Refine
Year of publication
- 2020 (160) (remove)
Document Type
- Article (105)
- Doctoral Thesis (46)
- Lecture (3)
- Course Material (2)
- Master's Thesis (2)
- Bachelor Thesis (1)
- Diploma Thesis (1)
Language
- English (160) (remove)
Has Fulltext
- yes (160)
Keywords
- B-splines (2)
- Delay Management (2)
- Line Planning (2)
- Line Pool Generation (2)
- NURBS (2)
- Open Source Library (2)
- Optimization in Public Transportation (2)
- Public Transport Planning (2)
- Software for Public Transport Planning (2)
- Stop Location (2)
Faculty / Organisational entity
- Kaiserslautern - Fachbereich Maschinenbau und Verfahrenstechnik (35)
- Kaiserslautern - Fachbereich Mathematik (25)
- Kaiserslautern - Fachbereich Informatik (19)
- Kaiserslautern - Fachbereich Chemie (17)
- Kaiserslautern - Fachbereich Physik (17)
- Kaiserslautern - Fachbereich Biologie (14)
- Kaiserslautern - Fachbereich Sozialwissenschaften (12)
- Kaiserslautern - Fachbereich Elektrotechnik und Informationstechnik (7)
- Kaiserslautern - Fachbereich Bauingenieurwesen (6)
- Kaiserslautern - Fachbereich Wirtschaftswissenschaften (6)
Learning From Networked-data: Methods and Models for Understanding Online Social Networks Dynamics
(2020)
Abstract
Nowadays, people and systems created by people are generating an unprecedented amount of
data. This data has brought us data-driven services with a variety of applications that affect
people’s behavior. One of these applications is the emergent online social networks as a method
for communicating with each other, getting and sharing information, looking for jobs, and many
other things. However, the tremendous growth of these online social networks has also led to many
new challenges that need to be addressed. In this context, the goal of this thesis is to better understand
the dynamics between the members of online social networks from two perspectives. The
first perspective is to better understand the process and the motives underlying link formation in
online social networks. We utilize external information to predict whether two members of an online
social network are friends or not. Also, we contribute a framework for assessing the strength of
friendship ties. The second perspective is to better understand the decay dynamics of online social
networks resulting from the inactivity of their members. Hence, we contribute a model, methods,
and frameworks for understanding the decay mechanics among the members, for predicting members’
inactivity, and for understanding and analyzing inactivity cascades occurring during the decay.
The results of this thesis are: (1) The link formation process is at least partly driven by interactions
among members that take place outside the social network itself; (2) external interactions might
help reduce the noise in social networks and for ranking the strength of the ties in these networks;
(3) inactivity dynamics can be modeled, predicted, and controlled using the models contributed in
this thesis, which are based on network measures. The contributions and the results of this thesis
can be beneficial in many respects. For example, improving the quality of a social network by introducing
new meaningful links and removing noisy ones help to improve the quality of the services
provided by the social network, which, e.g., enables better friend recommendations and helps to
eliminate fake accounts. Moreover, understanding the decay processes involved in the interaction
among the members of a social network can help to prolong the engagement of these members. This
is useful in designing more resilient social networks and can assist in finding influential members
whose inactivity may trigger an inactivity cascade resulting in a potential decay of a network.
The advent of heterogeneous many-core systems has increased the spectrum
of achievable performance from multi-threaded programming. As the processor components become more distributed, the cost of synchronization and
communication needed to access the shared resources increases. Concurrent
linearizable access to shared objects can be prohibitively expensive in a high
contention workload. Though there are various mechanisms (e.g., lock-free
data structures) to circumvent the synchronization overhead in linearizable
objects, it still incurs performance overhead for many concurrent data types.
Moreover, many applications do not require linearizable objects and apply
ad-hoc techniques to eliminate synchronous atomic updates.
In this thesis, we propose the Global-Local View Model. This programming model exploits the heterogeneous access latencies in many-core systems.
In this model, each thread maintains different views on the shared object: a
thread-local view and a global view. As the thread-local view is not shared,
it can be updated without incurring synchronization costs. The local updates
become visible to other threads only after the thread-local view is merged
with the global view. This scheme improves the performance at the expense
of linearizability.
Besides the weak operations on the local view, the model also allows strong
operations on the global view. Combining operations on the global and the
local views, we can build data types with customizable consistency semantics
on the spectrum between sequential and purely mergeable data types. Thus
the model provides a framework that captures the semantics of Multi-View
Data Types. We discuss a formal operational semantics of the model. We
also introduce a verification method to verify the correctness of the implementation of several multi-view data types.
Frequently, applications require updating shared objects in an “all-or-nothing” manner. Therefore, the mechanisms to synchronize access to individual objects are not sufficient. Software Transactional Memory (STM)
is a mechanism that helps the programmer to correctly synchronize access to
multiple mutable shared data by serializing the transactional reads and writes.
But under high contention, serializable transactions incur frequent aborts and
limit parallelism, which can lead to severe performance degradation.
Mergeable Transactional Memory (MTM), proposed in this thesis, allows accessing multi-view data types within a transaction. Instead of aborting
and re-executing the transaction, MTM merges its changes using the data-type
specific merge semantics. Thus it provides a consistency semantics that allows
for more scalability even under contention. The evaluation of our prototype
implementation in Haskell shows that mergeable transactions outperform serializable transactions even under low contention while providing a structured
and type-safe interface.
LinTim is a scientific software toolbox that has been under development since 2007, giving the possibility to solve the various planning steps in public transportation. Although the name originally derives from "Lineplanning and Timetabling", the available functions have grown far beyond this scope.
This document is the documentation for version 2020.02.
For more information, see https://www.lintim.net
Using molecular dynamics simulation, we study the cutting of an Fe single crystal using
tools with various rake angles α. We focus on the (110)[001] cut system, since here, the crystal
plasticity is governed by a simple mechanism for not too strongly negative rake angles. In this
case, the evolution of the chip is driven by the generation of edge dislocations with the Burgers
vector b = 1
2
[111], such that a fixed shear angle of φ = 54.7◦
is established. It is independent of
the rake angle of the tool. The chip form is rectangular, and the chip thickness agrees with the
theoretical result calculated for this shear angle from the law of mass conservation. We find that the
force angle χ between the direction of the force and the cutting direction is independent of the rake
angle; however, it does not obey the predictions of macroscopic cutting theories, nor the correlations
observed in experiments of (polycrystalline) cutting of mild steel. Only for (strongly) negative rake
angles, the mechanism of plasticity changes, leading to a complex chip shape or even suppressing the
formation of a chip. In these cases, the force angle strongly increases while the friction angle tends
to zero.
More than ten years ago, ER-ANT1 was shown to act as an ATP/ADP antiporter and to exist in the endoplasmic reticulum (ER) of higher plants. Because structurally different transporters generally mediate energy provision to the ER, the physiological function of ER-ANT1 was not directly evident.
Interestingly, mutant plants lacking ER-ANT1 exhibit a photorespiratory phenotype. Although many research efforts were undertaken, the possible connection between the transporter and photorespiration also remained elusive. Here, a forward genetic approach was used to decipher the role of ER-ANT1 in the plant context and its association to photorespiration.
This strategy identified that additional absence of a putative HAD-type phosphatase partially restored the photorespiratory phenotype. Localisation studies revealed that the corresponding protein is targeted to the chloroplast. Moreover, biochemical analyses demonstrate that the HAD-type phosphatase is specific for pyridoxal phosphate. These observations, together with transcriptional and metabolic data of corresponding single (ER-ANT1) and double (ER-ANT1, phosphatase) loss-of-function mutant plants revealed an unexpected connection of ER-ANT1 to vitamin B6 metabolism.
Finally, a scenario is proposed, which explains how ER-ANT1 may influence B6 vitamer phosphorylation, by this affects photorespiration and causes several other physiological alterations observed in the corresponding loss-of-function mutant plants.
Biological clocks exist across all life forms and serve to coordinate organismal physiology with periodic environmental changes. The underlying mechanism of these clocks is predominantly based on cellular transcription-translation feedback loops in which clock proteins mediate the periodic expression of numerous genes. However, recent studies point to the existence of a conserved timekeeping mechanism independent of cellular transcription and translation, but based on cellular metabolism. These metabolic clocks were concluded based upon the observation of circadian and ultradian oscillations in the level of hyperoxidized peroxiredoxin proteins. Peroxiredoxins are enzymes found almost ubiquitously throughout life. Originally identified as H2O2 scavengers, recent studies show that peroxiredoxins can transfer oxidation to, and thereby regulate, a wide range of cellular proteins. Thus, it is conceivable that peroxiredoxins, using H2O2 as the primary signaling molecule, have the potential to integrate and coordinate much of cellular physiology and behavior with metabolic changes. Nonetheless, it remained unclear if peroxiredoxins are passive reporters of metabolic clock activity or active determinants of cellular timekeeping. Budding yeast possess an ultradian metabolic clock termed the Yeast Metabolic Cycle (YMC). The most obvious feature of the YMC is a high amplitude oscillation in oxygen consumption. Like circadian clocks, the YMC temporally compartmentalizes cellular processes (e.g. metabolism) and coordinates cellular programs such as gene expression and cell division. The YMC also exhibits oscillations in the level of hyperoxidized peroxiredoxin proteins.
In this study, I used the YMC clock model to investigate the role of peroxiredoxins in cellular timekeeping, as well as the coordination of cell division with the metabolic clock. I observed that cytosolic 2-Cys peroxiredoxins are essential for robust metabolic clock function. I provide direct evidence for oscillations in cytosolic H2O2 levels, as well as cyclical changes in oxidation state of a peroxiredoxin and a model peroxiredoxin target protein during the YMC. I noted two distinct metabolic states during the YMC: low oxygen consumption (LOC) and high oxygen consumption (HOC). I demonstrate that thiol-disulfide oxidation and reduction are necessary for switching between LOC and HOC. Specifically, a thiol reductant promotes switching to HOC, whilst a thiol oxidant prevents switching to HOC, forcing cells to remain in LOC. Transient peroxiredoxin inactivation triggered rapid and premature switching from LOC to HOC. Furthermore, I show that cell division is normally synchronized with the YMC and that deletion of typical 2-Cys peroxiredoxins leads to complete uncoupling of cell division from metabolic cycling. Moreover, metabolic oscillations are crucial for regulating cell cycle entry and exit. Intriguingly, switching to HOC is crucial for initiating cell cycle entry whilst switching to LOC is crucial for cell cycle completion and exit. Consequently, forcing cells to remain in HOC by application of a thiol reductant leads to multiple rounds of cell cycle entry despite failure to complete the preceding cell cycle. On the other hand, forcing cells to remain in LOC by treating with a thiol oxidant prevents initiation of cell cycle entry.
In conclusion, I propose that peroxiredoxins – by controlling metabolic cycles, which are in turn crucial for regulating the progression through cell cycle – play a central role in the coordination of cellular metabolism with cell division. This proposition, thus, positions peroxiredoxins as active players in the cellular timekeeping mechanism.
In this thesis, we present the basic concepts of isogeometric analysis (IGA) and we consider Poisson's equation as model problem. Since in IGA the physical domain is parametrized via a geometry function that goes from a parameter domain, e.g. the unit square or unit cube, to the physical one, we present a class of parametrizations that can be viewed as a generalization of polar coordinates, known as the scaled boundary parametrizations (SB-parametrizations). These are easy to construct and are particularly attractive when only the boundary of a domain is available. We then present an IGA approach based on these parametrizations, that we call scaled boundary isogeometric analysis (SB-IGA). The SB-IGA derives the weak form of partial differential equations in a different way from the standard IGA. For the discretization projection
on a finite-dimensional space, we choose in both cases Galerkin's method. Thanks to this technique, we state an equivalence theorem for linear elliptic boundary value problems between the standard IGA, when it makes use of an SB-parametrization,
and the SB-IGA. We solve Poisson's equation with Dirichlet boundary conditions on different geometries and with different SB-parametrizations.
Micro machining with micro pencil grinding tools (MPGTs) is an emerging technology that can be used to manufacture closed microchannel structures in hard and brittle materials as well as hardened steels like 16MnCr5. At their current operating conditions, these tools have a comparatively short tool life. In previous works, MPGTs in combination with a minimum quantity lubrication (MQL) system were used to manufacture microchannels in 16MnCr5 hardened steel. The study has shown that steel adhesions clog the abrasive layer of MPGTs, most likely resulting from insufficient lubrication. In this paper, a metalworking fluid (MWF) supply method was developed to improve the process: a submerged micro grinding process, in which machining takes place inside a pool of MWF. In this study, the effect of seven types of MWFs on material adhesions at the bottom surface of the tool is evaluated. Equivalent good MWFs are then compared in a micro pendulum grinding experiment till failure.
In a (linear) parametric optimization problem, the objective value of each feasible solution is an affine function of a real-valued parameter and one is interested in computing a solution for each possible value of the parameter. For many important parametric optimization problems including the parametric versions of the shortest path problem, the assignment problem, and the minimum cost flow problem, however, the piecewise linear function mapping the parameter to the optimal objective value of the corresponding non-parametric instance (the optimal value function) can have super-polynomially many breakpoints (points of slope change). This implies that any optimal algorithm for such a problem must output a super-polynomial number of solutions. We provide a method for lifting approximation algorithms for non-parametric optimization problems to their parametric counterparts that is applicable to a general class of parametric optimization problems. The approximation guarantee achieved by this method for a parametric problem is arbitrarily close to the approximation guarantee of the algorithm for the corresponding non-parametric problem. It outputs polynomially many solutions and has polynomial running time if the non-parametric algorithm has polynomial running time. In the case that the non-parametric problem can be solved exactly in polynomial time or that an FPTAS is available, the method yields an FPTAS. In particular, under mild assumptions, we obtain the first parametric FPTAS for each of the specific problems mentioned above and a (3/2 + ε) -approximation algorithm for the parametric metric traveling salesman problem. Moreover, we describe a post-processing procedure that, if the non-parametric problem can be solved exactly in polynomial time, further decreases the number of returned solutions such that the method outputs at most twice as many solutions as needed at minimum for achieving the desired approximation guarantee.
This contribution presents the results of a replication study on the learning effect of tablet-supported video analysis compared to traditional teaching sequences using non-digital experimental materials in the subject areas of uniform and accelerated motion in high school physics lessons. In addition to the replication of the preliminary study results recently published in this journal (Becker et al 2018, 2019), the investigation of the effect on the cognitive load as well as the emotional state of the students is another focal point. Compared to the preliminary study, the sample size was significantly increased from N = 109 to N = 294. The individual effects of the preliminary study could be replicated in this way. For both topics, a significant reduction of extraneous cognitive load and a positive effect on intervention-induced emotions could be demonstrated. Moreover, the theoretically founded causal relationship between emotion, cognitive load, and learning achievement could be empirically verified by means of structural equation modeling.