The molecular vibration-rotation hamiltonian

By use of commutation relations and sum rules Watson [1] has simplified the Darling and Dennison hamiltonian and obtained

The quantity H - U is thus identical to the analytical expression of the classical hamiltonian.

By reconsidering completely the question of the derivation of the quantum mechanical hamiltonian we intend to prove that the U term comes only from the particular method chosen to derive the quantum mechanical hamiltonian from its wave mechanical representations. From this we conclude that in the usual model, the quantum mechanical vibration-rotation hamiltonian has the same form as the classical one.     

On excitation transfer and relaxation models in low-temperature systems

Starting from Redfield's reduced density formalism, we derive the coupled relaxation equations and expressions for the rate constants applicable to excited dimer systems In a comparative discussion the limitations are shown of relaxation models derived previously.     

Gene delivery by electroporation after dielectrophoretic positioning of cells in a non-uniform electric field

We report the use of dielectrophoresis (DEP) to position U-937 monocytes within a non-uniform electric field, prior to electroporation (EP) for gene delivery. DEP positioning and EP pulsing were both accomplished using a common set of inert planar electrodes, micro-fabricated on a glass substrate. A single-shell model of the cell's dielectric properties and finite-element modeling of the electric field distribution permitted us to predict the major features of cell positioning. The extent to which electric pulses increased the permeability of the cell membranes to fluorescent molecules and to pEGFPLuc DNA plasmids were found to depend on prior positioning. For a given set of pulse parameters, EP was either irreversible (resulting in cytolysis), reversible (leading to gene delivery), or not detectable, depending on where cells were positioned. Our results clearly demonstrate that position-dependent EP of cells in a non-uniform electric field can be controlled by DEP.     

A study of defects in ultra-thin transparent coatings on polymers

2 or more). Received: 1 September 1998/Accepted: 6 October 1998     

CHO Cells Adhering to Nitrogen‐Rich Plasma‐Polymerised Ethylene Exhibit High Production of a Specific Recombinant Protein

In many industrial applications, inadequate cell attachment can be a limitation, especially when serum‐free media are used. Nitrogen‐rich plasma‐polymerised ethylene (PPE:N) exhibits high concentrations of polar groups that can help to promote the attachment of weakly adherent cell types. Tissue plasminogen activator‐producing Chinese hamster ovary (CHO) cells, adapted to suspension, were grown in the presence PPE:N flakes and were found to adhere to them. The growth rate was reduced, but cell viability was enhanced and their metabolism was more efficient, with generally higher recombinant protein productivity. Finally, cell adhesion on PPE:N surfaces was found to be independent of integrins, and was probably mediated by certain non‐specific interactions with the PPE:N surface.

     

New ideas in neutrino detection

What is new in the field of neutrino detection? In addition to new projects probing both the low and high ends of the neutrino energy scale, an inexpensive, effective technique is being developed to allow tagging of antineutrinos in water Cherenkov (WC) detectors via the addition to water of a solute with a large neutron cross-section and energetic γ daughters. Gadolinium is an excellent candidate since in recent years it has become very inexpensive, now less than $8 per kilogram in the form of commercially available gadolinium trichloride. This non-toxic, non-reactive substance is highly soluble in water. Neutron capture on gadolinium yields an 8.0 MeV gamma cascade easily seen in detectors like Super-Kamiokande. The uses of GdCl₃ as a possible upgrade for the Super-Kamiokande detector — with a view toward improving its performance as an antineutrino detector for supernova neutrinos and reactor neutrinos — are discussed, as are the ongoing R&;D efforts which aim to make this dream a reality within the next two years.     

Comparison of microwave and lower-frequency discharges for plasma polymerization

A plasma sustained by surface waves (SW) has been used to study the deposition rate R of hydrocarbon and fluorocarbon plasma polymer films as a function of excitation frequency f=/2 in the range 12–400 MHz. The SW technique allows one to vary only f while keeping constant all other parameters known to influence R, for example, power density in the plasma P. A plot of R/P at a total pressure of 200 m Torr (27 Pa) displays two plateaus, that at f<30 MHz being about five times lower than that at f100 MHz. This is attributed to the fact that electron energy distribution functions differ fundamentally at radio- (f50 MHz) and microwave (f100 MHz) frequencies, for the gas pressure range considered.     

Editorial

Plasmas and Polymers -