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The Cryogenic AntiCoincidence Detector for ATHENA X-IFU: Improvement of the Test Setup Toward the Demonstration Model
摘要： The ATHENA X-IFU development program foresees to build and characterize an instrument Demonstration Model (DM), in order to probe the system critical technologies before the mission adoption. In this respect, we are now developing the DM of the X-IFU Cryogenic AntiCoincidence Detector (CryoAC), which will be delivered to the Focal Plane Assembly development team for the integration with the TES array. Before the delivery, we will characterize and test the CryoAC DM in our CryoLab at INAF/IAPS. In this paper, we report the main results of the activities performed to improve our cryogenic test setup, making it suitable for the DM integration. These activities mainly consist in the development of a mechanical setup and a cryogenic magnetic shielding system, whose effectiveness has been assessed by FEM simulations and a measurement at warm. The preliminary performance test has been performed by means of the last CryoAC single-pixel prototype, the AC-S8 pre-DM sample.
关键词： Magnetic shielding,AntiCoincidence detectors,ATHENA,X-rays: detectors
更新于2025-09-04 15:30:14
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Reference Module in Materials Science and Materials Engineering || Compton Scattering
摘要： Compton effect which was invented by Arthur Holly Compton (Compton, 1923a,b) was a milestone in the development of quantum mechanics. In 1929, DuMond and collaborators (DuMond, 1929) firstly explained the shape of Compton profile of beryllium within the Fermi–Dirac statistics. After that a couple of basic studies on Compton profiles and the electron momentum densities were performed in the 1930s (DuMond and Kirkpatrick, 1930). With the development of new generation of photon detectors, this technique was re-established in the mid-1960s. Several reviews on development of this technique are available in literature (Williams, 1977; Cooper, 1985; Lovesey and Collins, 1995; Cooper et al., 2004; Schülke, 2007; Ahuja, 2010). With the advent of third generation synchrotron radiation (SR) sources along with the further improvement in the detector technology, Compton scattering (CS) is now established as a well recognized tool to study electronic properties of variety of materials. Even CS is being employed to study the magnetic behavior of materials using circularly polarized SRs.
关键词： electronic properties,Compton Scattering,synchrotron radiation,magnetic behavior
更新于2025-09-04 15:30:14
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Frequency rising sub-THz emission from solar flare ribbons
摘要： Observations of solar ?ares at sub-THz frequencies (millimetre and sub-millimetre wavelengths) over the last two decades often show a spectral component rising with frequency. Unlike a typical gyrosynchrotron spectrum decreasing with frequency or a weak thermal component from hot coronal plasma, the observations can demonstrate a high ?ux level (up to ～104 solar ?ux units at 0.4 THz) and fast variability on sub-second timescales. Although, many models have been put forward to explain the puzzling observations, none of them has clear observational support. Here we propose a scenario to explain the intriguing sub-THz observations. We show that the model, based on free-free emission from the plasma of ?are ribbons at temperatures 104?106 K, is consistent with all existing observations of frequency-rising sub-THz ?are emission. The model provides a temperature diagnostic of the ?aring chromosphere and suggests fast heating and cooling of the dense transition region plasma.
关键词： Sun: ?ares,Sun: radio radiation,Sun: activity,Sun: chromosphere,Sun: magnetic ?elds,Sun: X-rays, gamma rays
更新于2025-09-04 15:30:14
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Physical nature of electrically detected magnetic resonance through spin dependent trap assisted tunneling in insulators
摘要： We show that electrically detected magnetic resonance (EDMR), through spin dependent trap assisted tunneling (SDTT) in amorphous SiC, exhibits approximately equal amplitudes at very high (8.5 T) and very low (0.013 T) magnetic fields at room temperature. This result strongly supports an SDTT/EDMR model in which spins at two nearby sites involved in a tunneling event are coupled for a finite time in circumstances somewhat analogous to spin pair coupling in the spin dependent recombination/EDMR model of Kaplan, Solomon, and Mott (KSM) [Kaplan, Solomon, and Mott, J. Phys. Lett. 39, 51 (1978)]. Since a comparable near zero magnetic field change in resistance is also observed in these samples, our results support the idea that this magnetoresistance response is also the result of a KSM-like mechanism involving SDTT. Additionally, we observe a large enhancement in SDTT/EDMR at high field (8.5 T) for temperatures below 50 K, which suggests the potential utility of SDTT in spin based quantum computation and other spintronic applications.
关键词： spin dependent trap assisted tunneling,electrically detected magnetic resonance,spintronics,amorphous SiC,magnetoresistance
更新于2025-09-04 15:30:14
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Modification of GaN thin film on sapphire substrate optical properties under weak magnetic fields
摘要： We present a study of the modifications to the optical transmittance of GaN thin film on sapphire substrate due to weak magnetic field (WMF) treatment. Measurements were performed in the 320-1100 nm wavelength range at 300 K, evidencing a change in transmission spectra for wavelengths above 700-800 nm after the WMF treatment. We use a model with three layers to simulate transmittance spectra. We have found that changes of the optical thickness induced by WMF are not sufficient to explain discrepancies between experimental and simulated spectra. To obtain a complete agreement it is necessary to consider a change in the refractive index of GaN and/or in the reflection coefficients for the interface air-GaN. We interpret such WMF-related effects as due to the diffusion of point defects after dissolution of metastable complexes from inner boundaries to surface of the structure. These defects modify optical properties of the GaN film.
关键词： reflectance,transmittance,weak magnetic field,gallium nitride
更新于2025-09-04 15:30:14
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High resolution VLBI polarization imaging of AGN with the maximum entropy method
摘要： Radio polarization images of the jets of Active Galactic Nuclei (AGN) can provide a deep insight into the launching and collimation mechanisms of relativistic jets. However, even at VLBI scales, resolution is often a limiting factor in the conclusions that can be drawn from observations. The maximum entropy method (MEM) is a deconvolution algorithm that can outperform the more common CLEAN algorithm in many cases, particularly when investigating structures present on scales comparable to or smaller than the nominal beam size with ‘super-resolution’. A new implementation of the MEM suitable for single- or multiple-wavelength VLBI polarization observations has been developed and is described here. Monte Carlo simulations comparing the performances of CLEAN and MEM at reconstructing the properties of model images are presented; these demonstrate the enhanced reliability of MEM over CLEAN when images of the fractional polarization and polarization angle are constructed using convolving beams that are appreciably smaller than the full CLEAN beam. The results of using this new MEM software to image VLBA observations of the AGN 0716+714 at six different wavelengths are presented, and compared to corresponding maps obtained with CLEAN. MEM and CLEAN maps of Stokes I, the polarized flux, the fractional polarization and the polarization angle are compared for convolving beams ranging from the full CLEAN beam down to a beam one-third of this size. MEM’s ability to provide more trustworthy polarization imaging than a standard CLEAN-based deconvolution when convolving beams appreciably smaller than the full CLEAN beam are used is discussed.
关键词： techniques: high angular resolution,BL Lacertae objects: individual: 0716+714,techniques: image processing,galaxies: magnetic fields,galaxies: active
更新于2025-09-04 15:30:14
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Molecular beam epitaxy growth of Mn4?Ni N thin films on MgO(0?0?1) substrates and their magnetic properties
摘要： We grew Mn4?xNixN epitaxial thin ?lms on MgO(0 0 1) by molecular beam epitaxy, as well as studied their crystalline qualities and magnetic properties. The ?lms were decomposed into Ni8N or Mn-Ni alloys when x ≥ 2, as con?rmed by X-ray di?raction and re?ection high-energy electron di?raction, but this decomposition was mitigated by reducing the substrate growth temperature. The lattice constants decreased with increased Ni substitution except when the Mn ratio was high, while the crystal orientation tended to degrade. The magnetic properties were measured via vibrating sample magnetometer, and it was found that the saturation magneti- zation (MS) and perpendicular magnetic anisotropy (PMA) diminished with a small amount of Ni substitution. Speci?cally, the MS value was remarkably decreased from 86.3 ± 1.1 emu/cm3 (Mn4N) to 19.0 ± 0.5 emu/cm3 (Mn3.85Ni0.25N), and the magnetic anisotropy constant was decreased from approximately 0.94–0.027 Merg/ cm3, respectively. The PMA vanished with further Ni substitution. Ultimately, a small MS and a PMA were simultaneously achieved with a small amount of Ni substitution. These properties support spin transfer torque, which can be applied to the emerging non-volatile memory devices using domain wall motion.
关键词： A3. Molecular beam epitaxy,A1. Crystal structure,B1. Mn4N,B2. Magnetic materials,B1. MgO,B1. Ni4N
更新于2025-09-04 15:30:14
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Synthesis and characterizations of a novel CoFe2O4@CuS magnetic nanocomposite and investigation of its efficiency for photocatalytic degradation of penicillin G antibiotic in simulated wastewater
摘要： In the present study, efficiency of a new magnetic nanocomposite (CoFe2O4@CuS) for photocatalytic degradation of PG in aqueous solutions was investigated. Structural characteristics of synthesized magnetic nanoparticles were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), Thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), Energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. Also, the effect of important parameters such as pH (3–11), nanoparticle dosage (0.1-0.8 g/L), PG concentration (10–100 mg/L) and contact time (10–120 min) were investigated. Results of FT-IR, XRD, EDX and Raman analyses showed successful synthesis of CoFe2O4@CuS magnetic nanocomposite. SEM and TEM images showed that the size of CoFe2O4@CuS magnetic nanocomposite was below 100 nm. Also, results of VSM analyses showed that CoFe2O4@CuS magnetic nanocomposite still has magnetic properties (Ms = 7.76 emu/g). According to the results of study, in photocatalytic degradation process of PG by CoFe2O4@CuS magnetic nanocomposite by UV light and in optimum condition (pH = 5, nanocomposite dose: 0.2 g/L, PG concentration: 10 mg/L and contact time: 120 min), maximum degradation of PG was 70.7%. Also the photocatalytic reaction almost followed the pseudo-first order kinetics. In addition, after five consecutive runs, the catalyst efficiency wasn't reduced significantly.
关键词： CoFe2O4@CuS,Magnetic nanocomposite,Penicillin G,Antibiotic
更新于2025-09-04 15:30:14
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Differential quenching of the angular momentum of the B and Q bands of a porphyrin as a result of extended ring π-conjugation
摘要： A novel porphyrin, whose p-system has been extended via the presence of two additional carbon–carbon triple bonds on opposite meso-positions and by fusion of a single naphthalene unit simultaneously bridging the third meso-position and the b-carbon of one of the pyrroles, has been synthesized in good yield. Absorption, magnetic circular dichroism, emission, and theoretical spectra are reported for the fused and unfused trans-naphthalene free base and zinc porphyrins. The fusing of one of the naphthalene moieties results in significant changes to the absorption spectrum and, very unusually, the bridged meso-b-pyrrole fusion results in quenching of the MCD Faraday pseudo-A term in the porphyrin’s B band (S2). This unique effect was interpreted as resulting from the origin of the electronic structure of the second excited state (the B state). The x and y polarizations are completely mixed by the electronic effects of the non-symmetric extended conjugation of the p ring. Analysis of the origin of the MCD signal indicates that the presence of this novel mixed polarization leads to negligible angular momentum in the important B state. To our knowledge, this is the first report in which the magnetic moment in a porphyrin’s intensely absorbing B band has been quenched while the angular momentum in the Q band, the first excited state, remains as normal. This implies that the photophysical properties of the B state are likely very different than those of the Q state, which has novel and significant implications for applications, especially in non-linear spectroscopy.
关键词： TD-DFT calculations,Extended porphyrin,Magnetic Circular Dichrosim (MCD),Q band,B band,angular momentum
更新于2025-09-04 15:30:14
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Tailoring the Linear and Second-Order Nonlinear Optical Responses of the Titanium-MIL-125 Metal-Organic Framework through Ligand Functionalization: A First Principles Study
摘要： Density functional theory calculations have been performed to investigate the linear and second order nonlinear optical (NLO) properties of titanium-based MIL-125 metal-organic frameworks in crystalline form, in which the 1,4-benzene-dicarboxylate (BDC) linkers are modified by introducing different functional groups or by extending BDC ligand to contain two (MIL-126) and three (MIL-127) benzene rings. Our results reveal that the functionalization of BDC linker tends to increase the dielectric constants and the magnitude of birefringence of MIL-125, especially for the aminated derivatives. Correspondingly, the incorporation of substituent group will improve the phase matching performance of MIL-125. As for the second harmonic generation (SHG) susceptibility, the SHG activity of the pristine MIL-125 is comparable to KDP, which can be attributed mostly to the contributions of TiO5(OH) octahedra. It is noted that after introducing substituent group into BDC linker, the organic part will have a remarkable influence on the SHG intensity. However, the specific effect on the NLO response is dependent on the type of functional group incorporated into BDC ligand, and only the inclusion of amine group that is strongly electron-donating can obviously enhance the SHG activity of MIL-125. In addition, MIL-126 and MIL-127 with longer aromatic linking unit are not suitable to act as NLO materials due to their poor phase matching abilities, but they are the promising candidates for the low dielectric constant materials. The present study can provide theoretical insights to design new second-order NLO materials based on MIL-125.
关键词： Nonlinear Optical Properties,Density Functional Theory,Hybrid Materials,Ligand Functionalization,Metal-Organic Framework,Plasmonics,Optical,Magnetic
更新于2025-09-04 15:30:14