Proof of a conjecture on hadamard 2-groups

AbstractBy expanding on the results of James Davis, we prove by construction that every abelian 2-group that meets the exponent bound has a difference set

Study of quasi-optical circuit techniques in varactor multipliers

Quasi-optical circuit techniques in varactor multiplier

Artifacts at 4.5 and 8.0 um in Short Wavelength Spectra from the Infrared Space Observatory

Spectra from the Short Wavelength Spectrometer (SWS) on ISO exhibit artifacts at 4.5 and 8 um. These artifacts appear in spectra from a recent data release, OLP 10.0, as spurious broad emission features in the spectra of stars earlier than ~F0, such as alpha CMa. Comparison of absolutely calibrated spectra of standard stars to corresponding spectra from the SWS reveals that these artifacts result from an underestimation of the strength of the CO and SiO molecular bands in the spectra of sources used as calibrators by the SWS. Although OLP 10.0 was intended to be the final data release, these findings have led to an additional release addressing this issue, OLP 10.1, which corrects the artifacts.Comment: 14 pages, AASTex, including 5 figures. Accepted by ApJ Letter

Metastable Feshbach Molecules in High Rotational States

We experimentally demonstrate Cs2 Feshbach molecules well above the dissociation threshold, which are stable against spontaneous decay on the timescale of one second. An optically trapped sample of ultracold dimers is prepared in an l-wave state and magnetically tuned into a region with negative binding energy. The metastable character of these molecules arises from the large centrifugal barrier in combination with negligible coupling to states with low rotational angular momentum. A sharp onset of dissociation with increasing magnetic field is mediated by a crossing with a g-wave dimer state and facilitates dissociation on demand with a well defined energy.Comment: 4 pages, 5 figure

The distribution of value in the mobile phone supply chain

The supply chains of the mobile phone industry span national and firm boundaries. To analyze how value is distributed among the participants, a framework based on theories of firm strategy is applied, and a novel methodology is used to measure value capture in three phone models introduced from 2004 to 2008. The research shows that carriers capture the greatest value (in terms of gross profit) from each handset, followed closely by handset makers, with suppliers a distant third. However, the situation is reversed in terms of operating profit. Carriers shoulder the burden of network installation, maintenance, and upgrading, which absorbs much of the value from their subscription fees. Handset maker nationality, which may also influence supplier choice, is a key determinant of the geographic distribution of value capture. The results are also used to estimate the relationship of handset subsidies to carrier profits, which has been an issue of concern for antitrust authorities in several countries. The analysis shows how the framework can be used to calculate how much service charges might be inflated to cover the subsidies. © 2011 Elsevier Ltd. All rights reserved

Summarizing the state of the terrestrial biosphere in few dimensions

In times of global change, we must closely monitor the state of the planet in order to understand gradual or abrupt changes early on. In fact, each of the Earth's subsystems – i.e. the biosphere, atmosphere, hydrosphere, and cryosphere – can be analyzed from a multitude of data streams. However, since it is very hard to jointly interpret multiple monitoring data streams in parallel, one often aims for some summarizing indicator. Climate indices, for example, summarize the state of atmospheric circulation in a region. Although such approaches are also used in other fields of science, they are rarely used to describe land surface dynamics. Here, we propose a robust method to create indicators for the terrestrial biosphere using principal component analysis based on a high-dimensional set of relevant global data streams. The concept was tested using 12 explanatory variables representing the biophysical states of ecosystems and land-atmosphere water, energy, and carbon fluxes. We find that two indicators account for 73 % of the variance of the state of the biosphere in space and time. While the first indicator summarizes productivity patterns, the second indicator summarizes variables representing water and energy availability. Anomalies in the indicators clearly identify extreme events, such as the Amazon droughts (2005 and 2010) and the Russian heatwave (2010), they also allow us to interpret the impacts of these events. The indicators also reveal changes in the seasonal cycle, e.g. increasing seasonal amplitudes of productivity in agricultural areas and in arctic regions. We assume that this generic approach has great potential for the analysis of land-surface dynamics from observational or model data

X-ray narrow line region variability as a geometry probe: The case of NGC 5548

We study the long time scale variability of the gas responsible for the X-ray narrow emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the location and geometry of the emitting gas. Using X-ray spectra taken with the Chandra-LETGS and HETGS instruments and with XMM-Newton RGS and combining them with long-term monitoring observations of the Rossi X-ray Timing Explorer (RXTE), we perform a correlation analysis in order to try constrain the time scale on which the narrow line emitting gas responds to variations of the continuum flux. With the inclusion of the 2007 Chandra-LETGS observation we have an additional observation at an historically low flux level. We conclude that the NLR in NGC 5548 is in the form of an ionization cone, compact in size, and located between 1 and 15 pc from the central source, depending on the exact geometry of the NLR.Comment: 6 pages, 4 figures, accepted for publication in A&