Boundary Scattering,Symmetric Spaces and the Principal Chiral Model on the Half-Line

We investigate integrable boundary conditions (BCs) for the principal chiral model on the half-line, and rational solutions of the boundary Yang-Baxter equation (BYBE). In each case we find a connection with (type I, Riemannian, globally) symmetric spaces G/H: there is a class of integrable BCs in which the boundary field is restricted to lie in a coset of H; these BCs are parametrized by G/H×G/H; there are rational solutions of the BYBE in the defining representations of all classical G parametrized by G/H; and using these we propose boundary S-matrices for the principal chiral model, parametrized by G/H×G/H, which correspond to our boundary conditions.An erratum to this article can be found at     

Evidence for large gap anisotropy in superconducting Pb from phonon imaging

We report the first ballistic phonon images of superconducting Pb. Unusual absorption lines are observed for phonon wave vectors in 111 planes. We show that a highly anisotropic energy gap can lead to sharply defined directions of phonon attenuation. Overhauser and Daemen [Phys. Rev. Lett. 61, 1885 (1988)] postulated a spin-density-wave ground state for Pb that leads to directions of strongly reduced gap. By applying their idea to the actual Fermi surface of Pb, we predict phonon attenuation directions consistent with the data.     

Generating an adaptive multiresolution image analysis with compact cupolets

We present an efficient control scheme for stabilizing unstable periodic orbits of chaotic systems. The resulting orbits are called cupolets and have been proven to be useful in the representation of oscillatory or quasi periodic signals such as appear in music and image compression (Short et al., AES 118th Convention preprint 6446, May 2005; Short et al., AES 119th Convention preprint 6588, October 2005). In this paper we show that these cupolets can be used effectively to produce an adaptive basis for the space of real-valued functions of a discrete variable. From this basis, we construct a multiresolution analysis which allows for the approximation of signals at different resolution levels and apply it to image compression. This adaptive multiresolution analysis provides an interesting continuum between Fourier analysis and wavelet analysis.     

Charge compensation for imaging large insulating samples by using secondary ion tandem mass spectrometry

A charge compensation technique has been developed for secondary ion mass spectrometry and imaging of insulating samples as large as 1 cm² using a triple quadrupole-based microprobe. The microprobe secondary ion extraction field is synchronized with a periodic primary Cs⁺ beam to allow a sheetlike beam of 5-eV electrons to pass over the sample surface when the extraction field is zeroed. Electrons are attracted to, and neutralize, any points on the sample that have accumulated positive charge. Positive secondary ion images from Teflon®, a well-known insulator, illustrate the effectiveness of charge compensation. Locating and identifying analytes on dry filter paper by using tandem mass spectrometry are also demonstrated.     

测量时间的热力学成本

精确测量时间之能力已对社会产生了巨大影响,从海洋航行计时器(在十八世纪推进航海),到星载原子钟(今天全球定位系统(GPS)之基础设备)。但是,物理学对我们测量时间的能力有什么基本的限制呢？在一篇新论文中,来自西班牙巴塞罗那Autonomous 大学的Paul Erker 和他的同事认为,在这样的限制中热力学起关键作用。考虑一个简单的量子钟模型,他们在准确性和分辨率两个特性之间建立了定量关系,并借助于模型钟的热耗散和熵增,计算了运行模型钟的“热力学成本”。时间无情地流逝,从过去流向未来,就我们的感知而言,热力学占据核心地位。因此,这些结果将我们测量时间的能力与时间流逝本身联系起来。     

Schmelzpunktsbestimmungen

Ohne Zusammenfassung