Quantum dynamics of ultracold Na+ Na2 collisions

Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na2 molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations are carried out on both pairwise additive and nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws are followed for energies below 10(-5) K. Vibrational relaxation processes dominate elastic processes for temperatures below 10(-3)-10(-4) K. For temperatures below 10(-5) K, the rate coefficients for vibrational relaxation (v=1-->0) are 4.8x10(-11) and 5.2x10(-10) cm(3) s(-1) for the additive and nonadditive potentials, respectively. The large difference emphasizes the importance of using accurate potential energy surfaces for such calculations.     

Fluctuations and stability of superfluid turbulence at mK temperatures

Turbulent flow of superfluid 4He at mK temperatures around an oscillating microsphere is known to be unstable at low driving forces, switching intermittently between turbulent and laminar phases. The lifetimes of the turbulent phases are exponentially distributed, and the mean lifetimes grow exponentially with the square of the driving force. These experimental results are attributed to statistical fluctuations of the density L of the vortex line length. As a result, a normal probability distribution of L2 is found having a standard deviation of 2.9 x 10(14) m(-4) and a spectral bandwidth Deltaomega approximately 13 s(-1).     

Test of the equivalence principle using a rotating torsion balance

We used a continuously rotating torsion balance instrument to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result Deltaa(N),(Be-Ti)=(0.6+/-3.1)x10(-15) m/s2 improves limits on equivalence-principle violations with ranges from 1 m to infinity by an order of magnitude. The E?tv?s parameter is eta(Earth,Be-Ti)=(0.3+/-1.8)x10(-13). By analyzing our data for accelerations towards the center of the Milky Way we find equal attractions of Be and Ti towards galactic dark matter, yielding eta(DM,Be-Ti)=(-4+/-7)x10(-5). Space-fixed differential accelerations in any direction are limited to less than 8.8x10(-15) m/s2 with 95% confidence.     

Collisions between metastable hydrogen atoms at thermal energies

The complex interaction potentials arising in the approach of two metastable hydrogen 2s atoms are calculated and the cross sections for ionization, excitation transfer, and elastic scattering are predicted. The measured cross section for associative ionization at E = 4.1 meV equals 2x10(-15) cm (2). We calculate a total ionization cross section of 2x10(-13) cm (2), varying as E(-2/3) at higher energies. Thus it appears that dissociative ionization is the major ionization channel. We find also that double excitation transfer into two excited H(2p) atoms is still more probable with the large cross section of 9x10(-12) cm (2) at E = 4.1 meV varying as E(-1/2) at higher energies. The detection of the resulting Lyman alpha photons would provide a diagnostic test of our predictions.     

Intense high-energy proton beams from Petawatt-laser irradiation of solids

An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.     

Sensitive detection of cold cesium molecules formed on Feshbach resonances

We observe the dynamic formation of quasibound Cs2 molecules near Feshbach resonances in a cold sample of atomic cesium. Using an external probe beam, more than 15 weakly coupled molecular states are detected with high sensitivity, whose collisional formation cross sections are as small as sigma=2 x 10(-16) cm(2). By modeling the molecule formation and dissociation processes with rate equations, we conclude that at an atomic density of 10(13) cm(-3) and temperature of 5 microK, more than 5(1)x10(5) Cs2 molecules in a single rovibrational state coexist with 10(8) Cs atoms in our trap.     

Self-diffusion in core-shell composite 12CO2/13CO2 nanoparticles

A new technique for the generation of multilayered molecular nanoparticles is presented. Core-shell composite nanoparticles of CO(2) with varied composition have been investigated by Fourier-transform infrared spectroscopy over 600 s at 78 K. The isotopically different zones of the particles turned out to have completely different spectra in the nu(3) region: a tub structure (mantle) and a head-and-shoulders structure (core). From the aggregation behavior of both components the particle formation time was found to be 0.1 s. Low-temperature self-diffusion of airborne molecular nanoparticles has been monitored for the first time. The self-diffusion coefficient for (12)CO(2)/(13)CO2 nanocomposites at 78 K was determined from the time evolution of the nu(1) + nu(3) combination band to about 7 x 10(-20) m(2)/s. The work represents a major advance toward nanoengineering of molecular nanoparticles at low temperatures.     

Ultrashort-pulse laser ellipsometric pump-probe experiments on gold targets

Ultrashort-pulse laser pump-probe ellipsometry has been performed on gold targets at intensities 2 x 10(12)-5 x 10(13) W/cm(2). We measured time-resolved p- and s-polarized reflectivity (r(p) and r(s)) and the s-p phase difference (delta). When plotted as Y=[2|r(s)||r(p)|sin((delta)]/(|r(s)|(2)+|r(p)|(2)) versus X=|r(p)|(2)/|r(s)|(2), the experimental data follow approximately the same curve in X-Y space, even for different pump intensities. Although the input energy density is about 40 eV/atom and the plasma expansion is rapid (up to 10 km/sec), our data are consistent with a partially transparent blowoff having an atomic polarizability (-1.75+0.2i)x 10(-24) cm(3). We attribute this behavior to recombination in the expanding plasma. The Saha equation predicts recombination and formation of negative ions and a low density of free electrons in the low-density vapor, and solutions of the Maxwell equations approximately reproduce the data.     

Rb(5PJ)与He,N2的碰撞精细结构混合和猝灭

在气体样品池条件下,研究了Rb(5PJ) (He,N2)碰撞能量转移过程.用调频半导体激光器激发Rb原子至Rb(5P3/2)态,在不同的He或N2气压下,测量了直接5P3/2→5S1/2荧光和转移5P1/2→5S1/2荧光.对于Rb(5PJ)与He的碰撞,只发生精细结构转移(略去碰撞猝灭效应),电子态能量仅能转移为He原子的平动能.在与N2的碰撞中,向分子振转态的转移是重要的.本实验中,Rb的密度为4.5×1011 cm-3,由辐射陷获理论得到5P1/2→5S1/2的有效辐射率为2.47×107 s-1.利用速率方程分析,可以得到碰撞转移速率系数,对于He,5P3/2→5S1/2转移速率系数kHe21=2.61×10 12 cm3·s.对于N2,测量5PJ He和5PJ N2两种情况下直接荧光与敏化荧光的相对强度比,利用最小二乘法确定5Pa/2→5S1/2转移速率系数kN212=2.36×10-11 cm3·s,5PJ态猝灭速率系数kN2=1.44×10-11 cm3·s-1.由实验结果证实了Cs-N2主要是直线式碰撞传能机制,与其他实验结果进行了比较.     

2—溴甲基萘荧光和室温磷光性质研究

研究了２－溴甲基萘（２－ＢｒＭＮ）的荧光及磷光性质。２－溴甲基萘是一种优良的荧光试剂,λｅｘ／λｅｍ＝２７４／３３４ｎｍ,其浓度在１．０×１０＾－６～１．２×１０＾－４ｍｏｌ·Ｌ＾－１范围内与荧光强度呈良好的线性关系,相关系数ｒ＝０．９９９,最低检测限为４．７×１０＾－８ｍｏｌ·Ｌ＾－１。以β－环糊精（β－ＣＤ）作保护剂和１,２－二溴丙烷（ＤＢＰ）为重原子微扰剂的２－ＢｒＭＮ／β－ＣＤ／ＤＢＰ体系     

Search for electron neutrino appearance in a 250 km long-baseline experiment

We present a search for electron neutrino appearance from accelerator-produced muon neutrinos in the K2K long-baseline neutrino experiment. One candidate event is found in the data corresponding to an exposure of 4.8 x 10(19) protons on target. The expected background in the absence of neutrino oscillations is estimated to be 2.4+/-0.6 events and is dominated by misidentification of events from neutral current pi(0) production. We exclude the nu(micro) to nu(e) oscillations at 90% C.L. for the effective mixing angle in the 2-flavor approximation of sin((2)2theta(microe)( approximately 1/2sin((2)2theta(13))>0.15 at Deltam(2)(microe)=2.8 x 10(-3) eV(2), the best-fit value of the nu(micro) disappearance analysis in K2K. The most stringent limit of sin((2)2theta(microe)<0.09 is obtained at Deltam(2)(microe)=6 x 10(-3) eV(2).     

Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with T(c)?≈?45?K

We report on a new iron selenide superconductor with a T(c) onset of 45?K and the nominal composition Li(x)(C(5)H(5)N)(y)Fe(2-z)Se(2), synthesized via intercalation of dissolved alkaline metal in anhydrous pyridine at room temperature. This superconductor exhibits a broad transition, reaching zero resistance at 10?K. Magnetization measurements reveal a superconducting shielding fraction of approximately 30%. Analogous phases intercalated with Na, K and Rb were also synthesized and characterized. The superconducting transition temperature of Li(x)(C(5)H(5)N)(y)Fe(2-z)Se(2) is clearly enhanced in comparison to those of the known superconductors FeSe(0.98) (T(c)?～?8?K) and A(x)Fe(2-y)Se(2) (T(c)?～?27-32?K) and is in close agreement with critical temperatures recently reported for Li(x)(NH(3))(y)Fe(2-z)Se(2). Post-annealing of intercalated material (Li(x)(C(5)H(5)N)(y)Fe(2-z)Se(2)) at elevated temperatures drastically enlarges the c-parameter of the unit cell (～44%) and increases the superconducting shielding fraction to nearly 100%. Our findings indicate a new synthesis route leading to possibly even higher critical temperatures for materials in this class: by intercalation of organic compounds between Fe-Se layers.     

双水相体系中食用色素与蛋白质作用光谱行为研究

在聚乙二醇-2000(PEG)-硫酸铵-食用色素双水相体系中,研究了PEG相中食用色素与蛋白质复合物光谱行为。实验了溶液酸度,盐浓度,PEG用量,反应时间,反应温度,共存物质等对体系测定的影响。结果表明,在pH 8的缓冲溶液条件下,樱桃红(BS)与人血清白蛋白(HSA)复合物的最大吸收在541 nm处,比单纯樱桃红红移13 nm,复合物表观摩尔吸光系数为9.4×104 L·mol-1·cm-1,用摩尔比法求得最大结合数为40,蛋白质浓度在0～21.07 mg·L-1范围内具有线性关系。用加入不同类型表面活性剂方法,探讨了食用色素樱桃红与蛋白质之间的作用机理。     

Proton relaxation NMR study of polycrystalline progesterone.

Polycrystalline progesterone (4-pregnene-3,20-dione, C21H30O2) has been investigated by proton NMR methods between 80 and 350 K. A reduction in dipolar second moment is ascribed to methyl group reorientation. Minima in the spin-lattice relaxation time found in measurements at five frequencies from 7 to 200 MHz are attributed to reorientation of two of the three methyl groups in each molecule, characterized by activation energy Ea = 10.9 +/- 0.8 kJ/mol and tau o = (2.3 +/- 0.2) x 10(-13) s. Additional relaxation at lower temperatures is attributed to reorientation of the third methyl group with Ea approximately 3.4 kJ/mol. Measurements were also made of relaxation in the rotating frame.     

Ideal laser-beam propagation through high-temperature ignition Hohlraum plasmas

We demonstrate that a blue (3omega, 351 nm) laser beam with an intensity of 2 x 10(15) W cm(-2) propagates nearly within the original beam cone through a millimeter scale, T(e)=3.5 keV high density (n(e)=5 x 10(20) cm(-3)) plasma. The beam produced less than 1% total backscatter at these high temperatures and densities; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.     

Enhanced electric dipole moment of the muon in the presence of large neutrino mixing

The electric dipole moment (edm) of the muon ( d(e)(&mgr;)) is evaluated in supersymmetric models with nonzero neutrino masses and large neutrino mixing arising from the seesaw mechanism. It is found that if the seesaw mechanism is embedded in the framework of a left-right symmetric gauge structure, the interactions responsible for the right-handed neutrino Majorana masses lead to an enhancement in d(e)(&mgr;) to values as large as 5x10(-23)e cm, with a correlated value of (g-2)(&mgr;) approximately 13x10(-10). This should provide a strong motivation for improving the edm of the muon to the level of 10(-24)e cm as has recently been proposed.     

Highly efficient third-order optical nonlinearities in donor-substituted cyanoethynylethene molecules

We investigated the third-order nonlinear optical properties of several donor-substituted cyanoethynylethene molecules in the zero-frequency limit. We observed nonlinearities that are extraordinarily large relative to the small molecular mass of these molecules and that are within a factor of 50 from the fundamental limit. At a wavelength of 1.5 microm, the rotational average of the third-order molecular polarizability is 53 +/- 13 x 10(-48) m5 V(-2) (3.8 x 10(-33) esu) for the best molecule, which corresponds to 1.7 x 10(-48) m5 V(-2) per delocalized electron. The high nonlinear efficiency of these molecules is due to the compact two-dimensional conjugated system and the effective donor-acceptor substitution patterns.     

Forward-backward asymmetries of lepton pairs in events with a large-transverse-momentum jet at hadron colliders

We discuss forward-backward charge asymmetries for lepton-pair production in association with a large-transverse-momentum jet at hadron colliders. The lepton charge asymmetry relative to the jet direction A(j)(FB) gives a new determination of the effective weak mixing angle sin((2)theta(lept)(eff)(M(2)(Z)) with a statistical precision after cuts of approximately 10(-3) (8x10(-3)) at LHC (Tevatron). This is to be compared with the current uncertainty at LEP and SLD from the asymmetries alone, 2x10(-4). The identification of b jets also allows for the measurement of the bottom-quark-Z asymmetry A(b)(FB) at hadron colliders, the resulting statistical precision for sin((2)theta(lept)(eff)(M(2)(Z)) being approximately 9x10(-4) (2x10(-2) at Tevatron), also lower than the reported precision at e(+)e(-) colliders, 3x10(-4).     

甲基麝香草酚兰-Mn(Ⅱ)-H2O2催化体系测定痕量锰

硼砂-氢氧化钠缓冲介质中利用锰(Ⅱ)催化过氧化氢氧化甲基麝香草酚兰褪色为指示反应, 建立了测定锰的动力学光度新方法. 方法的测定范围是0.20～40.00 μg·L-1, 表观活化能E=73.24 kJ·mol-1,表观速率常数k=5.62×10-4·s-1, 方法检出限为6.4×10-10 g·mL-1. 结合离子交换分离用于蒙药样品中痕量锰的测定, 结果满意.     

Absolute frequency measurement of a 1.5-microm acetylene standard by use of a combined frequency chain and femtosecond comb

We have developed and characterized a pair of Doppler-free acetylene-stabilized diode laser frequency standards as optical communications references. The Allan deviation sigma/f of an individual system reaches a minimum of 4 x 10(-14) at a sampling time of 5000 s, and the long-term lock-point repeatability is found to be 0.4 kHz (one standard uncertainty), corresponding to a fractional uncertainty of 2 x 10(-12). Using a combination of a frequency chain and a self-referenced femtosecond comb, we have measured the frequency of line P(16) of the v1 + v3 overtone band of 13C2H2 to be 194,369,569,385.9 (3.0) kHz. The uncertainty of this number is limited solely by the reproducibility of the standards.