A study on conformational changes by electron charges in viologen single molecules by using STM

The topography of self-assembled viologen derivatives (VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH) molecules on an octanethiol (C(8)) self-assembled monolayer (SAM) modified gold surface was measured using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). We demonstrate here a novel matrix SAM appropriate for isolation of the viologen molecules. The C(8) was used for a matrix SAM, in which the VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH were inserted at molecular lattice defects. The isolated single molecules of viologen derivatives inserted in the matrix SAM were observed as protrusions in STM topography using a constant current mode. We measured the topographic heights (VC(8)SH: 1.53nm, VC(10)SH: 2.01nm, HSC(8)VC(8)SH: 2.71nm, and HSC(10)VC(10)SH: 3.3nm) of the molecular protrusions using STM. Also, changes in the central axis of viologen molecules were observed as VC(8)SH (0.5-0.73nm), VC(10)SH (0.4-0.74nm), HSC(8)VC(8)SH (0.67-0.84nm), and HSC(10)VC(10)SH (0.67-0.99nm), respectively.     

基于LED光源的一氧化碳气体检测仪的设计

文章描绘并分析了一氧化碳分子的红外吸收光谱,推导了一氧化碳分子的吸收线型,估算了分子吸收系数,给出了气室设计的最佳长度。通过光谱分析发现,一氧化碳基频吸收比倍频吸收强约两个数量级,因此基频对应的4．60μm吸收谱带更适合于高灵敏度的一氧化碳气体检测。文中设计了一种基于LED光源的红外一氧化碳检测仪,结果表明,利用单LED光源、双探测器及反射式气室结构能够有效抑制环境变化、LED功率波动及探测器漂移等产生的噪声的干扰,进而具有较低的探测灵敏度,探测限为100×10-6。     

Studying the Possibility of Using Avalanche Photodetectors in the Single-photon Registration Mode to Create Quantum Random-number Generators

The possibility of using avalanche photodiodes that operate in the single-photon registration mode as a source of a random physical quantity in generators of random number sequences was evaluated. The operating modes of avalanche photodiodes were determined that allow generation of streams of random events, whose statistical characteristics are similar to those of a Poisson stream. Estimates of the similarity of the properties of generated random binary sequences to the properties of a uniformly distributed sequence are presented.     

Use of Large-Area Photodiodes for Improving the Characteristics of an Electromagnetic Calorimeter Based on Lead Tungstate Crystals

It is shown that an increase in the area of photodetectors allows the PHOS electromagnetic calorimeter of the ALICE experiment to operate at room temperature with better spectrometric characteristics. The linearity of the calorimeter response has been investigated in the 1–110 GeV energy range using both Hamamatsu S8664-1010 avalanche photodiodes with a large area (10 × 10 mm²) and arrays of MPPC Hamamatsu S12572-015C silicon photomultipliers with a sensitive area of 6 × 6 mm². The calorimeter based on avalanche photodiodes is linear in the energy range under investigation compared to a calorimeter composed of silicon-photomultiplier arrays.     

Single-shot beam-position monitor for x-ray free electron laser

We have developed an x-ray beam-position monitor for detecting the radiation properties of an x-ray free electron laser (FEL). It is composed of four PIN photodiodes that detect backscattered x-rays from a semitransparent diamond film placed in the beam path. The signal intensities from the photodiodes are used to compute the beam intensity and position. A proof-of-principle experiment at a synchrotron light source revealed that the error in the beam position is reduced to below 7 μm by using a nanocrystal diamond film prepared by plasma-enhanced chemical vapor deposition. Owing to high dose tolerance and transparency of the diamond film, the monitor is suitable for routine diagnostics of extremely intense x-ray pulses from the FEL.     

Using GaAsP photodiodes to characterize ultrashort pulses under high numerical aperture focusing in microscopy

We demonstrate for the first time that the two-photon response of GaAsP photodiodes can be used to conveniently characterize the spatial and temporal profiles of ultrashort pulses at the focus of a high numerical aperture system.     

Holder for fast photodiodes in TO-18 package

The design of a holder for fast photodiodes is described. These holders have been tested with commercially available photodiodes in a standard TO-18 package using delta light pulses from a synchronously pumped cw dye laser. Results of the measurements are presented and the holder is shown to perform well even for an experimental photodiode with a rise time of less than 40 ps and a FWHM of 80 ps.     

Tests of multipixel Geiger photodiodes in liquid and gaseous xenon

To evaluate the applicability of multipixel Geiger photodiodes in experiments searching for dark matter, such device from different manufacturers were studied in liquid and gaseous xenon. The detection efficiency for scintillation radiation at a wavelength of 175 nm was <1%. Measurements in gaseous xenon have shown the presence of a component in the visible or infrared region and the absence of this component in liquid xenon. It has been concluded that further studies in this field must be performed using wavelength-shifting materials and photodiodes featuring the highest quantum sensitivity in the region of emission of the reemitter.     

Biomechanical and microstructural benefits of physical exercise associated with risedronate in bones of ovariectomized rats

Several treatments have been developed aiming the prevention of bone loss. There are discussions about the best prophylactic and therapeutic procedures for osteoporosis. This study evaluated the effects of physical exercise associated with risedronate as a prophylactic and therapeutic procedure in osteopenic bones of rats submitted to ovariectomy. We used 48 Wistar rats divided into: ovariectomized or subjected to sham surgery. Ovariectomized rats were divided into the following sub‐groups: OVX, 12 weeks sedentary; OVX‐EX, treadmill training for 12 weeks; OVX‐RA, 12 weeks with risedronate administration; and OVX‐EX‐RA, 12 weeks with risedronate administration and treadmill training. Rats subjected to sham surgery were divided into the following sub‐groups: SH, 12 weeks sedentary; SH‐EX, treadmill training for 12 weeks; SH‐RA, 12 weeks with risedronate administration; and SH‐EX‐RA, 12 weeks with risedronate administration and training on the treadmill. The effectiveness of the treatment was evaluated in tibias using biomechanical, radiological, histomorphometric, and immunohistochemical analyses. Data were analyzed by statistical tests, with significance level of P < 0.05. Results of mechanical tests showed that the SH‐RA group had lower values compared with OVX‐RA group; densitometry showed no significant differences; according to histomorphometric methods, OVX group presented lower results than the SH‐EX, OVX‐RA, SH‐EX‐RA, and OVX‐EX‐RA groups, and SH‐EX‐RA and OVX‐EX‐RA groups showed values higher than SH‐RA, SH, and OVX‐EX groups. The SH‐EX‐RA and OVX‐EX‐RA groups had decreased immunostaining for tartrate‐resistant acid phosphatase and receptor activator of nuclear factor kappa‐B ligand and increased osteoprotegerin immunostaining. In this experimental model, it was concluded that the physical training associated with use of risedronate exerted positive effects on biomechanical and microstructural properties in bones of ovariectomized rats. Microsc. Res. Tech. 77:431–438, 2014. © 2014 Wiley Periodicals, Inc.     

Investigation of a LYSO crystal for a low-energy calorimeter

The results of studying a calorimeter cell in the low-energy region, ~50 MeV, which consists of a LYSO crystal and two avalanche photodiodes, are presented. The use of two photodiodes per crystal made it possible to perform a preliminary measurement of the calorimeter energy resolution using one calorimeter cell and cosmic muons. The coefficient of the stochastic contribution to the calorimeter energy resolution and the crystal luminescence time were measured (0.115% and 50 ns, respectively).     

Highly sensitive micropixel avalanche photodiodes for scintillation counters of the T2K neutrino experiment

Highly sensitive micropixel avalanche photodiodes with a metal-resistor-semiconductor structure (MRS APDs) operating in the restricted Geiger discharge mode and scintillation detectors with wavelength-shifting optical fibers developed for the T2K neutrino oscillation experiment have been investigated. Dependencies of basic MRS APD parameters on the bias voltage, photon wavelength, and temperature have been measured. Characteristics of the scintillation detectors with wavelength-shifting optical fibers and avalanche photodiodes are described.     

A method for automatic tuning and stabilization of the energy threshold in scintillation detectors

A method is proposed for automatic tuning and stabilization of the energy threshold in scintillation detectors by maintaining the constancy of the average detector counting rate from ?? rays of natural radiation background or cosmic rays. Stabilization is automatically performed by controlling the photodetector supply voltage, which makes it possible to stabilize the detector threshold with an error of 0.73?C2.40%, depending on the used circuitry. The stabilization electronics for scintillation detectors with avalanche multipixel photodiodes and photomultipliers is described. A circuit ensuring the increased precision of threshold stabilization is also proposed.     

变厚度板中水平剪切波的传播特性分析

为研究超声导波在储罐壁板等变壁厚结构中的传播特性，建立了SH波在空间自由边界中的传播模型，基于各向同性弹性介质Navier-Stokes方程，推导了变厚度板中SH波的频散方程，分析了变厚度板中水平剪切波走时t与倾斜角θ间的相互作用关系；通过简谐点源的远场响应并引入板厚与传播位移的非线性关系，得出了变厚度板中SH波的远场响应方程。在此基础上，仿真分析和实验验证了水平剪切波在不同倾斜角变厚度板中的传播特性，结果表明：在变厚度板的薄端激励水平剪切波并沿结构表面传播时，无频散现象，且无波包分离现象；但随着变厚度板倾斜角θ增大，水平剪切波的走时和接收信号幅值均逐渐递减，且呈非线性关系。     

Using single-photon detectors for quantum key distribution in an experimental fiber-optic communication system

This paper gives experimental results of quantum key distribution on a fiber-optic setup at a telecom wavelength of 1555 nm. A self-compensated two-channel optical circuit is used. Quantum key distribution was performed by coding the phase states of single photons radiated by a pulsed semiconductor laser in two alternative nonorthogonal bases. Specially developed single photon counters based on InGaAs: InP avalanche photodiodes were employed as high-sensitivity photodetectors. The results of investigation of the quantum efficiency, probability of afterpulses, and noise level for various operating modes of the detectors at temperatures from −40 to −60°C are given. A key distribution rate of 450 bit/s was obtained for a single-mode fiber-optic quantum communication channel between the receiver and sender 25 km long at a laser pulse clock frequency of 5 MHz and an average number of photons per pulse of about 0.2. For the achieved photodetector characteristics, the average number of errors in the quantum key did not exceed 3.7%.     

Effect of medicaments used in endodontic regeneration on the morphological characteristics of bovine radicular dentin: Experimental immature tooth model

The purpose of this study was to evaluate the effect of different combinations of irrigating solutions and intracanal dressings in the pretreatment of bovine radicular dentin, using an experimental immature tooth model. Eighty healthy bovine teeth, simulated with incomplete rhizogenesis, were randomly distributed according to the protocols of root canal dentin pretreatment for a regenerative endodontic procedure (n = 10): Control (irrigation with distilled water); SH (irrigation with 1.5% Sodium Hypochlorite); EDTA (irrigation with 17% EDTA); SH/EDTA (irrigation with 1.5% SH + 17% EDTA); SH/CH/EDTA (irrigation with 1.5% SH + calcium hydroxide paste +17% EDTA); SH/MTAP/EDTA (irrigation with 1.5% SH + modified triple antibiotic paste + EDTA 17%); SH/TAP/EDTA (irrigation with 1.5% SH + triple antibiotic paste +17% EDTA) and SH/DAP/EDTA (irrigation with 1.5% SH + double antibiotic paste + EDTA 17%). After the completion of the protocol, the demineralization, the exposure of collagen fibers, and the dentin erosion was evaluated under scanning electron microscopy (SEM), by applying a score system (1–3) to classify the observed features. Statistical analysis was performed (Kruskal‐Wallis and Dunn Multiple Comparison tests—p < .05). SH/TAP/EDTA and SH/DAP/EDTA groups presented the highest rates of demineralization in both the coronal and middle thirds of the root (p < .05). In the SH/MTAP/EDTA group, the samples presented moderate demineralization. The samples from the SH/CH/EDTA group presented similar findings to the control group (p < .05). Conventional triple antibiotic (TAP) and double antibiotic (DAP) pastes promoted more pronounced morphological changes on the dentin surface.     

Ultrafast spectroscopy diagnostic to measure localized ion temperature and toroidal velocity fluctuations

A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence. A large-area prism-coupled transmission grating and high-throughput collection optics are employed to observe C?VI emission centered near λ=529?nm. The diagnostic achieves 0.25 nm resolution over a 2.0 nm spectral band via eight discrete spectral channels. A turbulence-relevant time resolution of 1?μs is achieved using cooled high-speed avalanche photodiodes and ultralow-noise preamplifiers. The system sensitivity is designed to provide measurements of normalized ion temperature fluctuations on the order of δT(i)/T(i)≤1%.     

Effects of chemical agents on physical properties and structure of primary pulp chamber dentin

This study evaluated the effects of chemical agents on the physical properties and structure of primary pulp chamber dentin using surface roughness, microhardness tests, and scanning electron microscopy (SEM). Twenty‐five primary teeth were sectioned exposing the pulp chamber and were divided into five groups (n = 5): NT, no treatment; SH1, 1% sodium hypochlorite (NaOCl); SH1U, 1% NaOCl + Endo‐PTC^®; SH1E, 1% NaOCl + 17% EDTA; and E, 17% EDTA. After dentin treatment, the specimens were submitted to roughness, microhardness testing, and SEM analysis. Roughness and microhardness data were submitted to one‐way ANOVA and Tukey's test (P < 0.05). The SH1E group showed the highest roughness, followed by the E group (P < 0.05) when compared with the NT, SH1, and SH1U groups. Microhardness values of SH1 and SH1U showed no significant difference as compared to the NT (control) group (P > 0.05). Microhardness values could not be obtained in the EDTA groups (SH1E and E). The presence of intertubular dentin with opened dentin tubules was observed in the NT, SH1, and SH1U groups. SH1E showed eroded and disorganized dentin with few opened tubules and the intertubular/peritubular dentin was partially removed. Considering the physical and structural approaches and the chemical agents studied, it can be concluded that NaOCl and NaOCl associated with Endo‐PTC^® were the agents that promoted the smallest changes in surface roughness, microhardness, and structure of the pulp chamber dentin of primary teeth. Microsc. Res. Tech. 77:52–56, 2014. © 2013 Wiley Periodicals, Inc.     

Avalanche photodiode based detector for beam emission spectroscopy

An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements (≈10(8)-10(10)?photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).     

Single-Photon Detection with the Use of a Gated Silicon Avalanche Photodiode

Silicon avalanche photodiodes were investigated in the single-photon mode with time gating. The dependences of the probability densities of dark- and signal-pulse generation on the gate-pulse duration were found to obey a normal distribution. The likelihood ratio was used to optimize the duration and repetition frequency of gate pulses and the constant reverse-bias voltage of the avalanche photodiode.     

硅光电探测器的发展与应用

半导体光电探测器由于体积小、灵敏度商、响应速度快、易于集成,是最理想的光电探测器,典型的包括PIN光电二极管、雪崩二极管以及硅光电倍增管.论述了它们的工作原理,以及在光纤通信、传感系统、高能物理、核医学等领域的广泛应用.