Anregung von Atomen durch getwistetes Licht

Twisted light has received a lot of attention in recent years. And there are justified reasons for this. The properties of twisted light are unusual and differ fundamentally from the plane-wave properties. The phase fronts of these light beams have a helical structure, giving them the name twisted. This helical phase structure originates from the well-defined orbital angular momentum (OAM) that they carry along their propagation direction and in addition to the spin angular momentum (SAM). Moreover, they have a characteristic intensity profile, which consists of concentric rings with a central minimum, and a phase singularity in the beam center. This thesis is based on two main parts, each dealing with a different aspect of twisted light. These investigations are carried out using Bessel beams, one type of twisted light. Twisted light beams are cylindrically symmetrical. Therefore, they are defined on the basis of circularly polarized light. This fact leads to the first question: Is it possible to generate twisted light in other polarization states? In this work, we derive how this can be achieved by using the superposition principle and how this can be used to construct linearly, radially, or azimuthally polarized Bessel beams. The focus in the second part is on excitations of atoms by twisted Bessel beams. In particular, we analyze how the use of twisted light can modify individual atomic multipole transitions. The obtained results show that for an efficient modification a precise localization of the target atom is required. In the last chapter, both aspects are combined. We analyze transitions between magnetic hyperfine states in a single trapped atom (or ion), which is exposed to an additional external magnetic field. The presented calculations for these multipole excitations are based on a formalism that accounts for the alignment of the applied external magnetic field with respect to the light propagation direction, and additionally different polarization states of the radiation field are considered. The obtained results indicate that twisted light could be of particular interest for precision experiments. One possible application is the use in single-ion clocks. The work shows that high multipole orders of the vortex beams allow excitations in the intensity minimum in the center of these beams without causing large disturbances, and thus may enable a significant reduction of the light shift in atomic transitions.Getwisteten Lichtstrahlen wurde in den letzten Jahren viel Aufmerksamkeit gewidmet. Dafür gibt es berechtigte Gründe. Die Eigenschaften von getwisteten Lichtstrahlen sind ungewöhnlich und unterscheiden sich grundlegend von den Eigenschaften ebener Wellen: Ihre Phasenfronten weisen eine helikale Struktur auf, woraus der Name getwisted hervorgeht. Diese helikale Phasenstruktur resultiert aus dem wohldefinierten Orbitalen-Drehimpuls (OAM), den sie entlang ihrer Ausbreitungsrichtung und zusätzlich zum Spin-Drehimpuls (SAM) haben. Charakterisch ist das ringförmige Intensitätsprofil mit dem zentralen Minimum, ebenso wie die Phasensingularität im Strahlzentrum. Diese Arbeit ist im Wesentlichen in zwei Hauptteile gegliedert, die sich jeweils mit einem anderen Aspekt des getwisteten Lichts befassen. Diese Untersuchungen werden mit Besselstrahlen, einer Art des getwisteten Lichts, durchgeführt. Getwistete Lichtstrahlen sind zylindersymmetrisch, aus diesem Grund werden sie in der Basis von zirkular polarisiertem Licht definiert. Diese Tatsache führt zur ersten Fragestellung: Ist es möglich getwistetes Licht in anderen Polarisationszuständen zu generieren? Wir zeigen, wie dies mit dem Superpositionsprinzip realisiert werden kann und wie damit verschiedene Polarisationszustände von Besselstrahlen, wie z.B. lineare, radiale oder azimuthale Polarisation, konstruiert werden können. Der zweite Teil fokussiert sich auf die Anregung von Atomen durch getwistete Besselstrahlen. Insbesondere analysieren wir, wie der Einsatz von getwistetem Licht einzelne atomare Multipolübergänge modifizieren kann. Die erzielten Ergebnisse zeigen, dass eine genaue Positionierung des Atoms notwendig ist, um eine effiziente Modifikation zu erreichen. Im letzten Kapitel werden diese beiden Aspekte kombiniert. Dort untersuchen wir Übergänge zwischen magnetischen Hyperfeinstrukturzuständen in einem einzelnen gefangenen Atom (bzw. Ion), das einem zusätzlichen Magnetfeld ausgesetzt ist. Die erzielten Ergebnisse machen kenntlich, dass getwistetes Licht für Präzisionsexperimente von Interesse sein könnte. Eine denkbare Anwendung wäre die Verwendung in Einzelionen-Uhren. Die Arbeit zeigt, dass hohe Multipolordnungen der Vortex-Lichtstrahlen Anregungen im Intensitätsminimum im Zentrum dieser Strahlen ermöglichen, ohne große Störungen zu bewirken und somit eine deutliche Reduktion der Lichtverschiebung in atomaren Übergängen möglich machen

Strengthening organic food value chains in Germany - first results of the EU-project HalthyGrowth – From niche to volume with integrity and trust

Our presentation starts with a short overview of the diversity of organic food chains in Germany. We show that several different supply chains coexist. Smaller businesses tend to focus on market niches and particular consumer groups and values. The in-depth analysis identifies the strengths and weaknesses of different types of organic food chains. Exemplarily, we highlight factors that can strengthen value chains for organic food

Site-Specific Conditions Change the Response of Bacterial Producers of Soil Structure-Stabilizing Agents Such as Exopolysaccarides and Lipopolysaccarides to Tillage Intensity

Agro-ecosystems experience huge losses of land every year due to soil erosion induced by poor agricultural practices such as intensive tillage. Erosion can be minimized by the presence of stable soil aggregates, the formation of which can be promoted by bacteria. Some of these microorganisms have the ability to produce exopolysaccharides and lipopolysaccharides that "glue" soil particles together. However, little is known about the influence of tillage intensity on the bacterial potential to produce these polysaccharides, even though more stable soil aggregates are usually observed under less intense tillage. As the effects of tillage intensity on soil aggregate stability may vary between sites, we hypothesized that the response of polysaccharide-producing bacteria to tillage intensity is also determined by site-specific conditions. To investigate this, we performed a high-throughput shotgun sequencing of DNA extracted from conventionally and reduced tilled soils from three tillage system field trials characterized by different soil parameters. While we confirmed that the impact of tillage intensity on soil aggregates is site-specific, we could connect improved aggregate stability with increased absolute abundance of genes involved in the production of exopolysaccharides and lipopolysaccharides. The potential to produce polysaccharides was generally promoted under reduced tillage due to the increased microbial biomass. We also found that the response of most potential producers of polysaccharides to tillage was site-specific, e.g., Oxalobacteraceae had higher potential to produce polysaccharides under reduced tillage at one site, and showed the opposite response at another site. However, the response of some potential producers of polysaccharides to tillage did not depend on site characteristics, but rather on their taxonomic affiliation, i.e., all members of Actinobacteria that responded to tillage intensity had higher potential for exopolysaccharide and lipopolysaccharide production specifically under reduced tillage. This could be especially crucial for aggregate stability, as polysaccharides produced by different taxa have different "gluing" efficiency. Overall, our data indicate that tillage intensity could affect aggregate stability by both influencing the absolute abundance of genes involved in the production of exopolysaccharides and lipopolysaccharides, as well as by inducing shifts in the community of potential polysaccharide producers. The effects of tillage intensity depend mostly on site-specific conditions

Effekte einer mehrwöchigen standardisierten Deoxynivalenolaufnahme über einen mit Fusarium spp. infizierten Weizen auf das Futteraufnahmeverhalten und den Gesundheitsstatus bei Pferden

Effects of a deoxynivalenol contaminated diet on feed intake and health status in horses

Strategies for medium-sized value-based food chains during growing process with a particular focus on the business logic and management concept

Growth of values-based food chains holds particular challenges. The disconnection between producers and consumers require strategies that maintain and communicate values throughout the food chain. The objective of this paper is to analyze strategies organic food businesses have chosen to deal with growth, and in particular, strategies that focus on consumers’ expectations and producers’ business strategies. A literature review on the challenges of growing organic food chains provided the conceptual framework. The analysis of three case studies of organic food businesses shows that the values of food chains and the related business strategies aiming to maintain and transmit these values differ significantly. One case study business is closely linked to the farmers and the chain is characterized by the quality of products and process. The second case study focuses on reliability between chain partners, while the third is based on good cooperation aiming to secure income and employment

Direct measurement of neutrons induced in lead by cosmic muons at a shallow underground site

Neutron production in lead by cosmic muons has been studied with a Gadolinium doped liquid scintillator detector. The detector was installed next to the Muon-Induced Neutron Indirect Detection EXperiment (MINIDEX), permanently located in the T\"ubingen shallow underground laboratory where the mean muon energy is approximately 7 GeV. The MINIDEX plastic scintillators were used to tag muons; the neutrons were detected through neutron capture and neutron-induced nuclear recoil signals in the liquid scintillator detector. Results on the rates of observed neutron captures and nuclear recoils are presented and compared to predictions from GEANT4-9.6 and GEANT4-10.3. The predicted rates are significantly too low for both versions of GEANT4. For neutron capture events, the observation exceeds the predictions by factors of $1.65\,\pm\,0.02\,\textrm{(stat.)}\,\pm\,0.07\,\textrm{(syst.)}$ and $2.58\,\pm\,0.03\,\textrm{(stat.)}\,\pm\,0.11\,\textrm{(syst.)}$ for GEANT4-9.6 and GEANT4-10.3, respectively. For neutron nuclear recoil events, which require neutron energies above approximately 5 MeV, the factors are even larger, $2.22\,\pm\,0.05\,\textrm{(stat.)}\,\pm\,0.25\,\textrm{(syst.)}$ and $3.76\,\pm\,0.09\,\textrm{(stat.)}\,\pm\,0.41\,\textrm{(syst.)}$, respectively. Also presented is the first statistically significant measurement of the spectrum of neutrons induced by cosmic muons in lead between 5 and 40 MeV. It was obtained by unfolding the nuclear recoil spectrum. The observed neutron spectrum is harder than predicted by GEANT4. An investigation of the distribution of the time difference between muon tags and nuclear recoil signals confirms the validity of the unfolding procedure and shows that GEANT4 cannot properly describe the time distribution of nuclear recoil events. In general, the description of the data is worse for GEANT4-10.3 than for GEANT4-9.6.Comment: 29 pages, 22 figures, 4 table

Extended experience in parieto-occipital expansion surgery by meander technique—clinical and radiological evaluation

Introduction: Brachycephaly and anterior and posterior plagiocephaly appear as an isolated entity or manifest in syndromic conditions. In severe cases, possible treatment options currently comprise either cranioplasty or osteogenetic distraction. The aim of this paper is to retrospectively review the perioperative course of a series of children treated by posterior meander expansion technique at our institution with focus on the course of postoperative intracranial volume and eventual tonsillar descent evolution. Methods: Forty-two children received a posterior cranial vault remodeling by means of a posterior meander technique during a 7-year period. Hospital records were reviewed, and pre- and postoperative MRIs were analyzed for intracranial volume, cephalic and asymmetry index, and tonsillar position over time. Results: Median age at surgery was 11.5 months (range 17 days-10 years). Nineteen children had a symmetrical cranial deformity, twenty-three an asymmetrical synostosis. Half of the cohort showed a syndromic condition. Transfusions were administered in the majority (92.2%) of the cases. A significant postoperative increase of intracranial volume was present from 1188.9 ± 370.4 cm(3) to 1324.8 ± 352.9 cm(3) (p < 0.001). The asymmetry index showed a significant improvement postoperatively: 0.86 ± 0.06 versus 0.91 ± 0.05 (p < 0.001), while the cephalic index showed a non-statistical change (0.91 ± 0.11 versus 0.88 ± 0.08). Tonsillar herniation, bilateral or homolateral, showed no significant changes at early control, while a nonsignificant amelioration of tonsillar descent was seen among children older than 12 months at late imaging follow-up. Conclusion: Among the osteoplastic techniques, the posterior meander technique offers several advantages, such as early mobilization of the child, less bony defects, absence of implants, and a small complication rate. However, further comparative studies among different surgical techniques are needed