Event-by-Event Jet Quenching

High momentum jets and hadrons can be used as probes for the quark gluon plasma (QGP) formed in nuclear collisions at high energies. We investigate the influence of fluctuations in the fireball on jet quenching observables by comparing propagation of light quarks and gluons through averaged, smooth QGP fireballs with event-by-event jet quenching using realistic inhomogeneous fireballs. We find that the transverse momentum and impact parameter dependence of the nuclear modification factor R_AA can be fit well in an event-by-event quenching scenario within experimental errors. However the transport coefficient qhat extracted from fits to the measured nuclear modification factor R_AA in averaged fireballs underestimates the value from event-by-event calculations by up to 50%. On the other hand, after adjusting qhat to fit R_AA in the event-by-event analysis we find residual deviations in the azimuthal asymmetry v_2 and in two-particle correlations, that provide a possible faint signature for a spatial tomography of the fireball.Comment: 8 pages, 5 figures; v2: new figure added, small changes and fixes, this version published in Phys. Lett.

Degenerate four-wave mixing in triply-resonant Kerr cavities

We demonstrate theoretical conditions for highly-efficient degenerate four-wave mixing in triply-resonant nonlinear (Kerr) cavities. We employ a general and accurate temporal coupled-mode analysis in which the interaction of light in arbitrary microcavities is expressed in terms a set of coupling coefficients that we rigorously derive from the full Maxwell equations. Using the coupled-mode theory, we show that light consisting of an input signal of frequency $\omega_0-\Delta \omega$ can, in the presence of pump light at $\omega_0$, be converted with quantum-limited efficiency into an output shifted signal of frequency $\omega_0 + \Delta \omega$, and we derive expressions for the critical input powers at which this occurs. We find that critical powers in the order of 10mW assuming very conservative cavity parameters (modal volumes $\sim10$ cubic wavelengths and quality factors $\sim1000$. The standard Manley-Rowe efficiency limits are obtained from the solution of the classical coupled-mode equations, although we also derive them from simple photon-counting "quantum" arguments. Finally, using a linear stability analysis, we demonstrate that maximal conversion efficiency can be retained even in the presence of self- and cross-phase modulation effects that generally act to disrupt the resonance condition.Comment: 13 pages, 8 figures. To appear in Physical Review

Crystallization and preliminary X-ray diffraction analysis of levansucrase (LsdA) from Gluconacetobacter diazotrophicus SRT4

The endophytic bacterium Gluconacetobacter diazotrophicus SRT4 secretes a constitutively expressed levansucrase (LsdA; EC 2.4.1.10), which converts sucrose to fructo-oligosaccharides and levan. Fully active LsdA was purified to high homogeneity by non-denaturing reversed-phase HPLC and was crystallized at room temperature by the hanging-drop vapour-diffusion method using ammonium sulfate and ethanol as precipitants. The crystals are extremely sensitive, but native data have been collected to 2.5 A under cryogenic conditions using synchrotron radiation. LsdA crystals belong to the orthorhombic space group P22(1)2(1) or P2(1)2(1)2, with unit-cell parameters a = 53.80, b = 119.39, c = 215.10 A

A low-voltage low-power front-end for wearable EEG systems

A low-voltage and low-power front-end for miniaturized, wearable EEG systems is presented. The instrumentation amplifier, which removes the electrode drift and conditions the signal for a 10-bit A/D converter, combines a chopping strategy with quasi-FGMOS (QFG) transistors to minimize low frequency noise whilst enabling operation at 1 V supply. QFG devices are also key to the A/D converter operating at 1.2 V with 70dB of SNR and an oversampling ratio of 64. The whole system consumes less than 2uW at 1.2V.Published versio

ENGINEERING PROPERTIES OF SUGARCANE FIBRES

Abstract THE PHYSICAL properties and the mass and heat transfer coefficients for sugarcane bagasse were determined to provide information for process design and manufacturing of products. In this report, true density (ρ s ) and apparent density (ρ) were measured by the pycnometer method. Superficial area (As) and pore size distribution of fibres were determined by nitrogen adsorption and mercury porosimetry. Equilibration cells were used in order to obtain sorption isotherms. Water content and surface temperature of the sugarcane fibres were monitored using a modified Thermal Gravimetric Analyzer (TGA). The method of slope was used to calculate the effective water diffusion coefficient. The mass (h M ) and heat coefficients (h H ) were determined by experimental data, and then compared with one convective transfer correlation .s). The fibre is a porous material consisting of macropores and its internal structure differs from that of the pith. The experimental values of h H were more elevated than those calculated with correlations due to the effects of conduction and radiation. The principal mass transfer mechanism was the internal resistance, D e increased with temperature in an Arrhenius type function. Introduction Bagasse is the residue left after the crushing of sugarcane for juice extraction. The largest and most traditional use of bagasse is burning it in boilers to generate process steam A revision of the published results and industrial experience realised by In order to expand the use of bagasse, it is essential that information on fibre characteristics and the factors which affect the performance of that fibre be available. Specific knowledge of the bagasse material is useful to predict its behaviour during transformation processes. Physical properties involved in the heat and mass transfer, such as density and porosity, play an important role in the design, the estimation of other properties, the characterisation of materials, and the prediction of heat transfer operations during processing and handling. The engineering properties are important in the process design and manufacturing of products. The mathematical models are fitted using data as a function of one or more experimental parameters, such as temperature, water content, porosity, heat, and mass transfer coefficients or others. In order to do this, the aim of the present work is to describe physical characteristics, adsorption capacity, mass and heat transfer coefficient and water diffusivity of bagasse. Materials and methods Material preparation The sugarcane bagasse provided by sugarcane factories in Zacatepec, Morelos, Mexico was depithed while wet, dried, sieved, and classified by size manually using a stereoscopic microscope. The highest frequency fractions (9.62% and 7.53%) of fibre (12 to14 and 20 to 24 mesh screen/sieve, respectively) were used for all tests. A vernier caliper was used for measuring the length and diameter of the selected fibres. Volume and area were calculated using these data. Physical characteristics are shown in Equation 1-Heat balance equation. Experiments were conducted to measure the moisture lost during drying. The rate of moisture lost (dX/dt), determined in the period of constant-rate drying, and fibre surface temperature data were used for determine the convective coefficients of heat and mass transfer. It is assumed the heat of water vaporisation is constant and equal to the heat of water vapour condensation. A correlation presented by Eckert and Drake Calculation of the effective moisture diffusivity The effective moisture diffusivity (D e ) in solids is a physical property of the system and can be estimated from drying rate data. Assuming that the drying process is entirely controlled by internal mass transfer resistance (falling rate drying period), uniform initial moisture distribution and negligible external resistance, the solution of Fick's diffusion equation developed for particles with cylinder geometry by Crank (1975) for a series of six terms is applicable and is in the form of equation 4. Equation 4-Solution of Fick's diffusion equation for a cylinder. The effective moisture diffusivity was calculated using the slope method Surface area and pore size The size, area and pores distribution were measured by nitrogen adsorption and mercury porosimetry methods, respectively. A nitrogen adsorption surface area analyser (Micromeritics, ASAP-2000) and standard methods ASTM D 3663-92 and ASTM D 4222-91 were used to evaluate the surface area and pore size, and adsorption and desorption by nitrogen isotherms. A mercury porosymeter (Poromaster, Quantachrome) was used between 0 and 60 000 psi for measured macropores. The pore volume distribution over pore diameter is expressed in terms of the distribution function F v (eq. 5): where V is pore volume. The function is such that area under the function in any pore diameter range yields volume of pores in that range. Sorption isotherms Sorption isotherms were determined gravimetrically at 25°C and 70°C. Triplicate samples of fibres dried at 90°C, sieved on sieves mesh number 16-14 (1.19-1.41 mm) and weighed, were transferred to vacuum desiccators. Sulfuric acid solutions at different concentrations were used to achieve the internal, relative humidity in desiccators The Guggenheim-Anderson-DeBoer (GAB) equation (eq. 6) was used in modelling water sorption Equation 7-Temperature dependent GAB constant. Results Fibre dimensions Surface area, pore and diameter volume measured by nitrogen adsorption and mercury porosimetry are shown in The pore volume distribution over pore diameter is expressed in terms of the distribution function Fv. The fibres reveal two pore distributions, one in the range of 0.1 at 1 μm and one in the range 4-100 μm with pore diameter maxima of 0.5774, 5.387 and 29.85 μm. This material mainly contains macropores >0.05 μm. Sorption isotherm The values of GAB constant and the correction factors are presented in The isotherm presents a sigmoid or S-shape. For the same moisture content, water activity increased with temperature. This behaviour is frequently observed in cellulose-based materials The high level of moisture adsorption is caused by the high hydrophilic nature of the sugarcane fibre compared to other natural fibres, like the agave fibre which shows a low adsorption of 0.3 g water/g dry fibre at 0.8 a w (Bessadok, 2009). Cane fibre has a high cellulose composition of 32-48