High-Performance Dual Raman Spectrometer

12 pages, 16 figures.The transformation of an old Raman double monochromator into a dual spectrometer capable of working either as the origin al instrument or as a very high sensitivity scanning single monochromator with multichannel charge-coupled device (CCD) array detection is described. The merits and limitations of this instrument, particularly suited for medium/low resolu tion (0.3 to 2 cm2 1) Raman spectroscopy in the gas phase, are discussed. Example spectra of O2, N2, CO2, H2O, and CCl4 are shown.The Dirección General de Investigación Científica y Técnica (DGICYT), of Spain, is acknowledged for financial support (Research Project PB91-0133).Peer reviewe

Einfluss von Stromstärke und Zyklentiefe auf graphitische Anoden

At ageing tests with commercial Lithium-Ion Batteries unexpected strong degradation can be observed at certain test settings. At some of those conditions the anode, which is graphite based, has a phase change which can be the root cause for the ageing. The phase change causes a volume change in the materials. For the analysis in this work commercially available cells with different chemistries are investigated. The cells differ in design and capacity were systematically and accelerated aged, before they were disassembled and analysed for ageing effects. Goal of the work is to clarify whether there is a stronger degradation of the graphitic anode due to current density and cycle depth. The results show no structural change of the activ material, but an effect at the border between anode and electrolyte, which limit the power and lifetime of the cell

Systematic aging of commercial LiFePO4|Graphite cylindrical cells including a theory explaining rise of capacity during aging

The contribution introduces a new theory explaining the capacity increase that is often observed in early stages of life of lithium-ion batteries. This reversible and SOC-depending capacity rise is explained by the passive electrode effect in this work. The theory assumes a slow, compensating flow of active lithium between the passive and the active part of the anode, where the passive part represents the geometric excess anode with respect to the cathode. The theory is validated using a systematic test of 50 cylindrical 8 Ah LiFePO4|Graphite battery cells analyzed during cyclic and calendaric aging. The cyclic aging has been performed symmetrically at 40 °C cell temperature, varying current rates and DODs. The calendar aging is executed at three temperatures and up to four SOCs. The aging is dominated by capacity fade while the increase of internal resistance is hardly influenced. Surprisingly shallow cycling between 45 and 55% SOC shows stronger aging than aging at higher DOD and tests at 4 C exhibit less aging than aging at lower C-rates. Aging mechanisms at 60 °C seem to deviate from those at 40 °C or lower.The data of this aging matrix is used for further destructive and non-destructive characterization in future contributions

New method evaluating currents keeping the voltage constant for fast and highly resolved measurement of Arrhenius relation and capacity fade

The evaluation of floating currents is a powerful method to characterize capacity fade induced by calendaric aging and enables a highly resolved representation of the Arrhenius relation. The test arrangement is simple and could constitute a cheap alternative to state-of-the-art calendaric aging tests including check-up tests. Therefore the currents to maintain a constant voltage are evaluated. This method is validated by analyzing nine cylindrical 8 Ah LiFePO4|Graphite battery cells during calendaric aging at 25 °C, 40 °C and 60 °C at 3.6 V (100% SOC). The 3.6 V are kept by applying constant voltage while the floating currents are logged. The floating currents correlate with the rate of capacity loss measured during capacity tests. The floating currents reveal to be rather constant at 25 °C, linearly increasing at 40 °C and decreasing from a higher level at 60 °C. Additional tests with three test cells, with the temperature rising from 40 to 60 °C in steps of 5 K, exhibit non-constant currents starting from 50 °C on with high variations amongst the tested cells. Once stored above 50 °C, the cells exhibit increased floating currents compared to the measurement at the same temperature before exceeding 50 °C

Fire-related traits for plant species of the Mediterranean Basin

1 página.Plant trait information is essential for understanding plant evolution, vegetation dynamics, and vegetation responses to disturbance and management. Furthermore, in Mediterranean ecosystems, changes in fire regime may be more relevant than direct changes in climatic conditions, making the knowledge of fire-related traits especially important. Thus the purpose of this data set was to compile the most updated and comprehensive information on fire-related traits for vascular plant species of the Mediterranean Basin, that is, traits related to plant persistence and regeneration after fire. Data were collected from an extensive literature review and from field and experimental observations. The data source is documented for each value. Since life history traits may vary spatially or with environmental conditions, we did not aggregate them by species; i.e., traits and species are repeated in different records if they were observed by different researchers and/or in different locations. Life history traits included in the data set are: life form, resprouting ability (after fire, after clipping, or after other disturbances that remove all the aboveground biomass), resprouting bud source, heat-stimulated germination, other germination cues, seed bank location and longevity, post-fire seedling emergence and survival, maturity age of resprouts and saplings, and seed mass. Several traits are unknown for many species; consequently, the data set reflects the state of the knowledge on the topic. However, since the ability to resprout is a trait of paramount relevance in fire-prone environments, it was considered a core trait in the data set, and thus species whose resprouting capacity was unknown were not included. Life form is also provided for all taxa. The structure of the database allows different levels of information (and accuracy) for each entry, and thus some traits may include different types of data (quantitative, semi-quantitative, or categorical) from different sources. The data set is structured in 8263 records and 11 columns, obtained from 301 published and unpublished sources of information. It includes 952 taxa determined at specific or infraspecific level, which comprise 859 species, 384 genera, and 79 families. Although this is the most comprehensive data set of fire-relevant plant traits for Mediterranean species, there is still a considerable need for observations and experiments, especially in little-studied Mediterranean areas, such as northern Africa.Peer reviewe