Destruction of long range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites

The quantum spin systems Cu2M BO5 M Al,Ga with the ludwigite crystal structure consist of a structurally ordered Cu2 sublattice in the form of three leg ladders, interpenetrated by a structurally disordered sublattice with a statistically random site occupation by magnetic Cu2 and nonmagnetic Ga3 or Al3 ions. A microscopic analysis based on density functional theory calculations for Cu2GaBO5 reveals a frustrated quasi two dimensional spin model featuring five inequivalent antiferromagnetic exchanges. A broad low temperature 11B nuclear magnetic resonance points to a considerable spin disorder in the system. In zero magnetic field, antiferromagnetic order sets in below TN approximation 4.1 K and 2.4 K for the Ga and Al compounds, respectively. From neutron diffraction, we find that the magnetic propagation vector in Cu2GaBO5 is commensurate and lies on the Brillouin zone boundary in the H0L plane, qm 0.45, 0, 0.7 , corresponding to a complex noncollinear long range ordered structure with a large magnetic unit cell. Muon spin relaxation is monotonic, consisting of a fast static component typical for complex noncollinear spin systems and a slow dynamic component originating from the relaxation on low energy spin fluctuations. Gapless spin dynamics in the form of a diffuse quasielastic peak is also evidenced by inelastic neutron scattering. Most remarkably, application of a magnetic field above 1 T destroys the static long range order, which is manifested in the gradual broadening of the magnetic Bragg peaks. We argue that such a crossover from a magnetically long range ordered state to a spin glass regime may result from orphan spins on the structurally disordered magnetic sublattice, which are polarized in magnetic field and thus act as a tuning knob for field controlled magnetic disorde

Adsorption of casein at the silica-solution interface

113-116<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">The effects of various factors such as the concentration of casein, <span style="font-size: 11.0pt;line-height:115%;font-family:" calibri","sans-serif";mso-ascii-theme-font:="" minor-latin;mso-fareast-font-family:"times="" new="" roman";mso-fareast-theme-font:="" minor-fareast;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:arial;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">pH of the protein solution, presence of low molecular weight electrolytes and detergents and temperature of the adsorption medium have been studied on the adsorption of casein onto silica.</span

Protein adsorption: A fascinating phenomenon

101-112This review article presents the current state-of-art of protein adsorption and briefly reviews the major findings of the adsorption of a variety of proteins onto different solid surfaces. The article al so highlights some of the modern theories of protein adsorption like the Random sequential adsorption theory, DRSA theory and Lattice theory and briefly describes some major optical techniques for studying the static and dynamics of the adsorption process

Polymerization kinetics of acrylonitrile initiated by K₂S₂O₈-Ag⁺- EDT A redox system

831-836The kinetics of polymerization of acrylonitrile has been studied employing K2S2O8- EDTA - Ag+ redox couple under atmospheric oxygen. The rate expression Rp α[Monomer]0.45 [K2S2O8]0.42, [Ag+]0.46, [EDTA]0.80 has been obtained and a plausible mechanism suggested to explain the experimental fi ndings. The effect of varying concentrations of monomer and redox components, temperature, added salts, solvents, H+ ions and surfactants on the polymerization kinetics have also been studied