Warm air in combination with frozen soil is a major cause of wintertime drought damage in evergreen plants in subalpine and boreal environments. We analyzed diurnal tree stem diameter variation ...(SDV), which reflects soil water uptake, canopy-level water vapor flux (F(w)), stand photosynthesis (P(s)), photosynthetically active radiation (PAR), soil and air temperatures (T(s) and T(air), respectively) and soil liquid water content (theta) to determine under what conditions photosynthesis is possible in wintertime and how crucial water uptake from soil is for photosynthesis. Measurements were made under field conditions in a Scots pine forest in southern Finland during winter 2002-2003. We found four wintertime periods when there was measurable P(s) and SDV, the latter always starting 2-7 days after photosynthesis and both usually ending on the same day. Stand photosynthesis began when T(air) reached 3-4 degrees C and ended when T(air) dropped below -7 degrees C. The trees appeared to rely on stored stem water first and started taking up water from the soil a few days later, when the transpirational demand became strong enough. The more difficult it was to access soil water because of low T(s) or low theta, the longer the trees used water stored in their stems. Even partial stem freezing did not prevent photosynthesis or soil water uptake.
New insights into nocturnal nucleation Ortega, I. K; Suni, T; Boy, M ...
Atmospheric chemistry and physics,
05/2012, Letnik:
12, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Formation of new aerosol particles by nucleation and growth is a significant source of aerosols in the atmosphere. New particle formation events usually take place during daytime, but in some ...locations they have been observed also at night. In the present study we have combined chamber experiments, quantum chemical calculations and aerosol dynamics models to study nocturnal new particle formation. All our approaches demonstrate, in a consistent manner, that the oxidation products of monoterpenes play an important role in nocturnal nucleation events. By varying the conditions in our chamber experiments, we were able to reproduce the very different types of nocturnal events observed earlier in the atmosphere. The exact strength, duration and shape of the events appears to be sensitive to the type and concentration of reacting monoterpenes, as well as the extent to which the monoterpenes are exposed to ozone and potentially other atmospheric oxidants.
Thinning is a routine forest management operation that changes tree spacing, number, and size distribution and affects the material flows between vegetation and the atmosphere. Here, using direct ...micrometeorological ecosystem‐scale measurements, we show that in a boreal pine forest, thinning decreases the deposition velocities of fine particles as expected but does not reduce the carbon sink, water vapor flux, or ozone deposition. The thinning decreased the all‐sided leaf area index from 8 to 6, and we suggest that the redistribution of sources and sinks within the ecosystem compensated for this reduction in foliage area. In the case of water vapor and O3, changes in light penetration and among‐tree competition seem to increase individual transpiration rates and lead to larger stomatal apertures, thus enhancing also O3 deposition. In the case of CO2, increased ground vegetation assimilation and decreased autotrophic respiration seem to cancel out opposite changes in canopy assimilation and heterotrophic respiration. Current soil‐vegetation‐atmosphere transfer models should be able to reproduce these observations.
The integrated land ecosystem-atmosphere processes study (iLEAPS) is an international research project focussing on the fundamental processes that link land-atmosphere exchange, climate, the water ...cycle, and tropospheric chemistry. The project, iLEAPS, was established 2004 within the International Geosphere-Biosphere Programme (IGBP). During its first decade, iLEAPS has proven to be a vital project, well equipped to build a community to address the challenges involved in understanding the complex Earth system: multidisciplinary, integrative approaches for both observations and modeling. The iLEAPS community has made major advances in process understanding, land-surface modeling, and observation techniques and networks. The modes of iLEAPS operation include elucidating specific iLEAPS scientific questions through networks of process studies, field campaigns, modeling, long-term integrated field studies, international interdisciplinary mega-campaigns, synthesis studies, databases, as well as conferences on specific scientific questions and synthesis meetings. Another essential component of iLEAPS is knowledge transfer and it also encourages community- and policy-related outreach activities associated with the regional integrative projects. As a result of its first decade of work, iLEAPS is now setting the agenda for its next phase (2014–2024) under the new international initiative, future Earth. Human influence has always been an important part of land-atmosphere science but in order to respond to the new challenges of global sustainability, closer ties with social science and economics groups will be necessary to produce realistic estimates of land use and anthropogenic emissions by analysing future population increase, migration patterns, food production allocation, land management practices, energy production, industrial development, and urbanization.
Hermetic packaging is often an essential requirement to enable proper functionality throughout the device’s lifetime and ensure the optimal performance of a micro electronic mechanical system (MEMS) ...device. Solid-liquid interdiffusion (SLID) bonding is a novel and attractive way to encapsulate MEMS devices at a wafer level. SLID bonding utilizes a low-melting-point metal to reduce the bonding process temperature; and metallic seal rings take out less of the valuable surface area and have a lower gas permeability compared to polymer or glass-based sealing materials. In addition, ductile metals can adopt mechanical and thermo-mechanical stresses during their service lifetime, which improves their reliability. In this study, the principles of Au-Sn and Cu-Sn SLID bonding are presented, which are meant to be used for wafer-level hermetic sealing of MEMS resonators. Seal rings in 15.24 cm silicon wafers were bonded at a width of 60 μm, electroplated, and used with Au-Sn and Cu-Sn layer structures. The wafer bonding temperature varied between 300 °C and 350 °C, and the bonding force was 3.5 kN under the ambient pressure, that is, it was less than 0.1 Pa. A shear test was used to compare the mechanical properties of the interconnections between both material systems. In addition, important factors pertaining to bond ring design are discussed according to their effects on the failure mechanisms. The results show that the design of metal structures can significantly affect the reliability of bond rings.
Atomic layer deposition (ALD) can be used to grow pinhole-free nanometer-thin conformal inorganic films at low temperatures, making it of interest for many applications in MEMS ...(microelectromechanical systems). Stiction during device operation remains one of the mechanisms leading to permanent failure of operating silicon-based MEMS. This work investigated whether stiction in MEMS could be decreased by applying rough thin inorganic ALD films. Test structures based on the cantilever-beam-array (CBA) method were fabricated and coated with 2–50nm thick ALD layers varying in chemical nature and roughness: Al2O3, TiO2, MoN and Ta(Al)N. Smooth ALD films (AFM rms roughness below or equal to ca. 0.5nm) were not observed to decrease stiction markedly. Crystalline films with roughness in the nanometer range (AFM rms ca. 1–3nm) decreased stiction, resulting in a decrease of adhesion energy by up to four orders of magnitude as compared to Si and other smooth films. On the basis of this work, rough crystalline nanoscale ALD films are candidates for anti-stiction layers in MEMS.
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