University of Crete

About: University of Crete is a education organization based out in Rethymno, Greece. It is known for research contribution in the topics: Population & Galaxy. The organization has 8681 authors who have published 21684 publications receiving 709078 citations. The organization is also known as: Panepistimio Kritis.

Alleviating the sparsity problem of collaborative filtering using trust inferences

Abstract: Collaborative Filtering (CF), the prevalent recommendation approach, has been successfully used to identify users that can be characterized as “similar” according to their logged history of prior transactions. However, the applicability of CF is limited due to the sparsity problem, which refers to a situation that transactional data are lacking or are insufficient. In an attempt to provide high-quality recommendations even when data are sparse, we propose a method for alleviating sparsity using trust inferences. Trust inferences are transitive associations between users in the context of an underlying social network and are valuable sources of additional information that help dealing with the sparsity and the cold-start problems. A trust computational model has been developed that permits to define the subjective notion of trust by applying confidence and uncertainty properties to network associations. We compare our method with the classic CF that does not consider any transitive associations. Our experimental results indicate that our method of trust inferences significantly improves the quality performance of the classic CF method.

Modeling of thermal transport in pillared-graphene architectures.

Abstract: Carbon nanotubes (CNT) and graphene are considered as potential future candidates for many nano/microscale integrated devices due to their superior thermal properties. Both systems, however, exhibit significant anisotropy in their thermal conduction, limiting their performance as three-dimensional thermal transport materials. From thermal management perspective, one way to tailor this anisotropy is to consider designing alternative carbon-based architectures. This paper investigates the thermal transport in one such novel architecture—a pillared-graphene (PG) network nanostructure which combines graphene sheets and carbon nanotubes to create a three-dimensional network. Nonequilibrium molecular dynamics simulations have been carried out using the AIREBO potential to calculate the thermal conductivity of pillared-graphene structures along parallel (in-plane) as well as perpendicular (out-of-plane) directions with respect to the graphene plane. The resulting thermal conductivity values for PG systems are di...

Structure and stability of SiC nanotubes

Abstract: We propose structural and electronic properties of recently synthesized SiC nanotubes. The nanotubes with a Si to C ratio of 1:1 exhibit rich morphologies and are shown to belong to two distinct categories that are close in energies but show significant differences in electronic and transport properties. Similarities and differences are invoked with the case of BN nanotubes to explain the observed surface reconstruction.

High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies

Abstract: We present R � 600, 10Y37 � m spectra of 53 ultraluminous infrared galaxies (ULIRGs), taken using the Infrared SpectrographonboardSpitzer.Thespectra showfine-structureemissionlines of neon,oxygen,sulfur,silicon, argon, chlorine, iron, and phosphorous; molecular hydrogen lines, and C2H2, HCN, and OHabsorption features. We em- ploy diagnostics based on the fine-structure lines, the polycyclic aromatic hydrocarbon (PAH) features and the 9.7 � m silicate absorption feature, to show that the infrared emission from most ULIRGs is powered mostly by star formation, with only � 20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of (Ne v) k14.32injustunderhalfthesample,however,impliesthatanAGNcontributessignificantlytothemid-IRfluxin � 42% of ULIRGs.ThestarburstsandAGNsinULIRGsappearmoreextincted,andforthestarburstsmorecompactthanthose in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with LP10 11.5 L� , although the NLR gas in ULIRGs may be more dense. We show thatthe(Neii)k12.81+(Neiii)k15.56 luminositycorrelateswithbothinfraredluminosityandtheluminosityof the 6.2 and 11.2 � m PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show thatULIRGswithsilicateabsorptionstrengthsSsilof 0:8PSsilP2:4 arelikelytobepoweredmainlybystarformation, but that ULIRGs with Ssil P0:8, and possibly those with Ssil k2:4, contain an IR-luminous AGN. Subject headingg galaxies: active — galaxies: evolution — galaxies: starburst — infrared: galaxies Online material: color figures