Capillary electrochromatography : fundamentals and applications

III+226hlm.;24c

Eddy covariance flux measurements of gaseous elemental mercury over a grassland

Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg-0) are important to improve our understanding of global Hg cycling and, ultimately, human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg-0 flux estimates. It currently remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg-0. Here, we show a detailed validation of direct Hg-0 flux measurements based on the eddy covariance technique (Eddy Mercury) using a Lumex RA-915 AM mercury monitor. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m(-2) h(-1) (maximum) with a 50% cutoff at 0.074 ng m(-2) h(-1). We present eddy covariance NEE measurements of Hg-0 over a low-Hg soil (41-75 ng Hg g(-1) in the topsoil, referring to a depth of 0-10 cm), conducted in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). The statistical estimate of the Hg-0 flux detection limit under outdoor conditions at the site was 5.9 ng m(-2) h(-1') (50% cutoff). We measured a net summertime emission over a period of 34 d with a median Hg-0 flux of 2.5 ng m(-2) h(-1) (with a -0.6 to 7.4 ng m(-2) h(-1) range between the 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m(-2) h(-1)) than night-time fluxes (1.0 ng m(-2) h(-1)). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation. Partial stomata closure led to a midday depression in CO2 uptake, which did not recover during the afternoon. The median CO2 flux was only 24% of the median CO2 flux measured during the same period in the previous year (2017). We suggest that partial stomata closure also dampened Hg-0 uptake by vegetation, resulting in a NEE of Hg-0 that was dominated by soil emission. Finally, we provide suggestions to further improve the precision and handling of the "Eddy Mercury" system in order to assure its suitability for long-term NEE measurements of Hg-0 over natural background surfaces with low soil Hg concentrations (< 100 ng g(-1)). With these improvements, Eddy Mercury has the potential to be integrated into global networks of micrometeorological tower sites (FluxNet) and to provide the long-term observations on terrestrial atmosphere Hg-0 exchange necessary to validate regional and global mercury models

Storage life of new torch tip

Svařování v ochranné atmosféře MIG/MAG je nejpoužívanější a nejrozšířenější metoda svařování. Použití této metody je velmi rozsáhlé. Její jediné omezení je pouze ve venkovním prostředí při práci v terénu, kdy při působení vnějších vlivů (větru) dochází k porušení ochranné obálky plynu. Tato ochranná obálka brání přístupu vzduchu ke svarové lázni a při jejím porušení hrozí vznik nekvalitního svarového spoje se spoustou pórů. Důležitou součástí svařovacího zařízení je kontaktní špička, která napájí svařovací drát elektrickým proudem. Kontaktních špiček existuje celá řada, od nejlevnějších až po ty dražší. Požadavkem je zvýšit životnost špiček na maximum, aby se minimalizovaly časy jejich výměn. O zvýšení životnosti se pokusila i australská firma se špičkou MIGfast použitím keramického izolátoru. U této špičky výrobce deklaroval až pětkrát delší životnost oproti konvenčním špičkám. Námi provedené zkoušky ovšem ukázaly velmi negativní výsledek v porovnání s běžně používanými konvenčními špičkami.Welding in a MIG/MAG protection atmosphere is the the most used and most widespread method for welding. This method is very extensively used. Its only limitation is in an outdoor environment while working in the field, when the effects of external influences (wind) can breach the gas containment. The containment prevents the access of air to the weld pool and a breach can lead to the formation of a poor quality welded joint with a lot of pores. An important part of the welding device is the contact tip, which energizes the welding wire by electric current. There are many types of contact tips from the cheapest to more expensive ones. The requirement is to increase the lifetime of tips to the maximum in order to minimize replacement times. An Australian company making MIGfast tips has tried to increase the lifetime by using a ceramic insulator. This tip producer claimed as much as five times longer lifetime than conventional tips. Tests carried out by us, however, showed a very negative result in comparison with commonly used conventional tips.

Comparison of CMT TWIN with other MIG/MAG processes

Vývoj svařovací technologie je hnán neustále kupředu především z důvodu snižování výrobních nákladů a nákladů na dodatečné rovnání svařenců vlivem tepelných deformací. Proto přední výrobci svařovacího zařízení přichází s novými metodami a technologiemi. Jednou z novinek je i vysoce výkonná tandemová technologie CMT Twin od společnosti Fronius. Experiment provedený v diplomové práci potvrzuje, že se jedná o velmi hospodárný proces. V porovnání s konvenčním svařováním je CMT Twin z pohledu výrobních nákladů na provedení svaru levnější variantou a vnáší do materiálu méně tepla. Aplikace zařízení CMT Twin vyžaduje průmyslového robota, tudíž metoda je předurčena pro sériovou až hromadnou výrobu. CMT Twin najde uplatnění například v automobilovém či lodním průmyslu.The development of welding technology is constantly going forward mainly due to the reduction of production costs and the costs of additional straightening of weldments due to the welding distortion. Therefore, the leading producers of welding machine are coming with new methods and technologies. One of the innovations is also the tandem technology CMT Twin from the company Fronius. The experiment carried out in the diploma thesis confirmed that this is a very cost effective process. The CMT Twin is from the point of view of production costs of the weld cheaper variant and bring less heat into the material compared with conventional welding. Application equipment CMT Twin requires industrial robot, so the method is predestined for the series up to mass production. The CMT Twin finds application, for example in the automotive and shipbuilding industry.

Subjective body and life. An Essay on the way of thinking of Michel Henry

v českém jazyce: Ústředním tématem této diplomové práce je fenomenologie těla a s ní spojené zkoumání aktu zjevování jako takového v díle francouzského filosofa Michela Henryho. Fenomenologickou pozici tohoto myslitele se pokusíme vymezit především v konfrontaci s intencionální fenomenologií Edmunda Husserla, která původ zjevování spojuje se světem. Proti této klasické variantě fenomenologie postavíme Henryho fenomenologii života. Tímto způsobem pojatý život je přitom neviditelný či nezjevný, neboť se nám jakožto radikálně imanentní nemůže ukázat v rámci exteriority světa. Redefinice klasické koncepce zjevování by nám v každém případě měla umožnit přístup k tomu, co nás v tomto textu především zajímá, totiž subjektivní či transcendentální tělo, které se nám dává v ničím nezprostředkovaném afektivním sebe-zakoušení své neviditelné interiority. Z těchto důvodů označíme spolu s Henrym subjektivní tělo za imanentní bytí, které je zároveň zjevováním. Na základě odmítnutí klasické koncepce vědomí, které je redukováno na intencionální vztah k předmětu, a odhalením transcendentálního vnitřního těla na půdě subjektivity tak představíme čtenáři Henryho vlastní, radikální fenomenologii interiority, fenomenologii života.v anglickém jazyce: The fundamental theme of this diploma paper is the phenomenology of the body which is related to the investigation of the act of the appearing itself in the works of the French philosopher Michel Henry. The phenomenological approach of this thinker is going to be defined primarily by the confrontation with intentional phenomenology of Edmund Husserl, which in the matter of the appearance keeps itself within the bounds of the relation to the world. This classical version of the phenomenology will be compared with Henrys phenomenology of the life. The life which is understood in such a manner is invisible or unapparent because it is radically immanent and never appears in the exteriority of the world. Anyhow, the redefinition of the classical conception of the appearance should make possible access to the most important and the most interesting thing for us that is to say to subjective or transcendental body, which appears and experiences itself directly in its affective self- experience of the invisible interiority. Therefore, the subjective body is going to be described upon these grounds together with Henry as immanent being that is at the same time appearance. Thus we are going to present philosophy of Michel Henry, which is called radical phenomenology of interiority that is...Institute of Philosophy and Religious StudiesÚstav filosofie a religionistikyFaculty of ArtsFilozofická fakult

Mercury in tundra vegetation of Alaska: Spatial and temporal dynamics and stable isotope patterns

Vegetation uptake of atmospheric mercury (Hg) is an important mechanism enhancing atmospheric Hg deposition via litterfall and senescence. We here report Hg concentration and pool sizes of different plant functional groups and plant species across nine tundra sites in northern Alaska. Significant spatial differences were observed in bulk vegetation Hg concentrations at Toolik Field station (52 ± 9 μg kg−1), Eight Mile Lake Observatory (40 ± 0.2 μg kg−1), and seven sites along a transect from Toolik Field station to the Arctic coast (36 ± 9 μg kg−1). Hg concentrations in non-vascular vegetation including feather and peat moss (58 ± 6 μg kg−1 and 34 ± 2 μg kg−1, respectively) and brown and white lichen (41 ± 2 μg kg−1 and 34 ± 2 μg kg−1, respectively), were three to six times those of vascular plant tissues (8 ± 1 μg kg−1 in dwarf birch leaves and 9 ± 1 μg kg−1 in tussock grass). A high representation of nonvascular vegetation in aboveground biomass resulted in substantial Hg mass contained in tundra aboveground vegetation (29 μg m−2), which fell within the range of foliar Hg mass estimated for forests in the United States (15 to 45 μg m−2) in spite of much shorter growing seasons. Hg stable isotope signatures of different plant species showed that atmospheric Hg(0) was the dominant source of Hg to tundra vegetation. Mass-dependent isotope signatures (δ202Hg) in vegetation relative to atmospheric Hg(0) showed pronounced shifts towards lower values, consistent with previously reported isotopic fractionation during foliar uptake of Hg(0). Mass-independent isotope signatures (Δ199Hg) of lichen were more positive relative to atmospheric Hg(0), indicating either photochemical reduction of Hg(II) or contributions of inorganic Hg(II) from atmospheric deposition and/or dust. Δ199Hg and Δ200Hg values in vascular plant species were similar to atmospheric Hg(0) suggesting that overall photochemical reduction and subsequent re-emission was relatively insignificant in these tundra ecosystems, in agreement with previous Hg(0) ecosystem flux measurements