HTSS

The following summary of the essentials of the phenomenon and theory of superconductivity serves to introduce terminology and permits the high transition temperatures (Tc) superconductors (HTSs) to be seen in a historical... 

A significant step in the history of the HTSs was the discovery in 1966 of superconductivity in the oxygen-deficient perovskite SrTi03 5, containing some barium or calcium substituted for strontium. Although the Tc value was very low (0.55 K), in retrospect it can be seen as the first superconducting ceramic. In 1979 a Tc of approximately 13 K was discovered for BaPb075Bi025O3, which also has the perovskite structure. 

Reference to the texts by F.C. Moon [38] and that edited by H. Maeda and K. Togano [39] is recommended. The Proceedings issue [40] covers the present status of the materials, processing and applications and the article by D. Larbalestier et al. [3, pp. 368-77] reviews HTSs for power applications. 

Efforts directed to develop HTSs to commercial products are confined to the RE-123 compounds, where RE = rare earth element, Y, Nd, Sm, etc., and the Bi-based materials. As far as the former type is concerned the discussion is confined to YBCO, the most prominent of the RE-123 family. YBCO has the advantage of a higher Jc value at 77K than the Bi-based materials ( 1010 Am-2 compared to 109 Am-2) although the comparison is not an easy one to make since the values are so dependent on specimen form, doping, applied field, etc. More importantly, the Bi-based powders have a flat, clay-like morphology and this is very significant when it comes to fabrication. In contrast YBCO particles tend to be equiaxed. 

For the reasons summarized below, the coherence length , and irreversibility field Hirr are two parameters of special significance in the processing of HTSs. 

In summary, under the usual operating conditions the ceramic HTSs are characterized by the presence of flux vortices and materials engineers are... 

Leads and fault current-limiters Current leads and fault current-limiters are the first large scale commercial applications of Bi-based HTSs. Current leads significantly improve efficiency of liquid helium-cooled magnets. 

Because the Jc in the a-b plane of Bi-HTSs is several orders of magnitude larger than that in the c-direction, it is necessary to have the latter normal to the lead length. The following tape-casting route is one which was developed to achieve optimum texture. 

Johansen, T.H. (2000) Pinning-induced stress during activation of bulk HTSs as trapped-held magnets, Supercond. Sci. Technol. 13, 830-5. 

Refore. staring the freeze-drying process a production plant htss to be leak-tested as part of (he routine program. A leak (i ) in a vacuum plant is rlcfired as... 

The Hierarchical Tree Substructure Search (HTSS) system [25-27] generates a single rooted decision tree from database structures by gradually refining classification of... 

The HTSS system has been previously used for substructure searches of the Beilstein database on the Orbit online system, but this service was withdrawn in 1992 and replaced by the Dialog online system [28], which allows one to perform substructure searches of the Beilstein database using another substructure search system called S4. 

Hicks MG, Jochum C. Substructure search systems. 1. Performance comparison of the MACCS, DARC, HTSS, CAS Registry, MYSSS, and S4 substructure search systems. J Chem Inf Comput Sci 1990 30 191-199. 

HighTemperature steody state (HTSS) — Pseudo-homogeneous model (PSHM)... 

M. Margules Sitzungsber, Akad. HTss. Wien, Math. Naturwiss. Kl., 104(2)1243 (1895). 

Tarascon et al, 1987). The properties of HTSs cannot be explained by BCS theory currently, there is not even a well-established basis to account for these properties. 

A fifth package in this structure management category, HTSS (LexTex, Inc.), has been recently announced but has not been evaluated. HTSS will be included in later reviews. 

By 1986, when we were ready to buy chemical structure software, there was a number of systems on offer. A year earlier the position might have been very different. The main contenders were MACCS, DARC and OSAC, a program derived from the reaction storage and searching program, ORAC. In addition, HTSS and SABRE were of interest although we had doubts about their state of development at the time. 

A rather different approach to substructure searching is used by at least two systems. One of these is the Chemical Information System (CIS) developed by Richard Feldmann and his colleagues at the National Cancer Institute, and its various off-shoots which include the Chemical Databank System (CDS) at the SERC Laboratory in Daresbury. The other is the Hierarchic Tree Substructure Search (HTSS) developed in Hungary. ... 

HTSS is also rather similar, except that in building the hierarchic tree structure, once all the immediate neighbours for the central atom have been processed, what amounts to a relaxation procedure is applied to extend the tree search file, taking... 

M Z Nagy, S Kozics, T Veszpremi and P Brack HTSS, 1136 Budapest, Balzac u 43, Hungary... 

The HTSS system avoids this problem by making the atom-by-atom search phase unnecessary. 

In the case of the HTSS system the radius of the environment can be selected at the generation of the database, according to the problems to be answered. The usual radius, which can be used for a very broad range of problems, is three, i.e., the effects of the first, second and third neighbours of each and every atom are taken into account. 

In traditional search systems no direct information is available on the relative position of the concentric environments within the molecules. In the HTSS system this additional connectivity information is also taken into account due to the new method of information storage. 

It is obvious that atom-by-atom search is not necessary if an adequately precise description of the environments is used. Therefore the problems and limitations related to atom-by-atom search can be avoided in the HTSS system. 

Since in the decision tree related structures are located in non-distant parts of the tree, the system is well suited to the simultaneous retrieval of a set of similar structures, therefore the HTSS system is able to retrieve very complex Markush queries with good response times. A biographical multiwindow technique has been implemented in the user interface of the HTSS system to enable the easy entry of Markush queries. Functional groups can be defined by the user as special atom types. 

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