| 1. |
|
|
| 2. |
|
|
| 3. |
- Gong, S., et al.
(författare)
-
Orientation effect on heat transfer coefficient of a downward surface for flow boiling in a rectangular channel under low flow rate
- 2020
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 153
-
Tidskriftsartikel (refereegranskat)abstract
- Natural convection boiling in channel with Arc-Shaped will be encountered in the IVR-ERVC (In-Vessel Retention measure by External Reactor Vessel Cooling) system in nuclear power plant under severe accident. The flow and heat transfer characters in this situation is simulated by flow boiling of deionized water in an inclined rectangular channel under low flow rates. This paper aims to separate various parameters (such as orientation, mass flow rate and inlet quality, etc.) to investigate their individual effects on heat transfer coefficient (HTC) in a rectangular channel with cross section of 17 mm × 10 mm. By using a preheater at the inlet of the rectangular channel, the inlet quality could be controlled and the two-phase flow situation could be observed before the fluids entering into the main heater region on one side of the channel wall in downstream. Thus the characteristics of HTC on the main heater could be investigated at different flow patterns. The channel orientations vary from 15 to 90°, the mass flow rates vary from 110 to 288 kg/(m2s) and the qualities vary from 0.003 to 0.036, respectively. Experimental results show that the mass flow rate and quality effects on the HTC are very weak in this study. However, the orientation angle effect on HTC shows an transition region within 45°~60°, while it slowly changes when the orientation angle is smaller than 45° and bigger than 60°. Such tendency could be well formulated by the error function. Compared with different empirical formulas of saturated boiling HTC, it is found that the Liu & Winterton correlation can well predict the experimental HTC results in 90° orientation channel. Based on such correlation and coupled with the error function, a new model was developed by considering the orientation effect, which has an error of ±15% comparing with the experimental data.
|
|
| 4. |
- Li, W., et al.
(författare)
-
On improvement of a conditional mornitoring technique for condition-based maintenance
- 2019
-
Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888982566
-
Konferensbidrag (refereegranskat)abstract
- The condition-based maintenance (CMB) is a hot research topic to overcome the drawbacks belonging to the periodic maintenance used in nuclear power plants nowadays. Auto-Associative Kernel Regression (AAKR) is a widely applied condition monitoring technique which is the basis of a CBM. In this paper, the traditional AAKR is improved by using the ensemble learning technique. The modified AAKR is tested by steady-state operational data of a Tennessee-Eastman chemical process and the results show that it can significantly improve the auto- and cross-sensitivity without reducing the accuracy. This indicates a significant improvement in performance of this condition monitoring technique.
|
|
| 5. |
- Polyakov, A. Y., et al.
(författare)
-
Electrical and luminescent properties and the spectra of deep centers in GaMnN/InGaN light-emitting diodes
- 2004
-
Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 33:3, s. 241-247
-
Tidskriftsartikel (refereegranskat)abstract
- Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external magnetic field (so-called -spin-LEDs-). The contact annealing temperature was kept to 750°C, which is the thermal stability limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and the n-GaN in the top contact layer.
|
|
| 6. |
- Qi, Z., et al.
(författare)
-
Application of nonlinear principal component analysis technique to nuclear power plants
- 2019
-
Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888982566
-
Konferensbidrag (refereegranskat)abstract
- Traditionally, manual calibration of sensors is required and performed during each refueling outage. If the traditional time-directed calibration is replaced by an online monitoring technique, the maintenance cost will be significantly reduced since only the abnormal sensors identified in on-line monitoring need to be re-calibrated or replaced off-line. The Nonlinear Principal Component Analysis (NLPCA), such as Auto-Associative Neural Network (AANN) and Auto-Associative Kernel Principal Component Analysis (AAKPCA), can describe the nonlinear correlation between sensors such as power, temperature, pressure and flowrate. In this paper, AANN and AAKPCA model are tested by simulated redundant data and Tennessee-Eastman process data. The results show that both of them have a high ability of prediction and a low sensitivity. Therefore, they are can be used in on-line monitoring.
|
|
| 7. |
- Qi, Z., et al.
(författare)
-
Sensor fault detection in nuclear power plant using auto-associative neural network
- 2019
-
Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : American Society of Mechanical Engineers (ASME). - 9784888983051
-
Konferensbidrag (refereegranskat)abstract
- Fault diagnosis system usually includes a prediction module and a diagnosis module. The prediction module is supposed to predict sensor values based on sensor observations, and the diagnosis module is used to determine whether a sensor has degradation or failure by comparing the difference between sensor observations and predictions. Auto-Associative Neural Network (AANN) is a widely applied data-driven prediction method consisting of input layer, mapping layer, bottleneck layer, de-mapping layer and output layer. AANN compresses the information contained in the input data (i.e. sensor observations) into bottleneck layer through mapping layer, and then reconstructs the sensor values at output layer based on the extracted nonlinear features stored in bottleneck layer through de-mapping layer. This paper focuses on the feasibility study of AANN model in fault diagnosis for nuclear power plants. The performance of AANN model was studied by using simulation data, and the AANN model was optimized by combining prejudgment and secondary prediction. The results show that the optimized AANN model can improve the performance comparing to original AANN model, and can be applied to the fault diagnosis for nuclear power plant sensors.
|
|
| 8. |
- Thinh, N. Q., et al.
(författare)
-
Identification of Ga-interstitial defects in GaNyP1−y and AlxGa1−xNyP1−y
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : APS. - 1098-0121 .- 1550-235X. ; 70:12, s. 121201-
-
Tidskriftsartikel (refereegranskat)abstract
- Two Ga -interstitial (Gai) defects are identified by optically detected magnetic resonance as common grown-in defects in molecular beam epitaxial GaNyP1−y and AlxGa1−xNyP1−y. Characteristic hyperfine structure arising from spin interaction between an unpaired electron and a Ga nucleus is clearly resolved. The observed strong and nearly isotropic hyperfine interaction reveals an electron wave function of A1 symmetry that is highly localized at the Gai and thus a deep-level defect. Our analysis based on first-principles calculations suggests that these defects are complexes containing one Gai2+ .
|
|
| 9. |
|
|
| 10. |
- Thinh, N.Q., et al.
(författare)
-
Properties of Ga-interstitial defects in AlxGa 1-xNyP1-y
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:12
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed account of the experimental results from optically detected magnetic resonance (ODMR) studies of grown-in defects in (Al)GaNP alloys, prepared by molecular beam epitaxy, is presented. The experimental procedure and an in-depth analysis by a spin Hamiltonian lead to the identification of two Gai defects (Gai-A and Gai-B). New information on the electronic properties of these defects and the recombination processes leading to the observation of the ODMR signals will be provided. These defects are deep-level defects. In conditions when the defect is directly involved in radiative recombination of the near-infrared photoluminescence band, the energy level of the Gai-B defect was estimated to be deeper than ~1.2 eV from either the conduction or valence band edge. In most cases, however, these defects act as nonradiative recombination centers, reducing the efficiency of light emission from the alloys. They can thus undermine the performance of potential photonic devices. High thermal stability is observed for these defects. ©2005 The American Physical Society.
|
|
| 11. |
- Zhang, Y., et al.
(författare)
-
A feasibility study on application of redundancy sensors estimation technique to nuclear power plants
- 2019
-
Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888983051
-
Konferensbidrag (refereegranskat)abstract
- Traditional periodic maintenance techniques being employed in nuclear power plants usually fail to detect the potential degradation in performance of a sensor timely, and may increase workload and radiation exposure of the maintenance staff. The Redundancy Sensors Estimation Technique (RSET) to be presented in this paper is a noninvasive and in-situ monitoring technique based on measurement theory. The technique allows staff to monitor redundant sensors on-line and to assess their performance instantly. If such a REST can be applied to a nuclear power plant, it is expected that it will improve the safety of the plant and reduce the costs of operation and maintenance. This paper is concerned with a feasibility study on the REST's application to a nuclear power plant. The results show that the RSET, featuring a strong generalization ability, can offer state estimation and fault diagnosis to signals from redundant sensors accurately. By adding drift data to the test dataset, the RSET can determine the signal drift accurately. The core algorithm of RSET can be explained by mathematical formulas and has high prediction accuracy. In conclusion, RSET can detect the performance degradation of redundant sensors in advance during the operation of plant.
|
|
| 12. |
- Zhu, Y. -C, et al.
(författare)
-
Experimental Study of Critical Heat Flux on a Graphite Film
- 2020
-
Ingår i: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics. - : Science Press. - 0253-231X. ; 41:3, s. 643-647
-
Tidskriftsartikel (refereegranskat)abstract
- Saturated pool boiling experiment with heater surfaces of smooth graphite films was conducted under atmospheric pressure, and the deionized water was used as working fluid. The test results showed that the graphite film began to expand and fracture in some parts of the surface as the heat flux reached 1.83 MW/m2. Then the expanded area enlarged and the resistance of the graphite film rapidly increased with the increase of the heat flux, until the whole film was expanded and the surface was ruptured uniformly under a heat flux of 2.40 MW/m2, while the resistance increased slowly during this process. Ultimately, the graphite film was burned out at a heat flux of 3.17 MW/m2. Consequently, the critical heat flux of the graphite film could be enhanced by an adaptively expanding processing with an enhancement ratio of 73%. The visualization results through a high-speed camera showed that compared with the smooth surface, the quantity of nucleation was greater, the bubble departure diameter was smaller, and the bubble departure frequency was higher on an expanded graphite surface under the same heat flux condition.
|
|
| 13. |
- Buyanova, Irina A., et al.
(författare)
-
Effect of momentum relaxation on exciton spin dynamics in diluted magnetic semiconductor ZnMnSe CdSe superlattices
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:16
-
Tidskriftsartikel (refereegranskat)abstract
- cw hot photoluminescence (PL) complemented by transient PL measurements is employed to evaluate momentum and spin relaxation of heavy hole (HH) excitons in ZnMnSe CdSe superlattices. The rate of acoustic-phonon assisted momentum relaxation is concluded to be comparable to the total rate of exciton decay processes, about (2-3) × 1010 s-1, independent of applied magnetic fields. In magnetic fields when the Zeeman splitting ? of the exciton states is below the energy of the longitudinal optical (LO) phonon (?LO), a surprisingly strong suppression of spin relaxation rate from the bottom of the upper spin band is observed, which becomes comparable to that of momentum scattering via acoustic phonons. On the other hand, dramatic acceleration of the spin relaxation process by more than one order of magnitude is found for the excitons with a high momentum K. The findings are interpreted as being due to electron and hole spin flip processes via exchange interaction with isolated Mn2+ ions. Experimental evidence for the efficient interaction between the hot excitons and Mn impurities is also provided by the observation of spin flip transitions within Mn2+ - Mn2+ pairs that accompany the momentum relaxation of the hot HH excitons. In higher magnetic fields ?= ?LO, abrupt shortening of the spin flip time is observed. It indicates involvement of a new and more efficient spin relaxation process and is attributed to direct LO-assisted exciton spin relaxation with a subpicosecond spin relaxation time. © 2005 The American Physical Society.
|
|
| 14. |
- Buyanova, Irina A., et al.
(författare)
-
Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures
- 2007
-
Ingår i: 2006 E-MRS Fall Meeting. - : Wiley. ; , s. 159-173
-
Konferensbidrag (refereegranskat)abstract
- In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II-VIs (e.g. ZnMnSe/Zn(Cd)Se) and III-Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron-hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by efficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.
|
|
| 15. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Analysis of band anticrossing in GaNxP1-x alloys
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70, s. 085209-
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent absorption, photoluminescence excitation, and spectroscopic ellipsometry measurements are employed to accurately determine compositional and temperature dependences of the conduction band (CB) states in GaNP alloys. The CB edge and the higher lying Γc CB minimum (CBM) are shown to exhibit an apparently anticrossing behavior, i.e., the N-induced redshift of the bandgap energy is accompanied by a matching blueshift of the Γc CBM. The obtained data can be phenomenologically described by the band anticrossing model. By considering strong temperature dependence of the energy of the interacting N level, which has largely been overlooked in earlier studies of GaNP, the interacting N level can be attributed to the isolated substitutional NP and the coupling parameter is accurately determined.
|
|
| 16. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Band alignment in novel GaInNP/GaAs heterostructures.
- 2007
-
Ingår i: 31th Workshop on Compound Semiconductor Devices and Integrated Circuits WOCSDICE 2007,2007. ; , s. 183-186
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Direct experimental evidence for unusual effects of hydrogen on the electronic and vibrational properties of GaNxP1−x alloys : a proof for a general property of dilute nitrides
- 2004
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:24, s. 245215-245219
-
Tidskriftsartikel (refereegranskat)abstract
- Direct experimental evidence for dramatic effects of hydrogen incorporation on the electronic structure and lattice properties of GaNxP1−x alloys is presented. By employing photoluminescence excitation spectroscopy, postgrowth hydrogenation is shown to reopen the band gap of the GaNP alloys and to efficiently reduce the N-induced coupling between the conduction band states. By Raman spectroscopy, these effects are shown to be accompanied by hydrogen-induced breaking of the Ga-P bond in the alloy, evident from disappearance of the corresponding vibrational mode. According to the performed Raman and x-ray diffraction measurements, the hydrogenation is also found to cause a strong expansion of the GaNP lattice, which changes the sign of strain from tensile in the as-grown GaNP epilayers to compressive in the posthydrogenated structures, due to the formation of complexes between N and H.
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Hydrogen passivation of nitrogen in GaNAs and GaNP alloys : How many H atoms are required for each N atom?
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:2, s. 021920-
-
Tidskriftsartikel (refereegranskat)abstract
- Secondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the dominant mechanism for neutralization of N-induced modifications in the electronic structure of the materials. Though the exact number of H atoms involved in passivation may depend on the conditions of the H treatment and the host matrixes, it is generally found that more than three H atoms are required to bind to a N atom to achieve full passivation for both alloys. © 2007 American Institute of Physics.
|
|
| 24. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Intrinsic modulation doping in InP-based structures : properties relevant to device applications
- 1999
-
Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 201-202, s. 786-789
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we study device-relevant issues, such as doping efficiency and thermal stability, of recently proposed intrinsic modulation doping approach where intrinsic defects (PIn antisites) are used as a carrier source instead of impurity dopants. The InP/InGaAs heterostructure designed to resemble high electron mobility transistor (HEMT) structures, where all the layers were grown at a normal growth temperature 480°C except for the top InP layer which was grown at 265°C, was used as a prototype device. A comparison between the intrinsically doped structure with extrinsically doped HEMTs, which have an identical design except that the top InP layer was instead Si-doped and was grown at 480°C, reveals a high efficiency of the intrinsic doping. The thermal stability of the intrinsically doped HEMT is examined by annealing at temperatures 400-500°C relevant to possible processing steps needed in device fabrication. The observed severe reduction of the carrier concentration after annealing performed without phosphorous gas protection is attributed to the known instability of an InP surface at T>400°C. Thermal stability of the intrinsically doped HEMT is shown to be improved by using an InP cap layer grown at 480°C.
|
|
| 25. |
|
|
| 26. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Modeling of band gap properties of GaInNP alloys lattice matched to GaAs
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:3, s. 31907-
-
Tidskriftsartikel (refereegranskat)abstract
- Compositional and temperature dependences of the band gap energies of GaInNP alloys, which are lattice matched to GaAs, are determined and modeled by a band anticrossing (BAC) interaction between the localized state of the isolated NP and extended host states. The BAC parameters are deduced as EN =2.1±0.1 eV and CMN =1.7±0.2 eV. The low value of the coupling parameter CMN implies weaker coupling of the N level with the host matrix, presumably due to short range ordering effects, similar to the case of GaInNAs alloys with a high In content. The obtained information is important for future modeling of the electronic structure of the alloys. © 2006 American Institute of Physics.
|
|
| 27. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
On the origin of spin loss in GaMnN/InGaN Light-Emitting Diodes
- 2004
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84, s. 2599-
-
Tidskriftsartikel (refereegranskat)abstract
- Spin polarization of GaMnN/InGaN light-emitting diodes grown by molecular beam epitaxy is analyzed. In spite of the ferromagnetic behavior of the GaMnN spin injector, the diodes are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN spin detector, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection.
|
|
| 28. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Role of nitrogen in photoluminescence up-conversion in GaInNP/GaAs heterostructures
- 2007
-
Ingår i: AIP Conference Proceedings / Volume 893. - : American Institute of Physics (AIP). ; , s. 381-382
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Alloying of disordered GaInP with nitrogen is shown to lead to very efficient PLU in GaInNP/GaAs heterostructures grown by gas source molecular beam epitaxy (GS‐MBE). This is attributed to the N‐induced changes in the band alignment at the GaInNP/GaAs heterointerface from the type I for the N‐free structure to the type II in the samples with N compositions exceeding 0.5%. Based on the performed excitation power dependent measurements, a possible mechanism for the energy upconversion is suggested as being due to the two‐step two‐photon absorption. The photon recycling effect is shown to be important for the structures with N=1%, from time‐resolved PL measurements. © 2007 American Institute of Physics
|
|
| 29. |
|
|
| 30. |
- Buyanova, Irina, et al.
(författare)
-
Spin dynamics in ZnO-based materials
- 2010
-
Ingår i: Journal of Superconductivity and Novel Magnetism. - New York, USA : Springer-Verlag New York. - 1557-1939 .- 1557-1947. ; 23:1, s. 161-165
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we address the issue of spin relaxation and its relevance to spin detection in ZnO-based materials, by spin-polarized, time-resolved magneto-optical spectroscopy. We have found that spin relaxation is very fast, i.e. about 100 ps for donor bound excitons in wurtzite ZnO, despite of a weak spin–orbit interaction. We also reveal that alloying of ZnO with Cd enhances spin relaxation, prohibiting ZnCdO/ZnO structures for efficient optical spin detection. On the other hand, a variation in strain field induced by lattice mismatch with substrates does not seem to lead to a noticeable change in spin relaxation. The observed fast spin relaxation, together with the limitation imposed by the band structure, are thus identified as the two most important factors that limit the efficiency of optical spin detection in the studied ZnO-based materials.
|
|
| 31. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Thermal stability and doping efficiency of intrinsic modulation doping in InP-based structures
- 1999
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:12, s. 1733-
-
Tidskriftsartikel (refereegranskat)abstract
- Doping efficiency and thermal stability of intrinsic modulation doping in InP/InGaAs heterostructures, where intrinsic defects (PInantisites) are used as an electron source, are investigated. A high efficiency of the intrinsic doping is demonstrated from a comparison between the intrinsically doped and conventional extrinsically doped structures. The thermal stability of the intrinsically doped heterostructures is shown to be largely affected by the thermal stability of the InP surface.
|
|
| 32. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Transient Spectroscopy of Optical Spin Injection in ZnMnSe/ZnCdSe Quantum Structures
- 2005
-
Ingår i: Journal of Superconductivity. - Journal of Superconductivity and Novel Magnetism, vol. 18 : Springer. - 0896-1107 .- 1572-9605.
-
Konferensbidrag (refereegranskat)abstract
- We show, by time-resolved magneto-photoluminescence (PL) spectroscopy in combination with selective laser excitation, that optical polarization of the ZnCdSe spin detector induced by spin injection from the ZnMnSe spin injector persists over a much longer time scale than the lifetime of the ZnMnSe excitons. This finding provides compelling experimental evidence that the dominant mechanism for the observed spin injection in the ZnMnSe/ZnCdSe structures should not be due to injection of the excitonic spins of the diluted magnetic semiconductor (DMS). It is rather due to e.g. a delayed spin injection arising from tunneling of individual carriers or/and trapped spins in ZnMnSe.
|
|
| 33. |
- Campa, Daniele, et al.
(författare)
-
Leukocyte telomere length in relation to pancreatic cancer risk: a prospective study.
- 2014
-
Ingår i: Cancer Epidemiology Biomarkers & Prevention. - 1538-7755 .- 1055-9965. ; 23:11, s. 2447-2454
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Several studies have examined leukocyte telomere length (LTL) as a possible predictor for cancer at various organ sites. The hypothesis originally motivating many of these studies was that shorter telomeres would be associated with an increase in cancer risk, the results of epidemiologic studies have been inconsistent, however, and suggested positive, negative, or null associations. Two studies have addressed the association of LTL in relation to pancreatic cancer risk and the results are contrasting. Methods: we measured LTL in a prospective study of 331 pancreatic cancer cases and 331 controls in the context of the European Prospective Investigation into Cancer and Nutrition (EPIC). Results: We observed that the mean LTL was higher in cases (0.59±0.20) than in controls (0.57±0.17), although this difference was not statistically significant (p=0.07), and a basic logistic regression model showed no association of LTL with pancreas cancer risk. When adjusting for levels of HbA1c and C-Peptide, however, there was a weakly positive association between longer LTL and pancreatic cancer risk , OR=1.13 (1.01-1.27). Additional analyses by cubic spline regression suggested a possible non-linear relationship between RTL and pancreatic cancer risk (P=0.022), with a statistically non-significant increase in risk at very low LTL, as well as a significant increase at high LTL. Conclusion: Taken together, the results from our study do not support LTL as a uniform and strong predictor of pancreatic cancer. Impact: The results of this manuscript can provide insights into telomere dynamics and highlight the complex relationship between LTL and pancreatic cancer risk.
|
|
| 34. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Dominant factors limiting efficiency of optical spin detection in ZnO-based materials
- 2008
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 092103-
-
Tidskriftsartikel (refereegranskat)abstract
- Two dominant factors limiting efficiency of optical spin detection in ZnO-based materials system are identified from time-resolved optical orientation and magneto-optical studies. The first is related to the fundamental band structure of the materials characterized by a weak spin-orbit interaction. It leads to cancellation of circular polarization from the optical transitions between the conduction band and the A and B valence band states, which would otherwise carry the desired information on spin polarization of carriers. The second limiting factor is shown to be efficient carrier/exciton spin relaxation, i.e., about 45-80 ps.
|
|
| 35. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Efficient spin depolarization in ZnCdSe spin detector : an important factor limiting optical spin injection efficiency in ZnMnSe/CdZnSe spin light-emitting structures
- 2004
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85, s. 5260-
-
Tidskriftsartikel (refereegranskat)abstract
- Spin depolarization of a ZnCdSe quantum-well spin detector (SD) in ZnMnSe/ZnCdSe light-emitting quantum structures is investigated by cw and time-resolved optical orientation spectroscopy. It is shown that spin depolarization is governed by three distinct spin relaxation processes with the corresponding polarization decay times of 850, 30, and <10 ps. The dominant and the fastest process is attributed to spin relaxation accompanying energy relaxation of hot excitons (and hot carriers) within the SD, providing evidence that it can be an important source of spin loss, leading to the observed limited efficiency of optical spin injection in the structures.
|
|
| 36. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Efficient spin relaxation in InGaN/GaN and InGaN/GaMnN quantum wells : An obstacle to spin detection
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:19, s. 192107-
-
Tidskriftsartikel (refereegranskat)abstract
- Transient magneto-optical spectroscopy of InGaNGaN and InGaNGaMnN quantum wells reveals a spin relaxation process with a characteristic time of 50 ps. We show that the observed spin relaxation is mediated by spin flips of individual carriers rather than by direct exciton spin flips, and is proposed to occur near the bottom of the exciton band (K=0). Nearly complete thermalization between spin sublevels of the excitons, observed immediately after the pulsed photoexcitation, is attributed to even faster spin relaxation of photogenerated hot carriers/excitons accompanying momentum and energy relaxation at high K vectors. © 2005 American Institute of Physics.
|
|
| 37. |
- Chen, Weimin, et al.
(författare)
-
Exciton spin relaxation in diluted magnetic semiconductor Zn1-xMnxSe/CdSe superlattices : Effect of spin splitting and role of longitudinal optical phonons
- 2003
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:12
-
Tidskriftsartikel (refereegranskat)abstract
- Exciton spin relaxation in diluted magnetic semiconductor (DMS) structures based on ZnMnSe is closely examined as a function of exciton spin splitting in an external magnetic field. A drastic increase in spin relaxation is observed when exciton spin splitting exceeds the longitudinal optical (LO) phonon energy. Direct experimental evidence has been provided from (1) spin injection from the DMS to an adjacent nonmagnetic quantum well that can be modulated by the LO-assisted spin relaxation and (2) hot exciton photoluminescence within the DMS where a spin flip is accompanied by the emission of one LO phonon.
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
|
|
| 41. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Prospects of potential semiconductor spin detectors
- 2007
-
Ingår i: Advances in Nanomaterials and Processing, Pts 1 and 2. - : Trans Tech Publications Inc.. ; , s. 839-842
-
Konferensbidrag (refereegranskat)abstract
- We review our recent experimental findings by optical orientation spectroscopy that show efficient spin relaxation within semiconductor spin detectors to be an important factor limiting efficiency of spin injection in spin light-emitting structures based on ZnCdSe/ZnMnSe and InGaN/GaMnN. We provide evidence for the physical mechanism responsible for the observed efficient spin relaxation that accompanies momentum and energy relaxation of excitons/carriers. These findings call for increasing efforts in suppressing spin relaxation in spin detectors.
|
|
| 42. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Spin depolarization in semiconductor spin detectors
- 2006
-
Ingår i: Proc. of SPIE Vol. 6118. - : SPIE - International Society for Optical Engineering. ; , s. 611804-1-611804-12
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A brief review is given of our recent experimental results from in-depth investigations of spin depolarization and underlying physical mechanisms within semiconductor spin detectors based on II-VIs (e.g. Zn(Cd)Se quantum wells) and III-Vs (e.g. InGaN quantum wells), which are relevant to applications for spin-LEDs based on ZnMnSe/Zn(Cd)Se and GaMnN/InGaN structures. By employing cw and time-resolved magneto-optical and optical spin orientation spectroscopy in combination with tunable laser excitation, we show that spin depolarization within these spin detectors is very efficient and is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.
|
|
| 43. |
|
|
| 44. |
|
|
| 45. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Spin relaxation in InGaN/Ga(Mn)N quantum wells
- 2005
-
Ingår i: Bulletin of the American physical society. - 0003-0503. ; 50, s. 609-609
-
Tidskriftsartikel (refereegranskat)abstract
- Proc. 2005 APS March Meeting, March 21-25, 2005; Los Angeles, CA, USA
|
|
| 46. |
|
|
| 47. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Transport properties of intrinsically and extrinsically modulation doped InP/InGaAs heterostructures
- 1999
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T79, s. 103-105
-
Tidskriftsartikel (refereegranskat)abstract
- Transport properties in a new type of modulation doped InP/InGaAs systems, where the n-type doping is provided by intrinsic PIn-antisite defects rather than foreign impurities, are studied by Shubnikov-de-Haas (SdH) oscillations and low-field Hall effect measurements. A close comparison of transport properties is made between these intrinsically modulation doped structures with extrinsically doped structures, with the emphasis on two of the most important physical processes i.e. doping efficiency and scattering mechanism. It is found that the efficiency of the intrinsic modulation doping is at least as high as the extrinsic modulation doping. The mobilities of the two dimensional electron gas (2DEG) derived from Hall and SdH measurements are shown to be higher in the intrinsically doped structures as compared to the extrinsically doped structures. This is attributed to a reduced scattering of the 2DEG by the remote parent dopants, due to e.g. an increased screening of the scattering potential by the excess free electrons present in the intrinsic doping region due to auto-ionization of the PIn antisite.
|
|
| 48. |
|
|
| 49. |
|
|
| 50. |
- Dagnelund, Daniel, 1980-, et al.
(författare)
-
Effect of growth conditions on grown-in defect formation and luminescence efficiency in GaInNP epilayers grown by molecular-beam epitaxy.
- 2008
-
Ingår i: Physica status solidi (c)Special Issue: E-MRS 2007 Spring Meeting – Symposium F and Conference on Photonic Materials. - Weinheim : Wiley-VCH Verlagsgesellschaft. ; , s. 460-463
-
Konferensbidrag (refereegranskat)abstract
- A detailed study of the impact of different growth conditions (i.e. ion bombardment, nitrogen flow and In content) on the defect formation in Ga(In)NP epilayers grown on GaP substrates by solid-source molecular beam epitaxy is performed. Reduced nitrogen ion bombardment during the growth is shown to significantly reduce formation of defects acting as competing recombination centers, such as a Ga interstitial defect and other unidentified defects revealed by optically detected magnetic resonance. Further, high nitrogen flow is found to be even more effective than the ion bombardment in introducing the defects. The incorporation of In by 5.1% is, on the other hand, found not to affect the introduction of defects. The results provide a useful insight into the formation mechanism of the defects that will hopefully shed light on a control of the defect introduction in the alloys by optimizing growth conditions.
|
|
