New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the ...CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from −0.05 to 0.95 (−0.05 to 0.4) in Feynman
x
for protons (anti-protons), respectively.
p
T
integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman
x
. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.
We describe an advanced microfluidic hydrogen-air fuel cell (FC) that exhibits exceptional durability and high performance, most notably yielding stable output power (>100 days) without the use of an ...anode-cathode separator membrane. This FC embraces an entirely passive device architecture and, unlike conventional microfluidic designs that exploit laminar hydrodynamics, no external pumps are used to sustain or localize the reagent flow fields. The devices incorporate high surface area/porous metal and metal alloy electrodes that are embedded and fully immersed in liquid electrolyte confined in the channels of a poly(dimethylsiloxane) (PDMS)-based microfluidic network. The polymeric network also serves as a self-supporting membrane through which oxygen and hydrogen are supplied to the cathode and alloy anode, respectively, by permeation. The operational stability of the device and its performance is strongly dependent on the nature of the electrolyte used (5 M H2SO4 or 2.5 M NaOH) and composition of the anode material. The latter choice is optimized to decrease the sensitivity of the system to oxygen cross-over while still maintaining high activity towards the hydrogen oxidation reaction (HOR). Three types of high surface area anodes were tested in this work. These include: high-surface area electrodeposited Pt (Pt); high-surface area electrodeposited Pd (Pd); and thin palladium adlayers supported on a "porous" Pt electrode (Pd/Pt). The FCs display their best performance in 5 M H2SO4 using the Pd/Pt anode. This exceptional stability and performance was ascribed to several factors, namely: the high permeabilities of O2, H2, and CO2 in PDMS; the inhibition of the formation of insoluble carbonate species due to the presence of a highly acidic electrolyte; and the selectivity of the Pd/Pt anode toward the HOR. The stability of the device for long-term operation was modeled using a stack of three FCs as a power supply for a portable display that otherwise uses a 3 V battery.
In noncentral collisions between ultrarelativistic heavy ions, the freeze-out distribution is anisotropic, and its major longitudinal axis may be tilted away from the beam direction. The shape and ...orientation of this distribution are particularly interesting, as they provide a snapshot of the evolving source and reflect the space-time aspect of anisotropic flow. Experimentally, this information is extracted by measuring pion Hanbury-Brown-Twiss (HBT) radii as a function of angle with respect to the reaction plane. The connection between measured radius oscillations and the underlying geometry is necessarily model-dependent; many existing formulas are strictly valid only for Gaussian sources with no collective flow. With a realistic transport model of the collision, which generates flow and non-Gaussian sources, we find that these formulas approximately reflect the anisotropy of the freeze-out distribution.
We describe the fabrication and performance of a passive, microfluidics-based H2−O2 microfluidic fuel cell using thin film Pt electrodes embedded in a poly(dimethylsiloxane) (PDMS) device. The ...electrode array is fully immersed in a liquid electrolyte confined inside the microchannel network, which serves also as a thin gas-permeable membrane through which the reactants are fed to the electrodes. The cell operates at room temperature with a maximum power density of around 700 μW/cm2, while its performance, as recorded by monitoring the corresponding polarization curves and the power density plots, is affected by the pH of the electrolyte, its concentration, the surface area of the Pt electrodes, and the thickness of the PDMS membrane. The best results were obtained in basic solutions using electrochemically roughened Pt electrodes, the roughness factor, R f, of which was around 90 relative to a smooth Pt film. In addition, the operating lifetime of the fuel cell was found to be longer for the one using higher surface area electrodes.
We describe the fabrication and performance of an integrated microelectrochemical reactor-a design possessing utility for multiple applications that include electrochemical sensing, the generation ...and manipulation of in-channel microfluidic pH gradients, and fluid actuation and flow. The device architecture is based on a three-electrode electrochemical cell design that incorporates a Pt interdigitated array (IDA) working (WE), a Pt counter (CE), and Ag pseudo-reference (RE) electrodes within a microfluidic network in which the WE is fully immersed in a liquid electrolyte confined in the channels. The microchannels are made from a conventional poly(dimethylsiloxane)(PDMS) elastomer, which serves also as a thin gas-permeable membrane through which gaseous reactants in the external ambient environment are supplied to the working electrode by diffusion. Due to the high permeability of oxygen through PDMS, the microfluidic cell supports significantly (>order of magnitude) higher current densities in the oxygen reduction reaction (ORR) than those measured in conventional (quiescent) electrochemical cells for the same electrode areas. We demonstrate in this work that, when operated at constant potential under mass transport control, the device can be utilized as a membrane-covered oxygen sensor, the response of which can be tuned by varying the thickness of the PDMS membrane. Depending on the experimental conditions under which the electrochemical ORR is performed, the data establish that the device can be operated as both a programmable pH gradient generator and a microfluidic pump.
This work describes an integrated microfluidic (μ-fl) device that can be used to effect separations that discriminate single-nucleotide polymorphisms (SNP) based on kinetic differences in the ...lability of perfectly matched (PM) and mismatched (MM) DNA duplexes during alkaline dehybridization. For this purpose a 21-base single-stranded DNA (ssDNA) probe sequence was immobilized on agarose-coated magnetic beads, that in turn can be localized within the channels of a poly(dimethylsiloxane) microfluidic device using an embedded magnetic separator. The PM and MM ssDNA targets were hybridized with the probe to form a mixture of PM and MM DNA duplexes using standard protocols, and the hydroxide ions necessary for mediating the dehybridization were generated electrochemically in situ by performing the oxygen reduction reaction (ORR) using O2 that passively permeates the device at a Pt working electrode (Pt-WE) embedded within the microfluidic channel system. The alkaline DNA dehybridization process was followed using fluorescence microscopy. The results of this study show that the two duplexes exhibit different kinetics of dehybridization, rate profiles that can be manipulated as a function of both the amount of the hydroxide ions generated and the mass-transfer characteristics of their transport within the device. This system is shown to function as a durable platform for effecting hybridization/dehybridization cycles using a nonthermal, electrochemical actuation mechanism, one that may enable new designs for lab-on-a-chip devices used in DNA analysis.
We explore the potential of net-baryon, net-proton and net-charge kurtosis measurements to investigate the properties of hot and dense matter created in relativistic heavy-ion collisions. Contrary to ...calculations in a grand-canonical ensemble we explicitly take into account exact electric and baryon charge conservation on an event-by-event basis. This drastically limits the width of baryon fluctuations. A simple model to account for this is to assume a grand-canonical distribution with a sharp cut-off at the tails. We present baseline predictions of the energy dependence of the net-baryon, net-proton and net-charge kurtosis for central (
b
≤2.75 fm) Pb+Pb/Au+Au collisions from
E
lab
=2
A
GeV to
from the UrQMD model. While the net-charge kurtosis is compatible with values around zero, the net-baryon number decreases to large negative values with decreasing beam energy. The net-proton kurtosis becomes only slightly negative for low
.
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