Enabling Coarse X-ray Fluorescence Imaging Scans with Enlarged Synchrotron Beam by Means of Mosaic Crystal Defocusing Optics

Trace elements, functionalized nanoparticles and labeled entities can be localized with sub-mm spatial resolution by X-ray fluorescence imaging (XFI). Here, small animals are raster scanned with a pencil-like synchrotron beam of high energy and low divergence and the X-ray fluorescence is recorded with an energy-dispersive detector. The ability to first perform coarse scans to identify regions of interest, followed by a close-up with a sub-mm X-ray beam is desirable, because overall measurement time and X-ray dose absorbed by the (biological) specimen can thus be minimized. However, the size of X-ray beams at synchrotron beamlines is usually strongly dependent on the actual beamline setup and can only be adapted within specific pre-defined limits. Especially, large synchrotron beams are non-trivial to generate. Here, we present the concept of graphite-based, convex reflection optics for the one-dimensional enlargement of a 1 mm wide synchrotron beam by a factor of 5 to 10 within a 1 m distance. Four different optics are tested and characterized and their reflection properties compared to ray tracing simulations. The general shape and size of the measured reflection profiles agree with expectations. Enhancements with respect to homogeneity and efficiency can be expected with improved optics manufacturing. A mouse phantom is used for a proof-of-principle XFI experiment demonstrating the applicability of coarse and fine scans with the suggested optics design.     

The hawk/goose story: The classical ethological experiments of Lorenz and Tinbergen, revisited.

We present a historical account of the story behind the famous hawk/goose experiments of Lorenz and Tinbergen in a wider context of cognitive ethology. We discuss their significance, for ethological experimentation in general, and specifically for understanding innate constraints on cognition. As examples of the continuing significance of the hawk/goose paradigm of selective habituation, we discuss its relation to “exposure therapy” of human phobias and the use of hawk silhouettes as deterrents for songbirds. Finally we rephrase Uexküll's thesis of taxon-specific worlds (“Umwelten”) as a “Theory of World.” (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A fast Monte Carlo algorithm for studying bottle-brush polymers

Obtaining reliable estimates of the statistical properties of complex macromolecules by computer simulation is a task that requires high computational effort as well as the development of highly efficient simulation algorithms. We present here an algorithm combining local moves, the pivot algorithm, and an adjustable simulation lattice box for simulating dilute systems of bottle-brush polymers with a flexible backbone and flexible side chains under good solvent conditions. Applying this algorithm to the bond fluctuation model, very precise estimates of the mean square end-to-end distances and gyration radii of the backbone and side chains are obtained, and the conformational properties of such a complex macromolecule are studied. Varying the backbone length (from Nb=67 to Nb=1027), side chain length (from N=0 to N=24 or 48), the scaling predictions for the backbone behavior as well as the side chain behavior are checked. We are also able to give a direct comparison of the structure factor between experimental data and the simulation results.     

一体化的信号源分析仪

与美国同行争分夺秒抢占市场先机不同,欧洲测量仪器厂商Rohde&Schwarz公司的产品策略则相对稳健,他们的产品更专注于功能的多样化     

Personal Trusted Devices for Web Services: Revisiting Multilevel Security

In this paper we revisit the concept of mandatory access control and investigate its potential with personal digital assistants (PDA). Only if applications are clearly separated and Trojans cannot leak personal information can these PDAs become personal trusted devices. Limited processing power and memory can be overcome by using Web services instead of full-fledged applications – a trend also in non-mobile computing. Web services, however, introduce additional security risks, some of them specific for mobile users. We propose an identification scheme that can be effectively used to protect privacy and show how this system builds upon a light-weight version of mandatory access control.     

Covalent Adaptable Microstructures via Combining Two-Photon Laser Printing and Alkoxyamine Chemistry: Toward Living 3D Microstructures

Manufacturing programmable materials, whose mechanical properties can be adapted on demand, is highly desired for their application in areas ranging from robotics, to biomedicine, or microfluidics. Herein, the inclusion of dynamic and living bonds, such as alkoxyamines, in a printable formulation suitable for two-photon 3D laser printing is exploited. On one hand, taking advantage of the dynamic covalent character of alkoxyamines, the nitroxide exchange reaction is investigated. As a consequence, a reduction of the Young´s Modulus by 50%, is measured by nanoindentation. On the other hand, due to its “living” characteristic, the chain extension becomes possible via nitroxide mediated polymerization. In particular, living nitroxide mediated polymerization of styrene results not only in a dramatic increase of the volume (≈8 times) of the 3D printed microstructure but also an increase of the Young's Modulus by two orders of magnitude (from 14 MPa to 2.7 GPa), while maintaining the shape including fine structural details. Thus, the approach introduces a new dimension by enabling to create microstructures with dynamically tunable size and mechanical properties.     

Reliability of a two-way circular consecutively connected system with multistate components

A two-way circular consecutively connected system with multistate components (two-way circular CCSMC) consists of n cyclically ordered components e₁,…,e_n, i.e. e_i+1, succeeds e₁, iε«ng l, …, n − 1ång;, e, succeeds e_n- Each component is capable of sending a signal in left-hand and right-hand directions. All components operate independently. The whole system is functioning if both left-hand and right-hand signals are received by each component. A recursive procedure evaluating the reliability of a two-way circular CCSMC is presented.     

A parallel algorithm evaluating the reliability of a system with known minimal cuts (paths)

A system with known minimal cuts is considered. In order to compute its reliability a binary tree is constructed with nodes being assigned numerical values. The value of each non-leaf node is a linear combination of its child nodes' values. The values of leaf nodes can be computed in a very simple way. The value of the root node is the system's reliability. The presented method is a memory saving one. Moreover, it is possible to apply parallel computation to the nodes located on the same level, which may significantly reduce the computing time.