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The mechanical degradation of polysaccharides was investigated using dynamic high and ultra-high-pressure homogenization (HPH). The objectives were to reduce the molar mass of polymer chains, and simultaneously, the apparent and intrinsic viscosity of polysaccharides in solution. The influence of homogenization pressure (up to 200 MPa) and cycles was compared on polysaccharides with different physical and structure properties: namely, guar gum, hydroxyethylcellulose (HEC), sodium carboxymethylcellulose (Na-CMC), sodium alginate (Na-alginate) and gum arabic. HPH was applied on semi-dilute solutions. The apparent changes in molar mass, gyration radius and intrinsic viscosity were deduced from size exclusion chromatography coupled on-line with multi-angle laser light scattering, differential viscometer detector and differential refractive index detector (SEC/MALS/DV/DRI), while the evolution of the critical overlap concentration (C∗) was obtained by viscosimetry. A method based on a succession of homogenization cycles and polymer pre-concentration steps was developed to determine the minimum molar mass achieved at constant pressure. Molar mass, and intrinsic viscosity were shown to fall simultaneously while logically C∗ increased during HPH for all polysaccharides, except gum arabic, probably because of its globular and branched structure. This highlights that the differences of polysaccharide structures and conformation (linear, branched…) exhibit a stronger impact on HPH treatments than polymer charge or molar mass. Finally, via an empirical approach linking the decrease of both molar masses and viscosities, we have evidenced a specific scaling exponent that should characterize the flexibility of the treated polymer (i.e. its ability to be degraded by HPH). 相似文献
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Adrián E. Yuchechen S. Gabriela Lakkis Pablo O. Canziani 《International journal of remote sensing》2017,38(12):3483-3501
Annual anomalies of Lambertian equivalent reflectivity (LER) retrieved from the total ozone mapping spectrometer spanning the period November 1978–November 2005 were studied in the Southern Hemisphere, in a region bounded by 0° S and 60° S, and their trends were estimated. With the exception of few regions where the variable may represent the contribution of both cloudiness and snow, trends in LER anomalies provided an evolution of total cloudiness. On average, the study region experienced a net increase in LER values of 0.78 reflectivity units (RU) decade?1; if only significant trend values are considered this figure increased to 1.18 RU decade?1. The region that showed the largest upward trend, up to 4 RU decade?1, was located over the eastern Pacific, off the coasts of Chile and Peru, where the presence of marine stratocumulus is frequent. Despite the overall positive trend there were regions that yielded a negative one, most notably the tropical latitudes of South America and Africa. The yearly zonal means also showed a positive trend at all latitudes, but significance occurred beyond 20° S only. Correlation maps between LER anomalies and five different circulation indices were also introduced. The indices with the highest and lowest number of significant correlation values were the Madden–Julian oscillation at 70° E and the quasi-biennial Oscillation, respectively. 相似文献
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We examined whether IL-2 regulates alloimmune responses by studying allograft survival in wild-type (IL-2+/+) and IL-2 gene-knockout (IL-2-/-) mice. The acute rejection of vascularized, cardiac allografts and the generation of allospecific CTLs were not impaired in the absence of IL-2. In contrast, blocking the B7-CD28 T cell costimulation pathway with CTLA4Ig induced long-term allograft survival (> 100 days) in IL-2+/+ recipients but failed to do so in IL-2-/- mice or in wild-type mice that had been treated with IL-2-neutralizing Ab around the time of transplantation. Allografts rejected by IL-2-/- recipients exhibited extensive mononuclear cell infiltrates despite CTLA4Ig administration. In vivo allostimulation in the absence of IL-2 led to exaggerated T lymphocyte proliferation and impaired apoptosis of activated T cells in untreated and CTLA4Ig-treated mice. These findings indicate that endogenous IL-2 is required for the induction of long-term allograft survival, and that IL-2 regulates alloimmune responses by preparing activated T lymphocytes for alloantigen-induced apoptosis. 相似文献
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El Assad S. Lakkis I. Saillard J. 《Antennas and Propagation, IEEE Transactions on》1993,41(5):620-624
Using the physical optics approximation, the radar image of a target can be constructed from a knowledge of the monostatic backscattered field or hologram for all frequencies and all aspects angles. The target image is the two-dimensional Fourier transform of the hologram. This is based on the same principle as conventional holography. In the near-field the image is computed by the coherent summation of back-projected range responses which are derived from complex impulse responses. Consequently, the image can be interpreted as a tomographic reconstruction. If the target is within the antenna beam at each radar position in the linear synthetic-aperture radar (SAR) geometry, then the algorithm for the coherent summation of impulse response derivatives (IRDs) can be applied. Experimental results for the near-field of a wheat field and a Peugeot 504 automobile are presented to verify the effectiveness of the method 相似文献
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Wireless Networks - The Internet of Things (IoT) technology has recently experienced popularity and growth in every facet of life, and it has been applied to every industry in recent years. The... 相似文献
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SF Nagueh NM Lakkis KJ Middleton D Killip WA Zoghbi MA Qui?ones WH Spencer 《Canadian Metallurgical Quarterly》1999,99(3):344-347
BACKGROUND: Nonsurgical septal reduction therapy (NSRT) decreases left ventricular outflow tract (LVOT) gradient and improves symptoms in patients with hypertrophic obstructive cardiomyopathy (HOCM). NSRT effects on LV/left ventricular diastolic function are currently unknown. METHODS AND RESULTS: HOCM patients (n=29) had Doppler echocardiography at baseline and 6 months after NSRT to evaluate changes in LV volume, pre-A-wave pressure, early diastolic mitral annulus velocity (Ea) by tissue Doppler, and tau. At 6 months, a significant reduction in LVOT gradient (from 53.6+/-15 to 6+/-5 mm Hg; P<0.001) was accompanied by improvement in exercise duration (from 284+/-147 to 408+/-178 seconds; P=0.04) and New York Health Association class (from III to I; P<0.001). Pre-A pressure (18+/-6 to 14+/-5 mm Hg; P<0.01) and tau (62+/-8 to 51+/-8 ms; P<0.01) decreased, whereas Ea (5.8+/-1.8 to 8+/-1.8 cml/s; P<0.01) and LV end-diastolic volume (117+/-16 to 130+/-22 mL; P<0.01) increased. CONCLUSIONS: NSRT improves LV relaxation and compliance, which contributes to the symptomatic relief seen at 6 months. 相似文献
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F. Moukalled R. Nuwayhid I. Lakkis 《Numerical Heat Transfer, Part A: Applications》2013,63(6):687-705
Steady and unsteady heat transfer in a radially diluted and centrally cooled nuclear fuel rod are investigated numerically. The nuclear fuel cell is radially diluted by the addition of a non-heat-generating material of high melting point, high specific heat, and high resistance to oxidation and ignition, with the intention of increasing its time delay before melting, when convection is totally lost. Results show a great reduction in the maximum wall temperature under steady operation and a substantial increase in the time delay under transient conditions, with its value increasing with increasing the amount of added diluent. Moreover, results indicate the presence of an optimum value of the ratio of inner to outer channel flow rates for which the maximum inner and outer wall temperatures are minimum. Finally, the distribution of the added diluent is shown to mildly affect the steady and unsteady performance of the reactor. 相似文献
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The synergic extraction of Co(ll) and Ni(Il) with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP) in presence of crown-ether (Cw) 18C6 or DC18C6 (cis-syn-cis and cis-anti-cis isomers) in toluene from 1M chloride medium is quantitatively described. A slope analysis of the distribution curves shows that the composition of the extracted species depends on the cations found in the aqueous solution : from a LiCl or (CH3.)NC14 solution, the extracted species are M(PMBP) 2.Cw (M = Co, Ni) whereas the KCw+,M(PMBP)3 ion pair is extracted from 1M KC1 solution. In the two cases, higher D-values in extraction with DC18C6 are only due to a poorer lipophilicity of 18C6; both ethers are weaker synergists than lipophilic ammonium salts. 相似文献