41,189 research outputs found
A Characteristic Planetary Feature in Double-Peaked, High-Magnification Microlensing Events
A significant fraction of microlensing planets have been discovered in
high-magnification events, and a significant fraction of these events exhibit a
double-peak structure at their peak. However, very wide or very close binaries
can also produce double-peaked high-magnification events, with the same gross
properties as those produced by planets. Traditionally, distinguishing between
these two interpretations has relied upon detailed modeling, which is both
time-consuming and generally does not provide insight into the observable
properties that allow discrimination between these two classes of models. We
study the morphologies of these two classes of double-peaked high-magnification
events, and identify a simple diagnostic that can be used to immediately
distinguish between perturbations caused by planetary and binary companions,
without detailed modeling. This diagnostic is based on the difference in the
shape of the intra-peak region of the light curves. The shape is smooth and
concave for binary lensing, while it tends to be either boxy or convex for
planetary lensing. In planetary lensing this intra-peak morphology is due to
the small, weak cusp of the planetary central caustic located between the two
stronger cusps. We apply this diagnostic to five observed double-peaked
high-magnification events to infer their underlying nature. A corollary of our
study is that good coverage of the intra-peak region of double-peaked
high-magnification events is likely to be important for their unique
interpretation.Comment: 6 pages, 3 figure
Detection of advanced persistent threat using machine-learning correlation analysis
As one of the most serious types of cyber attack, Advanced Persistent Threats (APT) have caused major concerns on a global scale. APT refers to a persistent, multi-stage attack with the intention to compromise the system and gain information from the targeted system, which has the potential to cause significant damage and substantial financial loss. The accurate detection and prediction of APT is an ongoing challenge. This work proposes a novel machine learning-based system entitled MLAPT, which can accurately and rapidly detect and predict APT attacks in a systematic way. The MLAPT runs through three main phases: (1) Threat detection, in which eight methods have been developed to detect different techniques used during the various APT steps. The implementation and validation of these methods with real traffic is a significant contribution to the current body of research; (2) Alert correlation, in which a correlation framework is designed to link the outputs of the detection methods, aims to identify alerts that could be related and belong to a single APT scenario; and (3) Attack prediction, in which a machine learning-based prediction module is proposed based on the correlation framework output, to be used by the network security team to determine the probability of the early alerts to develop a complete APT attack. MLAPT is experimentally evaluated and the presented sy
Offspring from maternal nutrient restriction in mice show variations in adult glucose metabolism similar to human fetal growth restriction.
Fetal growth restriction (FGR) is a pregnancy condition in which fetal growth is suboptimal for gestation, and this population is at increased risk for type 2 diabetes as adults. In humans, maternal malnutrition and placental insufficiency are the most common causes of FGR, and both result in fetal undernutrition. We hypothesized that maternal nutrient restriction (MNR) in mice will cause FGR and alter glucose metabolism in adult offspring. Pregnant CD-1 mice were subjected to MNR (70% of average ad libitum) or control (ad libitum) from E6.5 to birth. Following birth, mice were fostered by mothers on ad libitum feeds. Weight, blood glucose, glucose tolerance and tissue-specific insulin sensitivity were assessed in male offspring. MNR resulted in reduced fetal sizes but caught up to controls by 3 days postnatal age. As adults, glucose intolerance was detected in 19% of male MNR offspring. At 6 months, liver size was reduced (P = 0.01), but pAkt-to-Akt ratios in response to insulin were increased 2.5-fold relative to controls (P = 0.004). These data suggest that MNR causes FGR and long-term glucose intolerance in a population of male offspring similar to human populations. This mouse model can be used to investigate the impacts of FGR on tissues of importance in glucose metabolism
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Room-Temperature Power-Stabilized Narrow-Linewidth Tunable Erbium-Doped Fiber Ring Laser Based on Cascaded Mach-Zehnder Interferometers with Different Free Spectral Range for Strain Sensing
An automatically power-stabilized (with power fluctuation <0.155 dB), narrow-linewidth (0.0171 nm), wavelength-tunable (10.69 nm) erbium-doped fiber laser has been proposed by cascading two fiber Mach-Zehnder interferometers (MZI) without using any temperature controlling device. One of the MZIs (here called the 1st MZI) is composed of two 3 dB couplers to form interference patterns while the other MZI (here termed the 2nd MZI) is constructed with a tapered seven-core fiber (SCF) and based on the principle of supermode interference. For the two MZIs, the free spectral range (FSR), the passband bandwidth and the extinction ratio (ER) at 1560 nm are 0.37 nm, 0.19 nm, 16.6 dB and 13.93 nm, 7.93 nm, 10.1 dB, respectively. Due to the major difference between the two FSR values, the 1st MZI and the 2nd MZI respectively play a role in controlling the laser linewidth and suppressing the homogeneous broadening effect to reach to a satisfactory level of power stability. The 2nd MZI is also used to fine tune the laser wavelength by applying strain to the tapered SCF (TSCF) over the spectral range of 1570.22-1559.33 nm, with an incremental step of 0.37 nm being used. The side-mode suppression ratio (SMSR) of the tunable fiber laser can be up to 45 dB. By appropriately adjusting the polarization controller, dual wavelength lasing can also be achieved. For single wavelength lasing, the 3 dB laser linewidth is 0.0171 nm. The power fluctuation, without a temperature controlling device being used and operating at room temperature, is found to be less than 0.155 dB over 1 hour while the central wavelength drift is less than 0.19 nm
Strangelet dwarfs
If the surface tension of quark matter is low enough, quark matter is not
self bound. At sufficiently low pressure and temperature, it will take the form
of a crystal of positively charged strangelets in a neutralizing background of
electrons. In this case there will exist, in addition to the usual family of
strange stars, a family of low-mass large-radius objects analogous to white
dwarfs, which we call "strangelet dwarfs". Using a generic parametrization of
the equation of state of quark matter, we calculate the mass-radius
relationship of these objects.Comment: 10 pages, LaTeX, added discussion of CFL phase and strangelet
pollution, version to appear in journal. arXiv admin note: text overlap with
arXiv:0808.067
Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}
The mechanism of ferromagnetism stability in sandwich clusters
V(CH) has been studied by first-principles calculation and
model analysis. It is found that each of the three types of bonds between V and
benzene (Bz) plays different roles. V 3d orbital, extending along the
molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the
-bond. It is quite localized and singly occupied, which contributes
1 to the magnetic moment but little to the magnetic coupling of
neighboring V magnetic moments. The in-plane d, d orbitals
are hybridized with the LUMO of Bz and constitute the -bond. This
hybridization is medium and crucial to the magnetic coupling though the
states have no net contribution to the total magnetic moment.
d, d and HOMO of Bz form a quite strong -bond to hold the
molecular structure but they are inactive in magnetism because their energy
levels are far away from the Fermi level. Based on the results of
first-principles calculation, we point out that the ferromagnetism stability is
closely related with the mechanism proposed by Kanamori and Terakura [J.
Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the
presence of edge Bz's in the cluster introduces an important modification. A
simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure
Validity of abundances derived from spaxel spectra of the MaNGA survey
We measured the emission lines in the spaxel spectra of MaNGA galaxies in
order to determine the abundance distributions therein. It has been suggested
that the strength of the low-ionization lines, R_2, N_2, and S_2 may be
increased (relative to Balmer lines) in (some) spaxel spectra of the MaNGA
survey due to a contribution of the radiation of the diffuse ionized gas.
Consequently, the abundances derived from the spaxel spectra through
strong-line methods may suffer from large errors. We examined this expectation
by comparing the behaviour of the line intensities and the abundances estimated
through different calibrations for slit spectra of HII regions in nearby
galaxies, for fibre spectra from the SDSS, and for spaxel spectra of the MaNGA
survey. We found that the S_2 strength is increased significantly in the fibre
and spaxel spectra. The mean enhancement changes with metallicity and can be as
large as a factor of 2. The mean distortion of R_2 and N_2 is less than a
factor of 1.3. This suggests that Kaufmann et al.'s demarcation line between
AGNs and HII regions in the BPT diagram is a useful criterion to reject spectra
with significantly distorted strengths of the N_2 and R_2 lines. We find that
the three-dimensional R calibration, which uses the N_2 and R_2 lines, produces
reliable abundances in the MaNGA galaxies. The one-dimensional N2 calibration
produces either reliable or wrong abundances depending on whether excitation
and N/O abundance ratio in the target region (spaxel) are close to or differ
from those parameters in the calibrating points located close to the
calibration relation. We then determined abundance distributions within the
optical radii in the discs of 47 MaNGA galaxies. The optical radii of the
galaxies were estimated from the surface brightness profiles constructed based
on the MaNGA observations.Comment: 19 pages, 15 figures, accepted for publication in A&
Correlation effects during liquid infiltration into hydrophobic nanoporous mediums
Correlation effects arising during liquid infiltration into hydrophobic
porous medium are considered. On the basis of these effects a mechanism of
energy absorption at filling porous medium by nonwetting liquid is suggested.
In accordance with this mechanism, the absorption of mechanical energy is a
result expenditure of energy for the formation of menisci in the pores on the
shell of the infinite cluster and expenditure of energy for the formation of
liquid-porous medium interface in the pores belonging to the infinite cluster
of filled pores. It was found that in dependences on the porosity and,
consequently, in dependences on the number of filled pores neighbors, the
thermal effect of filling can be either positive or negative and the cycle of
infiltration-defiltration can be closed with full outflow of liquid. It can
occur under certain relation between percolation properties of porous medium
and the energy characteristics of the liquid-porous medium interface and the
liquid-gas interface. It is shown that a consecutive account of these
correlation effects and percolation properties of the pores space during
infiltration allow to describe all experimental data under discussion
Precision W-boson and top-quark mass determinations at a muon collider
Precise determinations of the masses of the boson and of the top quark
could stringently test the radiative structure of the Standard Model (SM) or
provide evidence for new physics. We analyze the excellent prospects at a muon
collider for measuring and in the and threshold
regions. With an integrated luminosity of 10 (100) fb, the -boson
mass could be measured to a precision of 20 (6) MeV, and the top-quark mass to
a precision of 200 (70) MeV, provided that theoretical and experimental
systematics are understood. A measurement of MeV for fixed
would constrain a 100 GeV SM Higgs mass within about GeV, while
MeV for fixed would constrain to about GeV.Comment: 27 pages, 11 figures, postscript file available via anonymous
ftp://ucdhep.ucdavis.edu/han/mumu/mwmt.p
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