Search results

1

Multi-Scale Simulations of Semiconductor Nanostructures

100%

Zieliński M.

Acta Physica Polonica A

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2012

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vol. 122

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issue 2

312-315

EN

We demonstrate a multi-domain scheme for calculation of electronic and optical properties of semiconductor nanostructures. Three progressively smaller computational domains are used for strain simulation, single particle states calculation and computation of the Coulomb scattering matrix elements. Proposed approach offers a significant reduction of computational time and memory savings without sacrificing the accuracy of obtained spectra. We illustrate this method on the example of InAs/InP self-assembled quantum dots.

2

Exact Diagonalization Approach for Atomistic Calculation of Piezoelectric Effects in Semiconductor Quantum Dots

64%

Świderski M., Zieliński M.

Acta Physica Polonica A

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2016

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vol. 129

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issue 1a

A-79-A-82

EN

We present an exact diagonalization approach for atomistic calculation of excitonic properties of semiconductor nanostructures under piezoelectric field. The method allows for efficient treatment of both single particle and many-body states at a small computational cost and results in a very good agreement with the full diagonalization treatment. We illustrate our approach by analyzing the effect of a piezoelectric field on a spectra of a self-assembled InAs/GaAs lens-shaped quantum dot. We study the influence of linear and quadratic piezoelectric terms on the quantum dot electronic structure and importantly we found that the non-linear, density functional based theory of piezoelectricity produces results very similar to those obtained by a well-established linear approach utilizing empirical parameters.

3

The influence of CFBC fly ash addition on phase composition of air-entrained concrete

64%

Glinicki M. A., Zieliński M.

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2008

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vol. 56

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issue 1

4

ERRATUM

51%

Zieliński M., Jaskólski W., Aizpurua J., Bryant G.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

443-445

EN

Erratum: M. Zieliński, W. Jaskólski, J. Aizpurua, G.W. Bryant, Strain and Spin-Orbit Effects in Self-Assembled Quantum Dots, Acta Phys. Pol. A, 108, 929, 2005.

5

Coupling and Strain Effects in Vertically Stacked Double InAs/GaAs Quantum Dots: Tight-Binding Approach

51%

Jaskólski W., Zieliński M., Bryant G.

Acta Physica Polonica A

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2004

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vol. 106

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issue 2

193-205

EN

The empirical tight-binding approach is used to study atomic-scale effects on electronic coupling in vertically stacked, self-assembled InAs/GaAs quantum dots. A model with unstrained dots is first studied to isolate the atomistic coupling effects from the strain effects. The strain effects are next considered by means of the valence force field method. Electron levels in coupled quantum dots follow closely the simple analogy of coupled dots as artificial molecules. The electron ground state of double dot has always bonding-like character. The coupling of hole states is more complicated because the coupling depends both of the hole envelope function and the atomic character of the hole state. It is shown that the character of the hole ground state of double dot changes from antibonding to bonding-like, when the distance between the dots decreases. It reorders hole levels, changes state symmetries, and makes changes in optical spectra. The calculated red-shift of the lowest transition for closely-spaced dots agrees well with experimental data. We present also some preliminary results on strain effects in such nanocrystals.

6

Atomistic Calculation of Coulomb Interactions in Semiconductor Nanocrystals: Role of Surface Passivation and Composition Details

51%

Chwastyk M., Różanski P., Zieliński M.

Acta Physica Polonica A

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2012

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vol. 122

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issue 2

324-328

EN

We report a theoretical investigation of electronic properties of semiconductor InAs and GaAs nanocrystals. Our calculation scheme starts with the single particle calculation using atomistic tight-binding model including spin-orbital interaction and d-orbitals. Then the exciton binding energies are calculated with screened Coulomb interaction. We study the role of surface passivation effects by varying value of surface passivation potential. We compare results obtained with dot center positioned on different lattice sites thus containing different number of anion and cations. We conclude that passivation of surface states affects significantly single particle energies and the value of electron-hole Coulomb attraction. Interestingly, due to limited screening, the short-range (on-site) contribution to the electron-hole Coulomb attraction plays significant role for small nanocrystals with radius smaller than 1 nm.

7

Strain and Spin-Orbit Effects in Self-Assembled Quantum Dots

51%

Zieliński M., Jaskólski W., Aizpurua J., Bryant G.

Acta Physica Polonica A

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2005

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vol. 108

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issue 5

929-940

EN

The effects of strain and spin-orbit interaction in self-assembled lens-shaped InAs/GaAs quantum dots are investigated. Calculations are performed with empirical tight-binding theory supplemented by the valence force field method to account for effects of strain caused by lattice mismatch at the InAs-GaAs interface. It is shown that both effects influence strongly the electron and hole energy structure: splitting of the energy levels, the number of bound states, density distributions, and transition rates. We show that piezoelectric effects are almost negligible in quantum dots of the size investigated.

8

Structure Characterization and Catalytic Properties of Cr_2O_3 Doped with MgO Supported on MgF_2

45%

Goslar J., Wojciechowska M., Zieliński M., Tomska-Foralewska I., Przystajko W.

Acta Physica Polonica A

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2005

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vol. 108

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issue 2

323-330

EN

A characterization of double oxide systems containing Cr_2O_3 doped with MgO and supported on MgF_2 was carried out. The catalysts were prepared by impregnation and co-impregnation methods and characterized by the Brunauer-Emmett-Teller method, EPR, and temperature programmed reduction. The results proved the interactions between supported oxides and the presence of spinel-like phase after treatment at 400ºC. Magnesium oxide clearly influences the catalytic activity as well as selectivity of chromium catalysts supported on MgF_2. The MgO-Cr_2O_3/MgF_2 systems were active and selective in the reaction of CO oxidation at the room temperature and in the dehydrogenation of cyclohexene.

9

X-ray Characterization of Films Formed by Pulsed Laser Deposition on Cold Substrates from YBaCuO Targets

39%

Pełka J., Paszkowicz W., Gierłowski P., Lewandowski S., Zieliński M., Barbanera S., Knapp M.

Acta Physica Polonica A

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2002

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vol. 101

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issue 5

787-794

EN

Grazing-incidence X-ray diffraction supplemented with atomic force microscopy and secondary ion mass spectroscopy were applied to the characterization of films deposited by laser ablation on cold substrates from YBaCuO targets and subsequently irradiated with additional laser pulses of lower energy density. Evolution of X-ray diffraction pattern was observed as a function of irradiation dose. For the as-deposited films the pattern was typical of the amorphized solids. For the films irradiated with doses higher than the threshold, the pattern was enriched with the diffraction peaks, whose general features, like peak positions, widths and relative intensities were almost independent of the dose. The size of the crystallites was deduced from the peak widths to be not smaller than 12-16 nm. Comparison of the pattern with patterns of known phases indicates that, apart of the amorphous component, a structure with an admixture of some new metastable or high temperature phase(s) is formed during the process of pulsed laser annealing. The atomic force microscopy observations revealed that the surface roughness shows a pronounced minimum at low irradiation doses. The secondary ion mass spectroscopy investigation confirms that the strongest chemical changes (increase in concentration of yttrium and copper) due to irradiation with higher doses are observed in the near-surface film material.

10

Magnons in Cubic MBE-Grown A_{1-x}Mn_{x}Te Layers (A = Cd, Zn, Mg)

33%

Szuszkiewicz W., Hennion B., Jouanne M., Morhange J., Dynowska E., Janik E., Wojtowicz T., Zieliński M., Furdyna J.

Acta Physica Polonica A

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1998

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vol. 94

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issue 3

583-587

EN

One-magnon excitations in MBE-grown A_{1-x}Mn_{x}Te layers (where A = Cd, Zn, Mg and x>0.7) were investigated by means of the Raman scattering measurements at low temperatures (≈20 K). The composition dependence of the anisotropy energy - as extracted from these measurements - is discussed. Further, the elastic neutron scattering measurements were performed in layers of cubic MnTe, which constitute the end point material of the ternary alloys series. Abundance of variously oriented antiferromagnetic domains in MnTe layers as a function of temperature was studied. We confirm occurrence of a pronounced magnetostriction effect.

11

A Pilot Study of the Novel J-PET Plastic Scintillator with 2-(4-styrylphenyl)benzoxazole as a Wavelength Shifter

18%

Wieczorek A., Moskal P., Niedźwiecki S., Bednarski T., Białas P., Czerwiński E., Danel A., Gajos A., Gruntowski A., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowal J., Kowalski P., Kozik T., Krzemień W., Kubicz E., Molenda M., Pałka M., Raczyński L., Rudy Z., Rundel O., Salabura P., Sharma N., Silarski M., Słomski A., Smyrski J., Strzelecki A., Uchacz T., Wiślicki W., Zieliński M., Zoń N.

Acta Physica Polonica A

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2015

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vol. 127

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issue 5

1487-1490

EN

For the first time a molecule of 2-(4-styrylphenyl)benzoxazole containing benzoxazole and stilbene groups is applied as a scintillator dopant acting as a wavelength shifter. In this article a light yield of the plastic scintillator, prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt% of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% ± 2% of the anthracene light output. There is a potential to improve this value in the future by the optimization of the additives concentrations.

12

Multiple Scattering and Accidental Coincidences in the J-PET Detector Simulated Using GATE Package

18%

Kowalski P., Moskal P., Wiślicki W., Raczyński L., Bednarski T., Białas P., Bułka J., Czerwiński E., Gajos A., Gruntowski A., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowal J., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Rudy Z., Salabura P., Sharma N., Silarski M., Słomski A., Smyrski J., Strzelecki A., Wieczorek A., Wochlik I., Zieliński M., Zoń N.

Acta Physica Polonica A

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2015

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vol. 127

|

issue 5

1505-1512

EN

Novel positron emission tomography system, based on plastic scintillators, is developed by the J-PET collaboration. In order to optimize geometrical configuration of built device, advanced computer simulations are performed. Detailed study is presented of background given by accidental coincidences and multiple scattering of gamma quanta.

13

GPU Accelerated Image Reconstruction in a Two-Strip J-PET Tomograph

18%

Białas P., Kowal J., Strzelecki A., Bednarski T., Czerwiński E., Gajos A., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowalski P., Kozik T., Krzemień W., Kubicz E., Moskal P., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Salabura P., Sharma N., Silarski M., Słomski A., Smyrski J., Wieczorek A., Wiślicki W., Zieliński M., Zoń N.

Acta Physica Polonica A

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2015

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vol. 127

|

issue 5

1500-1504

EN

We present a fast GPU implementation of the image reconstruction routine, for a novel two strip PET detector that relies solely on the time of flight measurements.

14

Analysis Framework for the J-PET Scanner

18%

Krzemień W., Gajos A., Gruntowski A., Stola K., Trybek D., Bednarski T., Białas P., Czerwiński E., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowal J., Kowalski P., Kozik T., Kubicz E., Moskal P., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Salabura P., Sharma N., Silarski M., Słomski A., Smyrski J., Strzelecki A., Wieczorek A., Wiślicki W., Zieliński M., Zoń N.

Acta Physica Polonica A

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2015

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vol. 127

|

issue 5

1491-1494

EN

J-PET analysis framework is a flexible, lightweight, ROOT-based software package which provides the tools to develop reconstruction and calibration procedures for PET tomography. In this article we present the implementation of the full data-processing chain in the J-PET framework which is used for the data analysis of the J-PET tomography scanner. The framework incorporates automated handling of PET setup parameters' database as well as high level tools for building data reconstruction procedures. Each of these components is briefly discussed.

15

Hit Time and Hit Position Reconstruction in the J-PET Detector Based on a Library of Averaged Model Signals

18%

Moskal P., Sharma N., Silarski M., Bednarski T., Białas P., Bułka J., Czerwiński E., Gajos A., Kamińska D., Kapłon L., Kochanowski A., Korcyl G., Kowal J., Kowalski P., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Salabura P., Słomski A., Smyrski J., Strzelecki A., Wieczorek A., Wiślicki W., Wochlik I., Zieliński M., Zoń N.

Acta Physica Polonica A

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2015

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vol. 127

|

issue 5

1495-1499

EN

In this article we present a novel method of hit time and hit position reconstruction in long scintillator detectors. We take advantage of the fact that for this kind of detectors amplitude and shape of registered signals depend strongly on the position where particle hits the detector. The reconstruction is based on determination of the degree of similarity between measured and averaged signals stored in a library for a set of well-defined positions along the scintillator. Preliminary results of validation of the introduced method with experimental data obtained by means of the double strip prototype of the J-PET detector are presented.

16

Analysis Procedure of the Positronium Lifetime Spectra for the J-PET Detector

18%

Dulski K., Zgardzińska B., Białas P., Curceanu C., Czerwiński E., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska-Kamińska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Mohammed M., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Raj J., Rudy Z., Sharma N., Sharma S., Shivani S., Shopa R., Silarski M., Skurzok M., Wieczorek A., Wiślicki W., Zieliński M., Moskal P.

Acta Physica Polonica A

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2017

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vol. 132

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issue 5

1637-1640

EN

Positron annihilation lifetime spectroscopy has shown to be a powerful tool to study the nanostructures of porous materials. Positron emission tomograph is a device allowing imaging of metabolic processes e.g. in human bodies. A newly developed device, the Jagiellonian PET will allow positron annihilation lifetime spectroscopy in addition to imaging, thus combining both analyses providing new methods for physics and medicine. In this contribution we present a computer program that is compatible with the Jagiellonian PET software. We compare its performance with the standard program LT 9.0 by using positron annihilation lifetime spectroscopy data from hexane measurements at different temperatures. Our program is based on an iterative procedure, and our fits prove that it performs as good as LT 9.0.

17

Time Calibration of the J-PET Detector

18%

Skurzok M., Silarski M., Alfs D., Białas P., Shivani, Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska-Kamińska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Mohammed M., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Raj J., Rudy Z., Sharma N., Sharma S., Shopa R., Wieczorek A., Wiślicki W., Zgardzińska B., Zieliński M., Moskal P.

Acta Physica Polonica A

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2017

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vol. 132

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issue 5

1641-1644

EN

The Jagiellonian positron emission tomograph project carried out in the Institute of Physics of the Jagiellonian University is focused on construction and tests of the first prototype of PET scanner for medical diagnostic which allows for the simultaneous 3D imaging of the whole human body using organic scintillators. The J-PET prototype consists of 192 scintillator strips forming three cylindrical layers which are optimized for the detection of photons from the electron-positron annihilation with high time-and high angular resolutions. In this article we present time calibration and synchronization of the whole J-PET detection system by irradiating each single detection module with a ²²Na source and a small detector providing common reference time for synchronization of all the modules.

18

Preliminary Studies of J-PET Detector Spatial Resolution

18%

Pawlik-Niedźwiecka M., Niedźwiecki S., Alfs D., Białas P., Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Mohammed M., Pałka M., Raczyński L., Raj J., Rudy Z., Shivani, Silarski M., Skurzok M., Sharma N., Sharma S., Shopa R., Strzelecki A., Wieczorek A., Wiślicki W., Zgardzińska B., Zieliński M., Moskal P.

Acta Physica Polonica A

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2017

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vol. 132

|

issue 5

1645-1648

EN

The J-PET detector, based on long plastic scintillator strips, was recently constructed at the Jagiellonian University. It consists of 192 modules axially arranged into three layers, read out from both sides by digital constant-threshold front-end electronics. This work presents preliminary results of measurements of the spatial resolution of the J-PET tomograph performed with ²²Na source placed at selected position inside the detector chamber.

19

A Method to Produce Linearly Polarized Positrons and Positronium Atoms with the J-PET Detector

18%

Mohammed M., Białas P., Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Raj J., Rudy Z., Sharma N., Sharma S., Shivani, Skurzok M., Silarski M., Wieczorek A., Wiślicki W., Zgardzińska B., Zieliński M., Moskal P.

Acta Physica Polonica A

|

2017

|

vol. 132

|

issue 5

1486-1489

EN

A method for creating linearly polarized positrons and ortho-positronium (o-Ps) atoms with the J-PET detector is presented. The unique geometry and properties of the J-PET tomography enable one to design a positron source such that the quantization axis for the estimation of the linear polarization of produced o-Ps can be determined on the event by event basis in a direction of the positron motion. We intend to use ²²Na or other β⁺ decay isotopes as a source of polarized positrons. Due to the parity violation in the beta decay, the emitted positrons are longitudinally polarized. The choice of the quantization axis is based on the known position of the positron emitter and the reconstructed position of the positronium annihilation. We show that the J-PET tomography is equipped with all needed components.

20

Human Tissue Investigations Using PALS Technique - Free Radicals Influence

18%

Jasińska B., Zgardzińska B., Chołubek G., Pietrow M., Gorgol M., Wiktor K., Wysogląd K., Białas P., Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Hiesmayr B., Jodłowska-Jędrych B., Kamińska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Mohammed M., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Sharma N., Sharma S., Shopa R., Silarski M., Skurzok M., Wieczorek A., Wiktor H., Wiślicki W., Zieliński M., Moskal P.

Acta Physica Polonica A

|

2017

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vol. 132

|

issue 5

1556-1558

EN

The positron annihilation lifetime spectroscopy was applied to the samples of the human uterine leiomyomas and the normal myometrium tissues taken from the selected place of the uterus during a surgery. The method indicated differences in values of the measured positron annihilation lifetime spectroscopy parameters (lifetimes and intensities) between healthy and diseased tissue samples. The additional measurements were performed either in darkness or in presence of visible light which influenced the free radicals present in both kind of tissues and, as a result, made changes in free annihilation and o-Ps decay lifetime and intensity values.

Refine search results

Multi-Scale Simulations of Semiconductor Nanostructures

Exact Diagonalization Approach for Atomistic Calculation of Piezoelectric Effects in Semiconductor Quantum Dots

The influence of CFBC fly ash addition on phase composition of air-entrained concrete

ERRATUM

Coupling and Strain Effects in Vertically Stacked Double InAs/GaAs Quantum Dots: Tight-Binding Approach

Atomistic Calculation of Coulomb Interactions in Semiconductor Nanocrystals: Role of Surface Passivation and Composition Details

Strain and Spin-Orbit Effects in Self-Assembled Quantum Dots

Structure Characterization and Catalytic Properties of Cr_2O_3 Doped with MgO Supported on MgF_2

X-ray Characterization of Films Formed by Pulsed Laser Deposition on Cold Substrates from YBaCuO Targets

Magnons in Cubic MBE-Grown A_{1-x}Mn_{x}Te Layers (A = Cd, Zn, Mg)

A Pilot Study of the Novel J-PET Plastic Scintillator with 2-(4-styrylphenyl)benzoxazole as a Wavelength Shifter

Multiple Scattering and Accidental Coincidences in the J-PET Detector Simulated Using GATE Package

GPU Accelerated Image Reconstruction in a Two-Strip J-PET Tomograph

Analysis Framework for the J-PET Scanner

Hit Time and Hit Position Reconstruction in the J-PET Detector Based on a Library of Averaged Model Signals

Analysis Procedure of the Positronium Lifetime Spectra for the J-PET Detector

Time Calibration of the J-PET Detector

Preliminary Studies of J-PET Detector Spatial Resolution

A Method to Produce Linearly Polarized Positrons and Positronium Atoms with the J-PET Detector

Human Tissue Investigations Using PALS Technique - Free Radicals Influence