25,776 research outputs found
A Canonical Ensemble Approach to the Fermion/Boson Random Point Processes and its Applications
We introduce the boson and the fermion point processes from the elementary
quantum mechanical point of view. That is, we consider quantum statistical
mechanics of canonical ensemble for a fixed number of particles which obey
Bose-Einstein, Fermi-Dirac statistics, respectively, in a finite volume.
Focusing on the distribution of positions of the particles, we have point
processes of the fixed number of points in a bounded domain. By taking the
thermodynamic limit such that the particle density converges to a finite value,
the boson/fermion processes are obtained. This argument is a realization of the
equivalence of ensembles, since resulting processes are considered to describe
a grand canonical ensemble of points. Random point processes corresponding to
para-particles of order two are discussed as an application of the formulation.
A statistics of a system of composite particles at zero temperature are also
considered as a model of determinantal random point processes.Comment: 26pages, Some typos are corrected, to be published in Commun. Math.
Phy
Tunable Exchange Interaction in Quantum Dot Devices
We theoretically discuss the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction
between semiconductor quantum dots (QDs). When each QD having a local spin is
coupled to the conduction electrons in semiconductors, an indirect exchange
interaction, i.e., the RKKY interaction, is induced between two local spins.
The RKKY interaction between QDs, which is mediated by the Fermi sea in
semiconductors, is modulated by changing the Fermi energy, and the magnitude or
even the sign of the exchange interaction can be tuned, which leads to a
tunable magnetic transition in QD devices. We estimate the magnitude of the
RKKY interaction in QDs as a function of the electron density and the inter-dot
distance
Star formation activity in the southern Galactic HII region G351.63-1.25
The southern Galactic high mass star-forming region, G351.6-1.3, is a HII
region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located
at a distance of 2.4 kpc. In this paper, we focus on the investigation of the
associated HII region, embedded cluster and the interstellar medium in the
vicinity of G351.6-1.3. We address the identification of exciting source(s) as
well as the census of stellar populations. The ionised gas distribution has
been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three
continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated
morphology and the 1280 MHz map comprises six resolved high density regions
encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age
main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have
carried out near-infrared observations in the JHKs bands using the SIRIUS
instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The
near-infrared images reveal the presence of a cluster embedded in nebulous
fan-shaped emission. The log-normal slope of the K-band luminosity function of
the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the
near-infrared excess stars is estimated to be 43%. These indicate that the age
of the cluster is consistent with 1 Myr. The champagne flow model from a flat,
thin molecular cloud is used to explain the morphology of radio emission with
respect to the millimetre cloud and infrared brightness.Comment: 18 pages, 8 figures, To be published in MNRA
Bound states in two spatial dimensions in the non-central case
We derive a bound on the total number of negative energy bound states in a
potential in two spatial dimensions by using an adaptation of the Schwinger
method to derive the Birman-Schwinger bound in three dimensions. Specifically,
counting the number of bound states in a potential gV for g=1 is replaced by
counting the number of g_i's for which zero energy bound states exist, and then
the kernel of the integral equation for the zero-energy wave functon is
symmetrized. One of the keys of the solution is the replacement of an
inhomogeneous integral equation by a homogeneous integral equation.Comment: Work supported in part by the U.S. Department of Energy under Grant
No. DE-FG02-84-ER4015
Star formation activity in the Galactic H II region Sh2-297
We present a multiwavelength study of the Galactic H II region Sh2-297,
located in Canis Major OB1 complex. Optical spectroscopic observations are used
to constrain the spectral type of ionizing star HD 53623 as B0V. The classical
nature of this H II region is affirmed by the low values of electron density
and emission measure, which are calculated to be 756 cm^-3 and 9.15 x 10^5
cm^-6 pc using the radio continuum observations at 610 and 1280 MHz, and VLA
archival data at 1420 MHz. To understand local star formation, we identified
the young stellar object (YSO) candidates in a region of area ~ 7.5' x 7.5'
centered on Sh2-297 using grism slitless spectroscopy (to identify the Halpha
emission line stars), and near infrared (NIR) observations. NIR YSO candidates
are further classified into various evolutionary stages using color-color (CC)
and color-magnitude (CM) diagrams, giving 50 red sources (H-K > 0.6) and 26
Class II-like sources. The mass and age range of the YSOs are estimated to be ~
0.1 - 2 Msolar and 0.5 - 2 Myr using optical (V/V-I) and NIR (J/J-H) CM
diagrams. The mean age of the YSOs is found to be ~ 1 Myr, which is of the
order of dynamical age of 1.07 Myr of the H II region. Using the estimated
range of visual extinction (1.1 - 25 mag) from literature and NIR data for the
region, spectral energy distribution (SED) models have been implemented for
selected YSOs which show masses and ages to be consistent with estimated
values. The spatial distribution of YSOs shows an evolutionary sequence,
suggesting triggered star formation in the region. The star formation seems to
have propagated from the ionizing star towards the cold dark cloud LDN1657A
located west of Sh2-297.Comment: 19 pages, 13 figures, 3 tables. Accepted for publication in The
Astrophysical Journa
NGC 7538 : Multiwavelength Study of Stellar Cluster Regions associated with IRS 1-3 and IRS 9 sources
We present deep and high-resolution (FWHM ~ 0.4 arcsec) near-infrared (NIR)
imaging observations of the NGC 7538 IRS 1-3 region (in JHK bands), and IRS 9
region (in HK bands) using the 8.2m Subaru telescope. The NIR analysis is
complemented with GMRT low-frequency observations at 325, 610, and 1280 MHz,
molecular line observations of H13CO+ (J=1-0), and archival Chandra X-ray
observations. Using the 'J-H/H-K' diagram, 144 Class II and 24 Class I young
stellar object (YSO) candidates are identified in the IRS 1-3 region. Further
analysis using 'K/H-K' diagram yields 145 and 96 red sources in the IRS 1-3 and
IRS 9 regions, respectively. A total of 27 sources are found to have X-ray
counterparts. The YSO mass function (MF), constructed using a theoretical
mass-luminosity relation, shows peaks at substellar (~0.08-0.18 Msolar) and
intermediate (~1-1.78 Msolar) mass ranges for the IRS 1-3 region. The MF can be
fitted by a power law in the low mass regime with a slope of Gamma ~ 0.54-0.75,
which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2
is obtained for the star to brown dwarf ratio in the IRS 1-3 region. GMRT maps
show a compact HII region associated with the IRS 1-3 sources, whose spectral
index of 0.87+-0.11 suggests optical thickness. This compact region is resolved
into three separate peaks in higher resolution 1280 MHz map, and the 'East'
sub-peak coincides with the IRS 2 source. H13CO+ (J=1-0) emission reveals peaks
in both IRS 1-3 and IRS 9 regions, none of which are coincident with visible
nebular emission, suggesting the presence of dense cloud nearby. The virial
masses are approximately of the order of 1000 Msolar and 500 Msolar for the
clumps in IRS 1-3 and IRS 9 regions, respectively.Comment: 27 pages, 18 figures, 5 tables. Accepted for publication in MNRA
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