Microscopic theory of the activated behavior of the quantized Hall effect

The thermally activated behavior of the gate defined narrow Hall bars is studied by analyzing the existence of the incompressible strips within a Hartree-type approximation. We perform self-consistent calculations considering the linear response regime, supported by a local conductivity model. We investigate the variation of the activation energy depending on the width of samples in the range of $2d\sim [1-10] \mu m$. We show that the largest activation energy of high-mobility narrow samples, is at the low field edge of Hall filling factor 2 plateau (exceeding half of the cyclotron energy), whereas for relatively wide samples the higher activation energy is obtained at the high field edge of Hall plateau. In contrast to the single-particle theories based on the localization of electronic states, we found that the activation energy is almost independent of the properties of the density of states.Comment: 8 pages, 4 figure

Evanescent incompressible strips as origin of the observed Hall resistance overshoot

In this work we provide a systematic explanation to the unusual non-monotonic behavior of the Hall resistance observed at two-dimensional electron systems. We use a semi-analytical model based on the interaction theory of the integer quantized Hall effect to investigate the existence of the anomalous, \emph{i.e} overshoot, Hall resistance $R_{H}$. The observation of the overshoot resistance at low magnetic field edge of the plateaus is elucidated by means of overlapping evanescent incompressible strips, formed due to strong magnetic fields and interactions. Utilizing a self-consistent numerical scheme we also show that, if the magnetic field is decreased the $R_{H}$ decreases to its expected value. The effects of the sample width, temperature, disorder strength and magnetic field on the overshoot peaks are investigated in detail. Based on our findings, we predict a controllable procedure to manipulate the maxima of the peaks, which can be tested experimentally. Our model does not depend on specific and intrinsic properties of the material, provided that a single particle gap exists.Comment: A theoretical follow-up paper of arXiv:1007.258

Exchange-correlation enhancement of the Lande-g* factor in integer quantized Hall plateaus

We study the emergent role of many-body effects on a two dimensional electron gas (2DEG) within the Thomas-Fermi-Poisson approximation, including both the exchange and correlation interactions in the presence of a strong perpendicular magnetic field. It is shown that, the indirect interactions widen the odd-integer incompressible strips spatially, whereas the even-integer filling factors almost remain unaffected.Comment: 8 pages,4 figure

Quantum Hall Resistance Overshoot in 2-Dimensional Electron Gases - Theory and Experiment

We present a systematical experimental investigation of an unusual transport phenomenon observed in two dimensional electron gases in Si/SiGe heterostructures under integer quantum Hall effect (IQHE) conditions. This phenomenon emerges under specific experimental conditions and in different material systems. It is commonly referred to as Hall resistance overshoot, however, lacks a consistent explanation so far. Based on our experimental findings we are able to develop a model that accounts for all of our observations in the framework of a screening theory for the IQHE. Within this model the origin of the overshoot is attributed to a transport regime where current is confined to co-existing evanescent incompressible strips of different filling factors.Comment: 26 pages, 10 figure

Interaction mediated asymmetries of the quantized Hall effect

Experimental and theoretical investigations on the integer quantized Hall effect in gate defined narrow Hall bars are presented. At low electron mobility the classical (high temperature) Hall resistance line RH(B) cuts through the center of all Hall plateaus. In contrast, for our high mobility samples the intersection point, at even filling factors \nu = 2; 4 ..., is clearly shifted towards larger magnetic fields B. This asymmetry is in good agreement with predictions of the screening theory, i. e. taking Coulomb interaction into account. The observed effect is directly related to the formation of incompressible strips in the Hall bar. The spin-split plateau at \nu= 1 is found to be almost symmetric regardless of the mobility. We explain this within the so-called effective g-model.Comment: 4 pages, 3 figure

Thrombospondin-1 and VEGF in inflammatory bowel disease

Background and aim: Angiogenesis is an important process in the pathogenesis of chronic inflammation. We aimed to study the angiogeneic balance in inflammatory bowel disease (IBD) by evaluating the expression of vascular endothelial growth factor (VEGF) and thrombospondin-1 (TSP-1) on colonic epithelial cells, together with the expression of inducible nitric oxide synthase (iNOS). Methods: Twenty-one ulcerative colitis (UC), 14 Crohn’s disease (CD), 11 colorectal cancer patients, and 11 healthy controls colonic biopsy samples were evaluated immunohistochemically. Results: The expressions of TSP-1, VEGF, and iNOS in UC and CD groups were higher than expression in healthy control group, all with statistical significance. However, in colorectal cancer group, VEGF and iNOS expressions were increased importantly, but TSP-1 expression was not statistically different from healthy control group’s expression. Both TSP-1 and VEGF expressions were correlated with iNOS expression distinctly but did not correlate with each other. Conclusions: Both pro-angiogeneic VEGF and antiangiogeneic TSP-1 expressions were found increased in our IBD groups, but in colorectal cancer group, only VEGF expression was increased. TSP-1 increases in IBD patients as a response to inflammatory condition, but this increase was not enough to suppress pathologic angiogenesis and inflammation in IBD.Keywords: inflammatory bowel disease; thrombospondin-1; VEGF; iNOS; colon cance

Effectiveness of ranitidine bismuth citrate and proton pump inhibitor based triple therapies of Helicobacter pylori in Turkey

Background : Helicobacter pylori infection is the main cause of gastritis, gastroduodenal ulcer disease, MALT lymphoma, and adenocarcinoma of the stomach. The reported prevalence of H. pylori in the adult population in Turkey is 67.6%–81.3%. A national meta-analysis showed that the average H. pylori eradication rate with proton pump inhibitor-based triple regimens in Turkey had decreased from 84% in 1997 to 55.3% in 2004, suggesting a need to evaluate alternative regimens. Materials and methods : The study was a prospective, single-center trial with a parallel group design. After the selection procedure, consecutive out-patients were assigned to one of six study groups using random sampling numbers. All patients received amoxicillin 1,000 mg b.i.d. and clarithromycin 500 mg b.i.d. along with ranitidine bismuth citrate 400 mg b.i.d., or omeprazole 20 mg b.i.d., or lansoprazole 30 mg b.i.d., or rabeprazole 20 mg b.i.d., or pantoprazole 40 mg b.i.d., or esomeprazole 40 mg b.i.d. for 14 days. Results : When we look at the eradication rates of the treatment groups, only two groups (ranitidine bismuth citrate and rabeprazole groups) had eradication rates greater than 80%, both at intention to treat and per protocol analyses. The other four groups (omeprazole, lansoprazole, pantoprazole, and esomeprazole groups) showed statistically significant lower eradication rates both at intention to treat (between 57.6 and 66.7%) and per protocol (between 60.3 and 72.1%) analyses when compared with ranitidine bismuth citrate and rabeprazole groups (p<.05). Conclusion : Ranitidine bismuth citrate and/or rabeprazole based triple therapies must be preferred for the first-line treatment of H. pylori infection

Acaricidal activity of Foeniculum vulgare against Rhipicephalus annulatus is mainly dependent on its constituent from trans-anethone

Globally, the economic losses due to hard ticks infestation and the control of the associated diseases have been calculated at USD $13.9-18.7 billion per year. The economic impact is related to its direct damage to the skins, blood loss, anemia, severe immunological reactions and indirect losses that related to the effects of hemoparasites, cost of treatment for clinical cases and expenses incurred in the control of ticks. The current study evaluated the acaricidal activities of fennel Foeniculum vulgare essential oil and its main components; trans-anethole and fenchone; against R. annulatus. GC-MS analysis revealed that this oil contained 16 components representing 99.9% of the total identified compounds with E-anethole being the predominant component(64.29%), followed by fenchone (9.94%). The fennel oil and trans-anethole showed significant acaricidal activities. The LC50 of the fennel oil was attained at concentrations of 12.96% for adult ticks and 1.75% for tick larvae meanwhile the LC50 of trans-anethole was reached at concentrations of 2.36% for adult tick and 0.56% for tick larvae. On the contrary, fenchone showed no any significant adulticidal activities and its LC50 attained at a concentration of 9.11% for tick larvae. Regarding repellence activities, trans-anethole achieved 100% repellency at the concentration of 10% while fennel showed 86% repellency at the same concentration. Fenchone showed no repellency effect. Treatment of larvae with fennel, trans-anethole, and fenchone LC50 concentrations significantly inhibited the acetylcholinesterase activity. Meanwhile, glutathione s-transferase activity was significantly decreased in fennel treated larvae but no significant effect was found in the larvae of trans-anethole and fenchone groups. These results indicate that the acaricide effect of fennel oil may attributed to its high content of trans-anethole. This was supported by potent adulticidal, larvicidal, and repellency effects of trans-anethole against Rhipeciphalus annulatus tick and therefore it could be included in the list of acaricide of plant origin

Effect of exchange-correlation potential on the plasmon dispersions in a doped symmetrical double quantum well

We have calculated the plasmon dispersion relations in a doped double quantum well with and without exchange-correlation potential added to the effective potential of the system. The calculations were done for high and low doping densities by solving the Schrödinger and Poisson equations self-consistently. Our numerical results show that the exchange-correlation potential is quite important at high doping densities of donor impurities for plasmon dispersions at large wave vectors. On the other hand, the ratio of subband populations nl to donor density ND is more affected at low densities. © 2007 WILEY-VCH Verlag GmbH &amp; Co. KGaA