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1
Mahmood, Salman, Zainal Arif Burhanudin, and Nor Hisham Hamid. "Field Emission Model of CNT Based Ionization Gas Sensor." Advanced Materials Research 667 (March 2013): 135–43. http://dx.doi.org/10.4028/www.scientific.net/amr.667.135.
Повний текст джерелаАнотація:
A new model to study the gas detection mechanism of carbon nanotube (CNT) based ionization gas sensor has been developed. The model incorporates the effect of electron field emission due to the presence of CNT. The model is then embedded in the standard Particle-In-Cell / Monte-Carlo-Collision (PIC-MCC) codes. This enhanced PIC-MCC codes serve as a tool to optimize CNT based ionization gas sensor. The functionality of the new model is validated by running simulations of DC discharges in argon and comparing the results with published experimental and simulated works. From the simulation, one order of magnitude decrease in the breakdown voltages and three orders of magnitude faster response time was observed.
2
Lee, Ha Rim, Da Woon Kim, Alfi Rodiansyah, Boklae Cho, Joonwon Lim, and Kyu Chang Park. "Investigation of the Effect of Structural Properties of a Vertically Standing CNT Cold Cathode on Electron Beam Brightness and Resolution of Secondary Electron Images." Nanomaterials 11, no. 8 (July 26, 2021): 1918. http://dx.doi.org/10.3390/nano11081918.
Повний текст джерелаАнотація:
Carbon nanotube (CNT)-based cold cathodes are promising sources of field emission electrons for advanced electron devices, particularly for ultra-high-resolution imaging systems, due to their high brightness and low energy spread. While the electron field emission properties of single-tip CNT cathodes have been intensively studied in the last few decades, a systematic study of the influencing factors on the electron beam properties of CNT cold cathodes and the resolution of the secondary electron images has been overlooked in this field. Here, we have systematically investigated the effect of the structural properties of a CNT cold cathode on the electron beam properties and resolution of secondary electron microscope (SEM) images. The aspect ratio (geometric factor) and the diameter of the tip of a vertically standing CNT cold cathode significantly affect the electron beam properties, including the beam size and brightness, and consequently determine the resolution of the secondary electron images obtained by SEM systems equipped with a CNT cold cathode module. Theoretical simulation elucidated the dependence of the structural features of CNT cold cathodes and electron beam properties on the contribution of edge-emitted electrons to the total field emission current. Investigating the correlations between the structural properties of CNT cold cathodes, the properties of the emitted electron beams, and the resolution of the secondary electron images captured by SEM equipped with CNT cold cathode modules is highly important and informative as a basic model.
3
Ludwick, Jonathan, Nathaniel Hernandez, Geet Tripathi, Marc Cahay, Tyson Back, and Kevin L. Jensen. "Influence of thermal contact resistance on the field emission characteristics of a carbon nanotube." Journal of Vacuum Science & Technology B 40, no. 4 (July 2022): 042804. http://dx.doi.org/10.1116/6.0002001.
Повний текст джерелаАнотація:
A recent algorithm developed by Tripathi et al. [J. Appl. Phys. 128, 025017 (2020); Erratum, J. Appl. Phys. 131, 169901 (2022)] is modified to study the effects of thermal contact resistance on the field emission (FE) properties of a carbon nanotube (CNT). The model takes into account the temperature dependence of the CNT electrical and thermal conductivities. The boundary condition proposed by Huang et al. [Phys. Rev. Lett. 93, 7 (2004)] is used to include the effects of thermal contact resistance at a CNT/chuck interface located at [Formula: see text], i.e., [Formula: see text], where r is the CNT radius, [Formula: see text] is the heat conduction coefficient at [Formula: see text], and [Formula: see text] is the thermal resistivity of the CNT/chuck interface. The chuck is assumed to be a perfect heat sink at temperature [Formula: see text]. For a given set of CNT parameters and values of the applied external electric field, it is shown that current constriction at the CNT/chuck contact point leads to self-heating effects which increase with the value of the thermal contact resistance, leading to an increase in the temperature profile along the CNT (including the temperature at its tip) and the FE current above their values obtained assuming the CNT/chuck interface is at the heat sink temperature [Formula: see text]. The fractional change of the emission current versus applied external electric field is calculated for increasing values of the parameter [Formula: see text].
4
Saleh, Tawfik A., Mohammad N. Siddiqui, and Abdulrahman A. Al-Arfaj. "Synthesis of Multiwalled Carbon Nanotubes-Titania Nanomaterial for Desulfurization of Model Fuel." Journal of Nanomaterials 2014 (2014): 1–6. http://dx.doi.org/10.1155/2014/940639.
Повний текст джерелаАнотація:
This work reported on the development of novel nanomaterials of multiwalled carbon nanotubes doped with titania (CNT/TiO2) for the adsorptive desulfurization of model fuel oils. Various analytical techniques such as field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of the nanomaterials. The initial results indicated the effectiveness of the prepared CNT/TiO2nanomaterials in removing sulfur compounds from model fuel oil. The adsorption of DBT, BT, and thiophene from model fuel onto the derived sorbents was performed using batch mode system. These CNT/TiO2nanomaterials initially afforded approximately 45% removal of DBT, 55% BT, and more than 65% thiophene compounds from model fuels. The CNT/TiO2nanomaterials provided an excellent activity towards interaction with organosulfur compounds. More experiments are underway to optimize the parameters for the adsorptive desulfurization processes. We believe that these nanomaterials as adsorbents will find useful applications in petroleum industry because of their operational simplicity, high efficiency, and high capacity.
5
Zu, Yifan, Xuesong Yuan, Xiaotao Xu, Matthew T. Cole, Yu Zhang, Hailong Li, Yong Yin, Bin Wang, and Yang Yan. "Design and Simulation of a Multi-Sheet Beam Terahertz Radiation Source Based on Carbon-Nanotube Cold Cathode." Nanomaterials 9, no. 12 (December 12, 2019): 1768. http://dx.doi.org/10.3390/nano9121768.
Повний текст джерелаАнотація:
Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order TM 5 , 1 mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%.
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Zhang, Yang, Xinchuan Liu, Liye Zhao, Yuanxun Li, and Zhenjun Li. "Simulation and Optimization of CNTs Cold Cathode Emission Grid Structure." Nanomaterials 13, no. 1 (December 22, 2022): 50. http://dx.doi.org/10.3390/nano13010050.
Повний текст джерелаАнотація:
Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs’ electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.
7
Qistina, Omar, Ali Salmiaton, Thomas S. Y. Choong, Yun Hin Taufiq-Yap, and Shamsul Izhar. "Optimization of Carbon Nanotube-Coated Monolith by Direct Liquid Injection Chemical Vapor Deposition Based on Taguchi Method." Catalysts 10, no. 1 (January 2, 2020): 67. http://dx.doi.org/10.3390/catal10010067.
Повний текст джерелаАнотація:
Carbon nanotubes (CNTs) have the potential to act as a catalyst support in many sciences and engineering fields due to their outstanding properties. The CNT-coated monolith was synthesized over a highly active Ni catalyst using direct liquid injection chemical vapor deposition (CVD). The aim was to study the optimum condition for synthesizing CNT-coated monoliths. The Taguchi method with L9 (34) orthogonal array design was employed to optimize the experimental conditions of CNT-coated monoliths. The design response was the percentage of carbon yield expressed by the signal-to-noise (S/N) value. The parameters including the mass ratio of Ni to citric acid (Ni:CA) (A), the injection rate of carbon source (B), time of reaction (C), and operating temperature (D) were selected at three levels. The results showed that the optimum conditions for CNT-coated monolith were established at A1B2C1D2 and the most influential parameter was D followed by B, C, and A. The ANOVA analysis showed the design was significant with R-squared and standard deviation of the factorial model equal to 0.9982 and 0.22, respectively. A confirmation test was conducted to confirm the optimum condition with the actual values of the average percentage of carbon yield deviated 1.4% from the predicted ones. The CNT-coated monoliths were characterized by various techniques such as field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy.
8
Bulyarskiy, Sergey V., Alexander A. Dudin, Alexander V. Lakalin, Andrey P. Orlov, Alexander A. Pavlov, Roman M. Ryazanov, and Artemiy A. Shamanaev. "Effect of heating and resistance on emission properties of carbon nanotubes." Characterization and Application of Nanomaterials 3, no. 2 (November 21, 2020): 49. http://dx.doi.org/10.24294/can.v3i2.567.
Повний текст джерелаАнотація:
We have studied the effect of the series resistance on the heating of the cathode, which is based on carbon nanotubes and serves to realize the field emission of electrons into the vacuum. The experiment was performed with the single multi-walled carbon nanotube (MCNT) that was separated from the array grown by CVD method with thin-film Ni-Ti catalyst (nickel 4 nm/Ti 10 nm). The heating of the cathode leads to the appearance of a current of the thermionic emission. The experimental voltage current characteristic exhibited the negative resistance region caused by thermal field emission. This current increases strongly with increasing voltage and contributes to the degradation of the cold emitter. The calculation of the temperature of the end of the cathode is made taking into account the effect of the phenomenon that warms up and cools the cathode. We have developed a method for processing of the emission volt-ampere characteristics of a cathode, which relies on a numerical calculation of the field emission current and the comparison of these calculations with experiments. The model of the volt-ampere characteristic takes into account the CNT’s geometry, properties, its contact with the catalyst, heating and simultaneous implementation of the thermionic and field emission. The calculation made it possible to determine a number of important parameters, including the voltage and current of the beginning of thermionic emission, the temperature distribution along the cathode and the resistance of the nanotube. The phenomenon of thermionic emission from CNTs was investigated experimentally and theoretically. The conditions of this type emission occurrence were defined. The results of the study could form the basis of theory of CNT emitter’s degradation.
9
Behling, Rolf. "Electric Field Enhancing Artifacts as Precursors for Vacuum High-Voltage Breakdown." Instruments 3, no. 4 (December 17, 2019): 64. http://dx.doi.org/10.3390/instruments3040064.
Повний текст джерелаАнотація:
Abrupt formation of plasma in a high-voltage insulating vacuum gap and subsequent discharge of electrodes limits the reliability of a class of vacuum electronic devices, such as X-ray tubes. It has been suggested that electron field emission from negatively charged electrodes would precede and initiate such discharge. Heating and evaporation of material upon field emission would cause dense plasma to develop in periods of nanoseconds. High-pressure plasma would expand from the cathode, eventually bridging the gap. Nevertheless, the very reason for the unredictable initial development of discharge events after long periods of reliable operation is still matter of debate. Experience from industrial processes suggests hydrocarbon contamination to degrade the electric stability of high-voltage gaps. While former attempts aimed at explaining high field emission by carbonaceous 2D structures or surface resonance effects, this paper discusses whether 3D structures may grow slowly, until their evaporation in a matter of nanoseconds. Similar to the production of carbon nanotubes, protruding structures might comprise carbon and, in addition, metallic nanoparticles, which would boost production of vapor during their explosion. The hypothesis was tested by scanning electron and energy-dispersive X-ray inspection of two cathodes of medical X-ray tubes, covered with metallic seed nanoparticles, which served as model systems. A third cleaner cathode was inspected for comparison. Although certain suggested conditions of carbon feed, elevated substrate temperature and nanoparticle contamination of the surfaces were met, images showed only a very weak sign of growth of suspicious carbon structures. It seems, therefore, unlikely that CNT-like structures are a major cause of high-voltage breakdown between electrodes of X-ray tubes.
10
Hussain, Md Zakir, Sabah Khan, Rajamani Nagarajan, Urfi Khan, and Vishnu Vats. "Fabrication and Microhardness Analysis of MWCNT/MnO2 Nanocomposite." Journal of Materials 2016 (October 10, 2016): 1–10. http://dx.doi.org/10.1155/2016/6070468.
Повний текст джерелаАнотація:
Recent research has shown that carbon nanotube (CNT) acts as a model reinforcement material for fabricating nanocomposites. The addition of CNT as a reinforcing material into the matrix improves the mechanical, thermal, tribological, and electrical properties. In this research paper multiwalled carbon nanotube (MWCNT), with different weight percentage (5%, 10%, and 15%), was reinforced into manganese dioxide (MnO2) matrix using solution method. The different weight % of MWCNT/MnO2 nanocomposite powders was compacted and then sintered. The phase analysis, morphology, and chemical composition of the nanocomposites were examined by X-ray diffractometer, Field Emission Scanning Electron Microscope (FESEM), and Energy Dispersive X-Ray (EDX), respectively. The XRD analysis indicates the formation of MWCNT/MnO2 nanocomposites. The FESEM surface morphology analysis shows that MnO2 nanotube is densely grown on the surface of MWCNT. Further, microhardness of MWCNT/MnO2 nanocomposite was measured and it was found that 10 wt% has higher microhardness in comparison to 5 and 15 wt%. The microhardness of the composites is influenced by mass density, nanotube weight fraction, arrangement of tubes, and dispersion of MWCNT in H2SO4(aq) solution.
11
Arumugasamy, Prakash, and Dipanjan Mitra. "Evaluating the evidence of multipolar surface magnetic field in PSR J0108–1431." Monthly Notices of the Royal Astronomical Society 489, no. 4 (August 19, 2019): 4589–605. http://dx.doi.org/10.1093/mnras/stz2299.
Повний текст джерелаАнотація:
ABSTRACT PSR J0108–1431 is an old pulsar where the X-ray emission is expected to have a thermal component from the polar cap and a non-thermal component from the magnetosphere. Although the phase-integrated spectra are fit best with a single non-thermal component modelled with a power law (PL) of photon index Γ = 2.9, the X-ray pulse profiles do show the presence of phase-separated thermal and non-thermal components. The spectrum extracted from half the rotational phase away from the X-ray peak fits well with either a single blackbody (BB) or a neutron star atmosphere (NA) model, whereas the spectrum from the rest of the phase range is dominated by a PL. From Bayesian analysis, the estimated BB area is smaller than the expected polar cap area for a dipolar magnetic field with a probability of 86 per cent, whereas the area estimate from the NA model is larger with a probability of 80 per cent. Due to the ambiguity in the thermal emission model, the polar cap area cannot be reliably estimated and hence cannot be used to understand the nature of the surface magnetic field. Instead, we can infer the presence of multipolar magnetic field from the misalignment between the pulsar’s thermal X-ray peak and the radio emission peak. For J0108–1431, we estimated a phase-offset Δϕ > 0.1 between the thermal polar cap emission peak and the radio emission peak and argue that this is best explained by the presence of a multipolar surface magnetic field.
12
Kavanagh, R. D., A. A. Vidotto, D. Ó. Fionnagáin, V. Bourrier, R. Fares, M. Jardine, Ch Helling, C. Moutou, J. Llama, and P. J. Wheatley. "MOVES – II. Tuning in to the radio environment of HD189733b." Monthly Notices of the Royal Astronomical Society 485, no. 4 (March 7, 2019): 4529–38. http://dx.doi.org/10.1093/mnras/stz655.
Повний текст джерелаАнотація:
ABSTRACT We present stellar wind modelling of the hot Jupiter host HD189733, and predict radio emission from the stellar wind and the planet, the latter arising from the interaction of the stellar wind with the planetary magnetosphere. Our stellar wind models incorporate surface stellar magnetic field maps at the epochs 2013 June/July, 2014 September, and 2015 July as boundary conditions. We find that the mass-loss rate, angular momentum loss rate, and open magnetic flux of HD189733 vary by 9 per cent, 40 per cent, and 19 per cent over these three epochs. Solving the equations of radiative transfer, we find that from 10 MHz–100 GHz the stellar wind emits fluxes in the range of 10−3–5 μJy, and becomes optically thin above 10 GHz. Our planetary radio emission model uses the radiometric Bode’s law, and neglects the presence of a planetary atmosphere. For assumed planetary magnetic fields of 1–10 G, we estimate that the planet emits at frequencies of 2–25 MHz, with peak flux densities of 102 mJy. We find that the planet orbits through regions of the stellar wind that are optically thick to the emitted frequency from the planet. As a result, unattenuated planetary radio emission can only propagate out of the system and reach the observer for 67 per cent of the orbit for a 10 G planetary field, corresponding to when the planet is approaching and leaving primary transit. We also find that the plasma frequency of the stellar wind is too high to allow propagation of the planetary radio emission below 21 MHz. This means a planetary field of at least 8 G is required to produce detectable radio emission.
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Bastian, T. S., W. D. Cotton, and G. Hallinan. "Radio Emission from UV Cet: Auroral Emission from a Stellar Magnetosphere." Astrophysical Journal 935, no. 2 (August 1, 2022): 99. http://dx.doi.org/10.3847/1538-4357/ac7d57.
Повний текст джерелаАнотація:
Abstract The archetypical flare star UV Cet was observed by MeerKAT on 2021 October 5–6. A large radio outburst with a duration of ∼2 hr was observed between 886 and 1682 MHz, with a time resolution of 8 s and a frequency resolution of 0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is characterized by three peaks containing a multitude of broadband arcs or partial arcs in the time-frequency domain. In general, the arcs are highly right-hand circularly polarized. At the end of the third peak, brief bursts occur that are significantly elliptically polarized. We present a simple model that appears to be broadly consistent with the characteristics of the radio emission from UV Cet. Briefly, the stellar magnetic field is modeled as a dipole aligned with the rotational axis of the star. The radio emission mechanism is assumed to be due to the cyclotron maser instability, where x-mode radiation near the electron gyrofrequency is amplified. While the elliptically polarized bursts may be intrinsic to the source, rather stringent limits are imposed on the plasma density in the source and along the propagation path. We suggest that the elliptically polarized radiation may instead be the result of reflection on an overdense plasma structure at some distance from the source. The radio emission from UV Cet shares both stellar and planetary attributes.
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Rodríguez-Ramírez, J. C., P. Kushwaha, E. M. de Gouveia Dal Pino, and R. Santos-Lima. "A hadronic emission model for black hole-disc impacts in the blazar OJ 287." Monthly Notices of the Royal Astronomical Society 498, no. 4 (September 4, 2020): 5424–36. http://dx.doi.org/10.1093/mnras/staa2664.
Повний текст джерелаАнотація:
ABSTRACT A supermassive black hole (SMBH) binary in the core of the blazar OJ 287 has been invoked in previous works to explain its observed optical flare quasi-periodicity. Following this picture, we investigate a hadronic origin for the X-ray and γ-ray counterparts of the November 2015 major optical flare of this source. An impact outflow must result after the lighter SMBH (the secondary) crosses the accretion disc of the heavier one (the primary). We then consider acceleration of cosmic ray (CR) protons in the shock driven by the impact outflow as it expands and collides with the active galactic nucleus (AGN) wind of the primary SMBH. We show that the emission of these CRs can reproduce the X-ray and γ-ray flare data self-consistently with the optical component of the 2015 November major flare. The derived emission models are consistent with a magnetic field B ∼ 5 G in the emission region and a power-law index of q ∼ 2.2 for the energy distribution of the emitting CRs. The mechanical luminosity of the AGN wind represents $\lesssim 50{{\ \rm per\ cent}}$ of the mass accretion power of the primary SMBH in all the derived emission profiles.
15
Pétri, J., and D. Mitra. "Joint radio and X-ray modelling of PSR J1136+1551." Monthly Notices of the Royal Astronomical Society 491, no. 1 (October 24, 2019): 80–91. http://dx.doi.org/10.1093/mnras/stz2974.
Повний текст джерелаАнотація:
ABSTRACT Multiwavelength observations of pulsar emission properties are powerful means to constrain their magnetospheric activity and magnetic topology. Usually a star centred magnetic dipole model is invoked to explain the main characteristics of this radiation. However, in some particular pulsars where observational constraints exist, such simplified models are unable to predict salient features of their multiwavelength emission. This paper aims to carefully model the radio and X-ray emission of PSR J1136+1551 with an off-centred magnetic dipole to reconcile both wavelength measurements. We simultaneously fit the radio pulse profile with its polarization and the thermal X-ray emission from the polar cap hotspots of PSR J1136+1551. We are able to pin down the parameters of the non-dipolar geometry (which we have assumed to be an offset dipole) and the viewing angle, meanwhile accounting for the time lag between X-ray and radio emission. Our model fits the data if the off-centred magnetic dipole lies about 20 per cent below the neutron star surface. We also expect very asymmetric polar cap shapes and sizes, implying non-antipodal and non-identical thermal emission from the hotspots. We conclude that a non-dipolar surface magnetic field is an essential feature to explain the multiwavelength aspects of PSR J1136+1551 and other similar pulsars.
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Pittard, J. M., G. E. Romero, and G. S. Vila. "Particle acceleration and non-thermal emission in colliding-wind binary systems." Monthly Notices of the Royal Astronomical Society 504, no. 3 (April 22, 2021): 4204–25. http://dx.doi.org/10.1093/mnras/stab1107.
Повний текст джерелаАнотація:
ABSTRACT We present a model for the creation of non-thermal particles via diffusive shock acceleration in a colliding-wind binary. Our model accounts for the oblique nature of the global shocks bounding the wind–wind collision region and the finite velocity of the scattering centres to the gas. It also includes magnetic field amplification by the cosmic ray induced streaming instability and the dynamical back reaction of the amplified field. We assume that the injection of the ions and electrons is independent of the shock obliquity and that the scattering centres move relative to the fluid at the Alfvén velocity (resulting in steeper non-thermal particle distributions). We find that the Mach number, Alfvénic Mach number, and transverse field strength vary strongly along and between the shocks, resulting in significant and non-linear variations in the particle acceleration efficiency and shock nature (turbulent versus non-turbulent). We find much reduced compression ratios at the oblique shocks in most of our models compared to our earlier work, though total gas compression ratios that exceed 20 can still be obtained in certain situations. We also investigate the dependence of the non-thermal emission on the stellar separation and determine when emission from secondary electrons becomes important. We finish by applying our model to WR 146, one of the brightest colliding wind binaries in the radio band. We are able to match the observed radio emission and find that roughly 30 per cent of the wind power at the shocks is channelled into non-thermal particles.
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Krause, Martin G. H., and Martin J. Hardcastle. "Can the Local Bubble explain the radio background?" Monthly Notices of the Royal Astronomical Society 502, no. 2 (January 16, 2021): 2807–14. http://dx.doi.org/10.1093/mnras/stab131.
Повний текст джерелаАнотація:
ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.
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Wang, L. J., M. Y. Ge, J. S. Wang, S. S. Weng, H. Tong, L. L. Yan, S. N. Zhang, Z. G. Dai, and L. M. Song. "The braking index of PSR B0540−69 and the associated pulsar wind nebula emission after spin-down rate transition." Monthly Notices of the Royal Astronomical Society 494, no. 2 (April 7, 2020): 1865–70. http://dx.doi.org/10.1093/mnras/staa884.
Повний текст джерелаАнотація:
ABSTRACT In 2011 December, PSR B054−69 experienced a spin-down rate transition (SRT), after which the spin-down power of the pulsar increased by $\sim 36{{\ \rm per\ cent}}$. About 1000 d after the SRT, the X-ray luminosity of the associated pulsar wind nebula (PWN) was found to brighten by $32\pm 8{{\ \rm per\ cent}}$. After the SRT, the braking index n of PSR B0540−69 changes from n = 2.12 to 0.03 and then keeps this value for about five years before rising to n = 0.9 in the following years. We find that most of the current models have difficulties in explaining the measured braking index. One exceptive model of the braking index evolution is the increasing dipole magnetic field of PSR B0540−69. We suggest that the field increase may result from some instabilities within the pulsar core that enhance the poloidal component at the price of toroidal component of the magnetic field. The increasing dipole magnetic field will result in the X-ray brightening of the PWN. We fit the PWN X-ray light curve by two models: one assumes a constant magnetic field within the PWN during the brightening and the other assumes an enhanced magnetic field proportional to the energy density of the PWN. It appears that the two models fit the data well, though the later model seems to fit the data a bit better. This provides marginal observational evidence that magnetic field in the PWN is generated by the termination shock. Future high-quality and high-cadence data are required to draw a solid conclusion.
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Pais, Matteo, and Christoph Pfrommer. "Simulating TeV gamma-ray morphologies of shell-type supernova remnants." Monthly Notices of the Royal Astronomical Society 498, no. 4 (September 18, 2020): 5557–73. http://dx.doi.org/10.1093/mnras/staa2827.
Повний текст джерелаАнотація:
ABSTRACT Supernova remnant (SNR) shocks provide favourable sites of cosmic ray (CR) proton acceleration if the local magnetic field direction is quasi-parallel to the shock normal. Using the moving-mesh magnetohydrodynamical (MHD) code arepo we present a suite of SNR simulations with CR acceleration in the Sedov–Taylor phase that combine different magnetic field topologies, density distributions with gradients and large-scale fluctuations, and – for our core-collapse SNRs – a multiphase interstellar medium with dense clumps with a contrast of 104. Assuming the hadronic gamma-ray emission model for the TeV gamma-ray emission, we find that large-amplitude density fluctuations of δρ/ρ0 ≳ 75 per cent are required to strongly modulate the gamma-ray emissivity in a straw man’s model in which the acceleration efficiency is independent of magnetic obliquity. However, this causes strong corrugations of the shock surface that are ruled out by gamma-ray observations. By contrast, magnetic obliquity-dependent acceleration can easily explain the observed variance in gamma-ray morphologies ranging from SN1006 (with a homogeneous magnetic field) to Vela Junior and RX J1713 (with a turbulent field) in a single model that derives from plasma particle-in-cell simulations. Our best-fitting model for SN1006 has a large-scale density gradient of ∇n ≃ 0.0034 cm−3 pc−1 pointing from south-west to north-east and a magnetic inclination with the plane of the sky of ≲10°. Our best-fitting model for Vela Junior and RX J1713 adopts a combination of turbulent magnetic field and dense clumps to explain their TeV gamma-ray morphologies and moderate shock corrugations.
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Lam, Ka Ho, Che-Yu Chen, Zhi-Yun Li, Haifeng Yang, Erin G. Cox, Leslie W. Looney, and Ian Stephens. "The transition of polarized dust thermal emission from the protostellar envelope to the disc scale." Monthly Notices of the Royal Astronomical Society 507, no. 1 (July 23, 2021): 608–20. http://dx.doi.org/10.1093/mnras/stab2105.
Повний текст джерелаАнотація:
ABSTRACT Polarized dust continuum emission has been observed with Atacama Large Millimeter/submillimeter Array in an increasing number of deeply embedded protostellar systems. It generally shows a sharp transition going from the protostellar envelope to the disc scale, with the polarization fraction typically dropping from ${\sim } 5{{\ \rm per\ cent}}$ to ${\sim } 1{{\ \rm per\ cent}}$ and the inferred magnetic field orientations becoming more aligned with the major axis of the system. We quantitatively investigate these observational trends using a sample of protostars in the Perseus molecular cloud and compare these features with a non-ideal magnetohydrodynamic disc formation simulation. We find that the gas density increases faster than the magnetic field strength in the transition from the envelope to the disc scale, which makes it more difficult to magnetically align the grains on the disc scale. Specifically, to produce the observed ${\sim } 1{{\ \rm per\ cent}}$ polarization at ${\sim } 100\, \mathrm{au}$ scale via grains aligned with the B-field, even relatively small grains of $1\, \mathrm{\mu m}$ in size need to have their magnetic susceptibilities significantly enhanced (by a factor of ∼20) over the standard value, potentially through superparamagnetic inclusions. This requirement is more stringent for larger grains, with the enhancement factor increasing linearly with the grain size, reaching ∼2 × 104 for millimetre-sized grains. Even if the required enhancement can be achieved, the resulting inferred magnetic field orientation in the simulation does not show a preference for the major axis, which is inconsistent with the observed pattern. We thus conclude that the observed trends are best described by the model where the polarization on the envelope scale is dominated by magnetically aligned grains and that on the disc scale by scattering.
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Barrow, Kirk S. S. "Blue galaxies: modelling nebular He ii emission in high redshift galaxies." Monthly Notices of the Royal Astronomical Society 491, no. 3 (November 26, 2019): 4509–22. http://dx.doi.org/10.1093/mnras/stz3290.
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ABSTRACT Using cosmological simulations to make useful, scientifically relevant emission line predictions is a relatively new and rapidly evolving field. However, nebular emission lines have been particularly challenging to model because they are extremely sensitive to the local photoionization balance, which can be driven by a spatially dispersed distribution of stars amidst an inhomogeneous absorbing medium of dust and gas. As such, several unmodelled mysteries in observed emission line patterns exist in the literature. For example, there is some question as to why He ii λ4686/H β ratios in observations of lower metallicity dwarf galaxies tend to be higher than model predictions. Since hydrodynamic cosmological simulations are best suited to this mass and metallicity regime, this question presents a good test case for the development of a robust emission line modelling pipeline. The pipeline described in this work can model a process that produces high He ii λ4686/H β ratios and eliminate some of the modelling discrepancy for ratios below 3 per cent without including AGNs, X-ray binaries, high mass binaries, or a top-heavy stellar initial mass function. These ratios are found to be more sensitive to the presence of 15 Myr or longer gaps in the star formation histories than to extraordinary ionization parameters or specific star formation rates. They also closely correspond to the WR phase of massive stars. In addition to the investigation into He ii λ4686/H β ratios, this work charts a general path forward for the next generation of nebular emission line modelling studies.
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Cook, R. H. W., N. Seymour, K. Spekkens, N. Hurley-Walker, P. J. Hancock, M. E. Bell, J. R. Callingham, et al. "Searching for dark matter signals from local dwarf spheroidal galaxies at low radio frequencies in the GLEAM survey." Monthly Notices of the Royal Astronomical Society 494, no. 1 (March 17, 2020): 135–45. http://dx.doi.org/10.1093/mnras/staa726.
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ABSTRACT The search for emission from weakly interacting massive particle (WIMP) dark matter annihilation and decay has become a multipronged area of research not only targeting a diverse selection of astrophysical objects, but also taking advantage of the entire electromagnetic spectrum. The decay of WIMP particles into standard model particles has been suggested as a possible channel for synchrotron emission to be detected at low radio frequencies. Here, we present the stacking analysis of a sample of 33 dwarf spheroidal (dSph) galaxies with low-frequency (72–231 MHz) radio images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. We produce radial surface brightness profiles of images centred upon each dSph galaxy with background radio sources masked. We remove 10 fields from the stacking due to contamination from either poorly subtracted, bright radio sources or strong background gradients across the field. The remaining 23 dSph galaxies are stacked in an attempt to obtain a statistical detection of any WIMP-induced synchrotron emission in these systems. We find that the stacked radial brightness profile does not exhibit a statistically significant detection above the 95 per cent confidence level of ∼1.5 mJy beam−1. This novel technique shows the potential of using low-frequency radio images to constrain fundamental properties of particle dark matter.
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Walters, N., J. Farihi, T. R. Marsh, S. Bagnulo, J. D. Landstreet, J. J. Hermes, N. Achilleos, A. Wallach, M. Hart, and C. J. Manser. "A test of the planet–star unipolar inductor for magnetic white dwarfs." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 5, 2021): 3743–58. http://dx.doi.org/10.1093/mnras/stab617.
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ABSTRACT Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in antiphase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no antiphase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the Hertzsprung–Russell diagram based on structure and composition.
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Mohd Nazmi, Nor Atiq Syakila, Wan Nazwanie Wan Abdullah, Farook Adam, Wan Nur Aini Wan Mokhtar, Noor Fatimah Yahaya, and Nurasmat Mohd Shukri. "Iron Oxide Catalyst for Oxidative Desulfurization of Model Diesel Fuel." Materials Science Forum 1010 (September 2020): 418–23. http://dx.doi.org/10.4028/www.scientific.net/msf.1010.418.
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— The catalytic oxidative desulfurization (Cat-ODS) process has been introduced as a new technology to achieve ultra-low sulphur levels in diesel fuels. In this study, the performance of the alumina supported iron oxide based catalysts doped with cobalt, synthesized via wet impregnation method on the Cat-ODS of the model diesel with the total sulphur 500ppm was investigated using tert-butyl hydroperoxide (TBHP) as an oxidizing agent and N,N-dimethylformamide as an extraction solvent. A series of dopant was being screened. Co/Fe-Al2O3 (10:90) and Co/Fe-Al2O3 (20:80) prepared at 400°C. Overall, the catalytic activity decreased as dopant ratio increased. Catalyst with 10 wt% of Co was successfully removed 96% of thiophene, 100% of DBT and 92% of 4,6-DMDBT in model diesel. Further investigation, potential catalyst that calcined at 400°C contributed higher sulphur removal compared to the catalyst calcined at 500°C. X-ray diffraction analysis (XRD) result showed that Co/Fe-Al2O3 (10:90) prepared at 400°C was amorphous, while micrograph of the field emission scanning electron microscopy (FESEM) illustrated an inhomogeneous distribution of various particle sizes. The energy dispersive X-ray analysis (EDX) result have confirmed the presence of Fe and Co in all of the prepared catalyst.
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Saberi, M., W. H. T. Vlemmings, E. De Beck, R. Montez, and S. Ramstedt. "Detection of CI line emission towards the oxygen-rich AGB star omi Ceti." Astronomy & Astrophysics 612 (April 2018): L11. http://dx.doi.org/10.1051/0004-6361/201833080.
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We present the detection of neutral atomic carbon CI(3P1–3P0) line emission towards omi Cet. This is the first time that CI is detected in the envelope around an oxygen-rich M-type asymptotic giant branch (AGB) star. We also confirm the previously tentative CI detection around V Hya, a carbon-rich AGB star. As one of the main photodissociation products of parent species in the circumstellar envelope (CSE) around evolved stars, CI can be used to trace sources of ultraviolet (UV) radiation in CSEs. The observed flux density towards omi Cet can be reproduced by a shell with a peak atomic fractional abundance of 2.4 × 10−5 predicted based on a simple chemical model where CO is dissociated by the interstellar radiation field. However, the CI emission is shifted by ~4 km s−1 from the stellar velocity. Based on this velocity shift, we suggest that the detected CI emission towards omi Cet potentially arises from a compact region near its hot binary companion. The velocity shift could, therefore, be the result of the orbital velocity of the binary companion around omi Cet. In this case, the CI column density is estimated to be 1.1 × 1019 cm−2. This would imply that strong UV radiation from the companion and/or accretion of matter between two stars is most likely the origin of the CI enhancement. However, this hypothesis can be confirmed by high-angular resolution observations.
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Berry, I. D., S. P. Owocki, M. E. Shultz, and A. ud-Doula. "Electron scattering emission in the light curves of stars with centrifugal magnetospheres." Monthly Notices of the Royal Astronomical Society 511, no. 4 (February 4, 2022): 4815–25. http://dx.doi.org/10.1093/mnras/stac322.
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ABSTRACT Strongly magnetic, rapidly rotating B-type stars with relatively weak winds form centrifugal magnetospheres (CMs), as the stellar wind becomes magnetically confined above the Kepler co-rotation radius. Approximating the magnetic field as a dipole tilted by an angle β with respect to the rotation axis, the CM plasma is concentrated in clouds at and above the Kepler radius along the intersection of the rotational and magnetic equatorial planes. Stellar rotation can bring such clouds in front of the stellar disc, leading to absorption of the order of 0.1 mag ($\sim 10 {{\ \rm per\ cent}}$ of continuum flux). However, some stars with prominent CMs, such as σ Ori E, show an emission bump in addition to absorption dips, which has been so far unexplained. We show that emission can occur from electron scattering towards the observer when CM clouds are projected off the stellar limb. Using the rigidly rotating magnetosphere model, modified with a centrifugal breakout density scaling, we present a model grid of photometric light curves spanning parameter space in observer inclination angle i, magnetic obliquity angle β, critical rotation fraction W, and optical depth at the Kepler radius τK. We show that τK of order unity can produce emission bumps of the magnitude ∼0.05 seen in σ Ori E. We discuss the implications for modelling the light curves of CM stars, as well as future work for applying the radiative transfer model developed here to 3D magnetohydrodynamic simulations of CMs.
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Rodríguez Montero, Francisco, Sergio Martin-Alvarez, Debora Sijacki, Adrianne Slyz, Julien Devriendt, and Yohan Dubois. "Momentum deposition of supernovae with cosmic rays." Monthly Notices of the Royal Astronomical Society 511, no. 1 (December 22, 2021): 1247–64. http://dx.doi.org/10.1093/mnras/stab3716.
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ABSTRACT The cataclysmic explosions of massive stars as supernovae are one of the key ingredients of galaxy formation. However, their evolution is not well understood in the presence of magnetic fields or cosmic rays (CRs). We study the expansion of individual supernova remnants (SNRs) using our suite of 3D hydrodynamical (HD), magnetohydrodynamical (MHD) and CRMHD simulations generated using ramses. We explore multiple ambient densities, magnetic fields, and fractions of supernova energy deposited as CRs (χCR), accounting for CR anisotropic diffusion and streaming. All our runs have comparable evolutions until the end of the Sedov-Taylor phase. However, our CRMHD simulations experience an additional CR pressure-driven snowplough phase once the CR energy dominates inside the SNR. We present a model for the final momentum deposited by supernovae that captures this new phase: $p_{\rm SNR} = 2.87\times 10^{5} (\chi _{\text{CR}} + 1)^{4.82}\left(\frac{n}{\text{cm}^{-3}}\right)^{-0.196} M_{\odot }$ km s−1. Assuming a 10 per cent fraction of SN energy in CRs leads to a 50 per cent boost of the final momentum, with our model predicting even higher impacts at lower ambient densities. The anisotropic diffusion of CRs assuming an initially uniform magnetic field leads to extended gas and CR outflows escaping from the supernova poles. We also study a tangled initial configuration of the magnetic field, resulting instead in a quasi-isotropic diffusion of CRs and earlier momentum deposition. Finally, synthetic synchrotron observations of our simulations using the polaris code show that the local magnetic field configuration in the interstellar medium modifies the overall radio emission morphology and polarization.
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Birenbaum, Gal, and Omer Bromberg. "Modelling the linear polarization of GRB afterglows across the electromagnetic spectrum." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 8, 2021): 4275–88. http://dx.doi.org/10.1093/mnras/stab1936.
Повний текст джерелаАнотація:
ABSTRACT Linear polarization measurements in the optical band show polarization degrees of a few per cent at late times. Recently, polarization at sub-per-cent level was also detected in radio by ALMA, opening the window for multiwavelength polarimetry and stressing the importance of properly modelling polarization in GRB afterglows across the EM spectrum. We introduce a numerical tool that can calculate the polarization from relativistically moving surfaces by discretizing them to small patches of uniform magnetic field, calculating the polarized emission from each cell assuming synchrotron radiation and summing it to obtain the total degree of polarization. We apply this tool to afterglow shocks with random magnetic fields confined to the shock plane, considering electron radiative cooling. We analyse the observed polarization curves in several wavelengths above the cooling frequency and below the minimal synchrotron frequency and point to the characteristic differences between them. We present a method to constrain the jet opening angle and the viewing angle within the context of our model. Applying it to GRB 021004, we obtain angles of ∼10○ and ∼8○ respectively and conclude that a non-negligible component of radial magnetic field is required to explain the ${\sim}1{{\ \rm per\ cent}}$ polarization level observed 3.5 days after the burst.
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Gullberg, B., Ian Smail, A. M. Swinbank, U. Dudzevičiūtė, S. M. Stach, A. P. Thomson, O. Almaini, et al. "An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: high-resolution dust continuum morphologies and the link between sub-millimetre galaxies and spheroid formation." Monthly Notices of the Royal Astronomical Society 490, no. 4 (October 14, 2019): 4956–74. http://dx.doi.org/10.1093/mnras/stz2835.
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ABSTRACT We present an analysis of the morphology and profiles of the dust continuum emission in 153 bright sub-millimetre galaxies (SMGs) detected with ALMA at signal-to-noise ratios of >8 in high-resolution 0.18 arcsec (∼1 kpc) 870 $\mu$m maps. We measure sizes, shapes, and light profiles for the rest-frame far-infrared emission from these luminous star-forming systems and derive a median effective radius (Re) of 0.10 ± 0.04 arcsec for our sample with a median flux of S870 = 5.6 ± 0.2 mJy. We find that the apparent axial ratio (b/a) distribution of the SMGs peaks at b/a ∼ 0.63 ± 0.02 and is best described by triaxial morphologies, while their emission profiles are best fitted by a Sérsic model with n ≃ 1.0 ± 0.1, similar to exponential discs. This combination of triaxiality and n ∼ 1 Sérsic index are characteristic of bars and we suggest that the bulk of the 870 $\mu$m dust continuum emission in the central ∼2 kpc of these galaxies arises from bar-like structures. As such we caution against using the orientation of shape of the bright dust continuum emission at $\eqsim$ resolution to assess either the orientation of any disc on the sky or tits inclination. By stacking our 870 $\mu$m maps we recover faint extended dust continuum emission on ∼4 kpc scales which contributes 13 ± 1 per cent of the total 870 $\mu$m emission. The scale of this extended emission is similar to that seen for the molecular gas and rest-frame optical light in these systems, suggesting that it represents an extended dust and gas disc at radii larger than the more active bar component. Including this component in our estimated size of the sources we derive a typical effective radius of ≃0.15 ± 0.05 arcsec or 1.2 ± 0.4 kpc. Our results suggest that kpc-scale bars are ubiquitous features of high star-formation rate systems at $z$ ≫ 1, while these systems also contain fainter and more extended gas and stellar envelopes. We suggest that these features, seen some 10–12 Gyr ago, represent the formation phase of the earliest galactic-scale components: stellar bulges.
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Simpson, J. M., Ian Smail, U. Dudzevičiūtė, Y. Matsuda, B.-C. Hsieh, W.-H. Wang, A. M. Swinbank, et al. "An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2–COSMOS field." Monthly Notices of the Royal Astronomical Society 495, no. 3 (January 2020): 3409–30. http://dx.doi.org/10.1093/mnras/staa1345.
Повний текст джерелаАнотація:
ABSTRACT We present an ALMA study of the ∼180 brightest sources in the SCUBA-2 850-μm map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS – a full survey of the ∼1000 sources in this field. In this pilot study, we have obtained 870-μm continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources ($S_{850\, \mu \rm m}\gt $ 6.2 mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of $S_{870\, \mu \rm m}$ = 0.7–19.2 mJy. We detect more than one SMG counterpart in 34 ± 2 per cent of sub-millimetre sources, increasing to 53 ± 8 per cent for SCUBA-2 sources brighter than $S_{850\, \mu \rm m}\gt $ 12 mJy. We estimate that approximately one-third of these SMG–SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, $S_{870\, \mu \rm m}\gtrsim$ 3 mJy), and illustrate this with the serendipitous detection of bright [C ii] 157.74-μm line emission in two SMGs, AS2COS 0001.1 and 0001.2 at z = 4.63, associated with the highest significance single-dish source. Using our source catalogue, we construct the interferometric 870-μm number counts at $S_{870\, \mu \rm m}\gt $ 6.2 mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with magphys to estimate their photometric redshifts. We find a median photometric redshift for the $S_{870\, \mu \rm m}\gt $ 6.2 mJy AS2COSMOS sample of z = 2.87 ± 0.08, and clear evidence for an increase in the median redshift with 870-μm flux density suggesting strong evolution in the bright end of the 870-μm luminosity function.
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Inoue, Shigeki, Naoki Yoshida, and Hidenobu Yajima. "The CO universe: modelling CO emission and H2 abundance in cosmological galaxy formation simulations." Monthly Notices of the Royal Astronomical Society 498, no. 4 (September 10, 2020): 5960–71. http://dx.doi.org/10.1093/mnras/staa2744.
Повний текст джерелаАнотація:
ABSTRACT We devise a physical model of formation and distribution of molecular gas clouds (MGCs) in galaxies. We use the model to predict the intensities of rotational transition lines of carbon monoxide (CO) and the molecular hydrogen (H2) abundance. Using the outputs of IllustrisTNG cosmological simulations, we populate MGCs of unresolved sizes in individual simulated galaxies, where the effect of the interstellar radiation field with dust attenuation is also taken into account. We then use the publicly available code despotic (Derive the Energetics and SPectra of Optically Thick Interstellar Clouds) to compute the CO line luminosities and H2 densities without assuming the CO-to-H2 conversion factor (αCO). Our method allows us to study the spatial and kinematic structures traced by CO(1–0) and higher transition lines. We compare the CO luminosities and H2 masses with recent observations of galaxies at low and high redshifts. Our model reproduces well the observed CO–luminosity function and the estimated H2 mass in the local UniverseAbout 10 per cent of molecules in the Universe reside in dwarf galaxies with stellar masses lower than 109 M⊙, but the galaxies are generally ‘CO-dark’ and have typically high αCO. Our model predicts generally lower CO line luminosities than observations at redshifts z ≳ 1–2. We argue that the difference can be explained by the highly turbulent structure suggested for the high-redshift star-forming galaxies.
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He, Hao, Chao Yuan, Er Jun Liang, and Shun Fang Li. "Field Emission of Gallium-Doped Carbon Nanotubes." Advanced Materials Research 535-537 (June 2012): 61–66. http://dx.doi.org/10.4028/www.scientific.net/amr.535-537.61.
Повний текст джерелаАнотація:
Field emission property of Ga-doped carbon nanotube (CNT) film has been studied and compared with those of un-doped, N-doped as well as B and N co-doped CNT films. It is found that the Ga-doped CNT film exhibits superior field emission property to the other films. The turn-on field for Ga-doped CNT film is well below 1.0 V/μm, lower than those for un-doped (2.22 V/μm), N-doped (1.1 V/μm), B and N co-doped (4.4 V/μm) CNT films. Its current density reaches 5000 μA/cm2at 2.6 V/μm which is well above those for un-doped (1400 μA/cm2), N-doped (3000 μA/cm2) as well as B and N co-doped (2) CNT films at applied electric field of 5.7 V/μm. First principles calculations were carried out to obtain the binding energy and electronic nature altering of a CNT by Ga doping. It is shown that Ga-doped CNT (8,0) alters from semiconductor to intrinsic metal and a binding energy of 2.7527 eV is obtained. The field emission property can not simply be explained by the defect concentration, but can be understood by significant altering in the local density of states near the Fermi level introduced by dopants.
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Raichoor, Anand, Arnaud de Mattia, Ashley J. Ross, Cheng Zhao, Shadab Alam, Santiago Avila, Julian Bautista, et al. "The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: large-scale structure catalogues and measurement of the isotropic BAO between redshift 0.6 and 1.1 for the Emission Line Galaxy Sample." Monthly Notices of the Royal Astronomical Society 500, no. 3 (October 28, 2020): 3254–74. http://dx.doi.org/10.1093/mnras/staa3336.
Повний текст джерелаАнотація:
ABSTRACT We present the Emission Line Galaxy (ELG) sample of the extended Baryon Oscillation Spectroscopic Survey from the Sloan Digital Sky Survey IV Data Release 16. We describe the observations and redshift measurement for the 269 243 observed ELG spectra, and then present the large-scale structure catalogues, used for the cosmological analysis, and made of 173 736 reliable spectroscopic redshifts between 0.6 and 1.1. We perform a spherically averaged baryon acoustic oscillations (BAO) measurement in configuration space, with density field reconstruction: the data two-point correlation function shows a feature consistent with that of the BAO, the BAO model being only weakly preferred over a model without BAO (Δχ2 < 1). Fitting a model constrained to have a BAO feature provides a 3.2 per cent measurement of the spherically averaged BAO distance DV(zeff)/rdrag = 18.23 ± 0.58 at the effective redshift zeff = 0.845.
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Wang, M. S., Jan Yong Wang, C. H. Jin, Qing Chen, and Lian Mao Peng. "Observations of Carbon Nanotube Field Emission Failure in the Transmission Electron Microscope." Materials Science Forum 475-479 (January 2005): 4071–76. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.4071.
Повний текст джерелаАнотація:
The failure of individual multiwall carbon nanotubes (CNTs) during electron field emission was investigated in situ inside the transmission electron microscope (TEM). Long time emission of a single CNT at the level of tens µA or higher may lead to unrecoverable damage to the CNT. High-resolution TEM observations of the emission failure process shown that the failure was usually companied by structure damage or break of the CNT, and the failure or degradation of the emission characteristics of the CNT was typically initiated at the CNT/substrate contact, defect site or at the open end via the field evaporation or oxidation of the tip of the CNT.
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Sisk-Reynés, Júlia, James H. Matthews, Christopher S. Reynolds, Helen R. Russell, Robyn N. Smith, and M. C. David Marsh. "New constraints on light axion-like particles using Chandra transmission grating spectroscopy of the powerful cluster-hosted quasar H1821+643." Monthly Notices of the Royal Astronomical Society 510, no. 1 (December 2, 2021): 1264–77. http://dx.doi.org/10.1093/mnras/stab3464.
Повний текст джерелаАнотація:
ABSTRACT Axion-like particles (ALPs) are predicted by several Beyond the Standard Model theories, in particular, string theory. In the presence of an external magnetic field perpendicular to the direction of propagation, ALPs can couple to photons. Therefore, if an X-ray source is viewed through a magnetized plasma, such as a luminous quasar in a galaxy cluster, we may expect spectral distortions that are well described by photon–ALP oscillations. We present a 571 ks combined high- and low-energy transmission grating Chandra observation of the powerful radio-quiet quasar H1821+643, hosted by a cool-core cluster at redshift 0.3. The spectrum is well described by a double power-law continuum and broad+narrow iron line emission typical of type-1 active galactic nuclei (AGNs), with remaining spectral features ${\lt}2.5{{\ \rm per\ cent}}$. Using a cell-based approach to describe the turbulent cluster magnetic field, we compare our spectrum with photon–ALP mixing curves for 500 field realizations, assuming that the thermal-to-magnetic pressure ratio β remains constant up to the virial radius. At $99.7{{\ \rm per\ cent}}$ credibility and taking β = 100, we exclude all couplings gaγ > 6.3 × 10−13 GeV−1 for most ALP masses <10−12 eV. Our results are moderately more sensitive to constraining ALPs than the best previous result from Chandra observations of the Perseus cluster, albeit with a less constrained field model. We reflect on the promising future of ALP studies with bright AGNs embedded in rich clusters, especially with the upcoming Athena mission.
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Fairchild, Steven B., Chelsea E. Amanatides, Thiago A. de Assis, Paul T. Murray, Dmitri Tsentalovich, Jeffrey L. Ellis, Salvador Portillo, et al. "Field emission cathodes made from knitted carbon nanotube fiber fabrics." Journal of Applied Physics 133, no. 9 (March 7, 2023): 094302. http://dx.doi.org/10.1063/5.0123120.
Повний текст джерелаАнотація:
Field electron emission cathodes were constructed from knitted fabrics comprised entirely of carbon nanotube (CNT) fibers. The fabrics consisted of a top layer array of ∼2 mm high looped structures and a bottom layer that was 1 mm thick with a flat underlying surface. Field emission (FE) experiments were performed on 25.4 mm diameter CNT fabric cathodes in both direct current (DC) and pulsed voltage (PV) modes, and the results were compared to those obtained from a CNT film cathode. The DC measurements were performed at a maximum voltage of 1.5 kV. The CNT fabric cathode emitted 20 mA, which was an 8× increase over the emission current from the CNT film cathode. The DC results were analyzed using the corrected form of the Fowler–Nordheim FE theory initially developed by Murphy and Good, which allows for the determination of the formal emission area and effective gap-field enhancement factor. The PV experiments resulted in Ampere level emission currents from both CNT fabric and CNT film cathodes. For a 25 kV, 500 ns voltage pulse, the CNT fabric cathode emitted 4 A, which was 2× more current than the CNT film cathode. Scanning electron microscopy imaging after PV testing revealed that the fibers remained intact after >5000 pulses. These results indicate that knitted CNT fabrics offer a promising approach for developing large area, conformable, robust FE cathodes for vacuum electronic devices.
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Guhan, V., V. Geethalakshmi, R. Jagannathan, S. Panneerselvam, and K. Bhuvaneswari. "ASSESSING THE IMPACT OF CLIMATE CHANGE IN PONNANIYAR BASIN OF TAMIL NADU BASED ON REGCM 4.4 SIMULATIONS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3/W6 (July 26, 2019): 21–24. http://dx.doi.org/10.5194/isprs-archives-xlii-3-w6-21-2019.
Повний текст джерелаАнотація:
<p><strong>Abstract.</strong> Climate change induced extreme weather events such as drought and flood condition are likely to become more common and associated impacts on crop production will be more without proper irrigation planning. The present investigation was undertaken for assessing the impact of Climate change on tomato yield and water use efficiency (WUE) using AquaCrop model and RegCM 4.4 simulations. The water driven AquaCrop model was validated based on observation of field experiment conducted with four different dates of sowing (1st November, 15th November, 1st December, 15th December) at Ponnaniyar basin, Tiruchirappalli. Validation of AquaCrop model indicated the capability of AquaCrop in predicting tomato yield, biomass and WUE close to the observed data. Seasonal maximum and minimum temperatures over Tiruchirappalli are projected to increase in the mid-century under both RCP4.5 and RCP8.5 scenarios. Maximum temperature is expected to increase up to 1.7&thinsp;&deg;C/2.5&thinsp;&deg;C in SWM and 1.9&thinsp;&deg;C/2.9&thinsp;&deg;C in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways. Minimum temperature is expected to increase up to 1.6&thinsp;&deg;C/2.2&thinsp;&deg;C in SWM and 1.6&thinsp;&deg;C/2.1&thinsp;&deg;C in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways. Seasonal rainfall over Tiruchirappalli is expected to decrease with RCP4.5 and RCP8.5scenarios with different magnitude. Rainfall is expected to change to the tune of &minus;1/&minus;11 per cent in SWM and &minus;2/&minus;14 per cent in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways.</p>
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Lim, Yu Dian, Liangxing Hu, Xin Xia, Zishan Ali, Shaomeng Wang, Beng Kang Tay, Sheel Aditya, and Jianmin Miao. "Field emission properties of SiO2-wrapped CNT field emitter." Nanotechnology 29, no. 1 (November 29, 2017): 015202. http://dx.doi.org/10.1088/1361-6528/aa96ed.
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Li, Hui, Xiao Gang Zhou, Chao Yuan, and Gen Sheng Dou. "Experimental Preparation and Properties of Modified CNT Field Emitters for the Field Emission Display Panel." Advanced Materials Research 148-149 (October 2010): 1327–30. http://dx.doi.org/10.4028/www.scientific.net/amr.148-149.1327.
Повний текст джерелаАнотація:
Carbon nanotube used as the cathode material, the diode-type field emission display panel was developed with low-cost screen-printing method and precise photolithography process. The modified CNT field emitter was fabricated for improving the field emission characteristic, and the detailed fabrication process was also presented. The indium-tin-oxide film on the cathode back-plane was divided to form the CNT cathode electrode, and the insulation slurry was screen-printed to form the insulation layer. Field emission characteristic of whole display device was measured. The sealed field emission display panel showed good emission properties and high display image brightness.
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Wu, Chao, and Xiao Feng Jin. "Optimization Design and Fabrication of Annular Field Emitter for Field Emission Display Panel." Key Engineering Materials 467-469 (February 2011): 1520–23. http://dx.doi.org/10.4028/www.scientific.net/kem.467-469.1520.
Повний текст джерелаАнотація:
With high-effective screen-printing technique, the diode field emission display (FED) panel with carbon nanotube (CNT) as cathode material was fabricated. For improving the field emission properties, the annular field emitter was developed. The bar cathode indium tin oxide (ITO) electrode was formed by the divided ITO film with the photolithography process. After the sintering process, the printed silver slurry was solidified to form the rectangular ring electrode. The prepared CNT paste was printed to form the cold cathode emitter. Field emission characteristics of sealed FED panel were measured, and the emission image was also presented. A series of low-cost manufacture process was employed in the device fabrication course. The fabricated FED panel exhibited better field emission performance and large emission current.
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Liao, Qin Liang, Yue Zhang, Yun Hua Huang, Jun Jie Qi, and Zheng Zhang. "Investigation on the Plasma-Induced Electron Emission Properties of ZnO Nanorod and Carbon Nanotube Arrays." Materials Science Forum 654-656 (June 2010): 1150–53. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.1150.
Повний текст джерелаАнотація:
The plasma-induced emission properties of ZnO nanorod and carbon nanotube (CNT) arrays were investigated under the pulse electric field. The formation of plasma on the array surface was found and high intensity electron beams were obtained from the two kinds of arrays. The plasma-induced emission properties of the ZnO nanorod and CNT arrays have big differences. Under the same electric field, the CNT arrays have higher emission current than the ZnO nanorod arrays. With the emission currents changing, the electron emissions of the ZnO nanorod arrays always are very uniform; but that of the CNT arrays are non-uniform. The plasma expansion velocity of the ZnO nanorod arrays is lower than that of the CNT arrays. Accordingly, the emission stability of the ZnO nanorod arrays is better than that of the CNT arrays.
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Al-Rabadi, Anas, and Marwan Mousa. "Field emission - based many-valued processing using carbon nanotube controlled switches - Part 2: Architecture effectuation." Facta universitatis - series: Electronics and Energetics 25, no. 1 (2012): 15–30. http://dx.doi.org/10.2298/fuee1201015a.
Повний текст джерелаАнотація:
A novel field emission Carbon Nanotube (CNT) - based controlled switch is introduced in the second part of the article. For the architecture effectuation of the new CNT field emission - based switching device, four field emission tubes having single CNT as emitters were previously tested and compared to a tungsten-tip tube, and the corresponding Fowler-Nordheim analysis was performed. Measurements conducted with the CNT suggested that mixer current could be 30 times greater if either SWCNT or MWCNT were used in place of metal emitters, increasing the microwave output power by 30 dB. Laser radiation was utilized to increase field emission current from a cathode with a dense field of CNT by a factor of 18. The extension of the new device from the two-valued to the general mvalued case is introduced, and the implementation of many-valued Galois circuits and systems is also shown.
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Wu, Chao, Wen Sheng Xing, and Yu Kui Li. "Field Emission Characteristics of FED with Carbon Nanotube Field Emitters Using Improved Cathode Electrode." Advanced Materials Research 148-149 (October 2010): 1315–18. http://dx.doi.org/10.4028/www.scientific.net/amr.148-149.1315.
Повний текст джерелаАнотація:
Silver slurry was used as conducting material, and the improved silver cathode electrode was fabricated. The CNT paste formed as field emitters was screen-printed on the surface of silver cathode electrode. The diode FED panel with CNT field emitters was sealed, and the fabrication of cathode substrate and anode substrate was described. The screen-printing technology and the sintering process were employed in the course of device fabrication for the silver cathode electrode. The field emission current was measured and the emission image was presented. The packaged FED showed good field emission characteristics and better field emission uniformity, which the manufacture process was also low-cost, feasible and simple.
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Alberts, Stacey, Kyoung-Soo Lee, Alexandra Pope, Mark Brodwin, Yi-Kuan Chiang, Jed McKinney, Rui Xue, et al. "Measuring the total infrared light from galaxy clusters at z = 0.5–1.6: connecting stellar populations to dusty star formation." Monthly Notices of the Royal Astronomical Society 501, no. 2 (October 31, 2020): 1970–98. http://dx.doi.org/10.1093/mnras/staa3357.
Повний текст джерелаАнотація:
ABSTRACT Massive galaxy clusters undergo strong evolution from z ∼ 1.6 to z ∼ 0.5, with overdense environments at high-z characterized by abundant dust-obscured star formation and stellar mass growth which rapidly give way to widespread quenching. Data spanning the near- to far-infrared (IR) can directly trace this transformation; however, such studies have largely been limited to the massive galaxy end of cluster populations. In this work, we present ‘total light’ stacking techniques spanning $3.4\!-\!500\, \mu$m aimed at revealing the total cluster emission, including low-mass members and potential intracluster dust. We detail our procedures for WISE, Spitzer, and Herschel imaging, including corrections to recover the total stacked emission in the case of high fractions of detected galaxies. We apply our techniques to 232 well-studied log$\, M_{200}/\mathrm{M}_{\odot }\sim 13.8$ clusters in multiple redshift bins, recovering extended cluster emission at all wavelengths. We measure the averaged IR radial profiles and spectral energy distributions (SEDs), quantifying the total stellar and dust content. The near-IR profiles are well described by an NFW model with a high (c ∼ 7) concentration. Dust emission is similarly concentrated, albeit suppressed at $r\lesssim 0.3\,$Mpc. The measured SEDs lack warm dust, consistent with the colder SEDs of low-mass galaxies. We derive total stellar masses consistent with the theoretical Mhalo−M⋆ relation and specific star formation rates that evolve strongly with redshift, echoing that of log$\, M_{\star }/\mathrm{M}_{\odot }\gtrsim 10$ cluster galaxies. Separating out the massive population reveals the majority of cluster far-IR emission ($\sim 70\!-\!80{{\ \rm per\ cent}}$) is provided by the low-mass constituents, which differs from field galaxies. This effect may be a combination of mass-dependent quenching and excess dust in low-mass cluster galaxies.
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Mirakhor, M. S., S. A. Walker, J. Bagchi, A. C. Fabian, A. J. Barth, F. Combes, P. Dabhade, L. C. Ho, and M. B. Pandge. "Exploring the hot gaseous halo around an extremely massive and relativistic jet launching spiral galaxy with XMM−Newton." Monthly Notices of the Royal Astronomical Society 500, no. 2 (October 31, 2020): 2503–13. http://dx.doi.org/10.1093/mnras/staa3404.
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ABSTRACT We present a deep XMM−Newton observation of the extremely massive, rapidly rotating, relativistic-jet-launching spiral galaxy 2MASX J23453268−0449256. Diffuse X-ray emission from the hot gaseous halo around the galaxy is robustly detected out to a radius of 160 kpc, corresponding roughly to 35 per cent of the virial radius (≈450 kpc). We fit the X-ray emission with the standard isothermal β model, and it is found that the enclosed gas mass within 160 kpc is $1.15_{-0.24}^{+0.22} \times 10^{11} \, \rm {M}_{\odot }$. Extrapolating the gas mass profile out to the virial radius, the estimated gas mass is $8.25_{-1.77}^{+1.62} \times 10^{11} \, \rm {M}_{\odot }$, which makes up roughly 65 per cent of the total baryon mass content of the galaxy. When the stellar mass is considered and accounting for the statistical and systematic uncertainties, the baryon mass fraction within the virial radius is $0.121_{-0.043}^{+0.043}$, in agreement with the universal baryon fraction. The baryon mass fraction is consistent with all baryons falling within r200, or with only half of the baryons falling within r200. Similar to the massive spiral galaxies NGC 1961 and NGC 6753, we find a low value for the metal abundance of ≈ 0.1 Z⊙, which appears uniform with radius. We also detect diffuse X-ray emission associated with the northern and southern lobes, possibly attributed to inverse Compton scattering of cosmic microwave background photons. The estimated energy densities of the electrons and magnetic field in these radio lobes suggest that they are electron-dominated by a factor of 10−200, depending on the choice of the lower cut-off energy of the electron spectrum.
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Hoag, A., T. Treu, L. Pentericci, R. Amorin, M. Bolzonella, M. Bradač, M. Castellano, et al. "Constraining Lyman-alpha spatial offsets at 3 < z < 5.5 from VANDELS slit spectroscopy." Monthly Notices of the Royal Astronomical Society 488, no. 1 (July 1, 2019): 706–19. http://dx.doi.org/10.1093/mnras/stz1768.
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Abstract We constrain the distribution of spatially offset Lyman-alpha emission (Ly α) relative to rest-frame ultraviolet emission in ∼300 high redshift (3 < z < 5.5) Lyman-break galaxies (LBGs) exhibiting Ly α emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (≃0.2 deg2 total). Because slit spectroscopy only provides one spatial dimension, we use Bayesian inference to recover the underlying two-dimensional Ly α spatial offset distribution. We model the distribution using a two-dimensional circular Gaussian, defined by a single parameter σr,Ly α, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 < z < 5.5), we find $\sigma _{r,\mathrm{Ly}\,\alpha }=1.70^{+0.09}_{-0.08}$ kpc ($68\hbox{ per cent}$ conf.), corresponding to ∼0${^{\prime\prime}_{.}}$25 at 〈z〉 = 4.5. We also find that σr,Ly α decreases significantly with redshift. Because Ly α spatial offsets can cause slit losses, the decrease in σr,Ly α with redshift can partially explain the increase in the fraction of Ly α emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If σr,Ly α continues to decrease into the reionization epoch, then the decrease in Ly α transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the intergalactic medium, slit losses may explain some of the drop in Ly α transmission observed at z > 6. Spatially resolved observations of Ly α and UV continuum at 6 < z < 8 are needed to settle the issue.
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Danilenko, A., A. Karpova, D. Ofengeim, Yu Shibanov, and D. Zyuzin. "XMM–Newton observations of a gamma-ray pulsar J0633+0632: pulsations, cooling and large-scale emission." Monthly Notices of the Royal Astronomical Society 493, no. 2 (February 28, 2020): 1874–87. http://dx.doi.org/10.1093/mnras/staa287.
Повний текст джерелаАнотація:
ABSTRACT We report results of XMM–Newton observations of a γ-ray pulsar J0633+0632 and its wind nebula. We reveal, for the first time, pulsations of the pulsar X-ray emission with a single sinusoidal pulse profile and a pulsed fraction of 23 ± 6 per cent in the 0.3–2 keV band. We confirm previous Chandra findings that the pulsar X-ray spectrum consists of thermal and non-thermal components. However, we do not find the absorption feature that was previously detected at about 0.8 keV. Thanks to the greater sensitivity of XMM–Newton, we get stronger constraints on spectral model parameters compared to previous studies. The thermal component can be equally well described by either blackbody or neutron star atmosphere models, implying that this emission is coming from either hot pulsar polar caps with a temperature of about 120 eV or from the colder bulk of the neutron star surface with a temperature of about 50 eV. In the latter case, the pulsar appears to be one of the coolest among other neutron stars of similar ages with estimated surface temperatures. We discuss cooling scenarios relevant to this neutron star. Using an interstellar absorption–distance relation, we also constrain the distance to the pulsar to the range of 0.7–2 kpc. Besides the pulsar and its compact nebula, we detect regions of weak large-scale diffuse non-thermal emission in the pulsar field and discuss their possible nature.
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Smith, M. D., and P. W. J. L. Brand. "H2 profiles of C-type bow shocks." Monthly Notices of the Royal Astronomical Society 245, no. 1 (July 1, 1990): 108. http://dx.doi.org/10.1093/mnras/245.1.108.
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Summary We present emission-line profiles of molecular hydrogen from curved C-shocks within molecular clouds. Shock configurations arising from the supersonic motion of jets and bullets within a dense cloud are chosen. Bow shock speeds in the range vw = 40-200 km s-1 are investigated. Breakdown through dissociation and selfionization restricts the C-shock section to the bow tail. We find that profiles ire essentially single-peaked and narrow with full widths (at 10 per cent maximum intensity, deconvolved) of up to about 50,40 and 30 km s-1 for cones, hemispherical caps and paraboloids, respectively. Exceptional field alignments can produce lines as wide as 75 km s-1 in the conical shock model. Line asymmetry is critically dependent on the orientation to the observer and, for low-velocity bows, the magnetic field direction. The peak is never significantly shifted away from the radial component of the pre-shock velocity. These results are consistent with observed profiles from H2 peaks associated with Herbig-Haro objects but not with the particularly broad H2 lines in OMC-1 and DR2 1
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Liu, Xingzhen, Weijin Qian, Yawei Chen, Mingliang Dong, Taxue Yu, Weijun Huang, and Changkun Dong. "Construction of CNT-MgO-Ag-BaO Nanocomposite with Enhanced Field Emission and Hydrogen Sensing Performances." Nanomaterials 13, no. 5 (February 27, 2023): 885. http://dx.doi.org/10.3390/nano13050885.
Повний текст джерелаАнотація:
CNTs and CNT-MgO, CNT-MgO-Ag, and CNT-MgO-Ag-BaO nanocomposites were grown on alloy substrates using an electrophoretic deposition method and their field emission (FE) and hydrogen sensing performances were investigated. The obtained samples were characterized by SEM, TEM, XRD, Raman, and XPS characterizations. The CNT-MgO-Ag-BaO nanocomposites showed the best FE performance with turn-on and threshold fields of 3.32 and 5.92 V.μm−1, respectively. The enhanced FE performances are mainly attributed to the reductions of the work function, and the enhancement of the thermal conductivity and emission sites. The current fluctuation of CNT-MgO-Ag-BaO nanocomposites was only 2.4% after a 12 h test at the pressure of 6.0 × 10−6 Pa. In addition, for the hydrogen sensing performances, the CNT-MgO-Ag-BaO sample showed the best increase in amplitude of the emission current among all the samples, with the mean IN increases of 67%, 120%, and 164% for 1, 3, and 5 min emissions, respectively, under the initial emission currents of about 1.0 μA.
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Wei, Xianqi, Xiaoli Wang, Xin Li, and Weihua Liu. "Electronic Pulses from Pulsed Field Emission of CNT Cathodes." Journal of Nanomaterials 2018 (2018): 1–6. http://dx.doi.org/10.1155/2018/4396430.
Повний текст джерелаАнотація:
We presented a demonstration of infrared laser irradiated field emission electronic pulse based on carbon nanotube (CNT) cathodes. Electronic pulses greatly depended on pulsed infrared laser and were almost synchronous with laser pulses. We have designed a pulsed field emission cathode based on CNTs and investigated correlation between electronic pulse and laser pulse, acquiring the shortest width of electronic pulses about 50 ms and turn-on field less than 0.14 V/μm. Besides, we have studied the thermal effect on the pulsed field emission of CNT cathodes caused by laser heating. Interestingly, the thermal effect has caused an enhancement of emission current but resulted in a waveform distortion on short electronic pulses. The application of laser pulses on CNT cathodes would extend conventional electron sources to a pulsed electron source and offered a possibility of pulsed field emission. These results were encouraging us to prepare further studies of ultrafast electronic pulses for high-frequency electron sources.