State Transformations and Ice Nucleation in Amorphous (Semi-) Solid Organic Aerosol

Amorphous (semi-)solid organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy have been used in conjunction with a cold stage to examine water uptake and ice nucleation on individual amorphous (semi-)solid particles at atmospherically relevant temperatures (200–273 K). Three organic compounds considered proxies for atmospheric secondary organic aerosol (SOA) were used in this investigation: sucrose, citric acid and glucose. Internally mixed particles consisting of each organic and ammonium sulfate were also investigated. Results from water uptake experiments followed the shape of a humidity-induced glass transition (Tg(RH)) curve and were used to construct state diagrams for each organic and corresponding mixture. Experimentally derived Tg(RH) curves are in good agreement with theoretical predictions of Tg(RH) following the approach of Koop et al. (2011). A unique humidity-induced glass transition point on each state diagram, Tg\u27(RH), was used to quantify and compare results from this study to previous works. Values of Tg\u27(RH) determined for sucrose, glucose and citric acid glasses were 236, 230 and 220 K, respectively. Values of Tg\u27(RH) for internally mixed organic/sulfate particles were always significantly lower; 210, 207 and 215 K for sucrose/sulfate, glucose/sulfate and citric acid/sulfate, respectively. All investigated SOA proxies were observed to act as heterogeneous ice nuclei at tropospheric temperatures. Heterogeneous ice nucleation on pure organic particles occurred at Sice = 1.1–1.4 for temperatures below 235 K. Particles consisting of 1:1 organic-sulfate mixtures took up water over a greater range of conditions but were in some cases also observed to heterogeneously nucleate ice at temperatures below 202 K (Sice= 1.25–1.38). Polynomial curves were fitted to experimental water uptake data and then incorporated into the Community Aerosol Radiation Model for Atmospheres (CARMA) along with the predicted range of humidity-induced glass transition temperatures for atmospheric SOA from Koop et al. (2011). Model results suggest that organic and organic/sulfate aerosol could be glassy more than 60% of the time in the midlatitude upper troposphere and more than 40% of the time in the tropical tropopause region (TTL). At conditions favorable for ice formation (Sice \u3e 1), particles in the TTL are expected to be glassy more than 50% of the time for temperatures below 200 K. Results from this study suggests that amorphous (semi-)solid organic particles are often present in the upper troposphere and that heterogeneous ice formation on this type of particle may play an important role in cirrus cloud formation

The Longitudinal Polarimeter at HERA

The design, construction and operation of a Compton back-scattering laser polarimeter at the HERA storage ring at DESY are described. The device measures the longitudinal polarization of the electron beam between the spin rotators at the HERMES experiment with a fractional systematic uncertainty of 1.6%. A measurement of the beam polarization to an absolute statistical precision of 0.01 requires typically one minute when the device is operated in the multi-photon mode. The polarimeter also measures the polarization of each individual electron bunch to an absolute statistical precision of 0.06 in approximately five minutes. It was found that colliding and non-colliding bunches can have substantially different polarizations. This information is important to the collider experiments H1 and ZEUS for their future longitudinally polarized electron program because those experiments use the colliding bunches only.Comment: 21 pages (Latex), 14 figures (EPS

Integration von Telelearning- und Teleworking-Applikationen

Aus der Kurzfassung: 'Ca. 5 % der deutschen Arbeitnehmer gehören zu einer der weltweit am rasantesten wachsenden Berufsgruppen: den Telearbeitern. Rund elf Millionen Amerikaner arbeiten bereits regelmäßig daheim - Tendenz steigend. Europa ist vergleichsweise rückständig, doch soll es in Deutschland bis zur Jahrtausendwende schon 800.000 Teleworker geben. [9] Damit diese Arbeitsform ihr Produktivitätspotential ganz entfaltet, gilt es jedoch, Teleworker ausreichend auf ihr neues Arbeitsumfeld und die neue Technik vorzubereiten

Integration von Telelearning- und Teleworking-Applikationen

Aus der Kurzfassung: 'Ca. 5 % der deutschen Arbeitnehmer gehören zu einer der weltweit am rasantesten wachsenden Berufsgruppen: den Telearbeitern. Rund elf Millionen Amerikaner arbeiten bereits regelmäßig daheim - Tendenz steigend. Europa ist vergleichsweise rückständig, doch soll es in Deutschland bis zur Jahrtausendwende schon 800.000 Teleworker geben. [9] Damit diese Arbeitsform ihr Produktivitätspotential ganz entfaltet, gilt es jedoch, Teleworker ausreichend auf ihr neues Arbeitsumfeld und die neue Technik vorzubereiten

From local watershed management to integrated river basin management at national and transboundary levels

Watersheds face a range of degradation challenges associated with human activities, such as pollution, deforestation and changes in sediment generation. The way they are managed has a profound cascading effect on natural resources and communities in the wider basin. Although watersheds play a critical role as the basic hydrological unit within a river basin they are often neglected in river basin management. Over the past decade, principles and practices have evolved to ensure that integrated water resources management (IWRM) approaches used at the broader basin level to address sustainable development and management of land and water resources also apply at the smaller watershed level. This technical report is a synthesis of the knowledge, lessons learned and good practices presented and discussed at the International Conference on Watershed Management held in Chiang Mai, Thailand 9-11 March 2011