A heuristic approach for new-item cold start problem in recommendation of micro open education resources

© Springer International Publishing AG, part of Springer Nature 2018. The recommendation of micro Open Education Resources (OERs) suffers from the new-item cold start problem because little is known about the continuously published micro OERs. This paper provides a heuristic approach to inserting newly published micro OERs into established learning paths, to enhance the possibilities of new items to be discovered and appear in the recommendation lists. It considers the accumulation and attenuation of user interests and conform with the demand of fast response in online computation. Performance of this approach has been proved by empirical studies

Construction of plant transformation vectors carrying beet necrotic yellow vein virus coat protein gene (ii)- plant transformation

Fragments containing the coat protein gene of beet necrotic yellow vein virus were cloned in two plant transformation vectors: pCAMBIA3301M with the bar gene as selectable marker, and pCAMBIA1304M, with resistance to hygromycin. Three constructs were made of each vector: CPL, containing coat protein gene with leader sequence; CPS with coat protein gene, and CPSas with coat protein gene in antisense orientation. Vectors pC3301MCPL, pC3301MCPS. and pC3301MCPSas were used in Agrobacterium—mediated transformation of Nicotiana tabacum (tobacco), Nicotiana excelsior and Nicotiana benthamiana. Regenerants that developed roots on selective media were tested for the presence of CP fragments and the bar gene, but most regenerants were nontransformed (50-83% escapes). After all rooted plants had been selfed, and T1 seed germinated on selective media, only plants descending from one N. excelsior regenerant transformed with pC3301MCPS were positive for presence of bar gene and CPS fragment. Tobacco and Nicotiana benthamiana were transformed with constructs pC1304MCPS and pC1304MCPSas. Transformation efficiency was much higher and approximately 50% of regenerants that rooted on media with 20 mg l−1 hygromycin were positive for the presence of CP fragments. All T1 plants were positive for presence of CP fragments

CCD standards for U and I in the open cluster NGC 7790

Photometric U and I standard sequences in the field of the open cluster NGC 7790 are presented. The intention is to achieve wide ranges in magnitude and colour, making these sequences suitable for calibrating deep CCD photometry. The 84 standard stars extend the BVR sequences of Odewahn et al. ([CITE]) to the near UV and IR, respectively

Surface photometry of galaxies in low density regions

We perform detailed surface photometry, based on B- and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies which were studied by Hopp et al. (1994) in the direction of three nearby voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different environments, and of a bright field galaxy sample. According to the obtained photometric characteristics, our sample is a mixture of intrinsically bright and faint galaxies, about 60% of them belonging to the bright subsample ($M_{B}~\langle~-19.0$). These bright ones show mean characteristics of typical Freeman's disks and are mainly located in the background of the observed voids. The faint subsample ($M_{B}~\geq~-19.0$) has parameters typical for the low-surface-brightness (LSB) galaxies. There are a few well isolated galaxies both among the bright and faint subsamples. About 40% of studied galaxies reveal ellipticity and position angle variations along of the radius. The $(B-R)$ colour indices of the observed galaxies span over a wide range of 0.5-1.8 mag with a median value at 1.11 mag, rather blue. About 30% of the observed galaxies reveal radial colour gradients at a 5σ significance level. These galaxies show typically red centers and are getting bluer towards the periphery. The most isolated galaxies in our sample show relatively blue colours ($B_{T}-R_{T}~\simeq$ 0.8). About 40% of the studied galaxies have surface brightness profiles which can be described by the model of single exponential disk. 38% of our galaxies have more complicated profiles and either can be approximated by two exponentials or show the presence of a small bulge. 20% of the observed galaxies have central light depression and outer irregularities – typical for some dwarf galaxies. These profile type frequencies are similar to those of faint field galaxy sample. The evolutionary history of both the isolated and clustered galaxies obviously results in similar photometric and structural characteristics. Thus the photometric methods alone are inadequate for selecting galaxies with different isolation properties