C-axis optical properties of high Tc cuprates

A review is given of the experimental status of the interlayer coupling energy in the cuprates. A second c-axis plasmon is identified in the double layer compound Y123 for various dopings. The anomalous transport properties along the c-direction and in the planar directions are compared to model calculations based on strongly anisotropic scattering. An excellent description of the optical data at optimal doping is obtained if an anomalously large anisotropy of the scattering rate between cold spots and hot spots is assumed. This raises questions as to the physical meaning of these parameters.Comment: 4 pages, LaTeX, espcrc2.sty, 3 figures in encapsulated postscript forma

Center for Fishery and Applied Hydrobiology “Little Danube”, Experimental School Estate “Radmilovac”: Synergy of Research, Economy and Society

In every society, initiators and promoters of the development are individuals, teams or institutions with a vision, good ideas, seriousness, but above enthusiasm to work hard. They trace the road and drive activities related to research and/or economy. In the Serbian aquaculture sector such institutions is the Faculty of Agriculture and its Center for Fishery and Applied Hydrobiology (CEFAH) (or the “Little Danube”), which operates within the Experimental school estate “Radmilovac”. The Center started to be established in 2007. Unlike other similar Centers built by state resources intended for research and scientific work, the “Little Danube” was created much more as a result of enthusiasm of a group of researchers and their readiness to cooperate with national and international institutions, but also by enthusiasm of individuals ready to financially or materially help some of the Center’s programs. The Center’s activities are directed towards improving and developing the research and economy in aquaculture. Today the Center in “Radmilovac” and its laboratories located in the building of the Faculty of Agriculture represent an education and research polygon for aquaculture development. The education part is aimed at all levels: from pre-school and elementary school level by educational visits to the “Little Danube”, where they get to know different fish species and other aquatic organisms, their culture, fishing, fishing tools; to PhD level students and researchers that increase their knowledge and skills in the Center. CEFAH is a scientific polygon: in its aquaria, tanks, RAS systems, as well as in a number of earthen ponds a range of various experiments in different areas of aquaculture are carried out and knowledge is transferred directly in aquaculture economy. The development of Serbian aquaculture is directly affected by the connection of the Center with the economy through realization of biotechnology projects, fish selective breeding programs, and experiments

Superconductivity, phase fluctuations and the c-axis conductivity of bilayer high temperature superconductors

We present a theory of the interplane conductivity of bilayer high temperature superconductors, focusing on the effect of quantal and thermal fluctuations on the oscillator strengths of the superfluid stiffness and the bilayer plasmon. We find that the opening of the superconducting gap and establishment of superconducting phase coherence each lead to redistribution of spectral weight over wide energy scales. The factor-of-two relation between the superfluid stiffness and the change below $T_c$ in the oscillator strength of the absorptive part of the conductivity previously derived for single-layer systems, is found to be substantially modified in bilayer systems.Comment: 11 pages, 14 figure

Correlation between the Josephson coupling energy and the condensation energy in bilayer cuprate superconductors

We review some previous studies concerning the intra-bilayer Josephson plasmons and present new ellipsometric data of the c-axis infrared response of almost optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8}. The c-axis conductivity of this compound exhibits the same kind of anomalies as that of underdoped YBa_{2}Cu_{3}O_{7-delta}. We analyze these anomalies in detail and show that they can be explained within a model involving the intra-bilayer Josephson effect and variations of the electric field inside the unit cell. The Josephson coupling energies of different bilayer compounds obtained from the optical data are compared with the condensation energies and it is shown that there is a reasonable agreement between the values of the two quantities. We argue that the Josephson coupling energy, as determined by the frequency of the intra-bilayer Josephson plasmon, represents a reasonable estimate of the change of the effective c-axis kinetic energy upon entering the superconducting state. It is further explained that this is not the case for the estimate based on the use of the simplest ``tight-binding'' sum rule. We discuss possible interpretations of the remarkable agreement between the Josephson coupling energies and the condensation energies. The most plausible interpretation is that the interlayer tunneling of the Cooper pairs provides the dominant contribution to the condensation energy of the bilayer compounds; in other words that the condensation energy of these compounds can be accounted for by the interlayer tunneling theory. We suggest an extension of this theory, which may also explain the high values of T_{c} in the single layer compounds Tl_{2}Ba_{2}CuO_{6} and HgBa_{2}CuO_{4}, and we make several experimentally verifiable predictions.Comment: 16 pages (including Tables) and 7 figures; accepted for publication in Physical Review

Stanje ribarstva u Srbiji

Fishery in Serbia comprises of aquaculture and fishery. Aquaculture in Serbia concerns fish culturing. For production of other aquatic animals, mainly ornamental plants and crayfish, only occasional interest and small scale production in aquarium type of units exists. Fish are produced in carp and trout fish farms (over 95%), to a smaller extent in cages, enclosed or partitioned natural or man made aquatic ecosystems. Aquaria fish culture is mainly low scale, with a small number of specialized breeders and one public aquarium (M a r k o v i ć i M i t r o v i ć T u t u n d ž i ć, 2003, 2005; M a r k o v i ć i P o l e k s i ć, 2007, M a r k o v i ć i sar., 2009). In Serbia freshwater species cultured are: common carp, white and gray bighead, wells, pike perch, rainbow trout and to a lesser degree Northern pike, tench, brown trout, beluga, Russian starlet. There is 13 500 – 14 000 ha of fish farms in Serbia, with 99.9% of carp farms and 0.1% of trout farms. The total fish production in recent years is between 10 000 and 15 000 tons with 70 to 75% of consumable fish. All three types of production systems are present: extensive, semi-intensive and intensive. Extensive production is sporadic and is present only at a few carp production units, mostly not economic for semi-intensive production due to remoteness from other production units or neglect. The principal type of production (75 – 80%) is semi-intensive production of cyprinids, with common carp as the main species. Common carp is present with more than 80% of the total production in warmwater fish farms. The traditional (old) type of feeding is slowly changing. Cereals are more often, at over 50% of production surfaces, totally of partially replaced by complete, peletted and even more extruded feed. This has resulted in an increase of production per surface unit in recent years. Intensive production systems in carp culture are less present, at a small number of earthen ponds with aeration systems, mainly for fish fry production, and in cages. However, rainbow trout, the only salmonid species cultured for consummation, is exclusively produced in intensive systems at trout farms in Serbia. The number of people involved full-time in fish production in Serbia is about 1100 and approximately 400 seasonal workers that are hired mainly prior to harvest. With the rising of standard and returning to traditional habits during religious fasting, as well as with a slow increase of “healthy food” supporters, fish consumption has a growing trend. However, although fish production is increasing in recent years, the country’s production and open-water capture fishery barely represent a quarter of the total needs of inhabitants. This results in increase of import, mainly marine and frizzed fish, but also freshwater fish. Open-water capture fishery is performed in Serbia’s fishing waters. They are represented by 66 000 km of water currents (rivers and streams), flood plains, backwaters, 50 lakes, 150 reservoir lakes and around 30 000 km of canal systems, hydromeliorative systems, as well as all other waters with fish. All fishing waters are divided into 6 fishing regions (Serbia – Vojvodina, Serbia – West, Serbia – South West, Srbia - South, Serbia – East, Serbia – Center) since year 2007. Sports fishing is obtainable at all regions but commercial fishery is aloud only at two regions (Serbia – Vojvodina, Serbia – west), and in rivers Tisa, Sava and Danube. Number of fisherman with purchased license in the last couple of years is between 50 000 and 100 000. Number of commercial fishermen is between 500 and 2000 in the last ten years. The amount of captured fish is between 2000 and 3000 tons in the few past years

Differential requirements for actin during yeast and mammalian endocytosis

Key features of clathrin-mediated endocytosis have been conserved across evolution. However, endocytosis in Saccharomyces cerevisiae is completely dependent on a functional actin cytoskeleton, whereas actin appears to be less critical in mammalian cell endocytosis. We reveal that the fundamental requirement for actin in the early stages of yeast endocytosis is to provide a strong framework to support the force generation needed to direct the invaginating plasma membrane into the cell against turgor pressure. By providing osmotic support, pressure differences across the plasma membrane were removed and this reduced the requirement for actin-bundling proteins in normal endocytosis. Conversely, increased turgor pressure in specific yeast mutants correlated with a decreased rate of endocytic patch invagination

Penetration of Josephson vortices and measurement of the c-axis penetration depth in Bi2Sr2CaCu2O8+δBi_{2}Sr_{2}CaCu_{2}O_{8+\delta}: Interplay of Josephson coupling, surface barrier and defects

The first penetration field H_{J}(T) of Josephson vortices is measured through the onset of microwave absorption in the locked state, in slightly overdoped $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}}$ single crystals (T_{c} ~ 84 K). The magnitude of H_{J}(T) is too large to be accounted for by the first thermodynamic critical field H_{c1}(T). We discuss the possibility of a Bean-Livingston barrier, also supported by irreversible behavior upon flux exit, and the role of defects, which relates H_{J}(T) to the c-axis penetration depth $\lambda_{c}(T)$. The temperature dependence of the latter, determined by a cavity perturbation technique and a theoretical estimate of the defect-limited penetration field are used to deduce from H_{J}(T) the absolute value of $\lambda_{c}(0)=(35 \pm 15) \mu m$.Comment: 9 pages, 6 figure

Decoupling of a Current-Biased Intrinsic Josephson Junction from its Environment

We have observed a dissipative phase diffusion branch in arrays of hysteretic high-Tc intrinsic Josephson junctions. By comparing the data with a thermal activation model we extract the impedance seen by the junction in which phase diffusion is occurring. At the plasma frequency this junction is isolated from its environment and it sees its own large (~ kilo Ohm) impedance. Our results suggest that stacks of Josephson junctions may be used for isolation purposes in the development of a solid state quantum computer

Influence of Chemical Structure on the Stability and Conductance of Porphyrin Single-Molecule Junctions

Quantum Matter and Optic