| 1. |
|
|
| 2. |
- Jin, Ying-Hui, et al.
(författare)
-
Chemoprophylaxis, diagnosis, treatments, and discharge management of COVID-19 : An evidence-based clinical practice guideline (updated version)
- 2020
-
Ingår i: Military Medical Research. - : Springer Science and Business Media LLC. - 2054-9369. ; 7:1
-
Tidskriftsartikel (refereegranskat)abstract
- The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of a rapidly spreading illness, coronavirus disease 2019 (COVID-19), affecting more than seventeen million people around the world. Diagnosis and treatment guidelines for clinicians caring for patients are needed. In the early stage, we have issued "A rapid advice guideline for the diagnosis and treatment of 2019 novel coronavirus (2019-nCoV) infected pneumonia (standard version)"; now there are many direct evidences emerged and may change some of previous recommendations and it is ripe for develop an evidence-based guideline. We formed a working group of clinical experts and methodologists. The steering group members proposed 29 questions that are relevant to the management of COVID-19 covering the following areas: chemoprophylaxis, diagnosis, treatments, and discharge management. We searched the literature for direct evidence on the management of COVID-19, and assessed its certainty generated recommendations using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. Recommendations were either strong or weak, or in the form of ungraded consensus-based statement. Finally, we issued 34 statements. Among them, 6 were strong recommendations for, 14 were weak recommendations for, 3 were weak recommendations against and 11 were ungraded consensus-based statement. They covered topics of chemoprophylaxis (including agents and Traditional Chinese Medicine (TCM) agents), diagnosis (including clinical manifestations, reverse transcription-polymerase chain reaction (RT-PCR), respiratory tract specimens, IgM and IgG antibody tests, chest computed tomography, chest x-ray, and CT features of asymptomatic infections), treatments (including lopinavir-ritonavir, umifenovir, favipiravir, interferon, remdesivir, combination of antiviral drugs, hydroxychloroquine/chloroquine, interleukin-6 inhibitors, interleukin-1 inhibitors, glucocorticoid, qingfei paidu decoction, lianhua qingwen granules/capsules, convalescent plasma, lung transplantation, invasive or noninvasive ventilation, and extracorporeal membrane oxygenation (ECMO)), and discharge management (including discharge criteria and management plan in patients whose RT-PCR retesting shows SARS-CoV-2 positive after discharge). We also created two figures of these recommendations for the implementation purpose. We hope these recommendations can help support healthcare workers caring for COVID-19 patients.
|
|
| 3. |
- Li, Wei, et al.
(författare)
-
Non-lab and semi-lab algorithms for screening undiagnosed diabetes : A cross-sectional study
- 2018
-
Ingår i: EBioMedicine. - : ELSEVIER SCIENCE BV. - 2352-3964. ; 35, s. 307-316
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The terrifying undiagnosed rate and high prevalence of diabetes have become a public emergency. A high efficiency and cost-effective early recognition method is urgently needed. We aimed to generate innovative, user-friendly nomograms that can be applied for diabetes screening in different ethnic groups in China using the non-lab or noninvasive semi-lab data. Methods: This multicenter, multi-ethnic, population-based, cross-sectional study was conducted in eight sites in China by enrolling subjects aged 20-70. Sociodemographic and anthropometric characteristics were collected. Blood and urine samples were obtained 2 h following a standard 75 g glucose solution. In the final analysis, 10,794 participants were included and randomized into model development (n - 8096) and model validation (n = 2698) group with a ratio of 3:1. Nomograms were developed by the stepwise binary logistic regression. The nomograms were validated internally by a bootstrap sampling method in the model development set and externally in the model validation set. The area under the receiver operating characteristic curve (AUC) was used to assess the screening performance of the nomograms. Decision curve analysis was applied to calculate the net benefit of the screening model. Results: The overall prevalence of undiagnosed diabetes was 9.8% (1059/10794) according to ADA criteria. The non-lab model revealed that gender, age, body mass index, waist circumference, hypertension, ethnicities, vegetable daily consumption and family history of diabetes were independent risk factors for diabetes. By adding 2 h post meal glycosuria qualitative to the non-lab model, the semi-lab model showed an improved Akaike information criterion (AIC: 4506 to 3580). The AUC of the semi-lab model was statistically larger than the non-lab model (0.868 vs 0.763, P < 0.001). The optimal cutoff probability in semi-lab and non-lab nomograms were 0.088 and 0.098, respectively. The sensitivity and specificity were 76.3% and 81.6%, respectively in semi-lab nomogram, and 72.1% and 673% in non-lab nomogram at the optimal cut off point. The decision curve analysis also revealed a bigger decrease of avoidable OGTT test (52 per 100 subjects) in the semi-lab model compared to the non-lab model (36 per 100 subjects) and the existed New Chinese Diabetes Risk Score (NCDRS, 35 per 100 subjects). Conclusion: The non-lab and semi-lab nomograms appear to be reliable tools for diabetes screening, especially in developing countries. However, the semi-lab model outperformed the non-lab model and NCDRS prediction systems and might be worth being adopted as decision support in diabetes screening in China.
|
|
| 4. |
- Tang, Ting-Ting, et al.
(författare)
-
Impaired thymic export and apoptosis contribute to regulatory T-cell defects in patients with chronic heart failure.
- 2011
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203 .- 1932-6203. ; 6:9, s. e24272-
-
Tidskriftsartikel (refereegranskat)abstract
- Animal studies suggest that regulatory T (T(reg)) cells play a beneficial role in ventricular remodeling and our previous data have demonstrated defects of T(reg) cells in patients with chronic heart failure (CHF). However, the mechanisms behind T(reg-)cell defects remained unknown. We here sought to elucidate the mechanism of T(reg-)cell defects in CHF patients.
|
|
| 5. |
- Aad, G, et al.
(författare)
-
- 2015
-
swepub:Mat__t
|
|
| 6. |
- Buyanova, Irina A., et al.
(författare)
-
Optical properties of GaNAs/GaAs structures
- 2001
-
Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 143-147
-
Tidskriftsartikel (refereegranskat)abstract
- We review our recent results on optical characterization of MBE-grown GaNAs/GaAs quantum structures with N content up to 4.5%, by employing photoluminescence (PL), PL excitation, and time-resolved PL spectroscopies. The dominant PL mechanism has been determined as recombination of excitons trapped by potential fluctuations of the band edge, due to composition disorder and strain nonuniformity of the alloy. The estimated value of the localization potential is around 60 meV for the low-temperature grown structures and can be reduced by increasing the growth temperature or using post-growth rapid thermal annealing (RTA). © 2001 Elsevier Science S.A.
|
|
| 7. |
- Buyanova, Irina A., et al.
(författare)
-
Strain relaxation in GaNxP1-x alloy : Effect on optical properties
- 2001
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 308-310, s. 106-109
-
Tidskriftsartikel (refereegranskat)abstract
- By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x=1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. © 2001 Elsevier Science B.V. All rights reserved.
|
|
| 8. |
- 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.
|
|
| 9. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Band alignment in the GaNAs/GaAs quantum structures
- 2001
-
Konferensbidrag (refereegranskat)abstract
- The band alignment in the GaN_xAs_1-x/GaAs quantum well (QW) structures with low N composition is studied by employing time-resolved photoluminescence (PL) spectroscopy, PL polarization measurements and optically-detected cyclotron resonance (ODCR) studies. The type I band line-up is concluded based on the following experimental results. Firstly, radiative lifetime of the near band gap PL emission in the GaNAs/GaAs MQW structures is nearly identical to that for the spatially direct PL transitions in the GaNAs epilayers. Secondly, the observed polarization of the PL emission in GaNAs QWs (preferentially along the growth direction) is more consistent with the type I band line-up in the GaNAs/GaAs QWs. Thirdly, since the ODCR peaks arising from the free electrons and free holes in GaAs disappear under resonant excitation of the GaNAs MQWs, the photo-excited holes are spatially confined within the GaNAs layers under the resonant excitation condition.
|
|
| 10. |
|
|
| 11. |
- 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.
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Effect of growth temperature on photoluminescence of GaNAs/GaAs quantum well structures
- 1999
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:24, s. 3781-
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of growth temperature on the optical properties of GaAs/GaNxAs1-x quantum wells is studied in detail using photoluminescence (PL) spectroscopies. An increase in growth temperature up to 580 °C is shown to improve the optical quality of the structures, while still allowing one to achieve high (>3%) N incorporation. This conclusion is based on: (i) an observed increase in intensity of the GaNAs-related near-band-edge emission; (ii) a reduction in band-edge potential fluctuations, deduced from the analysis of the PL line shape; and (iii) a decrease in concentration of some extended defects detected under resonant excitation of the GaNAs. The thermal quenching of the GaNAs-related PL emission, however, is almost independent of the growth temperature and is attributed to a thermal activation of an efficient nonradiative recombination channel located in the GaNAs layers.
|
|
| 15. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaNxP1-x alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t2 component of the X3c (or L1c CBM or a level arising from a complex of N and H (in some form) are also discussed.
|
|
| 16. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Evidence for type I band alignment in GaNAs/GaAs quantum structures by optical spectroscopies
- 2002
-
Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1074-1077
-
Tidskriftsartikel (refereegranskat)abstract
- Type I band line-up in GaNxAs1−x/GaAs multiple quantum wells (MQW) with xless-than-or-equals, slant3% is concluded based on the following experimental results: (i) a comparable radiative decay time of the GaNAs-related photoluminescence (PL) measured from single GaNAs epilayers and the GaNAs/GaAs MQW structures, (ii) the observed PL polarization, and (iii) the spatial confinement of photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs MQW.
|
|
| 17. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Experimental evidence for N-induced strong coupling of host conduction band states in GaNP : insight into the dominant mechanism for giant band-gap bowing
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 69, s. 201303-
-
Tidskriftsartikel (refereegranskat)abstract
- Direct evidence for N-induced strong coupling of host conduction band (CB) states in GaNxP1-x is provided by photoluminescence excitation. It is manifested as: (1) a drastic change in the ratio of oscillator strengths between the optical transitions involving the CB minimum (CBM) and the high-lying Γ CB state; (2) a strong blueshift of the Γ CB state with increasing x accompanying a redshift of the CBM, (3) pinning of the localized N states and a newly emerging t2 (L or X3) CB state. These findings shed new light on the issue of the dominant mechanism responsible for the giant band-gap bowing of dilute nitrides.
|
|
| 18. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Hydrogen-induced improvements in optical quality of GaNAs alloys
- 2003
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:21, s. 3662-3665
-
Tidskriftsartikel (refereegranskat)abstract
- Strong suppression of potential fluctuations in the band edges of GaNAs alloys due to postgrowth hydrogen treatment, which is accompanied by a reopening of the alloy band gap, is revealed from temperature-dependent photoluminescence (PL) and PL excitation measurements. The effect likely indicates preferential trapping of hydrogen near the lattice sites with the highest nitrogen content. A remarkable improvement in the radiative efficiency of the alloys at room temperature is also demonstrated and is ascribed to efficient hydrogen passivation of competing nonradiative centers.
|
|
| 19. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Mechanism for Light Emission in GaNAs/GaAs Structures Grown by Molecular Beam Epitaxy
- 1999
-
Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 216:1, s. 125-129
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed photoluminescence (PL) study reveals that the low-temperature PL emission in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well structures grown by molecular beam epitaxy is governed by recombination of localized excitons. This conclusion is based on the analysis of the PL lineshape, its dependence on the excitation power and measurement temperature, as well as PL transient data. The depth of the localization potential is estimated as about 60 meV, varying slightly among the different structures.
|
|
| 20. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy
- 1999
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:4, s. 501-
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employing PL, PL excitation, and time-resolved PL spectroscopies. It is shown that even though quantum confinement causes a strong blueshift of the GaNAs PL emission, its major characteristic properties are identical in both QW structures and epilayers. Based on the analysis of the PL line shape, its dependence on the excitation power and measurement temperature, as well as transient data, the PL emission is concluded to be caused by a recombination of excitons trapped by potential fluctuations in GaNAs.
|
|
| 21. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Mechanism for rapid thermal annealing improvements in undoped GaNxAs1-x/GaAs structures grown by molecular beam epitaxy
- 2000
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:15, s. 2325-
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1-x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1-x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies.
|
|
| 22. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
On a possible origin of the 2.87 eV optical transition in GaNP
- 2006
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18:2, s. 449-457
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature dependent photoluminescence excitation spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered for the GaNxP1-x alloys. Whereas the appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with the N content in the alloys. This questions the possible association of this feature with an N-related localized state. On the basis of the results of temperature dependent measurements, it is concluded that the state involved has a non-Γ character. Excitation of the known N-related localized states via this state is found to be non-selective, unlike that between the N-related centres. The observed properties are shown to be barely consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the '2.87 eV' state as being due to either a t 2 component of the X3c (or L1c) CBM or a level arising from a complex of N and H (in some form) are also discussed. © 2006 IOP Publishing Ltd.
|
|
| 23. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
On the Origin of Light Emission in GaNxP1-x
- 2002
-
Konferensbidrag (refereegranskat)abstract
- Temperature dependent photoluminescence (PL) and absorption measurements are employed to clarify mechanism for light emission in GaNP alloys with low (< 4.1) nitrogen content. The PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent red shift of the PL maximum position. On the other hand, band-to-band recombination in the alloy remains predominantly non-radiative presumably due to the presence of a large number of competing recombination channels.
|
|
| 24. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Optical and electronic properties of GaNAs/GaAs structures
- 2000
-
Konferensbidrag (refereegranskat)abstract
- We review our recent results from studies of electronic properties of GaNAs/GaAs structures with low nitrogen content, by photoluminescence (PL), PL excitation, time-resolved PL spectroscopies as well as optically detected magnetic resonance (ODMR) and cyclotron resonance (ODCR) studies. The issues to be addressed include key material-related properties and fundamental electronic parameters of the GaNAs alloy, relevant to device applications, such as identification of the dominant recombination processes in the alloy, compositional dependence of the electron effective mass and band alignment in the GaNAs/GaAs heterostructures.
|
|
| 25. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Optical characterization of GaNAs
- 2001
-
Ingår i: MRS Fall Meeting,2001.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 26. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Origin of bandgap bowing in GaNP alloys
- 2004
-
Ingår i: IEE Proceedings - Optoelectronics. - : Institution of Engineering and Technology (IET). - 1350-2433 .- 1359-7078.
-
Konferensbidrag (refereegranskat)abstract
- By employing photoluminescence excitation (PLE) spectroscopy, the authors provide direct evidence for N-induced strong coupling and repelling of host conduction band (CB) states in GaNxP1-x. This strong coupling is manifested as (i) a drastic change in the ratio of oscillator strengths between the optical transition near Eg/rGamma and that near the CB minimum (CBM); (ii) a strong blue shift of the a1(Γ) state with increasing N composition accompanying a red shift of the CBM; (iii) pinning of the energies of the N-related levels; and (iv) the appearance of t2(L) or t2(X3) upon N incorporation of which the energy position is insensitive to N compositions. These findings shed new light on the controversial issue of the dominant mechanism responsible for the giant bandgap bowing of dilute nitrides.
|
|
| 27. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Photoluminescence characterization of GaNAs/GaAs structures grown by molecular beam epitaxy
- 2000
-
Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 75:2-3, s. 166-169
-
Tidskriftsartikel (refereegranskat)abstract
- A number of optical spectroscopies, including photoluminescence (PL), PL excitation and cathodoluminescence, are employed for characterization of GaNAs epilayers and GaAs/GaNxAs1-x quantum well structures grown by gas source molecular beam epitaxy at low temperature. The existence of strong potential fluctuations in the band edge of the GaNAs alloy is concluded, even for the samples with high optical quality, from a detailed analysis of the characteristic properties of the GaNAs-related PL emission. Based on the observed similarity in the PL properties between the GaNAs epilayers and the QW structures, the potential fluctuations are suggested to be mainly due to composition disorder and strain nonuniformity of the alloy. ⌐ 2000 Elsevier Science S.A. All rights reserved.
|
|
| 28. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Radiative recombination mechanism in GaNxP1-x alloys
- 2002
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80, s. 1740-
-
Tidskriftsartikel (refereegranskat)abstract
- Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.
|
|
| 29. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Raman Studies of GaNP Alloy
- 2002
-
Konferensbidrag (refereegranskat)abstract
- Raman scattering (RS) spectroscopy is employed to characterize the effect of nitrogen on structural properties of GaNxP1-x alloy with nitrogen composition up to 3 %. Two-mode behavior of the alloy is clearly shown. The frequency of the GaP-like LO phonons is found to decrease with N composition as -1.13 cm-1 x. This dependence is proposed to be largely due to the biaxial strain in the GaNP epilayers, as a result of lattice mismatch to the GaP substrate. The frequency of the GaN-like phonons is found to be more sensitive to nitrogen content, increasing with the rate of +2.6 cm-1x. The addition of nitrogen is also found to cause a dramatic quenching of the two-phonon Raman scattering and an appearance of the zone edge GaP-like vibrations. These effects are suggested to reflect local distortion in the GaNP lattice induced by nitrogen, as well as possible clustering of N atoms.
|
|
| 30. |
|
|
| 31. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Resonant excitation spectroscopies of GaNAs/GaAs quantum structures
- 2000
-
Konferensbidrag (refereegranskat)abstract
- We employ resonant optical excitation and Raman spectroscopies to study optical properties of GaNAs-based quantum structures grown by gas source molecular beam epitaxy (GS MBE). Under above band gap non-resonant excitation the PL spectra of GaNAs are shown to be dominated by the commonly observed featureless localised exciton emission. In contrast, when excitation energy is tuned close to the band edge of GaNAs alloy a series of additional narrow lines can be detected in the PL spectra. The peak positions of these lines are at about 10 meV (strongest), and at 20, 32, and 36 below the excitation energy. The dominant 10 meV line can only be excited within very narrow spectral range coinciding with the free exciton emission in GaNAs. Based on performed spectral, temperature dependent, and polarization studies the strongest 10 meV and the weaker 20 meV lines are tentatively attributed to disorder activated Raman scattering which is strongly enhanced close to the mobility edge of the GaNAs. The 32 and 36 meV lines are, on the other hand, caused by Raman scattering involving GaAs-like TO and LO phonons.
|
|
| 32. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Structural properties of a GaNxP1-x alloy : Raman studies
- 2001
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:25, s. 3959-
-
Tidskriftsartikel (refereegranskat)abstract
- Raman measurements in backscattering configuration are employed to characterize the effect of nitrogen on the structural properties of a GaNxP1-x alloy with x<=3%. The following effects of N incorporation on the vibrational spectra of GaNP are observed. First, frequencies of GaP-like and GaN-like longitudinal optical phonons exhibit strong compositional dependence, due to a combined effect of alloying and biaxial strain. Second, a dramatic quenching of two-phonon Raman scattering and an emergence of zone-edge GaP-like vibrations are observed. These effects are tentatively attributed to a local distortion of the GaNP lattice and/or compositional disorder in the alloy.
|
|
| 33. |
|
|
| 34. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Time-resolved studies of photoluminescence in GaNxP1-x alloys : Evidence for indirect-direct band gap crossover
- 2002
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:1, s. 52-
-
Tidskriftsartikel (refereegranskat)abstract
- Time resolved photoluminescence spectroscopy is employed to monitor the effect of N incorporation on the band structure of GaNP alloys. Abrupt shortening in radiative lifetime of near-band gap emissions, arising from excitonic radiative recombination within N-related centers, is found to occur at very low N compositions of around 0.5%, i.e., within the same range as the appearance of the direct-band gap-like transitions in the photomodulated transmission spectra of GaNP reported previously. The effect has been attributed to an enhancement in oscillator strength of optical transitions due to band crossover from indirect to direct-band gap of the alloy.
|
|
| 35. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Type I band alignment in the GaNxAs1-x/GaAs quantum wells
- 2001
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:3, s. 333031-333034
-
Tidskriftsartikel (refereegranskat)abstract
- Three independent experimental techniques, namely, time-resolved photoluminescence (PL) spectroscopy, PL polarization, and optically detected cyclotron resonance, are employed to determine the band alignment of GaNxAS1-x/GaAs quantum structures with a low-N composition. It is concluded that band lineup is type I based on the following experimental results: (i) comparable radiative decay time of the GaNAs-related emission measured from single GaNAs epilayers and from GaNAs/GaAs quantum well (QW) structures, (ii) polarization of the GaNAs-related emission, and (iii) spatial confinement of the photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs QW's.
|
|
| 36. |
|
|
| 37. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Nature and Formation of Non-Radiative Defects in GaNAs and InGaAsN
- 2002
-
Ingår i: MRS Fall Meeting 2001,2001. - Materials Research Society Symposium - Proceedings, Vol. 692 : MRS. ; , s. 67-72
-
Konferensbidrag (refereegranskat)abstract
- The optically detected magnetic resonance (ODMR) technique has been employed to examine the nature and formation mechanism of non-radiative defects in GaNAs and InGaAsN. In both alloys, two defects were observed and were shown to be deep-level, non-radiative recombination centers. One of the defects has been identified as a complex involving an AsGa antisite. These two defects gain more importance with increasing N composition up to 3%, presumably due to an increase in their concentration. With a further higher N composition, the defects start to lose importance in carrier recombination that is attributed to an increasingly important role of other new non-radiative channels introduced with a high N composition. On the other hand, effect of In composition up to 3% seems to be only marginal. Both defects were shown to be preferably introduced in the alloys during low-temperature growth by molecular beam epitaxy (MBE), but can be rather efficiently removed by post-growth rapid thermal annealing.
|
|
| 38. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Optical and Microwave Double Resonance of III-nitrides
- 1999
-
Ingår i: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 764-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
|
|
| 39. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Optical Detection of Cyclotron Resonance (ODCR) in GaNAs/GaAs Quantum Well Structures
- 2000
-
Konferensbidrag (refereegranskat)abstract
- ODCR has been employed to study effective masses and carrier recombination in GaNAs/GaAs multi-quantum well (MQW) structures, prepared by MBE with the nitrogen composition up to 4.5 above GaAs bandgap excitation consists of the excitonic recombination within the GaNAs MQW, the band edge PL emissions from GaAs and a broad 0.8-eV PL of unknown origin. When monitoring these emissions under the above GaAs excitation, the ODCR spectrum is dominated by the electron and hole CR in GaAs, with effective mass values 0.07m0 and 0.5m_0, respectively. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs MQW. Under resonant excitation of the GaNAs MQW only a broad ODCR signal can be observed corresponding to an effective mass value 0.1m_0, attributed to the electron CR in the GaNAs MQW, where a higher electron effective mass value and a much lower mobility are expected.
|
|
| 40. |
- Chen, Weimin, et al.
(författare)
-
P-N defect in GaNP studied by optically detected magnetic resonance
- 2003
-
Ingår i: Proceedings of the 22nd International Conference on Defects in Semiconductors. - : Elsevier BV. ; , s. 399-402
-
Konferensbidrag (refereegranskat)abstract
- We provide experimental evidence for an intrinsic defect in GaNP from optically detected magnetic resonance (ODMR). This defect is identified as a P-N complex, exhibiting hyperfine structure due to interactions with a nuclear spin I=12 of one P atom and also a nuclear spin I=1 due to one N atom. The introduction of the defect is assisted by the incorporation of N within the studied N composition range of up to 3.1%, under non-equilibrium growth conditions during gas-source molecular beam epitaxy. The corresponding ODMR spectrum was found to be isotropic, suggesting an A1 symmetry of the defect state. The localization of the electron wave function at the P-N defect in GaNP is found to be even stronger than that for the isolated PGa antisite in its parent binary compound GaP. © 2003 Elsevier B.V. All rights reserved.
|
|
| 41. |
- Cui, Xiaolei, et al.
(författare)
-
Temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystal
- 2017
-
Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 111:23
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystals are investigated. The dynamic current-time measurement results at different temperatures directly demonstrate that the electrical properties of the perovskite single crystal are dependent on the work temperature. We find that the Poole-Frankel conduction mechanism fits the current-voltage curves at small bias voltage (0-1 V) under darkness, which is mainly attributed to the surface defect states. The capability of carriers de-trapping from defects varies with different work temperatures, resulting in an increased current as the temperature increases under both darkness and illumination. In addition, the different transient photocurrent responses of incident light at two wavelengths (470 nm, 550 nm) further confirm the existence of defect states on the single crystal surface. Published by AIP Publishing.
|
|
| 42. |
- Elman, Jeremy A., et al.
(författare)
-
Issues and recommendations for the residual approach to quantifying cognitive resilience and reserve
- 2022
-
Ingår i: Alzheimer's Research and Therapy. - : Springer Science and Business Media LLC. - 1758-9193. ; 14:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Cognitive reserve and resilience are terms used to explain interindividual variability in maintenance of cognitive health in response to adverse factors, such as brain pathology in the context of aging or neurodegenerative disorders. There is substantial interest in identifying tractable substrates of resilience to potentially leverage this phenomenon into intervention strategies. One way of operationalizing cognitive resilience that has gained popularity is the residual method: regressing cognition on an adverse factor and using the residual as a measure of resilience. This method is attractive because it provides a statistical approach that is an intuitive match to the reserve/resilience conceptual framework. However, due to statistical properties of the regression equation, the residual approach has qualities that complicate its interpretation as an index of resilience and make it statistically inappropriate in certain circumstances. Methods and results: We describe statistical properties of the regression equation to illustrate why the residual is highly correlated with the cognitive score from which it was derived. Using both simulations and real data, we model common applications of the approach by creating a residual score (global cognition residualized for hippocampal volume) in individuals along the AD spectrum. We demonstrate that in most real-life scenarios, the residual measure of cognitive resilience is highly correlated with cognition, and the degree of this correlation depends on the initial relationship between the adverse factor and cognition. Subsequently, any association between this resilience metric and an external variable may actually be driven by cognition, rather than by an operationalized measure of resilience. We then assess several strategies proposed as potential solutions to this problem, such as including both the residual and original cognitive measure in a model. However, we conclude these solutions may be insufficient, and we instead recommend against “pre-regression” strategies altogether in favor of using statistical moderation (e.g., interactions) to quantify resilience. Conclusions: Caution should be taken in the use and interpretation of the residual-based method of cognitive resilience. Rather than identifying resilient individuals, we encourage building more complete models of cognition to better identify the specific adverse and protective factors that influence cognitive decline.
|
|
| 43. |
- Felici, M, et al.
(författare)
-
High Energy Optical Transitions in Ga(PN) : Contribution from Perturbed Valence Band
- 2005
-
Ingår i: AIP Conference Proceedings / Volume 772. - : American Institute of Physics (AIP). - 0735402574 ; , s. 265-
-
Konferensbidrag (refereegranskat)abstract
- The GaP1–xNx conduction band is investigated experimentally (by excitation photoluminescence) andtheoretically (by pseudopotential supercells) for N concentrations up to x=3.5%and photon energies ranging from the optical absorption edge to3.2 eV. With increasing x: (i) a direct-like absorption edgedevelops smoothly and red-shifts rapidly overtaking energy-pinned cluster states; (ii)a broad absorption plateau appears between the X1c and the1c critical points of GaP; (iii) the 1c absorption edgebroadens and gradually disappears. Empirical pseudopotential calculations for GaP1-xNx randomalloy supercells account well for all the PLE results byconsidering N induced changes in the valence band overlooked sofar. ©2005 American Institute of Physics
|
|
| 44. |
- Hai, P. N., et al.
(författare)
-
Direct determination of electron effective mass in GaNAs/GaAs quantum wells
- 2000
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:12, s. 1843-1845
-
Tidskriftsartikel (refereegranskat)abstract
- Electron effective mass (m*e) in GaNxAs1-x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The m*e values of 0.12m0 and 0.19m0 are directly determined for the 70-A-thick QWs with N composition of 1.2% and 2.0%, respectively. This sizable increase in the electron effective mass is consistent with the earlier theoretical predictions based on the strong interaction of the lowest conduction band states with the upper lying band states or impurity band induced by the incorporation of N. ⌐ 2000 American Institute of Physics.
|
|
| 45. |
- Hai, P. N., et al.
(författare)
-
Properties of GaAsN/GaAs quantum wells studied by optical detection of cyclotron resonance
- 2001
-
Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 218-220
-
Tidskriftsartikel (refereegranskat)abstract
- Effective masses and carrier recombination in GaNAs/GaAs quantum wells (QWs) with nitrogen composition up to 4.5%, have been studied by optical detection of cyclotron resonance (ODCR). When monitoring the PL emissions under the conditions of above-GaAs barrier excitation, the ODCR spectrum is dominated by the electron CR in GaAs with an effective mass value 0.066m0. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs QW. Under resonant excitation of the GaNAs QWs, only a broad ODCR signal can be observed, corresponding to an effective mass value of 0.12m0 and 0.19m0 when the N composition is about 1.2 and 2%, respectively. This is attributed to the electron CR in the GaNAs QW with a lower electron mobility. This sizeable increase in the electron effective mass is in agreement with earlier theoretical predictions. ⌐ 2001 Elsevier Science B.V.
|
|
| 46. |
- He, Jiansen, et al.
(författare)
-
Direct Measurement of the Dissipation Rate Spectrum around Ion Kinetic Scales in Space Plasma Turbulence
- 2019
-
Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 880:2
-
Tidskriftsartikel (refereegranskat)abstract
- The energy of turbulence in the universe, which cascades from large fluid scales to small kinetic scales, is believed to be dissipated through conversion to thermal or nonthermal kinetic energy. However, identifying the dissipation processes and measuring the dissipation rate in turbulence remain challenging. Based on unprecedented high-quality measurements of space plasma turbulence by the Magnetospheric Multiscale mission, we propose a novel approach to measure the scale-dependent spectrum of the energy conversion rate between the fluctuating electromagnetic energy and plasma kinetic energy. The energy conversion rate spectrum is found to show a positive bulge around the ion kinetic scale, which clearly indicates the dissipation of the turbulent energy. The energy dissipation rate around the ion scale is estimated to be 0.5 x 10(6) J kg(-1) s(-1). This work provides basic information on local dissipation in magnetosheath turbulence and sets up a new paradigm for studying the dissipation of universal plasma turbulence.
|
|
| 47. |
- Hede, Thomas, et al.
(författare)
-
HULIS in Nanoaerosol Clusters; Investigations of Surface Tension and Aggregate Formation using Molecular Dynamics Simulations
- 2011
-
Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Cloud condensation nuclei act as cores for water vapor condensation, and their composition and chemical properties may enhance or depress the ability for droplet growth. In this study we use molecular dynamics simulations to show that humic-like substances of larger systems (8.6 nm in diameter) mimic experimental data well referring to reduction of surface tension. The structural properties examined show the ability for the humic-like substances to aggregate inside the nanoaerosol clusters.
|
|
| 48. |
- Hede, Thomas, 1975-, et al.
(författare)
-
Model HULIS compounds in nanoaerosol clusters : investigations of surface tension and aggregate formation using molecular dynamics simulations
- 2011
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:13, s. 6549-6557
-
Tidskriftsartikel (refereegranskat)abstract
- Cloud condensation nuclei act as cores for water vapour condensation, and their composition and chemical properties may enhance or depress the ability for droplet growth. In this study we use molecular dynamics simulations to show that model humic-like substances (HULIS) in systems containing 10 000 water molecules mimic experimental data well referring to reduction of surface tension. The model HULIS compounds investigated in this study are cis-pinonic acid (CPA), pinic acid (PAD) and pinonaldehyde (PAL). The structural properties examined show the ability for the model HULIS compounds to aggregate inside the nanoaerosol clusters.
|
|
| 49. |
- Kang, Yu, et al.
(författare)
-
On the Mechanism of Protein Adsorption onto Hydroxylated and Nonhydroxylated TiO2 Surfaces
- 2010
-
Ingår i: The Journal of Physical Chemistry C. - Washington DC, USA : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:34, s. 14496-14502
-
Tidskriftsartikel (refereegranskat)abstract
- Protein adsorption onto implant surfaces is of great importance for the regulation of implant bioactivity. Surface modification of implants is a promising way in the molecular design of biocompatible materials against nonspecific adsorption of proteins. On the basis of these fundamental facts, we focus in this work on the different behavior of protein adsorption on hydroxylated and nonhydroxylated rutile TiO2 (110) surfaces through molecular dynamics simulations. Our investigation indicates that the distribution of the water molecules at the interface induced by the surface modification plays an important role in the protein adsorption. The surface with modified hydroxyl groups was observed to have much greater affinity to the protein, as reflected by the larger protein-surface electrostatic interaction and by the larger amount of adsorbed residues. The highly ordered structure of the modified hydroxyl groups on the hydroxylated surface diminishes the possibility of hydrogen bond formation between the surface and the water molecules above it, which in turn makes it easier for the protein to move closer to the surface with hydroxyl modification.
|
|
| 50. |
- Li, Xin, et al.
(författare)
-
Cloud droplet activation mechanisms of amino acid aerosol particles : insight from molecular dynamics simulations
- 2013
-
Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 65, s. 65-
-
Tidskriftsartikel (refereegranskat)abstract
- Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN) materials in laboratory experiments. We present a molecular dynamics (MD) study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol-cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these L-amino acids are serine (SER), glycine (GLY), alanine (ALA), valine (VAL), methionine (MET) and phenylalanine (PHE) and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard-Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.
|
|
