Revisiting Content Availability in Distributed Online Social Networks

Online Social Networks (OSN) are among the most popular applications in today's Internet. Decentralized online social networks (DOSNs), a special class of OSNs, promise better privacy and autonomy than traditional centralized OSNs. However, ensuring availability of content when the content owner is not online remains a major challenge. In this paper, we rely on the structure of the social graphs underlying DOSN for replication. In particular, we propose that friends, who are anyhow interested in the content, are used to replicate the users content. We study the availability of such natural replication schemes via both theoretical analysis as well as simulations based on data from OSN users. We find that the availability of the content increases drastically when compared to the online time of the user, e. g., by a factor of more than 2 for 90% of the users. Thus, with these simple schemes we provide a baseline for any more complicated content replication scheme.Comment: 11pages, 12 figures; Technical report at TU Berlin, Department of Electrical Engineering and Computer Science (ISSN 1436-9915

Detection of single trial power coincidence for the identification of distributed cortical processes in a behavioral context

Poster presentation: The analysis of neuronal processes distributed across multiple cortical areas aims at the identification of interactions between signals recorded at different sites. Such interactions can be described by measuring the stability of phase angles in the case of oscillatory signals or other forms of signal dependencies for less regular signals. Before, however, any form of interaction can be analyzed at a given time and frequency, it is necessary to assess whether all potentially contributing signals are present. We have developed a new statistical procedure for the detection of coincident power in multiple simultaneously recorded analog signals, allowing the classification of events as 'non-accidental co-activation'. This method can effectively operate on single trials, each lasting only for a few seconds. Signals need to be transformed into time-frequency space, e.g. by applying a short-time Fourier transformation using a Gaussian window. The discrete wavelet transform (DWT) is used in order to weight the resulting power patterns according to their frequency. Subsequently, the weighted power patterns are binarized via applying a threshold. At this final stage, significant power coincidence is determined across all subgroups of channel combinations for individual frequencies by selecting the maximum ratio between observed and expected duration of co-activation as test statistic. The null hypothesis that the activity in each channel is independent from the activity in every other channel is simulated by independent, random rotation of the respective activity patterns. We applied this procedure to single trials of multiple simultaneously sampled local field potentials (LFPs) obtained from occipital, parietal, central and precentral areas of three macaque monkeys. Since their task was to use visual cues to perform a precise arm movement, co-activation of numerous cortical sites was expected. In a data set with 17 channels analyzed, up to 13 sites expressed simultaneous power in the range between 5 and 240 Hz. On average, more than 50% of active channels participated at least once in a significant power co-activation pattern (PCP). Because the significance of such PCPs can be evaluated at the level of single trials, we are confident that this procedure is useful to study single trial variability with sufficient accuracy that much of the behavioral variability can be explained by the dynamics of the underlying distributed neuronal processes

Transfer of employment practices, varieties of capitalism, and national employment systems: a review

"Nationale Beschäftigungssysteme verändern sich vor allem aufgrund der Aktivitäten multinationaler Unternehmen. In diesem Beitrag wird die Veränderungsanfälligkeit nationaler Beschäftigungssysteme untersucht, indem seit 1994 veröffentlichte, wichtige empirische Studien zum Transfer von Personalpraktiken innerhalb multinationaler Unternehmen aufgearbeitet werden. Drei Zusammenhänge, die aus neo-institutionalistischer Perspektive motiviert werden, bestätigen sich in den Studien. Erstens werden Praktiken der Arbeitsbeziehungen seltener transferiert als andere Personalpraktiken ('HR-Praktiken'). Zweitens werden HR-Praktiken häufiger aus einer liberalen Marktökonomie in eine koordinierte Marktökonomie transferiert als in umgekehrter Richtung. Drittens weist die Einführung bestimmter 'angelsächsischer' HR-Praktiken auf einen Dominanzeffekt hin. Insgesamt zeigen die Befunde, dass sich nationale Beschäftigungssysteme in Reaktion auf die Entscheidungen multinationaler Unternehmen asymmetrisch verändern. Der Beitrag benennt abschließend bestimmte Grenzen der vorliegenden Analyse und wirft interessante künftige Forschungsfragen auf." (Autorenreferat)"National employment systems are changing primarily through the activities of multinational enterprises (MNEs). In order to understand in how far national employment systems are susceptible to change, the authors revisit important quantitative empirical studies published since 1994 on the transfer of employment practices within MNEs. Three propositions are derived from a neo-institutional approach, and evidence for all of the three was found when re-analyzing the empirical papers. Firstly, human resource practices are more often transferred than industrial relations practices. Secondly, HR practices are more often transferred from a liberal market economy (such as the USA) to a coordinated market economy (such as Germany) than vice versa. Thirdly, some adoption of HR practices common in the USA points to a dominance effect. Overall, the findings show that an uneven change in national employment systems is to be expected from the transfer of practices within MNEs. The limits of the analysis and further routes for research are discussed in the concluding section of the paper." (author's abstract

Chloroplast Transition Metal Regulation for Efficient Photosynthesis

Schmidt SB, Eisenhut M, Schneider A. Chloroplast Transition Metal Regulation for Efficient Photosynthesis. Trends in Plant Science. 2020;25(8):817-828

Screening of Arabidopsis mutants for functional genomic studies

Eight photosynthetic Arabidopsis mutants were screened for co-segregation of a photosynthetic phenotype with the T-DNA insertion. These mutants were selected from 80 photosynthetic mutants with genetic background of Columbia-0. Two different screening approaches were used to study the T-DNA insertion in the genome of mutant Arabidopsis lines. The sulphonamide sulfadiazine was found to be an effective selective agent and a single copy of sulfonamide resistant gene was found to be completely resistant to the optimal concentration i.e., 5mg mL-1. The maximum number of Arabidopsis mutant plants had confirmed insertions. Some of the plants did not show any amplification with gene specific primer combination, and it was assumed that either they were wild type plants or they had random T-DNA insertion and the insertion was not found in the gene under study but it could be found in any where in the genome. Some mutant plants were morphologically different from the wild type plants e.g., ALP105. These plants grew as small in size and dark green in color. After PCR screening with gene specific and T-DNA border primers all such mutant plants were confirmed as heterozygous T-DNA insertion plants

AAV-Mediated Overexpression of the CB1 Receptor in the mPFC of Adult Rats Alters Cognitive Flexibility, Social Behavior, and Emotional Reactivity

The endocannabinoid (ECB) system is strongly involved in the regulation of cognitive processing and emotional behavior and evidence indicates that ECB signaling might affect these behavioral abilities by modulations of prefrontal cortical functions. The aim of the present study was to examine the role of the CB1 receptor in the medial prefrontal cortex (mPFC) on cognitive flexibility and emotional behavior. Therefore, the CB1 receptor was overexpressed by adeno-associated virus vector-mediated gene transfer specifically in the mPFC of adult Wistar rats. Animals were then tested in different anxiety-related paradigms for emotional reactivity [e.g., elevated plus maze (EPM), light/dark emergence test (EMT), social interaction] and the attentional set shift task (ASST) – an adaptation of the human Wisconsin card sorting test – for cognitive abilities and behavioral flexibility. A subtle increase in exploratory behavior was found in CB1 receptor overexpressing animals (CB1-R) compared to Empty vector injected controls (Empty) in the EMT and EPM, although general locomotor activity did not differ between the groups. During social interaction testing, social contact behavior toward the unknown conspecific was found to be decreased, whereas social withdrawal was increased in CB1-R animals and they showed an inadequate increase in exploratory behavior compared to control animals. In the ASST, impaired reversal learning abilities were detected in CB1-R animals compared to controls, indicating reduced behavioral flexibility. In conclusion, upregulation of the CB1 receptor specifically in the rat mPFC induces alterations in emotional reactivity, leads to inadequate social behavior, and impairs cognitive flexibility. These findings might be relevant for neuropsychiatric disorders, since higher cortical CB1 receptor expression levels as well as similar behavioral impairments as observed in the present study have been described in schizophrenic patients

Inhibitory effects of rat bone marrow-derived dendritic cells on naïve and alloantigen-specific CD4+ T cells: a comparison between dendritic cells generated with GM-CSF plus IL-4 and dendritic cells generated with GM-CSF plus IL-10

BACKGROUND: Unlike mouse immature bone marrow (BM)-derived dendritic cells (DC), rat immature BMDC have not been thoroughly characterised in vitro for the mechanisms underlying their suppressive effect. To better characterise these mechanisms we therefore analysed the phenotypes and immune inhibitory properties of rat BMDC generated with GM-CSF plus IL-4 (= IL-4 DC) and with GM-CSF plus IL-10 (= IL-10 DC). RESULTS: Both IL-4 DC and IL-10 DC exhibited lower surface expression of MHC class II and costimulatory molecules than mature splenic DC. They had a strong inhibitory effect on responsive T cells in vitro and despite their weak function as antigen-presenting cells they induced anergic T cells. However, only anergic T cells induced by IL-4 DC had a suppressive effect on responsive T cells. Induction of suppressive/tolerogenic T cells by IL-4 DC required direct contact between antigen-specific T cells and IL-4 DC. In addition, IL-4 DC and IL-10 DC prolonged allograft survival in an antigen-specific manner. CONCLUSION: A unique phenotype of immature BMDC was isolated from the cultures. The mechanisms underlying the suppressive effect may be caused by their inability to deliver adequate costimulatory signals for T-cell activation. In addition, IL-4 DC but not IL-10 DC induce anergic T cells with suppressive function. This indicates that IL-4 DC and IL-10 DC may differ in the quality of their costimulation although no differences in the surface expression of costimulatory molecules were found