267,141 research outputs found
Two- and three-dimensional blade vortex interactions
A three-dimensional time dependent Navier-Stokes analysis was applied to the rotor blade vortex interaction (BVI) problem. The numerical procedure is an iterative implicit procedure using three point central differences to represent spatial derivatives. A series of calculations were made to determine the time steps, pseudo-time steps, iterations, artificial dissipation level, etc. required to maintain a nondissipative vortex. Results show the chosen method to have excellent non-dissipative properties provided the correct parameters are chosen. This study was used to set parameters for both two- and three-dimensional blade vortex interaction studies. The two-dimensional study considered the interaction between a vortex and a NACA0012 airfoil. The results showed the detailed physics during the interaction including the pressure pulse propagating from the blade. The simulated flow physics was qualitatively similar to that experimentally observed. The 2-D BVI phenomena is the result of the buildup and violent collapse of the shock waves and local supersonic pockets on the blade surfaces. The resulting pressure pulse build-up appears to be centered at the blade leading edge. The three-dimensional interaction study considered the case of a vortex at 20 deg incidence to the blade leading edge. Although the qualitative results were similar to that of the two-dimensional interaction, details clearly showed the three-dimensional nature of the interaction process
An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres I. Formation of the G-band in metal-poor dwarf stars
Recent developments in the three-dimensional (3D) spectral synthesis code
Linfor3D have meant that, for the first time, large spectral wavelength
regions, such as molecular bands, can be synthesised with it in a short amount
of time. A detailed spectral analysis of the synthetic G-band for several dwarf
turn-off-type 3D atmospheres (5850 <= T_eff [K] <= 6550, 4.0 <= log g <= 4.5,
-3.0 <= [Fe/H] <= -1.0) was conducted, under the assumption of local
thermodynamic equilibrium. We also examine carbon and oxygen molecule formation
at various metallicity regimes and discuss the impact it has on the G-band.
Using a qualitative approach, we describe the different behaviours between the
3D atmospheres and the traditional one-dimensional (1D) atmospheres and how the
different physics involved inevitably leads to abundance corrections, which
differ over varying metallicities. Spectra computed in 1D were fit to every 3D
spectrum to determine the 3D abundance correction. Early analysis revealed that
the CH molecules that make up the G-band exhibited an oxygen abundance
dependency; a higher oxygen abundance leads to weaker CH features. Nitrogen
abundances showed zero impact to CH formation. The 3D corrections are also
stronger at lower metallicity. Analysis of the 3D corrections to the G-band
allows us to assign estimations of the 3D abundance correction to most dwarf
stars presented in the literature. The 3D corrections suggest that A(C) in CEMP
stars with high A(C) would remain unchanged, but would decrease in CEMP stars
with lower A(C). It was found that the C/O ratio is an important parameter to
the G-band in 3D. Additional testing confirmed that the C/O ratio is an equally
important parameter for OH transitions under 3D. This presents a clear
interrelation between the carbon and oxygen abundances in 3D atmospheres
through their molecular species, which is not seen in 1D.Comment: 19 pages, 13 figures, 4 tables. Accepted for publication in A&
Keyakinan Epistemologis Siswa Lintas Level Akademik Terhadap Fisika
This research applied qualitative research which used descriptive method in order to describe the general epistemological beliefs of middle school students in two schools with different academic levels. The subjects of this research were the eleventh graders of SMA Al-azhar Palu and six the ninth graders of SMP Al-azhar Palu. The selection of respondents and the collection data of epistemological beliefs using EBAPS (Epistemological Beliefs Assessment for Physics Science). Interviews were carried out to elicit students' epistemological beliefs information. Analysis showed that the two academic levels have the same beliefs on dimensional Structure of Scientific Knowledge (SSK), Nature of Knowing and Learning (NKL) and Real-Life Applicability (RLA), and have different beliefs on Evolving dimensions of Knowledge (EK) and Source of Ability to Learn (SAL)
Assessing the impact of representational and contextual problem features on student use of right-hand rules
Students in introductory physics struggle with vector algebra and these
challenges are often associated with contextual and representational features
of the problems. Performance on problems about cross product direction is
particularly poor and some research suggests that this may be primarily due to
misapplied right-hand rules. However, few studies have had the resolution to
explore student use of right-hand rules in detail. This study reviews
literature in several disciplines, including spatial cognition, to identify ten
contextual and representational problem features that are most likely to
influence performance on problems requiring a right-hand rule. Two quantitative
measures of performance (correctness and response time) and two qualitative
measures (methods used and type of errors made) were used to explore the impact
of these problem features on student performance. Quantitative results are
consistent with expectations from the literature, but reveal that some features
(such as the type of reasoning required and the physical awkwardness of using a
right-hand rule) have a greater impact than others (such as whether the vectors
are placed together or separate). Additional insight is gained by the
qualitative analysis, including identifying sources of difficulty not
previously discussed in the literature and revealing that the use of
supplemental methods, such as physically rotating the paper, can mitigate
errors associated with certain features
Splitting the Wino Multiplet by Higher-Dimensional Operators in Anomaly Mediation
In a class of AMSB models, the splitting in the Wino multiplet turns out to
be very small, such as the often-quoted 170 MeV in minimal AMSB, which
originates from MSSM loops. Such a small mass gap is potentially a window into
higher scale physics, as it may be sensitive to higher-dimensional operators.
We show that still within AMSB one can get a much larger splitting in the Wino
multiplet--a few GeV--if the scale of the new physics is comparable to the
gravitino mass (which is indeed often the scale of new physics in anomaly
mediation).Comment: 18 pages; v2: references added, matching journal versio
Valence Bond States: Link models
An isotropic anti-ferromagnetic quantum state on a square lattice is
characterized by symmetry arguments only. By construction, this quantum state
is the result of an underlying valence bond structure without breaking any
symmetry in the lattice or spin spaces. A detailed analysis of the correlations
of the quantum state is given (using a mapping to a 2D classical statistical
model and methods in field theory like mapping to the non-linear sigma model or
bosonization techniques) as well as the results of numerical treatments
(regarding exact diagonalization and variational methods). Finally, the
physical relevance of the model is motivated. A comparison of the model to
known anti-ferromagnetic Mott-Hubbard insulators is given by means of the
two-point equal-time correlation function obtained i) numerically from the
suggested state and ii) experimentally from neutron scattering on cuprates in
the anti-ferromagnetic insulator phase.Comment: 20 pages, 15 figures; added references, corrected some typos, new
sections. Published versio
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