Chemical models of the hydrophobic interaction: Apparent molal volumes and heat capacities of three symmetrical bolaform electrolytes and their homologous monomers in aqueous solution at 25°C

The densities and volumetric specific heats of aqueous solutions of Bu₃NHBr, Pent₃NHCl, and three diazonium salts, HN?Oct₃?NHBr₂, HN?Dec₃?NHCl₂, and Bu₃N?Oct?NBu₃Br₂, have been measured at 25°C. From these data, the apparent molal volumes φ _v and apparent molal heat capacities φ _c have been calculated and are reported here. In the series of compounds chosen, the diazonium (higher homologs) can be regarded as dimers of the alkyl-substituted ammonium ions (lower homologs), and these systems are examined as chemical models for the hydrophobic interaction. With the three homologous pairs studied here, the chemical model predicts that the strong interaction (limitingly, chemical binding) of two hydrocarbon chains in water leads to a major decrease in both φ _v and φ _c of the interacting solutes, ca.?22 cm³-mole^?1 and ?200 J-^oK^?1-mole^?1. These predictions constitute limiting behavior — useful, but not sufficient, to explain the observed concentration dependence of φ _v and φ _c in aqueous solutions of the lower homologs Bu₃NHBr, Pent₃NHCl, and Bu₄NBr. An explanation for the concentration dependence of φ _c is suggested with reference to ultrasonic relaxation data.     

Detection of Escherichia coli O157:H7 bacteria by a combination of immunofluorescent staining and capillary electrophoresis

As the number of incidents of bacterial infections continues to rise around the globe, simpler, faster, and more sensitive diagnostic techniques are required to improve the safety of the food supply and to screen for potential bacterial infections in humans. We present here direct and indirect approaches for the detection of bacteria, which are based upon a combination of immunofluorescent staining and capillary electrophoresis. In the direct approach, Escherichia coli O157:H7 bacteria stained with fluorescein-tagged specific antibodies are detected by CE, while in the indirect approach fluorescein-tagged specific antibodies to E. coli are first captured by E. coli O157:H7 bacteria and then released and detected by CE. We have identified suitable bacteria staining and CE protocols, which involved a 10 mM Tris-borate-EDTA (TBE) buffer, 0.25 micro g antibody/1 million bacteria, and capillaries dynamically coated with poly-N-hydroxyethylacrylamide (polyDuramide). We have also successfully detected the presence of E. coli O157:H7 in contaminated meat. The total time required for analysis was 6-8 h, which is less than that realized in most commercial assays presently available.     

Electrochemical determination of acetaminophen at a carbon electrode modified in the presence of β-cyclodextrin: role of the activated glassy carbon and the electropolymerised β-cyclodextrin

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10^–3 cm² s^–1 and 3.4 × 10^–3 cm² s^–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10^–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE.

     

Solitons in nonlinear media with an infinite range of nonlocality: first observation of coherent elliptic solitons and of vortex-ring solitons

We present an experimental study on wave propagation in highly nonlocal optically nonlinear media, for which far-away boundary conditions significantly affect the evolution of localized beams. As an example, we set the boundary conditions to be anisotropic and demonstrate the first experimental observation of coherent elliptic solitons. Furthermore, exploiting the natural ability of such nonlinearities to eliminate azimuthal instabilities, we perform the first observation of stable vortex-ring solitons. These features of highly nonlocal nonlinearities affected by far-away boundary conditions open new directions in nonlinear science by facilitating remote control over soliton propagation.     

Boundary force effects exerted on solitons in highly nonlinear media

We study the effects caused by remote boundaries on soliton dynamics in nonlinear media with a large range of nonlocality, and demonstrate theoretically and experimentally how asymmetric boundary forces can lead to soliton steering and oscillation in predetermined trajectories.     

Remarks on formulating an adhesion problem using Euler’s elastica (draft)

Three formulations for the problem of an elastica adhering to a rigid surface are discussed and compared. These include stationary principles, the surface integral of Eshelby’s energy-momentum tensor, and the material (configurational) force balance. The configuration at static equilibrium is predicted in closed form for a pair of structures that arise in nano- and microscale applications.     

Free electron laser pumped by a powerful traveling electromagneticwave

A three-wave free-electron laser (FEL) was operated with a powerful 8.4-GHz electromagnetic pump wave replacing the usual magnetostatic wiggler. The presence of a uniform axial magnetic field B₀ produced cyclotron-harmonic idler waves. Peaks in the emission spectrum corresponding to cyclotron harmonics were observed covering a frequency range from 16.5 to 130 GHz. The frequency spectrum of this novel FEL mechanism was tuned continuously by the variation of B₀     

Starting energy and current for a large diameter finite lengthbackward wave oscillator operated at the fundamental mode

We study the starting conditions for a large diameter (diameter/wavelength=4.8) finite length backward wave oscillator designed for 24-GHz operation at the fundamental TM₀₁ mode. This geometry is very promising for high power handling capability. We analyze two separate threshold conditions. First, finite length effects give rise to a threshold in electron beam energy below which oscillations cannot be sustained at any beam current. The second is the more familiar current threshold known as a start current. It is also found that the growth rate for the fundamental mode can be much larger than those of other higher order modes thus leading to coherent operation of large diameter sources free from mode competition