Thermodynamics and reentrant phase transition for logarithmic nonlinear charged black holes in massive gravity

We investigate a new class of $(n+1)$-dimensional topological black hole solutions in the context of massive gravity and in the presence of logarithmic nonlinear electrodynamics. Exploring higher dimensional solutions in massive gravity coupled to nonlinear electrodynamics is motivated by holographic hypothesis as well as string theory. We first construct exact solutions of the field equations and then explore the behavior of the metric functions for different values of the model parameters. We observe that our black holes admit the multi-horizons caused by a quantum effect called anti-evaporation. Next, by calculating the conserved and thermodynamic quantities, we obtain a generalized Smarr formula. We find that the first law of black holes thermodynamics is satisfied on the black hole horizon. We study thermal stability of the obtained solutions in both canonical and grand canonical ensembles. We reveal that depending on the model parameters, our solutions exhibit a rich variety of phase structures. Finally, we explore, for the first time without extending thermodynamics phase space, the critical behavior and reentrant phase transition for black hole solutions in massive gravity theory. We realize that there is a zeroth order phase transition for a specified range of charge value and the system experiences a large/small/large reentrant phase transition due to the presence of nonlinear electrodynamics.Comment: 14 pages (one column), 12 captioned figure

Tribological behaviour of AZ31 magnesium alloy reinforced by bimodal size B4C after precipitation hardening

This study investigated dry sliding wear properties of AZ31 magnesium alloy and B4C-reinforced AZ31 composites containing 5, 10, and 20 wt.% B4C with bimodal sizes under different loadings (10–80 N) at various sliding speeds (0.1–1 m/s) via the pin-on-disc configuration. Microhardness evaluations showed that when the distribution of B4C particles was uniform the hardness of the composites increased by enhancing the reinforcement content. The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content. For this purpose, wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses. The determined wear mechanisms were abrasion, oxidation, delamination, adhesion, and plastic deformation as a result of thermal softening and melting. The wear evaluations revealed that the composites containing 5 and 10 wt.% B4C had a significantly higher wear resistance in all the conditions. However, 20 wt.% B4C/AZ31 composite had a lower resistance at high sliding speeds (0.5–1 m/s) and high loadings (40–80 N) in comparison with the unreinforced alloy. The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear

Composition and diversity of phytoplankton from mangrove estuaries in Sarawak, Malaysia

The composition and diversity of phytoplankton were studied along with physico-chemical parameters of water of two mangrove-dominated estuaries i.e., Kuala Sibuti (KS) and Kuala Nyalau (KN), Sarawak, Malaysia. A total of 46 species of phytoplankton with the mean density of 147000 cells L-1 were recorded from KS estuary i.e., 3 species of Cyanophyceae; 22 species of Bacillariophyceae; 20 species of Dinophyceae and 1 species of Chlorophyceae. The recorded mean density of phytoplankton was 113000 cells L-1 with 33 species from 19 genera from KN estuary, in which 19 species were from Bacillariophyceae; 12 species were from Dinophyceae; 1 species was from Cyanophyceae and 1 species was from Chlorophyceae. In both the estuaries, the species composition was found to be in an order of Diatom>Dinoflagellate>Cyanophyceae>Chlorophyceae. Canonical Correspondence Analysis (CCA) revealed that the abundance of Bacillariophyceae and Dinoflagellates was influenced by salinity and conductivity along with ammonium and phosphate while the abundance of Chlorophyceae was influenced by temperature, TDS, DO and pH in KS. The influence of salinity and conductivity along with PO4 and NH4 on the abundance of Bacillariophyceae, Dinoflagellates and Chlorophyceae were observed in KN

Seasonal variation of water characteristics in Kuala Sibuti river estuary in Miri, Sarawak, Malaysia

This paper presents the water characteristics of Kuala Sibuti river estuary, which is margined by pristine mangrove forest. For this purpose, nutrients, chlorophyll a and environmental parameters were investigated for 12 months. Physical, chemical and biological parameters of this estuarine water followed a seasonal rhythm and induced by the annual cycle of the monsoon. Surface water temperature ranged from 27.4°C to 32.2°C with a wide variety of salinity from 0.70 PSU to 27.10 PSU followed by Dissolved Oxygen (DO) from 1.94 to 6.71 mg/L. The concentration of chlorophyll a was found to be varied from 0.02 to 0.16 mg/m3. Nitrate, phosphate and ammonium concentrations ranged from 0.40 to 3.53mg/L, 0.01 to 1.92 mg/L and 0.06 to 1.24 mg/L, respectively. Pearson correlation coefficients showed a significant relationship between nitrate and TDS, nitrate and pH, ammonium and salinity, temperature and salinity, temperature and TDS, phosphate and light attenuation in this estuarine environment. The estuary was found to be mesohaline in nature. Estuarine Water Quality Index (EWQI) calculated from phosphate (PO4), suspended matter (SM) and dissolved oxygen (DO) indicate very good quality (4.95). Significantly seasonal difference for salinity, water temperature and, TDS were observed probably related to tidal flow and upstream river runoff

Phytoplankton in tropical mangrove estuaries: role and interdependency

Mangrove estuaries are claimed to be productive and important breeding grounds for fishery resources. The role of particulate organic matter (POM), especially derived from decomposed litter detritus, is well documented in mangrove estuaries. However, being a primary producer, phytoplankton may play a significant role, which has not been well discussed, in governing the productivity of mangrove estuaries. Based on relevant published literature, this paper focuses on the role of phytoplankton in mangrove estuaries in the tropical coastal region and their interdependency. Analysis reveals that there are two-way interactions between phytoplankton and mangrove estuaries. The POM enriched water in mangrove estuaries acts as an ideal medium for phytoplankton succession. Simultaneously, diversified phytoplankton assemblages play a significant role in the food web of the estuarine mangrove ecosystem. Biomass and diversity of phytoplankton are influenced by nutrient and environmental parameters in mangrove estuaries and, concurrently, phytoplankton play a significant role in fish diversity and primary production in the same system. This review reveals that the inconsistent relationships between mangroves and coastal production could probably be due to the influence of seasonal changes. This paper unveils the latent potential and role of phytoplankton in tropical mangrove estuaries, which could be a source of thought for future research in this arena

Inter-linkage among some physico-chemical and biological factors in the tropical mangrove estuary

The interaction between abiotic and biotic parameters in an ecosystem usually shows health and functioning of the system. Thus, some physico-chemical parameters, phytoplankton abundance, chlorophyll a and primary production of the mangrove estuary in Sarawak, Malaysia were extensively investigated from January 2013 to December 2013 in order to establish the inter-linkage among them. The Pearson correlation coefficient revealed a significant relation between atmospheric and water temperatures (r = 0.692). Similarly, surface water temperature showed a significant positive correlation with salinity (r = 0.744), TDS (r = 0.708) and conductivity (r = 0.776). The light extinction coefficient (LEC, K) changed negatively in relation to TDS (r =-0.623), conductivity (r =-0.644) and surface water temperature (r =-0.766). Ammonium showed a negative correlation with rainfall (r =-0.620) but a positive correlation with salinity (r = 0.600). The biological variable such as phytoplankton abundance was found to be positively correlated with chlorophyll a (r = 0.692), ammonium (r = 0.645) and silica (r = 0.644) and negatively with rainfall (r =-0.644). The canonical correspondence analysis revealed a strong positive correlation between environmental parameters and phytoplankton species. The analysis of variance disclosed significant seasonal differences in salinity, water temperature, TDS, conductivity, LEC, ammonium and chlorophyll a

Community composition and diversity of phytoplankton in relation to environmental variables and seasonability in a tropical mangrove estuary

This paper presents the aspects of phytoplankton communities along a tropical mangrove estuary inSarawak, Malaysia. Data were collected monthly from the study area from January 2013 to December2013 and was pooled into seasons to examine the influence of seasonality. The estuary revealedrelatively species-rich, and a total of 102 species under 43 genera were recorded comprising 6 speciesof Cyanophyceae; 4 species of Chlorophyceae; 62 species of Bacillariophyceae and 30 species ofDinophyceae. The species composition, as well as the mean abundance (cellsL-1) of phytoplankton,were found in order of Bacillariophyceae>Dinophyceae> Cyanophyceae> Chlorophyceae. Mean abun-dance of phytoplankton ranged from 5694 to 88890 cellsL−1over the study period with its highervalue in the dry season. Species recorded from the estuary were dominated byPleurosigma normanii,Coscinodiscussp,Coscinodiscus centralis,Coscinodiscus granii,Dinophysis caudata,Ceratium carriense,Ceratium fusus, andCeratium lineatum. Abundance of phytoplankton demonstrated positive correlationwith chlorophylla(r=0.69), ammonium (r=0.64) and silica (r=0.64). Significant differences (ANOSIMand nMDS) were observed in the species community structure between intermediate and the wetseason. Canonical correspondence analysis (CCA) showed that most of the species assemblages werepositively correlated with surface water temperature, salinity, pH, ammonium and nitrate in theintermediate and dry season towards larger species composition in the respective seasons whereassilica showed influence on the species assemblage in the wet season. The findings suggest that theSibuti mangrove estuary is productive in terms of diversified phytoplanktons and their variability inassemblage, those are influenced by the hydrological and biological factors

Food and feeding habits of Nemipterus japonicus and Nemipterus peronii from coastal water of Bintulu, Sarawak, South China Sea

Aim: Knowing that feeding habit of fishes is important for ecosystem management and conservation purposes. In this regard, a total of 240 fish stomachs of each species of Nemipterus japonicas (11.9-26.0 cm in length) and Nemipterus peronii (11.6 -25.3 cm in length) from the coastal area of Bintulu were examined monthly for one year from April 2013 to March 2014. Methodology: Food items were analyzed using frequency of occurrence, numerical and fullness methods. Each species were grouped into three different length sized groups (large, medium and small). The degree of stomach fullness was classified into five categories (empty, one quarter full, half full, three quarter full and full). Results: N. japonicus was an active feeder with a higher percentage (38.03%) of full stomachs, while N. peronii was poor feeder with higher percentage (27.05%) of one-quarter full stomachs. Diet composition contained seven major categories that included fish, crustaceans, molluscs, echinoderms, polychaetes, nematodes and unidentified food items. Crustaceans (mainly crabs) were preferred in both the N. japonicus and N. peronei at 13.54-35.71% of occurrence and 13.07-33.56%, respectively. Food items in both the species varied with season with maximum in intermediate and minimum in wet season. Interpretation: Findings revealed that N. japonicas and N. peronii are carnivorous, and may change their feeding habits from shrimp to crabs, and then to fish as they grow

Megalencephalic leukoencephalopathy with subcortical cysts : characterization of disease variants

Objective : To provide an overview of clinical and MRI characteristics of the different variants of the leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC) and identify possible differentiating features. Methods : We performed an international multi-institutional, cross-sectional observational study of the clinical and MRI characteristics in patients with genetically confirmed MLC. Clinical information was obtained by questionnaires for physicians and retrospective chart review. Results : We included 204 patients with classic MLC, 187 of whom had recessive mutations in MLC1 (MLC1 variant) and 17 in GLIALCAM (MLC2A variant) and 38 patients with remitting MLC caused by dominant GLIALCAM mutations (MLC2B variant). We observed a relatively wide variability in neurologic disability among patients with classic MLC. No clinical differences could be identified between patients with MLC1 and MLC2A. Patients with MLC2B invariably had a milder phenotype with preservation of motor function, while intellectual disability and autism were relatively frequent. Systematic MRI review revealed no MRI features that distinguish between MLC1 and MLC2A. Radiologic improvement was observed in all patients with MLC2B and also in 2 patients with MLC1. In MRIs obtained in the early disease stage, absence of signal abnormalities of the posterior limb of the internal capsule and cerebellar white matter and presence of only rarefied subcortical white matter instead of true subcortical cysts were suggestive of MLC2B. Conclusion : Clinical and MRI features did not distinguish between classic MLC with MLC1 or GLIALCAM mutations. Absence of signal abnormalities of the internal capsule and cerebellar white matter are MRI findings that point to the remitting phenotype

Megalencephalic leukoencephalopathy with subcortical cysts: Characterization of disease variants

OBJECTIVE: To provide an overview of clinical and MRI characteristics of the different variants of the leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC) and identify possible differentiating features. METHODS: We performed an international multi-institutional, cross-sectional observational study of the clinical and MRI characteristics in patients with genetically confirmed MLC. Clinical information was obtained by questionnaires for physicians and retrospective chart review. RESULTS: We included 204 patients with classic MLC, 187 of whom had recessive mutations in MLC1 (MLC1 variant) and 17 in GLIALCAM (MLC2A variant) and 38 patients with remitting MLC caused by dominant GLIALCAM mutations (MLC2B variant). We observed a relatively wide variability in neurologic disability among patients with classic MLC. No clinical differences could be identified between patients with MLC1 and MLC2A. Patients with MLC2B invariably had a milder phenotype with preservation of motor function, while intellectual disability and autism were relatively frequent. Systematic MRI review revealed no MRI features that distinguish between MLC1 and MLC2A. Radiologic improvement was observed in all patients with MLC2B and also in 2 patients with MLC1. In MRIs obtained in the early disease stage, absence of signal abnormalities of the posterior limb of the internal capsule and cerebellar white matter and presence of only rarefied subcortical white matter instead of true subcortical cysts were suggestive of MLC2B. CONCLUSION: Clinical and MRI features did not distinguish between classic MLC with MLC1 or GLIALCAM mutations. Absence of signal abnormalities of the internal capsule and cerebellar white matter are MRI findings that point to the remitting phenotype