Mechanical unfolding of RNA hairpins

Mechanical unfolding trajectories, generated by applying constant force in optical tweezer experiments, show that RNA hairpins and the P5abc subdomain of the group I intron unfold reversibly. We use coarse-grained Go-like models for RNA hairpins to explore forced-unfolding over a broad range of temperatures. A number of predictions that are amenable to experimental tests are made. At the critical force the hairpin jumps between folded and unfolded conformations without populating any discernible intermediates. The phase diagram in the force-temperature (f,T) plane shows that the hairpin unfolds by an all-or-none process. The cooperativity of the unfolding transition increases dramatically at low temperatures. Free energy of stability, obtained from time averages of mechanical unfolding trajectories, coincide with ensemble averages which establishes ergodicity. The hopping time between the the native basin of attraction (NBA) and the unfolded basin increases dramatically along the phase boundary. Thermal unfolding is stochastic whereas mechanical unfolding occurs in "quantized steps" with great variations in the step lengths. Refolding times, upon force quench, from stretched states to the NBA is "at least an order of magnitude" greater than folding times by temperature quench. Upon force quench from stretched states the NBA is reached in at least three stages. In the initial stages the mean end-to-end distance decreases nearly continuously and only in the last stage there is a sudden transition to the NBA. Because of the generality of the results we propose that similar behavior should be observed in force quench refolding of proteins.Comment: 23 pages, 6 Figures. in press (Proc. Natl. Acad. Sci.

Eastern Enlargement of the EU: Bulgaria and Romania’s Accession- Geo-economic and Geopolitical Implications for the Balkans

The project’s aim is to look beyond the journalistic flash stories and the repetitive high pathos analysis of EU's Balkan Enlargement and explore in depth the geopolitical implications of such an important development. In other words, this thesis looks at two major questions, and namely, what are the geopolitical and geo-economic consequences for the Balkans, arising from Bulgaria and Romania’s accession to the EU and in a broader context what are the geo-economic and geopolitical changes that are shaping in the Balkans in the first decade of the 21st century? To answer these broader questions the research concentrates on series of other closely related, but narrowly focused questions, namely: How the EU policies of inclusion and exclusion in the Balkans could contribute to severe economic, political and cultural ghettoization of the Balkans in short to mid term perspective? What are the Geo-economic and Geopolitical Perspectives for the integrated Eastern component? (Bulgaria and Romania) Pathways from the West Periphery or Western Periphery Paths: Options for the Excluded Component? (Bosnia& Herzegovina, Albania, Kosovo, Serbia & Montenegro, Macedonia) Are we currently observing grandeur changes and the emergence of Bulgaria and Romania as a region with a new very important geopolitical value due to the concurrence of major developments? How can these two countries capitalize on their advanced Euro-Atlantic integration stage and lobby for a more engaged EU policy towards the whole region and specifically the West Balkans? The first section of the first chapter gives the historical framework of Balkan economic relations and the evolution from historical confrontation to cooperation.In the next section I explore the recent geopolitical developments and namely the emerging East-West split , running through the heart of the Balkan peninsula, with its east part in the final stages of EU integration (Bulgaria and Romania) and the ‘Wild West’ of the Balkans with no prospective of mid to long-term EU integration. The second chapter explores the geo-economic implications of Bulgaria and Romania’s EU accession for the region. The third chapter explores the major geo-political changes that are currently shaping the Balkans and more narrowly the geo-political implications of Bulgaria and Romania’s EU accession to the region.eu enlargement; eu accession; european union; bulgaria; romania; eastern enlargement; geopolitics; geo-economics; political economy; balkans

Laser nanotraps and nanotweezers for cold atoms: 3D gradient dipole force trap in the vicinity of Scanning Near-field Optical Microscope tip

Using a two-dipole model of an optical near-field of Scanning Near-field Optical Microscope tip, i. e. taking into account contributions of magnetic and electric dipoles, we propose and analyze a new type of 3D optical nanotrap found for certain relations between electric and magnetic dipoles. Electric field attains a minimum value in vacuum in the vicinity of the tip and hence such a trap is quite suitable for manipulations with cold atoms.Comment: 9 pages, 6 figure

Are there plasminos in superconductors?

Hot and/or dense, normal-conducting systems of relativistic fermions exhibit a particular collective excitation, the so-called plasmino. We compute the one-loop self-energy, the dispersion relation and the spectral density for fermions interacting via attractive boson exchange. It is shown that plasminos also exist in superconductors.Comment: 15 pages, 14 figures, revte

Chiral transition and mesonic excitations for quarks with thermal masses

We study the effect of a thermal quark mass, m_T, on the chiral phase transition and mesonic excitations in the light quark sector at finite temperature in a simple chirally-symmetric model. We show that while nonzero m_T lowers the chiral condensate, the chiral transition remains of second order. It is argued that the mesonic excitations have large decay rate at energies below 2m_T, owing to the Landau damping of the quarks and the van Hove singularities of the collective modes.Comment: 5 pages, 6 figures, typos correcte

Spontaneous emission rate of an excited atom placed near a nanofiber

The spontaneous decay rates of an excited atom placed near a dielectric cylinder are investigated. A special attention is paid to the case when the cylinder radius is small in comparison with radiation wavelength (nanofiber or photonic wire). In this case, the analytical expressions of the transition rates for different orientations of dipole are derived. It is shown that the main contribution to decay rates is due to quasistatic interaction of atom dipole momentum with nanofiber and the contributions of guided modes are exponentially small. On the contrary, in the case when the radius of fiber is only slightly less than radiation wavelength, the influence of guided modes can be substantial. The results obtained are compared with the case of dielectric nanospheroid and ideally conducting wire.Comment: 19 pages, 16 Postscript figure

Vanishing Thermal Mass in the Strongly Coupled QCD/QED medium

In this paper we perform a nonperturbative analysis of a thermal quasifermion in thermal QCD/QED by studying its self-energy function through the Dyson-Schwinger equation with the hard-thermal-loop resummed improved ladder kernel. Our analysis reveals several interesting results, some of which may force us to change the image of the thermal quasifermion: (1) The thermal mass of a quasifermion begins to decrease as the coupling gets stronger and finally disappears in the strong coupling region,(2) the imaginary part of the chiral invariant mass function (i.e., the decay width of the quasifermion) persists to have $O(g^2 T \log (1/g))$ behavior. Present results suggest that in the recently produced strongly coupled quark-gluon-plasma, the thermal mass of a quasifermion should vanish. We also briefly comment on evidence of the existence of a massless, or an ultrasoft mode.Comment: 6 pages, 8 figures, Published versio