2,669 research outputs found
Four decades of health economics through a bibliometric lens
This paper takes a bibliometric tour of the past 40 years of health economics using bibliographic"metadata"from EconLit supplemented by citation data from Google Scholar and the authors'topical classifications. The authors report the growth of health economics (33,000 publications since 1969 -- 12,000 more than in the economics of education) and list the 300 most-cited publications broken down by topic. They report the changing topical and geographic focus of health economics (the topics'Determinants of health and ill-health'and'Health statistics and econometrics'both show an upward trend, and the field has expanded appreciably into the developing world). They also compare authors, countries, institutions, and journals in terms of the volume of publications and their influence as measured through various citation-based indices (Grossman, the US, Harvard and the JHE emerge close to or at the top on a variety of measures).Health Monitoring&Evaluation,Health Systems Development&Reform,Health Economics&Finance,Rural Development Knowledge&Information Systems,Health Law
Homology of artinian and Matlis reflexive modules, I
Let R be a commutative local noetherian ring, and let L and L' be R-modules.
We investigate the properties of the functors Tor_i^R(L,-) and Ext^i_R(L,-).
For instance, we show the following:
(a) if L is artinian and L' is noetherian, then Hom_R(L,L') has finite
length;
(b) if L and L' are artinian, then the tensor product L \otimes_R L' has
finite length;
(c) if L and L' are artinian, then Tor_i^R(L,L') is artinian, and
Ext^i_R(L,L') is noetherian over the completion \hat R; and
(d) if L is artinian and L' is Matlis reflexive, then Ext^i_R(L,L'),
Ext^i_R(L',L), and Tor_i^R(L,L') are Matlis reflexive.
Also, we study the vanishing behavior of these functors, and we include
computations demonstrating the sharpness of our results.Comment: 24 page
Olivines in angrite LEW 87051: Phenos or xenos
Nyquist et al. recently reported the presence of live Mn-53 in angrite LEW 86010 when it crystallized. Hence, melting must have occurred within approx. 10 Ma of the accretion of the angrite parent body, and LEW 86010 is the oldest known differentiated meteorite. This discovery has made it even more desirable to understand teh petrogenesis of angrites, which presumably were all formed at a similar time. As part of the continuing work on angrite petrogenesis, crystallization experiments were conducted on LEW 87051, the other Antarctic angrite, to clarify its petrogenesis. Several aspects of the experimental work is reported. Although the details are not understood, it is clear that the Cr abundance in the experimental olivines must be controlled by spinel crystallization
Ascent of module structures, vanishing of Ext, and extended modules
Let (R,\m) and (S,\n) be commutative Noetherian local rings, and let
be a flat local homomorphism such that \m S = \n and the
induced map on residue fields R/\m \to S/\n is an isomorphism. Given a
finitely generated -module , we show that has an -module structure
compatible with the given -module structure if and only if \Ext^i_R(S,M)=0
for each .
We say that an -module is {\it extended} if there is a finitely
generated -module such that . Given a short exact
sequence of finitely generated -modules, with
two of the three modules extended, we obtain conditions forcing the
third module to be extended. We show that every finitely generated module over
the Henselization of is a direct summand of an extended module, but that
the analogous result fails for the \m-adic completion.Comment: 16 pages, AMS-TeX; final version to appear in Michigan Math. J.;
corrected proof of Main Theorem and made minor editorial changes; v3 has
dedication to Mel Hochste
Presentations of rings with non-trivial semidualizing modules
Let R be a commutative noetherian local ring. A finitely generated R-module C
is semidualizing if it is self-orthogonal and satisfies the condition
Hom_R(C,C) \cong R. We prove that a Cohen-Macaulay ring R with dualizing module
D admits a semidualizing module C satisfying R\ncong C \ncong D if and only if
it is a homomorphic image of a Gorenstein ring in which the defining ideal
decomposes in a cohomologically independent way. This expands on a well-known
result of Foxby, Reiten and Sharp saying that R admits a dualizing module if
and only if R is Cohen--Macaulay and a homomorphic image of a local Gorenstein
ring.Comment: 16 pages, uses XY-pic; v.2 reorganized, main theorem revised,
examples adde
Age and origin of enigmatic megaherbs from the subantarctic islands
Biogeographic relationships in the southern hemisphere have puzzled biologists for the last two centuries. Once joined to form the supercontinent Gondwana, Africa, Antarctica, Australia, New Zealand and South America are widely separated by the Pacific and Indian oceans. Sir Joseph Hooker was the first to suggest that Antarctica served as a corridor for plant migration not unlike the land-bridges in the northern hemisphere. While the Antarctic flora was largely erased by glaciation during the Pleistocene, at least some of these Antarctic plant communities found refuge on the subantarctic islands. Here we provide support for the hypothesis that giant herbs persisted in the subantactic islands prior to the onset of Pleistocene glaciation, then dispersed northward in response to glacial advance. Our findings provide further evidence that Antarctica has played a pivotal role in shaping southern hemisphere biogeography
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