13,537 research outputs found
A MEMS electrostatic particle transportation system
We demonstrate here an electrostatic MEMS system
capable of transporting particles 5-10ÎŒm in diameter in
air. This system consists of 3-phase electrode arrays
covered by insulators (Figs. 1, 2). Extensive testing of
this system has been done using a variety of insulation
materials (silicon nitride, photoresist, and Teflon),
thickness (0- 12ÎŒm), particle sizes (1-10ÎŒm), particle
materials (metal, glass, polystyrene, spores, etc),
waveforms, frequencies, and voltages. Although
previous literature [1-2] claimed it impractical to
electrostatically transport particles with sizes 5-10ÎŒm
due to complex surface forces, this effort actually
shows it feasible (as high as 90% efficiency) with the
optimal combination of insulation thickness, electrode
geometry, and insulation material. Moreover, we suggest a qualitative theory for our particle transportation system which is consistent with our data and finite-element electrostatic simulations
Behavior of Interfaces Between Structural and Geologic Media
The main objective of this paper is to identify and discuss the subject of the effect of interface behavior on the overall soil-structure interaction in building foundation systems. A brief review of the previous approaches based on the assumption of compatibility between the structure and soil is followed by a discussion of the recent efforts toward inclusion of relative slip, debonding and rebonding at interfaces. Here available models in the context of the lumped parameter and finite element approaches are reviewed. A number of models used in static and dynamic analyses are presented, and the difficulties associated with those based on relative displacement, particularly in relation to the (arbitrary) choices of normal and shear stiffness, are discussed. Some ideas toward a simple but potentially promising model based on the use of thin element of soil (or structural medium) as interface is presented. The importance of appropriate laboratory tests is established and is followed by a review of available laboratory test devices for static and dynamic interfaces. Finally, a brief description of a new multi-degree-of-freedom device including testing of interface under vertical, horizontal, torsional and rocking modes is described together with preliminary test results
Case Studies Through Material Modelling and Computation
This paper describes a number of case studies by using numerical procedures conducted by the author and his co-workers over a number of years. The case studies involve a wide range of static and dynamic stress-deformation, seepage and stability, and consolidation problems. The numerical procedures use simple linear and nonlinear elastic models, to advanced but simplified hierarchical plasticity based models for geologic materials and interfaces/joints. The evolution from the use of simple to advanced models is guided by the realization that it is essential to employ models that are capable of handling the complexities in geotechnical systems. In addition to use of the conventional and empirical methods, it is advisable to develop and utilize improved and simplified techniques based on basic principles of mechanics. This approach can allow the geotechnical engineer access to models and procedures towards improved and rational solutions for case studies and for practical applications
Ultracold neutron depolarization in magnetic bottles
We analyze the depolarization of ultracold neutrons confined in a magnetic
field configuration similar to those used in existing or proposed
magneto-gravitational storage experiments aiming at a precise measurement of
the neutron lifetime. We use an extension of the semi-classical Majorana
approach as well as an approximate quantum mechanical analysis, both pioneered
by Walstrom et al. [Nucl. Instr. Meth. Phys. Res. A 599, 82 (2009)]. In
contrast with this previous work we do not restrict the analysis to purely
vertical modes of neutron motion. The lateral motion is shown to cause the
predominant depolarization loss in a magnetic storage trap. The system studied
also allowed us to estimate the depolarization loss suffered by ultracold
neutrons totally reflected on a non-magnetic mirror immersed in a magnetic
field. This problem is of preeminent importance in polarized neutron decay
studies such as the measurement of the asymmetry parameter A using ultracold
neutrons, and it may limit the efficiency of ultracold neutron polarizers based
on passage through a high magnetic field.Comment: 18 pages, 6 figure
Spin flip loss in magnetic storage of ultracold neutrons
We analyze the depolarization of ultracold neutrons confined in a magnetic
field configuration similar to those used in existing or proposed
magneto-gravitational storage experiments aiming at a precise measurement of
the neutron lifetime. We use an approximate quantum mechanical analysis such as
pioneered by Walstrom \emph{et al} [Nucl. Instrum. Methods Phys. Res. A 599, 82
(2009)]. Our analysis is not restricted to purely vertical modes of neutron
motion. The lateral motion is shown to cause the predominant depolarization
loss in a magnetic storage trap.Comment: 12 pages, 3 figures, for Proceedings of Neutron Lifetime Worksho
Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation
Pendlebury [Phys. Rev. A , 032102 (2004)] were
the first to investigate the role of geometric phases in searches for an
electric dipole moment (EDM) of elementary particles based on Ramsey-separated
oscillatory field magnetic resonance with trapped ultracold neutrons and
comagnetometer atoms. Their work was based on the Bloch equation and later work
using the density matrix corroborated the results and extended the scope to
describe the dynamics of spins in general fields and in bounded geometries. We
solve the Schr\"odinger equation directly for cylindrical trap geometry and
obtain a full description of EDM-relevant spin behavior in general fields,
including the short-time transients and vertical spin oscillation in the entire
range of particle velocities. We apply this method to general macroscopic
fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure
Measuring Technology Achievement of Nations and the Capacity to Participate in the Network Age
human development, democracy
See-saw fermion masses in an SO(10) GUT
In this work we study an SO(10) GUT model with minimum Higgs representations
belonging only to the 210 and 16 dimensional representations of SO(10). We add
a singlet fermion S in addition to the usual 16 dimensional representation
containing quarks and leptons. There are no Higgs bi-doublets and so charged
fermion masses come from one-loop corrections. Consequently all the fermion
masses, Dirac and Majorana, are of the see-saw type. We minimize the Higgs
potential and show how the left-right symmetry is broken in our model where it
is assumed that a D-parity odd Higgs field gets a vacuum expectation value at
the grand unification scale. From the renormalization group equations we infer
that in our model unification happens at 10^{15} GeV and left-right symmetry
can be extended up to some values just above 10^{11} GeV. The Yukawa sector of
our model is completely different from most of the standard grand unified
theories and we explicitly show how the Yukawa sector will look like in the
different phases and briefly comment on the running of the top quark mass. We
end with a brief analysis of lepton number asymmetry generated from the
interactions in our model.Comment: 30 pages, 10 figure
A Singular Perturbation Analysis for \\Unstable Systems with Convective Nonlinearity
We use a singular perturbation method to study the interface dynamics of a
non-conserved order parameter (NCOP) system, of the reaction-diffusion type,
for the case where an external bias field or convection is present. We find
that this method, developed by Kawasaki, Yalabik and Gunton for the
time-dependant Ginzburg-Landau equation and used successfully on other NCOP
systems, breaks down for our system when the strength of bias/convection gets
large enough.Comment: 5 pages, PostScript forma
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