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In order to measure the quality of the results of a RS, there is a wide range of metrics which are used to evalúate both the prediction and recommendation quality of these systems [17,1,18,6].CF based RS estímate the valué of an item not voted by a user via the ratings made on that item by a set of similar users. The overall quality in the prediction is called accuracy [3] and the mean absolute error (MAE) is normally used to obtain it [17]. The system's ability to make estimations is called coverage and it indicates the percentage of prediction which we can make using the set of similar users selected (usually, the more similar users we select and the more votes the selected users have cast, the better the coverage we achieve). In RS, besides aiming to improve the quality measures of the predictions (accuracy and coverage), there are other issues that need be taken into account [56,41,51]: avoiding overspecialization phenomena, finding good Ítems, credibility of recommendations, precisión and recall measures, etc.The rest of the paper is divided into the following sections (with the same numbering shown here):2. State of the art, in which a review is made of the most relevant contributions that exist in the CF aspects covered in the paper: cold-start and application of neural networks to the RS. 3. General hypothesis and motivations: what we aim to contribute and the indications that lead us to believe that carrying out research into this subject will provide satisfactory results that support the hypothesis set out. 4. Design of the user cold-start similarity measure: explanation and formalization of the design of the similarity measure proposed as a linear combination of simple similarity measures, by adjusting the weights using optimization techniques based on neural networks. 5. Collaborative filtering specifications: formalization of the CF methodology which specifies the way to predict and recommend, as well as to obtain the quality valúes of the predictions and recommendations. This is the formalization that supports the design of experiments carried out in the paper. The methodology is provided which describes the use of leave-one-out cross validation applied to obtaining the MAE, coverage, precisión and recall. 6. Design of the experiments with which the quality results are obtained provided by the user cold-star similarity measure proposed and by a set of current similarity measures for which we aim to improve the results. We use the Netflix (http:// www.netflixprize.com) and Movielens (http://www.movielens.org) databases. 7. Graphical results obtained in the experiments, complemented with explanations of the behavior of each quality measure. 8. Most relevant conclusions obtained. State of the art The cold-start issueThe cold-start problem [48,1] occurs when it is not possible to make reliable recommendations due to an initial lack of ratings. We can distinguish three kinds of cold-start problems: new community, new item and new user. The last kind is the most important in RS that are already in operat...

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The immunological bone marrow (BM) microenvironment plays a major role in controlling growth and survival of clonal plasma cells (PC); this might translate into different patterns of expression of molecules involved in immune responses on PC from different types of monoclonal gammopathies (MG). We have studied the expression of a group of nine such molecules on both BMPC and the plasma of 61 newly diagnosed MG patients (30 MG of undetermined significance (MGUS), 27 multiple myeloma (MM) and four plasma cell leukemia (PCL)) and five normal individuals. Clonal PC from all MG displayed significantly increased levels of CD56, CD86 and CD126, and decreased amounts of CD38 (Po0.001). Additionally, HLA-I and b2-microglobulin were abnormally highly expressed in MGUS, while CD40 expression was decreased in MM and PCL (Po0.05). Interestingly, a progressive increase in the soluble levels of b2-microglobulin was found from MGUS to MM and PCL patients (P ¼ 0.03). In contrast, all groups showed similar surface and soluble amounts of CD126, CD130 and CD95, except for increased soluble levels of CD95 observed in PCL. Overall, those phenotypic differences are consistent with increased antigen presentation and costimulatory capacities in MGUS, which progressively deteriorate in malignant MG (MM and PCL).

Recommender systems play an important role in reducing the negative impact of information overload on those websites where users have the possibility of voting for their preferences on Ítems. The most normal technique for dealing with the recommendation mechanism is to use collaborative filtering, in which it is essential to discover the most similar users to whom you desire to make recommendations. The hypothesis of this paper is that the results obtained by applying traditional similarities measures can be improved by taking contextual information, drawn from the entire body of users, and using it to calcúlate the singularity which exists, for each item, in the votes cast by each pair of users that you wish to compare. As such, the greater the measure of singularity result between the votes cast by two given users, the greater the impact this will have on the similarity. The results, tested on the Movielens, Netflix and FilmAffinity databases, corrobórate the excellent behaviour of the singularity measure proposed.

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In the present study, we analyzed the cell cycle distribution of bone marrow (BM) cells in 120 untreated multiple myeloma patients using a DNA/CD38 double-staining technique at flow cytometry in which plasma cells (PCs) can be clearly discriminated from residual BM cells based on their CD38 expression. This approach allows us to determine the proliferative activity of both PCs and residual normal BM cells. The percentage of S-phase cells in the myelomatous population was found to be significantly lower than that of the residual normal BM cells (P < .001). Regarding the proliferative activity of myelomatous cells, patients with a high number of S-phase PCs (> 3%) showed a significantly (P < .05) increased incidence of anemia and hypercalcemia; higher values of beta 2-microglobulin (beta 2M), urea, and creatinine; and higher numbers of peripheral blood natural killer cells, as well as a poor prognosis as assessed both by response duration and overall survival. With respect to the residual BM normal fraction, a low proliferative activity was significantly (P < .05) associated with the presence of anemia and neutropenia together with increased numbers of BM PCs, a higher incidence of Bence Jones myelomas, and DNA diploidy. Multivariate analysis showed that the number of S-phase PCs was the most important independent prognostic factor, allowing us to discriminate two subgroups of patients with different prognoses, even within the same clinical stage. Moreover, the S-phase PCs, together with beta 2M, age, and performance status, represent the best combination of disease characteristics for stratifying patients according to prognosis and allow the establishment of a simple and powerful staging system for multiple myeloma patients. In addition, this classification can be used for planning treatment in patients who are candidates for transplantation.