Estimation of fixed-point temperatures - A practical approach

Phase transition temperatures can be used for thermometer calibrations in accordance with the ITS-90. For this the thermometer is inserted into a fixed-point cell filled with a highly pure substance. While the substance is melting or freezing the temperature inside the cell remains almost constant and the thermometer measures a plateau in the temperature curve. From this plateau the phase transition temperature needs to be estimated for the calibration of the thermometer. This can be done using different mathematical methods, taking into account various systematic deviations as well as reproducibilities of the results depending on the chosen method, the fixed-point material’s purity and above all the amount of fixed-point material. Hence this article presents results from measurements in miniature fixed-point cells filled with zinc of various purities. The plateau curves were measured at different heating rates and comparatively analysed using five different estimation methods.     

Hydrothermal catalytic production of fuels and chemicals from aquatic biomass

One of the promising avenues for biomass processing is the use of water as a reaction medium for wet or aquatic biomass. This review focuses on the hydrothermal catalytic production of fuels and chemicals from aquatic biomass. Two different regimes for conversion of aquatic biomass in hydrothermal conditions are discussed in detail. The first is hydrothermal liquefaction, and the second is hydrothermal gasification. The goals of these processes are to produce liquid‐fuel‐range hydrocarbons and methane or hydrogen, respectively. The catalytic upgrading of biocrude resulting from noncatalytic liquefaction and the stability and degradation of catalysts in high temperature water are also discussed. The review concludes with a brief discussion of the outlook for and opportunities within the field of hydrothermal catalytic valorization of biomass. Copyright © 2012 Society of Chemical Industry     

The Tensile Response and Fracture Behavior of Four High Strength Specialty Steels

In this technical paper the role of alloy chemistry and secondary processing on tensile response and final fracture behavior of four high strength steels is presented and discussed. The conjoint influence of composition, secondary processing and intrinsic microstructural features in governing stress versus strain response and tensile properties is highlighted. The macroscopic mode and intrinsic microscopic features that result from final fracture of the four high strength steels is discussed. The intrinsic microscopic mechanisms governing tensile deformation and final fracture behavior of the high strength steels are outlined in light of the specific role played by composition, intrinsic microstructural effects and nature of loading.     

Advanced Alumina Composites Reinforced with Titanium-Based Alloys

New (inter)metallic-ceramic composites for high-temperature structural and functional applications are prepared via high-energy ball milling. During compaction by pressureless sintering, dense Al₂O₃/Ti-based alloy composites are formed that consist of inter-connected networks of the ceramic and the (inter)metallic phases. Ti-Al-V/Al₂O₃ and Ti-Al-Nb/Al₂O₃ composites show enhanced damage tolerance over monolithic Al₂O₃, i.e ., fracture toughnesses up to 5.6 MPa·m^0.5 and bending strengths up to 527 MPa. The resistance against abrasive wear is almost doubled with respect to monolithic Al₂O₃ ceramic. Electrical resistivity scales with the ceramic volume fraction and ranges between 0.3 mΩ·cm and 55.1 mΩ·cm, with only a weak temperature dependence ≤700°C.     

Externality, internality, and (in)dispensability of grammatical features in speech production: Evidence from Czech declension and conjugation.

In 3 picture–word experiments, the authors explored the activation of 2 grammatical features in Czech during lexical access: declensional class of nouns and conjugational class of verbs. Experiments 1 and 2 demonstrated congruency effects of declensional and conjugational class, respectively. Picture naming times were reliably longer if the declensional or conjugational classes of the pictures' names and the distractors were incongruent. Experiment 3 explored the origin of the congruency effect in more detail. Congruency effects were obtained for declensional class regardless of whether the target name and the distractor differed in form, speaking for competition at the lemma level. These findings are discussed in comparison with gender congruency effects. The authors propose a differentiation between externally and internally specified features of lemmas, especially with respect to the time course of their activation. Internal features that become available only when the lemma is activated (e.g., gender, declensional or conjugational class of nouns and verbs) can be bypassed or not, depending on the grammatical specification of the earlier available external features (like case or number). Following this argument, supposedly inconsistent findings regarding grammatical gender and declensional or conjugational class can be explained straightforwardly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Raman investigation of single oxidized carbon nanotubes

The oxidation process of single-walled carbon nanotubes via nitric acid treatment was followed by IR-, UV-Vis-NIR, and single bundle Raman spectroscopy. The introduction of functional, oxygen-containing groups is revealed by an additional absorption band at 1725 cm⁻¹, characteristic of carbonyl stretch vibrations. No significant shift of the optical absorption bands could be detected after oxidation. The combination of atomic force microscopy and confocal scanning resonance-enhanced Raman microscopy was used to investigate thin bundles and, eventually, individual nanotubes in detail. These experiments enabled determination of the dependence of the Raman intensity of the G-line (around 1590 cm⁻¹) on the bundle height for both non-oxidized and oxidized tubes. The Raman cross-section of the oxidized tubes was found to be reduced by a factor of ˜4, compared to the pristine tubes. This observation is ascribed to all tubes within a bundle that are oxidized to the same degree.     

An Improved Method for Solution of the Linear Diffusion Equation

Abstract

The diffusion equation is often solved numerically, using finite-difference techniques. The linear one-dimensional diffusion equation may also be solved by the method of variation of parameters, which yields a solution in the form of an infinite series of products of eigenfunctions and time-varying coefficients. The series form of solution has advantages over finite-difference techniques, but the rate of convergence is often not sufficient to yield useful results. This paper presents an alternative form of the series solution for one-dimensional, Cartesian, homogeneous, and temperature-independent property conditions. The methodology, which exhibits excellent convergence, is applicable to several related problems.     

Thermodynamic Measurements in a Strongly Interacting Fermi Gas

Strongly interacting Fermi gases provide a clean and controllable laboratory system for modeling strong interparticle interactions between fermions in nature, from high temperature superconductors to neutron matter and quark-gluon plasmas. Model-independent thermodynamic measurements, which do not require theoretical models for calibrations, are very important for exploring this important system experimentally, as they enable direct tests of predictions based on the best current non-perturbative many-body theories. At Duke University, we use all-optical methods to produce a strongly interacting Fermi gas of spin-1/2-up and spin-1/2-down ⁶Li atoms that is magnetically tuned near a collisional (Feshbach) resonance. We conduct a series of measurements on the thermodynamic properties of this unique quantum gas, including the energy E, entropy S, and sound velocity  c. Our model-independent measurements of E and S enable a precision study of the finite temperature thermodynamics. The E(S) data are directly compared to several recent predictions. The temperature in both the superfluid and normal fluid regime is obtained from the fundamental thermodynamic relation T=? E/? S by parameterizing the E(S) data using two different power laws that are joined with continuous E and T at a certain entropy S _c, where the fit is optimized. We observe a significant change in the scaling of E with S above and below S _c. Taking the fitted value of S _c as an estimate of the critical entropy for a superfluid-normal fluid phase transition in the strongly interacting Fermi gas, we estimate the critical parameters. Our E(S) data are also used to experimentally calibrate the endpoint temperatures obtained for adiabatic sweeps of the magnetic field between the ideal and strongly interacting regimes. This enables the first experimental calibration of the temperature scale used in experiments on fermionic pair condensation, where the ideal Fermi gas temperature is measured before sweeping the magnetic field to the strongly interacting regime. Our calibration shows that the ideal gas temperature measured for the onset of pair condensation corresponds closely to the critical temperature T _c estimated in the strongly interacting regime from the fits to our E(S) data. We also calibrate the empirical temperature employed in studies of the heat capacity and obtain nearly the same T _c. We determine the ground state energy by three different methods, using sound velocity measurements, by extrapolating E(S) to S=0 and by measuring the ratio of the cloud sizes in the strongly and weakly interacting regimes. The results are in very good agreement with recent predictions. Finally, using universal thermodynamic relations, we estimate the chemical potential and heat capacity of the trapped gas from the E(S) data.     

Friction Properties of Fluorinated Carbon Nanodiscs and Nanocones

The tribologic properties of carbon nanodiscs and nanocones and their fluorinated derivatives are investigated and correlated to their structure and chemical composition (atomic fluorine/carbon ratio). Two families of products are studied obtained by fluorination of ill ordered and highly graphitized carbon nanodiscs and nanocones. The studies clearly point out that friction properties of the nanoparticles are strongly dependent on the structure of the initial carbonaceous compounds. Better tribologic behaviour is obtained when the initial nanoparticles structure is highly ordered (graphitized particles). In that case, an optimum of fluorination rate is put in evidence.