42 research outputs found
A Parametric Study of Erupting Flux Rope Rotation. Modeling the "Cartwheel CME" on 9 April 2008
The rotation of erupting filaments in the solar corona is addressed through a
parametric simulation study of unstable, rotating flux ropes in bipolar
force-free initial equilibrium. The Lorentz force due to the external shear
field component and the relaxation of tension in the twisted field are the
major contributors to the rotation in this model, while reconnection with the
ambient field is of minor importance. Both major mechanisms writhe the flux
rope axis, converting part of the initial twist helicity, and produce rotation
profiles which, to a large part, are very similar in a range of shear-twist
combinations. A difference lies in the tendency of twist-driven rotation to
saturate at lower heights than shear-driven rotation. For parameters
characteristic of the source regions of erupting filaments and coronal mass
ejections, the shear field is found to be the dominant origin of rotations in
the corona and to be required if the rotation reaches angles of order 90
degrees and higher; it dominates even if the twist exceeds the threshold of the
helical kink instability. The contributions by shear and twist to the total
rotation can be disentangled in the analysis of observations if the rotation
and rise profiles are simultaneously compared with model calculations. The
resulting twist estimate allows one to judge whether the helical kink
instability occurred. This is demonstrated for the erupting prominence in the
"Cartwheel CME" on 9 April 2008, which has shown a rotation of \approx 115
degrees up to a height of 1.5 R_sun above the photosphere. Out of a range of
initial equilibria which include strongly kink-unstable (twist Phi=5pi), weakly
kink-unstable (Phi=3.5pi), and kink-stable (Phi=2.5pi) configurations, only the
evolution of the weakly kink-unstable flux rope matches the observations in
their entirety.Comment: Solar Physics, submitte
From bi-layer to tri-layer Fe nanoislands on Cu3Au(001)
Self assembly on suitably chosen substrates is a well exploited root to
control the structure and morphology, hence magnetization, of metal films. In
particular, the Cu3Au(001) surface has been recently singled out as a good
template to grow high spin Fe phases, due to the close matching between the
Cu3Au lattice constant (3.75 Angstrom) and the equilibrium lattice constant for
fcc ferromagnetic Fe (3.65 Angstrom). Growth proceeds almost layer by layer at
room temperature, with a small amount of Au segregation in the early stage of
deposition. Islands of 1-2 nm lateral size and double layer height are formed
when 1 monolayer of Fe is deposited on Cu3Au(001) at low temperature. We used
the PhotoElectron Diffraction technique to investigate the atomic structure and
chemical composition of these nanoislands just after the deposition at 140 K
and after annealing at 400 K. We show that only bi-layer islands are formed at
low temperature, without any surface segregation. After annealing, the Fe atoms
are re-aggregated to form mainly tri-layer islands. Surface segregation is
shown to be inhibited also after the annealing process. The implications for
the film magnetic properties and the growth model are discussed.Comment: Revtex, 5 pages with 4 eps figure
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
The Origin, Early Evolution and Predictability of Solar Eruptions
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt
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Assessing the quality of models of the ambient solar wind
In this paper we present an assessment of the status of models of the global Solar Wind in the inner heliosphere. We limit our discussion to the class of models designed to provide solar wind forecasts, excluding those designed for the purpose of testing physical processes in idealized configurations. In addition, we limit our discussion to modeling of the ‘ambient’ wind in the absence of coronal mass ejections. In this assessment we cover use of the models both in forecast mode and as tools for scientific research. We present a brief history of the development of these models, discussing the range of physical approximations in use. We discuss the limitations of the data inputs available to these models and its impact on their quality. We also discuss current model development trends
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
PROFIL WISATAWAN MUSEUM RADYA PUSTAKA SURAKARTA
Anggit Margaret, C9407031 2011. Profil Wisatawan Museum
Radya Pustaka Surakarta. Program Studi Diploma III Usaha Perjalanan
Wisata Fakultas Sastra Dan Seni Rupa Universitas Sebelas Maret Surakarta.
Penelitian tugas akhir ini mengkaji tentang Profil Wisatawan di
Museum Radya Pustaka Surakarta. Tujuan dari penelitian ini adalah untuk
mengetahui dari daerah mana saja wisatawan yang berkunjung ke Museum
Radya Pustaka, bagaimana ciri-ciri wisatawan yang berkunjung ke Museum
Radya Pustaka serta harapan-harapan yang diinginkan wisatawan terhadap
Museum Radya Pustaka.
Penelitian dilakukan dengan metode kualitatif. Pengumpulan data
dilakukan melalui wawancara dengan narasumber wisatawan yang berkujung
di Museum Radya Pustaka Surakarta tempat penulis melakukan penelitian,
serta studi pustaka dan studi dokumen guna menambah sumber data.
Hasil penelitian menunjukkan bahwa (1) Sebagian besar wisatawan
yang datang berasal dari Semarang sebesar 32%. (2) Mayoritas wisatawan
yang berkunjung ke Museum Radya Pustaka berusia antara 17-25 tahun dan
kebanyakan dari mereka adalah pelajar atau mahasiswa dengan prosentase
52%. (3) Sebagian besar wisatawan yang datang ke Museum Radya Pustaka
adalah bertujuan untuk melakukan penelitian yaitu sebesar 34%. (4) Harapan
wisatawan yang berkunjung terhadap kelangsungan Museum Radya Pustaka
sebagian besar adalah agar ditingkatkan lagi pengelolaan dan keamanan
museum, agar kejadian hilangnya benda-benda koleksi museum tidak terulang
lagi dikemudian hari.
Kesimpulan dari hasil penelitian ini bahwa wisatawan yang berkujung
ke Museum Radya Pustaka Surakarta mayoritas berasal dari Semarang,
mayoritas berusia 17-25 tahun dan kebanyakan dari mereka adalah berprofesi
sebagai pelajar dan mahasiswa. Kebanyakan wisatawan yang datang bertujuan
untuk melakukan penelitian, serta harapan wisatawan terhadap Museum
Radya Pustaka adalah supaya lebih ditingkatkan lagi pengelolaan dan
keamanan museum
4-[(4-Methylphenyl)sulfanyl]butan-2-one
In the title compound, C11H14OS, all non-H atoms are essentially coplanar, with a mean deviation of 0.023 Å. In the crystal, centrosymmetrically related molecules are weakly connected into dimers by pairs of C - H⋯O interactions. The dimers are further linked along the a axis by weak C - H⋯π and C - H⋯S interactions
4-Ethoxy-3-methoxybenzaldehyde
In the title compound, C10H12O3, all non-H atoms are approximately coplanar, with an r.m.s. deviation of 0.046 Å. In the crystal, very weak C-H⋯O interactions link the molecules into sheets parallel to (101)
1-Ferrocenyl-3-(2-methylanilino)propan-1-one
In the ferrocene-containing Mannich base, [Fe(C5H 5)(C15H16NO)], the dihedral angle between the mean planes of the benzene ring and the substituted cyclopentadienyl ring is 84.63 (7)°. The conformation of the title compound significantly differs from those found in corresponding m-tolylamino and p-tolylamino derivatives. In the crystal, C - H⋯O interactions connect the molecules into chains, which further interact by means of C - H⋯π interactions. It is noteworthy that the amino H atom is shielded and is not involved in hydrogen bonding. © 2012 International Union of Crystallography