| 1. |
-
- 2019
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Abbasi, R., et al.
(författare)
-
IceCat-1: The IceCube Event Catalog of Alert Tracks
- 2023
-
Ingår i: Astrophysical Journal, Supplement Series. - : IOP Publishing Ltd. - 1538-4365 .- 0067-0049. ; 269:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present a catalog of likely astrophysical neutrino track-like events from the IceCube Neutrino Observatory. IceCube began reporting likely astrophysical neutrinos in 2016, and this system was updated in 2019. The catalog presented here includes events that were reported in real time since 2019, as well as events identified in archival data samples starting from 2011. We report 275 neutrino events from two selection channels as the first entries in the catalog, the IceCube Event Catalog of Alert Tracks, which will see ongoing extensions with additional alerts. The Gold and Bronze alert channels respectively provide neutrino candidates with a 50% and 30% probability of being astrophysical, on average assuming an astrophysical neutrino power-law energy spectral index of 2.19. For each neutrino alert, we provide the reconstructed energy, direction, false-alarm rate, probability of being astrophysical in origin, and likelihood contours describing the spatial uncertainty in the alert's reconstructed location. We also investigate a directional correlation of these neutrino events with gamma-ray and X-ray catalogs, including 4FGL, 3HWC, TeVCat, and Swift-BAT.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Romagnoni, A, et al.
(författare)
-
Comparative performances of machine learning methods for classifying Crohn Disease patients using genome-wide genotyping data
- 2019
-
Ingår i: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1, s. 10351-
-
Tidskriftsartikel (refereegranskat)abstract
- Crohn Disease (CD) is a complex genetic disorder for which more than 140 genes have been identified using genome wide association studies (GWAS). However, the genetic architecture of the trait remains largely unknown. The recent development of machine learning (ML) approaches incited us to apply them to classify healthy and diseased people according to their genomic information. The Immunochip dataset containing 18,227 CD patients and 34,050 healthy controls enrolled and genotyped by the international Inflammatory Bowel Disease genetic consortium (IIBDGC) has been re-analyzed using a set of ML methods: penalized logistic regression (LR), gradient boosted trees (GBT) and artificial neural networks (NN). The main score used to compare the methods was the Area Under the ROC Curve (AUC) statistics. The impact of quality control (QC), imputing and coding methods on LR results showed that QC methods and imputation of missing genotypes may artificially increase the scores. At the opposite, neither the patient/control ratio nor marker preselection or coding strategies significantly affected the results. LR methods, including Lasso, Ridge and ElasticNet provided similar results with a maximum AUC of 0.80. GBT methods like XGBoost, LightGBM and CatBoost, together with dense NN with one or more hidden layers, provided similar AUC values, suggesting limited epistatic effects in the genetic architecture of the trait. ML methods detected near all the genetic variants previously identified by GWAS among the best predictors plus additional predictors with lower effects. The robustness and complementarity of the different methods are also studied. Compared to LR, non-linear models such as GBT or NN may provide robust complementary approaches to identify and classify genetic markers.
|
|
| 6. |
- Adcox, K, et al.
(författare)
-
PHENIX detector overview
- 2003
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 499:2-3, s. 469-479
-
Tidskriftsartikel (refereegranskat)abstract
- The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented. (C) 2002 Elsevier Science B.V. All rights reserved.
|
|
| 7. |
- Jayakumar, O. D., et al.
(författare)
-
Structural and magnetic properties of (In1-xFex)(2)O-3 (0.0 <= x <= 0.25) system : Prepared by gel combustion method
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5
-
Tidskriftsartikel (refereegranskat)abstract
- (In1-xFex)(2)O-3 polycrystalline samples with x=(0.0,0.05,0.10,0.15,0.20, and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature (T-C) well above room temperature.
|
|
| 8. |
|
|
| 9. |
- Araujo, Carlos Moyses, et al.
(författare)
-
Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites
- 2014
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 4686-
-
Tidskriftsartikel (refereegranskat)abstract
- We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.
|
|
| 10. |
- Jayakumar, O. D., et al.
(författare)
-
1D Morphology Stabilization and Enhanced Magnetic Properties of Co : ZnO Nanostructures on Codoping with Li: A Template-Free Synthesis
- 2009
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:10, s. 4450-4455
-
Tidskriftsartikel (refereegranskat)abstract
- ID natiostructures of Zn1-xCoxO (x = 0, 0.03 and 0.05) and Co and Li codoped ZnO (Zn0.85Li0.10Co0.05O) were prepared by a soft chemical method. We report a very interesting observation of morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution. It is also remarkable to note that the morphology completely reverts back to rod shape by Li incorporation. In addition to this unusual observation, the Li incorporation enhances the room-temperature ferromagnetic (RTFM) properties. These experimental observations are well-supported by theory work as well. These results are significant, as the I D RTFM will have implications in spintronic devices.
|
|
| 11. |
- Jayakumar, O. D., et al.
(författare)
-
Enhancement of ferromagnetic properties in Zn0.95Co0.05O nanoparticles by indium codoping : An experimental and theoretical study
- 2010
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:23, s. 232510-
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of Zn0.95-xCo0.05InxO (x = 0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When "In." is codoped with Co with x = 0.0 to 0.07 in Zn0.95-xCo0.05InxO, a systematic increase in magnetic moment is observed up to x = 0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations.
|
|
| 12. |
- Jayakumar, O. D., et al.
(författare)
-
Experimental and theoretical investigations of dopant, defect, and morphology control on the magnetic and optical properties of transition metal doped ZnO nanoparticles
- 2014
-
Ingår i: Springer Series in Materials Science. - New Delhi : Springer Nature. - 0933-033X. ; 180, s. 341-370
-
Tidskriftsartikel (refereegranskat)abstract
- The control of size, shape, and physical properties by surface modifications are of immense interest in materials which are of technological importance. The ZnO-based wide bandgap semiconductor nanoparticles have gained significant interest in the research community due to its large exciton binding energy (60 meV). Further substantial renewed interest in ZnO-based compounds is due to the possible realization of p-type conduction and ferromagnetic behavior when doped with transition metals. In this report we present interesting results on the ZnO nanoparticle system in which the control of dopants, morphology, and the surface modification can influence significantly the physical properties of the ZnO nanoparticles. First, we present the methods to control the morphology of the ZnO particle to obtain nanorods. As an example we show the effect of Li dopant on the morphology control of Co and Ni doped ZnO. The effect of morphology on the magnetic properties of these compounds is discussed further. We also demonstrate the effect of the n-type charge carriers on the magnetic and optical properties by doping aliovalent cations in Zn(Co)O. Following this we comment on the magnetic property manipulations by surfactant treatment of transition metal (TM) doped ZnO and defect stabilization in ZnO by Mg doping. The magnetic coupling is RKKY-like both with and without Li co-doping. Finally, we provide the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials by first-principles modeling. These theoretical analyses demonstrate that Li co-doping has primarily two effects in bulk Zn1-xMxO (with M = Co or Ni). First, the Li-on-Zn acceptors increase the local magnetic moment by depopulating the M 3d minority spin-states. Second, Li-on- Zn prefer to be closer to the M atoms to compensate the M-O bonds and to locally depopulate the 3d states, and this will help in forming high aspect nanostructures. The observed room temperature ferromagnetism in Li co-doped Zn1-xMxO nanorods can therefore be explained by the better rod morphology in combination with locally ionizing the magnetic M atoms.
|
|
| 13. |
- Jayakumar, O. D., et al.
(författare)
-
Experimental and theoretical investigations on magnetic behavior of (Al,Co) co-doped ZnO nanoparticles
- 2010
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 2:8, s. 1505-1511
-
Tidskriftsartikel (refereegranskat)abstract
- We present the structural and magnetic properties of Zn0.95-xCo0.05AlxO (x = 0.0 to 0.1) nanoparticles, synthesized by a novel sol-gel route followed by pyrolysis. Powder X-ray diffraction data confirms the formation of a single phase wurtzite type ZnO structure for all the compositions. The Zn0.95Co0.05O nanoparticles show diamagnetic behavior at room temperature. However, when Al is co-doped with Co with x = 0.0 to 0.10 in Zn0.95-xCo0.05AlxO, a systematic increase in ferromagnetic moment is observed up to x = 0.07 at 300 K. Above x = 0.07 (e.g. for x = 0.10) a drastic decrease in ferromagnetic nature is observed which is concomitant with the segregation of poorly crystalline Al rich ZnO phase as evidenced from TEM studies. Theoretical studies using density functional calculations on Zn0.95-xCo0.05AlxO suggest that the partial occupancy of S2 states leads to an increased double exchange interaction favoring the ferromagnetic ground states. Such ferromagnetic interactions are favorable beyond a threshold limit. At a high level doping of Al, the exchange splitting is reduced, which suppresses the ferromagnetic ordering.
|
|
| 14. |
- Jayakumar, O. D., et al.
(författare)
-
Surfactant-induced enhanced room temperature ferromagnetism in Zn0.96Mn0.03Li0.01O nanoparticles : Prepared by solid-state pyrolitic reaction
- 2007
-
Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 307:2, s. 315-320
-
Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis of nanoparticles of Zn0.96Mn0.03Li0.01O by a low-temperature solid-state pyrolitic reaction, followed by a surfactant-assisted calcination at 400 degrees C. The X-ray diffraction and transmission electron microscopy analyses showed the formation of impurity free nanocrystals of Mn doped Li co-cloped ZnO with wurtzite structure. XPS data revealed that Mn exists in + 2 oxidation state. DC magnetization measurements as a function of field and temperature showed enhanced room temperature ferromagnetism for the surfactant-treated Zn0:96Mn0.03Li0.01O. FMR signal observed in the EPR spectrum further confirmed its ferromagnetic nature.
|
|
| 15. |
- Jayakumar, O. D., et al.
(författare)
-
Tunable Ferromagnetism accompanied by Morphology Control in Li-doped Zn0.97Ni0.03O
- 2010
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:41, s. 17428-17433
-
Tidskriftsartikel (refereegranskat)abstract
- We report morphological and ferromagnetic property control in ZnO nanorod structures by an optimum doping of Ni and Li. Nanostructures of Zn0.97-xNi0.03LixO (x = 0, 0.03, 0.05, 0.08, and 0.10) are prepared by a solvothermal method. High aspect ratio (5-15) ZnO nanorods transform to particles (with 1-3 aspect ratio) influenced by 3 at. % Ni substitution in ZnO (Zn0.97Ni0.03O). It is remarkable to note that the Zn1.97Ni0.03O particles completely retain the nanorod shape with significantly increased aspect ratio (15-30) when 3 at.c/a Li ions are codoped in (Zn0.99Li0.03Ni0.30O). Li substitution tits enhances ferromagnetism with largest magnetization (0.8 emu.g(-1)) observed for Zn0.94Li0.03Ni0.03O. For Li concentration >3 at.%, the aspect ratio as well as the magnetization decreased considerably. These experimental observations are explained by first-principles modeling. At low Li-on-Zn acceptor concentrations, the total magnetization is increased by lower Ni d-state populations, whereas at higher Li concentrations the population of ZnO host states decreases the ferromagnetism by induced magnetic moments on the oxygens. We discuss the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials, which are expected to play pivotal role in developing spintronic devices.
|
|
| 16. |
- Nagar, Sandeep, et al.
(författare)
-
Room Temperature Ferromagnetism and Lack of Ferroelectricity in Thin Films of 'Biferroic?' YbCrO3
- 2009
-
Ingår i: Novel Materials and Devices for Spintronics. - : Materials Research Society. - 9781605111568 ; , s. 163-168
-
Konferensbidrag (refereegranskat)abstract
- Search for novel multi-functional materials, especially multiferroics, which are ferromagnetic above room temperature and at the same time exhibit a ferroelectric behavior much above room temperature, is an active topic of extensive studies today Ability to address an entity with an external field, laser beam, and also electric potential is a welcome challenge to develop multifunctional devices enabled by nanoscience While most of the studies to date have been on various forms of Bi and Ba based Ferrites, rare earth chromites are a new class of materials which appear to show some promise However m the powder and bulk form these materials are at best canted antiferromagnets with the magnetic transition temperatures much below room temperature In this presentation we show that thin films of YbCrO3 deposited by Pulsed Laser Deposition exhibit robust ferromagnetic properties above room temperature It is indeed a welcome surprise and a challenge to understand the evolution of above room temperature ferromagnetism in such a thin film The thin films are amorphous in contrast to the powder and bulk forms which are crystalline The magnetic properties are those of a soft magnet with low coercivity We present extensive investigations of the magnetic and ferroelectric properties, and spectroscopic studies using XAS techniques to understand the electronic states of the constituent atoms in this novel Chromite While the amorphous films are ferromagnetic much above room temperature, we show that any observation of ferroelectric property in these films is an artifact of a leaky highly resistive material
|
|
| 17. |
- Okabayashi, M., et al.
(författare)
-
Control of the resistive wall mode with internal coils in the DIII-D tokamak
- 2005
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 45:12, s. 1715-1731
-
Tidskriftsartikel (refereegranskat)abstract
- Internal coils, 'I-Coils', were installed inside the vacuum vessel of the DIII-D device to generate non-axisymmetric magnetic fields to act directly on the plasma. These fields are predicted to stabilize the resistive wall mode (RWM) branch of the long-wavelength external kink mode with plasma beta close to the ideal wall limit. Feedback using these I-Coils was found to be more effective as compared to using external coils located outside the vacuum vessel. Locating the coils inside the vessel allows for a faster response and the coil geometry also allows for better coupling to the helical mode structure. Initial results were reported previously (Strait E.J. et al 2004 Phys. Plasmas 11 2505). This paper reports on results from extended feedback stabilization operations, achieving plasma parameters up to the regime of Cβ ≈ 1.0 and open loop growth rates of γopenτw ≳ 25 where the RWM was predicted to be unstable with only the 'rotational viscous stabilization mechanism'. Here Cβ ≈ (β - βno-wall.limit)/(βideal.wall.limit - βno-wall.limit) is a measure of the beta relative to the stability limits without a wall and with a perfectly conducting wall, and τw is the resistive flux penetration time of the wall. These feedback experimental results clarified the processes of dynamic error field correction and direct RWM stabilization, both of which took place simultaneously during RWM feedback stabilization operation. MARS-F modelling provides a critical rotation velocity in reasonable agreement with the experiment and predicts that the growth rate increases rapidly as rotation decreases below the critical. The MARS-F code also predicted that for successful RWM magnetic feedback, the characteristic time of the power supply should be limited to a fraction of the growth time of the targeted RWM. The possibility of further improvements in the presently achievable range of operation of feedback gain values is also discussed.
|
|
| 18. |
- Persson, Clas, et al.
(författare)
-
Morphology and Magnetic Coupling in ZnO:Co and ZnO:Ni Co-Doped with Li
- 2011
-
Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 119:2, s. 95-98
-
Tidskriftsartikel (refereegranskat)abstract
- Zn0.95Co0.05O and Zn0.97Ni0.03O nanorods, prepared by a solvothermal method, show intriguing morphology and magnetic properties when co-doped with Li. At low and moderate Li incorporation (below 10 and 3 at.% Li in the Co- and Ni-doped samples, respectively) the rod aspect ratio is increased and room temperature ferromagnetic properties are enhanced, whereas the ferromagnetic coupling in Zn0.97Ni0.03O is decreased for Li concentrations > 3 at.%. First-principles theoretical analyses demonstrate that Li co-doping has primarily two effect 3 in bulk Zn1-xMxO (with M = Co or Ni). First, the Li-on-Zn acceptors increase the local magnetic moment by depopulating the M 3d minority spin-states. The magnetic coupling is Ruderman-Kittel-Kasuya-Yosida-like both without and with Li co-doping. Second, Li-on-Zn prefer to be close to the M atoms to compensate the M-O bonds and to locally depopulate the 3d states, and this will help forming high aspect nanostructures. The observed room temperature ferromagnetism in Li co-doped Zn1-xMxO nanorods can therefore be explained by the better rod morphology in combination with ionizing the magnetic M atoms.
|
|
| 19. |
- Wu, Yan, et al.
(författare)
-
Room Temperature Ferromagnetism and Fast Ultraviolet Photoresponse of Inkjet-Printed Mn-Doped ZnO Thin Films
- 2010
-
Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 46:6, s. 2152-2155
-
Tidskriftsartikel (refereegranskat)abstract
- We have synthesized Mn-doped ZnO thin films by inkjet printing using a two-step annealing process at 200 C for the decomposition of the organic compounds, and at various temperatures above 400 degrees C to tailor room temperature ferromagnetism. Highly c axis oriented 80 to 400 nm thin films on ( 001) Si substrates are obtained with a magnetic moment as large as 2.1 mu(B)/Mn2+. X-ray absorption and emission spectra measurements at the O K edge and the Mn L edge suggest strong p-d hybridization between the Mn2+ and O2-. Furthermore, Mn L edge XAS indicates the emergence of Mn3+ /Mn4+ mixed valence states for films annealed above 500 degrees C that leads to suppression of ferromagnetic ordering. All of these films show large and fast ultraviolet (UV) photoresponse with the decay times of about 0.5 ms, suggesting the potential for designing multifunctional UV sensors.
|
|
