Optimal structural topologies with transmissible loads

In optimal topological design of structures one obtains the configuration of optimal structures when the design domain, the displacement boundary conditions and the applied loads are specified. In the optimal structure one often notices a marked difference between the main bearing structure and the load transfer zones. The latter are composed of relatively light elements the exact nature of which is not always very distinct. The main purpose of this paper is to allow the main bearing part of the structure to emerge. Moreover the actual location of the load along its line of action is not always a design requirement. In order to include this relaxed condition regarding the loading position the concept of transmissible or sliding forces is introduced in topological design of structures. A transmissible force is a force of given magnitude and direction which can be applied at any point along the line of action of the force. The optimization formulation is similar to standard topological design procedure in addition to the condition of transmissability of the forces. It is shown that this condition reduces to an equal displacement constraint along the line of action of the forces. The method is illustrated by typical structural examples. It is observed that this numerical method produces indeed crisp images of the main structural components, unblurred by the secondary load transfer elements. It is also indicated that many results are often replicas of Prager structures which were previously obtained by analytical methods. Received March 3, 1999     

Liposome-cell interaction: transfer and intracellular release of a trapped fluorescent marker

When small, unilamellar lipid vesicles containing a high concentration of the fluorescent dye 6-carboxyfluorescein are incubated with either frog retinas or human lymphocytes, fluroescence distributes widely throughout each cell. Since "self-quenching" largely prevents the dye from fluorescing as long as it remains sequestered in vesicles, it is clear that a considerable amount of dye is released from the vesicles and diluted into the much larger volume of the cell.     

Fibrous myopathy. A rheumatic complication of drug abuse

A progressive fibrous myopathy may result from chronic intramuscular drug abuse. This complication may mimic other rheumatic disorders and early recognition may prevent disability. The patient described here presented with fixed flexion and extension contracture of hips and knees, respectively, after abusing meperidine and other agents for 3 years. Soft tissues of thighs and buttocks were "wood hard," EMG showed absence of action potentials in affected muscles, and biopsy revealed extensive replacement of muscle with dense, acellular fibrous tissue. Possible mechanisms are discussed.     

Application of local variations and maximum sensitivities selection for optimal placement of shunt capacitor banks under nonsinusoidal operating conditions

A new iterative algorithm is proposed for optimal sizing and placement of fixed and switched capacitor banks in radial distribution lines in the presence of linear and nonlinear loads. The method is a combination of maximum sensitivities selection (to improve convergence by selecting candidate buses) and local variations (to improve accuracy in the permissible solution region) and is implemented using the HARMFLOW codes. Objective functions include minimum energy losses, peak losses and capacitor costs while IEEE-519 power quality limits are used as constraints. The 18 bus IEEE distorted system is used to investigate the advantages and limitations of the proposed algorithm and compare its performance with the maximum sensitivities selection (MSS) method. The contributions of the proposed algorithm, as compared to prior publications, are the consideration of harmonic couplings and reactions of actual nonlinear loads, improved convergence and more accurate solutions.     

A data acquisition and image processing system for scanning tunneling microscopy

We have built a dedicated data acquisition and image processing system for scanning tunneling microscopy (STM). Data acquisition is accomplished by a fast 8-bit add-on frame grabber which may be synchronized either to standard TV frequencies or to asynchronous slow scan data sources such as STM or SEM. A 32-bit minicomputer is used for image processing by means of a comprehensive interactive-language which also allows the data acquisition process to be controlled. To speed up time-consuming computations, a floating-point array processor was linked to the system.     

Charging effect in electron-irradiated ice

To maintain the original distribution pattern of diffusible elements in biological samples, electron probe microanalysis is carried out with frozen hydrated bulk specimens and cryosections, analysed at temperatures below 130 K. Ice has a very low intrinsic conductivity at this working temperature and surface- and space-charging appears, when uncoated specimens are irradiated with non-penetrating electrons. Although coating with a grounded conductor abolishes the surface potential, the build-up of an internal space-charge field is possible, depending on the sample thickness and beam voltage used. Consequently, the geometry of the X-ray source volume and the spectral distribution of the emitted continuous and characteristic X-rays are affected. To simulate the situation for microanalysis of frozen hydrated specimens the charging process in electron irradiated ice is studied by recording simultaneous specimen currents from the top and bottom of ice layer preparations. The external currents yield information on the build-up of internal space-charge fields which result from the balance of charge injection, storage, and transport. Irradiation of uncoated bulk specimens with a finely focused beam results in the build-up of a space-charge field close to the surface, which causes a reduction of the depth of microprobe analysis. In coated bulk specimens the induced conductivity renders possible a current flow to the front electrode, thereby limiting the space-charge field. Sections with an effective rear electrode will not charge appreciably if the electron range is larger than about half the section thickness.     

Charge transfer in thin films of donor–acceptor complexes studied by infrared spectroscopy

The degree of charge transfer in thin films of organic charge transfer (CT)-complexes, which are deposited via thermal evaporation, is examined via infrared-spectroscopy. We demonstrate a linear relationship between the shift in the excitation energy of the CN-stretching mode of CT-complexes with the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the charge transfer. The measured correlation corresponds very well with DFT calculations. For Na-TCNQ we observe a splitting in the peak of the CN-stretching mode, which can be explained by the coupling of two modes and was confirmed by the calculations. In CT-complexes with partial charge transfer the appearance of an electronic excitation is demonstrated.