3,309 research outputs found
Dissolution of calcium carbonate: observations and model results in the subpolar North Atlantic
We investigate the significance of in situ dissolution of calcium carbonate above its saturation horizons using observations from the open subpolar North Atlantic [sNA] and to a lesser extent a 3-D biogeochemical model. The sNA is particularly well suited for observation-based detections of in situ, i.e. shallow-depth CaCO3 dissolution [SDCCD] as it is a region of high CaCO3 production, deep CaCO3 saturation horizons, and precisely-defined pre-formed alkalinity. Based on the analysis of a comprehensive alkalinity data set we find that SDCCD does not appear to be a significant process in the open sNA. The results from the model support the observational findings by indicating that there is not a significant need of SDCCD to explain observed patterns of alkalinity in the North Atlantic. Instead our investigation points to the importance of mixing processes for the redistribution of alkalinity from dissolution of CaCO3 from below its saturation horizons. However, mixing has recently been neglected for a number of studies that called for SDCCD in the sNA and on global scale
Topology and Phases in Fermionic Systems
There can exist topological obstructions to continuously deforming a gapped
Hamiltonian for free fermions into a trivial form without closing the gap.
These topological obstructions are closely related to obstructions to the
existence of exponentially localized Wannier functions. We show that by taking
two copies of a gapped, free fermionic system with complex conjugate
Hamiltonians, it is always possible to overcome these obstructions. This allows
us to write the ground state in matrix product form using Grassman-valued bond
variables, and show insensitivity of the ground state density matrix to
boundary conditions.Comment: 4 pages, see also arxiv:0710.329
Relativistic entanglement of two massive particles
We describe the spin and momentum degrees of freedom of a system of two
massive spin-- particles as a 4 qubit system. Then we explicitly
show how the entanglement changes between different partitions of the qubits,
when considered by different inertial observers. Although the two particle
entanglement corresponding to a partition into Alice's and Bob's subsystems is,
as often stated in the literature, invariant under Lorentz boosts, the
entanglement with respect to other partitions of the Hilbert space on the other
hand, is not. It certainly does depend on the chosen inertial frame and on the
initial state considered. The change of entanglement arises, because a Lorentz
boost on the momenta of the particles causes a Wigner rotation of the spin,
which in certain cases entangles the spin- with the momentum states. We
systematically investigate the situation for different classes of initial spin
states and different partitions of the 4 qubit space.
Furthermore, we study the behavior of Bell inequalities for different
observers and demonstrate how the maximally possible degree of violation, using
the Pauli-Lubanski spin observable, can be recovered by any inertial observer.Comment: 17 pages, 4 figure
Støvplagen ved Maskintærskning.
Støvplagen ved Maskintærskning
A Framework for Evaluating Security in the Presence of Signal Injection Attacks
Sensors are embedded in security-critical applications from medical devices
to nuclear power plants, but their outputs can be spoofed through
electromagnetic and other types of signals transmitted by attackers at a
distance. To address the lack of a unifying framework for evaluating the
effects of such transmissions, we introduce a system and threat model for
signal injection attacks. We further define the concepts of existential,
selective, and universal security, which address attacker goals from mere
disruptions of the sensor readings to precise waveform injections. Moreover, we
introduce an algorithm which allows circuit designers to concretely calculate
the security level of real systems. Finally, we apply our definitions and
algorithm in practice using measurements of injections against a smartphone
microphone, and analyze the demodulation characteristics of commercial
Analog-to-Digital Converters (ADCs). Overall, our work highlights the
importance of evaluating the susceptibility of systems against signal injection
attacks, and introduces both the terminology and the methodology to do so.Comment: This article is the extended technical report version of the paper
presented at ESORICS 2019, 24th European Symposium on Research in Computer
Security (ESORICS), Luxembourg, Luxembourg, September 201
Dissolution of calcium carbonate: observations and model results in the North Atlantic
International audienceWe investigate the significance of in situ dissolution of calcium carbonate above its saturation horizons. The study relies on observations from the open subpolar North Atlantic [sNA] and on a 3-D biogeochemical model. The sNA is particularly well suited for observation-based detections of in situ, i.e. shallow depth CaCO3 dissolution [SDCCD] as it is a region of high CaCO3 production, deep CaCO3 saturation horizons, and precisely-defined pre-formed alkalinity. Based on the analysis of a comprehensive alkalinity data set we find that SDCCD does not appear to be a significant process in the open sNA. The results from the model support the observational findings and do not indicate a significant need of SDCCD to explain observed patterns of alkalinity in the North Atlantic. Instead our investigation points to the importance of mixing processes for the redistribution of alkalinity from dissolution of CaCO3 from below its saturation horizons. However, mixing has recently been neglected for a number of studies that called for SDCCD in the sNA and on global scale
Lorentz invariance of entanglement classes in multipartite systems
We analyze multipartite entanglement in systems of spin-1/2 particles from a
relativistic perspective. General conditions which have to be met for any
classification of multipartite entanglement to be Lorentz invariant are
derived, which contributes to a physical understanding of entanglement
classification. We show that quantum information in a relativistic setting
requires the partition of the Hilbert space into particles to be taken
seriously. Furthermore, we study exemplary cases and show how the spin and
momentum entanglement transforms relativistically in a multipartite setting.Comment: v2: 5 pages, 4 figures, minor changes to main body, journal
references update
- …