Search results for "Temperature"
showing 10 items of 3798 documents
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N-isopropylacrylamide)
2003
The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (M w = 1 600 kg/mol) poly(N-isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, T cp decreases steadily with rising polymer concentration up to 10 wt.-%. The application of shear supports phase separation and reduces T cp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected wit…
A thermodynamic study to evidence the alpha,omega-dichloroalkane/ block copolymer mixed aggregates formation: effect of the copolymer architecture.
2006
Abstract The thermodynamics of α , ω -dichloroalkanes in aqueous solutions of (ethylene oxide)11(propylene oxide)16(ethylene oxide)11 (L35) and (propylene oxide)8(ethylene oxide)23(propylene oxide)8 (10R5) was determined at 298 and 305 K. Modeling the experimental data allowed to calculate the standard free energy ( Δ G D o / w ) and the volume ( Δ V D / w ) for the additive–copolymer mixed aggregates formation per additive molecule. Δ G D o / w for Cl2CH2 and Cl2(CH2)2 evidenced that the process is controlled by the forces exercising between the chlorine atoms and the OH groups of the copolymer micelles protruded into the aqueous phase. Cl2(CH2)3 experiences both the hydrophilic and hydrop…
Apparent molar volumes of lithium nitrate in 1-propanol + water in the temperature range from 288.15 to 318.15 K
2002
Abstract Densities of 1-propanol+water+lithium chloride mixtures have been measured with an oscillating-tube densimeter over a large range of concentrations of the salt and 1-propanol at 288.15, 298.15, 308.15, and 318.15 K. From these densities, apparent molar volumes of lithium chloride in 1-propanol+water mixtures have been calculated for each temperature, and apparent molar volumes at infinite dilution have been evaluated. An empirical correlation for partial molar volumes of lithium chloride in 1-propanol+water mixtures with solvent composition and temperature has been derived.
The dynamics of 57Fe nuclei in Fe(II)-DNA and [Fe(II)(1-methyl-2-mercaptoimidazole)2]-DNA condensates.
2002
Abstract Alcoholic solutions of FeCl 2 and Fe II (Hmmi) 2 Cl 2 (Hmmi=1-methyl-2-mercaptoimidazole) induce calf thymus DNA condensation from aqueous solutions buffered at pH 7.4. A 1:1 Fe II –(DNA monomer) stoichiometry is assumed. The 57 Fe Mossbauer hyperfine parameters suggest an octahedral coordination environment, severely distorted, in both Fe II –(DNA monomer) and [Fe II (Hmmi) 2 ]–(DNA monomer) condensates. The dynamic properties of iron nuclei in freeze-dried samples were investigated by means of variable temperature 57 Fe Mossbauer spectroscopy. Mean square displacements, 〈 x 2 〉( T ), were calculated, such as the effective vibrating mass and the Mossbauer lattice temperature of th…
ChemInform Abstract: Synthesis and Magnetic Properties of Bis(μ-hydroxo)bis((2,2′-bipyridyl)copper(II)) Squarate. Crystal Structure of Bis(μ-hydroxo)…
1990
Abstract The compound [Cu2(bipy)2(OH)2](C4O4)·5.5H2O, where bipy and C4O42− correspond to 2,2′-bipyridyl and squarate (dianion of 3,4-dihydroxy-3-cyclo- butene-1,3-dione) respectively, has been synthesized. Its magnetic properties have been investigated in the 2–300 K temperature range. The ground state is a spin-triplet state, with a singlet-triplet separation of 145 cm−1. The EPR powder spectrum confirms the nature of the ground state. Well-formed single crystals of the tetrahydrate, [Cu2(bipy)2(OH)2](C4O4)·4H2O, were grown from aqueous solutions and characterized by X-ray diffraction. The system is triclinic, space group P 1 , with a = 9.022(2), b = 9.040(2), c = 8.409(2) A, α = 103.51(2…
A 45-year sub-annual reconstruction of seawater temperature in the Bay of Brest, France, using the shell oxygen isotope composition of the bivalve Gl…
2020
A reconstruction of sea surface temperature (SST) spanning 45 years (1966–2011) was developed from δ18O obtained from the aragonitic shells of Glycymeris glycymeris, collected from the Bay of Brest, France. Bivalve sampling was undertaken monthly between 2014 and 2015 using a dredge. In total, 401 live specimens and 243 articulated paired valves from dead specimens were collected, of which 24 individuals were used to reconstruct SST. Temperatures determined using the palaeotemperature equation of Royer et al. compared well with observed SST during the growing season between 1998 and 2010 (Pearson’s correlation: p = 0.002, r = 0.760). Furthermore, a significant negative correlation was foun…
Decadal climate variability of the North Sea during the last millennium reconstructed from bivalve shells (Arctica islandica)
2014
Uninterrupted, annually resolved paleoclimate records are crucial to contextualize the current global change. Such information is particularly relevant for the Europe realm for which weather and climate projections are still very challenging if not virtually impossible. This study presents the first precisely dated, annually resolved, multiregional Arctica islandica chronologies from the North Sea which cover the time interval ad 1040–2010 and contain important information on supra-regional climatic conditions (sea surface temperature (SST), ocean productivity, wind stress). Shell growth varied periodically on timescales of 3–8, 12–16, 28–36, 50–80, and 120–240 years, possibly indicating a…
Temperature monitoring in archaeological animal bone samples in the Near East arid area, before, during and after excavation
2008
Summary In order to estimate experimentally the intensity and amplitude of thermal shocks during and after excavation, we monitored temperatures of archaeological bones on the field at three Syrian sites of the arid steppe, Qaramel, Dja'de and Aswad. Water cleaning and sun drying appear to be the most damaging steps, with temperature variations of ca. 11,000 °C/h and 84 °C/h, respectively. Ancient DNA (aDNA) bone samples kept between −7 and +12 °C from their extraction to the lab suffered much lower thermal variations (6 °C/h). Estimation of the temperature variations at different depths in the soil suggests that aDNA has suffered negative thermal conditions shortly after burial and again d…
Study of uniformity of plasmas produced in a wall-stabilized arc
2003
In this contribution the plasma of an arc discharge in a mixture of helium and argon is studied. The gas mixture is introduced uniformly along the arc column between each of the stabilizing plates. From the measured lateral distribution of radiation (HeI, HI, ArI, ArII, NI, FI line intensity and width measurements), after Abel inversion, the radial temperature distributions were obtained at various positions of the arc column. Beside the expected radial temperature gradients, a distinct temperature gradient along the arc column was found.
Temperature at Small Scales: A Lower Limit for a Thermodynamic Description
2011
We analyze the concept of equilibrium temperature in a set of interacting argon atoms, confined in a nanostructure, a zeolite with an intricate distribution of channels through which the atoms may move. The temperature is computed following two procedures: by averaging over the kinetic energy of the particles and over the forces acting on them. It is shown that for external surfaces and for regions which do not fall under the whole pattern of potential energy distribution, smaller than a quarter of a crystal unit cell, both temperatures, kinetic and configurational, show significant differences. The configurational temperature accounts for the different interactions on the particles in the …