Vacuum Region Research Articles

Field-Gradient-Focusing Ion Guide for Enhanced Transfer Efficiency of Low-Mass Ions.

Efficient transmission of low-mass ions in a rough vacuum pressure region has always been a challenging issue in mass spectrometry (MS). In this study, a novel ion guide, namely, field-gradient-focusing ion guide (FGF-IG), was proposed to improve the transfer efficiency of ions, especially low-mass ions in a rough vacuum region. The FGF-IG has 12 electrodes whose surfaces gradually narrowed and tilted inward, and its electric field gradually varies from dodecapole (or multipole) to quadrupole along the ion transfer route. The field radius was gradually decreased from 6 to 2 mm in the multipole region (65 mm in length) and finally remained unchanged as 2 mm in the quadrupole region (20 mm in length). By integrating into a miniature mass spectrometer (mini-MS) with a continuous atmospheric pressure interface, this ion guide was optimized in terms of inlet capillary position, radio frequency amplitude, and direct current voltage applied on it. Results showed that a reduced low-mass discrimination effect and improved efficiency of simultaneously transferring mid and low m/z ions were achieved for FGF-IG compared with a conventional ion funnel. Under optimized conditions, a limit of detection of 1 ng/mL was obtained for both reserpine (m/z 609) and arginine (m/z 175) ions by integrating FGF-IG into the mini-MS. The sensitivity of smaller arginine ions using FGF-IG was enhanced by ∼10 times than that obtained using the conventional ion funnel (10 ng/mL) in comparative experiments. The idea of smooth transfer from dodecapole to quadrupole fields could be extended to other multipole fields, as well as in lab-scale MS instruments.

Entanglement structures in quantum field theories: Negativity cores and bound entanglement in the vacuum

The many-body entanglement between two finite (size-$d$) disjoint vacuum regions of noninteracting lattice scalar field theory in one spatial dimension, i.e., a ${({d}_{A}\ifmmode\times\else\texttimes\fi{}{d}_{B})}_{\mathrm{mixed}}$ Gaussian continuous variable system, is locally transformed into a tensor-product core of ${({1}_{A}\ifmmode\times\else\texttimes\fi{}{1}_{B})}_{\mathrm{mixed}}$ entangled pairs. Accessible entanglement within these core pairs exhibits an exponential hierarchy and as such identifies the structure of dominant region modes from which vacuum entanglement could be extracted into a spatially separated pair of quantum detectors. Beyond the core, the remaining modes of the halo are determined to be $AB$ separable in isolation, as well as separable from the core. However, state preparation protocols that distribute entanglement in the form of ${({1}_{A}\ifmmode\times\else\texttimes\fi{}{1}_{B})}_{\mathrm{mixed}}$ core pairs are found to require additional entanglement in the halo that is obscured by classical correlations. This inaccessible (bound) halo entanglement is found to mirror the accessible entanglement, but with a step behavior as the continuum is approached. It remains possible that alternate initialization protocols that do not utilize the exponential hierarchy of core-pair entanglement may require less inaccessible entanglement. Entanglement consolidation is expected to persist in higher dimensions and may aid classical and quantum simulations of asymptotically free gauge field theories, such as quantum chromodynamics.

No Gravitational Wave from Orbiting Supermassive Kerr Black Hole—a model of matter distribution and propagation of gravitational waves inside the event horizon

The matter distribution of the extremely high-energy and dense plasma inside a supermassive rotating black hole has been theoretically investigated, starting from Einstein’s equation with the source term, in the coordinate close to the free-falling frame along the geodesics of interior matter, where the state of the force balance can be described with the formalism of modified Newtonian dynamics. For a model of equal-rotation velocity of matter, where the main component of plasma is rotating around a common axis with the same velocity close to the light velocity, with a high Lorentz factor (gamma rate), it is concluded that the matter distribution is condensed to a region with a much smaller radius than that of the event horizon of the Kerr spacetime. The gravitational waves that are generated from the condensed matter region due to the orbital motion of the binary, return towards the source, after ceasing at the critical sphere in the vacuum region of spinning Kerr spacetime. At the stage where returning waves encounter with foreword waves, the gravitational waves are deformed to standing waves that carry no energy outside of the event horizon. We conclude that no gravitational wave is radiated from the supermassive black hole binary

Физические процессы в датчике низкого вакуума типа Пирани

Auger electron spectroscopy and thermoresistive methods are used to study the physical processes leading to gas cooling of heated molybdenum filaments in a wide temperature range of 350 - 1300 K and pressures of 760 - 10-3 Torr, corresponding to the operating range of a Pirani-type vacuum sensor. Nitrogen was used as the gas. It is shown that nitrogen atoms chemisorbed on the surface do not contribute to gas cooling, which occurs only due to physisorbed N2 molecules. In the intermediate vacuum region of 10-3 – 1 Torr, the heater is cooled due to the equilibrium between the flux of incident and thermally desorbed molecules, which is well described by the Hertz-Knudsen formula and first-order desorption with an activation energy of ~ 0.55 eV. On the contrary, at high pressures close to atmospheric, this cooling occurs due to the thermal desorption of gas molecules from an almost filled monolayer, which reduces its relative efficiency by many orders of magnitude.

Physical processes in the Pirani type low vacuum sensor

Auger electron spectroscopy and thermoresistive methods are used to study the physical processes leading to gas cooling of heated molybdenum filaments in a wide temperature range of 350-1300 K and pressures of 760-10-3 Torr, corresponding to the operating range of a Pirani-type vacuum sensor. Nitrogen was used as the gas. It is shown that nitrogen atoms chemisorbed on the surface do not contribute to gas cooling, which occurs only due to physisorbed N2 molecules. In the intermediate vacuum region of 10-3-1 Torr, the heater is cooled due to the equilibrium between the flux of incident and thermally desorbed molecules, which is well described by the Hertz--Knudsen formula and first-order desorption with an activation energy of ~0.55 eV. On the contrary, at high pressures close to atmospheric, this cooling occurs due to the thermal desorption of gas molecules from an almost filled monolayer, which reduces its relative efficiency by many orders of magnitude. Keywords: vacuum, adsorption, Pirani sensor, molybdenum, thermal desorption, nitrogen.

The quantum character of the Scalar Field Dark Matter

ABSTRACT The scalar field dark matter (SFDM) model, also called Fuzzy, Wave, Bose–Einstein, and Ultra-light Dark Matter, has received a lot of attention because it has been able to provide simpler and more natural explanations for various features of galaxies, such as the number of satellite galaxies and the cusp-core problem. We recently showed that this model is able to explain the vast polar orbits of satellite galaxies around their host, the so-called VPO, and to explain the X-ray and gamma-ray emissions in the vacuum regions of our galaxy, that is, the Fermi Bubbles. In all these phenomena, the quantum character of SFDM has been crucial. In this work, we study the quantum effects of SFDM at the cosmological level, to see these effects not only at the galactic scale, but also at the cosmological scale. Using a convenient ansatz, we were able to integrate the perturbed equations to show that the shape of the SFDM haloes resembling atoms is a generic result. The main conclusion of this work is that quantum mechanics, the successful microworld theory, could also explain the dark side of the Cosmos.

Molecular Dynamics Study of Adsorption Phenomenon of Aromatic Hydrocarbon Ionomer in Catalytic Layer of Polymer Electrolyte Fuel Cell

In response to the current global energy crisis and environmental problems, fuel cells are an optional solution. Among them, polymer electrolyte fuel cell (PEFC) has high expectations because of its low operating temperature and suitability for applications in households and mobility devices. Since PEFC requires the use of proton exchange membranes, the transmission efficiency and durability of the exchange membrane is a major concern. To improve the proton transport efficiency, which is generally required, a catalytic layer is integrated into the PEFC. The catalyst layer of PEFC generally contains platinum catalyst covered with the ionomer membrane. Proton conductivity increases with ionomer thickness, while oxygen permeability decreases with ionomer thickness. Therefore, in order to improve the power generation efficiency of PEFC, it is important to design the catalyst layer. In addition, the fluorinated ionomer membrane material (such as Nafion) used for PEFC has good proton conductivity and chemical stability, but the synthesis cost is relatively high. As a consequence, new materials such as composite materials and non-fluorine-based materials have received a lot of attention in recent years. In this study, we focus on a new ionomer material of aromatic hydrocarbon (named SPP-BP) and elucidate the adsorption state of the ionomer on the platinum surface on a nanoscale using molecular dynamics (MD) simulations. Then, the structural properties and water diffusion characteristics of the ionomers of new material (SPP-BP) and conventional Nafion were analyzed based on the MD simulation results.The degree of polymerization (m, p, s) of the monomers were given as 20, 5, and 23 (molecular weight 7.38 kDa), respectively, based on the reported experimental values of SPP-BP. For the polymer composition, molecular models of a random type (r-type), which shows a randomness of monomers, were used. A molecular model of Nafion was also created as the conventional fluorinated membrane materials for comparison with the SPP-BP. The platinum surface was built with a three layers of platinum atoms in a face-centered cubic lattice structure. Regarding the calculation potentials, the DREIDING forcefield was used for the interactions with the molecules. While for the intermolecular potential, the Spohr potential was used for Pt-H2O and Pt-H3O+ interactions, and the others were applied with the Lennard Jones (LJ). The parameters of those potentials were based on the previous studies.In the ionomer membrane, water content is an important indicator that affects the transfer of protons and substances. Based on the water absorption results obtained in the experiment, the water content of SPP-BP was calculated to be between 1.8 and 7.2. Therefore, the water content during the MD simulation was used 3, 5, and 7. The computational size was 55.5 Å × 52.9 Å in the transverse direction of the ionomer membrane (X and Y directions), and the thickness of the membrane adsorbed on the platinum surface was about 50-60 Å. A vacuum region of about 40 Å was set at the top of the system. To calculate the diffusion coefficient and the cluster character of water, multiple simulations with different initial structure were considered. Furthermore, in order to compare to the Nafion, the number of polymers and the computational size was adjusted for containing the same water content.Based on the simulation results, the density distribution of water, hydrophilic sulfo groups, and main body of polymer was analyzed. By the analysis of density distribution, the structure of the ionomer at the interface-vacuum, near the Pt surface and inside was studied. In addition, the orientation of the sulfo group of SPP-BP and Nafion near the Pt surface was analyzed. Besides, the water cluster characteristics and water diffusion properties of the ionomers of SPP-BP and Nafion were also investigated.Acknowledgements: This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan through the fund for ECCEED'30 Projects (No. JPNP20003). Numerical simulations were performed on the Supercomputer system "AFI-NITY" at the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University.

Modeling the diffusion of muonium in silica aerogel and its application to a novel design of multi-layer target for thermal muon generation

The generation of thermal muons by laser ionization of muonium (μ+e−) confined in multi-layer silica aerogel structures is simulated. Thermal muonium generated inside the silica aerogel is emitted into the sandwiched vacuum regions between the aerogel layers separated by a few millimeters. The model for muonium emission is validated against emission measurements from single aerogel samples. The efficiency of thermal muon generation in this configuration is predicted to increase by several times compared with a single-layer design.

Two-dimensional shaping of Solov'ev equilibrium with vacuum using external coils

In this work, we demonstrate a method for constructing the Solov'ev equilibrium with any given 2D shape surrounded by a vacuum region using external poloidal field coils, based on the method previously developed by T. Xu and R. Fitzpatrick [Nuclear Fusion, 59, 064002 (2019)]. The computational domain consists of two parts: the plasma region, where the solution is the same as the Solov'ev solution, and the vacuum region, where the magnetic field generated by external coils as well as plasma current is determined using the Green function method through a matching condition near the separatrix. However, the method is not limited to the Solov'ev equilibrium in particular. The accuracy, efficiency, and robustness of such a scheme suggest that this method may be applied to the 2D shaping of a tokamak plasma with a vacuum region using external coils in general.

Positivity-preserving entropy stable schemes for the 1-D compressible Navier-Stokes equations: First-order approximation

This is the first of two companion papers that introduce a new class of positivity-preserving, entropy stable schemes for the 1-D compressible Navier-Stokes equations. In this paper, we develop and analyze a novel first–order finite volume scheme that is discretized on Legendre-Gauss-Lobatto grids used for high-order spectral collocation methods. The scheme is constructed by regularizing the Navier-Stokes equations by adding artificial dissipation in the form of the Brenner-Navier-Stokes diffusion operator. The key distinctive property of the proposed scheme is that it is proven to satisfy the discrete entropy inequality and to guarantee the pointwise positivity of density, temperature, pressure, and internal energy for 1–D compressible viscous flows, while using high–order spectral collocation summation-by-parts operators for discretizing the Navier–Stokes viscous terms. To eliminate time step stiffness caused by the high-order approximation of the viscous terms, we develop two new limiters that bound the magnitude of velocity and temperature gradients and preserve the entropy stability and positivity properties of the baseline scheme. Numerical results demonstrating positivity-preserving and discontinuity-capturing capabilities of the new scheme are presented for viscous and inviscid flows with nearly vacuum regions and very strong shocks and contact discontinuities.

Boosting Electrocatalytic CO 2 Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Adsorption and dissociation of mercury species on the surface of 1T-MnO2/graphene

In this paper, the adsorption of HgCl and HgO mercury species is studied on the 1T-MnO2/graphene heterostructure, using the Density Functional Theory (DFT) within the framework of Generalized Gradient Approximation of Perdew-Burke and Ernzerhof (GGA-PBE) along with atomic pseudopotentials. The heterostructure is modelled using the periodic slab scheme, with a vacuum region of 26 Å. In this investigation, the surface of interest is the monolayer of 1T-MnO2 coupled to a monolayer of graphene and its interaction with the HgCl and HgO species of mercury. The graphene monolayer only acts as a substrate to support the 1T-MnO2 monolayer; for that reason, in all of the processes of adsorption of the HgCl and HgO species of mercury onto the heterostructure, the atomic positions of the graphene remain fixed.In order to study the most energetically favorable adsorption model, the especial sites TO1, TO2, TM1 and TM2 in the 1T-MnO2/graphene surface are considered as well as the different orientations of the HgCl and HgO molecules on the heterostructure surface. In both cases, it is concluded that the most energetically favorable site is TO2 with adsorption energy values of −1.668 eV and −1.904 eV respectively. The analysis of the possible molecular dissociation scenarios shows that the HgCl and HgO species are strongly adsorbed (chemically) by the surface of the heterostructure. In particular, after of the adsorption process, the HgO molecule is dissociated by the 1T-MnO2/graphene heterostructure, where the oxygen atom is removed, and the mercury atom is adsorbed by the surface of the heterostructure. This scenario is highest favorable for the adsorption of Hg on the heterostructure. These results obtained indicate that the heterostructure behaves as a formidable substrate for the capture of the HgCl and HgO species. Lastly, the effect of their adsorption over the surface of the 1T-MnO2/graphene heterostructure in terms of electronic properties is analyzed for the most energetically stable configurations in each case.

Density functional calculations of atomic structure, charging effect, and static dielectric constant of two-dimensional systems based on B-splines

We have implemented a total-energy minimization scheme to allow for relaxation of atomic positions in density functional calculations for two-dimensional (2D) materials using a mixed basis set. The basis functions consist of products of 2D plane waves in the plane of the material and localized B-splines along the perpendicular direction. By using the mixed basis approach (MBA), we have studied the atomic relaxation and charge polarization of 2D systems under an applied electric field. In contrast to the conventional super-cell approach (SCA) which adopts repeated slabs sandwiched between vacuum regions, MBA makes no requirement of compensating background charge for treating electrically charged 2D systems due to carrier injection. With MBA we can avoid using a periodic sawtooth potential for systems under the applied field as commonly adopted in SCA. Furthermore, we introduced a simple method to determine the out-of-plane dielectric constants of 2D materials without the ambiguity of defining their effective thickness. This is achieved by calculating the linear response in charge polarization to the applied field. Selected 2D systems, including graphene and transition-metal dichalcogenides are tested. Our MBA results are consistent with previous SCA calculations when both approaches are equally applicable. However, for charged systems with high carrier density, we find significant deviation from SCA results obtained by imposing artificial charge neutrality condition.

Delta shocks and vacuum states for the isentropic magnetogasdynamics equations for Chaplygin gas as pressure and magnetic field vanish

This paper is concerned with the Riemann problem for the isentropic Chaplygin gas magnetogasdynamics equations and the formation of $$\delta $$ -shocks and vacuum states as pressure and magnetic field vanish. Firstly, the Riemann problem of the isentropic magnetogasdynamics equations for Chaplygin gas is solved analytically. Secondly, it is rigorously proved that, as both the pressure and the magnetic field vanish, the Riemann solution containing two shocks tends to a $$\delta $$ -shock solution to the transport equations, and the intermediate density between the two shocks tends to a weighted $$\delta $$ -measure which form the $$\delta $$ -shock; while the Riemann solution containing two rarefaction waves tends to a two-contact-discontinuity solution to the transport equations if we do not consider the virtual velocity in the vacuum region, the intermediate state between the two contact discontinuities is a vacuum state. Moreover, we also give some numerical simulations to confirm the theoretical analysis.

Formation of Point Shocks for 3D Compressible Euler

We consider the 3D isentropic compressible Euler equations with the ideal gas law. We provide a constructive proof of the formation of the first point shock from smooth initial datum of finite energy, with no vacuum regions, with nontrivial vorticity present at the shock, and under no symmetry assumptions. We prove that for an open set of Sobolev‐class initial data that are a small L∞ perturbation of a constant state, there exist smooth solutions to the Euler equations which form a generic stable shock in finite time. The blowup time and location can be explicitly computed, and solutions at the blowup time are smooth except for a single point, where they are of cusp‐type with Hölder C1/3 regularity. Our proof is based on the use of modulated self‐similar variables that are used to enforce a number of constraints on the blowup profile, necessary to establish global existence and asymptotic stability in self‐similar variables. © 2022 Wiley Periodicals LLC.

Weakly nonlinear surface waves on the plasma–vacuum interface

We consider the free boundary problem for a plasma–vacuum interface in ideal incompressible magnetohydrodynamics. Unlike the classical statement, where the vacuum magnetic field obeys the div-curl system of pre-Maxwell dynamics, we do not neglect the displacement current in the vacuum region and consider the Maxwell equations for electric and magnetic fields. Our aim is to construct highly oscillating surface wave solutions in weakly nonlinear regime to this plasma–vacuum interface problem.Under a necessary and sufficient stability condition for a piecewise constant background state, we construct approximate solutions at any arbitrarily large order of accuracy to the free boundary problem in three space dimensions when the initial discontinuity displays high frequency oscillations. Moreover, such approximate surface waves have nontrivial residual non-oscillatory components.

Simulating a pulsed-power-driven plasma with ideal MHD

We describe a simple practical numerical method for simulating plasma driven within a vacuum chamber by a pulsed power generator. Typically, in this type of simulation, the vacuum region adjacent to the plasma is approximated as a highly resistive, light fluid; this involves computationally expensive solvers describing the diffusion of the magnetic field through this fluid. Instead, we provide a recipe for coupling pulsed power generators to the magnetohydrodynamics (MHD) domain by approximating the perfectly insulating vacuum as a light, perfectly conducting, inviscid MHD fluid and discuss the applicability of this counter-intuitive technique. This much more affordable ideal MHD representation is particularly useful in situations where a plasma exhibits interesting three-dimensional phenomena, either due to the design of the experiment or due to developing instabilities. We verified that this coupling recipe works by modeling an exactly solvable flux compression generator as well as a self-similar Noh-like solution and demonstrated convergence to the theoretical solution. We also showed examples of simulating complex three-dimensional pulsed power devices with this technique. We release our code implementation to the public (see https://github.com/beresnyak/verif_coupling).

About graphite evaporation dynamics caused by radiation in near zone of magnetoplasma compressor discharge

The results of processes above the surface of graphite samples which exposed with powerful vacuum ultraviolet (VUV) radiation experimental studies are presented. The characteristic radiation exposure time was 3...100 μs, the radiation energy in the vacuum region of the spectrum was 1...2 kJ. The main characteristics of the processes were recorded on direct, shadow photographs and interferograms. The temporal dynamics of the expansion of the plasma layer formed during evaporation of the flat graphite targets surface by VUV radiation, as well as the dynamics of buffer gas compression and shock wave motion are analyzed. It is shown that the temperature of the carbon plasma above the samples surface reached 1 eV. Research is relevant in the fields of space, plasma technologies, the development of the element base of microelectronics and fundamental studies of the powerful radiation interaction with matter.

Improving the Self-Healing of Cementitious Materials with a Hydrogel System.

Despite cement’s superior performance and inexpensive cost compared to other industrial materials, crack development remains a persistent problem in concrete. Given the comparatively low tensile strength, when cracks emerge, a pathway is created for gas and water to enter the cementitious matrix, resulting in steel reinforcement corrosion which compromises the durability of concrete. Superabsorbent hydrogels have been developed as a novel material for enhancing the characteristics of cementitious materials in which they have been demonstrated to decrease autogenous shrinkage and encourage self-healing. This study will detail the design and application of polyelectrolyte hydrogel particles as internal curing agents in concrete and provide new findings on relevant hydrogel–ion interactions. When hydrogel particles are mixed into concrete, they generate their stored water to fuel the curing reaction that results in less cracking and shrinkage, thereby prolonging the service life of the concrete. The interaction of hydrogels with cementitious materials is addressed in this study; the effect of hydrogels on the characteristics and self-healing of cementitious materials was also studied. Incorporating hydrogel particles into cement decreased mixture shrinkage while increasing the production of particular inorganic phases within the vacuum region formerly supplied by the swollen particle. In addition, considering the control paste, cement pastes containing hydrogels exhibited less autogenous shrinkage. The influence of hydrogels on autogenous shrinkage was found to be chemically dependent; the hydrogel with a delayed desorption rate displayed significantly low shrinkage in cement paste.

Dynamics of nonlinear hyperbolic equations of Kirchhoff type

In this paper, we study the initial boundary value problem of the important hyperbolic Kirchhoff equation $$\begin{aligned} u_{tt}-\left( a \int _\text{\O}mega |\nabla u|^2 \mathrm {d}x +b\right) \Delta u = \lambda u+ |u|^{p-1}u , \end{aligned}$$ where a, $$b>0$$ , $$p>1$$ , $$\lambda \in {\mathbb {R}}$$ and the initial energy is arbitrarily large. We prove several new theorems on the dynamics such as the boundedness or finite time blow-up of solution under the different range of a, b, $$\lambda $$ and the initial data for the following cases: (i) $$1<p<3$$ , (ii) $$p=3$$ and $$a>1/\Lambda $$ , (iii) $$p=3$$ , $$a \le 1/\Lambda $$ and $$\lambda <b\lambda _1$$ , (iv) $$p=3$$ , $$a < 1/\Lambda $$ and $$\lambda >b\lambda _1$$ , (v) $$p>3$$ and $$\lambda \le b\lambda _1$$ , (vi) $$p>3$$ and $$\lambda > b\lambda _1$$ , where $$\lambda _1 = \inf \left\{ \Vert \nabla u\Vert ^2_2 :~ u\in H^1_0(\text{\O}mega )\ \mathrm{and}\ \Vert u\Vert _2 =1\right\} $$ , and $$\Lambda = \inf \left\{ \Vert \nabla u\Vert ^4_2 :~ u\in H^1_0(\text{\O}mega )\ \mathrm{and}\ \Vert u\Vert _4 =1\right\} $$ . Moreover, we prove the invariance of some stable and unstable sets of the solution for suitable a, b and $$\lambda $$ , and give the sufficient conditions of initial data to generate a vacuum region of the solution. Due to the nonlocal effect caused by the nonlocal integro-differential term, we show many interesting differences between the blow-up phenomenon of the problem for $$a>0$$ and $$a=0$$ .