Oscillatory waves in inhomogeneous neural media

In this Letter we show that an inhomogeneous input can induce wave propagation failure in an excitatory neural network due to the pinning of a stationary front or pulse solution. A subsequent reduction in the strength of the input can lead to a Hopf instability of the stationary solution resulting in breatherlike oscillatory waves.     

Determination of ciprofloxacin and enrofloxacin in edible animal tissues by terbium-sensitized luminescence.

A terbium-sensitized luminescence method is described for the determination of the sum of residues of enrofloxacin and its major metabolite ciprofloxacin in edible animal tissues. Several parameters affecting both detection and extraction were studied. Analytes were extracted from spiked samples of chicken and trout tissues with pH 7.4 buffer-dichloromethane. The organic extract was evaporated and the residue dissolved in aqueous nitric acid and defatted with hexane. Determination was carried out directly in the aqueous phase (in a micellar medium). The calibration curves were linear up to 75 micrograms l-1. The detection limit was 3.5 micrograms kg-1 (for a 5 g sample) and the repeatability was 7.0% (n = 7). The sensitivity was similar for both quinolones and therefore calibration can be carried out with either ciprofloxacin or enrofloxacin. In any case, the differences were < 10%.     

Drying processes in the presence of temperature gradients--pore-scale modelling

The influence of temperature gradients on the drying of water-saturated porous networks has been studied. We have focussed on the influence of the temperature on the drying process via the equilibrium vapor density rhoe, because this is the most sensitive parameter with respect to variations of the temperature T. We have used a 2D model which accounts for both capillary and buoyancy forces. Invasion events by air or water are handled by standard rules of invasion percolation in a gradient (IPG). Vapor fluxes are calculated by solving a discretized version of the Laplace equation. In the model the temperature T varies linearly from the open side T0 to the closed side TL. The temperature gradients strongly influence the cluster evolution during the process, because they facilitate vapor transport through wet regions. When T0TL, the front movement is enhanced and the air ingress in the wet region behind the front is inhibited. The behavior of 3D systems differs from that of 2D systems, because the point where air percolates the system and the point where the water network breaks up in isolated clusters do not coincide. Before the latter fragmentation point the temperature will mainly influence the drying rates. After this point also the water distribution becomes sensitive to the temperature profile.     

Experimental investigations and DICTRA simulations on formation of diffusion-controlled fcc-rich surface layers on cemented carbides

Wear resistant fcc-rich surface layers were produced on cemented carbides by nitridation of W-Ti-Ta-Nb-Co-C compositions at 1400 °C in nitrogen atmosphere. A 15 ± 3 μm thick (Ti,Ta,Nb,W)(C,N) top-layer formed on the surface of the cemented carbides. The driving force for formation of the fcc-rich layers was the difference in nitrogen activity between the sintering atmosphere and the cemented carbide bulk, which promoted in-diffusion of nitrogen and out-diffusion of Ti, Ta and Nb. The diffusion-controlled process was modeled by DICTRA considering that all diffusion occurred in the liquid binder phase of a dispersed system model with a labyrinth factor of λ(f) = f. Good agreement between experimental and simulations regarding layer thickness, phase fraction distribution and element profiles was obtained for the presented model.     

1.25–2.5 Gb/s Simple Nyquist Transmitters for Coherent UDWDM-PON with Enhanced Spectral Efficiency

We present a coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with enhanced spectral efficiency. The benefit of using Gaussian or Nyquist pulse-shaping filters at the transmitter is evaluated through numerical simulations and experiments. The transmitters consist of directly phase modulated distributed feedback (DFB) lasers through beat signals whose duty-cycle and amplitude are digitally adjusted. The results show that transmitting a Nyquist-shaped signal achieves a 25% spectral saving allowing to place 2.5 Gb/s/user data in 6.25 GHz channels. Furthermore, the proposed transmitter tolerates differential link-losses of 15 dB at Rx sensitivity of ?44 dBm at BER=10^?3 with intradyne detection.     

Modelling of heat transfer by conduction in a transition region between a porous medium and an external fluid

We study the modelling of purely conductive heat transfer between a porous medium and an external fluid within the framework of the volume averaging method. When the temperature field for such a system is classically determined by coupling the macroscopic heat conduction equation in the porous medium domain to the heat conduction equation in the external fluid domain, it is shown that the phase average temperature cannot be predicted without a generally negligible error due to the fact that the boundary conditions at the interface between the two media are specified at the macroscopic level.Afterwards, it is presented an alternative modelling by means of a single equation involving an effective thermal conductivity which is a function of point inside the interfacial region.The theoretical results are illustrated by means of some numerical simulations for a model porous medium. In particular, temperature fields at the microscopic level are presented.Roman Letters _sf interfacial area of thes-f interface contained within the macroscopic system m² - A _sf interfacial area of thes-f interface contained within the averaging volume m² - C _p mass fraction weighted heat capacity, kcal/kg/K - g vector that maps to _s , m - h vector that maps to _f , m - K _eff effective thermal conductivity tensor, kcal/m s K - l _s,l _f microscopic characteristic length m - L macroscopic characteristic length, m - n _fs outwardly directed unit normal vector for thef-phase at thef-s interface - n outwardly directed unit normal vector at the dividing surface. - R ₀ REV characteristic length, m - T _i macroscopic temperature at the interface, K - error on the external fluid temperature due to the macroscopic boundary condition, K - T ^* macroscopic temperature field obtained by solving the macroscopic Equation (3), K - V averaging volume, m³ - V _s,V _f volume of the considered phase within the averaging volume, m³. - _mp volume of the porous medium domain, m³ - _ex volume of the external fluid domain, m³ - _s , _f volume of the considered phase within the volume of the macroscopic system, m³ - dividing surface, m² - x, z spatial coordinates Greek Letters _s, _f volume fraction - ratio of the effective thermal conductivity to the external fluid thermal conductivity - ^* macroscopic thermal conductivity (single equation model) kcal/m s K - _s, _f microscopic thermal conductivities, kcal/m s K - spatial average density, kg/m³ - microscopic temperature, K - ^* microscopic temperature corresponding toT ^*, K - spatial deviation temperature K - error in the temperature due to the macroscopic boundary conditions, K - ^* _i macroscopic temperature at the interface given by the single equation model, K - spatial average - ^s , ^f intrinsic phase average.     

The One-Pot Palladium Catalyzed Wittig Reaction with Allylic Alcohols. Scope and Limitations

Some allylic alcohols react with aldehydes and triphenylphosphine in a one-pot formal Wittig reaction under Pd° catalysis. The method has been extended to cinnamyl alcohol, 1, 2-methyl-2-propen-1-01, 7, and 3-buten-2-01, 11, and to heterocyclic aldehydes.     

Undulator beamline optimization with integrated chicanes for X‐ray free‐electron‐laser facilities

An optimization of the undulator layout of X‐ray free‐electron‐laser (FEL) facilities based on placing small chicanes between the undulator modules is presented. The installation of magnetic chicanes offers the following benefits with respect to state‐of‐the‐art FEL facilities: reduction of the required undulator length to achieve FEL saturation, improvement of the longitudinal coherence of the FEL pulses, and the ability to produce shorter FEL pulses with higher power levels. Numerical simulations performed for the soft X‐ray beamline of the SwissFEL facility show that optimizing the advantages of the layout requires shorter undulator modules than the standard ones. This proposal allows a very compact undulator beamline that produces fully coherent FEL pulses and it makes possible new kinds of experiments that require very short and high‐power FEL pulses.     

Crystallization of bisulfite derivatives of enantiomerically enriched verbenone

After separation of crystalline bisulfite derivatives of enantiomerically enriched (1S)- and (1R)-verbenones, steam distillation of the filtrates afforded (1S)- and (1R)-verbenones whose optical purity was higher by 30 and 20%, respectively, than that of the initial enantiomers.