Decarboxylative aldol reactions of allyl beta-keto esters via heterobimetallic catalysis

Mild and selective heterobimetallic-catalyzed decarboxylative aldol reactions involving allyl beta-keto esters have been developed. The reaction is promoted by Pd(0)- and Yb(III)-DIOP complexes at room temperature and involves the in situ formation of a ketone enolate from allyl beta-keto esters followed by addition of the enolate to aldehydes. The reaction is a new example of heterobimetallic catalysis in which the optimized reaction conditions require the addition of both metals.     

A mild synthesis of bis(indolyl)methanes using a deep eutectic solvent

Deep eutectic solvents (such as the combination of urea and choline chloride) are effective solvents/organocatalysts for the condensation of indole and aryl or alkenyl aldehydes to form bis(indolyl)methanes. The reaction conditions are quite mild and do not require additional Bronsted or Lewis acid catalyst, though they fail with ketones or aliphatic aldehydes. Given the inexpensive, non-toxic, and recyclable nature of the DES, these reaction conditions are simple and highly environmentally friendly.     

Optical detection of cold atoms without spontaneous emission

We have demonstrated nondestructive detection of cold atoms with a probe laser by a frequency-modulation spectroscopy technique. We were able to tune the probe laser and its sidebands far from atomic resonance to reduce the spontaneous emission to less than 0.2 photon per atom during detection.     

Realizing a stable magnetic double-well potential on an atom chip

We discuss design considerations and the realization of a magnetic double-well potential on an atom chip using current-carrying wires. Stability requirements for the trapping potential lead to a typical size of order microns for such a device. We also present experiments using the device to manipulate cold, trapped atoms.     

Fiber-based tunable dispersion compensation

Tunable dispersion has been implemented in various technology platforms, including fiber gratings, planar waveguides, thin film etalons, and bulk optic technologies. This paper will focus on fiber grating based tunable dispersion compensation, because fiber gratings are at present one of the best developed TDC technologies available. The paper is divided into three parts. In the first part we describe grating based TDC technologies and discuss their advantages and disadvantages. We focus on thermally tuned linearly chirped fiber gratings, as these have to date been the most successful grating technology for 40 Gbit/s. We also compare grating TDCs to two other prominent tunable dispersion technologies: thin film etalons and planar waveguide ring resonators. In the second section we describe the techniques used to fabricate high performance dispersion compensation gratings as well as the theory of the primary defect of fiber grating dispersion compensation: group delay ripple (GDR). In the third section we describe the telecom system related issues for tunable gratings, including characterization of grating performance, tunability requirements and results from actual system trials using tunable FBGs.     

Biofuel Combustion Chemistry: From Ethanol to Biodiesel

Biofuels, such as bio‐ethanol, bio‐butanol, and biodiesel, are of increasing interest as alternatives to petroleum‐based transportation fuels because they offer the long‐term promise of fuel‐source regenerability and reduced climatic impact. Current discussions emphasize the processes to make such alternative fuels and fuel additives, the compatibility of these substances with current fuel‐delivery infrastructure and engine performance, and the competition between biofuel and food production. However, the combustion chemistry of the compounds that constitute typical biofuels, including alcohols, ethers, and esters, has not received similar public attention. Herein we highlight some characteristic aspects of the chemical pathways in the combustion of prototypical representatives of potential biofuels. The discussion focuses on the decomposition and oxidation mechanisms and the formation of undesired, harmful, or toxic emissions, with an emphasis on transportation fuels. New insights into the vastly diverse and complex chemical reaction networks of biofuel combustion are enabled by recent experimental investigations and complementary combustion modeling. Understanding key elements of this chemistry is an important step towards the intelligent selection of next‐generation alternative fuels.