11,507 research outputs found
Obscured clusters.I. GLIMPSE30 - Young Milky Way Star Cluster Hosting Wolf-Rayet Stars
Young massive clusters are perfect astrophysical laboratories for study of
massive stars. Clusters with Wolf-Rayet (WR) stars are of special importance,
since this enables us to study a coeval WR population at a uniform metallicity
and known age. GLIMPSE30 (G30) is one of them. The cluster is situated near the
Galactic plane (l=298.756deg, b=-0.408deg) and we aimed to determine its
physical parameters and to investigate its high-mass stellar content and
especially WR stars. Our analysis is based on SOFI/NTT JsHKs imaging and low
resolution (R~2000) spectroscopy of the brightest cluster members in the K
atmospheric window. For the age determination we applied isochrone fits for MS
and Pre-MS stars. We derived stellar parameters of the WR stars candidates
using a full nonLTE modeling of the observed spectra. Using a variety of
techniques we found that G30 is very young cluster, with age t~4Myr. The
cluster is located in Carina spiral arm, it is deeply embedded in dust and
suffers reddening of Av~10.5+-1.1mag. The distance to the object is
d=7.2+-0.9kpc. The mass of the cluster members down to 2.35Msol is ~1600Msol.
Cluster's MF for the mass range of 5.6 to 31.6Msol shows a slope of
Gamma=-1.01+-0.03. The total mass of the cluster obtained by this MF down to
1Msol is about 3x10^3Msol. The spectral analysis and the models allow us to
conclude that in G30 are at least one Ofpe/WN and two WR stars. The WR stars
are of WN6-7 hydrogen rich type with progenitor masses more than 60Msol. G30 is
a new member of the exquisite family of young Galactic clusters, hosting WR
stars. It is a factor of two to three less massive than some of the youngest
super-massive star clusters like Arches, Quintuplet and Central cluster and is
their smaller analog.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
A Bloch-Sphere-Type Model for Two Qubits in the Geometric Algebra of a 6-D Euclidean Vector Space
Geometric algebra is a mathematical structure that is inherent in any metric
vector space, and defined by the requirement that the metric tensor is given by
the scalar part of the product of vectors. It provides a natural framework in
which to represent the classical groups as subgroups of rotation groups, and
similarly their Lie algebras. In this article we show how the geometric algebra
of a six-dimensional real Euclidean vector space naturally allows one to
construct the special unitary group on a two-qubit (quantum bit) Hilbert space,
in a fashion similar to that used in the well-established Bloch sphere model
for a single qubit. This is then used to illustrate the Cartan decompositions
and subalgebras of the four-dimensional special unitary group, which have
recently been used by J. Zhang, J. Vala, S. Sastry and K. B. Whaley [Phys. Rev.
A 67, 042313, 2003] to study the entangling capabilities of two-qubit
unitaries.Comment: 14 pages, 2 figures, in press (Proceedings of SPIE Conference on
Defense & Security
EEG–fMRI mapping of asymmetrical delta activity in a patient with refractory epilepsy is concordant with the epileptogenic region determined by intracranial EEG
We studied a patient with refractory focal epilepsy using continuous EEG-correlated fMRI. Seizures were characterized by head turning to the left and clonic jerking of the left arm, suggesting a right frontal epileptogenic region. Interictal EEG showed occasional runs of independent nonlateralized slow activity in the delta band with right frontocentral dominance and had no lateralizing value. Ictal scalp EEG had no lateralizing value. Ictal scalp EEG suggested right-sided central slow activity preceding some seizures. Structural 3-T MRI showed no abnormality. There was no clear epileptiform abnormality during simultaneous EEG–fMRI. We therefore modeled asymmetrical EEG delta activity at 1–3 Hz near frontocentral electrode positions. Significant blood oxygen level-dependent (BOLD) signal changes in the right superior frontal gyrus correlated with right frontal oscillations at 1–3 Hz but not at 4–7 Hz and with neither of the two frequency bands when derived from contralateral or posterior electrode positions, which served as controls. Motor fMRI activations with a finger-tapping paradigm were asymmetrical: they were more anterior for the left hand compared with the right and were near the aforementioned EEG-correlated signal changes. A right frontocentral perirolandic seizure onset was identified with a subdural grid recording, and electric stimulation of the adjacent contact produced motor responses in the left arm and after discharges. The fMRI localization of the left hand motor and the detected BOLD activation associated with modeled slow activity suggest a role for localization of the epileptogenic region with EEG–fMRI even in the absence of clear interictal discharges
Milling characteristics and distribution of phytic acid and zind in long-, medium- and short-grain rice
Milling and polishing are important operations during the production of white rice. The degree of milling and polishing has a significant effect on the nutritional aspects of white rice, especially on minerals, due to a non-uniform distribution of nutrients in the kernel. Information on the distribution of nutrients in rice will greatly help in understanding the effect of milling and aid in designing procedures that improve technological and sensory properties of rice while retaining its essential nutrients as much as possible. In this study, three kernel shapes (short-, medium- and long-grain) of rice were selected for the study of milling characteristics and distribution of zinc (Zn) and phytic acid using abrasive milling and X-ray fluorescent microscope imaging approaches. Milling characteristics differed with kernel shapes and cultivars. Mass loss (y, %) correlated well with milling duration (x, s) and was fitted using a polynomial equation of y=ax2+bx+c (R2=0.99). Different kernel shapes of rice resulted in different patterns. Breakage in milling increased with longer duration of milling. The relation between breakage (y, %) and milling duration (x, s) fitted the exponential equation y=aebx. Levels of phytic acid, as well as Zn, decreased with prolonged milling. Phytic acid decreased at a higher rate than Zn. The analysis of different milling runs showed that the concentration of phytic acid decreased from the surface region inward, whereas X-ray fluorescent images indicated that the highest concentration of phosphorus was at the interface of the embryo and perisperm. Our results help in understanding the milling characteristics of different rice cultivars. Understanding these characteristics offers opportunities to optimize milling procedures for maximum phytate removal at minimum mineral losses and yield los
Group Theory and Dynamics of Neutrino Mixing
There is a direct group-theoretical connection between neutrino mixing and
horizontal symmetry that can be established without any dynamical input. Such a
connection is reviewed and expanded in this article. For certain symmetry
groups \G including and , it is shown that a generic U(1)\x\G
Higgs potential of a valon yields exactly the alignments dictated by the
group-theoretic approach, but energy can now be used to discriminate different
alignments. This mechanism possibly explains why starting from an group,
the tribimaximal mixing matrix with an enhanced symmetry is more
preferable than the one without it.Comment: One footnote and one reference added. To appear in Physical Review
Ghost field realizations of the spinor strings based on the linear W(1,2,s) algebras
It has been shown that certain W algebras can be linearized by the inclusion
of a spin-1 current. This Provides a way of obtaining new realizations of the W
algebras. In this paper, we investigate the new ghost field realizations of the
W(2,s)(s=3,4) algebras, making use of the fact that these two algebras can be
linearized. We then construct the nilpotent BRST charges of the spinor
non-critical W(2,s) strings with these new realizations.Comment: 10 pages, no figure
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