Thermo-infrared-spectroscopy analysis of the interaction of naphthylammonium–montmorillonite with sodium nitrite

The deep blue organoclay color pigment (OCCP), naphthylazonaphthylammonium–montmorillonite, was synthesized in an aqueous suspension by treating montmorillonite with naphthylammonium chloride followed after 2 h by NaNO₂. The reddish-brown azo dye naphthylazonaphthylamine (commercial name “Solvent Brown 3”) was synthesized in an aqueous solution in the absence of clay from the same reagents. X-ray diffraction and thermo-infrared (IR) spectroscopy of organoclay prepared by treating montmorillonite with naphthylammonium chloride showed that the organoclay contained two types of tactoids with intercalated naphthylammonium cations and with naphthylammonium–naphthylamine associations. Naphthylammonium clay was obtained after thoroughly washing the latter organoclay. IR spectra of naphthylamine, naphthylammonium chloride, naphthylammonium clay, naphthylammonium–naphthylamine clay (with some naphthylammonium-clay), OCCP, and Solvent Brown 3 in KBr disks were recorded before and after thermal treatments up to 120 °C. IR spectrum of the OCCP was similar to that of Solvent Brown 3. An NH₃ ⁺ group was identified in the spectrum of the OCCP but not in that of Solvent Brown 3. In the latter spectrum, an NH₂ group was identified, suggesting that the amine group of the azo dye in the OCCP was protonated. It appears that the difference in color between OCCP and Solvent Brown 3 resulted from the protonation of the azo molecule in the interlayer space of the clay.     

The Poisson equation with local nonregular similarities

Moffatt and Duffy [1] have shown that the solution to the Poisson equation, defined on rectangular domains, includes a local similarity term of the form: r²log(r)cos(2θ). The latter means that the second (and higher) derivative of the solution with respect to r is singular at r = 0. Standard high‐order numerical schemes require the existence of high‐order derivatives of the solution. Thus, for the case considered by Moffatt and Duffy, the high‐order finite‐difference schemes loose their high‐order convergence due to the nonregularity at r = 0. In this article, a simple method is outlined to regain the high‐order accuracy of these schemes, without the need of any modification in the scheme's algorithm. This is a significant consideration when one wants to use a given finite‐difference computer code for problems with local nonregular similarity solutions. Numerical examples using the modified scheme in conjunction with a sixth‐order finite difference approximation are provided. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17:336–346, 2001     

Generating molecular rovibrational coherence by two-photon femtosecond photoassociation of thermally hot atoms

The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.     

Confinement and lattice quantum-electrodynamic electric flux tubes simulated with ultracold atoms

We propose a method for simulating (2+1)D compact lattice quantum-electrodynamics, using ultracold atoms in optical lattices. In our model local Bose-Einstein condensates' (BECs) phases correspond to the electromagnetic vector potential, and the local number operators represent the conjugate electric field. The well-known gauge-invariant Kogut-Susskind Hamiltonian is obtained as an effective low-energy theory. The field is then coupled to external static charges. We show that in the strong coupling limit this gives rise to "electric flux tubes" and to confinement. This can be observed by measuring the local density deviations of the BECs, and is expected to hold even, to some extent, outside the perturbative calculable regime.     

Black box polynomial identity testing of generalized depth-3 arithmetic circuits with bounded top fan-in

In this paper we consider the problem of determining whether an unknown arithmetic circuit, for which we have oracle access, computes the identically zero polynomial. This problem is known as the black-box polynomial identity testing (PIT) problem. Our focus is on polynomials that can be written in the form f([`(x)]) = ?<sub>i = 1</sub><sup>k</sup> h<sub>i</sub> ([`(x)]) ·g_i ([`(x)])f(\bar x) = \sum\nolimits_{i = 1}^k {h_i (\bar x) \cdot g_i (\bar x)} , where each h _i is a polynomial that depends on only ρ linear functions, and each g _i is a product of linear functions (when h _i = 1, for each i, then we get the class of depth-3 circuits with k multiplication gates, also known as ΣΠΣ(k) circuits, but the general case is much richer). When max _i (deg(h _i · g _i )) = d we say that f is computable by a ΣΠΣ(k; d;ρ) circuit. We obtain the following results.

Chemical Modification of a Bacterial Siderophore by a Competitor in Dual-Species Biofilms

Chemical communication between competing bacteria in multi-species environments often enables both species to adapt and survive, and perhaps even thrive. P. aeruginosa and S. aureus are two bacterial pathogens found in natural biofilms, especially in the lungs of cystic fibrosis (CF) patients, where recent studies showed that there is often cooperation between the two species, leading to increased disease severity and antibiotic resistance. However, the mechanisms behind this cooperation are poorly understood. In this study, we analyzed co-cultured biofilms in various settings, and we applied untargeted mass spectrometry-based metabolomics analyses, combined with synthetic validation of candidate compounds. We unexpectedly discovered that S. aureus can convert pyochelin into pyochelin methyl ester, an analogue of pyochelin with reduced affinity for iron (III). This conversion allows S. aureus to coexist more readily with P. aeruginosa and unveils a mechanism underlying the formation of robust dual-species biofilms.