现本人需要如下4篇外文文献，为了方便结算，烦请应助者分开应助（附上相应的文献名），每篇25果果。
【作 者】A. J. Leighton and R. V. Higgins
【题 名】Improved Method for Calculating Areas and Shape Factors of Flow Nets.
【系 列】 Report of investigations - Bureau of Mines -- 7111
【出版项】 1968, U.S. Dept. of the Interior, Bureau of Mines (Pittsburgh, Pa)
【作 者】A. J. Leighton and R. V. Higgins
【题 名】Numerical Methods for Determining Streamlines and Isopressures for Use in Fluid-Flow Studies.
【系 列】Report of investigations - Bureau of Mines -- 7621
【出版项】1972, U.S. Dept. of the Interior, Bureau of Mines (Pittsburgh, Pa)
【作 者】A. J. Leighton and R. V. Higgins
【题 名】Principles and Computer Techniques for Calculating Performance of a Five-Spot Waterflood-Two-Phase Flow.
【系 列】Report of investigations - Bureau of Mines -- 6305
【出版项】1963, U.S. Dept. of the Interior, Bureau of Mines (Pittsburgh, Pa)
【作 者】A. J. Leighton and R. V. Higgins
【题 名】Pressure Distribution in Irregularly Bounded Reservoirs.
【系 列】Report of investigations - Bureau of Mines -- 7666
【出版项】1972, U.S. Dept. of the Interior, Bureau of Mines (Pittsburgh, Pa)
