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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 91 to 98 of 98 (0.041 seconds)| 91 |
Secure Quantum EncryptionSt-Jules, Michael January 2016 (has links)
To the field of cryptography, quantum mechanics is a game changer. The exploitation of quantum mechanical properties through the manipulation of quantum information, the information encoded in the state of quantum systems, would allow many protocols in use today to be broken as well as lead to the expansion of cryptography to new protocols. In this thesis, quantum encryption, i.e. encryption schemes for quantum data, is defined, along with several definitions of security, broadly divisible into semantic security and ciphertext indistinguishability, which are proven equivalent, in analogy to the foundational result by Goldwasser and Micali. Private- and public-key quantum encryption schemes are also constructed from quantum-secure cryptographic primitives, and their security is proven. Most of the results are in the joint paper Computational Security of Quantum Encryption, to appear in the 9th International Conference on Information Theoretic Security (ICITS2016).
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Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses: The PENELOPE Laser SystemLöser, Markus 22 January 2018 (has links)
The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control
filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.
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Evaluation of the Nguni cattle reproductive performance in the communal property association and privately owned enterprises across ecological zones of Mpumalanga ProvinceSambo, Johan Mackson January 2020 (has links)
Thesis (M.A. Agricultural Management (Animal Production)) -- University of Limpopo, 2020 / The Nguni is indigenous multi-purpose cattle breed that plays an important role in
both commercial and communal farming systems in South Africa (SA).
Unfortunately, the breed is currently under threat of diminishing due to farmers’
preference for exotic breeds and cross breeding. In recognition of the above, the
Industrial Development Corporation, the Mpumalanga Department of Agriculture,
Rural Development, Land and Environmental Affairs and the University of Limpopo
established the Nguni cattle breed preservation project. In this project, a herd of 30
Nguni heifers and 1 bull were allocated to 34 Communal Property Associations
(CPA) and 40 private farming enterprises each. With its three distinct ecological
zones (High, Mid and Low-veld), the Mpumalanga province poses a challenge to
the Nguni preservation project since cattle have to adapt to different ecological
zones in order to grow and reproduce efficiently. Knowledge of cattle herd
productivity improves the understanding of the functional attributes and is useful in
determining the constraints and the potential of communal beef cattle production
systems. Significant differences between ecological zones were observed for age
at first calving, weaning rate, calves’ birth weight and calves’ weaning weight
(p < 0.05). Calving of heifers in the Mid-veld zone occurred earlier (24 months) on
both ownership types compared to Highveld (28.09 months for private and 26.00 for
CPA) and the Lowveld (28.35 months for both ownerships). Nguni cattle on the
Highveld performed better in terms of weaning rate under both private and CPA
ownerships, where the weaning rate were 93% and 80%, respectively. Calves birth
weight was lower in both ownership types in the Midveld zone (22.17 kg), whereas
in the CPA, the Lowveld zone had higher calves birth weights (26.80 kg). In the
private ownership, the highest calves’ birth weight (25.35 kg) was on the Highveld.
The calves weaning weight were significantly higher (p < 0.05) on Highveld in
private ownership (190.16 kg) and lowest (160.39 kg) in the Midveld zone. For the
CPA, the highest calves weaning weight was also on the Highveld (187.55) and
lowest on Midveld (167.50 kg). A full range of backup services that are offered to
the communities by stakeholders in the form of a beef package that includes veld
and pasture management, nutrition management, beef performance, animal
recording keeping, genetic evaluation and animal health management program
needs thorough attention.
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Étude de la différenciation des lymphocytes T CD8+ effecteurs et mémoires : rôle de la cellule présentatrice d’antigène et de la voie de signalisation NotchMathieu, Mélissa 09 1900 (has links)
Lors d’une infection par un pathogène, des lymphocytes T CD8+ naïfs (LTn) spécifiques de l’antigène sont activés, prolifèrent et se différencient en LT effecteurs (LTe). Les LTe produisent différentes cytokines et acquièrent une activité cytotoxique menant à l’élimination du pathogène. Seulement 5 à 10 % des LTe survivront et se différencieront en LT mémoires (LTm), qui sont capables de répondre plus rapidement lors d’une seconde infection par le même pathogène, contribuant au succès de la vaccination. Toutefois, la compréhension de l’ensemble des mécanismes régulant le développement des LTe et des LTm demeure incomplète. Afin de mieux comprendre les signaux requis pour la différenciation des LT CD8+ lors de la réponse immune, nous avons posé deux hypothèses.
Nous avons d’abord proposé que différentes cellules présentatrices d’antigène (CPA) fournissent différents signaux au moment de la reconnaissance antigénique influençant ainsi le devenir des LT CD8+. Vu leur potentiel d’utilisation en immunothérapie, nous avons comparé la capacité d’activation des LT CD8+ par les lymphocytes B activés via le CD40 (CD40-B) et les cellules dendritiques (CD). Nous avons montré que l’immunisation avec des CD40-B induit une réponse effectrice mais, contrairement à l’immunisation avec des CD, pratiquement aucun LTm n’est généré. Les LTe générés sont fonctionnels puisqu’ils sécrètent des cytokines, ont une activité cytotoxique et contrôlent une infection avec Listeria monocytogenes (Lm). Nous proposons qu’une sécrétion plus faible de cytokines par les CD40 B ainsi qu’une interaction plus courte et moins intime avec les LT CD8+ comparativement aux CD contribuent au défaut de différenciation des LTm observé lors de la vaccination avec les CD40-B.
Ensuite, nous posé l’hypothèse que, parmi les signaux fournis par les CPA au moment de la reconnaissance antigénique, la voie de signalisation Notch influence le développement des LTe, mais aussi des LTm CD8+ en instaurant un programme génétique particulier. D’abord, grâce à un système in vitro, le rôle de la signalisation Notch dans les moments précoces suivant l’activation du LT CD8+ a été étudié. Ce système nous a permis de démontrer que la voie de signalisation Notch régule directement l’expression de la molécule PD-1. Ensuite, grâce à des souris où il y a délétion des récepteurs Notch1 et Notch2 seulement chez les LT CD8+ matures, un rôle de la voie de signalisation Notch dans la réponse immune des LT CD8+ a été démontré. Nos résultats démontrent que suite à une infection avec Lm ou à une immunisation avec des CD, la signalisation Notch favorise le développement de LTe, exprimant fortement KLRG1 et faiblement CD127, destinés à mourir par apoptose. Toutefois, la signalisation Notch n’a pas influencé la génération de LTm. De façon très intéressante, l’expression des récepteurs Notch influence la production d’IFN- en fonction du contexte d’activation. En effet, suite à une infection avec Lm, l’absence des récepteurs Notch n’affecte pas la production d’IFN- par les LTe, alors qu’elle est diminuée suite à une immunisation avec des CD suggérant un rôle dépendant du contexte pour la voie de signalisation Notch.
Nos résultats permettent une meilleure compréhension des signaux fournis par les différentes CPA et de la voie de signalisation Notch, donc des mécanismes moléculaires régulant la différenciation des LT CD8+ lors de la réponse immunitaire, ce qui pourrait ultimement permettre d’améliorer les stratégies de vaccination. / Following an infection with a pathogen, antigen-specific naive CD8+ T lymphocytes (Tn) will proliferate and differentiate into effector (Te) cells. Those Te cells will produce different cytokines and acquire a cytotoxic activity, leading to pathogen clearance. Only 5 to 10 % of Te cells will survive and differentiate into memory CD8+ T lymphocytes (Tm) able to respond rapidly following a second encounter with the same pathogen, contributing to the success of vaccination. However, the mechanisms regulating Te and Tm cells development remain incompletely understood. To better understand the signals required for CD8+ T lymphocytes during an immune response, we proposed two hypotheses.
First, we propose that different antigen presenting cells (APCs) can deliver different signals to CD8+ T lymphocytes at the time of priming leading to different outcome. Given their potential for use in immunotherapy, we compared the ability of CD40 activated B lymphocytes (CD40-B) and dendritic cells (DCs) to activate CD8+ T lymphocytes. We have shown that CD40-B cell immunisation leads to an effector response but very few Tm cells are generated compared to DC immunisation. The Te cells generated following CD40-B cell immunisation are functional because they secrete cytokine, are cytotoxic and control a Listeria monocytogenes (Lm) infection. We propose that CD40-B cells secrete less cytokines and interact during shorter period of time with the CD8+ T lymphocytes, without engulfment, contributing to the decreased Tm generation observed following immunisation with CD40-B cells.
Second, among the signals provided by APC at the time of CD8+ T lymphocyte priming, we have hypothesised that the Notch signalling pathway influences Te and Tm cell differentiation by inducing a particular genetic program. Using an in vitro system, we first studied the role of the Notch signalling pathway in the hours following CD8+ T lymphocyte priming. We demonstrated that Notch signalling directly regulates PD-1 expression. Then, studying mice where Notch1 and Notch2 receptor genes are deleted only in mature CD8+ T lymphocytes, we characterised the role of the Notch signalling pathway on Te and Tm differentiation during an immune response. Our results show that following Lm infection or a DC immunisation, the Notch signalling pathway promotes the differentiation of short lived effector cells Te cells (KLRG1highCD127low) meant to die by apoptosis. However, the Notch signalling pathway did not influence the generation of CD8+ Tm cells. Most interestingly, IFN- regulation by the Notch signalling pathway depends on the activation context. Indeed, following Lm infection, lack of Notch receptors does not impact IFN- secretion by Te cells while it is significantly decreased following a DC immunisation suggesting a context dependant role for the Notch signalling pathway.
Our findings provide a better understanding of the key signals provided by APC as well as the Notch signalling pathway, and thus the molecular mechanisms leading to CD8+ lymphocyte effector and memory generation which is crucial as this knowledge may ultimately lead to improved vaccination.
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台灣五大會計師事務所女性審計人員升遷問題之研究 / A Study of Upward Mobility of Female Auditors in Big 5 Public Accounting石倉安, Shi, Tsang-An Unknown Date (has links)
台灣五大會計師事務所審計部門的從業人員長久以來一直是女性多於男性，每年新進的人員亦以女性居多，然而在高階職位上卻是男性遠多於女性。換言之，若女性審計人員在事務所裡沒有遭受任何升遷上的障礙，以每年新進人員女性多於男性的情況比例計算，在高階職位上女性的人數亦應多於男性，然而真實的情況卻正好相反。故本研究參考之前研究者的研究發現，彙總出台灣五大會計師事務所女性審計人員可能面臨到的升遷障礙，包括性別歧視、性騷擾、家庭與工作衝突和缺乏良師益友（mentor）等，以問卷調查方式蒐集實證資料，並進行統計分析。另外，本研究詢問研究對象所知的審計人員離職原因以及五大會計師事務所現行的工作場所家庭政策，以了解男性與女性審計人員在離職原因上有無差異和事務所提供的家庭福利政策，得到的結果如下：
1.性別歧視：不管從性別、職位和事務所別的角度來看，受試者均趨向於不同意女性審計人員遭受到性別歧視；而在參加選修課程與社交活動的情形上，男性與女性亦沒有顯著的差異。
2.性騷擾：曾經遭受性騷擾的受試者雖然皆為女性，然而僅有12位，比例為8.43%，比之前的研究低許多。
3.工作與家庭衝突：已婚女性比已婚男性感受到較大的衝突程度，而且家中若有生活無法自理、需要特別照顧的家人或小孩的女性，其衝突程度會比沒有需要特別照顧的家人或小孩的女性來得高。反觀已婚的男性受試者，不管家中有無需要特別照顧的家人或小孩，其工作與家庭衝突的程度並沒有顯著的差異。
4.女性缺乏mentor：女性擁有mentor的比例與男性相同；相同職位的男性與女性擁有mentor的比例亦相似。而且深入分析後發現，女性與男性的mentor，在職位上的差異不大，且擁有mentor的女性受試者，對mentor所能提供協助的同意程度，與男性受試者差異不大。
5.離職原因：女性因為「結婚生子」而離職排名第4，為其主要離職原因，男性則否。衡量性別歧視的「升遷機會受限」，則非男女審計人員的主要離職原因。
6.工作場所家庭政策：五大會計師事務所皆有提供產假與留職停薪這兩項福利政策，然而，較具彈性的「半職（part-time）」只有兩個事務所提供；「彈性上班時間」只有一個事務所提供，顯示目前五大事務所的工作場所家庭政策仍不夠多元。
綜上所述，本研究所探討的四個女性升遷障礙：性別歧視、性騷擾、工作與家庭衝突和缺乏mentor等，僅有工作與家庭衝突得到支持。因此在沒有進一步地證據支持另外三項升遷障礙前，工作與家庭衝突似乎是目前五大會計師事務所女性審計人員所共同面臨到的升遷問題，故會計師事務所管理當局應提供更多元的工作場所家庭政策，以降低女性審計人員的工作與家庭衝突。
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Attaques par canaux auxiliaires: nouvelles attaques, contre-mesures et mises en oeuvreFernandes Medeiros, Stéphane 28 April 2015 (has links)
Les attaques par canaux auxiliaires sont apparues dans la deuxième moitié des années 1990. Ces attaques exploitent différentes informations qu’il est possible de collecter lors de l’exécution d’un algorithme sur un appareil cryptographique. Il est ainsi possible, entre autres, de mesurer la consommation d’énergie d’un appareil cryptographique, ou encore d’observer le temps d’exécution d’un certain algorithme sur un appareil. C’est à ces deux sources d’in- formation que nous nous intéressons dans ce travail. Après une présentation des concepts utiles à la lecture du travail et de l’état de l’art des attaques et des contre-mesures du domaine, nous abordons les résultats de nos recherches effectuées lors de ce travail de thèse. Nous présentons d’abord nos contributions aux attaques par mesure de consommation d’énergie :(1) une approche com- binant apprentissage semi-supervisé et attaques par templates pour retrouver le poids de Hamming des différents bytes d’une clé de chiffrement et (2) une approche utilisant des techniques d’apprentissage automatique pour attaquer une implantation protégée d’AES. Ensuite, nous abordons les contre-mesures investiguées durant nos recherches qui se résument (1) en la possibilité de rendre l’ordre des instructions d’AES le plus aléatoire possible en jouant sur la relation de dépendance entre celles-ci ainsi qu’en (2) l’étude de l’application partielle (sur un sous-ensemble de données) de certaines contre-mesures, afin de protéger les données sensibles d’un algorithme. Enfin, nous terminons ce travail par l’emploi de la programmation orientée aspects comme manière d’implanter des contre-mesures pour les attaques temporelles (sur RSA) et pour les attaques par mesures de consommation d’énergie (sur AES). / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
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Legal and regulatory aspects of mobile financial servicesPerlman, Leon Joseph 11 1900 (has links)
The thesis deals with the emergence of bank and non-bank entities that provide a range of unique
transaction-based payment services broadly called Mobile Financial Services (MFS) to unbanked,
underserved and underbanked persons via mobile phones.
Models of MFS from Mobile Network Operators (MNOs), banks, combinations of MNOs and banks, and
independent Mobile Financial Services Providers are covered. Provision by non-banks of ‘bank-type’
services via mobile phones has been termed ‘transformational banking’ versus the ‘additive banking’
services from banks. All involve the concept of ‘branchless banking’ whereby ‘cash-in/cash out’ services
are provided through ‘agents.’
Funds for MFS payments may available through a Stored Value Product (SVP), particularly through a
Stored Value Account SVP variant offered by MNOs where value is stored as a redeemable fiat- or mobile
‘airtime’-based Store of Value.
The competitive, legal, technical and regulatory nature of non-bank versus bank MFS models is discussed,
in particular the impact of banking, payments, money laundering, telecommunications, e-commerce and
consumer protection laws. Whether funding mechanisms for SVPs may amount to deposit-taking such that
entities could be engaged in the ‘business of banking’ is discussed. The continued use of ‘deposit’ as the
traditional trigger for the ‘business of banking’ is investigated, alongside whether transaction and paymentcentric
MFS rises to the ‘business of banking.’
An extensive evaluation of ‘money’ based on the Orthodox and Claim School economic theories is
undertaken in relation to SVPs used in MFS, their legal associations and import, and whether they may be
deemed ‘money’ in law.
Consumer protection for MFS and payments generally through current statute, contract, and payment law
and common law condictiones are found to be wanting. Possible regulatory arbitrage in relation to MFS in
South African law is discussed.
The legal and regulatory regimes in the European Union, Kenya and the United States of America are
compared with South Africa. The need for a coordinated payments-specific law that has consumer
protections, enables proportional risk-based licensing of new non-bank providers of MFS, and allows for a
regulator for retail payments is recommended. The use of trust companies and trust accounts is
recommended for protection of user funds.
| vi / Public, Constitutional and International Law / LLD
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Legal and regulatory aspects of mobile financial servicesPerlman, Leon Joseph 11 1900 (has links)
The thesis deals with the emergence of bank and non-bank entities that provide a range of unique
transaction-based payment services broadly called Mobile Financial Services (MFS) to unbanked,
underserved and underbanked persons via mobile phones.
Models of MFS from Mobile Network Operators (MNOs), banks, combinations of MNOs and banks, and
independent Mobile Financial Services Providers are covered. Provision by non-banks of ‘bank-type’
services via mobile phones has been termed ‘transformational banking’ versus the ‘additive banking’
services from banks. All involve the concept of ‘branchless banking’ whereby ‘cash-in/cash out’ services
are provided through ‘agents.’
Funds for MFS payments may available through a Stored Value Product (SVP), particularly through a
Stored Value Account SVP variant offered by MNOs where value is stored as a redeemable fiat- or mobile
‘airtime’-based Store of Value.
The competitive, legal, technical and regulatory nature of non-bank versus bank MFS models is discussed,
in particular the impact of banking, payments, money laundering, telecommunications, e-commerce and
consumer protection laws. Whether funding mechanisms for SVPs may amount to deposit-taking such that
entities could be engaged in the ‘business of banking’ is discussed. The continued use of ‘deposit’ as the
traditional trigger for the ‘business of banking’ is investigated, alongside whether transaction and paymentcentric
MFS rises to the ‘business of banking.’
An extensive evaluation of ‘money’ based on the Orthodox and Claim School economic theories is
undertaken in relation to SVPs used in MFS, their legal associations and import, and whether they may be
deemed ‘money’ in law.
Consumer protection for MFS and payments generally through current statute, contract, and payment law
and common law condictiones are found to be wanting. Possible regulatory arbitrage in relation to MFS in
South African law is discussed.
The legal and regulatory regimes in the European Union, Kenya and the United States of America are
compared with South Africa. The need for a coordinated payments-specific law that has consumer
protections, enables proportional risk-based licensing of new non-bank providers of MFS, and allows for a
regulator for retail payments is recommended. The use of trust companies and trust accounts is
recommended for protection of user funds.
| vi / Public, Constitutional and International Law / LL. D.
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