Hadron-nucleon Total Cross Section Fluctuations from Hadron-nucleus Total Cross Sections

The extent to which information about fluctuations in hadron-nucleon total cross sections in the frozen approximation can be extracted from very high energy hadron-nucleus total cross section measurements for a range of heavy nuclei is discussed. The corrections to the predictions of Glauber theory due to these fluctuations are calculated for several models for the distribution functions, and differences of the order of 50 mb are found for heavy nuclei. The generating function for the moments of the hadron-nucleon cross section distributions can be approximately determined from the derivatives of the hadron-nucleus total cross sections with respect to the nuclear geometric cross section. The argument of the generating function, however, it limited to the maximum value of a dimensionless thickness function obtained at zero impact parameter for the heaviest nuclear targets: about 1.8 for pions and 3.0 for nucleons.Comment: 14 pages, revtex 3.0, 4 figures available upon reques

Nonperturbative Effects in Gluon Radiation and Photoproduction of Quark Pairs

We introduce a nonperturbative interaction for light-cone fluctuations containing quarks and gluons. The $\bar qq$ interaction squeezes the transverse size of these fluctuations in the photon and one does not need to simulate this effect via effective quark masses. The strength of this interaction is fixed by data. Data on diffractive dissociation of hadrons and photons show that the nonperturbative interaction of gluons is much stronger. We fix the parameters for the nonperturbative quark-gluon interaction by data for diffractive dissociation to large masses (triple-Pomeron regime). This allows us to predict nuclear shadowing for gluons which turns out to be not as strong as perturbative QCD predicts. We expect a delayed onset of gluon shadowing at $x \leq 10^{-2}$ shadowing of quarks. Gluon shadowing turns out to be nearly scale invariant up to virtualities $Q^2\sim 4 GeV^2$ due to presence of a semihard scale characterizing the strong nonperturbative interaction of gluons. We use the same concept to improve our description of gluon bremsstrahlung which is related to the distribution function for a quark-gluon fluctuation and the interaction cross section of a $\bar qqG$ fluctuation with a nucleon. We expect the nonperturbative interaction to suppress dramatically the gluon radiation at small transverse momenta compared to perturbative calculations.Comment: 58 pages of Latex including 11 figures. Shadowing for soft gluons and Fig. 6 are added as well as a few reference

Color Transparency versus Quantum Coherence in Electroproduction of Vector Mesons off Nuclei

So far no theoretical tool for the comprehensive description of exclusive electroproduction of vector mesons off nuclei at medium energies has been developed. We suggest a light-cone QCD formalism which is valid at any energy and incorporates formation effects (color transparency), the coherence length and the gluon shadowing. At medium energies color transparency (CT) and the onset of coherence length (CL) effects are not easily separated. Indeed, although nuclear transparency measured by the HERMES experiment rises with Q^2, it agrees with predictions of the vector dominance model (VDM) without any CT effects. Our new results and observations are: (i) the good agreement with the VDM found earlier is accidental and related to the specific correlation between Q^2 and CL for HERMES kinematics; (ii) CT effects are much larger than have been estimated earlier within the two channel approximation. They are even stronger at low than at high energies and can be easily identified by HERMES or at JLab; (iii) gluon shadowing which is important at high energies is calculated and included; (iv) our parameter-free calculations explain well available data for variation of nuclear transparency with virtuality and energy of the photon; (v) predictions for electroproduction of \rho and \phi are provided for future measurements at HERMES and JLab.Comment: Latex 57 pages and 17 figure

Study of touchless sensors for the measurement of control surface positions onboard an aircraft

The Flight Test Instrumentation branch of the Institute of Flight Mechanics at the DLR Braunschweig has been involved in the development of instrumentation and data acquisition systems of several aircraft and helicopters. The data acquired during the flight tests have been very gainfully used to analyse the performance of the aircraft and helicopters. One of the problems faced by the engineers has been in the measurement of the positions of various control surfaces of a non-instrumented aircraft. This is because of the problems in installing the potentiometric sensors and its subsequent calibration. The installation requires the dismantling of all control surfaces, fabrication of proper fixtures for mounting the potentiometers and reassembly of the surfaces. The potentiometric sensors require frequent replacements and recalibration due to a number of factors such as wear and tear, noise due to the improper positioning of wiper arm and vibration. These drawbacks provided the much needed impetus to search for alternative solutions to overcome the above problems. The objective of the present work was to make a study of various techniques that are currently being used for position measurement and to identify methods or sensors that would suit touchless measurement of control surface positions onboard an aircraft. This report discusses the existing techniques in brief and identifies some new techniques for measurement of the position of control surfaces such as ailerons, flaps, rudder and elevator. The measuring ranges of these types of instruments vary from less than a millimeter to several hundreds of mm for linear displacement and from less than 1 degree to about 350 for angular measurements. An alternative to the potentiometers could be the non-contact type of sensors using the variation in capacitance and inductance due to displacement. These type of sensors are being extensively used in aerospace applications because of their performance. The main advantages of the non-contact sensors are that they are free from any physical contact with the measured and also do not load the structure. A significant amount of work has been done at various locations in research and development of techniques for non contact distance gauging though not necessarily for aeronautical applications. Optical, acoustic, X-rays and magnetic sensors have been considered. (orig./AKF)SIGLEAvailable from TIB Hannover: RN 4165(1994,45) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman