On linear vertex-arboricity of complementary graphs

The linear vertex-arboricity ρ(G) of a graph G is defined to be the minimum number of subsets into which the vertex set of G can be partitioned such that each subset induces a linear forest. In this paper, we give the sharp upper and lower bounds for the sum and product of linear vertex-arboricities of a graph and its complement. Specifically, we prove that for any graph G of order p. and for any graph G of order p = (2n + 1)², where n ? Z⁺, 2n + 2 ≦ ρ(G) + ρ(G ).     

Induced renal artery stenosis in rabbits: magnetic resonance imaging, angiography, and radionuclide determination of blood volume and blood flow

To investigate the ability of MRI to detect alterations due to renal ischemia, a rabbit renal artery stenosis (RAS) model was developed. Seven rabbits had RAS induced by surgically encircling the artery with a polyethylene band which had a lumen of 1 mm, 1 to 2 weeks prior to imaging. The stenosis was confirmed by angiography, and the rabbits were then imaged in a 1.4 T research MRI unit. T1 was calculated using four inversion recovery sequences with different inversion times. Renal blood flow, using 113Sn-microspheres, and regional water content by drying were then measured. The average T1 of the inner medulla was shorter for the ischemia (1574 msec) than for the contralateral kidney (1849 msec), while no change ws noted in the cortex. Ischemic kidneys had less distinct outer medullary zones on IR images with TI = 600 msec than did contralateral or control kidneys. Blood flow to both the cortex and medulla were markedly reduced in ischemic kidneys compared with contralateral kidneys (119.5 vs. 391 ml/min/100 gm for cortex and 19.8 vs. 50.8 ml/min/100 gm for medulla). Renal water and blood content were less affected. Our rabbit model of renal artery stenosis with MRI, radionuclide, and angiographic correlation has the potential to increase our understanding of MR imaging of the rabbit kidney.     

A FACILE AND NEW METHOD FOR THE SYNTHESIS OF α-ARYL-N-METHYLNITRONES IN SOLVENT-FREE MEDIA USING SILICA GEL-NaOH

Substituted α-aryl-N-methylnitrones are prepared by the condensation reaction of N-methylhydroxylamine hydrochloride and benzaldehydes in solvent-free media using silica-gel–NaOH catalyst system. The yields are excellent regardless of the electron-donating or electron-accepting nature of the substituents on benzaldehyde. Similar ketones are unreactive under these conditions, rendering chemoselectivity of the method.     

Synthesis, structure and catalytic activity of an oxo-bridged dinuclear oxovanadium complex of an isonicotinohydrazide ligand

A mononuclear dioxo vanadium(V) complex of a hydrazone ONO donor ligand, [V^VO₂(L¹)] (1), was synthesized by the reaction of V₂O₅ and terephthalic acid with H₂L¹ in 1:1:1 mol ratio, while an oxo-bridged bis(vanadium(IV)oxo) complex, [μ ₂–O–{V^IVO(L²)}₂] (2), was synthesized by the treatment of isonicotinic acid hydrazide, salicylaldehyde and CoSO₄·7H₂O with bis(acetylacetonato)oxovanadium(IV) (H₂L¹ = isonicotinic acid(2-hydroxy-benzylidene)-hydrazide, H₂L² = isonicotinic acid (1-methyl-3-oxo-butylidene)-hydrazide). The complexes were characterized by elemental analyses and spectroscopic methods. The crystal structure of complex 2 was determined by X-ray analysis. The complexes were tested as catalysts for the oxidation of cycloalkenes and benzyl alcohol using H₂O₂ as terminal oxidant. Excellent selectivity was achieved in the oxidation of cyclohexene.     

Thermally Stable Magnetic Polyurethane Nanocomposites Prepared from Functionalized Polybutadiene: Novel Approach to the Polybutadiene Chemical Modification

Russian Journal of Applied Chemistry - In this work, preparation and characterization of new classes of polybutadiene-based polyols and polyurethanes investigated with consecutive reactions namely,...     

Proton radioactivity half-lives with nuclear asymmetry factor

The dependence of proton emission half-lives on the nuclear asymmetry parameter is investigated using the WKB method and two types of empirical formula.Using the single-folding formalism with asymmetry-depend-ent nuclear radius and surface diffuseness of nuclear matter,the nuclear potential and consequently the half-life are functions of the asymmetry factor.Despite small values of asymmetry in neutron-deficient proton emitters,notice-able changes in the half-lives are observed.The addition of an asymmetry parameter term to the two forms of empir-ical formulas leads to a reduction in the rms error for ground state and isomeric transitions.A noticeable reduction of about 43%is obtained for isomeric transitions in the second form of the empirical formula.Considering ground state transitions in two categories,odd-even and odd-odd emitters,and adopting deformation and asymmetry-dependent empirical formulas,the rms decreases remarkably.The low est values of rms errors,viz.0.1492,0.2312,and 0.1999,are obtained for the aforementioned empirical formulas for ground state transitions of odd-even and odd-odd emit-ters and for all isomeric transitions,respectively.     

Tuning methane content in gas hydrates via thermodynamic modeling and molecular dynamics simulation

Storage and transportation of natural gas as gas hydrate (“gas-to-solids technology”) is a promising alternative to the established liquefied natural gas (LNG) or compressed natural gas (CNG) technologies. Gas hydrates offer a relatively high gas storage capacity and mild temperature and pressure conditions for formation. Simulations based on the van der Waals–Platteeuw model and molecular dynamics (MD) are employed in this study to relate the methane gas content/occupancy in different hydrate systems with the hydrate stability conditions including temperature, pressure, and secondary clathrate stabilizing guests. Methane is chosen as a model system for natural gas. It was found that the addition of about 1% propane suffices to increase the structure II (sII) methane hydrate stability without excessively compromising methane storage capacity in hydrate. When tetrahydrofuran (THF) is used as the stabilizing agent in sII hydrate at concentration between 1% and 3%, a reasonably high methane content in hydrate can be maintained (∼85–100, v/v) without dealing with pressures more than 5 MPa and close to room temperature.     

Simulations of p-tert-butylcalix[4]arene with multiple occupancies of small guest molecules

Classical molecular dynamics simulations were used to study low-density beta(0)-phase p-tert-butylcalix[4]arene inclusion compounds with multiple calix occupancies of xenon, carbon dioxide, methane, and hydrogen guest molecules with guest-host ratios ranging from 1:4 to 4:1. Custom parameterized force fields were used for the guests and the AMBER force field for the calixarene units was validated in our previous work (Chem. Eur. J. 2006, 12, 5231). The inclusion energy and unit cell volume of the calixarene inclusion compound were determined for various guest occupancies and for occupancies greater than 1:1, strong guest-guest interaction effects are observed. The structure and energetics of the 2:1 CO(2)/beta(0)-phase inclusion compound were compared to those of the low-temperature 2:1 CO(2)/calixarene in which the guest molecules occupy both cage and interstitial sites.     

Determination of NMR Lineshape Anisotropy of Guest Molecules within Inclusion Complexes from Molecular Dynamics Simulations

Nonspherical cages in inclusion compounds can result in non‐uniform motion of guest species in these cages and anisotropic lineshapes in NMR spectra of the guest. Herein, we develop a methodology to calculate lineshape anisotropy of guest species in cages based on molecular dynamics simulations of the inclusion compound. The methodology is valid for guest atoms with spin 1/2 nuclei and does not depend on the temperature and type of inclusion compound or guest species studied. As an example, the nonspherical shape of the structure I (sI) clathrate hydrate large cages leads to preferential alignment of linear CO₂ molecules in directions parallel to the two hexagonal faces of the cages. The angular distribution of the CO₂ guests in terms of a polar angle θ and azimuth angle ? and small amplitude vibrational motions in the large cage are characterized by molecular dynamics simulations at different temperatures in the stability range of the CO₂ sI clathrate. The experimental ¹³C NMR lineshapes of CO₂ guests in the large cages show a reversal of the skew between the low temperature (77 K) and the high temperature (238 K) limits of the stability of the clathrate. We determine the angular distributions of the guests in the cages by classical MD simulations of the sI clathrate and calculate the ¹³C NMR lineshapes over a range of temperatures. Good agreement between experimental lineshapes and calculated lineshapes is obtained. No assumptions regarding the nature of the guest motions in the cages are required.