449 research outputs found
Measuring the equation of state of a hard-disc fluid
We use video microscopy to study a two-dimensional (2D) model fluid of
charged colloidal particles suspended in water and compute the pressure from
the measured particle configurations. Direct experimental control over the
particle density by means of optical tweezers allows the precise measurement of
pressure as a function of density. We compare our data with theoretical
predictions for the equation of state, the pair-correlation function and the
compressibility of a hard-disc fluid and find good agreement, both for the
fluid and the solid phase. In particular the location of the transition point
agrees well with results from Monte Carlo simulations.Comment: 7 pages, to appear in EPL, slightly corrected versio
Dynamics of stick-slip in peeling of an adhesive tape
We investigate the dynamics of peeling of an adhesive tape subjected to a
constant pull speed. We derive the equations of motion for the angular speed of
the roller tape, the peel angle and the pull force used in earlier
investigations using a Lagrangian. Due to the constraint between the pull
force, peel angle and the peel force, it falls into the category of
differential-algebraic equations requiring an appropriate algorithm for its
numerical solution. Using such a scheme, we show that stick-slip jumps emerge
in a purely dynamical manner. Our detailed numerical study shows that these set
of equations exhibit rich dynamics hitherto not reported. In particular, our
analysis shows that inertia has considerable influence on the nature of the
dynamics. Following studies in the Portevin-Le Chatelier effect, we suggest a
phenomenological peel force function which includes the influence of the pull
speed. This reproduces the decreasing nature of the rupture force with the pull
speed observed in experiments. This rich dynamics is made transparent by using
a set of approximations valid in different regimes of the parameter space. The
approximate solutions capture major features of the exact numerical solutions
and also produce reasonably accurate values for the various quantities of
interest.Comment: 12 pages, 9 figures. Minor modifications as suggested by refere
Geometry-dependent electrostatics near contact lines
Long-ranged electrostatic interactions in electrolytes modify their contact
angles on charged substrates in a scale and geometry dependent manner. For
angles measured at scales smaller than the typical Debye screening length, the
wetting geometry near the contact line must be explicitly considered. Using
variational and asymptotic methods, we derive new transcendental equations for
the contact angle that depend on the electrostatic potential only at the three
phase contact line. Analytic expressions are found in certain limits and
compared with predictions for contact angles measured with lower resolution. An
estimate for electrostatic contributions to {\it line} tension is also given.Comment: 3 .eps figures, 5p
New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides
A new DTA (Differential Thermal Analysis) device was designed and installed
in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure
thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be
carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The
calibration of the DTA apparatus under pressure was successfully performed
using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard
calibration references. The thermal properties of these metals have been
studied under pressure. The values of DV (volume variation between liquid and
solid at Tm), ROsm (density of the solid at Tm) and ALPHAm (linear thermal
expansion coefficient at Tm) have been extracted. A very good agreement was
found with the existing literature and new data were added. This HP-DTA
apparatus is very useful for studying the thermodynamics of those systems where
one or more volatile elements are present, such as high TC superconducting
oxides. DTA measurements have been performed on Bi,Pb(2223) tapes up to 2 kbar
under reduced oxygen partial pressure (p(O2) = 0.07 bar). The reaction leading
to the formation of the 2223 phase was found to occur at higher temperatures
when applying pressure: the reaction DTA peak shifted by 49C at 2 kbar compared
to the reaction at 1 bar. This temperature shift is due to the higher stability
of the Pb-rich precursor phases under pressure, as the high isostatic pressure
prevents Pb from evaporating.Comment: 6 figures, 3 tables, Thermodynamics, Thermal property, Bi-2223,
fundamental valu
Dynamics of Crossover from a Chaotic to a Power Law State in Jerky Flow
We study the dynamics of an intriguing crossover from a chaotic to a power
law state as a function of strain rate within the context of a recently
introduced model which reproduces the crossover. While the chaotic regime has a
small set of positive Lyapunov exponents, interestingly, the scaling regime has
a power law distribution of null exponents which also exhibits a power law. The
slow manifold analysis of the model shows that while a large proportion of
dislocations are pinned in the chaotic regime, most of them are pushed to the
threshold of unpinning in the scaling regime, thus providing insight into the
mechanism of crossover.Comment: 5 pages, 3 figures. In print in Phy. Rev. E Rapid Communication
Entropic Tension in Crowded Membranes
Unlike their model membrane counterparts, biological membranes are richly
decorated with a heterogeneous assembly of membrane proteins. These proteins
are so tightly packed that their excluded area interactions can alter the free
energy landscape controlling the conformational transitions suffered by such
proteins. For membrane channels, this effect can alter the critical membrane
tension at which they undergo a transition from a closed to an open state, and
therefore influence protein function \emph{in vivo}. Despite their obvious
importance, crowding phenomena in membranes are much less well studied than in
the cytoplasm.
Using statistical mechanics results for hard disk liquids, we show that
crowding induces an entropic tension in the membrane, which influences
transitions that alter the projected area and circumference of a membrane
protein. As a specific case study in this effect, we consider the impact of
crowding on the gating properties of bacterial mechanosensitive membrane
channels, which are thought to confer osmoprotection when these cells are
subjected to osmotic shock. We find that crowding can alter the gating energies
by more than in physiological conditions, a substantial fraction of
the total gating energies in some cases.
Given the ubiquity of membrane crowding, the nonspecific nature of excluded
volume interactions, and the fact that the function of many membrane proteins
involve significant conformational changes, this specific case study highlights
a general aspect in the function of membrane proteins.Comment: 20 pages (inclduing supporting information), 4 figures, to appear in
PLoS Comp. Bio
Dynamical scaling and isotope effect in temporal evolution of mesoscopic structure during hydration of cement
The evolution of mesoscopic structure for cement-water mixtures turning into
colloidal gels remains far from being understood. Recent neutron scattering
investigations (Phys. Rev. Lett. 93, 255704 (2004); Phys. Rev. B. 72, 224208
(2005); Phys. Rev. B. 82, 064203 (2010)),, reveal the role of hydrogen bond in
temporal evolution of the mesoscopic structure during hydration of cement which
is the most consumed synthetic material. The present neutron scattering
investigation on hydration of cement with a mixture of light and heavy water
points to incomprehensibility of the temporal evolution of the mesoscopic
structure in terms of earlier observations on hydration with pure light or
heavy water. Unlike in the case of hydration with light water, disagreement has
been observed with the hypothesis of dynamical scaling for hydration of cement
with a mixture of the two types of water. The dynamics of evolution of the
mesoscopic structure has been observed to be nonlinear in regard to the
composition of hydration medium.Comment: 16 Pages, 5 Figure
Between the Post and the Com-Post:Examining the Postdigital ‘Work’ of a Prefix
In examining the work of the prefix ‘post’, we aim to contribute to the current postdigital dialogue. Our paper does not provide a rationale for the use of ‘postdigital’ in the title of this journal: that has been thoroughly explored elsewhere. We want instead to consider the work the prefix might do. We look at ‘post’, as it appears to ‘act’ in the terms of ‘postmodernism’ and ‘posthumanism’, suggesting that modernism and humanism are in need of questioning and reworking. We also examine what gets ‘post-ed’, or sometimes ‘com-posted’. (Com- is another interesting prefix, meaning ‘with’.) We then consider how these inquiries inform our understanding of a ‘postdigital reality’ that humans now inhabit. We understand this as a space of learning, struggle, and hope, where ‘old’ and ‘new’ media are now ‘cohabiting artefacts’ that enmesh with the economy, politics and culture. In entering this postdigital age, there really is no turning back from a convergence of the traditional and the digital. However, this is not simply a debate about technological and non-technological media. The postdigital throws up new challenges and possibilities across all aspects of social life. We believe this opens up new avenues too, for considering ways that discourse (language-in-use) shapes how we experience the postdigital
STRATEGIJA GOSPODARSKOG RAZVOJA REPUBLIKE HRVATSKE
Polazište rada ide za tim da pri definiranju strategije gospodarskog razvoja valja poći od nalaza teorije o determinantama rasta i od poruka empirijskog procesa gospodarskog razvoja iz proteklih 46 poslijeratnih godina. Analizom prvog ukazuje se na šest ključnih determinanti rasta, s posebnim akcentom na ulogu znanja (odnosno, ljudskog kapitala) i infrastrukture (fizičke i socijalne), a analizom drugog na ulogu konkurencije, ali istodobno i na potencijal države u stimuliranju procesa rasta. Država mora napustiti funkciju proizvodnje i alokacije dobara, jer se ove ostvaruju najbolje kroz tržišnu konkurenciju, ali mora voditi brigu o: unapređivanju infrastrukture, ulaganjima u ljudski kapital i poticanju znanstvenih istraživanja i inovacija koje doprinose porastu opće produktivnosti činilaca. Briga o unapređivanju (fizičke i socijalne) infrastrukture implicira između inoga, kreiranje niz aktivnosti na liniji poticanja razvoja tržišta i konkurentne mikroekonomije, jasnog definiranja i zaštite vlasničkih prava, privlačenja kapitala, otvorenosti i stabilne makroekonomije. Slijedi, u našem se primjeru kao sastavni element strategije i pretpostavka razvoja nameće ubrzana tranzicija iz "naslijeđenog" komandnog u poduzetničko gospodarstvo i pretvorba društva u cjelini u istinsko "tržišno društvo". Privatizacija "društvenog vlasništva" i aktiviranje financijskog tržišta preduvjet su ostvarivanja te tranzicije, pa je time u mnogome determiniran i izbor modela provedbe privatizacije, odnosno pretvorbe društvenih poduzeća. Zadnji odjeljak rada bavi se pitanjem odnosa razvoja i kvalitete upravljanja (shvaćenog kao zadaće političke vlasti da rukovodi poslovima nacije), odnosno pitanjem što predstavlja dobro upravljanje - upravljanje koje ne koči, već potiče razvoj
Hippurate as a metabolomic marker of gut microbiome diversity: Modulation by diet and relationship to metabolic syndrome
Reduced gut microbiome diversity is associated with multiple disorders including metabolic syndrome (MetS) features, though metabolomic markers have not been investigated. Our objective was to identify blood metabolite markers of gut microbiome diversity, and explore their relationship with dietary intake and MetS. We examined associations between Shannon diversity and 292 metabolites profiled by the untargeted metabolomics provider Metabolon Inc. in 1529 females from TwinsUK using linear regressions adjusting for confounders and multiple testing (Bonferroni: P < 1.71 × 10−4). We replicated the top results in an independent sample of 420 individuals as well as discordant identical twin pairs and explored associations with self-reported intakes of 20 food groups. Longitudinal changes in circulating levels of the top metabolite, were examined for their association with food intake at baseline and with MetS at endpoint. Five metabolites were associated with microbiome diversity and replicated in the independent sample. Higher intakes of fruit and whole grains were associated with higher levels of hippurate cross-sectionally and longitudinally. An increasing hippurate trend was associated with reduced odds of having MetS (OR: 0.795[0.082]; P = 0.026). These data add further weight to the key role of the microbiome as a potential mediator of the impact of dietary intake on metabolic status and health
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