Ulf Persson

Configurations of Kodaira fibers on rational elliptic surfaces.

I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l Legend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 The list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 I. D i s c r i m i n a n t cons ide ra t i ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 If. Po l a r s of p lane curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 IlI. In t r ins ic g e o m e t r y on g e n u s two curves . . . . . . . . . . . . . . . . . . . . . . . 19 IV. Ell iptic qua r t i c s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 V. R a t i o n a l qua r t i c s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 The reduc ib le case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 To r s ion g r o u p s of ra t iona l elliptic surfaces . . . . . . . . . . . . . . . . . . . . . . . 43 Epi logue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Temperature and pressure dependence of NH 3 and C 2 H 4 absorption cross sections at CO 2 laser wavelengths

Absorption cross sections at CO(2) laser wavelengths have been measured for ethylene and ammonia. The dependence of the cross sections on pressure and temperature have been investigated for pressures and temperatures normally occurring in the atmosphere. The changes in cross section are, e.g., 5% for ethylene at the P(14) 00 degrees 1-10 degrees 0 line and 10% for ammonia at the R(8) 00 degrees 1-10 degrees 0 line for a temperature change of 30 K. A comparison with theoretical calculations is made for ammonia.

Differential reflectance of natural and man-made materials at CO 2 laser wavelengths

The differential reflectance of several naturally occurring and man-made materials at CO(2) laser wavelengths is determined. The computer-controlled measurement system has two CO(2) lasers and determines the differential reflectance of each material by measuring the ratio of the reflected signals at two wavelengths simultaneously. These results can be used to improve the accuracy of air pollution measurement systems which derive their return signals from topographic targets.

Geography of spin surfaces

due to Noether’s inequality (the left-most inequality) and the Bogomolov-Miyaoka-Yau inequality (the right-most inequality). See [l] for details. It is generally believed that those are the only restrictions, i.e. “all invariants can occur”. Evidence for this conjecture was supplied by [12] where it was essentially shown that all invar~ants with negative index (i.e. c: ,< 8~) can occur, and work by Chen [4,5] essentially did the same for the harder case of positive index. In fact a few gaps still remain, but those are mainly due to technical reasons and do not reflect anything intrinsic. The combined result reads as follows:

Analysis of errors caused by optical interference effects in wavelength-diverse CO2 laser long-path systems.

The measurement errors in a CO2 laser differential absorption system caused by optical interference effects are analyzed. Major sources of errors are identified and design suggestions to improve the system accuracy are made. The effects of temperature changes, short measurement paths, and spectral features of the measured species are taken into account.

Air pollution monitoring with a Q-switched CO 2 -laser lidar using heterodyne detection

A differential absorption lidar (DIAL) using a Q-switched CO(2) laser and a heterodyne receiver has been developed. The DIAL system is highly automated with computer-controlled laser-line selection and signal processing. The transmitter operates at a pulse-repetition frequency of 20 kHz and has an average output power of 1.8 W. A wideband HgCdTe detector is used together with a high speed adding buffer to detect the return signals. The system has been used in a field experiment to monitor ethylene emission from a petrochemical factory.

Surfaces with triple points

In this paper we compute upper bounds for the number of ordinary triple points on a hypersurface in

Computer-automated CO2-laser long-path absorption system for air quality monitoring in the working environment.

P^3

Ethylene mass flow measurements with an automatic CO 2 laser long-path absorption system

and give a complete classification for degree six (degree four or less is trivial, and five is elementary). But the real purpose is to point out the intricate geometry of examples with many triple points, and how it fits with the general classification of surfaces.

Bounded Cognitive Resources and Arbitrary Domains

A compact computer-controlled CO2-laser long-path absorption system has been developed. It is specifically designed to monitor gaseous pollutants in the working environment. The instrument uses a closed-cycle cooling system for the lasers and operates with room-temperature pyroelectric detectors. The high degree of automation and the compact design make the system easy to use. It has been used to measure several different species such as ammonia and methyl ethyl ketone in various industrial environments.