Novel Rearrangement of Sulfur Ylides and Application to the Synthesis of Tagetitoxin

This thesis presents the work undertaken towards the total synthesis of tagetitoxin. This phytotoxin was isolated in 1981 from a strain of Pseudomonas syringae bacteria, and was shown to specifically inhibit eukaryotic RNA polymerase III from a broad phylogenetic range. A structure has been proposed for tagetitoxin as a highly functionalised 9-oxa-3-thiabicyclo[3.3.1]nonane, but some ambiguity still remains over its absolute configuration and the position of carbonyl substituents. A synthetic route would allow to confirm or revise the proposed structure, provide a possible entry to analogues and increase supplies of the toxin for biological studies on transcription mechanism. A novel one-carbon ring expansion of 1,3-oxathiolanes was developed in view of constructing the core structure of tagetitoxin. A series of model substrates were successfully converted to the corresponding 1,4-oxathianes using ethyl (triethylsilanyl)diazoacetate and a copper catalyst. The reaction is expected to occur via an intermediate sulfur ylide, which rearranges to give the ring-expanded product. This methodology will be applied to a fully functionalised bicyclic precursor to assemble the tagetitoxin frame. Synthetic studies are described towards the synthesis of the precursor. An aldol reaction between methyl l,3-oxathiolane-5-carboxylate and a protected 2-azido-3,4- dihydroxybutanal was envisaged to form a functionalised branched 5-mercaptomethyl- 5-hydroxypentanal. Intramolecular thioacetal formation would give the fully substituted bicyclic substrate for ring-expansion. Three approaches to the azidoaldehyde fragment were carried out, which were based on regioselective azide opening of chiral epoxyalcohols. The methyl l,3-oxathiolane-5- carboxylate fragment was derived from L-serine, using a one pot cyclisation / sulfur deprotection reaction. Model reactions however showed that the enolate of the 1,3- oxathiolane ester was not stable under aldol conditions, possibly due to [beta]-elimination of the sulfur

Current and voltage based bit errors and their combined mitigation for the Kirchhoff-law-Johnson-noise secure key exchange

We classify and analyze bit errors in the current measurement mode of the Kirchhoff-law-Johnson-noise (KLJN) key distribution. The error probability decays exponentially with increasing bit exchange period and fixed bandwidth, which is similar to the error probability decay in the voltage measurement mode. We also analyze the combination of voltage and current modes for error removal. In this combination method, the error probability is still an exponential function that decays with the duration of the bit exchange period, but it has superior fidelity to the former schemes.Comment: 9 pages, accepted for publication in Journal of Computational Electronic

A paradox in bosonic energy computations via semidefinite programming relaxations

We show that the recent hierarchy of semidefinite programming relaxations based on non-commutative polynomial optimization and reduced density matrix variational methods exhibits an interesting paradox when applied to the bosonic case: even though it can be rigorously proven that the hierarchy collapses after the first step, numerical implementations of higher order steps generate a sequence of improving lower bounds that converges to the optimal solution. We analyze this effect and compare it with similar behavior observed in implementations of semidefinite programming relaxations for commutative polynomial minimization. We conclude that the method converges due to the rounding errors occurring during the execution of the numerical program, and show that convergence is lost as soon as computer precision is incremented. We support this conclusion by proving that for any element p of a Weyl algebra which is non-negative in the Schrodinger representation there exists another element p' arbitrarily close to p that admits a sum of squares decomposition.Comment: 22 pages, 4 figure

Phosphoproteomics data classify hematological cancer cell lines according to tumor type and sensitivity to kinase inhibitors

This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

On KLJN-based secure key distribution in vehicular communication networks

In a former paper [Fluct. Noise Lett., 13 (2014) 1450020] we introduced a vehicular communication system with unconditionally secure key exchange based on the Kirchhoff-Law-Johnson-Noise (KLJN) key distribution scheme. In this paper, we address the secure KLJN key donation to vehicles. This KLJN key donation solution is performed lane-by-lane by using roadside key provider equipment embedded in the pavement. A method to compute the lifetime of the KLJN key is also given. This key lifetime depends on the car density and gives an upper limit of the lifetime of the KLJN key for vehicular communication networks.Comment: Accepted for publicatio

Cable Capacitance Attack against the KLJN Secure Key Exchange

The security of the Kirchhoff-law-Johnson-(like)-noise (KLJN) key exchange system is based on the Fluctuation-Dissipation-Theorem of classical statistical physics. Similarly to quantum key distribution, in practical situations, due to the non-idealities of the building elements, there is a small information leak, which can be mitigated by privacy amplification or other techniques so that the unconditional (information theoretic) security is preserved. In this paper, the industrial cable and circuit simulator LTSPICE is used to validate the information leak due to one of the non-idealities in KLJN, the parasitic (cable) capacitance. Simulation results show that privacy amplification and/or capacitor killer (capacitance compensation) arrangements can effectively eliminate the leak.Comment: Accepted for publication in the journal: Informatio

The Elasticity of Taxable Income with Respect to Marginal Tax Rates: A Critical Review

This paper critically surveys the large and growing literature estimating the elasticity of taxable income with respect to marginal tax rates (ETI) using tax return data. First, we provide a theoretical framework showing under what assumptions this elasticity can be used as a sufficient statistic for efficiency and optimal tax analysis. We discuss what other parameters should be estimated when the elasticity is not a sufficient statistic. Second, we discuss conceptually the key issues that arise in the empirical estimation of the elasticity of taxable income using the example of the 1993 top individual income tax rate increase in the United States to illustrate those issues. Third, we provide a critical discussion of most of the taxable income elasticities studies to date, both in the United States and abroad, in light of the theoretical and empirical framework we laid out. Finally, we discuss avenues for future research.

Three Acts of Resistance during the 2014–16 West Africa Ebola Epidemic

Abstract Community engagement is commonly regarded as a crucial entry point for gaining access and securing trust during humanitarian emergencies. In this article, we present three case studies of community engagement encounters during the West African Ebola outbreak. They represent strategies commonly implemented by the humanitarian response to the epidemic: communication through comités de veille villageois in Guinea, engagement with NGO-affiliated community leadership structures in Liberia and indirect mediation to chiefs in Sierra Leone. These case studies are based on ethnographic fieldwork carried out before, during and after the outbreak by five anthropologists involved in the response to Ebola in diverse capacities. Our goal is to represent and conceptualise the Ebola response as a dynamic interaction between a response apparatus, local populations and intermediaries, with uncertain outcomes that were negotiated over time and in response to changing conditions. Our findings show that community engagement tactics that are based on fixed notions of legitimacy are unable to respond to the fluidity of community response environments during emergencies.</jats:p

A Characterization of the ALMA Phasing System at 345 GHz

The development of the Atacama Large Millimeter/submillimeter Array (ALMA) phasing system (APS) has allowed ALMA to function as an extraordinarily sensitive station for very long baseline interferometry (VLBI) at frequencies of up to 230 GHz (~1.3 mm). Efforts are now underway to extend use of the APS to 345 GHz (~0.87 mm). Here we report a characterization of APS performance at 345 GHz based on a series of tests carried out between 2015-2021, including a successful global VLBI test campaign conducted in 2018 October in collaboration with the Event Horizon Telescope (EHT).Comment: 22 pages, 11 figures, 7 tables, accepted for publication in PAS