bluuebunny/crossref_metadata_2025 huggingface dataset:
Previous land use alters plant allocation and growth in forest herbs
Authors: FRATERRIGO JENNIFER M. , TURNER MONICA G. , PEARSON SCOTT M.
Published: April 2006

Former human practices can persistently influence forest ecosystems, particularly by altering the distribution and abundance of vegetation. Previous research has focused on the role of colonization success in governing plant community patterns in abandoned forests, but few studies have explored how changes in the performance of adult plants may contribute to changes in plant populations.

We examined patterns of biomass allocation and growth of 12 herbaceous plant species in southern Appalachian forest stands that have developed after agricultural abandonment or logging at least 55 years ago, to determine whether plant performance varied with land‐use history. Soil nutrient availability and canopy closure were also investigated.

Adult plant biomass allocation varied appreciably among stands with different histories. Herbs in farmed stands generally allocated the most to leaves and the least to stems, while reference stands showed the opposite pattern. Plants in previously farmed sites had the highest rate of growth, although we observed considerable interspecific variation in plant performance. Stem allocation and relative growth rate were positively correlated in reference stands, but not in farmed or logged stands. Similarly, the growth of plants was clearly associated with soil nutrient concentration in reference stands but not in farmed or logged stands.

Differences in understorey density and soil nutrient availability may account for the observed patterns. Total herbaceous cover was appreciably lower in farmed and logged stands (58% and 51%) than in reference stands (78%), and soil phosphorus was higher in farmed stands than in logged and reference stands. Thus, competition for light and nutrients may be lower in farmed and logged stands than in reference stands, despite there being no difference in canopy closure with land‐use history.

Overall, these results suggest that land‐use history may influence environmental variables in ways that can enhance the performance of some herbaceous species. However, not all species may respond similarly to these changes.
Self‐organized vegetation patterning as a fingerprint of climate and human impact on semi‐arid ecosystems
Authors: BARBIER NICOLAS , COUTERON PIERRE , LEJOLY JEAN , DEBLAUWE VINCENT , LEJEUNE OLIVIER
Published: April 2006

Spatially periodic vegetation patterns are well known in arid and semi‐arid regions around the world.

Mathematical models have been developed that attribute this phenomenon to a symmetry‐breaking instability. Such models are based on the interplay between competitive and facilitative influences that the vegetation exerts on its own dynamics when it is constrained by arid conditions, but evidence for these predictions is still lacking. Moreover, not all models can account for the development of regularly spaced spots of bare ground in the absence of a soil prepattern.

We applied Fourier analysis to high‐resolution, remotely sensed data taken at either end of a 40‐year interval in southern Niger. Statistical comparisons based on this textural characterization gave us broad‐scale evidence that the decrease in rainfall over recent decades in the sub‐Saharan Sahel has been accompanied by a detectable shift from homogeneous vegetation cover to spotted patterns marked by a spatial frequency of about 20 cycles km−1.

Wood cutting and grazing by domestic animals have led to a much more marked transition in unprotected areas than in a protected reserve.

Field measurements demonstrated that the dominant spatial frequency was endogenous rather than reflecting the spatial variation of any pre‐existing heterogeneity in soil properties.

All these results support the use of models that can account for periodic vegetation patterns without invoking substrate heterogeneity or anisotropy, and provide new elements for further developments, refinements and tests.

This study underlines the potential of studying vegetation pattern properties for monitoring climatic and human impacts on the extensive fragile areas bordering hot deserts. Explicit consideration of vegetation self‐patterning may also improve our understanding of vegetation and climate interactions in arid areas.
The epidemiology of Argulus spp. (Crustacea: Branchiura) infections in stillwater trout fisheries
Authors: Taylor N G H , Sommerville C , Wootten R
Published: April 2006

Problem infections caused by species of the crustacean ectoparasite, Argulus, in UK stillwater trout fisheries appear to have increased in recent years. A cross‐sectional study of 77 such fisheries was conducted to establish the perceived problem and the extent and severity of this problem, and to identify associated risk factors. An interview‐based study was conducted in 2001 using a standardized questionnaire based on the management and infection status of each fishery in the previous year. Logistic regression was used to identify potential risk factors. Argulus spp. were perceived to cause economic losses in infected fisheries through a reduction in the number of anglers due to reduced aesthetic appeal and catchability of fish. Of the sites studied, 29% experienced such a problem infection in 2000. Argulus foliaceus was identified in all but one case and was found to be widely distributed throughout the UK. The remaining case was identified as Argulus coregoni. Three risk factors were associated with problem infections: the presence of an algal bloom, slow rates of stock turnover and whether water level dropped by <1 m during the summer months.
Brain transplantation of human neural stem cells transduced with tyrosine hydroxylase and GTP cyclohydrolase 1 provides functional improvement in animal models of Parkinson disease
Authors: Kim Seung U. , Park In H. , Kim Tae H. , Kim Kwang S. , Choi Hyun B. , Hong Seok H. , Bang Jung H. , Lee Myung A. , Joo In S. , Lee Chong S. , Kim Yong S.
Published: April 2006

Parkinson disease is a neurodegenerative disease characterized by loss of midbrain dopaminergic neurons resulting in movement disorder. Neural stem cells (NSC) of the CNS have recently aroused a great deal of interest, not only because of their importance in basic research of neural development, but also for their therapeutic potential in neurological disorders. We have recently generated an immortalized human NSC cell line, HB1.F3, via retrovirus‐mediated v‐myc transfer. This line is capable of self‐renewal, is multipotent, and expresses cell specific markers for NSC, ATP‐binding cassettes transporter (ABCG2) and nestin. Next, we co‐transduced the F3 NSC line with genes encoding tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GTPCH1) in order to generate dopamine‐producing NSC. The F3.TH.GTPCH human NSC line expresses TH and GTPCH phenotypes as determined by RT‐PCR, western blotting and immunocytochemistry, and shows a 800 to 2000‐fold increase in production of l‐dihydroxyphenyl alanine in HPLC analysis. A marked improvement in amphetamine‐induced turning behavior was observed in parkinsonian rats implanted with F3.TH.GTPCH cells, but not in control rats receiving F3 NSC. In the animals showing functional improvement, a large number of TH‐positive F3.TH.GTPCH NSC were found at injection sites. These results indicate that human NSC, genetically transduced with TH and GTPCH1 genes, have great potential in clinical utility for cell replacement therapy in patients suffering from Parkinson disease.
Religious Homogamy and Marital Quality: Historical and Generational Patterns, 1980 – 1997
Authors: Myers Scott M.
Published: April 2006

Despite significant social changes in the past 50 years, research continues to find a strong and enduring link between religious homogamy and marital quality. Yet, research has not explicitly examined whether this link has changed over time or over generations. To address historical and generational trends, I use national, longitudinal data collected between 1980 and 1997 that represents 3,211 respondents in the parental and offspring generations and 2 measures each of marital quality and religious homogamy. The findings show that the relationship between religious homogamy and marital quality weakened significantly between 1980 and 1997 from intragenerational change and generational replacement. The homogamy–marital quality link was weaker in both generations partly because of the increasing relative influence of gender, work, and family issues. Additionally, a decline in perceptions of religious authority has altered the religion–marital quality connection, though mostly among the younger generation. Even so, religiously homogamous couples still report higher marital quality.
Substitute or Complement? Spousal Influence on Volunteering
Authors: Rotolo Thomas , Wilson John
Published: April 2006

Social scientists have documented the influence of family statuses on volunteering, ignoring intrafamily effects. Using newly issued data from the Current Population Survey on the volunteer behavior of 19,626 American couples, we test two competing theories concerning spousal influences on volunteering. Substitution theory predicts that spouses will trade off volunteer work; complementarity theory predicts that spouses’ volunteer work is positively linked. Using structural equation methods to control for simultaneity bias, we find support for the complementarity theory. The wife’s influence, however, is stronger than the husband’s. Spousal influence is stronger if both spouses volunteer in the same domain. The findings underline the importance of close relationships in mobilizing volunteer workers.
Developmental Outcomes for Children of Young Mothers
Authors: Pogarsky Greg , Thornberry Terence P. , Lizotte Alan J.
Published: April 2006

This study tested the association between mother’s early age at first birth and various life outcomes for her children in later adolescence and early adulthood. Data were analyzed from the Rochester Youth Development Study, an ongoing panel study of adolescents enrolled in seventh or eighth grade in Rochester Public Schools in 1988 (N =729). Boys born to mothers who began childbearing before age 19 had elevated risks of drug use, gang membership, unemployment, and early parenthood. Girls born to young mothers only had elevated risks of early parenthood. Of the mediators tested, low maternal education had the largest mediating effects. The findings suggest that the risks associated with being born to a young mother are substantial but perhaps disproportionately so for boys.
Children’s Economic Well‐Being in Married and Cohabiting Parent Families
Authors: Manning Wendy D. , Brown Susan
Published: April 2006

Increasingly, children are living with cohabiting parents. Prior work on the material well‐being of children living in cohabiting families is extended by including the biological relationship of children to adults, examining the racial and ethnic variations, and investigating the multiple indicators of material well‐being. We draw on the 1999 National Survey of America’s Families (N =34,509). Our findings suggest that children can potentially benefit from living with a cohabiting partner whose resources are shared with family members. Although children living with married rather than cohabiting parents fare better in terms of material well‐being, this advantage is accounted for by race and ethnic group and parents’ education. Marriage appears to provide more material advantages to White children than to Black or Latino children.
Unsociable Work? Nonstandard Work Schedules, Family Relationships, and Children’s Well‐Being
Authors: Strazdins Lyndall , Clements Mark S. , Korda Rosemary J. , Broom Dorothy H. , D’Souza Rennie M.
Published: April 2006

Many children live in families where one or both parents work evenings, nights, or weekends. Do these work schedules affect family relationships or well‐being? Using cross‐sectional survey data from dual‐earner Canadian families (N= 4,306) with children aged 2 – 11 years (N= 6,156), we compared families where parents worked standard weekday times with those where parents worked nonstandard schedules. Parents working nonstandard schedules reported worse family functioning, more depressive symptoms, and less effective parenting. Their children were also more likely to have social and emotional difficulties, and these associations were partially mediated through family relationships and parent well‐being. For some families, work in the 24‐hour economy may strain the well‐being of parents and children.
Informal Caregiving at Working Age: Effects of Job Characteristics and Family Configuration
Authors: Henz Ursula
Published: April 2006

This article addresses the relationship between employment and providing informal care for sick, disabled, or elderly people in Great Britain. Hazard rate models for taking up caring and leaving work when caring are estimated using retrospective family, employment, and caring data from the British Family and Working Lives Survey 1994 – 1995 for 9,139 British men and women. Family roles but not employment characteristics were relevant for men and women taking up caring. Being in a lower social class was, however, an important predictor of female carers leaving the labor market. Starting caring and quitting the labor market were not affected by women working part time, nor by most aspects of job flexibility that were considered.
Race‐Ethnic Differences in Nonmarital Fertility: A Focus on Mexican American Women
Authors: Wildsmith Elizabeth , Raley R. Kelly
Published: April 2006

We use the National Survey of Family Growth to identify race‐ethnic differences in nonmarital fertility, paying particular attention to Mexican American women. On the basis of a sample of 9,054 White, Black, and Mexican American women, we use event history methods to explore the role of family background, a woman’s own employment and school enrollment, and cohabitation on nonmarital fertility. We additionally determine whether these relationships vary by socioeconomic background. The above factors are all significantly related to the risk of a nonmarital birth and reduce Mexican American–White differentials. Interestingly, higher fertility within cohabiting unions among Mexican American women, despite lower levels of cohabitation, contributes to their higher nonmarital fertility relative to White women.
Differences Between Partners From Heterosexual, Gay, and Lesbian Cohabiting Couples
Authors: Kurdek Lawrence A.
Published: April 2006

Partners from four types of couples without children (gay unmarried, lesbian unmarried, heterosexual unmarried, and heterosexual married, Ns=1,412, 1,310, 1,036, and 1,728, respectively) were compared to partners from heterosexual married couples with children (N =3,116) on mean levels of variables from a model of relationship adjustment as well as on the strength of links posited by the model. Although 82% of the mean‐level comparisons were significant, only 36% of the comparisons had effect sizes that were at least small in strength. Type of couple affected links between variables in only 33% of the instances, with effect sizes trivial in strength. Findings support the view that despite variability in structure, close dyadic relationships work in similar ways.
Application of annatto dye formulations in different fruit and vegetable products
Authors: Satyanarayana Akula , Prabhakara Rao Pamidighantam , Balaswamy Karakala , Velu Veeraputhiran , Rao Dubasi Govardhana
Published: April 2006

The orange‐yellow colour extracted from annatto (Bixa orellana L.) seeds is mainly used as a food colourant. Spray‐dried water‐soluble and acid‐stable annatto dye formulations were used to colour the fruit and vegetable products such as lime squash, orange squash, mixed fruit jam and tooty‐fruity (papaya candy). Spray‐dried acid‐stable annatto (ASA) dye formulation has shown more stability than the spray‐dried water‐soluble annatto (WSA) dye formulation during the 180 days of storage period in lime and orange squashes. The levels of norbixin concentrations in different fruit and vegetable products were standardised as 12.5 (lime squash); 50 (orange squash); 150 (mixed fruit jam) and 50–100 mg/kg (tooty‐fruity). In the case of tooty‐fruity, only 36% norbixin was observed to penetrate into the fruit matrix irrespective of the concentration of the norbixin present in the sugar syrup during processing. The ASA dye formulation was not exempt from degradation of norbixin formulation, but has shown good compatibility by preventing the precipitation of the dye during storage in the high‐acidic products of lime and orange squashes stored in transparent glass bottles. The WSA dye formulation has shown good compatibility and stability in products like jams and tooty‐fruity during the storage period.
Consumer information on hygiene inspections of food premises
Authors: Worsfold Denise
Published: April 2006

The purpose of this investigation was to learn more about the public's perceptions of hygiene standards in eating places and their interest in the provision of more consumer information on the inspection of food premises. A telephone survey found that people who eat out regularly claimed that the standard of food hygiene of food premises was important to them when deciding where to dine. A minority had concerns/complaints about the hygiene standards of eating places they had used. Consumers believe that they have the right to know the results of a hygiene inspection. Most would welcome a reliable system to help them judge hygiene standards. Half of them thought that it was difficult to find information on the hygiene standards of eating places. If access to information was made easier, some consumers claimed they would eat out more often. Respondents preferred the use of ‘stars’ to inform them on hygiene standards. Although current public awareness of hygiene award schemes is low, respondents were in favour of them. Independent evaluation of existing award schemes and hygiene inspection report scores should be carried out before a national scheme is launched.
Regulatory Domains of Snf1-Activating Kinases Determine Pathway Specificity
Authors: Rubenstein Eric M. , McCartney Rhonda R. , Schmidt Martin C.
Published: April 2006

In
Saccharomyces cerevisiae
, the Snf1 kinase can be activated by any one of three upstream kinases, Sak1, Tos3, or Elm1. All three Snf1-activating kinases contain serine/threonine kinase domains near their N termini and large C-terminal domains with little sequence conservation and previously unknown function. Deletion of the C-terminal domains of Sak1 and Tos3 greatly reduces their ability to activate the Snf1 pathway. In contrast, deletion of the Elm1 C-terminal domain has no effect on Snf1 signaling but abrogates the ability of Elm1 to participate in the morphogenetic-checkpoint signaling pathway. Thus, the C-terminal domains of Sak1, Tos3, and Elm1 help to determine pathway specificity. Additional deletion mutants of the Sak1 kinase revealed that the N terminus of the protein is essential for Snf1 signaling. The deletion of 43 amino acids from within the N terminus of Sak1 (residues 87 to 129) completely blocks Snf1 signaling and activation loop phosphorylation in vivo. The Sak1 kinase domain (lacking both N-terminal and C-terminal domains) is catalytically active and specific in vitro but is unable to promote Snf1 signaling in vivo when expressed at normal levels. Our studies indicate that the kinase domains of the Snf1-activating kinases are not sufficient by themselves for their proper function and that the nonconserved N-terminal and C-terminal domains are critical for the biological activities of these kinases.
Conserved Fungal Genes as Potential Targets for Broad-Spectrum Antifungal Drug Discovery
Authors: Liu Mengping , Healy Matthew D. , Dougherty Brian A. , Esposito Kim M. , Maurice Trina C. , Mazzucco Charles E. , Bruccoleri Robert E. , Davison Daniel B. , Frosco Marybeth , Barrett John F. , Wang Ying-Kai
Published: April 2006

The discovery of novel classes of antifungal drugs depends to a certain extent on the identification of new, unexplored targets that are essential for growth of fungal pathogens. Likewise, the broad-spectrum capacity of future antifungals requires the target gene(s) to be conserved among key fungal pathogens. Using a genome comparison (or concordance) tool, we identified 240 conserved genes as candidates for potential antifungal targets in 10 fungal genomes. To facilitate the identification of essential genes in
Candida albicans
, we developed a repressible
C. albicans MET3
(Ca
MET3
) promoter system capable of evaluating gene essentiality on a genome-wide scale. The Ca
MET3
promoter was found to be highly amenable to controlled gene expression, a prerequisite for use in target-based whole-cell screening. When the expression of the known antifungal target
C. albicans ERG1
was reduced via down-regulation of the Ca
MET3
promoter, the Ca
ERG1
conditional mutant strain became hypersensitive, specifically to its inhibitor, terbinafine. Furthermore, parallel screening against a small compound library using the Ca
ERG1
conditional mutant under normal and repressed conditions uncovered several hypersensitive compound hits. This work therefore demonstrates a streamlined process for proceeding from selection and validation of candidate antifungal targets to screening for specific inhibitors.
The C-Module DNA-Binding Factor Mediates Expression of the
Dictyostelium
Aggregation-Specific Adenylyl Cyclase ACA
Authors: Siol Oliver , Dingermann Theodor , Winckler Thomas
Published: April 2006

Aggregation of
Dictyostelium discoideum
amoebae into multicellular structures is organized by cyclic AMP (cAMP), which acts as a chemoattractant, as a second messenger, and as a morphogen. Aggregation of
D. discoideum
cells depends on the expression of adenylyl cyclase ACA, which provides extracellular cAMP for signal relay and intracellular cAMP for the induction of genes required at multicellular stages. We have identified a DNA-binding activity specific for a highly A+T-enriched motif in the upstream region of the ACA-encoding gene,
acaA
. The factor shows DNA-binding characteristics very similar to those of C-module-binding factor (CbfA). Although CbfA was originally identified as a putative regulator of the activity of
D. discoideum
retrotransposon TRE5-A, it also was found to be essential for aggregation of
D. discoideum
cells. The identified DNA-binding activity was absent in mutant cells depleted of CbfA, and CbfA could be precipitated using an
acaA
promoter fragment. We propose that CbfA binds to the
acaA
promoter to provide a basal transcription activity that is required for induction of ACA expression after the onset of
D. discoideum
development.
Targeted Gene Silencing in the Model Mushroom
Coprinopsis cinerea
(
Coprinus cinereus
) by Expression of Homologous Hairpin RNAs
Authors: Wälti Martin A. , Villalba Cristina , Buser Reto M. , Grünler Anke , Aebi Markus , Künzler Markus
Published: April 2006

The ink cap
Coprinopsis cinerea
is a model organism for studying fruiting body (mushroom) formation in homobasidiomycetes. Mutant screens and expression studies have implicated a number of genes in this developmental process. Functional analysis of these genes, however, is hampered by the lack of reliable reverse genetics tools for
C. cinerea
. Here, we report the applicability of gene targeting by RNA silencing for this organism. Efficient silencing of both an introduced
GFP
expression cassette and the endogenous
cgl1
and
cgl2
isogenes was achieved by expression of homologous hairpin RNAs. In latter case, silencing was the result of a hairpin construct containing solely
cgl2
sequences, demonstrating the possibility of simultaneous silencing of whole gene families by a single construct. Expression of the hairpin RNAs reduced the mRNA levels of the target genes by at least 90%, as determined by quantitative real-time PCR. The reduced mRNA levels were accompanied by cytosine methylation of transcribed and nontranscribed DNA at both silencing and target loci in the case of constitutive high-level expression of the hairpin RNA but not in the case of transient expression. These results suggest the presence of both posttranscriptional and transcriptional gene silencing mechanisms in
C. cinerea
and demonstrate the applicability of targeted gene silencing as a powerful reverse genetics approach in this organism.
Giardia lamblia
Attachment Force Is Insensitive to Surface Treatments
Authors: Hansen W. R. , Tulyathan O. , Dawson S. C. , Cande W. Z. , Fletcher D. A.
Published: April 2006

Giardia lamblia
cell populations show 90% detachment from glass under normal forces of 2.43 ± 0.33 nN applied by centrifugation. Detachment forces were not significantly different for cells attached to positively charged, hydrophobic, or inert surfaces than for cells attached to plain glass. The insensitivity of attachment force to surface treatment is consistent with a suction-based mechanism of attachment.
OPTICAL ABSORPTION AND OH- TRANSMISSION SPECTRA IN Mg:Er:LiNbO3 CRYSTALS
Authors: ZHEN XIHE , LI QIANG , XU YUHENG
Published: April 2006

Mg:Er:LiNbO 3 crystals were grown by the Czochralski method. Their UV-Vis absorption edges and OH - transmission spectra were measured in terms of the defect structure. The absorption edges shift towards a shorter wavelength with increasing Mg concentration. The dependence of the shift mechanism of the absorption edge on the defect structure was discussed in detail. The OH - absorption bands shift from 3486 cm-1 to 3535 cm-1 when the Mg concentration exceeds a threshold value. It is considered that the 3535 cm-1 absorption band corresponds to the (MgNb) 3-– OH - complexes.
PRODUCTION AND CHARACTERIZATION OF Ba2NdSbO6 COMPLEX PEROVSKITE AS A SUBSTRATE FOR YBa2Cu3O7-δ SUPERCONDUCTING FILMS
Authors: MADUEÑO Q. , LANDÍNEZ TÉLLEZ D. A. , ROA-ROJAS J.
Published: April 2006

We report systematic studies of Ba 2 NdSbO 6 as substrates for the production of YBa 2 Cu 3 O 7-δ superconducting thin films. Chemical stability and crystallographic coupling between Ba 2 NdSbO 6 and YBCO were examined by characterizing Ba 2 NdSbO 6- YBa 2 Cu 3 O 7-δ (0 to 100 vol.%) polycrystalline composites. X-ray diffraction experiments showed that Ba 2 NdSbO 6 belongs to the complex cubic perovskite family. Moreover, we determine that these materials are chemically stables, e.g. there is no chemical reaction at the interface, and the lattice parameters evidenced a matching ~ 2%. Morphological characterization of our samples was performed through scanning electron microscopy, which revealed the existence of separated grains of Ba 2 NdSbO 6 and YBa 2 Cu 3 O 7-δ. Compositional analysis of samples was performed by energy dispersive X-ray experiments, which showed the inexistence of impurities or undesired chemical elements. DC susceptibility measurements permitted us to determine that the presence of Ba 2 NdSbO 6 does not affect the critical temperature of the superconducting transition of YBa 2 Cu 3 O 7-δ. Our results evidenced that Ba 2 NdSbO 6 is an excellent candidate as a substrate for the fabrication of YBa 2 Cu 3 O 7-δ superconducting thin films.
ACTIVE WALKS: THE FIRST TWELVE YEARS (PART II)
Authors: LAM LUI
Published: April 2006

Active Walk (AW) is a paradigm for self-organization and pattern formation in simple and complex systems, originated by Lam in 1992. In an AW, the walker changes the deformable landscape as it walks, and is influenced by the changed landscape in choosing its next step. Active walk models have been applied successfully to various biological, physical, geological and economic systems from both the natural and social sciences. More recently, it has been used to model human history. In Part I of this review, the birth of the AW paradigm, its basic concepts and formulations, a solvable two-site model, and the experiments and AW modeling of surface-reaction filamentary patterns are presented. Part II here continues with properties of AW, and applications of AW in nonliving and living systems — including those from the social sciences and human history. (In particular, unsuspected quantitative laws and a prediction about the Chinese history are given.) A comment on the relationship between physics, social science and complex systems is provided. The review concludes with open problems in the form of workable research projects and general discussions.
SYNCHRONIZATION AND ASYNCHRONIZATION IN A LATTICE OF COUPLED LORENZ-TYPE MAPS
Authors: LIN WEN-WEI , SHIEH SHIH-FENG , WANG YI-QIAN
Published: April 2006

In this paper, we study synchronization and asynchronization in a Coupled Lorenz-type Map Lattice (CLML). Lorenz-type map forms a chaotic system with an appropriate discontinuous function. We prove that in a CLML with suitable coupling strength, there is a subset of full measure in the phase space such that chaotic synchronization occurs for any orbit starting from this subset and there is a dense subset of measure zero in the phase space such that synchronization will never occur. We also provide numerical observations to explain our results.
DETAILED STUDY OF LIMIT CYCLES AND GLOBAL BIFURCATIONS IN A CIRCADIAN RHYTHM MODEL
Authors: SIMON PETER L. , VOLFORD ANDRÁS
Published: April 2006

A two variable model describing the circadian fluctuation of two proteins (PER and TIM) in cells is considered. The original model was set up by Leloup and Goldbeter [1998], the present form was developed by Tyson et al. [1999]. Periodic solutions with 24-h period were investigated in those papers. Here the possible phase portraits and bifurcations are studied in detail. The saddle-node and Hopf bifurcation curves are determined in the plane of two parameters by using the parametric representation method [Simon et al., 1999]. It is shown that there are four cases according to their mutual position (as the remaining parameters of the system are varied). Using these curves the number and type of the stationary points are determined in all four cases. The global bifurcation diagram, which is a system of bifurcation curves that divide the given parameter plane into regions according to topological equivalence of global phase portraits, is also determined. Finally, the so-called constant period curves are computed numerically. These curves consist of those parameter pairs on the parameter plane for which the system has a limit cycle with a given period. It turns out that in a wide range of parameters the system has limit cycles with period close to 24-h.
SIMPLE VECTOR FIELDS WITH COMPLEX BEHAVIOR
Authors: AGUIAR MANUELA A. D. , CASTRO SOFIA B. S. D. , LABOURIAU ISABEL S.
Published: April 2006

We construct examples of vector fields on a three-sphere, amenable to analytic proof of properties that guarantee the existence of complex behavior. The examples are restrictions of symmetric polynomial vector fields in R4 and possess heteroclinic networks producing switching and nearby suspended horseshoes. The heteroclinic networks in our examples are persistent under symmetry preserving perturbations. We prove that some of the connections in the networks are the transverse intersection of invariant manifolds. The remaining connections are symmetry-induced. The networks lie in an invariant three-sphere and may involve connections exclusively between equilibria or between equilibria and periodic trajectories. The same construction technique may be applied to obtain other examples with similar features.
MODELING NONLINEAR TIME SERIES USING IMPROVED LEAST SQUARES METHOD
Authors: NAKAMURA TOMOMICHI , SMALL MICHAEL
Published: April 2006

We improve the least squares (LS) method for building models of a nonlinear dynamical system given finite time series which are contaminated by observational noise. When the noise level is low, the LS method gives good estimates for the parameters, however, the models selected as the best by information criteria often tend to be over-parameterized or even degenerate. We observe that the correct model is not selected as the best model despite belonging to the chosen model class. To overcome this, we propose a simple but very effective idea to use the LS method more appropriately. We apply the method for model selection. Numerical studies indicate that the method can be used to apply information criteria more effectively, and generally avoid over-fitting and model degeneracy.
MULTI-SCALE ISO-SURFACE EXTRACTION FOR VOLUME VISUALIZATION
Authors: FANG SHIAOFEN , ADADA MARWAN
Published: April 2006

This paper describes a new multi-scale approach for the extraction of iso-surfaces from volume datasets. The goal is to automatically identify iso-surfaces that best approximate the boundary surfaces at different levels of details. Using histogram analysis, iso-values are extracted from histograms of boundary voxels defined by gradient thresholding or zero-crossing boundaries. Multi-scale smoothing of the histogram using Gaussian filters of various sizes allows the iso-surfaces to be defined hierarchically over a scale space map. It provides an interactive environment and volume navigation tools for the exploration of large volume datasets by visualizing the layers of the volume space in a multi-scale manner.
A HAPTIC NEEDLE MANIPULATION SIMULATOR FOR CHINESE ACUPUNCTURE LEARNING AND TRAINING
Authors: HENG PHENG-ANN , WONG TIEN-TSIN , LEUNG KA-MAN , CHUI YIM-PAN , SUN HANQIU
Published: April 2006

This paper presents a haptic needle manipulation simulator for Chinese acupuncture learning and training. Students can learn and practise acupuncture in the proposed 3D interactive virtual environment that supports force feedback interface for needle insertion. So that, students not only "see" but also "touch" the virtual patient. With the high performance computers, highly informative and flexible visualization of acupuncture points of various related meridian and collateral can be highlighted to guide the students during training. Such a virtual reality system can provide an interesting and effective learning environment for Chinese acupuncture.
A VR ENHANCED COLLABORATIVE SYSTEM FOR 3D CONFOCAL MICROSCOPIC IMAGE PROCESSING AND VISUALIZATION
Authors: GUAN Y. Q. , CAI Y. Y. , OPAS M. , XIONG Z. W. , LEE Y. T.
Published: April 2006

With the rapid advancement in high-resolution confocal imaging, various forms of microscopy deliver substantial amount of valuable 3D cell biological information. Currently, image processing, modeling, visualization and analysis on confocal microscopic datasets are, however, still more or less following the traditional fashion that is 2D centric via a slice-by-slice strategy. Such image sequence based operations not only leads to lengthy processing times but also can potentially cause problems in data communication and interpretation, and knowledge discovery in a global 3D cellular level. In this paper, we describe our solution for processing, visualization and quantification of 3D confocal images with the CellStudio system we developed. CellStudio has a collaborative feature allowing 3D confocal data to be collected and retrieved across the net. CellStudio is also an integrated solution enabling 3D confocal image processing, volumetric visualization and interactive quantification performed in a network connected PC/Window platform.
The Extracellular Matrix Environment in Suture Morphogenesis and Growth
Authors: Opperman Lynne A. , Rawlins Joseph T.
Published: April 2006

Sutures are the major bone growth sites of the craniofacial skeleton and form in response to developmental approximation of and interaction between two opposing osteogenic fronts. Premature obliteration of these craniofacial bone growth sites or craniosynostosis results in compensatory growth at other bone growth sites, with concomitant craniofacial dysmorphology. While much is now known about the growth and transcriptional factor regulation of suture formation and maintenance, little about the nature of the extracellular environment within sutures and their surrounding bones has been described. This review elucidates the nature of the sutural extracellular matrix and its role in mediating suture maintenance and growth through the regulation of cellular and biomechanical signaling.
Variation in Mineral Properties in Normal and Mutant Bones and Teeth
Authors: Boskey Adele L. , Young Marian F. , Kilts Tina , Verdelis Kostas
Published: April 2006

Hydroxyapatite mineral is deposited in an organized fashion in the matrices of bones and teeth. The amount of mineral present, the composition of the mineral, and the size of the mineral crystals varies with both tissue and animal age, diet, health status, and the tissue being examined. Here, we review methods for measuring these differences in mineral properties and provide some illustrations from bones and teeth of animals in which the small leucine-rich proteoglycans (biglycan and decorin) were ablated. Differences in mineral properties between biglycan-deficient bones and teeth are related to the functions of this small proteoglycan in these tissues.
Collagenase in Cranial Morphogenesis
Authors: Holmbeck Kenn
Published: April 2006

Collagen is the most abundant extracellular matrix protein in connective tissues of higher animals. The growth of connective tissues is intimately linked to the ability to model and remodel the collagen-rich matrices of the organism at critical points during development and growth to allow expansion and adaptation of tissue interfaces. The mammalian cranium is one such place where collagen remodeling is required for proper growth, and this review explores the consequences of abrogated collagen remodeling as they materialize in a mouse model deficient for the membrane type 1 matrix metalloproteinase.
Role of Matrix Gla Protein in Parathyroid Hormone Inhibition of Osteoblast Mineralization
Authors: Gopalakrishnan Rajaram , Suttamanatwong Supaporn , Carlson Ann E. , Franceschi Renny T.
Published: April 2006

Parathyroid hormone (PTH) exerts biphasic effects on bone, dependent on the frequency and dose of administration. The catabolic actions of PTH on bone have been associated with continuous treatment, an increase in osteoblast-mediated resorption of bone via osteoclast activation, and inhibition of osteoblast activity and mineralization. Downregulation of differentiation markers and inhibition of mineralization by PTH have been reported in primary calvarial explants and osteoblast cell lines. Using MC3T3-E1 osteoblast-like cells, we have shown that matrix Gla protein (MGP) can be induced by PTH, and that this induction may explain the PTH-mediated inhibition of osteoblast biomineralization. MGP is a known inhibitor of mineralization, and mice deficient in Mgp show severe vascular calcification and premature bone mineralization. This review discusses the role of MGP in mineralization, comparing bone and vascular mineralization. In addition to MGP, the regulation and possible role of osteopontin, another known regulator of osteoblast mineralization, in PTH-mediated regulation of bone and vascular mineralization is discussed.
The Use of Animal Models to Explore Amelogenin Variants in Amelogenesis Imperfecta
Authors: Gibson Carolyn W. , Kulkarni Ashok B. , Wright J. Timothy
Published: April 2006

Amelogenin proteins are secreted by ameloblast cells during tooth development. Because of extensive alternative splicing of the amelogenin primary RNA transcript, and because systematic proteolysis results in many additional peptides during enamel maturation, it has been difficult to assign function to individual amelogenins. Targeted deletions and transgenic mice have been generated in order to better understand amelogenin protein functionin vivo. From these murine models, we have determined that amelogenins are responsible for normal enamel thickness and structure, but not for initiation of enamel mineral formation at the dentin-enamel junction. Although it is now clear that the amelogenin (AmelX) gene exists in a nested orientation and that AmelX is expressed at a low level in various developing tissues, the significance of these findings is incompletely understood. Future studies are expected to answer remaining questions concerning structure/function relationships among these ‘enamel proteins’.
Proteomics and Genetics of Dental Enamel
Authors: Hu Jan C.-C. , Yamakoshi Yasuo , Yamakoshi Fumiko , Krebsbach Paul H. , Simmer James P.
Published: April 2006

The initiation of enamel crystals at the dentino-enamel junction is associated with the expression of dentin sialophosphoprotein (DSPP, a gene normally linked with dentin formation), three ‘structural’ enamel proteins – amelogenin (AMELX), enamelin (ENAM), and ameloblastin (AMBN) – and a matrix metalloproteinase, enamelysin (MMP20). Enamel formation proceeds with the steady elongation of the enamel crystals at a mineralization front just beneath the ameloblast distal membrane, where these proteins are secreted. As the crystal ribbons lengthen, enamelysin processes the secreted proteins. Some of the cleavage products accumulate in the matrix, others are reabsorbed back into the ameloblast. Once crystal elongation is complete and the enamel layer reaches its final thickness, kallikrein 4 (KLK4) facilitates the breakdown and reabsorption of accumulated enamel matrix proteins. The importance of the extracellular matrix proteins to proper tooth development is best illustrated by the dramatic dental phenotypes observed in the targeted knockouts of enamel matrix genes in mice (Dspp,Amelx,Ambn,Mmp20) and in human kindreds with defined mutations in the genes (DSPP,AMELX,ENAM,MMP20,KLK4) encoding these matrix proteins. However, ablation studies alone cannot give specific mechanistic information on how enamel matrix proteins combine to catalyze the formation of enamel crystals. The best approach for determining the molecular mechanism of dental enamel formation is to reconstitute the matrix and synthesize enamel crystals in vitro. Here, we report refinements to the procedures used to isolate porcine enamel and dentin proteins, recent advances in the characterization of enamel matrix protein posttranslational modifications, and summarize the results of human genetic studies that associate specific mutations in the genes encoding matrix proteins with a range of dental phenotypes.
The Consequences of Being Born Small – An Adaptive Perspective
Authors: Gluckman P.D. , Hanson M.A.
Published: April 2006

Absolute definitions of fetal growth are being replaced by definitions that focus on an optimal life-course trajectory. The fetus makes responses to its environment that are determined by the maternal macro-environment, health and physiology. The processes of maternal constraint create significant variations within the normal range of maternal environments and function, and in the fetal environment, which are reflected in different patterns of growth. Deficient nutrient provision may induce immediate adaptation in the form of fetal growth impairment, but will also induce adaptive responses that have evolved for predictive advantage; that is, for a later phase of the life cycle. This latter class of response, probably mediated by epigenetic processes, explains many outcomes of a less-than-optimal pregnancy, including impaired growth, increased visceral obesity, impaired cognitive development, advanced maturation and a greater risk of metabolic and related disease in later life. While these adaptive processes evolved and were appropriate in the environments of prehistory, they are increasingly mismatched with modern environments. Such considerations suggest different approaches to intervention and prevention in population-specific contexts.
Hormonal Regulation of Postnatal Growth in Children Born Small for Gestational Age
Authors: Cianfarani S. , Ladaki C. , Geremia C.
Published: April 2006

Children born small for gestational age (SGA) are at high risk of permanent short stature, with approximately 10% continuing to have stature below the third centile throughout childhood and adolescence and into adulthood. The mechanisms involved in catch-up growth, and those that prevent catch-up growth, are still unknown. To date, no reliable anthropometric or endocrine parameter predictive of postnatal catch-up growth has been identified. However, subtle abnormalities in the growth hormone-insulin-like growth factor axis, the hypothalamic-pituitary-adrenal axis and thyroid function have been described, and a mechanism involving intrauterine programming of hypothalamic-pituitary function has been proposed.
Growth and the Premature Baby
Authors: Gibson A. , Carney S. , Wales J.K.H.
Published: April 2006

There is considerable evidence to show that babies born prematurely have poor postnatal growth, and the more premature the baby, the greater the impairment is likely to be and the longer it will persist. Nutrition has been shown to play an important part in this, but adequate nutrition is difficult, if not impossible, to achieve in these infants. In the most immature infants, growth retardation may continue for many months and catch-up may be delayed and incomplete. Evidence from long-term studies suggests that preterm infants will be shorter and lighter than term controls and that reduced stature and head size may be linked with lower intelligence. Although there is evidence linking better growth to better neurodevelopmental outcome, with reports suggesting that this can be achieved with dietary manipulation, there are also data that suggest that there could be a link between increased postnatal growth and increased morbidity and mortality in later childhood and adult life. Here, we provide an overview of current understanding of growth impairment in infants born prematurely and the effects in later life.
Regulation of Fat Storage via Suppressed Thermogenesis: A Thrifty Phenotype That Predisposes Individuals with Catch-Up Growth to Insulin Resistance and Obesity
Authors: Dulloo A.G.
Published: April 2006

Catch-up growth during infancy and childhood is increasingly recognized as a major risk factor for later development of insulin-related complications and chronic diseases, namely abdominal obesity, type 2 diabetes and cardiovascular disease. As catch-up growth per se is characterized by insulin resistance, hyperinsulinaemia and an accelerated rate of fat storage (i.e., catch-up fat) even in the absence of hyperphagia, the possibility arises that suppressed thermogenesis in certain organs/tissues – for the purpose of enhancing the efficiency of catch-up fat – also plays a role in the pathophysiological consequences of catch-up growth. Here, the evidence for the existence of an adipose-specific control of thermogenesis, the suppression of which contributes to catch-up fat, is reviewed. Recent findings suggest that such suppression of thermogenesis is accompanied by hyperinsulinaemia, insulin resistance in skeletal muscle and insulin hyperresponsiveness in adipose tissue, all of which precede the appearance of excess body fat, central fat distribution and elevations in intramyocellular triglyceride or circulating lipid concentrations. These findings underscore a role for suppressed thermogenesis per se as an early event in the pathophysiology of catch-up growth. It is proposed that, in its evolutionary adaptive role to spare glucose for the rapid rebuilding of an adequate fat reserve (for optimal survival capacity during intermittent famine), suppressed thermogenesis in skeletal muscle constitutes a thrifty phenotype that confers to the phase of catch-up growth its high sensitivity to the development of insulin resistance and hyperinsulinaemia. In the context of the complex interactions between earlier reprogramming and a modern lifestyle characterized by nutritional abundance and low physical activity, this thrifty ‘catch-up fat phenotype’ is a central event that predisposes individuals with catch-up growth to abdominal obesity, type 2 diabetes and cardiovascular disease.