Momentum Transfer Distributions Research Articles

Fabricating a Structured Single‐Atom Catalyst via High‐Resolution Photopolymerization 3D Printing

AbstractThis study introduces a novel solution to the design of structured catalysts, integrating single‐piece 3D printing with single‐atom catalysis. Structured catalysts are widely employed in industrial processes, as they provide optimal mass and heat transfer, leading to a more efficient use of catalytic materials. They are conventionally prepared using ceramic or metallic bodies, which are then washcoated and impregnated with catalytically active layers. However, this approach may lead to adhesion issues of the latter. By employing photopolymerization printing, a stable and active single‐atom catalyst is directly shaped into a stand‐alone, single‐piece structured material. The battery of characterization methods employed in the present study confirms the uniform distribution of catalytically active species and the structural integrity of the material. Computational fluid dynamics simulations are applied to demonstrate enhanced momentum transfer and light distribution within the structured body. The materials are finally evaluated in the continuous‐flow photocatalytic oxidation of benzyl alcohol to benzaldehyde, a relevant reaction to prepare biomass‐derived building blocks. The innovative approach reported herein to manufacture a structured single‐atom catalyst circumvents the complexities of traditional synthetic methods, offering scalability and efficiency improvements, and highlights the transformative role of 3D printing in catalysis engineering to revolutionize catalysts’ design.

Laser fusion cutting: The missing link between gas dynamics and cut edge topography

In laser cutting, the fundamental role of the gas flow for melt removal and kerf formation is generally accepted. Beyond this vague understanding, however, the underlying physical mechanisms are not yet fully understood. In particular, detailed data concerning the momentum and heat transfer between the gas and melt have seldom been reported. This study addresses the local interactions between the cutting gas and kerf surface (melt film surface) in a fundamental way based on a combined experimental, theoretical, and numerical approach. Typical solid-state laser cut edges are analyzed considering the characteristic surface structures and the basic influences of the gas flow on the global and local melt movement. Here, apparent structures in the micrometer range indicate the effect of vortical gas structures close to the wall. Theoretical investigation of the gas boundary layer is conducted by semiempirical equations and the transfer of basic results from the boundary layer theory. It is shown that the boundary layer is in transition between the laminar and turbulent flow, and local flow separations and shock-boundary layer interactions primarily induce spatially periodic and quasistationary instability modes. An improved numerical model of the cutting gas flow confirms the theoretical results and exhibits good agreement with experimental cut edges, reproducing relevant instability modes and quantifying the local momentum and heat transfer distributions between the gas and melt. With the knowledge gained about the underlying physical mechanisms, promising approaches for improvements of the fusion cutting performance are proposed.

Nuclear form factor of xenon from photoproduction of vector mesons in Xe-Xe ultraperipheral collisions at the LHC

Using the Gribov-Glauber model for photon-nucleus scattering and a generalization of the vector meson dominance model for the hadronic structure of the photon, we calculate cross sections of light and heavy vector meson photoproduction in ultraperipheral Xe-Xe collisions at 5.44 TeV at the Large Hadron Collider. Analyzing the momentum transfer distribution in this process, we examine the feasibility to extract the nuclear isoscalar form factor of Xe isotopes, which are needed in searches for dark matter with Xenon-based detectors.

On the Blast Mitigation Ability of Multiple V-Shape Deflectors

This paper presents a 2D numerical study of v-shape deflectors subjected to high explosive charge detonation. The literature provides many papers concerning the appropriate geometry of blast protection deflectors. Such structures require a relatively high distance between the ground and the vehicle chassis. In most cases, the placement of a deflector is not possible or it cannot cover the whole area under a chassis. An interesting question that arises is to what extent a set of small deflectors would be able to mitigate blast effects. The content of this paper constitutes an answer to this question. Three analyses were conducted: (1) multiplication of triangle components, (2) effect of deflector size, and (3) geometry-induced shock dynamics. The problem was solved with the use of modelling and simulation methods, in particular, CFD-FEM implemented in the LS-DYNA code. It was considered a plain issue in computational fluid dynamics, where space discretization for each option was built with two-dimensional elements to ensure efficient calculations. Deflectors were described using a rigid wall boundary condition, and an adequate simplified detonation model was assumed. The primary measure of the results was reaction force history, with momentum transfer and pressure distribution maps considered supplementary. The studies performed showed that both minimizing the v-shape deflector size and surrounding it with adjacent structures had a negative impact on its blast mitigation effectiveness. However, for each multi-v-shape deflector, some improvement was present, and, therefore, in situations where the installation of a typical protector is not possible due to dimensional requirements, it may offer a compromise solution.

Electron scattering from 208Pb and 132Xe ions at the SCRIT facility

We constructed the SCRIT (Self-Confining Radioactive Ion Target) electron scattering facility to realize electron scattering off short-lived unstable nuclei at RIKEN in Japan. Electron scattering is one of the most powerful and reliable tools to study structures of atomic nuclei. However, it has been extremely difficult to apply electron scattering to unstable nuclei because of target preparation problems. SCRIT is a novel ion-trapping technique that achieves high luminosity of more than 1027 cm-?2s-?1 with a small amount of target ions. Following completion of the facility, a series of commissioning experiments of the entire facility with several stable nuclear targets, including 208Pb and 132Xe, were performed. Momentum transfer distributions of elastic scattering from those targets were successfully measured at several electron beam energies, and the charge density distribution of the 132Xe nucleus was extracted for the first time.

Coherent and incoherent vector meson electroproduction in the future electron - ion colliders: The hot - spot predictions

One of the more promising observables to probe the high energy regime of the QCD dynamics in the future Electron - Ion Colliders (EIC) is the exclusive vector meson production cross section in coherent and incoherent interactions. Such processes measure the average spatial distribution of gluons in the target as well the fluctuations and correlations in the gluon density. In this paper we present a comprehensive analysis of the energy, photon virtuality, atomic number and momentum transfer dependencies of the coherent and incoherent cross sections considering two different models for the nuclear profile function. In particular, we present the predictions of the hot - spot model, which assumes the presence of subnucleonic degrees of freedom and an energy-dependent profile. Our results indicate that the analysis of the ratio between the incoherent and coherent cross sections and the momentum transfer distributions in the future EIC can be useful to constrain the description of the hadronic structure at high energies.

Exclusive ρ and J/Ψ photoproduction in ultraperipheral pA collisions: Predictions of the gluon saturation models for the momentum transfer distributions

In this letter we complement previous studies on exclusive vector meson photoproduction in hadronic collisions presenting a comprehensive analysis of the t-spectrum measured in exclusive ρ and J/Ψ photoproduction in pA collisions at the LHC. We compute the differential cross sections considering two phenomenological models for the gluon saturation effects and present predictions for pPb and pCa collisions. Moreover, we compare our predictions with the recent preliminary CMS data for the exclusive ρ photoproduction. We demonstrate that the gluon saturation models are able to describe the CMS data at small – t. On the other hand, the models underestimate the few data point at large – t. Our results indicate that future measurements of the large – t region can be useful to probe the presence or absence of a dip in the t-spectrum and discriminate between the different approaches to the gluon saturation effects.

Photoproduction of light vector mesons in Xe–Xe ultraperipheral collisions at the LHC and the nuclear density of Xe-129

We make predictions for cross sections of ρ and ϕ vector meson photoproduction in ultraperipheral Xe–Xe collisions at sNN=5.44TeV. Analyzing the momentum transfer distribution of ρ mesons in this process, we explore the feasibility of extracting the nuclear density of 129Xe, which is needed in searches for dark matter with Xenon-based detectors.

Quasielastic neutrino charged-current scattering off C12 : Effects of the meson exchange currents and large nucleon axial mass

The quasi-elastic scattering of muon neutrino and electrons on a carbon target are analyzed using the relativistic distorted-wave impulse approximation (RDWIA). We also evaluate the contribution of the two-particle and two-hole meson exchange current ($2p-2h$ MEC) to electroweak response functions. The nuclear model dependence of the (anti)neutrino cross sections is studied within the RDWIA+MEC approach and RDWIA model with the large nucleon axial mass. It is shown that the results for the squared momentum transfer distribution $d\sigma/dQ^2$ and for invariant mass of the final hadronic system distribution $d\sigma/dW$ obtained within these models are substantially different.

Neutrinoless ββ decay mediated by the exchange of light and heavy neutrinos: the role of nuclear structure correlations

Neutrinoless decay nuclear matrix elements calculated with the shell model and energy-density functional theory typically disagree by more than a factor of two in the standard scenario of light-neutrino exchange. In contrast, for a decay mediated by sterile heavy neutrinos the deviations are reduced to about 50%, an uncertainty similar to the one due to short-range effects. We compare matrix elements in the light- and heavy-neutrino-exchange channels, exploring the radial, momentum transfer and angular momentum-parity matrix element distributions, and considering transitions that involve correlated and uncorrelated nuclear states. We argue that the shorter-range heavy-neutrino exchange is less sensitive to collective nuclear correlations, and that discrepancies in matrix elements are mostly due to the treatment of long-range correlations in many-body calculations. Our analysis supports previous studies suggesting that isoscalar pairing correlations, which affect mostly the longer-range part of the neutrinoless decay operator, are partially responsible for the differences between nuclear matrix elements in the standard light-neutrino-exchange mechanism.

First Elastic Electron Scattering from ^{132}Xe at the SCRIT Facility.

The first elastic electron scattering has been successfully performed at the self-confining radioactive-isotope ion target (SCRIT) facility, the world's first electron scattering facility for SCRIT technique achieved high luminosity (over 10^{27} cm^{-2} s^{-1}, sufficient for determining the nuclear shape) with only 10^{8} target ions. While ^{132}Xe used in this time as a target is a stable isotope, the charge density distribution was first extracted from the momentum transfer distributions of the scattered electrons by comparing the results with those calculated by a phase shift calculation.

Investigating the impact of the gluon saturation effects on the momentum transfer distributions for the exclusive vector meson photoproduction in hadronic collisions

The exclusive vector meson production cross section is one of the most promising observables to probe the high energy regime of the QCD dynamics. In particular, the squared momentum transfer (t) distributions are an important source of information about the spatial distribution of the gluons in the hadron and about fluctuations of the color fields. In this paper we complement previous studies on exclusive vector meson photoproduction in hadronic collisions presenting a comprehensive analysis of the t-spectrum measured in exclusive ρ, ϕ and J/Ψ photoproduction in pp and PbPb collisions at the LHC. We compute the differential cross sections taking into account gluon saturation effects and compare the predictions with those obtained in the linear regime of the QCD dynamics. Our results show that gluon saturation suppresses the magnitude of the cross sections and shifts the position of the dips towards smaller values of t.

Accessing transverse nucleon and gluon distributions in heavy nuclei using coherent vector meson photoproduction at high energies in ion ultraperipheral collisions

By using the theoretical approaches describing well the available data on $t$-integrated coherent photoproduction of light and heavy vector mesons in Pb-Pb ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) in Run 1, we calculate the momentum transfer distributions for this process for $\rho$ and $J/\psi$ vector mesons in the kinematics of Run 2 at the LHC. We demonstrate that nuclear shadowing not only suppresses the absolute value of the cross sections, but also shifts the momentum transfer distributions toward smaller values of the momentum transfer $|t|$. This result can be interpreted as a broadening in the impact parameter space of the effective nucleon density in nuclei by 14\% in the case of $\rho$ and the nuclear gluon distribution by $5-11$\% in the case of $J/\psi$.

Rapidity and momentum transfer distributions of coherent J/ψ photoproduction in ultraperipheral pPb collisions at the LHC

Based on accurate calculations of the flux of equivalent photons of the proton and heavy nuclei and the pQCD framework for the gluon distribution in the proton and nuclei, we analyze the rapidity and momentum transfer distributions of coherent J/ψ photoproduction in ultraperipheral proton-Pb collisions at the LHC. We demonstrate that unlike the case of proton-proton UPCs marred by certain theoretical uncertainties and experimental limitations, after a cut excluding the region of small momentum transfers, ultraperipheral proton-Pb collisions offer a clean way to study the gluon distribution in the proton down to x ≈ 10−5. Our analysis of the momentum transfer distributions shows that an interplay of J/ψ production by low-energy photons on the nucleus and by high-energy photons on the proton in proton-Pb UPCs can result in some excess of events at small p t in a definite region of the rapidity y.

Accurate evaluation of pressure effects on the electronic stopping cross section and mean excitation energy of atomic hydrogen beyond the Bethe approximation

Atomic hydrogen is used as a fundamental reference target system to explore pressure effects on the electronic stopping cross section, Se, of swift bare ions such as protons and α-particles. This is achieved by considering the hydrogen atom under pressure as a padded spherically-confined quantum system. Within this scheme, Se is calculated rigorously in the first Born approximation taking into account the full target excitation spectrum and momentum transfer distribution for different confinement conditions (pressures) and fixed projectile charge states. Pressure effects on the target mean excitation energy, I, are also formally calculated and compared with corresponding accurate calculations based on the Local Plasma Approximation (LPA). Even though atomic hydrogen is the simplest target system, its accurate treatment to account for the role of pressure in the stopping dynamics is found to provide useful means to understand the behavior of more complex systems under similar conditions. It is found that: (i) the region of projectile velocities for which the Bethe approximation remains valid is shifted towards higher values as pressure increases; (ii) shell corrections are enhanced relative to the free-atom case as pressure increases, and (iii) the LPA seems to underestimate I as pressure is increased. The results of this work for atomic hydrogen may serve as accurate benchmark reference values for studies of pressure effects on Se and I using different methodologies.

Quantitative, depth-resolved determination of particle motion using multi-exposure, spatial frequency domain laser speckle imaging

Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer dynamics. To verify with experimental data, controlled phantom experiments with characteristic tissue optical properties were performed using a structured light speckle imaging system. Three main geometries were explored: 1) diffusive dynamic layer beneath a static layer, 2) static layer beneath a diffuse dynamic layer, and 3) directed flow (tube) submerged in a dynamic scattering layer. Data fits were performed using the Monte Carlo model, which accurately reconstructed the type of particle flow (diffusive or directed) in each layer, the layer thickness, and absolute flow speeds to within 15% or better.

Selection of interface for discharge prediction in a compound channel flow

River engineers often analyze the overbank fl ows using subdivision techniques through the selection of assumed interface planes. A wrong selection of interface planes between the main channel and fl oodplain accounts for transfer of improper momentum, which inculcates error in estimation of discharge for compound channel section. Distribution of apparent shear stress between the main channel and fl oodplain gives an insight into the magnitude of momentum transfer based on which the discharge estimation using divided channel methods is decided. In the present study, experimental results of momentum transfer at various interface plains for straight and meandering compound channels are presented. Momentum transfer and boundary shear distribution are found to be dependent on the dimensionless parameters viz., overbank fl ow depth ratio, width ratio, sinuosity, and the orientation of the interfaces. The developed equation helps to predict the discharge carried by compound channels of different geometry and sinuosity. The present study indicates that for a straight compound channel, the horizontal division method provides better discharge results for low overbank fl ow depth and diagonal division method is good for higher overbank fl ow depths. The best discharge results for a meandering compound channel are obtained through diagonal division method for low overbank fl ow depths and vertical division method is good for higher overbank fl ow depths. The adequacies of the present results are verifi ed using present experimental data, and the data collected from the large channel facility (FCF) at Wallingford, UK. These methods agree well when applied to some natural river data.

Confinement approach to pressure effects on the dipole and the generalized oscillator strength of atomic hydrogen

Initial calculations to explore the role of pressure on generalized oscillator strengths (GOSs) for the hydrogen atom are presented. Our work is based on models of quantum confinement where the hydrogen atom is assumed to be spatially confined in a spherical cavity bounded by a barrier potential of finite height. For a given confinement radius and barrier height the energy spectrum for all available bound states and a number of continuum states (pseudocontinuum) is obtained by solving the Schr\"odinger equation using a finite-differences method. In contrast with the free atom case, the GOS momentum-transfer distribution for the $1s\ensuremath{\rightarrow}nl$ transitions is enhanced in amplitude and width as pressure increases. A turnover of this behavior takes place at a critical pressure, indicating the approach to the limit of confining capacity for the system to hold the $nl$ state. As a consequence of this behavior, the corresponding dipole oscillator strength (DOS) values provide a useful way to characterize the critical pressures for the fading and ultimate bleaching of the spectroscopic emission lines. It is also found that the height of the barrier---simulating different confining media---also affects these properties. These findings may be equally applicable to the study of inelastic energy loss from swift bare ions incident on matter under high pressures, photoabsorption, and photoionization cross sections of caged atoms as well as on optical properties of hydrogenic impurities trapped in spherical quantum dots.

Neutrino energy reconstruction in quasielastic-like scattering in the MiniBooNE and T2K experiments

Neutrino oscillation probabilities, which are being measured in long-baseline experiments, depend on neutrino energy. The energy in a neutrino beam, however, is broadly smeared so that the neutrino energy in a particular event is not directly known, but must be reconstructed from final state properties. In this paper we investigate the contributions from different reaction mechanisms on the energy-reconstruction method widely used in long-baseline neutrino experiments. Difference between the true-QE and QE-like cross sections in MiniBooNE experiment is investigated in details. It is shown, that fake QE-like events lead to significant distortions in neutrino energy reconstruction. Flux-folded and unfolded cross sections for QE-like scattering are calculated as functions of both true and reconstructed energies. Flux-folded momentum transfer distributions are calculated as functions of both true and reconstructed momentum transfer. Distributions versus reconstructed values are compared with the experimental data. Also presented are the conditional probability densities of finding a true energy for a given reconstructed energy. It is shown, how the energy reconstruction procedure influences the measurement of oscillation parameters in T2K experiment. For the reconstruction procedure based on quasielastic (QE) kinematics, all other reaction channels beside true-QE scattering show a shift of the reconstructed energy towards lower values as compared to the true energy. On average in the MiniBooNE and T2K experiments the shift is 100 - 200 MeV and depends on energy. The oscillation signals are similarly affected. These uncertainties may limit the extraction of a CP violating phase from an oscillation result.

Coherence loss and revivals in atomic interferometry: a quantum-recoil analysis

The coherence effects induced by external photons coupled to matter waves inside a Mach–Zehnder three-grating interferometer are analyzed. Alternatively to atom–photon entanglement scenarios, the model considered here only relies on the atomic wavefunction and the momentum shift induced in it by the photon scattering events. A functional dependence is thus found between the observables, namely the fringe visibility and the phase shift, and the transversal momentum transfer distribution. Good quantitative agreement is found when comparing the results obtained from our model with the experimental data.