42292049
Fitting semiparametric cure models
Survival data with a sizable cure fraction are commonly encountered in some cancer clinical researches and the semiparametric proportional hazards cure model has been recently investigated to analyze such data. However the estimation method of the model requires a special C program. The restrictive assumptions of the model also limit its application in broader settings. We present a new computational method for the cure model in this article. The method combines the computational methods for logistic regression and the Cox proportional hazards models and is easy to implement in many statistical packages. We also show how this method allows a number of useful extensions of the model to relax the restrictive assumptions. An illustrative example with survival times of lymphoma patients is provided.
21181741
An alternative estimation method for the accelerated failure time frailty model
Frailty models based on the proportional hazards model are useful to analyze correlated or clustered failure time data. However, there has been some recent interest in a frailty model based on the popular accelerated failure time model for correlated failure time data ([Pan, W., 2001. Using frailties in the accelerated failure time model. Lifetime Data Anal. 7(1), 55-64], for example). In this paper we review recent advances on this model in the literature. We propose a general estimation method based on M-estimators and the EM algorithm to estimate the parameters in the model. To evaluate the performance of the proposed method, we carry out a simulation study. The results of the simulation study show that the proposed method performs well in comparison with existing estimation methods. As an illustration, the model and the proposed method are applied to analyze the effects of sublingual nitroglycerin and oral isosorbide dinitrate on angina pectoris of coronary heart disease patients [Danahy, D.T., Burwell, D.T., Aronow, W.S., Prakash, R., 1977. Sustained hemodynamic and antianginal effect of high dose oral isosorbide dinitrate. Circulation 55, 381-387].
11039476
On the chromatic uniqueness of certain bipartite graphs
Let K(p, q), p ⩽ q, denote the complete bipartite graph in which the two partite sets consist of p and q vertices, respectively. We denote by K-r(p, q), the family of all graphs obtained by deleting any r distinct edges from K(p, q). Teo and Koh showed that K-1(p, q) is chromatically unique (in short χ-unique) for all p, q such that 3 ⩽ p ⩽ q. In this paper, we obtain a sufficient condition for a graph in K-2(p, q) to be χ-unique. Using this result, we then prove that each graph in K-2(p, p + d) is χ-unique for p ⩾ 4and 0 ⩽ d ⩽ 3. For d ⩾ 4, the graphs in K-2(p, q + d) are χ-unique if p > (A + √B)/4d2, where A and B are polynomials in d. We also show that each graph (≇K(4, 4) – K(1, 3)) in K-3(p, p + d) is χ-unique, for p ⩾ 4 and d=0, 1; and all graphs in K-3(p, p + 2) are χ-unique if and only if all graphs in K-4(p + 1, p + 1) are χ-unique, where p ⩾ 4. Finally we prove that every graph in K-4(p, p + 1) is χ-unique for p ⩾ 5.
33972996
Chromatic equivalence classes of certain cycles with edges
Abstract Let P(G) denote the chromatic polynomial of a graph G . Two graphs G and H are chromatically equivalent, written G∼H , if P(G)=P(H) . A graph G is chromatically unique if for any graph H , G∼H implies that G is isomorphic with H . In this paper, we give the necessary and sufficient conditions for a family of generalized polygon trees to be chromatically unique.
16284083
Minimizing Complexity in Cellular Automata Models of Self-Replication
Understanding self-replication from an information processing perspective is important because, among other things, it can shed light on molecular mechanisms of biological reproduction and on prebiotic chemical evolution. Intuition, biological knowledge, and early computational models of self-replication all suggested that self-replication is an inherently complex process. In this paper we describe recent computational studies that challenge this viewpoint. We summarize our recent work with cellular automata models of simple yet non-trivial self-replicating structures called unsheathed loops. For example, one unsheathed loop consists of only six components and requires only 20 rules to specify the local intercomponent interactions needed to bring about replication. The implication of this work is that, when viewed as an emergent property of numerous local, concurrent interactions between components, self-replicating systems can be substantially simpler than is generally recognized.
18522080
Example of supersonic solutions to a steady state Euler-Poisson system
Abstract We give an example of supersonic solutions to a one-dimensional steady state Euler–Poisson system arising in the modeling of plasmas and semiconductors. The existence of the supersonic solutions which correspond to large current density is proved by Schauder’s fixed point theorem. We show also the uniqueness of solutions in the supersonic region.
15008277
The interoperability problem: bringing together mobile agents and agent communication languages
Interoperability is a central issue far both the mobile agents community and the wider agents community. Unfortunately, the interoperability concerns are different between the two communities. As a result, inter-agent communication is an issue that has been addressed in a limited manner by the mobile agents community. Supplementing mobile agents with the ability to interact a a higher level with other mobile or static agents, or agentified information sources is a necessity in the vastly heterogeneous arena where mobile agents are called to compete. An agent communication language (ACL) has been interpreted by the agents community as a tool with the capacity to integrate disparate sources of information. Such a perspective does not seem to be shared by the mobile agents community. We investigate the origins of the differences of perspective on agent to agent communication and examine the reasons for the relative lack of interest on ACLs by mobile agents researchers and explore the integration of ACLs into mobile agents frameworks.