Excitation Temperature Research Articles

Luminescence and energy transfer of Ce3+, Eu2+ co-doped Ba2Mg(BO3)2 for potential anti-counterfeiting applications

The phosphors Ba2Mg(BO3)2 activated with Ce3+ and Eu2+ ions are prepared by a solid-state reaction method at high-temperature and the Rietveld structure refinement of the host compound is performed. The synchrotron radiation VUV - UV excitation, UV – vis emission and luminescence decay spectra, as well as the dependencies of luminescence intensity and lifetime on doping content and temperature are systematically investigated. In addition, the electron-vibrational interaction (EVI) of Eu2+ ions with coordination surroundings and the Ce3+→Eu2+ energy transfer (ET) dynamics are studied in detail. Based on above discussion, the potential applications of co-doped phosphors in excitation wavelength and temperature dual-response optical anti-counterfeiting are demonstrated.

Influence of silicon particle morphology on laser-induced plasma properties

In this work, Si particles of varying sizes and a bulk Si wafer are exposed to high-energy nanosecond-pulsed laser excitation. The subsequent laser-induced plasma is characterized using a suite of diagnostic techniques, including spatiotemporal species imaging via high-speed videography and high-resolution gated spectroscopy. The intensity and location of various species in the plasma (e.g., Si I and Si II) are tracked as a function of time over two time regimes, 2–10 μs and 20–80 μs, and show differences in impurities and peak intensities between the various particle sizes and compared to the Si wafer. Electron densities under these conditions decrease from ≈1.8 to 0.8 × 1017 cm−3 from 2 to 8 μs, while plasma excitation temperatures determined from the Boltzmann method range from 9200 to 8000 K over the same time window. The powdered Si samples have characteristically larger and more intense plasmas than the wafer sample. The laser-induced air-shock from energetic materials (LASEM) method was employed on these materials, in concert with their acoustic response, to establish their relative microsecond energy releases. While the powders have similar laser-induced shock velocities, they appear to have differences in their acoustic response which roughly scales as a function of plasma carbon content. The proposed reasons for these shock and acoustic trends are discussed, which include particle size and morphology, surface impurities, and dispersion and flow within the plasma.

N-bearing complex organics toward high-mass protostars

Context. Complex organic species are known to be abundant toward low- and high-mass protostars. No statistical study of these species toward a large sample of high-mass protostars with the Atacama Large Millimeter/submillimeter Array (ALMA) has been carried out so far. Aims. We aim to study six N-bearing species: methyl cyanide (CH3CN), isocyanic acid (HNCO), formamide (NH2CHO), ethyl cyanide (C2H5CN), vinyl cyanide (C2H3CN) and methylamine (CH3NH2) in a large sample of line-rich high-mass protostars. Methods. From the ALMA Evolutionary study of High Mass Protocluster Formation in the Galaxy survey, 37 of the most line-rich hot molecular cores with ~1" angular resolution are selected. Next, we fit their spectra and find column densities and excitation temperatures of the N-bearing species mentioned above, in addition to methanol (CH3OH) to be used as a reference species. Finally, we compare our column densities with those in other low- and high-mass protostars. Results. CH3OH, CH3CN and HNCO are detected in all sources in our sample, whereas C2H3CN and CH3NH2 are (tentatively) detected in ~78 and ~32% of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH2CHO; Tex ≳ 250 K), warm (C2H3CN, HN13CO and CH313CN; 100 K ≲ Tex ≲ 250 K) and cold species (CH3OH and CH3NH2; Tex ≲ 100 K). This temperature segregation reflects the trend seen in the sublimation temperature of these molecules and validates the idea that complex organic emission shows an onion-like structure around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor ~3 around the mean. Conclusions. The constant column density ratios point to a common formation environment of complex organics or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars (within factors ~2–3).

A Large (≈ 1 pc) Contracting Envelope Around the Prestellar Core L1544* *This work is based on observations carried out with the IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Prestellar cores, the birthplace of Sun-like stars, form from the fragmentation of the filamentary structure that composes molecular clouds, from which they must inherit at least partially the kinematics. Furthermore, when they are on the verge of gravitational collapse, they show signs of subsonic infall motions. How extended these motions are, which depends on how the collapse occurs, remains largely unknown. We want to investigate the kinematics of the envelope that surrounds the prototypical prestellar core L1544, studying the cloud-core connection. To our aims, we observed the HCO+ (1–0) transition in a large map. HCO+ is expected to be abundant in the envelope, making it an ideal probe of the large-scale kinematics in the source. We modeled the spectrum at the dust peak by means of a nonlocal thermodynamical equilibrium radiative transfer. In order to reproduce the spectrum at the dust peak, a large (∼1 pc) envelope is needed, with low density (tens of cm−3 at most) and contraction motions, with an inward velocity of ≈ 0.05 km s−1. We fitted the data cube using the Hill5 model, which implements a simple model for the optical depth and excitation temperature profiles along the line of sight, in order to obtain a map of the infall velocity. This shows that the infall motions are extended, with typical values in the range 0.1–0.2 km s−1. Our results suggest that the contraction motions extend in the diffuse envelope surrounding the core, which is consistent with recent magnetic field measurements in the source, which showed that the envelope is magnetically supercritical.

A Multiwavelengh study towards Galactic HII region G10.32-0.26

AbstractWe present the results of high-resolution continuum and molecular line observations towards the Galactic HII region, G10.32-0.26. The continuum map with ALMA reveals the five cores with masses ranging from 2.5–9.2 Me. The results show that the brightest peak, Peak 1, is an HCHII region with an excitation temperature of : 12000 K, an electron density of 3.4×107 cm3, and a radius of 14 au. The central object is estimated to be a B0.5 star. The class II 6.7 GHz CH3OH maser coincides with Peak 1, implying class II CH3OH maser is associated with a later evolutionary stage of star formation. Using KaVA and KVN observation, we detect the class I 44 and 95 GHz CH3OH masers near the weakest peak, Peak 5. We successfully imaged class I 95 GHz CH3OH masers with VLBI for the first time. In Peak 5, the high-velocity SiO emission also exists. The continuum emission can be modelled with grey-body dust emission with Td∼30 K, and the molecular species are poor near Peak 5, suggesting Peak 5 is in an early stage of star formation.

The Study of the Influence of Temperature and Low Frequency on the Performance of the Laminated MFC Piezoelectric Energy Harvester

MFC (Microfiber composite) piezoelectric transducers are one of the smart composite materials used among others in alternative energy sources and autonomous wireless sensors which exploit vibrational energy. This work presents the theoretical and experimental investigations of the integration of MFC piezoelectric transducers on epoxy glass fiber composite material and explores the capacity of power generation based on a variety of ambient temperatures and frequencies. The study examined the use of ambient vibrational energy to power small electronic devices of wireless sensor networks which eliminates the need for external power, periodic battery replacement costs, and chemical waste from conventional batteries. The test was conducted using a laboratory stand equipped with a thermal chamber and an Instron ElectroPulse waveform generator which induces a concentric cyclic load to the laminated beam. Laminated MFC was loaded with a low–frequency range, controlled displacement under different moderate temperatures. The test was conducted at temperatures ranging from 25 to 60 degrees Celsius and at frequencies ranging from 5 to 25 Hz. The results show that the voltage generated by the transducer is highly affected by both temperature and frequency of excitation.

Emission enhancement in laser-induced breakdown spectroscopy from sample heating with a continuous-wave diode laser

In this work an affordable, energy-efficient technique to enhance the sensitivity of the laser-induced breakdown spectroscopy technique is presented. This method is based in applying the beam of a continuous wave (CW) diode laser into the spot where the focused beam of a pulsed Nd:YAG, high-power laser induces the plasma. With the present set-up the CW beam heats the sample's surface to 300 °C. It was found that pre-heating the target in this way increased the line intensity of both neutrals and ions by a factor of up to 4.5. It was also found that the plasma excitation temperature and the electron density of the heated sample did not differ significantly from those at room temperature. However the amount of ablated material did change significantly when the sample was heated, with the crater in the latter case as much as 8.9 times larger than that obtained at ambient temperature. We conclude that the intensification in the pre-heated-sample case stems not from increased electronic plasma density or temperature but rather from a larger plume size resulting from an increased amount of ablated material when the target is heated.

The effect of scattering calculations on non-LTE modelling of the C3O and C5O abundances in TMC-1

ABSTRACT Tricarbon and pentacarbon monoxides have been detected towards the Taurus Molecular Cloud (TMC-1) with relatively important abundances. Understanding the chemical formation of these molecules requires interpreting their observational spectra by mean of non-local thermodynamical equilibrium modelling. For this purpose, we report rate coefficients of C3O and C5O induced by collision with He for temperatures up to 100 K. These data are obtained by calculating inelastic cross sections for the 31 low-lying rotational levels of C3O and C5O using the close-coupling approach. The comparison of the new rate coefficients with those of HC3N and HC5N, previously used to interpret the observational spectra of C3O and C5O, reveals differences of up to an order of magnitude. The effect of the new collisional rate coefficients in radiative transfer calculations is checked by computing the excitation temperatures for some transitions and simulating the C3O and C5O column densities observed towards TMC-1. Our findings suggest that the use of HCnN as template for CnO may lead to local thermodynamic equilibrium conditions for gas densities as low as ∼103 cm−3. Regarding the interpretation of the observational spectra, using radiative transfer modelling based on the actual CnO collisional rate coefficients instead of rotational diagram analysis leads to underestimate the column densities reported in the literature by up to 25 per cent and accordingly the C3O/ C5O abundance ratio by up to 50 per cent. We expect that the new rate coefficients and the radiative transfer calculations presented in this work will encourage further modellings of the CnO abundance and accordingly constrain the chemistry.

Sequence-specific eDNA extraction using hydrophobic magnetic ionic liquids attached with oligonucleotide strand

Isolation of high-purity nucleic acids, especially sequence-specific DNA, from complex samples is critical to the downstream nucleic acid analysis. In this work, an oligonucleotide strand-attached magnetic ionic liquid (OSMIL) was designed and prepared for DNA extraction. The attached oligonucleotide strand has a sequence complementary to that of a specific DNA to be extracted. The OSMIL has good hydrophobicity and magnetic response properties. At the extraction temperature, OSMIL was in a liquid state, which was favorable for maximizing the adsorption of DNA; while at the separation temperature, OSMIL was in a solid state (with an average particle size of 897 nm) and could be attracted by an external magnet in 3s, which was favorable for the separation and recovery of DNA. The sequence-specific DNA extraction process with OSMIL is simple and fast. After extraction, the DNA-enriched OSMILs were quickly attracted and separated by an external magnetic field. The extracted DNA was evaluated by a NanoDrop (wavelength detection at 260–280 nm) and the OSMIL can be recycled and reused. The enrichment factor was 0.81. Through single-factor experimental analysis, the effects of OSMIL extraction volume, thermal excitation temperature, thermal excitation time, pH, and other factors on the DNA extraction process were systematically investigated. The RSD of repeatability experiment was 1.19% (n = 3), showing the method has good repeatability. The extraction method presented here has been shown to extract DNA with specific sequences from mixtures containing DNA of different sequences and from mixtures containing proteins, respectively. In addition, the OSMIL has been applied to extract target environmental DNA with specific sequences from different water environments with high extraction efficiency. In the long run, OSMIL has great potential for identifying existing organisms in environmental samples or exploring unknown organisms.

Rare earth effect on laser produced plasma dynamics during pulsed laser deposition of doped cobalt ferrite

The addition of rare earth elements the ferrites can lead to significant changes in structural, magnetic and electric properties of bulk materials and also of thin films deposited by pulsed laser deposition. The present study relies on the analysis of the laser induced plasma of three sets of cobalt ferrite targets doped with various concentrations of RE elements (Dy, Gd, Yb) and proposes a correlation of the derived results with structural investigations of the films obtained during the same experiment. ICCD imaging and space-and time-resolved optical emission spectroscopy techniques were used to obtain information on the dynamics and excitation temperatures of various species found in the laser produced plasmas (LPP). Initial investigations on the global behavior of the LPP revealed that the addition of RE reduced the drift velocities of the formed plasma structures, the lowest ones being observed for the targets doped with the heaviest RE (Yb). Space-and time-resolved spectroscopy measurements applied for all main elements (Fe, Co and RE - both neutral and ionic species) showed a complex dynamic system, with decreased/increased kinetic energies for neutrals/ions at high dopant concentrations, suggesting a possible re-sputtering effect at the films surface. The individual excitation temperatures of the main elements derived from Boltzmann plots increased as the RE content was augmented via radiative collision events due to their larger diameters compared with Co, Fe or O. The spatial distribution of electron temperature can be explained by the charge separation occurring with the addition of RE in the investigated systems.

Multiple gas phases in supernova remnant IC 443: mapping shocked H2 with VLT/KMOS

ABSTRACT Supernovae and their remnants provide energetic feedback to the ambient interstellar medium (ISM), which is often distributed in multiple gas phases. Among them, warm molecular hydrogen (H2) often dominates the cooling of the shocked molecular ISM, which has been observed with the H2 emission lines at near-infrared wavelengths. Such studies, however, were either limited in narrow filter imaging or sparsely sampled mid-infrared spectroscopic observations with relatively poor angular resolutions. Here we present near-infrared (H and K bands) spectroscopic mosaic observations towards the A, B, C, and G regions of the supernova remnant (SNR) IC 443, with the K-band Multi-Object Spectrograph (KMOS) onboard the Very Large Telescope (VLT). We detected 20 rotational–vibrational transitions of H2, one H line (Brγ), and two [Fe ii] lines, which dominate broad-band images at both H and K bands. The spatial distribution of H2 lines at all regions is clumpy on scales from ∼0.1 down to ∼0.008 pc. The fitted excitation temperature of H2 is between 1500 and 2500 K, indicating warm shocked gas in these regions. The multigas phase comparison shows stratified shock structures in all regions, which explains the coexistence of multiple types of shocks in the same regions. Lastly, we verify the candidates of young stellar objects previously identified in these regions with our spectroscopic data, and find none of them are associated with young stars. This sets challenges to the previously proposed scenario of triggered star formation by SNR shocks in IC 443.

Star and Cluster Formation in the Sh2-112 Filamentary Cloud Complex

We present the star formation activity around the emission nebula Sh2-112. At a distance of ∼2.1 kpc, this H ii complex, itself 3 pc in radius, is illuminated by the massive star (O8 V) BD+45 3216. The associated molecular cloud extends in angular scales of 2.°0 × 0.°83, corresponding to linear sizes of 73 pc by 30 pc, along the Galactic longitude. The high-resolution (30″) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of A V ∼ 2.78 mag, varying up to a maximum of ∼17 mag. Our analysis led to identification of a rich population (∼500) of young (average age of ∼1 Myr) stars, plus a numerous number (∼350) of Hα emitters, spatially correlated with the filamentary clouds. Located near the edge of the cloud, the luminous star BD+45 3216 has created an arc-like pattern as the ionizing radiation encounters the dense gas, forming a blister-shaped morphology. We found three distinct young stellar groups, all coincident with relatively dense parts of the cloud complex, signifying ongoing star formation. Moreover, the cloud filament (excitation temperature ∼10 K) traced by the CO isotopologues and extending nearly ∼80 pc is devoid of ionized gas except at the dense cores (excitation temperature ∼28–32 K) wherein significant ionized emission excited by OB stars (dynamical age ∼0.18–1.0 Myr) pertains. The radial velocity is dynamic (median ∼−3.65 km s−1) along the main filament, increasing from Galactic east to west, indicating mass flow to form the massive stars/clusters at the central hubs.

Investigation on spheroidization of refractory tungsten powders by laminar DC plasma torch

The spherical tungsten powders were prepared by a low-power DC laminar plasma torch. At a discharge current of 50 A, the tungsten powder fed downstream cannot be spheroidized by using Ar discharge, while a small number of spherical particles can be observed with upstream feeding. When N2 is added to the working gas, the input power is increased to maintain the same discharge current, which leads to the increase of plasma jet length, thereby expanding the effective high temperature region. Optical emission spectroscopy measurements show that the electron excitation temperature of N2-Ar mixed discharge is higher than that of argon discharge. In addition, compared with argon plasma, N2-Ar mixed gas plasma has larger thermal conductivity due to the molecular dissociation. Therefore, the heat is more efficiently transferred from the plasma to the tungsten particles. The improvement of plasma jet and heat transfer characteristics by introducing nitrogen into the discharge contributes to the increase of spheroidization rate. EDS analysis shows that the oxygen content in the tungsten particles decreases after spheroidization, which is caused by the evaporation of tungsten oxide during plasma treatment.

Study of the type-I to type-II band alignment transition in InAs(Sb)/GaAs quantum dot nanostructures

InAs(Sb)/GaAs self-assembled quantum dots (QDs) were grown by molecular beam epitaxy though incorporating Sb into InAs with increased beam equivalent pressure ratio, x = Sb2/(Sb2+As2), of x = 0, 0.15, 0.25, and 0.5. From photoluminescence measurements, we observed a transition of the band alignment from type-I for the InAs QDs to type-II for InAsSb QDs. Thus, after adding Sb into the QDs these type II InAsSb QDs have different characteristics from the well-studied type-I InAs QDs regarding to their excitation intensity dependence, temperature dependence, and time dependence of the luminescence. Additionally, the Sb distribution in the QDs and the wetting layer was studied. These results indicate that we are able to fabricate InAsSb QDs with a type II band alignment, which may be good optical materials for the development of intermediate-band photovoltaic cells.

Impact of Excitation Intensity-Dependent Fluorescence Intensity Ratio of Upconversion Nanoparticles on Wide-Field Thermal Imaging

Erbium ion (Er3+)-doped upconversion nanoparticles (UCNPs) are frequently used for nanothermometry because their fluorescence intensity ratio (FIR) between two green emission bands at ∼525 and ∼545 nm is sensitive to temperature variation. One of the prerequisites for nanothermometry is that the FIR be independent of excitation intensity at constant temperature. In this work, the effect of excitation intensity on the FIR of core–double-shell NaYF4:Yb3+,Er3+@NaYF4:Yb3+,Nd3+@NaYF4 UCNPs was investigated in two environments. The first environment is in aqueous solution, and the second is a monolayer of UCNPs on top of a silica–silicon substrate in air. The experimental results showed that the FIR decreases with the excitation intensity at constant temperature in each case. We further found that the excitation intensity-dependent FIR indeed deteriorated the thermal images acquired by wide-field upconversion fluorescence microscopy, in which a Gaussian laser beam was used to excite UCNPs uniformly coated on a silica–silicon substrate. The nonuniform excitation intensity of the incident laser beam resulted in thermal images that showed nonuniform temperature distributions in a 100 μm range field of view, even though the whole sample was maintained at constant temperature in air. To tackle this problem, we first measured the excitation intensity and temperature dependence of the FIR and the excitation laser intensity distribution on the sample. We then developed a correction scheme to correct the thermal images. With our correction process, the temperature distribution on the sample can be accurately mapped even with nonuniform illumination.

CO(J = 1 – 0) Observations toward the Filamentary Cloud in the Galactic Region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50

We present observations of the J = 1 – 0 transition lines of 12CO, 13CO, and C18O toward the Galactic region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50, using the Purple Mountain Observatory 13.7 m millimeter telescope. Based on the 13CO data, one main filament and five subfilaments are found together as a network structure in the velocity interval of [−42.5, −30.0] km s−1. The kinematic distance of this molecular cloud is estimated to be ∼4.5 kpc. The median length, width, excitation temperature, and line mass of these filaments are ∼49 pc, ∼2.9 pc, ∼8.9 K, and ∼39 M ⊙ pc−1, respectively. The velocity structures along these filaments exhibit oscillatory patterns, which are likely caused by the fragmentation or accretion process along these filaments. The maximum accretion rate is estimated to be ∼700 M ⊙ pc−1. A total of ∼162 13CO clumps and ∼103 young stellar objects are identified in this region. Most of the clumps are in gravitationally bound states. Three H ii regions (G154.359+2.606, SH2-211, and SH2-212) are found to be located in the apexes of the filaments. Intense star-forming activity is found along the entire filamentary cloud. The observed results may help us to better understand the link between filaments and massive star formation.

The Star Formation–Gas Density Relation in Four Galactic GMCs: Effects of Stellar Feedback

We present maps of four Galactic giant molecular clouds (GMCs) in the J = 2-1 emission of both CO and 13CO. We use an LTE analysis to derive maps of the CO excitation temperature and column density and the distribution of total molecular gas column density, Σgas. The depletion of CO by freeze-out onto cold dust grains is accounted for by an approximation to the results of Lewis et al., which were derived from far-IR observations with Herschel. The surface density of young stellar objects (YSOs) is obtained from published catalogs. The mean YSO surface density exhibits a power-law dependence on Σgas, with exponents in the range 0.9–1.9. Gas column density probability distribution functions show power-law tails extending to high column densities. The distributions of sonic Mach number, M S , are sharply peaked at MS ∼ 5–8 for 3 GMCs; a fourth has a broad distribution up to M S = 30, possibly a result of feedback effects from multiple OB stars. An analysis following the methodology of Pokhrel et al. finds that our sample of GMCs shows power-law relations that are somewhat shallower than those found by Pokhrel et al. for the star formation rate versus 〈Σgas〉 and versus 〈Σgas〉/t ff in a different sample of clouds. We discuss possible differences in the two samples of star-forming clouds and the effects of stellar feedback on the relation between gas density and star formation rate.

Discharge Characteristics of Atmospheric Pressure Ar/N₂/O₂ a Plasma Jet Under a Square Wave Pulse

Plasma jets have broad application in the fields of sterilization and material processing. In recent years, studies have shown that adding a small amount of active gas into a single inert gas can change the distribution of active particles in the plasma. This not only produces the desired active species but also changes the length of the jet to make it more suitable for plasma applications. In this article, the characteristics of plasma jets were studied under an argon atmosphere with a small amount of nitrogen and oxygen. By measuring the voltage and current waveforms, luminescence images, and emission spectra under the three mixed gases, the main parameters such as discharge power, the three main particle emission spectrum intensities (the OH spectral line, the second positive band of nitrogen molecules and its diffraction band, argon atomic line), electron excitation temperature, molecular vibration temperature, and molecular rotation temperature are calculated. The results show two discharges in one cycle under the square wave pulse voltage. The addition of nitrogen and oxygen reduces the peak current of the Ar plasma jet but increases the power. The addition of N2 increases and stabilizes the length of the jet, while oxygen decreases the length. The spectral line intensities of OH and Ar atoms decrease with the increase in N2 doping concentration, while the spectral line intensity of nitrogen gas increases. The addition of oxygen reduces the intensity of all the three emission spectra. The electron excitation temperature is the highest in the mixed gas (Ar/N2/O2) and the lowest in pure argon. In the mixed gas (Ar/N2), the vibration temperature and rotation temperature are basically unchanged. After the addition of oxygen, the vibration temperature remained unchanged, but the rotation temperature increased slightly.

Vibrationally excited HCN transitions in circumstellar envelopes of carbon-rich AGB stars

Context. The most abundant molecule after H2 and CO in the circumstellar envelopes (CSEs) of carbon-rich asymptotic giant branch (AGB) stars is HCN. Its rotational lines within vibrationally excited states are exceptional tracers of the innermost region of carbon-rich CSEs. Aims. We aim to constrain the physical conditions of CSEs of carbon-rich stars using thermal lines of the HCN molecule. Additionally, we also search for new HCN masers and probe the temporal variations for HCN masers, which should shed light on their pumping mechanisms. Methods. We observed 16 carbon-rich AGB stars in various HCN rotational transitions, within the ground and 12 vibrationally excited states, with the Atacama Pathfinder Experiment (APEX) 12-metre sub-millimetre telescope. Results. We detect 68 vibrationally excited HCN lines from 13 carbon-rich stars, including 39 thermal transitions and 29 maser lines, suggesting that vibrationally excited HCN lines are ubiquitous in carbon-rich stars. Population diagrams constructed for two objects from the sample, for thermal transitions from different vibrationally excited states, give excitation temperatures around 800–900 K, confirming that they arise from the hot innermost regions of CSEs (i.e. r <20 R*). Among the detected masers, 23 are newly detected, and the results expand the total number of known HCN masers lines towards carbon-rich stars by 47%. In particular, the J = 2−1 (0, 3le, 0), J = 3−2 (0, 2, 0), and J = 4−3 (0, 11f, 0) masers are detected in an astronomical source for the first time. Our observations confirm temporal variations of the 2−1 (0, 11e, 0) maser on a timescale of a few years. Our analysis of the data suggests that all detected HCN masers are unsaturated. A gas kinetic temperature of ≳700 K and an H2 number density of >108 cm−3 are required to excite the HCN masers. In some ways, HCN masers in carbon-rich stars might be regarded as an analogy of SiO masers in oxygen-rich stars.

A Novel Slug Heat Test Theoretical and Indoor Model Research for Determining Thermal Property Parameters of Aquifers and Rock-Soil Skeletons

As important parameters for characterizing heat transfer, thermal property parameters of aquifers and rock-soil skeletons have important research significance in the development and utilization of geothermal resources. The slug heat test is inspired by the slug test, and the heat is instantaneously excited in the test well so as to change the temperature of test section in the test well instantaneously. Based on the thermal radial convection-dispersion theory and the principle of heat conservation, the theoretical model of the slug heat test is established, and the model is solved by Laplace transform and inverse transform to obtain multiple sets of standard curves under different conditions. The slug heat tests were conducted in the indoor model, the slug heat test data under different hydrodynamic conditions were fitted with the standard curves and the thermal property parameters, including effective thermal conductivity, stagnant thermal conductivity, thermal mechanical dispersion coefficient, thermal dispersive degree, thermal diffusivity, heat capacity of aquifer, heat capacity and thermal conductivity of rock-soil skeletons, were accurately obtained. The test results are in good agreement with the empirical values. Meanwhile, the effective thermal conductivity of the aquifer also clearly increases with the increase of flow rate. The excitation temperature difference had little effect on the effective thermal conductivity of the aquifer. At the same time, numerical simulation methods are used to establish a numerical model consistent with the indoor test model, and the numerical model is assigned with the thermal property parameters obtained from the indoor slug heat test, and the measured values of temperature changes in the test well during the slug heat test under different hydrodynamic and excitation strength conditions are compared with the simulated values for verification. The research results show that the slug heat test has the characteristics of high applicability, simple operation and rapid testing, and can effectively determine the thermal properties parameters of aquifers and rock-soil skeletons.