Equilibrium spherically curved 2D Lennard-Jones systems

To learn about basic aspects of nano-scale spherical molecular shells during their formation, spherically curved two-dimensional N-particle Lennard-Jones systems are simulated, studying curvature evolution paths at zero-temperature. For many N-values (N<800) equilibrium configurations are traced as a function of the curvature radius R. Sharp jumps for tiny changes in R between trajectories with major differences in topological structure correspond to avalanche-like transitions. For a typical case, N=25, equilibrium configurations fall on smooth trajectories in state space which can be traced in the E-R plane. The trajectories show-up with local energy minima, from which growth in N at steady curvature can develop.Comment: 10 pages, 2 figures, to be published in Journal of Chemical Physic

REGIONALY IMPORTANT SINCRO.GRID SMART GRID PROJECT

Regional transmission and distribution challenges has evolved and changed a lot in recent years. Four contradictory influences increasingly affected the operations of Slovenian and Croatian electricity systems. Regional electricity systems experienced increasing support of RES integration to meet the EU targets, a lower electricity consumption due to the economic crisis, a growing lack of centralized electricity production for electric system support and the high interconnectivity between the neighboring control zones. TSOs and DSOs observed growing network overvoltage issues as well as a decrease in secondary reserve capacities. Such situation starts to impact national and regional renewable integration targets affecting the security of supply at European level. SINCRO.GRID joint investment project addressed the above-mentioned issues in a sustainable manner. Such cross-border systemic approach will bring synergetic benefits. It will enable an acceptable level of security of operation for at least the next ten years hosting levels of RES in line with the trends foreseen to reach the 2030 targets safely. The project is going to integrate new active elements in the transmission and distribution grids. It leans on the following main pillars: deployment of six compensation devices, deployment of advanced dynamic thermal rating (DTR) systems, deployment of electricity storage systems, integration of distributed renewable generation (DG) and deployment of a virtual cross-border control center (VCBCC). A key aspect of the SINCRO.GRID project lies in the synergy brought by the simultaneous innovative deployment of a portfolio of mature technology-based solutions bring high benefits and positive externalities for the region and European Union

REGIONALY IMPORTANT SINCRO.GRID SMART GRID PROJECT

Regional transmission and distribution challenges has evolved and changed a lot in recent years. Four contradictory influences increasingly affected the operations of Slovenian and Croatian electricity systems. Regional electricity systems experienced increasing support of RES integration to meet the EU targets, a lower electricity consumption due to the economic crisis, a growing lack of centralized electricity production for electric system support and the high interconnectivity between the neighboring control zones. TSOs and DSOs observed growing network overvoltage issues as well as a decrease in secondary reserve capacities. Such situation starts to impact national and regional renewable integration targets affecting the security of supply at European level. SINCRO.GRID joint investment project addressed the above-mentioned issues in a sustainable manner. Such cross-border systemic approach will bring synergetic benefits. It will enable an acceptable level of security of operation for at least the next ten years hosting levels of RES in line with the trends foreseen to reach the 2030 targets safely. The project is going to integrate new active elements in the transmission and distribution grids. It leans on the following main pillars: deployment of six compensation devices, deployment of advanced dynamic thermal rating (DTR) systems, deployment of electricity storage systems, integration of distributed renewable generation (DG) and deployment of a virtual cross-border control center (VCBCC). A key aspect of the SINCRO.GRID project lies in the synergy brought by the simultaneous innovative deployment of a portfolio of mature technology-based solutions bring high benefits and positive externalities for the region and European Union

Advances in the management of gout: Critical appraisal of febuxostat in the control of hyperuricemia

Gout recently passed rheumatoid arthritis to become the most common inflammatory arthritis in the United States (US). However, epidemiologic studies indicate that the quality of gout management is suboptimal owing to both patient and physician issues. Only three options for urate-lowering therapy are currently available in the US: allopurinol, probenecid, and recently, febuxostat. Probenecid is generally safe except for the occurrence of urolithiasis, but is only effective for the subset of patients with better kidney function. Allopurinol use is limited due to its side effects, potential toxicity of uncertain magnitude in patients with renal disease, and failure to achieve targeted serum urate levels. In part this failure may be due to the necessity for it to be titrated for optimal therapeutic effect. Febuxostat is a new medication that may offer several advantages and can be given as an alternative to allopurinol. We review the basic biology and clinical performance of febuxostat, and consider the potential utility of this agent in comparison to the older, better-established gout therapeutics

Dynamics of Air-Fluidized Granular System Measured by the Modulated Gradient Spin-echo

The power spectrum of displacement fluctuation of beads in the air-fluidized granular system is measured by a novel NMR technique of modulated gradient spin-echo. The results of measurement together with the related spectrum of the velocity fluctuation autocorrelation function fit well to an empiric formula based on to the model of bead caging between nearest neighbours; the cage breaks up after a few collisions \cite{Menon1}. The fit yields the characteristic collision time, the size of bead caging and the diffusion-like constant for different degrees of system fluidization. The resulting mean squared displacement increases proportionally to the second power of time in the short-time ballistic regime and increases linearly with time in the long-time diffusion regime as already confirmed by other experiments and simulations.Comment: 4 figures. Submited to Physical Review Letters, April 200

Complexation of DNA with Cationic Surfactant

Transfection of an anionic polynucleotide through a negatively charged membrane is an important problem in genetic engineering. The direct association of cationic surfactant to DNA decreases the effective negative charge of the nucleic acid, allowing the DNA-surfactant complex to approach a negatively charged membrane. The paper develops a theory for solutions composed of polyelectrolyte, salt, and ionic surfactant. The theoretical predictions are compared with the experimental measurements.Comment: 9 pages, 3 figure

Critical swelling of particle-encapsulating vesicles

We consider a ubiquitous scenario where a fluctuating, semipermeable vesicle is embedded in solution while enclosing a fixed number of solute particles. The swelling with increasing number of particles or decreasing concentration of the outer solution exhibits a continuous phase transition from a fluctuating state to the maximum-volume configuration, whereupon appreciable pressure difference and surface tension build up. This criticality is unique to particle-encapsulating vesicles, whose volume and inner pressure both fluctuate. It implies a universal swelling behavior of such vesicles as they approach their limiting volume and osmotic lysis.Comment: 4 pages, 1 figur

Theoretical model for the formation of caveolae and similar membrane invaginations

We study a physical model for the formation of bud-like invaginations on fluid lipid membranes under tension, and apply this model to caveolae formation. We demonstrate that budding can be driven by membrane-bound proteins, provided that they exert asymmetric forces on the membrane that give rise to bending moments. In particular, caveolae formation does not necessarily require forces to be applied by the cytoskeleton. Our theoretical model is able to explain several features observed experimentally in caveolae, where proteins in the caveolin family are known to play a crucial role in the formation of caveolae buds. These include 1), the formation of caveolae buds with sizes in the 100-nm range and 2), that certain N- and C-termini deletion mutants result in vesicles that are an order-of-magnitude larger. Finally, we discuss the possible origin of the morphological striations that are observed on the surfaces of the caveolae

Fluctuation spectrum of fluid membranes coupled to an elastic meshwork: jump of the effective surface tension at the mesh size

We identify a class of composite membranes: fluid bilayers coupled to an elastic meshwork, that are such that the meshwork's energy is a function $F_\mathrm{el}[A_\xi]$ \textit{not} of the real microscopic membrane area $A$, but of a \textit{smoothed} membrane's area $A_\xi$, which corresponds to the area of the membrane coarse-grained at the mesh size $\xi$. We show that the meshwork modifies the membrane tension $\sigma$ both below and above the scale $\xi$, inducing a tension-jump $\Delta\sigma=dF_\mathrm{el}/dA_\xi$. The predictions of our model account for the fluctuation spectrum of red blood cells membranes coupled to their cytoskeleton. Our results indicate that the cytoskeleton might be under extensional stress, which would provide a means to regulate available membrane area. We also predict an observable tension jump for membranes decorated with polymer "brushes"

A Sucrose Solution Application to the Study of Model Biological Membranes

The small-angle X-ray and neutron scattering, time resolved X-ray small-angle and wide-angle diffraction coupled with differential scanning calorimetry have been applied to the investigation of unilamellar and multilamellar dimyristoylphosphatidylcholine (DMPC) vesicles in sucrose buffers with sucrose concentrations from 0 to 60%. Sucrose buffer decreased vesicle size and polydispersity and increased an X-ray contrast between phospholipid membrane and bulk solvent sufficiently. No influence of sucrose on the membrane thickness or mutual packing of hydrocarbon chains has been detected. The region of sucrose concentrations 30%-40% created the best experimental conditions for X-ray small-angle experiments with phospholipid vesicles.Comment: PDF: 10 pages, 6 figures. MS Word sours