囚禁离子与调制热库相互作用时的退相干特征

解析地分析了在囚禁离子中由热库导致量子退相干的控制问题,提出了一个基于热库调制的抑制退相干的一般方法.热库的调制可利用外加的光场与离子相互作用来实现.应用这个方法,适当地选择热库调制参数,可以有效消除量子退相干.计算表明:在高的调制频率下,用这个机制来抑制退相干的效果与宇称激励机制相似.宇称激励机制不仅要求外场是±π脉冲而且要求脉冲既快又强,而热库调制机制仅要求外场频率足够高,因此,热库调制机制优于宇称激励机制.     

355 nm激光作用下质子化丙酮-水团簇的多光子电离质谱

为研究由氢键形成的超分子体系内的质子化构型,利用355 nm多光子电离(MPI)技术结合飞行时间质谱（TOF-MS）得到丙酮和水的系列团簇质谱.实验观察到的主要产物是质子化的丙酮水团簇.其团簇构型归纳为(CH3COCH3)n(H2O)n－2H+,(CH3COCH3)n(H2O)n－1H+和(CH3COCH3)n(H2O)nH+.利用Gaussian 98程序优化了团簇的离子态构型,通过频率验证了构型的稳定性,并给出了相关能量和零点修正能.     

Trapping mechanism of superconductivity suppression induced by Pr substitution in the Ho1−xPrxBa2Cu3O7−δ system

Pr concentration dependence of the superconducting transition temperature T_c in the Ho_1−xPr_xBa₂Cu₃O_7−δ system is determined from measurements of DC electrical resistance. This dependence coincides with that for the parallely studied Y_1−xPr_xBa₂Cu₃O_7−δ reference system. Both systems have the same value of the critical concentration x_c=0.58, in accordance with nearly equal ionic radii of Ho³⁺ and Y³⁺ ions. It has been shown that the T_c(x) curve can be described with a single mechanism based on a decreasing number of sheet holes trapped by Pr^IV-ions, if one takes also into account that the number of these ions changes with x.     

Residual water suppression by indirect covariance NMR

Residual water solvent signals in 2D NMR experiments adversely affect appearance and subsequent analysis of spectra. A method for water suppression that is based on indirect covariance processing is described. It produces a symmetric spectrum with a water signal that is substantially decreased or completely absent. The method, which can be combined with other water suppression schemes, is demonstrated for 2D TOCSY, NOESY, and ROESY spectra of the protein, ubiquitin in aqueous solution.     

STUDIES ON THE CELL PHENOTYPE CHARACTERISTICS OF HYBRID CELLS CROSSED BETWEEN RAT NUCLEATED ERYTHROBLASTS AND MOUSE PLASMOCYTOMA (SP~2/O) CELL LINE

The present study is designed to investigate the regulatory effect of mammalian erythroblasts, prior to naturally-occurring denucleation, on malignancy of mouse plasmocytoma cells and the possibility of reactivation of the pyknotic late erythroblast nuclei in hybrid cells crossed between rat intermediate or late erythroblasts of 15-day Wistar rat embryonic livers, and mouse plasmocytoma (SP~2/O) cell lines. Results indicated that:(ⅰ) Suppression of tumorigenicity and reversion of the malignant phenotype were observed in hybrid cells in a similar way as those of cybrid cells crossed between reticulocytes and myeloma cells as we reported previously, thus providing further evidence to support the hypothesis that some regulatory substances already existed in mammalian intermediate and late erythroblasts long before nuclear extrusion. (ⅱ) Appearance of positive histochemical reaction for hemoglobins in cytoplasm and electrophoretic bands of rat and mouse globin chains in hybrid cell lysate were i. The tran     

Amplification of noble gas ion lines in the afterglow of a pulsed hollow cathode discharge and possible benefit for analytical glow discharge mass spectrometry

A high-current pulsed hollow cathode discharge was used to study the role of atomic and ionic metastables involved in ionization plasma processes. We observed the enhancement of the spectral emission lines of noble gas ions in the afterglow. A study of the processes that involve atomic and ionic metastables is of great interest since it should lead to a better understanding of and enhanced control over the ionization mechanisms crucial to analytical glow discharge mass spectrometry (GDMS) analysis. Figure Time profile of Ti, Ti⁺, and Ne⁺ spectral lines     

Biophysical approaches to G protein-coupled receptors: Structure, function and dynamics

G protein-coupled receptors (GPCR) represent a large family of drug targets for which there is no high-resolution structural information. In order to understand the mechanisms of ligand recognition and receptor activation, there is a strong need for novel biophysical methods. In this Perspective we provide an overview of recent experimental approaches used to explore the molecular architecture and dynamics of GPCR and their interactions with ligands and G proteins using biophysical, non-crystallographic, methods.     

Ionization equilibrium in the electron-proton gas

Using Fefferman's analysis of the quantum electron-proton gas, we give a rigorous proof of ionization equilibrium in this system. Ionization equilibrium phases are obtained as low-density and low-temperature limits, letting the chemical potential(T) approach the ground-state energy of the hydrogen atom as the temperatureT tends to zero. The rate of ionization is determined by the slope of(T) atT=0 and is correctly given by the Saha formula. We also discuss a simpler model where a single quantum particle interacts with a classical gas of hard spheres.     

The ionization of trichloroacetic acid and evidence for an unusual type of ion pairing

Osmotic and activity coefficients are reported for aqueous solutions of the lithium and potassium salts of iodic acid and trichloroacetic acid. The degree of ionization of the parent acids at various concentrations was estimated from ion exchange measurements, and these values were compared with those obtained from Raman measurements. It was concluded that one obtains comparable values of α, the degree of dissociation, of iodic acid whether these are estimated from hydrogen ion concentrations or anion concentrations. Lack of agreement between like measurements of α for trichloroacetic acid leads to the postulation of an unusual ion pair in which the proton is strongly associated with the chlorine end of the anion. A similar type of ion pairing is suggested in solutions of the aromatic sulfonic acids.