Numerical simulations of compressible Rayleigh-Taylor turbulence in stratified fluids

We present results from numerical simulations of Rayleigh-Taylor turbulence, performed using a recently proposed lattice Boltzmann method able to describe consistently a thermal compressible flow subject to an external forcing. The method allowed us to study the system both in the nearly-Boussinesq and strongly compressible regimes. Moreover, we show that when the stratification is important, the presence of the adiabatic gradient causes the arrest of the mixing process.Comment: 15 pages, 11 figures. Proceedings of II Conference on Turbulent Mixing and Beyond (TMB-2009

Physical constraints on the coefficients of Fourier expansions in cylindrical coordinates

It is demonstrated that (i) the postulate of infinite differentiability in Cartesian coordinates and (ii) the physical assumption of regularity on the axis of a cylindrical coordinate system provide significant simplifying constraints on the coefficients of Fourier expansions in cylindrical coordinates. These constraints are independent of any governing equations. The simplification can provide considerable practical benefit for the analysis (especially numerical) of actual physical problems. Of equal importance, these constraints demonstrate that if A is any arbitrary physical vector, then the only finite Fourier terms of A_r and A_θ are those with m=1 symmetry. In the Appendix, it is further shown that postulate (i) may be inferred from a more primitive assumption, namely, the arbitrariness of the location of the cylindrical axis of the coordinate system

Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments

The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of 3-rows we obtain ({\it i}) the pinning frequency $f_p$, ({\it ii}) the onset frequency $f_c$ for ML ($\propto$ ordering velocity) and ({\it iii}) the fraction $L_{ML}/L$ of coherently moving 3-row regions in the channel. The field dependence of these quantities shows that, at matching, where $L_{ML}$ is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where $L_{ML}$ is small, both the pinning force and the ordering velocity are enhanced. Further, we find that $f_c \propto f_p^2$, consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.Comment: 10 pages, 7 figure, submitted to PRB. Discussion has been improved and a figure has been adde

Phase-shift calculation using continuum-discretized states

We present a method for calculating scattering phase shifts which utilizes continuum-discretized states obtained in a bound-state type calculation. The wrong asymptotic behavior of the discretized state is remedied by means of the Green's function formalism. Test examples confirm the accuracy of the method. The $\alpha+n$ scattering is described using realistic nucleon-nucleon potentials. The $3/2^-$ and $1/2^-$ phase shifts obtained in a single-channel calculation are too small in comparison with experiment. The $1/2^+$ phase shifts are in reasonable agreement with experiment, and gain contributions both from the tensor and central components of the nucleon-nucleon potential.Comment: 16 pages, 5 figure

The Law of Cross-Border Securitization: Lex Juris

Denna uppsats kretsar kring beslutsfattande och metodik vid fastighetsinvesteringar i potentiella tillväxtnoder. Då fastighetssektorn är så omfattande har vi valt att avgränsa oss till en speciell typ av fastigheter, närmare bestämt logistikfastigheter. Ytterligare en fördjupning har skett, där vi valt ut en specifik investering i området, för att fördjupa oss om denna. Det specifika fall vi valt att ta mestadels av vår data från är Rosersbergs industriområde, även känt som Stockholm Nord Logistikcenter. Som en referenspunkt till Stockholm Nord Logistikcenter har vi i arbetet även skrivit översiktligt om Arenastaden, som är belägen i Solna. En del tidigare forskning har gjort på området Logistik, och somliga av dessa studier har vi även tagit del av för att utvinna information inom ämnet som även kunnat användas i vårt arbete. Dock har den studien vi främst använt oss av varit inriktad på logistik i sin helhet och inte ett specifikt fall. På cirka 9 år har området utanför Rosersberg villastad förvandlats från en skog, inom ett bullerområde utanför en mindre bostadsort, till en logistiknod där ett tiotal stora företag bedriver verksamhet i tusentals kvadratmeter lokaler. Allt detta i något som tros komma att bli ett av de största logistikcentrena i hela Sverige, och med tanke för de framtidsplaner som finns är det inte osannolikt. Den största drivkraften för projektet har varit Kilenkrysset, men detta med hjälp av gott samarbetsvilja från offentlig sektor. Vår studie kretsar kring vilka faktorer som påverkat till att denna investering blivit lyckad, samt vilken typ av företag det är som bedrivit arbetet. Vi har även gått in på hur orten Rosersberg, som tidigare legat i lä, påverkats av detta händelseförlopp. Innan projektet i Rosersberg initierades av Kilenkrysset har många frågor angående området diskuterats inom kommunen under många årtionden, dock har man aldrig kommit till skott på grund av bristande intresse och samhällsnytta. Utifrån det vi kunnat utläsa av den tillgängliga data vi samlat, har vi kunnat dra slutsatsen att utvecklingen bidragit till att göra platsen attraktiv för företag, men likväl för människor att numera bo i. Under arbetet har vi tagit kontakt med fyra respondenter som intervjuats, varav tre av dessa respondenter kommer från koncernen Kilenkrysset. Flera företag, bland annat NCC, har kontribuerat till utvecklingen i Rosersbergs industriområde, men Kilenkrysset är de som varit överlägset störst i området. Vi har även haft kontakt med en före detta anställd på bygg- och trafiknämnden i Sigtuna kommun för att få en objektiv, och mer överskådlig bild över hur samarbetet mellan offentlig sektor och investerare sett ut. För att bättre kunna förstå hur beslutsfattande skötts inom Kilenkrysset, både under och innan projektets fortgående, har vi studerat företaget mer grundligt. Information har framtagits kring företagets uppstart och dess historia, och hur det beslutsfattandet som till sist ledde dem till Rosersberg sett ut. Man kan klart se att både företaget i sin helhet och dess ledning är säregna, vilket man även ur materialet kan observera hur detta gynnat dem under projektets fortlöpande. Men även negativa aspekter har tagits upp angående deras beslutsfattande och tillvägagångssätt. Detta för att ge en rättvisande bild av vilka för- och nackdelar som i realiteten kretsar runt dessa metoder.This essay revolves around the desicion making process in real estate investments, where the investment contributes to the economic growth of the surrounding area. Due to the sheer size of the sector, we have chosen to limit our study to a specific type of real estate, which we decided to be logistic property. We have also chosen to study a specific case in more detail, to be able to understand how these projects develops. The case we chose was the investment of Rosersbergs Industrial park, also known as Stockholm Nord Logistic Centre. As a point of reference to this project we have chosen to briefly look into another, quite similar in size, project; Arenastaden in Solna. There have been studies made on Logistics in the past, some of which we have chosen to use as sources of information on our study. The study we used as the main source studied logistics on a different scale than ours, where the whole logistics market in Stockholm was studied. In merely 9 years the area surrounding Rosersberg has transformed, from unexploited land suffering from airport noise, into a rapidly growing logistics center where dozens of companies have chosen to exist. All this in an area many believe will be one of the biggest logistic centers in Sweden, which is not unlikely due to the future plans of the area. The company that initiated the project, which also has been the driving force is Kilenkrysset AB, with a lot of assistance from a supportive municipality. Before the company's initiative in the area, the municipality has been contemplating since the 60's what to do with the area, and how to make it grow. The issue before the company came along was almost solely economical; because there was no solid plan or investor to take care of the area and the infrastructure surrounding it. Based on the data we collected the area has improved its attraction both to companies, as well as to the residents in the area. Our study will attempt to determine which of the variables had the greatest importance on the end result of the project. As well as to study which type of company that decides to take on these kinds of projects. We have also studied how the surrounding area in Rosersberg has grown as a result of this specific investment. To gather information on the subject, we have contacted four respondents, which consists of three people from the Kilenkrysset organization. The reason why the majority of the interviewed respondents has been from one single company is because they have by far been the biggest investor in the area. The construction company NCC has also been part of the development in the area, but have sold most of their property to Kilenkrysset. The last respondent is from the building and traffic department within the municipality (Bygg- och trafiknämnden). Since we want to understand how decision making is handled within these types of organizations, we have chosen to study Kilenkrysset more thoroughly. Information about their history and the decision making process that eventually lead them to Rosersberg. From the information collected we can conclude that the company and its management have quite an extraordinary way of doing business. It is also obvious how their way of thinking has benefited them throughout their project in Rosersberg. But every technique has consequences, and we will also enlighten these consequences to try to observe both the pros and the cons about these methods

Electron Transport Through Molecules: Gate Induced Polarization and Potential Shift

We analyze the effect of a gate on the conductance of molecules by separately evaluating the gate-induced polarization and the potential shift of the molecule relative to the leads. The calculations use ab initio density functional theory combined with a Green function method for electron transport. For a general view, we study several systems: (1) atomic chains of C or Al sandwiched between Al electrodes, (2) a benzene molecule between Au leads, and (3) (9,0) and (5,5) carbon nanotubes. We find that the polarization effect is small because of screening, while the effect of the potential shift is significant, providing a mechanism for single-molecule transistors.Comment: 4 pages, 4 figure