Macroscopic invisibility cloaking of visible light

Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices

The application of dental implants to the cleft palate patients

Many single crystal semiconductors are grown by variants of the Bridgman technique in which a cylindrical ampoule containing a molten semiconductor is translated through a thermal gradient, resulting in directional solidification and the growth of a single crystal. During crystal growth, the shape and location of the solid-liquid interface together with the local temperature gradient control the mechanism of solidification (i.e. planar, cellular or dendritic), the likelihood of secondary grain nucleation/twin formation (i.e. loss of single crystallinity), solute (dopant) segregation, dislocation generation, etc. and thus determine the crystals’ quality [1]. For crystals grown by the vertical Bridgman (VB) technique, optimum properties are obtained with a low (∼1–5mm/hr) constant solidification velocity and a planar or near planar (slightly convex towards liquid) interface shape maintained throughout growth [2,3]. The solidification rate and the interface shape are both sensitive functions of the internal temperature gradient (both axial and radial) during solidification, which is governed by the heat flux distribution incident upon the ampoule, the latent heat release at the interface, and heat transport (by a combination of conduction, buoyancy surface tension driven convection and radiation) within the ampoule [4,5]. The solid-liquid interface’s instantaneous location, velocity and shape during crystal growth are therefore difficult to predict and to control, especially for those semiconductor materials with low thermal conductivity (i.e. CdZnTe alloys) [6]. Thus the development of ultrasonic technologies to non-invasively sense the interface location and shape throughout VB crystal growth processes has become a key step in developing a better understanding of the growth process and for enabling eventual sensor-based manufacturing

Leadership: Current Theories, Research, and Future Directions

This review examines recent theoretical and empirical developments in the leadership literature, beginning with topics that are currently receiving attention in terms of research, theory, and practice. We begin by examining authentic leadership and its development, followed by work that takes a cognitive science approach. We then examine new-genre leadership theories, complexity leadership, and leadership that is shared, collective, or distributed. We examine the role of relationships through our review of leader member exchange and the emerging work on followership. Finally, we examine work that has been done on substitutes for leadership, servant leadership, spirituality and leadership, cross-cultural leadership, and e-leadership. This structure has the benefit of creating a future focus as well as providing an interesting way to examine the development of the field. Each section ends with an identification of issues to be addressed in the future, in addition to the overall integration of the literature we provide at the end of the article

Leadership as purpose: Exploring the role of purpose in leadership practice

This article initiates a long overdue discussion regarding purpose within leadership, an integral yet often taken-for-granted and subsumed function of leadership. Specifically, the article problematicizes the manifestation of purpose in everyday organizational leadership practices through the work of the moral philosopher Alasdair MacIntyre. The article argues that purpose requires greater attention if it is to become manifest in both the corporate and the societal orientations of leaders in organizations. In support of this argument we identify the implications of singularly focusing upon corporate purpose to the exclusion of societal purpose against the backdrop of the credit crunch aftermath. The article develops a theoretical argument that, when conceptualized as a process of sensemaking, leadership can provide an opportunity for notions of societal purpose to come to the fore in countervailing balance with corporate purposes. We conclude by suggesting a research agenda centred on further explicating and developing the idea of leadership as purpose