bluuebunny/crossref_metadata_2025 huggingface dataset:
Rare Species and the Use of Indicator Groups for Conservation Planning
Authors: Lawler Joshua J. , White Denis , Sifneos Jean C. , Master Lawrence L.
Published: May 2003

Abstract:Indicators of biodiversity have been proposed as a potential tool for selecting areas for conservation when information about species distributions is scarce. Although tests of the concept have produced varied results, sites selected to address indicator groups can include a high proportion of other species. We tested the hypothesis that species at risk of extinction are not likely to be included in sites selected to protect indicator groups. Using a reserve‐selection approach, we compared the ability of seven indicator groups—freshwater fish, birds, mammals, freshwater mussels, reptiles, amphibians, and at‐risk species of those six taxa—to provide protection for other species in general and at‐risk species in particular in the Middle Atlantic region of the United States. Although sites selected with single taxonomic indicator groups provided protection for between 61% and 82% of all other species, no taxonomic group provided protection for more than 58% of all other at‐risk species. The failure to cover at‐risk species is likely linked to their rarity. By examining the relationship between a species' probability of coverage by each indicator group and the extent of its geographic range within the study area, we found that species with more restricted ranges were less likely to be protected than more widespread species. Furthermore, we found that although sites selected with indicator groups composed primarily of terrestrial species ( birds and mammals ) included relatively high percentages of those species ( 82–85% ) they included smaller percentages of strictly aquatic species (27–55%). Finally, of both importance and possible utility, we found that at‐risk species themselves performed well as an indicator group, covering an average of 84% of all other species.
Mexico's Community‐Managed Forests as a Global Model for Sustainable Landscapes
Authors: Bray David Barton , Merino‐Pérez Leticia , Negreros‐Castillo Patricia , Segura‐Warnholtz Gerardo , Torres‐Rojo Juan Manuel , Vester Henricus F. M.
Published: May 2003

Abstract:Researchers concerned with sustainable management of forests in the tropics have argued that the road to improved stewardship of forest resources is the transfer of responsibility to the local communities who get their livelihoods from them. On the other hand, conservationists have declared that the only way to stem the tide of deforestation is to place as many tracts as possible under strict protection. In this context, Mexico presents a national laboratory for studying the social and ecological benefits of delivering forests to local people. As a little‐noticed result of the Mexican Revolution in the second decade of the twentieth century, well over half of the forests of Mexico were placed in community‐held lands. In historic struggles that passed through several phases, most of these communities have now gained substantial control over the use of their forests. Because of the substantial degree of social capital in rural forms of organization in Mexico, this control of forest resources has led to an estimated 290–479 community forest enterprises ( CFEs ), through which communities are producing timber on their own lands. New studies are beginning to suggest that important gains in both social and economic justice, good forest management, and biodiversity protection are resulting from the actions of these CFEs. As more forests globally are being devolved to local communities, it is important to carry out more research on the Mexican model of community forest management for timber production.
Estimating Decline and Distributional Change in Amphibians
Authors: Skelly David K. , Yurewicz Kerry L. , Werner Earl E. , Relyea Rick A.
Published: May 2003

Abstract: Concern over species declines has prompted researchers to use historical data as a basis for comparison with present‐day information from the same sites to assess changes in presence/absence distributions. A review of the literature revealed that these resurveys typically lasted for 1 or 2 years, and many were based on museum records or other data relying on known historical presences. Using data on nine amphibian species from a set of 32 ponds at the E. S. George Reserve ( ESGR ) in Michigan, we evaluated the importance of the duration of a resurvey and the type of historical data used ( information on historical presences and absences vs. historical presences only ). We compared data we collected between 1996 and 2000 with information from the same ponds collected between 1967 and 1974. By systematically degrading the 1996–2000 data, we determined that a resurvey lasting 1 year would yield an estimated 45% decline in the number of presences, whereas a resurvey lasting 2 years would yield an estimated 28% decline. In contrast, a 5‐year resurvey would yield an estimated 3% decline in the number of presences. In addition, when our historical data were limited to known presences in the past, even a 5‐year resurvey yielded an estimated 30% decline in the number of presences. Our results suggest that estimates of decline and distributional change can be extremely sensitive to the duration of resurvey effort and the type of historical data used. The pattern we found in analyses of ESGR data is echoed in published studies in which multiple‐year resurveys tended to yield smaller estimates of decline than single‐year resurveys. Based on our findings, we suggest that future resurveys extend for long enough to estimate the value of additional data and that geographic scales of inference be chosen based on the amount and quality of historical information.
Modeling Factors Affecting the Severity of Outbreeding Depression
Authors: Edmands Suzanne , Timmerman Charles C.
Published: May 2003

Abstract: Hybridization between populations may cause either increased fitness ( “hybrid vigor” ) or decreased fitness ( “outbreeding depression” ). Translocation between populations may therefore in some cases be a successful means of combating genetic erosion and preserving evolutionary potential, whereas in other cases it may make the situation worse by inducing outbreeding depression. Because genetic distance alone is a poor predictor of the success or failure of hybridization, we developed a computer model ( ELAB ) to explore other factors affecting the consequences of hybridization. Our model simulates diploid, unisexual populations following Mendelian rules, and in this study we used it to test the effect of a variety of parameters on both the magnitude and duration of outbreeding depression. We focused our simulations on the effects of ( 1 ) divergence between populations, ( 2 ) the genetic basis of outbreeding depression ( disruption of local adaptation vs. intrinsic coadaptation ), ( 3 ) population parameters such as mutation rate and recombination rate, and ( 4 ) alternative management schemes ( 50:50 mixture vs. one migrant per generation ). The magnitude of outbreeding depression increased linearly with genetic distance, whereas the duration of outbreeding depression showed a more complex curvilinear relationship. With genetic distance held constant, magnitude increased with larger population size, lower mutation rate, cross‐fertilization, and higher recombination rate, whereas duration increased with larger population size and partial self‐fertilization. Fitness problems caused by disruption of local adaptation were stronger but more transient than those caused by a disruption of intrinsic coadaptation. Finally, simulations showed that, depending on the genetic basis of outcrossing problems, recurrent transfer of only one migrant per generation into a population of 100 individuals could cause as much or more damage as a one‐time 50:50 mixture.
Conservation Implications of Chamorro Consumption of Flying Foxes as a Possible Cause of Amyotrophic Lateral Sclerosis–Parkinsonism Dementia Complex in Guam
Authors: Monson Clark S. , Banack Sandra Anne , Cox Paul Alan
Published: May 2003

Abstract: In the Pacific island of Guam, flying fox (  Pteropus mariannus and P. tokudae ) populations historically persisted for centuries despite subsistence foraging by the indigenous Chamorro people. However, the militarization of Guam in the twentieth century, with an increased emphasis on a cash rather than a subsistence economy, led to two features that had deleterious effects on the flying fox populations: easy access to firearms greatly increased hunter yields and disposable income facilitated commercial traffic in flying foxes. As a result, consumption of flying foxes dramatically increased, leading to the extinction of one indigenous species and near extinction of another. The demise of the flying fox populations was mirrored by a subsequent decrease in the health of the Chamorro people. Amyotrophic lateral sclerosis–Parkinsonism dementia complex ( ALS‐PDC ), a neurological disease with aspects of ALS, Alzheimer's, and Parkinson's disease, became a major cause of adult death in some villages. It has been recently hypothesized that consumption of flying foxes by the Chamorro may have generated sufficiently high cumulative doses of neurotoxins to result in the observed high levels of ALS‐PDC among the Chamorros in Guam because flying foxes forage on cycad seeds that are rich in neurotoxins. Commercialization of traffic in wild flying fox populations may have therefore produced grave health consequences for the Chamorro people.
Initial Effects of Clearcutting and Alternative Silvicultural Practices on Terrestrial Salamander Abundance
Authors: Knapp Shannon M. , Haas Carola A. , Harpole Douglas N. , Kirkpatrick Roy L.
Published: May 2003

Abstract: Several studies have demonstrated the negative effects of clearcutting on terrestrial plethodontid salamander populations. However, none has experimentally compared clearcutting with multiple alternative timber‐harvest methods. Using a randomized, replicated design, we compared the short‐term effects ( 1–4 years after harvest ) of clearcutting to effects of leavetree, group selection, and two shelterwood cuts on terrestrial salamanders in the southern Appalachian Mountains of Virginia and West Virginia ( U.S.A. ). Treatment plots were 2 ha each. We also compared salamander age class ( percent juvenile ), fecundity ( percentage of females carrying eggs and average number of eggs per gravid female ), size of gravid females, and species composition and diversity between treatments with canopy removal ( cut ) and those without canopy removal ( uncut ). All treatments with canopy removal had significantly fewer salamanders than the control treatment, but salamander abundances on alternative treatments with canopy removal did not differ significantly from salamander abundances on the clearcuts. There were no significant differences between cut and uncut treatments in the proportion of females that were gravid or in the average number of eggs in gravid females; however, gravid Plethodon cinereus females weighed more on the cut treatments and gravid Desmognathus ochrophaeus females weighed more on uncut treatments. There were no significant differences between cut and uncut treatments in the proportion of the sample that was juvenile, except in the largest species tested, P. glutinosus, which had a significantly higher proportion of juveniles in the uncut treatments. We conclude that initial declines in terrestrial plethodontid abundance caused by timber harvesting may be minimized across the landscape by concentrating high‐intensity timber harvesting ( clearcutting ) in small areas (  a few hectares in size  ).
Effects of Habitat Disturbance on Stream Salamanders: Implications for Buffer Zones and Watershed Management
Authors: Willson John D. , Dorcas Michael E.
Published: May 2003

Abstract: With human populations increasing worldwide, habitat destruction and degradation are among the greatest threats facing wildlife. To minimize the impacts of development on aquatic habitats, numerous conservation measures have been implemented, including the use of riparian buffer zones along streams and rivers. We examined the effectiveness of current buffer‐zone systems for management of small watersheds in conserving stream‐dwelling salamander populations in 10 small streams ( draining <40.5 ha ) in the western Piedmont of North Carolina. We captured salamanders by means of funnel traps and systematic dipnetting and used a geographic information system to calculate the percentage of disturbed habitat within the watershed of each stream and within 10.7‐, 30.5‐, and 61.0 ‐m buffer zones around each stream, upstream from our sampling locations. Although the relative abundance of salamanders was strongly inversely proportional to the percentage of disturbed habitat in the entire watersheds (  R2 = 0.71 for Desmognathus fuscus and 0.48 for Eurycea cirrigera ), we found little to no correlation between the relative abundance of salamanders and the percentage of disturbed habitat present within buffer zones (  R2 = 0.06–0.27 for D. fuscus and 0.01–0.07 for E. cirrigera ). Thus, conservation efforts aimed at preserving salamander populations in headwater streams must consider land use throughout entire watersheds, rather than just preserving small riparian buffer zones.
Estimating Natural Selection Acting on Stream‐Dwelling Atlantic Salmon: Implications for the Restoration of Extirpated Populations
Authors: Hendry Andrew P. , Letcher Benjamin H. , Gries Gabe
Published: May 2003

Abstract:Efforts to restore populations to locations from which they have been extirpated may be hampered by maladaptation in the introduced group because they came from a different environment. Estimates of natural selection acting on the new population can be used to deduce maladaptation and tailor efforts to reduce its effects. We estimated natural selection acting on Atlantic salmon (  Salmo salar ) undergoing restoration to the Connecticut River ( U.S.A. ). More than 3500 mark‐recapture records in a small tributary ( West Brook, Massachusetts ) were used to estimate selection acting on body length, body mass, condition factor, and growth. Estimates were obtained for three to four different cohorts, two age classes ( second and third years of life ), and two seasons ( winter and summer ). We found little evidence that any of the traits were subject to strong directional selection (  favoring larger or smaller trait values ). Interestingly, fish that were larger or had higher condition factors rarely survived at higher rates, a result conflicting with the conventional “bigger is better” expectation. We also found little evidence that any of the traits were subject to strong or consistent stabilizing selection (  favoring trait values near the mean ). Our results suggest that the specific traits we examined are not limiting adaptation and are probably not preventing the population from becoming self‐sustaining. Future efforts should concentrate on other potentially limiting traits, such as the timing of smolt migration. Our results also suggest that any additional introductions of exogenous fish need not be concentrated on the size or growth of juveniles in potential source populations.
Spontaneous Pattern Formation and Genetic Diversity in Habitats with Irregular Geographical Features
Authors: Sayama Hiroki , Kaufman Les , Bar‐Yam Yaneer
Published: May 2003

Abstract:The role of spontaneous pattern formation, the appearance of inhomogeneities that are not directly imposed by external forces, has not been closely examined in the context of the origin and maintenance of genetic diversity in wild populations. Using individual‐based computer simulations, we demonstrated that such patterns form in spatially distributed species with local demes under disruptive selection. In our model systems, spatial patterns of genetic diversity arose and changed over time even in the context of a spatially homogenous environment. The spatial distribution and dynamics of the fittest genotypes were controlled by the movement of boundaries between domains of the different genotypes. The rate of diversity decay was dramatically slower than predicted by traditional models. Therefore, spontaneous pattern formation may lead to the maintenance of genetic diversity of a species in a contiguous habitat, despite reproductive mixing. Moreover, the diversity persisted significantly longer in larger habitats and habitats with irregular geographical features. Habitat structure was intimately linked to the preservation of genetic diversity. Spontaneous pattern formation should be considered along with other spatial effects in the design of conservation areas.
Validation Tests of Predictive Models of Butterfly Occurrence Based on Environmental Variables
Authors: Fleishman Erica , Nally Ralph Mac , Fay John P.
Published: May 2003

Abstract:Ecologists often seek to predict species distributions as functions of abiotic environmental variables. Statistical models are useful for making predictions about the occurrence of species based on variables derived from remote sensing or geographic information systems. We previously used 14 topographically based environmental variables from 49 locations in the Toquima Range ( Nevada, U.S.A. ) and species inventories conducted over 4 years ( 1996–1999 ) to model logistically the occurrence of resident butterfly species. To test the models, we collected new validation data in 39 locations in the nearby Shoshone Mountains in 2000–2001. We used a series of “classification rules” based on conventional logistic and Bayesian criteria to assess the success rates of predictions. The classification rules represented a gradient of stringency in the “certainty” with which predictions were made. More stringent rules reduced the number of predictions made but greatly increased the success rate of predictions. For comparisons of classification rules making similar numbers of predictions, conventional logistic and Bayesian criteria produced similar outcomes. Success rates for predicted absences were uniformly higher than for predicted presences. Increasing the temporal extent of data from 1 to 2 years elevated success rates for predicted presences but decreased success rates for predicted absences, leaving the overall success rates essentially the same. Although species occurrence rates ( the proportion of locations in which each species was found ) were correlated between the modeling and validation data sets, occurrence rates for many species increased or decreased substantially; erroneous predictions were more likely for those taxa. Model fit ( measured by the explained deviance ) was an indicator of the probable success rate of predicted presences but not of predicted absences or overall success rates. We suggest that classification rules for predicting likely presences and absences may be decoupled to improve overall predictive success. Our general framework for modeling species occurrence is applicable to virtually any taxonomic group or ecosystem.
A Novel Application of the Trivers‐Willard Model to the Problem of Genetic Rescue
Authors: Linklater Wayne L.
Published: May 2003

Abstract:Translocation is increasingly used to maintain evolutionary processes, particularly the genetic rescue of fragmented populations, but it is sometimes a costly and unsuccessful conservation tool. Succeeding at genetic rescue depends on the transfer of alleles between populations in the same way that successful parenthood consists in transferring alleles to the next generation. Moreover, there are large differences in the reproductive potential of males and females and growing evidence of sex‐biased survivorship after translocation in sexually selected species. Under these circumstances the Trivers‐Willard model ( TWM ), a founding and influential theory in behavioral ecology, makes predictions about how a parent should invest in the offspring of a different sex based on their ability to invest. Like parents, conservation managers also modify their investment in translocations to improve success. Thus, there are remarkable parallels between the predictions of modern evolutionary theory about parental investment in offspring of different sex and the investments of conservation managers in the translocation of alleles between populations via animals of different sex. The TWM for sex‐biased parental investment could be a theoretical guide to the problem of maximizing the transfer of alleles for genetic rescue.
Childhood Brain Tumors: Children's and Siblings' Concerns Regarding the Diagnosis and Phase of Illness
Authors: Freeman Katherine , O'Dell Christine , Meola Carol
Published: May 2003

Our objective was to identify commonly reported problems and helpful resources important to children with brain or spinal cord tumors and siblings during phases of illness. Affected children and siblings from 40 families responded to a regional survey. Items encompassed four general content areas: health care provider interactions, medical information/education, health care utilization, and psycho social. Children rated individual items as helpful, a problem, and for importance; relative frequencies were derived. One-third or more affected children reported important problems: hospitalization/surgery—help with schoolwork; hospital discharge—help with changes in physical activity, appearance, moods, special needs at school ; adjuvant treatment-Internet information, help with moods; and remission—socializing. One-third or more siblings reported important problems: diagnosis—information about etiology and prognosis, manner of physician and parents in providing information; hospitalization/surgery—information about prognosis, help with schoolwork; hospital discharge—help with schoolwork; adjuvant treatment—help with changes in sister or brother's appearance, phys ical activity, moods, and information about the treatment; end of life—treatment of sister's or brother's pain, information about dying, family harmony, support from friends, help with schoolwork, and preparation for the death. Consideration of problems and helpful resources will provide the framework for developing and evaluating intervention strategies at each phase of illness.
A Substantive Theory of Keeping the Spirit Alive: The Spirit Within Children With Cancer and Their Families
Authors: Woodgate Roberta Lynn , Degner Lesley Faith
Published: May 2003

Despite increasing survivorship, childhood cancer is nonetheless still a very traumatic phenomenon. Children and families must confront many new stressors and challenges. Understanding what families experience is essential if pediatric oncology nurses hope to provide sensitive and comprehensive care. To help discover meaningful descriptions and interpretations of families' experiences with childhood cancer, process-oriented qualitative research needs to be undertaken. A longitudinal qualitative study guided by the philosophy of interpretive interac tionism was conducted to arrive at an understanding of childhood cancer from the children's and families' perspectives. A theoretical purposive sample of 39 families residing in western Canada participated. Children (41/2-to-18 years of age) with a variety of cancer diagnoses and their families (parents and siblings) participated. Data collection methods included formal and informal interviewing and participant observation. Data were analyzed by the constant comparative method of grounded theory and analysis of illness narratives. Although the original intent of this study was to focus on the children's cancer symptoms, the children and families could not easily separate their cancer symptom experiences from the whole cancer experience and all its associated "rough spots." They first needed to talk about the overall cancer experience, which led to the development of the study's first substantive theory—Keeping the Spirit Alive: The Spirit Within. This substantive theory provided an understanding of how children and families used the process of keeping the spirit alive in response to them having to experience the phenomenon of the cancer: "getting through all the rough spots." Description of this theory is the focus of this article. Ways that nurses can assist children and families in maintaining a sense of spirit are presented.
Distressing Events for Children and Adolescents With Cancer: Child, Parent, an Nurse Perceptions
Authors: Hedström Mariann , Haglund Kristina , Skolin Inger , von Essen Louise
Published: May 2003

Distressing events for children with cancer (N = 121), 0 to 19 years of age, were investigated. Data were gathered through interviews with 50 children, 65 par ents, and 118 nurses. Each participant was asked: "Has there been any especially distressing event for you/your child/the child with regard to disease and treat ment?" Data were analyzed by content analysis. The categories that emerged from the analysis were grouped into a physical and an emotional dimension. The most frequently mentioned aspects of distress referred to the physical dimension: pain resulting from diagnostic procedures and treatments, nausea, and fatigue. The most frequently mentioned physical aspect of distress was, for children 0 to 3, 4 to 7, and 8 to 12 years of age, pain resulting from diagnostic procedures and treatments, and for children ≥ 13 years of age, nausea. The most frequently mentioned aspects of distress referred to the emotional dimension were catego rized as confinement, feeling of alienation, and worry before medical procedures. The most frequently mentioned emotional aspect of distress was, for children 0 to 3 years of age, confinement; 4 to 7 years of age, feeling of alienation; 8 to 12 years of age, worry about death; and ≥ 13 years of age, changed appearance. For children 0 to 3, 4 to 7, and ≥13 years of age, aspects of distress of a physical character were mentioned most frequently. For children 8 to 12 years of age, aspects of distress of an emotional character were mentioned most frequently. © 2003 by Association of Pediatric Oncology Nurses
Visualization Schemas and a Web-Based Architecture for Custom Multiple-View Visualization of Multiple-Table Databases
Authors: North Chris , Conklin Nathan , Indukuri Kiran , Saini Varun
Published: May 2003

Relational databases provide significant flexibility to organize, store, and manipulate an infinite variety of complex data collections. This flexibility is enabled by the concept of relational data Schemas, which allow data owners to easily design custom databases according to their unique needs. However, user interfaces and information visualizations for accessing and utilizing databases have not kept pace with this level of flexibility. Visualizations need to integrate multiple tables and diverse visualization tools into custom solutions. This paper describes advances to Snap-Together Visualization, introduces Visualization Schemas, and presents an extensible system architecture. The Snap model for custom multiple-view visualization establishes an analogy to the relational data model, enabling coordinated data design and visualization design. Visualization Schemas are a natural extension to data Schemas, and provide a user interface that enables data owners to rapidly construct and disseminate custom visualizations without programming. The web-based software architecture supports run-time extensibility, enabling end-user integration and dissemination of diverse data and visualization tools from the field.
The InfoSky visual explorer: Exploiting Hierarchical Structure and Document Similarities
Authors: Andrews Keith , Kienreich Wolfgang , Sabol Vedran , Becker Jutta , Droschl Georg , Kappe Frank , Granitzer Michael , Auer Peter , Tochtermann Klaus
Published: May 2003

InfoSky is a system enabling users to explore large, hierarchically structured document collections. Similar to a real-world telescope, InfoSky employs a planar graphical representation with variable magnification. Documents of similar content are placed close to each other and are visualised as stars, forming clusters with distinct shapes. For greater performance, the hierarchical structure is exploited and force-directed placement is applied recursively at each level on much fewer objects, rather than on the whole corpus. Collections of documents at a particular level in the hierarchy are visualised with bounding polygons using a modified weighted Voronoi diagram. Their area is related to the number of documents contained. Textual labels are displayed dynamically during navigation, adjusting to the visualisation content. Navigation is animated and provides a seamless zooming transition between summary and detail view. Users can map metadata such as document size or age to attributes of the visualisation such as colour and luminance. Queries can be made and matching documents or collections are highlighted. Formative usability testing is ongoing; a small baseline experiment comparing the telescope browser to a tree browser is discussed.
Multivariate Visualization with Data Fusion
Authors: Wong Pak Chung , Foote Harlan , Kao David L , Leung Ruby , Thomas Jim
Published: May 2003

We discuss a fusion-based visualization method to analyze a multivariate climate dataset and its metadata. The primary difference between a conventional visualization and a fusion-based visualization is that the former draws on a single image whereas the latter draws on multiple see-through layers, which are then overlaid on each other to form the final visualization. We propose optimized colormaps to highlight subtle features that would not be shown with conventional colormaps. We present fusion techniques that integrate multiple single-purpose visualization techniques into the same viewing space. Our highly flexible fusion approach allows scientists to explore multiple parameters concurrently by mixing and matching images without frequently reconstructing new visualizations from the data for every possible combination. Although our primary visualization application is climate modeling, we show with examples that our fundamental design - fusing layers of data images for multivariate visualization - can be generalized for other information visualization applications.
A Taxonomy of Glyph Placement Strategies for Multidimensional Data Visualization
Authors: Ward Matthew O
Published: May 2003

Glyphs are graphical entities that convey one or more data values via attributes such as shape, size, color, and position. They have been widely used in the visualization of data and information, and are especially well suited for displaying complex, multivariate data sets. The placement or layout of glyphs on a display can communicate significant information regarding the data values themselves as well as relationships between data points, and a wide assortment of placement strategies have been developed to date. Methods range from simply using data dimensions as positional attributes to basing placement on implicit or explicit structure within the data set. This paper presents an overview of multivariate glyphs, a list of issues regarding the layout of glyphs, and a comprehensive taxonomy of placement strategies to assist the visualization designer in selecting the technique most suitable to his or her data and task. Examples, strengths, weaknesses, and design considerations are given for each category of technique. We conclude with some general guidelines for selecting a placement strategy, along with a brief description of some of our future research directions.
One-dimensional “turbulence” in a discrete lattice
Authors: Daumont Isabelle , Peyrard Michel
Published: May 2003

We study a one-dimensional discrete analog of the von Kármán flow, widely investigated in turbulence. A lattice of anharmonic oscillators is excited by both ends in order to create a large scale structure in a highly nonlinear medium, in the presence of a dissipative term proportional to the second order finite difference of the velocities, similar to the viscous term in a fluid. In a first part, the energy density is investigated in real and Fourier space in order to characterize the behavior of the system on a local scale. At low amplitude of excitation the large scale structure persists in the system but all modes are however excited and exchange energy, leading to a power law spectrum for the energy density, which is remarkably stable against changes in the model parameters, amplitude of excitation, or damping. In the spirit of shell models, this regime can be described in terms of interacting scales. At higher amplitude of excitation, the large scale structure is destroyed and the dynamics of the system can be viewed as resulting from the creation, interaction, and decay of localized excitations, the discrete breathers, the one-dimensional equivalents of vortices in a fluid. The spectrum of the energy density is well described by the spectrum of the breathers, and shows an exponential decay with the wave vector. Due to this exponential behavior, the spectrum is dominated by the most intense breathers. In this regime, the probability distribution of the increments of velocity between neighboring points is remarkably similar to the experimental results of turbulence and can be described by distributions deduced from nonextensive thermodynamics as in fluids. In a second part the power dissipated in the whole lattice is studied to characterize the global behavior of the system. Its probability distribution function shows non-Gaussian fluctuations similar to the one exhibited recently in a large class of “inertial systems,” i.e., systems that cannot be divided into mesoscopic regions which are independent. The properties of the nonlinear excitations of the lattice provide a partial understanding of this behavior.
Cooling nonlinear lattices toward energy localization
Authors: Piazza Francesco , Lepri Stefano , Livi Roberto
Published: May 2003

We describe the energy relaxation process produced by surface damping on lattices of classical anharmonic oscillators. Spontaneous emergence of localized vibrations dramatically slows down dissipation and gives rise to quasistationary states where energy is trapped in the form of a gas of weakly interacting discrete breathers. In one dimension, strong enough on-site coupling may yield stretched-exponential relaxation which is reminiscent of glassy dynamics. We illustrate the mechanism generating localized structures and discuss the crucial role of the boundary conditions. For two-dimensional lattices, the existence of a gap in the breather spectrum causes the localization process to become activated. A statistical analysis of the resulting quasistationary state through the distribution of breathers’ energies yield information on their effective interactions.
Breathers and thermal relaxation in Fermi–Pasta–Ulam arrays
Authors: Reigada Ramon , Sarmiento Antonio , Lindenberg Katja
Published: May 2003

Breather stability and longevity in thermally relaxing nonlinear arrays depend sensitively on their interactions with other excitations. We review numerical results for the relaxation of breathers in Fermi–Pasta–Ulam arrays, with a specific focus on the different relaxation channels and their dependence on the interparticle interactions, dimensionality, initial condition, and system parameters.
Study of intrinsic localized vibrational modes in micromechanical oscillator arrays
Authors: Sato M. , Hubbard B. E. , English L. Q. , Sievers A. J. , Ilic B. , Czaplewski D. A. , Craighead H. G.
Published: May 2003

Intrinsic localized modes (ILMs) have been observed in micromechanical cantilever arrays, and their creation, locking, interaction, and relaxation dynamics in the presence of a driver have been studied. The micromechanical array is fabricated in a 300 nm thick silicon–nitride film on a silicon substrate, and consists of up to 248 cantilevers of two alternating lengths. To observe the ILMs in this experimental system a line-shaped laser beam is focused on the 1D cantilever array, and the reflected beam is captured with a fast charge coupled device camera. The array is driven near its highest frequency mode with a piezoelectric transducer. Numerical simulations of the nonlinear Klein–Gordon lattice have been carried out to assist with the detailed interpretation of the experimental results. These include pinning and locking of the ILMs when the driver is on, collisions between ILMs, low frequency excitation modes of the locked ILMs and their relaxation behavior after the driver is turned off.
Discrete breathers in Josephson arrays
Authors: Mazo J. J. , Orlando T. P.
Published: May 2003

Since the original proposal of 1996 by Florı́a et al. [Europhys. Lett. 36, 539 (1996)] of intrinsic localization in Josephson ladders, many efforts have been devoted to the theoretical, numerical, and experimental study of such dynamical states in Josephson arrays. Such efforts have already produced around 20 papers on the subject. In this article we will try to review the basic aspects of the physics of discrete breathers in Josephson arrays.
Discrete quantum breathers: What do we know about them?
Authors: Fleurov V.
Published: May 2003

The knowledge about discrete quantum breathers, accumulated during the last two decades, is reviewed. “Prehistory” of the problem is described and some important properties differentiating localized and extended vibrational modes are outlined. The state of art of our understanding of the principal features of the quantum discrete breathers is presented.
Intermittency of energy in rapid granular shear flows
Authors: Jalali Payman , Li Mo , Ritvanen Jouni , Sarkomaa Pertti
Published: May 2003

Hard-disk simulations are used for two-dimensional rapid granular shear flows of circular disks between two rotating cylinders. The intermittency effects associated with the rate of the energy dissipation of collisions are studied. The statistics of intermittent signals of energy dissipation reveals that a power law governs the dynamics of rapid shear granular flows. A dynamical system approach based on the Gledzer–Ohkitani–Yamada shell model of turbulence is employed to reproduce signals for energy dissipation that are statistically consistent with those from simulations. The results suggest that rapid granular flows can be analyzed by appropriate turbulent models.
Estimation of entropies and dimensions by nonlinear symbolic time series analysis
Authors: Finn J. M. , Goettee J. D. , Toroczkai Z. , Anghel M. , Wood B. P.
Published: May 2003

Symbolic nonlinear time series analysis methods have the potential for analyzing nonlinear data efficiently with low sensitivity to noise. In symbolic nonlinear time series analysis a time series for a fixed delay is partitioned into a small number (called the alphabet size) of cells labeled by symbols, creating a symbolic time series. Symbolic methods involve computing the statistics of words made from the symbolic time series. Specifically, the Shannon entropy of the distribution of possible words for a range of word lengths is computed. The rate of increase of the entropy with word length is the metric (Kolmogorov–Sinai) entropy. Methods of computing the metric entropy for flows as well as for maps are shown. A method of computing the information dimension appropriate to symbolic analysis is proposed. In terms of this formulation, the information dimension is determined by the scaling of entropy as alphabet size is modestly increased, using the information obtained from large word length. We discuss the role of sampling time and the issue of using these methods when there may be no generating partition.
Renormalization and destruction of 1/γ2 tori in the standard nontwist map
Authors: Apte A. , Wurm A. , Morrison P. J.
Published: May 2003

Extending the work of del-Castillo-Negrete, Greene, and Morrison [Physica D 91, 1 (1996); 100, 311 (1997)] on the standard nontwist map, the breakup of an invariant torus with winding number equal to the inverse golden mean squared is studied. Improved numerical techniques provide the greater accuracy that is needed for this case. The new results are interpreted within the renormalization group framework by constructing a renormalization operator on the space of commuting map pairs, and by studying the fixed points of the so constructed operator.
If “discrete breathers” is the answer, what is the question?
Authors: Tsironis G. P.
Published: May 2003

Intense work on discrete breathers or intrinsic localized modes in recent years has revealed a wealth of new properties of classical energy localization. Relaxation and mobility in particular may be two of the critical links with biomolecular processes. We review some of the basic discrete breather properties that we think are pertinent to biomolecules and make conjectures as to their possible biological utility.
Dissipative discrete breathers: Periodic, quasiperiodic, chaotic, and mobile
Authors: Martı́nez P. J. , Meister M. , Florı́a L. M. , Falo F.
Published: May 2003

The properties of discrete breathers in dissipative one-dimensional lattices of nonlinear oscillators subject to periodic driving forces are reviewed. We focus on oscillobreathers in the Frenkel–Kontorova chain and rotobreathers in a ladder of Josephson junctions. Both types of exponentially localized solutions are easily obtained numerically using adiabatic continuation from the anticontinuous limit. Linear stability (Floquet) analysis allows the characterization of different types of bifurcations experienced by periodic discrete breathers. Some of these bifurcations produce nonperiodic localized solutions, namely, quasiperiodic and chaotic discrete breathers, which are generally impossible as exact solutions in Hamiltonian systems. Within a certain range of parameters, propagating breathers occur as attractors of the dissipative dynamics. General features of these excitations are discussed and the Peierls–Nabarro barrier is addressed. Numerical scattering experiments with mobile breathers reveal the existence of two-breather bound states and allow a first glimpse at the intricate phenomenology of these special multibreather configurations.
Collision properties of quasi-one-dimensional spin wave solitons and two-dimensional spin wave bullets
Authors: Slavin A. N. , Büttner O. , Bauer M. , Demokritov S. O. , Hillebrands B. , Kostylev M. P. , Kalinikos B. A. , Grimalsky V. V. , Rapoport Yu.
Published: May 2003

Collision properties of quasi-one-dimensional spin wave envelope solitons propagating in narrow ferrite film waveguides and of two-dimensional self-focused spin wave packets (spin wave bullets) propagating in wide ferrite film samples are studied both experimentally and numerically. The experiments, performed by means of a space- and time-resolved Brillouin light scattering technique, have shown that quasi-one-dimensional spin wave envelope solitons retain their shapes after collisions, while two-dimensional spin wave bullets are destroyed in collisions. The experiments have also shown that the introduction of a fixed phase shift between the colliding envelope solitons leads to a qualitative change in their interaction at the collision point. Numerical modeling of head-on collisions of nonlinear spin wave packets based on two different approaches provides a good qualitative description of the observed collision phenomena.
Low frequency oscillations in semi-insulating GaAs: A nonlinear analysis
Authors: Rubinger R. M. , da Silva R. L. , de Oliveira A. G. , Ribeiro G. M. , Albuquerque H. A. , Rodrigues W. N. , Moreira M. V. B.
Published: May 2003

We have observed low frequency current oscillations in a semi-insulating GaAs sample grown by low temperature molecular beam epitaxy. For this, an experimental setup proper to measure high impedance samples with small external noise was developed. Spontaneous oscillations in the current were observed for some bias conditions. Although measurements were carried out from room temperature down to liquid helium, the dynamical analysis was carried out around 200 K where the signal to noise ratio was fairly favorable. To increase the data quality we have also used a noise reduction algorithm suitably developed for nonlinear systems. We observed attractors having low embedding dimension, limit cycle bifurcations, and chaotic behavior characteristic of nonlinear dynamical processes in route to chaos. Attractor reconstruction, Poincaré sections, Lyapunov exponents, and correlation dimension were also analyzed.
Open-shell localized Hartree–Fock approach for an efficient effective exact-exchange Kohn–Sham treatment of open-shell atoms and molecules
Authors: Della Sala Fabio , Görling Andreas
Published: May 2003

Within the framework of the symmetrized Kohn–Sham (KS) formalism an effective exact-exchange approach, the open-shell localized Hartree–Fock (OSLHF) method, is derived. The derivation relies on an approximation of energy denominators in KS one-particle Greens functions, the approximation of average magnitudes of eigenvalue differences, which is introduced. With the OSLHF method open-shell molecules can be treated efficiently and numerically stable without running into the symmetry problem encountered in conventional KS methods. The self-interaction free Hamiltonian operator of the OSLHF approach is in all cases non-spin-polarized and exhibits the full molecular point group symmetry in real space. Results for atoms as well as small and medium size molecules are presented. A procedure is introduced which yields special basis sets required for an efficient construction of the Slater potential which enters the effective KS potential of localized Hartree–Fock methods.
Damping of persistent oscillations of quadratic optical solitons
Authors: Rosanov Nikolay N. , Krepostnov Pavel I. , Popov Vitalii O.
Published: May 2003

We investigate the dynamics of optical soliton formation in media with quadratic nonlinearity under conditions of long-living oscillations produced by the soliton’s internal modes. We compare the predictions of the second-order perturbation approach, combining it with the energy conservation law, with the direct numerical simulations using the transparent boundary conditions. We demonstrate that these two approaches correlate well and describe the nonlinear radiation damping of the internal modes.
Wave scattering by discrete breathers
Authors: Flach S. , Miroshnichenko A. E. , Fistul M. V.
Published: May 2003

We present a theoretical study of linear wave scattering in one-dimensional nonlinear lattices by intrinsic spatially localized dynamic excitations or discrete breathers. These states appear in various nonlinear systems and present a time-periodic localized scattering potential for plane waves. We consider the case of elastic one-channel scattering, when the frequencies of incoming and transmitted waves coincide, but the breather provides with additional spatially localized ac channels whose presence may lead to various interference patterns. The dependence of the transmission coefficient on the wave number q and the breather frequency Ωb is studied for different types of breathers: acoustic and optical breathers, and rotobreathers. We identify several typical scattering setups where the internal time dependence of the breather is of crucial importance for the observed transmission properties.
Interpretation of heart rate variability via detrended fluctuation analysis and αβ filter
Authors: Echeverrı́a J. C. , Woolfson M. S. , Crowe J. A. , Hayes-Gill B. R. , Croaker G. D. H. , Vyas H.
Published: May 2003

Detrended fluctuation analysis (DFA), suitable for the analysis of nonstationary time series, has confirmed the existence of persistent long-range correlations in healthy heart rate variability data. In this paper, we present the incorporation of the αβ filter to DFA to determine patterns in the power-law behavior that can be found in these correlations. Well-known simulated scenarios and real data involving normal and pathological circumstances were used to evaluate this process. The results presented here suggest the existence of evolving patterns, not always following a uniform power-law behavior, that cannot be described by scaling exponents estimated using a linear procedure over two predefined ranges. Instead, the power law is observed to have a continuous variation with segment length. We also show that the study of these patterns, avoiding initial assumptions about the nature of the data, may confer advantages to DFA by revealing more clearly abnormal physiological conditions detected in congestive heart failure patients related to the existence of dominant characteristic scales.