Particle number fractionalization of an atomic Fermi-Dirac gas in an optical lattice

We show that a dilute two-species gas of Fermi-Dirac alkali-metal atoms in a periodic optical lattice may exhibit fractionalization of the particle number when the two components are coupled via a coherent electromagnetic field with a topologically nontrivial phase profile. This results in fractional eigenvalues of the spin operator with vanishing fluctuations. The fractional part can be accurately controlled by modifying the effective detuning of the electromagnetic field.     

Preparation of amino acid nanoparticles at varying saturation conditions in an aerosol flow reactor

In this article, we describe the synthesis of new and ion-selective nanofiltration (NF) membranes using polyvinylidene fluoride (PVDF) nanofibers and hyperbranched polyethylenimine (PEI) as building blocks. These new nanofibrous composite (NFC) membranes consist of crosslinked hyperbranched PEI networks supported by PVDF nanofibrous scaffolds that are electrospun onto commercial PVDF microfiltration (MF) membranes. A major objective of our study was to fabricate positively charged NF membranes that can be operated at low pressure with high water flux and improved rejection for monovalent cations. To achieve this, we investigated the effects of crosslinker chemistry on membrane properties (morphology, composition, hydrophobicity, and zeta potential) and membrane performance (salt rejection and permeate flux) in aqueous solutions (2,000?mg/L) of four salts (NaCl, MgCl₂, Na₂SO₄, and MgSO₄) at pH 4, 6, and 8. We found that an NFC?CPVDF membrane with a network of PEI macromolecules crosslinked with trimesoyl chloride has a high water flux (~30?L?m^?2?h^?1) and high rejections for MgCl₂ (~88 %) and NaCl (~65 %) at pH 6 using a pressure of 7?bar. The overall results of our study suggest that PVDF nanofibers and hyperbranched PEI are promising building blocks for the fabrication of high performance NF membranes for water purification.     

Screening the Thermodynamics of Trimethylaluminum‐Hydrolysis Products and Their Co‐Catalytic Performance in Olefin‐Polymerization Catalysis

Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)_n(AlMe₃)_m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe₃ molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co‐catalytic activity in olefin‐polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.     

Modification of Lignins. I. Reaction of Lignins with Chlorophosphazenes

Lignin is a potential raw material for several applications. The immediate future should result in the development of lignin modifications yielding new polymers with special properties such as flame and/or thermal resistance. In this report a new reaction of lignins with chlorophosphazenes is discussed. The effect of different types of lignin and chlorophosphazene oligomers on the properties of the reaction product was investigated. The reactions were found to result in products with flame as well as with a base and acid hydrolitic resistance.     

Changes in the Prevalence of Vocal Symptoms Among Teachers During a Twelve-Year Period

Vocal symptoms and voice disorders among teachers were studied in 1988 using a questionnaire designed to obtain information on six vocal symptoms that had appeared during the past 2 years. Twelve percent of the 478 respondents reported vocal symptoms occurring weekly or more often. The study was repeated using the same questionnaire in 2001. The results of this second study (n=241) indicate that vocal symptoms had increased considerably. Twenty-nine percent of the teachers reported symptoms occurring weekly or more often, and 20% reported two symptoms or more occurring at least once a week, which is significantly more than in 1988. Accordingly, voice disorders are probably a growing problem among teachers. Several factors may explain these increases. In 2001, the teachers complained more often about increases in the size of their classes. Factors that disturbed normal work routines, such as noisy or misbehaving pupils, had also increased significantly. A growing number of misbehaving pupils probably cause increased background noise and stress and, thus, increase the vocal symptoms in teachers.