bluuebunny/crossref_metadata_2025 huggingface dataset:
COLLISION BROADENING THROUGH SEQUENCES OF SCATTERING EVENTS: THEORY, CONSEQUENCES AND MODELING WITHIN SEMICLASSICAL MONTE CARLO
Authors: REGISTER LEONARD F. , FISHER BJÖRN
Published: April 2003

Recent developments in the understanding of the theory and consequences of collision broadening through sequences of scattering events are reviewed and expanded upon, particularly in regard to semiclassical Monte Carlo simulation. Using basic theory backed up by quantum transport simulations, it is demonstrated that the requirement for energy conservation in the coupled carrier-phonon system prohibits the accumulation of the uncertainty in the carrier energy associated with collision broadening through a sequence of scattering events. This accumulation, however, had been possible with the conventional treatment of collision broadening in semiclassical Monte Carlo. Accordingly, an improved, more physically accurate algorithm for connecting sequences of collision broadened scattering events within semiclassical Monte is described. The potential consequences of collision broadening are then reassessed using both the quantum transport simulations and semiclassical Monte Carlo simulations incorporating the new algorithm, including full-band Monte Carlo simulations for the first time. The broadening assisted runaway of the high-energy tail of the carrier distribution possible with the conventional algorithm is shown to be an artifact of that algorithm, not of the form of the collision broadening used (Lorentzian, etc.) as often assumed. Simulation results obtained with the new algorithm also demonstrate that for important cases, Golden-Rule-based Monte Carlo simulations can remain accurate despite the presence of significant collision broadening. A notable class of exceptions, however, is when collision broadening allows for a threshold or scattering bottle-neck to be overcome, although the ultimate requirement for energy conservation remains critical. Specifically, it is shown that collision broadening lowers but does not eliminate the impact ionization threshold energy, producing simulated impact ionization coefficients for holes in silicon that accurately track experimental results as a function of field. Similarly, the quantum transport simulations illustrate how collision broadening can significantly affect optical absorption, but that simply subjecting low energy carriers to scattering induced collision broadening does not allow them to overcome large potential barriers.
TRANSPORT IN A POLARIZATION-INDUCED 2D ELECTRON GAS
Authors: RIDLEY B. K. , ZAKHLENIUK N. A.
Published: April 2003

AlGaN/GaN structures constitute a new class of 2D systems in that a large population of electrons can be produced without doping as a result of spontaneous and strain-induced polarization. Electron transport can, in principle, be mediated solely by phonon scattering and, for the first time, it is possible to realistically envisage the formation of a drifted Maxwellian or Fermi-Dirac distribution in hot-electron transport. We first describe a simple model that relates electron density in a heterostructure to barrier width and then explore electron-electron (e-e) energy and momentum exchange in some depth. We then illustrate the novel hot-electron transport properties that can arise when only phonon and e-e scattering are present. These include S-type NDR, electron cooling and squeezed electrons.
IMPACT IONIZATION AND HIGH FIELD EFFECTS IN WIDE BAND GAP SEMICONDUCTORS
Authors: REIGROTZKI M. , MADUREIRA J. R. , KULIGK A. , FITZER N. , REDMER R. , GOODNICK S. M. , DÜR M.
Published: April 2003

Impact ionization plays a crucial role for electron transport in wide-bandgap semiconductors at high electric fields. Therefore, a realistic band structure has to be used in calculations of the microscopic scattering rate, as well as high field quantum corrections such as the intercollisional field effect. Here we consider both, and evaluate the impact ionization rate for wide-bandgap materials such as ZnS. A pronounced softening of the impact ionization threshold is obtained, as found earlier for materials like Si and GaAs. This field dependent impact ionization rate is included within a full-band ensemble Monte Carlo simulation of high field transport in ZnS. Although the impact ionization rate itself is strongly affected, little effect is observed on measurable quantities such as the impact ionization coefficient or the electron distribution function itself.
ELECTRICAL TRANSPORT IN ORGANIC SEMICONDUCTORS
Authors: CAMPBELL I. H. , SMITH D. L.
Published: April 2003

Organic semiconductors have processing and performance advantages for low cost and/or large area applications that have led to their rapid commercialization. Organic semiconductors are π conjugated materials, either small molecules or polymers. Their electrical transport properties are fundamentally distinct from those of inorganic semiconductors. Organic semiconductor thin films are amorphous or polycrystalline and their electronic structures consist of a distribution of localized electronic states with different energies. The localized sites are either individual molecules or isolated conjugated segments of a polymer chain. Electrical transport results from carrier hopping between neighboring sites. At room temperature, equilibration between neighboring sites of different energy is fast enough that carrier transport can be described using a mobility picture. Hopping transport in these disordered systems leads to a mobility that can depend strongly on both the electric field and carrier density. This article presents experimental measurements and theoretical analysis of the electrical transport properties of representative organic semiconductors.
PHYSICS AND CHEMISTRY OF INTRINSIC TIME-DEPENDENT DIELECTRIC BREAKDOWN IN SiO2 DIELECTRICS
Authors: McPHERSON J. W.
Published: April 2003

A molecular physics-based complementary model, which includes both field-induced and current-induced degradation mechanisms, is used to help resolve the E versus 1/E time-dependent dielectric breakdown (TDDB) model controversy that has existed for many years. The Complementary Model indicates either the E or 1/E–TDDB model can be valid for certain specified field, temperature, and molecular bonding-energy ranges. For bond strengths <3 eV, the bond breakage rate is generally dominated by field-enhanced thermal processes at lower fields and elevated temperatures where the E-model is valid. At higher fields, lower temperatures and higher bond strengths the bond breakage mechanism must be hole-catalyzed and the TDDB physics is described well by the 1/E-model. Neither the E-model nor 1/E-model works well for oxide thickness below tox < 4 nm where direct tunneling effects dominate in these hyper-thin films. The increase in DT leakage leads to more hole injection and trapping in the SiO 2. This enhanced dielectric degradation rate with tox reduction can be easily incorporated into the Complementary Model where hole capture serves to catalyze Si–O bond breakage.
OXIDE WEAROUT, BREAKDOWN, AND RELIABILITY
Authors: DUMIN D. J.
Published: April 2003

The subject of oxide wearout, breakdown, and reliability will be reviewed, largely, from an historical perspective. Five topics will be discussed: oxide breakdown, oxide leakage currents, trap generation, statistics, and reliability. An early model of oxide breakdown, developed by Klein and Solomon, will be described and will be shown to be generally applicable to oxide manufactured today, and to other solid insulators, as well. Both hard and soft breakdown were included in this model and will be discussed here. The importance of stress-induced-leakage-currents (SILCs) and direct tunneling currents will be discussed in the context of device applications, thinner oxides, and oxide reliability. The diminishing importance of breakdown in ultra thin oxides in ultra small devices will be contrasted with the increasing importance of oxide leakage currents. Trap generation is important in the triggering of breakdown and in the formation of SILCs. Trap generation will be discussed in some detail. Various statistical formulations of oxide breakdown, and how these distributions are related to trap generation, will be discussed. All of these effects will be related to oxide reliability and oxide integrity. An extensive bibliography has been included to help the reader obtain more detailed information concerning the concepts being discussed.
Reliability of Flash Nonvolatile Memories
Authors: Mielke Neal , Chen Jian
Published: April 2003

This paper reviews the reliability of Flash nonvolatile memories, with particular to dielectric degradation. These memories are manufactured with the same materials and processing steps as are other types of IC's, but unique features of Flash memories create very different reliability challenges. These features stem from the three unique functions of the Flash cell: to program, to erase, and to retain charge for years. Each of these functions has its own characteristic degradation mechanisms. A fascinating aspect of Flash reliability is the insight that can be gained into dielectric degradation mechanisms. In normal use, Flash dielectries experience levels of electric field, hot-carrier bombardment, and charge fluence that other IC processes experience only in capacitor breakdown studies and other accelerated stresses. Catastrophic breakdown does not occur, however, because the stress from charging and discharging the floating-gate capacitor is fundamentally self-limiting. At the same time, dielectric leakage of a few electrons a day can be measurable in a Flash cell. The combination of high stress, self-limiting degradation, and high leakage sensitivity allows prebreakdown dielectric degradation to be studied in great detail. Although Flash memory technology poses unique development challenges, engineering optimization can make these memories highly reliable.
BREAKDOWN MODES AND BREAKDOWN STATISTICS OF ULTRATHIN SiO2 GATE OXIDES
Authors: SUÑE JORDI , JIMENEZ DAVID , MIRANDA ENRIQUE
Published: April 2003

The dielectric breakdown of ultra-thin silicon dioxide films used as gate insulator in MOSFETs is one of the most important reliability issues in CMOS technology. In this paper, two main aspects of oxide breakdown are considered: the modeling of the breakdown statistics and the properties of the two main breakdown modes, namely Soft Breakdown and Hard Breakdown. The most invoked models for the breakdown statistics that relate defect generation and breakdown are reviewed. Particular attention is paid to the percolation models and to a recent cell-based analytic picture. The scaling of the breakdown distribution with oxide thickness is considered and it is shown that both pictures are equivalent for ultra-thin oxides. It is shown that soft and hard breakdown show coincident statistics and this is used to conclude that both breakdown models are triggered by the formation of the same kind of defect-related conduction paths. The big differences in the post-breakdown conduction properties are attributed to phenomena occurring during the very fast breakdown current runaway that determine the area of the final breakdown spot. The properties of soft and hard breakdown are explained within the common framework of a model based on quantum-point-contact conduction. This mesoscopic approach to the post-breakdown conduction is shown to explain the main experimental results including conductance quantization after hard breakdown, the area and thickness independence of the soft-breakdown I(V) characteristics and the statistical correlation between current level and normalized conductance. Finally, we deal with some open questions and relevant issues that are now subject of intensive investigations. The fact that some breakdown events can be tolerated for some digital applications is considered. In this regard, the distinction between breakdown and device failure distributions is made and some implications for device reliability are discussed. It is argued that energy dissipation during the breakdown runaway can determine the breakdown efficiency, the prevalence ratio of soft to hard breakdown, and their variations with stress conditions, experimental setup (series impedance) and sample characteristics.
MOSFET Gate Oxide Reliability: Anode Hole Injection Model and its Applications
Authors: Yeo Yee-Chia , Lu Qiang , Hu Chenming
Published: April 2003

We review the development of the anode hole injection (AHI) model for reliability projection of the silicon dioxide gate dielectric. The experimental and theoretical foundation of the AHI model is presented. Recent development and implications for the reliability of ultra-thin oxides are discussed. AHI is used to illuminate the questions of E versus 1/E models and field-driven versus voltage-driven models. Building on the concept of effective thinning, the AHI model is applied for the interpretation of defect-induced breakdown data and for optimizing oxide screening conditions. Circuit level reliability projection as a function of operating time, temperature, and power supply voltage is also illustrated.
RF MOS MEASUREMENTS
Authors: SISCHKA FRANZ , GNEITING THOMAS
Published: April 2003

The trend to higher integration and higher transmission speed challenges modeling engineers to develop accurate device models up to the Gigahertz range. An absolute prerequisite for achieving this goal are reliable measurements, which have to be checked for data consistency and plausibility. This is especially true for RF data, and also for checking and verifying the applied de-embedding techniques. If this is not the case, RF modeling can become quite time consuming, with a lot of guesswork and ad-hoc judgements, and, basically, frustrating and not correct. If, however, the underlying measurements are flawless and consistent, and provided the applied the models are understood well, RF modeling becomes very effective and provides accurate design kits which will satisfy the chip designer's main goal: right the fist time.
MOSFET MODELING AND PARAMETER EXTRACTION FOR RF IC'S
Authors: JE MINKYU , KWON ICKJIN , SHIN HYUNGCHEOL , LEE KWYRO
Published: April 2003

After reviewing the basic concept and general strategies, we have examined a variety of examples of modeling and parameter extraction methods for RF MOSFET's. Modeling and parameter extraction techniques popular in III-V FET modeling were reviewed and recent efforts to model the RF MOSFET and extract the model parameters were examined in light of the differences between the MOSFET and the III-V FET. A very simple and accurate parameter extraction method studied in our laboratory for three-terminal modeling considering charge conservation is also introduced. Our works have two important implications. One is that the consideration for charge conservation is important not only for accurate device modeling and circuit simulation but even more for proper parameter extraction. Another is that one accurate large-signal I-V model is enough to be used for DC, low-frequency analog, as well as RF circuit simulation. Four-terminal modeling based on new equivalent circuits to address the high-frequency effects arising in a MOSFET is very complicated and not practical for CAD applications, even without considering the substrate coupling terms. As a temporary alternative, the macro-modeling approach is examined with various examples.
MOSFET MODELING FOR RF IC DESIGN
Authors: CHENG YUHUA
Published: April 2003

High frequency (HF) AC and noise modeling of MOSFETs for radio frequency (RF) integrated circuit (IC) design is discussed. Equivalent circuits representing both intrinsic and extrinsic components in a MOSFET are analyzed to obtain a physics-based RF model. Modeling of the intrinsic device and the extrinsic components is disussed by accounting for the important physical effects at both DC and HF. Based on the Y-parameter analysis of the equivalent circuit model, procedures of the HF model parameter extraction are also developed. With the discussed approaches, a sub-circuit RF model incorporating the modeling of parasitics is presented. This model is compared with the measured data for both y parameter and fr characteristics. Good model accuracy is achieved against the measurements for a 0.25μm RF CMOS technology. The non-quasi-static (NQS) modeling issue has also been discussed by using the BSIM3v3 based RF model to predict the HF characteristics of devices with serious NQS effects. Further, noise modeling issues are discussed by analyzing the theoretical and experimental results in both the flicker noise and thermal noise modeling. Modeling efforts to in corporate new physical effects are needed to predict better the flicker noise characteristics in today's MOSFETs. A detailed analysis of the HF noise parameters has been conducted to establish the relationship between the noise parameters preferred by circuit designers and obtained by HF noise measurement. Analytical calcultion of the noise parameters has also been discussed to understand the noise characteristics with/without some parasitic components such as gate and substrate resistances as well as the influence of the induced gate noise. The HF noise predictivities of several HF noise models are also examined with the measured data. The results show that the BSIM3v3 based RF model can predict the channel thermal noise better than the other models.
SOI CMOS TRANSISTORS FOR RF AND MICROWAVE APPLICATIONS
Authors: FLANDRE D. , RASKIN J.-P. , VANHOENACKER-JANVIER D.
Published: April 2003

The new communication markets are vey demanding: high frequency, high degree of integration, low power consumption. Silicon-on-Insulator offers many advantages and this paper illustrates the potentialities of this technology for RF and microwave applictions. After an overview of the SOI material, the properties of the SOI MOSFET's are analyzed and compared to bulk Si MOSFET's. The models of transmission lines and inductors on SOI are compared and further used in the on-wafer characterization of the transistors. Various models for the transistors are presented and their limitations are given. A new model is described, valid from DC to the microwave region. This model agrees very well with the measurements for various transistor dimensions. Finally, variuos RF and microware circuits are presented. Ths paper does not fully describe all the properties and applications of SOI but the numerous references offered to the reader help him to gather more informations.
RF CMOS RELIABILITY
Authors: NASEH SASAN , DEEN M. JAMAL
Published: April 2003

In this chapter the effects of hot carrier on the reliability of NMOS transistors are investigated. First, it is explained why the hot carrier issue can be important in RF CMOS circuits. Important mechanisms of hot carrier generation are reviewed and some of the techniques used in the measurement of hot carrier damages are explained. Next, results of measurement of DC hot carrier stress on the NMOS transistors are presented. The main focus here is the RF performance of the NMOS devices and circuits mode of them, but DC parameters of the device such as its I-V characteristics and threshold voltage are presented, as they directly affect the RF performance. Finally, using the measurements of hot carrier effects on single NMOS transistors, the effects of hot carriers on three parameters of a low noise amplifier, matching, power gain and stability, are predicted using circuit simulation.
FINSLER LAPLACIANS AND MINIMAL-ENERGY MAPS
Authors: CENTORE PAUL
Published: April 2003

For any Finsler manifold, there is a geometrically natural Laplacian operator, called the mean-value Laplacian, which generalizes the Riemannian Laplacian. We show that, like the Riemannian Laplacian (for functions), we can see the vanishing of the mean-value Laplacian at some function f as the minimizing of an energy functional e(f) by f. This energy functional e depends on a Riemannian metric canonically associated to the Finsler metric and on a canonically associated volume form. We relate this construction to a more general construction of Jost, and define a notion of harmonic mappings between Finsler manifolds.
HOLOMORPHIC AND KILLING VECTOR FIELDS ON COMPACT BALANCED HERMITIAN MANIFOLDS
Authors: GANCHEV GEORGI , IVANOV STEFAN
Published: April 2003

We extend the classical theorems for nonexistence of Killing and holomorphic vector fields on compact Kähler manifolds to compact balanced Hermitian manifolds. We express the obstructions to the existence of Killing and holomorphic vector fields on compact balanced Hermitian manifolds in terms of the Ricci tensors of the Levi–Civita connection as well as in terms of the Ricci tensors of the Chern connection. We show that every affine vector field with respect to the Chern connection on a compact balanced Hermitian manifold is holomorphic.
ANALYTIC CONTINUATION OF VECTOR BUNDLES WITH Lp –CURVATURE
Authors: HARRIS ADAM , TONEGAWA YOSHIHIRO
Published: April 2003

This article addresses the problem of removable singularities for a Hermitian-holomorphic vector bundle ℰ, defined on the complement of an analytic set A of complex codimension at least two in a complex n-dimensional manifold X. In particular it is shown here that there exists a unique holomorphic bundle [Formula: see text] on X, such that [Formula: see text], when the curvature of ℰ belongs to Ln (X\A). This result is in fact sharp, as counterexamples exist for the extensibility of ℰ with curvature in Lp, p < n. Extension across general closed subsets of finite (2n - 4)-dimensional Hausdorff measure then follows directly from a slicing theorem of Bando and Siu.
GROTHENDIECK GROUP INVARIANTS FOR PARTLY SELF-ADJOINT OPERATOR ALGEBRAS
Authors: POWER S. C.
Published: April 2003

Partially ordered Grothendieck group invariants are introduced for general operator algebras and used in the classification of direct systems and direct limits of finite-dimensional complex incidence algebras with common reduced digraph H (systems of H-algebras). In particular the dimension distribution groupG (A; C), defined for an operator algebra A and a self-adjoint subalgebra C, generalizes both the K0 group of a σ-unital C*-algebra B and the spectrum (fundamental relation) R(A) of a regular limit A of triangular digraph algebras. This invariant is more economical and computable than the regular Grothendieck group [Formula: see text] which nevertheless forms the basis for a complete classification of regular systems of H-algebras.
TWO CLASSES OF HYPERBOLIC SURFACES IN ℙ3
Authors: SHIFFMAN BERNARD , ZAIDENBERG MIKHAIL
Published: April 2003

We construct two classes of singular Kobayashi hyperbolic surfaces in ℙ3. The first consists of generic projections of the Cartesian square V = C × C of a generic genus g ≥ 2 curve C smoothly embedded in ℙ5. These surfaces have C-hyperbolic normalizations; we give some lower bounds for their degrees and provide an example of degree 32. The second class of examples of hyperbolic surfaces in ℙ3 is provided by generic projections of the symmetric square V′ = C2 of a generic genus g ≥ 3 curve C. The minimal degree of these surfaces is 16, but this time the normalizations are not C-hyperbolic.
ON THE COMPLETE HYPERBOLICITY AND THE TAUTNESS OF THE HARTOGS DOMAINS
Authors: THAI DO DUC , DUC PHAM VIET
Published: April 2003

Let X be a complex space and φ a plurisubharmonic function on X. Consider the Hartogs domain Ωφ (X) given by [Formula: see text]. In this article, the necessary and sufficient conditions on the complete hyperbolicity and the tautness of the Hartogs domain Ωφ (X) are given.
ON A LOCAL ANALOGUE OF THE GROTHENDIECK CONJECTURE
Authors: ABRASHKIN VICTOR A.
Published: April 2003

We prove that the functor from the category of all complete discrete valuation fields with finite residue fields of characteristic ≠2 to the category of profinite filtered groups given by taking the Galois group of corresponding field together with its filtration by higher ramification subgroups is fully faithful. If [K; ℚp]<∞ we also study the opportunity to recover K from the knowledge of the filtered group ΓK(p)/ΓK(p)(a), where a>0, ΓK(p) is the absolute Galois group of the maximal p-extension of K and filtration is induced by ramification filtration.
IMPROVED FORMS OF SOME VANISHING THEOREMS IN RIEMANNIAN SPIN GEOMETRY
Authors: BRANSON THOMAS , HIJAZI OUSSAMA
Published: April 2003

We improve the hypotheses on some vanishing theorems for first order differential operators on bundles over a Riemannian spin manifold. The improved hypotheses are uniform, in the sense that they are the same for each of an infinite sequence of bundles in each even dimension. They are also elementary, in the sense that they involve only the bottom eigenvalue of the Yamabe operator on scalars, and the pointwise action of the Weyl conformal curvature tensor on two-forms. In particular, they do not make reference to the higher spin bundles on which the conclusion holds.
THE UNIVERSAL COVER OF AN AFFINE THREE-MANIFOLD WITH HOLONOMY OF SHRINKABLE DIMENSION ≤ TWO
Authors: CHOI SUHYOUNG
Published: April 2003

An affine manifold is a manifold with an affine structure, i.e. a torsion-free flat affine connection. We show that the universal cover of a closed affine 3-manifold M with holonomy group of shrinkable dimension (or discompacité in French) less than or equal to two is diffeomorphic to R3. Hence, M is irreducible. This follows from two results: (i) a simply connected affine 3-manifold which is 2-convex is diffeomorphic to R3, whose proof using the Morse theory takes most of this paper; and (ii) a closed affine manifold of holonomy of shrinkable dimension less or equal to d is d-convex. To prove (i), we show that 2-convexity is a geometric form of topological incompressibility of level sets. As a consequence, we show that the universal cover of a closed affine three-manifold with parallel volume form is diffeomorphic to R3, a part of the weak Markus conjecture. As applications, we show that the universal cover of a hyperbolic 3-manifold with cone-type singularity of arbitrarily assigned cone-angles along a link removed with the singular locus is diffeomorphic to R3. A fake cell has an affine structure as shown by Gromov. Such a cell must have a concave point at the boundary.
FACTORIALITY OF HARMONIC TRACES ON STRING ALGEBRAS
Authors: HAYASHI TOMOHIRO
Published: April 2003

A criterion for factoriality of harmonic traces on string algebras was given by S. Popa in a subfactor setting [9]. In this paper, we shall generalize the validity of the criterion to more general graphs. The proof is more elementally than in subfactors cases.
PLURICANONICAL SYSTEMS ON SURFACES WITH SMALL K2
Authors: LANGER ADRIAN
Published: April 2003

We prove that the bicanonical system of a surface of general type with K2=4 has no base components and we describe clusters contracted by 3KX and 4KX for regular surfaces with small [Formula: see text]. In particular, we answer the question when 3KX or 4KX define embeddings of a canonical surface.
BOUNDEDNESS OF NONBIRATIONAL EXTREMAL CONTRACTIONS
Authors: PROKHOROV YURI G.
Published: April 2003

We consider KX-negative extremal contractions f:x→(Z,o), where X is an algebraic threefold with only ε-log terminal ℚ-factorial singularities and (Z,o) is a two (respectively, one)-dimensional germ. The main result is that KX is 1, 2, 3, 4 or 6-complementary or we have, so-called, exceptional case and then the singularity (Z∈o) is bounded (respectively, the multiplicity of the central fiber f-1(o) is bounded).
ENERGY ESTIMATES AND LIOUVILLE THEOREMS FOR HARMONIC MAPS
Authors: RIGOLI MARCO , SETTI ALBERTO G.
Published: April 2003

We obtain lower and upper energy estimates for harmonic maps between Riemannian manifolds under natural curvature conditions leading to various Liouville-type theorems. Some of the methods described may also be applied to vanishing-type problems for vector bundle-valued harmonic forms.
CALABI–YAU THREEFOLDS WITH A CURVE OF SINGULARITIES AND COUNTEREXAMPLES TO THE TORELLI PROBLEM
Authors: SZENDRÖI BALÁZS
Published: April 2003

Birational Calabi–Yau threefolds in the same deformation family provide a "weak" counterexample to the global Torelli problem, as long as they are not isomorphic. In this paper, it is shown that deformations of certain desingularized weighted projective hypersurfaces provide examples of families containing birational varieties. The constructed examples are shown to be nonisomorphic using a specialization argument.
LOWER BOUNDS OF THE SLOPE OF FIBRED THREEFOLDS
Authors: BARJA MIGUEL A.
Published: April 2003

We study from a geographical point of view fibrations of threefolds over smooth curves f:T→B such that the general fibre is of general type. We prove the non-negativity of certain relative invariants under general hypotheses and give lower bounds for [Formula: see text] depending on other relative invariants. We also study the influence of the relative irregularity q(T)-g(B) on these bounds. A more detailed study of the lowest cases of the bounds is given.
THE HITCHIN–KOBAYASHI CORRESPONDENCE FOR TWISTED TRIPLES
Authors: BRADLOW STEVEN B. , KAMBER FRANZ W. , GLAZEBROOK JAMES F.
Published: April 2003

We introduce the twisted coupled vortex equations defined over a closed Kähler manifold X. There is an associated notion of stability for certain triples of holomorphic data on X. We establish a Hitchin–Kobayashi correspondence which relates the existence of solutions to these equations and the stability of a corresponding triple.
THE PLURICOMPLEX GREEN FUNCTION ON PSEUDOCONVEX DOMAINS WITH A SMOOTH BOUNDARY
Authors: HERBORT GREGOR
Published: April 2003

In this article we deal with the behavior of the pluricomplex Green function GD(·;w), of a pseudoconvex domain D in [Formula: see text], when the pole tends to a boundary point. In [7], it was shown that, given a boundary point w0 of a hyperconvex domain D, then there is a pluripolar set E⊂D, such that lim sup w→w0 GD(z;w)=0 for z∈D\E. Under an additional assumption on D, that can be viewed as natural, one can avoid the pluripolar exceptional set. Our main result is that on a bounded domain [Formula: see text] that admits a Hoelder continuous plurisubharmonic exhaustion function ρ:D→[-1,0), the pluricomplex Green function GD(·,w) tends to zero uniformly on compact subsets of D, if the pole w tends to a boundary point w0 of D.
KONTSEVICH'S UNIVERSAL FORMULA FOR DEFORMATION QUANTIZATION AND THE CAMPBELL–BAKER–HAUSDORFF FORMULA
Authors: KATHOTIA VINAY
Published: April 2003

We relate a universal formula for the deformation quantization of Poisson structures (⋆-products) on ℝd proposed by Maxim Kontsevich to the Campbell–Baker–Hausdorff (CBH) formula. We show that Kontsevich's formula can be viewed as exp (P) where P is a bi-differential operator that is a deformation of the given Poisson structure. For linear Poisson structures (duals of Lie algebras) his product takes the form exp (C+L) where exp (C) is the ⋆-product given by the universal enveloping algebra via symmetrization, essentially the CBH formula. This is established by showing that the two products are identical on duals of nilpotent Lie algebras where the operator L vanishes. This completely determines part of Kontsevich's formula and leads to a new scheme for computing the CBH formula. The main tool is a graphical analysis for bi-differential operators and the computation of certain iterated integrals that yield the Bernoulli numbers.
PROJECTIVE CONVEXITY IN ℙ3 IMPLIES GRASSMANN CONVEXITY
Authors: SHAPIRO B. , SHAPIRO M.
Published: April 2003

In this note we introduce the notion of Grassmann convexity analogous to the well-known notion of convexity for curves in real projective spaces. We show that the curve in G2,4 osculating to a convex closed curve in ℙ3 is Grassmann-convex. This proves that the tangent developable (i.e. the hypersurface formed by all tangents) of any convex curve in ℙ3 has the "degree" equal to 4. Here by "degree" of a real projective hypersurface we mean the maximal total multiplicity of its intersection with a line.
PLANE CURVES WITH SMALL LINEAR ORBITS II
Authors: ALUFFI PAOLO , FABER CAREL
Published: April 2003

The "linear orbit" of a plane curve of degree d is its orbit in ℙd(d+3)/2 under the natural action of PGL(3). We classify curves with positive dimensional stabilizer, and we compute the degree of the closure of the linear orbits of curves supported on unions of lines. Together with the results of [3], this encompasses the enumerative geometry of all plane curves with small linear orbit. This information will serve elsewhere as an ingredient in the computation of the degree of the orbit closure of an arbitrary plane curve.
POLES OF THE CURRENT |f|2λ OVER AN ISOLATED SINGULARITY
Authors: BARLET D. , MAIRE H.-M.
Published: April 2003

Let (X, 0) be the germ of a normal space of dimension n+1 with an isolated singularity at 0 and let f be a germ of holomorphic function with an isolated regularity at 0. We prove that the meromorphic extension of the current [Formula: see text] has a pole of order k at λ=-m-r for m∈ℕ large enough and r∈[0, 1[ if , and only if, e-2iπr is an eigenvalue with nilpotency order k of the monodromy of f acting on Hn(F)/J, where F is the Milnor fibre of f and J is the image of the restriction map Hn(X\{0})→Hn(F).
GEOMETRY OF THE MODULI OF HIGHER SPIN CURVES
Authors: JARVIS TYLER J.
Published: April 2003

This article treats various aspects of the geometry of the moduli [Formula: see text] of r-spin curves and its compactification [Formula: see text]. Generalized spin curves, or r-spin curves, are a natural generalization of 2-spin curves (algebraic curves with a theta-characteristic), and have been of interest lately because of the similarities between the intersection theory of these moduli spaces and that of the moduli of stable maps. In particular, these spaces are the subject of a remarkable conjecture of E. Witten relating their intersection theory to the Gelfand–Dikii (KdVr) heirarchy. There is also a W-algebra conjecture for these spaces [16] generalizing the Virasoro conjecture of quantum cohomology.

For any line bundle [Formula: see text] on the universal curve over the stack of stable curves, there is a smooth stack [Formula: see text] of triples (X, ℒ, b) of a smooth curve X, a line bundle ℒ on X, and an isomorphism [Formula: see text]. In the special case that [Formula: see text] is the relative dualizing sheaf, then [Formula: see text] is the stack [Formula: see text] of r-spin curves.

We construct a smooth compactification [Formula: see text] of the stack [Formula: see text], describe the geometric meaning of its points, and prove that its coarse moduli is projective.

We also prove that when r is odd and g>1, the compactified stack of spin curves [Formula: see text] and its coarse moduli space [Formula: see text] are irreducible, and when r is even and [Formula: see text] is the disjoint union of two irreducible components. We give similar results for n-pointed spin curves, as required for Witten's conjecture, and also generalize to the n-pointed case the classical fact that when [Formula: see text] is the disjoint union of d(r) components, where d(r) is the number of positive divisors of r. These irreducibility properties are important in the study of the Picard group of [Formula: see text] [15], and also in the study of the cohomological field theory related to Witten's conjecture [16, 34].
QUANTUM HOMOLOGY OF FIBRATIONS OVER S2
Authors: MCDUFF DUSA J.
Published: April 2003

This paper studies the (small) quantum homology and cohomology of fibrations p:P→S2 whose structural group is the group of Hamiltonian symplectomorphisms of the fiber (M, ω). It gives a proof that the rational cohomology splits additively as the vector space tensor product H*(M)⊗H*(S2), and investigates conditions under which the ring structure also splits, thus generalizing work of Lalonde–McDuff–Polterovich and Seidel. The main tool is a study of certain operations in the quantum homology of the total space P and of the fiber M, whose properties reflect the relations between the Gromov–Witten invariants of P and M. In order to establish these properties we further develop the language introduced in [22] to describe the virtual moduli cycle (defined by Liu–Tian, Fukaya–Ono, Li–Tian, Ruan and Siebert).
HARTOGS-TYPE EXTENSION THEOREMS FOR SEPARATELY HOLOMORPHIC MAPPINGS ON COMPACT SETS
Authors: THAI DO DUC , MAI NGUYEN THI TUYET
Published: April 2003

We give several Hartogs-type extension theorems for separately holomorphic mappings on compact sets into complex spaces which either have the Hartogs extension property or are weakly Brody hyperbolic. Moreover, a characterization for the Hartogs extension property of holomorphically convex Kähler complex spaces by separate analyticity is given.
NONEMPTINESS OF BRILL–NOETHER LOCI
Authors: BRAMBILA-PAZ L. , MERCAT V. , NEWSTEAD P. E. , ONGAY F.
Published: April 2003

Let X be a non-singular algebraic curve of genus g. We prove that the Brill–Noether locus [Formula: see text] is non-empty if d=nd′+d′′ with 0<d′′< 2n, 1≤s≤g, d′≥(s-1)(s+g)/s, n≤d′′+(n-k)g, (d′′,k) ≠(n, n). These results hold for an arbitrary curve of genus ≥ 2, and allow us to construct a region in the associated "Brill–Noether (μ, λ)-map" of points for which the Brill–Noether loci are non-empty. Even for the generic case, the region so constructed extends beyond that defined by the so-called "Teixidor parallelograms". For hyperelliptic curves, the same methods give more extensive and precise results.
TOWARD A CLASSIFICATION OF ALMOST HOMOGENEOUS MANIFOLDS III — SL(2)×C* ACTIONS
Authors: GUAN ZHUANG-DAN DANIEL
Published: April 2003

In this paper we finished the classification of SL(2, C)×Gm almost homogeneous projective 3-folds which we started in [8, 9]. For some technical reasons we leave the proofs of Propositions 1.2 and 1.3 to [8] and that of Propositon 2.7 to [9]. But we include all other proofs, especially those of Propositions 2.1 and 2.2 in this paper and try to give an intuitive picture of the process. The proofs of Lemmas 2.1 and 2.2 as well as those of Sec. 3 (Theorems 3.1–3.4) are the main results of this paper.

Most of this work was done in the fall of 1991. I thank those who had tried their best to understand my proofs, for their helpful comments and criticisms.
ON WłODARCZYK'S EMBEDDING THEOREM
Authors: HAUSEN JÜRGEN
Published: April 2003

We prove the following version of Włodarczyk's Embedding Theorem: Every normal complex algebraic [Formula: see text]-variety Y admits an equivariant closed embedding into a toric prevariety X on which [Formula: see text] acts as a one-parameter-subgroup of the big torus T⊂X. If Y is ℚ-factorial, then X may be chosen to be simplicial and of affine intersection.
HERMITIAN METRIC WITH CONSTANT HOLOMORPHIC SECTIONAL CURVATURE ON CONVEX DOMAINS
Authors: CHEUNG WING SUM , WONG BUN
Published: April 2003

Let D be a bounded convex domain in [Formula: see text] with a Hermitian metric [Formula: see text] of constant negative holomorphic sectional curvature such that all components [Formula: see text] blow up to infinity on the boundary of D. Then D is biholomorphic to the Euclidean ball.
FANO MANIFOLDS WITH GEOMETRIC STRUCTURES MODELED AFTER HOMOGENEOUS CONTACT MANIFOLDS
Authors: HONG JAEHYUN
Published: April 2003

In this paper we present a study on geometric structures modeled after homogeneous contact manifolds and show that on Fano manifolds these geometric structures are locally isomorphic to the standard geometric structures on the model spaces. This conclusion is analogous to those of [13, 7]. We expect that this work will help prove the conjecture that a compact quaternionic Kähler manifold of positive scalar curvature is a quaternionic symmetric space [21].
ON -K2 FOR NORMAL SURFACE SINGULARITIES II
Authors: CHEN HAO , ISHII SHIHOKO
Published: April 2003

In this paper we continue our study [1] of the set of nonzero -K2 of normal surface singularities. The main results are (1) Every accumulation point of the set is the sum of -K2 of several normal surface singularities; (2) There are accumulation points of the set which are not -K2 of any one normal surface singularity, which means that the set {-K2} is not closed.
ABELIAN FIBRATIONS AND RATIONAL POINTS ON SYMMETRIC PRODUCTS
Authors: HASSETT BRENDAN , TSCHINKEL YURI
Published: April 2003

Given a variety over a number field, are its rational points potentially dense, i.e. does there exist a finite extension over which rational points are Zariski dense? We study the question of potential density for symmetric products of surfaces. Contrary to the situation for curves, rational points are not necessarily potentially dense on a sufficiently high symmetric product. Our main result is that rational points are potentially dense for the Nth symmetric product of a K3 surface, where N is explicitly determined by the geometry of the surface. The basic construction is that for some N, the Nth symmetric power of a K3 surface is birational to an Abelian fibration over ℙN. It is an interesting geometric problem to find the smallest N with this property.
A CLASS OF HARMONIC SUBMERSIONS AND MINIMAL SUBMANIFOLDS
Authors: APRODU MONICA ALICE , APRODU MARIAN , BRÎNZĂNESCU VASILE
Published: April 2003

We introduce the class of pseudo-horizontally homothetic maps from a Riemann manifold to a Kähler manifold, and we study some of their properties. For example, we prove that a pseudo-horizontally homothetic submersion is harmonic if and only if it has minimal fibres, and a pseudo-horizontally homothetic harmonic submersion pulls back complex submanifolds into minimal submanifolds.
ON MATRIX QUANTUM GROUPS OF TYPE An
Authors: PHUNG HO Hai
Published: April 2003

Given a Hecke symmetry R, one can define a matrix bialgebra ER and a matrix Hopf algebra HR, which are called function rings on the matrix quantum semi-group and matrix quantum groups associated to R. We show that for an even Hecke symmetry, the rational representations of the corresponding quantum group are absolutely reducible and that the fusion coefficients of simple representations depend only on the rank of the Hecke symmetry. Further we compute the quantum rank of simple representations. We also show that the quantum semi-group is "Zariski" dense in the quantum group. Finally we give a formula for the integral.
A MINIMAX SELECTOR FOR A CLASS OF HAMILTONIANS ON COTANGENT BUNDLES
Authors: ITURRIAGA RENATO , SÁNCHEZ-MORGADO HÉCTOR
Published: April 2003

We construct a minimax selector for eventually quadratic Hamiltonians on cotangent bundles. We use it to give a relation between Hofer's energy and Mather's action minimizing function. We also study the local flatness of the set of twist maps.
CONTINUOUS–TRACEC*-ALGEBRAS NOT ISOMORPHIC TO THEIR OPPOSITE ALGEBRAS
Authors: PHILLIPS N. CHRISTOPHER
Published: April 2003

We give examples of locally trivial continuous-trace C *-algebra not isomorphic to their opposite algebras. Our examples include a unital C *-algebra which is both stably isomorphic to and homotopy equivalent to its opposite algebra, a unital C *-algebra which is homotopy equivalent to but not stably isomorphic to its opposite algebra, and a unital C *-algebra which is not even stably homotopy equivalent to its opposite algebra.
GEOMETRY OF THE MODULI SPACES OF HARMONIC MAPS INTO LIE GROUPS VIA GAUGE THEORY OVER RIEMANN SURFACES
Authors: MUKAI-HIDANO MARIKO , OHNITA YOSHIHIRO
Published: April 2003

This paper aims to investigate the geometry of the moduli spaces of harmonic maps of compact Riemann surfaces into compact Lie groups or compact symmetric spaces. The approach here is to study the gauge theoretic equations for such harmonic maps and the moduli space of their solutions. We discuss the S1-action, the hyper-presymplectic structure, the energy function, the Hitchin map, the flag transforms on the moduli space, several kinds of subspaces in the moduli space, and the relationship among them, especially the structure of the critical point subset for the energy function on the moduli space. As results, we show that every uniton solution is a critical point of the energy function on the moduli space, and moreover we give a characterization of the fixed point subset fixed by S1-action in terms of a flag transform.
LOCALLY COMPACT QUANTUM GROUPS IN THE UNIVERSAL SETTING
Authors: KUSTERMANS JOHAN
Published: April 2003

In this paper we associate to every reduced C *-algebraic quantum group (A, Δ) (as defined in [11]) a universal C *-algebraic quantum group (Au, Δu). We fine tune a proof of Kirchberg to show that every *-representation of a modified L 1-space is generated by a unitary corepresentation. By taking the universal enveloping C *-algebra of a dense sub *-algebra of A we arrive at the C *-algebra Au. We show that this C *-algebra Au carries a quantum group structure which is a rich as its reduced companion. We also establish a bijective correspondence between quantum group morphisms and certain co-actions.
GEOMETRIC REALIZATION AND K-THEORETIC DECOMPOSITION OF C*-ALGEBRAS
Authors: SCHOCHET C. L.
Published: April 2003

Suppose that A is a separable C*-algebra and that G* is a (graded) subgroup of the ℤ/2-graded group K*(A). Then there is a natural short exact sequence [Formula: see text] In this note we demonstrate how to geometrically realize this sequence at the level of C*-algebras. We KK-theoretically decompose A as [Formula: see text] where K*(At) is the torsion subgroup of K*(A) and K*(Af) is its torsionfree quotient. Then we further decompose At: it is KK-equivalent to ⊕p Ap where K*(Ap) is the p-primary subgroup of the torsion subgroup of K*(A). We then apply this realization to study the Kasparov group K*(A) and related objects.
REMARKS ON THE SIMILARITY DEGREE OF AN OPERATOR ALGEBRA
Authors: PISIER GILLES
Published: April 2003

The "similarity degree" of a unital operator algebra A was defined and studied in two recent papers of ours, where in particular we showed that it coincides with the "length" of an operator algebra. This paper brings several complements: we give direct proofs (with slight improvements) of several known facts on the length which were only known via the degree, and we show that the length of a type II1 factor with property Γ is at most 5, improving on a previous bound (≤ 44) due to E. Christensen.
QUANTUM 'az + b' GROUP ON COMPLEX PLANE
Authors: WORONOWICZ S. L.
Published: April 2003

'az + b' is the group of affine transformations of complex plane [Formula: see text]. The coefficients a, [Formula: see text]. In quantum version a, b are normal operators such that ab = q2ba, where q is the deformation parameter. We shall assume that q is a root of unity, more precisely [Formula: see text], where N is an even natural number. To construct the group we write an explicit formula for the Kac Takesaki operator W. It is shown that W is a manageable multiplicative unitary in the sense of [3, 18]. Then using the general theory we construct a C *-algebra A and a comultiplication Δ ∈ Mor (A, A ⊗ A). A should be interpreted as the algebra of all continuous functions vanishing at infinity on quantum 'az + b'-group. The group structure is encoded by Δ. The existence of coinverse also follows from the general theory [18]. In the appendix, we briefly discuss the case of real q.
APPROXIMATION PROPERTIES FOR CROSSED PRODUCTS BY ACTIONS AND COACTIONS
Authors: NILSEN MAY M. , SMITH ROGER R.
Published: April 2003

We investigate approximation properties for C*-algebras and their crossed products by actions and coactions by locally compact groups. We show that Haagerup's approximation constant is preserved for crossed products by arbitrary amenable groups, and we show why this is not always true in the non-amenable case. We also examine similar questions for other forms of the approximation property.
HARDER–NARASIMHAN FILTRATION ON NON KÄHLER MANIFOLDS
Authors: BRUASSE LAURENT
Published: April 2003

In this paper we are interested in the behavior of the degree map on holomorphic bundles over compact complex manifolds. We do not assume the manifold to be Kähler and we define the degree by means of a Gauduchon metric. We show that the degree is bounded above over all coherent subsheaves of a vector bundle and that the supremum is reached. Then we prove the existence of the Harder–Narasimhan filtration in this general context.