基于文桥振荡器的T-T滤波器设计

对经典文桥振荡器的环路增益分析,将该环路作为T-T滤波器的环路,设计一个带通滤波器,然后通过添加一个积分器设计一个低通滤波器,实现了T-T滤波器的滤波功能。该滤波器仅仅使用2个集成运放,电路不仅拥有低通、带通滤波功能,而且拥有高的Q值,还能实现极点频率和品质因数的正交调节,调节电阻还可产生两路正交正弦信号。通过计算机仿真,证实所设计的电路正确有效。

Study on the energy level limitations of triplet-triplet annihilation upconversion with anthracene-isomerized dimers as annihilators

The enhancement in the efficiency of triplet-triplet annihilation upconversion(TTA-UC)is mainly determined by the triplet energy transfer(TET)and triplet-triplet annihilation(TTA)between the sensitizers and annihilators.The TET process works efficiently by adjusting the concentration ratio of the sensitizers and annihilators.The efficiency of TTA is determined by the properties of the annihilator.Because TTA is a Dexter-type energy transfer and is affected by the diffusion rate,the energy levels of the excited states and the molecular size are both crucial in TTA.In this study,four isomerized dimers of 9,10-diphenlanthracene(DPA)and anthracene(An)were designed and prepared as annihilators for TTA-UC.The singlet and triplet energy levels could be adjusted by altering the connection position while maintaining the molecular weight and size.When PtOEP was used as the sensitizer,the maximum upconversion efficiency of 9-[4-(9-anthracenyl)phenyl]-10-phenylanthracene(9DPA-9An)was~11.18%.This is four times higher than that of 9,10-diphenyl-2,9-bianthracene(2DPA-9An,2.63%).The calculation of the energies of T_(1)and the higher triplet state(T_(3),because E(T_(2))is similar to the E(T)of these dimers)for these dimers has provided insights into the underlying reasons.These indicated that the energy gap value of 2×E(T_(1))-E(T_(3))is the determining factor for TTA efficiency.This work may provide a better understanding of the excited-state energy levels,which is crucial for designing novel annihilators to enhance the TTA-UCefficiency.

Triplet-triplet annihilation upconversion materials as electrophoretic inks

Luminescent materials that can be reversibly switched by electric field stimulation are attractive since the potential application for optoelectronic devices.Here we report a triplet-triplet annihilation upconversion(TTA-UC)system with electrophoretic response which is developed as the electrophoretic ink.The TTA-UC system consists of an ionic derivative of 9,10-diphenyl anthracene(DPA)as the annihilator and Pt(II)octaethylporphyrin(PtOEP)as the sensitizer.Upon applying an electric field,migration and enrichment of positively charged DPA derivatives towards the cathode results in a 20%enhancement of TTA-UC.A quasi-solid film for electrically writing is made using the electrophoretic TTA system as the ink and a platinum electrode as a pen.The prototype of TTA-UC ink demonstrates unique luminescence functions upon electrically writing and erasing,providing a promising strategy to develop electronic devices for display,information storage and encryption.

Annihilation Solitons and Chaotic Solitons for the （2＋1）-Dimensional Breaking Soliton System

By means of an improved mapping method and a variable separation method, a series of variable separation solutions including solitary wave solutions, periodic wave solutions and rational function solutions） to the （2＋1）-dimensional breaking soliton system is derived. Based on the derived solitary wave excitation, we obtain some special annihilation solitons and chaotic solitons in this short note.

APPLICATION OF THE POSITRON ANNIHILATION TECHNIQUE

The principles of positron annihilation and four positron experimental techniques are described. The application of positron annihilation technique in material science. atomic physics and other related fields are discussed.

Positron Annihilation Mechanism Correlated with Microstructure of C60-Contained Chitosan

Positron annihilation lifetime spectra measurements were performed on C_(60)-containing chitosan as a function of temperature ranging from 290 to 380K.Both the ortho-positronium annihilation lifetimeт_(3) and its intensity Is increase with increasing temperature,however,the values of I_(3) in C_(60)-containing chitosan are smaller than that in pure chitosan,and the slope ofт_(3) with temperature is also suppressed after C_(60) linked.The existing three models for positron annihilation in polymer have been compared to analyze the experiment result.It is realized that only the spur reaction model,combined with the free volume model,can explain it satisfactorily.The ortho-positronium lifetime and intensity were affected by the local physicochemical environment of material,i.e.,free-volume structure,electron scavenging and trapping sites,etc.The linked C_(60) that play a significant chemical inhibition and quenching role on positronium formation and annihilation isfirst observed.The microstructure change brought by C_(60) group has also been discussed.

Evolution of native point defects in ZnO bulk probed by positron annihilation spectroscopy

This paper studies the evolution of native point defects with temperature in ZnO single crystals by positron lifetime and coincidence Doppler broadening （CDB） spectroscopy, combined with the calculated results of positron lifetime and electron momentum distribution. The calculated and experimental results of the positron lifetime in ZnO bulk ensure the presence of zinc monovacancy, and zinc monovacancy concentration begins to decrease above 600 ℃ annealing treatment. CDB is an effective method to distinguish the elemental species, here we combine this technique with calculated electron momentum distribution to determine the oxygen vacancies, which do not trap positrons due to their positive charge. The CDB spectra show that oxygen vacancies do not appear until 600℃ annealing treatment, and increase with the increase of annealing temperature. This study supports the idea that green luminescence has a close relation with oxygen vacancies.

Comparison between photon annihilation-then-creation and photon creation-then-annihilation thermal states:Non-classical and non-Gaussian properties

We investigate the nonclassical properties of arbitrary number photon annihilation-then-creation operation （AC） and creation-then-annihilation operation （CA） to the thermal state （TS）, whose normalization factors are related to the polylog- arithm function. Then we compare their quantum characters, such as photon number distribution, average photon number, Mandel Q-parameter, purity and the Wigner function. Because of the noncommutativity between the annihilation operator and the creation operator, the ACTS and the CATS have different nonclassical properties. It is found that nonclassical properties are exhibited more strongly after AC than after CA. In addition we also examine their non-Gaussianity. The result shows that the ACTS can present a slightly bigger non-Gaussianity than the CATS.

Effects of Flavour-Dependent qq Annihilation on the Mixing Angle of the Isoscalar Octet-Singlet and Schwinger’s Nonet Mass Formula

By incorporating the flavour-dependent quark--antiquark annihilation amplitude into the mass-squared matrix describing the mixing of the isoscalar states of a meson nonet,the new version of Schwinger's nonet mass formula,which holds with a high accuracy for the 0^(-+),1^(--),2^(++),2^(-+)and 3^(--)nonets,is derived and the mixing angle of the isoscalar octet--singlet for these nonets is obtained.In particular,the mixing angle of the isoscalar octet-singlet for the pseudoscalar nonet is determined to take the value of-12.92°,which is in agreement with the value range from-13°to-17°deduced from a rather exhaustive and up-to-date analysis of data.It is also pointed out that the omission of the flavour-dependent qq annihilation effect might be a factor resulting in the invalidity of Schwinger’s original nonet mass formula for the pseudoscalar nonet.

POSITRON ANNIHILATION AND CONDUCTIVITY MEASUREMENTS ON POLYANILINE

The positron lifetime spectra and electrical conductivities have been measured for polyaniline as a function of protonation level ([H+] from 10-7-1000.8 mol/L). Weobserved that (1) the short lifetime τ1, which was related to electron density in bulk,decreased with the protonation level; (2) the intermediate lifetime τ2≈360ps, almost remaining constant, whereas its intensity I2 increased with increasing protonation level which was related to the conductivity of material. These results are discussed in terms of conducting island model.

Microstructural Investigation of PM-355 Nuclear Track Detector Subjected to Low-Dose Gamma Irradiation: A Positron Annihilation Lifetime Study

Samples of the PM-355 polymeric solid state nuclear track detector were exposed to low gamma absorbed doses from 1 kGy (0.1 Mrad) up to 9 kGy (0.9 Mrad). Positron annihilation lifetime (PAL) in conjunction with transmission electron microscopy (TEM) and Thermo-gravimetric analysis (TGA) were performed on irradiated and pristine samples at room temperature. The observed lifetime spectra were resolved into three components where the ortho-positronium (o-Ps) lifetime component was associated with the pick-off annihilation of positronium trapped by the free volume. PAL studies of irradiated PM-355 samples showed that ortho-positronium (o-Ps) lifetime increases with an increase in dose up to 4 kGy and decreases at higher doses. In contrast, the intensity of the o-Ps component, I3, decreases with the dose up to about 2 kGy, followed by a much smooth decrease up to 7 kGy, and then it levels off. TGA analysis indicated that the PM-355 detector decomposed in one main breakdown stage. These results are discussed on the basis of chemical and physical changes occurring at the microscopic level in the PM-355 due to irradiation. Crosslinking dominates for doses between 1 and 4 kGy, while the degradation mechanism (Chain scission) prevails for doses up to 9 kGy.

Positron Annihilation Study on the Microstructural Stability in Rapidly Solidified Al_(92.3)Fe_(4.3)V_(0.7)Si_(1.7)Mm_(1.0) Alloy

Rapidly solidified Al92.3Fe4.3V0.7Si1.7Mm1.0 alloy has been studied by positron lifetime spectroscopy and the variations on the intedecial defects with the annealing temperature were revealed by an analysis of the lifetime results. The intedece characteristics derived from the positron-lifetime results could be used to give a satisfactory interpretation of the dependence of mechanical properties on the annealing temperature

Interaction behaviours of solitoffs:fission, fusion, reconnection and annihilation

The interactions between solitoffs are extensively investigated. Besides the known solitoff fission and fusion interac- tions, two new types of solitoff interactions are discovered, named the solitoff reconnection and the solitoff annihilation. Taking the asymmetric Nizhnik-Novikov Veselov equation as an illustrative system, five types of solitoff interactions are graphically revealed on the basis of the analytical solution obtained by the modified tanh function expansion method.

A PRELIMINARY STUDY OF EMBRITTLEMENT OF Co-BASED AMORPHOUS ALLOYS BY POSITRON ANNIHILATION

Measurements of the Doppler broadening S-lineshape parameter of positron annihilation and brittleness have been performed for two Co-based amorphous alloy prior to crystallization. It is shown that the brittleness is related to the S-parameter, that is, microdefects may be one of the important factors affecting the embrittlement of the Co-based amorphous alloys.

EFFECT OF POLYMERIZATION DEGREE ON MICROSTRUCTURE OF POLYETHYLENE GLYCOL STUDIED BY POSITRON ANNIHILATION

Positron lifetimes in polyethylene glycol (PEG) polymer have been measured as a function of polymerization degree N (N = 25 - 500). It is observed that all the positron parameters are strongly dependent on N when N≤250, and then tend to constant levels when N≥250. The variations of the longest-lived component (I3,τ3) show that the size of free- volume holes has a minimum at N - 100 and the hole concentration decreases with N. These trends may be due to the variations in crystallinity, the chain ends, entanglements and the Van der Waals interaction between segments. The variations of the second component (I2,τ2) with N reflect the changes of defect properties in crystalline regions of PEG.

Effects of thermal aging on Fe ion-irradiated Fe–0.6%Cu alloy investigated by positron annihilation

Thermal aging effects on surface of 2.5 Me V Fe ion-irradiated Fe–0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50 and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near-surface region from the S parameters and inflection point form at S–W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies.

INVESTIGATION OF BEHAVIOUR OF B IN Ni_3Al ALLOYS BY POSITRON ANNIHILATION TECHNIQUE

The behuviour of B atoms added to mono-and poly-crystalline Ni_3AI alloys has been investi- gated hy positron annihilation technique(PA T).If the additive of B was less than 1.37 at-%, some of B atoms solid-solutioned interstitially into matrix and distorted the lattice,thus the lifetime (τ) of positron (e^+) Or matrix dilated:the others of them segregated on vacancy-like defects and formed "filling effect",thus the mean lifetime (τ)and S parameters decreased.If B added was increased up to 2.22 at-%,more defects having larger free volume were induced by horide eutectic occurred along grain boundaries and grain interior,thus the τ in vacancy-like defects.τ and S parameters increased remarkably.

Positron Annihilation Study on TiC Powders

By means of the positron annihilation technique (PAT), superfine TiC powders obtained by ball-milling process were characterized. The results showed that there was a clear correlation between the change in TiC powders and that in the PAT parameters. In the high energy ball-milling process, TiC powders were severely deformed, which caused large increase in the amount of defects and severe distortion of lattice. On the other hand, the extreme refinement of grain size of powders resulted in the increase of grain boundary area and enhancement of system free energy. The spacing between deformed domains in 96 h milled samples is somewhat smaller than those in 48 h milled samples, indicating the size of Type II defects in 96 h milled samples is somewhat smaller than that in 48 h milled samples.

Free Volume Properties of Interpenetrating Polymer Networks Probed by Positron Annihilation

Positron annihilation lifetime (PAL) spectroscopy was applied to investigate the free volume properties of two types of simultaneous interpenetrating polymer networks (SINs), stoichiometric SINs and non--stoichiometric SINs. PU/VER SINs are all composed of polyurethane(PU) and vinyl ester resin (VER)with different compositions. Mean free volume size in PU/VER deceased with the increase of VER weight percentage, and the relative intensity, relevant to free volume content, increased with VER contents. The effect of chemical bonds between PU networks and VER networks to free volume properties was observed. Results revealed that chemical bonds between the two networks led to molecular denser packing, free volume contraction and made stoichoimetric PU/VER SINs a miscible system.

Effect of vacancy charge state on positron annihilation in silicon

The charge-state-dependent lattice relaxation of mono-vacancy in silicon is studied using the first-principles pseu- dopotential plane-wave method. We observe that the structural relaxation for the first-neighbor atoms of the mono-vacancy is strongly dependent on its charge state. The difference in total electron density between with and without charge states in mono-vacancy and its relevant change due to the localized positron are also examined by means of first-principles simu- lation, demonstrating the strong interplay between positron and electron. Our calculations reveal that the positron lifetime decreases with absolute charge value increasing.