1,714 research outputs found
Structured Near-Optimal Channel-Adapted Quantum Error Correction
We present a class of numerical algorithms which adapt a quantum error
correction scheme to a channel model. Given an encoding and a channel model, it
was previously shown that the quantum operation that maximizes the average
entanglement fidelity may be calculated by a semidefinite program (SDP), which
is a convex optimization. While optimal, this recovery operation is
computationally difficult for long codes. Furthermore, the optimal recovery
operation has no structure beyond the completely positive trace preserving
(CPTP) constraint. We derive methods to generate structured channel-adapted
error recovery operations. Specifically, each recovery operation begins with a
projective error syndrome measurement. The algorithms to compute the structured
recovery operations are more scalable than the SDP and yield recovery
operations with an intuitive physical form. Using Lagrange duality, we derive
performance bounds to certify near-optimality.Comment: 18 pages, 13 figures Update: typos corrected in Appendi
State of Utah v. Jindall : Brief of Appellant
Security principles, like least privilege, are among the resources in the security body of knowledge that survived the test of time. The implementation of these principles in a software architecture is difficult, as there are no systematic rules on how to apply them in practice. As a result, they are often neglected, which lowers the overall security level of the software system and increases the cost necessary to fix this later in de development life-cycle.
This report improves the support for least privilege in software architectures by (i) defining the foundations to identify potential violations of the principle herein and (ii) elicitating architectural transformations that positively impact the security properties of the architecture, while preserving the semantics thereof. These results have been implemented and validated in a number of case studies.nrpages: 74status: publishe
Optimum Quantum Error Recovery using Semidefinite Programming
Quantum error correction (QEC) is an essential element of physical quantum
information processing systems. Most QEC efforts focus on extending classical
error correction schemes to the quantum regime. The input to a noisy system is
embedded in a coded subspace, and error recovery is performed via an operation
designed to perfectly correct for a set of errors, presumably a large subset of
the physical noise process. In this paper, we examine the choice of recovery
operation. Rather than seeking perfect correction on a subset of errors, we
seek a recovery operation to maximize the entanglement fidelity for a given
input state and noise model. In this way, the recovery operation is optimum for
the given encoding and noise process. This optimization is shown to be
calculable via a semidefinite program (SDP), a well-established form of convex
optimization with efficient algorithms for its solution. The error recovery
operation may also be interpreted as a combining operation following a quantum
spreading channel, thus providing a quantum analogy to the classical diversity
combining operation.Comment: 7 pages, 3 figure
Ziekenhuismanagement als afstemmings- en structureringsprobleem : historie en perspectief
Rede in verkorte vorm uitgesproken bij de aanvaarding van het ambt van bijzonder hoogleraar ziekenhuismanagement, vanwege de Nederlandse Vereniging van Ziekenhuisdirecteuren, in de Faculteit Geneeskunde en Gezondheidswetenschappen van de Erasmus Universiteit Rotterdam op vrijdag 15 april 198
Cram\'er-Rao Bounds for Holographic Positioning
Multiple antennas arrays play a key role in wireless networks for
communications but also for localization and sensing applications. The use of
large antenna arrays at high carrier frequencies (in the mmWave range) pushes
towards a propagation regime in which the wavefront is no longer plane but
spherical. This allows to infer the position and orientation of a transmitting
source from the received signal without the need of using multiple anchor
nodes, located in known positions. To understand the fundamental limits of
large antenna arrays for localization, this paper combines wave propagation
theory with estimation theory, and computes the Cram\'er-Rao Bound (CRB) for
the estimation of the source position on the basis of the three Cartesian
components of the electric field, observed over a rectangular surface area. The
problem is referred to as holographic positioning and is formulated by taking
into account the radiation angular pattern of the transmitting source, which is
typically ignored in standard signal processing models. We assume that the
source is a Hertzian dipole, and address the holographic positioning problem in
both cases, that is, with and without a priori knowledge of its orientation. To
simplify the analysis and gain further insights, we also consider the case in
which the dipole is located on the line perpendicular to the surface center.
Numerical and asymptotic results are given to quantify the CRBs, and to
quantify the effect of various system parameters on the ultimate estimation
accuracy. It turns out that surfaces of practical size may guarantee a
centimeter-level accuracy in the mmWave bands.Comment: 15 pages, 9 figures, IEEE Transactions on Signal Processin
Design of a Low Micro Vibration High Precision CubeSat Reaction Wheel
Rolling element bearings are known to generate higher order harmonics. These harmonics can reach up to the 10th or higher engine order [1]. When wheels are used in a wide speed range, these higher order harmonics can pass and excite rotor eigenfrequencies and rotor modes, severely increasing the exported μ-vibrations at these frequencies. The amplification of these frequencies will then be governed by the quality factor (Q-factor) of the rotor. Single piece rotors have several advantages such as affordable tight tolerances, uniform mass and elimination of assembly errors, but such monolithic metallic structure feature high Q-factors. Material choice is a first way to address this [2], but damping will stay limited. To further increase the internal damping and reduce the Q-factor, Constrained layer damping is employed
The use of the DR CALUX bioassay and indicator polychlorinated biphenyls for screening of elevated levels of dioxins and dioxin-like polychlorinated biphenyls in eel.
The DR CALUX bioassay is a very suitable screening method for dioxins and dioxin-like-PCBs in feed and food. This was, e. g. demonstrated in a survey in the Netherlands to control the dioxin levels in eel. The DR CALUX assay, but also indicator polychlorinated biphenyls (PCB) were evaluated as a screening method. Based on the limit for polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/F) [at that time 8 pg toxic equivalents (TEQ)/g eel], and the relation between PCDD/F and dioxin-like-PCB, a decision limit of 30 pg TEQ/g eel was used for screening of 153 field samples. Suspected samples (21) and part of the higher contaminated negative samples (35) were analyzed by GC/MS for dioxins, non-ortho, mono-ortho and indicator PCB, revealing 13 samples exceeding the action limit of 30 pg TEQ/g eel. Only one sample slightly exceeded the dioxin level of 8 pg TEQ/g eel. The relatively low sensitivity for mono-ortho PCB was overcome by the use of reference samples, as shown by the correlation of 0.93 between GC/MS and CALUX determined total TEQ levels. The present data show that the DR CALUX assay can be used for screening of total TEQ levels in eel. The use for dioxins only requires a safe, and therefore relatively low, decision limit. The indicator PCB also showed a good correlation with total TEQ levels, mainly due to the large contribution of the mono-ortho PCB at higher concentrations. The relation with dioxins was very poor and as such indicator PCB seem less suitable than the DR CALUX assay for screening for dioxins only. The present study clearly shows that part of the wild eel samples contains high total TEQ levels and will exceed the future European Union limit of 12 pg TEQ/g eel for dioxins and dioxin-like PCB. Especially at high TEQ levels, dioxin-like PCB contribute most to the total TEQ. In practice, wild eel presents only a minor part of the eel consumed
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