101 research outputs found
Malnutrition and Associated Risk Factors Among Disabled Children. Special Considerations in the Pediatric Surgical “Fragile” Patients
No full textCrystallization behavior and mechanical properties of poly(aryl ether ether ketone)/poly(ether imide) blends
No full text
Poly(Butylene Terephthalate) Based Composites Containing Alumina Whiskers: Influence of Filler Functionalization on Dielectric Properties
No full textPoly(butylene terephthalate) (PBT) is one of the most widely used semicrystalline thermoplastics polyester because of its superior thermal and mechanical properties, high dimensional stability and excellent processability. In this research PBT-based nanocomposites, including various amounts (up to 10 wt%) of commercial alumina whiskers, have been prepared by using a Brabender internal chamber mixer and analysed in terms of morphological features and dielectric properties. Specific attention has been focused on the effect of the filler functionalization considering 3-glycidoxy propylmethoxysilane (GPS) or 3-methacryloxypropyltrimethoxysilane (MPS) as coupling agents. Tests, performed on compounds filled with neat and functionalized alumina whiskers, show a clear dependence of relative dielectric permittivity , invariance of dissipation factor ( ), and a sensible increase of volume electrical resistivity with the filler’s content and are encouraging for a future introduction of such composites in many electrical applications
Adaptation of intestinal cell membrane enzymes to low temperature in the Antarctic teleost Pagothenia bernacchii
No full texthe enzymatic activity (expressed as milliunits per milligram total proteins) of three intestinal brush-border membrane enzymes, leucine aminopeptidase, alkaline phosphatase and maltase, measured over a range of temperatures between 1.5 and 37-degrees-C, has been found to be much higher in the Antarctic fish Pagothenia bernacchii than in the temperate fish Anguilla anguilla. To explain this experimental observation the apparent Michaelis-Menten constant, the maximal velocity, the activation energy values and the thermal stability of these three enzymes were measured. The apparent Michaelis-Menten constant values of leucine amino peptidase and alkaline phosphatase were different in the intestine mucosal homogenate of the two fish at each measured temperature (from a minimum of 2.5 to a maximum of 37-degrees-C). However, the values found at 2.5-degrees-C for the Antarctic species and 15-degrees-C for the eel where comparable. Furthermore, its value was unchanged in eel intestine apical membranes, both in the presence and without enzyme lipid microenvironment. While the maximal enzymatic activities of the leucine aminopeptidase and maltase did not decrease without their enzyme lipid microenvironment, produced by treatment with Triton X-100, the impairment of alkaline phosphatase maximal activity cannot be significantly differentiated from a non-specific inhibitory effect of the detergent. The activation energy values of leucine amino peptidase, alkaline phosphatase and maltase were lower in the Antarctic fish (11.7, 5.6 and 11.8 kcal.mol-1, respectively) than in the eel (13.6, 7.6 and 13.1 kcal . mol-1, respectively). The thermal stability of alkaline phosphatase and maltase is different in Pagothenia bernacchii and Anguilla anguilla intestinal homogenate
Epoxy-Nanocomposites with Ceramic Reinforcement for Electrical Insulation
No full textCeramic nanoparticles, that is, SiO 2 , TiO 2 ,
and Al 2 O 3 nanoparticles, with increasingly high thermal
conductivity ( k ), represent good candidates for improving
the thermophysical properties of epoxy resins. In this study,
the influence of filler addition on the thermal, mechanical,
and dielectric properties were investigated by means of
differential scanning calorimetry, dynamic mechanical anal-
ysis, and dielectric spectroscopy to measure k , storage and
loss moduli, dielectric permittivity, and volume resistivity.
Moreover, morphological investigations by scanning
electron microscopy were performed to confirm the particle
dispersion into the epoxy matrix. The results show that both
the elastic modulus and glass-transition temperature
increased with particle content. An enhancement of k was
also observed at high filler contents because of the forma-
tion of heat conductive pathways within the matrix. The
nanocomposites’ relative permittivity at 50 Hz was lower,
whereas the dielectric loss was slightly higher compared
with that of the neat epoxy matrix. A decrease in the relative
permittivity with increasing frequency, both for the unfilled
epoxy resin and epoxy–nanocomposites, was observed
Thermo-mechanical and electrical properties of epoxy composites containing ceramic nanofillers
No full textNa(+)-D-glucose cotransport by intestinal BBMVs of the Antarctic fish Trematomus bernacchii.
No full textIntestinal nutrient absorption in fish adapted to low temperature was investigated by isolating, with a Mg2+-precipitation procedure, brush-border membrane vesicles (BBMVs) from intestines of the Antarctic teleost Trematomus bernacchii. In particular, D-glucose transport was analyzed by measuring both 1) fluorescence changes of the electrical potential-sensitive dye 3,3'-diethylthiadicarbocyanine iodide. [DiS-C-2(5)] and 2) intravesicular uptake of D-[C-14]glucose. Results demonstrated that transport of D-glucose across intestinal BBMs of the Antarctic fish is stimulated by the presence of a transmembrane Na+ gradient (out > in) and was specifically inhibited by phloridzin. Furthermore, Na+-dependent D-glucose uptake was strongly enhanced by the presence of an electrical potential (inside-negative) across the membrane. There was a marked difference in temperature dependence of Na+-sugar cotransport between the Antarctic fish and temperate fish, such as the European yellow eel. Na+-dependent D-glucose uptake in T. bernacchii intestinal BBMV reached its maximal rate at -2-0 degrees C (close to fish living temperature) and was exponentially inactivated by incubation at higher temperatures. Kinetic analysis of D-glucose influx indicated the presence of a single Na+-dependent carrier process (apparent maximal carrier-mediated influx = 0.233 +/- 0.009 nmol . mg protein(-1). min(-1); apparent half-saturation constant for carrier-mediated influx - 0.157 +/- 0.026 mmol/l) and a nonsaturable transfer component (apparent diffusional permeability of membrane to the sugar = 0.233 +/- 0.016 mu l . mg protein(-1). min(-1)). The Na+-dependent carrier-mediated mechanism was specific for sugars, since it ws partially inhibited by the presence in the extravesicular medium of other monosaccharides, but not by ascorbic acid or amino acids of different types. These data suggest that in the intestine of Antarctic fish luminal D-glucose transport takes place by a specific Na+-dependent electrogenic secondary active transport working well at subzero temperatures
Membrane lipid and protein adaptations in Antarctic fish
No full textThe success of Notothenioids to survive in the Antarctic involves, among other things, adaptive modifications of proteins and membrane lipids, because only the conservation of their biochemical characteristics and physiological state allows physiological processes to proceed at the low temperature of the Antarctic sea.
Biological membranes are complex structures whose composition (mainly lipid and protein) and arrangement vary widely both between, and within, cells depending upon function (Gennis, 1989).
The phospholipid bilayer holds multiple essential properties for cell membrane function since it:
(i) acts as a physical barrier to solute diVusion;
(ii) regulates the utilization of energy in transmembrane ion gradients;
(iii) mediates the transmembrane movement of specific solutes;
(iv) provides an organizing matrix for the assembly of multicomponent metabolic and signal transduction pathways;
(v) supplies precursors for the generation of lipid-derived second messengers.
Biological membranes may contain different types of proteins related to different cellular functions such as transmembrane transport (channels and carriers), substrate hydrolysis (enzymes), hormone and neurotransmitter recognition (receptors) and protein contributions to the mechanical structure of the membrane. Membrane proteins may be associated with the lipid bilayer in different ways. They have been distinguished as peripheral or integral proteins according to whether they penetrate to a lesser or greater extent into the bilayer and can therefore be isolated by mild or more severe treatments.
The amount of lipid in biological membranes ranges between 20 and 80% of the dry weight and, because of the lipids, particular structural and physical properties of the membrane occur
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