bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitized photon avalanche nanothermometry in Pr3+ and Yb3+ co-doped NaYF4 colloidal nanoparticles
Authors: Korczak Zuzanna , Dudek Magdalena , Majak Martyna , Misiak Małgorzata , Marciniak Łukasz , Szalkowski Marcin , Bednarkiewicz Artur
Published: March 2023

Photon avalanche (PA) is a highly nonlinear luminescence phenomenon that occurs in lanthanide doped materials. PA exhibits a very steep power law relationship between luminescence intensity and the optical pump power. Due to the mechanism of PA emission, even weak perturbations to the energy looping and energy distribution within excited levels of lanthanide emitters are expected to significantly modify luminescent properties. Therefore, in this work, we experimentally study the impact of temperature (from – 175 to 175 °C, with 25 °C steps) on the sensitized PA emission in NaYF4 nanoparticles co-doped with 15% of Yb3+ and 0.5% of Pr3+ ions under 852 nm pumping wavelength. Significant variations of the PA nonlinearity (S = 4.5–9), PA gain (from 50 up to 175), and PA threshold (from 100 up to 700 kW/cm2) were observed under temperature rise from – 175 to 175 °C, respectively. The relative temperature sensitivities based on luminescence intensity changes were larger than 1.5% °C–1 in the whole temperature range, reaching the maximal value of 7.5% °C–1 at 0 °C. Moreover, a new thermometric parameter was proposed, namely, the PA pump power threshold, which exhibited over 0.5% °C–1 relative sensitivities in the same wide temperature range. Owing to PA properties, the temperature sensitivity range and the corresponding relative sensitivities may be intentionally tuned by selecting the appropriate pump intensity in respect to the power dependence relationship. These studies not only provide a better understanding of fundamental processes and susceptibility of the sensitized photon avalanche emission to temperature variation, but also show the possibility of using PA materials as sensitive (nano)thermometers.
Multiple ultrasounds assisted phase separation and monotectic solidification of liquid ternary Al81.5Cu14.7Bi3.8 immiscible alloy
Authors: Wu Wenhua , Wang Dongzhen , Zhai Wei , Wang Jianyuan , Wei Bingbo
Published: March 2023

Multiple power ultrasounds were employed to investigate the phase transition process of ternary Al81.5Cu14.7Bi3.8 immiscible alloy by various exerting modes. As the ultrasonic sources increased, the liquid phase separation pattern transformed from (Bi)-rich layered macrosegregation into the uniform distribution of secondary (Bi) droplets. Meanwhile, the primary (Al) phase evolved from coarse dendrites into plenty of small spherical grains and also tended to be uniformly dispersed. The subsequently formed ternary (Al) + (Al2Cu) + (Bi) monotectic structure, featured by the alternative (Al) and (Al2Cu) lamellar structure with fine (Bi) grains distributed, was coarsened first and then refined. Numerical simulations showed that the transient cavitation and the acoustic streaming strength were significantly enhanced by increasing ultrasonic beams, with the fourfold ultrasounds producing the most prominent effects on the phase separation process. The intensive and enlarged cavitation areas greatly accelerated the nucleation of both the secondary liquid phase and primary solid phase, which refined the growing (Bi) droplets and (Al) dendrites. The strength and morphology of acoustic streaming were the key factors in offsetting Stokes motion and carrying the growing grains to various regions, resulting in a uniform microstructure. Furthermore, increasing ultrasonic sources improved the friction and wear properties of the solidified alloy, which indicated that the Al81.5Cu14.7Bi3.8 immiscible alloy may become an excellent wear-resistant material owing to the uniform monotectic structure fabricated by the fourfold ultrasounds.
Research on temperature drift mechanism and compensation method of silicon piezoresistive pressure sensors
Authors: Wu Ruirui , Li Huaijiang , Gao Lei
Published: March 2023

Silicon piezoresistive pressure sensors have played a key role in the detection field due to their small size, high sensitivity, and high integration. However, the factors such as its material particularity, the temperature dependence of the piezoresistive coefficient, the variation of carrier motion in the material caused by heat-induced stress, doping concentration, and resistance mismatch may cause the sensor to generate temperature drift. In this paper, the mechanism of temperature drift of silicon-based pressure sensor is analyzed initially, and then a comparison between BP neural network and wavelet neural network is done, which shows the root mean square error of the wavelet neural network is much smaller than that of the BP neural network and better linearity.
Thermal rectification in thin film metalattice structures: A computational study
Authors: Eichfeld Devon A. , Chen Weinan , Dabo Ismaila , Foley Brian M. , Ramos-Alvarado Bladimir
Published: March 2023

Thermal rectification is an asymmetric heat transfer process where directionally dependent transport occurs along a given axis. In this work, geometric parameters that govern thermal rectification in solids composed of various semiconducting materials were investigated utilizing metalattice data for seven materials with pore sizes ranging between 2 and 30 nm. Using numerical simulation, thermal rectification was calculated at different thermal biases in single material systems, including silicon, cubic boron nitride, and diamond, among others. The largest thermal rectification for each material was exhibited in bilayer sample stacks that were thermally matched (i.e., the thermal resistance of each layer in the stack is equal in either forward or reverse direction). Of the materials tested, diamond provided the highest thermal rectification for all cases, with its best case achieving a thermal rectification of 57.2%. This novel thermal functionality will find application in advanced applications for temperature regulation, including resonator systems where thermal effects may significantly alter and/or degrade performance.
A review study on methanol steam reforming catalysts: Evaluation of the catalytic performance, characterizations, and operational parameters
Authors: Rostami Mohsen , Farajollahi Amir Hamzeh , Amirkhani Rasool , Farshchi Mahdi Ebrahimi
Published: March 2023

Conventional fossil-based energy sources have numerous environmental demerits; sustainable and renewable sources are attracting the undivided attention of researchers owing to their valuable physical and chemical features. Several industrial-scale technologies are employing hydrogen as a green energy source as the most preferential source. Not only is hydrogen a potent energy carrier but also it is not detrimental to the environment. Among many other hydrogen production processes, steam reforming of methanol (SRM) is deemed a practical method due to its low energy consumption. Cu, Ni, noble metals, etc., are the salient catalysts in SRM. Many researchers have conducted thorough studies incorporating improvement of the catalysts’ activity, mechanism predictions, and the impacts of operational parameters and reformers. This review concentrates on the SRM catalysts, supports, promoters, and the effect of the operational parameters on the process efficiency and H2 production yield. In this regard, the methanol conversion, H2 and CO selectivity, and operating parameters are notably contingent on the surface characterization and chemistry of the catalysts. Herein, Cu-, Ni-, and noble metal-based catalysts on various metal oxide supports, such as Al2O3 and ZnO, are assessed meticulously in the SRM process from the standpoint of mechanism and catalyst characterization. Most of the peer-reviewed studies had encountered agglomeration, metal particle sintering at high temperatures, coke formation, and deactivation of catalysts as the prevalent barriers. Hence, the novel methods of conquering the above-mentioned obstacles are evaluated in this review. Employment of diverse synthetic methods, bimetallic catalysts, distinct catalyst promoters, and unconventional supports, such as metal–organic frameworks, carbon nanotubes, and zeolites, are the salient routes to overcome the metal dispersion and thermal stability issues. In addition, the influence of operational parameters (temperature of the process, steam/carbon ratio, and feed flow rate) has been weighed painstakingly, along with introducing the research gap and future perspectives in the territory of SRM catalysts.
Linearly polarized light emission from GaN micro-LEDs for 3D display
Authors: Huang Jinpeng , Xu Yi , Zhou Binru , Zhan Huming , Cao Peng , Wang Junxi , Li Jinmin , Yi Xiaoyan , Pan Anlian , Wang Liancheng
Published: March 2023

A three-dimensional (3D) display provides an immersive user experience and represents the frontier of display technology. The 3D display based on polarizer films is relatively mature. However, the currently used polarizer films lead to bulk systems and low efficiency. Micro-light-emitting diodes (micro-LEDs) have the advantages of small size, high contrast, low power consumption, and high response frequency. The 3D micro-LED displays combine the characteristics of 3D display and the advantages of micro-LEDs simultaneously, which can be used in portable electronics or micro-LED projectors and provides users with 3D experience. Here, linearly polarized (LP) micro-LEDs with varied chip diameters are numerically and experimentally investigated. Subwavelength metal gratings are integrated directly on the p-GaN of micro-LEDs. A maximum extinction ratio of 14.17 dB and a corresponding energy loss of 50% are achieved directly from LP micro-LEDs under the injection current density of 200 A/cm2. The size-dependent effect of LP micro-LED is also investigated and it is found that smaller sized LP micro-LEDs have smaller extinction ratio due to sidewall light leakage. The reported GaN-based LP micro-LEDs have excellent potential to be utilized in 3D micro-LED displays.
Relaxation time scales of interfacial water upon fluid to ripple to gel phase transitions of bilayers
Authors: Malik Sheeba , Karmakar Smarajit , Debnath Ananya
Published: March 2023

The slow relaxation of interface water (IW) across three primary phases of membranes is relevant to understand the influence of IW on membrane functions at supercooled conditions. To this objective, a total of ∼16.26μs all-atom molecular dynamics simulations of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine lipid membranes are carried out. A supercooling-driven drastic slow-down in heterogeneity time scales of the IW is found at the fluid to the ripple to the gel phase transitions of the membranes. At both fluid-to-ripple-to-gel phase transitions, the IW undergoes two dynamic crossovers in Arrhenius behavior with the highest activation energy at the gel phase due to the highest number of hydrogen bonds. Interestingly, the Stokes–Einstein (SE) relation is conserved for the IW near all three phases of the membranes for the time scales derived from the diffusion exponents and the non-Gaussian parameters. However, the SE relation breaks for the time scale obtained from the self-intermediate scattering functions. The behavioral difference in different time scales is universal and found to be an intrinsic property of glass. The first dynamical transition in the α relaxation time of the IW is associated with an increase in the Gibbs energy of activation of hydrogen bond breaking with locally distorted tetrahedral structures, unlike the bulk water. Thus, our analyses unveil the nature of the relaxation time scales of the IW across membrane phase transitions in comparison with the bulk water. The results will be useful to understand the activities and survival of complex biomembranes under supercooled conditions in the future.
Electronic density response of warm dense matter
Authors: Dornheim Tobias , Moldabekov Zhandos A. , Ramakrishna Kushal , Tolias Panagiotis , Baczewski Andrew D. , Kraus Dominik , Preston Thomas R. , Chapman David A. , Böhme Maximilian P. , Döppner Tilo , Graziani Frank , Bonitz Michael , Cangi Attila , Vorberger Jan
Published: March 2023

Matter at extreme temperatures and pressures—commonly known as warm dense matter (WDM)—is ubiquitous throughout our Universe and occurs in astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion and is realized in the laboratory using different techniques. A particularly important property for the understanding of WDM is given by its electronic density response to an external perturbation. Such response properties are probed in x-ray Thomson scattering (XRTS) experiments and are central for the theoretical description of WDM. In this work, we give an overview of a number of recent developments in this field. To this end, we summarize the relevant theoretical background, covering the regime of linear response theory and nonlinear effects, the fully dynamic response and its static, time-independent limit, and the connection between density response properties and imaginary-time correlation functions (ITCF). In addition, we introduce the most important numerical simulation techniques, including path-integral Monte Carlo simulations and different thermal density functional theory (DFT) approaches. From a practical perspective, we present a variety of simulation results for different density response properties, covering the archetypal model of the uniform electron gas and realistic WDM systems such as hydrogen. Moreover, we show how the concept of ITCFs can be used to infer the temperature from XRTS measurements of arbitrary complex systems without the need for any models or approximations. Finally, we outline a strategy for future developments based on the close interplay between simulations and experiments.
Ultrafast 2D-IR spectroscopy of intensely optically scattering pelleted solid catalysts
Authors: Donaldson Paul M. , Howe Russell F. , Hawkins Alexander P. , Towrie Mike , Greetham Gregory M.
Published: March 2023

Solid, powdered samples are often prepared for infrared (IR) spectroscopy analysis in the form of compressed pellets. The intense scattering of incident light by such samples inhibits applications of more advanced IR spectroscopic techniques, such as two-dimensional (2D)-IR spectroscopy. We describe here an experimental approach that enables the measurement of high-quality 2D-IR spectra from scattering pellets of zeolites, titania, and fumed silica in the OD-stretching region of the spectrum under flowing gas and variable temperature up to ∼500 ◦C. In addition to known scatter suppression techniques, such as phase cycling and polarization control, we demonstrate how a bright probe laser beam comparable in strength with the pump beam provides effective scatter suppression. The possible nonlinear signals arising from this approach are discussed and shown to be limited in consequence. In the intense focus of 2D-IR laser beams, a free-standing solid pellet may become elevated in temperature compared with its surroundings. The effects of steady state and transient laser heating effects on practical applications are discussed.
Slow spectral diffusion of the NO stretching mode of [RuCl5(NO)]2− in D2O studied by 2D-IR spectroscopy and molecular dynamics simulations
Authors: Fujii Yuki , Aikawa Kyoko , Tayama Jumpei , Banno Motohiro , Ohta Kaoru , Tominaga Keisuke
Published: March 2023

The vibrational dynamics of the NO stretching mode of [RuCl5(NO)]2− in D2O were investigated by nonlinear infrared (IR) spectroscopy. We performed IR pump–probe measurements to obtain the vibrational lifetime of this molecule. The lifetime is 31 ps, which is sufficiently long enough to study the vibrational frequency fluctuation on a slower time scale with high precision. By two-dimensional IR spectroscopy, the frequency–frequency time correlation function (FFTCF) of the NO stretching mode was characterized with a delta function plus a double-exponential function. The time constant of the slower component was ∼10 ps. We also found that the time constant does not strongly depend on temperature. In order to investigate the microscopic origin of this component, we performed classical molecular dynamics simulations. It was found that the hydration structure around the NO group was influenced by the negatively charged Cl ligands. To calculate the FFTCF decay, we employed an approximate theoretical model based on the vibrational solvatochromism theory. It was demonstrated that water fluctuations around the Cl ligands projected on the NO group correspond to the 10 ps decay component in the FFTCF. The fluctuation is related to the orientational dynamics of the water molecules attracted by the Cl ligands. By comparing the FFTCF parameters of the present solute with those of previously reported metal complexes and SCN− in D2O, we conclude that the presence of different electrostatic environments around the vibrational probe and the other interaction sites of the solute is important for understanding the slow decay component in the FFTCFs.
Predicting residue cooperativity during protein folding: A combined, molecular dynamics and unsupervised learning approach
Authors: Prabhakar Praveen Ranganath , Ray Dhiman , Andricioaei Ioan
Published: March 2023

Allostery in proteins involves, broadly speaking, ligand-induced conformational transitions that modulate function at active sites distal to where the ligand binds. In contrast, the concept of cooperativity (in the sense used in phase transition theory) is often invoked to understand protein folding and, therefore, function. The modern view on allostery is one based on dynamics and hinges on the time-dependent interactions between key residues in a complex network, interactions that determine the free-energy profile for the reaction at the distal site. Here, we merge allostery and cooperativity, and we discuss a joint model with features of both. In our model, the active-site reaction is replaced by the reaction pathway that leads to protein folding, and the presence or absence of the effector is replaced by mutant-vs-wild type changes in key residues. To this end, we employ our recently introduced time-lagged independent component analysis (tICA) correlation approach [Ray et al. Proc. Natl. Acad. Sci. 118(43) (2021), e2100943118] to identify the allosteric role of distant residues in the folded-state dynamics of a large protein. In this work, we apply the technique to identify key residues that have a significant role in the folding of a small, fast folding-protein, chignolin. Using extensive enhanced sampling simulations, we critically evaluate the accuracy of the predictions by mutating each residue one at a time and studying how the mutations change the underlying free energy landscape of the folding process. We observe that mutations in those residues whose associated backbone torsion angles have a high correlation score can indeed lead to loss of stability of the folded configuration. We also provide a rationale based on interaction energies between individual residues with the rest of the protein to explain this effect. From these observations, we conclude that the tICA correlation score metric is a useful tool for predicting the role of individual residues in the correlated dynamics of proteins and can find application to the problem of identifying regions of protein that are either most vulnerable to mutations or—mutatis mutandis—to binding events that affect their functionality.
Characteristics of reattached oblique detonation induced by a double wedge
Authors: Yao Kepeng , Yang Pengfei , Li Haoyang , Wang Chun , Jiang Zonglin
Published: March 2023

The stationary characteristics of the oblique detonation wave (ODW) induced by the double wedge with an expansion corner are investigated using two-dimensional Navier–Stokes equations along with a two-step induction-exothermic kinetic model. The results show that the detached ODW can be reattached by expansion waves induced by the double wedge so that the standing window of ODW can be expanded. The re-standing position of ODW depends on the location and strength of the expansion waves, which are governed by the first wedge length L and the corner angle between the first and second wedge surface θC. There is a critical angle reattachment that determines whether the ODW can be reattached by expansion waves, and this critical angle increases as wedge length increases. However, the detached ODW cannot be reattached when the wedge length is increased to a critical value regardless of the wedge corner. The re-standing position moves downstream with the increment of θC until the last Mach wave tangent to the subsonic zone behind the strong overdriven ODW because no more Mach waves interact with the initiation zone. Moreover, the comparison of viscous and inviscid fields demonstrates that a shorter wedge length is necessary for the viscous field to reattach the ODW because the recirculation zone forms a gas wedge that extends the first wedge surface.
Microstructural diversity, nucleation paths, and phase behavior in binary mixtures of charged colloidal spheres
Authors: Lorenz Nina , Gupta Ishan , Palberg Thomas
Published: March 2023

We study low-salt, binary aqueous suspensions of charged colloidal spheres of size ratio Γ = 0.57, number densities below the eutectic number density nE, and number fractions of p = 1.00–0.40. The typical phase obtained by solidification from a homogeneous shear-melt is a substitutional alloy with a body centered cubic structure. In strictly gas-tight vials, the polycrystalline solid is stable against melting and further phase transformation for extended times. For comparison, we also prepare the same samples by slow, mechanically undisturbed deionization in commercial slit cells. These cells feature a complex but well reproducible sequence of global and local gradients in salt concentration, number density, and composition as induced by successive deionization, phoretic transport, and differential settling of the components, respectively. Moreover, they provide an extended bottom surface suitable for heterogeneous nucleation of the β-phase. We give a detailed qualitative characterization of the crystallization processes using imaging and optical microscopy. By contrast to the bulk samples, the initial alloy formation is not volume-filling, and we now observe also α- and β-phases with low solubility of the odd component. In addition to the initial homogeneous nucleation route, the interplay of gradients opens various further crystallization and transformation pathways leading to a great diversity of microstructures. Upon a subsequent increase in salt concentration, the crystals melt again. Wall-based, pebble-shaped β-phase crystals and facetted α-crystals melt last. Our observations suggest that the substitutional alloys formed in bulk experiments by homogeneous nucleation and subsequent growth are mechanically stable in the absence of solid–fluid interfaces but thermodynamically metastable.
The effect of time resolution on the observed first passage times in diffusive dynamics
Authors: Song Kevin , Makarov Dmitrii E. , Vouga Etienne
Published: March 2023

Single-molecule and single-particle tracking experiments are typically unable to resolve fine details of thermal motion at short timescales where trajectories are continuous. We show that, when a diffusive trajectory xt is sampled at finite time intervals δt, the resulting error in measuring the first passage time to a given domain can exceed the time resolution of the measurement by more than an order of magnitude. Such surprisingly large errors originate from the fact that the trajectory may enter and exit the domain while being unobserved, thereby lengthening the apparent first passage time by an amount that is larger than δt. Such systematic errors are particularly important in single-molecule studies of barrier crossing dynamics. We show that the correct first passage times, as well as other properties of the trajectories such as splitting probabilities, can be recovered via a stochastic algorithm that reintroduces unobserved first passage events probabilistically.
Breathing modes of skyrmion strings in a synthetic antiferromagnet multilayer
Authors: Barker Christopher E. A. , Haltz Eloi , Moore Thomas. A. , Marrows Christopher H.
Published: March 2023

Skyrmions are small topologically protected magnetic structures that hold promise for applications from data storage to neuromorphic computing and they have been shown to possess internal microwave frequency excitations. Skyrmions in a synthetic antiferromagnet have been predicted to be smaller and faster than their ferromagnetic equivalents and also shown to possess more internal modes. In this work, we consider the breathing modes of skyrmions in a four repetition synthetic antiferromagnetic multilayer by means of micromagnetic simulations and examine the further splitting of the modes into different arrangements of out-of-phase, in-phase, and modes with more complex phase relationships. This results in a lowering of frequencies, which is promising for skyrmion sensing applications in a synthetic antiferromagnet.
Climate forcing of regional fire years in the upper Great Lakes Region, USA
Authors: Sutheimer Colleen M. , Meunier Jed , Drobyshev Igor , Stambaugh Michael C. , Hotchkiss Sara C. , Rebitzke Eric , Radeloff Volker C.
Published: March 2023

Background Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories. Aims To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America. Methods We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate–fire relationships. Key results Historically, fire frequency and seasonality were variable within and among Great Lakes’ ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891. Conclusions We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region. Implications Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate–fire interactions due to climate change.
A mutant fitness assay identifies bacterial interactions in a model ocean hot spot
Authors: Schreier Jeremy E. , Smith Christa B. , Ioerger Thomas R. , Moran Mary Ann
Published: March 2023

Bacteria that assemble in phycospheres surrounding living phytoplankton cells metabolize a substantial proportion of ocean primary productivity. Yet the type and extent of interactions occurring among species that colonize these micron-scale “hot spot” environments are challenging to study. We identified genes that mediate bacterial interactions in phycosphere communities by culturing a transposon mutant library of copiotrophic bacterium
Ruegeria pomeroyi
DSS-3 with the diatom
Thalassiosira pseudonana
CCMP1335 as the sole source of organic matter in the presence or absence of other heterotrophic bacterial species. The function of genes having significant effects on
R. pomeroyi
fitness indicated explicit cell–cell interactions initiated in the multibacterial phycospheres. We found that
R. pomeroyi
simultaneously competed for shared substrates while increasing reliance on substrates that did not support the other species’ growth. Fitness outcomes also indicated that the bacterium competed for nitrogen in the forms of ammonium and amino acids; obtained purines, pyrimidines, and cofactors via crossfeeding; both initiated and defended antagonistic interactions; and sensed an environment with altered oxygen and superoxide levels. The large genomes characteristic of copiotrophic marine bacteria are hypothesized to enable responses to dynamic ecological challenges occurring at the scale of microns. Here, we discover >200 nonessential genes implicated in the management of fitness costs and benefits of membership in a globally significant bacterial community.
The exocyst complex is an essential component of the mammalian constitutive secretory pathway
Authors: Pereira Conceição , Stalder Danièle , Anderson Georgina S.F. , Shun-Shion Amber S. , Houghton Jack , Antrobus Robin , Chapman Michael A. , Fazakerley Daniel J. , Gershlick David C.
Published: March 2023

Secreted proteins fulfill a vast array of functions, including immunity, signaling, and extracellular matrix remodeling. In the trans-Golgi network, proteins destined for constitutive secretion are sorted into post-Golgi carriers which fuse with the plasma membrane. The molecular machinery involved is poorly understood. Here, we have used kinetic trafficking assays and transient CRISPR-KO to study biosynthetic sorting from the Golgi to the plasma membrane. Depletion of all canonical exocyst subunits causes cargo accumulation in post-Golgi carriers. Exocyst subunits are recruited to and co-localize with carriers. Exocyst abrogation followed by kinetic trafficking assays of soluble cargoes results in intracellular cargo accumulation. Unbiased secretomics reveals impairment of soluble protein secretion after exocyst subunit knockout. Importantly, in specialized cell types, the loss of exocyst prevents constitutive secretion of antibodies in lymphocytes and of leptin in adipocytes. These data identify exocyst as the functional tether of secretory post-Golgi carriers at the plasma membrane and an essential component of the mammalian constitutive secretory pathway.
Pressure-Induced Color Change in the Lutetium Dihydride LuH2
Authors: Shan Pengfei , Wang Ningning , Zheng Xiquan , Qiu Qingzheng , Peng Yingying , Cheng Jinguang
Published: March 2023

The lutetium dihydride LuH2 is stable at ambient conditions. Here we show that its color undergoes sequential changes from dark blue at ambient pressure to pink at ∼ 2.2 GPa and then to bright red at ∼ 4 GPa upon compression in a diamond anvil cell. Such a pressure-induced color change in LuH2 is reversible and it is very similar to that recently reported in the N-doped lutetium hydride [Nature
615, 244 (2023)]. However, our preliminary resistance measurements on LuH2 under pressures up to ∼ 7 GPa evidenced no superconductivity down to 1.5 K.
A probabilistic framework for uncertainty quantification in positron emission particle tracking
Authors: Offner Avshalom , Manger Sam , Vanneste Jacques
Published: March 2023

Positron emission particle tracking (PEPT) is an imaging method for the visualization of fluid motion, capable of reconstructing three-dimensional trajectories of small tracer particles suspended in nearly any medium, including fluids that are opaque or contained within opaque vessels. The particles are labeled radioactively, and their positions are reconstructed from the detection of pairs of back-to-back photons emitted by positron annihilation. Current reconstruction algorithms are heuristic and typically based on minimizing the distance between the particles and the so-called lines of response (LoRs) joining the detection points, while accounting for spurious LoRs generated by scattering. Here we develop a probabilistic framework for the Bayesian inference and uncertainty quantification of particle positions from PEPT data. We formulate a likelihood by describing the emission of photons and their noisy detection as a Poisson process in the space of LoRs. We derive formulas for the corresponding Poisson rate in the case of cylindrical detectors, accounting for both undetected and scattered photons. We illustrate the formulation by quantifying the uncertainty in the reconstruction of the position of a single particle on a circular path from data generated by state-of-the-art Monte Carlo simulations. The results show how the observation time

Δ
t

can be chosen optimally to balance the need for a large number of LoRs with the requirement of small particle displacement imposed by the assumption that the particle is static over

Δ
t

. We further show how this assumption can be relaxed by inferring jointly the position and velocity of the particle, with clear benefits for the accuracy of the reconstruction.
Stability of the

2p2 3Pe

state of two-electron atoms near to critical nuclear charge
Authors: Zheng Ruo Yu , Jiao Li Guang , Liu Aihua , Ma Jia , Montgomery Jr Henry E , Ho Yew Kam , Fritzsche Stephan
Published: March 2023

Critical stability of the metastable bound

2

p

2

 

3

P

e

state of two-electron atoms near the critical nuclear charge Z

c
(smaller than which the bound state ceases to exist) is investigated by employing the explicitly correlated Hylleraas-configuration interaction basis function. Our numerical calculation shows that, when the nuclear charge decreases to Z

c
, the ionization energy of the system approaches zero linearly and this behavior is fully consistent with the Hellmann–Feynman theorem. Radial and angular physical quantities as well as the inner and outer electron radial density distributions are calculated to reveal the classical geometric structure of the two-electron atom. The inner electron can be well modeled by a hydrogenic model in the 2 p state and its density distribution does not change much as the nuclear charge is changed. The outer electron, which is still localized in a finite region near the nucleus before the system transforms into a well-defined resonance, is shifted notably into a far-distance region. The critical stability of the system near the bound-continuum limit is therefore dominated by the outer electron.
Orbital magnetization of three-dimensional Dirac electrons in the quantum limit
Authors: Kawamura Shogo , Fuseya Yuki
Published: March 2023

In this study, we evaluated the dependence of magnetization of three-dimensional Dirac electrons in the quantum limit on the magnetic field and temperature. The magnetization was calculated by differentiating the free energy with respect to the magnetic field. The field and temperature dependence of the chemical potential were entirely considered under the canonical ensemble condition. The total magnetization M consisted of two contributions from the conduction

M

c

and valence

M

v

bands.

M

v

was insensitive to temperature and exhibited sub-linear field dependence, which is consistent with the previous research on Dirac electrons. By contrast,

M

c

was sensitive to both temperature and magnetic field, yielding a non-trivial contribution to the total M. As a result, the properties of total M changed at approximately

k

B

T
≃

E

F

, where

E

F

is the Fermi energy measured from the band bottom and

k

B

is the Boltzmann constant. At low temperatures

k
B

T
≲

E
F

, M exhibited sub-linear field dependence, whereas M exhibited super-linear field dependence at high temperatures

k

B

T
≳

E

F

. This qualitative change in the field dependence of M will play a significant role in the magnetization of Dirac electrons with small

E

F

.
First of its kind: a test artifact for direct laser writing
Authors: Fritzsche Sven , Pauw Brian R , Weimann Christiane , Sturm Heinz
Published: March 2023

With femtosecond-laser direct writing (fs-LDW) maturing in all aspects as a manufacturing technology, a toolset for quality assurance must be developed. In this work we introduce a first of its kind test artifact. Test artifacts are standardized 3D models with specific geometric features to evaluate the performance of writing parameters. Test artifacts are already common in other 3D additive manufacturing technologies e.g. selective laser melting. The test artifact introduced in this work was developed in particular to accommodate (1) the high geometrical resolution of fs-LDW structures and (2) the limited possibilities to examine the resulting structure. Geometric accuracy, surface adhesion as well as confocal Raman spectroscopy results were considered when evaluating the design of the test artifact. We will explain the individual features and design considerations of our fs-LDW test artifact. The difference between two slicers, Cura and 3DPoli, and the implications on measured feature sizes and the general shape is quantified. The measured geometries are used to derive a general design guide for a specific combination of photoresists, laser power and scanning speed and to analyze the geometric accuracy of a structure produced using these guidelines. The shown test artifact is publicly available as STL file on GitHub (https://github.com/BAMresearch/2PP-TestArtifact) and in the supplement.
Students’ understanding of electrostatic force as a vector quantity at the undergraduate level
Authors: Chhabra Mahima , Das Ritwick
Published: March 2023

Electrostatic force is the preliminary and fundamental topic that forms the bedrock on which the conceptual framework of electromagnetism is built. Being a ‘vector’ quantity, electromagnetic force naturally inherits direction as well as magnitude. The conceptualization of such physical quantities may pose a challenge. The present work explores how students conceptualize the construct of electrostatic force from the viewpoint of its vector nature. Our effort is directed towards engaging students in problems aimed at their understanding of the concept of electrostatic force (a physical quantity) and analyse their responses for identifying the conceptual challenges. Our observations reveal that a significant fraction of conceptual difficulties in the concept of electrostatic force are due to insufficient understanding of operations involving vector quantities. The implications of this work indicate that the pedagogical aspects in physics classroom and curriculum design needs to be researched holistically so as to bridge-in the gaps obstructing the desired cognitive framework of students.
Energy and mass misconceptions
Authors: Riggs Peter J
Published: March 2023

Eight misconceptions involving energy and mass are identified and corrected. Examples are included in order to illustrate errors in the presented misconceptions. It is important to identify such misconceptions so that physics/chemistry courses and textbooks do not perpetuate them.
A treatment plan optimization method with direct minimization of number of energy jumps for proton arc therapy
Authors: Zhang Gezhi , Long Yong , Lin Yuting , Chen Ronald C , Gao Hao
Published: March 2023

Objective. The optimization of energy layer distributions is crucial to proton arc therapy: on one hand, a sufficient number of energy layers is needed to ensure the plan quality; on the other hand, an excess number of energy jumps (NEJ) can substantially slow down the treatment delivery. This work will develop a new treatment plan optimization method with direct minimization of (NEJ), which will be shown to outperform state-of-the-art methods in both plan quality and delivery efficiency. Approach. The proposed method jointly optimizes the plan quality and minimizes the NEJ. To minimize NEJ, (1) the proton spots x is summed per energy layer to form the energy vector y; (2) y is binarized via sigmoid transform into y

1
; (3) y
1 is multiplied with a predefined energy order vector via dot product into y
2; (4) y
2 is filtered through the finite-differencing kernel into y
3 in order to identify NEJ; (5) only the NEJ of y
3 is penalized, while x is optimized for plan quality. The solution algorithm to this new method is based on iterative convex relaxation. Main results. The new method is validated in comparison with state-of-the-art methods called energy sequencing (ES) method and energy matrix (EM) method. In terms of delivery efficiency, the new method had fewer NEJ, less energy switching time, and generally less total delivery time. In terms of plan quality, the new method had smaller optimization objective values, lower normal tissue dose, and generally better target coverage. Significance. We have developed a new treatment plan optimization method with direct minimization of NEJ, and demonstrated that this new method outperformed state-of-the-art methods (ES and EM) in both plan quality and delivery efficiency.
Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code
Authors: Eremin D , Berger B , Engel D , Kallähn J , Köhn K , Krüger D , Xu L , Oberberg M , Wölfel C , Lunze J , Awakowicz P , Schulze J , Brinkmann R P
Published: March 2023

The present work investigates electron transport and heating mechanisms using an (r, z) particle-in-cell simulation of a typical rf-driven axisymmetric magnetron discharge with a conducting target. Due to a strong geometric asymmetry and a blocking capacitor, the discharge features a large negative self-bias conducive to sputtering applications. Employing decomposition of the electron transport parallel and perpendicular to the magnetic field lines, it is shown that for the considered magnetic field topology the electron current flows through different channels in the (r, z) plane: a ‘transverse’ one, which involves current flow through the electrons’ magnetic confinement region (EMCR) above the racetrack, and two ‘longitudinal’ ones, where electrons’ guiding centers move along the magnetic field lines. Electrons gain energy from the electric field along these channels following various mechanisms, which are rather distinct from those sustaining dc-powered magnetrons. The longitudinal power absorption involves mirror-effect heating (MEH), nonlinear electron resonance heating, magnetized bounce heating (MBH), and the heating by the ambipolar field at the sheath-presheath interface. The MEH and MBH represent two new mechanisms missing from the previous literature. The MEH is caused by a reversed electric field needed to overcome the mirror force generated in a nonuniform magnetic field to ensure sufficient flux of electrons to the powered electrode, and the MBH is related to a possibility for an electron to undergo multiple reflections from the expanding sheath in the longitudinal channels connected by the arc-like magnetic field. The electron heating in the transverse channel is caused mostly by the essentially collisionless Hall heating in the EMCR above the racetrack, generating a strong

E

×

B

azimuthal drift velocity. The latter mechanism results in an efficient electron energization, i.e. energy transfer from the electric field to electrons in the inelastic range. Since the main electron population energized by this mechanism remains confined within the discharge for a long time, its contribution to the ionization processes is dominant.
Electron dynamics in planar radio frequency magnetron plasmas: I. The mechanism of Hall heating and the µ-mode
Authors: Eremin Denis , Engel Dennis , Krüger Dennis , Wilczek Sebastian , Berger Birk , Oberberg Moritz , Wölfel Christian , Smolyakov Andrei , Lunze Jan , Awakowicz Peter , Schulze Julian , Brinkmann Ralf Peter
Published: March 2023

The electron dynamics and the mechanisms of power absorption in radio-frequency (RF) driven, magnetically enhanced capacitively coupled plasmas at low pressure are investigated. The device in focus is a geometrically asymmetric cylindrical magnetron with a radially nonuniform magnetic field in axial direction and an electric field in radial direction. The dynamics is studied analytically using the cold plasma model and a single-particle formalism, and numerically with the inhouse energy and charge conserving particle-in-cell/Monte Carlo collisions code ECCOPIC1S-M. It is found that the dynamics differs significantly from that of an unmagnetized reference discharge. In the magnetized region in front of the powered electrode, an enhanced electric field arises during sheath expansion and a reversed electric field during sheath collapse. Both fields are needed to ensure discharge sustaining electron transport against the confining effect of the magnetic field. The corresponding azimuthal

E

×

B

-drift can accelerate electrons into the inelastic energy range which gives rise to a new mechanism of RF power dissipation. It is related to the Hall current and is different in nature from Ohmic heating, as which it has been classified in previous literature. The new heating is expected to be dominant in many magnetized capacitively coupled discharges. It is proposed to term it the ‘µ-mode’ to separate it from other heating modes.
Mechanisms leading to plasma activated water high in nitrogen oxides
Authors: Matějka F , Galář P , Khun J , Scholtz V , Kůsová K
Published: March 2023

Plasma activated water (PAW) is a unique highly reactive medium, traditionally used in medicine and agriculture because of its decontamination and disinfection abilities. Recently, we have shown that this medium can also be beneficial for tailoring the surface chemistry of semiconductor nanostructures if its composition is tuned to contain a high concentration of nitrogen-related species (HiN:PAW). However, pathways leading to the production of HiN:PAW remained unclear, which we address in this article. By monitoring the composition of the produced PAW and the concentration of selected species in the discharge under different activation geometries and discharge conditions, we identify the activation geometries favourable for the production of HiN:PAW using two phenomenological factors, a barrier parameter P and a maximum effective radius of the vessel r
max. A key point is the presence of a barrier area in the discharge reactor, which forms as a result of the favourable activation geometry and a discharge with prevailing more reactive atomic species. This area acts as a partial barrier between the discharge and the surrounding air atmosphere, limiting, but still allowing a flow of source N2 molecules from the surrounding atmosphere. The minimal and ideal build-up times of 10 and 30 min, respectively, for the discharge to stabilize are also reported. Using the reported experimental settings, we were able to produce HiN:PAW containing a mixture of various reactive species beneficial for the surface modification of nanoparticles, with the NO3
− to H2O2 ratio of at least 20 × 103: 1, in contrast to approximately 1:1 under more traditional conditions.
On projection method for numerical solution of hypersingular integral equations of the first kind combined with quadrature methods
Authors: Elahi M R , Mahmoudi Y , Salimi Shamloo A , Jahangiri Rad M
Published: March 2023

The Fredholm integral equations of the first kind with two regular and hypersingular kernels are considered on [−1, 1]. The hypersingular kernel is considered smooth enough with no additional conditions. A projection method based on second kind Chebyshev polynomials approximation, combined with quadrature integration method, is developed to obtain high accurate approximations. The proposed method reduces the underlying integral equation to a system of algebraic equations. Several illustrative examples are provided to show the efficiency of the method.