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W Just

Publications and source records attributed to W Just.

At least 19 recordsLinked to original sources
PubMed2002

Comparison of time-delayed feedback schemes for spatiotemporal control of chaos in a reaction-diffusion system with global coupling.

Time-delayed feedback control for stabilizing time periodic spatial patterns is investigated in a generic reaction-diffusion system with global coupling. We focus on the case of low-dimensional chaos where unstable patterns admit only a single unstable mode. Spatial degrees of freedom are taken into account to define different control schemes. The efficiency of these schemes is discussed, where control forces are motivated by physical requirements as well as by the possibility of obtaining analytically exact results. We find that control schemes that contain the full feedback of the inhibitor variable may finally destroy the control performance. Thus schemes that omit the inhibitor might be more efficient. Our numerical findings are explained in terms of Floquet spectra and compared with analytical solutions of particular coupling schemes.

Journal Article↗
PubMed2001

Invariant densities of delayed maps in the limit of large time delay.

The marginal invariant density of chaotic attractors of scalar systems with time delayed feedback has an asymptotic form in the limit of large delay. It is well known that the dimension and the entropy of such attractors obey interesting scaling laws in this limit, but very little has been said about properties of the invariant density. We present general considerations, detailed analytical results in low order perturbation theory for a particular model, and numerics for understanding the asymptotic behavior of the projections of the invariant density. Our approach clarifies how the analytical properties of the model determine the behavior of the marginal invariant densities for large delay times.

Journal Article↗
PubMed2001

Spatiotemporal dynamics near a supercritical Turing-Hopf bifurcation in a two-dimensional reaction-diffusion system.

Pattern formation in semiconductor heterostructures is studied on the basis of a spatially two-dimensional model of reaction-diffusion type. In particular, we investigate the neighborhood of a codimension-two Turing-Hopf instability by analytical methods. Amplitude equations are derived which predict the absence of mixed modes but extended ranges of bistability between homogeneous oscillatory states and hexagonal Turing patterns. Our results are confirmed by numerical simulations. The features are not confined to a neighborhood of the bifurcation point so that the conclusions of the weakly nonlinear analysis explain the observations in large portions of the parameter space at least qualitatively

Journal Article↗
PubMed2001

Periodic orbits and topological entropy of delayed maps.

The periodic orbits of a nonlinear dynamical system provide valuable insight into the topological and metric properties of its chaotic attractors. In this paper we describe general properties of periodic orbits of dynamical systems with feedback delay. In the case of delayed maps, these properties enable us to provide general arguments about the boundedness of the topological entropy in the high delay limit. As a consequence, all the metric entropies can be shown to be bounded in this limit. The general considerations are illustrated in the cases of Bernoulli-like and Hénon-like delayed maps.

Journal Article↗
PubMed2001

Exclusion of SOX9 as the testis determining factor in Ellobius lutescens: evidence for another testis determining gene besides SRY and SOX9.

In mammals the initiation of testis determination usually depends on the Y-chromosomal gene SRY. A few species, however, escape from this rule with a testis determination that is independent of SRY. The mole vole Ellobius lutescens is one of these species. It is not known how testis determination is initiated in this species but it has been suggested that a gene from the sex determination cascade usually acting downstream of SRY is mutated and has taken over the testis-determining function. At present SOX9 is the only candidate gene for which a testis-determining function in the absence of SRY has been observed. To test the hypothesis that testis differentiation in E. lutescens is initiated by SOX9, segregation analysis of SOX9 alleles was performed in an E. lutescens family. As there is no marker data available in this species we screened both Ellobius SOX9 introns for polymorphisms suitable for segregation studies. A biallelic polymorphism was found in the second intron of the SOX9 gene and analysis of this marker in the Ellobius family revealed an inheritance pattern completely independent of the sex of the animals. Thus, SOX9 can be excluded from being the testis-determining factor in E. lutescens. These results provide evidence for another possibly yet unknown gene besides SRY and SOX9 able to exert testis-determining function.

Alleles↗
PubMed2001

Recurrent mutations in the COL1A2 gene in patients with osteogenesis imperfecta.

A new recurrent point mutation in the COL1A2 gene was found in a patient with type III osteogenesis imperfecta (OI). A G-to-T transversion in nucleotide position 1121 leads to an amino acid substitution Gly238Cys. This is the first report on the most N-terminal cysteine substitution in COL1A2 reported so far. Until now, at this position, only serine substitutions were observed five times in unrelated patients showing a highly variable expression of OI. It is obvious that endogenic and/or exogenic modifiers are involved in this classical autosomal dominant (or rarely recessive) mendelian disorder. An apparent preferential substitution by cysteine and serine residues is discussed with reference to post-transcriptional or post-translational collagen assembly control.

Amino Acid Substitution↗
PubMed2001

Computational complexity of multiple sequence alignment with SP-score.

It is shown that the multiple alignment problem with SP-score is NP-hard for each scoring matrix in a broad class M that includes most scoring matrices actually used in biological applications. The problem remains NP-hard even if sequences can only be shifted relative to each other and no internal gaps are allowed. It is also shown that there is a scoring matrix M(0) such that the multiple alignment problem for M(0) is MAX-SNP-hard, regardless of whether or not internal gaps are allowed.

Algorithms↗
PubMed2000

Radioiodinated N-(2-diethylaminoethyl)benzamide derivatives with high melanoma uptake: structure-affinity relationships, metabolic fate, and intracellular localization.

Several radioiodinated N-(dialkylaminoalkyl)benzamides have been used for planar scintigraphy and single-photon emission computed tomography (SPECT) of melanoma metastases. In a quest for improved melanoma uptake and tissue selectivity, structure-activity studies for N-(2-diethylaminoethyl)benzamides with variation of phenyl substituents were performed using C57Bl/6 mice bearing B16 melanoma. Compounds 2 (4-amino-5-bromo-N-(2-diethylaminoethyl)-3-[(131)I]iodo-2-methoxybenz amide) and 6 (4-acetamido-N-(2-diethylaminoethyl)-5-[(131)I]iodo-2-methoxybenzamid e) showed at 6 h post iv injection, for example, melanoma uptake of 16.6 and 23.2% ID/g, respectively (mean values, n = 3). Uptake was 3-5 times higher (P < 0.01) than observed with benzamides known from the literature and was probably facilitated by the relatively slow urinary excretion of 2 or 6. In contrast, analogues lacking either the MeO, Ac, AcNH, or Br substituents exhibited reduced tumor uptake and high urinary excretion of radioactivity in various benzamide metabolites. Uptake of radioiodinated benzamides in B16 melanoma is not mediated by a specific mechanism such as sigma-receptor binding. 2 and 6 exhibited similar melanoma uptake values but quite different sigma(1)-receptor affinities of K(i) = 0.278 +/- 0.018 and 5.19 +/- 0.40 microM, respectively. Uptake studies with IMBA (N-(2-diethylaminoethyl)-3-[(131)I]iodo-4-methoxybenzamide) or BZA (N-(2-diethylaminoethyl)-4-[(131)I]iodobenzamide) showed that with increasing dose of unlabeled compound the measured uptake of label was unchanged (IMBA) or even enhanced (BZA) while receptor binding of label decreased. Differential and equilibrium density-gradient centrifugation revealed that most of the radioactivity from labeled IMBA was associated with fractions containing melanin granules. Thus, structure-activity studies indicate that blood clearance rates and metabolic stability are the main determinants for benzamide uptake in melanoma. The high uptake and slow clearance of 6 offer considerable potential for melanoma imaging in patients, and this compound may also prove to be useful for radionuclide therapy.

Animals↗
PubMed2000

Developmental profile of Sry transcripts in mouse brain.

Transient activation of the gene Sry in the gonadal ridge during a brief period of embryonic development is believed to function as a key signal for sex determination. However, a number of reports suggest that Sry expression is not as restricted in space and time as one would expect if its role was confined to directing male-specific differentiation in the early gonadal anlage. We have previously reported the occurrence of Sry/SRY transcripts in adult murine and human brain. The present communication is concerned with the study of the ontogenetic time course of Sry transcripts in mouse brain as detected by reverse transcription-polymerase chain reaction (RT-PCR). Particular emphasis was placed on the identification of two different forms of Sry mRNA, which can be linear or circular. To this aim, we used specific RT-PCR strategies to distinguish between both. Sry transcripts were found in male brain tissue of all ontogenetic stages investigated. Circular, presumably untranslatable, transcripts were found in embryonic brains of day 11 through 19. In contrast, postnatal Sry transcripts were linear, and thus translatable, and were found in diencephalon, midbrain, and cortex. The change from one transcript form to the other suggests that expression of the Sry gene in mouse brain is developmentally regulated, presumably by a switch in promoter selection. This supports the notion that Sry expression in brain is biologically significant.

Adult↗
PubMed2000

Relation between coupled map lattices and kinetic ising models

A spatially one-dimensional coupled map lattice possessing the same symmetries as the Miller-Huse model is introduced. Our model is studied analytically by means of a formal perturbation expansion which uses weak coupling and the vicinity to a symmetry breaking bifurcation point. In parameter space four phases with different ergodic behavior are observed. Although the coupling in the map lattice is diffusive, antiferromagnetic ordering is predominant. Via coarse graining the deterministic model is mapped to a master equation which establishes an equivalence between our system and a kinetic Ising model. Such an approach sheds some light on the dependence of the transient behavior on the system size and the nature of the phase transitions.

Journal Article↗
PubMed2000

Influence of stable Floquet exponents on time-delayed feedback control

The performance of time-delayed feedback control is studied by linear stability analysis. Analytical approximations for the resulting eigenvalue spectrum are proposed. Our investigations demonstrate that eigenbranches that develop from the stable Lyapunov exponents of the free system also have a strong influence on the control properties, either by hybridization or by a crossing of branches which interchanges the role of the leading eigenvalue. Our findings are confirmed by numerical analysis of two particular examples, the Toda and the Rossler models. More important is the verification by actual electronic circuit experiments. Here, the observed reduction of control domains can be attributed to these additional eigenvalue branches. The investigations lead to a thorough analytical understanding of the stability properties in time-delayed feedback systems.

Journal Article↗
PubMed2000

A comparison of the expression pattern of five genes of the family of small leucine-rich proteoglycans during mouse development.

For five members of the family of the small leucine-rich proteoglycans (SLRPs), the expression pattern during fetal development was analyzed. RNA in situ hybridization on whole body sections of mouse embryos was performed for biglycan (Bgn), decorin (Dcn), fibromodulin (Fmod), chondroadherin (Chad), and lumican (Lum). Special attention was given to the question of whether these patterns coincide only with sites of collagen secretion in connective tissue during tissue modeling or if expression can be observed at specific sites of organ differentiation also. In general, Fmod, Lum, and Bgn are expressed at sites of cartilage and bone formation and interstitial tissue deposition; Chad is expressed only at sites of cartilage; and Dcn is expressed only at sites of interstitial tissue deposition. However, there are some distinct developmental stages where no collagen secretion is known to occur. For example, this applies for the expression of Fmod in the forming somites of stage 9.5 postconception (p.c.), for Dcn and Lum in later stage embryos in the pituitary gland and dorsal root ganglia, and for Bgn and Dcn during differentiation in the kidney. These studies provide further evidence for a role of these molecules during connective tissue organization but also for an involvement at specific sites of organ differentiation.

Animals↗
PubMed1999

ZOO-FISH analysis in a species of the order Chiroptera: Glossophaga soricina (Phyllostomidae).

Glossophaga soricina is a flower-visiting bat which lives in the neotropics. The diploid chromosome number is 2n = 32 with a fundamental number of autosomal arms, FN, of 60. G. soricina belongs to the Microchiroptera which have a lower diploid DNA content and a higher AT composition in their DNA compared with other mammals. By ZOO-FISH analysis with human chromosome-specific DNA probes, the human autosomes were found conserved in 41 segments. This is an arrangement similar to other mammals which have been analyzed. Several chromosomal associations already known from ZOO-FISH studies in other species were also present in G. soricina.

Animals↗
PubMed1999

(CAG)nCAA and GGN repeats in the human androgen receptor gene are not associated with prostate cancer in a French-German population.

Alleles of the CAG and the GGC repeat in the first exon of the human androgen receptor (AR) gene have been shown to be associated with the risk of (advanced) prostate cancer. These studies had been carried out in the United States. We have analysed these polymorphisms in a French-German collection of 105 controls, 132 sporadic cases, and a sample of prostate cancer families comprising 85 affected and 46 not affected family members. The allele distributions were very similar in all four groups and chi square statistics on contingency tables did not detect any significant differences. The relative risk (odds ratio, OR) were calculated using logistic regression and did not reach significance despite sufficient numbers of patients and controls. Typical results were OR = 1.007; 95% Confidence Interval (CI) 0.97-1.1, P = 0.87 for CAG as continuous variable and OR = 1.2 (95% CI 0.7-2.0), P = 0.47 for CAG classes < 22 and > = 22 repeats. Similar results were obtained for subgroups defined by age or Gleason score. We conclude that these polymorphisms can not be used as predictive parameters for prostate cancer in the French or German population.

Aged↗
PubMed1998

Sex determination in Ellobius lutescens: the story of an enigma.

The unusual karyotype of Ellobius lutescens (2n = 17,X in males and females) has attracted permanent interest and prompted a series of hypotheses on sex determination in this species since its first description by Matthey (1953). The developing knowledge about the sex chromosomes and sex determination as well as the availability of new cytogenetic and molecular genetic techniques prompted studies to test the compatibility between current hypotheses and new findings and rendered modifications of the hypotheses necessary. After a long period dominated by the question what the sex chromosome constitution of this species might be and where the testis determining factor could be located, the presence of Sry had been eventually excluded and sex determination attributed to a hypothetical mutated gene acting downstream of Sry. An X-chromosomal or autosomal location of this gene can be assessed by cosegregation of sex with X-chromosome markers. Some preliminary results concerning X-chromosome dinucleotide repeat markers are reported. However, these markers were homomorphic in Ellobius lutescens. We now report evidence that Zfy is also missing in Ellobius lutescens and E. tancrei (males and females XX), a finding from which we conclude that the entire Y chromosome has been lost from these species. Perspectives concerning future studies are discussed.

Animals↗
PubMed1997

XX-agonadism in a fetus with multiple dysraphic lesions: a new syndrome.

We report on a 19-week-old fetus with a 46,XX karyotype, normal female external genitalia, complete gonadal agenesis, large encephalocele, spina bifida, and omphalocele. We postulate a new syndrome. Hitherto no consistent malformation patterns have been observed in agonadism patients. True agonadism, including even the unusual finding of an XX gonosomal status, is obviously not as rare as suggested.

Abnormalities, Multiple↗