A spatio-temporal study of rheo-oscillations in a sheared lamellar phase using ultrasound

We present an experimental study of the flow dynamics of a lamellar phase sheared in the Couette geometry. High-frequency ultrasonic pulses at 36 MHz are used to measure time-resolved velocity profiles. Oscillations of the viscosity occur in the vicinity of a shear-induced transition between a high-viscosity disordered fluid and a low-viscosity ordered fluid. The phase coexistence shows up as shear bands on the velocity profiles. We show that the dynamics of the rheological data result from two different processes: (i) fluctuations of slip velocities at the two walls and (ii) flow dynamics in the bulk of the lamellar phase. The bulk dynamics are shown to be related to the displacement of the interface between the two differently sheared regions in the gap of the Couette cell. Two different dynamical regimes are investigated under applied shear stress: one of small amplitude oscillations of the viscosity ( %) and one of large oscillations ( %). A phenomenological model is proposed that may account for the observed spatio-temporal dynamics.Received: 2 December 2003, Published online: 9 March 2004PACS: 83.10.Tv Structural and phase changes - 43.58. + z Acoustical measurements and instrumentation - 47.50. + d Non-Newtonian fluid flows     

An experimental test of alternative models of bidding in ascending auctions

The theory and behavior of the clock version of the ascending auction has been well understood for at least 20 years. The more widely used oral outcry version of the ascending auction that allows bidders to submit their own bids has been the subject of some recent controversy mostly in regard to whether or not jump bidding, i.e. bidders submitting bids higher than required by the auctioneer, should be allowed. Isaac, Salmon & Zillante (2005) shows that the standard equilibrium for the clock auction does not apply to the non-clock format and constructs an equilibrium bid function intended to match with field data on ascending auctions. In this study, we will use economic experiments to provide a direct empirical test of that model while simultaneously providing empirical evidence to resolve the policy disputes centered around the place of jump bidding in ascending auctions.Received: March 2005The authors would like to thank Florida State University for providing the funding for the experiments in this paper and Bradley Andrews for programming assistance.     

The NMR spectra and conformations of cyclic compounds–III: The conformations of some pinane derivatives

The 220 MHz ¹H spectra of isoverbanone, nopinone and verbanone are reported. The spectra of the first two are completely assigned but that of verbanone only partially. The coupling constants obtained provide information about the conformation of these molecules. The isoverbanone molecule is almost Y shaped, but that of nopinone is between a Y shape and a half-chair conformation with the six membered ring bent away form the gem dimethyl groups. These conformations are consistent with the known steric interactions in these molecules.     

An experimental investigation of the decays K± → π0π0π±: The slope parameter and its charge asymmetry

The slope parameter and its charge asymmetry have been measured for the τ′ decay mode of the charged K mesons. No charge asymmetry in the parameter is observed to the precision level of 1.25%, indicating the absence of CP violating transitions. The result for the slope parameter is consistent with previous measurements and taken with other results on K_π³ decay modes supports the conclusion that the $\text{ΔI =}\text{1}\text{2}$ rule is not exact.     

Anelli con unica decomponibilità in fattori primi ed un problema di intersezioni complete

La prima redazione manoscritta di questo lavoro, che avevo iniziato e quasi concluso personalmente, presentava una lacuna tutt'altro che facile da colmare nella dimostrazione del teorema di Noether. P. Salmon ha superato questa difficoltà mediante gli sviluppi contenuti al n. 9, E.E' inoltre dovuto a Salmon il teorema 1 del n. 9 con cui viene sostituita una proprietà più limitata da me ottenuta in altro modo. Coll'uso del risultato di Salmon si perviene compiutamente al primo teorema del n. 11.Aldo Andreotti.     

A Tris(triazolate) Ligand for a Highly Active and Magnetically Recoverable Palladium Catalyst of Selective Alcohol Oxidation Using Air at Atmospheric Pressure

High efficiency and selectivity, easy magnetic recovery and recycling, and use of air as the oxidant at atmospheric pressure are major objectives for oxidation catalysis in terms of sustainable and green processes. A tris(triazolyl) ligand, so far only used in copper‐catalyzed alkyne azide cycloadditions, was found to be extremely efficient in SiO₂/γ‐Fe₂O₃‐immobilized palladium complexes. It was characterized by inductively coupled plasma (ICP) analysis, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray photoelectron spectra (XPS) and found to fulfill the combined conditions for the selective oxidation of alcohols to aldehydes and ketones.     

Dielectric and charge transport properties of the spin crossover complex [Fe(Htrz)2(trz)](BF4)

Spin crossover compounds are considered to be a viable alternative for creating display, memory and switching devices due to the bistability of their magnetic, optical, mechanical and electrical properties. This Letter presents the study of the dielectric and transport properties of the [Fe(Htrz)₂(trz)](BF₄) (Htrz = 1H‐1,2,4‐triazole) complex in a wide temperature and frequency range. Our results reveal a singular behavior of the dielectric modulus upon the spin transition in conjunction with the switching of the conductivity between the high spin and low spin states.

     

Surface plasmons reveal spin crossover in nanometric layers

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale.