Review of the state of the art of preparative thin-layer chromatography

The state of the art of preparative thin-layer chromatography (PTLC) based on the literature published from 2007 through 2016 is reviewed. Classical capillary flow PTLC, forced flow PTLC, precoated and laboratory prepared plates, instruments, and micropreparative TLC are all covered, including techniques, instruments, and applications. Prospects for future applications and advances in PTLC are suggested.     

Reciprocity and power-flow theorems for the scattering of plane elastic waves in a half space

In this paper we present six field-reciprocity relations, and an additional six power-reciprocity relations for the far-zone scattered field if time-harmonic plane elastic waves are incident upon an obstacle in a half space. The incident waves are successively selected as to be either a P-wave, a SV-wave or a Rayleigh surface wave, each propagating in a prescribed direction. In the derivations we employ an explicit integral representation for the far-zone scattered field amplitude. The latter is obtained by expanding the half-space Green's displacement tensor in the far-zone region. Then, starting with the general Betti-Rayleigh theorem, the reciprocity identities are systematically inferred by inspection. We also present energy-conservation relations due to a single incident P-, SV- or Rayleigh wave.     

Microscale Crystals of Cytochrome c and Calixarene on Electrodes: Interprotein Electron Transfer between Defined Sites

The assembly of redox proteins on electrodes is an important step in biosensor development. Recently, p‐sulfonato‐calix[4]arene was shown to act as “molecular glue” for the assembly and crystallization of cytochrome c (cyt c). Electrochemical data are presented for microscale cyt c–calixarene crystals grown on self‐assembled monolayers (SAM)‐modified Au electrodes. The crystals were characterized by cyclic voltammetry and exceptionally high concentrations of electroactive cyt c were obtained. The peak currents were found to increase linearly with the square root of the scan rate, thus allowing an evaluation of the rate constant for electron self‐exchange. This study revealed high electroactivity accompanied by fast interprotein electron transfer in crystals, which may have implications for the construction of novel bioelectronic devices.     

Oscillatory flow in microchannels

Commonly used, lumped-parameter expressions for the impedance of an incompressible viscous fluid subjected to harmonic oscillations in a channel were compared with exact expressions, based on solutions of the Navier-Stokes equations for slots and channels of circular and rectangular cross-section, and were found to differ by as much as 30% in amplitude. These differences resulted in predicted discrepancies by as much as 400% in frequency response amplitude for simple second-order systems based on size scales and frequencies encountered in microfluidic devices. These predictions were verified experimentally for rectangular microchannels and indicate that underdamped fluidic systems operating near the corner frequency of any included flow channel should be modeled with exact expressions for impedance to avoid potentially large errors in predicted behavior.List of symbols A Channel cross-sectional area (m²) - A_c Membrane area (m²) - a Rectangular duct and slot half-width or radius (m) - b Rectangular duct half-depth and slot depth (m) - C Capacitance (m³/Pa) - C - D_h Channel hydraulic diameter (m) - E Voltage (V) - f Darcy friction factor - F Force (N) - I Channel inertance (Pa s²/m³) - i - Imaginary part of a complex number - J_k Bessel function of the first kind of order k - System transfer function - K Sum of minor loss factors - k Membrane stiffness (N/m) - L Channel length (m) - n Outward unit normal vector - P Fluid pressure (Pa) - p_n - Q Volumetric flow rate (m³/s) - R Channel resistance (Pa s/m³) - Real part of a complex number - Re Reynolds number, - V Velocity (m/s) - _V Volume (m³) - w Axial component of velocity (m/s) - Harmonic amplitude of membrane centerline displacement - Fluid impedance (kg/m⁴ s) - Duct aspect ratio, b/a - ² Nondimensional frequency parameter, - Nondimensional corner frequency, - Membrane shape factor - C/C - µ Fluid dynamic viscosity (Pa s) - Fluid kinematic viscosity (m²/s) - Mass density (kg/m³) - Radian frequency - _c R_s/I_s cutoff or corner frequency - _n Undamped natural frequency - Channel shape parameter in Eqs. 29 and 30 - Damping ratio - ( )_e Exact property - ( )_s Simplified property - (^–) Spatial average - Complex quantity     

A PDE representation of the density of the minimal entropy martingale measure in stochastic volatility markets

Under general conditions stated in Rheinländer [An entropy approach to the stein/stein model with correlation. Preprint, 2003, ETH Zürich.], we prove that in a stochastic volatility market the Radon–Nikodym density of the minimal entropy martingale measure (MEMM) can be expressed in terms of the solution of a semilinear PDE. The semilinear PDE is suggested by the dynamic programming approach to the utility indifference pricing problem of contingent claims. One of our main results is the existence and uniqueness of a classical solution of the semilinear PDE in the case of a general stochastic volatility model with additive noise correlated with the asset price. Our results are applied to the Stein–Stein and Heston stochastic volatility models.     

Anticipative calculus for Lévy processes and stochastic differential equations*

We develop an anticipative calculus for Lévy processes with finite second moment for analysing anticipating stochastic differential equations. The calculus is based on the chaos expansion of square-integrable random variables in terms of iterated integrals with respect to the compensated Poisson random measure. We define a space of smooth and generalized random variables in terms of such chaos expansions, and present anticipative stochastic integration, the Wick product and the so-called 𝒮-transform. These concepts serve as tools for studying general Wick type stochastic differential equations with anticipative initial conditions. We apply the 𝒮-transform to find the unique solutions to a class of linear stochastic differential equations. The solutions can be expressed in terms of the Wick product.     

Thermodynamic properties and ordering in liquid NaK alloys

The thermodynamic activities of sodium and potassium were determined by vapour-phase absorption spectrophotometry of atomic resonance lines. Both components exhibit significant positive deviations from ideality. Excess Gibbs energies computed from the activity data were combined with available heat-of-mixing data to yield values for excess entropies. The entropy of mixing which was found to be ideal in the sodium-rich liquid alloys provides no support for the earlier speculations about the existence of Na₂K molecules therein. The partial molar excess entropy of sodium in dilute solution in potassium was found to be surprisingly large and negative for a system of this type. A plausible model, involving sodium-sodium pairing, is proposed to account for the loss of configurational entropy.     

Distinguishability of stacks in ZnTe/ZnSe quantum dots via spectral analysis of Aharonov-Bohm oscillations

We have investigated the active-layer-thickness dependence of exciton-photon interactions in CuI microcavities. The active layer thickness was changed from λ/2 to 2λ, where λ corresponds to an effective resonant wavelength of the lowest-lying exciton. In the CuI active layer, thermal strain removes the degeneracy of the heavy-hole (HH) and light-hole (LH) excitons at the Γ point. Angle-resolved reflectance spectra measured at 10 K demonstrate the strong coupling between the HH and LH excitons and cavity photon, resulting in the formation of three cavity-polariton branches: the lower, middle, and upper polariton branches. The energies of the three cavity-polariton modes as a function of incidence angle are reasonably explained using a phenomenological Hamiltonian to describe the exciton-photon strong coupling. It is found that the interaction energies of the cavity-polariton modes, the so-called vacuum Rabi-splitting energies, are systematically controlled from 29 (50) to 48 (84) meV for the LH (HH) exciton by changing the active layer thickness from λ/2 to 2λ. The active-layer-thickness dependence of the Rabi-splitting energies is semi-quantitatively explained by a simple model.     

Biomedical Applications of Selected Ion Monitoring

In 1961 Henneberg [1] employed selected ion monitoring (SIM) to study hydrocarbons eluting from a gas chromatographic column, and in 1966 the first biological application was reported by Sweeley, Elliott, Fries, and Ryhage [2]. Since these efforts and the early impetus given by Hammar, Holmstedt, and co-workers [3–6], SIM has found widespread application in biological, medicinal, and environmental research. Recent review articles have described ion monitoring work with magnetic sector instruments [7,8,8a,8b], quadrupole instruments [9], and time-of-flight instruments [19]. These articles provide comprehensive coverage of applications through 1972. This review emphasizes medicinal and biological applications through 1973 and attempts to evaluate current methods and recent developments.     

Influence of the annealing conditions on the polarization and electromechanical response of high‐energy‐electron‐irradiated poly(vinylidene fluoride trifluoroethylene) copolymer

In this study, we investigated the influence of annealing conditions before irradiation on the ferroelectric and electromechanical properties of uniaxially stretched high‐energy‐electron‐irradiated poly(vinylidene fluoride trifluoroethylene) (HEEIP) copolymer (68/32 mol %) films. For films annealed at one fixed temperature before the irradiation (one‐step annealing), the highest crystallinity, which was highly desirable for enhancing the electromechanical response, was obtained only for films annealed between 132 and 136 °C. In addition, annealing over 10 h in this temperature window resulted in a large increase in the crystal lamellar thickness, which was required for reducing the polarization hysteresis to a minimum in the HEEIP samples. For improvements in the mechanical qualities of the uniaxially stretched films, a two‐step annealing procedure was investigated; that is, before the irradiation, the films were first annealed at a lower temperature to release the mechanical stress in the films due to the stretching and then were annealed in the high‐temperature window to raise the crystallinity and crystalline size. The experimental results indicated that this approach could produce uniaxially stretched HEEIP films with much improved mechanical qualities. Furthermore, the uniaxially stretched HEEIP films with this two‐step annealing exhibited the same electromechanical response as or an even higher one than that from the one‐step‐annealed HEEIP films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 797–806, 2003