755 research outputs found
Atomistic Models of DNA Charge Transfer
No full textIn Chap. 4, Koslowski and Cramer address the phenomenon of charge transport in DNA using a simple, but chemically specific approach intimately related to the Su-Schrieffer-Heeger model. In that model, the Hamiltonian is carefully parameterized using the ab-initio density-functional calculations. In the presence of an excess positive charge, the emerging potential energy surfaces for hole transfer are found to correspond to the formation of small polarons localized mainly on the individual bases. Thermally activated hopping between these states is analyzed using the Marcus theory of charge transfer. Their results are fully compatible with the conjecture of long-range charge transfer in DNA via two competing mechanisms, and the computations provide the corresponding charge-transfer rates both in the short-range superexchange and in the long-range hopping regime as the output of a single atomistic theory. Furthermore, it reproduces the order of magnitude of the current flow in DNA-gold nanojunctions, the over all shape of the current-voltage curves and their dependence upon the DNA sequence
DNA charge transfer: An atomistic model
No full textIn this work, we address the phenomenon of charge transport in DNA using a simple, but chemically specific, approach that is intimately related to the Su-Schrieffer-Heeger (SSH) model. The emerging potential energy surface for hole transport is analyzed using Marcus' theory of charge transfer. Our results are fully compatible with the conjecture of charge transfer in DNA via two competing mechanisms, and the computations provide the corresponding charge-transfer rates both in the short-range superexchange and in the long-range hopping regime as the output of a single atomistic theory. Finally, the model allows the computation of the transport properties of systems containing modified bases and of more complex arrangements of base pairs as an additional element of verification
Charge transfer through the nucleosome: A theoretical approach
No full textIn this work, we approach the problem of charge transfer in deoxyribonucleic acid (DNA) from a theoretical and numerical perspective. We focus on a DNA geometry characteristic of the eukaryotic genome and study transport along a superhelix that contains 292 nucleobases. The electronic structure is described within the Su-Schrieffer-Heeger model in an atomistic parameterization, which has been extended by a nonretarded reaction field to take dielectric polarization effects into account. The emerging potential energy surface is analyzed using the Marcus theory of electron transfer. The computed reaction coefficients are compared to their counterparts originating from idealized geometries and to experimental findings. This comparison and the palindromic nature of the DNA sequence used here permit the assessment of fluctuations in the local orientation of the bases and their impact upon transport properties
Theory and simulation of DNA charge transfer: From junctions to networks
No full textIn this work, we address charge transfer within complex arrangements of nucleobases from a theoretical and numerical point of view. We study dendrimers constructed from T-shaped double-stranded DNA three-way junctions (3WJs). The electronic structure of these junctions is computed on an atomistic level using a chemically specific Su-Schrieffer-Heeger Hamiltonian, which has been extended by a nonretarded reaction field to take solvent polarization effects into account. Hopping rates through isolated 3WJs are derived by analyzing the emerging potential energy surfaces using Marcus' theory of charge transfer. We find highly anisotropic transport; the corresponding rates are used to compute the global trapping kinetics on DNA dendrimers with a central absorbing core. As a potential application, we discuss a DNA-based drug delivery system
Static and dynamic aspects of DNA charge transfer: a theoretical perspective
No full textIn this work, we approach the impact of dynamic and static disorder on DNA charge transfer from a theoretical and numerical perspective. Disordered or defect geometries are either realized via molecular dynamics simulations using a classical force field or by experimentally determined DNA bulge structures. We apply a chemically specific, atomically resolved extended Su-Schrieffer-Heeger model to compute the energy parameters relevant to DNA charge transfer. For both models studied here, the effective donor-acceptor couplings-and hence the charge transfer rates-significantly depend upon the geometry. Dynamic disorder leads to a correlation time in this quantity of the order of 30 fs, and the transfer rates universally exhibit a broad, yet well-defined, exponential distribution. For DNA bulges, the angle characterizing the defect controls the charge transfer efficiency. The results are discussed and extensively compared to experimental findings and other calculations
Identiteter och världsbild : "hårdkokt" skriftbruk i Thorsten Jonssons noveller
No full textidentity and worldview – “hard-boiled” writing in Thorsten Jonsson’s short storiesThis article deals with the Swedish author Thorsten Jonsson (1910–50) and his first short story collection Som det brukar vara (1939) [‘As it usually is’]. The nar- rative represents a new modernistic literary trend in Swedish prose in the 1930s. i take my starting point in Burgess & ivanič’s (2010) theories of the act of writing involving many different identities, and particularly what Burgess & ivanič iden- tify as the discursive self. By contemporary readers and critics the discursive self in the short story collection was often connected with an American hard-boiled literary ideal, often linked to ernest Hemingway’s writings. in this article i dis- cuss the common textual features of the two authors’ first collections, but also the differences that emerge when looking through the linguistic surface. The analysis shows that Thorsten Jonsson’s discursive self is based upon a northern Swedish culture, Hemingway’s on an urban American one. </p
Measures of excess liquidity
No full textThe aim of this note is to provide an overview of various measures of excess liquidity, which can be defined as the deviation of the actual stock of money from an estimated equilibrium level. Given their dynamic nature, the excess liquidity measures under review are - in the light of long and variable lags of monetary policy - very useful tools to quantify future price pressures. In addition, excess liquidity measures consider inflation as a purely monetary phenomenon: neither the output gap nor liquidity gap - although both form an integral part of the concepts - an be held responsible for inducing a persistent rise in the price level. Despite strong theoretical support, the usefulness of excess liquidity measures depends on the stability of money demand, a question which has of course to be answered in the realm of empirical research. --P-star,excess liquidity,monetary policy,ECB
A case for money in the ECB monetary policy strategy
No full textOne major outcome of the review of the ECBs two pillar monetary policy strategy, which was published on 8 May 2003, has been the de facto downgrading of the hitherto prominent role assigned to the stock of money. According to the authors judgement, however, there is a strong theoretical and empirical rationale for the ECB monetary policy to pay close attention to the information content of money in the form of M3. However, the authors argue the ECB should make use of the so-called price gap or real money gap concept rather than the reference value as the latter runs the risk of giving misleading policy recommendations and compromising the indicator quality of the stock of money. Making use of M3 seems all the more rational as currently no better inflation indicator appears to exist in providing inflation forecasts in the euro area. --P-star,real money gap,excess liquidity,ECB
Why is unemployment so high in Bulgaria?
No full textThe author seeks to determine the main factors behind poor labor market outcomes in Bulgaria. Unemployment in Bulgaria is high and of long duration. The accumulation of the unemployment stock has been caused by relatively high inflows into unemployment coupled with limited outflows. These features of the Bulgarian labor market are typical of other transition economies in Central Europe and exploring their sources is of broad interest. The author focuses on determinants of and constraints to job creation. He uses data on job creation and job destruction from a survey of employment in all registered firms. He finds that the source of large inflows into unemployment is intensive enterprise restructuring associated with a high pace of job reallocation. However, job creation falls short of job destruction. Three main factors account for the limited job creation and hiring, and thus for low outflows from unemployment: a) The unfriendly business environment, reflected by a low rate of new firm formation, and a relatively small, small and medium enterprise sector. b) Labor market rigidities, including excessive hiring and firing costs. c) Skill and spatial mismatches brought about by enterprise restructuring, as well as low skills and marginalization of the long-term unemployed who cannot successfully compete for new jobs. The author recommends a three pronged strategy to improve labor market performance: (1) removing bureaucratic constraints to entry and expansion of firms; (2) enhancing labor market flexibility through lowering hiring and firing costs; and (3) improving the educational system so as to equip workers with broad and portable skills.Environmental Economics&Policies,Labor Policies,Labor Markets,Public Health Promotion,Health Monitoring&Evaluation,Environmental Economics&Policies,Labor Markets,Health Monitoring&Evaluation,Labor Standards,Banks&Banking Reform
Improvements to the Secure Construction and Utilization of Greedy Embeddings in Friend-to-Friend Overlays
No full textRouting based on greedy network embeddings enables efficient and privacy-preserving routing in overlays where connectivity is restricted to mutually trusted nodes. In previous works, we proposed security enhancements to the embedding and routing procedures to protect against denial-of-service attacks by malicious overlay participants. In this work, we propose an improved timeout scheme to reduce the stabilization overhead of secure tree maintenance in response to node failures and malicious behavior. Furthermore, we present an attack-resistant packet replication scheme that leverages alternative paths discovered during routing
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