frank wagner

We present an algorithm for finding the minimum cut of an undirected edge-weighted graph. It is s... more We present an algorithm for finding the minimum cut of an undirected edge-weighted graph. It is simple in every respect. It has a short and compact description, is easy to implement, and has a surprisingly simple proof of correctness. Its runtime matches that of the fastest algorithm known. The runtime analysis is straightforward. In contrast to nearly all approaches so far, the algorithm uses no flow techniques. Roughly speaking, the algorithm consists of about ͉V͉ nearly identical phases each of which is a maximum adjacency search.

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Supersimple theories

A simple min-cut algorithm

Journal of The ACM, 1997

We present an algorithm for finding the minimum cut of an undirected edge-weighted graph. It is s... more We present an algorithm for finding the minimum cut of an undirected edge-weighted graph. It is simple in every respect. It has a short and compact description, is easy to implement, and has a surprisingly simple proof of correctness. Its runtime matches that of the fastest algorithm known. The runtime analysis is straightforward. In contrast to nearly all approaches so far, the algorithm uses no flow techniques. Roughly speaking, the algorithm consists of about ͉V͉ nearly identical phases each of which is a maximum adjacency search.

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Modeling Hypergraphs by Graphs with the Same Mincut Properties

Information Processing Letters, 1993

Abstract An elegant and general way to apply graph partitioning algorithms to hypergraphs would b... more

Correction Method for RS80-A Humicap Humidity Profiles and Their Validation by Lidar Backscattering Profiles in Tropical Cirrus Clouds

Journal of Atmospheric and Oceanic Technology, 2005

... The model of RS80-A humidity sensor response given by Eqs ... 5. Validation of RS80-A Humicap... more

One-year observations of particle lidar ratio over the tropical Indian Ocean with Raman lidar

Geophysical Research Letters, 2001

Observations of the extinction-to-backscatter ratio (lidar ratio) of South and Southeast Asian ae... more Observations of the extinction-to-backscatter ratio (lidar ratio) of South and Southeast Asian aerosol particles are presented for the wavelength of 532 nm. Raman lidar measurements were performed in the Maldives (4.1 • N, 73.3 • E) in the framework of the Indian Ocean Experiment (INDOEX) in 1999/2000. These observations in the tropics are an important contribution to a growing global lidarratio climatology which is needed for an improved determination of the particle optical depth with ground-based and spaceborne lidars. The lidar ratio was found to be a useful quantity to trace back different pollution sources and to identify less and considerably light-absorbing particles. During the winter/spring seasons heavily polluted air from India and Southeast Asia was advected to the lidar site. Under these conditions lidar ratios up to 110 sr were observed in the lofted pollution plumes above 1000 m height. According to backward trajectories the highest lidar ratios were found for airmasses which crossed the eastern and northeastern parts of India. Large lidar ratios >70 sr indicate small, considerably absorbing aerosol particles. Below 1000 m height, the lidar ratio typically ranged from 30-60 sr. The marine boundary layer contained a mixture of marine and anthropogenic particles. Under clean, marine conditions in October 1999, lidar ratios <30 sr were found.

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European pollution outbreaks during ACE 2: Lofted aerosol plumes observed with Raman lidar at the Portuguese coast

Journal of Geophysical Research, 2001

During the Second Aerosol Characterization Experiment (ACE 2) in the summer of 1997, four polluti... more During the Second Aerosol Characterization Experiment (ACE 2) in the summer of 1997, four pollution outbreaks from the European continent were monitored at Sagres (37°N, 9°W), Portugal, by applying the Raman lidar technique at a wavelength of 532 nm. The findings are presented in terms of vertical profiles of the volume extinction coefficient of the particles, the backscatter coefficient, the extinction-to-backscatter ratio (lidar ratio), the relative humidity, and the geometrical and optical depths of the marine boundary layer and the continental aerosol layers aloft. The lidar-derived optical depths are compared with results of simultaneously conducted star photometer observations. During all outbreaks, similar aerosol profiles were observed. Above the cold marine boundary layer the warm continental pollution plume extended from about 500 to a maximum height of 3500 m. Strong temperature inversions prohibited mixing of the two layers. The ACE 2 mean optical depths of the marine boundary layer and the aerosol layers aloft were about 0.05 and 0.1, respectively. Maximum values of the optical depth in the pollution plumes were close to 0.25 at 532 nm. On average, the free-tropospheric layers contributed about 60% to the total optical depth at the coast. Volume extinction coefficients were mainly between 30 and 70 Mm-1, and the lidar ratios ranged from 30 to 80 sr in the polluted continental air.

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Vertical profiling of the Indian aerosol plume with six-wavelength lidar during INDOEX: A first case study

Geophysical Research Letters, 2000

During the Intensive Field Phase (IFP) of the Indian Ocean Experiment (INDOEX) lasting from 15 Fe... more During the Intensive Field Phase (IFP) of the Indian Ocean Experiment (INDOEX) lasting from 15 February to 26 March 1999, a large number of pollution outbreaks from India and southeast Asia were observed with a unique six-wavelength aerosol lidar at Maldives International Airport, Hulule (4.1°N, 73.3°E). An example is presented here. Above the polluted marine boundary layer a 3-km deep aerosol layer was advected from the Indian subcontinent. The aerosol optical depths of the marine boundary layer and the free-troposphere layer were approximately 0.2 and 0.4 at 532 nm, respectively. Inversions using spectrally resolved particle backscatter and extinction data indicate an effective particle radius of 0.17 µm, volume and surface concentrations around 13 µm³ cm-3 and 600 µm² cm-3, respectively, and considerable absorption by the free-tropospheric particles.

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Vertical profiling of optical and physical particle properties over the tropical Indian Ocean with six-wavelength lidar 2. Case studies

Journal of Geophysical Research, 2001

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European pollution outbreaks during ACE 2: Optical particle properties inferred from multiwavelength lidar and star-Sun photometry

Journal of Geophysical Research, 2002

1] On the basis of multiwavelength backscatter and 532-nm extinction profiling with lidar at Sagr... more 1] On the basis of multiwavelength backscatter and 532-nm extinction profiling with lidar at Sagres (37°N, 9°W), southern Portugal, and optical depth observations with a star photometer at the lidar site and a Sun photometer atop a nearby mountain, several European pollution outbreaks were characterized during the Second Aerosol Characterization Experiment (ACE 2) in the summer of 1997. A sophisticated analysis scheme applied to the lidar-photometer data set is described. The observations are mainly presented in terms of profiles of the 532-nm extinction-to-backscatter ratio (lidar ratio) and of Å ngström exponents calculated for the wavelength ranges 400-532 nm and 532-800 nm. The lidar ratio indicates the aerosol type (marine, soil, pollution) whereas the Å ngström exponents are sensitive to changes in the particle size distribution (accumulation mode, coarse mode). Results of an extensive correlation analysis considering all determined optical parameters, relative humidity, and measurement height are discussed. Finally, the spectrally resolved optical depth and the column Å ngström exponents for the lofted outbreak plumes determined from the lidar profiles are compared with respective values derived from the star and Sun photometer measurements.

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Optical properties of the Indo-Asian haze layer over the tropical Indian Ocean

Journal of Geophysical Research, 2003

1] Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman... more 1] Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4°N, 73°E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532-nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000-m height. On average, the freetropospheric aerosol layers contributed 30-60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm À1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction-to-backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50-80 sr for highly absorbing particles from northern India. The shift of the lidar-ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent with an aerosol black-carbon content of up to 20%. The Å ngström exponent (for short wavelengths 355/400/532 nm) ranged mostly from 1 to 1.6 for Southeast Asian particles, from 0.8 to 1.4 for North Indian pollution, and from 0.6 to 1 for South Indian air masses. The comparably low Indian Å ngström exponents (indicating a comparably large mean particle radius) are possibly caused by the high contribution of biomass combustion to the aerosol formation in India. Results of a correlation analysis based on the lidar ratio, extinction coefficient, Å ngström exponents, and relative humidity are presented. In most cases only a weak relationship or no relationship was found between the different parameters.

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Vertical profiling of optical and physical particle properties over the tropical Indian Ocean with six-wavelength lidar 1. Seasonal cycle

Journal of Geophysical Research, 2001

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