Water quality assessment and pollution threat to safe water supply for three river basins in Malaysia.

Pollution in raw water poses increasing threats to safe water supply in many developing countries. Therefore, a comprehensive water quality assessment is essential to provide various stakeholders the information to deal with this problem. This study applies chemometrics to interpret a recent 10-year water quality data from three major river basins (Selangor River basin, Langat River basin, and Klang River basin) frequented by water supply disruptions in Selangor, Malaysia. We present the application of selected chemometrics approaches, namely agglomerative hierarchical cluster analysis, principal component analysis, factor analysis and Man-Kendall trend analysis. The results showed three spatial groups of monitoring stations with similar land use practices and pollution characteristics. Besides spatial differences, periodic variations were observed when similar pollutants exhibited different pollution loads during rainy and dry periods. We found that nitrogen species, total suspended solids, and dissolved solids represented the major pollution loads in the studied basins. The results further confirmed a significant increasing trend in ammonia pollution. Our study demonstrates how ammonia pollutant is likely to pose a threat to water supply and highlights the vulnerability of Selangor's water resource system to water pollution. The results of this study could facilitate decision making towards more holistic strategies, specifically, incorporating ammonia treatment facilities into the conventional water treatment plant will help achieve smooth water supply operations.

Band Anti-Crossing Model in Dilute-As GaNAs Alloys.

The band structure of the dilute-As GaNAs material is explained by the hybridization of localized As-impurity states with the valance band structure of GaN. Our approach employs the use of Density Functional Theory (DFT) calculated band structures, along with experimental results, to determine the localized As-impurity energy level and coupling parameters in the band anti-crossing (BAC) k ∙ p model for N-rich alloys. This model captures the reduction of bandgap with increasing arsenic incorporation and provides a tool for device-level design with the material within the context of the k ∙ p formalism. The analysis extends to calculating the effect of the arsenic impurities on hole (heavy, light and split-off) effective masses and predicting the trend of the bandgap across the entire composition range.

Shear-Induced Changes of Electronic Properties in Gallium Nitride.

We show that sliding on the surface of GaN can permanently change the surface band structure, resulting in an increased degree of band bending by more than 0.5 eV. We hypothesize that shear and contact stresses introduce vacancies that cause a spatially variant band bending. Band bending is observed by shifts and broadening of core-level binding energies toward lower values in X-ray photoelectron spectroscopy. The extent of band bending is controlled by humidity, number of sliding cycles and applied load, presenting opportunities for scalable tuning of the degree of band bending on a GaN surface. Scanning transmission electron microscopy revealed that the epitaxy of GaN was preserved up to the surface with regions of defects near the surface. The hypothesized mechanism of band bending is shear-induced defect generation, which has been shown to affect the surface states. The ability to introduce band bending at the GaN surface is promising for applications in photovoltaics, photocatalysis, gas sensing, and photoelectrochemical processes.

Subcritical water extraction of low methoxyl pectin from pomelo (Citrus grandis (L.) Osbeck) peels.

Low methoxyl (LM) pectin was extracted from pomelo peels using subcritical water in a dynamic mode. The effects of pressure and temperature were analyzed through a face-centred central composite design. Extraction yield and the rate of extraction were found to be predominantly influenced by temperature. Optimization of the subcritical water extraction (SWE) yielded an optimized operating condition of 120°C and 30bar with a predicted pectin yield of 18.8%. The corresponding experimental yield was 19.6%, which is in close agreement with the predicted data. The pectin obtained from the optimized condition was further analyzed for its physicochemical properties. The kinetics of the SWE was also evaluated whereby the one-site kinetic desorption model was found to be in good agreement with experimental data (R2>0.94).

First-Principle Study of the Optical Properties of Dilute-P GaN1-xPx Alloys.

An investigation on the optical properties of dilute-P GaN1-xPx alloys by First-Principle Density Functional Theory (DFT) methods is presented, for phosphorus (P) content varying from 0% up to 12.5%. Findings on the imaginary and real part of the dielectric function are analyzed and the results are compared with previously reported theoretical works on GaN. The complex refractive index, normal-incidence reflectivity and birefringence are presented and a difference in the refractive index in the visible regime between GaN and GaNP alloys of ~0.3 can be engineered by adding minute amounts of phosphorus, indicating strong potential for refractive index tunability. The optical properties of the GaN1-xPx alloys indicate their strong potential for implementation in various III-nitride-based photonic waveguide applications and Distributed Bragg Reflectors (DBR).

Ultra-Broadband Optical Gain in III-Nitride Digital Alloys.

A novel III-Nitride digital alloy (DA) with ultra-broadband optical gain is proposed. Numerical analysis shows a 50-period InN/GaN DA yields minibands that are densely quantized by numerous confined states. Interband transitions between the conduction and valence minibands create ultra-broadband optical gain spectra with bandwidths up to ~1 µm that can be tuned from the red to infrared. In addition, the ultra-broadband optical gain, bandwidth, and spectral coverage of the III-Nitride DA is very sensitive to layer thickness and other structural design parameters. This study shows the promising potential of the III-Nitride DAs with tunable ultra-broadband interband optical gain for use in semiconductor optical amplifiers and future III-Nitride photonic integration applications.

Investigations of the Optical Properties of GaNAs Alloys by First-Principle.

We present a Density Functional Theory (DFT) analysis of the optical properties of dilute-As GaN1-xAsx alloys with arsenic (As) content ranging from 0% up to 12.5%. The real and imaginary parts of the dielectric function are investigated, and the results are compared to experimental and theoretical values for GaN. The analysis extends to present the complex refractive index and the normal-incidence reflectivity. The refractive index difference between GaN and GaNAs alloys can be engineered to be up to ~0.35 in the visible regime by inserting relatively low amounts of As-content into the GaN system. Thus, the analysis elucidates on the birefringence of the dilute-As GaNAs alloys and comparison to other experimentally characterized III-nitride systems is drawn. Our findings indicate the potential of GaNAs alloys for III-nitride based waveguide and photonic circuit design applications.

Pathway Towards High-Efficiency Eu-doped GaN Light-Emitting Diodes.

A physically intuitive current injection efficiency model for a GaN:Eu quantum well (QW) has been developed to clarify the necessary means to achieve device quantum efficiency higher than the state-of-the-art GaN:Eu system for red light emission. The identification and analysis of limiting factors for high internal quantum efficiencies (IQE) are accomplished through the current injection efficiency model. In addition, the issue of the significantly lower IQE in the electrically-driven GaN:Eu devices in comparison to the optically-pumped GaN:Eu devices is clarified in the framework of this injection efficiency model. The improved understanding of the quantum efficiency issue through current injection efficiency model provides a pathway to address the limiting factors in electrically-driven devices. Based on our developed injection efficiency model, several experimental approaches have been suggested to address the limitations in achieving high IQE GaN:Eu QW based devices in red spectral regime.

AlN/GaN Digital Alloy for Mid- and Deep-Ultraviolet Optoelectronics.

The AlN/GaN digital alloy (DA) is a superlattice-like nanostructure formed by stacking ultra-thin ( ≤ 4 monolayers) AlN barriers and GaN wells periodically. Here we performed a comprehensive study on the electronics and optoelectronics properties of the AlN/GaN DA for mid- and deep-ultraviolet (UV) applications. Our numerical analysis indicates significant miniband engineering in the AlN/GaN DA by tuning the thicknesses of AlN barriers and GaN wells, so that the effective energy gap can be engineered from ~3.97 eV to ~5.24 eV. The band structure calculation also shows that the valence subbands of the AlN/GaN DA is properly rearranged leading to the heavy-hole (HH) miniband being the top valence subband, which results in the desired transverse-electric polarized emission. Furthermore, our study reveals that the electron-hole wavefunction overlaps in the AlN/GaN DA structure can be remarkably enhanced up to 97% showing the great potential of improving the internal quantum efficiency for mid- and deep-UV device application. In addition, the optical absorption properties of the AlN/GaN DA are analyzed with wide spectral coverage and spectral tunability in mid- and deep-UV regime. Our findings suggest the potential of implementing the AlN/GaN DA as a promising active region design for high efficiency mid- and deep-UV device applications.

III-Nitride Digital Alloy: Electronics and Optoelectronics Properties of the InN/GaN Ultra-Short Period Superlattice Nanostructures.

The III-Nitride digital alloy (DA) is comprehensively studied as a short-period superlattice nanostructure consisting of ultra-thin III-Nitride epitaxial layers. By stacking the ultra-thin III-Nitride epitaxial layers periodically, these nanostructures are expected to have comparable optoelectronic properties as the conventional III-Nitride alloys. Here we carried out numerical studies on the InGaN DA showing the tunable optoelectronic properties of the III-Nitride DA. Our study shows that the energy gap of the InGaN DA can be tuned from ~0.63 eV up to ~2.4 eV, where the thicknesses and the thickness ratio of each GaN and InN ultra-thin binary layers within the DA structure are the key factors for tuning bandgap. Correspondingly, the absorption spectra of the InGaN DA yield broad wavelength tunability which is comparable to that of bulk InGaN ternary alloy. In addition, our investigation also reveals that the electron-hole wavefunction overlaps are remarkably large in the InGaN DA structure despite the existence of strain effect and build-in polarization field. Our findings point out the potential of III-Nitride DA as an artificially engineered nanostructure for optoelectronic device applications.

First-Principle Electronic Properties of Dilute-P GaN(1-x)P(x) Alloy for Visible Light Emitters.

A study on the electronic properties of the dilute-P GaN(1-x)P(x)alloy using First-Principle Density Functional Theory (DFT) calculations is presented. Our results indicate a band gap energy coverage from 3.645 eV to 2.697 eV, with P-content varying from 0% to 12.5% respectively. In addition, through line fitting of calculated and experimental data, a bowing parameter of 9.5 ± 0.5 eV was obtained. The effective masses for electrons and holes are analyzed, as well as the split-off energy parameters where findings indicate minimal interband Auger recombination. The alloy also possesses the direct energy band gap property, indicating its strong potential as a candidate for future photonic device applications.

Large Optical Gain AlInN-Delta-GaN Quantum Well for Deep Ultraviolet Emitters.

The optical gain and spontaneous emission characteristics of low In-content AlInN-delta-GaN quantum wells (QWs) are analyzed for deep ultraviolet (UV) light emitting diodes (LEDs) and lasers. Our analysis shows a large increase in the dominant transverse electric (TE) polarized spontaneous emission rate and optical gain. The remarkable enhancements in TE-polarized optical gain and spontaneous emission characteristics are attributed to the dominant conduction (C)-heavy hole (HH) transitions achieved by the AlInN-delta-GaN QW structure, which could lead to its potential application as the active region material for high performance deep UV emitters. In addition, our findings show that further optimizations of the delta-GaN layer in the active region are required to realize the high performance AlInN-based LEDs and lasers with the desired emission wavelength. This work illuminates the high potential of the low In-content AlInN-delta-GaN QW structure to achieve large dominant TE-polarized spontaneous emission rates and optical gains for high performance AlN-based UV devices.

Dilute-As AlNAs Alloy for Deep-Ultraviolet Emitter.

The band structures of dilute-As AlNAs alloys with As composition ranging from 0% up to 12.5% are studied by using First-Principle Density Functional Theory (DFT) calculation. The energy band gap shows remarkable reduction from 6.19 eV to 3.87 eV with small amount of As content in the AlNAs alloy, which covers the deep ultraviolet (UV) spectral regime. A giant bowing parameter of 30.5 eV ± 0.5 eV for AlNAs alloy is obtained. In addition, our analysis shows that the crossover between crystal field split-off (CH) band and heavy hole (HH) bands occurs in the dilute-As AlNAs alloy with As-content of ~1.5%. This result implies the possibility of dominant transverse electric (TE)-polarized emission by using AlNAs alloy with dilute amount of As-content. Our findings indicate the potential of dilute-As AlNAs alloy as the new active region material for TE-polarized III-Nitride-based deep UV light emitters.

InGaN/Dilute-As GaNAs Interface Quantum Well for Red Emitters.

The design of InGaN/dilute-As GaNAs interface quantum well (QW) leads to significant redshift in the transition wavelength with improvement in electron-hole wave function overlap and spontaneous emission rate as compared to that of the conventional In0.2Ga0.8N QW. By using self-consistent six-band k·p band formalism, the nitride active region consisting of 30 Å In0.2Ga0.8N and 10 Å GaN0.95As0.05 interface QW leads to 623.52 nm emission wavelength in the red spectral regime. The utilization of 30 Å In0.2Ga0.8N/10 Å GaN0.95As0.05 interface QW also leads to 8.5 times enhancement of spontaneous emission rate attributed by the improvement in electron-hole wavefunction overlap, as compared to that of conventional 30 Å In0.35Ga0.65N QW for red spectral regime. In addition, the transition wavelength of the interface QW is relatively unaffected by the thickness of the dilute-As GaNAs interface layer (beyond 10 Å). The analysis indicates the potential of using interface QW concept in nitride-based light-emitting diodes for long wavelength emission.

Acanthoic acid inhibits LPS-induced inflammatory response in human gingival fibroblasts.

Periodontitis is a chronic disease that affects the gums and destroys connective tissue. Acanthoic acid (AA), a diterpene in Acanthopanax koreanum, has been reported to have anti-inflammatory activities. The aim of this study was to investigate the anti-inflammatory effects of AA on lipopolysaccharide (LPS)-induced inflammatory response in human gingival fibroblasts (HGFs). HGFs were treated with Porphyromonas gingivalis LPS in the presence or absence of AA. The production of inflammatory cytokines IL-8 and IL-6 were measured by ELISA. The expression of NF-κB and TLR4 were detected by Western blotting. The results showed that AA inhibited LPS-induced IL-8 and IL-6 production in a dose-dependent manner. In addition, AA inhibited LPS-induced TLR4 expression and NF-κB activation. In conclusion, AA inhibits LPS-induced inflammatory response in HGFs through inhibition TLR4-mediated NF-κB signaling pathway.

Aspect ratio engineering of microlens arrays in thin-film flip-chip light-emitting diodes.

Light extraction efficiency of thin-film flip-chip InGaN-based light-emitting diodes (LEDs) with a TiO2 microlens arrays was calculated by employing the finite-difference time-domain method. The microlens arrays, formed by embedding hexagonal close-packed TiO2 sphere arrays in a polystyrene (PS) layer, were placed on top of the InGaN LED to serve as an intermediate medium for light extraction. By tuning the thickness of the PS layer, in-coupling and out-coupling efficiencies were optimized to achieve maximum light extraction efficiency. A thicker PS layer resulted in higher in-coupling efficiency, while a thinner PS layer led to higher out-coupling efficiency. Thus, the maximum light extraction efficiency becomes a trade-off between in-coupling and out-coupling efficiency. In addition, the cavity formed by the PS layer also affects light extraction from the LED. Our study reveals that a maximum light extraction efficiency of 86% was achievable by tuning PS thickness to 75 nm with maximized in-coupling and out-coupling efficiency accompanied by the optimized resonant cavity condition.

Infection and cellular defense dynamics in a novel 17ß-estradiol murine model of chronic human group B streptococcus genital tract colonization reveal a role for hemolysin in persistence and neutrophil accumulation.

Genital tract carriage of group B streptococcus (GBS) is prevalent among adult women; however, the dynamics of chronic GBS genital tract carriage, including how GBS persists in this immunologically active host niche long term, are not well defined. To our knowledge, in this study, we report the first animal model of chronic GBS genital tract colonization using female mice synchronized into estrus by delivery of 17ß-estradiol prior to intravaginal challenge with wild-type GBS 874391. Cervicovaginal swabs, which were used to measure bacterial persistence, showed that GBS colonized the vaginal mucosa of mice at high numbers (10(6)-10(7) CFU/swab) for at least 90 d. Cellular and histological analyses showed that chronic GBS colonization of the murine genital tract caused significant lymphocyte and PMN cell infiltrates, which were localized to the vaginal mucosal surface. Long-term colonization was independent of regular hormone cycling. Immunological analyses of 23 soluble proteins related to chemotaxis and inflammation showed that the host response to GBS in the genital tract comprised markers of innate immune activation including cytokines such as GM-CSF and TNF-α. A nonhemolytic isogenic mutant of GBS 874391, Δcyle9, was impaired for colonization and was associated with amplified local PMN responses. Induction of DNA neutrophil extracellular traps, which was observed in GBS-infected human PMNs in vitro in a hemolysin-dependent manner, appeared to be part of this response. Overall, this study defines key infection dynamics in a novel murine model of chronic GBS genital tract colonization and establishes previously unknown cellular and soluble defense responses to GBS in the female genital tract.

Orf virus interleukin-10 inhibits cytokine synthesis in activated human THP-1 monocytes, but only partially impairs their proliferation.

The sheep parapoxvirus orf virus (ORFV) induces acute, pustular skin lesions in humans. ORFV encodes an orthologue of interleukin-10 (IL-10) that, whilst it closely resembles ovine IL-10 (91 % amino acid identity), shows only 75 % amino acid identity to human IL-10 (hIL-10). The anti-inflammatory potential of ORFV IL-10 in human ORFV infection was investigated by examining its immunosuppressive effects on THP-1 monocytes. ORFV IL-10 and hIL-10 were shown to have equivalent inhibitory effects on the synthesis of proinflammatory cytokines in lipopolysaccharide-activated monocytes, but differed in their abilities to inhibit monocyte proliferation. Structural modelling of ORFV IL-10 revealed differences from hIL-10 in residues predicted to interact with IL-10 co-receptor 2 (IL-10R2), whereas there were very few differences in the residues predicted to interact with IL-10R1. These findings suggest that the partial ability of ORFV IL-10 to inhibit THP-1 monocyte proliferation may be due to the absence of critical residues that mediate the interaction with human IL-10R2.

Epidemiology of fatty liver in a hospital-based study in Taiwan.

BACKGROUND: The aim of this study was to assess the epidemiology of fatty liver in Taiwan. METHODS: We retrospectively analyzed the medical records of all patients receiving health examinations at China Medical College Hospital from January through December 2000. A total of 1,012 subjects were included for analysis. Data were analyzed using the t test, chi-square analysis, and multivariate logistic regression. RESULTS: Our cohort was comprised of 41.8% women and 58.2% men; mean age was 49.2 years. The prevalence of fatty liver was 36.9% in all subjects, and prevalence was higher in men than in women. After controlling for other covariates, the multivariate logistic regression analysis showed that the significant factors related to fatty liver were male sex, obesity, hyperglycemia, hypertriglyceridemia, elevated glutamate pyruvate transaminase level, and hyperuricemia. Elevated glutamate oxaloacetate transaminase level was negatively associated with fatty liver. CONCLUSIONS: The prevalence of fatty liver is high in Taiwan. This study establishes background data for further investigation.