The effect of intraspecific sample size on type I and type II error rates in comparative studies

Comparative studies have increased greatly in number in recent years due to advances in statistical and phylogenetic methodologies. For these studies, a trade-off often exists between the number of species that can be included in any given study and the number of individuals examined per species. Here, we describe a simple simulation study examining the effect of intraspecific sample size on statistical error in comparative studies. We find that ignoring measurement error has no effect on type I error of nonphylogenetic analyses, but can lead to increased type I error under some circumstances when using independent contrasts. We suggest using ANOVA to evaluate the relative amounts of within- and between-species variation when considering a phylogenetic comparative study. If within-species variance is particularly large and intraspecific sample sizes small, then either larger sample sizes or comparative methods that account for measurement error are necessary.     

Phylogenetic analysis of ecomorphological divergence, community structure, and diversification rates in dusky salamanders (Plethodontidae: Desmognathus)

An important dimension of adaptive radiation is the degree to which diversification rates fluctuate or remain constant through time. Focusing on plethodontid salamanders of the genus Desmognathus, we present a novel synthetic analysis of phylogeographic history, rates of ecomorphological evolution and species accumulation, and community assembly in an adaptive radiation. Dusky salamanders are highly variable in life history, body size, and ecology, with many endemic lineages in the southern Appalachian Highlands of eastern North America. Our results show that life-history evolution had important consequences for the buildup of plethodontid-salamander species richness and phenotypic disparity in eastern North America, a global hot spot of salamander biodiversity. The origin of Desmognathus species with aquatic larvae was followed by a high rate of lineage accumulation, which then gradually decreased toward the present time. The peak period of lineage accumulation in the group coincides with evolutionary partitioning of lineages with aquatic larvae into seepage, stream-edge, and stream microhabitats. Phylogenetic simulations demonstrate a strong correlation between morphology and microhabitat ecology independent of phylogenetic effects and suggest that ecomorphological changes are concentrated early in the radiation of Desmognathus. Deep phylogeographic fragmentation within many codistributed ecomorph clades suggests long-term persistence of ecomorphological features and stability of endemic lineages and communities through multiple climatic cycles. Phylogenetic analyses of community structure show that ecomorphological divergence promotes the coexistence of lineages and that repeated, independent evolution of microhabitat-associated ecomorphs has a limited role in the evolutionary assembly of Desmognathus communities. Comparing and contrasting our results to other adaptive radiations having different biogeographic histories, our results suggest that rates of diversification during adaptive radiation are intimately linked to the degree to which community structure persists over evolutionary time.     

Nanosecond dynamics of a mimicked membrane-water interface observed by time-resolved stokes shift of LAURDAN

We studied the dipolar relaxation of the surfactant-water interface in reverse micelles of AOT-water in isooctane in the nanosecond and subnanosecond time ranges by incorporating the amphipathic solvatochromic fluorescent probes LAURDAN and TOE. A negative component was observed in the fluorescence decays in the red edge of the emission spectrum-the signature of an excited state reaction-with LAURDAN but not for TOE. The deconvolution of the transient reconstructed spectra of LAURDAN based on a model constructed by adding together three log-normal Gaussian equations made it possible to separate the specific dynamic solvent response from the intramolecular excited state reactions of the probe. The deconvoluted spectrum of lowest energy displayed the largest Stokes shift. This spectral shift was described by unimodal kinetics on the nanosecond timescale, whereas the relaxation kinetics of water-soluble probes have been reported to be biphasic (on the subnanosecond and nanosecond timescales) due to the heterogeneous distribution of these probes in the water pool. Most of this spectral shift probably resulted from water relaxation as it was highly sensitive to the water to surfactant molar ratio (w(0)) (60-65 nm at w(0) = 20-30). A small part of this spectral shift (9 nm at w(0) = 0) probably resulted from dipolar interaction with the AOT polar headgroup. The measured relaxation time values were in the range of the rotational motion of the AOT polar headgroup region as assessed by LAURDAN and TOE fluorescence anisotropy decays.     

Retrospective analysis of sequential dose-finding designs

The continual reassessment method (CRM) is a dose-finding design using a dynamic sequential updating scheme. In common with other dynamic schemes the method estimates a current dose level corresponding to some target percentile for experimentation. The estimate is based on all included subjects. This continual reevaluation is made possible by the use of a simple model. As it stands, neither the CRM, nor any of the other dynamic schemes, allow for the correct estimation of some target percentile, based on retrospective data apart from the exceptional situation in which the simplified model exactly generates the observations. In this article we focus on the very specific issue of retrospective analysis of data generated by some arbitrary mechanism and subsequently analyzed via the continual reassessment method. We show how this can be done consistently. The proposed methodology is not restricted to that particular design and is applicable to any sequential updating scheme in which dose levels are associated with percentiles via model inversion.     

New manganese complexes with 2-salicyloylhydrazono-1,3-dithiolane ligand and various coordination solvents

The new complexes with 2-salicyloylhydrazono-1,3-dithiolane ligand (H₂L) have been obtained with good yields (≈85%) by reacting manganese (II) acetate tetrahydrate or manganese (II) acetylacetonate with 2-salicyloylhydrazono-1,3-dithiolane ligand in DMF, THF or Py (L′). These compounds have been fully characterized by spectroscopic methods and single crystal X-ray diffraction. In the solid state, supramolecular networks are described and discussed in terms of weak H-bonds and short contacts. The new monomeric complexes will be considered as candidates to obtain polynuclear complexes.     

Topological Characteristics of Random Multihop Wireless Networks

Multihop wireless networks are treated as random symmetric planar point graphs, where all the nodes have the same transmission power and radius, and vertices of a graph are drawn randomly over certain geographical region. Several basic and important topological properties of random multihop wireless networks are studied, including node degree, connectivity, diameter, bisection width, and biconnectivity. It is believed that such study has very useful implication in real applications.Keqin Li is currently a full professor of computer science in State University of New York at New Paltz. His research interests are mainly in design and analysis of algorithms, parallel and distributed computing, and computer networking, with particular interests in approximation algorithms, parallel algorithms, job scheduling, task dispatching, load balancing, performance evaluation, dynamic tree embedding, scalability analysis, parallel computing using optical interconnects, optical networks, and wireless networks. He has published over 190 journal articles, book chapters, and research papers in refereed international conference proceedings. He has also co-edited six international conference proceedings and a book entitled Parallel Computing Using Optical Interconnections published by Kluwer Academic Publishers in 1998. His current research (2001–2004) is supported by US National Science Foundation.Dr. Li has served in various capacities for numerous international conferences as program/steering/advisory committee member, workshop chair, track chair, and special session organizer. He received best paper awards in 1996 International Conference on Parallel and Distributed Processing Techniques and Applications, 1997 IEEE National Aerospace and Electronics Conference, and 2000 IEEE International Parallel and Distributed Processing Symposium. He received a recognition award from International Association of Science and Technology for Development in October 1998. He is listed in Whos Who in Science and Engineering, 7th edition, 2003–2004; Whos Who in America, 58th edition, 2004; Whos Who in the World, 20th edition, 2003. Dr. Li is a senior member of IEEE and a member of IEEE Computer Society and ACM.     

Computation of Minimal Uniform Transmission Range in Ad Hoc Wireless Networks

Power conservation is a critical issue for ad hoc wireless networks. The main objective of the paper is to find the minimum uniform transmission range of an ad hoc wireless network, where each node uses the same transmission power, while maintaining network connectivity. Three different algorithms, Prims Minimum Spanning Tree (MST), its extension with Fibonacci heap implementation, and an area-based binary search are developed to solve the problem. Their performance is compared by simulation study together with Kruskals MST, a known solution proposed by Ramanathan and Rosales-Hain for topology control by transmission power adjustment, and an edge-based binary search used by the same study in order to find the per-node-minimality after Kruskals algorithm is applied. Our results show that Prims MST outperforms both Kruskals MST and the two binary searches. The performance between Prims MST implemented with binary heap and Fibonacci heap is fairly close, with the Fibonacci implementation slightly outperforming the other.Qing Dai received her M.S. degree in Computer Science from Florida Atlantic University on August 2003, and M.S. degree in Microbiology from Upstate University on July 2000. She is currently a software engineer at Motorola, Plantation, FL.Jie Wu is a Professor at Department of Computer Science and Engineering, Florida Atlantic University. He has published over 200 papers in various journals and conference proceedings. His research interests are in the areas of wireless networks and mobile computing, routing protocols, fault-tolerant computing, and interconnection networks. He served on many conference organization committees. Dr. Wu is on the editorial board of IEEE Transactions on Parallel and Distributed Systems and was a co-guest-editor of IEEE Computer and Journal of Parallel and Distributed Computing. He is the author of the text Distributed System Design published by the CRC press. He was also the recipient of the 1996–97 and 2001–2002 Researcher of the Year Award at Florida Atlantic University. Dr. Wu has served as an IEEE Computer Society Distinguished Visitor. He is a Member of ACM and a Senior Member of IEEE.