Temperature-dependent photoluminescence properties of porous fluorescent SiC.

A comprehensive study of surface passivation effect on porous fluorescent silicon carbide (SiC) was carried out to elucidate the luminescence properties by temperature dependent photoluminescence (PL) measurement. The porous structures were prepared using an anodic oxidation etching method and passivated by atomic layer deposited (ALD) Al2O3 films. An impressive enhancement of PL intensity was observed in porous SiC with ALD Al2O3, especially at low temperatures. At temperatures below 150 K, two prominent PL emission peaks located at 517 nm and 650 nm were observed. The broad emission peak at 517 nm was attributed to originate from the surface states in the porous structures, which was supported by X-ray photoelectron spectra characterization. The emission peak at 650 nm is due to donor-acceptor-pairs (DAP) recombination via nitrogen donors and boron-related double D-centers in fluorescent SiC substrates. The results of the present work suggest that the ALD Al2O3 films can effectively suppress the non-radiative recombination for the porous structures on fluorescent SiC. In addition, we provide the evidence based on the low-temperature time-resolved PL that the mechanism behind the PL emission in porous structures is mainly related to the transitions via surface states.

Terahertz time-domain spectroscopy of zone-folded acoustic phonons in 4H and 6H silicon carbide.

We investigate the dielectric properties of the 4H and 6H polytypes of silicon carbide in the 0.1-19 THz range, below the fundamental transverse-optical phonons. Folding of the Brillouin zone due to the specific superlattice structure of the two polytypes leads to activation of acoustic phonon modes. We use a combination of ultrabroadband terahertz time-domain spectroscopy and simulations based on density-functional perturbation theory to observe and characterize these modes, including band splitting due to the dissimilar carbon and silicon sublattices of the structures, and an indirect measurement of the anisotropic sound velocities in the two polytypes.

Genotyping and molecular detection of multidrug-resistant Mycobacterium tuberculosis among tuberculosis lymphadenitis cases in Addis Ababa, Ethiopia.

Multidrug-resistant tuberculosis (MDR-TB) has emerged as a major public health problem. Drug-resistance surveillance data show that 3.9% of new and 21% of previously treated TB cases were estimated to have had rifampicin/ multidrug-resistant tuberculosis (MDR/RR-TB) in 2015. This implies that the MDR-TB is increasing alarmingly. Hence, a better understanding of drug resistance mechanisms and genotypes associated with multidrug resistance in M. tuberculosis is crucial for improving diagnostic and therapeutic methods to treat individuals with MDR-TB. The aim of this study was to analyze molecular drug resistance mutations of MDR-TB isolates from the cases of TB-lymphadenitis in relation to its genetic lineages. A cross-sectional study was conducted on culture positive cases from July to October, 2014 in Addis Ababa, Ethiopia. Sixty isolates were included to analyze drug resistance mutated gene responsible for MDR-TB in relation to its molecular genotyping. Mycobacterial culture, GenoTypeMTBDR plus and Spoligotyping were used to undertake the study. Of 60 TBLN isolates, 8.3% were identified MDR-TB cases and one isolate was isoniazid mono-resistant. Eleven isolates in T3-ETH genetic sub lineage were sensitive to both RMP and INH, while only 2 isolates were MDR-TB. Most of the RMP- resistant isolates showed mutation in codon S531L and all isolates mutated in the katG gene conferring INH resistant strains had mutations in codon of S315T1. Screening for the rpoB and katG gene mutation of tuberculosis lymphadenitis is useful in Ethiopia for an early detection and treatment of MDR-TB. Besides, there is a drug resistance variation among different lineages of Tuberculosis lymphadenitis which has important consequences for the development of efficient control strategies.

Determination and Analysis of Film Reject Rate at Eight Selected Governmental Diagnostic X-Ray Facilities in Tigray Region, Northern Ethiopian.

BACKGROUND: In radiography examination, it is common to encounter patients undergoing repeated X-ray exposure after the rejection of a film image due to poor image quality. This subjects the patients to unnecessary radiation exposure and extra cost for the facility. This fact has required to investigate the causes of film rejection in common X-ray examinations. AIMS: This study aims to obtain images, which are adequate for the clinical diagnostic purpose with minimum radiation dose to the patient in X-ray radiographic examination using film rejects analysis. METHODS: A prospective, crosssectional study design was carried out for 3 months. The film rejection rate data were collected using standardized checklist as recommended by the National Radiation Protection Authority and International Atomic Energy Agency. Daily recordings were compiled by frontline radiographers and senior physicians. STATISTICAL ANALYSIS USED: Data were analyzed descriptively using SPSS of version 23 software. RESULTS: Overall rejection rate was 319 (10.02%) in 3183 X-ray exposures. The rejection rates by hospitals are 33.7% in Adwa, 13% in Aksum, 9.6% in Suhul, 9.2% in AbiAdi, 7.7% in Humera, 7% in Wukro, 4.3% in Lemlem Karl, and 2.9% in Alamata General Hospitals. CONCLUSIONS: Rejected films were found to have been caused by numerous factors including incorrect exposure, poor technical judgment, patient motion, and improper film processing. Hence, strategies need to be developed within medical imaging departments to improve the situation.

Amplification of resonant field enhancement by plasmonic lattice coupling in metallic slit arrays.

Nonlinear spectroscopic investigation in the terahertz (THz) range requires significant field strength of the light fields. It is still a challenge to obtain the required field strengths in free space from table-top laser systems at sufficiently high repetition rates to enable quantitative nonlinear spectroscopy. It is well known that local enhancement of the THz field can be obtained for instance in narrow apertures in metallic films. Here we show by simulation, analytical modelling and experiment that the achievable field enhancement in a two-dimensional array of slits with micrometer dimensions in a metallic film can be increased by at least 60% compared to the enhancement in an isolated slit. The additional enhancement is obtained by optimized plasmonic coupling between the lattice modes and the resonance of the individual slits. Our results indicate a viable route to sensitive schemes for THz spectroscopy with slit arrays manufactured by standard UV photolithography, with local field strengths in the multi-ten-MV/cm range at kHz repetition rates, and tens of kV/cm at oscillator repetition rates.

Molecular typing of mycobacteria isolated from tuberculous lymphadenitis cases in Addis Ababa, Ethiopia.

BACKGROUND: In Ethiopia, one of the world's 22 high tuberculosis (TB) burden countries, one third of the tuberculosis (TB) cases are attributed to tuberculosis lymphadenitis (TBLN). However, information on the molecular type of the mycobacterial species and strains that cause TBLN in the country is scarce. OBJECTIVE: To identify the species and strains of mycobacteria that cause TBLN in Ethiopia. METHODS AND RESULTS: A cross-sectional study was conducted among 206 presumed TBLN cases to characterise positive culture isolates. Mycobacterium tuberculosis complex species and strains were identified using region of difference 9 deletion and SITVIT WEB, respectively. Of the 206 fine-needle aspirate samples collected, 74 (36%) were culture-positive: 73 (98.6%) of the isolates were M. tuberculosis, and the remaining 1.4% were M. bovis. Further characterisation of the 73 M. tuberculosis isolates led to 26 distinct spoligotype international types (SITs) and 13 newly identified patterns. The most prevalent strains were SIT149, SIT53, SIT26 and SIT37 of sublineages T3-ETH, T1, CASI-DELHI and T3, respectively; these accounted for 52.6% of the total number of strains. CONCLUSION: TBLN was mainly caused by M. tuberculosis and highly clustered strains SIT149, SIT53, SIT26 and SIT37 of sublineages T3-ETH, T1, CASI-DELHI and T3, respectively.

Strain diversity of mycobacteria isolated from pulmonary tuberculosis patients at Debre Birhan Hospital, Ethiopia.

BACKGROUND: Ethiopia ranks seventh in the list of 22 high tuberculosis (TB) burden countries, with an incidence rate of 379 cases per 100,000 population for TB all forms. However, information on the genomic diversity of Mycobacterium tuberculosis in Ethiopia is limited. OBJECTIVE: To investigate the molecular characteristics of M. tuberculosis strains implicated in pulmonary TB in the study area. METHODS AND RESULTS: A cross-sectional study was conducted using socio-demographic, clinical and culture data combined with molecular typing analysis. The proportion of TB and M. tuberculosis isolates was not associated with risk factors (P > 0.05). Of 99 sputum samples, 80.8% were culture-positive. Speciation of isolates showed that 88.8% were M. tuberculosis. Further characterisation led to the identification of 27 different spoligotype patterns of M. tuberculosis; the most dominant shared types were SIT149, SIT53 and SIT54. Of the 27 strains, three strains were new and were reported to the SITVIT database. More than two thirds of the strains belonged to the Euro-American lineage. CONCLUSION: This study shows the presence of several clusters and new strains of M. tuberculosis circulating in pulmonary TB patients in the study area, suggesting recent transmission. Nationwide studies are recommended to map the population structure of M. tuberculosis and set control measures.

Susceptibility of clinical isolates of Leishmania aethiopica to miltefosine, paromomycin, amphotericin B and sodium stibogluconate using amastigote-macrophage in vitro model.

Cutaneous Leishmaniasis (CL) caused by Leishmania aethiopica is a public health and social problem with a sequel of severe and mutilating skin lesions. It is manifested in three forms: localized CL (LCL), mucosal CL (MCL) and diffuse CL (DCL). Unresponsiveness to sodium stibogluconate (Sb(V)) is common in Ethiopian CL patients. Using the amastigote-macrophage in vitro model the susceptibility of 24 clinical isolates of L. aethiopica derived from untreated patients was investigated. Eight strains of LCL, 9 of MCL, and 7 of DCL patients together with a reference strain (MHOM/ET/82/117/82) were tested against four antileishmanial drugs: amphotericin B, miltefosine, Sb(V) and paromomycin. In the same order of drugs, IC(50) (µg/ml±SD) values for the 24 strains tested were 0.16±0.18, 5.88±4.79, 10.23±8.12, and 13.63±18.74. The susceptibility threshold of isolates originating from the 3 categories of patients to all 4 drugs was not different (p>0.05). Maximal efficacy was superior for miltefosine across all the strains. Further susceptibility test could validate miltefosine as a potential alternative drug in cases of sodium stibogluconate treatment failure in CL patients.

Antiretroviral therapy abrogates association between arginase activity and HIV disease severity.

Arginase-induced L-arginine deprivation is emerging as a key mechanism for the downregulation of immune responses. We hypothesised that arginase activity increases with disease severity in HIV-seropositive patients. Our results show that peripheral blood mononuclear cells (PBMCs) from 23 HIV-seropositive patients with low CD4(+) T cell counts (≤350 cells/µl) expressed significantly more arginase compared with 21 patients with high CD4(+) T cell counts. Furthermore, we found a significant association between the two principal prognostic markers used to monitor HIV disease (CD4(+) T cell count and plasma viral load) and PBMC arginase activity in antiretroviral therapy naïve patients but not in patients undergoing therapy.

Increased level of arginase activity correlates with disease severity in HIV-seropositive patients.

Infection with human immunodeficiency virus (HIV) results in a chronic infection that progressively impairs the immune system. Although depletion of CD4(+) T cells is frequently used to explain immunosuppression, chronicity of infection and progressive loss of CD4(+) T cells are not sufficient to fully account for immune dysregulation. Arginase-induced l-arginine deprivation is emerging as a key mechanism for the down-regulation of immune responses. Here, we hypothesized that the level of arginase activity increases with disease severity in HIV-seropositive patients. We determined the levels of arginase activity in peripheral blood mononuclear cells from HIV-seropositive patients and uninfected control participants. Our results show that peripheral blood mononuclear cells from HIV-seropositive patients with low CD4(+) T cell counts expressed statistically significantly higher levels of arginase activity, compared with patients with high CD4(+) T cell counts or uninfected control participants. Furthermore, we found a statistically significant correlation between high level of arginase activity and high viral load in HIV-seropositive patients.

A clinical isolate of Leishmania donovani with ITS1 sequence polymorphism as a cause of para-kala-azar dermal leishmaniasis in an Ethiopian human immunodeficiency virus-positive patient on highly active antiretroviral therapy.

The diagnosis of para-kala-azar dermal leishmaniasis (PKDL/VL), either as an immune reconstitution inflammatory syndrome (IRIS)-associated syndrome or as a complication of visceral leishmaniasis (VL) during human immunodeficiency virus (HIV) co-infection in patients with or without highly active antiretroviral therapy, represents a challenge for prompt treatment. The aim of this study was to identify the causative Leishmania species and to clarify whether the post-kala-azar dermal leishmaniasis (PKDL)-like lesions appeared as a result of IRIS or not. A 31-year-old Ethiopian male patient, with stage IV HIV/acquired immune deficiency syndrome (AIDS), was clinically diagnosed with PKDL/VL. He had developed a generalized maculopapular rash on his face after initiation of highly active antiretroviral therapy. The Leishmania isolate obtained from the skin lesions was analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and sequencing of the ribosomal DNA internal transcribed spacer 1 (ITS1) and partial coding sequences of the heat shock protein 70 gene (hsp70). Restriction analysis of the ITS1 PCR product gave a unique RFLP pattern not seen before for any Leishmania isolate. Sequencing of both the ITS1 and hsp70 PCR products identified the causative species as Leishmania donovani, and further revealed the existence of five different sequence variants of the ITS1 among the 10 clones sequenced. The results indicate that PKDL/VL resulted from an infection by L. donovani. The sequence variants of ITS1 might be due to the presence of multiple strains/clones or the existence of intragenomic variations in the multicopy ITS1, or a combination of both.

Hippocampal pyramidal cell disarray in schizophrenia as a bilateral phenomenon.

In a continuing quantitative study of hippocampal cell orientation in schizophrenic subjects and nonschizophrenic control subjects, a pattern of right hemispheric cell disorganization in schizophrenic subjects, as robust as that previously described in the left hemisphere, was shown. The study was based on tissue from 11 schizophrenic and seven approximately age-matched control subjects from a Veterans Administration Medical Center. Using a new measuring technique that proved complementary and superior to the method formerly used, we determined the axes of orientation for approximately 10,800 neurons. A significant difference in cell disorganization was found between schizophrenic and control subjects. From separate analyses of the interface zones among the various hippocampal cell sectors, this difference was found to be significant at the interfaces between cornu ammonis zones 1 and 2 and zones 2 and 3. Analysis of the pattern of disorganization numbers suggests a bimodal distribution in which the cell orientation values of one group of schizophrenic subjects overlap those of the nonschizophrenic control group, while the cell orientation values of a second group significantly exceed those of the control population. Although some recent studies have suggested that schizophrenia may be related exclusively to the left hemisphere, the results of this study indicate that schizophrenia-related structural changes involve the right hemisphere as well. Thus, schizophrenia may be a bilateral rather than unilateral disorder.