Metal Ejection Research Articles

ANISOTROPIC ACTIVE GALACTIC NUCLEUS OUTFLOWS AND ENRICHMENT OF THE INTERGALACTIC MEDIUM. II. METALLICITY

We investigate the large-scale influence of outflows from AGNs in enriching the IGM with metals in a cosmological context. We combine cosmological simulations of large scale structure formation with a detailed model of metal enrichment, in which outflows expand anisotropically along the direction of least resistance, distributing metals into the IGM. The metals carried by the outflows are generated by two separate stellar populations: stars located near the central AGN, and stars located in the greater galaxy. Using this algorithm, we performed a series of 5 simulations of the propagation of AGN-driven outflows in a cosmological volume of size (128/h Mpc)^3 in a Lambda-CDM universe, and analyze the resulting metal enrichment of the IGM. We found that the metallicity induced in the IGM is greatly dominated by AGNs having bolometric luminosity L > 10^9 L_sun, sources with 10^8 < L / L_sun < 10^9 having a negligible contribution. Our simulations produced an average IGM metallicity of [O/H] = -5 at z = 5.5, which then rises gradually, and remains relatively flat at a value [O/H] = -2.8 between z = 2 and z = 0. The ejection of metals from AGN host galaxies by AGN-driven outflows is found to enrich the IGM to > 10 - 20% of the observed values, the number dependent on redshift. The enriched IGM volume fractions are small at z > 3, then rise rapidly to the following values at z = 0: 6 - 10% of the volume enriched to [O/H] > -2.5, 14 - 24% volume to [O/H] > -3, and 34 - 45% volume to [O/H] > -4. At z > 2, there is a gradient of the induced enrichment, the metallicity decreasing with increasing IGM density, enriching the underdense IGM to higher metallicities, a trend more prominent with increasing anisotropy of the outflows. This can explain observations of metal-enriched low-density IGM at z = 3 - 4.

Observation of Hole Formation Process in Plasma Arc Drilling

Drilling is widely applied in materials processing. Novel drilling methods, including electrical discharge machining, laser drilling, and plasma arc drilling, have emerged in recent years to overcome such problems as tool wear and low efficiency in the drilling of thick plates or difficult-to-machine materials. Plasma arc drilling is an effective and high-speed drilling method for thick plates. However, the mechanisms of plasma arc drilling, such as the hole formation and dross formation processes, have not yet been fully elucidated. In this study, a number of experiments under different drilling conditions were conducted to investigate the hole formation process in mild steel plate of 12 mm in thickness, using a high-speed video camera. Hole formation in plasma arc drilling is a highly complex process since both melting and vaporization are involved. The mechanisms of molten metal ejection as a material removal process were verified. The formation and removal of dross at the entrance and exit sides were elucidated by our observations of molten metal ejection. Further experiments were carried out to investigate the effect of the anode motion peculiar to plasma arc drilling. The results clarified the hole formation process and some specific related phenomena. The insights gained into the hole formation process will be useful in improving hole quality and reducing dross around the hole.

Effects of the integrated galactic IMF on the chemical evolution of the solar neighbourhood

The initial mass function determines the fraction of stars of different intial mass born per stellar generation. In this paper, we test the effects of the integrated galactic initial mass function (IGIMF) on the chemical evolution of the solar neighbourhood. The IGIMF (Weidner & Kroupa 2005) is computed from the combination of the stellar intial mass function (IMF), i.e. the mass function of single star clusters, and the embedded cluster mass function, i.e. a power law with index beta. By taking into account also the fact that the maximum achievable stellar mass is a function of the total mass of the cluster, the IGIMF becomes a time-varying IMF which depends on the star formation rate. We applied this formalism to a chemical evolution model for the solar neighbourhood and compared the results obtained by assuming three possible values for beta with the results obtained by means of a standard, well-tested, constant IMF. In general, a lower absolute value of beta implies a flatter IGIMF, hence a larger number of massive stars and larger metal ejection rates. This translates into higher type Ia and II supernova rates, higher mass ejection rates from massive stars and a larger amount of gas available for star formation, coupled with lower present-day stellar mass densities. (abridged) We also discuss the importance of the present day stellar mass function (PDMF) in providing a way to disentangle among various assumptions for beta. Our results indicate that the model adopting the IGIMF computed with beta ~2 should be considered the best since it allows us to reproduce the observed PDMF and to account for most of the chemical evolution constraints considered in this work.

Enhanced control over metal composition in mixed Ga/Zn and Ga/Cu coordinated pyrogallol[4]arene nanocapsules

The stepwise synthesis of mixed metal-organic C-alkylpyrogallol[4]arene nanocapsules allows control over the metal ratios in the resulting assemblies via sequential incorporation and ejection of different metals.

Specificity of Acyl Transfer from 2-Mercaptobenzamide Thioesters to the HIV-1 Nucleocapsid Protein

The HIV-1 nucleocapsid protein (NCp7) is a small, highly conserved protein with two zinc-binding domains that are essential for the protein's function. Molecules that bind to and inactivate NCp7 are currently being evaluated as new antiviral drugs. In particular, derivatives based on a 2-mercaptobenzamide thioester template have been shown to specifically eject zinc from the C-terminal zinc-binding domain (ZD2) of NCp7 via acyl transfer from the thioester to a cysteine sulfur. In this study, mutational analysis of the NCp7 amino acid sequence has been used to investigate the specificity of the interaction between ZD2 and a 2-mercaptobenzamide thioester compound using UV-vis spectroscopy and mass spectrometry to monitor the rate of metal ejection from NCp7 mutant peptides and sites of acylation, respectively. We were able to extend the previously reported mechanism of action of these thioester compounds to include a secondary S to N intramolecular acyl transfer that occurs after the primary acyl transfer from the thioester to a cysteine side chain in the protein. Structural models of the thioester/ZD2 complex were then examined to identify the most likely binding orientation. We determined that position x+1 (where x is Cys36) needs to be an aromatic residue for reactivity and a hydrogen-bond donor in position x+9 is important for optimal reactivity. A basic residue (lysine or arginine) is required at position x+2 for the correct fold, while a lysine residue is needed for reactivity involving S to N acyl transfer. We report highly specific interactions between 2-mercaptobenzamide thioester compounds and NCp7 that offer a structural basis for refining and designing new antiretroviral therapeutics, directed toward a target that is resistant to viral mutation.

The missing metals problem - III. How many metals are expelled from galaxies?

We revisit the metal budget at z ≃ 2, and include the contribution of the intergalactic medium (IGM). Past estimates of the metal budget have indicated that, at redshift z ≃ 2.5, 90 per cent of the expected metals were missing. In the first two papers of this series, we have already shown that ∼30 per cent of the metals are observed in all z ∼ 2.5 galaxies detected in current surveys. This fraction could increase to ≤60 per cent if we extrapolate the faint end of the luminosity function (LF), leaving >40 per cent of the metals missing. Here, we extend our analysis to the metals outside galaxies (i.e. in the IGM), using (i) observational data and (ii) analytical calculations. Our results for both are strikingly similar. (i) Observationally, we find that, besides the small (5 per cent) contribution of damped Lya absorbers (DLAs), the forest and sub-DLAs contribute substantially to make ≤30-45 per cent of the metal budget; however, neither of these appear to be sufficient to close the metal budget. The forest accounts for 15-30 per cent depending on the ultraviolet background, and sub-DLAs for ≥2 to ≤17 per cent depending on the ionization fraction. Combining the metals in galaxies and in the IGM, it appears now that >65 per cent of the metals have been accounted for, and the 'missing metals problem' is substantially eased. (ii) We perform analytical calculations based on the effective yield-mass (y eff -V c ) relation, whose deficit for small galaxies is considered as evidence for supernova-driven outflows. As a test of the method, we show that, at z = 0, the calculation self-consistently predicts the total amount of metals expelled from galaxies. At z = 2, we find that the method predicts that 25-50 per cent of the metals have been ejected from galaxies into the IGM, consistent with the observations (≥35 per cent). The metal ejection is predominantly by L B < (1/3) L * B (z = 2) galaxies, which are responsible for 90 per cent of the metal enrichment, while the 50 percentile is at L ∼ (1/10) L * B (z = 2). As a consequence, if indeed 50 per cent of the metals have been ejected from galaxies, three to five bursts of star formation are required per galaxy prior to z = 2. The ratio between the mass of metals outside galaxies to those in stars has changed from z = 2 to z = 0; it was 1: 2 or 1: 1 and is now 1: 8 or 1: 9. This evolution implies that a significant fraction of the IGM metals will cool and fall back into galaxies.

Effect of turbulent diffusion on iron abundance profiles

We compare the observed peaked iron abundance profiles for a small sample of groups and clusters with the predictions of a simple model involving the metal ejection from the brightest galaxy and the subsequent diffusion of metals by stochastic gas motions. Extending the analysis of Rebusco et al., we found that for five out of eight objects in the sample an effective diffusion coefficient of the order of 1029 cm2 s−1 is needed. For AWM4, Centaurus and AWM7 the results are different suggesting substantial intermittence in the process of metal spreading across the cluster. There is no obvious dependence of the diffusion coefficient on the mass of the system. We also estimated the characteristic velocities and the spatial scales of the gas motions needed to balance the cooling losses by the dissipation of the same gas motions. A comparison of the derived spatial scales and the sizes of observed radio bubbles inflated in the ICM by a central active galactic nucleus (AGN) suggests that the AGN/ICM interaction makes an important (if not a dominant) contribution to the gas motions in the cluster cores.

Cr(VI) containing electric furnace dusts and filter cake from a stainless steel waste treatment plant: Part 2 – Formation mechanisms and leachability

The present study describes the formation mechanisms and leachability of Cr(VI) from electric furnace dust and filter cake from the ferrochromium and stainless steel industries. The results show that stainless steel dust is formed by the entrainment of charge materials, volatilisation of elements and ejection of slag and metal by spitting or bursting of gas bubbles. Ferrochrome dust is formed by the ejection of slag and metal from the electrode holes, the entrainment of charge fines, vaporisation as well as the precipitation of reaction products in the off gas duct. Toxicity characteristics leaching procedure (TCLP) and American Society for Testing and Materials (ASTM) D3987–85 tests show that these wastes are all hazardous materials according to South African legislation, owing to the high degree of Cr (VI) leachability. Cr(VI) in the wastes is easily leached by distilled water, and cannot be stockpiled without prior treatment.

Enrichment of the ICM of galaxy clusters due to ram-pressure stripping

We investigate the impact of galactic mass loss triggered by ram-pressure stripping of cluster galaxies on the evolution of the intra-cluster medium (ICM). We use combined N-body and hydrodynamic simulations together with a phenomenological galaxy formation model and a prescription of the effect of ram-pressure stripping on the galaxies. We analyze the effect of galaxy -- ICM interaction for different model clusters with different masses and different merger histories. Our simulations show that ram-pressure stripping can account for ~ 10% of the overall observed level of enrichment in the ICM within a radius of 1.3 Mpc. The efficiency of metal ejection of cluster galaxies depends at the first few Gyr of the simulation mainly on the cluster mass and is significantly increased during major merger events. Additionally we show that ram-pressure stripping is most efficient in the center of the galaxy cluster and the level of enrichment drops quite fast at larger radii. We present emission weighted metallicity maps of the ICM which can be compared with X-ray observations. The resulting distribution of metals in the ICM shows a complex pattern with stripes and plumes of metal rich material. The metallicity maps can be used to trace the present and past interactions between the ICM and cluster galaxies.

Color functions of stellar systems

Model calculations of the photometric evolution of rather dense stellar systems, such as globular clusters, are presented. On “luminosity-effective temperature” diagrams of these systems, low-mass stars are concentrated near the minimum and maximum temperatures for a given luminosity and are deficient in the intermediate region. This sort of double-peaked distribution of the stars can be avoided in open models with ejection of excess metals into the surrounding medium. The distributions of the stars with respect to effective temperature on a “ luminosity-effective temperature” diagram are sensitive to the history of star formation in the system and to possible time variations in the initial mass function. In open systems with a single-peak distribution function, the asymmetry in the distribution varies over wide limits with the lower bound for the initial mass function and this can be used to establish whether the first generations of stars might have been more massive than in the present epoch.

Studies on the Mechanism of Inactivation of the HIV-1 Nucleocapsid Protein NCp7 with 2-Mercaptobenzamide Thioesters

The HIV-1 nucleocapsid protein (NCp7) is a small basic protein with two CysCysHisCys zinc-binding domains that specifically recognizes the Psi-site of the viral RNA. NCp7 plays a number of crucial roles in the viral lifecycle, including reverse transcription and RNA encapsidation. Several classes of potential anti-HIV compounds have been designed to inactivate NCp7 through zinc ejection, including a special class of thioester compounds. We have investigated the mechanism of action of two N-substituted-S-acyl-2-mercaptobenzamide compounds (compounds 1 and 2) that target NCp7. UV/Visible spectroscopy studies demonstrated that both thioesters were able to eject metal from NCp7. NMR and mass spectroscopy studies showed that the thioester compounds specifically ejected zinc from the carboxyl-terminal zinc-binding domain of NCp7 by covalent modification of Cys(39). Exposure of NCp7 to compounds 1 and 2 destroyed its ability to specifically bind RNA, whereas NCp7 already bound to RNA was protected from zinc ejection by the thioesters. The thiol component of the thioesters (compound 3, 2-mercaptobenzoyl-beta-alaninamide) did not eject zinc from NCp7, but when compound 3 was incubated with acetyl CoA prior to incubation with NCp7, we observed extensive metal ejection. Thus, the thiol released by the reaction of compounds 1 and 2 could be re-acylated in vivo by acyl CoA to form a new thioester compound that is able to react with NCp7. These studies provide a better understanding of the mechanism of action of thioester compounds, which is important for future design of anti-HIV-1 compounds that target NCp7.

Cosmological Feedback from High‐Redshift Dwarf Galaxies

We model how repeated supernova explosions in high-redshift dwarf starburst galaxies drive superbubbles and winds out of the galaxies. We compute the efficiencies of metal and mass ejection and energy transport from the galactic potentials, including the effect of cosmological infall of external gas. The starburst bubbles quickly blow out of small, high-redshift, galactic disks, but must compete with the ram pressure of the infalling gas to escape into intergalactic space. We show that the assumed efficiency of the star formation rate dominates the bubble evolution and the metal, mass, and energy feedback efficiencies. With star formation efficiency f*=0.01, the ram pressure of infall can confine the bubbles around high-redshift dwarf galaxies with circular velocities v_c>52 km/s. We can expect high metal and mass ejection efficiencies, and moderate energy transport efficiencies in halos with v_c~30-50 km/s and f*~0.01 as well as in halos with v_c~100 km/s and f*>>0.01. Such haloes collapse successively from 1-2 sigma peaks in LambdaCDM Gaussian density perturbations as time progresses. These dwarf galaxies can probably enrich low and high-density regions of intergalactic space with metals to 10^-3-10^-2 Zsun as they collapse at z~8 and z<5 respectively. They also may be able to provide adequate turbulent energy to prevent the collapse of other nearby halos, as well as to significantly broaden Lyman-alpha absorption lines to v_rms~20-40 km/s. We compute the timescales for the next starbursts if gas freely falls back after a starburst, and find that, for star formation efficiencies as low as f*<0.01, the next starburst should occur in less than half the Hubble time at the collapse redshift. This suggests that episodic star formation may be ubiquitous in dwarf galaxies.

Parametric Studies on Improved Laser Cutting Performance of Magnesium Alloy with Two Flow Nozzles

We describe a newly proposed method of cutting a magnesium alloy using a high-energy CO2 laser. Improved laser cutting was achieved when the movement of the molten metal in the kerf was controlled by supplying assist gas from two nozzles positioned above and below the cutting sample. In order to analyze the gas flow and the movement of the molten metal in detail, a flow visualization experiment that simulated the molten metal ejection was also performed using an acrylic work-piece and water as the operation fluid. The results of this simulation were then compared with those of a computational fluid dynamics calculation. Such comprehensive model analysis revealed that the well-balanced gas flows from the two nozzles could enable the desirable flow and fast velocity to be generated both in the kerf and underneath the workpiece, under the conditions where high-quality laser cutting is achieved.

Very High Iron Abundance of the Hot Gas around the cD Galaxy of the MKW 4 Cluster

We observed a nearby X-ray-bright poor cluster MKW 4 with Chandra. The iron abundance is found to increase dramatically from 0.3 to 1.3 solar within 150'' of the cD galaxy NGC 4073. Then MKW 4 is the second cluster to exhibit a significantly high metallicity of greater than 1 solar, after the Centaurus Cluster. Weakness of the central cool component helps us to obtain the metallicity free from the multitemperature effects. The scale of temperature decrease toward the center region is clearly different from that of abundance increment, indicating that these are not the same phenomena. Since the stellar-to-intracluster mass ratio around NGC 4073 is very high compared to other cD type clusters, it is no doubt that the abundance increment is due to metal ejection from the cD galaxy. The iron-to-stellar mass ratio around NGC 4073 is 6.2 × 10-3, and thus most of the ejected iron still remains in the vicinity of NGC 4073. By comparing the stellar distribution with that of iron, the steady state outflow speed of iron is roughly estimated to be 2.4 km s-1, which is faster than the Coulomb diffusion.

The Clustering of Intergalactic Metals

We measure the spatial clustering of metals in the intergalactic medium from z = 1.7 to 3.0, as traced by 643 CIV and 104 SiIV N >= 10^12 cm^-2 absorption systems in 19 high signal-to-noise (40-80) and high resolution (R = 45000) quasar spectra. The number densities and two-point correlation functions of both these species are largely constant with redshift, suggesting the bulk of metal ejection occurred at z >= 3. However, at z = M_s, and use numerical simulations to derive best-fit values of R_s ~ 2 comoving Mpc and M_s ~ 5x10^11 solar masses at z = 3. This does not exclude that metals could have been produced at higher redshifts in smaller, but equally rare, objects. At the level of detection of this survey, IGM enrichment is likely to be incomplete and inhomogeneous, with a filling factor ~ 10%.

Dynamics simulation of ejection of metal under a shock wave

In this paper, the dynamic process of ejection from a metal surface groove under ashock wave is investigated by molecular dynamics simulation combined with ahybrid tight-binding-like potential. By taking ‘snapshots’ and analysing thepressure, we classify reflection rarefaction waves and second-uploadingcompression waves propagating in the material, and find one negative-pressureregion and one high-pressure region induced by two wave series. The velocities ofboth the ejected atom and the free surface of the groove increase with theangle of the groove. When the half-angle of the groove is more than 60°,there is no ejected body, and this result is consistent with experiment.

Superbubble Metallicities and X-ray Luminosities

We show that X-ray emission and dynamical properties of superbubbles around OB associations are affected by metal ejection from the enclosed Type II supernovae (SNe). The SN and massive star yields may significantly change the superbubble interior metallicity and enhance its X-ray luminosity.

Metal Enrichment of the Intergalactic Medium in Cosmological Simulations

Observations have established that the diffuse intergalactic medium (IGM) at z ~ 3 is enriched to ~10-2.5 solar metallicity and that the hot gas in large clusters of galaxies (ICM) is enriched to - Z☉ at z = 0. Metals in the IGM may have been removed from galaxies (in which they presumably form) during dynamical encounters between galaxies, by ram-pressure stripping, by supernova-driven winds, or as radiation-pressure-driven dust efflux. This study develops a method of investigating the chemical enrichment of the IGM and of galaxies, using already completed cosmological simulations. To these simulations we add dust and (gaseous) metals, assuming instantaneous recycling and distributing the dust and metals in the gas according to three simple parameterized prescriptions, one for each enrichment mechanism. These prescriptions are formulated to capture the basic ejection physics, and calibrated when possible with empirical data. Our method allows exploration of a large number of models, yet for each model yields a specific (not statistical) realization of the cosmic metal distribution that can be compared in detail to observations. Our results indicate that dynamical removal of metals from 108.5 M☉ galaxies cannot account for the observed metallicity of low column density Lyα absorbers and that dynamical removal from 1010.5 M☉ galaxies cannot account for the ICM metallicities. Dynamical removal also fails to produce a strong enough mass-metallicity relation in galaxies. In contrast, either wind or radiation-pressure ejection of metals from relatively large galaxies can plausibly account for all three sets of observations (though it is unclear whether metals can be distributed uniformly enough in the low-density regions without overly disturbing the IGM and whether clusters can be enriched quite as much as observed). We investigate in detail how our results change with variations in our assumed parameters and how results for the different ejection processes compare.

Metal Enrichment of the Intergalactic Medium atz = 3 by Galactic Winds

Studies of quasar absorption lines reveal that the low-density intergalactic medium (IGM) at z ~ 3 is enriched to between 10-3 and 10-2 solar metallicity. This enrichment may have occurred in an early generation of Population III stars at redshift z 10, by protogalaxies at 6 z 10, or by larger galaxies at 3 z 6. This paper addresses the third possibility by calculating the enrichment of the IGM at z 3 by galaxies of baryonic mass 108.5 M☉. We use already completed cosmological simulations, to which we add a prescription for chemical evolution and metal ejection by winds, assuming that the winds have properties similar to those observed in local starbursts and Lyman break galaxies. Results are given for a number of representative models, and we also examine the properties of the galaxies responsible for the enrichment as well as the physical effects responsible for wind escape and propagation. We find that winds of velocity 200-300 km s-1 are capable of enriching the IGM to the mean level observed, although many low-density regions would remain metal free. Calibrated by observations of Lyman break galaxies, our calculations suggest that most galaxies at z 3 should drive winds that can escape and propagate to large radii. The primary effect limiting the enrichment of low-density intergalactic gas in our scenario is then the travel time from high- to low-density regions, implying that the metallicity of low-density gas is a strong function of redshift.

Investigation of striation formation in thin stainless steel tube during pulsed Nd:YAG laser cutting process by numerical simulation

The formation of a striation pattern in a thin stainless steel tube was investigated by numerical simulation during a pulsed Nd:YAG laser cutting process. The simulated results were compared with the experimental results, which were performed under the same conditions for simulation. The simulated results showed good agreement with the experimental results. Although the formation of the striation pattern was influenced by various laser parameters, the laser power density had become the most important factor in the formation of striation patterns, since the laser power density is the most influential in the heating of metal, and the striation formation is caused by the ejection of molten metal and evaporation during laser cutting process. Although a high power density resulted in clear regular striation patterns, relatively low power density caused the formation of a hot spot, which hindered the formation of regular striation patterns and caused less striation. The numerical simulation calculations can be used to predict the shape of striation patterns and to offer a way to provide a smooth cut wall.