Analytical Models in Electron Backscattering

The different aspects of electron backscattering from solid films are calculated in terms of simple analytical models for thin films and bulk targets, for normal and oblique incidence. Well-known models regard only one scattering aspect, e.g.: single Rutherford scattering by Everhart\u27s model, diffusion from a point source by Archard\u27s model, diffusion from sources continuously distributed over the depth of the target by Thümmel\u27s model. A few analytical models have been developed recently regarding single scattering and continuous diffusion, e.g. by Werner and by the author. These models allow us to calculate analytically the backscattering coefficient for bulk targets versus atomic number, for thin films versus thickness and incident electron energy, the angular intensity distribution, the total and angular energy distributions, and the surface density distribution of backscattered electrons. The numerical results of these models are compared with experimental results thus revealing the limits of the present models

Ion and Electron Emission from Liquid Metal Sources

In liquid metal ion sources, the emission is located at the apex of a liquid cone (the often so-called Taylor cone), formed by electrostatic forces and surface tension. Reversal of the extraction voltage polarity results in electron emission from the liquid metal surface. For small apex radii, ≤ 1 μm, steady field emission of electrons has been observed, whereas for apex radii ≥ 10 μm, explosive pulsed emission occurs. Since the onset voltage for electron emission has been found to be considerably lower than the critical voltage for the formation of the Taylor cone, it has been concluded that dc (direct current) electron emission from a field stabilized cone is not possible. In situ high-voltage transmission electron microscopy observations seem to confirm this conclusion, although in one case, a field-stabilized liquid micro-cone during electron emission has been observed for a liquid-gallium-indium-tin source. The literature on liquid metal ion and electron sources is reviewed. From in situ transmission electron microscopy observations of the cone formation, relations for cone angle and jet length dependent on ion emission current are derived. Growth and emission of microdroplets at liquid indium ion sources have been imaged. In the case of electron field emission from liquid indium sources, no liquid cone formation has been observed

Coordinated Implementation of Chikungunya Virus Reverse Transcription–PCR

A preformulated chikungunya virus real-time reverse transcription–PCR, quality-confirmed oligonucleotides, and noninfectious virus controls were distributed by the European Network for the Diagnosis of Imported Viral Diseases. An international proficiency study with 31 participants demonstrated that ad hoc implementation of molecular diagnostics was feasible and successful

Recombinant Envelope-Proteins with Mutations in the Conserved Fusion Loop Allow Specific Serological Diagnosis of Dengue-Infections

Dengue virus (DENV) is a mosquito-borne flavivirus and a major international public health concern in many tropical and sub-tropical areas worldwide. DENV is divided into four major serotypes, and infection with one serotype leads to immunity against the same, but not the other serotypes. The specific diagnosis of DENV-infections via antibody-detection is problematic due to the high degree of cross-reactivity displayed by antibodies against related flaviviruses, such as West Nile virus (WNV), Yellow Fever virus (YFV) or Tick-borne encephalitis virus (TBEV). Especially in areas where several flaviviruses co-circulate or in the context of vaccination e.g. against YFV or TBEV, this severely complicates diagnosis and surveillance. Most flavivirus cross-reactive antibodies are produced against the highly conserved fusion loop (FL) domain in the viral envelope (E) protein. We generated insect-cell derived recombinant E-proteins of the four DENV-serotypes which contain point mutations in the FL domain. By using specific mixtures of these mutant antigens, cross-reactivity against heterologous flaviviruses was strongly reduced, enabling sensitive and specific diagnosis of the DENV-infected serum samples in IgG and IgM-measurements. These results have indications for the development of serological DENV-tests with improved specificity

Hybrid identities? The self-positioning of young transmigrants

In dem Beitrag geht es um das Aufwachsen im Kontext transnationaler Migration als Herausforderung an die Identitätskonstruktion von Jugendlichen. Grundlage ist der Begriff \u27hybride Identitäten\u27, der im Umfeld der Cultural Studies theoretisch begründet wurde und der in der deutschen Erziehungswissenschaft in der Regel verwendet wird, um die kreativen und produktiven Aspekte der Identitätskonstruktionen in Migrationskontexten herauszustellen. Ausgehend von Überlegungen Stuart Halls fassen die Verfasserinnen \u27hybride Identität\u27 als einen spezifischen diskursiven Modus der Selbstverortung in (dominanten) national-kulturellen Repräsentationssystemen. Sie analysieren Auszüge aus Interviews mit zwei jugendlichen Transmigrantinnen, deren Erfahrungen jeweils charakteristisch für zwei unterschiedliche \u27Migrationstypen\u27 (\u27Gastarbeitermigration\u27; \u27Neue Migration\u27) sind. Dabei wird deutlich, dass sowohl Parallelen als auch Differenzen in den Selbstverortungen der jungen Frauen, die sich mit unterschiedlichen Kategorien dominanter Zuschreibungen auseinandersetzen, auf der Grundlage des Konzepts \u27hybrider Identitäten\u27 erfasst werden können. (DIPF/Orig.)In this article the authors deal with the question how growing-up in the context of transnational migration challenges the identity construction of young people. They focus their discussion on the concept of \u27hybrid identities\u27, which was devised as part of the theoretical projects of \u27Cultural Studies\u27. Within German educational science this concept is usually employed in order to stress the creative and productive aspects of identity construction in the context of migration. Based on theoretical reflections by Stuart Hall, the authors define \u27hybrid identity\u27 as a specific mode of identity discourse and the according positioning of the self within (dominant) national-cultural systems of representation. They analyze extracts from interviews with two young female transmigrants, whose experiences are characteristic for two different \u27types of migration\u27 (\u27guest-worker migration\u27; \u27new migration\u27). The authors thereby show that the concept of \u27hybrid identities\u27 is suitable to capture both parallels and differences of self-positioning processes of the young women, who have to tackle different categories of dominant identity ascriptions. (DIPF/Orig.

Immunological reactivity of a human immunodeficiency virus type I derived peptide representing a consensus sequence of the GP120 major neutralizing region V3

To reduce the opportunities for human immunodeficiency virus type 1 (HIV-1) to evade vaccine induced immunity, the development of subunit vaccines must focus on the characterization of immunogenic epitopes, which are major targets for the immune system. The most dominant site for elicitation of neutralising immune response is located on the external envelope glycoprotein gp120 within the third variable domain (V3). To overcome virus type specificity of antibodies directed to the V3-domain we designed a 36 amino acids long gp120/V3-consensus peptide (V3-C36) based on published biological data and sequence comparisons of various HIV-1 virus isolates. This peptide contains a conserved core sequence which is suggested to form a surface-exposed beta-turn. This peptide also includes T-cell epitopes defined in mice and humans, an ADCC-epitope and two highly conserved cysteine residues which were oxidized to form a cystine derivate, thus allowing correct peptide folding. In ELISA-tests, this peptide reacts with at least 90% of randomly selected sera of European and African patients infected with HIV-1 and is recognized by three different HIV-1/V3 "type-specific" antisera (MN, RF, IIIB-strain). Using this peptide as immunogen in rabbits, antisera could be raised with highly cross-reactive and HIV-1/IIIB strain neutralizing properties. Moreover, HTLV/HIV-1/IIIB specific cytotoxic T-lymphocytes (CTLs) of BALB/c mice infected with a gp120 recombinant vaccinia virus recognized the central 16- and 12-mer peptides of the V3-C36 consensus peptide in cytolytic assays, indicating perfect compatibility of the consensus peptide with the IIIB-primed CTLs. The DNA-sequence encoding the V3-consensus loop region might be an important component in newly designed recombinant subunit vaccines. In addition, due to its broad serological reactivity, the V3-consensus peptide might play an important role in special diagnostic purposes

Studies on processing, particle formation, and immunogenicity of the HIV-1 gag gene product: a possible component of a HIV vaccine

Antigens in a particulate conformation were shown to be highly immunogenic in mammals. For this reason, the particle forming capacity of derivatives of the HIV-1 group specific core antigen p55 gag was assayed and compared dependent on various expression systems: recombinant bacteria, vaccinia- and baculoviruses were established encoding the entire core protein p55 either in its authentic sequence or lacking the myristylation consensus signal. Moreover, p55 gag was expressed in combination with the protease (p55-PR) or with the entire polymerase (p55-pol), respectively. Budding of 100-160 nm p55 core particles, resembling immature HIV-virions, was observed in the eucaryotic expression systems only. In comparison to the vaccinia virus driven expression of p55 in mammalian cells, considerably higher yields of particulate core antigen were obtained by infection of Spodoptera frugiperda (Sf9) insect cells with the recombinant Autographa californica nuclear polyhedrosis (AcMNPV) baculovirus. Mutation of the NH2-terminal myristylation signal sequence prevented budding of the immature core particles. Expression of the HIV p55-PR gene construct by recombinant baculovirus resulted in complete processing of the p55 gag precursor molecule in this system. The introduction of an artificial frameshift near the natural frameshift site resulted in constitutive expression of the viral protease and complete processing of p55, both in Escherichia coli and in vaccinia virus infected cells. Interestingly, significant processing of p55 resembling that of HIV infected H9 cells could also be achieved in the vaccinia system by fusing the entire pol gene to the gag gene. Moreover, processing was not found to be dependent on amino-terminal myristylation of the gag procursor molecule, which is in contrast to observations with type C and type D retrovirus. However, complete processing of p55 into p24, p17, p9 and p6 abolished particle formation. Purified immature HIV-virus like particles were highly immunogenic in rabbits, leading to a strong humoral immune response after immunization. Empty immature p55 gag particles represent a noninfectious and attractive candidate for a basic vaccine component

Random Access Direct Parallel Detection of Electron Energy Loss Spectra with a New Photodiode Array

A new type of photodiode array (PDA) which allows the individual access of single diodes is used to record energy loss electrons directly without electron photon conversion. The detector is part of an electron energy loss parallel detection system which consists of a sector field spectrometer and a quadrupole lens system to magnify the spectra electron-optically. The parallel detector is a new random access PDA (RAPDA) which allows the individual access of single diodes. Therefore, different parts of the spectrum with dramatically different electron rates (zero loss peak, plasmon loss, ionization edges) can be recorded, each with optimum acquisition time and number of read-outs. This method allows the use of all available information in one recording of a spectrum for an increased intensity range compared to self-scanning PD As (SSPDAs) where all the diodes have to be read out in a row. Direct illumination of the diodes increases the sensitivity of the detector by two orders of magnitude for 40 keV electrons compared to detectors with electron photon conversion. No apparent radiation damage of the diodes was observed if the detector was cooled down to temperatures below -80°C

Electrochemical Performance and Stability of Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ for Oxygen Transport Membranes

Mixed ionic-electronic conducting (MIEC) ceramics as oxygen transport membranes (OTMs) can provide high oxygen permeation rates at comparably low energy demands. For this purpose, Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ (BSCF) shows the best performance under ideal operating conditions. Thermal and chemical stability investigations, electrical behavior σ(T,pO₂,t), and oxygen exchange parameter extraction by means of electrical conductivity relaxation resulted in a far better understanding of the BSCF system

A Computer Controlled Scanning Transmission Electron Microscope Equipped with an Energy Analyzer for Special Investigations on Electron Diffraction- and Channeling Patterns

A scanning electron microscope was equipped with a double tilting stage, driven by stepping motors, to investigate electron channeling patterns (ECPs) and large angle convergent beam patterns (LACBPs) of single crystals. Transmitted electrons may be energy-selected by a magnetic sector-field energy analyzer. The recording of experimental data and the experimental arrangement are controlled by a microprocessor system, including a picture storage unit of 512 x 512 pixels of 16 bit. Recorded patterns can be stored on 1 Megabyte floppies. A set of useful programs allows one to perform calculations with stored patter ns, e.g., contrast enhancement or -inversion, noise reduction, difference or quotient of two patterns etc. The possibility of background subtraction (e.g., in patterns recorded with characteristic energy loss electrons) allows one to get true K-loss convergent beam patterns. Other recording modes allow one to get two CBPs simultaneously recorded with electrons of different energy losses, to measure angle dependences of energy selected electrons, or to take electron energy loss spectra. A special processor program generates a theoretically calculated CBP or ECP on the TV screen and prints out a list of all band edges up to a chosen limit of Miller indices (hkl). The program requires the coordinates of two known poles and some crystallographic properties of the investigated material. Thus complete indexing of recorded diffraction patterns is easily possible. The system has been applied, e.g., to investigate localization effects of electron Bloch-waves in graphite