Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5\mathrm{Ge_{2}Sb_{2}Te_{5}}

In this article, we use hybrid density functional (HSE06) to study the crystal and electronic structures and optical properties of well known phase change memory material $\mathrm{Ge_{2}Sb_{2}Te_{5}}$. We calculate the structural parameters, band gaps and dielectric functions of three stable structures of this material. We also analyze the electron charge distribution using the Bader's theory of charge analysis. We find that hybrid density functional slightly overestimate the value of 'C' parameter. However, overall, our results calculated with the use of hybrid density functional (HSE06) are very close to available experimental values than calculated with the use of PBE functional. Specifically, the electronic band gap values of this material calculated with HSE06 are in good agreement with the available experimental data in the literature. Furthermore, we perform the charge analysis and find that naive ionic model fails to explain the charge distribution between the constituent atoms, showing the complex nature of this compound.Comment: 10 pages, 3 tables, 3 figure

Динамика биохимических показателей грануляционной ткани экспериментальных инфицированных ран при лечении биологически активными препаратами

РАНЫ И ТРАВМЫ /лек терБИОПРЕПАРАТЫГРАНУЛЯЦИОННАЯ ТКАН

Computational Studies of Electron Transport in Nanoscale Devices

In this thesis, a combination of density functional theory (DFT) based calculations and nonequilibrium Green’s functions are employed to investigate electron transport in molecular switches, molecular cords and nanoscale devices.   Molecular electronic devices have been proposed as an approach to complement today’s silicon based electronic devices. However, engineering of such miniature devices and design of functional molecular components still present significant challenges.   First, the way to connect a molecule to conductive electrodes has to be controlled. We study, in a nanoelectrode-nanoparticle platform, how structural changes affect the measured conductance and how current fluctuations due to these structural changes can be decreased. We find that, for reproducible measurements, it is important to have the molecules chemically bonded to the surfaces of adjacent nanoparticles. Furthermore, we show by a combination of DFT and theoretical modeling that we can identify signals from single-molecules in inelastic electron spectroscopy measurements on these devices.   Second, active elements based on molecules, some examples being switches, rectifiers or memory devices, have to be designed. We study molecular conductance switches that can be operated by light and/or temperature. By tuning the substituents on the molecules, we can optimize the shift of the most conducting molecular orbital and increase the effective coupling between the molecule and the electrodes when going from the OFF to the ON-state of the switches, giving high switching ratio (up to three orders of magnitude). We also study so called mechanoswitches that are activated by a mechanical force elongating the molecules, which means that these switches could operate as sensors.   Furthermore, we have studied two different classes of compounds that may function either as rigid molecular spacers with a well-defined conductance or as molecular cords. In both cases, we find that it is of great importance to match the conjugation of the anchoring groups with the molecular backbone for high conductance.   The last part of the thesis is devoted to another interesting semiconductor material, diamond. We have accurately calculated the band structure and effective masses for this material. Furthermore, these results have been used to calculate the Hall coefficient, the resistivity and the Seebeck coefficient

Theoretical studies of a nanoparticle bridge platform for molecular electronics measurements

The main focus of this thesis is the theoretical investigations of a nanogap platform used for molecular electronics measurements under ambient conditions. The nanogap is about 20 nm wide, while the molecules investigated here (octanethiol(OT) and octanedithiol(ODT)) are about 1-1.5 nm long making it impossible to bridge the gap with one molecule. Two different approaches are investigated. In the first approach the electrodes of the nanogap are coated with a layer of OT molecules, and large gold nanoparticles (diameter of about 30 nm) are trapped in the gap creating two molecular junctions with assemblies of molecules. In the second approach the electrodes are kept clean, but instead the gold nanoparticles are coated with doubly functionalized molecules (ODT) and trapped in the gap. Here the nanoparticles are limited in size to about 5 nm, hence it is necessary to consider nanoparticle-molecule chains or small networks to bridge the gap. The first principles modeling of the structure of the metal-molecule junctions combined with elastic and inelastic transport properties is performed using the density functional theory (DFT) combined with the non-equilibrium Green’s functions (DFT-NEGF) method. In the first approach with the coated electrodes and the large nanoparticles, simulations show that structural irregularities at the electrode interface can lead to a significant variation of the conductance through the molecular film. Due to the size of the nanoparticles, the shape and orientation of the facets will have great influence on how many molecules are connected, affecting the measured resistance of the device. With the second approach utilizing the functionalized nanoparticles, more stable junctions are obtained since the nanogap is bridged by molecular junctions chemisorbed in both ends. To make chemical bonds to both sides of the junctions, the outer functional group needs to be protected before the trapping of nanoparticles in the gap. Deprotected nanoparticles agglomerate and cannot be trapped. We have inves- tigated the most probable configurations of the molecules in these junctions. During deprotection of the functional group in the gap, a conduction increase have been observed. We have found that the removal of the protection group is not responsible for the increased conduction. Instead, since the deprotected molecule is shorter and the nanoparticles are mobile during deprotection, a reorganization of the nanopar- ticles in the gap occurs. This reorganization leads to decreasing of the tunneling length for the electrons, hence increasing the conduction. We also demonstrate, that we can obtain the inelastic electron tunneling spectroscopy (IETS) signature of an octanedithiol molecule in this platform. This is done on the network of chemisorbed ODT junctions, where we are able to relate the low-bias Au-S and C-S stretch modes of the molecule to observed peaks in IETS. From this we estimate that the main contribution in the signal comes from chains containing 5, 6 and 7 molecular junctions. To identify the peaks, we have calculated the theoretical spectra for one molecule, from which we are able to extract the important vibrational modes, and their couplings to the electrons. This we then use in a model, including the Coulomb blockade observed in the nanoparticles, to fit the theoretical spectra to the measured one.

Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode

Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced.  A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region

Förhoppningarna över CAR-T celler som behandlingsmetod mot hematologisk cancer

Olika typer av blodcancer är några av de vanligast förekommande cancerformerna i världen. Ju tidigare sjukdomen upptäcks och beroende på vilken typ av blodcancer någon drabbats av ser prognosen i många fall god ut då dagens behandlingsmetoder under flera år effektiviserats. Dock finns det fall där patienter inte svarar på traditionella terapier som cytostatika och stålning eller gånger där sjukdomen kommer tillbaka i aggressivare former. I dessa fall krävs andra metoder för att försöka behandla och bota cancern.   En metod som på senare tid fått mycket uppmärksamhet i forskarvärlden är användandet av kroppens egna immunceller som behandlingsform mot blodcancer. Genom att rena fram en patients egna T-celler från ett blodprov, kan dessa sedan genetiskt modifieras till att känna igen specifika tumörassocierade antigener (TAA) som bara vissa typer av cancerceller uttrycker. Metoden går ut på att T-cellerna får chimära antigen-receptorer (CAR), som uttrycks på cellytan, där CAR-T cellerna sedan injiceras tillbaka till patienten. CAR-T cellerna känner igen cancercellerna och attackerar sedan, med målet att patienten efter behandlingen inte ska ha några cancerceller kvar i kroppen.   Kliniska försök gjorda på patienter med olika typer av blodcancer har visat lovande resultat, särskilt gällande patienter som fått återfall av blodcancertypen Akut Lymfatisk Leukemi (ALL). De som fått delta i studierna har haft mycket dåliga prognoser och har innan blivit behandlade med de konventionella behandlingsterapierna, men utan eller med mycket dåligt resultat. Förhoppningar som väckts från dessa forskningsresultat har lett till diskussion att CAR-T celler kan komma att förändra cancervården och i framtiden kanske vara en lika vanlig behandlingsmetod som strålning eller kemoterapi. Dock kvarstår många problem som forskarna måste lyckas lösa innan CAR-T celler kan räknas som konventionell. Bland annat finns stora risker att patienter vid behandling kan drabbas av cytokinfrisläppningssyndrom (CRS, eng. cytokine release syndrome), där immunförsvaret kan attackera kroppens egna organ som i värsta fall kan leda till döden. Cancercellerna kan även komma tillbaka efterbehandling, då de har utvecklat en resistens mot CAR-T cellerna. Metoder för att undvika dessa toxiska responser och göra T-cellerna mer effektiva är bara några av de problem som kvarstår

Förhoppningarna över CAR-T celler som behandlingsmetod mot hematologisk cancer

Olika typer av blodcancer är några av de vanligast förekommande cancerformerna i världen. Ju tidigare sjukdomen upptäcks och beroende på vilken typ av blodcancer någon drabbats av ser prognosen i många fall god ut då dagens behandlingsmetoder under flera år effektiviserats. Dock finns det fall där patienter inte svarar på traditionella terapier som cytostatika och stålning eller gånger där sjukdomen kommer tillbaka i aggressivare former. I dessa fall krävs andra metoder för att försöka behandla och bota cancern.   En metod som på senare tid fått mycket uppmärksamhet i forskarvärlden är användandet av kroppens egna immunceller som behandlingsform mot blodcancer. Genom att rena fram en patients egna T-celler från ett blodprov, kan dessa sedan genetiskt modifieras till att känna igen specifika tumörassocierade antigener (TAA) som bara vissa typer av cancerceller uttrycker. Metoden går ut på att T-cellerna får chimära antigen-receptorer (CAR), som uttrycks på cellytan, där CAR-T cellerna sedan injiceras tillbaka till patienten. CAR-T cellerna känner igen cancercellerna och attackerar sedan, med målet att patienten efter behandlingen inte ska ha några cancerceller kvar i kroppen.   Kliniska försök gjorda på patienter med olika typer av blodcancer har visat lovande resultat, särskilt gällande patienter som fått återfall av blodcancertypen Akut Lymfatisk Leukemi (ALL). De som fått delta i studierna har haft mycket dåliga prognoser och har innan blivit behandlade med de konventionella behandlingsterapierna, men utan eller med mycket dåligt resultat. Förhoppningar som väckts från dessa forskningsresultat har lett till diskussion att CAR-T celler kan komma att förändra cancervården och i framtiden kanske vara en lika vanlig behandlingsmetod som strålning eller kemoterapi. Dock kvarstår många problem som forskarna måste lyckas lösa innan CAR-T celler kan räknas som konventionell. Bland annat finns stora risker att patienter vid behandling kan drabbas av cytokinfrisläppningssyndrom (CRS, eng. cytokine release syndrome), där immunförsvaret kan attackera kroppens egna organ som i värsta fall kan leda till döden. Cancercellerna kan även komma tillbaka efterbehandling, då de har utvecklat en resistens mot CAR-T cellerna. Metoder för att undvika dessa toxiska responser och göra T-cellerna mer effektiva är bara några av de problem som kvarstår

Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode

Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced.  A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region