We have investigated the quantum efficiency of monolayer MoS2 light-emitting devices through detailed temperature and power-dependent photoluminescence studies and rate equation analysis. The ...internal quantum efficiency can reach 45 and 8.3% at 83 and 300 K, respectively. However, efficiency droop is clearly measured with increasing carrier injection due to the unusually large Auger recombination coefficient, which is found to be ∼10–24 cm6/s at room temperature, nearly 6 orders of magnitude higher than that of conventional bulk semiconductors. The significantly elevated Auger recombination in the emerging two-dimensional (2D) semiconductors is primarily an indirect process and is attributed to the abrupt bounding surfaces and the enhanced correlation, mediated by magnified Coulomb interactions, between electrons and holes confined in a 2D structure.
Solar cell generations over 40% efficiency King, R. R.; Bhusari, D.; Larrabee, D. ...
Progress in photovoltaics,
September 2012, Letnik:
20, Številka:
6
Journal Article, Conference Proceeding
Temperature-dependent (T-dependent) Raman scattering can provide valuable informations on thermal properties, phonon anharmonicity and electron-phonon coupling of graphene-based materials. Graphene ...are found to exhibit extrinsic T-dependent Raman behavior at low temperature in vacuum or N2 gas, showing a behavior of heavily doped graphene. To obtain intrinsic properties of graphene-based materials, we focused on the comparative T-dependent Raman study on graphite and silicon in the temperature range of 4 K∼1000 K by different excitation lasers and different hot-stages or cryogenic stations. In contrast to the monotonic increase of full width at half maximum (FWHM) with temperature for the Si mode in silicon, FWHM for the G mode in graphite exhibits a minimum when T∼700K, which can be explained by the contributions from phonon anharmonicity and electron-phonon coupling. The result shows that the previous theoretical works underestimate the contribution from phonon anharmonicity above ∼ 600 K. The electron-phonon coupling strength of 0.026 is revealed, smaller than that of graphene. The peak position of G peak of graphite shows a nonlinear decrease with increasing temperature, which agrees well with the previous theoretical calculation. Our results find that the contribution of phonon anharmonicity to both peak position and FWHM is more prominent for the G mode in graphite than the Si mode in silicon.
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To explore the characteristics of Helicobacter pylori resistance in China and the association between antibiotic resistance and several clinical factors.
H. pylori strains were collected from ...patients in 13 provinces or cities in China between 2010 and 2016. Demographic data including type of disease, geographic area, age, gender and isolation year were collected to analyse their association with antibiotic resistance. Antibiotic resistance was detected using the Etest test and the Kirby-Bauer disc diffusion method.
H. pylori were successfully cultured from 1117 patients. The prevalence of metronidazole, clarithromycin (CLA), azithromycin, levofloxacin (LEV), moxifloxacin, amoxicillin (AMO), tetracycline and rifampicin resistance was 78.2, 22.1, 23.3, 19.2, 17.2, 3.4, 1.9 and 1.5%, respectively. No resistance to furazolidone was observed. The resistance rates to LEV and moxifloxacin were higher in strains isolated from patients with gastritis compared to those with duodenal ulcer and among women. Compared to patients ≥40 years old, younger patients exhibited lower resistance rates to CLA, azithromycin, LEV and moxifloxacin. The resistance rates to CLA and AMO were higher in strains isolated more recently, and we also found that the prevalence of resistance to metronidazole, CLA, azithromycin and AMO were significantly different among different regions of China.
The resistance rates to metronidazole, CLA and LEV were high in China. Patient age, gender, disease and location were associated with the resistance of H. pylori to some antibiotics. Furazolidone, AMO and tetracycline are better choices for H. pylori treatment in China.
Plant polyphenols, especially flavonoids, are of great interest due to their wide range of biological activities. Quercetin, a ubiquitous flavonoid, is known to have antioxidant and antibacterial ...effects. In this study, we investigated the effect of quercetin on performance, egg quality, cecal microflora populations, and antioxidant status in laying hens. Two hundred forty 28-wk-old Hessian laying hens, with an average laying rate of lay 85% at the start, were randomly allotted to 4 treatments and fed 1 of 4 diets (negative control, 0.2, 0.4, and 0.6 g of quercetin/kg of diet) for 8 wk. Layer performance responses, egg quality parameters, cecal microflora populations and antioxidant status were measured at the end of the experiment. Results showed that feed conversion decreased as the quercetin level increased. Laying rate had a quadratic correlation with the level of quercetin (P = 0.056) and was maximized by the supplementation level of 0.2 g/kg of diet. However, no significant quercetin effect was observed on egg quality. Regression analysis showed that the population of total aerobes and coliforms decreased and the population of Bifidobacteria increased as the level of quercetin increased. Regression analysis also showed the activities of Cu-Zn-superoxide dismutase increased as the level of quercetin increased (P < 0.05). Results of the study suggest that the appropriate level of supplementation is 0.367 to 0.369 g of quercetin/kg of feed based on the improvement of laying rate (with 88.55 as maximum value) and feed conversion (with 2.0725 as minimum value). Our observations provided further evidence that dietary supplementation of quercetin improved performance by modulation of intestinal environment and liver superoxide dismutase content in laying hens. Quercetin has the potential as functional feed additive in animal production.
Please cite this paper as: Mazzoni A, Althabe F, Liu N, Bonotti A, Gibbons L, Sánchez A, Belizán J. Women’s preference for caesarean section: a systematic review and meta‐analysis of observational ...studies. BJOG 2011;118:391–399.
Background The striking increase in caesarean section rates in middle‐ and high‐income countries has been partly attributed to maternal request. We conducted a systematic review and meta‐analysis of women’s preferences for caesarean section.
Objectives To review the published literature on women’s preferences for caesarean section.
Search strategy A systematic search of MEDLINE, EMBASE, LILACS and PsychINFO was performed. References of all included articles were examined.
Selection criteria We included studies that quantitatively evaluated women’s preferences for caesarean section in any country. We excluded articles assessing health providers’ preferences and qualitative studies.
Data collection and analysis Two reviewers independently screened s of all identified citations, selected potentially eligible studies, and assessed their full‐text versions. We conducted a meta‐analysis of proportions, and a meta‐regression analysis to determine variables significantly associated with caesarean section preference.
Main results Thirty‐eight studies were included (n = 19 403). The overall pooled preference for caesarean section was 15.6% (95% CI 12.5–18.9). Higher preference for caesarean section was reported in women with a previous caesarean section versus women without a previous caesarean section (29.4%; 95% CI 24.4–34.8 versus 10.1%; 95% CI 7.5–13.1), and those living in a middle‐income country versus a high‐income country (22.1%; 95% CI 17.6–26.9 versus 11.8%; 95% CI 8.9–15.1).
Authors’ conclusions Only a minority of women in a wide variety of countries expressed a preference for caesarean delivery. Further research is needed to better estimate the contribution of women’s demand to the rising caesarean section rates.
Summary
Background An uncommon histiocytosis primarily involving the lymph nodes, Rosai–Dorfman disease (RDD, originally called sinus histiocytosis with massive lymphadenopathy) involves extranodal ...sites in 43% of cases; cutaneous RDD (C‐RDD) is a rare form of RDD limited to the skin. The clinicopathological diagnosis of C‐RDD may sometimes be difficult, with different clinical profiles from those of its nodal counterpart, and occasionally misleading histological pictures. There have been few multipatient studies of C‐RDD and documentation of its histological spectrum is rare.
Objectives To identify the clinical and histopathological profiles, associated features, and the chronological changes of this rare histiocytosis.
Methods From 1991 to 2002, patients diagnosed as having C‐RDD were collected in four academic hospitals. Clinical presentations, treatments, and courses of each case were documented. In total, 21 biopsy specimens obtained from these patients were re‐evaluated and scored microscopically with attention to the uncommon patterns and chronological evolution both clinically and histologically.
Results We examined six patients with C‐RDD, three men and three women. The mean age at the first visit was 43·7 years. The clinical presentations were mostly papules, nodules and plaques, varying with the duration and depth of lesions. Although the anatomical distribution was wide, the face was most commonly involved. Evolutional changes were identified clinically, as the lesions typically began with papules or plaques and grew to form nodules with satellite lesions and resolved with fibrotic plaques before complete remission. No patient had lymphadenopathy or extracutaneous lesions during follow‐up (mean 50·5 months). At the end of follow‐up, the lesions in four patients had completely resolved irrespective of treatment; two patients had persistent lesions. The histopathological pattern of the main infiltrate, the components of cells and the stromal responses showed dynamic changes according to the duration of lesions. The characteristic Rosai–Dorfman cells (RD cells) were found in association with a nodular or diffuse infiltrate in 15 lesions (71%). Four lesions (19%) demonstrated a patchy/interstitial pattern. One lesion (5%) assumed the pattern of a suppurative granuloma. RD cells were less readily found in these atypical patterns. Conspicuous proliferation of histiocytes associated with RD cells was found in three lesions, including xanthoma, localized Langerhans cell histiocytosis and xanthogranuloma. Along with lymphocytes, plasma cells were present in all lesions, often in large numbers with occasional binucleated or trinucleated cells. Variably found in the lesions were neutrophils (nine lesions, 43%) and eosinophils (13 lesions, 62%). The former occasionally formed microabscesses, while the latter were often few in number. Vascular proliferation was a relatively constant feature (90%). Fibrosis was found in 10 lesions (48%).
Conclusions Our study further confirms that C‐RDD is a distinct entity with different age and possibly race distributions from RDD. Compared with its nodal counterpart, C‐RDD demonstrates a wider histopathological spectrum with different clinicopathological phases depending on duration of the lesions. Awareness of these features is helpful in making a correct diagnosis. The associations of C‐RDD with other histiocytoses may have important implications for the pathogenesis of this rare histiocytosis.
This paper proposes a novel and perfect absorber based on patterned graphene and vanadium dioxide hybrid metamaterial, which can not only achieve wide-band perfect absorption and dual-channel ...absorption in the terahertz band, but also realize their conversion by adjusting the temperature to control the metallic or insulating phase of VO
. Firstly, the absorption spectrum of the proposed structure is analyzed without graphene, where the absorption can reach as high as 100% at one frequency point (f = 5.956 THz) when VO
is in the metal phase. What merits attention is that the addition of graphene above the structure enhances the almost 100% absorption from one frequency point (f = 5.956 THz) to a wide frequency band, in which the broadband width records 1.683 THz. Secondly, when VO
is the insulating phase, the absorption of the metamaterial structure with graphene outperforms better, and two high absorption peaks are formed, logging 100% and 90.7% at f
= 5.545 THz and f
= 7.684 THz, respectively. Lastly, the adjustment of the Fermi level of graphene from 0.8 eV to 1.1 eV incurs an obvious blueshift of the absorption spectra, where an asynchronous optical switch can be achieved at fK
= 5.782 THz and fK
= 6.898 THz. Besides, the absorber exhibits polarization sensitivity at f
= 5.545 THz, and polarization insensitivity at f
= 7.684 THz with the shift in the polarization angle of incident light from 0° to 90°. Accordingly, this paper gives insights into the new method that increases the high absorption width, as well as the great potential in the multifunctional modulator.
Primary ovarian insufficiency (POI) is a common cause of infertility in around 1-2% of women aged <40 years. However, the mechanisms that cause POI are still poorly understood. Here we showed that ...germ cell-specific knockout of an essential autophagy induction gene Atg7 led to subfertility in female mice. The subfertility of Atg7 deletion females was caused by severe ovarian follicle loss, which is very similar to human POI patients. Further investigation revealed that germ cell-specific Atg7 knockout resulted in germ cell over-loss at the neonatal transition period. In addition, our in vitro studies also demonstrated that autophagy could protect oocytes from over-loss by apoptosis in neonatal ovaries under the starvation condition. Taken together, our results uncover a new role for autophagy in the regulation of ovarian primordial follicle reservation and hint that autophagy-related genes might be potential pathogenic genes to POI of women.
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