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Supermassive black holes (SMBHs) of $\sim 10^9\, \rm M_{\odot }$ are generally believed to be the central engines of the luminous quasars observed at z ≳ 6, but their astrophysical origin remains elusive. To investigate the formation of these distant quasars, we perform a suite of zoom-in simulations on a favourable halo, with a mass of $\sim 10^{13}\, \rm M_{\odot }$ at z = 6 and a history of multiple major mergers, ideal for BH growth. We test BH seeds of $10 {\!-\!} 10^6\, \rm M_{\odot }$, and various accretion and feedback models, including thin-disc and slim-disc accretion. We find that abundant gas supply and efficient angular momentum transport by gravitational torques are critical to BH accretion, and that the final BH mass depends strongly on the seed mass and radiative efficiency which in turn depends on feedback model. In our simulations, heavy seeds of $\gtrsim 10^4\, \rm M_{\odot }$ can grow rapidly to SMBHs of $10^8 {\!-\!} 10^9\, \rm M_{\odot }$ by z ∼6 in both thin and slim disc accretion models, provided that the duty cycle of near-Eddington accretion with an Eddington ratio λEdd ≳ 0.6 is maintained at $\gtrsim 40{{\ \rm per\ cent}}$. In particular, for a $10^5\, \rm M_{\odot }$ seed, both our fiducial model and the supercritical accretion model with no spin produce bright quasars with SMBHs of $\sim 10^9\, \rm M_{\odot }$ at z ∼ 7.5. On the other hand, the light seeds of $\lesssim 10^3\, \rm M_{\odot }$ failed to grow to $10^8\, \rm M_{\odot }$ by z ∼ 6 in our simulations. We caution that the results are inconclusive due to limitations of our numerical methods and physical models, and we stress the need for further investigations on the growth of BH seeds with more advanced methods.

We consider a retailer that sells a perishable product, making joint pricing and inventory ordering decisions over a finite time horizon of T periods with lost sales. Exploring a real-life data set from a leading supermarket chain, we identify several distinctive challenges faced by such a retailer that have not been jointly studied in the literature: the retailer does not have perfect information on (1) the demand-price relationship, (2) the demand noise distribution, (3) the inventory perishability rate, and (4) how the demand-price relationship changes over time. Furthermore, the demand noise distribution is nonparametric for some products but parametric for others. To tackle these challenges, we design two types of data-driven pricing and ordering (DDPO) policies for the cases of nonparametric and parametric noise distributions. Measuring performance by regret, that is, the profit loss caused by not knowing (1)–(4), we prove that the T-period regret of our DDPO policies are in the order of [Formula: see text] and [Formula: see text] in the cases of nonparametric and parametric noise distributions, respectively. These are the best achievable growth rates of regret in these settings (up to logarithmic terms). Implementing our policies in the context of the aforementioned real-life data set, we show that our approach significantly outperforms the historical decisions made by the supermarket chain. Moreover, we characterize parameter regimes that quantify the relative significance of the changing environment and product perishability. Finally, we extend our model to allow for age-dependent perishability and demand censoring and modify our policies to address these issues. This paper was accepted by David Simchi-Levi, Management Science Special Section on Data-Driven Prescriptive Analytics.

We know that cancer is rich in neutrophil extracellular traps (NETs) and NETs can promote breast cancer (BC) metastasis, but whether NETs-related genes are associated with the prognosis of BC patients is unclear. As part of this study, we used the TCGA database to obtain 1113 BC samples and 113 normal samples and screened for 102 differentially expressed genes associated with NETs. Following that, we modeled the prognostic risk for six genes (CYBA, RAC2, ITGAL, C3 down-regulated and VDAC1, SLC25A5 up-regulated) using multivariate Cox regression and LASSO regression analyses. In order to determine the risk groups for BC patients, we calculated a risk score and then classified the patients into high and low risk groups based on their median risk value. A significant difference in survival rates was found between high-risk and low-risk BC patients (p

Interface engineering has been widely proved to be an effective approach to improving the overall efficiency of organic solar cells (OSCs). Among the enhanced photovoltaic parameters, a high fill factor (FF) is more responsible for a stable and efficient device. Herein, a simple and effective strategy with a view to improving the FF is demonstrated by modification of hole transporting layers (HTLs). By using a non-planar conjugated tetrathiafulvalene derivative (named TTF-pm) and poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) as double HTLs, the conventional device based on PTB7-Th:PC71BM bulk heterojunction delivers a boosted power conversion efficiency (PCE) of 9.80% and an impressive FF of 74.05%. The analyses presented indicate that the enhanced FF is mostly attributed to the optimized morphology of active layer, improved mobility and suppressed charge recombination via interfacial modification. Moreover, the device stability is also improved benefiting from the optimized film morphology. In addition, a PCE of 16.5% for non-fullerene organic solar cells based on PM6:Y6 blend film using the new HTLs is obtained, which is 7.8% higher than the control. This study highlights the potential of TTF derivatives as new HTLs for high and stable performance in the field of organic photovoltaics.

This study examines how the low-carbon pilot city policy (LCPCP) affects energy efficiency from the angles of green technology innovation and upgrading industrial structure by using panel data collected from Chinese cities between 2007 and 2019. The research results include: (1) Based on the time-varying difference-in-differences method, LCPCP has significantly improved energy efficiency, while such results remain significant after replacing the method of measuring the dependent variable and testing with the placebo test and the method of PSM-DID. (2) The heterogeneity analysis shows that compared to resource-based cities (RBC), LCPCP has a greater impact in non-resource-based cities (NRBC). Compared to the Central regions (CR) and Western regions (WR), LCPCP has a stronger impact in the Eastern region (ER). (3) A mechanism inspection shows that LCPCP can promote energy efficiency through both upgrading industrial structure and green technology innovation. LCPCP is of great importance for improving energy efficiency.

Combining cosmological hydrodynamic simulations and radiative transfer (RT) calculations, we present predictions of multi-wavelength radiative properties of the first galaxies at z ∼ 6–5. We find that intermittent star formation due to supernova (SN) feedback causes the escape fraction of UV photons to fluctuate rapidly, which then produces the observed diversity of SEDs for high-z galaxies. The simulated galaxies make rapid transition between UV-bright and IR-bright phase, and our RT calculations suggest that dust temperatures in the first galaxies are higher than z < 3 galaxies with ∼ 60 K.

Recent observations have successfully detected UV or infrared flux from galaxies at the epoch of reionization. However, the origin of their radiative properties has not been fully understood yet. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present theoretical predictions of multi-wavelength radiative properties of the first galaxies at z=6-15. We find that most of the gas and dust are ejected from star-forming regions due to supernova (SN) feedback, which allows UV photons to escape. We show that the peak of SED rapidly shifts between UV and infrared wavelengths on a timescale of 100 Myr due to intermittent star formation and feedback. When dusty gas covers the star-forming regions, the galaxies become bright in the observed-frame sub-millimeter wavelengths. In addition, we find that the escape fraction of ionizing photons also changes between 1-40% at z>10. The mass fraction of HII region changes with the star formation history, resulting in the fluctuations of metal lines and Lyman-alpha line luminosities. In the starbursting phase of galaxies with the halo mass $\sim 10^{11}\,{\rm M_{\odot}}$ ($10^{12}\,{\rm M_{\odot}}$), the simulated galaxy has $L_{\rm [O\,III]} \sim 10^{42}\, (10^{43})\, {\rm erg\,s^{-1}}$, which is consistent with the observed star-forming galaxies at z>7. Our simulations suggest that deep [C II] observation with ALMA can trace the distribution of neutral gas extending over $\sim 20$ physical kpc. We also find that the luminosity ratio $L_{\rm [O\,III]}/L_{\rm [C\,II]}$ decreases with bolometric luminosity due to metal enrichment. Our simulations show that the combination of multi-wavelength observations by ALMA and JWST will be able to reveal the multi-phase ISM structure and the transition from starbursting to outflowing phases of high-z galaxies., 5 pages, 4 figures, Proceedings IAU Symposium No. 352 "Uncovering early galaxy evolution in the ALMA and JWST era", Viana do Castelo, Portugal, June 2019

With the increasing demands of wireless communication and sensing such as mobile cellular networks and the Internet of Things, radio spectrum is becoming a scarcer resource more than ever. The electromagnetic waves emitted from a radio transmitter typically occupy a certain information channel that is divided into either time [e.g., time division duplex (TDD)] or frequency [e.g. frequency division duplex (FDD)], and, within this channel, all of the receivers or sensors colocated with the transmitter are normally paralyzed.

Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6, during the so-called epoch of reionization. While a few of these UV identified galaxies revealed significant dust reservoirs, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies, and companions of rare quasars. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at $z>6$ is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at $z=3-6$. However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star forming galaxies at $z=6.6813\pm0.0005$ and $z=7.3521\pm0.0005$. These objects are not detected in existing rest-frame UV data, and were only discovered through their far-infrared [CII] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at $z\sim7$. This population of heavily dust-obscured galaxies appears to contribute 10-25 per cent to the $z>6$ cosmic star formation rate density., 16 pages, 7 figures, 4 tables, published in Nature

ART$^2$ is a 3D multi-wavelength Monte Carlo radiative transfer (RT) code that couples continuum and emission lines to track the propagation of photons and their interactions with the interstellar medium (ISM). The previous version of ART$^2$, which included continuum and Ly$\alpha$ line, has been extensively applied to hydrodynamics simulations to study multi-band properties of galaxies and ISM. Here, we describe new implementations of non-local thermodynamic equilibrium RT of molecular and atomic fine structure emission lines, and the parallelization of the code using a number of novel methods. The new ART$^2$ can efficiently and self-consistently produce a full spectrum that includes both continuum and lines such as [CII], [NII], [OIII], Ly$\alpha$, and CO. These essential features, together with the multi-phase ISM model and the adaptive grid, make ART$^2$ a multi-purpose code to study multi-wavelength properties of a wide range of astrophysical systems from planetary disks to large-scale structures. To demonstrate the capability of the new ART$^2$, we applied it to two hydrodynamics simulations: the zoom-in Milky Way Simulation to obtain panchromatic properties of individual galaxies, and the large-scale IllustrisTNG100 Simulation to obtain global properties such as the line intensity mappings. These products are essential for a broad array of studies such as the correlations between physical and panchromatic properties and their evolution. By enabling direct comparison between numerical simulations and multi-band observations, ART$^2$ provides a crucial theoretical framework for the interpretations of existing observations, the plan for future surveys, and the synergy between multi-band galaxy surveys and line intensity mappings. Therefore, ART$^2$ is a powerful and versatile tool to bridge the gap between theories and observations of cosmic structures., Comment: Accepted for publication in MNRAS; 20 pages, 26 figures

We consider an electric utility company that serves retail electricity customers over a discrete-time horizon. In each period, the company observes the customers' consumption as well as high-dimensional features on customer characteristics and exogenous factors. These features exhibit three types of heterogeneity—over time, customers, or both. Based on the consumption and feature observations, the company can dynamically adjust the retail electricity price at the customer level. The consumption depends on the features: there is an underlying structure of clusters in the feature space, and the relationship between consumption and features is different in each cluster. Initially, the company knows neither the underlying cluster structure nor the corresponding consumption models. We measure the company's performance by its average regret, i.e., the profit loss per period per customer, relative to a clairvoyant who knows the underlying cluster structure and the consumption model in each cluster. We design a data-driven policy of joint spectral clustering and feature-based pricing, and show that its average regret converges to zero at the fastest achievable rate. We conduct case studies based on real-life smart meter data from Texas and simulation experiments. Relative to the company policy, our policy increases company profits by 146% over a three-month period.

We present results from a new cosmological hydrodynamics simulation campaign of protocluster (PC) regions, FOREVER22: FORmation and EVolution of galaxies in Extremely-overdense Regions motivated by SSA22. The simulations cover a wide range of cosmological scales using three different zoom set-ups in a parent volume of $(714.2~\rm cMpc)^{3}$: PCR (Proto-Cluster Region; $V= (28.6~{\rm cMpc})^{3} $, SPH particle mass, $m_{\rm{SPH}} = 4.1 \times 10^{6}~\rm M_{\odot}$ and final redshift, $z_{\rm end}=2.0$), BCG (Brightest proto-Cluster Galaxy; $V \sim (10~{\rm cMpc})^{3} $, $m_{\rm SPH} = 5.0\times10^{5}~\rm M_{\odot}$ and $z_{\rm end}=4.0$ ), and First ( $V \sim (3~{\rm cMpc})^{3} $, $m_{\rm SPH} = 7.9 \times 10^{3}~\rm M_{\odot}$ and $z_{\rm end}=9.5$) runs, that allow to focus on different aspects of galaxy formation. In the PCR runs, we follow 10 PCs, each harbouring 1 - 4 SMBHs with $M_{\rm BH} \ge 10^{9}~\rm M_{\odot}$. One of the PC cores shows a spatially close arrangement of seven starburst galaxies with ${\rm SFR} \gtrsim 100~\rm M_{\odot}~yr^{-1}$ each, that are dust-obscured and would appear as submillimeter galaxies with flux $\gtrsim 1~$ mJy at $1.1~ \rm mm$ in observations. The BCG runs show that the total SFRs of haloes hosting BCGs are affected by AGN feedback, but exceed $1000~\rm M_{\odot}~yr^{-1}$ at $z \lesssim 6$. The First runs resolve mini-haloes hosting population (Pop) III stars and we show that, in PC regions, the dominant stellar population changes from Pop III to Pop II at $z \gtrsim 20$, and the first galaxies with ${\rm SFR} \gtrsim 18~\rm M_{\odot}~yr^{-1}$ form at $z \sim 10$. These can be prime targets for future observations with the James Webb Space Telescope. Our simulations successfully reproduce the global star formation activities in observed PCs and suggest that PCs can kickstart cosmic reionization., Comment: 24 pages, 19 figures, accepted for publication in MNRAS

The galaxy Malin 1 contains the largest stellar disk known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity $V_{\rm max}$ of 430 ${\rm km\ s^{-1}}$, contains a 100 kpc gas/stellar disk with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disk, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disk back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy disks as extreme as Malin 1 within the current galaxy formation framework., 5 page, 5 figures; resubmitted to MNRAS Letters after first referee report; Comments welcome. Animations of gas/stars can be found here at https://youtu.be/Ibl4Cyybw2Q and https://youtu.be/3aIpCu6e9dQ, or downloaded at http://www.tng-project.org/movies/tng/TNG_Malin_1_gas.mpeg and http://www.tng-project.org/movies/tng/TNG_Malin_1_star.mpeg

Recent observations have successfully detected UV-bright and infrared-bright galaxies in the epoch of reionization. However, the origin of their radiative properties has not been understood yet. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present predictions of multiwavelength radiative properties of the first galaxies at z ∼ 6–15. Using zoom-in initial conditions, we investigate three massive galaxies and their satellites in different environment and halo masses at z = 6: $M_{\rm h}= 2.4\times 10^{10}\,$, $1.6\times 10^{11}\, $, and $0.7\times 10^{12}\, {\rm M_{\odot }}$. We find that most of the gas and dust are ejected from star-forming regions by supernova feedback, which allows the UV photons to escape. We show that the peak of the spectral energy distribution (SED) rapidly changes between UV and infrared wavelengths on a time-scale of ∼ 100 Myr due to intermittent star formation and feedback, and the escape fraction of UV photons fluctuates in the range of 0.2–0.8 at z < 10 with a time-averaged value of 0.3. When dusty gas covers the star-forming regions, the galaxies become bright in the observed-frame sub-millimeter wavelengths. We predict the detectability of high-z galaxies with the Atacama Large Millimeter Array (ALMA). For a sensitivity limit of $0.1\, {\rm mJy}$ at $850\, {\rm \mu m}$, the detection probability of galaxies in haloes $M_{\rm h}\gtrsim 10^{11}\, \, {\rm M_{\odot }}$ at z ≲ 7 exceeds fifty per cent. We argue that supernova feedback can produce the observed diversity of SEDs for high-z galaxies.

In recent years, the discovery of massive quasars at z~7 has provided a striking challenge to our understanding of the origin and growth of supermassive black holes in the early Universe. Mounting observational and theoretical evidence indicates the viability of massive seeds, formed by the collapse of supermassive stars, as a progenitor model for such early, massive accreting black holes. Although considerable progress has been made in our theoretical understanding, many questions remain regarding how (and how often) such objects may form, how they live and die, and how next generation observatories may yield new insight into the origin of these primordial titans. This review focusses on our present understanding of this remarkable formation scenario, based on discussions held at the Monash Prato Centre from November 20--24, 2017, during the workshop "Titans of the Early Universe: The Origin of the First Supermassive Black Holes.", Comment: Solicited review article (accepted) for Publications of the Astronomical Society of Australia. 38 pages, 15 figures, 1 table

In this paper, we present our design of a v-band patch array for compact, lightweight, and power efficient drone radar. The 60 GHz radar has a bandwidth of 7GHz. Several compact V-band antennas, such as Yagi, patch, aperture coupled and dual-slits patch antenna are studied and compared. The impact of different antenna design on the compact radar board geometry and quality of performance was analyzed.

We study the orbital properties of dark matter haloes by combining a spectral method and cosmological simulations of Milky Way-sized galaxies. We compare the dynamics and orbits of individual dark matter particles from both hydrodynamic and $N$-body simulations, and find that the fraction of box, tube and resonant orbits of the dark matter halo decreases significantly due to the effects of baryons. In particular, the central region of the dark matter halo in the hydrodynamic simulation is dominated by regular, short-axis tube orbits, in contrast to the chaotic, box and thin orbits dominant in the $N$-body run. This leads to a more spherical dark matter halo in the hydrodynamic run compared to a prolate one as commonly seen in the $N$-body simulations. Furthermore, by using a kernel based density estimator, we compare the coarse-grained phase-space densities of dark matter haloes in both simulations and find that it is lower by $\sim0.5$ dex in the hydrodynamic run due to changes in the angular momentum distribution, which indicates that the baryonic process that affects the dark matter is irreversible. Our results imply that baryons play an important role in determining the shape, kinematics and phase-space density of dark matter haloes in galaxies., 12 pages, 9 figures

The "Disk of satellites" (DoS) around Milky Way is a highly debated topic with conflicting interpretations of observations and their theoretical models. We perform a comprehensive analysis of all dwarfs detected in the Milky Way and find that the DoS structure depends strongly on the plane identification method and the sample size. In particular, we demonstrate that a smaller sample size produces a higher anisotropy of the spatial distribution and a stronger clustering of the angular momentum of the satellites. Moreover, we calculate the evolution of the 11 classical satellites with proper motion measurements and find that the thin DoS they currently reside in is transient. Furthermore, we analyze two cosmological simulations using the same initial conditions of a Milky Way-sized galaxy, an N-body run with dark matter only and a hydrodynamic one with both baryonic and dark matter, and find that the hydrodynamic simulation produces more anisotropic distribution of satellites than the N-body one. Our results suggest that an anisotropic distribution of satellites in galaxies can originate from baryonic processes in the hierarchical structure formation model, but the claimed highly-flattened, coherently-rotating DoS of the Milky Way may be a small-number selection effect. These findings may help resolve the contradictory claims of DoS in other galaxies and the discrepancy among numerical simulations., Comment: Published in ApJ. 7 pages, 5 figures

The ground-breaking detections of gravitational waves from black hole mergers by LIGO have rekindled interest in primordial black holes (PBHs) and the possibility of dark matter being composed of PBHs. It has been suggested that PBHs of tens of solar masses could serve as dark matter candidates. Recent analytical studies demonstrated that compact ultra-faint dwarf galaxies can serve as a sensitive test for the PBH dark matter hypothesis, since stars in such a halo-dominated system would be heated by the more massive PBHs, their present-day distribution can provide strong constraints on PBH mass. In this study, we further explore this scenario with more detailed calculations, using a combination of dynamical simulations and Bayesian inference methods. The joint evolution of stars and PBH dark matter is followed with a Fokker-Planck code PhaseFlow. We run a large suite of such simulations for different dark matter parameters, then use a Markov Chain Monte Carlo approach to constrain the PBH properties with observations of ultra-faint galaxies. We find that two-body relaxation between the stars and PBH drives up the stellar core size, and increases the central stellar velocity dispersion. Using the observed half-light radius and velocity dispersion of stars in the compact ultra-faint dwarf galaxies as joint constraints, we infer that these dwarfs may have a cored dark matter halo with the central density in the range of 1-2 $\rm{M_{\odot}/pc^3}$, and that the PBHs may have a mass range of 2-14 $\rm{M_{\odot}}$ if they constitute all or a substantial fraction of the dark matter., Comment: 11 page, 6 figures, submitted to MNRAS; comments welcome

A large number of high-redshift galaxies have been discovered via their narrow-band Lyα line or broad-band continuum colours in recent years. The nature of the escaping process of photons from these early galaxies is crucial to understand galaxy evolution and the cosmic reionization. Here, we investigate the escape of Lyα, non-ionizing UV-continuum (λ = 1300-1600 A in rest frame), and ionizing photons (λ < 912 A) from galaxies by combining a cosmological hydrodynamic simulation with three-dimensional multiwavelength radiative transfer calculations. The galaxies are simulated in a box of 5^3 h^−3 Mpc^3 with high resolutions using the Aquila initial condition which reproduces a Milky Way-like galaxy at redshift z = 0. We find that the escape fraction (f_esc) of these different photons shows a complex dependence on redshift and galaxy properties: $f_{\rm esc}^{\rm \rm {Ly{\alpha }}}$ and $f_{\rm esc}^{\rm UV}$ appear to evolve with redshift, and they show similar, weak correlations with galaxy properties such as mass, star formation, metallicity, and dust content, while $f_{\rm esc}^{\rm Ion}$ remains roughly constant at ∼0.2 from z ∼ 0 to 10, and it does not show clear dependence on galaxy properties. $f_{\rm esc}^{\rm \rm {Ly{\alpha }}}$ correlates more strongly with $f_{\rm esc}^{\rm UV}$ than with $f_{\rm esc}^{\rm Ion}$. In addition, we find a relation between the emergent Lyα luminosity and the ionizing photon emissivity of Lyman Alpha Emitters (LAEs). By combining this relation with the observed luminosity functions of LAEs at different redshift, we estimate the contribution from LAEs to the reionization of intergalactic medium (IGM). Our result suggests that ionizing photons from LAEs alone are not sufficient to ionize IGM at z ≳ 6, but they can maintain the ionization of IGM at z ∼ 0–5.

Recent observations show that a large number of Lyman-alpha emitters (LAEs) at high redshift z >= 3 have unusually high Lya equivalent widths (EW > 400 angstrom). However, the origin of these high EWs is an open question. Here, we investigate the impacts of photon trapping on the Lya EW and other properties by tracking the Lya radiative transfer in spherical galactic clouds. We find that the delayed escape of the Lya photons can change the Lya properties significantly. During the transition phase from optically thick to optically thin where the Lya photons can escape simultaneously, the EW can be boosted to ~ 1000 angstrom, the Lya luminosity can be increased by a factor of a few, and the line profile can be significantly broadened. The boost factor appears to depend on the galaxy properties such as mass and star formation rate and timescale, therefore future investigation combing 3D Lya RT calculations with cosmological simulations of galaxy formation and evolution is needed to fully understand the Lya properties of early star-forming galaxies., 7 pages, 7 figures, accepted for publication in MNRAS

Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at $\sim 2\times 10^{5}\, {\rm{M_{\odot}}}$, but the origin of this peaked distribution is highly debated. Here we investigate the formation and evolution of star clusters in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts. We find that massive star clusters in the range of $\sim 10^{5.5} - 10^{7.5}\, {\rm{M_{\odot}}}$ form preferentially in the highly-shocked regions produced by galaxy interactions. The nascent cluster-forming clouds have high gas pressures in the range of $P/k \sim 10^8 - 10^{12}\, \rm{K}\,\rm{cm^{-3}}$, which is $\sim 10^4 - 10^8$ times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super star cluster cloud in the Antennae Galaxies. Furthermore, these massive star clusters have quasi-lognormal initial mass functions with a peak around $\sim 10^{6}\, {\rm{M_{\odot}}}$. The number of clusters declines with time due to destructive processes, but the shape and the peak of the mass functions do not change significantly during the course of galaxy collisions. Our results suggest that gas-rich galaxy mergers may provide a favorable environment for the formation of massive star clusters such as globular clusters, and that the lognormal mass functions and the unique peak may originate from the extreme high-pressure conditions of the birth clouds and may survive the dynamical evolution., Comment: Accepted in ApJ. 16 pages, 9 figures

Narrow-band Lya line and broad-band continuum have played important roles in the discovery of high-redshift galaxies in recent years. Hence, it is crucial to study the radiative transfer of both Lya and continuum photons in the context of galaxy formation and evolution in order to understand the nature of distant galaxies. Here, we present a three-dimensional Monte Carlo radiative transfer code, All-wavelength Radiative Transfer with Adaptive Refinement Tree (ART^2), which couples Lya line and multi-wavelength continuum, for the study of panchromatic properties of galaxies and interstellar medium. This code is based on the original version of Li et al., and features three essential modules: continuum emission from X-ray to radio, Lya emission from both recombination and collisional excitation, and ionization of neutral hydrogen. The coupling of these three modules, together with an adaptive refinement grid, enables a self-consistent and accurate calculation of the Lya properties. As an example, we apply ART^2 to a cosmological simulation that includes both star formation and black hole growth, and study in detail a sample of massive galaxies at redshifts z=3.1 - 10.2. We find that these galaxies are Lya emitters (LAEs), whose Lya emission traces the dense gas region, and that their Lya lines show a shape characteristic of gas inflow. Furthermore, the Lya properties, including photon escape fraction, emergent luminosity, and equivalent width, change with time and environment. Our results suggest that LAEs evolve with redshift, and that early LAEs such as the most distant one detected at z ~ 8.6 may be dwarf galaxies with a high star formation rate fueled by infall of cold gas, and a low Lya escape fraction.

We investigate the nature of CO emission from z~6 quasars by combining non-LTE radiative transfer calculations with merger-driven models of z~6 quasar formation that arise naturally in LCDM cosmological simulations. We consider four model quasars formed in 10^12-10^13 M_sun halos from different merging histories. Our main results follow. Owing to massive starbursts and funneling of dense gas into the nuclear regions of merging galaxies, the CO is highly excited and the flux density peaks between J=5-8. The CO morphology of z~6 quasars often exhibits multiple emission peaks which arise from H2 concentrations which have not yet fully coalesced. Quasars at z~6 display a large range of sightline dependent line widths such that the lines are narrowest when the rotating H2 gas associated with the quasar is viewed face-on (when L_B is largest), and broadest when the gas is seen edge-on (when L_B is lowest). Thus for all models selection effects exist such that quasars selected for optical luminosity are preferentially face-on which may result in detected CO line widths narrower than the median. The sightline averaged line width is reflective of the circular velocity (V_c) of the host halo, and ranges from sigma~300-650 km/s. For optically selected QSOs, 10-25% (halo-mass dependant) of sightlines have narrow line widths compatible with the sole CO detection at z>6, J1148+5251. When accounting for both the temporal evolution of CO line widths, as well as the redshift evolution of halo V_c, these models self-consistently account for the CO line widths of both z~2 sub-mm galaxies and QSO's. Finally, the dynamical mass derived from the sightline averaged line widths provides a good estimate of the total mass, and allows for a stellar bulge and SMBH consistent with the local M_BH-M_bulge relation. [abridged]

We calculate the observable properties of the most massive high-redshift galaxies in the hierarchical formation scenario where stellar spheroid and supermassive black hole growth are fueled by gas-rich mergers. Combining high-resolution hydrodynamical simulations of the hierarchical formation of a z~6 quasar, stellar population synthesis models, template AGN spectra, prescriptions for interstellar and intergalactic absorption, and the response of modern telescopes, the photometric evolution of galaxies destined to host z~6 quasars are modeled at redshifts z~4-14. These massive galaxies, with enormous stellar masses of M_star ~10^11.5-10^12 M_sun. and star formation rates of SFR~10^3-10^4 M_sun yr^-1 at z>~7, satisfy a variety of photometric selection criteria based on Lyman-break techniques including V-band dropouts at z>~5, i-band dropouts at z>~6, and z-band dropouts at z>~7. The observability of the most massive high-redshift galaxies is assessed and compared with a wide range of existing and future photometric surveys including SDSS, GOODS/HUDF, NOAO WDFS, UKIDSS, the IRAC Shallow Survey, Pan-STARRS, LSST, and SNAP. Massive stellar spheroids descended from z~6 quasars will likely be detected at z~4 by existing surveys, but owing to their low number densities the discovery of quasar progenitor galaxies at z>7 will likely require future surveys of large portions of the sky (>~0.5%) at wavelengths lambda>1 micron. The detection of rare, star-bursting, massive galaxies at redshifts z>~6 would provide support for the hierarchical formation of the earliest quasars and characterize the primitive star-formation histories of the most luminous elliptical galaxies., Version accepted by ApJ (5/21/2007), for high-resolution figures see http://kicp.uchicago.edu/~brant/astro-ph/massive_high_redshift_galaxies/

Bitstream Modulated transmitters based on Delta Sigma Modulation have been proved to be promising for efficient amplification of non-constant envelope signal. Such transmitters preserve signal linearity by converting the signal to binary envelope and shaping the quantization noise out of signal band. To further suppress the noise near the in band signal that is left from noise shaping, active FIR filter structure consisting of multiple identical amplifier units is proposed. In this paper, the Channelized Active Noise Elimination (CANE) technique is employed to create an effective band-pass FIR filter by delaying, up-converting the baseband signal and then combining them in RF. A special power combining network is designed to maintain the overall PA efficiency while the noise power is suppressed. An S-band transmitter prototype with 2-channels has been built and tested. The results demonstrated that the CANE technique can achieve filtering with software reconfigured flexibility while maintaining the power efficiency.

We study the impact of baryons on the distribution of dark matter in a Milky Way-size halo by comparing a high-resolution, moving-mesh cosmological simulation with its dark matter-only counterpart. We identify three main processes related to baryons -- adiabatic contraction, tidal disruption and reionization -- which jointly shape the dark matter distribution in both the main halo and its subhalos. The relative effect of each baryonic process depends strongly on the subhalo mass. For massive subhalos with maximum circular velocity $v_{\rm max} > 35 km/s$, adiabatic contraction increases the dark matter concentration, making these halos less susceptible to tidal disruption. For low-mass subhalos with $v_{\rm max} < 20 km/s$, reionization effectively reduces their mass on average by $\approx$ 30% and $v_{\rm max}$ by $\approx$ 20%. For intermediate subhalos with $20 km/s < v_{\rm max} < 35 km/s$, which share a similar mass range as the classical dwarf spheroidals, strong tidal truncation induced by the main galaxy reduces their $v_{\rm max}$. Moreover, the stellar disk of the main galaxy effectively depletes subhalos near the central region. As a combined result of reionization and increased tidal disruption, the total number of low-mass subhalos in the hydrodynamic simulation is nearly halved compared to that of the $\textit{N-}$body simulation. We do not find dark matter cores in dwarf galaxies, unlike previous studies that employed bursty feedback-driven outflows. The substantial impact of baryons on the abundance and internal structure of subhalos suggests that galaxy formation and evolution models based on $\textit{N}$-body simulations should include these physical processes as major components., 22 pages, accepted for publication in MNRAS

Using a model for self-regulated growth of black holes (BHs) in mergers involving gas-rich galaxies, we study the relationship between quasars and the population of merging galaxies and predict the merger-induced star formation rate density of the Universe. Mergers drive nuclear gas inflows, fueling starbursts and 'buried quasars' until accretion feedback expels the gas, rendering a briefly visible optical quasar. Star formation is shut down and accretion declines, leaving a passively evolving remnant with properties typical of red, elliptical galaxies. Based on evolution of these events in our simulations, we demonstrate that the observed statistics of merger rates, luminosity functions (LFs) and mass functions, SFR distributions, specific SFRs, quasar and quasar host galaxy LFs, and elliptical/red galaxy LFs are self-consistent and follow from one another as predicted by the merger hypothesis. We use our simulations to de-convolve both quasar and merging galaxy LFs to determine the birthrate of black holes of a given final mass and merger rates as a function of stellar mass. We use this to predict the merging galaxy LF in several observed wavebands, color-magnitude relations, mass functions, absolute and specific SFR distributions and SFR density, and quasar host galaxy LFs, as a function of redshift from z=0-6. We invert this and predict e.g. quasar LFs from observed merger LFs or SFR distributions. Our results agree well with observations, but idealized models of quasar lightcurves are ruled out by comparison of merger and quasar observations at >99.9% confidence. Using only observations of quasars, we estimate the contribution of mergers to the SFR density of the Universe even to high redshifts z~4.

We present numerical experiments that demonstrate that the nonlinear development of the Toomre instability in disks of isothermal gas, stars, and dark matter reproduces the observed Schmidt Law for star formation. The rate of gas collapse depends exponentially on the (minimum) value of the Toomre parameter in the disk. We demonstrate that spurious fragmentation occurs in the absence of sufficient resolution in our SPH model. Our models also reproduce observed star formation thresholds in disk galaxies. We finally briefly discuss the application of our models to the study of globular cluster formation in merging galaxies.

Penning discharge (PD) sputtering deposition technique is developed and first used in synthesis of nanostructured aluminum nitride (AlN) films. The advantage of the present PD is that discharge current is linearly dependent on power supply voltage. Maximal discharge current up to 180 mA is obtained for power supply voltage of 5 kV with a ballast resistor of 25 kΩ. In contrast, the discharge voltage is only 290 V. Installation of smaller value of the ballast resistor will yield larger discharge current, whereas discharge voltage remains nearly unchanged, which is an important factor employed to the synthesis of high quality of AlN films. The preferred orientations of nanoscale AlN particles distributions on the surface of the substrates are observed. The increase of the power voltage (discharge current) for sputtering deposition yields different patterns of the nanoscale particles, but sizes of the particles are unchanged. Typical A 1– TO and A1– LO bands in Raman spectra of the films are identified, respectively.

(Z)-2-Enynyl-2-hydroxy-imidazolidine-4,5-diones 2 are synthesized for the first time via Cu(I)-mediated (Z)-selective geminal coupling among two molecules of terminal alkynes, carbodiimides, and oxalyl chloride. Further transformation of 2a is performed to yield a highly functionalized spiro heterocyclic compound 5.

Identifying the processes that determine the initial mass function of stars (IMF) is a fundamental problem in star formation theory. One of the major uncertainties is the exact chemical state of the star forming gas and its influence on the dynamical evolution. Most simulations of star forming clusters use an isothermal equation of state (EOS). However, theoretical predictions and observations suggest that the effective polytropic exponent gamma in the EOS varies with density. We address these issues and study the effect of a piecewise polytropic EOS on the formation of stellar clusters in turbulent, self-gravitating molecular clouds using three-dimensional, smoothed particle hydrodynamics simulations. To approximate the results of published predictions of the thermal behavior of collapsing clouds, we increase the polytropic exponent gamma from 0.7 to 1.1 at some chosen density n_c, which we vary. The change of thermodynamic state at n_c selects a characteristic mass scale for fragmentation M_ch, which we relate to the peak of the observed IMF. Our investigation generally supports the idea that the distribution of stellar masses depends mainly on the thermodynamic state of the star-forming gas. The thermodynamic state of interstellar gas is a result of the balance between heating and cooling processes, which in turn are determined by fundamental atomic and molecular physics and by chemical abundances. Given the abundances, the derivation of a characteristic stellar mass can thus be based on universal quantities and constants., 13 pages, 7 figures, accepted by A&A

We study gravitational instability and consequent star formation in a wide range of isolated disk galaxies, using three-dimensional, smoothed particle hydrodynamics simulations at resolution sufficient to fully resolve gravitational collapse. Stellar feedback is represented by an isothermal equation of state. Absorbing sink particles are inserted in dynamically bound, converging regions with number density $n > 10^3$ cm$^{-3}$ to directly measure the mass of gravitationally collapsing gas available for star formation. Our models quantitatively reproduce not only the observed Schmidt law, but also the observed star formation threshold in disk galaxies. Our results suggest that the dominant physical mechanism determining the star formation rate is just the strength of gravitational instability, with feedback primarily functioning to maintain a roughly constant effective sound speed., ApJL accepted, version with high quality color images can be found in http://research.amnh.org/~yuexing/astro-ph/0407247.pdf

Potential of porous carbons for practical applications is often limited by their intrinsic fragility and poor processability. Here, a facile approach to fabricate hierarchically macro-/microporous carbon monolith (CM) with high strength and integrated structure is developed, which offers great possibilities for structure-to-functionality applications. Through a fiber-reinforced sol–gel process and an ambient pressure drying approach, aerogel-like CMs can be designed and fabricated in customizable forms. In particular, a novel scroll-type carbon monolith (S-CM) is constructed, which can mimic a roll-to-roll tube reactor and thus avoid the packing problems arising from the granules or powders of conventional activated carbons. The resulting CM exhibits a high CO2 adsorption capacity of 15.9 mmol g−1 at 25 bar and a breakthrough capacity of 1 mmol g−1 at 1 bar. Moreover, owing to the integrated structure and good electrical conductivity, the scroll-type S-CM can be easily regenerated by employing a low-energy electrothermal desorption technique. The specialized design of the CMs should fulfill industrial directives and may provide an access route to more efficient porous carbons for structure-oriented and process-intensified applications.

(Z)-2-Enynyl-2-hydroxy-imidazolidine-4,5-diones 2 are synthesized for the first time via Cu(I)-mediated (Z)-selective geminal coupling among two molecules of terminal alkynes, carbodiimides, and oxalyl chloride. Further transformation of 2a is performed to yield a highly functionalized spiro heterocyclic compound 5.

We study the convergence properties of smoothed particle hydrodynamics (SPH) using numerical tests and simple analytic considerations. Our analysis shows that formal numerical convergence is possible in SPH only in the joint limit $N \rightarrow \infty$, $h \rightarrow 0$, and $N_{nb} \rightarrow \infty$, where $N$ is the total number of particles, $h$ is the smoothing length, and $N_{nb}$ is the number of neighbor particles within the smoothing volume used to compute smoothed estimates. Previous work has generally assumed that the conditions $N \rightarrow \infty$ and $h \rightarrow 0$ are sufficient to achieve convergence, while holding $N_{nb}$ fixed. We demonstrate that if $N_{nb}$ is held fixed as the resolution is increased, there will be a residual source of error that does not vanish as $N \rightarrow \infty$ and $h \rightarrow 0$. Formal numerical convergence in SPH is possible only if $N_{nb}$ is increased systematically as the resolution is improved. Using analytic arguments, we derive an optimal compromise scaling for $N_{nb}$ by requiring that this source of error balance that present in the smoothing procedure. For typical choices of the smoothing kernel, we find $N_{nb} \propto N^{1/2}$. This means that if SPH is to be used as a numerically convergent method, the required computational cost does not scale with particle number as $O(N)$, but rather as $O(N^{1+\delta})$, where $\delta \approx 1/2$, with a weak dependence on the form of the smoothing kernel., Comment: The revised version accepted in ApJ, with typos corrected and references added

We derive a semi-analytic solution for the structure of conduction-mediated transition layers above an X-ray illuminated accretion disk, and calculate explicitly the X-ray line radiation resulting from both resonance line scattering and radiative recombination in these layers. The vertical thermal structure of the illuminated disk is found to depend on the illuminating continuum: for a hard power law continuum, there are two stable phases connected by a single transition layer; while for a softer continuum, there may exist three stable phases connected by two separate transition layers, with an intermediate stable layer in between. We show that the structure can be written as a function of the electron scattering optical depth through these layers, which leads to unique predictions of the equivalent width of the resulting line radiation from both recombination cascades and resonance line scattering. We find that resonance line scattering plays an important role, especially for the case where there is no intermediate stable layer., 27 pages, 6 figures, submitted to ApJ