636 research outputs found
Generalized Bruhat Cells and Completeness of Hamiltonian Flows of Kogan-Zelevinsky Integrable Systems
Let be any connected and simply connected complex semisimple Lie group,
equipped with a standard holomorphic multiplicative Poisson structure. We show
that the Hamiltonian flows of all the Fomin-Zelevinsky twisted generalized
minors on every double Bruhat cell of are complete in the sense that all
the integral curves of their Hamiltonian vector fields are defined on
. It follows that all the Kogan-Zelevinsky integrable systems on
have complete Hamiltonian flows, generalizing the result of Gekhtman and
Yakimov for the case of . We in fact construct a class of
integrable systems with complete Hamiltonian flows associated to {\it
generalized Bruhat cells} which are defined using arbitrary sequences of
elements in the Weyl group of , and we obtain the results for double Bruhat
cells through the so-called open {\it Fomin-Zelevinsky embeddings} of (reduced)
double Bruhat cells in generalized Bruhat cells. The Fomin-Zelevinsky
embeddings are proved to be Poisson, and they provide global coordinates on
double Bruhat cells, called {\it Bott-Samelson coordinates}, in which all the
Fomin-Zelevinsky minors become polynomials and the Poisson structure can be
computed explicitly.Comment: Title slightly changed; Section 1.3 expanded; some typos correcte
A scaling relation between merger rate of galaxies and their close pair count
We study how to measure the galaxy merger rate from the observed close pair
count. Using a high-resolution N-body/SPH cosmological simulation, we find an
accurate scaling relation between galaxy pair counts and merger rates down to a
stellar mass ratio of about 1:30. The relation explicitly accounts for the
dependence on redshift (or time), on pair separation, and on mass of the two
galaxies in a pair. With this relation, one can easily obtain the mean merger
timescale for a close pair of galaxies. The use of virial masses, instead of
stellar masses, is motivated by the fact that the dynamical friction time scale
is mainly determined by the dark matter surrounding central and satellite
galaxies. This fact can also minimize the error induced by uncertainties in
modeling star formation in the simulation. Since the virial mass can be read
from the well-established relation between the virial masses and the stellar
masses in observation, our scaling relation can be easily applied to
observations to obtain the merger rate and merger time scale. For major merger
pairs (1:1-1:4) of galaxies above a stellar mass of 4*10^10 M_sun/h at z=0.1,
it takes about 0.31 Gyr to merge for pairs within a projected distance of 20
kpc/h with stellar mass ratio of 1:1, while the time taken goes up to 1.6 Gyr
for mergers with stellar mass ratio of 1:4. Our results indicate that a single
timescale usually used in literature is not accurate to describe mergers with
the stellar mass ratio spanning even a narrow range from 1:1 to 1:4.Comment: accepted for publication in Ap
Simulation of an Axion Search Experiment
The resolution of the strong CP problem postulates a new dark matter candidate known as the axion. Axions can couple with photons in the presence of a strong magnetic field. Light shining through wall method (LSW) uses a lead wall inside a cavity with a strong magnetic field to coupled axions with photons then detect axions when the axions cross the lead wall and convert back to photons. The axion signal and thermal noise are simulated and by comparing the simulated signals after they have been rectified and integrated, the sensitivity of the planned experiment was determined
The multidimensional dependence of halo bias in the eye of a machine: a tale of halo structure, assembly and environment
We develop a novel approach in exploring the joint dependence of halo bias on
multiple halo properties using Gaussian process regression. Using a
CDM -body simulation, we carry out a comprehensive study of the
joint bias dependence on halo structure, formation history and environment. We
show that the bias is a multivariate function of halo properties that falls
into three regimes. For massive haloes, halo mass explains the majority of bias
variation. For early-forming haloes, bias depends sensitively on the recent
mass accretion history. For low-mass and late-forming haloes, bias depends more
on the structure of a halo such as its shape and spin. Our framework enables us
to convincingly prove that is a lossy proxy of
formation time for bias modelling, whereas the mass, spin, shape and formation
time variables are non-redundant with respect to each other. Combining mass and
formation time largely accounts for the mass accretion history dependence of
bias. Combining all the internal halo properties fully accounts for the density
profile dependence inside haloes, and predicts the clustering variation of
individual haloes to a level at . When an
environmental density is measured outside from the halo
centre, it outperforms and largely accounts for the bias dependence on the
internal halo structure, explaining the bias variation above a level of .Comment: MNRAS accepte
Recommended from our members
Monolithic ultrasound fingerprint sensor.
This paper presents a 591×438-DPI ultrasonic fingerprint sensor. The sensor is based on a piezoelectric micromachined ultrasonic transducer (PMUT) array that is bonded at wafer-level to complementary metal oxide semiconductor (CMOS) signal processing electronics to produce a pulse-echo ultrasonic imager on a chip. To meet the 500-DPI standard for consumer fingerprint sensors, the PMUT pitch was reduced by approximately a factor of two relative to an earlier design. We conducted a systematic design study of the individual PMUT and array to achieve this scaling while maintaining a high fill-factor. The resulting 110×56-PMUT array, composed of 30×43-μm2 rectangular PMUTs, achieved a 51.7% fill-factor, three times greater than that of the previous design. Together with the custom CMOS ASIC, the sensor achieves 2 mV kPa-1 sensitivity, 15 kPa pressure output, 75 μm lateral resolution, and 150 μm axial resolution in a 4.6 mm×3.2 mm image. To the best of our knowledge, we have demonstrated the first MEMS ultrasonic fingerprint sensor capable of imaging epidermis and sub-surface layer fingerprints
Mississippi State Axion Search: A Light Shining though a Wall ALP Search
The elegant solutions to the strong CP problem predict the existence of a
particle called axion. Thus, the search for axion like particles (ALP) has been
an ongoing endeavor. The possibility that these axion like particles couple to
photons in presence of magnetic field gives rise to a technique of detecting
these particles known as light shining through a wall (LSW). Mississippi State
Axion Search (MASS) is an experiment employing the LSW technique in search for
axion like particles. The apparatus consists of two radio frequency (RF)
cavities, both under the influence of strong magnetic field and separated by a
lead wall. While one of the cavities houses a strong RF generator, the other
cavity houses the detector systems. The MASS apparatus looks for excesses in RF
photons that tunnel through the wall as a signature of candidate axion-like
particles. The concept behind the experiment as well as the projected
sensitivities are presented here.Comment: Xth Patras Workshop on Axions, WIMPs and WISPs; 4 Pages, 5 figure
Photometric Metallicity Calibration with SDSS and SCUSS and its Application to distant stars in the South Galactic Cap
Based on SDSS g, r and SCUSS (South Galactic Cap of u-band Sky Survey)
photometry, we develop a photometric calibration for estimating the stellar
metallicity from and colors by using the SDSS spectra of 32,542 F-
and G-type main sequence stars, which cover almost deg in the
south Galactic cap. The rms scatter of the photometric metallicity residuals
relative to spectrum-based metallicity is dex when , and
dex when . Due to the deeper and more accurate magnitude of SCUSS
band, the estimate can be used up to the faint magnitude of . This
application range of photometric metallicity calibration is wide enough so that
it can be used to study metallicity distribution of distant stars. In this
study, we select the Sagittarius (Sgr) stream and its neighboring field halo
stars in south Galactic cap to study their metallicity distribution. We find
that the Sgr stream at the cylindrical Galactocentric coordinate of
kpc, kpc exhibits a relative rich metallicity
distribution, and the neighboring field halo stars in our studied fields can be
modeled by two-Gaussian model, with peaks respectively at [Fe/H] and
[Fe/H].Comment: 8 pages, 7 figures, Accepted for publication in MNRA
- …