Constraints on heterotic M-theory from s-cobordism

We interpret heterotic M-theory in terms of h-cobordism, that is the eleven-manifold is a product of the ten-manifold times an interval is translated into a statement that the former is a cobordism of the latter which is a homotopy equivalence. In the non-simply connected case, which is important for model building, the interpretation is then in terms of s-cobordism, so that the cobordism is a simple-homotopy equivalence. This gives constraints on the possible cobordisms depending on the fundamental groups and hence provides a characterization of possible compactification manifolds using the Whitehead group - a quotient of algebraic K-theory of the integral group ring of the fundamental group - and a distinguished element, the Whitehead torsion. We also consider the effect on the dynamics via diffeomorphisms and general dimensional reduction, and comment on the effect on F-theory compactifications.     

1,1‐Di(9‐fluorenyl)­ethyl acetate,a by‐­product from the acetyl­ation of 9‐fluorenyl­lithium

The preparation of sp‐9‐acetyl­fluorene from the reaction of 9‐­fluorenyl­lithium with acetyl chloride also provided 9‐(1‐acetoxy­ethyl­idene)­fluorene (`di­acetyl­fluorene') and 1,1‐di(9‐fluorenyl)­ethanol, (II), as by‐products recently characterized by X‐ray analysis. A third by‐product, 1,1‐di(9‐fluorenyl)­ethyl acetate, (III), C₃₀H₂₄O₂, has now been unequivocally identified for the first time, and emanates from the acetyl­ation of the oxy­anion of (II). In the asymmetric unit, compound (III) exists as two almost identical structures which differ slightly, but significantly, in conformation. Neither possesses the significant fluorene‐ring bowing or the perpendicularity of the two ring planes exhibited by (II). The angle between the least‐squares planes of the two fluorene rings of (III) is 58.45 (9) and 60.95 (10)°, respectively, for the two conformations, and their corresponding bonding parameters also differ slightly in a number of instances.     

Thermodynamics of Amino Acid Methyl Ester Hydrochlorides—Crown Ether Complexes in Methanol at 25°C

Stability constants, free energies, and enthalpies and entropies of the complexation of L-alanine methyl ester hydrochloride (L-Ala-HCl), L-phenylalanine methyl ester hydrochloride (L-Phe-HCl), and valine methyl ester hydrochloride (L-Val-HCl) with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexano-18-crown-6 (DC18C6), and dicyclohexano-24-crown-8 (DC24C8) in methanol are reported for 20°C. No significant variation in the stability constants and free energies of complexation is observed, indicating that the various crown ethers are poorly selective in binding the amino acids. However, the nature of the crown ether and the amino acid and their pattern of substitution cause a remarkable variation in the enthalpies and entropies of complexation. This indicates a strong enthalpy–entropy compensation effect. The enthalpy–entropy compensation effect for the crown ether complexes of the amino acid methyl ester hydrochlorides reported herein is compared with that of the crown ethers complexes of the amino alcohols and the free amino acid. It is found that the enthalpy–entropy compensation effect holds equally for the three classes of complexes.     

Local equivalence ratio measurements in turbulent partially premixed flames using laser-induced breakdown spectroscopy

One of the most recently applied laser-based techniques in combustion environment is the laser-induced breakdown spectroscopy (LIBS). The technique has been extensively and successfully applied to elemental concentration measurements in solids and liquids. The LIBS signal is much weaker in gases and hence more work is required for quantitative measurements in flames. In the present work we used two orthogonal Nd:YAG lasers that operate at the fundamental wavelength with laser pulse energy of about 100 mJ/pulse. A Princeton-Instruments IMAX ICCD camera attached to a PI-Echelle spectrometer was used for signal detection. The lasers are focused using two 5-cm lenses. Several calibration points have been collected in well defined and homogeneous mixtures of air and fuel in order to be used as references for the measurements in turbulent partially premixed flames. This work shows that the application of the LIBS technique in a turbulent combustion environment is feasible and signal is enhanced by applying an orthogonal dual-pulse arrangement for air–fuel.     

Chromatographic Application on Calixarene Bonded Stationary Phases: A Stability Indicating LC-Method for Determination of Celecoxib in Tablet Formulation

A method is described for extraction and quantification of celecoxib in tablets. The extraction was achieved through centrifugation of the fine powder of the tablets in Acetonitrile (ACN). The extract was examined by LC. The chromatographic separation was carried out on a Caltrex AIII column, a relatively new packing material consisting of silica-bonded calix[8]arene, using isocratic binary mobile phase of ACN and H₂O (55%:45%, v/v). A diode array detector was used at 254 nm for detection. The method was validated for system suitability, linearity, precision, limits of detection and quantitation, specificity, stability and robustness. The limits of detection and quantitation were 0.122 and 0.488 μg mL^?1, respectively. The recovery value of this method was 101.88% and the reproducibility was within 2.08.     

Chromatographic Application on Calixarene Bonded Stationary Phases: A Stability Indicating Method for Simultaneous Determination of Paracetamol, Caffeine and Acetylsalicylic Acid in Excedrin Tablets

A simple, rapid and accurate, routine-LC method is described for simultaneous determination of paracetamol, caffeine and acetylsalicylic acid in a tablet formulation. This study represents a new application for the calixarene stationary phases. The chromatographic separation of the three pharmaceuticals was achieved on a Caltrex BIIE column (250 × 4 mm, 5 μm) using a binary mobile phase of 14% ACN and 86% 50 mM NaH₂PO₄ pH 3.0 at 1 mL min^?1 flow rate. Detection was at 214 nm. Separation was achieved in less than 15 min. The method was validated for system efficiency, linearity, accuracy, precision, limit of detection and quantification, specificity, stability and robustness. The limits of detection were 4.88, 9.77 and 78.13 ng per 10 μL of their injected volumes, respectively. The recovery values of this method were between 94.63 and 101.85 and the reproducibility was within 3.88. The method could also be used for separation and determination of salicylic acid which is considered the most important degradation product of acetylsalicylic acid.     

Column performance of uranyl ion exchange on tin(IV) antimonite hydrous oxide

Column chromatographic technique has been utilized to study the column performance of uranyl ion separation on tin(IV) antimonite hydrous oxide matrix. Different flow rates were applied, at 0.6 ionic strength and pH 3, to evaluate the effect of different flow rate on column breakthrough behaviour. Van Demeeter equation was used to emphasize the optimum column conditions. High equivalent to theoretical plate, breakthrough capacity (Q _0.5) were also calculated.     

Polyamide capsules via soft templating with oil drops—1. Morphological studies of the capsule wall

Poly(terephthalamide) microcapsules can be reproducibly and easily prepared by interfacial polycondensation around emulsion droplets in water. Oil drops of cyclohexane/chloroform mixture stabilized with poly(vinyl alcohol) containing terephthaloylchloride serve as soft template. The interfacial polycondensation starts immediately after addition of an amine mixture (hexamethylenediamine/diethylenetriamine). Light and scanning electron microscopy prove the formation of capsules with size distribution in the range from a few up to 100 μm depending on particular composition of the reaction mixture. The morphology of the capsule wall is characterized by precipitated particles. If instead of pure organic solvents a reactive oil phase is used as template, the capsules can serve in subsequent reactions as templates for the synthesis of composite particles. In this way, styrene can be radically polymerized inside the capsule leading to composite capsules. The capsule morphology is determined by the partition of all components between all phases.     

9‐(1‐Acetoxy­ethyl­idene)­fluorene (`diacetyl­fluorene'), a by‐product from the acetyl­ation of 9‐fluorenyl­lithium

Treatment of 9‐fluorenyl­lithium with acetyl chloride produces 9‐acetyl­fluorene, (I), and several by‐products, among which is `di­acetyl­fluorene', now characterized definitively as 9‐(1‐acetoxy­ethyl­idene)­fluorene [IUPAC name: (1‐fluoren‐9‐yl­idene­)ethyl acetate], (II), C₁₇H₁₄O₂, derived from acetyl­ation of initially formed (I). Various parameters disclose substantial structural distortion within (II) emanating from A^(1,3) strain associated with the 9‐(acetoxy­ethyl­idenyl)­fluorene system.     

以脉冲萃取柱利用三异辛胺从高浓度铀溶液中回收铀

利用三异辛胺（TOA）纯化Gattar小型试验工厂的高浓度铀溶液（洗脱液的铀浓度7 g·L^-1）,研究了脉冲萃取柱的性能。利用实验室级脉冲萃取柱进行了实验室规模的溶剂萃取实验和后续实验。结果表明,在室温、pH=1和有机相与水相的比例（V_O/V_A）约为1.8∶1时,加入二（2-乙基己基）磷酸（D2EHPA）使其与TOA的比例（V_D2EHPA/V_TOA）为2∶3,可使萃取克服Cl^-的抑制效应,提高效率。将结论用于考察试验工厂级萃取柱的流体力学和传质性能,结果表明用脉冲萃取柱萃取铀可以达到97%的萃取效率,具有可行性。