scholarly journals The New Opacities and B-Star Pulsations

1994 ◽  
Vol 162 ◽  
pp. 55-66
Author(s):  
W.A. Dziembowski
Keyword(s):  
Normal Modes ◽  
Local Maximum ◽  
High Order ◽  
Driving Mechanism ◽  
Instability Domain ◽  
B Stars ◽  
Sequence Band ◽  
Metal Abundance ◽  
New Feature ◽  
The One

Over thirty years ago Baker & Kippenhahn (1962) demonstrated that an instability driven by the opacity mechanism is the cause of Cepheid pulsations. Recently it has been shown that the same mechanism is responsible for oscillations observed in β Cephei, SPB and perhaps in other variable B-type stars. The search for the driving mechanism in hot stars began in the late sixties with no success until the opacities calculated with the OPAL code (Iglesias, Rogers and Wilson 1990, 1992) became available. The crucial new feature in the opacity is the local maximum at T ≈ 2 × 105 K caused by iron lines which was ignored in earlier calculations. Recently, stellar opacity data from an independent project (OP) became available (Seaton et al., 1993). The agreement between the two opacity data is satisfactory.In B stars the opacity mechanism drives two distinct categories of normal modes. The one relevant to β Cep stars encompasses low order p- and g-modes with periods 0.1–0.3 d. The other includes high-order g-modes with periods ranging up above 4 d. Excitation of such modes may explain most of the slow variability observed in B stars. The theoretical instability domain in the H-R diagram is very sensitive to metal abundance. For the standard value of Z = 0.02, the total instability domain in the main sequence band extends from spectral type O9.5 to B9. In types later than B2 only high-order g-modes are unstable.

scholarly journals g-Mode instability in the main sequence B-type stars

1994 ◽  
Vol 162 ◽  
pp. 69-69
Author(s):  
W.A. Dziembowski ◽  
P. Moskalik ◽  
A.A. Pamyatnykh
Keyword(s):  
Main Sequence ◽  
High Order ◽  
Large Region ◽  
Excitation Mechanism ◽  
Instability Domain ◽  
Mode Instability ◽  
Period Range ◽  
Photometric Variability ◽  
B Stars ◽  
Sequence Band

We show that the OPAL opacities, in addition to explaining the origin of β Cep stars pulsations, also predict existence of a large region in the Main Sequence band at lower luminosities, where high-order g-modes of low harmonic degrees, l, are unstable. The excitation mechanism remains the same and is due to the usual κ-effect acting in the metal opacity bump (T ≈ 2 × 105K). The new instability domain nearly bridges the gap in spectral types between δ Set and β Cep stars. Periods of unstable modes are in the range 0.4–3.5 days for l = 1 and l = 2. We propose that this excitation mechanism causes photometric variability in the Slowly Pulsating B-type stars (SPB stars, Waelkens 1991) and perhaps in other B stars whose variability in the same period range has been reported.

scholarly journals New Results on Pulsating OB Stars

1995 ◽  
Vol 155 ◽  
pp. 44-55 ◽  
Author(s):  
Paweł Moskalik
Keyword(s):  
Data Model ◽  
Physical Mechanism ◽  
High Order ◽  
Early Type ◽  
Instability Strip ◽  
Model Calculations ◽  
B Stars ◽  
Ob Stars ◽  
Early Type Stars ◽  
Theoretical Results

AbstractUntil very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.

ANALISIS TERHADAP SOAL PENILAIAN AKHIR SEMESTER TINGKAT SD/MI DALAM PERSPEKTIF HIGH ORDER THINK SKILLS

2020 ◽  
Vol 12 (33) ◽  
Author(s):  
Yudha Andana Prawira ◽  
Titim Kurnia
Keyword(s):  
Critical Thinking ◽  
Critical Reflection ◽  
Descriptive Analysis ◽  
High Order ◽  
Point Of View ◽  
The Other ◽  
National Education ◽  
The One ◽  
High Level ◽  
High Level Thinking

The National Education World is currently trying to improve the ability of its students to think critically and creatively. One of these efforts has been pursued through evaluations that also lead to critical reflection. This research is a descriptive analysis of the final semester evaluation questions that are examined from the point of view of high-level thinking [HOTS]. The reference to the HOTS criteria is that the researcher refers to the opinions of King and his friends. From the manuscript data, the issues examined are samples from the Bandung area. The results of the analysis show that 10 out of 15 HOTS ranges proposed by King are already included in the scripts made by the teachers. On the one hand, it shows the teacher's creativity in compiling questions. On the other hand, all these questions do not refer to the HOTS criteria as planned. Therefore, there is a need to increase teachers' skills in compiling scripts as HOTS. This increase can be done through teacher training.Keywords: Evaluation, HOTS, critical thinking and creativity thingking

Local maximum principle satisfying high-order non-oscillatory schemes

2015 ◽  
Vol 81 (11) ◽  
pp. 689-715 ◽  
Author(s):  
Ritesh Kumar Dubey ◽  
Biswarup Biswas ◽  
Vikas Gupta
Keyword(s):  
Maximum Principle ◽  
Local Maximum ◽  
High Order

SPECTRAL PROPERTIES OF DERIVATIVE OPERATORS IN THE BASIS-SPLINE COLLOCATION METHOD

1995 ◽  
Vol 06 (01) ◽  
pp. 143-167 ◽  
Author(s):  
J.C. WELLS ◽  
V.E. OBERACKER ◽  
M.R. STRAYER ◽  
A.S. UMAR
Keyword(s):  
Collocation Method ◽  
Spectral Properties ◽  
High Order ◽  
Collocation Methods ◽  
Finite Difference Schemes ◽  
Spline Collocation ◽  
Spline Collocation Method ◽  
The Difference ◽  
Order Spline ◽  
The One

We discuss the basis-spline collocation method for the lattice solution of boundary-value differential equations, drawing particular attention to the difference between lattice and continuous collocation methods. Spectral properties of the basis-spline lattice representation of the first and second spatial derivatives are studied for the case of periodic boundary conditions with homogeneous lattice spacing and compared to spectra obtained using traditional finite-difference schemes. Basis-spline representations are shown to give excellent resolution on small-length scales and to satisfy the chain rule with good fidelity for the lattice-derivative operators using high-order splines. Application to the one-dimensional Dirac equation shows that very high-order spline representations of the Hamiltonian on odd lattices avoid the notorious spectral-doubling problem.

Vibration of an elastic strip with varying curvature

1992 ◽  
Vol 339 (1655) ◽  
pp. 587-625 ◽  
Keyword(s):  
Total Internal Reflection ◽  
Normal Modes ◽  
Mode Shapes ◽  
Elastic Strip ◽  
Interesting Phenomenon ◽  
One Dimensional ◽  
End Conditions ◽  
The One ◽  
Fixed End ◽  
Good Agreement

The vibrational behaviour of an elastic strip with varying curvature is investigated. The case of vibration which is predominantly transverse is considered, and it is shown that when the strip is S-shaped, certain of the normal modes may be confined to the vicinity of the inflection point of the S by a process of total internal reflection from points where the curvature reaches critical values. This confinement can produce modes with extraordinarily low damping factors. Asymptotic analysis is compared with experimental measurements on a strip in several S-shaped configurations, and very good agreement is demonstrated for modal frequencies and shapes. Mathematically, the lower modes turn out to be analogous to those of the one-dimensional harmonic oscillator in quantum mechanics. This mode confinement behaviour occurs for all waveguide branches except the lowest, ‘bending beam ’, branch. In this particular case, wave propagation is insensitive to curvature. However, an interesting phenomenon associated with curvature is found : the successive mode shapes do not display the normal alternation of symmetry and antisymmetry with respect to the centre of the strip. The effect is shown to result from the constraint on axial movement produced by fixed end conditions. For the geometry of the experiments, this constraint raises the frequencies of antisymmetric modes in a characteristic way while leaving the symmetric modes unaltered, thus changing the mode sequence. Theory is developed which gives reasonable quantitive agreement with the observations.

scholarly journals MOMENTUM DISTRIBUTION OF ITINERANT ELECTRONS IN THE ONE-DIMENSIONAL FALICOV–KIMBALL MODEL

2003 ◽  
Vol 17 (27) ◽  
pp. 4897-4911 ◽  
Author(s):  
PAVOL FARKAŠOVSKÝ
Keyword(s):  
Momentum Distribution ◽  
Ground States ◽  
Local Maximum ◽  
Singular Behavior ◽  
Coulomb Interactions ◽  
Unusual Behavior ◽  
One Dimensional ◽  
Itinerant Electrons ◽  
Half Filling ◽  
The One

The momentum distribution nk of itinerant electrons in the one-dimensional Falicov–Kimball model is calculated for various ground-state phases. In particular, we examine the periodic phases with period two, three and four (that are ground-states for all Coulomb interactions) as well as the phase separated states (that are ground states for small Coulomb interactions). For all periodic phases examined the momentum distribution is a smooth function of k with no sign of any discontinuity or singular behavior at the Fermi surface k=kF. An unusual behavior of nk (a local maximum) is found at k=3kF for electron concentrations outside half-filling. For the phase separated ground states the momentum distribution nk exhibits discontinuity at k=k0<kF. This behavior is interpreted in terms of a Fermi liquid.

MESOSCOPIC DESCRIPTION OF DYNAMICAL SYSTEMS: HIERARCHY OF RECURSIVE EQUATIONS FOR THE MOMENTS OF THE DENSITY DISTRIBUTION WITH AN APPLICATION TO CHARGED PARTICLE BEAM DYNAMICS

2004 ◽  
Vol 18 (04n05) ◽  
pp. 655-665
Author(s):  
SALVATORE DE MARTINO ◽  
SILVIO DE SIENA ◽  
RENATO FEDELE ◽  
STEPHAN TZENOV
Keyword(s):  
Charged Particle ◽  
Density Distribution ◽  
Particle Beam ◽  
High Order ◽  
Beam Dynamics ◽  
Charged Particle Beam ◽  
Recursion Relations ◽  
Control Stability ◽  
The One ◽  
Recursive Equations

The quantumlike formalism in the form of Madelung fluid has been applied to describe the collective dynamics of a mesoscopic aggregate of particles in a potential field. The scheme has been specialized to the one-degree-of-freedom dynamics of a charged particle beam in an accelerator in the presence of high-order multipole nonlinearities. A hierarchy of recursive equations satisfied by the moments of the density distribution has been obtained. It has been shown that the recursion relations can be in principle solved if a finite number of the first several moments is known. Beam dynamics in the presence of octupole and decapole nonlinearities has been studied as an example, demonstrating the above scheme. It has been shown that an appropriate mechanism can be introduced to control stability and coherence of states when high-order nonlinearities have to be taken into account.

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