Direct object-shape comparison by light-in-flight speckle interferometry

A method is proposed for direct optical comparison of the three-dimensional shapes of objects by light-in-flight speckle holography. The basic idea of this technique is to use an ultrashort laser pulse with a short coherence length to produce interference patterns that present a single contouring of the object. A simple experiment using plane diffuse objects was performed to verify the method.     

Selective removal of enzymes from substrate and products. An alternative to immobilization for enzymes acting on macromolecular or solid substrates

A new approach for the control and interruption of enzymatic reactions via selective enzyme immobilization has been developed. The technique was exemplified by the use of three model enzymes with the corresponding macromolecular substrates: α-amylase/starch, trypsin/ insoluble collagen, and alkaline phosphatase/plasmid DNA. Prior to incubation with its substrate, each enzyme was provided withde novo thiol-groups by a two-step reaction involvingN-succinimidyl-3-(2-pyridyldithio) propionate (SPDP) and DTT. The chemical modification was achieved such that at least 80% of the native enzyme activity was preserved in all cases. In order to interrupt rapidly the reactions in which the enzymes were used, the modified enzyme was immobilized by reaction via its thiol groups on a thiolsulfinate-agarose derivative. The gel-bound enzyme could then be easily removed from unreacted substrate and product by filtration or centrifugation. Comparative studies showed that the immobilized enzymes had much lower activities in the reactions studied than the corresponding soluble ones. The potential for enzyme reuse was also demonstrated with the a-amylase derivatives, which were quantitatively released and eluted in fully active form from the agarose. We have shown that it is possible to achieve practically complete enzyme immobilization in short times and thus to control the progress of the reactions. Because of its simplicity and high efficiency, this approach may represent an interesting alternative for biotechnological processes involving macromolecular or solid substrates.     

Total Synthesis of Sialylgalactosylgloboside: Stage-Specific Embryonic Antigen 4

A versatile total synthesis of sialylgalactosylgloboside (SGG, 1), carrying the stage-specific embryonic antigen 4 (SSEA-4) is reported, illustrating a more general strategy for the synthesis of complex globo-series glycosphingolipids. Starting from readily available building blocks 7, 8, and 10, two different approaches to the synthesis of the key tetrasaccharide 6 have been developed in a highly convergent manner. Further glycosylations with galactosyl trichloroacetimidate (5) and sialyl phosphite (2) donors successively afforded the penta- and hexasaccharides 3 and 11. The latter was finally converted into the target molecule (SGG, 1) with the help of a azidosphingosine glycosylation procedure, favored in this case by the stereocontrolling properties of the 2a-O-pivaloyl protecting group. Valuable intermediates 6 and 3, having the oligosaccharidic skeletons of Gb(4) and Gb(5) (SSEA-3), respectively, were obtained in the course of the synthesis.     

Interaction between ethyl(hydroxyethyl)cellulose and sodium dodecyl sulphate in aqueous solution

Using sodium activity, viscosity, and cloudpoint measurements, it has been shown that sodium dodecyl sulphate (SDS) binds to ethyl(hydroxyethyl)cellulose in a cooperative manner. In the absence of salt the binding leads to an increase in the clouding temperature, but when a small amount of salt (0.01 molal) is present first a drastic decrease and then an equally drastic increase in the cloud point temperature is observed. The binding of SDS also initially leads to an increase in viscosity followed by a decreased viscosity at higher SDS concentrations. A molecular mechanism explaining the observed behavior is given.     

Metallic stripe in two dimensions: stability and spin-charge separation

The problems of charge stripe formation, spin-charge separation, and stability of the antiphase domain wall (ADW) associated with a stripe are addressed using an analytical approach to the t- J(z) model. We show that a metallic stripe together with its ADW is the ground state of the problem in the low doping regime. The stripe is described as a system of spinons and magnetically confined holons strongly coupled to the two dimensional spin environment with holon-spin-polaron elementary excitations filling a one-dimensional band.     

The mechanical point impedance of the human head, with and without skin penetration

The fact that a titanium screw can be implanted into the mastoid portion of the human skull, at the same time establishing a permanent, reaction-free skin penetration, has made it possible to attach a new bone conduction hearing aid directly to the skull. To understand and improve this new method of bone stimulation, the mechanical point impedance of the titanium screw-skull system was measured. The conventional point impedance of the skin-covered mastoid portion of the temporal bone was also measured and the difference in magnitude between the two impedances was calculated. An impedance head (Brüel & Kjaer 8001) and an FFT analyzer (Hewlett-Packard 5423) were used for mechanical point impedance measurements. Seven patients have been investigated. The magnitude of the impedance for the screw-skull system was found to be generally between 10 and 30 dB higher than that for the conventional skin-covered mastoid bone. One conclusion is that the conventional point impedance of the skin-covered mastoid portion of the human skull is essentially due to the properties of the skin and subcutaneous soft tissue. Another conclusion is that a much lower stimulation velocity is needed, with skin penetration, to produce a given hearing sensation.     

Flow analysis based on a pulsed flow of solution: theory, instrumentation and applications

The increased demands placed on solution propulsion by programmed flow systems, such as sequential injection analysis, lab-on-value technology, bead injection and multi-commutation, has highlighted the inability of many conventional pumps to generate a smooth, consistent flow. A number of researchers have examined ways to overcome the inadvertent, uncontrolled pulsation caused by the mechanical aciton of peristaltic pumps. In contrast, we have developed instruments that exploit the characteristics of a reproducible pulsed flow of solution. In this paper, we discuss our instrumental approaches and some applications that have benefited from the use of a reproducible pulsed flow rather than the traditional linear flow approach. To place our approach in the context of the continuously developing field of flow analysis, an overview of other programmed flow systems is also presented.