bluuebunny/crossref_metadata_2025_split huggingface dataset:
A review of transition experiences in perinatally and behaviourally acquired HIV‐1 infection; same, same but different?
Authors: Lam Phung Khanh , Fidler Sarah , Foster Caroline 
Published: May 2017

AbstractIntroduction: Despite sharing common psychosocial and developmental experiences, adolescents living with perinatally and behaviourally acquired HIV‐1 infection are different in terms of timing of HIV infection and developmental stage at infection. Therefore, it is of interest to identify similarities and differences between these two groups of adolescents living with HIV in their experiences, facilitators and barriers during the transition process.Methods: A detailed literature search of peer‐reviewed published papers was conducted on PubMed to identify relevant original research or viewpoints published up to September 2016. Conference abstracts and other unpublished data sources were not included.Results: Existing published literature, mainly using qualitative methods, explores the transition from paediatric to adult healthcare provision, as experienced by these two groups of young people. Reports highlight the variation and similarities in their experiences and challenges of transition. Findings from the USA and Europe predominate, while experience from Africa and Asia is lacking, despite the importance of these regions in the global epidemic.Conclusions: Published transition data remain limited, and there are few studies focusing on behaviourally infected adolescents and key population groups (e.g. adolescents who use drugs, lesbian/gay/transgender individuals). Robust definitions of the transition process and standardized outcome measures are required to facilitate cross‐study and geographic comparisons.
Synoptic‐to‐planetary scale wind variability enhances phytoplankton biomass at ocean fronts
Authors: Whitt D. B. , Taylor J. R. , Lévy M. 
Published: May 2017

AbstractIn nutrient‐limited conditions, phytoplankton growth at fronts is enhanced by winds, which drive upward nutrient fluxes via enhanced turbulent mixing and upwelling. Hence, depth‐integrated phytoplankton biomass can be 10 times greater at isolated fronts. Using theory and two‐dimensional simulations with a coupled physical‐biogeochemical ocean model, this paper builds conceptual understanding of the physical processes driving upward nutrient fluxes at fronts forced by unsteady winds with timescales of 4–16 days. The largest vertical nutrient fluxes occur when the surface mixing layer penetrates the nutricline, which fuels phytoplankton in the mixed layer. At a front, mixed layer deepening depends on the magnitude and direction of the wind stress, cross‐front variations in buoyancy and velocity at the surface, and potential vorticity at the base of the mixed layer, which itself depends on past wind events. Consequently, mixing layers are deeper and more intermittent in time at fronts than outside fronts. Moreover, mixing can decouple in time from the wind stress, even without other sources of physical variability. Wind‐driven upwelling also enhances depth‐integrated phytoplankton biomass at fronts; when the mixed layer remains shallower than the nutricline, this results in enhanced subsurface phytoplankton. Oscillatory along‐front winds induce both oscillatory and mean upwelling. The mean effect of oscillatory vertical motion is to transiently increase subsurface phytoplankton over days to weeks, whereas slower mean upwelling sustains this increase over weeks to months. Taken together, these results emphasize that wind‐driven phytoplankton growth is both spatially and temporally intermittent and depends on a diverse combination of physical processes.
Large eddy simulation (LES) of wind‐driven circulation in a peri‐alpine lake: Detection of turbulent structures and implications of a complex surrounding orography
Authors: Santo Marco A. , Toffolon Marco , Zanier Giulia , Giovannini Lorenzo , Armenio Vincenzo 
Published: May 2017

AbstractWe investigate wind‐driven circulation in a peri‐alpine lake (Lake Ledro ‐ Italy) using LES‐COAST. Lake Ledro is interesting because its own dimensions are suited for LES and it is surrounded by complex orography, affecting wind distribution. We consider the winter condition when stratification is nearly absent. Two types of time‐varying wind stress are used: spatially homogeneous and spatially inhomogeneous respectively. The analysis of the eddy viscosities shows substantial differences with respect to the ocean case characterized by absence of coastal boundaries and homogeneous, steady wind. The quantities exhibit a noticeable inhomogeneous behavior: the horizontal eddy viscosity is larger in the water body far from the boundaries, whereas the vertical one is larger close to the lateral boundaries due to the presence of a boundary layer. The energetic bottom boundary layer, typically occurring in lakes, is not present. This because of the intrinsic unsteadiness of the thermal wind blowing over the lake and due to the absence of large amplitude internal waves, the latter present only in case of stable stratification. In the inhomogeneous wind case, up‐welling and down‐welling areas are not confined along the shoreline only, but are also generated in the water body due to substantial horizontal velocity divergence, and turbulent mixing, quantified by eddy viscosities, TKE and its dissipation rate, appears enhanced with respect to the homogeneous wind case. Finally, downwelling/upwelling areas along the windward/leeward coastline respectively were observed, whose quantitative estimation may give explanation for the bloom of cyanobacteria at the lake surface observed in winter.
Biological and physical controls on the flux and characteristics of sinking particles on the Northwest Atlantic margin
Authors: Hwang Jeomshik , Manganini Steven J. , Park JongJin , Montluçon Daniel B. , Toole John M. , Eglinton Timothy I. 
Published: May 2017

AbstractsBiogenic matter characteristics and radiocarbon contents of organic carbon (OC) were examined on sinking particle samples intercepted at three nominal depths of 1000 m, 2000 m, and 3000 m (∼50 m above the seafloor) during a 3 year sediment trap program on the New England slope in the Northwest Atlantic. We have sought to characterize the sources of sinking particles in the context of vertical export of biogenic particles from the overlying water column and lateral supply of resuspended sediment particles from adjacent margin sediments. High aluminum (Al) abundances and low OC radiocarbon contents indicated contributions from resuspended sediment which was greatest at 3000 m but also significant at shallower depths. The benthic source (i.e., laterally supplied resuspended sediment) of opal appears negligible based on the absence of a correlation with Al fluxes. In comparison, CaCO3 fluxes at 3000 m showed a positive correlation with Al fluxes. Benthic sources accounted for 42 ∼ 63% of the sinking particle flux based on radiocarbon mass balance and the relationship between Al flux and CaCO3 flux. Episodic pulses of Al at 3000 m were significantly correlated with the near‐bottom current at a nearby hydrographic mooring site, implying the importance of current variability in lateral particle transport. However, Al fluxes at 1000 m and 2000 m were coherent but differed from those at 3000 m, implying more than one mode of lateral supply of particles in the water column.
Advanced numerical model of lightning development: Application to studying the role of LPCR in determining lightning type
Authors: Iudin D. I. , Rakov V. A. , Mareev E.A. , Iudin F. D. , Syssoev A. A. , Davydenko S. S. 
Published: May 2017

AbstractAn advanced 3‐D numerical model of lightning development is presented. The key features of the model include the probabilistic branching, bidirectional propagation, nonzero internal electric field, simultaneous growth of multiple branches, physical timing, channel decay, and, for the first time, probabilistic propagation field threshold. The new model can be used for computing electrical parameters of individual branches, including conductivity, current, and longitudinal electric field, each as a function of time, in different parts of the discharge tree. For illustrative purposes, the model was applied to studying the occurrence of lightning flashes of different type depending on the cloud charge structure, with emphasis on the lower positive charge region (LPCR). We demonstrated with the new model that the presence of relatively large (excessive) LPCR can prevent the occurrence of negative CG flashes by “blocking” the progression of descending negative leader from reaching ground. The blocking effect of excessive LPCR was found to occur when the vertical component of electric field near the cloud bottom was negative (downward directed). Further, we showed that significant reduction or absence of LPCR can eliminate the possibility of negative CG flashes and lead to normal‐polarity IC flashes instead. The model predicts the polarity‐asymmetry, which suggests that the amount of collected charge depends not only on the number of branches but also on the dynamics of their conductivity (lifetime) and the local cloud charge density.
Charged particle behavior in localized ultralow frequency waves: Theory and observations
Authors: Li Li , Zhou Xu‐Zhi , Zong Qiu‐Gang , Rankin Robert , Zou Hong , Liu Ying , Chen Xing‐Ran , Hao Yi‐Xin 
Published: May 2017

AbstractThe formation and variability of the Van Allen radiation belts are highly influenced by charged particles accelerated via drift‐resonant interactions with ultralow frequency (ULF) waves. In the prevailing theory of drift resonance, the ULF wave amplitude is assumed independent of magnetic longitude. This assumption is not generally valid in Earth's magnetosphere, as supported by numerous observations that point to the localized nature of ULF waves. Here we introduce a longitude dependence of the ULF wave amplitude, achieved via a von Mises function, into the theoretical framework of ULF wave‐particle drift resonance. To validate the revised theory, the predicted particle signatures are compared with observational data through a best fit procedure. It is demonstrated that incorporation of nonlocal effects in drift‐resonance theory provides an improved understanding of charged particle behavior in the inner magnetosphere through the intermediary of ULF waves.
Long‐period long‐duration seismic events during hydraulic fracturing: Implications for tensile fracture development
Authors: Hu Hongru , Li Aibing , Zavala‐Torres Ricardo 
Published: May 2017

AbstractLong‐period long‐duration (LPLD) seismic events are observed from a microseismic data set acquired by surface receivers in the Eagle Ford Shale. These events are characterized by low frequencies of 10–60 Hz and long durations of 30–60 s. The seismograms are dominated with P waves, and the frequency spectra have peaks at several isolated frequencies, similar to volcanic tremors. The LPLD events are located close to the horizontal hydraulic treatment well and migrate away from the well with time. These observations suggest that the LPLD events are related to hydraulic fracturing and are possibly caused by the jerky opening and resonance of fluid‐filled cracks. Imaging this type of LPLD events can potentially map fluid flow and tensile fracture development during hydraulic fracturing.
A new interpretation of the ability of global models to simulate the MJO
Authors: Ling Jian , Zhang Chidong , Wang Shuguang , Li Chongyin 
Published: May 2017

AbstractStatistical diagnostics have led to a common perception that only few global models can reproduce the Madden‐Julian Oscillation (MJO). Here we demonstrate, using a method of tracking individual MJO events, that this perception is incorrect. Of 27 global model simulations diagnosed, all produced large‐scale slowly eastward propagating signals in precipitation, which are taken as manifestations of the MJO. The difference is some model produced them frequently, others infrequently. There is no statistically significant distinction between the strength and propagation speeds of MJO events produced by most of these models. A hypothesis is proposed to interpret our results: A model can produce the MJO only in a particular background state. If the background state of a model can be constantly in a condition that is conducive to its production of the MJO, this model simulates the MJO frequently. If not, this model can still produce the MJO but only infrequently when its seasonal background state occasionally migrates into a condition that is conducive to its production of the MJO. Preliminary results from testing this hypothesis are presented.
Interactions between energetic electrons and realistic whistler mode waves in the Jovian magnetosphere
Authors: de Soria‐Santacruz M. , Shprits Y. Y. , Drozdov A. , Menietti J. D. , Garrett H. B. , Zhu H. , Kellerman A. C. , Horne R. B. 
Published: May 2017

AbstractThe role of plasma waves in shaping the intense Jovian radiation belts is not well understood. In this study we use a realistic wave model based on an extensive survey from the Plasma Wave Investigation on the Galileo spacecraft to calculate the effect of pitch angle and energy diffusion on Jovian energetic electrons due to upper and lower band chorus. Two Earth‐based models, the Full Diffusion Code and the Versatile Electron Radiation Belt code, are adapted to the case of the Jovian magnetosphere and used to resolve the interaction between chorus and electrons at L = 10. We also present a study of the sensitivity to the latitudinal wave coverage and initial electron distribution. Our analysis shows that the contribution to the electron dynamics from upper band chorus is almost negligible compared to that from lower band chorus. For 100 keV electrons, we observe that diffusion leads to redistribution of particles toward lower pitch angles with some particle loss, which could indicate that radial diffusion or interchange instabilities are important. For energies above >500 keV, an initial electron distribution based on observations is only weakly affected by chorus waves. Ideally, we would require the initial electron phase space density before transport takes place to assess the importance of wave acceleration, but this is not available. It is clear from this study that the shape of the electron phase space density and the latitudinal extent of the waves are important for both electron acceleration and loss.
Linear theory of the current sheet shear instability
Authors: Fujimoto Keizo , Sydora Richard D. 
Published: May 2017

AbstractThe present study investigates the linear properties of the current sheet shear instability (CSSI) based on the two‐fluid equations. The mode is typically excited in the thin current layer formed around the X line during a quasi‐steady phase of collisionless reconnection and is considered to give rise to the anomalous momentum transport. The linear analyses are carried out for a realistic current sheet as evolved in collisionless reconnection, where the current density profile is produced by the nonuniform ion and electron flows and the pressure balance is maintained due to the temperature gradients. The density profile is assumed to be uniform, so that the lower hybrid drift instability is mostly suppressed. We confirm that the eigenfunctions in the numerical analysis are well consistent with the profiles in a kinetic simulation, implying that the two‐fluid approximation is valid for the CSSI. The mass ratio dependencies of the wave number and growth rate are remarkable for the electron‐scale current sheet, indicating that both the electrons and ions contribute to the wave generation. From the analytical analysis, it is found that these mass ratio dependencies originate from the fact that the ion momentum balance is coupled with the electron dynamics in the electron‐scale current layer. In particular, the electron inertia and electron flow shear play a significant role in generating the CSSI through the induction electric and magnetic fields.
Quasi‐linear diffusion coefficients for highly oblique whistler mode waves
Authors: Albert J. M. 
Published: May 2017

AbstractQuasi‐linear diffusion coefficients are considered for highly oblique whistler mode waves, which exhibit a singular “resonance cone” in cold plasma theory. The refractive index becomes both very large and rapidly varying as a function of wave parameters, making the diffusion coefficients difficult to calculate and to characterize. Since such waves have been repeatedly observed both outside and inside the plasmasphere, this problem has received renewed attention. Here the diffusion equations are analytically treated in the limit of large refractive index μ. It is shown that a common approximation to the refractive index allows the associated “normalization integral” to be evaluated in closed form and that this can be exploited in the numerical evaluation of the exact expression. The overall diffusion coefficient formulas for large μ are then reduced to a very simple form, and the remaining integral and sum over resonances are approximated analytically. These formulas are typically written for a modeled distribution of wave magnetic field intensity, but this may not be appropriate for highly oblique whistlers, which become quasi‐electrostatic. Thus, the analysis is also presented in terms of wave electric field intensity. The final results depend strongly on the maximum μ (or μ∥) used to model the wave distribution, so realistic determination of these limiting values becomes paramount.
The sea‐level budget along the Northwest Atlantic coast: GIA, mass changes, and large‐scale ocean dynamics
Authors: Frederikse Thomas , Simon Karen , Katsman Caroline A. , Riva Riccardo 
Published: May 2017

AbstractSea‐level rise and decadal variability along the northwestern coast of the North Atlantic Ocean are studied in a self‐consistent framework that takes into account the effects of solid‐earth deformation and geoid changes due to large‐scale mass redistribution processes. Observations of sea and land level changes from tide gauges and GPS are compared to the cumulative effect of GIA, present‐day mass redistribution, and ocean dynamics over a 50 year period (1965–2014). GIA explains the majority of the observed sea‐level and land motion trends, as well as almost all interstation variability. Present‐day mass redistribution resulting from ice melt and land hydrology causes both land uplift and sea‐level rise in the region. We find a strong correlation between decadal steric variability in the Subpolar Gyre and coastal sea level, which is likely caused by variability in the Labrador Sea that is propagated southward. The steric signal explains the majority of the observed decadal sea‐level variability and shows an upward trend and a significant acceleration, which are also found along the coast. The sum of all contributors explains the observed trends in both sea‐level rise and vertical land motion in the region, as well as the decadal variability. The sum of contributors also explains the observed acceleration within confidence intervals. The sea‐level acceleration coincides with an accelerating density decrease at high latitudes.
The formation processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean
Authors: Chang Yu‐Lin , Miyazawa Yasumasa , Oey Lie‐Yauw , Kodaira Tsubasa , Huang Shihming 
Published: May 2017

AbstractIn this study, we investigate the processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean based on the in situ chlorophyll data obtained from 52 cruises conducted by the Japan Meteorological Agency together with idealized numerical simulations. Both the observation and model results suggest that chlorophyll/phytoplankton concentrations are higher in cold than in warm eddies in near‐surface water (z > −70 m). In the idealized simulation, the isopycnal movements associated with upwelling/downwelling transport phytoplankton and nutrients to different vertical depths during eddy formation (stage A). Phytoplankton and nutrients in cold eddies is transported toward shallower waters while those in warm eddies move toward deeper waters. In the period after the eddy has formed (stage B), sunlight and initially upwelled nutrients together promote the growth of phytoplankton in cold eddies. Phytoplankton in warm eddies decays due to insufficient sunlight in deeper waters. In stage B, upwelling and downwelling coexist in both warm and cold eddies, contributing nearly equally to vertical displacement. The upwelling/downwelling‐induced nitrate flux accounts for a small percentage (∼3%) of the total nitrate flux in stage B. The vertical velocity caused by propagating eddies, therefore, is not the primary factor causing differences in phytoplankton concentrations between stage‐B warm and cold eddies.
Implementation of absolute quantification in small‐animal SPECT imaging: Phantom and animal studies
Authors: Gerdekoohi Shabnam Khorasani , Vosoughi Naser , Tanha Kaveh , Assadi Majid , Ghafarian Pardis , Rahmim Arman , Ay Mohammad Reza 
Published: May 2017

AbstractPurposePresence of photon attenuation severely challenges quantitative accuracy in single‐photon emission computed tomography (SPECT) imaging. Subsequently, various attenuation correction methods have been developed to compensate for this degradation. The present study aims to implement an attenuation correction method and then to evaluate quantification accuracy of attenuation correction in small‐animal SPECT imaging.MethodsImages were reconstructed using an iterative reconstruction method based on the maximum‐likelihood expectation maximization (MLEM) algorithm including resolution recovery. This was implemented in our designed dedicated small‐animal SPECT (HiReSPECT) system. For accurate quantification, the voxel values were converted to activity concentration via a calculated calibration factor. An attenuation correction algorithm was developed based on the first‐order Chang's method. Both phantom study and experimental measurements with four rats were used in order to validate the proposed method.ResultsThe phantom experiments showed that the error of −15.5% in the estimation of activity concentration in a uniform region was reduced to +5.1% when attenuation correction was applied. For in vivo studies, the average quantitative error of −22.8 ± 6.3% (ranging from −31.2% to −14.8%) in the uncorrected images was reduced to +3.5 ± 6.7% (ranging from −6.7 to +9.8%) after applying attenuation correction.ConclusionThe results indicate that the proposed attenuation correction algorithm based on the first‐order Chang's method, as implemented in our dedicated small‐animal SPECT system, significantly improves accuracy of the quantitative analysis as well as the absolute quantification.