Energy Requirement of Control: Comments on Szilard's Engine and Maxwell's Demon

In mathematical physical analyses of Szilard's engine and Maxwell's demon, a general assumption (explicit or implicit) is that one can neglect the energy needed for relocating the piston in Szilard's engine and for driving the trap door in Maxwell's demon. If this basic assumption is wrong, then the conclusions of a vast literature on the implications of the Second Law of Thermodynamics and of Landauer's erasure theorem are incorrect too. Our analyses of the fundamental information physical aspects of various type of control within Szilard's engine and Maxwell's demon indicate that the entropy production due to the necessary generation of information yield much greater energy dissipation than the energy Szilard's engine is able to produce even if all sources of dissipation in the rest of these demons (due to measurement, decision, memory, etc) are neglected.Comment: New, simpler and more fundamental approach utilizing the physical meaning of control-information and the related entropy production. Criticism of recent experiments adde

Infrared aircraft measurements of stratospheric composition over Antarctica during September 1987

The JPL Mark IV interferometer recorded high resolution, infared solar spectra from the NASA DC-8 aircraft during flights over Antarctica in September 1987. The atmospheric absorption features in these spectra were analyzed to determine the overburdens of O3, NO, NO2, HNO3, ClONO2, HCl, HF, CH4, N2O, CO, H2O and CFC-12. The spectra were obtained at latitudes which ranged between 64 degrees S and 86 degrees S, allowing the composition in the interior of the polar vortex to be compared with that at the edge. The latitude dependence observed for NO, HO2, HNO3, ClONO2, HCl and HF are summerized. The values at 30 deg S were observed on the ferry flight from New Zealand to Hawaii. The dashed lines connecting the two were interpolated across the region for which there are no measurements. The chemically perturbed region is seen to consist of a collar of high HNO3 and ClONO2 surrounding a core in which the overburdens of these and of HCl and NO2 are very low. Clear increases in the overburdens of HF and HNO3 were observed during the course of September in the vortex core. HCl and NO2 exhibited smaller, less significant increases. The overburdens of the tropospheric source gases, N2O, CH4, CF2Cl2, and H2O were observed to much smaller over Antarctica than at mid-latitudes. This, together with the fact that HF over Antarctica was more that double its mid-latitude value, suggests that downwelling has occurred

An interstellar precursor mission

A mission out of the planetary system, with launch about the year 2000, could provide valuable scientific data as well as test some of the technology for a later mission to another star. Primary scientific objectives for the precursor mission concern characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science instruments are suggested. Individual spacecraft systems for the mission were considered, technology requirements and problem areas noted, and a number of recommendations made for technology study and advanced development. The most critical technology needs include attainment of 50-yr spacecraft lifetime and development of a long-life NEP system

On the Meaning of the Principle of General Covariance

We present a definite formulation of the Principle of General Covariance (GCP) as a Principle of General Relativity with physical content and thus susceptible of verification or contradiction. To that end it is useful to introduce a kind of coordinates, that we call quasi-Minkowskian coordinates (QMC), as an empirical extension of the Minkowskian coordinates employed by the inertial observers in flat space-time to general observers in the curved situations in presence of gravitation. The QMC are operationally defined by some of the operational protocols through which the inertial observers determine their Minkowskian coordinates and may be mathematically characterized in a neighbourhood of the world-line of the corresponding observer. It is taken care of the fact that the set of all the operational protocols which are equivalent to measure a quantity in flat space-time split into inequivalent subsets of operational prescriptions under the presence of a gravitational field or when the observer is not inertial. We deal with the Hole Argument by resorting to de idea of the QMC and show how it is the metric field that supplies the physical meaning of coordinates and individuates point-events in regions of space-time where no other fields exist. Because of that the GCP has also value as a guiding principle supporting Einstein's appreciation of its heuristic worth in his reply to Kretschmann in 1918

Modelling of anal sphincter tone based on pneumatic and cable-driven mechanisms

Motivated by the need for improving a haptics-based simulation tool for learning and training digital rectal examinations, a sphincter tone model and its actuation is conceived and developed. Two approaches are presented: One based on pneumatics actuation and the other using cable-driven mechanical actuation using servo motors. Clinical scenarios are modelled as profiles based on studies of anorectal manometry and adapted with clinical input. Both designed mechanisms and scenarios were experimentally evaluated by six experts, Nurse Practitioners in Continence and Colorectal Surgeons. Results show that both mechanisms produce enough pressure on examining finger and profiles are able to generate a wide range of healthy and abnormal cases. Either approach could be used to provide a more realistic experience during training of sphincter tone assessment

Functional correlates of optic flow motion processing in Parkinson’s disease

The visual input created by the relative motion between an individual and the environment, also called optic flow, influences the sense of self-motion, postural orientation, veering of gait, and visuospatial cognition. An optic flow network comprising visual motion areas V6, V3A, and MT+, as well as visuo-vestibular areas including posterior insula vestibular cortex (PIVC) and cingulate sulcus visual area (CSv), has been described as uniquely selective for parsing egomotion depth cues in humans. Individuals with Parkinson’s disease (PD) have known behavioral deficits in optic flow perception and visuospatial cognition compared to age- and education-matched control adults (MC). The present study used functional magnetic resonance imaging (fMRI) to investigate neural correlates related to impaired optic flow perception in PD. We conducted fMRI on 40 non-demented participants (23 PD and 17 MC) during passive viewing of simulated optic flow motion and random motion. We hypothesized that compared to the MC group, PD participants would show abnormal neural activity in regions comprising this optic flow network. MC participants showed robust activation across all regions in the optic flow network, consistent with studies in young adults, suggesting intact optic flow perception at the neural level in healthy aging. PD participants showed diminished activity compared to MC particularly within visual motion area MT+ and the visuo-vestibular region CSv. Further, activation in visuo-vestibular region CSv was associated with disease severity. These findings suggest that behavioral reports of impaired optic flow perception and visuospatial performance may be a result of impaired neural processing within visual motion and visuo-vestibular regions in PD.Published versio

Observables, gauge invariance, and the role of the observers in the limit from general relativity to special relativity

Some conceptual issues concerning general invariant theories, with special emphasis on general relativity, are analyzed. The common assertion that observables must be required to be gauge invariant is examined in the light of the role played by a system of observers. Some features of the reduction of the gauge group are discussed, including the fact that in the process of a partial gauge fixing the reduction at the level of the gauge group and the reduction at the level of the variational principle do not commute. Distinctions between the mathematical and the physical concept of gauge symmetry are discussed and illustrated with examples. The limit from general relativity to special relativity is considered as an example of a gauge group reduction that is allowed in some specific physical circumstances. Whether and when the Poincar\'e group must be considered as a residual gauge group will come out as a result of our analysis, that applies, in particular, to asymptotically flat spaces.Comment: 17 page

The benefits of organic farming for biodiversity

Previous studies suggest widespread positive responses of biodiversity to organic farming. Many of these studies, however, have been small-scale. This project tested the generality of habitat and biodiversity differences between matched pairs of organic and non-organic farms containing cereal crops in lowland England on a large-scale across a range of taxa including plants, insects, birds and bats. The extent of both cropped and un-cropped habitats together with their composition and management on a range of scales were also compared. Organic farms was likely to favour higher levels of biodiversity and indeed organic farms tended to support higher numbers of species and overall abundance across most taxa. However, the magnitude of the response differed strikingly; plants showed stronger and more consistent responses than other taxa. Some, but not all, differences in biodiversity between systems appear to be a consequence of differences in habitat quantity

"It's just horrible": a qualitative study of patients' and carers' experiences of bowel dysfunction in Multiple Sclerosis

Background: Around 50% of people with multiple sclerosis (MS) experience neurogenic bowel dysfunction (constipation and / or faecal incontinence), reducing quality of life and increasing carer burden. No previous qualitative studies have explored the experiences of bowel problems in people with MS, or the views of their family carers. Objective: To understand 'what it is like' to live with bowel dysfunction and the impact this has on people with MS and carers. Methods: Using exploratory qualitative methods, 47 semi-structured interviews were conducted with participants recruited from specialist hospital clinics and community sources using purposive and chain-referral sampling. Data were analysed using a pragmatic inductive-deductive method. Results: Participants identified multiple psychological, physical and social impacts of bowel dysfunction. Health care professional support ranged from empathy and appropriate onward referral, to lack of interest or not referring to appropriate services. Participants want bowel issues to be discussed more openly, with clinicians instigating a discussion early after MS diagnosis and repeating enquiries regularly. Conclusions: Bowel dysfunction impacts on the lives of people with MS and their carers; their experience with care services is often unsatisfactory. Understanding patient and carer preferences about management of bowel dysfunction can inform clinical care and referral pathways