938 research outputs found
Feasibility study of electromechanical cylinder drivetrain for offshore mechatronic systems
Currently, there is an increasing focus on the environmental impact and energy consumption of the oil and gas industry. In offshore drilling equipment, electric motors tend to replace traditionally used hydraulic motors, especially in rotational motion control applications. However, force densities available from linear hydraulic actuators are still typically higher than those of electric actuators. Therefore, usually the remaining source of hydraulic power is thereby the hydraulic cylinder. This paper presents a feasibility study on the implementation of an electromechanical cylinder drivetrain on an offshore vertical pipe handling machine. The scope of this paper is to investigate the feasibility of a commercial off-the-shelf drivetrain. With a focus on the motion performance, numerical modeling and simulation are used when sizing and selecting the components of the considered electromechanical cylinder drivetrain. The simulation results are analyzed and discussed together with a literature study regarding advantages and disadvantages of the proposed solution considering the design criteria of offshore drilling equipment. It is concluded that the selected drivetrain can only satisfy the static motion requirements since the required transmitted power is higher than the recommended permissible power of the transmission screw. Consequently, based on the recommendation of the manufacturer, avoidance of overheating cannot be guaranteed for the drivetrain combinations considered for the case study presented in this paper. Hence, to avoid overheating, the average speed of the motion cycle must be decreased. Alternatively, external cooling or temperature monitoring and control system that prevents overheating could be implemented
Glucagon-like peptide-1 is a marker of systemic inflammation in patients treated with high-dose chemotherapy and autologous stem cell transplantation
Size Effects in Carbon Nanotubes
The inter-shell spacing of multi-walled carbon nanotubes was determined by
analyzing the high resolution transmission electron microscopy images of these
nanotubes. For the nanotubes that were studied, the inter-shell spacing
is found to range from 0.34 to 0.39 nm, increasing with
decreasing tube diameter. A model based on the results from real space image
analysis is used to explain the variation in inter-shell spacings obtained from
reciprocal space periodicity analysis. The increase in inter-shell spacing with
decreased nanotube diameter is attributed to the high curvature, resulting in
an increased repulsive force, associated with the decreased diameter of the
nanotube shells.Comment: 4 pages. RevTeX. 4 figure
Disclination vortices in elastic media
The vortex-like solutions are studied in the framework of the gauge model of
disclinations in elastic continuum. A complete set of model equations with
disclination driven dislocations taken into account is considered. Within the
linear approximation an exact solution for a low-angle wedge disclination is
found to be independent from the coupling constants of the theory. As a result,
no additional dimensional characteristics (like the core radius of the defect)
are involved. The situation changes drastically for 2\pi vortices where two
characteristic lengths, l_\phi and l_W, become of importance. The asymptotical
behaviour of the solutions for both singular and nonsingular 2\pi vortices is
studied. Forces between pairs of vortices are calculated.Comment: 13 pages, published versio
Order N photonic band structures for metals and other dispersive materials
We show, for the first time, how to calculate photonic band structures for
metals and other dispersive systems using an efficient Order N scheme. The
method is applied to two simple periodic metallic systems where it gives
results in close agreement with calculations made with other techniques.
Further, the approach demonstrates excellent numerical stablity within the
limits we give. Our new method opens the way for efficient calculations on
complex structures containing a whole new class of material.Comment: Four pages, plus seven postscript figures. Submitted to Physical
Review Letter
Theory of extraordinary optical transmission through subwavelength hole arrays
We present a fully three-dimensional theoretical study of the extraordinary
transmission of light through subwavelength hole arrays in optically thick
metal films. Good agreement is obtained with experimental data. An analytical
minimal model is also developed, which conclusively shows that the enhancement
of transmission is due to tunneling through surface plasmons formed on each
metal-dielectric interfaces. Different regimes of tunneling (resonant through a
''surface plasmon molecule", or sequential through two isolated surface
plasmons) are found depending on the geometrical parameters defining the
system.Comment: 4 pages, 4 figure
On the metal-insulator transition in the two-chain model of correlated fermions
The doping-induced metal-insulator transition in two-chain systems of
correlated fermions is studied using a solvable limit of the t-J model and the
fact that various strong- and weak-coupling limits of the two-chain model are
in the same phase, i.e. have the same low-energy properties. It is shown that
the Luttinger-liquid parameter K_\rho takes the universal value unity as the
insulating state (half-filling) is approached, implying dominant d-type
superconducting fluctuations, independently of the interaction strength. The
crossover to insulating behavior of correlations as the transition is
approached is discussed.Comment: 7 pages, 1 figur
Exact SO(8) Symmetry in the Weakly-Interacting Two-Leg Ladder
A perturbative renormalization group analysis of interacting electrons on a
two-leg ladder reveals that at half-filling any weakly repulsive system scales
onto an exactly soluble Gross-Neveu model with a hidden SO(8) symmetry. The
half-filled ground state is a Mott insulator with short-range d-wave pair
correlations. We extract the exact energies, degeneracies, and quantum numbers
of *all* the low energy excited multiplets. One energy (mass) m octets contains
Cooper pair, magnon, and density-wave excitations, two more octets contain
single-particle excitations, and a mass \sqrt{3}m antisymmetric tensor contains
28 "bound states". Exact single-particle and spin gaps are found for the
lightly-doped (d-wave paired one-dimension Bose fluid) system. We also
determine the four other robust phases occuring at half-filling for partially
attractive interactions. All 5 phases have distinct SO(8) symmetries, but share
S.C. Zhang's SO(5) as a common subgroup.Comment: RevTex, 35 pages with 15 figure
Analysis of quantum conductance of carbon nanotube junctions by the effective mass approximation
The electron transport through the nanotube junctions which connect the
different metallic nanotubes by a pair of a pentagonal defect and a heptagonal
defect is investigated by Landauer's formula and the effective mass
approximation. From our previous calculations based on the tight binding model,
it has been known that the conductance is determined almost only by two
parameters,i.e., the energy in the unit of the onset energy of more than two
channels and the ratio of the radii of the two nanotubes. The conductance is
calculated again by the effective mass theory in this paper and a simple
analytical form of the conductance is obtained considering a special boundary
conditions of the envelop wavefunctions. The two scaling parameters appear
naturally in this treatment. The results by this formula coincide fairly well
with those of the tight binding model.
The physical origin of the scaling law is clarified by this approach.Comment: RevTe
Making Micro- and Nano-beams by Channeling in Micro- and Nano-structures
A particle beam of very small cross-section is useful in many accelerator
applications including biological and medical ones. We show the capability of
the channeling technique using a micron-sized structure on a surface of a
single crystal, or using a nanotube, to produce beam of a cross-section down to
1 square micrometer (or nanometer). The channeled beam can be deflected and
thus well separated in angle and space from the primary and scattered
particles. Monte Carlo simulation is done to evaluate the characteristics of a
channeled microbeam. Emittances down to 0.1-0.001 nanometer radian, and flux up
to 1 million particles per square micron per second, can be achieved for
protons and ions.Comment: 8 pages, 4 figure
- …