Positions Of Transitions Research Articles

Longitudinal zonation pattern in Arabidopsis root tip defined by a multiple structural change algorithm.

Background and Aims The Arabidopsis thaliana root is a key experimental system in developmental biology. Despite its importance, we are still lacking an objective and broadly applicable approach for identification of number and position of developmental domains or zones along the longitudinal axis of the root apex or boundaries between them, which is essential for understanding the mechanisms underlying cell proliferation, elongation and differentiation dynamics during root development. Methods We used a statistics approach, the multiple structural change algorithm (MSC), for estimating the number and position of developmental transitions in the growing portion of the root apex. Once the positions of the transitions between domains and zones were determined, linear models were used to estimate the critical size of dividing cells (LcritD) and other parameters. Key Results The MSC approach enabled identification of three discrete regions in the growing parts of the root that correspond to the proliferation domain (PD), the transition domain (TD) and the elongation zone (EZ). Simultaneous application of the MSC approach and G2-to-M transition (CycB1;1DB:GFP) and endoreduplication (pCCS52A1:GUS) molecular markers confirmed the presence and position of the TD. We also found that the MADS-box gene XAANTAL1 (XAL1) is required for the wild-type (wt) PD increase in length during the first 2weeks of growth. Contrary to wt, in the xal1 loss-of-function mutant the increase and acceleration of root growth were not detected. We also found alterations in LcritD in xal1 compared with wt, which was associated with longer cell cycle duration in the mutant. Conclusions The MSC approach is a useful, objective and versatile tool for identification of the PD, TD and EZ and boundaries between them in the root apices and can be used for the phenotyping of different genetic backgrounds, experimental treatments or developmental changes within a genotype. The tool is publicly available at www.ibiologia.com.mx/MSC_analysis.

Influence of annealing temperature and Sn doping on the optical properties of hematite thin films determined by spectroscopic ellipsometry

Hematite (α-Fe2O3) thin films were prepared by sol-gel route and investigated for application in H2 generation by photo-assisted water splitting. The photoelectrochemical (PEC) performance was shown to increase significantly for films deposited on SnO2:F/glass subjected to high temperature (T) annealing (>750 °C). Strong correlation was found between photogenerated current, donor concentration, and Sn concentration as determined by Mott-Schottky analysis and X-ray photoelectron spectroscopy. The effects of thermal annealing and Sn addition in the resulting microstructure and optical properties of hematite films deposited on fused silica substrates were determined by a combination of structural characterization techniques and spectroscopic ellipsometry. Thermal annealing (>600 °C) induces a higher optical absorption that is associated directly to film densification and grain growth; however, it promotes no changes in the energy positions of the main Fe2O3 electronic transitions. The band gap energy was found to be 2.21 eV and independent of microstructure and of Sn concentration for all studied films. On the other hand, Sn can be incorporated in the Fe2O3 lattice for concentration up to Sn/Fe ∼2%, leading to an increase in energy split of the main absorption peak, attributed to a distortion of the Fe2O3 lattice. For higher concentrations, Sn incorporation leads to a reduction in absorption, associated with higher porosity and the formation of a secondary Sn-rich phase. In summary, the variation in the optical properties induced by thermal annealing and Sn addition cannot account for the order of magnitude increase of the current density generated by photoanodes annealed at high T (>750 °C); thus, it is concluded that the major contribution for the enhanced PEC performance comes from improved electronic properties induced by the n-type doping caused by Sn diffusion from the SnO2:F substrate.

Ground-state ordering of theJ1−J2model on the simple cubic and body-centered cubic lattices

The $J_1$--$J_2$ Heisenberg model is a "canonical" model in the field of quantum magnetism in order to study the interplay between frustration and quantum fluctuations as well as quantum phase transitions driven by frustration. Here we apply the Coupled Cluster Method (CCM) to study the spin-half $J_1$--$J_2$ model with antiferromagnetic nearest-neighbor bonds $J_1 >0$ and next-nearest-neighbor bonds $J_2 >0$ for the simple cubic (SC) and body-centered cubic (BCC) lattices. In particular, we wish to study the ground-state ordering of these systems as a function of the frustration parameter $p=z_2J_2/z_1J_1$, where $z_1$ ($z_2$) is the number of nearest (next-nearest) neighbors. We wish to determine the positions of the phase transitions using the CCM and we aim to resolve the nature of the phase transition points. We consider the ground-state energy, order parameters, spin-spin correlation functions as well as the spin stiffness in order to determine the ground-state phase diagrams of these models. We find a direct first-order phase transition at a value of $p = 0.528$ from a state of nearest-neighbor N\'eel order to next-nearest-neighbor N\'eel order for the BCC lattice. For the SC lattice the situation is more subtle. CCM results for the energy, the order parameter, the spin-spin correlation functions and the spin stiffness indicate that there is no direct first-order transition between ground-state phases with magnetic long-range order, rather it is more likely that two phases with antiferromagnetic long-range are separated by a narrow region of a spin-liquid like quantum phase around $p=0.55$. Thus the strong frustration present in the $J_1$--$J_2$ Heisenberg model on the SC lattice may open a window for an unconventional quantum ground state in this three-dimensional spin model.

Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations.

We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)2···(RSR)n] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals. Linear two-coordination, the most common coordination geometry in mercury chemistry, yields a sharp 2p to 6s + 5d electronic transition. This transition varies in intensity for Hg bonded to thiol groups in macromolecular NOM. The intensity variation is explained by contributions from next-nearest, low-charge, thioether-type RSR ligands at 3.0-3.3 Å from Hg. Thus, Hg in NOM has two strong bonds to thiol S and k additional weak Hg···S contacts, or 2 + k coordination. The calculated stabilization energy is -5 kcal/mol per RSR ligand. Detection of distant ligands beyond the first coordination shell requires precise measurement of, and comparison to, spectra of reference compounds as well as accurate calculation of spectra for representative molecular models. The combined experimental and theoretical approaches described here for Hg can be applied to other closed-shell atoms, such as Ag(I) and Au(I). To facilitate further calculation of XANES spectra, experimental data, a new crystallographic structure of a key mercury thioether complex, Cartesian coordinates of the computed models, and examples of input files are provided as Supporting Information .

Dielectric response and ac-conductivity studies of Gd<sub>2</sub>O<sub>3</sub>- contained K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> piezoelectric ceramics

We report the role of Gd2O3 substitution on the dielectric properties of alkali niobate K0.5Na0.5NbO3 (KNN) ceramics. This system exhibits relaxor behaviour for 0.5 wt% of Gd2O3 in KNN matrix and shows enhanced dielectric permittivity (er = 4147 at T = 628 K) and low loss (Tanδ ~ 0.008) at frequency f = 1 MHz. The position of crystallographic phase transitions of Orthorhombic to Tetragonal (T1) and Tetragonal to Cubic (T2) shifts significantly from 480 K to 413 K and 668 K to 582 K, respectively. The temperature and the frequency dependence of the position of maximum dielectric permittivity Tm obeys the Vogel–Fulcher law, with the attempt frequency f0 = 5.32×1011 Hz, freezing temperature Tf = 598 K and activation energy EA= 0.038 eV for KNN + 0.5 wt% Gd2O3. The temperature dependence of AC-conductivity σac (T) analysis in the range 300 K < T < 600 K reveals the existence of variable range hopping of charge carriers with average hopping length RH in the range 7.93-29.24 nm and 5.55-26.41 nm for ξ = 0 and ξ = 0.5, respectively. The diffuseness exponent ‘γ’ (~1.74) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals the weakly coupled relaxor behavior.

Absorption linelists for HD18O and D2 18O molecules based on the experimental energy levels and calculated intensities

Detailed and accurate absorption linelists are generated for the HD18O and D218O molecules in the 0–9400 cm–1 spectral range. These linelists, known as empirical lists, are based on the experimental energy levels available from the literature and ab initio transition intensities obtained through variational computations. Positions of empirical transitions are determined at a level of the bes t experimental accuracy, and even better in case of weak or blended lines. Average accuracy of calculated intensities is about 10%. Empirical lists of absorption lines of water isotopologues currently replace incomplete or low accuracy experimental data in the canonical databases like HITRAN.

Fluctuation Effects in Phase-Frustrated Multiband Superconductors

In this paper, we compute the phase diagrams of an effective model of a three-dimensional multiband superconductor which is phase-frustrated by interband Josephson couplings. Four different computations are performed and compared: (i) standard mean field theory, (ii) cluster mean field theory, (iii) large-scale Monte Carlo computations including phase fluctuations but no gauge field fluctuations, and (iv) large-scale Monte Carlo computations including phase fluctuations and gauge field fluctuations. Here, phase fluctuations refer to fluctuations in the phases of the components of the superconducting order parameter. Our findings may be summarized as follows: (i) The standard mean field theory treatment fails in locating correctly the positions of the phase transitions, as well as the character of the transitions between the different states. (ii) A cluster mean field calculations taking into account order parameter fluctuations in a local environment improves the results considerably. This shows that phase fluctuations in the superconducting order parameter are important in these three-dimensional systems. The origin of the strong phase fluctuations is frustration due to interband Josephson couplings. However, a novel chiral metallic phase found in previous works using large-scale Monte Carlo computations is not obtained either within the single-site mean field theory or the improved cluster mean field theory of order parameter fluctuations. (iii) Including all phase fluctuations, but no gauge field fluctuations, in the effective model in large-scale Monte Carlo computations yields results essentially in agreement with the cluster mean field calculations. (iv) Including all phase fluctuations and gauge field fluctuations in the effective model in large-scale Monte Carlo computations shows that the inclusion of gauge field fluctuations is crucial in bringing about the novel chiral metallic state in three dimensions.

Dimer formation of perylene: An ultracold spectroscopic and computational study

The electronic spectra of perylene inside helium nanodroplets recorded by the depletion method are presented. The results show two broad peaks in addition to sharp monomer vibronic transitions due to dimer formation. In order to understand the details of the spectra, first the dimer formation is studied by DFT and SCS-MP2 calculations and then the electronic spectra are calculated at the minima of the potential energy surface (PES). Theoretical calculations show that there are two low-lying energetically degenerate dimer structures; namely a parallel displaced one and a rotated stacked one. PES around these minima is very flat with a number of local minima at higher energies which at the experimental temperatures cannot be populated. Even though thermodynamically these two structures are equally populated, dynamical considerations point out that in helium droplet the parallel displaced geometry is encouraged by the natural alignment of the molecules due to the acquired angular momentum following the pick-up process. The calculated spectrum of the parallel displaced geometry predicts the positions of the dimer transitions within 30nm of the experimental spectrum. Furthermore, the difference between the two dimer transitions is accurately predicted to be about 25nm while the experimental difference was about 20nm. Such a small difference could only be detected due to the ultracold conditions helium nanodroplets provided.

Solution of the explosive percolation quest. II. Infinite-order transition produced by the initial distributions of clusters.

We describe the effect of power-law initial distributions of clusters on ordinary percolation and its generalizations, specifically, models of explosive percolation processes based on local optimization. These aggregation processes were shown to exhibit continuous phase transitions if the evolution starts from a set of disconnected nodes. Since the critical exponents of the order parameter in explosive percolation transitions turned out to be very small, these transitions were first believed to be discontinuous. In this article we analyze the evolution starting from clusters of nodes whose sizes are distributed according to a power law. We show that these initial distributions change dramatically the position and order of the phase transitions in these problems. We find a particular initial power-law distribution producing a peculiar effect on explosive percolation, namely, before the emergence of the percolation cluster, the system is in a "critical phase" with an infinite generalized susceptibility. This critical phase is absent in ordinary percolation models with any power-law initial conditions. The transition from the critical phase is an infinite-order phase transition, which resembles the scenario of the Berezinskii-Kosterlitz-Thouless phase transition. We obtain the critical singularity of susceptibility at this peculiar infinite-order transition in explosive percolation. It turns out that susceptibility in this situation does not obey the Curie-Weiss law.

Phase diagrams of DNA-photosensitive surfactant complexes: effect of ionic strength and surfactant structure.

Realization of all-optically controlled and efficient DNA compaction is the major motivation in the study of interactions between DNA and photosensitive surfactants. In this article, using recently published approach of phase diagram construction [Y. Zakrevskyy, P. Cywinski, M. Cywinska, J. Paasche, N. Lomadze, O. Reich, H.-G. Löhmannsroben, and S. Santer, J. Chem. Phys. 140, 044907 (2014)], a strategy for substantial reduction of compaction agent concentration and simultaneous maintaining the light-induced decompaction efficiency is proposed. The role of ionic strength (NaCl concentration), as a very important environmental parameter, and surfactant structure (spacer length) on the changes of positions of phase transitions is investigated. Increase of ionic strength leads to increase of the surfactant concentration needed to compact DNA molecule. However, elongation of the spacer results to substantial reduction of this concentration. DNA compaction by surfactants with longer tails starts to take place in diluted solutions at charge ratios Z < 1 and is driven by azobenzene-aggregation compaction mechanism, which is responsible for efficient decompaction. Comparison of phase diagrams for different DNA-photosensitive surfactant systems allowed explanation and proposal of a strategy to overcome previously reported limitations of the light-induced decompaction for complexes with increasing surfactant hydrophobicity.

L-SHELL DIELECTRONIC SATELLITE TRANSITIONS OF Fe XVII

We have used the relativistic multi-reference Moller-Plesset perturbation theory to calculate the positions of the dielectronic satellite transitions involving doubly excited 3l3l' configurations that are associated with the X-ray spectrum of Fe XVII. A comparison of these positions with the wavelengths employed in astrophysical modeling codes shows discrepancies of up to 36 mA. Inspection of the spectrum of Capella recorded with the high energy transmission grating on the Chandra X-Ray Observatory reveals several features enhanced by Fe XVI lines formed by dielectronic recombination, one of which may be of future diagnostic use as it is fairly well isolated and in large part formed by dielectronic recombination.

Photoluminescence Study on O-plasma Treated ZnO Thin Films

A temperature dependent (10K-290K) photoluminescence (PL) study for two differently prepared ZnO thin films (as-grown and O-plasma treated) is presented. Four characteristic peaks were identified for both samples: (i) neutral donor-bound excitons ( $D^oX$ ), (ii) two electron satellites (TES), (iii) phonon replica of $D^oX$ ( $D^oX$ -1LO), and (iv) donor-acceptor pair transition (DAP). As the sample temperature increased, $D^oX$ -1LO and DAP transitions became indistinct. This was accompanied by newly-rising emission of free electron-acceptor transitions (e, $A^o$ ). The spectral evolution with temperature for as-grown samples also showed the optical emission from free excitons, which became dominant at higher temperatures. Some features related to O-plasma were identified in PL spectra: (i) different positions of TES transitions (28meV lower than $D^oX$ for as-grown samples and 35meV for O-plasma treated samples), (ii) the decrease of spectral intensity in both emissions of $D^oX$ and DAP after O-plasma treatment, and (iii) no noticeable transition from free excitons after the O-plasma treatment.

A new layered triangular antiferromagnet Li4FeSbO6: spin order, field-induced transitions and anomalous critical behavior

Structure, electrochemical, magnetic and resonance properties of new layered antimonate Li(4)FeSbO(6) were comprehensively studied using powder X-ray diffraction, cyclic voltammetry, magnetic susceptibility, heat capacity, electron spin resonance and Mössbauer spectroscopy. In the crystal structure the iron ions form the triangular network within (LiFeSbO(6))(3-) layers alternating with nonmagnetic lithium layers. The electrochemical activity studied implies an Fe(3+)/Fe(4+) redox couple at 4.3 V (ox.) and 3.9 V (red.) thereby revealing that Li can be reversibly extracted. The long-range antiferromagnetic order was found to occur at the Néel temperature, T(N) ≈ 3.6 K, confirmed both by the magnetic susceptibility data and specific heat ones. The effective magnetic moment is estimated to be 5.93 μ(B)/f.u. and satisfactorily agrees with theoretical estimations assuming high-spin configuration of Fe(3+) (S = 5/2). In the magnetically ordered state, though, the magnetization demonstrates rather peculiar behavior. An additional anomaly on the M(T) curves appears at T(2) < T(N) in moderate magnetic field. The positions of transitions at T(N) and T(2) separate increasingly with increasing external field. Multiple measurements consistently demonstrated field-sensitive moving of magnetic phase boundaries constituting a unique phase diagram for the compound under study. The complex low-dimensional (2D) nature of magnetic coupling was confirmed by the dynamic magnetic properties study. Electron spin resonance from Fe(3+) ions in paramagnetic phase is characterized by a temperature independent effective g-factor of 1.99 ± 0.01. However, the distortion and broadening of the ESR line were found to take place upon approaching the magnetically ordered state from above. The divergence of the temperature-dependent linewidth is analyzed in terms of both critical behavior close to long-range magnetic order and the Berezinskii-Kosterlitz-Thouless (BKT)-type transition. Heat capacity measurements even at zero field manifested an appearance of the additional anomaly at temperatures below the Néel temperature. The temperature dependence of ESR intensity, linewidth and shift of the resonant field imply an extended region of short-range order correlations in the compound studied. The rich variety of the anomalies in magnetic and resonance properties makes this new antimonate a very interesting system to investigate the multiple phase transitions and competing exchange interaction due to the critical role of the layered structure organization accompanied by the frustration effects in triangular antiferromagnets.

The infrared spectrum of HOOH+ trapped in solid neon

When a Ne:H(2)O(2) mixture is codeposited at 4.3 K with a beam of neon atoms that have been excited in a microwave discharge, three new, photosensitive absorptions appear which can be assigned to the three infrared-active vibrational fundamentals of trans-HOOH(+). When the Ne:H(2)O(2) deposition system is pretreated with the vapors of D(2)O, the product absorptions include new peaks which can be attributed to vibrational fundamentals of trans-HOOD(+) and trans-DOOD(+). Density functional calculations of the vibrational fundamentals of the three hydrogen peroxide cation isotopologues support the proposed assignments. Broad, photosensitive product absorptions also appear near the positions of vibrational transitions of O(3)(-), and may be contributed by a weakly bound complex of that species with H(2)O.

Excitons in semiconductor carbon nanotubes: A momentum-space perspective

We give an exposition of an approach toward excitons in semiconductor carbon nanotubes allowing for separation of the short-range and long-range parts of the electron–hole Coulomb interaction. The approach is applied to account for the exciton fine structure and excitonic effects in optical absorption. It is shown that the energy positions of the Eii optical transitions with i>2 are strongly affected by the short-range part of the electron–hole Coulomb interaction.

Rotational spectroscopy of 2-methylfuran from 8.7 to 960 GHz

The rotational spectrum of 2-methylfuran has been measured from 8.7 to 960GHz using a chirped-pulse waveguide spectrometer to collect the centimeter-wave data and a direct absorption flow cell spectrometer to collect the millimeter- and submillimeter-wave data. Over 19,000 transitions in the vibrational ground state spectrum and over 6000 transitions in the spectrum of the first excited state of the methyl torsion were assigned. Fits were performed with both XIAM and ERHAM. Both programs successfully predicted the position and relative intensity of forbidden c-type transitions, but the fits from ERHAM had substantially lower RMS values than those from XIAM for roughly equivalent numbers of adjustable parameters.

Phase transitions for modified Erdős–Rényi processes

A fundamental and very well studied region of the Erd\"os-R\'enyi process is the phase transition at n/2 edges in which a giant component suddenly appears. We examine the process beginning with an initial graph. We further examine the Bohman-Frieze process in which edges between isolated vertices are more likely. While the positions of the phase transitions vary, the three processes belong, roughly speaking, to the same universality class. In particular, the growth of the giant component in the barely supercritical region is linear in all cases.

Effect of Moringa Oleifera Oil Blending on Fractional Crystallization Behavior of Palm Oil

The objective of this study was to see the effect of Moringa oleifera oil blending on the fractional crystallization behavior of palm oil. Palm oil blended with Moringa oleifera oil at 20% (w/w) was subjected to crystallization using a dry process at 21 and 18°C and a solvent process at 15 and 10°C. After recording the quantitative recoveries of the liquid and solid fractions, their fatty acid and triacylglycerol compositions, and the thermal profiles were determined by using gas liquid chromatography, high performance liquid chromatography, and differential scanning calorimetry, respectively. Results showed that the yield recoveries of liquid fractions under solvent-assisted crystallization were higher than those obtained by dry-crystallization conditions. Almost all of the liquid fractions isolated had experienced a significant (p < 0.05) increase in oleic acid as well as triolein contents. Among the solid fractions, those isolated by dry-crystallization were found to be higher (p < 0.05) in oleic acid and triolein contents than the reference stearin sample. Although the thermal profiles of the solid and liquid fractions derived by different methods looked similar to those of the two reference samples, remarkable differences were noticed with regard to the onset of crystallization and the position of the thermal transitions.

Unveiling Electronic Transitions in Three Novel Chiral Azo-Compounds Using Linear and Nonlinear Circular Dichroism: A Theoretical−Experimental Study

Herein, we report on the experimental and theoretically study of the linear absorption, electronic circular dichroism (ECD) spectra, as well as the two-photon absorption circular-linear dichroism measurements of three different chiral azo derivatives in dimethylsulfoxide solution. Using potential energy surfaces and frontier orbital analysis, we established the most stable conformation for each molecule and elucidated their different electronic transitions. Our theoretical calculations allowed us to unambiguously identify the spectral position of such transitions and correlate them with the spectral profiles observed in the two-photon absorption spectra. To further elucidate the characteristics of the main electronic transitions in terms of spectral shape and position, we carried out measurements of the polarization dependent two-photon absorption cross sections and determined the two-photon circular-linear dichroism spectra of these azo dyes.

Robust embedding of longitudinal position into tape servo signals

In linear tape open technology, the longitudinal position (LPOS) on magnetic tape is embedded into the timing-based servo format by modulating the positions of magnetic transitions during the servo-writing process. An efficient method for embedding LPOS information into tape servo signals that is robust to LPOS detection errors is presented. The proposed concept is based on the serial concatenation of three data-processing stages: a lossless compression stage with a fixed compression ratio, an error-correction coding (ECC) stage and a runlength-limited coding stage. Various algorithms have been designed to compress and decompress the LPOS information. Error-correction codes, such as Hamming codes, Reed–Solomon codes and Golay codes, are used to protect LPOS and manufacturing information from detection errors. Finally, the random-error and the burst-error performance of various compression/ECC schemes are evaluated by computing the LPOS word error rate for servo signals corrupted by additive white Gaussian noise and by determining the burst-error correction capability of the proposed LPOS formats, respectively.