Imaging Studies of photodamage and self-healing in disperse orange 11 dye-doped PMMA

We report on optical imaging studies of self-healing after laser-induced photodamage in disperse orange 11 dye doped into poly(methyl methacrylate) (PMMA) polymer. In particular, the high spatial-contrast image of the damage track made by a line focus pump laser allows the recovery rates to be measured as a function of burn dose using the relationship between transverse distance and pump intensity profile. The time evolution of the damaged population results in an intensity-independent time constant of {\tau} = 490\pm23 min, in agreement with independent measurements of the time evolution of amplified spontaneous emission. Also observed is a damage threshold above which the material does not fully recover.Comment: 5 pages, 8 figure

Testing the diffusion hypothesis as a mechanism of self-healing in Disperse orange 11 doped in PMMA

In this work, we show that reversible photodegradation of Disperse Orange 11 doped in PMMA is not due to dye diffusion - a common phenomenon observed in many dye-doped polymers. The change in linear absorbance due to photodegradation of the material shows an isobestic point, which is consistent with the formation of a quasi-stable damaged species. Spatially-resolved amplified spontaneous emission and fluorescence, both related to the population density, are measured by scanning the pump beam over a burn mark. A numerical model of the time evolution of the population density due to diffusion is inconsistent with the experimental data suggesting that diffusion is not responsible.Comment: 5 pages, 6 figure

Determination of the Optimum Population Density of Seedlings during Transplanting for the Productivity Improvement of Tef [Eragrostis tef (Zucc.)] Trotter] in Central zone of Tigray, Etiopia

A study was conducted in 2012/13 cropping seasons across two locations (Adet in N/adet district and Axum in L/Maychew district) to determine the appropriate population density for transplanting Tef. Field experiment was conducted during the 2012 and 2013-cropping season from (June to December) to address the question whether or not the population for transplanting determines the yielding components of for Tef. The trial consisted of seven treatments and arranged in Randomized Complete Block Design (RCBD) with three replications. All agronomic data were collected and the difference was analyzed by Gene stat (16th edition). At Adet and Axum, the transplanted treatments had shorter maturity days, highest plant height, highest panicle length, more number of tillers per tuber and less lodging index percentages.  In addition to this, the transplanted treatments T5 (20cm*10cm spacing) and T6 (20cm*15cm spacing) scored the highest grain yield (3086 Kg/ha and 3076 Kg/ha respectively).  These treatments also scored the highest biomass yield (9593 Kg/ha and 9685 Kg/ha respectively). Hence based on these results, for transplanting Tef seedlings a row spacing of 20cm and plant spacing of 10cm-15cm is recommended for better Tef grain and biomass yield and for improved grain quality of the crop. Keywords: Tef, transplanting, broadcasting, row planting, grain yield, biomass yiel

Mechanism of self-healing of amplified spontaneous emission in the dye-doped polymer disperse orange 11 dye in PMMA polymer

We study the mechanisms of photodegradation and self-healing of 1-amino-2- methylanthraquinone (Disperse Orange 11) in solid poly(methyl methacrylate) under 532nm Nd:YAG laser excitation as measured by amplified spontaneous emission (ASE). We used photochromism in conjuction with ASE dynamical studies to gain an understanding of the character of species formed during photodegradation. Based on our experiments, we propose the mechanism of dimer formation from dipole coupled tautomers and summarize our results with an energy level diagram that is consistent with the full set of measurements. We use a simple population dynamics model to explain the proposed mechanism. As expected from our proposed mechanisms we find an intensity-dependent photodegradation rate and a constant recovery rate. This understanding can be used to design materials for devices that are more robust against the common problem of photodegradation

Investigation on Redefining the Silt Content of Sand in Concrete Production

This study investigates redefining the silt content of sand in concrete production. Fine aggregate has properties that differ from natural sands; for this reason, the plastic and hardened properties of concrete produced using manufactured fine aggregate differ from the properties of concrete made with natural sands. In most current standards used for construction purposes, the fines or material passing the N200 sieve content limitations have been intended for natural sands. Even though there are standards that have tried to stipulate for manufactured fine aggregate, the limits allow small amounts. The manufactured fine aggregate producers have faced difficulty meeting the standards specification and washing aggregate to lower silt content. This results in incrementing costs and develops environmental issues. The high proportion of silt fines found in the manufactured sand has been investigated in this research and the impact of the material on the properties of concrete both in fresh and hardened state. Thus concrete specimens with a w/c ratio of 0.58, 0.54, and 0.45 with different silt content of fine aggregate, ranging from 0% to 15%, were cast and tested on the Normal Strength Concrete, Intermediate Strength Concrete, and High Strength Concrete. Finally, the results of the tests have shown that better workability and better strength can be achieved with a concrete mix of up to 15 % silt content. The first trial faces workability and finishable difficulties. This was adjusted with a fairly increased water-cement ratio instead of using chemical solutions. Keywords: Concrete production, Manufactured fine aggregate, Redefining silt content DOI: 10.7176/CER/17-2-03 Publication date: May 31st 202

Offshore Membrane Enclosures for Growing Algae (OMEGA: A System for Biofuel Production, Wastewater Treatment, and CO2 Sequestration

We are developing Offshore Membrane Enclosures for Growing Algae (OMEGA). OMEGAs are closed photo-bioreactors constructed of flexible, inexpensive, and durable plastic with small sections of semi-permeable membranes for gas exchange and forward osmosis (FO). Each OMEGA modules is filled with municipal wastewater and provided with CO2 from coastal CO2 sources. The OMEGA modules float just below the surface, and the surrounding seawater provides structural support, temperature control, and mixing for the freshwater algae cultures inside. The salinit7 gradient from inside to outside drives forward osmosis through the patches of FO membranes. This concentrates nutrients in the wastewater, which enhances algal growth, and slowly dewaters the algae, which facilitates harvesting. Thy concentrated algal biomass is harvested for producing biofuels and fertilizer. OMEGA system cleans the wastewater released into the surrounding coastal waters and functions as a carbon sequestration system

Effect of Tuber Size, Storage Time and Storage Environment on Dormancy and Sprouting Characteristics of Some Potato (Solanum Tuberosum L.) Cultivars

A study was conducted to investigate the influence of tuber size, storage time and storage environment on storage losses and seed tuber quality of three selected potato cultivars under diffused light storage (DLS) structures in three locations in 2012/2013 in the Tigray region, North Ethiopia. The treatments consisted of two environments (locations), three potato cultivars (Gera, Gudene and Jalene) and four tuber size categories [very small (20-30mm), small (31-40mm), medium (41-50mm), and large (51-65mm)] arranged in Randomized Complete Block Design with three replications. Data pertaining to sprouting characteristics were recorded for 28 weeks at monthly interval. The larger tubers had better sprouting ability than the rest of the tuber sizes. Gudene and Jalene cultivars recorded more number of sprouts per tuber at F.weyni storage environment. In contrast Gera cultivar recorded few numbers of sprouts until week 28. So, de-sprouting treatment is recommended for Gera cultivar. Number of sprouts per tuber, length and thickness of sprouts increased with increasing storage time. At F.weyni storage environment, large tuber size categories of all three potato cultivars had more number of sprouts per tuber than in the other storage environments. Generally, storing medium (41-50mm) and large (51-65mm) tuber size categories of potato tubers is recommended for a sustainable quality seed supply; Potato tubers should be stored at warm storage environments when short term storage is desired; however they should be stored at cool environments for long term storage. Keywords: dormancy, sprouting, potato, tuber size, cultivar, diffused light storag

Diverse syntrophic partnerships from deep-sea methane vents revealed by direct cell capture and metagenomics

Microorganisms play a fundamental role in the cycling of nutrients and energy on our planet. A common strategy for many microorganisms mediating biogeochemical cycles in anoxic environments is syntrophy, frequently necessitating close spatial proximity between microbial partners. We are only now beginning to fully appreciate the diversity and pervasiveness of microbial partnerships in nature, the majority of which cannot be replicated in the laboratory. One notable example of such cooperation is the interspecies association between anaerobic methane oxidizing archaea (ANME) and sulfate-reducing bacteria. These consortia are globally distributed in the environment and provide a significant sink for methane by substantially reducing the export of this potent greenhouse gas into the atmosphere. The interdependence of these currently uncultured microbes renders them difficult to study, and our knowledge of their physiological capabilities in nature is limited. Here, we have developed a method to capture select microorganisms directly from the environment, using combined fluorescence in situ hybridization and immunomagnetic cell capture. We used this method to purify syntrophic anaerobic methane oxidizing ANME-2c archaea and physically associated microorganisms directly from deep-sea marine sediment. Metagenomics, PCR, and microscopy of these purified consortia revealed unexpected diversity of associated bacteria, including Betaproteobacteria and a second sulfate-reducing Deltaproteobacterial partner. The detection of nitrogenase genes within the metagenome and subsequent demonstration of 15N2 incorporation in the biomass of these methane-oxidizing consortia suggest a possible role in new nitrogen inputs by these syntrophic assemblages

Essays on Tax Evasion and Government Spending in Developing Countries

The dissertation aims at broadening our understanding of tax evasion and government spending in developing countries. It comprises three essays. The first essay deals with estimation of tax evasion in a cross-section of developing countries by estimating their underground economies using the currency demand method. By including enforcement parameters of the tax authorities as another factor of tax evasion in the currency demand equation, it presents theory-consistent tax evasion measurement. Our estimation strategy includes the use of the Arellano-Bond dynamic panel data method that is suitable for correcting the endogeneity problem in the currency demand estimation. The study finds substantial underground economy in developing countries, ranging from 2-67 percent of GDP. The second essay is concerned with time series measurement of the underground economy in South Africa using the currency demand method. Unlike other similar studies on South Africa, it gives sufficient attention to the unit root problem that is common in time series analysis of the currency demand method. Using the Error Correction Method (ECM), it investigates the relationship between the tax rate and the currency demand, and presents yearly estimates of the underground economy for the period 1965-2002. The third essay deals with the behavior of government spending in South Africa for the period 1960-2002. Since South Africa went through various political and macroeconomic shocks during this period, we augment measures of these shocks to the standard median voter model to assess the determinants of government spending in South Africa. Using the Error Correction Method (ECM), we investigate the long-run and short-run behavior of government spending. We find that, in addition to the tax share and the income of the median voter, macroeconomic and political shocks were also significant factors in determining government spending in South Africa. This study broadens our understanding of the behavior of government spending in the presence of political and macroeconomic shocks that are common in small open developing economies