Journal articles on the topic 'Sub-K coolers'
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1
Gupta, Sandeep K., Aijaz A. Dar, Thayalan Rajeshkumar, Subramaniam Kuppuswamy, Stuart K. Langley, Keith S. Murray, Gopalan Rajaraman, and Ramaswamy Murugavel. "Discrete {GdIII4M} (M = GdIII or CoII) pentanuclear complexes: a new class of metal-organophosphate molecular coolers." Dalton Transactions 44, no. 13 (2015): 5961–65. http://dx.doi.org/10.1039/c4dt03655g.
Abstract:
A higher magnetic entropy change is observed for the homometallic {GdIII5} complex (25.8 J kg−1 K−1) as compared to the heterometallic {GdIII4CoII} complex (20.3 J kg−1 K−1).
2
Lei, Yongqing, Biao Zhong, Tao Yang, Xuelu Duan, Meng Xia, Chaoyu Wang, Jiajin Xu, Ziheng Zhang, Jingxin Ding, and Jianping Yin. "Laser cooling of Yb3+:LuLiF4 crystal below cryogenic temperature to 121 K." Applied Physics Letters 120, no. 23 (June 6, 2022): 231101. http://dx.doi.org/10.1063/5.0094705.
Abstract:
Optical cooling techniques of solid-state refrigerators, especially those toward the cryogenic temperature range, have attracted considerable attention in the fields of space exploration, precise measurement, material sciences, and so forth. Here, we report the laser cooling of the 7.5% Yb3+-doped LuLiF4 crystal down to 121 K reaching NIST's designated range of cryogenic temperatures (<123 K). Further results based on the cooling window indicate a promising cooling limit of 59 K, provided with enhancement in pump absorbance and heat load management of the sample. Our work, therefore, can motivate an all-solid-state optical refrigeration application beyond the liquid nitrogen boiling point, thus bringing great opportunity to realize cryogenic coolers and radiation-balanced lasers in miniaturized systems.
3
Lee, Jongmin, Wenmei Liu, Hannah Löffler, and Pierre Boillat. "New Characterizations for PEFC Under Sub-Zero Temperature." ECS Meeting Abstracts MA2023-02, no. 37 (December 22, 2023): 1791. http://dx.doi.org/10.1149/ma2023-02371791mtgabs.
Abstract:
The operation of fuel cells at sub-zero temperature results in direct deposition of ice or production of supercooled water that freezes upon interacting with nucleation seeds. Ice formation can lead to irreversible mechanical damages in membrane electrode assembly (MEA), particularly at interfaces, which is detrimental to the performance and safety of fuel cells. The mitigation strategies are focused on temperature elevation, including assisted heating, catalytic heating, and starvation (low potential) heating; however, these are associated with parasitic loss that reduces overall efficiency of the system. An alternative method is to develop porous media that are capable of ensuring oxygen transport pathways in the presence of ice or retaining supercooled water without phase transition until the cell reaches above 0ºC. The development of ice-resistant porous media for sub-zero operation is hindered by limitations on material characterization and performance evaluation techniques. The most common characterization technique is differential scanning calorimetry (DSC), by which water-saturated porous media is subjected to rapid temperature cycles to measure melting and freezing peaks. The DSC is a well-established and convenient technique that is suitable for statistical analysis; however, the sample size is limited to the mm-scale, and water must be injected in hydrophobic media prior to the DSC measurement where water saturation level and morphology are unpredictable. In situ testing of novel materials are performed on single cell hardware, in which the temperature is controlled by circulating a coolant through endplates or cooling channels that are placed several mm to cm away from an MEA. Such pseudo-active cooling system results in a significant difference (and delay) between the coolant and cell temperatures, influenced by heat production due to cell operation as well as freezing/melting. On the other hand, free heating operation starting from sub-zero is not desirable, since product heat is dissipated to current collectors and endplates that have much greater mass per active area in comparison to stack. As a result, most of sub-zero tests are performed on isothermal condition. Our previous works [1,2] introduced a unique single fuel cell hardware featuring temperature control and heat flux measurement (TCHM) system. Thermoelectric coolers and tangential gradient heat flux sensors enable a precise control of temperature in the MEA and detection of freezing and melting events during the cell operation. We have advanced the TCHM controlling software and integrated them on the custom fuel cell test bench. In this work, two novel techniques are introduced for sub-zero application for fuel cell porous media: (1) advanced calorimetry and (2) non-isothermal cold start. The advantages of our advanced calorimetry include testing of a large sample area up to 12cm2 and control of water quantity in a gas diffusion layer (GDL). Through neutron imaging, we validated capillary water injection method in the GDL and reduced saturation level with drying gas purging. Using techniques, we analyzed the effect of GDL structures and hydrophobicity on repeated freezing-thaw cycle to assist design of ice-resistant material. Additionally, we successfully implemented non-isothermal cold-start at -20 ºC in addition to isothermal condition, as seen in Figure 1. After the calibration of the TCHM units, the heating load was emulated to match that of the stack, corresponding to the heating rate between 10-15 K/min. The methods introduced in this study are expected to make a significant contribution towards the development of GDLs and catalyst layers that suppress ice formation and related mechanical damages. In particular, the non-isothermal cold-start provides a flexible, precise temperature control in the MEA, which can bridge the gap between the single cell and stack testing. Reference [1] J. Lee, E.R. Carreon-Ruiz, M. Siegwart, P. Boillat, Segmentation for Preventing Ice Propagation in Operating Fuel Cells, Meet. Abstr. MA2021-02 (2021) 1066. https://doi.org/10.1149/MA2021-02361066mtgabs. [2] M. Siegwart, F. Huang, M. Cochet, T.J. Schmidt, J. Zhang, P. Boillat, Spatially Resolved Analysis of Freezing during Isothermal PEFC Cold Starts with Time-of-Flight Neutron Imaging, Journal of The Electrochemical Society. 167 (2020) 064510. https://doi.org/10.1149/1945-7111/ab7d91. Figure 1
4
Matsuki, Yoh, Takeshi Kobayashi, Jun Fukazawa, Frédéric A. Perras, Marek Pruski, and Toshimichi Fujiwara. "Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions." Physical Chemistry Chemical Physics 23, no. 8 (2021): 4919–26. http://dx.doi.org/10.1039/d0cp05658h.
Abstract:
DNP enhancement, paramagnet-induced quenching/depolarization and build-up times are studied in a heterogeneous catalyst between 30 and 100 K. He-cooled MAS DNP at 30 K provides up to 100-fold better time performance than N2-cooled MAS DNP at 90 K.
5
Belkhodja, Y., J. Loreau, A. van der Avoird, Y. Berger, and P. Asselin. "Intermolecular dynamics of NH3-rare gas complexes in the ν2 umbrella region of NH3 investigated by rovibrational laser jet-cooled spectroscopy and ab initio calculations." Physical Chemistry Chemical Physics 23, no. 18 (2021): 10864–74. http://dx.doi.org/10.1039/d1cp00316j.
6
Xi, Xiaotong, Biao Yang, Zhaozhao Gao, Liubiao Chen, Yuan Zhou, and Junjie Wang. "Experimental study on a helium-4 sorption cryocooler." IOP Conference Series: Materials Science and Engineering 1240, no. 1 (May 1, 2022): 012022. http://dx.doi.org/10.1088/1757-899x/1240/1/012022.
Abstract:
Abstract The sorption cooler is one of the commonly used Sub-Kelvin temperature refrigeration technologies, used in space exploration and ground experiments to provide a low temperature below 1 K. In this paper, a sorption cooler using helium-4 as the working gas has been developed. At a heat sink temperature of 3 K, the lowest no-load temperature of the developed sorption cooler is 843 mK and the hold time below 1 K is 4 hours. The effects of different sorption pump temperatures and sorption pump cooling rates on the refrigeration performance were studied through experiments. The test results show that during the condensation process, when the temperature of the sorption pump is higher than 45 K, the pump temperature has little effect on the liquefaction efficiency, and speeding up the cooling rate of the sorption pump is conducive to obtaining a lower refrigeration temperature.
7
Sistani, M., M. S. Seifner, M. G. Bartmann, J. Smoliner, A. Lugstein, and S. Barth. "Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires." Nanoscale 10, no. 41 (2018): 19443–49. http://dx.doi.org/10.1039/c8nr05296d.
Abstract:
Electrical characterization of Ge0.81Sn0.19 nanowires has been performed revealing high electrical conductivity and semiconductor behaviour when cooled to 10 K. The impact on slightly elevated temperatures on the device stability of this metastable material is described.
8
Vaghela, Hitensinh, Ketan Choukekar, Pratik Patel, Vinit Shukla, Anuj Garg, Srinivasa Muralidhara, Vikas Gaur, Shk Madeenavalli, and Bikash Dash. "Augmentation scheme of 80 K helium test facility to 65 K using sub-cooled liquid nitrogen." Indian Journal of Cryogenics 45, no. 1 (2020): 90–96. http://dx.doi.org/10.5958/2349-2120.2020.00015.1.
9
Zhang, Lili, Yongzhang Cui, Wenlong Mao, Xiangzhuo Sheng, and Guanmin Zhang. "The Condensation Characteristics of Propane in Binary and Ternary Mixtures on a Vertical Plate." Energies 16, no. 16 (August 8, 2023): 5873. http://dx.doi.org/10.3390/en16165873.
Abstract:
Natural gas is one of the most common forms of energy in our daily life, and it is composed of multicomponent hydrocarbon gas mixtures (mainly of methane, ethane and propane). It is of great significant to reveal the condensation mechanism of multicomponent mixtures for the development and utilization of natural gas. A numerical model was adopted to analyze the heat and mass transfer characteristics of propane condensation in binary and ternary gas mixtures on a vertical cold plate. Multicomponent diffusion equations and the volume of fluid method (VOF) are used to describe the in-phase and inter-phase transportation. The conditions of different wall sub-cooled temperatures (temperature difference between the wall and saturated gas mixture) and the inlet molar fraction of methane/ethane are discussed. The numerical results show that ethane gas is more likely to accumulate near the wall compared with the lighter methane gas. The thermal resistance in the gas boundary layer is one hundred times higher than that of the liquid film, revealing the importance of diffusion resistance. The heat transfer coefficients increased about 11% (at ΔT = 10 K) and 7% (at ΔT = 40 K), as the molar fraction of ethane increased from 0 to 40%. Meanwhile, the condensation heat transfer coefficient decreased by 53~56% as the wall sub-cooled temperature increased from 10 K to 40 K.
10
Kováč, P., L. Kopera, T. Melišek, M. Búran, I. Hušek, D. Berek, and J. Kováč. "Water ice-cooled MgB2 coil made by wind and react process." Superconductor Science and Technology 35, no. 5 (March 17, 2022): 055001. http://dx.doi.org/10.1088/1361-6668/ac521c.
Abstract:
Abstract A wind and react (W&R) coil of inner diameter 53 mm has been made from multi-core MgB2/Nb/CuNi wire manufactured by the internal magnesium diffusion (IMD) process. The W&R coil is wound from non-insulated rectangular wire of 1 mm2 with only 5 µm thick stainless steel foil used for interlayer insulation. The transport current performance of the coil and short wire samples was measured in a liquid He bath at external magnetic fields of 4.5–8.5 T and also in self-field conditions in sub-cooled water ice at temperatures between 33 K and 38 K. The presented MgB2 coil exhibits stable behavior at water ice cooling, and its high space factor allows a high current density of winding in comparison to the data from the already published MgB2 coils. The presented results demonstrate that MgB2 windings can be used safely in He-free conditions inside sub-cooled water ice, and this technique can be further optimized and used for future MgB2 coils.
11
Lu, X. F., Q. Y. Zhang, A. Y. Chen, P. Zhu, Z. W. Zhou, B. Fu, and S. S. Li. "Design and Commissioning of a 700 W@3 K Sub-cooled Helium Test Facility." IOP Conference Series: Materials Science and Engineering 755 (June 30, 2020): 012143. http://dx.doi.org/10.1088/1757-899x/755/1/012143.
12
Romojaro, Pablo, Ciro Alfonso, Luca Fiorito, Alejandro Cuesta-Matesanz, Juan Carlos Guillamot, Augusto Hernandez-Solis, Alexey Stankovskiy, and Gert Van den Eynde. "Nuclear Data Uncertainty Analysis to Meet the Target Accuracy Requirements on the MYRRHA keff." EPJ Web of Conferences 284 (2023): 08012. http://dx.doi.org/10.1051/epjconf/202328408012.
Abstract:
MYRRHA is a flexible experimental facility being designed at the SCK CEN, in Mol, Belgium. Cooled by lead-bismuth, it is conceived to operate both in sub-critical mode, as an accelerator driven system, and in critical mode, as a fast reactor. In order to comply with MYRRHA reactor design requirements, uncertainties due to nuclear data must be quantified. Significant gaps between the uncertainties and the target accuracies have been systematically shown in the past. In this paper, first, a Sensitivity and Uncertainty analysis with JEFF-3.3 nuclear data library of the effective neutron multiplication factor keff of the latest MYRRHA reactor design - v1.8 - is presented. Then, since target accuracy for keff of 300 pcm is exceeded, a Target Accuracy Requirement assessment is performed in order to find out the required accuracy on cross section data to meet the requested target accuracy. To reach the requested target accuracy, a reduction of the uncertainty in the fission and capture cross sections of 240Pu JEFF-3.3 evaluation is needed.
13
Sathe, V. G., Soma Banik, Aditi Dubey, S. R. Barman, A. M. Awasthi, and Luca Olivi. "Signature of Austenitic to Martensitic Phase Transition in Ni2MnGa in Mn and Ni K-Edge XANES Spectra." Advanced Materials Research 52 (June 2008): 175–80. http://dx.doi.org/10.4028/www.scientific.net/amr.52.175.
Abstract:
The XANES studies at Mn, Ni and Ga K-edge of Ni2MnGa compound have been carried out at room and low temperatures. The Mn K-edge and Ni K-edge spectra shows modulation in the post edge features when the sample is cooled below martensitic transition temperature. It is strongly reflected in the XANES of Mn K-edge where the peak after the edge gets totally suppressed when the sample is in martensitic phase. This peak shows a hysteretic behaviour when thermal cycling was done across the martensitic transition temperature. This clearly shows that the peak height is a measure of austenitic phase present at a particular temperature. This demonstrates the strong correlations of electronic states and crystal structures in these compounds.
14
Saukhimov, A. A., M. A. Hobosyan, G. C. Dannangoda, N. N. Zhumabekova, S. E. Kumekov, and K. S. Martirosyan. "Fabrication of Yttrium Ferrite Nanoparticles by Solution Combustion Synthesis." Eurasian Chemico-Technological Journal 16, no. 1 (December 22, 2013): 27. http://dx.doi.org/10.18321/ectj165.
Abstract:
<p>The ternary oxide system Y-Fe-O presents fascinating magnetic properties that are sensitive to the crystalline size of particles. There is a major challenge to fabricate these materials in nano-crystalline forms due to particle conglomeration during nucleation and synthesis. In this paper we report the fabrication of nano sized crystalline yttrium ferrite by solution combustion synthesis (SCS) where yttrium and iron nitrates were used as metal precursors with glycine as a fuel. The magnetic properties of the product can be selectively controlled by adjusting the ratio of glycine to metal nitrates. Yttrium ferrite nano-powder was obtained by using three concentration of glycine (3, 6 and 10 wt.%) in the initial exothermic mixture. Increasing glycine content was found to increase the reaction temperature of the system. The structural and magnetic properties of yttrium ferrite before and after annealing at temperature of 1000 °C were investigated by X-ray diffractometry, Differential Scanning Calorimetry (DSC) and cryogenic magnetometry (PPMS, Quantum Design). X-ray diffraction showed that, a broad diffraction peak was found for all samples indicating the amorphous nature of the product. Particle size and product morphology analysis identified that, Nitrate/glycine combustion caused considerable gas evolution, mainly carbon dioxide, N<sub>2</sub> and H<sub>2</sub>O vapor, which caused the synthesized powders to become friable and loosely agglomerated for glycine concentration from 3 wt.% up to 10 wt.%. The study of the magnetic properties of produced materials in a metastable state was performed by measuring dependencies of Magnetization (M) on temperature, and magnetization on magnetic field strength between 5 K and 300 K. Magnetization measurements on temperature zero-fieldcooled and field-cooled show different patterns when the fraction of glycine is increased. The analysis of zero-field-cooled (ZFC), field-cooled (FC) and magnetization curves of annealed samples confirmed that nanoparticles exhibit superparamagnetic behavior. The increasing concentration of glycine leads to an increased blocking temperature.</p>
15
Booth, A. M., M. H. Barley, D. O. Topping, G. McFiggans, A. Garforth, and C. J. Percival. "Solid state and sub-cooled liquid vapour pressures of substituted dicarboxylic acids using Knudsen Effusion Mass Spectrometry (KEMS) and Differential Scanning Calorimetry." Atmospheric Chemistry and Physics 10, no. 10 (May 26, 2010): 4879–92. http://dx.doi.org/10.5194/acp-10-4879-2010.
Abstract:
Abstract. Solid state vapour pressures of a selection of atmospherically important substituted dicarboxylic acids have been measured using Knudsen Effusion Mass Spectrometry (KEMS) over a range of 20 K (298–318 K). Enthalpies of fusion and melting points obtained using Differential Scanning Calorimetry (DSC) were used to obtain sub-cooled liquid vapour pressures. They have been compared to estimation methods used on the E-AIM website. These methods are shown to poorly represent – OH groups in combination with COOH groups. Partitioning calculations have been performed to illustrate the impact of the different estimation methods on organic aerosol mass compared to the use of experimental data.
16
Grosdidier, Thierry, Y. Samih, Nathalie Allain-Bonasso, Bernard Bolle, Z. X. Zou, Y. Quin, Sheng Zhi Hao, and Chuang Dong. "Grain Refinement and Hardening Induced by Heavy Deformation Using Low Energy High Current Pulsed Electron Beam Surface Treatment." Materials Science Forum 667-669 (December 2010): 499–504. http://dx.doi.org/10.4028/www.scientific.net/msf.667-669.499.
Abstract:
The low energy high current pulse electron beam (LEHCPEB) irradiation induces ultra fast dynamic temperature fields in the surface of the material to which is associated dynamic stress fields that causes intense deformation at the material surface and sub-surface. Improved surface properties (hardness, corrosion resistance) can be obtained using the LEHCPEB treatment. Under the “Melting” mode, the top surface (few µm) which is melted and rapidly solidified (107 K/s), can solidify has nano-domains formed from the highly under-cooled melt. The thermal stress wave that propagates in the sub-surface imposes strain hardening and grain size refinement. This induces a sub-surface hardening that can extent over about 100 µm. The use of the “Heating” mode is less conventional. This mode can promote grain size refinement, hardening as well as texture modification without modification of the sample geometry.
17
Iwasa, Y., R. Wheatley, J. Bascunan, B. Haid, and Haigun Lee. "A solid-nitrogen cooled Nb/sub 3/Sn NMR magnet operating in the range 8-10 K." IEEE Transactions on Appiled Superconductivity 13, no. 2 (June 2003): 1636–39. http://dx.doi.org/10.1109/tasc.2003.812851.
18
Wang, Jian, Li Wang, Yiyong Liu, and Wei Zhang. "Effect Analyses of Thermal Deformation on Magnetic Performance of the CPMU Prototype in SSRF." IOP Conference Series: Materials Science and Engineering 1240, no. 1 (May 1, 2022): 012144. http://dx.doi.org/10.1088/1757-899x/1240/1/012144.
Abstract:
Abstract A cryogenic permanent magnet undulator (CPMU) prototype cooled by sub-cooled liquid nitrogen was developed in Shanghai Synchrotron Radiation Facility (SSRF) in 2016. The CPMU prototype mainly consist of NdFeB based hybrid magnet arrays with a period of 20 mm and a magnetic length of 1.6 m, a pair of girders to support the magnetic arrays, parallel SLN2 cooling loops attached to the girders, thermal spacers connecting the girders and the copper LN2 tubes, electric heaters to heat the girders and regulate the magnet working temperature at around 120 K, and stems made of stainless steel to support the girders. During the first magnetic field measurement, the RMS phase error of the CPMU prototype changed from 3.2 degree at room temperature to 4.5 degree at 135 K. By shimming the magnetic field, its RMS phase error is reduced to 3.5 at low temperature finally. This paper presents detailed analyses of temperature distribution and thermal deformation along the CPMU girder during cool down process. By comparison with test results, the deterioration of the RMS phase error is well explained. The analyses can provide guidance for magnetic field shimming and avoid or reduce the deterioration of the RMS phase error at low temperature.
19
Kameno, Seiji, Satoko Sawada-Satoh, C. M. Violette Impellizzeri, Kotaro Kohno, Sergio Martín, Daniel Espada, Naomasa Nakai, et al. "Probing the Jet–Torus Interaction in the Radio Galaxy NGC 1052 by Sulfur-bearing Molecules." Astrophysical Journal 944, no. 2 (February 1, 2023): 156. http://dx.doi.org/10.3847/1538-4357/acb499.
Abstract:
Abstract The radio galaxy NGC 1052 casts absorption features of sulfur-bearing molecules, H2S, SO, SO2, and CS toward the radio continuum emission from the core and jets. Using the Atacama Large Millimeter/submillimeter Array, we have measured the equivalent widths of SO absorption features in multiple transitions and determined the temperatures of 344 ± 43 K and 26 ± 4 K in submillimeter and millimeter wavelengths, respectively. Since submillimeter and millimeter continuum represents the core and jets, the high and low temperatures of the absorbers imply a warm environment in the molecular torus and cooler downstream flows. The high temperature in the torus is consistent with the presence of 22 GHz H2O maser emission, vibrationally excited HCN and HCO+ absorption lines, and sulfur-bearing molecules in the gas phase released from dust. The origin of the sulfur-bearing gas is ascribed to the evaporation of the icy dust component through a jet–torus interaction. Shock heating is the sole plausible mechanism to maintain such a high temperature of gas and dust in the torus. The implication of the jet–torus interaction also supports the collimation of the sub-relativistic jets by the gas pressure of the torus.
20
Morito, Shigekazu, Ryota Igarashi, Keiichiro Kamiya, Takuya Ohba, and Tadashi Maki. "Effect of Cooling Rate on Morphology and Crystallography of Lath Martensite in Fe-Ni Alloys." Materials Science Forum 638-642 (January 2010): 1459–63. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.1459.
Abstract:
The development of blocks and subblocks in the lath martensite was observed with SEM/EBSD and TEM/Kikuchi diffraction patterns analyses. Morphology of lath martensite formed below Ms temperature was observed using step quenching method in 18 mass% Ni maraging steel. The development of lath martensite structure can be described as follow; lath groups with single K-S variant start to form at the austenite grain boundary. Next, other sub-blocks appear adjacent to the lath groups formed first and these lath groups form macroscopic blocks observed in optical microscopy. The morphologies of the lath martensite in Fe -23 mass% Ni alloy cooled at different cooling rates after austenitization were also observed. The packet size and block thickness decreases with increasing cooling rate, although the sub-block thickness do not change. A packet locally contains small packets with different relationship of close packed planes, and the amount of small packets increases with increasing the cooling rate.
21
Carleo, Ilaria, Paolo Giacobbe, Gloria Guilluy, Patricio E. Cubillos, Aldo S. Bonomo, Alessandro Sozzetti, Matteo Brogi, et al. "The GAPS Programme at TNG XXXIX. Multiple Molecular Species in the Atmosphere of the Warm Giant Planet WASP-80 b Unveiled at High Resolution with GIANO-B ∗." Astronomical Journal 164, no. 3 (August 18, 2022): 101. http://dx.doi.org/10.3847/1538-3881/ac80bf.
Abstract:
Abstract Detections of molecules in the atmosphere of gas giant exoplanets allow us to investigate the physico-chemical properties of the atmospheres. Their inferred chemical composition is used as tracer of planet formation and evolution mechanisms. Currently, an increasing number of detections is showing a possible rich chemistry of the hotter gaseous planets, but whether this extends to cooler giants is still unknown. We observed four transits of WASP-80 b, a warm transiting giant planet orbiting a late-K dwarf star with the near-infrared GIANO-B spectrograph installed at the Telescopio Nazionale Galileo and performed high-resolution transmission spectroscopy analysis. We report the detection of several molecular species in its atmosphere. Combining the four nights and comparing our transmission spectrum to planetary atmosphere models containing the signature of individual molecules within the cross-correlation framework, we find the presence of H2O, CH4, NH3, and HCN with high significance, tentative detection of CO2, and inconclusive results for C2H2 and CO. A qualitative interpretation of these results, using physically motivated models, suggests an atmosphere consistent with solar composition and the presence of disequilibrium chemistry and we therefore recommend the inclusion of the latter in future modeling of sub-1000 K planets.
22
Lee, G. K. H., J. Blecic, and Ch Helling. "Dust in brown dwarfs and extra-solar planets." Astronomy & Astrophysics 614 (June 2018): A126. http://dx.doi.org/10.1051/0004-6361/201731977.
Abstract:
Context. The cloud formation process starts with the formation of seed particles, after which, surface chemical reactions grow or erode the cloud particles. If seed particles do not form, or are not available by another means, an atmosphere is unable to form a cloud complex and will remain cloud free. Aims. We aim to investigate which materials may form cloud condensation seeds in the gas temperature and pressure regimes (Tgas = 100–2000 K, pgas = 10−8–100 bar) expected to occur in planetary and brown dwarf atmospheres. Methods. We have applied modified classical nucleation theory which requires surface tensions and vapour pressure data for each solid species, which are taken from the literature. Input gas phase number densities are calculated assuming chemical equilibrium at solar metallicity. Results. We calculated the seed formation rates of TiO2[s] and SiO[s] and find that they efficiently nucleate at high temperatures of Tgas = 1000–1750 K. Cr[s], KCl[s] and NaCl[s] are found to efficiently nucleate across an intermediate temperature range of Tgas = 500–1000 K. We find CsCl[s] may serve as the seed particle for the water cloud layers in cool sub-stellar atmospheres. The nucleation rates of four low temperature ice species (Tgas = 100–250 K), H2O[s/l], NH3[s], H2S[s/l], and CH4[s], are also investigated for the coolest sub-stellar and planetary atmospheres. Conclusions. Our results suggest a possibly (Tgas, pgas) distributed hierarchy of seed particle formation regimes throughout the substellar and planetary atmospheric temperature-pressure space. With TiO2[s] providing seed particles for the most refractory cloud formation species (e.g. Al2O3[s], Fe[s], MgSiO3[s], Mg2SiO4[s]), Cr[s] providing the seed particles for MnS[s], Na2S[s], and ZnS[s] sulfides, and K/Na/Rb/Cs/NH4-Cl binding solid species providing the seed particles for H2O[s/l] and NH4-H2PO4/SH[s] clouds. A detached, high-altitude aerosol layer may form in some sub-stellar atmospheres from the nucleation process, dependent on the upper atmosphere temperature, pressure and availability of volatile elements. In order to improve the accuracy of the nucleation rate calculation, further research into the small cluster thermochemical data for each cloud species is warranted. The validity of these seed particle scenarios will be tested by applying it to more complete cloud models in the future.
23
Shelley, Petroc, Thomas J. Bannan, Stephen D. Worrall, M. Rami Alfarra, Carl J. Percival, Arthur Garforth, and David Topping. "Measured Solid State and Sub-Cooled Liquid Vapour Pressures of Benzaldehydes Using Knudsen Effusion Mass Spectrometry." Atmosphere 12, no. 3 (March 19, 2021): 397. http://dx.doi.org/10.3390/atmos12030397.
Abstract:
Benzaldehydes are components of atmospheric aerosol that are poorly represented in current vapour pressure predictive techniques. In this study the solid state (PSsat) and sub-cooled liquid saturation vapour pressures (PLsat) were measured over a range of temperatures (298–328 K) for a chemically diverse group of benzaldehydes. The selected benzaldehydes allowed for the effects of varied geometric isomers and functionalities on saturation vapour pressure (Psat) to be probed. PSsat was measured using Knudsen effusion mass spectrometry (KEMS) and PLsat was obtained via a sub-cooled correction utilising experimental enthalpy of fusion and melting point values measured using differential scanning calorimetry (DSC). The strength of the hydrogen bond (H-bond) was the most important factor for determining PLsat when a H-bond was present and the polarisability of the compound was the most important factor when a H-bond was not present. Typically compounds capable of hydrogen bonding had PLsat 1 to 2 orders of magnitude lower than those that could not H-bond. The PLsat were compared to estimated values using three different predictive techniques (Nannoolal et al. vapour pressure method, Myrdal and Yalkowsky method, and SIMPOL). The Nannoolal et al. vapour pressure method and the Myrdal and Yalkowsky method require the use of a boiling point method to predict Psat. For the compounds in this study the Nannoolal et al. boiling point method showed the best performance. All three predictive techniques showed less than an order of magnitude error in PLsat on average, however more significant errors were within these methods. Such errors will have important implications for studies trying to ascertain the role of these compounds on aerosol growth and human health impacts. SIMPOL predicted PLsat the closest to the experimentally determined values.
24
Zhang, Rui, Mengxue Du, Evgeny Zhuravlev, René Androsch, and Christoph Schick. "Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry." Polymers 13, no. 12 (June 19, 2021): 2008. http://dx.doi.org/10.3390/polym13122008.
Abstract:
By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time.
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Murray, B. J., S. L. Broadley, T. W. Wilson, J. D. Atkinson, and R. H. Wills. "Heterogeneous freezing of water droplets containing kaolinite particles." Atmospheric Chemistry and Physics 11, no. 9 (May 6, 2011): 4191–207. http://dx.doi.org/10.5194/acp-11-4191-2011.
Abstract:
Abstract. Clouds composed of both ice particles and supercooled liquid water droplets exist at temperatures above ~236 K. These mixed phase clouds, which strongly impact climate, are very sensitive to the presence of solid particles that can catalyse freezing. In this paper we describe experiments to determine the conditions at which the clay mineral kaolinite nucleates ice when immersed within water droplets. These are the first immersion mode experiments in which the ice nucleating ability of kaolinite has been determined as a function of clay surface area, cooling rate and also at constant temperatures. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and cooled at rates of between 0.8 and 10 K min−1 or held at constant sub-zero temperatures. The time and temperature at which individual 10–50 μm diameter droplets froze were determined by optical microscopy. For a cooling rate of 10 K min−1, the median nucleation temperature of 10–40 μm diameter droplets increased from close to the homogeneous nucleation limit (236 K) to 240.8 ± 0.6 K as the concentration of kaolinite in the droplets was increased from 0.005 wt% to 1 wt%. This data shows that the probability of freezing scales with surface area of the kaolinite inclusions. We also show that at a constant temperature the number of liquid droplets decreases exponentially as they freeze over time. The constant cooling rate experiments are consistent with the stochastic, singular and modified singular descriptions of heterogeneous nucleation; however, freezing during cooling and at constant temperature can be reconciled best with the stochastic approach. We report temperature dependent nucleation rate coefficients (nucleation events per unit time per unit area) for kaolinite and present a general parameterisation for immersion nucleation which may be suitable for cloud modelling once nucleation by other important ice nucleating species is quantified in the future.
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Zhao, Yue Feng, and Jing Li. "Development of Microwave Limb Sounder." Key Engineering Materials 500 (January 2012): 204–11. http://dx.doi.org/10.4028/www.scientific.net/kem.500.204.
Abstract:
Microwave limb sounding is powerful to measure atmospheric compositions, temperature and pressure with high vertical resolution. During the past few decades many countries have developed several Microwave limb sounders to improve our understanding of stratospheric ozone chemistry and dynamics, the interaction of composition and climate and pollution in the upper troposphere. This issue will outline five existed MLS instrument and analyze their adopted techniques for lower noise and higher sensitivity as well as their capabilities comparisons. In American, the Jet Propulsion Laboratory (JPL) has already developed three MLS instruments: the UARS-MLS, EOS-MLS and CAMEO-SMLS which is ready for launch in 2011. In Japan, its JEM/SMILES is the first MLS instrument to use superconductor-insulator-superconductor (SIS) mixers with a mechanical 4-K refrigerator in space. In Sweden, the millimeter and sub millimeter limb-emission sounder on Odin uses actively cooled Schottky receivers with auto-correlators and wide hand AOS.
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Ayres, Thomas R. "In the Trenches of the Solar-stellar Connection. V. High-resolution Ultraviolet and X-Ray Observations of Sun-like Stars: The Curious Case of Procyon." Astrophysical Journal 923, no. 2 (December 1, 2021): 192. http://dx.doi.org/10.3847/1538-4357/ac1fec.
Abstract:
Abstract A joint X-ray (0.2–2 keV) and ultraviolet (1150–3000 Å) time-domain study has been carried out on three nearby bright late-type stars, bracketing the Sun in properties. Alpha Cen A (HD 128620: G2 V) is a near twin to the Sun, although slightly more massive and luminous, slightly metal-rich, but older. Alpha Cen B (HD 128621: K1 V) is cooler than the Sun, somewhat less massive and lower in luminosity. Procyon (HD 61421: F5 IV–V) is hotter, more massive and more luminous than the Sun, half the age, but more evolved. Stellar observations were from Chandra X-ray Observatory and Hubble Space Telescope (HST). The Sun provided a benchmark through high-energy spectral scans from solar irradiance satellites and novel high-dispersion full-disk profiles of key UV species—Mg ii, C ii, and Si iv—from the Interface Region Imaging Spectrograph. Procyon’s flux history was strikingly constant at all wavelengths, in contrast to the other three cycling-dynamo stars. Procyon also displays a strong subcoronal (T ∼ 1 × 105 K) emission excess, relative to chromospheric Mg ii (T ≲ 104 K), although its X-rays (T ∼ 2 MK) appear to be more normal. At the same time, the odd sub-Gaussian shapes, and redshifts, of the subgiant’s “hot lines” (such as Si iv and C iv) are remarkably similar to the solar counterparts (and α Cen AB). This suggests a Sun-like origin, namely a supergranulation network supplied by magnetic flux from a noncycling “local dynamo.”
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Dong, Zenghao, Jianquan Liu, Chao Huang, Xinyi Niu, and Lihan Hai. "Analysis on heat transfer performance sub-channels of sodium-cooled fast reactor fuel assemblies based on entransy." Nuclear Technology and Radiation Protection 38, no. 3 (2023): 145–54. http://dx.doi.org/10.2298/ntrp2303145d.
Abstract:
In this paper, the symmetric heat transfer performance of sodium-cooled fast reactor fuel assemblies was analyzed and studied. The model is analytically optimized based on sub-channel calculations. The deviations of the numerical simulation results from the pre-existing experimental data in the literature are within 10 %, with an average deviation of 2.5 %, which tested the reliability of the model. The calculated results demonstrated that the distribution of the axial power, temperature, and coolant of the reactor core is approximately symmetric M-shape. The reactor core coolant has a monotonic increase in axial distribution with the cladding temperature and the temperature peaks all appear at the reactor core outlet. The individual fuel assemblies' internal temperature is relatively sensitive to the axial power distribution, and there are troughs around the imports and exports. The simulated results showed that the center temperature of the hottest rod reactor core block reached 965.65 K. This pa- per provides a better guide to understanding the overall heat transfer effect by optimizing the heat transfer model.
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Melis, A., R. Chiello, G. Comoretto, R. Concu, A. Magro, G. Naldi, A. Navarrini, et al. "A Digital Beamformer for the PHAROS2 Phased Array Feed." Journal of Astronomical Instrumentation 09, no. 03 (September 2020): 2050013. http://dx.doi.org/10.1142/s2251171720500130.
Abstract:
PHased Arrays for Reflector Observing Systems (PHAROS) is a C-band (4–8[Formula: see text]GHz) Phased Array Feed (PAF) receiver designed to operate from the primary focus of a large single-dish radio astronomy antenna. It consists of an array of 220-element Vivaldi antennas ([Formula: see text] polarization), cryogenically cooled at roughly 20[Formula: see text]K along with low noise amplifiers (LNAs), and of analogue beamformers cryogenically cooled at roughly 80[Formula: see text]K. PHAROS2, the upgrade of PHAROS, is a PAF demonstrator developed in the framework of the Square Kilometer Array Advanced Instrumentation Program (SKA AIP) with the goal of investigating the potential of the PAF technologies at high frequencies in view of their possible application on the SKA dish telescopes. The PHAROS2 design includes new cryogenically cooled LNAs with state-of-the-art performance, a digital beamformer capable of synthesizing four beams from a sub-array of 24 single-polarization antenna elements, and a C-band multi-channel Warm Section receiver capable of analogue filtering and down-converting the signals from the antennas to a suitable frequency range at the input of the digital backend, providing an instantaneous bandwidth of 275[Formula: see text]MHz for each signal. In this paper, we describe the design and performance of the PHAROS2 digital backend/beamformer, based on the Italian Tile Processing Module (ITPM) hardware, which was initially developed for the SKA Low Frequency Aperture Array (LFAA). The backend was adapted to perform the beamforming for our PAF application. We describe the implementation of the beamformer on the Field Programmable Gate Arrays (FPGAs) of the ITPM and how the backend was successfully used to synthesize four independent beams, both in the laboratory (across the entire 275[Formula: see text]MHz instantaneous bandwidth) and during on-field observations at the BEST-2 array (across 16[Formula: see text]MHz instantaneous bandwidth), which is a subset of the Northern Cross Radio Telescope (located in the district of Bologna, Italy). The beamformer design allows re-scaling to a greater number of beams and wider bandwidths.
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Ciliax, B. J., K. L. Kirk, and R. D. Leapman. "Stability of Fluorinated Organic Compounds as Measured by Parallel-Detection EELS." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 2 (August 12, 1990): 408–9. http://dx.doi.org/10.1017/s0424820100135642.
Abstract:
The use of fluorine-labelling to localize specific organic compounds at the sub-cellular level by means of electron energy loss spectroscopy (EELS) was suggested over ten years ago. Since then, however, there have been differing reports about the susceptibility of fluorinated compounds to fluorine loss in the electron beam; damage doses appear to range over several orders of magnitude. Recent advances in EELS, i.e. the availability of parallel detectors, have generated renewed interest in this labelling technique. We therefore have undertaken a more systematic study of radiation damage in a series of aromatic and aliphatic fluorinated compounds as a function of dose and temperature.Energy loss spectra were recorded using a VG Microscopes HB501 STEM equipped with a Gatan model 666 parallel-detection spectrometer. The vacuum at the specimen was better than 5×10−9 mbar and the specimen could be cooled from room temperature to 100 K. Samples were prepared by air drying thin layers of the compounds dissolved in appropriate solvents on to ˜10 nm carbon or aluminum evaporated films supported on 200 mesh copper grids.
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Lines, S., N. J. Mayne, I. A. Boutle, J. Manners, G. K. H. Lee, Ch Helling, B. Drummond, et al. "Simulating the cloudy atmospheres of HD 209458 b and HD 189733 b with the 3D Met Office Unified Model." Astronomy & Astrophysics 615 (July 2018): A97. http://dx.doi.org/10.1051/0004-6361/201732278.
Abstract:
Aims. To understand and compare the 3D atmospheric structure of HD 209458 b and HD 189733 b, focusing on the formation and distribution of cloud particles, as well as their feedback on the dynamics and thermal profile. Methods. We coupled the 3D Met Office Unified Model (UM), including detailed treatments of atmospheric radiative transfer and dynamics, to a kinetic cloud formation scheme. The resulting model self-consistently solves for the formation of condensation seeds, surface growth and evaporation, gravitational settling and advection, cloud radiative feedback via absorption, and crucially, scattering. We used fluxes directly obtained from the UM to produce synthetic spectral energy distributions and phase curves. Results. Our simulations show extensive cloud formation in both HD 209458 b and HD 189733 b. However, cooler temperatures in the latter result in higher cloud particle number densities. Large particles, reaching 1 μm in diameter, can form due to high particle growth velocities, and sub-μm particles are suspended by vertical flows leading to extensive upper-atmosphere cloud cover. A combination of meridional advection and efficient cloud formation in cooler high latitude regions, results in enhanced cloud coverage for latitudes above 30° and leads to a zonally banded structure for all our simulations. The cloud bands extend around the entire planet, for HD 209458 b and HD 189733 b, as the temperatures, even on the day side, remain below the condensation temperature of silicates and oxides. Therefore, the simulated optical phase curve for HD 209458 b shows no “offset”, in contrast to observations. Efficient scattering of stellar irradiation by cloud particles results in a local maximum cooling of up to 250 K in the upper atmosphere, and an advection-driven fluctuating cloud opacity causes temporal variability in the thermal emission. The inclusion of this fundamental cloud-atmosphere radiative feedback leads to significant differences with approaches neglecting these physical elements, which have been employed to interpret observations and determine thermal profiles for these planets. This suggests that readers should be cautious of interpretations neglecting such cloud feedback and scattering, and that the subject merits further study.
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Sahoo, M. R., A. Barik, S. Kuila, Sweta Tiwary, R. Ghosh, P. D. Babu, S. D. Kaushik, and P. N. Vishwakarma. "Magnetic and electrical transport studies of polycrystalline Sr1− x Bi x Fe12O19 (x = 0, 0.01, and 0.02)." Journal of Physics D: Applied Physics 55, no. 26 (April 4, 2022): 265001. http://dx.doi.org/10.1088/1361-6463/ac5a8d.
Abstract:
Abstract Bismuth-substituted strontium hexaferrites, Sr1−x Bi x Fe12O19 for x = 0, 0.01 and 0.02, are studied via powder neutron diffraction (ND), magnetization (M) studies, Mössbauer spectroscopy, and electrical transport. ND results show an indication of increasing Fe2+ at 12k crystallographic sites (which is supported by Mössbauer results), with increasing Bi in the sample. They also suggest an increase in strain due to Bi substitution for the polyhedral associated with 2a and 2b spin-up and 4f1 spin-down sites. The M measurements over a wide temperature range (3–823 K), shows irreversibility in zero field cooled (ZFC) and field cooled data right below the Curie temperature, along with the Hopkinson peak in the ZFC data. The temperature dependence of saturated magnetization follows the Bloch relation but that of the coercive field shows unconventional behavior. The coercive field data is fitted using an equation devised by taking into consideration of all the three anisotropies. The critical exponents at the ferromagnetic–paramagnetic phase transition boundary, calculated using modified Arrott plots, are slightly overvalued as per mean-field theory. The temperature dependence of resistivity displays nearest-neighbor hopping conduction in all the three samples. The conductivity increases with increasing Bi in the sample, due to the increasing Fe2+ content, which facilitates the electron hopping between Fe sites. The magnetoresistance measured at various sub-room temperatures for all the compounds shows the interplay of anisotropy magnetoresistance (AMR) and giant magnetoresistance (GMR). Low temperature data are dominated by GMR and gradual participation of AMR increases as room temperature is approached.
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Brand, J., J. G. A. Wouterloot, C. Codella, F. Massi, and A. Giannetti. "A multi-molecular line study of the star-forming globule CB88-230." Astronomy & Astrophysics 628 (August 2019): A98. http://dx.doi.org/10.1051/0004-6361/201935731.
Abstract:
Context. This paper relates to low-mass star formation in globules, and the interaction of newly-formed stars with their environment. We follow up on the results of our earlier observations of this globule. Aims. Our aim is to study the gas- and dust environment of the young stellar object (YSO) in globule CB88 230, the large-scale molecular outflow triggered by the jet driven by the YSO, and their interaction. Methods. We carried out submillimetre continuum and multi-line molecular observations with several single-dish facilities, mapping the core of the globule and the large-scale outflow associated with the YSO. Results. Dust continuum and molecular line maps (of 12CO, C18O, CS, CH3OH) show a flattened (axes ratio 1.5−1.7), asymmetric core with a full width at half maximum (FWHM)-diameter of 0.16−0.21 pc. Line profiles of 12CO, 13CO(2–1, 3–2), and CS(2–1) show self-absorption near the YSO; the absorption dip is at a slightly (~0.3 km s−1) redder velocity than that of the quiescent gas, possibly indicating infall of cooler envelope gas. The mass of the core, determined from C18O(1–0) observations, is about 8 M⊙, while the virial mass is in the range 5−8M⊙, depending on the assumed density distribution. We detect a slight velocity gradient (~0.98 km s−1 pc−1), though rotational energy is negligible with respect to gravitational and turbulent energy of the core. A fit to the spectral energy distribution of the core gives a dust temperature Td ≈ 18 K and a gas mass of ca. 2 M⊙ (assuming a gas-to-dust ratio of 100). More careful modelling of the sub-mm emission (not dominated by the relatively hot central regions) yields M ≈ 8M⊙. From the molecular line observations we derive gas temperatures of 10−20 K. A Bayesian analysis of the emission of selected molecules observed towards the YSO, yields Tkin ≈ 21.4 K (68% credibility interval 14.5−35.5 K) and volume density n(H2) ≈ 4.6 × 105 cm−3 (8.3 × 104−9.1 × 105 cm−3). We have mapped the well-collimated large-scale outflow in 12CO(3–2). The outflow has a dynamical age of a few 104 yr, and contains little mass (a few 10−2 M⊙). A misalignment between the axis of this large-scale outflow and that of the hot jet close to the YSO indicates that the outflow direction may be changing with time.
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Faley, Michael I., Joshua Williams, Penghan Lu, and Rafal E. Dunin-Borkowski. "TiN-NbN-TiN and Permalloy Nanostructures for Applications in Transmission Electron Microscopy." Electronics 12, no. 9 (May 8, 2023): 2144. http://dx.doi.org/10.3390/electronics12092144.
Abstract:
We fabricated superconducting and ferromagnetic nanostructures, which are intended for applications in transmission electron microscopy (TEM), in a commercial sample holder that can be cooled using liquid helium. Nanoscale superconducting quantum-interference devices (nanoSQUIDs) with sub-100 nm nanobridge Josephson junctions (nJJs) were prepared at a distance of ~300 nm from the edges of a 2 mm × 2 mm × 0.05 mm substrate. Thin-film TiN-NbN-TiN heterostructures were used to optimize the superconducting parameters and enhance the oxidation and corrosion resistance of nJJs and nanoSQUIDs. Non-hysteretic I(V) characteristics of nJJs, as well as peak-to-peak quantum oscillations in the V(B) characteristics of the nanoSQUIDs with an amplitude of up to ~20 µV, were obtained at a temperature ~5 K, which is suitable for operation in TEM. Electron-beam lithography, high-selectivity reactive ion etching with pure SF6 gas, and a naturally created undercut in the Si substrate were used to prepare nanoSQUIDs on a SiN membrane within ~500 nm from the edge of the substrate. Permalloy nanodots with diameters down to ~100 nm were prepared on SiN membranes using three nanofabrication methods. High-resolution TEM revealed that permalloy films on a SiN buffer have a polycrystalline structure with an average grain dimension of approximately 5 nm and a lattice constant of ~0.36 nm. The M(H) dependences of the permalloy films were measured and revealed coercive fields of 2 and 10 G at 300 and 5 K, respectively. These technologies are promising for the fabrication of superconducting electronics based on nJJs and ferromagnetic nanostructures for operation in TEM.
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Hasan, N., V. Ganni, A. Fila, and F. Casagrande. "Design of Cryogenic Heat Exchangers and associated Sub-Systems for Controlled Cool-down and Testing of Superconducting Magnets at FRIB." IOP Conference Series: Materials Science and Engineering 1240, no. 1 (May 1, 2022): 012063. http://dx.doi.org/10.1088/1757-899x/1240/1/012063.
Abstract:
Abstract The Facility for Rare Isotope Beams (FRIB) is a continuous wave heavy ion beam linear accelerator designed for a maximum beam energy of 400 kW and using in-flight (fragment) production and separation to generate rare isotope beams. Spatial separation of the isotopes is achieved by using superconducting magnets with a high magnetic field, large aperture, and iron-dominated core. There are a total of 14 superconducting magnets used in the fragment separator section of the facility. Designs for these magnets are relatively new, and it poses challenges in several aspects of the cryogenic design and operation such as, compact coil and cryostat design, thermal shield design, and a controlled cool-down to the operating temperature while avoiding high thermal stresses. Helically coiled finned-tube cryogenic heat exchanger designs are considered for the controlled cool-down of superconducting magnets with up to 22.4 tonnes of cold mass. These heat exchangers use liquid nitrogen cooled helium gas to cool the superconducting magnets. They demonstrate high thermal effectiveness and mechanical flexibility that are essential for the variable operating temperatures (300 – 80 K) experienced during a cool-down process. This paper presents an overview of the process design, analysis, fabrication and operation of cool-down heat exchangers and their associated sub-systems developed at FRIB.
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van der Geer, S. B., M. J. de Loos, E. J. D. Vredenbregt, and O. J. Luiten. "Ultracold Electron Source for Single-Shot, Ultrafast Electron Diffraction." Microscopy and Microanalysis 15, no. 4 (July 3, 2009): 282–89. http://dx.doi.org/10.1017/s143192760909076x.
Abstract:
AbstractUltrafast electron diffraction (UED) enables studies of structural dynamics at atomic length and timescales, i.e., 0.1 nm and 0.1 ps, in single-shot mode. At present UED experiments are based on femtosecond laser photoemission from solid state cathodes. These photoemission sources perform excellently, but are not sufficiently bright for single-shot studies of, for example, biomolecular samples. We propose a new type of electron source, based on near-threshold photoionization of a laser-cooled and trapped atomic gas. The electron temperature of these sources can be as low as 10 K, implying an increase in brightness by orders of magnitude. We investigate a setup consisting of an ultracold electron source and standard radio-frequency acceleration techniques by GPT tracking simulations. The simulations use realistic fields and include all pairwise Coulomb interactions. We show that in this setup 120 keV, 0.1 pC electron bunches can be produced with a longitudinal emittance sufficiently small for enabling sub-100 fs bunch lengths at 1% relative energy spread. A transverse root-mean-square normalized emittance of εx = 10 nm is obtained, significantly better than from photoemission sources. Correlations in transverse phase-space indicate that the transverse emittance can be improved even further, enabling single-shot studies of biomolecular samples.
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Ohno, Kazumasa, and Jonathan J. Fortney. "Nitrogen as a Tracer of Giant Planet Formation. I. A Universal Deep Adiabatic Profile and Semianalytical Predictions of Disequilibrium Ammonia Abundances in Warm Exoplanetary Atmospheres." Astrophysical Journal 946, no. 1 (March 1, 2023): 18. http://dx.doi.org/10.3847/1538-4357/acafed.
Abstract:
Abstract A major motivation of spectroscopic observations of giant exoplanets is to unveil planet formation processes from atmospheric compositions. Several recent studies suggested that atmospheric nitrogen, like carbon and oxygen, can provide important constraints on planetary formation environments. Since nitrogen chemistry can be far from thermochemical equilibrium in warm atmospheres, we extensively investigate under what conditions, and with what assumptions, the observable NH3 abundances can diagnose an atmosphere’s bulk nitrogen abundance. In the first paper of this series, we investigate atmospheric T–P profiles across equilibrium temperature, surface gravity, intrinsic temperature, atmospheric metallicity, and C/O ratio using a 1D radiative–convective equilibrium model. Models with the same intrinsic temperature and surface gravity coincide with a shared “universal” adiabat in the deep atmosphere, across a wide equilibrium temperature range (250–1200 K), which is not seen in hotter or cooler models. We explain this behavior in terms of the classic “radiative zero solution” and then establish a semianalytical T–P profile of the deep atmospheres of warm exoplanets. This profile is then used to predict vertically quenched NH3 abundances. At solar metallicity, our results show that the quenched NH3 abundance only coincides with the bulk nitrogen abundance (within 10%) at low intrinsic temperature, corresponding to a planet with a sub-Jupiter mass (≲1 M J) and old age (≳1 Gyr). If a planet has a high-metallicity (≳10× solar) atmosphere, the quenched NH3 abundance significantly underestimates the bulk nitrogen abundance at almost all planetary masses and ages. We suggest modeling and observational strategies to improve the assessment of bulk nitrogen from NH3.
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Wells, R. D., B. V. Rackham, N. Schanche, R. Petrucci, Y. Gómez Maqueo Chew, B. O. Demory, A. J. Burgasser, et al. "A large sub-Neptune transiting the thick-disk M4 V TOI-2406." Astronomy & Astrophysics 653 (September 2021): A97. http://dx.doi.org/10.1051/0004-6361/202141277.
Abstract:
Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Aims. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star’s low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models. Methods. We first infer properties of the host star by analysing the star’s near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. Results. We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties Teff = 3100 ± 75 K, M* = 0.162 ± 0.008M⊙, R* = 0.202 ± 0.011R⊙, and [Fe∕H] = −0.38 ± 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with Rp = 2.94 ± 0.17R⊕ and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3σ, prompting questions about the dynamical history of the system. Conclusions. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet’s mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population.
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Blakeley, Matthew P., Samar S. Hasnain, and Svetlana V. Antonyuk. "Sub-atomic resolution X-ray crystallography and neutron crystallography: promise, challenges and potential." IUCrJ 2, no. 4 (June 30, 2015): 464–74. http://dx.doi.org/10.1107/s2052252515011239.
Abstract:
The International Year of Crystallography saw the number of macromolecular structures deposited in the Protein Data Bank cross the 100000 mark, with more than 90000 of these provided by X-ray crystallography. The number of X-ray structures determined to sub-atomic resolution (i.e.≤1 Å) has passed 600 and this is likely to continue to grow rapidly with diffraction-limited synchrotron radiation sources such as MAX-IV (Sweden) and Sirius (Brazil) under construction. A dozen X-ray structures have been deposited to ultra-high resolution (i.e.≤0.7 Å), for which precise electron density can be exploited to obtain charge density and provide information on the bonding character of catalytic or electron transfer sites. Although the development of neutron macromolecular crystallography over the years has been far less pronounced, and its application much less widespread, the availability of new and improved instrumentation, combined with dedicated deuteration facilities, are beginning to transform the field. Of the 83 macromolecular structures deposited with neutron diffraction data, more than half (49/83, 59%) were released since 2010. Sub-mm3crystals are now regularly being used for data collection, structures have been determined to atomic resolution for a few small proteins, and much larger unit-cell systems (cell edges >100 Å) are being successfully studied. While some details relating to H-atom positions are tractable with X-ray crystallography at sub-atomic resolution, the mobility of certain H atoms precludes them from being located. In addition, highly polarized H atoms and protons (H+) remain invisible with X-rays. Moreover, the majority of X-ray structures are determined from cryo-cooled crystals at 100 K, and, although radiation damage can be strongly controlled, especially since the advent of shutterless fast detectors, and by using limited doses and crystal translation at micro-focus beams, radiation damage can still take place. Neutron crystallography therefore remains the only approach where diffraction data can be collected at room temperature without radiation damage issues and the only approach to locate mobile or highly polarized H atoms and protons. Here a review of the current status of sub-atomic X-ray and neutron macromolecular crystallography is given and future prospects for combined approaches are outlined. New results from two metalloproteins, copper nitrite reductase and cytochromec′, are also included, which illustrate the type of information that can be obtained from sub-atomic-resolution (∼0.8 Å) X-ray structures, while also highlighting the need for complementary neutron studies that can provide details of H atoms not provided by X-ray crystallography.
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Mikal-Evans, Thomas, Nikku Madhusudhan, Jason Dittmann, Maximilian N. Günther, Luis Welbanks, Vincent Van Eylen, Ian J. M. Crossfield, Tansu Daylan, and Laura Kreidberg. "Hubble Space Telescope Transmission Spectroscopy for the Temperate Sub-Neptune TOI-270 d: A Possible Hydrogen-rich Atmosphere Containing Water Vapor." Astronomical Journal 165, no. 3 (February 3, 2023): 84. http://dx.doi.org/10.3847/1538-3881/aca90b.
Abstract:
Abstract TOI-270 d is a temperate sub-Neptune discovered by the Transiting Exoplanet Survey Satellite (TESS) around a bright (J = 9.1 mag) M3V host star. With an approximate radius of 2 R ⊕ and equilibrium temperature of 350 K, TOI-270 d is one of the most promising small exoplanets for atmospheric characterization using transit spectroscopy. Here we present a primary transit observation of TOI-270 d made with the Hubble Space Telescope Wide Field Camera 3 (WFC3) spectrograph across the 1.126–1.644 μm wavelength range, and a 95% credible upper limit of 8.2 × 10−14 erg s−1 cm−2 Å−1 arcsec−2 for the stellar Lyα emission obtained using the Space Telescope Imaging Spectrograph. The transmission spectrum derived from the TESS and WFC3 data provides evidence for molecular absorption by a hydrogen-rich atmosphere at 4σ significance relative to a featureless spectrum. The strongest evidence for any individual absorber is obtained for H2O, which is favored at 3σ significance. When retrieving on the WFC3 data alone and allowing for the possibility of a heterogeneous stellar brightness profile, the detection significance of H2O is reduced to 2.8σ. Further observations are therefore required to robustly determine the atmospheric composition of TOI-270 d and assess the impact of stellar heterogeneity. If confirmed, our findings would make TOI-270 d one of the smallest and coolest exoplanets to date with detected atmospheric spectral features.
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Zani, A., F. Alessandria, A. Andreani, A. Castoldi, S. Coelli, D. Cortis, D. D’Angelo, et al. "The ASTAROTH Project: enhanced low-energy sensitivity to Dark Matter annual modulation." Journal of Physics: Conference Series 2156, no. 1 (December 1, 2021): 012060. http://dx.doi.org/10.1088/1742-6596/2156/1/012060.
Abstract:
Abstract ASTAROTH is a novel R&D project which aims at improving the physics reach of future direct dark matter detection experiments based on NaI(Tl) scintillating crystals. There is a strong need to test the long standing DAMA positive observation of an annual modulation that could be due to Dark Matter (DM), with the same target material and in a model independent way. ASTAROTH aim is the enhancement of the sensitivity to the annual modulation signal, compared with present technology, by lowering the detection energy threshold in order to observe sub-keV recoils for the first time. This can be achieved by reading the scintillation light from the NaI(Tl) crystals with arrays of Silicon PhotoMultipliers (SiPM), and placing the detectors in a cryogenic environment. SiPMs feature lower dark noise than Photomultiplier Tubes (PMTs) at T < 150 K and allow for higher light collection. The cooling medium is liquid Argon, as it is an excellent scintillator that can be instrumented to act as a veto against several backgrounds. Here we present the status of the ASTAROTH project, introducing the innovative design of the detector chamber that will be used for the demonstration of the technology. Then, we will show the preliminary results of our first ever measurements performed on a single NaI(Tl) crystal read out by one SiPM array in a cryogenic set-up cooled with liquid nitrogen.
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Sutlieff, Ben J., Alexander J. Bohn, Jayne L. Birkby, Matthew A. Kenworthy, Katie M. Morzinski, David S. Doelman, Jared R. Males, et al. "High-contrast observations of brown dwarf companion HR 2562 B with the vector Apodizing Phase Plate coronagraph." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 5, 2021): 3224–38. http://dx.doi.org/10.1093/mnras/stab1893.
Abstract:
ABSTRACT The vector Apodizing Phase Plate (vAPP) is a class of pupil plane coronagraph that enables high-contrast imaging by modifying the Point Spread Function (PSF) to create a dark hole of deep flux suppression adjacent to the PSF core. Here, we recover the known brown dwarf HR 2562 B using a vAPP coronagraph, in conjunction with the Magellan Adaptive Optics (MagAO) system, at a signal-to-noise of S/N = 3.04 in the lesser studied L-band regime. The data contained a mix of field and pupil-stabilized observations, hence we explored three different processing techniques to extract the companion, including Flipped Differential Imaging (FDI), a newly devised Principal Component Analysis (PCA)-based method for vAPP data. Despite the partial field-stabilization, the companion is recovered sufficiently to measure a 3.94 $\mu\mathrm{ m}$ narrow-band contrast of (3.05 ± 1.00) × 10−4 ($\Delta \, {\rm m}_{3.94 \mu {\rm m}}$ = 8.79 ± 0.36 mag). Combined with archival GPI and SPHERE observations, our atmospheric modelling indicates a spectral type at the L/T transition with mass M = 29 ± 15 MJup, consistent with literature results. However, effective temperature and surface gravity vary significantly depending on the wavebands considered (1200 ≤ Teff(K) ≤ 1700 and 4.0 ≤ log(g)(dex) ≤ 5.0), reflecting the challenges of modelling objects at the L/T transition. Observations between 2.4 and 3.2 $\mu\mathrm{ m}$ will be more effective in distinguishing cooler brown dwarfs due to the onset of absorption bands in this region. We explain that instrumental scattered light and wind-driven halo can be detrimental to FDI+PCA and thus must be sufficiently mitigated to use this processing technique. We thus demonstrate the potential of vAPP coronagraphs in the characterization of high-contrast substellar companions, even in sub-optimal conditions, and provide new complementary photometry of HR 2562 B.
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Hartono, Gendoet, Adjat Sudrajat, and Ildrem Syafri. "Gumuk gunung api purba bawah laut di Tawangsari - Jomboran, Sukoharjo - Wonogiri, Jawa Tengah." Indonesian Journal on Geoscience 3, no. 1 (March 28, 2008): 37–48. http://dx.doi.org/10.17014/ijog.3.1.37-48.
Abstract:
http://dx.doi.org/10.17014/ijog.vol3no1.20084This paper discusses the study on the basalt volcanic rocks and the volcano morphology indicating the existence of an ancient submarine volcano in Tawangsari-Jomboran sub-regency, Sukoharjo- Wonogiri, Central Java. In general, this basalt volcanic rocks were identified as andesite breccia which might be grouped into the Mandalika Formation of Oligosen-Miosen age (Surono et al., 1992). The origin of the Mandalika Formation in relation to the classic sedimentation process and the submarine volcanism is still needed to be evaluated. The present study was based on the detailed descriptions of the rocks both in the field and in the laboratory. The autoclastic basalt outcrops consisting of breccias show the characteristics of the igneous rock fragment component embedded in the groundmass with the same composition, namely igneous rock, dark grey to black in colour; porphyritic texture, rough surface, brecciated; pillow structures, massive, fine vesicularities, amygdaloidal filled with calcite, and radial fractures; calk-alkaline andesite composition ( SiO = 54.71% , K O = 1.15% ). This rock body attains the dimension of 2 - 5 m length, and 40 cm - 1 m in diameter with the direction of the deposition varies following the direction of the eruption source. Brecciated structures on the surface was controlled by the high cooling rate and the low flow, while the interior of the rock is massive because it was not in a direct contact to the cooler mass outside. Autoclastic basalt breccias and or the pillow basalt lava was interpreted to be formed by the undulating low gradient of morphology with the average angle of <10o. On the other hand, the low basaltic magma viscosity produced the effusive eruption related to the formation of the low angle morphology. The distance between the hills generally composed of pillow basalt is between 500 m - 1 km. The typical pillow structure of the igneous rock as described above is interpreted to be the product of the lava flow related to the effusive eruption from a submarine volcano located under or close to the seawater surface.
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Baratella, M., V. D’Orazi, K. Biazzo, S. Desidera, R. Gratton, S. Benatti, A. Bignamini, et al. "The GAPS Programme at TNG." Astronomy & Astrophysics 640 (August 2020): A123. http://dx.doi.org/10.1051/0004-6361/202038511.
Abstract:
Context. The detailed chemical composition of stars is important in many astrophysical fields, among which is the characterisation of exoplanetary systems. Previous studies seem to indicate an anomalous chemical pattern of the youngest stellar population in the solar vicinity that has sub-solar metal content. This can influence various observational relations linking the properties of exoplanets to the characteristics of the host stars, for example the giant planet-metallicity relation. Aims. In this framework, we aim to expand our knowledge of the chemical composition of intermediate-age stars and understand whether these peculiarities are real or related to spectroscopic analysis techniques. Methods. We analysed high-resolution optical and near-infrared spectra of intermediate-age stars (<700 Myr) that have been observed simultaneously with HARPS-N and GIANO-B spectrographs in GIARPS mode. To overcome issues related to the young ages of the stars, we applied a new spectroscopic method that uses titanium lines to derive the atmospheric parameters, in particular surface gravities and microturbulence velocity parameter. We derived abundances of C I, Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Cr I, Cr II, Fe I, Fe II, Ni I, and Zn I. Results. The lack of systematic trends between elemental abundances and effective temperatures validates our methods. However, we observed that the coolest stars in the sample, where Teff < 5400 K, display higher abundances for the ionised species, in particular Cr II, and for high-excitation potential C I lines. Conclusions. We found a positive correlation between the higher abundances measured of C I and Cr II and the activity index log RHK′. Instead, we found no correlations between the C abundances obtained from CH molecular band at 4300 Å and both effective temperatures and activity. Thus, we suggest that these are better estimates for C abundances in young and cool stars. Finally, we found an indication of an increasing abundance ratio [X/H] with the condensation temperature for HD 167389, indicating possible episodes of planet engulfment.
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Xi, Xiaotong, Biao Yang, Jue Wang, Liubiao Chen, and Junjie Wang. "The Low-Temperature Adsorption Characteristics of Activated Carbon With 3He and 4He as Sorption Cooler Cryogens." Journal of Thermal Science and Engineering Applications 13, no. 5 (March 16, 2021). http://dx.doi.org/10.1115/1.4050224.
Abstract:
Abstract As a commonly used sub-Kelvin refrigeration technology, helium sorption coolers play an important role in space and ground applications. The adsorption characteristics of the porous material inside the sorption cooler at low temperature have a crucial influence on its performance. At present, the analysis and calculation of sorption coolers are mainly based on helium 4 (4He) as the working gas, and there is a lack of systematic research on the low-temperature adsorption characteristics of helium-3 (3He) and its coupling effect characteristics of temperature, pressure, and mass distribution in different components. In this paper, a molecular model of activated carbon that is similar to the actual structure was constructed, and the adsorption isobars and isosteric heat of 3He and 4He at 0.8–5 K were comparatively studied based on the grand canonical Monte Carlo (GCMC) method. Besides, the influence of adsorption characteristics of 3He and 4He on the condensation efficiency, the mass distribution after condensation equilibrium, and the self-cooling loss of the sorption cooler were analyzed. The results show that for the 3He sorption cooler, the main factor affecting the condensation efficiency is the adsorbed helium in the sorption pump, while for the 4He sorption cooler, it is the adsorbed helium and the gas in the dead volume. For both 3He and 4He sorption coolers, the condensation efficiency increases as the sorption pump temperature increases or the heat sink temperature decreases, while the self-cooling loss decreases as the heat sink temperature decreases or the operating temperature increases.
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Hirose, Sakyo, Tomoyasu Usui, Takanobu Hiroto, Bhasi Nair, Xavier Moya, and Neil D. Mathur. "Large conventional and inverse electrocaloric effects in PbMg0.5W0.5O3 multilayer capacitors above and below the Néel temperature." Journal of Physics: Energy, June 7, 2023. http://dx.doi.org/10.1088/2515-7655/acdc53.
Abstract:
Abstract Bulk PbMg0.5W0.5O3 (PMW) is an antiferromagnet in which an electric field of 12 V μm-1 is sufficient to initiate a nominally reversible transition to a dipole aligned (ferroelectric) phase if operating just below the Néel temperature T N, near room temperature [J. Li et al., Adv. Funct. Mater. 31 (2021) 2101176]. Here we describe multilayer capacitors (MLCs) of PMW that permit 27 V μm-1 to be applied without breakdown. Below T N, nominally reversible initiation (completion) of the antiferroelectric ferroelectric (AF FE) transition over a wide (narrow) range of temperatures yields large inverse electrocaloric (EC) effects that peak at ΔTj ~ –2.6 K when applying 27 V μm-1 at 293 K (ΔTj denotes directly measured temperature jumps). Above T N, nominally reversible initiation of the paraelectric ferroelectric (PE-FE) transition yields large conventional EC effects that peak at ΔTj ~ +5.2 K when applying 27 V μm-1 at 302 K. This good performance near room temperature implies that MLCs of PMW could be exploited in prototype EC coolers.
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Xie, Hengli, Huaiyuan Yin, and Chunzhen Fan. "Realization of an adaptive radiative cooler with multilayer filter and VO2-based Fabry-Perot cavity." Chinese Physics Letters, March 12, 2024. http://dx.doi.org/10.1088/0256-307x/41/4/044202.
Abstract:
Abstract A high-performance adaptive radiative cooler comprising of multilayer filter and VO2-based Fabry-Perot (FP) cavity has been proposed. The bottom FP cavity adopts four layers of VO2/NaCl/PVC/Ag. Based on the phase transition of VO2, the average emissivity in the transparent window can be switched from 3.7% to 96.3%. Additionally, the average emissivity can also be adjusted with external strain to the PVC layer, providing another way to attain the desired cooling effect. The upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window. At high temperature, the adaptive emitter automatically activates radiative cooling. The net cooling power is up to 156.4 W/m2 at an ambient temperature of 303 K. Our adaptive emitter still exhibits stable selective emissivity at different incident angle and heat transfer coefficient. At low temperature, the radiative cooling automatically deactivates, and the average emissivity decreases to only 3.8%. Therefore, our work not only provides new insights into the design of high-performance adaptive radiative coolers, but also advances the development of intelligent thermal management.
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Guo, Yuefeng, Xingkang Su, Guan Wang, Xianwen Li, and Long Gu. "Numerical Study of Turbulent Heat Transfer of Annular Fuel Assembly in a Sodium-cooled Fast Reactor by a SST k-ω-k θ -ε θ Model." Journal of Nuclear Science and Technology, February 5, 2024. http://dx.doi.org/10.1080/00223131.2024.2310563.
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Unnikrishnan, Govind, Michael Gröbner, and Hanns-Christoph Nägerl. "Sub-Doppler laser cooling of $^{39}$K via the 4S$\to$5P transition." SciPost Physics 6, no. 4 (April 18, 2019). http://dx.doi.org/10.21468/scipostphys.6.4.047.
Abstract:
We demonstrate sub-Doppler laser cooling of ^{39}39K using degenerate Raman sideband cooling via the 4S_{1/2} \rightarrow1/2→5P_{1/2}1/2 transition at 404.8 nm. By using an optical lattice in combination with a magnetic field and optical pumping beams, we obtain a spin-polarized sample of up to 5.6 \times 10^{7}5.6×107 atoms cooled down to a sub-Doppler temperature of 4 \upmuμK, reaching a peak density of 3.9 \times 10^{9}3.9×109 atoms/cm^{3}3, a phase-space density greater than 10^{-5}10−5, and an average vibrational level of \langle \nu \rangle=0.6⟨ν⟩=0.6 in the lattice. This work opens up the possibility of implementing a single-site imaging scheme in a far-detuned optical lattice utilizing shorter wavelength transitions in alkali atoms, thus allowing improved spatial resolution.
50
Yuan Hong-Rui, Liu Tao, Zhu Tian-Xin, Liu Yun, Li Xiang, Chen Yang, and Duan Chuan-Xi. "High-resolution jet-cooled laser absorption spectroscopy of SF<sub>6</sub> at 10.6 μm." Acta Physica Sinica, 2023, 0. http://dx.doi.org/10.7498/aps.72.20222285.
Abstract:
Sulfur hexafluoride (SF<sub>６</sub>) is a greenhouse gas of very long lifetime. Its infrared absorption spectrum is very important for modeling the atmospheric radiation balances. SF<sub>６</sub> is also a prototypical system for studying the principles and techniques of laser isotope separation using powerful infrared lasers. As a very heavy molecule, the infrared spectrum of SF<sub>６</sub> at room temperature is very dense, which poses a great challenge for monitoring the relative abundances of different SF<sub>６</sub> isotopomers by direct absorption spectroscopy. Supersonic jet expansions have been used widely to simplify gas phase molecular spectra. In this work, astigmatic multi-pass absorption cell and distributed feed-back quantum cascade lasers (QCLs) are used to measure jet-cooled rovibrational absorption spectrum of <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> at 10.6 μm. The spectrometer works in a segmented rapid-scan mode. The gas mixtures (SF<sub>6</sub>:Ar:He = 0.12:1:100) are expanded through a 80 mm×300 μm pulsed slit nozzle. Two QCLs running at room temperature are used and each one covers a spectral range of about 3.0 cm<sup>-1</sup>. The <i>v</i><sub>3</sub> fundamental bands of both <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> are observed. The rotational temperature of <sup>32</sup>SF<sub>６</sub> and <sup>33</sup>SF<sub>６</sub> in the ground state in the supersonic jet is estimated to be about 10 K and the linewidth is about 0.0008 cm<sup>-1</sup> by comparing the simulated and observed spectrum with the PGOPHER program. A new weak vibrational band centered around 941.0 cm<sup>-1</sup> is observed and tentatively assigned to the <i>v</i><sub>1</sub>+<i>v</i><sub>2</sub>+<i>v</i><sub>3</sub>-(<i>v</i><sub>1</sub>+<i>v</i><sub>2</sub>)hot band of <sup>32</sup>SF<sub>６</sub>. The effective Hamiltonian used to analyze the rovibrational spectrum of SF<sub>６</sub> is briefly introduced. A simplified rotational analysis for this hot band is performed with the XTDS program developed by the Dijon group. The band-origin of this hot band is determined to be 941.1785(21) cm<sup>-1</sup>. The rotational temperature of this hot band is estimated to be about 50 K. A new scheme by measuring the jet-cooled absorption spectrum of this hot band of <sup>32</sup>SF<sub>6</sub> and the <i>v</i><sub>3</sub> fundamental band of <sup>33</sup>SF<sub>６</sub> is proposed for measuring the relative abundance of <sup>33</sup>SF<sub>６</sub>／<sup>32</sup>SF<sub>６</sub>.