Long-time Persistence Research Articles

Diversity of Rich Fen Vegetation and Related Plant Specialists in Mountain Refugia of the Iberian Peninsula

In temperate mountains, fens have been reported as relict habitats subject to geographical fragmentation and broad climatic gradients, but few studies have analyzed the influence of these factors on plant diversity. Here we investigate the effect of isolation on the vegetation diversity of rich fens (Caricion davallianae) in the mountains of the Iberian Peninsula, the distribution limit of these habitats in south-western Europe. We used plot-based vegetation data from the Pyrenees and the Cantabrian mountain range to evaluate their regional species-pool, occurrence of specialists, beta-diversity and the effect of geo-climatic variables on their species-richness and species-composition. We found a lower ratio of rare specialists in the Pyrenees than in the Cantabrian range, but similar estimates in the species pools, total species-richness per plot and beta-diversity. The isolation of the two mountain regions resulted in different species assemblages best predicted by summer precipitation and bedrock types, showing region-based differences in the response of vegetation and plant specialists to the environment. The tighter correlation between local climate and diversity estimates in the Cantabrian range suggests relict character of rich fens in that region, where climatic conditions have restricted local distribution of formerly more widely distributed specialists. Although there is no relevant evidence of vegetation impoverishment in that region, historical isolation has probably resulted in the existence of fragmentary plant communities. We conclude that fen vegetation may experience long-time persistence in climatically sub-optimal mountain refugia, but related plant specialists may be sensitive to climatic changes and subject to the extinction of local populations.

The life cycle and fitness domain of gregarine (Apicomplexa) parasites

Theoretical demographic models with accompanying experimental programs provide an important framework to study the life history of organisms. In this paper we examine the fitness characteristics of gregarine parasites (Apicomplexa) and how these evolutionary long-lived parasites are shaped by their own life cycle stages inside and outside a definitive insect host. Although gregarines have been investigated in experimental works, their fitness and population characteristics have not been subject to modeling efforts to help understand their longevity or interactions with their host species. We develop a dynamic, mechanistic population model represented by a system of two differential equations for two of the parasite stages: the mature parasite, or trophont, inside a definitive insect host, and the infectious oocyst stage in the water environment of the host. In contrast to many classical macroparasite models, the force of infection between oocysts and hosts is of sigmoid type. Inside the host, production of the water borne infectious state is modeled by linear production rate in the trophont population with a density-independent trophont mortality. We examine stability of model's equilibria for different parameter values and different host populations. This leads to the definition of a fitness parameter that acts as a bifurcation parameter for the model. The model shows good cause for the establishment and long-time persistence of this common, widespread parasite. It is parameterized by extensive data gathered at Cedar Point Biological Station, and numerical calculations based on those parameters illustrate the dynamics. Possible applications include parasite control in aquacultures.

Quantitative determination of IgM antibodies reduces the pitfalls in the serodiagnosis of tick-borne encephalitis

BackgroundTick-borne encephalitis (TBE) is the most important arbovirus disease in parts of Europe and Asia. Its laboratory diagnosis depends on the detection of specific IgM antibodies which can be impeded by (1) long-time persistence of IgM antibodies after infection, (2) vaccine-induced IgM antibodies, and (3) cross-reactive IgM antibodies from other flavivirus infections. ObjectivesTo assess the extent of interference factors in the serodiagnosis of TBE that might lead to the false positive assignment of a recent infection. Study designWe quantified TBE virus-specific IgM and IgG antibodies in sera collected at different time points from cohorts of (1) 61 TBE patients, (2) 131 TBE vaccinees, and (3) 42 patients with recent dengue or West Nile virus infections. ResultsAll of the TBE patients were IgM- and IgG-positive upon hospitalization and 87% of acute TBE sera had IgM antibody titers of >500 Arbitrary Units (AU). These titers rapidly declined and only 16% of TBE patients had low IgM titers ≥9months after infection. Vaccine-induced as well as flavivirus cross-reactive IgM antibodies were rarely detectable and of low titer. ConclusionsMost of the potential problems of TBE serodiagnosis can be resolved by the quantification of IgM antibodies in a single serum sample taken upon hospitalization. High IgM values (>500AU in our assay) are indicative of a recent infection. Lower IgM values, however, may require the analysis of a follow-up sample and/or a specific neutralization assay to exclude the possibilities of IgM persistence, vaccine-induced IgM antibodies or heterologous flavivirus infections.

Long-term persistence of molecular response after discontinuation of interferon-alpha in two patients with chronic myeloid leukaemia.

Dear Sir, By describing the long-time persistence of major and complete molecular responses in two patients with chronic myeloid leukaemia (CML) after cessation of interferon-α therapy, we would like to take part in the debate regarding discontinuation of treatment in CML patients. The first case, a 64-year old man, was diagnosed with CML in September 1990. Treatment was discontinued, at the patient’s request, in June 2002 during a major molecular remission. The second case, a 34-year old male was diagnosed with CML in March 1997. Interferon-α was stopped in December 2005 due to an acute myocardial infarction. The patient had been in complete molecular remission since September 1999. Following discontinuation of interferon-α, both patients were evaluated twice a year by real time quantitative and/or nested polymerase chain reaction (PCR) analysis of BCR-ABL mRNA from peripheral blood. To date, the patients are in persistent major molecular remission (BCR-ABL:ABL-ABL ratio: 0.0103) and complete molecular remission at 107 and 65 months, respectively, since treatment cessation. In the past, allogeneic haemopoietic stem-cell transplantation (HSCT) was indicated to be the only cure for CML because disease recurrence was not observed in most transplanted patients who achieved a complete molecular response1. However, imatinib, a tyrosine-kinase inhibitor, currently represents the standard of care for patients with newly diagnosed CML. It produces a major molecular response in a large proportion of patients and, over time, can also induce a complete molecular response2. Unfortunately, disease recurrence is reported early after treatment cessation in about 60% of patients in complete molecular remission, although the majority of patients remain responsive to re-treatment after recurrence. Conversely, about 40% of patients maintain a complete molecular response after withdrawal of tyrosine kinase inhibitor treatment. It is interesting to note that previous treatment with interferon-α does not increase the percentage of patients with persistent complete molecular remission3. In our opinion, it is reasonable to consider that in CML the long-time persistence of molecular response after therapy cessation does not depend on the type of treatment adopted, i.e. interferon-α, HSCT, or tyrosine-kinase inhibitors, with the last being by far the most effective therapy. However, if CML is an incurable disease, it is difficult to explain why it does not recur in about 40% of patients after withdrawal of tyrosine-kinase inhibitors; contrariwise, if CML is a curable disease, there is the same difficulty in explaining why it does recur in about 60% of patients in complete molecular remission. As a consequence, we may consider that assessment of BCR-ABL transcripts by PCR analysis is not a fully reliable method for evaluating disease status. Along with clinical features such as low Sokal score, male sex and duration of imatinib treatment, predictive of maintaining complete molecular response after suspension of imatinib, a more sensitive and standardised PCR technology should be designed in order to identify those patients in whom treatment could be withdrawn. In addition, considering that we did not observe progression of disease after discontinuation of interferon-α, even in the patient in major molecular remission, and that other authors did not observe disease recurrence in patients in complete cytogenetic remission4 (not necessarily in complete molecular remission), it is reasonable to hypothesise that other biological markers should be identified to assess the real status of disease5. In conclusion, in spite of the fact that discontinuation of treatment is not warranted outside the context of clinical studies, our observation adds support to the concept that CML may be cured without HSCT, at least in some patients.

From Modes to Movement in the Behavior of Caenorhabditis elegans

Organisms move through the world by changing their shape, and here we explore the mapping from shape space to movements in the nematode Caenorhabditis elegans as it crawls on an agar plate. We characterize the statistics of the trajectories through the correlation functions of the orientation angular velocity, orientation angle and the mean-squared displacement, and we find that the loss of orientational memory has significant contributions from both abrupt, large amplitude turning events and the continuous dynamics between these events. Further, we discover long-time persistence of orientational memory in the intervals between abrupt turns. Building on recent work demonstrating that C. elegans movements are restricted to a low-dimensional shape space, we construct a map from the dynamics in this shape space to the trajectory of the worm along the agar. We use this connection to illustrate that changes in the continuous dynamics reveal subtle differences in movement strategy that occur among mutants defective in two classes of dopamine receptors.

Porous silicon based β-FeSi2 and photoluminescence

Highly-pure iron powder was covered on porous silicon for fabricating semiconducting β-FeSi2 structures. X-ray diffraction and Raman scattering results confirm the formation of pure-phase β-FeSi2 after high-temperature annealing at 1100°C and then long-time persistence at 900°C. Scanning electron microscope observations reveal that large-size (>μm) β-FeSi2 grains mainly form in the pores of porous silicon and some nanocrystals grow on local surfaces. The temperature-dependent photoluminescence spectra disclose that the observed ∼1.54 μm emission arises from free exciton recombination, which is confirmed via the activation energy (0.25 eV) measurement. Our method provides a way to synthesize single-phase β-FeSi2 materials.

Potential of active and passive immunizations for the prevention and therapy of transmissible spongiform encephalopathies

Transmissible spongiform encephalopathies are fatal neurodegenerative disorders that affect humans and certain animals and are caused by prions. In most cases, infection occurs by ingestion of prions. Their long-time persistence in the environment creates a reservoir of potentially infectious matter that renders the eradication of the disease problematic. Unfortunately, no cure is available to date. Yet, for both the treatment of infected and the protection of uninfected individuals, active and passive immunizations have been shown to have a beneficial effect on the course of the disease. The current review provides an overview of such antibody-based approaches and assesses their feasibility and potential in prophylaxis and therapy of transmissible spongiform encephalopathies.

Long-time persistence of Korteweg–de Vries solitons as transient dynamics in a model of inclined film flow

The Kuramoto–Sivashinsky-perturbed Korteweg–de Vries (KS–KdV) equation$$ \partial_tu=-\partial_x^3u-\tfrac{1}{2}\partial_x(u^2)-\varepsilon(\partial_x^2+\partial_x^4)u, $$with $0<\varepsilon\ll1$ a small parameter, arises as an amplitude equation for small amplitude long waves on the surface of a viscous liquid running down an inclined plane in certain regimes when the trivial solution, the so-called Nusselt solution, is sideband unstable. Although individual pulses are unstable due to the long-wave instability of the flat surface, the dynamics of KS–KdV is dominated by travelling pulse trains of $O(1)$ amplitude. As a step toward explaining the persistence of pulses and understanding their interactions, we prove that for $n=1$ and $2$ the KdV manifolds of $n$-solitons are stable in KS–KdV on an $O(1/\varepsilon)$ time-scale with respect to $O(1)$ perturbations in $H^n(\mathbb{R})$.

Memory effect in electron glasses: Theoretical analysis via a percolation approach

We present a theory for the memory effect in electron glasses. In fast gate voltage sweeps it is manifested as a dip in the conductivity around the equilibration gate voltage. We show that this feature, also known as anomalous field effect, arises from the long-time persistence of correlations in the electronic configuration. We argue that the gate voltage at which the memory dip saturates is related to an instability caused by the injection of a critical number of excess carriers. This saturation threshold naturally increases with temperature. On the other hand, we argue that the gate voltage beyond which memory is erased, is temperature independent. Using standard percolation arguments, we calculate the anomalous field effect as a function of gate voltage, temperature, carrier density and disorder. Our results are consistent with experiments, and in particular, they reproduce the observed scaling of the width of the memory dip with various parameters.

Biogeography and origin of Lilium longiflorum and L. formosanum (Liliaceae) endemic to the Ryukyu Archipelago and Taiwan as determined by allozyme diversity

Allozyme diversity on 13 isozyme loci was investigated for two bulbous species, Lilium longiflorum and L. formosanum, endemic to the subtropical archipelago of continental origin located in East Asia. Degrees of allozyme variability and divergence for L. longiflorum were very high for insular endemic species, indicating relatively longtime persistence of the present widespread distribution across many islands in this phenotypically little-changed species. Lilium formosanum exhibited rather lower variability and divergence than did L. longiflorum and was genetically close to the southern peripheral populations of L. longiflorum with 0.978 as its highest genetic identity value. Combined with other biological and insular geohistorical information, our results suggest that L. longiflorum was established around the end of the Pliocene when the current distribution area was still a continuous part of the ancient Asian continent, and L. formosanum was derived from southern populations of L. longiflorum around the late Pleistocene when the mainland of Taiwan was completely separated from the adjacent islands and the main continent. Depauperization of allozyme variability in some L. longiflorum populations was found on islands with lower altitudes. This reflects bottleneck effects after the complete or almost complete submergence of such low islands during the archipelago's development.

Can staphylococcal superantigens be neutralized by healthy infants?

It has long been thought that bacterial superantigens invariably cause pathology by causing the powerful stimulation of large numbers of T cells, a phenomenon seen in several models, which leads to high levels of cytokine release. Clinically this scenario manifests as toxic shock syndrome following burns, trauma, or in relation to menstruation. More limited local T-cell stimulation, probably caused by superantigens, has been described in atopic dermatitis, food poisoning and psoriasis. The implication of studies so far has been that antibodies provide protection against these molecules; the most vulnerable group should therefore be infants. However, careful prospective observation of a group of 49 healthy Swedish infants over their first year challenges this disease model 1 Lindberg E et al. Long-time persistence of superantigen-producing Staphylococcus aureus strains in the intestinal microflora of healthy infants. Pediatr. Res. 2000; 48: 741-747 Crossref PubMed Scopus (76) Google Scholar . These healthy infants had fecal flora sampled and tested at intervals; it was observed that Staphylococcus aureus colonization rates rose from 16% on the third day of life to 73% by six months of age. The organisms resembled those known to colonize the skin. Strains of S. aureus were identified using their characteristic polymorphic DNA patterns. It was found that individual strains frequently persisted for several months in stool samples. Following culture, Staphylococci in 23 infants were capable of producing superantigens (over a quarter synthesized more than one superantigen). Some 25% of toxin-producing strains were found in numbers of >108 per gram of feces. Levels of colonization or toxin production did not correspond to any obvious clinical symptom in the infants.

Spatial Noise Stabilizes Periodic Wave Patterns in Oscillatory Systems on Finite Domains

Invasions in oscillatory systems generate in their wake spatiotemporal oscillations, consisting of either periodic wavetrains or irregular oscillations that appear to be spatiotemporal chaos. We have shown previously that when a finite domain, with zero-flux boundary conditions, has been fully invaded, the spatiotemporal oscillations persist in the irregular case, but die out in a systematic way for periodic traveling waves. In this paper, we consider the effect of environmental inhomogeneities on this persistence. We use numerical simulations of several predator-prey systems to study the effect of random spatial variation of the kinetic parameters on the die-out of regular oscillations and the long-time persistence of irregular oscillations. We find no effect on the latter, but remarkably, a moderate spatial variation in parameters leads to the persistence of regular oscillations, via the formation of target patterns. In order to study this target pattern production analytically, we turn to λ-ω systems. Numerical simulations confirm analagous behavior in this generic oscillatory system. We then repeat this numerical study using piecewise linear spatial variation of parameters, rather than random variation, which also gives formation of target patterns under certain circum- stances, which we discuss. We study this in detail by deriving an analytical approximation to the targets formed when the parameter λ0 varies in a simple, piecewise linear manner across the do- main, using perturbation theory. We end by discussing the applications of our results in ecology and chemistry.

IL-4 addition during differentiation of CD34 progenitors delays maturation of dendritic cells while promoting their survival

Dendritic cells (DC) are the most effective cells for antigen presentation in primary immune responses. Human cord blood CD34+ progenitors cultured in the presence of GM-CSF and TNF alpha generate a heterogeneous population of DC including Langerhans-like DC (LLDC) and monocytes. We describe here that IL-4 exerts different effecs in such culture according to the cells considered. Thus, IL-4 favors DC components at the expense of monocytic development, and permits long-time persistence of DC which can be maintained up to one month in culture. These results show an IL-4-dependent inhibition of proliferation and emergence of CD14+ cells. Notably, however, IL-4 also acts on the DC precursors. Thus, IL-4 enhances survival and delays maturation of LLDC from CD1a+ CD14- precursors. In addition, IL-4 also favors orientation of CD14+ CD1a- DC/monocyte precursors towards dermal-type CD1a+ DC. DC recovered from IL-4 treated cultures display reduced allostimulatory capacity, but this function is restored upon IL-4 weaning. Finally, a short (48h) IL-4 pulse is sufficient to favor DC development. The present study demonstrates that IL-4 positively regulates DC development at several levels on distinct precursor cells.

Long-time persistence of D 2 dopamine receptor occupancy after discontinuation of haloperidol decanoate

Long-time persistence of D 2 dopamine receptor occupancy after discontinuation of haloperidol decanoate

A topological study of the dynamical effects of entanglements

The constraint that extended molecules such as polymers cannot pass through each other is formulated in terms of a topological invariant. A simple model of the motion of a labelled loop entangled in a uniform background of amorphous loops is studied. A dynamical weighting factor is found which effectively removes configurational changes that would lead to the labelled loop passing through the strands of the background material. A perturbation treatment of this weighting factor is presented which describes the effects of the entanglements in terms of random environmental forces possessing considerable space and time correlations. A detailed analytic calculation is presented for the case of a labelled molecule with a rigid-ring configuration. This calculation illustrates the limited validity of perturbation theory in dealing with entanglements and suggests the existence of a transition in time to a random 'tube'-like behaviour, where the centre-of-mass motion of the ring depends on the time as t1/4 instead of the usual diffusive t1/2. The origin of this behaviour can be located in the long-time persistence of the bond vector correlation function of the labelled ring.

Submarine Canyons: Multiple Causes and Long-Time Persistence

The actual investigation of submarine canyons as field work was begun about 50 years ago. A large amount of factual information has accumulated as result of operations of deep diving vehicles, first in the Pacific Coast canyons and more recently in the remarkable dives of the Woods Hole minisubmarine Alvin into East Coast canyons. Taking the results of these recent dives and combining them with earlier investigations, including much work done by the French in the Mediterranean as well as our extensive studies off California and Baja California, we can now say with some confidence that these amazing deep excavations into the sea floor off so many coastal areas can be explained. New methods such as side scanning have also given us a greater understanding of the exact character of submarine canyons, particularly in the Bay of Biscay. The development of multichannel sonar has greatly increased our knowledge of the nature of continental margins and hence their history. This has given us more insight into the history of canyon development, particularly off the east Coast where drilling for oil and gas has become so important. In the past we have seen a great variety of hypotheses for explaining submarine canyons. Unfortunately almost all of these have been based on information from a small selection of the canyons, usually from one area. From the new information, it is evident that canyons are of composite origin and that many of the hypotheses suggested in the past were partly correct but did not appreciate that coordination of other processes was required. Thus there is growing evidence that, in the history of many canyons, there was a period in which subaerial erosion was an important precursor, but that present features are predominantly the result of marine erosion. Those advocating turbidity currents as the unique cause of canyons failed to appreciate that debris flows down the incipient valleys, as ell as other types of landslides, could be an almost equally important factor in marine erosion. The great effect of biologic activity on the rock walls of incipient canyons has been almost completely neglected in explanations, and various types of currents such as those of the tides have been left largely out of the picture. Perhaps the most important feature absent in these various hypotheses has been the realization that canyons may well be the result of a long period of formation, much longer than the short episodes of Pleistocene glacial sea-level lowering features which commonly cut into hard crystalline rock. New information is showing that the canyons may date back to at least the Cretaceous.

Observation of Sidebands on the EPR Lines in Low-Dimensional Systems

The observation of sidebands on the EPR lines is reported in one- and two-dimensional exchange-coupled paramagnets, TMMC and K 2 MnF 4 . These subsidiary resonances appear at half the main Zeeman fields and provide direct evidences of the long-time persistence of spin correlation functions in the low-dimensional systems.

Exchange Narrowing in One-Dimensional Systems

Magnetic relaxation in one-dimensional exchange-coupled ${(\mathrm{C}{\mathrm{H}}_{3})}_{4}$NMn${\mathrm{Cl}}_{3}$ is found to be dramatically different than it is in three-dimensional exchange-narrowed paramagnets. A theory which accounts properly for the special long-time persistence of spin-correlation functions in one dimension is shown to explain the observed behavior.