Computational Screening of a Single-Atom Catalyst Supported by Monolayer Nb2S2C for Oxygen Reduction Reaction.

The search for high-performance catalysts to improve the catalytic activity for an oxygen reduction reaction (ORR) is crucial for developing a proton exchange membrane fuel cell. Using the first-principles method, we have performed computational screening on a series of transition metal (TM) atoms embedded in monolayer Nb2S2C to enhance the ORR activity. Through the scaling relationship and volcano plot, our results reveal that the introduction of a single Ni or Rh atom through substitutional doping into monolayer Nb2S2C yields promising ORR catalysts with low overpotentials of 0.52 and 0.42 V, respectively. These doped atoms remain intact on the monolayer Nb2S2C even at elevated temperatures. Importantly, the catalytic activity of the Nb2S2C doped with a TM atom can be effectively correlated with an intrinsic descriptor, which can be computed based on the number of d orbital electrons and the electronegativity of TM and O atoms.

The effect of vacancy defects on the electromechanical properties of monolayer NiTe2 from first principles calculations.

The electromechanical properties of monolayer 1-T NiTe2 under charge actuation were investigated using first-principles density functional theory (DFT) calculations. Monolayer 1-T NiTe2 in its pristine form has a work area density per cycle of up to 5.38 MJ m-3 nm upon charge injection and it can generate a strain and a stress of 1.51% and 0.96 N m-1, respectively. We found that defects in the form of vacancies can be exploited to modulate the electromechanical properties of this material. The presence of Ni-vacancies can further enhance the generated stress by 22.5%. On the other hand, with Te-vacancies, it is possible to improve the work area density per cycle by at least 145% and also to enhance the induced strain from 1.51% to 2.92%. The effect of charge polarity on the contraction and expansion of monolayer 1T-NiTe2 was investigated. Due to its excellent environmental stability and good electromechanical properties, monolayer NiTe2 is considered to be a promising electrode material for electroactive polymer (EAP) based actuators.

A first-principles study of two-dimensional NbSe2H/g-ZnO van der Waals heterostructures as a water splitting photocatalyst.

Based on first-principles calculations, we propose a new two-dimensional (2D) van der Waals (vdW) heterostructure that can be used as a photocatalyst for water splitting. The heterostructure consists of vertically stacked 2D NbSe2H and graphene-like ZnO (g-ZnO). Depending on the stacking orders, we identified two configurations that have high binding energies with an energy band gap of >2.6 eV. These 2D systems form a type-II heterostructure which enables the separation of photoexcited electrons and holes. The presence of a strong electrostatic potential difference across the 2D NbSe2H and g-ZnO interface is expected to suppress the electron-hole recombination leading to an enhancement in the efficiency of the photocatalytic activity. Our study also shows that the 2D NbSe2H/g-ZnO vdW heterostructure has good thermodynamic properties for water splitting. Furthermore, the optical absorption of the 2D NbSe2H/g-ZnO vdW heterostructure extends into the visible light region. Our results suggest that the 2D NbSe2H/g-ZnO vdW heterostructure is a promising photocatalytic material for water splitting.

A first-principles comparative study of lithium, sodium, potassium and calcium storage in two-dimensional Mg2C.

Two-dimensional (2D) materials have recently emerged as potential candidates for high-capacity lithium-ion batteries anode materials because of their compelling physicochemical and structural properties. In the present study, we use first-principles calculations to investigate the performance of 2D Mg2C as anode materials for Li, Na, K and Ca-ions batteries. The calculated average open-circuit voltage are 0.37, 0.50, 0.03 and 0.06 eV vs Li, Na, K, Ca. No significant structural deformations are observed on the 2D Mg2C upon the adsorption of Li, Na, K or Ca and the metallic characteristic of the 2D Mg2C is retained. The metallic behaviour of both pristine and adsorbed Mg2C ensures the desirable electric conductivity, implying the advantages of 2D Mg2C for batteries. The Na and K atoms show an extremely high diffusivity on the 2D Mg2C with a low energy barrier of 0.08 and 0.04 eV respectively, which is about an order of magnitude smaller than that of Li atom. For the Na and K atoms, the theoretical storage capacity can reach up to 1770 mAh g-1, nearly two times that of the Li atom of 885 mAh g-1. Our study suggests that the 2D Mg2C is a promising anode material which offers a fast ion diffusion and high storage capacity.

The removal of metallic single-walled carbon nanotubes using an aqueous two-phase system.

Here we report our findings on the removal of metallic single-walled carbon nanotubes using an aqueous two-phase system. The aqueous two-phase system contained as received carbon nanotubes, polyethylene glycol, dextran, N-methylpyrrolidone, cetyltrimethylammonium bromide, and water which phase separated into top and bottom phases. The top phase was dominated by polyethylene glycol whereas the bottom phase was dominated by dextran. The dextran-rich phase contained more semiconducting species while metallic species was more abundant in the polyethylene glycol rich-phase. It was found via Fourier-Transform Infrared Spectroscopy that cetyltrimethylammonium bromide only present in the dextran-rich phase. A selectivity mechanism is tentatively proposed and discussed.

The upper and lower airway responses to nasal challenge with house-dust mite Blomia tropicalis.

BACKGROUND: The house dust mite Blomia tropicalis (B. tropicalis) was found to be the most prevalent domestic mite in Singapore. However, its pathogenicity in allergic airway diseases remains to be investigated. METHODS: Twenty adults with persistent allergic rhinitis (PAR) were studied. Five had a history of asthma, and all were asymptomatic except one who was under treatment with low-dose inhaled corticosteroid. Nasal challenge was carried out by nasal spray with phosphate-buffered saline (PBS) and with increasing concentrations of crude B. tropicalis extracts (0.6, 6.0 and 60 micro g/ml) at 15 min intervals. Subjective symptom scores and absolute number of sneezes were recorded together with objective measurements of spirometry (forced expiratory volume in 1 s, FEV1) and acoustic rhinomanometry (volume of the nasal cavity). These were performed at baseline, 5 min after each incremental challenge, and 30 min, 1 h, 3 h, 5 h and 7 h after the last challenge. Meanwhile, concentrations of mediators in nasal secretions (tryptase, leukotriene C4 (LTC4) and eosinophil cationic protein (ECP)) were measured in nasal aspirate samples at similar time intervals. An identical (control) challenge procedure with PBS alone was repeated in seven patients after a washout period of at least 2 weeks. RESULTS: Significant increases in the subjective and objective nasal symptoms, together with a significant increase of tryptase and LTC4 concentrations in nasal secretion, were found 5 min after each challenge with B. tropicalis, but not with PBS. There was no definitive pattern of the late-phase nasal response in either subjective symptoms or objective measurements. Three patients (3/5) with a history of asthma showed a fall in FEV1 readings (33%, 22% and 11% from baseline, respectively) at 7 h post challenge with concomitant mild wheezing in the night. CONCLUSIONS: Our study demonstrates direct evidence of allergic nasal response to B. tropicalis in sensitized adults. It shows that nasal provocation may also provoke concomitant asthmatic symptoms during the late-phase reaction, especially in people with a history of asthma.

Rhinitis: do diagnostic criteria affect the prevalence and treatment?

BACKGROUND: Rhinitis is one of the world's most common health problems. Diagnostic criteria used in community surveys may affect reported prevalence and treatment. METHODS: A proportionately stratified random sample study was performed to investigate the prevalence, comorbidities and management of community-based patients with rhinitis in the tropical urban city of Singapore. RESULTS: The prevalence of at least one, two, three, or four nasal symptoms on most days during the past year in our study population was 25.5%, 13.1%, 6.5%, and 3.0%, respectively. Based on the definition of 'rhinitis' by the International Consensus Report (ICR), the prevalence was 13.1% in Singapore. There was significantly higher prevalence of self-reported allergy, asthma, and common cold/influenza-like illness among the rhinitis group. In the 53% of rhinitis subjects seeking for medical help, 71% visited a primary care physician and 20% an otolaryngologist. Treatments as reported by patients were decongestants (topical or oral) 27%, antibiotics 12%, antihistamines 6%, nasal steroids 3%, surgery 2%, traditional methods 28%, and 22% did not know what medication they had. Subjects considered the effectiveness of treatment unsatisfactory because the majority of them had only partial or no relief with any treatment. CONCLUSIONS: The standardization of the definition of rhinitis in epidemiological studies is of crucial importance, especially when comparing the prevalence between studies. Appropriate patient education by physicians with a good understanding of the nature of rhinitis and the available treatment options (e.g. evidenced-based efficacy, safety, and a good cost-benefit ratio) will maximize patient compliance and treatment outcomes.

Evaluation of nasal cavity by acoustic rhinometry in Chinese, Malay and Indian ethnic groups.

Acoustic rhinometry (AR) evaluates the geometry of the nasal cavity by measuring the minimum cross-sectional area (MCA) and nasal volume (V) by means of acoustic reflection. Understanding the normal and pathologic conditions of the internal nasal cavity using AR is important in the diagnosis of structural abnormalities in patients. The aim of this study was to investigate the normal range of AR parameters in healthy volunteers from three ethnic groups in Singapore: Chinese, Malay and Indian. We also attempted to evaluate the role of these measurements in the documentation of structural abnormalities in the nose. A total of 189 Singaporeans, aged > or = 18 years, were recruited from a nationwide survey study. They comprised 83 Chinese, 35 Malays and 71 Indians. Eighty-nine subjects had a rhinoscopically normal nose (Group 1), 77 had significant septal deviation (Group 2) and 23 had inferior turbinate hypertrophy (Group 3). AR was performed to measure the MCA at the anterior 1-5 cm from the nostril and the volume (V) between points at the nostril and 5 cm into the nose. A mean MCA (mMCA; equal to (L + R)/2) and a total volume (Vt; equal to L + R) were then calculated for each subject, where L and R refer to the measurements made for the left and right nostrils, respectively. The results showed that there was no statistically significant difference in mMCA (p = 0.80) and Vt (p = 0.60) among the three ethnic subgroups of Group 1. Statistically significant differences were found only between Groups 1 and 3 (p < 0.001 for both mMCA and Vt) and between Groups 2 and 3 (p = 0.001 for mMCA and p = 0.013 for Vt). Although there was no significant difference between Groups 1 and 2, significant differences in MCA (p = 0.001) and V (p = 0.040) were found between the narrower sides (smaller volume) and the wider sides in Group 2, indicating volume compensation between the nasal cavities. In conclusion, our study demonstrates that there is no significant difference in the normal range of AR measurements among Chinese, Malay and Indian ethnic groups. AR is able to determine the structural abnormality of the internal nasal cavity caused by septal deviation and inferior turbinate hypertrophy.

Effects of nitric oxide on normal and ischemic cochlea of the guinea pig.

To determine whether nitric oxide (NO)/peroxynitrite plays any role in neurodestruction observed in ischemic cochlea of the guinea pig, the effects of NO donors like S-nitrosocysteine (S-NC) and nitroglycerin (NTG), peroxynitrite generators like 3-morpholinosydnonimine (SIN-1), peroxynitrite inhibitors like superoxide dismutase plus catalase (SOD/Cat), as well as NOS inhibitors like N(G)-nitro-l-arginine methyl ether (L-NAME), were tested on normal and ischemic cochleae. Various concentrations of S-NC and SIN-1 were introduced into the perilymphatic space of normal guinea pig cochlea. Quantitative scanning electron microscopy of inner and outer hair cells was carried out 2 days later. To determine the level of NO in the cochlea after 20 to 120 min of ischemia, nitrites/nitrates in the perilymph were measured. The effects of NO on the ischemic cochlea were tested by infusion of SOD/Cat, L-NAME, S-NC, and NTG into the perilymphatic space just before decapitation. Introduction of fixative into the cochlea was delayed for 15 min to investigate the effects of the chemicals on nerve endings at the base of inner hair cells. The results showed that the level of nitrites/nitrates tended to decline with increasing time of ischemia. There was no significant hair cell loss in the cochleae treated with SIN-1 or S-NC. At 15 min after ischemia, most of the nerve endings at the base of the inner hair cells were protected from damage when 1 mM S-NC or NTG was infused into the perilymph. Taken together, the results indicate that NO/peroxynitrite is unlikely to be involved in the neurodestruction in the ischemic cochlea. In fact, exogenous NO may have a neural protective effect.

Complications of foreign bodies in the esophagus.

Major complications of foreign bodies in the esophagus carry significant morbidity and mortality risks. A retrospective case control study was performed to assess the factors associated with major complications. In total, 273 patients seen within a 7-year period were divided into 2 groups; 253 had no or minor complications, and 20 had major complications. Age, sex, duration of the foreign body, total white cell count (TWC), and nature and site of the foreign body were analyzed in the 2 groups. The major complication rate was 7.3%. Duration of the foreign body and TWC were the only statistically significant factors associated with major complications. Six patients required open neck exploration, 1 had an open thoracotomy, and 13 were treated by endoscopic removal. There were 2 deaths. Given the significant morbidity and mortality risks, we conclude that patients with a prolonged history of a foreign body in the esophagus and a raised TWC should be treated urgently.

Ototoxicity of sodium nitroprusside is not due to nitric oxide.

Sodium nitroprusside (SNP) has been used as a donor for nitric oxide (NO) to study the effects of NO on the mammalian cochlea. In the present study, we set out to determine whether NO was the chemical responsible for the ototoxic effects seen after the application of SNP at the round window membrane of the adult guinea pig cochlea. In the first instance, NO released from S-nitrosocysteine, a compound not related to cyanide, has no toxic effect on the hair cells of the cochlea. Light-exposed SNP that could no longer produce NO, light-exposed SNP to which acetylcysteine (ATC) or hydroxycobalamin (HCL) was added to eliminate cyanide, and freshly prepared SNP to which ATC or HCL was added were also tested. Six groups of animals consisting of three animals in each group were used. The single chemical or combination of chemicals stated above was soaked in a piece of gelfoam that was then applied to the round window membrane of the animal under ketamine-xylasine anesthesia. The animals were reanesthetized 3 days later and perfused for scanning electron microscopy and hair cell quantitative analysis. The results showed that, in animals given S-nitrosocysteine, no hair cell loss was noted, while light-exposed SNP led to severe hair cell damage similar to that seen after the administration of fresh SNP. In animals treated with the mixture of light-exposed SNP and ATC or HCL, or fresh SNP with ATC or HCL, ototoxicity was significantly attenuated. These results have convincingly demonstrated that NO at a certain level is not destructive to auditory hair cells and the hair cell loss observed after SNP application is most likely due to the cyanide released from the SNP instead of NO.

Increased production of interferon-gamma by tumour infiltrating T lymphocytes in nasopharyngeal carcinoma: indicative of an activated status.

Undifferentiated nasopharyngeal carcinomas (UNPC) are characterised by an association with Epstein-Barr virus and an abundant lymphoid stroma. We studied the functional status of the infiltrating T cells in ten UNPC biopsies using an immunohistochemical approach. Twelve non-NPC biopsies were included as controls. Tumour cells of UNPC were positive for HLA class I (10/10) and II (8/10), LMP1 (3/10), and CD86 (6/10). Tumour infiltrating T cells (TILs) were detected with antibodies directed at CD3, CD4, and CD8, and shown to be comparable to that in the control biopsies. Although expression of CD28 was shown to be decreased in TILs, expression of CD25 and IFN-gamma at a relatively high percentage could be consistently detected in the UNPC biopsies. These data suggest that TILs in UNPC are in an activated status, and this T cell response is possibly directed at the tumour cells.

Effects of BDNF and NT-3 on hair cell survival in guinea pig cochlea damaged by kanamycin treatment.

The aim of this study was to determine whether neurotrophic factors such as brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) would protect auditory hair cells from ototoxicity by aminoglycoside antibiotic. Twenty-seven Wistar guinea pigs were divided into three groups of nine animals each. BDNF and NT-3 (100 microg/ml) were delivered into the right scala tympani of guinea pig cochlea through a cannula-osmotic pump device. Artificial perilymph (AP) was used as control. Immediately after implantation of the device, each animal was given five successive doses of kanamycin (400 mg/kg). At 15, 30 and 60 days after infusion, surviving inner and outer hair cells were counted at each turn of every cochlea with a Philips 515 scanning electron microscope. Multiple comparison tests were carried out among the groups, using ANOVA and Dunnett T3/Tukey HSD. Protective effects of NT-3 on hair cells were observed at 30 and 60 days after kanamycin injection. BDNF had no protective effect on hair cells at 15 and 60 days, but some at 30 days. This study suggests that NT-3 and BDNF may protect against cochlear hair cell damage caused by kanamycin treatment. Possible mechanisms for the otoprotective effects were discussed. No single mechanism postulated can explain fully the results seen in this study. It is possible that the mechanisms act in concert to produce the observed effects, or there are as yet undiscovered mechanisms or secondary messengers responsible for the otoprotective effects.

The significance and technical aspects of quantitative measurements of inflammatory mediators in allergic rhinitis.

The pathophysiology of allergic rhinitis induced by various inhalant allergens through an IgE mediated mechanism, has been well demonstrated. The participation of many important inflammatory cells and mediators released by these cells in the human nasal allergic reaction provides insight into the relationship between the responsiveness to allergen exposure and nasal symptoms of allergic rhinitis. This paper summarizes our previous studies on some important mediators in the nasal secretions of atopic patients during different phases after nasal allergen challenge and during natural allergen exposure. The microsuction technique proves to be an especially useful and reliable nasal sampling method permitting quantitative analysis of important mediators such as histamine, tryptase, leukotriene C4 and eosinophil cationic protein in nasal secretions. The measurement of these mediators during allergic reactions provides accurate data on the activity of some important inflammatory cells (i.e., mast cells, basophils, and eosinophils) and their responses to therapy.

Otitis externa--the clinical pattern in a tertiary institution in Singapore.

Otitis externa is a common condition in the tropics. Most of the data related to the condition have arisen from Western sources. Locally, the aetiology and the pathogens identified have not been systematically studied. A prospective study involving 107 patients was conducted. Otomycosis was frequently encountered. Coagulase negative Staphylococcus and Aspergillus niger were the most common bacteria and fungus cultured respectively. Gentamicin and polymyxin B were the most effective topical agents against Pseudomonas aeruginosa. Self-cleaning of the ears was the most common predisposing factor.

Localization of nitric oxide synthase and NADPH-diaphorase in guinea pig and human cochleae.

The distributions of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) and nitric oxide synthase (NOS) in mammalian cochlea were studied at light and electron microscope levels by NADPH-d histochemistry and brain NOS (bNOS) immunohistochemistry. The cochleae from 15 albino guinea pigs were perilymphatically fixed with 2% periodate-lysine-paraformaldehyde, decalcified in 10% EDTA and processed for light and electron microscopy after NADPH-d or NOS staining in frozen and vibratome sections respectively. One human cochlea was available for light microscope examination of NADPH-d or bNOS stained sections. Light microscope results revealed that type I neurons and nerve fibers of the spiral ganglion cells were labeled by bNOS immunohistochemistry as well as NADPH-d histochemistry in both guinea pig and human cochleae. At subcellular level, NADPH-d reaction product was localized in the mitochondria of the neuronal cytoplasm and axoplasm and in the cytoplasm of the vascular endothelium. The immunoreaction products of bNOS were evenly distributed in the neuronal cytoplasm and axoplasm. Myelinated and unmyelinated fibers in the intraganglionic spiral bundle and the inner spiral and inner radial fibers below the inner hair cells were labeled for bNOS. The nerve endings below the outer hair cells were not stained. NOS immunoreaction product was also found in the outer hair cells, Schwann cells of myelinated nerve fibers, Deiter's cells, pillar cells and the tympanic lamina cells. No difference was found in the staining pattern of both NADPH-d and NOS reaction products between human and guinea pig cochleae at the light microscope level. The results suggest that NO plays an important role in the maintenance of auditory function in the mammal.

Ototoxicity of sodium nitroprusside.

Nitric oxide (NO) not only has normal physiological roles like vasodilation and neurotransmission in the living organism, it could also have possible neurodestructive effects under certain pathological conditions. The present study aimed to determine whether direct exposure of guinea pig cochlea to a NO donor like sodium nitroprusside (SNP), or a nitric oxide synthase (NOS) inhibitor like N(G)-nitro-L-arginine methyl ester (L-NAME), would cause damage to the auditory hair cells. A piece of gelfoam was placed on the round window of the right ear of adult albino guinea pigs. It was then soaked with 0.1 ml of SNP (3.4 microM), 0.1 ml of L-NAME (9.3 microM or 18.5 microM) or 0.1 ml of injection water, the vehicle used to dissolve the above chemicals. Twelve animals receiving SNP were perfused 1 day, 2, 3 and 7 days later, with three animals being used for each survival period. Six animals receiving L-NAME were allowed to survive up to 7 days before perfusion. Eight animals receiving injection water or 0.45% saline were used as controls. With the scanning electron microscope, the inner and outer hair cells were counted over a 1 mm length of the basilar membrane in each turn of every cochlea. The results showed that, in animals treated with L-NAME at both concentrations stated, no significant loss of either inner or outer hair cells was noted in any part of the cochlea studied. However, as early as 1 day after SNP treatment, a striking loss of inner and outer hair cells was observed in the three lower turns of the cochlea. Damage to the outer hair cells was extended to the apical turn with increasing survival period, but no significant loss of inner hair cells was evident in the apical turn at any of the survival periods studied. To rule out the possibility that the effects were due to the presence of cyanide, a metabolite of SNP, hydroxycobalamin was introduced into the scala tympani of three animals through a cannula-osmotic pump device during SNP treatment. There was no significant difference in the results between the groups with and without hydroxycobalamin infusion 7 days after SNP treatment. The present study suggests that an excessive production of NO in the inner ear could lead to extensive loss of hair cells.