8,247 research outputs found
Baryon Oscillations and Consistency Tests for Photometrically-Determined Redshifts of Very Faint Galaxies
Weak lensing surveys that can potentially place strong constraints on dark
energy parameters can only do so if the source redshift means and error
distributions are very well known. We investigate prospects for controlling
errors in these quantities by exploiting their influence on the power spectra
of the galaxies. Although, from the galaxy power spectra alone, sufficiently
precise and simultaneous determination of redshift biases and variances is not
possible, a strong consistency test is. Given the redshift error rms, galaxy
power spectra can be used to determine the mean redshift of a group of galaxies
to subpercent accuracy. Although galaxy power spectra cannot be used to
determine the redshift error rms, they can be used to determine this rms
divided by the Hubble parameter, a quantity that may be even more valuable for
interpretation of cosmic shear data than the rms itself. We also show that
galaxy power spectra, due to the baryonic acoustic oscillations, can
potentially lead to constraints on dark energy that are competitive with those
due to the cosmic shear power spectra from the same survey.Comment: 8 pages, 6 figures, submitted to Ap
On the Three-dimensional Lattice Model
Using the restricted star-triangle relation, it is shown that the -state
spin integrable model on a three-dimensional lattice with spins interacting
round each elementary cube of the lattice proposed by Mangazeev, Sergeev and
Stroganov is a particular case of the Bazhanov-Baxter model.Comment: 8 pages, latex, 4 figure
One-point Statistics of the Cosmic Density Field in Real and Redshift Spaces with A Multiresolutional Decomposition
In this paper, we develop a method of performing the one-point statistics of
a perturbed density field with a multiresolutional decomposition based on the
discrete wavelet transform (DWT). We establish the algorithm of the one-point
variable and its moments in considering the effects of Poisson sampling and
selection function. We also establish the mapping between the DWT one-point
statistics in redshift space and real space, i.e. the algorithm for recovering
the DWT one-point statistics from the redshift distortion of bulk velocity,
velocity dispersion, and selection function. Numerical tests on N-body
simulation samples show that this algorithm works well on scales from a few
hundreds to a few Mpc/h for four popular cold dark matter models.
Taking the advantage that the DWT one-point variable is dependent on both the
scale and the shape (configuration) of decomposition modes, one can design
estimators of the redshift distortion parameter (beta) from combinations of DWT
modes. When the non-linear redshift distortion is not negligible, the beta
estimator from quadrupole-to-monopole ratio is a function of scale. This
estimator would not work without adding information about the scale-dependence,
such as the power-spectrum index or the real-space correlation function of the
random field. The DWT beta estimators, however, do not need such extra
information. Numerical tests show that the proposed DWT estimators are able to
determine beta robustly with less than 15% uncertainty in the redshift range 0
< z < 3.Comment: 39 pages, 12 figures, ApJ accepte
Measuring Baryon Acoustic Oscillations with Millions of Supernovae
Since type Ia Supernovae (SNe) explode in galaxies, they can, in principle,
be used as the same tracer of the large-scale structure as their hosts to
measure baryon acoustic oscillations (BAOs). To realize this, one must obtain a
dense integrated sampling of SNe over a large fraction of the sky, which may
only be achievable photometrically with future projects such as the Large
Synoptic Survey Telescope. The advantage of SN BAOs is that SNe have more
uniform luminosities and more accurate photometric redshifts than galaxies, but
the disadvantage is that they are transitory and hard to obtain in large number
at high redshift. We find that a half-sky photometric SN survey to redshift z =
0.8 is able to measure the baryon signature in the SN spatial power spectrum.
Although dark energy constraints from SN BAOs are weak, they can significantly
improve the results from SN luminosity distances of the same data, and the
combination of the two is no longer sensitive to cosmic microwave background
priors.Comment: 4 pages, 3 figures, ApJL accepte
Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption
We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.Comment: 7 pages, 9 figures, accepted for publication in MNRAS, replaced by
the version after proo
Identifying Hidden Visits from Sparse Call Detail Record Data
Despite a large body of literature on trip inference using call detail record
(CDR) data, a fundamental understanding of their limitations is lacking. In
particular, because of the sparse nature of CDR data, users may travel to a
location without being revealed in the data, which we refer to as a "hidden
visit". The existence of hidden visits hinders our ability to extract reliable
information about human mobility and travel behavior from CDR data. In this
study, we propose a data fusion approach to obtain labeled data for statistical
inference of hidden visits. In the absence of complementary data, this can be
accomplished by extracting labeled observations from more granular cellular
data access records, and extracting features from voice call and text messaging
records. The proposed approach is demonstrated using a real-world CDR dataset
of 3 million users from a large Chinese city. Logistic regression, support
vector machine, random forest, and gradient boosting are used to infer whether
a hidden visit exists during a displacement observed from CDR data. The test
results show significant improvement over the naive no-hidden-visit rule, which
is an implicit assumption adopted by most existing studies. Based on the
proposed model, we estimate that over 10% of the displacements extracted from
CDR data involve hidden visits. The proposed data fusion method offers a
systematic statistical approach to inferring individual mobility patterns based
on telecommunication records
High-Q-factor Al [subscript 2]O[subscript 3] micro-trench cavities integrated with silicon nitride waveguides on silicon
We report on the design and performance of high-Q integrated optical micro-trench cavities on silicon. The microcavities are co-integrated with silicon nitride bus waveguides and fabricated using wafer-scale silicon-photonics-compatible processing steps. The amorphous aluminum oxide resonator material is deposited via sputtering in a single straightforward post-processing step. We examine the theoretical and experimental optical properties of the aluminum oxide micro-trench cavities for different bend radii, film thicknesses and near-infrared wavelengths and demonstrate experimental Q factors of > 10[superscript 6]. We propose that this high-Q micro-trench cavity design can be applied to incorporate a wide variety of novel microcavity materials, including rare-earth-doped films for microlasers, into wafer-scale silicon photonics platforms
Recommended from our members
Ly alpha flux power spectrum and its covariance
We analyse the flux power spectrum and its covariance using simulated Lyα forests. We find that pseudo-hydro techniques are good approximations of hydrodynamical simulations at high redshift. However, the pseudo-hydro techniques fail at low redshift because they are insufficient for characterizing some components of the low-redshift intergalactic medium, notably the warmâhot intergalactic medium. Hence, to use the low-redshift Lyα flux power spectrum to constrain cosmology, one would need realistic hydrodynamical simulations. By comparing (one-dimensional) mass statistics with flux statistics, we show that the non-linear transform between density and flux quenches the fluctuations so that the flux power spectrum is much less sensitive to cosmological parameters than the one-dimensional mass power spectrum. The covariance of the flux power spectrum is nearly Gaussian. As such, the uncertainties of the underlying mass power spectrum could still be large, even though the flux power spectrum can be precisely determined from a small number of lines of sight
Tunable singlet-triplet splitting in a few-electron Si/SiGe quantum dot
We measure the excited-state spectrum of a Si/SiGe quantum dot as a function
of in-plane magnetic field, and we identify the spin of the lowest three
eigenstates in an effective two-electron regime. The singlet-triplet splitting
is an essential parameter describing spin qubits, and we extract this splitting
from the data. We find it to be tunable by lateral displacement of the dot,
which is realized by changing two gate voltages on opposite sides of the
device. We present calculations showing the data are consistent with a spectrum
in which the first excited state of the dot is a valley-orbit state.Comment: 4 pages with 3 figure
- âŠ