STUDIES ON PHOTOTROPISM OF YOUNG SPORANGIOPHORES OF PILOBOLUS KLEINII*

Abstract— Young sporangiophores of the fungus, Pilobolus kleinii, respond to unilateral illumination by bending or by growing toward light of wavelengths between 312 and 530 mμ, with peaks of sensitivity near 360 and 450 mμ. Young sporangiophores exhibit a negative phototropic response to wavelengths shorter than 300 mμ, with a strong negative response at 280 mμ. Since the action spectrum did not correspond to the absorption spectrum of the pigmented zone as measured in vivo, and since colorless sporangiophores formed on media containing diphenylamine were capable of phototropic response, it is unlikely that the conspicuous orange-yellow pigment in young sporangiophores is the photoreceptor for phototropism. The results of probing with small beams of light and the behavior of sporangiophores submerged in mineral oil, together with measurements of the refractive index of the tip and base indicate that the photosensitive region is located in the tip of the young sporangiophore.     

Short‐Range Order of Methylammonium and Persistence of Distortion at the Local Scale in MAPbBr3 Hybrid Perovskite

Short‐range investigation by means of variable‐temperature neutron total scattering and pair distribution function analysis revealed that the local environment around the methylammonium (MA) cation in MAPbBr₃ hybrid perovskite is maintained through the different phase transitions observed as a function of temperature. In addition, the orthorhombic distortion of the lattice is present at any temperature. Local structure around MA changes from static to configurationally averaged or dynamic with temperature but the local structure of the low‐temperature orthorhombic phase is preserved.     

Crystal structure and the paraelectric-to-ferroelectric phase transition of nanoscale BaTiO3

We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles.     

An activated sulfonylating agent that undergoes general base-catalyzed hydrolysis by amines in preference to aminolysis

Activated sulfonyl derivatives, similar to acyl ones, usually undergo aminolysis with amines in water as nucleophilic attack by the amine is preferred to hydrolysis. However, despite being active sulfonyl derivatives, four-membered heterocyclic sulfonamides, beta-sultams, do not undergo aminolysis in aqueous solution but preferentially react to give hydrolysis products only. The rate of the reaction of beta-sultams in buffered solutions of simple primary amines shows a first-order dependence on amine concentrations attributed to general base-catalyzed hydrolysis by the amine. Even N-benzyl-4,4-dimethyl-3-oxo-beta-sultam, which is both a beta-sultam and a beta-lactam, undergoes hydrolysis at the sulfonyl center rather than aminolysis at either the sulfonyl or acyl center. The solvent kinetic isotope effects (SKIE, k(H(2)O)/k(D(2)O)) for the amine-catalyzed hydrolyses are 1.4 and 1.9 for the hydrolysis of N-benzoyl-beta-sultam and N-benzyl-4,4-dimethyl-3-oxo-beta-sultam, respectively, compatible with a general base-catalyzed mechanism. The amine-catalyzed hydrolysis gives a Bronsted beta value of +0.9 for both N-benzoyl beta-sultam and N-benzyl-4,4-dimethyl-3-oxo-beta-sultam, indicating that the general base amine is almost fully protonated in the transition state. A general base-catalyzed mechanism for hydrolysis rather than nucleophilic attack was also deduced for the reaction of N-benzyl-4,4-dimethyl-3-oxo-beta-sultam with carboxylate anions based on a SKIE of 1.7-1.9 and rate constants which fit the Bronsted plot for amines. In contrast to acyl transfer reactions, those for sulfonyl transfer appear to show an inverse reactivity-selectivity relationshipthe most active compounds being the most selective. The lack of reactivity of beta-sultams toward amine nucleophiles appears to be related to the mechanism of ring opening of beta-sultams with a decreased reactivity toward amines relative to hydroxide ion, probably related to the expulsion of the relatively poor leaving group amide anion.     

Ion chromatographic analysis of amines, alkanolamines, and associated anions in concrete

In order to assess the effectiveness of applying penetrating corrosion inhibitors to the surface of reinforced concrete, it is necessary to devise accurate methods for their detection and quantification. In this paper, methods for ion chromatographic analysis of a variety of amines, alkanolamines, and associated anions, which may be used as corrosion inhibitors for steel reinforcement in concrete, are described. By careful adjustment of the conditions for analysis, these inhibitors were readily identified and quantified in concrete/cement pore solutions or digests. Characterisation of the cationic inhibitors, ethanolamine, quaternary methylammonium, dimethylethanolamine, cyclohexylamine, guanidine, and arginine, and the anionic inhibitors, nitrite, molybdate, acetate, benzoate, and azelate, was carried out conductimetrically. To enhance the sensitivity of detection, amperometry was used for the analysis of triethanolamine and low concentrations of ethanolamine. Ion chromatography was also used as a means of obtaining a distribution profile of the concentrations of inhibitor ions present throughout a concrete structure.     

Why is the universe so large?

S. W. Hawking's proposal for the wave function of the universe, if correct, determines the conditional probabilities for all properties of the universe. In a simple minisuperspace model it predicts that at any given nonzero energy density, the universe is most probably infinitely large.     

The determination of wear elements in lubricating oils by neutron activation analysis

Used lubricating oil analysis programs are currently employed by both the military and industry in an attempt to minimize some of the costs associated with equipment failure. The periodic determination of water elements in the lubricant of an oil-wetted system can provide very useful information on the condition or health of the system and an early indication of impending failure. In the present study, the application of Neutron Activation Analysis (NAA) to used oil analysis was investigated. The method developed allowed for the determination of fifteen elements (Ag, Al, Cl, Cr, Cu, Fe, In, Mg, Mn, Mo, Na, Ni, Sn, Ti and Zn) associated with engine wear or deterioration. Results obtained for the analysis of used naval diesel oils exhibited good agreement with results obtained by Atomic Absorption Spectrophotometry (AAS) methods. A drawback of the NAA procedure is that the determination of Fe, a major wear element in most systems, involves an analysis time of approximately one week.     

Alpha decay of the new isotope 174Hg

Neutron deficient mercury isotopes were produced in the reaction ³⁶Ar + ¹⁴⁴Sm using bombarding energies of 180–230 MeV. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7069±11) keV and (2.1 _?0.7 ^+1.8 ) ms, respectively, was assigned to the new mercury isotope ¹⁷⁴Hg.