基于蒙特卡罗模拟的透射式XRD背景的定量分析

XRD背景主要来源于空气、装置和样品中光子的散射,XRD分析需准确扣除背景,常用的扣背景方法具有一定的局限。蒙特卡罗模拟可实现光子的甄别与统计,因此可将其用于XRD背景来源的定量分析。相干散射的模拟中需考虑物质的Form Factor,这可由Baró等的拟合式、独立原子模型或德拜公式给出;在20 keV能量及透射几何模式下,通过对骨、尼龙、水等物质的XRD模拟,对探测器中光子来源进行了区分和统计。结果表明,德拜公式计算的空气背景大于独立原子模型;空气散射在小角度时背景占比大,随散射角的增加从100%减小至40%以下,而样品中康普顿散射的计数占比则从0增大至60%以上。该方法可对不同样品组成以及复杂装置结构的XRD背景进行定量分析。

Neutral Pion Electromagnetic Form Factor as a Bound System of 3 + 1 Dimensional QCD

We investigate a neutral pion electromagnetic form factor in momentum space and obtain Gaussian-like function for it. The characteristic form of our neutral pion electromagnetic form factor is consistent with the results published by Jefferson Lab Hall A Collaboration. .

Planar morphology and controlling factors of the gullies in the Yuanmou Dry-hot Valley based on field investigation

The plane form of a gully can provide a basis for evaluating the gully volume and erosion rate, acting process, and evolutionary stage. For describing the planar characteristics of a permanent gully and understanding their controlling factors, this study, utilizing a total station and GPS RTK, measured the shoulder lines and channel curves of 112 gullies in six sites of the Yuanmou Dry-hot Valley and then mapped them by Arc GIS software and calculated nine parameters. The results showed that the channel lengths range from 10.88 to 249.11 m; the widths range from 6.20 to 40.99 m; the perimeters range from 54.11 to 541.67 m; the gully areas range from 153.02 to 6,930.30 m2; the left-side areas range from 92.93 to 4,027.20 m2; and the right-side areas range from 63.65 to 3,539.77 m2. The slightly sinuous and straight gullies account for 73.21% of the total gullies; the quantity of the right skewed gullies is 8.93% greater than that of the left skewed ones based on the symmetry ratio; the shape ratios range from 1.12 to 1.40 and the morphology ratios from 0.038 to 1.294; the fractal dimension is 1.192. Gullies in different sites have diverse planar characteristics. Except for the symmetry index, which was close to a negatively skewed distribution, all of the other parameters had the characteristic of positively skewed distribution. The gully area is related to the length and width, but the gully length has a weak correlation with the width. The evolutionary stage, topographic conditions, strata, soil properties, and piping erosion played very important roles in the gully planar morphology. This study could provide useful information for controlling gully erosion and safeguarding human habitation and engineering buildings.

A Diquark-Quark Model with Its Use in Nucleon Form Factorst

The nucleon electromagnetic form factors are investigated within a simple diquark-quark model using the light-front formalism. In this model, baryon is described as a bound state of one quark and one clustering diquark. The calculational results are compared with the experimental ones. We also regard the quarks in a baryon as pointlike constituent quarks.

Local Quark-Hadron Duality and Magnetic Form Factors of Bound Proton

We discuss the consequence of local duality for elastic scattering, and derive a model-independent equation between structure functions at x ～ 1 and elastic electromagnetic form factors. Then the electromagnetic form factors of proton are discussed using the quark-hadron duality theory. We also debate the form factor of proton in a bound state.It may be an effective approach to study the form factor of proton in media.

Quantifying.Associations among Dimensions of Ears and Their Form Factors in Maize(Zea Mays)Using Dimensional Analysis

Ear morphological traits such as volume and shape are important features of maize and the quantitative associations among them can help understand kernel yield determination. 150 mature ears each of 4 maize cultivars were collected from field experiments, and ear length(L), diameter(D), area(S) and volume(V) were recorded for individual ears, kernel weight per ear also recorded for a portion of the examined ears. Following principles of dimensional analysis, 8 theoretical equations of 3 sets,which relate ear higher dimensions to its length and diameter, were developed and parameterized and validated with the field observations. The 3 optimized equations showed that the shape of ears in maize can be featured with 3 dimensionless form factors, namely diameter-to-length ratio(c=D/L), areal form factor(b=S/L/D), and volumetric form factor(a=V/L/D/D). Statistically,all of them were significantly different among cultivars, and a's values varied from 0.582 to 0.612, and b's 0.839-0.868, and c's 0.242-0.308. Volumetric form factor and areal form factor could estimate precisely ear volume and area respectively, but diameter-to-length ratio was not suitable to estimate ear diameter by its length. Ear volume explained almost all variation of ear kernel weight and product L*D*D did the same substantially. Dimensional analysis proved to be promising in understanding relationship among morphological traits of ears in maize. Its application in crop researches should improve our knowledge of the physical properties of crop plants.

Nucleon Form Factors and N-△ Transitions in a Hypercentral Constituent Quark Model with Meson Cloud

We study the nucleon form factors and the nucleon-△（1232） transitions in a framework of hypercentral constituent quark model. The pion meson cloud effect is taken into account explicitly. Our results show that the pion cloud contributes substantially to the nucleon form factors as well as to the helicity amplitudes of △（1232）, and it gives an improved agreement compared to the experimental.

Electric and Magnetic Form Factors of Proton in Relativistic Constituent QuarkModel

Based on relativistic constituent quark (RCQ) model, the electric and magnetic form factors are analyzed. The ratio of the two form factors for the proton , which is an image of its charge and magnetization distributions, is calculated in the light-front formulism of RCQ model. Recently, this ratio was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the polarization technique. The new data presented span the range and are well described by a linear Q2 fit. Also, the ratio reaches a constant value while Q2 becomes larger than 2 (GeV)2. Our calculation results are presented and appear to be consistent with the experimental ones.

Microscopic Calculations of Core-Polarization Effect on Inelastic Electron Scattering Form Factors for Different Parity States in （14^）

Inelastic electron scattering form factors has been calculated for different parity for the two （C3） transitions of 14^N for （5.83MeV） （f^π, T = 20） level and, （5.106MeV） （f^π, T = 30） level in the frame work of shell model. The model space wave functions are generated by using the Cohen-Kurath （CK） interaction, where 4He is assumed as a core and ten nucleons are distributed over the lp-shell which forms the model space. Core-polarization effects （CP） （the effects from outside lp-shell model space） are included through the first order perturbation theory. The core-polarization effects increase the form factor to be up near the experimental data which are not sufficient to give a good comparison with the calculating data.

A CLOSED FORM SOLUTION OF STRESS INTENSITY FACTORS FOR THREE DIMENSIONAL FINITE BODIES WITH ECCENTRIC CRACKS

In this paper, a new analytical-engineering method of closed form solution about stress intensity factors for three dimensional finite bodies with eccentric cracks is derived by means of energy release rate method. The results of stress intensity factors can be obtained. The results provided ir this method are in nice agreement with those of the famous alternating method by which only special cases can be solved.

Gravitational form factors of the proton from near-threshold vector meson photoproduction

We systematically analyze the quark and gluon gravitational form factors(GFFs)of the proton by connecting the energy-momentum tensor and near-threshold vector meson photoproduction(NTVMP).Specifically,the quark contributions of GFFs are determined by applying global fitting to the cross section of the lightest vector mesonρ0 photoproduction.Combined with the gluon GFFs obtained from heavy quarkonium J/ψphotoproduction data,the complete GFFs are obtained and compared with the experimental results and lattice quantum chromodynamics determinations.In addition,we use the resonance via Padé(RVP)method based on the Schlessinger point method to obtain a model-independent quark D-term distribution through direct analytical continuation of deeply virtual Compton scattering experimental data.If errors are considered,the results obtained with RVP are essentially consistent with those obtained by NTVMP.Moreover,the comprehensive information on GFFs helps to uncover the mass distribution and mechanical properties inside the proton.This study is not only an important basis for delving into the enigmatic properties of the proton,but also has significance for theoretically guiding future JLab and EIC experimental measurements.

CFD-Based Method of Determining Form Factor k for Different Ship Types and Different Drafts

The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.

Numerical Study on Scale Effect of Form Factor for DTMB5415, KCS,KVLCC2, and 4000TEU Container Ship

Four ships,a twin-propeller naval ship,two single-propeller container ships,and a single-propeller very large crude carrier(VLCC),were studied to investigate the scale effect of the form factor.The viscous flow fields of the ships at different scales were solved numerically via the Reynolds-averaged Navier–Stokes method combined with the shear stress transport k–ωturbulence model.The numerical method was validated through comparisons with experimental data,and numerical uncertainty analysis was carried out based on the ITTC recommended procedure.On this basis,scale effects of the form factor were analyzed using different friction lines,and scale effects of flow fields and the mean axial wake fractions were further analyzed in details.The results showed that the form factor exhibited scale effects when adopting the ITTC-1957 line,and it increased with the increase in the Reynolds number.The scale effect of the form factor reduces the prediction precision of the full-scale ship resistance.The friction line has a significant effect on the form factor.The form factor exhibits little dependence on the Reynolds number when using the numerical friction line or the Katsui line,which is useful for full-scale ship resistance predictions.With the increasing Reynolds number,the boundary layer thickness becomes thinner and the axial velocity contour contracts toward the center plane,and there is nearly a linear relationship between the reciprocal of mean axial wake fraction on propeller disc and Reynolds number in logarithmic scale for the three types of ship forms.

Numerical Prediction of Form Factor and Wave Interference of A Trimaran for Different Outrigger Positions

Trimaran hydrodynamics have been an important research topic in recent years.Trimarans have even been chosen for naval surface combatants.In this case,investigation of a trimaran with different outrigger positions is important and necessary for better hydrodynamic performance.This paper focuses on the numerical investigation of trimaran hydrodynamics.The trimaran model used in this study is a 1/80 scale high-speed displacement frigate-type concept developed by the Center for Innovation in Ship Design(CISD)at Naval Surface Warfare Center,Carderock Division(NSWCCD).The numerical simulations were conducted for different outrigger positions at low and moderate Froude numbers by using commercial CFD software solving URANS equations.A verification and validation study was carried out for the numerical method in one configuration and one ship velocity.The existing experimental results for the trimaran resistance in the literature were used for validation.Five different outrigger positions were analyzed and the form factor of each configuration was calculated by the Prohaska method.The total resistance was decomposed to its components using the form factor.The interference factor was calculated for each configuration in terms of total resistance,residual resistance and wave resistance.Also,wave profiles using the longitudinal wave cuts in different locations were obtained both numerically and experimentally.It was concluded that the outrigger position had different effects on the interference,total resistance and wave profile at different Froude numbers.It was also shown that the CFD results were in good agreement with the experimental data in all configurations.In conclusion,this study presents the results of interference effects for different trimaran configurations in terms of wave resistance in addition to the total resistance and residual resistance.The numerical method was validated not only with the total resistance test data but also the longitudinal wave profiles along the hull.

Theoretical Study of the Nuclear Charge Distributions of Tin Isotopes

Nuclear binding energies, charge radii and the charge distributions of even-even tin （Sn） isotopes are calculated using relativistic mean field theory, and the theoretical results are found to be in accordance with the experimental data. The nuclear charge form factors for Sn isotopes are calculated using the phase-shift analysis method. It is shown that the minima of the charge form factors shift upward and inward with an increase in the neutron number of the Sn isotopes.

Determining Nuclear Form factor for Detection of Dark Matter in Relativistic Mean Field Theory

In this work, we derive the nuclear form factor for the spin-independent collision between the WIMPs and nucleus in terms of the relativistic mean field （RMF） theory. Comparison with the traditional form factors which are commonly used in literature is given and it is found that our results are slightly above that of the 2PF model by 4% to 8%, but deviate from the Helm form factor by 15% to 25% for the whole recoil energy spectrum of 0 -100 keV. Moreover, taking Xe and Ge as examples, we show the dependence of the form Factor on the recoil energy.

Thomson scattering off a pair （electron-positron） plasma

Thomson scattering off a pair （electron-positron） plasma is theoretically investigated in the collisionless and collisional limits respectively. Our calculations show that the power spectrum of the Thomson scattering off a collisionless pair plasma is just proportional to the velocity distribution function of the particles in the plasma. Collective modes in the plasma do not have any effects on the Thomson scattering spectrum because of the correlation between the negatively- and positively-charged particles. In the collisional limit, the power spectrum of the Thomson scattering presents three spikes： two peaks correspond to two contra-propagating sound waves and one peak corresponds to an entropy wave.

Re-study of Nucleon Pole Contribution in J/ψ → NN^-π Decay

We re-study nucleon pole contribution in J/ψ → NN^-π decays by including the imaginary part for the propagator of the off-shell nucleon with energy above π N threshold. It is found that when including the imaginary part in the propagator, the branching ratio of the decay width will descend about 11% compared with the result without including the imaginary part, no matter whether including the off-shell form factors or not. It also leads to a phase of up to 25° for the off-shell nucleon propagator at invariant mass around 1400 MeV. This effect needs to be considered for detailed partial wave analysis of N^＊ resonances around this mass region.

B_((s))→D^(∗∗)_((s))form factors in HQEFT and model independent analysis of relevant semileptonic decays with NP effects

The form factors of B(s)decays into P-wave excited charmed mesons(including D∗0(2300),D1(2430),D1(2420),D∗2(2460)and their strange counterparts,denoted generically as D∗∗(s))are systematically calculated via QCD sum rules in the framework of heavy quark effective field theory(HQEFT).We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors,including the scalar and tensor ones only relevant for possible new physics effects.The expressions for the form factors in terms of several universal wave functions are derived via heavy quark expansion.These universal functions can be evaluated through QCD sum rules.Then,the numerical results of the form factors are presented.With the form factors given here,a model independent analysis of relevant semileptonic decays B(s)→D∗∗(s)lν¯l is performed,including the contributions from possible new physics effects.Our predictions for the differential decay widths,branching fractions,and ratios of branching fractions R(D∗∗(s))may be tested in more precise experiments in the future.

Deuteron electromagnetic form factors and tensor polarization observables in the framework of the hard-wall AdS/QCD model

We study the electromagnetic form factors and tensor polarization observables of the deuteron in the framework of the hard-wall AdS/QCD model.We find a profile function for the bulk twistτ=6 vector field,which describes the deuteron on the boundary and fix the infrared boundary cut-off of AdS space in accordance with the ground state mass of the deuteron.We obtain the deuteron charge monopole,quadrupole,and magnetic dipole form factors and tensor polarization observables from the bulk Lagrangians for the deuteron and photon field interactions.We plot the momentum transfer dependence of the form factors and tensor polarization observables and compare our numerical results with those in the soft-wall model and experimental data.