NVU dynamics. I. Geodesic motion on the constant-potential-energy hypersurface

An algorithm is derived for computer simulation of geodesics on the constant potential-energy hypersurface of a system of N classical particles. First, a basic time-reversible geodesic algorithm is derived by discretizing the geodesic stationarity condition and implementing the constant potential energy constraint via standard Lagrangian multipliers. The basic NVU algorithm is tested by single-precision computer simulations of the Lennard-Jones liquid. Excellent numerical stability is obtained if the force cutoff is smoothed and the two initial configurations have identical potential energy within machine precision. Nevertheless, just as for NVE algorithms, stabilizers are needed for very long runs in order to compensate for the accumulation of numerical errors that eventually lead to "entropic drift" of the potential energy towards higher values. A modification of the basic NVU algorithm is introduced that ensures potential-energy and step-length conservation; center-of-mass drift is also eliminated. Analytical arguments confirmed by simulations demonstrate that the modified NVU algorithm is absolutely stable. Finally, simulations show that the NVU algorithm and the standard leap-frog NVE algorithm have identical radial distribution functions for the Lennard-Jones liquid

Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

The properties of nanoconfined fluids can be strikingly different from those of bulk liquids. A basic unanswered question is whether the equilibrium and dynamic consequences of confinement are related to each other in a simple way. We study this question by simulation of a liquid comprising asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times - spanning six decades as a function of temperature, density, and degree of confinement - collapse when plotted versus excess entropy. The data also collapse when plotted versus excess isochoric heat capacity, a behaviour that follows from the existence of isomorphs in the bulk and confined states.Comment: 8 pages; accepted for publication in Phys. Rev. Lett. Includes the Supplemental Materia

Scaling of viscous dynamics in simple liquids:theory, simulation and experiment

Supercooled liquids are characterized by relaxation times that increase dramatically by cooling or compression. Many liquids have been shown to obey power-law density scaling, according to which the relaxation time is a function of density to some power over temperature. We show that power-law density scaling breaks down for larger density variations than usually studied. This is demonstrated by simulations of the Kob-Andersen binary Lennard-Jones mixture and two molecular models, as well as by experimental results for two van der Waals liquids. A more general form of density scaling is derived, which is consistent with results for all the systems studied. An analytical expression for the scaling function for liquids of particles interacting via generalized Lennard-Jones potentials is derived and shown to agree very well with simulations. This effectively reduces the problem of understanding the viscous slowing down from being a quest for a function of two variables to a search for a single-variable function.Comment: 7 pages, 5 figure

Plants as De-Worming Agents of Livestock in the Nordic Countries: Historical Perspective, Popular Beliefs and Prospects for the Future

Preparations derived from plants were the original therapeutic interventions used by man to control diseases (including parasites), both within humans and livestock. Development of herbal products depended upon local botanical flora with the result that different remedies tended to develop in different parts of the world. Nevertheless, in some instances, the same or related plants were used over wide geographic regions, which also was the result of communication and/or the importation of plant material of high repute. Thus, the Nordic countries have an ancient, rich and diverse history of plant derived anthelmintic medications for human and animal use. Although some of the more commonly used herbal de-wormers were derived from imported plants, or their products, many are from endemic plants or those that thrive in the Scandinavian environment. With the advent of the modern chemotherapeutic era, and the discovery, development and marketing of a seemingly unlimited variety of highly efficacious, safe synthetic chemicals with very wide spectra of activities, herbal remedies virtually disappeared from the consciousness – at least in the Western world. This attitude is now rapidly changing. There is a widespread resurgence in natural product medication, driven by major threats posed by multi-resistant pest, or disease, organisms and the diminishing public perceptions that synthetic chemicals are the panacea to health and disease control. This review attempts to provide a comprehensive account of the depth of historical Nordic information available on herbal de-wormers, with emphasis on livestock and to provide some insights on potentially rewarding areas of "re-discovery" and scientific evaluation in this field

Positional differences of physical traits and physiological characteristics in female volleyball players – the role of age

The purpose of this study was to examine the variation in physical and physiological characteristics according to playing position in adolescent and adult female volleyball players. Adolescent (n=62, aged 15.6±1.1 years) and adult volleyball players (n=58, aged 24.9±5.3 years) were examined for anthropometric characteristics and body composition, and they performed a physical working capacity test, a 3-minute step test, the Wingate anaerobic test, sit-and-reach test, handgrip strength test, and countermovement vertical jump with arm-swing test (CMJa). Adult players were taller and had a higher percentage of fat-free mass, better performance in cardiorespiratory power, anaerobic power, handgrip muscle strength and CMJa than adolescents (Cohen’s d>0.45). Positional differences in body height (centers were the tallest, whereas liberos were the shortest, p<.001) were found for both age groups. However, positional differences in body mass and fat-free mass were observed only in adolescents (centers were heavier than liberos, p<.05), whereas differences in CMJa were only in adults (hitters jumped higher than liberos, p<.05). Thus, the differences in body mass, fat-free mass and CMJa among playing positions in female volleyball were age-dependent. These findings might help coaches and trainers to develop position-specific training programs

Tiltrekke og beholde sykepleiere i offentlig sektor : Hvordan unngå sykepleiermangel?

Det har i lang tid vært oppmerksomhet rundt sykepleiermangelen, og hvordan utfordringene knyttet til denne problemstillingen forventes å øke i årene fremover. Formålet med denne masterutredningen er å undersøke faktorer som er viktig for å beholde og tiltrekke kvalifiserte sykepleiere. Utredningen bygger på en deskriptiv og eksplorerende intervjustudie, gjennomført ved bruk av kvalitativ metode. Data ble innhentet gjennom semistrukturerte intervju med 13 sykepleiere i alderen 23 til 28 år, som arbeider i ulike offentlige helseinstitusjoner i Bergen og omegn. Det teoretiske grunnlaget for utredningen er litteraturene om temaene motivasjon, belønninger og turnover, som vektlegger indre- og ytre motivasjon, samt forklarer hvorfor ansatte ønsker å slutte i sin jobb. Faglig interesse og et ønske om å hjelpe andre viser seg å være de viktigste årsakene til valg av sykepleieryrket. Sykepleiere som har valgt arbeidsplass basert på sine interesser, gir uttrykk for å trives i høyere grad enn sykepleiere som ikke har gjort dette. Selv om lønn ikke fremstår som viktig for valg av yrket eller arbeidsmotivasjonen, er dette en faktor som fører til mistrivsel på lang sikt. Det skyldes at sykepleiere føler seg avhengig av å jobbe ubekvemme tider for at den totale lønnen skal være tilfredsstillende, samt at det er en stor skjevhet mellom lønn og innsats. Når det gjelder innsats opplever sykepleierne et høyt arbeidspress grunnet bemanningsproblemer. Faktorer som ser ut til å ha positiv effekt på trivselen til sykepleierne, er arbeidsmiljø, arbeidsforhold og ikke-finansielle belønninger som anerkjennelse og ros. Videreutdanning tilbudt av arbeidsplassen er også et effektivt insentiv til å beholde sykepleiere.nhhma

Isomorphs in model molecular liquids

Isomorphs are curves in the phase diagram along which a number of static and dynamic quantities are invariant in reduced units. A liquid has good isomorphs if and only if it is strongly correlating, i.e., the equilibrium virial/potential energy fluctuations are more than 90% correlated in the NVT ensemble. This paper generalizes isomorphs to liquids composed of rigid molecules and study the isomorphs of two systems of small rigid molecules, the asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for both systems we find that the isochoric heat capacity, the excess entropy, the reduced molecular center-of-mass self part of the intermediate scattering function, the reduced molecular center-of-mass radial distribution function to a good approximation are invariant along an isomorph. In agreement with theory, we also find that an instantaneous change of temperature and density from an equilibrated state point to another isomorphic state point leads to no relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be more approximative than those of the asymmetric dumbbell model, which is consistent with the OTP model being less strongly correlating. For both models we find "master isomorphs", i.e., isomorphs have identical shape in the virial/potential energy phase diagram.Comment: 20 page