A new diketopyrrolopyrrole-based co-polymer for ambipolar field-effect transistors and solar cells

A new thieno3,2-b]thiophenediketopyrrolopyrrole-benzo1,2-b:4,5-b']dithio phene based narrow optical gap co-polymer (PTTDPP-BDT) has been synthesized and characterized for field-effect transistors and solar cells. In field-effect transistors the polymer exhibited ambipolar charge transport behaviour with maximum hole and electron mobilities of 10(-3) cm(2) V-1 s(-1) and 10(-5) cm(2)V(-1) s(-1), respectively. The respectable charge transporting properties of the polymer were consistent with X-ray diffraction measurements that showed close molecular packing in the solid state. The difference in hole and electron mobilities was explained by density functional theory calculations, which showed that the highest occupied molecular orbital was delocalized along the polymer backbone with the lowest unoccupied molecular orbital localized on the bis(thieno3,2-b]thiophene)diketopyrrolopyrrole units. Bulk heterojunction photovoltaic devices with the fullerene acceptor PC70BM were fabricated and delivered a maximum conversion efficiency of 3.3% under AM1.5G illumination. (C) 2012 Elsevier B.V. All rights reserved.

En Masse relay selection algorithms for multi-source, multi-relay, decode-and-forward cooperative systems

Opportunistic relay selection in a multiple source-destination (MSD) cooperative system requires quickly allocating to each source-destination (SD) pair a suitable relay based on channel gains. Since the channel knowledge is available only locally at a relay and not globally, efficient relay selection algorithms are needed. For an MSD system, in which the SD pairs communicate in a time-orthogonal manner with the help of decode-and-forward relays, we propose three novel relay selection algorithms, namely, contention-free en masse assignment (CFEA), contention-based en masse assignment (CBEA), and a hybrid algorithm that combines the best features of CFEA and CBEA. En masse assignment exploits the fact that a relay can often aid not one but multiple SD pairs, and, therefore, can be assigned to multiple SD pairs. This drastically reduces the average time required to allocate an SD pair when compared to allocating the SD pairs one by one. We show that the algorithms are much faster than other selection schemes proposed in the literature and yield significantly higher net system throughputs. Interestingly, CFEA is as effective as CBEA over a wider range of system parameters than in single SD pair systems.

Diketopyrrolopyrrole-Based Conjugated Polymers and Small Molecules for Organic Ambipolar Transistors and Solar Cells

The present highlight discusses major work in the synthesis of low bandgap diketopyrrolopyrrole (DPP)-based polymers with donor-acceptor-donor (D-A-D) approach and their application in organic electronics. It examines the past and recent significant advances which have led to development of low bandgap DPP-based materials with phenyl and thiophene as donors. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4241-4260

Performance Analysis of Heat Sinks With Phase-Change Materials Subjected to Transient and Cyclic Heating

Phase-change cooling technique is a suitable method for thermal management of electronic equipment subjected to transient or cyclic heat loads. The thermal performance of a phase-change based heat sink under cyclic heat load depends on several design parameters, namely, applied heat flux, cooling heat transfer coefficient, thermophysical properties of phase-change materials (PCMs), and physical dimensions of phase-change storage system during melting and freezing processes. A one-dimensional conduction heat transfer model is formulated to evaluate the effectiveness of preliminary design of practical PCM-based energy storage units. In this model, the phase-change process of the PCM is divided into melting and solidification subprocesses, for which separate equations are written. The equations are solved sequentially and an explicit closed-form solution is obtained. The efficacy of analytical model is estimated by comparing with a finite-volume-based numerical solution for both transient and cyclic heat loads.

Three-Dimensional Nanoarchitecture of BiFeO3 Anchored TiO2 Nanotube Arrays for Electrochemical Energy Storage and Solar Energy Conversion

Here, we report the synthesis of TiO2/BiFeO3 nano-heterostnicture (NH) arrays by anchoring BiFeO3 (BFO) particles on on TiO2 nanotube surface and investigate their pseudocapacitive and photoelectrochemical properties considering their applications in green energy fields. The unique TiO2/BFO NHs have been demonstrated both as energy conversion and storage materials. The capacitive behavior of the NHs has been found to be significantly higher than that of the pristine TiO2 NTs, which is mainly due to the anchoring of redox active BFO nanoparticles. A specific capacitance of about 440 F g(-1) has been achieved for this NHs at a current density of 1.1 A g(-1) with similar to 80% capacity retention at a current density of 2.5 A g(-1). The NHs also exhibit high energy and power performance (energy density of 46.5 Wh kg(-1) and power density of 1.2 kW kg(-1) at a current density of 2.5 A g(-1)) with moderate cycling stability (92% capacity retention after 1200 cycles). Photoelectrochemical investigation reveals that the photocurrent density of the NHs is almost 480% higher than the corresponding dark current and it shows significantly improved photoswitching performance as compared to pure TiO2 nanotubes, which has been demonstrated based the interfacial type-II band alignment between TiO2 and BFO.

Fast and slow climate responses to CO2 and solar forcing: A linear multivariate regression model characterizing transient climate change

Climate change in response to a change in external forcing can be understood in terms of fast response to the imposed forcing and slow feedback associated with surface temperature change. Previous studies have investigated the characteristics of fast response and slow feedback for different forcing agents. Here we examine to what extent that fast response and slow feedback derived from time-mean results of climate model simulations can be used to infer total climate change. To achieve this goal, we develop a multivariate regression model of climate change, in which the change in a climate variable is represented by a linear combination of its sensitivity to CO2 forcing, solar forcing, and change in global mean surface temperature. We derive the parameters of the regression model using time-mean results from a set of HadCM3L climate model step-forcing simulations, and then use the regression model to emulate HadCM3L-simulated transient climate change. Our results show that the regression model emulates well HadCM3L-simulated temporal evolution and spatial distribution of climate change, including surface temperature, precipitation, runoff, soil moisture, cloudiness, and radiative fluxes under transient CO2 and/or solar forcing scenarios. Our findings suggest that temporal and spatial patterns of total change for the climate variables considered here can be represented well by the sum of fast response and slow feedback. Furthermore, by using a simple 1-D heat-diffusion climate model, we show that the temporal and spatial characteristics of climate change under transient forcing scenarios can be emulated well using information from step-forcing simulations alone.

Comparison of Convective and Radiative Heating Modes on the Thermophysical Changes of a Cerium Nitrate Droplet

In this paper, we try to establish the equivalence or similarity in the thermal and physiochemical changes in precursor droplets (cerium nitrate) in convective and radiative fields. The radiative field is created through careful heating of the droplet using a monochromatic light source (CO2 laser). The equivalence is also established for different modes of convection like droplet injected into a high-speed flow and droplet experiencing a convective flow due to acoustic streaming (levitated) only. The thermophysical changes are studied in an aqueous cerium nitrate droplet, and the dissociation of cerium nitrate to ceria is modeled using modified Kramers' reaction rate formulation. It is observed that vaporization, species accumulation, and chemical characteristics obtained in a convectively heated droplet are retained in a radiatively heated droplet by careful adjustment of the laser intensity. The timescales and ceria yield match reasonably well for both the cases. It is also noted that similar conclusions are drawn in both levitated droplet and a nonlevitated droplet.

Numerical Investigations for Leakage and Windage Heating in Straight-Through Labyrinth Seals

The ability to quantify leakage flow and windage heating for labyrinth seals with honeycomb lands is critical in understanding gas turbine engine system performance and predicting its component life. Variety of labyrinth seal configurations (number of teeth, stepped or straight, honeycomb cell size) are in use in gas turbines, and for each configuration, there are many geometric factors that can impact a seal's leakage and windage characteristics. This paper describes the development of a numerical methodology aimed at studying the effect of honeycomb lands on leakage and windage heating. Specifically, a three-dimensional computational fluid dynamics (CFD) model is developed utilizing commercial finite volume-based software incorporating the renormalization group (RNG) k-epsilon turbulence model with modified Schmidt number. The modified turbulence model is benchmarked and fine-tuned based on several experiments. Using this model, a broad parametric study is conducted by varying honeycomb cell size, pressure ratio (PR), and radial clearance for a four-tooth straight-through labyrinth seal. The results show good agreement with available experimental data. They further indicate that larger honeycomb cells predict higher seal leakage and windage heating at tighter clearances compared to smaller honeycomb cells and smooth lands. However, at open seal clearances larger honeycomb cells have lower leakage compared to smaller honeycomb cells.

Absorption-resorption heating cycles with the new working pairs R21-NMP and R21-DMA

The new working pairs, R21-NMP and R21-DMA, find potential application as working pairs for the single stage Resorption Heat Pump (RHP) and the Resorption Heat Transformer (RHT) cycles. A thermodynamic cycle analysis with these pairs shows that single stage RHPs have high COPs in their entire range of operation. RHTs show higher temperature boosts (up to 47 K) than the simple absorption heat transformers. Absorber temperatures of up to 400 K can be achieved in a single stage RHT system using R21 as the refrigerant. However, absorption-resorption systems have inherent limitations on the range of operating temperatures. Besides, they necessitate a higher pump work as compared to simple single stage absorption heating systems.

Fluorescent probe studies of biomembranes and model systems. The design and use of anionic site reporters

The fluorescence properties of a homologous series of fluorescent alkylamines are described. The binding of the probes to crythrocyte membranes increases with the length of the alkyl chain. The probes are shown to interact more strongly with membranes than with protein and lipid model systems. The binding of the probes to the membrane is sensitive to the cation concentration of the medium.

Steric effects on the ultraviolet absorption of 1,2-enedioic and related systems

1,2-Enedioic systems, being sterically perturbed from planarity do not show the effect of the extended conjugation expected of a (formal) trienic entity. In the absence of a model which approximates to a uniplanar situation, the strategy of replacing an ester group in the enedioates by a cyano (for which less stringent steric demand may be presumed) and noting the correction concomitant to this replacement was adopted to arrive at a notional figure for the position of maximal absorption in the planar enedioates. From this the conclusion, subject to substantiation by molecular mechanical or quantum chemical calculations, was drawn that even the E-isomeric and comparatively less substituted enedioates are highly sterically perturbed. An alternative to an earlier explanation of the bathochromic shift of absorption maxima encountered in the 5-cyclic ene-ester and ene-nitrile, relative to the 6-cyclic analogues (observed also with the enedioates and cyanovinyl ester systems), seen later to have been based on unwarranted premises, has been advanced. A comment on the absorption characteristics of enedioic anhydrides has been appended.

Optimal infinite-horizon feedback laws for a general class of constrained discrete-time systems: stability and moving-horizon approximations

Stability results are given for a class of feedback systems arising from the regulation of time-varying discrete-time systems using optimal infinite-horizon and moving-horizon feedback laws. The class is characterized by joint constraints on the state and the control, a general nonlinear cost function and nonlinear equations of motion possessing two special properties. It is shown that weak conditions on the cost function and the constraints are sufficient to guarantee uniform asymptotic stability of both the optimal infinite-horizon and movinghorizon feedback systems. The infinite-horizon cost associated with the moving-horizon feedback law approaches the optimal infinite-horizon cost as the moving horizon is extended.

The 31p nmr Spectra of Isomeric Diaminohexa-hlorocyclotetraphosphazatetraenes; Examples of a2b2 and aa'bb' spin Systems

The 31P nmr spectra of 2,4- and 2,6-diamino-derivatives of octachlorocyclotetraphosphazatetraene, N4P4Cl6(NR1R2)2 (R1 = H, R2 = But; R1 = H, R2 = CH2Ph; R1 = Me, R2 = Ph), have been measured. The 2,4- and 2,6-isomers were analysed as AA'BB' and A2B2 spin systems respectively. In the 2,4-isomers the spin-spin couplings 2J(PNP) and 4J(PNPNP) were of opposite sign.

The Relay Selection and Transmission Trade-off in Cooperative Communication Systems

A common and practical paradigm in cooperative communication systems is the use of a dynamically selected `best' relay to decode and forward information from a source to a destination. Such systems use two phases - a relay selection phase, in which the system uses transmission time and energy to select the best relay, and a data transmission phase, in which it uses the spatial diversity benefits of selection to transmit data. In this paper, we derive closed-form expressions for the overall throughput and energy consumption, and study the time and energy trade-off between the selection and data transmission phases. To this end, we analyze a baseline non-adaptive system and several adaptive systems that adapt the selection phase, relay transmission power, or transmission time. Our results show that while selection yields significant benefits, the selection phase's time and energy overhead can be significant. In fact, at the optimal point, the selection can be far from perfect, and depends on the number of relays and the mode of adaptation. The results also provide guidelines about the optimal system operating point for different modes of adaptation. The analysis also sheds new insights on the fast splitting-based algorithm considered in this paper for relay selection.