Theoretical Momentum Research Articles

Impact of liquid crossflow on the discharge coefficient of a gas jet hole on a flat plate

This study combines the experimental and numerical simulation methods to deeply analyze the impact of liquid crossflow on the discharge coefficient of a gas jet hole on a flat plate. Experiments were conducted to examine the influence of momentum flux ratio and theoretical momentum flux ratio on the discharge coefficient under various crossflow Reynolds numbers. It was found that the variation of the discharge coefficient with the theoretical momentum flux ratio clearly reflects the impact of the crossflow boundary layer velocity profile on the discharge coefficient. The rapid growth of velocity in the boundary layer near the wall in the direction normal to the wall surface, or the decrease in the thickness of the boundary layer, both enhance the shearing effect of the crossflow, leading to a decrease in the discharge coefficient. Analysis of the cavity morphology at the hole exit captured by high-speed camera revealed that the averaged profile of the gas–liquid boundary on the symmetrical plane of the jet below the hole can be approximated as a straight line within the scale of the hole diameter, and the sine of the angle between this line and the upper wall surface is roughly equivalent to the normalized discharge coefficient. This relationship was physically interpreted through the analysis of effective and equivalent flow cross-sectional shapes derived from numerical simulation at different crossflow Reynolds numbers and theoretical momentum flux ratios. Additionally, this paper introduces an innovative method for predicting jet flow rate based on image processing technology. A notable feature of this method is that it does not require the measurement of the pressure inside the gas chamber.

Momentum induced by steam injection into a subcooled pool

Boiling Water Reactors (BWR) and Advanced Pressurized Water Reactors (APWR) often use spargers to release steam from the primary coolant system into a pool with subcooled water to prevent containment overpressure. Direct contact Condensation (DCC) creates sources of mass, heat, and momentum determined by the condensation regimes in a subcooled pool. Thermal stratification can develop in the pool if buoyancy forces created by the heat source dominate the momentum source. Only part of the stratified pool volume can be used as the heat sink which is a safety concern. Modeling of steam injection and its effect on a large pool is computationally expensive due to the considerable spatial and temporal scale differences between the steam-water interface dynamics and global pool circulation. To enable the prediction of realistic plant transients, Effective Heat Source (EHS) and Effective Momentum Source (EMS) models were proposed. These models aim to calculate the time-averaged integral effects of the steam injection on the pool without resolving the dynamics of the interface and DCC phenomena.This work aims to develop the empirical correlations that predict the time-averaged effective momentum induced by steam injection into a subcooled pool. The experimental data were collected in a Separate Effect Facility (SEF-POOL) at LUT, Finland. The force acting on the injection pipe was measured in SEF-POOL to estimate the effective momentum rate created by steam injection. The condensation regime coefficient C, defined as the ratio of effective momentum rate to the theoretical momentum rate of injected steam, is presented as a function of Jakob and Mach numbers. We found that the pitch-to-diameter ratios (P/D) had a significant effect on both the effective (time averaged) momentum rate and instantaneous forces measured in the low Jakob number region, which might be attributed to the interactions between neighboring nozzles.

A new approach for limiting the Lorentz violation term (cμν) through analyzing e−e+ → μ−μ+ scattering in a strong magnetic field

The present study explores a novel approach to establish a new bound on the Lorentz violation parameter cμν in the muon sector. It is achieved by analyzing the scattering cross-section of electron-positron into muon-antimuon under the influence of a strong magnetic field while considering the anomalous magnetic moment. By the standard model extension, the detected discrepancy between the theoretical and experimental values of the anomalous magnetic moment can be attributed to Lorentz violation. New bounds on the Lorenz-violating coefficients cμν can be obtained by analyzing the theoretical scattering cross section's magnitude at a specific energy for both theoretical and experimental muon anomalous magnetic momentum values. The recently established bounds for the muon is around cTT+0.029cXX+0.07cYY+0.039cZZ<5.76×10−7.

Appropriateness of HSE06 exchange-correlation energies for post transition metal sesquioxides Ga2O3 and In2O3: Peculiarities in electronic states, momentum densities and thermoluminescence

Compton scattering measurements using 59.54 keV γ-rays have been reported for sesquioxides Ga2O3 and In2O3. To precisely compare the experimental and theoretical momentum densities, different exchange and correlation potentials within density functional theory and its hybridisation with Hartree-Fock (PBESOL0 and HSE06) have been considered. χ2 fitting analysis depicts HSE06 as a better choice for both sesquioxides. Present band structures, density of states and UV–vis measurements unambiguously support the use of HSE06 for such oxides and resolves issues related to appropriateness of exchange and correlation potentials. Higher covalent character in Ga2O3 than In2O3 using Mulliken's population is well explained by equal-valence-electron-density scaled CPs. Most prominent and firstly reported features in band structures of In2O3 are presence of parabolic trapping centres at Γ, H and N points with three direct band gaps of similar energy (3.37 eV), which may lead to its higher luminescence properties including potential applications in thermoluminescence dosimeters.

Axis-symmetric diesel spray flame model coupled with momentum flux distribution measurement and improved soot phi-T map

An axis-symmetrical diesel spray flame model coupled with momentum flux distribution measurement was developed as a tool for nozzle orifice development. Momentum flux distributions at several distances from the nozzle orifice exit are measured by a force sensor with a small-diameter aperture which traverses a cross-section. A theoretical momentum flux profile is determined by fitting with the measured momentum flux profile at the cross-section. The spray velocity profile and equivalence ratio profiles are quantified from the theoretical momentum flux profile. By interpolating the profiles of the measured cross-sections, the axis-symmetrical diesel spray flame model can calculate the equivalence ratio and other physical values as a function of the distance from the nozzle exit ( x) and the radius from the spray axis ( r). The equivalence ratio distribution in a cross-section involving the spray axis is converted into soot formation and oxidation distribution by coupling with the improved soot ϕ -T map. The conventional soot-NOx ϕ -T map did not show the borderline between the soot formation and oxidation. To quantify the residence time of the fuel element during soot formation, the narrow soot peninsula was expanded up to its maximum by replacing the soot yield with the soot particle diameter. Instead of contour lines for the of NO mole fraction, contour lines for the OH mole fraction were implemented to reveal the border between soot formation and soot oxidation on the ϕ -T map. The borderline appears clearly, consisting of a horizontal line in the lower-temperature region and a rising line in the higher-temperature region. The converted soot formation and oxidation regions in the axis-symmetric spray flame model exhibit a strong correlation with the measured soot distributions in a quasi-steady diesel spray flame. The shear-stress, which induces turbulence affecting soot formation/oxidation, is also quantified from the velocity distribution.

Ultralow-power spiking neural networks for 1024-ary orbital angular momentum shift keying free-space optical communication

The theoretical unbounded orbital angular momentum (OAM) states can be exploited as data bits in the OAM shift keying (OAM-SK) free-space optical (FSO) communications. In order to cope with the atmospheric turbulence (AT) and misalignment in practical applications, various machine learning algorithms, or neural networks (NNs), have been put forward to decode the OAM states. However, to recognize the hybrid spatial modes representing a large bit states, the massive learnable nodes, longer computation time and more training parameters are required to improve the capability of the NNs, resulting in energy efficiency burden to the hardware device. In this paper, the event-based spiking neural network (SNN) is utilized to recognize the hybrid spatial modes consisting of superposed coaxial Laguerre–Gaussian modes with l ranging from 0 to 9 and p = 0, which is termed as spiking OAM-recognition neural network (Spiking-ORNN). In comparison to the previous solution of running deep NNs on graphics processing units, the neuromorphic solution of running Spiking-ORNN on neuromorphic chips exhibits 4300× higher energy efficiency without obvious sacrifice of recognition accuracy (less than 0.5%). Moreover, we experimentally demonstrate a 10 m 1024-ary OAM-SK FSO communication for the transmission of an image with a 10 bit grey level, wherein the peak signal-to-noise ratio of the received image can exceed 41.4 dB under the AT of =10−15 m−2/3. We anticipate that our results can stimulate further researches on the utilization of the brain-like SNN chips to reduce the energy consumptions based on the artificial-intelligence-enhanced optoelectronic systems.

Einstein’s questioning and speculations lead to theoretical photon momentum

Theoretical photon momentum results from (1) using Einstein’s paper questioning whether a body’s inertia depended on its energy content, and (2) using two previously published papers that followed Einstein’s 1954 speculations that (a) it is possible physics is based on a discontinuum theory, and (b) the continuum concept along with space and time must be discarded.

Analysis of dual band and survey photometry of two low mass ratio contact binary systems

The study presents photometric analysis of the completely eclipsing contact binary systems TYC 8351-1081-1 and ASAS J210406-0522.3. TYC 8351-1081-1 is an extremely low mass ratio (q=0.086) system with high degree of contact (f=0.66) while ASAS J210406-0522.3 is found to be in marginal contact (f=0.08) with a relatively low mass ratio of 0.272. There is good thermal contact in both systems with only a small difference in the temperature of the components. The systems have been observed by a number sky surveys over the past 20 years. We compare the light curve solutions from up to three of these surveys and find that survey photometric data manually analysed is robust and yields results comparable to dedicated ground based photometry. There is evidence of significant luminosity transfer from the primary to the secondary, on the order of 0.5LJ for TYC 8351-1081-1 and 0.06LJ for ASAS J210406-0522.3. There appears to be no change in period of either system over the past 20 years and theoretical angular momentum loss is below current measurement threshold in both cases. We also show that the mass ratio and separation are well above the theoretical values for orbital instability in both cases. As would be expected, the density of the secondary components is significantly higher relative to the primary.

Validation of hybrid WC1LYP functional for ferroelectric LiNbO3 and LiTaO3 using Compton spectroscopy and first-principles computations

Electronic structure and theoretical momentum densities (EMDs) of LiNbO3 and LiTaO3 using linear combination of atomic orbitals (LCAO) scheme are deduced. Present energy bands and density of states using local density approximation, generalised gradient approximation and hybrid (HF + DFT) PBE0 and WC1LYP schemes show a direct band gap (varying between 3.13- 5.13 eV and 3.11–5.18 eV for LiNbO3 and LiTaO3, respectively) at Γ point of Brillouin zones. The WC1LYP hybrid functional based EMDs depict reasonable agreement with present experimental Compton lines (using 100 mCi Am-241 γ-ray Compton spectrometer) than other investigated exchange-correlation potentials, thereby suggesting the applicability of hybrid model like WC1LYP in such ferroelectrics. Accuracy of energy bands is also ensured via electronic and optical properties using modified Becke–Johnson potential as facilitated in the full-potential linearized augmented plane wave method. Presently reported UV–vis measurements for optical band gaps are in consonance with the hybrid potential (WC1LYP) for the both ferroelectrics, which further confirms usefulness of hybrid scheme. Moreover, equal–valence–electron–density scaled experimental data reveal more covalent character of LiNbO3 than that in LiTaO3, which is in agreement with the present LCAO based Mulliken's population analysis.

Direct observation of the momentum distribution and renormalization factor in lithium

We have measured the momentum distribution and renormalization factor ${Z}_{{k}_{F}}$ in liquid and solid lithium by high-resolution Compton scattering. High-resolution data over a wide momentum range exhibit a clear feature of the renormalization and a sharp drop of momentum densities at the Fermi momentum ${k}_{F}$. These results are compared with those computed by quantum Monte Carlo simulation performed both on a disordered crystal and a liquid exhibiting very good agreement. Asymptotic behavior of the experimental and theoretical momentum distributions are examined to estimate ${Z}_{{k}_{F}}$. The experimentally obtained ${Z}_{{k}_{F}}=0.{43}_{\ensuremath{-}0.01}^{+0.11}$ for liquid Li and $0.{54}_{\ensuremath{-}0.02}^{+0.11}$ for solid Li are in good agreement with theoretical results of $0.54\ifmmode\pm\else\textpm\fi{}0.01$ and $0.64\ifmmode\pm\else\textpm\fi{}0.01$, respectively.

Revisiting electron-correlation effects on valence shake-up satellites of neon

We report an electron momentum spectroscopy study on valence shake-up satellites of neon. A symmetric noncoplanar $(e,2e)$ experiment was performed at an incident electron energy of 1.2 keV, and the recoil-ion-momentum--dependent $(e,2e)$ cross sections or momentum profiles of the shake-up satellites have been obtained. Furthermore, theoretical momentum profiles have been calculated on the basis of the distorted-wave Born approximation using configuration interaction wave functions of the initial neutral and final ionic states. Comparison between experiment and theory has revealed that contrary to a general expectation, electron correlation in the initial neutral state has a significant influence on the shapes of momentum profiles for neon satellites. It has been shown that the Dyson orbitals of transitions to the $2{p}^{4}(^{1}\mathrm{S})3s\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{S}$ and $2{p}^{4}(^{1}\mathrm{D})3p\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{P}$ ionic states are more localized than those of the associated primary ionizations due to electron-correlation effects.

Theoretical and experimental cross sections for electron scattering from halothane

We report a joint theoretical and experimental study on elastic scattering of electrons from halothane (CF3CHBrCl). The theoretical differential, integral and momentum transfer cross sections were obtained with the Schwinger multichannel method implemented with pseudopotentials (SMCPP), and with the independent atom model with screening corrected additivity rule including interference effects (IAM-SCAR+I). The differential cross sections measurements were conducted for incident electron energies of 10, 20, 30 and 50 eV, while the scattered electron angular range varied from 7° to 100°. At these energies the present experimental differential cross sections are in reasonable agreement with both SMCPP and IAM-SCAR+I calculations. As expected, the two theoretical methodologies agree well with each other as the electron impact energy increases. We also discuss the presence of low-energy resonances and a bound anion state identified in our SMCPP calculations.

Experimental and theoretical study of valence electronic structure of tetrabromomethane by (e,2e) electron momentum spectroscopy

We report a measurement of the valence orbital momentum profiles of tetrabromomethane (${\mathrm{CBr}}_{4}$) using symmetric noncoplanar $(e,2e)$ experiments at the impact energies of about 600 and 1200 eV. The experimental momentum profiles for the individual orbitals $5{t}_{1}, 13{t}_{2}, 5e, 12{t}_{2}$, and $9{a}_{1}$ and the branching ratio of $5{t}_{1}$ to $13{t}_{2}$ and $5e$ to $13{t}_{2}$ are obtained and compared with two kinds of calculations under the plane-wave impulse approximation. One is theoretical momentum profiles that have been calculated at the equilibrium geometry, the other is those that involve vibrational effects using a thermal sampling molecular dynamics method. The calculations considering molecular vibrations are in better agreement with experiment than the equilibrium geometry calculations, indicating the important role of nuclear motions on the valence orbital electronic structures of ${\mathrm{CBr}}_{4}$. The distorted-wave effects are observed in the experimental momentum profiles of $5{t}_{1}, 5e$, and $12{t}_{2}$ which display dynamic dependencies on the impact energies. A multicenter interference or bond oscillation effect has been observed from the momentum profile ratios of $5{t}_{1}$ to $13{t}_{2}$ and $5e$ to $13{t}_{2}$ which has direct information about the bond length of a molecule.

Measurement of the orbital angular momentum of an astigmatic Hermite–Gaussian beam

Here we study three different types of astigmatic Gaussian beams, whose complex amplitude in the Fresnel diffraction zone is described by the complex argument Hermite polynomial of the order (n, 0). The first type is a circularly symmetric Gaussian optical vortex with and a topological charge n after passing through a cylindrical lens. On propagation, the optical vortex "splits" into n first-order optical vortices. Its orbital angular momentum per photon is equal to n. The second type is an elliptical Gaussian optical vortex with a topological charge n after passing through a cylindrical lens. With a special choice of the ellipticity degree (1: 3), such a beam retains its structure upon propagation and the degenerate intensity null on the optical axis does not “split” into n optical vortices. Such a beam has fractional orbital angular momentum not equal to n. The third type is the astigmatic Hermite-Gaussian beam (HG) of order (n, 0), which is generated when a HG beam passes through a cylindrical lens. The cylindrical lens brings the orbital angular momentum into the original HG beam. The orbital angular momentum of such a beam is the sum of the vortex and astigmatic components, and can reach large values (tens and hundreds of thousands per photon). Under certain conditions, the zero intensity lines of the HG beam "merge" into an n-fold degenerate intensity null on the optical axis, and the orbital angular momentum of such a beam is equal to n. Using intensity distributions of the astigmatic HG beam in foci of two cylindrical lenses, we calculate the normalized orbital angular momentum which differs only by 7 % from its theoretical orbital angular momentum value (experimental orbital angular momentum is –13,62, theoretical OAM is –14.76).

Compton spectroscopy and electronic structure study for tetragonal barium titanate

The Compton profile of tetragonal BaTiO3 is measured using 20Ci 137Cs Compton spectrometer. The experimental data have been analyzed using theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) with density functional theory (DFT) and the hybridization of Hartree-Fock and DFT (WC1LYP scheme). It observed that hybrid scheme WC1LYP provides a better agreement with the experimental data than other approximations of exchange-correlation (with generalized gradient approximation like PBESol, SOGGA and local density approximation like LDAPZ) as considered in the present work. In addition, the energy bands and density of states have been reported using LCAO-WC1LYP scheme. The WC1LYP hybrid method confirms wide band gap semiconducting nature of tetragonal BaTiO3. Further, a relative nature of bonding among CaTiO3, SrTiO3 and BaTiO3 has also been discussed using equal-valence-electron-density profiles and Mulliken's population analysis which predict a trend of increasing iconicity in the order CaTiO3→BaTiO3→SrTiO3.

Electronic and optical response of Cr-doped MoSe2 and WSe2: Compton measurements and first-principles strategies

In this paper, we present energy bands, density of states and Mulliken's population (MP) data using the linear combination of atomic orbitals (LCAO) method. To compare the theoretical momentum densities, we have also employed 100mCi 241Am Compton spectrometer to measure the Compton profiles of Cr0.5X0.5Se2 (X=Mo and W). The experimental Compton data have been used to check the performance of various exchange and correlation energies for the present mixed dichalcogenides within the LCAO scheme. It is seen that CPs based on the hybridization of Hartree-Fock and density functional theory give a better agreement with the experimental data than other schemes employed in the present investigations. All theoretical approximations show an indirect band gap between the Γ and K points of the Brillouin zone. Further, equal-valence-electron-density scaled experimental data predict a more ionic character in Cr0.5W0.5Se2 than in Cr0.5Mo0.5Se2, which is in tune with our MP data. Going beyond the computation of electronic properties using LCAO, we have also reported accurate electronic and optical properties using the modified Becke-Johnson (mBJ) potential within the full potential augmented plane wave (FP-LAPW) method. Optical properties computed using the FP-LAPW-mBJ method show the feasibility of using both the mixed dichalcogenides in photovoltaic devices.

High Resolution Electron Momentum Spectroscopy Study on Ethanol: Orbital Electron Momentum Distributions for Individual Conformers

The outer-valence binding energy spectra of ethanol in the energy range of 9–21 eV are measured by a high-resolution electron momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The electron momentum distributions for the ionization peaks corresponding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calculations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured electron momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical electron momentum distributions for the molecular orbitals of individual conformers (i.e., 8a′ of trans and 9a of gauche), but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution electron momentum spectrometer, by inspecting the molecular electronic structure, is a promising technique to identify different conformers in a mixed sample.

Bewitching sex workers, blaming wives: HIV/AIDS, stigma, and the gender politics of panic in western Kenya

ABSTRACTSince access to HIV testing, counselling, and drug therapy has improved so dramatically, scholars have investigated ways this ‘scale-up’ has interacted with HIV/AIDS-related stigma in sub-Saharan Africa. Drawing on data collected during ethnographic research in a trading centre in western Kenya, this paper critically analyses two violent and localised case studies of panic over the ill health of particular community residents as a nuanced lens through which to explore the dynamic interplay of gender politics and processes of HIV/AIDS-related stigma in the aftershocks of the AIDS crisis. Gaining theoretical momentum from literatures focusing on stigma, gender, witchcraft, gossip, and accusation, we argue that the cases highlight collective anxieties, as well as local critiques of shifting gender roles and the strain of globalisation and legacies of uneven development on myriad forms of relationships. We further contend that these heightened moments of panic and accusation were deployments of power that ultimately sharpened local gender politics and conflicts on the ground in ways that complicated the social solidarity necessary to tackle social and health inequalities. The paper highlights one community’s challenge to eradicate the stigma associated with HIV/AIDS during a period of increased access to HIV services.

Alignment dependence of photoelectron momentum distributions of atomic and molecular targets probed by few-cycle circularly polarized laser pulses

We present theoretical photoelectron momentum distributions (PMDs) for ionization from Ar($3p$) and ${\mathrm{H}}_{2}{}^{+}$(${\ensuremath{\sigma}}_{g}$) orbitals by few-cycle, high-intensity, near-infrared laser fields circularly polarized in the $xy$ plane. The three-dimensional time-dependent Schr\odinger equation is solved numerically within the single-active-electron approximation for Ar and within the fixed nuclei approximation for ${\mathrm{H}}_{2}{}^{+}$. The PMDs are investigated for alignment of the probed target orbitals relative to the polarization plane of the laser field. In the atomic case, the PMDs in the polarization plane for aligned $3p$ Ar orbitals are, up to an overall scaling factor, insensitive to alignment of the probed orbital, while the lateral PMDs show a signature of the orbital node when that node is sufficiently close to the polarization plane. For the molecular case of ${\mathrm{H}}_{2}{}^{+}$(${\ensuremath{\sigma}}_{g}$), our results show a significant impact of alignment on the PMDs due to the anisotropic molecular potential and the alignment-dependent coupling between the ground state and excited states.

Vibrational Effects on Electron Momentum Distributions of Outer-Valence Orbitals of Oxetane.

Vibrational effects on electron momentum distributions (EMDs) of outer-valence orbitals of oxetane are computed with a comprehensive consideration of all vibrational modes. It is found that vibrational motions influence EMDs of all outer-valence orbitals noticeably. The agreement between theoretical and experimental momentum profiles of the first five orbitals is greatly improved when including molecular vibrations in the calculation. In particular, the large turn-up at low momentum in the experimental momentum profile of the 3b1 orbital is well interpreted by vibrational effects, indicating that, besides the low-frequency ring-puckering mode, C-H stretching motion also plays a significant role in affecting EMDs of outer-valence orbitals of oxetane. The case of oxetane exhibits the significance of checking vibrational effects when performing electron momentum spectroscopy measurements.