3,124 research outputs found
Phantom maps and chromatic phantom maps
In the first part, we determine conditions on spectra X and Y under which
either every map from X to Y is phantom, or no nonzero maps are. We also
address the question of whether such all or nothing behaviour is preserved when
X is replaced with V smash X for V finite. In the second part, we introduce
chromatic phantom maps. A map is n-phantom if it is null when restricted to
finite spectra of type at least n. We define divisibility and finite type
conditions which are suitable for studying n-phantom maps. We show that the
duality functor W_{n-1} defined by Mahowald and Rezk is the analog of
Brown-Comenetz duality for chromatic phantom maps, and give conditions under
which the natural map Y --> W_{n-1}^2 Y is an isomorphism.Comment: 18 page
Quillen model structures for relative homological algebra
An important example of a model category is the category of unbounded chain
complexes of R-modules, which has as its homotopy category the derived category
of the ring R. This example shows that traditional homological algebra is
encompassed by Quillen's homotopical algebra. The goal of this paper is to show
that more general forms of homological algebra also fit into Quillen's
framework. Specifically, a projective class on a complete and cocomplete
abelian category A is exactly the information needed to do homological algebra
in A. The main result is that, under weak hypotheses, the category of chain
complexes of objects of A has a model category structure that reflects the
homological algebra of the projective class in the sense that it encodes the
Ext groups and more general derived functors. Examples include the "pure
derived category" of a ring R, and derived categories capturing relative
situations, including the projective class for Hochschild homology and
cohomology. We characterize the model structures that are cofibrantly
generated, and show that this fails for many interesting examples. Finally, we
explain how the category of simplicial objects in a possibly non-abelian
category can be equipped with a model category structure reflecting a given
projective class, and give examples that include equivariant homotopy theory
and bounded below derived categories.Comment: 29 pages. v4: Published in Math. Proc. Cambridge Philos. Soc. v5:
Minor corrections to published version appear on last pag
Exploring the relationship between tourism and offshore finance in small island economies: lessons from Jersey
Many islands host tourism and offshore finance but research tends to focus on either industry without examining the nature of the relationship(s) between these two where they co-exist. This paper examines the nature of the relationships using a case study of the British Channel Island of Jersey. Both industries demand labour, land and capital that are frequently scarce in small islands. Given their common characteristics and, drawing lessons from Jersey, the paper then considers the nature and the dynamics of their relationship, and the issue of resource competition between the two sectors. In light of the unusual context of small polities and the political power of external actors, the paper also analyses the dynamics of the central relationship between tourism, offshore finance and the state in islands. Finally, the paper considers the overall impact of the relationship between tourism and offshore finance and how it affects the economic development trajectory of small islands.tax havens, island tourism, island development
Bias-Correcting the Realized Range-Based Variance in the Presence of Market Microstructure Noise
Market microstructure noise is a challenge to high-frequency based estimation of the integrated variance, because the noise accumulates with the sampling frequency. In this paper, we analyze the impact of microstructure noise on the realized range-based variance and propose a bias-correction to the rangestatistic. The new estimator is shown to be consistent for the integrated variance and asymptotically mixed Gaussian under simple forms of microstructure noise, and we can select an optimal partition of the high-frequency data in order to minimize its asymptotic conditional variance. The finite sample properties of our estimator are studied with Monte Carlo simulations and we implement it on high-frequency data from TAQ. We find that a bias-corrected range-statistic often has much smaller confidence intervals than the realized variance. --Bias-Correction,Integrated Variance,Market Microstructure Noise,Realized Range-Based Variance,Realized Variance
Cuboid syndrome
This issue of eMedRef provides information to clinicians on the pathophysiology, diagnosis, and therapeutics of cuboid syndrome
Validation of a smartphone app to map social networks of proximity
Social network analysis is a prominent approach to investigate interpersonal
relationships. Most studies use self-report data to quantify the connections
between participants and construct social networks. In recent years smartphones
have been used as an alternative to map networks by assessing the proximity
between participants based on Bluetooth and GPS data. While most studies have
handed out specially programmed smartphones to study participants, we developed
an application for iOS and Android to collect Bluetooth data from participants
own smartphones. In this study, we compared the networks estimated with the
smartphone app to those obtained from sociometric badges and self-report data.
Participants (n=21) installed the app on their phone and wore a sociometric
badge during office hours. Proximity data was collected for 4 weeks. A
contingency table revealed a significant association between proximity data
(rho = 0.17, p<0.0001), but the marginal odds were higher for the app (8.6%)
than for the badges (1.3%), indicating that dyads were more often detected by
the app. We then compared the networks that were estimated using the proximity
and self-report data. All three networks were significantly correlated,
although the correlation with self-reported data was lower for the app (rho =
0.25) than for badges (rho = 0.67). The scanning rates of the app varied
considerably between devices and was lower on iOS than on Android. The
association between the app and the badges increased when the network was
estimated between participants whose app recorded more regularly. These
findings suggest that the accuracy of proximity networks can be further
improved by reducing missing data and restricting the interpersonal distance at
which interactions are detected.Comment: 20 pages, 5 figure
Using Bluetooth Low Energy in smartphones to map social networks
Social networks have an important role in an individual's health, with the
propagation of health-related features through a network, and correlations
between network structures and symptomatology. Using Bluetooth-enabled
smartphones to measure social connectivity is an alternative to traditional
paper-based data collection; however studies employing this technology have
been restricted to limited sets of homogenous handsets. We investigated the
feasibility of using the Bluetooth Low Energy (BLE) protocol, present on users'
own smartphones, to measure social connectivity. A custom application was
designed for Android and iOS handsets. The app was configured to simultaneously
broadcast via BLE and perform periodic discovery scans for other nearby
devices. The app was installed on two Android handsets and two iOS handsets,
and each combination of devices was tested in the foreground, background and
locked states. Connectivity was successfully measured in all test cases, except
between two iOS devices when both were in a locked state with their screens
off. As smartphones are in a locked state for the majority of a day, this
severely limits the ability to measure social connectivity on users' own
smartphones. It is not currently feasible to use Bluetooth Low Energy to map
social networks, due to the inability of iOS devices to detect another iOS
device when both are in a locked state. While the technology was successfully
implemented on Android devices, this represents a smaller market share of
partially or fully compatible devices.Comment: 6 pages, 1 tabl
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