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101.
102.
We prove the existence of uncountably many nonisomorphic topological projective planes, each universal in the sense that it contains an isomorphic copy of every pseudoline arrangement. 相似文献
103.
This paper estimates a non-parametric production frontier for a population of 117 corn/livestock farms in the Corn Belt region in 1987, employing a hyperbolic graph efficiency approach. There are 7 outputs, 39 variable inputs, 4 fixed inputs, and one bad input (residual nitrogen). Three graph efficiency models are estimated. A profit maximization model is specified to estimate a production frontier constrained only by the fixed factors. Two other models involving tax constraints are also estimated. One involves a tax directly on nitrogen and the other involves a tax directly on residual nitrogen, making the disposal of residual nitrogen costly. The nitrogen tax constraint is more effective in reducing residual nitrogen loadings and causes a larger reduction in income than the residual tax constraint. 相似文献
104.
Richard C. Bradley 《Journal of Theoretical Probability》1996,9(3):659-678
Schmidt(10) showed that if the family of distributions of the partial sums of a strictly stationary random sequence is tight, then that random sequence is a coboundary. Here an analog of that result is proved for some sequences of random matrices, with partial sums replaced by matrix products. 相似文献
105.
Richard Kerner 《Letters in Mathematical Physics》1996,36(4):441-454
We present a possible generalization of the exterior differential calculus, based on the operator d such that d3=0, but d20. The entities dx
i
and d2
x
k
generate an associative algebra; we shall suppose that the products dx
i
dx
k
are independent of dx
k
dx
i
, while theternary products will satisfy the relation: dx
i
dx
k
dx
m
=jdx
k
dx
m
dx
i
=j
2dx
m
dx
m
dx
i
dx
k
, complemented by the relation dx
i
d2
x
k
=jd2
x
k
dx
i
, withj:=e2i/3.We shall attribute grade 1 to the differentials dx
i
and grade 2 to the second differentials d2
x
k
; under the associative multiplication law the grades add up modulo 3.We show how the notion ofcovariant derivation can be generalized with a 1-formA so thatD:=d+A, and we give the expression in local coordinates of thecurvature 3-form defined as :=d2
A+d(A
2)+AdA+A
3.Finally, the introduction of notions of a scalar product and integration of theZ
3-graded exterior forms enables us to define the variational principle and to derive the differential equations satisfied by the 3-form . The Lagrangian obtained in this way contains the invariants of the ordinary gauge field tensorF
ik
and its covariant derivativesD
i
F
km
. 相似文献
106.
107.
Downey Rodney G.; Lempp Steffen; Shore Richard A. 《Journal London Mathematical Society》1996,54(3):417-439
We show that there is a degree a REA in and low over 0' suchthat no minimal degree below 0' jumps to a degree above a. Wealso show that every nonlow recursively enumerable degree boundsa nonlow minimal degree. 相似文献
108.
Richard Steiner 《Applied Categorical Structures》1993,1(3):247-284
The theory of directed complexes is a higher-dimensional generalisation of the theory of directed graphs. In a directed graph, the simple directed paths form a subset of the free category which they generate; if the graph has no directed cycles, then the simple directed paths constitute the entire category. Generalising this, in a directed complex there is a class of split subsets which is contained in and generates a free -category; when a simple loop-freeness condition is satisfied, the split sets constitute the entire -category. The class of directed complexes is closed under the natural product and join constructions. The free -categories generated by directed complexes include the important examples associated to cubes and simplexes. 相似文献
109.
110.
Synthesis, single-crystal structure determination, and magnetic properties are reported for manganese carbodiimide, MnNCN. The presumably unstable but inert phase adopts the trigonal system (R3m) with a = 3.3583(4) A, c = 14.347(2) A, V = 140.13(3) A3, and Z = 3. Divalent manganese is octahedrally coordinated by nitrogen atoms at 2.26 A, and the NCN(2-) unit adopts the linear [N=C=N](2-) carbodiimide shape with two C=N double bonds of 1.23 A. MnNCN contains high-spin Mn(II) with five unpaired electrons and behaves like an antiferromagnet with an ordering temperature below 30 K. 相似文献