381 research outputs found
Lamellar and inverse micellar structures of skin lipids: Effect of templating
The outermost layer of skin, the stratum corneum (SC), comprises rigid
corneocytes in a layered lipid matrix. Using atomistic simulations we find that
the equilibrium phase of the SC lipids is inverse micellar. A model of the
corneocyte is used to demonstrate that lamellar layering is induced by the
patterned corneocyte wall. The inverse micellar phase is consistent with in
vivo observations in the lacunar spaces and at the stratum granulosum - SC
boundary region, and suggests a functional role in the lipid synthesis pathway
in vivo.Comment: pdflatex 5 pages, 10 page supplementary material. Published Physical
Review Letters. Added link to website with animation
An investigation of the SCOZA for narrow square-well potentials and in the sticky limit
We present a study of the self consistent Ornstein-Zernike approximation
(SCOZA) for square-well (SW) potentials of narrow width delta. The main purpose
of this investigation is to elucidate whether in the limit delta --> 0, the
SCOZA predicts a finite value for the second virial coefficient at the critical
temperature B2(Tc), and whether this theory can lead to an improvement of the
approximate Percus-Yevick solution of the sticky hard-sphere (SHS) model due to
Baxter [R. J. Baxter, J. Chem. Phys. 49, 2770 (1968)]. For SW of non vanishing
delta, the difficulties due to the influence of the boundary condition at high
density already encountered in an earlier investigation [E. Schoell-Paschinger,
A. L. Benavides, and R. Castaneda-Priego, J. Chem. Phys. 123, 234513 (2005)]
prevented us from obtaining reliable results for delta < 0.1. In the sticky
limit this difficulty can be circumvented, but then the SCOZA fails to predict
a liquid-vapor transition. The picture that emerges from this study is that for
delta --> 0, the SCOZA does not fulfill the expected prediction of a constant
B2(Tc) [M. G. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)], and that
for thermodynamic consistency to be usefully exploited in this regime, one
should probably go beyond the Ornstein-Zernike ansatz.Comment: 40 pages, 13 figures. Previous Sec. 2 on the Yukawa potential has
been removed. Only the square-well potential is considered in this versio
Phase Behavior of Short Range Square Well Model
Various Monte Carlo techniques are used to determine the complete phase
diagrams of the square well model for the attractive ranges
and . The results for the latter case are in agreement with
earlier Monte Carlo simulations for the fluid-fluid coexistence curve and yield
new results for the liquidus-solidus lines. Our results for
are new. We find that the fluid-fluid critical point is metastable for both
cases, with the case being just below the threshold value for
metastability. We compare our results with prior studies and with experimental
results for the gamma-II crystallin.Comment: 8 figures, 1 tabl
Genital manifestations of tropical diseases
Genital symptoms in tropical countries and among returned travellers can arise from a variety of bacterial, protozoal, and helminthic infections which are not usually sexually transmitted. The symptoms may mimic classic sexually transmitted infections (STIs) by producing ulceration (for example, amoebiasis, leishmaniasis), wart-like lesions (schistosomiasis), or lesions of the upper genital tract (epididymo-orchitis caused by tuberculosis, leprosy, and brucellosis; salpingitis as a result of tuberculosis, amoebiasis, and schistosomiasis). A variety of other genital symptoms less suggestive of STI are also seen in tropical countries. These include hydrocele (seen with filariasis), which can be no less stigmatising than STI, haemospermia (seen with schistosomiasis), and hypogonadism (which may occur in lepromatous leprosy). This article deals in turn with genital manifestations of filariasis, schistosomiasis, amoebiasis, leishmaniasis, tuberculosis and leprosy and gives clinical presentation, diagnosis, and treatment
Water permeation through stratum corneum lipid bilayers from atomistic simulations
Stratum corneum, the outermost layer of skin, consists of keratin filled
rigid non-viable corneocyte cells surrounded by multilayers of lipids. The
lipid layer is responsible for the barrier properties of the skin. We calculate
the excess chemical potential and diffusivity of water as a function of depth
in lipid bilayers with compositions representative of the stratum corneum using
atomistic molecular dynamics simulations. The maximum in the excess free energy
of water inside the lipid bilayers is found to be twice that of water in
phospholipid bilayers at the same temperature. Permeability, which decreases
exponentially with the free energy barrier, is reduced by several orders of
magnitude as compared to with phospholipid bilayers. The average time it takes
for a water molecule to cross the bilayer is calculated by solving the
Smoluchowski equation in presence of the free energy barrier. For a bilayer
composed of a 2:2:1 molar ratio of ceramide NS 24:0, cholesterol and free fatty
acid 24:0 at 300K, we estimate the permeability P=3.7e-9 cm/s and the average
crossing time \tau_{av}=0.69 ms. The permeability is about 30 times smaller
than existing experimental results on mammalian skin sections.Comment: latex, 8 pages, 6 figure
Gas-solid coexistence of adhesive spheres
In this note we investigate using basic free energy considerations the
location of the gas-liquid critical point with respect to solidification for
narrow attractive interactions down to the Baxter limit. Possible experimental
and simulation realizations leading to a stable critical point are briefly
discussed.Comment: 2 pages, 2 figures, submitte
Energy and technological refurbishment of the School of Architecture Valle Giulia, Rome
Modern architecture built in historical urban contexts represents a demanding issue when its energy efficiency should be improved. Indeed, the strongest efforts have to be made to maintain the architectural identity and its harmony with the surrounding cultural heritage. This study deals with the main building of the School of Architecture Valle Giulia in Rome, designed by Enrico Del Debbio in the 30’s. Further constraints are related to several interventions of airspace expansion starting from 1958 which involved the building starting from 1958. So, preservation would mean highlighting its historic change but, adapting the built environment to the contemporary users’ needs. As above-mentioned, the building belongs to the Valle delle Accademie, within the historic park of Villa Borghese, so that to acquire landscaping values. Those latter ones call for ulterior requirements when any new design process is conceived. The study provides a global renewal of the building accounting for the current low Indoor Environmental Quality in both summer and winter seasons and the lack of suitability to the contemporary University student’s needs. The interaction between building performance and HVAC systems was studied by collecting data and architectural surveys conducted by all the architects who modified the building. This procedure was chosen since thermo-physical investigations are considered destructive due to required perforations to identify the actual wall layers. Moreover, thermographic surveys were carried out to validate the modelled building response. The result of the study is the identification of viable interventions to improve the accessibility and fruition of the building as well as its energy performance. A specific cost-benefit analysis was done to prioritize the design options along with considering the measures needed to preserve all the architectural features and values
Thermodynamic investigation of a shared cogeneration system with electrical cars for northern Europe climate
Transition to alternative energy systems is indicated by EU Commission as a suitable path to energy efficiency and energy saving in the next years. The aims are to decrease greenhouses gases emissions, relevance of fossil fuels in energy production and energy dependence on extra-EU countries. These goals can be achieved increasing renewable energy sources and/or efficiency on energy production processes. In this paper an innovative micro-cogeneration system for household application is presented: it covers heating, domestic hot water and electricity demands for a residential user. Solid oxide fuel cells, heat pump and Stirling engine are utilised as a system to achieve high energy conversion efficiency. A transition from traditional petrol cars to electric mobility is also considered and simulated here. Different types of fuel are considered to demonstrate the high versatility of the simulated cogeneration system by changing the pre-reformer of the fuel cell. Thermodynamic analysis is performed to prove high efficiency with the different fuels
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