Climate change impacts on dryland cropping systems in the Central Great Plains,USA     

Jonghan Ko  Lajpat R. Ahuja  S. A. Saseendran  Timothy R. Green  Liwang Ma  David C. Nielsen  Charles L. Walthall 《Climatic change》2012,111(2):445-472

Agricultural systems models are essential tools to assess potential climate change (CC) impacts on crop production and help guide policy decisions. In this study, impacts of projected CC on dryland crop rotations of wheat-fallow (WF), wheat-corn-fallow (WCF), and wheat-corn-millet (WCM) in the U.S. Central Great Plains (Akron, Colorado) were simulated using the CERES V4.0 crop modules in RZWQM2. The CC scenarios for CO₂, temperature and precipitation were based on a synthesis of Intergovernmental Panel on Climate Change (IPCC 2007) projections for Colorado. The CC for years 2025, 2050, 2075, and 2100 (CC projection years) were super-imposed on measured baseline climate data for 15–17 years collected during the long-term WF and WCF (1992–2008), and WCM (1994–2008) experiments at the location to provide inter-annual variability. For all the CC projection years, a decline in simulated wheat yield and an increase in actual transpiration were observed, but compared to the baseline these changes were not significant (p > 0.05) in all cases but one. However, corn and proso millet yields in all rotations and projection years declined significantly (p < 0.05), which resulted in decreased transpiration. Overall, the projected negative effects of rising temperatures on crop production dominated over any positive impacts of atmospheric CO₂ increases in these dryland cropping systems. Simulated adaptation via changes in planting dates did not mitigate the yield losses of the crops significantly. However, the no-tillage maintained higher wheat yields than the conventional tillage in the WF rotation to year 2075. Possible effects of historical CO₂ increases during the past century (from 300 to 380 ppm) on crop yields were also simulated using 96 years of measured climate data (1912–2008) at the location. On average the CO₂ increase enhanced wheat yields by about 30%, and millet yields by about 17%, with no significant changes in corn yields.  相似文献   

Asian Dust effects on Total Suspended Particulate (TSP) compositions at Gosan in Jeju Island, Korea   总被引：2，自引：0，他引：2  

Chang-Hee Kang  Won-Hyung Kim  Hee-Jung Ko  Sang-Bum Hong   《Atmospheric Research》2009,94(2):345-355

The compositions of TSP between AD and NAD storm periods were compared to study their long-term variations and chemical characteristics. TSP samples were collected at Gosan site in Jeju Island of Korea from February to May of 1992–2004. The major ionic and elemental species of TSP aerosols were analyzed. During AD periods, the concentrations of crust components (nss-Ca²⁺, Al, Fe, Ca, Mg, Ba, Sr, Ti) increased remarkably, and the concentrations of anthropogenic components (nss-SO₄²⁻, NO₃⁻, S, Zn, Pb, Cr, Ni, Cd), with the exception of NH₄⁺, increased weakly. The concentration ratios of all major components between AD and NAD periods showed ranges from 1.2 to 8.5, except for NH₄⁺. The slope of the linear regression indicated that the contribution of CO₃²⁻ may have comprised up to 17% of the total anions. Our results suggested that the AD storm greatly influenced TSP compositions. Linear regression analyses indicated that NH₄⁺ was not correlated with NO₃⁻, but highly correlated with nss-SO₄²⁻ during both periods. The nss-SO₄²⁻ was also correlated with NH₄⁺, K⁺, nss-Mg²⁺, and nss-Ca²⁺ during both periods. Interestingly, NO₃⁻ was associated with nss-Ca²⁺ and nss-Mg²⁺ during AD periods. Of the metal elements, Fe, Ca, Mg, Ti, Mn, Ba, Sr, V, and Co were highly correlated with Al during both periods, signifying that these metals were mostly originated from soils.  相似文献   

Seasonal and annual loads of hydrophobic organic contaminants from the Susquehanna River basin to the Chesapeake Bay     

Ko FC  Baker JE 《Marine pollution bulletin》2004,48(9-10):840-851

Water from the Susquehanna River was collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCB) congeners to estimate seasonal and annual riverine loads to the Chesapeake Bay. Temporal variations in the chemical loads resulted from the large changes in the water flow rates and in the particle-associated contaminant concentrations. Concentrations of PCBs and PAHs in river particles (ng/g) were twice as great as those in the northern Chesapeake Bay, indicating that the Susquehanna River is an important source of these contaminants to the bay. The river carries a majority of its hydrophobic organic contaminants (HOCs) in the particulate phase. During periods of high flow, large amounts of suspended particles in the river result in elevated HOC levels and increased loadings of these contaminants to the bay. From 1997 to 1998, 60% of the total annual HOC loading occurred in the early spring coincident with high river flows. The total PCB and PAH annual loadings from the Susquehanna River to the Chesapeake Bay were 76 and 3160 kg/year, respectively and 75% of the loaded organic contaminants were in the particulate phase. Principal component analysis of PAH and PCB congener patterns in the particles reveals that the river suspended particles were dominated by autochthonous production in the summer and by resuspended sediment and watershed erosion during the winter and early spring.  相似文献   

Sloshing behaviours of rectangular and cylindrical liquid tanks subjected to harmonic and seismic excitations     

Yung‐Hsiang Chen  Wei‐Shien Hwang  Chia‐Hao Ko 《地震工程与结构动力学》2007,36(12):1701-1717

A numerical and experimental study on the sloshing behaviours of cylindrical and rectangular liquid tanks is addressed. A three‐dimensional boundary element method for space with the second‐order Taylor series expansion in time is established to simulate the sloshing phenomenon and its related physical quantities inside a liquid tank subjected to horizontal harmonic oscillations or recorded earthquake excitations. The small‐scale model experiments are carried out to verify some results of numerical methods in this study. The comparisons between numerical and experimental results show that the numerical method is reliable for both kinds of ground excitations. Finally, the water wave and the base shear force of a rectangular tank due to harmonic excitation are also presented at different frequencies. A huge cylindrical water tank subjected to a recorded earthquake excitation is used for application and discussion. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Analyses of nitrogen and argon in single lunar grains: towards a quantification of the asteroidal contribution to planetary surfaces     

Ko Hashizume  Bernard Marty  Rainer Wieler 《Earth and Planetary Science Letters》2002,202(2):201-216

We performed nitrogen and argon isotopic analyses in single 200-μm-sized ilmenite grains of lunar regolith samples 71501, 79035 and 79135. Cosmogenic and trapped components were discriminated using stepwise heating with a power-controlled CO₂ laser. Cosmogenic ¹⁵N and ³⁸Ar correlate among different ilmenite grains, yielding a mean ¹⁵N_c/³⁸Ar_c production ratio of 14.4±1.0 atoms/atom. This yields a ¹⁵N production rate in bulk lunar samples of 3.8-5.6 pg (g rock)⁻¹ Ma⁻¹, which agrees well with previous estimates. The trapped δ¹⁵N values show large variations (up to 300‰) among different grains of a given soil, reflecting complex histories of mixing between different end-members. The ³⁶Ar/¹⁴N ratio, which is expected to increase with increasing contribution of solar ions, varies from 0.007 to 0.44 times the solar abundance ratio. The trapped δ¹⁵N values correlate roughly with the ³⁶Ar/¹⁴N ratios from a non-solar end-member characterized by a ³⁶Ar/¹⁴N ratio close to 0 and variable but generally positive δ¹⁵N values, to lower δ¹⁵N values accompanied by increasing ³⁶Ar/¹⁴N ratios, supporting the claim of Hashizume et al. (2000) that solar nitrogen is largely depleted in ¹⁵N relative to meteoritic or terrestrial nitrogen. Nevertheless, the ³⁶Ar/¹⁴N ratio of the ¹⁵N-depleted (solar) end-member is lower than the solar abundance ratio by a factor of 2.5-5. We explain this by a reprocessing of implanted solar wind atoms, during which part of the chemically inert rare gases were lost. We estimate that the flux of non-solar N necessary to account for the observed δ¹⁵N values is comparable to the flux of micrometeorites and interplanetary dust particles estimated for the Earth. Hence we propose that the variations in δ¹⁵N values observed in lunar regolith can be simply explained by mixing between solar wind contributions and micrometeoritic ones infalling on the Moon. Temporal variations of δ¹⁵N values among samples of different antiquities could be due to changes in the micrometeoritic flux through time, in which case such flux has increased by up to an order of magnitude during the last 0.5 Ga.  相似文献   

Wind-induced vibration control of bridges using liquid column damper   总被引：1，自引：0，他引：1  

薛素铎  高赞明  徐幼麟 《地震工程与工程振动(英文版)》2002,1(2):271-280

The potential application of tuned liquid column damper (TLCD) for suppressing wind-induced vibration of long span bridges is explored in this paper. By installing the TLCD in the bridge deck, a mathematical model for the bridge-TLCD system is established. The governing equations of the system are developed by considering all three displacement components of the deck in vertical, lateral, and torsional vibrations, in which the interactions between the bridge deck, the TLCD, the aeroelastic forces, and the aerodynamic forces are fully reflected. Both buffeting and flutter analyses are carried out. The buffeting analysis is performed through random vibration approach, and a critical flutter condition is identified from flutter analysis. A numerical example is presented to demonstrate the control effectiveness of the damper and it is shown that the TLCD can be an effective device for suppressing wind-induced vibration of long span bridges, either for reducing the buffeting response or increasing the critical flutter wind velocity of the bridge.  相似文献   

A high resolution numerical study of Gulf of Mexico fronts and eddies     

D. E. Dietrich  C. A. Lin  Dr. A. Mestas-Nunez  D. S. Ko 《Meteorology and Atmospheric Physics》1997,64(3-4):187-201

Summary The Gulf of Mexico (GOM) circulation is simulated using the DieCAST ocean model, with a horizontal resolution of 1/12° and 20 vertical layers. The results compare well with observations of both large and small scale features, including Loop Current frontal occlusions associated with frontal eddies. The simulation is carried out without any data assimilation. The frontal eddies tend to be spaced at about 90° intervals around the Loop Current, leading to a Loop Current head shaped like a square with rounded corners. The pattern rotates as the eddies circle the Loop, and frontal eddies elongate as they squeeze through the Florida Strait. Major warm core eddies separate regularly from the Loop Current and propagate to the western GOM. Old warm core eddies in the western Gulf dissipate through bottom drag effects, which also generate cyclonic parasitic eddies. Newly arrived warm core eddies merge with old ones in the western GOM. Recently separated elongated Loop Current eddies can rotate and reattach temporarily to the Loop Current. The barotropic flow component develops eddies between the main separated warm core eddy and the Loop Current due to eastward dispersion, as the main eddy itself propagates westward into the Gulf.With 10 Figures  相似文献   

High-pressure phase transition in MnTiO3 from the ilmenite to the LiNbO3 structure     

Jaidong Ko  Charles T. Prewitt 《Physics and Chemistry of Minerals》1988,15(4):355-362

Crystals of a high-pressure phase of MnTiO₃ have been synthesized at pressures of 60 kbar using the SAM-85 cubic-anvil high pressure apparatus. Although all crystals examined were twinned on (10 \(\bar 1\) \(\bar 2\) ), a set of diffraction intensities that are essentially unaffected by the twinning were obtained. Three possible structure models were considered: (1) the corundum (completely disordered Mn and Ti), (2) the partially-disordered ilmenite, and (3) the LiNbO₃ structures. The R factors of the corundum and the disordered ilmenite models were much larger than that of LiNbO₃. Using structure factors unaffected by twinning, the final LiNbO₃-type refinement gave R _w=0.037 and R=0.034. The averaged bond lengths for Mn-O and Ti-O were consistent with ones calculated using Shannon and Prewitt's (1969) radii. The study concludes that MnTiO₃ II actually has an ordered LiNbO₃-type structure rather than the disordered one as reported previously. From the analysis of the two MnTiO₃ structures, the transition can be related to a cation reordering process, in which half of the cations participate, accompanied by the rotation of oxygens to accommodate the cations.  相似文献   

Inversion of the geomagnetic field determined by palaeomagnetic investigations of quaternary sediments     

Alois Kočí 《Studia Geophysica et Geodaetica》1969,13(3):326-331

Résumé Au cours des recherches paléomagnétiques en Tchécoslovaquie, on a constaté und double polarité de la magnétisation rémanente des sédiments quaternaires. Des recherches plus détaillées de la localité Červeny kopec près de Brno, qui représente une région de sédiments avec une suite initerrompue de couches déposées au cours d'un million d'années dernières, datées par la méthode de correlation astronomique, fournissent certains résultats importants sur l'époque au cours de laquelle s'est passé l'inversion du champ géomagnétique. Selon nos recherches de jusqu'à présent, on peut déterminer la fin de l'époque inverse de Matuyama par 0,930 million d'années environ. Après elle succède la pèriode de transition, dont la durée est de 60 000 ans environ, au cours de laquelle se sont passé des changements rapides dans le champ géomagnétique et au cours de laquelle existent des roches possédant une magnétisation avec inclinaison soit positive, soit négative. L'époque de polarité normale de Brunhes commence selon nos constatations autour de 0,870 million d'années.

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Address: Bočni II, Praha 4-Spořilov  相似文献   

A new phase transition in MnTiO3: LiNbO3-perovskite structure     

Nancy L. Ross  Jaidong Ko  Charles T. Prewitt 《Physics and Chemistry of Minerals》1989,16(7):621-629

The stable polymorph of MnTiO₃ at room temperature and pressure has the ilmenite structure. At high temperatures and pressures, MnTiO₃ ilmenite transforms to a LiNbO₃ structure through a cation reordering process (Ko and Prewitt 1988). Single crystals of both phases have been studied with X-ray diffraction to 5.0 GPa. We have obtained the first experimental verification of the close relationship between the LiNbO₃ and perovskite structures, first postulated by Megaw (1968). MnTiO₃ with the LiNbO₃ structure (MnTiO₃ II) transforms directly to an orthorhombic perovskite structure (MnTiO₃ III) between 2.0 and 3.0 GPa. The transition involves a change of volume of -5%, is reversible and has pronounced hysteresis. Only pressure is required to drive the transition because it involves no breaking of bonds; it simply involves rotation of the [TiO₆] octahedra about their triad axes accompanied by displacement of the Mn cations to the distorted twelve-coordinated sites formed by the rotations. An unusual aspect of this transition is that twinned MnTiO₃ II crystals transform to untwinned MnTiO₃ III crystals with increasing pressure. The twin plane of MnTiO₃ II, , corresponds to the (001) mirror plane of the orthorhombic perovskite structure. MnTiO₃ III examined at 4.5 GPa is very distorted from the ideal cubic perovskite structure. The O(2)-O(2)-O(2) angle describing the tilting in the ab plane is 133.3(7)°, in contrast to 180° for a cubic perovskite and the O(2)-O(2)-O(2) angle describing the tilting in the ac plane is 109.3(4)°, as opposed to 90° in a cubic perovskite.  相似文献