Hole-depletion of ladders in Sr14_{14}Cu24_{24}O41_{41} induced by correlation effects

The hole distribution in Sr$_{14}$Cu$_{24}$O$_{41}$ is studied by low temperature polarization dependent O K Near-Edge X-ray Absorption Fine Structure measurements and state of the art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semi-empirical models, we show that correlations and antiferromagnetic ordering favor the strong chain hole-attraction. For the remaining small number of holes accommodated on ladders, leg-sites are preferred to rung-sites. The small hole affinity of rung-sites explains naturally the 1D - 2D cross-over in the phase diagram of (La,Y,Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$Comment: 6 pages, 8 figure

WATER DOSAGE USING THE COEFFICIENT OF IRRIGATION

Cilj istraživanja je bio utvrditi koeficijente navodnjavanja, a zatim koristeći koeficijente odrediti početak navodnjavanja, na temelju izračunavanja svakodnevne evapotranspiracije. Koeficijent navodnjavanja predstavlja potrošnju vode (mm) po jednom stupnju srednje temperature zraka (0C). Trogodišnja istraživanja (1999-2000) provedena su u Međimurju, na kulturama: jabuke, šećerne repe i krumpira i na tipu tla semiglej. Navodnjavanje kultura obavljeno je mini rasprskivačima. Obrok navodnjavanja izračunat je standardnom metodom i iznosio je kod jabuke 47,9 mm, a kod šećerne repe i krumpira 36,0 mm. Koeficijent navodnjavanja izračunat je za dekadno razdoblje na temelju sljedećih podataka: vlažnost tla, oborine, srednje dnevne temperature zraka i količina vode dodane navodnjavanjem. Prosječni trogodišnji koeficijent navodnjavanja za jabuku se kretao od 0,16 mm/0C u prvoj dekadi svibnja do 0,40 mm/0C u prvoj dekadi kolovoza, za šećernu repu od 0,10 mm/0C u prvoj dekadi svibnja do 0,23 mm/0C u drugoj dekadi srpnja i za krumpir od 0,11 mm/0C u prvoj dekadi svibnja do 0,21 mm/0C u drugoj dekadi srpnja. Potrošnja vode za pojedini dan može se izračunati množenjem koeficijenta navodnjavanja i srednje dnevne temperature zraka (0C). Kada se zbrajanjem potroši količina vode dodana prethodnim obrokom navodnjavanja, potrebno je ponovno primijeniti navodnjavanje. Određene vrijednosti koeficijenta navodnjavanja mogu se koristiti za određivanje početka navodnjavanja i u širem području s istim ili sličnim pedološkim i klimatskim uvjetima.The goal of the investigations was to determine the onset of irrigation using the coefficient of irrigation, which is based on the calculation of everyday evapotranspiration. The coefficient of irrigation represents the water consumption (mm) per one degree of mean daily air temperature (oC). Three-year investigations (1999-2001) were carried out in Međimurje, on the soil type Calcaric Fluvisol (Anthrosol). Irrigation was applied by means of mini sprinklers. Irrigation rate was calculated by the standard method and amounted to 47.9 mm apple, 36.0 mm for sugarbeet and potato. The coefficient of irrigation was estimated for ten-day periods (decades) according to the data on: soil moisture, precipitation, mean daily air temperature and the amount of water added with irrigation. The average three-year coefficient of irrigation ranged for apple from 0.16 mm/oC in the first decade of May to 0.40 mm/oC in the first decade of August, sugarbeet from 0.10 mm/oC in the first decade of May to 0.23 mm/oC in the second decade of August and for potato from 0.11 mm/oC in the first decade of May to 0.21 mm/oC in the second decade of July. Water consumption for a particular day is calculated by multiplying the coefficient of irrigation by the mean daily air temperature (oC). When, in adding up the consumption of water per days, the previously added irrigation rate is spent, irrigation should be applied again. This practical procedure of determining the onset of irrigation can also be applied in crop production also in a wider area with equal or similar pedological and climatic conditions

Molecular Mechanics and SCF MO Conformational Analysis of Indol-3-ylacetic Acid Phytohormone (Auxin)

Conformational analysis of indol-3-ylacetic acid (IAA)-plant growth hormone has been performed using molecular mechanics and the ab initio SCF MO theory. The equilibrium geometry of IAA has been determined. Relative energies of alternative conformations, their charge distribution, dipole moment and energy barriers between them have been calculated. The position of the carboxyl group relative to the indole ring depends on two torsion angles, Tl(C2-C3-C8-C9) and T2(C3-C8-C9=02). Rotational barriers for these two angles were explored and it emerged that both rotations (about the C3-C8and C8-C9 bonds) can be accomplished in a reasonable time period at room temperature (the barrier height is about 4.6-10.9 (TI) and 1.7-3.8 (T2) kJ/mol respectively, according to ab initio calculations. Ab initio (GAMESS)and molecular mechanics (DISCOVER (CVFF and cff91), SYBYL(TRIPOS) and MM2(87), calculations revealed qualitatively the same shape of potential energy surface (E =f(Tl, T2)). However, energy differences between various conformations depend on the basis set (ab initio calculations) and force field (molecular mechanics) used

Dielectric relaxation of DNA aqueous solutions

We report on a detailed characterization of complex dielectric response of Na-DNA aqueous solutions by means of low-frequency dielectric spectroscopy (40 Hz - 110 MHz). Results reveal two broad relaxation modes of strength 20<\Delta\epsilon_LF<100 and 5<\Delta\epsilon_HF<20, centered at 0.5 kHz<\nu_LF<70 kHz and 0.1 MHz<\nu_HF<15 MHz. The characteristic length scale of the LF process, 50<L_LF<750nm, scales with DNA concentration as c_DNA^{-0.29\pm0.04} and is independent of the ionic strength in the low added salt regime. Conversely, the measured length scale of the LF process does not vary with DNA concentration but depends on the ionic strength of the added salt as I_s^{-1} in the high added salt regime. On the other hand, the characteristic length scale of the HF process, 3<L_HF<50 nm, varyes with DNA concentration as c_DNA^{-0.5} for intermediate and large DNA concentrations. At low DNA concentrations and in the low added salt limit the characteristic length scale of the HF process scales as c_DNA^{-0.33}. We put these results in perspective regarding the integrity of the double stranded form of DNA at low salt conditions as well as regarding the role of different types of counterions in different regimes of dielectric dispersion. We argue that the free DNA counterions are primarily active in the HF relaxation, while the condensed counterions play a role only in the LF relaxation. We also suggest theoretical interpretations for all these length scales in the whole regime of DNA and salt concentrations and discuss their ramifications and limitations.Comment: 15 pages, 9 figure

Sage Extracts as Inhibitors of Steel Corrosion in 4% HCl

In this paper the research of corrosion protection of steel by processing corrosion environment using various concentrations of sage extracts (Salvia officinalis) (0.5 g/dm(3), 1 g/dm(3) and 1.5 g/dm(3)) in a 4% solution of HCl was carried out. Measurements were performed using gravimetric and electrochemical methods (Tafel extrapolation method and electrochemical impedance spectroscopy). The results have showed that sage is recommendable as a possible inhibitor in 4% solutions of HCl. The research also confirms that electrochemical impedance spectroscopy is a reliable method to use for rapid corrosion tests, since the results confirm the gravimetric measurements of corrosion indicators. Determination of corrosion rate and the degree of protection using Tafel diagrams calculated on the basis of corrosion current did not give reliable results. The results show that sage may be used as a "green inhibitor" for protection of steel in a shorter period of time. The degree of protection ranges up to 64.5% for steel 2; however, since sage is environmentally friendly, it is a suitable corrosion inhibitor for shorter periods of time

Using XML and XSLT for flexible elicitation of mental-health risk knowledge

Current tools for assessing risks associated with mental-health problems require assessors to make high-level judgements based on clinical experience. This paper describes how new technologies can enhance qualitative research methods to identify lower-level cues underlying these judgements, which can be collected by people without a specialist mental-health background. Methods and evolving results: Content analysis of interviews with 46 multidisciplinary mental-health experts exposed the cues and their interrelationships, which were represented by a mind map using software that stores maps as XML. All 46 mind maps were integrated into a single XML knowledge structure and analysed by a Lisp program to generate quantitative information about the numbers of experts associated with each part of it. The knowledge was refined by the experts, using software developed in Flash to record their collective views within the XML itself. These views specified how the XML should be transformed by XSLT, a technology for rendering XML, which resulted in a validated hierarchical knowledge structure associating patient cues with risks. Conclusions: Changing knowledge elicitation requirements were accommodated by flexible transformations of XML data using XSLT, which also facilitated generation of multiple data-gathering tools suiting different assessment circumstances and levels of mental-health knowledge

Magnetic field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional tau phase organic conductors

We present an electrical transport study of the 2-dimensional (2D) organic conductor tau-(P-(S,S)-DMEDT-TTF)_2(AuBr)_2(AuBr_2)_y (y = 0.75) at low temperatures and high magnetic fields. The inter-plane resistivity rho_zz increases with decreasing temperature, with the exception of a slight anomaly at 12 K. Under a magnetic field B, both rho_zz and the in-plane resistivity plane rho_xx show a pronounced negative and hysteretic magnetoresistance with Shubnikov de Haas (SdH)oscillations being observed in some (high quality)samples above 15 T. Contrary to the predicted single, star-shaped, closed orbit Fermi surface from band structure calculations (with an expected approximate area of 12.5% of A_FBZ), two fundamental frequencies F_l and F_h are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the area of the first Brillouin zone(A_FBZ), with effective masses F_l = 4.0 +/- 0.5 and F_h = 7.3 +/- 0.1. The angular dependence, in tilted magnetic fields of F_l and F_h, reveals the 2D character of the FS and Angular dependent magnetoresistance (AMRO) further suggests a FS which is strictly 2-D where the inter-plane hopping t_c is virtually absent or incoherent. The Hall constant R_xy is field independent, and the Hall mobility increases by a factor of 3 under moderate magnetic fields. Our observations suggest a unique physical situation where a stable 2D Fermi liquid state in the molecular layers are incoherently coupled along the least conducting direction. The magnetic field not only reduces the inelastic scattering between the 2D metallic layers, but it also reveals the incoherent nature of interplane transport in the AMRO spectrum. The apparent ferromagnetism of the hysteretic magnetoresistance remains an unsolved problem.Comment: 33 pages, 11 figure

Inhomogeneous superconductivity in organic conductors: role of disorder and magnetic field

Several experimental studies have shown the presence of spatially inhomogeneous phase coexistence of superconducting and non superconducting domains in low dimensional organic superconductors. The superconducting properties of these systems are found to be strongly dependent on the amount of disorder introduced in the sample regardless of its origin. The suppression of the superconducting transition temperature $T_c$ shows clear discrepancy with the result expected from the Abrikosov-Gor'kov law giving the behavior of $T_c$ with impurities. Based on the time dependent Ginzburg-Landau theory, we derive a model to account for the striking feature of $T_c$ in organic superconductors for different types of disorder by considering the segregated texture of the system. We show that the calculated $T_c$ quantitatively agrees with experiments. We also focus on the role of superconducting fluctuations on the upper critical fields $H_{c2}$ of layered superconductors showing slab structure where superconducting domains are sandwiched by non-superconducting regions. We found that $H_{c2}$ may be strongly enhanced by such fluctuations.Comment: to appear in Journal of Physics: Condensed Matte