Neutron scattering and molecular correlations in a supercooled liquid

We show that the intermediate scattering function $S_n(q,t)$ for neutron scattering (ns) can be expanded naturely with respect to a set of molecular correlation functions that give a complete description of the translational and orientational two-point correlations in the liquid. The general properties of this expansion are discussed with special focus on the $q$-dependence and hints for a (partial) determination of the molecular correlation functions from neutron scattering results are given. The resulting representation of the static structure factor $S_n(q)$ is studied in detail for a model system using data from a molecular dynamics simulation of a supercooled liquid of rigid diatomic molecules. The comparison between the exact result for $S_n(q)$ and different approximations that result from a truncation of the series representation demonstrates its good convergence for the given model system. On the other hand it shows explicitly that the coupling between translational (TDOF) and orientational degrees of freedom (ODOF) of each molecule and rotational motion of different molecules can not be neglected in the supercooled regime.Further we report the existence of a prepeak in the ns-static structure factor of the examined fragile glassformer, demonstrating that prepeaks can occur even in the most simple molecular liquids. Besides examining the dependence of the prepeak on the scattering length and the temperature we use the expansion of $S_n(q)$ into molecular correlation functions to point out intermediate range orientational order as its principle origin.Comment: 13 pages, 7 figure

DT/T beyond linear theory

The major contribution to the anisotropy of the temperature of the Cosmic Microwave Background (CMB) radiation is believed to come from the interaction of linear density perturbations with the radiation previous to the decoupling time. Assuming a standard thermal history for the gas after recombination, only the gravitational field produced by the linear density perturbations present on a $\Omega\neq 1$ universe can generate anisotropies at low z (these anisotropies would manifest on large angular scales). However, secondary anisotropies are inevitably produced during the nonlinear evolution of matter at late times even in a universe with a standard thermal history. Two effects associated to this nonlinear phase can give rise to new anisotropies: the time-varying gravitational potential of nonlinear structures (Rees-Sciama RS effect) and the inverse Compton scattering of the microwave photons with hot electrons in clusters of galaxies (Sunyaev-Zeldovich SZ effect). These two effects can produce distinct imprints on the CMB temperature anisotropy. We discuss the amplitude of the anisotropies expected and the relevant angular scales in different cosmological scenarios. Future sensitive experiments will be able to probe the CMB anisotropies beyong the first order primary contribution.Comment: plain tex, 16 pages, 3 figures. Proceedings of the Laredo Advance School on Astrophysics "The universe at high-z, large-scale structure and the cosmic microwave background". To be publised by Springer-Verla

First-year Sloan Digital Sky Survey-II (SDSS-II) supernova results: consistency and constraints with other intermediate-redshift datasets

We present an analysis of the luminosity distances of Type Ia Supernovae from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey in conjunction with other intermediate redshift (z<0.4) cosmological measurements including redshift-space distortions from the Two-degree Field Galaxy Redshift Survey (2dFGRS), the Integrated Sachs-Wolfe (ISW) effect seen by the SDSS, and the latest Baryon Acoustic Oscillation (BAO) distance scale from both the SDSS and 2dFGRS. We have analysed the SDSS-II SN data alone using a variety of "model-independent" methods and find evidence for an accelerating universe at >97% level from this single dataset. We find good agreement between the supernova and BAO distance measurements, both consistent with a Lambda-dominated CDM cosmology, as demonstrated through an analysis of the distance duality relationship between the luminosity (d_L) and angular diameter (d_A) distance measures. We then use these data to estimate w within this restricted redshift range (z<0.4). Our most stringent result comes from the combination of all our intermediate-redshift data (SDSS-II SNe, BAO, ISW and redshift-space distortions), giving w = -0.81 +0.16 -0.18(stat) +/- 0.15(sys) and Omega_M=0.22 +0.09 -0.08 assuming a flat universe. This value of w, and associated errors, only change slightly if curvature is allowed to vary, consistent with constraints from the Cosmic Microwave Background. We also consider more limited combinations of the geometrical (SN, BAO) and dynamical (ISW, redshift-space distortions) probes.Comment: 13 pages, 7 figures, accepted for publication in MNRA

Gap-filling eddy covariance methane fluxes:Comparison of machine learning model predictions and uncertainties at FLUXNET-CH4 wetlands

Time series of wetland methane fluxes measured by eddy covariance require gap-filling to estimate daily, seasonal, and annual emissions. Gap-filling methane fluxes is challenging because of high variability and complex responses to multiple drivers. To date, there is no widely established gap-filling standard for wetland methane fluxes, with regards both to the best model algorithms and predictors. This study synthesizes results of different gap-filling methods systematically applied at 17 wetland sites spanning boreal to tropical regions and including all major wetland classes and two rice paddies. Procedures are proposed for: 1) creating realistic artificial gap scenarios, 2) training and evaluating gap-filling models without overstating performance, and 3) predicting half-hourly methane fluxes and annual emissions with realistic uncertainty estimates. Performance is compared between a conventional method (marginal distribution sampling) and four machine learning algorithms. The conventional method achieved similar median performance as the machine learning models but was worse than the best machine learning models and relatively insensitive to predictor choices. Of the machine learning models, decision tree algorithms performed the best in cross-validation experiments, even with a baseline predictor set, and artificial neural networks showed comparable performance when using all predictors. Soil temperature was frequently the most important predictor whilst water table depth was important at sites with substantial water table fluctuations, highlighting the value of data on wetland soil conditions. Raw gap-filling uncertainties from the machine learning models were underestimated and we propose a method to calibrate uncertainties to observations. The python code for model development, evaluation, and uncertainty estimation is publicly available. This study outlines a modular and robust machine learning workflow and makes recommendations for, and evaluates an improved baseline of, methane gap-filling models that can be implemented in multi-site syntheses or standardized products from regional and global flux networks (e.g., FLUXNET)

Innovative Architectures For Ops/obs Advanced Photonic Networks

In this work we present new architectures having new sets of link connections for mesh network (Manhattan St. type) and a for ring topology, with both using unidirectional and (one case) bi-directional links. For the comparative analysis we adopt two types of optical node configurations for both ring and mesh topologies, using 2x2 and 3x3 input/output connections. Other node functionalities such as add/drop do not impact directly on optical layer performance considered here. The traffic was analyzed in these new network topologies in terms of average number of hops and throughput under uniform traffic distribution. Our results are based on analytic studies and computer simulations. ©2009IEEE.673677Yoo, S.J., Optical Packet and Burst Switching Technologies for the Future Photonic Internet (2006) J. Lightwave Technology, 24 (12). , DecemberBonani, L.H., Rudge Barbosa, F., Moschim, E., Arthur, R., Analysis of Eletronic Buffers in Optical Packet/Burst Switched Mesh Networks International Conference on Transparent Optical Networks-ICTON-2008, June 2008 - Athens, GreeceRudge Barbosa, F., Optical Packet Switching Node for Metro-Access Networks Proceed. 29th. ECOC'2003, Rimini, Italia, Sept. 2003, , paper PD-160Ramaswami, R., Sivarajan, K.N., (2002) Optical Networks: A Practical Perspective, , Morgan Kaufmann Publishers, 2nd EditionMartins, I.B., Bonani, L.H., Barbosa, F.R., Moschim, E., Dynamic Traffic Analysis of Metro Access Optical Packet Switching Networks having Mesh Topologies Proc. Int. Telecom Symp., ITS'2006, Sept. 2006, Fortaleza, BrazilBravi, E., Cotter, E., Traffic Analysis of Optical Networks Based on Wavelenght Division Multiplexed Clockwork Routing Proceeding Int.Conf.Communications-ICC-2007-Glasgow, ScotlandRodriguez-Moral, A., Bonenfant, P., Baroni, S., Wu, R., Optical Data Networking: Protocols, Tecnologies, and Architetures for Next Generation Optical Transport Networks and Optical Internetworks (2000) IEEE J. Lightwave Technology, 18 (12). , DecemberYao, S., Mukherjee, B., Yoo, S.J., Dixit, S., A Unified Study of Contention Resolution Schemes in Optical packet switching Networks (2003) IEEE J. Lightwave Tech, 21 (3), p. 672. , MarchChlamtac, I., Fumagalli, A., An Optical Switch Architecture for Manhattan Networks (1993) IEEE J.Select. Areas Communic., 11 (4), p. 550. , MayMartins, I.B., Barbosa, F.R., Improved Method for Evaluation of Network Throughput na Protection in Future Optically Switched Metropolitan Networks Proc the Fifth Advanced International Conference on Telecommunications - AICT'2009, May 2009, Venice/Mestre, Ital

Optical Packet Switching And Routing Using In-band Frequency Header Labeling

We demonstrate a novel optical packet switching and routing system applicable to future photonic networks. Our solution is based on μs optical packets that have an RF frequency tone as header label and a digital payload transparent to rate and format in the range 1-5 Gb/s. The optical switching nodes are bufferless, with 2×2 topology, and add-drop functionalities. At the network nodes only the RF header is processed, leaving the payload undisturbed. Information between end-users is processed only at end-users locations. Packet switching, routing and contentions are resolved on a packet-by-packet basis in few μS at nodes through electronic logic control circuits, and fast optical switches. This solution is fully compatible with WDM networks.2529Yao, S., Mukherjee, B., Advances in Photonic Packet Switching: An overview (2000) IEEE Communic. Mag., pp. 84-94. , FebChiaroni, D., Status and Applications of Optical Packet Switching (2001) ECOC'2001, , paper WeM.1, Amsterdam, SeptBlumenthal, D.J., Photonic Packet and All-Optical Label Switching Techniques and Technologies (2002) OFC'2002, , paper WO3, Anaheim, USA, MarchBarbosa, F.R., Sachs, A.C., Ferreira, R.S., Furtado, M.T., New Photonic System for Optical Packet Switching (2002) 6th World Multiconference on Systemics, Cybernetics and Informatics - SCI'2002, , Orlando FL, USA, July(2002), Ericsson Telecom AB, "Apparatus, Method and System for Optical Packet Switching using Frequency Headers", International Patent Application PCT/BR02/00015, Munich, FebBonani, L.H., Sachs, A.C., Furtado, M.T., Moschim, E., Yamakami, A., Non-Uniformly Distributed Traffic in Optical Networks with Optical Packet Switching Functionalities (2002) Brazilian Symposium on Microwaves and Optoelectronics - SBMO'2002, , Recife, Brasil, AgoRocha, M.L., Rossi, S.M., Barros, M.X., Pezzolo, L., Rosolem, J.B., Paradisi, A., Experimental Performance Evaluation of 5-node IP over WDM laboratory test-bed (2002) Electron. Lett., 38. , accepted for publicationYoo, S.J.B., Optical-label based Packet Routing System with contention resolution in Wavelength, Time and Space domains OFC'2002, , paper WO2, Anaheim CA, US