2,746 research outputs found
Possible Solution of the long-standing discrepancy in the Microlensing Optical Depth Toward the Galactic Bulge by correcting the stellar number count
We find that significant incompleteness in stellar number counts results in a
significant overestimate of the microlensing optical depth and event
rate per star per year toward the Galactic bulge from the first two
years of the MOA-II survey. We find that the completeness in Red Clump Giant
(RCG) counts decreases proportional to the galactic latitude ,
as , ranging between 1 and
0.7 at . The previous measurements using all sources
by Difference Image Analysis (DIA) by MACHO and MOA-I suffer the same bias. On
the other hand, the measurements using a RCG sample by OGLE-II, MACHO and EROS
were free from this bias because they selected only the events associated with
the resolved stars. Thus, the incompleteness both in the number of events and
stellar number count cancel out. We estimate and by correcting
this incompleteness. In the central fields with , we find
star
yr and
for the 427 events with days using all sources brighter
than mag. Our revised all-source measurements are about
2- smaller than the other all-source measurements and are consistent
with the RCG measurements within 1-. We conclude that the long-standing
problem on discrepancy between the high with all-source samples by DIA
and low with RCG samples can probably be explained by the incompleteness
of the stellar number count. A model fit to these measurements predicts
star yr at
and for sources with , where the future space
mission WFIRST will observe.Comment: 39 pages, 15 figures, 5 tables, accepted for publication in ApJ.
arXiv admin note: substantial text overlap with arXiv:1305.018
Direct imaging constraints on planet populations detected by microlensing
Results from gravitational microlensing suggested the existence of a large
population of free-floating planetary mass objects. The main conclusion from
this work was partly based on constraints from a direct imaging survey. This
survey determined upper limits for the frequency of stars that harbor giant
exoplanets at large orbital separations. Aims. We want to verify to what extent
upper limits from direct imaging do indeed constrain the microlensing results.
We examine the current derivation of the upper limits used in the microlensing
study and re-analyze the data from the corresponding imaging survey. We focus
on the mass and semi-major axis ranges that are most relevant in context of the
microlensing results. We also consider new results from a recent M-dwarf
imaging survey as these objects are typically the host stars for planets
detected by microlensing. We find that the upper limits currently applied in
context of the microlensing results are probably underestimated. This means
that a larger fraction of stars than assumed may harbor gas giant planets at
larger orbital separations. Also, the way the upper limit is currently used to
estimate the fraction of free-floating objects is not strictly correct. If the
planetary surface density of giant planets around M-dwarfs is described as
df_Planet ~ a^beta da, we find that beta ~ 0.5 - 0.6 is consistent with results
from different observational studies probing semi-major axes between ~0.03 - 30
AU. Having a higher upper limit on the fraction of stars that may have gas
giant planets at orbital separations probed by the microlensing data implies
that more of the planets detected in the microlensing study are potentially
bound to stars rather than free-floating. The current observational data are
consistent with a rising planetary surface density for giant exoplanets around
M-dwarfs out to ~30 AU.Comment: Accepted for publication in A&A as Research Note, 3 page
Frequency Coded Chipless RFID Tag using Spurline Resonators
A novel compact chipless RFID tag using spurline resonators is discussed in this paper. The detection of the tag's ID is using the spectral signature of a spurline resonator circuit. The tag has a data capacity of 8-bits in the range 2.38 to 4.04 GHz. The tag consists of a spurline multiresonating circuit and two cross polarised antennas. The prototype of the tag is fabricated on a substrate C-MET/LK4.3 of dielectric constant 4.3 and loss tangent 0.0018. The measured results show that group delay response can also be used to decode the tag’s identity
Comparison of two models for bridge-assisted charge transfer
Based on the reduced density matrix method, we compare two different
approaches to calculate the dynamics of the electron transfer in systems with
donor, bridge, and acceptor. In the first approach a vibrational substructure
is taken into account for each electronic state and the corresponding states
are displaced along a common reaction coordinate. In the second approach it is
assumed that vibrational relaxation is much faster than the electron transfer
and therefore the states are modeled by electronic levels only. In both
approaches the system is coupled to a bath of harmonic oscillators but the way
of relaxation is quite different. The theory is applied to the electron
transfer in with free-base porphyrin () being the donor, zinc porphyrin () being the bridge and
quinone () the acceptor. The parameters are chosen as similar as
possible for both approaches and the quality of the agreement is discussed.Comment: 12 pages including 4 figures, 1 table, 26 references. For more info
see http://eee.tu-chemnitz.de/~kili
Knowledge of Risk Factors of Cancer Among Nepali Immigrants in Japan
Cancer accounts for 30% mortality in Japan. Increasing the basic knowledge on Cancer is vital to decrease the burden of cancer treatment and medical expenses. Since Nepal is the largest South Asian community in Japan, it is necessary to assess their awareness of Cancer. The purpose of this study was to identify cancer awarenessamong Nepali immigrants in Japan. A descriptive, cross-sectional study was conducted Hokkaido prefecture, Japan. A snowball sample of 100 Nepali immigrants aged 20-45 years participated in this study. SPSS V.22.0 was used for regression and descriptive analysis. Most immigrants (67%) were in between 31 and 45 years old and male (73%). Almost 21% did not have health insurance in Japan. The smoking rate was low (12%) while the alcohol rate was high (65%) among immigrants. Internet was reported to be the most common source of information. A total of 87% of immigrants showed a strong need for cancer education. The total range of score was 0-9. Female, university-level education, family history of chronic illness, and immigrants with the daily habit of healthy diet had better knowledge about risk factors of Cancer. Multiple regressions showed education level, length of stay, and healthy diet habit as a significant factor for knowledge about cancer (R2 = 0.34, p<0.01). There was limited knowledge on risk factors of cancer among Nepali immigrants. This study showed a strong need for awareness about cancer and screening tests to ameliorate the increased risk of cancer.
Keywords: Risk factors, Cancer, Immigrants, Knowledge, Nepal
The Optical Gravitational Lensing Experiment. Catalog of stellar proper motions in the OGLE-II Galactic bulge fields
We present a proper motion (\mu) catalogue of 5,080,236 stars in 49 Optical
Gravitational Lensing Experiment II (OGLE-II) Galactic bulge (GB) fields,
covering a range of -11 deg. <l< 11 deg. and -6 deg. <b<3 deg., the total area
close to 11 square degrees. The proper motion measurements are based on 138 -
555 I-band images taken during four observing seasons: 1997-2000. The catalogue
stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue
includes Red Clump Giants (RCGs) and Red Giants in the GB, and main sequence
stars in the Galactic disc. The proper motions up to \mu = 500 mas/yr were
measured with the mean accuracy of 0.8-3.5 mas/yr, depending on the brightness
of a star. This catalogue may be useful for studying the kinematic of stars in
the GB and the Galactic disk.Comment: 13 pages, 16 figures, MNRAS in pres
XMM observation of 1RXS J180431.1-273932: a new M-type X-ray binary with a 494 s-pulse period neutron star?
Low-mass X-ray binaries are binary systems composed of a compact object and a
low-mass star. Recently, a new class of these systems, known as symbiotic
-ray binaries (with a neutron star with a M-type giant companion), has been
discovered. Here, we present long-duration observations of the
source 1RXS J180431.1-273932. Temporal and spectral analysis of the source was
performed along with a search for an optical counterpart. We used a
Lomb-Scargle periodogram analysis for the period search and evaluated the
confidence level using Monte-Carlo simulations. The source is characterized by
regular pulses so that it is most likely a neutron star. A modulation of
s (3 error) was found with a confidence level of 99%.
Evidence of variability is also present, since the data show a rate of change
in the signal of counts s hr. A longer
observation will be necessary in order to determine if the source shows any
periodic behavior. The spectrum can be described by a power law with photon
index and a Gaussian line at 6.6 keV. The X-ray flux in the
0.2--10 keV energy band is erg s cm. The
identification of an optical counterpart (possibly an M6III red-giant star with
an apparent visual magnitude of ) allows a conservative distance
of kpc to be estimated. Other possibilities are also discussed. Once
the distance was estimated, we got an -ray luminosity of L_X\ut<6\times
10^{34} erg s, which is consistent with the typical -ray luminosity
of a symbiotic LMXB system.Comment: in press on A&
Large Magellanic Cloud Microlensing Optical Depth with Imperfect Event Selection
I present a new analysis of the MACHO Project 5.7 year Large Magellanic Cloud
(LMC) microlensing data set that incorporates the effects of contamination of
the microlensing event sample by variable stars. Photometric monitoring of
MACHO LMC microlensing event candidates by the EROS and OGLE groups has
revealed that one of these events is likely to be a variable star, while
additional data has confirmed that many of the other events are very likely to
be microlensing. This additional data on the nature of the MACHO microlensing
candidates is incorporated into a simple likelihood analysis to derive a
probability distribution for the number of MACHO microlens candidates that are
true microlensing events. This analysis shows that 10-12 of the 13 events that
passed the MACHO selection criteria are likely to be microlensing events, with
the other 1-3 being variable stars. This likelihood analysis is also used to
show that the main conclusions of the MACHO LMC analysis are unchanged by the
variable star contamination. The microlensing optical depth toward the LMC is =
1.0 +/- 0.3 * 10^{-7}. If this is due to microlensing by known stellar
populations, plus an additional population of lens objects in the Galactic
halo, then the new halo population would account for 16% of the mass of a
standard Galactic halo. The MACHO detection exceeds the expected background of
2 events expected from ordinary stars in standard models of the Milky Way and
LMC at the 99.98% confidence level. The background prediction is increased to 3
events if maximal disk models are assumed for both the MilkyWay and LMC, but
this model fails to account for the full signal seen by MACHO at the 99.8%
confidence level.Comment: 20 pages, 2 postscript figues, accepted by Ap
Circadian patterns of Wikipedia editorial activity: A demographic analysis
Wikipedia (WP) as a collaborative, dynamical system of humans is an
appropriate subject of social studies. Each single action of the members of
this society, i.e. editors, is well recorded and accessible. Using the
cumulative data of 34 Wikipedias in different languages, we try to characterize
and find the universalities and differences in temporal activity patterns of
editors. Based on this data, we estimate the geographical distribution of
editors for each WP in the globe. Furthermore we also clarify the differences
among different groups of WPs, which originate in the variance of cultural and
social features of the communities of editors
- …