Reduction of TCE and Chromate by Granular Iron in the Presence of Dissolved CaCO₃

Iron permeable reactive barriers (PRBs) have been installed at sites contaminated with various reducible organic and inorganic chemicals, particularly chlorinated solvents, worldwide. Many geochemical factors can affect the performance of iron PRBs. Chemicals such as nitrate and Cr(VI) may act as competing oxidants when co-exist with chlorinated solvents. Previous studies observed declines in the rate of TCE degradation by granular iron in the presence of nitrate. Passive oxide formation on the iron surface and an increase in corrosion potential of the iron were determined to be the mechanisms for the decline. Cr(VI), being a stronger oxidant than nitrate, may have a similar but greater effect on the iron reactivity. In addition, chromium oxide as well as dissolved CaCO3, a common groundwater constituent, form secondary precipitates and are likely to further affect the iron reactivity. The primary objective of this study was to determine the effects of Cr(VI) and dissolved CaCO3 on the iron reactivity towards TCE and Cr(VI) reduction and to provide mechanistic explanations for the observation. In addition, the applicability of a modified reactive transport model (Jeen, 2005) to the system in which chromate and CaCO3 co-exist with TCE was evaluated. Column experiments, including measurements of corrosion potential and surface film composition using Raman spectroscopy were conducted. Five column tests were carried out with input solutions consisting of different combinations of TCE (5 mg/L), Cr(VI) (10 mg/L) and dissolved CaCO3 (300 mg/L) for eight months. The results from the column receiving only Cr(VI) showed that Cr(VI) was reduced rapidly by the granular iron and was not detected beyond 10 cm from the influent end of the column by the end of the experiment. However, Cr(VI) profiles migrated from the influent end further into the column overtime, suggesting progressive passivation of the iron near the influent end of the column. The gradual increase in corrosion potential (up to 180 mV positive shift) at the port 3 cm from the inlet with the migration of Cr(VI) profiles suggests the formation and accumulation of higher valent iron oxides, such as hematite and goethite, together with Cr(III) products on the iron surface, passivating iron material. Raman spectroscopic measurements confirmed the presence of passive iron oxides at the end of the experiment. For the column receiving Cr(VI) + TCE, the co-existence of TCE did not affect Cr(VI) reduction kinetics. However, the presence of Cr(VI) affected TCE degradation significantly. Two segments in the migration of TCE profiles are identified: the first segment near the influent end of the column, where the iron was still active towards Cr(VI) reduction but inactive towards TCE degradation, and the second segment where Cr(VI) was fully removed and the TCE degradation continued to follow pseudo-first-order kinetics. The migrations in Cr(VI) and TCE profiles suggest that iron was passivated by Fe(III)/Cr(III) products, and Cr(VI), being a stronger oxidant, was reduced much more rapidly than TCE. It is expected that the first segment of TCE profiles would extend gradually with the migration of Cr(VI) profiles over time. When dissolved CaCO3 was added to the columns with Cr(VI) and TCE, either as single contaminant, or as co-contaminants, the pH values near the influent end of the columns remained relatively low (~ pH 7), thus, the presence of dissolved CaCO3 resulted in a stable corrosion potential and faster degradation rates of TCE and Cr(VI). Over time, however, Cr(VI) reduction and iron corrosion produced OH- and shifted the carbonate-bicarbonate equilibrium, resulting in the precipitation of secondary carbonate minerals, as detected by Raman analysis in the three columns containing CaCO3. The precipitation and accumulation of the secondary minerals on the iron surface gradually decreased iron reactivity, as indicated from the progressive migrations of TCE profiles in the column receiving TCE +CaCO3 and of second segment TCE of profiles in the column receiving TCE + Cr(VI) + CaCO3. Over the experimental period, the enhancement of dissolved CaCO3 was much greater than the iron passivation by secondary mineral precipitates. Based on the laboratory experiments, Jeen (2005) developed an empirical formula relating the decrease in iron reactivity to the accumulation of secondary minerals, and incorporated this formula into kinetic expression of an existing multi-component reactive transport model (MIN3P). The same code was used in this study to simulate the experimental data. The model reproduced the observations from the columns in which TCE co-exists with Cr(VI) and CaCO3 quite well, which suggests this model has applicability to predict the long-term performance of an iron PRB when treating groundwater containing Cr(VI), TCE and CaCO3, though there are some potential areas for improvements, including inconsistent volume fractions of secondary carbonate minerals and Fe(III)/Cr(III) products between experimental measurements and model simulation results, the reactive surface area concept, and inability to adapt changes in iron corrosion rates. The long-term performance for a hypothetical scenario in using an iron PRB (40 cm thick) to treat groundwater where TCE (5 mg/L) co-exists with Cr(VI) (10 mg/L ) in the presence of CaCO3 (300 mg/L) was simulated. The simulation indicated that Cr(VI) was completely treated over a period of 30 years, however, TCE broke through before 20 years, and substantial porosity was lost due to the accumulation of carbonate precipitates. The prediction could be valuable in the design of PRBs or in the development of effective maintenance procedures for PRBs treating groundwater co-contaminated with chromate and TCE

Fighting Depression at Christmas

Depression is a hard thing to understand and an even harder thing to explain. But you don’t have to ‘get it’ to help your loved ones this holiday season. Posting about factors that contribute to depression from In All Things - an online hub committed to the claim that the life, death, and resurrection of Jesus Christ has implications for the entire world. http://inallthings.org/fighting-depression-at-christmas

GROVE: A Retrieval-augmented Complex Story Generation Framework with A Forest of Evidence

Conditional story generation is significant in human-machine interaction, particularly in producing stories with complex plots. While Large language models (LLMs) perform well on multiple NLP tasks, including story generation, it is challenging to generate stories with both complex and creative plots. Existing methods often rely on detailed prompts to guide LLMs to meet target conditions, which inadvertently restrict the creative potential of the generated stories. We argue that leveraging information from exemplary human-written stories facilitates generating more diverse plotlines. Delving deeper into story details helps build complex and credible plots. In this paper, we propose a retrieval-au\textbf{G}mented sto\textbf{R}y generation framework with a f\textbf{O}rest of e\textbf{V}id\textbf{E}nce (GROVE) to enhance stories' complexity. We build a retrieval repository for target conditions to produce few-shot examples to prompt LLMs. Additionally, we design an ``asking-why'' prompting scheme that extracts a forest of evidence, providing compensation for the ambiguities that may occur in the generated story. This iterative process uncovers underlying story backgrounds. Finally, we select the most fitting chains of evidence from the evidence forest and integrate them into the generated story, thereby enhancing the narrative's complexity and credibility. Experimental results and numerous examples verify the effectiveness of our method.Comment: Findings of EMNLP 202

Few-shot Semantic Segmentation with Support-induced Graph Convolutional Network

Few-shot semantic segmentation (FSS) aims to achieve novel objects segmentation with only a few annotated samples and has made great progress recently. Most of the existing FSS models focus on the feature matching between support and query to tackle FSS. However, the appearance variations between objects from the same category could be extremely large, leading to unreliable feature matching and query mask prediction. To this end, we propose a Support-induced Graph Convolutional Network (SiGCN) to explicitly excavate latent context structure in query images. Specifically, we propose a Support-induced Graph Reasoning (SiGR) module to capture salient query object parts at different semantic levels with a Support-induced GCN. Furthermore, an instance association (IA) module is designed to capture high-order instance context from both support and query instances. By integrating the proposed two modules, SiGCN can learn rich query context representation, and thus being more robust to appearance variations. Extensive experiments on PASCAL-5i and COCO-20i demonstrate that our SiGCN achieves state-of-the-art performance.Comment: Accepted in BMVC2022 as oral presentatio

Atypical location of primary cardiac lymphoma in the left heart with atypical clinical presentation: A case report and literature review

BackgroundPrimary cardiac lymphoma (PCL) is a rare and aggressive cardiac tumor with very poor prognosis that occurs mostly in the right cardiac cavity. Early diagnosis and treatment may improve its prognosis. In the present report, we describe the diagnosis and treatment of a primary cardiac diffuse large B-cell lymphoma (PC-DLBCL) with atypical location and clinical presentation. Additionally, a literature review was conducted to summarize the current knowledge of the disease.Case PresentationA 71-year-old man visited his local hospital because of syncope, recurrent chest tightness, shortness of breath, palpitations, and profuse sweating for more than 20 days. Chest radiography revealed a mediastinal mass. Cardiac computed tomography (CT) showed multiple enlarged mediastinal lymph nodes. Transthoracic echocardiography (TTE) showed a cardiac mass in the posterior–inferior wall of the left atrium. He was then transferred to our hospital for positron emission tomography-CT (PET-CT) which showed active uptake of fluorodeoxyglucose both in the cardiac mass and in the multiple enlarged mediastinal lymph nodes. Biopsy of the enlarged mediastinal lymph nodes was carried out by using video-assisted thoracic surgery (VATS) technique, and pathological examination confirmed the subtype of PC-DLBCL, Stage IV, NCCN IPI 3. Therefore, the patient received a combination of chemotherapy and immunotherapy with R-CDOP (rituximab, cyclophosphamide, liposome doxorubicin, vincristine, and prednisone). After four courses of treatment in 4 months, the cardiac lymphoma and the enlarged mediastinal lymph nodes achieved complete remission with mild side effects of the chemotherapy.ConclusionEarly diagnosis and a precise choice of chemotherapy and immunotherapy based on cardiac imaging and pathological examination may improve the prognosis of PC-DLBCL in an atypical location