720 research outputs found
Ring Current Proton Decay Timescales Derived from Van Allen Probe Observations
The Earth's ring current is highly dynamic and is strongly influenced by the
solar wind. The ring current alters the planet's magnetic field, defining
geomagnetic storms. In this study, we investigate the decay timescales of ring
current protons using observations from the Van Allen Probes. Since proton
fluxes typically exhibit exponential decay after big storms, the decay time
scales are calculated by performing linear regression on the logarithm of the
fluxes. We found that in the central region of the ring current, proton decay
timescales generally increase with increasing energies and increasing L-shells.
The ~10s keV proton decay timescales are about a few days, while the ~100 keV
proton decay time scale is about ~10 days, and protons of 269 keV have decay
timescales up to ~118 days. These findings provide valuable insights into the
ring current dynamics and can contribute to the development of more accurate
ring current models.Comment: 8 pages, 7 figure
Combining stable carbon isotope analysis and petroleum-fingerprinting to evaluate petroleum contamination in the Yanchang oilfield located on loess plateau in China
This study evaluated petroleum contamination in the Yanchang (Shaanxi Yanchang Petroleum (Group) Co., Ltd.) oilfield, located in the loess plateau region of northern Shaanxi, China. Surface soil and sediment samples were collected from the wasteland, farmland, and riverbed in this area to assess the following parameters: total petroleum hydrocarbon (TPH), n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and carbon isotope ratios (delta C-13). The results showed that TPH and PAH levels in the study area were 907-3447 mg/kg and 103.59-563.50 mu g/kg, respectively, significantly higher than the control samples (TPH 224 mg/kg, PAHs below method quantification limit, MQL). Tests using delta C-13 to detect modified TPH (2238.66 to 6639.42 mg/kg) in the wastelands adjacent to the oil wells revealed more significant contamination than tests using extraction gravimetric analysis. In addition, "chemical fingerprint" indicators, such as low to high molecular weight (LMW/HMW) hydrocarbons, carbon preference index (CPI), and pristine/phytane (Pr/Ph), further confirmed the presence of heavy petroleum contamination and weathering. This has resulted in a nutrient imbalance and unsuitable pH and moisture conditions for microbial metabolic activities. This study evaluates petroleum contamination, which can inform contamination remediation on a case by case basis
Boric Acid Cross-linked 3D Polyvinyl Alcohol Gel Beads by NaOH-Titration Method as a Suitable Biomass Immobilization Matrix
Granule-base immobilization of biomass is a potential method for a decent quality granular sludge cultivation. In this study, 3D polyvinyl alcohol (PVA) gel beads were chemically cross-linked via a simple NaOH-titration method. The PVA gel beadsā porous morphology was characterized using scanning electron microscope (SEM) and BrunauerāEmmetteāTeller (BET), and their mechanical properties were evaluated by swelling rate and compressive stress tests. When cross-linking time was 10 min, high quality gel beads (P10) were synthesized, which demonstrated a homogeneous porous structure, good swelling rate, and high compressive strength. A mechanism for synthesis of the gel beads was proposed based on the results of Fourier transform infrared (FTIR) and X-ray diffractometer (XRD) analysis. Briefly, the intermolecular hydrogen bonds of PVA were firstly broken by NaOH to generate active bond of OāNa, which easily reacted with B(OH)4 ā to produce the PVA-boric acid gel beads. P10 showed excellent biocompatibility for anaerobic ammonia oxidation (anammox) biomassā immobilization. After incubation for three months, well granule-base immobilized sludge on P10 was developed in up-flow reactor. The sludge had high abundance of anammox biomass and was in balance with other functional bacteria. This work provides a simple method for the rapid preparation of 3D PVA gel beads and verifies their potential in granule-base immobilization of biomass.</p
Object-aware Adaptive-Positivity Learning for Audio-Visual Question Answering
This paper focuses on the Audio-Visual Question Answering (AVQA) task that
aims to answer questions derived from untrimmed audible videos. To generate
accurate answers, an AVQA model is expected to find the most informative
audio-visual clues relevant to the given questions. In this paper, we propose
to explicitly consider fine-grained visual objects in video frames
(object-level clues) and explore the multi-modal relations(i.e., the object,
audio, and question) in terms of feature interaction and model optimization.
For the former, we present an end-to-end object-oriented network that adopts a
question-conditioned clue discovery module to concentrate audio/visual
modalities on respective keywords of the question and designs a
modality-conditioned clue collection module to highlight closely associated
audio segments or visual objects. For model optimization, we propose an
object-aware adaptive-positivity learning strategy that selects the highly
semantic-matched multi-modal pair as positivity. Specifically, we design two
object-aware contrastive loss functions to identify the highly relevant
question-object pairs and audio-object pairs, respectively. These selected
pairs are constrained to have larger similarity values than the mismatched
pairs. The positivity-selecting process is adaptive as the positivity pairs
selected in each video frame may be different. These two object-aware
objectives help the model understand which objects are exactly relevant to the
question and which are making sounds. Extensive experiments on the MUSIC-AVQA
dataset demonstrate the proposed method is effective in finding favorable
audio-visual clues and also achieves new state-of-the-art question-answering
performance.Comment: Accepted by AAAI-202
The hole sealing technology of solid-liquid materials with three pluggings and two injections for gas extraction hole in the coal mine
The sealing quality of the gas extraction holes determines the extracted gas concentration. Based on this, the paper reveals the basic principle of hole sealing by analyzing the gas leakage mechanism of the borehole. The hole sealing technology of solid-liquid materials with three pluggings and two injections for the gas extraction hole is proposed, and the hole sealing device and material are developed. Through testing the granularity distribution of the solid material, as well as the surface tension and contact angle of the slurry, the hole sealing material that can meet the requirements of accessible, sticky, and anti-deformation is selected. The sealing material enters microcracks and bonds coal rock more easily. First, the solid material is injected for hole sealing. Second, the liquid material can be injected repeatedly to maintain a high concentration for holes with poor sealing and gas concentration attenuation in the late stage of gas extraction. Field tests show that the gas concentration of solid material is 1.3 times that of the conventional material after 30 days of sealing. The liquid material injected after the concentration decline enables the gas extraction concentration to be recovered at 85 %
Quench behavior of high temperature superconductor (RE)Ba2Cu3Ox CORC cable
High temperature superconductor (HTS) (RE)Ba2Cu3Ox (REBCO) conductor on round core cable (CORC) shows great advantages on high current capacity and power density. In REBCO CORC cables, current is redistributed among tapes through terminal contact resistances (TCR) when a local quench occurs. Therefore, its quench behaviour is different from single tape situation. To better understand the underlying physical process of local quenches in CORC cables, a new 3D multi-physics modelling tool for CORC cables is developed and presented in this paper. In this model, the REBCO tape is treated as a thin shell without thickness, and four models are coupled: T-formulation model, A-formulation model, a heat transfer model and an equivalent circuit model. The T-formulation is applied to the conductor shell only to calculate current distribution, which will be input into A-formulation model; the A-formulation is applied to the whole 3D domain to calculate magnetic field, which is then fed back to the T-formulation model. The hot spot induced quenches of CORC cables are analysed. The results show that the thermal stability of CORC cable can be considerably improved by reducing TCR. The minimum quench energy (MQE) increases rapidly with the reduction of TCR when the resistance is in a middle range, which is about 5 Ī¼Ī© ā¤ Rt ā¤ 200 Ī¼Ī© in this study. When TCR is too low (Rt 50 Ī¼Ī©), the MQE shows no obvious variation with TRC. With low TCR, a hot spot in one tape may induce an over-current quench on other tapes. This will not happen in a cable with high TCR. In this case, the tape with hot spot will quench and burn out before inducing a quench on other tapes. The modelling tool developed can be used to design CORC cables with improved thermal stability
- ā¦