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Anisotropy in a high Landau level due to effective electron-electron interactions
No full textQuantization of Hall resistivity in strongly correlated two-dimensional electronic systems at high magnetic fields generally indicates the stabilization of novel electronic quantum liquid phases of matter. This is the nature of the integer and fractional quantum Hall states that stabilize at integer and fractional odd-denominator (not always, though) filling factors of the Landau level. Away from certain filling factors that represent quantum Hall liquid states, different phases, some of them with unusually high magneto-transport anisotropy have been known to stabilize specially in high Landau levels. In this work, we try to understand this anisotropic behaviour in terms of effective electron-electron interaction potentials. To this effect, we implement a full projection of the original Coulomb interaction potential in the suitable Landau level. We find out that, in high Landau levels, thus for relatively weak magnetic fields, a semi-classical description of the interaction potential between electrons appear to be an adequate choice. The features of this semi-classical interaction potential in this limit suggest ways how the energetic balance between density waves and/or liquid crystalline phases might be sensitively affected. © 2013 The Korean Physical Society
Anisotropic quantum hall liquids at intermediate magnetic fields
No full textThe observation of significant magnetoresistance anisotropy of a two-dimensional electronic system in very clean GaAs/AlGaAs heterostructure samples in presence of moderately large perpendicular magnetic fields is a striking example of novel anisotropic behavior in the quantum Hall regime. Anisotropy appears to be the strongest at quantum Hall even-denominator filled states for filling factors ν\u3e4 where several Landau levels are occupied. A possible explanation of these findings is due to the existence of charge density waves that are known to cause interesting phase transitions at high Landau levels. An alternative explanation of this phenomenon is to argue that the strongly correlated electronic system has stabilized in an orientationally ordered anisotropic quantum Hall liquid state. Quantum Monte Carlo calculations with a translationally invariant wave function in which rotation symmetry is broken indicate that this might be the case. © 2012 Springer Science+Business Media, LLC
Two-dimensional motion of a parabolically confined charged particle in a perpendicular magnetic field
No full textThe classical two-dimensional motion of a parabolically confined charged particle in presence of a perpendicular magnetic is studied. The resulting equations of motion are solved exactly by using a mathematical method which is based on the introduction of complex variables. The two-dimensional motion of a parabolically charged particle in a perpendicular magnetic field is strikingly different from either the two-dimensional cyclotron motion, or the oscillator motion. It is found that the trajectory of a parabolically confined charged particle in a perpendicular magnetic field is closed only for particular values of cyclotron and parabolic confining frequencies that satisfy a given commensurability condition. In these cases, the closed paths of the particle resemble Lissajous figures, though significant differences with them do exist. When such commensurability condition is not satisfied, path of particle is open and motion is no longer periodic. In this case, after a sufficiently long time has elapsed, the open paths of the particle fill a whole annulus, a region lying between two concentric circles of different radii. © 2013 Versita Warsaw and Springer-Verlag Wien
Gradations of guessing: Preliminary sketches and suggestions
No full textGuessing is considered a central function of scientific inquiry by most scientists and philosophers, but it has mostly been neglected as an object of philosophical analysis. I supply an initial remedy to this neglect that provides a general definition of guessing that applies to scientific inquiry. In addition, I combat the assumption that the meaning of guessing is monosemic by providing examples of various types, or gradations, of guessing. The variation of these types indicates that guessing is not merely an unambiguous, simplistic process at which philosophers of science can merely hand-wave before moving on to deduction and induction. Rather, accounting for the gradations of guessing contributes to the argument that guessing is a logical process that is an appropriate object of philosophical analysis instead of a process that necessarily falls outside of rational reconstruction. As a logical process, guessing is clearly distinguished from induction and deduction. This distinction provides an important domain of philosophical inquiry that merits further investigation, especially within philosophy of science
Modeling of environmental adaptation: Amenity versus productivity and modernization
No full textWe develop an aggregated model to study rational environmental adaptation policies that compensate negative consequences of climate change. The model distinguishes three categories of adaptation measures that (a) compensate the decrease of environmental amenity value, (b) compensate the decrease of total productivity, (c) develop and introduce new hazard-protected capital and technology. We analyze the optimal balance among consumption, capital investment, and different categories of adaptation investments under exogenous climate change. It appears that the climate change damage and subsequent adaptation do not lead to a higher level of capital modernization in the long run as compared to the benchmark case with no climate change. A synergism between productivity-related and amenity-related adaptation activities arises because the productivity-related adaptation positively impacts the economy and creates better possibilities for the amenity adaptation
Mixture of D-vine copulas for modeling dependence
No full textThe identification of an appropriate multivariate copula for capturing the dependence structure in multivariate data is not straightforward. The reason is because standard multivariate copulas (such as the multivariate Gaussian, Student-t, and exchangeable Archimedean copulas) lack flexibility to model dependence and have other limitations, such as parameter restrictions. To overcome these problems, vine copulas have been developed and applied to many applications. In order to reveal and fully understand the complex and hidden dependence patterns in multivariate data, a mixture of D-vine copulas is proposed incorporating D-vine copulas into a finite mixture model. As a D-vine copula has multiple parameters capturing the dependence through iterative construction of pair-copulas, the proposed model can facilitate a comprehensive study of complex and hidden dependence patterns in multivariate data. The proposed mixture of D-vine copulas is applied to simulated and real data to illustrate its performance and benefits. © 2013 Elsevier B.V. All rights reserved
Comparison of dried plum puree, rosemary extract, and BHA/BHT as antioxidants in irradiated ground beef patties
No full textFresh ground beef patties with (1) no antioxidant (control), (2) 0.02% butylated hydroxyanisole/butylated hydroxytoluene (BHA/BHT), (3) 3% dried plum puree, or (4) 0.25% rosemary extract were aerobically packaged, irradiated at target doses of 0, 1.5, or 2.0 kGy (1.7 and 2.3 kGy actual doses), and stored at 4 ° C. The samples were evaluated for lipid oxidation on 0, 3, 7, 14, 21, and 28 days of storage after irradiation. When compared to the control, all antioxidant treatments were effective in retarding (P \u3c 0.05) irradiation-induced lipid oxidation during storage as determined by 2-thiobarbituric acid reactive substances (TBARs) values. Rosemary extracts had the same antioxidant effect (P \u3e 0.05) as BHA/BHT in irradiated and nonirradiated beef patties, followed by the dried plum puree treatment. Irradiation increased TBARs values, but no differences were noted in oxidation between irradiation dose levels