ALBERT

Description: Reconfigurable digital filter is being widely used in applications such as communication and signal processing. Its performance, power consumption, and logic resource utilization are the major factors to be taken into consideration when designing the filters. This paper proposes a concise canonic signed digit coefficient grouping method aiming at reducing the number of common subexpressions (CSs). Further, we statistically analyze every CS occurance for numerous sorts of the finite-impulse response (FIR) filters and obtain characterization of the distribution behavior for all the possible CS patterns in a 16-bit coefficient. Thus, a novel processing element structure is proposed to form a medium-grain array for computationally efficient realization of reconfigurable FIR filter. The experiment results suggest such design implementations typically achieve 21% reduction in silicon area, 20% decrease in power consumption, and 14% improvement in operation speed in comparison to other conventional FIR architectures.

Description: Digital microfluidic biochips (DMFBs) are gaining increasing attention with promising applications for automating and miniaturizing laboratory procedures in biochemistry. In DMFBs, cross-contamination of droplets with different biomolecules is a major issue, which causes significant errors in bioassays. Washing operations are introduced to clean the cross-contamination spots. However, existing works have oversimplified assumptions on the washing behavior, which either assume infinite washing capacity, or ignore the routing conflicts between functional and washing droplets. This paper proposes the first integrated functional and washing droplet routing flow, which considers practical issues including the finite washing capacity constraint, and the routing conflicts between functional and washing droplets. Washing droplets of different sizes are also proposed to wash the congested cross-contamination spots. Effectiveness of the proposed method is validated by real-life biochemical applications.

Description: It is known that bus-oriented escape routing and area routing are necessary in a high-speed printed circuit board (PCB) design. In this paper, given a set of global routed buses in a high-speed PCB design, it is assumed that the routed nets in a single bus are represented as a bus-oriented net between two escaped boundary pins. Based on the construction of a virtual wall between two circuit components, the connection transformation of the given bus-oriented nets inside a closed region and the construction of a covering graph for the represented intervals, an iterative modified left-edge algorithm is proposed to minimize the number of the assigned layers and assign all the bus-oriented nets onto the available layers. Compared with Tsai’s algorithm, the experimental results show that our proposed algorithm reduces 15.0% of the layer number and 21.9% of CPU time for six tested examples on the average, respectively. Compared with Chin’s algorithm, the experimental results show that our proposed algorithm use less CPU time to reduce 15.0% of the layer number for six tested examples on the average.

Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.

Description: Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.

Description: Applications executed on multicore embedded systems interact with system software [such as the operating system (OS)] and hardware, leading to widely varying thermal profiles which accelerate some aging mechanisms, reducing the lifetime reliability. Effectively managing the temperature therefore requires: 1) autonomous detection of changes in application workload and 2) appropriate selection of control levers to manage thermal profiles of these workloads. In this paper, we propose a technique for workload change detection using density ratio-based statistical divergence between overlapping sliding windows of CPU performance statistics. This is integrated in a runtime approach for thermal management, which uses reinforcement learning to select workload-specific thermal control levers by sampling on-board thermal sensors. Identified control levers override the OSs native thread allocation decision and scale hardware voltage–frequency to improve average temperature, peak temperature, and thermal cycling. The proposed approach is validated through its implementation as a hierarchical runtime manager for Linux, with heuristic-based thread affinity selected from the upper hierarchy to reduce thermal cycling and learning-based voltage–frequency selected from the lower hierarchy to reduce average and peak temperatures. Experiments conducted with mobile, embedded, and high performance applications on ARM-based embedded systems demonstrate that the proposed approach increases workload change detection accuracy by an average ${3.4times }$ , reducing the average temperature by 4 °C–25 °C, peak temperature by 6 °C–24 °C, and thermal cycling by 7%–35% over state-of-the-art approaches.

Description: This paper proposes a three-tier algorithmic framework as the basis for the flexible design of data-driven structural health monitoring (SHM) systems. The three major functions of the SHM system, including data normalization, feature extraction, and hypothesis testing (HT), are mapped to the three layers of the framework. The first tier of the framework is devoted to data normalization. Machine learning (ML) methods are adopted to normalize available data sets by binning data sets to similar environmental and operational conditions (EOCs) of the system. Specifically, affinity propagation clustering is used to delineate data into groups of similar EOC. Once data are normalized by EOC, the second tier of the framework extracts features from the data to serve as condition parameters (CPs) for damage assessment. To ascertain the health state of the structure, the third tier of the framework is devoted to statistical analysis of the CP through HT. An intrinsic goal of the study is to explore the modularity of the three tier framework as a means of offering SHM system designers opportunity to explore and test different computational block sets at each layer to maximize the detection capability of the SHM system. Various realizations of the three-tier modular framework are presented and applied to acceleration and EOC data collected from an operational 3-kW wind turbine. In total, 354 data sets are collected from the turbine, including tower lateral accelerations in two orthogonal directions at six heights, wind speed and wind direction; 317 of the data sets correspond to the wind turbine in a healthy state and 37 with the wind turbine in a damage state. Using quantitative metrics derived from receiver operating characteristic (ROC) curves, the damage classification capabilities of the framework are validated and shown to accurately identify intentionally introduced damage in the turbine.

Description: Studying local earthquakes in the area Baltic-Bothnia Megashear using the data of the POLENET/LAPNET temporary array Olga Usoltseva and Elena Kozlovskaya Solid Earth, 7, 1095-1108, doi:10.5194/se-7-1095-2016, 2016 We address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET seismic array. We relocate the seismic events, calculate a 3-D tomographic P wave velocity model of the uppermost crust and investigate a focal mechanism of the event. Our results demonstrate that the Baltic-Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account when estimating seismic hazard.

Description: Studying local earthquakes in the area Baltic-Bothnia Megashear using the data of the POLENET/LAPNET temporary array Olga Usoltseva and Elena Kozlovskaya Solid Earth, 7, 1095-1108, doi:10.5194/se-7-1095-2016, 2016 We address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET seismic array. We relocate the seismic events, calculate a 3-D tomographic P wave velocity model of the uppermost crust and investigate a focal mechanism of the event. Our results demonstrate that the Baltic-Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account when estimating seismic hazard.

Description: Combined deep sampling and mass-based approaches to assess soil carbon and nitrogen losses due to land-use changes in karst area of southwestern China Yecui Hu, Zhangliu Du, Qibing Wang, and Guichun Li Solid Earth, 7, 1075-1084, doi:10.5194/se-7-1075-2016, 2016 We quantified the SOC and TN losses induced by land-use changes in a typical karst region of southwestern China. Converting from natural forest to croplands greatly led to SOC and TN losses (as higher as 37.8 %), but the magnitude depended on sampling depth and calculation method. We recommend to account for SOC and TN stocks on equivalent soil mass basis together with deep sampling. This study has significant implications on the projected land management in the degraded karst areas.

Description: Experimental sand burial affects seedling survivorship, morphological traits, and biomass allocation of Ulmus pumila var. sabulosa in the Horqin Sandy Land, China Jiao Tang, Carlos Alberto Busso, Deming Jiang, Ala Musa, Dafu Wu, Yongcui Wang, and Chunping Miao Solid Earth, 7, 1085-1094, doi:10.5194/se-7-1085-2016, 2016 In order to test the tolerance of sandy elm after emergence, an experiment was conducted to evaluate the changes of survivorship, morphological traits and biomass allocation buried by various experimental burial depths. The results showed that partial sand burial did not influence survivorship but increased seedling height, diameter, taproot length, total biomass, and relative growth rates. It decreased total leaf area and changed biomass allocation, transferring more biomass to aboveground.

Description: Characteristics of an avalanche-feeding and partially debris-covered glacier and its response to atmospheric warming in Mt. Tomor, Tian Shan, China Puyu Wang, Zhongqin Li, and Huilin Li The Cryosphere Discuss., doi:10.5194/tc-2016-138,2016 Manuscript under review for TC (discussion: open, 0 comments) A cirque-valley glacier with complex topography and partially debris-covered area was investigated in the Mt. Tomor, Tian Shan. The glacier is analogous to temperate one on movement and temperature regimes. The strongest ablation and most significant terminus retreat and area reduction occurred at the end of last century and the beginning of this century. Since inhibition of debris cover to melting, it is expected to keep shrinkage in the coming decades, but the terminus retreat is to be slower.

Description: On the temporal variability of the surface solar radiation by means of spectral representations Marc Bengulescu, Philippe Blanc, and Lucien Wald Adv. Sci. Res., 13, 121-127, doi:10.5194/asr-13-121-2016, 2016 The continuous wavelet (CWT) and the Hilbert–Huang transforms (HHT) are compared for the analysis of the temporal variability on ten years of daily means of the surface solar irradiance. In both cases, the variability exhibits a plateau between scales of two days and three months that has decreasing power with increasing scale, a spectral peak corresponding to the annual cycle, and a low power regime in-between. The HHT is shown to be suitable for inspecting the variability of the measurements.

Description: Development of high-resolution multi-scale modelling system for simulation of coastal-fluvial urban flooding Agnieszka Indiana Olbert, Joanne Comer, Stephen Nash, and Michael Hartnett Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-238,2016 Manuscript under review for NHESS (discussion: open, 0 comments) A novel nested flood model (MSN_Flood) is applied to simulate complex coastal-fluvial urban flooding in order to critically examine the model's capability to forecast evolution of urban inundation. The model demonstrates high accuracy of outputs without incurring the computational expense of high spatial resolution over the entire model domain. MSN_Flood provides full characteristics of water levels and flow regimes necessary for flood hazard identification and flood risk assessment.

Description: Development of high-resolution multi-scale modelling system for simulation of coastal-fluvial urban flooding Agnieszka Indiana Olbert, Joanne Comer, Stephen Nash, and Michael Hartnett Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-238,2016 Manuscript under review for NHESS (discussion: open, 0 comments) A novel nested flood model (MSN_Flood) is applied to simulate complex coastal-fluvial urban flooding in order to critically examine the model's capability to forecast evolution of urban inundation. The model demonstrates high accuracy of outputs without incurring the computational expense of high spatial resolution over the entire model domain. MSN_Flood provides full characteristics of water levels and flow regimes necessary for flood hazard identification and flood risk assessment.

Description: Turbulence kinetic energy budget during the afternoon transition – Part 2: A simple TKE model Erik Nilsson, Marie Lothon, Fabienne Lohou, Eric Pardyjak, Oscar Hartogensis, and Clara Darbieu Atmos. Chem. Phys., 16, 8873-8898, doi:10.5194/acp-16-8873-2016, 2016 A new simple model for turbulence kinetic energy (TKE) and its budget is presented for the sheared convective atmospheric boundary layer. It is used to study effects of buoyancy and shear on TKE evolution during the afternoon transition, especially near the surface. We also find a region of weak turbulence during unstable afternoon conditions below the inversion top, which we refer to as a "pre-residual layer".

Description: Turbulence kinetic energy budget during the afternoon transition – Part 1: Observed surface TKE budget and boundary layer description for 10 intensive observation period days Erik Nilsson, Fabienne Lohou, Marie Lothon, Eric Pardyjak, Larry Mahrt, and Clara Darbieu Atmos. Chem. Phys., 16, 8849-8872, doi:10.5194/acp-16-8849-2016, 2016 The evolution of near-surface turbulence kinetic energy (TKE) and its budget in the afternoon transition has been studied based on field measurements. The study shows that TKE transport is an important budget term that needs to be taken into account in modeling of TKE. A non-local parametrization of dissipation using a TKE–length scale model which takes into account of boundary layer depth also gave improved results compared to a local parametrization.

Description: Ice nucleation efficiency of AgI: review and new insights Claudia Marcolli, Baban Nagare, André Welti, and Ulrike Lohmann Atmos. Chem. Phys., 16, 8915-8937, doi:10.5194/acp-16-8915-2016, 2016 Silver iodide is one of the best-investigated ice nuclei. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Nevertheless, many open questions remain. This paper gives an overview of silver iodide as an ice nucleus and tries to identify the factors that influence the ice nucleation ability of silver iodide.

Description: A comprehensive biomass burning emission inventory with high spatial and temporal resolution in China Ying Zhou, Xiaofan Xing, Jianlei Lang, Dongsheng Chen, Shuiyuan Cheng, Lin Wei, Xiao Wei, and Chao Liu Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-560,2016 Manuscript under review for ACP (discussion: open, 0 comments) A 1-km gridded and comprehensive biomass burning emission inventory is developed for mainland China in 2012, based on the county-level activity data and updated source-specific emission factors. Several important parameters for emissions estimation are investigated. This paper presents the detailed emission inventory for air quality modelling and supports the development of a targeted control strategy for biomass pollution.

Description: How stratospheric are deep stratospheric intrusions? LUAMI 2008 Thomas Trickl, Hannes Vogelmann, Andreas Fix, Andreas Schäfler, Martin Wirth, Bertrand Calpini, Gilbert Levrat, Gonzague Romanens, Arnoud Apituley, Keith M. Wilson, Robert Begbie, Jens Reichardt, Holger Vömel, and Michael Sprenger Atmos. Chem. Phys., 16, 8791-8815, doi:10.5194/acp-16-8791-2016, 2016 A rather homogeneous deep stratospheric intrusion event was mapped by vertical sounding over central Europe and by model calculations along the transport path. The very low minimum H 2 O mixing ratios demonstrate almost negligible mixing with tropospheric air during the downward transport. The vertical distributions of O 3 and aerosol were transferred from the source region to Europe without major change. A rather shallow outflow from the stratosphere was found.

Description: Air–surface exchange of gaseous mercury over permafrost soil: an investigation at a high-altitude (4700 m a.s.l.) and remote site in the central Qinghai-Tibet Plateau Zhijia Ci, Fei Peng, Xian Xue, and Xiaoshan Zhang Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-515,2016 Manuscript under review for ACP (discussion: open, 0 comments) We performed filed measurements and controlled field experiments to examine the flux, temporal variation and influencing factors of air–surface Hg(0) exchange at a high-altitude and remote site in the central Qinghai-Tibet Plateau. We found that the environmental conditions greatly influenced the air–surface Hg dynamics. Our results have important implications to the Hg biogeochemical cycle in the soils of Qinghai-Tibet Plateau under the rapid climate warming and environmental change.

Description: Ice nucleation efficiency of AgI: review and new insights Claudia Marcolli, Baban Nagare, André Welti, and Ulrike Lohmann Atmos. Chem. Phys., 16, 8915-8937, doi:10.5194/acp-16-8915-2016, 2016 Silver iodide is one of the best-investigated ice nuclei. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Nevertheless, many open questions remain. This paper gives an overview of silver iodide as an ice nucleus and tries to identify the factors that influence the ice nucleation ability of silver iodide.

Description: Controls on phase composition and ice water content in a convection-permitting model simulation of a tropical mesoscale convective system Charmaine N. Franklin, Alain Protat, Delphine Leroy, and Emmanuel Fontaine Atmos. Chem. Phys., 16, 8767-8789, doi:10.5194/acp-16-8767-2016, 2016 Simulations of tropical convection are used to investigate the processes that control the phase composition of tropical clouds. It is shown that the growth of ice is less dependent on vertical velocity than is liquid water, with the control on ice water content being the ice sizes and available liquid water. Results show that in the purely ice region of convective updraughts, the buoyancy is controlled by the ice sizes, demonstrating the importance of microphysical processes on convective dynamics.

Description: Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities Mijung Song, Pengfei F. Liu, Sarah J. Hanna, Rahul A. Zaveri, Katie Potter, Yuan You, Scot T. Martin, and Allan K. Bertram Atmos. Chem. Phys., 16, 8817-8830, doi:10.5194/acp-16-8817-2016, 2016 To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α -pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2  ×  10 −1 to  ∼  6  ×  10 6  Pa s from 30 to 90 % RH, and greater than  ∼  2  ×  10 8  Pa s (similar to or greater than the viscosity of tar pitch) for RH  ≤  17 %. These viscosities correspond to Stokes–Einstein-equivalent diffusion coefficients for large organic molecules of  ∼  2  ×  10 −15  cm 2  s −1 for 30 % RH, and lower than  ∼  3  ×  10 −17  cm 2  s −1 for RH  ≤  17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h for 30 % RH, and higher than  ∼  100 h for RH  ≤  17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00–17:00 LT) during certain times of the year.

Description: Air–surface exchange of gaseous mercury over permafrost soil: an investigation at a high-altitude (4700 m a.s.l.) and remote site in the central Qinghai-Tibet Plateau Zhijia Ci, Fei Peng, Xian Xue, and Xiaoshan Zhang Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-515,2016 Manuscript under review for ACP (discussion: open, 0 comments) We performed filed measurements and controlled field experiments to examine the flux, temporal variation and influencing factors of air–surface Hg(0) exchange at a high-altitude and remote site in the central Qinghai-Tibet Plateau. We found that the environmental conditions greatly influenced the air–surface Hg dynamics. Our results have important implications to the Hg biogeochemical cycle in the soils of Qinghai-Tibet Plateau under the rapid climate warming and environmental change.

Description: Aerosol source apportionment from 1-year measurements at the CESAR tower in Cabauw, the Netherlands Patrick Schlag, Astrid Kiendler-Scharr, Marcus Johannes Blom, Francesco Canonaco, Jeroen Sebastiaan Henzing, Marcel Moerman, André Stephan Henry Prévôt, and Rupert Holzinger Atmos. Chem. Phys., 16, 8831-8847, doi:10.5194/acp-16-8831-2016, 2016 This work provides chemical composition data of atmospheric aerosols acquired during 1 year in the rural site of Cabauw, the Netherlands. In some periods, we found unexpected high particle mass concentrations exceeding the WHO limits. Using these composition data, we found that reducing ammonia emissions in this region would largely reduce the main aerosol component ammonium nitrate, whereas the local mitigation of the organics turned out to be difficult due to the lack of a designated source.

Description: Turbulence kinetic energy budget during the afternoon transition – Part 2: A simple TKE model Erik Nilsson, Marie Lothon, Fabienne Lohou, Eric Pardyjak, Oscar Hartogensis, and Clara Darbieu Atmos. Chem. Phys., 16, 8873-8898, doi:10.5194/acp-16-8873-2016, 2016 A new simple model for turbulence kinetic energy (TKE) and its budget is presented for the sheared convective atmospheric boundary layer. It is used to study effects of buoyancy and shear on TKE evolution during the afternoon transition, especially near the surface. We also find a region of weak turbulence during unstable afternoon conditions below the inversion top, which we refer to as a "pre-residual layer".

Description: Comparing contact and immersion freezing from continuous flow diffusion chambers Baban Nagare, Claudia Marcolli, André Welti, Olaf Stetzer, and Ulrike Lohmann Atmos. Chem. Phys., 16, 8899-8914, doi:10.5194/acp-16-8899-2016, 2016 The relative importance of contact freezing and immersion freezing at mixed-phase cloud temperatures is the subject of debate. We performed experiments using continuous-flow diffusion chambers to compare the freezing efficiency of ice-nucleating particles for both these nucleation modes. Silver iodide, kaolinite and Arizona Test Dust were used as ice-nucleating particles. We could not confirm the dominance of contact freezing over immersion freezing for our experimental conditions.

Description: Assessment of cloud related fine mode AOD enhancements based on AERONET SDA product A. Arola, T. F. Eck, H. Kokkola, M. R. A. Pitkänen, and S. Romakkaniemi Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-600,2016 Manuscript under review for ACP (discussion: open, 0 comments) One of the issues that hinder the measurement-based assessment of aerosol-cloud interactions by remote sensing methods is that typically aerosols and clouds cannot be measured simultaneously by passive remote sensing methods. AERONET includes so-called SDA product that provides the fine mode AOD also in mixed cloud-aerosol observations. These measurements have not been yet fully exploited in studies of aerosol-cloud interactions. We applied SDA for this kind of analysis.

Description: Controls on phase composition and ice water content in a convection-permitting model simulation of a tropical mesoscale convective system Charmaine N. Franklin, Alain Protat, Delphine Leroy, and Emmanuel Fontaine Atmos. Chem. Phys., 16, 8767-8789, doi:10.5194/acp-16-8767-2016, 2016 Simulations of tropical convection are used to investigate the processes that control the phase composition of tropical clouds. It is shown that the growth of ice is less dependent on vertical velocity than is liquid water, with the control on ice water content being the ice sizes and available liquid water. Results show that in the purely ice region of convective updraughts, the buoyancy is controlled by the ice sizes, demonstrating the importance of microphysical processes on convective dynamics.

Description: Turbulence kinetic energy budget during the afternoon transition – Part 1: Observed surface TKE budget and boundary layer description for 10 intensive observation period days Erik Nilsson, Fabienne Lohou, Marie Lothon, Eric Pardyjak, Larry Mahrt, and Clara Darbieu Atmos. Chem. Phys., 16, 8849-8872, doi:10.5194/acp-16-8849-2016, 2016 The evolution of near-surface turbulence kinetic energy (TKE) and its budget in the afternoon transition has been studied based on field measurements. The study shows that TKE transport is an important budget term that needs to be taken into account in modeling of TKE. A non-local parametrization of dissipation using a TKE–length scale model which takes into account of boundary layer depth also gave improved results compared to a local parametrization.

Description: Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities Mijung Song, Pengfei F. Liu, Sarah J. Hanna, Rahul A. Zaveri, Katie Potter, Yuan You, Scot T. Martin, and Allan K. Bertram Atmos. Chem. Phys., 16, 8817-8830, doi:10.5194/acp-16-8817-2016, 2016 To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α -pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2  ×  10 −1 to  ∼  6  ×  10 6  Pa s from 30 to 90 % RH, and greater than  ∼  2  ×  10 8  Pa s (similar to or greater than the viscosity of tar pitch) for RH  ≤  17 %. These viscosities correspond to Stokes–Einstein-equivalent diffusion coefficients for large organic molecules of  ∼  2  ×  10 −15  cm 2  s −1 for 30 % RH, and lower than  ∼  3  ×  10 −17  cm 2  s −1 for RH  ≤  17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h for 30 % RH, and higher than  ∼  100 h for RH  ≤  17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00–17:00 LT) during certain times of the year.

Description: How stratospheric are deep stratospheric intrusions? LUAMI 2008 Thomas Trickl, Hannes Vogelmann, Andreas Fix, Andreas Schäfler, Martin Wirth, Bertrand Calpini, Gilbert Levrat, Gonzague Romanens, Arnoud Apituley, Keith M. Wilson, Robert Begbie, Jens Reichardt, Holger Vömel, and Michael Sprenger Atmos. Chem. Phys., 16, 8791-8815, doi:10.5194/acp-16-8791-2016, 2016 A rather homogeneous deep stratospheric intrusion event was mapped by vertical sounding over central Europe and by model calculations along the transport path. The very low minimum H 2 O mixing ratios demonstrate almost negligible mixing with tropospheric air during the downward transport. The vertical distributions of O 3 and aerosol were transferred from the source region to Europe without major change. A rather shallow outflow from the stratosphere was found.

Description: A low-cost acoustic permeameter Stephen A. Drake, John S. Selker, and Chad W. Higgins Geosci. Instrum. Method. Data Syst. Discuss., doi:10.5194/gi-2016-13,2016 Manuscript under review for GI (discussion: open, 0 comments) Intrinsic permeability of snow is an important parameter that regulates snow/atmosphere exchange. Current permeability measurements require specialized equipment to acquire in the field and have increased variability with increasing snow heterogeneity. To facilitate a field-based, volume-averaged measure of permeability we designed and assembled an acoustic permeameter. Using reticulated foam samples of known permeability, the mean relative error from known values was less than 20 %.

Description: Automatic georeferencing of astronaut auroral photography Maik Riechert, Andrew P. Walsh, Alexander Gerst, and Matthew G. G. T. Taylor Geosci. Instrum. Method. Data Syst., 5, 289-304, doi:10.5194/gi-5-289-2016, 2016 Astronauts on board the International Space Station have taken thousands of high-quality images of the northern and southern lights (aurorae). Because the images were not taken as part of a specific research project, no information about exactly where the camera was pointing was available. We have used the stars in the images to reconstruct this information. Now we can tell the latitudes and longitudes of the aurorae in the images and use them for research. The data are publicly available.

Description: On the propagation of diel signals in river networks using analytic solutions of flow equations Morgan Fonley, Ricardo Mantilla, Scott J. Small, and Rodica Curtu Hydrol. Earth Syst. Sci., 20, 2899-2912, doi:10.5194/hess-20-2899-2016, 2016 We design and implement a theoretical experiment to show that, under low-flow conditions, observed streamflow discrepancies between early and late summer can be attributed to different flow velocities in the river network. By developing an analytic solution to represent flow along a given river network, we emphasize the dependence of streamflow amplitude and time delay on the geomorphology of the network. We also simulate using a realistic river network to highlight the effects of scale.

Description: On the propagation of diel signals in river networks using analytic solutions of flow equations Morgan Fonley, Ricardo Mantilla, Scott J. Small, and Rodica Curtu Hydrol. Earth Syst. Sci., 20, 2899-2912, doi:10.5194/hess-20-2899-2016, 2016 We design and implement a theoretical experiment to show that, under low-flow conditions, observed streamflow discrepancies between early and late summer can be attributed to different flow velocities in the river network. By developing an analytic solution to represent flow along a given river network, we emphasize the dependence of streamflow amplitude and time delay on the geomorphology of the network. We also simulate using a realistic river network to highlight the effects of scale.

Description: Simultaneous calibration of hydrological models in geographical space András Bárdossy, Yingchun Huang, and Thorsten Wagener Hydrol. Earth Syst. Sci., 20, 2913-2928, doi:10.5194/hess-20-2913-2016, 2016 This paper explores the simultaneous calibration method to transfer model parameters from gauged to ungauged catchments. It is hypothesized that the model parameters can be separated into two categories: one reflecting the dynamic behavior and the other representing the long-term water balance. The results of three numerical experiments indicate that a good parameter transfer to ungauged catchments can be achieved through simultaneous calibration of models for a number of catchments.

Description: Reinforced concrete infrastructure assets built during the last century are required to stay in-service beyond their intended design lives, which requires techniques that allow the effects of deterioration and overloading to be monitored to ensure these assets are still fit for purpose. One such indicator of distress in a reinforced concrete structure is crack movement; models have been proposed that allow the internal stresses within a structure to be estimated if crack width and slip can be measured. This paper introduces a technique that uses digital image correlation (DIC) to measure not only crack width but also crack slip. The effect of curvature on this measurement technique is discussed and a method for minimizing the errors due to curvature is presented. The technique is used to measure crack width and slip in reinforced concrete beams with both small crack slip and significant crack slip. The results suggest that the technique can be used to measure crack movement in beams once the effects of curvature are accounted for. Future research in this area will focus on development of this technique for use in the field.

Description: Ultrasonic guided waves are an attractive tool for structural health monitoring due to their capability to rapidly assess large regions of a structure. Yet, most guided wave based methods for detecting, locating, and classifying structural damage rely on our ability to accurately predict guided wave behavior. Characterizing and predicting guided wave behavior is difficult, particularly in mechanically complex materials such as fiber-reinforced composites. In this paper, we address this challenge through a sparse wavenumber analysis framework. Sparse wavenumber analysis integrates physics-based models, signal processing algorithms for compressive sensing, and a small number of local measurements to predict global wave behavior. We implement sparse wavenumber analysis for three wave systems: standing waves on a string, Lamb waves in an isotropic plate, and guided waves in a unidirectional, anisotropic plate. Through the use of simulation and experimental data, we show that sparse wavenumber analysis can accurately recover the sparse representations (i.e., the eigenmodes) of each system and then use these representations to predict global wave behavior. For the anisotropic plate, we accurately predict 149765 experimental time-domain measurements from only 36 local measurements.

Description: Guided wave sensors are widely used in a number of industries and have found particular application in the oil and gas industry for the inspection of pipework. Traditionally this type of sensor was used for one-off inspections, but in recent years there has been a move towards permanent installation of the sensor. This has enabled highly repeatable readings of the same section of pipe, potentially allowing improvements in defect detection and classification. This paper proposes a novel approach using independent component analysis to decompose repeat guided wave signals into constituent independent components. This separates the defect from coherent noise caused by changing environmental conditions, improving detectability. This paper demonstrates independent component analysis applied to guided wave signals from a range of industrial inspection scenarios. The analysis is performed on test data from pipe loops that have been subject to multiple temperature cycles both in undamaged and damaged states. In addition to processing data from experimental damaged conditions, simulated damage signals have been added to “undamaged” experimental data, so enabling multiple different damage scenarios to be investigated. The algorithm has also been used to process guided wave signals from finite element simulations of a pipe with distributed shallow general corrosion, within which there is a patch of severe corrosion. In all these scenarios, the independent component analysis algorithm was able to extract the defect signal, rejecting coherent noise.

Description: Integrated structural health monitoring and damage prognosis (SHM-DP) methodologies, coupled with sensor-based nondestructive evaluation (NDE) techniques, are becoming increasingly important for the near-real-time condition assessment (i.e., SHM) and future performance predictions (i.e., DP) of aging mechanical systems, civil structures, and infrastructure networks, as well as automotive, naval, and aerospace vehicles. A successful SHM-DP strategy, capable of identifying all critical damage mechanisms while accounting for all relevant sources of uncertainty, can be used as an advanced tool to effectively and optimally manage the life-cycle of the monitored system, recursively forecast its remaining useful life (RUL), and ultimately reduce the overall ownership cost through dynamic reliability-based inspection and maintenance (RBIM) plans, system downtime minimization, catastrophic failure prevention, and potential RUL extension. In this perspective, fatigue damage propagation is one of the most critical and unpredictable deterioration processes for a large variety of structural and mechanical systems that are subjected repeatedly to cyclic and/or random operational loading during their service life. Within this limited scope, the authors developed a comprehensive NDE-based SHM-DP framework for recursively predicting the time-varying system reliability and the remaining fatigue life (RFL) of monitored systems subjected to deterioration by multi-site fatigue damage propagation. This paper provides a brief overview of the proposed framework and then uses a set of experimental fatigue test data to perform a thorough statistical performance assessment of the developed methodology at the local reliability component level (i.e., single damage mechanism and single damage location) including NDE detectability and measurement uncertainty as well as both load and model parameter uncertainty.

Description: Accurate and reliable damage characterization (i.e., damage detection, localization, and evaluation of extent) in civil structures and infrastructure is an important objective of structural health monitoring (SHM). Highly accurate and reliable characterization of damage at early stages requires continuous or quasi-continuous direct sensing of the critical parameters. Direct sensing requires deploying dense arrays of sensors, to enhance the probability that damage will result in signals that can be directly acquired by the sensors. However, coverage by dense arrays of sensors over the large areas that are of relevance represents an enormous challenge for current technologies. Large area electronics (LAE) is an emerging technology that can enable the formation of dense sensor arrays spanning large areas (several square meters) on flexible substrates. This paper explores the requirements and technology for a sensing sheet for SHM based on LAE and crystalline silicon CMOS integrated circuits (ICs). The sensing sheet contains a dense array of thin-film full-bridge resistive strain sensors, along with the electronics for strain readout, full-system self-powering, and communication. Research on several stages is presented for translating the sensing sheet to practical SHM applications. This includes experimental characterization of an individual sensor’s response when exposed to cracks in concrete and steel; theoretical and experimental performance evaluation of various geometrical parameters of the sensing sheet; and development of the electronics necessary for sensor readout, power management, and sensor-data communication. The concept of direct sensing has been experimentally validated, and the potential of a sensing sheet to provide direct sensing and successful damage characterization has been evaluated in the laboratory setting. A prototype of the sensing sheet has also been successfully developed and independently characterized in the laboratory, meeting the- required specifications. Thus, a sensing sheet for SHM applications shows promise both in terms of practicality and effectiveness.

Description: Global combustion sources of organic aerosols: model comparison with 84 AMS factor-analysis data sets Alexandra P. Tsimpidi, Vlassis A. Karydis, Spyros N. Pandis, and Jos Lelieveld Atmos. Chem. Phys., 16, 8939-8962, doi:10.5194/acp-16-8939-2016, 2016 In this work we use a global chemistry climate model together with a comprehensive global AMS data set in order to provide valuable insights into the temporal and geographical variability of the contribution of the emitted particles and the chemically processed organic material from combustion sources to total OA. This study reveals the high importance of SOA from anthropogenic sources on global OA concentrations and identifies plausible sources of discrepancy between models and measurements.

Description: Modeling investigation of light absorbing aerosols in the central Amazon during the wet season Qiaoqiao Wang, Jorge Saturno, Xuguang Chi, David Walter, Jost V. Lavric, Daniel Moran- Zuloaga, Florian Ditas, Christopher Pöhlker, Joel Brito, Samara Carbone, Paulo Artaxo, and Meinrat O. Andreae Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-586,2016 Manuscript under review for ACP (discussion: open, 0 comments) We use a chemical transport model to interpret observed aerosol concentrations and absorption over the Amazon basin during the wet season. With daily temporal resolution for open fire emissions and modified aerosol optical properties, our model successfully captures the observed variation of aerosol concentrations and absorption over the Amazon basin. The simulation indicates important influence of open fire mainly from northern South America and from Northern Africa in the wet season.

Description: Morphology and Mixing of BC Particles Collected in Central California During the CARES Field Study Ryan C. Moffet, Rachel E. O'Brien, Peter Alpert, Stephen T. Kelly, Don Q. Pham, Mary K. Gilles, Daniel Knopf, and Alexander Laskin Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-634,2016 Manuscript under review for ACP (discussion: open, 0 comments) Atmospheric black carbon (BC), commonly known as soot, is an important constituent of the earth's that imparts a warming similar to that of carbon dioxide. However, BC is much shorter lived and has uncertain warming due to its mixture with other solid and liquid components. Here, advanced microscopic methods have provided a detailed look at thousands of BC particles sampled from central California; these measurements will lead towards a better understanding of the effects that BC has on climate.

Description: 4-D-VAR assimilation of disdrometer data and radar spectral reflectivities for raindrop size distribution and vertical wind retrievals François Mercier, Aymeric Chazottes, Laurent Barthès, and Cécile Mallet Atmos. Meas. Tech., 9, 3145-3163, doi:10.5194/amt-9-3145-2016, 2016 The aim of this study is to retrieve vertical profiles of raindrop size distributions and vertical winds from radar and ground measurements. This is crucial to understand the phenomena acting on the raindrops at small scale during their fall and then to be able to merge measurements of rain at different heights and scales (from radar, rain gauges, satellites etc.). It could also help to improve the treatment of radar data and to better parameterize rain in numerical weather prediction models.

Description: Diversity and mineral substrate preference in endolithic microbial communities from marine intertidal outcrops (Isla de Mona, Puerto Rico) Estelle Couradeau, Daniel Roush, Brandon Scott Guida, and Ferran Garcia-Pichel Biogeosciences Discuss., doi:10.5194/bg-2016-254,2016 Manuscript under review for BG (discussion: open, 0 comments) Endolithic (inside rock) microbial communities are dominated by cyanobacteria, among which the true boring cyanobacteria actively perforate the mineral and play a significant role in the erosion of coastal outcrops that may increase with ocean acidification. We interrogated the microbial communities associated with various intertidal substrates of Mona Island (PR) and brought the first evidence that there exists a mineralogical substrate preference among the pioneers true boring cyanobacteria.

Description: Influence of the spatial distribution of gravity wave activity on the middle atmospheric circulation and transport Petr Šácha, Friederike Lilienthal, Christoph Jacobi, and Petr Pišoft Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-548,2016 Manuscript under review for ACP (discussion: open, 0 comments) With a mechanistic model for the middle and upper atmosphere we performed sensitivity simulations to study a possible effect of a localized GW breaking hotspot in the Eastern Asia/Northern Pacific region and also more generally, possible influence of spatial distribution of gravity wave activity on the middle atmospheric circulation and transport. We show implications for polar vortex stability, in-situ planetary wave generation and longitudinal variability and strength of the B.–D. circulation.

Description: Influence of enhanced Asian NO x emissions on ozone in the Upper Troposphere and Lower Stratosphere (UTLS) in chemistry climate model simulations Chaitri Roy, Suvarna Fadnavis, Rolf Müller, Ayantika Dey Chaudhary, and Felix Ploeger Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-582,2016 Manuscript under review for ACP (discussion: open, 0 comments) In the monsoon season, Asian NO x emissions are rapidly transported to the UTLS and can impact ozone in the UTLS. From chemistry climate model simulations, we show that increasing Asian NO x emissions have led to enhanced ozone radiative forcing over South east Asia which leads to significant warming over the Tibetan plateau and increase precipitations over India. However, a further increase in NO x emissions elicited negative precipitation via ozone heating over the Tibetan plateau.

Description: A reduced-complexity model for sediment transport and step-pool morphology Matteo Saletti, Peter Molnar, Marwan A. Hassan, and Paolo Burlando Earth Surf. Dynam., 4, 549-566, doi:10.5194/esurf-4-549-2016, 2016 This study presents a new reduced-complexity model with few parameters linked to basic physical processes, which aims to reproduce the transport of sediment as bed load and the formation and stability of channel morphology in steep mountain streams. The model is able to simulate the formation and stability of steps, bed structures commonly encountered in steep channels, by assuming that their formation is due to intense sediment transport during high flows causing jamming of particles.

Description: A new test statistic for climate models that includes field and spatial dependencies using Gaussian Markov random fields Alvaro Nosedal-Sanchez, Charles S. Jackson, and Gabriel Huerta Geosci. Model Dev., 9, 2407-2414, doi:10.5194/gmd-9-2407-2016, 2016 We have developed a new metric for climate model evaluation that quantifies the significance of modeling errors across multiple fields. Our approach dramatically reduces the amount of data that is required to evaluate field and space dependencies and increases the community's potential to make use of the extremely valuable but limited satellite observational record. Our objective is to improve the strategies that currently exist for more formal data-driven model development.

Description: Looking beyond general metrics for model comparison – lessons from an international model intercomparison study Tanja de Boer-Euser, Laurène Bouaziz, Jan De Niel, Claudia Brauer, Benjamin Dewals, Gilles Drogue, Fabrizio Fenicia, Benjamin Grelier, Jiri Nossent, Fernando Pereira, Hubert Savenije, Guillaume Thirel, and Patrick Willems Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-339,2016 Manuscript under review for HESS (discussion: open, 0 comments) In this study the rainfall–runoff models of eight international research groups were compared for a set of subcatchments of the Meuse basin to investigate the influence of certain model components on the modelled discharge. Although the models showed similar performances based on general metrics, clear differences could be observed for specific events. The differences during drier conditions could indeed be linked back to differences in model structures.

Description: Phase segmentation of X-ray computer tomography rock images using machine learning techniques: an accuracy and performance study Swarup Chauhan, Wolfram Rühaak, Hauke Anbergen, Alen Kabdenov, Marcus Freise, Thorsten Wille, and Ingo Sass Solid Earth, 7, 1125-1139, doi:10.5194/se-7-1125-2016, 2016 Machine learning techniques are a promising alternative for processing (phase segmentation) of 3-D X-ray computer tomographic rock images. Here the performance and accuracy of different machine learning techniques are tested. The aim is to classify pore space, rock grains and matrix of four distinct rock samples. The porosity obtained based on the segmented XCT images is cross-validated with laboratory measurements. Accuracies of the different methods are discussed and recommendations proposed.

Description: Comparison and validation of global and regional ocean forecasting systems for the South China Sea Xueming Zhu, Hui Wang, Guimei Liu, Charly Régnier, Xiaodi Kuang, Dakui Wang, Shihe Ren, Zhiyou Jing, and Marie Drévillon Nat. Hazards Earth Syst. Sci., 16, 1639-1655, doi:10.5194/nhess-16-1639-2016, 2016 This paper examined the performances of two operational ocean forecasting systems, Mercator Océan in France and SCSOFS in China, based on observed satellite and in situ data obtained in 2012. The comparison and validation are focused on the ocean circulations, the structures of temperature and salinity, and some mesoscale activities in the South China Sea. Finally, some recommendations have been proposed for both systems to improve their performances in the near future.

Description: Pore-scale tomography and imaging: applications, techniques and recommended practice Matthias Halisch, Holger Steeb, Steven Henkel, and Charlotte M. Krawczyk Solid Earth, 7, 1141-1143, doi:10.5194/se-7-1141-2016, 2016 No abstract available.

Description: An ice-sheet-wide framework for englacial attenuation from ice-penetrating radar data T. M. Jordan, J. L. Bamber, C. N. Williams, J. D. Paden, M. J. Siegert, P. Huybrechts, O. Gagliardini, and F. Gillet-Chaulet The Cryosphere, 10, 1547-1570, doi:10.5194/tc-10-1547-2016, 2016 Ice penetrating radar enables determination of the basal properties of ice sheets. Existing algorithms assume stationarity in the attenuation rate, which is not justifiable at an ice sheet scale. We introduce the first ice-sheet-wide algorithm for radar attenuation that incorporates spatial variability, using the temperature field from a numerical model as an initial guess. The study is a step toward ice-sheet-wide data products for basal properties and evaluation of model temperature fields.

Description: HCOOH distributions from IASI for 2008–2014: comparison with ground-based FTIR measurements and a global chemistry-transport model Matthieu Pommier, Cathy Clerbaux, Pierre-François Coheur, Emmanuel Mahieu, Jean-François Müller, Clare Paton-Walsh, Trissevgeni Stavrakou, and Corinne Vigouroux Atmos. Chem. Phys., 16, 8963-8981, doi:10.5194/acp-16-8963-2016, 2016 This work presents for the first time 7 years of formic acid (HCOOH) measurements recorded by the satellite instrument, IASI. The comparison of the data set with ground-based FTIR measurements and a CTM shows the interannual and the seasonal variation are well captured. Global distributions are provided, highlighting the long-range transport of tropospheric HCOOH over the oceans and the detection of source regions e.g. over India, USA, and Africa.

Description: Current Understanding of the Driving Mechanisms for Spatiotemporal Variations of Atmospheric Speciated Mercury: A Critical Review Huiting Mao, Irene Cheng, and Leiming Zhang Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-563,2016 Manuscript under review for ACP (discussion: open, 0 comments) Understanding of spatial and temporal variations of atmospheric speciated mercury can advance our knowledge of mercury cycling in various environments. This review summarized spatiotemporal variations of TGM/GEM, GOM, and PBM in various environments including oceans, continents, high elevation, the free troposphere, and low to high latitudes. Remaining questions/issues and recommendations were provided for future research on spatiotemporal variations of atmospheric Hg.

Description: Comparison of MODIS and VIIRS cloud properties with ARM ground-based observations over Finland Moa K. Sporre, Ewan J. O'Connor, Nina Håkansson, Anke Thoss, Erik Swietlicki, and Tuukka Petäjä Atmos. Meas. Tech., 9, 3193-3203, doi:10.5194/amt-9-3193-2016, 2016 Satellite measurements of cloud top height and liquid water path are compared to ground-based remote sensing to evaluate the satellite retrievals. The overall performance of the satellite retrievals of cloud top height are good, but they become more problematic when several layers of clouds are present. The liquid water path retrievals also agree well, and the average differences are within the estimated measurement uncertainties.

Description: Remote sensing of tropospheric turbulence using GPS radio occultation Esayas Shume and Chi Ao Atmos. Meas. Tech., 9, 3175-3182, doi:10.5194/amt-9-3175-2016, 2016 Radio occultation (RO) measurements are sensitive to the small-scale irregularities in the atmosphere. In this study, we present a new technique to estimate tropospheric turbulence strength (namely, scintillation index) by analyzing RO amplitude fluctuations in impact parameter domain. GPS RO observations from the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites enabled us to calculate global maps of scintillation measures, revealing the seasonal, latitudinal, and longitudinal characteristics of the turbulent troposphere. Such information are both difficult and expensive to obtain especially over the oceans. To verify our approach, simulation experiments using the multiple phase screen (MPS) method were conducted. The results show that scintillation indices inferred from the MPS simulations are in good agreement with scintillation measures estimated from COSMIC observations.

Description: CFC-11, CFC-12 and HCFC-22 ground-based remote sensing FTIR measurements at Reunion Island and comparisons with MIPAS/ENVISAT data Minqiang Zhou, CCorinne Vigouroux, Bavo Langerock, Pucai Wang, Geoff Dutton, Christian Hermans, Nicolas Kumps, Jean-Marc Metzger, Geoff Toon, and Martine De Mazière Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-235,2016 Manuscript under review for AMT (discussion: open, 0 comments) Profiles of CFC-11, CFC-12 and HCFC-22 have been obtained from FTIR measurements above the Saint-Denis and Maïdo sites at Reunion Island (21ºS, 55ºE) with low vertical resolution. The trends derived from the FTIR measurements are -0.86±0.12% and 2.75±0.12% for CFC-11 and HCFC-22, respectively, for the period 2004 to 2016 , and -0.76±0.05% for CFC-12 for 2009 to 2016, which are consistent with ground-based in-situ observations. Our FTIR data and the collocated MIPAS data are in good agreement.

Description: Evaluation And Attribution Of OCO-2 XCO 2 Uncertainties John Worden, Gary Doran, Susan Kulawik, Annmarie Eldering, David Crisp, Chris Frankenberg, Christian O'Dell, and Kevin Bowman Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-175,2016 Manuscript under review for AMT (discussion: open, 0 comments) This paper evaluates the uncertainties of the total column carbon dioxide (XCO 2 ) measurements from the NASA OCO-2 instrument by comparing observed variations in small geographical regions to the calculated uncertainties of the data within this region. In general we find that the XCO 2 uncertainties are consistent with calculated values of approximately 0.2 ppm over the ocean whereas variations over land likely have larger uncertainties of at least ~ 0.7 ppm.

Description: Long-range atmospheric transport of volatile monocarboxylic acids with Asian dust over high mountain snow site, central Japan Tomoki Mochizuki, Kimitaka Kawamura, Kazuma Aoki, and Nobuo Sugimoto Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-623,2016 Manuscript under review for ACP (discussion: open, 0 comments) High abundances of formic and acetic acids in the snow pit samples (6 m in depth) collected at snowfield site near Mt. Tateyama, central Japan. Formic and acetic acids are highly abundant in the snow with dust layers in which Ca was enriched. We propose that alkaline metals in Asian dusts largely titrate gaseous organic acids during long-range atmospheric transport.

Description: Characterization of anthropogenic methane plumes with the Hyperspectral Thermal Emission Spectrometer (HyTES): a retrieval method and error analysis Le Kuai, John R. Worden, King-Fai Li, Glynn C. Hulley, Francesca M. Hopkins, Charles E. Miller, Simon J. Hook, Riley M. Duren, and Andrew D. Aubrey Atmos. Meas. Tech., 9, 3165-3173, doi:10.5194/amt-9-3165-2016, 2016 This paper describes the retrieval algorithm to estimate the lower tropospheric methane concentrations using Hyperspectral Thermal Emission Spectrometer (HyTES) airborne measurements. This project aims to map and detect methane plumes from the oil leaking or dairy emission. Our results demonstrate an example of the quantitative retrievals, imaged a big methane plume from storage tanks near Kern River Oil Field. The methane enhancement is well above the uncertainties of the estimates.

Description: Anaerobic methane oxidation in an East African great lake (Lake Kivu) Fleur A. E. Roland, François Darchambeau, Cédric Morana, Sean A. Crowe, Bo Thamdrup, and Alberto V. Borges Biogeosciences Discuss., doi:10.5194/bg-2016-300,2016 Manuscript under review for BG (discussion: open, 0 comments) We studied methane consumption in a tropical Great Lake (Lake Kivu, East Africa). Lake Kivu has huge methane concentrations in its deep anoxic waters, but is a very poor emitter of methane to the atmosphere, which suppose a strong methane consumption in the water column. During this study, we put in evidence high aerobic and anaerobic consumption rates, whose relative importance varied with the season (higher aerobic rates in dry season, when the oxic compartment is wider).

Description: Improving together: better science writing through peer learning Mathew A. Stiller-Reeve, Céline Heuzé, William T. Ball, Rachel H. White, Gabriele Messori, Karin van der Wiel, Iselin Medhaug, Annemarie H. Eckes, Amee O'Callaghan, Mike J. Newland, Sian R. Williams, Matthew Kasoar, Hella Elisa Wittmeier, and Valerie Kumer Hydrol. Earth Syst. Sci., 20, 2965-2973, doi:10.5194/hess-20-2965-2016, 2016 Scientific writing must improve and the key to long-term improvement of scientific writing lies with the early-career scientist (ECS). We introduce the ClimateSnack project, which aims to motivate ECSs to start writing groups around the world to improve their skills together. Writing groups offer many benefits but can be a challenge to keep going. Several ClimateSnack writing groups formed, and this paper examines why some of the groups flourished and others dissolved.

Description: River water quality changes in New Zealand over 26 years (1989–2014): Response to land use and land disturbance Jason P. Julian, Kirsten M. de Beurs, Braden Owsley, Robert J. Davies-Colley, and Anne-Gaelle E. Ausseil Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-323,2016 Manuscript under review for HESS (discussion: open, 0 comments) New Zealand (NZ) is a natural laboratory for investigating water quality responses to land use change because its landscape is managed intensively. We interpreted water quality state and trends (1989–2014) of 77 river sites across NZ. We show that the greatest long-term impacts on river water quality in NZ have been densely stocked pastures (due to high nutrient inputs), followed by plantation forestry (due to sediment/nutrient runoff during harvesting).

Description: A post-wildfire response in cave dripwater chemistry Gurinder Nagra, Pauline C. Treble, Martin S. Andersen, Ian J. Fairchild, Katie Coleborn, and Andy Baker Hydrol. Earth Syst. Sci., 20, 2745-2758, doi:10.5194/hess-20-2745-2016, 2016 Our current understanding of wildfires on Earth is filled with knowledge gaps. One reason for this is our poor record of fire in natural archives. We open the possibility for speleothems to be "a missing piece to the fire-puzzle". We find by effecting surface evaporation and transpiration rates, wildfires can have a multi-year impact on speleothem, forming dripwater hydrology and chemistry. We open a new avenue for speleothems as potential palaeo-fire archives.

Description: Improving together: better science writing through peer learning Mathew A. Stiller-Reeve, Céline Heuzé, William T. Ball, Rachel H. White, Gabriele Messori, Karin van der Wiel, Iselin Medhaug, Annemarie H. Eckes, Amee O'Callaghan, Mike J. Newland, Sian R. Williams, Matthew Kasoar, Hella Elisa Wittmeier, and Valerie Kumer Hydrol. Earth Syst. Sci., 20, 2965-2973, doi:10.5194/hess-20-2965-2016, 2016 Scientific writing must improve and the key to long-term improvement of scientific writing lies with the early-career scientist (ECS). We introduce the ClimateSnack project, which aims to motivate ECSs to start writing groups around the world to improve their skills together. Writing groups offer many benefits but can be a challenge to keep going. Several ClimateSnack writing groups formed, and this paper examines why some of the groups flourished and others dissolved.

Description: The inverse problem of synthetic aperture imaging radiometers (SAIRs) has been demonstrated to be not well posed. The regularization methods are crucial for providing unique and stable solutions in the reconstruction of radiometric brightness temperature (BT) maps. Different to deterministic ones, a new approach is presented by referring to the rule of Bayesian inference, providing a probability model of regularized constraints to combat the ill-posedness of finite-dimensional discrete inverse problems. In addition, the SAIR inverse problem can be converted into the probability estimation of the reconstructed BT. Furthermore, in application to both uniformly and nonuniformly spaced arrays, our method can obtain the optimal solution adaptively and avoid the dilemma of choosing the optimal regularization parameter. Finally, simulation results illustrating the effectiveness and performance of the proposed method are provided.

Description: A range-cell-focusing algorithm is proposed in order to improve the quality of the target image. In a synthetic aperture radar (SAR) imaging system, the range resolution depends on the frequency bandwidth and determines the ability to distinguish between targets that are very close to each other. In cases where the resolution and the SNR from the environment are not adequate, targets cannot be accurately visualized. In order to successively classify targets that are close, we are combining an enhanced-multiple-signal-classification spectrum as a weighting function to reproduce the raw data. The proposed algorithm improves classification and separation for close targets while suppressing artifacts in the final images. The targets of interest are stationary point scatterers. The results are obtained from both simulated and experimental data to demonstrate that the proposed algorithm provides better performance than a conventional SAR imaging algorithm, the range migration algorithm.

Description: This letter presents a multiscale edge detection method for multilook polarimetric synthetic aperture radar (PolSAR) images based on the nonsubsampled contourlet transform (NSCT). The NSCT can provide flexible multiscale and directional decomposition. In the multiscale decomposition, the coefficients of the nonsubsampled pyramid in the NSCT are calculated via maximizing the polarimetric contrast between the adjacent subband levels, instead of using the difference of the adjacent subbands as used in the additive noise model. By this way, we make the NSCT applicable to PolSAR data and multiband data. Then, the edges are detected in the NSCT domain based on a fusion of the directional subband coefficients at different scales. Experimental results with both simulated and real PolSAR data show that the present approach is robust to noise and the extracted edges are complete and continuous.

Description: A method for defining the spatial resolution of a Global Navigation Satellite System reflectometry delay–Doppler map (DDM) and of any derived geophysical product is proposed. An effective spatial resolution is derived as a function of measurement geometry and delay–Doppler (DD) interval, and as a more appropriate representation of resolution than the geometric resolution previously used in the literature. The definition more accurately accounts for variations in the scattered power across different pixels of the DDM and more accurately includes the power spreading effect caused by the Woodward ambiguity function. The dependence of the effective resolution on incidence angle, receiver altitude, and DD interval is analyzed and compared with the dependence of the geometric resolution with similar parameters.

Description: Laser scanner-captured 3-D point cloud data analysis is becoming more commonly used for remote sensing and plant science applications. Because of nonrigidity and complexity, reconstructing a 3-D model of a plant is extremely challenging. Existing algorithms often fail to find correct correspondences for plantlike thin structures. We address the problem of finding 3-D junction points in plant point cloud data as a first step of this correspondence matching process. Temporarily, we transform the 3-D problem into 2-D by performing appropriate coordinate transformations to the neighborhood of each 3-D point. Our proposed method has two steps. First, a statistical dip test of multimodality is performed to detect the nonlinearity of the local 2D structure. Then, each branch is approximated by sequential random-sample-consensus line fitting and a Euclidean clustering technique. The straight line parameters of each branch are extracted using total-least-squares estimation. Finally, the straight line equations are solved to determine if they intersect in the local neighborhood. Such junction points are good candidates for subsequent correspondence algorithms. Using these detected junction points, we formulate a correspondence algorithm as a subgraph matching problem and show that, without using traditional descriptor similarity-based matching, good correspondences can be obtained by simply considering geodesic distances among graph nodes. Experiments on synthetic and real ( Arabidopsis plant) data show that the proposed method outperforms the state of the art.

Description: Repeat-track analysis is commonly utilized to generate elevation change time series from satellite radar altimetry over ice sheets. It requires surface gradient (SG) correction due primarily to orbital drifts and radar-related empirical corrections caused by radar scatters from ice surface and potential subsurface. In this letter, two approaches, namely, the use of a digital elevation model (DEM) and the modified repeat-track analysis, which uses the accumulated Envisat altimetry profiles, are applied to correct the SG over both Greenland ice sheet (GrIS) and Antarctic ice sheet (AIS). By comparing the root mean square (rms) of elevation change time series after SG correction, the percentage of data (rms< 1 m) obtained by using modified repeat-track analysis is found to be 85% and 88% for the GrIS and AIS, respectively, as opposed to 45% and 44% if the DEM method is used. Furthermore, three cases are studied to assess empirical corrections for elevation retrieved from both ice-1 and ice-2 algorithms over the AIS. We conclude that the modified repeat-track analysis is more effective to remove topographic induced error. For the ice-2 algorithm, waveform shape parameters are needed in addition to applying corrections from changes in backscatter coefficients. The trend of elevation changes from the ice-1 algorithm with only backscatter analysis agrees with that from the ice-2 algorithm with corrections from backscatter coefficient changes and waveform shape parameters. This study could provide a potential data processing recipe for generating improved satellite radar altimetry elevation time series over ice sheets.

Description: Extracting ships from complex backgrounds is the bottleneck of ship detection in high-resolution optical satellite images. In this letter, we propose a nearly closed-form ship rotated bounding box space used for ship detection and design a method to generate a small number of highly potential candidates based on this space. We first analyze the possibility of accurately covering all ships by labeling rotated bounding boxes. Moreover, to reduce search space, we construct a nearly closed-form ship rotated bounding box space. Then, by scoring for each latent candidate in the space using a two-cascaded linear model followed by binary linear programming, we select a small number of highly potential candidates. Moreover, we also propose a fast version of our method. Experiments on our data set validate the effectiveness of our method and the efficiency of its fast version, which achieves a close detection rate in near real time.

Description: In this letter, a two-stage method for airport detection on remote sensing images is proposed. In the first stage, a new algorithm composed of several line-based processing steps is used for extraction of candidate airport regions. In the second stage, the scale-invariant feature transformation and Fisher vector coding are used for efficient representation of the airport and nonairport regions and support vector machines employed for classification. In order to evaluate the performance of the proposed method, extensive experiments are conducted on airports around the world with different layouts. The measures used in the evaluation are accuracy, sensitivity, and specificity. The proposed method achieved an accuracy of 94.6%, which was benchmarked with two previous methods to prove its superiority.

Description: High-resolution wide-swath synthetic aperture radar (SAR) systems are very attractive for the observation of dynamic processes on the Earth's surface, but they require the downlink of a huge volume of data. In order to comply with azimuth ambiguity requirements, in fact, a pulse repetition frequency much higher than the required processed Doppler bandwidth is often desirable. The volume of downlinked data, however, can be drastically reduced by performing Doppler filtering and decimation on board. A finite-impulse-response filter with a relatively small number of taps suffices to suppress the additional ambiguous components and to recover the original impulse response. This strategy is of special relevance for staggered SAR systems, which are typically characterized by a high oversampling factor. The proposed data reduction technique is also baseline for Tandem-L, where onboard Doppler filtering, resampling, and decimation will be jointly implemented.

Description: In this letter, we generate anisotropic bicontinuous media with different vertical and horizontal correlation functions. With the computer-generated bicontinuous medium, we then use numerical solutions of Maxwell equations in 3-dimensions (NMM3D) to calculate the anisotropic effective permittivities and the effective propagation constants of V and H polarizations. The copolarization phase difference (CPD) of VV and HH is then derived. The CPDs have recently been applied to the retrieval of snow water equivalent, snow depth, and anisotropy. The NMM3D simulation results are also compared with the results of the strong permittivity fluctuations in the low frequency limit and compared against the Maxwell–Garnett mixing formula.

Description: The IEEE GRS Society is grateful for the support given by the organizations listed and invites applications for Institutional Listings from other firms interested in the field of geoscience and remote sensing.

Description: The mucosal microanatomy of the large intestine is characterized by the presence of crypts of Lieberkühn, which is associated predominantly with goblet cells. Such cellular-level intestinal microstructures undergo morphological changes during the progression of bowel diseases, such as colon cancer or ulcerative colitis. As an indicator of gastric cancers, intestinal metaplasia in the large intestine is characterized by the appearance of goblet cells in gastric epithelium, and therefore, visualization of intestinal microstructure changes in cross-sectional view, particularly in vivo , in a high-speed fashion would assist early disease diagnosis and its treatment. In this paper, we investigated the capability of micro-optical coherence tomography $(mutext{OCT})$ for high-speed cellular-level crypt and goblet cell structures imaging ex vivo and in vivo . The adopted $mutext{OCT}$ system achieved a resolution of 2.0 $mutext{m}$ in both the lateral and axial directions in air. Ex vivo and video-rate in vivo images acquired in 3-D at respective imaging rates of 20 and 60 frames/s are presented and compared with the histology images. Imaging results show that the detailed microstructures, such as the crypt lumen and the goblet cells, could be clearly identified and are also comparable with those in histology images. Such comparisons also indicate that high-resolution $mutext{OCT}$ could be a powerful tool to perform “optical biopsy” in colorectal tissue. This is the first work, to the best of our knowledge, on cellular-level structure imaging in intestinal mucosa using spectral-- omain OCT.

Description: Influence of different high-index oxide overlayers on the performance of a fiber optic SPR sensor coated with bimetallic layer of aluminum (Al)/copper (Cu) is reported. The oxides considered for the analysis are Al 2 O 3 , Sc 2 O 3 , Lu 2 O 3, GeO 2 , SnO 2 , TeO 2 , MgO, ITO, and ZnO, which on-coated over Al/Cu bimetallic layer causes an enhancement in electric field intensity at the oxide–analyte interface and increases the red shift in the resonance wavelength with the increase in the refractive index of the analyte solution. In addition, the figure of merit is also drastically improved. All the performance parameters are found to be different for different oxides. On the basis of comparison, the best possible oxide along with Al/Cu bimetallic layer and its requisite thickness is predicted. The sensor with Al/Cu/TeO 2 is found to possess the best performance parameters. A fiber optic SPR sensor with coatings of Al/Cu/TeO 2 layers over unclad core of the fiber is fabricated and its performance parameters are compared with the theoretically obtained values. Further, the sensitivity (5.98 µm/RIU) and the figure of merit (35.95) for 1.33 refractive index of the analyte are found to be better than those of previously reported sensors to the best of our knowledge.

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Description: GaN p-i-n ultraviolet avalanche photodiodes (UV-APDs) were fabricated from epitaxial structures grown on low-dislocation-density free-standing GaN substrates to form $4times 4$ UV-APD arrays with a device size of $75times 75~mu text{m}^{{ {2}}}$ . The devices in the UV-APD array showed a uniform and reliable distribution of breakdown voltage ( $V_{text {BR}}$ ) and leakage current density. The average $V_{text {BR}}$ of the 16 devices in one of the UV-APD arrays was 96±0.6 V, and the average dark current density ( $J_{R_{}{text {Dark}}}$ ) and photocurrent density ( $J_{R_{}{text {Photo}}}$ ) were measured to be (6.5±1.8) $times 10^{-7}$ and (5.7±1.1) $times 10^{{text {-6}}}$ A/cm $^{{{2}}}$ at the reverse bias voltage of $V_{R}=48$ V (50% of the average onset point of $V_{text {BR}}$ ), respectively. The reliable device performance was confirmed by performing multiple reverse bias $I$ – $V$ scans for the selected devices in the UV-APD array. We also observed the significantly enhanced spectral resp- nsivity from the 142 to 5485 mA/W due to the strong carrier impact ionization at high reverse bias.

Description: The combination of a thin dielectric grating with a thin metal film is shown to reveal the existence of multiple plasmons, some are short range and others long range both represented by resonant dips in the reflectivity. Usually the plasmons come in pairs, where one is excited at the substrate metal interface while the other at the grating metal interface. One of these dips is sensitive to the refractive index (RI) of the medium adjacent to the metal surface while the other to that near the grating interfaces. Using an optimum design it is possible to obtain high sensitivity to the RI variations of one of the adjacent media but not to the other, hence a self-referenced biosensor can be built using this design. Two configurations are shown to reveal unique features in the angular mode: 1) the possibility of using both angular and intensity sensitivity to detect variations in the RI of the analyte, 2) the possibility of using the excited multiple sharp plasmons that cause multiple resonances (dips) in the reflectivity, where part of these resonances are red-shifted due to variations in the RI of the analyte, while the others are blue shifted. Hence, by measuring the shift of one with respect to the other the angular sensitivity is improved, 3) multiple dips can be used for reference, and 4) high figure of merit is obtained. The thin dielectric grating is shown to have two roles, one to provide the momentum matching whereas the other is to act effectively as a dielectric layer underneath the metal film to enable the excitation of both the long and short range surface plasmons.

Description: An optimized broadband source emitting from 1064 to 1600 nm was specially designed for coherent anti-Stokes Raman scattering spectroscopy. This source is based on the use of a ytterbium-doped photonic crystal fiber with a large core in which a supercontinuum is generated from a signal wave at 1064 nm regenerated by ytterbium ions pumping. A particularly flat spectrum with high spectral power density and perfectly synchronized spectral components is obtained.

Description: We experimentally demonstrate switchable dual-wavelength mode-locking of thulium-doped fiber laser (TDFL), using single-wall carbon nanotubes as saturable absorber. Due to the cavity birefringence-induced comb filter, switchable mode-locking can be individually realized for the proposed TDFL among three wavelengths of 1947, 1945, and 1943 nm, with almost the same 3-dB spectral bandwidth of 2.2 nm, repetition rate of 13.6 MHz, and pulsewidth of 1.8 ps. Furthermore, after finely adjusting the intra-cavity birefringence, we are able to demonstrate switchable dual-wavelength mode-locking at either 1947/1945 or 1945/1943 nm. The optical spectra of dual-wavelength mode-locking have almost the same characteristics and can maintain stable operation for a long period.

Description: A capillary covered silica hollow core fiber (HCF) has been designed and tested for the measurement of displacement based on antiresonant reflecting optical waveguide. A section of the silica HCF was inserted into a silver coated capillary. A Fabry–Perot resonator can be formed in the silica cladding. The leaky mode of the guided light can be achieved at resonant wavelengths of the Fabry–Perot resonator, which results in lossy dips in the transmission spectrum. The transmission power of the dip is sensitive with the displacement of the capillary since the effective reflectivity of the Fabry–Perot resonator is affected by the location between the capillary and the silica HCF. The experimental results show that the sensitivity of up to 0.578 dB/μm is achieved, and the proposed sensor is insensitive with the temperature.

Description: We report high-responsivity GaN/InGaN heterojunction phototransistors (HPTs) grown on sapphire substrates. Under the ultraviolet (UV) photon illumination from the front side of the wafer, an HPT shows broad photoresponse spectrum with the short-wavelength cutoff wavelength well beyond $lambda = 280$ nm, and the UV-to-visible-band rejection ratio is $> 8 times 10^{3}$ . The responsivity ( $R_{lambda }$ ) of HPT is greater than 8 A/W at $lambda = 373$ nm, and is greater than 3 A/W at $lambda = 280$ nm as the device is biased at $V_{mathrm{ CE}}=10$ V. As the HPT is biased at the near breakdown voltage ( $V_{mathrm{ CE}}> 35$ V), the responsivity performance was enhanced due to the carrier multiplication, resulting in $R_{lambda }> 100$ A/W at $V_{mathrm{ CE}}= 40$ V for $P_{mathrm{ opt}}=1.73~mu text{W}$ /cm 2 at $lambda = 373$ nm. These results demonstrate that GaN/InGaN HPTs can achieve low light detection with a broadband photon response in the near-UV-to-deep-UV spectral ranges.

Description: The S-transform (ST), as a time–frequency analysis tool, has been widely used, but the amplitude preserving property is a little poor near the boundary of the selected discrete signal. The reason lies that the summation of the product between the analytical window and the comprehensive window over the sliding step deviates from unity near the boundary in the discrete cases. In order to hold the amplitude preserving property for the discrete signal recovery analysis, an amplitude preserving S-transform (APST) is proposed based on a novel analytical window selection. First, lots of numerical tests are used to analyze the shortcomings of the ST near the boundary for the selected discrete signal and demonstrate the effectiveness and the validity of the proposed APST using the novel analytical window. After that, the proposed APST is used for seismic data attenuation compensation, during which the attenuation function is estimated based on the minimum phase assumption using a statistical variable-step hyperbolic smoothing method. Numerical examples on synthetic and field data demonstrate the validity of the proposed method using the seismogram and time–frequency spectrum comparisons. Besides, the proposed APST can be easily extended into a generalized ST which is more flexible compared with the ST, and it can also be used in seismology, remote sensing, and other related discrete signal analysis fields.

Description: The multiplexing and the amplification of 2- $mu text{m}$ vortex beams are experimentally verified in a Ho:YAG crystal rod amplifier. Spatially multiplexed vortex beams are studied and the amplification results are presented and discussed. The integrity of the launched vortex beams is well maintained through the amplification process. Further discussions are provided to increase the gain as well as for power scaling. Due to the nature of Ho:YAG material and the geometry of the rod amplifier, our system shows the potential of working as a power amplifier for vortex beams.

Description: This paper addresses fundamental scaling issues that hinder phase retrieval (PR) in high dimensions. We show that, if the measurement matrix can be put into a generalized block-diagonal form, a large PR problem can be solved on separate blocks, at the cost of a few extra global measurements to merge the partial results. We illustrate this principle using two distinct PR methods, and discuss different design trade-offs. Experimental results indicate that this block-based PR framework can reduce computational cost and memory requirements by several orders of magnitude.

Description: Objective: This work evaluates current 3-D image registration tools on clinically acquired abdominal computed tomography (CT) scans. Methods: Thirteen abdominal organs were manually labeled on a set of 100 CT images, and the 100 labeled images (i.e., atlases) were pairwise registered based on intensity information with six registration tools (FSL, ANTS-CC, ANTS-QUICK-MI, IRTK, NIFTYREG, and DEEDS). The Dice similarity coefficient (DSC), mean surface distance, and Hausdorff distance were calculated on the registered organs individually. Permutation tests and indifference-zone ranking were performed to examine the statistical and practical significance, respectively. Results: The results suggest that DEEDS yielded the best registration performance. However, due to the overall low DSC values, and substantial portion of low-performing outliers, great care must be taken when image registration is used for local interpretation of abdominal CT. Conclusion: There is substantial room for improvement in image registration for abdominal CT. Significance: All data and source code are available so that innovations in registration can be directly compared with the current generation of tools without excessive duplication of effort.

Description: Wireless networks face the challenge of increasing energy consumption while satisfying the unprecedented demand for higher data rates. Energy-efficient transmission has been regarded as a key technology for the next-generation wireless system. Meanwhile, to reduce the cost, in practice, a base station usually has less radio chains than the antennas, which makes antenna selection an appealing transmission strategy. This letter addresses the problem of joint optimization of energy-efficient beamforming and antenna selection for downlink multiuser systems. The nonconvexity arising from both the nonlinear fractional programming and the $ell _{0}$ -(quasi)norm presents the main difficulty in solving the joint optimization problem. Nevertheless, we develop an effective algorithm to address this problem. Numerical results are given to validate the effectiveness and the performance of the developed algorithm.

Description: Gallium-nitride (GaN)-based light-emitting diodes (LEDs) are highly efficient sources for general purpose illumination. Visible light communications (VLC) uses these sources to supplement existing wireless communications by offering a large, licence-free region of optical spectrum. Here, we report on progress in the development of micro-scale GaN LEDs (micro-LEDs), optimized for VLC. These blue-emitting micro-LEDs are shown to have very high electrical-to-optical modulation bandwidths, exceeding 800 MHz. The data transmission capabilities of the micro-LEDs are illustrated by demonstrations using ON–OFF-keying, pulse-amplitude modulation, and orthogonal frequency division multiplexing modulation schemes to transmit data over free space at the rates of 1.7, 3.4, and 5 Gb/s, respectively.