A vast network of cellular circadian clocks regulates 24‐hour rhythms of behavior and physiology in mammals. Complex environments are characterized by multiple, and often conflicting time signals demanding flexible mechanisms of adaptation of endogenous rhythms to external time. Traditionally this process of circadian entrainment has been conceptualized in a hierarchical scheme with a light‐reset master pacemaker residing in the hypothalamus that subsequently aligns subordinate peripheral clocks with each other and with external time. Here we review new experiments (...) using conditional mouse genetics suggesting that resetting of the circadian system occurs in a more “federated” and tissue‐specific fashion, which allows for increased noise resistance and plasticity of circadian timekeeping under natural conditions. (shrink)

In mammals, a network of cellular circadian clocks organizes physiology and behavior along the 24‐h day cycle. The traditional hierarchical model of circadian clock organization with a central pacemaker and peripheral slave oscillators has recently been challenged by studies combining tissue‐specific mouse mutants with transcriptome analyses. First, a surprisingly small number of tissue rhythms are lost when only local clocks are ablated and, second, transcriptional circadian rhythms appear to be regulated by a complex mix of local and (...) systemic factors. As reviewed here, these findings suggest a more integrated model of clock network interaction with the central pacemaker as the main source of behavioral and systemic–physiological rhythms and peripheral clocks controlling some local rhythms while at the same time acting as gatekeepers that temporally adjust cellular responses to external stimuli. (shrink)

MPZL3 is a nuclear‐encoded, mitochondrially localized, immunoglobulin‐like V‐type protein that functions as a key regulator of epithelial cell differentiation, lipid metabolism, ROS production, glycemic control, and energy expenditure. Recently, MPZL3 has surfaced as an important modulator of sebaceous gland function and of hair follicle cycling, an organ transformation process that is also governed by peripheral clock gene activity and PPARγ. Given the phenotype similarities and differences between Mpzl3 and Pparγ knockout mice, we propose that MPZL3 serves as a signaling (...) hub that is regulated by core clock gene products and/or PPARγ to translate signals from these nuclear transcription factors to the mitochondria to modulate circadian and metabolic regulation. Conservation between murine and human MPZL3 suggests that human MPZL3 may have similarly complex functions in health and disease. We summarize current knowledge and discuss future directions to elucidate the full spectrum of MPZL3 functions in mammalian physiology. (shrink)

Acidity, generated in hypoxia or hypermetabolic states, perturbs homeostasis and is a feature of solid tumors. That acid peripherally disperses lysosomes is a three‐decade‐old observation, yet one little understood or appreciated. However, recent work has recognized the inhibitory impact this spatial redistribution has on mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of metabolism. This finding argues for a paradigm shift in localization of mTORC1 activator Ras homolog enriched in brain (RHEB), a conclusion several others have now independently (...) reached. Thus, mTORC1, known to sense amino acids, mitogens, and energy to restrict biosynthesis to times of adequate resources, also senses pH and, via dampened mTOR‐governed synthesis of clock proteins, regulates the circadian clock to achieve concerted responses to metabolic stress. While this may allow cancer to endure metabolic deprivation, immune cell mTOR signaling likewise exhibits pH sensitivity, suggesting that suppression of antitumor immune function by solid tumor acidity may additionally fuel cancers, an obstacle potentially reversible through therapeutic pH manipulation. (shrink)

It has long been suspected that attentional processes differ between olfaction and the other senses. Here, we test whether voluntary dishabituation, seen, for example, when we re-attend to the ticking of a clock, can occur in olfaction. Participants were seated in an odorized room, where at various intervals they had to evaluate what they could smell. An experimental group had one nostril open and the other closed, except during the evaluations, so that the closed side was subject to centrally driven (...) habituation, but not peripheral adaptation. A control group had both nostrils closed except during evaluations. Following exposure, the experimental group could not report the room's odor in either the centrally habituated nostril or the nostril that remained open, while the control group could. This effect could result from a number of causes, including olfaction's unique neuroanatomy, functional constraints imposed by detecting volatile chemicals, and as a consequence of limited cortical resources, with implications for the functional value of consciousness. (shrink)

Previous research has reported that ethical values of business students are lower than those of their peers in other majors. The purpose of this study was to investigate whether a self-selection bias with respect to ethical values exists among students enrolled as business majors when compared with students planning to enter the engineering profession. Engineering students are exposed to a similar technical orientation in academic curricula and also supply the market for managers.A survey instrument was administered to 195 students enrolled (...) in undergraduate business and engineering programs and a graduate business program. The research instrument measured how business and engineering students perceive their own ethical beliefs and actions and how they perceived the ethical beliefs and actions of their peers. (shrink)

O artigo traz resultados de uma investigação de mestrado que teve por objetivo pesquisar as concepções de um grupo de professores a respeito das funções que os mesmos exercem frente à sociedade contemporânea. Partiu-se da premissa de que suas concepções guardam relação com suas práticas educativas e pedagógicas. Trata-se de uma pesquisa desenvolvida na perspectiva qualitativa, com cinquenta e um professores que atuam em seis escolas estaduais da cidade de Ponta Grossa-PR. Elegeu-se como aporte teórico autores que tratam da formação (...) de professores e da profissão docente, como Freire, Imbernón, Ens e Behrens, Tozetto, Sacristán e Tedesco. Os dados foram coletados por meio de questionários, categorizados e analisados seguindo os pressupostos na Análise de Conteúdo. Três categorias foram configuradas a partir de significantes presentes nas respostas dos professores participantes: Categoria I – Professor como um sujeito transformador: educação em uma forma ampla, Categoria II – Professor como profissional do conhecimento, e Categoria III – Professor enquanto sujeito que desempenha vários papéis sociais. Essas categorias nos possibilitaram inferir que as concepções dos professores em relação ao seu papel na sociedade contemporânea vão além da função social da escola, pois centram-se primeiramente na figura de um profissional transformador do mundo; seguida da noção de profissional do conhecimento e, por fim, da ideia de um profissional que desempenha vários papéis sociais. A pesquisa também apontou uma necessária redefinição da profissão docente para que os professores assumam novas competências profissionais na contemporaneidade. Palavras-chave: Profissão docente. Função dos professores. Sociedade contemporânea. Concepções. (shrink)

Daylight is the primary cue used by circadian clocks to entrain to the day/night cycle so as to synchronize physiological processes with periodic environmental changes induced by Earth rotation.However, the temporal daylight pattern is not the same every day due to erratic weather fluctuations or regular seasonal changes. Then, how do circadian clocks operate properly in varying weather and seasons? In this paper, we discuss the strategy unveiled by recent studies of the circadian clock of Ostreococcus tauri, the (...) smallest free‐living eukaryotic organism. It combines mechanisms controlling light inputs and clock sensitivity, shaping both the dynamics of the core circadian oscillator and its forcing by light so as to ensure stable and precise synchronization in all weather and seasons.Editor's suggested further reading in BioEssays: Another place, another timer: Marine species and the rhythms of life Abstract. (shrink)

Philosophers of mind, both in the conceptual analysis tradition and in the empirical informed school, have been implicitly neglecting the potential conceptual role of the Peripheral Nervous System (PNS) in understanding sensory and perceptual states. Instead, the philosophical as well as the neuroscientific literature has been assuming that it is the Central Nervous System (CNS) alone, and more exactly the brain, that should prima facie be taken as conceptually and empirically crucial for a philosophical analysis of such states This (...) is the first monograph that focuses on the PNS and its constitutive role in sensory states, including pain, mechanoception, proprioception, tactile perception, and so forth. -/- The author argues that the brain-centeredness of current philosophy of mind is a prejudice, and proposes a series of original ways in which classic puzzles in the philosophy of mind can be solved once the hypothesis that PNS is a constitutive element of mental states is taken seriously. The author calls this “the Peripheral Mind Hypothesis”, and employs it in a vast range of issues, such as functionalism, physicalism, mental content, embodiment, as well as some issues in neuroethics. -/- Making equal use of conceptual analysis, empirical data from neuroscience, first-person phenomenological data, and philosophical speculation, this work offers a fresh look at, and novel solutions to many philosophical problems. (shrink)

It is often said that some kind of peripheral (or inattentional) conscious awareness accompanies our focal (attentional) consciousness. I agree that this is often the case, but clarity is needed on several fronts. In this paper, I lay out four distinct theses on peripheral awareness and show that three of them are true. However, I then argue that a fourth thesis, commonly associated with the so-called "self-representational approach to consciousness," is false. The claim here is that we have (...) outer focal consciousness accompanied often (or even always) by inner peripheral (self-)awareness. My criticisms stem from both methodological and phenomenological considerations. In doing so, I offer a diagnosis as to why the fourth thesis has seemed true to so many and also show how the so-called "transparency of experience," frequently invoked by representationalists, is importantly relevant to my diagnosis. Finally, I respond to several objections and to further attempts to show that thesis four is true. What emerges is that if one wishes to hold that some form of self-awareness accompanies all outer-directed conscious states, one is better off holding that such self-awareness is itself unconscious, as is held for example by standard higher-order theories of consciousness. (shrink)

The clock hypothesis of relativity theory equates the proper time experienced by a point particle along a timelike curve with the length of that curve as determined by the metric. Is it possible to prove that particular types of clocks satisfy the clock hypothesis, thus genuinely measure proper time, at least approximately? Because most real clocks would be enormously complicated to study in this connection, focusing attention on an idealized light clock is attractive. The present paper extends and (...) generalized partial results along these lines with a theorem showing that, for any timelike curve in any spacetime, there is a light clock that measures the curve’s length as accurately and regularly as one wishes. (shrink)

Cellular circadian clocks represent ancient anticipatory systems which co‐evolved with the first cells to safeguard their survival. Cyanobacteria represent one of the most ancient cells, having essentially invented photosynthesis together with redox‐based cellular circadian clocks some 2.7 billion years ago. Bioelectricity phenomena, based on redox homeostasis associated electron transfers in membranes and within protein complexes inserted in excitable membranes, play important roles, not only in the cellular circadian clocks and in anesthetics‐sensitive cellular sentience (awareness of environment), but (...) also in the coupling of single cells into tissues and organs of unitary multicellular organisms. This integration of cellular circadian clocks with cellular basis of sentience is an essential feature of the cognitive CBC‐Clock basis of cellular life. (shrink)

Circalunar clocks, which allow organisms to time reproduction to lunar phase, have been experimentally proven but are still not understood at the molecular level. Currently, a new generation of researchers with new tools is setting out to fill this gap. Our essay provides an overview of classic experiments on circalunar clocks. From the unpublished work of the late D. Neumann we also present a novel phase response curve for a circalunar clock. These experiments highlight avenues for molecular work (...) and call for rigor in setting up and analyzing the logistically complex experiments on circalunar clocks. Re‐evaluating classic experiments, we propose that (1) circalunar clocks in different organisms will have divergent mechanisms and physiological bases, (2) they may have properties very different from the well‐studied circadian clocks and (3) they may have close mechanistic and molecular relations to seasonal rhythms and diapause. (shrink)

The present study employed the gaze-contingent window paradigm to investigate parafoveal and peripheral cueing and masking effects on saccadic selectivity in a triple-conjunction visual search task. In the cueing conditions, the information shown outside the gaze-contingent window was restricted to the feature or feature pair shared between the target and a particular distractor type. In the masking conditions, no stimulus features were shown outside the window. Significant cueing and masking effects on saccadic selectivity were observed for saccades directed at (...) items within the window, where all features were visible across experimental conditions. Cueing a particular feature or feature pair biased saccadic selectivity towards this feature or feature pair, while masking generally reduced saccadic selectivity. These findings support the concept of visual guidance being a preattentive process that operates in parallel across the display. © 2001 Published by Elsevier Science Ltd. (shrink)

Sound propagation within certain non-relativistic condensed matter models obeys a relativistic wave equation despite such systems admitting entirely non-relativistic descriptions. A natural question that arises upon consideration of this is, “do devices exist that will experience the relativity in these systems?” We describe a thought experiment in which ‘acoustic observers’ possess devices called sound clocks that can be connected to form chains. Careful investigation shows that appropriately constructed chains of stationary and moving sound clocks are perceived by observers (...) on the other chain as undergoing the relativistic phenomena of length contraction and time dilation by the Lorentz factor, \, with \ the speed of sound. Sound clocks within moving chains actually tick less frequently than stationary ones and must be separated by a shorter distance than when stationary to satisfy simultaneity conditions. Stationary sound clocks appear to be length contracted and time dilated to moving observers due to their misunderstanding of their own state of motion with respect to the laboratory. Observers restricted to using sound clocks describe a universe kinematically consistent with the theory of special relativity, despite the preferred frame of their universe in the laboratory. Such devices show promise in further probing analogue relativity models, for example in investigating phenomena that require careful consideration of the proper time elapsed for observers. (shrink)

This paper aims at tracking down, by looking at late medieval and early modern discussions over the ontological status of artifacts, the main steps of the process through which nature became theorized on a mechanistic model in the early 17th century. The adopted methodology consists in examining how inventions such as mechanical clocks and automata forced philosophers to modify traditional criteria based on an intrinsic principle of motion and rest for defining natural beings. The paper studies different strategies designed (...) in the transitional period 1300–1600 for making these inventions compatible with classical definitions of nature and artifacts. In the first part of the paper, it is shown that, even if virtually all medieval philosophers acknowledged an ontological distinction between artifacts and natural beings, these different strategies demonstrate a growing concern about the consistency of the art/nature distinction. The next part of the paper studies how mechanical clocks, even before the Scientific Revolution, served as theoretical models for applying mechanistic views to different objects (be they cosmological, physical or biological). The epistemological function of clocks appears to stem from different factors (like the specific manufacturing of late medieval clocks as well as the evolution of 16th-century mechanics) that are listed in this second part of the paper. These factors, combined with the definitional issues raised by automata, explain that clocks became the symbol of a new approach to natural philosophy, characterized by the collapse of the art/nature distinction and the “mechanization of nature”. (shrink)

Scientists, both modern and contemporary, commonly try to discern patterns in nature. They also frequently use arguments by analogy to construct an understanding of the natural mechanisms responsible for producing such patterns. For Robert Boyle, the famous clock at Strasbourg provided a perfect paradigm for understanding the connection between these two scientific activities. Unfortunately, it also posed a serious threat to his realistic pretensions. All sorts of internal mechanisms could produce precisely the same movements across the face of a clock. (...) Given God's immense creative capacities, Boyle realized that standard epistemological constraints could never ensure, not even to the least degree of probability, that scientific theories about the unobservable mechanisms of nature were descriptively accurate. Like most moderns, he fortified his epistemology theologically in order to retain his realistic stance. John Locke, however, took counsel from Ecclesiastes to repudiate Boyle's realism, while Samuel Clarke mobilized biblical images to dismiss the clockwork paradigm altogether.A contemporary review of this modern controversy reveals that there is still much to learn from the clock at Strasbourg. Among other things, the realism/antirealism issue is of central importance to understanding today's science, Nancey Murphy's protests notwithstanding. Moreover, the kind of realistic stance that is essential, not only to the truth but to the very intelligibility of certain types of scientific explanation, demands more than the critical realism of Ian Barbour. To be taken seriously, the models used in such contexts must be taken literally. (shrink)

Across a wide range of cultural forms, including philosophy, cultural theory, literature and art, the figure of the clock has drawn suspicion, censure and outright hostility. In contrast, even while maps have been shown to be complicit with forms of domination, they are also widely recognised as tools that can be critically reworked in the service of more liberatory ends. This paper seeks to counteract the tendency to see clocks in this way, arguing that they have many more interesting (...) possibilities than they are usually given credit for. An analysis of approaches to clocks in continental philosophy critiques the way they have too often been dismissed as unworthy of further analysis, and argues that this dismissal is based upon an inadequate understanding of how clocks operate. Seeking to move towards more critical and curious approaches, the paper draws inspiration from critical cartography in order to call for the development of a ‘critical horology’ which would emphasise both the fundamentally political nature of clocks, and the potential for designing them otherwise. A discussion of temporal design provides a range of examples of how clocks might open up new horizons within the politics of time. (shrink)

This paper (i) gives necessary and sufficient conditions that clocks in an inertial lattice can be synchronized, (ii) shows that these conditions do not imply a universal light speed, and (iii) shows that the terrestrial redshift experiment provides evidence that clocks in a small inertial lattice in a gravitational field can be synchronized.

Recent evidence indicates that inhibition of protein translation may be a common pathogenic mechanism for peripheral neuropathy associated with mutant tRNA synthetases (aaRSs). aaRSs are enzymes that ligate amino acids to their cognate tRNA, thus catalyzing the first step of translation. Dominant mutations in five distinct aaRSs cause Charcot‐Marie‐Tooth (CMT) peripheral neuropathy, characterized by length‐dependent degeneration of peripheral motor and sensory axons. Surprisingly, loss of aminoacylation activity is not required for mutant aaRSs to cause CMT. Rather, at (...) least for some mutations, a toxic‐gain‐of‐function mechanism underlies CMT‐aaRS. Interestingly, several mutations in two distinct aaRSs were recently shown to inhibit global protein translation in Drosophila models of CMT‐aaRS, by a mechanism independent of aminoacylation, suggesting inhibition of translation as a common pathogenic mechanism. Future research aimed at elucidating the molecular mechanisms underlying the translation defect induced by CMT‐mutant aaRSs should provide novel insight into the molecular pathogenesis of these incurable diseases. (shrink)

Recent work in the physics literature demonstrates that, in particular classes of rotating spacetimes, physical light rays in general do not traverse null geodesics. Having presented this result, we discuss its philosophical significance, both for the clock hypothesis (and, in particular, a recent purported proof thereof for light clocks), and for the operational meaning of the metric field. 1. Introduction2. Fletcher's Theorem2.1. Maudlin on the clock hypothesis in special relativity2.2. Fletcher’s result in special relativity2.3. Fletcher’s theorem in general relativity3. (...) Electromagnetism and the Geometrical-Optical Limit 3.1. Maxwell’s equations in curved spacetime3.2. The geometrical-optical limit3.3. Rotating spacetimes3.4. Aren’t Gödel spacetimes unphysical?4. The Clock Hypothesis and Chronogeometry 4.1. Natural and mathematical observations4.2. Clock registry discord4.3. Chronogeometry5. Conclusion. (shrink)

1. Introduction. The germ of the clock paradox was contained in Einstein's fundamental paper on the special theory of relativity, where he declares that the retardation of a moving clock “still holds good if the clock moves from A to B in any polygonal line, and also when the points A and B coincide.” This remark soon gave rise to a criticism which was to play a prominent role in the discussions of the consistency of the theory of relativity. It (...) was charged that this theory allows the paradoxical conclusion that at the instant of the return of a moving clock U1 to its point of departure A, the time shown by Ul is both earlier and later than the corresponding reading of a clock U2 which has remained stationary at A during U1's journey. Critics based this contention on the following assumptions, for which they claimed the sanction of relativity: The relative motion of U1 and U2 is such that the kinematic process seen by an observer on one of these clocks is of the same character as that seen by an observer on the other, and this symmetry allows each of these two clocks to be used as a reference frame from which to describe the motion of the other, and there is reciprocity between these two reference frames such that in each of them, the moving clock must be slow upon returning to the stationary one. (shrink)

It is the prevailing paradigm in contemporary physics to model the dynamical evolution of physical systems in terms of a real parameter conventionally denoted as 't' ('little tee'). We typically call such dynamical models laws of nature' and t we call 'physical time'. It is common in the philosophy of time to regard t as time itself, and to take the global structure of general relativity as the ultimate guide to physical time, and so consequently the true nature of time. (...) In this paper we defend the idea that physical time, t, is rather better defined as an operational modelling parameter: we measure relations between changing physical quantities using bespoke physical systems---i.e. clocks---that coordinate local coincidences. We argue that the sorts of physical systems that make good clocks---what we call precision clocks---are those that exhibit self-sustained oscillations known as limit cycles, which are ubiquitous in open, driven, stable, dissipative systems. We develop the physical and philosophical ramifications of this conception of physical time, particularly the notion that physical time does not track something 'out there' in the world. As a result, we speculate that physical time is perhaps not as different from manifest time as many philosophers of time (and apparently general relativity) seem to suggest. (shrink)

Somites are transient structures which represent the most overt segmental feature of the vertebrate embryo. The strict temporal regulation of somitogenesis is of critical developmental importance since many segmental structures adopt a periodicity based on that of the somites. Until recently, the mechanisms underlying the periodicity of somitogenesis were largely unknown. Based on the oscillations of c-hairy1 and lunatic fringe RNA, we now have evidence for an intrinsic segmentation clock in presomitic cells. Translation of this temporal periodicity into a spatial (...) periodicity, through somite formation, requires Notch signaling. While the Hox genes are certainly involved, it remains unknown how the metameric vertebrate axis becomes regionalized along the antero–posterior (AP) dimension into the occipital, cervical, thoracic, lumbar, and sacral domains. We discuss the implications of cell division as a clock mechanism underlying the regionalization of somites and their derivatives along the AP axis. Possible links between the segmentation clock and axial regionalization are also discussed. (shrink)

When addressing the notion of proper time in the theory of relativity, it is usually taken for granted that the time read by an accelerated clock is given by the Minkowski proper time. However, there are authors like Harvey Brown that consider necessary an extra assumption to arrive at this result, the so-called clock hypothesis. In opposition to Brown, Richard TW Arthur takes the clock hypothesis to be already implicit in the theory. In this paper I will present a view (...) different from these authors by taking into account Einstein’s notion of natural clock and showing its relevance to the debate. (shrink)

A clock can do two things: it can give the time, and it can measure time. Perhaps the first function is the more humanly important. But one might say that a clock can only give the time by measuring time; at some point it is ‘fed’ the time, or the date, and if it subsequently keeps good time—measures time accurately—one can use it to read off later times or dates.

Objective: Clock variance is an important statistic in many clinical and developmental studies. Existing methods require a large number of trials for accurate clock variability assessment, which is problematic in studies using clinical or either young or aged participants. Furthermore, these existing methods often implicitly convolute clock and memory processes, making it difficult to disentangle whether the clock or memory system are driving the observed deviations. Here we assessed whether twenty repeated productions of a well-engrained interval (1 second), a task (...) that does not incorporate memory updating nor the processing of feedback, could provide an accurate assessment of clock variability. Method: Sixty-eight undergraduate students completed two tasks: a 1-second production task in which they were asked to produce a 1-second duration by ending a tone by a keypress, and a multi-duration reproduction task. Durations presented in the reproduction task were tones lasting 1.17, 1.4 and 1.68 seconds. No feedback was presented in either task, and the order of presentation was counterbalanced between participants. Results: The observed central tendency in the reproduction task was better explained by models including the measures of clock variability derived from the 1-second production task than by models without it. Three clock variability measures were calculated for each participant (standard deviation, root mean squared residuals (RMSR) from an estimated linear slope, and RMSR scaled by mean production duration). The model including the scaled RMSR was prefered over the alternative models, and no notable effects of the order of presentation were observed. These results suggest that (1) measures of variability should account for drift, (2) the presentation of another timing task before a 1-second production task did not influence the assessment of the clock variability, and (3) the observed variability adheres to the scalar property and predicts temporal performance, and is thus a usable index of clock variability. Conclusion: This study shows that just 20 repeated productions of 1 second provide a reliable index of clock variability. As administering this task is fast and easy, it could prove to be useful in a large variety of developmental and clinical populations. (shrink)

Einstein’s equivalence principle has a number of problems, and it is often applied incorrectly. Clocks on the earth do not seem to be affected by the sun’s gravitational potential. The most commonly accepted reason given is a faulty application of the equivalence principle. While no valid reason is available within either the special or general theories of relativity, ether theories can provide a valid explanation. A clock bias of the correct magnitude and position dependence can convert the Selleri transformation (...) of ether theories into an apparent Lorentz transformation, which gives rise to an apparent equivalence of inertial frames. The results indicate that the special theory is invalid and that only an apparent relativity exists. (shrink)

Adrian Heathcote and I agree that a stopped clock does not show—as the adage has it—the right time twice a day, but he thinks, as I do not, that it does show what time it stopped. To think that it does is to treat the position of its hands as evidence of its stopping at the time it did. Add to the justified-true-belief analysis of knowledge the requirement that the evidence on the basis of which the believer is justified be (...) evidence of what is believed in this sense, and you have the long-sought fourth condition to block Gettier cases. I argue that requiring that one’s evidence be evidence in this sense is incompatible with the fallibilism on which Gettier cases are predicated. (shrink)

On receiver-based teleosemantic theories of representation, the chemical states of the circadian clocks in animal, plant and cyanobacterial cells constitute signals of future states of affairs, often the rising and setting of the sun. This signalling is much more rigid than sophisticated representational systems like human language, but it is not simple on all dimensions. In most organisms the clock regulates many different circadian rhythms. The process of entrainment ensures that the mapping between chemical states of the clock and (...) the daily light-dark cycle is adjusted to deal with seasonal changes. In regulating anticipatory behaviour, the states of the clock look forward both to the time the behaviour is supposed to happen and the later time when the anticipated circumstances are supposed to arise. The case of the circadian clock shows that purely indicative signals can arise in very basic biological systems and brings into sharp relief the trade-offs involved in characterizing representational systems. On receiver-based teleosemantic theories, future-directed signals are not restricted to complex multicellular organisms but are ubiquitous in the biological world. (shrink)

In the eighteenth century, the sciences and their applications adopted a new attitude based on quantification and, increasingly, on a notion of precision. Within this process, instruments played a significant role. However, while new devices such as the micrometer, telescope, and pendulum clock embodied a formerly unknown potential of precision, this could only be realized by defining a set of practices regulating their application and control. The paper picks up the case of pendulum clocks used in eighteenth-century observatories in (...) order to show the process of learning in the course of which the pendulum clock first became a precision instrument. By examining the results of an especially developed statistical analysis, conducted to compare the performance of eighteenth-century clocks, it highlights the diversity of conditions, attitudes, and manners of handling that are characteristic for the epoch. In this way, it underlines the necessity of standardization of timekeeping practices rather than exclusively focusing on the technological development of clocks. Ultimately, the paper discusses the role of makers and users in order to show the evolution of a “precision instrument.”. (shrink)

There are a number of problematic features within the current treatment of time in physical theories, including the “timelessness” of the Universe as encapsulated by the Wheeler–DeWitt equation. This paper considers one particular investigation into resolving this issue; a conditional probability interpretation that was first proposed by Page and Wooters. Those authors addressed the apparent timelessness by subdividing a faux Universe into two entangled parts, “the clock” and “the remainder of the Universe”, and then synchronizing the effective dynamics of the (...) two subsystems by way of conditional probabilities. The current treatment focuses on the possibility of using a realistic clock system; namely, a coherent-state description of a damped harmonic oscillator. This clock proves to be consistent with the conditional probability interpretation; in particular, a standard evolution operator is identified with the position of the clock playing the role of time for the rest of the Universe. Restrictions on the damping factor are determined and, perhaps contrary to expectations, the optimal choice of clock is not necessarily one of minimal damping. (shrink)

Period homeostasis is the defining characteristic of a biological clock. Strict period homeostasis is found for the ultradian clocks of eukaryotic microbes. In addition to being temperature-compensated, the period of these rhythms is unaffected by differences in nutrient composition or changes in other environmental variables. The best-studied examples of ultradian clocks are those of the ciliates Paramecium tetraurelia and Tetrahymena sp. and of the fission yeast, Schizosaccharomyces pombe. In these single cell eukaryotes, up to seven different parameters display (...) ultradian rhythmicity with the same, species- and strain-specific period. In fission yeast, the molecular genetic analysis of ultradian clock mechanisms has begun with the systematic analysis of mutants in identified candidate genes. More than 40 “clock mutants” have already been identified, most of them affected in components of major regulatory and signalling pathways. These results indicate a high degree of complexity for a eukaryotic clock mechanism. BioEssays 22:16–22, 2000. ©2000 John Wiley & Sons, Inc. (shrink)

A passenger boards a fast train. It takes her some distance, makes a u-turn, and returns to the starting platform. She reports that according to her clock, the trip took n seconds. An observer on the platform, using his own clock, gets a different reading. He records a longer time interval m. These claims are compatible with the clocks being in perfect order. Modern Physics tells us that time is a relativistic notion. The duration of the trip, understood as (...) the temporal distance between the departure and the return event, will depend on the chosen frame of reference. The passenger and the observer belong to different frames. This is the source of the discrepancy. Suppose that the passenger and the observer speak a language that is like ours with possible differences arising from the assumption that no one in their community knows about modern physics. Let us call this language '19th Century English'. Imagine that the agents, in different conversations, utter sentences (1) and (2) respectively. (shrink)

Pandemic disruptions to schooling threw into sharper relief the entanglements of economy, gender norms, and education that had been there, and throughout the modern world, all along. The particular entanglement this paper aims to unravel is the reliance of education on a certain kind of attentiveness, historically provided by a feminized teaching force and mothers, that itself rests on the cultivation of particular sensibilities regarding time.

Oersted has been a puzzle for historians of science. Unflatteringly regarded by contemporaries in Britain and France as a metaphysician, he astonished and galvanised the learned world in 1820 with his discovery of electromagnetism. Suddenly famous, he was belatedly honoured; but, like Röntgen with X-rays, did no more serious work on the discovery that brought him renown, leaving that to Ampère and Faraday while he concentrated on an aesthetics that would bridge arts and sciences, and on building up scientific institutions (...) at home in Denmark in the wake of the Napoleonic wars and the British bombardment of Copenhagen. He lived in exciting times under the last absolutist monarchy in western Europe; and as he lay dying, his country was lapsing into civil war over the Schleswig–Holstein question, following the 1848 revolutions all over Europe. Although not geographically remote, Denmark was peripheral as far as science was concerned and was a very small country in which the int .. (shrink)

The twin paradox of relativity theory is reviewed. A distinction is made between physical clocks and biological ones. It is suggested that metabolic activity might be a better measure of aging than physical time. Further it is suggested that entropy changes representing metabolic activity would be a good way to describe aging. Using the above criterion it appears that a traveling twin will be older than his brother.

Two ideal standard clocks, effectively isolated from interaction with other physical systems, and in a region of the universe free of gravitational fields, are assumed to move in any arbitrary manner so that they coincide on at least two occasions. In general, the reading of one of them will become retarded relative to the other in the interval between successive coincidences. This relative retardation is predicted by the restricted theory of relativity, taken together with the assumption that the 'rate' (...) of a clock depends only on its velocity and not on its acceleration. The recognized procedure for calculating the retardation in terms of clock 'rates' is set out, and is illustrated by its application to a simple hypothetical experiment in which one clock remains at rest and the other travels away from and back to it with constant speed in a straight line. There is nothing paradoxical in the predicted retardation as such. The so-called 'clock paradox' arises because an alternative, and apparently valid, calculation procedure, also based on clock 'rates', leads to a contradictory result. The term 'paradox' is something of a euphemism since the two predictions are contradictories. It is shown that the paradox does not arise when direct use is made of the Lorentz transformation without introducing the additional, and non-essential, step in reasoning involved in utilizing the clock 'rates'. It is then shown that the paradox arises only through using these clock 'rates' without due regard to the exact significance of the quantities so described; once this is recognized the paradox is resolved completely within the framework of the restricted theory, which then provides a unique and unambiguous prediction of the relative retardation. Once the paradox is thus resolved, the general theory of relativity can add nothing significant to the analysis. It is shown that the application of the principle of equivalence is essentially trivial; in effect, Einstein and Tolman evaded the real logical issue raised by the contradictory predictions by denying the applicability of the restricted theory and then utilizing, by means of the principle of equivalence, results obtained from it. This tortuous procedure succeeded in evading the paradox rather than in resolving it; it would obviously be quite invalid were the restricted theory indeed inapplicable to the problem. (shrink)

We consider a sequence of absolute-space kinematical theories which differ more or less from the special theory of relativity (STR) in the amount of clock retardation which they predict, but which agree with STR with respect to roundtrip light experiments, such as Michelson-Morley and Kennedy-Thorndike. This sequence of theories is imbedded in the synchrony-free formulation of STR developed by Winnie by modifying the equal passage time principle. The paper has bearing on the relationship between the slow clock transport behavior of (...) clocks and the one-way velocity of light. Experiments which claim to measure the latter are discussed. (shrink)

Girolamo Cardano's writings on medicine reflect both the complexity and diversity of the Renaissance medical world and the breadth of his own interests. This book draws on selected themes of in Cardano's medical writings to explore the relation between medicine and Renaissance.

dickenson briefly mentions that peripheral opioid receptors somehow become active following inflammation and that the appearance of endogenous opioid peptides at the injury site may be related to immune cell proliferation. Recent findings elucidate the underlying mechanisms in more detail and provide an incentive for the development of a novel generation of analgesics devoid of typical central opioid side effects.

Publication in this journal recently of a paper by A. Grünbaum has induced me to submit a treatment of the same subject. Like Grünbaum, I shall use the framework of special relativity, but my analysis will be different. Some of his arguments, I believe, are inadmissable. I shall pose the problem in a form different from his, but the solution to be described will be applicable to his case as well.