scholarly journals What are the challenges for modelling isoprene and monoterpene emission dynamics of subarctic plants?

2016 ◽  
Author(s):  
Jing Tang ◽  
Guy Schurgers ◽  
Hanna Valolahti ◽  
Patrick Faubert ◽  
Päivi Tiiva ◽  
...  
Keyword(s):  
Response Curve ◽  
Large Scale ◽  
Ecosystem Model ◽  
The Arctic ◽  
Emission Rates ◽  
Short Term ◽  
Response Curves ◽  
Arctic Plants ◽  
Scale Modelling

Abstract. The Arctic is warming at twice the global average speed, and the warming-induced increases in biogenic volatile organic compounds (BVOC) emissions from arctic plants are expected to be drastic. The current global models' estimations of minimal BVOC emissions from the Arctic are based on very few observations and have been challenged by increasing field data. This study applied a dynamic ecosystem model, LPJ-GUESS, as a platform to investigate short-term and long-term BVOC emission responses to climate warming. Field observations in a subarctic heath tundra with long-term (13 years) warming treatments were extensively used for parameterizing and evaluating BVOC related processes. We proposed an adjusted temperature (T) response curve for arctic plants with much stronger T sensitivity than the commonly-used algorithms for large-scale modelling. The simulated emission responses to 2 °C warming between the adjusted and original T response curves in the model were evaluated against the observed warming responses (WR) at short-term scales. Moreover, the model's responses to higher levels' warming (4 °C and 8 °C) were also investigated as a sensitivity test. The model was able to reproduce vegetation CO2 fluxes as well as day-to-day variability of isoprene and monoterpene emissions. The modelled BVOC WR, especially for isoprene, were better captured by using the adjusted T response curve, comparing with using the original one. A few days' underestimation of leaf T led to the underestimated emission rates as well as WR. During 1999–2012, the modelled annual mean isoprene and monoterpene emissions were 20 and 8 mg C m−2 yr−1, with an increase in emission by 55 % and 57 % for 2 °C summertime warming, respectively. Warming by 4 °C and 8 °C further elevated isoprene emission for all years compared with 2 °C warming, but the impacts on monoterpene emissions levelled off because of a decreased coverage of monoterpene-emitters among the evergreen prostrate dwarf shrubs. The high WR captured by the adjusted T response curve highlight the strong T sensitivity of arctic plants. At short-term scale, the WR seem to be strongly impacted by leaf T; while at long-term scale, the WR are a combined effect of plant functional type (PFT) dynamics as well as instantaneous BVOC responses to warming. The identified essential issues associated with estimating arctic BVOC emissions are: (1) leaf T estimation/extrapolation based on air T; (2) PFT parameterization accounting for BVOC emission features as well as PFT's responses to warming; and (3) representation of vegetation dynamics in the past and the future.

scholarly journals Challenges in modelling isoprene and monoterpene emission dynamics of Arctic plants: a case study from a subarctic tundra heath

2016 ◽  
Vol 13 (24) ◽  
pp. 6651-6667 ◽  
Author(s):  
Jing Tang ◽  
Guy Schurgers ◽  
Hanna Valolahti ◽  
Patrick Faubert ◽  
Päivi Tiiva ◽  
...  
Keyword(s):  
Response Curve ◽  
Large Scale ◽  
Ecosystem Model ◽  
The Arctic ◽  
Short Term ◽  
Response Curves ◽  
Arctic Plants ◽  
Scale Modelling

Abstract. The Arctic is warming at twice the global average speed, and the warming-induced increases in biogenic volatile organic compounds (BVOCs) emissions from Arctic plants are expected to be drastic. The current global models' estimations of minimal BVOC emissions from the Arctic are based on very few observations and have been challenged increasingly by field data. This study applied a dynamic ecosystem model, LPJ-GUESS, as a platform to investigate short-term and long-term BVOC emission responses to Arctic climate warming. Field observations in a subarctic tundra heath with long-term (13-year) warming treatments were extensively used for parameterizing and evaluating BVOC-related processes (photosynthesis, emission responses to temperature and vegetation composition). We propose an adjusted temperature (T) response curve for Arctic plants with much stronger T sensitivity than the commonly used algorithms for large-scale modelling. The simulated emission responses to 2 °C warming between the adjusted and original T response curves were evaluated against the observed warming responses (WRs) at short-term scales. Moreover, the model responses to warming by 4 and 8 °C were also investigated as a sensitivity test. The model showed reasonable agreement to the observed vegetation CO2 fluxes in the main growing season as well as day-to-day variability of isoprene and monoterpene emissions. The observed relatively high WRs were better captured by the adjusted T response curve than by the common one. During 1999–2012, the modelled annual mean isoprene and monoterpene emissions were 20 and 8 mg C m−2 yr−1, with an increase by 55 and 57 % for 2 °C summertime warming, respectively. Warming by 4 and 8 °C for the same period further elevated isoprene emission for all years, but the impacts on monoterpene emissions levelled off during the last few years. At hour-day scale, the WRs seem to be strongly impacted by canopy air T, while at the day–year scale, the WRs are a combined effect of plant functional type (PFT) dynamics and instantaneous BVOC responses to warming. The identified challenges in estimating Arctic BVOC emissions are (1) correct leaf T estimation, (2) PFT parameterization accounting for plant emission features as well as physiological responses to warming, and (3) representation of long-term vegetation changes in the past and the future.

scholarly journals Two Stage Continuous Gesture Recognition Based on Deep Learning

Electronics ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 534
Author(s):  
Huogen Wang
Keyword(s):  
Gesture Recognition ◽  
Large Scale ◽  
Short Term Memory ◽  
Short Term ◽  
Hand Motion ◽  
Spatiotemporal Features ◽  
Spatiotemporal Information ◽  
Video Frames ◽  
Depth Sequences

The paper proposes an effective continuous gesture recognition method, which includes two modules: segmentation and recognition. In the segmentation module, the video frames are divided into gesture frames and transitional frames by using the information of hand motion and appearance, and continuous gesture sequences are segmented into isolated sequences. In the recognition module, our method exploits the spatiotemporal information embedded in RGB and depth sequences. For the RGB modality, our method adopts Convolutional Long Short-Term Memory Networks to learn long-term spatiotemporal features from short-term spatiotemporal features obtained from a 3D convolutional neural network. For the depth modality, our method converts a sequence into Dynamic Images and Motion Dynamic Images through weighted rank pooling and feed them into Convolutional Neural Networks, respectively. Our method has been evaluated on both ChaLearn LAP Large-scale Continuous Gesture Dataset and Montalbano Gesture Dataset and achieved state-of-the-art performance.

scholarly journals Changes to the chemical state of the northern hemisphere atmosphere during the second half of the twentieth century

2016 ◽  
Author(s):  
Mike J. Newland ◽  
Patricia Martinerie ◽  
Emmanuel Witrant ◽  
Detlev Helmig ◽  
David R. Worton ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Major Influence ◽  
Secondary Products ◽  
Alkyl Nitrates ◽  
Mixing Ratios ◽  
Wide Range

Abstract. The NOX (NO and NO2) and HOX (OH and HO2) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NOX and HOX are highly variable in space and time, and so the measurements of these species are of very limited value for examining long term, large scale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the formation of which is dependent on the atmospheric NO / HO2 ratio. We derive long term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 4–5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NOX, lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increase from around 1970 to the late 1990's consistent with large changes to the [NO] / [HO2] ratio in the northern hemisphere atmosphere during this period. These could represent historic changes to NOX sources and sinks. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.

Contrasting tactical and strategic dynamics on a Clausewitz landscape

2019 ◽  
Vol 17 (2) ◽  
pp. 143-153
Author(s):  
Rodrick Wallace
Keyword(s):  
Statistical Models ◽  
Limit Theorems ◽  
Large Scale ◽  
Evolutionary Process ◽  
Short Term ◽  
Local Resources ◽  
Human Organization ◽  
The World ◽  
Short Time

Statistical models based on the asymptotic limit theorems of control and information theories allow formal examination of the essential differences between short-time “tactical” confrontations and a long-term “strategic” conflict dominated by evolutionary process. The world of extended coevolutionary conflict is not the world of sequential “muddling through.” The existential strategic challenge is to take cognitive control of a long-term dynamic in which one may, in fact, be “losing” most short-term confrontations. Winning individual battles can be a relatively direct, if not simple or easy, matter of sufficient local resources, training, and resolve. Winning extended conflicts is not direct, and requires management of subtle coevolutionary phenomena subject to a dismaying punctuated equilibrium more familiar from evolutionary theory than military doctrine. Directed evolution has given us the agricultural base needed for large-scale human organization. Directed coevolution of the inevitable conflicts between the various segments of that organization may be needed for its long-term persistence.

scholarly journals Rapid retreat of permafrost coastline observed with aerial drone photogrammetry

2019 ◽  
Vol 13 (5) ◽  
pp. 1513-1528 ◽  
Author(s):  
Andrew M. Cunliffe ◽  
George Tanski ◽  
Boris Radosavljevic ◽  
William F. Palmer ◽  
Torsten Sachs ◽  
...  
Keyword(s):  
Coastal Erosion ◽  
Average Rate ◽  
Temporal Frequency ◽  
Shoreline Change ◽  
Yukon Territory ◽  
Aerial Photographs ◽  
The Arctic ◽  
Storm Events ◽  
Short Term

Abstract. Permafrost landscapes are changing around the Arctic in response to climate warming, with coastal erosion being one of the most prominent and hazardous features. Using drone platforms, satellite images, and historic aerial photographs, we observed the rapid retreat of a permafrost coastline on Qikiqtaruk – Herschel Island, Yukon Territory, in the Canadian Beaufort Sea. This coastline is adjacent to a gravel spit accommodating several culturally significant sites and is the logistical base for the Qikiqtaruk – Herschel Island Territorial Park operations. In this study we sought to (i) assess short-term coastal erosion dynamics over fine temporal resolution, (ii) evaluate short-term shoreline change in the context of long-term observations, and (iii) demonstrate the potential of low-cost lightweight unmanned aerial vehicles (“drones”) to inform coastline studies and management decisions. We resurveyed a 500 m permafrost coastal reach at high temporal frequency (seven surveys over 40 d in 2017). Intra-seasonal shoreline changes were related to meteorological and oceanographic variables to understand controls on intra-seasonal erosion patterns. To put our short-term observations into historical context, we combined our analysis of shoreline positions in 2016 and 2017 with historical observations from 1952, 1970, 2000, and 2011. In just the summer of 2017, we observed coastal retreat of 14.5 m, more than 6 times faster than the long-term average rate of 2.2±0.1 m a−1 (1952–2017). Coastline retreat rates exceeded 1.0±0.1 m d−1 over a single 4 d period. Over 40 d, we estimated removal of ca. 0.96 m3 m−1 d−1. These findings highlight the episodic nature of shoreline change and the important role of storm events, which are poorly understood along permafrost coastlines. We found drone surveys combined with image-based modelling yield fine spatial resolution and accurately geolocated observations that are highly suitable to observe intra-seasonal erosion dynamics in rapidly changing Arctic landscapes.

scholarly journals Modelling large timescale and small timescale service variability

2019 ◽  
Vol 293 (1) ◽  
pp. 123-140
Author(s):  
Marco Gribaudo ◽  
Illés Horváth ◽  
Daniele Manini ◽  
Miklós Telek
Keyword(s):  
Service Time ◽  
Large Scale ◽  
Service Time Distribution ◽  
Efficient Computation ◽  
Short Term ◽  
Service Unit ◽  
Long Term Effect ◽  
Short And Long Term ◽  
Short Term Variability

Abstract The performance of service units may depend on various randomly changing environmental effects. It is quite often the case that these effects vary on different timescales. In this paper, we consider small and large scale (short and long term) service variability, where the short term variability affects the instantaneous service speed of the service unit and a modulating background Markov chain characterizes the long term effect. The main modelling challenge in this work is that the considered small and long term variation results in randomness along different axes: short term variability along the time axis and long term variability along the work axis. We present a simulation approach and an explicit analytic formula for the service time distribution in the double transform domain that allows for the efficient computation of service time moments. Finally, we compare the simulation results with analytic ones.

scholarly journals Short- and Long-Term Effects of Nonconsciously Processed Ambient Scents in a Servicescape: Findings From Two Field Experiments

2019 ◽  
Vol 22 (4) ◽  
pp. 440-455 ◽  
Author(s):  
Anna Girard ◽  
Marcel Lichters ◽  
Marko Sarstedt ◽  
Dipayan Biswas
Keyword(s):  
Large Scale ◽  
Field Experiments ◽  
Field Studies ◽  
Long Term Effects ◽  
Short Term ◽  
Railway Company ◽  
Short And Long Term ◽  
Ambient Scents ◽  
Short Term Effects

Ambient scents are being increasingly used in different service environments. While there is emerging research on the effects of scents, almost nothing is known about the long-term effects of consumers’ repeated exposure to ambient scents in a service environment as prior studies on ambient scents have been lab or field studies examining short-term effects of scent exposure only. Addressing this limitation, we examine the short- and long-term effects of ambient scents. Specifically, we present a conceptual framework for the short- and long-term effects of nonconsciously processed ambient scent in olfactory-rich servicescapes. We empirically test this framework with the help of two large-scale field experiments, conducted in collaboration with a major German railway company, in which consumers were exposed to a pleasant, nonconsciously processed scent. The first experiment demonstrates ambient scent’s positive short-term effects on consumers’ service perceptions. The second experiment—a longitudinal study conducted over a 4-month period—examines scent’s long-term effects on consumers’ reactions and demonstrates that the effects persist even when the scent has been removed from the servicescape.

Robot perceptual adaptation to environment changes for long-term human teammate following

2020 ◽  
pp. 027836491989662
Author(s):  
Sriram Siva ◽  
Hao Zhang
Keyword(s):  
Large Scale ◽  
Feature Learning ◽  
Optimal Solution ◽  
Human Detection ◽  
Perceptual Adaptation ◽  
Short Term ◽  
Environment Changes ◽  
Depth Sensors ◽  
Robot Perception

Perception is one of the several fundamental abilities required by robots, and it also poses significant challenges, especially in real-world field applications. Long-term autonomy introduces additional difficulties to robot perception, including short- and long-term changes of the robot operation environment (e.g., lighting changes). In this article, we propose an innovative human-inspired approach named robot perceptual adaptation (ROPA) that is able to calibrate perception according to the environment context, which enables perceptual adaptation in response to environmental variations. ROPA jointly performs feature learning, sensor fusion, and perception calibration under a unified regularized optimization framework. We also implement a new algorithm to solve the formulated optimization problem, which has a theoretical guarantee to converge to the optimal solution. In addition, we collect a large-scale dataset from physical robots in the field, called perceptual adaptation to environment changes (PEAC), with the aim to benchmark methods for robot adaptation to short-term and long-term, and fast and gradual lighting changes for human detection based upon different feature modalities extracted from color and depth sensors. Utilizing the PEAC dataset, we conduct extensive experiments in the application of human recognition and following in various scenarios to evaluate ROPA. Experimental results have validated that the ROPA approach obtains promising performance in terms of accuracy and efficiency, and effectively adapts robot perception to address short-term and long-term lighting changes in human detection and following applications.

SECULAR VARIATIONS IN THE 14C CONCENTRATION OF DOUGLAS FIR TREE RINGS

1966 ◽  
Vol 3 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Willy Dyck
Keyword(s):  
Large Scale ◽  
Carbon Fixation ◽  
Douglas Fir ◽  
Sunspot Activity ◽  
Short Term ◽  
Fixation Rate ◽  
Pumping Rate ◽  
Counting Error ◽  
Annual Growth Rings

Measurements of the 14C concentration in a Douglas fir from Vancouver Island indicate a maximum variation of 44‰, during the past 1 100 years. The magnitude and trend of these variations are similar to those observed by de Vries (1958) in oak from Germany and by Willis et al. (1960) in sequoias from California, confirming earlier observations that atmospheric mixing of CO2 takes place rapidly on a large scale.14C measurements of successive annual growth rings from the piths of two firs (346 years and 1 142 years old) show no variations beyond those attributable to the statistical counting error of ± 6‰. Thus, cyclic variations in sunspot activity and (or) climate, if present during these intervals, did not affect the 14C concentration in the biosphere appreciably.A mechanism, based on a climate-sensitive carbon pumping rate of the biosphere coupled with the temperature-dependent oceanic CO2 content is postulated to explain, qualitatively, the observed short-term (150 years or less) and long-term (1 000 years or more) 14C variations in the land biosphere. Short-term fluctuations are directly proportional to temperature because variations in the carbon fixation rate lead to a pulsating CO2 content of the atmosphere. Long-term changes are inversely proportional to temperature because large quantities of carbon, normally stored in deeper regions of the ocean, are exchanged between biosphere and hydrosphere.

scholarly journals Quantitative Monetary Easing and Risk in Financial Asset Markets

2006 ◽  
Vol 6 (1) ◽  
pp. 1-54 ◽  
Author(s):  
Takeshi Kimura ◽  
David H. Small
Keyword(s):  
Interest Rates ◽  
Large Scale ◽  
Corporate Bonds ◽  
Asset Markets ◽  
Low Grade ◽  
Short Term ◽  
Government Bonds ◽  
Risk Premiums ◽  
Portfolio Rebalancing

In this paper, we empirically examine the portfolio-rebalancing effects stemming from the policy of “quantitative monetary easing” recently undertaken by the Bank of Japan when the nominal short-term interest rate was virtually at zero. Portfolio-rebalancing effects resulting from the open market purchase of long-term government bonds under this policy have been statistically significant. Our results also show that the portfolio-rebalancing effects were beneficial in that they reduced risk premiums on assets with counter-cyclical returns, such as government and high-grade corporate bonds. But, they may have generated the adverse effects of increasing risk premiums on assets with pro-cyclical returns, such as equities and low-grade corporate bonds. These results are consistent with a CAPM framework in which business-cycle risk importantly affects risk premiums. Our estimates capture only some of the effects of quantitative easing and thus do not imply that the complete set of effects were adverse on net for Japan’s economy. However, our analysis counsels caution in accepting the view that, ceteris paribus, a massive large-scale purchase of long-term government bonds by a central bank provides unambiguously positive net benefits to financial markets at zero short-term interest rates.

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