Classical and quantum transport through entropic barriers modeled by hardwall hyperboloidal constrictions

We study the quantum transport through entropic barriers induced by hardwall constrictions of hyperboloidal shape in two and three spatial dimensions. Using the separability of the Schrödinger equation and the classical equations of motion for these geometries, we study in detail the quantum transmission probabilities and the associated quantum resonances, and relate them to the classical phase structures which govern the transport through the constrictions. These classical phase structures are compared to the analogous structures which, as has been shown only recently, govern reaction type dynamics in smooth systems. Although the systems studied in this paper are special due their separability they can be taken as a guide to study entropic barriers resulting from constriction geometries that lead to non-separable dynamics.     

The directed genus of the de Bruijn graph

Define the directed genus, Γ(G), of an Eulerian digraph G to be the minimum value of p for which G has a 2-cell embedding in the orientable surface of genus p so that every face of the embedding is bounded by a directed circuit in G. The directed genus of the de Bruijn graph D_n is shown to be

     

Flaxseed Increases Animal Lifespan and Reduces Ovarian Cancer Severity by Toxically Augmenting One-Carbon Metabolism

We used an LC-MS/MS metabolomics approach to investigate one-carbon metabolism in the plasma of flaxseed-fed White Leghorn laying hens (aged 3.5 years). In our study, dietary flaxseed (via the activity of a vitamin B6 antagonist known as “1-amino d-proline”) induced at least 15-fold elevated plasma cystathionine. Surprisingly, plasma homocysteine (Hcy) was stable in flaxseed-fed hens despite such highly elevated cystathionine. To explain stable Hcy, our data suggest accelerated Hcy remethylation via BHMT and MS-B12. Also supporting accelerated Hcy remethylation, we observed elevated S-adenosylmethionine (SAM), an elevated SAM:SAH ratio, and elevated methylthioadenosine (MTA), in flaxseed-fed hens. These results suggest that flaxseed increases SAM biosynthesis and possibly increases polyamine biosynthesis. The following endpoint phenotypes were observed in hens consuming flaxseed: decreased physiological aging, increased empirical lifespan, 9–14% reduced body mass, and improved liver function. Overall, we suggest that flaxseed can protect women from ovarian tumor metastasis by decreasing omental adiposity. We also propose that flaxseed protects cancer patients from cancer-associated cachexia by enhancing liver function.     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of temperature on the enthalpy of mixing of polyelectrolyte solutions

The effect of temperature on the enthalpies of mixing of sodium dextran sulphate and sodium alginate with sodium chloride has been determined and the results compared with the predictions based on the line charge theory. Better agreement between experimental and calculated values is obtained at the higher reaction temperature, as previously found for the enthalpies of dilution. Measurement of the additional enthalpy changes occurring when different alkali metal chlorides are mixed with the sodium salt of the polyanion gives the sequence Li⁺ > Na⁺ > K⁺ in order of decreasing overall endothermic enthalpies of reaction. The same sequence is observed with polysulphates and polycarboxylates at different temperatures.     

Substrate-based design of the first class of angiotensin-converting enzyme-related carboxypeptidase (ACE2) inhibitors

Angiotensin-converting enzyme-related carboxypeptidase (ACE2) is a recently identified zinc metalloprotease with carboxypeptidase activity that was identified using our genomics platform. We implemented a rational design approach to identify potent and selective ACE2 inhibitors. To this end, picomolar inhibitors of ACE2 were designed and synthesized.     

Determination of butyltin species in natural waters using aqueous phase ethylation and off-line room temperature trapping

Monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) were determined in natural water samples by aqueous phase ethylation with sodium tetraethylborate (STEB), room temperature trapping of the resulting volatile derivatives on Tenax TA^®, followed by gas chromatography-quartz furnace atomic absorption spectrometry (GC-QFAAS). Recoveries of butyltin spikes from natural water samples were 90-109% at concentrations of ∼100 ng Sn/l. The method precision at ∼100 ng Sn/l was ≤6% RSD for butyltins spiked into natural waters. The detection limits for 1 l water samples were <1 ng Sn/l for all butyltin species. Sample throughput of the method is high (greater than three samples per hour) due to the two-stage nature of the procedure, which allows derivatisation/trapping and GC-QFAAS quantitation to be performed separately. Off-line trapping is also advantageous as it extends the life of the GC column and quartz furnace to at least 12 months due to minimisation of carry-over of co-purged material.