Mechanical explanation of nature and its limits in Kant’s Critique of judgment

In this paper I discuss two questions. What does Kant understand by mechanical explanation in the Critique of judgment? And why does he think that mechanical explanation is the only type of the explanation of nature available to us? According to the interpretation proposed, mechanical explanations in the Critique of judgment refer to a particular species of empirical causal laws. Mechanical laws aim to explain nature by reference to the causal interaction between the forces of the parts of matter and the way in which they form into complex material wholes. Just like any other empirical causal law, however, mechanical laws can never be known with full certainty. The conception according to which we can explain all of nature by means of mechanical laws, it turns out, is based on what Kant calls ‘regulative’ or ‘reflective’ considerations about nature. Nothing in Kant’s Critique of judgment suggests that these considerations can ever be justified by reference to how the natural world really is. I suggest that what, upon first consideration, appears to be a thoroughly mechanistic conception of nature in Kant is much more limited than one might have expected.     

Prokaryotic diversity and its limits: microbial community structure in nature and implications for microbial ecology

Recent advances in the estimation of prokaryotic diversity have brought us insight into two questions: what is the extent of prokaryotic diversity, and perhaps more importantly, why bother finding out. In this review, we highlight the insights about the extent of diversity that may be gained by considering patterns that occur, or are likely to occur, in the relative abundance of prokaryotic taxa. We posit that global reservoirs of diversity are an important driving force behind patterns in localised diversity seen in leaves, intestines and wastewater treatment reactors. Thus, where the reservoir community is very large and relatively even, chance alone will prevent physically identical communities from having the same, or sometimes even stable, communities. By contrast, communities that tend to be similar (even when not physically identical) and stable are observed where the source diversity is low. Thus the relationship between structure and function in a community can only be understood, predicted and engineered through an understanding of the source of diversity from which the community is drawn.     

Characterization of the low temperature thermoluminescence band Zv in leaf: an explanation for its variable nature

Out of the six thermoluminescence bands reported for a mature leaf, one band (Zv) appearing at the lowest temperatures is dependent on the temperature of illumination. The characteristics of this band in fresh leaf are compared with those is a leaf heated to 60 degrees C for 5 min. It is concluded here that this band, following illumination at temperatures lower than 173 K, is part of Arnold and Azzi's Z band (Arnold, W. and Azzi, J.R. (1971) Photochem. Photobiol. 14, 233--240). However, it is part of peak I when observed subsequent to illumination beyond 173 K. An explanation for the appearance of this band at different temperatures is proposed.     

Characterization of the low temperature thermoluminescence band Zv in leaf an explanation for its variable nature

Out of the six thermoluminescence bands reported for a mature leaf, one band (Z_v) appearing at the lowest temperatures is dependent on the temperature of illumination. The characteristics of this band in fresh leaf are compared with those in a leaf heated to 60°C for 5 min. It is concluded here that this band, following illumination at temperatures lower than 173 K, is part of Arnold and Azzi's Z band (Arnold, W. and Azzi, J.R. (1971) Photochem. Photobiol. 14, 233–240). However, it is a part of peak I when observed subsequent to illumination beyond 173 K. An explanation for the appearance of this band at different temperatures is proposed.     

The role and limits of a gradient based explanation of morphogenesis: a theoretical consideration

Development of an organism is a multi-dimensional process leading to the generation of complex species-specific structures. This specificity suggests machine-like organisation. The uneven distribution (gradient) of soluble substances (morphogens) and specific receptor-ligand interactions are known to cause differential gene expression. Therefore gradients of morphogens are used as a causal explanation of developmental processes. However each attempt to describe development causally should take into account both the local fine organisation and global robustness of morphogenesis. The classical view of the role of morphogens will be critically considered and possible alternative proposed. The core idea of my proposal is that the main function of morphogenetic substances could be a context dependent modification of cell behaviour. Both history and different features of morphogenetic fields create the framework for the activity of morphogenes.     

Meat made us moral: a hypothesis on the nature and evolution of moral judgment

In the first part of the article, an account of moral judgment in terms of emotional dispositions is given. This account provides an expressivist explanation of three important features of moral demands: inescapability, authority independence and meriting. In the second part of the article, some ideas initially put forward by Christopher Boehm are developed and modified in order to provide a hypothesis about the evolution of the ability to token moral judgments. This hypothesis makes evolutionary sense of inescapability, authority independence and meriting. It does so by referring to the selection pressures generated in the Late Pleistocene by large-game hunting. If the hypothesis is correct, we can say that, in a sense, meat made us moral.     

Neural crest cell plasticity and its limits

The neural crest (NC) yields pluripotent cells endowed with migratory properties. They give rise to neurons, glia, melanocytes and endocrine cells, and to diverse 'mesenchymal' derivatives. Experiments in avian embryos have revealed that the differentiation of the NC 'neural' precursors is strongly influenced by environmental cues. The reversibility of differentiated cells (such as melanocytes or glia) to a pluripotent precursor state can even be induced in vitro by a cytokine, endothelin 3. The fate of 'mesenchymal' NC precursors is strongly restricted by Hox gene expression. In this context, however, facial skeleton morphogenesis is under the control of a multistep crosstalk between the epithelia (endoderm and ectoderm) and NC cells.     

Mechanical study of spinal interbody implants--characteristics and limits of standardized testing]

Spinal interbody fusion has proved to be a useful procedure for the surgical stabilization of spinal segments, for which fusion cases made of metal or reinforced polymers are increasingly being used. For the mechanical testing of spinal interbody implants, a test setup has been developed on the basis of an ASTM proposal. Initially, testing of lumbar fusion cages made of CFRP (carbon fibre reinforced polymer) was carried out. The implants (UNION Cages, Medtronic Sofamor Danek), which are characterised by their radiolucency on radiography, NMR and CT scans, have a cube-shaped body with three table-tracks on the under and upper surfaces. The cages were tested at different loads. Modifications of the proposed standardized method were carried out to enable implementation of implant-oriented testing. The tested cages were shown to have adequate axial compression, shear and torsional strengths with regard to the implant body. The maximum axial compression force tolerated by the table-tracks was less than the maximal potential loading of the lumbar spine, and, with account being taken of implant design, consequences with regard to surgical technique were drawn. As dictated by the geometry of the table-tracks, parallel grooves have to be made intra-operatively in the vertebral end plates. Axial compressive loads then act on the implant body, and the table-tracks are protected from damage. To avoid in vivo failure, the tested cages should be implanted only when this specific surgical technique is employed. Using supplementary anterior or posterior instrumentation, in vivo failure of the table-tracks under physiological spinal loading is not to be expected.     

Mechanical limits of bacterial flagellar motors probed by electrorotation.

We used the technique of electrorotation to apply steadily increasing external torque to tethered cells of the bacterium Escherichia coli while continuously recording the speed of cell rotation. We found that the bacterial flagellar motor generates constant torque when rotating forward at low speeds and constant but considerably higher torque when rotating backward. At intermediate torques, the motor stalls. The torque-speed relationship is the same in both directional modes of switching motors. Motors forced backward usually break, either suddenly and irreversibly or progressively. Motors broken progressively rotate predominantly at integral multiples of a unitary speed during the course of both breaking and subsequent recovery, as expected if progressive breaking affects individual torque-generating units. Torque is reduced by the same factor at all speeds in partially broken motors, implying that the torque-speed relationship is a property of the individual torque-generating units.     

Mechanical limits to maximum weapon size in a giant rhinoceros beetle

The horns of giant rhinoceros beetles are a classic example of the elaborate morphologies that can result from sexual selection. Theory predicts that sexual traits will evolve to be increasingly exaggerated until survival costs balance the reproductive benefits of further trait elaboration. In Trypoxylus dichotomus, long horns confer a competitive advantage to males, yet previous studies have found that they do not incur survival costs. It is therefore unlikely that horn size is limited by the theoretical cost–benefit equilibrium. However, males sometimes fight vigorously enough to break their horns, so mechanical limits may set an upper bound on horn size. Here, I tested this mechanical limit hypothesis by measuring safety factors across the full range of horn sizes. Safety factors were calculated as the ratio between the force required to break a horn and the maximum force exerted on a horn during a typical fight. I found that safety factors decrease with increasing horn length, indicating that the risk of breakage is indeed highest for the longest horns. Structural failure of oversized horns may therefore oppose the continued exaggeration of horn length driven by male–male competition and set a mechanical limit on the maximum size of rhinoceros beetle horns.     

Spasticity; its nature and treatment

There are a number of physiological means of relaxing spasticity, including active resistive exercise, cold hydrotherapy, heat, electrical stimulation of antagonistic muscles, passive stretch in diagonal movement patterns, and the Von Bechterew reflex. Although none of them will cure spasticity, temporary relaxation may permit a patient to achieve better functioning of an affected joint. The choice of procedure will depend on the nature of the lesion and the muscular distribution of the spasticity.     

Mechanical properties and polysaccharide nature of the cell walls of maize root

Changes in mechanical properties and chemical nature of the cell walls of the different zones along elongating maize ( Zea mays L. cv. LG 11) roots were analyzed and the following results were obtained. (1) The apical region 2 to 5 mm from the tip of 15 mm long roots showed rapid elongation whereas the region 8–10 mm from the tip showed very little growth. (2) The minimum stress-relaxation time (To) and the mean stress-relaxation rate (R) of the cell wall were small whereas the maximum stress-relaxation time (Tm) was large in the region where cell elongation was optimum. The To and R increased and the Tm decreased gradually towards the base of the root. (3) The amounts of non-cellulosic polysaccharides of the cell wall were highest in the region 1.5–2.5 mm from the tip, decreasing until 5 mm from the tip, and then increasing towards the base. However, the proportion of this fraction in the total cell wall polysaccharides was highest in the extreme tip (cap and meristem, 0–1 mm) and decreased towards the base. (4) Major neutral sugars constituting the non-cellulosic polysaccharides of the cell wall were xylose, arabinose, galactose and glucose, with minor amounts of rhamnosc. mannose and fucose. The 1–15 mm region was on the whole rich in glucose and xylose and contained arabinose to a lesser extent. However, the chemical nature in the apical region, (0–2 mm, was rather special, being rich in galactose and fucose. (5) The cell wall of maize roots contained, as a whole, only little pectic substances but was high in hemicellulose 1 (rich in xylose, arabinose and glucose) and hemicellulose 2 (rich in glucose and xylose). (6) It appeared that in the elongating region (apical 2 to 5 mm) the cell elongation rate (CET) showed a rather good correlation with the parameters of mechanical properties (To, Tm and R) and with neutral sugar compositions in the non-cellulosic polysaccharides.