A precision machine for mounting tissue for Mohs micrographic surgery

BACKGROUND: Mounting specimens onto chucks, so the cryostat knife follows the exact path of the surgeon's knife, poses difficulties even for experienced histotechnologists. Oftentimes, the frozen planar surface of the tissue falls at an angle that requires gimballing the chuck holder to compensate. OBJECTIVE: To demonstrate the use of a precision tissue mounting machine and associated fast freezing chucks. METHODS: Specimens of pickled pig skin were marked with blue dye on the cut surface. The pieces were mounted onto chucks with the blue surface exposed, and then sectioned in a cryostat. RESULTS: A complete section with all edges was obtained after eight turns of the cryostat handwheel, at 12 microns per turn. CONCLUSIONS: A precision machine used in conjunction with a properly adjusted chuck holder can yield results unobtainable by other methods.     

Alternative software architectures for parallel protocol executionwith synchronous IPC

The use of parallelism in enhancing protocol execution performance is examined. In particular the use of a separate concurrent task for each protocol layer is discussed. Two layers of the OSI protocol system were implemented and run on a multiprocessor, with from one to five processors at each end of the connection. Potentially concurrent entities included user tasks as data source and sink, the OSI session layer (kernel functional unit only), the OSI transport layer (classes 0 and 2), vestigial network tasks, and tasks to buffer data between layers. Three substantially different design architectures with from nine to twelve tasks at each end of the connection were compared. The design differences centered on different ways to provide interlayer coordination and buffering; the protocol code was kept identical. The implementation used a real-time kernel which provides synchronous (request-reply) interprocess communication. The variation in throughput between designs covered a range of approximately two to one. The best design is found to be symmetrical decentralized two-way pipeline with courier communications     

Interruptibility as a constraint on hybrid systems

It is widely mooted that a plausible computational cognitive model should involve both symbolic and connectionist components. However, sound principles for combining these components within a hybrid system are currently lacking; the design of such systems is oftenad hoc. In an attempt to ameliorate this we provide a framework of types of hybrid systems and constraints therein, within which to explore the issues. In particular, we suggest the use of system independent constraints, whose source lies in general considerations about cognitive systems, rather than in particular technological or task-based considerations. We illustrate this through a detailed examination of an interruptibility constraint: handling interruptions is a fundamental facet of cognition in a dynamic world. Aspects of interruptions are delineated, as are their precise expression in symbolic and connectionist systems. We illustrate the interaction of the various constraints from interruptibility in the different types of hybrid systems. The picture that emerges of the relationship between the connectionist and the symbolic within a hybrid system provides for sufficient flexibility and complexity to suggest interesting general implications for cognition, thus vindicating the utility of the framework.     

Universality in ant behaviour

Prediction for social systems is a major challenge. Universality at the social level has inspired a unified theory for urban living but individual variation makes predicting relationships within societies difficult. Here, we show that in ant societies individual average speed is higher when event duration is longer. Expressed as a single scaling function, this relationship is universal because for any event duration an ant, on average, moves at the corresponding average speed except for a short acceleration and deceleration at the beginning and end. This establishes cause and effect within a social system and may inform engineering and control of artificial ones.     

Colloidal Processing of Zirconium Diboride Ultra‐High Temperature Ceramics

Colloidal processing of the Ultra‐High Temperature Ceramic (UHTC) zirconium diboride (ZrB₂) to develop near?net‐shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB₂ suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex‐shaped components that can be densified at lower sintering temperatures without pressure.     

An electroanalytical study of the composition of molten sodium metaphosphate

Phosphate glasses are known to be mixtures of chain phosphates. The presence of the lower polymers has been confirmed by electrochemical techniques and the proportions of the orthophosphate monomer in sodium metaphosphate melts have been estimated at temperatures between 660–810°C. The orthophosphate had not been detected in phosphate glasses using paper chromatography, but it is considered that quenching tends to increase polymerization and thus causes loss of the monomer.     

Effect of particle size on the shaping of ceramics by slip casting

The effect of the nanometric-ranged particle size of the starting powder through a simple and well-established shaping method, slip casting, has been studied. Several alumina suspensions with the same viscosity (but different solid content suspensions) and different particle size (11, 44, 190 and 600 nm) were prepared and shaped into a dense body. The green and sintered densities ranged between 30–67% and 63–99% of the theoretical value, respectively. These values, together with the microstructure observations reveal the effect of the solid content of the suspensions and the characteristics of the ceramic powder, leading to the determination of an optimal particle size. Based on both processability (rheological behaviour) and microstructure (density and grain size) it has been determined that particles with sizes ranging 100–300 nm are the best for preparing concentrated suspensions with low viscosity and bodies with density close to the theoretical value when using conventional pressureless sintering densification.