bluuebunny/crossref_metadata_2025 huggingface dataset:
High thermal conductivity of free-standing skeleton in graphene foam
Authors: Gao Jianshu , Xie Danmei , Wang Xinwei , Zhang Xin , Yue Yanan
Published: December 2020

Due to the high-porosity structure, the low thermal transport property of graphene foam (GF) is expected. However, the interconnected skeleton can still act as excellent thermal conductor branches if phonon scattering is not severely affected in the structure of graphene flakes. Such a property has not been validated experimentally due to the difficulty in sample manipulation and the fragility of the structure. In this work, we report the characterization results of thermal properties of the free-standing skeleton in GF. Three individual skeleton samples from one GF piece are prepared under the same condition. The thermal diffusivity of GF skeletons is characterized in the range of 3.26–3.48 × 10−4 m2/s, and the thermal conductivity is determined to be 520–555 W/(m K), which is two orders of magnitude larger than the value of bulk GF. These high thermal conductivity values originate from the intrinsic thermal property of graphene, while the contact interfaces, wrinkled structures, and defects induced in the synthesis process do not affect the phonon transport property significantly, which proves that the three-dimensional hierarchical graphene structure can still be implemented in energy-intensive applications.
A broadband metamaterial absorber with temperature scalability to 400 °C
Authors: Qiao Jian , Liu Yufu
Published: December 2020

A broadband metamaterial absorber intended for applications at elevated temperatures was designed and fabricated. Its performance was measured over a temperature range from room temperature to approximately 400 °C. The absorber consists of a lossy resistive frequency selective surface (RFSS) on a dielectric substrate and a metallic ground plane with high-temperature stability scalable to approximately 400 °C. The top RFSS layer, made of conductive composites, was prepared using a mixture of graphite microflakes and water glass, and it showed good chemical and thermal stability up to 400 °C. Its sheet resistance was adjustable over a wide range with different proportions of graphite flakes and decreased gradually with increasing temperature. The metamaterial absorber demonstrated broadband absorption with a reflection coefficient of less than −10 dB in the X-band frequency range (8.2–12.4 GHz), resulting in the absorption of more than 90%. The influence of testing temperature on the reflection coefficient was correlated with the variation in the sheet resistance. The proposed metamaterial absorber is a promising candidate for use in high-temperature microwave absorption applications.
Gate tunable vertical geometry phototransistor based on infrared HgTe nanocrystals
Authors: Gréboval Charlie , Noumbé Ulrich Nguétchuissi , Chu Audrey , Prado Yoann , Khalili Adrien , Dabard Corentin , Dang Tung Huu , Colis Silviu , Chaste Julien , Ouerghi Abdelkarim , Dayen Jean-Francois , Lhuillier Emmanuel
Published: December 2020

Infrared nanocrystals are promising building blocks for the design of low-cost infrared sensors. Vertical geometry diode is, among possible geometries, the one that has led to the best performance so far. However, this geometry suffers from a lack of tunability after its fabrication, slowing down possible improvements. Here, we demonstrate gate control on a vertical diode in which the active layer is made of HgTe NCs absorbing in the extended short-wave infrared (2.5 μm). To reach this goal, we take advantage of the electrostatic transparency of graphene, combined with the high capacitance LaF3 ionic glass to design a gate tunable photodiode. The latter behaves as a work function-tunable electrode which lets the gate-induced electric field tune the carrier density within the nanocrystal film. In particular, we show that the gate allows to tune the band profile leading to more efficient charge extraction and thus an enhanced photoresponse (×4 compared to the device with a floating gate). This work also demonstrates that photoelectron extraction can still be improved in the existing diode, by better controlling the doping profile of the stack.
A study of the effect of serration shape and flexibility on trailing edge noise
Authors: Zhou Peng , Liu Qian , Zhong Siyang , Fang Yi , Zhang Xin
Published: December 2020

In this study, we investigated the performance of flexible trailing edge serrations of various shapes for airfoil self-noise reduction through anechoic wind tunnel experiments. A flat plate model was tested at zero angle of attack. The chord-based Reynolds number was between 1.6 × 105 and 4 × 105. The boundary layers were fully tripped near the leading edge. Add-on type trailing edge serrations were cut from flexible polyethylene terephthalate sheets. It is observed that compared with rigid serrations, flexible serrations can achieve an additional broadband noise reduction up to 2 dB–3 dB at high frequencies, and the effect also depends on the geometry of the serrations. Complementary deformation measurement and aerodynamic force measurement show that flexible serrations can align better with the flow and are expected to reduce the crossflow intensity near the serration roots, which has been related to the extraneous high-frequency noise generated by serrations in previous studies. An inviscid model is proposed to predict the wake structure and the loadings for serrations of various shapes. Although the model over-predicts the crossflow speed due to the omission of the viscous effect, the relative intensity corresponding to different serration geometry is consistent with experimental observations. Last, we show that the recent analytical noise prediction model [B. Lyu and L. J. Ayton, “Rapid noise prediction models for serrated leading and trailing edges,” J. Sound Vib. 469, 115136 (2020)] for a serrated trailing edge still significantly overpredicts the noise reduction capacity by serrations and does not reveal the role of serration shape properly. This indicates the necessity to include the non-frozen turbulent properties near serrations in the future prediction models.
Effect of plastic deformation on phonon thermal conductivity of
α
-Ag2S
Authors: Liang Xin , Chen Chuang , Dai Feihu
Published: December 2020

α-Ag2S is a ductile inorganic semiconductor recently identified, which can undergo considerable plastic deformation without the aid of dislocations. Together with its intrinsically poor electrical conductivity, it is one ideal system to study the effect of plastic deformation on phonon thermal transport. In this work, we show that the room temperature phonon thermal conductivity of α-Ag2S monotonically increases with compressive strain by about 32% at a compressive strain of 0.7. No deformation-induced phase transition occurs. Electrical conductivity and the Seebeck coefficient are basically invariant with deformation. No transport anisotropy is observed between the directions that are parallel and perpendicular to the compression direction. The stored energy in α-Ag2S measured by differential scanning calorimetry increases with strain but is remarkably larger than plastically deformed Cu at large strains. Possible origins for the increasing phonon thermal conductivity with plastic deformation are discussed. The present work provides original experimental observations on the effect of plastic deformation on phonon thermal conductivity, and it has important implications for the development of α-Ag2S-based ductile thermoelectric semiconductors and devices.
Probing the deformation of [12]cycloparaphenylene molecular nanohoops adsorbed on metal surfaces by tip-enhanced Raman spectroscopy
Authors: Li Hang , Zhang Yu-Fan , Zhang Xian-Biao , Farrukh Aftab , Zhang Yang , Zhang Yao , Dong Zhen-Chao
Published: December 2020

[n]Cycloparaphenylene ([n]CPP) molecules have attracted broad interests due to their unique properties resulting from the distorted and strained aromatic hoop structures. In this work, we apply sub-nanometer resolved tip-enhanced Raman spectroscopy (TERS) to investigate the adsorption configurations and structural deformations of [12]CPP molecules on metal substrates with different crystallographic orientations. The TERS spectra for a [12]CPP molecule adsorbed on the isotropic Cu(100) surface are found to be essentially the same over the whole nanohoop, indicating an alternately twisted structure that is similar to the [12]CPP molecule in free space. However, when the [12]CPP molecules are adsorbed on the anisotropic Ag(110) surface, the molecular shape is found to be severely deformed into two types of adsorption configurations: one showing an interesting “Möbius-like” feature and the other showing a symmetric bending structure. Their TERS spectral features are found to be site-dependent over the hoop and even show peak splitting for the out-of-plane C–H bending vibrations. The deformed structural models gain strong support from the spatial distribution of “symmetric” TERS spectra at different positions on the hoop. Further TERS imaging, with a spatial resolution down to ∼2 Å, provides a panoramic view on the local structural deformations caused by different tilting of the benzene units in real space, which offers insights into the subtle changes in the aromatic properties over the deformed hoop owing to inhomogeneous molecule−substrate interactions. The ability of TERS to probe the molecular structure and local deformation at the sub-molecular level, as demonstrated here, is important for understanding surface science as well as molecular electronics and optoelectronics at the nanoscale.
Experimental and theoretical investigation of resonances in low-energy NO–H2 collisions
Authors: Shuai Quan , de Jongh Tim , Besemer Matthieu , van der Avoird Ad , Groenenboom Gerrit C. , van de Meerakker Sebastiaan Y. T.
Published: December 2020

The experimental characterization of scattering resonances in low energy collisions has proven to be a stringent test for quantum chemistry calculations. Previous measurements on the NO–H2 system at energies down to 10 cm−1 challenged the most sophisticated calculations of potential energy surfaces available. In this report, we continue these investigations by measuring the scattering behavior of the NO–H2 system in the previously unexplored 0.4 cm−1–10 cm−1 region for the parity changing de-excitation channel of NO. We study state-specific inelastic collisions with both para- and ortho-H2 in a crossed molecular beam experiment involving Stark deceleration and velocity map imaging. We are able to resolve resonance features in the measured integral and differential cross sections. Results are compared to predictions from two previously available potential energy surfaces, and we are able to clearly discriminate between the two potentials. We furthermore identify the partial wave contributions to these resonances and investigate the nature of the differences between collisions with para- and ortho-H2. Additionally, we tune the energy spreads in the experiment to our advantage to probe scattering behavior at energies beyond our mean experimental limit.
A review of the state-of-the-art nanofluid spray and jet impingement cooling
Authors: Tyagi Praveen Kumar , Kumar Rajan , Mondal Pranab Kumar
Published: December 2020

Nanofluid spray/jet impingement cooling is widespread and finds applications in many scientific and industrial paradigms. Because of these ubiquities of nanofluid spray/jet impingement cooling, this branch of fluid dynamics has attracted great attention from the scientific community. The performance of nanofluid spray/jet impingement cooling very often depends on the nanoparticle concentration, shape, and size of the nanoparticle, as well as the mass flow rate of the nanofluid. These aspects lead to interesting variants of the thermo-hydrodynamic analysis of the nanofluid, which are studied meticulously, and some new functionalities are established such as high heat flux removal capacity, temperature uniformity, lower flow rate demand, and no thermal resistance to the heated test surface. We provide an overview of nanofluid spray/jet impingement cooling with an emphasis on the parametric effects, such as the Reynolds number, jet to test surface distance, the Prandtl number, the confinement of the jets, test plate inclination, and the roughness of the test surface, on the underlying phenomenon. Also, we aptly discuss the essential features of the nanofluid spray/jet impingement cooling, which includes spray properties, cooling fluid properties, substrate properties, and environmental conditions, which affect the heat transfer of spray cooling.
Universal mechanisms for self-termination of rapid cardiac rhythm
Authors: Biasci Valentina , Sacconi Leonardo , Cytrynbaum Eric N. , Pijnappels Daniël A. , De Coster Tim , Shrier Alvin , Glass Leon , Bub Gil
Published: December 2020

Excitable media sustain circulating waves. In the heart, sustained circulating waves can lead to serious impairment or even death. To investigate factors affecting the stability of such waves, we have used optogenetic techniques to stimulate a region at the apex of a mouse heart at a fixed delay after the detection of excitation at the base of the heart. For long delays, rapid circulating rhythms can be sustained, whereas for shorter delays, there are paroxysmal bursts of activity that start and stop spontaneously. By considering the dependence of the action potential and conduction velocity on the preceding recovery time using restitution curves, as well as the reduced excitability (fatigue) due to the rapid excitation, we model prominent features of the dynamics including alternation of the duration of the excited phases and conduction times, as well as termination of the bursts for short delays. We propose that this illustrates universal mechanisms that exist in biological systems for the self-termination of such activities.
Can face masks offer protection from airborne sneeze and cough droplets in close-up, face-to-face human interactions?—A quantitative study
Authors: Akhtar Javed , Garcia Abner Luna , Saenz Leonardo , Kuravi Sarada , Shu Fangjun , Kota Krishna
Published: December 2020

Day-to-day observations reveal numerous medical and social situations where maintaining physical distancing is either not feasible or not practiced during the time of a viral pandemic, such as, the coronavirus disease 2019 (COVID-19). During these close-up, face-to-face interactions, a common belief is that a susceptible person wearing a face mask is safe, at least to a large extent, from foreign airborne sneeze and cough droplets. This study, for the first time, quantitatively verifies this notion. Droplet flow visualization experiments of a simulated face-to-face interaction with a mask in place were conducted using the particle image velocimetry setup. Five masks were tested in a snug-fit configuration (i.e., with no leakage around the edges): N-95, surgical, cloth PM 2.5, cloth, and wetted cloth PM 2.5. Except for the N-95 mask, the findings showed leakage of airborne droplets through all the face masks in both the configurations of (1) a susceptible person wearing a mask for protection and (2) a virus carrier wearing a mask to prevent the spreading of the virus. When the leakage percentages of these airborne droplets were expressed in terms of the number of virus particles, it was found that masks would not offer complete protection to a susceptible person from a viral infection in close (e.g., <6 ft) face-to-face or frontal human interactions. Therefore, consideration must be given to minimize or avoid such interactions, if possible. This study lends quantitative support to the social distancing and mask-wearing guidelines proposed by the medical research community.
NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions
Authors: Schneider S. , Säckel C. , Brodrecht M. , Breitzke H. , Buntkowsky G. , Vogel M.
Published: December 2020

We use 1H, 2H, and 7Li NMR to investigate the molecular dynamics of glass-forming LiCl-7H2O and LiCl-7D2O solutions confined to MCM-41 or SBA-15 silica pores with diameters in the range of d = 2.8 nm–5.4 nm. Specifically, it is exploited that NMR experiments in homogeneous and gradient magnetic fields provide access to local and diffusive motions, respectively, and that the isotope selectivity of the method allows us to characterize the dynamics of the water molecules and the lithium ions separately. We find that the silica confinements cause a slowdown of the dynamics on all length scales, which is stronger at lower temperatures and in narrower pores and is more prominent for the lithium ions than the water molecules. However, we do not observe a temperature-dependent decoupling of short-range and long-range dynamics inside the pores. 7Li NMR correlation functions show bimodal decays when the pores are sufficiently wide (d > 3 nm) so that bulk-like ion dynamics in the pore centers can be distinguished from significantly retarded ion dynamics at the pore walls, possibly in a Stern layer. However, we do not find evidence for truly immobile fractions of water molecules or lithium ions and, hence, for the existence of a static Stern layer in any of the studied silica pores.
Assessing the orbital-optimized unitary Ansatz for density cumulant theory
Authors: Misiewicz Jonathon P. , Turney Justin M. , Schaefer Henry F. , Sokolov Alexander Yu.
Published: December 2020

The previously proposed Ansatz for density cumulant theory that combines orbital-optimization and a parameterization of the 2-electron reduced density matrix cumulant in terms of unitary coupled cluster amplitudes (OUDCT) is carefully examined. Formally, we elucidate the relationship between OUDCT and orbital-optimized unitary coupled cluster theory and show the existence of near-zero denominators in the stationarity conditions for both the exact and some approximate OUDCT methods. We implement methods of the OUDCT Ansatz restricted to double excitations for numerical study, up to the fifth commutator in the Baker–Campbell–Hausdorff expansion. We find that methods derived from the Ansatz beyond the previously known ODC-12 method tend to be less accurate for equilibrium properties and less reliable when attempting to describe H2 dissociation. New developments are needed to formulate more accurate density cumulant theory variants.
Probe of antiferromagnetic transition via thermal-excited incoherent spin current
Authors: Peng Yibo , Sha Rongxin , Wang Mengyi , Liu Min , Guo Fangzhun , Zhang Ziyang , Zou Ailiang , Xu Yuekui , Qiu Zhiyong
Published: December 2020

Spin Seebeck effect (SSE) for an yttrium iron garnet (YIG)/nickel oxide (NiO)/platinum (Pt) trilayer device was studied in a wide temperature range. It is found that the SSE signal is nonmonotonic in the temperature domain and shows a maximum around the Néel temperature of the NiO layer, which is similar to the temperature dependence of the spin pumping signal in the same device. This result identified that the thermal-excited incoherent spin currents are also sensitive to the fluctuation of an antiferromagnetic system and can be used to probe the antiferromagnetic phase transition. Furthermore, the antiferromagnetic NiO layer is considered to be valuable for the optimization of spin transport efficiency at YIG/Pt interface, which enhances the SSE signal around room temperature.
Full-dimensional, ab initio potential energy surface for glycine with characterization of stationary points and zero-point energy calculations by means of diffusion Monte Carlo and semiclassical dynamics
Authors: Conte Riccardo , Houston Paul L. , Qu Chen , Li Jeffrey , Bowman Joel M.
Published: December 2020

A full-dimensional, permutationally invariant potential energy surface (PES) for the glycine amino acid is reported. A precise fit to energies and gradients calculated at the density functional theory (DFT)/B3LYP level of electronic-structure theory with Dunning’s aug-cc-pVDZ basis set is performed involving 20 000 low-energy points and associated Cartesian gradients plus about 50 000 additional higher-energy points. The fact that newly calculated DFT/B3LYP energies for the main stationary points are close to the coupled-cluster single-double-triple [CCSD(T)] values, recently reported in the literature, provides reassurance about the accuracy of the constructed PES. Eight conformers and numerous saddle points are identified and characterized by describing geometries, relative stability, and harmonic frequencies. Stochastic and dynamical approaches are employed to study the vibrational ground state. Specifically, diffusion Monte Carlo simulations and approximate quantum dynamics, performed by means of the adiabatic switching semiclassical initial value representation technique, provide zero-point energies in excellent agreement with each other. The PES we report is sufficiently complete to permit spectroscopic and dynamical studies on glycine, which may be of interest to the biochemical and astrochemistry communities.
Unsynchronized motion of inner and outer membranes of compound capsules in shear flow
Authors: Xu Han , Bai Bo Feng
Published: December 2020

Despite its significance in understanding behaviors of biological cells with nucleus or designing functions of complex artificial capsules in applications, the dynamics of elastic capsules enclosing complicated internal structures in flow is still largely unexplored. In this study, by using our own three-dimensional front-tracking finite-difference model, we present a numerical investigation into the dynamics of a compound capsule in a simple shear flow whose inner and outer membranes have the same prolate ellipsoidal shape at the rest state. Particular interest is focused on the unsynchronized motion of the inner and outer membranes. Regarding the dynamical regime, both the inner and outer capsules can undergo either synchronized or unsynchronized dynamical regimes (i.e., swinging or tumbling), which strongly depends on the inner-to-outer capillary number ratio Cain/Caout, the inner-to-outer volume ratio ϕ, and the prolate aspect ratio a/b. Particularly, via establishing a phase diagram based on a/b and ϕ at Cain/Caout = 1, we find that the inner and outer membranes can exist simultaneously in different dynamical regimes, even if they have the same deformability and the same shape. More importantly, if the detailed oscillation behavior is also concerned besides the capsule’s dynamical regime, such as the transient shape and the oscillating period, unsynchronization is always obvious between the inner and outer capsules. Specifically, the inner capsule exhibits a slower oscillation than the outer capsule no matter if they lie in the swinging or tumbling regime.
Corrigendum to: Young Deadly Free: impact evaluation of a sexual health youth peer education program in remote Australian communities
Authors: Lobo Roanna , D'Costa Belinda , Forbes Linda , Ward James
Published: December 2020

Background:Aboriginal and Torres Strait Islander people in remote and very remote communities in Australia experience high rates of sexually transmissible infections (STIs), 4- to 29-fold the rates reported for non-Aboriginal people living in remote areas. Young people aged 16–29 years are particularly vulnerable to STIs. The Young Deadly Free (YDF) sexual health youth peer education program was implemented in 15 remote or very remote communities in four Australian jurisdictions in an effort to address endemic STI rates in these communities. The present study sought to evaluate the effect of YDF for Aboriginal young people. Methods: Young people (n = 128) participated in youth peer educator training to deliver peer education sessions on sexual health topics to other young people in their communities. Pre and post surveys were used to examine changes in STI knowledge, attitudes and behavioural intentions of the young people attending the peer education sessions. GHRANITE software extracted deidentified STI testing data for young people attending 13 community health services. Results: Young people (n = 426) attended peer education sessions delivered by trained youth peer educators. Pre and post surveys were completed by 174 and 172 young people respectively (median age 20 years). Gains were reported in STI knowledge, intentions to test (χ2 = 10.58, d.f. = 4, n = 142, P Conclusions: Peer education can enhance the sexual health literacy of young Aboriginal people residing in remote communities. The extent to which knowledge gains result in behaviours that prevent STI transmission requires further evaluation. Normalising STI testing among Aboriginal young people would help reduce feelings of shame.
Xenophobia, misogyny and rape culture
Authors: Kopytowska Monika
Published: December 2020

The present article explores the interface between online misogyny and xenophobia in the context of both
socio-cultural factors which are conducive to verbal aggression against women and cyberspace’s technological affordances. The
former, as will be argued, can be linked to “rape culture”, where the notions of rape and sexual violence are used not only as
instruments of subjugation and domination, but also as tools to legitimize racial, ethnic, or religious hatred. In the case of the
latter, anonymity, interactivity and connectivity will be discussed as factors which facilitate generating, amplifying and
perpetuating hateful and aggressive content online. Applying the Media Proximization Approach (Kopytowska 2013, 2015a, 2018a,
2018b, 2020) and drawing on
previous research examining online xenophobic discourses and hate speech, the article scrutinizes hate speech targeting female
politicians, namely Angela Merkel, current Chancellor of Germany, and Ewa Kopacz, former Polish Prime Minister, for their
pro-refugee stance and migration policy. Data-wise, the examples analyzed will be taken from the corpora comprising comments
following online articles in
niezalezna.pl
(a Polish conservative
news portal) and YouTube videos on migrants and refugees.
Twitter and abortion
Authors: Pérez-Arredondo Carolina , Graells-Garrido Eduardo
Published: December 2020

This paper explores the misogynistic abuse against female Chilean politicians who openly supported a pro-choice bill that allowed the access to abortion in limited circumstances. We analysed the verbal abuse targeted at these politicians during the legislation of the abortion bill (2015–2017) and the linguistic and discursive patterns of online abuse. To that end, we collected tweets from this legislation period and created a subset with specific milestones of the parliamentary debate. Further, we undertook a corpus-assisted analysis of the data, focusing on collocations and keywords, which were then analysed in the light ofvan Leeuwen’s (2008)framework on the representation of social actors and legitimation strategies. Results evidence that violence against women in power can take forms other than the explicit sexual, physical, and psychological threats that are commonly identified. Violence targets these women as it is claimed that they are unsuitable to legislate for allegedly having tolerated and protected crime. Therefore, the corrective function of abuse takes the form of legal actions against their crimes.
Ipomoea carnea subsp. fistulosa (bush morning glory).
Authors: Rojas-Sandoval Julissa , Shaltout Kamal Hussien
Published: December 2020

Ipomoea carnea subsp. fistulosa is a species of morning glory that has been introduced worldwide as an ornamental and hedge (living fence) plant. The species has escaped from cultivation to become naturalized and invasive mostly in disturbed sites, riparian areas and wetlands, and it behaves as a weed in cultivated fields, such as rice plantations. It is a strong competitor for resources (e.g. nutrients and water), with the potential to outcompete native plants. The species has been listed as a noxious weed in the USA and as invasive in India, Nepal, Egypt, South Africa, Swaziland, Cuba, and in many islands in the Pacific region.
Active damping of ultrasonic receiving sensors through engineered pressure waves
Authors: Dixon Steve , Kang Lei , Feeney Andrew , Somerset William E
Published: December 2020

Transducers for ultrasonic sensing and measurement are often operated with a short burst signal, for example a few cycles at a specific excitation voltage and frequency on the generating transducer. The vibration response of a narrowband transducer in detection is usually dominated by resonant ringing, severely affecting its ability to detect two or more signals arriving at the receiver at similar times. Prior researchers have focused on strategies to damp the ringing of a transducer in transmission, to create a temporally short output pressure wave. However, if the receiving transducer is narrowband, the incident pressure waves can create significant ringing of this receiving transducer, irrespective of how temporally short the incident pressure waves are on the receiving transducer. This can reduce the accuracy of common measurement processes, as signals are temporally long and multiple wave arrivals can be difficult to distinguish from each other. In this research, a method of damping transducers in reception is demonstrated using a flexural ultrasonic transducer (FUT). This narrowband transducer can operate effectively as a transmitter or receiver of ultrasound, and due to its use in automotive applications, is the most common ultrasonic transducer in existence. An existing mathematical analog for the transducers is used to guide the design of an engineered pressure wave to actively damp the receiving FUT. Experimental measurements on transducers show that ultrasonic receiver resonant ringing can be reduced by 80%, without significantly compromising sensitivity and only by using a suitable driving voltage waveform on the generating transducer.
Experimental investigation of C-shape embedded multi-channel plasma igniter in a single-head swirl combustor
Authors: Cai Banghuang , Song Huimin , Zhang Zhibo , Jia Min , Wang Weizhen , Lin Dong
Published: December 2020

A C-shape embedded multi-channel plasma igniter (CEMPI) is presented in this paper. Compared with traditional spark igniter (SI), it has a deeper penetration depth of fire kernel. The fuel supply pressure was kept at 0.2 MPa for the ignition tests. The ignition processes of two igniters at different air flow in a single-head swirl combustor were captured by using the technology of CH* chemiluminescence imaging. The influence of air flow on the ignition process and the ignition characteristics of two igniters were studied. The results show that the ignition dynamic process can be divided into four stages: fire kernel growth stage, flame stagnation stage, flame propagation stage and overall flame stage. To some extent, increasing air flow can shorten the ignition delay caused by flame stagnation, improve the flame propagation speed, and form overall flame earlier, which is conducive to fast ignition. Compared with SIs, CEMPIs can produce larger and more powerful fire kernel, which can penetrate deeper into the central recirculation zone and touch combustible mixture to generate initial flame. It also has a faster flame propagation speed to reduce the ignition time significantly. In addition, the CEMPI can widen the lean ignition boundary and has a more significant ignition advantage when the air flow is small.
Device performance of chemical vapor deposition monocrystal diamond radiation detectors correlated with the bulk diamond properties
Authors: Su Kai , He Qi , Zhang Jinfeng , Ren Zeyang , Liu Linyue , Zhang Jincheng , Ouyang Xiaoping , Hao Yue
Published: December 2020

Diamond radiation detectors (DRDs) based on type-IIa chemical vapor deposition (CVD) monocrystal diamond are more suitable for engineering applications with high consistency requirements due to the lower cost and property controllability. However, their saturated charge collection efficiencies (CCEs) have huge differences. Six type-IIa CVD monocrystal diamond plates were analyzed by the Fourier transform infrared spectrometer, high resolution x-ray diffraction, Raman spectroscopy, photoluminescence and secondary ion mass spectroscopy. Then DRDs were fabricated by them and the CCEs were measured under the irradiation of 241Am source. The results show that the most important factor restricting CCEs are the impurities in the diamond plates, while dislocations with a density <1 × 107 cm−2 for all samples have weaker impact in our case. The reason is that the carrier mobility-lifetime (μτ) product of diamond is more strongly influenced by impurities in this dislocation density range. Thinning diamond plate, if the thickness is kept above 100 μm, is not a good means to obtain high performance DRDs. Therefore, to further improve the detector performance, ultra-high purity diamond growth is most important. Moreover, a diamond test and selection scheme for high performance DRDs is also demonstrated.
Optical polarizability of erbium-oxygen complexes in sol-gel-based silica films
Authors: Abedrabbo Sufian , Lahlouh Bashar , Fiory Anthony T , Ravindra Nuggehalli M
Published: December 2020

For erbium (Er)-doped amorphous oxides, such as those that are used in compact lightwave devices interfaced with silicon, values of the refractive indices are commonly obtained empirically. This work, combining experimental and theoretical studies, examines silica as the exemplary host and the influence of Er doping on the refractive index. Analysis of data is presented for the spectral refractive index in the ultraviolet to near infrared wavelength range of heavily Er-doped silica thin films prepared by spin coating a sol-gel precursor on silicon and subsequent vacuum annealing. Effective medium Lorentz–Lorenz data analysis determines that the dopant component has a refractive index of 1.76 ± 0.24 with wavelength dispersion constrained to within 2%. Considering the dopant as a localized ErO6 impurity complex, a corresponding theoretical refractive index of 1.662 is derived by calculating the optical polarizability and volume of the impurity. Data presented for room-temperature (∼293 K) photoluminescence in the vicinity of 1.54 μm are shown to be consistent with random variability in impurity sites. Inherent advantages of studying colloid-based materials are discussed. To the best of the authors’ knowledge, such a detailed study of the refractive index associated with Er impurities in silica is being reported for the first time in the literature.
Crystal reorientation and plastic deformation of single-layer MoS2 and MoSe2 under uniaxial stress
Authors: Alencar Ananias B , de Oliveira Alan B , Chacham Helio
Published: December 2020

We investigate theoretically, through of first-principles calculations, the effect of the application of large in-plane uniaxial stress on single-layer of MoS2, MoSe2, and MoSSe alloys. For stress applied along the zigzag (zz) direction, we predict an anomalous behavior near the point fracture. This behavior is characterized by the reorientation of the MoS2 structure along the applied stress from zz to armchair due to the formation of transient square-lattice regions in the crystal, with an apparent crystal rotation of 30 degrees. After reorientation, a large plastic deformation

ε
=

3

−
1

remains after the stress is removed. This behavior is also observed in MoSe2 and in MoSSe alloys. This phenomenon is observed both in stress-constrained geometry optimizations and in ab initio molecular dynamics simulations at finite temperature and applied stress.
Markov models from the square root approximation of the Fokker–Planck equation: calculating the grid-dependent flux
Authors: Donati Luca , Weber Marcus , Keller Bettina G
Published: December 2020

Molecular dynamics (MD) are extremely complex, yet understanding the slow components of their dynamics is essential to understanding their macroscopic properties. To achieve this, one models the MD as a stochastic process and analyses the dominant eigenfunctions of the associated Fokker–Planck operator, or of closely related transfer operators. So far, the calculation of the discretized operators requires extensive MD simulations. The square-root approximation of the Fokker–Planck equation is a method to calculate transition rates as a ratio of the Boltzmann densities of neighboring grid cells times a flux, and can in principle be calculated without a simulation. In a previous work we still used MD simulations to determine the flux. Here, we propose several methods to calculate the exact or approximate flux for various grid types, and thus estimate the rate matrix without a simulation. Using model potentials we test computational efficiency of the methods, and the accuracy with which they reproduce the dominant eigenfunctions and eigenvalues. For these model potentials, rate matrices with up to

O

(

1

0

6

)

states can be obtained within seconds on a single high-performance compute server if regular grids are used.
Field validation of an actuated convergent-beam acoustic Doppler profiler for high resolution flow mapping
Authors: Harding Samuel , Dorward Mairi , Sellar Brian , Richmond Marshall
Published: December 2020

Energetic river and tidal flow environments feature complex hydrodynamic conditions. Conventional acoustic Doppler profiling instrumentation typically requires assumptions of flow homogeneity over the spatial scales of the divergent beam separation. This removes the ability to measure spatio-temporal variability within the flow. However, velocity variability within these spatial scales is often important in the design of structures and devices exposed to such flow, informing dynamic and peak hydrodynamic load predictions. The research presented outlines the development and testing of a flow measurement instrument consisting of multiple spatially-separated single beam acoustic Doppler profilers converging on a remote focal point, the location of which can be programmatically adjusted through actuation. This increases the spatial resolution at which remote field measurements can be made in energetic flow environments. Field testing of the instrument was conducted in a tidal channel at Sequim Bay Inlet, WA, USA. Results are compared with independent reference measurements made by a co-located, motion-corrected acoustic Doppler velocimeter. This comparison, across tidal velocities of 0.4–0.7 m s−1, showed a mean velocity error of 0.5%–13.2% across nine sample locations within a 3.00 m × 2.25 m plane. To the authors’ knowledge, this is the first publication of flow velocity results from non-intrusive acoustic measurements at an off-axis, focal point location that features 3D positional control.
Single-particle optical-trapping Raman spectroscopy for the detection and identification of aerosolized airborne biological particles
Authors: Ai Yukai , Alali Haifa , Pan Yongle , Videen Gorden , Wang Chuji
Published: December 2020

The detection and identification of bioaerosol particles, especially a potential threat from aerosolized biowarfare agents (BWAs), has become increasingly important. Here, we report on single-particle optical-trapping Raman spectroscopy (OT-RS) for the detection and identification of airborne biological particles. OT enables the capture of single particles in air for several minutes or longer, more than sufficient to capture the Raman spectra and minimize the interference from background aerosol particles. Simultaneously, the embedded imaging system can provide real-time information on the shape and size of the trapped particles. Several kinds of bioaerosol particles were analyzed using OT-RS including four BWA surrogates: Bacillus globigii, Yersinia rhodei, MS2, and Bacillus subtilis, along with some interfering bioaerosol particles commonly presented in the atmosphere. Similarities and differences of the Raman spectra of these biological particles are discussed. In addition, the BWA surrogates are well classified by using the principal component analysis. The results demonstrate that single-particle OT-RS can be used not only for the potential detection of BWAs but also for the identification of BWAs.
Bioinspired design and assembly of a multilayer cage-shaped sensor capable of multistage load bearing and collapse prevention
Authors: Cheng Xu , Liu Zhi , Jin Tianqi , Zhang Fan , Zhang Hang , Zhang Yihui
Published: December 2020

Flexible bioinspired mesostructures and electronic devices have recently attracted intense attention because of their widespread application in microelectromechanical systems (MEMS), reconfigurable electronics, health-monitoring systems, etc. Among various geometric constructions, 3D flexible bioinspired architectures are of particular interest, since they can provide new functions and capabilities, compared to their 2D counterparts. However, 3D electronic device systems usually undergo complicated mechanical loading in practical operation, resulting in complex deformation modes and elusive failure mechanisms. The development of mechanically robust flexible 3D electronics that can undergo extreme compression without irreversible collapse or fracture remains a challenge. Here, inspired by the multilayer mesostructure of Enhydra lutris fur, we introduce the design and assembly of multilayer cage architectures capable of multistage load bearing and collapse prevention under large out-of-plane compression. Combined in situ experiments and mechanical modeling show that the multistage mechanical responses of the developed bionic architectures can be fine-tuned by tailoring the microstructural geometries. The integration of functional layers of gold and piezoelectric polymer allows the development of a flexible multifunctional sensor that can simultaneously achieve the dynamic sensing of compressive forces and temperatures. The demonstrated capabilities and performances of fast response speed, tunable measurement range, excellent flexibility, and reliability suggest potential uses in MEMS, robotics and biointegrated electronics.
Ratio of arterial blood pressures at borders of window surrounding systolic peak indicates patent ductus arteriosus in preterm infants
Authors: Bennis Frank C , Andriessen Peter , van Pul Carola , Kramer Boris W , Delhaas Tammo
Published: December 2020

Objective. Presence of a patent ductus arteriosus (PDA) in neonates is assessed by echocardiography. Echocardiographic assessment has disadvantages, primarily its discontinuous nature. We hypothesize that the continuously measured ratio of arterial blood pressures (ABP) at the borders of a window surrounding the systolic peak ratio discriminates non-PDA from PDA patients. Approach. Preterm infants (gestational age <32 weeks) with and without PDA were included. Patients were divided into controls (n = 8) and PDA patients (n = 22), the latter with a subset of patients with closed PDA after three doses Ibuprofen (n = 10). For each patient, a six-hour ABP segment from 12 AM to 6 AM on the day of echocardiographic assessment patency or closure of the DA was selected. The mean ratio of the ABP values a samples before and p samples after the systolic peak (R
ABP) was calculated for each segment. If R
ABP < 1, the patient was predicted to have a PDA. The a and p with the least misclassifications were selected (−64 and +104 ms). Main results.
R
ABP was significantly lower in PDA patients (median 0.95, IQR 0.06) compared to controls (median 1.05, IQR 0.10; p = 0.0024). R
ABP correctly predicted 19 out of 22 patients (86.4%) and six out of eight controls (75%). R
ABP increased after closure in nine out of 10 patients (median 1.01, IQR 0.04; p = 0. 0182). Significance.
R
ABP may discriminate preterm PDA patients from non-PDA patients and can be calculated continuously from clinical data measured during standard of care.
A unified theory of zonal flow shears and density corrugations in drift wave turbulence
Authors: Singh Rameswar , Diamond P H
Published: December 2020

A unified theory of zonal flow shears and density corrugations in drift wave turbulence is presented. Polarization and density advection beat excitation are studied in combination with modulational response. Noise is driven by two-time flux correlation. While the effective zonal flow eddy viscosity can go negative, the zonal diffusivity is positive definite. There is no inverse cascade of density corrugation. The connection between avalanches and corrugations is discussed. The zonal cross-correlation is identified and calculated. Conditions for alignment of zonal shears and corrugation gradients are determined, and the implications for staircase structure are discussed. We show that the synergy of beat noise and modulational effects is stronger than either alone. Strong zonal flows can be excited well below the modulational instability threshold. In the context of L–H transition, zonal noise quenches turbulence overshoot by eliminating the threshold for zonal flow excitation. The power threshold for L–H transition is lowered.
Intra-cavity dynamics in a microplasma channel by side-on imaging
Authors: Kreuznacht Simon , Böke Marc , Schulz-von der Gathen Volker
Published: December 2020

Here, a microplasma channel was investigated. The design was developed from a recently presented modular microplasma array. The setup consists of three stacked layers: a magnet, a dielectric foil and two nickel foils that are separated by a 120 μm wide gap. The magnet is grounded while the two nickel foils are powered. The channel is in two dimensions identical (50 μm high and 120 μm wide) to a single cavity of the microplasma arrays while it is two orders of magnitude longer. Unlike the microplasma arrays, the channel provides an additional optical access to the inside of the cavity from the side. The setup was operated with a triangular voltage with a frequency of 10 kHz and an amplitude of up to 700 V at atmospheric pressure. Phase resolved emission images were used to investigate the microplasma channel dynamics with line of sight from the top and from the side to the inside of the cavity. The top view images revealed that the discharge in the microplasma channel and the microplasma arrays behave similar. The already known asymmetric discharge behavior, the self-pulsing and the wavelike ignition was also observed in the microplasma channel. For the wavelike ignition in the channel a simple one dimensional model was proposed. With the additional side view images the asymmetric discharge behavior was examined more thoroughly. Unlike in the microplasma arrays, the discharge expands here in both half periods of the applied voltage above the upper edge of the powered electrodes. The discharge extends over a larger width in the half period, in which the potential of the upper electrodes is increasing, while it extends over a larger height in the other half period. Phase resolved images were also used to investigate the ignition phase of the discharge. The discharge ignites in the two half periods on a different height. This was explained by modeling the drift and diffusion of the charged particles between two discharge pulses. The new insights into the discharge dynamics in the microplasma channel will help to understand the behavior of the discharge in the microplasma arrays.
Uncertainty analysis of a shape memory alloy model for dynamic analysis
Authors: Hou Hetao , Li Jinpeng , Chen Cheng , Qiu Canxing
Published: December 2020

Superelastic shape memory alloys (SMAs) are capable of recovering large inelastic deformation and dissipating energy under loading reversals, and therefore present promising application in vibration control of engineering structures subjected to dynamic loads. Properties of SMAs are often optimised based on experimental results and treated as deterministic for dynamic analysis of structures with SMA-based devices. This study applies the Metropolis–Hasting algorithm to characterise the uncertainties within an SMA material model and to provide insight into its parameter uncertainty. Cyclic tests of SMA bars are first conducted and the experimental data are analysed using the Markov chain Monte Carlo method. The statistical properties of SMA model parameters are calculated based on posterior parameter distributions. The influence of SMA model parameter uncertainty is further explored on energy dissipation capacity under cyclic tests. The first four L-moment method is applied to transform the posterior parameter distributions into standard normal distribution to further evaluate the influence of model parameter uncertainty on energy dissipation in dynamic analysis.