6,374 research outputs found
Helmholtz resonance in a piezoelectricâhydraulic pump-based hybrid actuator
This paper demonstrates that a hydraulically acting Helmholtz resonator can exist in a piezoelectricâhydraulic pump (PHP) based hybrid actuator, which in turn affects the volumetric efficiency of the PHP. The simulation and experimental results illustrate the effect of Helmholtz resonance on the flow rate performance of the PHP. The study also shows how to shift the Helmholtz resonant frequency to a higher value through changing parameters such as the cylinder diameter and the effective bulk modulus of the working fluid, which will improve the volumetric efficiency and broaden the operating frequency range of the PHP actuator.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90809/1/0964-1726_20_1_015010.pd
XMM-Newton Observations of NGC 507: Super-solar Metal Abundances in the Hot ISM
We present the results of the X-ray XMM-Newton observations of NGC 507, a
dominant elliptical galaxy in a small group of galaxies, and report
'super-solar' metal abundances of both Fe and a-elements in the hot ISM of this
galaxy. We find Z_Fe = 2-3 times solar inside the D25 ellipse of NGC 507. This
is the highest Z_Fe reported so far for the hot halo of an elliptical galaxy;
this high Iron abundance is fully consistent with the predictions of stellar
evolution models, which include the yield of both type II and Ia supernovae.
The spatially resolved, high quality XMM spectra provide enough statistics to
formally require at least three emission components: two soft thermal
components indicating a range of temperatures in the hot ISM, plus a harder
component, consistent with the integrated output of low mass X-ray binaries
(LMXBs). The abundance of a-elements (most accurately determined by Si) is also
found to be super-solar. The a-elements to Fe abundance ratio is close to the
solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was
originated from SNe Type Ia. The a-element to Fe abundance ratio remains
constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are
well mixed in a scale much larger than the extent of the stellar body.Comment: 29 pages, 6 figures, Accepted in ApJ (v613, Oct. 1, 2004); Minor
revisions after referee's comments; A high-resolution pdf file available at
http://hea-www.harvard.edu/~kim/pap/N507_XMM.pd
Switching sliding mode force tracking control of piezoelectric-hydraulic pump-based friction element actuation systems for automotive transmissions
In this study, a nonlinear sliding-mode controller is designed for force tracking of a piezoelectric-hydraulic pump (PHP)-based actuation system, which is developed to replace the current electro-hydraulic actuation systems for automatic transmission (AT) friction elements, such as band brakes or clutches. By utilizing the PHP, one can eliminate the various hydraulic components (oil pump, regulating valve and control valve) in current ATs and achieve a simpler configuration with more efficient operation. With the derived governing equation of motion of the PHP-based actuation system integrated with the friction element (band brake), a switching control law is synthesized based on the sliding-mode theory. To evaluate the effectiveness of the proposed control law, its force tracking performance for the engagement of a friction element during an AT ##IMG## [http://ej.iop.org/images/0964-1726/18/8/085004/sms306895ieqn1.gif] {1 to 2} up-shift is examined experimentally. It is shown that one can successfully track the desired force trajectory for AT shift control with small tracking error. This study demonstrates the potential of the PHP as a new controllable actuation system for AT friction elements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65109/2/sms9_8_085004.pd
Origins of anomalous electronic structures of epitaxial graphene on silicon carbide
On the basis of first-principles calculations, we report that a novel
interfacial atomic structure occurs between graphene and the surface of silicon
carbide, destroying the Dirac point of graphene and opening a substantial
energy gap there. In the calculated atomic structures, a quasi-periodic
domain pattern emerges out of a larger commensurate
periodic interfacial reconstruction,
resolving a long standing experimental controversy on the periodicity of the
interfacial superstructures. Our theoretical energy spectrum shows a gap and
midgap states at the Dirac point of graphene, which are in excellent agreement
with the recently-observed anomalous angle-resolved photoemission spectra.
Beyond solving unexplained issues of epitaxial graphene, our atomistic study
may provide a way to engineer the energy gaps of graphene on substrates.Comment: Additional references added; published version; 4 pages, 4 figure
Adoption of dynamic simulation for an energy performance rating tool for Korean residential buildings : EDEM-SAMSUNG
Currently, there is a high emphasis on reducing the energy consumption and carbon emissions of buildings worldwide. Korea is facing an emerging issue of energy savings in buildings in perspective of new green economic policy. In this context, various policy measures including the energy efficiency ratings for buildings are being implemented for domestic and non-domestic buildings. In practice, design teams tend to prefer easy to use assessment tools to optimise energy performance and carbon ratings while they are concerned about calculation accuracy and the accurate representation of the dynamics involved associated with the characteristics of Korean residential buildings. This paper presents an assessment tool, named âEDEM-Samsungâ that aims to address these challenges for Korean residential apartments, which often encounter complex design issues. EDEM-Samsung is a tool that enables users to make rapid decisions identifying the effect of design parameter changes on energy and carbon ratings with an effective user interface and without compromising accuracy. This paper describes the architecture and functionalities of the tool, and the advantages offered to Korean designers
Isobar of an ideal Bose gas within the grand canonical ensemble
We investigate the isobar of an ideal Bose gas confined in a cubic box within
the grand canonical ensemble, for a large yet finite number of particles, N.
After solving the equation of the spinodal curve, we derive precise formulae
for the supercooling and the superheating temperatures which reveal an N^{-1/3}
or N^{-1/4} power correction to the known Bose-Einstein condensation
temperature in the thermodynamic limit. Numerical computations confirm the
accuracy of our analytical approximation, and further show that the isobar
zigzags on the temperature-volume plane if N is greater than or equal to 14393.
In particular, for the Avogadro's number of particles, the volume expands
discretely about 10^5 times. Our results quantitatively agree with a previous
study on the canonical ensemble within 0.1% error.Comment: 6 pages, 2 figures; Reference added. Accepted for publication in
Phys. Rev.
On A two-variable p-adic l_q function
We prove that a two-variable p-adic l_q-function has the series p-adic
expansion which interpolates a linear combinations of terms of the generalized
q-Euler polynomials at non positive integers. The proof of this original
construction is due to Kubota and Leopoldt in 1964, although the method given
this note is due to WashingtonComment: 11S8
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