1,094 research outputs found
A study of the flocculation of phospholipids as a model of membrane interactions
Dispersion of the pure phospholipids phosphatidylcholine (lecithin) and phosphatidyiserine were prepared in solutions of different ionic type and concentration. The dispersions were prepared so as to give particies, spherules, of the phospholipids which were of a fairly constant diameter, i.e. they were quasi-monodisperse suspensions. The dispersions were subjected to a laminar flow shear gradient was to affect collisions between the particles of the dispersions and thus to bring about flocculation or aggregation of the suspensions. By measuring the total number of particles in the dispersions at timed intervals a parameter was calculated for each aggregation, the collision efficiency. The collision efficiency is a measure of the rate of aggregation and can also be used to calculate the enrgy of the adhesive interaction of the particles. The values of the collision efficiency for the flocculation of lecithin spherules showed that for the monovalent cations the order of increasing efficacy was Potassium: Sodium: Lithium which is the order of decreasing ionic radius. The results for divalent cations showed that these were more effective by at least two orders of magnitude. Further divalent cations exhibited a reversal of charge behaviour at concentrations above about 10-3 molar. The order of increasing efficacy did not reflect the order of decreasing ionic radius and was Magnesium: Strontium: Barium: Calcium, which suggest that lecithin may have a specific affinity for Calcium. The trivalent cation Lanthanum was more effective than the divalent cations and showed a charge reversal at a lower concentration. Temperature was found to have little effect on the rate of flocculation of lecithin dispersion. For the flocculation of phosphatidylserine dispersions higher concentrations of sodium and calcium ions were found to be necessary, than for the flocculation of lecithin dispersions. This was to be expected because phosphatidylserine spherules are considered to bear a considerable negative surface charge, whereas those of lecitihin are considered to be uncharged. The collision efficiency, measured in ionic conditions where the spherules are probably uncharged, was used to calculate a value for the London-Hamaker constant. Values in the range 7x10
Pyrethroid resistance in Italian populations of the mite Varroa destructor: a focus on the Lombardy region
Varroa destructor Anderson et Trueman (Acari Varroidae) is a major pest of honey bees and synthetic acaricide treatments remain the most effective tool to contain its infestations. In 1991, pyrethroid resistance was first reported in Lombardy, and is now spread worldwide. Recently, three different mutations (L925V/I/M) occurring in the voltage-gated sodium channel have been associated with tau-fluvalinate resistance. Furthermore, in the literature, indirect evidence from laboratory bioassays have indicated that high levels of esterases may be involved in mites resistant to tau-fluvalinate. This study provides an update on the actual spread of target-site resistance to tau-fluvalinate in V. destructor samples collected in the Lombardy region. TaqMan assays showed that mutation L925V is present in this area, however only low frequencies of this resistant allele were detected. The majority of resistant mites were found in the homozygous form (11%), and only a small fraction possessed the heterozygous genotype (2%). Additionally, a protocol was set up to detect esterase activity directly in single mites. Slight variability was observed among different populations collected in Lombardy. Additional studies are needed to confirm the involvement of esterases in resistance to pyrethroids in V. destructor and whether this can be correlated to changes in enzyme activity
Controlling pulse propagation in optical fibers through nonlinearity and dispersion management
In case of the nonlinear Schr\"odinger equation with designed group velocity
dispersion, variable nonlinearity and gain/loss; we analytically demonstrate
the phenomenon of chirp reversal crucial for pulse reproduction. Two different
scenarios are exhibited, where the pulses experience identical dispersion
profiles, but show entirely different propagation behavior. Exact expressions
for dynamical quasi-solitons and soliton bound-states relevant for fiber
communication are also exhibited.Comment: 4 pages, 5 eps figure
Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions
A UV photolytic process was studied for the production of methane from carbonaceous chondrites under simulated Martian conditions. Methane evolution rates from carbonaceous chondrites were found to be positively correlated to temperature (â80 to 20°C) and the concentration of carbon in the chondrites (0.2 to 1.69 wt%); and decreased over time with Murchison samples exposed to Martian conditions. The amount of evolved methane (EM) per unit of UV energy was 7.9 Ă 10â13 mol Jâ1 for UV irradiation of Murchison (1.69 wt%) samples tested under Martian conditions (6.9 mbar and 20°C). Using a previously described Mars UV model (Moores et al., 2007), and the EM given above, an annual interplanetary dust particle (IDP) accreted mass of 2.4 Ă 105 kg carbon per year yields methane abundances between 2.2 to 11 ppbv for model scenarios in which 20 to 100% of the accreted carbon is converted to methane, respectively. The UV/CH4 model for accreted IDPs can explain a portion of the globally averaged methane abundance on Mars, but cannot easily explain seasonal, temporal, diurnal, or plume fluctuations of methane. Several impact processes were modeled to determine if periodic emplacement of organics from carbonaceous bolides could be invoked to explain the occurrence of methane plumes produced by the UV/CH4process. Modeling of surface impacts of high-density bolides, single airbursts of low-density bolides, and multiple airbursts of a cascading breakup of a low-density rubble-pile comet were all unable to reproduce a methane plume of 45 ppbv, as reported by Mumma et al
Palliative treatment of malignant esophageal-cardiac stricture in the ederly
The aging of the population and longer life expectancy
entails an increased number of elderly patients with esophageal
cancer and benign pathologies referred for surgical
treatment. Esophageal cancer is a pathology that
mainly involves elderly patients. The aim of this study is
to assess the effects of age on the outcome of surgery
for esophageal cancer and benign pathologies in patients
treated in our department
S-, P- and D-wave resonances in positronium-sodium and positronium-potassium scattering
Scattering of positronium (Ps) by sodium and potassium atoms has been
investigated employing a three-Ps-state coupled-channel model with Ps(1s,2s,2p)
states using a time-reversal-symmetric regularized electron-exchange model
potential fitted to reproduce accurate theoretical results for PsNa and PsK
binding energies. We find a narrow S-wave singlet resonance at 4.58 eV of width
0.002 eV in the Ps-Na system and at 4.77 eV of width 0.003 eV in the Ps-K
system. Singlet P-wave resonances in both systems are found at 5.07 eV of width
0.3 eV. Singlet D-wave structures are found at 5.3 eV in both systems. We also
report results for elastic and Ps-excitation cross sections for Ps scattering
by Na and K.Comment: 9 pages, 5 figures, Accepted in Journal of Physics
The architectures of media power: editing, the newsroom, and urban public space
This paper considers the relation of the newsroom and the city as a lens into the more general relation of production spaces and mediated publics. Leading theoretically from Lee and LiPumaâs (2002) notion of âcultures of circulationâ, and drawing on an ethnography of the Toronto Star, the paper focuses on how media forms circulate and are enacted through particular practices and material settings. With its attention to the urban milieus and orientations of media organizations, this paper exhibits both affinities with but also differences to current interests in the urban architectures of media, which describe and theorize how media get âbuilt intoâ the urban experience more generally. In looking at editing practices situated in the newsroom, an emphasis is placed on the phenomenological appearance of media forms both as objects for material assembly as well as more abstracted subjects of reflexivity, anticipation and purposiveness. Although this is explored with detailed attention to the settings of the newsroom and the city, the paper seeks to also provide insight into the more general question of how publicness is material shaped and sited
Mechanochemical bottom-up synthesis of phosphorus-linked, heptazine-based carbon nitrides using sodium phosphide
Herein, we present the bottom-up, mechanochemical synthesis of phosphorus-bridged heptazine-based carbon nitrides (g-h-PCN). The structure of these materials was determined through a combination of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), 31P magic angle spinning nuclear magnetic resonance (MAS NMR), density functional theory (DFT) and electron energy loss spectroscopy (EELS). Compared to traditional furnace-based techniques, the presented method utilizes milder conditions, as well as shorter reaction times. Both samples of g-h-PCN directly after milling and aging and after an hour of annealing at 300 °C (g-h-PCN300) show a reduction in photoluminescent recombination, as well as a nearly two-time increase in photocurrent under broad spectrum irradiation, which are appealing properties for photocatalysis
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