Numerical renormalization group study of the correlation functions of the antiferromagnetic spin-12\frac{1}{2} Heisenberg chain

We use the density-matrix renormalization group technique developed by White \cite{white} to calculate the spin correlation functions $=(-1)^l \omega(l,N)$ for isotropic Heisenberg rings up to $N=70$ sites. The correlation functions for large $l$ and $N$ are found to obey the scaling relation $\omega(l,N)=\omega(l,\infty)f_{XY}^{\alpha} (l/N)$ proposed by Kaplan et al. \cite{horsch} , which is used to determine $\omega(l,\infty)$. The asymptotic correlation function $\omega(l,\infty)$ and the magnetic structure factor $S(q=\pi)$ show logarithmic corrections consistent with $\omega(l,\infty)\sim a\sqrt{\ln{cl}}/l$, where $c$ is related to the cut-off dependent coupling constant $g_{eff}(l_0)=1/\ln(cl_0)$, as predicted by field theoretical treatments.Comment: Accepted in Phys. Rev. B. 4 pages of text in Latex + 5 figures in uuencoded form containing the 5 postscripts (mailed separately

Nonequilibrium electron transport using the density matrix renormalization group

We extended the Density Matrix Renormalization Group method to study the real time dynamics of interacting one dimensional spinless Fermi systems by applying the full time evolution operator to an initial state. As an example we describe the propagation of a density excitation in an interacting clean system and the transport through an interacting nano structure

Turbulent mixing layers in supersonic protostellar outflows, with application to DG Tauri

Turbulent entrainment processes may play an important role in the outflows from young stellar objects at all stages of their evolution. In particular, lateral entrainment of ambient material by high-velocity, well-collimated protostellar jets may be the cause of the multiple emission-line velocity components observed in the microjet-scale outflows driven by classical T Tauri stars. Intermediate-velocity outflow components may be emitted by a turbulent, shock- excited mixing layer along the boundaries of the jet. We present a formalism for describing such a mixing layer based on Reynolds decomposition of quantities measuring fundamental properties of the gas. In this model, the molecular wind from large disc radii provides a continual supply of material for entrainment. We calculate the total stress profile in the mixing layer, which allows us to estimate the dissipation of turbulent energy, and hence the luminosity of the layer. We utilize MAPPINGS IV shock models to determine the fraction of total emission that occurs in [Fe II] 1.644 {\mu}m line emission in order to facilitate comparison to previous observations of the young stellar object DG Tauri. Our model accurately estimates the luminosity and changes in mass outflow rate of the intermediate-velocity component of the DG Tau approaching outflow. Therefore, we propose that this component represents a turbulent mixing layer surrounding the well-collimated jet in this object. Finally, we compare and contrast our model to previous work in the field.Comment: 18 pages, 13 figures, accepted for publication in MNRA

Acetonitrile­[2-(1-{bis­[2,4,6-tris­(trifluoro­meth­yl)phen­yl]phosphan­yloxy}-1-methyl­eth­yl)pyridine]­methyl­palladium(II) hexa­fluoridoanti­monate dichloro­methane hemisolvate

In the title compound, [Pd(CH3)(C26H14F18NOP)(C2H3N)][SbF6]·0.5CH2Cl2, the Pd2+ cation has a distorted square-planar environment, being coordinated by the acetonitrile [Pd—N = 2.078 (8) Å] and methyl [Pd—C = 2.052 (9) Å] groups and the bidentate ligand 2-(1-{bis­[2,4,6-tris­(trifluoro­meth­yl)phen­yl]phosphan­yloxy}-1-methyl­eth­yl)pyridine (L). In L, one –CF3 group is rotationally disordered between two orientations in a 1:1 ratio. The solvent mol­ecule was treated as disordered between two positions related by an inversion center with occupancies fixed at 0.5. The crystal packing exhibits weak inter­molecular C—H⋯F contacts

Global Impacts from Improved Tropical Forages: A Meta-Analysis Revealing Overlooked Benefits and Costs, Evolving Values and New Priorities

The wider use and improved performance of planted tropical forages can substantially change social, economic and environmental landscapes. By reviewing impact-related studies published in the past two decades, this paper shows how evolving development priorities have influenced the types of impacts being documented. A meta-analysis was used to examine 98 studies according to: (1) breadth of reported effects, as related to development goals of social equity, economic growth and environmental sustainability; (2) extent of effects, ranging from intermediate to longer-term impacts; and (3) measurement precision (identification, description and quantification). Impacts have been assessed for fewer than half of the documented 118M ha with improved forages. Although Brazil accounts for 86% of the known planted area, widespread irregular reporting of technology adoption affects accuracy of global estimates. Over 80% of the impact-related studies reported economic effects, while fewer than 20% were quantitative estimates of longer-term economic impacts. Inconsistent valuation methods and assumptions prevented valid summation of total economic impacts. Social effects were reported in fewer than 60% of studies and emphasised household-level outcomes on gender and labour, with most reported effects being non-quantitative. Environmental effects were reported slightly more often than social effects, with recent increases in quantitative estimates of carbon accumulation. Few studies analysed tradeoffs. Independent reviewers conducted approximately 15% of the studies. Newer development priorities of environmental sustainability, system intensification, organisational participation and innovation capacities require broader approaches to assess impacts. Increased marketing and coordination with development and environmental organisations can generate greater demands for improved forages

Dark-Matter Decays and Self-Gravitating Halos

We consider models in which a dark-matter particle decays to a slightly less massive daughter particle and a noninteracting massless particle. The decay gives the daughter particle a small velocity kick. Self-gravitating dark-matter halos that have a virial velocity smaller than this velocity kick may be disrupted by these particle decays, while those with larger virial velocities will be heated. We use numerical simulations to follow the detailed evolution of the total mass and density profile of self-gravitating systems composed of particles that undergo such velocity kicks as a function of the kick speed (relative to the virial velocity) and the decay time (relative to the dynamical time). We show how these decays will affect the halo mass-concentration relation and mass function. Using measurements of the halo mass-concentration relation and galaxy-cluster mass function to constrain the lifetime--kick-velocity parameter space for decaying dark matter, we find roughly that the observations rule out the combination of kick velocities greater than 100 km/s and decay times less than a few times the age of the Universe.Comment: 17 pages, 10 figures, replaced with published versio

Salicylaldehyde hydrazones: buttressing of outer sphere hydrogen-bonding and copper-extraction properties

Salicylaldehyde hydrazones are weaker copper extractants than their oxime derivatives, which are used in hydrometallurgical processes to recover ~20 % of the world’s copper. Their strength, based on the extraction equilibrium constant Ke, can be increased by nearly three orders of magnitude by incorporating electron-withdrawing or hydrogen-bond acceptor groups (X) ortho to the phenolic OH group of the salicylaldehyde unit. Density functional theory calculations suggest that the effects of the 3-X substituents arise from a combination of their influence on the acidity of the phenol in the pH-dependent equilibrium, Cu2+ + 2Lorg ⇌ [Cu(L–H)2]org + 2H+, and on their ability to ‘buttress’ interligand hydrogen bonding by interacting with the hydrazone N–H donor group. X-ray crystal structure determination and computed structures indicate that in both the solid state and the gas phase, coordinated hydrazone groups are less planar than coordinated oximes and this has an adverse effect on intramolecular hydrogen-bond formation to the neighbouring phenolate oxygen atoms

Synthesis and Complete Characterization of a Gallium-Mixed-Pnicogen Four-Membered-Ring Compound: I2GaAs (SiMe3) 2Ga (I) 2P (SiMe3) 2

The first four-membered ring compound containing two gallium atoms bridged by two different Group 15 elements, I2GaAs(SiMe3)2Ga(I)2P(SiMe3)2 (1) to be completely characterized was synthesized by both the equilibration of [I2GaAs(SiMe3)2]2 (2) and [I2GaP(SiMe3)2]2 (3) in a 1:1 mole ratio, and the direct reaction of Gal3 with As(SiMe3)3 and P(SiMe3)3 in a 2:1:1 mole ratio. Single crystal x-ray structures were determined for both 1 and 3. Crystals of 1 belong to the orthorhombic system, space group Pbca, with a = 17.349(3), b = 13.9187(21), c = 13.7570(24) Ä. V = 3322.0(10) A3, DcaIc = 1.879 g cnr3 for Z = 4; the average Ga-As/P bond length is 2.44 Ä. and crystals of 1 are isomorphous with those of 2. Crystals of 3 belong to the monoclinic system, space group P2\lc, with a = 11.040(9), b = 10.228(4), c = 19.619(9) A, V = 2169.4(22) A3, Dcalc = 1.816 g cm"3 for Z = 4; the average Ga-P bond length is 2.39 Ä

Evolution of X-ray cluster scaling relations in simulations with radiative cooling and non-gravitational heating

We investigate the redshift dependence of X-ray cluster scaling relations drawn from three hydrodynamic simulations of the LCDM cosmology: a Radiative model that incorporates radiative cooling of the gas, a Preheating model that additionally heats the gas uniformly at high redshift, and a Feedback model that self-consistently heats cold gas in proportion to its local star-formation rate. While all three models are capable of reproducing the observed local Lx-Tx relation, they predict substantially different results at high redshift (to z=1.5), with the Radiative, Preheating and Feedback models predicting strongly positive, mildly positive and mildly negative evolution, respectively. The physical explanation for these differences lies in the structure of the intracluster medium. All three models predict significant temperature fluctuations at any given radius due to the presence of cool subclumps and, in the case of the Feedback simulation, reheated gas. The mean gas temperature lies above the dynamical temperature of the halo for all models at z=0, but differs between models at higher redshift with the Radiative model having the lowest mean gas temperature at z=1.5. We have not attempted to model the scaling relations in a manner that mimics the observational selection effects, nor has a consistent observational picture yet emerged. Nevertheless, evolution of the scaling relations promises to be a powerful probe of the physics of entropy generation in clusters. First indications are that early, widespread heating is favored over an extended period of heating that is associated with galaxy formation.Comment: Accepted for publication in ApJ. Minor changes following referee's comment