Studies on the focusing performance of a Gabor lens depending on nonneutral plasma properties
- The concept of the Gabor lens goes back to an idea by Dennis Gabor, who proposed a magnetron-type trap as an effective diverging lens for electron beams (collecting lens for positive ion beams).
Electrons confined inside the lens volume by orthogonal magnetic and electric fields, create an electric space charge field that causes a radial symmetric focusing force on an ion beam passing through the lens volume.
Since the beginning of the 1990s, a new design of this lens type as well as numerical models to describe the confined plasma cloud have been developed at the Institute for Applied Physics (IAP, Johann Wolfgang Goethe-University Frankfurt).
Thanks to an improved understanding of the plasma confinement as a function of the external fields, two lenses have successfully been tested for low beam currents and remain in operation.
In the scope of this work, the performance of a prototype Gabor lens for the transport of intense, i.e. space charge dominated ion beams, was investigated at the High Current Test Injector (HOSTI) of GSI Helmholtzzentrum für Schwerionenforschung GmbH for the first time.
To ensure an optimal focusing performance of the Gabor lens a homogeneous and stable electron confinement is required. Therefore, new non-interceptive diagnostic methods were developed to investigate the parameters and state of the confined nonneutral plasma column as a function of the external fields.
An essential part of the studies was the time-resolved diagnostic of an occurring plasma instability and the determination of the electron temperature via optical spectroscopy. The latter necessitated the detailed investigation of atomic excitation as well as the measurement of optical-emission cross sections.
A comparison of the results from both experiments i.e. the beam transport measurements at GSI and the diagnostic experiments performed at IAP concerning the plasma state, gave first indications of possible interaction processes between the nonneutral plasma and the ion beam.
The phylogeny of the genus Gazella and the phylogeography and population genetics of arabian species
- Biodiversity is caused by a fundamental evolutionary process: speciation. When species can spread into new habitats and are allowed to colonize new ecological niches, speciation can become accelerated and is then called radiation. This can happen, e.g., when formerly separated land masses become connected. A prime example of such a scenario is the Arabian Peninsula that connects Africa and Asia since the Oligocene (approx. 30 Ma ago). Since then, the peninsula promoted several faunal exchanges between both continents. The mammalian genus Gazella is an excellent candidate for investigating this faunal exchange. Species are distributed on both, the African and Asian continent as well as on the Arabian Peninsula that is located in between. The aim of my thesis was to cast new light on the evolution and speciation of the genus and, furthermore, to evaluate the currently problematic taxonomy to infer suggestions for improved conservation actions for threatened gazelle species. Therefore, I investigated the taxon Gazella genetically and identified factors that promoted the speciation of this diverse genus. I assessed intraspecific genetic variability for species that inhabited the Arabian Peninsula to infer the past demography of those species and to estimate the history of species divergence and past population parameters.
In the first part of my thesis I inferred a mitochondrial phylogeny based on cytochrome b gene sequences using samples of all nine extant species of Gazella and also of closely related taxa (chapter 2). Besides the monophyly of the genus Gazella two reciprocally monophyletic clades were detected that evolved in allopatry: one predominantly African and one predominantly Asian clade. Within both clades species pairs could be inferred with species being ecologically adapted to different habitats: one species is a desert-dweller (probably the ancestral character state combination), while the other one is adapted to rather mountainous and humid habitats. These adaptations also correlate with the behavior of the species with the mountainous forms being sedentary, territorial and living in small groups and the desert forms being migratory, non-territorial and living in larger herds.
The second part of my thesis focuses on the Arabian gazelle species. In a study about G. subgutturosa I could show that the Arabian form G. marica (sand gazelle)—previously recognized as a subspecies of G. subgutturosa—is genetically distinct from the nominate form (chapter 3). Moreover, a phylogenetic tree based on cytochrome b gene sequences revealed a polyphyly of G. subgutturosa and G. marica with sand gazelles being more closely related to G. leptoceros and G. cuvieri of North Africa. Consequently, I suggested the restoration to full species level for G. marica corroborating earlier conservation practices of breeding both taxa separately in captivity.
In case of G. dorcas such a genetic differentiation could not be detected (chapter 4). Despite the large distribution range from Mali in the west to Saudi Arabia in the east only low genetic variation was detectable in mitochondrial sequence data. Statistically parsimony network analyses revealed pronounced haplotype sharing across regions. Using a coalescence approach I observed a steep population decline that started about 25,000 years ago and which is still ongoing. The decline could be correlated with human hunting activities in the Sahara. Hence, hunting of G. dorcas (already in ancient times) had a much larger impact on gazelle populations than previously thought and even led to the extinction of the Arabian form of G. dorcas.
In chapter 5 of my thesis I provided a rigorous test to genetically distinguish between the potential species G. gazella and G. arabica. Previously recognized as a single species mitochondrial sequence analyses provided first hints for the separation of both taxa. But without the investigation of nuclear loci the observed pattern could also be the result of male biased dispersal combined with female philopatry. Therefore, I amplified mitochondrial sequence markers and nuclear microsatellite loci for both taxa and found support for the earlier view of two separate species. No signs of recurrent gene flow could be detected between neighboring populations of G. arabica and G. gazella. The split of both species could be estimated one million years ago and the recommendation of breeding both taxa separately in captivity for conservation purposes is fully justified.
Several populations of G. arabica suffer from a severe decline. In chapter 6 I asked whether the population occurring on the Farasan archipelago—being at stable individual numbers for decades—may serve as potential source for future reintroduction on the Arabian mainland, although the gazelles show a reduced body size. Analyzing the genetic differentiation of Farasan gazelles, a genetic cluster could be inferred being endemic to the archipelago. However, only approx. 70% of Farasan individuals were assigned to this specific cluster, while the others showed at least intermediate or even complete assignment to the mainland cluster. This indicates ongoing introgression that is probably mediated by human translocations of gazelles from and onto the islands. Considering the uniform dwarfism of Farasan gazelles, reasons for the smaller body size might be direct consequences of resource limitations, i.e., phenotypic plasticity. If the population decline on the mainland will hold on Farasan gazelles could serve as stocks for future reintroductions.
Medial prefrontal cortex stimulation modulates the processing of conditioned fear
Laura D. Müller
Sara V. Tupak
Martin J. Herrmann
- The extinction of conditioned fear depends on an efficient interplay between the amygdala and the medial prefrontal cortex (mPFC). In rats, high-frequency electrical mPFC stimulation has been shown to improve extinction by means of a reduction of amygdala activity. However, so far it is unclear whether stimulation of homologues regions in humans might have similar beneficial effects. Healthy volunteers received one session of either active or sham repetitive transcranial magnetic stimulation (rTMS) covering the mPFC while undergoing a 2-day fear conditioning and extinction paradigm. Repetitive TMS was applied offline after fear acquisition in which one of two faces (CS+ but not CS−) was associated with an aversive scream (UCS). Immediate extinction learning (day 1) and extinction recall (day 2) were conducted without UCS delivery. Conditioned responses (CR) were assessed in a multimodal approach using fear-potentiated startle (FPS), skin conductance responses (SCR), functional near-infrared spectroscopy (fNIRS), and self-report scales. Consistent with the hypothesis of a modulated processing of conditioned fear after high-frequency rTMS, the active group showed a reduced CS+/CS− discrimination during extinction learning as evident in FPS as well as in SCR and arousal ratings. FPS responses to CS+ further showed a linear decrement throughout both extinction sessions. This study describes the first experimental approach of influencing conditioned fear by using rTMS and can thus be a basis for future studies investigating a complementation of mPFC stimulation to cognitive behavioral therapy (CBT).
Dysregulated expression of lipid storage and membrane dynamics factors in Tia1 knockout mouse nervous tissue
Melanie Vanessa Heck
- During cell stress, the transcription and translation of immediate early genes are prioritized, while most other messenger RNAs (mRNAs) are stored away in stress granules or degraded in processing bodies (P-bodies). TIA-1 is an mRNA-binding protein that needs to translocate from the nucleus to seed the formation of stress granules in the cytoplasm. Because other stress granule components such as TDP-43, FUS, ATXN2, SMN, MAPT, HNRNPA2B1, and HNRNPA1 are crucial for the motor neuron diseases amyotrophic lateral sclerosis (ALS)/spinal muscular atrophy (SMA) and for the frontotemporal dementia (FTD), here we studied mouse nervous tissue to identify mRNAs with selective dependence on Tia1 deletion. Transcriptome profiling with oligonucleotide microarrays in comparison of spinal cord and cerebellum, together with independent validation in quantitative reverse transcriptase PCR and immunoblots demonstrated several strong and consistent dysregulations. In agreement with previously reported TIA1 knock down effects, cell cycle and apoptosis regulators were affected markedly with expression changes up to +2-fold, exhibiting increased levels for Cdkn1a, Ccnf, and Tprkb vs. decreased levels for Bid and Inca1 transcripts. Novel and surprisingly strong expression alterations were detected for fat storage and membrane trafficking factors, with prominent +3-fold upregulations of Plin4, Wdfy1, Tbc1d24, and Pnpla2 vs. a −2.4-fold downregulation of Cntn4 transcript, encoding an axonal membrane adhesion factor with established haploinsufficiency. In comparison, subtle effects on the RNA processing machinery included up to 1.2-fold upregulations of Dcp1b and Tial1. The effect on lipid dynamics factors is noteworthy, since also the gene deletion of Tardbp (encoding TDP-43) and Atxn2 led to fat metabolism phenotypes in mouse. In conclusion, genetic ablation of the stress granule nucleator TIA-1 has a novel major effect on mRNAs encoding lipid homeostasis factors in the brain, similar to the fasting effect.
Ataxin-2 Modulates the Levels of Grb2 and Src but Not Ras Signaling
Ewout R. Brunt
- Ataxin-2 (ATXN2) is implicated mainly in mRNA processing. Some ATXN2 associates with receptor tyrosine kinases (RTK), inhibiting their endocytic internalization through interaction of proline-rich domains (PRD) in ATXN2 with SH3 motifs in Src. Gain of function of ATXN2 leads to neuronal atrophy in the diseases spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS). Conversely, ATXN2 knockout (KO) mice show hypertrophy and insulin resistance. To elucidate the influence of ATXN2 on trophic regulation, we surveyed interactions of ATXN2 with SH3 motifs from numerous proteins and observed a novel interaction with Grb2. Direct binding in glutathione S-transferase (GST) pull-down assays and coimmunoprecipitation of the endogenous proteins indicated a physiologically relevant association. In SCA2 patient fibroblasts, Grb2 more than Src protein levels were diminished, with an upregulation of both transcripts suggesting enhanced protein turnover. In KO mouse embryonal fibroblasts (MEF), the protein levels of Grb2 and Src were decreased. ATXN2 absence by itself was insufficient to significantly change Grb2-dependent signaling for endogenous Ras levels, Ras-GTP levels, and kinetics as well as MEK1 phosphorylation, suggesting that other factors compensate for proliferation control. In KO tissue with postmitotic neurons, a significant decrease of Src protein levels is prominent rather than Grb2. ATXN2 mutations modulate the levels of several components of the RTK endocytosis complex and may thus contribute to alter cell proliferation as well as translation and growth.
The other-race effect in 3-year-old German and Cameroonian children
Isabel A. Vöhringer
- Recognizing individual faces is an important human ability that highly depends on experience. This is reflected in the so called other-race effect; adults are better at recognizing faces from their own ethnic group, while very young infants do not show this specialization yet. Two experiments examined whether 3-year-old children from two different cultural backgrounds show the other-race effect. In Experiment 1, German children (N = 41) were presented with a forced choice paradigm where they were asked to recognize female Caucasian or African faces. In Experiment 2, 3-year-olds from Cameroon (N = 66) participated in a similar task using the same stimulus material. In both cultures the other-race effect was present; children were better at recognizing individual faces from their own ethnic group. In addition, German children performed at a higher overall level of accuracy than Cameroonians. The results are discussed in relation to cultural aspects in particular.
Development of β-Lactamase as a Tool for Monitoring Conditional Gene Expression by a Tetracycline-Riboswitch in Methanosarcina acetivorans
Miriam M. Geist
Julia E. Weigand
- The use of reporter gene fusions to assess cellular processes such as protein targeting and regulation of transcription or translation is established technology in archaeal, bacterial, and eukaryal genetics. Fluorescent proteins or enzymes resulting in chromogenic substrate turnover, like β -galactosidase, have been particularly useful for microscopic and screening purposes. However, application of such methodology is of limited use for strictly anaerobic organisms due to the requirement of molecular oxygen for chromophore formation or color development. We have developed β -lactamase from Escherichia coli (encoded by bla) in conjunction with the chromogenic substrate nitrocefin into a reporter system usable under anaerobic conditions for the methanogenic archaeon Methanosarcina acetivorans. By using a signal peptide of a putative flagellin from M. acetivorans and different catabolic promoters, we could demonstrate growth substrate-dependent secretion of β -lactamase, facilitating its use in colony screening on agar plates. Furthermore, a series of fusions comprised of a constitutive promoter and sequences encoding variants of the synthetic tetracycline-responsive riboswitch (tc-RS) was created to characterize its influence on translation initiation in M. acetivorans. One tc-RS variant resulted in more than 11-fold tetracycline-dependent regulation of bla expression, which is in the range of regulation by naturally occurring riboswitches. Thus, tc-RS fusions represent the first solely cis-active, that is, factor-independent system for controlled gene expression in Archaea.
Acceptance and Rejection of 'foreign' Legal Doctrine by the Council of Lubeck around 1500
- From the late middle ages to early modern times (ca. 1200-1600) the Lübeck City Council was the most important courthouse in the Baltic. About 100 cities and towns on its shores lived according to the law of Lübeck. The paper deals with the old theory that Imperial law, i.e. mainly the learned Ius commune, was generally rejected by the council on the grounds of its foreign nature. The paper rejects this view with the help of 8 case studies. There exist rather spectacular statements against Imperial Law, but a closer look reveals that they have to be seen in the light of a specific practical context. They must not be confounded with general statements in which the council had no interest. Its attitude towards Learned Law was flexible and purely pragmatic.
Some corrections to "The Beetles of Northeastern North America"
Ross H. Arnett, Jr.
- The following are some oft he corrections that have been submitted for „Bettles of Northeastern North America“, by Norville M. Downie and Ross H. Arnett.
Redescriptions, new combinations, synonymies, and new records of South American Lepturini (Coleoptera: Cerambycidae: Lepturinae)
Oscaldo R. Di Iorio
- Some Neotropical Lepturini are studied: Euryptera latipennis Audinet-Serville, 1828 (type species) redescription, Strangalia dimidiate (Redtenbacher, 1868) new combination (= Strangalia melanophthisis (Berg, 1889) new combination, new synonymy, and lectotype designation), Strangalia fulvicornis (bates, 1872), new record from Argentina; Strangalia melanùra (Redtenbacher, 1868) new combination from Brazil; Strangalia rubricollis (Bates, 1870) new record from Peru. “Leptura” bonariensis Burmeister , 1865 is not a true Leptura, being exotic for Argentina and for the Neotropical fauna; the type-specimen was mislabeled as coming from Buenos Aires. Elytral patterns, posterior tarsi, antennae, 5th apparent urosternite, and elytral apices of E. lapipennis, and S. dimidiate are illustrated. A key to Argentinian genera and species is provided.