bluuebunny/crossref_metadata_2025_split huggingface dataset:
Digital Control
Authors: Yamamoto Yutaka , Nagahara Masaaki 
Published: February 2018

AbstractThis article gives a brief account on digital control, particularly sampled‐data control where signals are sampled with a uniform rate. We first review basic notions such as sampling and hold, digital‐to‐analog (DA) converter, z‐transform, and pulse transfer functions. The relationship of sampling theorem with aliasing and controllability is also reviewed. We then discuss standard classical design methodologies and problems inherent to them. The problem lies in the fact that sampled‐data systems operate on two time sets ‐ continuous and discrete. This is usually the cause of difficulties encountered in the classical design methods, in particular the oscillatory intersample behavior called ripples. This problem is resolved by introducing a new technique called lifting. It is seen that lifting makes linear continuous‐time time‐invariant plant an infinite‐dimensional discrete‐time system, thereby making the total system a time‐invariant discrete‐time system. Time‐invariant notions, such as steady‐state response, frequency response, transfer functions, can then be fully recovered. This framework makes it possible to formulate and solve robust control such as H2 and H‐infinity control and improve upon the continuous‐time performance dramatically. The same design philosophy is then applied to digital signal processing, where one can use this robust control method to optimize the intersample signals optimally. Robust sampled‐data control is suitably applied to the signal processing context, and is seen to optimally reproduce intersample high‐frequency signals. Applications to digital signal processing are discussed. The article concludes with reviews on the existing literature and recent advances in sampled‐data control as well as discussing some future directions.
Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017
Authors: Aiuppa Alessandro , de Moor J. Maarten , Arellano Santiago , Coppola Diego , Francofonte Vincenzo , Galle Bo , Giudice Gaetano , Liuzzo Marco , Mendoza Elvis , Saballos Armando , Tamburello Giancarlo , Battaglia Angelo , Bitetto Marcello , Gurrieri Sergio , Laiolo Marco , Mastrolia Andrea , Moretti Roberto 
Published: February 2018

AbstractA vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented‐long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2 rich, as testified by high CO2/SO2 ratios (mean: 12.2 ± 6.3) and low H2O/CO2 ratios (mean: 2.3 ± 1.3). The volcanic CO2 flux also peaked in November 2015 (mean: 81.3 ± 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile‐rich fast‐overturning (3.6–5.2 m3 s−1) magma, supplying CO2‐rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite‐based MODIS thermal observations), the gas emissions transitioned to more SO2‐rich composition, and the SO2 flux increased by a factor ∼40% (11.4 ± 5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 versus ∼3 m3 s−1) shallow magma convection. Based on thermal energy records, we estimate that only ∼0.8 of the 4.4 m3 s−1 of magma actually reached the surface to manifest into a convecting lava lake, suggesting inefficient transport of magma in the near‐surface plumbing system.
Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere
Authors: Andriopoulou Maria , Nakamura Rumi , Wellenzohn Simon , Torkar Klaus , Baumjohann Wolfgang , Torbert R. B. , Lindqvist Per‐Arne , Khotyaintsev Yuri V. , Dorelli John , Burch James L. 
Published: February 2018

AbstractUsing spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.
Crustal Metasomatism at the Slab‐Mantle Interface in a Continental Subduction Channel: Geochemical Evidence From Orogenic Peridotite in the Sulu Orogen
Authors: Li Hai‐Yong , Chen Ren‐Xu , Zheng Yong‐Fei , Hu Zhaochu , Xu Lijuan 
Published: February 2018

AbstractTo understand crust‐mantle interactions in a continental subduction channel, we carried out a combined study of whole‐rock elements and Sr‐Nd isotopes, mineral elements, and whole‐rock and mineral O isotopes in orogenic peridotite and its host gneiss from the Sulu orogen in China. The results indicate that the peridotite originated from highly depleted subcontinental lithospheric mantle beneath the North China Craton and underwent three episodes of metasomatism via crustally derived fluids. The peridotite was offscraped from the subcontinental lithospheric mantle wedge base and experienced petrographic transformation from a spinel peridotite to a garnet peridotite during continental subduction from forearc to subarc depths. The peridotite underwent the first episode of metasomatism via aqueous solutions at high‐pressure conditions. Afterward, the peridotite underwent a second episode of metasomatism by carbonate melts at ultrahigh‐pressure conditions and a third episode of metasomatism by aqueous solutions at high‐pressure conditions. While the aqueous solution was derived from the metamorphic dehydration of the subducting/exhuming continental crust at the forearc depths, the carbonate melts were produced by partial melting of the ultrahigh‐pressure metasedimentary rocks in the exhuming continental crust at subarc depths. These metasomatic agents did not originate from the gneiss directly hosting the peridotite but from another part of the deeply subducted continental crust that was not in direct contact with the peridotite. Therefore, the orogenic peridotite recorded the geochemical transfer from the subducting crust into the mantle in the continental subduction zone.
Locations of Injection‐Induced Earthquakes in Oklahoma Controlled by Crustal Structures
Authors: Pei Shunping , Peng Zhigang , Chen Xiaowei 
Published: February 2018

AbstractIn recent years, many small‐ to moderate‐size earthquakes occurred in central northern Oklahoma, likely associated with wastewater injection. The most recent one is the M5.8 Pawnee earthquake occurred on 3 September 2016. It is still not clear what controls the locations of these injection‐induced earthquakes. Here we conduct 2‐D Pg wave tomography with anisotropy to image seismogenic structures in this region, using more than 10 years of Pg arrivals recorded by 81 seismic stations. Our high‐resolution Pg wave tomography shows two high‐velocity zones with northwest fast direction alternated by low‐velocity zones with northeast fast direction. The two dominant anisotropy directions are consistent with conjugated microfractures from surface faults and two nodal planes from focal mechanisms of moderate‐size earthquakes. Most moderate‐size (M > 4) earthquakes occurred either close to the boundaries between high‐ and low‐seismic velocity zones or within the high‐velocity zones, suggesting that they are associated with geological boundaries of different basement rock properties or with strong material properties in the upper crust. We suggest that although these moderate‐size earthquakes were induced by fluid injection, their spatial locations were likely controlled by local geologic structures.
Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography
Authors: Halpaap Felix , Rondenay Stéphane , Ottemöller Lars 
Published: February 2018

AbstractThe Western Hellenic Subduction Zone is characterized by a transition from oceanic to continental subduction. In the southern oceanic portion of the system, abundant seismicity reaches depths of 100 km to 190 km, while the northern continental portion rarely exhibits deep earthquakes. Our study investigates how this oceanic‐continental transition affects fluid release and related seismicity along strike. We present results from local earthquake tomography and double‐difference relocation in conjunction with published images based on scattered teleseismic waves. Our tomographic images recover both subducting oceanic and continental crusts as low‐velocity layers on top of high‐velocity mantle. Although the northern and southern trenches are offset along the Kephalonia Transform Fault, continental and oceanic subducting crusts appear to align at depth. This suggests a smooth transition between slab retreat in the south and slab convergence in the north. Relocated hypocenters outline a single‐planed Wadati‐Benioff Zone with significant along‐strike variability in the south. Seismicity terminates abruptly north of the Kephalonia Transform Fault, likely reflecting the transition from oceanic to continental subducted crust. Near 90 km depth, the low‐velocity signature of the subducting crust fades out and the Wadati‐Benioff Zone thins and steepens, marking the outline of the basalt‐eclogite transition. Subarc melting of the mantle is only observed in the southernmost sector of the oceanic subduction, below the volcanic part of the arc. Beneath the nonvolcanic part, the overriding crust appears to have undergone large‐scale silica enrichment. This enrichment is observed as an anomalously low Vp/Vs ratio and requires massive transport of dehydration‐derived fluids updip through the subducting crust.
First Reprocessing of Southern Hemisphere ADditional OZonesondes Profile Records: 3. Uncertainty in Ozone Profile and Total Column
Authors: Witte Jacquelyn C. , Thompson Anne M. , Smit Herman G. J. , Vömel Holger , Posny Françoise , Stübi Rene 
Published: February 2018

AbstractReprocessed ozonesonde data from eight SHADOZ (Southern Hemisphere ADditional OZonesondes) sites have been used to derive the first analysis of uncertainty estimates for both profile and total column ozone (TCO). The ozone uncertainty is a composite of the uncertainties of the individual terms in the ozone partial pressure (PO3) equation, those being the ozone sensor current, background current, internal pump temperature, pump efficiency factors, conversion efficiency, and flow rate. Overall, PO3 uncertainties (ΔPO3) are within 15% and peak around the tropopause (15 ± 3 km) where ozone is a minimum and ΔPO3 approaches the measured signal. The uncertainty in the background and sensor currents dominates the overall ΔPO3 in the troposphere including the tropopause region, while the uncertainties in the conversion efficiency and flow rate dominate in the stratosphere. Seasonally, ΔPO3 is generally a maximum in the March–May, with the exception of SHADOZ sites in Asia, for which the highest ΔPO3 occurs in September–February. As a first approach, we calculate sonde TCO uncertainty (ΔTCO) by integrating the profile ΔPO3 and adding the ozone residual uncertainty, derived from the McPeters and Labow (2012, doi:10.1029/2011JD017006) 1σ ozone mixing ratios. Overall, ΔTCO are within ±15 Dobson units (DU), representing ~5–6% of the TCO. Total Ozone Mapping Spectrometer and Ozone Monitoring Instrument (TOMS and OMI) satellite overpasses are generally within the sonde ΔTCO. However, there is a discontinuity between TOMS v8.6 (1998 to September 2004) and OMI (October 2004–2016) TCO on the order of 10 DU that accounts for the significant 16 DU overall difference observed between sonde and TOMS. By comparison, the sonde‐OMI absolute difference for the eight stations is only ~4 DU.
Foehn Event Triggered by an Atmospheric River Underlies Record‐Setting Temperature Along Continental Antarctica
Authors: Bozkurt D. , Rondanelli R. , Marín J. C. , Garreaud R. 
Published: February 2018

AbstractA record‐setting temperature of 17.5°C occurred on 24 March 2015 at the Esperanza station located near the northern tip of the Antarctic Peninsula (AP). We studied the event using surface station data, satellite imagery, reanalysis data, and numerical simulations. The Moderate Resolution Imaging Spectroradiometer Antarctic Ice Shelf Image Archive provides clear evidence for disintegration and advection of sea ice, as well as the formation of melt ponds on the ice sheet surface at the base of the AP mountain range. A deep low‐pressure center over the Amundsen‐Bellingshausen Sea and a blocking ridge over the southeast Pacific provided favorable conditions for the development of an atmospheric river with a northwest‐southeast orientation, directing warm and moist air toward the AP, and triggering a widespread foehn episode. A control simulation using a regional climate model shows the existence of local topographically induced warming along the northern tip of the AP (∼60% of the full temperature signal) and the central part of the eastern AP (>90% of the full temperature signal) with respect to a simulation without topography. These modeling results suggest that more than half of the warming experienced at Esperanza can be attributed to the foehn effect (a local process), rather than to the large‐scale advection of warm air from the midlatitudes. Nevertheless, the local foehn effect also has a large‐scale advection component, since the atmospheric river provides water vapor for orographic precipitation enhancement and latent heat release, which makes it difficult to completely disentangle the role of local versus large‐scale processes in explaining the extreme event.
A Comparison of the Response of the Hadley Circulation to Different Tropical SST Meridional Structures During the Equinox Seasons
Authors: Feng Juan , Li Jianping , Jin Fei‐Fei , Zheng Fei 
Published: February 2018

AbstractThe response of the Hadley circulation (HC) to different tropical sea surface temperature (SST) patterns during the equinox seasons (i.e., boreal spring and autumn) is analyzed. Although the HC shows quasi‐equatorially symmetric structure in both equinox seasons, both the climatology and the interannual variations of the HC display considerable differences, that is, being more equatorially asymmetric (symmetric) during autumn (spring). After decomposing the variations of the HC and zonal SST into the equatorially asymmetric (i.e., HC's equatorially asymmetric variation (HEA) for HC and SST's equatorially asymmetric variation (SEA) for SST) and symmetric (i.e., HC's equatorially symmetric variation (HES) for HC and SST's equatorially symmetric variation (SES) for SST) components, the differences in the HC between spring and autumn are shown to derive mainly from the HEA. Meanwhile, the contrast in the response of the HEA to SEA against HES to SES is greater in spring than in autumn, suggesting the HC is more sensitive to the SST conditions in spring. The variation of the HEA is related to different signals in spring and autumn that is linked to the central Pacific El Niño during spring but to the Atlantic Multidecadal Oscillation during autumn. The different contributors are associated with the differences in both the spatial extent and temporal variations in the HEA. In contrast, both spring and autumn HES are closely linked to the canonical El Niño, favoring similar variations in spring and autumn HES. The results here provide a possible explanation of the different variations in the HC during spring and autumn and highlight the seasonal dependence of the response of the HC to SST.
An Assessment of Regional Variations in Martian Modified Impact Crater Morphology
Authors: Craddock Robert A. , Bandeira Lourenço , Howard Alan D. 
Published: February 2018

AbstractImpact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by eolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding landscape. To look for signs of potential regional differences in crater modification processes, we conducted an analysis of different morphometric parameters related to modified impact craters located in the Margaritifer Sinus, Sinus Sabaeus, Iapygia, Mare Tyrrhenum, Aeolis, and Eridania quadrangles, including depth, crater wall slope, crater floor slope, the curvature between the interior wall and the crater floor slope, and the curvature between the interior wall and surrounding landscape. A Welch's t test analysis comparing these parameters shows that fresh impact craters (Type 4) have consistent morphologies regardless of their geographic location examined in this study, which is not unexpected. Modified impact craters both in the initial (Type 3) and terminal stages (Type 1) of modification also have statistically consistent morphologies. This would suggest that the processes that operated in the late Noachian were globally ubiquitous, and that modified craters eventually reached a stable crater morphology. However, craters preserved in advanced (but not terminal) stages of modification (Type 2) have morphologies that vary across the quadrangles. It is possible that these variations reflect spatial differences in the types and intensity of geologic processes that operated during the Noachian, implying that the ancient climate also varied across regions.
Effect of Mars Atmospheric Loss on Snow Melt Potential in a 3.5 Gyr Mars Climate Evolution Model
Authors: Mansfield Megan , Kite Edwin S. , Mischna Michael A. 
Published: February 2018

AbstractPost‐Noachian Martian paleochannels indicate the existence of liquid water on the surface of Mars after about 3.5 Gya (Irwin et al., 2015, https://doi.org/10.1016/j.geomorph.2014.10.012; Palucis et al., 2016, https://doi.org/10.1002/2015JE004905). In order to explore the effects of variations in CO2 partial pressure and obliquity on the possibility of surface water, we created a zero‐dimensional surface energy balance model. We combine this model with physically consistent orbital histories to track conditions over the last 3.5 Gyr of Martian history. We find that melting is allowed for atmospheric pressures corresponding to exponential loss rates of dP/d
or faster, but this rate is within 0.5σ of the rate calculated from initial measurements made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, if we assume all the escaping oxygen measured by MAVEN comes from atmospheric CO2 (Lillis et al., 2017, https://doi.org/10.1002/2016JA023525; Tu et al., 2015, https://doi.org/10.1051/0004-6361/201526146). Melting at this loss rate matches selected key geologic constraints on the formation of Hesperian river networks, assuming optimal melt conditions during the warmest part of each Mars year (Irwin et al., 2015, https://doi.org/10.1016/j.geomorph.2014.10.012; Kite, Gao, et al., 2017, https://doi.org/10.1038/ngeo3033; Kite, Sneed et al., 2017, https://doi.org/10.1002/2017GL072660; Stopar et al., 2006, https://doi.org/10.1016/j.gca.2006.07.039). The atmospheric pressure has a larger effect on the surface energy than changes in Mars's mean obliquity. These results show that initial measurements of atmosphere loss by MAVEN are consistent with atmospheric loss being the dominant process that switched Mars from a melt‐permitting to a melt‐absent climate (Jakosky et al., 2017, https://doi.org/10.1126/science.aai7721), but non‐CO2 warming will be required if <2 Gya paleochannels are confirmed or if most of the escaping oxygen measured by MAVEN comes from H2O.
Linking Soil Moisture Variation and Abundance of Plants to Geomorphic Processes: A Generalized Model for Erosion‐Uplifting Landscapes
Authors: Ding Junyan , Johnson Edward A. , Martin Yvonne E. 
Published: February 2018

AbstractThe diffusive and advective erosion‐created landscapes have similar structure (hillslopes and channels) across different scales regardless of variations in drivers and controls. The relative magnitude of diffusive erosion to advective erosion (D/K ratio) in a landscape development model controls hillslope length, shape, and drainage density, which regulate soil moisture variation, one of the critical resources of plants, through the contributing area (A) and local slope (S) represented by a topographic index (TI). Here we explore the theoretical relation between geomorphic processes, TI, and the abundance and distribution of plants. We derived an analytical model that expresses the TI with D, K, and A. This gives us the relation between soil moisture variation and geomorphic processes. Plant tolerance curves are used to link plant performance to soil moisture. Using the hypothetical tolerance curves of three plants, we show that the abundance and distribution of xeric, mesic, and hydric plants on the landscape are regulated by the D/K ratio. Where diffusive erosion is the major erosion process (large D/K ratio), mesic plants have higher abundance relative to xeric and hydric plants and the landscape has longer and convex‐upward hillslope and low channel density. Increasing the dominance of advective erosion increases relative abundance of xeric and hydric plants dominance, and the landscape has short and concave hillslope and high channel density.