Family forest owners’ perception of management and thinning operations in young dense forests: a survey from Sweden

Family forest owners (FFOs) own 48% of Sweden’s productive forest land and are responsible for 59% of the annual gross felling. They are thus important suppliers of raw materials to the forest industry and the energy sector. Environmental goals on the national and international level promote an increased use of renewable resources in order to replace fossil-based fuels, but since the current supply of forest products is already fully utilized by the industry, there is a need to find new types of biomass assortment. One way to increase the biomass supply is to replace traditional pre-commercial thinning operations, where fallen stems are left in the forest to rot, with whole-tree harvesting of small-diameter trees using novel technologies and methods. This will however require willingness of the FFOs to shift their management practices. The objectives of this study were, therefore, to elucidate FFOs’ perceptions of management and thinning operations in young dense forests, identify if there are differences depending on their demographic backgrounds, and clarify which factors could potentially affect their willingness to implement whole-tree harvesting in young dense forests. Data were collected through a survey administered to a random sample of 842 FFOs, with a response rate of 53.4% (n = 450). The results show that FFOs in general are positive towards implementing whole-tree harvesting in young dense stands, and are often also willing to promote the development of suitable stands. Factors such as forest size, geographical location, distance from home to their forest, degree of self-employment and current need for cleaning were found to significantly affect their attitudes. The study highlights that the development of cost efficient harvesting techniques and working methods is important if the industry wants to increase the FFOs’ willingness to engage in whole-tree harvesting in young dense forest stands and thereby increase the supply of biomass

High mobility n-channel organic field-effect transistors based on soluble C60 and C70 fullerene derivatives

We report on n-channel organic field-effect transistors (OFETs) based on the solution processable methanofullerenes [6,6]-phenyl-C61-butyric acid ester ([60]PCBM) and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM). Despite the fact that both derivatives form glassy films when processed from solution, their electron mobilities are high and on the order of 0.21 cm2/V s and 0.1 cm2/V s, for [60]PCBM and [70]PCBM, respectively. Although the derived mobility of [60]PCBM is comparable to the best values reported in the literature, the electron mobility of [70]PCBM is the highest value reported to date for any C70 based molecule. We note that this is the only report in which C60 and C70 methanofullerenes exhibit comparable electron mobilities. The present findings could have significant implications in the area of large-area organic electronics and organic photovoltaics where C60 derivatives have so far been the most widely used electron acceptor materials.

Epigenetic and Genetic Contributions to Adaptation in Chlamydomonas.

Epigenetic modifications, such as DNA methylation or histone modifications, can be transmitted between cellular or organismal generations. However, there are no experiments measuring their role in adaptation, so here we use experimental evolution to investigate how epigenetic variation can contribute to adaptation. We manipulated DNA methylation and histone acetylation in the unicellular green alga Chlamydomonas reinhardtii both genetically and chemically to change the amount of epigenetic variation generated or transmitted in adapting populations in three different environments (salt stress, phosphate starvation, and high CO2) for two hundred asexual generations. We find that reducing the amount of epigenetic variation available to populations can reduce adaptation in environments where it otherwise happens. From genomic and epigenomic sequences from a subset of the populations, we see changes in methylation patterns between the evolved populations over-represented in some functional categories of genes, which is consistent with some of these differences being adaptive. Based on whole genome sequencing of evolved clones, the majority of DNA methylation changes do not appear to be linked to cis-acting genetic mutations. Our results show that transgenerational epigenetic effects play a role in adaptive evolution, and suggest that the relationship between changes in methylation patterns and differences in evolutionary outcomes, at least for quantitative traits such as cell division rates, is complex

Association between visual impairment and sleep duration: analysis of the 2009 National Health Interview Survey (NHIS)

BACKGROUND: Visual impairment (VI) is associated with increased mortality and health factors such as depression and cardiovascular disease. Epidemiologic studies consistently show associations between sleep duration with adverse health outcomes, but these have not systematically considered the influence of VI. The aim of this study was to ascertain the independent association between VI and sleep duration using the National Health Interview Survey (NHIS) data. We also examined whether race/ethnicity influenced these associations independently of sociodemographic and medical characteristics. METHODS: Our analysis was based on the 2009 NHIS, providing valid sleep and vision data for 29,815 participants. The NHIS is a cross-sectional household interview survey utilizing a multistage area probability design. Trained personnel from the US census bureau gathered data during face-to-face interview and obtained socio-demographic, self-reported habitual sleep duration and physician-diagnosed chronic conditions. RESULTS: The mean age of the sample was 48 years and 56% were female. Short sleep and long sleep durations were reported by 49% and 23% of the participants, respectively. Visual impairment was observed in 10%. Multivariate-adjusted logistic regression models showed significant associations between VI and short sleep (OR = 1.6, 95% CI = 1.5-1.9 and long sleep durations (OR = 1.6, 95% CI = 1.3-1.9). These associations persisted in multivariate models stratified by race-ethnic groups. CONCLUSION: Visual impairment was associated with both short and long sleep durations. Analysis of epidemiologic sleep data should consider visual impairment as an important factor likely to influence the amount of sleep experienced habitually

Molecular weight growth pathways in fuel-rich combustion

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2000.Includes bibliographical references.Polycyclic aromatic hydrocarbons (P AH) and soot are formed when a hydrocarbon fuel is oxidized under fuel-rich conditions. The distinction between what constitutes the largest P AH molecule and the smallest soot particle is arbitrary; the formation processes of both can be placed under the heading of molecular weight growth. Evidence exists for the carcinogenicity of many P AH molecules. Soot is used as a component of dyes and as an additive to rubbers as well as being an undesirable atmospheric pollutant. Both are emitted from many typical combustion processes such as diesel engines, wood fires, furnaces, etc. Though the area has received much attention, the fundamental chemical mechanisms for formation of both P AH and soot are still uncertain. Much debate has centered on the identity of the soot surface growth reactant, in particular whether the dominant surface growth reactant is P AH or acetylene. Though several models of soot formation exist, none has demonstrated through comparison to experimental data a thorough knowledge of the fundamental chemical processes of soot formation. The goal of this research was to further the understanding of these fundamental chemical processes. Since the chemistry of P AH and soot are intertwined, PAH was a necessary subcomponent of the soot formation research. The research was accomplished by obtaining soot particle size distribution data for the jet-stirred reactor/ plug-flow reactor (JSR/PFR), development of kinetics modeling methods, and the development of a kinetics model of soot formation. The JSR/PFR has been used extensively in the past to investigate P AH and soot formation, providing much data for concentrations of light-gas species, P AH, and soot under various conditions of equivalence ratio, temperature, and PFR additives. No experimental data have been obtained for soot particle size distribution in the JSR/PFR, so a study was undertaken here to obtain the soot particle size distributions for two conditions previously studied by Marr, premixed atmospheric ethylene combustion at equivalence ratio 2.2 and temperatures of 1520 K and 1620 K. Thermophoretic sampling was used to obtain soot samples for transmission electron micrograph analysis. Software was written and used to obtain soot particle sizes from electron micrographs. The chemical environment in a fuel-rich flame consists of many hundreds of species and thousands of chemical reactions. To isolate particular portions of the chemistry, a calculational technique was developed, data incorporation, that replaces chosen portions of the chemistry in kinetics models with functions of data concentrations. This technique was then used to isolate the process of P AH molecular weight growth and soot nucleation through the use of a discrete sectional model, and rate coefficients for hydrogen-atom abstraction, acetylene-addition, and PAH radical addition to PAH were obtained by comparisons to data from Marr for the 1620 K condition described above and the same condition with naphthalene injection into the PFR. The data incorporation technique was then used to expand the discrete sectional model to include sections describing soot, and the experimental soot size distribution data described above was used with previously available PFR data to obtain values for rate coefficients of PAHaddition to soot and coagulation of soot particles. Five PFR conditions were used to develop the soot formation model in these calculations, and the dominant mechanisms of soot formation present under these conditions appear to be present in the model. Quantitative agreement is obtained to all of the available data, including simultaneous agreement of soot mass and particle size, without significant deviation in the rate coefficients required to obtain agreement. Calculations were performed using both PAH and acetylene as the dominant soot surface growth reactant. It was found that P AH had far more consistent rate coefficient values (constant to within a factor of 4) than acetylene ( constant to within a factor of 59) to describe the data for all of the conditions. An analysis of the above five sets of conditions in the PFR, an additional three for the PFR, and three for premixed one-dimensional flames of acetylene, ethylene, and benzene, for which concentrations of acetylene, P AH. and soot, and in the case of the one-dimensional flames, soot particle size data, were available, were analyzed with the aim of understanding the dominant characteristics of the soot surface growth reactant. Soot mass growth rates were calculated for all of the conditions, and deviate markedly between the PFR and one-dimensional flames. Soot growth rate increases and oscillates in the PFR and sharply declines in the one-dimensional flames in the region of soot growth after initial particle inception. Under all of these conditions, PAH show the characteristics required of the dominant surface growth reactant: increases and oscillations in the PFR and sharp declines in the one-dimensional flames. For acetylene to be the dominant surface growth reactant, anomalous behavior of acetylene-suot reactivity would be required that cannot be explained by soot aging or radical intermediates. This leads to the observation that the long-held notion of declining soot reactivity in premixed one-dimensional flames similar to the ones studied here is a result of variations in the PAH intermediates and not a real phenomenon in the region after soot particle inception. An approximate method of uncertainty analysis of kinetics models was used to place an uncertainty bound of a factor of 3 on the rate coefficient parameters calculated. The approximate method was compared to more precise techniques and used to show that the uncertainty of concentration predictions with PAH kinetics models is of very large magnitude. The approximate uncertainty analysis technique was also used to show that the data incorporation technique reduces the uncertainty in calculated rate parameters by over two orders of magnitude. A kinetics model reduction algorithm was developed and implemented to reduce a PAH kinetics model fro.n 722 reactions and 187 species to 93 reactions and 52 species, maintaining naphthalene conc1;;ntration to within 9% of the original model. This technique was also used by Dinaro to redm:e a benzene oxidation model from 545 to 41 reactions for use in super-critical water oxidation applications.by David Franklin Kronholm.Ph.D

Air-Stable n-Channel Organic Transistors Based on a Soluble C84 Fullerene Derivative

Air-stable n-channel organic transistors are fabricated using a newly synthesized soluble fullerene derivative. The airstable nature of this molecule allows the realization of complementary circuits under ambient conditions without encapsulation. As shown in the figure, the I-V characteristics of the devices are retained even after exposure to air for a week. To the best of our knowledge, this is the first demonstration of an air-stable electron-transporting fullerene-based molecule

Electron Trapping in Higher Adduct Fullerene-Based Solar Cells

Here, the performance of bulk-heterojunction solar cells based on a series of bisadduct analogues of commonly used derivatives of C60 and C70, such PCBMs and their thienyl versions, is investigated. Due to their higher lowest unoccupied molecular orbital an increase in open-circuit voltage and thus performance is expected. It is shown that the occurrence of a multitude of different isomers results in a decrease in the electron transport for some of the materials. Surprisingly, the solar-cell characteristics are very similar for all materials. This apparent discrepancy is explained by a significant amount of shallow trapping occurring in the fullerene phase that does not hamper the solar cell performance due the filling of these shallow traps during illumination. Furthermore, the trisadduct analogue of [60]PCBM has been investigated, which, despite an even further increase in open-circuit voltage, results in a significantly reduced device performance due to a strong deterioration of the electron mobility in the fullerene phase.