Simulations of a weakly conducting droplet under the influence of an alternating electric field

We investigate the electrohydrodynamics of an initially spherical droplet under the influence of an external alternating electric field by conducting axisymmetric numerical simulations using a charge-conservative volume-of-fluid based finite volume flow solver. The mean amplitude of shape oscillations of a droplet subjected to an alternating electric field for leaky dielectric fluids is the same as the steady-state deformation under an equivalent root mean squared direct electric field for all possible electrical conductivity ratio $(K_r)$ and permittivity ratio $(S)$ of the droplet to the surrounding fluid. In contrast, our simulations for weakly conducting media show that this equivalence between alternating and direct electric fields does not hold for $K_r \ne S$. Moreover, for a range of parameters, the deformation obtained using the alternating and direct electric fields is qualitatively different, i.e. for low $K_r$ and high $S$, the droplet becomes prolate under alternating electric field but deforms to an oblate shape in the case of the equivalent direct electric field. A parametric study is conducted by varying the time period of the applied alternating electric field, the permittivity and the electrical conductivity ratios. It is observed that while increasing $K_r$ has a negligible effect on the deformation dynamics of the droplet for $K_r<S$, it enhances the deformation of the droplet when $K_r>S$ for both alternating and direct electric fields. We believe that our results may be of immense consequence in explaining the morphological evolution of droplets in a plethora of scenarios ranging from nature to biology.Comment: 10 pages, 8 figure

Collective excitations and low temperature transport properties of bismuth

We examine the influence of collective excitations on the transport properties (resistivity, magneto- optical conductivity) for semimetals, focusing on the case of bismuth. We show, using an RPA approximation, that the properties of the system are drastically affected by the presence of an acoustic plasmon mode, consequence of the presence of two types of carriers (electrons and holes) in this system. We found a crossover temperature T* separating two different regimes of transport. At high temperatures T > T* we show that Baber scattering explains quantitatively the DC resistivity experiments, while at low temperatures T < T* interactions of the carriers with this collective mode lead to a T^5 behavior of the resistivity. We examine other consequences of the presence of this mode, and in particular predict a two plasmon edge feature in the magneto-optical conductivity. We compare our results with the experimental findings on bismuth. We discuss the limitations and extensions of our results beyond the RPA approximation, and examine the case of other semimetals such as graphite or 1T-TiSe_2

La Terrasse Ebebda (centre du Cameroun) : preuve d’une migration de la confluence Mbam-Sanaga

La compréhension de la mise en place de la terrasse située à la confluence Mbam- Sanaga, et le fonctionnement de cette zone, ont conduit à certaines observations qui ont permis la reconstitution du paléochenal de cette confluence. Une étude comparative a été menée sur les différents sites afin de ressortir des similitudes entre les fleuves et terrasse. Ainsi à l’issue des prélèvements effectués, des analyses ont donné les résultats permettant de décrire sa mise en place. Le recueil géomorphologique et sédimentologique réalisé, dégage les caractères suivants: les mesures faites sur des galets indiquent un écoulement global NE-SW, perpendiculaire à l’orientation de leur grand axe SE-NW; les galets et les alluvions prélevés sur les trois sites, présentent des indices leur attribuant un agent de transport et d’usure de type fluviatile; Le cortège minéralogique des trois systèmes présente les minéraux des roches volcaniques dans le Mbam et la Terrasse. Preuve que la mise en place de la terrasse a été faite par le Mbam et non la Sanaga comme vulgairement appelée «terrasse de la Sanaga»; la carte géomorphologique de la confluence permet de reconstituer le profil au moment de la mise en place des alluvions et d’envisager une évolution future de ce fleuve ; la dénivellation de l’ordre de vingt mètres entre la terrasse et le Mbam laisse envisager que, le creusement latéral que subit le fleuve Sanaga du coté Sud du pont en direction de la localité d’Ebebda pourra affecter les populations de cette localité dans les années avenir.Mots-clés : Sanaga, Mbam, terrasse alluviale, Ebebda, sédimentologie, géomorphologie.The Ebebda Terrace (Central Cameroon) : evidence of migrating Mbam-Sanaga River confluenceUnderstanding of the implementation of the terrace situated at the Sanaga-Mbam confluence, and the operation of this area led to the reconstruction of a paleochannel. A study conducted at the three sites, as well as the analyses, done; permit us to describe its implementation. Geomorphological and sedimentological collection made liberates the following characters: measurements made on pebbles indicate a NE-SW flow perpendicular to the orientation of the major axis, pebbles and silt collected from the three sites have indices assigning agent transport and fluvial wear; mineralogical the three systems present minerals of volcanic rocks in the Mbam and Terrace. The geomorphological map of the confluence can reconstruct the profile at the time of implementation of alluvium and consider the future of the river. The slope in the order of twenty meters between the terrace and the Mbam, shows that the river suffers a widening effect by its sides in south and may affect the surrounding populations later.Keywords : Sanaga, Mbam, terrace alluvial, Ebebda, sedimentology, geomorphology

Die Detektionsgrenze der MR-Spektroskopie mittels intermolekularen Nullquantenkohärenzen in inhomogenen Magnetfeldern

Die Magnetresonanzspektroskopie (MRS) ermöglicht die Messung relativer Veränderungen oder sogar die absolute Quantifizierung von bestimmten Metaboliten im lebenden Organismus. Voraussetzung für hochwertige MR-Spektren ist eine hervorragende Homogenität des Hauptmagnetfeldes (B0). Feldverzerrungen kann man mit externen Shim-Spulen bis zu einem bestimmten Grad kompensieren und damit die von ihnen verursachte spektrale Linienverbreiterung reduzieren. Dennoch sind anatomische Bereiche oder Probenregionen, die Strukturen mit stark unterschiedlichen magnetischen Eigenschaften (Suszeptibilitätssprünge) beinhalten (wie z.B. Luft-WasserÜbergänge, Knochen-Muskel-Grenzregionen oder Gewebe, die mit exogenem Kontrastmittel (z.B. Eisenoxidpartikeln) markiert sind) von einer MRS-Untersuchung in der Regel ausgeschlossen. Sogenannte „resolution enhancement“ Methoden, wie die MRS mittels intermolekularen Nullquantenkohärenzen (iZQC) [1] wurden dazu entwickelt, um MRS auch in sehr inhomogenen Magnetfeldern zu ermöglichen. Erfolgreiche Anwendungen der iZQC-MRS wurden bisher in der Gegenwart von linearen Magnetfeldgradienten entlang eines Probenröhrchens [1], in einem driftenden 25-T-Magneten [2], und in vivo in Kaltblütern [3] sowie in Warmblütern [4-7] demonstriert. Um die Anwendbarkeit der iZQC-MRS für andere Proben oder Organe (z.B. Epithel der Lunge, grüne Blätter, Gewebe mit exogenen Kontrastmitteln) zu analysieren, muss man erst ihr Verhalten unter kritischen Bedingungen und ihre Grenzen ermitteln. Frühere Analysen der Methode befassten sich nur mit der Theorie in der Gegenwart von makroskopischen Feldverzerrungen. Viel grundlegender für reale Proben sind aber die Effekte der mesoskopischen und mikroskopischen Inhomogenitäten, die im Rahmen dieser Arbeit zum ersten Mal untersucht wurden [8]

Year in review 2005: Critical Care – resource management

During 2005 Critical Care published several original papers dealing with resource management. Emphasis was placed on sepsis, especially the coagulation cascade, prognosis and resuscitation. The papers highlighted important aspects of the pathophysiology of coagulation and inflammation in sepsis, as well as dealing with the proper use of newly developed compounds. Several aspects of prognosis in critically ill patients were investigated, focusing on biological markers and clinical indexes. Resuscitation received great attention, dealing with the effects of fluid infusion in hemodynamics and the lung. The information obtained can be used to address unknown effects of established therapies, to enlighten current clinical discussion on controversial topics, and to introduce novel medical resources and strategies. Future clinical work will rely heavily on these preclinical and laboratory data

Performance Effects of Adding a Parallel Capacitor to a Pulse Inductive Plasma Accelerator Powertrain

Pulsed inductive plasma accelerators are electrodeless space propulsion devices where a capacitor is charged to an initial voltage and then discharged through a coil as a high-current pulse that inductively couples energy into the propellant. The field produced by this pulse ionizes the propellant, producing a plasma near the face of the coil. Once a plasma is formed if can be accelerated and expelled at a high exhaust velocity by the Lorentz force arising from the interaction of an induced plasma current and the magnetic field. While there are many coil geometries that can be employed to inductively accelerate a plasma, in this paper the discussion is limit to planar geometries where the coil take the shape of a flat spiral. A recent review of the developmental history of planar-geometry pulsed inductive thrusters can be found in Ref. [1]. Two concepts that have employed this geometry are the Pulsed Inductive Thruster (PIT) and the Faraday Accelerator with Radio-frequency Assisted Discharge (FARAD)

Novel mechanisms of G-protein-coupled receptors functions: AT1 angiotensin receptor acts as a signaling hub and focal point of receptor cross-talk

AT1 angiotensin receptor (AT1R), a prototypical G protein-coupled receptor (GPCR), is the main receptor, which mediates the effects of the renin-angiotensin system (RAS). AT1R plays a crucial role in the regulation of blood pressure and salt-water homeostasis, and in the development of pathological conditions, such as hypertension, heart failure, cardiovascular remodeling, renal fibrosis, inflammation, and metabolic disorders. Stimulation of AT1R leads to pleiotropic signal transduction pathways generating arrays of complex cellular responses. Growing amount of evidence shows that AT1R is a versatile GPCR, which has multiple unique faces with distinct conformations and signaling properties providing new opportunities for functionally selective pharmacological targeting of the receptor. Biased ligands of AT1R have been developed to selectively activate the β-arrestin pathway, which may have therapeutic benefits compared to the conventional angiotensin converting enzyme inhibitors and angiotensin receptor blockers. In this review, we provide a summary about the most recent findings and novel aspects of the AT1R function, signaling, regulation, dimerization or oligomerization and its cross-talk with other receptors, including epidermal growth factor (EGF) receptor, adrenergic receptors and CB1 cannabinoid receptor. Better understanding of the mechanisms and structural aspects of AT1R activation and cross-talk can lead to the development of novel type of drugs for the treatment of cardiovascular and other diseases. © 201

Estimates of higher-dimensional vacuum condensates from the instanton vacuum

We calculate the values of non-factorizable dimension-7 vacuum condensates in the instanton vacuum. We comment on a method, recently proposed by Oganesian, to estimate the dimension-7 condensates by factorization of dimension-10 condensates in various inequivalent ways. The instanton estimates could be used to analyze the stability of QCD sum rules with increasing dimensions.Comment: 8 pages, Late

Charge carrier interaction with a purely electronic collective mode: Plasmarons and the infrared response of elemental bismuth

We present a detailed optical study of single crystal bismuth using infrared reflectivity and ellipsometry. Colossal changes in the plasmon frequency are observed as a function of temperature due to charge transfer between hole and electron Fermi pockets. In the optical conductivity, an anomalous temperature dependent mid-infrared absorption feature is observed. An extended Drude model analysis reveals that it can be connected to a sharp upturn in the scattering rate, the frequency of which exactly tracks the temperature dependent plasmon frequency. We interpret this absorption and increased scattering as the first direct optical evidence for a charge carrier interaction with a collective mode of purely electronic origin; here electron-plasmon scattering. The observation of a \emph{plasmaron} as such is made possible only by the unique coincidence of various energy scales and exceptional properties of semi-metal bismuth.Comment: 4 pages, 4 figure