Number Of Group Members Research Articles

The relationship between group size, intoxication and continuing to drink after bar attendance

ObjectiveThe present study was undertaken to explore multilevel determinants of planning to continue to drink alcohol after leaving public drinking events. We assessed whether individual-level factors, group-related factors, or event-level bar characteristics were associated with post-bar drinking. MethodWe recruited a total of 642 participants from 30 participating bars in urban Southern California. Groups who arrived to patron a bar were interviewed upon their entrance and exit. Given data nesting, we employed a multilevel modeling approach to data analysis. ResultsMore than one-third (40%) of our sample reported the intention to continue drinking as they exited the bar. Results of our multilevel model indicated eight individual-level variables significantly associated with intending to continue to drink. Time of night moderated the relationship between BrAC change and intentions to continue to drink. Although none of the group factors were significant in our model, a significant cross-level interaction between BrAC change and number of group members indicated the effect of intoxication on planning to continue to drink increases as group members increase. At the bar level, the presence of temporary bars and server offers of non-alcoholic drinks significantly decreased intentions to continue to drink. ConclusionsGiven the large percentage of participants who reported the intention to continue drinking after exiting a bar, this study draws attention to the fact that field studies of drinking behavior may assess drinking mid-event rather than at the end of a drinking event.

Collective States, Multistability and Transitional Behavior in Schooling Fish

The spontaneous emergence of pattern formation is ubiquitous in nature, often arising as a collective phenomenon from interactions among a large number of individual constituents or sub-systems. Understanding, and controlling, collective behavior is dependent on determining the low-level dynamical principles from which spatial and temporal patterns emerge; a key question is whether different group-level patterns result from all components of a system responding to the same external factor, individual components changing behavior but in a distributed self-organized way, or whether multiple collective states co-exist for the same individual behaviors. Using schooling fish (golden shiners, in groups of 30 to 300 fish) as a model system, we demonstrate that collective motion can be effectively mapped onto a set of order parameters describing the macroscopic group structure, revealing the existence of at least three dynamically-stable collective states; swarm, milling and polarized groups. Swarms are characterized by slow individual motion and a relatively dense, disordered structure. Increasing swim speed is associated with a transition to one of two locally-ordered states, milling or highly-mobile polarized groups. The stability of the discrete collective behaviors exhibited by a group depends on the number of group members. Transitions between states are influenced by both external (boundary-driven) and internal (changing motion of group members) factors. Whereas transitions between locally-disordered and locally-ordered group states are speed dependent, analysis of local and global properties of groups suggests that, congruent with theory, milling and polarized states co-exist in a bistable regime with transitions largely driven by perturbations. Our study allows us to relate theoretical and empirical understanding of animal group behavior and emphasizes dynamic changes in the structure of such groups.

A two-phase algorithm for consensus building in AHP-group decision making

Group decision making through the AHP has received significant attention in contemporary research, the primary focus of which has been on the issues of consistency and consensus building. In this paper, we concentrate on the latter and present a two-phase algorithm based on the optimal clustering of decision makers (members of a group) into sub groups followed by consensus building both within sub groups and between sub groups. Two-dimensional Sammon’s mapping is proposed as a tool for generating an approximate visualization of sub groups identified in multidimensional vector space, while the consensus convergence model is suggested for reaching agreement amongst individuals in and between sub groups. As a given, all decision makers evaluate the same decision elements within the AHP framework and produce individual scores of these decision elements. The consensual scores are obtained through the iterative procedure and the final scores are declared as the group decision. The results of two selected numerical examples are compared with two sets of results: the results obtained by the commonly used geometric mean aggregation method and also the results obtained if the consensus convergence model is applied directly without the prior clustering of the decision makers. The comparisons indicated the expected differences among the aggregation schemes and the final group scores. The matrices of respect values in the consensus convergence model, obtained for cases when the decision makers are optimally clustered and when they are not, show that in the latter case the decision makers receive lower weights of respect from other members in the group. Various tests showed that our approach is efficient in cases when no clusters can be visually and undoubtedly identified, especially if the number of group members is high.

Towards scalable key management for secure multicast communication

A secure multicast communication is used to deliver encrypted messages from a sender to a group of authorized receivers. A practical approach is to use a common key only known by the authorized users to encrypt the transmitted messages. The common key must be renewed to ensure forward/backward secrecy when a group member joins/ leaves the group. In this case, the rekeying problem becomes a critical issue for secure multicast communication. Many researchers have focused on solving the rekeying problem. In 2010, Lin et al. proposed two multicast key management schemes without the rekeying process. However, the transmission size in their schemes is dependent on the number of group members. In this article, we adopt the time-bound concept to propose two new key management schemes without the rekeying process. The point is that the required transmission size in the proposed schemes is constant. Performance analysis is given to demonstrate that our schemes have better performance as compared with the recently proposed key management schemes in terms of transmission size and computational cost. Under several security assumptions, we prove that the proposed schemes are secure key management schemes for multicast communication.DOI: http://dx.doi.org/10.5755/j01.itc.41.2.846

Securing Group Communication in Partially Distributed Systems

This paper deals with symmetric key exchange in partially distributed systems. Unlike the traditional distributed approaches for key exchange utilized when we have a centralized KDC (Key Distribution Center), which is a trusted server responsible for key exchange between the users involved in group communication or a KDC for each node, we divide the group of nodes in regions with each having its own KDC. Each user can communicate securely with members of its own region as well as with those belonging to other regions. We use a hierarchical approach to represent the partial distributed structure of the distributed system using key graphs. The outcome is a secure group communication providing authenticity, confidentiality and integrity of messages delivered between groups. Each secure group is represented in form of a triplet (U, N, R) where U is the set of users, N is the set of keys held by the users and R represents a relation on U and R. This approach has been developed keeping in view the scalability issues of the distributed systems where number of group members may increase or decrease with time. For the same reason we use rekeying strategies to redistribute the keys every time a user joins or leaves the group. This approach is irrespective of frequency of joins and leaves. Keywords - Group communication, multicast, partially distributed systems, rekeying, security

Groups in Mendeley: Owners' descriptions and group outcomes

AbstractUsing four factors borrowed from traditional social group theories, we examined owners' group descriptions in Mendeley to study the applicability of traditional social group theories for large, loosely‐formed online groups. We manually annotated the descriptions for 529 Mendeley groups, and correlated the appearances of the factors with two measures of the groups' outcomes: the changes in the numbers of group members and the changes of the articles shared within the groups between 2011 and 2012. Our results suggest that, in general, all four factors are important in online groups, which indicates the usefulness of traditional group theories in the study of online groups. In addition, although a majority of the factors have helped the growth of group size being higher than average increase, several factors have caused the increase of the shared articles within the groups to be smaller than average increase.

Group Size in Animal Societies: The Potential Role of Social and Ecological Limitations in the Group-Living Fish, Paragobiodon xanthosomus

The number of group members in an animal society can have a major influence on group members’ life history, survival, and reproductive success. Identifying the factors that limit group size is therefore fundamental for a complete understanding of social behavior. Here, I examined the relationships between resource availability, social conflict, and group size in the coral-dwelling fish, Paragobiogon xanthosomus (Gobiidae). The size of the largest (breeding) female and the minimum size difference required for hierarchy stability strongly but not perfectly predicted maximum group size, suggesting that social conflicts and hierarchy structure set the upper limit on group size. Deviations in group size around the predicted maximum were explained by variation in average body size ratios but not by variation in coral size, suggesting that coral size does not directly influence group size. In contrast, coral size was a significant predictor of body size ratios, and possible explanations for this relationship are discussed. Group size may be limited by the social conflicts that characterize size-based dominance hierarchies. Ecological factors, namely coral size, may in turn play an indirect role via an effect on body size ratios.

Applying Fuzzy Technologies to Equivalence Learning in Protein Classification

When sequencing a new genome, its function and structure are important concerns, and inferring methods are based on protein sequence similarity methods. However, sequence groups differ in their parameters such as the number of group members and intra- and inter-class variability. A method that performs well on one group may not perform well on another group. Thus, learning similarity in a supervised manner could provide a general framework to set a similarity function to a specific sequence class. Here we describe a novel method that learns a similarity function between proteins by using a binary classifier and pairs of equivalent sequences (belonging to the same class) as positive samples, and non- equivalent sequences (belonging to different classes) as negative training samples. For sequence pair representation, we propose to use advanced techniques from fuzzy theory, including a sigmoid-type function for normalization and the class of Dombi operators that provide a more robust method. Using some additional constraints, the learned function turns out to be a valid kernel or metric function, and we present a new way of learning it, along with a new parameter-weighting technique. Using a dataset of archeal, bacterial, and eukaryotic 3-phosphoglycerate-kinase sequences (3PGK) and clusters from COG, we evaluate this equivalence learning method from a protein classification point of view. A receiver operator characteristic (ROC) analysis shows that we get a much more robust and accurate methodology for protein classification when these techniques are applied together. (See online Supplementary Material at www.liebertonline.com).

Constructing UC Secure and Constant-Round Group Key Exchange Protocols via Secret Sharing

Group key exchange (GKE) is one of the basic building blocks in securing group communication. A number of solutions to GKE problem have been proposed, but most of them are not scalable and require a number of rounds linear with the number of group members. We present a method of constructing constant-round and identity-based protocol via secret sharing for GKE within universally composability (UC) framework. The resultant protocol focuses on round efficiency and three rounds of communication are required. The protocol allows the batch verification of messages signed by all other group participants. Moreover, compared with other identity-based protocols, the key generation center (KGC) in our protocol is not always online.

A ID-based revocable group signature scheme

In the case that third parties can not be trusted,the traditional ID signature security system does not suit for the group signature.A secure ID-based group signature scheme was proposed.Even when the Key Generation Center(KGC)was implausible,its safety could be ensured,and the group members could be safely added or deleted without changing the keys of other effective group members and public group key.At the same time,the lengths of key and signature were unrelated to the number of group members.

Ownership Structure and Minority Expropriation in Non-Listed Firms: The Case for Multiple Large Shareholders

This paper investigates minority expropriation problems in closely-held corporations, where control is shared by a small number of blockholders. Using a large sample of Spanish firms for the years 1996 through 2000, we find that firms whose characteristics make them more vulnerable to minority expropriation tend to have controlling groups with stakes that are far removed from the 50% threshold, where expropriation is higher. However, because of adjustment costs, firms do not achieve an optimal ownership structure. Performance improves when the controlling group's ownership stake is higher and, for a given ownership stake, when the number of group members increases.

Exploring Performance of Hypercube Structure for Multicast in Mobile Ad Hoc Networks

Performance of multicast routing protocol in mobile ad hoc networks is mostly characterized by underlying forwarding structure. Currently, general structures based on tree/mesh based scheme cannot handle with transmission efficiency, robustness to dynamic topology, scalability, and load balancing functionalities at the same time. To handle above key performance factors concurrently, we propose a new virtual backbone architecture for multicast, which is based on hierarchical hypercube structure. Due to the natural properties of hypercube structure, we can achieve efficiency, robustness and load balance in mobile ad hoc networks where links are frequently broken owing to nodes' free immigration. Furthermore, scalability problem is naturally resolved by hierarchical structure. Finally, through simulation results, we have proven good scalability by demonstrating that our structure can provide higher packet delivery ratio with low control overhead and better scalability than tree/mesh based scheme without regard to the number of group members.

Coordination, independence or synchronization of individual vigilance in the eastern grey kangaroo?

Vigilance activity is usually considered an adaptive advantage of group living conferring protection against predators. An individual of a prey species is assumed to benefit from an increase in the number of group members by reducing its own investment in vigilance. However, the proximate mechanism generating the decrease in vigilance with increasing group size is unclear. Most models of this relation assume that either individuals coordinate their scans in nonoverlapping bouts of vigilance or animals scan independently of one another. We studied the relation between vigilance and group size in the eastern grey kangaroo, Macropus giganteus, analysing vigilance at two structural levels, individual vigilance and collective vigilance of the group. We tested both assumptions, coordination and independence of scanning. The time that an individual spent vigilant decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased up to a group size of seven individuals but decreased thereafter. Analyses revealed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, both the onset and the end of individuals' scanning bouts were synchronized between group members, producing waves of collective vigilance. Bouts of vigilance and nonvigilance activity tended to be synchronized. Our results appear to support a hypothesis of allelomimetic vigilance.

A new dynamic group signature scheme

In this paper, a new dynamic group signature scheme is proposed. It allows the group manager to increase or delete group members flexibly. Furthermore, the length of group signatures, as well as the computational effort for signing, verifying and opening are very small and independent of the number of group members and deleted group members. So it is efficient.

A Computationally Efficient Key-Hiding Based Group Re-Keying Scheme For Secure Multicasting

Multicast security is becoming an important networking issue because of the growing number of network applications that rely on multicast communication. Scalable group re-keying is one of the biggest challenges that needs to be addressed in order to support secure multicasting. In this paper, we present and analyze a new group re-keying algorithm for establishing cryptographic keys in multicast groups. Our re-keying algorithm is based on hiding the cryptographic group key in a numerical matrix. Our algorithm does not need computationally expensive encryption/decryption for group re-keying. Re-keying message construction and group key retrieval processes need only simple logical operations. For a given re-keying matrix, the computational cost for group re-keying is constant regardless of the number of group members.

A Novel Overlay Multicast Protocol in Mobile Ad Hoc Networks: Design and Evaluation

Despite significant research in mobile ad hoc networks, multicast still remains a research challenge. Recently, overlay multicast protocols for MANET have been proposed to enhance the packet delivery ratio by reducing the number of reconfigurations caused by nongroup members' unexpected migration in tree or mesh structure. However, since data is delivered by using replication at each group member, delivery failure on one group member seriously affects all descendent members' packet delivery ratio. In addition, delivery failure can occur by collision between numbers of unicast packets where group members densely locate. In this paper, we propose a new overlay multicast protocol to enhance packet delivery ratio in two ways. One is to construct a new type of overlay data delivery tree, and the other is to apply a heterogeneous data forwarding scheme depending on the density of group members. While the former aims to minimize influence of delivery failure on one group member, the latter intends to reduce excessive packet collision where group members are densely placed. Our simulation results show distinct scalability improvement of our approach without regard to the number of group members or source nodes.

Multiring techniques for scalable battlespace group communications

Network-centric warfare must leverage off a common network to support different purposes. While group communications based on a single virtual ring overlay may satisfy the most important requirements for survivability and security, scalability may for cc redesign because a single ring generally has higher delay and delay jitter. In order to provide scalability as the number of group members grows, large single rings may be broken into, smaller multirings interconnected together. Thus, comparing the characteristics of different multiring techniques provides insight into which battlespace applications may be supported via virtual rings. In this article we consider different approaches to providing scalable battlespace group communications using multi-ring techniques, classifying the techniques according to the primary military requirements of QoS, security, and survivability. Some important design issues of multiring techniques, such as the number of ring levels and number of rings per level, are dependent on, application QoS requirements and the underlying network infrastructure in terms of topology (dense vs. sparse) and link bandwidths (bottleneck capacities). Through our survey, we conclude that while no existing multiring scheme provides the single solution to battlespace group communications, some aspects of existing multiring schemes do match specific scenarios and provide us useful insights for designing new schemes for battlespace group communication. To our knowledge, this is the first article to survey and categorize multiring algorithms.

Shapes of clusters and groups of galaxies: comparison of model predictions with observations

We study the properties of the 3-dimensional and projected shapes of haloes using high resolution numerical simulations and observational data where the latter comes from the 2PIGG (Eke et al. 2004) and SDSS-DR3GC group catalogues (Merchan & Zandivarez 2005). We investigate the dependence of halo shape on characteristics such as mass and number of members. In the 3-dimensional case, we find a significant correlation between the mass and halo shape; massive systems are more prolate than small haloes. We detect a source of strong systematics in estimates of the triaxiality of a halo, which is found to be a strong function of the number of members; LCDM haloes usually characterised by triaxial shapes, slightly bent toward prolate forms, appear more oblate when taking only a small subset of the halo particles. The ellipticities of observed 2PIGG and SDSS-DR3GC groups are found to be strongly dependent on the number of group members, so that poor groups appear more elongated than rich ones. However, this is again an artifact caused by poor statistics and not an intrinsic property of the galaxy groups, nor an effect from observational biases. We interpret these results with the aid of a GALFORM mock 2PIGG catalogue. When comparing the group ellipticities in mock and real catalogues, we find an excellent agreement between the trends of shapes with number of group members. When carefully taking into account the effects of low number statistics, we find that more massive groups are consistent with more elongated shapes. Finally, our studies find no significant correlations between the shape of observed 2PIGG or SDSS-DR3GC groups with the properties of galaxy members such as colour or spectral type index.

A novel group signature with one time secret key

A new group signature with one time secret key is proposed. The main merits are that it only needs the trusted center issuing the partial secret key one time for each group member; and that the group member can generate his different secret key each time when he wants to sign a message. The group public key is constant and the size of the signature is independent of the number of group members. The total computation cost of signature and verification requires only 8 modular exponentiations.

Key establishment in large dynamic groups using one-way function trees

We present, implement, and analyze a new scalable centralized algorithm, called OFT, for establishing shared cryptographic keys in large, dynamically changing groups. Our algorithm is based on a novel application of one-way function trees. In comparison with the top-down logical key hierarchy (LKH) method of Wallner et al., our bottom-up algorithm approximately halves the number of bits that need to be broadcast to members in order to rekey after a member is added or evicted. The number of keys stored by group members, the number of keys broadcast to the group when new members are added or evicted, and the computational efforts of group members, are logarithmic in the number of group members. Among the hierarchical methods, OFT is the first to achieve an approximate halving in broadcast length, an idea on which subsequent algorithms have built. Our algorithm provides complete forward and backward security: Newly admitted group members cannot read previous messages, and evicted members cannot read future messages, even with collusion by arbitrarily many evicted members. In addition, and unlike LKH, our algorithm has the option of being member contributory in that members can be allowed to contribute entropy to the group key. Running on a Pentium II, our prototype has handled groups with up to 10 million members. This algorithm offers a new scalable method for establishing group session keys for secure large-group applications such as broadcast encryption, electronic conferences, multicast sessions, and military command and control.