ALBERT

Description: Regional and local patterns in depth to water table, hydrochemistry and peat properties of bogs and their laggs in coastal British Columbia Hydrology and Earth System Sciences, 17, 3421-3435, 2013 Author(s): S. A. Howie and H. J. van Meerveld In restoration planning for damaged raised bogs, the lagg at the bog margin is often not given considerable weight and is sometimes disregarded entirely. However, the lagg is critical for the proper functioning of the bog, as it supports the water mound in the bog. In order to include the lagg in a restoration plan for a raised bog, it is necessary to understand the hydrological characteristics and functions of this rarely studied transition zone. We studied 13 coastal British Columbia (BC) bogs and identified two different gradients in depth to water table, hydrochemistry and peat properties: (1) a local bog expanse–bog margin gradient, and (2) a regional gradient related to climate and proximity to the ocean. Depth to water table generally increased across the transition from bog expanse to bog margin. In the bog expanse, pH was above 4.2 in the Pacific Oceanic wetland region (cooler and wetter climate) and below 4.3 in the Pacific Temperate wetland region (warmer and drier climate). Both pH and pH-corrected electrical conductivity increased significantly across the transition from bog expanse to bog margin, though not in all cases. Na + and Mg 2+ concentrations were generally highest in exposed, oceanic bogs and lower in inland bogs. Ash content in peat samples increased across the bog expanse–bog margin transition, and appears to be a useful abiotic indicator of the location of the bog margin. The observed variation in the hydrological and hydrochemical gradients across the bog expanse–bog margin transition highlights both local and regional diversity of bogs and their associated laggs.

Description: Imperfect scaling in distributions of radar-derived rainfall fields Hydrology and Earth System Sciences Discussions, 10, 11385-11422, 2013 Author(s): M. J. van den Berg, L. Delobbe, and N. E. C. Verhoest Fine scale rainfall observations for modeling exercises are often not available, but rather coarser data derived from a variety of sources are used. Effectively using these data sources in models often requires the probability distribution of the data at the applicable scale. Although numerous models for scaling distributions exist, these are often based on theoretical developments, rather than on data. In this study, we develop a model based on the α-stable distribution of rainfall fields, and tested on 5 min radar data from a Belgian weather radar. We use these data to estimate functions that describe parameters of the distribution over various scales. Moreover, we study how the mean of the distribution and the intermittency change with scale, and validate and design functions to describe the shape parameter of the distribution. This information was combined into an effective model of the distribution. Finally, the model was fitted to data from numerous storms, and the resulting parameters were compared to investigate the change in scaling behavior through time.

Description: Spatially resolved information on karst conduit flow from in-cave dye-tracing Hydrology and Earth System Sciences Discussions, 10, 11311-11335, 2013 Author(s): U. Lauber, W. Ufrecht, and N. Goldscheider Artificial tracers are powerful tools to investigate karst systems. Tracers are commonly injected into sinking streams or dolines, while springs serve as monitoring sites. The obtained flow and transport parameters represent mixed information from the vadose, epiphreatic and phreatic zones, i.e., the aquifer remains a black box. Accessible active caves constitute valuable but underexploited natural laboratories to gain detailed insights into the hydrologic functioning of the aquifer. Two multi-tracer tests in the catchment of a major karst spring (Blautopf, Germany) with injections and monitoring in two associated water caves aimed at obtaining spatially and temporally resolved information on groundwater flow in different compartments of the system. Two tracers were injected in the caves to characterize the hydraulic connections between them and with the spring. Two injections at the land surface, far from the spring, aimed at resolving the aquifer's internal drainage structure. Tracer breakthrough curves were monitored by field fluorimeters in caves and at the spring. Results demonstrate the dendritic drainage structure of the aquifer. It was possible to obtain relevant flow and transport parameters for different sections of this system. The highest mean flow velocities (275 m h −1 ) were observed in the near-spring epiphreatic section (open-channel flow), while velocities in the phreatic zone (pressurized flow) were one order of magnitude lower. Determined conduit water volumes confirm results of water balances and hydrograph analyses. In conclusion, experiments and monitoring in caves can deliver spatially resolved information on karst aquifer heterogeneity and dynamics that cannot be obtained by traditional investigative methods.

Description: On the lack of robustness of hydrologic models regarding water balance simulation – a diagnostic approach on 20 mountainous catchments using three models of increasing complexity Hydrology and Earth System Sciences Discussions, 10, 11337-11383, 2013 Author(s): L. Coron, V. Andréassian, C. Perrin, M. Bourqui, and F. Hendrickx This paper investigates the robustness of rainfall–runoff models when their parameters are transferred in time. More specifically, we studied their ability to simulate water balance on periods with different hydroclimatic characteristics. The testing procedure consisted in a series of parameter transfers between 10-yr periods and the systematic analysis of mean-volume errors. This procedure was applied to three conceptual models of different structural complexity over 20 mountainous catchments in southern France. The results showed that robustness problems are common. Errors on 10-yr-mean flows were significant for all three models and calibration periods, even when the entire record was used for calibration. Various graphical and numerical tools were used to show strong similarities between the shapes of mean flow biases calculated on a 10-yr-long sliding window when various parameter sets are used. Unexpected behavioural similarities were observed between the three models tested, considering their large differences in structural complexity. While the actual causes for robustness problems in these models remain unclear, this work stresses the limited transferability in time of the water balance adjustments made through parameter optimization. Although absolute differences between simulations obtained with different calibrated parameter sets were sometimes substantial, relative differences in simulated mean flows between time periods remained similar regardless of the calibrated parameter sets.

Description: Bayesian networks modelling in support to cross-cutting analysis of water supply and sanitation in developing countries Hydrology and Earth System Sciences, 17, 3397-3419, 2013 Author(s): C. Dondeynaz, J. López Puga, and C. Carmona Moreno Despite the efforts made towards the Millennium Development Goals targets during the last decade, improved access to water supply or basic sanitation still remains unavailable for millions of people across the world. This paper proposes a set of models that use 25 key variables and country profiles from the WatSan4Dev data set involving water supply and sanitation (Dondeynaz et al., 2012). This paper suggests the use of Bayesian network modelling methods because they are more easily adapted to deal with non-normal distributions, and integrate a qualitative approach for data analysis. They also offer the advantage of integrating preliminary knowledge into the probabilistic models. The statistical performance of the proposed models ranges between 20 and 5% error rates, which are very satisfactory taking into account the strong heterogeneity of variables. Probabilistic scenarios run from the models allow an assessment of the relationships between human development, external support, governance aspects, economic activities and water supply and sanitation (WSS) access. According to models proposed in this paper, gaining a strong poverty reduction will require the WSS access to reach 75–76% through: (1) the management of ongoing urbanisation processes to avoid slums development; and (2) the improvement of health care, for instance for children. Improving governance, such as institutional efficiency, capacities to make and apply rules, or control of corruption is positively associated with WSS sustainable development. The first condition for an increment of the HDP (human development and poverty) remains of course an improvement of the economic conditions with higher household incomes. Moreover, a significant country commitment to the environment, associated with civil society freedom of expression constitutes a favourable setting for sustainable WSS services delivery. Intensive agriculture using irrigation practises also appears as a mean for sustainable WSS thanks to multi-uses and complementarities. With a WSS sector organised at national level, irrigation practices can support the structuring and efficiency of the agriculture sector. It may then induce rural development in areas where WSS access often is set back compared to urban areas 1 . External financial support, called Official Development Assistance (ODA CI), plays a role in WSS improvement but comes last in the sensitivity analyses of models. An overall 47% of the Official Development Assistance goes first to poor countries, and is associated to governance aspects: (1) political stability and (2) country commitment to the environment and civil society degree of freedom. These governance aspects constitute a good framework for aid implementation in recipient countries. Modelling is run with the five groups of countries as defined in Dondeynaz et al. (2012). Models for profile 4 (essential external support) and profile 5 (primary material consumption) are specifically detailed and analysed in this paper. For countries in profile 4, fighting against water scarcity and progressing desertification should be the priority. However, for countries in profile 5, efforts should first concentrate on consolidation of political stability while supporting diversification of the economic activities. Nevertheless, for both profiles, reduction of poverty should remain the first priority as previously indicated. 1 JMP statistics, 2004 http://www.wssinfo.org/data-estimates/table/ , last access: 22 July 2013.

Description: Technical Note: A comparison of model and empirical measures of catchment-scale effective energy and mass transfer Hydrology and Earth System Sciences, 17, 3389-3395, 2013 Author(s): C. Rasmussen and E. L. Gallo Recent work suggests that a coupled effective energy and mass transfer (EEMT) term, which includes the energy associated with effective precipitation and primary production, may serve as a robust prediction parameter of critical zone structure and function. However, the models used to estimate EEMT have been solely based on long-term climatological data with little validation using direct empirical measures of energy, water, and carbon balances. Here we compare catchment-scale EEMT estimates generated using two distinct approaches: (1) EEMT modeled using the established methodology based on estimates of monthly effective precipitation and net primary production derived from climatological data, and (2) empirical catchment-scale EEMT estimated using data from 86 catchments of the Model Parameter Estimation Experiment (MOPEX) and MOD17A3 annual net primary production (NPP) product derived from Moderate Resolution Imaging Spectroradiometer (MODIS). Results indicated positive and significant linear correspondence ( R 2 = 0.75; P 〈 0.001) between model and empirical measures with an average root mean square error (RMSE) of 4.86 MJ m −2 yr −1 . Modeled EEMT values were consistently greater than empirical measures of EEMT. Empirical catchment estimates of the energy associated with effective precipitation ( E PPT ) were calculated using a mass balance approach that accounts for water losses to quick surface runoff not accounted for in the climatologically modeled E PPT . Similarly, local controls on primary production such as solar radiation and nutrient limitation were not explicitly included in the climatologically based estimates of energy associated with primary production ( E BIO ), whereas these were captured in the remotely sensed MODIS NPP data. These differences likely explain the greater estimate of modeled EEMT relative to the empirical measures. There was significant positive correlation between catchment aridity and the fraction of EEMT partitioned into E BIO ( F BIO ), with an increase in F BIO as a fraction of the total as aridity increases and percentage of catchment woody plant cover decreases. In summary, the data indicated strong correspondence between model and empirical measures of EEMT with limited bias that agree well with other empirical measures of catchment energy and water partitioning and plant cover.

Description: Mobile broadband services have expanded considerably in recent years, driving operators to improve and densify their radio access network (RAN). It has become clear that small cells as well as macrocells must be included in a heterogeneous network, due to the scale of densification required. In order to maximize the end user experience, some level of radio coordination between these small and macrocells is needed ?? this coordination will be signaled across a mobile backhaul network. Mobile backhaul typically refers to the network between the base station site and the network controller site, but can also include interconnection between base station sites. Mobile backhaul includes a spectrum of networks and network technologies, including the RAN and core networks. There is considerable market interest on the development of small cell backhaul solutions that are an evolution of existing backhaul networks. Packet synchronisation mechanisms that are being developed are key to support the mobile backhaul application. Various standards bodies such as the Next Generation Mobile Networks Alliance (NGMN), Small Cell Forum (SCF), Metro Ethernet Forum (MEF), and Broadband Forum (BBF) are also studying what the implications would be on their defined mobile backhaul network architectures.

Description: Heterodyne generation of parallel random bit streams from chaotic emission of an optically injected semiconductor laser is investigated. The continuous-wave optical injection invokes chaotic dynamics in the laser. The broadband chaotic emission is detected through optical heterodyning and electrical heterodyning into different channels. The channels digitize the signals into parallel independent random bit streams. Because of efficient utilization of different portions of the chaos bandwidth, heterodyne detections enable parallel generation of random bit streams, offer high total output bit rates, and require no high-bandwidth analogue-to-digital converters. In the experiment, two optical heterodyne channels and four electrical heterodyne channels are implemented. Each channel is required to digitize only 2.5 GHz of a much broader chaos bandwidth. The sampling rate is 10 GHz with five least significant bits selected from every 8-bit sample. The total output bit rate reaches 100 Gb/s and 200 Gb/s for optical and electrical heterodyning, respectively. The standard test suite of the National Institute of Standards and Technology verifies the randomness of both individual and interleaved output bit streams.

Description: In this article, we introduce the EstiNet OpenFlow network simulator and emulator, and present its support for testing the functions and evaluating the performances of software-defined networks?? OpenFlow controller??s application programs. EstiNet uses an unique kernel reentering simulation methodology to enable unmodified real applications to run on nodes in its simulated network. As a result, without any modification, real NOX/POX or Floodlight OpenFlow controllers can readily run on a host in an EstiNet simulated network to control thousands of simulated OpenFlow switches. EstiNet has the characteristics of a simulator and an emulator at the same time. It combines the advantages of the simulation and emulation approaches without their respective shortcomings. EstiNet uses real OpenFlow controller programs, real network application programs, and the real TCP/IP protocol stack in the Linux kernel to generate correct, accurate, and repeatable SDN application performance results. In this article, we compare EstiNet with ns-3 and Mininet regarding their capabilities, performance, and scalability.

Description: This article discusses novel wireless and optical technologies to address the radical new challenges of small cell mobile backhaul (MBH). Specifically, we examine 60 GHz and 70??80 GHz millimeter-wave technologies for high-capacity last mile and pre-aggregation backhaul, and orthogonal frequency-division multiple access passive optical networks as the optical technology complement for enabling flexible cost-efficient hybrid backhaul coverage. Flexible high-capacity hybrid millimeter wave/optical MBH network operation is next verified via network simulations in the context of a demanding, urban small-cell backhaul application. Finally, a novel software defined networking tool called the backhaul resource manager is introduced for automated dynamic resource provisioning and capacity-aware path computation that improves fairness, network utilization and end-to-end user quality of experience. The introduction of the novel wireless, optical, and software-defined technologies thus has the potential to truly revolutionize the future MBH network.

Description: In this article we discuss different technology alternatives for small cell backhaul, and we present high-frequency microwave technology as a very interesting alternative for wireless backhauling of small cells. In fact, we demonstrate that high-frequency microwave technology can be used for NLOS wireless backhauling of small cells, which opens up new applications for microwave technology. We discuss urban NLOS channel propagation at high frequencies, and we show both measurement and simulation results to validate the use of high-frequency microwave technology for NLOS small cell backhaul.

Description: A novel design and assembly technology is developed for a three-dimensional (3-D) flexible thermal flow sensor based on convective heat transfer to reduce detection error caused by position variation of a sensor inside the flow of narrow and curved geometries, such as coronary artery. The 3-D sensor has three independent sensing elements equally distributed around the catheter tube. This arrangement introduces three independent information channels, and cross-comparisons are used to provide accurate flow measurement. The resistance of the sensing elements is measured at ${sim}{1}-1.2~{rm k}Omega$ with the temperature coefficient of resistance at $0.086%/^{circ}{rm C}$ . Using a constant-current circuit, the three sensing elements are heated to ${sim}10^{circ}{rm C}$ above ambient temperature. Flow testing is implemented in a pipe channel at two positions: on the wall and along the center line. Experimental results from these two positions are discussed and computational fluid dynamic simulation based on Newtonian fluid properties is implemented, showing comparable results within an acceptable range of experimental to simulation errors. Therefore, we demonstrate the capability of 3-D thermal flow sensor for detecting the position of the catheter in the flow channel, thereby providing an accurate flow measurement.

Description: Currently, online social networks such as Facebook, Twitter, Google+, LinkedIn, and Foursquare have become extremely popular all over the world and play a significant role in people??s daily lives. People access OSNs using both traditional desktop PCs and new emerging mobile devices. With more than one billion users worldwide, OSNs are a new venue of innovation with many challenging research problems. In this survey, we aim to give a comprehensive review of state-of-the-art research related to user behavior in OSNs from several perspectives. First, we discuss social connectivity and interaction among users. Also, we investigate traffic activity from a network perspective. Moreover, as mobile devices become a commodity, we pay attention to the characteristics of social behaviors in mobile environments. Last but not least, we review malicious behaviors of OSN users, and discuss several solutions to detect misbehaving users. Our survey serves the important roles of both providing a systematic exploration of existing research highlights and triggering various potentially significant research in these topics.

Description: We discuss the fabrication and performance of an all-polymer, flexural plate wave gravimetric sensor using flexible, piezoelectric Polyvinylidene fluoride as the substrate and an inkjet-printed interdigital transducer (IDT) employing conductive poly(3, 4-ethylenedioxythiophene) poly(styrenesulfonate) to excite Lamb waves within the film. Lamb waves are measured both electronically, using a second IDT, and mapped directly using a scanning laser Doppler vibrometer. Pulsed wave excitation is utilized to isolate the weak acoustic signal from the electromagnetic crosstalk, enabling the measurement of relative changes in the resonant frequency, $Delta f/f_{0}$ , in response to added mass, $Delta m$ , to the sensing area. A gravimetric mass sensitivity equivalent to $Delta f/(f_{0}Delta m)=-153~{rm cm}^{2}/{rm g}$ is measured by mass loading the sensor with printed polymer layers. It is found that the low stiffness of the substrate contributes significantly to the response of the sensor, yielding a measured overall sensitivity of $Delta f/(f_{0}Delta m)=-83~{rm cm}^{2}/{rm g}$ .

Description: In this paper, we propose a novel technological approach for the implementation of large-area flexible artificial skin based on arrays of piezoelectric polymer transducers. Polyvinylidene fluoride (PVDF) transducers are chosen for the high electromechanical transduction frequency bandwidth (up to 1 kHz). A low-cost and scalable technique for extracting PVDF signals is used to directly provide the piezoelectric film with patterned electrodes. If the skin is meant to cover large areas of a robot body, specific requirements have to be fulfilled from the point of view of the overall system and of the technology. Experimental tests on the prototype skin modules demonstrate the feasibility of the proposed approach and reveal the potentiality to build large area flexible skin.

Description: This paper presents ultra-thin silicon chips (flex–chips) on flexible foils, realized through post-processing steps such as wafer thinning, dicing, and transferring the thinned chips to flexible polyimide foils. The cost effective chemical etching is adopted for wafer thinning and the transfer printing approach, to transfer quasi 1-D structures such as micro/nanoscale wires and ribbons, that is adapted for transferring large ultra-thin flex–chips (widths 4.5–15 mm, lengths 8–36 mm, and thickness ${approx}{rm 15}~mu{rm m}$ ). The post-processing capability is demonstrated with passive structures such as metal interconnects realized on the flex–chips before carrying out the chip thinning step. The resistance values of metal interconnects do not show any appreciable change because of bending of chips for the tested range viz., radius of curvature 9 mm and above. Further, the bending mechanics of silicon membranes on foil is investigated to evaluate the bending limits before a mechanical fracture/failure occurs. The distinct advantages of this paper are: attaining bendability through post-processing of chips, cost effective fabrication process, and easy transfer of chips to the flexible substrates without using conventional and sophisticated equipment such as pick and place set up.

Description: A sensor was made of a polymer composite composed of electrically-conductive carbon nanotubes embedded in elastic polyurethane. The composite was prepared using a polyurethane filter membrane, enmeshing it, and melding together with carbon nanotubes. Testing has shown that the composite can be elongated as much as 400% during which the electrical resistance is increased 270 times. The composite is also sensitive to compression and to organic solvent vapors. These properties indicate the composite could have applications as a highly-deformable strain and chemical vapors sensing element and also as flexible electromagnetic shielding or protection against lightning. As an example of the use of the composite as a strain sensor, the pressure variation between a shoe and floor during walking and knee flexion during cycling has been monitored.

Description: This paper presents a novel concept for stretchable conductors. Metal coated polymer spheres were densely packed in biocompatible silicone tubes. The resistivity of the conductors were in the approximate range of $1times 10^{-4}~Omega{rm m}$ at 0% strain and 50% strain could be applied before degrading their electrical performance. Initial results showed good reproducibility and no drift in resistance values up to 1000 cycles with 0%–25% strain. This make the conductors well suited for digital low speed data transmission. The initial application is intended for integration of electronics in clothing; the conductors have been tested with success transmitting data from a commercial digital combined humidity and temperature sensor.

Description: Recently, there are innovative mechanoluminescent (ML) particles made available, each of which repeatedly emits light in response to small applied stresses even in elastic region. When dispersedly coated onto a structure, each particle acts as a sensitive mechanical sensor, while the two-dimensional emission pattern of the whole assembly reflects the dynamical stress distribution inside the structure and the mechanical information around the crack and defect. To use the remarkable advantage of the ML sensor in flexibility, electricity/lead-free, low-cost, and so forth, and to answer social needs for historical-log of stress/damage accumulation on social infra-structure, we investigate historical-log recording system for crack opening and fatigue crack growth, and finally succeed to record it with responding position and intensity reflecting the trace of propagating crack tip and stress intensity factor around the tip. Furthermore, crack mouse opening displacement accompanied by general traffic of bridge in use is successfully detected.

Description: Spectrum sharing potentially holds the promise of solving the emerging spectrum crisis. However, technology innovators face the conundrum of developing spectrum sharing technologies without the ability to experiment and test with real incumbent systems. Interference with operational incumbents can prevent critical services, and the cost of deploying and operating an incumbent system can be prohibitive. Thus, the lack of incumbent systems and frequency authorization for technology incubation and demonstration has stymied spectrum sharing research. To this end, industry, academia, and regulators all require a test facility for validating hypotheses and demonstrating functionality without affecting operational incumbent systems. This article proposes a four-phase program supported by our spectrum accountability architecture. We propose that our comprehensive experimentation and testing approach for technology incubation and demonstration will accelerate the development of spectrum sharing technologies.

Description: This special issue focuses on the sensors and sensing systems having features like flexibility, bendability, conformability, stretchability, and presence over large areas and 3D surfaces. Like conventional sensors, flexible sensors are also used to measure parameters and agents like pH, temperature, humidity, force, gasses, velocity, flow etc. In addition, they possess the ability to bend. This requires special front-end processing techniques compatible with the flexible materials that these sensors are made of. In response to the call for papers for this special issue, 114 manuscripts were received. Of those, 39 were found not to fit to the scope of the special issue and were separated to be handled by the permanent editors of the Journal. The peer review process resulted in 29 innovative manuscripts to be published here submitted from over 45 institutions, with a few trailing manuscripts to be published at a later issue due to time constraints. Of the work presented here, nine papers describe sensors for health and medical applications. Five papers detail sensors for the general fields of environmental and structural health monitoring. Four are on robotic applications. Although majority of the manuscripts focus on a single sensing function such as fluidic flow, force, pH, temperature or presence of a specific gas, four papers present multifunctional flexible sensors.

Description: Thin, highly compliant sensing skins could provide valuable information for a host of grasping and locomotion tasks with minimal impact on the host system. We describe the design, fabrication, and characterization of a novel soft multi-axis force sensor made of highly deformable materials. The sensor is capable of measuring normal and in-plane shear forces. This soft sensor is composed of an elastomer (modulus: 69 kPa) with embedded microchannels filled with a conductive liquid. Depending on the magnitude and the direction of an applied force, all or part of the microchannels will be compressed, changing their electrical resistance. The two designs presented in this paper differ in their flexibility and channel configurations. The channel dimensions are approximately 200 $,times,$ 200 $mu{rm m}$ and 300 $,times,$ 700 $mu{rm m}$ for the two prototypes, respectively. The overall size of each sensor is 50 $,times,$ 60 $,times,$ 7 mm. The first prototype demonstrated force sensitivities along the two principal in-plane axes of 37.0 and ${-}{rm 28.6}~{rm mV/N}$ . The second prototype demonstrated the capability to detecting and differentiating normal and in-plane forces. In addition, this paper presents the results of a parameter study for different design configurations.

Description: We have developed a fabric sensor knitted of tension-sensitive electro-conductive yarns. Each yarn has an elastic core, around which is wound two other separate, tension-sensitive electro-conductive threads, making this sensor inherently flexible and stretchable and allowing it to conform to any complicated surface on a robot, acting as a robotic skin. The pile-shaped surface of the sensor enhances its ability to detect tangential traction, while also enabling it to sense a normal load. Our aim is to use this sensor in applications involving relative sliding between its surface and a touched object, such as contact recognition, slip detection, and surface identification through a sliding motion. We carefully analyzed the static and dynamic characteristics of this sensor while varying the load and stretching force to fully understand its response and determine its degree of flexibility and stretchability. We found that a discrete wavelet transformation may be used to indicate stick/slip states while the sensor is sliding over surfaces. This method was then used to detect slippage events acting on the sensor's surface, and to decode textures in a classification test using an artificial neural network. Because of its flexibility and sensitivity, this sensor can be used widely as a robotic skin in humanoid robots.

Description: Carbon nanotubes (CNTs) are demonstrated as one of the most interesting materials for gas sensing. The possibility to obtain CNT thin-films via solution-processing techniques has paved the way for low-cost applications of such sensors. In this paper, we demonstrate that high performance gas sensors based on CNT thin-films can be obtained by direct spray deposition onto flexible substrates. The results obtained for ${rm NH}_{3}$ sensing using CNT films deposited on polyimide show exceptionally high as well as immediate response to the test gas, with performance comparable with that obtained on oxidized silicon substrates. In addition, a good repeatability of the sensor response to defined gas concentrations is demonstrated. This represents a major step toward low-cost large-scale production of this class of devices.

Description: We present a calibration technique for an acoustic imaging microphone array, combined with a digital camera. Computer vision and acoustic time of arrival data are used to obtain microphone coordinates in the camera reference frame. Our new method allows acoustic maps to be plotted onto the camera images without the need for additional camera alignment or calibration. Microphones and cameras may be placed in an ad-hoc arrangement and, after calibration, the coordinates of the microphones are known in the reference frame of a camera in the array. No prior knowledge of microphone positions, inter-microphone spacings, or air temperature is required. This technique is applied to a spherical microphone array and a mean difference of 3 mm was obtained between the coordinates obtained with this calibration technique and those measured using a precision mechanical method.

Description: In this paper, we present a transform scheme where a secondary transform is applied after the conventional DCT for intra as well as inter prediction residues. Our approach is applicable to any block-based video codec that employs transforms along the horizontal and vertical direction separably. The secondary transform is applied to the lower K ( ${rm K}={4}$ or 8) frequency coefficients of the output of conventional DCT at block with dimensions 8 and larger. The proposed transform scheme has low complexity as it is applied only to the top-left portion of the DCT output, especially in the context of large blocks such as 32 $,times,$ 32 where an alternate non-DCT 32 $,times,$ 32 transform would have a prohibitive implementation hardware cost. The proposed technique is single-pass, and the choice of whether to use the secondary transform is solely based on the prediction direction for intra residue, and on transform unit location in the prediction unit for the inter residue. The scheme requires no additional signaling information or R-D search. Our simulation results show that the proposed transform scheme provides significant BD-rate improvement over the conventional DCT-based coding scheme. Finally, we also show how to implement the proposed secondary transforms with low latency in hardware.

Description: In this paper, we describe a novel algorithm for unsupervised segmentation of images with low depth of field (DOF). First of all, a multi-scale reblurring model is used to detect the object of interest (OOI) in saliency space. Then, to determine the boundary of OOI, an active contour model based on hybrid energy function is proposed. In this model, a global energy item related with the saliency map is adopted to find the global minimum, and a local energy term regarding the low DOF image is used to improve the segmentation precision. In addition, an adaptive parameter is attached to this model to balance the weight of global and local energy. Furthermore, an unsupervised curve initialization method is designed to reduce the number of evolution iterations. Finally, we conduct experiments on various low DOF images, and the results demonstrate the high robustness and precision of the proposed approach.

Description: In this paper, we propose a novel method that treats pose estimation as a problem with the constraints of human segmentation consistency from single images. Different from the previous paper, we integrate pose estimation and object segmentation into a joint optimization. With the support of segmentation consistency, we can obtain more reliable pose results. Through analyzing the energy function of pose estimation and human segmentation, we convert the pose estimation into a binary optimization problem that has the same formation as segmentation. The top-down pose shape cues, bottom-up visual cues, and the consistency constraints that penalize the mismatching of pose and human foreground are incorporated into our final objective function. Qualitative and quantitative experimental results demonstrate the merits of our method in pose estimation on Ramanan benchmark and Buffy data sets.

Description: A real-time and accurate object detection framework, ${rm C}^{4}$ , is proposed in this paper. ${rm C}^{4}$ achieves 20 fps speed and the state-of-the-art detection accuracy, using only one processing thread without resorting to special hardware such as GPU. The real-time accurate object detection is made possible by two contributions. First, we conjecture (with supporting experiments) that contour is what we should capture and signs of comparisons among neighboring pixels are the key information to capture contour cues. Second, we show that the CENTRIST visual descriptor is suitable for contour based object detection, because it encodes the sign information and can implicitly represent the global contour. When CENTRIST and linear classifier are used, we propose a computational method that does not need to explicitly generate feature vectors. It involves no image preprocessing or feature vector normalization, and only requires $O(1)$ steps to test an image patch. ${rm C}^{4}$ is also friendly to further hardware acceleration. It has been applied to detect objects such as pedestrians, faces, and cars on benchmark data sets. It has comparable detection accuracy with state-of-the-art methods, and has a clear advantage in detection speed.

Description: Previous image clutter metrics were proposed on the thought that clutter was just a perceptual effect, while we identify clutter as both perceptual and cognitive effects. Under this identification, we give a new definition of image clutter metric by analyzing the research results in the fields of visual psychology and psychophysics. According to the definition, we further put forward a DisSIMilarity (DSIM) based image clutter metric, which can also be taken as a kind of HVS-based signal-to-clutter ratio. The earlier image clutter metrics produced limited success in predicting targeting performance mainly since they did not consider brain cognitive characteristics. We develop a brain cognitive dissimilarity measure (BCDM) as a quantitative estimate of the selection weights which are allocated by brain attentional mechanism to affect visual selection processes. A human vision perceptual dissimilarity measure (VPDM), fully embodying vision perceptual properties, is first established between the target and clutter images, and then we utilize the BCDM between the two images as selection weights to pool the VPDM to be a clutter metric, which can be called DSIM metric. The metric is tested in Search_2 dataset provided by TNO Human Factors Research Institute of Netherlands. Error analysis and correlation tests demonstrate that the DSIM metric makes a more significant improvement than previously proposed metrics in predicting 62 observers' targeting performances including detection probability, false alarm probability and search time.

Description: Despite continuous improvements in optical flow in the last three decades, the ability for optical flow algorithms to handle illumination variation is still an unsolved challenge. To improve the ability to interpret apparent object motion in video containing illumination variation, an illumination-robust optical flow method is designed. This method decouples brightness into reflectance and illumination components using a stochastic technique; reflectance is given higher weight to ensure robustness against illumination, which is suppressed. Illumination experiments using the Middlebury and University of Oulu databases demonstrate the decoupled method's improvement when compared with state-of-the-art. In addition, a novel technique is implemented to visualize optical flow output, which is especially useful to compare different optical flow methods in the absence of the ground truth.

Description: Accurate grain segmentation on 3D superalloy images is very important in materials science and engineering. From grain segmentation, we can derive the underlying superalloy grains' micro-structures, based on how many important physical, mechanical, and chemical properties of the superalloy samples can be evaluated. Grain segmentation is, however, usually a very challenging problem because: 1) even a small 3D superalloy sample may contain hundreds of grains; 2) carbides and noises may degrade the imaging quality; and 3) the intensity within a grain may not be homogeneous. In addition, the same grain may present different appearances, e.g., different intensities, under different microscope settings. In practice, a 3D superalloy image may contain multichannel information where each channel corresponds to a specific microscope setting. In this paper, we develop a multichannel edge-weighted centroidal Voronoi tessellation (MCEWCVT) algorithm to effectively and robustly segment the superalloy grains from 3D multichannel superalloy images. MCEWCVT performs segmentation by minimizing an energy function, which encodes both the multichannel voxel-intensity similarity within each cluster in the intensity domain and the smoothness of segmentation boundaries in the 3D image domain. In the experiment, we first quantitatively evaluate the proposed MCEWCVT algorithm on a four-channel Ni-based 3D superalloy data set (IN100) against the manually annotated ground-truth segmentation. We further evaluate the MCEWCVT algorithm on two synthesized four-channel superalloy data sets. The qualitative and quantitative comparisons of 18 existing image segmentation algorithms demonstrate the effectiveness and robustness of the proposed MCEWCVT algorithm.

Description: Local binary pattern (LBP) is sensitive to noise. Local ternary pattern (LTP) partially solves this problem. Both LBP and LTP, however, treat the corrupted image patterns as they are. In view of this, we propose a noise-resistant LBP (NRLBP) to preserve the image local structures in presence of noise. The small pixel difference is vulnerable to noise. Thus, we encode it as an uncertain state first, and then determine its value based on the other bits of the LBP code. It is widely accepted that most of the image local structures are represented by uniform codes and noise patterns most likely fall into the non-uniform codes. Therefore, we assign the value of an uncertain bit hence as to form possible uniform codes. Thus, we develop an error-correction mechanism to recover the distorted image patterns. In addition, we find that some image patterns such as lines are not captured in uniform codes. Those line patterns may appear less frequently than uniform codes, but they represent a set of important local primitives for pattern recognition. Thus, we propose an extended noise-resistant LBP (ENRLBP) to capture line patterns. The proposed NRLBP and ENRLBP are more resistant to noise compared with LBP, LTP, and many other variants. On various applications, the proposed NRLBP and ENRLBP demonstrate superior performance to LBP/LTP variants.

Description: It is known that if the objective of a wireless sensor network is not to reconstruct individual sensor readings at a fusion center but rather to compute a linear function of them, then the interference property of the wireless channel can be beneficially harnessed by letting nodes transmit simultaneously. Recently, an analog computation scheme was proposed to show that it is possible to take the advantage of the interference property even if nonlinear functions are to be computed. The scheme involves some pre-processing on the sensor readings and post-processing on the superimposed signals observed by the fusion center. Correspondingly, this paper provides a thorough base for a theory of analog-computing functions over wireless channels by specifying what is the maximum achievable. This means it is determined for networks of arbitrary topology which functions are generally analog-computable over the channel and how many wireless resources are needed. It turns out that the considerations are closely related to the famous 13th Hilbert problem and that analog-computations can be universally performed in the sense that the pre-processing at sensor nodes is independent of the function to be computed. Universality reduces the complexity of transmitters and the signaling overhead, and it is shown that this property is preserved if nodes leave or join the network. Analog-computability is therefore of high practical relevance as it allows for an efficient computation of functions in sensor networks.

Description: We study the application of matrix completion in the process of calibrating physical devices. In particular we propose an algorithm together with reconstruction bounds for calibrating circular ultrasound tomography devices. We use the time-of-flight (ToF) measurements between sensor pairs in a homogeneous medium to calibrate the system. The calibration process consists of a low-rank matrix completion algorithm to de-noise and estimate random and structured missing ToFs, and the classic multi-dimensional scaling method to estimate the sensor positions from the ToF measurements. We provide theoretical bounds on the calibration error. Several simulations are conducted to evaluate the theoretical results presented in this paper.

Description: We propose a particle filtering technique to track multiple maneuvering targets in the presence of clutter. We treat data association and state estimation, which are the two important sub-problems in tracking, as separate problems. We develop a game-theoretic framework to solve the data association, in which we model each tracker as a player and the set of measurements as strategies. We develop utility functions for each player, and then use a regret-based learning algorithm to find the equilibrium of this game. The game-theoretic approach allows us to associate measurements to all the targets simultaneously. Further, in contrast to the traditional Monte-Carlo data association algorithms that use samples of the association vector obtained from a proposal distribution, our method finds the association in a deterministic fashion. We then use Monte-Carlo sampling on the reduced dimensional state of each target, independently, and thereby mitigate the curse-of-dimensionality problem that is known to occur in particle filtering. We provide a number of numerical results to demonstrate the performance of our proposed filtering algorithm.

Description: To overcome the difficulties in applying gradient-based operators to color images, Di Zenzo introduced the color tensor, an operator that provides a gradient field for multichannel images. An elegant application for this operator was developed in the domain of multichannel image visualization: Socolinsky and Wolff proposed to reintegrate Di Zenzo's gradient by solving a Poisson equation, yielding a greyscale representation of the multispectral contrast of the input image. Di Zenzo's gradients are, however, generally not integrable and some approximation must be introduced. Thus, the resulting image can suffer from artifacts such as the smearing of edges. In this paper, we focus on the integrability of Di Zenzo's gradients. We show that the integrability of the obtained field can be improved dramatically through a simple desaturation of the color image (as in the HSV color space). This result can be readily extended to multispectral images by defining an analogue to saturation. We present several results explaining what happens to color tensors as the saturation changes. Significantly we show that small changes of the saturation in the linear image space can result in large improvements in the integrability of tensor gradients calculated in logarithmic color space. This result is important for two reasons. 1) Log-differences are more perceptually meaningful. 2) In log-space we can operate with retinex algorithms, which are well known techniques for contrast enhancement. We propose that they can be used to “put back” any contrast that might be lost in the desaturation step and, more importantly, they can enhance contrast at the same time as reintegrating the gradient field because of their relation to partial differential equations. Finally, we evaluate our method psychophysically. Compared with other commonly used image fusion methods, experiments show that our data fusion using the Di Zenzo color tensor after desaturating the image and where a si- ple contrast boost is applied is strongly preferred.

Description: In this paper we deal with the problem of detecting an extended target embedded in homogeneous Gaussian interference with unknown but structured covariance matrix. We model the possible target echo, from each range bin under test, as a deterministic signal with an unknown scaling factor accounting for the target response. At the design stage, we exploit some a-priori knowledge about the operating environment enforcing the inverse interference plus noise covariance matrix to belong to a set described via unitary invariant continuous functions. Hence, we derive the constrained Maximum Likelihood (ML) estimates of the unknown parameters, under both the $H_{0}$ and $H_{1}$ hypotheses, and design the Generalized Likelihood Ratio Test (GLRT) for the considered decision problem. At the analysis stage, we assess the performance of the devised GLRT for some covariance matrix uncertainty sets of practical relevance both for spatial and Doppler processing. The results highlight that correct use of the a-priori knowledge can lead to a detection performance quite close to the optimum receiver which supposes the perfect knowledge of the interference plus noise covariance matrix.

Description: Describes the above-named upcoming special issue or section. May include topics to be covered or calls for papers.

Description: In this paper, we present a novel memory-efficient high-throughput scalable architecture for multi-level 2-D DWT. We studied the existing DWT architectures and observed that data scanning method has a significant impact on the memory efficiency of DWT architecture. We propose a novel parallel stripe-based scanning method based on the analysis of the dependency graph of the lifting scheme. With the new scanning method for multi-level 2D DWT, a high memory efficient scalable parallel pipelined architecture is developed. The proposed architecture requires no frame memory and a temporal memory of size only $3 N +682$ for the 3-level DWT decomposition with an image of size $N times N$ pixels with 32 pixels processed concurrently. The elimination of frame memory and the small temporal memory lead to significant reduction in overall size. The proposed architecture has a regular structure and achieves 100% hardware utilization. The synthesis results in 90 nm CMOS process show that the proposed architecture achieves a better area-delay product by 60% and higher throughput by 97% when compared to the best existing design for the CDF (Cohen-Daubechies-Favreau) 9/7 2-D DWT.

Description: A scalable monolithically integrated photonic space switch is proposed which uses a combination of Mach–Zehnder modulators and semiconductor optical amplifiers (SOAs) for improved crosstalk performance and reduced switch loss. This architecture enables the design of high-capacity, high-speed, large-port count, low-energy switches. Extremely low crosstalk of better than −50 dB can be achieved using a 2 × 2 dilated hybrid switch module. A “building block” approach is applied to make large port count optical switches possible. Detailed physical layer multiwavelength simulations are used to investigate the viability of a 64 × 64 port switch. Optical signal degradation is estimated as a function of switch size and waveguide induced crosstalk. A comparison between hybrid and SOA switching fabrics highlights the power-efficient, high-performance nature of the hybrid switch design, which consumes less than one-third of the energy of an equivalent SOA-based switch. The significantly reduced impairments resulting from this switch design enable scaling of the port count, compared to conventional SOA-based switches.

Description: We consider a multiple-input multiple-output (MIMO) interference channel (IC), where a single data stream per user is transmitted and each receiver treats interference as noise. The paper focuses on the open problem of computing the outermost boundary (so-called Pareto boundary-PB) of the achievable rate region under linear transceiver design. The Pareto boundary consists of the strict PB and non-strict PB. For the two user case, we compute the non-strict PB and the two ending points of the strict PB exactly. For the strict PB, we formulate the problem to maximize one rate while the other rate is fixed such that a strict PB point is reached. To solve this non-convex optimization problem which results from the hard-coupled two transmit beamformers, we propose an alternating optimization algorithm. Furthermore, we extend the algorithm to the multi-user scenario and show convergence. Numerical simulations illustrate that the proposed algorithm computes a sequence of well-distributed operating points that serve as a reasonable and complete inner bound of the strict PB compared with existing methods.

Description: We have studied plasmonic slot nanoresonators (PSNRs) embedded in a gold-coated microfiber. Light is coupled from the plasmonic waveguide into the PSNR, showing strong localization in three dimensions. Single bow-tie and rectangular PSNRs, as well as cascades of multiple bow-tie PSNRs, have been considered. The intensity enhancement and the resonance wavelength depend on both the PSNR and microfiber dimensions. The PSNRs embedded in plasmonic microfibers could find wide range of applications, such as surface enhanced Raman scattering, optical filtering, bio-sensing, and spectroscopy.

Description: This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy performance as the system is interference-limited. In the literature, assuming that the receiver operates in half duplex (HD) mode, the aforementioned problem has been addressed via use of cooperating nodes who act as jammers to confound the eavesdropper. This paper investigates an alternative solution, which assumes the availability of a full duplex (FD) receiver. In particular, while receiving data, the receiver transmits jamming noise to degrade the eavesdropper channel. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. For the case in which global channel state information is available, we aim to design the optimal jamming covariance matrix that maximizes the secrecy rate and mitigates loop interference associated with the FD operation. We consider both fixed and optimal linear receiver design at the destination, and show that the optimal jamming covariance matrix is rank-1, and can be found via an efficient 1-D search. For the case in which only statistical information on the eavesdropper channel is available, the optimal power allocation is studied in terms of ergodic and outage secrecy rates. Simulation results verify the analysis and demonstrate substantial performance gain over conventional HD operation at the destination.

Description: This paper addresses the problem of logical topology design for optical backbone networks subject to stochastic traffic demands. The network design problem is broken into three tasks: traffic routing, capacity allocation, and link placement. While the routing and capacity allocation subproblem can be formulated using convex optimization, it is prohibitive to add the link placement component to the nonlinear formulation since the link placement problem involves integer variables. To address this issue, we develop a linear formulation for the routing and capacity allocation subproblem by applying tools from robust optimization. We show that this linear formulation performs comparably to the optimal nonlinear formulation. Our formulation can then be used to solve the link-placement subproblem for stochastic traffic. We show that optimal logical topologies for deterministic traffic demands are not necessarily optimal for stochastic traffic demands. We develop algorithms for finding logical topologies optimized for stochastic traffic.

Description: We report novel rocking long period gratings (R-LPGs) made by introducing permanent periodic twist along a standard single mode fiber. Very high coupling efficiency of 32.5 dB was achieved with 23 periods and a 2° rocking angle. The responses of R-LPGs to temperature, strain, and torsion were tested. Compared with a normal LPG written under the same conditions, the R-LPGs were found to have a similar sensitivity to temperature, five times smaller sensitivity to strain, and insensitive to twist.

Description: This paper presents a complete analytical framework for modeling memoryless nonlinear effects in an intensity modulation and direct detection optical wireless communication system based on orthogonal frequency division multiplexing. The theory employs the Bussgang theorem, which is widely accepted as a means to characterize the impact of nonlinear distortions on normally distributed signals. This paper proposes a new method to generalize this approach, and it describes how a closed-form analytical expression for the system bit error rate can be obtained for an arbitrary memoryless distortion. Major distortion effects at the transmitter stage such as quantization and nonlinearity from the light emitting diode are analyzed. Four known orthogonal-frequency-division-multiplexing-based modulation schemes for optical communication are considered in this paper: direct-current-biased optical OFDM, asymmetrically clipped optical OFDM, pulse-amplitude-modulated discrete multitone modulation, and unipolar orthogonal frequency division multiplexing.

Description: This paper presents a downlink scheme that permits the coexistence, on a passive optical network branch, of future DSP-based optical network units (ONUs) that can receive advanced modulation signals and legacy ONUs that can receive only on–off keying (OOK) signals. In the proposed scheme, the two types of signals, advanced modulation signals and OOK signals, are multiplexed by using a hierarchical star quadrature amplitude modulation (QAM) format and transmitted simultaneously on a single carrier. The design criteria and the feasibility of the proposal are discussed. The coexistence of 10G-class ONUs and DSP-based ONUs using hierarchical star 8-QAM format is numerically analyzed and experimentally evaluated. The results confirm that a 10-Gbps OOK signal and 30-Gbps star 8-QAM signal can be received with 30.5-dB loss budget by an APD and intradyne detector with DSP, respectively. The ability of the proposed approach to expand the coverage area is also introduced.

Description: A novel filter for nonlinear and non-Gaussian systems is proposed in this paper. The unscented Kalman filter is designed to give a preliminary estimation of the state. An additional RBF-network is added to the UKF innovation term to compensate for the non-Gaussianity of the whole system. The Renyi's entropy of the innovation is introduced and parameters of the RBF-network are updated using minimum entropy criterion at each time step. It has been shown that the proposed algorithm has a high accuracy in estimation because entropy can characterize all the randomness of the residual while UKF only cares for the mean and the covariance. It has been proved that with properly chosen bandwidth $Sigma$ , the minimum entropy problem of the innovation is convex. Therefore, the proposed adaptive nonlinear filter will be globally convergent and the misadjustment will be proportional to the step size $mu$ . The effectiveness of the proposed method is shown by simulation.

Description: Analysis of projected changes in the occurrence of heat waves in Hungary Advances in Geosciences, 35, 115-122, 2013 Author(s): R. Pongrácz, J. Bartholy, and E. B. Bartha Heat wave events are important temperature-related hazards due to their impacts on human health. In 2004, a Heat Health Warning System including three levels of heat wave warning was developed on the basis of a retrospective analysis of mortality and meteorological data in Hungary to anticipate heat waves that may result in a large excess of mortality. Projected changes in the frequency of different heat wave warning levels are analysed for the 21st century. For this purpose, outputs of regional climate model PRECIS (Providing REgional Climates for Impacts Studies) are used taking into account three different global emissions scenarios (A2, A1B, B2). The results clearly show an increase in occurrence and length of heat waves with respect to the underlying emissions scenarios and regional climate model used. Moreover, the potential season of heat wave occurrences is projected to be lengthened by two months in 2071–2100 compared to 1961–1990.

Description: Review Article: On the relation between the seismic activity and the Hurst exponent of the geomagnetic field at the time of the 2000 Izu swarm Natural Hazards and Earth System Science, 13, 2189-2194, 2013 Author(s): F. Masci and J. N. Thomas Many papers document the observation of earthquake-related precursory signatures in geomagnetic field data. However, the significance of these findings is ambiguous because the authors did not adequately take into account that these signals could have been generated by other sources, and the seismogenic origin of these signals have not been validated by comparison with independent datasets. Thus, they are not reliable examples of magnetic disturbances induced by the seismic activity. Hayakawa et al. (2004) claim that at the time of the 2000 Izu swarm the Hurst exponent of the Ultra-Low-Frequency (ULF: 0.001–10 Hz) band of the geomagnetic field varied in accord with the energy released by the seismicity. The present paper demonstrates that the behaviour of the Hurst exponent was insufficiently investigated and also misinterpreted by the authors. We clearly show that during the Izu swarm the changes of the Hurst exponent were strongly related to the level of global geomagnetic activity and not to the increase of the local seismic activity.

Description: Forest fire danger rating in complex topography – results from a case study in the Bavarian Alps in autumn 2011 Natural Hazards and Earth System Science, 13, 2157-2167, 2013 Author(s): C. Schunk, C. Wastl, M. Leuchner, C. Schuster, and A. Menzel Forest fire danger rating based on sparse meteorological stations is known to be potentially misleading when assigned to larger areas of complex topography. This case study examines several fire danger indices based on data from two meteorological stations at different elevations during a major drought period. This drought was caused by a persistent high pressure system, inducing a pronounced temperature inversion and its associated thermal belt with much warmer, dryer conditions in intermediate elevations. Thus, a massive drying of fuels, leading to higher fire danger levels, and multiple fire occurrences at mid-slope positions were contrasted by moderate fire danger especially in the valleys. The ability of fire danger indices to resolve this situation was studied based on a comparison with the actual fire danger as determined from expert observations, fire occurrences and fuel moisture measurements. The results revealed that, during temperature inversion, differences in daily cycles of meteorological parameters influence fire danger and that these are not resolved by standard meteorological stations and fire danger indices (calculated on a once-a-day basis). Additional stations in higher locations or high-resolution meteorological models combined with fire danger indices accepting at least hourly input data may allow reasonable fire danger calculations under these circumstances.

Description: The Mediterranean Sea system: a review and an introduction to the special issue Ocean Science, 9, 789-803, 2013 Author(s): T. Tanhua, D. Hainbucher, K. Schroeder, V. Cardin, M. Álvarez, and G. Civitarese The Mediterranean Sea is a semi-enclosed sea characterized by high salinities, temperatures and densities. The net evaporation exceeds the precipitation, driving an anti-estuarine circulation through the Strait of Gibraltar, contributing to very low nutrient concentrations. The Mediterranean Sea has an active overturning circulation, one shallow cell that communicates directly with the Atlantic Ocean, and two deep overturning cells, one in each of the two main basins. It is surrounded by populated areas and is thus sensitive to anthropogenic forcing. Several dramatic changes in the oceanographic and biogeochemical conditions have been observed during the past several decades, emphasizing the need to better monitor and understand the changing conditions and their drivers. During 2011 three oceanographic cruises were conducted in a coordinated fashion in order to produce baseline data of important physical and biogeochemical parameters that can be compared to historic data and be used as reference for future observational campaigns. In this article we provide information on the Mediterranean Sea oceanographic situation, and present a short review that will serve as background information for the special issue in Ocean Science on "Physical, chemical and biological oceanography of the Mediterranean Sea". An important contribution of this article is the set of figures showing the large-scale distributions of physical and chemical properties along the full length of the Mediterranean Sea.

Description: Corrigendum to "NEMO on the shelf: assessment of the Iberia–Biscay–Ireland configuration" published in Ocean Sci., 9, 745–771, 2013 Ocean Science, 9, 787-787, 2013 Author(s): C. Maraldi, J. Chanut, B. Levier, N. Ayoub, P. De Mey, G. Reffray, F. Lyard, S. Cailleau, M. Drévillon, E. A. Fanjul, M. G. Sotillo, P. Marsaleix, and the Mercator Research and Development Team No abstract available.

Description: Preface "Landslide hazard and risk assessment at different scales" Natural Hazards and Earth System Science, 13, 2169-2171, 2013 Author(s): P. Reichenbach, A. Günther, and T. Glade

Description: We present a methodology for infrasonic remote sensing of winds in the stratosphere that does not require discrete ground-truth events. Our method uses measured time delays between arrays of sensors to provide group velocities (referred to here as celerities) and then minimizes the difference between observed and predicted celerities by perturbing an initial atmospheric specification. Because we focus on interarray propagation effects, it is not necessary to simulate the full propagation path from source to receiver. This feature allows us to use a relatively simple forward model that is applicable over short-regional distances. By focusing on stratospheric returns, we show that our non-linear inversion scheme converges much better if the starting model contains a strong stratospheric duct. Using the Horizontal Wind Model (HWM)/Mass Spectrometer Incoherent Scatter (MSISE) empirical climatology as a starting model, we demonstrate that the inversion scheme is robust to large uncertainties in backazimuth, but that uncertainties in the measured trace velocity and celerity require the use of prior constraints to ensure suitable convergence. The inversion of synthetic data, using realistic estimates of measurement error, shows that our scheme will nevertheless improve upon a starting model under most scenarios. The inversion scheme is applied to infrasound data recorded from a large event on 2010 December 25, which is presumed to be a bolide, using data from a nine-element infrasound network in Utah. We show that our recorded data require a stronger zonal wind speed in the stratosphere than is present in the HWM profile, and are more consistent with the Ground-to-Space (G2S) profile.

Description: Coda- Q is a stochastic parameter reflecting the heterogeneities of medium that seismic waves travel through. We confirmed that coda- Q would vary with the stress loaded to an elastic medium using numerical simulations of seismic wave propagation. When the stress is loaded, cracks in the crust could either close or newly open. The closure and opening of the cracks are not random but depending on the magnitude and the direction of the stress and the crack aspect ratio. The cracks in the medium after loading stress could be aligned in a specific orientation, and elastic wave velocity field would become anisotropic due to the alignment of specific crack orientations. Elastic wave velocity is in general faster along the direction corresponding with the crack orientation while slower along the perpendicular direction. In the numerical simulation, the effect of anisotropy in elastic wave velocity field due to the selective closure and opening of the cracks is calculated using a 2-D finite difference method assuming elastic wave velocity to be a function of the magnitude of loaded stress. The coda- Q calculated from seismic waves simulated for a model varies when the averaged normal stress changes. Our simulation indicated that the sensitivity of coda- Q –1 , that is the reciprocal of the coda- Q , would be 1.0 10 –2 (1.0 MPa –1 ) against the magnitude of the confining pressure and 1.0 10 –3 (1.0 deg –1 ) against the direction of principal stress. We would like to conclude that coda- Q , a stochastic parameter reflecting heterogeneities of subsurface medium, could become a quantitative state indicator of the stress field of the medium where seismic waves propagate through. Spatiotemporal variation of coda- Q reflects change in the stress field in the crust.

Description: The Chemistry CATT-BRAMS model (CCATT-BRAMS 4.5): a regional atmospheric model system for integrated air quality and weather forecasting and research Geoscientific Model Development, 6, 1389-1405, 2013 Author(s): K. M. Longo, S. R. Freitas, M. Pirre, V. Marécal, L. F. Rodrigues, J. Panetta, M. F. Alonso, N. E. Rosário, D. S. Moreira, M. S. Gácita, J. Arteta, R. Fonseca, R. Stockler, D. M. Katsurayama, A. Fazenda, and M. Bela Coupled Chemistry Aerosol-Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS, version 4.5) is an on-line regional chemical transport model designed for local and regional studies of atmospheric chemistry from the surface to the lower stratosphere suitable both for operational and research purposes. It includes gaseous/aqueous chemistry, photochemistry, scavenging and dry deposition. The CCATT-BRAMS model takes advantage of BRAMS-specific development for the tropics/subtropics as well as the recent availability of preprocessing tools for chemical mechanisms and fast codes for photolysis rates. BRAMS includes state-of-the-art physical parameterizations and dynamic formulations to simulate atmospheric circulations down to the meter. This on-line coupling of meteorology and chemistry allows the system to be used for simultaneous weather and chemical composition forecasts as well as potential feedback between the two. The entire system is made of three preprocessing software tools for user-defined chemical mechanisms, aerosol and trace gas emissions fields and the interpolation of initial and boundary conditions for meteorology and chemistry. In this paper, the model description is provided along with the evaluations performed by using observational data obtained from ground-based stations, instruments aboard aircrafts and retrieval from space remote sensing. The evaluation accounts for model applications at different scales from megacities and the Amazon Basin up to the intercontinental region of the Southern Hemisphere.

Description: Influence of microphysical schemes on atmospheric water in the Weather Research and Forecasting model Geoscientific Model Development Discussions, 6, 4563-4601, 2013 Author(s): F. Cossu and K. Hocke This study examines how different microphysical parameterization schemes influence orographically-induced precipitation and the distributions of hydrometeors and water vapour for mid-latitude summer conditions in the Weather Research and Forecasting (WRF) model. A high-resolution two-dimensional idealized simulation is used to assess the differences between the schemes in which a moist air flow is interacting with a bell-shaped 2 km high mountain. Periodic lateral boundary conditions are chosen to recirculate atmospheric water in the domain. It is found that the 13 selected microphysical schemes conserve the water in the model domain. The gain or loss of water is less than 0.81% over a simulation time interval of 61 days. The differences of the microphysical schemes in terms of the distributions of water vapour, hydrometeors and accumulated precipitation are presented and discussed. The Kessler scheme, the only scheme without ice-phase processes, shows final values of cloud liquid water 14 times greater than the other schemes. The differences among the other schemes are not as extreme, but still they differ up to 79% in water vapour, up to 10 times in hydrometeors and up to 64% in accumulated precipitation at the end of the simulation. The microphysical schemes also differ in the surface evaporation rate. The WRF single-moment 3-class scheme has the highest surface evaporation rate compensated by the highest precipitation rate. The different distributions of hydrometeors and water vapour of the microphysical schemes induce differences up to 49 W m −2 in the downwelling shortwave radiation and up to 33 W m −2 in the downwelling longwave radiation.

Description: How do body-wave traveltimes constrain the Earth's radial (1-D) seismic structure? Existing 1-D seismological models underpin 3-D seismic tomography and earthquake location algorithms. It is therefore crucial to assess the quality of such 1-D models, yet quantifying uncertainties in seismological models is challenging and thus often ignored. Ideally, quality assessment should be an integral part of the inverse method. Our aim in this study is twofold: (i) we show how to solve a general Bayesian non-linear inverse problem and quantify model uncertainties, and (ii) we investigate the constraint on spherically symmetric P -wave velocity ( V P ) structure provided by body-wave traveltimes from the EHB bulletin (phases Pn , P , PP and PKP ). Our approach is based on artificial neural networks, which are very common in pattern recognition problems and can be used to approximate an arbitrary function. We use a Mixture Density Network to obtain 1-D marginal posterior probability density functions (pdfs), which provide a quantitative description of our knowledge on the individual Earth parameters. No linearization or model damping is required, which allows us to infer a model which is constrained purely by the data. We present 1-D marginal posterior pdfs for the 22 V P parameters and seven discontinuity depths in our model. P -wave velocities in the inner core, outer core and lower mantle are resolved well, with standard deviations of ~0.2 to 1 per cent with respect to the mean of the posterior pdfs. The maximum likelihoods of V P are in general similar to the corresponding ak135 values, which lie within one or two standard deviations from the posterior means, thus providing an independent validation of ak135 in this part of the radial model. Conversely, the data contain little or no information on P -wave velocity in the D '' layer, the upper mantle and the homogeneous crustal layers. Further, the data do not constrain the depth of the discontinuities in our model. Using additional phases available in the ISC bulletin, such as PcP , PKKP and the converted phases SP and ScP , may enhance the resolvability of these parameters. Finally, we show how the method can be extended to obtain a posterior pdf for a multidimensional model space. This enables us to investigate correlations between model parameters.

Description: We have developed a network optimization method for regional-scale microseismic monitoring networks and applied it to optimize the densification of the existing seismic network in northeastern Switzerland. The new network will build the backbone of a 10-yr study on the neotectonic activity of this area that will help to better constrain the seismic hazard imposed on nuclear power plants and waste repository sites. This task defined the requirements regarding location precision (0.5 km in epicentre and 2 km in source depth) and detection capability [magnitude of completeness M c  = 1.0 ( M L )]. The goal of the optimization was to find the geometry and size of the network that met these requirements. Existing stations in Switzerland, Germany and Austria were considered in the optimization procedure. We based the optimization on the simulated annealing approach proposed by Hardt & Scherbaum, which aims to minimize the volume of the error ellipsoid of the linearized earthquake location problem ( D -criterion). We have extended their algorithm to: calculate traveltimes of seismic body waves using a finite difference ray tracer and the 3-D velocity model of Switzerland, calculate seismic body-wave amplitudes at arbitrary stations assuming the Brune source model and using scaling and attenuation relations recently derived for Switzerland, and estimate the noise level at arbitrary locations within Switzerland using a first-order ambient seismic noise model based on 14 land-use classes defined by the EU-project CORINE and open GIS data. We calculated optimized geometries for networks with 10–35 added stations and tested the stability of the optimization result by repeated runs with changing initial conditions. Further, we estimated the attainable magnitude of completeness ( M c ) for the different sized optimal networks using the Bayesian Magnitude of Completeness (BMC) method introduced by Mignan et al. The algorithm developed in this study is also applicable to smaller optimization problems, for example, small local monitoring networks. Possible applications are volcano monitoring, the surveillance of induced seismicity associated with geotechnical operations and many more. Our algorithm is especially useful to optimize networks in populated areas with heterogeneous noise conditions and if complex velocity structures or existing stations have to be considered.

Description: Fluid injection in and withdrawal from wells are basic procedures in mining activities and deep resources exploitation, such as oil and gas extraction, permeability enhancement for geothermal exploitation and waste fluid disposal. All of these activities have the potential to induce seismicity, as exemplified by the 2006 Basel earthquake ( M L 3.4). Despite several decades of experience, the mechanisms of induced seismicity are not known in detail, which prevents effective risk assessment and/or mitigation. In this study, we provide an interpretation of induced seismicity based on computation of Coulomb stress changes that result from fluid injection/withdrawal at depth, mainly focused on the interpretation of induced seismicity due to stimulation of a geothermal reservoir. Seismicity is, theoretically, more likely where Coulomb stress changes are larger. For modeling purposes, we simulate the thermodynamic evolution of a system after fluid injection/withdrawal. The associated changes in pressure and temperature are subsequently considered as sources of incremental stress changes, which are then converted to Coulomb stress changes on favourably oriented faults, taking into account the background regional stress. Numerical results are applied to the water injection that was performed to create the fractured reservoir at the enhanced-geothermal-system site, Soultz-sous-Forets (France). Our approach describes well the observed seismicity, and provides an explanation for the different behaviors of a system when fluids are injected or withdrawn.

Description: We report on a broad-band high-resolution attenuation model for the North China Craton and surrounding regions based on regional Lg -wave data. Vertical broad-band waveforms recorded at 39 stations from 176 crustal earthquakes are collected to extract the Lg -wave amplitude spectra between 0.05 and 10.0 Hz. We use the dual-station method to generate a preliminary Q Lg model and use it as the initial model. Then, we combine the dual- and single-station data together to jointly invert the Q Lg distribution and Lg source excitation functions. These inversions are conducted independently at individual frequencies without using any a priori assumption about the frequency dependences in Q Lg and source terms. The maximum spatial resolution is approximately 1° x 1° in well-covered areas for frequencies between 0.05 and 2.0 Hz. The Q Lg image is then used to determine the relationship between the attenuation and different geological structures. Results show an average Q 0 (1 Hz Q Lg ) of 374 for the entire North China Craton with an increasing trend from east to west. Average Q 0 values are 337, 361 and 421 for the east, central and west blocks, respectively. For the surrounding regions, the Eastern Tibetan plateau has a very low Q 0 of 188, while the Northeast China Plate and the Tianshan–Xingmeng fold belts are characterized by high Q 0 values of 506 and 424, respectively. We also investigate regional variations of the Lg attenuation in low-frequency band between 0.2 and 1.0 Hz.

Description: We present a systematic study on the influence of pressure (0.1–600 MPa), temperature (750–1200 °C), carbon dioxide fugacity (log f CO 2  = –4.41 to 3.60) and time (2–12 hr) on the chemical and physical properties of carbonate rock. Our experiments aim to reproduce the conditions at the periphery of magma chamber where carbonate host rock is influenced by, but not readily assimilated by, magma. This permits the investigation of the natural conditions at which circulating fluids/gases promote infiltration reactions typical of metasomatic skarns that can involve large volumes of subvolcanic carbonate basements. Results show that, providing that carbon dioxide is retained in the pore space, decarbonation does not proceed at any magmatic pressure and temperature. However, when the carbon dioxide is free to escape, decarbonation can occur rapidly and is not hindered by a low initial porosity or permeability. Together with carbon dioxide and lime, portlandite, a mineral commonly found in voluminous metasomatic skarns, readily forms during carbonate decomposition. Post-experimental analyses highlight that thermal microcracking, a result of the highly anisotropic thermal expansion of calcite, exerts a greater influence on rock physical properties (porosity, ultrasonic wave velocities and elastic moduli) than decarbonation. Our data suggest that this will be especially true at the margins of dykes or magma bodies, where temperatures can reach up to 1200 °C. However, rock compressive strength is significantly reduced by both thermal cracking and decarbonation, explained by the relative weakness of lime + portlandite compared to calcite, and an increase in grain size with increasing temperature. Metasomatic skarns, whose petrogenetic reactions may involve a few tens of cubic kilometres, could therefore represent an important source of volcanic instability.

Description: The scattering of plane SH waves incident on a circular sectorial canyon is considered. An accurate region-matching technique is applied to derive a rigorous series solution. Appropriate wavefunctions are employed to describe antiplane motions. Judicious basis functions, involving Gegenbauer polynomials, are well utilized to correctly capture the singular behaviour in stress fields near the canyon bottom. The enforcement of matching conditions on the auxiliary boundary leads to the determination of unknown coefficients. Plotted results demonstrate the influence of pertinent parameters on surface and subsurface motions. Both steady-state and transient results are included. The solution technique proposed achieves a considerable reduction in the computational effort, facilitating benchmark computations. The derived series solution enriches the limited list of series solutions presently known for canyon problems related to SH -wave scattering.

Description: We present 3-D models of the P- and S -wave velocity distributions in the crust and uppermost mantle beneath Sicily, Calabria (Southern Italy), and surrounding submerged areas, obtained by tomographic inversion of traveltimes of regional body waves phases. Our method combines double-difference tomographic inversion with a post-processing procedure [Weighted Average Model method (WAM)]. This procedure was applied to a set of models consistent with the experimental data. We tested the ability of the WAM procedure to mitigate the uncertainty associated with the arbitrary nature of the many input parameters required for each inversion. The local reliability and resolution of the obtained models have been assessed through: synthetic tests, experimental tests carried out with independent data sets and unconventional tests based on the analysis of the internal consistency of the P - and S -velocity models. The tomographic images provide a detailed sketch of P- and S- wave velocity anomalies. These clearly show the shape of the Sicilian-Maghrebian belt beneath Sicily and Calabrian Arc at different depths. Low V P and Vs bodies are imaged beneath Stromboli and Marsili volcanoes in the southern Tyrrhenian, whereas high and low seismic velocities alternate beneath the Etna giving inferences on the possible depth of the mantle melting feeding the volcano. In the upper crust, the main sedimentary basins and tectonic features are also well imaged. Finally, tomographic cross sections show the trend of the Moho in the study area, where its depth ranges between 35 and 40 km beneath the Sicilian belt and between 15 and 22 km in the southern Tyrrhenian basin and Ionian Sea.

Description: We used two tracks of ALOS PALSAR images to investigate the focal mechanism and slip distribution of the 2011 March 24, M W 6.8 Burma strike-slip earthquake. Three different SAR techniques, namely conventional interferometry, SAR pixel offsets (SPO) and multiple-aperture InSAR (MAI), were employed to obtain the coseismic surface deformation fields along the ~30 km length of the fault rupture. Along-track measurements from SPO and MAI techniques show a high correlation, and were subsequently used to precisely determine the location and extent of the surface fault trace. The best-fitting fault model geometry derived from an iterative inversion technique suggests that the rupture occurred on a near-vertical sinistral strike-slip fault west of the Nam Ma fault with a strike of 70°. A maximum slip of 4.2 m occurs at a depth of 2.5 km, with significant slip constrained only to the upper 10 km of the crust.

Description: Knowledge of the mantle reflectivity structure is highly dependent on our ability to efficiently extract, and properly interpret, small seismic arrivals. Among the various data types and techniques, long-period SS/PP precursors and high-frequency receiver functions are routinely utilized to increase the confidence of the recovered mantle stratifications at distinct spatial scales. However, low resolution and a complex Fresnel zone are glaring weaknesses of SS precursors, while over-reliance on receiver distribution is a formidable challenge for the analysis of converted waves from oceanic regions. A promising high frequency alternative to receiver functions is P ' P ' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of ~5 and ~200 km, respectively, owing to their spectral content, shallow angle of incidence and near-symmetric Fresnel zones. This study presents a novel processing method for both SS (or PP) and P ' P ' precursors based on deconvolution, stacking, Radon transform and depth migration. A suite of synthetic tests is performed to quantify the fidelity and stability of this method under different data conditions. Our multiresolution survey of the mantle at targeted areas near Nazca-South America subduction zone reveal both olivine and garnet related transitions at depths below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P ' P ' reflections within the transition zone, and the anomalous amplitudes near the plate boundary zone indicate a sharp (~10 km thick) transition that likely resonates with the frequency content of P ' P ' precursors. The migration of SS precursors in this study shows no evidence of split 660 reflections, but potential majorite–ilmenite (590–640 km) and ilmenite–perovskite transitions (740–750 km) are identified based on similarly processed high-frequency P ' P ' precursors. Additional findings of severely scattered energy in the lithosphere and distinct lower mantle reflections at ~800 km could be potentially important but require further verifications. Overall, our improved imaging methods and the strong sensitivity of P ' P ' precursors to the existence, depth, sharpness and strength of reflective structures offer significant future promise for the understanding of mantle mineralogy and dynamics.

Description: Time-dependent probabilistic seismic hazard assessment requires a stochastic description of earthquake occurrences. While short-term seismicity models are well-constrained by observations, the recurrences of characteristic on-fault earthquakes are only derived from theoretical considerations, uncertain palaeo-events or proxy data. Despite the involved uncertainties and complexity, simple statistical models for a quasi-period recurrence of on-fault events are implemented in seismic hazard assessments. To test the applicability of statistical models, such as the Brownian relaxation oscillator or the stress release model, we perform a systematic comparison with deterministic simulations based on rate- and state-dependent friction, high-resolution representations of fault systems and quasi-dynamic rupture propagation. For the specific fault network of the Lower Rhine Embayment, Germany, we run both stochastic and deterministic model simulations based on the same fault geometries and stress interactions. Our results indicate that the stochastic simulators are able to reproduce the first-order characteristics of the major earthquakes on isolated faults as well as for coupled faults with moderate stress interactions. However, we find that all tested statistical models fail to reproduce the characteristics of strongly coupled faults, because multisegment rupturing resulting from a spatiotemporally correlated stress field is underestimated in the stochastic simulators. Our results suggest that stochastic models have to be extended by multirupture probability distributions to provide more reliable results.

Description: Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress–strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress–strain response measured during standard laboratory tests. Subsequently, AE frequency–magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of event magnitude tends to decay as power law while the spatial distribution of sources exhibits a fractal character, in agreement with experimental observations. Moreover, the model can capture the decrease of seismic b value associated with the macrorupture of the rock sample and the transition of AE spatial distribution from diffuse, in the pre-peak stage, to strongly localized at the peak and post-peak stages, as reported in a number of published laboratory studies. In future studies, the validated FEM/DEM-AE modelling technique will be used to obtain further insights into the micromechanics of rock failure with potential applications ranging from laboratory-scale microcracking to engineering-scale processes (e.g. excavations within mines, tunnels and caverns, petroleum and geothermal reservoirs) to tectonic earthquakes triggering.

Description: We used strong-motion records from the 2012 May 20 and 29 Emilia-Romagna earthquakes ( M w 6.1 and 5.9, respectively) and four aftershocks with magnitudes ranging between 4.9 and 5.5 to analyse the S -wave spectral amplitude decay with distance and estimate acceleration source functions and site effects. The data set consists of six earthquakes, 44 stations and 248 records with hypocentral distances in the range 10 〈 r  〈 100 km. We rotated the accelerograms to calculate transverse and radial components of the acceleration spectrum. We found non-parametric attenuation functions that describe the spectral amplitude decay of SH and SV waves with distance at 60 different frequencies between 0.1 and 40 Hz. These attenuation functions provide an estimate of the quality factor Q at each frequency analysed. Assuming that geometrical spreading is 1/ r for r  ≤ r x and 1/( r x r ) 0.5 for r  〉 r x with r x  = 60 km and normalizing at 15 km (the recording distance where the attenuation functions start to decay), we find that the average Q for SH waves can be approximated by Q SH  = 82 ± 1 f  1.2±0.02 and by Q SV  = 79 ± 1 f  1.24±0.03 for SV waves in the frequency range 0.10 ≤ f  ≤ 10.7 Hz. At higher frequencies, 11.8 ≤ f  ≤ 40 Hz, the frequency dependence of Q weakens and is approximated by Q SH  = 301 ± 1 f   0.36±0.04 and Q SV  = 384 ± 1 f  0.28±0.04 . These results indicate that the S -wave attenuation is radially isotropic at local distances in the epicentral area. Nevertheless, we used these attenuation parameters separately to correct the radial (with Q SV ) and transverse (with Q SH ) components of the acceleration spectra and to separate source and site effects using a non-parametric spectral inversion scheme. We found that the source function of the main event and the bigger aftershocks show enhanced low frequency radiation between 0.4 and 3.0 Hz. We converted the source functions into far-field source acceleration spectra and interpreted the resulting source spectra in terms of Brune's model. The stress drops obtained range between approximately 0.9 and 2.9 MPa. Although all the recording stations used are located in the Po Plain, the site functions obtained from the spectral inversion show important amplification variability between the sites. We compared these site functions with the average horizontal to vertical spectral ratios calculated for each station, and we found consistent results for most stations.

Description: The sensitivity of global climate to the episodicity of fire aerosol emissions Atmospheric Chemistry and Physics Discussions, 13, 23691-23717, 2013 Author(s): S. K. Clark, D. S. Ward, and N. M. Mahowald One of the major ways in which forest and grass fires have an impact on global climate is through the release of aerosols. Most studies focusing on calculating the radiative forcing and other climate impacts of fire aerosols use monthly mean emissions derived from the Global Fire Emissions Database that captures only the seasonal cycle of fire aerosol emissions. Here we present the results of a sensitivity study that investigates the climate response to the episodicity of the fires, based on the standard approach which releases emissions every day, and contrasts that to the response when fires are represented as intense pulses of emissions that occur only over 1–2 days on a monthly, yearly, or five-yearly basis. Overall we find that in the modified cases with increased levels of episodicity, the all sky direct effect radiative forcing increases, the clear sky direct effect radiative forcing remains relatively constant, and the magnitude of the indirect effect radiative forcing decreases by about 1 W m −2 (from −1.6 to −0.6 W m −2 ). In the long term, we find that an increase in aerosol emission episodicity leads to an asymmetric change in indirect radiative forcing in the Northern Hemisphere compared to the Southern Hemisphere contributes to a slight shift in the annual average position of the intertropical convergence zone (ITCZ). This shift is found to have a mixed effect on the overall performance of the model at predicting precipitation rates in the tropics. Given these results we conclude that future studies that look to assess the present day global climate impacts of fire aerosols should consider the need to accurately represent fire episodicity.

Description: Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates Biogeosciences Discussions, 10, 14861-14885, 2013 Author(s): K. Schmidt, C. L. De La Rocha, M. Gallinari, and G. Cortese Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d −1 , became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

Description: Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles Atmospheric Chemistry and Physics, 13, 9097-9118, 2013 Author(s): Z. A. Kanji, A. Welti, C. Chou, O. Stetzer, and U. Lohmann Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature ( T ) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 〈 T 〈 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone concentrations of 0.4–4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode measurements, respectively. Ice active fractions as well as ice active surface site densities ( n s ) are reported and observed to increase as a function of decreasing temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. We also present the first results to show a suppression of heterogeneous ice nucleation activity without the condensation of a coating of (in)organic material. In immersion mode, low ozone exposed Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka, whereas high ozone exposed ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder than that of untreated ATD. In deposition mode, low exposure Ka had ice active fractions of an order of magnitude higher than untreated Ka, whereas high ozone exposed ATD had ice active fractions up to a factor of 4 lower than untreated ATD. From our results, we derive and present parameterizations in terms of n s ( T ) that can be used in models to predict ice nuclei concentrations based on available aerosol surface area.

Description: Antecedent flow conditions and nitrate concentrations in the Mississippi River Basin Hydrology and Earth System Sciences Discussions, 10, 11451-11484, 2013 Author(s): J. C. Murphy, R. M. Hirsch, and L. A. Sprague The influence of antecedent flow conditions on nitrate concentrations was explored at eight sites in the Mississippi River Basin, USA. Antecedent moisture conditions have been shown to influence nutrient export from small, relatively homogenous basins, but this influence has not been observed at a regional or continental scale. Antecedent flow conditions were quantified as the ratio between the mean daily flow of the previous year and the mean daily flow from the period of record ( Q ratio), and the Q ratio was statistically related to nitrate anomalies (the unexplained variability in nitrate concentration after filtering out season, long-term trend, and contemporaneous flow effects) at each site. Nitrate anomaly and Q ratio were negatively related at three of the four major tributary sites and upstream in the Mississippi River, indicating that when the previous year was drier than average, at these sites, nitrate concentrations were higher than expected. The strength of these relationships increased when data were subdivided by contemporaneous flow conditions. Five of the eight sites had significant negative relationships ( p ≤ 0.05) at high or moderately high contemporaneous flows, suggesting nitrate that accumulates in these basins during a drought is flushed during subsequent storm events. At half of the sites, when flow during the previous year was 50% drier than average, nitrate concentration can be from 9 and 27% higher than nitrate concentrations that follow a year with average daily flow. Conversely, nitrate concentration can be from 8 and 21% lower than expected when the previous year was 50% wetter than average. These relationships between nitrate concentration and Q ratio serve as the basis for future studies that can better define specific hydrologic processes occurring during and after a drought, which influence nitrate concentration, such as the duration or magnitude of low flows, and the timing of low and high flows.

Description: We report on the results of numerical investigations into the effects of slot geometry of horizontal slot microdisk resonators on their performance as optical biosensors. We find that for resonator-based biosensors, the mode overlap is the limiting factor for the performance. With this finding, we suggest that slot resonators are superior to conventional, evanescent-field based resonators primarily for the surface sensing, where a high optical field created by the thin slots can be used. Possible mixing of modes reduces the mode overlap and thus need to be avoided by proper design of the resonator structure. We further propose an optimized triple-slot structure to double the possible detector sensitivity.

Description: We demonstrated 3.2-Tb/s (32 $,times,$ 120-Gb/s) unrepeatered transmission over 445-km fiber with ${rm A}_{rm eff}$ -managed-span. This was achieved by employing co-propagating second-order pumped Raman amplification and remote optically pumped amplifier, which was counter-propagating second-order Raman pumped. This letter also discusses design tradeoff on the nonlinear tolerance and Raman gain efficiency within ${rm A}_{rm eff}$ -managed-span for performance enhancement of unrepeatered transmission.

Description: We report a new approach to photonic generation of binary phase-coded microwave signals based on the asymmetric phase modulation indexes of a phase modulator in the TE and TM polarization states. The proposed system is extremely simplified compared with any other techniques reported in the previous literature since we only use one phase modulator. The microwave carrier frequency is widely tunable, and the $pi$ phase shift of the microwave signal is independent of the amplitude of the electrical driving signal. The proposed technique is theoretically analyzed and experimentally verified at carrier frequencies of 10 and 25 GHz, respectively.

Description: This letter reports a cost-effective transmitter solution for future generations of long reach passive optical networks (PONs). It is based on the direct adaptive orthogonal frequency division multiplexing modulation of a hybrid III/V-on-silicon laser. Because of low-noise and good linearity of the hybrid laser, modulation formats as high as 32-quadrature amplitude modulation are achieved. Data-rates of 21.5 and 12.4 Gb/s are demonstrated, respectively, in optical back-to-back and 50 km single-mode fiber (SMF)-link free from amplifiers, while on-off keying transmission is limited to ${〈}{rm 7}~{rm Gb}/{rm s}$ at 20 km SMF. The proposed solution stands as a cost-effective solution for next-generation time and wavelength division multiplexing PONs with extended reach, as the hybrid laser can further be made tunable.

Description: We propose a photonic technique for millimeter-wave ultra-wideband (MMW-UWB) signal generation via direct frequency up-conversion using a dual-parallel Mach–Zehnder modulator (DPMZM). By properly setting the dc bias voltages of the DPMZM, the baseband UWB pulse is up-converted to the MMW band without pulse distortion. In addition, the excessive residual local oscillator component is perfectly suppressed. The electrical spectrum of the up-converted UWB signal satisfies the Federal Communications Commission spectral mask very well.

Description: We developed a multiframe observation method of femtosecond laser pulse propagating in transparent medium based on optical polarigraphy technique. An echelon was introduced into the probe light and divided it into multipulses both in time and space, allowing a multiframe detection of the intense laser pulse propagating in materials. Using this method, we realized a multiframe observation of a single femtosecond laser pulse propagating in CS2 with ultrafast self-modulation such as filamentation. This imaging method has been demonstrated to be of a femtosecond time resolution and a frame rate of ${sim}{rm THz}$ .

Description: An in-line submillimeter hole fabricated by micro-drilling plastic optical fiber (POF) directly has been proposed as a compact refractive index sensor. Since the hole behaves as a concave lens if it is filled with a liquid having lower refractive index than that of the fiber core, transmittance increases in proportion to the refractive index. Analysis of the sensor transmittance has been performed using a simple ray optics model. Through immersing a 1.5-mm POF with a 0.35-mm-radius hole into various liquids, transmittance of the sensor has been measured at 670 nm. It has been shown that the experimental and analytical results are in excellent agreement.

Description: We experimentally demonstrate two types of silicon-on-insulator microring devices: 1) a slotted conventional microring resonator (MRR) using a multimode interferometer (MMI) coupler as the coupling element; and 2) an MMI-coupled slotted Mach–Zehnder interferometer (MZI) racetrack microring. We achieved a high bandwidth of 1.1 nm and a quality factor Q of ${sim}{1300}$ at the wavelength of 1510 nm for the conventional MRRs with a radius of 20 $mu{rm m}$ . A high extinction ratio (17–25 dB) is exhibited over a wavelength range from 1490 to 1520 nm. At the 1515-nm resonance wavelength, the MMI-coupled MZI racetrack microring demonstrates a quasi-free spectral range of 22.6 nm with a high extinction ratio of 25 dB. The demonstrated devices have many applications such as biochemical and gas sensing and modulation in communication systems.

Description: We report an experimental demonstration of a nonuniformly spaced photonic microwave delay-line filter implemented using an incoherent broadband optical source and a spatially discrete chirped fiber Bragg grating (SD-CFBG). The SD-CFBG performs simultaneously three functions: 1) to slice the spectrum of the broadband optical source for generating the filter taps; 2) to provide nonuniform time delays; and 3) to control the weights of the filter taps. Since negative or complex coefficients are equivalently generated based on the nonuniform sampling, a filter with an arbitrary spectra response is achieved. To verify the effectiveness of the proposed method, a flat-top bandpass microwave filter with seven all-positive nonuniformly spaced taps at 12 GHz is experimentally demonstrated. The proposed method offers a cost-effective and easy-to-implement solution for photonic microwave filters having arbitrary frequency responses.

Description: An Si photonic transmitter is integrated in a 130-nm silicon-on-insulator complementary metal–oxide–semiconductor technology. A high-speed photonic ring modulator is designed for 25-Gb/s operation with an 8-dB extinction ratio. The ring is driven with a $2.4hbox{-}{rm V}_{rm pp}$ swing using a low-power inverter driver. With a reference receiver, the 25-Gb/s link is measured with a bit error rate (BER) of $10^{-12}$ . The total transmitter power consumption is 17 mW at 25 Gb/s for an energy efficiency of 680 fJ/b excluding laser and ring tuning power.

Description: A higher order statistics (HOS)-based method is proposed in this letter to estimate the nonlinear amplitude-to-phase (AM/PM) conversion function of power amplifiers (PAs) in communications systems. By utilizing the symmetry property of the modulated signal, the proposed method estimates the AM/PM conversion function using only the PA output signal, from which the phase predistorter (PD) function can be derived. Simulation results show that the HOS-based method can accurately determine the phase PD function required to compensate for the AM/PM distortion in the PA, yielding a linearization performance close to that of non-blind methods in terms of adjacent channel power ratio and error vector magnitude.

Description: Tidally induced velocity variations of the Beardmore Glacier, Antarctica, and their representation in satellite measurements of ice velocity The Cryosphere, 7, 1375-1384, 2013 Author(s): O. J. Marsh, W. Rack, D. Floricioiu, N. R. Golledge, and W. Lawson Ocean tides close to the grounding line of outlet glaciers around Antarctica have been shown to directly influence ice velocity, both linearly and non-linearly. These fluctuations can be significant and have the potential to affect satellite measurements of ice discharge, which assume displacement between satellite passes to be consistent and representative of annual means. Satellite observations of horizontal velocity variation in the grounding zone are also contaminated by vertical tidal effects, the importance of which is highlighted here in speckle tracking measurements. Eight TerraSAR-X scenes from the grounding zone of the Beardmore Glacier are analysed in conjunction with GPS measurements to determine short-term and decadal trends in ice velocity. Diurnal tides produce horizontal velocity fluctuations of 〉50% on the ice shelf, recorded in the GPS data 4 km downstream of the grounding line. This variability decreases rapidly to 〈5% only 15 km upstream of the grounding line. Daily fluctuations are smoothed to 〈1% in the 11-day repeat pass TerraSAR-X imagery, but fortnightly variations over this period are still visible and show that satellite-velocity measurements can be affected by tides over longer periods. The measured tidal displacement observed in radar look direction over floating ice also allows the grounding line to be identified, using differential speckle tracking where phase information cannot be easily unwrapped.

Description: A new data set of soil mineralogy for dust-cycle modeling Atmospheric Chemistry and Physics Discussions, 13, 23943-23993, 2013 Author(s): E. Journet, Y. Balkanski, and S. P. Harrison The mineralogy of airborne dust affects the impact of dust particles on direct and indirect radiative forcing, on atmospheric chemistry and on biogeochemical cycling. It is determined partly by the mineralogy of the dust-source regions and partly by size-dependent fractionation during erosion and transport. Here we present a data set that characterizes the clay and silt sized fractions of global soil units in terms of the abundance of 12 minerals that are important for dust-climate interactions: quartz, feldspars, illite, smectite, kaolinite, chlorite, vermiculite, mica, calcite, gypsum, hematite and goethite. The basic mineralogical information is derived from the literature, and is then expanded following explicit rules, in order to characterize as many soil units as possible. We present three alternative realisations of the mineralogical maps that account for the uncertainties in the mineralogical data. We examine the implications of the new database for calculations of the single scattering albedo of airborne dust and thus for dust radiative forcing.

Description: Calibration of the passive cavity aerosol spectrometer probe for airborne determination of the size distribution Atmospheric Measurement Techniques, 6, 2349-2358, 2013 Author(s): Y. Cai, J. R. Snider, and P. Wechsler This work describes calibration methods for the particle sizing and particle concentration systems of the passive cavity aerosol spectrometer probe (PCASP). Laboratory calibrations conducted over six years, in support of the deployment of a PCASP on a cloud physics research aircraft, are analyzed. Instead of using the many calibration sizes recommended by the PCASP manufacturer, a relationship between particle diameter and scattered light intensity is established using three sizes of mobility-selected polystyrene latex particles, one for each amplifier gain stage. In addition, studies of two factors influencing the PCASP's determination of the particle size distribution – amplifier baseline and particle shape – are conducted. It is shown that the PCASP-derived size distribution is sensitive to adjustments of the sizing system's baseline voltage, and that for aggregates of spheres, a PCASP-derived particle size and a sphere-equivalent particle size agree within uncertainty dictated by the PCASP's sizing resolution. Robust determinations of aerosol concentration, and size distribution, also require calibration of the PCASP's aerosol flowrate sensor. Sensor calibrations, calibration drift, and the sensor's non-linear response are documented.

Description: Contribution of snow and glacier melt to discharge for highly glacierised catchments in Norway Hydrology and Earth System Sciences Discussions, 10, 11485-11517, 2013 Author(s): M. Engelhardt, T. V. Schuler, and L. M. Andreassen Glacierised catchments significantly alter the streamflow regime due to snow and glacier meltwater contribution to discharge. In this study, we modelled the mass balance and discharge rates for three highly glacierised catchments (〉50% glacier cover) in western Norway over the period 1961–2012. The spatial pattern of the catchments follows a gradient in climate continentality from west to east. The model uses gridded temperature and precipitation values from seNorge ( http://senorge.no ) as input which are available at a daily resolution. It accounts for accumulation of snow, transformation of snow to firn and ice, evaporation and melt. The model was calibrated for each catchment based on measurements of seasonal glacier mass-balances and daily discharge rates. For validation, daily melt rates were compared with measurements from sonic rangers located in the ablation zones of two of the glaciers and an uncertainty analysis was performed for the third catchment. The discharge contributions from snowmelt, glacier melt and rain were analysed with respect to spatial variations and temporal evolution. The model simulations reveal an increase of the relative contribution from glacier melt for the three catchments from less than 10% in the early 1990s to 15–30% in the late 2000s. The decline in precipitation by 10–20% in the same period was therefore overcompensated resulting in an increase of the annual discharge by 5–20%. Annual discharge sums and annual glacier melt are strongest correlated with annual and winter precipitation at the most maritime glacier and, with increased climate continentality, variations in both glacier melt contribution and annual discharge are becoming stronger correlated with variations in summer temperatures.

Description: Beyond multifractional Brownian motion: new stochastic models for geophysical modelling Nonlinear Processes in Geophysics, 20, 643-655, 2013 Author(s): J. Lévy Véhel Multifractional Brownian motion (mBm) has proved to be a useful tool in various areas of geophysical modelling. Although a versatile model, mBm is of course not always an adequate one. We present in this work several other stochastic processes which could potentially be useful in geophysics. The first alternative type is that of self-regulating processes : these are models where the local regularity is a function of the amplitude, in contrast to mBm where it is tuned exogenously. We demonstrate the relevance of such models for digital elevation maps and for temperature records. We also briefly describe two other types of alternative processes, which are the counterparts of mBm and of self-regulating processes when the intensity of local jumps is considered in lieu of local regularity: multistable processes allow one to prescribe the local intensity of jumps in space/time, while this intensity is governed by the amplitude for self-stabilizing processes .

Description: Decadal trends in the Antarctic sea ice extent ultimately controlled by ice-ocean feedback The Cryosphere Discussions, 7, 4585-4632, 2013 Author(s): H. Goosse and V. Zunz The large natural variability of the Antarctic sea ice is a key characteristic of the system that might be responsible for the small positive trend in sea ice extent observed since 1979. In order to gain insight in the processes responsible for this variability, we have analysed in a control simulation performed with a coupled climate model a strong positive ice-ocean feedback that amplifies sea ice variations. When sea ice concentration increases in a region, in particular close to the ice edge, the mixed layer depth tends to decrease. This can be caused by a net inflow of ice and thus of freshwater that stabilizes the water column. Another stabilizing mechanism at interannual time scales that appears more widespread in our simulation is associated with the downward salt transport due to the seasonal cycle of ice formation: brine is released in winter when ice is formed and mixed over a deep layer while the freshwater flux caused by ice melting is included in a shallow layer, resulting in a net vertical transport of salt. Because of this stronger stratification due to the presence of sea ice, more heat is stored at depth in the ocean and the vertical oceanic heat flux is reduced, which contributes to maintain a higher ice extent. This positive feedback is not associated with a particular spatial pattern. Consequently, the spatial distribution of the trend in ice concentration is largely imposed by the wind changes that can provide the initial perturbation. A positive freshwater flux could alternatively be the initial trigger but the amplitude of the final response of the sea ice extent is finally set up by the amplification related to ice-ocean feedback. Initial conditions have also an influence as the chance to have a large increase in ice extent is higher if starting from a state characterized by a low value.

Description: Growth of sulphuric acid nanoparticles under wet and dry conditions Atmospheric Chemistry and Physics Discussions, 13, 24087-24125, 2013 Author(s): L. Škrabalová, D. Brus, T. Anttila, V. Ždímal, and H. Lihavainen New particle formation, which greatly influences the number concentrations and size distributions of an atmospheric aerosol, is often followed by a rapid growth of freshly formed particles. The initial growth of a newly formed aerosol is the crucial process determining the fraction of nucleated particles growing into cloud condensation nuclei sizes, which have a significant influence on climate. In this study, we report the laboratory observations of the growth of nanoparticles produced by nucleation of H 2 SO 4 and water in a laminar flow tube at temperatures of 283, 293 and 303 K, under dry (a relative humidity of 1%) and wet conditions (relative humidity of 30%) and residence times of 30, 45, 60 and 90 s. The initial H 2 SO 4 concentration spans the range from 2 × 10 8 to 1.4 × 10 10 molecule cm −3 and the calculated wall losses of H 2 SO 4 were assumed to be diffusion limited. The detected particle number concentrations, measured by the Ultrafine Condensation Particle Counter (UCPC) and Differential Mobility Particle Sizer (DMPS), were found to depend strongly on the residence time. Hygroscopic particle growth, presented by growth factors, was found to be in good agreement with the previously reported studies. The experimental growth rates ranged from 20 nm h −1 to 890 nm h −1 at RH 1% and from 7 nm h −1 to 980 nm h −1 at RH 30% and were found to increase significantly with the increasing concentration of H 2 SO 4 . Increases in the nucleation temperature had a slight enhancing effect on the growth rates under dry conditions. The influence of relative humidity on growth was not consistent – at lower H 2 SO 4 concentrations, the growth rates were higher under dry conditions while at H 2 SO 4 concentrations greater than 1×10 9 molecule cm −3 the growth rates were higher under wet conditions. The growth rates show only a weak dependence on the residence time. The experimental observations were compared with predictions made using a numerical model, which investigates the growth of particles with three different extents of neutralization by the ammonia NH 3 : (1) pure H 2 SO 4 – H 2 O particles (2) particles formed by ammonium bisulphate, (NH 4 )HSO 4 (3) particles formed by ammonium sulphate, (NH 4 ) 2 SO 4 . The highest growth rates were found for ammonium sulphate particles. Since the model accounting for the initial H 2 SO 4 concentration predicted the experimental growth rates correctly, our results suggest that the commonly presumed diffusional wall losses of H 2 SO 4 are not so significant. We therefore assume that there are not only losses of H 2 SO 4 on the wall but also a flux of H 2 SO 4 molecules from the wall into the flow tube, the effect being more profound under dry conditions and at higher temperatures of the tube wall. Based on a comparison with the atmospheric observations, our results indicate that sulphuric acid alone can not explain the growth rates of particles formed in the atmosphere.

Description: Experimental quantification of contact freezing in an electrodynamic balance Atmospheric Measurement Techniques, 6, 2373-2382, 2013 Author(s): N. Hoffmann, A. Kiselev, D. Rzesanke, D. Duft, and T. Leisner Heterogeneous nucleation of ice in a supercooled water droplet induced by external contact with a dry aerosol particle has long been known to be more effective than freezing induced by the same nucleus immersed in the droplet. However, the experimental quantification of contact freezing is challenging. Here we report an experimental method to determine the temperature-dependent ice nucleation probability of size-selected aerosol particles. The method is based on the suspension of supercooled charged water droplets in a laminar flow of air containing aerosol particles as contact freezing nuclei. The rate of droplet–particle collisions is calculated numerically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. The calculation is verified by direct counting of aerosol particles collected by a levitated droplet. By repeating the experiment on individual droplets for a sufficient number of times, we are able to reproduce the statistical freezing behavior of a large ensemble of supercooled droplets and measure the average rate of freezing events. The freezing rate is equal to the product of the droplet–particle collision rate and the probability of freezing on a single contact, the latter being a function of temperature, size and composition of the contact ice nuclei. Based on these observations, we show that for the types of particles investigated so far, contact freezing is the dominating freezing mechanism on the timescale of our experiment.

Description: δ 18 O water isotope in the i LOVECLIM model (version 1.0) – Part 1: Implementation and verification Geoscientific Model Development, 6, 1481-1491, 2013 Author(s): D. M. Roche A new 18 O stable water isotope scheme is developed for three components of the i LOVECLIM coupled climate model: atmospheric, oceanic and land surface. The equations required to reproduce the fractionation of stable water isotopes in the simplified atmospheric model ECBilt are developed consistently with the moisture scheme. Simplifications in the processes are made to account for the simplified vertical structure including only one moist layer. Implementation of these equations together with a passive tracer scheme for the ocean and a equilibrium fractionation scheme for the land surface leads to the closure of the (isotopic-) water budget in our climate system. Following the implementation, verification of the existence of usual δ 18 O to climatic relationships are performed for the Rayleigh distillation, the Dansgaard relationship and the δ 18 O –salinity relationship. Advantages and caveats of the approach taken are outlined. The isotopic fields simulated are shown to reproduce most expected oxygen-18–climate relationships with the notable exception of the isotopic composition in Antarctica.

Description: Contribution of directly connected and isolated impervious areas to urban drainage network hydrographs Hydrology and Earth System Sciences, 17, 3473-3483, 2013 Author(s): Y. Seo, N.-J. Choi, and A. R. Schmidt This paper addresses the mass balance error observed in runoff hydrographs in urban watersheds by introducing assumptions regarding the contribution of infiltrated rainfall from pervious areas and isolated impervious area (IIA) to the runoff hydrograph. Rainfall infiltrating into pervious areas has been assumed not to contribute to the runoff hydrograph until Hortonian excess rainfall occurs. However, mass balance analysis in an urban watershed indicates that rainfall infiltrated to pervious areas can contribute directly to the runoff hydrograph, thereby offering an explanation for the long hydrograph tail commonly observed in runoff from urban storm sewers. In this study, a hydrologic analysis based on the width function is introduced, with two types of width functions obtained from both pervious and impervious areas, respectively. The width function can be regarded as the direct interpretation of the network response. These two width functions are derived to obtain distinct response functions for directly connected impervious areas (DCIA), IIA, and pervious areas. The results show significant improvement in the estimation of runoff hydrographs and suggest the need to consider the flow contribution from pervious areas to the runoff hydrograph. It also implies that additional contribution from flow paths through joints and cracks in sewer pipes needs to be taken into account to improve the estimation of runoff hydrographs in urban catchments.

Description: δ 18 O water isotope in the i LOVECLIM model (version 1.0) – Part 3: A palaeo-perspective based on present-day data–model comparison for oxygen stable isotopes in carbonates Geoscientific Model Development, 6, 1505-1516, 2013 Author(s): T. Caley and D. M. Roche Oxygen stable isotopes (δ 18 O) are among the most useful tools in palaeoclimatology/palaeoceanography. Simulation of oxygen stable isotopes allows testing how the past variability of these isotopes in water can be interpreted. By modelling the proxy directly in the model, the results can also be directly compared with the data. Water isotopes have been implemented in the global three-dimensional model of intermediate complexity i LOVECLIM, allowing fully coupled atmosphere–ocean simulations. In this study, we present the validation of the model results for present-day climate against the global database for oxygen stable isotopes in carbonates. The limitation of the model together with the processes operating in the natural environment reveal the complexity of use the continental calcite-δ 18 O signal of speleothems for a global quantitative data–model comparison exercise. On the contrary, the reconstructed surface ocean calcite-δ 18 O signal in i LOVECLIM does show a very good agreement with the late Holocene database (foraminifers) at the global and regional scales. Our results indicate that temperature and the isotopic composition of the seawater are the main control on the fossil-δ 18 O signal recorded in foraminifer shells when all species are grouped together. Depth habitat, seasonality and other ecological effects play a more significant role when individual species are considered. We argue that a data–model comparison for surface ocean calcite δ 18 O in past climates, such as the Last Glacial Maximum (≈ 21 000 yr), could constitute an interesting tool for mapping the potential shifts of the frontal systems and circulation changes throughout time. Similarly, the potential changes in intermediate oceanic circulation systems in the past could be documented by a data (benthic foraminifers)-model comparison exercise whereas future investigations are necessary in order to quantitatively compare the results with data for the deep ocean.

Description: Phenology as a strategy for carbon optimality: a global model Biogeosciences Discussions, 10, 15107-15152, 2013 Author(s): S. Caldararu, D. W. Purves, and P. I. Palmer Phenology is essential to our understanding of biogeochemical cycles and the climate system. We develop a global mechanistic model of leaf phenology based on the hypothesis that phenology is a strategy for optimal carbon gain at the canopy level so that trees adjust leaf gains and losses in response to environmental factors such as light, temperature and soil moisture, to achieve maximum carbon assimilation. We fit this model to five years of satellite observations of leaf area index (LAI) using a Bayesian fitting algorithm. We show that our model is able to reproduce phenological patterns for all vegetation types and use it to explore variations in growing season length and the climate factors that limit leaf growth for different biomes. Phenology in wet tropical areas is limited by leaf age physiological constraints while at higher latitude leaf seasonality is limited by low temperature and light availability. Leaf growth in grassland regions is limited by water availability but often in combination with other factors. This model will advance the current understanding of phenology for ecosystem carbon models and our ability to predict future phenological behaviour.

Description: We introduce a method to create lossy versions of one image, either by successively merging the constant regions of the original image, or by iteratively splitting the regions from a created lossy image using horizontal or vertical line segments. Merging and split decisions are greedily taken, according to the best slope towards next point in the rate-distortion curve. For each created lossy image, the region contours and the optimal depth values can be entropy coded in three ways: with a new algorithm, or with two existing lossless coding algorithms. The obtained results compare favorably with the existing lossy methods.

Description: Water reflection, a typical imperfect reflection symmetry problem, plays an important role in image content analysis. Existing techniques of symmetry recognition, however, cannot recognize water reflection images correctly because of the complex and various distortions caused by the water wave. Hence, we propose a novel water reflection recognition technique to solve the problem. First, we construct a novel feature space composed of motion blur invariant moments in low-frequency curvelet space and of curvelet coefficients in high-frequency curvelet space. Second, we propose an efficient algorithm including two sub-algorithms: low-frequency reflection cost minimization and high-frequency curvelet coefficients discrimination to classify water reflection images and to determine the reflection axis. Through experimenting on authentic images in a series of tasks, the proposed techniques prove effective and reliable in classifying water reflection images and detecting the reflection axis, as well as in retrieving images with water reflection.