Efficient generation of a photon pair in a bulk periodically poled potassium titanyl phosphate

In this report, we demonstrate the efficient generation of collinearly propagating photon pairs in a bulk periodically poled potassium titanyl phosphate pumped by a cw laser. The detected coincidence counts are more than 7400/s with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW. This is very promising for some applications, such as quantum key distribution, proof of the Bell-inequality, preparation of single photon states in broadband wave packets, Franson-type interference and so on.     

Observation of two resonant structures in e+ e- -->pi+ pi- psi(2S) via initial-state radiation at Belle

The cross section for e+ e- --> pi+ pi- psi(2S) between threshold and sqrt[s]=5.5 GeV is measured using 673 fb(-1) of data on and off the Upsilon(4S) resonance collected with the Belle detector at KEKB. Two resonant structures are observed in the pi+ pi- psi(2S) invariant-mass distribution, one at 4361 +/- 9 +/- 9 MeV/c2 with a width of 74 +/- 15 +/- 10 MeV/c2, and another at 4664 +/- 11 +/- 5 MeV/c2 with a width of 48 +/- 15 +/- 3 MeV/c2, if the mass spectrum is parametrized with the coherent sum of two Breit-Wigner functions. These values do not match those of any of the known charmonium states.     

Complete suppression of metastable phase and significant enhancement of magnetic properties of B-rich PrFeB nanocomposites prepared by devitrifying amorphous ribbons

The effect of refractory element addition on phase transformation, crystallization behavior and magnetic properties of Pr_8.5Fe_81.5B₁₀ (addition-free) and Pr_8.5Fe_81.5M₂B₁₀ (M=V, Cr, Nb, Zr, Ti) ribbons has been investigated. The annealed addition-free ribbon as well as the samples with V or Cr additions are mainly composed of the metastable Pr₂Fe₂₃B₃ phase, whereas annealed ribbons with Nb, Zr or Ti additions primarily consist of Pr₂Fe₁₄B and a minor amount of Fe₃B/boride. The complete suppression of the metastable Pr₂Fe₂₃B₃ phase due to Nb, Zr or Ti additions leads to a significant enhancement of the magnetic properties. For example, the remanence, the coercivity and the energy product are remarkably increased from 2.5 kG, 0.4 kOe and 0.2 MG Oe for the addition-free material to 9.2 kG, 4.7 kOe and 7.6 MG Oe for the specimens with Nb addition. The successful elimination of the metastable Pr₂Fe₂₃B₃ phase is believed to profit from two factors: (a) Nb, Zr or Ti atoms substitute the Pr site, comparatively increase the Pr content, and thus inhibit the nucleation of Pr-lean Pr₂Fe₂₃B₃ phases, and (b) the formation of Nb, Zr, or Ti borides consumes some part of B, which hinders the generation of the B-rich Pr₂Fe₂₃B₃ phase.     

Study of decay mechanisms in B--->Lambdac+ppi- decays and observation of low-mass structure in the Lambdac+p system

Using a sample of 152 x 10(6) BB pairs accumulated with the Belle detector at the KEKB e+e- collider, we study the decay mechanism of three-body charmed decay B- --> Lambdac+ ppi-. The intermediate two-body decay B--->Sigmac (2455)0 p is observed for the first time with a branching fraction of (3.7 +/- 0.7 +/- 0.4 +/- 1.0) x 10(-5) and a statistical significance of 8.4sigma. We also observe a low-mass enhancement in the (Lambdac+p) system, which can be parametrized as a Breit-Wigner function with a mass of (3.35(-0.02)(+0.01) +/-0.02) GeV/c2 and a width of (0.07(-0.03)(+0.04) +/-0.04) GeV/c2. We measure its branching fraction to be (3.9(-0.7)(+0.8) +/- 0.4 +/- 1.0) x 10(-5) with a statistical significance of 6.2sigma. The errors are statistical, systematic, and that of the Lambdac+-->pK- pi+ decay branching fraction.     

Single-element objective lens for soft x-ray differential interference contrast microscopy

High-resolution soft x-ray differential interference contrast (DIC) imaging was demonstrated through the use of a single-element objective, the XOR pattern, in a full-field soft x-ray microscope. DIC images of the magnetic domains in a 59 nm thick amorphous Gd25Fe75 layer were obtained and magnetic phase contributions were directly imaged. With its elemental, chemical, and magnetic specificity, compatibility with various sample environments, and ease of implementation, we expect this soft x-ray DIC technique to become one of the standard modes of operation for existing full-field soft x-ray microscopes.     

Improved constraints on D0-D0 mixing in D0 --> K+ pi- decays from the Belle detector

We report the results of a search for D0-D0 mixing in D0 --> K+ pi- decays based on 400 fb(-1) of data accumulated by the Belle detector at KEKB. Both assuming CP conservation and allowing for CP violation, we fit the decay-time distribution for the mixing parameters x and y, as well as for the parameter R(D), the ratio of doubly Cabibbo-suppressed decays to Cabibbo-favored decays. The 95% confidence level region in the (x'2,y') plane is obtained using a frequentist method. Assuming CP conservation, we find x'2 < 0.72 x 10(-3) and -9.9 x 10(-3) < y' < 6.8 x 10(-3) at the 95% confidence level; these are the most stringent constraints on the mixing parameters to date. The no-mixing point (0,0) has a confidence level of 3.9%. Assuming no mixing, we measure R(D) = (0.377 +/- 0.008 +/- 0.005)%.     

利用紫外Mie散射激光雷达探测澳门地区沙尘暴事件

研制了一台工作波长为355nm的紫外高能Mie散射激光雷达,并利用该激光雷达在2010年一次沙尘暴事件期间对澳门上空的大气进行了探测,得到了澳门地区不同时刻的气溶胶消光系数垂直廓线。利用Fernald方法反演得到的气溶胶近地面消光系数随时间的变化与当地气象数据具有较好的一致性,气溶胶消光系数与当地可吸入颗粒物浓度的相关性达到了0.93。气溶胶垂直廓线显示,在沙尘暴来临期间存在明显的沙尘气溶胶凝集层。通过气溶胶轨迹倒推,分析了沙尘气溶胶的来源及路径。观测结果表明,该激光雷达可以在特殊天气条件下对澳门地区气溶胶进行有效探测,这将有助于深化对澳门上空气溶胶特性的研究。     

Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray diffraction

Strong resonant enhancements of the charge-order and spin-order superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The pronounced photon-energy and polarization dependences of these diffraction intensities allow for a critical determination of the local symmetry of the ordered spin and charge carriers. We found that not only the antiferromagnetic order but also the charge-order superstructure resides within the NiO2 layers; the holes are mainly located on in-plane oxygens surrounding a Ni2+ site with the spins coupled antiparallel in close analogy to Zhang-Rice singlets in the cuprates.     

Temperature dependence of protein backbone motion from carbonyl 13C and amide 15N NMR relaxation

The NMR spin-lattice relaxation rate (R1) and the rotating-frame spin-lattice relaxation rate (R1rho) of amide 15N and carbonyl 13C (13C') of the uniformly 13C- and 15N-labeled ubiquitin were measured at different temperatures and field strengths to investigate the temperature dependence of overall rotational diffusion and local backbone motion. Correlation between the order parameter of the N-H vector, SNH2, and that of the carbonyl carbon, S2C', was investigated. The effective S2C' was estimated from the direct fit of the experimental relaxation rates and from the slope of 2R2-R1 vs. B2 using Lipari-Szabo formalism. The average SNH2 decreased by 5.9%, while the average S2C' decreased by 4.6% from 15 to 47 degrees C. At the extreme low and high temperatures the difference in the temperature dependence of the order parameters vanishes. At the intermediate temperatures they do not change by the same amount but they follow the same trend. On the same peptide plane along the protein sequence, S2C' and SNH2 are highly correlated. The results suggest that fast local motion experienced at the site of the N-H vector and carbonyl nucleus is more complicated than previously thought and it cannot be easily described by one single type of motion in a broad range of temperature.     

Multipeak fitting analysis of Raman spectra on DLCH film

The hydrogenated diamond‐like carbon (DLCH) film with 1‐µm thickness is deposited by direct hydrocarbon gas ion beam method on silicon wafer and annealed at 400 °C. Detailed Raman spectra feature are fitted from nine sets of different peak fitting functions, including Gaussian, Lorentzian and Breit‐Wigner‐Fano (BWF) functions. These fitting results obtained from a two‐peak combination show some specific variances on the G peak position, FWHM_G and I_D/I_G ratio for as‐deposited and as‐annealed DLCH films. The most popular two‐peak fitting method with full Gaussian function tends to exhibit a higher ratio of the G peak position shift and higher I_D/I_G ratio than others fitting methods, the drastic difference among the most popular G (G) & G (D) and B (G) & L (D) schemes also have brought out in I_D/I_G ratio. However, for a more complex four‐peak Gaussian function fitting Raman spectra, the I_D/I_G ratio is close to that of a two‐peak fitting function with a mixture functions of BWF (G) and L (D). Furthermore, a series of systematic peak fitting procedures and comparisons of Raman spectra have been discussed in this study. Copyright © 2009 John Wiley & Sons, Ltd.