Electrostatic adhesion of ion and triboelectric-charged particles

The adhesion of ∼10 μm charged toner particles is of considerable importance in the electrophotographic process for copying or printing documents. If the non-electrostatic short-range adhesion force is reduced with nanoparticle surface additives, the toner adhesion is dominated by an electrostatic force. However, the measured adhesion of triboelectrically charged toner is greater than the prediction of an electrostatic image force model that assumes a uniform surface charge distribution. The enhanced electrostatic adhesion of triboelectrically charged toner is attributed to a non-uniform surface charge distribution. To provide support for this interpretation, the adhesion of ion-charged toner is of interest since a more uniform surface charge distribution is expected. Electric field detachment measurements on ion-charged toner for different charge levels show that the adhesion of ion-charged toner is indeed less than that of triboelectrically charged toner.     

Analysis of the electrostatic force on a dielectric particle with partial charge distribution

This paper presents the analysis of the electrostatic force acting on a charged dielectric particle on a grounded plane. The force has been determined by a numerical field calculation method to make clear the effect of particle dielectric constant and charge distribution on the particle surface. The charge is treated to be distributed in three ways: (a) uniformly over entire surface, (b) partially on the upper, or (c) on the lower part of a particle. The calculation results show that, if a particle with dielectric constant ?_p = 3 is partially charged on the lower part by a zenith angle π/2, π/4 and π/8, the force shall be higher by 0.7, 4.3 and 20 times, respectively, than that for a uniform charging with the same charge amount. On the other hand, the force becomes weaker when charge is on the upper part. The effect of the particle dielectric constant is found to be dependent on the charge distribution. With charge uniform on the entire surface or on the upper part, the force always increases with the dielectric constant. However, when surface charge is restricted to a small area at the lower part of the particle (θ_q < π/4), the force may decrease with increasing the dielectric constant.     

Δ++π−-electroproduction near threshold and the Q2 dependence of the contact interaction

The Q² dependence of σ (γvp→π^?Δ⁺⁺) was measured. Close to threshold σ (γvp→π^?Δ⁺⁺) is roughly proportional to 1/(m²_? + Q²)². The data are consistent with dominance of the contact term and imply that the contact term has the Q² dependence of the ? propagator.     

DSE Perspective on QCD Modeling,Distribution Amplitudes,and Form Factors

We describe results for the pion distribution amplitude (PDA) at the non-perturbative scale μ = 2 GeV by projecting the Poincaré-covariant Bethe–Salpeter wave-function onto the light-front and use it to investigate the ultraviolet behavior of the electromagnetic form factor, F _π (Q ²), on the entire domain of spacelike Q ². The significant dilation of this PDA compared to the known asymptotic PDA is a signature of dynamical chiral symmetry breaking on the light front. We investigate the transition region of Q ² where non-perturbative behavior of constituent-like quarks gives way to the partonic-like behavior of quantum chromodynamics (QCD). The non-perturbative approach is based on the Dyson–Schwinger equation (DSE) framework for continuum investigations in QCD. The leading-order, leading-twist perturbative QCD result for Q ² F _π (Q ²) underestimates the new DSE computation by just 15 % on \({Q^2\gtrsim 8\,}\) GeV², in stark contrast with the result obtained using the asymptotic PDA.     

Electroproduction of π+ n, π- p andK + Λ,K + 2211; 0 final states above the resonance region

The reactionsΣ _v p→π⁺ n,K ⁺ Λ,K ⁺ ∑ ⁰ andΣ _v n→π⁺ n were studied at invariant hadronic masses around 2.2. GeV forQ ²=0.06, 0.28, 0.70, and 1.35 GeV². The main results are: At small |t| the π⁺ production is dominated by longitudinally polarized photons and can be described by one pion exchange. At low |t| the transverse (π⁺ n) cross section drops steeply withQ ², but remains roughly constant forQ ²≧0.5 GeV². For |t?≧0.8 GeV², (π⁺ n/dt) is almost independent ofQ ². The integrated cross section (π⁺ n) shows a similarQ ²-dependence asσ _tot (γ _v p) forQ ²≧0.28 GeV². The ratioσ(π^- p)/σ(π⁺ n) atQ ²=0.70 and 1.35 GeV² for |t|≧0.6 GeV² is smaller than in photoproduction and close to 1/4. The ratioσ(K ⁺ ∑ ⁰ decreases steeply withQ ² following roughly the predictions of the quark-parton model.     

Elastic and transition form factors of light pseudoscalar mesons from QCD sum rules

We revisit F _π(Q ²) and F _Pγ(Q ²), P = π, η, η′, making use of the local-duality (LD) version of QCD sum rules. We give arguments that the LD sum rule provides reliable predictions for these form factors at Q ² ≥ 5–6 GeV², the accuracy of the method increasing with Q ² in this region. For the pion elastic form factor, the well-measured data at small Q ² give a hint that the LD limit may be reached already at relatively low values of momentum transfers, Q ² ≈ 4–8 GeV²; we therefore conclude that large deviations from LD in the region Q ² = 20–50 GeV² seem very unlikely. The data on the (η, η′) → γγ* form factors meet the expectations from the LD model. However, the BaBar results for the π ⁰ → γγ* form factor imply a violation of LD growing with Q ² even at Q ² ≈ 40 GeV², at odds with the η, η′ case and with the general properties expected for the LD sum rule.     

Structure of30Si from the spectroscopy of highly excited states

Highly excited states in³⁰Si were investigated using the²⁷Al(α, p γ) reaction. Proton-γ ray angular correlations were measured atE _α=12, 14.1 and 15MeV. At 15MeV linear polarizations ofγ-rays were measured in coincidence with protons using a five-crystal Compton-polarimeter. Lifetimes were measured atE _α=14.6 MeV using the Dopper-shift attenuation method. Unambigious spin-parity assignments were obtained for the levels at 6,865 (3⁺), 7,001 (5⁺), 7,079 (3⁺), 7,810 (4), 9,371 (6⁺), 7,613 (4^?), 8,196 (5^?), 8,596 (4^?), 8,963 (5^?), 9,111 (6^?), 9,350 (4^?), 9,507 (5^?), 9,777 (6^?), 10,188 (5^?), 10,305 (3^?), 10,561 (6^?), 10,725 (7^?), 11,477 (6^?) and 11,544 (7^?)keV excitation energy, respectively. The structure of³⁰Si is understood both in terms of the shell model and the collective model. The levels at 5,487, 6,505, 8,196, 9,777 and 11,544keV, respectively, are theI ^π=3^? through 7^? members of a well developedK ^π=3^? rotational band with intrinsic quadrupole moment |Q ₀|=350 _?70 ⁺²⁵⁰ mb. There is evidence of further rotational bands, among them aK ^π=3^? band with |Q ₀|=800 _?80 ⁺⁴²² mb.     

A model for chiral symmetry breaking in QCD

A recently proposed model for dynamical breaking of chiral symmetry in QCD is extended and developed for the calculation of pion and chiral symmetry breaking parameters. The pion is explicitly realized as a massless Goldstone boson and as a bound state of the constituent quarks. We compute, in the limit of exact chiral symmetry, M_Q, the constituent quark mass $\text{?}{}_{\mathrm{\pi }}$ the pion decay coupling, $\text{〈}\text{u}\text{u〉}$, the constituent quark loop density, μ_π²/m_q, the ratio of the Goldstone boson mass squared to the bare quark mass, and 〈r²〉_π, the pion electromagnetic charge radius squared.     

A partial wave analysis of the (Kππ) system in the reaction π− p→(K +π−π0)Λ at 3.95 GeV/c

Results from a partial wave analysis of theKππ system produced in the hypercharge exchange reaction π^? p→(K ⁺π^?π⁰)Λ at 3.95 GeV/c are presented. SignificantQ ₁ production is observed but no evidence is found forQ ₂ production thus confirming the results obtained in a previous decay Dalitz plot analysis of the same reaction. The relative phase behaviour of the 1⁺(K?) partial waves obtained with the present analysis provides additional confirmation of the resonance interpretation of theQ ₁ enhancement. Information is also obtained about its production properties and the role played by the Λ polarization in the hypercharge exchange reaction. This is compared with the results obtained in the reactionK ^? p→(π⁺π^?π⁰)Λ at 4 GeV/c.     

Line energy,line tension and drop size

The relation between drop radius, r, the force to move the three phase contact line and the advancing and receding contact angles θ_A and θ_R is studied. To keep the line energy (energy per 2πr, also named line tension) independent of r, the modified Young equation predicts that the advancing and receding contact angles, θ_A and θ_R, change considerably with r. As shown by many investigators, θ_A and θ_R change negligibly, if at all, with r. We quantify recent evidences showing that the line energy is a function of the Laplace pressure and show that this way the modified Young equation is correct and still θ_A and θ_R should hardly change with r. According to our model, the small surface deformation associated with the unsatisfied normal component of the Young equation results in higher intermolecular interactions at the three phase contact line which corresponds to a higher retention force. This time increasing effect is supported by recent experiments.     

Higher-twist effects in QCD,deep inelastic scattering,and the Drell-Yan process

Inclusion of specific effects associated with constituent binding in hadronic wave functions is shown to lead to important non-scaling, nonfactorizing 1/Q ² contributions to cross sections for semi-inclusive deep-inelastic scattering, the Drell-Yan process, and other hard scattering reactions. These 1/Q ² higher-twist terms are predicted to be dominant in well defined kinematic regions such as largex and/or largez. The provide angular distributions typical of longitudinally polarized virtual photons andW's, including sin² θ terms in meson induced Drell-Yan processes and ine ⁺ e ^?→πX, as well as unusual (1?y) terms in deep-inelastic scattering. Calculations are also presented of the quark structure functions of the pionq _π(x, Q ²) and for the quark to pion fragmentation functionD _π(z, Q ²). Predictions are made for the azimuthal angle dependence of the cross sections for \(\pi N \to \mu {\text{ }}\bar \mu X\) andlN→l′πX.     

On some relationships between energy,charge and electrostatic potential at the nucleus and the interpretation of chemical shifts in XPS

Some relations between total energy, 2p binding energy and electrostatic potential and electron density at the nucleus have been studied for iron mainly by Xα calculations. For a number of elements belonging to the 3rd and 4th periods, transition energy and radial integrals {r^?1} of valence electrons have been calculated to study the energy — charge correlations in XPS.     

Modellunabhängige Beschreibung kugelsymmetrischer Ladungsverteilungen bei der Streuung schneller Elektronen an Atomkernen

A method is given to evaluate in a model independent way cross sections for scattering of fast electrons by nuclei. For this purpose the charge distribution in the nucleus will not, as usual, be described by means of the charge densityρ(r), but by the first moment functionT(Q): $$T(Q) = \int\limits_0^Q {r(Q')dQ'} .$$ The integration has to be performed over this part of the charge distribution in which the charge will increase from the value 0 to the valueQ. ThusT(Q) gives the first moment of this part. It will be shown that this function can be fixed by elastic scattering within certain limits.     

Production mechanism in the four-body reaction π+n → pπ+π−π0 at 5.1 and 9 GeV/c

The π⁺n → pπ⁺π^?π⁰ reaction is studied in the longitudinal phase space (LPS). The cross sections, mass spectra and four-momentum transfer distributions are discussed in each LPS sector. The dominant processes seem to be the ΔQ = 0 and G parity positive exchange, and ΔQ = 0, 1 and G parity negative exchange. A low baryon diffraction dissociation is also present.     

Limits on the impact parameters occuring in specific K−p interactions at 8.25 GeV/c

We have determined a lower limit of the impact parameter for the reactions associated with the channels K^?p → K^?pπ⁺π^?K^?p → λπ⁺π^?π⁰. The limit was found to be highest for the diffractive parts of the first channel (～ 0.52 fm) and smallest for the forward Λ in the second channel (～0.21 fm).We have also examined the elements of the inverse correlation matrix for the transfer: the off-diagonal elements are small (consistent with zero) for n = 4?7 body products. The log 〈Q_i·Q_j〉 of the correlation matrix as a function of $\text{Гi?jГ}$ falls on a straight line and the eigenvalue λ₁ of the transverse momentum transfer eigenfunction was found to increase slightly from ～0.6 for 4-body to ～0.7 for 7-body products. The 〈cosφ_ij〉 of the Q_i, Q_j shows similar behaviour to the 〈Q_i·Q_j〉     

Beyond leading order QCD perturbative corrections to the pion form factor

The order α_s²(Q²) corrections to the pion form factor, F_π(Q²), are calculated using perturbative quantum chromodynamics and dimensional regularization. In the $\text{MS}$ renormalization scheme these corrections are large. This means that reliable perturbative predictions cannot be made until momentum transfers, Q, of about 300–400 GeV are reached or unless one can sum the large perturbative terms to all orders. Attempts to reorganize the perturbation series so that the first term gives a better approximation of the complete sum indicate that at Q = 10 GeV the pion form factor may be about a factor of two larger than the leading order result.     

Surface charge estimation on hemispherical dielectric samples from EFM force gradient measurements

A numerical model capable of estimating the surface charge density(σ_S) and the dielectric constant(k_e) of a hemispherical sample from force gradient measurements is proposed. Force gradients are commonly detected by a biased conductive tip during electrostatic force microscopy(EFM) probing but provide limited quantitative assessment of the charge in the sample. The proposed model gives an analytical solution for the force exerted over a biased conical tip. Theoretical numerical results, presented in the form of multitraces of minimum force gradients for fixed bias voltages and tip-sample distances allow the translation of EFM force gradient measurements into functions of σ_S and k_e.     

Study of the γD → ppπ− reaction in the Δ(1236) region for well defined kinematical conditions

The γD → ppπ^? reaction cross section, in the Δ(1236) region, is measured in a counter experiment with high statistical accuracy. Particular emphasis is put on the accurate determination of the complete kinematics. For low values of the undetected nucleon momentum (p_r, ≈ 50 MeV/c), the validity of the spectator nucleon model is experimentally checked and the γn → pπ^? elementary reaction cross section is extracted and compared with other experimental data. When the recoiling nucleon momentum increases (p_r ≈ 150 MeV/c), significant departures from the spectator nucleon model are found. Presumably they are the signature of final state interaction effects.     

A signal of a narrowπNN resonance inpp →ppπ − π +

We report on the first exclusive measurement of the 2π production in NN collisions atT _p=750 MeV using a H₂ cluster jet target and the WASA/PROMICE detector at CELSIUS. In the invariant-mass spectrum $M_{pp\pi ^ - } $ we observe a narrow peak at 2.063(2) GeV with a 4σ deviation relative to the MC simulations for the conventional nonresonant 2π production process. The finding is in agreement with the hypothesis of a narrowπNN resonance withI(J^P)=even (0^?), calledd′, postulated recently to describe the peculiar resonance-like behavior of the pionic double charge exchange on nuclei.