W波段带状注速调管准光输出结构改进设计

本文使用等效偶极子理论和相位叠加原理对准光输出结构进行了理论分析, 并在此基础上对准光渐变输出结构进行了一系列的改进设计, 通过对冷腔特性包括特性阻抗、耦合系数、有载Q值、模式分布均匀性等方面的详细研究, 发现抛物线渐变准光输出腔相比于直线渐变、三角形渐变和切比雪夫渐变结构具有更好的冷场性质, 对改善带状注速调放大器的互作用效率和工作带宽有一定的优势. 在此设计基础上加工了5间隙直线渐变结构准光输出耦合器. 关键词： W波段 带状注速调管 准光输出结构     

瓶颈开口角对二维颗粒流的影响

实验研究了平面传送带上颗粒流的特性，主要包括传送带出口处开口宽度以及瓶颈开口角度对颗粒流的影响.实验结果发现，改变瓶颈开口角度θ，当θ大于15°时，颗粒流量Q随着cosθ呈线性变化.同时，颗粒流量Q与传送带速度v以及开口大小R也密切相关，而在θ小于15°时，颗粒流量Q基本不随开口角度变化.     

Measurements of total and positronium-formation cross sections for the scattering of positrons by alkali atoms

We present a review of our recent measurements of total cross sections (Q _T's) for the scattering of positrons by Na, K, and Rb, and positronium-formation cross sections (Q _Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For ourQ _Ps measurements, our approach involves setting upper and lower limits onQ _Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the scattering cell. Comparison with theoretical calculations shows that our measuredQ _T's andQ _Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in then=1 andn=2 states. In the 3–10 eV energy range, this calculation predicts a peak in theQ _T's andQ _Ps's for K which also appears in our measurements. The absence of such a peak in our measuredQ _T's andQ _Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations ofQ _T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and RbQ _T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb.     

Centrifugal distortion effects in the microwave spectra of 1,3-dioxane, tetrahydropyran and piperidine

Applying a bootstrap approach to transition assignment, a first-order centrifugal distortion analysis has been performed on 1,3-dioxane, tetrahydropyran, and piperidine (axial NH conformer). Q-branch transition frequencies for J up to 32 have been combined with previously published or remeasured frequencies for low J, R-, and Q-branch transitions to yield values for the quartic centrifugal distortion parameters. Comparison is made between the results obtained using two forms of the quartic Hamiltonian.     

Measurements of total cross sections for positron-K and-Rb scattering

A modification of the apparatus that we have been using to measure absolute total cross sections (Q _T′s) for positron and electron scattering by alkali metal atoms has enabled us to more easily obtainQ _T′s at low energies (<10 eV). Our positron-K and-RbQ _T measurements now extend from 1 to 98 eV and we have made the correspondingQ _T measurements for electrons in the same system using the same technique (a beam transmission technique). Our measured positron-K and-RbQ _T values show a peak in the vicinity of 6 eV and decrease substantially as the positron energy is reduced below 6 eV, in sharp contrast to the results obtained in recent 5-state close-coupling approximation calculations. At higher energies (above 10 eV), we have found that the same calculations are in quite good agreement with our measured positron-K and-RbQ _T′s. Our measurements of the correspondingQ _T′s for electrons below 10 eV do not show a peak, but rather continue to increase as the energy is decreased.     

Effect of mean-square amplitude of atomic vibrations on the creep behaviour of cubic crystals

Correlation between the activation energyQ of high-temperature creep and the Debye-Waller thermal parameterB, which is proportional to the mean-square amplitude of atomic vibrations, has been examined in the case of 17 faced-centred cubic, body-centred cubic and diamond-structure cubic elements. It is observed thatQ is a function ofB, irrespective of the crystal structure;Q decreases asB increases. The correlation is governed by the power-lawQ=Q ₀(B/B ₀) ^M0 , whereQ ₀=0.095eV andM ₀=−0.62 are numerical constants determined by least-squares fit method, and the constantB ₀=1 nm².     

Measurement of event shapes in deep inelastic scattering at HERA

Inclusive event-shape variables have been measured in the current region of the Breit frame for neutral current deep inelastic ep scattering using an integrated luminosity of collected with the ZEUS detector at HERA. The variables studied included thrust, jet broadening and invariant jet mass. The kinematic range covered was 10 &lt; Q ² &lt; 20 480 GeV ² and , where Q² is the virtuality of the exchanged boson and x is the Bjorken variable. The Q dependence of the shape variables has been used in conjunction with NLO perturbative calculations and the Dokshitzer-Webber non-perturbative corrections (`power corrections') to investigate the validity of this approach. Received: 13 November 2002 / Published online: 7 March 2003     

Q-value for the Fermi beta-decay of <Superscript>46</Superscript>V

By comparing the Q -values for the ⁴⁶Ti ( ³He , t ⁴⁶V and ⁴⁷Ti ( ³He , t ⁴⁷V reactions to the isobaric analogue states the Q -value for the superallowed Fermi decay of ⁴⁶V has been determined as Q _EC( ^46V ) = (7052.11±0.27) keV. The result is compatible with the values from two recent direct mass measurements but is at variance with the previously most precise reaction Q -value. As additional input quantity we have determined the neutron separation energy S _n( ^47Ti ) = (8880.51±0.25) keV.     

Cyclic period-3 window in antiferromagnetic potts and Ising models on recursive lattices

The magnetic properties of the antiferromagnetic Potts model with two-site interaction and the antiferromagnetic Ising model with three-site interaction on recursive lattices have been studied. A cyclic period-3 window has been revealed by the recurrence relation method in the antiferromagnetic Q-state Potts model on the Bethe lattice (at Q < 2) and in the antiferromagnetic Ising model with three-site interaction on the Husimi cactus. The Lyapunov exponents have been calculated, modulated phases and a chaotic regime in the cyclic period-3 window have been found for one-dimensional rational mappings determined the properties of these systems.     

Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders

In future measurements of the dilepton (Z/γ ^∗) transverse momentum, Q _T , at both the Tevatron and LHC, the achievable bin widths and the ultimate precision of the measurements will be limited by experimental resolution rather than by the available event statistics. In a recent paper the variable a _T , which corresponds to the component of Q _T that is transverse to the dilepton thrust axis, has been studied in this regard. In the region, Q _T < 30 GeV, a _T has been shown to be less susceptible to experimental resolution and efficiency effects than the Q _T . Extending over all Q _T , we now demonstrate that dividing a _T (or Q _T ) by the measured dilepton invariant mass further improves the resolution. In addition, we propose a new variable, f_h^*\phi _{\rm \eta }^{*}, that is determined exclusively from the measured lepton directions; this is even more precisely determined experimentally than the above variables and is similarly sensitive to the Q _T . The greater precision achievable using such variables will enable more stringent tests of QCD and tighter constraints on Monte Carlo event generator tunes.     

Extraction of the CKM matrix element V<Subscript>us</Subscript> from the hyperon semileptonic decays

The chiral constituent quark model with configuration mixing ( c \chi CQM _config , which is successful in explaining the weak vector and axial-vector form factors for the strangeness-changing as well as strangeness-nonchanging hyperon semileptonic decays at Q ² = 0 , has been extended to determine the CKM matrix element V _us for the strangeness-changing decays. The implications of the effect of the SU(3) symmetry breaking, Q²-dependence and radiative corrections on the form factors and V _us have also been investigated. It is found that the results with SU(3) symmetry breaking show considerable improvement over the SU(3) symmetric results when compared with the existing experimental data. The inclusion of the Q²-dependence and radiative corrections in form factors have only a small effect on the prediction of V _us as is expected from the theory.     

Polarized Fluorescence of Jet‐Cooled Indole

The polarization of indole fluorescence on excitation in the P, Q, and R branches of a purely electron transition has been investigated. Relations are given to calculate the fluorescence polarization with arbitrary orientation of the dipole moments of transitions with absorption and emission and with excitation in the Q branch of the vibronic line. The coincidence of the measured (7.3%) and calculated (7.7%) values of the polarization degree confirms the reported intramolecular orientation of the dipole moment of transition. The measured fluorescence polarization degree on nonselective excitation is about 3%.     

Peierls Instability for the Holstein Model with Rational Density

We consider the static Holstein model, describing a chain of fermions interacting with a classical phonon field, when the interaction is weak and the density is a rational number p = P/Q, with P, Q relative prime integers. We show that the energy of the system, as a function of the phonon field, has one (if Q is even) or two (if Q is odd) stationary points, defined up to a lattice translation, which are local minima in the space of fields periodic with period equal to the inverse of the density.     

Near-threshold η-meson production in the dd↦He η reaction

The dd↦⁴Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed.     

Measurement of high-Q e<Superscript>-</Superscript>p neutral current cross sections at HERA and the extraction of xF<Subscript>3</Subscript>

Cross sections for e^-p neutral current deep inelastic scattering have been measured at a centre-of-mass energy of 318 GeV using an integrated luminosity of 15.9 pb^-1 collected with the ZEUS detector at HERA. Results on the double-differential cross-section in the range 185 &lt; Q ² &lt; 50 000 GeV² and 0.0037 &lt; x &lt; 0.75, as well as the single-differential cross-sections , and for Q ² &gt; 200 GeV², are presented. To study the effect of Z-boson exchange, has also been measured for Q ² &gt; 10 000 GeV². The structure function xF₃ has been extracted by combining the e^-p results presented here with the recent ZEUS measurements of e⁺p neutral current deep inelastic scattering. All results agree well with the predictions of the Standard Model. Received: 2 August 2002 / Revised version: 30 January 2003 / Published online: 24 March 2003     

The Q-dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron,proton and neutron

The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution to the magnetic moment of the target nucleus with an energy-weighted integral of the difference of the helicity-dependent photoabsorption cross sections. Originally conceived for real photons, the GDH integral can be generalised to the case of photons with virtuality Q². For spin-1/2 targets such as the nucleon, it then represents the non-perturbative limit of the first moment of the spin structure function g ₁ (x,Q ² ) in deep inelastic scattering (DIS). The data collected by HERMES with a deuterium target are presented together with a re-analysis of previous measurements on the proton. This provides an unprecedented and complete measurement of the generalised GDH integral for photon-virtuality ranging over 1.2&lt;Q ² &lt;12.0 GeV² and for photon-nucleon invariant mass squared W² ranging over 1&lt;W ² &lt;45 GeV², thus covering simultaneously the nucleon-resonance and the deep inelastic scattering regions. These data allow the study of the Q²-dependence of the full GDH integral, which is sensitive to both the Q²-evolution of the resonance form factors and contributions of higher twist. The contribution of the nucleon-resonance region is seen to decrease rapidly with increasing Q². The DIS contribution is sizeable over the full measured range, even down to the lowest measured Q². As expected, at higher Q² the data are found to be in agreement with previous measurements of the first moment of g₁. From data on the deuteron and proton, the GDH integral for the neutron has been derived and the proton-neutron difference evaluated. This difference is found to satisfy the fundamental Bjorken sum rule at Q ² = 5 GeV². Received: 20 October 2002 / Published online: 15 January 2003     

Measurements of Optical Trapping Efficiency for Micron-Sized Dielectric Particles in Various Surrounding Media

The maximum axial trapping efficiency Q_max has been measured in water, ethanol, butanol and octanol for polystyrene latex spheres having a diameter of 2–15μm. The effects of the diameter of the particle as well as the refractive index and the viscosity of surrounding medium have been investigated. For particles of d≥7 μm, Q_max is almost independent of particle size, while it decreases as the diameters decrease to d≦5 μm. It is also noted that Q_max is affected by the viscosity rather than the refractive index of the surrounding medium.     

Hund's rules reformulated as inequalities and some related inequalities for exchange integrals,Slater-Condon parameters energy differences and correlation energies

Measurements have been made of the neutron scattering structure factors of liquid nitrogen and liquid oxygen at 77 K and 84 K respectively in the Q-value range of 3 to 36 Å^-1. ‘White’ incident thermal neutrons were produced in the wavelength range of 0·3 to 3·0 Å by a pulsed electron linac and detected in a total-scattering time-of-flight spectrometer. Qualitative agreement has been obtained between these present data and a simple molecular form factor in the Q-value range of 12–36 Å^-1.

Using reactor data [1], structure factors over a total Q-value range of 0·3 to 36 Å^-1 were obtained. Fourier transforms of the structure factor curves yield pair distribution functions which show a distinct separation of the inter and intra-molecular distances in the liquid. A comparison is made with results for the solid phase.     

Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator

Microwave surface resistance (R _s) of silver-doped YBa₂Cu₃O_7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm × 10 mm LaAlO₃ substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwave surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the R _s measurement, that is, the relative change in the Q value with the change in the R _s value is determined for each resonator.