The prospect of building a future energy system on hydrogen has stimulated much research effort in developing hydrogen storage technologies. One of the potential materials newly developed is sodium amidoborane (NaNH 2 BH 3 ) which evolves $7.5 wt% hydrogen at temperatures as low as 91 C. In this paper, two methods of synthesizing pure NaNH 2 BH 3 were reported. One method is by reacting NaH and ammonia borane in THF at low temperatures, and the other is by reacting NaNH 2 and ammonia borane in THF at ambient temperature. Non-isothermal testing on the thermolysis of solid NaNH 2 BH 3 showed that hydrogen evolution was composed of two exothermic steps. More than 1 equiv. H 2 was evolved rapidly at temperatures below 87 C. After evolving 2 equiv. H 2 , NaH was identified in solid products and coexisted with amorphous BN.
The overwhelmingly homochiral nature of life has left a puzzle as to whether mirror-image biological systems based on a chirally inverted version of molecular machinery could also have existed. Here we report that two key steps in the central dogma of molecular biology, the template-directed polymerization of DNA and transcription into RNA, can be catalysed by a chemically synthesized D-amino acid polymerase on an L-DNA template. We also show that two chirally mirrored versions of the 174-residue African swine fever virus polymerase X could operate in a racemic mixture without significant enantiomeric cross-inhibition to the activity of each other. Furthermore, we demonstrate that a functionally active L-DNAzyme could be enzymatically produced using the D-amino acid polymerase. The establishment of such molecular systems with an opposite handedness highlights the potential to exploit enzymatically produced mirror-image biomolecules as research and therapeutic tools.
Immersion, interaction, and imagination are three features of virtual reality (VR). Existing VR systems possess fairly realistic visual and auditory feedbacks, and however, are poor with haptic feedback, by means of which human can perceive the physical world via abundant haptic properties. Haptic display is an interface aiming to enable bilateral signal communications between human and computer, and thus to greatly enhance the immersion and interaction of VR systems. This paper surveys the paradigm shift of haptic display occurred in the past 30 years, which is classified into three stages, including desktop haptics, surface haptics, and wearable haptics. The driving forces, key technologies and typical applications in each stage are critically reviewed. Toward the future high-fidelity VR interaction, research challenges are highlighted concerning handheld haptic device, multimodal haptic device, and high fidelity haptic rendering. In the end, the importance of understanding human haptic perception for designing effective haptic devices is addressed. IntroductionIn 1965, Ivan Sutherland proposed the concept "the ultimate display", which represents the birth of virtual reality (VR) [1] . In his seminal work, he introduced three features of VR: immersion, interaction, and imagination. In past 50 years, thanks to the research in computer graphics and sound synthesis, existing VR systems possess fairly realistic visual and auditory feedback. However, haptic feedback is far from user's perceptual expectations. The experiences of haptic sensation in most VR systems are rather poor compared to the abundant haptic properties that human can perceive in the physical world.Haptic feedback is indispensable for enhancing immersion, interaction, and imagination of VR systems.Interaction can be enhanced by haptic feedback as users can directly manipulate virtual objects, and obtain ·Review· Dangxiao WANG et al: Haptic display for virtual reality: progress and challenges immediate haptic feedback. Immersion of the VR system can be enhanced in terms of providing more realistic sensation to mimic the physical interaction process. Imagination of users can be inspired when haptics can provide more cues for user to mentally construct an imagined virtual world beyond spatial and/ or temporal limitations.The haptic sensation obtained through virtual interaction is severely poor compared to the sensation obtained through physical interaction. In our physical life, the haptic channel is pervasively used, such as perception of stiffness, roughness and temperature of the objects in external world, or manipulation of these objects and motion or force control tasks such as grasping, touching or walking etc. In contrary, in virtual world, haptic experiences are fairly poor in both quantity and quality. Most commercial VR games and movies only provide visual and auditory feedbacks, and a few of them provide simple haptic feedback such as vibrations. With the booming of VR in many areas such as medical simulation and product design, there is a...
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