Active Learning with Statistical Models

For many types of machine learning algorithms, one can compute the statistically `optimal' way to select training data. In this paper, we review how optimal data selection techniques have been used with feedforward neural networks. We then show how the same principles may be used to select data for two alternative, statistically-based learning architectures: mixtures of Gaussians and locally weighted regression. While the techniques for neural networks are computationally expensive and approximate, the techniques for mixtures of Gaussians and locally weighted regression are both efficient and accurate. Empirically, we observe that the optimality criterion sharply decreases the number of training examples the learner needs in order to achieve good performance.Comment: See http://www.jair.org/ for any accompanying file

Distribution and turnover of Langerhans cells during delayed immune responses in human skin

The changes in distribution and turnover of T6+ Langerhans cells (LC) in the skin during delayed immune responses to tuberculin, and in the lesions of tuberculoid leprosy and cutaneous Leishmaniasis were investigated. In each situation, there was a dermal accumulation of monocytes and T cells and epidermal thickening with keratinocyte Ia expression. In the tuberculin response a dramatic change in the distribution of LC was observed. By 41 h, T6+ LC were displaced to the upper zone of the thickening epidermis followed by an almost complete loss of LC from the epidermis by approximately 72 h. After 7 d, T6+ cells started to reappear in the epidermis, which regained almost normal numbers of T6+ LC by 14 d. After antigen administration and initiation of the delayed immune response, enhanced numbers of T6+ cells appeared in association with the mononuclear cell infiltrate of the upper dermal lesions. Their numbers peaked by 72 h, were reduced at 7 d, and again enhanced by 14 d, when the epidermis was being repopulated. Similar numbers of T6+ cells were found in the chronic lesions of tuberculoid leprosy and cutaneous Leishmaniasis but not lepromatous leprosy. The cells of the dermis were identified as typical LC by the presence of Birbeck granules and surface T6 antigen at the electron microscope level. These cells were closely associated with lymphocytes. We have quantified the number of LC, evaluated their directional flux into the epidermis and dermis, determined nearest neighbors, and made predictions as to their fate

Interactions of asbestos-activated macrophages with an experimental fibrosarcoma

Supernatants from in vivo asbestos-activated macrophages failed to show any cytostatic activity against a syngeneic fibrosarcoma cell line in vitro. UICC chrysotile-induced peritoneal exudate cells also failed to demonstrate any growth inhibitory effect on the same cells in Winn assays of tumor growth. Mixing UICC crocidolite with inoculated tumor cells resulted in a dose-dependent inhibition of tumor growth; this could, however, be explained by a direct cytostatic effect on the tumor cells of high doses of crocidolite, which was observed in vitro

Mouse spleen lymphoblasts generated in vitro. Their replication and differentiation in vitro

Mouse spleen lymphoblasts induced with lipopolysaccharide and fetal calf serum were obtained in high yield and purity in their first proliferative cell cycle by floatation in dense bovine plasma albumin columns (3). The blasts were maintained in vitro for 3 more days. The cultures were examined in bulk on each day, and in addition, those cells in S phase initially were tagged with [(3)H]thymidine and followed continuously in vitro. Grain count dilution data indicated that most blasts divided but twice over a 2- to 3-day interval in vitro. [(3)H]Thymidine pulse radiolabeling and flow microfluorometry suggested that at least 50-70 percent of the proliferating blasts withdrew from proliferative activity after 2-3 days of culture. Morphologic studies demonstrated that lymphoblasts persisted as such for 1-2 days in vitro and then matured into typical plasma cells. Many of the blastprogeny had small nuclei and considerable basophilic cytoplasm on Giemsa-stained cell smears; abundant rough endoplasmic reticulum by electron microscopy; and readily detectable cytoplasmic Ig by immunocytochemistry. Reversion of blasts to small lymphocytes could not be detected; however, some blasts persisted even after 3 days of culture. The viability of the cultured lymphoblast was followed by initially tagging the cells with [(3)H]thymidine as well as several other techniques. Little cell death was documented during the first day of culture. The number of labeled progeny increased twofold whereas the grain count halved. But 40- 50 percent of the cell-associated label was lost during each of the second and third days, and fewer labeled progeny than predicted by grain count dilution were identified. The culture medium could not be implicated in this loss of lymphoblast progeny, and we suggest that the maturation of the lymphoblast to a short-lived plasma cell was responsible. Therefore mitogen-stimulated B blasts seem to mature into typical plasma cells after just two cycles of cell division. The plasma cells resemble those produced in situ during an immune response in their cytologic features, withdrawal from active proliferative activity, and short life-span

Business Value Is not only Dollars - Results from Case Study Research on Agile Software Projects

Business value is a key concept in agile software development. This paper presents results of a case study on how business value and its creation is perceived in the context of agile projects. Our overall conclusion is that the project participants almost never use an explicit and structured approach to guide the value creation throughout the project. Still, the application of agile methods in the studied cases leads to satisfied clients. An interesting result of the study represents the fact that the agile process of many projects differs significantly from what is described in the agile practitioners’ books as best practices. The key implication for research and practice is that we have an incentive to pursue the study of value creation in agile projects and to complement it by providing guidelines for better client’s involvement, as well as by developing structured methods that will enhance the value-creation in a project