattice diffusion coefficient, D_Hg, with temperature, under saturated mercury partial pressure, obeyed the equation: D_Hg=3×10⁻³ exp(−1.2 eV/kT) cm² s⁻¹. It was found to have a strong composition dependence but was insensitive to changes of substrate material or crystal orientation. Autoradiography was used to show that mercury also exploited defect structure to diffuse rapidly from the surface. Dislocation diffusion analysis is used to model defect tails in MOVPE Cd_xHg_1–xTe profiles.     

Effect of channel fade rate on throughput of three GHARQ-II schemesover Rayleigh fading channel

The performance of three GHARQ-II schemes, based on punctured convolutional codes, used over a simulated Rayleigh fading channel subject to additive white Gaussian noise are compared. Various fade rates and signal to noise ratios are considered     

54式12.7mm高射机枪拆解

1枪身与枪架分解前,应先检查膛是否内有枪弹(航向照准器与前照准器的连接杆未装入) 2拧松枪架两侧的支耳座盖紧定手柄,以解脱支耳座盖对枪身耳轴的约束;抽出固定枪身后部的插销,可将枪身从枪架上卸下     

On some Bayesian/regularization methods for image restoration

Methods are reviewed for choosing regularized restorations in image processing. In particular, a method developed by Galatsanos and Katsaggelos (see ibid., vol.1, p.322-336, 1992) is given a Bayesian interpretation and is compared with other Bayesian and non-Bayesian alternatives. A small illustrative example is provided and a complement is provided for the discussion of noise variance estimation of Galatsanos et al.     

Mercury diffusion in Hg1−xCdxTe

A radiotracer technique has been used to measure both mercury self-diffusion and surface concentration values in bulk and liquid phase epitaxy, LPE, grown Hg_1−xCd_xTe. A high resolution sectioning technique has allowed profiling of thin epitaxial layers in submicron steps. Hg_1-xCd_xTe samples with composition values betweenx _Cd= 0.16 and 0.23 were isothermally annealed in carefully controlled and monitored diffusion con-ditions. Mercury reservoirs containing Hg²⁰³ were used to provide vapour diffusion sources during closed tube isothermal anneals in the temperature range 300° C to 400° C. Evidence has been found which may indicate the presence of two components in the radio-tracer profiles for both bulk and epitaxially grown material. In some cases it was possible to estimate two diffusion coefficients,D ₁andD ₂, from the near surface and deeply penetrating components, respectively. Our results forD ₁andD ₂are compared with other work. For bulk material annealed at 400° C under a saturated mercury pressureD ₁= 2.0 x 10^-12cm²s^-1 andD ₂= 1.1 x 10^-11cm²s⁻¹. Diffusion coefficients at 310° C under saturated mercury pressure, have been measured in bulk and epitaxial material. Close agreement was found between these results with an average value ofD ₁= 1.4 x 10⁻¹³cm²s⁻¹. We believe this to be the first time radiotracer results for epitaxial material have been presented. We have collated diffusion data, as a function of reciprocal temperature, from several workers and suggest there is evidence for a change in the activation energy for mercury diffusion around 350° C. This may be due to a change in the dominant diffusion mechanism.     

Performance and Modeling of the MWIR HgCdTe Electron Avalanche Photodiode

The operation of the mid-wave infrared (MWIR) HgCdTe cylindrical electron injection avalanche photodiode (e-APD) is described. The measured gain and excess noise factor are related to the collection region fill factor. A two-dimensional diffusion model calculates the time-dependent response and steady-state pixel point spread function for cylindrical diodes, and predicts bandwidths near 1 GHz for small geometries. A 2 μm diameter spot scan system was developed for point spread function and crosstalk measurements at 80 K. An electron diffusion length of 13.4 μm was extracted from spot scan data. Bandwidth data are shown that indicate bandwidths in excess of 300 MHz for small unit cells geometries. Dark current data, at high gain levels, indicate an effective gain normalized dark density count as low as 1000 counts/μs/cm² at an APD gain of 444. A junction doping profile was determined from capacitance–voltage data. Spectral response data shows a gain-independent characteristic.     

Functionalized Nanostructures with Liquid‐Like Behavior: Expanding the Gallery of Available Nanostructures

Recently, we have developed a novel family of functionalized nanostructures that exhibit liquid‐like behavior in the absence of solvents and preserve their nanostructure in the liquid state. The gallery of nanostructures developed so far includes functionalized silica and magnetic iron oxide nanoparticles, layer‐like organosilicate nanoparticles, polyoxometalate clusters, and organic–inorganic hybrid networks. In an effort to demonstrate the wider applicability of this concept and to provide a deeper insight into this class of materials, the present work cites additional paradigms of functionalized nanostructures with similar behavior as above. In one case, surface functionalization of anatase nanoparticles (TiO₂, an inorganic nanostructure) with a quaternary ammonium organosilane leads to ionically modified nanoparticles that, when electrostatically combined with a poly(ethylene glycol) (PEG)‐tailed sulfonate anion, exhibit liquid‐like behavior in the absence of solvents. In a different but quite interesting case of a bionanostructure, ion‐exchange functionalization of a DNA oligonucleotide with a PEG‐tailed quaternary ammonium cation leads to an easily separable liquid derivative with attractive features. These examples show the versatility of this concept over a range of nanostructures.     

Securing light clients in blockchain with DLCP

In blockchain, full nodes (FNs) are peers that store and verify entire chains of transactions. In contrast, light clients (LCs) are those with limited resources, and for this reason, they request only block headers from FNs for transaction verification—using protocols like Simple Payment Verification (SPV). In an approach to prevent FN tampering on transaction verification (byzantine fault), LCs request block headers from multiple FNs and compare received responses. One problem with this approach is that an LC must connect to each FN and perform the same cryptographic operations with each one repeatedly, which leads to client‐side complexity and slower response. We propose an alternate approach to tackle this issue, in which LCs can encrypt a request for block headers only once, and send that request to a predetermined set of FNs to access, process, and reply back in a single response. Our approach, called Distributed Lightweight Client Protocol (DLCP), enables LCs to verify with little effort if FNs have agreed on a response. From an experimental evaluation, we observed that DLCP provided lower latency and reduced computing and communication overhead in comparison with the existing conventional approach.