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Biomedical subjects

K P Hadeler

Publications and source records attributed to K P Hadeler.

At least 19 recordsLinked to original sources
PubMed2005

Optimal harvesting and optimal vaccination.

Two optimization problems are considered: Harvesting from a structured population with maximal gain subject to the condition of non-extinction, and vaccinating a population with prescribed reduction of the reproduction number of the disease at minimal costs. It is shown that these problems have a similar structure and can be treated by the same mathematical approach. The optimal solutions have a 'two-window' structure: Optimal harvesting and vaccination strategies or policies are concentrated on one or two preferred age classes. The results are first shown for a linear age structure problem and for an epidemic situation at the uninfected state (minimize costs for a given reduction of the reproduction number) and then extended to populations structured by size, to harvesting at Gurtin-MacCamy equilibria and to vaccination at infected equilibria.

Age Distribution↗
PubMed2005

Insensitivity of cardiovascular function to low power cm-/mm-microwaves.

A previous study failed to disclose an effect of short (15 min) exposure to low level energy microwaves (3 microW/cm2) emitted by a commercially available automobile radar system (77 GHz) for adaptive cruise control (ACC) on cardiovascular function. The present study explored whether a 15 min exposure to higher level energy microwaves of frequencies varying from 5.8 to 110 GHz influences cardiovascular function. To this end heart rate, skin temperature (thermocouple), skin conductance (Ag/AgCl electrodes), systolic and diastolic blood pressure (automatic cuff) were recorded in 50 test persons before, during and after a 15 min exposure to a sequential pattern of microwaves varying from 5.8 to 110 GHz (59.7 microW/cm2). After an equilibration period of 30 min the first group of test persons and after additional 30 min the second group of test persons were exposed. The study has been performed in a strict double blind design. While significant effects on the measured parameters were observed depending on time ("calming" effect), no significant difference was observed between exposure and sham exposure to microwaves. In view of the small scatter of the data the present study rules out physiologically relevant effects of moderate energy (59.7 microW/cm2) microwaves varying from 5.8 to 110 GHz on cardiovascular function.

Adolescent↗
PubMed2004

Influence of low power cm-/mm-microwaves on cardiovascular function.

The present study has been designed to investigate physiological effects of short (15 min) exposure to low level energy microwaves (< 10 microW cm(-2)). To this end heart rate, PQ, QS and ST (electrocardiography), respiration (conductive stretch band around the thorax), skin temperature (thermocouple), skin conductance (Ag/AgCl electrodes), systolic and diastolic blood pressure (automatic cuff) were continuously recorded in a group of 50 test persons before, during and after a 15 min exposure to 3 microW cm(-2) high frequency (77 GHz) microwaves. After an equilibration period of 30 min the first group of test persons and after additional 30 min the second group of test persons were exposed. The study has been performed in a strict double blind design. While significant effects on the measured parameters were observed depending on time ('calming' effect), no significant difference was observed between exposure and sham exposure to microwaves. In view of the small scatter of the data the present study rules out physiologically relevant effects of low level energy on the autonomic nervous system and cardiovascular function.

Adolescent↗
PubMed2001

PAProC: a prediction algorithm for proteasomal cleavages available on the WWW.

The first version of PAProC (Prediction Algorithm for Proteasomal Cleavages) is now available to the general public. PAProC is a prediction tool for cleavages by human and yeast proteasomes, based on experimental cleavage data. It will be particularly useful for immunologists working on antigen processing and the prediction of major histocompatibility complex class I molecule (MHC I) ligands and cytotoxic T-lymphocyte (CTL) epitopes. Likewise, in cases in which proteasomal protein degradation has been indicated in disease, PAProC can be used to assess the general cleavability of disease-linked proteins. On its web site (http://www.paproc.de), background information and hyperlinks are provided for the user (e.g., to SYFPEITHI, the database for the prediction of MHC I ligands).

Algorithms↗
PubMed2000

An algorithm for the prediction of proteasomal cleavages.

Proteasomes, major proteolytic sites in eukaryotic cells, play an important part in major histocompatibility class I (MHC I) ligand generation and thus in the regulation of specific immune responses. Their cleavage specificity is of outstanding interest for this process. In order to generalize previously determined cleavage motifs of 20 S proteasomes, we developed network-based model proteasomes trained by an evolutionary algorithm with experimental cleavage data of yeast and human 20 S proteasomes. A window of ten flanking amino acid residues proved sufficient for the model proteasomes to reproduce the experimental results with 98-100 % accuracy. Actual experimental data were reproduced significantly better than randomly selected cleavage sites, suggesting that our model proteasomes were able to extract rules inherent to proteasomal cleavage data. The affinity parameters of the model, which decide for or against cleavage, correspond with the cleavage motifs determined experimentally. The predictive power of the model was verified for unknown (to the program) test conditions: the prediction of cleavage numbers in proteins and the generation of MHC I ligands from short peptides. In summary, our model proteasomes reproduce and predict proteasomal cleavages with high degree of accuracy. They present a promising approach for predicting proteasomal cleavage products in future attempts and, in combination with existing algorithms for MHC I ligand prediction, will be tested to improve cytotoxic T lymphocyte epitope prediction.

Algorithms↗
PubMed2000

Ticks and tick-borne diseases: a vector-host interaction model for the brown ear tick (Rhipicephalus appendiculatus).

An analytical model is derived for the interaction of the brown ear tick (Rhipicephalus appendiculatus) with its hosts. Such models are rare due to the complexity and lack of information on the entire stages of ticks life cycles. Most models are simulations rather than analytical. The vector is categorized into a discrete number of compartments according to its life cycle. The starting model in this article consists of a system of differential equations with constant coefficients. A general model on a stage structured population with unlimited host density is developed. From the characteristic polynomial of the system a sensitivity analysis for the population parameters is carried out in detail. The model is then improved by incorporating host abundance and availability. This is done on the basis of a demand-driven and ratio-dependent functional response model. The improved model adequately represents the dynamics of a stage-structured vector population under conditions of varying host density. The model allows the qualitative evaluation of several management strategies and is expected to guide future research work.

Animals↗
PubMed1997

Backward bifurcation in epidemic control.

For a class of epidemiological SIRS models that include public health policies, the stability at the uninfected state and the prevalence at the infected state are investigated. Backward bifurcation from the uninfected state and hysteresis effects are shown to occur for some range of parameters. In such cases, the reproduction number does not describe the necessary elimination effort; rather the effort is described by the value of the critical parameter at the turning point. An explicit expression is given for this quantity. The phenomenon of subcritical bifurcation in epidemic modeling is also discussed in terms of group models, pair formation, and macroparasite infection.

Disease Outbreaks↗
PubMed1995

Deterministic models for the eradication of poliomyelitis: vaccination with the inactivated (IPV) and attenuated (OPV) polio virus vaccine.

Currently two polio vaccines, IPV and OPV, are in use which differ markedly in their epidemiological parameters. A simple epidemiological model in terms of ordinary differential equations is proposed to study the effects of vaccination campaigns using these vaccines. The numbers of interest are the reproduction number of the disease in the presence of vaccination and the critical vaccination coverage necessary to prevent an outbreak. For these numbers explicit representations are determined which can be used in comparing different vaccination strategies.

Adult↗
PubMed1990

The discrete Rosenzweig model.

Discrete time versions of the Rosenweig predator-prey model are studied by analytic and numerical methods. The interaction of the Hopf bifurcation leading to periodic orbits and the period-doubling bifurcation is investigated. It is shown that for certain choices of the parameters there is stable coexistence of both species together with a local attractor at which the prey is absent.

Animals↗
PubMed1989

Predator-prey populations with parasitic infection.

A predator-prey model, where both species are subjected to parasitism, is developed and analyzed. For the case where there is coexistence of the predator with the uninfected prey, an epidemic threshold theorem is proved. It is shown that in the case where the uninfected predator cannot survive only on uninfected prey, the parasitization could lead to persistence of the predator provided a certain threshold of transmission is surpassed.

Animals↗
PubMed1988

Models for pair formation in bisexual populations.

Birth, death, pair formation, and separation are described by a system of three nonlinear homogeneous ordinary differential equations. The qualitative properties of the system are investigated, in particular the conditions for existence and global stability of the bisexual state.

Animals↗
PubMed1988

Epidemiological models for sexually transmitted diseases.

The classical models for sexually transmitted infections assume homogeneous mixing either between all males and females or between certain subgroups of males and females with heterogeneous contact rates. This implies that everybody is all the time at risk of acquiring an infection. These models ignore the fact that the formation of a pair of two susceptibles renders them in a sense temporarily immune to infection as long as the partners do not separate and have no contacts with other partners. The present paper takes into account the phenomenon of pair formation by introducing explicitly a pairing rate and a separation rate. The infection transmission dynamics depends on the contact rate within a pair and the duration of a partnership. It turns out that endemic equilibria can only exist if the separation rate is sufficiently large in order to ensure the necessary number of sexual partners. The classical models are recovered if one lets the separation rate tend to infinity.

Epidemiologic Methods↗
PubMed1986

The hypercycle, traveling waves, and Wright's equation.

A formal relation between the hypercycle equation and the delay differential equation of E. M. Wright is exhibited using a traveling waves approach. Several unsolved questions in either problem can be related and interpreted, in particular new motivation for the study of Wright's equation is obtained.

Alleles↗
PubMed1984

Population dynamics of killing parasites which reproduce in the host.

For a parasitic infection in human hosts a model is derived from basic assumptions on the population structure of the host, in particular mortality depending on age and parasite load, and on the reproduction and transmission of parasites. The model assumes the form of a system of partial differential equations. The paper contains proofs of local and global existence and existence and uniqueness of nontrivial stationary states, and a discussion of the relation to birth and death processes and other models for parasitic infections.

Age Factors↗
PubMed1980

Dynamic models for animal orientation.

The orientation of an animal moving in a plane towards a point-like mark is investigated. The control exerted by the optomotor (tracking) response on the motion of the animal is interpreted as an external force acting on the animal itself, which is modeled as a dipole or as a single point. The optomotor response is assumed as a rather general function of distance and angle. Differential equations governing the motion are derived and analyzed qualitatively and numerically. The role of distance-dependence and of the width of the visual field is investigated in detail and related to some typical kinds of paths in the plane, such as hitting the mark, coming close to the mark within a short distance, circular or undulating motion around the mark.

Animals↗