bluuebunny/crossref_metadata_2025 huggingface dataset:
On-the-fly dynamics simulations of transient anions
Authors: Kossoski F. , Varella M. T. do N. , Barbatti M.
Published: December 2019

A novel theoretical framework for describing the dynamics of transient anions is presented. An ensemble of classical trajectories is propagated on-the-fly, where resonance energies are computed with bound state techniques, and resonance widths are modeled with a combination of bound state and scattering calculations. The methodology was benchmarked against quantum dynamics results for model potential energy curves, and excellent agreement was attained. As a first application, we considered the electron induced dissociation of chloroethane. We found that electron attachment readily stretches the C–Cl bond, which stabilizes the transient anion within ∼10 fs and leads to the release of fast chloride ions. Both magnitude and shape of the computed dissociative electron attachment cross sections are very similar to the available experimental data, even though we found the results to be very sensitive on the accuracy of the underlying methods. These encouraging results place the proposed methodology as a promising approach for studies on transient anions’ dynamics of medium sized molecules.
Structures and bonding properties of CPt2−/ and CPt2H−/: Anion photoelectron spectroscopy and quantum chemical calculations
Authors: Lu Sheng-Jie , Xu Xi-Ling , Xu Hong-Guang , Zheng Wei-Jun
Published: December 2019

We present a combined anion photoelectron spectroscopic and quantum chemical investigation on the structures and bonding properties of CPt2−/0 and CPt2H−/0. The experimental vertical detachment energies of CPt2− and CPt2H− are measured to be 1.91 ± 0.08 and 3.54 ± 0.08 eV, respectively. CPt2− is identified as a C2v symmetric Pt—C—Pt bent structure, and CPt2 has a D∞h symmetric Pt—C—Pt linear structure. Both anionic and neutral CPt2H adopt a Pt—C—Pt—H chain-shaped structure, in which the ∠PtCPt and ∠CPtH bond angles of CPt2H− are larger than those of CPt2H. The Pt—C bonds in CPt2−/0 and CPt2H−/0 exhibit covalent double bonding characters. The Pt=C bonds are much stronger than the C—H bond that may explain why the C atom CPt2H−/0 prefers to form Pt=C bonds rather than C—H bonds. It may also explain why platinum can insert into the C—H bond to activate the C—H bond as reported in the literature.
Coherent exciton-phonon coupling in perovskite semiconductor nanocrystals studied by two-dimensional electronic spectroscopy
Authors: Zhao Wei , Qin Zhengyuan , Zhang Chunfeng , Wang Guodong , Dai Xingcan , Xiao Min
Published: December 2019

Perovskite semiconductor nanocrystals of lead halides exhibit excellent electronic and optical properties that are suitable for many optoelectronic applications. In this report, we investigate the underlying mechanism of the optical response of the material by probing coherent interaction between the exciton and lattice vibration by two-dimensional electronic spectroscopy. Coherent exciton-phonon coupling has been observed with time-domain oscillations in the dynamics of signals related to either ground or excited electronic states. Furthermore, the spectra of the coherent phonon derived from the dynamics of biexciton formation have larger amplitudes for higher frequency modes, which is attributed to the phonon bottleneck effect. Moreover, the composition-dependent coherent coupling between the exciton and lattice vibration in mixed halide samples reveals a critical role played by the anharmonicity and fluctuation of lattice vibration in the excited-state dynamics of perovskite nanocrystals.
Multi-objective optimization of multilayer passive magnetic shield based on genetic algorithm
Authors: Li Jundi , Wang Zhuo , Quan Wei
Published: December 2019

The performance of a multilayer magnetic shield directly affects and limits the sensitivity improvement of an atomic magnetometer. To better meet the requirements of spin-exchange relaxation free atomic magnetometer for the environmental magnetic field, the magnetic shield should be optimized. At present, the optimizations have focused only on a single objective, such as the axial shielding factor. However, the importance of other goals should not be neglected. In this paper, multiobjective optimization of the shield is carried out to obtain a better comprehensive performance. First, according to the structural characteristics of the multilayer shield, a multiobjective optimization model is established. Then, a multiobjective genetic algorithm is utilized to optimize the shield. After optimization, a Pareto optimal solution set is obtained. Furthermore, depending on the desired design requirements, two sets of optimal combinations of target values and variable parameters are selected, based on the fuzzy comprehensive evaluation method and the lowest magnetic noise. This method can obtain a balance between different optimization objectives and effectively improve the comprehensive performance of the shield.
Evidence for lambda doublet propensity in the UV photodissociation of ozone
Authors: Gunthardt Carolyn E. , Aardema Megan N. , Hall Gregory E. , North Simon W.
Published: December 2019

The photodissociation of O3 at 266 nm has been studied using velocity mapped ion imaging. We report temperature-dependent vector correlations for the O2(a1Δg, v = 0, j = 18–20) fragments at molecular beam temperatures of 70 K, 115 K, and 170 K. Both the fragment spatial anisotropy and the v-j correlations are found to be increasingly depolarized with increasing beam temperature. At all temperatures, the v-j correlations for the j = 19 state were shown to be reduced compared to those of j = 18 and 20, while no such odd/even rotational state difference was observed for the spatial anisotropy, consistent with previous measurements. We find that temperature-dependent differences in the populations and v-j correlations between the odd and even rotational states can be explained by a Λ-doublet propensity model. Although symmetry conservation should lead to formation of only the A′ Λ-doublet component, and only even rotational states, out-of-plane rotation of the parent molecule breaks the planar symmetry and permits the formation of the A″ Λ-doublet component and odd rotational states. A simple classical model to treat the effect of parent rotation on the v-j correlation and the odd/even rotational population alternation reproduces both the current measurements and previously reported rotational distributions, suggesting that the “odd” behavior originates from a Λ-doublet propensity, and not from a mass independent curve crossing effect, as previously proposed.
A black phosphorus nanoconveyor belt system
Authors: Hua Anping , Zhao Junhua , Wei Ning
Published: December 2019

Nanocoveyor belt systems (NCBSs) are considered key components of micro-/nanoelectromechanical systems (M/NEMS). However, it is still a tremendous challenge to find suitable NCBSs and reveal their transmission mechanism at the nano-/microscale in some special applications. Here, we report black phosphorus (BP) NCBS using molecular dynamics (MD) simulations, which consist of a drive nanowheel, a driven nanowheel, and a nanoconveyor belt. Our MD results show that the time to achieve a stable transmission ratio strongly depends on the ambient temperature, the chirality and size of the NCBS, and the velocity of the drive nanowheel. The aaa-type BP-NCBS have better transmission efficiency and stability than other types due to their greater friction and better structural stability. In particular, the friction force between the two nanowheels and the belt dominates the transmission mechanism of the NCBS, in which the logarithmic relationship between the friction force and the transmission velocity of the corresponding two BP sheets from MD simulations agrees well with that from available continuum modeling. This study provides physical insights into the transmission mechanism of different NCBSs and should be of great help for designing other more perfect NCBSs in M/NEMS.
Characterization of large-volume Frisch grid detector fabricated from as-grown CdZnTeSe
Authors: Roy Utpal N. , Camarda Giuseppe S. , Cui Yonggang , James Ralph B.
Published: December 2019

CdZnTe (CZT) has been under continuous development as a room-temperature radiation detector for the past 2–3 decades. Due to its intrinsic defects, such as a high concentration subgrain boundary network, it has been very challenging to consistently produce high-quality CZT detectors with high yield, particularly for detector volumes exceeding a few cubic centimeters. In this paper, we report characterization of a relatively large-volume Frisch-grid detector (dimensions: 11 × 10.8 × 19.4 mm3) fabricated from a new material Cd0.9Zn0.1Te0.985Se0.015. The detector was fabricated from an as-grown ingot with a 2-in. diameter grown by the Traveling Heater Method. The detector sample was evaluated by infrared transmission microscopy to study the presence of Te inclusions. X-ray topography using a synchrotron light source was deployed to measure the presence of subgrain boundaries and their networks. The detector performance was measured for an optimized Frisch-grid length to extract the best energy resolution at room temperature.
New source design will increase ultracold neutron production rate
Authors: Mandel Savannah
Published: December 2019

Physicists propose a design for a next-generation source of ultracold neutrons which can produce a high current of ultracold neutrons.
Protecting plasma devices with carbon velvet
Authors: Mandel Savannah
Published: December 2019

Scientists study scanning electron microscopy on carbon velvet to learn how to minimize secondary electron emission.
Social perception of situations of sexual cyberviolence: The role of sexist attitudes and the victim’s transgression of gender roles / Percepción social de situaciones de ciberviolencia sexual: el rol de las actitudes sexistas y la transgresión de rol de género de la víctima
Authors: Durán Mercedes , Rodríguez-Domínguez Carmen
Published: December 2019

Sexist attitudes have been identified as an important variable which fosters a climate of social permissiveness towards sexual violence towards women. However, its impact on social reactions to scenarios of sexual cyberviolence is unknown. This study examines whether the impact of this variable along with the victim’s transgression of their gender role may condition social reactions towards this kind of technological violence in a sample of 301 university students between the ages of 18 and 27. The results point to sexist attitudes and transgression of the gender role traditionally attributed to women as predictors of negative social assessments of sexual cyberviolence; furthermore, the interaction between both factors is especially decisive in social judgements on the victims’ guilt. These results complement those of previous studies on the perception of offline sexual violence and highlight the important role of sexist beliefs in negative reactions towards victims of sexual cyberviolence who may be perceived as transgressors of traditional gender roles.
Role of Mac‐1 integrin in generation of extracellular vesicles with antibacterial capacity from neutrophilic granulocytes
Authors: Lőrincz Ákos M. , Bartos Balázs , Szombath Dávid , Szeifert Viktória , Timár Csaba I. , Turiák Lilla , Drahos László , Kittel Ágnes , Veres Dániel S. , Kolonics Ferenc , Mócsai Attila , Ligeti Erzsébet
Published: December 2019

Production of extracellular vesicles (EVs) involved in intercellular communication is a common capacity of most cell types. Upon encountering opsonized microorganisms, neutrophilic granulocytes release EVs that compromise bacterial growth. We carried out a systematic investigation of the involvement of potential opsonin receptors in EV‐generation from human and murine neutrophils. Applying flow cytometric, proteomic and functional analysis as well as using genetically modified mice, we demonstrate that formation of antibacterial EVs depends upon stimulation of the multifunctional Mac‐1 integrin complex, also called as complement receptor 3 (CR3), whereas activation of immunoglobulin binding Fc receptors or pattern recognition receptors alone or in combination is ineffective. Mac‐1/CR3 stimulation and downstream tyrosine kinase signalling affect both the numbers, the cargo content and the antibacterial capacity of the produced vesicles. In contrast, Mac‐1/CR3 signalling is not required for spontaneous EV formation, clearly indicating the existence of separate molecular pathways in EV biogenesis. We propose that EVs are “tailor‐made” with different composition and functional properties depending on the environmental circumstances.
A pair of E3 ubiquitin ligases compete to regulate filopodial dynamics and axon guidance
Authors: Boyer Nicholas P. , McCormick Laura E. , Menon Shalini , Urbina Fabio L. , Gupton Stephanie L.
Published: December 2019

Appropriate axon guidance is necessary to form accurate neuronal connections. Axon guidance cues that stimulate cytoskeletal reorganization within the growth cone direct axon navigation. Filopodia at the growth cone periphery have long been considered sensors for axon guidance cues, yet how they respond to extracellular cues remains ill defined. Our previous work found that the filopodial actin polymerase VASP and consequently filopodial stability are negatively regulated via nondegradative TRIM9-dependent ubiquitination. Appropriate VASP ubiquitination and deubiquitination are required for axon turning in response to the guidance cue netrin-1. Here we show that the TRIM9-related protein TRIM67 outcompetes TRIM9 for interacting with VASP and antagonizes TRIM9-dependent VASP ubiquitination. The surprising antagonistic roles of two closely related E3 ubiquitin ligases are required for netrin-1–dependent filopodial responses, axon turning and branching, and fiber tract formation. We suggest a novel model in which coordinated regulation of VASP ubiquitination by a pair of interfering ligases is a critical element of VASP dynamics, filopodial stability, and axon guidance.
The human fetal thymus generates invariant effector γδ T cells
Authors: Tieppo Paola , Papadopoulou Maria , Gatti Deborah , McGovern Naomi , Chan Jerry K.Y. , Gosselin Françoise , Goetgeluk Glenn , Weening Karin , Ma Ling , Dauby Nicolas , Cogan Alexandra , Donner Catherine , Ginhoux Florent , Vandekerckhove Bart , Vermijlen David
Published: December 2019

In the mouse thymus, invariant γδ T cells are generated at well-defined times during development and acquire effector functions before exiting the thymus. However, whether such thymic programming and age-dependent generation of invariant γδ T cells occur in humans is not known. Here we found that, unlike postnatal γδ thymocytes, human fetal γδ thymocytes were functionally programmed (e.g., IFNγ, granzymes) and expressed low levels of terminal deoxynucleotidyl transferase (TdT). This low level of TdT resulted in a low number of N nucleotide insertions in the complementarity-determining region-3 (CDR3) of their TCR repertoire, allowing the usage of short homology repeats within the germline-encoded VDJ segments to generate invariant/public cytomegalovirus-reactive CDR3 sequences (TRGV8-TRJP1-CATWDTTGWFKIF, TRDV2-TRDD3-CACDTGGY, and TRDV1-TRDD3-CALGELGD). Furthermore, both the generation of invariant TCRs and the intrathymic acquisition of effector functions were due to an intrinsic property of fetal hematopoietic stem and precursor cells (HSPCs) caused by high expression of the RNA-binding protein Lin28b. In conclusion, our data indicate that the human fetal thymus generates, in an HSPC/Lin28b-dependent manner, invariant γδ T cells with programmed effector functions.
The basic residues in the Orai1 channel inner pore promote opening of the outer hydrophobic gate
Authors: Yamashita Megumi , Ing Christopher E. , Yeung Priscilla See-Wai , Maneshi Mohammad M. , Pomès Régis , Prakriya Murali
Published: December 2019

Store-operated Orai1 channels regulate a wide range of cellular functions from gene expression to cell proliferation. Previous studies have shown that gating of Orai1 channels is regulated by the outer pore residues V102 and F99, which together function as a hydrophobic gate to block ion conduction in resting channels. Opening of this gate occurs through a conformational change that moves F99 away from the permeation pathway, leading to pore hydration and ion conduction. In addition to this outer hydrophobic gate, several studies have postulated the presence of an inner gate formed by the basic residues R91, K87, and R83 in the inner pore. These positively charged residues were suggested to block ion conduction in closed channels via mechanisms involving either electrostatic repulsion or steric occlusion by a bound anion plug. However, in contrast to this model, here we find that neutralization of the basic residues dose-dependently abolishes both STIM1-mediated and STIM1-independent activation of Orai1 channels. Molecular dynamics simulations show that loss of the basic residues dehydrates the pore around the hydrophobic gate and stabilizes the pore in a closed configuration. Likewise, the severe combined immunodeficiency mutation, Orai1 R91W, closes the channel by dewetting the hydrophobic stretch of the pore and stabilizing F99 in a pore-facing configuration. Loss of STIM1-gating in R91W and in the other basic residue mutants is rescued by a V102A mutation, which restores pore hydration at the hydrophobic gate to repermit ion conduction. These results indicate that the inner pore basic residues facilitate opening of the principal outer hydrophobic gate through a long-range effect involving hydration of the outer pore.
Highly coupled transport can be achieved in free-exchange transport models
Authors: Hussey Grant A. , Thomas Nathan E. , Henzler-Wildman Katherine A.
Published: December 2019

Secondary active transporters couple the transport of an ion species down its concentration gradient to the uphill transport of another substrate. Despite the importance of secondary active transport to multidrug resistance, metabolite transport, and nutrient acquisition, among other biological processes, the microscopic steps of the coupling mechanism are not well understood. Often, transport models illustrate coupling mechanisms through a limited number of “major” conformations or states, yet recent studies have indicated that at least some transporters violate these models. The small multidrug resistance transporter EmrE has been shown to couple proton influx to multidrug efflux via a mechanism that incorporates both “major” and “minor” conformational states and transitions. The resulting free exchange transport model includes multiple leak pathways and theoretically allows for both exchange and cotransport of ion and substrate. To better understand how coupled transport can be achieved in such a model, we numerically simulate a free-exchange model of transport to determine the step-by-step requirements for coupled transport. We find that only moderate biasing of rate constants for key transitions produce highly efficient net transport approaching a perfectly coupled, stoichiometric model. We show how a free-exchange model can enable complex phenotypes, including switching transport direction with changing environmental conditions or substrates. This research has broad implications for synthetic biology, as it demonstrates the utility of free-exchange transport models and the fine tuning required for perfectly coupled transport.
The role of kinetic inductance on the performance of YBCO SQUID magnetometers
Authors: Ruffieux S , Kalaboukhov A , Xie M , Chukharkin M , Pfeiffer C , Sepehri S , Schneiderman J F , Winkler D
Published: December 2019

Inductance is a key parameter when optimizing the performance of superconducting quantum interference device (SQUID) magnetometers made from the high temperature superconductor YBa2Cu3O7−x
(YBCO) because lower SQUID inductance L leads to lower flux noise, but also weaker coupling to the pickup loop. In order to optimize the SQUID design, we combine inductance simulations and measurements to extract the different inductance contributions, and measure the dependence of the transfer function V
Φ and flux noise

S

Φ

1

/

2

on L. A comparison between two samples shows that the kinetic inductance contribution varies strongly with film quality, hence making inductance measurements a crucial part of the SQUID characterization. Thanks to the improved estimation of the kinetic inductance contribution, previously found discrepancies between theoretical estimates and measured values of V
Φ and

S

Φ

1

/

2

could to a large extent be avoided. We then use the measurements and improved theoretical estimations to optimize the SQUID geometry and reach a noise level of

S

B

1

/

2

 = 44 fT/

Hz

for the best SQUID magnetometer with a 8.6 mm × 9.2 mm directly coupled pickup loop. Lastly, we demonstrate a method for reliable one-time sensor calibration that is constant in a temperature range of several kelvin despite the presence of temperature dependent coupling contributions, such as the kinetic inductance. The found variability of the kinetic inductance contribution has implications not only for the design of YBCO SQUID magnetometers, but for all narrow linewidth SQUID-based devices operated close to their critical temperature.
Molecular opacities of low-lying states of oxygen molecule*
Authors: Liang Gui-Ying , Peng Yi-Geng , Li Rui , Wu Yong , Wang Jian-Guo
Published: December 2019

The

X
3

Σ
g
−

, A′3Δu,

A
3

Σ
u
+

, 13Πg, and

B
3

Σ
u
−

electronic states of oxygen molecule (O2) are calculated by the multi-configuration self-consisted filed (MRCI) + Q method with the scalar relativistic correction and core–valence correlation correction. The obtained spectroscopic constants of the low-lying bound states are in excellent agreement with measurements. Based on the accurately calculated structure parameters, the opacities of the oxygen molecule at the temperatures of 1000 K, 2000 K, 2500 K, and 5000 K under a pressure of 100 atm (1 atm = 1.01325 × 105 Pa) and the partition functions between 10 K and 104 K are obtained. It is found that with the increase of temperature, the opacities for transitions in a long wavelength range are enlarged because of the larger population on excited electronic states at the higher temperatures.
Infrared light-emitting diodes based on colloidal PbSe/PbS core/shell nanocrystals*
Authors: Hyun Byung-Ryool , Marus Mikita , Zhong Huaying , Li Depeng , Liu Haochen , Xie Yue , Koh Weon-kyu , Xu Bing , Liu Yanjun , Sun Xiao Wei
Published: December 2019

Colloidal PbSe nanocrystals (NCs) have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ranges. However, the fast degradation of colloidal PbSe NCs in ambient conditions hampers their widespread applications in infrared optoelectronics. It is well-known that the inorganic thick-shell over core improves the stability of NCs. Here, we present the synthesis of PbSe/PbS core/shell NCs showing wide spectral tunability, in which the molar ratio of lead (Pb) and sulfur (S) precursors, and the concentration of sulfur and PbSe NCs in solvent have a significant effect on the efficient PbS shell growth. The infrared light-emitting diodes (IR-LEDs) fabricated with the PbSe/PbS core/shell NCs exhibit an external quantum efficiency (EQE) of 1.3 % at 1280 nm. The ligand exchange to optimize the distance between NCs and chloride treatment are important processes for achieving high performance on PbSe/PbS NC-LEDs. Our results provide evidence for the promising potential of PbSe/PbS NCs over the wide range of infrared optoelectronic applications.
Effects of square micro-pillar array porosity on the liquid motion of near surface layer*
Authors: Qiao Xiaoxi , Zhang Xiangjun , Chen Ping , Tian Yu , Meng Yonggang
Published: December 2019

The influence rules of square micro-pillar array porosity on the liquid motion characteristics of the near-surface layer are investigated by quartz crystal microbalance (QCM). QCM is a powerful and promising technique in studying the interfacial behavior, which exhibits great advantages in investigating the effects of surface microstructure, roughness, and array. In our experiments, three different arrays with the same height of about 280 nm and center distance of 200 μm, but different diameters of about 78 μm, 139 μm, and 179 μm are investigated. The results indicate that when the surface array has a large porosity, its influence on the liquid motion of the near surface layer is slight, thus resulting in a small increase of half-bandwidth variation due to the additional friction energy dissipation. When the surface array has a small porosity, the array tends to make the liquid film trapped in the array oscillating with the substrate, then there may be a layer of liquid film behaving like rigid film, and it also will make the liquid motion near the array layer more complicated. Thus for the #3 surface with a small porosity, both the absolute values of frequency shift |Δf
3| and half-bandwidth variation ΔΓ
3 increase obviously. The experimental results show good consistence with the theoretical model of Daikhin and Urbakh. This study sheds light on understanding the influence mechanism of surface array porosity on the liquid motion of near-surface layer.
Quantum intelligence on protein folding pathways*
Authors: Mao Wen-Wen , Lv Li-Hua , Ji Yong-Yun , Li You-Quan
Published: December 2019

We study the protein folding problem on the base of our quantum approach by considering the model of protein chain with nine amino-acid residues. We introduce the concept of distance space and its projections on a XY-plane, and two characteristic quantities, one is called compactness of protein structure and another is called probability ratio involving shortest path. The concept of shortest path enables us to reduce the 388 × 388 density matrix to a 2 × 2 one from which the von Neumann entropy reflecting certain quantum coherence feature is naturally defined. We observe the time evolution of average distance and compactness solved from the classical random walk and quantum walk, we also compare the features of the time-dependence of Shannon entropy and von Neumann entropy. All the results not only reveal the fast quantum folding time but also unveil the existence of quantum intelligence hidden behind in choosing protein folding pathways.
Effect of system–reservoir correlations on temperature estimation*
Authors: Zhu Wen-Li , Wu Wei , Luo Hong-Gang
Published: December 2019

In many previous temperature estimation schemes, the temperature of a sample is directly read out from the final steady state of a quantum probe, which is coupled to the sample. However, in these studies, information of correlations between system (the probe) and reservoir (the sample) is usually eliminated, leading the steady state of the probe is a canonical equilibrium state with respect solely to system’s Hamiltonian. To explore the influence of system–reservoir correlations on the estimation precision, we investigate the equilibration dynamics of a spin interacting with a finite temperature bosonic reservoir. By incorporating an intermediate harmonic oscillator or a collective coordinate into the spin, the system–reservoir correlations can be correspondingly encoded in a Gibbs state of an effective Hamilton, which is size consistent with the original bare spin. Extracting information of temperature from this corrected steady state, we find the effect of the system-reservoir correlations on the estimation precision is highly sensitive to the details of the spectral density function of the measured reservoir.
Optical and electrical properties of InGaZnON thin films*
Authors: Yao Jian Ke , Ye Fan , Fan Ping
Published: December 2019

The substrate temperature (T
s) and N2 partial pressure (P
N2) dependent optical and electrical properties of sputtered InGaZnON thin films are studied. With the increased T
s and P
N2, the thin film becomes more crystallized and nitrified. The Hall mobility, free carrier concentration (N
e), and electrical conductivity increase with the lowered interfacial potential barrier during crystal growing. The photoluminescence (PL) intensity decreases with the increased N
e. The band gap (E
g) narrows and the linear refractive index (n
1) increases with the increasing concentration of N in the thin films. The Stokes shift between the PL peak and absorption edge decreases with E
g. The n
1, dispersion energy, average oscillator wavelength, and oscillator length strength all increase with n
1. The single oscillator energy decreases with n
1. The nonlinear refractive index and third order optical susceptibility increase with n
1. The Seebeck coefficient, electron effective mass, mean free path, scattering time, and plasma energy are all N
e dependent.
Graphene’s photonic and optoelectronic properties – A review
Authors: Wirth-Lima A J , Alves-Sousa P P , Bezerra-Fraga W
Published: December 2019

Due to its remarkable electrical and optical properties, graphene continues to receive more and more attention from researchers around the world. An excellent advantage of graphene is the possibility of controlling its charge density, and consequently, the management of its conductivity and dielectric constant, among other parameters. It is noteworthy that the control of these properties enables the obtaining of new optical/electronic devices, which would not exist based on conventional materials. However, to work in this area of science, it is necessary to have a thorough knowledge regarding the electrical/optical properties of graphene. In this review paper, we show these graphene properties very well detailed.
Geant4 simulation of proton-induced single event upset in three-dimensional die-stacked SRAM device*
Authors: Ye Bing , Mo Li-Hua , Liu Tao , Luo Jie , Li Dong-Qing , Zhao Pei-Xiong , Cai Chang , He Ze , Sun You-Mei , Hou Ming-Dong , Liu Jie
Published: December 2019

Geant4 Monte Carlo simulation results of the single event upset (SEU) induced by protons with energy ranging from 0.3 MeV to 1 GeV are reported. The SEU cross section for planar and three-dimensional (3D) die-stacked SRAM are calculated. The results show that the SEU cross sections of the planar device and the 3D device are different from each other under low energy proton direct ionization mechanism, but almost the same for the high energy proton. Besides, the multi-bit upset (MBU) ratio and pattern are presented and analyzed. The results indicate that the MBU ratio of the 3D die-stacked device is higher than that of the planar device, and the MBU patterns are more complicated. Finally, the on-orbit upset rate for the 3D die-stacked device and the planar device are calculated by SPACE RADIATION software. The calculation results indicate that no matter what the orbital parameters and shielding conditions are, the on-orbit upset rate of planar device is higher than that of 3D die-stacked device.
Molecular dynamics simulation of atomic hydrogen diffusion in strained amorphous silica*
Authors: Zhang Fu-Jie , Zhou Bao-Hua , Liu Xiao , Song Yu , Zuo Xu
Published: December 2019

Understanding hydrogen diffusion in amorphous SiO2 (a-SiO2), especially under strain, is of prominent importance for improving the reliability of semiconducting devices, such as metal–oxide–semiconductor field effect transistors. In this work, the diffusion of hydrogen atom in a-SiO2 under strain is simulated by using molecular dynamics (MD) with the ReaxFF force field. A defect-free a-SiO2 atomic model, of which the local structure parameters accord well with the experimental results, is established. Strain is applied by using the uniaxial tensile method, and the values of maximum strain, ultimate strength, and Young’s modulus of the a-SiO2 model under different tensile rates are calculated. The diffusion of hydrogen atom is simulated by MD with the ReaxFF, and its pathway is identified to be a series of hops among local energy minima. Moreover, the calculated diffusivity and activation energy show their dependence on strain. The diffusivity is substantially enhanced by the tensile strain at a low temperature (below 500 K), but reduced at a high temperature (above 500 K). The activation energy decreases as strain increases. Our research shows that the tensile strain can have an influence on hydrogen transportation in a-SiO2, which may be utilized to improve the reliability of semiconducting devices.
Orientation-dependent depolarization of supercontinuum in BaF2 crystal*
Authors: Li Zi-Xi , Gong Cheng , Shao Tian-Jiao , Hua Lin-Qiang , Bian Xue-Bin , Liu Xiao-Jun
Published: December 2019

We present a systematic investigation of the depolarization properties of a supercontinuum accompanied with femtosecond laser filamentation in barium fluoride (BaF2) crystal. It is found that the depolarization of the supercontinuum depends strongly on the crystal orientations with respect to the incident laser polarization. At most crystal orientations, the depolarization of the supercontinuum rises with the increase of the input laser energies and finally saturates. While at 45°, the depolarization of the supercontinuum is not changed and keeps nearly negligible with the increase of the input laser energies. These peculiar depolarization properties of the supercontinuum can be ascribed to the orientation dependence of the cross-polarized wave (XPW) generation and ionization-induced plasma scattering in the BaF2 crystal.
Smooth and Beta-Beating-Free Optics Transitions for HL-LHC
Authors: De Maria R. , Solfaroli M.
Published: December 2019

In the CERN LHC, optics transitions are mainly required to control the beam size at the four experimental interaction points. The current method, based on linearly-interpolated optics functions over a small set of matched optics and parabolic time-domain segments, introduces non-zero beta-beating and it is not optimal in time. This contribution presents an alternative approach, based on continuously-matched optics solutions distributed in time domain by using a realistic model of the superconducting circuits, which optimises the overall process duration. This method requires a change in the paradigm used in the control system and it is proposed for the future High Luminosity LHC (HL-LHC) runs.
US contribution to the High Luminosity LHC Upgrade: focusing quadrupoles and crab cavities
Authors: Apollinari Giorgio , Carcagno Ruben , Ambrosio Giorgio , Feher Sandor , Ristori Leonardo
Published: December 2019

In the early 2000’s, the US High Energy Physics community contributing to the Large Hadron Collider (LHC) launched the LHC Accelerator R&D Program (LARP), a long-vision focused R&D program, intended to contribute to a quick LHC commissioning and to bring the Nb3Sn and other technologies to a maturity level that would allow applications in HEP machines. Around 2015, the technologies developed by LARP, CERN and other institutions were mature enough to allow the spin-off of a major upgrade project to the LHC complex, the High Luminosity LHC (HL-LHC) [3]. This paper will focus on the US contribution to HL-LHC, namely the large-aperture low-β focusing Nb3Sn quadrupoles and the Radio Frequency Dipole (RFD) Crab Cavities, located in close proximity to the ATLAS and CMS experiments. This contribution, called the HL-LHC Accelerator Upgrade Project (HL-LHC AUP), focuses on production of these quadrupoles and cavities by sharing the work among a consortium of US Laboratories (FNAL, LBNL, BNL and SLAC) and Universities and in close connection with the CERN-led HL-LHC Collaboration. The collaboration achieved commonality of specifications and uniformity of performance. Final development of design, construction and first results from the prototypes are described to indicate the status of these critical components for HL-LHC.
Study of Beam-Gas Interactions at the LHC for the Physics Beyond Colliders Fixed-Target Study
Authors: Boscolo Meneguolo C , Abramov A , Bruce R , Cerutti F , Ferro-Luzzi M , Giovannozzi M , Mereghetti A , Molson J , Redaelli S
Published: December 2019

Among several working groups formed in the framework of the Physics Beyond Colliders study, launched at CERN in September 2016, there is one investigating specific fixed- target experiment proposals. Of particular interest is the study of high-density unpolarized or polarized gas targets to be installed in the LHC, upstream of the LHCb detector, using storage cells to enhance the target density. This work studies the impact of the interactions of 7 TeV proton beams with such gas targets on the LHC machine in terms of particle losses.
Study on beam-induced heating in injection section of Hefei Light Source
Authors: Xu Derong , Xu Wei
Published: December 2019

Ceramic chambers distributed with metal striplines on the inner surface are installed in the injection section at Hefei Light Source (HLS). Heating on the ceramics chambers has been observed during machine operation. An air compressor is used to cool these chambers due to concerns of overheating during top-up operation mode. To understand the sources of the heating, a series of experiments are performed with various beam currents and bunch filling patterns. The study shows that the heating is mainly caused by the narrow-band impedances of the ceramic chambers and their adjacent vacuum components.
Status report of the SINBAD-ARES RF photoinjector and linac commissioning
Authors: Panofski E , Assmann R W , Burkart F , Dorda U , Floettmann K , Huening M , Marchetti B , Marx D , Mayet F , Walker P A , Yamin S
Published: December 2019

The accelerator R&D facility SINBAD (Short innovative bunches and accelerators at DESY) will drive multiple independent experiments, including the acceleration of ultrashort electron bunches and the testing of advanced high-gradient acceleration concepts. The SINBAD-ARES (Accelerator Research Experiment at SINBAD) setup hosts a normal conducting RF photoinjector generating a low-charge electron beam, which is afterwards accelerated by an S-band linac section. The linac as well as a magnetic chicane will allow the production of ultrashort bunches with excellent arrival-time stability. The high brightness beam has then the potential to serve as a test beam for next-generation compact acceleration schemes. The setup of the SINBAD-ARES facility will proceed in stages. We report on the current status of the ARES RF gun commissioning and linac setup.
Simulation studies for a EEHG seeded FEL in the XUV
Authors: Grattoni V. , Faatz B. , Paraskaki G. , Ackermann S. , Assmann R. W. , Lechner C. , Zemella J. , Kazemi M. M. , Lang T. , Hillert W. , Reiche S.
Published: December 2019

Echo-enabled harmonic generation (EEHG) is a promising technique for seeded free electron lasers (FELs) not only to go down to wavelengths of 4 nm but also to simplify the schemes that are currently used to achieve a similar wavelength range (double cascade HGHG). Thus a study optimizing the EEHG performance in the wavelength range from 60 to 4nm has been performed. The more critical working point, at 4 nm, is here analyzed in terms of seed laser stability for two different seed laser frequencies: visible and UV.
Wake-T: a fast particle tracking code for plasma-based accelerators
Authors: Ferran Pousa A , Assmann R , Martinez de la Ossa A
Published: December 2019

The design and study of plasma-based accelerators relies typically on costly 3D Particle-In-Cell (PIC) simulations due to the complexity of the laser-plasma and beam-plasma interactions. However, under certain assumptions, more efficient and simple models can be implemented to describe the dynamics of the accelerated beams. Wake-T (Wakefield particle Tracker) is a new code for analytical and numerical particle tracking in plasma-based accelerators which is orders of magnitude faster than conventional PIC codes. This allows for fast parameter scans and is well suited for the initial design and optimization of these novel accelerators.
Numerical Study of Photonic-Crystal-Based Dielectric Accelerators
Authors: Torrisi G. , Mauro G. S. , Celona L. , Mascali D. , Gammino S. , Sorbello G. , De Angelis C. , Locatelli A.
Published: December 2019

All-dielectric electromagnetic band gap (EBG) waveguides structures promise significant improvement of accelerating gradient of laser-driven acceleration with the potential to miniaturize the accelerator itself. In this work we study photonic crystal structures designed for acceleration of relativistic electrons. We explore the performance of the all-dielectric EBG accelerating structures thanks to full wave electromagnetic simulations of couplers and accelerating waveguides. The characteristic interaction impedance, accelerating gradient and all the key parameters that are typically used to characterize linear accelerators are evaluated and used to compare the properties of the accelerating mode field distribution in different geometries.
Moderation of positive muons by helium gas
Authors: Li Yang , Bao Yu , Fan Ruirui , Li Xiao , Ning Changjun , Tong Xin , Wang Pengcheng
Published: December 2019

Efficiently creating beams of spin-polarized positive muons with energies between eV and keV (so-called slow muon beams) is important for further development and application of muon spin rotation, relaxation, and resonance techniques. One existing moderation method involves the use of wide-band-gap materials as moderators such as rare gas solids and solid nitrogen thin films (band-gap energy between 11 eV and 22eV). Based on this moderation method, we have studied the use of helium gas as a moderator, with the goal of producing the slow muon beam more efficiently. Because of helium’s high (24.6 eV) ionization energy and because the cross section for muonium formation is suppressed in helium gas, we expect the production of slow muons using helium gas to be highly efficient.
Negative Muonium Ion Production With a C12A7 Electride Film
Authors: Otani M. , Fukao Y. , Futatsukawa K. , Kawamura N. , Matoba S. , Mibe T. , Miyake Y. , Shimomura K. , Yamazaki T. , Hasegawa K. , Kitamura R. , Kondo Y. , Morishita T. , Iijima T. , Inami K. , Sue Y. , Yotsuzuka M. , Iinuma H. , Nakazawa Y. , Ishida K. , Saito N. , Yasuda H.
Published: December 2019

Negative muonium atom (μ
+
e
–
e
–, Mu–) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980’s in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative muonium production measurement with several materials including a C12A7 electride film will be presented.
Advanced Beam Dynamics Design for the Superconducting Heavy Ion Accelerator HELIAC
Authors: Schwarz Malte , Aulenbacher Kurt , Barth Winfried , Basten Markus , Burandt Christoph , Busch Marco , Conrad Thorsten , Dziuba Florian , Gettmann Viktor , Heilmann Manuel , Kürzeder Thorsten , Lauber Simon , List Julian , Miski-Oglu Maksym , Podlech Holger , Rubin Anna , Yaramyshev Stepan
Published: December 2019

The standalone superconducting (SC) continuous wave (CW) heavy ion linac HELIAC (HElmholtz LInear ACcelerator) is a common project of GSI and HIM under key support of IAP Frankfurt and in collaboration with Moscow Engineering Physics Institute (MEPhI) and Moscow Institute for Theoretical and Experimental Physics (KI-ITEP). It is intended for future experiments with heavy ions near the Coulomb barrier within super-heavy element (SHE) research and aims at developing a linac with multiple CH cavities as key components downstream the High Charge State Injector (HLI) at GSI. The design is challenging due to the requirement of intense beams in CW mode up to a mass-to-charge ratio of 6, while covering a broad output energy range from 3.5 to 7.3MeV/u with minimum energy spread. In 2017 the first superconducting section of the linac has been successfully commissioned and extensively tested with beam at GSI. In the light of experience gained in this research so far, the beam dynamics layout for the entire linac has recently been updated and optimized with particular emphasis on realistic assumptions of cavity gap and drift lengths as well as gap voltage distributions for CH3-CH11.
Upgrade of the 3-MeV Linac for testing of Accelerator Components at J-PARC
Authors: Kondo Y. , Morishita T. , Hirano K. , Ito T. , Kikuzawa N. , Kitamura R. , Oguri H. , Ohkoshi K. , Shinozaki S. , Shinto K. , Fang Z. , Fukui Y. , Futatsukawa K. , Ikegami K. , Miyao T. , Nanmo K. , Otani M. , Shibata T. , Hori T. , Nemoto Y. , Sato Y. , Kobayashi F. , Takahashi D. , Tasaki R. , Ito Y. , Kato Y. , Ishiyama T. , Sawabe Y.
Published: December 2019

We have upgraded a 3-MeV linac at J-PARC. The ion source is same as the J-PARC linac’s, and the old 30-mA RFQ is replaced by a spare 50-mA RFQ, therefore, the beam energy is 3 MeV and the nominal beam current is 50 mA. The main purpose of this system is to test the spare RFQ, but also used for testing of various components required in order to keep the stable operation of the J-PARC accelerator. The accelerator has been already commissioned, and measurement programs have been started. In this paper, present status of this 3-MeV linac is presented.
Longitudinal Measurements and Beam Tuning in the J-PARC Linac MEBT1
Authors: Otani M. , Futatsukawa K. , Miyao T. , Liu Y. , Hirano K. , Kondo Y. , Miura A. , Oguri H.
Published: December 2019

The Japan Proton Accelerator Research Complex (J-PARC) linac is operated with design peak current of 50 mA from 2018. For operation with such a high beam current, it is important to understand transverse and longitudinal beam properties especially in low-velocity region. A medium energy beam transport (MEBT1) line between the 3-MeV radio-frequency quadrupole linac (RFQ) and the 50-MeV drift-tube linac (DTL) is a 3-m-long transport line to match the beam to the DTL and produces a macro pulse configuration for a 3-GeV rapid-cycling synchrotron (RCS). In this paper, recent measurements and beam tuning results in MEBT1 will be presented.
Charge stripping at high energy heavy ion Linacs
Authors: Barth W , Fomichev A , Grigorenko L , Kulevoy T. , Polozov S , Yaramyshev S
Published: December 2019

For each heavy-ion accelerator facility charge stripping is a key technology – the stripping charge state, its efficiency to produce ions in the selected charge state, and the beam quality after stripping substantially determine the entire accelerator performance. Modern heavy ion accelerator facilities such as the future Facility for Antiproton and Ion Research (FAIR) at GSI, Darmstadt, Germany provide for high-intensity heavy-ion beams beyond 200 MeV/u. Heavy ions generated in an ion source at comparatively low charge states are pre-accelerated in a Linac to a few MeV/u, after charge stripping the average charge state is increased and one (or several) ion charge states are selected for further acceleration. This enables more efficient acceleration up to the final beam energy, compared to acceleration of ions with a low charge state. C-foil stripping allows for highest mean charge state and best stripping efficiency into the desired charge state. Therefore minimum acceleration voltage could be expected utilizing C-foil stripping. Due to the high power deposited by the ions in the stripping media and radiation damages if solids are used, self-recovering stripper media must be used in any case. First layout scenarios for a 200 MeV/u heavy ion Linac considering efficient heavy ion stripping will be presented.