Feshbach resonances in 40K

De wisselwerking tussen deeltjes bepaalt de eigenschappen van alle materie. Als het mogelijk is de wisselwerking in te stellen, kunnen deze eigenschappen worden veranderd. Er is een mechanisme bekend om de wisselwerking tussen sommige atoomsoorten te veranderen: de zogeheten Feshbach-resonanties. Deze resonanties kunnen optreden in ultrakoude atomen. Het mechanisme werkt alleen als de atomen in gasvorm zijn en tot dichtbij het absolute nulpunt zijn gekoeld. Feshbach-resonanties in ultrakoude atomen zijn al enige tijd bekend. De juiste magnetische veldsterktes waarbij deze resonanties optreden zijn echter nog onbekend en moeten voor elke atoomsoort opnieuw worden bepaald. Antje Ludewig bepaalde voor de kaliumisotoop 40K de waarden van 23 magnetische velden, waar de wisselwerking kan worden toegepast. Deze waarden worden gebruikt om theoretische modellen te verbeteren, zodat het makkelijker wordt Feshbach-resonanties in andere atoomsoorten te voorspellen. Als de wisselwerking tussen ultrakoude atomen ingesteld kan worden, kunnen ultrakoude atomen gebruikt worden als modelsysteem voor het oplossen van andere problemen in de natuurkunde zoals hoge-temperatuursupergeleiding of het gedrag van neutronensterren

Bouncing trimer: a random self-propelled particle, chaos and periodical motions

A trimer is an object composed of three centimetrical stainless steel beads equally distant and is predestined to show richer behaviours than the bouncing ball or the bouncing dimer. The rigid trimer has been placed on a plate of a electromagnetic shaker and has been vertically vibrated according to a sinusoidal signal. The horizontal translational and rotational motions of the trimer have been recorded for a range of frequencies between 25 and 100 Hz while the amplitude of the forcing vibration was tuned for obtaining maximal acceleration of the plate up to 10 times the gravity. Several modes have been detected like e.g. rotational and pure translational motions. These modes are found at determined accelerations of the plate and do not depend on the frequency. By recording the time delays between two successive contacts when the frequency and the amplitude are fixed, a mapping of the bouncing regime has been constructed and compared to that of the dimer and the bouncing ball. Period-2 and period-3 orbits have been experimentally observed. In these modes, according to observations, the contact between the trimer and the plate is persistent between two successive jumps. This persistence erases the memory of the jump preceding the contact. A model is proposed and allows to explain the values of the particular accelerations for which period-2 and period-3 modes are observed. Finally, numerical simulations allow to reproduce the experimental results. That allows to conclude that the friction between the beads and the plate is the major dissipative process.Comment: 22 pages, 10 figure

Phase-sensitive detection of Bragg scattering at 1D optical lattices

We report on the observation of Bragg scattering at 1D atomic lattices. Cold atoms are confined by optical dipole forces at the antinodes of a standing wave generated by the two counter-propagating modes of a laser-driven high-finesse ring cavity. By heterodyning the Bragg-scattered light with a reference beam, we obtain detailed information on phase shifts imparted by the Bragg scattering process. Being deep in the Lamb-Dicke regime, the scattered light is not broadened by the motion of individual atoms. In contrast, we have detected signatures of global translatory motion of the atomic grating.Comment: 4 pages, 4 figure

School-Based Mental Health Services and Programs: A Review of the Literature

In Chapter 1, a rationale, a statement regarding the focus of my paper, and historical backgrounds of both community-based mental health services and the history surrounding school-based mental health (SBMH) services were provided. In Chapter 2, I review 15 studies dated between 2003 and 2017 addressing the results of school-based mental health programs involving either an in-school parental component or services delivered by clinicians in school settings and the implications SBMH presents for the educational system and its personnel. Studies reviewed are summarized in chronological order and include both quantitative data pertaining to changes in behavioral and academic qualities in children and adolescents deemed “at risk” or diagnosed with mental health disorders, as well as qualitative input related to factors contributing to the success of school-based interventions. In the final chapter, I summarize my findings and provide my conclusions and recommendations for future research

The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus

Background: Cat breeders observed a frequent occurrence of internal hydrocephalus in Persian cats with extreme brachycephalic head morphology. Objective: To investigate a possible relationship among the grade of brachycephaly, ventricular dilatation, and skull dysmorphologies in Persian cats. Animals: 92 Persian-, 10 Domestic shorthair cats. Methods: The grade of brachycephaly was determined on skull models based on CT datasets. Cranial measurements were examined with regard to a possible correlation with relative ventricular volume, and cranial capacity. Persians with high (peke-face Persians) and lower grades of brachycephaly (doll-face Persians) were investigated for the presence of skull dysmorphologies. Results: The mean cranial index of the peke-face Persians (0.97 ± 0.14) was significantly higher than the mean cranial index of doll-face Persians (0.66 ± 0.04; P < 0.001). Peke-face Persians had a lower relative nasal bone length (0.15 ± 0.04) compared to doll-face (0.29 ± 0.08; P < 0.001). The endocranial volume was significantly lower in doll-face than peke-face Persians (89.6 ± 1.27% versus 91.76 ± 2.07%; P < 0.001). The cranial index was significantly correlated with this variable (Spearman´s r: 0.7; P < 0.0001). Mean ventricle: Brain ratio of the peke-face group (0.159 ± 0.14) was significantly higher compared to doll-face Persians (0.015 ± 0.01; P < 0.001). Conclusion and Clinical Relevance: High grades of brachycephaly are also associated with malformations of the calvarial and facial bones as well as dental malformations. As these dysmorphologies can affect animal welfare, the selection for extreme forms of brachycephaly in Persian cats should be reconsidered

Dimensional Crossover in Bragg Scattering from an Optical Lattice

We study Bragg scattering at 1D optical lattices. Cold atoms are confined by the optical dipole force at the antinodes of a standing wave generated inside a laser-driven high-finesse cavity. The atoms arrange themselves into a chain of pancake-shaped layers located at the antinodes of the standing wave. Laser light incident on this chain is partially Bragg-reflected. We observe an angular dependence of this Bragg reflection which is different to what is known from crystalline solids. In solids the scattering layers can be taken to be infinitely spread (3D limit). This is not generally true for an optical lattice consistent of a 1D linear chain of point-like scattering sites. By an explicit structure factor calculation we derive a generalized Bragg condition, which is valid in the intermediate regime. This enables us to determine the aspect ratio of the atomic lattice from the angular dependance of the Bragg scattered light.Comment: 4 pages, 5 figure

Broad Feshbach resonance in the 6Li-40K mixture

We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model we select the optimal resonance to study the 6Li/40K mixture. Experimentally, we obtain the asymmetric Fano lineshape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/40K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance in this mixture, Delta B=1.5(5) G. Our results offer good perspectives for the observation of universal crossover physics using this mass-imbalanced fermionic mixture.Comment: 4 pages, 2 figure

Ten microsatellite loci for the strawberry poison frog (Oophaga pumilio)

We describe primers and PCR conditions to amplify nine new tetranucleotide loci and one new dinucleotide locus isolated from the strawberry poison frog (Oophaga pumilio). In 21 individuals from Costa Rica, the number of alleles ranged from 4 to 16, observed heterozygosities from 40 to 100%, and polymorphic information content ranged from 0.60 to 0.90 per locus. Evidence for linkage disequilibrium was found only between two loci, but this pattern was not found in other populations tested. All primer pairs cross-amplified in Oophaga vicentei from Panama

Understanding and manipulating non-templated peptide bond formation by macrocyclase enzymes

Peptide macrocycles are attractive molecules because they are drug-like, protease resistant, cell permeable, and possess a rigid structure. They have been shown to possess various biological activities and to be able to inhibit protein-protein interactions and other complex targets. Although several macrocyclases have been characterized to date, only two can catalyze the formation of cyclic peptides containing less than 9 amino acids in their core. PatGmac, from the biosynthesis of cyanobactins, is a versatile catalyst with very broad substrate specificity. It can utilize varied peptide sequences, incorporate unnatural amino acids, including substrates that are peptide “chimeras” containing triazoles, peg linkers and sugars (Figure 1A, bottom). Despite its remarkable substrate promiscuity, PatGmac is extremely slow, with turnover rates in the vicinity of once per day. In search for a more efficient macrocyclase we studied GmPOPB, a prolyl oligopeptidase from the mushroom Galerina marginata. GmPOPB (fast macrocyclase) participates in the biosynthesis of the toxic amanitins, catalyzing both peptide bond hydrolysis and peptide bond formation with equal efficiency (Figure 1A, top). We determined crystal structures of apoGmPOPB and GmPOPB mutants bound to a peptidase and a macrocyclase substrate unveiling a mechanism by which the enzyme controls which reaction will be catalyzed. We have also performed an extensive kinetic analysis of this enzyme in comparison to the slow PatGmac. Crucial differences exist between the fast and the slow macrocyclases. Substrate positioning plays an important role towards catalytic efficiency. For the fast macrocyclase GmPOPB there is product inhibition and the rate-limiting step for the reaction is product release. For the slow macrocyclase PatGmac product release is not rate determining for the majority of the substrates tested, and the rate-limiting step is coupled to chemistry. Guided by our kinetic studies, we have designed modified peptide substrates, which eliminate the requirement for a long peptide substrate from 25 amino acids to 13 amino acids for the fast macrocyclase. We are currently designing enzyme variants to improve the catalytic efficiency of the slow macrocyclase and to broaden the substrate scope of the fast macrocyclase. We hope our findings will result in a better, more efficient and substrate permissible macrocyclase that can be used for the biocatalytic generation of cyclic peptide libraries to be tested for biological function. Please click Additional Files below to see the full abstract

Characterization of a dual function macrocyclase enables design and use of efficient macrocyclization substrates

H.L. is funded by the George & Stella Lee Scholarship and Criticat EPSRC. This project was also funded by the European Research Council project 339367 NCB-TNT and by the BBSRC (K015508/1). JHN is 1000 talent scholar of the Chinese Academy of Sciences at the University of Sichuan.Peptide macrocycles are promising therapeutic molecules because they are protease resistant, structurally rigid, membrane permeable and capable of modulating protein-protein interactions. Here, we report the characterization of the dual function macrocyclase-peptidase enzyme involved in the biosynthesis of the highly toxic Amanitin toxin family of macrocycles. The enzyme first removes 10 residues from the N-terminus of a 35-residue substrate. Conformational trapping of the amino acid peptide forces the enzyme to release this intermediate rather than proceed to macrocyclization. The enzyme rebinds the 25 amino acid peptide in a different conformation and catalyzes macrocyclization of the N-terminal 8 residues. Structures of the enzyme bound to both substrates and biophysical analysis characterize the different binding modes rationalizing the mechanism. Using these insights simpler substrates with only five C-terminal residues were designed, allowing the enzyme to be more effectively exploited in biotechnology.Publisher PDFPeer reviewe