@article{213,
abstract = {For any integers d,n ≥2, let X ⊂ Pn be a non‐singular hypersurface of degree d that is defined over the rational numbers. The main result in this paper is a proof that the number of rational points on X which have height at most B is O(Bn − 1 + ɛ), for any ɛ > 0. The implied constant in this estimate depends at most upon d, ɛ and n. 2000 Mathematics Subject Classification 11D45 (primary), 11G35, 14G05 (secondary).},
author = {Timothy Browning and Heath-Brown, Roger and Starr, Jason M},
journal = {Proceedings of the London Mathematical Society},
number = {2},
pages = {273 -- 303},
publisher = {John Wiley and Sons Ltd},
title = {{The density of rational points on non-singular hypersurfaces, II}},
doi = {https://doi.org/10.1112/S0024611506015784},
volume = {93},
year = {2006},
}
@article{2134,
abstract = {Predissociation of the N+2 C 2Σ+u(v') vibrational levels with v' ≥ 3 was observed via dispersed C 2Σ+u → X 2Σ+g fluorescence in the spectral range of 165–208 nm after resonant 1s−1π*(vr) excitation of N2 and its subsequent autoionization into the N+2 C state. This range is dominated by lines in atomic nitrogen, by overlapped C 2Σ+u(v') → X 2Σ+g(v'') vibrational band sequences with Δv = const and broad unresolved band systems (D, (2))2Πg(v') → A2Πu(v'') in the N+2 molecular ion. With very high fluorescence resolution of about 0.1 nm FWHM individual C 2Σ+u(v') → X 2Σ+g(v'') vibrational bands have been resolved. Calculation of the observed fluorescence spectra by taking into account predissociation and molecular rotation describes well the shape of both individual vibrational bands C 2Σ+u(v') → X 2Σ+g(v'') and the whole band system.},
author = {Ehresmann, Arno and Werner, Lutz and Klumpp, Stefan and Demekhin, Ph V and Mikhail Lemeshko and Sukhorukov, V. L and Schartner, Karl H and Schmoranzer, Hans P},
journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
number = {6},
pages = {L119 -- L126},
publisher = {IOP Publishing Ltd.},
title = {{Predissociation of the N+2(C 2Σ+u) state observed via C 2Σ+u → X 2Σ+g fluorescence after resonant 1s−1π* excitation of N2 molecule}},
doi = {10.1088/0953-4075/39/6/L03},
volume = {39},
year = {2006},
}
@article{2142,
abstract = {Fluorescence from fragments formed after the de-excitation of the N*2(1s−1π*) resonance has been measured in the spectral range of 135–190 nm. This range is dominated by lines in atomic nitrogen and lines formed by overlapping C2Σ+u(v') → X2Σ+g(v'') bands with Δv = const in the N+2 molecular ion which result from the spectator Auger decays of the N*2(1s−1π*(vr)) resonances. Ab initio calculations of the corresponding potential curves and transition probabilities showed that the observed irregular intensity dependence of the C2Σ+u(v') → X2Σ+g(v'')(Δv = const) fluorescence lines on the vibrational quantum number vr is due to transitions between vibrational levels during the reaction N2(v0 = 0)→ N*2(1s−1π*(vr)) Longrightarrow C2Σ+u(v') → X2Σ+g(v'').},
author = {Ehresmann, Arno and Werner, Lutz and Klumpp, Stefan and Lucht, S and Schmoranzer, Hans P and Mickat, Sascha and Schill, Rüdiger H and Schartner, Karl H and Demekhin, Philipp and Mikhail Lemeshko and Sukhorukov, Victor L},
journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
number = {2},
pages = {283 -- 304},
publisher = {IOP Publishing Ltd.},
title = {{Studying the N+2(C2Σ+u → X2Σ+g) fluorescence excited via the 1s−1π* resonance}},
doi = {10.1088/0953-4075/39/2/006},
volume = {39},
year = {2006},
}
@article{2144,
abstract = {Temperature dependent preedge and extended x-ray absorption fine structure measurements at the Zr K edge for the perovskite-type zirconates Pb Zr0.515 Ti0.485 O3 (PZT), PbZr O3 (PZ), and BaZr O3 are performed. To carry out a more accurate study of the weak reconstruction of the local atomic structure we employed a combination of two techniques: (i) analysis of the preedge fine structure, and (ii) analysis of the Fourier transform of the difference between χ (k) functions obtained at different temperatures. A detailed investigation of local atomic structure in the cubic phase for all the crystals is also performed. It is shown that neither the displacive nor the order-disorder model can describe correctly the changes of local atomic structure during phase transitions in PZ and PZT. A spherical model describing the local atomic structure of perovskite-type crystals suffering structural phase transitions is proposed.},
author = {Vedrinskiǐ, Rostislav V and Nazarenko, Elena S and Mikhail Lemeshko and Nassif, Vivian M and Proux, Olivier and Novakovich, Alexander A and Joly, Yves},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {13},
publisher = {American Physical Society},
title = {{Temperature dependent XAFS studies of local atomic structure of the perovskite-type zirconates}},
doi = {10.1103/PhysRevB.73.134109},
volume = {73},
year = {2006},
}
@article{215,
abstract = {For any n≥3, let F ∈ Z[X0,...,Xn ] be a form of degree d *≥5 that defines a non-singular hypersurface X ⊂ Pn . The main result in this paper is a proof of the fact that the number N (F ; B) of Q-rational points on X which have height at most B satisfiesN (F ; B) = Od,ε,n (Bn −1+ε ), for any ε > 0. The implied constant in this estimate depends at most upon d, ε and n. New estimates are also obtained for the number of representations of a positive integer as the sum of three dth powers, and for the paucity of integer solutions to equal sums of like polynomials.*},
author = {Timothy Browning and Heath-Brown, Roger},
journal = {Bulletin of the London Mathematical Society},
number = {3},
pages = {401 -- 410},
publisher = {Wiley-Blackwell},
title = {{The density of rational points on non-singular hypersurfaces, I}},
doi = {10.1112/S0024609305018412},
volume = {38},
year = {2006},
}
@article{216,
abstract = {For any N ≥ 2, let Z ⊂ ℙN be a geometrically integral algebraic variety of degree d. This article is concerned with the number Nz(B) of ℚ-rational points on Z which have height at most B. For any ε > 0, we establish the estimate NZ(B) = O d,ε,N(Bdim Z+ε), provided that d ≥ 6. As indicated, the implied constant depends at most on d, ε, and N.},
author = {Timothy Browning and Heath-Brown, Roger and Salberger, Per},
journal = {Duke Mathematical Journal},
number = {3},
pages = {545 -- 578},
publisher = {Unknown},
title = {{Counting rational points on algebraic varieties}},
doi = {10.1215/S0012-7094-06-13236-2},
volume = {132},
year = {2006},
}
@article{218,
abstract = {This paper is concerned with the average order of certain arithmetic functions, as they range over the values taken by binary forms.},
author = {de la Bretèche, Régis and Timothy Browning},
journal = {Acta Arithmetica},
number = {3},
pages = {291 -- 304},
publisher = {Instytut Matematyczny},
title = {{Sums of arithmetic functions over values of binary forms}},
doi = {10.4064/aa125-3-6},
volume = {125},
year = {2006},
}
@inproceedings{7326,
abstract = {Often the properties of a single cell are considered as representative for a complete polymer electrolyte fuel cell stack or even a fuel cell system. In some cases this comes close, however, in many real cases differences on several scales become important. Cell interaction phenomena in fuel cell stacks that arise from inequalities between adjacent cells are investigated in detail experimentally. For that, a specialized 2-cell stack with advanced localized diagnostics was developed. The results show that inequalities propagate by electrical coupling, inhomogeneous cell polarization and inducing in-plane current in the common bipolar plate. The effects of the different loss-mechanisms are analyzed and quantified. },
author = {Büchi, Felix N. and Freunberger, Stefan Alexander and Santis, Marco},
booktitle = {ECS Transactions},
location = {Cancun, Mexico},
number = {1},
pages = {963--968},
publisher = {ECS},
title = {{What is learned beyond the scale of single cells?}},
doi = {10.1149/1.2356215},
volume = {3},
year = {2006},
}
@article{7327,
abstract = {Propagation of performance changes to adjacent cells in polymer electrolyte fuel cell stacks is studied by means of voltage monitoring and local current density measurements in peripheral cells of the stack. A technical fuel cell stack has been modified by implementing two independent reactant and coolant supplies in order to deliberately change the performance of one cell (anomalous cell) and study the coupling phenomena to adjacent cells (coupling cells), while keeping the working conditions of the later cell-group unaltered.
Two anomalies are studied: (i) air starvation and (ii) thermal anomaly, in a single anomalous cell in the stack and their coupling to adjacent cells. The results have shown that anomalies inducing considerable changes in the local current density of the anomalous cell (such as air starvation) propagate to adjacent cells affecting their performance. The propagation of local current density changes takes place via the common bipolar plate due to its finite thickness and in-plane conductivity. Consequently, anomalies which do not strongly influence the local current density distribution (such as a thermal anomaly under the studied working conditions) do not propagate to adjacent cells.},
author = {Santis, Marco and Freunberger, Stefan Alexander and Papra, Matthias and Wokaun, Alexander and Büchi, Felix N.},
issn = {0378-7753},
journal = {Journal of Power Sources},
number = {2},
pages = {1076--1083},
publisher = {Elsevier},
title = {{Experimental investigation of coupling phenomena in polymer electrolyte fuel cell stacks}},
doi = {10.1016/j.jpowsour.2006.06.007},
volume = {161},
year = {2006},
}
@article{7328,
abstract = {An experimental technique for measuring the current density distribution with a resolution smaller than the channel/rib scale of the flow field in polymer electrolyte fuel cells (PEFCs) is presented. The electron conductors in a plane perpendicular to the channel direction are considered as two-dimensional resistors. Hence, the current density is obtained from the solution of Laplace's equation with the potentials at current collector and reaction layer as boundary conditions. Using ohmic drop for calculating the local current, detailed knowledge of all resistances involved is of prime importance. In particular, the contact resistance between the gas diffusion layer (GDL) and flow field rib, as well as GDL bulk conductivity, are strongly dependent on clamping pressure. They represent a substantial amount of the total ohmic drop and therefore require careful consideration. The detailed experimental setup as well as the concise procedure for quantitative data evaluation is described. Finally, the method is applied successfully to a cell operated on pure oxygen and air up to high current densities. The results show that electrical and ionic resistances seem to govern the current distribution at low current regimes, whereas mass transport limitations locally hamper the current production at high loads.},
author = {Freunberger, Stefan Alexander and Reum, Mathias and Evertz, Jörg and Wokaun, Alexander and Büchi, Felix N.},
issn = {0013-4651},
journal = {Journal of The Electrochemical Society},
number = {11},
publisher = {The Electrochemical Society},
title = {{Measuring the current distribution in PEFCs with sub-millimeter resolution}},
doi = {10.1149/1.2345591},
volume = {153},
year = {2006},
}
@article{7329,
abstract = {A novel measurement principle for measuring the current distribution in polymer electrolyte fuel cells (PEFCs) is introduced. It allows, in contrast to all other known techniques, for the first time for a resolution smaller than the channel/rib scale of the flow field in PEFCs. The current density is obtained by considering the electron conductors in the cell as a two-dimensional resistor with the voltage drop caused by the current. The method was applied to a cell operated on oxygen up to high current densities. The results show that the ohmic resistances govern the current distribution in the low current regime, whereas mass transport limitations hamper the current production under the land at high loads.},
author = {Freunberger, Stefan Alexander and Reum, Mathias and Wokaun, Alexander and Büchi, Felix N.},
issn = {1388-2481},
journal = {Electrochemistry Communications},
number = {9},
pages = {1435--1438},
publisher = {Elsevier},
title = {{Expanding current distribution measurement in PEFCs to sub-millimeter resolution}},
doi = {10.1016/j.elecom.2006.05.032},
volume = {8},
year = {2006},
}
@article{7330,
abstract = {Polymer electrolyte fuel cells (PE fuel cells) working with air at low stoichiometries (<2.0) and standard electrochemical components show a high degree of inhomogeneity in the current density distribution over the active area. An inhomogeneous current density distribution leads to a non-uniform utilization of the active area, which could negatively affect the time of life of the cells. Furthermore, it is also believed to lower cell performance. In this work, the homogenization of the current density, realized by means of tailored cathodes with along-the-air-channel redistributed catalyst loadings, is investigated. The air stoichiometry range for which a homogenization of the current density is achieved depends upon the gradient with which the catalyst is redistributed along the air channel. A gentle increasing catalyst loading profile homogenizes the current density at relatively higher air stoichiometries, while a steeper profile is suited better for lower air stoichiometries. The results show that a homogenization of the current density by means of redistributed catalyst loading has negative effects on cell performance. Model calculations corroborate the experimental findings on homogenization of the current density and deliver an explanation for the decrease in cell performance.},
author = {Santis, M. and Freunberger, Stefan Alexander and Reiner, A. and Büchi, F.N.},
issn = {0013-4686},
journal = {Electrochimica Acta},
number = {25},
pages = {5383--5393},
publisher = {Elsevier},
title = {{Homogenization of the current density in polymer electrolyte fuel cells by in-plane cathode catalyst gradients}},
doi = {10.1016/j.electacta.2006.02.008},
volume = {51},
year = {2006},
}
@article{7331,
abstract = {A previously developed mathematical model for water management and current density distribution in a polymer electrolyte fuel cell (PEFCs) is employed to investigate the effects of cooling strategies on cell performance. The model describes a two-dimensional slice through the cell along the channels and through the entire cell sandwich including the coolant channels and the bipolar plate. Arbitrary flow arrangements of fuel, oxidant, and coolant stream directions can be described. Due to the serious impact of temperature on all processes in the PEFC, both the relative direction of the coolant stream to the gas streams and its mass flow turns out to significantly affect the cell performance. Besides influencing the electrochemical reaction and all kinds of mass transfer temperature, variations predominantly alter the local membrane hydration distribution and subseqently its conductivity.},
author = {Freunberger, Stefan Alexander and Wokaun, Alexander and Büchi, Felix N.},
issn = {0013-4651},
journal = {Journal of The Electrochemical Society},
number = {5},
publisher = {The Electrochemical Society},
title = {{In-plane effects in large-scale PEFCs: II. The influence of cooling strategy on cell performance}},
doi = {10.1149/1.2185282},
volume = {153},
year = {2006},
}
@article{7332,
abstract = {A quasi-two-dimensional, along-the-channel mass and heat-transfer model for a proton exchange membrane fuel cell (PEFC) is described and validated against experimental current distribution data. The model is formulated in a dimensional manner, i.e., local transport phenomena are treated one-dimensional in through-plane direction and coupled in-plane by convective transport in the gas and coolant channels. Thus, a two-dimensional slice running through the repetitive unit of a cell from the anode channel via membrane-electrode assembly (MEA) and cathode channel to the coolant channel and from inlet to outlet is modeled. The aim of the work is to elucidate the influence of operating conditions such as feed gas humidities and stoichiometric ratios on the along-the-channel current density distribution and to identify the distinct underlying voltage loss mechanisms. Furthermore, a complicated technical flow field is modeled by a combination of co- and counterflow subdomains and compared with experimental current densities.},
author = {Freunberger, Stefan Alexander and Santis, Marco and Schneider, Ingo A. and Wokaun, Alexander and Büchi, Felix N.},
issn = {0013-4651},
journal = {Journal of The Electrochemical Society},
number = {2},
publisher = {The Electrochemical Society},
title = {{In-plane effects in large-scale PEMFCs}},
doi = {10.1149/1.2150150},
volume = {153},
year = {2006},
}
@unpublished{573,
abstract = {Mitchison and Jozsa recently suggested that the "chained-Zeno" counterfactual computation protocol recently proposed by Hosten et al. is counterfactual for only one output of the computer. This claim was based on the existing abstract algebraic definition of counterfactual computation, and indeed according to this definition, their argument is correct. However, a more general definition (physically adequate) for counterfactual computation is implicitly assumed by Hosten et. al. Here we explain in detail why the protocol is counterfactual and how the "history tracking" method of the existing description inadequately represents the physics underlying the protocol. Consequently, we propose a modified definition of counterfactual computation. Finally, we comment on one of the most interesting aspects of the error-correcting protocol. },
author = {Hosten, Onur and Rakher, Matthew and Barreiro, Julio and Peters, Nicholas and Kwiat, Paul},
pages = {12},
publisher = {ArXiv},
title = {{Counterfactual computation revisited}},
year = {2006},
}
@unpublished{574,
abstract = {Vaidman, in a recent article adopts the method of 'quantum weak measurements in pre- and postselected ensembles' to ascertain whether or not the chained-Zeno counterfactual computation scheme proposed by Hosten et al. is counterfactual; which has been the topic of a debate on the definition of counterfactuality. We disagree with his conclusion, which brings up some interesting aspects of quantum weak measurements and some concerns about the way they are interpreted. },
author = {Hosten, Onur and Kwiat, Paul},
pages = {2},
publisher = {ArXiv},
title = {{Weak measurements and counterfactual computation}},
year = {2006},
}
@inproceedings{577,
abstract = {Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) are high-efficiency single-photon detectors which have multi-photon counting capability. While both the VLPCs and the SSPMs have inferred internal quantum efficiencies above 93%, the actual measured values for both the detectors were in fact limited to less than 88%, attributed to in-coupling losses. We are currently improving this overall detection efficiency via a) custom anti-reflection coating the detectors and the in-coupling fibers, b) implementing a novel cryogenic design to reduce transmission losses and, c) using low-noise electronics to obtain a better signal-to-noise ratio.},
author = {Rangarajan, Radhika and Altepeter, Joseph B and Jeffrey, Evan R and Stoutimore, Micah J and Peters, Nicholas A and Onur Hosten and Kwiat, Paul G},
publisher = {SPIE},
title = {{High-efficiency single-photon detectors}},
doi = {10.1117/12.686117},
volume = {6372},
year = {2006},
}
@inproceedings{578,
abstract = {A source of single photons allows secure quantum key distribution, in addition, to being a critical resource for linear optics quantum computing. We describe our progress on deterministically creating single photons from spontaneous parametric downconversion, an extension of the Pittman, Jacobs and Franson scheme [Phys. Rev A, v66, 042303 (2002)]. Their idea was to conditionally prepare single photons by measuring one member of a spontaneously emitted photon pair and storing the remaining conditionally prepared photon until a predetermined time, when it would be "deterministically" released from storage. Our approach attempts to improve upon this by recycling the pump pulse in order to decrease the possibility of multiple-pair generation, while maintaining a high probability of producing a single pair. Many of the challenges we discuss are central to other quantum information technologies, including the need for low-loss optical storage, switching and detection, and fast feed-forward control.},
author = {Peters, Nicholas A and Arnold, Keith J and VanDevender, Aaron P and Jeffrey, Evan R and Rangarajan, Radhika and Onur Hosten and Barreiro, Julio T and Altepeter, Joseph B and Kwiat, Paul G},
publisher = {SPIE},
title = {{Towards a quasi-deterministic single-photon source}},
doi = {10.1117/12.684702},
volume = {6305},
year = {2006},
}
@article{579,
abstract = {The logic underlying the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to surprising effects. Counterfactual computation constitutes a striking example: the potential outcome of a quantum computation can be inferred, even if the computer is not run 1. Relying on similar arguments to interaction-free measurements 2 (or quantum interrogation3), counterfactual computation is accomplished by putting the computer in a superposition of 'running' and 'not running' states, and then interfering the two histories. Conditional on the as-yet-unknown outcome of the computation, it is sometimes possible to counterfactually infer information about the solution. Here we demonstrate counterfactual computation, implementing Grover's search algorithm with an all-optical approach4. It was believed that the overall probability of such counterfactual inference is intrinsically limited1,5, so that it could not perform better on average than random guesses. However, using a novel 'chained' version of the quantum Zeno effect6, we show how to boost the counterfactual inference probability to unity, thereby beating the random guessing limit. Our methods are general and apply to any physical system, as illustrated by a discussion of trapped-ion systems. Finally, we briefly show that, in certain circumstances, counterfactual computation can eliminate errors induced by decoherence. },
author = {Onur Hosten and Rakher, Matthew T and Barreiro, Julio T and Peters, Nicholas A and Kwiat, Paul G},
journal = {Nature},
number = {7079},
pages = {949 -- 952},
publisher = {Nature Publishing Group},
title = {{Counterfactual quantum computation through quantum interrogation}},
doi = {10.1038/nature04523},
volume = {439},
year = {2006},
}
@inproceedings{583,
abstract = {Visible light photon counters (VLPCs) and solid-state photomultipliers (SSPMs) facilitate efficient single-photon detection. We are attempting to improve their efficiency, previously limited to < 88% by coupling losses, via anti-reflection coatings, better electronics and cryogenics.},
author = {Rangarajan, Radhika and Peters, Nicholas A and Onur Hosten and Altepeter, Joseph B and Jeffrey, Evan R and Kwiat, Paul G},
publisher = {IEEE},
title = {{Improved single-photon detection}},
doi = {10.1109/CLEO.2006.4628641},
year = {2006},
}