Displaying publications 181 - 200 of 372 in total

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  1. Gliricidia (Gliricidia sepium) Green manures as a potential source of N for maize production in the tropics
    Bah AR, Rahman ZA
    ScientificWorldJournal, 2001 Nov 22;1 Suppl 2:90-5.
    PMID: 12805783
    Use of cheap, N-rich, and environmentally benign legume green manures to correct N deficiency in infertile soils is a very attractive option in the humid tropics. Understanding the influence of management and climate on their effectiveness, and quantifying their contribution to crop productivity, is therefore crucial for technology adoption and adaptation. Mineral N buildup and the contribution to N uptake in maize were studied in an Ultisol amended with fresh Gliricidia leaves. Net mineral N accumulation was compared in mulched and incorporated treatments in a field incubation study. The 15 N isotope dilution technique was used to quantify N supplied to maize by Gliricidia leaves in an alley cropping. Mineral N accumulation was slow, but was much greater after incorporation than after mulching. Also, N buildup was always higher in the topsoil (0 to 10 cm) than in the subsoil (10 to 20 cm). More NO3-N was leached than NH4-N, and the effect was greater in the incorporated treatment. Surface-applied Gliricidia leaves significantly increased N uptake by maize, and supplied >30% of the total N in the stover and >20% of that in the corn grain, even in the presence of hedgerows. Thus Gliricidia leaf mulch has immense potential to improve productivity in tropical soils.
    Matched MeSH terms: Tropical Climate
  2. Seasonal variation in respiratory syncytial virus chest infection in the tropics
    Chan PW, Chew FT, Tan TN, Chua KB, Hooi PS
    Pediatr Pulmonol, 2002 Jul;34(1):47-51.
    PMID: 12112797 DOI: 10.1002/ppul.10095
    Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infection (LRTI) in young children. We determined if there was a seasonal variation in Malaysia in the incidence of RSV infection in young children admitted with LRTI, and possible associations of RSV infection with local meteorological parameters. A total of 5,691 children, aged less than 24 months and hospitalized with LRTI (i.e., bronchiolitis and pneumonia) between 1982-1997, were included in this study. Nasopharyngeal samples were collected and examined for RSV by immunofluorescence, viral culture, or both. Seasonal variations were determined by analyzing the monthly RSV-positive isolation rate via time series analysis. Possible correlations with local meteorological parameters were also evaluated.RSV was isolated in 1,047 (18.4%) children. Seasonal variations in RSV infection rate were evident and peaked during the months of November, December, and January (test statistics [T] = 53.7, P < 0.001). This seasonal variation was evident for both bronchiolitis and pneumonia categories (T = 42.8 and 56.9, respectively, P < 0.001). The rate of RSV infection appeared to correlate with the monthly number of rain days (r = 0.26, P < 0.01), and inversely with the monthly mean temperature (r = -0.38, P < 0.001). In the tropics, seasonal variations in the incidence of RSV infection are evident, with an annual peak in November, December, and January. This information provides a guide for healthcare provisions and implementation of RSV prevention.
    Matched MeSH terms: Tropical Climate
  3. Severe upper airway obstruction in the tropics requiring intensive care
    Chan PW, Goh A, Lum L
    Pediatr Int, 2001 Feb;43(1):53-7.
    PMID: 11208000
    BACKGROUND: The clinical profile of severe upper airway obstruction, a challenging acute pediatric emergency, has not been extensively documented in the developing nations of the tropics.

    METHODS: The diagnostic categories, severity of illness and outcome from 63 episodes of severe upper airway obstruction in 56 children admitted to the Pediatric Intensive Care Unit between January 1994 and December 1999 were reviewed. Outcome variables studied included requirement for ventilation, mortality and complications. Severity of illness was determined with the Pediatric Risk of Mortality (PRISM) II score.

    RESULTS: Viral croup (29%) was the most common diagnosis, followed by mediastinal malignancy (13%), bacterial tracheitis (11%) and Pierre Robin syndrome (11%). There were no admissions for acute epiglottitis. Thirty episodes (48%) required ventilation for a median duration of 4.0 days. Bacterial tracheitis (100%) and subglottic stenosis (100%) were the most likely diagnoses requiring ventilation. Difficulty in intubation was encountered in 13 episodes (43%) involving, in particular, patients with bacterial tracheitis (83%; P = 0.006). Only two patients required a tracheostomy. The overall mortality was 11%. The PRISM score for all categories was generally low (mean 10.3 +/- 1.0; median 9.0). Non-survivors had a significantly higher PRISM II score than survivors (27.4 +/- 9.7 vs 8.1 +/- 4.9, respectively; P = 0.002) and were more likely to include children with bacterial tracheitis and mediastinal malignancy.

    CONCLUSIONS: There is marked heterogeneity in the causes of upper airway obstruction in the tropics with viral croup remaining the most common. A significant proportion required ventilation, but outcome is generally favorable, except in those with bacterial tracheitis and mediastinal malignancy.

    Matched MeSH terms: Tropical Climate
  4. Adsorption, desorption, and mobility of metsulfuron methyl in Malaysian agricultural soils
    Abdullah AR, Sinnakkannu S, Tahir NM
    Bull Environ Contam Toxicol, 2001 Jun;66(6):762-9.
    PMID: 11353379
    Matched MeSH terms: Tropical Climate
  5. The role of extreme events in the impacts of selective tropical forestry on erosion during harvesting and recovery phases at Danum Valley, Sabah
    Douglas I, Bidin K, Balamurugan G, Chappell NA, Walsh RP, Greer T, et al.
    Philos Trans R Soc Lond B Biol Sci, 1999 Nov 29;354(1391):1749-61.
    PMID: 11605619
    Ten years' hydrological investigations at Danum have provided strong evidence of the effects of extremes of drought, as in the April 1992 El Niño southern oscillation event, and flood, as in January 1996. The 1.5 km2 undisturbed forest control catchment experienced a complete drying out of the stream for the whole 1.5 km of defined channel above the gauging station in 1992, but concentrated surface flow along every declivity from within a few metres of the catchment divide after the exceptional rains of 19 January 1996. Under these natural conditions, erosion is episodic. Sediment is discharged in pulses caused by storm events, collapse of debris dams and occasional landslips. Disturbance by logging accentuates this irregular regime. In the first few months following disturbance, a wave of sediment is moved by each storm, but over subsequent years, rare events scour sediment from bare areas, gullies and channel deposits. The spatial distribution of sediment sources changes with time after logging, as bare areas on slopes are revegetated and small gullies are filled with debris. Extreme storm events, as in January 1996, cause logging roads to collapse, with landslides leading to surges of sediment into channels, reactivating the pulsed sediment delivery by every storm that happened immediately after logging. These effects are not dampened out with increasing catchment scale. Even the 721 km2 Sungai Segama has a sediment yield regime dominated by extreme events, the sediment yield in that single day on 19 January 1996 exceeding the annual sediment load in several previous years. In a large disturbed catchment, such road failures and logging-activity-induced mass movements increase the mud and silt in floodwaters affecting settlements downstream. Management systems require long-term sediment reduction strategies. This implies careful road design and good water movement regulation and erosion control throughout the logging process.
    Matched MeSH terms: Tropical Climate
  6. Termite assemblages, forest disturbance and greenhouse gas fluxes in Sabah, East Malaysia
    Eggleton P, Homathevi R, Jones DT, MacDonald JA, Jeeva D, Bignell DE, et al.
    Philos Trans R Soc Lond B Biol Sci, 1999 Nov 29;354(1391):1791-802.
    PMID: 11605622
    A synthesis is presented of sampling work conducted under a UK government-funded Darwin Initiative grant undertaken predominantly within the Danum Valley Conservation Area (DVCA), Sabah, East Malaysia. The project concerned the assemblage structure, gas physiology and landscape gas fluxes of termites in pristine and two ages of secondary, dipterocarp forest. The DVCA termite fauna is typical of the Sunda region, dominated by Termes-group soil-feeders and Nasutitermitinae. Selective logging appears to have relatively little effect on termite assemblages, although soil-feeding termites may be moderately affected by this level of disturbance. Species composition changes, but to a small extent when considered against the background level of compositional differences within the Sunda region. Physiologically the assemblage is very like others that have been studied, although there are some species that do not fit on the expected body size-metabolic rate curve. As elsewhere, soil-feeders and soil-wood interface-feeders tend to produce more methane. As with the termite assemblage characteristics, gross gas and energy fluxes do not differ significantly between logged and unlogged sites. Although gross methane fluxes are high, all the soils at DVCA were methane sinks, suggesting that methane oxidation by methanotrophic bacteria was a more important process than methane production by gut archaea. This implies that methane production by termites in South-East Asia is not contributing significantly to the observed increase in levels of methane production worldwide. Biomass density, species richness, clade complement and energy flow were much lower at DVCA than at a directly comparable site in southern Cameroon. This is probably due to the different biogeographical histories of the areas.
    Matched MeSH terms: Tropical Climate
  7. Quantitative application of fecal sterols using gas chromatography-mass spectrometry to investigate fecal pollution in tropical waters: western Malaysia and Mekong Delta, Vietnam
    Isobe KO, Tarao M, Zakaria MP, Chiem NH, Minh le Y, Takada H
    Environ Sci Technol, 2002 Nov 1;36(21):4497-507.
    PMID: 12433157
    This is the first report on fecal pollution using molecular markers in Southeast Asia where serious sewage pollution has occurred. A simple and sensitive analytical method using gas chromatography-mass spectrometry for 10 sterols in various environmental samples was developed to monitor extensive areas of tropical Asia. First, the method was applied to wastewater to confirm that >95% of sterols existed in the particulate phase. Then the approach was applied to a tropical Asian region, Malaysia and Vietnam, with a selection of 59 sampling stations in total. River water and sediment samples were collected and analyzed for chemical markers (coprostanol and other sterols) and microbiological markers (fecal coliforms and fecal streptococci). Particulate coprostanol concentrations ranged from <0.0001 to 13.47 microg/L in tropical river and estuarine waters, indicating severe fecal pollution in populous areas. Coprostanol concentrations in the sediments ranged from 0.005 to 15.5 microg/g-dry. The sedimentary coprostanol concentrations were lower than those reported in some urban areas of industrialized countries. This is probably because frequent heavy rain induces intensive input of eroded soil, which dilutes fecal material in river sediments. The relationship between the concentrations of fecal sterols and bacterial indicators was examined in an attempt to develop public health criteria for coprostanol levels applicable to the tropical region. Coprostanol concentrations of 30-100 ng/L or percent coprostanol levels of 2% corresponded to approximately 1000 fecal coliforms per 100 mL, which is set for secondary contact limit in many countries. These coprostanol concentrations were lower than those proposed as criteria in temperate countries, probably owing to greater survival of bacteria in warmer tropical waters. On the basis of these criteria, extensive monitoring of sediments suggests that poor sanitary conditions exist in most of the urbanized area of Malaysia and in several urban and rural sites in Vietnam.
    Matched MeSH terms: Tropical Climate
  8. Exposure to air pollution zones in a tropical city
    Armstrong RW
    Geogr Med, 1984;14:49-64.
    PMID: 6207076
    Matched MeSH terms: Tropical Climate
  9. Effect of interactions on the nutrient status of a tropical soil treated with green manures and inorganic phosphate fertilizers
    Bah AR, Rahman ZA, Hussin A
    ScientificWorldJournal, 2004 Jun 08;4:393-414.
    PMID: 15252691
    Integrated nutrient management systems using plant residues and inorganic P fertilizers have high potential for increasing crop production and ensuring sustainability in the tropics, but their adoption requires in-depth understanding of nutrient dynamics in such systems. This was examined in a highly weathered tropical soil treated with green manures (GMs) and P fertilizers in two experiments conducted in the laboratory and glasshouse. The treatments were factorial combinations of the GMs (Calopogonium caeruleum, Gliricidia sepium, and Imperata cylindrica) and P fertilizers (phosphate rocks [PRs] from North Carolina, China, and Algeria, and triple superphosphate) replicated thrice. Olsen P, mineral N, pH, and exchangeable K, Ca, and Mg were monitored in a laboratory incubation study for 16 months. The change in soil P fractions and available P was also determined at the end of the study. Phosphorus available from the amendments was quantified at monthly intervals for 5 months by 33P-32P double isotopic labeling in the glasshouse using Setaria sphacelata as test crop. The GMs were labeled with 33P to determine their contribution to P taken up by Setaria, while that from the P fertilizers was indirectly measured by labeling the soil with 32P. The P fertilizers hardly changed Olsen P and exchangeable cations during 16 months of incubation. The legume GMs and legume GM+P did not change Olsen P, lowered exchangeable Ca, and increased exchangeable K about threefold (4.5 cmol[+]kg(-1) soil) in the first 4 months, even as large amounts of NH4-N accumulated (approximately 1000 mg kg soil(-1)) and soil pH increased to more than 6.5. Afterwards, Olsen P and exchangeable Ca and Mg increased (threefold) as NH4+-N and soil pH declined. The legume GMs also augmented reversibly sorbed P in Al-P and Fe-P fractions resulting in high residual effect in the soil, while fertilizer-P was irreversibly retained. The GMs increased PR-P utilization by 40 to over 80%, mobilized soil P, and markedly enhanced uptake of N, K, Ca, and Mg. Thus GMs+PRs is an appropriate combination for correcting nutrient deficiencies in tropical soils.
    Matched MeSH terms: Tropical Climate
  10. Some aspects of dentistry in Sabah
    Golding KM
    Aust Dent J, 1971 Dec;16(6):389-93.
    PMID: 5291233
    Matched MeSH terms: Tropical Climate
  11. Fulltext A biogeographical study on tropical flora of southern China
    Zhu H
    Ecol Evol, 2017 12;7(23):10398-10408.
    PMID: 29238563 DOI: 10.1002/ece3.3561
    The tropical climate in China exists in southeastern Xizang (Tibet), southwestern to southeastern Yunnan, southwestern Guangxi, southern Guangdon, southern Taiwan, and Hainan, and these southern Chinese areas contain tropical floras. I checked and synonymized native seed plants from these tropical areas in China and recognized 12,844 species of seed plants included in 2,181 genera and 227 families. In the tropical flora of southern China, the families are mainly distributed in tropical areas and extend into temperate zones and contribute to the majority of the taxa present. The genera with tropical distributions also make up the most of the total flora. In terms of geographical elements, the genera with tropical Asian distribution constitute the highest proportion, which implies tropical Asian or Indo-Malaysia affinity. Floristic composition and geographical elements are conspicuous from region to region due to different geological history and ecological environments, although floristic similarities from these regions are more than 90% and 64% at the family and generic levels, respectively, but lower than 50% at specific level. These differences in the regional floras could be influenced by historical events associated with the uplift of the Himalayas, such as the southeastward extrusion of the Indochina geoblock, clockwise rotation and southeastward movement of Lanping-Simao geoblock, and southeastward movement of Hainan Island. The similarity coefficients between the flora of southern China and those of Indochina countries are more than 96% and 80% at family and generic levels, indicating their close floristic affinity and inclusion in the same biogeographically floristic unit.
    Matched MeSH terms: Tropical Climate
  12. Fulltext Standardized Assessment of Biodiversity Trends in Tropical Forest Protected Areas: The End Is Not in Sight
    Beaudrot L, Ahumada JA, O'Brien T, Alvarez-Loayza P, Boekee K, Campos-Arceiz A, et al.
    PLoS Biol, 2016 Jan;14(1):e1002357.
    PMID: 26785119 DOI: 10.1371/journal.pbio.1002357
    Extinction rates in the Anthropocene are three orders of magnitude higher than background and disproportionately occur in the tropics, home of half the world's species. Despite global efforts to combat tropical species extinctions, lack of high-quality, objective information on tropical biodiversity has hampered quantitative evaluation of conservation strategies. In particular, the scarcity of population-level monitoring in tropical forests has stymied assessment of biodiversity outcomes, such as the status and trends of animal populations in protected areas. Here, we evaluate occupancy trends for 511 populations of terrestrial mammals and birds, representing 244 species from 15 tropical forest protected areas on three continents. For the first time to our knowledge, we use annual surveys from tropical forests worldwide that employ a standardized camera trapping protocol, and we compute data analytics that correct for imperfect detection. We found that occupancy declined in 22%, increased in 17%, and exhibited no change in 22% of populations during the last 3-8 years, while 39% of populations were detected too infrequently to assess occupancy changes. Despite extensive variability in occupancy trends, these 15 tropical protected areas have not exhibited systematic declines in biodiversity (i.e., occupancy, richness, or evenness) at the community level. Our results differ from reports of widespread biodiversity declines based on aggregated secondary data and expert opinion and suggest less extreme deterioration in tropical forest protected areas. We simultaneously fill an important conservation data gap and demonstrate the value of large-scale monitoring infrastructure and powerful analytics, which can be scaled to incorporate additional sites, ecosystems, and monitoring methods. In an era of catastrophic biodiversity loss, robust indicators produced from standardized monitoring infrastructure are critical to accurately assess population outcomes and identify conservation strategies that can avert biodiversity collapse.
    Matched MeSH terms: Tropical Climate
  13. Locomotor constraints favour the evolution of the human pygmy phenotype in tropical rainforests
    Venkataraman VV, Yegian AK, Wallace IJ, Holowka NB, Tacey I, Gurven M, et al.
    Proc Biol Sci, 2018 11 07;285(1890).
    PMID: 30404871 DOI: 10.1098/rspb.2018.1492
    The convergent evolution of the human pygmy phenotype in tropical rainforests is widely assumed to reflect adaptation in response to the distinct ecological challenges of this habitat (e.g. high levels of heat and humidity, high pathogen load, low food availability, and dense forest structure), yet few precise adaptive benefits of this phenotype have been proposed. Here, we describe and test a biomechanical model of how the rainforest environment can alter gait kinematics such that short stature is advantageous in dense habitats. We hypothesized that environmental constraints on step length in rainforests alter walking mechanics such that taller individuals are expected to walk more slowly due to their inability to achieve preferred step lengths in the rainforest. We tested predictions from this model with experimental field data from two short-statured populations that regularly forage in the rainforest: the Batek of Peninsular Malaysia and the Tsimane of the Bolivian Amazon. In accordance with model expectations, we found stature-dependent constraints on step length in the rainforest and concomitant reductions in walking speed that are expected to compromise foraging efficiency. These results provide the first evidence that the human pygmy phenotype is beneficial in terms of locomotor performance and highlight the value of applying laboratory-derived biomechanical models to field settings for testing evolutionary hypotheses.
    Matched MeSH terms: Tropical Climate
  14. Termites mitigate the effects of drought in tropical rainforest
    Ashton LA, Griffiths HM, Parr CL, Evans TA, Didham RK, Hasan F, et al.
    Science, 2019 01 11;363(6423):174-177.
    PMID: 30630931 DOI: 10.1126/science.aau9565
    Termites perform key ecological functions in tropical ecosystems, are strongly affected by variation in rainfall, and respond negatively to habitat disturbance. However, it is not known how the projected increase in frequency and severity of droughts in tropical rainforests will alter termite communities and the maintenance of ecosystem processes. Using a large-scale termite suppression experiment, we found that termite activity and abundance increased during drought in a Bornean forest. This increase resulted in accelerated litter decomposition, elevated soil moisture, greater soil nutrient heterogeneity, and higher seedling survival rates during the extreme El Niño drought of 2015-2016. Our work shows how an invertebrate group enhances ecosystem resistance to drought, providing evidence that the dual stressors of climate change and anthropogenic shifts in biotic communities will have various negative consequences for the maintenance of rainforest ecosystems.
    Matched MeSH terms: Tropical Climate
  15. Indoor thermal fogging application of pesguard FG 161, a mixture of d-tetramethrin and cyphenothrin, using portable sprayer against vector mosquitoes in the tropical environment
    Yap HH, Lee YW, Zairi J, Jahangir K, Adanan CR
    J Am Mosq Control Assoc, 2001 Mar;17(1):28-32.
    PMID: 11345415
    Indoor bioefficacy of the thermal fogging application of Pesguard FG 161, a formulation containing both knockdown and killing agents (active ingredient [AI]: d-tetramethrin 4% [w/w] and cyphenothrin 12% [w/w]) was compared with Resigen5 (AI: s-bioallethrin 0.8% [w/w], permethrin 125/75] 18.7% [w/w], and piperonyl butoxide 16.8% [w/w]), another pyrethroid formulation, as larvicides and adulticides against Aedes aegypti, Aedes albopictus, Anopheles sinensis, and Culex quinquefasciatus using a portable Agrofog AF35 sprayer indoors in houses on Penang Island, Malaysia. Pesguard FG 161 at the concentrations tested was effective against all 4 mosquito species tested. The water-based Pesguard FG 161 performed far better as a larvicide than the diesel-based formulation. Resigen was also effective as a larvicide and adulticide against all 4 mosquito species tested. Larvae of Ae. aegypti were most susceptible to water-based Pesguard FG 161, followed by Cx. quinquefasciatus, An. sinensis, and Ae. albopictus. Even at the lowest concentrations tested, Pesguard FG 161 showed adequate adulticidal properties. At higher dosages, water-based Pesguard FG 161 proved effective as a larvicide against all 4 mosquito species.
    Matched MeSH terms: Tropical Climate
  16. Fulltext Utilization of Point-of-Care Ultrasound to Detect Splenic Microabscesses in Pediatric Melioidosis
    Sakulchit T, Ngu L, Chor YK, Ong GY
    Cureus, 2021 Mar 08;13(3):e13760.
    PMID: 33842136 DOI: 10.7759/cureus.13760
    Melioidosis is an infectious disease most commonly found in places with tropical climates. Definitive diagnosis can be confirmed by culture or pathological results of blood or infected organ. However, imaging study is helpful in providing early provisional diagnosis and guiding therapy. Point-of-care ultrasound can be currently performed bedside by non-radiological staff such as emergency physicians or intensivists. We present the case of a pediatric patient who got diagnosed with melioidosis after detection of multiple splenic and hepatic abscesses by point-of-care ultrasound, leading to early diagnosis and appropriate empirical antibiotic selection, resulting in good treatment outcome.
    Matched MeSH terms: Tropical Climate
  17. Synchronous flowering of the rubber tree (Hevea brasiliensis) induced by high solar radiation intensity
    Yeang HY
    New Phytol, 2007;175(2):283-9.
    PMID: 17587376
    How tropical trees flower synchronously near the equator in the absence of significant day length variation or other meteorological cues has long been a puzzle. The rubber tree (Hevea brasiliensis) is used as a model to investigate this phenomenon. The annual cycle of solar radiation intensity is shown to correspond closely with the flowering of the rubber tree planted near the equator and in the subtropics. Unlike in temperate regions, where incoming solar radiation (insolation) is dependent on both day length and radiation intensity, insolation at the equator is due entirely to the latter. Insolation at the upper atmosphere peaks twice a year during the spring and autumn equinoxes, but the actual solar radiation that reaches the ground is attenuated to varying extents in different localities. The rubber tree shows one or two flowering seasons a year (with major and minor seasons in the latter) in accordance with the solar radiation intensity received. High solar radiation intensity, and in particular bright sunshine (as distinct from prolonged diffuse radiation), induces synchronous anthesis and blooming in Hevea around the time of the equinoxes. The same mechanism may be operational in other tropical tree species.
    Matched MeSH terms: Tropical Climate
  18. The sunshine-mediated trigger of synchronous flowering in the tropics: the rubber tree as a study model
    Yeang HY
    New Phytol, 2007;176(4):730-5.
    PMID: 17997756
    Matched MeSH terms: Tropical Climate
  19. Distinctive phyllosphere bacterial communities in tropical trees
    Kim M, Singh D, Lai-Hoe A, Go R, Abdul Rahim R, Ainuddin AN, et al.
    Microb Ecol, 2012 Apr;63(3):674-81.
    PMID: 21990015 DOI: 10.1007/s00248-011-9953-1
    Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of 'true' tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and pyrosequenced targeting the V1-V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in the phyllosphere were unique to plant leaves in that very few operational taxonomic units (0.5%) co-occurred in the surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average, 17%), a pattern not previously recognized. Sequences belonging to Acidobacteria were classified into subgroups 1-6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plants and Acidobacteria in tropical rain forest, which needs to be investigated further. The similarity of phyllosphere bacterial communities amongst the tree species sampled shows a significant tendency to follow host plant phylogeny, with more similar communities on more closely related hosts.
    Matched MeSH terms: Tropical Climate
  20. Effect of tropical outdoor weathering on the surface roughness and mechanical properties of maxillofacial silicones
    Rahman AM, Jamayet NB, Nizami MMUI, Johari Y, Husein A, Alam MK
    J Prosthet Dent, 2021 Jan 17.
    PMID: 33472753 DOI: 10.1016/j.prosdent.2020.07.026
    STATEMENT OF PROBLEM: The climate of tropical Southeast Asia includes high humidity and ultraviolet radiation that reduce the lifespan of silicone prostheses by inducing changes in their mechanical properties and color stability. Studies on the surface roughness (SR) and mechanical properties of different silicone elastomers (SEs) subjected to the natural tropical weather of Southeast Asia are lacking.

    PURPOSE: The purpose of this in vitro study was to evaluate the SR, tensile strength (TS), and percentage elongation (% E) of different SEs subjected to outdoor weathering in the Malaysian climate.

    MATERIAL AND METHODS: Type-II dumbbell-shaped specimens (N-120) (nonweathered=15, weathered=15) were made from 3 room-temperature vulcanized (A-2000, A-2006, and A-103) and 1 heat-temperature vulcanized (M-511) silicone (Factor II). For 6 months, weathered specimens were subjected to outdoor weathering inside a custom exposure rack. Simultaneously, the nonweathered specimens were kept in a dehumidifier. Subsequently, the SR was measured with a profilometer; TS and % E were measured by using a universal testing machine. Two-way ANOVA was used to compare the means of the tested properties of the nonweathered and weathered specimens, and pairwise comparison was carried out between the silicones (α=.05).

    RESULTS: After outdoor weathering, the SR, TS, and % E were adversely affected by weathering in the Malaysian environment. Among the silicone materials, A-2000 showed the least TS changes (2.51 MPa), while A-2006 demonstrated significant changes in percentage elongation after outdoor weathering (266.5%). M-511 exhibited the highest mean value (2.50 μm) for SR changes. In addition, A-103 SE showed statistically significant differences in most pairwise comparisons for all 3 dependent variables.

    CONCLUSIONS: Based on the evaluation of mechanical properties, A-103 can be suggested as a suitable silicone for maxillofacial prostheses fabricated for tropical climates. However, A-2000 can be a suitable alternative, although significant changes to surface roughness were detected after outdoor weathering.

    Matched MeSH terms: Tropical Climate
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