Magnetic properties of nanoscale crystalline maghemite obtained by a new synthetic route

In this work we describe the synthesis and characterization of maghemite nanoparticles obtained by a new synthetic route. The material was synthesized using triethylamine as a coprecipitation agent in the presence of the organic ligand N,N′-bis(3,5-di-tert-butyl-catechol)-2,4-diaminotoluene (LCH₃). Mössbauer spectrum at 4 K shows typical hyperfine parameters of maghemite and Transmission Electron Microscopy images reveal that the nanoparticles have a mean diameter of 3.9 nm and a narrow size distribution. AC magnetic susceptibility in zero field presents an Arrhenius behavior with unreasonable relaxation parameters due to the strong influence of dipolar interaction. In contrast when the measurements are performed in a 1 kOe field, the effect of dipolar interactions becomes negligible and the obtained parameters are in good agreement with the static magnetic properties. The dynamic energy barrier obtained from the AC susceptibility results is larger than the expected from the average size observed by HRTEM results, evidencing the strong influence of the surface contribution to the anisotropy.     

Interface induced crystal structures of dioctyl-terthiophene thin films

Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.     

High-resolution calorimetric study of pb(mg_{1/3}nb_{2/3})o_{3} single crystal

Motivated by the long-standing unresolved enigma of the relaxor ferroelectric ground state, we performed a high-resolution heat capacity and polarization study of the field-induced phase transition in the relaxor ferroelectric single crystal Pb(Mg_{1/3}Nb_{2/3})O_{3} (PMN) oriented along the [110] direction. We show that the discontinuous evolution of polarization as a function of the electric field or temperature is a consequence of a true first order transition from a glassy to ferroelectric state, which is accompanied by an excess heat capacity anomaly and released latent heat. We also find that in a zero field there is no ferroelectric phase transition in bulk PMN at any temperature, indicating that the nonergodic dipolar glass phase persists down to the lowest temperatures.     

Comparative study of the in vitro bioactivities of Bupleurum rigidum and B. fruticescens

Decoctions of the aerial parts of either Bupleurum rigidum or B. fruticescens are equally used in certain parts of Spain for the treatment of topical and musculoskeletal inflammations. In the present paper, their phytochemical profile and pharmacological value has been compared. After chromatographic and spectral analyses we could establish the presence of rutin and absence of chlorogenic acid in B. fruticescens, whilst the contrary applies to B. rigidum, providing a means to chemically differentiate extracts and dry materials from the two species. Their free radical scavenging and antiperoxidative activities were similar, with B. fruticescens being more active overall. The infusions of both Bupleurum species also showed similar anti-inflammatory activity when tested by NF-kappaB assay (40% and 42% at 60 microg x mL(-1)), as well as in a hexosaminidase exocytosis assay (30% at 50 microg x mL(-1)). Antimigratory effects on rat melanoma B16F10 showed significant activity for both infusions, with B. rigidum twice as potent as B. fruticescens, the activity of the latter not being fully explained by its content of rutin. Taking all these results together, we can conclude that, in the selected experimental models, there exist an in vitro bioequivalence of the infusions from both species, which is in agreement with the majority of ethnopharmacological reports.     

Water in planetary and cometary atmospheres: H2O/HDO transmittance and fluorescence models

We developed a modern methodology to retrieve water (H₂O) and deuterated water (HDO) in planetary and cometary atmospheres, and constructed an accurate spectral database that combines theoretical and empirical results. On the basis of a greatly expanded set of spectroscopic parameters, we built a full non-resonance cascade fluorescence model and computed fluorescence efficiencies for H₂O (500 million lines) and HDO (700 million lines). The new line list was also integrated into an advanced terrestrial radiative transfer code (LBLRTM) and adapted to the CO₂ rich atmosphere of Mars, for which we adopted the complex Robert–Bonamy formalism for line shapes. We retrieved water and D/H in the atmospheres of Mars, comet C/2007 W1 (Boattini), and Earth by applying the new formalism to spectra obtained with the high-resolution spectrograph NIRSPEC/Keck II atop Mauna Kea (Hawaii). The new model accurately describes the complex morphology of the water bands and greatly increases the accuracy of the retrieved abundances (and the D/H ratio in water) with respect to previously available models. The new model provides improved agreement of predicted and measured intensities for many H₂O lines already identified in comets, and it identifies several unassigned cometary emission lines as new emission lines of H₂O. The improved spectral accuracy permits retrieval of more accurate rotational temperatures and production rates for cometary water.     

Optimal consumption,training, working time,and leisure over the life cycle

In this paper, we analyze the joint determination of optimal consumption and allocation of time between learning (accumulation of human capital), working for wages (used for consumption and accumulation of financial capital), and leisure. Using Hopf bifurcation theory, we are able to show that cyclical training, working, leisuring, and consumption are optimal under certain constellations of parameters.This research was supported by the Austrian Science Foundation under Contract No. P6601.     

Vibrational study of phase transitions and conductivity mechanism in H3OUO2PO4.3 H2O (HUP)

Infrared and Raman spectra of polycrystalline H₃OUO₂PO₄.3 H₂O (HUP) have been envestigated at various temperatures between 50 K and 300 K. The most temperature sensitive bands corresponding to PO₄ and H₂O librations, U-OPO₃ stretching and OH stretching vibrations indicate four different phases of HUP and allow to propose a phase transition mechanism from a quasiliquid state of protonated species in R.T. phase to a fully ordered crystal below 100 K. Protonic conductivity mechanism of room and low temperature phases is discussed.     

Optimal Pricing of a Product Diffusing in Rich and Poor Populations

We consider a market consisting of two populations, termed rich and poor for convenience. If a product is priced such that it is very expensive for the poor, but affordable to the rich, then it becomes a status symbol for the poor and this makes it more desirable for the poor. At a lower price, the product is affordable by both populations. However, as more of the poor buy the product, it ceases to be a status symbol and becomes less appealing to the rich. We present a two-state nonlinear optimal control problem that aims to obtain profit-maximizing prices over time in this environment. We find that there are three categories of optimal price paths. One is status-symbol pricing with high initial price, declining over time. The other two are mass-market pricing, with price declining in one, and price increasing and then decreasing in the other.     

Simple Monte Carlo and the Metropolis algorithm

We study the integration of functions with respect to an unknown density. Information is available as oracle calls to the integrand and to the non-normalized density function. We are interested in analyzing the integration error of optimal algorithms (or the complexity of the problem) with emphasis on the variability of the weight function. For a corresponding large class of problem instances we show that the complexity grows linearly in the variability, and the simple Monte Carlo method provides an almost optimal algorithm. Under additional geometric restrictions (mainly log-concavity) for the density functions, we establish that a suitable adaptive local Metropolis algorithm is almost optimal and outperforms any non-adaptive algorithm.     

Preparation and nitrosation of 3,4-dimethyl-3-penten-2-one (e)- and (z)-oximes. Formation of 3,3,4,5-tetramethyl-3H-pyrazole 1,2-dioxide and of 2-isoxazoline derivatives

The stereoisomeric (E)- and (Z)-oximes of 3,4-dimethyl-3-penten-2-one were prepared and nitrosated with butyl nitrite in methanol. The (E)-oxime gave 3,3,4,5-tetramethyl-3H-pyrazole 1,2-dioxide in nearly quantitative yield, while the (Z)-oxime reacted less readily, giving a lower yield of the same product, with five other products identified as isoxazoline derivatives. Three of these were 4-hydroxy-, 4-methoxy-, and 4-nitro-3,4,5,5-tetramethyl-2-isoxazoline. The fourth was the O-(3,4,5,5-tetramethyl-2-isoxazolin-4-yl) derivative of the starting (Z)-oxime, and the fifth was 4-methylene-3,5,5-trimethyl-2-isoxazoline.