Self-diffusion coefficients of charged particles: Prediction of Nonlinear volume fraction dependence

We report on calculations of the translational and rotational short-time self-diffusion coefficients $D^t_s$ and $D^r_s$ for suspensions of charge-stabilized colloidal spheres. These diffusion coefficients are affected by electrostatic forces and many-body hydrodynamic interactions (HI). Our computations account for both two-body and three-body HI. For strongly charged particles, we predict interesting nonlinear scaling relations $D^t_s\propto 1-a_t\phi^{4/3}$ and $D^r_s\propto 1-a_r\phi^2$ depending on volume fraction $\phi$, with essentially charge-independent parameters $a_t$ and $a_r$. These scaling relations are strikingly different from the corresponding results for hard spheres. Our numerical results can be explained using a model of effective hard spheres. Moreover, we perceptibly improve the known result for $D^t_s$ of hard sphere suspensions.Comment: 8 pages, LaTeX, 3 Postscript figures included using eps

Flux Expulsion - Field Evolution in Neutron Stars

Models for the evolution of magnetic fields of neutron stars are constructed, assuming the field is embedded in the proton superconducting core of the star. The rate of expulsion of the magnetic flux out of the core, or equivalently the velocity of outward motion of flux-carrying proton-vortices is determined from a solution of the Magnus equation of motion for these vortices. A force due to the pinning interaction between the proton-vortices and the neutron-superfluid vortices is also taken into account in addition to the other more conventional forces acting on the proton-vortices. Alternative models for the field evolution are considered based on the different possibilities discussed for the effective values of the various forces. The coupled spin and magnetic evolution of single pulsars as well as those processed in low-mass binary systems are computed, for each of the models. The predicted lifetimes of active pulsars, field strengths of the very old neutron stars, and distribution of the magnetic fields versus orbital periods in low-mass binary pulsars are used to test the adopted field decay models. Contrary to the earlier claims, the buoyancy is argued to be the dominant driving cause of the flux expulsion, for the single as well as the binary neutron stars. However, the pinning is also found to play a crucial role which is necessary to account for the observed low field binary and millisecond pulsars.Comment: 23 pages, + 7 figures, accepted for publication in Ap

Quantum steering of electron wave function in an InAs Y-branch switch

We report experiments on gated Y-branch switches made from InAs ballistic electron wave guides. We demonstrate that gating modifies the electron wave functions as well as their interference pattern, causing the anti-correlated, oscillatory transconductances. Such previously unexpected phenomenon provides evidence of steering the electron wave function in a multi-channel transistor structure.Comment: 15 pages, including 3 figure

Observation of one electron charge in an enhancement-mode InAs single electron transistor at 4.2K

We propose and demonstrate experimentally a novel design of single-electron quantum dots. The structure consists of a narrow band gap quantum well that can undergo a transition from the hole accumulation regime to the electron inversion regime in a single-top-gate transistor configuration. We have observed large size quantization and Coulomb charging energies over 10meV. This quantum dot design can be especially important for scalable quantum computing.Comment: 5 figure

Fuel quality-processing study. Volume 2: Literature survey

The validity of initial assumptions about raw materials choices and relevant upgrading processing options was confirmed. The literature survey also served to define the on-site (at the turbine location) options for fuel treatment and exhaust gas treatment. The literature survey also contains a substantial compilation of specification and physical property information about liquid fuel products relevant to industrial gas turbines

The effect of renovation of long-term temperate grassland on N2O emissions and N leaching from contrasting soils

pre-printRenovation of long-term grassland is associated with a peak in soil organic N mineralisation which, coupled with diminished plant N uptake can lead to large gaseous and leaching N losses. This study reports on the effect of ploughing and subsequent N fertilisation on the N2O emissions and DON/NO3− leaching, and evaluates the impact of ploughing technique on the magnitude and profile of N losses. This study was carried out on isolated grassland lysimeters of three Irish soils representing contrasting drainage properties (well-drained Clonakilty, moderately-drained Elton and poorly-drained Rathangan). Lysimeters were manually ploughed simulating conventional (CT) and minimum tillage (MT) as two treatments. Renovation of grassland increased N2O flux to a maximum of 0.9 kg N2O–N ha− 1 from poorly-drained soil over four days after treatment. Although there was no difference between CT and MT in the post-ploughing period, the treatment influenced subsequent N2O after fertiliser applications. Fertilisation remained the major driver of N losses therefore reducing fertilisation rate post-planting to account for N mineralised through grassland renovation could reduce the losses in medium to longer term. Leaching was a significant loss pathway, with the cumulative drainage volume and N leached highly influenced by soil type. Overall, the total N losses (N2O + N leached) were lowest from poorly and moderately draining soil and highest for the well draining soil, reflecting the dominance of leaching on total N losses and the paramount importance of soil properties

H ingestion into He-burning convection zones in super-AGB stellar models as a potential site for intermediate neutron-density nucleosynthesis

We investigate the evolution of super-AGB (SAGB) thermal pulse (TP) stars for a range of metallicities (Z) and explore the effect of convective boundary mixing (CBM). With decreasing metallicity and evolution along the TP phase, the He-shell flash and the third dredge-up (TDU) occur closer together in time. After some time (depending upon the CBM parametrization), efficient TDU begins while the pulse-driven convection zone (PDCZ) is still present, causing a convective exchange of material between the PDCZ and the convective envelope. This results in the ingestion of protons into the convective He-burning pulse. Even small amounts of CBM encourage the interaction of the convection zones leading to transport of protons from the convective envelope into the He layer. H-burning luminosities exceed 10⁹ (in some cases 10¹⁰) L⊙. We also calculate models of dredge-out in the most massive SAGB stars and show that the dredge-out phenomenon is another likely site of convective-reactive H-¹²C combustion. We discuss the substantial uncertainties of stellar evolution models under these conditions. Nevertheless, the simulations suggest that in the convective-reactive H-combustion regime of H ingestion the star may encounter conditions for the intermediate neutron capture process (i-process). We speculate that some CEMP-s/r stars could originate in i-process conditions in the H ingestion phases of low-Z SAGB stars. This scenario would however suggest a very low electron-capture supernova rate from SAGB stars. We also simulate potential outbursts triggered by such H ingestion events, present their light curves and briefly discuss their transient properties

Validation and analysis of regional present-day climate and climate change simulations over Europe

In the European Commission (EC) project "Regionalization of Anthropogenic Climate Change Simulations, RACCS, recently terminated, 11 European institutions have carried out tests of dynamical and statistical regionalization techniques. The outcome of the "dynamical part" of the project, utilizing a series of high resolution LAMs and a variable resolution global model (all of which we shall refer to as RCMs, Regional Climate Models), is presented here. The per- formance of the dqterent LAMs had first, in a preceding EC project, been tested with "perfect" boundary forcing fields (ECMWF analyses) and also multi-year present-day climate simula- tions with AMIP "perfect ocean " or mixed layer ocean GCM boundary conditions had been validated against available climatological data. The present report involves results of vali- dation and analysis of RCM present-day climate simulations and anthropogenic climate change experiments. Multi-year (5 - 30 years) present-day climate simulations have been per- formed with resolutions between 19 and 70 km (grid lengths) and with boundary conditions from the newest CGCM simulations. The climate change experiments involve various 2xCO2 - ]xCO2 transient greenhouse gas experiments and in one case also changing sulphur aerosols. A common validation and inter-comparison was made at the coordinating institution, MPIfor Meteorology. The validation of the present-day climate simulations shows the importance of systematic errors in the low level general circulation. Such errors seem to induce large errors in precipitation and surface air temperature in the RCMs as well as in the CGCMs providing boundary conditions. Over Europe the field of systematic errors in the mean sea level pressure (MSLP) usually involve an area of too low pressure, often in the form of an east-west trough across Europe with too high pressure to the north and south. New storm-track analyses confirm that the areas of too low pressure are caused by enhanced cyclonic activity and similarly that the areas of too high pressure are caused by reduced such activity. The precise location and strength of the extremes in the MSLP error field seems to be dependent on the physical param- eterization package used. In model pairs sharing the same package the area of too low pressure is deepened further in the RCM compared to the corresponding CGCM, indicating an increase of the excessive cyclonic activity with increasing resolution. From the experiments performed it seems not possible to decide to what extent the systematic errors in the general circulation are the result of local errors in the physical parameterization schemes or remote errors trans- mitted to the European region via the boundary conditions. Additional errors in precipitation and temperature seems to be due to direct local effects of errors in certain parameterization schemes and errors in the SSTs taken from the CGCMs. For all seasons many biases are fOund to be statistically significant compared to estimates of the internal model variability of the time- slice mean values. In the climate change experiments statistically significant European mean temperature changes which are large compared to the corresponding biases are found. How- ever, the changes in the deviations from the European mean temperature as well as the changes in precipitation are only partly sign wcan ce and are of the same order of magnitude or smaller than the corresponding biases found in the present-day climate simulations. Cases of an inter- action between the systematic model errors and the radiative forcing show that generally the errors are not canceling out when the changes are computed. Therefore, reliable regional cli- mate changes can only be achieved after model improvements which reduce their systematic errors sufficiently. Also in future RCM experiments sujiciently long time-slices must be used in order to obtain statistically sign ijicant climate changes on the sub-continental scale aimed at with the present regionalization technique