Collective Interaction-Driven Ratchet for Transporting Flux Quanta

We propose and study a novel way to produce a DC transport of vortices when applying an AC electrical current to a sample. Specifically, we study superconductors with a graduated random pinning density, which transports interacting vortices as a ratchet system. We show that a ratchet effect appears as a consequence of the long range interactions between the vortices. The pinned vortices create an asymmetric periodic flux density profile, which results in an asymmetric effective potential for the unpinned interstitial vortices. The latter exhibit a net longitudinal rectification under an applied transverse AC electric current.Comment: 4 pages, 5 postscript figure

Local cabbage (Brassica oleracea var. capitata L.) populations from Serbian Province of Vojvodina

In previous experiments, we were able to augment cabbages (Brassica oleracea L. var. capitata L.) with two new local open pollinated (OP) populations and one cultivar. The type of use indicated that these are cabbages with thinner and juicier leaves, which predisposes their heads for fine grating and also makes their leaves readily bendable and easy to roll up when pickled. The populations were collected in Vojvodina, North Province of Serbia, country located at the crossroads of Central and Southeastern Europe. Fresh cabbages are late-maturing white cabbages suitable for fresh consumption and biological fermentation. The third is a newly developed cultivar, bred by family selection. This cultivar has slight coloring by anthocyan that is red coloring of the head and rosette leaves. The fourth genotype in our trial was the local cultivar NS-Futoski. The morphological characters among OP populations were analysed by using principal component analysis (PCA). The first three principal components (PCs) gave Eigen values greater than 1.0 and explained 99.99% of the total variability among the cultivars and populations for all the traits investigated.Key words: Cabbage, local population, head characteristics

Variability of characteristics in new experimental hybrids of early cabbage (Brassica oleracea var. capitata L.)

Early hybrids take a significant share of the Serbian fresh vegetables market; however, all early hybrids are foreign. New domestic experimental hybrids of early cabbage have been analyzed and results are presented in this paper. In order to get a better insight in the variability among the tested hybrids, we have analyzed them for 14 characteristics by the principal component analysis (PCA) method. This paper deals with four principal components that explain 87.2% of the total variance. Out of the 14 traits analyzed, only seven traits had the highest communality with the first principal component and these were plant height, rosette diameter, the weight of the whole plant, head weight, the usable part of the head, head height and head diameter. All characteristics were positively correlated with the first principal component. Cabbage characteristics that constitute the first principal component are in fact the main objectives in programs of breeding early maturing cabbage. These characteristics explained 45.3% of the variability of the tested hybrids. If value of any of these seven characteristics is increased, the values of the other six characteristics increased proportionally. The results of this work have therefore contributed to a better understanding of the clustering of variability of the studied characteristics. These characteristics directly impact the formation of market value of new hybrids, and make them recognizable on the market.Key words: Cabbage, head weight, principal component analysis, useful portion

Stability of head weight in cabbage accessions (Brassica oleracea var. capitata L.)

An understanding of the causes of genotype x environment interaction can help in identifying traits and environments for better cultivar evaluation. The fact that head formation depends on other factors besides the cabbage accessions involved, makes it necessary to investigate accessions responses to agroecological growing conditions. Studied in the present paper was the stability of 21 cabbage accessions (10 cultivars and 11 F1-hybrids) with regard to head weight over three growing seasons. Joint analysis of variance revealed highly significant differences among the cabbage accessions, study years and accessions x year interactions. The parameter stability test showed that seven of the accessions (Kopenhaski and Elisa-F1 as early type; Tucana-F1 as summer type; Srpski melez, SG-3014, Ljubljanski and Rodeo-F1 as late type) significantly deviated from the regression line. Four of the seven accessions are cultivars and three F1-hybrids. These accessions had quite different regression coefficients around or above the value of one. Analysis of stability parameters for head weight showed the following accessions to be very stable: Copenhagen market (an early variety), Grenadier-F1 (a summer cabbage) and Ljubljanski (a late variety).Key words: Stability, variety, cabbage, interaction, growing

Probing superconducting phase fluctuations from the current noise spectrum of pseudogaped metal-superconductor tunnel junctions

We study the current noise spectra of a tunnel junction of a metal with strong pairing phase fluctuation and a superconductor. It is shown that there is a characteristic peak in the noise spectrum at the intrinsic Josephson frequency $\omega_J=2eV$ when $\omega_J$ is smaller than the pairing gap but larger than the pairing scattering rate. In the presence of an AC voltage, the tunnelling current noise shows a series of characteristic peaks with increasing DC voltage. Experimental observation of these peaks will give direct evidence of the pair fluctuation in the normal state of high-$T_c$ superconductors and from the half width of the peaks the pair decay rate can be estimated.Comment: 4 pages, 3 figure

Parity Effect in Ground State Energies of Ultrasmall Superconducting Grains

We study the superconductivity in small grains in the regime when the quantum level spacing $\delta\varepsilon$ is comparable to the gap $\Delta$. As $\delta\varepsilon$ is increased, the system crosses over from superconducting to normal state. This crossover is studied by calculating the dependence of the ground state energy of a grain on the parity of the number of electrons. The states with odd numbers of particles carry an additional energy $\Delta_P$, which shows non-monotonic dependence on $\delta\varepsilon$. Our predictions can be tested experimentally by studying the parity-induced alternation of Coulomb blockade peak spacings in grains of different sizes.Comment: 4 pages, revtex, multicol.st