Electric Control of the Exciton Fine Structure in Non-Parabolic Quantum Dots

We show that the non-parabolic confinement potential is responsible for the non-monotonic behavior and sign change of the exciton fine-structure splitting (FSS) in optically active self-assembled quantum dots. This insight is important for the theoretical understanding and practical control by electric fields of the quantum state of the emitted light from a biexciton cascade recombination process. We find that a hard-wall (box) confinement potential leads to a FSS that is in better agreement with experimentally measured FSS than a harmonic potential. We then show that a finite applied electric field can be used to remove the FSS entirely, thus allowing for the creation of maximally entangled photons, being vital to the growing field of quantum communication and quantum key distribution.Comment: 5 pages, 4 figure

Impact of Screening on Prognosis in the Multiple Endocrine Neoplasia Type 2 Syndromes: Natural History and Treatment Results in 105 Patients

We evaluated the effects of screening for multiple endocrine neoplasia type 2A (MEN-2A) in 12 families. Genealogical studies going back to 1730 show a common ancestry for seven Swedish families and one American family. The total number of patients included 105 individuals, 68 of whom were diagnosed by our screening program. Our screening methods for medullary carcinoma of the thyroid (MTC) had an optimal sensitivity and specificity. The frequency of gene carriers detected in MEN-2A families was 55%. Screening will lead to early diagnosis and early therapy, which in turn, will significantly decrease morbidity, incidence of surgical complications, and mortality related to the tumors of this hereditary syndrome

Spin and Photon Coherence and Entanglement in Semiconductor Quantum Dots

The aim of this thesis is to theoretically investigate two possible applications of semiconductor quantum dots for the growing field of quantum information and communication. The first one is the generation of entangled photons, which can be created by the radiative recombination of a quantum dot biexciton. This non-classical state of light is for instance used for teleportation of quantum information over distance. Although other methods of creating entangled photons exist, they suffer from problems such as inefficiency and unreliability, and an alternative which can produce an entangled photon pair on-demand within a given time interval would be most welcome. The second application is the implementation of a quantum bit using the intrinsic angular momentum of a single electron confined to a quantum dot. The quantum bit is the basic element of any quantum computer and is used to store quantum information.The work is divided into four main parts. We begin with an introduction which contains a short description about entanglement and quantum information followed by a brief review about the electron structure of semiconductors. This review aims to provide knowledge about some key methods and results from the semiconductor physics, which we will need in the following chapters.In the second part we will turn our attention to the generation of entangled light by the recombination of semiconductor biexcitons, which are composed of two excitons. We will discover that the excitons show an energy structure which requires extending the semiconductor theory from the introduction to be able to properly describe the observed effects. Once the exciton energy structure is known, we will examine a method to improve the quality of the emitted light with respect to entanglement.The third part considers effects from interactions between nuclear and electron spins. Focusing on storing one quantum bit using a single electron spin, we investigate the possible loss of information caused by interaction with the nuclear spins. We find that the temporal fluctuations of the nuclear spins give rise to an upper limit on the electron coherence time, during which quantum information can be accurately stored. We also investigate possible techniques to reduce the fluctuations and prolong the coherence time.In the fourth part we combine knowledge about the nuclear spins with the biexciton recombination process to investigate what effect exciton-nuclear spin interaction has on the entangled light. We find that the interaction with nuclear spins degrades the entanglement of the emitted light. To restore the quality of the entanglement, we investigate the effect of polarizing the nuclear spins and find that this can improve the entanglement

Tanulmányok a Neveléstudomány Köréből

Localization and magnetic properties of electrons in a thin, cyclic quasi one-dimensional GaAs wire with a central potential barrier were studied using the Hartree-Fock and LSDA (Local Spin Density Approximation, exchange only) and compared to more time consuming Quantum Monte-Carlo calculations. Within LSDA, evidence of true localization was found as well as evidence for the existence of both ferromagnetic as well as anti-ferromagnetic states. Also signs of two-dimensional spin localization was found, without associated localized electrons

Electron Localization and Spin Polarization in a Quantum Circle

Localization and magnetic properties of electrons in a thin, cyclic quasi one-dimensional GaAs wire with a central potential barrier were studied using the Hartree-Fock and LSDA (Local Spin Density Approximation, exchange only) and compared to more time consuming Quantum Monte-Carlo calculations. Within LSDA, evidence of true localization was found as well as evidence for the existence of both ferromagnetic as well as anti-ferromagnetic states. Also signs of two-dimensional spin localization was found, without associated localized electrons

Provrötning av marina substrat i laboratorie- och pilotskala : Delstudie i projektet Biogas – Nya substrat från havet

Denna rapport omfattar delstudie 4 av projektet Biogas-Nya substrat från havet. Inom delstudien har ett antal provrötningar av substrat från havet (vass, musslor, alger och skrapsill) genomförts. Syftet med delstudien var att få fram metanpotentialen för de olika substraten och att öka kunskapen kring hur dessa substrat uppför sig i en biogasprocess. Projektet var ett samverkansprojekt delfinansierat av EU Regionala fonden för Småland och öarna. Projektledare var Regionförbundet i Kalmar län. Inledningsvis genomfördes ett antal satsvisa försök med samtliga substrat. Metanpotentialerna för vassen, musslorna, algerna respektive skarpsillen var 400, 270, ca 210 och 460 Ndm3/kg VS. Ymp hämtades från Kalmar Biogas ABs industriella rötkammare. Vassen samrötades också med industriellt avfall i ett kontinuerligt våtrötningsförsök. Försöket genomfördes i två total omrörda tankreaktorer med volymen 30 l/st. Tillsatsen av vass gav en utökad metanproduktion med 220 Ndm3/kgVS. Vassen och musslorna studerades också i torrötningsförsök. Försöken i laboratorieskala genomfördes vid Avdelningen för Bioteknik i Lund medan försöket med musslor i pilotskala genomfördes vid Avdelningen för Bioenergiteknik, Linnéuniversitet. Metanpotentialen för vassen var i torrötningsförsöket ca 220 Ndm3/kg VS vilket är lika med potentialen i våtrötningsförsöket. För musslorna erhölls en metanpotential på 330 Ndm3/kg VS i laboratorieskaleförsöket. Pilotskaleförsöket visade att hydrolysen etablerades på likartat sätt som i laboratorieskaleförsöket. Metanhalten var ca 70 %. En visuell inspektion av musslorna efter rötningen visade också att endast skalen återstod. Det är dock inte möjligt att ange en metanpotential från detta försök beroende på ett antal tekniska problem med processen. Processen byggdes inför detta försök och det fanns inte tid att testköra den samma före försökets start.Arbetet med de satsvisa försöken och det kontinuerliga våtrötningsförsöket av vass genomfördes i samarbete med Kalmar Biogas AB. Detta bland annat genom att Kalmar Biogas AB tillhandahöll sin försöksanläggning med satsvisa och kontinuerliga reaktorer till projektet

Rötning av fjäderfägödsel med gödselförädling i tillämpad skala

Ett tjugotal lantbrukare i Mönsterås kommun planerar för att bygga en stor biogas­anläggning som kommer att ha fastgödsel från höns som huvudsubstrat. Den gemen­samma biogasanläggning kan bli den största i sitt slag i Sverige, med en biogas­produktion på ca 70 GWh biogas/år för produktion av drivmedel. Den genererade rötresten kan kväve­försörja ca 12 000 ha/år växtodling och fosforförsörja ca 20 000 ha/år. Den rötade gödseln bidrar i princip till all växtnäring i rötresten, där fjäderfä­gödseln kommer att bidra med ca 80 % av rötrestens innehåll av kväve och fosfor. Ett hinder för att realisera denna anläggning är att det idag saknas erfarenhet från praktisk drift av rötningsanläggningar med betydande inblandning av fjäderfägödsel. Fjäderfä­gödsel är både ett fosfor- och kväverikt substrat, och innehåller dessutom både tunga och lätta partiklar som riskerar att bilda sediment och svämtäcken i rötkammaren. Idag betraktas fjäderfägödsel framför allt som ett fosforgödselmedel eftersom huvuddelen av kvävet inte är direkt upptagbart av växter, men rötning av fjäderfägödsel ökar andelen direktverkanande kväve. För att optimera hantering, spridning och utnyttjande av kväve och fosfor i fjäderfägödsel är det önskvärt att processa denna gödsel för att generera fyra stycken gödselmedel med olika kväve- och fosforkvot. För att kunna studera dessa fråge­ställningar och bredda gödselbasen för rötning har Vinnova, under 2016-2018, finansierat denna tillämpade studie. Under ett tillämpat försök genomfördes rötning i pilotskala av kväverik hönsgödsel som huvudsubstrat. Rötningsprocessen gick att driva stabilt vid en ammoniumkvävehalt på närmare 6 g/l inom det mesofila temperaturområdet i en totalomblandad rötkammare med volymetrisk metanproduktion som uppgick till 1,1 m3 CH4/m3 slamvolym & dag. Järnklorid tillfördes rötkammaren för att hålla biogasens innehåll av svavelväte vid ca 100 ppm. För att hålla ammoniumhalten vid angiven nivå tillfördes vatten motsvarande halva inflödet in i rötkammaren, för att späda ner kvävet till denna nivå. Efter rötningen av substratblandningen ökade dess ammoniuminnehåll med 3,7 gånger. Under pilotförsöket producerades ca 13 m3 rötrest som sparades och lagrades 4–8 månader innan den förädlades i två steg till två olika gödselmedel. I första steget genomfördes fasseparation med en dekantercentrifug följt av indunstning av surgjord tunnfas. Baserat på dessa försök beräknas fassepareringen kunna generera ett fast gödselmedel vars vikt motsvarar 23 % av i rötningsprocessen producerad rötrest. Det fasta gödselmedlets innehåll av fosfor utgör dryga 70 % av rötrestens fosforinnehåll. Vidare beräknas indunstningen kunna generera ett uppkoncentrerat flytande gödsel­medel vars vikt motsvarar 2o % av i rötningsprocessen producerad rötrest. Det flytande gödselmedlets innehåll av ammoniumkvävet utgör dryga 70 % av rötrestens ammonium­innehåll.       Det producerade koncentratgödselmedlet liksom tunnfasgödselmedlet hade en hög andel lättillgängligt kväve, vilket är en viktig delförutsättning för att uppnå höga skördar vid växtodling. Gödselmedel från Mönsterås Biogas planerade biogasanläggning kan i framtiden bidra till att jordbruket i Kalmar län med omnejd kan gå mot en hållbar intensifiering av livsmedelsproduktionen.Digestion of poultry manure with digestate processing in pilot scale tests Twenty farmers in the municipality of Mönsterås in southern Sweden are jointly planning to build a large biogas plant. The plant will digest a very high proportion of poultry manure, resulting in significantly greater biogas yield than normally expected, and higher nitrogen contents in the digestate. A major obstacle to realising the biogas plant is controlling digestion operation under high nitrogen levels resulting from the considerable amounts of poultry manure substrate. Poultry manure also contains both heavy and light particles that can cause challenges with poor stability in the digestion process, formation of sediments and crust in digester tanks. The high nitrogen contents together with high phosphorus and solids concentrations will also create difficulties for digestate management and use as fertiliser.  Today solid poultry manure is mainly used as a phosphorus fertiliser, not only due to high concentration of phosphorus but also due to relatively poor utilisation of the nitrogen by crops. However, due to the high concentration of phosphorus, the application rate needed to meet plant needs is lower than modern solid manure spreaders can evenly apply. Over application and inefficient use of nitrogen increases risk of nutrient losses to waters and the environment. To study these issues for biogas production, Vinnova (Sweden's innovation agency) has supported this research project in applied digestion and digestate processing. The project contained the following components: i) 6 months digestion tests with prospective substrates in a pilot-plant with 5 m3 active digesting volume, provided with mixers and pumps commonly used in full-scale plants, ii) laboratory tests to determine biogas potential for feedstocks, and to determine the potential for increased gas production by post-digestion, iii) applied trials of separating and concentrating the digestate with centrifuge followed by industrial evaporation of the liquid phase, iv) analysis of the nutrient value and the function of the concentrated fertilizer in organic farming. The biological and technical operational performance in the pilot test was evaluated in a complete stirred tank reactor at mesophilic temperature during co-digestion of poultry manure, liquid manure and glycerol. The poultry manure contributed with approx. 70% of dry matter in the substrate mixture and 80% of the nitrogen and phosphorus. The digestion process was stable with NH4-N levels close to 6 g/l. To control hydrogen sulphide in the biogas to approx. 100 ppm, ferric chloride was added to the digester. Volumetric methane production reached 1,1 m3 CH4/ m3 digester and day. Significant formation of sediment occurred in both digester and in pipes, however, no crust formation was observed in the digester. The outflow of ammonia from the digester by the digestate was 3.7 times higher than the ammonia inflow by the substrate mixture. Thirteen tonnes of digestate was produced during the pilot test. The digestate was separated with a decanter centrifuge generating a solid fraction corresponding to 23% of digestate weight and approx. 70% of the phosphorus in the digestate. Sulfuric acid was added to the liquid fraction generated by the centrifuge before evaporation to stabilize the ammonium nitrogen. Industrial evaporation of the liquid fraction produced a concentrate corresponding to 23% of digestate weight and containing approx. 70% of the ammonium nitrogen in the digestate. The pilot test generated four different fertilisers, (digestate, solid fraction, liquid fraction and concentrate) each with very different physical and chemical properties. Digestate processing increased the N/P ration of the liquid fraction and concentrate allowing more balanced N and P supply to crop demand, reducing the risk of nutrient losses to waters but also increasing the resource use efficiency of the plant nutrients. Processing was also successful at concentrating the two of the fertilisers, enabling cost effective long-distance transport for use in areas with low animal density and a need for the soil amendment properties of from manure. These project results have contributed to plans for a full-scale plant by developing the basis of design and the credibility for implementation, resulting in an investment grant and the formation of a new economically stronger company.  Based on the results from the project, the estimated production of biogas in a full-scale plant is 70 GWh /year for renewable automotive fuels. Post-digestion of the digestate with 10 days retention time can increase biogas production with an extra 3 GWh/year (4%). The solid and liquid products can fertilise 12 000 ha/year of organic cultivation with nitrogen and up to 20 000 up to ha/year with phosphorus

Laser photodetachment of radioactive 128^{128}I−^−

International audienceThe first experimental investigation of the electron affinity (EA) of a radioactive isotope has been conducted at the CERN-ISOLDE radioactive ion beam facility. The EA of the radioactive iodine isotope (128)I (t (1/2) = 25 min) was determined to be 3.059 052(38) eV. The experiment was conducted using the newly developed Gothenburg ANion Detector for Affinity measurements by Laser PHotodetachment (GANDALPH) apparatus, connected to a CERN-ISOLDE experimental beamline. (128)I was produced in fission induced by 1.4 GeV protons striking a thorium/tantalum foil target and then extracted as singly charged negative ions at a beam energy of 20 keV. Laser photodetachment of the fast ion beam was performed in a collinear geometry inside the GANDALPH chamber. Neutral atoms produced in the photodetachment process were detected by allowing them to impinge on a glass surface, creating secondary electrons which were then detected using a channel electron multiplier. The photon energy of the laser was tuned across the threshold of the photodetachment process and the detachment threshold data were fitted to a Wigner law function in order to extract the EA. This first successful demonstration of photodetachment at an isotope separator on line facility opens up the opportunity for future studies of the fundamental properties of negatively charged radioactive isotopes such as the EA of astatine and polonium

Laser photodetachment of radioactive ions: towards the determination of the electronegativity of astatine

Negatively charged ions are mainly stabilized through the electron correlation effect. A measure of the stability of a negative ion is the electron affinity, which the energy gain by attaching an electron to a neutral atom. This fundamental quantity is, due to the almost general lack of bound excited states, the only atomic property that can be determined with high accuracy for negative ions. We will present the results of the first laser photodetachment studies of radioactive negative ions at CERN-ISOLDE. The photodetachment threshold for the radiogenic iodine isotope 128I was measured successfully, demonstrating the performance of the upgraded GANDALPH experimental beam line. The first detection of photo-detached astatine atoms marks a milestone towards the determination of the EA of this radioactive element