bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se2 absorber materials
Authors: Ferguson Andrew J. , Farshchi Rouin , Paul Pran K. , Dippo Pat , Bailey Jeff , Poplavskyy Dmitry , Khanam Afrina , Tuomisto Filip , Arehart Aaron R. , Kuciauskas Darius
Published: June 2020

Using a combination of optical and electrical measurements, we develop a model for metastable defects in Ag-alloyed Cu(In,Ga)Se2, one of the leading thin film photovoltaic materials. By controlling the pre-selenization conditions of the back contact prior to the growth of polycrystalline (Ag,Cu)(In,Ga)Se2 absorbers and subsequently exposing them to various stresses (light soaking and dark-heat), we explore the nature and role of metastable defects on the electro-optical and photovoltaic performance of high-efficiency solar cell materials and devices. Positron annihilation spectroscopy indicates that dark-heat exposure results in an increase in the concentration of the selenium–copper divacancy complex (VSe–VCu), attributed to depassivation of donor defects. Deep-level optical spectroscopy finds a corresponding increase of a defect at Ev + 0.98 eV, and deep-level transient spectroscopy suggests that this increase is accompanied by a decrease in the concentration of mid-bandgap recombination centers. Time-resolved photoluminescence excitation spectroscopy data are consistent with the presence of the VSe–VCu divacancy complex, which may act as a shallow trap for the minority carriers. Light-soaking experiments are consistent with the VSe–VCu optical cycle proposed by Lany and Zunger, resulting in the conversion of shallow traps into recombination states that limit the effective minority carrier recombination time (and the associated carrier diffusion length) and an increase in the doping density that limits carrier extraction in photovoltaic devices.
Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D
Authors: Casali L. , Osborne T. H. , Grierson B. A. , McLean A. G. , Meier E. T. , Ren J. , Shafer M. W. , Wang H. , Watkins J. G.
Published: June 2020

Impurity seeding studies in the small angle slot (SAS) divertor at DIII-D have revealed a strong relationship between the detachment onset and pedestal characteristics with both target geometry and impurity species. N2 seeding in the slot has led to the first simultaneous observation of detachment on the entire suite of boundary diagnostics viewing the SAS without degradation of core confinement. SOLPS-ITER simulations with D+C+N, full cross field drifts, and n–n collisions activated are performed for the first time in DIII-D to interpret the behavior. This highlights a strong effect of divertor configuration and plasma drifts on the recycling source distribution with significant consequences on plasma flows. Flow reversal is found for both main ions and impurities affecting strongly the impurity transport and providing an explanation for the observed dependence on the strike point location of the detachment onset and impurity leakage found in the experiments. Matched discharges with either nitrogen or neon injection show that while nitrogen does not significantly affect the pedestal, neon leads to increased pedestal pressure gradients and improved pedestal stability. Little nitrogen penetrates in the core, but a significant amount of neon is found in the pedestal consistent with the different ionization potentials of the two impurities. This work demonstrates that neutral and impurity distributions in the divertor can be controlled through variations in strike point locations in a fixed baffle structure. Divertor geometry combined with impurity seeding enables mitigated divertor heat flux balancing core contamination, thus leading to enhanced divertor dissipation and improved core-edge compatibility, which are essential for ITER and for future fusion reactors.
The accurate measurement of spin orbit torque by utilizing the harmonic longitudinal voltage with Wheatstone bridge structure
Authors: Wang Bo , Guo Yonghai , Han Bo , Yan Ze , Wang Tao , Yang Dezheng , Fan Xiaolong , Cao Jiangwei
Published: June 2020

The microscopic mechanism for the current-induced spin–orbit torque (SOT) in magnetic heterostructures is still under debate. The accurate measurement of SOT effective fields and their thickness dependence is the basis for understanding this issue. In this work, we measured the SOT effective fields for Pt/NiFe bilayers by utilizing the harmonic longitudinal voltage (HLV) method with a Wheatstone bridge structure. Benefiting from the elimination of the linear resistance in the bridge structure and the large magnetoresistance difference resulting from the large length–width ratio of the bridge element, we achieved very high measurement accuracy for both field-like and damping-like effective fields in the Pt/NiFe bilayers. On this basis, we demonstrated the possibility of the SOT measurement with a relatively low current density (∼109 A/m2) by utilizing the HLV method with a Wheatstone bridge structure and found that the method we proposed is also applicable to the Pt/CoFeB system with a low anisotropic magnetoresistance ratio.
Broadband metamaterial microwave absorber based on asymmetric sectional resonator structures
Authors: Cheng Yongzhi , Luo Hui , Chen Fu
Published: June 2020

In this paper, we present a novel design of broadband metamaterial microwave absorber (MWA) based on asymmetric sectional resonator structures (SRSs), which has been verified by simulation, calculation based on circuit theory, and experiment. The broadband perfect absorption of the MWA can be obtained by assembling four asymmetric SRSs with different sizes. The numerical results indicate that the bandwidth of the broadband MWA based on asymmetric SRSs is about 16.2 times of the ones based on single SRS or four complete symmetric SRSs. The broadband perfect absorption of the proposed MWA mainly originates from the excitation of the fundamental resonance mode of the SRS. The numerical results also demonstrate that the broadband MWA exhibits an angle-insensitivity microwave absorption capacity, which is manifested as a high absorption level at large incident angles for both transverse electric and transverse magnetic modes. Thus, the proposed broadband MWA turns out to be suitable for a wide variety of potential applications in stealth technology and energy harvesting.
Drift Alfvén energetic particle stability with circulating particles
Authors: Li Y. , Hu S. , Zheng W. , Xiao Y.
Published: June 2020

We develop from scratch a comprehensive linear stability eigenvalue code based on a finite element method, namely, the drift Alfvén energetic particle stability (DAEPS) code, to investigate the physics of various stable and unstable modes observed in toroidal fusion plasmas, which has the advantage of accurate calculation of the mode characteristics near marginal stability. The DAEPS code is dedicated to providing a thorough understanding of low frequency modes in collisionless plasmas, e.g., shear Alfvén wave SAW and drift Alfvén wave physics with an energetic particle (EP) effect. DAEPS can calculate the linear frequency and growth rate for these modes by keeping correct asymptotic behavior in ballooning space. In this work, we demonstrate that the DAEPS code is able to analyze linear electromagnetic modes excited by circulating particles, including the thermal particle excited beta-induced Alfvén eigenmode and EP excited toroidicity-induced Alfvén eigenmode, where the verifications are performed successfully with other codes and theories, where the finite orbit width is discovered to play an important stabilizing role, which are usually ignored by traditional theory.
Thermal droop in III-nitride based light-emitting diodes: Physical origin and perspectives
Authors: Meneghini Matteo , De Santi Carlo , Tibaldi Alberto , Vallone Marco , Bertazzi Francesco , Meneghesso Gaudenzio , Zanoni Enrico , Goano Michele
Published: June 2020

This tutorial paper focuses on the physical origin of thermal droop, i.e., the decrease in the luminescence of light-emitting diodes (LEDs) induced by increasing temperature. III-nitride-based LEDs are becoming a pervasive technology, covering several fields from lighting to displays, from automotive to portable electronics, and from horticulture to sensing. In all these environments, high efficiency is a fundamental requirement, for reducing power consumption and system cost. Over the last decade, a great deal of effort has been put in the analysis of the efficiency droop, the decrease in LED internal quantum efficiency (IQE) induced by high current density. On the other hand, an IQE decrease is observed also for increasing temperature, a phenomenon usually referred to as thermal droop. For commercial LEDs, the IQE decrease related to thermal droop can be comparable to that of efficiency droop: for this reason, understanding thermal droop is a fundamental step for making LEDs capable of operating at high temperature levels. In several fields (including street lighting, automotive, photochemical treatments, projection, entertainment lighting, etc.), compact and high-flux light sources are required: typically, to reduce the size, weight, and cost of the systems, LEDs are mounted in compact arrays, and heat sinks are reduced to a minimum. As a consequence, LEDs can easily reach junction temperatures above 85–100 °C and are rated for junction temperatures up to 150–175 °C (figures from commercially available LED datasheets: Cree XHP70, Osram LUW HWQP, Nichia NVSL219CT, Samsung LH351B, and LedEngin LZP-00CW0R) and this motivates a careful analysis of thermal droop. This paper discusses the possible physical causes of thermal droop. After an introduction on the loss mechanisms in junctions, we will individually focus on the following processes: (i) Shockley–Read–Hall (SRH) recombination and properties of the related defects; (ii) Auger recombination and its temperature dependence, including the discussion of trap-assisted Auger recombination; (iii) impact of carrier transport on the thermal droop, including a discussion on carrier delocalization, escape, and freeze out; (iv) non-SRH defect-related droop mechanisms. In addition, (v) we discuss the processes that contribute to light emission at extremely low current levels and (vi) the thermal droop in deep ultraviolet LEDs, also with reference to the main parasitic emission bands. The results presented within this paper give a tutorial perspective on thermal droop; in addition, they suggest a pathway for the mitigation of this process and for the development of LEDs with stable optical output over a broad temperature range.
Three-dimensional measurements of fundamental plasma parameters in pulsed ICP operation
Authors: Han Jia , Pribyl Patrick , Gekelman Walter , Paterson Alex
Published: June 2020

Radio frequency inductively coupled plasma sources are widely used in low temperature industrial processing. Recent computer simulations and experiments indicate significant improvement in processing results with the use of pulsed plasmas. We report three dimensional spatial and temporal measurements of fundamental plasma parameters in a pulsed Argon plasma in an industrial etch tool modified for diagnostic access. The pulse repetition rate is 1 kHz with 50% duty cycle. The density does not decay to zero at the end of the afterglow period, and this affects the initial conditions for the beginning of the next powered phase. At 5 mTorr, the plasma starts in the E-mode for each pulse and grows into a “ring” shape density profile. Subsequently, the profile evolves to peak in the middle of the chamber as it reaches a steady state toward the end of the active-glow. At 25 mTorr, the plasma density profile always peaks at the center of the chamber throughout the entire pulse.
Dielectric polarizability of alkali and alkaline-earth modified silicate glasses at microwave frequency
Authors: Lanagan Michael T. , Cai Ling , Lamberson Lisa A. , Wu Jingshi , Streltsova Elena , Smith Nicholas J.
Published: June 2020

The dielectric properties of alkali and alkaline earth-modified silicate glasses were characterized in the frequency range where electronic and ionic polarizabilities contribute to permittivity. From the Clausius–Mossotti (CM) model, dielectric polarizability of each cation-oxygen constituent was determined from the permittivity and molar volume. The silicon–oxygen polarizability of silica glass (5.24 Å3) is significantly higher than that of crystalline quartz (4.87 Å3), suggesting that additional polarization modes contribute to glass permittivity. A full range of alkali species (Li, Na, K, Rb, and Cs) were then added as glass network modifiers through a series of binary silicate glasses, and the silicon–oxygen polarizability increased to 5.38 Å3. A similar trend was observed for alkaline-earth aluminosilicate glasses in which the polarizability increased with the addition of cationic modifiers to 5.89 Å3. CM analysis provides a method to explore the fundamental relationship between the glass structure and its unique polarization response in the microwave frequency range. Microwave permittivity values are predicted over broad compositional ranges for alkali and alkaline earth-modified silicate glasses using the CM relationship.
Three-dimensional vortical structures generated by plasma synthetic jets in crossflow
Authors: Zong H. , Kotsonis M.
Published: June 2020

In the present study, phase-locked tomographic particle image velocimetry measurements are performed to obtain the complex three-dimensional vortex system created by the interaction of plasma synthetic jets with external crossflow. Three orifice configurations (round, transverse slot, and longitudinal slot) are investigated. For the round orifice case, the vortex system consists of a starting vortex ring surrounding the jet head, a hanging vortex pair residing in the two lateral sides of the jet body, several shear layer vortices bridging the two legs of the hanging vortex pair, and a hairpin vortex induced by the low-speed secondary jet. For the slot orifice cases, the above vortex system is also present; nevertheless, the interconnections of the vortices are further intersected by the rib vortices that are branched out of the elongated vortex ring during axis switching. The counter-rotating vortex pair observed in the far field is essentially evolving from the hanging vortex pair in the near field.
Fluvial instabilities
Authors: Dey Subhasish , Ali Sk Zeeshan
Published: June 2020

Fluvial instabilities originate from an interplay between the carrier fluid and the erodible loose boundary at their interface, manifesting a variety of sedimentary architectures with length scales spanning from a few millimeters to hundreds of meters. This review sheds light on the current state-of-the-science of the subject, explaining the fluvial instabilities from three broad perspectives. They are micro-scale, meso-scale, and macro-scale instabilities. The interactions between the near-bed hydrodynamics and the sediment dynamics in generating various kinds of instabilities, including their natures and driving mechanisms, are thoroughly appraised in the light of laboratory experimental results, field observations, and theoretical backgrounds. Besides, this review addresses the current challenges, delineating key points as a future research scope.
1.5 – 1.6 μm semiconductor lasers with an asymmetric periodic optically coupled waveguide
Authors: Bagaeva O.O. , Danilov A.I. , Ivanov A.V. , Kurnosov V.D. , Kurnosov K.V. , Kurnyavko Yu.V. , Ladugin M.A. , Marmalyuk A.A. , Romantsevich V.I. , Ryaboshtan Yu.L. , Simakov V.A. , Svetogorov V.N. , Chernov R.V.
Published: June 2020

High-power 1.5 – 1.6-μm semiconductor lasers with an asymmetric periodic optically coupled waveguide are developed and their current – voltage, light – current, and spectral characteristics are experimentally studied. The characteristics of these lasers are compared with the characteristics of traditional lasers based on double separate-confinement heterostructures. It is shown that the developed lasers have lower divergence and almost the same threshold and power characteristics as conventional lasers with Fabry – Perot resonators. The developed lasers with a cavity length of 1.6 mm and a mesa-stripe contact width of 3 μm mounted in a housing 11 mm in diameter have a power no lower than 200 mW at a pump current not exceeding 700 mA with a divergence of 25 – 35° versus 45° typical for conventional lasers.
Laser cooling of atoms at narrow optical transitions in fields with a polarisation gradient
Authors: Il’enkov R.Ya. , Prudnikov O.N. , Taichenachev A.V. , Yudin V.I.
Published: June 2020

The efficiency of the polarisation mechanisms of laser cooling of atoms is analysed using narrow optical transitions for which the recoil energy is greater than or comparable to the natural line width. By the example of atoms with the J
g = 1 → J
e = 2 optical transition (J
g and J
e are the total angular momenta of the ground and excited states) in the resonant light fields of σ
+ – σ
– and lin⊥lin configurations, the analysis of the minimum achievable energies of laser-cooled atoms is performed. It is shown that the polarisation mechanisms of laser cooling under conditions of a significant influence of recoil effects become less efficient and do not lead to average kinetic energies of an ensemble of atoms below the Doppler limit.
Miniature quantum frequency standard based on the phenomenon of coherent population trapping in vapours of 87Rb atoms
Authors: Skvortsov M.N. , Ignatovich S.M. , Vishnyakov V.I. , Kvashnin N.L. , Mesenzova I.S. , Brazhnikov D.V. , Vasil’ev V.A. , Taichenachev A.V. , Yudin V.I. , Bagayev S.N. , Blinov I.Yu. , Pal’chikov V.G. , Samokhvalov Yu.S. , Parekhin D.A.
Published: June 2020

We report the results of the development and production of a quantum frequency standard (QFS) based on the coherent population trapping (CPT) resonance observed on the D1 absorption line of 87Rb atoms. The effect of various physical factors on the QFS frequency is studied, and the optimal physical parameters of the device to attain the best frequency stability are determined. The measured relative frequency instability (Allan deviation) is ∼9 × 10−12 for the averaging time of 1 s, 3 ×10−13 for 1000 s, and 1.5 ×10−12 for 24 hours. For a volume of 60 cm3, the power consumption of the entire device is 300 mW. The designed QFS can be used in a new-generation satellite navigation systems with increased accuracy and reliability, as well as for solving a number of other problems of science and technology.
Trapping of lithium atoms in a large hollow optical dipole trap
Authors: Vinogradov V.A. , Karpov K.A. , Lukashov S.S. , Turlapov A.V.
Published: June 2020

We describe the trapping of lithium atoms in an optical dipole trap about 1 mm in size, with a nearly rectangular potential. The trap has the shape of a cylinder with flat bases. The confinement region is bounded by thin walls produced by light with a frequency blue-detuned from an atomic transition (resonance) frequency by 19 GHz. Before trapping, the gas is collected and cooled in a magneto-optical trap whose centre nearly coincides with the centre of the dipole trap. After switching off the magneto-optical trap, we have photographed the atoms remaining in the dipole trap.
Effect of boundary conditions on fluctuations of the Bose condensate of interacting atoms
Authors: Tarasov S.V.
Published: June 2020

For a gas of trapped interacting atoms forming a Bose condensate, we demonstrate a possibility of a significant influence of the boundary conditions on the statistics of the number of particles in the fundamental mode of the system. The analysis is carried out in the Bogoliubov – Popov low-temperature approximation for model homogeneous cubic traps with periodic or combined periodic and zero boundary conditions. It is shown that the effect of the boundary conditions does not weaken even in the region of parameters corresponding to the relatively strong interaction in the Thomas – Fermi asymptotic case, and does not disappear when proceeding to the thermodynamic limit.
Study of saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell
Authors: Goncharov A.N. , Klimacheva O.A. , Mel’nikova A.O.
Published: June 2020

The saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell are studied. The line width (FWHM) for the observed saturated-absorption resonance on the 33P0 → 33D1 transition turns out to be ∼220 MHz. Experiments are performed using a system based on a 766-nm diode laser with amplification and frequency doubling in a nonlinear BiBO crystal. The results obtained are of interest for sub-Doppler cooling on the 33P2 → 33D3 transition.
Forest fires in Mexico: an approach to estimate fire probabilities
Authors: Galván Luis , Magaña Víctor
Published: June 2020

The probabilities of forest fires in Mexico are estimated using information on precipitation and temperature, along with data on type of vegetation, human activities near forests and fire prevention policies. The proposed model addresses the factors that account for extreme wildfire hazard, and may provide a basis for fire prevention actions, reducing vulnerability factors.
Tourism and little penguins: a comparative study of survival and reproductive parameters
Authors: Agnew Philippa , Houston David M.
Published: June 2020

Abstract ContextTourism operations that provide the opportunity for wildlife viewing can support conservation management through public education, habitat protection, population management, research activities and revenue generation. However, alongside these potential benefits there can be negative effects on the species that include the possibility of reduced breeding success, survival and, subsequently, population growth. AimWe sought to establish whether a tourism operation affected little penguins Eudyptula minor by comparing reproductive and survival parameters of two managed populations in Oamaru, New Zealand. One population was the focus of a tourism operation, whereas the other (located nearby) did not provide any public access. The tourism operation implemented strategies to reduce human disturbance, including the reduction of noise, light and movement from visitors during viewing, and by ensuring that visitors were restricted to designated viewing areas. MethodsNesting boxes were installed at both colonies that facilitated weekly monitoring of the populations. The monitoring program (1993–2017) included weekly checks of every nesting box in the colony for the presence of eggs, chicks and adults. Chicks were weighed before fledging, and both fledglings and breeding adults were individually marked. Key resultsLay dates, breeding success, chick fledge mass and survival rates were not measurably different between the two populations, indicating that there was little evidence of negative effects on the penguins at the tourist site. ConclusionsThe slight differences observed between the colonies during the time series were attributed to environmental damage sustained at the non-tourist site and a difference in the proportion of un-monitored nest sites available to the penguins when the study was initiated. ImplicationsNotwithstanding the present findings, long-term and consistent monitoring of wildlife populations facing increasing pressure from tourism is essential to ensure effects are detected and that management procedures implemented to reduce potential effects.
Common homozygosity for predicted loss-of-function variants reveals both redundant and advantageous effects of dispensable human genes
Authors: Rausell Antonio , Luo Yufei , Lopez Marie , Seeleuthner Yoann , Rapaport Franck , Favier Antoine , Stenson Peter D. , Cooper David N. , Patin Etienne , Casanova Jean-Laurent , Quintana-Murci Lluis , Abel Laurent
Published: June 2020

Significance

Human genes homozygous for apparent loss of function (LoF) variants are increasingly reported in a sizeable proportion of individuals without overt clinical phenotypes. Here, we found 166 genes with 179 predicted LoF variants for which the frequency of homozygous individuals exceeds 1% in at least one of the populations present in databases ExAC and gnomAD. These putatively dispensable genes showed relaxation of selective constraints, suggesting that a considerable proportion of these genes may be undergoing pseudogenization. Eight of these LoF variants displayed robust signals of positive selection, including two variants in genes involved in resistance to infectious diseases. The identification of dispensable genes will facilitate the identification of functions that are now redundant, or possibly even advantageous, for human survival.
Global variation in the thermal tolerances of plants
Authors: Lancaster Lesley T. , Humphreys Aelys M.
Published: June 2020

Significance

Knowledge of how thermal tolerances are distributed across major clades and biogeographic regions is important for understanding biome formation and climate change responses. However, most research has concentrated on animals, and we lack equivalent knowledge for other organisms. Here, we compile global data on heat and cold tolerances of plants, showing that many, but not all, broad-scale patterns known from animals are also true for plants. Importantly, failing to account simultaneously for influences of local environments, and evolutionary and biogeographic histories, can mislead conclusions about underlying drivers. Our study unravels how and why plant cold and heat tolerances vary globally and highlights that all plants, particularly at mid-to-high latitudes and in their nonhardened state, are vulnerable to ongoing climate change.
Estimating US fossil fuel CO
2
emissions from measurements of
14
C in atmospheric CO
2
Authors: Basu Sourish , Lehman Scott J. , Miller John B. , Andrews Arlyn E. , Sweeney Colm , Gurney Kevin R. , Xu Xiaomei , Southon John , Tans Pieter P.
Published: June 2020

Significance

The vast majority of the world’s nations have pledged to reduce emissions of CO
2
and other greenhouse gases and to track and report emissions using accounting methods based on economic statistics and emissions factors. Here, we present an independent method of emissions monitoring based directly on atmospheric observations and the strong fossil fuel CO
2
detection capability afforded by precise measurements of
14
CO
2
in air samples obtained largely from NOAA’s air sampling network. The national total we derive for 2010 is larger than from available inventories, including the US EPA, but is within error bounds of the updated Vulcan emission data product. These results suggest that reported emissions can now be subject to independent and objective evaluation using atmospheric
14
CO
2
measurements.
A continuous reaction network that produces RNA precursors
Authors: Yi Ruiqin , Tran Quoc Phuong , Ali Sarfaraz , Yoda Isao , Adam Zachary R. , Cleaves H. James , Fahrenbach Albert C.
Published: June 2020

Significance

RNA may have been the original polymer to arise spontaneously on the early Earth through natural geochemistry. Although direct physical evidence regarding early Earth’s geochemistry is extremely limited, complex chemical reaction networks are thought to have played an important role in chemical evolution. The present study demonstrates an experimental model reaction network that generates a number of compounds that can lead to RNA synthesis in a single mixture starting from simple organic and inorganic feedstocks. Models of this type will help explain which conditions are needed to produce RNA in primitive planetary settings.
A cost-effectiveness analysis of the number of samples to collect and test from a sexual assault
Authors: Wang Zhengli , MacMillan Kevin , Powell Mark , Wein Lawrence M.
Published: June 2020

Significance

Within the context of sexual assaults, we address a fundamental issue in criminal investigations: how much evidence to collect and process. Using data from the San Francisco Police Department, we show that machine learning algorithms outperform sexual assault forensic examiners at identifying probative samples. Relative to selective testing of samples, testing all DNA samples in a sexual assault kit more than doubles the number of sexual assault kits generating a DNA profile that can be entered into the criminal DNA database, at only a slightly lower benefit-to-cost ratio. Our results suggest that the yield of DNA profiles for the database would increase another 47.2% by collecting samples from the three most probative locations (as deemed by the machine learning algorithm).
High-throughput photocapture approach for reaction discovery
Authors: Bayly Alison A. , McDonald Benjamin R. , Mrksich Milan , Scheidt Karl A.
Published: June 2020

Significance

Mass spectrometry (MS) has inspired powerful modes of reaction discovery. Chemists often rely on MS methods, such as liquid-chromatography MS and gas chromatography MS, to rapidly assess hundreds of small-scale reactions. These chromatography-based MS techniques are preferred as they typically provide data consistent with scaled-up yields. Other MS approaches that more rapidly analyze reactions frequently provide results inconsistent with scaled-up yields. Herein we describe the development of a high-throughput platform that overcomes the analytical bottleneck presented by chromatography-based MS techniques while retaining consistency with scaled-up results. Our MS method, which combines diazirine photocapture and self-assembled monolayers for desorption/ionization MS, enabled the analysis of ∼2,000 reactions in <2.5 h to realize an intermolecular photoredox reaction.
“It’s writtenniistobut it sounds likeknee stew.”
Authors: Genee Inge
Published: June 2020

This paper argues for pragmatism rather than linguistic purity in orthography design for endangered Indigenous languages such as Blackfoot, emphasizing the need to see orthography standardization as a dynamic process rather than a static result. It explores the ongoing lack of community agreement about the best way to write the Blackfoot language and lack of widespread proficiency in the use of its standard orthography, and then describes ways in which this is mitigated in the Blackfoot Language Resources and Digital Dictionary project, a suite of web resources created to support language maintenance and revitalization work. The website uses a combination of relaxed searches, alternative spelling fields, and multimedia content to increase accessibility of the resources for users lacking proficiency in the standard orthography.
Physics postgraduate teaching assistants’ grading approaches: conflicting goals and practices
Authors: Marshman Emily , Maries Alexandru , Sayer Ryan T , Henderson Charles , Yerushalmi Edit , Singh Chandralekha
Published: June 2020

Grading can shape students’ learning and encourage use of effective problem solving practices. Teaching assistants (TAs) are often responsible for grading student solutions and providing feedback, thus, their perceptions of grading may impact grading practices in the physics classroom. Understanding TAs’ perceptions of grading is instrumental for curriculum developers as well as professional development leaders interested in improving grading practices. In order to identify TAs’ perceptions of grading, we used a data collection tool designed to elicit TAs’ considerations when making grading decisions as well as elicit possible conflicts between their stated goals and actual grading practices. The tool was designed to explicate TAs’ attitudes towards research-based grading practices that promote effective problem solving approaches. TAs were first asked to state their goals for grading in general. Then, TAs graded student solutions in a simulated setting while explicating and discussing their underlying considerations. The data collection tool was administered at the beginning of TAs’ first postgraduate teaching appointment and again after one semester of teaching experience. We found that almost all of the TAs stated that the purpose of grading was formative, i.e. grading should encourage students to learn from their mistakes as well as inform the instructor of common student difficulties. However, when making grading decisions in a simulated setting, the majority of TAs’ grading considerations focused on correctness and they did not assign grades in a way that encourages use of effective problem solving approaches. TAs’ perceptions of grading did not change significantly during one semester of teaching experience.
Never far from shore: productive patterns in physics students’
use of the digital learning environment Algodoo
Authors: Euler Elias , Prytz Christopher , Gregorcic Bor
Published: June 2020

In this paper, we present three types of activity that we have observed during
students’ free exploration of a software called
Algodoo
, which allows students to explore a range of
physics phenomena within the same digital learning environment. We discuss how,
by responding to any of the three activity types we identify in the
students’ use of Algodoo, physics teachers can
springboard into a range of relevant physics discussions while supporting and
valuing student agency and divergent thinking. Thus, while one might not expect
students’ undirected use of a digital tool such as
Algodoo to be particularly worthwhile for the physics
classroom, we highlight how students are never ‘far from the shore’
of a productive physics discussion.
Analysis of ultra-short bunches in free-electron lasers
Authors: Campbell L T , Freund H P , Henderson J R , McNeil B W J , Traczykowski P , van der Slot P J M
Published: June 2020

Free-electron lasers (FELs) operate at wavelengths from millimeter waves through hard x-rays. At x-ray wavelengths, FELs typically rely on self-amplified spontaneous emission (SASE). Typical SASE emission contains multiple temporal ‘spikes’ which limit the longitudinal coherence of the optical output; hence, alternate schemes that improve on the longitudinal coherence of the SASE emission are of interest. In this paper, we consider electron bunches that are shorter than the SASE spike separation. In such cases, the spontaneously generated radiation consists of a single optical pulse with better longitudinal coherence than is found in typical SASE FELs. To investigate this regime, we use two FEL simulation codes. One (MINERVA) uses the slowly-varying envelope approximation (SVEA) which breaks down for extremely short pulses. The second (PUFFIN) is a particle-in-cell simulation code that is considered to be a more complete model of the underlying physics and which is able to simulate very short pulses. We first anchor these codes by showing that there is substantial agreement between the codes in simulation of the SPARC SASE FEL experiment at ENEA Frascati. We then compare the two codes for simulations using electron bunch lengths that are shorter than the SASE slice separation. The comparisons between the two codes for short bunch simulations elucidate the limitations of the SVEA in this regime but indicate that the SVEA can treat short bunches that are comparable to the cooperation length.
A comparative study of materials assembled from recombinant K31 and K81 and extracted human hair keratins
Authors: Parker Rachael N , Trent Alexis , Roth Stefaniak Kristina L , Van Dyke Mark E , Grove Tijana Z
Published: June 2020

Natural biopolymers have found success in tissue engineering and regenerative medicine applications. Their intrinsic biocompatibility and biological activity make them well suited for biomaterials development. Specifically, keratin-based biomaterials have demonstrated utility in regenerative medicine applications including bone regeneration, wound healing, and nerve regeneration. However, studies of structure-function relationships in keratin biomaterials have been hindered by the lack of homogeneous preparations of materials extracted and isolated from natural sources such as wool and hair fibers. Here we present a side-by-side comparison of natural and recombinant human hair keratin proteins K31 and K81. When combined, the recombinant proteins (i.e. rhK31 and rhK81) assemble into characteristic intermediate filament-like fibers. Coatings made from natural and recombinant dimers were compared side-by-side and investigated for coating characteristics and cell adhesion. In comparison to control substrates, the recombinant keratin materials show a higher propensity for inducing involucrin and hence, maturation in terms of potential skin cell differentiation.
Influence of stratospheric sudden warming on the tropical intraseasonal convection
Authors: Wang Feiyang , Han Yuanyuan , Zhang Shiyan , Zhang Ruhua
Published: June 2020

Madden–Julian oscillation (MJO), the dominant mode of intraseasonal variability in the tropical troposphere, has recently been shown to have a great impact on Northern Hemisphere (NH) extratropical stratosphere. But the influence of the variability in the extratropical stratosphere on MJO is seldom reported. In this study, the influence of major, mid–winter NH stratospheric sudden warmings (SSWs) on the MJO is investigated using meteorological reanalysis datasets. Our analysis reveals that SSWs also exert considerable influence on tropical intraseasonal convection. The occurrences of MJO phases 6 and 7 significantly increase during around 20 d after the onset of SSWs, corresponding to enhanced convective activity over the equatorial Central and Western Pacific. Then in the following days, the coherent eastward propagation of tropical intraseasonal convection resembles the periodic variation in a typical MJO. These results suggest that the extratropical stratosphere affects the organized tropical intraseasonal convection, and variability of the tropical intraseasonal convection related to MJO can be better grasped by taking extratropical stratospheric variability into account. Considering the complex interaction between MJO and extratropical stratosphere, further work on comprehensive understanding of the relationship between SSWs and MJO is required in future studies.
Research on Integrated Deployment Method of Digital Earth Thematic Application Model
Authors: Danpu Zhao , Xianqing Tai , Zhijie Ma
Published: June 2020

Nowadays, the digital earth not only relates to the technologies of surveying and mapping geography, but also includes the analysis and cross-application of various scientific data related to geographic information. It requires a computing environment and management for the corresponding thematic application models which supports the online analysis on the digital earth. So we proposed an integrated deployment method for digital earth thematic application models based on container cloud, which provides a flexible and scalable information integration and analysis architecture for digital earth. Firstly, a Docker image building module is designed to facilitate the user to quickly build the application model into a image. Then the Docker technology is used to implement the containerization of the application model to provide a stable running environment for the application model. Finally, the Kubernetes is used to dynamically manage the cluster resources to realize rapid expansion of computing resources. In addition, the HDFS is deployed, and the image files and various scientific data respectively store with Hbase and Apache file systems. It can ensure the read and write speed of the application model and the related data and log files. It also used zabbix framework to manage the monitoring index of the container cloud cluster to ensure the execution effect of the application model. Through the tests of typical application model, it is verified that the method can integrated deploy and apply the cross-domain, hetero-architecture, multi-version and multi-class application models on the digital earth.
Semi-supervised classification of hyperspectral images based on two branch autoencoder
Authors: Lei Z , Yi Z , Peng L , Hui S X
Published: June 2020

In this paper, we propose a novel semi-supervised method based on two branch autoencoder (TBAE) for hyperspectral images. A branch is classification function, and another branch is decoder function. Both of functions promote each other in training process. The encoder is fit for both classifier and decoder. The encoder and the decoder guide feature extraction from unlabeled samples. The encoder and the classifier guide classification for all labeled samples. We can get more information from unlabeled samples for classification. Finally, we use convolutional autoencoder (CAE) to extend TBAE and obtain TBCAE. Compared with ANN and CNN, TBAE and TBCAE have a better performance in the case of a small number of labeled samples. Use different datasets to verify these methods and print visualization of hidden layer and the reconstructed data. The results demonstrate that the proposed framework obtains credible results with a small number of labeled samples.
A multi-scale 3D convolution neural network for spectral-spatial classification of hyperspectral imagery
Authors: Qi Wenchao , Zhang Xia
Published: June 2020

Along with the remarkable achievements of various neural networks in the field of computer vision, deep learning methods have gradually been applied to hyperspectral image (HSI) classification. Traditional classification methods have several outstanding issues, including the insufficient hand-craft features and time-consuming and laborious feature extraction. We therefore propose a multi-scale, 3D convolutional neural network (CNN) framework (MSCNN), trained in an end-to-end manner for hyperspectral image classification. Using the original hyperspectral image as an input, the MSCNN framework leverages two branches of a 3D residual neural network to extract deep and abstract HSI features. Then, the HSI spectral-spatial features of different scales are fused and fed into the SoftMax layer to achieve an end-to-end hyperspectral image classification. Besides, data augmentation, dynamic learning rate, and regularization methods are used to promote the rapid convergence of MSCNN and avoid model over-fitting. Three well-known hyperspectral datasets (Indian Pines, University of Pavia and Pavia Center) were used to evaluate the classification performance of the proposed MSCNN method. The results indicate that, compared with the existing deep learning methods, the proposed MSCNN method achieves the best classification performance within the 20 training epochs. The overall accuracy (OA), average accuracy (AA), and kappa statistic (K) of MSCNN are 97.16%, 98.69% and 0.9665, respectively, for Indian Pines; 99.17%, 98.97% and 0.9888 for University of Pavia; and 99.87%, 99.70% and 0.9981 for Pavia Center.
A New Level of Detail Concept for Building Indoor Scene
Authors: Pang Yueyong , Yang Qiqi , Zhou Liangchen , Lin Bingxian , Lv Guonian
Published: June 2020

Concomitant with the acceleration of urbanization, the indoor scene of buildings becoming increasingly complex in recent years. In order to meet the needs of diverse indoor application analysis, the multi-level of detail (LOD) model of indoor scene has been paid increasing attention. However, there are two kinds of LODs in the fields of geographic information and building information, which cannot be effectively integrated. From the perspective of geographic scenario, this paper proposes a new concept of LOD to realize the construction of indoor scene model under different details. According to the effects on indoor space, the indoor components are divided into three semantic levels: enclosing component, connecting component and decorating component. Finally, several examples of indoor models combining semantic LOD, geometric LOD and process LOD are introduced.
Extraction of raft cultivation of remotely sensed high-spatial-resolution images based on LBV and wavelet transforms
Authors: Wei Baoquan , Zhao Jianhua , Li Ying , Suo Anning
Published: June 2020

A method to extract information on raft cultivation based on the LBV (The general radiance level L, visible-infrared radiation balance B, and band radiance variation vector V) transform and wavelet multi-scale decomposition was proposed. This paper selects the spectral information of typical objects and uses regression analysis to solve for the coefficients of regression. The LBV transformation of remotely sensed high-spatial-resolution imagery was derived according to the spatial characteristics of the object space, color space, and LBV variable space to obtain the B band that can be used to identify maritime targets. Multi-scale wavelet decomposition was then used to calculate the eigenvalues of the components of each sub-image by using different windows to analyze the texture features of the maritime objects, and to explore the rules of texture extraction of raft cultivation from high-spatial-resolution images. Experiments on remotely sensed ZY-3 images from Liandao Island show the following: (1) compared with the original image, the LBV-transformed image was clearer and finer details were visible in it. They helped identify and extract ground objects. (2) The eigenvalues extracted by wavelet decomposition were beneficial for the segmentation of the image. As the dimensionality of the eigenvalue increased, the accuracy of raft cultivation extraction showed an upward trend. (3) The proposed method is applicable to texture feature extraction owing to its clear rules and directionality.
Comparison to Changes of Lake Ice Phenology and Air Temperature over Northern Europe, Tibetan Plateau and Mongolian Plateau
Authors: Xingxing Wang , Yubao Qiu , Lemmetyinen Juha , Pengfei Xie , Cheng Bin , Wenshan Liang
Published: June 2020

Lake ice is a sensitive factor for the Earth’s environment and climate change research. In the comparative study on climate change to the Earth three-pole (Antarctic, Arctic, and Tibetan Plateau), the lake ice phenology can be used to represent seasonal climate changes. In this paper, the lake ice phenology and the corresponding daily temperature for 48 lakes in Northern Europe, Tibetan Plateau and Mongolia Plateau were used as the typical case for comparative research. Based on passive microwave remote sensing data. The results showed that the average lake ice cover duration experienced a consistent decreasing for the three regions from 1978-2018. However, in the northern Tibetan Plateau, though the lake ice cover duration showed a shortening trend from 1978 to 2000, it displayed a prolonged trend from 2000 to 2018. Moreover, the air temperature changes of the lake area had a significant correlation with the changes of ice cover duration in each region, and the change of 0 °C isotherm in the Northern Europe lakes are more sensitive than the Mongolian Plateau and the Tibetan Plateau. The air temperature played a major role in the change of lake ice phenology, but there were still other factors that affected the lake ice phenology changes, especially in northern Tibetan Plateau. By comparing the analysis of the ice cover duration in the three regions and the effect of air temperature on the lake ice cover duration change, it provides more evidences for the study on climate change research in different regions.
An Cnn-Based Operational Approach For Land Cover Mapping in China
Authors: Zhao Xuemei , Gao Lianru , Chen Zhengchao , Zhang Bing
Published: June 2020

National land cover map with 30m resolution, an important database for studying the interaction between human and the environment, is a tedious work. The rise of deep learning technique provides a new idea for the work. This paper reports a novel method based on deep convolutional neural networks for the national land cover mapping task. The proposed method has four major parts: classification system, data sources, training samples selection, and training & inferencing. The produced deep learning (DL)-based land cover map is compared with two highly accepted land cover maps (the reference land cover map and the GLC30). Overall accuracies of GLC30 and DL-land cover map are 76.45% and 82.59% when considering the reference land cover map as the ground truth. Overall accuracies of the reference land cover map and the DL-land cover map are 74.25% and 78.87% when the GLC30 is treated as the ground truth.