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Background/Objectives: The incidence of nontuberculous mycobacterial (NTM) infections has increased globally; however, the clinical manifestations and optimal treatment strategies for extrapulmonary NTM infections remain poorly defined. This study assessed the clinical manifestations and treatment outcomes of extrapulmonary NTM infections. Methods: Data from adult patients with suspected extrapulmonary NTM infections at a tertiary-care hospital from 2009-2022 were categorized into NTM disease and isolation groups. Diagnosis of NTM disease relied on stringent criteria, whereas isolation required NTM isolation without meeting the criteria for infection. Results: Among 75 patients evaluated, 32 (42%) were diagnosed with NTM disease and 43 (57%) with NTM isolation. History of immunosuppressant use within the past 3 months (p = 0.070) and injection (p = 0.001) were more frequent in the disease group. The median interval from symptom onset to evaluation was 106.6 and 20 days in the disease and isolation groups, respectively. The prevalence of positive NTM polymerase chain reaction results (36.4%, p = 0.003) and acid-fast bacillus staining (39.1%, p < 0.001) was significantly higher in the disease group than in the isolation group. Mycobacterium intracellulare (21.9%), M. abscessus (15.6%), M. chelonae (9.4%), and M. fortuitum complex (9.4%) were the most frequently identified species. Of the 27 patients in the disease group who received treatment, 13 improved, four experienced treatment failure, seven were lost to follow-up, and three died during treatment, with one death directly attributable to NTM disease. Conclusions: NTM disease exhibits a spectrum of clinical manifestations. Accurate diagnosis is crucial for initiating effective treatment.
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INTRODUCTION: Whooping cough, also known as pertussis, remains a significant challenge as a vaccine-preventable disease worldwide. Since the switch from the whole-cell Pertussis (wP) vaccine to the acellular Pertussis vaccine (aP), cases of whooping cough have increased in countries using the aP vaccine. Understanding the immune system's response to pertussis vaccines and infection is crucial for improving current vaccine efficacy. AREAS COVERED: This review of the literature using PubMed records offers an overview of the qualitative differences in antibody and T cell responses to B. pertussis (BP) in vaccination and infection, and their potential association with decreased efficacy of the aP vaccine in preventing infection and subclinical colonization. We further discuss how asymptomatic infections and carriage are widespread among vaccinated human populations, and explore methodologies that can be employed for their detection, to better understand their impact on adaptive immune responses and identify key features necessary for protection against the disease. EXPERT OPINION: An underappreciated human BP reservoir, stemming from the decreased capacity of the aP vaccine to prevent subclinical infection, offers an alternative explanation for the increased incidence of clinical disease and recurrent outbreaks.
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Imunidade Adaptativa , Bordetella pertussis , Vacina contra Coqueluche , Vacinação , Coqueluche , Humanos , Coqueluche/prevenção & controle , Coqueluche/imunologia , Vacina contra Coqueluche/imunologia , Vacina contra Coqueluche/administração & dosagem , Bordetella pertussis/imunologia , Imunidade Adaptativa/imunologia , Vacinação/métodos , Eficácia de Vacinas , Linfócitos T/imunologia , Anticorpos Antibacterianos/imunologia , Anticorpos Antibacterianos/sangue , AnimaisRESUMO
HYPOTHESIS: Soft materials, particularly elastomers, are extensively studied, but investigations into purely soft gel contact systems are limited due to their complex dual phases consisting of polymer and free liquids. While Dual Wavelength-Reflection Interference Confocal Microscopy (DW-RICM) is effective for noninvasively visualizing interfaces from a bottom view, it faces challenges in gel studies due to close refractive indices of polymeric networks and free liquids. We hypothesize that modulating the refractive index of soft gels using nanoparticles (NPs) enhances the visualization of contact zone beneath the free surface, providing insights into the configuration of phase-separated free oil within gel-on-gel contact systems. EXPERIMENTS: Gel-on-gel contact systems were fabricated using immiscible organogels and hydrogels. Titanium dioxide (TiO2) NPs were introduced into the organogel to modulate refractive indices. Given the lack of prior studies on the hidden contact zone between gels, various techniques, including DW-RICM, side-view imaging, and inverted optical microscopy, were employed to observe and validate our findings. Comparative analyses were conducted with elastomer-on-rigid, elastomer-on-gel, and gel-on-rigid contact systems. FINDINGS: Our investigation demonstrated that a minimal amount of TiO2 NPs effectively delineates the direct contact radius between organogel polymeric networks and hydrogel surfaces. Comparative experiments showed that TiO2 addition did not alter the gels' mechanical and surface properties but significantly enhanced information on gel contact deformation. This enhanced visualization technique has the potential to advance our understanding of adhesive contacts in gels, providing valuable insights into interface phenomena involving biological soft tissues and cells.
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Enterococcus faecalis is a Gram-positive bacterium that is frequently found in the periapical lesion of patients with apical periodontitis. Its biofilm formation in root canal is closely related to the development of refractory apical periodontitis by providing increased resistance to endodontic treatments. Phage therapy has recently been considered as an efficient therapeutic strategy in controlling various periodontal pathogens. We previously demonstrated the bactericidal capacities of Enterococcus phage vB_EfaS_HEf13 (phage HEf13) against clinically-isolated E. faecalis strains. Here, we investigated whether phage HEf13 affects biofilm formation and pre-formed biofilm of clinically-isolated E. faecalis, and its combinatory effect with endodontic treatments, including chlorhexidine (CHX) and penicillin. The phage HEf13 inhibited biofilm formation and disrupted pre-formed biofilms of E. faecalis in a dose- and time-dependent manner. Interestingly, phage HEf13 destroyed E. faecalis biofilm exopolysaccharide (EPS), which is known to be a major component of bacterial biofilm. Furthermore, combined treatment of phage HEf13 with CHX or penicillin more potently inhibited biofilm formation and disrupted pre-formed biofilm than either treatment alone. Confocal laser scanning microscopic examination demonstrated that these additive effects of the combination treatments on disruption of pre-formed biofilm are mediated by relatively enhanced reduction in thickness distribution and biomass of biofilm. Collectively, our results suggest that the effect of phage HEf13 on E. faecalis biofilm is mediated by its EPS-degrading property, and its combination with endodontic treatments more potently suppresses E. faecalis biofilm, implying that phage HEf13 has potential to be used as a combination therapy against E. faecalis infections.
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Our study analyzed 95 solid organ transplant (SOT) and 78 hematopoietic stem cell transplant (HSCT) recipients with prior coronavirus disease 2019 (COVID-19). Patients who underwent transplantation within 30 days of COVID-19 infection comprised the early group, and those who underwent transplantation post-30 days of COVID-19 infection comprised the delayed group. In the early transplantation group, no patient, whether undergoing SOT and HSCT, experienced COVID-19-associated complications. In the delayed transplantation group, one patient each from SOT and HSCT experienced COVID-19-associated complications. Additionally, among early SOT and HSCT recipients, two and six patients underwent transplantation within seven days of COVID-19 diagnosis, respectively. However, no significant differences were observed in the clinical outcomes of these patients compared to those in other patients. Early transplantation following severe acute respiratory syndrome coronavirus 2 infection can be performed without increased risk of COVID-19-associated complications. Therefore, transplantation needs not be delayed by COVID-19 infection.
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COVID-19 , Transplante de Órgãos , Humanos , Teste para COVID-19 , SARS-CoV-2 , TransplantadosRESUMO
Raindrops falling on window-panes spread upon contact, whereas hail can cause dents or scratches on the same glass window upon contact. While the former phenomenon resembles classical wetting, the latter is dictated by contact and adhesion theories. The classical Young-Dupre law applies to the wetting of pure liquids on rigid solids, whereas conventional contact mechanics theories account for rigid-on-soft or soft-on-rigid contacts with small deformations in the elastic limit. However, the crossover between adhesion and wetting is yet to be fully resolved. The key lies in the study of soft-on-soft interactions with material properties intermediate between liquids and solids. In this work, we translate adhesion to wetting by experimentally probing the static signature of hydrogels in contact with soft PDMS of varying elasticity of both the components. Consequently, we probe this transition across six orders of magnitude in terms of the characteristic elasto-adhesive parameter of the system. In doing so, we reveal previously unknown phenomenology and a theoretical model which smoothly bridges adhesion of glass spheres with total wetting of pure liquids on any given substrate.
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Sessile hydrogel drops on rigid surfaces exhibit a wetting/contact morphology intermediate between liquid drops and glass spheres. Using density functional theory, we reveal the contact forces acting between a hydrogel and a rigid glass surface. We show that while transitioning from liquid-like to solid-like hydrogels, there exists a critical hydrogel elasticity that enables a switch from attractive-to-repulsive interaction with the underlying rigid glass surface. Our theoretical model is validated by experimental observations of sessile polyacrylamide hydrogels of varying elasticity on glass surfaces. Further, the proposed model successfully approaches Young's law in the pure liquid limit and work of adhesion in the glassy limit. Lastly, we show a modified contact angle relation, taking into account the hydrogel elasticity to explain the features of a distinct hydrogel foot.
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BACKGROUND: Serratia marcescens is a gram-negative bacterium that is widespread in the environment. S. marcescens bacteremia can be fatal during pregnancy and cause persistent chorioamnionitis. This study reports an outbreak of Serratia marcescens bloodstream infection (BSI) among high-risk pregnant women in an obstetric ward. The purpose of this study is to report our experience with the usefulness of the ATP test in hospital environmental management and to confirm that bloodstream infections of patients with the same strain were correlated by WGS testing. METHODS: This retrospective study collected the data of inpatients with S. marcescens bacteremia in obstetric ward for high-risk pregnant women from August 22, 2021, to October 14, 2021. We performed: an adenosine triphosphate (ATP) bioluminescence test in the environment with a high-contact area; environmental culture; on-site monitoring and staff education; and whole-genome sequencing (WGS) to evaluate genetic relationships among S. marcescens isolates. RESULTS: S. marcescens BSI occurred in four consecutive patients. None of the patients had central venous catheters. An ATP bioluminescence test revealed that high-contact areas and areas for injection preparation were not clean (≥ 1000 relative light units). However, S. marcescens was not identified in the environmental cultures, likely due to intensive environmental cleaning and discarding of potentially contaminated specimens before the culture test. On-site monitoring and education were conducted for 1 month. There were no further reports of BSI until 6 months after the last patient was discharged. WGS performed on three isolates from three patients indicated that the isolated S. marcescens was likely from the same strain. CONCLUSIONS: We controlled an S. marcescens outbreak by improving environmental cleaning as well as education of and behavior changes in healthcare workers. Using the ATP bioluminescence test can provide feedback on environmental cleaning and education. WGS played a role in determining the spread of BSI caused by the same strain.
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Bacteriemia , Infecção Hospitalar , Sepse , Infecções por Serratia , Gravidez , Humanos , Feminino , Recém-Nascido , Infecção Hospitalar/epidemiologia , Infecção Hospitalar/microbiologia , Gestantes , Serratia marcescens/genética , Estudos Retrospectivos , Infecções por Serratia/epidemiologia , Infecções por Serratia/microbiologia , Sepse/epidemiologia , Surtos de Doenças , Bacteriemia/epidemiologia , Bacteriemia/microbiologia , Hospitais , Trifosfato de Adenosina , Unidades de Terapia Intensiva NeonatalRESUMO
Though remdesivir benefits COVID-19 patients, its use in those with renal dysfunction is currently limited due to concerns about possible toxic effects of accumulated sulfobutylether-ß-cyclodextrin (SBECD) on liver and kidney. We examined renal and hepatic function for a month in renally-impaired COVID-19 patients who were treated or not treated with remdesivir to assess the safety of the drug. A retrospective study was performed in adult COVID-19 patients with glomerular filtration rates of <30 ml/min/1.73 m2 at admission to a tertiary care hospital between November 2020 and March 2022. Data on serum creatinine and liver chemistry were collected serially. A total of 101 patients with impaired renal function were analyzed, comprising 64 remdesivir-treated patients and 37 who did not receive any antiviral agent. Although remdesivir-treated patients were more likely to be infected with the Omicron variant (79.7% vs. 48.6%), baseline characteristics did not differ significantly between the two groups. Among patients who initially did not require dialysis, 18.4% (7/38) of remdesivir-treated patients developed acute kidney injury (AKI) at days 4-6, compared with 51.7% (15/29) of non-remdesivir-treated patients. Liver injury severity worsened in 3.1% (2/64) of remdesivir-treated patients and 5.4% (2/37) of non-remdesivir-treated patients at days 4-6. In addition, there was no significant increase in AKI and liver injury over time in remdesivir-treated patients, and there were no cases of discontinuation of remdesivir due to adverse reactions. Concerns regarding the safety of SBECD should not lead to hasty withholding of remdesivir treatment in renally-impaired COVID-19 patients.
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Injúria Renal Aguda , Monofosfato de Adenosina/análogos & derivados , Alanina/análogos & derivados , COVID-19 , Adulto , Humanos , SARS-CoV-2 , Estudos Retrospectivos , Tratamento Farmacológico da COVID-19 , Injúria Renal Aguda/induzido quimicamente , Injúria Renal Aguda/epidemiologiaRESUMO
BACKGROUND: Nocardiosis is a rare, but potentially life-threatening condition. It is difficult to diagnose, and bacterial culture identification can be time consuming. We investigated the characteristics of nocardiosis and the suitability of the treatment approach in Korea. MATERIALS AND METHODS: This retrospective study was conducted at 5 medical institutions between 2011 and 2021. We reviewed the medical records of patients with microbiologically confirmed nocardiosis. Appropriate antibiotic selection was defined as follows: (1) selecting antibiotics according to the species, (2) if the species of Nocardia was unknown, trimethoprim-sulfamethoxazole-based therapy or linezolid-based therapy was administered, and (3) selection of antibiotics using the antibiotic susceptibility test. The appropriate treatment periods for antibiotics were defined as treatment maintained from 3 to 12 months, depending on involvement of the organs. Descriptive analysis and Fisher exact test were used. Statistical significance was set at P-values of <0.05. RESULTS: Thirty patients were enrolled. Of these patients, 18 (60.0%) were male. The median age was 70.5 years. Among the diagnosed patients, 12 (40.0%) had an immunocompromised status. Eight (30.0%) patients received optimal treatment for the appropriate treatment period. Appropriate dosing duration was observed in 3 of the 12 (25.0%) immunocompromised patients. There was no significant difference between the presence or absence of immunosuppression and the adequacy of treatment for nocardiosis (P = 1.000). Skin and soft tissue (14 patients) were most frequently involved in this study. Nocardia species (spp.) were isolated from culture at a median of 6.0 days. There were 7 cases with N. farcinica (23.3%). CONCLUSION: We found that 60.0% of the patients with nocardiosis did not have an immunocompromised status. Further, 26.7% of the total patients received adequate treatment for nocardiosis. The reasons for suboptimal management of nocardiosis in Korea are presumed to be diagnostic difficulties, lack of awareness about nocardiosis, and difficulties in selecting antibiotics for Nocardia spp. among clinicians. The lack of antibiotic susceptibility tests for Nocardia spp. could be the source of these problems. Nocardiosis should be suspected in cases of recurrent infections with skin and soft tissue, musculoskeletal, or respiratory system involvement with or without an immunocompromised status. Clinical microbiological support is required for the diagnosis and selection of antibiotics in Korea. High clinical index of suspicion and clinical microbiological support are required for the accurate diagnosis of nocardiosis in Korea.
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Gel materials with tailored functions and tissue-like properties have gained significant interest in emerging applications, including tissue engineering scaffolds, flexible electronics, and soft robotics. In this work, we developed a stretchable, flexible, adhesive, and conductive organohydrogel through physical cross-linking of the poly (N-[tris (hydroxymethyl) methyl] acrylamide-co-acrylamide) (denoted as P(THMA-AM)) network in the presence of cellulose nanofiber (CNF), sodium chloride, and glycerol. The gel matrix is rich in intermolecular interactions, including hydrogen bonding and ionic interactions, which contribute to a highly compact and cohesive structure without the requirement of any chemical crosslinkers. Moreover, the plasticizing effect of glycerol can mitigate the self-entanglement of CNFs, enhancing their mobility and ultimately conferring the organohydrogel with exceptional stretchability and flexibility. The resulting organohydrogel exhibited superior mechanical properties, self-adhesion, and ionic conductivity, making it an excellent candidate for strain-sensing applications, particularly in distinguishing and monitoring human movements.
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BACKGROUND: Due to high mortality and limited treatment options, the rise in carbapenemase-producing Enterobacterales (CPE) has become a major concern. This study aimed to evaluate the incidence and characteristics of subsequent CPE bacteraemia in rectal CPE carriers and investigate the risk factors for CPE bacteraemia compared with non-carbapenemase-producing (non-CP) Enterobacterales bacteraemia. METHODS: A retrospective analysis was conducted on adult patients who were confirmed to have CPE colonisation by stool surveillance culture at a tertiary hospital from January 2018 to February 2022. All episodes of Enterobacterales bacteraemia up to 6 months after CPE colonisation were identified. RESULTS: Of 1174 patients identified as rectal CPE carriers, 69 (5.8%; 95% CI 4.6-7.3%) experienced subsequent CPE bacteraemia during the 6 months after the diagnosis of CPE colonisation. Colonisation by a Klebsiella pneumoniae carbapenemase (KPC) producer (or CP-K. pneumoniae), colonisation by multiple CPE species, chronic kidney disease and haematological malignancy were independently associated with CPE bacteraemia in CPE carriers. When CPE carriers developed Enterobacterales bacteraemia, the causative agent was more frequently non-CP Enterobacterales than CPE (63.6% vs. 36.4%). Among these patients, colonisation with a KPC producer, CPE colonisation at multiple sites, shorter duration from colonisation to bacteraemia (< 30 days) and recent intraabdominal surgery were independent risk factors for CPE bacteraemia rather than non-CP Enterobacterales bacteraemia. CONCLUSIONS: In CPE carriers, non-CP Enterobacterales were more often responsible for bacteraemia than CPE. Empirical antibiotic therapy for CPE should be considered when sepsis is suspected in a CPE carrier with risk factors for CPE bacteraemia.
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Bacteriemia , Infecções por Enterobacteriaceae , Adulto , Humanos , Estudos Retrospectivos , Proteínas de Bactérias , beta-Lactamases , Bacteriemia/epidemiologia , Klebsiella pneumoniae , Fatores de Risco , Infecções por Enterobacteriaceae/epidemiologiaRESUMO
Virtual memory T (TVM) cells are a T cell subtype with a memory phenotype but no prior exposure to foreign antigen. Although TVM cells have antiviral and antibacterial functions, whether these cells can be pathogenic effectors of inflammatory disease is unclear. Here we identified a TVM cell-originated CD44super-high(s-hi)CD49dlo CD8+ T cell subset with features of tissue residency. These cells are transcriptionally, phenotypically and functionally distinct from conventional CD8+ TVM cells and can cause alopecia areata. Mechanistically, CD44s-hiCD49dlo CD8+ T cells could be induced from conventional TVM cells by interleukin (IL)-12, IL-15 and IL-18 stimulation. Pathogenic activity of CD44s-hiCD49dlo CD8+ T cells was mediated by NKG2D-dependent innate-like cytotoxicity, which was further augmented by IL-15 stimulation and triggered disease onset. Collectively, these data suggest an immunological mechanism through which TVM cells can cause chronic inflammatory disease by innate-like cytotoxicity.
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Alopecia em Áreas , Linfócitos T CD8-Positivos , Humanos , Interleucina-15 , Memória Imunológica , Subpopulações de Linfócitos TRESUMO
There have been few studies comparing the clinical characteristics and outcomes of SARS-CoV-2 pneumonia in individuals with and without moderately to severely immunocompromised conditions. We reviewed adult patients with SARS-CoV-2 infection who had radiologic evidence of pneumonia at a tertiary hospital in Seoul, South Korea, from February 2020 to April 2022. Moderately to severely immunocompromised status was defined as medical conditions or treatments that resulted in increased risk of severe COVID-19 and weakened immune response to COVID-19 vaccine as recommended by Centers for Disease Control and Prevention. The time to pneumonia development was defined as the time from symptom onset to the time when radiologic evidence of pneumonia was obtained. Viral clearance was defined as a Ct value > 30. COVID-19-related death was defined as 90-day death following imaging-confirmed pneumonia without any other plausible cause of death. A total of 467 patients with SARS-CoV-2 pneumonia were analyzed. Of these, 102 (22%) were moderately to severely immunocompromised. The median (IQR) time to pneumonia development was significantly longer in moderately to severely immunocompromised patients (9.5 [6-14] days) than the comparator (6 [3-8] days), p < 0.001), as was the median time to viral clearance (21 versus 12 days, p < 0.001). Moderately to severely immunocompromised status (aOR, 18.39; 95% CI, 5.80-58.30; p < 0.001) was independently associated with COVID-19-related death. Patients with moderately to severely immunocompromised conditions are likely to experience a more protracted course of SARS-CoV-2 pneumonia and a worse outcome than those without these conditions.
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COVID-19 , SARS-CoV-2 , Estados Unidos , Adulto , Humanos , Vacinas contra COVID-19 , Hospedeiro Imunocomprometido , Centros de Atenção TerciáriaRESUMO
PURPOSE: Regulatory T cells (Tregs) exert immunosuppressive functions and hamper antitumor immune responses in the tumor microenvironment. Understanding the heterogeneity of intratumoral Tregs, and how it changes with tumor progression, will provide clues regarding novel target molecules of Treg-directed therapies. EXPERIMENTAL DESIGN: From 42 patients with renal cell carcinoma and 5 patients with ovarian cancer, immune cells from tumor and peripheral blood were isolated. We performed multicolor flow cytometry and RNA-sequencing to characterize the phenotypes and heterogeneity of intratumoral Tregs. In vitro functional assays were performed to evaluate suppressive capacity of Tregs and effect of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1)-mediated depletion. The CT26 tumor model was used to evaluate the association between intratumoral Tregs and tumor growth, and examine the in vivo role of CEACAM1+ intratumoral Tregs on antitumor immunity. RESULTS: We found that CEACAM1 was selectively expressed on intratumoral Tregs, whereas its expression on peripheral Tregs or other immune cells was low. The CEACAM1+ intratumoral Tregs accumulated with tumor progression, whereas the CEACAM1- subset did not. Notably, we found that CEACAM1 marked intratumoral Tregs that exhibited highly suppressive and activated phenotypes with substantial clonal expansion. Depletion of CEACAM1-expressing cells from tumor-infiltrating leukocytes led to increased effector functions of tumor-infiltrating T cells. Moreover, CEACAM1+ cell depletion further enhanced anti-PD-1-mediated reinvigoration of exhausted CD8+ T cells. CONCLUSIONS: CEACAM1 marks highly suppressive subset of intratumoral Tregs, and can be a target for selective depletion of intratumoral Tregs. These results may inform future studies on CEACAM1-mediated depletion in patients with cancer.
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Neoplasias , Linfócitos T Reguladores , Humanos , Molécula 1 de Adesão Celular/metabolismo , Antígenos CD/genética , Antígenos CD/metabolismo , Neoplasias/genética , Neoplasias/terapia , Microambiente TumoralRESUMO
Oral streptococci are considered as an opportunistic pathogen associated with initiation and progression of various oral diseases. However, since the currently-available treatments often accompany adverse effects, alternative strategy is demanded to control streptococci. In the current study, we investigated whether short-chain fatty acids (SCFAs), including sodium acetate (NaA), sodium propionate (NaP), and sodium butyrate (NaB), can inhibit the growth of oral streptococci. Among the tested SCFAs, NaP most potently inhibited the growth of laboratory and clinically isolated strains of Streptococcus gordonii under anaerobic culture conditions. However, the growth inhibitory effect of NaP on six different species of other oral streptococci was different depending on their culture conditions. Metabolic changes such as alteration of methionine biosynthesis can affect bacterial growth. Indeed, NaP enhanced intracellular methionine levels of oral streptococci as well as the mRNA expression level of methionine biosynthesis-related genes. Collectively, these results suggest that NaP has an inhibitory effect on the growth of oral streptococci, which might be due to alteration of methionine biosynthesis. Thus, NaP can be used an effective bacteriostatic agent for the prevention of oral infectious diseases caused by oral streptococci.
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Propionatos , Streptococcus , Propionatos/farmacologia , Ácidos Graxos Voláteis , Acetato de Sódio , MetioninaRESUMO
HYPOTHESIS: The conventional solid-solid contact is well studied in the literature. However, a number of practical applications, such as adhesive patches and biomimetic surfaces, require a much deeper understanding of soft contact where there is a distinct time-dependent adhesion behavior due to the dual-phase structure (solids and liquids). To understand this, currently existing solid-solid contact behavior is extrapolated to soft contact, wherein the size-effect of the gel film and the preload are typically neglected. When introducing the finite-size effect and preload, gels could experience distinctive long-term contact dynamics in contact with another material. EXPERIMENTS: We reconstruct the evolving surface profile of the gel films intercalated between a glass sphere and glass slide using dual wavelength-reflection interference contrast microscopy. The macro-sized glass sphere compresses the gel. The indentation depth is comparable to the gel film thickness, wherein the conventional contact theories are inapplicable. FINDINGS: The gel surface experiences two deformation stages. The natural preload and elastic force develop the contact area in the early state. In the later state, the viscous free molecules of the gel develop the ridge. We discover that the residual surface stress relaxes over 85 hr. Our findings on the long-term gel deformation provide a new perspective on soft adhesion, from developing soft adhesives to understanding biological tissues.
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Vidro , Fenômenos Mecânicos , Géis , ViscosidadeRESUMO
The vegetation changes in the abandoned rice fields with different abandonment histories were analyzed across the country of South Korea. The successional process was confirmed by changes in vegetation profiles and species composition. The vegetation profile showed the process of starting with grassland, passing through the shrub stage, and turning into a tree-dominated forest. DCA ordination based on vegetation data showed that the process began with grasslands consisting of Persicaria thunbergii, Juncus effusus var. decipiens, Phalaris arundinacea, etc., then partially went through shrubland stages consisting of Salix gracilistyla, S. integra, young Salix koreensis, etc., and ultimately changed to a Salix koreensis dominated forest. In order to study the relationship between the succession process of the abandoned rice paddies and riparian vegetation, information on riparian vegetation was collected in the same watershed as the abandoned rice paddies investigated. Riparian vegetation tended to be distributed in the order of grasslands consisting of Phragmites japonica, Miscanthus sacchariflorus, P. arundinacea, etc., shrubland dominated by Salix gracilistyla, S. integra, etc., and a S. koreensis community dominated forest by reflecting the flooding regime as far away from the waterway. The result of stand ordination based on the riparian vegetation data also reflected the trend. From this result, we confirmed that the temporal sequence of the vegetation change that occurred in the abandoned rice fields resembled the spatial distribution of the riparian vegetation. Consequently, succession of the abandoned rice fields restored the riparian forest, which has almost disappeared in Korea and other Asian countries that use rice as their staple food.