D-branes from Matrix Factorizations

B-type D-branes can be obtained from matrix factorizations of the Landau-Ginzburg superpotential. We here review this promising approach to learning about the spacetime superpotential of Calabi-Yau compactifications. We discuss the grading of the D-branes, and present applications in two examples: the two-dimensional torus, and the quintic.Comment: 10 pages. Talk given by J.W. at Strings '04, June 28-July 2, Pari

A single ion as a three-body reaction center in an ultracold atomic gas

We report on three-body recombination of a single trapped Rb^+ ion and two neutral Rb atoms in an ultracold atom cloud. We observe that the corresponding rate coefficient K_3 depends on collision energy and is about a factor of 1000 larger than for three colliding neutral Rb atoms. In the three-body recombination process large energies up to several 0.1eV are released leading to an ejection of the ion from the atom cloud. It is sympathetically recooled back into the cloud via elastic binary collisions with cold atoms. Further, we find that the final ionic product of the three-body processes is again an atomic Rb^+ ion suggesting that the ion merely acts as a catalyzer, possibly in the formation of deeply bound Rb_2 molecules.Comment: 5 pages, 4 figure

Makro- und mikroelektrochemische Untersuchungen zum lokalen Korrosionsverhalten ultrafeinkörniger und technischer Aluminiumlegierungen

The modification of conventional and well established material may have the ability to negotiate upcoming requirements and standards in the aircraft industry. Therefore, ultrafinegrained (UFG) metals and alloys have been in the focus of strong research interest due to their exceptional mechanical properties in the last years. These properties are predominantly achieved due to a smaller grain size and higher dislocation density. However, one can also expect that the high surface fraction of grain boundaries and dislocations will influence the corrosion behavior of these materials. In particular, the above-mentioned structural characteristics may play an important role in passivity and localized breakdown. Open literature dealing with the electrochemical behavior of ultrafine-grained metals and alloys, give no clear consensus on the effect of the crystalline nature of the material on the corrosion behavior. Depending on the study, an improved as well as an impaired corrosion behavior of ultrafine-grained materials as compared with conventional grained (CG) alloys of the same type has been observed. The present study investigates the effect of severe plastic deformation on the corrosion performance of Al-Mg model-alloys and AA2024-T351 with respect to pitting and intergranular corrosion. Ultrafine-grained specimens were produced by equal-channel angular pressing (ECAP) and increasing the number of extruded passes. The alloys were electrochemically investigated in various NaCl solutions and compared with their conventionally grained counterparts. The results of potentiodynamic polarization experiments indicate that the anodic behavior is strongly affected by the deformation technique in respect to the CG samples. Corrosion attack takes place in form of laterally spreaded crystallographic filiform corrosion for the CG specimens, whilst UFG Al-Mg alloys tend with increasing pass number to deep localized pitting corrosion. Futhermore, the susceptibility to intergranular corrosion was investigated by potentiostatic experiments. Major differences are present in the corrosion morphology based on the large microstructural modification. The bulk material shows primarily intergranular corrosion along their textured grain boundaries (GB). In contrast, the ECAP material with a higher number of passes exhibits predominantly pitting corrosion, whereas the ECAP material with one pass shows a transition state. The results suggest that the UFG microstructure controls the corrosion towards pitting due to a complete rearrangement of GBs, indicating a kind of desensitization effect from the ECAP process. In addition, the electrochemical behavior of pure matrix material as well as single intermetallic particle connected with matrix on aluminum 2024-T3 has been studied in the sub 10 micrometer range by using a combination of optical lithographic structuring and microcapillary cell technique. Due to the fact that conventional micro scale techniques are not reasonably practicable to isolate well defined geometric areas below these dimensions. We demonstrate a novel method using an optical pinhole mask overcoming some limitations of the microcapillary technique. With this advanced technique we investigated the electrochemical behavior of an aluminium alloy AA2024-T3, to obtain a more detailed insight into corrosion characteristics and particle dissolution.Die Modifikation altbewährter als auch klassischer Werkstoffe kann trotz der sukzessiven Substitution vorhandener Flugzeugstrukturen durch neuartige Materialien, wie glas- und kohlefaserverstärkte Kunststoffe, eine vielversprechende Alternative zur Bewältigung steigender Anforderungen im Flugzeugbau, sein. Vor allem hoch- und höchstfeste Aluminiumlegierungen spielen speziell in modernen Luftfahrtsystemen immer noch eine große Rolle. Aufgrund der vielversprechenden mechanischen Eigenschaften haben ultrafeinkörnige (engl.: ultrafine grained, UFG) Werkstoffe, mit Korngrößen im Submikrometerbereich, in den letzten Jahren immer mehr an Bedeutung gewonnen. Ihre außergewöhnlichen mechanischen Eigenschaften erhalten diese Werkstoffe durch eine verkleinerte Korngröße als auch durch eine erhöhte Versetzungsdichte. Inwieweit sich diese mikrostrukturellen Merkmale auf das Korrosionsverhalten auswirken, ist bis zum jetzigen Zeitpunkt ungeklärt und wird kontrovers diskutiert. Im Rahmen der vorliegenden Arbeit wurden für einphasige AlMg- als auch einer technischen AlCuMg-Legierung (AA2024) ultrafeinkörnige Gefügestrukturen mittels Equal Channel Angular Pressing (ECAP) erzeugt und in Abhängigkeit des Umformgrades elektrochemisch charakterisiert. Die zwei Legierungen wurden jeweils in chloridhaltiger Umgebung auf ihre Anfälligkeit für Loch- und interkristalline Korrosion untersucht. Die durch den Verformungsprozess initiierten Gefügeveränderungen wirken sich besonders stark auf die Angriffsmorphologie aus. Mit steigendem Umformgrad konnte für die AlMg-Legierung ein Übergang von kristallographischem Lochfraß zu lokalisierter Lochkorrosion beobachtet werden. Das Verhalten wurde weniger mit der kleineren Korngröße als mit einer erhöhten Versetzungsdichte erklärt. Für die technische AlCuMg-Legierung lässt sich feststellen, dass mit steigendem Umformungsgrad die Anfälligkeit für interkristalline Korrosion abnimmt. Im Gegensatz zur grobkörnigen Variante erfolgt der Angriff unter interkristallinen Bedingungen lochfraßähnlich. Ähnlich wie für die AlMg-Modelllegierung lenkt die ultrafeinkörnige Mikrostruktur die Angriffsmorphologie in Richtung lokaler Lochkorrosion. Oberflächenanalytische Untersuchungen ergaben dabei, dass der Umformprozess die chemische Zusammensetzung der ursprünglichen Korngrenzen und somit den Werkstoff „desensibilisiert“. Eine modellhafte Darstellung der Ergebnisse für beide Legierungstypen und -varianten wurde des Weiteren entworfen. Zur lokalen Bestimmung des elektrochemischen Verhaltens lokaler Gefügebestandteile wurde der Versuch unternommen mittels photolithographischem Ansatz Mikrobereichsmessungen zur Charakterisierung einzelner Legierungsbestandteile durchzuführen. Mit Hilfe dieser Technik konnten elektrochemische Messflächen mit Durchmessern unter 10 Mikrometer freigelegt und mittels Mikrokapillartechnik elektrochemisch untersucht werden. Anhand von Reinstaluminium konnte die Technik eindrucksvoll verifiziert werden. Untersuchungen einzelner Sekundärphasen der technischen Legierung ergaben dagegen keine eindeutigen Ergebnisse

Queen pheromones in Temnothorax ants: control or honest signal?

Background The division of reproductive labor among group members in insect societies is regulated by "queen pheromones". However, it remains controversial whether these are manipulative, i.e., actively suppress worker reproduction, or honestly signal the fertility status of the queen to which workers react in their own interest by refraining from laying eggs. Manipulative queen control is thought to lead to an evolutionary arms race between queens and workers, resulting in complex queen bouquets that diverge strongly among different populations and species. In contrast, honest signals would evolve more slowly and might therefore differ less strongly within and among species. Results We aimed at determining the tempo of the evolution of queen signals in two ways. First, we investigated whether queens of Temnothorax ants are capable of controlling egg laying by workers of their own, closely, and distantly related species. Second, we compared the species- and caste-specific patterns of cuticular hydrocarbons, which are assumed to convey information on reproductive status. In mixed-species colonies, queens were not able to fully suppress egg-laying and male production by workers of unrelated species, while workers did not reproduce under the influence of a queen from their own species. Furthermore, the chemical profiles differed more strongly among queens of different species than among the respective workers. Conclusions Our results suggest that cuticular hydrocarbons associated with fecundity are not fully conserved in evolution and evolve slightly faster than worker-specific components in the blend of cuticular hydrocarbons. While this higher rate of evolution might reflect an arms race between queens and workers, the observation that workers still respond to the presence of a queen from another species support the honest signal hypothesis. Future studies need to examine alternative explanations for a higher rate of evolution of queen-specific substances, such as an involvement of such compounds in mating

Efficient Bioelectrochemical Conversion of Industrial Wastewater by Specific Strain Isolation and Community Adaptation

The aim of this study was the development of a specifically adapted microbial community for the removal of organic carbon from an industrial wastewater using a bioelectrochemical system. In a first step, ferric iron reducing microorganisms were isolated from the examined industrial wastewater. In a second step, it was tested to what extent these isolates or a cocultivation of the isolates with the exoelectrogenic model organism Geobacter sulfurreducens (G. sulfurreducens) were able to eliminate organic carbon from the wastewater. To establish a stable biofilm on the anode and to analyze the performance of the system, the experiments were conducted first under batch-mode conditions for 21 days. Since the removal of organic carbon was relatively low in the batch system, a similar experiment was conducted under continuous-mode conditions for 65 days, including a slow transition from synthetic medium to industrial wastewater as carbon and electron source and variations in the flow rate of the medium. The overall performance of the system was strongly increased in the continuous- compared to the batch-mode reactor and the highest average current density (1,368 mA/m2) and Coulombic efficiency (54.9%) was measured in the continuous-mode reactor inoculated with the coculture consisting of the new isolates and G. sulfurreducens. The equivalently inoculated batch-mode system produced only 82-fold lower current densities, which were accompanied by 42-fold lower Coulombic efficiencies

Opening Mirror Symmetry on the Quintic

Aided by mirror symmetry, we determine the number of holomorphic disks ending on the real Lagrangian in the quintic threefold. The tension of the domainwall between the two vacua on the brane, which is the generating function for the open Gromov-Witten invariants, satisfies a certain extension of the Picard-Fuchs differential equation governing periods of the mirror quintic. We verify consistency of the monodromies under analytic continuation of the superpotential over the entire moduli space. We reproduce the first few instanton numbers by a localization computation directly in the A-model, and check Ooguri-Vafa integrality. This is the first exact result on open string mirror symmetry for a compact Calabi-Yau manifold.Comment: 26 pages. v2: minor corrections and improvement

Low-dose intranasal versus oral midazolam for routine body MRI of claustrophobic patients

The purpose of this study was to assess prospectively the potential of low-dose intranasal midazolam compared to oral midazolam in claustrophobic patients undergoing routine body magnetic resonance imaging (MRI). Seventy-two adult claustrophobic patients referred for body MRI were randomly assigned to one of two treatment groups (TG1 and TG2). The 36 patients of TG1 received 7.5mg midazolam orally 15min before MRI, whereas the 36 patients of TG2 received one (or, if necessary, two) pumps of a midazolam nasal spray into each nostril immediately prior to MRI (in total, 1 or 2mg). Patients' tolerance, anxiety and sedation were assessed using a questionnaire and a visual analogue scale immediately before and after MRI. Image quality was evaluated using a five-point-scale. In TG1, 18/36 MRI examinations (50%) had to be cancelled, the reduction of anxiety was insufficient in 12/18 remaining patients (67%). In TG2, 35/36 MRI examinations (97%) were completed successfully, without relevant adverse effects. MRI image quality was rated higher among patients of TG2 compared to TG1 (p<0.001). Low-dose intranasal midazolam is an effective and patient-friendly solution to overcome anxiety in claustrophobic patients in a broad spectrum of body MRI. Its anxiolytic effect is superior to that of the orally administrated for

Effectiveness and cost-efficiency of phosphate binders in hemodialysis

Health political background: In 2006, the prevalence of chronic renal insufficiency in Germany was 91,718, of which 66,508 patients were on dialysis. The tendency is clearly growing. Scientific background: Chronic renal insufficiency results in a disturbance of the mineral balance. It leads to hyperphosphataemia, which is the strongest independent risk factor for mortality in renal patients. Usually, a reduction in the phosphate intake through nutrition and the amount of phosphate filtered out during dialysis are not sufficient to reduce the serum phosphate values to the recommended value. Therefore, phosphate binders are used to bind ingested phosphate in the digestive tract in order to lower the phosphate concentration in the serum. Four different groups of phosphate binders are available: calcium- and aluminium salts are the traditional therapies. Sevelamer and Lanthanum are recent developments on the market. In varying doses, all phosphate binders are able to effectively lower phosphate concentrations. However, drug therapies have achieved recommended phosphate levels in only 50 percent of patients during the last years. Research questions: How effective and efficient are the different phosphate binders in chronic renal insufficient patients? Methods: The systematic literature search yielded 1,251 abstracts. Following a two-part selection process with predefined criteria 18 publications were included in the assessment. Results: All studies evaluated conclude that serum phosphate, serum calcium and intact parathyroid hormone can be controlled effectively with all phosphate binders. Only the number of episodes of hypercalcaemia is higher when using calcium-containing phosphatebinders compared to Sevelamer and Lanthanum. Regarding the mortality rate, the cardiovascular artery calcification and bone metabolism no definite conclusions can be drawn. In any case, the amount of calcification at study start seems to be crucial for the further development of the cardiovascular calcification. Economic studies show higher costs for Sevelamer and Lanthanum compared to calcium-containing phosphate binders. Discussion: Only a few well documented primary studies on the effectiveness of phosphate binders are available. Particularly long-term studies with a robust study design and transparent documentation are lacking. Ten of the eleven primary studies included in this report were conducted in only 539 patients from five patient collectives. Conclusions: From a medical point of view, Sevelamer shows some superiority over calcium-containing phosphate binders based on the current data, at least for special indications. The validity of the present Health Technology Assessment (HTA) report is significantly limited due to the limited number of available publications, the low sample size of treated patients, as well as the fact that the majority of studies are based on the same patient collectives. Prospective long-term studies not funded by the industry with adequate sample sizes and comparable study designs are called for to make authoritative statements regarding the medical effectiveness and safety of Sevelamer and Lanthanum, as well as regarding their economic efficiency