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The recent trend of rapid urbanization makes it imperative to understand urban characteristics such as infrastructure, population distribution, jobs, and services that play a key role in urban livability and sustainability. A healthy debate exists on what constitutes optimal structure regarding livability in cities, interpolating, for instance, between mono- and poly-centric organization. Here anonymous and aggregated flows generated from three hundred million users, opted-in to Location History, are used to extract global Intra-urban trips. We develop a metric that allows us to classify cities and to establish a connection between mobility organization and key urban indicators. We demonstrate that cities with strong hierarchical mobility structure display an extensive use of public transport, higher levels of walkability, lower pollutant emissions per capita and better health indicators. Our framework outperforms previous metrics, is highly scalable and can be deployed with little cost, even in areas without resources for traditional data collection., The growing availability of human mobility data can help assess the structure and dynamics of urban environments and their relation to the performance of cities. Here the authors introduce a metric of hierarchy in urban travel and find correlations between levels of hierarchy and other urban indicators.

Developing synthetic methodology to crystallize extended covalent structures has been an important pursuit of reticular chemistry. Here, we report a homogeneous synthetic route for imine covalent organic frameworks (COFs) where crystallites emerge from clear solutions without forming amorphous polyimine precipitates. The key feature of this route is the utilization of tert-butyloxycarbonyl group protected amine building blocks, which are deprotected in situ and gradually nucleate the crystalline framework. We demonstrate the utility of this approach by crystallizing a woven covalent organic framework (COF-112), in which covalent organic threads are interlaced to form a three-dimensional woven framework. The homogeneous imine COF synthesis also enabled the control of nucleation and crystal growth leading to uniform nanocrystals, through microwave-Assisted reactions, and facile preparation of oriented thin films., Material synthesis and characterization was supported by BASF SE (Ludwigshafen, Germany) and King Abdulaziz City for Science and Technology as part of a joint KACST–UC Berkeley collaboration (Center of Excellence for Nanomaterials and Clean Energy Applications). Work performed at the Advanced Light Source (beamline 7.3.3 and 11.3.1) and at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract no. DE-AC02-05CH11231. We also acknowledge the Kavli energy nanoscience institute at UC Berkeley for support of research on nanostructuring of reticular materials. Y.M. and O.T. acknowledge support from ShanghaiTech Startup Funding and Shanghai Science and Technology Committee (17ZR1418600), Y.Z. acknowledges support from a SIP fellowship. L.G. acknowledges support from the Army Research Office for the Multidisciplinary University Research Initiatives award WG11NF-15-1-0047. F.G. acknowledges the Spanish Ministry of Economy and Competitiveness for funding through the Ramón y Cajal program.

In the book The Essential Tension (1979) Thomas Kuhn described the conflict between tradition and innovation in scientific research—i.e., the desire to explore new promising areas, counterposed to the need to capitalize on the work done in the past. While it is probable that along their careers many scientists felt this tension, only few works have tried to quantify it. Here, we address this question by analyzing a large-scale dataset, containing all the papers published by the American Physical Society (APS) in 26 years, which allows for a better understanding of scientists’ careers evolution in Physics. We employ the Physics and Astronomy Classification Scheme (PACS) present in each paper to map the scientific interests of 103,246 authors and their evolution along the years. Our results indeed confirm the existence of the “essential tension” with scientists balancing between exploring the boundaries of their area and exploiting previous work. In particular, we found that although the majority of physicists change the topics of their research, they stay within the same broader area thus exploring with caution new scientific endeavors. Furthermore, we quantify the flows of authors moving between different subfields and pinpoint which areas are more likely to attract or donate researchers to the other ones. Overall, our results depict a very distinctive portrait of the evolution of research interests in Physics and can help in designing specific policies for the future., This material is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U.S. Army Research Office under contract/grant number W911NF-18-1-0376. A.A. acknowledges support from Santander via the “Universities International Mobility Awards “program and of the FPI doctoral fellowship program from MINECO, Spain (grant FIS2014-55867-P). S.M. acknowledges partial financial support from the Agencia Estatal de Investigacion (AEI, Spain) and Fondo Europeo de Desarrollo Regional under Project PACSS Project No. RTI2018-093732-B-C22 (MCIU, AEI/FEDER,UE) and through the María de Maeztu Program for units of Excellence in R&D (MDM-2017-0711). Y.M. acknowledges partial support from the Government of Aragón, Spain through a grant to the group FENOL (E36-17R), by MINECO and FEDER funds (grant FIS2017-87519-P) and by Intesa Sanpaolo Innovation Center.

The regional circulation in the northwestern Gulf of Mexico during late spring-summer is modulated by upwelling-favorable winds that can cause coastal upwelling in the western region and by freshwater inputs from the Mississippi-Atchafalaya Rivers. Spatial variability and temporal dynamics of phytoplankton community composition were examined during two upwelling-favorable periods using data obtained with an Imaging FlowCytobot (IFCB) from two cruises on the Texas-Louisiana shelf in June 2013 and 2014 and from the Texas Observatory for Algal Succession Time series (TOAST) at Port Aransas (Texas). Phytoplankton spatial distributions were determined by the influence of upwelling and river discharged waters. In the 2013 cruise, upwelling was detected in a large portion of the western region and the phytoplankton assemblages were dominated by diatoms, mostly chain-forming taxa. As revealed by the TOAST time series, the upwelling onset caused a dramatic increase in diatom carbon biomass. In the areas not affected by upwelling, variation in the river plume distribution that resulted from the circulation and the different discharge magnitudes for each year influenced the spatial distributions of the phytoplankton community composition. Dinoflagellates and other flagellated taxa were notably dominant during the 2013 cruise, whereas both diatoms and flagellated groups dominated the assemblages during the 2014 cruise. High stratification promoted by freshwater input, notably higher during 2013 than 2014, likely favored the dominance of flagellated groups in 2013. This study provides evidence of the influence of coastal upwelling in the phytoplankton community of the northwestern Gulf of Mexico and contributes to the knowledge of the drivers of community composition in this high-productivity area., This research was supported by grants from a Marie Curie international outgoing fellowship (GA-302562) from the European Community to S.A., and NOAA/ECOHAB (NA09NOS4780196) and NOAA/PCMHAB (NA15NOS4780173) to L.C. We thank L. Harred for collecting the IFCB data during the cruises. We extend our gratitude to the crew of the R/V Manta for their assistance on the cruises, and to S. DiMarco for providing the environmental data from his NOAA/MCH cruises (NA09NOS4780208). We thank E. Buskey and the Mission-Aransas NERR program, the NOAA/OAR/ESRL PSD, the National Data Buoy Center and the Texas Automated Buoy System, and the U.S. Army Corps of Engineers for providing data of Port Aransas Ship Channel station, satellite SST, wind and water temperature, and freshwater discharge, respectively, and R. Mooney for technical assistance with the IFCB at TOAST.

Chirality is a geometrical property by which an object is not super-imposable onto its mirror image, thereby imparting a handedness. Chirality determines many important properties in nature—from the strength of the weak interactions according to the electroweak theory in particle physics to the binding of enzymes with naturally occurring amino acids or sugars, reactions that are fundamental for life. In condensed matter physics, the prediction of topologically protected magnetic skyrmions and related spin textures in chiral magnets has stimulated significant research. If the magnetic dipoles were replaced by their electrical counterparts, then electrically controllable chiral devices could be designed. Complex oxide BaTiO/SrTiO nanocomposites and PbTiO/SrTiO superlattices are perfect candidates, since “polar vortices,” in which a continuous rotation of ferroelectric polarization spontaneously forms, have been recently discovered. Using resonant soft X-ray diffraction, we report the observation of a strong circular dichroism from the interaction between circularly polarized light and the chiral electric polarization texture that emerges in PbTiO/SrTiO superlattices. This hallmark of chirality is explained by a helical rotation of electric polarization that second-principles simulations predict to reside within complex 3D polarization textures comprising ordered topological line defects. The handedness of the texture can be topologically characterized by the sign of the helicity number of the chiral line defects. This coupling between the optical and novel polar properties could be exploited to encode chiral signatures into photon or electron beams for information processing., The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract DE-AC02-05CH11231. Electron microscopy of superlattice structures was performed at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. P.G.-F. recognizes support from Ramón y Cajal Grant RyC-2013-12515. A.R.D. acknowledges support from the Army Research Office under Grant W911NF-14-1-0104 and the US Department of Energy, Office of Basic Energy Sciences under Grant DE-SC0012375 for synthesis and structural study of the materials. A.K.Y. and C.T.N. were supported by the Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC02-05CH11231. S.-L.H. acknowledges support from the National Science Foundation under the Materials Research Science and Engineering Centers program under Grant DMR-1420620. J.Í. acknowledges support from the Luxembourg National Research Fund under Grant C15/MS/10458889 NEWALLS. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant FIS2015-64886-C5-2-P. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative, under Grant GBMF5307.

Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized., A. D. and I. R. acknowledge the financial support from the EU project ACMOL (FET Young Explorers, No. 618082). A. D. received additional support from EU Marie Sklodowska-Curie project SPINMAN (No. SEP-210189940) and from the Ministerio de Economía y Competitividad de España (No. FPDI-2013-16641). I. R. acknowledges additional financial support from the EU H2020 programme PETMEM project (Grant No. 688282). I. R. thanks the Cambridge CSD3 HPC centre for providing part of the computing resources. W. H. A., L. C. and D. V. acknowledge the financial support from the Deutsche Forschungsgemeinschaft through TRR80/F6, TRR80/G7 and the FOR1346/P3. E. Muñoz acknowledges financial support by Fondecyt (Chile) No. 1141146. M. M. Radonjić acknowledges the support from Ministry of Education, Science, and Technological Development of the Republic of Serbia under project ON171017. S. Kirchner acknowledges support by the National Key R&D Program of the MOST of China, grant No. 2016YFA0300202, the National Science Foundation of China, grant No. 11774307 and No. 11474250, and the U.S. Army RDECOM – Atlantic Grant No. W911NF-17-1-0108.

Recent years have witnessed an explosion of extensive geolocated datasets related to human movement, enabling scientists to quantitatively study individual and collective mobility patterns, and to generate models that can capture and reproduce the spatiotemporal structures and regularities in human trajectories. The study of human mobility is especially important for applications such as estimating migratory flows, traffic forecasting, urban planning, and epidemic modeling. In this survey, we review the approaches developed to reproduce various mobility patterns, with the main focus on recent developments. This review can be used both as an introduction to the fundamental modeling principles of human mobility, and as a collection of technical methods applicable to specific mobility-related problems. The review organizes the subject by differentiating between individual and population mobility and also between short-range and long-range mobility. Throughout the text the description of the theory is intertwined with real-world applications., HB, GG, RM and MT were partially supported by the US Army Research Office under Agreement Number W911NF-17-1-0127. FS is supported by EPSRC First Grant EP/P012906/1. JJR received funding from the Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and FEDER (EU) under the project ESOTECOS (FIS2015-63628-C2-2-R), and also from the European Commission H2020 project BigData4ATM (699260) under the SESAR Joint Undertaking.

Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO>3/SrTiO>3 superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a>1/a>2 phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities., A.R.D. acknowledges support from the Army Research Office under grant W911NF-14-1-0104 and the Department of Energy, Office of Science, Office of Basic Energy Sciences under grant no. DE-SC0012375 for synthesis and structural study of the materials. Z.H. acknowledges support from NSF-MRSEC grant number DMR-1420620 and NSF-MWN grant number DMR-1210588. A.K.Y. acknowledges support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. C.T.N. acknowledge support from the Office of Basic Energy Sciences, US Department of Energy DE-AC02-05CH11231. S.L.H. acknowledges support from the National Science Foundation under the MRSEC programme (DMR-1420620). M.R.M. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant number DGE-1106400. K.-D.P., V.K. and M.B.R. acknowledge support from the US Department of Energy, Office of Basic Sciences, Division of Material Sciences and Engineering, under Award No. DE-SC0008807. A.F. acknowledges support from the Swiss National Science Foundation. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grant number FIS2015-64886-C5-2-P. J.I. is supported by the Luxembourg National Research Fund (Grant FNR/C15/MS/10458889 NEWALLS). L.-Q.C. is supported by the US Department of Energy, Office of Basic Energy Sciences under Award FG02-07ER46417. R.R. and L.W.M. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, under grant GBMF5307. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-C02-05CH11231. Nanodiffraction measurements were supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Electron microscopy of superlattice structures was performed at the Molecular Foundry at Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231).

8 pags., 3 figs., 3 apps., Aaronson and Arkhipov showed that predicting or reproducing the measurement statistics of a general linear optics circuit with a single Fock-state input is a classically hard problem. Here we show that this problem, known as boson sampling, is as hard as simulating the short time evolution of a large but simple spin model with long-range XY interactions. The conditions for this equivalence are the same for efficient boson sampling, namely, having a small number of photons (excitations) as compared to the number of modes (spins). This mapping allows efficient implementations of boson sampling in small quantum computers and simulators and sheds light on the complexity of time evolution with critical spin models., B.P. and A.A.-G. acknowledge the Air Force Office of Scientific Research for support under Award No. FA9550-12-1- 0046. A.A.-G. acknowledges the Army Research Office under Award No. W911NF-15-1-0256 and the Vannevar Bush Faculty Fellowship under Award No. N00014-16-1-2008. J.J.G.R. acknowledges support from the Spanish MINECO/FEDER Project No. FIS2012-33022 and CAM PRICYT Project No. QUITEMAD+S2013/ICE-2801.

Millimeter wave radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D electron system under bichromatic excitation in order to study the evolution of the oscillatory diagonal magnetoresistance, Rxx as the millimeter wave intensity is changed systematically for various frequency combinations. The results indicate that at low magnetic fields, the lower frequency millimeter wave excitation sets the observed Rxx response, as the higher frequency millimeter wave component determines the Rxx response at higher magnetic fields. The observations are qualitatively explained in terms of the order of the involved transitions. The results are also modeled using the radiation-driven electron orbit theory., B.G., R.L.S., and magnetotransport studies at Georgia State University have been funded by U.S. Department of Energy, Office of Basic Energy Sciences, Material Sciences and Engineering division under the Grant No. DE-SC0001762. H.C.L., microwave/millimeter/terahertz study, and 2D material study have been funded by Army Research Office under W911NF-14-2-0076 and W911NF-15-1-0433. J.I. is supported by the MINECO (Spain) under Grant No. MAT2014-58241-P and ITN Grant No. 234970 (EU).

Jian, Liu et al., By using a combination of heteroepitaxial growth, structure refinement based on synchrotron x-ray diffraction, and first-principles calculations, we show that the symmetry-protected Dirac line nodes in the topological semimetallic perovskite SrIrO3 can be lifted simply by applying epitaxial constraints. In particular, the Dirac gap opens without breaking the Pbnm mirror symmetry. In virtue of a symmetry-breaking analysis, we demonstrate that the original symmetry protection is related to the n-glide operation, which can be selectively broken by different heteroepitaxial structures. This symmetry protection renders the nodal line a nonsymmorphic Dirac semimetallic state. The results highlight the vital role of crystal symmetry in spin-orbit-coupled correlated oxides and provide a foundation for experimental realization of topological insulators in iridate-based heterostructures., We thank C. Fang, P. J. Ryan, and J.-W. Kim for insightful discussions. We thank J. Rubio for experiment assistance. J.L. is sponsored by the Science Alliance Joint Directed Research and Development Program at the University of Tennessee.We are thankful for support from the director of the Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231 through the Quantum Materials FWP.We acknowledge additional support of the material synthesis facility through the DOD ARO MURI, E3S, and DARPA. D.K. acknowledges the support from the Austrian Science Fund (FWF): J3523-N27. We acknowledge support from the Grant Agency of the Czech Republic Grant no. 14-37427. Financial support from the Spanish MINECO (MAT2012-33207) is acknowledged. We acknowledge ESRF for the provision of beam time. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. J.M.R. and D.P. acknowledge support from the Army Research Office under Grant No. W911NF-15-1-0017 and the High Performance Computing Modernization Program (HPCMP) of the DOD for providing computational resources that have contributed to the research results reported herein.

The recent analysis of the composition of the frozen surface of comet 67P/Churyumov-Gerasimenko has revealed a significant number of complex organic molecules. Methyl isocyanate (CHNCO) is one of the more abundant species detected on the comet surface. In this work we report extensive characterization of its rotational spectrum resulting in a list of 1269 confidently assigned laboratory lines and its detection in space towards the Orion clouds where 399 lines of the molecule have been unambiguously identified. We find that the limited mm-wave laboratory data reported prior to our work require some revision. The abundance of CHNCO in Orion is only a factor of ten below those of HNCO and CHCN. Unlike the molecular abundances in the coma of comets, which correlate with those of warm molecular clouds, molecular abundances in the gas phase in Orion are only weakly correlated with those measured on the comet surface. We also compare our abundances with those derived recently for this molecule towards Sgr B2 (Halfen et al. 2015, ApJ, 812, L5). A more accurate abundance of CHNCO is provided for this cloud based on our extensive laboratory work., The Spanish authors thank MINECO for funding support from the CONSOLIDER-Ingenio program “ASTROMOL” CSD 2009-00038, AYA2012-32032, CTQ 2013-40717 P, CTQ 2010-19008, and the ERC synergy grant ERC-2013-Syg-610256-NANOCOSMOS. They also thank Junta de Castilla y León under grants VA070A08 and VA175U13. Z.K. acknowledges a grant from the Polish National Science Centre, decision number DEC/2011/02/A/ST2/00298. J.-C.G. and J.C. thank the ANR-13-BS05-0008-02 IMOLABS. J.-C.G. thanks the Program PCMI (INSU-CNRS) and the Centre National d’Études Spatiales (CNES) for funding support. The OSU authors acknowledge funding from NASA, NSF, and the Army Research Office.

11 págs.; 14 figs., The reflection and transmission amplitudes of waves in disordered multimode waveguides are studied by means of numerical simulations based on the invariant embedding equations. In particular, we analyze the influence of surface-type disorder on the behavior of the ensemble average and fluctuations of the reflection and transmission coefficients, reflectance, transmittance, and conductance. Our results show anomalous effects stemming from the combination of mode dispersion and rough-surface scattering: For a given waveguide length, the larger the mode transverse momentum is, the more strongly is the mode scattered. These effects manifest themselves in the mode selectivity of the transmission coefficients, anomalous backscattering enhancement, and speckle pattern both in reflection and transmission, reflectance and transmittance, and also in the conductance and its universal fluctuations. It is shown that, in contrast to volume impurities, surface scattering in quasi-one-dimensional structures (waveguides) gives rise to the coexistence of the ballistic, diffusive, and localized regimes within the same sample. © 1999 The American Physical Society., Acknowledges support from the Spanish CSIC, DGES Grant No. PB97-1221 and CICYT Grant No. TIC95-0563- CO5-03. The work of A.A.M. was supported in part by Army Research Office Grant No. DAAH 04-96-1-0187. I.V.Y. gratefully acknowledges support by EPSRC Grant No. GR/K95505.

9 págs.; 9 figs.; 1 apéndice, A rigorous formulation for the scattering of surface plasmon polaritons (SPP's) from a one-dimensional surface defect of any shape that yields the electromagnetic field in the vacuum half-space above the vacuum-metal interface is developed by the use of an impedance boundary condition. The electric and magnetic near fields, the angular distribution of the far-field radiation into vacuum due to SPP-photon coupling, and the SPP reflection and transmission coefficients are calculated by numerically solving the k-space integral equation upon which the formulation is based. In particular, we consider Gaussian-shaped defects (either protuberances or indentations) and study the dependence of the above-mentioned physical quantities on their 1/e half-width a and height h. SPP reflection is significant for narrow defects (a ≲ λ/5, for either protuberances or indentations, where λ is the wavelength of the SPP); maximum reflection (plasmon mirrors) is achieved for a ≈ λ/10. For increasing defect widths, protuberances and indentations behave differently. The former give rise to a monotonic increase of radiation at the expense of SPP transmission for increasing defect half-width. However, indentations exhibit a significant increase of radiation (decrease of SPP transmission) for half-widths of the order of or smaller than the wavelength, but tend to total SPP transmission in an oscillatory manner upon further increasing the half-width. Both the position of the maximum radiation and the oscillation period depend on the defect height, which in all other cases only affects the process quantitatively. Light emitters might thus be associated with either wide indentations or protuberances with widths that are of the order of or smaller than the wavelength. ©1999 The American Physical Society., This work was supported in part by Army Research Office Grant No. DAAH 0-96-1-0187, and by both the Spanish DGES (Grants No. PB96-0844-C02-02 and PB97-1221) and the Consejo Superior de Investigaciones Científicas.

11 págs.; 10 figs., The Green's-theorem integral equation formulation is employed to study numerically the coupling into surface plasmon polaritons by illuminating a finite metal grating with a Gaussian beam from the vacuum half-space above the metal surface. A flat surface impedance boundary condition is used to simplify the scattering integral equations. The grating coupler period is chosen so that the first diffracted order excites a surface plasmon polariton and the zeroth diffracted order is the only radiating order. In particular, the surface magnetic field and the angular distribution of scattered intensity are calculated. These functions provide in turn the total intensity of the radiation scattered into the vacuum and the total power flow carried by the surface plasmon polariton, from which the energy balance is monitored. In this way, the zeroth order and coupling efficiencies are studied as functions of the angle of incidence θ0 and the grating coupler height sc, with the aim of analyzing the influence of the length of the illuminated coupler. Our results show that, when the illuminated coupler length is decreased, the photon-surface plasmon polariton coupling resonance broadens as a function of both θ0 and sc, and that larger values of sc. are required to optimize this coupling resonance. In addition, the coupling geometry is exploited to obtain the reflection and transmission coefficients, and the intensity of the scattered volume waves, of a surface plasmon polariton thus excited that impinges on another finite metal grating, called a grating scatterer. Two frequencies of the incoming surface plasmon polariton are considered that lie very close to the lower band edge of the gap in the surface plasmon polariton dispersion relation for the infinite grating scatterer. If the frequency is in the band, a strongly oscillating, resonant behavior of the transmission coefficient as a function of the grating length is obtained. For a frequency in the gap, transmission is negligible unless the grating is short enough that the surface plasmon polariton can tunnel through it. ©1996 American Physical Society, Financial support from the Spanish Consejo Superior de Investigaciones Científicas and the Dirección General de Investigación Científica y Técnica (Grant No. PB93- 0973-C02) is acknowledged. This work was supported in part by Army Research Office Grant No. DAAL 03-92-G- 0239.

Final technical report, This work includes the study of the soils of the provinces of Huesca and Zaragoza with a total extension of 8.2000000 acres corresponding to 3.300.000 Hectares; the main part of it concerns the drawing of soil maps of these provinces at a scale 1:250.000 and the complementary part deals with the laboratory study of the samples of soils and the wording of the explicatory report., The research reported in this document has been made possible through the support and sponsorship of the U.S. Department of the Army through its European Research Office. Contract No. DA-91-591-EUC-1424 1st. April 1960 to 30th March 1961.

Trabajo financiado por U.S. Department of Army. Número de contrato DR-91-508-EUC-357. Final technical report number 1, july 1958-july 1959

Final technical report, The study of the soils of the provinces of Navarra and Logroño, both of which belong to the Ebro river basin, comprises two essential parts: on. the one hand, the mapping of the soils of the above mentioned provinces and, on the other, the preparation of the corresponding explicative report., The research reported in this document has been made possible through the support and sponsorship of the U.S. Department of the Army through its European Research Office. Contract No. DA-91-591-EUC-1085 1st. March 1959 to 30th February 1960.

Final technical report, The purpose of the research work proposed is the study of the physical properties of the soils by means of the interpretation of aerial photographs. This study is to be carried out in two years and thus it is not possible to give definite conclusions at the end of the first year, although the results we have obtained are highly satisfactory. In our opinion and after the experience of the first year, the working problem of the study of the physical properties of the soils through aerial photographs, can be examined from two different aspects. The first of them could be called the "deductive" method and consists in acquiring knowledge of the physical properties of the soils by means of sucoessive interpretations of aerial photographs; through photointerpretation we study the physical Geography of an area, its hydrographic net, natural vegetation and .man-introduced cultivations, the forms of erosion end the nature of the geological material, All these interpretations, together with the clitmate, allow to "deduce" the nature of the soils of that area, as all the pedological processes which the different geological materials have undergone can be know perfectly well, which also shows the intensity of physical and chemical desintegration of the materials that form the starting point of soil formation., The research reported in this document has been made possible through the support and sponsorship of the U.S. Department of the Army through its European Research Office.Contract No. DA-91-591-EUC-2652 1st. April 1963 to 31th March 1964.

Final Technical Report., Ten homogeneous areas typical of different geological soil materlals of Iha peninsula (Spain) were selected for study. All soil characteristics were studied "In situ", io set up a basis for correlating these data with the photolnlerpretatlons from the avallable aerial photographs. The aerlal photographs were taken In 1956 and the scale was approximate! y 1: 30.000. The physlographlc characteristics of each area are summarized and the geological, botanical and pedologlcai characteristics are discussed. A study of the photo-elements of the aerial photographs and the terrain elements such as drainage, topography, erosion, etc, was made and correlated with the tralflcabfllty conditions of each area. These studies have led to certain conclusions that can be applied directly In some cases. However, they cannot be applied universally. It is felp that the eflects of the climatic environment on the material must be studied to develop definitive relationships. The work Is illustrated with graphs of climate, geomorphology, sle. reoscoplc aerial photographs and photographic views of the selected test areas. A summary key Is included which provides a summary of lhe proper lies of the test areas., European Research Office, United States Army contract number DA-91-591-EUC-3713

4 pags., 4 figs., The potential for a subpicosecond amorphous-to-crystalline, disorder-to-order transition was explored by measuring the dielectric function of a-GeSb films following femtosecond laser excitation. Subpicosecond nonthermal structural changes both above and below the threshold for permanent crystallization were observed., The work at Harvard is supported by the National Science Foundation (Contract No. DMR-9807144) and the Army Research Office (Contract No. DAAG55-98-1-0077). A. M.-T. Kim recognizes support from the Deutscher Akademischer Auslandsdienst (DAAD) and J. Siegel from the European Union through the TMR Program (Grant No. ERB40001GT954352).