Network externalities in a dynamic monopoly

We reconsider the role of network externalities in a dynamic spatial monopoly where the firm must invest in order to accumulate capacity, while consumers may have either linear or quadratic preferences. We (1) characterise saddle point equilibria, (2) prove that the extent of market coverage is increasing in the network effect and (3) unlike the existing static literature on the same problem, the monopolist may not make introductory price offers. Then, we briefly deal with the socially optimal solution, showing that, in general, a planner would serve more consumers than a profit-seeking monopolist.      

Chemoenzymatic synthesis of conduritol analogues

Several conduritol and conduramine analogues have been synthesized from β-substituted naphthalenes via a chemoenzymatic approach, in a high regio- and stereocontrolled way.     

A chemoselective deprotection of trimethylsilyl acetylenes catalyzed by silver salts

Trimethylsilyl acetylenes can be selectively deprotected in the presence of a catalytic amount of silver salts. AgNO₃ and AgOTf proved to be the most effective catalyst in a mixture of methanol, water and dichloromethane. Other functional groups, and especially silyl ethers, are not affected in these conditions.     

C-Metallated reformatsky intermediates. Structure and reactivity.

¹³C-NMR analysis of the Reformatsky intermediates from t-b$\text{u}$tyl-α-bromo acetate, t-b$\text{u}$tyl-α-bromo isobutyrate and t-b$\text{u}$tyl-α-bromo pr$\text{o}$pionate have evidenced C-metallated species. Their ability to act as n$\text{u}$cleophilic reagents under mild conditions and their selectivity towards h$\text{a}$logen-and oxygen containing electrophiles is reported.     

Simultaneous Determination of Trichothecenes A, B, and D in Maize Food Products by LC–MS–MS

Two new methods of analysis, based on liquid chromatography–tandem mass spectrometry, for simultaneous determination of trichothecenes A, B, and D in maize flour and oil have been developed and validated in accordance with European Commission decision 2002/657/EC (recovery, CCα, CCβ, and precision). The trichothecenes were extracted from maize flour by matrix solid-phase dispersion, with recoveries ≥79%, and from maize oil by liquid–liquid extraction, with recoveries ≥78%. Limits of quantitation ranged between 0.03 and 50 μg kg^?1, depending on the electrospray response to each analyte and on the matrix. Monitoring of flour and oil samples with this HPLC–MS–MS method revealed the presence of deoxynivalenol, T-2 toxin, and diacetoxyscirpenol at very low concentrations.     

Microwave assisted digestion of atmospheric aerosol samples followed by inductively coupled plasma mass spectrometry determination of trace elements

A microwave digestion method in a closed vessel was developed for the determination of trace metals in atmospheric aerosols using inductively coupled plasma mass spectrometry (ICP-MS). A recovery study for the elements V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Cd, Sb, and Pb was conducted using multi-elemental standard solutions, NIST 1633b Trace Elements in Coal Fly Ash, and NIST 1648 Urban Particulate Matter. A simple digestion method using only HNO3/H2O2 gave good recoveries (90%-108%) for all elements except Cr in SRM 1648, but yielded low recoveries for SRM 1633b. A more robust method using HNO3/H2O2/HF/H3BO3 yielded higher recoveries (82%-103%) for the lighter elements (V-Zn) in SRM 1633b, and improved the Cr recovery in SRM 1648, but decreased the Se recovery in both SRMs. A comparative analysis of aerosol samples obtained at a remote mountain location Nathiagali, Pakistan (2.5 km above mean sea level), and Mayville, New York, downwind from the highly industrialized Midwestern United States, was carried out using Instrumental Neutron Activation Analysis (INAA) for the elements Cr, Mn, Fe, Co, Zn, As, Se, and Sb. The simple digestion method yielded excellent agreement for Cr, Fe, Zn, As, Se, and Sb, with slopes of the ICP-MS vs. INAA regressions of 0.90-1.00 and R2 values of 0.96-1.00. The regressions for Mn and Co had slopes of 0.82 and 0.84 with R2 values of 0.83 and 0.82, respectively. Addition of HF/H3BO3 did not improve the correlation for any of the elements and degraded the precision somewhat. The technique provides sensitivity and accuracy for trace elements in relatively small aerosol samples used in atmospheric chemistry studies related to SO2 oxidation in cloud droplets. The ability to determine concentrations of a very large number of elements from a single analysis will permit source apportionment of various trace pollutants and hence strategies to control the sources of air pollution. This is particularly important as the health effects of particulate matter are increasingly recognized.     

Heterocycles from amino acids. A novel synthetic approach for imidazo[1,5-a]pyridines and imidazo[1,5-a]quinolines

From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5-a]pyridine ( 3 ) and imidazo[1,5-a]quinoline ( 10 ) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl-1,2,4-triazinone ( 18 ) could be obtained.     

1,3-Dipolar cycloadditions of azomethine ylides with dipolarophiles. II. Synthesis of pyrrolizidines

Substituted pyrrolizidines have been synthesized by 1,3-dipolar cycloaddition of various dipolarophiles with the azomethine ylide generated by treatment of proline with benzaldehyde in dimethylsulfoxide. The regio- and stereochemical outcome of the reaction as well as the stability of the isomers obtained are discussed.     

Zinc (0)-Mediated Formation of Carbon-Carbon Bond from γ-Bromo Crotonate

The coupling reaction of allylic halides with diffferent organometallic reagents has been widely utilized for synthetic purpose.¹ Unfortunately, with the exception of primary halides which give mostly α attack and of hindered substrates which prefer γ attack, the lack of regioselectivity is a great handicap for the generalization of the method.