32,882 research outputs found
Nuclear Equation of State and Internal Structure of Magnetars
Recently, neutron stars with very strong surface magnetic fields have been
suggested as the site for the origin of observed soft gamma repeaters (SGRs).
We investigate the influence of a strong magnetic field on the properties and
internal structure of such strongly magnetized neutron stars (magnetars). The
presence of a sufficiently strong magnetic field changes the ratio of protons
to neutrons as well as the neutron appearance density. We also study the pion
production and pion condensation in a strong magnetic field. We discuss the
pion condensation in the interior of magnetars as a possible source of SGRs.Comment: 5 pages with 3 figures, To appear in the Proceedings of the 5th
Huntsville Gamma Ray Burst Symposium, Huntsville, Alabama, USA, Oct. 18-22,
199
Quantum MHV diagrams
Over the past two years, the use of on-shell techniques has deepened our understanding of the S-matrix of gauge theories and led to the calculation of many new scattering amplitudes. In these notes we review a particular on-shell method developed recently, the quantum MHV diagrams, and discuss applications to one-loop amplitudes. Furthermore, we briefly discuss the application of D-dimensional generalised unitarity to the calculation of scattering amplitudes in non-supersymmetric Yang-Mills
Use of the NESS Handmaster to restore handfunction in tetraplegia: clinical experiences in ten patients
Objective: To explore possible functional effects of the Handmaster in tetraplegia and to determine suitable patients for the system. \ud
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Patients: Patients with a cervical spinal cord injury between C4 and C6, motor group 0-3. Important selection criteria were a stable clinical situation and the absence of other medical problems and complications. \ud
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Design: Ten patients were consecutively selected from the in- and outpatient department of a large rehabilitation hospital in The Netherlands. Each patient was fitted with a Handmaster by a qualified therapist and underwent muscle strength and functional training for at least 2 months. \ud
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Methods: Functional evaluation comprised the performance of a defined set of tasks and at least one additional task as selected by patients themselves. Tasks were performed both with and without the Handmaster. Finally, patients were asked for their opinion on Handmaster use as well as their willingness to future use. \ud
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Results: In six patients a stimulated grasp and release with either one or both grasp modes (key- and palmar pinch) of the Handmaster was possible. Four patients could perform the set of tasks using the Handmaster, while they were not able to do so without the Handmaster. Eventually, one patient continued using the Handmaster during ADL at home. \ud
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Conclusion: The Handmaster has a functional benefit in a limited group of patients with a C5 SCI motor group 0 and 1. Suitable patients should have sufficient shoulder and biceps function combined with absent or weak wrist extensors. Though functional use was the main reason for using the Handmaster, this case series showed that therapeutic use can also be considered. \ud
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Constraining the neutron star equation of state using XMM-Newton
We have identified three possible ways in which future XMM-Newton
observations can provide significant constraints on the equation of state of
neutron stars. First, using a long observation of the neutron star X-ray
transient CenX-4 in quiescence one can use the RGS spectrum to constrain the
interstellar extinction to the source. This removes this parameter from the
X-ray spectral fitting of the pn and MOS spectra and allows us to investigate
whether the variability observed in the quiescent X-ray spectrum of this source
is due to variations in the soft thermal spectral component or variations in
the power law spectral component coupled with variations in N_H. This will test
whether the soft thermal spectral component can indeed be due to the hot
thermal glow of the neutron star. Potentially such an observation could also
reveal redshifted spectral lines from the neutron star surface. Second,
XMM-Newton observations of radius expansion type I X-ray bursts might reveal
redshifted absorption lines from the surface of the neutron star. Third,
XMM-Newton observations of eclipsing quiescent low-mass X-ray binaries provide
the eclipse duration. With this the system inclination can be determined
accurately. The inclination determined from the X-ray eclipse duration in
quiescence, the rotational velocity of the companion star and the
semi-amplitude of the radial velocity curve determined through optical
spectroscopy, yield the neutron star mass.Comment: 4 pages, 1 figure, proceedings of the XMM-Newton workshop, June 2007,
accepted for publication in A
Commutator Leavitt path algebras
For any field K and directed graph E, we completely describe the elements of
the Leavitt path algebra L_K(E) which lie in the commutator subspace
[L_K(E),L_K(E)]. We then use this result to classify all Leavitt path algebras
L_K(E) that satisfy L_K(E)=[L_K(E),L_K(E)]. We also show that these Leavitt
path algebras have the additional (unusual) property that all their Lie ideals
are (ring-theoretic) ideals, and construct examples of such rings with various
ideal structures.Comment: 24 page
The two dimensional Hubbard model:a theoretical tool for molecular electronics
When speaking about molecular electronics, the obvious question which occurs
is how does one study it theoretically. The simplest theoretical model suitable
for application in molecular electronics is the two dimensional Hubbard model.
The aim of the present paper is to introduce this model, and give some examples
of the systems which it can describe. After a short mathematically oriented
discussion, it will be shown how to calculate the electrical conductivity of a
particular planar system: a rectangular lattice with mutually independent
conductivities along the two axes,but without using the 2D Hamiltonian. This
system could find applications in high Tc studies. It will finally be shown
that the electrical conductivity of graphene can be determined not by using the
full formalism of the Hubbard model, but by a slight reformulation of the
Hamiltonian of the 1D Hubbard modelComment: Lecture given at the 16 Int.School of Cond.Matt.Physics,August
29.,-September 3 2010.,Varna (Bulgaria
Penerapan Model Pembelajaran Savi untuk Meningkatkan Kemampuan Komunikasi Matematis dan Motivasi Belajar Mahasiswa Ditinjau dari Jurusan Asal Sekolah
Penelitian ini dilatarbelakangi karena banyaknya kemampuan komunikasi matematis dari mahasiswa yang masih rendah, faktor yang menyebabkan kemampuan komunikasi matematik rendah karena pembelajaran yang dilakukan di kelas terlalu monoton atau terpusat pada dosen, motivasi belajar yang masih rendah dari mahasiswa dan latar belakang jurusan asal sekolah yang berbeda-beda. Tujuan penelitian ini yaitu Untuk menganalisis peningkatan kemampuan komunikasi matematis antara mahasiswa yang menggunakan model pembelajaran SAVI dengan yang menggunakan model pembelajaran ekspositori ditinjau dari asal jurusan sekolah serta untuk mengetahui perbedaan motivasi yang menggunakan model pembelajaran SAVI dengan yang menggunakan model pembelajaran ekspositori ditinjau asal jurusan sekolah. Metode penelitian yang digunakan adalah metode kuantitatif dan kualitatif (mix method). Sampel yang dianalisis sebanyak 68 orang mahasiswa. Instrumen yang digunakan untuk pengumpulan data berupa tes uraian dan wawancara. Hasil tes uraian dianalisis untuk menentukan kemampuan komunikasi matematisnya dan hasil wawancara dianalisis untuk tingkat motivasi mahasiswa. Hasil penelitian ini menunjukkan bahwa, hasil kemampuan komunikasi matematis antara mahasiswa yang menggunakan model pembelajaran SAVI lebih baik dengan yang menggunakan model pembelajaran ekspositori ditinjau dari asal jurusan sekolah serta terdapat perbedaan motivasi yang menggunakan model pembelajaran SAVI dengan yang menggunakan model pembelajaran ekspositori ditinjau asal jurusan sekolah
Detection of a 1258 Hz high-amplitude kilohertz quasi-periodic oscillation in the ultra-compact X-ray binary 1A 1246-588
We have observed the ultra-compact low-mass X-ray binary (LMXB) 1A 1246-588
with the Rossi X-ray Timing Explorer (RXTE). In this manuscript we report the
discovery of a kilohertz quasi-periodic oscillation (QPO) in 1A 1246-588. The
kilohertz QPO was only detected when the source was in a soft high-flux state
reminiscent of the lower banana branch in atoll sources. Only one kilohertz QPO
peak is detected at a relatively high frequency of 1258+-2 Hz and at a single
trial significance of more than 7 sigma. Kilohertz QPOs with a higher frequency
have only been found on two occasions in 4U 0614+09. Furthermore, the frequency
is higher than that found for the lower kilohertz QPO in any source, strongly
suggesting that the QPO is the upper of the kilohertz QPO pair often found in
LMXBs. The full-width at half maximum is 25+-4 Hz, making the coherence the
highest found for an upper kilohertz QPO. From a distance estimate of ~6 kpc
from a radius expansion burst we derive that 1A 1246-588 is at a persistent
flux of ~0.2-0.3 per cent of the Eddington flux, hence 1A 1246-588 is one of
the weakest LMXBs for which a kilohertz QPO has been detected. The
root-mean-square (rms) amplitude in the 5-60 keV band is 27+-3 per cent, this
is the highest for any kilohertz QPO source so far, in line with the general
anti-correlation between source luminosity and rms amplitude of the kilohertz
QPO peak identified before. Using the X-ray spectral information we produce a
colour-colour diagram. The source behaviour in this diagram provides further
evidence for the atoll nature of the source.Comment: 4 pages, 3 figures, accepted for publication in MNRA
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