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Time domain analysis: an alternative way to interpret PGSE experiment.

We report a theoretical development which aims at interpreting Pulsed Gradient Spin Echo data for diffusing fluids in saturated porous media. It consists in analyzing the time dependence of PGSE amplitudes for each single gradient strength, and introduces a new diffusion coefficient D(q) as being continuously dependent on the length scale in the material. Both experimental measurements on water saturated bead packings and simulated experiments in 2D and 3D model systems are interpreted with this approach. D(q) is shown to give a new insight in the micro-macro transition. Its evolution vs. the length scale is non trivial, and can be sensitive to local slow kinetic effects.

Magnetic Resonance Spectroscopy↗

Modeling the interplay of generic and genetic mechanisms in cleavage, blastulation, and gastrulation.

Early development of multicellular organisms is marked by a rapid initial increase in their cell numbers, accompanied by spectacular morphogenetic processes leading to the gradual formation of organs of characteristic shapes. During morphogenesis, through differentiation under strict genetic control, cells become more and more specialized. Morphogenesis also requires coordinated cell movement and elaborate interactions between cells, governed by fundamental physical or generic principles. As a consequence, early development must rely on an intricate interplay of generic and genetic mechanisms. We present the results of computer simulations of the first nontrivial morphogenetic transformations in the life of multicellular organisms: initial cleavages, blastula formation, and gastrulation. The same model, which is based on the physical properties of individual cells and their interactions, describes all these processes. The genetic code determines the values of the model parameters. The model accurately reproduces the major steps of early development. It predicts that physical constraints strongly influence the timing of gastrulation. Gastrulation must occur prior to the appearance of dynamical instability, which would destabilize and eventually derail normal development. Within our model, to avoid the instability, we suddenly change the values of some of the model parameters. We interpret this change as a consequence of specific gene activity. After changing the physical characteristics of some cells, normal development resumes, and gastrulation proceeds.

Algorithms↗

A new criterion for selection of pharmacokinetic multiexponential equations.

In linear pharmacokinetics, the time course of the plasma concentration of a drug, Ct, is expressed by the sum of exponential terms, (formula; see text) This article proposes a new statistical criterion for discriminating between alternate polyexponential models. According to this new criterion, the model that best interprets a set of experimental data points is that which minimizes the area between the approximate confidence limits of Ct.

Doxorubicin↗

Statistical modelling in specific case analysis.

In spite of the problems associated with the development of a statistical approach in specific case analysis, the potential of two statistical methods, logistic regression and Bayesian belief networks, has been investigated and found encouraging in the context of a database relating to child murders with a sexual connotation. Continual collaboration between statisticians and detectives would be needed in the collection of the data, the choice and construction of the models, and the interpretation of the results.

Adult↗

Estimates of mechanical work and energy transfers: demonstration of a rigid body power model of the recovery leg in gait.

Many studies concerning the mechanical work and efficiency of human motion have used models based on segmental energy. It has been shown theoretically that such work estimates may be in error due to offsetting compensations in power sources underlying the energy profiles. Further, mechanical energy transfers calculated from these energy models have been interpreted as metabolic energy-saving mechanisms. This paper examines the use of mechanical power analysis to calculate work and energy transfer estimates, using the motion of the recovery leg in walking and running for one subject as a demonstrative example. Work and energy transfer estimates from both energy and power models are compared and contrasted. The energy model underestimates the work of the recovery leg in both walking (54% of power model estimate) and running (38%), due to muscle powers at joints opposing each other in energy generation and absorption. Energy transfers calculated with energy models are shown to suffer the same problem of offsetting power sources. In contrast, the power model identifies four energy transfer mechanisms (pendulum, whip, tendon, and joint force transfers), which contribute to energy change within the leg in varying amounts. For the recovery leg, the joint force and whip transfer mechanisms have the greatest magnitude, while the pendulum and tendon transfers are much smaller. These energy transfers can be observed on a time-varying basis throughout a motion sequence and illustrate differences in energy distribution between walking and running. These power-based transfers are discussed in terms of their nature regarding metabolic energy cost and mechanical energy distribution within a multisegmented system. It is suggested that the work and energy transfers calculated from the power analysis are more accurate than those calculated from mechanical energy models and are more useful for understanding performance.

Biomechanical Phenomena↗

Animal models in peritoneal dialysis research: a need for consensus.

The development of an adequate animal model for peritoneal research remains an object of concern. In vivo peritoneal dialysis (PD) research is hampered by the large variety of available models that make interpretation of results and comparison of studies very difficult. Species and strain of experimental animals, method of peritoneal access, study duration, measures of solute transport and ultrafiltration, and sampling for histology differ substantially among the various research groups. A collective effort to discuss the shortcomings and merits of the different experimental models may lead to a consensus on a standardized animal model of PD.

Animals↗

Boltzmann-type distribution of side-chain conformation in proteins.

We analyze packing imperfections in globular proteins as reflected in deviations of torsion angles from the equilibrium values for the isolated side chains. The distribution of conformations of methionine and lysine residues in a database of high-resolution structures is compared with energies of model compounds calculated with high-level quantum-mechanics. The distribution of the C-C and C-S torsion angles (chi(3)) correlates well with the Boltzmann factor of the torsion energy, exp(-betaE) of the model compounds C(2)H(5)-C(2)H(5) and C(2)H(5)-S-CH(3). An exponential relation was again found between the relative occurrence of g+, g- and t conformations for C(alpha)-C(beta) bonds in long side chains and the energy differences of rotamers of alpha-amino n-butyric acid, when dependence on backbone conformation was taken into account. The distribution of all 27 rotamers of methionine was correlated with the energy differences between the model's rotamers, corrected for clashes with nearby residues, the correlation being good for a set with backbone in the beta-conformation, but less clear for backbone alpha-conformation. In all correlations, the value of the coefficient beta corresponds to a temperature of circa 300 K. These results can be interpreted with a model that considers the structure of a folded protein as resulting from packing imperfectly complementary parts, with a requirement of an overall low energy. Compromises are required to optimize the fit of nonbonded contacts with surrounding groups, and side chains assume conformations away from the energy minimum. An exponential distribution is a most probable distribution, and this can be established easily under conditions other than thermal equilibrium.

Butanes↗

Interpreting the effectiveness of involuntary outpatient commitment: a conceptual model.

Many experimental trials of community mental health interventions fail to develop testable conceptual models of the specific mechanisms and pathways by which relevant outcomes may occur, thus falling short of usefully interpreting what happens inside the experimental "black box." This paper describes a conceptual model of involuntary outpatient commitment (OPC) for persons with severe and persistent mental disorders. The model represents an attempt to "unpack" the effects of OPC by incorporating several interacting variables at various stages. According to this model, court-mandated outpatient treatment may improve long-term outcomes both directly and indirectly in several ways: by stimulating case management efforts, mobilizing supportive resources, improving individual compliance with treatment in the community, reducing clients' psychiatric symptoms and dangerous behavior, improving clients' social functioning, and finally by reducing the chance of illness relapse and rehospitalization. A randomized clinical trial of OPC is underway in North Carolina that will test the direct and indirect effects suggested by this model, using longitudinal data from the multiple perspectives of mental health clients, family members, and case managers.

Ambulatory Care↗

Acute tetrodotoxin-induced neurotoxicity after ingestion of puffer fish.

This study documents the effects of puffer-fish poisoning on peripheral nerve. Excitability measurements investigated membrane properties of sensory and motor axons in four patients. The median nerve was stimulated at the wrist, with compound muscle potentials recorded from abductor pollicis brevis and compound sensory potentials from digit 2. Stimulus-responses, strength-duration time constant (tau(SD)), threshold electrotonus, and current-threshold relations were recorded. The urine of each patient tested positive for tetrodotoxin. Compared with controls, axons were of higher threshold, compound muscle action potentials and compound sensory nerve action potentials were reduced in amplitude, latency was prolonged, and tau(SD) was reduced. In recovery cycles, refractoriness, superexcitability, and late subexcitability were decreased. Threshold electrotonus of motor axons exhibited distinctive abnormalities with less threshold decline than normal on depolarization and greater threshold increase on hyperpolarization (p < 0.0005 for each patient). The changes in excitability were reproduced in a mathematical model by reducing sodium (Na(+)) permeabilities by a factor of two. This study confirms that the neurotoxic effects of puffer-fish poisoning can be explained by tetrodotoxin blockade of Na(+) channels. It demonstrates the ability of noninvasive nerve excitability studies to detect Na(+) channel blockade in vivo and also the utility of mathematical modeling to aid interpretation of altered excitability properties in disease.

Action Potentials↗

Circadian rhythms in Neurospora crassa: interactions between clock mutations.

Mutations at four loci in Neurospora crassa that alter the period of the circadian rhythm have been used to construct a series of double mutant strains in order to detect interactions between these mutations. Strains carrying mutations at three of these loci have altered periods on minimal media: prd-1, several alleles at the olir (oligomycin resistance) locus and four alleles at the frq locus. A mutation at the fourth locus, cel, which results in a defect in fatty acid synthesis, also leads to lengthening of the period when the medium is supplemented with linoleic acid (18:2). The cel mutation was crossed into strains carrying the frq, prd-1 and olir mutations, and the periods of the double mutant strains with and without 18:2 supplementation were determined. In addition, data from the literature for other combinations of loci and/or chemical effects on the period have been reanalyzed.--It was found that both prd-1 and olir are epistatic to the effects of 18:2 on cel; in the series of cel frq double mutant strains, the period-lengthening effect of 18:2 is inversely proportional to the period of the frq parent, indicating an interaction between frq and cel; period effects reported in the literature can be described as changes by a fixed ratio or percentage of the period rather than by a fixed number of hours, and the data, therefore, can support a multiplicative as well as an additive model.--Several biochemical interpretations of these interactions are discussed, based on simple chemical kinetics, enzyme inhibition kinetics and the control of flux through metabolic pathways.

Circadian Rhythm↗

Biological Foundation Models for Complex Disease Research and Clinical Translation.

Complex diseases, including cancer, rare genetic disorders, neurodevelopmental and psychiatric conditions, and neurodegenerative diseases, arise from interactions among genetic variation, gene regulation, and cellular states that are difficult to capture using a single data type or biological scale. Biological foundation models address this challenge by treating nucleotides and genes as tokens and learning representations that can be transferred to downstream biomedical and clinical tasks. In this review, we examine two major model classes, genomic sequence foundation models and cell foundation models, and compare their tokenization strategies, model architectures, pretraining objectives, and adaptation methods. We summarize their emerging applications in regulatory variant interpretation, disease-associated cell-state analysis, drug-response prediction, and therapeutic target discovery across complex diseases. We distinguish applications supported by experimental or retrospective validation from those that remain primarily computational or conceptual. We further discuss key challenges to clinical translation, including multimodal data integration, model interpretability, benchmarking, patient-specific prediction, and privacy protection. We highlight future opportunities to integrate biological foundation models with emerging frameworks of medical digital twins, agentic AI, and federated learning. By linking model design to translational goals, this review provides a practical framework for evaluating biological foundation models and their readiness for complex disease research and clinical use.

biological foundation model↗

A computer-based approach to describe the 13C NMR chemical shifts of alkanes by the generalized spectral moments of iterated line graphs

A recently introduced strategy to quantitative structure-property relationship studies is used to model the sum of 13C NMR chemical shifts of alkanes. This graph theoretical approach is based on the spectral moments of the iterated line graph sequence (ILGS). The statistical quality of the model developed by using the present approach is compared to those obtained by using spectral moments of the bond matrix or the embedding frequencies of alkanes as independent variables. The embedding frequencies were computed on the basis of the spectral moments of the ILGS. The emphasis of this work is on the structural interpretation of the results. Consequently, the contributions of the different structural fragments of alkanes to the 13C NMR chemical shift sum are computed by the three theoretical approaches. The advantages and disadvantages of the use of these approaches are analyzed on the basis of computational expenditure, i.e. computer time and memory, and the statistical quality, complexity, and structural interpretation of the models developed.

Journal Article↗

Implementation of a model for service delivery and organisation in mental healthcare: a qualitative exploration of service provider views.

The purpose of the present study was to investigate factors influencing the implementation of a model for service delivery and organisation in mental healthcare. A qualitative case-study approach was employed involving in-depth interviews with 25 service providers from across mental health and social care in one local authority area in northern England. Purposive sampling achieved a broad coverage across geographical areas, voluntary and statutory services, and primary, secondary and specialist mental healthcare. The findings indicate that implementation was influenced by three interrelated factors: the means by which the model was introduced to the workforce; use of the model itself by service providers; and the broader service context. Thus, negative reactions to the way the model was initially presented strongly influenced service providers' subsequent views of it. Moreover, observations regarding the broader context of mental healthcare revealed a service that was ill-equipped to manage change because of over-stretched resources and that was disinclined to accept imposed change because of poor staff morale. Finally, differential interpretation of the model's tiers by service providers led to defensive practice that manifested itself as over-referral of service users within the system. Changing practice behaviour is a complex process, particularly at a service level that consists of numerous professional groups with differing cultural norms. Successful reorganisation of services is unlikely if those responsible for delivering care are not part of the process of change. Moreover, unsuccessful attempts to change professional practice may exacerbate existing tensions within a workforce, which may be to the detriment of those requiring care. A full diagnostic analysis of the system, including service providers' concerns, should be carried out before introducing change or reconfiguring services.

Attitude of Health Personnel↗

A supersonic molecular beam study of the reaction of tetrakis(dimethylamido)titanium with self-assembled alkyltrichlorosilane monolayers.

The reaction of a transition metal coordination complex, Ti[N(CH(3))(2)](4), with self-assembled monolayers (SAMs) possessing-OH, -NH(2), and -CH(3) terminations has been examined using supersonic molecular beam techniques. The emphasis here is on how the reaction probability varies with incident kinetic energy (E(i)=0.4-2.07 eV) and angle of incidence (theta(i)=0 degrees -60 degrees ). The most reactive surface is the substrate underlying the SAMs-SiO(2) with a high density of -OH(a) (>5 x 10(14) cm(-2)), "chemical oxide." On chemical oxide, the dynamics of adsorption are well described by trapping, precursor-mediated adsorption, and the initial probability of adsorption depends only weakly on E(i) and theta(i). The dependence of the reaction probability on substrate temperature is well described by a model involving an intrinsic precursor state, where the barrier for dissociation is approximately 0.2-0.5 eV below the vacuum level. Reaction with the SAMs is more complicated. On the SAM with the unreactive, -CH(3), termination, reactivity decreases continuously with increasing E(i) while increasing with increasing theta(i). The data are best interpreted by a model where the Ti[N(CH(3))(2)](4) must first be trapped on the surface, followed by diffusion through the SAM and reaction at the SAMSiO(2) interface with residual -OH(a). This process is not activated by E(i) and most likely occurs in defective areas of the SAM. On the SAMs with reactive end groups, the situation is quite different. On both the-OH and -NH(2) SAMs, the reaction with the Ti[N(CH(3))(2)](4) as a function of E(i) passes through a minimum near E(i) approximately 1.0 eV. Two explanations for this intriguing finding are made-one involves the participation of a direct dissociation channel at sufficiently high E(i). A second explanation involves a new mechanism for trapping, which could be termed penetration facilitated trapping, where the Ti[N(CH(3))(2)](4) penetrates the near surface layers, a process that is activated as the molecules in the SAM must be displaced from their equilibrium positions.

Journal Article↗

The nature of memory processes underlying recognition judgments in the process dissociation procedure.

The hypothesis is tested that the memory processes involved in recognition judgments in the process dissociation procedure are the same as those involved in standard source-monitoring tasks. It is shown how source-monitoring response categories can be mapped onto process dissociation response categories. On the basis of this abbreviation, an experiment was conducted in which it was possible to compare, using a multinomial modeling approach, the parameters representing memory processes in the process dissociation procedure with those involved in source monitoring. For the two different encoding conditions realized, the results are compatible with the hypothesis that the same processes are involved in source monitoring and in recognition judgments in the process dissociation procedure. Implications for the interpretation of the model's parameters are discussed.

Adolescent↗

Modelling covariate effects in observer agreement studies: the case of nominal scale agreement.

Correction for chance-expected agreement has become an accepted technique in the analysis of observer agreement data and may be particularly useful when the level of agreement achieved in different populations is compared. However, formal methods for making comparisons of chance-corrected agreement or, more generally, for studying the effects of covariates on chance-corrected agreement have not received much attention. For nominal scale agreement data we show how Tanner and Young's model for observer agreement can be applied to this problem. The models discussed can be fitted using existing software and certain model parameters have interpretations in terms of positive and negative agreement odds ratios. The proposed methodology facilitates investigation of issues such as confounding of covariate effects and interaction between covariates in their effect on chance-corrected agreement. The methods outlined therefore allow observer agreement data to be analyzed in a manner strongly analogous to the logistic modelling of the association between disease and suspected risk factors. The methods are illustrated using data on the comparability of primary and proxy respondent reports of the primary respondents participation in physically vigorous leisure time activity.

Analysis of Variance↗

A review of cost-effectiveness analyses in rheumatology and related disciplines.

A MEDLINE search of the 1996 and 1997 literature yielded two reviews of the methodology of cost-effectiveness analyses (CEAs) in the field of rheumatology and eight original CEAs evaluating slow-acting antirheumatic agents (two studies), total hip arthroplasty for patients with osteoarthritis (one study), educational intervention for patients with fibromyalgia (one study), interventions for patients with low back pain (three studies), and hormone replacement therapy for women with osteoporosis (one study). Most CEAs relied on modelling of data that were assembled from various sources; however, in one CEA a cost-effectiveness comparison was based on data collected prospectively within a randomized clinical trial. Extensive sensitivity analyses were conducted by a majority of the studies. The CEAs of slow-acting antirheumatic agents provided results that were difficult to interpret given extensive modelling and reliance on expert estimates. Only one CEA was supported by an industry grant. Most of the studies were of high quality and met current methodologic requirements, including the use of discounting, sensitivity analysis, and incremental analysis. However, the major shortcoming of these recent studies continues to be the use of estimated costs instead of prospectively measured resource utilization data presented in terms of separate physical units.

Cost-Benefit Analysis↗

Assessment of the validity of a population pharmacokinetic model for epirubicin.

AIMS: The aim of this study was to evaluate a population model for epirubicin clearance using internal and external validation techniques. METHODS: Jackknife samples were used to identify outliers in the population dataset and individuals influencing covariate selection. Sensitivity analyses were performed in which serum aspartate transaminase (AST) values (a covariate in the population model) or epirubicin concentrations were randomly changed by +/-10%. Cross-validation was performed five times, on each occasion using 80% of the data for model development and 20% to assess the performance of the model. External validation was conducted by assessing the ability of the population model to predict concentrations and clearances in a separate group of 79 patients. RESULTS: Structural parameter estimates from all jackknife samples were within 7.5% of the final population estimates and examination of log likelihood values indicated that the selection of AST in the final model was not due to the presence of outliers. Alteration of AST or epirubicin concentrations by +/-10% had a negligible effect on population parameter estimates and their precision. In the cross-validation analysis, the precision of clearance estimates was better in patients with AST concentrations>150 U l-1. In the external validation, epirubicin concentrations were over-predicted by 81.4% using the population model and clearance values were also poorly predicted (imprecision 43%). CONCLUSIONS: The results of internal validation of population pharmacokinetic models should be interpreted with caution, especially when the dataset is relatively small.

Adult↗