The accuracy of comparative estimating

Economic work measurement can now be successfully achieved in many areas by the integrated use of the various systems in the M.T.M. family. A related area is that of comparative estimating in which jobs are allocated by the planner to a time interval and then assigned the single time associated with that interval. This paper examines two different methods of time (distance) interval selection— one from each area, and discusses the implications of these different bases on managerial decision making. It is suggested that in practice comparative estimating may have much to offer, and the paper concludes with comments on planner estimation error, showing that there appears to be a unique best solution for any particular environment, although this may be insensitive near the optimum.     

ROBUST DATA LINK PROTOCOLS FOR CONNECTION-LESS SERVICE OVER SATELLITE LINKS

The performance of the connection-less network service (CLNS) over a satellite link with features such as high propagation delay and a varying (often high) level of errors, can be improved using the connection oriented data link (CODL) service. However, although existing CODL protocols satisfy the requirements of a connection oriented network protocol (e.g. X.25), they are not optimal for the CLNS over satellite links. The interaction of link error recovery procedures with the error recovery procedures implemented by CLNS users, the unnecessary delay due to link protocol sequencing and recovery procedures, and the interaction between applications with different quality of service (QoS) requirements cause most CODL protocols to have a detrimental impact on the performance of the CLNS. This study presents a new link protocol, which improves the quality of the CLNS (e.g. IP), especially considering the enhancement of the performance of connection-oriented transport protocols (e.g. TCP). The performance improvement using the new link protocols is demonstrated by implementation in a satellite interworking unit.     

Hydration of the stratum corneum

Topically applied water, occlusion and topically applied glycerol were used to investigate and characterize some of the changes which occur in the hydrated stratum corneum. The effects of these treatments were monitored using non-invasive techniques under controlled conditions. The Servomed Evaporimeter was used to determine natural water flux from the skin surface before and after treatment. The performance of the Evaporimeter in this type of study had previously been improved by attaching a paper baffle to the detector. This eliminated the variance in output caused by atmospheric movement. Experiments were carried out at temperatures below the threshold of thermal sweating and emotional sweating was minimized. Skin surface topography was characterized by means of a new type of profilometer. The instrument's design allowed a diamond stylus to traverse the living skin surface without significantly altering its structure. Changes in skin surface roughness were further elucidated using scanning electron microscopy and macrophotography. In vivo penetration of glycerol was assessed by chemical analysis of stratum corneum layers of treated skin. Samples were obtained by sequential stripping of the stratum corneum using adhesive tape. Topically applied water produced only a transient benefit because of rapid evaporation. More prolonged hydration was achieved by suppressing transepidermal water loss with polyethylene film. This occlusive hyperhydration was characterized by a significant reduction in profile roughness and by a smoother macroscopic appearance. Glycerol achieved the same effects by reducing the magnitude of the natural water flux from the skin surface and by reducing the rate of evaporation of water from applied aqueous glycerol solution or cosmetic product. Both effects were seen as the result of lowered water activity in the proximity of glycerol. Smoothing effects of glycerol on the skin surface, and improved appearance, persisted for at least 24 h. This persistence was explained by evidence for diffusion of glycerol into the stratum corneum where it formed a reservoir. Hydration of the skin is known to affect its barrier function and thereby exert a profound effect on penetration of both lipophilic and hydrophilic molecules. Clinically, this effect may be achieved using liberal applications of occlusive petroleum jelly and ointments. The results presented in this paper suggest that the use of humectants could achieve useful hydration using cosmetically acceptable materials.