Relaxation behaviour at the spin-flop phase transition in the quasi-1D antiferromagnet CsMnCl3·2H2O

The low-frequency relaxation behaviour of the linear-chain antiferromagnet CsMnCl3·2H2O at the spin-flop transition has been determined from dynamic susceptibility measurements on a single crystal placed in direct contact with liquid helium. The experiments were performed between 1.4 and 4.2 K in the frequency range 0.1 Hz–3.0 kHz with a frequency-sweeping SQUID susceptometer. Below Tλ = 2.17 K, the relaxation rate τ−1 manifests an exponential temperature dependence, τ−1 = ω0e−E/kT, where E/k = 3.19±0.04 K is approximately equal to the magnitude of the intrachain exchange interaction constant Ja/k. Above Tλ the apparent deviation from the exponential behaviour has been explained satisfactorily by using the thermal conduction model of relaxation. The field-dependent factor ω0 is directly proportional to the ratio of the adiabatic χs to the isothermal χT susceptibilities

Theoretical investigation of Stokes shifts and reaction pathways

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 38-40).Solar thermal fuels and fluorescent solar concentrators provide two ways in which the energy from the sun can be harnessed and stored. While much progress has been made in recent years, there is still much more to learn about the way that these applications work and more efficient materials are needed to make this a feasible source of renewable energy. Theoretical chemistry is a powerful tool which can provide insight into the processes involved and the properties of materials, allowing us to predict substances that might improve the efficiency of these devices. In this work, we explore how the delta self-consistent field method performs for the calculation of Stokes shifts for conjugated dyes. We also develop a new reaction path finding method which uses a combination of trigonometric functions and information about the initial and final states in the reaction to generate an approximate path. We show that this path finding method works well for several model systems including a seven atom Lennard-Jones cluster. The ability to calculate excited state properties at a reasonably low cost and to find convergent reaction pathways is extremely beneficial for understanding and improving solar devices.by Laken M. Top.S.M

Climate Influences the Content and Chemical Composition of Foliar Tannins in Green and Senesced Tissues of \u3ci\u3eQuercus rubra\u3c/i\u3e

Environmental stresses not only influence production of plant metabolites but could also modify their resorption during leaf senescence. The production-resorption dynamics of polyphenolic tannins, a class of defense compound whose ecological role extends beyond tissue senescence, could amplify the influence of climate on ecosystem processes. We studied the quantity, chemical composition, and tissue-association of tannins in green and freshly-senesced leaves of Quercus rubra exposed to different temperature (Warming and No Warming) and precipitation treatments (Dry, Ambient, Wet) at the Boston-Area Climate Experiment (BACE) in Massachusetts, USA. Climate influenced not only the quantity of tannins, but also their molecular composition and cell-wall associations. Irrespective of climatic treatments, tannin composition in Q. rubra was dominated by condensed tannins (CTs, proanthocyanidins). When exposed to Dry and Ambient*Warm conditions, Q. rubra produced higher quantities of tannins that were less polymerized. In contrast, under favorable conditions (Wet), tannins were produced in lower quantities, but the CTs were more polymerized. Further, even as the overall tissue tannin content declined, the content of hydrolysable tannins (HTs) increased under Wet treatments. The molecular composition of tannins influenced their content in senesced litter. Compared to the green leaves, the content of HTs decreased in senesced leaves across treatments, whereas the CT content was similar between green and senesced leaves in Wet treatments that produced more polymerized tannins. The content of total tannins in senesced leaves was higher in Warming treatments under both dry and ambient precipitation treatments. Our results suggest that, though climate directly influenced the production of tannins in green tissues (and similar patterns were observed in the senesced tissue), the influence of climate on tannin content of senesced tissue was partly mediated by the effect on the chemical composition of tannins. These different climatic impacts on leaves over the course of a growing season may alter forest dynamics, not only in decomposition and nutrient cycling dynamics, but also in herbivory dynamics

Linear differential equations with finite differential Galois group

For a finite irreducible subgroup H⊂PSL(Cn) and an irreducible, H-invariant curve Z⊂P(Cn) such that C(Z)H=C(t), a standard differential operator Lst∈C(t)[d/dt] is constructed. For n=2 this is essentially Klein's work. For n>2 an actual calculation of Lst is done by computing an evaluation of invariants C[X1,…,Xn]H→C(t) and applying a scalar form of a theorem of E. Compoint in a “Procedure”. Also in some cases where Z is unknown evaluations are produced. This new method is tested for n=2 and for three irreducible subgroups of SL3. This supplements [18]. The theory developed here relates to and continues classical work of H.A. Schwarz, G. Fano, F. Klein and A. Hurwitz

Draft genome sequence of Pseudomonas moraviensis R28-S

We report the draft genome sequence of Pseudomonas moraviensis R28-S, isolated from the municipal wastewater treatment plant of Moscow, ID. The strain carries a native mercury resistance plasmid, poorly maintains introduced IncP-1 antibiotic resistance plasmids, and has been useful for studying the evolution of plasmid host range and stability

Metformin:A Narrative Review of Its Potential Benefits for Cardiovascular Disease, Cancer and Dementia

The biguanide metformin has been used as first-line therapy in type 2 diabetes mellitus (T2DM) treatment for several decades. In addition to its glucose-lowering properties and its prevention of weight gain, the landmark UK Prospective Diabetes Study (UKPDS) demonstrated cardioprotective properties in obese T2DM patients. Coupled with a favorable side effect profile and low cost, metformin has become the cornerstone in the treatment of T2DM worldwide. In addition, metformin is increasingly being investigated for its potential anticancer and neuroprotective properties both in T2DM patients and non-diabetic individuals. In the meantime, new drugs with powerful cardioprotective properties have been introduced and compete with metformin for its place in the treatment of T2DM. In this review we will discuss actual insights in the various working mechanisms of metformin and the evidence for its beneficial effects on (the prevention of) cardiovascular disease, cancer and dementia. In addition to observational evidence, emphasis is placed on randomized trials and recent meta-analyses to obtain an up-to-date overview of the use of metformin in clinical practice