117,286 research outputs found
New lamellar phase with pores in the chain-melting regime of an anionic phospholipid dispersion
No full textThe anionic phospholipid DMPG (dimyristoyl phosphatidylglycerol) may exhibit in water, instead of a unique melting transition of the hydrocarbon chains, a "melting regime" for pH values above 5, where the phosphate groups are deprotonated, and for low ionic strength, where charge screening is weak. The chain-melting process of DMPG starts at Tmon (onset of the melting regime at ∼ 20°C), but the complete fluid phase exists only above Tmoff (offset of the melting regime at ∼ 30°C). In a recent paper we developed a SAXS model for a bilayer with pores to explain SAXS results obtained for concentrations up to 70 mM DMPG (F. Spinozzi, L. Paccamiccio, P. Mariani, and L. Q. Amaral, Langmuir, in print, 2010). A new lamellar phase with pores, starting 3°C above T mon and existing up to 4°C above Tm off, was also identified at the higher investigated DMPG concentrations (up to 300 mM DMPG). In this paper we focus in more detail the SAXS curves obtained in the concentration interval 70-300 mM DMPG. The slope of the scattering profile in the very small q range, as well as the anomalous increase in the intensity of the bilayer band centered around 0.12 Å-1 after Tmoff, have been in particular analyzed. By using a model of water-penetrated bilayers, the volume fractions of DMPG and water molecules inside the bilayer was derived as a function of temperature
Reasoning About Inter-procedural Security Requirements in IoT Applications
No full textThe importance of information security dramatically increased and will further grow due to the shape and nature of the modern computing industry. Software is published at a continuously increasing pace. The Internet of Things and security protocols are two examples of domains that pose a great security challenge, due to how diverse the needs for those software may be, and a generalisation of the capabilities regarding the toolchain necessary for testing is becoming a necessity. Oftentimes, these software are designed starting from a formal model, which can be verified with appropriate model checkers. These models, though, do not represent the actual implementation, which can deviate from the model and hence certain security properties might not be inherited from the model, or additional issues could be introduced in the implementation. In this paper we describe a proposal for a novel technique to assess software security properties from LLVM bitcode. We perform various static analyses, such as points-to analysis, call graph and control-flow graph, with the aim of deriving from them an ‘accurate enough’ formal model of the paths taken by the program, which are then going to be examined via consolidated techniques by matching them against a set of defined rules. The proposed workflow then requires further analysis with more precise methods if a rule is violated, in order to assess the actual feasibility of such path(s). This step is required as the analyses performed to derive the model to analyse are over-approximating the behaviour of the software
Melting regime of the anionic phospholipid DMPG: new Lamellar phase and porous bilayer model
No full textAqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG) at pH above the
apparent pK of DMPG and concentrations in the interval 70-300 mM have been investigated by small (SAXS) and
wide-angle X-ray scattering, differential scanning calorimetry, and polarized optical microscopy. The order-disorder
transition of the hydrocarbon chains occurs along an interval of about 10 C (between Tm
on ∼ 20 C and Tm
off ∼ 30 C).
Such melting regime was previously characterized at lower concentrations, up to 70 mM DMPG, when sample
transparency was correlated with the presence of pores across the bilayer. At higher concentrations considered here, the
melting regime persists but is not transparent. Defined SAXS peaks appear and a new lamellar phase Lp with pores is
proposed to exist above 70 mM DMPG, starting at ∼23 C (∼3 C above Tm
on) and losing correlation after Tm
off. A new
model for describing the X-ray scattering of bilayers with pores, presented here, is able to explain the broad band
attributed to in-plane correlation between pores. The majority of cell membranes have a net negative charge, and the
opening of pores across the membrane tuned by ionic strength, temperature, and lipid composition is likely to have
biological relevance
“Pressure and Temperature effects on phase behaviour and structural properties of lipids mixture”
No full textLight Communication for Controlling Industrial Robots
No full textOptical Wireless Communication (OWC) is regarded as an auspicious communication approach that can outperform the existing wireless technology. It utilizes LED lights, whose subtle variation in radiant intensity generate a binary data stream. This is perceived by a photodiode, that converts it to electric signals for further interpretation. This article aims at exploring the use of this emerging technology in order to control wirelessly industrial robots, overcoming the need for wires, especially in environments where radio waves are not working due to environmental factors or not allowed for safety reasons. We performed experiments to ensure the suitability and efficiency of OWC based technology for the aforementioned scope and “in vitro" tests in various Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) configurations to observe the system throughput and reliability. The technology performance in the “clear LoS" and in the presence of a transparent barrier, were also analyzed
On the importance of anandamide structural features for its interactions with dipalmitoylphospahtidylcholine bilayers: effects on PLA2 activity
No full textThe acylethanolamide anandamide (AEA) occurs in a variety of mammalian tissues and, as a result of its action on cannabinoid receptors, exhibits several cannabimimetic activities. Moreover, some of its effects are mediated through interaction with an ion channel-type vanilloid receptor. However, the chemical features of AEA suggest that some of its biological effects could be related to physical interactions with the lipidic part of the membrane. The present work studies the effect of AEA-induced structural modifications of the dipalmitoylphosphatidylcholine (DPPC) bilayer on phospholipase A2 (PLA2) activity, which is strictly dependent on lipid bilayer features. This study, performed by 2-dimethylamino-(6-lauroyl)-naphthalene fluorescence, demonstrates that the effect of AEA on PLA2 activity is concentration-dependent. In fact, at low AEA/DPPC molar ratios (from R = 0.001 to R = 0.04), there is an increase of the enzymatic activity, which is completely inhibited for R = 0.1. X-ray diffraction data indicate that the AEA affects DPPC membrane structural properties in a concentration-dependent manner. Because the biphasic effect of increasing AEA concentrations on PLA2 activity is related to the induced modifications of membrane bilayer structural properties, we suggest that AEA-phospholipid interactions may be important to produce, at least in part, some of the similarly biphasic responses of some physiological activities to increasing concentrations of AEA
Pressure effects on lipidic direct phases: the dodecyltrimethyl ammonium chloride-water system
No full textThe direct lyotropic polymorphism of dodecyltrimethylammonium chloride (DTAC) was investigated by synchrotron X-ray diffraction at different water concentrations under compression up to 2 kbar, i.e., in the pressure intermediate range where interesting biophysical transformations occur and the functional characteristics of cell membranes are altered. The results show that pressure induces the transition from the hexagonal phase to the micellar Pm3n cubic phase in hydrated samples (c between 0.5 and 0.6, c being the weight concentration of lipid in the mixture) and the transition from the bicontinuous Ia3d cubic phase to the hexagonal phase in drier samples (c = 0.8). By increasing the pressure on very dry samples, a lamellar Lα phase was observed to form transitorily at the Ia3d cubic-hexagonal phase transition. Phase compressibility and then the lipid and water partial molecular compressibilities were derived as a function of pressure and concentration. As a result, we assessed the very low compressibility of the hydration water within the lipid phases, and we demonstrated that the compressibility of DTAC is very dependent on pressure. Moreover, the molecular parameters of DTAC calculated in the different phases during compression confirmed that pressure induces small but continuous conformational changes, definitely different from the large changes observed in lipid molecules forming type II structures. © 2006 American Chemical Society
“Compressing inverse lyotropic phases: effects on dioleoyl phosphatidyl ethanolamine at low hydration”
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
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