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The purpose of the project is to investigate the possibility of using modern machine learning to model nonlinear analog devices like the Power Amplifier (PA), and study the feasibility of using such models in wireless systems design. Orthogonal frequency division multiplexing (OFDM) is one of the most prominent modulation technique used in several standards like 802.11a,802.11n, 802.11ac and more. Telecommunication systems like LTE, LTE/Aand WiMAX are also based on OFDM. Nevertheless, OFDM system shows high peak to average power (PAPR) in time domain because it comprises of many subcarriers added via inverse fast Fourier transform(IFFT). HighPAPR results in an increased symbol error rate, while degrading the efficiency of the PA. Digital predistortion (DPD) still suffers from high symbol error rate (SER) and reduced PA efficiency, when there is an increase in peak back off(PBO). A receiver based nonlinearity distortion reduction approach can be justified by the fact that base stations have high computation power. A iterative-decision-feedback mitigation technique can be implemented as a receiver side compensation assuming memoryless PA nonlinearities. For successful distortion reduction the iterative-decision based technique required the knowledge of the transmitter PA. The author proposes to identify the nonlinear PA model using machine learning techniques like nonlinear regression and deep learning. The results show promising improvement in SER reduction with small PA model learning time. / Syftet med detta projekt är att undersöka möjligheterna att använda modernmaskininlärning för att beskriva ickelinjära analoga enheter såsom effektförstärkareoch att studera hur användbart det är att använda sådana modeller föratt designa trådlösa kommunikationssystem. OFDM (ortogonal frekvensmultiplex)är en av de vanligast förekommande modulationsteknikerna, som användsi standarder såsom 802.11a, 802.11n, 802.11ac and andra. Telekommunikationssystemsom LTE, LTE/A och WiMAX baseras också på OFDM. Dock resulterarOFDM i hög toppeffekt i förhållande till medeleffekten (hög PAPR) i tidsdomänen,eftersom signalen består av många delkanaler som summeras mha inversdiskret fouriertransform (IFFT). En hög PAPR resulterar i ökad symbolfelshaltoch försämrar effektiviteten hos effektförstärkaren. Digital predistortion (DPD)kan förbättra situationen men ger fortfarande hög symbolfelshalt och försämradförstärkareffektivitet, när man drar ned sändeffekten för undvika kvarvarandeickelineariteter. Att minska förvrängningen från ickelineariteterna vid mottagarenkan motiveras i system där basstationerna har hög beräkningsförmåga. Enmetod för att reducera förvrängningarna kan implementeras på mottagarsidan,baserad på iterativ beslutsåterkoppling, under antagandet om att sändarens effektförstärkarehar en minneslös ickelinearitet. För att störningsreduceringenska fungera väl, krävs god kunskap om sändarens effektförstärkare. Författarenföreslår att identifiera en ickelinjär modell för förstärkaren mha maskininlärningstekniker,såsom ickelinjär regression och djup inlärning. Resultaten visarlovande förbättringar av symbolfelshalten med en låg inlärningstid för förstärkarmodellen.

No / Mobile social networks (MSNs) facilitate connections between mobile users and allow them to find other potential users who have similar interests through mobile devices, communicate with them, and benefit from their information. As MSNs are distributed public virtual social spaces, the available information may not be trustworthy to all. Therefore, mobile users are often at risk since they may not have any prior knowledge about others who are socially connected. To address this problem, trust inference plays a critical role for establishing social links between mobile users in MSNs. Taking into account the nonsemantical representation of trust between users of the existing trust models in social networks, this paper proposes a new fuzzy inference mechanism, namely MobiFuzzyTrust, for inferring trust semantically from one mobile user to another that may not be directly connected in the trust graph of MSNs. First, a mobile context including an intersection of prestige of users, location, time, and social context is constructed. Second, a mobile context aware trust model is devised to evaluate the trust value between two mobile users efficiently. Finally, the fuzzy linguistic technique is used to express the trust between two mobile users and enhance the human's understanding of trust. Real-world mobile dataset is adopted to evaluate the performance of the MobiFuzzyTrust inference mechanism. The experimental results demonstrate that MobiFuzzyTrust can efficiently infer trust with a high precision.

Thesis advisor: Pablo Guerron-Quintana / This thesis consists of two self-contained essays on topics in applied macroeconomics. In the first chapter, I study how heterogeneous sensitivities to weather fluctuations and interregional production networks impact the measurement of weather shocks’ impact on economic activity in the United States. I start the analysis by building a general equilibrium model where the impact of weather fluctuations on productivity is state-sector dependent, and networks expose sectors to weather shocks from other regions through the use of intermediate inputs. Then, I quantify the relevance of these mechanisms, combining the model’s predictions with annual data on sectoral GDP and average temperatures by state from 1970 to 2019. My estimates show that models that do not consider these characteristics underestimate the aggregateimpact of weather fluctuations by at least a factor of 3. In particular, when the whole economy faces an unexpected increase in temperature of 1 Celsius degree, the contraction in economic activity increases from -0.13 to -0.37 percent once heterogeneity is considered and -1.14 percent when networks are included. In the second chapter, I propose a new methodology to disentangle between terms of trade movements caused by global shocks and those resulting from country-specific terms-of-trade fluctuations. This methodology extends the so-called maximum-share approach in two ways. Firstly, a global shock is identified as the shock with the highest explanatory power on the forecast error variance of a set of exogenous variables. This is in contrast to the typical approach of using only one variable as a source of information to identify a shock. Secondly, country-specific terms-of-trade shocks are identified as shocks that satisfy two conditions: (i) maximum explanation power on terms-of-trade variability and (ii) orthogonality to global shocks, allowing me to isolate the main drivers of terms of trade that are not related to global fluctuations. I apply this methodology to data on ten small open economies(SOEs) and show that global shocks contribute - on average- to 33 percent of their business cycle fluctuations. The contribution of global shocks to terms-of-trade variability is close to 20 percent, meaning that around 80 percent of terms-of-trade movements have country-specific origins. Interestingly, on average, country-specific terms-of-trade shocks are responsible for less than 10 percent of SOE business cycle variability. These results help to reconcile current estimates on the importance of terms of trade and suggest an intensive evaluation of the origins of terms-of-trade movements by policymakers before any intervention. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

Yes / To investigate factors associated with movement behaviours among White British (WB) and South Asian (SA) children aged 6-8 years during school terms and holidays. Cross-sectional. Three primary schools from the Bradford area, UK. One hundred and sixty WB and SA children aged 6-8 years. Sedentary behaviour (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) measured by accelerometry during summer, winter and spring and during school terms and school holidays. Data were analysed using multivariate mixed-effects multilevel modelling with robust SEs. Factors of interest were ethnicity, holiday/term, sex, socioeconomic status (SES), weight status, weekend/weekday and season. One hundred and eight children (67.5%) provided 1157 valid days of data. Fifty-nine per cent of children were WB (n=64) and 41% (n=44) were SA. Boys spent more time in MVPA (11 min/day, p=0.013) compared with girls and SA children spent more time in SB (39 min, p=0.017) compared with WB children in adjusted models. Children living in higher SES areas were more sedentary (43 min, p=0.006) than children living in low SES areas. Children were more active during summer (15 min MVPA, p<0.001; 27 LPA, p<0.001) and spring (15 min MVPA, p=0.005; 38 min LPA, p<0.001) and less sedentary (−42 min and −53 min, p<0.001) compared with winter. Less time (8 min, p=0.012) was spent in LPA during school terms compared with school holidays. Children spent more time in MVPA (5 min, p=0.036) during weekend compared with weekdays. Overweight and obese children spent more time in LPA (21 min, p=0.021) than normal-weight children. The results of our study suggest that significant child level factors associated with movement behaviours are ethnicity, sex, weight-status and area SES. Significant temporal factors are weekends, school holidays and seasonality. Interventions to support health enhancing movement behaviours may need to be tailored around these factors.

No / Trade credit terms offer firms contractual solutions to informational asymmetries between buyers and sellers. The credit period permits buyers to reduce uncertainty concerning product quality prior to payment, while the seller can reduce uncertainty concerning buyer payment intentions by prescribing payment before/on delivery or through two¿part payment terms and other mechanisms. Variation in trade credit terms also offers firms price discriminating opportunities. This study, drawing on the responses of 700 large firms in the US, UK and Australia, explores trade credit terms through the twin objectives of reducing information asymmetries and discriminatory pricing. Support is found for both theories.

Jede lebendige Sprache ist durch ihren Gebrauch ständigem Wandel unterworfen, der jede Ebene der Sprache betreffen kann – von der Phonologie über die Semantik bis hin zur Grammatik. Die vorliegende Arbeit hat es sich zur Aufgabe gemacht, den semantischen und lexikalischen Wandel des Ägyptischen zu beleuchten. Das Ägyptische ist in seinen verschiedenen Sprachstufen über mehr als vier Jahrtausende hinweg zu verfolgen, und gehört damit zu den am längsten bezeugten Einzelsprachen der Menschheitsgeschichte. Dies und die gute Quellenlage des Ägyptischen machen es zu einem prädestinierten Gegenstand für diachrone Untersuchungen. Nach einer quantitativen Erhebung der Lexeme eines ausgewählten Textkorpus’, der die Grundlage der Arbeit liefert, wurden im zweiten Teil der Dissertation vier Wortfelder exemplarisch auf ihr Wandelverhalten hin untersucht. Diese Wortfelder, Verwandtschafts- und Körperteilbezeichnungen sowie Wahrnehmungsverben und kognitive Verben, gehören zum Grundvokabular einer jeden Sprache, was die Vergleichbarkeit der Ergebnisse garantieren soll. Neben der Beschreibung konkreter Wandelphänomene wurde dabei Fragen nach dem Ablauf, dem Umfang und den Typen von semantischem und lexikalischem Wandel im Ägyptischen nachgegangen. Ziel war es unter anderem, generalisierbare Aussagen zu treffen, die für die allgemeinen Fragestellungen der Sprachwandelforschung, der Diachronen Semantik und der Historischen Linguistik von Relevanz sind, indem sie mit Ergebnissen früherer Untersuchungen zu den verschiedensten Sprachen verglichen bzw. zu ihrer Überprüfung herangezogen werden können. Als Ergebnis der Untersuchung konnten neben der Beschreibung interessanter Einzelbeobachtungen schließlich einige Regularitäten des semantischen und lexikalischen Wandels des Ägyptischen aufgestellt werden. Diese wurden zum Teil bereits durch andere Sprachen bestätigt und können nach weiterer Überprüfung möglicherweise als universale Tendenzen des semantischen Wandels formuliert werden. / Every spoken language is subject to constant change due to its use. This change can affect every level of the language, from phonology to semantics to grammar. The present dissertation is set out to illuminate the semantic and lexical change of the Egyptian language, which can be followed over four thousand years and is therefore one of the longest attested languages of mankind. This and its excellent state of sources make it the ideal subject of a diachronic study. After a quantitative analysis of the lexemes of a carefully chosen set of texts, which provides the foundation of the study, the main part of the dissertation examines four semantic fields with regard to its mode of change. These semantic fields, kinship terms and terms for body parts as well as verbs for cognition and perception, are part of the basic vocabulary of every language, which guarantees the comparability of the results. In addition to the description of individual processes of change, the paper pursues questions of the course, the range, and the types of semantic and lexical change of the Egyptian language. The intention was to form general statements which are of relevance to questions of the study of language change, the Diachronic Semantics as well as the Historical Linguistics, by serving as comparison as well as verification to studies of other languages. As a result of the present paper, some general regularities of the semantic and lexical change of the Egyptian language were established, in addition to the observation of some interesting individual processes of language change. These regularities were already partially confirmed by observations made in other languages and could, after further examination, turn out to be universal tendencies of semantic change.

<p>This thesis examines usage of English colour terms in context, based on an extensive computerised text corpus, the Bank of English. It describes the ways in which English colour terms may be used to refer to nuances outside their normal area of designation and to attributes outside the colour domain. Usage patterns are analysed on three different levels: with regard to the overall frequency of occurrences, nominal domains and individual tokens, respectively. </p><p>Cognitive linguistics supplies the theoretical framework employed in the analyses of the observed patterns. The study identifies three types of usage where colour terms refer to peripheral colour nuances or to concepts outside the colour domain: classifying, figurative and marked usage. </p><p>When a colour term has a classifying function, it can be used outside the normal area of designation. This usage is analysed as a type of reference-point construction where a term referring to a salient point in the colour domain is used to subcategorise an entity whose actual colour may be only a peripheral member of the category named by the colour term. An analysis of the OED and the Bank of English shows that this type of usage is primarily restricted to a few of the most salient basic terms. </p><p>This study points to the close affinities between classifying and figurative usage. Figurative expressions of colour terms frequently have a classifying function. I argue that figurative meanings are derived through two types of metonymy: +SALIENT ATTRIBUTE FOR OBJECT+ and +SALIENT CONCRETE ATTRIBUTE FOR SALIENT ABSTRACT ATTRIBUTE+. </p><p>Marked usage arises when specific colour terms are used in nominal domains where the specificity is not expected. This phenomenon is consequently confined to non-basic colour terms. </p><p>On the basis of the established patterns of usage and the frequency of occurrences, this thesis suggests that the colour category may be analysed as a radial category, with the basic colour terms forming the centre. </p>

This thesis examines usage of English colour terms in context, based on an extensive computerised text corpus, the Bank of English. It describes the ways in which English colour terms may be used to refer to nuances outside their normal area of designation and to attributes outside the colour domain. Usage patterns are analysed on three different levels: with regard to the overall frequency of occurrences, nominal domains and individual tokens, respectively. Cognitive linguistics supplies the theoretical framework employed in the analyses of the observed patterns. The study identifies three types of usage where colour terms refer to peripheral colour nuances or to concepts outside the colour domain: classifying, figurative and marked usage. When a colour term has a classifying function, it can be used outside the normal area of designation. This usage is analysed as a type of reference-point construction where a term referring to a salient point in the colour domain is used to subcategorise an entity whose actual colour may be only a peripheral member of the category named by the colour term. An analysis of the OED and the Bank of English shows that this type of usage is primarily restricted to a few of the most salient basic terms. This study points to the close affinities between classifying and figurative usage. Figurative expressions of colour terms frequently have a classifying function. I argue that figurative meanings are derived through two types of metonymy: +SALIENT ATTRIBUTE FOR OBJECT+ and +SALIENT CONCRETE ATTRIBUTE FOR SALIENT ABSTRACT ATTRIBUTE+. Marked usage arises when specific colour terms are used in nominal domains where the specificity is not expected. This phenomenon is consequently confined to non-basic colour terms. On the basis of the established patterns of usage and the frequency of occurrences, this thesis suggests that the colour category may be analysed as a radial category, with the basic colour terms forming the centre.