Search

Earthquakes change the gravity field of the area affected by the earthquake due to mass redistribution in the upper layers of the Earth. In addition, for sub-oceanic earthquakes deformation of the ocean floor causes relative sea-level changes and mass redistribution of water that has again a significant effect on the gravity field. Two such recent, large sub-oceanic earthquakes are the 27 February 2010 Chile Maule earthquake with a magnitude of Mw 8.8 and the 11 March 2011 Japan Tohoku earthquake with a magnitude of Mw 9.0. The goal of ESA’s satellite GOCE—launched in March 2009—is to map the Earth’s gravity field with unprecedented accuracy and resolution. To this end, GOCE carries a gravity gradiometer. Although the mean gravity field is to be mapped, the sheer size of both earthquakes and associated mass redistribution make them both potential candidates for detecting the co-seismic gravity changes in the GOCE gradiometer data. We assess the detectability of gravity field changes in the GOCE gravity gradients by modelling these earthquakes using a forward model. Furthermore, we analyse the GOCE data before and after the respective earthquakes and assess their quality. Based on these analyses we conclude that despite its small signal size at GOCE altitude the Japan earthquake may be visible in the gravity gradients when more post-earthquake data become available. Because of the short data period before the Chile earthquake this signal will probably not be visible.

The Global Geodetic Observing System (GGOS) is the contribution of the International Association of Geodesy (IAG) to the Global Earth Observing System of Systems (GEOSS). The implementation of common standards and conventions in all components of GGOS is of crucial importance to ensure highest accuracy of geodetic and geophysical products. Consistency with relevant external standards and conventions is mandatory to achieve interoperability with GEOSS.

We study the problem of authentication based on a weak key in the information-theoretic setting. A key is weak if its min-entropy is an arbitrary small fraction of its bit length. This problem has recently received considerable attention, with different solutions optimizing different parameters. We study the problem in an extended setting, where the weak key is a one-time session key that is derived from a public source of randomness with the help of a (potentially also weak) long-term key. Our goal now is to authenticate a message by means of the weak session key in such a way that (nearly) no information on the long-term key is leaked. Ensuring privacy of the long-term key is vital for the long-term key to be re-usable. Previous work has not considered such a privacy issue, and previous solutions do not seem to satisfy this requirement. We show the existence of a practical four-round protocol that provides message authentication from a weak session key and that avoids non-negligible leakage on the long-term key. The security of our scheme also holds in the quantum setting where the adversary may have limited quantum side information on the weak session key. As an application of our scheme, we show the existence of an identification scheme in the bounded quantum storage model that is secure against a man-in-the-middle attack and that is truly password-based: it does not need any high entropy key, in contrast to the scheme proposed by Damgard et al.

We propose a framework for analyzing classical sampling strategies for estimating the Hamming weight of a large string from a few sample positions, when applied to a multi-qubit quantum system instead. The framework shows how to interpret the result of such a strategy and how to define its accuracy when applied to a quantum system. Furthermore, we show how the accuracy of any strategy relates to its accuracy in its classical usage, which is well understood for the important examples. We show the usefulness of our framework by using it to obtain new and simple security proofs for the following quantum-cryptographic schemes: BB84 quantum-key-distribution, and quantum oblivious-transfer from bit-commitment.

The determination of the Earth’s gravitational potential from gravity gradients measured at satellite altitude along a non-polar orbit is an ill-posed problem, which lacks stability due to the polar gaps and the downward continuation from satellite altitude to the Earth’s surface. Even in the discrete world of observations the problem is still ill-conditioned, and some kind of regularization is indispensable to provide physically meaningful solutions up to high-degree and order. However, for large-scale problems the determination of the optimal regularization parameter is very expensive in terms of CPU-time, and strategies have to be developed to find this parameter with a minimum number of arithmetic operations. For the pair Tikhonov-Phillips/Morozov discrepancy principle the performance is analyzed for the gravity field recovery from GOCE SGG observations of two methods for accelerating the standard CG-algorithm recently proposed by Frommer & Maass. Moreover, the choice of a number of method-dependent parameters is investigated based on the analysis of several simulations up to degree and order 200 for white noise and colored noise observations and GOCE-like orbits.

Prior to 1912, the structure of matter was unknown to a large extent, though in some cases models were proposed. This was especially the case with gases, the kinetical theory of gases being able to explain many features of the gaseous state. At the other end of the scale, the regularity of crystals had led to the idea that the molecules in a crystal were arranged in an orderly fashion, though there was no direct proof for the proposed arrangements. Of liquids and amorphous bodies nothing was known at all. The first tool for ascertaining such structures has been the diffraction of X-rays by matter, later on to be followed by the diffraction of electrons and of neutrons. In the present article, only diffraction of X-rays will be treated. Many of the considerations in this field will be useful for diffraction of neutrons and electrons as well1.