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Search Results: 1 - 10 of 9648 matches for " Philip Lo "
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The Effect of Atmospheric Plasma Paint Stripping on the Fatigue Crack Growth Properties of Aluminium Substrates  [PDF]
Ali Merati, Marko Yanishevsky, Tessa Despinic, Philip Lo
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2017, DOI: 10.4236/jmmce.2017.54014
Abstract: Paint removal is a common maintenance requirement for aircraft as well as naval and land vehicles, since external paint gets damaged and loses much of its corrosion protection effectiveness with time. Paint removal is also conducted when metallic aircraft structures are inspected periodically for fatigue cracks and corrosion. The conventional methods of removing paint employed throughout the Canadian Forces mainly include chemical stripping and abrasive media blasting. Chemical stripping involves the use of hazardous chemicals, which are high in Volatile Organic Compounds (VOC) and Hazardous Air Pollutants (HAP). Abrasive media blasting typically results in a substantial quantity of solid waste consisting of paint and blast residues. Such waste is subject to control under increasingly stringent environmental and safety regulations and its disposal is costly. The new Atmospheric Plasma (AP) paint removal process purports to be a high chemical energy, low thermal energy (cold plasma process), that should not damage temperature sensitive substructures, such as heat treated aerospace aluminium alloys. Fatigue strength is one of the key properties in aircraft structures. In order for AP paint stripping to be accepted as an aerospace industry standard paint removal process, it must be thoroughly tested to demonstrate that it does not adversely affect the fatigue properties of the substrate. This paper investigates effect of the paint removal process on fatigue crack growth of 7075-T6 and 2024-T3 aluminium panels.
Alternate Environmentally Friendly De-Painting Process for Aircraft Structures-Atmospheric Plasma  [PDF]
Ali Merati, Marko Yanishevsky, Tessa Despinic, Philip Lo, Vladimir Pankov
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2017, DOI: 10.4236/jmmce.2017.54019
Abstract: During the lifetime of aircraft structures, paint removal and re-application cycles are conducted to restore appearance and to enable inspection for fatigue cracks and corrosion damages. Current paint removals processes, including chemical and abrasive media blasting, yield large amounts of volatile organic compounds and hazardous air pollutants, and generate large quantities of waste which require proper disposal/treatment. They also have the potential to mask surface cracks and decrease the effectiveness of Liquid Penetrant Inspections (LPI). This study compares current paint stripping methods to a novel Atmospheric Plasma (AP) system, which claims to be a more environmentally friendly method. Aluminium and steel coupons were prepared with military aircraft quality topcoat and primer paint schemes and subjected to the three aforemen-tioned paint stripping processes. The results were then characterized in terms of paint removal effectiveness, potential damages to the metallic substrates, and effect on the LPI process. Hardness and conductivity measurements as well as metallographic sectioning and microscopy, were used to characterize the stripped samples. The results indicated that AP had no negative ramifications on detecting fatigue cracks in the substrates, and did not alter the temper, mechanical properties of the aerospace alloys studied. The AP process has the potential to replace current hazardous and less environmentally friendly paint removal methods; though a full systematic qualification and evaluation process is still required for it to be considered as an accepted industrial paint removal process.
Neutral Order Parameters in Metallic Criticality in d=2+1 from a Hairy Electron Star
Mohammad Edalati,Ka Wai Lo,Philip W. Phillips
Physics , 2011, DOI: 10.1103/PhysRevD.84.066007
Abstract: We use holography to study the spontaneous condensation of a neutral order parameter in a (2+1)-dimensional field theory at zero-temperature and finite density, dual to the electron star background of Hartnoll and Tavanfar. An appealing feature of this field theory is the emergence of an IR Lifshitz fixed-point with a finite dynamical critical exponent $z$, which is due to the strong interaction between critical bosonic degrees of freedom and a finite density of fermions (metallic quantum criticality). We show that under some circumstances the electron star background develops a neutral scalar hair whose holographic interpretation is that the boundary field theory undergoes a quantum phase transition, with a Berezinski-Kosterlitz-Thouless character, to a phase with a neutral order parameter. Including the backreaction of the bulk neutral scalar on the background, we argue that the two phases across the quantum critical point have different $z$, a novelty that exists in certain quantum phase transitions in condensed matter systems. We also analyze the system at finite temperature and find that the phase transition becomes, as expected, second-order. Embedding the neutral scalar into a higher form, a variety of interesting phases could potentially be realized for the boundary field theory. Examples which are of particular interest to condensed matter physics include an antiferromagnetic phase where a vector condenses and break the spin symmetry, a quadrupole nematic phase which involves the condensation of a symmetric traceless tensor breaking rotational symmetry, or different phases of a system with competing order parameters.
Pomeranchuk Instability in a non-Fermi Liquid from Holography
Mohammad Edalati,Ka Wai Lo,Philip W. Phillips
Physics , 2012, DOI: 10.1103/PhysRevD.86.086003
Abstract: The Pomeranchuk instability, in which an isotropic Fermi surface distorts and becomes anisotropic due to strong interactions, is a possible mechanism for the growing number of experimental systems which display transport properties that differ along the $x$ and $y$ axes. We show here that the gauge-gravity duality can be used to describe such an instability in fermionic systems. Our holographic model consists of fermions in a background which describes the causal propagation of a massive neutral spin-two field in an asymptotically AdS spacetime. The Fermi surfaces in the boundary theory distort spontaneously and become anisotropic once the neutral massive spin-two field develops a normalizable mode in the bulk. Analysis of the fermionic correlators reveals that the low-lying fermionic excitations are non-Fermi liquid-like both before and after the Fermi surface shape distortion. Further, the spectral weight along the Fermi surface is angularly dependent and can be made to vanish along certain directions.
Non-Fermi Liquid behavior at the Orbital Ordering Quantum Critical Point in the Two-Orbital Model
Ka Wai Lo,Wei-Cheng Lee,Philip W. Phillips
Physics , 2012, DOI: 10.1209/0295-5075/101/50007
Abstract: The critical behavior of a two-orbital model with degenerate $d_{xz}$ and $d_{yz}$ orbitals is investigated by multidimensional bosonization. We find that the corresponding bosonic theory has an overdamped collective mode with dynamical exponent $z=3$, which appears to be a general feature of a two-orbital model and becomes the dominant fluctuation in the vicinity of the orbital-ordering quantum critical point. Since the very existence of this $z=3$ overdamped collective mode induces non-Fermi liquid behavior near the quantum critical point, we conclude that a two-orbital model generally has a sizable area in the phase diagram showing non-Fermi liquid behavior. Furthermore, we show that the bosonic theory resembles the continuous model near the d-wave Pomeranchuk instability, suggesting that orbital order in a two-orbital model is identical to nematic order in a continuous model. Our results can be applied to systems with degenerate $d_{xz}$ and $d_{yz}$ orbitals such as iron-based superconductors and bilayer strontium ruthenates Sr$_3$Ru$_2$O$_7$.
Non-equilibrium Transport in the Strange Metal and Pseudogap phases of the Cuprates
Ka Wai Lo,Seungmin Hong,Philip W. Phillips
Physics , 2013, DOI: 10.1103/PhysRevB.88.235114
Abstract: We propose that the non-equilibrium current measured in the $a-b$ plane of an underdoped cuprate (in either the strange metal or pseudogap regime) in contact with either an overdoped cuprate or a standard Fermi liquid can be used diagnose how different the pseudogap and strange metals are from a Fermi liquid. Naively one expects the strange metal to be more different from a Fermi liquid than is the pseudogap. We compute the expected non-equilibrium transport signal with the three Green functions that are available in the literature: 1) marginal Fermi liquid theory, 2) the phenomenological ansatz for the pseudogap regime and 3) the Wilsonian reduction of the Hubbard model which contains both the strange metal and pseudogap. All three give linear IV curves at low bias voltages. Significant deviations from linearity at higher voltages obtain only in the marginal Fermi liquid approach. The key finding, however, is that IV curves for the strange metal/Fermi liquid contact that exceed that of the pseudogap/Fermi liquid system. If this is borne out experimentally, this implies that the strange metal is less orthogonal to a Fermi liquid than is the pseudogap. Within the Wilsonian reduction of the Hubbard model, this result is explained in terms of a composite-particle picture. Namely, the pseudogap corresponds to a confinement transition of the charge degrees of freedom present in the strange metal. In the strange metal the composite excitations break up and electron quasiparticles scatter off bosons. The bosons here, however, do not arise from phonons but from the charge degrees of freedom responsible for dynamical spectral weight transfer.
Comparison of Outcomes of Velopharyngeal Surgery between the Inferiorly and Superiorly Based Pharyngeal Flaps
Kachin Wattanawong,Ying-Chien Tan,Lun-Jou Lo,Philip KT Chen
Chang Gung Medical Journal , 2007,
Abstract: Background: Pharyngeal flaps have been widely used for the correction of velopharyngealincompetence. The aim of this study was to compare the outcomes ofvelopharyngeal surgery between those who received the superiorly and inferiorlybased pharyngeal flaps.Methods: A retrospective review of medical records of patients with cleft palates whoreceived pharyngeal flap surgery for the correction of velopharyngeal incompetenceat one craniofacial center was performed. The superiorly based flapswere elevated and inset using the fish-mouth method. The inferiorly basedflaps were sutured to the soft palate where a distally based mucosa flap wasturned over to cover the raw surface of the flap pedicle. The velopharyngealfunctions were categorized as adequate, marginal, or inadequate.Complications associated with the operation were documented. Statisticalcomparisons between the two groups were made.Results: There were 65 patients in each group. No statistically significant differenceswere found for sex distribution and age at operation. The outcomes of thevelopharyngeal surgery were better in the group of patients who received theinferiorly based pharyngeal flaps (p = 0.030). The complications were notsignificantly different between the two groups, and were all relatively mild.Conclusion: The inferiorly based pharyngeal flap was more effective than the superiorlybased pharyngeal flap for the correction of velopharyngeal incompetence. Aprobable explanation may be the fibrotic changes and scar contracture occurringin the pedicle of the superiorly based pharyngeal flap that may haveimpaired the velopharyngeal closure.
On the use of projectors for Hamiltonian systems and their relationship with Dirac brackets
Cristel Chandre,Lo?c De Guillebon,Aurore Back,Emanuele Tassi,Philip Morrison
Physics , 2012, DOI: 10.1088/1751-8113/46/12/125203
Abstract: The role of projectors associated with Poisson brackets of constrained Hamiltonian systems is analyzed. Projectors act in two instances in a bracket: in the explicit dependence on the variables and in the computation of the functional derivatives. The role of these projectors is investigated by using Dirac's theory of constrained Hamiltonian systems. Results are illustrated by three examples taken from plasma physics: magnetohydrodynamics, the Vlasov-Maxwell system, and the linear two-species Vlasov system with quasineutrality.
Dynamical Gap and Cuprate-like Physics from Holography
Mohammad Edalati,Robert G. Leigh,Ka Wai Lo,Philip W. Phillips
Physics , 2010, DOI: 10.1103/PhysRevD.83.046012
Abstract: We study the properties of fermion correlators in a boundary theory dual to the Reissner-Nordstr\"om AdS_{d+1} background in the presence of a bulk dipole (Pauli) interaction term with strength p. We show that by simply changing the value of the parameter p we can tune continuously from a Fermi liquid (small p), to a marginal Fermi liquid behavior at a critical value of p, to a generic non-Fermi liquid at intermediate values of p, and finally to a Mott insulator at large values of the bulk Pauli coupling. As all of these phases are seen in the cuprate phase diagram, the holographic model we study has the key elements of the strong coupling physics typified by Mott systems. In addition, we extend our analysis to finite temperature and show that the Mott gap closes. Of particular interest is that it closes when the ratio of the gap to the critical temperature is of the order of ten. This behavior is very much similar to that observed in the classic Mott insulator VO_2. We then analyze the non-analyticities of the boundary theory fermion correlators for generic values of frequency and momentum by calculating the quasi-normal modes of the bulk fermions. Not surprisingly, we find no evidence for the dipole interaction inducing an instability in the boundary theory. Finally, we briefly consider the introduction of superconducting condensates, and find that in that case, the fermion gap is driven by scalar-fermion couplings rather than by the Pauli coupling.
The Characteristics and Distribution of Dental Anomalies in Patients with Cleft
Ting-Ting Wu,Philip K.T. Chen,Lun-Jou Lo,Min-Chi Cheng
Chang Gung Medical Journal , 2011,
Abstract: Background: Dental anomalies associated with different severities of cleft lip and palatehave been rarely reported. This retrospective study investigates the characteristics of dental anomalies associated with different types of cleft, and compares the dental anomaly traits based on sex and severity of cleft.Methods: Cleft patients born in 1995 with qualified diagnostic records from 7 to 11years were included for evaluation. Records were retrieved from database ofChang Gung Craniofacial Center, including panoramic radiographs and intraoral photographs. In total, 196 patients with complete records were includedin the evaluation. This study compares the dental anomalies associated witheach type of cleft.Results: The frequency of dental anomalies in the maxillary incisor area in the cleftpalate (CP) group (20%) was significantly lower than that in other groups.The frequency of missing maxillary lateral incisors (MLIs) increased as thecleft severity increased. Supernumerary teeth and missing lower incisorsexhibited the opposite trend. No sexual dimorphism appeared in terms of thefrequencies of peg laterals and missing MLIs. The distribution patterns ofmissing MLIs and peg laterals in males, but not in females, were consistentfor the three types of unilateral clefts.Conclusion: Regarding the characteristics of dental anomalies among the three unilateralclefts, missing MLIs, supernumerary teeth, and missing lower incisors werefound to be related to cleft severity. The maxillary lateral incisor was themost affected tooth in the cleft area. The frequency of missing MLIs and peglaterals was not sexual dimorphic, but the distribution pattern was differentbetween the sexes
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