Journal of Mathematical Sciences: Advances and Applications[1] R. P. Bambah, Four squares and a k-th power, Quart. J.
Math. Oxford 5 (1954), 191-202.
[2] B. J. Birch and H. Davenport, On a theorem of Davenport and
Heilbronn, Acta Mathematica 100 (1958), 259-279.
[3] H. Davenport and H. Heilbronn, On indefinite quadratic forms in
five variables, Journal of London Math. Soc. 21 (1946), 185-193.
[4] A. Ghosh, The distribution 
modulo one, Proc. London Math. Soc. 42
(1981), 252-269.
[5] G. Harman, The values of ternary quadratic forms at prime
arguments, Mathematika 51 (2004), 83-96.
[6] Kee Wai Lau and Ming-Chit Liu, Approximation by four squares and a
k-th power, Southeast Asian Bull. Math. 2 (1978), 33-36.
[7] W. P. Li and T. Z. Wang, Diophantine approximation with one prime
and three squares of primes, The Ramanujan Journal (in press).
[8] R. C. Vaughan, Diophantine approximation by prime numbers, I,
Proc. London Math. Soc. 28 (1974), 373-384.
[9] R. C. Vaughan, Diophantine approximation by prime numbers, II,
Proc. London Math. Soc. 28 (1974), 385-401.
