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.