133,030 research outputs found
Absorbing new subjects: holography as an analog of photography
No full textI discuss the early history of holography and explore how perceptions, applications, and forecasts of the subject were shaped by prior experience. I focus on the work of Dennis Gabor (1900–1979) in England,Yury N. Denisyuk (b. 1924) in the Soviet Union, and Emmett N. Leith (1927–2005) and Juris Upatnieks (b. 1936) in the United States. I show that the evolution of holography was simultaneously promoted and constrained by its identification as an analog of photography, an association that influenced its assessment by successive audiences of practitioners, entrepreneurs, and consumers. One consequence is that holography can be seen as an example of a modern technical subject that has been shaped by cultural influences more powerfully than generally appreciated.
Conversely, the understanding of this new science and technology in terms of an older one helps
to explain why the cultural effects of holography have been more muted than anticipated by forecasters
between the 1960s and 1990s
The castellated architecture of Aberdeenshire
No full textby Sir Andrew Leith Hay of RannesHandschriftliches Exlibris: "Captain G. S. Bell 3rd Gordon Highlanders Balnagask 1918" 990040392790205503_0001 Exemplar der ETH-BI
Learning-Based Constraint Satisfaction With Sensing Restrictions
No full textIn this paper we consider graph-coloring problems, an important subset
of general constraint satisfaction problems that arise in wireless resource
allocation. We constructively establish the existence of fully decentralized
learning-based algorithms that are able to find a proper coloring
even in the presence of strong sensing restrictions, in particular sensing
asymmetry of the type encountered when hidden terminals are present.
Our main analytic contribution is to establish sufficient conditions on the
sensing behaviour to ensure that the solvers find satisfying assignments
with probability one. These conditions take the form of connectivity requirements
on the induced sensing graph. These requirements are mild,
and we demonstrate that they are commonly satisfied in wireless allocation
tasks. We argue that our results are of considerable practical importance
in view of the prevalence of both communication and sensing restrictions
in wireless resource allocation problems. The class of algorithms analysed
here requires no message-passing whatsoever between wireless devices,
and we show that they continue to perform well even when devices are
only able to carry out constrained sensing of the surrounding radio environment
Low-Delay Proportional Fair Rate Allocation for 802.11ac WLAN Downlink
No full textIn this paper we consider a next generation edge architecture where traffic is routed via a proxy located close to the network edge (e.g. within a cloudlet). This creates freedom to implement new transport layer behaviour over the wireless path between proxy and clients. We use this freedom to develop a novel approach to achieving high rate, low latency communication on the downlink. This works by adjusting the send rates to clients so as to regulate the aggregation level of transmitted frames which in turn robustly regulates the queueing delay at the AP. We derive the low-delay proportional fair rate allocation in the presence of aggregation and using this consider primal-dual and PI controller approaches for achieving the low-delay proportional fair rate allocation. We find that the primal-dual approach is fragile in the sense that it is sensitive to modelling errors, and in contrast the PI controller approach is much more robust. We present numerical simulation results evaluating the performance
Fair virtualization of 802.11 networks
No full textWe consider virtualization of network capacity in 802.11 WLANs and mesh networks. We show that allocating total airtime slices to ISPs is analogous to allocating a fraction of available time-slots in TDMA. We establish that the max-min fair flow rate allocation within an ISP airtime slice can be characterized independently of the rate allocation policy employed in other slices. Building on these observations, we present a lightweight, distributed algorithm for allocating airtime slices among ISP and max-min fair flow rates within each slice
Low-delay high-rate operation of 802.11ac WLAN downlink: Nonlinear controller analysis & design
No full textIn this paper we present a novel nonlinear control design for regulating the aggregation level in 802.11 WLANs so as to ensure robust low-delay operation at high data rates. The controller compensates for system nonlinearities and so can be used for the full range of WLAN operation. We develop an implementation of the nonlinear control design and use this to evaluate performance using both simulations and hardware measurements
Proportional Fairness in 802.11 Wireless LANs
No full textWe provide the first rigorous analysis of proportional fairness in 802.11 WLANs. This analysis corrects prior approximate studies. We show that there exists a unique proportional fair rate allocation and completely characterise the allocation in terms of a new air-time quantity, the total air-time
Interior of ANZ Bank head office, Westside corner Collins & Queen Streets, Melbourne, [1] [picture] /
No full textCondition: Good.; Title devised by cataloguer based on inscription on sleeve.; Part of Wolfgang Sievers photographic archive.; Sievers number: 2968-D.; Inscription on sleeve: Arch: Leith Bartlett.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.pic-an24876735
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