Author name cluster

Michael Brand

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

4 papers

1 author row

TAAS Journal 2024 Journal Article

Applying Trust for Operational States of ICT-Enabled Power Grid Services

Michael Brand
Anand Narayan
Sebastian Lehnhoff

Digitalization enables the automation required to operate modern cyber-physical energy systems (CPESs), leading to a shift from hierarchical to organic systems. However, digitalization increases the number of factors affecting the state of a CPES (e.g., software bugs and cyber threats). In addition to established factors like functional correctness, others like security become relevant but are yet to be integrated into an operational viewpoint, i.e., a holistic perspective on the system state. Trust in organic computing is an approach to gain a holistic view of the state of systems. It consists of several facets (e.g., functional correctness, security, and reliability), which can be used to assess the state of CPES. Therefore, a trust assessment on all levels can contribute to a coherent state assessment. This article focuses on the trust in ICT-enabled grid services in a CPES. These are essential for operating the CPES, and their performance relies on various data aspects like availability, timeliness, and correctness. This article proposes to assess the trust in involved components and data to estimate data correctness, which is crucial for grid services. The assessment is presented considering two exemplary grid services, namely state estimation and coordinated voltage control. Furthermore, the interpretation of different trust facets is also discussed.

Details DOI

TCS Journal 2017 Journal Article

P-RAM vs. RP-RAM

Michael Brand

One of the fundamental open questions in computational complexity is whether the class of problems solvable by use of stochasticity under the Random Polynomial time (RP) model is larger than the class of those solvable in deterministic polynomial time (P). However, this question is only open for Turing machines, not for Random Access Machines (RAMs). Simon (1981) [31] was able to show that for a sufficiently equipped Random Access Machine, the ability to switch states nondeterministically entails no computational advantage. On the other hand, in the same paper, Simon describes a different (and arguably more natural) model for RAM stochasticity. According to Simon's proposal, instead of receiving a new random bit at each execution step, the RAM program is able to execute the pseudofunction RAND ( y ), which returns a uniformly distributed random integer in the range [ 0, y ). Whether the ability to allot a random integer in this fashion is more powerful than the ability to allot a random bit remained an open question for the last 30 years. In this paper, we close Simon's open problem by fully characterising the class of languages recognisable in polynomial time by each of the RAMs regarding which the question was posed. We show that for some of these stochasticity does not entail any advantage, but, more interestingly, we show that for others it does. These results carry over also to BPP-like and coRP-like acceptance criteria.

Details DOI

TCS Journal 2015 Journal Article

No easy puzzles: Hardness results for jigsaw puzzles

Michael Brand

We show that solving (bounded-degree) jigsaw puzzles requires Θ ( n 2 ) edge matching comparisons both in the worst case and in expectation, making all jigsaw puzzles as hard to solve as the trivial upper bound. This result applies to bounded-degree puzzles of all shapes, whether pictorial or apictorial. For non-bounded degree puzzles, we show that Ω ( n log ⁡ n ) is a tight bound.

Details DOI

I&C Journal 2014 Journal Article

Constant-time sorting

Michael Brand

We present an algorithm for sorting an arbitrary number of arbitrary-length integers in constant time on a random access machine (RAM). The algorithm forms a Straight Line Program (SLP).

Details DOI