TO overcome the discomfort, nerve strain and fatigue to both passengers and crew on multi‐engined aircraft resulting from the noise and vibrations of engines running at slightly varying speeds, the need of an accurate, easily read indication of such variations is readily apparent. A direct comparison of r.p.m. indicators is ineffective because the permissible tolerance on each indicator might result in a total difference of the order of 50 r.p.m. even though the speed of the engines under comparison is the same. The development of the 3‐phase electric tachometer indicators overcame this difficulty by comparing the relative frequencies of two or more tachometer generators (not the voltages), before this has been translated into an indicated r.p.m., by means of a small synchronous motor operating a magnetic drag unit; the desired result is obtained even though the possibility of permissible errors in a yet serviceable indicator has not been obviated. These two frequencies arc used to operate what is, in reality, a beat‐frequency indicator with a pointer rotating in proportion to the difference in speed. As the difference in speed of the two engines results in a difference in the frequencies developed by the two tachometer generators, so the pointer of the synchroscope will rotate either clockwise or anti‐clockwise according to which engine is running faster. When both engines are running at the same speed the frequencies will be alike and the pointer will remain stationary. Any difference in voltage output of the two generators will not affect this final indication, but will have some bearing on the speed difference at which the pointer begins to rotate where this rate of rotation is directly proportionate to the difference in engine speed. However, as a large variation between engine speeds will not cause any pointer rotation at all, but merely be shown as a flickering of the pointer, this is of no material importance.
The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions…
The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones.
Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are “stacked” inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone.
The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing.
This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate.
The study here responds to the view that the crucial problem in strategic management (research) is firm heterogeneity – why firms adopt different strategies and…
The study here responds to the view that the crucial problem in strategic management (research) is firm heterogeneity – why firms adopt different strategies and structures, why heterogeneity persists, and why competitors perform differently. The present study applies complexity theory tenets and a “neo-configurational perspective” of Misangyi et al. (2016) in proposing complex antecedent conditions affecting complex outcome conditions. Rather than examining variable directional relationships using null hypotheses statistical tests, the study examines case-based conditions using somewhat precise outcome tests (SPOT). The complex outcome conditions include firms with high financial performances in declining markets and firms with low financial performances in growing markets – the study focuses on seemingly paradoxical outcomes. The study here examines firm strategies and outcomes for separate samples of cross-sectional data of manufacturing firms with headquarters in one of two nations: Finland (n = 820) and Hungary (n = 300). The study includes examining the predictive validities of the models. The study contributes conceptual advances of complex firm orientation configurations and complex firm performance capabilities configurations as mediating conditions between firmographics, firm resources, and the two final complex outcome conditions (high performance in declining markets and low performance in growing markets). The study contributes by showing how fuzzy-logic computing with words (Zadeh, 1966) advances strategic management research toward achieving requisite variety to overcome the theory-analytic mismatch pervasive currently in the discipline (Fiss, 2007, 2011) – thus, this study is a useful step toward solving the crucial problem of how to explain firm heterogeneity.
Possible reasons for using kites to kill gazelles are comprehensively reviewed in this article. Even though they are now well inventoried and documented, desert kites are…
Possible reasons for using kites to kill gazelles are comprehensively reviewed in this article. Even though they are now well inventoried and documented, desert kites are still not well understood, as exemplified by the recurrent controversies about their function and dating. According to the dominant view, kites were hunting structures used to drive and to mass kill large herds of wild ungulates, particularly gazelles. Although kites were intensively used during the Early Bronze Age, some of them could have been built and used before that. Beyond these issues, the cultural and socioeconomic aspects of the kites phenomenon are even less understood, and therefore, we focus on changing reasons for the long-lasting use of kites as hunting devices. We contend that the reasons why they were used during the period of utilization for hunting gazelles changed, in most cases, in response to socioeconomic development. It is hypothesized, for example, that, as a result of urban development, kites may have been increasingly (but not exclusively) used to kill gazelles to trade their products with urban communities and farmers, even though they had other uses as well which are also considered. The main hypothesis presented in this article enables diverse opinions about the types of uses and reasons for utilizing desert kites to be reconciled, including in particular varied reasons given in the literature about why they were used for killing gazelles.
EACH September the eyes of the aeronautical World turn towards the S.B.A.C. Air Display and Exhibition with interest unequalled by any other event. It is fitting that the…
EACH September the eyes of the aeronautical World turn towards the S.B.A.C. Air Display and Exhibition with interest unequalled by any other event. It is fitting that the Display is now held each year at the airfield of the Royal Aircraft Establishment, one of the world's most prominent aeronautical research centres. This interest becomes increasingly keen too, as the preview day comes closer, because new prototypes of unorthodox designs often appear a short time before the Show to illustrate the results of years of careful planning, development and research of the particular company. These designs often mould the path of progress for smaller countries without the economic resources to forge the way ahead alone. Most British citizens are very proud of their country's place in aviation today, both in the military and civil fields. This is understood by most foreigners because it is clear that Britain has won a place in aeronautical development second to none.