On the relative intensity of Poisson’s spot

The Fresnel diffraction phenomenon referred to as Poisson’s spot or spot of Arago has, beside its historical significance, become relevant in a number of fields. Among them are for example fundamental tests of the super-position principle in the transition from quantum to classical physics and the search for extra-solar planets using star shades. Poisson’s spot refers to the positive on-axis wave interference in the shadow of any spherical or circular obstacle. While the spot’s intensity is equal to the undisturbed field in the plane wave picture, its intensity in general depends on a number of factors, namely the size and wavelength of the source, the size and surface corrugation of the diffraction obstacle, and the distances between source, obstacle and detector. The intensity can be calculated by solving the Fresnel–Kirchhoff diffraction integral numerically, which however tends to be computationally expensive. We have therefore devised an analytical model for the on-axis intensity of Poisson’s spot relative to the intensity of the undisturbed wave field and successfully validated it both using a simple light diffraction setup and numerical methods. The model will be useful for optimizing future Poisson-spot matter-wave diffraction experiments and determining under what experimental conditions the spot can be observed

The Elastic Modulus of Nano-Sized Zinc Determined by Laser Ultrasonic Method

The nano — sized materials are the advanced materials developed in the eighties[1]and being called nanocrystalline materials, ultra — fine grained materials or nanophase materials. Because there are a lot of interfaces within the nano — scaled materials, the volume fraction occupied by the interface is comparable with that of particles. The particle size effect and disordering effect of interface exist in the materials. They are referred to have“gaslike” structure. So the nano — sized materials have a number of advantages excelling to the traditional materials properties. Many new phenomena have been discovered from the investigations of their optical and electric properties. However few works are related to their mechanical and ultrasonic properties

The reality of the imaginary : architectural and the digital image

Wissenschaftliches Kolloquium vom 19. bis 22. April 2007 in Weimar an der Bauhaus-Universität zum Thema: ‚Die Realität des Imaginären. Architektur und das digitale Bild

Critical Theory of Ornament – On The Change of Status of Aesthetics in Architectural Modernism

Gegen die Kahlschlagmetapher von der "Liquidierung des Ornaments" steht im Zentrum der Dissertation die These vom Statuswandel des Ornaments in der architektonischen Moderne. Am Punkt des technologischen Paradigmenwechsels wird das Ornament im Spannungsfeld diskutiert zwischen der Maschinenproduktion zu Beginn des 20. Jhd. und der Virtualisierung der Kultur im Computerzeitalter, d.h. zwischen der vermeintlichen Abschaffung des Ornaments durch Loos (1910) und Eisenmans performativen Entwurfsverfahren (1990). Die Frage stellt sich, inwiefern die Ornamentproblematik der Moderne nicht als Vorgeschichte zur spezifischen Problematik der medialisierten Massenkultur und ihrer digitalen Bildlogik heute zu lesen wäre. Mit V. Sklovskij und S. Freud, M. Tafuri und K. M. Hays, aber auch zwischen Adornos Ästhetik der "Nicht-Identität" und Derridas "Parergonalität" geht es um die semiologische Reformulierung des Ornaments: im Übergang der Ästhetik der Moderne vom Dualismusprinzip zum Wiederholungsprinzip, von der affirmativen Rückbezüglichkeit zur kritischen Performativität und von der Objektproduktion zur Medialisierung der Kultur.Challen-ging the idea of the "liquidation" of ornament as an indicator of modernity, the thesis focuses on ornament after its proclaimed abolition in architectural moder-nism. With Critical Theory as its conceptual basis, its main argument is that, in modern architecture, classical ornament has undergone a radical change of status. Wittnessing a process of "intellectualisation of perception" in modern aesthetics, the debates on the ornament in early modernism appear as directly leading up to today's practice of digitalization of everyday culture. In a critical juxtaposition of both modern semio-tics and philosophical aesthetics, ornament is shown at the center of a shift in 20th Century architectural aesthetics, from ornament-as-object to ornament-as-per-formative-production and from the duality principle to repetition compulsion. Departing from A. Loos’ Freudian ornament theory, moving on to Russian constructivism, Mies’ pictorial nihilism, Neue Sachlichkeit and the Surrealists’ automation techniques, the thesis focuses on the semiological reconceptualization of ornament between the two anti-podes of modern architecture: Loos and Eisenman

What's new - delete the on and off of architecture - Wotans verwunschenes Schloß

Wissenschaftliches Kolloquium vom 27. bis 30. Juni 1996 in Weimar an der Bauhaus-Universität zum Thema: ‚Techno-Fiction. Zur Kritik der technologischen Utopien

Architecture and Philosophy: The Failure of Translation

In the connection between architecture and philosophy, the “and” connects and separates at the same time. In classical rhetoric, the concept and technique of ekphrasis stands for this. Ekphrasis means transfer from the medium of sensual experience into the medium of lan-guage and back into the realm of sensual imagination. As will be shown here, however, the “and” unfolds its full functionality only in the failure of ekphrasis. Only in failure does the “and” become the medium of in-tellectuality and sensuality, that is, when the “and” no longer designates a center and a place of symmetry, but when it describes a marginal con-dition, when it shifts the discourse toward the margins, when it clears the space and gives freedom a place. An example of the creative failure of ekphrasis is the Memorial to the Murdered Jews of Europe in Berlin by Peter Eisenman. In the failed translation of sensory and cognitive ex-perience, Eisenman forces architecture and philosophy into a unity that cannot be resolved into a dialectical third. Thus, the memorial creates a void in the center of Berlin that becomes a trigger of sensual and intellec-tual imagination for the unimaginable of the Holocaust

Photosystem II: Thermodynamics and Kinetics of Electron Transport from QA- to QB(QB- ) and Deleterious Effects of Copper(II)

Studies on thermodynamics and kinetics of electron transfer from QA- to QB(QB-) were performed by monitoring laser flash induced changes of the relative fluorescence emission as a function of temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane fragments. In addition, effects of bivalent metal ions on PS II were investigated by measuring conventional fluorescence induction curves, oxygen evolution, manganese content and atrazine binding mostly in PS II membrane fragments. It was found: a) the normalized level of the fluorescence remaining 10 s after the actinic flash (Ft/F0) steeply increases at temperatures below -10 to - 20 °C, b) the fast phase of the transient fluorescence change becomes markedly retarded with decreasing temperatures, c) among different cations (Cu2+, Zn2+, Cd2+, Ni2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 μᴍ and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number of binding sites. The content of about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 μᴍ. Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state of QA- reoxidation by QB(QB- ) is characterized by standard enthalpies ΔH° of 95 kJ mol-1 and 60 kJ mol-1 and standard entropies ΔS° of 370 kJ K-1 mol-1 and 240 kJ K-1 mol-1 in isolated thylakoids and PS II membrane fragments, respectively, ii) the activation energies of QA- reoxidation by plastoquinone bound to the QB site are about 30 kJ mol-1 (thylakoids) and 40 kJ mol-1 (PS II membrane fragments) in 220 K < T < 300 K, and iii) Cu2+ causes at least a two-fold effect on PS II by modifying the atrazine binding affinity at lower concentrations ( ~ 5 μᴍ) and interference with the redox active tyrosine Yz at slightly higher concentration ( ~ 10 μᴍ) leading to blockage of oxygen evolution

Magnetic microstructure of nanostructured Fe, studied by small angle neutron scattering

Small angle neutron scattering (SANS) was applied to achieve insight into the magnetic correlations in nanostructured Fe. The results confirm the expected microstructure involving ferromagnetic grains and a nonmagnetic or weakly magnetic interface region, the interfaces occupying about half the specimen volume. The SANS measurements further reveal that in nanostructured Fe the magnetic correlations are not confined to single grains, but are extended across the interfaces and result in the alignment of the magnetization over several hundreds of grains. An external field of 1.5 kOe is not sufficient for complete magnetic alignment of the entire specimen. However, the long-range magnetic correlations are considerably disturbed by this field. Reducing the external magnetic field to zero causes the magnetic correlations to resume microstructural characteristics similar to what they had in the original stat

MALDI-TOF MS Analysis of Urinary Nucleosides

As RNA turnover seems to be impaired in cancer patients, modified nucleosides have been evaluated as potential tumor markers. Modified nucleosides are mainly formed post-transcriptionally in tRNA, set free during RNA metabolism, and excreted in urine. Especially methylated nucleosides play an important role, as their levels are higher in urine from cancer patients. For structural elucidation of known and unknown nucleosides from urine samples of cancer patients, MALDI-TOF MS and MALDI-PSD were used for the first time. This technique generally ensures high sensitivity, mass resolution, and accuracy. In our analytical approach we prepurified nucleosides from urine by affinity chromatography and subsequently separated them by semipreparative high performance liquid chromatography. The different fractions were collected separately and analyzed by MALDI-TOF MS and PSD-MALDI using a mixture of six low molecular weight calibrants for internal or external calibration. The molecular totals formulas based on a mass accuracy of 10 ppm and below were calculated and a systematic data base search was performed. The inherent problem of the MALDI-technique, the reduced sensitivity for low molecular weight substances caused by matrix suppression effects, was reduced by our technique. We identified several nucleosides in urine, which were previously identified via retention times and UV spectra of standards after HPLC analysis. Eight further nucleosides were observed. This work demonstrates for the first time the potential of MALDI-TOF and PSD-MALDI in combination with semipreparative HPLC for assignment of nucleosides in urine. The particularly high mass accuracy of this mass spectrometric method provides opportunities for identifying unknown compounds