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| 2. |
- Ashraf, H., et al.
(författare)
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Study of electric field enhanced emission rates of an electron trap in n-type GaN grown by hydride vapor phase epitaxy
- 2010
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 108:10
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Tidskriftsartikel (refereegranskat)abstract
- Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from E-c -0.48 +/- 0.02 eV to E-c-0.35 +/- 0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55 +/- 0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data.
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| 3. |
- Ashraf, M., et al.
(författare)
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MHD flow and heat transfer of micropolar fluid between two porous disks
- 2012
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Ingår i: Applied mathematics and mechanics. - : Springer Science and Business Media LLC. - 0253-4827 .- 1573-2754. ; 33:1, s. 51-64
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study is carried out for the axisymmetric steady laminar incompressible flow of an electrically conducting micropolar fluid between two infinite parallel porous disks with the constant uniform injection through the surface of the disks. The fluid is subjected to an external transverse magnetic field. The governing nonlinear equations of motion are transformed into a dimensionless form through von Karman's similarity transformation. An algorithm based on a finite difference scheme is used to solve the reduced coupled ordinary differential equations under associated boundary conditions. The effects of the Reynolds number, the magnetic parameter, the micropolar parameter, and the Prandtl number on the flow velocity and temperature distributions are discussed. The results agree well with those of the previously published work for special cases. The investigation predicts that the heat transfer rate at the surfaces of the disks increases with the increases in the Reynolds number, the magnetic parameter, and the Prandtl number. The shear stresses decrease with the increase in the injection while increase with the increase in the applied magnetic field. The shear stress factor is lower for micropolar fluids than for Newtonian fluids, which may be beneficial in the flow and thermal control in the polymeric processing.
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| 5. |
- Langner, J., et al.
(författare)
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A multi-model study of impacts of climate change on surface ozone in Europe
- 2012
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:21, s. 10423-10440
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Tidskriftsartikel (refereegranskat)abstract
- The impact of climate change on surface ozone over Europe was studied using four offline regional chemistry transport models (CTMs) and one online regional integrated climate-chemistry model (CCM), driven by the same global projection of future climate under the SRES A1B scenario. Anthropogenic emissions of ozone precursors from RCP4.5 for year 2000 were used for simulations of both present and future periods in order to isolate the impact of climate change and to assess the robustness of the results across the different models. The sensitivity of the simulated surface ozone to changes in climate between the periods 20002009 and 2040-2049 differs by a factor of two between the models, but the general pattern of change with an increase in southern Europe is similar across different models. Emissions of isoprene differ substantially between different CTMs ranging from 1.6 to 8.0 Tg yr(-1) for the current climate, partly due to differences in horizontal resolution of meteorological input data. Also the simulated change in total isoprene emissions varies substantially across models explaining part of the different climate response on surface ozone. Ensemble mean changes in summer mean ozone and mean of daily maximum ozone are close to 1 ppb(v) in parts of the land area in southern Europe. Corresponding changes of 95-percentiles of hourly ozone are close to 2 ppb(v) in the same region. In northern Europe ensemble mean for mean and daily maximum show negative changes while there are no negative changes for the higher percentiles indicating that climate impacts on O-3 could be especially important in connection with extreme summer events.
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| 7. |
- Muniza Faraz, Sadia, et al.
(författare)
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Interface state density of free-standing GaN Schottky diodes
- 2010
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Ingår i: Semiconductor Science and Technology. - : Iop Publishing Ltd. - 0268-1242 .- 1361-6641. ; 25:9, s. 095008-
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Tidskriftsartikel (refereegranskat)abstract
- Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance-voltage (C-V) measurement, the net doping concentration of n-GaN is 4 x 10(17) cm(-3), resulting in a lower reverse breakdown of around -12 V. The interface state density (N-SS) as a function of E-C-E-SS is found to be in the range 4.23 x 10(12)-3.87 x 10(11) eV(-1) cm(-2) (below the conduction band) from Ec-0.90 to E-C-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.
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| 8. |
- Myrelid, Pär, et al.
(författare)
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Complications in surgery for Crohns disease after preoperative antitumour necrosis factor therapy
- 2014
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Ingår i: British Journal of Surgery. - : Wiley. - 0007-1323 .- 1365-2168. ; 101:5, s. 539-545
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Tidskriftsartikel (refereegranskat)abstract
- Background: The use of biological therapy (biologicals) is established in the treatment of Crohns disease. This study aimed to determine whether preoperative treatment with biologicals is associated with an increased rate of complications following surgery for Crohns disease with intestinal anastomosis. Methods: All patients receiving biologicals and undergoing abdominal surgery with anastomosis or strictureplasty were identified at six tertiary referral centres. Demographic data, and preoperative, operative and postoperative details were registered. Patients who were treated with biologicals within 2 months before surgery were compared with a control group who were not. Postoperative complications were classified according to anastomotic, infectious or other complications, and graded according to the Clavien-Dindo classification. Results: Some 111 patients treated with biologicals within 2 months before surgery were compared with 187 patients in the control group. The groups were well matched. There were no differences between the treatment and control groups in the rate of complications of any type (34.2 versus 28.9 per cent respectively; P = 0.402), anastomotic complications (7.2 versus 8.0 per cent; P = 0.976) and non-anastomotic infectious complications (16.2 versus 13.9 per cent; P = 0.586). In univariable regression analysis, biologicals were not associated with an increased risk of any complication (odds ratio (OR) 1.33, 95 per cent confidence interval 0.81 to 2.20), anastomotic complication (OR 0.89, 0.37 to 2.17) or infectious complication (OR 1.09, 0.62 to 1.91). Conclusion: Treatment with biologicals within 2 months of surgery for Crohns disease with intestinal anastomosis was not associated with an increased risk of complications.
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