bluuebunny/crossref_metadata_2025 huggingface dataset:
Disputas marítimas en el Caribe colombiano: la pesca de tortugas en el archipiélago de San Andrés y Providencia, 1910-1930
Authors: Crawford Sharika
Published: October 2017

There has been a long history of turtle hunting in the Greater Caribbean, especially in Colombian waters around the archipelago of San Andrés and Providence. This article is focused on Colombia’s efforts to affirm its national borders and to strengthen its control over its territorial waters, and on how the new regulations that these measures entail affect turtle hunters in the Caribbean Sea. Using travel stories, newspapers from Jamaica, Colombia and the United States, as well as diplomatic correspondence, interviews and secondary sources, this study analyzes the national and regional implications of these problems. This makes it possible to conclude that the islanders, in the company of Colombian officials, attempted to defend their insular territory and its maritime borders against both real and imaginary threats. Their efforts were aimed at restricting the extraction of marine resources within the country’s territorial waters, as part of the government’s interest in reinforcing the integrity of the Colombian nation-state in the Caribbean.
Neural and computational processes underlying dynamic changes in self-esteem
Authors: Will Geert-Jan , Rutledge Robb B , Moutoussis Michael , Dolan Raymond J
Published: October 2017

Self-esteem is shaped by the appraisals we receive from others. Here, we characterize neural and computational mechanisms underlying this form of social influence. We introduce a computational model that captures fluctuations in self-esteem engendered by prediction errors that quantify the difference between expected and received social feedback. Using functional MRI, we show these social prediction errors correlate with activity in ventral striatum/subgenual anterior cingulate cortex, while updates in self-esteem resulting from these errors co-varied with activity in ventromedial prefrontal cortex (vmPFC). We linked computational parameters to psychiatric symptoms using canonical correlation analysis to identify an ‘interpersonal vulnerability’ dimension. Vulnerability modulated the expression of prediction error responses in anterior insula and insula-vmPFC connectivity during self-esteem updates. Our findings indicate that updating of self-evaluative beliefs relies on learning mechanisms akin to those used in learning about others. Enhanced insula-vmPFC connectivity during updating of those beliefs may represent a marker for psychiatric vulnerability.
AMPylation targets the rate-limiting step of BiP’s ATPase cycle for its functional inactivation
Authors: Preissler Steffen , Rohland Lukas , Yan Yahui , Chen Ruming , Read Randy J , Ron David
Published: October 2017

The endoplasmic reticulum (ER)-localized Hsp70 chaperone BiP contributes to protein folding homeostasis by engaging unfolded client proteins in a process that is tightly coupled to ATP binding and hydrolysis. The inverse correlation between BiP AMPylation and the burden of unfolded ER proteins suggests a post-translational mechanism for adjusting BiP’s activity to changing levels of ER stress, but the underlying molecular details are unexplored. We present biochemical and crystallographic studies indicating that irrespective of the identity of the bound nucleotide AMPylation biases BiP towards a conformation normally attained by the ATP-bound chaperone. AMPylation does not affect the interaction between BiP and J-protein co-factors but appears to allosterically impair J protein-stimulated ATP-hydrolysis, resulting in the inability of modified BiP to attain high affinity for its substrates. These findings suggest a molecular mechanism by which AMPylation serves as a switch to inactivate BiP, limiting its interactions with substrates whilst conserving ATP.
Allosteric fine-tuning of the conformational equilibrium poises the chaperone BiP for post-translational regulation
Authors: Wieteska Lukasz , Shahidi Saeid , Zhuravleva Anastasia
Published: October 2017

BiP is the only Hsp70 chaperone in the endoplasmic reticulum (ER) and similar to other Hsp70s, its activity relies on nucleotide- and substrate-controllable docking and undocking of its nucleotide-binding domain (NBD) and substrate-binding domain (SBD). However, little is known of specific features of the BiP conformational landscape that tune BiP to its unique tasks and the ER environment. We present methyl NMR analysis of the BiP chaperone cycle that reveals surprising conformational heterogeneity of ATP-bound BiP that distinguishes BiP from its bacterial homologue DnaK. This unusual poise enables gradual post-translational regulation of the BiP chaperone cycle and its chaperone activity by subtle local perturbations at SBD allosteric ‘hotspots’. In particular, BiP inactivation by AMPylation of its SBD does not disturb Hsp70 inter-domain allostery and preserves BiP structure. Instead it relies on a redistribution of the BiP conformational ensemble and stabilization the domain-docked conformation in presence of ADP and ATP.
Theta-burst microstimulation in the human entorhinal area improves memory specificity
Authors: Titiz Ali S , Hill Michael R H , Mankin Emily A , M Aghajan Zahra , Eliashiv Dawn , Tchemodanov Natalia , Maoz Uri , Stern John , Tran Michelle E , Schuette Peter , Behnke Eric , Suthana Nanthia A , Fried Itzhak
Published: October 2017

The hippocampus is critical for episodic memory, and synaptic changes induced by long-term potentiation (LTP) are thought to underlie memory formation. In rodents, hippocampal LTP may be induced through electrical stimulation of the perforant path. To test whether similar techniques could improve episodic memory in humans, we implemented a microstimulation technique that allowed delivery of low-current electrical stimulation via 100 μm-diameter microelectrodes. As thirteen neurosurgical patients performed a person recognition task, microstimulation was applied in a theta-burst pattern, shown to optimally induce LTP. Microstimulation in the right entorhinal area during learning significantly improved subsequent memory specificity for novel portraits; participants were able both to recognize previously-viewed photos and reject similar lures. These results suggest that microstimulation with physiologic level currents—a radical departure from commonly used deep brain stimulation protocols—is sufficient to modulate human behavior and provides an avenue for refined interrogation of the circuits involved in human memory.
Many si/shRNAs can kill cancer cells by targeting multiple survival genes through an off-target mechanism
Authors: Putzbach William , Gao Quan Q , Patel Monal , van Dongen Stijn , Haluck-Kangas Ashley , Sarshad Aishe A , Bartom Elizabeth T , Kim Kwang-Youn A , Scholtens Denise M , Hafner Markus , Zhao Jonathan C , Murmann Andrea E , Peter Marcus E
Published: October 2017

Over 80% of multiple-tested siRNAs and shRNAs targeting CD95 or CD95 ligand (CD95L) induce a form of cell death characterized by simultaneous activation of multiple cell death pathways preferentially killing transformed and cancer stem cells. We now show these si/shRNAs kill cancer cells through canonical RNAi by targeting the 3’UTR of critical survival genes in a unique form of off-target effect we call DISE (death induced by survival gene elimination). Drosha and Dicer-deficient cells, devoid of most miRNAs, are hypersensitive to DISE, suggesting cellular miRNAs protect cells from this form of cell death. By testing 4666 shRNAs derived from the CD95 and CD95L mRNA sequences and an unrelated control gene, Venus, we have identified many toxic sequences - most of them located in the open reading frame of CD95L. We propose that specific toxic RNAi-active sequences present in the genome can kill cancer cells.
SAV1 promotes Hippo kinase activation through antagonizing the PP2A phosphatase STRIPAK
Authors: Bae Sung Jun , Ni Lisheng , Osinski Adam , Tomchick Diana R , Brautigam Chad A , Luo Xuelian
Published: October 2017

The Hippo pathway controls tissue growth and homeostasis through a central MST-LATS kinase cascade. The scaffold protein SAV1 promotes the activation of this kinase cascade, but the molecular mechanisms remain unknown. Here, we discover SAV1-mediated inhibition of the PP2A complex STRIPAKSLMAP as a key mechanism of MST1/2 activation. SLMAP binding to autophosphorylated MST2 linker recruits STRIPAK and promotes PP2A-mediated dephosphorylation of MST2 at the activation loop. Our structural and biochemical studies reveal that SAV1 and MST2 heterodimerize through their SARAH domains. Two SAV1–MST2 heterodimers further dimerize through SAV1 WW domains to form a heterotetramer, in which MST2 undergoes trans-autophosphorylation. SAV1 directly binds to STRIPAK and inhibits its phosphatase activity, protecting MST2 activation-loop phosphorylation. Genetic ablation of SLMAP in human cells leads to spontaneous activation of the Hippo pathway and alleviates the need for SAV1 in Hippo signaling. Thus, SAV1 promotes Hippo activation through counteracting the STRIPAKSLMAP PP2A phosphatase complex.
Cross-species functional diversity within the PIN auxin efflux protein family
Authors: O'Connor Devin Lee , Elton Samuel , Ticchiarelli Fabrizio , Hsia Mon Mandy , Vogel John P , Leyser Ottoline
Published: October 2017

In Arabidopsis, development during flowering is coordinated by transport of the hormone auxin mediated by polar-localized PIN-FORMED1 (AtPIN1). However Arabidopsis has lost a PIN clade sister to AtPIN1, Sister-of-PIN1 (SoPIN1), which is conserved in flowering plants. We previously proposed that the AtPIN1 organ initiation and vein patterning functions are split between the SoPIN1 and PIN1 clades in grasses. Here we show that in the grass Brachypodium sopin1 mutants have organ initiation defects similar to Arabidopsis atpin1, while loss of PIN1 function in Brachypodium has little effect on organ initiation but alters stem growth. Heterologous expression of Brachypodium SoPIN1 and PIN1b in Arabidopsis provides further evidence of functional specificity. SoPIN1 but not PIN1b can mediate flower formation in null atpin1 mutants, although both can complement a missense allele. The behavior of SoPIN1 and PIN1b in Arabidopsis illustrates how membrane and tissue-level accumulation, transport activity, and interaction contribute to PIN functional specificity.
Ruin philosophy, poetic discourse and the collapse of meta-narratives in Aleksandr Kushner's poetry of the 1970s
Authors: Schönle Andreas
Published: October 2017

This article offers an analysis of the trope of ruin in the poetry of Aleksandr Kushner (born 1936), in particular through a close reading of two of his poems: “In a slippery graveyard, alone” and “Ruins”. The analysis of these poems is preceded by an overview of ruin philosophy from Burke and Diderot to Simmel and Benjamin, with particular emphasis on the way the trope of ruin contemplation stages a confrontation between the self and what transcends it (death, history, nature, etc.). This philosophical background serves as a heuristic tool to shed light on the poetry of Kushner. Through the trope of ruin, Kushner explores the legitimacy of poetic speech after the collapse of all meta-narratives. Kushner has no truck with Diderot's solipsism, nor with Hegel's bold narrative of progress, nor with Simmel's peaceful reconciliation with the creative forces of nature. Nor, really, does he intend to bear witness to history, the way Benjamin does in the faint anticipation of some miracle. Instead, Kushner posits the endurance of a community united not around a grand project, but around the idea of carrying on in the face of everything, muddling through despite the lack of hopes for a transformational future and making the most of fleeting moments of positivity that emerge out of the fundamental serendipity of history.
Glycaspis brimblecombei (Hemiptera: Psyllidae) attack patterns on different Eucalyptus genotypes
Authors: Tuller Juliana , Oliveira Karla Nunes , Silva Jhonathan Oliveira , de Faria Maurício Lopes , do Espírito-Santo Mario Marcos , Serrão José Eduardo , Zanuncio José Cola
Published: October 2017

Background

The red gum lerp psyllid, Glycaspis brimblecombei Moore (Hemiptera: Psyllidae), an eucalypt insect pest from Australia, was reported in Brazil in 2003. This study evaluated damage patterns of this pest on Eucalyptus camaldulensis Dehn (Myrtaceae) and its hybrids E. urophylla X E. camaldulensis (urocam) and E. urophylla X E. grandis (urograndis). In addition, parasitism rates of Psyllaephagus bliteus Riek (Hymenoptera: Encyrtidae) on G. brimblecombei collected on different eucalypt genotypes are reported.

Methods

Plantation plots of three eucalypt genotypes were evaluated over one year. The eucalypt leaves were collected and examined for attack by G. brimblecombei. Nymph parasitism of G. brimblecombei by P. bliteus was recorded.

Results

Damage by G. brimblecombei was lower on the hybrid genotypes and on the adaxial surface of the eucalypt leaves. G. brimblecombei egg and nymph density were negatively correlated with monthly rainfall. Nymph parasitism of G. brimblecombei by P. bliteus was low (2.9%) independent of genotype and did not vary throughout the year.

Discussion

Our data indicate the use of less susceptible eucalypt genotypes (e.g., hybrids) as an alternative to G. brimblecombei management. Because of the current low mortality rates for G. brimblecombei resulting from P. bliteus parasitism, biological control with this natural enemy is not recommended as a management strategy for G. brimblecombei.
The head turn paradigm to assess auditory laterality in cats: influence of ear position and repeated sound presentation
Authors: Konerding Wiebke S. , Zimmermann Elke , Bleich Eva , Hedrich Hans-Jürgen , Scheumann Marina
Published: October 2017

In most humans, speech is predominantly processed by the left hemisphere. This auditory laterality was formerly thought to be an exclusive human characteristic, but is now suggested to have pre-human origins. In studies on auditory laterality in nonhuman animals, the head turn paradigm has become very popular due to its non-invasive character. Although there are implications that the head turn direction indicates functional dominance of the contralateral hemisphere in processing a given sound, the validity of the paradigm is under debate. To validate the paradigm via comparison with imaging or electrophysiological methods, it is first necessary to establish turning biases at the individual level. Recently, the domestic cat, a common model in hearing research, has been found to show turning biases at the group level. To assess individual turning asymmetries in cats, we repeatedly presented kitten isolation calls and assessed whether differences in conveyed arousal changed the previously described left-wards lateralisation of conspecific vocalizations. Based on responses to 50 playback presentations (25 of high and 25 of low arousal), we calculated individual head turn indices. Based on the total data set, we found no consistent individual turning bias, irrespective of call category or sex of the receiver. Although the playback paradigm was chosen carefully to reduce any effects of lateralized loudness perception or changes in motivation due to habituation, individual head turn biases changed significantly in concordance with habituation to repeated playback-presentations and was predictable by small deflections in ear position prior to listening. When splitting the data set according to a decline in responsiveness after seven playback presentations, we revealed an initial left turning bias for most of our subjects (i.e., significant at the group level). We propose that this left turning bias is related to right hemisphere dominance in processes like vigilance behaviour or general arousal rather than on auditory processing, as such. Our findings suggest that both the experimental sequence and sound level differences, induced by asymmetric ear positions, strongly influence the outcome of the head turn paradigm and should be taken into account when evaluating auditory laterality at the behavioural level.
Statins: antimicrobial resistance breakers or makers?
Authors: Ko Humphrey H.T. , Lareu Ricky R. , Dix Brett R. , Hughes Jeffery D.
Published: October 2017

Introduction

The repurposing of non-antibiotic drugs as adjuvant antibiotics may help break antimicrobial resistance (AMR). Statins are commonly prescribed worldwide to lower cholesterol. They also possess qualities of AMR “breakers”, namely direct antibacterial activity, synergism with antibiotics, and ability to stimulate the host immune system. However, statins’ role as AMR breakers may be limited. Their current extensive use for cardiovascular protection might result in selective pressures for resistance, ironically causing statins to be AMR “makers” instead. This review examines statins’ potential as AMR breakers, probable AMR makers, and identifies knowledge gaps in a statin-bacteria-human-environment continuum. The most suitable statin for repurposing is identified, and a mechanism of antibacterial action is postulated based on structure-activity relationship analysis.

Methods

A literature search using keywords “statin” or “statins” combined with “minimum inhibitory concentration” (MIC) was performed in six databases on 7th April 2017. After screening 793 abstracts, 16 relevant studies were identified. Unrelated studies on drug interactions; antifungal or antiviral properties of statins; and antibacterial properties of mevastatin, cerivastatin, antibiotics, or natural products were excluded. Studies involving only statins currently registered for human use were included.

Results

Against Gram-positive bacteria, simvastatin generally exerted the greatest antibacterial activity (lowest MIC) compared to atorvastatin, rosuvastatin, and fluvastatin. Against Gram-negative bacteria, atorvastatin generally exhibited similar or slightly better activity compared to simvastatin, but both were more potent than rosuvastatin and fluvastatin.

Discussion

Statins may serve as AMR breakers by working synergistically with existing topical antibiotics, attenuating virulence factors, boosting human immunity, or aiding in wound healing. It is probable that statins’ mechanism of antibacterial activity involves interference of bacterial cell regulatory functions via binding and disrupting cell surface structures such as wall teichoic acids, lipoteichoic acids, lipopolysaccharides, and/or surface proteins. The widespread use of statins for cardiovascular protection may favor selective pressures or co-selection for resistance, including dysbiosis of the human gut microbiota, sublethal plasma concentrations in bacteremic patients, and statin persistence in the environment, all possibly culminating in AMR.

Conclusion

Simvastatin appears to be the most suitable statin for repurposing as a novel adjuvant antibiotic. Current evidence better supports statins as potential AMR breakers, but their role as plausible AMR makers cannot be excluded. Elucidating the mechanism of statins’ antibacterial activity is perhaps the most important knowledge gap to address as this will likely clarify statins’ role as AMR breakers or makers.
Ichthyofilaria argentinensis sp. nov. (Nematoda: Philometridae) parasite of Merluccius hubbsi (Pisces: Merlucciidae)
Authors: Silvia-Incorvaia I
Published: October 2017

The present work deals with a new nematode species, Ichthyofilaria argentinensis, found in the swim bladder of the Argentine common hake, Merluccius hubbsi Marini, 1933, from the Southwest Atlantic sector between 34º and 48ºS. Ichthyofilaria argentinensis sp. nov. is characterized by its smooth cuticle and fusiform body. The mouth is simple and does not have lips. The robust oesophagus is divided into two sections, an anterior muscular and a posterior glandular, from which a free glandular appendage arises, directed backwards.
Underway pH measurements in upwelling conditions: The California Current
Authors: Del-Valls TA
Published: October 2017

This paper reports the use of underway spectrophotometric pH as part of a series of measurements (together with underway salinity, temperature and some discrete measurements of chlorophyll a) made in the California Current coastal upwelling area. The values of pH obtained (measured at 25ºC) ranged from 7.6 near the coastline (in the centre of the upwelling) to 8.3 at the western boundary of the study area (close to the oceanic environment); pH values were more uniform away from the influence of upwelling. Variations in the pH, temperature and chlorophyll a were all approximately in phase. In particular, higher pH values –indicative of photosynthetic activity– were well correlated with the chlorophyll a measurements. These results illustrate the need to consider both small and mesoscale processes when investigating carbon dioxide exchange across the air-sea interface in such systems, and also show that spectrophotometric pH measurements are sufficiently sensitive (and can be measured sufficiently rapidly) to describe various biogeochemical processes in such systems.
Induction of metamorphosis with KCl in three species of sea urchins and its implications in the production of juveniles
Authors: Carpizo-Ituarte E , Salas-Garza A , Parés-Sierra G
Published: October 2017

A common practice for inducing metamorphosis in larvae of marine invertebrates is the use of a wide variety of artificial inducers. Excess K+ and Cs+ in seawater have proved to be very effective for this purpose, but not universally effective to induce metamorphosis in different phyla of marine invertebrates. In the present study we tested the response of three species of sea urchins to excess K+ in seawater as an artificial inducer. Excess K+ in seawater was presented to the larvae as continuous (24 h) or pulse exposure in concentrations ranging from 0.01 to 100 mM. Results showed that excess K+ in the form of KCl added to seawater was an effective metamorphic inducer of the three species of sea urchins tested; the purple sea urchin Strongylocentrotus purpuratus, the red sea urchin S. franciscanus and the white sea urchin Lytechinus pictus. The response was dependent on concentration and time of exposure. Continuous exposure (24 h or more) to excess K+ (100 mM) resulted lethal to the larvae of the three species. Excess K+ (100 mM) for 15 min resulted the most effective pulse-period to induce metamorphosis in the three species. This method of induction allows us to produce synchronous metamorphosed postlarvae useful for aquaculture and studies of signal transduction mechanisms during metamorphosis of sea urchins.
The Influence of Crystal Size Distributions on the Rheology of Magmas: New Insights From Analog Experiments
Authors: Klein Johannes , Mueller Sebastian P. , Castro Jonathan M.
Published: October 2017

This study examines the influence of particle‐size distributions on the rheology of particle suspensions by using analog experiments with spherical glass beads in silicone oil as a magma equivalent. The analyses of 274 individual particle‐bearing suspensions of varying modality (unimodality, bimodality, trimodality, and tetramodality), as well as of polymodal suspensions with specific defined skewness and variance, are the first data set of its kind and provide important insights into the relationship between the solid particles of a suspension and its rheological behavior. Since the relationship between the rheology of particle‐bearing suspensions and its maximum packing fraction
is well established by several theoretical models, the results of the analog experiments of this study reveal that the polydispersity γ exerts the largest influence on
. Consequently, the estimation of the polydispersity γ of a particle‐size distribution is essential for estimating the viscosity of that given suspension.
Elastic Anisotropy Reversal During Brittle Creep in Shale
Authors: Geng Zhi , Bonnelye Audrey , Chen Mian , Jin Yan , Dick Pierre , David Christian , Fang Xin , Schubnel Alexandre
Published: October 2017

We conducted two brittle creep experiments on shale samples under upper crustal conditions (confining pressure of 80 MPa at 26°C and 75°C). We deformed the samples to failure, with bedding oriented perpendicular to the maximum compressive stress direction, using the stress‐stepping methodology. In both experiments, the failure stress was ~64% higher than the short‐term peak strength. Throughout each differential stress step, ultrasonic wave velocities initially decreased and then gradually increased with deformation/time. The magnitude of these variations depends both on the direction of measurement with respect to the bedding and the temperature, and it is largest for velocities measured parallel to the bedding and at high temperature. Elastic wave anisotropy was completely reversed at 75°C, following a limited amount of axial strain (~0.6%). Scanning electron microscope investigation confirmed evidence of a time‐dependent pressure solution, localized compaction, crack sealing/healing, and mineral rotation. Our observations reveal that elastic anisotropy can evolve rapidly in both time and space, which has implications on the stress state and its rotation near fault zones.
Rapid Cenozoic Subsidence in the Gulf of Mexico Resulting From Hess Rise Conjugate Subduction
Authors: Wang Huilin , Gurnis Michael , Skogseid Jakob
Published: October 2017

Enigmatic surface deflections occurred in North America starting from the Cretaceous, including the continental‐scale drainage reorganization and the long‐wavelength subsidence in the Western Interior Seaway. These surface undulations cannot be simply explained by sea level change or flexure loading. Coinciding with the large‐scale surface deflection, the Gulf of Mexico (GOM) has an immense Paleocene sediment deposition probably caused by tectonic subsidence. Increasing evidence indicates a distinct seismic anomaly localized in the mantle below the GOM. With geodynamic models, we show that the Hess Rise conjugate coincides with the position of the seismic anomaly. The basalt‐eclogite transition in the Hess conjugate can lead to a localized dynamic subsidence in the GOM, which is superimposed on the broad surface deflection caused by the Farallon slab. The Hess conjugate, transformed to eclogite, could tilt the surface southward in the U.S. and help frame the GOM as a main depocenter in the Cenozoic.
Evolving Impacts of Multiyear La Niña Events on Atmospheric Circulation and U.S. Drought
Authors: Okumura Yuko M. , DiNezio Pedro , Deser Clara
Published: October 2017

Wintertime precipitation over the southern U.S. is known to decrease with interannual cooling of the equatorial Pacific associated with La Niña, which often persists 2 years or longer. Composite analysis based on a suite of observational and reanalysis data sets covering the period 1901–2012 reveals distinct evolution of atmospheric teleconnections and U.S. precipitation anomalies during multiyear La Niña events. In particular, atmospheric circulation anomalies strengthen and become more zonally elongated over the North Pacific in the second winter compared to the first winter. U.S. precipitation deficits also remain large, while the region of reduced precipitation shifts northeastward in the second winter. This occurs despite a significant weakening of the equatorial Pacific cooling in the second winter and suggests that the large‐scale atmospheric circulation is more sensitive to tropical sea surface temperature anomalies of broader meridional extent. Given the extended climatic impacts, accurate prediction of La Niña duration is crucial.
Constraints on Inner Core Anisotropy Using Array Observations of P′P′
Authors: Frost Daniel A. , Romanowicz Barbara
Published: October 2017

Recent studies of PKPdf travel times suggest strong anisotropy (4% or more) in the quasi‐western inner core hemisphere. However, the availability of paths sampling at low angles to the Earth's rotation axis (the fast axis) is limited. To augment this sampling, we collected a travel time data set for the phase P′P′df (PKPPKPdf), for which at least one inner core leg is quasi‐polar, at two high latitude seismic arrays. We find that the inferred anisotropy is weak (on the order of 0.5 to 1.5%), confirming previous results based on a much smaller P′P′ data set. While previous models of inner core anisotropy required very strong alignment of anisotropic iron grains, our results are more easily explained by current dynamic models of inner core growth. We observe large travel time anomalies when one leg of P′P′df is along the South Sandwich to Alaska path, consistent with PKPdf observations, and warranting further investigation.
Crustal and Uppermost Mantle Structure Across the Tibet‐Qinling Transition Zone in NE Tibet: Implications for Material Extrusion Beneath the Tibetan Plateau
Authors: Ye Zhuo , Li Jiangtao , Gao Rui , Song Xiaodong , Li Qiusheng , Li Yingkang , Xu Xiao , Huang Xingfu , Xiong Xiaosong , Li Wenhui
Published: October 2017

Based on a dense linear seismic array traversing the eastern margin of the Tibetan Plateau into the Qinling Belt, we conducted a joint inversion of receiver functions and surface wave dispersion curves under P wave velocity constraints and simultaneously derived a crustal and uppermost mantle Vs profile with a Vp/Vs profile. Our observations indicate that the Qinling Belt, of which the lower crust exhibits Vp/Vs values less than 1.8 that are indicative of an intermediate to felsic composition, is currently not serving as a channel accommodating the extrusion of middle to lower crustal materials of the Tibetan Plateau. Channelized ductile mantle flow from beneath the Tibetan Plateau through the Qinling Belt would be feasible only at sublithospheric depths (i.e., in the asthenosphere). Our results suggest that the extrusion of ductile middle to lower crustal materials accompanied by fault‐related tectonics and isostatic buoyancy resulting from lithospheric detachment (triggered by asthenospheric flow) may have jointly engendered the plateau uplift and expansion in the Tibet‐Qinling transition zone.
Pressure Dependence of Creep in Forsterite Olivine: Comparison of Measurements From the D‐DIA and Griggs Apparatus
Authors: Kaboli S. , Burnley P. C. , Xia G. , Green H. W.
Published: October 2017

We present measurements of the creep strength of forsterite olivine at 1200°C from 1 to 7.5 GPa made using a Griggs apparatus at low pressures and a D‐DIA apparatus at high pressures. The same starting material is used for all experiments allowing us to compare measurements made with the two instruments. We find that results from the two apparatus are comparable if the stress measurements made from the alumina piston in the D‐DIA experiments are used as a proxy for the load that the olivine sample supports. The reproducibility of the D‐DIA experiments are improved if microstructural observations of the post experimental integrity of the sample and piston are used to judge experimental validity. Interpretation of the joint dataset indicate that the pressure dependence of creep (ΔV*) for our sample material cannot be described by a constant value over this pressure range, but changes from ~15 cm3/mol at low pressure to closer to ~4 cm3/mol at high pressure. These results are consistent with changes in the mix of deformation mechanisms operating in forsterite as pressure increases.
The Effect of a Guide Field on Local Energy Conversion During Asymmetric Magnetic Reconnection: MMS Observations
Authors: Genestreti K. J. , Burch J. L. , Cassak P. A. , Torbert R. B. , Ergun R. E. , Varsani A. , Phan T. D. , Giles B. L. , Russell C. T. , Wang S. , Akhavan‐Tafti M. , Allen R. C.
Published: October 2017

We compare case studies of Magnetospheric Multiscale (MMS)‐observed magnetopause electron diffusion regions (EDRs) to determine how the rate of work done by the electric field,
varies with shear angle. We analyze MMS‐observed EDR event with a guide field approximately the same size as the magnetosheath reconnecting field, which occurred on 8 December 2015. We find that
was largest and positive near the magnetic field reversal point, though patchy lower amplitude
also occurred on the magnetosphere side EDR near the electron crescent point. The current associated with the large
near the X point was carried by electrons with a velocity distribution function (VDF) resembling the magnetosheath inflow, shifted in the −v∥ direction. At the magnetosphere side EDR, the current was carried by electrons with a crescent‐like VDF. We compare this 8 December event to 10 other EDRs with different guide field strengths. The dual‐region
was observed in three other moderate‐shear EDR events, whereas three high‐shear events had a strong positive
near the electron crescent point and one low‐shear event had a strong positive
only near the BL=0 point. The dual‐region
was seen for one of three “intermediate”‐shear EDRs with guide fields of ∼0.2–0.3. We propose a physical relationship between the shear angle and mode of energy conversion where (a) a guide field provides an efficient mechanism for carrying a current at the field reversal point (streaming) and (b) a guide field may limit the formation of crescent electron VDFs, limiting the current carried near the stagnation point.
The MMS Dayside Magnetic Reconnection Locations During Phase 1 and Their Relation to the Predictions of the Maximum Magnetic Shear Model
Authors: Trattner K. J. , Burch J. L. , Ergun R. , Eriksson S. , Fuselier S. A. , Giles B. L. , Gomez R. G. , Grimes E. W. , Lewis W. S. , Mauk B. , Petrinec S. M. , Russell C. T. , Strangeway R. J. , Trenchi L. , Wilder F. D.
Published: October 2017

Several studies have validated the accuracy of the maximum magnetic shear model to predict the location of the reconnection site at the dayside magnetopause. These studies found agreement between model and observations for 74% to 88% of events examined. It should be noted that, of the anomalous events that failed the prediction of the model, 72% shared a very specific parameter range. These events occurred around equinox for an interplanetary magnetic field (IMF) clock angle of about 240°. This study investigates if this remarkable grouping of events is also present in data from the recently launched MMS. The MMS magnetopause encounter database from the first dayside phase of the mission includes about 4,500 full and partial magnetopause crossings and flux transfer events. We use the known reconnection line signature of switching accelerated ion beams in the magnetopause boundary layer to identify encounters with the reconnection region and identify 302 events during phase 1a when the spacecraft are at reconnection sites. These confirmed reconnection locations are compared with the predicted location from the maximum magnetic shear model and revealed an 80% agreement. The study also revealed the existence of anomalous cases as mentioned in an earlier study. The anomalies are concentrated for times around the equinoxes together with IMF clock angles around 140° and 240°. Another group of anomalies for the same clock angle ranges was found during December events.
A Single Deformed Bow Shock for Titan‐Saturn System
Authors: Omidi N. , Sulaiman A. H. , Kurth W. , Madanian H. , Cravens T. , Sergis N. , Dougherty M. K. , Edberg N. J. T.
Published: October 2017

During periods of high solar wind pressure, Saturn's bow shock is pushed inside Titan's orbit exposing the moon and its ionosphere to the solar wind. The Cassini spacecraft's T96 encounter with Titan occurred during such a period and showed evidence for shocks associated with Saturn and Titan. It also revealed the presence of two foreshocks: one prior to the closest approach (foreshock 1) and one after (foreshock 2). Using electromagnetic hybrid (kinetic ions and fluid electrons) simulations and Cassini observations, we show that the origin of foreshock 1 is tied to the formation of a single deformed bow shock for the Titan‐Saturn system. We also report the observations of a structure in foreshock 1 with properties consistent with those of spontaneous hot flow anomalies formed in the simulations and previously observed at Earth, Venus, and Mars. The results of hybrid simulations also show the generation of oblique fast magnetosonic waves upstream of the outbound Titan bow shock in agreement with the observations of large‐amplitude magnetosonic pulsations in foreshock 2. We also discuss the implications of a single deformed bow shock for new particle acceleration mechanisms and also Saturn's magnetopause and magnetosphere.
Crustal Thickness Beneath Libya and the Origin of Partial Melt Beneath AS Sawda Volcanic Province From Receiver Function Constraints
Authors: Lemnifi Awad A. , Elshaafi Abdelsalam , Browning John , Aouad Nassib S. , El Ebaidi Saad K. , Liu Kelly K. , Gudmundsson Agust
Published: October 2017

This study investigates crustal thickness and properties within the Libyan region. Results obtained from 15 seismic stations belonging to the Libyan Center for Remote Sensing and Space Science are reported, in addition to 3 seismic stations publically available, using receiver functions. The results show crustal thicknesses ranging from 24 km to 36 km (with uncertainties ranging between ±0.10 km and ±0.90 km). More specifically, crustal thickness ranges from 32 km to 36 km in the southern portion of the Libyan territory then becomes thinner, between 24 km and 30 km, in the coastal areas of Libya and thinnest, between 24 km and 28 km, in the Sirt Basin. The observed high Vp/Vs value of 1.91 at one station located at the AS Sawda Volcanic Province in central Libya indicates the presence of either partial melt or an abnormally warm area. This finding suggests that magma reservoirs beneath the Libyan territory may still be partially molten and active, thereby posing significant earthquake and volcanic risks. The hypothesis of an active magma source is further demonstrated though the presence of asthenospheric upwelling and extension of the Sirt Basin. This study provides a new calculation of unconsolidated sediment layers by using the arrival time of the P to S converted phases. The results show sediments thicknesses of 0.4 km to 3.7 km, with the Vp/Vs values ranging from 2.2 to 4.8. The variations in crustal thickness throughout the region are correlated with surface elevation and Bouguer gravity anomalies, which suggest that they are isostatically compensated.
Pressure‐Dependent Elastic and Transport Properties of Porous and Permeable Rocks: Microstructural Control
Authors: Pimienta Lucas , Sarout Joel , Esteban Lionel , David Christian , Clennell Michael B.
Published: October 2017

Although several studies aimed at linking electrical and hydraulic transport properties in rocks, the existing models remain at most incomplete. Based on this observation, in addition to the transport properties, this contribution investigates the pressure dependence of P wave velocities and porosity for three porous rocks. Apart from hydraulic conductivity, all physical properties show an important dependence to the confining pressure. In particular, electrical resistivity reaches an asymptote at low confining pressures. Using the measured P wave velocities and effective medium theories, the microcrack density (ρ) and its evolution with confining pressure are estimated. For the three rocks, the microcrack density at which electrical resistivity reaches a plateau is of ρ ~0.13. This value corresponds to the threshold for crack percolation in media containing microcracks exclusively. This suggests that in porous and microcracked rocks, electrical resistivity is controlled by two independent hydraulic pathways of tubes and cracks acting in parallel. In contrast, this percolation threshold is not observed in the permeability data. A simple conceptual model is finally introduced that explains the fundamental differences between transport properties.
A Model and Satellite‐Based Analysis of the Tropospheric Ozone Distribution in Clear Versus Convectively Cloudy Conditions
Authors: Strode Sarah A. , Douglass Anne R. , Ziemke Jerald R. , Manyin Michael , Nielsen J. Eric , Oman Luke D.
Published: October 2017

Satellite observations of in‐cloud ozone concentrations from the Ozone Monitoring Instrument and Microwave Limb Sounder instruments show substantial differences from background ozone concentrations. We develop a method for comparing a free‐running chemistry‐climate model (CCM) to in‐cloud and background ozone observations using a simple criterion based on cloud fraction to separate cloudy and clear‐sky days. We demonstrate that the CCM simulates key features of the in‐cloud versus background ozone differences and of the geographic distribution of in‐cloud ozone. Since the agreement is not dependent on matching the meteorological conditions of a specific day, this is a promising method for diagnosing how accurately CCMs represent the relationships between ozone and clouds, including the lower ozone concentrations shown by in‐cloud satellite observations. Since clouds are associated with convection as well as changes in chemistry, we diagnose the tendency of tropical ozone at 400 hPa due to chemistry, convection and turbulence, and large‐scale dynamics. While convection acts to reduce ozone concentrations at 400 hPa throughout much of the tropics, it has the opposite effect over highly polluted regions of South and East Asia.
Relationships Between Gravity Waves Observed at Earth's Surface and in the Stratosphere Over the Central and Eastern United States
Authors: de Groot‐Hedlin Catherine D. , Hedlin Michael A. H. , Hoffmann Lars , Alexander M. Joan , Stephan Claudia C.
Published: October 2017

Observations of tropospheric gravity waves (GWs) made by the new and extensive USArray Transportable Array (TA) barometric network located east of the Rockies, in the central and eastern United States and of stratospheric (30–40 km above sea level) GWs made by the Atmospheric Infrared Sounder (AIRS) are compared over a 5 year time span from 2010 through 2014. GW detections in the period band from 2 to 6 h made at the Earth's surface during the thunderstorm season from May through August each year exhibit the same broad spatial and temporal patterns as observed at stratospheric altitudes. At both levels, the occurrence frequency of GWs is higher at night than during the day and is highest to the west of the Great Lakes. Statistically significant correlations between the variance of the pressure at the TA, which is a proxy for GWs at ground level, with 8.1 μm brightness temperature measurements from AIRS and rain radar precipitation data, which are both proxies for convective activity, indicate that GWs observed at the TA are related to convective sources. There is little, if any, time lag between the two. Correlations between GWs in the stratosphere and at ground level are weaker, possibly due to the AIRS observational filter effect, but are still statistically significant at nighttime. We conclude that convective activity to the west of the Great Lakes is the dominant source of GWs both at ground level and within the stratosphere.
Molecular Halogens Above the Arctic Snowpack: Emissions, Diurnal Variations, and Recycling Mechanisms
Authors: Wang Siyuan , Pratt Kerri A.
Published: October 2017

Elevated levels of reactive bromine and chlorine species in the springtime Arctic boundary layer contribute to ozone depletion and mercury oxidation, as well as reactions with volatile organic compounds. Recent laboratory and field studies have revealed that snowpack photochemistry leads to Br2 and Cl2 production, the mechanisms of which remain poorly understood. In this work, we use a photochemical box model, with a simplified snow module, to examine the halogen chemistry occurring during the March 2012 Bromine, Ozone, and Mercury Experiment (BROMEX) near Utqiaġvik (Barrow), Alaska. Elevated daytime Br2 levels (e.g., 6–30 parts per trillion (ppt) at around local noon) reported in previous studies and in this work may be explained by Br + BrNO2/BrONO2 reactions under conditions of depleted O3 (<~10 ppb) and background NO2 (10–100 ppt). Even at low background NOx levels at Utqiaġvik, ClONO2 is predicted to be important in the production of Cl2 via multiphase reaction with Cl−. In the late afternoon, photolysis alone cannot explain the rapid decrease of Cl2 observed in the Arctic boundary layer. Heterogeneous reactions of Cl2 on aerosol particles and surface snowpack are suggested to play a key role in atmospheric Cl2 removal and possible BrCl production. Given the importance of the snowpack in the multiphase chemistry of the Arctic boundary layer, future measurements should focus on vertically resolved measurements of NOx and reactive halogens, as well as simultaneous particulate and snow halide measurements, to further evaluate and isolate the halogen production and vertical propagation mechanisms through one‐dimensional modeling.
Sources and Potential Photochemical Roles of Formaldehyde in an Urban Atmosphere in South China
Authors: Wang Chuan , Huang Xiao‐Feng , Han Yu , Zhu Bo , He Ling‐Yan
Published: October 2017

Formaldehyde (HCHO) is an important intermediate in tropospheric photochemistry. However, study of its evolution characteristics under heavy pollution conditions in China is limited, especially for high temporal resolutions, making it difficult to analyze its sources and environmental impacts. In this study, ambient levels of HCHO were monitored using a proton‐transfer reaction mass spectrometer at an urban site in the Pearl River Delta of China. Continuous monitoring campaigns were conducted in the spring, summer, fall, and winter in 2016. The highest averaged HCHO concentrations were observed in autumn (5.1 ± 3.1 ppbv) and summer (5.0 ± 4.4 ppbv), followed by winter (4.2 ± 2.2 ppbv) and spring (3.4 ± 1.6 ppbv). The daily maximum of HCHO occurs in the early afternoon and shows good correlations with O3 and the secondary organic aerosol tracer during the day, revealing close relationships between ambient HCHO and secondary formations in Shenzhen, especially in summer and autumn. The daytime HCHO is estimated to be the major contributor to O3 formation and OH radical production, indicating that HCHO plays a key role in the urban atmospheric photochemical reactions. Anthropogenic secondary formation was calculated to be the dominant source of HCHO using a photochemical age‐based parameterization method, with an average proportion of 39%. The contributions of biogenic sources in summer (41%) and autumn (39%) are much higher than those in spring (26%) and winter (28%), while the contributions of anthropogenic primary sources in spring (20%) and winter (18%) are twice those in summer (9%) and autumn (9%).