Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions

When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that exchanges no energy and specularly reflects and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped fraction of particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.Comment: 46 pages including 14 figure

A New Ridge Regression Causality Test in the Presence of Multicollinearity

This paper analyzes and compares the properties of the most commonly applied versions of the Granger causality (GC) test to a new ridge regression GC test (RRGC), in the presence of multicollinearity. The investigation has been carried out using Monte Carlo simulations. A large number of models have been investigated where the number of observations, strength of collinearity, and data generating processes have been varied. For each model we have performed 10000 replications and studied seven different versions of the test. The main conclusion from our study is that the traditional OLS version of the GC test over-rejects the true null hypothesis when there are relatively high (but empirically common levels of) multicollinearity, while it is established that the new RRGC test will remedy or substantially decrease this problem.Granger causality test; multicollinearity; ridge parameters; size and power

Modelling Graphene Field-Effect Transistors

Today, transistors with 20 nanometer (nm) channel length are in mass production and many researchers believe that we are reaching a limit with downsizing conventionally used silicon metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. To keep up with the trend of making the transistor smaller, new channel materials are studied, and graphene has come into the spotlight. Graphene became a serious contender mostly due to its high mobility, but other properties such as high velocity saturation and the two-dimensional (2D) nature of the material have gained more attention in recent years [2–4]. The first graphene field-effect transistor (GFET) was reported in 2004, since many transistors with graphene as a channel material have been successfully fabricated [3]. It is important to have accurate simulation models that showcase all the peculiar behaviours of GFETs. Even though several new models with high accuracy, have been presented in recent years, few theoretical explanations exist. This thesis work focuses greatly on the theory behind two different simulation models for GFETs. Several parameter approximations are investigated, with focus on the possibility of showcasing negative differential resistance (NDR). In conclusion, we can see that the drift-diffusion (DD) model show good agreement with data and showcases NDR, while the virtual source (VS) model is more unstable and does not give NDR. I hope this thesis can act as a knowledge base, to facilitate for future simulation models.Transistor av materialet grafen. En av världens största uppfinningar är också den minsta av dom alla. Transistorn storlek är endast 1/5000 av ett hårstrå. Men låt inte detta lura er, tack vare denna smarta uppfinning utför din mobil mer och mer avancerade uppgifter. Transistorn sägs vara en av de största uppfinningarna i modern historia. Uppfinningen har nämnts i samma klass som bilen och telefonen. Idag finns transistorn i nästan all modern elektronik, vilket inte är så chockerande då 2 913 276 327 576 980 000 000 stycken transistorer har tillverkats industriellt sedan 1947 [5]. Siffran blir inte mer greppbar bara för att man ser hur många transistorer det är per person på jorden; 388 436 843 677 stycken transistorer per person. Trots detta, är inte transistorn något som diskuteras i vardagliga sammanhang. Så vad är en transistor? Enkelt uttryckt så är det en elektronikkomponent, som kan efterliknas vid en ventil. Vanligtvis har transistorn tre terminaler, vid varje terminal kan spänningen regleras. Beroende på spänningsstyrkorna ändras strömsignalen genom komponenten. Har du märkt att våra tv-apparater, datorer och telefoner tycks bli mindre, lättare och smidigare trots att de har högre prestanda, kan lagra mer information och arbetar snabbare? Detta är till stor del tack vare utvecklingen av transistorerna. Idag finns det transistorer så små som 20 nanometer (nm) i massproduktion [3]. Okej, tänker du då, hur stort är 20 nm? Det är en mycket bra fråga, som inte är helt enkel att svara på. Generellt brukar man säga att ett hårstrå på ditt huvud är 0.1 mm, det betyder att 20 nm endast är 1/5000 av ett hårstrå. Transistorerna vi tillverkar idag är med andra ord otroligt små. De flesta transistorer som används idag görs av Kisel. Men när dessa ska tillverkas så små som 20 nm börjar det bli problem med materialet Kisel. Det blir läckage och oönskade kapacitanser som gör att mer energi krävs för att få önskad effekt. Forskare behövde därför fundera på om det är möjligt att byta ut Kisel mot något bättre material. Materialet grafen kom upp som tänkbar ersättare. Grafen är gjort av Kol-atomer och är ett otroligt starkt material. Materialet är dessutom bättre än någon metall på att leda ström. I denna rapport tittar jag närmare på speciella egenskaper hos grafen. Jag går sedan vidare till teorin bakom grafen-transistorer, här beskriver jag vad som händer när man ändrar spänningen vid de olika terminalerna. Jag har skapat visuella bilder för att se vad som händer inne i transistorn. Till sist, beskriver jag hur man kan skapa en matematisk modell som beskriver strömmen som går genom grafen-transistorn. Målet med mitt arbete var att på ett grundläggande sätt förklara teorin bakom de matematiska modellerna för grafen-transistorer. Ofta måste förenklingar göras då det är svårt att beskriva allt i en transistor matematiskt. Jag har undersökt vad tidigare forskare har gjort och jämfört olika förenklingar samt hur dessa påverkar strömsignalen

Intressenternas uppfattning av European Sustainability Reporting Standards

Oftare än sällan hör vi att det rapporteras om vilka utmaningar vi står inför kopplat till klimatförändringar och användning av icke förnybara resurser. Företagen bär ansvar både för ekonomisk hållbarhet och social hållbarhet likväl ansvar för sin inverkan på miljön. Ett direktiv om hållbarhetsrapportering, kallat Corporate Sustainability Reporting Directive (CSRD), har instiftats som ett initiativ från EU i deras arbete för att uppfylla FN:s mål i Agenda 2030, i och med detta direktiv kom förslag på de nya rapporteringsstandarderna European Sustainability Reporting Standards (ESRS). För att få standarderna så bra som möjligt gavs intressenter möjligheten att lämna feedback på standarderna. Syftet med detta arbete är att undersöka intressentfeedback inskickad till EU om vad intressenter som antingen är producenter eller konsumenter av hållbarhetsrapporter ser för utmaningar och möjligheter till följd av de nya ESRS-standarderna. Denna studie har genomförts genom en kvalitativ undersökning med en induktiv ansats då detta arbete utgår ifrån text och tolkning av intressenternas åsikter. Det teoretiska ramverket är grundas i intressentteorin. Den empiriska delen strävar efter att identifiera teman som belyser de utmaningar och möjligheter olika intressenter associerar med de nya standarderna. Resultaten visar att intressenter från båda grupperna välkomnar de föreslagna utkasten till ESRS-standarder och erkänner deras betydelse för att främja EU:s arbete mot en hållbar utveckling, de lyfter att det är ett bra initiativ. Samtidigt som de belyser oroligheter kring dubbelarbete och oro för att väsentlighetsprincipen utnyttjas påpekas en avsaknad av branschstandarder. Båda intressent-grupperna lyfter betydligt fler utmaningar jämfört med vad de ser som möjligheter, vilket kan härledas till den omfattande tiden som företagen lägger på att ge feedback. Sammanfattningsvis erbjuder denna studie en inblick i trender rörande hur olika intressentgrupper har resonerat i sin feedback av ESRS. Den belyser de utmaningar som intressenter ser med de nya standarderna, såväl som de potentiella möjligheter som intressenter ser med de nya standarderna.More often than not we hear reports in various channels highlighting the challenges associated with climate change and non-renewable resources. Companies bear responsibility for both economic and social sustainability, as well as for their environmental impact. In its efforts to align with the UN's Agenda 2030 goals, the EU has introduced the Corporate Sustainability Reporting Directive (CSRD). This directive has led to the proposal of new standards known as European Sustainability Reporting Standards (ESRS). To optimize these standards, stakeholders were invited to provide feedback. The aim of this study is to analyze the feedback submitted to the EU by various Scandinavian stakeholders, examining their perspectives on the challenges and opportunities these standards present, particularly in relation to their roles as producers or consumers of sustainability reports. This study was conducted as a qualitative inquiry, employing an inductive approach based on textual analysis and human interpretation. The theoretical framework is grounded in stakeholder theory. The empirical section endeavors to identify themes that shed light on the challenges and opportunities different stakeholders associate with the new standards. The findings reveal that stakeholders from both groups welcome the proposed ESRS standard drafts recognizing its significance in promoting sustainable development. Even though there are differences among the stakeholder groups, they commend it as a positive initiative. However, they also raise concerns about potential redundant efforts, the misuse of the materiality principle, and the lack of industry-specific standards. Notably, these groups tend to emphasize the challenges more than the opportunities, a perspective that may stem from the extensive time invested in providing feedback. In conclusion, this study provides insight into trends regarding how various stakeholder groups have reasoned in their feedback of the ESRS. It highlights the challenges they perceive with the new standards, as well as the potential opportunities

Frequentist versus Bayesian approaches to multiple testing

Multiple tests arise frequently in epidemiologic research. However, the issue of multiplicity adjustment is surrounded by confusion and controversy, and there is no uniform agreement on whether or when adjustment is warranted. In this paper we compare frequentist and Bayesian frameworks for multiple testing. We argue that the frequentist framework leads to logical difficulties, and is unable to distinguish between relevant and irrelevant multiplicity adjustments. We further argue that these logical difficulties resolve within the Bayesian framework, and that the Bayesian framework makes a clear and coherent distinction between relevant and irrelevant adjustments. We use Directed Acyclic Graphs to illustrate the differences between the two frameworks, and to motivate our arguments

Numerical Simulations of Restrained Shrinkage Cracking in Glass Fibre Reinforced Shotcrete Slabs

Modern tunnels in hard rock are usually constructed by drill and blast with the rock reinforced by shotcrete (sprayed concrete) in combination with rock bolts. The irregular rock surface and the projection method of shotcrete lead to a tunnel lining of varying thickness with unevenly distributed stresses that affect the risk of cracking during shrinkage of the young and hardening material. Depending on water conditions, shotcrete is sprayed directly either onto the rock surface or over a drainage system, creating a fully restrained or an end-restrained structural system. In this paper, a method for nonlinear numerical simulations has been demonstrated, for the study of differences in stress build-up and cracking behaviour of restrained shotcrete slabs subjected to shrinkage. Special focus was given to the effects of the irregular shape and varying thickness of the shotcrete. The effects of glass fibre reinforcement and bond were implemented in the study by changing the fracture energy in bending and in the interaction between shotcrete and the substrate. The study verifies that an end-restrained shotcrete slab is prone to shrinkage induced cracking and shows the importance of a continuous bond to avoid wide shrinkage cracks when shotcrete is sprayed directly onto the rock

Sensitivity Analysis of G-estimators to Invalid Instrumental Variables

Instrumental variables regression is a tool that is commonly used in the analysis of observational data. The instrumental variables are used to make causal inference about the effect of a certain exposure in the presence of unmeasured confounders. A valid instrumental variable is a variable that is associated with the exposure, affects the outcome only through the exposure (exclusion criterion), and is not confounded with the outcome (exogeneity). These assumptions are generally untestable and rely on subject-matter knowledge. Therefore, a sensitivity analysis is desirable to assess the impact of assumptions violation on the estimated parameters. In this paper, we propose and demonstrate a new method of sensitivity analysis for G-estimators in causal linear and non-linear models. We introduce two novel aspects of sensitivity analysis in instrumental variables studies. The first is a single sensitivity parameter that captures violations of exclusion and exogeneity assumptions. The second is an application of the method to non-linear models. The introduced framework is theoretically justified and is illustrated via a simulation study. Finally, we illustrate the method by application to real-world data and provide practitioners with guidelines on conducting sensitivity analysis.Comment: Published version of the pape

Skärgårdsnavigering i nyktert och alkoholpåverkat tillstånd

I detta examensarbete görs en undersökning mellan två simulatorkörningar under vilka ett lastfartyg navigeras i en skärgårdsfarled av ett bryggteam bestående av befälhavare, styrman och en utkik. Den ena simulatorkörningen navigeras i nyktert tillstånd och den andra simulatorkörningen navigeras i ett alkoholpåverkat tillstånd. Undersökningen kartlägger skillnader i navigationen, bryggprocedurer, plotting och i kommunikationen mellan simulatorkörningarna. I arbetet ges också en kort beskrivning över alkoholens väg genom människans kropp och vad som händer med människans kropp under de olika faserna av alkoholpåverkat tillstånd från 0 till 1,0 ‰ alkoholhalt i blodet på en människa. Resultatet av den här undersökningen ger en ytlig inblick i hur alkoholen kan påverka arbetet som utförs på ett lastfartygs kommandobrygga när det framförs i en skärgårdsfarled av ett bryggteam bestående av befälhavare, styrman och en utkik.In this Bachelor’s thesis we study two simulated voyages, where a ship is navigated in an archipelago fairway by a bridge team consisting of a master, a mate and a lookout. During the first voyage the crew was sober and during the other the crew was in a state influence of alcohol. The study focuses on the differences in existing navigation, bridge procedures, plotting and communication between the two voyages. The study also gives a brief description of the alcohols, way through the human body and what happens to the human body during the different phases of alcohol influnce from 0 to 1.0 ‰ in the blood on a human. The results of this study provides a cursory glimpse how alcohol affects the work carried out on a cargo ship´s bridge when navigating in a archipelago fairway by a bridge team consisting of a master, mate and a lookout