bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variations of the meteor echo heights at Beijing and Mohe, China
Authors: Liu Libo , Liu Huixin , Chen Yiding , Le Huijun , Sun Yang‐Yi , Ning Baiqi , Hu Lianhuan , Wan Weixing 
Published: December 2016

AbstractDetecting the changing of the upper atmosphere is an important and challenging issue. The change in the meteor peak heights observed by a meteor radar should contain information of the neutral density in the meteoroid ablation region. In this work, observations from the VHF all‐sky meteor radars operated at Beijing (40.3°N, 116.2°E) and Mohe (53.5°N, 122.3°E), China, are collected to explore the temporal patterns of the meteor peak heights. The daily meteor peak height is determined through a least squares fitting of the height profile of meteor radar echoes under a normal distribution assumption. There are considerable seasonal variations in the meteor peak heights, being dominated by an annual component at Beijing and a semiannual one at Mohe. Moreover, the Ensemble Empirical Mode Decomposition (EEMD) is employed to determine the overall trends in the series of the meteor peak heights. The EEMD analysis reveals an overall decrease in the meteor peak heights at both stations, indicating the descending trend in neutral density near 90 km altitude at middle latitudes. The meteor peak heights show a rather weak solar activity effect at Beijing, which is different from the positive effects reported at some other sites.
Hot oxygen escape from Mars: Simple scaling with solar EUV irradiance
Authors: Cravens T. E. , Rahmati A. , Fox Jane L. , Lillis R. , Bougher S. , Luhmann J. , Sakai S. , Deighan J. , Lee Yuni , Combi M. , Jakosky B. 
Published: December 2016

AbstractThe evolution of the atmosphere of Mars and the loss of volatiles over the lifetime of the solar system is a key topic in planetary science. An important loss process for atomic species, such as oxygen, is ionospheric photochemical escape. Dissociative recombination of O2+ ions (the major ion species) produces fast oxygen atoms, some of which can escape from the planet. Many theoretical hot O models have been constructed over the years, although a number of uncertainties are present in these models, particularly concerning the elastic cross sections of O atoms with CO2. Recently, the Mars Atmosphere and Volatile Evolution mission has been rapidly improving our understanding of the upper atmosphere and ionosphere of Mars and its interaction with the external environment (e.g., solar wind), allowing a new assessment of this important loss process. The purpose of the current paper is to take a simple analytical approach to the oxygen escape problem in order to (1) study the role that variations in solar radiation or solar wind fluxes could have on escape in a transparent fashion and (2) isolate the effects of uncertainties in oxygen cross sections on the derived oxygen escape rates. In agreement with several more elaborate numerical models, we find that the escape flux is directly proportional to the incident solar extreme ultraviolet irradiance and is inversely proportional to the backscatter elastic cross section. The amount of O lost due to ion transport in the topside ionosphere is found to be about 5–10% of the total.
Development of intermediate‐scale structure at different altitudes within an equatorial plasma bubble: Implications for L‐band scintillations
Authors: Bhattacharyya A. , Kakad B. , Gurram P. , Sripathi S. , Sunda S. 
Published: December 2016

AbstractAn important aspect of the development of intermediate‐scale length (approximately hundred meters to few kilometers) irregularities in an equatorial plasma bubble (EPB) that has not been considered in the schemes to predict the occurrence pattern of L‐band scintillations in low‐latitude regions is how these structures develop at different heights within an EPB as it rises in the postsunset equatorial ionosphere due to the growth of the Rayleigh‐Taylor instability. Irregularities at different heights over the dip equator map to different latitudes, and their spectrum as well as the background electron density determine the strength of L‐band scintillations at different latitudes. In this paper, VHF and L‐band scintillations recorded at different latitudes together with theoretical modeling of the scintillations are used to study the implications of this structuring of EPBs on the occurrence and strength of L‐band scintillations at different latitudes. Theoretical modeling shows that while S4 index for scintillations on a VHF signal recorded at an equatorial station may be >1, S4 index for scintillations on a VHF signal recorded near the crest of the equatorial ionization anomaly (EIA) generally does not exceed the value of 1 because the intermediate‐scale irregularity spectrum at F layer peak near the EIA crest is shallower than that found in the equatorial F layer peak. This also explains the latitudinal distribution of L‐band scintillations. Thus, it is concluded that there is greater structuring of an EPB on the topside of the equatorial F region than near the equatorial F layer peak.
Three‐scale structure of diffusion region in the presence of cold ions
Authors: Divin A. , Khotyaintsev Yu. V. , Vaivads A. , André M. , Toledo‐Redondo S. , Markidis S. , Lapenta G. 
Published: December 2016

AbstractKinetic simulations and spacecraft observations typically display the two‐scale structure of collisionless diffusion region (DR), with electron and ion demagnetization scales governing the spatial extent of the DR. Recent in situ observations of the nightside magnetosphere, as well as investigation of magnetic reconnection events at the Earth's magnetopause, discovered the presence of a population of cold (tens of eV) ions of ionospheric origin. We present two‐dimensional particle‐in‐cell simulations of collisionless magnetic reconnection in multicomponent plasma with ions consisting of hot and cold populations. We show that a new cold ion diffusion region scale is introduced in between that of hot ions and electrons. Demagnetization scale of cold ion population is several times (∼4–8) larger than the initial cold ion gyroradius. Cold ions are accelerated and thermalized during magnetic reconnection and form ion beams moving with velocities close to the Alfvén velocity.
Spatiotemporal variations of characteristic repeating earthquake sequences along the Middle America Trench in Mexico
Authors: Dominguez Luis A. , Taira Taka'aki , Santoyo Miguel A. 
Published: December 2016

AbstractSearching for repeating earthquakes allows the examination of spatiotemporal variation of slip budget in the subduction of the Cocos plate in the Guerrero‐Oaxaca region of Mexico. As different transient phenomena continuously load and unload stresses around asperities in an area where megathrust earthquakes nucleate, repeating earthquakes act as track markers for slip on the plate interface. We systematically examined 14 years of waveform records from 2001 through 2014 to identify repeating earthquakes along the subducting segment of the Cocos plate. An analysis of waveform similarity resulted in a significant number (224) of earthquake sequences with highly correlated waveforms (correlation coefficient cc ≥ 0.95 and spectral coherency coh ≥ 0.95). The reported set of correlated waveforms shows a well‐defined clustering in space and substantial temporal variability. We find a significant increase of repeating earthquake activity after the 20 March 2012 Ometepec (Mw7.4) and 18 April 2014 Tecpan (Mw7.2) earthquakes as a result of the postseismic relaxation. In contrast, the rupture zone of the 1985 (Mw8.1) Michoacán earthquake is completely devoid of repeating sequences, suggesting a strongly coupled segment. Examining the temporal behavior of repeating earthquake activity provides a new tool to better understand how creeping of the subduction thrust controls stress release and postseismic relaxation.
Uppermost mantle seismic velocity structure beneath USArray
Authors: Buehler J. S. , Shearer P. M. 
Published: December 2016

AbstractWe apply Pn tomography beneath the entire USArray footprint to image uppermost mantle velocity structure and anisotropy, as well as crustal thickness constraints, beneath the United States. The sparse source distribution in the eastern United States and the resulting longer raypaths provide new challenges and justify the inclusion of additional parameters that account for the velocity gradient in the mantle lid. At large scale, Pn velocities are higher in the eastern United States compared to the west, but we observe patches of lower velocities around the New Madrid seismic zone and below the eastern Appalachians. For much of the mantle lid below the central and eastern United States we find a moderate positive velocity gradient. In the western United States, we observe a moderate gradient in the region of the Juan de Fuca subduction zone, but no significant gradient to the south and east of this region. In terms of anisotropy, we find that the Pn fast axes generally do not agree with SKS splitting orientations, suggesting significant vertical changes in anisotropy in the upper mantle. In particular the circular pattern of the fast polarization direction of SKS in the western United States is much less pronounced in the Pn results, and in the eastern US the dominant Pn fast direction is approximately north‐south, whereas the SKS fast polarizations are oriented roughly parallel to the absolute plate motion direction.
Isoprene suppression of new particle formation: Potential mechanisms and implications
Authors: Lee Shan‐Hu , Uin Janek , Guenther Alex B. , de Gouw Joost A. , Yu Fangqun , Nadykto Alex B. , Herb Jason , Ng Nga L. , Koss Abigail , Brune William H. , Baumann Karsten , Kanawade Vijay P. , Keutsch Frank N. , Nenes Athanasios , Olsen Kevin , Goldstein Allen , Ouyang Qi 
Published: December 2016

AbstractSecondary aerosols formed from anthropogenic pollutants and natural emissions have substantial impacts on human health, air quality, and the Earth's climate. New particle formation (NPF) contributes up to 70% of the global production of cloud condensation nuclei (CCN), but the effects of biogenic volatile organic compounds (BVOCs) and their oxidation products on NPF processes in forests are poorly understood. Observations show that isoprene, the most abundant BVOC, suppresses NPF in forests. But the previously proposed chemical mechanism underlying this suppression process contradicts atmospheric observations. By reviewing observations made in other forests, it is clear that NPF rarely takes place during the summer when emissions of isoprene are high, even though there are sufficient concentrations of monoterpenes. But at present it is not clear how isoprene and its oxidation products may change the oxidation chemistry of terpenes and how NOx and other atmospheric key species affect NPF in forest environments. Future laboratory experiments with chemical speciation of gas phase nucleation precursors and clusters and chemical composition of particles smaller than 10 nm are required to understand the role of isoprene in NPF. Our results show that climate models can overpredict aerosol's first indirect effect when not considering the absence of NPF in the southeastern U.S. forests during the summer using the current nucleation algorithm that includes only sulfuric acid and total concentrations of low‐volatility organic compounds. This highlights the importance of understanding NPF processes as function of temperature, relative humidity, and BVOC compositions to make valid predictions of NPF and CCN at a wide range of atmospheric conditions.
The influence of ozone forcing on blocking in the Southern Hemisphere
Authors: Dennison Fraser W. , McDonald Adrian , Morgenstern Olaf 
Published: December 2016

AbstractWe investigate the influence of ozone depletion and recovery on tropospheric blocking in the Southern Hemisphere. Blocking events are identified using a persistent positive anomaly method applied to 500 hPa geopotential height. Using the National Institute for Water and Atmospheric Research‐United Kingdom Chemistry and Aerosols chemistry‐climate model, we compare reference runs that include forcing due to greenhouse gases (GHGs) and ozone‐depleting substances to sensitivity simulations in which ozone‐depleting substances are fixed at their 1960 abundances and other sensitivity simulations with GHGs fixed at their 1960 abundances. Blocking events in the South Atlantic are shown to follow stratospheric positive anomalies in the Southern Annular Mode (SAM) index; this is not the case for South Pacific blocking events. This relationship means that summer ozone depletion, and corresponding positive SAM anomalies, leads to an increased frequency of blocking in the South Atlantic while having little effect in the South Pacific. Similarly, ozone recovery, having the opposite effect on the SAM, leads to a decline in blocking frequency in the South Atlantic, although this may be somewhat counteracted by the effect of increasing GHGs.
Development of an improved aerosol product over the Indian subcontinent: Blending model, satellite, and ground‐based estimates
Authors: Singh Randhir , Singh Charu , Ojha Satya P. , Kumar A. Senthil , Kumar A. S. Kiran 
Published: December 2016

AbstractA comprehensive assessment of the aerosol optical depth (AOD) at 550 nm from European Centre for Medium‐Range Weather Forecasts (ECMWF), Moderate Resolution Imaging Spectroradiometer (MODIS), and Multiangle Imaging Spectroradiometer (MISR) has been performed with respect to the Aerosol Robotic Network (AERONET) measurements at 35 locations over the Indian subcontinent. For all of the stations, the mean relative errors for the collocated ECMWF, MODIS, and MISR AOD are 46.15%, 41.81%, and 39.98%, respectively. Compared with AERONET, ECMWF estimates suffer from a negative bias, whereas MODIS and MISR estimates suffer from a positive bias. The correlation of ECMWF, MODIS, and MISR AOD with AERONET observation is 0.73, 0.80, and 0.78, respectively. Analysis shows that approximately 52.12% of ECMWF, 60.51% of MODIS, and 62.63% of MISR AOD fall within the error envelopes (± 0.05 ± 0.15AODAERONET) of validation data from AERONET. This analysis indicates that both modeled and space‐based AOD measurements have large discrepancies over the Indian subcontinent. Due to the aerosol's significant role in altering the Earth radiation budget, there is an urgent need to develop an AOD product with reduced error. Therefore, a new AOD product at 550 nm has been developed using an optimum interpolation (OI) technique. For this purpose, a model‐derived AOD from ECMWF, remotely sensed AOD from MODIS, MISR, and in situ measured AOD from AERONET have been blended using the OI technique. A new product has been generated for 13 years (2003 to 2015) at 0.25° by 0.25° latitude/longitude and daily temporal resolution over the Indian subcontinent. When compared with AERONET observations, the new product has a negligible bias, with a mean relative error of 12.31% and a correlation of 0.99.
Sensitivity of midnineteenth century tropospheric ozone to atmospheric chemistry‐vegetation interactions
Authors: Hollaway M. J. , Arnold S. R. , Collins W. J. , Folberth G. , Rap A. 
Published: December 2016

AbstractWe use an Earth System model (HadGEM2‐ES) to investigate the sensitivity of midnineteenth century tropospheric ozone to vegetation distribution and atmospheric chemistry‐vegetation interaction processes. We conduct model experiments to isolate the response of midnineteenth century tropospheric ozone to vegetation cover changes between the 1860s and present day and to CO2‐induced changes in isoprene emissions and dry deposition over the same period. Changes in vegetation distribution and CO2 suppression of isoprene emissions between midnineteenth century and present day lead to decreases in global isoprene emissions of 19% and 21%, respectively. This results in increases in surface ozone over the continents of up to 2 ppbv and of 2–6 ppbv in the tropical upper troposphere. The effects of CO2 increases on suppression of isoprene emissions and suppression of dry deposition to vegetation are small compared with the effects of vegetation cover change. Accounting for present‐day climate in addition to present‐day vegetation cover and atmospheric CO2 concentrations leads to increases in surface ozone concentrations of up to 5 ppbv over the entire northern hemisphere (NH) and of up to 8 ppbv in the NH free troposphere, compared with a midnineteenth century control simulation. Ozone changes are dominated by the following: (1) the role of isoprene as an ozone sink in the low NOx midnineteenth century atmosphere and (2) the redistribution of NOx to remote regions and the free troposphere via PAN (peroxyacetyl nitrate) formed from isoprene oxidation. We estimate a tropospheric ozone radiative forcing of 0.264 W m−2 and a sensitivity in ozone radiative forcing to midnineteenth century to present‐day vegetation cover change of −0.012 W m−2.
Japanese space weather research activities
Authors: Ishii M. 
Published: December 2016

AbstractIn this paper, we present existing and planned Japanese space weather research activities. The program consists of several core elements, including a space weather prediction system using numerical forecasts, a large‐scale ground‐based observation network, and the cooperative framework “Project for Solar‐Terrestrial Environment Prediction (PSTEP)” based on a Grant‐in Aid for Scientific Research on Innovative Areas.
Ethyl 2‐(tert‐Butoxycarbonyloxyimino)‐2‐cyanoacetate (Boc‐Oxyma): An Efficient Reagent for the Racemization Free Synthesis of Ureas, Carbamates and Thiocarbamates via Lossen Rearrangement
Authors: Manne Srinivasa Rao , Thalluri Kishore , Giri Rajat Subhra , Chandra Jyoti , Mandal Bhubaneswar 
Published: December 2016

AbstractBoc‐Oxyma (Ethyl 2‐(tert‐butoxycarbonyloxyimino)‐2‐cyanoacetate) has been reported previously as an efficient coupling reagent for the synthesis of amides, peptides, esters, thioesters and hydroxamic acids. It is known for its excellent racemization suppression capability, and also as an environment friendly reagent as it generates only Oxyma as solid byproduct that can be recovered easily and recycled for the synthesis of the same reagent. In this update, we report a simple, efficient, environment friendly, chemoselective and racemization free method for the synthesis of ureas, carbamates and thiocarbamates from hydroxamic acids via Lossen rearrangement by using Boc‐Oxyma. We have achieved racemization free di‐ and tri‐peptidyl ureas with very good yield by using this protocol. A rigorous mechanistic investigation is also incorporated.magnified image
Au108S24(PPh3)16: Bestätigung des allgemeinen Konzeptes metalloider Cluster durch einen hochsymmetrischen nanoskaligen Goldcluster
Authors: Kenzler Sebastian , Schrenk Claudio , Schnepf Andreas 
Published: December 2016

AbstractDie Reduktion von (Ph3P)AuCl mit NaBH4 in Gegenwart von HSC(SiMe3)3 führt zu einem der größten bisher beschriebenen metalloiden Goldcluster: Au108S24(PPh3)16 (1). In 1 sind die Goldatome im zentralen oktaedrischen Au44‐Kern wie in metallischem Gold angeordnet und von 48 oxidierten Goldatomen einer Au48S24‐Schale, einem neuartigen Baustein in der Goldchemie, umgeben. Die schützende Au48S24‐Schale wird durch 16 zusätzliche Au(PPh3)‐Einheiten abgeschlossen, was zu einer kompletten Abschirmung des Goldkerns führt. In 1 werden die Au‐Au‐Abstände von innen nach außen stärker molekular. 1 zeigt neue Strukturmotive im Bereich metalloider Goldcluster, die zum Teil jedoch typisch für Metallatome in metalloiden Clustern [MnRm (n>m)] sind.
AIEgen with Fluorescence–Phosphorescence Dual Mechanoluminescence at Room Temperature
Authors: Yang Jie , Ren Zichun , Xie Zongliang , Liu Yingjie , Wang Can , Xie Yujun , Peng Qian , Xu Bin , Tian Wenjing , Zhang Fan , Chi Zhenguo , Li Qianqian , Li Zhen 
Published: December 2016

AbstractWe report the first example of an AIEgen (DPP‐BO) with fluorescence–phosphorescence dual emission under mechanical stimulation. By carefully analyzing the crystal structure of DPP‐BO, the efficient intermolecular and intramolecular interactions should account for its unique mechanoluminescence (ML) properties, especially the abnormal phosphorescence, as further confirmed by controlled experiments and theoretical calculations for the presence of ISC transitions. These results provide important information for understanding the complex ML process, possibly opening up a new way to study the inherent mechanism of ML by broadening the application of AIEgens.
Pre‐contact fish choice and foraging efficiency at Tula, American Sāmoa
Authors: RIETH TIMOTHY M. , MORRISON ALEX E. 
Published: December 2016

ABSTRACTMarine foraging is an under‐studied aspect of Sāmoan archaeology, although it clearly played a primary role in subsistence, with implications for settlement and demography. A pair of previous ichthyoarchaeological studies identified general stability in fish exploitation during ∼1500–2000 year sequences. We present a foraging‐theory‐based analysis of fish remains from Tula Village, Tutuila Island. Our results identify a decrease in foraging efficiency, but there is no unequivocal evidence for resource depression. To frame this issue at a broader level, we re‐analyse published data for Fatu‐ma‐Futi, Tutuila Island, and To‘aga, Ofu Island. Our results are consistent with previous analyses in suggesting little change in the prevalence of particular fish families and the contribution of large‐bodied prey at these two sites. However, a degree of localised variability in dominant fish taxa is evident. Our analysis has implications for studies of resilience in nearshore marine environments, as well as methodological issues for data generated to examine foraging efficiency and resource depression.
Tandem Thorpe Reaction/Palladium Catalyzed Asymmetric Allylic Alkylation: Access to Chiral β‐enaminonitriles with Excellent Enantioselectivity
Authors: Bai Da‐Chang , Liu Xiu‐Yan , Li Hao , Ding Chang‐Hua , Hou Xue‐Long 
Published: December 2016

AbstractA new type of nucleophile, a 3‐imino nitrile carbanion generated in situ by Thorpe reaction of acetonitrile with a base, was developed successfully and applied in a Pd‐catalyzed asymmetric allylic alkylation with mono‐substituted allyl reagents under Pd/SIOCPhox catalysis, affording β‐enaminonitrile products in high yields with excellent regio‐ and enantioselectivities.
Teaching young children to make accurate portion size estimations using a stimulus equivalence paradigm
Authors: Hausman Nicole L. , Borrero John C. , Fisher Alyssa , Kahng SungWoo 
Published: December 2016

The prevalence of obesity among children and adolescents has increased over the past four decades. Obesity can be conceptualized as a problem related to energy balance, where more energy is consumed than is expended through physical activity. One way that children may have a positive energy balance is through the overconsumption of foods (i.e., eating large portion sizes). Therefore, interventions that teach children to make accurate portion size estimations may be important to maintain overall health. In the current study, seven children between the ages of 4 and 7 years were taught to make accurate portion size estimations using a stimulus equivalence paradigm. Results suggested that the stimulus equivalence paradigm was effective in teaching five of seven participants to make more accurate portion size estimations during posttraining. Furthermore, five of seven participants estimated the target portion size of a novel food during extension sessions. These findings extend the current literature related to teaching children to make accurate portion size estimations. Although this was a translational study, results might help to inform existing nutrition education programs aimed at teaching children healthier eating habits.