The Effect of Impacts on the Martian Climate

Evidence for the presence of liquid water early in Mars history continues to accumulate. The most recent evidence for liquid water being pervasive early in Mars history is the discoveries of sulfate and gypsum layers by the Mars Exploration Rovers and Mars Express. However, the presence of liquid water at the surface very early in Mars history presents a conundrum. The early sun was most likely approximately 75% fainter than it is today. About 65-70 degrees of greenhouse warming is needed to bring surface temperatures to the melting point of water. To date climate models have not been able to produce a continuously warm and wet early Mars. This may be a good thing as there is morphological and mineralogical evidence that the warm and wet period had to be relatively short and episodic. The rates of erosion appear to correlate with the rate at which Mars was impacted thus an alternate possibility is transient warm and wet conditions initiated by large impacts. It is widely accepted that even relatively small impacts (approximately 10 km) have altered the past climate of Earth to such an extent as to cause mass extinctions. Mars has been impacted with a similar distribution of objects. The impact record at Mars is preserved in the abundance of observable craters on it surface. Impact induced climate change must have occurred on Mars

High-pressure lattice dynamics in wurtzite and rocksalt indium nitride investigated by means of Raman spectroscopy

We present an experimental and theoretical lattice-dynamical study of InN at high hydrostatic pressures. We perform Raman scattering measurements on five InN epilayers, with different residual strain and free electron concentrations. The experimental results are analyzed in terms of ab initio lattice-dynamical calculations on both wurtzite InN (w-InN) and rocksalt InN (rs-InN) as a function of pressure. Experimental and theoretical pressure coefficients of the optical modes in w-InN are compared, and the role of residual strain on the measured pressure coefficients is analyzed. In the case of the LO band, we analyze and discuss its pressure behavior considering the double-resonance mechanism responsible for the selective excitation of LO phonons with large wave vectors in w-InN. The pressure behavior of the L− coupled mode observed in a heavily doped n-type sample allows us to estimate the pressure dependence of the electron effective mass in w-InN. The results thus obtained are in good agreement with k⋅p theory. The wurtzite-to-rocksalt phase transition on the upstroke cycle and the rocksalt-to-wurtzite backtransition on the downstroke cycle are investigated, and the Raman spectra of both phases are interpreted in terms of DFT lattice-dynamical calculations. ©2013 American Physical SocietyWork was supported by the Spanish Ministerio de Economia y Competitividad through Projects MAT2010-16116, MAT2010-21270-C04-04 and MALTA Consolider Ingenio 2010 (CSD2007-00045).Ibánez, J.; Oliva, R.; Manjón Herrera, FJ.; Segura, A.; Yamaguchi, T.; Nanishi, Y.; Cuscó, R.... (2013). High-pressure lattice dynamics in wurtzite and rocksalt indium nitride investigated by means of Raman spectroscopy. Physical Review B. 88:115202-1-115202-13. https://doi.org/10.1103/PhysRevB.88.115202S115202-1115202-1388Wu, J. (2009). When group-III nitrides go infrared: New properties and perspectives. Journal of Applied Physics, 106(1), 011101. doi:10.1063/1.3155798Pinquier, C., Demangeot, F., Frandon, J., Pomeroy, J. W., Kuball, M., Hubel, H., … Gil, B. (2004). Raman scattering in hexagonal InN under high pressure. Physical Review B, 70(11). doi:10.1103/physrevb.70.113202Pinquier, C., Demangeot, F., Frandon, J., Chervin, J.-C., Polian, A., Couzinet, B., … Maleyre, B. (2006). Raman scattering study of wurtzite and rocksalt InN under high pressure. Physical Review B, 73(11). doi:10.1103/physrevb.73.115211Yao, L. D., Luo, S. D., Shen, X., You, S. J., Yang, L. X., Zhang, S. J., … Xie, S. S. (2010). Structural stability and Raman scattering of InN nanowires under high pressure. Journal of Materials Research, 25(12), 2330-2335. doi:10.1557/jmr.2010.0290Ibáñez, J., Manjón, F. J., Segura, A., Oliva, R., Cuscó, R., Vilaplana, R., … Artús, L. (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters, 99(1), 011908. doi:10.1063/1.3609327Uehara, S., Masamoto, T., Onodera, A., Ueno, M., Shimomura, O., & Takemura, K. (1997). Equation of state of the rocksalt phase of III–V nitrides to 72 GPa or higher. Journal of Physics and Chemistry of Solids, 58(12), 2093-2099. doi:10.1016/s0022-3697(97)00150-9Duan, M.-Y., He, L., Xu, M., Xu, M.-Y., Xu, S., & Ostrikov, K. (Ken). (2010). Structural, electronic, and optical properties of wurtzite and rocksalt InN under pressure. Physical Review B, 81(3). doi:10.1103/physrevb.81.033102Davydov, V. Y., Klochikhin, A. A., Smirnov, A. N., Strashkova, I. Y., Krylov, A. S., Lu, H., … Gwo, S. (2009). Selective excitation ofE1(LO)andA1(LO)phonons with large wave vectors in the Raman spectra of hexagonal InN. Physical Review B, 80(8). doi:10.1103/physrevb.80.081204Cuscó, R., Ibáñez, J., Alarcón-Lladó, E., Artús, L., Yamaguchi, T., & Nanishi, Y. (2009). Raman scattering study of the long-wavelength longitudinal-optical-phonon–plasmon coupled modes in high-mobility InN layers. Physical Review B, 79(15). doi:10.1103/physrevb.79.155210Ernst, S., Goñi, A. R., Syassen, K., & Cardona, M. (1995). LO-Phonon-plasmon modes in n-GaAs and n-InP under pressure. Journal of Physics and Chemistry of Solids, 56(3-4), 567-570. doi:10.1016/0022-3697(94)00242-8Ernst, S., Goñi, A. R., Syassen, K., & Cardona, M. (1996). Plasmon Raman scattering and photoluminescence of heavily dopedn-type InP near the Γ-X crossover. Physical Review B, 53(3), 1287-1293. doi:10.1103/physrevb.53.1287Lin, Y. C., Chiu, C. H., Fan, W. C., Chia, C. H., Yang, S. L., Chuu, D. S., … Chou, W. C. (2007). Raman scattering of longitudinal-optical-phonon-plasmon coupling in Cl-doped ZnSe under high pressure. Journal of Applied Physics, 102(12), 123510. doi:10.1063/1.2826936Gonze, X., Beuken, J.-M., Caracas, R., Detraux, F., Fuchs, M., Rignanese, G.-M., … Allan, D. C. (2002). First-principles computation of material properties: the ABINIT software project. Computational Materials Science, 25(3), 478-492. doi:10.1016/s0927-0256(02)00325-7Goedecker, S., Teter, M., & Hutter, J. (1996). Separable dual-space Gaussian pseudopotentials. Physical Review B, 54(3), 1703-1710. doi:10.1103/physrevb.54.1703Troullier, N., & Martins, J. L. (1991). Efficient pseudopotentials for plane-wave calculations. Physical Review B, 43(3), 1993-2006. doi:10.1103/physrevb.43.1993Wu, M. F., Zhou, S. Q., Vantomme, A., Huang, Y., Wang, H., & Yang, H. (2006). High-precision determination of lattice constants and structural characterization of InN thin films. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 24(2), 275-279. doi:10.1116/1.2167970Ueno, M., Yoshida, M., Onodera, A., Shimomura, O., & Takemura, K. (1994). Stability of the wurtzite-type structure under high pressure: GaN and InN. Physical Review B, 49(1), 14-21. doi:10.1103/physrevb.49.14Serrano, J., Bosak, A., Krisch, M., Manjón, F. J., Romero, A. H., Garro, N., … Kuball, M. (2011). InN Thin Film Lattice Dynamics by Grazing Incidence Inelastic X-Ray Scattering. Physical Review Letters, 106(20). doi:10.1103/physrevlett.106.205501Giannozzi, P., de Gironcoli, S., Pavone, P., & Baroni, S. (1991). Ab initiocalculation of phonon dispersions in semiconductors. Physical Review B, 43(9), 7231-7242. doi:10.1103/physrevb.43.7231Gonze, X., & Lee, C. (1997). Dynamical matrices, Born effective charges, dielectric permittivity tensors, and interatomic force constants from density-functional perturbation theory. Physical Review B, 55(16), 10355-10368. doi:10.1103/physrevb.55.10355Weinstein, B. A. (1977). Phonon dispersion of zinc chalcogenides under extreme pressure and the metallic transformation. Solid State Communications, 24(9), 595-598. doi:10.1016/0038-1098(77)90369-6Yakovenko, E. V., Gauthier, M., & Polian, A. (2004). High-pressure behavior of the bond-bending mode of AIN. Journal of Experimental and Theoretical Physics, 98(5), 981-985. doi:10.1134/1.1767565Ibáñez, J., Segura, A., García-Domene, B., Oliva, R., Manjón, F. J., Yamaguchi, T., … Artús, L. (2012). High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN. Physical Review B, 86(3). doi:10.1103/physrevb.86.035210Serrano, J., Romero, A. H., Manjón, F. J., Lauck, R., Cardona, M., & Rubio, A. (2004). Pressure dependence of the lattice dynamics of ZnO: Anab initioapproach. Physical Review B, 69(9). doi:10.1103/physrevb.69.094306Cuscó, R., Ibáñez, J., Domenech-Amador, N., Artús, L., Zúñiga-Pérez, J., & Muñoz-Sanjosé, V. (2010). Raman scattering of cadmium oxide epilayers grown by metal-organic vapor phase epitaxy. Journal of Applied Physics, 107(6), 063519. doi:10.1063/1.3357377Cuscó, R., Alarcón-Lladó, E., Ibáñez, J., Yamaguchi, T., Nanishi, Y., & Artús, L. (2009). Raman scattering study of background electron density in InN: a hydrodynamical approach to the LO-phonon–plasmon coupled modes. Journal of Physics: Condensed Matter, 21(41), 415801. doi:10.1088/0953-8984/21/41/415801Cuscó, R., Ibáñez, J., Alarcón-Lladó, E., Artús, L., Yamaguchi, T., & Nanishi, Y. (2009). Photoexcited carriers and surface recombination velocity in InN epilayers: A Raman scattering study. Physical Review B, 80(15). doi:10.1103/physrevb.80.155204Wang, X., Che, S.-B., Ishitani, Y., & Yoshikawa, A. (2006). Experimental determination of strain-free Raman frequencies and deformation potentials for the E2 high and A1(LO) modes in hexagonal InN. Applied Physics Letters, 89(17), 171907. doi:10.1063/1.2364884Perlin, P., Jauberthie-Carillon, C., Itie, J. P., San Miguel, A., Grzegory, I., & Polian, A. (1992). Raman scattering and x-ray-absorption spectroscopy in gallium nitride under high pressure. Physical Review B, 45(1), 83-89. doi:10.1103/physrevb.45.83Perlin, P., Suski, T., Ager, J. W., Conti, G., Polian, A., Christensen, N. E., … Haller, E. E. (1999). Transverse effective charge and its pressure dependence in GaN single crystals. Physical Review B, 60(3), 1480-1483. doi:10.1103/physrevb.60.1480Halsall, M. P., Harmer, P., Parbrook, P. J., & Henley, S. J. (2004). Raman scattering and absorption study of the high-pressure wurtzite to rocksalt phase transition of GaN. Physical Review B, 69(23). doi:10.1103/physrevb.69.235207Goñi, A. R., Siegle, H., Syassen, K., Thomsen, C., & Wagner, J.-M. (2001). Effect of pressure on optical phonon modes and transverse effective charges inGaNandAlN. Physical Review B, 64(3). doi:10.1103/physrevb.64.035205Watson, G. H., Daniels, W. B., & Wang, C. S. (1981). Measurements of Raman intensities and pressure dependence of phonon frequencies in sapphire. Journal of Applied Physics, 52(2), 956-958. doi:10.1063/1.328785Manjón, F. J., Errandonea, D., Romero, A. H., Garro, N., Serrano, J., & Kuball, M. (2008). Lattice dynamics of wurtzite and rocksalt AlN under high pressure: Effect of compression on the crystal anisotropy of wurtzite-type semiconductors. Physical Review B, 77(20). doi:10.1103/physrevb.77.205204Domènech-Amador, N., Cuscó, R., Artús, L., Stoica, T., & Calarco, R. (2012). Longer InN phonon lifetimes in nanowires. Nanotechnology, 23(8), 085702. doi:10.1088/0957-4484/23/8/085702Gorczyca, I., Plesiewicz, J., Dmowski, L., Suski, T., Christensen, N. E., Svane, A., … Speck, J. S. (2008). Electronic structure and effective masses of InN under pressure. Journal of Applied Physics, 104(1), 013704. doi:10.1063/1.2953094Cardona, M., & Güntherodt, G. (Eds.). (1984). Light Scattering in Solids IV. Topics in Applied Physics. doi:10.1007/3-540-11942-6Artús, L., Cuscó, R., Ibáñez, J., Blanco, N., & González-Díaz, G. (1999). Raman scattering by LO phonon-plasmon coupled modes inn-type InP. Physical Review B, 60(8), 5456-5463. doi:10.1103/physrevb.60.5456Ib��ez, J., Cusc�, R., & Art�s, L. (2001). Raman Scattering Determination of Free Charge Density Using a Modified Hydrodynamical Model. physica status solidi (b), 223(3), 715-722. doi:10.1002/1521-3951(200102)223:33.0.co;2-oKasic, A., Schubert, M., Saito, Y., Nanishi, Y., & Wagner, G. (2002). Effective electron mass and phonon modes inn-type hexagonal InN. Physical Review B, 65(11). doi:10.1103/physrevb.65.115206Demangeot, F., Pinquier, C., Frandon, J., Gaio, M., Briot, O., Maleyre, B., … Gil, B. (2005). Raman scattering by the longitudinal optical phonon in InN: Wave-vector nonconserving mechanisms. Physical Review B, 71(10). doi:10.1103/physrevb.71.104305Thakur, J. S., Haddad, D., Naik, V. M., Naik, R., Auner, G. W., Lu, H., & Schaff, W. J. (2005). A1(LO)phonon structure in degenerate InN semiconductor films. Physical Review B, 71(11). doi:10.1103/physrevb.71.115203Inushima, T., Higashiwaki, M., & Matsui, T. (2003). Optical properties of Si-doped InN grown on sapphire (0001). Physical Review B, 68(23). doi:10.1103/physrevb.68.235204Kasic, A., Valcheva, E., Monemar, B., Lu, H., & Schaff, W. J. (2004). InNdielectric function from the midinfrared to the ultraviolet range. Physical Review B, 70(11). doi:10.1103/physrevb.70.115217Wu, J., Walukiewicz, W., Shan, W., Yu, K. M., Ager, J. W., Haller, E. E., … Schaff, W. J. (2002). Effects of the narrow band gap on the properties of InN. Physical Review B, 66(20). doi:10.1103/physrevb.66.201403Kim, J. G., Kamei, Y., Hasuike, N., Harima, H., Kisoda, K., Sasamoto, K., & Yamamoto, A. (2010). Effective mass of InN estimated by Raman scattering. physica status solidi (c), 7(7-8), 1887-1889. doi:10.1002/pssc.200983567Christensen, N. E., & Gorczyca, I. (1994). Optical and structural properties of III-V nitrides under pressure. Physical Review B, 50(7), 4397-4415. doi:10.1103/physrevb.50.4397Ovsyannikov, S. V., Shchennikov, V. V., Karkin, A. E., Polian, A., Briot, O., Ruffenach, S., … Moret, M. (2010). Pressure cycling of InN to 20 GPa: In situ transport properties and amorphization. Applied Physics Letters, 97(3), 032105. doi:10.1063/1.3466913Davydov, V. Y., Klochikhin, A. A., Smirnov, M. B., Emtsev, V. V., Petrikov, V. D., Abroyan, I. A., … Inushima, T. (1999). Phonons in Hexagonal InN. Experiment and Theory. physica status solidi (b), 216(1), 779-783. doi:10.1002/(sici)1521-3951(199911)216:13.0.co;2-

Structure of the interstellar medium around Cas A

We present a three-year series of observations at 24 microns with the Spitzer Space Telescope of the interstellar material in a 200 x 200 arcmin square area centered on Cassiopeia A. Interstellar dust heated by the outward light pulse from the supernova explosion emits in the form of compact, moving features. Their sequential outward movements allow us to study the complicated three-dimensional structure of the interstellar medium (ISM) behind and near Cassiopeia A. The ISM consists of sheets and filaments, with many structures on a scale of a parsec or less. The spatial power spectrum of the ISM appears to be similar to that of fractals with a spectral index of 3.5. The filling factor for the small structures above the spatial wavenumber k ~ 0.5 cycles/pc is only ~ 0.4%.Comment: 29 pages including 10 figures; accepted by The Astrophysical Journa

High-pressure Raman scattering in wurtzite indium nitride

Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We perform Raman-scattering measurements at high hydrostatic pressures on c-face and a-face InN layers to investigate the high-pressure behavior of the zone-center optical phonons of wurtzite InN. Linear pressure coefficients and mode Grneisen parameters are obtained, and the experimental results are compared with theoretical values obtained from ab initio lattice-dynamical calculations. Good agreement is found between the experimental and calculated results. © 2011 American Institute of Physics.Work supported by the Spanish MICINN (Projects MAT2010-16116, MAT2008-06873-C02-02, MAT2010-21270-C04-04, and CSD2007-00045), the Catalan Government (BE-DG 2009), and the Spanish Council for Research (PIE2009-CSIC).Ibanez, J.; Manjón Herrera, FJ.; Segura, A.; Oliva, R.; Cusco, R.; Vilaplana Cerda, RI.; Yamaguchi, T.... (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters. 99:119081-119083. https://doi.org/10.1063/1.3609327S11908111908399Veal, T., McConville, C., & Schaff, W. (Eds.). (2009). Indium Nitride and Related Alloys. doi:10.1201/9781420078107Gallinat, C. S., Koblmüller, G., Brown, J. S., Bernardis, S., Speck, J. S., Chern, G. D., … Wraback, M. (2006). In-polar InN grown by plasma-assisted molecular beam epitaxy. Applied Physics Letters, 89(3), 032109. doi:10.1063/1.2234274Li, S. X., Wu, J., Haller, E. E., Walukiewicz, W., Shan, W., Lu, H., & Schaff, W. J. (2003). Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys. Applied Physics Letters, 83(24), 4963-4965. doi:10.1063/1.1633681Gorczyca, I., Plesiewicz, J., Dmowski, L., Suski, T., Christensen, N. E., Svane, A., … Speck, J. S. (2008). Electronic structure and effective masses of InN under pressure. Journal of Applied Physics, 104(1), 013704. doi:10.1063/1.2953094Domènech-Amador, N., Cuscó, R., Artús, L., Yamaguchi, T., & Nanishi, Y. (2011). Raman scattering study of anharmonic phonon decay in InN. Physical Review B, 83(24). doi:10.1103/physrevb.83.245203Serrano, J., Bosak, A., Krisch, M., Manjón, F. J., Romero, A. H., Garro, N., … Kuball, M. (2011). InN Thin Film Lattice Dynamics by Grazing Incidence Inelastic X-Ray Scattering. Physical Review Letters, 106(20). doi:10.1103/physrevlett.106.205501Pinquier, C., Demangeot, F., Frandon, J., Pomeroy, J. W., Kuball, M., Hubel, H., … Gil, B. (2004). Raman scattering in hexagonal InN under high pressure. Physical Review B, 70(11). doi:10.1103/physrevb.70.113202Pinquier, C., Demangeot, F., Frandon, J., Chervin, J.-C., Polian, A., Couzinet, B., … Maleyre, B. (2006). Raman scattering study of wurtzite and rocksalt InN under high pressure. Physical Review B, 73(11). doi:10.1103/physrevb.73.115211Yao, L. D., Luo, S. D., Shen, X., You, S. J., Yang, L. X., Zhang, S. J., … Xie, S. S. (2010). Structural stability and Raman scattering of InN nanowires under high pressure. Journal of Materials Research, 25(12), 2330-2335. doi:10.1557/jmr.2010.0290Cuscó, R., Ibáñez, J., Alarcón-Lladó, E., Artús, L., Yamaguchi, T., & Nanishi, Y. (2009). Raman scattering study of the long-wavelength longitudinal-optical-phonon–plasmon coupled modes in high-mobility InN layers. Physical Review B, 79(15). doi:10.1103/physrevb.79.155210Wagner, J.-M., & Bechstedt, F. (2003). First-principles study of phonon-mode softening under pressure: the case of GaN and AlN. physica status solidi (b), 235(2), 464-469. doi:10.1002/pssb.200301603Weinstein, B. A. (1977). Phonon dispersion of zinc chalcogenides under extreme pressure and the metallic transformation. Solid State Communications, 24(9), 595-598. doi:10.1016/0038-1098(77)90369-6Yakovenko, E. V., Gauthier, M., & Polian, A. (2004). High-pressure behavior of the bond-bending mode of AIN. Journal of Experimental and Theoretical Physics, 98(5), 981-985. doi:10.1134/1.1767565Reparaz, J. S., Muniz, L. R., Wagner, M. R., Goñi, A. R., Alonso, M. I., Hoffmann, A., & Meyer, B. K. (2010). Reduction of the transverse effective charge of optical phonons in ZnO under pressure. Applied Physics Letters, 96(23), 231906. doi:10.1063/1.3447798Perlin, P., Jauberthie-Carillon, C., Itie, J. P., San Miguel, A., Grzegory, I., & Polian, A. (1992). Raman scattering and x-ray-absorption spectroscopy in gallium nitride under high pressure. Physical Review B, 45(1), 83-89. doi:10.1103/physrevb.45.83Manjón, F. J., Errandonea, D., Romero, A. H., Garro, N., Serrano, J., & Kuball, M. (2008). Lattice dynamics of wurtzite and rocksalt AlN under high pressure: Effect of compression on the crystal anisotropy of wurtzite-type semiconductors. Physical Review B, 77(20). doi:10.1103/physrevb.77.205204Jephcoat, A. P., Hemley, R. J., Mao, H. K., Cohen, R. E., & Mehl, M. J. (1988). Raman spectroscopy and theoretical modeling of BeO at high pressure. Physical Review B, 37(9), 4727-4734. doi:10.1103/physrevb.37.4727Ibáñez, J., Segura, A., Manjón, F. J., Artús, L., Yamaguchi, T., & Nanishi, Y. (2010). Electronic structure of wurtzite and rocksalt InN investigated by optical absorption under hydrostatic pressure. Applied Physics Letters, 96(20), 201903. doi:10.1063/1.3431291Goñi, A. R., Siegle, H., Syassen, K., Thomsen, C., & Wagner, J.-M. (2001). Effect of pressure on optical phonon modes and transverse effective charges inGaNandAlN. Physical Review B, 64(3). doi:10.1103/physrevb.64.03520

High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN

We report on high-pressure optical absorption measurements on InN epilayers with a range of free-electron concentrations (5×1017–1.6×1019 cm−3) to investigate the effect of free carriers on the pressure coefficient of the optical band gap of wurtzite InN. With increasing carrier concentration, we observe a decrease of the absolute value of the optical band gap pressure coefficient of wurtzite InN. An analysis of our data based on the k·p model allows us to obtain a pressure coefficient of 32 meV/GPa for the fundamental band gap of intrinsic wurtzite InN. Optical absorption measurements on a 5.7-μm-thick InN epilayer at pressures above the wurtzite-to-rocksalt transition have allowed us to obtain an accurate determination of the indirect band gap energy of rocksalt InN as a function of pressure. Around the phase transition (∼15 GPa), a band gap value of 0.7 eV and a pressure coefficient of ∼23 meV/GPa are obtained. ©2012 American Physical SocietyThis work was supported by the Spanish Ministry of Science and Innovation through Project No. MAT2010-16116.Ibáñez, J.; Segura, A.; García-Domene, B.; Oliva, R.; Manjón Herrera, FJ.; Yamaguchi, T.; Nanishi, Y.... (2012). High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN. Physical Review B. 86:35210-1-35210-5. https://doi.org/10.1103/PhysRevB.86.035210S35210-135210-586Wu, J. (2009). When group-III nitrides go infrared: New properties and perspectives. Journal of Applied Physics, 106(1), 011101. doi:10.1063/1.3155798Ueno, M., Yoshida, M., Onodera, A., Shimomura, O., & Takemura, K. (1994). Stability of the wurtzite-type structure under high pressure: GaN and InN. Physical Review B, 49(1), 14-21. doi:10.1103/physrevb.49.14Uehara, S., Masamoto, T., Onodera, A., Ueno, M., Shimomura, O., & Takemura, K. (1997). Equation of state of the rocksalt phase of III–V nitrides to 72 GPa or higher. Journal of Physics and Chemistry of Solids, 58(12), 2093-2099. doi:10.1016/s0022-3697(97)00150-9Pinquier, C., Demangeot, F., Frandon, J., Chervin, J.-C., Polian, A., Couzinet, B., … Maleyre, B. (2006). Raman scattering study of wurtzite and rocksalt InN under high pressure. Physical Review B, 73(11). doi:10.1103/physrevb.73.115211Ibáñez, J., Manjón, F. J., Segura, A., Oliva, R., Cuscó, R., Vilaplana, R., … Artús, L. (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters, 99(1), 011908. doi:10.1063/1.3609327Li, S. X., Wu, J., Haller, E. E., Walukiewicz, W., Shan, W., Lu, H., & Schaff, W. J. (2003). Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys. Applied Physics Letters, 83(24), 4963-4965. doi:10.1063/1.1633681Franssen, G., Gorczyca, I., Suski, T., Kamińska, A., Pereiro, J., Muñoz, E., … Svane, A. (2008). Bowing of the band gap pressure coefficient in InxGa1−xN alloys. Journal of Applied Physics, 103(3), 033514. doi:10.1063/1.2837072Kamińska, A., Franssen, G., Suski, T., Gorczyca, I., Christensen, N. E., Svane, A., … Georgakilas, A. (2007). Role of conduction-band filling in the dependence of InN photoluminescence on hydrostatic pressure. Physical Review B, 76(7). doi:10.1103/physrevb.76.075203Shan, W., Walukiewicz, W., Haller, E. E., Little, B. D., Song, J. J., McCluskey, M. D., … Stall, R. A. (1998). Optical properties of InxGa1−xN alloys grown by metalorganic chemical vapor deposition. Journal of Applied Physics, 84(8), 4452-4458. doi:10.1063/1.368669Millot, M., Geballe, Z. M., Yu, K. M., Walukiewicz, W., & Jeanloz, R. (2012). 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GSH23.0-0.7+117, a neutral hydrogen shell in the inner Galaxy

GSH23.0-0.7+117 is a well-defined neutral hydrogen shell discovered in the VLA Galactic Plane Survey (VGPS). Only the blueshifted side of the shell was detected. The expansion velocity and systemic velocity were determined through the systematic behavior of the HI emission with velocity. The center of the shell is at (l,b,v)=(23.05,-0.77,+117 km/s). The angular radius of the shell is 6.8', or 15 pc at a distance of 7.8 kpc. The HI mass divided by the volume of the half-shell implies an average density n_H = 11 +/- 4 cm^{-3} for the medium in which the shell expanded. The estimated age of GSH23.0-0.7+117 is 1 Myr, with an upper limit of 2 Myr. The modest expansion energy of 2 * 10^{48} erg can be provided by the stellar wind of a single O4 to O8 star over the age of the shell. The 3 sigma upper limit to the 1.4 GHz continuum flux density (S_{1.4} < 248 mJy) is used to derive an upper limit to the Lyman continuum luminosity generated inside the shell. This upper limit implies a maximum of one O9 star (O8 to O9.5 taking into account the error in the distance) inside the HI shell, unless most of the incident ionizing flux leaks through the HI shell. To allow this, the shell should be fragmented on scales smaller than the beam (2.3 pc). If the stellar wind bubble is not adiabatic, or the bubble has burst (as suggested by the HI channel maps), agreement between the energy and ionization requirements is even less likely. The limit set by the non-detection in the continuum provides a significant challenge for the interpretation of GSH23.0-0.7+117 as a stellar wind bubble. A similar analysis may be applicable to other Galactic HI shells that have not been detected in the continuum.Comment: 18 pages, 6 figures. Figures 1 and 4 separately in GIF format. Accepted for publication in Astrophysical Journa

Density functional formalism in the canonical ensemble

Density functional theory, when applied to systems with $T\neq 0$, is based on the grand canonical extension of the Hohenberg-Kohn-Sham theorem due to Mermin (HKSM theorem). While a straightforward canonical ensemble generalization fails, work in nanopore systems could certainly benefit from such extension. We show that, if the asymptotic behaviour of the canonical distribution functions is taken into account, the HKSM theorem can be extended to the canonical ensemble. We generate $N$-modified correlation and distribution functions hierarchies and prove that, if they are employed, either a modified external field or the density profiles can be indistinctly used as independent variables. We also write down the $N$% -modified free energy functional and prove that its minimum is reached when the equilibrium values of the new hierarchy are used. This completes the extension of the HKSM theorem.Comment: revtex, to be submitted to Phys. Rev. Let

Transport properties of nitrogen doped p‐gallium selenide single crystals

Nitrogen doped gallium selenide single crystals are studied through Hall effect and photoluminescence measurements in the temperature ranges from 150 to 700 K and from 30 to 45 K, respectively. The doping effect of nitrogen is established and room temperature resistivities as low as 20 Ω cm are measured. The temperature dependence of the hole concentration can be explained through a single acceptor‐single donor model, the acceptor ionization energy being 210 meV, with a very low compensation rate. The high quality of nitrogen doped GaSe single crystals is confirmed by photoluminescence spectra exhibiting only exciton related peaks. Two phonon scattering mechanisms must be considered in order to give quantitative account of the temperature dependence of the hole mobility: scattering by 16.7 meV A′1 homopolar optical phonons with a hole‐phonon coupling constant g2=0.115 and scattering by 31.5 meV LO polar phonon with a hole Fröhlich constant αh⊥[email protected]

Response of soil health indicators to dung, urine and mineral fertilizer application in temperate pastures

Healthy soils are key to sustainability and food security. In temperate grasslands, not many studies have focused on soil health comparisons between contrasting pasture systems under different management strategies and treatment applications (e.g. manures and inorganic fertilisers). The aim of this study was to assess the responses of soil health indicators to dung, urine and inorganic N fertiliser in three temperate swards: permanent pasture not ploughed for at least 20 years (PP), high sugar ryegrass with white clover targeted at 30% coverage reseeded in 2013 (WC), and high sugar ryegrass reseeded in 2014 (HG). This study was conducted on the North Wyke Farm Platform (UK) from April 2017 to October 2017. Soil health indicators including soil organic carbon (SOC, measured by loss of ignition and elemental analyser), dissolved organic carbon (DOC), total nitrogen (TN), C:N ratio, soil C and N bulk isotopes, pH, bulk density (BD), aggregate stability, ergosterol concentration (as a proxy for fungi biomass), and earthworms (abundance, mass and density) were measured and analysed before and after application of dung and N fertilizer, urine and N fertiliser, and only N fertiliser. The highest SOC, TN, DOC, ergosterol concentration and earthworms as well as the lowest BD were found in PP, likely due to the lack of ploughing. Differences among treatments were observed due to the application of dung, resulting in an improvement in chemical indicators of soil health after 50 days of its application. Ergosterol concentration was significantly higher before treatment applications than at the end of the experiment. No changes were detected in BD and aggregate stability after treatment applications. We conclude that not enough time had passed for the soil to recover after the ploughing and reseeding of the permanent pasture, independently of the sward composition (HG or WC). Our results highlight the strong influence of the soil management legacy in temperate pasture and the positive effects of dung application on soil health over the short term. In addition, we point out the relevance of using standardised methods to report soil health indicators and some methodological limitations

Constraints on Type Ib/c and GRB Progenitors

Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.Comment: 36 pages, 6 figure