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Study of mechanisms of the Spark Plasma Sintering technique
Bouda, Václav; Chráska, Tomáš; Cinert, Jakub
2018 - English
This Doctoral thesis is written for the purpose of a deeper understanding of the spark plasma sintering processes. The main objective of the work is to deeply evaluate how the change of sintering parameters (length of electric pulse, heating rate and sintering pressure) can affect the material properties of a sintered sample. The sintering process was investigated in detail, especially the reliability of temperature measurement. It was found that the measured temperature is different to the real temperature of the sintered sample, moreover this temperature difference depends on the parameters of sintering and the electrical conductivity of sintered powder. On the base of measured data, the sintering process was optimised and the reproducibility of sintering was investigated. While samples sintered by non-pulsed current showed relatively a good reproducibility, the reproducibility of samples sintered by pulse current was significantly worse. The influence of the sintering parameters were studied on a carefully selected materials with regard to the previous measurement. The mechanical properties of the sintered samples were studied through a measurement of porosity, hardness and flexural strength. The phase composition of samples was characterised by XRD analysis. It was found that the pulsed current has not improved any mechanical properties of the sintered samples and contrarily its usage might result in worsening of mechanical properties of the sintered samples. All measurements in this work provide new knowledge about the Spark Plasma Sintering process and thereby contribute to a better understanding of the spark plasma sintering processes. These results might be well used in a further research.Předložená doktorská práce se zabývá hlubším porozuměním problematiky Spark Plasma Sintering, hlavním cílem práce je vyhodnocení vlivu parametru slinování (jako je například délka elektrického pulzu, rychlost ohřevu nebo sekvence ohřevu a aplikovaného tlaku) na mechanické vlastnosti slinutých vzorků. Proces byl detailně studován, zejména pak přesnost měření procesních teplot. Bylo zjištěno, že se teplota slinovaného prášku a teplota měřená výrazně liší. Tento teplotní rozdíl závisí na parametrech slinování, zejména na rychlosti ohřevu a na elektrické vodivosti slinovaného prášku. Na základě naměřených dat byl slinovací proces zoptimalizován a byla vyhodnocena jeho reprodukovatelnost. Jak ukazují naměřené údaje, při slinování stejnosměrným proudem lze dosáhnout poměrně dobré opakovatelnosti výroby, ovšem při použití pulzního proudu se reprodukovatelnost procesu znatelně zhoršuje. Vliv parametrů slinování byl vyhodnocován na široké řadě prášků a při vyhodnocení byly využity poznatky z předchozích měření, zejména byl brán ohled na reprodukovatelnost procesu slinování. Mechanické vlastnosti, respektive jejich změny byly u jednotlivých vzorků vyhodnocovány pomocí měření pórovitosti, tvrdosti a pevnosti v ohybu. U vzorků bylo dále zkoumáno jejich fázové složení a byla pozorována jejich mikrostruktura. Bylo zjištěno, že slinování pulzním proudem nepřináší oproti slinování stejnosměrným proudem žádné prokazatelné vylepšení materiálových vlastností vzorků, naopak u některých typů materiálů bylo prokázáno jejich zhoršení. Všechna tato měření přináší nový pohled na problematiku Spark Plasma Sintering a do značné části prohlubují současný stav znalostí této metody. Tyto výsledky mohou být využity při dalším výzkumu.
Available in digital repository of ČVUT.
Study of mechanisms of the Spark Plasma Sintering technique
This Doctoral thesis is written for the purpose of a deeper understanding of the spark plasma sintering processes. The main objective of the work is to deeply evaluate how the change of sintering ...
PHOTONIC SERVICES FOR NON-STANDARD APPLICATIONS OVER ALL-OPTICAL NETWORKS
Zvánovec, Stanislav; Radil, Jan; Škoda, Pavel
2017 - English
Available in digital repository of ČVUT.
PHOTONIC SERVICES FOR NON-STANDARD APPLICATIONS OVER ALL-OPTICAL NETWORKS
Supporting Exploratory Testing by Automated Navigation Using the Model of System Under Test
Jelínek, Ivan; Bureš, Miroslav; Frajták, Karel
2017 - English
Exploratory Testing (ET) is software testing technique, which is applicable to software
development projects, in which test basis (design documentation) is not available, or at
least not complete and consistent enough to allow the creation of e cient test cases. The
principle of this technique is simultaneous learning, creation of the test cases and testing
of the explored system under test (SUT).
The key factor for the e ciency of this technique a documentation of explored tester's
path in the SUT and the exercised test cases. When this is not being documented properly,
ET loses its potential e ciency. Documentation of the explored paths in the SUT also
allows more accurate reports of found defects, together with the possibility of the more
systematic creation of the test cases during the exploratory testing process, preventing
potential duplicities in executed tests. Created test cases can be used later in the next
testing phases (retesting of xed defects or regression testing, for instance).
Currently, a large ratio of web applications is usually developed without any or su -
cient underlying models. In the most of the cases, this is a consequence of required low
development costs and usually short time-to-market in the competitive software development
environment. Nevertheless, the model is still implicitly present in the SUT code and
with proper techniques, it is possible to reconstruct it from the SUT.
Using the browser extension and server application, the framework automatically records
selected actions of the exploratory testers in the SUT. Based on this recorded data,
a screen-
ow based model of the SUT is incrementally created and automatically updated.
Based on this model and tester's position in the SUT during the testing process, the
framework dynamically creates navigational test cases guiding the testers in the SUT and
supports its e cient exploration.
The recorded model consists of parts representing SUT pages, forms, input elements
of the pages, and action elements as submit buttons and links. Besides that, home page,
error pages and transition between SUT pages are de ned. The model constructs are
accompanied by technical information and meta{data to support the model construction
and generation of navigational test cases.
In the test leader role, the tester can also extend the model with additional meta{
data. For example, he can prioritize certain pages or selected actions as a result of a risk
analysis of the SUT. Moreover, he can de ne equivalence classes determining the suitable
test data for particular inputs (e.g. text boxes in the forms) for the later generation of the
navigational test cases. The SUT model is described formally and de ned constructs are
used to document the proposal and the experiments verifying the framework functionality
and practical e ciency.
During the dynamical generation of navigational test cases, several navigational strategies
can be selected. These strategies are based on combinations of the inputs like the
parts of the SUT previously explored by an individual tester or all testers in the team,
priority of the particular pages marked by the test team leader, or complexity of explored
page elements.
Performed experiments show that Exploratory Testing aided by this automated support
is less resource demanding than Exploratory Testing performed manually only. With this
support, also larger parts of the SUT were explored by the experiment participants in
the de ned time. Also, as defect injection experiments have shown, that the proposed
automated support helped the testing teams to detect more inserted software defects than
ET performed as a manual process only.
In particular, the main contributions of the dissertation thesis are as follows:
Design and experimental implementation of automated method, which makes Exploratory
Testing process more e cient in terms of spent resources, extent of explored
SUT and found defects.
Innovative combination of Exploratory Testing, Model{Based Testing and Reverse{
Engineering.
De nition of formal model of the underlying system under test, which serves as a
basis for the framework functionality.
Design of initial navigational strategies, ranking functions, and test data strategies,
used in the framework. These strategies are supporting the individual as well as team
exploratory testing.
Practical applicability of the proposed framework to industrial software development
and testing projects.
Available in digital repository of ČVUT.
Supporting Exploratory Testing by Automated Navigation Using the Model of System Under Test
Exploratory Testing (ET) is software testing technique, which is applicable to software development projects, in which test basis (design documentation) is not available, or at least not complete ...
Blood vessel segmentation in the analysis of retinal and diaphragm images
Novák, Daniel; Štěpánková, Olga; Vostatek, Pavel
2017 - English
The segmentation and characterization of structures in medical images represents an
important part of the diagnostic and research procedures in medicine. This thesis focuses
on the characterization methods in two application fields that make use of two imaging
modalities. The first topic is the characterization of the blood vessel structure in the
human retina and the second is the characterization of diaphragm movement during
breathing. The imaged blood vessel structures are considered important landmarks in
both applications.
The framework for the retinal image processing and analysis starts with the testing
of five publicly available blood vessel segmentation methods for retinal images. The
parameters of the methods are optimized on five databases with the ground truth for
blood vessels. An approach for predicting the method parameters is proposed based on
the optimization results. The parameter prediction approach is then applied to obtain
vessel segmentation on a new database and an automatic approach to the blood vessel
classification and computation of the arteriovenous ratio is proposed and evaluated on
the new database.
The framework for the diaphragm image processing and analysis is based on the measurement
of diaphragm motion. The motion is characterized by a set of features quantifying
the amplitude and frequency of the breathing pattern, as well as a portion of the nonharmonic
movements that occur. In addition, a set of static features like the diaphragm
slope and height are proposed. Two approaches for the motion measurement are proposed
and compared. A statistical evaluation of the proposed features is performed by
comparing measurements from people with and without spinal findings.
The results from the retinal image processing and analysis revealed the possibility of the
successful prediction of the parameters of the blood vessel segmentation methods. The
automatic approach for the automatic arteriovenous ratio estimation revealed a stronger
association with blood pressure than the manually estimated ratio. The results from the
diaphragm image processing and analysis confirmed differences in the position, shape and
breathing patterns between the healthy people and people suffering from spinal findings.
The blood vessel structure was shown to be a reliable marker for characterizing the
diaphragm motion.
Available in digital repository of ČVUT.
Blood vessel segmentation in the analysis of retinal and diaphragm images
The segmentation and characterization of structures in medical images represents an important part of the diagnostic and research procedures in medicine. This thesis focuses on the characterization ...
Visible Light Communications for Indoor Applications
Zvánovec, Stanislav; Chvojka, Petr
2017 - English
The field of visible light communications (VLC) has undergone a rapid development in
recent years. The increased utilization of light emitting diodes (LEDs) has opened new
possibilities for especially indoor services such as broadband internet connection and po-
sitioning. Thus, a research within VLC is the main focus of the thesis and is divided into
two main parts. At rst, the multiband carrier-less amplitude and phase (m-CAP) mod-
ulation, introducing a newly adopted format for spectrally e cient VLC links, is under
investigation using both theoretical and experimental approaches. The recommendations
for m-CAP transmitter site design are proposed. Next, the channel modeling of indoor
VLC is investigated with emphasis on the dynamically changing environments caused by
moving people and non-line of sight (NLOS) propagation and new statistical models are
derived.
Keywords:
channel modeling; multiband carrier-less amplitude and phase; visible light communications
Available in digital repository of ČVUT.
Visible Light Communications for Indoor Applications
The field of visible light communications (VLC) has undergone a rapid development in recent years. The increased utilization of light emitting diodes (LEDs) has opened new possibilities for ...
Dynamic Reconfiguration of Intrusion Detection Systems
Pevný, Tomáš; Rehák, Martin; Stiborek, Jan
2017 - English
Intrusion detection systems (IDS) used in network security are complex solutions that require
precise tuning prior to their deployment. Such tuning, however, is a problem. If done statically,
the fixed configuration fails to follow the dynamic trends in the network traffic. On the other
hand, configuration which is dynamically optimized using the complete traffic of the monitored
network (background traffic) is infeasible due to the lack of ground-truth. To tackle these issues,
researchers recently proposed to mix prerecorded static traces of labeled network traffic (i.e.
challenges) into the background traffic, where they serve as evaluation data, and the IDS is
dynamically adapted with respect to these challenges.
This thesis extends the challenge-based approach in two steps. In the first step, we adopt
techniques from game theory to model the interactions between IDS (defender) and an attacker
to make the adaptation process robust against the rational adversaries. We propose
a dynamically-defined two-player single stage game with complex utility function to precisely
capture incentives of both attacker and defender. Next, we combine the game definition with
the challenge-based principle so we can estimate the parameters of the security game online, use
traditional game-theoretical solution concept to solve the game, and immediately reconfigure
the IDS accordingly. The experimental evaluation proves that this approach outperforms the
trust-based baseline solution and thus allows us to improve the performance of the IDS against
rational attacker.
However, using fixed database of static challenges for dynamic adaptation of the IDS is still
far from optimal as it provides data with only limited variability, and manual updates of the
database cannot provide new data fast enough as new trends and techniques used by malware
authors emerge literally every day.
To solve these problems, we propose to replace legitimate challenges with dynamic simulation
of network behavior based on probabilistic generative model. We experimentally verified that
the proposed model generates network traffic similar to the traffic of real users. Next, we
automate the updating the database of malicious challenges via emulation of malicious behavior
with network traffic observed during execution of malware binaries in controlled environment
(sandbox). In order to address the lack of labeled malware binaries, we propose novel approach
for classification and clustering of unknown binaries based on their interactions with system
resources (files, network traffic, mutexes, registry keys and error messages generated by the
operating system). Moreover, the proposed model prioritizes the generated clusters to further
aid the manual analysis of the threat level required in the definition of the security game. The
performance of the classification and clustering of malware binaries is verified on large real-world
dataset.
Available in digital repository of ČVUT.
Dynamic Reconfiguration of Intrusion Detection Systems
Intrusion detection systems (IDS) used in network security are complex solutions that require precise tuning prior to their deployment. Such tuning, however, is a problem. If done statically, the ...
Coupled Learning and Planning for Active 3D Mapping
Svoboda, Tomáš; Zimmermann, Karel; Petříček, Tomáš
2017 - English
The thesis presents several results in the area of 3D perception, with focus on combining
learning and planning in active 3D mapping.
Autonomous robots, including those deployed in search and rescue operations or autonomous
vehicles, must build and maintain accurate representations of the surroundings
to operate e ciently and safely in human environment. These representations, or
maps, should encompass both low-level information about geometry of the scene and
high-level semantical information, including recognized categories or individual objects.
In the rst part we propose a method of 3D object recognition based on matching local
invariant features, which is further extended for 3D point cloud registration task and
evaluated on challenging real-world datasets. The method builds on a multi-stage feature
extraction pipeline composed of sparse keypoint detection to reduce complexity of
further stages, establishing local reference frames as a means to achieve invariance with
respect to rigid transformations without sacri cing descriptiveness of the underlying 3D
shape, and a compact description of the shape based on area-weighted normal projections.
For a moderate overlap between the laser scans, the registration method provides
a superior registration accuracy compared to state-of-the-art methods including Generalized
ICP, 3D Normal-Distribution Transform, Fast Point-Feature Histograms, and
4-Points Congruent Sets.
In the second part, two tasks from the area of active 3D mapping are being solved|
namely, simultaneous exploration and segmentation with a mobile robot in a search and
rescue scenario, and active 3D mapping using a sensor with steerable depth-measuring
rays, with applications in autonomous driving. For these tasks, we assume that the
localization is provided by an external source.
In the simultaneous exploration and segmentation task, we consider a mobile robot
exploring an unknown environment along a known path, using a static panoramic sensor
providing RGB and depth measurements, and controlling a narrow eld-of-view
thermal camera mounted on a pan-tilt unit. The task is to control the sensor along
the path to maximize accuracy of segmentation of the surroundings into human body
and background categories. Since demanding optimal control does not allow for online
replanning, we rather employ the optimal planner o ine to provide guiding trajectories
for learning a CNN-based control policy in a guided Q-learning framework. A policy
initialization is proposed which takes advantage of a special structure of the task and
allows e cient learning of the policy.
In the active 3D mapping task, our method simultaneously learns to reconstruct a
dense 3D occupancy map from sparse measurements and optimizes the reactive control
of depth-measuring rays. We propose a fast prioritized greedy algorithm to solve
the control subtask online, which needs to update the cost function in only a small
fraction of possible rays in each iteration. An approximation ratio of the algorithm is
derived. We experimentally demonstrate, using publicly available KITTI dataset, that
accuracy of the 3D improves signi cantly when learning-to-reconstruct is coupled with
the optimization of depth measuring rays.
Available in digital repository of ČVUT.
Coupled Learning and Planning for Active 3D Mapping
The thesis presents several results in the area of 3D perception, with focus on combining learning and planning in active 3D mapping. Autonomous robots, including those deployed in search and rescue ...
Virtual Distributed Computing Systems and Their Applications
Janeček, Jan; Fesl, Jan
2017 - English
This dissertation thesis deals with the architecture, benchmarking, optimization and
implementation of virtual distributed computing systems. Large distributed systems rep-
resenting the performance background of all modern cloud computing architectures have
become a very hot topic at present. This dissertation thesis o ers an introduction into
modern technologies showing a rapid impact on the system performance. One of them is
virtualization technology, whose real e ciency was a standalone part of the research. Large
distributed systems consume a huge amount of electric power, therefore their optimization
was also discussed. New ideas originated from the research were incorporated into the pro-
posal of a new distributed system called Centr aln mozek univerzity (CMU). This system
is able to manage and automatically optimize large virtualization infrastructures. It is also
accessible to the end-users. This system is currently used in teaching many subjects and
became a prototype of an educational system of new generation.
In particular, the main contributions of the dissertation thesis are as follows:
1. Methodology, design and implementation of a new software benchmark utility able
to measure virtualization e ciency of the distributed architecture.
2. New approach in a possible migration of the entire distributed systems between
various data centres.
3. New distributed algorithm for virtual machines consolidation, rapidly reducing the
energy consumption.
4. Design, description and implementation of the distributed virtualization system CMU.Diserta cn pr ace se zaob r a architekturami, testov an m, optimalizac a implementac
virtu aln ch distribuovan ych syst em u. Rozs ahl e distribuovan e syst emy, kter e stoj v pozad
v sech modern ch cloudov ych architektur, jsou v sou casn e dob e skute cn e zhav ym t ematem.
Pr ace obsahuje teoretick y uvod do modern ch virtualiza cn ch technologi , kter e rapidn e
ovliv nuj v ypo cetn v ykon. Efektivita virtualiza cn ch technologi byla jedn m z kl cov ych
t emat vlastn ho v yzkumu. Rozs ahl e v ypo cetn infrastruktury spot rebov avaj obrovsk e
mno zstv elektrick e energie, p ri cem z optimalizace spot reby byla dal s m p redm etem v yzkumu.
Inovativn my sleny, kter e vznikly ve f azi v yzkumu, byly integrov any do n avrhu a im-
plementace nov eho distribuovan eho virtualiza cn ho syst emu, kter y nese n azev Centr aln
mozek univerzity (CMU). Tento syst em je schopen pln e automatizovan e spravovat a op-
timalizovat distribuovan e infrastruktury pro virtualizaci. Syst em dok a ze zprost redkovat
p r stup pro vyu zit sv ych v ypo cetn ch prost redk u koncov ym u zivatel um. Takov ato kon-
cepce syst emu je sou casn e prototypem v yukov eho syst emu nov e generace, ve kter em je
vyu zita architektura datov ych center pro v yuku univerzitn ch p redm et u.
Keywords:
virtualization; distributed computing systems; cloud computing; live migration; green computing
Available in digital repository of ČVUT.
Virtual Distributed Computing Systems and Their Applications
This dissertation thesis deals with the architecture, benchmarking, optimization and implementation of virtual distributed computing systems. Large distributed systems rep- resenting the performance ...
Graph-based Detection of Malicious Network Communities
Rehák, Martin; Pevný, Tomáš; Jusko, Ján
2017 - English
In this thesis, we use graph based methods in conjunction with behavioral modeling to uncover
hidden malicious communities and peer-to-peer tra c.
The nature of malicious tra c, and its tendency to rally in order to communicate with
its owner opens a possibility to detect malicious tra c by revealing hidden sub-structures of
network tra c. In fact, besides discovering the presence of an infection, analyzing network
tra c also enables inference of valuable context information about the malicious campaign
as a whole, often leading to a more precise attribution than is possible using only a hostbased
solution. In this work, we focus on the detection approaches that observe the hidden
structures and exploit them to uncover malicious command & control (C&C) servers.
Peer-to-peer (P2P) protocol is a popular choice with malware authors to be used as a C&C
channel. Therefore, we propose a uni ed solution to identify P2P communities operating in a
monitored network. We propose an algorithm that is able to 1) progressively discover hosts in
the monitored network that cooperate in a P2P network and to 2) identify that P2P network.
Starting from a single known host, other hosts participating in the P2P network are identi ed
through the analysis of widely available and standardized IPFIX (NetFlow) data. It is able
to identify a large range of both legitimate and malicious P2P networks, is highly scalable
and the use of standard meta-data without access to tra c content makes it easy to deploy
and justify from privacy protection perspective.
Even malware families that do not rely on a P2P-based C&C channels resort to highly
dynamic C&C structures to counter security industry approaches based on blacklisting known
malicious domains. It is therefore important to automatically follow the migration of C&C
servers. We propose to use a well-known Probability Threat Propagation (PTP) with a novel
graph representation capturing connections from clients to servers. The proposed graph
representation is highly condensed, preserves privacy, allows us to nd malicious domains
that cannot be found using existing graph representations and is harder to evade by malware
authors.
We propose two behavioral models for HTTP tra c together with kernel-based similarity
and distance functions that can be conveniently used to extend the ndings of PTP. For
any domain marked as malicious by PTP we can nd other domains with identical or similar
behavior, which are likely also malicious. This signi cantly increases the number of discovered
malicious domains.
All proposed algorithms and representations are veri ed using extensive data sets spanning
hundreds of independent networks. The validity of proposed approaches was further veri ed
in a large-scale deployment within the Cisco Cognitive Threat Analytics.
Available in digital repository of ČVUT.
Graph-based Detection of Malicious Network Communities
In this thesis, we use graph based methods in conjunction with behavioral modeling to uncover hidden malicious communities and peer-to-peer tra c. The nature of malicious tra c, and its tendency to ...
Multi-Agent Planning by Plan Set Intersection
Pěchouček, Michal; Komenda, Antonín; Tožička, Jan
2017 - English
Coordination of a team of cooperative agents and their activities towards fulfillment
of goals is described by multi-agent planning. For deterministic environments,
where agents are not willing to share all their knowledge, the MA-STRIPS model
provides minimal extension from classical planning. MA-STRIPS exactly prescribes
what information can be freely communicated between the agents and what information
has to be kept private such that the shared or individual goals can be still
achieved.
This thesis proposes a novel multi-agent planning approach which distributively
intersects local plans of the agents towards a global solution of the multi-agent planning
problem. This core principle builds on local compilation to a classical planning
problem and compact representation of the local plans in the form of Finite State Machines.
The efficiency of the resulting planner is further boosted up by distributed
delete-relaxation heuristic, an approximative local plan analysis, and reduction of
agents’ internal problems.
The planning approach is analysed theoretically, in particular we prove its completeness
and soundness. Experimental evaluation shows its applicability in a full
privacy setting where only public information can be communicated and in less restricted
privacy settings. At a recent international competition of distributed multiagent
planners, the proposed planner showed top performance when compared
with other existing state-of-the-art multi-agent planners.
Available in digital repository of ČVUT.
Multi-Agent Planning by Plan Set Intersection
Coordination of a team of cooperative agents and their activities towards fulfillment of goals is described by multi-agent planning. For deterministic environments, where agents are not willing to ...
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