| 1. |
- Wang, Haidong, et al.
(författare)
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Global, regional, and national levels of neonatal, infant, and under-5 mortality during 1990-2013 : a systematic analysis for the Global Burden of Disease Study 2013
- 2014
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 384:9947, s. 957-979
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Remarkable financial and political efforts have been focused on the reduction of child mortality during the past few decades. Timely measurements of levels and trends in under-5 mortality are important to assess progress towards the Millennium Development Goal 4 (MDG 4) target of reduction of child mortality by two thirds from 1990 to 2015, and to identify models of success.METHODS: We generated updated estimates of child mortality in early neonatal (age 0-6 days), late neonatal (7-28 days), postneonatal (29-364 days), childhood (1-4 years), and under-5 (0-4 years) age groups for 188 countries from 1970 to 2013, with more than 29 000 survey, census, vital registration, and sample registration datapoints. We used Gaussian process regression with adjustments for bias and non-sampling error to synthesise the data for under-5 mortality for each country, and a separate model to estimate mortality for more detailed age groups. We used explanatory mixed effects regression models to assess the association between under-5 mortality and income per person, maternal education, HIV child death rates, secular shifts, and other factors. To quantify the contribution of these different factors and birth numbers to the change in numbers of deaths in under-5 age groups from 1990 to 2013, we used Shapley decomposition. We used estimated rates of change between 2000 and 2013 to construct under-5 mortality rate scenarios out to 2030.FINDINGS: We estimated that 6·3 million (95% UI 6·0-6·6) children under-5 died in 2013, a 64% reduction from 17·6 million (17·1-18·1) in 1970. In 2013, child mortality rates ranged from 152·5 per 1000 livebirths (130·6-177·4) in Guinea-Bissau to 2·3 (1·8-2·9) per 1000 in Singapore. The annualised rates of change from 1990 to 2013 ranged from -6·8% to 0·1%. 99 of 188 countries, including 43 of 48 countries in sub-Saharan Africa, had faster decreases in child mortality during 2000-13 than during 1990-2000. In 2013, neonatal deaths accounted for 41·6% of under-5 deaths compared with 37·4% in 1990. Compared with 1990, in 2013, rising numbers of births, especially in sub-Saharan Africa, led to 1·4 million more child deaths, and rising income per person and maternal education led to 0·9 million and 2·2 million fewer deaths, respectively. Changes in secular trends led to 4·2 million fewer deaths. Unexplained factors accounted for only -1% of the change in child deaths. In 30 developing countries, decreases since 2000 have been faster than predicted attributable to income, education, and secular shift alone.INTERPRETATION: Only 27 developing countries are expected to achieve MDG 4. Decreases since 2000 in under-5 mortality rates are accelerating in many developing countries, especially in sub-Saharan Africa. The Millennium Declaration and increased development assistance for health might have been a factor in faster decreases in some developing countries. Without further accelerated progress, many countries in west and central Africa will still have high levels of under-5 mortality in 2030.
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| 2. |
- Kumar, Mukesh, et al.
(författare)
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Bulk properties of InN films determined by experiments and theory
- 2014
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 403, s. 124-127
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Tidskriftsartikel (refereegranskat)abstract
- Built properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first principles beyond density functional theory. The quasi particle aspect is described in the framework of a quasi particle method (the GW approximation). The calculated band gap energy is similar to 0.8 eV whereas significance in the optical absorption occurs at similar to 1.2 eV, which are consistent with both luminescence and absorption results. The Bethe-Salpeter equation is utilized to model the two particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN.
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| 3. |
- Kumar, Mukesh, et al.
(författare)
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Cation vacancies in the alloy compounds of Cu2ZnSn(S1-xSex)(4) and CuIn(S1-xSex)(2)
- 2013
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 535, s. 318-321
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Tidskriftsartikel (refereegranskat)abstract
- The present work analyzes theoretically the formation energy of the cation vacancies V-Cu, V-In, V-Zn, and V-Sn in Cu2ZnSn(S1-xSex)(4) and CuIn(S1-xSex)(2) alloy compounds. An atomistic first-principles study is carried out by employing a generalized gradient approximation and a hybrid functional approach within the density functional theory, using the supercell approach to model the alloy compositions x = 0.00, 0.25, 0.50, 0.75, and 1.00. We find that the Cu vacancy is the most dominant cation vacancy with the lowest formation energy Delta H-f. The formation energy of V-Cu is very similar in both types of alloy compounds, while the formation energy of V-In in CuIn(S1-xSex)(2) is roughly the average value of the formation energies of V-Zn and V-Sn in Cu2ZnSn(S1-xSex)(4). Moreover, we find that the vacancy formation energies are larger in the S-rich compounds compared with the corresponding vacancies in the Se-rich compounds. The results suggest that the concentration of especially V-Cu can, to some extent, be controlled by anion alloying.
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| 4. |
- Kumar, Mukesh, et al.
(författare)
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Cu(Sb,Bi)(S,Se)2 as indium-free absorber material with high optical efficiency
- 2014
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Ingår i: Energy Procedia. - : Elsevier. ; , s. 176-183
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Konferensbidrag (refereegranskat)abstract
- Ternary Cu(Sb,Bi)(S,Se)2 compounds such as CuSbS2, CuSbSe2, CuBiS2, and CuBiSe2, are potential photovoltaic materials that contain earth abundant and low-cost elements. Employing an atomistic first-principles modeling within the density function theory we calculate the electronic and optical properties of Cu(Sb,Bi)(S,Se)2 compounds. We find that these four materials have indirect fundamental band gaps in the range of 1.1-1.7 eV. The indirect gap nature is different to the previous experimental measurements (direct gap). Calculations reveal that these materials have strong optical absorption compared to chalcopyrite CuIn(S,Se)2 and kesterite Cu2ZnSn(S,Se)4. The strong absorption of these compounds is explained by the localized p-states of cation Sb/Bi in the lower region of conduction band. Thereby, ternary Cu(Sb,Bi)(S,Se) 2 compounds have the potential to be used as absorber material in thin-film PV technologies.
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| 5. |
- Kumar, Mukesh, et al.
(författare)
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Cu3BiS3 as a potential photovoltaic absorber with high optical efficiency
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:6, s. 062109-
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Tidskriftsartikel (refereegranskat)abstract
- Cu3BiS3 is a potential photovoltaic material. Employing a first-principles approach, we calculate the structural, electronic, and optical properties of Cu3BiS3, and we demonstrate that Cu3BiS3 is an indirect band gap semiconductor in contrast to similar chalcogenide semiconductors. The fundamental band gap energy is estimated to be E-g approximate to 1.5-1.7 eV. The analysis reveals that Cu3BiS3 has a much stronger absorption coefficient (>10(5) cm(-1)) compared to other Cu-S based materials like CuInS2 and Cu2ZnSnS4. This is explained by the presence of localized Bi 6p states in the band gap region, generating a flat lowest conduction band.
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| 6. |
- Kumar, Mukesh, et al.
(författare)
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CuSbS2 and CuBiS2 as potential absorber materials for thin-film solar cells
- 2013
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Ingår i: Journal of Renewable and Sustainable Energy. - : AIP Publishing. - 1941-7012. ; 5:3, s. 031616-
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Tidskriftsartikel (refereegranskat)abstract
- The current thin-film photovoltaic (PV) technologies are dominated by CdTe and Cu(In,Ga)Se-2 compounds. However, due to the limited availably and toxicity of the elements in these technologies, the current research efforts are directed to search alternative earth abundant materials. Therefore, in this work, we analyze the CuSbS2 and CuBiS2 compounds as alternative absorber materials for future thin-film solar cells. Employing a first-principles approach within the density functional theory, we calculate the structural, electronic, and optical properties of CuSbS2 and CuBiS2 compounds. We show that these compounds have indirect fundamental band gap E-g = 1.5-1.7 eV. The indirect gap nature is different from the previous experimental measurements. However, due to the flat bands, the direct gap E-dg = 1.6-1.8 eV is suitable for solar energy technologies. Furthermore, calculations reveal that these compounds have strong absorption coefficients, which are about twice as large as in other Cu-S based PV materials like CuInS2 and Cu2ZnSnS4. Therefore, CuSbS2 and CuBiS2 have the potential to be used as absorber materials in thin-film PV technologies.
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| 7. |
- Kumar, Mukesh, et al.
(författare)
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Structural, electronic and optical properties of silver delafossite oxides : A first-principles study with hybrid functional
- 2013
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 422, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Ternary delafossite compounds are potential materials for optoelectronic devices. Employing a first-principles method, we calculate the structural, electronic, and optical properties of the silver based compounds AgMO2 (M=Al, Ga or In), which crystallize in delafossite structure. Our calculations show that these AgMO2 oxides have indirect band gaps and the gap energies are in the region of 1.6-3.0 eV whereas, the lowest direct band gap energies are estimated in the range of 2.6-4.3 eV. Furthermore, we find that AgMO2 compounds exhibit a strong anisotropy for the dielectric function and absorption spectra. The absorption onset for these compounds occurs well above the band gap energies. Overall, we show that the hybrid functional improves the lattice parameters and band gap energies and the calculated values are in good agreement with the experimental values.
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| 8. |
- Kumar, Mukesh, et al.
(författare)
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Study of band-structure, optical properties and native defects in A IBIIIO2 (AI = Cu or Ag, B III = Al, Ga or In) delafossites
- 2013
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 28:6, s. 065003-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, employing a first-principles approach, the structural, electronic, optical, as well as the defect physics of AIB IIIO2 (AI = Cu or Ag, BIII = Al, Ga or In) compounds are discussed. We show that all these delafossite compounds have indirect band gaps with gap energy in the range = 1.6-3.6 eV. We also estimate the lowest direct band gap energies to be in the range = 2.6-4.0 eV. Optical characteristics reveal that AIBIIIO2 compounds exhibit a significant anisotropy for both the real and imaginary parts of the dielectric function. Furthermore, we find that absorption onset for these compounds is energetically well above (>1.5 eV) the fundamental band gaps. Moreover, we demonstrate that the copper delafossites have larger absorption coefficients compared to the corresponding BIII cation silver delafossites in the visible range. Defect calculations reveal that Cu or Ag vacancy has the lowest formation energy followed by the O vacancy while the BIII cation vacancy has the highest formation energy.
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| 9. |
- Kumar, Mukesh, et al.
(författare)
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Ternary Cu3BiY3 (Y = S, Se, and Te) for thin-film solar cells
- 2013
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Ingår i: Mater Res Soc Symp Proc. - : Springer Science and Business Media LLC. - 9781605115153 ; , s. 235-240
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Konferensbidrag (refereegranskat)abstract
- Very recently, Cu3BiS3 has been suggested as an alternative material for photovoltaic (PV) thin-film technologies. In this work, we analyze the electronic and optical properties of Cu3BiY 3 with the anion elements Y = S, Se, and Te, employing a first-principles approach within the density function theory. We find that the three Cu2BiY3 compounds have indirect band gaps and the gap energies are in the region of 1.2-1.7 eV. The energy dispersions of the lowest conduction bands are small, and therefore the direct gap energies are only ∼0.1 eV larger than the fundamental gap energies. The flat conduction bands are explained by the presence of localized Bi p-states in the band gap region. Flat energy dispersion implies a large optical absorption, and the calculations reveal that the absorption coefficient of Cu3BiY 3 is larger than 105 cm-1 for photon energies of ∼2.5 eV. The absorption is stronger than other Cu-S based materials like CuInS2 and Cu2ZnSnS4. Thereby, Cu 3BiY3 has the potential to be a suitable material in thin-film PV technologies.
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| 10. |
- Zhao, Hanyue, et al.
(författare)
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Density functional theory study of ordered defect Cu-(In,Ga)-Se compounds
- 2012
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 9:7, s. 1600-1603
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Tidskriftsartikel (refereegranskat)abstract
- CuIn1-xGaxSe2 is used as absorber material in thin-film photovoltaics. Presence of defect arrays of 2V(Cu)(-) + X-Cu(2+) complexes (X = In or Ga) in the material results in the formation of ordered defect phases, like for instance Cu(In1-xGax)(3)Se-5 and Cu(In1-xGax)(5)Se-8. An understanding of these defects phases is of considerably importance since they can strongly affect the performance of the solar cell. Density functional theory calculation with a hybrid functional is carried out to study the electronic structures and optical properties of these ordered defect phases. Fundamental properties, such as the band bowing, the band alignment and the absorption coefficients, are presented, and their dependence on material composition is discussed.
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