Correlated mesoscopic fluctuations in integer quantum Hall transitions

We investigate the origin of the resistance fluctuations of mesoscopic samples, near transitions between Quantum Hall plateaus. These fluctuations have been recently observed experimentally by E. Peled et al. [Phys. Rev. Lett. 90, 246802 (2003); ibid 90, 236802 (2003); Phys. Rev. B 69, R241305 (2004)]. We perform realistic first-principles simulations using a six-terminal geometry and sample sizes similar to those of real devices, to model the actual experiment. We present the theory and implementation of these simulations, which are based on the linear response theory for non-interacting electrons. The Hall and longitudinal resistances extracted from the Landauer formula exhibit all the observed experimental features. We give a unified explanation for the three regimes with distinct types of fluctuations observed experimentally, based on a simple generalization of the Landauer-Buttiker model. The transport is shown to be determined by the interplay between tunneling and chiral currents. We identify the central part of the transition, at intermediate filling factors, as the critical region where the localization length is larger than the sample size.Comment: 18 pages 17 figure

Momentum average approximation for models with electron-phonon coupling dependent on the phonon momentum

We generalize the momentum average (MA) approximation to study the properties of models with momentum-dependent electron-phonon coupling. As in the case of the application of the original MA to the Holstein model, the results are analytical, numerically trivial to evaluate, exact for both zero bandwidth and for zero electron-phonon coupling, and are accurate everywhere in parameter space. Comparison with available numerical data confirms this accuracy. We then show that further improvements can be obtained based on variational considerations, using the one-dimensional breathing-mode Hamiltonian as a specific example. For example, by using this variational MA, we obtain ground state energies within at most 0.3% error of the numerical data.Comment: 15 pages, 10 figure

A reflection on learning crafts as a practice for self-development

This paper represents a reflection on craft as a process that stimulates self-development. Central to this approach is the perception of craft, not as a means of production, but as an exercise of relating to the world. The paper suggests that through the dialogue between the mind, body and environment craft practitioners experience a particular form of connection with the world that reshapes their perceptual and conceptual understanding of it. Rather than following an ego-driven tendency to control, a craftsperson is exposed to modes of ‘knowing’ and ‘being’ that embrace the inherent uncertainty of a complex world. The learning experience of a novice (lead author) demonstrates such a course of development in this paper. In particular, the liminal space that needs to be created for the dialogue between the self and the non-self is explored. This personal narrative is woven together with the experience of craft masters within different social contexts and value systems (from traditional to modern to postmodern) and their views on the process of being and becoming a craftsperson

The role of the lattice structure in determining the magnon-mediated interactions between charge carriers doped into a magnetically ordered background

We use two recently proposed methods to calculate exactly the spectrum of two spin-${1\over 2}$ charge carriers moving in a ferromagnetic background, at zero temperature, for three types of models. By comparing the low-energy states in both the one-carrier and the two-carrier sectors, we analyze whether complex models with multiple sublattices can be accurately described by simpler Hamiltonians, such as one-band models. We find that while this is possible in the one-particle sector, the magnon-mediated interactions which are key to properly describe the two-carrier states of the complex model are not reproduced by the simpler models. We argue that this is true not just for ferromagnetic, but also for antiferromagnetic backgrounds. Our results question the ability of simple one-band models to accurately describe the low-energy physics of cuprate layers.Comment: 15 pages, 10 figure

Sedimentological and stratigraphic framework of the several hundred thousand years old lacustrine record from Lake Van, Turkey

Within the frame of the International Continental scientific Drilling Program (ICDP) project PALEOVAN, a long and continuous sediment record from Lake Van, a closed lake situated in a climatically sensitive semiarid and tectonically active region in Eastern Anatolia, has been drilled in summer 2010. At two sites, Ahlat Ridge and Northern Basin, sedimentary records of 220 and 140 m were recovered, respectively. With basal ages possibly around 500'000 years, these records span several glacial-interglacial cycles and reach back until the lake’s initial transgression in the Middle Pleistocene. First results from ongoing analysis of core-catcher samples and newly opened cores document the sedimentological and geochemical succession. Two composite profiles of the drill sites were defined. Core catcher-based geochemical data such as proxies of lake’s productivity and catchment alterations show large variations and reflect a rich paleoenvironmental history. Most of the 220 m thick succession consists of carbonate mud, mostly sub-mm-thick laminated and interbedded by either homogenous mud or pyroclastic cm-thick layers. The lowermost sediments from the Ahlat Ridge site represent the initial lake transition as the drilling could not penetrate further and the seismic data indicates coincidence with the ‘acoustic’ basement. Such an early transgressive state of the lake’s history is also supported by the lithology consisting of a gravel unit as an indicator of a beach-like environment, which is overlain by sand deposits containing fresh-water gastropods (Bithynia). Above 200 mblf, the laminated mud clearly indicates that the lake was already deep enough to form anoxic bottom water as the laminations were preserved. This unique paleoclimate archive indicates that great changes of the depositional conditions occurred that hint to a fascinating evolution of the environment and has ideal prerequisites for the investigation of the Quaternary climate evolution in the Near East

Surface coupling effects on the capacitance of thin insulating films

A general form for the surface roughness effects on the capacitance of a capacitor is proposed. We state that a capacitor with two uncoupled rough surfaces could be treated as two capacitors in series which have been divided from the mother capacitor by a slit. This is in contrast to the case where the two rough surfaces are coupled. When the rough surfaces are coupled, the type of coupling decides the modification of the capacitance in comparison to the uncoupled case. It is shown that if the coupling between the two surfaces of the capacitor is positive (negative), the capacitance is less (higher) than the case of two uncoupled rough plates. Also, we state that when the correlation length and the roughness exponent are small, the coupling effect is not negligible

Analisis Pendapatan USAhatani Bawang Merah (Allium Ascalonicum) di Desa Sei.geringging Kecamatan Kampar Kiri Kabupaten Kampar

The purpose of this research are: 1) know the onion cultivation, 2) analyse the income of onion farming, and 3)know the management of onion farming in Sei. Geringging Village Kampar Kiri District Kampar Regency. This research conducted since April till July 2014. The samples in this research used random sampling method, namely taking a random sample of the population of onion farmers as much as 20 peoples. Onion cultivation in Sei. Geringging Village still conventional. Pre-planting treatment undertaken is tillage, then planting with a spacing of 15 x 15 cm. Fertilizers used in this farming are organic and inorganic fertilizers. Maintenance of onion farming includes the watering step and weeding step. Onion harvest is done when the age of onion plants 60 days old after planting. The analysis in this research are the gross revenue, production cost, net income, farm efficiency, and farm management. Gross revenue of onion farming is Rp.490.000.000, while production costs amounted to Rp.321.258.734, then net income of onion farming amounted to Rp.168.741.266 per 4 ha with RCR value amounted to 1,53, it means every Rp.1 cost will earn revenues of Rp.1,53, thus indicated that onion farming in Sei. Geringging Village economically efficient and feasible to be continued and developed. Management of onion farming in Sei. Geringging Village good enough, but there are some management functions that must be considered again such as the controlling function must be aware again