Burst dynamics during drainage displacements in porous media: Simulations and experiments

We investigate the burst dynamics during drainage going from low to high injection rate at various fluid viscosities. The bursts are identified as pressure drops in the pressure signal across the system. We find that the statistical distribution of pressure drops scales according to other systems exhibiting self-organized criticality. The pressure signal was calculated by a network model that properly simulates drainage displacements. We compare our results with corresponding experiments.Comment: 7 pages, 4 figures. Submitted to Europhys. Let

On integrability of Hirota-Kimura type discretizations

We give an overview of the integrability of the Hirota-Kimura discretization method applied to algebraically completely integrable (a.c.i.) systems with quadratic vector fields. Along with the description of the basic mechanism of integrability (Hirota-Kimura bases), we provide the reader with a fairly complete list of the currently available results for concrete a.c.i. systems.Comment: 47 pages, some minor change

Lindhard and RPA susceptibility computations in extended momentum space in electron doped cuprates

We present an approximation for efficient calculation of the Lindhard susceptibility $\chi^{L}(q,\omega)$ in a periodic system through the use of simple products of real space functions and the fast Fourier transform (FFT). The method is illustrated by providing $\chi^{L}(q,\omega)$ results for the electron doped cuprate Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ extended over several Brillouin zones. These results are relevant for interpreting inelastic X-ray scattering spectra from cuprates.Comment: 6 pages, 6 figures, accepted in Physical Review

Clostridium perfringens α-toxin interaction with red cells and model membranes.

The effects of Clostridium perfringens α-toxin on host cells have previously been studied extensively but the biophysical processes associated with toxicity are poorly understood. The work reported here shows that the initial interaction between the toxin and lipid membrane leads to measurable changes in the physical properties and morphology of the membrane. A Langmuir monolayer technique was used to assess the response of different lipid species to toxin. Sphingomyelin and unsaturated phosphatidylcholine showed the highest susceptibility to toxin lypolitic action, with a two stage response to the toxin (an initial, rapid hydrolysis stage followed by the insertion and/or reorganisation of material in the monolayer). Fluorescence confocal microscopy on unsaturated phosphatidylcholine vesicles shows that the toxin initially aggregates at discrete sites followed by the formation of localised "droplets" accumulating the hydrolysis products. This process is accompanied by local increases in the membrane dipole potential by about 50 (±42) mV. In contrast, red blood cells incubated with the toxin suffered a decrease of the membrane dipole potential by 50 (±40) mV in areas of high toxin activity (equivalent to a change in electric field strength of 10(7) V m(-1)) which is sufficient to affect the functioning of the cell membrane. Changes in erythrocyte morphology caused by the toxin are presented, and the early stages of interaction between toxin and membrane are characterised using thermal shape fluctuation analysis of red cells which revealed two distinct regimes of membrane-toxin interaction.Royal Society University Research Fellowshi

Breath-Hold Blood Oxygen Level-Dependent MRI: A Tool for the Assessment of Cerebrovascular Reserve in Children with Moyamoya Disease

BACKGROUND AND PURPOSE: There is a critical need for a reliable and clinically feasible imaging technique that can enable prognostication and selection for revascularization surgery in children with Moyamoya disease. Blood oxygen level-dependent MR imaging assessment of cerebrovascular reactivity, using voluntary breath-hold hypercapnic challenge, is one such simple technique. However, its repeatability and reliability in children with Moyamoya disease are unknown. The current study sought to address this limitation. MATERIALS AND METHODS: Children with Moyamoya disease underwent dual breath-hold hypercapnic challenge blood oxygen level-dependent MR imaging of cerebrovascular reactivity in the same MR imaging session. Within-day, within-subject repeatability of cerebrovascular reactivity estimates, derived from the blood oxygen level-dependent signal, was computed. Estimates were associated with demographics and intellectual function. Interrater reliability of a qualitative and clinically applicable scoring scheme was assessed. RESULTS: Twenty children (11 males; 12.1 ± 3.3 years) with 30 MR imaging sessions (60 MR imaging scans) were included. Repeatability was "good" on the basis of the intraclass correlation coefficient (0.70 ± 0.19). Agreement of qualitative scores was "substantial" (κ = 0.711), and intrarater reliability of scores was "almost perfect" (κ = 0.83 and 1). Younger participants exhibited lower repeatability (P = .027). Repeatability was not associated with cognitive function (P > .05). However, abnormal cerebrovascular reactivity was associated with slower processing speed (P = .015). CONCLUSIONS: Breath-hold hypercapnic challenge blood oxygen level-dependent MR imaging is a repeatable technique for the assessment of cerebrovascular reactivity in children with Moyamoya disease and is reliably interpretable for use in clinical practice. Standardization of such protocols will allow further research into its application for the assessment of ischemic risk in childhood cerebrovascular disease

A Smart Bluetooth-based Ad Hoc Management System for Appliances in Home Environments

The number of home devices integrating new technologies is continuously increasing. These advances allow us to improve our daily routines. In addition, the improvement in network infrastructure and the development of smart phones and mobile devices allow us access from any place to any of our systems over the Internet. Bearing in mind this idea, we have developed a low-cost ad hoc protocol based on Bluetooth technology that allows us to control all our home appliances and monitor the power consumption of our homes. Our proposal is based on an Android application installed on a mobile device which acts as server. The application allows users to program the various appliances. It is also able to check the status of the appliance, as well as controlling the power consumption of the house and its cost. The system is equipped with a smart algorithm able to manage all appliances and decide which ones should work as a function of various criteria such as time of day or power consumption. Finally, the system is able to detect faults in water and electricity supply for acting accordingly. All data received and sent by the server are stored in a database which the system can check and compare to make their own decisions.Sendra, S.; Laborda, A.; Díaz Santos, JR.; Lloret, J. (2015). A Smart Bluetooth-based Ad Hoc Management System for Appliances in Home Environments. Springer Verlag (Germany): LNCS. 8487:128-141. doi:10.1007/978-3-319-07425-2_10S1281418487Garcia, M., Sendra, S., Lloret, J., Canovas, A.: Saving energy and improving communications using cooperative group-based Wireless Sensor Networks. Telecommunication Systems 52(4), 2489–2502 (2013)Liu, Y., Zhou, G.: Technologies and Applications of Internet of Things. In: Proceedings of 2012 Fifth International Conference on Intelligent Computation Technology and Automation (ICICTA), Zhangjiajie, China, January 12-14, pp. 197–200 (2012)Aiello, M.: The Role of Web Services at Home. 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Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

We report the evolution of the surface electronic structure and surface material properties of a topological crystalline insulator (TCI) Pb1-xSnxSe as a function of various material parameters including composition x, temperature T and crystal structure. Our spectroscopic data demonstrate the electronic groundstate condition for the saddle point singularity, the tunability of surface chemical potential, and the surface states' response to circularly polarized light. Our results show that each material parameter can tune the system between trivial and topological phase in a distinct way unlike as seen in Bi2Se3 and related compounds, leading to a rich and unique topological phase diagram. Our systematic studies of the TCI Pb1-xSnxSe are valuable materials guide to realize new topological phenomena.Comment: 10 pages, 7 figures. Expanded version of arXiv:1403.156

In-Plane Orbital Texture Switch at the Dirac Point in the Topological Insulator Bi2Se3

Topological insulators are novel macroscopic quantum-mechanical phase of matter, which hold promise for realizing some of the most exotic particles in physics as well as application towards spintronics and quantum computation. In all the known topological insulators, strong spin-orbit coupling is critical for the generation of the protected massless surface states. Consequently, a complete description of the Dirac state should include both the spin and orbital (spatial) parts of the wavefunction. For the family of materials with a single Dirac cone, theories and experiments agree qualitatively, showing the topological state has a chiral spin texture that changes handedness across the Dirac point (DP), but they differ quantitatively on how the spin is polarized. Limited existing theoretical ideas predict chiral local orbital angular momentum on the two sides of the DP. However, there have been neither direct measurements nor calculations identifying the global symmetry of the spatial wavefunction. Here we present the first results from angle-resolved photoemission experiment and first-principles calculation that both show, counter to current predictions, the in-plane orbital wavefunctions for the surface states of Bi2Se3 are asymmetric relative to the DP, switching from being tangential to the k-space constant energy surfaces above DP, to being radial to them below the DP. Because the orbital texture switch occurs exactly at the DP this effect should be intrinsic to the topological physics, constituting an essential yet missing aspect in the description of the topological Dirac state. Our results also indicate that the spin texture may be more complex than previously reported, helping to reconcile earlier conflicting spin resolved measurements

Theory of Extrinsic and Intrinsic Tunnelling in Cuprate Superconductors

A theory capable of explaining intrinsic and extrinsic tunnelling conductance in underdoped cuprates has been devised that accounts for the existence of two energy scales, their temperature and doping dependencies. The asymmetry and inhomogeneity seen in extrinsic (normal metal - superconductor (NS)) tunnelling and the normal-state gapped intrinsic (SS) conductance is explained, as well as the superconducting gap and normal state pseudogap and the temperature dependence of the full gap.Comment: 14 pages, 10 figures, misprints correcte