Implausible Mechanism Research Articles

What's wrong with osteopathy?

This commentary critically examines the foundational assumptions, practices and claimed distinctiveness upon which osteopathy was built and continues to be structured. Five areas which are considered to be highly problematic for osteopathy, namely its weak theoretical basis, inherent biomedicalism, monointerventionism, default practitioner-centredness and predilection for implausible mechanisms. It is argued that these areas require considerable reflection and action as if not remedied, they constitute a major threat to the development, unity and legitimacy of the osteopathic profession. Ongoing reconceptualisation of underpinning theories, assumptions and associated skills informed by current evidence and knowledge from disciplines outside of the osteopathic domain is necessary for professional maturation. Implications for practice•Osteopathy's weak theoretical basis, biomedicalism, monointerventionism, practitioner-centredness and implausible mechanisms are problematic.•These constitute a major threat to the development, unity and legitimacy of osteopathy.•Ongoing critical reflection, practice reconceptualisation and research are needed for professional maturation.•Osteopaths should draw on theory and evidence from outside the osteopathic domain.

Fold Evolution before LUCA: Common Ancestry of SH3 Domains and OB Domains.

SH3 and OB are the simplest, oldest, and most common protein domains within the translation system. SH3 and OB domains are β-barrels that are structurally similar but are topologically distinct. To transform an OB domain to a SH3 domain, β-strands must be permuted in a multistep and evolutionarily implausible mechanism. Here, we explored relationships between SH3 and OB domains of ribosomal proteins, initiation, and elongation factors using a combined sequence- and structure-based approach. We detect a common core of SH3 and OB domains, as a region of significant structure and sequence similarity. The common core contains four β-strands and a loop, but omits the fifth β-strand, which is variable and is absent from some OB and SH3 domain proteins. The structure of the common core immediately suggests a simple permutation mechanism for interconversion between SH3 and OB domains, which appear to share an ancestor. The OB domain was formed by duplication and adaptation of the SH3 domain core, or vice versa, in a simple and probable transformation. By employing the folding algorithm AlphaFold2, we demonstrated that an ancestral reconstruction of a permuted SH3 sequence folds into an OB structure, and an ancestral reconstruction of a permuted OB sequence folds into a SH3 structure. The tandem SH3 and OB domains in the universal ribosomal protein uL2 share a common ancestor, suggesting that the divergence of these two domains occurred before the last universal common ancestor.

Common Ownership and Executive Incentives: The Implausibility of Compensation As an Anticompetitive Mechanism

Mutual funds, pension funds and other institutional investors are a growing presence in U.S. equity markets, and these investors frequently hold large stakes in shares of competing companies. Because these common owners might prefer to maximize the values of their portfolios of companies, rather than the value of individual companies in isolation, this new reality has lead to a concern that companies in concentrated industries with high degrees of common ownership might compete less vigorously with each other than they otherwise would. But what mechanism would link common ownership with reduced competition? Some commentators argue that one of the most plausible mechanisms is executive pay design. The idea is that executive pay at companies in concentrated industries with high common ownership may be designed to dampen the incentives of the companies’ managers to compete aggressively with peer firms. This essay challenges both the theoretical and empirical bases for this argument and contends that executive pay design is actually an implausible mechanism linking common ownership with reduced competition. For example, I show that, contrary to the claims of some commentators, the use of competition-enhancing executive relative performance evaluation as a compensation tool has increased dramatically in parallel with the increase in common ownership, exactly the opposite of what one would expect if common owners sought to dampen competition through pay design. Despite voicing skepticism regarding a possible association between common ownership and executive pay design, this essay also offers suggestions for improving empirical analyses going forward that should help to resolve the debate. If, however, as this essay argues, executive pay design is an implausible mechanism, this determination tends to undermine the broader claim that common ownership dampens inter-firm competition.

Moral externalization is an implausible mechanism for cooperation, let alone "hypercooperation".

To facilitate cooperation, moral externalization requires truthful and meticulous information about others' moral commitments (Stanford target article, sect. 6). By definition, this information does not exist in the low-information environments where humans display their "hypercooperativeness." Furthermore, collecting that information-if possible-entails costs that other mechanisms for correlated interaction avoid. Hence, moral externalization is an unlikely mechanism for cooperation, let alone "hypercooperation."

Bayesian Learning Without Recall

We analyze a model of learning and belief formation in networks in which agents follow Bayes rule yet they do not recall their history of past observations and cannot reason about how other agents' beliefs are formed. They do so by making rational inferences about their observations which include a sequence of independent and identically distributed private signals as well as the actions of their neighboring agents at each time. Successive applications of Bayes rule to the entire history of past observations lead to forebodingly complex inferences: due to lack of knowledge about the global network structure, and unavailability of private observations, as well as third party interactions preceding every decision. Such difficulties make Bayesian updating of beliefs an implausible mechanism for social learning. To address these complexities, we consider a Bayesian without Recall model of inference. On the one hand, this model provides a tractable framework for analyzing the behavior of rational agents in social networks. On the other hand, this model also provides a behavioral foundation for the variety of non-Bayesian update rules in the literature. We present the implications of various choices for the structure of the action space and utility functions for such agents and investigate the properties of learning, convergence, and consensus in special cases.

Dynamics of Suppression in Macaque Primary Visual Cortex

The response of a neuron in primary visual cortex (V1) to an optimal stimulus in its classical receptive field (CRF) can be reduced by the presence of an orthogonal mask, a phenomenon known as cross-orientation suppression. The presence of a parallel stimulus outside the CRF can have a similar effect, in this case known as surround suppression. We used a novel stimulus to probe the time course of cross-orientation suppression and found that it is very fast, starting even before the response to optimal excitatory stimuli. However, it occurs with some delay after the offset response, considered to be a measure of the earliest excitatory signals that reach the CRF. We also examined the time course of response to a stimulus presented outside the CRF and found that cross-orientation suppression begins substantially earlier than surround suppression measured in the same cells. Together, these findings suggest that cross-orientation suppression is attributable to either direct feedforward signal paths to V1 neurons or a circuit involving fast local interneurons within V1. Feedback from higher cortical areas is implicated in surround suppression, but our results make this an implausible mechanism for cross-orientation suppression. We conclude that suppression from inside and outside the CRF occur through different mechanisms.

The coupling of the electrostatic potential with the transport and adsorption mechanisms in ion‐exchange chromatography systems: Theory and experiments

AbstractThe coupling of the constitutive expression for the electrostatic potential as specified through Poisson's equation together with the constitutive equations for the mechanisms of convection, diffusion, electrophoretic migration, and adsorption provides the necessary set of constitutive expressions to be employed in the material balance equations of ion‐exchange chromatography systems to construct macroscopic continuum models that could be used to design and simulate the dynamic behavior of systems involving a single charged adsorbate or multiple charged adsorbates. A physically relevant and consistent macroscopic continuum model that can predict, as has been observed experimentally by UV confocal microscopy (UVCM), the presence or absence of the concentration overshoot phenomenon, based on the pH and ionic strength of the liquid solution, is discussed and expanded to describe the behavior of IEC systems involving competitive adsorption of two or more charged adsorbates. Furthermore, UVCM and confocal scanning laser microscopy (CSLM) experiments and the macroscopic continuum models that could be used to analyze their data are indicated. Results are also presented that have been obtained from molecular dynamics (MD) modeling and simulation studies (microscopic modeling and analysis) employing realistic atomistic models derived from fundamental physics, and indicate the physical mechanisms that are relevant and actively involved in the transport and adsorption of charged adsorbates in IEC systems, as well as their relative importance. The results obtained from the MD simulations show that when a charged macromolecule is adsorbed it is restrained by a strong dominant Coulombic interaction and is trapped by a hydration layer adjacent to the surface and these lead to zero lateral displacement of the adsorbed macromolecule. This finding indicates that surface diffusion could be a physically implausible mechanism in IEC systems involving charged adsorbate macromolecules. Also, the results obtained from the MD simulation studies show that the transport coefficients that characterize the mass transfer of a charged adsorbate in the liquid solution by diffusion and electrophoretic migration have magnitudes along the lateral direction that are different from those along the direction that is normal to the charged surface.

Transient fixation on a non‐native language associated with anaesthesia

Transient fixation on a non‐native language associated with anaesthesia

Molecular dynamics simulation studies of the transport and adsorption of a charged macromolecule onto a charged adsorbent solid surface immersed in an electrolytic solution.

Molecular dynamics simulations were performed in order to study the transport and adsorption of a charged macromolecule (desmopressin) onto a charged solid surface in an electrolytic solution. The strong Coulombic interaction from the charged solid surface represents the major force for accelerating, orienting, entrapping in the electrical double layer, and adsorbing the macromolecule onto the charged solid surface. The macromolecule is flattened as it approaches the charged surface, giving rise to a stronger surface exclusion effect that shields surface sites. When adsorbed, the macromolecule is restrained by a surface interaction more than one hundred times stronger than the thermal energy, of which 99.8% results from the strong dominant Coulombic interaction, and trapped by a hydration layer adjacent to the surface. This leads to zero lateral displacement of the adsorbed macromolecule and indicates that surface diffusion is a physically implausible mechanism in similar systems. Explicit solvent is required for realistic representation of the macromolecular structure and the surface interaction energy. The adsorbed macromolecule also decreased the electrostatic potential gradient perpendicular to the charged solid surface and introduced additional electrostatic potential gradients laterally. The results obtained from the molecular dynamics simulations confirm the importance of electrophoretic migration and support the physical mechanisms used in a macroscopic continuum model that predicts an overshoot in the concentration of a charged macromolecule in the adsorbed phase under certain conditions of pH and ionic strength.

Mechanics of layer-bound polygonal faulting in fine-grained sediments

Abstract: Extensive polygonal networks of normal faults have reportedly been identified within layer-bound sequences in about 28 sedimentary basins worldwide. The gentle regional dips, passive tectonic settings and geometry of the fault networks have led to the conclusion that faulting must have resulted from gravity-driven mechanical compaction. The faulted sequences comprise very fine-grained sediments, with lithofacies that range from smectitic claystones to almost pure chalks. In most, if not all, cases it is clear that volumetric contraction has occurred with horizontal contraction of the sediments complementing the heave of the faults. One explanation which has previously been offered is that the fine-grained sediments have shrunk due to syneresis, a process that involves spontaneous contraction of the solid network with expulsion of the pore fluid. However, syneresis is an implausible mechanism because it does not explain the observed lithological variation in the sediments concerned, why the initiation of faulting occurs in the depth range 100–1000 m, and why faulting continues for millions of years. A much simpler explanation is that shear failure inevitably results from one-dimensional compaction if the coefficient of friction is sufficiently low; and there is some evidence from laboratory measurements that the coefficient of friction is likely to be exceptionally low in these fine-grained sediments. Qualitatively, low coefficients of friction also explain why these compaction faults preferentially dip towards the basin margin where the regional dip of the bedding is greater than 1˚. Furthermore, they help to explain the origin of a polygonal fault system in the Eromanga Basin, South Australia, where the situation is complicated by the presence of a low velocity, ductile layer at the base of the faulted sequence.

Nitric oxide: physiology and pharmacology.

Nitric oxide: physiology and pharmacology.

Nitric Oxide

Nitric Oxide

A model of single-stage concomitant potassium—argon exchange in acidic lavas from the erlend volcanic complex, North of Shetland Islands

The linear disposition of data in 40Ar-40K correlation diagrams can be accounted for using a single-stage concomitant K-Ar exchange model. Such a model avoids the implausible mechanism of “equal Ar loss” in accounting for a negative intercept on the 40Ar axis, and demonstrates that no information of geological significance relates directly to the gradient of the correlation line. Bounds to the “primary formation age” and “age of exchange event” may be established using extreme values of the observed K content and using estimates of its value based on petrographic type. Application of the model method to discordant age data from an upper Cretaceous/lower Tertiary rhyolite—dacite—pitchstone sequence from well 2094-1A drilled on the Erlend Complex (61° 55′N, 00° 18′W) on the SE margin of Faeroe-Shetland Channel yields a Palaeocene formation age perturbed in the Neogene by an event which may relate to seawater penetration following regional subsidence. This apparent Palaeocene K-Ar formation age may be real, or may be a consequence of thermal overprinting of an actual Cretaceous age by the overlying lower Tertiary basalts.

“Hopeful monsters,” transposons, and Metazoan radiation

The appearance of many novel morphologies, frequently expressed taxonomically as new phyla, classes, or orders, occurs with such rapidity in evolutionary time that microevolutionary substitutions involving structural genes seem an implausible mechanism. It has been suggested that such novelties are produced by changes in developmental and regulatory structures and patterns rather than by an accumulation of single structural gene changes. The horizontal transmission of genetic material via RNA-based viruses between members of a population may rapidly create intrafertile sub-populations that differ markedly from their parents and form the basis of new morphological types, avoiding the usual fitness problems associated with "hopeful monsters."

Mixing and unmixing of magmas

Linear compositional variations of calc-alkaline rocks are difficult to explain in terms of mixing of two genetically unrelated magmas. At least two processes must be involved, a deep-seated one responsible for the long-term variations between suites of rocks erupted in successive episodes and a shallow-level one by which magma columns become vertically zoned during periods of repose between eruptions. The first process appears to involve resorption of differing proportions of mafic residue in a rising batch of magma. The second results from fractionation and collection of a buoyant liquid under the roof of a high-level reservoir. The effect of cooling and crystallization of a calc-alkaline intrusion is to produce a compositional change and decrease of density in the fractionated liquid that has a greater effect on the boundary layer than thermal contraction. The same effect may result from melting of felsic wall rocks or absorption of water. Many of the features that are commonly observed in calc-alkaline rocks can be explained in terms of these two processes without appealing to physically implausible mechanisms involving mixing of liquids of differing densities.

Speculations on the theory of adhesive wear

A new sliding model applicable to adhesive wear is offered which includes the influence of asperity interaction distance. This model reduces to that of Archard in the limit as the asperity interaction distance reduces to the length of the junction. The new model allows wear to be related to three independent quantities: number of asperity interactions, total real area of interaction, and the volume of slid interaction. On physical grounds, the first of these is shown to be an implausible mechanism, and the remaining two are shown to be plausible. Potential explanations are offered for the influence of asperity interaction distance on the probability of wear particle formation. A consideration of the plastic real area of contact, instead of the total real area of contact, is suggested as a means to increase the Archard wear particle formation probabilities by two orders of magnitude. The new sliding model may have implications on a number of subjects in addition to wear, including friction, and surface temperature analysis.