bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent magnetic vortex flow at a supergranular vertex
Authors: Requerey Iker S. , Cobo Basilio Ruiz , Gošić Milan , Bellot Rubio Luis R.
Published: December 2017

Context. Photospheric vortex flows are thought to play a key role in the evolution of magnetic fields. Recent studies show that these swirling motions are ubiquitous in the solar surface convection and occur in a wide range of temporal and spatial scales. Their interplay with magnetic fields is poorly characterized, however.

Aims. We study the relation between a persistent photospheric vortex flow and the evolution of a network magnetic element at a supergranular vertex.

Methods. We used long-duration sequences of continuum intensity images acquired with Hinode and the local correlation-tracking method to derive the horizontal photospheric flows. Supergranular cells are detected as large-scale divergence structures in the flow maps. At their vertices, and cospatial with network magnetic elements, the velocity flows converge on a central point.

Results. One of these converging flows is observed as a vortex during the whole 24 h time series. It consists of three consecutive vortices that appear nearly at the same location. At their core, a network magnetic element is also detected. Its evolution is strongly correlated to that of the vortices. The magnetic feature is concentrated and evacuated when it is caught by the vortices and is weakened and fragmented after the whirls disappear.

Conclusions. This evolutionary behavior supports the picture presented previously, where a small flux tube becomes stable when it is surrounded by a vortex flow.
Negative inductance circuits for metamaterial bandwidth enhancement
Authors: Avignon-Meseldzija Emilie , Lepetit Thomas , Ferreira Pietro Maris , Boust Fabrice
Published: December 2017

Passive metamaterials have yet to be translated into applications on a large scale due in large part to their limited bandwidth. To overcome this limitation many authors have suggested coupling metamaterials to non-Foster circuits. However, up to now, the number of convincing demonstrations based on non-Foster metamaterials has been very limited. This paper intends to clarify why progress has been so slow, i.e., the fundamental difficulty in making a truly broadband and efficient non-Foster metamaterial. To this end, we consider two families of metamaterials, namely Artificial Magnetic Media and Artificial Magnetic Conductors. In both cases, it turns out that bandwidth enhancement requires negative inductance with almost zero resistance. To estimate bandwidth enhancement with actual non-Foster circuits, we consider two classes of such circuits, namely Linvill and gyrator. The issue of stability being critical, both metamaterial families are studied with equivalent circuits that include advanced models of these non-Foster circuits. Conclusions are different for Artificial Magnetic Media coupled to Linvill circuits and Artificial Magnetic Conductors coupled to gyrator circuits. In the first case, requirements for bandwidth enhancement and stability are very hard to meet simultaneously whereas, in the second case, an adjustment of the transistor gain does significantly increase bandwidth.
Reverse maximum flow problem under the weighted Chebyshev distance
Authors: Tayyebi Javad , Mohammadi Abumoslem , Kazemi Seyyed Mohammad Reza
Published: December 2017

Given a networkG(V,A,u) with two specific nodes, a source nodesand a sink nodet, the reverse maximum flow problem is to increase the capacity of some arcs (i,j) as little as possible under bound constraints on the modifications so that the maximum flow value fromstotin the modified network is lower bounded by a prescribed valuev0. In this paper, we study the reverse maximum flow problem when the capacity modifications are measured by the weighted Chebyshev distance. We present an efficient algorithm to solve the problem in two phases. The first phase applies the binary search technique to find an interval containing the optimal value. The second phase uses the discrete type Newton method to obtain exactly the optimal value. Finally, some computational experiments are conducted to observe the performance of the proposed algorithm.
Acute Stroke Multimodal Imaging: Present and Potential Applications toward Advancing Care
Authors: Matos Diaz I. , Liang J. , Ostojic L. , Tansy Aaron
Published: December 2017

In the past few decades, the field of acute ischemic stroke (AIS) has experienced significant advances in clinical practice. A core driver of this success has been the utilization of acute stroke imaging with an increasing focus on advanced methods including multimodal imaging. Such imaging techniques not only provide a richer understanding of AIS in vivo, but also, in doing so, provide better informed clinical assessments in management and treatment toward achieving best outcomes. As a result, advanced stroke imaging methods are now a mainstay of routine AIS practice that reflect best practice delivery of care. Furthermore, these imaging methods hold great potential to continue to advance the understanding of AIS and its care in the future.
TSPO-PET Imaging to Assess Cerebral Microglial Activation in Multiple Sclerosis
Authors: Weiner Howard , Bakshi Rohit , Singhal Tarun
Published: December 2017

The adaptive immune system, particularly T cells and more recently B cells, is considered to play a major role in the pathogenesis of multiple sclerosis (MS). In addition to adaptive immune mechanisms, innate central nervous system (CNS) immunity, particularly mediated by microglia, may play a key role in MS pathogenesis. Microglial activation has been demonstrated throughout the MS disease course and at various locations in the CNS, including white and gray matter lesions as well as normal appearing white and gray matter. Activated microglia overexpress an 18 kilodalton mitochondrial translocator protein (TSPO), which is otherwise expressed at low levels during the resting state. Several positron emission tomography (PET) ligands targeting TSPO have been developed to enable the assessment of microglial activation. In this article, we review the biological basis, methodological aspects, and current status of TSPO-PET imaging in MS and discuss future research directions.
Magnetic Resonance Spectroscopy as a Biomarker for Chronic Traumatic Encephalopathy
Authors: Alosco Michael , Jarnagin Johnny , Rowland Benjamin , Liao Huijun , Stern Robert , Lin Alexander
Published: December 2017

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts (RHI). Currently, CTE can only be diagnosed after death by postmortem, as validated in vivo biomarkers of CTE do not yet exist. Proton magnetic resonance spectroscopy (MRS) measures brain tissue metabolism in vivo and could facilitate a “probable CTE” diagnosis during life. Here, we propose MRS as one potential biomarker for CTE through a review of CTE neuropathology, and the extant literature that has examined the acute and long-term effects of RHI exposure on brain chemistry. There is preliminary empirical support for MRS in the detection of later-life neurological impairment associated with RHI exposure, but further ante- and postmortem research is needed before MRS can be considered a diagnostic biomarker for CTE.
Role of Endovascular Aortic Repair in the Treatment of Infected Aortic Aneurysms Complicated by Aortoenteric or Aortobronchial Fistulae
Authors: Lee Hsin-Ling , Yang Yu-Jen , Kan Chung-Dann
Published: December 2017

Background The aim of this study was to compare outcomes and identify factors related to increased mortality of open surgical and endovascular aortic repair (EVAR) of primary mycotic aortic aneurysms complicated by aortoenteric fistula (AEF) or aortobronchial fistula (ABF).

Methods Patients with primary mycotic aortic aneurysms complicated by an AEF or ABF treated by open surgery or endovascular repair between January 1993 and January 2014 were retrospectively reviewed. Outcomes were compared between the open surgery and endovascular groups, and a Cox's proportional hazard model was used to determine factors associated with mortality.

Results A total of 29 patients included 14 received open surgery and 15 received endovascular repair. Positive initial bacterial blood culture results included Salmonella spp., oxacillin-resistant Staphylococcus aureus, and Klebsiella pneumoniae. Mortality within 1 month of surgery was higher in the open surgery than in the endovascular group (43 vs. 7%, respectively, p = 0.035). Shock, additional surgery to repair gastrointestinal (GI) or airway pathology, and aneurysm rupture were associated with a higher risk of death. Compared with patients without resection surgery, the adjusted hazard ratio of death within 4 years in patients with resection for GI/bronchial disease was 0.25. Survival within 6 months was better in the endovascular group (p = 0.016).

Conclusion The results of this study showed that EVAR/thoracic EVAR (TEVAR) is feasible for the management of infected aortic aneurysms complicated by an AEF or ABF, and results in good short-term outcomes. However, EVAR/TEVAR did not benefit long-term survival compared with open surgery.
Cognitive Development in Pediatric Epilepsy Surgery
Authors: Reuner Gitta , Ramantani Georgia
Published: December 2017

Epilepsy surgery is a very effective treatment option for children and adolescents with drug-resistant structural epilepsy, resulting in seizure freedom in the majority of cases. Beyond seizure freedom, the postsurgical stabilization or even improvement of cognitive development constitutes a fundamental objective. This study aims to address key features of cognitive development in the context of pediatric epilepsy surgery. Many surgical candidates present with severe developmental delay and cognitive deficits prior to surgery. Recent studies support that global cognitive development remains stable after surgery. Individual developmental trajectories are determined by the degree of presurgical developmental impairment, age at surgery, seizure freedom, antiepileptic drug tapering, and other case-specific factors. Compared with adults, children may better compensate for temporary postsurgical deficits in circumscribed cognitive functions such as memory. Particularly for left-sided temporal resections, children present a clear advantage in terms of postsurgical recovery with regard to verbal learning compared with adults. In the case of severe presurgical developmental impairment, minimal postsurgical improvements are often not measurable, although they are evident to patients' families and have a large impact on their quality of life. Multicenter studies with a standardized assessment protocol and longer follow-up intervals are urgently called for to provide deeper insights into the cognitive development after epilepsy surgery, to analyze the interaction between different predictors, and to facilitate the selection of appropriate candidates as well as the counseling of families.
Management des Delirs auf der Intensivstation
Authors: Braune Stephan , Gurlit Simone
Published: December 2017

Was ist neu?

Ende 2015 wurde die aktualisierte S3-Leitlinie „Analgesie, Sedierung und Delirmanagement in der Intensivmedizin“ publiziert 1.

Erkennung des Delirs Das mehrfach tägliche Delir-Screening mittels validierter Delir-Scores ist die Voraussetzung für ein effektives Delir-Management auf der Intensivstation und ein Qualitätsindikator in der Intensivmedizin.

Management des Delirs Grundlage der Prävention und Therapie des Delirs sind nicht-pharmakologische Basismaßnahmen. Diese werden flankiert von einer effektiven Analgesie, einer zurückhaltenden, ziel- und symptomorientierten Sedierung mit gut steuerbaren, möglichst wenig delirogenen Substanzen sowie bedarfsweise und symptomorientiert einer antipsychotischen Therapie.
Phäochromozytom richtig erkennen, behandeln und nachsorgen
Authors: Megerle Felix , Fassnacht Martin
Published: December 2017

Was ist neu?

Laborchemische Diagnostik Die Bestimmung der Metanephrine (Überbegriff für Normetanephrin und Metanephrin) im Plasma oder der fraktionierten Metanephrine im 24h-Sammelurin sind Diagnostik der ersten Wahl und haben die Bestimmung von Adrenalin und Noradrenalin bzw. Vanillinmandelsäure endgültig abgelöst. Werte > 3fach der oberen Norm werden als diagnostisch angesehen. Bei leicht bis moderat erhöhten Befunden empfiehlt sich weitere Bestätigungsdiagnostik.

Bildgebende Diagnostik Computertomografie (CT) und Magnetresonanztherapie (MRT) sind ebenbürtige Optionen. Eine funktionelle Bildgebung ist nach den neuen Leitlinien nur bei Malignitätsverdacht bzw. metastasierten Phäochromozytomen oder zur Detektion von Paragangliomen zwingend.

Genetische Diagnostik Bei mind. 30 % der Patienten mit Phäochromozytom lässt sich eine genetische Disposition feststellen. Inzwischen wurden 14 „Phäochromozytom-Paragangliom-Gene“ identifiziert. Daher wird grundsätzlich jedem Patienten eine genetische Aufklärung und Diagnostik angeboten.

Therapie Hier geht die Empfehlung zur minimalinvasiven Resektion, sofern dies technisch möglich ist und kein Malignitätsverdacht besteht. Alle Patienten mit hormonell aktivem Phäochromozytom sollten eine präoperative α-Blockade für 7 – 14 Tage erhalten.

Nachsorge Alle Patienten bedürfen einer regelmäßigen jährlichen Nachsorge für mindestens 10 Jahre. Bei nachgewiesener Mutation, großem Tumor oder jungem Patientenalter wird lebenslängliche Nachsorge empfohlen.
Google and advertising: digital capitalism in the context of Post-Fordism, the reification of language, and the rise of fake news
Authors: Graham Rosie
Published: December 2017

Google’s dominance over the web allows it to dictate various norms and practices that regulate the state of contemporary capitalism online. The way in which Google operates as a company and generates revenue is often sidelined in academic discussions regarding the cultural implications of how its search engine functions. Almost 90% of Google’s revenue is derived from advertising, despite Larry Page and Sergey Brin’s original academic paper regarding Google in which they argue that advertising produces mixed motives that make it an unfeasible way to fund search engines. This article outlines how Google’s model of advertising reflects and encourages wider changes in capitalism as it shifts from its twentieth-century Fordist incarnation to contemporary Post-Fordist arrangements of labour. In doing so, this article analyses Google’s two main advertising systems, AdWords and AdSense, and proposes that these financial models have significant effects upon online discourse. In discussing AdWords, this article details some of the tensions between the local and the global that develop when tracing flows of information and capital, specifically highlighting Google’s impact on the decline of online language diversity. In outlining AdSense, this article demonstrates how Google’s hegemonic control prescribes which parts of the web can be monetised and which remain unprofitable. In particular, in drawing from existing studies, evidence is provided that Google’s AdSense programme, along with Google’s relationship with Facebook, incentivised the rise of fake news in the 2016 US presidential election. This work builds on existing scholarship to demonstrate that Google’s economic influence has varied and far-reaching effects in a number of contexts and is relevant to scholars in a range of disciplines. As such, this article is intended as a discursive introduction to the topic and does not require specific disciplinary background knowledge. In doing so, this article does not attempt to provide the final word on Google’s relationship to digital capitalism, but rather, demonstrate the profitability of a Post-Fordist perspective, in order to enable a wider engagement with the issues identified.
GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell
Authors: Nelson George T. , Juang Bor-Chau , Slocum Michael A. , Bittner Zachary S. , Laghumavarapu Ramesh B. , Huffaker Diana L. , Hubbard Seth M.
Published: December 2017

Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.
Kriging modeling and SPSA adjusting PID with KPWF compensator control of IPMC gripper for mm-sized objects
Authors: Chen Yang , Hao Lina , Yang Hui , Gao Jinhai
Published: December 2017

Ionic polymer metal composite (IPMC) as a new smart material has been widely concerned in the micromanipulation field. In this paper, a novel two-finger gripper which contains an IPMC actuator and an ultrasensitive force sensor is proposed and fabricated. The IPMC as one finger of the gripper for mm-sized objects can achieve gripping and releasing motion, and the other finger works not only as a support finger but also as a force sensor. Because of the feedback signal of the force sensor, this integrated actuating and sensing gripper can complete gripping miniature objects in millimeter scale. The Kriging model is used to describe nonlinear characteristics of the IPMC for the first time, and then the control scheme called simultaneous perturbation stochastic approximation adjusting a proportion integration differentiation parameter controller with a Kriging predictor wavelet filter compensator is applied to track the gripping force of the gripper. The high precision force tracking in the foam ball manipulation process is obtained on a semi-physical experimental platform, which demonstrates that this gripper for mm-sized objects can work well in manipulation applications.
SH wave propagation in joined half-spaces composed of elastic metamaterials
Authors: Shi Xiaona , Shu Haisheng , Zhou Haiyong , Zhao Lei , Liu Ru , An Shuowei , Zhu Jie
Published: December 2017

Based on the effective-medium theory, the propagation of a shear horizontal (SH) wave in joined half-spaces composed of elastic metamaterials (EMMs) is investigated. From the dispersion relations, the effects of negative effective-medium parameters on the properties of a SH wave traveling near the interface are analyzed in detail. It is found that a SH wave can always appear and travel along the interface under specific effective-parameter combinations no matter whether the effective transverse wave velocity is imaginary or real. This is significantly different from the classical case (joined half-spaces composed of natural media), and the existence of these SH interfacial wave modes may have important impacts on EMM-based SH wave manipulation, especially wave isolation and object protection.
A combined theoretical and experimental approach of a new ternary metal oxide in molybdate composite for hybrid energy storage capacitors
Authors: Minakshi M. , Watcharatharapong T. , Chakraborty S. , Ahuja R.
Published: December 2017

Sustainable energy sources require an efficient energy storage system possessing excellent electrochemical properties. The better understanding of possible crystal configurations and the development of a new ternary metal oxide in molybdate composite as an electrode for hybrid capacitors can lead to an efficient energy storage system. Here, we reported a new ternary metal oxide in molybdate composite [(Mn1/3Co1/3Ni1/3)MoO4] prepared by simple combustion synthesis with an extended voltage window (1.8 V vs. Carbon) resulting in excellent specific capacity 35 C g−1 (58 F g−1) and energy density (50 Wh kg−1 at 500 W kg−1) for a two electrode system in an aqueous NaOH electrolyte. The binding energies measured for Mn, Co, and Ni 2p are consistent with the literature, and with the metal ions being present as M(II), implying that the oxidation states of the transition metals are unchanged. The experimental findings are correlated well through density functional theory based electronic structure calculations. Our reported work on the ternary metal oxide studies (Mn1/3Co1/3Ni1/3)MoO4 suggests that will be an added value to the materials for energy storage.
Mechanical low-frequency filter via modes separation in 3D periodic structures
Authors: D'Alessandro L. , Belloni E. , Ardito R. , Braghin F. , Corigliano A.
Published: December 2017

This work presents a strategy to design three-dimensional elastic periodic structures endowed with complete bandgaps, the first of which is ultra-wide, where the top limits of the first two bandgaps are overstepped in terms of wave transmission in the finite structure. Thus, subsequent bandgaps are merged, approaching the behaviour of a three-dimensional low-pass mechanical filter. This result relies on a proper organization of the modal characteristics, and it is validated by performing numerical and analytical calculations over the unit cell. A prototype of the analysed layout, made of Nylon by means of additive manufacturing, is experimentally tested to assess the transmission spectrum of the finite structure, obtaining good agreement with numerical predictions. The presented strategy paves the way for the development of a class of periodic structures to be used in robust and reliable wave attenuation over a wide frequency band.
Augmented potential, energy densities, and virial relations in the weak- and strong-interaction limits of DFT
Authors: Vuckovic Stefan , Levy Mel , Gori-Giorgi Paola
Published: December 2017

The augmented potential introduced by Levy and Zahariev [Phys. Rev. Lett. 113, 113002 (2014)] is shifted with respect to the standard exchange-correlation potential of the Kohn-Sham density functional theory by a density-dependent constant that makes the total energy become equal to the sum of the occupied orbital energies. In this work, we analyze several features of this approach, focusing on the limit of infinite coupling strength and studying the shift and the corresponding energy density at different correlation regimes. We present and discuss coordinate scaling properties of the augmented potential, study its connection to the response potential, and use the shift to analyze the classical jellium and uniform gas models. We also study other definitions of the energy densities in relation to the functional construction by local interpolations along the adiabatic connection. Our findings indicate that the energy density that is defined in terms of the electrostatic potential of the exchange-correlation hole is particularly well suited for this purpose.
Characterization of plastic and boron carbide additive manufactured neutron collimators
Authors: Stone M. B. , Siddel D. H. , Elliott A. M. , Anderson D. , Abernathy D. L.
Published: December 2017

Additive manufacturing techniques allow for the production of materials with complicated geometries with reduced costs and production time over traditional methods. We have applied this technique to the production of neutron collimators for use in thermal and cold neutron scattering instrumentation directly out of boron carbide. We discuss the design and generation of these collimators. We also provide measurements at neutron scattering beamlines which serve to characterize the performance of these collimators. Additive manufacturing of parts using neutron absorbing material may also find applications in radiography and neutron moderation.
Exploratory study and application of the angular wavelet analysis for assessing the spatial distribution of breakdown spots in Pt/HfO2/Pt structures
Authors: Muñoz-Gorriz J. , Monaghan S. , Cherkaoui K. , Suñé J. , Hurley P. K. , Miranda E.
Published: December 2017

The angular wavelet analysis is applied for assessing the spatial distribution of breakdown spots in Pt/HfO2/Pt capacitors with areas ranging from 104 to 105 μm2. The breakdown spot lateral sizes are in the range from 1 to 3 μm, and they appear distributed on the top metal electrode as a point pattern. The spots are generated by ramped and constant voltage stresses and are the consequence of microexplosions caused by the formation of shorts spanning the dielectric film. This kind of pattern was analyzed in the past using the conventional spatial analysis tools such as intensity plots, distance histograms, pair correlation function, and nearest neighbours. Here, we show that the wavelet analysis offers an alternative and complementary method for testing whether or not the failure site distribution departs from a complete spatial randomness process in the angular domain. The effect of using different wavelet functions, such as the Haar, Sine, French top hat, Mexican hat, and Morlet, as well as the roles played by the process intensity, the location of the voltage probe, and the aspect ratio of the device, are all discussed.
Transition path time distributions
Authors: Laleman M. , Carlon E. , Orland H.
Published: December 2017

Biomolecular folding, at least in simple systems, can be described as a two state transition in a free energy landscape with two deep wells separated by a high barrier. Transition paths are the short part of the trajectories that cross the barrier. Average transition path times and, recently, their full probability distribution have been measured for several biomolecular systems, e.g., in the folding of nucleic acids or proteins. Motivated by these experiments, we have calculated the full transition path time distribution for a single stochastic particle crossing a parabolic barrier, including inertial terms which were neglected in previous studies. These terms influence the short time scale dynamics of a stochastic system and can be of experimental relevance in view of the short duration of transition paths. We derive the full transition path time distribution as well as the average transition path times and discuss the similarities and differences with the high friction limit.
Adaptive enhanced sampling with a path-variable for the simulation of protein folding and aggregation
Authors: Peter Emanuel K.
Published: December 2017

In this article, we present a novel adaptive enhanced sampling molecular dynamics (MD) method for the accelerated simulation of protein folding and aggregation. We introduce a path-variable L based on the un-biased momenta p and displacements dq for the definition of the bias s applied to the system and derive 3 algorithms: general adaptive bias MD, adaptive path-sampling, and a hybrid method which combines the first 2 methodologies. Through the analysis of the correlations between the bias and the un-biased gradient in the system, we find that the hybrid methodology leads to an improved force correlation and acceleration in the sampling of the phase space. We apply our method on SPC/E water, where we find a conservation of the average water structure. We then use our method to sample dialanine and the folding of TrpCage, where we find a good agreement with simulation data reported in the literature. Finally, we apply our methodologies on the initial stages of aggregation of a hexamer of Alzheimer’s amyloid β fragment 25-35 (Aβ 25-35) and find that transitions within the hexameric aggregate are dominated by entropic barriers, while we speculate that especially the conformation entropy plays a major role in the formation of the fibril as a rate limiting factor.
Surface loop-gap resonators for electron spin resonance at W-band
Authors: Twig Ygal , Sorkin Anton , Cristea David , Feintuch Akiva , Blank Aharon
Published: December 2017

Electron spin resonance (ESR) is a spectroscopic method used to detect paramagnetic materials, reveal their structure, and also image their position in a sample. ESR makes use of a large static magnetic field to split the energy levels of the electron magnetic moment of the paramagnetic species. A strong microwave magnetic field is applied to excite the spins, and subsequently the ESR system detects their faint microwave signal response. The sensitivity of an ESR system is greatly influenced by the magnitude of the static field and the properties of the microwave resonator used to detect the spin signal. In general terms, the higher the static field (microwave frequency) and the smaller the resonator, the more sensitive the system will be. Previous work aimed at high-sensitivity ESR was focused on the development and testing of very small resonators operating at moderate magnetic fields in the range of ∼0.1-1.2 T (maximum frequency of ∼35 GHz). Here, we describe the design, construction, and testing of recently developed miniature surface loop-gap resonators used in ESR and operating at a much higher frequency of ∼95 GHz (W-band, corresponding to a field of ∼3.4 T). Such resonators can greatly enhance the sensitivity of ESR and also improve the resulting spectral resolution due to the higher static field employed. A detailed description of the resonator’s design and coupling mechanism, as well as the supporting probe head, is provided. We also discuss the production method of the resonators and probe head and, in the end, provide preliminary experimental results that show the setup’s high spin sensitivity and compare it to theoretical predictions.
Cross Sections for Electron Collisions with Ammonia
Authors: Itikawa Yukikazu
Published: December 2017

Cross-sectional data are surveyed for electron collisions with ammonia. Collision processes considered are total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, ionization, and dissociative electron attachment. After a review of the literature (up to March 2017), recommended values of the cross section are determined, as far as possible.
Homoepitaxy of non-polar ZnO/(Zn,Mg)O multi-quantum wells: From a precise growth control to the observation of intersubband transitions
Authors: Le Biavan N. , Hugues M. , Montes Bajo M. , Tamayo-Arriola J. , Jollivet A. , Lefebvre D. , Cordier Y. , Vinter B. , Julien F.-H. , Hierro A. , Chauveau J.-M.
Published: December 2017

We have developed a method to grow and characterize the state of the art non-polar ZnO/(Zn,Mg)O multi-quantum wells on m-plane ZnO substrates as a prerequisite for applications based on intersubband transitions. The epilayer interfaces exhibit a low roughness, and the layer thickness remains constant within one monolayer in these heterostructures. The optical properties have been studied in the UV and IR domains by means of photoluminescence and absorption experiments, respectively. In the UV, the photoluminescence is very well described by an excitonic transition, with the clear effect of quantum confinement as a function of the well thickness in the absence of the internal field. In the IR, the intersubband transitions can be precisely modeled if a large depolarization shift is taken into account. Overall, we demonstrate a very good control in the design and fabrication of ZnO quantum wells (QWs) for intersubband transitions. Our result gives a clear understanding of the ISBTs in ZnO QWs.
Multiply charged metal ions in high current pulsed vacuum arcs
Authors: Yushkov G. Yu. , Nikolaev A. G. , Frolova V. P. , Oks E. M. , Rousskikh A. G. , Zhigalin A. S.
Published: December 2017

We show that vacuum arc plasma discharges with a current of several kiloamperes and duration of a few microseconds can generate multiply charged metal ions with charge states greater than 10+. The physical mechanism behind this is discussed, suggesting an optimum arc current for higher charge states depending on the pulse duration and cathode material. Measurements of ion mass-to-charge ratio and images taken with nanosecond resolution suggest that, higher charge state ions are produced at characteristic distances of ∼10 mm from the cathode as the arc current peaks, and the process responsible for their generation is additional ionization as the discharge is pinched by its self-magnetic field. The maximum and mean ion charge states reveal a considerable increase for the all cathode materials studied: magnesium, aluminum, zirconium, tin, tantalum, gold, lead, and bismuth. For bismuth ions, the maximum charge state reaches a record-breaking value of 17+ and the mean of the charge state distribution is 12.6+. The results obtained are of interest for vacuum arc discharge physics and for ion beam technologies.
Pressure-induced structural evolution, optical and electronic transitions of nontoxic organometal halide perovskite-based methylammonium tin chloride
Authors: Wang Lingrui , Ou Tianji , Wang Kai , Xiao Guanjun , Gao Chunxiao , Zou Bo
Published: December 2017

Hybrid solar cells with organometal halide perovskites have already reached a power conversion efficiency exceeding 22.1%, but their toxic lead component remains a serious concern. Hence, the replacement of lead with nontoxic alternatives, such as tin, has attracted increasing interest. This study investigates the structural and optoelectronic properties of nontoxic perovskite methylammonium tin chloride (MASnCl3, MA: CH3NH3) under pressure. The synchrotron X-ray diffraction experiment shows that the sample transforms from the monoclinic to the triclinic phase and then amorphizes. The tilting and distortion of [SnCl6]4− octahedra are mainly responsible for the bandgap decreasing below 1.0 GPa. Upon further compression, an additional optical absorption peak appears, which is ascribed to the conduction band splitting of the triclinic MASnCl3. The high pressure behavior of MA cations indicates that the interaction between MA cations and [SnCl6]4− octahedra is strengthened. The pressure-induced electrical resistance evolution of MASnCl3 coincides with the structural changes. The intrinsic properties and the stability of nontoxic Sn-based hybrid perovskites provide better understanding and insights into their potential applications in photovoltaics.
Temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystal
Authors: Cui Xiaolei , Yuan Sijian , Zhang Huotian , Zhang Xin , Wang Pengfei , Tu Li , Sun Zhengyi , Wang Jiao , Zhan Yiqiang , Zheng Lirong
Published: December 2017

In this paper, the temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystals are investigated. The dynamic current-time measurement results at different temperatures directly demonstrate that the electrical properties of the perovskite single crystal are dependent on the work temperature. We find that the Poole-Frankel conduction mechanism fits the current-voltage curves at small bias voltage (0–1 V) under darkness, which is mainly attributed to the surface defect states. The capability of carriers de-trapping from defects varies with different work temperatures, resulting in an increased current as the temperature increases under both darkness and illumination. In addition, the different transient photocurrent responses of incident light at two wavelengths (470 nm, 550 nm) further confirm the existence of defect states on the single crystal surface.
A multiscale transport model for non-classical nanochannel electroosmosis
Authors: Bhadauria Ravi , Aluru N. R.
Published: December 2017

We present a multiscale model describing the electroosmotic flow (EOF) in nanoscale channels involving high surface charge liquid-solid interfaces. The departure of the EOF velocity profiles from classical predictions is explained by the non-classical charge distribution in the confined direction including charge inversion, reduced mobility of interfacial counter-ions, and subsequent enhancement of the local viscosity. The excess component of the local solvent viscosity is modeled by the local application of the Fuoss-Onsager theory and the Hubbard-Onsager electro-hydrodynamic equation based dielectric friction theory. The electroosmotic slip velocity is estimated from the interfacial friction coefficient, which in turn is calculated using a generalized Langevin equation based dynamical framework. The proposed model for local viscosity enhancement and EOF velocity shows good agreement of corresponding physical quantities against relevant molecular dynamics simulation results, including the cases of anomalous transport such as EOF reversal.
Identification of a new low energy 1u state in dicopper with resonant four-wave mixing
Authors: Visser B. , Beck M. , Bornhauser P. , Knopp G. , van Bokhoven J. A. , Marquardt R. , Gourlaouen C. , Radi P. P.
Published: December 2017

The low energy electronic structure of the copper dimer has been re-investigated using non-linear four-wave mixing spectroscopy and high level ab initio calculations. In addition to the measurement of the previously reported A, B, and C electronic states, a new state denoted A′ is identified with T0 = 20 100.4090(16) cm−1 (63Cu2). Rotational analysis of the A′–X (0,0) and (1,0) transitions leads to the assignment of A′ 1u. Ab initio calculations present the first theoretical description of the low energy states of the copper dimer in Hund’s case (c) and confirm the experimental assignment. The discovery of this new low energy excited state emphasizes that spin-orbit coupling is significant in states with d-hole electronic configurations and resolves a decades-long mystery in the initial assignment of the A state.
Note: Assessment of the SCAN+rVV10 functional for the structure of liquid water
Authors: Wiktor Julia , Ambrosio Francesco , Pasquarello Alfredo
Published: December 2017

The performance of the SCAN+rVV10 functional in modeling the structural properties of liquid water is studied through constant-volume ab initio molecular dynamics simulations with both classical and quantum nuclei. The radial distribution functions are found to be slightly overstructured with respect to experiment, but overall similar to those achieved with the bare SCAN and the rVV10 functionals. From the pressures calculated during the dynamics, it is inferred that the SCAN+rVV10 functional leads to a noticeable overestimation of the density of liquid water.
Single transverse mode protein laser
Authors: Dogru Itir Bakis , Min Kyungtaek , Umar Muhammad , Bahmani Jalali Houman , Begar Efe , Conkar Deniz , Firat Karalar Elif Nur , Kim Sunghwan , Nizamoglu Sedat
Published: December 2017

Here, we report a single transverse mode distributed feedback (DFB) protein laser. The gain medium that is composed of enhanced green fluorescent protein in a silk fibroin matrix yields a waveguiding gain layer on a DFB resonator. The thin TiO2 layer on the quartz grating improves optical feedback due to the increased effective refractive index. The protein laser shows a single transverse mode lasing at the wavelength of 520 nm with the threshold level of 92.1 μJ/mm2.
Effects of stressor characteristics on early warning signs of critical transitions and “critical coupling” in complex dynamical systems
Authors: Blume Steffen O. P. , Sansavini Giovanni
Published: December 2017

Complex dynamical systems face abrupt transitions into unstable and catastrophic regimes. These critical transitions are triggered by gradual modifications in stressors, which push the dynamical system towards unstable regimes. Bifurcation analysis can characterize such critical thresholds, beyond which systems become unstable. Moreover, the stochasticity of the external stressors causes small-scale fluctuations in the system response. In some systems, the decomposition of these signal fluctuations into precursor signals can reveal early warning signs prior to the critical transition. Here, we present a dynamical analysis of a power system subjected to an increasing load level and small-scale stochastic load perturbations. We show that the auto- and cross-correlations of bus voltage magnitudes increase, leading up to a Hopf bifurcation point, and further grow until the system collapses. This evidences a gradual transition into a state of “critical coupling,” which is complementary to the established concept of “critical slowing down.” Furthermore, we analyze the effects of the type of load perturbation and load characteristics on early warning signs and find that gradient changes in the autocorrelation provide early warning signs of the imminent critical transition under white-noise but not for auto-correlated load perturbations. Furthermore, the cross-correlation between all voltage magnitude pairs generally increases prior to and beyond the Hopf bifurcation point, indicating “critical coupling,” but cannot provide early warning indications. Finally, we show that the established early warning indicators are oblivious to limit-induced bifurcations and, in the case of the power system model considered here, only react to an approaching Hopf bifurcation.
Characterization and modeling of SET/RESET cycling induced read-disturb failure time degradation in a resistive switching memory
Authors: Su Po-Cheng , Hsu Chun-Chi , Du Sin-I , Wang Tahui
Published: December 2017

Read operation induced disturbance in SET-state in a tungsten oxide resistive switching memory is investigated. We observe that the reduction of oxygen vacancy density during read-disturb follows power-law dependence on cumulative read-disturb time. Our study shows that the SET-state read-disturb immunity progressively degrades by orders of magnitude as SET/RESET cycle number increases. To explore the cause of the read-disturb degradation, we perform a constant voltage stress to emulate high-field stress effects in SET/RESET cycling. We find that the read-disturb failure time degradation is attributed to high-field stress-generated oxide traps. Since the stress-generated traps may substitute for some of oxygen vacancies in forming conductive percolation paths in a switching dielectric, a stressed cell has a reduced oxygen vacancy density in SET-state, which in turn results in a shorter read-disturb failure time. We develop an analytical read-disturb degradation model including both cycling induced oxide trap creation and read-disturb induced oxygen vacancy reduction. Our model can well reproduce the measured read-disturb failure time degradation in a cycled cell without using fitting parameters.
Trapping and escape in a turbid medium
Authors: Krapivsky P. L. , Redner S.
Published: December 2017

We investigate the absorption of diffusing molecules in a fluid-filled spherical beaker that contains many small reactive traps. The molecules are absorbed either by hitting a trap or by escaping via the beaker walls. In the physical situation where the number N of traps is large and their radii a are small compared to the beaker radius R, the fraction of molecules E that escape to the beaker wall and the complementary fraction T that eventually are absorbed by the traps depend only on the dimensionless parameter combination λ = Na/R. We compute E and T as a function of λ for a spherical beaker and for beakers of other three-dimensional shapes. The asymptotic behavior is found to be universal: 1 − E ∼ λ for λ → 0 and E ∼ λ−1/2 for λ → ∞.
Guided ion beam and theoretical studies of the bond energy of SmS+
Authors: Armentrout P. B. , Demireva Maria , Peterson Kirk A.
Published: December 2017

Previous work has shown that atomic samarium cations react with carbonyl sulfide to form SmS+ + CO in an exothermic and barrierless process. To characterize this reaction further, the bond energy of SmS+ is determined in the present study using guided ion beam tandem mass spectrometry. Reactions of SmS+ with Xe, CO, and O2 are examined. Results for collision-induced dissociation processes with all three molecules along with the endothermicity of the SmS+ + CO → Sm+ + COS exchange reaction are combined to yield D0(Sm+–S) = 3.37 ± 0.20 eV. The CO and O2 reactions also yield a SmSO+ product, with measured endothermicities that indicate D0(SSm+–O) = 3.73 ± 0.16 eV and D0(OSm+–S) = 1.38 ± 0.27 eV. The SmS+ bond energy is compared with theoretical values characterized at several levels of theory, including CCSD(T) complete basis set extrapolations using all-electron basis sets. Multireference configuration interaction calculations with explicit spin-orbit calculations along with composite thermochemistry using the Feller-Peterson-Dixon method and all-electron basis sets were also explored for SmS+, and for comparison, SmO, SmO+, and EuO.
Separating grain-boundary and bulk recombination with time-resolved photoluminescence microscopy
Authors: Kuciauskas Darius , Lu Dingyuan , Grover Sachit , Xiong Gang , Gloeckler Markus
Published: December 2017

Two-photon excitation (2PE) microscopy allows contactless and non-destructive cross-sectional analysis of grain-boundary (GB) and grain-interior (GI) properties in polycrystalline solar cells, with measurements of doping uniformity, space-charge field distribution, and carrier dynamics in different regions of the device. Using 2PE time-resolved microscopy, we analyzed charge-carrier lifetimes near the GBs and in the GI of polycrystalline thin-film CdTe solar cells doped with As. When the grain radius is larger than the minority-carrier diffusion length, GI lifetimes are interpreted as the bulk lifetimes τB, and GB recombination velocity SGB is extracted by comparing recombination rates in the GI and near GBs. In As-doped CdTe solar cells, we find τB = 1.0–2.4 ns and SGB = (1–4) × 105 cm/s. The results imply the potential to improve solar cell voltage via GB passivation and reduced recombination center concentration in the GI.
A note on the Duffin-Kemmer-Petiau equation in (1+1) space-time dimensions
Authors: Lunardi José T.
Published: December 2017

In the last years, several papers addressed the supposed spin-1 sector of the massive Duffin-Kemmer-Petiau (DKP) equation restricted to (1+1) space-time dimensions. In this note, we show explicitly that this is a misleading approach, since the DKP algebra in (1+1) dimensions admits only a spin-0 representation. Our result also is useful to understand why several recent papers found coincident results for both spin-0 and spin-1 sectors of the DKP theory in (3+1) dimensions when the dynamics is restricted to one space dimension.
Direct measurements of meltwater runoff on the Greenland ice sheet surface
Authors: Smith Laurence C. , Yang Kang , Pitcher Lincoln H , Overstreet Brandon T. , Chu Vena W. , Rennermalm Åsa K. , Ryan Jonathan C. , Cooper Matthew G. , Gleason Colin J. , Tedesco Marco , Jeyaratnam Jeyavinoth , van As Dirk , van den Broeke Michiel R. , van de Berg Willem Jan , Noël Brice , Langen Peter L. , Cullather Richard I. , Zhao Bin , Willis Michael J. , Hubbard Alun , Box Jason E. , Jenner Brittany A. , Behar Alberto E.
Published: December 2017

Significance

Meltwater runoff is an important hydrological process operating on the Greenland ice sheet surface that is rarely studied directly. By combining satellite and drone remote sensing with continuous field measurements of discharge in a large supraglacial river, we obtained 72 h of runoff observations suitable for comparison with climate model predictions. The field observations quantify how a large, fluvial supraglacial catchment attenuates the magnitude and timing of runoff delivered to its terminal moulin and hence the bed. The data are used to calibrate classical fluvial hydrology equations to improve meltwater runoff models and to demonstrate that broad-scale surface water drainage patterns that form on the ice surface powerfully alter the timing, magnitude, and locations of meltwater penetrating into the ice sheet.