6,693 research outputs found
Definitions: Does disjunction mean dysfunction?
Our concern in this paper is with definitions that are not conjunctive. In particular, our concern is with definitions of things of a kind K which allege that there is a bunch of conditions, each of which is sufficient, but not necessary, for bestowing K-hood. Definitions of this kind, call them “disjunctive,” are often proposed for kinds of things that interest us, but they usually draw fairly muted applause. Many treat them as provisional, to be endured, rather than celebrated. Surely, it is thought, they do not provide all one might want from a definition. Because of water, art and other cases which apparently problematise the boundary between practice-mandated and theoretically-posited kinds, there will doubtless continue to be disagreements about the credentials of disjunctive definitions. Even so, we think we have gone some way towards offering a reasonable justification for the on-going debates and some apparatus for formulating the issues
Jackson’s armchair: The only chair in town?
Are all the facts about nations, cultures and economies really just facts about people's mental states and their interactions? Are all of the properties which determine whether or not a thing is a work of art really just physical properties of that thing? Is linguistics, the scientific investigation of language, best understood as a branch of psychology, the scientific investigation of the mind? Can psychology be reduced to biology? Can all biological phenomena be explained chemically? Is chemistry really just part of physics? Is there anything going on in the world which isn't a physical thing? Can there be freely-chosen, autonomous human action in a purely physical world? Frank Jackson has made a controversial claim about the way in which one should investigate questions like these. This paper is a qualified defence of that claim
Photonic Engineering for CV-QKD over Earth-Satellite Channels
Quantum Key Distribution (QKD) via satellite offers up the possibility of
unconditionally secure communications on a global scale. Increasing the secret
key rate in such systems, via photonic engineering at the source, is a topic of
much ongoing research. In this work we investigate the use of photon-added
states and photon-subtracted states, derived from two mode squeezed vacuum
states, as examples of such photonic engineering. Specifically, we determine
which engineered-photonic state provides for better QKD performance when
implemented over channels connecting terrestrial receivers with Low-Earth-Orbit
satellites. We quantify the impact the number of photons that are added or
subtracted has, and highlight the role played by the adopted model for
atmospheric turbulence and loss on the predicted key rates. Our results are
presented in terms of the complexity of deployment used, with the simplest
deployments ignoring any estimate of the channel, and the more sophisticated
deployments involving a feedback loop that is used to optimize the key rate for
each channel estimation. The optimal quantum state is identified for each
deployment scenario investigated.Comment: Updated reference lis
Inter-satellite Quantum Key Distribution at Terahertz Frequencies
Terahertz (THz) communication is a topic of much research in the context of
high-capacity next-generation wireless networks. Quantum communication is also
a topic of intensive research, most recently in the context of space-based
deployments. In this work we explore the use of THz frequencies as a means to
achieve quantum communication within a constellation of micro-satellites in
Low-Earth-Orbit (LEO). Quantum communication between the micro-satellite
constellation and high-altitude terrestrial stations is also investigated. Our
work demonstrates that THz quantum entanglement distribution and THz quantum
key distribution are viable deployment options in the micro-satellite context.
We discuss how such deployment opens up the possibility for simpler integration
of global quantum and wireless networks. The possibility of using THz
frequencies for quantum-radar applications in the context of LEO deployments is
briefly discussed.Comment: 7 pages, 6 figure
Detecting Orbital Angular Momentum of Light in Satellite-to-Ground Quantum Communications
Satellite-based quantum communications enable a bright future for
global-scale information security. However, the spin orbital momentum of light,
currently used in many mainstream quantum communication systems, only allows
for quantum encoding in a two-dimensional Hilbert space. The orbital angular
momentum (OAM) of light, on the other hand, enables quantum encoding in
higher-dimensional Hilbert spaces, opening up new opportunities for
high-capacity quantum communications. Due to its turbulence-induced decoherence
effects, however, the atmospheric channel may limit the practical usage of OAM.
In order to determine whether OAM is useful for satellite-based quantum
communications, we numerically investigate the detection likelihoods for OAM
states that traverse satellite-to-ground channels. We show that the use of OAM
through such channels is in fact feasible. We use our new results to then
investigate design specifications that could improve OAM detection -
particularly the use of advanced adaptive optics techniques. Finally, we
discuss how our work provides new insights into future implementations of
space-based OAM systems within the context of quantum communications.Comment: 7 pages, 7 figure
Mutual Fund Flows and Performance in Rational Markets
We develop a simple rational model of active portfolio management that provides a natural benchmark against which to evaluate observed relationship between returns and fund flows. We show that many effects widely regarded as anomalous are consistent with this simple explanation. In the model, investments with active managers do not outperform passive benchmarks because of the competitive market for capital provision, combined with decreasing returns to scale in active portfolio management. Consequently, past performance cannot be used to predict future returns, or to infer the average skill level of active managers. The lack of persistence in active manager returns does not imply that differential ability across managers is nonexistent or unrewarded, that gathering information about performance is socially wasteful, or that chasing performance is pointless. A strong relationship between past performance and the ow of funds exists in our model, indeed this is the market mechanism that ensures that no predictability in performance exists. Calibrating the model to the fund flows and survivorship rates, we nd these features of the data are consistent with the vast majority (80%) of active managers having at least enough skill to make back their fees.
Towards an effective structure of IT governance for organizations in developing economies
The pervasive use of IT is prominent amongst organizations in developing economies. However, there is growing evidence that these economies fail to capitalize on their IT investment to transform their organizations to be competitive both locally and globally. IT-related benefits are possible with appropriate governance of the IT-related resources, and we need to broaden our understanding on the IT governance mechanics suitable for organizations in the developing economies. In this study, we adopted an initial interpretive design to obtain a deeper understanding of the IT governance (ITG) environment and conceptions of the stakeholders on effective IT governance structures for the developing economies. We found that the presence of an IT Strategic Planning Committee, Multiple level of authority, and a Forum for informal discussions as the crucial components of an ITG structure in developing economies
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