多光束共振光压作用下钠原子束的偏转

本文报道了多光束共振光压作用下钠原子束偏转的实验研究结果。文中提出了用多光束与原子束相互作用以增大原子束的偏转量,并可大大降低对激光功率的要求。用一台染料激光器照射钠原子束得到1×10^-2rad的偏转角,偏转距离约7.2mm,并用激光诱导原子束荧光的方法检测原子束的偏转。     

Mössbauer study of magnetic ordering in57Co-doped Eu2CuO4 and Gd2CuO4

Zeeman splitting of Mossbauer spectra of⁵⁷Co doped into Eu₂CuO₄ and Gd₂CuO₄ indicates magnetic ordering of Cu moments for temperatures below about 150 K in Eu₂CuO₄ and below about 200 K in Gd₂CuO₄. Supported by NASA Grant NAG 3-847     

Astrophysical S-factors from asymptotic normalization coefficients

S-factors for direct capture reactions can be found at astrophysical energies from asymptotic normalization coefficients which provide the normalization of the tail of the overlap function. For example the overlap for ⁸B → ⁷Be+p defines the S-factor for ⁷Be (p, γ)⁸B. Peripheral transfer reactions offer a technique to determine these asymptotic normalization coefficients. As a test of the technique, the ¹⁶O(³He, d)¹⁷F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ¹⁷F. The S-factors for ¹⁶O(p, γ)¹⁷F calculated from these ¹⁷F → ¹⁶O+p asymptotic normalization coefficients are found to be in very good agreement with recent measurements. Following the same technique, the ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the asymptotic normalization coefficient for ⁷Be(p, γ)⁸B. This result provides an indirect determination of S ₁₇(0).     

Preparation of nanocrystalline metal hydrides by ball milling

The diffusion of hydrogen into metals during ball milling has been investigated. A system is described that enables the milling to be done under approximately constant hydrogen pressure and allows for the continuous measurement of the quantity of hydrogen absorbed. This method has been used to prepare nanocrystalline hydrides of a variety of early transition metals and alloys. X-ray diffraction studies are used to identify phases present before and after milling and the width of diffraction peaks is used to estimate average grain size. Changes in the microstructure of Fe-containing samples during hydrogen absorption have been investigated by Mössbauer effect. Studies of the influence of milling conditions and the effect of milling time are also presented.     

pH-responsive aggregates from double hydrophilic block copolymers carrying zwitterionic groups. Encapsulation of antiparasitic compounds for the treatment of leishmaniasis

A series of well-defined poly[(ethylene oxide)-b-2-(dimethylamino)ethyl methacrylate] (PEO-b-PDMAEMA) diblock copolymers were synthesized by atom transfer radical polymerization (ATRP) techniques. Post-polymerization reactions were performed to transform a portion of the tertiary amine groups of the PDMAEpsilonMA into phosphorozwitterions. The aggregation behavior of the prepared zwitterionic block copolymers was investigated by static and dynamic light scattering techniques at 25 and 37 degrees C, in weakly basic and acidic aqueous solutions. Antiparasitic drugs used for the treatment of Leishmania were incorporated into the copolymer aggregates. The effect of the solution pH, the zwitterion content, temperature, and the quantity of the incorporated drug on the aggregation behavior of the copolymers was tested.     

Symmetry and ferromagnetic clusters

Isomers of pure Fe₁₃ and icosahedral Fe₁₂X clusters are studied using the all-electron linear-combination-of-Gaussian-type-orbital (LCGTO) local-density-functional (LDF) methods that allow the spin and geometry of the cluster to be determined self-consistently. The Fe₁₃ ground state is icosahedral. The icosahedral cluster also has the greatest magnetic moment because of increased symmetry-required orbital degeneracy for electrons of different spins. The central atom of the icosahedral iron cluster has been varied to optimize the spin of the cluster keeping the oribital contribution to the magnetic moment quenched. Varying the central atom under this constraint can alter the magnetic moment by more than 20%. Similar studies have begun on 55-atom icosahedral iron clusters.     

Tethered particle motion as a diagnostic of DNA tether length

The tethered particle motion (TPM) technique involves an analysis of the Brownian motion of a bead tethered to a slide by a single DNA molecule. We describe an improved experimental protocol with which to form the tethers, an algorithm for analyzing bead motion visualized using differential interference contrast microscopy, and a physical model with which we have successfully simulated such DNA tethers. Both experiment and theory show that the statistics of the bead motion are quite different from those of a free semiflexible polymer. Our experimental data for chain extension versus tether length fit our model over a range of tether lengths from 109 to 3477 base pairs, using a value for the DNA persistence length that is consistent with those obtained under similar solution conditions by other methods. Moreover, we present the first experimental determination of the full probability distribution function of bead displacements and find excellent agreement with our theoretical prediction. Our results show that TPM is a useful tool for monitoring large conformational changes such as DNA looping.