Fast high--voltage amplifiers for driving electro-optic modulators

We describe five high-voltage (60 to 550V peak to peak), high-speed (1-300ns rise time; 1.3-300MHz bandwidth) linear amplifiers for driving capacitive or resistive loads such as electro-optic modulators. The amplifiers use bipolar transistors in various topologies. Two use electron tubes to overcome the speed limitations of high-voltage semiconductors. All amplifiers have been built. Measured performance data is given for each.Comment: 9pages, 6figures, 6tables, to appear in Review of Scientific Instrument

Integrated multidimensional sustainability assessment of energy system transformation pathways

Sustainable development embraces a broad spectrum of social, economic and ecological aspects. Thus, a sustainable transformation process of energy systems is inevitably multidimensional and needs to go beyond climate impact and cost considerations. An approach for an integrated and interdisciplinary sustainability assessment of energy system transformation pathways is presented here. It first integrates energy system modeling with a multidimensional impact assessment that focuses on life cycle-based environmental and macroeconomic impacts. Then, stakeholders’ preferences with respect to defined sustainability indicators are inquired, which are finally integrated into a comparative scenario evaluation through a multi-criteria decision analysis (MCDA), all in one consistent assessment framework. As an illustrative example, this holistic approach is applied to the sustainability assessment of ten different transformation strategies for Germany. Applying multi-criteria decision analysis reveals that both ambitious (80%) and highly ambitious (95%) carbon reduction scenarios can achieve top sustainability ranks, depending on the underlying energy transformation pathways and respective scores in other sustainability dimensions. Furthermore, this research highlights an increasingly dominant contribution of energy systems’ upstream chains on total environmental impacts, reveals rather small differences in macroeconomic effects between different scenarios and identifies the transition among societal segments and climate impact minimization as the most important stakeholder preferences

Improved high-fidelity transport of trapped-ion qubits through a multi-dimensional array

We have demonstrated transport of Be+ ions through a 2D Paul-trap array that incorporates an X-junction, while maintaining the ions near the motional ground-state of the confining potential well. We expand on the first report of the experiment [1], including a detailed discussion of how the transport potentials were calculated. Two main mechanisms that caused motional excitation during transport are explained, along with the methods used to mitigate such excitation. We reduced the motional excitation below the results in Ref. [1] by a factor of approximately 50. The effect of a mu-metal shield on qubit coherence is also reported. Finally, we examined a method for exchanging energy between multiple motional modes on the few-quanta level, which could be useful for cooling motional modes without directly accessing the modes with lasers. These results establish how trapped ions can be transported in a large-scale quantum processor with high fidelity.Comment: 16 page

Apparent Alkyl Transfer and Phenazine Formation via an Aryne Intermediate

Treatment of chlorotriaryl derivatives 3a and 3d or fluorotriaryl derivatives 3b and 3e with potassium diisopropylamide afforded alkyl-shifted phenazine derivatives 5a/5b, rather than the expected 9-membered triazaorthocyclophane 2a. The phenazine derivatives were isolated in 78–98% yield depending on the halogen and alkyl group present. In the absence of the halogen (chloro or fluoro), the apparent alkyl shift proceeds more slowly and cannot proceed via the intermediacy of the aryne intermediate. Mechanistic possibilities include intramolecular nucleophilic attack on an aryne intermediate leading to a zwitterionic intermediate and alkyl transfer via a 5-endo-tet process, or via a Smiles rearrangement

Impaired Nuclear Nrf2 Translocation Undermines the Oxidative Stress Response in Friedreich Ataxia

BACKGROUND: Friedreich ataxia originates from a decrease in mitochondrial frataxin, which causes the death of a subset of neurons. The biochemical hallmarks of the disease include low activity of the iron sulfur cluster-containing proteins (ISP) and impairment of antioxidant defense mechanisms that may play a major role in disease progression. METHODOLOGY/PRINCIPAL FINDINGS: We thus investigated signaling pathways involved in antioxidant defense mechanisms. We showed that cultured fibroblasts from patients with Friedreich ataxia exhibited hypersensitivity to oxidative insults because of an impairment in the Nrf2 signaling pathway, which led to faulty induction of antioxidant enzymes. This impairment originated from previously reported actin remodeling by hydrogen peroxide. CONCLUSIONS/SIGNIFICANCE: Thus, the defective machinery for ISP synthesis by causing mitochondrial iron dysmetabolism increases hydrogen peroxide production that accounts for the increased susceptibility to oxidative stress

Interactions of melatonin with mammalian mitochondria. Reducer of energy capacity and amplifier of permeability transition.

Melatonin, a metabolic product of the amino acid tryptophan, induces a dose-dependent energy drop correlated with a decrease in the oxidative phosphorylation process in isolated rat liver mitochondria. This effect involves a gradual decrease in the respiratory control index and significant alterations in the state 4/state 3 transition of membrane potential (ΔΨ). Melatonin, alone, does not affect the insulating properties of the inner membrane but, in the presence of supraphysiological Ca2+, induces a ΔΨ drop and colloid-osmotic mitochondrial swelling. These events are sensitive to cyclosporin A and the inhibitors of Ca2+ transport, indicative of the induction or amplification of the mitochondrial permeability transition. This phenomenon is triggered by oxidative stress induced by melatonin and Ca2+, with the generation of hydrogen peroxide and the consequent oxidation of sulfydryl groups, glutathione and pyridine nucleotides. In addition, melatonin, again in the presence of Ca2+, can also induce substantial release of cytochrome C and AIF (apoptosis-inducing factor), thus revealing its potential as a pro-apoptotic agent

Evaluating susceptibility of karst dolines (sinkholes) for collapse in Sango, Tennessee, USA

Dolines or sinkholes are earth depressions that develop in soluble rocks complexes such as limestone, dolomite, gypsum, anhydrite, and halite; dolines appear in a variety of shapes from nearly circular to complex structures with highly curved perimeters. The occurrence of dolines in the studied karst area is not random; they are the results of geomorphic, hydrologic and chemical processes that have caused partial subsidence, even total collapse of the land surface, when voids and caves are present in the bedrock and the regolith arch overbridging these voids is unstable. In the study area, the majority of collapses occur in the regolith (bedrock cover) that bridges voids in the bedrock. Because these collapsing dolines can damage property and cause even the loss of lives, there is a need to develop methods for evaluating karst hazards; such methods can be used by planners and practitioners for urban and economic development, especially in regions with a growing population. The purpose of this project is threefold: 1) to develop a karst feature database, 2) to investigate critical indicators associated with doline collapse, and 3) to design a doline susceptibility model for potential doline collapse based on external morphometric data. The study revealed the presence of short range spatial dependence in the distribution of the dolines’ morphometric parameters such as circularity, geographic orientation of the main doline axes and the length-to-width doline ratios; therefore, geostatistics can be used to spatially evaluate the susceptibility of the karst area for doline collapse using the probability of occurrence of these critical parameters. The partial susceptibility estimates were combined into final spatial probabilities enabling the identification of areas where undetected dolines may cause significant hazards