Band Jahn-Teller instability and formation of valence bond solid in a mixed-valent spinel oxide LiRh2O4

We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent configuration of Rh3+ and Rh4+. At room temperature, it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of t_{2g} holes within the xy band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital-disordered phase above 230 K.     

Comment on "Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation"

We present some strong evidence against the assignment of an ytterbium-related oxygen deficiency center (ODC) near 230 nm in Yb-doped aluminosilicate glass in the Letter by Yoo [Opt. Lett.32, 1626 (2007)]. The strong 230 nm absorption band is actually a charge-transfer band corresponding to the transfer of an electron from nearby oxygen ligands to the ytterbium ion and not related to ODCs.     

Q-switched mode-locked diode-pumped Nd:YVO4 laser with a saturable Bragg reflector

We demonstrated a diode-pumped passively Q-switched mode-locked Nd:YVO4 laser by using a relaxed saturable Bragg reflector (SBR). Stable mode-locked pulse train with the repetition rate of ～230 MHz was achieved and the pulse train was modulated by the Q-switched envelope with the repetition rate of ～150 kHz. The maximum output of 4 W was obtained under the pump power of 13.5 W. The optical-to-optical efficiency was 30%. We also discussed the transition of each process having emerged.     

Fabrication and evaluation of a freestanding pyroelectric detector made from single-crystal LiNbO(3) film

We have packaged a rectangular 3 mm x 4 mm, 10-mum-thick Z-cut lithium niobate (LiNbO(3)) film produced by crystal ion slicing (CIS) and evaluated its performance as a pyroelectric optical detector. We justify the difficulty of preparing the film by showing that the freestanding detector has much greater sensitivity than the same detector bonded to a substrate. We compare the sensitivity of three CIS-film detectors with that of a detector based on a 230-mum-thick LiNbO(3) plate and describe the detectors' spatial uniformity and noise-equivalent power.     

A quasiparticle SIN mixer for the 230 GHz frequency range

We report on quasiparticle mixing in the frequency range 220 to 230 GHz using SIN junctions. The lowest double sideband receiver noise temperature measured was about 230 K. This result shows that the SIN junction provides an interesting alternative for high frequency heterodyne receivers where pair tunneling in SIS junctions could give rise to interference from Josephson effects.     

MBE生长PbSe/PbSrSe量子阱结构的光致中红外发光的研究

研究了分子束外延技术生长的PbSe/PbSrSe多量子阱结构的中红外光致荧光现象.高分辨率X射线衍射（HRXRD）谱观察到了多量子阱所特有的多级卫星峰,表明量子阱界面陡峭.变温光致荧光谱测量显示量子阱结构对电子空穴有强的限制效应,在相同温度下,量子阱样品的荧光峰峰位相对PbSe体材料有一定的蓝移.发现量子阱样品的荧光强度同温度有关,温度从150 K上升到230 K时,荧光强度逐渐增大,温度继续升高,荧光强度缓慢下降,但在高于室温时,仍能观察到较强的荧光发射,这说明该量子阱结构材料具有应用于室温工作的中红外 关键词： PbSe/PbSrSe多层量子阱（MQWs） 光致中红外荧光 高分辨X射线衍射（HRXRD）     

Specific heat of superconducting Zn nanowires

We present heat capacity measurements on crystalline Zn nanowires with diameters of 230 and 23 nm, bracketing the superconducting coherence length of 155 nm. Transport measurements on superconducting nanowires have found a crossover from three-dimensional to one-dimensional behavior as the wire diameter was reduced below the coherence length. In contrast, the normalized heat capacity peak of the 23 nm Zn nanowires is found to be nearly identical to that of 230 nm wires and bulk Zn, indicating their thermodynamic properties remain three dimensional.     

Ultrasonic studies of phase transitions in stage-4 antimony pentachloride intercalated graphite

The c-axis shear elastic constant C₄₄ and transverse sound attenuation α_T for stage-4 SbCl₅ intercalated graphite from 4 to 300 K are studied with ultrasonic pulse-echo techniques. No transverse sound echo is observable above 230 K. At constant temperatures between 230 and 200 K, both C₄₄ and α_T drift spontaneously toward lower bounds over a period of hours. A decrease in C₄₄ by a factor of ～ 2 is observed. Below 195 K, the sample becomes metastable. From 195 to 4 K, C₄₄ increases by 60% for the quenched sample, and by 30% for the annealed sample. This abnormal behavior of the elastic property can be interpreted by a disordered-liquid to incommensurate-solid phase transition of the intercalant layer at 230 K. The time-dependence of C₄₄ and α_T is attributed to the growth of islands with a slightly incommensurate solid structure.     

MBE growth of ZnSe nanowires on oxidized silicon substrate

We report the growth of single crystalline ZnSe nanowires on oxidized Si(100) substrates by molecular-beam epitaxy using Au nano-particles as the catalysts. It was found that average length decreased while the average diameter increased as we increased the temperature from 230 to 320 ^°C. It was also found that crystal quality of the ZnSe nanowires prepared at 320 ^°C was poorer than the ZnSe nanowires prepared at 230 ^°C and 280 ^°C.     

230U重离子衰变的观测

利用35MeV的质子束轰击ThO₂粉末靶,通过²³²Th(p,3n)反应产生²³⁰Pa核,经用放射化学方法分离出²³⁰Pa核并制成²³⁰Pa→²³⁰U测量源.用聚乙烯对苯二酸酯固体核径迹探测器记录其发射的重离子径迹.经248天的收集,观测到了两个²³⁰U→²⁰⁸Ph+²²Ne衰变事件,相对于α衰变的分支比为(1.3±0.8)×10^－14.     

Extended analysis of the Kr V spectrum

The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s²4p5d, 4s²4p5s, 4s²4p6s, 4s²4p5p and 4s4p²4d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions.     

苏丹Ⅲ在不同溶剂中的紫外-可见光谱研究

研究了苏丹Ⅲ在不同溶剂中的紫外-可见吸收光谱,探讨了极性、非极性及混合溶剂对苏丹Ⅲ的紫外-可见光谱的影响。结果表明,苏丹Ⅲ的主要吸收峰位于200～230 nm,340～360 nm及490～510 nm区间。在200～230 nm的中紫外区,苏丹Ⅲ在极性溶剂中呈双峰吸收,非极性溶剂中随苏丹Ⅲ浓度增加吸收峰由双峰变为单峰,混合溶剂中吸收双峰消失,红移至310 nm处,呈单峰状。苏丹Ⅲ在环己烷、石油醚、甲醇、乙腈和香蕉水这5种溶剂中的摩尔吸光系数(ε)均在104数量级。     

Classification of Three-Dimensional Integrable Scalar Discrete Equations

We classify all integrable three-dimensional scalar discrete affine linear equations Q ₃ = 0 on an elementary cubic cell of the lattice . An equation Q ₃ = 0 is called integrable if it may be consistently imposed on all three-dimensional elementary faces of the lattice . Under the natural requirement of invariance of the equation under the action of the complete group of symmetries of the cube we prove that the only non-trivial (non-linearizable) integrable equation from this class is the well-known dBKP-system. SPT acknowledges partial financial support from a grant of Siberian Federal University (NM-project No 45.2007) and the RFBR grant 06-01-00814.     

负电子亲和势GaN光电阴极光谱响应特性研究

针对负电子亲和势（NEA） GaN光电阴极成功激活后的量子效率问题,利用自行研制的紫外光谱响应测试仪器,测试了成功激活的NEA GaN光电阴极的光谱响应,给出了230—400 nm波段内反射模式NEA GaN光电阴极的量子效率曲线.测试结果表明：反射模式下NEA GaN光电阴极在230nm具有高达37.4%的量子效率,在GaN光电阴极阈值365 nm处仍有3.75%的量子效率,230 nm和400 nm之间的抑制比率超过2个数量级.文中还结合国外的研究结果,综合分析了影响量子效率的因素. 关键词： 负电子亲和势 GaN光电阴极 光谱响应 反射模式     

Multiple-element photonic microwave true-time-delay beamforming incorporating a tunable chirped fiber Bragg grating with symmetrical bending technique

We experimentally demonstrate a novel scheme for a multiple-element photonic microwave true-time-delay device with high tunability based on a tunable chirped fiber Bragg grating without center wavelength shift. We achieve the different true time delay by controlling the grating period of a chirped fiber Bragg grating based on the symmetrical bending technique as a multiwavelength signal source is applied to carry microwave signals. The proposed method does not require the complex structure of systems, wavelength tuning, and synchronization of optical devices such as tunable bandpass filters and optical input signals. We achieve the tunabilty of the time delay for a microwave signal carried over an optical signal in a range from 1 to 230 ps.     

Like-charge attraction and hydrodynamic interaction

We demonstrate that the attractive interaction measured between like-charged colloidal spheres near a wall can be accounted for by a nonequilibrium hydrodynamic effect. We present both analytical results and Brownian dynamics simulations which quantitatively capture the one-wall experiments of Larsen and Grier [Nature (London) 385, 230 (1997)], using a single unmeasured parameter.     

Observation of Upsilon(4S) decays to pi(+)pi(-)Upsilon(1S) and pi(+)pi(-)Upsilon(2S)

Observation of Upsilon(4S) decays to pi(+)pi(-)C and pi(+)pi(-)Upsilon(2S)We present the first measurement of Upsilon(4S) decays to pi(+)pi(-)Upsilon(1S) based on a sample of 230 x 106(4S) mesons collected with the BABAR detector. We measure the product branching fractions Beta(Upsilon(4S) --> pi(+)pi(-)Upsilon(1S)) x BetaUpsilon(1S) --> mu(+)mu(-) = (2.23 +/- 0.25(stat) +/- 0.27(syst))x 10(-6) and Beta(Upsilon(4S) --> pi(+)pi(-)Upsilon(2S) x Beta(Upsilon(2S) --> mu(+)mu(-))=(1.69 +/-0.26(stat) +/- 0.20(syst)) x 10(-)6, from which we derive the partial widths Gamma(Upsilon(4S) --> pi(+)pi(-)Upsilon(1S))=(1.8 +/-0.4) keV and Gamma(Upsilon(4S) --> pi(+)pi(-)Upsilon(2S))=(2.7 +/- 0.8) keV.     

Fixed exciton number level density for a finite potential well

We present a calculation of the nuclear level density _ph(E) for a fixed number of particlesp and holesh, taking into account the energy dependence of the singleparticle level densityg(). We demonstrate the significant effects of the finite depth of the potential well (continuum effect) and the finite surface thickness of the nucleus on the value of _ph(E).Communicated by: X. Campi     

Measurement of the absolute branching fraction of D0-->K-pi+

We measure the absolute branching fraction for D(0)-->K(-)pi(+) using partial reconstruction of B(0)-->D(*+)Xl(-)nu(l) decays, in which only the charged lepton and the pion from the decay D(*+)-->D(0)pi(+) are used. Based on a data sample of 230 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D(0)-->K(-)pi(+)) = (4.007+/-0.037+/-0.072)%, where the first uncertainty is statistical and the second is systematic.     

Mutual inductance bridge for magnetic relaxation measurements at low temperatures

An apparatus using a mutual inductance bridge has been designed to measure real and imaginary parts of the magnetic ac susceptibility simultaneously in the frequency range from 1 Hz to 230 kHz at helium temperatures. From 230 kHz up to 3 MHz the real part can be determined. The susceptibility as a function of temperature or external magnetic field at constant frequency may be measured. In addition, frequency sweeps can be performed with temperature and magnetic field held constant. The experiment is controlled by an on-line computer.