Origin of stability of the high-temperature, low-pressure Rh2O3 III form of rhodium sesquioxide

We present a first principles study of the equilibrium structures and relative thermodynamic stability of the three observed polymorphs of rhodium(III) sesquioxide. The thermodynamic Gibbs free energies for each phase are calculated as a function of P and T based on the electronic total energy, as well as vibrational energy and vibrational entropy contributions in the local harmonic (LH) approximation. The results confirm that Rh₂O₃ I is a low-temperature, low-pressure form and Rh₂O₃ II is a high-pressure form. A breakdown in the LH approximation at high T is then discussed and to address this breakdown an empirically corrected local harmonic (ECLH) approximation is introduced. ECLH demonstrates that the high-temperature, low-pressure form Rh₂O₃ III is entropically stabilized and produces a partitioning of phase space that is consistent with published experimental investigations.     

Free-Radical Reaction of 2-Vinylcyclopropane-1,1-dicarboxylate with Alkynes

A free-radical reaction of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate with electron rich alkynes giving cyclopentene systems is described. This reaction can be achieved with p-toluenesulfonyl chloride and phenyldisulfide as radical precursors.     

EPR studies of phosphine photofragments in cancrinite matrix at 77K

The far-uv photolysis of phosphine sorbed in cancrinite matrix at 77 K has been studied by epr spectroscopy. Cancrinite is demonstrated to stabilise the photolytically generated radicals ·PH₂, ·P and ·H. Computer simulation of the entire lineshapes has been employed to assess the spin Hamiltonian parameters for both ·PH₂ and ·P. The intensity distribution pattern of the ·PH₂ spectrum at 77 K is indicative of a thermally-equilibrated population of rotational states of this radical in its matrix environment. The similarity of the epr data of ·PH₂ trapped in cancrinite to that isolated in rare gas matrices, as well as theisotropic nature of the³¹P and¹H hyperfine couplings in the former situation, suggest that ·PH₂ is trapped in pseudospherical cavities of cancrinite with minimal matrix perturbations. Marked departures are observed for theg- andA- values of cancrinite-trapped P atoms as compared with the gasphase counterparts.     

纺织品中游离甲醛含量的高效液相色谱法测定

建立了纺织品中游离甲醛的高效液相色谱检测法,采用SinoChrom ODS-BP色谱柱(250×4.6 mm i.d.,5μm),流动相为甲醇-水(70∶30,V/V),流速1.0 mL/min,检测波长360 nm。通过正交试验优化了甲醛衍生条件,应用F检验和t检验证实了本方法的准确性。方法相对标准偏差(RSD)为2.53%,回收率在95.0%~102.7%范围。     

Macroreticular Phenolic Cationites

Macroreticular cation exchangers can be prepared by polymerizing sulfonated phenols with formaldehyde under acidic conditions. The resins are highly porous with large surface areas. Their properties compare well with those based on styrene and divinylbenzene copolymers.     

Effect of Blowing Agent Type in Rigid Polyurethane Foam

Rigid polyurethane foams have been fabricated from polymeric MDI and polypropylene glycols (PPG) synthesized with two different initiator compositions using two different types of blowing agents, viz., the conventional HCFC 141b and environmently friendly HFC 365 mfc. It was found that the two blowing agents gave identically the same cream time, gel time, and tack‐free time. The HFC 365 mfc gave foams with smaller cell size, greater core density and compression strength, whereas HCFC 141b gave better dimensional stability and thermal insulation. For the same type of blowing agent, the initiator containing more toluene diamine gave greater core density, compression strength and thermal insulation     

Statistical Interaction Description of Pauli Crystals in 2D Systems of Harmonically Confined Fermions

It is conjectured that the Pauli exclusion principle alone may be responsible for a particular geometric arrangement of confined systems of identical fermions even when there is no interaction between them. These geometric structures, called Pauli crystals, are predicted for a two‐dimensional (2D) system of free fermions under harmonic confinement. In this work, the possibility of this outcome is pursued and a theoretical model is considered that may capture both qualitatively and quantitatively, the key features of the abovementioned setup. The results for $N=3$ and 6 particles show that the minimum energy configuration corresponds to and is in good quantitative agreement with the reported values of Pauli crystals seen in single‐shot imaging data obtained via the configuration density technique. Numerical results for larger systems of $N=15$ and 30 particles show that the crystalline configurations observed are not the same as the classical Wigner crystal structures that emerge should the confined charged particles interact with a Coulomb potential. An important question floated is whether such crystalline structures do really exist in a quantum system or whether they are artifacts of the methods used to analyze them.     

Free vibration characteristics of a functionally graded beam by finite element method

This paper presents the dynamic characteristics of functionally graded beam with material graduation in axially or transversally through the thickness based on the power law. The present model is more effective for replacing the non-uniform geometrical beam with axially or transversally uniform geometrical graded beam. The system of equations of motion is derived by using the principle of virtual work under the assumptions of the Euler–Bernoulli beam theory. The finite element method is employed to discretize the model and obtain a numerical approximation of the motion equation. The model has been verified with the previously published works and found a good agreement with them. Numerical results are presented in both tabular and graphical forms to figure out the effects of different material distribution, slenderness ratios, and boundary conditions on the dynamic characteristics of the beam. The above mention effects play very important role on the dynamic behavior of the beam.     

Polyurethanes: Versatile Materials and Sustainable Problem Solvers for Today’s Challenges

Polyurethanes are the only class of polymers that display thermoplastic, elastomeric, and thermoset behavior depending on their chemical and morphological makeup. In addition to compact polyurethanes, foamed variations in particular are very widespread, and they achieve their targeted properties at very low weights. The simple production of sandwich structures and material composites in a single processing step is a key advantage of polyurethane technology. The requirement of energy and resource efficiency increasingly demands lightweight structures. Polyurethanes can serve this requirement by acting as matrix materials or as flexible adhesives for composites. Polyurethanes are indispensable when it comes to high‐quality decorative coatings or maintaining the value of numerous objects. They are extremely adaptable and sustainable problem solvers for today’s challenges facing our society, all of which impose special demands on materials.