1,979 research outputs found
Global dynamic modeling of a transmission system
The work performed on global dynamic simulation and noise correlation of gear transmission systems at the University of Akron is outlined. The objective is to develop a comprehensive procedure to simulate the dynamics of the gear transmission system coupled with the effects of gear box vibrations. The developed numerical model is benchmarked with results from experimental tests at NASA Lewis Research Center. The modal synthesis approach is used to develop the global transient vibration analysis procedure used in the model. Modal dynamic characteristics of the rotor-gear-bearing system are calculated by the matrix transfer method while those of the gear box are evaluated by the finite element method (NASTRAN). A three-dimensional, axial-lateral coupled bearing model is used to couple the rotor vibrations with the gear box motion. The vibrations between the individual rotor systems are coupled through the nonlinear gear mesh interactions. The global equations of motion are solved in modal coordinates and the transient vibration of the system is evaluated by a variable time-stepping integration scheme. The relationship between housing vibration and resulting noise of the gear transmission system is generated by linear transfer functions using experimental data. A nonlinear relationship of the noise components to the fundamental mesh frequency is developed using the hypercoherence function. The numerically simulated vibrations and predicted noise of the gear transmission system are compared with the experimental results from the gear noise test rig at NASA Lewis Research Center. Results of the comparison indicate that the global dynamic model developed can accurately simulate the dynamics of a gear transmission system
Electricity consumption forecasting using Adaptive Neuro-Fuzzy Inference System (ANFIS)
Universiti Tun Hussein Onn Malaysia (UTHM) is a developing Malaysian Technical University. There is a great development of UTHM since its formation in 1993. Therefore, it is crucial to have accurate future electricity consumption forecasting for its future energy management and saving. Even though there are previous works of electricity consumption forecasting using Adaptive Neuro-Fuzzy Inference System (ANFIS), but most of their data are multivariate data. In this study, we have only univariate data of UTHM electricity consumption from January 2009 to December 2018 and wish to forecast 2019 consumption. The univariate data was converted to multivariate and ANFIS was chosen as it carries both advantages of Artificial Neural Network (ANN) and Fuzzy Inference System (FIS). ANFIS yields the MAPE between actual and predicted electricity consumption of 0.4002% which is relatively low if compared to previous works of UTHM electricity forecasting using time series model (11.14%), and first-order fuzzy time series (5.74%), and multiple linear regression (10.62%)
Vibration and noise analysis of a gear transmission system
This paper presents a comprehensive procedure to predict both the vibration and noise generated by a gear transmission system under normal operating conditions. The gearbox vibrations were obtained from both numerical simulation and experimental studies using a gear noise test rig. In addition, the noise generated by the gearbox vibrations was recorded during the experimental testing. A numerical method was used to develop linear relationships between the gearbox vibration and the generated noise. The hypercoherence function is introduced to correlate the nonlinear relationship between the fundamental noise frequency and its harmonics. A numerical procedure was developed using both the linear and nonlinear relationships generated from the experimental data to predict noise resulting from the gearbox vibrations. The application of this methodology is demonstrated by comparing the numerical and experimental results from the gear noise test rig
The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells
Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO2, but quantitative analysis of the role of facile TiCl4 treatment and thickness control of the compact TiO2 layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO2 layer to produce highly efficient planar PSCs. TiCl4 treatment of TiO2 layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl4 aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl4 treatment, PCE of 16.42% was achieved for PSCs with TiCl4 aqueous solution-treated TiO2 and 19.24% for PSCs with TiCl4 aqueous/ethanol solution-treated TiO2, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer
Exact Integration of the High Energy Scale in Doped Mott Insulators
We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99},
46404 (2007)) in which we constructed the exact low-energy theory of a doped
Mott insulator by explicitly integrating (rather than projecting) out the
degrees of freedom far away from the chemical potential. The exact low-energy
theory contains degrees of freedom that cannot be obtained from projective
schemes. In particular a new charge bosonic field emerges at low
energies that is not made out of elemental excitations. Such a field accounts
for dynamical spectral weight transfer across the Mott gap. At half-filling, we
show that two such excitations emerge which play a crucial role in preserving
the Luttinger surface along which the single-particle Green function vanishes.
In addition, the interactions with the bosonic fields defeat the artificial
local SU(2) symmetry that is present in the Heisenberg model. We also apply
this method to the Anderson-U impurity and show that in addition to the Kondo
interaction, bosonic degrees of freedom appear as well. Finally, we show that
as a result of the bosonic degree of freedom, the electron at low energies is
in a linear superposition of two excitations--one arising from the standard
projection into the low-energy sector and the other from the binding of a hole
and the boson.Comment: Published veriso
Electrokinetic behavior of two touching inhomogeneous biological cells and colloidal particles: Effects of multipolar interactions
We present a theory to investigate electro-kinetic behavior, namely,
electrorotation and dielectrophoresis under alternating current (AC) applied
fields for a pair of touching inhomogeneous colloidal particles and biological
cells. These inhomogeneous particles are treated as graded ones with physically
motivated model dielectric and conductivity profiles. The mutual polarization
interaction between the particles yields a change in their respective dipole
moments, and hence in the AC electrokinetic spectra. The multipolar
interactions between polarized particles are accurately captured by the
multiple images method. In the point-dipole limit, our theory reproduces the
known results. We find that the multipolar interactions as well as the spatial
fluctuations inside the particles can affect the AC electrokinetic spectra
significantly.Comment: Revised version with minor changes: References added and discussion
extende
Electrorotation of a pair of spherical particles
We present a theoretical study of electrorotation (ER) of two spherical
particles under the action of a rotating electric field. When the two particles
approach and finally touch, the mutual polarization interaction between the
particles leads to a change in the dipole moment of the individual particle and
hence the ER spectrum, as compared to that of the well-separated particles. The
mutual polarization effects are captured by the method of multiple images. From
the theoretical analysis, we find that the mutual polarization effects can
change the characteristic frequency at which the maximum angular velocity of
electrorotation occurs. The numerical results can be understood in the spectral
representation theory.Comment: Minor revisions; accepted by Phys. Rev.
Nonlinear ER effects in an ac applied field
The electric field used in most electrorheological (ER) experiments is
usually quite high, and nonlinear ER effects have been theoretically predicted
and experimentally measured recently. A direct method of measuring the
nonlinear ER effects is to examine the frequency dependence of the same
effects. For a sinusoidal applied field, we calculate the ac response which
generally includes higher harmonics. In is work, we develop a multiple image
formula, and calculate the total dipole moments of a pair of dielectric
spheres, embedded in a nonlinear host. The higher harmonics due to the
nonlinearity are calculated systematically.Comment: Presented at Conference on Computational Physics (CCP2000), held at
Gold Coast, Australia from 3-8, December 200
NMR studies of Successive Phase Transitions in Na0.5CoO2 and K0.5CoO2
59Co- and 23Na-NMR measurements have been carried out on polycrystalline and
c-axis aligned samples of Na0.5CoO2, which exhibits successive transitions at
temperatures T = 87 K (= Tc1) and T = 53 K (= Tc2). 59Co-NMR has also been
carried out on c-axis aligned crystallites of K0.5CoO2 with similar successive
transitions at Tc1 ~ 60 K and Tc2 ~ 20 K. For Na0.5CoO2, two sets of three NMR
lines of 23Na nuclei explained by considering the quadrupolar frequencies nuQ
~1.32 and 1.40 MHz have been observed above Tc1, as is expected from the
crystalline structure. Rather complicated but characteristic variation of the
23Na-NMR spectra has been observed with varying T through the transition
temperatures, and the internal fields at two crystallographically distinct Na
sites are discussed on the basis of the magnetic structures reported
previously. The internal fields at two distinct Co sites observed below Tc1 and
the 591/T1-T curves of Na0.5CoO2 and K0.5CoO2 are also discussed in a
comparative way.Comment: 7 pages, 10 figures, submitted to J. Phys. Soc. Jpn, correction is
made in right colum of p6 (35th line) as K0.5CoO2-->Na0.5CoO
The on-line comprehension of wh- movement structures in agrammatic Broca’s aphasia: Evidence from eyetracking
Dickey & Thompson (2004) present evidence that individuals with agrammatic Broca’s aphasia retain significant on-line gap-filling capacity, which improves in response to linguistically-motivated treatment (TUF; Thompson 2001). This paper presents data from an eyetracking study following up this result. Twelve agrammatic aphasic individuals’ and eight control participants’ eyes were tracked while they listened to stories ending with comprehension probes involving wh- movement (wh- object questions, object clefts). Aphasic participants’ responses to probes demonstrated impaired comprehension of wh- movement structures. However, their eye-movements indicated intact automatic processing of the movement sentences, even for wh- questions which they failed to comprehend
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