477 research outputs found
DelayAndPeriodicity
Systems with time delay play an important role in modeling of many physical
and biological processes. In this paper we describe generic properties of
systems with time delay, which are related to the appearance and stability of
periodic solutions. In particular, we show that delay systems generically have
families of periodic solutions, which are reappearing for infinitely many delay
times. As delay increases, the solution families overlap leading to increasing
coexistence of multiple stable as well as unstable solutions. We also consider
stability issue of periodic solutions with large delay by explaining asymptotic
properties of the spectrum of characteristic multipliers. We show that the
spectrum of multipliers can be splitted into two parts: pseudo-continuous and
strongly unstable. The pseudo-continuous part of the spectrum mediates
destabilization of periodic solutions.Comment: 24 pages, 9 figure
On the stability of periodic orbits in delay equations with large delay
We prove a necessary and sufficient criterion for the exponential stability
of periodic solutions of delay differential equations with large delay. We show
that for sufficiently large delay the Floquet spectrum near criticality is
characterized by a set of curves, which we call asymptotic continuous spectrum,
that is independent on the delay.Comment: postprint versio
Optimum ground states for spin- chains
We present a set of {\em optimum ground states} for a large class of
spin- chains. Such global ground states are simultaneously ground
states of the local Hamiltonian, i.e. the nearest neighbour interaction in the
present case. They are constructed in the form of a matrix product. We find
three types of phases, namely a {\em weak antiferromagnet}, a {\em weak
ferromagnet}, and a {\em dimerized antiferromagnet}. The main physical
properties of these phases are calculated exactly by using a transfer matrix
technique, in particular magnetization and two spin correlations. Depending on
the model parameters, they show a surprisingly rich structure.Comment: LaTeX, 22 pages, 6 embedded Postscript figure
The EMIF-AD Multimodal Biomarker Discovery study: design, methods and cohort characteristics.
There is an urgent need for novel, noninvasive biomarkers to diagnose Alzheimer's disease (AD) in the predementia stages and to predict the rate of decline. Therefore, we set up the European Medical Information Framework for Alzheimer's Disease Multimodal Biomarker Discovery (EMIF-AD MBD) study. In this report we describe the design of the study, the methods used and the characteristics of the participants.
Participants were selected from existing prospective multicenter and single-center European studies. Inclusion criteria were having normal cognition (NC) or a diagnosis of mild cognitive impairment (MCI) or AD-type dementia at baseline, age above 50 years, known amyloid-beta (Aβ) status, availability of cognitive test results and at least two of the following materials: plasma, DNA, magnetic resonance imaging (MRI) or cerebrospinal fluid (CSF). Targeted and untargeted metabolomic and proteomic analyses were performed in plasma, and targeted and untargeted proteomics were performed in CSF. Genome-wide SNP genotyping, next-generation sequencing and methylation profiling were conducted in DNA. Visual rating and volumetric measures were assessed on MRI. Baseline characteristics were analyzed using ANOVA or chi-square, rate of decline analyzed by linear mixed modeling.
We included 1221 individuals (NC n = 492, MCI n = 527, AD-type dementia n = 202) with a mean age of 67.9 (SD 8.3) years. The percentage Aβ+ was 26% in the NC, 58% in the MCI, and 87% in the AD-type dementia groups. Plasma samples were available for 1189 (97%) subjects, DNA samples for 929 (76%) subjects, MRI scans for 862 (71%) subjects and CSF samples for 767 (63%) subjects. For 759 (62%) individuals, clinical follow-up data were available. In each diagnostic group, the APOE ε4 allele was more frequent amongst Aβ+ individuals (p < 0.001). Only in MCI was there a difference in baseline Mini Mental State Examination (MMSE) score between the A groups (p < 0.001). Aβ+ had a faster rate of decline on the MMSE during follow-up in the NC (p < 0.001) and MCI (p < 0.001) groups.
The characteristics of this large cohort of elderly subjects at various cognitive stages confirm the central roles of Aβ and APOE ε4 in AD pathogenesis. The results of the multimodal analyses will provide new insights into underlying mechanisms and facilitate the discovery of new diagnostic and prognostic AD biomarkers. All researchers can apply for access to the EMIF-AD MBD data by submitting a research proposal via the EMIF-AD Catalog
Finding periodic orbits in state-dependent delay differential equations as roots of algebraic equations
In this paper we prove that periodic boundary-value problems (BVPs) for delay
differential equations are locally equivalent to finite-dimensional algebraic
systems of equations. We rely only on regularity assumptions that follow those
of the review by Hartung et al. (2006). Thus, the equivalence result can be
applied to differential equations with state-dependent delays (SD-DDEs),
transferring many results of bifurcation theory for periodic orbits to this
class of systems. We demonstrate this by using the equivalence to give an
elementary proof of the Hopf bifurcation theorem for differential equations
with state-dependent delays. This is an alternative and extension to the
original Hopf bifurcation theorem for SD-DDEs by Eichmann (2006).Comment: minor revision, correcting mistakes in formulation of Lemma 2.3 and
A.5 (which are also present in the Journal paper): center of neighborhood
must be in , which is the case for the main theore
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