Direct medical cost of type 2 diabetes in Singapore

10.1371/joumal.pone.0122795PLoS ONE103e012279

Continuous-wave lasing from InP/InGaAs nanoridges at telecommunication wavelengths

We report continuous-wave lasing from InP/InGaAs nanoridges grown on a patterned (001) Si substrate by aspect ratio trapping. Multi-InGaAs ridge quantum wells inside InP nanoridges are designed as active gain materials for emission in the 1500 nm band. The good crystalline quality and optical property of the InGaAs quantum wells are attested by transmission electron microscopy and microphotoluminescence measurements. After transfer of the InP/InGaAs nanoridges onto a SiO2/Si substrate, amplified Fabry-Perot resonant modes at room temperature and multi-mode lasing behavior in the 1400 nm band under continuous-wave optical pumping at 4.5 K are observed. This result thus marks an important step towards integrating InP/InGaAs nanolasers directly grown on microelectronic standard (001) Si substrates. Semiconductor nanowires are emerging as ideal building blocks for ultra-compact optoelectronic devices with low-energy dissipation.1 As a result of axially guided optical modes and feedback provided by end-facets, lasing behaviors have been observed in various II-VI and III-V compound semiconductor nanostructures.2–16 In particular, indium phosphide (InP) and indium gallium arsenide (InGaAs) nanolasers, emitting at silicon(Si)-transparent wavelengths, show great promise to fill a key missing on-chip component in Si photonic-based optical interconnects.17–21 However, most of the previously demonstrated InP/InGaAs nanolasers operate under pulsed-conditions.22–24 Continuous-wave (CW) lasing at telecom wavelengths has only been achieved in InP/InGaAs nanopillars grown on (111) Si substrates25 and InAsP/InP nanowires (inside Si photonic crystal cavity) grown on (111)B InP substrates, with lasing wavelengths situated at the 1200 and 1300 nm bands.26 Extending the lasing wavelengths to the 1400 nm and 1500 nm bands is desirable for high density inter/intra-chip data transmission. In this letter, we utilized InP/InGaAs nanoridges grown on a (001) Si substrate to demonstrate CW lasing behavior at the 1400 nm band. Compared with other hetero-epitaxial growth techniques, selective area growth combined with the aspect ratio trapping (ART) method provides a viable route to form well-aligned, millimeter-long horizontal in-plane nanowires on CMOS-standard (001) Si substrates.27–34 Previously, we have leveraged this approach to grow InP nanoridges with embedded InGaAs quantum wells (QWs) and quasi-quantum wires (QWRs) with strong photolumiescence.35,36 Here, we observe CW lasing at the telecommunication band from high quality multi-InGaAs ridge QWs inside the InP nanoridges directly grown on nanopatterned silicon. To explore the potential of the InP/InGaAs nanoridges as nanoscale light sources, we separated the InP/InGaAs nanoridges from the initial patterned Si substrate and transferred them onto a SiO2/Si substrate for optical characterization. We observed CW lasing at 4.5 K under optical excitation and strong optical mode modulation at room temperature. The InP/InGaAs nanoridges used in this experiment were grown on (001) Si substrates using a metal-organic chemical vapor deposition (MOCVD) system with a horizontal reactor (AIXTRON 200/4). [110] direction oriented SiO2 stripe patterns with a line pitch of 1 μm and a trench opening width of 450 nm were used to define the growth regions. Detailed sample preparation and the growth procedure have been reported elsewhere.35,36 Figure 1(a) presents the top-view scanning electron microscopy (SEM) image of the as-grown sample, showing a uniform morphology across a large area. The 70° tilted-view SEM image in Fig. 1(b) reveals symmetrical {111} faceting. A zoomed-in SEM image in Fig. 1(c) highlights the multi-QW active region. Notably, to enhance contrast, the InGaAs layers were selectively etched in a H2PO4:H2O2:H2O (3:1:50) solution. Five uniform InGaAs ridge QWs and the GaAs nucleation buffer are clearly identified

Telecom InP/InGaAs nanolaser array directly grown on (001) silicon-on-insulator

A compact, efficient, and monolithically grown III–V laser source provides an attractive alternative to bonding off-chip lasers for Si photonics research. Although recent demonstrations of microlasers on (001) Si wafers using thick metamorphic buffers are encouraging, scaling down the laser footprint to nanoscale and operating the nanolasers at telecom wavelengths remain significant challenges. Here, we report a monolithically integrated in-plane InP/InGaAs nanolaser array on (001) silicon-on-insulator (SOI) platforms with emission wavelengths covering the entire C band (1.55 μm). Multiple InGaAs quantum wells are embedded in high-quality InP nanoridges by selective-area growth on patterned (001) SOI. Combined with air-cladded InP/Si optical cavities, room-temperature operation at multiple telecom bands is obtained by defining different cavity lengths with lithography. The demonstration of telecom-wavelength monolithic nanolasers on (001) SOI platforms presents an important step towards fully integrated Si photonics circuits

Image operator learning coupled with CNN classification and its application to staff line removal

Many image transformations can be modeled by image operators that are characterized by pixel-wise local functions defined on a finite support window. In image operator learning, these functions are estimated from training data using machine learning techniques. Input size is usually a critical issue when using learning algorithms, and it limits the size of practicable windows. We propose the use of convolutional neural networks (CNNs) to overcome this limitation. The problem of removing staff-lines in music score images is chosen to evaluate the effects of window and convolutional mask sizes on the learned image operator performance. Results show that the CNN based solution outperforms previous ones obtained using conventional learning algorithms or heuristic algorithms, indicating the potential of CNNs as base classifiers in image operator learning. The implementations will be made available on the TRIOSlib project site.Comment: To appear in ICDAR 201

Room-temperature InP/InGaAs nano-ridge lasers grown on Si and emitting at telecom bands

Semiconductor nano-lasers grown on silicon and emitting at the telecom bands are advantageous ultra-compact coherent light sources for potential Si-based photonic integrated circuit applications. However, realizing room-temperature lasing inside nano-cavities at telecom bands is challenging and has only been demonstrated up to the E band. Here, we report on InP/InGaAs nano-ridge lasers with emission wavelengths ranging from the O, E, and S bands to the C band operating at room temperature with ultra-low lasing thresholds. Using a cycled growth procedure, ridge InGaAs quantum wells inside InP nano-ridges grown on patterned (001) Si substrates are designed as active gain materials. Room-temperature lasing at the telecom bands is achieved by transferring the InP/InGaAs nano-ridges onto a SiO2∕Si substrate for optical excitation. We also show that the operation wavelength of InP/InGaAs nano-lasers can be adjusted by altering the excitation power density and the length of the nano-ridges formed in a single growth run. These results indicate the excellent optical properties of the InP/InGaAs nano-ridges grown on (001) Si substrates and pave the way towards telecom InP/InGaAs nano-laser arrays on CMOS standard Si or silicon-on-insulator substrates

InGaAs/InP quantum wires grown on silicon with adjustable emission wavelength at telecom bands

We report the growth of vertically stacked InGaAs/InP quantum wires on (001) Si substrates with adjustable room-temperature emission at telecom bands. Based on a self-limiting growth mode in selective area metal–organic chemical vapor deposition, crescent-shaped InGaAs quantum wires with variable dimensions are embedded within InP nano-ridges. With extensive transmission electron microscopy studies, the growth transition and morphology change from quantum wires to ridge quantum wells (QWs) have been revealed. As a result, we are able to decouple the quantum wires from ridge QWs and manipulate their dimensions by scaling the growth time. With minimized lateral dimension and their unique positioning, the InGaAs/InP quantum wires are more immune to dislocations and more efficient in radiative processes, as evidenced by their excellent optical quality at telecom-bands. These promising results thus highlight the potential of combining low-dimensional quantum wire structures with the aspect ratio trapping process for integrating III–V nano-light emitters on mainstream (001) Si substrates

Environmental literacy on ecotourism: a study on student knowledge, attitude, and behavioral intentions in China and Taiwan

This study aims to gain further insights to Chinese and Taiwanese university students’ environmental literacy on ecotourism. A structural equation model is developed and validated in an effort to explore the differences between Chinese and Taiwanese university students in terms of their environmental knowledge, environmental attitude, and behavioral intentions. The results showed that the ecotourism perception of Chinese and Taiwanese university students affect their behavioral intentions. Chinese university students exhibited a higher correlation between ecotourism knowledge and behavioral intentions than their Taiwanese counterparts. The findings also revealed differences between the Chinese and Taiwanese students in their perception of ecotourism, and this disparity was particularly evident with regards to how ecotourism should be governed. A moderate difference in ecotourism behavioral intentions was also identified, in which Taiwanese university students were less likely to engage in self-empowerment or private empowerment, to be more educated in the field of ecotourism than their Chinese counterparts

Chaperones as integrators of cellular networks: Changes of cellular integrity in stress and diseases

Cellular networks undergo rearrangements during stress and diseases. In un-stressed state the yeast protein-protein interaction network (interactome) is highly compact, and the centrally organized modules have a large overlap. During stress several original modules became more separated, and a number of novel modules also appear. A few basic functions, such as the proteasome preserve their central position. However, several functions with high energy demand, such the cell-cycle regulation loose their original centrality during stress. A number of key stress-dependent protein complexes, such as the disaggregation-specific chaperone, Hsp104, gain centrality in the stressed yeast interactome. Molecular chaperones, heat shock, or stress proteins form complex interaction networks (the chaperome) with each other and their partners. Here we show that the human chaperome recovers the segregation of protein synthesis-coupled and stress-related chaperones observed in yeast recently. Examination of yeast and human interactomes shows that (1) chaperones are inter-modular integrators of protein-protein interaction networks, which (2) often bridge hubs and (3) are favorite candidates for extensive phosphorylation. Moreover, chaperones (4) become more central in the organization of the isolated modules of the stressed yeast protein-protein interaction network, which highlights their importance in the de-coupling and re-coupling of network modules during and after stress. Chaperone-mediated evolvability of cellular networks may play a key role in cellular adaptation during stress and various polygenic and chronic diseases, such as cancer, diabetes or neurodegeneration.Comment: 13 pages, 3 figures, 1 glossar

Detection of MicroRNA processing intermediates through RNA ligation approaches

MicroRNAs (miRNA) are small RNAs of 20–22 nt that regulate diverse biological pathways through the modulation of gene expression. miRNAs recognize target RNAs by base complementarity and guide them to degradation or translational arrest. They are transcribed as longer precursors with extensive secondary structures. In plants, these precursors are processed by a complex harboring DICER-LIKE1 (DCL1), which cuts on the precursor stem region to release the mature miRNA together with the miRNA*. In both plants and animals, the miRNA precursors contain spatial clues that determine the position of the miRNA along their sequences. DCL1 is assisted by several proteins, such as the double-stranded RNA binding protein, HYPONASTIC LEAVES1 (HYL1), and the zinc finger protein SERRATE (SE). The precise biogenesis of miRNAs is of utter importance since it determines the exact nucleotide sequence of the mature small RNAs and therefore the identity of the target genes. miRNA processing itself can be regulated and therefore can determine the final small RNA levels and activity. Here, we describe methods to analyze miRNA processing intermediates in plants. These approaches can be used in wild-type or mutant plants, as well as in plants grown under different conditions, allowing a molecular characterization of the miRNA biogenesis from the RNA precursor perspective.Fil: Moro, Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; ArgentinaFil: Rojas, Arantxa Maria Larisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Palatnik, Javier Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentina. Universidad Nacional de Rosario. Centro de Estudios Interdisciplinarios; Argentin