On computational approaches for size-and-shape distributions from sedimentation velocity analytical ultracentrifugation

Sedimentation velocity analytical ultracentrifugation has become a very popular technique to study size distributions and interactions of macromolecules. Recently, a method termed two-dimensional spectrum analysis (2DSA) for the determination of size-and-shape distributions was described by Demeler and colleagues (Eur Biophys J 2009). It is based on novel ideas conceived for fitting the integral equations of the size-and-shape distribution to experimental data, illustrated with an example but provided without proof of the principle of the algorithm. In the present work, we examine the 2DSA algorithm by comparison with the mathematical reference frame and simple well-known numerical concepts for solving Fredholm integral equations, and test the key assumptions underlying the 2DSA method in an example application. While the 2DSA appears computationally excessively wasteful, key elements also appear to be in conflict with mathematical results. This raises doubts about the correctness of the results from 2DSA analysis

Giant multiphoton absorption for THz resonances in silicon hydrogenic donors

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Ultrafast X-ray pulse characterization at free-electron lasers

The ability to fully characterize ultrashort, ultra-intense X-ray pulses at free-electron lasers (FELs) will be crucial in experiments ranging from single-molecule imaging to extreme-timescale X-ray science. This issue is especially important at current-generation FELs, which are primarily based on self-amplified spontaneous emission and radiate with parameters that fluctuate strongly from pulse to pulse. Using single-cycle terahertz pulses from an optical laser, we have extended the streaking techniques of attosecond metrology to measure the temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy, as well as their arrival on a time base synchronized to the external laser to within 6 fs r.m.s. Optical laser-driven terahertz streaking can be utilized at any X-ray photon energy and is non-invasive, allowing it to be incorporated into any pump–probe experiment, eventually characterizing pulses before and after interaction with most sample environments

Review of Terahertz Tomography Techniques

Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.Development and Optimization of THz NDT on Aeronautics Composite Multi-layered Structur