Soft x‐ray techniques to study mesoscale magnetism

Femtosecond pulses from linac-based free-electron lasers are unique tools for future time-resolved experiments. In March 2004, BESSY published the Technical Design Report (TDR) for a free-electron-laser user facility that covers the VUV to soft X-ray range (BESSY FEL) [1 Krämer, D., Jaeschke, E. and Eberhardt, W., eds. 2004. Technical Design Report, Berlin, , Germany: BESSY.  [Google Scholar]]. This second-generation FEL facility is seeded and uses the High-Gain Harmonic-Generation (HGHG) [2 Doyuran, A. 2001. Phys. Rev. Lett., 86: 5902 [Google Scholar]] scheme to produce coherent radiation down to the 1 nm range.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Existence and Uniqueness of Fixed Points for Markov Operators and Markov Processes

This paper concerns a Markov operator T on a space L₁, and aMarkov process P which defines a Markov operator on a spaceM of finite signed measures. For T, the paper presents necessaryand sufficient conditions for:

a the existence of invariant probabilitydensities (IPDs)

b the existence of strictly positive IPDs,and

c the existence and uniqueness of IPDs.

Similar resultson invariant probability measures for P are presented. The basicapproach is to pose a fixed-point problem as the problem ofsolving a certain linear equation in a suitable Banach space,and then obtain necessary and sufficient conditions for thisequation to have a solution. 1991 Mathematics Subject Classification:60J05, 47B65, 47N30.     

库仑加线性位基态解析解

应用新发展的单一轨迹积分方法求解库仑加线性位的基态量子波函数,得到基态能量和波函数的一般解析表达式,并讨论了解的收敛性.应用此方法讨论了重夸克偶素系统.     

Coherent soft X-ray magnetic scattering

X-ray sources are exceptional tools for studying the structure of matter down to atomic-length scales, but across a wide range of fields there are samples that have remained notoriously difficult to study, such as airborne particles, particles in solution, membrane proteins, and macromolecular complexes. The advancement of imaging techniques to address these elusive samples has been a big motivation for constructing new X-ray light sources. Fourth-generation light sources, commonly called X-ray free-electron lasers (XFELs) [1 Madey, J. 1971. Journal of Applied Physics, 42: 1906–1913. [Crossref], [Web of Science ®] , [Google Scholar]], represent a huge step forward, with upwards of nine orders of magnitude increase in peak brightness for hard X-rays. As of 2012, four such XFELs are already productively operational (in Germany [2 Ackermann, W. 2007. Nature Photonics, 1: 336–342. [Crossref], [Web of Science ®] , [Google Scholar]], the U.S. [3 Emma, P. 2010. Nature Photonics, 4: 641–647. [Crossref], [Web of Science ®] , [Google Scholar]], Japan [4 Ishikawa, T. 2012. Nature Photonics, 6: 540–544. [Crossref], [Web of Science ®] , [Google Scholar]], and Italy [5 Allaria, E. 2012. Nature Photonics, 6: 699–704. [Crossref], [Web of Science ®] , [Google Scholar]]), with at least five more planned for the next 10 years. These lasers produce femtosecond pulses of extremely intense coherent radiation through the positive feedback between a co-moving electron bunch and the radiation it emits when they traverse an extended undulator. This process creates remarkably strong, tunable probes that will undoubtedly change the way we examine nanoscale structure and dynamics.     

Resonant soft x‐ray scattering and reflectivity study of the phase‐separated structure of thin poly(styrene‐b‐methyl methacrylate) films

Combined soft X‐ray scattering and reflectometry techniques promise analysis of polymer thin film domain structure and composition without resorting to chemical modification or isotopic labeling. This work explores the capabilities of these techniques in polymer films of poly(styrene‐b‐methyl methacrylate) (P(S‐b‐MMA)). The results demonstrate that the techniques give detailed information on the domain structure of thin films using well‐known modeling procedures. Discrepancies were noted between the X‐ray optical parameters that are needed to best fit the reflectivity data to the model and the expected parameters. The sources of these discrepancies are discussed in terms of instrument configuration parameters, sample attributes, and, particularly, anisotropy of the chromophore parameters. The results show that fitting the soft X‐ray reflectivity data is much more sensitive to these X‐ray optical parameters than the soft X‐ray scattering data. Nevertheless, fits to both types of data yield quantitative measures of the polymer film's lamellar morphology that are consistent with each other and with literature values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Advances in nanomagnetism via X-ray techniques

This report examines the current status and the future directions of the field of nanomagnetism and assesses the ability of hard X-ray synchrotron facilities to provide new capabilities for making advances in this field. The report first identifies major research challenges that lie ahead in three broadly defined subfields of nanomagnetism: confined systems, clusters and complex oxides. It then examines the relevant experimental capabilities that are currently available at hard X-ray synchrotron light sources, using the Advanced Photon Source (APS) at Argonne as an example. Finally, recommendations are made for future development in X-ray facilities that will enhance the study of nanomagnetism, including new experimental directions, modifications that would enable in situ sample preparation, and measurements at high magnetic fields and/or low temperatures. In particular, in situ sample preparation is of high priority in many experiments, especially those in the area of surface magnetism.