25 research outputs found
Can we constrain galaxy geometry parameters using spatially integrated SED fitting?
Sophisticated spectral energy distribution (SED) models describe dust
attenuation and emission using geometry parameters. This treatment is natural
since dust effects are driven by the underlying star-dust geometry in galaxies.
An example is the Starduster SED model, which divides a galaxy into a stellar
disk, a stellar bulge, and a dust disk. This work utilises the Starduster SED
model to study the efficacy of inferring geometry parameters using spatially
integrated SED fitting. Our method fits the SED model to mock photometry
produced by combining a semi-analytic model with the same SED model. Our
fitting results imply that the disk radius can be constrained, while the
inclination angle, dust disk to stellar disk radius ratio, bulge radius and
intrinsic bulge to total luminosity ratio are unconstrained, even though 21
filters from UV to FIR are used. We also study the impact of S/N, finding that
the increase of S/N (up to 80) brings limited improvements to the results. We
provide a detailed discussion to explain these findings, and point out the
implications for models with more general geometry.Comment: 14 pages, 13 figures, Accepted for publication in MNRA
Dark-ages Reionization and Galaxy Formation Simulation -- XIX: Predictions of infrared excess and cosmic star formation rate density from UV observations
We present a new analysis of high-redshift UV observations using a
semi-analytic galaxy formation model, and provide self-consistent predictions
of the infrared excess (IRX) -- relations and cosmic star formation
rate density. We combine the Charlot & Fall dust attenuation model with the
Meraxes semi-analytic model, and explore three different parametrisations for
the dust optical depths, linked to star formation rate, dust-to-gas ratio and
gas column density respectively. A Bayesian approach is employed to
statistically calibrate model free parameters including star formation
efficiency, mass loading factor, dust optical depths and reddening slope
directly against UV luminosity functions and colour-magnitude relations at z ~
4-7. The best-fit models show excellent agreement with the observations. We
calculate IRX using energy balance arguments, and find that the large intrinsic
scatter in the IRX - plane is driven by the specific star formation
rate. Additionally, the difference among the three dust models suggests a
factor of two systematic uncertainty in the dust-corrected star formation rate
when using the Meurer IRX - relation at z > 4.Comment: 15 pages, 10 figure. Accepted for publication in MNRA
Dependence of galaxy clustering on UV-luminosity and stellar mass at
We investigate the dependence of galaxy clustering at on
UV-luminosity and stellar mass. Our sample consists of 10,000
Lyman-break galaxies (LBGs) in the XDF and CANDELS fields. As part of our
analysis, the relation is estimated for the sample,
which is found to have a nearly linear slope of . We subsequently measure the angular correlation function and
bias in different stellar mass and luminosity bins. We focus on comparing the
clustering dependence on these two properties. While UV-luminosity is only
related to recent starbursts of a galaxy, stellar mass reflects the integrated
build-up of the whole star formation history, which should make it more tightly
correlated with halo mass. Hence, the clustering segregation with stellar mass
is expected to be larger than with luminosity. However, our measurements
suggest that the segregation with luminosity is larger with
confidence (neglecting contributions from systematic errors). We compare this
unexpected result with predictions from the \textsc{Meraxes} semi-analytic
galaxy formation model. Interestingly, the model reproduces the observed
angular correlation functions, and also suggests stronger clustering
segregation with luminosity. The comparison between our observations and the
model provides evidence of multiple halo occupation in the small scale
clustering.Comment: 10 pages, 6 figures, 2 tables, accepted for publication in MNRA
Identification of Dominant Spoilage Bacteria in Chicken Feet with Pickled Peppers and Analysis of Their Spoilage Capacity
The dominant spoilage bacteria in chicken feet with pickled peppers were analyzed by high-throughput sequencing technology and isolated by the traditional culture method to evaluate their spoilage capacity by back inoculation. The results showed that the dominant genus identified was Bacillus, and four dominant strains were identified including B. methylotrophicus, B. velezensis, B. subtilis and B. safensis. All these strains were able to produce protease and lipase activity. Among them, B. safensis showed the strongest protease activity (51.19 U/mL), while B. methylotrophicus showed the strongest lipase activity (3.75 U/mL). The pH, total volatile basic nitrogen (TVB-N) content and thiobarbituric acid reactive substances (TBARS) value of the samples inoculated with each of the four Bacillus strains were higher than those of the uninoculated control group, indicating that all four Bacillus strains had spoilage capacity. This study will provided a theoretical basis for preventing and controlling the spoilage of chicken feet with pickled peppers and extending its shelf life
Validation of the neural network for 3D photon radiation field reconstruction under various source distributions
Introduction: This paper proposes a five-layer fully connected neural network for predicting radiation parameters in a radiation space based on detector readings.Methods: The network is trained and tested using gamma flux values from individual detector positions as input, and is used to predict the gamma radiation field in 3D space under different source term distributions. The method is evaluated using the mean percentage change error (PCT) for the test set under different source term distributions.Results: The results show that the neural network method can accurately predict radiation parameters with an average PCT error range of 0.53% to 3.11%, within the given measurement input error range of ± 10%. The method also demonstrates its ability to directly reconstruct the 3D radiation field with some simple source terms.Discussion: The proposed method has practical value in real operations within radiation spaces, and can be used to improve the accuracy and efficiency of predicting radiation parameters. Further research could explore the use of more complex source term distributions and the integration of other types of sensors for improved accuracy
Semi-analytic galaxy formation during the epoch of the reionisation
© 2020 Yisheng QiuSemi-analytic models play an important role in modelling the epoch of reionisation. This thesis presents three studies that are related to this topic. First, we measure clustering segregation with both UV-luminosity and stellar mass at z > 4, which is then compared with predictions from the Meraxes semi-analytic model. Our results suggest that the dependence of clustering strength on UV-luminosity is stronger than stellar mass, indicating that compared with stellar mass, UV-luminosity is more tightly correlated with halo mass. Secondly, we investigate dust extinction in the early Universe. Our method utilises the Meraxes semi-analytic model to produce intrinsic galaxy luminosity and adopts parametric relations to estimate dust extinction. A novelty of our approach is that intrinsic luminosity and dust extinction are determined simultaneously by calibrating both galaxy formation and dust models against only UV observations. Our results suggest that there is a factor of two systematic error in the estimations of the cosmic star formation rate density based on the dust law in the local Universe. Finally, we present a method to augment N-body simulations using a Monte Carlo algorithm, which increases the mass resolution of the simulations. The results can be used by semi-analytic models of reionisation to overcome the challenge that convergent predictions of the reionisation history require both high mass resolution and large simulation volume. The effectiveness of our method is tested using a high resolution small volume N-body simulation
Optimization problems involving the fractional Laplacian
In this article we study rearrangement optimization problems
related to boundary-value problems involving the fractional Laplacian.
We establish the existence and uniqueness of a solution
under suitable assumptions
Genome-Wide Expression Analysis Indicates that FNR of Escherichia coli K-12 Regulates a Large Number of Genes of Unknown Function
The major regulator controlling the physiological switch between aerobic and anaerobic growth conditions in Escherichia coli is the DNA binding protein FNR. To identify genes controlled by FNR, we used Affymetrix Antisense GeneChips to compare global gene expression profiles from isogenic MG1655 wild-type and Δfnr strains grown in glucose minimal media under aerobic or anaerobic conditions. We found that 297 genes contained within 184 operons were regulated by FNR and/or by O(2) levels. The expression of many genes known to be involved in anaerobic respiration and fermentation was increased under anaerobic growth conditions, while that of genes involved in aerobic respiration and the tricarboxylic acid cycle were repressed as expected. The expression of nine operons associated with acid resistance was also increased under anaerobic growth conditions, which may reflect the production of acidic fermentation products. Ninety-one genes with no presently defined function were also altered in expression, including seven of the most highly anaerobically induced genes, six of which we found to be directly regulated by FNR. Classification of the 297 genes into eight groups by k-means clustering analysis indicated that genes with common gene expression patterns also had a strong functional relationship, providing clues for studying the function of unknown genes in each group. Six of the eight groups showed regulation by FNR; while some expression groups represent genes that are simply activated or repressed by FNR, others, such as those encoding functions for chemotaxis and motility, showed a more complex pattern of regulation. A computer search for FNR DNA binding sites within predicted promoter regions identified 63 new sites for 54 genes. We suggest that E. coli MG1655 has a larger metabolic potential under anaerobic conditions than has been previously recognized
Systematic Mutagenesis of the Escherichia coli Genome
A high-throughput method has been developed for the systematic mutagenesis of the Escherichia coli genome. The system is based on in vitro transposition of a modified Tn5 element, the Sce-poson, into linear fragments of each open reading frame. The transposon introduces both positive (kanamycin resistance) and negative (I-SceI recognition site) selectable markers for isolation of mutants and subsequent allele replacement, respectively. Reaction products are then introduced into the genome by homologous recombination via the λRed proteins. The method has yielded insertion alleles for 1976 genes during a first pass through the genome including, unexpectedly, a number of known and putative essential genes. Sce-poson insertions can be easily replaced by markerless mutations by using the I-SceI homing endonuclease to select against retention of the transposon as demonstrated by the substitution of amber and/or in-frame deletions in six different genes. This allows a Sce-poson-containing gene to be specifically targeted for either designed or random modifications, as well as permitting the stepwise engineering of strains with multiple mutations. The promiscuous nature of Tn5 transposition also enables a targeted gene to be dissected by using randomly inserted Sce-posons as shown by a lacZ allelic series. Finally, assessment of the insertion sites by an iterative weighted matrix algorithm reveals that these hyperactive Tn5 complexes generally recognize a highly degenerate asymmetric motif on one end of the target site helping to explain the randomness of Tn5 transposition