Femtosecond single-mode diode-pumped Cr:LiSAF laser mode-locked with single-walled carbon nanotubes

A low threshold Cr:LiSAF laser pumped with an inexpensive single-mode laser diode emitting 120 mW was passively mode-locked with a novel ultrafast saturable absorber mirror based on single-walled carbon nanotubes (SWCNT-SAM). Pulses as short as 122 fs were achieved, tunable across 14 nm. A second pump diode coupled in polarization allowed to shorten the pulse duration to 106 fs, with up to 24-mW output power.     

Self‐Assembly of Aminocyclopropenium Salts: En Route to Deltic Ionic Liquid Crystals

Aminocyclopropenium ions have raised much attention as organocatalysts and redox active polymers. However, the self‐assembly of amphiphilic aminocyclopropenium ions remains challenging. The first deltic ionic liquid crystals based on aminocyclopropenium ions have been developed. Differential scanning calorimetry, polarizing optical microscopy and X‐ray diffraction provided insight into the unique self‐assembly and nanosegregation of these liquid crystals. While the combination of small headgroups with linear p‐alkoxyphenyl units led to bilayer‐type smectic mesophases, wedge‐shaped units resulted in columnar mesophases. Upon increasing the size and polyphilicity of the aminocyclopropenium headgroup, a lamellar phase was formed.     

Structural effects responsible for stability and solvolytic reactivity of sulfonium ions

The solvolysis rates of X‐substituted benzhydryltetrahydrothiophenium ions ( 1 ) in pure and aqueous alcohols were determined at 25 °C and compared with the rates of the corresponding benzhydryldimethylsulfonium ions ( 2 ). The linear free energy relationship equation log k = s_f(E_f + N_f) has been used to relate quantitatively the leaving group abilities of tetrahydrothiophene (THT) and dimethyl sulfide (Me₂S). It has been demonstrated that although generating a stronger base by heterolysis, substrates 1 solvolyze over lower barriers than 2 . Steric and electronic influences that determine the relative reactivities of sulfonium salts have been examined computationally at B3LYP level of theory by calculating the energy of exchange of electrofuges with different substituents between THT and dimethyl sulfide. Because of more efficiently delocalized positive charge in THT moiety, tetrahydrothiophenium ions are more stable than the corresponding dimethylsulfonium ions, regardless of an electrofuge. The Hammond–Leffler coefficient is negative (α < 0) for the rate determining heterolysis of sulfonium salts 1 and 2 . Copyright © 2011 John Wiley & Sons, Ltd.     

Absorption of ammonia in the melt of ammonium nitrate

The paper deals with the absorption of ammonia in a model fertilizer of ammonium nitrate. Volumetric overall mass transfer coefficient quantitatively characterizing the process was estimated on the basis of experimental data and kinetics modeling. The volumetric overall mass transfer coefficient depends on the temperature, content of water in the fertilizer and hydrodynamic conditions. Different hydrodynamic conditions were simulated by different speeds of the propeller stirrer. The empirical equation describing the volumetric overall mass transfer coefficient was proposed.     

Formic Acid,a Ubiquitous but Overlooked Component of the Early Earth Atmosphere

Terrestrial volcanism has been one of the dominant geological forces shaping our planet since its earliest existence. Its associated phenomena, like atmospheric lightning and hydrothermal activity, provide a rich energy reservoir for chemical syntheses. Based on our laboratory simulations, we propose that on the early Earth volcanic activity inevitably led to a remarkable production of formic acid through various independent reaction channels. Large-scale availability of atmospheric formic acid supports the idea of the high-temperature accumulation of formamide in this primordial environment.     

Plane rotations and Hamilton—Dirac mechanics

Canonical formalism for SO(2) is developed. This group can be seen as a toy model of the Hamilton-Dirac mechanics with constraints. The Lagrangian and Hamiltonian are explicitly constructed and their physical interpretations are given. The Euler-Lagrange and Hamiltonian canonical equations coincide with the Lie equations. It is shown that the constraints satisfy CCR. Consistency of the constraints is checked. Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005.