Effectiveness evaluation of STOL transport operations (phase 2)

A computer simulation program which models a commercial short-haul aircraft operating in the civil air system was developed. The purpose of the program is to evaluate the effect of a given aircraft avionics capability on the ability of the aircraft to perform on-time carrier operations. The program outputs consist primarily of those quantities which can be used to determine direct operating costs. These include: (1) schedule reliability or delays, (2) repairs/replacements, (3) fuel consumption, and (4) cancellations. More comprehensive models of the terminal area environment were added and a simulation of an existing airline operation was conducted to obtain a form of model verification. The capability of the program to provide comparative results (sensitivity analysis) was then demonstrated by modifying the aircraft avionics capability for additional computer simulations

Quantitative analysis of nip-induced tension by use of digital image processing

Winding paper in contact with a drum leads to the production of nip-induced tension which, to a high degree, influences the structure of the roll. Thus, comprehending the processes in the nip, including each parameter involved, is desirable to avoid roll defects.This paper deals with a new measurement technique that is able to observe the process of building up nip-induced tension in the outer layers of a roll. With the use of digital image processing, this method ensures the registration of the two-dimensional displacement field of the outer layers with fairly high precision. Based on the first principal of the equations of mechanics, it is possible to derive the stress and strain in the layers from the displacement field. Thus, it succeeds to calculate the tangential stress in the outer layers of a roll taking the compression as well as the slippage of the layers into account.In all experimental test series the tangential stress increases within the first 4 to 15 layers to a maximum value. Afterwards, there is still a considerable displacement of the layers relative to the core, but the layer-to-layer slippage is so small that the change in strain is negligible. Furthermore, it is shown that there is a reduced increase of nip-induced tension in the first approximate 50 layers near the core. Comparing the nip-induced displacement of different type of papers, there are clearly differences noticeable concerning the amount of displacement, as well as the rapidness of increase to the final displacement

Supercooling across first-order phase transitions in vortex matter

Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature T or magnetic field H (and thus the density of vortices). Our recent work on phase transitions with two control variables shows that the observable region of metastability of the supercooled phase would depend on the path followed in H-T space, and will be larger when T is lowered at constant H compared to the case when H is lowered at constant T. We discuss the effect of isothermal field variations on metastable supercooled states produced by field-cooling. This path dependence is not a priori applicable to metastability caused by reduced diffusivity or hindered kinetics.Comment: Tex, 8 pages, 3 Postscripts figures. Submitted to Pramana - J. Physic

Analysis of the kinematic and dynamic process during winding based on a systematology of models for winding mechanics

The winding process of web materials with low bending resistance is composed of several partial processes whose single effects are influenced by specific machine, process and material parameters. The interaction of these processes causes an essential increase in the difficulty of modeling the total process. Up to now there are numerous mainly experimental investigations concerning the particular effects of the winding process. But they are not sufficient to describe the total process regarding all influences of the machine technology and material properties.In this regard our institute has developed a systematology of models for winding mechanics which starts with the real winding process of the different winder classifications and resolves the complex total process step by step into partial models. Subsequently it is possible to study the effect of different parameters on the derived partial models based on various degrees of idealisation. By coupling different partial models the modelling of any partial process becomes possible.The fundamental knowledge of theoretical research work is the mechanic of solid bodies with its analytical methods for highly idealized [simple] models and numerical methods (finite elemente-method (FEM), finite-difference-method (FDM)) for complex, more realistic models

Vortex fluctuations in superconducting La-Sr-Cu-O

Vortex fluctuations in the $La_{2-x}Sr_{x}CuO_{4+\delta}$ system have been studied as a function of magnetic field, temperature and carrier concentration in order to determine the dimensionality of the fluctuations. For a $x=0.10$ sample, there is a unique crossing-temperature on the magnetization vs. temperature plots for all magnetic fields up to 7 T, and the data scale very well with 2D fluctuation theory. At lower x-values where $H_{c2}$ is much smaller, there are two well defined crossing points, one at low fields (typically less than 1 T) and another at high fields (typically 3-7 T). A fit of the data to fluctuation theory shows that the low field crossing data scale as 2D fluctuations and the high field crossing data scale as 3D fluctuations. It would appear that as the magnetic field approaches $H_{c2}$, there is a 2D to 3D cross-over where the low field 2D pancake vortex structure transforms into a 3D vortex structure

Surface plasmons at single nanoholes in Au-films

The generation of surface plasmon polaritons (SPP's) at isolated nanoholes in 100 nm thick Au films is studied using near-field scanning optical microscopy (NSOM). Finite-difference time-domain calculations, some explicitly including a model of the NSOM tip, are used to interpret the results. We find the holes act as point-like sources of SPP's and demonstrate that interference between SPP's and a directly transmitted wave allows for determination of the wavelength, phase, and decay length of the SPP. The near-field intensity patterns can be manipulated by varying the angle and polarization of the incident beam.Comment: 12 pages, 3 figure

Vortex Plastic Motion in Twinned Superconductors

We present simulations, without electrodynamical assumptions, of $B(x,y,H(t)), M(H(t))$, and $J_c(H(t))$, in hard superconductors, for a variety of twin-boundary pinning potential parameters, and for a range of values of the density and strength of the pinning sites. We numerically solve the overdamped equations of motion of up to 10^4 flux-gradient-driven vortices which can be temporarily trapped at $\sim 10^6$ pinning centers. These simulations relate macroscopic measurements (e.g., M(H), ``flame'' shaped $B(x,y)$ profiles) with the underlying microscopic pinning landscape and the plastic dynamics of individual vortices