NiTi形状记忆合金相变过程的正电子湮没研究

采用正电子湮没技术研究了NiTi合金在降温和升温过程中缺陷和电子密度随温度的变化.在降温过程中,当温度从295K降至225K时,合金的电子密度nb随温度的降低而下降,在225K时降至最小;随后,nb随温度的降低而升高.当温度从295K降至221K时,合金缺陷的开空间随温度的下降而升高,在221K时达到最大值;随后,缺陷的开空间随温度的下降而下降.在升温过程中,当温度从25K升至253K时,合金的电子密度nb随温度的升高而降低,并在253K时达到最小;当温度从253K升至295K时,合金电子密度nb随温度的升高而升高.在相变临界温度点Ms=222K,Mf=197.2K,As=237.5K,Af=255.5K附近,合金的电子密度nb及合金缺陷的开空间均有异常的变化.     

Luminescence spectra of doped and undoped lead tungstate crystals

TL spectra of undoped lead tungstate crystals exhibit glow peaks at 30 v K and 85 v K centred at 440 v nm, plus a peak at 50 v K at 530 v nm in an annealed sample. Annealing adds a 170 v K peak. Trivalent dopants of La 3+ and Y 3+ reduce the green luminescence, and Nb 5+ introduces a peak near 100 v K centred at 530 v nm; Sb introduces features between 40 v K and 90 v K and 150 and 180 v K. The luminescence emissions around 50 v K may be attributed to complex intrinsic defect centres, including (WO 4 ) m 3 . Of the four dopants studied in the present research, Sb +5 has the highest luminescence intensity. CL spectra show interesting anomalies near 170 v K which are linked to a phase change of water/ice nanoparticles trapped at dislocations.     

Static magnetic order in metallic K0.49CoO2

By means of muon-spin spectroscopy, we have found that K0.49CoO2 crystals undergo successive magnetic transitions from a high-T paramagnetic state to a magnetic ordered state below 60 K and then to a second ordered state below 16 K, even though K0.49CoO2 is metallic at least down to 4 K. An isotropic magnetic behavior and wide internal-field distributions suggest the formation of a commensurate helical spin density wave (SDW) state below 16 K, while a linear SDW state is likely to exist above 16 K. It was also found that exhibits a further transition at 150 K presumably due to a change in the spin state of the Co ions. Since the dependence of the internal-field below 60 K was similar to that for Na0.5CoO2, this suggests that magnetic order is more strongly affected by the Co valence than by the interlayer distance or interaction and/or the charge ordering.     

Proposed search for a(0)(0)(980)-f(0)(980) mixing in polarization phenomena

The K+ and K0 meson mass difference induces the mixing of the a(0)(0)(980) and f(0)(980) resonances, the amplitude of which, between the K+K- and K0(-)K(0) thresholds, is large in magnitude, of the order of m(K)m(2)(K0)sqrt[-m(2)(K+)] approximately sqrt[alpha] m(2)(K), and possesses the phase sharply varying by about 90 degrees. We suggest performing the polarized target experiments on the reaction pi(-)p-->etapi(0)n at high energy in which the fact of the existence of a(0)(0)(980)-f(0)(980) mixing can be unambiguously and very easily established through the presence of a strong jump in the azimuthal asymmetry of the etapi(0) S wave production cross section near the K(-)K thresholds. The presented estimates of the polarization effect to be expected in experiment are to a great extent model independent.     

First–principles study of potassium adsorption and diffusion on graphene

Potassium–ion batteries (KIBs) are a new–type of energy storage devices that have attracted increasing attention due to their low cost and the abundant resource of K in the Earth’s crust. Monolayer and multilayer graphene are promising electrode materials for KIBs. Herein, the adsorption and diffusion of potassium atoms on the surface of graphene were studied using the first–principles calculations including the van der Waals interaction. It was determined that K atoms can stably adsorb on the surface of graphene. The climbing image nudged elastic band method was employed to calculate the diffusion barriers of a single K atom and two K atoms on the surface of graphene. The results demonstrated that the diffusion barrier of a single K atom on graphene was low. The interaction between K atoms was considered and it facilitates the K atom diffusion to the second and third nearest–neighbour site of the K adatom, but prevents the K atom diffusion to the far nearest–neighbour site of the K adatom. Moreover, the difference in charge density demonstrates that there was a significant charge transfer from two K adatoms to its nearest–neighbour carbon atoms.     

The properties of K and coadsorbed CO + K on Ru (001): II. Electronic structure

The electronic properties of K and CO + K mixed layers on Ru(001) have been examined in detail with XPS, polarization and angle dependent UPS, and work function changes. The adsorption of K is accompanied by a gradual decrease of the K 2p binding energies and a normal work function behaviour which are discussed in detail. Adsorption of CO on K predosed surfaces also causes a K 2p binding energy decrease at all K coverages which can be understood as repulsion of substrate charge back into the K atom induced by CO orbitals overlapping with the substrate valence band. The complex change in work function caused by CO adsorption is explained by the combination of three effects, CO addition, charge exchange, and K displacement. All results in this and the first paper, in particular the additional peaks in the He I spectra and the HREELS results, are only compatible with the model of a sp²-rehybridized CO molecule in the vicinity of coadsorbed K.     

Exclusive branching-fraction measurements of semileptonic tau decays into three charged hadrons, into phipi(-)nu tau, and into phi K(-)nu tau

Using a data sample corresponding to an integrated luminosity of 342 fb(-1) collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a center-of-mass energy near 10.58 GeV, we measure B(tau(-)--> pi(-)pi(-)pi+nu(tau)(ex.K(S0))=(8.83+/-0.01+/-0.13)%, B(tau(-) -->K(-)pi(-)pi+nu tau(ex.K(S0))=(0.273+/-0.002+/-0.009)%, B(tau(-) -->K(-)pi(-)K+nu tau)=(0.1346+/-0.0010+/-0.0036)%, and B(tau(-) -->K(-)K(-)K+nu tau)=(1.58+/-0.13+/-0.12)x10;{-5}, where the uncertainties are statistical and systematic, respectively. These include significant improvements over previous measurements and a first measurement of B(tau(-) -->K(-)K(-)K+nu tau) in which no resonance structure is assumed. We also report a first measurement of B(tau(-) -->var phi(-)nu tau)=(3.42+/-0.55+/-0.25)x10(-5), a new measurement of B(tau(-) -->var phi K(-)nu tau)=(3.39+/-0.20+/-0.28)x10(-5) and a first upper limit on B(tau(-) -->K(-)K(-)K+nu tau(ex.var phi)).     

The role played by hydrogen in the ionic thermocurrents of beryl

Abstract

Ionic thermocurrents (ITC) were measured in pink (morganite) and colourless (goshenite) samples of natural beryl from 77K up to 250K at a constant rate b = 0.1 Ks^?1. The spectra present three distinct bands, at 170K, 200K and 220K. The band at 200K predominates in the untreated crystals. After thermal treatments between 700K and 1300K, the ITC bands at 170K and 220K become prominent, masking the 200K band. The reduction of Fe³⁺ into Fe²⁺ in two distinct positions in the beryl lattice justify this observation. Infrared (IR) spectra show that treatments above 1000K remove water from the channels of the beryls. Ultraviolet (UV) irradiation of these thermally treated samples enhance the two bands at 170K and 220K.     

X射线衍射分析长期钾素盈亏对土壤含钾类矿物的影响

利用1991年—2013年国家紫色土肥力与肥料效益监测站长期定位试验的土壤样品,采用X射线衍射(XRD)光谱分析技术,研究了22年长期钾素投入亏缺和盈余处理中性紫色土壤钾素含量及含钾类矿物的演变特征。XRD图谱分析发现,长期钾素亏缺处理导致土壤云母、钾长石等含钾类原生矿物加速风化,表现为连续施肥22年<连续施肥12年<原始土壤,同时促进了蒙脱石的形成;长期钾素盈余处理土壤云母、钾长石等原生矿物风化程度虽得到有效缓解,但较原始土壤相比仍有明显风化。土壤含钾类粘土矿物的演变与原生矿物变化相似,长期钾素亏缺导致土壤粘粒中伊利石发生了明显崩解,且随着施肥年限的增加,粘粒中伊利石的含量随之减少,长期钾素盈余处理明显缓解了伊利石的风化进程;但是无论是钾素亏缺或盈余处理都出现土壤中伊利石的风化崩解,同时伴随蒙脱石等膨胀型矿物的形成,现有的钾素盈余水平也不能阻止土壤含钾类矿物的风化崩解。另外,长期钾素亏缺导致土壤中速效钾和缓效钾含量逐年降低,22年分别降低62.0%和37.4%;而钾素盈余处理提高了土壤速效钾含量,但缓效钾呈现下降趋势;土壤伊利石的风化程度和土壤缓效钾的演变趋势相吻合。表明中性紫色土壤中伊利石是土壤缓效钾的主要来源,长期钾素亏缺会造成土壤钾素枯竭和含钾类矿物的加速风化崩解,降低土壤供钾能力。     

Temperature studies of Fe−Mn nodules

Sea nodules were extensively studied over a wide range of temperature ranging from 77K to 1175K using Mossbauer effect and ESR. The Mossbauer studies of the nodules at 77K and room temperature show a quadrupole doublet whereas at higher temperatures magnetic spectra were obtained starting at around 875K which ultimately gives a hyperfine field of around 390 KOe at 1175 K. The Mossbauer spectra recorded at 30K did not show any significant change in the room temperature spectra. The analysis of the spectra upto 775K showed two positions of Fe^R+, vie., octahedral and tetrahedral which were varified by ESR of the diluted samples.     

Thermal properties of single-walled carbon nanotube crystal

In this work, the thermal properties of a single-walled carbon nanotube (SWCNT) crystal are studied. The thermal conductivity of the SWCNT crystal is found to have a linear dependence on temperature in the temperature range from 1.9 K to 100.0 K. In addition, a peak (658 W/mK) is found at a temperature of about 100.0 K. The thermal conductivity decreases gradually to a value of 480 W/mK and keeps almost a constant in the temperature range from 100.0 K to 300.0 K. Meanwhile, the specific heat shows an obvious linear relationship with temperature in the temperature range from 1.9 K to 300.0 K. We discuss the possible mechanisms for these unique thermal properties of the single-walled carbon nanotube crystal.     

Transport spectroscopy through dopant atom array in silicon junctionless nanowire transistors

We demonstrate electron transport spectroscopy through a dopant atom array in n-doped silicon junctionless nanowire transistors within a temperature range from 6 K to 250 K. Several current steps are observed at the initial stage of the transfer curves below 75 K, which result from the electron transport from Hubbard bands to one-dimensional conduction band. The current-off voltages in the transfer curves have a strikingly positive shift below 20 K and a negative shift above 20 K due to the electrostatic screening induced by the ionized dopant atoms. There exists the minimum electron mobility at a critical temperature of 20 K, resulting from the interplay between thermal activation and impurity scattering. Furthermore, electron transport behaviors change from hopping conductance to thermal activation conductance at the temperature of 30 K.     

Untersuchungen über Elektronenhaftstellen in ZnS-Phosphoren

Glow curves of different ZnS phosphors were measured and analysed in the temperature region from 4.2 °K to 500 °K. It was attempted to clarify the origin of the glowpeaks observed above 77.4 °K and to attribute them to structural defects in the ZnS lattice. In glow curves started at 4.2 °K a strong dependence of the trap distribution on the method of preparation of phosphors was observed. In particular a ZnS(Cu) phosphor containing oxygen shows a broad continuum of shallow traps between 4.2 °K and 150 °K. In a ZnS(Cu, Ga) phosphor free of oxygen the trap density of the continuum of shallow traps is very small. Moreover this phosphor shows a sharp glowpeak at about 60 °K. The afterglow at the excitation temperatures of 4.2 °K and 77.4 °K was also studied. It is concluded that the rapid amptying of shallow and, to a lesser extent, of deep traps should be due to a tunneling process leading to luminous recombination of the trapped electrons with the activator levels.     

Branching fractions and CP asymmetries in B0-->K+ K- K0 S and B+-->K+ K0 S K0 S

We measure the branching fractions and CP asymmetries in the decays B0-->K(+)K(-)K(0)(S) and B+-->K(+)K(0)(S)K(0)(S) using a sample of approximately 122x10(6) BB pairs collected by the BABAR detector. From a time-dependent analysis of the K(+)K(-)K(0)(S) sample that excludes phiK(0)(S), the values of the CP-violation parameters are S=-0.56+/-0.25+/-0.04 and C=-0.10+/-0.19+/-0.10, where the first uncertainty is statistical and the second is systematic. We confirm that the final state is nearly purely CP even and extract the standard model parameter sin(2beta=0.57+/-0.26+/-0.04(+0.17)(-0) where the last error is due to uncertainty on the CP content. We present the first measurement of the CP-violating charge asymmetry A(CP)(B+-->K(+)K(0)(S)K(0)(S))=-0.04+/-0.11+/-0.02. The branching fractions are B(B0-->K+K-K0)=(23.8+/-2.0+/-1.6)x10(-6) and B(B+-->K(+)K(0)(S)K(0)(S))=(10.7+/-1.2+/-1.0)x10(-6).     

A new N~* resonance as a hadronic molecular state

We report our recent work on a hadronic molecule state of the K(K)N system with I=1/2 and J~P=1/2~+. We assume that the A(1405) resonance and the scalar mesons, f_0(980), a_0(980), are reproduced as quasi-bound states of (K)N and K(K), respectively. Performing non-relativistic three-body calculations with a variational method for this system, we find a quasibound state of the K(K)N system around 1910 MeV below the three-body breakup threshold. This state corresponds to a new baryon resonance of N~* with J~P = 1/2~+. We find also that this resonance has the cluster structure of the two-body bound states keeping their properties as in the isolated two-particle systems. We also briefly discuss another hadronic molecular state composed by two (K) and one (N), which corresponds to a Ξ~* resonance.     

Positron annihilation in the quenched and electron-irradiated NiSb intermetallic compound

Samples of the near equiatomic NiSb compound were irradiated by 3 MeV electrons at 20 K or quenched from 1103 K and 1333 K and subsequently annealed isochronally. The behaviour of defects created by quench or irradiation were studied by the positron annihilation technique. Only one recovery stage was found around 425 K for quenched specimens, but two distinct stages (100 K and 425 K) were observed after irradiation. The 425 K stage is ascribed to the migration of Ni vacancies giving dislocation loops. The recombination of mobile interstitials with vacancies after irradiation is assumed to occur between 100 K and 250 K. Doppler broadening and lifetime variations of positrons as a function of the measuring temperature in these irradiation samples are discussed.     

Differential thermal analysis at high pressures— VIII: Phase behaviour of solid cyclopentanone,cyclopentanol, and cyclohexanone up to 3 KBAR

The phase behaviour of solid cyclopentanone, cyclopentanol, and cyclohexanone was investigated from 80 K to the melting temperature and up to 3 Kbar, using a low-temperature high-pressure differential thermal analysis apparatus. The melting temperature of cyclopentanone rises from 221.7 K at atmospheric pressure to 278 K at 2900 bar. No solid solid transition was observed. The melting temperature of cyclohexanone rises from 242.4 K at atmospheric pressure to 312 K at 2840 bar. Its well-known solid solid transition at atmospheric pressure (220.3 K) splits into two different solid solid transitions at elevated pressures. The melting temperature of cyclopentanol rises from 256 K at atmospheric pressure to 328 K at 2600 bar. Cyclopentanol exhibits two well-known solid solid transitions (236.4 K and 202.5 K at 1 atm), but an additional metastable form has been observed in the present work. the transition temperature being 195 K at 1 atm. Volume changes accompanying the phase transitions have been calculated using the Clausius Clapeyron equation.     

聚苯硫醚熔体的压致凝固行为

采用施加压力的方法将聚苯硫醚熔体凝固,凝固后获得的聚苯硫醚样品经过降温和卸压后在常温常压下回收. X射线衍射和差示扫描量热分析表明:约20 ms时间的快速压缩过程可以抑制熔体结晶,制备出非晶态聚苯硫醚块材,样品的表面及中心都是非晶态.非晶态聚苯硫醚的玻璃化转变温度和晶化温度分别为318和362 K.常压下的退火实验表明,非晶态聚苯硫醚在425 K等温结晶的产物为正交相晶型.压致凝固法中熔体的凝固不是靠温度变化,而是靠压力变化,样品表面和内部处在一致的温度下同时受压凝固,避免了热传导对非晶尺寸的影响,因此非常有利于获得结构均匀的大尺寸非晶态材料.     

Exploring Bd,s-->KK decays through flavor symmetries and QCD factorization

We present a new analysis of Bd,s-->KK modes within the standard model (SM), relating them in a controlled way through SU(3)-flavor symmetry and QCD-improved factorization. We propose a set of sum rules for Bd,s-->K0K0 observables. We determine Bs-->KK branching ratios and CP asymmetries as functions of Adir(Bd-->K0K0), pointing out a conflict between BR(Bs-->K+K-) in the SM and data. Finally, we predict the amount of U-spin breaking between Bd-->pi+pi- and Bs-->K+K-.