Formation Of Clumps Research Articles

Nonrelativistic formation of scalar clumps as a candidate for dark matter

We propose a new mechanism for the formation of dark matter clumps in the radiation era. We assume that a light scalar field is decoupled from matter and oscillates harmonically around its vacuum expectation value. We include self-interactions and consider the nonrelativistic regime. The scalar dynamics are described by a fluid approach where the fluid pressure depends on both quantum and self-interaction effects. When the squared speed of sound of the scalar fluid becomes negative, an instability arises and the fluctuations of the scalar energy-density field start growing. They eventually become nonlinear and clumps form. Subsequently, the clumps aggregate and reach a universal regime. Afterwards, they play the role of cold dark matter. We apply this mechanism first to a model with a negative quartic term stabilised by a positive self-interaction of order six, and then to axion monodromy, where a subdominant cosine potential corrects a mass term. In the first case, the squared speed of sound becomes negative when the quartic term dominates, leading to a tachyonic instability. For axion monodromy, the instability starts very slowly after the squared speed of sound first becomes negative and then oscillates around zero. Initially the density perturbations perform acoustic oscillations due to the quantum pressure. Eventually, they start growing exponentially due to a parametric resonance. In both scenarios, the scalar-field clumps span a wide range of scales and masses, running from the size of atoms to that of galactic molecular clouds, and from $10^{-3} \, {\rm gram}$ to thousands of solar masses. Because of finite-size effects, both from the source and the lens, these dark matter clumps are far beyond the reach of microlensing observations.

THROMBOTIC MICROANGIOPATHY: A RARE SEQUELAE OF ENDOSCOPIC RETROGRADE CHOLANGIOPANCREATOGRAPHY

SESSION TITLE: Medical Student/Resident Critical Care Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Thrombotic microangiopathy (TMA) is characterized by many etiologies, however it is not often described as a complication of Endoscopic Retrograde Cholangiopancreatography (ERCP). Failure to identify the relationship between TMA and ERCP may result in delay of diagnosis and poor patient outcomes. We present a case of a young healthy female who developed TMA after ERCP. CASE PRESENTATION: A 26-year-old woman presented to the hospital with complaints of abdominal pain, nausea and vomiting. An abdominal CT scan showed cholelithiasis and choledocholithiasis and the patient was scheduled for ERCP. She tolerated the procedure well with no immediate complications. However, a day after procedure, labs showed elevated serum lipase and amylase levels with renewed abdominal pain. Two days after ERCP she developed fever, severe thrombocytopenia, anemia and acute kidney injury (AKI) evidenced by elevated serum creatinine. A preliminary diagnosis of thrombotic thrombocytopenic purpura (TMA) was considered. Plasma exchange therapy with platelet transfusion and high dose steroids was initiated. She also received multiple packed red cell transfusion for severe anemia. ADAMTS13 antibody testing returned low at 53% with negative anti-ADAMTS13 IgG. After 7 daily sessions of plasma exchange platelets improved, AKI and anemia resolved, and the patient was discharged from the hospital. DISCUSSION: Literature review shows only about 4 cases of ERCP induced TMA. A well-known complication of ERCP is pancreatitis and a rare unfortunate sequela of this is TMA. There is a known correlation between TMA and pancreatitis, though the mechanism by which this occurs is still not well understood. Endothelial damage, cytokine release and platelet activation are thought to be the pathophysiological links between these two conditions (1). Cytokines cause release of ultra-large von-Willebrand factor (VWf) molecules that attach to activated platelets promoting aggregation, clumping and thrombus formation. There is concomitant reduction in serum ADAMTS13, which would normally cleave the ultra-large VWf, due to pancreatic enzyme degradation. CONCLUSIONS: This case illustrates how complicated the diagnosis of TMA can be, but also points out how clinical judgment is imperative to prompt early treatment and increase favorable outcomes. TMA caused by ERCP is rare, but recognizing this link is important for immediate initiation of life saving treatment. Reference #1: 1. Malik, F., Ali, N., Ahsan, I., Ghani, A. R., & Fidler, C. (2016). Eculizumab refractory thrombotic thrombocytopenic purpura secondary to post-endoscopic retrograde cholangiopancreatography pancreatitis in a patient. Journal of community hospital internal medicine perspectives, 6(6), 32310. DISCLOSURES: No relevant relationships by Kitson Deane, source=Web Response No relevant relationships by Abidemi Idowu, source=Web Response

Photoelectric heating effects on the evolution of luminous disc galaxies

ABSTRACT Photoelectric heating (PEH) influences the temperature and density of the interstellar medium (ISM), potentially also affecting star formation. PEH is expected to have a stronger effect on massive galaxies, as they host larger dust reservoirs compared to dwarf systems. Accordingly, in this paper, we study PEH effects in Milky Way-like galaxies using a smoothed particle hydrodynamics code, which self-consistently implements the evolution of the gas, dust, and interstellar radiation field. Dust evolution includes dust formation by stars, destruction by SNe, and growth in dense media. We find that PEH suppresses star formation due to the excess heating that reduces the ISM density. This suppression is seen across the entire range of gas fractions, star-formation recipes, dust models, and PEH efficiencies investigated by our code. The suppression ranges from negligible values to approximately a factor of five depending on the specific implementation. Galaxy models having higher gas fractions experience higher star-formation suppression. The adopted dust model also alters the extent of star-formation suppression. Moreover, when PEH is switched on, galaxy models show higher gas outflow rates and have higher loading factors, indicative of enhanced SNe feedback. In gas-rich models (i.e. a gas fraction of 0.5), we also find that PEH suppresses the formation of disc clumps via violent disc instabilities, and thus suppresses bulge formation via clump migration to the central regions.

Dynamics of the Parker–Jeans Instability of Gaseous Disks Including the Effect of Cosmic Rays

Abstract The effect of cosmic rays on the Parker–Jeans instability in magnetized self-gravitating gaseous disks is studied using three-dimensional magnetohydrodynamic simulations with cosmic rays taken as a massless fluid with notable pressure. Cosmic-ray diffusion along the magnetic field is taken into account in the simulation. The initial configuration of the disk is a magnetized cold gas slab sandwiched between hot coronae (on top and bottom). We show that cosmic rays play an important role in the formation of filaments or clumps in some parameter regimes. In a certain range of the thickness of the gas slab, the cosmic-ray diffusion coefficient plays a decisive role in determining whether the filaments lie along or perpendicular to the magnetic field. We also consider the effect of rotation on the system.

Use of Polymerase Chain Reaction, Cell Adhesion, Hemagglutination and Bacterial Clump Formation Tests in Detection of Enteroaggregative Escherichia coli Strains

Enteroaggregative Escherichia coli (EAggEC) is one of the pathogenic E. coli strains which may cause diarrhoea. In vitro studies have shown that EAggEC strains could establish a "stacked-brick" like adherence pattern on the surface of tissue culture cells and such a pattern is termed as aggregative adherence (AA). The purpose of this study is to compare the methods of polymerase chain reaction (PCR), HeLa cell adhesion, hemagglutination, and bacteria clumping tests for the specific detection of EAggEC suspected strains. This study isolated 340 E. coli strains from clinical samples of diarrhea cases which were firstly screened with the PCR method for the presence of suspected EaggEC strains. Strains of negative PCR results were also confirmed with HeLa cell adhesion and bacteria clumping tests for the EAggEC activity. Results showed that of these 340 clinical isolates, only three are EAggEC strains. Thus, EAggEC strains accounted for 0.88% in total strains. Also, for the above described methods, the in vitro HeLa cells adhesion test gave the clearest results followed by the bacteria clumping test. The hemagglutination tests might generate ambiguous results.

DLX5 and HOXC8 enhance the chondrogenic differentiation potential of stem cells from apical papilla via LINC01013

BackgroundMesenchymal stem cell (MSC)-based cartilage tissue regeneration is a treatment with great potential. How to enhance the MSC chondrogenic differentiation is a key issue involved in cartilage formation. In the present study, we seek to expound the phenotypes and mechanisms of DLX5 in chondrogenic differentiation function in MSCs.MethodsStem cells from apical papilla (SCAPs) were used. The Alcian Blue staining, pellet culture system, and cell transplantation in rabbit knee cartilage defect were used to evaluate the chondrogenic differentiation function of MSCs. Western blot, real-time RT-PCR, and ChIP assays were used to evaluate the molecular mechanisms.ResultsDLX5 and HOXC8 expressions were upregulated during chondrogenic differentiation. In vitro results showed that DLX5 and HOXC8 enhanced the expression of chondrogenic markers including collagen II (COL2), collagen V (COL5), and sex-determining region Y box protein 9 (SOX9) and promoted the chondrogenic differentiation and the formation of cartilage clumps in the pellet culture system. Mechanically, DLX5 and HOXC8 formed protein complexes and negatively regulated the LncRNA, LINC01013, via directly binding its promoter. In vivo transplantation experiment showed that DLX5 and HOXC8 could restore the cartilage defect in the rabbit knee model. In addition, knock-down of LINC01013 enhanced the chondrogenic differentiation of SCAPs.ConclusionsIn conclusion, DLX5 and HOXC8 enhance the chondrogenic differentiation abilities of SCAPs by negatively regulating LINC01013 in SCAPs, and provided the potential target for promoting cartilage tissue regeneration.

Origin of star-forming rings around massive centres in massive galaxies at z < 4

ABSTRACT Using analytic modelling and simulations, we address the origin of an abundance of star-forming clumpy extended gas rings about massive central bodies in massive galaxies at z < 4. Rings form by high-angular-momentum streams and survive in galaxies of Mstar > 109.5–10 M⊙ where merger-driven spin flips and supernova feedback are ineffective. The rings survive after events of compaction to central nuggets. Ring longevity was unexpected based on inward mass transport driven by torques from violent disc instability. However, evaluating the torques from a tightly wound spiral structure, we find that the time-scale for transport per orbital time is long and $\propto \! \delta _{\rm d}^{-3}$, with δd the cold-to-total mass ratio interior to the ring. A long-lived ring forms when the ring transport is slower than its replenishment by accretion and the interior depletion by star formation rate, both valid for δd < 0.3. The central mass that lowers δd is a compaction-driven bulge and/or dark matter, aided by the lower gas fraction at z < 4, provided that it is not too low. The ring is Toomre unstable for clump and star formation. The high-z dynamic rings are not likely to arise form secular resonances or collisions. Active galactic nucleus feedback is not expected to affect the rings. Mock images of simulated rings through dust indicate qualitative consistency with observed rings about bulges in massive z ∼ 0.5–3 galaxies, in H α and deep HST imaging. ALMA mock images indicate that z ∼ 0.5–1 rings should be detectable. We quote expected observable properties of rings and their central nuggets.

Effects of convection-, vacuum-and freeze-drying on antioxidant, physicochemical properties, functional properties and storage stability of stink bean (Parkia speciosa) powder.

This study aims to investigate the antioxidant, physicochemical and functional properties of convection-, vacuum-and freeze-dried stink bean (Parkia speciosa) powder upon storage at various relative humidity (RH) at room temperature, 25°C. Both convection- and vacuum-dried samples exhibited stronger DPPH free radical scavenging activity (7.62 ± 1.77 and 10.38 ± 0.63mg AA/g·db respectively) and ferric ion-chelating (FIC) ability (16.55 ± 1.29 and 18.88 ± 2.36mg/mL·db respectively) compared to the fresh and freeze-dried samples. Stink bean powder had low water solubility index, water holding capacity and oil holding capacity but it had the potential as emulsifier in food systems. Apparent formation of clumps were observed after 25-day storage of powder at RH of 43%, 54% or 75% due to absorption of moisture from surroundings. Generally, the antioxidant properties and colour of the powders deteriorated after storage especially at higher RH. Vacuum drying would be the most suitable drying method to produce stink bean powder because of its enhanced antioxidant capacities, light colour and relatively more stable after storage.

Antimicrobial Role of RNASET2 Protein During Innate Immune Response in the Medicinal Leech Hirudo verbana.

The innate immune response represents a first-line defense against pathogen infection that has been widely conserved throughout evolution. Using the invertebrate Hirudo verbana (Annelida, Hirudinea) as an experimental model, we show here that the RNASET2 ribonuclease is directly involved in the immune response against Gram-positive bacteria. Injection of lipoteichoic acid (LTA), a key component of Gram-positive bacteria cell wall, into the leech body wall induced a massive migration of granulocytes and macrophages expressing TLR2 (the key receptor involved in the response to Gram-positive bacteria) toward the challenged/inoculated area. We hypothesized that the endogenous leech RNASET2 protein (HvRNASET2) might be involved in the antimicrobial response, as already described for other vertebrate ribonucleases, such as RNase3 and RNase7. In support of our hypothesis, HvRNASET2 was mainly localized in the granules of granulocytes, and its release in the extracellular matrix triggered the recruitment of macrophages toward the area stimulated with LTA. The activity of HvRNASET2 was also evaluated on Staphylococcus aureus living cells by means of light, transmission, and scanning electron microscopy analysis. HvRNASET2 injection triggered the formation of S. aureus clumps following a direct interaction with the bacterial cell wall, as demonstrated by immunogold assay. Taken together, our data support the notion that, during the early phase of leech immune response, granulocyte-released HvRNASET2 triggers bacterial clumps formation and, at the same time, actively recruits phagocytic macrophages in order to elicit a rapid and effective eradication of the infecting microorganisms from inoculated area.

Modeling the formation of dense clumps during molecular clouds collision

The paper presents the results of numerical modeling of the collision process of two molecular clouds (MC). The process of formation and growth of dense clumps and filament is investigated. The density distribution along the MC radius is modeling according to various laws, and the density at the center of molecular clouds also changes. The processes of deformation, fragmentation, and the formation of superdense clumps zones are analyzed. Calculations are carried out according to different scenarios of collision of two spherical clouds that are heterogeneous in size, displacement, and internal distribution. The Euler numerical code created by the authors is used to conduct a numerical experiment on high-performance computers. The appearance of zones with a high degree of compression of the substance during the formation of new clouds and the oscillations arising from this strongly depend on the initial momentum of the colliding molecular clouds. The paper presents an analysis of the redistribution of gas density that occurs during local compression in bow-shock core and outer layers of clouds. The mechanism of substance turbulization, fragmentation, and the creation of dense regions was analyzed and interpreted. Compressions arising in the gas core and wave-like rarefaction in the interstellar medium are interpreted as Kelvin-Helmholtz instability aftereffects.

Three-dimensional simulations of clump formation in stellar wind collisions

ABSTRACT The inner parsec of our Galaxy contains tens of Wolf–Rayet stars whose powerful outflows are constantly interacting while filling the region with hot, diffuse plasma. Theoretical models have shown that, in some cases, the collision of stellar winds can generate cold, dense material in the form of clumps. However, their formation process and properties are not well understood yet. In this work, we present, for the first time, a statistical study of the clump formation process in unstable wind collisions. We study systems with dense outflows (${\sim }10^{-5}\rm \ M_{\odot }\ yr^{-1}$), wind speeds of 500–$1500\rm \ km\ s^{-1}$, and stellar separations of ∼20–$200\rm \ au$. We develop three-dimensional high-resolution hydrodynamical simulations of stellar wind collisions with the adaptive-mesh refinement grid-based code ramses. We aim at characterizing the initial properties of clumps that form through hydrodynamic instabilities, mostly via the non-linear thin-shell instability (NTSI). Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes. Increasing either the wind speed or the degree of asymmetry increases the dispersion of the clump mass and ejection speed distributions. Nevertheless, the most massive clumps are very light (∼10−3–$10^{-2}\rm \ M_{\oplus }$), about three orders of magnitude less massive than theoretical upper limits. Applying these results to the Galactic Centre, we find that clumps formed through the NTSI should not be heavy enough either to affect the thermodynamic state of the region or to survive for long enough to fall on to the central supermassive black hole.

In vitro study of pharmacobezoar formation in simulated acetaminophen overdose

Objectives: There have been few studies of pharmacobezoar formation, but they can be an important contributor to overdose toxicity. Pharmacobezoars may explain the delayed peak or “double hump” pharmacokinetics, which were noted in previous case reports with delayed toxicity of acetaminophen (APAP). We validated the presence of APAP bezoar formation in a controlled modified in vitro environment simulating acute APAP overdose.Methods: This study involved the APAP and control groups (ferrous sulfate and chlorpheniramine). The APAP study group contained three subgroups of APAP with different dosage, i.e., 25 g (50 tabs)/37.5 g (75 tabs)/50 g (100 tabs). The positive control group containing ferrous sulfate, i.e., 15 g (50 tabs), has been reported previously to form pharmacobezoars in overdose. The negative control group containing chlorpheniramine, i.e., 200 mg (50 tabs), has not been reported to form pharmacobezoars in previous case studies. Tablets from each study group were placed into a separate pig stomach. Each stomach contained 28 ml USP standard simulated gastric acid. The stomach was placed in a plastic box filled with water maintaining at 37 °C. Each test group was examined for 4 h in the stomach. The primary outcome was the presence of clump formation. Positive clump formation was defined as tablets sticking together and the ability to maintain shape upon dissecting the pig stomach and lifting with fingers. Tablet clumps would then undergo dissolution testing with subsequent analysis of dissolution profiles.Results: Formation of tablets clumps was confirmed in APAP overdose in the in vitro environment. Clumps were noted to be present in the 37.5 g and 50 g APAP groups, while 25 g APAP was unlikely to form clumps. The dissolution profile of clump demonstrated slower release without reaching plateau at 60 min, as compared to corresponding individual tabs of APAP. f1 and f2 analyses showed the dissolution profile of clump was different compared to that of referenced individual tab.Conclusions: APAP clump formation was confirmed in acute overdose of 37.5 g or more. Dissolution tests revealed delayed and steady release of tablet residue from the clumps, which could explain prolonged or delayed toxicity in large APAP overdose.

Electrical charging overcomes the bouncing barrier in planet formation

In protoplanetary disks, solid objects (so-called planetesimals) are formed from dust. Micrometre-sized dust grains grow into millimetre-sized aggregates. Once those aggregates have diameters exceeding a few centimetres, they become subject to concentration mechanisms such as the streaming instability, permitting the formation of self-gravitating clusters, which might eventually collapse into kilometre-sized planetesimals. However, for the streaming instability to set in, clumps spanning sizes from centimetres to decimetres are required in the centre of a protoplanetary disk. In the size range between millimetres and centimetres, aggregates bounce off each other rather than sticking together, and growth is stalled. Here we show in microgravity experiments that collisions between millimetre-sized grains lead to sufficient electrical charging for aggregation to bridge this gap between the bouncing barrier and the onset of the streaming instability. We computationally simulate aggregation and find that models agree with the experimental data only if electrical charging is present. We therefore propose that collisional charging may promote early growth in the size gap that current models of planetesimal formation cannot account for. In our understanding of planetary formation, it is still unclear how millimetre-sized dust grains grow into centimetre-sized aggregates. Microgravity experiments now show that electrical charging of the grains leads to the formation of larger clumps.

Nonlinear evolution of energetic-particles-driven waves in dissipative plasma

The formation of holes and clumps has been investigated by using a one-dimensional electrostatic particle-in-cell code with the effect of background dissipation and dynamical friction. The results show that the background dissipation is the primary reason for frequency sweeping, and dynamical friction can enhance the frequency sweeping in the damped case. A finite velocity distribution of energetic particles (EPs) can modulate the range of frequency sweeping. The evolution of continuous formation of holes and clumps is observed in phase space. The central islands are torn in two parts, which shift away from the resonance center, and afterward, new central islands reappear. Finally, multiple modes resonating with energetic particles with damping are investigated. The results indicate that there is a nonlinear wave-wave coupling effect even when the overlapping of phase space islands never occurs, and this nonlinear effect can lead to an energy flow between waves and modulate the energy exchange between waves and EPs. The background dissipation decreases the efficiency of energy exchange between EPs and waves further.

Merger induced clump formation in distant infrared luminous starburst galaxies

While the formation of stellar clumps in distant galaxies is usually attributed to gravitational violent disk instabilities, we show here that major mergers also represent a competitive mechanism to form bright clumps. Using ∼0.1″ resolution ACS F814W images in the entire COSMOS field, we measured the fraction of clumpy emission in 109 main sequence (MS) and 79 Herschel-detected starbursts (off-MS) galaxies at 0.5 < z < 0.9, representative of normal versus merger induced star-forming activity, respectively. We additionally identify merger samples from visual inspection and from Gini-M20 morphological parameters. Regardless of the merger criteria adopted, the clumpiness distribution of merging systems is different from that of normal isolated disks at a > 99.5% confidence level. The former reaches higher clumpiness values up to 20% of the total galaxy emission. We confirm the merger induced clumpiness enhancement with novel hydrodynamical simulations of colliding galaxies with gas fractions typical of z ∼ 0.7. Multi-wavelength images of three starbursts in the CANDELS field support the young nature of clumps, which are likely merger products rather than older preexisting structures. Finally, for a subset of 19 starbursts with existing near-infrared rest frame spectroscopy, we find that the clumpiness is mildly anti-correlated with the merger phase, which decreases toward final coalescence. Our result can explain recent ALMA detections of clumps in hyperluminous high-z starbursts, while normal objects are smooth. This work raises a question as to the role of mergers on the origin of clumps in high redshift galaxies in general.

GEMMA CUP-ASSOCIATED MYB1, an Ortholog of Axillary Meristem Regulators, Is Essential in Vegetative Reproduction in Marchantiapolymorpha.

A variety of plants in diverse taxa can reproduce asexually via vegetative propagation, in which clonal propagules with a new meristem(s) are generated directly from vegetative organs. A basal land plant, Marchantia polymorpha, develops clonal propagules, gemmae, on the gametophyte thallus from the basal epidermis of a specialized receptacle, the gemma cup. Here we report an R2R3-MYB transcription factor, designated GEMMA CUP-ASSOCIATED MYB1 (GCAM1), which is an essential regulator of gemma cup development in M.polymorpha. Targeted disruption of GCAM1 conferred a complete loss of gemma cup formation and gemma generation. Ectopic overexpression of GCAM1 resulted in formation of cell clumps, suggesting a function of GCAM1 in suppression of cell differentiation. Although gemma cups are a characteristic gametophyte organ for vegetative reproduction in a taxonomically restricted group of liverwort species, phylogenetic and interspecific complementation analyses support the orthologous relationship of GCAM1 to regulatory factors of axillary meristem formation, e.g., Arabidopsis REGULATOR OF AXILLARY MERISTEMS and tomato Blind, in angiosperm sporophytes. The present findings in M.polymorpha suggest an ancient acquisition of a transcriptional regulator for production of asexual propagules in the gametophyte and the use of the regulatory factor for diverse developmental programs, including axillary meristem formation, during land plant evolution.

In-pond strain selection of euryhaline Tetraselmis sp. strains for reliable long-term outdoor culture as potential sources of biofuel and other products

Studies on microalgae species and strain selection have demonstrated the potential of a broad range of algal species suitable for large-scale mass production, but provided little data on the reliability and productivity of the cultures under outdoor conditions over a long period. Long-term studies as part of the development of large-scale microalgae mass production are essential at small scale to minimise expenditure in scaling-up and large-scale operations. The current study describes the long-term semi-continuous culture of 4 wild-type isolates of euryhaline Tetraselmis sp. grown in 1 m2 raceway ponds outdoors in 7% (w/w NaCl) saline water enriched with N and P without any additional carbon source under the environmental conditions in Perth, Western Australia. The long-term investigation indicated that Tetraselmis MUR-231 was not able to grow outdoors, while Tetraselmis strains MUR-167, MUR-230 and MUR-233 grew outdoors over long periods. Tetraselmis MUR-167 was cultured for over 16 months outdoors before terminated due to cell clump formation and heavy biofilm development on the pond walls, whereas Tetraselmis strains MUR-230 and MUR-233 were cultured in semi-continuous culture over 20 months. The latter two strains grew at high solar irradiance with daily maximum values of 58890 W m−2 and temperatures ranging from about 40 to 0 °C. Both strains had a similar average specific growth rate of 0.19 day−1 over the experimental period. Maximum biomass productivities were 9.11 g m−2 day−1 and 9.99 g m−2 day−1 for Tetraselmis MUR-230 and MUR-233, respectively. The maximum total lipid productivity of 4.30 g m−2 day−1 of Tetraselmis MUR-230 was slightly higher than Tetraselmis MUR-233 (4.05 g m−2 day−1). These results clearly indicate the potential of these two Tetraselmis strains for commercial application, such as a high lipid yielding feedstock under minimal culture management conditions in arid and semi-arid coastal regions such as northern Western Australia.

Northern Galactic Molecular Cloud Clumps in Hi-GAL: Clump and Star Formation within Clouds

Abstract We investigate how the properties of Galactic giant molecular clouds (GMCs) and their denser substructures (clumps) correlate with the local star formation rate (SFR). We trace clouds using the 12CO(3−2) transition, as observed by the CO High Resolution Survey. We identify their constituent clumps using thermal dust emission, as observed by the Herschel infrared GALactic plane survey. We estimate SFRs in these clouds using 70 μm emission. In total, we match 3674 clumps to 473 clouds in position–position–velocity space spanning the Galactic longitude range 10° < ℓ < 56°. We find that more massive clouds produce more clumps and more massive clumps. These clumps have average number densities an order of magnitude greater than their host clouds. We find a mean clump mass fraction of . This mass fraction weakly varies with mass and mass surface density of clouds, and shows no clear dependence on the virial parameter and line width of the clouds. The average clump mass fraction is only weakly dependent upon Galactocentric radius. Although the scatter in our measured properties is significant, the SFR for clouds is independent of clump mass fraction. However, there is a positive correlation between the depletion times for clouds and clump mass fraction. We find a star formation efficiency per freefall time of ϵ ff = 0.15% for GMCs but ϵ ff = 0.37% for clumps.

Clumpy galaxies in cosmological simulations: the effect of ISM model

ABSTRACT We study influence by models of interstellar medium (ISM) on properties of galaxies in cosmological simulations. We examine three models widely used in previous studies. The ISM models impose different equations of state on dense gas. Using zoom-in simulations, we demonstrate that switching the ISM models can control formation of giant clumps in massive discs at redshifts z ∼ 1–2, while their initial conditions and the other settings such as stellar feedback are unchanged. Thus, not only feedback but ISM models can also be responsible for clumpy morphologies of simulated galaxies. We find, however, that changing the ISM models hardly affects global properties of galaxies, such as the total stellar and gas masses, star formation rate, metallicity, and stellar angular momentum, irrespective of the significant difference of clumpiness; namely the ISM models only change clumpiness of discs. In addition, our approach provides a test to investigate impact by clump formation on the evolution of disc galaxies using the same initial conditions and feedback. We find that clump formation does not significantly alter the properties of galaxies and therefore could not be the causes of starburst or quenching.

Synthesis and characterization of Ag/TiO2/composite aerogel for enhanced adsorption and photo-catalytic degradation of toluene from the gas phase

Despite titanium dioxide has some remarkable properties as a photo-catalyst, its usage in the photo-catalysis processes is associated with several drawbacks, like high band gap energy and clumping of its particles. In this study, a composite aerogel was exploited as a support for titanium dioxide to prevent clump formation and increase the production of electron-hole pairs. The results revealed that both utilized nanoparticles, i.e. TiO2 and Ag, were uniformly dispersed on the surface of composite aerogel. The absorption region of the synthesized catalysts shifted to the visible region and, in fact, the additions of Ag to the composite aerogel reduce the band gap energy of TiO2 from 3.17 to 2.7 eV. Studies on the degradation of toluene in gas streams through a fluidized bed reactor showed that the photo-catalytic activity of TiO2 supported on the composite aerogel was much higher than that of the unsupported titanium dioxide, so that the degradation rates of toluene were 95.7% and 15%, respectively for supported and unsupported TiO2. The results indicated that the highest oxidation rate of toluene was obtained at 45% humidity. The Intermediate products formed during the degradation of toluene by the composite photo-catalyst were identified which were included formic acid, acetic acid, and benzaldehyde. Overall, the composite aerogel could be used as a useful support for the TiO2 catalyst, and the prepared photo-catalyst has a high potential to be used in the oxidation of toluene in gas-phase streams in industrial scale.