Palaeoclimate: ocean tides and Heinrich events

Climate varied enormously over the most recent ice age--for example, large pulses of ice-rafted debris, originating mainly from the Labrador Sea, were deposited into the North Atlantic at roughly 7,000-year intervals, with global climatic implications. Here we show that ocean tides within the Labrador Sea were exceptionally large over the period spanning these huge, abrupt ice movements, which are known as Heinrich events. We propose that tides played a catalytic role in liberating iceberg armadas during that time.     

Fractionation of polydisperse colloid with acousto-optically generated potential energy landscapes

The motion of colloidal particles on a periodic optical potential energy landscape in the presence of an external driving force may result in particle separation. In contrast to recent methods of holographic or interferometric generation of such landscapes, we use an acousto-optic deflector to create two-dimensional landscapes. We present what is believed to be the first experimental realization of fractionation with simultaneous sorting of four different sizes of colloidal microparticle into laterally separated parallel laminar streams.     

Oligomerization and cyclization of 1,2-ethanedithiol (EDT), HSCH2CH2SH,by selenium dioxide and iodine

The reaction of 1,2 ethanedithiol (EDT) with selenous acid in water or alcohol leads to selenopolysulfide chains or cycles, (C₂H₄SSeSC₂H₄SS)_n, with randomly distributed  SSeS and  SS moieties. The reaction in water produces incompletely reacted material, which on recrystallization, gives an oligomer corresponding to 5 EDT units (pentamer) as confirmed by molecular mass determination, Se analysis, ¹H- and ⁷⁷Se-NMR spectroscopy. In both the pentamer and cyclic forms the incidence of neighboring  SSeS moieties is higher than that expected statistically. The mechanism for the reaction of thiols with selenous acid provides some rationalization for this observation in as much as neighboring  SSeS groups, or groups that will lead rapidly to neighboring  SSeS groups are formed in general before  SS links can be formed. The Raman spectrum of these products show typical strong SS, SeS, and CS stretching bands at 510, 370, and 730 cm⁻¹. The high frequency of ν_CS is attributed to a preferred gauche conformation at the CS bonds. For comparison, polydisulfides were also prepared from EDT and iodine in methanol. These products consist of at least seven cyclic polymers ranging from the four-membered 1,2-dithietane to higher members. Heating above 100°C in chloroform for several hours gives a solution containing the four lowest molecular mass rings, which on standing for 24 h, precipitate highly insoluble material, which is probably chain or large-ring polymer. Molecular mass determination in camphor indicates that, like yellow sulphur, chain polymers are formed at the melting point of camphor (170°C). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 379–390, 1998     

Copper-catalyzed N-arylation of sulfonamides with aryl bromides under mild conditions

This Letter describes a copper catalyzed sulfonamide coupling reaction with aryl bromides to form N-aryl sulfonamides under mild conditions, including the first examples of Cu-catalyzed sulfonamide coupling at room temperature. The reaction protocol tolerates a broad range of substrates including a variety of primary and secondary sulfonamides and challenging heteroaryl bromides such as 2-bromothiazole.     

Optimized material requirements planning for semiconductor manufacturing

This paper describes a custom operational research algorithm, which is run nightly by IBM to create a material requirements plan for its semiconductor fabrication facility in Vermont, USA. To model alternative manufacturing processes and part substitutions, this application interweaves linear programming and heuristic methods to reap the benefits of each decision technology. At each level of the bills of materials supply chain with complex decision choices to be made, parallel linear programmes are invoked and their results are fed into a material requirements planning (MRP) heuristic, which processes parts through multiple iterations. The results from processing one level of the bills of materials supply chain are exploded to create demand for the next level and the interweaving of the two decision technologies continues. The algorithm creates recommended manufacturing releases and work-in-process priorities. These outputs point out opportunities for improvement in order to satisfy all demands on time. The output can be interpreted with well-known MRP assumptions.     

ParaCEST MRI contrast agents capable of derivatization via"click" chemistry

A comprehensive series of lanthanide chelates has been prepared with a tetrapropargyl DOTAM type ligand. The complexes have been characterized by a combination of (1)H NMR, single-crystal X-ray crystallography, CEST and relaxation studies and have also been evaluated for potential use as paramagnetic chemical exchange saturation transfer (ParaCEST) contrast agents in magnetic resonance imaging (MRI). We demonstrate the functionalization of several chelates by means of alkyne-azide "click" chemistry in which a glucosyl azide is used to produce a tetra-substituted carbohydrate-decorated lanthanide complex. The carbohydrate periphery of the chelates has a potent influence on the CEST properties as described herein.     

Investigating the role of c-Jun N-terminal kinases in the proliferation of Werner syndrome fibroblasts using diaminopyridine inhibitors

To develop more potent small molecules with enhanced free radical scavenger properties, a series of N-substituted isatin derivatives was synthesized, and the cytoprotective effect on the apoptosis of PC12 cells induced by H₂O₂ was screened. All these compounds were found to be active, and N-ethyl isatin was found with the most potent activity of 69.7% protective effect on PC12 cells. Structure-activity relationship analyses showed the bioactivity of N-alkyl isatins decline as the increasing of the chain of the alkyl group, furthermore odd-even effect was found in the activity, which is interesting for further investigation.     

Model and experimental studies for contact angles of surfactant solutions on rough and smooth hydrophobic surfaces

Despite the practical need, no models exist to predict contact angles or wetting mode of surfactant solutions on rough hydrophobic or superhydrophobic surfaces. Using Gibbs' adsorption equation and a literature isotherm, a new model is constructed based on the Wenzel and Cassie equations. Experimental data for aqueous solutions of sodium dodecyl sulfate (SDS) contact angles on smooth Teflon surfaces are fit to estimate values for the adsorption coefficients in the model. Using these coefficients, model predictions for contact angles as a function of topological f (Cassie) and r (Wenzel) factors and SDS concentration are made for different intrinsic contact angles. The model is also used to design/tune surface responses. It is found that: (1) predictions compare favorably to data for SDS solutions on five superhydrophobic surfaces. Further, the model predictions can determine which wetting mode (Wenzel or Cassie) occurred in each experiment. The unpenetrated or partially penetrated Cassie mode was the most common, suggesting that surfactants inhibit the penetration of liquids into rough hydrophobic surfaces. (2) The Wenzel roughness factor, r, amplifies the effect of surfactant adsorption, leading to larger changes in contact angles and promoting total wetting. (3) The Cassie solid area fraction, f, attenuates the lowering of contact angles on rough surfaces. (4) The amplification/attenuation is understood to be due to increased/decreased solid-liquid contact-area.