The aim of the current study was to examine the effects of bilingualism on letter and category fluency tasks. Participants were 1,600 monolingual and bilingual children from three cities in Iran: Tehran (Persian monolinguals), Tabriz (Turkish–Persian bilinguals), and Sanandaj (Kurdish–Persian bilinguals). We separately presented nine Persian letters and thirty-one categories to the participants, and asked them to generate as many words as possible using each of these initial letters and categories within a maximum of three minutes. Bilingual children generated more words than monolingual children in the letter fluency task; this effect was more pronounced in Grade 1 and for Turkish–Persian bilinguals. However, Persian monolinguals generated significantly more words than both bilingual groups in the category fluency task. Thus, bilingualism can be of both advantage and disadvantage, and produce a dissociative effect. We discuss the results on the basis of the specific nature and different cognitive demands of letter and category fluency tasks. We suggest that the degree of language proficiency of bilinguals should be considered as an important variable in future research on bilingualism.
The conventional approach to search for new materials is to synthesize a limited number of candidates. However, this approach might delay or prevent the discovery of better-performing materials due to the narrow composition space explored. Here, we fabricate binary alloy films with a composition gradient in a single shot in less than one minute. We apply this approach to study the stability of halide perovskites. We synthesize all possible binary compositions from MAPbI3 and MAPbBr3 and then study their optical properties, structure, and environmental stability in a high-throughput manner. We find that perovskite alloys experience three different degradation mechanisms depending on halogen content: bromine-rich perovskites degrade by hydration, iodine-rich perovskites by the loss of the organic component, and all other intermediate alloys by phase segregation. The proposed method offers an avenue for discovering new materials and processing parameters for a wide range of applications that rely on compositional engineering.
Ambient air processing is desirable for the industrial fabrication of perovskite solar cells. Here, we show that perovskite ink containing methylammonium and formamidinium in Nmethyl-2-pyrrolidone and N,N-dimethylformamide, a cosolvent composition that satisfies prerequisites for upscaling solar cell fabrication, degrades within a day in ambient air. From 1 H NMR spectroscopic analysis, we find that water proton exchange with methylammonium and formamidinium facilitates the aminolysis of formamidinium by methylamine. The addition of elemental sulfur inhibits this proton exchange process via sulfur−amine reactions, resulting in a stable perovskite ink with an extrapolated half-life of 6300 h. The control ink aged for 1 day does not form perovskite films for solar cell fabrication, while the sulfur-stabilized ink is reproducibly used to make devices with efficiencies >15% when aged for over 1 month. The stabilized ink is suitable for upscaling perovskite solar cell fabrication, with efficiencies up to 17% for blade-coated devices.
α-FAPbI3 (FA = formamidinium) perovskite offers an optimal bandgap for single-junction solar cells but converts into a more thermodynamically stable photoinactive δ-polymorph at room temperature. FA- or I-site substitutional alloying stabilizes α-FAPbI3; however, it leads to compositional segregation in operational devices. Here, we stabilize α-FAPbI3 single crystals through Pb-site doping with a heterovalent metal–bismuth (Bi). We show that undoped α-FAPbI3 has an α- to δ-phase half-life transition of <0.15 h, while the optimum concentration of Bi extends it by 4 orders of magnitude. Differential scanning calorimetry (DSC) reveals that Bi has effectively decreased the δ- to α-phase onset transition temperature. Density functional theory (DFT) calculations suggest a relatively clean gap, supporting previous findings on the improved photovoltaic performance of Bi-doped α-FAPbI3-based solar cells.
near the influential materials if the proximity effect is either an advantage or a disadvantage for an antenna system, depending on the size of an element materials, and small antenna is a small example ceramic chip antenna encapsulated in a cubic millimeters, using ESA and PSA as well. When designing a chip ceramic ESA, the dimensions of the mobile terminal device, the space for mounting the antenna, the space to be occupied by the antenna, and the antenna size [11]. FUNDAMENTAL LIMITATIONSmall antennas to reduce its size, gain and antenna efficiency degrade, and bandwidth tends to be narrower. Body limiting small antenna could have effective aperture as high as 98% of a half-wave dipole antenna when the antenna is optimally adapted to the load. There seems to be no limitation in reducing the size of the antennas, so did the antenna can be perfectly adequate. Perfect matching is impossible when an antenna is extremely low [12].Furthermore, the losses existing in the antenna structure and the corresponding circuit does not exceed the radiation resistance, which reduces the effective apertures that the efficiency of radiotherapy. With regard to the impedance of the antenna, the increase and decrease in the reactive component of the resistive elements results in a high Q factor and bandwidth will be reduced as a result. Reducing the size of the antenna and also makes them Q and bandwidth [13].The parameters affecting the fundamental limitations of small antennas are antenna Q (quality factor) of the bandwidth ratio g, the antenna size ka, where a is the radius of a sphere surrounding and antenna [14].ka is much smaller than unity. Q is proportion to ka ð Þ -3 .RBW is proportion to ka ð Þ 3 , RBW nearly equalsg is proportion ka ð Þ 4 . CONCLUSIONIn a number of applications such as wireless Personal Computer Memory Card International Association cards, ESA's have been implemented that have adequate impedance bandwidth, and they are well matched. Some case matching the impedance bandwidth would decrease or in some case increase. Such that main fundamental limitation on antennas size versus impedance bandwidth brigs order to what can appear to be mysterious changes in antenna performance [15][16][17]. It should be noted that a small antenna, that is, appropriately designed to satisfy the system requirements should not be near certain materials so that designed antenna performance is substantially harmed. It can be said generally that the smaller the antenna becomes, the large the influence of such nearby materials is likely to be. ACKNOWLEDGMENTThe authors would like to thank the management of CHARU-SAT and management of Chandubhai S Patel Institute of Technology for their continuous support and encouragement. ABSTRACT: In this letter, we present a compact dual-band dielectric resonator antenna for multi-input multi-output antenna is designed and fabricated. The proposed antenna consists of a single cylindrical dielectric resonator antenna (CDRA) excited from two orthogonal ports. The electromagnetic analysis is perfor...
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