Multiscale Intensity Models for Single Name Credit Derivatives

We study the pricing of defaultable derivatives, such as bonds, bond options, and credit default swaps in the reduced form framework of intensity‐based models. We use regular and singular perturbation expansions on the intensity of default from which we derive approximations for the pricing functions of these derivatives. In particular, we assume an Ornstein‐Uhlenbeck process for the interest rate, and a two‐factor diffusion model for the intensity of default. The approximation allows for computational efficiency in calibrating the model. Finally, empirical evidence on the existence of multiple scales is presented by the calibration of the model on corporate yield curves.     

An efficient highly regioselective synthesis of 2,3,4-trisubstituted pyrroles by cycloaddition of polarized ketene S,S- and N,S-acetals with activated methylene isocyanides

An efficient route for regioselective synthesis of 2,3,4- substituted pyrroles allowing precise control over the introduction of a number of substituents and functionalities (tosyl, carbalkoxy, aryl, cyano, nitro, acetyl, benzoyl, cyclic amines, etc.) at the three positions of the pyrrole ring has been developed via 1,3-dipolar cycloaddition of readily accessible polarized ketene S,S- and N,S-acetals with carbanions derived from activated methylene isocyanides.     

Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite

New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 400 and 520 degrees C were measured on a sample of potassium-carbonate-promoted hydrotalcite, which was a reversible chemisorbent for CO(2). The equilibrium chemisorption isotherms were Langmuirian in the low-pressure region (p(CO(2)) < 0.2 atm) with a large gas-solid interaction parameter. The isotherms deviated from Langmuirian behavior in the higher pressure region. A new analytical model that simultaneously accounted for Langmuirian chemisorption of CO(2) on the adsorbent surface and additional reaction between the gaseous and sorbed CO(2) molecules was proposed to describe the measured equilibrium data. The model was also capable of describing the unique loading dependence of the isosteric heat of chemisorption of CO(2) reported in the literature. The column breakthrough curves for CO(2) sorption from inert N(2) on the chemisorbent could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The CO(2) mass-transfer coefficients were (i) independent of feed gas CO(2) concentration in the range of the data at a given temperature and (ii) a weak function of temperature. The ratio of the mass-transfer zone length to the column length was very low due to highly favorable CO(2) sorption equilibrium.     

2-phenyl-4-bis(methylthio)methyleneoxazol-5-one: versatile template for diversity oriented synthesis of heterocycles

4-Bis(methylthio)methylene-2-phenyloxazol-5-one (1) has been shown to be a versatile template for the synthesis of novel heterocyclic scaffolds. The key protocol involves nucleophilic ring opening of 1 with various primary aliphatic, aromatic amines and diamines to give open-chain amide adducts which are transformed into 4-bis(methylthio)methylene-2-phenyl-1-alkyl/arylimidazol-5-(4H)-ones (5) in good yields in the presence of anhydrous NaOAc/AcOH. Similarly, the amide adducts 4h-i from 3,4-dimethoxyphenylethylamine and tryptamine undergo interesting rearrangement in the presence of POCl(3) to furnish 1-(2-phenyl-5-methylthio-4-thiazolyl)dihydroisoquinoline and β-carboline derivatives 8-9 in good yields. The amide adduct 14 from o-phenylenediamine on exposure to refluxing acetic acid or in the presence of Ag(2)CO(3) affords substituted 3H-1,5-benzodiazepinone, 2-(5-methylthio-2-phenyl-4-oxazolyl)-1H-benzimidazole and trisubstituted oxazole (15-17), whereas the bis-adduct from ethylenediamine yields ethylene bridge tethered bis-imidazole 23 and bis-oxazole 24 under similar reaction conditions. Probable mechanisms for the formation of various products have been suggested.     

Effect of MeV protons on the phase behaviour and thermal stability of polytetrafluoroethylene

Thermomechanical spectroscopy analysis was used to study the influence of accelerated protons on the molecular-topological properties of polytetrafluoroethylene (PTFE). The study showed changes in a wide number of polymer parameters as a result of bombardment with 1, 2 and 4 MeV protons at fluences up to 2 × 10¹⁵ protons/cm². The basic topological process occurring under proton bombardment is amorphicity, as found for γ-irradiation of PTFE. The flow temperature of bombarded PTFE significantly decreases with increasing the fluxes and energy of the accelerated protons. The general process resulting from proton bombardment is cleavage of C-F bonds, leading to formation of “centered” radicals ～CF₂CF · CF₂～ and HF. The thermal stability of bombarded PTFE is below than that of virgin polymer. The rate of thermal destruction noticeably increases and the temperature of the initiation of effective thermal decomposition decreases after bombardment. The gaseous products generated during thermal destruction of the bombarded and virgin PTFE are similar.     

Highlights of non-equilibrium,non-isobaric,non-isothermal desorption of nitrogen from a LiX zeolite column by rapid pressure reduction and rapid purge by oxygen

The effects of adsorption kinetics, column pressure drop, gas phase mass and heat dispersions, gas–solid heat transfer resistance, and adsorber adiabaticity on desorption of N₂ from a LiX zeolite column by O₂ purge as well as pressurization–depressurization of the column using pure N₂ were recently studied using a numerical model of these processes [Chai et al. in Ind Eng Chem Res 50:8703, 2011, Chai et al. in Adsorption 18:87, 2012, Chai et al. in AIChE J 59:365 2013; Rama Rao et al. in Adsorption 2013]. The role of adsorbent particle size and column length to diameter ratio in determining the durations and efficiency of these processes were also investigated. These studies revealed several important limiting and optimum conditions for optimum operation of these processes which can be useful in design of a practical rapid pressure swing adsorption (RPSA) process for medical oxygen concentrator (MOC) application. The purpose of this short review article is to consolidate and re-emphasize these important results in a single article to be used as a guideline for design of a RPSA-MOC unit.     

Iron(III) Catecholates for Cellular Imaging and Photocytotoxicity in Red Light

Iron(III) complexes [Fe( L )( L′ )(NO₃)]—in which L is phenyl‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 1 ), (anthracen‐9‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 2 ), (pyreny‐1‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 3 – 5 ), and L′ is catecholate ( 1 – 3 ), 4‐tert‐butyl catecholate ( 4 ), and 4‐(2‐aminoethyl)‐benzene‐1,2‐diolate ( 5 )—were synthesized and their photocytotoxic properties examined. The five electron‐paramagnetic complexes displayed a Fe^III/Fe^II redox couple near ?0.4 V versus a saturated calomel electrode (SCE) in DMF/0.1 m tetrabutylammonium perchlorate (TBAP). They showed unprecedented photocytotoxicity in red light (600–720 nm) to give IC₅₀≈15 μM in various cell lines by means of apoptosis to generate reactive oxygen species. They were ingested in the nucleus of HeLa and HaCaT cells in 4 h, thereby interacting favorably with calf thymus (ct)‐DNA and photocleaving pUC19 DNA in red light of 785 nm to form hydroxyl radicals.     

Gradient learning in spiking neural networks by dynamic perturbation of conductances

We present a method of estimating the gradient of an objective function with respect to the synaptic weights of a spiking neural network. The method works by measuring the fluctuations in the objective function in response to dynamic perturbation of the membrane conductances of the neurons. It is compatible with recurrent networks of conductance-based model neurons with dynamic synapses. The method can be interpreted as a biologically plausible synaptic learning rule, if the dynamic perturbations are generated by a special class of "empiric" synapses driven by random spike trains from an external source.     

Functionalized magnesium organometallics as versatile intermediates for the synthesis of polyfunctional heterocycles

In the last few years, we have demonstrated that the halogen/magnesium-exchange reaction is a unique method for preparing a variety of new functionalized aryl, alkenyl, heteroaryl magnesium compounds which has considerably extended the range of functionalized Grignard reagents available for synthetic purposes. A variety of functional groups such as an ester, nitrile, iodide, imine and even sensitive groups like nitro, hydroxyl and boronic ester can be tolerated in these organomagnesium compounds. We wish to describe the application of this halogen/magnesium-exchange reaction for the preparation of a broad range of five- and six-membered functionalized heteroaryl magnesium compounds and their reactions with various electrophiles providing a new entry to a range of polyfunctional heterocycles such as thiophene, furan, pyrrole, imidazole, thiazole, antipyrine, pyridine, quinoline and uracil derivatives.