89 research outputs found
High-precision determination of transition amplitudes of principal transitions in Cs from van der Waals coefficient C_6
A method for determination of atomic dipole matrix elements of principal
transitions from the value of dispersion coefficient C_6 of molecular
potentials correlating to two ground-state atoms is proposed. The method is
illustrated on atomic Cs using C_6 deduced from high-resolution Feshbach
spectroscopy. The following reduced matrix elements are determined < 6S_{1/2}
|| D || 6P_{1/2} > =4.5028(60) |e| a0 and
=6.3373(84) |e| a0 (a0= 0.529177 \times 10^{-8} cm.) These matrix elements are
consistent with the results of the most accurate direct lifetime measurements
and have a similar uncertainty. It is argued that the uncertainty can be
considerably reduced as the coefficient C_6 is constrained further.Comment: 4 pages; 3 fig
Topological Inflation
We consider the possibility that higher-curvature corrections could drive
inflation after the compactification to four dimensions. Assuming that the
low-energy limit of the fundamental theory is eleven-dimensional supergravity
to the lowest order, including curvature corrections and taking the descent
from eleven dimensions to four via an intermediate five-dimensional theory, as
favored by recent considerations of unification at some scale around GeV, we may obtain a simple model of inflation in four dimensions. The
effective degrees of freedom are two scalar fields and the metric. The scalars
arise as the large five-dimensional modulus and the self-interacting conformal
mode of the metric. The effective potential has a local maximum in addition to
the more usual minimum. However, the potential is quite flat at the top, and
admits topological inflation. We show that the model can resolve cosmological
problems and provide a mechanism for structure formation with very little fine
tuning.Comment: 25 pages, latex, 2 eps figures, minor changes, accepted for
publication in Phys. Rev.
Electrodeposition of copper into high aspect ratio PCB micro-via using megasonic agitation
This paper presents the use of micro-particle imaging velocimetry (micro-PIV) to analyse fluid flow and hence ion replenishment in PCB micro-via during the electroplating process. The cross section of a PCB via is fabricated in PMMA to allow optical access to the sample. Fluid flow within two 1:1 aspect ratio blind micro-vias, one with straight side walls and the other with tapered side walls were compared. Flow is also analysed in a 1:1 aspect ratio through via. Flow rates measured using micro-PIV are used to validate simulated flow models. The results show that there are increased flow rates within the blind via with tapered side walls. This goes some way to explaining the improved electroplating results obtained in industry when tapered vias are used. Initial experimental results using megasonic streaming to remove bubbles from blind micro-via and promote ion transportation within high aspect ratio PCB micro-via to enhance electrodeposition are also reported
Bactericidal synergism through enterocin AS-48 and chemical preservatives against Staphylococcus aureus
- …