Effect of process parameters on flow length and flash formation in injection moulding of high aspect ratio polymeric micro features

This paper reports an investigation of the effects of process parameters on the quality characteristics of polymeric parts produced by micro injection moulding (μIM) with two different materials. Four injection moulding process parameters (injection velocity, holding pressure, melt temperature and mould temperature) were investigated using Polypropylene (PP) and Acrylonitrile Butadiene Styrene (ABS). Three key characteristics of the mouldings were evaluated with respect to process settings and the material employed: part mass, flow length and flash formation. The experimentation employs a test part with four micro fingers with different aspect ratios (from 21 up to 150) and was carried out according to the Design of Experiments (DOE) statistical technique. The results show that holding pressure and injection velocity are the most influential parameters on part mass with a direct effect for both materials. Both parameters have a similar effect on flow length for both PP and ABS at all aspect ratios and have higher effects as the feature thickness decreased below 300 μm. The study shows that for the investigated materials the injection speed and packing pressure were the most influential parameters for increasing the amount of flash formation, with relative effects consistent for both materials. Higher melt and mould temperatures settings were less influential parameters for increasing the flash amount when moulding with both materials. Of the two investigated materials, PP was the one exhibiting more flash formation as compared with ABS, when corresponding injection moulding parameters settings for both materials were considered

Massive black hole seeds from low angular momentum material

(ABRIDGED) We present a model in which the seeds of supermassive black holes form from the lowest angular momentum gas in proto-galaxies at high redshift. We show that this leads to a correlation between black hole masses and spheroid properties, as observed today. We assume that gas in early-forming, rare halos has a distribution of specific angular momentum similar to that expected for dark matter halos. This distribution has a significant low angular momentum tail which implies that every proto-galaxy should contain gas that ends up in a high-density disc. In halos more massive than a critical threshold of \~10^8Msun, the discs are gravitationally unstable, and experience an efficient Lin-Pringle viscosity that allows mass inflow. This process continues until the first massive stars disrupt the disc. Black holes are created with a characteristic mass of ~10^5 Msun, independent of the redshift of formation. This serves as a lower bound for black-hole masses in galaxies today. The comoving mass density of black hole seeds grows with time, and saturates when cosmic reionization stops gas cooling in these low-mass systems. By z~15, the comoving mass density becomes comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. Hierarchical merging after z~15 naturally leads to a linear correlation between black-hole mass and stellar spheroid mass, with negligible black hole masses in disc-dominated galaxies.Comment: Replaced to match version accepted for publication in Mon. Not. R. Astron. So

Growing Massive Black Holes in a Local Group Environment: the Central Supermassive, Slowly Sinking, and Ejected Populations

We explore the growth of < 10^7 Msun black holes that reside at the centers of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea II (VL-2) as a framework to test two merger-driven semi-analytic recipes for black hole growth that include dynamical friction, tidal stripping, and gravitational wave recoil in over 20,000 merger tree realizations. First, we apply a Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the central black hole to a maximum mass limited by the Black Hole Fundamental Plane after every merger. Next, we present a new model that allows for low-level Prolonged Gas Accretion (PGA) during the merger. We find that both models can generate a Sgr A* mass black hole. We predict a population of massive black holes in local field dwarf galaxies - if the VL-2 simulation is representative of the growth of the Local Group, we predict up to 35 massive black holes (< 10^6 Msun) in Local Group field dwarfs. We also predict that hundreds of < 10^5 Msun black holes fail to merge, and instead populate the Milky Way halo, with the most massive of them at roughly the virial radius. In addition, we find that there may be hundreds of massive black holes ejected from their hosts into the nearby intergalactic medium due to gravitational wave recoil. We discuss how the black hole population in the Local Group field dwarfs may help to constrain the growth mechanism for Sgr A*.Comment: 25 pages, 19 figures, accepted for publication in MNRA

Performance of aquatic plant species for phytoremediation of arsenic-contaminated water

This study investigates the effectiveness of aquatic macrophyte and microphyte for phytoremediation of water bodies contaminated with high arsenic concentration. Water hyacinth (Eichhornia crassipes) and two algae (Chlorodesmis sp. and Cladophora sp.) found near arsenic-enriched water bodies were used to determine their tolerance toward arsenic and their effectiveness to uptake arsenic thereby reducing organic pollution in arsenic-enriched wastewater of different concentrations. Parameters like pH, chemical oxygen demand (COD), and arsenic concentration were monitored. The pH of wastewater during the course of phytoremediation remained constant in the range of 7.3–8.4, whereas COD reduced by 50–65 % in a period of 15 days. Cladophora sp. was found to survive up to an arsenic concentration of 6 mg/L, whereas water hyacinth and Chlorodesmis sp. could survive up to arsenic concentrations of 2 and 4 mg/L, respectively. It was also found that during a retention period of 10 days under ambient temperature conditions, Cladophora sp. could bring down arsenic concentration from 6 to <0.1 mg/L, Chlorodesmis sp. was able to reduce arsenic by 40−50 %; whereas, water hyacinth could reduce arsenic by only 20 %. Cladophora sp. is thus suitable for co-treatment of sewage and arsenic-enriched brine in an algal pond having a retention time of 10 days. The identified plant species provides a simple and cost-effective method for application in rural areas affected with arsenic problem. The treated water can be used for irrigation

The Demography of Super-Massive Black Holes: Growing Monsters at the Heart of Galaxies

Supermassive black holes (BHs) appear to be ubiquitous at the center of all galaxies which have been observed at high enough sensitivities and resolution with the Hubble Space Telescope. Their masses are found to be tightly linked with the masses and velocity dispersions of their host galaxies. On the other hand, BHs are widely held to constitute the central engines of quasars and active galactic nuclei (AGN) in general. It is however still unclear how BHs have grown, and whether they have co-evolved with their hosts. In this Review I discuss how, in ways independent of specific models, constraints on the growth history of BHs and their host galaxies have been set by matching the statistics of local BHs to the emissivity, number density, and clustering properties of AGNs at different cosmological epochs. I also present some new results obtained through a novel numerical code which evolves the BH mass function and clustering adopting broad distributions of Eddington ratios. I finally review BH evolution in a wider cosmological context, connecting BH growth to galaxy evolution.Comment: 70 pages. New Astronomy Reviews, in pres

Formation and Evolution of Supermassive Black Holes

The correlation between the mass of supermassive black holes in galaxy nuclei and the mass of the galaxy spheroids or bulges (or more precisely their central velocity dispersion), suggests a common formation scenario for galaxies and their central black holes. The growth of bulges and black holes can commonly proceed through external gas accretion or hierarchical mergers, and are both related to starbursts. Internal dynamical processes control and regulate the rate of mass accretion. Self-regulation and feedback are the key of the correlation. It is possible that the growth of one component, either BH or bulge, takes over, breaking the correlation, as in Narrow Line Seyfert 1 objects. The formation of supermassive black holes can begin early in the universe, from the collapse of Population III, and then through gas accretion. The active black holes can then play a significant role in the re-ionization of the universe. The nuclear activity is now frequently invoked as a feedback to star formation in galaxies, and even more spectacularly in cooling flows. The growth of SMBH is certainly there self-regulated. SMBHs perturb their local environment, and the mergers of binary SMBHs help to heat and destroy central stellar cusps. The interpretation of the X-ray background yields important constraints on the history of AGN activity and obscuration, and the census of AGN at low and at high redshifts reveals the downsizing effect, already observed for star formation. History appears quite different for bright QSO and low-luminosity AGN: the first grow rapidly at high z, and their number density decreases then sharply, while the density of low-luminosity objects peaks more recently, and then decreases smoothly.Comment: 31 pages, 13 figures, review paper for Astrophysics Update

Supermassive Black Hole Growth and Merger Rates from Cosmological N-body Simulations

Understanding how seed black holes grow into intermediate and supermassive black holes (IMBHs and SMBHs, respectively) has important implications for the duty-cycle of active galactic nuclei (AGN), galaxy evolution, and gravitational wave astronomy. Most studies of the cosmological growth and merger history of black holes have used semianalytic models and have concentrated on SMBH growth in luminous galaxies. Using high resolution cosmological N-body simulations, we track the assembly of black holes over a large range of final masses -- from seed black holes to SMBHs -- over widely varying dynamical histories. We used the dynamics of dark matter halos to track the evolution of seed black holes in three different gas accretion scenarios. We have found that growth of Sagittarius A* - size SMBH reaches its maximum mass M_{SMBH}~10^6Msun at z~6 through early gaseous accretion episodes, after which it stays at near constant mass. At the same redshift, the duty-cycle of the host AGN ends, hence redshift z=6 marks the transition from an AGN to a starburst galaxy which eventually becomes the Milky Way. By tracking black hole growth as a function of time and mass, we estimate that the IMBH merger rate reaches a maximum of R_{max}=55 yr^-1 at z=11. From IMBH merger rates we calculate N_{ULX}=7 per Milky Way type galaxy per redshift in redshift range 2<z<6.Comment: 12 pages, 8 figures, submitted to MNRA

Ultraluminous Starbursts from SMBH-induced outflows

I argue that there are two modes of global star formation. Disks and smaller spheroids form stars relatively inefficiently as a consequence of supernova-triggered negative feedback via a sequence of ministarbursts (S mode), whereas massive spheroids formed rapidly with high efficiency via the impact of AGN jet-triggered positive feedback (J mode) that generates and enhances ultraluminous starbursts. Supermassive black hole growth by accretion is favoured in the gas-rich protospheroid environment as mergers build up the mass of the host galaxy and provide a centrally concentrated gas supply. Quasi-spherical outflows arise and provide the source of porosity as the energetic jets from the accreting central SMBH are isotropised by the inhomogeneous interstellar medium in the protospheroid core. Super-Eddington outflows occur and help generate both the SMBH at high redshift and the strong positive feedback on protospheroid star formation that occurs as dense interstellar clouds are overpressured and collapse. SMBH form before the bulk of spheroid stars, and the correlation between spheroid velocity dispersion and supermassive black hole mass arises as AGN-triggered outflows limit the gas reservoir for spheroid star formation. The super-Eddington phase plausibly triggers a top-heavy IMF in the region of influence of the SMBH. The Compton-cooled Eddington-limited outflow phase results in a spheroid core whose phase space density scales as the inverse 5/2 power of the core mass, and whose mass scales as the 3/2 power of SMBH mass. This latter scaling suggests that SMBH growth (and hence spheroid formation) is anti-hierarchical.Comment: 6 pages. References added, minor corrections, to match published version, MNRAS in pres

The Formation and Evolution of the First Massive Black Holes

The first massive astrophysical black holes likely formed at high redshifts (z>10) at the centers of low mass (~10^6 Msun) dark matter concentrations. These black holes grow by mergers and gas accretion, evolve into the population of bright quasars observed at lower redshifts, and eventually leave the supermassive black hole remnants that are ubiquitous at the centers of galaxies in the nearby universe. The astrophysical processes responsible for the formation of the earliest seed black holes are poorly understood. The purpose of this review is threefold: (1) to describe theoretical expectations for the formation and growth of the earliest black holes within the general paradigm of hierarchical cold dark matter cosmologies, (2) to summarize several relevant recent observations that have implications for the formation of the earliest black holes, and (3) to look into the future and assess the power of forthcoming observations to probe the physics of the first active galactic nuclei.Comment: 39 pages, review for "Supermassive Black Holes in the Distant Universe", Ed. A. J. Barger, Kluwer Academic Publisher

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease