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J Arlt

Publications and source records attributed to J Arlt.

8 recordsLinked to original sources

Routes towards Anderson-like localization of Bose-Einstein condensates in disordered optical lattices.

We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.

Journal Article↗

Single molecule fluorescence imaging and its application to the study of DNA condensation.

Single molecule fluorescence imaging incorporated with optical tweezers and a laminar flow cell has been used to monitor the kinetic process of DNA condensation induced by spermidine. It was found that at least two steps were involved in the condensation process of the hydrodynamically-stretched linear DNA; a lag period followed by a rapid collapse of DNA. The lag time increased with the flow speed and the collapse time remained short within the range of the flow speed studied. The effect of salt concentration on the condensation process was examined, and the results suggest that the longer lag time observed in the higher salt buffer probably results from the displacement of bound cations and rearrangement of spermidine on the DNA. The flow-speed dependence of the lag time suggests that a nucleation event at the free end of the DNA, i.e. formation of a loop, may play a vital role in the kinetic process of condensation.

DNA↗

Creation and manipulation of three-dimensional optically trapped structures.

An interferometric pattern between two annular laser beams is used to construct three-dimensional (3D) trapped structures within an optical tweezers setup. In addition to being fully translatable in three dimensions, the trapped structure can be rotated controllably and continuously by introducing a frequency difference between the two laser beams. These interference patterns could play an important role in the creation of extended 3D crystalline structures.

Journal Article↗

Controlled rotation of optically trapped microscopic particles.

We demonstrate controlled rotation of optically trapped objects in a spiral interference pattern. This pattern is generated by interfering an annular shaped laser beam with a reference beam. Objects are trapped in the spiral arms of the pattern. Changing the optical path length causes this pattern, and thus the trapped objects, to rotate. Structures of silica microspheres, microscopic glass rods, and chromosomes are set into rotation at rates in excess of 5 hertz. This technique does not depend on intrinsic properties of the trapped particle and thus offers important applications in optical and biological micromachines.

Animals↗

Observation of harmonic generation and nonlinear coupling in the collective dynamics of a bose-einstein condensate

We report the observation of harmonic generation and strong nonlinear coupling of two collective modes of a condensed gas of rubidium atoms. Using a modified time averaged orbiting potential trap we changed the trap anisotropy to a value where the frequency of the m = 0 high-lying mode corresponds to twice the frequency of the m = 0 low-lying mode, thus leading to strong nonlinear coupling between these modes. By changing the anisotropy of the trap and exciting the low-lying mode we observed significant frequency shifts of this fundamental mode and also the generation of its second harmonic.

Journal Article↗

Observation of the scissors mode and evidence for superfluidity of a trapped bose-einstein condensed Gas

We report the observation of the scissors mode of a Bose-Einstein condensed gas of 87Rb atoms in a magnetic trap, which gives direct evidence of superfluidity in this system. The scissors mode of oscillation is excited by a sudden rotation of the anisotropic trapping potential. For a gas above T(c) (normal fluid) we detect the occurrence of oscillations at two frequencies, with the lower frequency corresponding to the rigid body value of the moment of inertia. Well below T(c) the condensate oscillates at a single frequency, without damping, as expected for a superfluid.

Journal Article↗

Is there any relationship between functional dyspepsia and chronic gastritis associated with Helicobacter pylori infection?

BACKGROUND/AIMS: The relationship between functional dyspepsia, H. pylori infection and chronic gastritis is controversial. Our aims were 1) To determine the prevalence of symptoms and the degree of association between symptoms and histopathological findings in different topographical gastric regions in patients with functional dyspepsia and H. pylori infection; 2) To determine the effect of eradication treatment on functional dyspepsia symptoms. METHODOLOGY: Prospective randomized study. 251 consecutive patients with dyspepsia (141 women and 110 men), mean age 48.08, SD 16.68 (without ulcer, gastric malignancy or reflux esophageal disease as determined by endoscopy), and with H. pylori infection, underwent upper endoscopy accompanied by the obtaining of 6 biopsies (cardia, corpus, antrum) at baseline, 3 and 6 months after treatment (pantoprazole 40 mg, once daily, amoxycillin 100 mg b.i.d., clarithromycine 500 mg b.i.d.). Inflammation, activity, H. pylori presence and other mucosal alterations were evaluated semi-quantitatively according to the Sydney system, before treatment and 6 months following treatment. An interview that was carried out before, and 6 months following the treatment, determined seven symptoms (scored as 0-3); epigastric burning and pressure, pain after meal, nausea, vomiting, bloating and belching, pain on empty stomach and anorexia. 95% confidence intervals were calculated for mean values of the symptoms and histological findings. The association between symptoms and histological findings was determined by the Kendall tau-b (K tau-b). Using the t test on a 5% level of significance we tested the null hypothesis that symptoms and histological findings were independent variables. RESULTS: The effectiveness of eradication after 3 months was 87.3% and after 6 months 92.0%. Reinfection rate after 6 months was 6.4% and the overall failure of eradication was 1.6%. Significant decline of chronic inflammation, activity and H. pylori was found in cardia, corpus and antrum (P = 0.001). Glandular atrophy was found to be lower in corpus and antrum (P = 0.001), whereas in cardia an increase was found. Intestinal metaplasia remained unchanged in all gastric regions, whereas a higher degree of foveolar hyperplasia was found, which was most pronounced in corpus and antrum (P = 0.01). There was a significant regression of lymphoid follicles in cardia and antrum (P = 0.001). On the first visit, the mean significant association between symptoms and histological findings was higher, with lower variation of K tau values as compared with the visit 6 months after treatment (K tau-b 0.171, SD 0.05, variation coefficient 30.5% vs. K tau-b 0.167, SD 0.07, variation coefficient 41.5%). According to the topographic distribution of gastritis at the time of the first visit, the mean significant association between symptoms and findings was found to be highest in antrum and corpus as opposed to the visit 6 months after treatment, where the values of association were found to be highest for variables from cardia and lowest for those in gastric corpus. After 6 months both the number of patients complaining of symptoms and dyspepsia score were lower (Wilcoxon P = 0.000). CONCLUSIONS: Advanced morphological changes of gastric mucosa were found to be significantly associated with symptoms of dysmotility. Pain on an empty stomach is predictive of antral inflammation. Cardia showed higher values of mean association with symptoms 6 months after therapy. Eradication treatment results in an improvement of both inflammatory changes and symptoms. In some patients persisting dysmotility symptoms were associated with persistent inflammation in cardia, which was also true for antrum, however to a lesser degree.

Adult↗