Investigation of nonlinear dynamics in and via femtosecond filaments in gases

Intense, ultrashort laser pulses are required for the study of many nonlinear optical effects and are of utmost relevance for various applications from ultrafast X-ray radiography in medicine up to remote sensing of the atmosphere. Increasing their intensity while interacting with matter eventually leads to the generation of laser-induced plasma. This plasma has fascinating optical properties such as a negative refractive index contribution proportional to the free electron density or the lack of a damage threshold, giving the prospect of a multitude of new applications based on the manipulation of light with plasma. The realization of such plasma-based applications requires a precise knowledge of its properties and temporal evolution, as the plasma remains for much longer than its generation event. A method to generate and investigate ultrashort laser pulses as well as laser-induced plasma is femtosecond filamentation. It represents the formation of an intense self-guided light channel in a medium for distances much longer than the Rayleigh range of the same beam focused in vacuum. It is formed by a dynamic balance of Kerr-induced self-focusing and plasma-induced defocusing. In this thesis, it is demonstrated that femtosecond filamentation can be employed as a tool to investigate the temporal evolution of laser-induced plasma. The study is realized in various atomic and molecular gas atmospheres via measuring the temporal evolution of the enhancement of third harmonic radiation generated by a femtosecond filament which is intercepted by a laser-induced plasma spot. Significant differences for the lifetime of the plasma in atomic and molecular gas atmospheres are found. Further, a novel method for the complete spatio-temporal characterization of a femtosecond filament along its length is presented. It is based on controlled filament termination at various positions along its length in combination with spatio-temporal pulse characterization and numerical backpropagation of the filament pulses to the termination point. The capabilities of the method are illustrated by revealing complex spatio-temporal dynamics and couplings during filament propagation

New Abrasive Materials and Their Influence on the Surface Quality of Bearing Steel After Grinding

This paper focuses on the influence of various types of abrasive grains on cutting properties during the grinding process for bearing steel. In this experiment, not only conventional super-hard abrasive materials but also a new type of abrasive material were employed in grinding wheels. The measurement results were compared, and an evaluation was made of the cutting properties of the new abrasive material. The options were then evaluated for their practical applicability. The measurement results indicated that a grinding wheel with Abral and SG grains is the most suitable for grinding hardened bearing steel in order to achieve the best roughness and geometrical accuracy

New Abrasive Materials and Their Influence on the Surface Quality of Bearing Steel After Grinding

This paper focuses on the influence of various types of abrasive grains on cutting properties during the grinding process for bearing steel. In this experiment, not only conventional super-hard abrasive materials but also a new type of abrasive material were employed in grinding wheels. The measurement results were compared, and an evaluation was made of the cutting properties of the new abrasive material. The options were then evaluated for their practical applicability. The measurement results indicated that a grinding wheel with Abral and SG grains is the most suitable for grinding hardened bearing steel in order to achieve the best roughness and geometrical accuracy

Complement evasion strategies of human pathogens - the evolutionary arms race

Although the complement system, a pivotal component of innate immunty, is centrally involved in host defense against pathogens, its overactivation or deregulation may excessively amplify inflammation and contribute to immunopathology. Periodontitis, an oral infection-driven chronic inflammatory disease, has been linked with complement disruption by periodontal bacteria, resulting in inflammation and pathogenesis. The mechanisms of this disruption have partially been revealed, yet in this thesis we investigated novel periodontal pathogens and/or complement evasion pathways in periodontitis. Furthermore, complement inhibition by S. aureus is a key step in its infection, but the impact of its proteases on complement, highlighted in our studies, has not been well characterized before. We focused on a major but relatively poorly studied periodontal bacterium T. forsythia. We showed that its two novel peptidases contribute to its complement resistance by cleaving several key complement components. Interestingly, both of the proteases were able to cleave C5 to release biologically active anaphylatoxins C5a, activity of which has been largely implicated in pathogenesis of periodontitis. Further, we showed that another important periopathogen, Prevotella intermedia, acquires resistance towards complement by binding complement inhibitor found in human serum, factor I, and its two major cofactors C4b-binding protein (C4BP) and Factor H. This mechanism contributes to complement resistance of this bacterium. We also found that major periopathogens have the ability to bind to the membrane-bound complement inhibitor CD46. Strikingly, even though this molecule improved initial attachment of bacteria to the epithelial cells, the final outcome was not beneficial for the bacteria – in cells without CD46 they persisted much longer without getting cleared, indicating activation of certain killing mechanisms upon CD46 stimulation. The phenomenon may be related to autophagy, which may be affected by CD46 as shown previously. Recent studies implicated an involvement of a novel gram-positive Filifactor alocis in the pathogenesis of the periodontal disease. Taking into account the key role of complement deregulation by periodontal bacteria, we focused on F. alocis capacity to manipulate this system. We pinpointed different strategies, such as production of proteases or non-productive binding of C3, employed by this bacterium. Finally, Staphylococcus aureus, is known for its impressive repertoire of complement inhibitors. We tested a panel of major proteases of S. aureus and identified their substrates within complement cascades. We also showed that two of the proteases are able to release C5a, similarly to proteases of periodontal bacteria. Taken together, we explored the knowledge about complement manipulation by various common human pathogens. We identified both unique as wells as common strategies of bacterial complement evasion. Exploring virulence mechanisms shared by different pathogens can give rationales for developing effective therapies for infectious diseases

A BIODIVERSITY SURVEY OF THE SOIL CRUSTS OF THE GEOGRAPHICALLY ISOLATED SAN NICHOLAS ISLAND, CALIFORNIA, USA AND DESCRIPTION OF SPECIES IN THREE GENERA (ATLANTICOTHIX, PYCNACRONEMA, KONICACRONEMA) PREVIOUSLY RESTRICTED TO BRAZIL USING A POLYPHASIC APPROACH TO CYANOBACTERIAL TAXONOMY

San Nicholas Island, California, USA is a geographically-isolated island that experiences a semiarid climate and exhibits significant topographic and geologic diversity. Access to the island is restricted to the public and, as a result, only one previous study has been done on the algal biodiversity of its biological soil crusts. The previous study used morphology as the sole basis of species identification, and it was the aim of this study to corroborate and expand upon the results by including molecular data. Using 16S rRNA and 16S–23S ITS sequences and phylogenetic analyses, a diverse set of taxa were identified and are presented herein. Multiple taxa were determined to be common to both studies based on morphological similarity, and several putative new genera and species were identified based on molecular analyses. Several genera were identified that had not been observed in the Northen Hemisphere, raising questions about the distribution of taxa at the genus and species level

CROSS-DATASET MALICIOUS ACTORS IDENTIFICATION

Techniques are described herein for convicting malicious actors across datasets of different origins. The algorithm allows correlation of the available ground truth knowledge from one dataset with observations in another dataset. In the network/endpoint security field this algorithm allows for conviction of malicious network traffic and identification of Command and Control infrastructure of newly detected malware, even if no direct communication between binaries and domains is observed

Experts and Questions : Exploring Perceptions of Corruption

Based on two survey experiments, the article explores the influence specific formulation of survey questions have on the results of corruption perception measurements. By comparing the survey experiment results, the article also highlights differences between perceptions of experts and the public.Článek na základě dvou provedených survey experimentů zkoumá, jak formulace dotazníkových otázek ovlivňuje výsledky měření vnímání korupce. Srovnání výsledků obou survey experimentů také poukazuje na rozdíl mezi vnímáním korupce ze strany veřejnosti a expertů

Description of six new cyanobacterial species from soil biocrusts on San Nicolas Island, California, in three genera previously restricted to Brazil

As the taxonomic knowledge of cyanobacteria from terrestrial environments increases, it remains important to analyze biodiversity in areas that have been understudied to fully understand global and endemic diversity. This study was completed as part of a larger algal biodiversity study of the soil biocrusts of San Nicholas Island, California, USA. Among the taxa isolated were several new species in three genera (Atlanticothrix, Pycnacronema, and Konicacronema) which were described from, and previously restricted to, Brazil. New taxa are described herein using a polyphasic approach to cyanobacterial taxonomy that considers morphological, molecular, ecological, and biogeographical factors. Morphological data corroborated by molecular analysis including sequencing of the 16S rRNA gene, and the associated 16S–23S ITS rRNA region was used to delineate three new species of Atlanticothrix, two species of Pycnacronema, and one species of Konicacronema. The overlap of gen- era from San Nicolas Island and Brazil suggests that cyanobacterial genera may be widely distributed across global hemispheres, whereas the presence of distinct lineages may indicate that this is not true at the species level. Our data suggest that based upon global wind patterns, cyanobacteria in both Northern and Southern hemispheres of the Americas may have a more re- cent common ancestor in Northern Africa, but this common ancestry is dis- tant enough that speciation has occurred since transatlantic dispersal

Distality of Attentional Focus and Its Role in Postural Balance Control

The role of attentional focusing in motor tasks has been highlighted frequently. The “internal–external” dimension has emerged, but also the spatial distance between body and attended location. In two experiments, an extended attentional focus paradigm was introduced to investigate distality effects of attentional foci on balance performance. First, the distality of the coordinates of the point of focus was varied between a proximal and distal position on an artificial tool attached to the body. Second, the distance of the displayed effect on the wall was varied between a 2.5 and 5 m condition. Subjects were instructed to focus on controlling either a proximal or distal spot on a tool attached to their head, represented by two laser pointers. Subsequently, they needed to visually track their own body-movement effect of one of the laser pointers at a wall while completing various single leg stance tasks. Center of pressure (COP) sway was analyzed using a linear method (classic sway variables) as well as a non-linear method (multiscale entropy). In addition, laser trajectories were videotaped and served as additional performance outcome measure. Experiment 1 revealed differences in balance performance under proximal compared to distal attentional focus conditions. Moreover, experiment 2 yielded differences in balance-related sway measures and laser data between the 2.5 and 5 m condition of the visually observable movement effect. In conclusion, varying the distality of the point of focus between proximal and distal impacted balance performance. However, this effect was not consistent across all balance tasks. Relevantly, the distality of the movement effect shows a significant effect on balance plus laser performance with advantages in more distal conditions. This research emphasizes the importance of the spatial distality of movement effects for human behavior