Nuclear weapon yield | EPFL Graph Search

The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotonnes (kt—thousands of tonnes of TNT), in megatonnes (Mt—millions of tonnes of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is equal to . Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 1012 calories. The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six megatonnes of TNT per tonne of bomb mass (25 TJ/kg). Yields of 5.2 megato

Enhanced biofuel production from microalgae by adding CO2 to stimulate lipid biosynthesis (biodiesel) and by hydrothermal processing (syngas)

Gabriela Anca Haiduc, Christian Ludwig, David Pauli, Jean-Paul Schwitzguebel, Frédéric Vogel

Introduction: Microalgae cultures represent an attractive source of biomass for biofuel and chemicals production since they can have higher energy yields per area than conventional biomass crops and can be grown on marginal land using waste, saline, or brackish water. Their use can thus avoid the food-fuel competition for land, resulting in major economic and social benefits. At the present stage however, major developments are needed for making microalgae-to-biofuels processes technologically and economically feasible. One substantial technical challenge is the development of cost-effective processes for efficient conversion of microalgae biomass to biofuels. Our research aims to enhance the production of biodiesel and of bio-Synthetic Natural Gas (SNG) from microalgae. Experimental : Several species of microalgae are grown at laboratory scale to compare the yield of biomass and lipid production. In addition to the potential use of oil for biodiesel production, we are currently working towards demonstrating the technical and economical feasibility of an innovative process, “SunCHem”, for SNG production via hydrothermal (HT) processing of microalgae. The process is envisioned as a closed-cycle with respect to nutrients, water and CO2, that are separated and reused for microalgae growth, resulting in unprecedented energy efficiency for both algae and fuel production. The possible effect of increasing injection of CO2 in the growth medium is under investigation, with the aim to mitigate CO2 and enhance biomass production. Results and Discussion: Before the feasibility of the process can be demonstrated several key challenges stemming from its closed-nature need to be tackled. One major challenge is the recycling of nutrient-rich effluents, which upon continuous operation might become enriched in potential toxicants that in turn affect the growth of algae. We demonstrated that the presence of trace metals (Ni, Cr) in the recycled effluent as a result of reactor wall corrosion and catalyst leaching resulted in adverse effect on the growth of microalgae. The effect was directly proportional to the heavy metal concentration, and for the highest concentrations tested (Ni 25 ppm or Cr 5 ppm) complete inhibition of cell growth was observed. It is known that algae, like many other organisms, can adapt to extreme environments, including those with heavy metal contamination, and resulting mutants or strains should be more suited to survive under those particular conditions. The potential of developing and using metal-tolerant mutant microalgae as a biomass source for the SunCHem process is under investigation. Experiments are undertaken to develop Cr- and Ni- tolerant mutants by selective breeding and then comparing the mutants and the wild-type strains for their sensitivity to the heavy-metal contaminated HT effluent and the resulting biomass yields obtained in each case. It is hoped that the use of the metal-tolerant mutants or strains will contribute to the cost-effectiveness of the process by offering an efficient alternative to the use of the more costly setups otherwise needed for effluent clean-up, thus providing a way to avoid the reduction in the biomass yield upon continuous operation of the SunCHem process. On the other hand, metal-tolerant and accumulating microalgae could be used to treat industrial wastewater. Conclusions: Another aspect of utmost importance is the evaluation of the availability for algae of the nutrients contained in the recycled effluents from the process. To this end, microalgae growth experiments will be performed using as sole nutrient source the salt brine delivered from the HT step. The biomass composition with and without recycled input from the hydrothermal process will be characterized. These tests will provide information on the recycling efficiency and speciation of nutrients and will help to identify potential nutrient management issues. If there is significant loss of a given key nutrient, it will have to be replaced in the bioreactor. A candidate for loss through volatilization could be N. Subsequent studies will explore the role of growth media and especially that of nutrients such as N, P, and minerals. Algae growth experiments will be performed using different synthetic media compositions and varying nutrient levels to assess the tolerance of algae to changes in nutrient level and quality. The issue is of special relevance as the possibility of recycling and reusing all the nutrients, including N and P, is a sine qua non condition for closing the loop in the process.

2010

O6-alkylguanine-DNA alkyltransferase as a new tool for functional proteomics

Anke Arnold

Recently the sequencing project of the human genome has been completed. The interest of the post-sequencing-era is shifting nowadays towards the investigation of the biological function and localization of the encoded proteins. Proteins are essential parts of all living organisms and participate in every process in the living cell. Despite their importance, the detailed function of the majority of all proteins remains still unknown. Therefore high-throughput methods are needed for the systematic examination of proteins. The first part of this thesis describes the development of a novel functional protein microarray, taking advantage of the highly selective reaction of the human O6-alkylguanine-DNA alkyltransferase (AGT) with O6-benzylguanine derivatives. By functionalization of otherwise bioinert glass surfaces with the substrate O6-benzylguanine, AGT fusion proteins can be selectively and covalently immobilized on a solid surface (Figure S1). Due to the high selectivity of the covalent immobilization the main advantage of this AGT based approach is that fusion proteins can be immobilized directly out of cell extracts without prior purification. By analyzing a set of literature known protein-protein interactions, protein-small molecule interactions and posttranslational modifications we demonstrate the feasibility of this approach (Chapter 3). Figure S1: Principle of an AGT-based protein microarray in which x can be any protein of interest Furthermore, the development of surface materials suitable for functional protein microarrays is described. The generated surfaces allow immobilization of proteins in defined orientation and density. Intrinsically bioinert polymer brushes were generated in collaboration with the Laboratory of Polymers at the EPFL. For the production of these bioinert brush-surfaces, surface-initiated atom transfer radical polymerization (SI-ATRP) was used (Chapter 4). Additionally we addressed the importance of the orientation of immobilized proteins on solid surfaces. The immobilization of fusion proteins with random orientation on aldehyde-coated glass slides was compared with immobilization in a defined orientation on O6-benzylguanine functionalyzed polymer brushes. Subsequently, retention of activity of the proteins upon immobilization on the two different surfaces was analyzed. We demonstrated that a defined orientation of immobilized proteins is advantageous over random immobilization due to the fact that proteins, immobilized using the AGT approach, are attached in a defined orientation with their active site facing the solution phase, whereas random immobilization of proteins can result in hidden active sites (Chapter 5). In the second part of this thesis the problem of insolubility of recombinant expressed proteins is addressed. We analyzed the protein expression of a set of proteins, which were prior determined to be insoluble when expressed in E. coli. The proteins were expressed as AGT fusion proteins either in E. coli or M. smegmatis, with the goal to identify a suitable host for soluble protein expression with high yield. The AGT approach was exploited to screen for expression of soluble proteins and for the determination of the expression yields. We showed that fusion to AGT does not influence the solubility of the expressed proteins and that the expression yield in E. coli does not significantly differ from the yield in M. smegmatis, where proteins were expressed with less degradation. However, we assessed E. coli. to be the more suitable host for multi-parallel protein expression due to its easy handling and fast growth (Chapter 6). The gained knowledge of this project was transferred to the investigation of proteins from Mycobacterium tuberculosis, which is presented in the last part of this thesis. A better understanding of M. tuberculosis, with the goal of unveiling and validating new therapeutic targets, is an imperative need to improve the control and treatment of tuberculosis disease. We focused in particular on the bacterial two component adaptation systems (TCS). Since these systems do not exist in mammals they present attractive candidates for new drug targets. In order to gain a better understanding of these adaptation systems we focused on one specific TCS, SenX/RegX, one of the first identified and well established TCS, which is believed to be implicated in virulence. A radioactive in vitro phosphorylation assay was developed, which allowed the identification of two new in vitro substrates for histidine kinase SenX, namely DevR and NarL. These results confirm the hypothesis that TCS might not only consist of two components, but that cross-talk between different TCS exist in order to adapt rapidly to environmental changes.

EPFL2007

Energy Yield and Electricity Management of Thin-Film and Crystalline Silicon Solar Cells

Yannick Samuel Riesen

In the case of high photovoltaic (PV) penetration into the electricity grid, the energy produced by a PV system that is effectively used (useful energy) depends on the energy yield and on how this energy is managed to avoid detrimental effects occurring at high PV injection, e.g. during the midday peak. The overall goal of this thesis is to provide guidelines for maximizing the useful energy of a PV system by quantifying losses incurred during operation at both the solar cell device and the system levels. Solar cells are usually optimized for the standard test conditions (STC). However, the conditions are generally different during operation. This work assesses how solar cell materials and designs can be optimized to maximize the energy yield for specific operating condition. We mainly focus on thin-film silicon solar cells because of their challenging metastable behavior. The temperature dependence of the performance of thin-film amorphous silicon (a-Si:H) and microcrystalline silicon solar cells is thus measured for different deposition parameters and cell designs. We observe that, by tuning the intrinsic layer thickness of a-Si:H cells, the cells with the best (STC) efficiency do not necessarily provide the highest energy output. We also explain the presence of a maximum in the value of the fill factor as a function of temperature. The temperature dependence study is then extended to thin-film silicon multi-junction, crystalline silicon heterojunction (SHJ) and other crystalline silicon solar cells. For thin-film silicon solar cells, spectral effects and degradation or recovery effects due to the metastable character of a-Si:H (due to the Staebler-Wronski effect) significantly impact the energy yield. Based on indoor and outdoor degradation/recovery experiments, we show that it is challenging to describe this metastability with a diode model. However, such a model with a current loss term and an additional temperature dependence for the saturation current and ideality factors accurately reproduces the current-voltage characteristics of a-Si:H solar cells over a wide range of irradiance levels and operating temperatures. On the system level, we model a PV system with local storage to evaluate several strategies to reduce the detrimental midday injection peaks. The impact of such measures on the useful energy is also investigated. We develop a simple control algorithm that minimizes the losses due to a feed-in limit and maximizes self-consumption without the need of a production forecast. We show that heat storage using a boiler or a heat pump performs as well as battery storage. In general, a feed-in limit reduces significantly peak injection but only a relatively small storage capacity is needed to reduce losses (due to this limit). Changes in tilt and orientation of modules also reduce losses resulting from feed-in limits and shrink the winter/summer production ratio by more than a factor of two. We also develop a statistical method that estimates - from loads measured every 15 min - when different electrical appliances in a household are commonly used. This model indicates that about 8% of the total load could be shifted easily to the midday period, thereby reducing the midday injection peak. Finally, we combine device and system aspects to show that varying cell technology (e.g. with different temperature response) has a limited but not negligible impact on system output.

EPFL2016