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We prove that several invariants of a possibly singular complex affine or projective variety of degree $d$ in the affine space $\mathbb{A}^{n}$, or $\mathbb{P}^n$, are bounded by a function of $d$ alone, provided $b_{1}=0$ for a resolution of singularities of the variety., Comment: To appear in the Journal of the Ramanujan Mathematical Society

In this exposition of the equality and inequality of Minkowski for multiplicity of ideals, we provide simple algebraic and geometric proofs. Connections with mixed multiplicities of ideals are explained., Comment: 28 pages

We generalize results by Wakabayashi and Orevkov about rational cuspidal curves on the projective plane to that on $\mathbb{Q}$-homology projective planes. It turns out that the result is exactly the same as the projective plane case under suitable assumptions. We also provide examples which demonstrate sharpness of the results. The ambient surface is singular in these examples., Comment: 14 Pages. Some errors corrected. arXiv admin note: text overlap with arXiv:1512.08840

We will prove that given a genus-2 fibration $f: X \rightarrow C$ on a smooth projective surface $X$ such that $b_1(X)=b_1(C)+2$, the fundamental group of $X$ is almost isomorphic to $\pi_1(C) \times \pi_1(E)$, where $E$ is an elliptic curve. We will also verify the Shafarevich Conjecture on holomorphic convexity of the universal cover of surfaces $X$ with genus-2 fibration $X\rightarrow C$ such that $b_1(X)>b_1(C)$., Comment: 23 Pages, Published in the International Journal of Mathematics

Affine varieties of dimension greater than two can be explored their structures with the help of fibrations by the affine line or plane and quotient morphisms by $\mathbb{G}_a$-actions. We consider $\mathbb{G}_a$-actions on affine threefolds and discuss the structure and the singularities of the quotient surface as well as the singular fibers of the quotient morphism. Relative $\mathbb{G}_a$ and $\mathbb{G}_m$-actions on $\mathbb{A}^4$ or on an affine 4-fold having $\mathbb{A}^3$-fibrations over $\mathbb{A}^1$ are discussed when the actions leave one variable invariant or the fibration invariant., Comment: This paper has been withdrawn by the authors due to an error in the proof of Thm.3.1 which is not true in the present version

We consider log deformations of affine surfaces with fibrations by the affine lines. Such a fibration is of affine type (resp. of complete type) if the base curve of the fibration is an affine curve (resp. a complete curve). The case of affine type is mainly treated in the article., Comment: 40 pages

We consider the Zariski-Lipman Conjecture on free module of derivations for algebraic surfaces. Using the theory of non-complete algebraic surfaces, and some basic results about ruled surfaces, we will prove the conjecture for several classes of affine and projective surfaces., Comment: Final version; to appear in Jour. London Math. Soc

The affine line minus one point is the underlying space of the algebraic torus of dimension one. However the fibration of an affine algebraic threefold by the affine line minus one point is not always the quotient morphism of the threefold by the algebraic torus. We investigate the structure of affine algebraic threefolds having fibrations by the affine line minus one point. Our results cover not only algebro-geometric but also topological properties of the threefolds. We also consider when the fibration by the affine line minus one point becomes the quotient morphism by an algebraic torus of dimension one., Comment: 39 pages, To appear in the Proceedings of the conference held in Osaka, March 2011

Inspired by a result of D. Cerveau on surjective derivations on a polynomial ring in two variables over a complex number field C, we consider a surjective derivation defined on an affine domain over C of dimension one or two. Though our proofs are mostly algebraic or algebro-geometric, the idea using a result of Dimca-Saito which is behind the arguments of Cerveau and based on the differential complex of the polynomial ring in n variables is inspiring and affects our arguments., Comment: 27 pages

We show that a homology plane of general type has at worst a single cyclic quotient singular point. An example of such a surface with a singular point does exist. We also show that the automorphism group of a smooth contractible surface of general type is cyclic., Comment: 63 pages

We classify surjective self-maps (of degree at least two) of affine surfaces according to the log Kodaira dimension., Comment: in the book: Affine Algebraic Geometry (edited by T. Hibi, yr 2007)

In this paper we prove that a normal Gorenstein surface dominated by the projective plane P^2 is isomorphic to a quotient P^2/G, where G is a finite group of automorphisms of P^2 (except possibly for one surface V_8'). We can completely classify all such quotients. Some natural conjectures when the surface is not Gorenstein are also stated., Comment: Nagoya Mathematical Journal, to appear

This report records a large number of open problems in Affine Algebraic Geometry that were proposed by participants in a Conference on Open Algebraic Varieties at the Centre de Recherches en Mathematiques in Montreal at December 1994., Comment: 21 pages, author-supplied DVI file available at http://www.math.duke.edu/preprints/95-00.dvi , AMSLaTeX