J-aggregation and disaggregation of indocyanine green in water

J-aggregates of indocyanine green sodium iodide in water are formed by heat treatment. Starting from a dimeric solution the activation energy of molecule attachment (E_att ≈ 0.41 ev) to J-aggregates is determined by analysing the temperature dependence of the rate of J-aggregate absorption growth. The activation energy of molecule detachment (E_det ≈ 0.51 eV) from J-aggregates is deduced from the temperature dependent rate of J-aggregate absorption decrease after strong dilution.     

Blue alkali dinitrosomethanides: synthesis, structure, and bonding

Explosive alkali dinitrosomethanides (M[HC(NO)2]; M = Li, Na, K, Cs) were prepared in a new, simple, high-yielding synthetic procedure, fully characterized, and shown to be stable at ambient temperature. Alkali dinitrosomethanides are of widespread interest to pharmaceutical and materials scientists alike.     

Investigation of statistically perturbed angular correlations of154Gd and156Gd in different liquid sources

The statistical perturbations of γγ-angular correlations involving the first 2⁺ rotational state of¹⁵⁴Gd and¹⁵⁶Gd have been time differentially investigated. We used liquid sources of 3⁺ ions of Gadolinium in lN perchloric acid, 0.5 N and 1N hydrochloric acid, 1.3N and 2.6 N sulfuric acid. Influences of the various chemical surroundings on the ratio λ₄/λ₂ of the attenuation parameters have been found. A simultaneous measurement of the angular correlation of the 874 keV–123 keV cascade and the 2,098 keV–89 keV cascade of¹⁵⁴Gd and¹⁵⁶Gd, respectively, has been performed in perchloric solution. From the ratio of the attenuation parameters λ₂, obtained by this experiment, we have derived the ratio of the magneticg-factors of the first 2⁺ levels of these isotopes asg ¹⁵⁴/g ¹⁵⁶=1.11±0.08.     

Film cooling on a convex surface: influence of external pressure gradient and Mach number on film cooling performance

 The film cooling performance on a convex surface subjected to zero and favourable pressure gradient free-stream flow was investigated. Adiabatic film cooling effectiveness values were obtained for five different injection geometries, three with cylindrical holes and two with shaped holes. Heat transfer coefficients were derived for selected injection configurations. CO₂ was used as coolant to simulate density ratios between coolant and free-stream close to gas turbine engine conditions. The film cooling effectiveness results indicate a strong dependency on the free-stream Mach number level. Results obtained at the higher free-stream Mach number show for cylindrical holes generally and for shaped holes at moderate blowing rates significant higher film cooling effectiveness values compared to the lower free-stream Mach number data. Free-stream acceleration generally reduced adiabatic film cooling effectiveness relative to constant free-stream flow conditions. The different free-stream conditions investigated indicate no significant effects on the corresponding heat transfer increase due to film injection. The determined heat flux ratios or film cooling performance indicated that coolant injection with shaped film cooling holes is much more efficient than with cylindrical holes especially at higher blowing rates. Heat flux penalties can occur at high blowing rates when using cylindrical holes. Received on 29 May 2000     

Microstructure evolution during tensile loading histories of a polyurea

The evolution in the hard/soft domain microstructure of an elastomeric‐like polyurea during different tensile loading histories was studied using in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS). The nonlinear stress–strain behavior is initially stiff with a rollover yield to a more compliant response; unloading is highly nonlinear showing substantial hysteresis while also exhibiting significant recovery. Reloading reveals a substantially more compliant “softened” behavior and dramatically reduced hysteresis. WAXS peaks monitor characteristic dimensions of regular features within the hard domains; the peak location remains unchanged with tensile deformation indicating no separation of the internal structure within a domain, but the peak intensity becomes anisotropic with deformation evolving in a reversible manner consistent with orientation due to stretch. The SAXS profiles provide information between major hard domains. SAXS peaks are found to shift with tensile loading in a relatively affine manner up to a tensile true strain of ～0.4, which, using a Bragg reduction to aid interpretation, reveals an axial increase and a transverse decrease in interdomain spacings; this evolution is reversible for strains less than ～0.4. Increasing axial strain beyond a true strain of ～0.4 is accompanied by a dramatic, progressive, and irreversible reduction in axial Bragg spacing, indicating a breakdown in the hard domain aggregate network structure. A four‐point pattern is seen to develop during stretching. The breakdown in networked structure during a first load cycle gives a new structure for subsequent load cycles, which is seen to evolve in a reversible manner for strains less than or equal to the prior maximum strain. However, for strains exceeding the prior maximum strain excursion, additional breakdown is found. These SAXS results show that a breakdown in the hard domain aggregate network structure is a governing mechanism for the large dissipation (hysteresis) loops of the first load cycle and are also responsible for the softened reloading response. The absence of structure breakdown during subsequent load cycles corresponds to the substantially reduced hysteresis loops as well as the stable softened behavior. DMA data on pristine and previously deformed samples show a more compliant storage modulus in the predeformed sample, supporting the softened cyclic stress–strain data and the structural breakdown observed in the SAXS; the loss modulus was unchanged with deformation, which correlates with the lossy features measured in DMA with time‐dependent viscosity rather than losses due to structural breakdown. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011