Showing papers by "Yang Yang published in 2008"

Synthesis, Characterization, and Photovoltaic Properties of a Low Band Gap Polymer Based on Silole-Containing Polythiophenes and 2,1,3-Benzothiadiazole

Abstract: A new low band gap silole-containing conjugated polymer, PSBTBT, was designed and synthesized. Photovoltaic properties of PSBTBT were initially investigated, and an average power conversion efficiency (PCE) of 4.7% with a best PCE of 5.1% was recorded under illumination (AM 1.5G, 100 mW/cm(2)). The response range of the device covers the whole visible range from 380 to 800 nm. These results indicate that PSBTBT is a promising polymer material for applications in polymer solar cells.

Bandgap and Molecular Energy Level Control of Conjugated Polymer Photovoltaic Materials Based on Benzo[1,2-b:4,5-b']dithiophene

Abstract: Bandgap and molecular energy level control are of great importance in improving photovoltaic properties of conjugated polymers. A common approach to tuning these parameters is to modify the structure of conjugated polymers by copolymerizing with different units. In this paper, research work focuses on the synthesis of benzo[1,2-b:4,5-b′]dithiophene (BDT) with different conjugated units and their photovoltaic performance. Eight new BDT-based polymers with commonly used conjugated units, including thiophene, benzo[c][1,2,5]thiadiazole (BT), thieno[3,4-b]pyrazine (TPZ), etc., were synthesized. The bandgaps of the polymers were tuned in the range of 1.0−2.0 eV, and their HOMO and LUMO energy levels could also be tuned effectively. The absorption spectra as well as electrochemical and photovoltaic properties of these polymers were investigated systematically. Some units exhibiting the same effect of bandgap lowering exhibited different effects on molecular energy levels of the polymers. For example, the TPZ un...

Effects of Solvent Mixtures on the Nanoscale Phase Separation in Polymer Solar Cells

Abstract: The mixed solvent approach has been demonstrated as a promising method to modify nanomorphology in polymer solar cells. This work aims to understand the unique role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non-equilibrium spin-coating process. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology with the additive. Supported by AFM, TEM and XPS results, we proposed a model and identified relevant parameters for the additive such as solubility and vapor pressures. Other additives are discovered to show the ability to improve polymer solar cell performance as well.

Highly efficient inverted polymer solar cell by low temperature annealing of Cs2CO3 interlayer

Abstract: We demonstrate a highly efficient inverted bulk heterojunction polymer solar cell based on regioregular poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester with a low temperature annealed interfacial buffer layer, cesium carbonate (Cs2CO3). This approach improves the power conversion efficiency of the inverted cell from 2.3% to 4.2%, with short-circuit current of 11.17mA∕cm2, open-circuit voltage of 0.59V, and fill factor of 63% under AM1.5G 100mW∕cm2 irradiation. This result is comparable to the previous regular structure device on the same system. Ultraviolet photoelectron spectroscopy shows that the work function of annealed Cs2CO3 layer decreases from 3.45to3.06eV. Further x-ray photoelectron spectroscopy results reveal that Cs2CO3 can decompose into low work function, doped cesium oxide Cs2O upon annealing, which is accountable for the work-function reduction and device efficiency improvement.

Synthesis of Cu-In-S ternary nanocrystals with tunable structure and composition

Abstract: Nearly monodisperse Cu−In−S ternary nanocrystals with tunable composition, crystalline structure, and size were synthesized by a hot-injection method using mixed generic precursors. Such ternary nanocrystals with zincblende and wurtzite structure were reported for the first time. This work correlates the crystalline structure of the binary ZnS nanoparticles with those of ternary Cu−In−S nanocrystals, demonstrating the feasibility of making their alloyed or core/shell structure. Furthermore, this work may provide suitable material candidates for low-cost, high-efficiency solar cell fabrication.

A Semi-transparent Plastic Solar Cell Fabricated by a Lamination Process†

Abstract: Polymer solar cells have attracted broad research interest because of their advantageous solution processing capability and formation of low-cost, flexible, and large area electronic devices. However, the efficiency of polymer solar cells is still low compared to that of inorganic solar cells. Therefore, it is a challenge to find a polymer that has all the required properties for high efficiency devices, such as strong and broad absorption, high carrier mobility, and appropriate energy levels. One possible solution to avoid the strict material requirements is to stack two or more devices with different spectral responses, which enables more efficient utilization of solar energy. Such a solution would require a semitransparent solarcell device with high efficiency in its absorption wavelength range, while high transparency would be required in the complementary wavelength range. Semitransparent solar cells are also interesting for other appealing applications, such as energy-generating color window glasses. It is desirable that such solar cell devices can be fabricated using a low-cost strategy, such as the roll-to-roll fabrication process. One critical issue in this fabrication process is how to form the active-layer/cathode mechanic and electronic contacts. The lamination process is one very promising technique to fulfill this requirement owing to its simplicity and low cost. It has been reported to produce two-layer heterojunction solar cells; however, the method is not applicable to bulk heterojunction solar cells, nor compatible with roll-to-roll fabrication process. In this Communication, an electronic glue-based lamination process combined with interface modification is presented as a one-step process for semitransparent polymer solar-cell fabrication. The finished device is metalfree, semitransparent, flexible, self-encapsulated, and highly efficient (with a maximum external quantum efficiency of 70 % and power efficiency of 3 % under AM 1.5 global 1 sun solar illumination conditions with spectral mismatch correction). This approach represents a critical step towards the ultimate goal of low-cost polymer solar cells. The device fabrication process is illustrated in Figure 1, and can be described by the following steps. In Step I, two transparent substrates coated with a transparent conductor such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or a high conductivity polymer, etc., are selected. In Step II, one substrate is coated with a very thin buffer layer (Cs2CO3 ) to act as the low-work-function cathode, followed by coating of the active polymer layer. Step III involves the coating of conductive polymer glue to the other transparent substrate. We used modified conducting polymer poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the electronic glue, which was spin-coated to form the adhesive anode. Step IV is the lamination process: after drying both the substrates, they are laminated together by exerting force so that the two substrates are tightly glued together. During this lamination, a plastic rod with proper hardness rolls the plastic substrate to remove air bubbles. Both substrates are heated to a temperature of 105–120 °C during the lamination process, and the finished devices are then kept on the hotplate for 5–10 min for the final heat treatment. The PEDOT:PSS was purposely modified to become adhesive, so that the two separate films formed good contact at the interface, both electronically and mechanically. In this work, this adhesive and conductive PEDOT:PSS layer was obtained by doping D-sorbitol or volemitol into PEDOT:PSS, as has been successfully demonstrated in polymer light emitting diodes. However, the efficiency of such a device is too low for application. The polymer blend used in this work is regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) in 1:1 w/w ratio. The 200 nm thick polymer blend film was deposited by the slow-growth method (or solvent annealing) to enhance device efficiency. Either glass or plastic can be used as the transparent substrate. Figure 1b shows a picture of an all-plastic solar cell. The device area is ca. 40 mm. With both cathode and anode being transparent, a semitransparent polymer solar cell is formed. The transparency (T%) of the device is shown in Figure 1c, together with the solar illumination spectrum. A transparency of around 70 % was obtained in the wavelength range where polymer/PCBM has no absorption, which makes this device suitable for application in stacking devices to make full use of the solar spectrum. This device fabrication method has many advantages over the regular procedure. First of all, no thermal evaporation process is involved in the process, and each layer is coated by a low-cost and easy solution process. Second, in contrast to the reactive metal cathode in regular devices, the cathode in C O M M U N IC A IO N

Proportional Fairness in Multi-Rate Wireless LANs

Abstract: In multi-rate wireless LANs, throughput-based fair bandwidth allocation can lead to drastically reduced aggregate throughput. To balance aggregate throughput while serving users in a fair manner, proportional fair or time-based fair scheduling has been proposed to apply at each access point (AP). However, since a realistic deployment of wireless LANs can consist of a network of APs, this paper considers proportional fairness in this much wider setting. Our technique is to intelligently associate users with APs to achieve optimal proportional fairness in a network of APs. We propose two approximation algorithms for periodical offline optimization. Our algorithms are the first approximation algorithms in the literature with a tight worst-case guarantee for the NP-hard problem. Our simulation results demonstrate that our algorithms can obtain an aggregate throughput which can be as much as 2.3 times more than that of the max-min fair allocation in 802.11b. While maintaining aggregate throughput, our approximation algorithms outperform the default user-AP association method in the 802.11b standard significantly in terms of fairness.

Control of the nanoscale crystallinity and phase separation in polymer solar cells

Abstract: Grazing-incidence x-ray diffraction and atomic force microscopy were performed on bulk heterojunction regioregular poly(3-hexylthiophene) (RR-P3HT) [6,6]-phenyl-C71-butyric acid methyl esters spin-cast films with different film processing conditions to correlate the crystalline nanostructure of P3HT with the corresponding solar cell performance. The increase in long wavelength absorption for solvent annealed films is related to highly conjugated crystal structure of RR-P3HT phase-separated in the active layer. Upon thermal annealing, the solvent annealed 50-nm-thick device shows high solar cell performance with fill factor up to 73% and power conversion efficiency of 3.80%.

Nanoparticle-assisted high photoconductive gain in composites of polymer and fullerene

Abstract: Polymer-inorganic nanocrystal composites offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility and distribution of the nanocrystals in the polymer matrices. Here we show that blending CdTe nanoparticles into a polymer-fullerene matrix followed by solvent annealing can achieve high photoconductive gain under low applied voltages. The surface capping ligand renders the nanoparticles highly soluble in the polymer blend, thereby enabling high CdTe loadings. An external quantum efficiency as high as approximately 8,000% at 350 nm was achieved at -4.5 V. Hole-dominant devices coupled with atomic force microscopy images show a higher concentration of nanoparticles near the cathode-polymer interface. The nanoparticles and trapped electrons assist hole injection into the polymer under reverse bias, contributing to efficiency values in excess of 100%.

Preparation of polymer-coated mesoporous silica nanoparticles used for cellular imaging by a “graft-from” method

Abstract: Multi-functional mesoporous silica nanoparticles (MSNs) coated with poly(N-isopropylacrylamide) (PNIPAM) composite nanomaterials have been designed and synthesized by atom transfer radical polymerization (ATRP) on the surface of MSN through the “grafting-from” approach. Such materials not only provide porous cores which can act as suitable reservoirs, but also possess thermosensitive polymer shells which can entrap hydrophilic guest molecules, like FITC, into the cores upon varying the temperature. The materials can easily carry guest molecules into human breast carcinoma cells (MCF-7) and show little cytotoxicity to the cells. It is demonstrated that such MSN@PNIPAM materials can be applied in biological systems for cellular imaging or as biosensors.

Synthesis and Characterization of Novel Three-Dimensional Metallic Co Dendritic Superstructures by a Simple Hydrothermal Reduction Route

Abstract: Novel three-dimensional (3D) Co dendritic superstructures with an average diameter of ca. 15 µm were successfully prepared by a simple hydrothermal reduction route. The as-obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometry. It was shown that the 3D Co superstructures were comprised of dozens of well-aligned metallic Co dendrites with hierarchical assemblies radiating from the center. On the dendritic hierarchical structures, several leaves with different lengths and widths are connected to the main branch. The length of the main branch is several micrometers, and that of each leaf is about 0.5–1.5 µm with a width of 100−600 nm. A rational formation mechanism was proposed on the basis of the contrasting experiment. Compared with bulk cobalt, the 3D Co superstructures exhibited a decreased saturation magnetization (Ms) but an enhanced coercivity (Hc) due to their peculiar morphology.

Efficient inverted solar cells using TiO(2) nanotube arrays.

Abstract: Using a vertical titania (TiO2) nanotube array, an inverted polymer solar cell was constructed with power conversion efficiency up to 2.71%. In this study, self-organized TiO2 nanotubes arrays were grown by anodizing Ti metal in glycerol electrolyte containing 0.5 wt% NH4 Fa nd 1.0 wt% H2O with 20 V potential. The tube length (∼100 nm) was controlled by the thickness of the sputtered titanium layer on the indium‐tin oxide (ITO) substrate. The diameter of the tube was approximately 15‐25 nm. After annealing in air at 500 ◦ C for 1 h, nanotubes arrays were crystallized to the anatase phase from the initial amorphous state. Following the infiltration of polymeric semiconductor (poly(3-hexylthiophene) and (6,6)-phenyl C60 butyric acid methyl ester, P3HT:PCBM), the filled TiO2 layer had an optical absorption over a range from UV to visible light. The high surface-to-volume ratio of the nanotube arrays structure increased the effective area of the active region. The high efficiency of our solar cell is attributed to the vertical TiO2 nanotube array’s enhanced conduction of photo-induced current due to its charge transport capability. (Some figures in this article are in colour only in the electronic version)

Facile Synthesis of Highly Transparent Polymer Nanocomposites by Introduction of Core–Shell Structured Nanoparticles

Abstract: A high transmittance is the prerequisite for optically functional materials to be successfully used in practical applications. However, introduction of inorganic nanoparticles even at low contents into transparent polymers often leads to opaque nanocomposites due to light scattering caused by the nanoparticles because of the refractive index (RI) mismatch between nanoparticles and polymer matrices. This article reports for the first time a strategy for facile synthesis of highly transparent polymer nanocomposites by introduction of core–shell structured nanoparticles with the same RI. This strategy is based on the assumption that the core–shell structured nanoparticles can be regarded as integral nanofillers that have one refractive index in the polymer medium. In this study, core–shell structured silica–titania (S-T) nanoparticles were synthesized through coating titania with continuous feeding via hydrolysis of tetrabutyl orthotitanate (TBOT) to silica core preprepared according to Stober’s method by ba...

Transparent and light-emitting epoxy nanocomposites containing ZnO quantum dots as encapsulating materials for solid state lighting

Abstract: Polymer nanocomposites are usually made by incorporating dried narroparticles into polymer matrices. This would easily lead to aggregation of nanoparticles and then would readily bring about opaqueness for narrocomposites based on functionally transparent polymers. In this work, preparation of highly transparent ZnO quantum dots (ZnO-QDs)/epoxy nanocomposites that can emit intense luminescence was reported for the first time by uniformly dispersing ZnO quantum dots in a transparent epoxy resin via a direct dispersion method. The direct dispersion of ZnO quantum dots without drying in the epoxy matrix could effectively avoid aggregation of fine quantum dots and showed a good dispersity of ZnO-QDs in the epoxy matrix. Such materials showed a high transparency in the visible region and exited a broad emission spectrum peaked at 442 nm. On the other hand, in traditional solid state lighting emission diodes, semiconductor quantum dots are used as phosphors that are attached to the die of the lighting emission diode (LED) lamps for emitting luminescence. In this work, the as-prepared ZnO-QDs/epoxy nanocomposites were successfully employed as packaging materials for solid state lighting emission diodes in which conventional phosphors are not required while the nanocomposite encapsulating materials are responsible for emitting luminescence and thus the encapsulated LED lamps have an innovative structure. Consequently, the as-prepared ZnO-QDs/epoxy nanocomposites are promising for use as novel encapsulating materials in LED technology due to the much simplified encapsulating process.

Ultra-broadband enhanced absorption of metal surfaces structured by femtosecond laser pulses

Abstract: We investigate the enhanced absorption properties in a wavelength range of 0.2-25 microm for NiTi alloy targets structured by femtosecond laser pulses in air. Three different types of surface structures are produced with varying laser fluences. Measured reflectances through integrating sphere technique show that their couplings of incident electromagnetic irradiations are improved greatly over the broadband wavelength range. In particular, for coral-like micro-structures on the metal surfaces, approximate 90% absorption can be achieved from ultraviolet to mid-infrared region. Cut-off wavelengths of the enhanced absorption for the varied dimensional surface structures are determined experimentally. Chemical analysis by X-ray photoelectron spectroscopy indicates that blackness of metal surfaces is not attributed to the change in elemental composition. The physics of such remarkable absorption for the structured metal surfaces are discussed as well.

Anisotropy in Organic Single‐Crystal Photovoltaic Characteristics

Abstract: Organic single crystals have been well researched for many years. Typical vapor-phase growth of organic crystals developed from vertical to horizontal growth in order to achieve improved crystalline quality. Recently, a field-effect study on these single-crystal semiconductors demonstrated high carrier mobilities, up to ca. 15 cm Vs, along with anisotropic charge-transport properties. These single-crystal transistors were usually fabricated with rigid and thick crystals (tens of micrometers to millimeters), which were fragile and difficult to process because of poor mechanical properties. Recently, a growth method affording thin, 150 nm thick, organic crystals demonstrated the processability of single-crystal transistors on flexible substrates, and these organic crystals could be patterned on individual channels for transistors. However, in addition to transistor studies of these organic crystals, other types of electronic applications, such as two-terminal devices, have not yet been realized, mainly because of the difficultly processing thick crystals. In this Communication, we report organic single-crystal photovoltaics fabricated from single pieces of thin tetracene crystals on bilayer heterojunctions with fullerene (C60) thin films. These organic singlecrystal devices exhibited excellent diode behavior with rectifying ratios of 10 and an external power conversion efficiency (PCE) of ca. 0.34 %. By employing these high-quality single crystals in two-terminal devices, high-performance optoelectronic devices, such as organic diodes, photovoltaics, and photodetectors, become possible alternatives for large-area, low-cost flexible electronics. The quality of the single crystals was examined by cross-polarized microscopy, X-ray powder diffraction (XRD), and single-crystal X-ray diffraction. The optical microscopy images (Fig. 1a and b) recorded at 0° and 90° from the entrance polarizer and exit analyzer, respectively, show large birefringence, confirming the anisotropic crystalline nature of the tetracene crystals. The XRD data exhibit strong and narrow first (001) and second order (002) reflections (Fig. 1c), indicating the tetracene crystal is c-oriented, with molecular-plane growth along the vertical direction. The crystal data obtained for tetracene confirm a C18H6 molecular formula with a molecule weight of 222.23 g mol. The lattice constants are a = 6.02 ± 0.025 A, b = 7.77 ± 0.032 A, c = 12.46 ± 0.054 A, a =101.11 ± 0.078°, b = 99.41 ± 0.092°, and c = 94.40 ± 0.088°, and tetracene crystallizes with a triclinic crystal structure in space group P 1. The coordinates for tetracene can be obtained in the crystallographic information file (CIF) format from the Cambridge Crystallographic Data Center (CCDC), and the above crystallographic data are consistent with the data in the CCDC. Both the strong birefringence and the XRD results indicate these organic single crystals are of high quality. A schematic structure of a single-crystal solar cell is shown in Figure 2a. The device structure comprised a poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS)coated indium tin oxide (ITO) substrate, a tetracene crystal, evaporated thin films of C60 and bathocuproine (BCP), and an aluminum thin-film electrode. We note that thin crystals (ca. 200 nm) used in this study conformed better on substrates C O M M U N IC A IO N

Facile Synthesis of Metallic Co Hierarchical Nanostructured Microspheres by a Simple Solvothermal Process

Abstract: The fabrication of hierarchical and complex micro/nanostructures using nanoparticles such as nanorods, nanoribbons, nanoplatelets, etc. as building blocks at different levels has become a hot topic in recent material research fields. In this study, facile synthesis of metallic cobalt hierarchical nanostructured microspheres was reported by a simple solvothermal process. The as-obtained products were well characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer−Emmett−Teller analysis, and vibrating sample magnetometery. It was shown that the Co hierarchical nanostructured microspheres with a diameter of several micrometers are assembled from nanoplatelets with a thickness of about 20 nm and a width of 0.5−1.5 µm. A rational mechanism of formation was proposed on the basis of a range of contrasting experiments. The as-synthesized material exhibits ferromagnetic characteristics and a high surface area, showing potential applications for catalysts and other ...

Identification of higenamine in Radix Aconiti Lateralis Preparata as a beta2-adrenergic receptor agonist1.

Abstract: Aim: To screen beta2-adrenergic receptor (β2-AR) agonists from Radix Aconiti Lateralis Preparata (RALP) as potential drug leads for asthma using a sensitive cell-based agonist assay. Methods: The β 2 -AR gene was stably expressed by Chinese hamster ovary (CHO) cells also stably expressing a cyclic adenosine monophosphate (AMP) response element-linked enhanced green fluorescent protein reporter gene. The cells were used to screen agonists from high-performance liquid chromatographic fractions of an extract of RALP. The fraction with the highest activity was selected for further compound isolation and the study of the structure-activity relationship. Its active compound was further identified by chromatography and mass spectrometry. Results: Bioactivity-directed fraction-ation of the crude extract of RALP led to the isolation and characterization of the effective compound, namely hignamine. It could dose-dependently relax the isolated guinea pig trachea strip precontraction with acetylcholine with EC 50 value of (2.60±0.36) × 10 −5 mol/L. Further in vivo studies also displayed that hignamine could protect experimental asthma model induced by histamine in guinea pigs to prolong the latent periods of asthma. Conclusion: Hignamine, as a β 2 -AR agonist existing in the extract of RALP, is the key compound contributing to the successful relief of the bronchoconstriction.

Si-CdSSe core/shell nanowires with continuously tunable light emission.

Abstract: Uniform Si-CdSSe core/shell nanowires were controllably synthesized by a multisource thermal evaporation route. Both the silicon core and the alloyed CdSSe shell are of high-quality and single crystalline. The silicon core is grown via the gold-catalyzed VLS route with a silicon wafer piece at the high temperature zone as the source. These preferentially grown Si nanowires further serve as templates for the afterward depositions of CdSSe shells using CdS/CdSe powders at the low temperature zone of the furnace as sources. The composition/band gap of the shells can be continuously modulated by the S/Se ratio of the evaporation sources, making these prepared heterostructures have strong and spectral position/color largely tunable light emission at the visible region. These kind of structures may have potential applications in multicolor nanoscaled light-emitting devices. This flexible growth route will also be applicable for controllable synthesis of other Si wire containing heterostructures.

On the origin of efficiency roll-off in InGaN-based light-emitting diodes

Abstract: The external quantum efficiency (EQE) of AlInGaN-based light-emitting diodes (LEDs) on sapphire and bulk GaN substrates was measured over a wide range of pulsed currents with small duty cycles. The current dependence of the EQE appeared to be a strong function of the In content but nearly independent of the dislocation density in the active region. The EQE of the InGaN LEDs peaked at very low currents and decreased dramatically at high currents, whereas the AlGaN UV LED attained a saturated EQE as current increases. In contrast to minimal peak shift in the UV LED, a monotonic current-induced blueshift of the peak energy was seen up to 1 kA/cm2 for the InGaN blue and green LEDs. These results suggest that the capture of delocalized carriers by nonradiative recombination centers such as misfit defects is the major nonthermal mechanism of efficiency roll-off in InGaN LEDs.

Transparent and Light-Emitting Epoxy Super-Nanocomposites Containing ZnO-QDs/SiO2 Nanocomposite Particles as Encapsulating Materials for Solid-State Lighting

Abstract: In this article, the ZnO quantum dots-SiO2 (Z-S) nanocomposite particles were first synthesized. Transparent Z-S/epoxy super-nanocomposites were then prepared by introducing calcined Z-S nanocomposite particles with a proper ratio of ZnO to SiO2 into a transparent epoxy matrix in terms of the filler-matrix refractive index matching principle. It was shown that the epoxy super-nanocomposites displayed intense luminescence with broad emission spectra. Moreover, the epoxy super-nanocomposites showed the interesting afterglow phenomenon with a long phosphorescence lifetime that was not observed for ZnO-QDs/epoxy nanocomposites. Finally, the transparent and light-emitting Z-S/epoxy super-nanocomposites were successfully employed as encapsulating materials for synthesis of highly bright LED lamps.

An ATM- and Rad3-related (ATR) Signaling Pathway and a Phosphorylation-Acetylation Cascade Are Involved

Abstract: Most agents that damage DNA act through posttranslational modifications of p53 and activate its downstream targets. However, whether cellular responses to nucleoside analogue-induced DNA damage also operate through p53 posttranslational modification has not been reported. In this study, the relationship between p53 activation and its posttranslational modifications was investigated in the human cancer cell lines A549 and HCT116 in response to 5-aza-2-deoxycytidine (5-aza-CdR) or cytarabine treatment. 5-Aza-CdR induces p53 posttranslational modifications through activation of an ATM- and Rad3-related (ATR) signaling pathway, and 5-aza-CdR-induced association of replication protein A with chromatin is required for the binding of ATR to chromatin. Upon treatment with 5-aza-CdR, ATR activation is clearly associated with p53 phosphorylation at Ser 15 , but not at Thr 18 , Ser 20 ,o r Ser 37 . This specific p53 phosphorylation at Ser 15 in turn results in acetylation of p53 at Lys 320 and Lys 373 /Lys 382 through transcriptional cofactors p300/CBP-associated factor and p300, respectively. These p53 posttranslational modifications are directly responsible for 5-aza-CdR induced p21 Waf1/Cip1 expression because the binding activity of acetylated p53 at Lys 320 /Lys 373 /Lys 382 to the p21 Waf1/Cip1 promoter, as well as p21 Waf1/Cip1 expression itself are

Solution-processed poly(3-hexylthiophene) vertical organic transistor

Abstract: The fabrication and operation of a solution-processed vertical organic transistor are now demonstrated. The vertical structure provides a large cross section and a short channel length to counter the inherent limitations of the organic materials. The operation of a vertical organic transistor relies on a transition metal oxide layer, V2O5, to lower the carrier injection barrier at the organic/metal interface. The effect of the oxide thickness was examined to verify the role of transition metal oxide in device operation. By studying the device performance at different temperatures and in solvent environments, an operating mechanism that occurs via an ion drift and doping process was proposed. The drift direction of the dissolved Li+ ion can be controlled by altering the gate voltage bias in order to change the carrier injection barrier.

Quantifying the relation between the morphology and performance of polymer solar cells using Monte Carlo simulations

Abstract: Morphology is a crucially important factor determining the efficiency of photocurrent generation in bulk heterojunction polymer solar cells. Morphology, which depends on the characteristics of the polymers as well as on the conditions of phase separation, affects the performance of solar cells by influencing the rate of exciton dissociation and the efficiency of charge carrier transport. Using Monte Carlo simulations, we investigate the effects of annealing time on the morphology of phase separation and charge transfer behavior inside the active layers of polymer solar cells. We find that a suitably defined correlation distance is an effective parameter that quantitatively characterizes different morphologies and can be used to establish a direct link with transmission electron microscopy images of real polymer solar cells. Optimal morphologies have been investigated, showing results that are consistent with experimental data.

Temperature dependent Raman spectroscopy of chemically derived graphene

Abstract: Reduced graphite oxide (GO) has shown promise as a scalable alternative to mechanically exfoliated specimens. Although many measurements show that reduced GO has properties approaching those of pristine graphene, it has been difficult to quantify the extent to which the graphitic network is restored upon reduction. Raman spectroscopy is widely used for the characterization of mechanically exfoliated graphene, but has not been fully explored for reduced GO. In this work, hydrazine suspensions of reduced GO are deposited on micro-hot-plates and examined over a range of temperatures by Raman spectroscopy. The work highlights the benefits of solution processing.

Multi-hop delay performance in wireless mesh networks

Abstract: Wireless Mesh Network (WMN) technology is an attractive solution to meet the demand of broad-band network access anywhere and anytime. In order to effectively support delay-sensitive applications such as video streaming and interactive gaming in a WMN, it is crucial to develop feasible methodologies and techniques for accurately analyzing, predicting and guaranteeing end-to-end delay performance over multi-hop wireless communication paths. In this paper, we extend the link-layer effective capacity model and derive a lower bound of delay-bound violation probability, or complementary cumulative distribution function, over multi-hop wireless connections. A fluid traffic model with cross traffic and a Rayleigh fading channel with additive Gaussian noise and Doppler spectrum are considered in our study. The average multi-hop delay and jitter performance bounds are also obtained. Analytical results are verified by extensive computer simulations under different traffic load and wireless channel conditions. We find that multi-hop delay performance is much more sensitive to traffic load and maximum Doppler rate than traffic correlation.

Active materials for photoelectric devices and devices that use the materials

Abstract: A conjugated polymer has a repeated unit having the structure of formula (I) wherein A1, A2, R1 and R2 are independently selected from the group consisting of a proton, an alkyl group comprising up to 18 carbon atoms, an alkoxy group comprising up to 18 carbon atoms, cyano, nitro, aryls and substituted aryls, and wherein Ar is selected from the group consisting of ethenylene, ethynylene, monocyclic arylene, bicyclic arylene, polycyclic arylene, monocyclic heteroarylene, bicyclic heteroarylene, polycyclic heteroarylene, and one to five such groups one of fused or linked.