Utilizing hot electrons

DOE PAGES

Nozik, Arthur J.

2018-03-01

In current solar cells, any photon energy exceeding the semiconductor bandgap is lost before being collected, limiting the cell performance. Hot carrier solar cells could avoid these losses. Now, a detailed experimental study and analysis shows that this strategy could lead to an improvement of the photoconversion efficiency in practice.

Utilizing hot electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nozik, Arthur J.

In current solar cells, any photon energy exceeding the semiconductor bandgap is lost before being collected, limiting the cell performance. Hot carrier solar cells could avoid these losses. Now, a detailed experimental study and analysis shows that this strategy could lead to an improvement of the photoconversion efficiency in practice.

Seed mediated synthesis of nanosized zinc oxide and its electron transporting activity in dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Rajkumar, C.; Arulraj, Arunachalam

2018-01-01

A zinc oxide (ZnO) nanoparticle has been synthesized using seed mediated method at a low temperature of 90 °C. To understand its optical, structural and morphological properties of as-synthesized ZnO, it was characterized using various analytical techniques. The obtained result reveals that ZnO nanoparticles possess hexagonal wurtzite crystal structure with an average crystallite size of ˜40 nm. The presence of hydroxyl, amine and alkyl groups was confirmed from Fourier transform infrared analysis. Furthermore, the synthesized ZnO powder has employed as photoanode for the fabrication of dye-sensitized solar cells using Doctor-blade technique. To evaluate its photo-conversion efficiency, the device has been assembled into a cell module and illuminated with the light intensity of 100 mW cm-2. The device exhibits the photo-conversion efficiency of 1.85% with the current density of 4.532 mA cm-2 and voltage of 0.61 V.

Radiation Effects Research and Device Evaluation

DTIC Science & Technology

2012-04-04

disadvantages over classic inorganic -based cells in that their photo-conversion efficiency is low (less than 8% presently), their specific power... fullerene solar cells,” Appl. Phys. Lett., 86, pp. 123509-1-3, 2005. 4. H.P. Hjalmarson, R.L. Pease, S.C. Witczak, M.R. Shaneyfelt, J.R. Schwank, A.H

Intravital multiphoton photoconversion with a cell membrane dye.

PubMed

Turcotte, Raphaël; Wu, Juwell W; Lin, Charles P

2017-02-01

Photoconversion, an irreversible shift in a fluorophore emission spectrum after light exposure, is a powerful tool for marking cellular and subcellular compartments and tracking their dynamics in vivo. This paper reports on the photoconversion properties of Di-8-ANEPPS, a commercially available membrane dye. When illuminated with near-infrared femtosecond laser pulses, Di-8-ANEPPS undergoes multiphoton photoconversion as indicated by the supralinear dependence of the conversion rate ρ pc on the incident power (ρpc∝Iexc2.27), and by the ability to photoconvert a thin optical section in a three-dimensional matrix. The characteristic emission spectrum changed from red to blue, and ratiometric analysis on single cells in vitro revealed a 65-fold increase in the blue to red wavelength ratio after photoconversion. The spectral shift is preserved in vivo for hours, making Di-8-ANEPPS a useful dye for intravital cell marking and tracking applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic solar cells: understanding the role of Förster resonance energy transfer.

PubMed

Feron, Krishna; Belcher, Warwick J; Fell, Christopher J; Dastoor, Paul C

2012-12-12

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by F¨orster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of F¨orster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

Optimizing the photochemical conversion of UV-vis light of silver-nanoparticles decorated TiO2 nanotubes based photoanodes

NASA Astrophysics Data System (ADS)

Gaidi, M.; Trabelsi, K.; Hajjaji, A.; Chourou, M. L.; Alhazaa, A. N.; Bessais, B.; El Khakani, M. A.

2018-01-01

Homogeneous decoration of TiO2 nanotubes (NTs) by Ag metallic nanoparticles (NPs) was carried out by a relatively simple photoreduction process. This Ag-NPs decoration was found to improve the photoconversion efficiency of the TiO2-NTs based photoanodes. The x-ray photoelectron spectroscopy and x-ray diffraction analyses confirmed that all the Ag-NPs are metallic and the underlying TiO2-NTs crystallize in the anatase phase after their annealing at 400 °C, respectively. Transmission electron microscopy observations have confirmed the effective decoration of the TiO2-NTs’ surface by Ag-NPs, and allowed to measure the average Ag-NPs size, which was found to increase linearly from (4 ± 2) nm to (16 ± 4) nm when the photoreduction time is increased from 5 to 20 min. The diffuse reflectivity of the Ag-NPs decorated TiO2-NTs was found to decrease significantly as compared to the undecorated TiO2-NTs. Interestingly, the Ag-NPs decorated TiO2-NTs exhibited a significantly enhanced photochemical response, under visible radiation, with regards to the undecorated NTs. This enhancement was found to reach its maximum for the TiO2-NTs decorated with Ag-NPs having the optimal average diameter of ˜8.5 nm. The maximum photoconversion efficiency of Ag-NPs decorated TiO2-NTs was about two times greater than for the undecorated ones. This improved photo-electro-chemical response is believed to be associated with the additional absorption of visible light of Ag-NPs through the localized surface plasmon resonance phenomenon. This interpretation is supported by the fact that the photoluminescence intensity of the Ag-NPs decorated TiO2-NTs was found to decrease significantly as compared to undecorated NTs, due to charge carriers trapping in the Ag NPs. This demonstrates that Ag-NPs decoration promotes photogenerated charges separation in the TiO2-NTs, increasing thereby their capacity for current photogeneration. The surface decoration of TiO2 NTs by noble metals NPs is expected to impact positively the use of TiO2-NTs based photoanodes in some energetic applications such as hydrogen generation and photo-electrochemical solar cells.

Optimizing the photochemical conversion of UV-vis light of silver-nanoparticles decorated TiO2 nanotubes based photoanodes.

PubMed

Gaidi, M; Trabelsi, K; Hajjaji, A; Chourou, M L; Alhazaa, A N; Bessais, B; El Khakani, M A

2018-01-05

Homogeneous decoration of TiO 2 nanotubes (NTs) by Ag metallic nanoparticles (NPs) was carried out by a relatively simple photoreduction process. This Ag-NPs decoration was found to improve the photoconversion efficiency of the TiO 2 -NTs based photoanodes. The x-ray photoelectron spectroscopy and x-ray diffraction analyses confirmed that all the Ag-NPs are metallic and the underlying TiO 2 -NTs crystallize in the anatase phase after their annealing at 400 °C, respectively. Transmission electron microscopy observations have confirmed the effective decoration of the TiO 2 -NTs' surface by Ag-NPs, and allowed to measure the average Ag-NPs size, which was found to increase linearly from (4 ± 2) nm to (16 ± 4) nm when the photoreduction time is increased from 5 to 20 min. The diffuse reflectivity of the Ag-NPs decorated TiO 2 -NTs was found to decrease significantly as compared to the undecorated TiO 2 -NTs. Interestingly, the Ag-NPs decorated TiO 2 -NTs exhibited a significantly enhanced photochemical response, under visible radiation, with regards to the undecorated NTs. This enhancement was found to reach its maximum for the TiO 2 -NTs decorated with Ag-NPs having the optimal average diameter of ∼8.5 nm. The maximum photoconversion efficiency of Ag-NPs decorated TiO 2 -NTs was about two times greater than for the undecorated ones. This improved photo-electro-chemical response is believed to be associated with the additional absorption of visible light of Ag-NPs through the localized surface plasmon resonance phenomenon. This interpretation is supported by the fact that the photoluminescence intensity of the Ag-NPs decorated TiO 2 -NTs was found to decrease significantly as compared to undecorated NTs, due to charge carriers trapping in the Ag NPs. This demonstrates that Ag-NPs decoration promotes photogenerated charges separation in the TiO 2 -NTs, increasing thereby their capacity for current photogeneration. The surface decoration of TiO 2 NTs by noble metals NPs is expected to impact positively the use of TiO 2 -NTs based photoanodes in some energetic applications such as hydrogen generation and photo-electrochemical solar cells.

Photoconversion in orange and red fluorescent proteins

PubMed Central

Kremers, Gert-Jan; Hazelwood, Kristin L.; Murphy, Christopher S.; Davidson, Michael W.; Piston, David W.

2009-01-01

We report that photoconversion is fairly common among orange and red fluorescent proteins, as a screen of 12 variants yielded 8 that exhibit photoconversion. Specifically, three red fluorescent proteins can be switched into a green state, and two orange variants can be photoconverted to the far red. The orange highlighters are ideal for dual-probe highlighter applications, and they exhibit the most red-shifted excitation of all fluorescent protein described to date. PMID:19363494

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

PubMed Central

Feron, Krishna; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

2012-01-01

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells. PMID:23235328

Vapor and healing treatment for CH3NH3PbI3-xClx films toward large-area perovskite solar cells

NASA Astrophysics Data System (ADS)

Gouda, Laxman; Gottesman, Ronen; Tirosh, Shay; Haltzi, Eynav; Hu, Jiangang; Ginsburg, Adam; Keller, David A.; Bouhadana, Yaniv; Zaban, Arie

2016-03-01

Hybrid methyl-ammonium lead trihalide perovskites are promising low-cost materials for use in solar cells and other optoelectronic applications. With a certified photovoltaic conversion efficiency record of 20.1%, scale-up for commercial purposes is already underway. However, preparation of large-area perovskite films remains a challenge, and films of perovskites on large electrodes suffer from non-uniform performance. Thus, production and characterization of the lateral uniformity of large-area films is a crucial step towards scale-up of devices. In this paper, we present a reproducible method for improving the lateral uniformity and performance of large-area perovskite solar cells (32 cm2). The method is based on methyl-ammonium iodide (MAI) vapor treatment as a new step in the sequential deposition of perovskite films. Following the MAI vapor treatment, we used high throughput techniques to map the photovoltaic performance throughout the large-area device. The lateral uniformity and performance of all photovoltaic parameters (Voc, Jsc, Fill Factor, Photo-conversion efficiency) increased, with an overall improved photo-conversion efficiency of ~100% following a vapor treatment at 140 °C. Based on XRD and photoluminescence measurements, We propose that the MAI treatment promotes a ``healing effect'' to the perovskite film which increases the lateral uniformity across the large-area solar cell. Thus, the straightforward MAI vapor treatment is highly beneficial for large scale commercialization of perovskite solar cells, regardless of the specific deposition method.Hybrid methyl-ammonium lead trihalide perovskites are promising low-cost materials for use in solar cells and other optoelectronic applications. With a certified photovoltaic conversion efficiency record of 20.1%, scale-up for commercial purposes is already underway. However, preparation of large-area perovskite films remains a challenge, and films of perovskites on large electrodes suffer from non-uniform performance. Thus, production and characterization of the lateral uniformity of large-area films is a crucial step towards scale-up of devices. In this paper, we present a reproducible method for improving the lateral uniformity and performance of large-area perovskite solar cells (32 cm2). The method is based on methyl-ammonium iodide (MAI) vapor treatment as a new step in the sequential deposition of perovskite films. Following the MAI vapor treatment, we used high throughput techniques to map the photovoltaic performance throughout the large-area device. The lateral uniformity and performance of all photovoltaic parameters (Voc, Jsc, Fill Factor, Photo-conversion efficiency) increased, with an overall improved photo-conversion efficiency of ~100% following a vapor treatment at 140 °C. Based on XRD and photoluminescence measurements, We propose that the MAI treatment promotes a ``healing effect'' to the perovskite film which increases the lateral uniformity across the large-area solar cell. Thus, the straightforward MAI vapor treatment is highly beneficial for large scale commercialization of perovskite solar cells, regardless of the specific deposition method. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08658b

CuSb(S,Se)2 thin film heterojunction photovoltaic devices

NASA Astrophysics Data System (ADS)

Welch, Adam W.

Thin film heterojunction solar cells based on CuSb(S,Se)2 absorbers are investigated for two primary reasons. First, antimony is more abundant and less expensive than elements used in current thin film photovoltaics, In, Ga, and Te, and so, successful integration of Sb based materials offers greater diversification and scalability of solar energy. Second, the CuSb(S,Se) 2 ternary is chemically, electronically, and optically similar to the well-known, high efficiency, CuIn(S,Se)2 based materials. It is therefore postulated that the copper antimony ternaries will have similar defect tolerant electronic transport that may allow for similar highly efficient photoconversion. However, CuSb(S,Se)2 forms a layered crystal structure, different from the tetrahedral coordination found in conventional solar absorbers, due to the non-bonding lone pair of electrons on the antimony site. Thus examination of 2D antimony ternaries will lend insight into the role of structure in photoconversion processes. To address these questions, the semiconductors of interest (CuSbS 2 & CuSbSe2) were first synthesized on glass by combinatorial methods, to more quickly optimize process condi- tions. Radio-frequency (RF) magnetron co-sputtering from Sb2(S,Se)3 and Cu 2(S,Se) targets were used, without rotation, to produce chemical and flux graded libraries which were then subjected to high throughput characterization of structure (XRD), composition (XRF), conductivity (4pp), and optical absorption (UV/Vis/NIR). This approach rapidly identified processes that generated phase pure material with tunable carrier concentration by applying excess Sb 2(S,Se)3 within a temperature window bound by the volatility of Sb2(S,Se)3 and stability of the ternary phase. The resulting phase pure thin films were then incor- porated into the traditional CuInGaSe2 (CIGS) substrate photovoltaic (PV) architecture, and the resulting device performance was correlated to gradients in composition, sputter flux, absorber thickness, and grain orientation. This combinatorial work was complimented by individual measurements of photoluminescence (PL), capacitance-voltage (CV), external quantum efficiency (EQE), terahertz (THz) spectroscopy, and photoelectrochemical (PEC) measurements. CuSbS2-based libraries produced devices with just 1% power conversion efficiency, mainly limited by high levels of recombination associated with high density of shallow trap states. Conversely, the selenide variant showed more promise, with initial cells producing significantly more photocurrent, nearly 60% of the theoretical maximum, and likewise 5% efficient devices, mainly due to fewer trap states. However, the selenide is still limited by short carrier diffusion lengths, therefore demonstrating that structure does seem to play limiting role in photoconversion processes. Overall, the CuSb(S,Se)2 material system is only likely to merit further exploration if it can be incorporated into an alternate device structure less dependent on collection by diffusion. There is a small possibility that oriented selenide films with anisotropic carrier lifetimes could improve performance, though this is unlikely considering initial oriented sulfide films did not demonstrate much improved performance. This work demonstrated the utility of the combinatorial device fabrication applied to the search for new, scalable photovoltaic materials. An innovative chemical system was quickly explored in-depth and optimized for devices; continued efforts of this type are likely to produce better materials, or at the very least, quickly expand the library of well-scrutinized photovoltaic materials.

Author Correction: III-V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration

NASA Astrophysics Data System (ADS)

Cariou, Romain; Benick, Jan; Feldmann, Frank; Höhn, Oliver; Hauser, Hubert; Beutel, Paul; Razek, Nasser; Wimplinger, Markus; Bläsi, Benedikt; Lackner, David; Hermle, Martin; Siefer, Gerald; Glunz, Stefan W.; Bett, Andreas W.; Dimroth, Frank

2018-06-01

In the version of this Article originally published, in the legend in Fig. 5a, the blue, green and red lines were incorrectly labelled as GaAs, Si and GaInP, respectively; instead, the labels should have read, respectively, GaInP, GaAs and Si. This has now been corrected.

Evaluating Dihydroazulene/Vinylheptafulvene Photoswitches for Solar Energy Storage Applications

PubMed Central

Wang, Zhihang; Udmark, Jonas; Börjesson, Karl; Rodrigues, Rita; Roffey, Anna; Abrahamsson, Maria

2017-01-01

Abstract Efficient solar energy storage is a key challenge in striving toward a sustainable future. For this reason, molecules capable of solar energy storage and release through valence isomerization, for so‐called molecular solar thermal energy storage (MOST), have been investigated. Energy storage by photoconversion of the dihydroazulene/vinylheptafulvene (DHA/VHF) photothermal couple has been evaluated. The robust nature of this system is determined through multiple energy storage and release cycles at elevated temperatures in three different solvents. In a nonpolar solvent such as toluene, the DHA/VHF system can be cycled more than 70 times with less than 0.01 % degradation per cycle. Moreover, the [Cu(CH3CN)4]PF6‐catalyzed conversion of VHF into DHA was demonstrated in a flow reactor. The performance of the DHA/VHF couple was also evaluated in prototype photoconversion devices, both in the laboratory by using a flow chip under simulated sunlight and under outdoor conditions by using a parabolic mirror. Device experiments demonstrated a solar energy storage efficiency of up to 0.13 % in the chip device and up to 0.02 % in the parabolic collector. Avenues for future improvements and optimization of the system are also discussed. PMID:28644559

Photocurrent enhanced by singlet fission in a dye-sensitized solar cell.

PubMed

Schrauben, Joel N; Zhao, Yixin; Mercado, Candy; Dron, Paul I; Ryerson, Joseph L; Michl, Josef; Zhu, Kai; Johnson, Justin C

2015-02-04

Investigations of singlet fission have accelerated recently because of its potential utility in solar photoconversion, although only a few reports definitively identify the role of singlet fission in a complete solar cell. Evidence of the influence of singlet fission in a dye-sensitized solar cell using 1,3-diphenylisobenzofuran (DPIBF, 1) as the sensitizer is reported here. Self-assembly of the blue-absorbing 1 with co-adsorbed oxidation products on mesoporous TiO2 yields a cell with a peak internal quantum efficiency of ∼70% and a power conversion efficiency of ∼1.1%. Introducing a ZrO2 spacer layer of thickness varying from 2 to 20 Å modulates the short-circuit photocurrent such that it is initially reduced as thickness increases but 1 with 10-15 Å of added ZrO2. This rise can be explained as being due to a reduced rate of injection of electrons from the S1 state of 1 such that singlet fission, known to occur with a 30 ps time constant in polycrystalline films, has the opportunity to proceed efficiently and produce two T1 states per absorbed photon that can subsequently inject electrons into TiO2. Transient spectroscopy and kinetic simulations confirm this novel mode of dye-sensitized solar cell operation and its potential utility for enhanced solar photoconversion.

Superior photoelectrochemical properties of ZnO nanorods/poly(3-hexylthiophene) hybrid photoanodes

NASA Astrophysics Data System (ADS)

Majumder, T.; Hmar, J. J. L.; Dhar, S.; Mondal, S. P.

2017-06-01

Photoelectrochemical properties of ZnO nanorods (ZnO NRs) and poly(3-hexylthiophene) (P3HT) polymer hybrid photoanodes have been studied. The hybrid photoanodes demonstrated higher photoconversion efficiency, incident photon to current conversion efficiency (IPCE) and lower interfacial resistance compared to pristine ZnO nanorods and P3HT based electrodes. The origin of superior photoelectrochemical properties of ZnO/P3HT photoanodes has been explained using carrier transport mechanism at semiconductor/electrolyte junction. The stability of ZnO NRs/P3HT photoanode has been demonstrated.

Are tyrosine residues involved in the photoconversion of the water-soluble chlorophyll-binding protein of Chenopodium album?

PubMed

Takahashi, S; Seki, Y; Uchida, A; Nakayama, K; Satoh, H

2015-05-01

Non-photosynthetic and hydrophilic chlorophyll (Chl) proteins, called water-soluble Chl-binding proteins (WSCPs), are distributed in various species of Chenopodiaceae, Amaranthaceae, Polygonaceae and Brassicaceae. Based on their photoconvertibility, WSCPs are categorised into two classes: Class I (photoconvertible) and Class II (non-photoconvertible). Chenopodium album WSCP (CaWSCP; Class I) is able to convert the chlorin skeleton of Chl a into a bacteriochlorin-like skeleton under light in the presence of molecular oxygen. Potassium iodide (KI) is a strong inhibitor of the photoconversion. Because KI attacks tyrosine residues in proteins, tyrosine residues in CaWSCP are considered to be important amino acid residues for the photoconversion. Recently, we identified the gene encoding CaWSCP and found that the mature region of CaWSCP contained four tyrosine residues: Tyr13, Tyr14, Tyr87 and Tyr134. To gain insight into the effect of the tyrosine residues on the photoconversion, we constructed 15 mutant proteins (Y13A, Y14A, Y87A, Y134A, Y13-14A, Y13-87A, Y13-134A, Y14-87A, Y14-134A, Y87-134A, Y13-14-87A, Y13-14-134A, Y13-87-134A, Y14-87-134A and Y13-14-87-134A) using site-directed mutagenesis. Amazingly, all the mutant proteins retained not only chlorophyll-binding activity, but also photoconvertibility. Furthermore, we found that KI strongly inhibited the photoconversion of Y13-14-87-134A. These findings indicated that the four tyrosine residues are not essential for the photoconversion. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

A copper(I) dye-sensitised TiO2-based system for efficient light harvesting and photoconversion of CO2 into hydrocarbon fuel.

PubMed

Yuan, Yong-Jun; Yu, Zhen-Tao; Zhang, Ji-Yuan; Zou, Zhi-Gang

2012-08-28

A new copper(I) complex with the ability to bind to TiO(2) was synthesised and successfully employed as a solar cell sensitizer. Furthermore, we demonstrated that the copper(I) dye-sensitised TiO(2)-based photocatalyst exhibits impressive effectiveness for the selective photoreduction of CO(2) to CH(4) under visible light.

Optimization of TiO{sub 2} photoelectrode with titanium isopropoxide for flexible dye sensitized solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anggraini, Putri Nur, E-mail: putr014@lipi.go.id; Retnaningsih, Lilis; Muliani, Lia

2016-04-19

Flexible DSSC uses plastic substrate such as polyethylene terephthalate (PET) to deposit photoelectrode, resulting in poor photoconversion efficiency of the solar cell due to the low temperature applied in the fabrication process. In this research, optimization process was examined in order to optimize the performance of flexible DSSC by adding titanium isopropoxide (TTIP) as a binder to TiO{sub 2} paste for DSSC photoelectrode. Small portion of TTIP with molar percentages of 0%, 5%, and 10% were added to a mixture of TiO{sub 2} nanocrystaline, butanol, DI water, and reflector powder. The mixtures were stirred using a magnetic stirrer for 24more » hours. Each of various pastes was then deposited on a plastic substrate with doctor blade method on 1 cm{sup 2} area. The films were sintered at temperature of 150 °C for 4 hours and soaked in dye solution for 24 hours. Furthermore, TiO{sub 2} photoelectrode and Pt counter electrode were assembled and injected by electrolyte. Flexible DSSCs were characterized by SEM and XRD to determine their morphological structures. J-V measurement was performed by sun simulator to calculate DSSC photoconversion efficiency. The optimum performance of flexible DSSC was achieved by DSSC with 10 mol% TTIP content.« less

Fabrication and improved photoelectrochemical properties of a transferred GaN-based thin film with InGaN/GaN layers.

PubMed

Cao, Dezhong; Xiao, Hongdi; Gao, Qingxue; Yang, Xiaokun; Luan, Caina; Mao, Hongzhi; Liu, Jianqiang; Liu, Xiangdong

2017-08-17

Herein, a lift-off mesoporous GaN-based thin film, which consisted of a strong phase-separated InGaN/GaN layer and an n-GaN layer, was fabricated via an electrochemical etching method in a hydrofluoric acid (HF) solution for the first time and then transferred onto quartz or n-Si substrates, acting as photoanodes during photoelectrochemical (PEC) water splitting in a 1 M NaCl aqueous solution. Compared to the as-grown GaN-based film, the transferred GaN-based thin films possess higher and blue-shifted light emission, presumably resulting from an increase in the surface area and stress relaxation in the InGaN/GaN layer embedded on the mesoporous n-GaN. The properties such as (i) high photoconversion efficiency, (ii) low turn-on voltage (-0.79 V versus Ag/AgCl), and (iii) outstanding stability enable the transferred films to have excellent PEC water splitting ability. Furthermore, as compared to the film transferred onto the quartz substrate, the film transferred onto the n-Si substrate exhibits higher photoconversion efficiency (2.99% at -0.10 V) due to holes (h + ) in the mesoporous n-GaN layer that originate from the n-Si substrate.

Evaluating Dihydroazulene/Vinylheptafulvene Photoswitches for Solar Energy Storage Applications.

PubMed

Wang, Zhihang; Udmark, Jonas; Börjesson, Karl; Rodrigues, Rita; Roffey, Anna; Abrahamsson, Maria; Nielsen, Mogens Brøndsted; Moth-Poulsen, Kasper

2017-08-10

Efficient solar energy storage is a key challenge in striving toward a sustainable future. For this reason, molecules capable of solar energy storage and release through valence isomerization, for so-called molecular solar thermal energy storage (MOST), have been investigated. Energy storage by photoconversion of the dihydroazulene/vinylheptafulvene (DHA/VHF) photothermal couple has been evaluated. The robust nature of this system is determined through multiple energy storage and release cycles at elevated temperatures in three different solvents. In a nonpolar solvent such as toluene, the DHA/VHF system can be cycled more than 70 times with less than 0.01 % degradation per cycle. Moreover, the [Cu(CH 3 CN) 4 ]PF 6 -catalyzed conversion of VHF into DHA was demonstrated in a flow reactor. The performance of the DHA/VHF couple was also evaluated in prototype photoconversion devices, both in the laboratory by using a flow chip under simulated sunlight and under outdoor conditions by using a parabolic mirror. Device experiments demonstrated a solar energy storage efficiency of up to 0.13 % in the chip device and up to 0.02 % in the parabolic collector. Avenues for future improvements and optimization of the system are also discussed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of advanced nanostructured multijunction photoanodes for enhanced solar hydrogen generation via water splitting

NASA Astrophysics Data System (ADS)

Ishihara, Hidetaka

As the worldwide demand for fossil-based fuel increases every day and the fossil reserve continues to be depleted, the need for alternative/renewable energy sources has gained momentum. Electric, hybrid, and hydrogen cars have been at the center of discussion lately among consumers, automobile manufacturers, and politicians, alike. The development of a fuel-cell based engine using hydrogen has been an ambitious research area over the last few decades-ever since Fujishima showed that hydrogen can be generated via the solar-energy driven photo-electrolytic splitting of water. Such solar cells are known as Photo-Electro-Chemical (PEC) solar cells. In order to commercialize this technology, various challenges associated with photo-conversion efficiency, chemical corrosion resistance, and longevity need to be overcome. In general, metal oxide semiconductors such as titanium dioxide (TiO 2, titania) are excellent candidates for PEC solar cells. Titania nanotubes have several advantages, including biocompatibility and higher chemical stability. Nevertheless, they can absorb only 5-7% of the solar spectrum which makes it difficult to achieve the higher photo-conversion efficiency required for successful commercial applications. A two-prong approach was employed to enhance photo-conversion efficiency: 1) surface modification of titania nanotubes using plasma treatment and 2) nano-capping of the titania nanotubes using titanium disilicide. The plasma surface treatment with N2 was found to improve the photo-current efficiency of titania nanotubes by 55%. Similarly, a facile, novel approach of nano-capping titania nanotubes to enhance their photocurrent response was also investigated. Electrochemically anodized titania nanotubes were capped by coating a 25 nm layer of titanium disilicide using RF magnetron sputtering technique. The optical properties of titania nanotubes were not found to change due to the capping; however, a considerable increase (40%) in the photocurrent density was observed for the nano-capped titania nanotubes due to the enhanced charge transfer process. Similarly, another metal oxide semiconductor was investigated tungsten trioxide (WO3), which has a much higher absorption capability (12%) in the solar spectrum. The WO3 porous nanostructures suffered from surface corrosion resulting in a large reduction in the photocurrent density as a function of time in the alkaline electrolytes. However, with a protective coating of Indium Tin Oxide (100 nm), the surface corrosion of WO3 porous nanostructures was reduced. A large increase in the photocurrent density of as much as 340% was observed after the ITO was applied to the WO3 porous nanostructures

Direct assembly synthesis of metal complex-semiconductor hybrid photocatalysts anchored by phosphonate for highly efficient CO2 reduction.

PubMed

Suzuki, Tomiko M; Tanaka, Hiromitsu; Morikawa, Takeshi; Iwaki, Masayo; Sato, Shunsuke; Saeki, Shu; Inoue, Masae; Kajino, Tsutomu; Motohiro, Tomoyoshi

2011-08-14

Hybrid photocatalysts consisting of a ruthenium complex and p-type photoactive N-doped Ta(2)O(5) anchored with an organic group were successfully synthesized by a direct assembly method. The photocatalyst anchored by phosphonate exhibited excellent photoconversion activity of CO(2) to formic acid under visible-light irradiation with respect to the reaction rate and stability. This journal is © The Royal Society of Chemistry 2011

Primed Conversion: The New Kid on the Block for Photoconversion.

PubMed

Mohr, Manuel Alexander; Pantazis, Periklis

2018-02-11

In 2015, a novel way to convert photoconvertible fluorescent proteins was reported that uses the intercept of blue and far-red light instead of traditional violet or near-UV light illumination. This Minireview describes and contrasts this distinct two-step mechanism termed primed conversion with traditional photoconversion. We provide a comprehensive overview of what is known to date about primed conversion and focus on the molecular requirements for it to take place. We provide examples of its application to axially confined photoconversion in complex tissues as well as super-resolution microscopy. Further, we describe why and when it is useful, including its advantages and disadvantages, and give an insight into potential future development in the field. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of photoanode surface coverage by a sensitizer on the photovoltaic performance of titania based CdS quantum dot sensitized solar cells.

PubMed

Prasad, Rajendra M B; Pathan, Habib M

2016-04-08

In spite of the promising design and architecture, quantum dot sensitized solar cells (QDSSCs) have a long way to go before they attain the actual projected photoconversion efficiencies. Such an inferior performance displayed by QDSSCs is primarily because of many unwanted recombination losses of charge carriers at various interfaces of the cell. Electron recombination due to back electron transfer at the photoanode/electrolyte interface is an important one that needs to be addressed, to improve the efficiency of these third generation nanostructured solar cells. The present work highlights the importance of conformal coverage of CdS quantum dots (QDs) on the surface of the nanocrystalline titania photoanode in arresting such recombinations, leading to improvement in the performance of the cells. Using the successive ionic layer adsorption and reaction (SILAR) process, photoanodes are subjected to different amounts of CdS QD sensitization by varying the number of cycles of deposition. The sensitized electrodes are characterized using UV-visible spectroscopy, cyclic voltammetry and transmission electron microscopy to evaluate the extent of surface coverage of titania electrodes by QDs. Sandwich solar cells are then fabricated using these electrodes and characterized employing electrochemical impedance spectroscopy and J-V characteristics. It is observed that maximum solar cell efficiency is obtained for photoanodes with conformal coating of QDs and any further deposition of sensitizer leads to QD aggregation and so reduces the performance of the solar cells.

Less severe processing improves carbon nanotube photovoltaic performance

NASA Astrophysics Data System (ADS)

Shea, Matthew J.; Wang, Jialiang; Flach, Jessica T.; Zanni, Martin T.; Arnold, Michael S.

2018-05-01

Thin film semiconducting single walled carbon nanotube (s-SWCNT) photovoltaics suffer losses due to trapping and quenching of excitons by defects induced when dispersing s-SWCNTs into solution. We study these aspects by preparing photovoltaic devices from (6,5) carbon nanotubes isolated by different processes: extended ultrasonication, brief ultrasonication, and shear force mixing. Peak quantum efficiency increases from 28% to 38% to 49% as the processing harshness decreases and is attributed to both increasing s-SWCNT length and reducing sidewall defects. Fill-factor and open-circuit voltage also improve with shear force mixing, highlighting the importance of obtaining long, defect-free s-SWCNTs for efficient photoconversion devices.

Conditions for a carrier multiplication in amorphous-selenium based photodetector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masuzawa, Tomoaki; Kuniyoshi, Shingo; Onishi, Masanori

2013-02-18

Amorphous selenium is a promising candidate for high sensitivity photodetector due to its unique carrier multiplication phenomenon. More than 10 carriers can be generated per incident photon, which leads to high photo-conversion efficiency of 1000% that allows real-time imaging in dark ambient. However, application of this effect has been limited to specific devices due to the lack in material characterization. In this article, mechanism of carrier multiplication has been clarified using time-of-flight secondary ion mass spectroscopy and Raman spectroscopy. A prototype photodetector achieved photo conversion efficiency of 4000%, which explains the signal enhancement mechanism in a-Se based photodetector.

Subcellular localization of proteins in the anaerobic sulfate reducer Desulfovibrio vulgaris via SNAP-tag labeling and photoconversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorur, A.; Leung, C. M.; Jorgens, D.

2010-06-01

Systems Biology studies the temporal and spatial 3D distribution of macromolecular complexes with the aim that such knowledge will allow more accurate modeling of biological function and will allow mathematical prediction of cellular behavior. However, in order to accomplish accurate modeling precise knowledge of spatial 3D organization and distribution inside cells is necessary. And while a number of macromolecular complexes may be identified by its 3D structure and molecular characteristics alone, the overwhelming number of proteins will need to be localized using a reporter tag. GFP and its derivatives (XFPs) have been traditionally employed for subcelllar localization using photoconversion approaches,more » but this approach cannot be taken for obligate anaerobic bacteria, where the intolerance towards oxygen prevents XFP approaches. As part of the GTL-funded PCAP project (now ENIGMA) genetic tools have been developed for the anaerobe sulfate reducer Desulfovibrio vulgaris that allow the high-throughput generation of tagged-protein mutant strains, with a focus on the commercially available SNAP-tag cell system (New England Biolabs, Ipswich, MA), which is based on a modified O6-alkylguanine-DNA alkyltransferase (AGT) tag, that has a dead-end reaction with a modified O6-benzylguanine (BG) derivative and has been shown to function under anaerobic conditions. After initial challenges with respect to variability, robustness and specificity of the labeling signal we have optimized the labeling. Over the last year, as a result of the optimized labeling protocol, we now obtain robust labeling of 20 out of 31 SNAP strains. Labeling for 13 strains were confirmed at least five times. We have also successfully performed photoconversion on 5 of these 13 strains, with distinct labeling patterns for different strains. For example, DsrC robustly localizes to the periplasmic portion of the inner membrane, where as a DNA-binding protein localizes to the center of the cell, where the chromosome is located. Two other proteins - Thiosulfate reductase and ATP binding protein were found to be cytoplasmically distributed, whereas a molybdenum transporter was found to locate to the cell periphery. We judge labeling outcome by (1) SDS gel electrophoresis, followed by direct fluorescence imaging of the gel to address specificity of labeling/confirm expected molecular weight, and subsequent Coomassie analysis to ensure comparable protein levels (2) fluorescence intensity of culture by plate reader for statistical sampling (after adjustment for respective cell numbers) and (3) fluorescence microscopy for addressing cell-to-cell signal variation and potential localization patterns. All three assays were usually found to be consistent with one another. While we have been able to improve the efficacy of photoconversion by drastically reducing (eliminating) non-specific binding with our altered labeling protocol, we are currently working on reducing non-specific photoconversion reaction arising occasionally in non-labeled cells. In addition, we have confirmed the presence of SNAP tagged constructs in three recently cloned E.coli strains under promotor control, and are in the process of utilizing them for evaluating the sensitivity of the photoconversion protocol. Fluorescent Activated Cell Sorting was successfully applied to labeled E.coli cells containing SNAP tagged AtpA protein. Different batches of sorted cells, representing low and high labeling intensity, were re-grown and re-labeled and displayed a labeling efficiency similar to the starter culture, supporting the notion that cell-to-cell differences in labeling reflect difference in protein expression, rather then genetic differences.« less

Enhancing the photoelectrochemical response of TiO2 nanotubes through their nanodecoration by pulsed-laser-deposited Ag nanoparticles

NASA Astrophysics Data System (ADS)

Trabelsi, K.; Hajjaji, A.; Gaidi, M.; Bessais, B.; El Khakani, M. A.

2017-08-01

We report on the pulsed laser deposition (PLD) based nanodecoration of titanium dioxide (TiO2) nanotube arrays (NTAs) by Ag nanoparticles (NPs). We focus here on the investigation of the effect of the number of laser ablation pulses (NLP) of the silver target on both the average size of the Ag-NPs and the photoelectrochemical conversion efficiency of the Ag-NP decorated TiO2-NT based photoanodes. By varying the NLP, we were able to not only control the size of the PLD-deposited Ag nanoparticles from 20 to ˜50 nm, but also to increase concomitantly the surface coverage of the TiO2 NTAs by Ag-NPs. The red-shifting of the surface plasmon resonance peak of the PLD-deposited Ag-NPs deposited onto quartz substrates confirmed the increase of their size as the NLP is increased from 500 to 10 000. By investigating the photo-electrochemical properties of Ag-NP decorated TiO2-NTAs, by means of linear sweep cyclic voltammetry under UV-Vis illumination, we found that the generated photocurrent is sensitive to the size of the Ag-NPs and reaches a maximum value at NLP =500 (i.e.,; Ag-NP size of ˜20 nm). For NLP = 500, the photoconversion efficiency of the Ag-NP decorated TiO2-NTAs is shown to reach a maximum of 4.5% (at 0.5 V vs Ag/AgCl). The photocurrent enhancement of Ag-NP decorated TiO2-NTAs is believed to result from the additional light harvesting enabled by the ability of Ag-NPs to absorb visible irradiation caused by various localized surface plasmon resonances, which in turn depend on the size and interdistance of the Ag nanoparticles.

Mesoporous inverse opal TiO2 film as light scattering layer for dye-sensitized solar cell.

PubMed

Jin, Mingshi; Kim, Sung Soo; Yoon, Minyoung; Li, Zhenghua; Lee, Yoon Yun; Kim, Ji Man

2012-01-01

The light harvesting efficiency of dye-sensitized solar cells was enhanced by using a scattering layer. Such as sphere type TiO2, inverse photonic crystal TiO2, hollow spherical TiO2. Among these materials, the TiO2 with inverse photonic crystal (IPC) structure, synthesized by self-assembly using spherical templates, has attracted much attention due to their photonic crystal characteristics and light scattering effects. However, when applied in the DSSCs, the surface area of IPC is very low that caused insufficient adsorption amount of dye molecules. In the present work, a scattering layer with mesoporous inverse photonic crystal (MIPC) TiO2 film was fabricated by the sol-gel reactions with surfactant-assisted sol-gel method using poly(methyl methacrylate) as the template and titanium (IV) isopropoxide as the TiO2 precursor. After removing the PMMA and surfactant, a highly ordered macroporous structure with mesopores were successfully obtained. The surface area and total pore volume of the MIPC were 82 m2/g and 0.31 cm3/g, respectively, which is much larger than those of the IPC. The DSSCs with the scattering layer of MIPC film exhibited 18 and 10% higher photo-conversion efficiency than those of cells only with a nano-crystalline TiO2 film and with scattering layer of IPC film. From UV-visible spectra of dye solutions, the MIPC film showed a higher amount of absorbed dye molecules than those of the reference and IPC films. Accordingly, an increase in the photo-current density through abundant adsorption of the dye, coupled with inherent light scattering ability can improve overall photo-conversion efficiency.

Graphene interfaced perovskite solar cells: Role of graphene flake size

NASA Astrophysics Data System (ADS)

Sakorikar, Tushar; Kavitha, M. K.; Tong, Shi Wun; Vayalamkuzhi, Pramitha; Loh, Kian Ping; Jaiswal, Manu

2018-04-01

Graphene interfaced inverted planar heterojunction perovskite solar cells are fabricated by facile solution method and studied its potential as hole conducting layer. Reduced graphene oxide (rGO) with small and large flake size and Polyethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) are utilized as hole conducting layers in different devices. For the solar cell employing PEDOT:PSS as hole conducting layer, 3.8 % photoconversion efficiency is achieved. In case of solar cells fabricated with rGO as hole conducting layer, the efficiency of the device is strongly dependent on flake size. With all other fabrication conditions kept constant, the efficiency of graphene-interfaced solar cell improves by a factor of 6, by changing the flake size of graphene oxide. We attribute this effect to uniform coverage of graphene layer and improved electrical percolation network.

Mesoporous titania-vertical nanorod films with interfacial engineering for high performance dye-sensitized solar cells.

PubMed

Ahmed, Irfan; Fakharuddin, Azhar; Wali, Qamar; Bin Zainun, Ayib Rosdi; Ismail, Jamil; Jose, Rajan

2015-03-13

Working electrode (WE) fabrication offers significant challenges in terms of achieving high-efficiency dye-sensitized solar cells (DSCs). We have combined the beneficial effects of vertical nanorods grown on conducting glass substrate for charge transport and mesoporous particles for dye loading and have achieved a high photoconversion efficiency of (η) > 11% with an internal quantum efficiency of ∼93% in electrode films of thickness ∼7 ± 0.5 μm. Controlling the interface between the vertical nanorods and the mesoporous film is a crucial step in attaining high η. We identify three parameters, viz., large surface area of nanoparticles, increased light scattering of the nanorod-nanoparticle layer, and superior charge transport of nanorods, that simultaneously contribute to the improved photovoltaic performance of the WE developed.

Transparent ALD-grown Ta2O5 protective layer for highly stable ZnO photoelectrode in solar water splitting.

PubMed

Li, Chengcheng; Wang, Tuo; Luo, Zhibin; Zhang, Dong; Gong, Jinlong

2015-04-30

This communication describes a highly stable ZnO/Ta2O5 photoanode with Ta2O5 deposited by atomic layer deposition. The ultrathin Ta2O5 protective layer prevents corrosion of ZnO and reduces surface carrier recombination, leading to a nearly two-fold increase of photo-conversion efficiency. The transparency of Ta2O5 to sunlight is identified as the main reason for the excellent stability of the photoelectrode for 5 hours.

Band edge movement and structural modifications in transition metal doped TiO2 nanocrystals for the application of DSSC

NASA Astrophysics Data System (ADS)

Patle, L. B.; Huse, V. R.; Chaudhari, A. L.

2017-10-01

Nanocrystalline undoped and transition metal ion doped (TM:Cu2+, Mn2+ and Fe3+) TiO2 nanoparticles, with 1 mol% were synthesized by a simple and cost effective modified co-precipitation method at room temperature and were successfully used as photoanode for dye sensitized solar cell (DSSC). The effect of transition metal ions into TiO2 nano crystalline powder has been systematically investigated using x-ray diffraction (XRD), UV-Vis spectroscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDX). The results of XRD confirm nanocrystalline anatase tetragonal structure of prepared undoped and TM doped TiO2 semiconductor. The influence of doping on band edge movement has been estimated using UV-visible spectroscopy. The SEM results indicate that microscopic effect of doping on morphology of the TiO2. The peaks of EDX signify incorporation of transition metal cations into TiO2 lattice. The effect of doping on flat band potential was estimated using interpolation on Mott-Schottky plot. The performances of DSSCs of undoped and doped TiO2 photoelectrodes were investigated under light illumination. In comparison with undoped and (Cu2+, Fe3+) doped TiO2 photoanodes we found that incorporation of Mn2+ into TiO2 exhibits improvement in photoconversion efficiency (η). There is increase in photoconversion efficiency of DSSCs with Mn2+ doped TiO2 by 6% as compared to that of undoped TiO2 photoanode.

Reversible structural transformation and enhanced performance of PEDOT:PSS-based hybrid solar cells driven by light intensity.

PubMed

Thomas, Joseph Palathinkal; Srivastava, Saurabh; Zhao, Liyan; Abd-Ellah, Marwa; McGillivray, Donald; Kang, Jung Soo; Rahman, Md Anisur; Moghimi, Nafiseh; Heinig, Nina F; Leung, Kam Tong

2015-04-15

Hybrid solar cells made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PSS) and appropriate amounts of a cosolvent and a fluorosurfactant on planar n-type silicon substrates showed a photoconversion efficiency (PCE) of above 13%. These cells also exhibited stable, reproducible, and high external quantum efficiency (EQE) that was not sensitive to light-bias intensity (LBI). In contrast, solar cells made of pristine PSS showed low PCE and high EQE only under certain measurement conditions. The EQE was found to degrade with increasing LBI. Here we report that the LBI-sensitive variation of EQE of the low-PCE cells is related to a reversible structural transformation from a quinoid to a benzoid structure of PEDOT.

Z-Scheme NiTiO 3 /g-C 3 N 4 Heterojunctions with Enhanced Photoelectrochemical and Photocatalytic Performances under Visible LED Light Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zhenyu; Zeng, Xiaoqiao; Li, Kai

Direct Z-scheme NiTiO3/g-C3N4 heterojunctions were successfully assembled by using simple calcination method and the photoelectrochemical and photocatalytic performance were investigated by light emitting diode (LED). The photoanode composed by the heterojunction with about 50 wt% NiTiO3 content exhibits the best photoelectrochemical activity with photoconversion efficiency up to 0.066%, which is 4.4 and 3.13 times larger than NiTiO3 or g-C3N4. The remarkably enhanced photoelectrochemical and photocatalytic activity of the heterojunction can be due to the efficiently photogenerated electron-hole separation by a Z-scheme mechanism.

Combinatorial chemical bath deposition of CdS contacts for chalcogenide photovoltaics

DOE PAGES

Mokurala, Krishnaiah; Baranowski, Lauryn L.; de Souza Lucas, Francisco W.; ...

2016-08-01

Contact layers play an important role in thin film solar cells, but new material development and optimization of its thickness is usually a long and tedious process. A high-throughput experimental approach has been used to accelerate the rate of research in photovoltaic (PV) light absorbers and transparent conductive electrodes, however the combinatorial research on contact layers is less common. Here, we report on the chemical bath deposition (CBD) of CdS thin films by combinatorial dip coating technique and apply these contact layers to Cu(In,Ga)Se 2 (CIGSe) and Cu 2ZnSnSe 4 (CZTSe) light absorbers in PV devices. Combinatorial thickness steps ofmore » CdS thin films were achieved by removal of the substrate from the chemical bath, at regular intervals of time, and in equal distance increments. The trends in the photoconversion efficiency and in the spectral response of the PV devices as a function of thickness of CdS contacts were explained with the help of optical and morphological characterization of the CdS thin films. The maximum PV efficiency achieved for the combinatorial dip-coating CBD was similar to that for the PV devices processed using conventional CBD. Finally, the results of this study lead to the conclusion that combinatorial dip-coating can be used to accelerate the optimization of PV device performance of CdS and other candidate contact layers for a wide range of emerging absorbers.« less

Crystal structure of the fluorescent protein from Dendronephthya sp. in both green and photoconverted red forms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pletneva, Nadya V.; Pletnev, Sergei; Pakhomov, Alexey A.

The fluorescent protein fromDendronephthyasp. (DendFP) is a member of the Kaede-like group of photoconvertible fluorescent proteins with a His62-Tyr63-Gly64 chromophore-forming sequence. Upon irradiation with UV and blue light, the fluorescence of DendFP irreversibly changes from green (506 nm) to red (578 nm). The photoconversion is accompanied by cleavage of the peptide backbone at the C α—N bond of His62 and the formation of a terminal carboxamide group at the preceding Leu61. The resulting double C α=C βbond in His62 extends the conjugation of the chromophore π system to include imidazole, providing the red fluorescence. Here, the three-dimensional structures of nativemore » green and photoconverted red forms of DendFP determined at 1.81 and 2.14 Å resolution, respectively, are reported. This is the first structure of photoconverted red DendFP to be reported to date. The structure-based mutagenesis of DendFP revealed an important role of positions 142 and 193: replacement of the original Ser142 and His193 caused a moderate red shift in the fluorescence and a considerable increase in the photoconversion rate. It was demonstrated that hydrogen bonding of the chromophore to the Gln116 and Ser105 cluster is crucial for variation of the photoconversion rate. The single replacement Gln116Asn disrupts the hydrogen bonding of Gln116 to the chromophore, resulting in a 30-fold decrease in the photoconversion rate, which was partially restored by a further Ser105Asn replacement.« less

A FRET-facilitated photoswitching using an orange fluorescent protein with the fast photoconversion kinetics.

PubMed

Subach, Oksana M; Entenberg, David; Condeelis, John S; Verkhusha, Vladislav V

2012-09-12

Fluorescent proteins photoswitchable with noncytotoxic light irradiation and spectrally distinct from multiple available photoconvertible green-to-red probes are in high demand. We have developed a monomeric fluorescent protein, called PSmOrange2, which is photoswitchable with blue light from an orange (ex./em. at 546 nm/561 nm) to a far-red (ex./em. at 619 nm/651 nm) form. Compared to another orange-to-far-red photoconvertable variant, PSmOrange2 has blue-shifted photoswitching action spectrum, 9-fold higher photoconversion contrast, and up to 10-fold faster photoswitching kinetics. This results in the 4-fold more PSmOrange2 molecules being photoconverted in mammalian cells. Compared to common orange fluorescent proteins, such as mOrange, the orange form of PSmOrange has substantially higher photostability allowing its use in multicolor imaging applications to track dynamics of multiple populations of intracellular objects. The PSmOrange2 photochemical properties allow its efficient photoswitching with common two-photon lasers and, moreover, via Förster resonance energy transfer (FRET) from green fluorescent donors. We have termed the latter effect a FRET-facilitated photoswitching and demonstrated it using several sets of interacting proteins. The enhanced photoswitching properties of PSmOrange2 make it a superior photoconvertable protein tag for flow cytometry, conventional microscopy, and two-photon imaging of live cells.

Graphitic carbon nitride (g-C3N4) coated titanium oxide nanotube arrays with enhanced photo-electrochemical performance.

PubMed

Sun, Mingxuan; Fang, Yalin; Kong, Yuanyuan; Sun, Shanfu; Yu, Zhishui; Umar, Ahmad

2016-08-09

Herein, we report the successful formation of graphitic carbon nitride coated titanium oxide nanotube array thin films (g-C3N4/TiO2) via the facile thermal treatment of anodized Ti sheets over melamine. The proportion of C3N4 and TiO2 in the composite can be adjusted by changing the initial addition mass of melamine. The as-prepared samples are characterized by several techniques in order to understand the morphological, structural, compositional and optical properties. UV-vis absorption studies exhibit a remarkable red shift for the g-C3N4/TiO2 thin films as compared to the pristine TiO2 nanotubes. Importantly, the prepared composites exhibit an enhanced photocurrent and photo-potential under both UV-vis and visible light irradiation. Moreover, the observed maximum photo-conversion efficiency of the prepared composites is 1.59 times higher than that of the pristine TiO2 nanotubes. The optical and electrochemical impedance spectra analysis reveals that the better photo-electrochemical performance of the g-C3N4/TiO2 nanotubes is mainly due to the wider light absorption and reduced impedance compared to the bare TiO2 nanotube electrode. The presented work demonstrates a facile and simple method to fabricate g-C3N4/TiO2 nanotubes and clearly revealed that the introduction of g-C3N4 is a new and innovative approach to improve the photocurrent and photo-potential efficiencies of TiO2.

Formation of artificial pores in nano-TiO2 photo-electrode films using acetylene-black for high-efficiency, dye-sensitized solar cells

PubMed Central

Cho, Tae-Yeon; Han, Chi-Whan; Jun, Yongseok; Yoon, Soon-Gil

2013-01-01

Acetylene-black paste without a light scattering layer was applied to meso-porous TiO2 photo-electrode films with a crystalline framework, a low residual carbon, and a tunable morphological pore size. The thermal-treated TiO2 photo-electrode films had an increased acetylene-black concentration with an increase in artificial pores and a decrease in residual carbon. The performance of dye-sensitized solar cells (DSSCs) was enhanced by the use of the TiO2 photo-anode pastes at various acetylene-black concentrations. The photo-conversion efficiency of the DSSCs using TiO2 photo-electrode films with 1.5 wt% acetylene-black was enhanced from 7.98 (no acetylene-black) to 9.75% without the integration of a light- scattering layer. PMID:23511122

PyFDAP: automated analysis of fluorescence decay after photoconversion (FDAP) experiments.

PubMed

Bläßle, Alexander; Müller, Patrick

2015-03-15

We developed the graphical user interface PyFDAP for the fitting of linear and non-linear decay functions to data from fluorescence decay after photoconversion (FDAP) experiments. PyFDAP structures and analyses large FDAP datasets and features multiple fitting and plotting options. PyFDAP was written in Python and runs on Ubuntu Linux, Mac OS X and Microsoft Windows operating systems. The software, a user guide and a test FDAP dataset are freely available for download from http://people.tuebingen.mpg.de/mueller-lab. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Fluorescent Photo-conversion: A second chance to label unique cells.

PubMed

Mellott, Adam J; Shinogle, Heather E; Moore, David S; Detamore, Michael S

2015-03-01

Not all cells behave uniformly after treatment in tissue engineering studies. In fact, some treated cells display no signs of treatment or show unique characteristics not consistent with other treated cells. What if the "unique" cells could be isolated from a treated population, and further studied? Photo-convertible reporter proteins, such as Dendra2 , allow for the ability to selectively identify unique cells with a secondary label within a primary labeled treated population. In the current study, select cells were identified and labeled through photo-conversion of Dendra2 -transfected human Wharton's Jelly cells (hWJCs) for the first time. Robust photo-conversion of green-to-red fluorescence was achieved consistently in arbitrarily selected cells, allowing for precise cell identification of select hWJCs. The current study demonstrates a method that offers investigators the opportunity to selectively label and identify unique cells within a treated population for further study or isolation from the treatment population. Photo-convertible reporter proteins, such as Dendra2 , offer the ability over non-photo-convertible reporter proteins, such as green fluorescent protein, to analyze unique individual cells within a treated population, which allows investigators to gain more meaningful information on how a treatment affects all cells within a target population.

Unique Three-Dimensional InP Nanopore Arrays for Improved Photoelectrochemical Hydrogen Production.

PubMed

Li, Qiang; Zheng, Maojun; Ma, Liguo; Zhong, Miao; Zhu, Changqing; Zhang, Bin; Wang, Faze; Song, Jingnan; Ma, Li; Shen, Wenzhong

2016-08-31

Ordered three-dimensional (3D) nanostructure arrays hold promise for high-performance energy harvesting and storage devices. Here, we report the fabrication of InP nanopore arrays (NPs) in unique 3D architectures with excellent light trapping characteristic and large surface areas for use as highly active photoelectrodes in photoelectrochemical (PEC) hydrogen evolution devices. The ordered 3D NPs were scalably synthesized by a facile two-step etching process of (1) anodic etching of InP in neutral 3 M NaCl electrolytes to realize nanoporous structures and (2) wet chemical etching in HCl/H3PO4 (volume ratio of 1:3) solutions for removing the remaining top irregular layer. Importantly, we demonstrated that the use of neutral electrolyte of NaCl instead of other solutions, such as HCl, in anodic etching of InP can significantly passivate the surface states of 3D NPs. As a result, the maximum photoconversion efficiency obtained with ∼15.7 μm thick 3D NPs was 0.95%, which was 7.3 and 1.4 times higher than that of planar and 2D NPs. Electrochemical impedance spectroscopy and photoluminescence analyses further clarified that the improved PEC performance was attributed to the enhanced charge transfer across 3D NPs/electrolyte interfaces, the improved charge separation at 3D NPs/electrolyte junction, and the increased PEC active surface areas with our unique 3D NP arrays.

Printable CIGS thin film solar cells

NASA Astrophysics Data System (ADS)

Fan, Xiaojuan

2014-03-01

Among the various thin film solar cells in the market, CuInGaSe thin film cells have been considered as the most promising alternatives to silicon solar cells because of their high photo-electricity efficiency, reliability, and stability. However, many fabrication of CIGS thin film are based on vacuum processes such as evaporation sputtering techniques which are not cost efficient. This work develops a method using paste or ink liquid spin-coated on glass that would be to conventional ways in terms of cost effective, non-vacuum needed, quick processing. A mixture precursor was prepared by dissolving appropriate amounts of chemicals. After the mixture solution was cooled, a viscous paste prepared and ready for spin-coating process. A slight bluish CIG thin film substrate was then put in a tube furnace with evaporation of metal Se by depositing CdS layer and ZnO nanoparticle thin film coating to a solar cell fabrication. Structure, absorption spectrum, and photo-conversion efficiency for the as-grown CIGS thin film solar cell under study.

PhOTO Zebrafish: A Transgenic Resource for In Vivo Lineage Tracing during Development and Regeneration

PubMed Central

Dempsey, William P.; Fraser, Scott E.; Pantazis, Periklis

2012-01-01

Background Elucidating the complex cell dynamics (divisions, movement, morphological changes, etc.) underlying embryonic development and adult tissue regeneration requires an efficient means to track cells with high fidelity in space and time. To satisfy this criterion, we developed a transgenic zebrafish line, called PhOTO, that allows photoconvertible optical tracking of nuclear and membrane dynamics in vivo. Methodology PhOTO zebrafish ubiquitously express targeted blue fluorescent protein (FP) Cerulean and photoconvertible FP Dendra2 fusions, allowing for instantaneous, precise targeting and tracking of any number of cells using Dendra2 photoconversion while simultaneously monitoring global cell behavior and morphology. Expression persists through adulthood, making the PhOTO zebrafish an excellent tool for studying tissue regeneration: after tail fin amputation and photoconversion of a ∼100µm stripe along the cut area, marked differences seen in how cells contribute to the new tissue give detailed insight into the dynamic process of regeneration. Photoconverted cells that contributed to the regenerate were separated into three distinct populations corresponding to the extent of cell division 7 days after amputation, and a subset of cells that divided the least were organized into an evenly spaced, linear orientation along the length of the newly regenerating fin. Conclusions/Significance PhOTO zebrafish have wide applicability for lineage tracing at the systems-level in the early embryo as well as in the adult, making them ideal candidate tools for future research in development, traumatic injury and regeneration, cancer progression, and stem cell behavior. PMID:22431986

Progress and Perspectives of Plasmon-Enhanced Solar Energy Conversion.

PubMed

Cushing, Scott K; Wu, Nianqiang

2016-02-18

Plasmonics allows extraordinary control of light, making it attractive for application in solar energy harvesting. In metal-semiconductor heterojunctions, plasmons can enhance photoconversion in the semiconductor via three mechanisms, including light trapping, hot electron/hole transfer, and plasmon-induced resonance energy transfer (PIRET). To understand the plasmonic enhancement, the metal's geometry, constituent metal, and interface must be viewed in terms of the effects on the plasmon's dephasing and decay route. To simplify design of plasmonic metal-semiconductor heterojunctions for high-efficiency solar energy conversion, the parameters controlling the plasmonic enhancement can be distilled to the dephasing time. The plasmonic geometry can then be further refined to optimize hot carrier transfer, PIRET, or light trapping.

Efficiency Improvement Using Molybdenum Disulphide Interlayers in Single-Wall Carbon Nanotube/Silicon Solar Cells.

PubMed

Alzahly, Shaykha; Yu, LePing; Shearer, Cameron J; Gibson, Christopher T; Shapter, Joseph G

2018-04-21

Molybdenum disulphide (MoS₂) is one of the most studied and widely applied nanomaterials from the layered transition-metal dichalcogenides (TMDs) semiconductor family. MoS₂ has a large carrier diffusion length and a high carrier mobility. Combining a layered structure of single-wall carbon nanotube (SWCNT) and MoS₂ with n-type silicon (n-Si) provided novel SWCNT/n-Si photovoltaic devices. The solar cell has a layered structure with Si covered first by a thin layer of MoS₂ flakes and then a SWCNT film. The films were examined using scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The MoS₂ flake thickness ranged from 5 to 90 nm while the nanosheet’s lateral dimensions size ranged up to 1 μm². This insertion of MoS₂ improved the photoconversion efficiency (PCE) of the SWCNT/n-Si solar cells by approximately a factor of 2.

Broadband and wide-angle light harvesting by ultra-thin silicon solar cells with partially embedded dielectric spheres.

PubMed

Yang, Zhenhai; Shang, Aixue; Qin, Linling; Zhan, Yaohui; Zhang, Cheng; Gao, Pingqi; Ye, Jichun; Li, Xiaofeng

2016-04-01

We propose a design of crystalline silicon thin-film solar cells (c-Si TFSCs, 2 μm-thick) configured with partially embedded dielectric spheres on the light-injecting side. The intrinsic light trapping and photoconversion are simulated by the complete optoelectronic simulation. It shows that the embedding depth of the spheres provides an effective way to modulate and significantly enhance the optical absorption. Compared to the conventional planar and front sphere systems, the optimized partially embedded sphere design enables a broadband, wide-angle, and strong optical absorption and efficient carrier transportation. Optoelectronic simulation predicts that a 2 μm-thick c-Si TFSC with half-embedded spheres shows an increment of more than 10  mA/cm² in short-circuit current density and an enhancement ratio of more than 56% in light-conversion efficiency, compared to the conventional planar counterparts.

Comprehensive analysis of the green-to-blue photoconversion of full-length Cyanobacteriochrome Tlr0924.

PubMed

Hardman, Samantha J O; Hauck, Anna F E; Clark, Ian P; Heyes, Derren J; Scrutton, Nigel S

2014-11-04

Cyanobacteriochromes are members of the phytochrome superfamily of photoreceptors and are of central importance in biological light-activated signaling mechanisms. These photoreceptors are known to reversibly convert between two states in a photoinitiated process that involves a basic E/Z isomerization of the bilin chromophore and, in certain cases, the breakage of a thioether linkage to a conserved cysteine residue in the bulk protein structure. The exact details and timescales of the reactions involved in these photoconversions have not been conclusively shown. The cyanobacteriochrome Tlr0924 contains phycocyanobilin and phycoviolobilin chromophores, both of which photoconvert between two species: blue-absorbing and green-absorbing, and blue-absorbing and red-absorbing, respectively. Here, we followed the complete green-to-blue photoconversion process of the phycoviolobilin chromophore in the full-length form of Tlr0924 over timescales ranging from femtoseconds to seconds. Using a combination of time-resolved visible and mid-infrared transient absorption spectroscopy and cryotrapping techniques, we showed that after photoisomerization, which occurs with a lifetime of 3.6 ps, the phycoviolobilin twists or distorts slightly with a lifetime of 5.3 ?s. The final step, the formation of the thioether linkage with the protein, occurs with a lifetime of 23.6 ms.

Fluorescent Photo-conversion: A second chance to label unique cells

PubMed Central

Mellott, Adam J.; Shinogle, Heather E.; Moore, David S.; Detamore, Michael S.

2014-01-01

Not all cells behave uniformly after treatment in tissue engineering studies. In fact, some treated cells display no signs of treatment or show unique characteristics not consistent with other treated cells. What if the “unique” cells could be isolated from a treated population, and further studied? Photo-convertible reporter proteins, such as Dendra2, allow for the ability to selectively identify unique cells with a secondary label within a primary labeled treated population. In the current study, select cells were identified and labeled through photo-conversion of Dendra2-transfected human Wharton's Jelly cells (hWJCs) for the first time. Robust photo-conversion of green-to-red fluorescence was achieved consistently in arbitrarily selected cells, allowing for precise cell identification of select hWJCs. The current study demonstrates a method that offers investigators the opportunity to selectively label and identify unique cells within a treated population for further study or isolation from the treatment population. Photo-convertible reporter proteins, such as Dendra2, offer the ability over non-photo-convertible reporter proteins, such as green fluorescent protein, to analyze unique individual cells within a treated population, which allows investigators to gain more meaningful information on how a treatment affects all cells within a target population. PMID:25914756

III-V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration

NASA Astrophysics Data System (ADS)

Cariou, Romain; Benick, Jan; Feldmann, Frank; Höhn, Oliver; Hauser, Hubert; Beutel, Paul; Razek, Nasser; Wimplinger, Markus; Bläsi, Benedikt; Lackner, David; Hermle, Martin; Siefer, Gerald; Glunz, Stefan W.; Bett, Andreas W.; Dimroth, Frank

2018-04-01

Silicon dominates the photovoltaic industry but the conversion efficiency of silicon single-junction solar cells is intrinsically constrained to 29.4%, and practically limited to around 27%. It is possible to overcome this limit by combining silicon with high-bandgap materials, such as III-V semiconductors, in a multi-junction device. Significant challenges associated with this material combination have hindered the development of highly efficient III-V/Si solar cells. Here, we demonstrate a III-V/Si cell reaching similar performances to standard III-V/Ge triple-junction solar cells. This device is fabricated using wafer bonding to permanently join a GaInP/GaAs top cell with a silicon bottom cell. The key issues of III-V/Si interface recombination and silicon's weak absorption are addressed using poly-silicon/SiOx passivating contacts and a novel rear-side diffraction grating for the silicon bottom cell. With these combined features, we demonstrate a two-terminal GaInP/GaAs//Si solar cell reaching a 1-sun AM1.5G conversion efficiency of 33.3%.

A facile green antisolvent approach to Cu2+-doped ZnO nanocrystals with visible-light-responsive photoactivities.

PubMed

Lu, Yi-Hsuan; Lin, Wei-Hao; Yang, Chao-Yao; Chiu, Yi-Hsuan; Pu, Ying-Chih; Lee, Min-Han; Tseng, Yuan-Chieh; Hsu, Yung-Jung

2014-08-07

An environmentally benign antisolvent method has been developed to prepare Cu(2+)-doped ZnO nanocrystals with controllable dopant concentrations. A room temperature ionic liquid, known as a deep eutectic solvent (DES), was used as the solvent to dissolve ZnO powders. Upon the introduction of the ZnO-containing DES into a bad solvent which shows no solvation to ZnO, ZnO was precipitated and grown due to the dramatic decrease of solubility. By adding Cu(2+) ions to the bad solvent, the growth of ZnO from the antisolvent process was accompanied by Cu(2+) introduction, resulting in the formation of Cu(2+)-doped ZnO nanocrystals. The as-prepared Cu(2+)-doped ZnO showed an additional absorption band in the visible range (400-800 nm), which conduced to an improvement in the overall photon harvesting efficiency. Time-resolved photoluminescence spectra, together with the photovoltage information, suggested that the doped Cu(2+) may otherwise trap photoexcited electrons during the charge transfer process, inevitably depressing the photoconversion efficiency. The photoactivity of Cu(2+)-doped ZnO nanocrystals for photoelectrochemical water oxidation was effectively enhanced in the visible region, which achieved the highest at 2.0 at% of Cu(2+). A further increase in the Cu(2+) concentration however led to a decrease in the photocatalytic performance, which was ascribed to the significant carrier trapping caused by the increased states given by excessive Cu(2+). The photocurrent action spectra illustrated that the enhanced photoactivity of the Cu(2+)-doped ZnO nanocrystals was mainly due to the improved visible photon harvesting achieved by Cu(2+) doping. These results may facilitate the use of transition metal ion-doped ZnO in other photoconversion applications, such as ZnO based dye-sensitized solar cells and magnetism-assisted photocatalytic systems.

Preparation of flexible TiO2 photoelectrodes for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Li, Wen-Ren; Wang, Hsiu-Hsuan; Lin, Chia-Feng; Su, Chaochin

2014-09-01

Dye-sensitized solar cells (DSSCs) based on nanocrystalline TiO2 photoelectrodes on indium tin oxide (ITO) coated polymer substrates have drawn great attention due to its lightweight, flexibility and advantages in commercial applications. However, the thermal instability of polymer substrates limits the process temperature to below 150 °C. In order to assure high and firm interparticle connection between TiO2 nanocrystals (TiO2-NC) and polymer substrates, the post-treatment of flexible TiO2 photoelectrodes (F-TiO2-PE) by mechanical compression was employed. In this work, Degussa P25 TiO2-NC was mixed with tert-butyl alcohol and DI-water to form TiO2 paste. F-TiO2-PE was then prepared by coating the TiO2 paste onto ITO coated polyethylene terephthalate (PET) substrate using doctor blade followed by low temperature sintering at 120 °C for 2 hours. To study the effect of mechanical compression, we applied 50 and 100 kg/cm2 pressure on TiO2/PET to complete the fabrication of F-TiO2-PE. The surface morphology of F-TiO2-PE was characterized using scanning electron microscopy. The resultant F-TiO2-PE sample exhibited a smooth, crack-free structure indicating the great improvement in the interparticle connection of TiO2-NC. Increase of compression pressure could lead to the increase of DSSC photoconversion efficiency. The best photoconversion efficiency of 4.19 % (open circuit voltage (Voc) = 0.79 V, short-circuit photocurrent density (Jsc) = 7.75 mA/cm2, fill factor (FF) = 0.68) was obtained for the F-TiO2-PE device, which showed great enhancement compared with the F-TiO2-PE cell without compression treatment. The effect of compression in DSSC performance was vindicated by the electrochemical impedance spectroscopy measurement.

Impact excitation and electron-hole multiplication in graphene and carbon nanotubes.

PubMed

Gabor, Nathaniel M

2013-06-18

In semiconductor photovoltaics, photoconversion efficiency is governed by a simple competition: the incident photon energy is either transferred to the crystal lattice (heat) or transferred to electrons. In conventional materials, energy loss to the lattice is more efficient than energy transferred to electrons, thus limiting the power conversion efficiency. Quantum electronic systems, such as quantum dots, nanowires, and two-dimensional electronic membranes, promise to tip the balance in this competition by simultaneously limiting energy transfer to the lattice and enhancing energy transfer to electrons. By exploring the optical, thermal, and electronic properties of quantum materials, we may perhaps find an ideal optoelectronic material that provides low cost fabrication, facile systems integration, and a means to surpass the standard limit for photoconversion efficiency. Nanoscale carbon materials, such as graphene and carbon nanotubes, provide ideal experimental quantum systems in which to explore optoelectronic behavior for applications in solar energy harvesting. Within essentially the same material, researchers can achieve a broad spectrum of energetic configurations, from a gapless semimetal to a large band-gap semiconducting nanowire. Owing to their nanoscale dimensions, graphene and carbon nanotubes exhibit electronic and optical properties that reflect strong electron-electron interactions. Such strong interactions may lead to exotic low-energy electron transport behavior and high-energy electron scattering processes such as impact excitation and the inverse process of Auger recombination. High-energy processes, which become very important under photoexcitation, may be particularly efficient in nanoscale carbon materials due to the relativistic-like, charged particle band structure and sensitivity to the dielectric environment. In addition, due to the covalently bonded carbon framework that makes up these materials, electron-phonon coupling is very weak. In carbon nanomaterials, strong electron-electron interactions combined with weak electron-phonon interactions results in excellent optical, thermal and electronic properties, the exploration of which promises to reveal fundamentally new physical processes and deliver advanced nanotechnologies. In this Account, we review the results of novel optoelectronic experiments that explore the intrinsic photoresponse of carbon nanomaterials integrated into nanoscale devices. By fabricating gate voltage-controlled photodetectors composed of atomically thin sheets of graphene and individual carbon nanotubes, we are able to fully explore electron transport in these systems under optical illumination. We find that strong electron-electron interactions play a key role in the intrinsic photoresponse of both materials, as evidenced by hot carrier transport in graphene and highly efficient multiple electron-hole pair generation in nanotubes. In both of these quantum systems, photoexcitation leads to high-energy electron-hole pairs that relax energy predominantly into the electronic system, rather than heating the lattice. Due to highly efficient energy transfer from photons into electrons, graphene and carbon nanotubes may be ideal materials for solar energy harvesting devices with efficiencies that could exceed the Shockley-Queisser limit.

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

NASA Astrophysics Data System (ADS)

Morfa, Anthony J.; Rowlen, Kathy L.; Reilly, Thomas H.; Romero, Manuel J.; van de Lagemaat, Jao

2008-01-01

Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle layers were fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase in optical electrical field inside the photoactive layer, the inclusion of such particle films lead to increased optical absorption and consequently increased photoconversion at solar-conversion relevant wavelengths. The resulting solar energy conversion efficiency for a bulk heterojunction photovoltaic device of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester was found to increase from 1.3%±0.2% to 2.2%±0.1% for devices employing thin plasmon-active layers. Based on six measurements, the improvement factor of 1.7 was demonstrated to be statistically significant.

Photo-electrochemical properties of graphene wrapped hierarchically branched nanostructures obtained through hydrothermally transformed TiO2 nanotubes

NASA Astrophysics Data System (ADS)

Rambabu, Y.; Jaiswal, Manu; Roy, Somnath C.

2017-10-01

Hierarchically structured nanomaterials play an important role in both light absorption and separation of photo-generated charges. In the present study, hierarchically branched TiO2 nanostructures (HB-MLNTs) are obtained through hydrothermal transformation of electrochemically anodized TiO2 multi-leg nanotubes (MLNT) arrays. Photo-anodes based on HB-MLNTs demonstrated 5 fold increase in applied bias to photo-conversion efficiency (%ABPE) over that of TiO2 MLNTs without branches. Further, such nanostructures are wrapped with reduced graphene oxide (rGO) films to enhance the charge separation, which resulted in ∼6.5 times enhancement in %ABPE over that of bare MLNTs. We estimated charge transport (η tr) and charge transfer (η ct) efficiencies by analyzing the photo-current data. The ultra-fine nano branches grown on the MLNTs are effective in increasing light absorption through multiple scattering and improving charge transport/transfer efficiencies by enlarging semiconductor/electrolyte interface area. The charge transfer resistance, interfacial capacitance and electron decay time have been estimated through electrochemical impedance measurements which correlate with the results obtained from photocurrent measurements.

Improved efficiency of ZnO hierarchical particle based dye sensitized solar cell by incorporating thin passivation layer in photo-anode

NASA Astrophysics Data System (ADS)

Das, Priyanka; Mondal, Biswanath; Mukherjee, Kalisadhan

2018-01-01

Present article describes the DSSC performances of photo-anodes prepared using hydrothermal route derived ZnO particles having dissimilar morphologies i.e. simple micro-rod and nano-tips decorated micro-rod. The surface of nano-tips decorated micro-rod is uneven and patterned which facilitate more dye adsorption and better scattering of the incident light resulting superior photo-conversion efficiency (PCE) ( η 1.09%) than micro-rod ZnO ( η 0.86%). To further improve the efficiency of nano-tips decorated micro-rod ZnO based DSSC, thin passivation layer of ZnO is introduced in the corresponding photo-anode and a higher PCE ( η 1.29%) is achieved. The compact thin passivation layer here expedites the transportation of photo-excited electrons, restricts the undesired recombination reactions and prevents the direct contact of electrolyte with conducting substrates. Attempt is made to understand the effect of passivation layer on the transportation kinetics of photo-excited electrons by analyzing the electrochemical impedance spectra of the developed cells.

Photoconversion changes bilin chromophore conjugation and protein secondary structure in the violet/orange cyanobacteriochrome NpF2164g3' [corrected].

PubMed

Lim, Sunghyuk; Rockwell, Nathan C; Martin, Shelley S; Dallas, Jerry L; Lagarias, J Clark; Ames, James B

2014-06-01

Cyanobacteriochromes (CBCRs) are cyanobacterial photoreceptors distantly related to phytochromes. All CBCRs examined to date utilize a conserved Cys residue to form a covalent thioether linkage to the bilin chromophore. In the insert-Cys CBCR subfamily, a second conserved Cys can covalently link to the bilin C10 methine bridge, allowing detection of near-UV to blue light. The best understood insert-Cys CBCR is the violet/orange CBCR NpF2164g3 from Nostoc punctiforme, which has a stable second linkage in the violet-absorbing dark state. Photoconversion of NpF2164g3 leads to elimination of the second linkage and formation of an orange-absorbing photoproduct. We recently reported NMR chemical shift assignments for the orange-absorbing photoproduct state of NpF2164g3. We here present equivalent information for its violet-absorbing dark state. In both photostates, NpF2164g3 is monomeric in solution and regions containing the two conserved Cys residues essential for photoconversion are structurally disordered. In contrast to blue light receptors such as phototropin, NpF2164g3 is less structurally ordered in the dark state than in the photoproduct. The insert-Cys insertion loop and C-terminal helix exhibit light-dependent structural changes. Moreover, a motif containing an Asp residue also found in other CBCRs and in phytochromes adopts a random-coil structure in the dark state but a stable α-helix structure in the photoproduct. NMR analysis of the chromophore is consistent with a less ordered dark state, with A-ring resonances only resolved in the photoproduct. The C10 atom of the bilin chromophore exhibits a drastic change in chemical shift upon photoconversion, changing from 34.5 ppm (methylene) in the dark state to 115 ppm (methine) in the light-activated state. Our results provide structural insight into the two-Cys photocycle of NpF2164g3 and the structurally diverse mechanisms used for light perception by the larger phytochrome superfamily.

Detection of esophageal cancer cell by photoelectrochemical Cu2O/ZnO biosensor (Conference Presentation)

NASA Astrophysics Data System (ADS)

Hsu, Chao-Hsin; Chu, Cheng-Hsun; Chen, Weichung; Wu, I.-Chen; Wu, Ming Tsang; Kuo, Chie-Tong; Tsiang, Raymond Chien-Chao; Wang, Hsiang-Chen

2016-03-01

We have demonstrated a Cu2O/ZnO nanorods (NRs) array p-n heterostructures photoelectrochemical biosensor. The electrodeposition of Cu2O at pH 12 acquired the preferably (111) lattice planes, resulting in the largest interfacial electric field between Cu2O and ZnO, which finally led to the highest separation efficiency of photogenerated charge carriers. High verticality ZnO nanorods by seed layer and thermal annealing assist the hydrothermal growth. The optimized Cu2O/ZnO NRs array p-n heterostructures exhibited enhanced PEC performance, such as elevated photocurrent and photoconversion efficiency, as well as excellent sensing performance for the sensitive detection of four strains of different races and different degree of cancer cell which made the device self-powered. We got spectral response characteristics and operating wavelength range of biosensor, and to verify the biological characteristics of cancer cells wafer react with different stages of cancer characterized by a cancer measured reaction experiment.

Hydroxamate anchors for improved photoconversion in dye-sensitized solar cells.

PubMed

Brewster, Timothy P; Konezny, Steven J; Sheehan, Stafford W; Martini, Lauren A; Schmuttenmaer, Charles A; Batista, Victor S; Crabtree, Robert H

2013-06-03

We present the first analysis of performance of hydroxamate linkers as compared to carboxylate and phosphonate groups when anchoring ruthenium-polypyridyl dyes to TiO2 surfaces in dye-sensitized solar cells (DSSCs). The study provides fundamental insight into structure/function relationships that are critical for cell performance. Our DSSCs have been produced by using newly synthesized dye molecules and characterized by combining measurements and simulations of experimental current density-voltage (J-V) characteristic curves. We show that the choice of anchoring group has a direct effect on the overall sunlight-to-electricity conversion efficiency (η), with hydroxamate anchors showing the best performance. Solar cells based on the pyridyl-hydroxamate complex exhibit higher efficiency since they suppress electron transfer from the photoanode to the electrolyte and have superior photoinjection characteristics. These findings suggest that hydroxamate anchoring groups should be particularly valuable in DSSCs and photocatalytic applications based on molecular adsorbates covalently bound to semiconductor surfaces. In contrast, analogous acetylacetonate anchors might undergo decomposition under similar conditions suggesting limited potential in future applications.

Controllable lasing performance in solution-processed organic-inorganic hybrid perovskites.

PubMed

Kao, Tsung Sheng; Chou, Yu-Hsun; Hong, Kuo-Bin; Huang, Jiong-Fu; Chou, Chun-Hsien; Kuo, Hao-Chung; Chen, Fang-Chung; Lu, Tien-Chang

2016-11-03

Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of optoelectronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 μJ cm -2 in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.

Efficiency Improvement Using Molybdenum Disulphide Interlayers in Single-Wall Carbon Nanotube/Silicon Solar Cells

PubMed Central

Alzahly, Shaykha; Yu, LePing; Gibson, Christopher T.

2018-01-01

Molybdenum disulphide (MoS2) is one of the most studied and widely applied nanomaterials from the layered transition-metal dichalcogenides (TMDs) semiconductor family. MoS2 has a large carrier diffusion length and a high carrier mobility. Combining a layered structure of single-wall carbon nanotube (SWCNT) and MoS2 with n-type silicon (n-Si) provided novel SWCNT/n-Si photovoltaic devices. The solar cell has a layered structure with Si covered first by a thin layer of MoS2 flakes and then a SWCNT film. The films were examined using scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The MoS2 flake thickness ranged from 5 to 90 nm while the nanosheet’s lateral dimensions size ranged up to 1 μm2. This insertion of MoS2 improved the photoconversion efficiency (PCE) of the SWCNT/n-Si solar cells by approximately a factor of 2. PMID:29690503

Accounting for Limited Detection Efficiency and Localization Precision in Cluster Analysis in Single Molecule Localization Microscopy

PubMed Central

Shivanandan, Arun; Unnikrishnan, Jayakrishnan; Radenovic, Aleksandra

2015-01-01

Single Molecule Localization Microscopy techniques like PhotoActivated Localization Microscopy, with their sub-diffraction limit spatial resolution, have been popularly used to characterize the spatial organization of membrane proteins, by means of quantitative cluster analysis. However, such quantitative studies remain challenged by the techniques’ inherent sources of errors such as a limited detection efficiency of less than 60%, due to incomplete photo-conversion, and a limited localization precision in the range of 10 – 30nm, varying across the detected molecules, mainly depending on the number of photons collected from each. We provide analytical methods to estimate the effect of these errors in cluster analysis and to correct for them. These methods, based on the Ripley’s L(r) – r or Pair Correlation Function popularly used by the community, can facilitate potentially breakthrough results in quantitative biology by providing a more accurate and precise quantification of protein spatial organization. PMID:25794150

Probing the Interplay between Dendritic Spine Morphology and Membrane-Bound Diffusion.

PubMed

Adrian, Max; Kusters, Remy; Storm, Cornelis; Hoogenraad, Casper C; Kapitein, Lukas C

2017-11-21

Dendritic spines are protrusions along neuronal dendrites that harbor the majority of excitatory postsynapses. Their distinct morphology, often featuring a bulbous head and small neck that connects to the dendritic shaft, has been shown to facilitate compartmentalization of electrical and cytoplasmic signaling stimuli elicited at the synapse. The extent to which spine morphology also forms a barrier for membrane-bound diffusion has remained unclear. Recent simulations suggested that especially the diameter of the spine neck plays a limiting role in this process. Here, we examine the connection between spine morphology and membrane-bound diffusion through a combination of photoconversion, live-cell superresolution experiments, and numerical simulations. Local photoconversion was used to obtain the timescale of diffusive equilibration in spines and followed by global sparse photoconversion to determine spine morphologies with nanoscopic resolution. These morphologies were subsequently used to assess the role of morphology on the diffusive equilibration. From the simulations, we could determine a robust relation between the equilibration timescale and a generalized shape factor calculated using both spine neck width and neck length, as well as spine head size. Experimentally, we found that diffusive equilibration was often slower, but rarely faster than predicted from the simulations, indicating that other biological confounders further reduce membrane-bound diffusion in these spines. This shape-dependent membrane-bound diffusion in mature spines may contribute to spine-specific compartmentalization of neurotransmitter receptors and signaling molecules and thereby support long-term plasticity of synaptic contacts. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Rational Design of Multifunctional Fe@γ-Fe2 O3 @H-TiO2 Nanocomposites with Enhanced Magnetic and Photoconversion Effects for Wide Applications: From Photocatalysis to Imaging-Guided Photothermal Cancer Therapy.

PubMed

Wang, Meifang; Deng, Kerong; Lü, Wei; Deng, Xiaoran; Li, Kai; Shi, Yanshu; Ding, Binbin; Cheng, Ziyong; Xing, Bengang; Han, Gang; Hou, Zhiyao; Lin, Jun

2018-03-01

Titanium dioxide (TiO 2 ) has been widely investigated and used in many areas due to its high refractive index and ultraviolet light absorption, but the lack of absorption in the visible-near infrared (Vis-NIR) region limits its application. Herein, multifunctional Fe@γ-Fe 2 O 3 @H-TiO 2 nanocomposites (NCs) with multilayer-structure are synthesized by one-step hydrogen reduction, which show remarkably improved magnetic and photoconversion effects as a promising generalists for photocatalysis, bioimaging, and photothermal therapy (PTT). Hydrogenation is used to turn white TiO 2 in to hydrogenated TiO 2 (H-TiO 2 ), thus improving the absorption in the Vis-NIR region. Based on the excellent solar-driven photocatalytic activities of the H-TiO 2 shell, the Fe@γ-Fe 2 O 3 magnetic core is introduced to make it convenient for separating and recovering the catalytic agents. More importantly, Fe@γ-Fe 2 O 3 @H-TiO 2 NCs show enhanced photothermal conversion efficiency due to more circuit loops for electron transitions between H-TiO 2 and γ-Fe 2 O 3 , and the electronic structures of Fe@γ-Fe 2 O 3 @H-TiO 2 NCs are calculated using the Vienna ab initio simulation package based on the density functional theory to account for the results. The reported core-shell NCs can serve as an NIR-responsive photothermal agent for magnetic-targeted photothermal therapy and as a multimodal imaging probe for cancer including infrared photothermal imaging, magnetic resonance imaging, and photoacoustic imaging. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PHYTOCHOME STRUCTURE AND SIGNALING MECHANISMS

PubMed Central

Rockwell, Nathan C.; Su, Yi-Shin; Lagarias, J. Clark

2009-01-01

Phytochromes are a widespread family of red/far-red responsive photoreceptors first discovered in plants, where they constitute one of the three main classes of photomorphogenesis regulators. All phytochromes utilize covalently attached bilin chromophores that enable photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) forms. Phytochromes are thus photoswitchable photosensors; canonical phytochromes have a conserved N-terminal photosensory core and a C-terminal regulatory region which typically includes a histidine-kinase-related domain. The discovery of new bacterial and cyanobacterial members of the phytochrome family within the last decade has greatly aided biochemical and structural characterization of this family, with the first crystal structure of a bacteriophytochrome photosensory core appearing in 2005. This structure and other recent biochemical studies have provided exciting new insights into the structure of phytochrome, the photoconversion process that is central to light sensing, and the mechanism of signal transfer by this important family of photoreceptors. PMID:16669784

The relative absorption cross-sections of photosystem I and photosystem II in chloroplasts from three types of Nicotiana tabacum.

PubMed

Melis, A; Thielen, A P

1980-02-08

In the present study we used three types of Nicotiana tabacum, cv John William's Broad Leaf (the wild type and two mutants, the yellow-green Su/su and the yellow Su/su var. Aurea) in order to correlat functional properties of Photosystem II and Photosystem I with the structural organization of their chloroplasts. The effective absorption cross-section of Photosystem II and Photosystem I centers was measured by means of the rate constant of their photoconversion under light-limiting conditions. In agreement with earlier results (Okabe, K., Schmid, G.H. and Straub, J. (1977) Plant Physiol. 60, 150--156) the photosynthetic unit size for both System II and System I in the two mutants was considerably smaller as compared to the wild type. We observed biphasic kinetics in the photoconversion of System II in all three types of N. tabacum. However, the photoconversion of System I occurred with monophasic and exponential kinetics. Under our experimental conditions, the effective cross-section of Photosystem I was comparable to that of the fast System II component (alpha centers). The relative amplitude of the slow System II component (beta centers) varied between 30% in the wild type to 70% in the Su/su var. Aurea mutant. The increased fraction of beta centers is correlated with the decreased fraction of appressed photosynthetic membranes in the chloroplasts of the two mutants. As a working hypothesis, it is suggested that beta centers are located on photosynthetic membranes directly exposed to the stroma medium.

Ultrathin high band gap solar cells with improved efficiencies from the world's oldest photovoltaic material.

PubMed

Todorov, Teodor K; Singh, Saurabh; Bishop, Douglas M; Gunawan, Oki; Lee, Yun Seog; Gershon, Talia S; Brew, Kevin W; Antunez, Priscilla D; Haight, Richard

2017-09-25

Selenium was used in the first solid state solar cell in 1883 and gave early insights into the photoelectric effect that inspired Einstein's Nobel Prize work; however, the latest efficiency milestone of 5.0% was more than 30 years ago. The recent surge of interest towards high-band gap absorbers for tandem applications led us to reconsider this attractive 1.95 eV material. Here, we show completely redesigned selenium devices with improved back and front interfaces optimized through combinatorial studies and demonstrate record open-circuit voltage (V OC ) of 970 mV and efficiency of 6.5% under 1 Sun. In addition, Se devices are air-stable, non-toxic, and extremely simple to fabricate. The absorber layer is only 100 nm thick, and can be processed at 200 ˚C, allowing temperature compatibility with most bottom substrates or sub-cells. We analyze device limitations and find significant potential for further improvement making selenium an attractive high-band-gap absorber for multi-junction device applications.Wide band gap semiconductors are important for the development of tandem photovoltaics. By introducing buffer layers at the front and rear side of solar cells based on selenium; Todorov et al., reduce interface recombination losses to achieve photoconversion efficiencies of 6.5%.

Mixed Valence Perovskite Cs2 Au2 I6 : A Potential Material for Thin-Film Pb-Free Photovoltaic Cells with Ultrahigh Efficiency.

PubMed

Debbichi, Lamjed; Lee, Songju; Cho, Hyunyoung; Rappe, Andrew M; Hong, Ki-Ha; Jang, Min Seok; Kim, Hyungjun

2018-03-01

New light is shed on the previously known perovskite material, Cs 2 Au 2 I 6 , as a potential active material for high-efficiency thin-film Pb-free photovoltaic cells. First-principles calculations demonstrate that Cs 2 Au 2 I 6 has an optimal band gap that is close to the Shockley-Queisser value. The band gap size is governed by intermediate band formation. Charge disproportionation on Au makes Cs 2 Au 2 I 6 a double-perovskite material, although it is stoichiometrically a single perovskite. In contrast to most previously discussed double perovskites, Cs 2 Au 2 I 6 has a direct-band-gap feature, and optical simulation predicts that a very thin layer of active material is sufficient to achieve a high photoconversion efficiency using a polycrystalline film layer. The already confirmed synthesizability of this material, coupled with the state-of-the-art multiscale simulations connecting from the material to the device, strongly suggests that Cs 2 Au 2 I 6 will serve as the active material in highly efficient, nontoxic, and thin-film perovskite solar cells in the very near future. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

TiO2/PbS/ZnS heterostructure for panchromatic quantum dot sensitized solar cells synthesized by wet chemical route

NASA Astrophysics Data System (ADS)

Bhat, T. S.; Mali, S. S.; Sheikh, A. D.; Korade, S. D.; Pawar, K. K.; Hong, C. K.; Kim, J. H.; Patil, P. S.

2017-11-01

So far we developed the efficient photoelectrodes which can harness the UV as well as the visible regime of the solar spectrum effectively. In order to exploit a maximum portion of solar spectrum, it is necessary to study the synergistic effect of a photoelectrode comprising UV and visible radiations absorbing materials. Present research work highlights the efforts to study the synchronized effect of TiO2 and PbS on the power conversion efficiency of quantum dot sensitized solar cell (QDSSC). A cascade structure of TiO2/PbS/ZnS QDSSC is achieved to enhance the photoconversion efficiency of TiO2/PbS system by incorporating a surface passivation layer of ZnS which avoids the recombination of charge carriers. A QDSSC is fabricated using a simple and cost-effective technique such as hydrothermally grown TiO2 nanorod arrays decorated with PbS and ZnS using successive ionic layer adsorption and reaction (SILAR) method. Synthesized electrode materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), High resolution-transmission electron microscopy (TEM), STEM-EDS mapping, optical and solar cell performances. Phase formation of TiO2, PbS and ZnS get confirmed from the XPS study. FE-SEM images of the photoelectrode show uniform coverage of PbS QDs onto the TiO2 nanorods which increases with increasing number of SILAR cycles. The ZnS layer not only improves the charge transport but also reduces the photocorrosion of lead chalcogenides in the presence of a liquid electrolyte. Finally, the photoelectrochemical (PEC) study is carried out using an optimized photoanode comprising TiO2/PbS/ZnS assembly. Under AM 1.5G illumination the TiO2/PbS/ZnS QDSSC photoelectrode shows 4.08 mA/cm2 short circuit current density in a polysulfide electrolyte which is higher than that of a bare TiO2 nanorod array.

Tessellated gold nanostructures from Au144(SCH2CH2Ph)60 molecular precursors and their use in organic solar cell enhancement

NASA Astrophysics Data System (ADS)

Bauld, Reg; Hesari, Mahdi; Workentin, Mark S.; Fanchini, Giovanni

2014-06-01

We report for the first time the fabrication of nanocomposite hole-blocking layers consisting of poly-3,4-ethylene-dioxythiophene:poly-styrene-sulfonate (PEDOT:PSS) thin films incorporating networks of gold nanoparticles assembled from Au144(SCH2CH2Ph)60, a molecular gold precursor. These thin films can be prepared reproducibly on indium tin oxide by spinning on it Au144(SCH2CH2Ph)60 solutions in chlorobenzene, annealing the resulting thin film at 400 °C, and subsequently spinning PEDOT:PSS on top. The use of our nanocomposite hole-blocking layers for enhancing the photoconversion efficiency of bulk heterojunction organic solar cells is demonstrated. By varying the concentration of Au144(SCH2CH2Ph)60 in the starting solution and the annealing time, different gold nanostructures were obtained ranging from individual gold nanoparticles (AuNPs) to tessellated networks of gold nanostructures (Tess-AuNPs). Improvement in organic solar cell efficiencies up to 10% relative to a reference cell is demonstrated with Tess-AuNPs embedded in PEDOT:PSS.

Enhancing energy transport in conjugated polymers

NASA Astrophysics Data System (ADS)

Holmes, Russell J.

2018-05-01

The conversion of light into usable chemical energy by plants is enabled by the precise spatial arrangement of light-absorbing photosynthetic systems and associated molecular complexes (1). In organic solar cells, there is also the need to control intermolecular spacing and molecular orientation, as well as thin-film crystallinity and morphology, so as to enable efficient energy migration and photoconversion (2). In an organic solar cell, light absorption creates excitons, tightly bound electron-hole pairs that must be efficiently dissociated into their component charge carriers in order to create an electrical current. Thus, long-range exciton migration must occur from the point of photogeneration to a dissociating site. On page 897 of this issue, Jin et al. (3) report on a conjugated polymer nanofiber system that yields exciton diffusion lengths greater than 200 nm. In comparison, organic solar cells are typically constructed with materials having exciton diffusion lengths one order of magnitude smaller than this value, which limits device thickness and optical absorption. Their approach exploits a sequential synthesis method that enables measurement of this long exciton diffusion length (see the figure).

Semiconductor Quantum Dots for Applications to Advanced Concepts for Solar Photon Conversion to Electricity and Solar Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nozik, Arthur J; Beard, Matthew C

The challenge of photoconversion research is to produce photovoltaic electricity at costs much less than those based on fossil fuels. Novel photoactive semiconductors and molecules of various types and structures are discussed for this purpose.

Tracking Single Cells in Live Animals Using a Photoconvertible Near-Infrared Cell Membrane Label

PubMed Central

Wu, Juwell; Runnels, Judith M.; Turcotte, Raphaël; Celso, Cristina Lo; Scadden, David T.; Strom, Terry B.; Lin, Charles P.

2013-01-01

We describe a novel photoconversion technique to track individual cells in vivo using a commercial lipophilic membrane dye, DiR. We show that DiR exhibits a permanent fluorescence emission shift (photoconversion) after light exposure and does not reacquire the original color over time. Ratiometric imaging can be used to distinguish photoconverted from non-converted cells with high sensitivity. Combining the use of this photoconvertible dye with intravital microscopy, we tracked the division of individual hematopoietic stem/progenitor cells within the calvarium bone marrow of live mice. We also studied the peripheral differentiation of individual T cells by tracking the gain or loss of FoxP3-GFP expression, a marker of the immune suppressive function of CD4+ T cells. With the near-infrared photoconvertible membrane dye, the entire visible spectral range is available for simultaneous use with other fluorescent proteins to monitor gene expression or to trace cell lineage commitment in vivo with high spatial and temporal resolution. PMID:23990881

Tracking single cells in live animals using a photoconvertible near-infrared cell membrane label.

PubMed

Carlson, Alicia L; Fujisaki, Joji; Wu, Juwell; Runnels, Judith M; Turcotte, Raphaël; Spencer, Joel A; Celso, Cristina Lo; Scadden, David T; Strom, Terry B; Lin, Charles P

2013-01-01

We describe a novel photoconversion technique to track individual cells in vivo using a commercial lipophilic membrane dye, DiR. We show that DiR exhibits a permanent fluorescence emission shift (photoconversion) after light exposure and does not reacquire the original color over time. Ratiometric imaging can be used to distinguish photoconverted from non-converted cells with high sensitivity. Combining the use of this photoconvertible dye with intravital microscopy, we tracked the division of individual hematopoietic stem/progenitor cells within the calvarium bone marrow of live mice. We also studied the peripheral differentiation of individual T cells by tracking the gain or loss of FoxP3-GFP expression, a marker of the immune suppressive function of CD4(+) T cells. With the near-infrared photoconvertible membrane dye, the entire visible spectral range is available for simultaneous use with other fluorescent proteins to monitor gene expression or to trace cell lineage commitment in vivo with high spatial and temporal resolution.

Crystal Structure of Deinococcus Phytochrome in the Photoactivated State Reveals a Cascade of Structural Rearrangements during Photoconversion.

PubMed

Burgie, E Sethe; Zhang, Junrui; Vierstra, Richard D

2016-03-01

Phytochromes are photochromic photoreceptors responsible for a myriad of red/far-red light-dependent processes in plants and microorganisms. Interconversion is initially driven by photoreversible isomerization of bilin, but how this alteration directs the photostate-dependent changes within the protein to actuate signaling is poorly understood. Here, we describe the structure of the Deinococcus phytochrome photosensory module in its near complete far-red light-absorbing Pfr state. In addition to confirming the 180° rotation of the D-pyrrole ring, the dimeric structure clearly identifies downstream rearrangements that trigger large-scale conformational differences between the dark-adapted and photoactivated states. Mutational analyses verified the importance of residues surrounding the bilin in Pfr stabilization, and protease sensitivity assays corroborated photostate alterations that propagate along the dimeric interface. Collectively, these data support a cooperative "toggle" model for phytochrome photoconversion and advance our understanding of the allosteric connection between the photosensory and output modules. Copyright © 2016 Elsevier Ltd. All rights reserved.

Direct X-ray photoconversion in flexible organic thin film devices operated below 1 V

PubMed Central

Basiricò, Laura; Ciavatti, Andrea; Cramer, Tobias; Cosseddu, Piero; Bonfiglio, Annalisa; Fraboni, Beatrice

2016-01-01

The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. In this work we investigate the direct X-ray photoconversion process in organic thin film photoconductors. The devices are realized by drop casting solution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible plastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays despite the low X-ray photon absorption typical of low-Z organic materials. We propose a model, based on the accumulation of photogenerated charges and photoconductive gain, able to describe the magnitude as well as the dynamics of the X-ray-induced photocurrent. This finding allows us to fabricate and test a flexible 2 × 2 pixelated X-ray detector operating at 0.2 V, with gain and sensitivity up to 4.7 × 104 and 77,000 nC mGy−1 cm−3, respectively. PMID:27708274

Conjugated block copolymers: A building block for high-performance organic photovoltaics

NASA Astrophysics Data System (ADS)

Guo, Changhe

State-of-the-art organic photovoltaics rely on kinetically trapped, partially phase-separated structures of donor/acceptor mixtures to create a high interfacial area for exciton dissociation and networks of bicontinuous phases for charge transport. Nevertheless, intrinsic structural disorder and weak intermolecular interactions in polymer blends limit the performance and stability of organic electronic devices. We demonstrate a potential strategy to control morphology and donor/acceptor heterojunctions through conjugated block copolymer poly(3-hexylthiophene)- block-poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (P3HT-b-PFTBT). Block copolymers can self-assemble into well-ordered nanostructures ideal for photovoltaic applications. When utilized as the photovoltaic active layer, P3HT-b-PFTBT block copolymer devices demonstrate thermal stability and photoconversion efficiency of 3% well beyond devices composed of the constituent polymer blends. Resonant soft X-ray scattering (RSOXS) is used to elucidate the structural origin for efficient block copolymer photovoltaics. Energy tuning in soft X-ray ranges gives RSOXS chemical sensitivity to characterize organic thin films with compositionally similar phases or complicated multiphase systems. RSOXS reveals that the remarkable performance of P3HT-b-PFTBT devices is due to self-assembly into nanoscale in-plane lamellar morphology, which not only establishes an equilibrium microstructure amenable for exciton dissociation but also provides pathways for efficient charge transport. Furthermore, we find evidence that covalent control of donor/acceptor interfaces in block copolymers has the potential to promote charge separation and optimize the photoconversion process by limiting charge recombination. To visualize the nanostructure in organic thin films, we introduce low energy-loss energy-filtered transmission electron microscopy (EFTEM) as an important alternative approach to generate contrast from differences in optoelectronic properties and enable chemical imaging of organic materials. The widely-studied polymer/fullerene system is used as a test sample to demonstrate the application of this technique for structure characterization in the active layer of organic solar cells. In addition, well-ordered equilibrium nanostructures and covalent control of donor/acceptor interfaces make P3HT-b-PFTBT an excellent model for studying the effect of crystalline texture in the active layer on charge transport and photovoltaic performance. Solvent additives are applied to induce a drastic texture change from mainly face-on to edge-on orientations in crystalline P3HT domains of block copolymer thin films. We find that P3HT- b-PFTBT block copolymer devices demonstrate similar optimal performance, regardless of the dramatic changes in the predominant crystalline orientations adopted in P3HT domains. Our results provide further insights into the molecular organization required for efficient charge transport and device operation.

Trapping charges at grain boundaries and degradation of CH3NH3Pb(I1-x Br x )3 perovskite solar cells.

PubMed

Nguyen, Bich Phuong; Kim, Gee Yeong; Jo, William; Kim, Byeong Jo; Jung, Hyun Suk

2017-08-04

The electrical properties of CH 3 NH 3 Pb(I 1-x Br x ) 3 (x = 0.13) perovskite materials were investigated under ambient conditions. The local work function and the local current were measured using Kelvin probe force microscopy and conductive atomic force microscopy, respectively. The degradation of the perovskite layers depends on their grain size. As the material degrades, an additional peak in the surface potential appears simultaneously with a sudden increase and subsequent relaxation of the local current. The potential bending at the grain boundaries and the intragrains is the most likely reason for the change of the local current surface of the perovskite layers. The improved understanding of the degradation mechanism garnered from this study helps pave the way toward an improved photo-conversion efficiency in perovskite solar cells.

Trapping charges at grain boundaries and degradation of CH3NH3Pb(I1-x Br x )3 perovskite solar cells

NASA Astrophysics Data System (ADS)

Phuong Nguyen, Bich; Kim, Gee Yeong; Jo, William; Kim, Byeong Jo; Jung, Hyun Suk

2017-08-01

The electrical properties of CH3NH3Pb(I1-x Br x )3 (x = 0.13) perovskite materials were investigated under ambient conditions. The local work function and the local current were measured using Kelvin probe force microscopy and conductive atomic force microscopy, respectively. The degradation of the perovskite layers depends on their grain size. As the material degrades, an additional peak in the surface potential appears simultaneously with a sudden increase and subsequent relaxation of the local current. The potential bending at the grain boundaries and the intragrains is the most likely reason for the change of the local current surface of the perovskite layers. The improved understanding of the degradation mechanism garnered from this study helps pave the way toward an improved photo-conversion efficiency in perovskite solar cells.

Elucidation of the structure-property relationship of p-type organic semiconductors through rapid library construction via a one-pot, Suzuki-Miyaura coupling reaction.

PubMed

Fuse, Shinichiro; Matsumura, Keisuke; Wakamiya, Atsushi; Masui, Hisashi; Tanaka, Hiroshi; Yoshikawa, Susumu; Takahashi, Takashi

2014-09-08

The elucidation of the structure-property relationship is an important issue in the development of organic electronics. Combinatorial synthesis and the evaluation of systematically modified compounds is a powerful tool in the work of elucidating structure-property relationships. In this manuscript, D-π-A structure, 32 p-type organic semiconductors were rapidly synthesized via a one-pot, Suzuki-Miyaura coupling with subsequent Knoevenagel condensation. Evaluation of the solubility and photovoltaic properties of the prepared compounds revealed that the measured solubility was strongly correlated with the solubility parameter (SP), as reported by Fedors. In addition, the SPs were correlated with the Jsc of thin-film organic solar cells prepared using synthesized compounds. Among the evaluated photovoltaic properties of the solar cells, Jsc and Voc had strong correlations with the photoconversion efficiency (PCE).

Design of Far-Red Sensitizing Squaraine Dyes Aiming Towards the Fine Tuning of Dye Molecular Structure.

PubMed

Morimoto, Takuya; Fujikawa, Naotaka; Ogomi, Yuhei; Pandey, Shyam S; Ma, Tingli; Hayase, Shuzi

2016-04-01

Model squaraine dyes having sharp and narrow absorptions mainly in the far-red wavelength region has been logically designed, synthesized and used for their application as sensitizer in the dyesensitized solar cells (DSSC). In order to have fine control on energetics, dyes having same mother core and alkyl chain length varying only in molecular symmetry and position of substituent were designed. It has been found that even keeping all other structural factor constant, only positional variation of substituent leads to not only in the variation of energetics by 0.1 eV but affects the photovoltaic characteristics also. Optimum concentration of dye de-aggregating agent was found to be 100 times with respect to the sensitizing dye concentration. Amongst dyes utilized in this work best performance was obtained for unsymmetrical dye SQ-40 giving a photoconversion efficiency of 4.01% under simulated solar irradiation at global AM 1.5.

ZnO Photoanode Effect on the Efficiency Performance of Organic Based Dye Sensitized Solar Cell

NASA Astrophysics Data System (ADS)

Mohamad, I. S.; Ismail, S. S.; Norizan, M. N.; Murad, S. A. Z.; Abdullah, M. M. A.

2017-06-01

Dye sensitized solar cell has been emerged as one of the most promising candidates for photovoltaics applications in good quality of their low manufacturing cost and impressive conversion energy. Titanium dioxide (TiO2) which is used as photoanode in the market has the advantage of wide bandgap energy but low in electron mobility (∼10 cm2/(V.s)). Ruthenium in the other hand, as the dye sensitizer is a rare noble metal and harmful to human health. Thus, this article reveals the performance of photo-to-electric conversion efficiency with the usage of Zinc Oxide as photoanode with higher electron mobility (155 cm2/(V.s)) compared to TiO2 utilizing three natural fruit dyes of Prunus domestica, Magnifera indica and Citrus limon. ZnO and TiO2 photoanodes were fabricated using sol gel and dr blade method respectively. The morphology of the photoanodes were characterized using Scanning Electron Microscope and the efficiency of the complete DSSC with all different fruit dyes were characterized using Semiconductor Parametric Analyzer. The different property of electron mobility photoanodes effect in DSSC proved to give better performance with the photoconversion efficiency of 3.082% using ZnO with Prunus domestica dye. This article also reveals that pH indicator does not affect the selection and the performance of DSSC.

Mechanisms of electron transport and recombination in ZnO nanostructures for dye-sensitized solar cells.

PubMed

Vega-Poot, Alberto G; Macías-Montero, Manuel; Idígoras, Jesus; Borrás, Ana; Barranco, Angel; Gonzalez-Elipe, Agustín R; Lizama-Tzec, Francisco I; Oskam, Gerko; Anta, Juan A

2014-04-14

ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plasmonic-enhanced graphene flake counter electrodes for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Kim, Hyun-Young; Lee, Myung Woo; Song, Da Hyun; Yoon, Hyeok Jin; Suh, Jung Sang

2017-06-01

A plasmonic-enhanced graphene flake counter electrode for dye-sensitized solar cells (DSSCs) was fabricated by immobilization of gold nanoparticles (NPs) on fluorine-doped tin oxide (FTO) glass and the deposition of a thin layer of graphene flakes. The graphene flakes, fabricated using a thermal plasma jet system, were very thin and pure and had good crystallinity. Even though their average size is larger than 100 nm, they had great dispersibility in common solvents. Their relatively large size and good crystallinity resulted in good conductivity, and their good dispersibility allowed us to fabricate relatively uniform films. The efficiency of the DSSC with a graphene flake/Au NP/FTO counter electrode was as much as 9.78%, which is higher than that with a conventional Pt/FTO (9.08%) or graphene flake/FTO (8.98%) counter electrode. Using cyclic voltammograms and electrochemical impedance spectroscopy and by measuring the incident photo-conversion efficiency, we proved that by the localized surface plasmon resonance effect of the Au NPs included between the graphene flakes and FTO, the charge-transfer resistance at the electrode/electrolyte interface was decreased. Consequently, the catalytic rate for I- regeneration improved, and the energy conversion efficiency of the DSSC with a graphene flake/Au NP/FTO counter electrode improved.

Photovoltaic properties of multilayered quantum dot/quantum rod-sensitized TiO₂ solar cells fabricated by SILAR and electrophoresis.

PubMed

Cerdán-Pasarán, Andrea; López-Luke, Tzarara; Esparza, Diego; Zarazúa, Isaac; De la Rosa, Elder; Fuentes-Ramírez, Rosalba; Alatorre-Ordaz, Alejandro; Sánchez-Solís, Ana; Torres-Castro, Alejandro; Zhang, Jin Z

2015-07-28

A multilayered semiconductor sensitizer structure composed of three differently sized CdSe quantum rods (QRs), labeled as Q530, Q575, Q590, were prepared and deposited on the surface of mesoporous TiO2 nanoparticles by electrophoretic deposition (EPD) for photovoltaic applications. By varying the arrangement of layers as well as the time of EPD, the photoconversion efficiency was improved from 2.0% with the single layer of CdSe QRs (TiO2/Q590/ZnS) to 2.9% for multilayers (TiO2/Q590Q575/ZnS). The optimal EPD time was shorter for the multilayered structures. The effect of CdS quantum dots (QDs) deposited by successive ionic layer adsorption and reaction (SILAR) was also investigated. The addition of CdS QDs resulted in the enhancement of efficiency to 4.1% for the configuration (TiO2/CdS/Q590Q575/ZnS), due to increased photocurrent and photovoltage. Based on detailed structural, optical, and photoelectrical studies, the increased photocurrent is attributed to broadened light absorption while the increased voltage is due to a shift in the relevant energy levels.

Bifunctional NaYF4:Er3+/Yb3+ submicron rods, implemented in quantum dot sensitized solar cell(Conference Presentation)

NASA Astrophysics Data System (ADS)

Guerrero, J. Pablo; Cerdán Pasarán, Andrea; López-Luke, Tzarara; Ramachari, D.; Esparza, Diego; De la Rosa Cruz, Elder; Romero Arellano, Victor Hugo

2016-09-01

In this work are presented the results obtained with solar cells sensitized with quantum dots of cadmium sulphide (CdS) incorporating luminescent materials (NaYF4:Yb/Er). The study revealed that through using a bifunctional layer of NaYF4:Yb/Er submicron rods, the infrared radiation is absorbed in 980nm to generate luminescence in the visible region to 530nm, under the UP-conversion process, in the same way simultaneously, NaYF4:Yb/Er layer causes scattering toward the quantum dots, the emission and scattering generated by this material is reabsorbed by the QD-CdS, and these in turn are absorbing in its range of solar radiation absorption, Thus generates an increase in the electron injection into the semiconductor of TiO2. The results of a cell incorporating NaYF4: Yb/Er at 0.07M shown photoconversion efficiencies of 3.39% improving efficiency with respect to the reference solar cell without using NaYF4: Yb/Er of 1.99%. The obtained values of current and voltage showed a strong dependence of the percentage of NaYF4 Yb/Er, and the mechanism of incorporation of this material.

A solar light driven dual photoelectrode photocatalytic fuel cell (PFC) for simultaneous wastewater treatment and electricity generation.

PubMed

Bai, Jing; Wang, Rui; Li, Yunpo; Tang, Yuanyuan; Zeng, Qingyi; Xia, Ligang; Li, Xuejin; Li, Jinhua; Li, Caolong; Zhou, Baoxue

2016-07-05

In this paper, a novel dual heterojunction Photocatalytic Fuel Cell (PFC) system based on BiVO4/TiO2 nanotubes/FTO photoanode and ZnO/CuO nanowires/FTO photocathode has been designed. Compared with the electrodes in PFCs reported in earlier literatures, the proposed heterojunction not only enhances the visible light absorption but also offers a higher photoconversion efficiency. In addition, the nanostructured heterojunction owns a large surface area that ensures a large amount of active sites for organics degradation. The performance of the PFC base on the dual photoelectrodes was also studied herein. The results indicated that the PFC in ths paper exhibits a superior performance and its JV(max) reached 0.116 mw cm(-2), which is higher than that in most of reported PFCs with a Pt-free photocathode. When hazardous organic compounds such as methyl orange, Congo red and methylene blue were decomposed, the degradation rates obtained is to be 76%, 83%, and 90% respectively after 80 mins reaction. The proposed heterojunction photoelectrodes provided great potential for cost-effective and high-efficiency organic pollutants degradation and electricity generation in a PFC system. Copyright © 2016 Elsevier B.V. All rights reserved.

A B-C-N hybrid porous sheet: an efficient metal-free visible-light absorption material.

PubMed

Lu, Ruifeng; Li, Feng; Salafranca, Juan; Kan, Erjun; Xiao, Chuanyun; Deng, Kaiming

2014-03-07

The polyphenylene network, known as porous graphene, is one of the most important and widely studied two-dimensional materials. As a potential candidate for photocatalysis and photovoltaic energy generation, its application has been limited by the low photocatalytic activity in the visible-light region. State-of-the-art hybrid density functional theory investigations are presented to show that an analogous B-C-N porous sheet outperforms the pristine polyphenylene network with significantly enhanced visible-light absorption. Compared with porous graphene, the calculated energy gap of the B-C-N hybrid crystal shrinks to 2.7 eV and the optical absorption peak remarkably shifts to the visible light region. The redox potentials of water splitting are well positioned in the middle of the band gap. Hybridizations among B_p, N_p and C_p orbitals are responsible for these findings. Valence and conduction band calculations indicate that the electrons and holes can be effectively separated, reducing charge recombination and improving the photoconversion efficiency. Moreover, the band gap and optical properties of the B-C-N hybrid porous sheet can be further finely engineered by external strain.

Extremely Efficient Multiple Electron-hole Pair Generation in Carbon Nanotube Photodiodes

NASA Astrophysics Data System (ADS)

Gabor, Nathaniel

2010-03-01

The efficient generation of multiple electron-hole (e-h) pairs from a single photon could improve the efficiency of photovoltaic solar cells beyond standard thermodynamic limits [1] and has been the focus of much recent work in semiconductor nanomaterials [2,3]. In single walled carbon nanotubes (SWNTs), the small Fermi velocity and low dielectric constant suggests that electron-electron interactions are very strong and that high-energy carriers should efficiently generate e-h pairs. Here, I will discuss observations of highly efficient generation of e-h pairs due to impact excitation in SWNT p-n junction photodiodes [4]. To investigate optoelectronic transport properties of individual SWNT photodiodes, we focus a laser beam over the device while monitoring the electronic characteristics. Optical excitation into the second electronic subband E22 ˜ 2 EGAP leads to striking photocurrent steps in the device I-VSD characteristics that occur at voltage intervals of the band gap energy EGAP/ e. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple e-h pairs from a single hot E22 carrier. We conclude that in the SWNT photodiode, a single photon with energy greater than 2EGAP is converted into multiple e-h pairs, leading to enhanced photocurrent and increased photo-conversion efficiency. [1] W. Shockley, and H. J. Queisser, Journal of Applied Physics 32, 510 (1961). [2] R. D. Schaller, and V. I. Klimov, Physical Review Letters 92 (18), 186601 (2004). [3] R. J. Ellingson, et al, Nano Letters, 5 (5), 865-871 (2005). [4] Nathaniel M. Gabor, Zhaohui Zhong, Ken Bosnick, Jiwoong Park, and Paul McEuen, Science, 325, 1367 (2009).

A hybrid nanostructure of platinum-nanoparticles/graphitic-nanofibers as a three-dimensional counter electrode in dye-sensitized solar cells.

PubMed

Hsieh, Chien-Kuo; Tsai, Ming-Chi; Su, Ching-Yuan; Wei, Sung-Yen; Yen, Ming-Yu; Ma, Chen-Chi M; Chen, Fu-Rong; Tsai, Chuen-Horng

2011-11-07

We directly synthesized a platinum-nanoparticles/graphitic-nanofibers (PtNPs/GNFs) hybrid nanostructure on FTO glass. We applied this structure as a three-dimensional counter electrode in dye-sensitized solar cells (DSSCs), and investigated the cells' photoconversion performance. This journal is © The Royal Society of Chemistry 2011

Quantum dot sensitized solar cell based on TiO2/CdS/Ag2S heterostructure

NASA Astrophysics Data System (ADS)

Pawar, Sachin A.; Patil, Dipali S.; Kim, Jin Hyeok; Patil, Pramod S.; Shin, Jae Cheol

2017-04-01

Quantum dot sensitized solar cell (QDSSC) is fabricated based on a stepwise band structure of TiO2/CdS/Ag2S to improve the photoconversion efficiency of TiO2/CdS system by incorporating a low band gap Ag2S QDs. Vertically aligned TiO2 nanorods assembly is prepared by a simple hydrothermal technique. The formation of CdS and Ag2S QDs over TiO2 nanorods assembly as a photoanode is carried out by successive ionic layer adsorption and reaction (SILAR) technique. The synthesized electrode materials are characterized by XRD, XPS, field emission scanning electron microscopy (FE-SEM), Optical, solar cell and electrochemical performances. The results designate that the QDs of CdS and Ag2S have efficiently covered exterior surfaces of TiO2 nanorods assembly. A cautious evaluation between TiO2/CdS and TiO2/CdS/Ag2S sensitized cells tells that CdS and Ag2S synergetically helps to enhance the light harvesting ability. Under AM 1.5G illumination, the photoanodes show an improved power conversion efficiency of 1.87%, in an aqueous polysulfide electrolyte with short-circuit photocurrent density of 7.03 mA cm-2 which is four fold higher than that of a TiO2/CdS system.

Nano-engineering of p-n CuFeO2-ZnO heterojunction photoanode with improved light absorption and charge collection for photoelectrochemical water oxidation

NASA Astrophysics Data System (ADS)

Karmakar, Keshab; Sarkar, Ayan; Mandal, Kalyan; Gopal Khan, Gobinda

2017-08-01

The effective utilization of abundant visible solar light for photoelectrochemical water splitting is a green approach for energy harvesting, to reduce the enormous rise of carbon content in the atmosphere. Here, a novel efficient design strategy for p-n type nano-heterojunction photoanodes is demonstrated, with the goal of improving water splitting efficiency by growing low band gap p-CuFeO2 nanolayers on n-ZnO nanorods by an easy and scalable electrochemical route. The photoconversion efficiency of p-n CuFeO2/ZnO photoanodes is found to be ˜450% higher than that of pristine ZnO nanorod electrodes under visible solar light illumination (λ > 420 nm, intensity 10 mW cm-2). The p-n CuFeO2/ZnO nano-engineering not only boosts the visible light absorption but also resolves limitations regarding effective charge carrier separation and transportation due to interfacial band alignment. This photoanode also shows remarkably enhanced stability, where the formation of p-n nano-heterojunction enhances the easy migration of holes to the electrode/electrolyte interface, and of electrons to the counter electrode (Pt) for hydrogen generation. Therefore, this work demonstrates that p-n nano-engineering is a potential strategy to design light-harvesting electrodes for water splitting and clean energy generation.

Plasmonic Enhancement Mechanisms in Solar Energy Harvesting

NASA Astrophysics Data System (ADS)

Cushing, Scott K.

Semiconductor photovoltaics (solar-to-electrical) and photocatalysis (solar-to-chemical) requires sunlight to be converted into excited charge carriers with sufficient lifetimes and mobility to drive a current or photoreaction. Thin semiconductor films are necessary to reduce the charge recombination and mobility losses, but thin films also limit light absorption, reducing the solar energy conversion efficiency. Further, in photocatalysis, the band edges of semiconductor must straddle the redox potentials of a photochemical reaction, reducing light absorption to half the solar spectrum in water splitting. Plasmonics transforms metal nanoparticles into antennas with resonances tuneable across the solar spectrum. If energy can be transferred from the plasmon to the semiconductor, light absorption in the semiconductor can be increased in thin films and occur at energies smaller than the band gap. This thesis investigates why, despite this potential, plasmonic solar energy harvesting techniques rarely appear in top performing solar architectures. To accomplish this goal, the possible plasmonic enhancement mechanisms for solar energy conversion were identified, isolated, and optimized by combining systematic sample design with transient absorption spectroscopy, photoelectrochemical and photocatalytic testing, and theoretical development. Specifically, metal semiconductor nanostructures were designed to modulate the plasmon's scattering, hot carrier, and near field interactions as well as remove heating and self-catalysis effects. Transient absorption spectroscopy then revealed how the structure design affected energy and charge carrier transfer between metal and semiconductor. Correlating this data with wavelength-dependent photoconversion efficiencies and theoretical developments regarding metal-semiconductor interactions identified the origin of the plasmonic enhancement. Using this methodology, it has first been proven that three plasmonic enhancement routes are possible: i) increasing light absorption in the semiconductor by light trapping through scattering, ii) transferring hot carriers from metal to semiconductor after light absorption in the metal, and iii) non-radiative excitation of interband transitions in the semiconductor by plasmon-induced resonant energy transfer (PIRET). The effects of the metal on charge transport and carrier recombination were also revealed. Next, it has been shown that the strength and balance of the three enhancement mechanisms is rooted in the plasmon's dephasing time, or how long it takes the collective electron oscillations to stop being collective. The importance of coherent effects in plasmonic enhancement is also shown. Based on these findings, a thermodynamic balance framework has been used to predict the theoretical maximum efficiency of solar energy conversion in plasmonic metal-semiconductor heterojunctions. These calculations have revealed how plasmonics is best used to address the different light absorption problems in semiconductors, and that not taking into account the plasmon's dephasing is the origin of low plasmonic enhancement Finally, to prove these guidelines, each of the three enhancement mechanisms has been translated into optimal device geometries, showing the plasmon's potential for solar energy harvesting. This dissertation identifies the three possible plasmonic enhancement mechanisms for the first time, discovering a new enhancement mechanism (PIRET) in the process. It has also been shown for the first time that the various plasmon-semiconductor interactions could be rooted in the plasmon's dephasing. This has allowed for the first maximum efficiency estimates which have combined all three enhancement mechanisms to be performed, and revealed that changes in the plasmon's dephasing leads to the disparity in reported plasmonic enhancements. These findings are combined to create optimal device design guidelines, which are proven by fabrication of several devices with top efficiencies in plasmonic solar energy conversion. The knowledge obtained will guide the design of efficient photovoltaics and photocatalysts, helping usher in a renewable energy economy and address current needs of climate change.

Molecular diodes in optical rectennas

NASA Astrophysics Data System (ADS)

Duché, David; Palanchoke, Ujwol; Terracciano, Luigi; Dang, Florian-Xuan; Patrone, Lionel; Le Rouzo, Judikael; Balaban, Téodore Silviu; Alfonso, Claude; Charai, Ahmed; Margeat, Olivier; Ackermann, Jorg; Gourgon, Cécile; Simon, Jean-Jacques; Escoubas, Ludovic

2016-09-01

The photo conversion efficiencies of the 1st and 2nd generat ion photovoltaic solar cells are limited by the physical phenomena involved during the photo-conversion processes. An upper limit around 30% has been predicted for a monojunction silicon solar cell. In this work, we study 3rd generation solar cells named rectenna which could direct ly convert visible and infrared light into DC current. The rectenna technology is at odds with the actual photovoltaic technologies, since it is not based on the use of semi-conducting materials. We study a rectenna architecture consist ing of plasmonic nano-antennas associated with rectifying self assembled molecular diodes. We first opt imized the geometry of plasmonic nano-antennas using an FDTD method. The optimal antennas are then realized using a nano-imprint process and associated with self assembled molecular diodes in 11- ferrocenyl-undecanethiol. Finally, The I(V) characterist ics in darkness of the rectennas has been carried out using an STM. The molecular diodes exhibit averaged rect ification ratios of 5.

Formation of anodic TiO2 nanotube arrays in NaOH added fluoride-ethylene glycol electrolyte for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Nyein, Nyein; Tan, Wai Kian; Kawamura, Go; Matsuda, Atsunori; Lockman, Zainovia

2017-07-01

TiO2 nanotube (TNT) arrays were formed by anodizing titanium foil in fluoride-ethylene glycol (EG) electrolyte added to it either water (H2O) or sodium hydroxide (NaOH) as oxidant. In NaOH added fluoride-EG electrolyte, 10 µm long TNT arrays were formed compared to 5 μm long nanotubes in H2O added fluoride-EG electrolyte. When NaOH was added to EG, the electrolyte pH was 9. As the pH of the electrolyte was rather high, surface etching of the nanotubes was reduced resulting in tubes with longer length. Moreover, the addition of NaOH into fluoride-EG resulted in the crystallization of anatase in the as-made TNT arrays. Annealing obviously improved the crystallinity of the oxide. The TNT arrays were then used as a photoanode in a dye-sensitized solar cell (DSSC). A photoconversion efficiency of 2.4 % was recorded with photocurrent of 6.9 mA/cm2.

Performance analysis of flexible DSSC with binder addition

NASA Astrophysics Data System (ADS)

Muliani, Lia; Hidayat, Jojo; Anggraini, Putri Nur

2016-04-01

Flexible DSSC is one of modification of DSSC based on its substrate. Operating at low temperature, flexible DSSC requires a binder to improve particles interconnection. This research was done to compare the morphology and performance of flexible DSSC that was produced with binder-added and binder-free. TiO2 powder, butanol, and HCl were mixed for preparation of TiO2 paste. Small amount of titanium isopropoxide as binder was added into the mixture. TiO2 paste was deposited on ITO-PET plastic substrate with area of 1x1 cm2 by doctor blade method. Furthermore, SEM, XRD, and BET characterization were done to analyze morphology and surface area of the TiO2 photoelectrode microstructures. Dyed TiO2 photoelectrode and platinum counter electrode were assembled and injected by electrolyte. In the last process, flexible DSSCs were illuminated by sun simulator to do J-V measurement. As a result, flexible DSSC containing binder showed higher performance with photoconversion efficiency of 0.31%.

Optimized protocol for combined PALM-dSTORM imaging.

PubMed

Glushonkov, O; Réal, E; Boutant, E; Mély, Y; Didier, P

2018-06-08

Multi-colour super-resolution localization microscopy is an efficient technique to study a variety of intracellular processes, including protein-protein interactions. This technique requires specific labels that display transition between fluorescent and non-fluorescent states under given conditions. For the most commonly used label types, photoactivatable fluorescent proteins and organic fluorophores, these conditions are different, making experiments that combine both labels difficult. Here, we demonstrate that changing the standard imaging buffer of thiols/oxygen scavenging system, used for organic fluorophores, to the commercial mounting medium Vectashield increased the number of photons emitted by the fluorescent protein mEos2 and enhanced the photoconversion rate between its green and red forms. In addition, the photophysical properties of organic fluorophores remained unaltered with respect to the standard imaging buffer. The use of Vectashield together with our optimized protocol for correction of sample drift and chromatic aberrations enabled us to perform two-colour 3D super-resolution imaging of the nucleolus and resolve its three compartments.

Phosphorene-AsP heterostructure as a potential excitonic solar cell material - A first principles study

NASA Astrophysics Data System (ADS)

Kishore, M. R. Ashwin; Ravindran, P.

2018-04-01

Solar energy conversion to produce electricity using photovoltaics is an emerging area in alternative energy research. Herein, we report on the basis of density functional calculations, phosphorene/AsP heterostructure could be a promising material for excitonic solar cells (XSCs). Our HSE06 functional calculations show that the band gap of both phosphorene and AsP fall exactly into the optimum value range according to XSCs requirement. The calculated effective mass of electrons and holes show anisotropic in nature with effective masses along Γ-X direction is lower than the Γ-Y direction and hence the charge transport will be faster along Γ-X direction. The wide energy range of light absorption confirms the potential use of these materials for solar cell applications. Interestingly, phosphorene and AsP monolayer forms a type-II band alignment which will enhance the separation of photogenerated charge carriers and hence the recombination rate will be lower which can further improve its photo-conversion efficiency if one use it in XSCs.

Fluorescent protein Dendra2 as a ratiometric genetically encoded pH-sensor.

PubMed

Pakhomov, Alexey A; Martynov, Vladimir I; Orsa, Alexander N; Bondarenko, Alena A; Chertkova, Rita V; Lukyanov, Konstantin A; Petrenko, Alexander G; Deyev, Igor E

2017-12-02

Fluorescent protein Dendra2 is a monomeric GFP-like protein that belongs to the group of Kaede-like photoconvertible fluorescent proteins with irreversible photoconversion from a green- to red-emitting state when exposed to violet-blue light. In an acidic environment, photoconverted Dendra2 turns green due to protonation of the phenolic group of the chromophore with pKa of about 7.5. Thus, photoconverted form of Dendra2 can be potentially used as a ratiometric pH-sensor in the physiological pH range. However, incomplete photoconversion makes ratiometric measurements irreproducible when using standard filter sets. Here, we describe the method to detect fluorescence of only photoconverted Dendra2 form, but not nonconverted green Dendra2. We show that the 350 nm excitation light induces solely the fluorescence of photoconverted protein. By measuring the red to green fluorescence ratio, we determined intracellular pH in live CHO and HEK 293 cells. Thus, Dendra2 can be used as a novel ratiometric genetically encoded pH sensor with emission maxima in the green-red spectral region, which is suitable for application in live cells. Copyright © 2017 Elsevier Inc. All rights reserved.

FRAP and Photoconversion in Multiple Arbitrary Regions of Interest Using a Programmable Array Microscope (PAM)

PubMed Central

Hagen, Guy M.; Caarls, Wouter; Lidke, Keith A.; de Vries, Anthony H. B.; Fritsch, Cornelia; Barisas, B. George; Arndt-Jovin, Donna J.; Jovin, Thomas M.

2011-01-01

Photomanipulation (photobleaching, photoactivation, or photoconversion) is an essential tool in fluorescence microscopy. Fluorescence recovery after photobleaching (FRAP) is commonly used for the determination of lateral diffusion constants of membrane proteins, and can be conveniently implemented in confocal laser scanning microscopy (CLSM). Such determinations provide important information on molecular dynamics in live cells. However, the CLSM platform is inherently limited for FRAP because of its inflexible raster (spot) scanning format. We have implemented FRAP and photoactivation protocols using structured illumination and detection in a programmable array microscope (PAM). The patterns are arbitrary in number and shape, dynamic and adjustable to and by the sample characteristics. We have used multi-spot PAM-FRAP to measure the lateral diffusion of the erbB3 (HER3) receptor tyrosine kinase labeled by fusion with mCitrine on untreated cells and after treatment with reagents that perturb the cytoskeleton or plasma membrane or activate co-expressed erbB1 (HER1, the EGF receptor EGFR). We also show the versatility of the PAM for photoactivation in arbitrary regions of interest, in cells expressing erbB3 fused with the photoconvertible fluorescent protein dronpa. PMID:19208387

Basic and applied research program. Semiannual report, July-December 1978

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butler, B.L.

1979-12-01

The status of research projects in the Basic and Applied Research Program at SERI is presented for the semiannual period ending December 31, 1978. The five tasks in this program are grouped into Materials Research and Development, Materials Processing and Development, Photoconversion Research, Exploratory Research, and Energy Resource and Assessment and have been carried out by personnel in the Materials, Bio/Chemical Conversion, and Energy Resource and Assessment Branches. Subtask elements in the task areas include coatings and films, polymers, metallurgy and corrosion, optical materials, surfaces and interfaces in materials research and development; photochemistry, photoelectrochemistry, and photobiology in photoconversion; thin glassmore » mirror development, silver degradation of mirrors, hail resistance of thin glass, thin glass manufacturing, cellular glass development, and sorption by desiccants in materials processing and development; and thermoelectric energy conversion, desiccant cooling, photothermal degradation, and amorphous materials in exploratory research. For each task or subtask element, the overview, scope, goals, approach, apparatus and equipment, and supporting subcontracts are presented, as applicable, in addition to the status of the projects in each task or subtask. Listing of publications and reports authored by personnel associated with the Basic and Applied Research Program and prepared or published during 1978 are also included.« less

Water content and the conversion of phytochrome regulation of lettuce dormancy

NASA Technical Reports Server (NTRS)

Vertucci, C. W.; Vertucci, F. A.; Leopold, A. C.

1987-01-01

In an effort to determine which biological reactions can occur in relation to the water content of seeds, the regulation of lettuce seed dormancy by red and far red light was determined at various hydration levels. Far red light had an inhibiting effect on germination for seeds at all moisture contents from 4 to 32% water. Germination was progressively stimulated by red light as seed hydration increased from 8 to 15%, and reached a maximum at moisture contents above 18%. Red light was ineffective at moisture contents below 8%. Seeds that had been stimulated by red light and subsequently dried lost the enhanced germinability if stored at moisture contents above 8%. The contrast between the presumed photoconversion of phytochrome far red-absorbing (Pfr) to (Pr) occurring at any moisture content and the reverse reaction occurring only if the seed moisture content is greater than 8% may be explained on the basis of the existence of unstable intermediates in the Pr to Pfr conversion. Our results suggest that the initial photoreaction involved in phytochrome conversion is relatively independent of water content, while the subsequent partial reactions become increasingly facilitated as water content increases from 8 to 18%.

Performance enhancement in organic photovoltaic solar cells using iridium (Ir) ultra-thin surface modifier (USM)

NASA Astrophysics Data System (ADS)

Pandey, Rina; Lim, Ju Won; Kim, Jung Hyuk; Angadi, Basavaraj; Choi, Ji Won; Choi, Won Kook

2018-06-01

In this study, Iridium (Ir) metallic layer as an ultra-thin surface modifier (USM) was deposited on ITO coated glass substrate using radio frequency magnetron sputtering for improving the photo-conversion efficiency of organic photovoltaic cells. Ultra-thin Ir acts as a surface modifier replacing the conventional hole transport layer (HTL) PEDOT:PSS in organic photovoltaic (OPV) cells with two different active layers P3HT:PC60BM and PTB7:PC70BM. The Ir USM (1.0 nm) coated on ITO glass substrate showed transmittance of 84.1% and work function of >5.0 eV, which is higher than that of ITO (4.5-4.7 eV). The OPV cells with Ir USM (1.0 nm) exhibits increased power conversion efficiency of 3.70% (for P3HT:PC60BM active layer) and 7.28% (for PTB7:PC70BM active layer) under 100 mW/cm2 illumination (AM 1.5G) which are higher than those of 3.26% and 6.95% for the same OPV cells but with PEDOT:PSS as HTL instead of Ir USM. The results reveal that the chemically stable Ir USM layer could be used as an alternative material for PEDOT:PSS in organic photovoltaic cells.

One-Dimensional Electron Transport Layers for Perovskite Solar Cells

PubMed Central

Thakur, Ujwal K.; Kisslinger, Ryan; Shankar, Karthik

2017-01-01

The electron diffusion length (Ln) is smaller than the hole diffusion length (Lp) in many halide perovskite semiconductors meaning that the use of ordered one-dimensional (1D) structures such as nanowires (NWs) and nanotubes (NTs) as electron transport layers (ETLs) is a promising method of achieving high performance halide perovskite solar cells (HPSCs). ETLs consisting of oriented and aligned NWs and NTs offer the potential not merely for improved directional charge transport but also for the enhanced absorption of incoming light and thermodynamically efficient management of photogenerated carrier populations. The ordered architecture of NW/NT arrays affords superior infiltration of a deposited material making them ideal for use in HPSCs. Photoconversion efficiencies (PCEs) as high as 18% have been demonstrated for HPSCs using 1D ETLs. Despite the advantages of 1D ETLs, there are still challenges that need to be overcome to achieve even higher PCEs, such as better methods to eliminate or passivate surface traps, improved understanding of the hetero-interface and optimization of the morphology (i.e., length, diameter, and spacing of NWs/NTs). This review introduces the general considerations of ETLs for HPSCs, deposition techniques used, and the current research and challenges in the field of 1D ETLs for perovskite solar cells. PMID:28468280

Lattice defects of ZnO and hybrids with GO: Characterization, EPR and optoelectronic properties

NASA Astrophysics Data System (ADS)

Ahmed, Gulzar; Hanif, Muddasir; Mahmood, Khalid; Yao, Rihui; Ning, Honglong; jiao, Dongling; Wu, Mingmei; Khan, Javid; Liu, Zhongwu

2018-02-01

We have prepared and combined ZnO nanoparticles (ZnO-NPs) with different graphene oxide (GO) contents (10%, 20% and 30%) via microwave processing. The procedure provided well-dispersed ZnO-NPs between and onto the rGO layers (GZCs). The annealing temperature and graphene oxide contents affected the UV-Vis absorption, PL emission, defect-states of the ZnO, EPR signals, photo-electrochemical response and charge transfer properties. The HRTEM microscopy images of the GZCs showed interpenetrating structures and clearly visible vacancy defects. The results indicated that the defect sites (Zn interstitials, oxygen vacancy, ionized zinc vacancy and oxygen interstitials) significantly decreased after hybridization with GO. The photo-conversion efficiency of the GZC-10% (η = 13.1 x 10-3%), is 13 times higher than the ZnO-NPs (η = 1.02 x 10-3%) illustrating higher exciton production and separation efficiency of the GZCs under photo-excitation. The GZC-10% has lower (8-15 Ω) charge transfer resistance (Rct) compared to all the GZCs under same experimental conditions, therefore an important reason of better performance of the GZC 10%. The EPR spectra showed presence of radicals in all the samples with GZC 10% most intense signal among the different GZCs.

Rational design of a tripartite-layered TiO2 photoelectrode: a candidate for enhanced power conversion efficiency in dye sensitized solar cells.

PubMed

Khan, Javid; Gu, Jiuwang; He, Shiman; Li, Xiaohui; Ahmed, Gulzar; Liu, Zhongwu; Akhtar, Muhammad Nadeem; Mai, Wenjie; Wu, Mingmei

2017-07-20

A tri-layered photoelectrode for dye-sensitized solar cells (DSSCs) is assembled using single crystal hollow TiO 2 nanoparticles (HTNPs), sub-micro hollow TiO 2 mesospheres (SHTMSs) and hierarchical TiO 2 microspheres (HTMSs). The bottom layer composed of single crystal hollow TiO 2 nanoparticles serves to absorb dye molecules, harvest light due to its hollow structure and keep a better mechanical contact with FTO conducting glass; the middle layer consisting of sub-micro hollow mesospheres works as a multifunctional layer due to its high dye adsorption ability, strong light trapping and scattering ability and slow recombination rates; and the top layer consisting of hierarchical microspheres enhances light scattering. The DSSCs made of photoanodes with a tripartite-layer structure (Film 4) show a superior photoconversion efficiency (PCE) of 9.24%, which is 7.4% higher than a single layered photoanode composed of HTNPs (Film 1: 8.90%), 4.6% higher than a double layer-based electrode consisting of HTNPs and SHTMSs (Film 2: 9.03%) and 2.6% higher than a double layer-based electrode made of HTNPs and HTMSs (Film 3: 9.11%). The significant improvements in the PCE for tri-layered TiO 2 photoanodes are mainly because of the combined effects of their higher light scattering ability, long electron lifetime, fast electron transport rate, efficient charge collection and a considerable surface area with high dye-loading capability. This study confirms that the facile tri-layered photoanode is an interesting structure for high-efficiency DSSCs.

A comparative study between titania and zirconia as material for scattering layer in dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Nursam, N. M.; Hidayat, J.; Shobih; Rosa, E. S.; Pranoto, L. M.

2018-04-01

The photoanode of dye-sensitized solar cells (DSSC) is typically composed of nanocrystalline titania (TiO2) layer that has been sensitized with light-absorbing dye molecules. Large portion of the light, however, could not be efficiently absorbed due to some physical reasons, such as TiO2 crystal size (typically 10-25 nm) that makes the photoanode remains partially transparent to the visible region in the solar spectrum. One of the ways to improve the light harvesting efficiency in DSSC could be achieved by employing an additional scattering layer over the TiO2 electron transport material. In this contribution, we evaluate the effect of light scattering properties on the performance of DSSC. Specifically, the light scattering properties provided from two different scattering materials, i.e. additional TiO2 scattering layer and zirconia (ZrO2) scattering layer, were compared. Both layers were deposited using screen printing technique under the same condition on top of 8 µm thick TiO2 photoanode layer. All samples subsequently received the same thermal annealing treatment at 500 °C and sensitized with ruthenium-based synthetic dyes. Our results revealed that the thickness of the scattering layer for both TiO2 and ZrO2 had a significant effect on the solar cell performance. The best photoconversion efficiency was achieved by samples that were coated with one screen-printing cycle, giving an overall efficiency of 3.50 % and 4.02% for TiO2 and ZrO2, respectively.

Highly Functional TNTs with Superb Photocatalytic, Optical, and Electronic Performance Achieving Record PV Efficiency of 10.1% for 1D-Based DSSCs.

PubMed

Qadir, Muhammad Bilal; Li, Yuewen; Sahito, Iftikhar Ali; Arbab, Alvira Ayoub; Sun, Kyung Chul; Mengal, Naveed; Memon, Anam Ali; Jeong, Sung Hoon

2016-09-01

Different nanostructures of TiO2 play an important role in the photocatalytic and photoelectronic applications. TiO2 nanotubes (TNTs) have received increasing attention for these applications due to their unique physicochemical properties. Focusing on highly functional TNTs (HF-TNTs) for photocatalytic and photoelectronic applications, this study describes the facile hydrothermal synthesis of HF-TNTs by using commercial and cheaper materials for cost-effective manufacturing. To prove the functionality and applicability, these TNTs are used as scattering structure in dye-sensitized solar cells (DSSCs). Photocatalytic, optical, Brunauer-Emmett-Teller (BET), electrochemical impedance spectrum, incident-photon-to-current efficiency, and intensity-modulated photocurrent spectroscopy/intensity-modulated photovoltage spectroscopy characterizations are proving the functionality of HF-TNTs for DSSCs. HF-TNTs show 50% higher photocatalytic degradation rate and also 68% higher dye loading ability than conventional TNTs (C-TNTs). The DSSCs having HF-TNT and its composite-based multifunctional overlayer show effective light absorption, outstanding light scattering, lower interfacial resistance, longer electron lifetime, rapid electron transfer, and improved diffusion length, and consequently, J SC , quantum efficiency, and record photoconversion efficiency of 10.1% using commercial N-719 dye is achieved, for 1D-based DSSCs. These new and highly functional TNTs will be a concrete fundamental background toward the development of more functional applications in fuel cells, dye-sensitized solar cells, Li-ion batteries, photocatalysis process, ion-exchange/adsorption process, and photoelectrochemical devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Guide to Computed Tomography System Specifications

DTIC Science & Technology

1990-08-01

particularly where anomalies are not known or expected, where nonimaging measurements of deviations from a norm defy experience or expectation, or...point. 2.9 Archival Requirements Archival requirements usually involve hardcopy, tape, and/or optical disk. These dictate a small subsystem choice, but...some kind of scintillating X-ray crystal, e.g., cadmium tungstate or bismuth germanate that is optically coupled to a photoconversion device like a

Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells.

PubMed

Hsieh, Chien-Kuo; Tsai, Ming-Chi; Yen, Ming-Yu; Su, Ching-Yuan; Chen, Kuei-Fu; Ma, Chen-Chi M; Chen, Fu-Rong; Tsai, Chuen-Horng

2012-03-28

We synthesized platelet graphitic-nanofibres (GNFs) directly onto FTO glass and applied this forest of platelet GNFs as a highly porous structural counter-electrode in dye-sensitized solar cells (DSSCs). We investigated the electrochemical properties of counter-electrodes made from the highly porous structural GNFs and the photoconversion performance of the cells made with these electrodes.

Infra-red photoresponse of mesoscopic NiO-based solar cells sensitized with PbS quantum dot

PubMed Central

Raissi, Mahfoudh; Pellegrin, Yann; Jobic, Stéphane; Boujtita, Mohammed; Odobel, Fabrice

2016-01-01

Sensitized NiO based photocathode is a new field of investigation with increasing scientific interest in relation with the development of tandem dye-sensitized solar cells (photovoltaic) and dye-sensitized photoelectrosynthetic cells (solar fuel). We demonstrate herein that PbS quantum dots (QDs) represent promising inorganic sensitizers for NiO-based quantum dot-sensitized solar cells (QDSSCs). The solar cell sensitized with PbS quantum dot exhibits significantly higher photoconversion efficiency than solar cells sensitized with a classical and efficient molecular sensitizer (P1 dye = 4-(Bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)-benzoic acid). Furthermore, the system features an IPCE (Incident Photon-to-Current Efficiency) spectrum that spreads into the infra-red region, reaching operating wavelengths of 950 nm. The QDSSC photoelectrochemical device works with the complexes tris(4,4′-ditert-butyl-2,2′-bipyridine)cobalt(III/II) redox mediators, underscoring the formation of a long-lived charge-separated state. The electrochemical impedance spectrocopy measurements are consistent with a high packing of the QDs upon the NiO surface, the high density of which limits the access of the electrolyte and results in favorable light absorption cross-sections and a significant hole lifetime. These notable results highlight the potential of NiO-based photocathodes sensitized with quantum dots for accessing and exploiting the low-energy part of the solar spectrum in photovoltaic and photocatalysis applications. PMID:27125454

Enhanced photocatalytic and photoelectrochemical activities of reduced TiO 2-x /BiOCl heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Rongrong; Zeng, Xiaoqiao; Ma, Lu

2016-04-01

A key issue to design highly efficient photoelectrodes for hydrogen production is how to prohibit the rapid carrier recombination. In order to use the visible light and reduce the recombination of electrons and holes, reduced TiO 2-x/BiOCl heterojunctions are successfully synthesized and the photoelectrodes are assembled in this work. The effects of various Bi/Ti molar ratios on the structural, morphological, optical, photoelectrochemical and photocatalytic activities of the resultant samples are investigated systematically. The TiO 2-x nanoparticles contain Ti 3+, Ti 2+, and oxygen vacancies (Ov), while the BiOCl nanosheets exposed {001} facet. Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS) results indicatemore » that the existence of Ti 3+, Ti 2+ and Ov expand the light-response range. Linear scan voltammetry and electrochemical impedance spectroscopy results indicate that more efficient electron transportation is presented in the heterojunctions with the appropriate Bi/Ti molar ratio. Consequently, the reduced TiO 2-x/BiOCl heterojunction with the most appropriate Bi/Ti molar ratio exhibits a high photocurrent density of 0.755 mA cm -2 with photoconversion efficiency up to 0.634%, 10.5 and 22.6 times larger than that of pure TiO 2 and BiOCl. Furthermore, this heterojunction exhibit 48.38 and 12.54 times enhancement for the visible-light decomposition of rhodamine B compared with pure TiO 2 and BiOCl.« less

All-solid-state Z-scheme system arrays of Fe2V4O13/RGO/CdS for visible light-driving photocatalytic CO2 reduction into renewable hydrocarbon fuel.

PubMed

Li, Ping; Zhou, Yong; Li, Haijin; Xu, Qinfeng; Meng, Xianguang; Meng, Xiangguang; Wang, Xiaoyong; Xiao, Min; Zou, Zhigang

2015-01-14

An all-solid-state Z-scheme system array consisting of an Fe2V4O13 nanoribbon (NR)/reduced graphene oxide (RGO)/CdS nanoparticle grown on the stainless-steel mesh was rationally designed for photoconversion of gaseous CO2 into renewable hydrocarbon fuels (methane: CH4).

Photoconversion of gasified organic materials into biologically-degradable plastics

DOEpatents

Weaver, P.F.; Pinching Maness.

1993-10-05

A process is described for converting organic materials (such as biomass wastes) into a bioplastic suitable for use as a biodegradable plastic. In a preferred embodiment the process involves thermally gasifying the organic material into primarily carbon monoxide and hydrogen, followed by photosynthetic bacterial assimilation of the gases into cell material. The process is ideally suited for waste recycling and for production of useful biodegradable plastic polymer. 3 figures.

Photoconversion of gasified organic materials into biologically-degradable plastics

DOEpatents

Weaver, Paul F.; Maness, Pin-Ching

1993-01-01

A process is described for converting organic materials (such as biomass wastes) into a bioplastic suitable for use as a biodegradable plastic. In a preferred embodiment the process involves thermally gasifying the organic material into primarily carbon monoxide and hydrogen, followed by photosynthetic bacterial assimilation of the gases into cell material. The process is ideally suited for waste recycling and for production of useful biodegradable plastic polymer.

Tracking protein dynamics with photoconvertible Dendra2 on spinning disk confocal systems.

PubMed

Woods, Elena; Courtney, Jane; Scholz, Dimitri; Hall, William W; Gautier, Virginie W

2014-12-01

Understanding the dynamic properties of cellular proteins in live cells and in real time is essential to delineate their function. In this context, we introduce the Fluorescence Recovery After Photobleaching-Photoactivation unit (Andor) combined with the Nikon Eclipse Ti E Spinning Disk (Andor) confocal microscope as an advantageous and robust platform to exploit the properties of the Dendra2 photoconvertible fluorescent protein (Evrogen) and analyse protein subcellular trafficking in living cells. A major advantage of the spinning disk confocal is the rapid acquisition speed, enabling high temporal resolution of cellular processes. Furthermore, photoconversion and imaging are less invasive on the spinning disk confocal as the cell exposition to illumination power is reduced, thereby minimizing photobleaching and increasing cell viability. We have tested this commercially available platform using experimental settings adapted to track the migration of fast trafficking proteins such as UBC9, Fibrillarin and have successfully characterized their differential motion between subnuclear structures. We describe here step-by-step procedures, with emphasis on cellular imaging parameters, to successfully perform the dynamic imaging and photoconversion of Dendra2-fused proteins at high spatial and temporal resolutions necessary to characterize the trafficking pathways of proteins. © 2014 The Authors. Journal of Microscopy published by John Wiley & Sons, Ltd on behalf of Royal Microscopical Society.

Impedance analysis of PbS colloidal quantum dot solar cells with different ZnO nanowire lengths

NASA Astrophysics Data System (ADS)

Fukuda, Takeshi; Takahashi, Akihiro; Wang, Haibin; Takahira, Kazuya; Kubo, Takaya; Segawa, Hiroshi

2018-03-01

The photoconversion efficiency of colloidal quantum dot (QD) solar cells has been markedly improved by optimizing the surface passivation and device structure, and details of device physics are now under investigation. In this study, we investigated the resistance and capacitance components at the ZnO/PbS-QD interface and inside a PbS-QD layer by measuring the impedance spectrum while the interface area was controlled by changing the ZnO nanowire length. By evaluating the dependence of optical intensity and DC bias voltage on the ZnO nanowire length, only the capacitance was observed to be influenced by the interface area, and this indicates that photoinduced carriers are generated at the surface of PbS-QD. In addition, since the capacitance is proportional to the surface area of the QD, the interface area can be evaluated from the capacitance. Finally, photovoltaic performance was observed to increase with increasing ZnO nanowire length owing to the large interface area, and this result is in good agreement with the capacitance measurement.

Performance of 7-cells Dye Sensitized Solar Module in Z-type Series Interconnection

NASA Astrophysics Data System (ADS)

Nur Anggraini, Putri; Muliani, Lia; Maulani Nursam, Natalita; Hidayat, Jojo

2018-01-01

Dye sensitized solar cells (DSSC) is becoming attractive research topic as third generation solar cells technology since it provides clean energy and low cost fabrication. In this study, DSSC was fabricated into module scale, which is important for practical applications. The module was prepared in sandwich structure consisting of TiO2 working electrode and Pt counter electrode on conductive substrate with an area of 100 mm x 100 mm, which was distributed into seven active cells. TiO2 paste was deposited on FTO glass as working electrode with a size of 10 mm x 98 mm per unit cell by screen printing method. Each cell was connected in Z-type series that able to produce high voltage. I - V measurement was applied in two methods consisting of laboratory testing using sun simulator under 500 W/m2 of illumination and outdoor testing using a digital multimeter under direct sunlight. The result shows that DSSC module has photoconversion efficiency of 1.08% and 1.17% for laboratory and outdoor testing, respectively. The module was also tested in three different times to monitor its stability performance.

Performance analysis of flexible DSSC with binder addition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muliani, Lia; Hidayat, Jojo; Anggraini, Putri Nur, E-mail: putri.nur.anggraini@gmail.com

2016-04-19

Flexible DSSC is one of modification of DSSC based on its substrate. Operating at low temperature, flexible DSSC requires a binder to improve particles interconnection. This research was done to compare the morphology and performance of flexible DSSC that was produced with binder-added and binder-free. TiO{sub 2} powder, butanol, and HCl were mixed for preparation of TiO{sub 2} paste. Small amount of titanium isopropoxide as binder was added into the mixture. TiO{sub 2} paste was deposited on ITO-PET plastic substrate with area of 1x1 cm{sup 2} by doctor blade method. Furthermore, SEM, XRD, and BET characterization were done to analyzemore » morphology and surface area of the TiO{sub 2} photoelectrode microstructures. Dyed TiO{sub 2} photoelectrode and platinum counter electrode were assembled and injected by electrolyte. In the last process, flexible DSSCs were illuminated by sun simulator to do J-V measurement. As a result, flexible DSSC containing binder showed higher performance with photoconversion efficiency of 0.31%.« less

Improvement of the photovoltaic parameters of perovskite solar cells using a reduced-graphene-oxide-modified titania layer and soluble copper phthalocyanine as a hole transporter.

PubMed

Nouri, Esmaiel; Mohammadi, Mohammad Reza; Xu, Zong-Xiang; Dracopoulos, Vassilios; Lianos, Panagiotis

2018-01-24

Functional perovskite solar cells can be made by using a simple, inexpensive and stable soluble tetra-n-butyl-substituted copper phthalocyanine (CuBuPc) as a hole transporter. In the present study, TiO 2 /reduced graphene oxide (T/RGO) hybrids were synthesized via an in situ solvothermal process and used as electron acceptor/transport mediators in mesoscopic perovskite solar cells based on soluble CuBuPc as a hole transporter and on graphene oxide (GO) as a buffer layer. The impact of the RGO content on the optoelectronic properties of T/RGO hybrids and on the solar cell performance was studied, suggesting improved electron transport characteristics and photovoltaic parameters. An enhanced electron lifetime and recombination resistance led to an increase in the short circuit current density, open circuit voltage and fill factor. The device based on a T/RGO mesoporous layer with an optimal RGO content of 0.2 wt% showed 22% higher photoconversion efficiency and higher stability compared with pristine TiO 2 -based devices.

Interfacial Charge-Carrier Trapping in CH3NH3PbI3-Based Heterolayered Structures Revealed by Time-Resolved Photoluminescence Spectroscopy.

PubMed

Yamada, Yasuhiro; Yamada, Takumi; Shimazaki, Ai; Wakamiya, Atsushi; Kanemitsu, Yoshihiko

2016-06-02

The fast-decaying component of photoluminescence (PL) under very weak pulse photoexcitation is dominated by the rapid relaxation of the photoexcited carriers into a small number of carrier-trapping defect states. Here, we report the subnanosecond decay of the PL under excitation weaker than 1 nJ/cm(2) both in CH3NH3PbI3-based heterostructures and bare thin films. The trap-site density at the interface was evaluated on the basis of the fluence-dependent PL decay profiles. It was found that high-density defects determining the PL decay dynamics are formed near the interface between CH3NH3PbI3 and the hole-transporting Spiro-OMeTAD but not at the CH3NH3PbI3/TiO2 interface and the interior regions of CH3NH3PbI3 films. This finding can aid the fabrication of high-quality heterointerfaces, which are required improving the photoconversion efficiency of perovskite-based solar cells.

Characterizing the multiexciton fission intermediate in pentacene through 2D spectral modeling

NASA Astrophysics Data System (ADS)

Tempelaar, Roel; Reichman, David

Singlet fission, the molecular process in which a singlet excitation splits into two triplet excitons, holds promise to enhance the photoconversion efficiency of solar cells. Despite advances in both experiments and theory, a detailed understanding of this process remains lacking. In particular, the nature of the correlated triplet pair state (TT), which acts as a fission intermediate, remains obscure. Recently, 2D spectroscopy was shown to allow for the direct detection of the extremely weak optical transition between TT and the ground state through coherently prepared vibrational wavepackets in the associated electronic potentials. Here, we present a microscopic model of singlet fission which includes an exact quantum treatment of such vibrational modes. Our model reproduces the reported 2D spectra of pentacene, while providing a detailed insight into the anatomy of TT. As such, our results form a stepping stone towards understanding singlet fission at a molecular level, while bridging the gap between the wealth of recent theoretical works on one side and experimental measurements on the other. R.T. acknowledges The Netherlands Organisation for Scientific Research NWO for support through a Rubicon Grant.

Photoelectrochemical (PEC) studies on Cu2SnS3 (CTS) thin films deposited by chemical bath deposition method.

PubMed

Shelke, H D; Lokhande, A C; Kim, J H; Lokhande, C D

2017-11-15

Cu 2 SnS 3 (CTS) thin films have been successfully deposited on a cost-effective stainless steel substrate by simple and inexpensive chemical bath deposition (CBD) method. The films are deliberated in provisos of their structural, morphological, optical and photoelectrochemical (PEC) properties before and after annealing treatment, using various physico-chemical techniques. The XRD studies showed the formation of triclinic phase of CTS films with nanocrystalline structure. Also, the crystallinity is enhanced with annealing and the secondary phase of Cu 2 S observed. Raman analysis confirmed the formation of CTS compound with secondary Cu 2 S phase. The SEM images also discovered mostly tiny spherical grains and significant progress in the size of grains after annealing. The films possess direct transitions with band gap energies of 1.35eV and 1.31eV before and after annealing, respectively. The improved photoconversion efficiency of CTS thin film based PEC cell is explained with the help of theoretical modeling of energy band diagram and correspondent circuit model of the impedance spectra. Copyright © 2017 Elsevier Inc. All rights reserved.

Quantum Dot Sensitized Solar Cells Based on TiO2/AgInS2

NASA Astrophysics Data System (ADS)

Pawar, Sachin A.; Jeong, Jae Pil; Patil, Dipali S.; More, Vivek M.; Lee, Rochelle S.; Shin, Jae Cheol; Choi, Won Jun

2018-05-01

Quantum dot heterojunctions with type-II band alignment can efficiently separate photogenerated electron-hole pairs and, hence, are useful for solar cell studies. In this study, a quantum dot sensitized solar cell (QDSSC) made of TiO2/AgInS2 is achieved to boost the photoconversion efficiency for the TiO2-based system by varying the AgInS2 layer's thickness. The TiO2 nanorods array film is prepared by using a simple hydrothermal technique. The formation of a AgInS2 QD-sensitized TiO2-nanorod photoelectrode is carried out by successive ionic layer adsorption and reaction (SILAR) technique. The effect of the QD layer on the performance of the solar cell is studied by varying the SILAR cycles of the QD coating. The synthesized electrode materials are characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy and solar cell performances. The results indicate that the nanocrystals have effectively covered the outer surfaces of the TiO2 nanorods. The interfacial structure of quantum dots (QDs)/TiO2 is also investigated, and the growth interface is verified. A careful comparison between TiO2/AgInS2 sensitized cells reveals that the trasfer of electrons and hole proceeds efficiently, the recombination is suppressed for the optimum thickness of the QD layer and light from the entire visible spectrum is utilised. Under AM 1.5G illumination, a high photocurrent of 1.36 mAcm-2 with an improved power conversion efficiency of 0.48% is obtained. The solar cell properties of our photoanodes suggest that the TiO2 nanorod array films co-sensitized by AgInS2 nanoclusters have potential applications in solar cells.

Solid state perovskite solar modules by vacuum-vapor assisted sequential deposition on Nd:YVO₄ laser patterned rutile TiO₂ nanorods.

PubMed

Fakharuddin, Azhar; Palma, Alessandro L; Di Giacomo, Francesco; Casaluci, Simone; Matteocci, Fabio; Wali, Qamar; Rauf, Muhammad; Di Carlo, Aldo; Brown, Thomas M; Jose, Rajan

2015-12-11

The past few years have witnessed remarkable progress in solution-processed methylammonium lead halide (CH3NH3PbX3, X = halide) perovskite solar cells (PSCs) with reported photoconversion efficiency (η) exceeding 20% in laboratory-scale devices and reaching up to 13% in their large area perovskite solar modules (PSMs). These devices mostly employ mesoporous TiO2 nanoparticles (NPs) as an electron transport layer (ETL) which provides a scaffold on which the perovskite semiconductor can grow. However, limitations exist which are due to trap-limited electron transport and non-complete pore filling. Herein, we have employed TiO2 nanorods (NRs), a material offering a two-fold higher electronic mobility and higher pore-filing compared to their particle analogues, as an ETL. A crucial issue in NRs' patterning over substrates is resolved by using precise Nd:YVO4 laser ablation, and a champion device with η ∼ 8.1% is reported via a simple and low cost vacuum-vapor assisted sequential processing (V-VASP) of a CH3NH3PbI3 film. Our experiments showed a successful demonstration of NRs-based PSMs via the V-VASP technique which can be applied to fabricate large area modules with a pin-hole free, smooth and dense perovskite layer which is required to build high efficiency devices.

Electrochemically deposited Cu2O cubic particles on boron doped diamond substrate as efficient photocathode for solar hydrogen generation

NASA Astrophysics Data System (ADS)

Mavrokefalos, Christos K.; Hasan, Maksudul; Rohan, James F.; Compton, Richard G.; Foord, John S.

2017-06-01

Herein, we report a novel photocathode for the water splitting reaction. The electrochemical deposition of Cu2O particles on boron doped diamond (BDD) electrodes and the subsequent decoration with NiO nanoparticles by a dip coating method to act as co-catalyst for hydrogen evolution reaction is described. The morphology analysis by scanning electron microscope (SEM) revealed that Cu2O particles are cubic and decorated sporadically with NiO nanoparticles. X-ray photoelectron spectroscopy (XPS) confirmed the electronic interaction at the interface between Cu2O and NiO through a binding energy shift of the main Cu 2p peak. The photoelectrochemical (PEC) performance of NiO-Cu2O/BDD showed a much higher current density (-0.33 mA/cm2) and photoconversion efficiency (0.28%) compared to the unmodified Cu2O/BDD electrode, which are only -0.12 mA/cm2 and 0.06%, respectively. The enhancement in PEC performance is attributable to the synergy of NiO as an electron conduction mediator leading to the enhanced charge separation and transfer to the reaction interface for hydrogen evolution as evidenced by electrochemical impedance spectroscopy (EIS) and charge carrier density calculation. Stability tests showed that the NiO nanoparticles loading content on Cu2O surface is a crucial parameter in this regard.

Enabling Earth-Abundant Pyrite (FeS2) Semiconductor Nanostructures for High Performance Photovoltaic Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Song

2014-11-18

This project seeks to develop nanostructures of iron pyrite, an earth-abundant semiconductor, to enable their applications in high-performance photovoltaic (PV) devices. Growth of high purity iron pyrite nanostructures (nanowires, nanorods, and nanoplates), as well as iron pyrite thin films and single crystals, has been developed and their structures characterized. These structures have been fundamentally investigated to understand the origin of the low solar energy conversion efficiency of iron pyrite and various passivation strategies and doping approaches have been explored in order to improve it. By taking advantage of the high surface-to-bulk ratio in nanostructures and effective electrolyte gating, we fullymore » characterized both the surface inversion and bulk electrical transport properties for the first time through electrolyte-gated Hall measurements of pyrite nanoplate devices and show that pyrite is n-type in the bulk and p-type near the surface due to strong inversion, which has important consequences to using nanocrystalline pyrite for efficient solar energy conversion. Furthermore, through a comprehensive investigation on n-type iron pyrite single crystals, we found the ionization of high-density bulk deep donor states, likely resulting from bulk sulfur vacancies, creates a non-constant charge distribution and a very narrow surface space charge region that limits the total barrier height, thus satisfactorily explains the limited photovoltage and poor photoconversion efficiency of iron pyrite single crystals. These findings suggest new ideas on how to improve single crystal pyrite and nanocrystalline or polycrystalline pyrite films to enable them for high performance solar applications.« less

X-ray Free Electron Laser Determination of Crystal Structures of Dark and Light States of a Reversibly Photoswitching Fluorescent Protein at Room Temperature

PubMed Central

Hutchison, Christopher D. M.; Cordon-Preciado, Violeta; Morgan, Rhodri M. L.; Dorlhiac, Gabriel; Sanchez-Gonzalez, Alvaro; Fitzpatrick, Ann; Fare, Clyde; Marangos, Jon P.; Hunter, Mark S.; DePonte, Daniel P.; Boutet, Sébastien; Owada, Shigeki; Tanaka, Rie; Tono, Kensuke; Iwata, So; van Thor, Jasper J.

2017-01-01

The photochromic fluorescent protein Skylan-NS (Nonlinear Structured illumination variant mEos3.1H62L) is a reversibly photoswitchable fluorescent protein which has an unilluminated/ground state with an anionic and cis chromophore conformation and high fluorescence quantum yield. Photo-conversion with illumination at 515 nm generates a meta-stable intermediate with neutral trans-chromophore structure that has a 4 h lifetime. We present X-ray crystal structures of the cis (on) state at 1.9 Angstrom resolution and the trans (off) state at a limiting resolution of 1.55 Angstrom from serial femtosecond crystallography experiments conducted at SPring-8 Angstrom Compact Free Electron Laser (SACLA) at 7.0 keV and 10.5 keV, and at Linac Coherent Light Source (LCLS) at 9.5 keV. We present a comparison of the data reduction and structure determination statistics for the two facilities which differ in flux, beam characteristics and detector technologies. Furthermore, a comparison of droplet on demand, grease injection and Gas Dynamic Virtual Nozzle (GDVN) injection shows no significant differences in limiting resolution. The photoconversion of the on- to the off-state includes both internal and surface exposed protein structural changes, occurring in regions that lack crystal contacts in the orthorhombic crystal form. PMID:28880248

Relations between the efficiency, power and dissipation for linear irreversible heat engine at maximum trade-off figure of merit

NASA Astrophysics Data System (ADS)

Iyyappan, I.; Ponmurugan, M.

2018-03-01

A trade of figure of merit (\\dotΩ ) criterion accounts the best compromise between the useful input energy and the lost input energy of the heat devices. When the heat engine is working at maximum \\dotΩ criterion its efficiency increases significantly from the efficiency at maximum power. We derive the general relations between the power, efficiency at maximum \\dotΩ criterion and minimum dissipation for the linear irreversible heat engine. The efficiency at maximum \\dotΩ criterion has the lower bound \

Maximum efficiency of ideal heat engines based on a small system: correction to the Carnot efficiency at the nanoscale.

PubMed

Quan, H T

2014-06-01

We study the maximum efficiency of a heat engine based on a small system. It is revealed that due to the finiteness of the system, irreversibility may arise when the working substance contacts with a heat reservoir. As a result, there is a working-substance-dependent correction to the Carnot efficiency. We derive a general and simple expression for the maximum efficiency of a Carnot cycle heat engine in terms of the relative entropy. This maximum efficiency approaches the Carnot efficiency asymptotically when the size of the working substance increases to the thermodynamic limit. Our study extends Carnot's result of the maximum efficiency to an arbitrary working substance and elucidates the subtlety of thermodynamic laws in small systems.

CONJUGATED POLYMERS AND POLYELECTROLYTES IN SOLAR PHOTOCONVERSION, Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schanze, Kirk S

2014-08-05

This DOE-supported program investigated the fundamental properties of conjugated polyelectrolytes, with emphasis placed on studies of excited state energy transport, self-assembly into conjugated polyelectroyte (CPE) based films and colloids, and exciton transport and charge injection in CPE films constructed atop wide bandgap semiconductors. In the most recent grant period we have also extended efforts to examine the properties of low-bandgap donor-acceptor conjugated polyelectrolytes that feature strong visible light absorption and the ability to adsorb to metal-oxide interfaces.

Photoconversion of organic materials into single-cell protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weaver, P.F.

A process is described for converting organic materials (such as biomass wastes) into sterile, high-grade bacterial protein suitable for use an animal feed or human food supplements. In a preferred embodiment the process involves thermally gasifying the organic material into primarily carbon monoxide, hydrogen and nitrogen products, followed by photosynthetic bacterial assimilation of the gases into cell material, which can be high as 65% protein. The process is ideally suited for waste recycling and for food production under zero-gravity or extra-terrestrial conditions.

Photoconversion of organic materials into single-cell protein

DOEpatents

Weaver, Paul F.

2001-01-01

A process is described for converting organic materials (such as biomass wastes) into sterile, high-grade bacterial protein suitable for use an animal feed or human food supplements. In a preferred embodiment the process involves thermally gasifying the organic material into primarily carbon monoxide, hydrogen and nitrogen products, followed by photosynthetic bacterial assimilation of the gases into cell material, which can be as high as 65% protein. The process is ideally suited for waste recycling and for food production under zero-gravity or extra-terrestrial conditions.

Photocatalytic conversion of CO(2) into renewable hydrocarbon fuels: state-of-the-art accomplishment, challenges, and prospects.

PubMed

Tu, Wenguang; Zhou, Yong; Zou, Zhigang

2014-07-16

Photocatalytic reduction of CO2 into hydrocarbon fuels, an artificial photosynthesis, is based on the simulation of natural photosynthesis in green plants, whereby O2 and carbohydrates are produced from H2 O and CO2 using sunlight as an energy source. It couples the reductive half-reaction of CO2 fixation with a matched oxidative half-reaction such as water oxidation, to achieve a carbon neutral cycle, which is like killing two birds with one stone in terms of saving the environment and supplying future energy. The present review provides an overview and highlights recent state-of-the-art accomplishments of overcoming the drawback of low photoconversion efficiency and selectivity through the design of highly active photocatalysts from the point of adsorption of reactants, charge separation and transport, light harvesting, and CO2 activation. It specifically includes: i) band-structure engineering, ii) nanostructuralization, iii) surface oxygen vacancy engineering, iv) macro-/meso-/microporous structuralization, v) exposed facet engineering, vi) co-catalysts, vii) the development of a Z-scheme system. The challenges and prospects for future development of this field are also present. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

2D layered insulator hexagonal boron nitride enabled surface passivation in dye sensitized solar cells.

PubMed

Shanmugam, Mariyappan; Jacobs-Gedrim, Robin; Durcan, Chris; Yu, Bin

2013-11-21

A two-dimensional layered insulator, hexagonal boron nitride (h-BN), is demonstrated as a new class of surface passivation materials in dye-sensitized solar cells (DSSCs) to reduce interfacial carrier recombination. We observe ~57% enhancement in the photo-conversion efficiency of the DSSC utilizing h-BN coated semiconductor TiO2 as compared with the device without surface passivation. The h-BN coated TiO2 is characterized by Raman spectroscopy to confirm the presence of highly crystalline, mixed monolayer/few-layer h-BN nanoflakes on the surface of TiO2. The passivation helps to minimize electron-hole recombination at the TiO2/dye/electrolyte interfaces. The DSSC with h-BN passivation exhibits significantly lower dark saturation current in the low forward bias region and higher saturation in the high forward bias region, respectively, suggesting that the interface quality is largely improved without impeding carrier transport at the material interface. The experimental results reveal that the emerging 2D layered insulator could be used for effective surface passivation in solar cell applications attributed to desirable material features such as high crystallinity and self-terminated/dangling-bond-free atomic planes as compared with high-k thin-film dielectrics.

The equivalence of minimum entropy production and maximum thermal efficiency in endoreversible heat engines.

PubMed

Haseli, Y

2016-05-01

The objective of this study is to investigate the thermal efficiency and power production of typical models of endoreversible heat engines at the regime of minimum entropy generation rate. The study considers the Curzon-Ahlborn engine, the Novikov's engine, and the Carnot vapor cycle. The operational regimes at maximum thermal efficiency, maximum power output and minimum entropy production rate are compared for each of these engines. The results reveal that in an endoreversible heat engine, a reduction in entropy production corresponds to an increase in thermal efficiency. The three criteria of minimum entropy production, the maximum thermal efficiency, and the maximum power may become equivalent at the condition of fixed heat input.

On the missing links in quantum dot solar cells: a DFT study on fluorophore oxidation and reduction processes in sensitized solar cells.

PubMed

Muzakir, Saifful Kamaluddin; Alias, Nabilah; Yusoff, Mashitah M; Jose, Rajan

2013-10-14

The possibility of achieving many electrons per absorbed photon of sufficient energy by quantum dots (QDs) drives the motivation to build high performance quantum dot solar cells (QDSCs). Although performance of dye-sensitized solar cells (DSCs), with similar device configuration as that of QDSCs, has significantly improved in the last two decades QDSCs are yet to demonstrate impressive device performances despite the remarkable features of QDs as light harvesters. We investigated the fundamental differences in the optical properties of QDs and dyes using DFT calculations to get insights on the inferior performance of QDSCs. The CdSe QDs and the ruthenium bipyridyl dicarboxylic acid dye (N3) were used as typical examples in this study. Based on a generalized equation of state correlating material properties and photoconversion efficiency, we calculated ground and excited state properties of these absorbers at the B3LYP/lanl2dz level of DFT and analyzed them on the basis of the device performance. Five missing links have been identified in the study which provides numerous insights into building high efficiency QDSCs. They are (i) fundamental differences in the emitting states of the QDs in the strong and weak confinement regimes were observed, which explained successfully the performance differences; (ii) the crucial role of bifunctional ligands that bind the QDs and the photo-electrode was identified; in most cases use of bifunctional ligands does not lead to a QD enabled widening of the absorption of the photo-electrode; (iii) wide QDs size distribution further hinders efficient electron injections; (iv) wide absorption cross-section of QDs favours photon harvesting; and (v) the role of redox potential of the electrolyte in the QD reduction process.

Intersubunit distances in full-length, dimeric, bacterial phytochrome Agp1, as measured by pulsed electron-electron double resonance (PELDOR) between different spin label positions, remain unchanged upon photoconversion.

PubMed

Kacprzak, Sylwia; Njimona, Ibrahim; Renz, Anja; Feng, Juan; Reijerse, Edward; Lubitz, Wolfgang; Krauss, Norbert; Scheerer, Patrick; Nagano, Soshichiro; Lamparter, Tilman; Weber, Stefan

2017-05-05

Bacterial phytochromes are dimeric light-regulated histidine kinases that convert red light into signaling events. Light absorption by the N-terminal photosensory core module (PCM) causes the proteins to switch between two spectrally distinct forms, Pr and Pfr, thus resulting in a conformational change that modulates the C-terminal histidine kinase region. To provide further insights into structural details of photoactivation, we investigated the full-length Agp1 bacteriophytochrome from the soil bacterium Agrobacterium fabrum using a combined spectroscopic and modeling approach. We generated seven mutants suitable for spin labeling to enable application of pulsed EPR techniques. The distances between attached spin labels were measured using pulsed electron-electron double resonance spectroscopy to probe the arrangement of the subunits within the dimer. We found very good agreement of experimental and calculated distances for the histidine-kinase region when both subunits are in a parallel orientation. However, experimental distance distributions surprisingly showed only limited agreement with either parallel- or antiparallel-arranged dimer structures when spin labels were placed into the PCM region. This observation indicates that the arrangements of the PCM subunits in the full-length protein dimer in solution differ significantly from that in the PCM crystals. The pulsed electron-electron double resonance data presented here revealed either no or only minor changes of distance distributions upon Pr-to-Pfr photoconversion. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Phase aggregation and morphology effects on nanocarbon optoelectronics.

PubMed

Xie, Yu; Lohrman, Jessica; Ren, Shenqiang

2014-12-05

Controllable morphology and interfacial interactions within bulk heterojunction nanostructures show significant effects on optoelectronic device applications. In this study, a nanocarbon heterojunction, consisting of single-walled carbon nanotubes (s-SWCNTs) and fullerene derivatives, is reported by assembling/blending its structures through solution-based processes. A uniform and dense graphene oxide hole transport layer is used to facilitate the photoconversion at a near infrared (NIR) wavelength. Effective interfacial interaction between the s-SWCNTs and fullerene is suggested by the redshifted photoabsorption and nanoscale/micron-scale fluorescence, which is associated with self-assembled nanocarbon morphology.

Genetic Evidence That the Red-Absorbing Form of Phytochrome B Modulates Gravitropism in Arabidopsis thaliana.

PubMed Central

Liscum, E.; Hangarter, R. P.

1993-01-01

Hypocotyls of dark-grown Arabidopsis seedlings exhibit strong negative gravitropism, whereas in red light, gravitropism is strongly reduced. Red/far-red light-pulse experiments and analysis of specific phytochrome-deficient mutants indicate that the red-absorbing (Pr) form of phytochrome B regulates normal hypocotyl gravitropism in darkness, and depletion of Pr by photoconversion to the far-red-absorbing form attenuates hypocotyl gravitropism. These studies provide genetic evidence that the Pr form of phytochrome has an active function in plant development. PMID:12231913

Co-Optima Targets Maximum Transportation Sector Efficiency, Energy

Science.gov Websites

Independence and Industry Growth | News | NREL Co-Optima Targets Maximum Transportation Sector Efficiency, Energy Independence and Industry Growth Co-Optima Targets Maximum Transportation Sector Efficiency, Energy Independence and Industry Growth February 6, 2017 Report cover on Co-Optima Year in Review

Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway.

PubMed

Brayshaw, Simon K; Schiffers, Stephanie; Stevenson, Anna J; Teat, Simon J; Warren, Mark R; Bennett, Robert D; Sazanovich, Igor V; Buckley, Alastair R; Weinstein, Julia A; Raithby, Paul R

2011-04-11

We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Performance Analysis and Optimization of Concentrating Solar Thermoelectric Generator

NASA Astrophysics Data System (ADS)

Lamba, Ravita; Manikandan, S.; Kaushik, S. C.

2018-06-01

A thermodynamic model for a concentrating solar thermoelectric generator considering the Thomson effect combined with Fourier heat conduction, Peltier, and Joule heating has been developed and optimized in MATLAB environment. The temperatures at the hot and cold junctions of the thermoelectric generator were evaluated by solving the energy balance equations at both junctions. The effects of the solar concentration ratio, input electrical current, number of thermocouples, and electrical load resistance ratio on the power output and energy and exergy efficiencies of the system were studied. Optimization studies were carried out for the STEG system, and the optimum number of thermocouples, concentration ratio, and resistance ratio determined. The results showed that the optimum values of these parameters are different for conditions of maximum power output and maximum energy and exergy efficiency. The optimum values of the concentration ratio and load resistance ratio for maximum energy efficiency of 5.85% and maximum exergy efficiency of 6.29% were found to be 180 and 1.3, respectively, with corresponding power output of 4.213 W. Furthermore, at higher concentration ratio (C = 600), the optimum number of thermocouples was found to be 101 for maximum power output of 13.75 W, maximum energy efficiency of 5.73%, and maximum exergy efficiency of 6.16%. Moreover, the optimum number of thermocouple was the same for conditions of maximum power output and energy and exergy efficiency. The results of this study may provide insight for design of actual concentrated solar thermoelectric generator systems.

The maximum efficiency of nano heat engines depends on more than temperature

NASA Astrophysics Data System (ADS)

Woods, Mischa; Ng, Nelly; Wehner, Stephanie

Sadi Carnot's theorem regarding the maximum efficiency of heat engines is considered to be of fundamental importance in the theory of heat engines and thermodynamics. Here, we show that at the nano and quantum scale, this law needs to be revised in the sense that more information about the bath other than its temperature is required to decide whether maximum efficiency can be achieved. In particular, we derive new fundamental limitations of the efficiency of heat engines at the nano and quantum scale that show that the Carnot efficiency can only be achieved under special circumstances, and we derive a new maximum efficiency for others. A preprint can be found here arXiv:1506.02322 [quant-ph] Singapore's MOE Tier 3A Grant & STW, Netherlands.

Effects of acetylacetone on the photoconversion of pharmaceuticals in natural and pure waters.

PubMed

Zhang, Guoyang; Wu, Bingdang; Zhang, Shujuan

2017-06-01

Acetylacetone (AcAc) has proven to be a potent photo-activator in the degradation of color compounds. The effects of AcAc on the photochemical conversion of five colorless pharmaceuticals were for the first time investigated in both pure and natural waters with the UV/H 2 O 2 process as a reference. In most cases, AcAc played a similar role to H 2 O 2 . For example, AcAc accelerated the photodecomposition of carbamazepine, oxytetracycline, and tetracycline in pure water. Meanwhile, the toxicity of tetracyclines and carbamazepine were reduced to a similar extent to that in the UV/H 2 O 2 process. However, AcAc worked in a way different from that of H 2 O 2 . Based on the degradation kinetics, solvent kinetic isotope effect, and the inhibiting effect of O 2 , the underlying mechanisms for the degradation of pharmaceuticals in the UV/AcAc process were believed mainly to be direct energy transfer from excited AcAc to pharmaceuticals rather than reactive oxygen species-mediated reactions. In natural waters, dissolved organic matter (DOM) played a crucial role in the photoconversion of pharmaceuticals. The role of H 2 O 2 became negligible due to the scavenging effects of DOM and inorganic ions. Interestingly, in natural waters, AcAc first accelerated the photodecomposition of pharmaceuticals and then led to a dramatic reduction with the depletion of dissolved oxygen. Considering the natural occurrence of diketones, the results here point out a possible pathway in the fate and transport of pharmaceuticals in aquatic ecosystems. Copyright © 2017 Elsevier Ltd. All rights reserved.

An optical marker based on the UV-induced green-to-red photoconversion of a fluorescent protein

PubMed Central

Ando, Ryoko; Hama, Hiroshi; Yamamoto-Hino, Miki; Mizuno, Hideaki; Miyawaki, Atsushi

2002-01-01

We have cloned a gene encoding a fluorescent protein from a stony coral, Trachyphyllia geoffroyi, which emits green, yellow, and red light. The protein, named Kaede, includes a tripeptide, His-Tyr-Gly, that acts as a green chromophore that can be converted to red. The red fluorescence is comparable in intensity to the green and is stable under usual aerobic conditions. We found that the green-red conversion is highly sensitive to irradiation with UV or violet light (350–400 nm), which excites the protonated form of the chromophore. The excitation lights used to elicit red and green fluorescence do not induce photoconversion. Under a conventional epifluorescence microscope, Kaede protein expressed in HeLa cells turned red in a graded fashion in response to UV illumination; maximal illumination resulted in a 2,000-fold increase in the ratio of red-to-green signal. These color-changing properties provide a simple and powerful technique for regional optical marking. A focused UV pulse creates an instantaneous plane source of red Kaede within the cytosol. The red spot spreads rapidly throughout the cytosol, indicating its free diffusibility in the compartment. The extensive diffusion allows us to delineate a single neuron in a dense culture, where processes originating from many different somata are present. Illumination of a focused UV pulse onto the soma of a Kaede-expressing neuron resulted in filling of all processes with red fluorescence, allowing visualization of contact sites between the red and green neurons of interest. PMID:12271129

Real-Time and Accurate Identification of Single Oligonucleotide Photoisomers via an Aerolysin Nanopore.

PubMed

Hu, Zheng-Li; Li, Zi-Yuan; Ying, Yi-Lun; Zhang, Junji; Cao, Chan; Long, Yi-Tao; Tian, He

2018-04-03

Identification of the configuration for the photoresponsive oligonucleotide plays an important role in the ingenious design of DNA nanomolecules and nanodevices. Due to the limited resolution and sensitivity of present methods, it remains a challenge to determine the accurate configuration of photoresponsive oligonucleotides, much less a precise description of their photoconversion process. Here, we used an aerolysin (AeL) nanopore-based confined space for real-time determination and quantification of the absolute cis/ trans configuration of each azobenzene-modified oligonucleotide (Azo-ODN) with a single molecule resolution. The two completely separated current distributions with narrow peak widths at half height (<0.62 pA) are assigned to cis/ trans-Azo-ODN isomers, respectively. Due to the high current sensitivity, each isomer of Azo-ODN could be undoubtedly identified, which gives the accurate photostationary conversion values of 82.7% for trans-to- cis under UV irradiation and 82.5% for cis-to- trans under vis irradiation. Further real-time kinetic evaluation reveals that the photoresponsive rate constants of Azo-ODN from trans-to- cis and cis-to -trans are 0.43 and 0.20 min -1 , respectively. This study will promote the sophisticated design of photoresponsive ODN to achieve an efficient and applicable photocontrollable process.

An autonomous photosynthetic device in which all charge carriers derive from surface plasmons.

PubMed

Mubeen, Syed; Lee, Joun; Singh, Nirala; Krämer, Stephan; Stucky, Galen D; Moskovits, Martin

2013-04-01

Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO₂) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H₂ molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability.

Light-current-induced acceleration of degradation of methylammonium lead iodide perovskite solar cells

NASA Astrophysics Data System (ADS)

Xiang, Yuren; Zhang, Fan; He, Junjie; Lian, Jiarong; Zeng, Pengju; Song, Jun; Qu, Junle

2018-04-01

The photo-conversion efficiency of perovskite solar cells (PSCs) has been improved considerably in recent years, but the poor stability of PSCs still prevents their commercialization. In this report, we use the rate of the integrated short-circuit current change (Drate) to investigate the performance degradation kinetics and identify the degradation of PSCs that is accelerated by the light current. The value of Drate increases by an order of magnitude from about 0.02 to 0.35 mA cm-2·min-1 after light-IV testing. The accelerated degradation progress is proven to be dominated by the hydration process and the migration of the iodine ions of the light current. The migration of the iodine ions enhances the hydration process through a chain reaction, enabling the formation of fast diffusion channels for both H2O and O2, which induce the rapid decomposition of the perovskite film and increase the density of the trap state. The X-ray photoelectron spectroscopy measurement data also indicate that the super oxygen may be formed due to the PCBM damage caused by the migration iodine ions. An understanding of the degradation acceleration mechanism would provide an insight into the effect of ion migration on the stability of PSCs.

Surfactant mediated synthesis of bismuth selenide thin films for photoelectrochemical solar cell applications.

PubMed

Desai, Neha D; Khot, Kishorkumar V; Ghanwat, Vishvanath B; Kharade, Suvarta D; Bhosale, Popatrao N

2018-03-15

In the present report, nanostructured bismuth selenide (Bi 2 Se 3 ) thin films have been successfully deposited by using arrested precipitation technique (APT) at room temperature. The effect of three different surfactants on the optostructural, morphological, compositional and photoelectrochemical properties of Bi 2 Se 3 thin films were investigated. Optical absorption data indicates direct and allowed transition with a band gap energy varied from 1.4 eV to 1.8 eV. The X-ray diffraction pattern (XRD) revealed that Bi 2 Se 3 thin films are crystalline in nature and confirmed rhombohedral crystal structure. SEM micrographs shows morphological transition from interconnected mesh to nanospheres like and finally granular morphology. Surface topography of Bi 2 Se 3 thin films was determined by AFM. Compositional analysis of all samples was carried out by energy dispersive X-ray spectroscopy (EDS). Finally, all Bi 2 Se 3 thin films shows good PEC performance with highest photoconversion efficiency 1.47%. In order to study the stability of Bi 2 Se 3 thin films four cycles are repeated after gap of one week each. Further PEC performance of all Bi 2 Se 3 thin films are also supported by electrochemical impedance (EIS) measurement study. Copyright © 2017 Elsevier Inc. All rights reserved.

Enhanced Photocatalytic Reduction of CO2 to CO through TiO2 Passivation of InP in Ionic Liquids.

PubMed

Zeng, Guangtong; Qiu, Jing; Hou, Bingya; Shi, Haotian; Lin, Yongjing; Hettick, Mark; Javey, Ali; Cronin, Stephen B

2015-09-21

A robust and reliable method for improving the photocatalytic performance of InP, which is one of the best known materials for solar photoconversion (i.e., solar cells). In this article, we report substantial improvements (up to 18×) in the photocatalytic yields for CO2 reduction to CO through the surface passivation of InP with TiO2 deposited by atomic layer deposition (ALD). Here, the main mechanisms of enhancement are the introduction of catalytically active sites and the formation of a pn-junction. Photoelectrochemical reactions were carried out in a nonaqueous solution consisting of ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4), dissolved in acetonitrile, which enables CO2 reduction with a Faradaic efficiency of 99% at an underpotential of +0.78 V. While the photocatalytic yield increases with the addition of the TiO2 layer, a corresponding drop in the photoluminescence intensity indicates the presence of catalytically active sites, which cause an increase in the electron-hole pair recombination rate. NMR spectra show that the [EMIM](+) ions in solution form an intermediate complex with CO2(-), thus lowering the energy barrier of this reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of three systems of solar water heating by thermosiphon

NASA Astrophysics Data System (ADS)

Hernández, E.; Guzmán, R. E.

2016-02-01

The main purpose of this project was to elaborate a comparison between three water heating systems; using two plane water heating solar collector and another using a vacuum tube heater, all of them are on top of the cafeteria's roof on building of the “Universidad Pontificia Bolivariana” in Bucaramanga, Colombia. Through testing was determined each type of water heating systems' performance, where the Stainless Steel tube collector reached a maximum efficiency of 71.58%, the Copper Tubing Collector a maximum value of 76.31% and for the Vacuum Tube Heater Collector a maximum efficiency of 72.33%. The collector with copper coil was the system more efficient. So, taking into account the Performance and Temperature Curves, along with the weather conditions at the time of the testing we determined that the most efficient Solar Heating System is the one using a Vacuum Tube Heater Collector. Reaching a maximum efficiency of 72.33% and a maximum temperature of 62.6°C.

Highly efficient blue- and white-organic light emitting diodes base on triple-emitting layer.

PubMed

Shin, Hyun Su; Lee, Seok Jae; Lee, Ho Won; Lee, Dong Hyung; Kim, Woo Young; Yoon, Seung Soo; Kim, Young Kwan

2013-12-01

We have demonstrated highly efficient blue phosphorescent organic light-emitting diodes (PHOLEDs) using iridium (III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate (Flrpic) doped in three kinds of host materials, such as 9-(4-(triphenylsilyl)phenyl)-9H-carbazole (SPC), N,N'-dicarbazolyl-3,5-benzene (mCP), and 2,2',2"-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] (TPBi) as triple-emitting layer (T-EML). The properties of device with T-EML using the stepwise structure was found to be superior to the other blue PHOLEDs and exhibited a maximum luminous efficiency of 23.02 cd/A, a maximum external quantum efficiency of 11.09%, and a maximum power efficiency of 14.89 lm/W, respectively. An optimal blue device has improving charge balance and triplet excitons confinement within emitting layers (EMLs) each. Additionally, we also fabricated white PHOLED using a phosphorescent red dopant, bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq)2acac) doped in mCP and TPBi between blue EMLs. The properties of white PHOLED showed a maximum luminous efficiency and a maximum external quantum efficiency of 33.03 cd/A and 16.95%, respectively. It also showed the white emission with CIEx,y coordinates of (x = 0.36, y = 0.39) at 10 V.

Surface modification and multiple exciton generation studies of lead(II) sulfide nanoparticles

NASA Astrophysics Data System (ADS)

Zemke, Jennifer M.

2011-12-01

Solar energy is a green alternative to fossil fuels but solar technologies to date have been plagued by low conversion efficiencies and high input costs making solar power inaccessible to much of the developing world. Semiconductor nanoparticles (NPs) may provide a route to efficient, economical solar devices through a phenomenon called multiple exciton generation (MEG). Through MEG, semiconductor NPs use a high-energy input photon to create more than one exciton (electron-hole pair) per photon absorbed, thereby exhibiting large photoconversion efficiencies. While MEG has been studied in many NP systems, and we understand some of the factors that affect MEG, a rigorous analysis of the NP-ligand interface with respect to MEG is missing. This dissertation describes how the NP ligand shell directly affects MEG and subsequent charge carrier recombination. Chapter I describes the motivation for studying MEG with respect to NP surface chemistry. Chapter II provides an in-depth overview of the transient absorption experiment used to measure MEG in the NP samples. Chapter III highlights the effect of oleic acid and sodium 2, 3-dimercaptopropane sulfonate on MEG in PbS NPs. The differences in carrier recombination were accounted for by two differences between these ligands: the coordinating atom and/or the secondary structure of the ligand. Because of these hypotheses, experiments were designed to elucidate the origin of these effects by controlling the NP ligand shell. Chapter IV details a viable synthetic route to thiol and amine-capped PbS NPs using sodium 3-mercaptopropane sulfonate as an intermediate ligand. With the versatile ligand exchange described in Chapter IV, the MEG yield and carrier recombination was investigated for ligands with varying headgroups but the same secondary structure. The correlation of ligand donor atom to MEG is outlined in Chapter V. Finally, Chapter VI discusses the conclusions and future outlook of the research reported in this dissertation. This dissertation includes previously published and unpublished co-authored material.

Resonantly pumped high efficiency Ho:YAG laser.

PubMed

Shen, Ying-Jie; Yao, Bao-Quan; Duan, Xiao-Ming; Dai, Tong-Yu; Ju, You-Lun; Wang, Yue-Zhu

2012-11-20

High-efficient CW and Q-switched Ho:YAG lasers resonantly dual-end-pumped by two diode-pumped Tm:YLF lasers at 1908 nm were investigated. A maximum slope efficiency of 74.8% in CW operation as well as a maximum output power of 58.7 W at 83.2 W incident pump power was achieved, which corresponded to an optical-to-optical conversion efficiency of 70.6%. The maximum pulse energy of 2.94 mJ was achieved, with a 31 ns FWHM pulse width and a peak power of approximately 94.7 kW.

Efficiency of autonomous soft nanomachines at maximum power.

PubMed

Seifert, Udo

2011-01-14

We consider nanosized artificial or biological machines working in steady state enforced by imposing nonequilibrium concentrations of solutes or by applying external forces, torques, or electric fields. For unicyclic and strongly coupled multicyclic machines, efficiency at maximum power is not bounded by the linear response value 1/2. For strong driving, it can even approach the thermodynamic limit 1. Quite generally, such machines fall into three different classes characterized, respectively, as "strong and efficient," "strong and inefficient," and "balanced." For weakly coupled multicyclic machines, efficiency at maximum power has lost any universality even in the linear response regime.

Influence of Nb-doped TiO2 blocking layers as a cascading band structure for enhanced photovoltaic properties

NASA Astrophysics Data System (ADS)

Koo, Bon-Ryul; Oh, Dong-Hyeun; Ahn, Hyo-Jin

2018-03-01

Nb-doped TiO2 (Nb-TiO2) blocking layers (BLs) were developed using horizontal ultrasonic spray pyrolysis deposition (HUSPD). In order to improve the photovoltaic properties of the dye-sensitized solar cells (DSSCs), we optimized the Nb doping level of the Nb-TiO2 BLs by controlling the Nb/Ti molar ratio (0, 5, 6, and 7) of the precursor solution for HUSPD. Compared to bare TiO2 BLs, the Nb-TiO2 BLs formed a cascading band structure using the positive shift of the conduction band minimum of the Nb-TiO2 positioned between fluorine-doped tin oxide (FTO) and TiO2. This results in the increase of the potential current and the suppression of the electron recombination. Hence, it led to the improvement of the electrical conductivity, due to the increased electron concentration by the Nb doping into TiO2. Therefore, the DSSC fabricated with the Nb-TiO2 BLs at a Nb/Ti molar ratio of 6 showed superior photoconversion efficiency (∼7.50 ± 0.20%) as a result of the improved short-circuit current density. This is higher than those with the other Nb-TiO2 BLs and without BL. This improvement of the photovoltaic properties for the DSSCs can be attributed to the synergistic effects of uniform and compact BL relative to the prevention of the backward electron transport at the FTO/electrolyte interface, efficient electron transport at interfaces relative to a cascading band structure of FTO/Nb-TiO2/TiO2 multilayers and the facilitated electron transport at the BLs relative to the increased electrical conductivity of the optimized Nb-TiO2 BLs.

A scanning probe investigation of the role of surface motifs in the behavior of p-WSe 2 photocathodes

DOE PAGES

Velazquez, Jesus M.; John, Jimmy; Esposito, Daniel V.; ...

2015-10-08

The spatial variation in the photoelectrochemical performance for the reduction of an aqueous one-electron redox couple, Ru(NH 3) 6 3+/2+, and for the evolution of H 2(g) from 0.5 M H 2SO 4(aq) at the surface of bare or Pt-decorated p-type WSe 2 photocathodes has been investigated in situ using scanning photocurrent microscopy (SPCM). The measurements revealed significant differences in the charge-collection performance (quantified by the values of external quantum yields, Φ ext) on various macroscopic terraces. Local spectral response measurements indicated a variation in the local electronic structure among the terraces, which was consistent with a non-uniform spatial distributionmore » of sub-band-gap states within the crystals. The photoconversion efficiencies of Pt-decorated p-WSe2 photocathodes were greater for the evolution of H 2(g) from 0.5 M H 2SO 4 than for the reduction of Ru(NH 3) 6 3+/2+, and terraces that exhibited relatively low values of Φext for the reduction of Ru(NH 3) 6 3+/2+ could in some cases yield values of Φ ext for the evolution of H 2(g) comparable to the values of Φ ext yielded by the highest-performing terraces. In conclusion, although the spatial resolution of the techniques used in this work frequently did not result in observation of the effect of edge sites on photocurrent efficiency, some edge effects were observed in the measurements; however the observed edge effects differed among edges, and did not appear to determine the performance of the electrodes.« less

Nearly 100% triplet harvesting in conventional fluorescent dopant-based organic light-emitting devices through energy transfer from exciplex.

PubMed

Liu, Xiao-Ke; Chen, Zhan; Zheng, Cai-Jun; Chen, Miao; Liu, Wei; Zhang, Xiao-Hong; Lee, Chun-Sing

2015-03-25

Nearly 100% triplet harvesting in conventional fluorophor-based organic light-emitting devices is realized through energy transfer from exciplex. The best C545T-doped device using the exciplex host exhibits a maximum current efficiency of 44.0 cd A(-1) , a maximum power efficiency of 46.1 lm W(-1) , and a maximum external quantum efficiency of 14.5%. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Versatile benzimidazole/triphenylamine hybrids: efficient nondoped deep-blue electroluminescence and good host materials for phosphorescent emitters.

PubMed

Gong, Shaolong; Zhao, Yongbiao; Wang, Meng; Yang, Chuluo; Zhong, Cheng; Qin, Jingui; Ma, Dongge

2010-09-03

Two new bipolar compounds, N,N,N',N'-tetraphenyl-5'-(1-phenyl-1H-benzimidazol-2-yl)-1,1':3',1''-terphenyl-4,4''-diamine (1) and N,N,N',N'-tetraphenyl-5'-(1-phenyl-1H-benzimidazol-2-yl)-1,1':3',1''-terphenyl-3,3''-diamine (2), were synthesized and characterized, and their thermal, photophysical, and electrochemical properties were investigated. Compounds 1 and 2 possess good thermal stability with high glass-transition temperatures of 109-129 degrees C and thermal decomposition temperatures of 501-531 degrees C. The fluorescence quantum yield of 1 (0.52) is higher than that of 2 (0.16), which could be attributed to greater pi conjugation between the donor and acceptor moieties. A nondoped deep-blue fluorescent organic light-emitting diode (OLED) using 1 as the blue emitter displays high performance, with a maximum current efficiency of 2.2 cd A(-1) and a maximum external efficiency of 2.9 % at the CIE coordinates of (0.17, 0.07) that are very close to the National Television System Committee's blue standard (0.15, 0.07). Electrophosphorescent devices using the two compounds as host materials for green and red phosphor emitters show high efficiencies. The best performance of a green phosphorescent device was achieved using 2 as the host, with a maximum current efficiency of 64.3 cd A(-1) and a maximum power efficiency of 68.3 lm W(-1); whereas the best performance of a red phosphorescent device was achieved using 1 as the host, with a maximum current efficiency of 11.5 cd A(-1), and a maximum power efficiency of 9.8 lm W(-1). The relationship between the molecular structures and optoelectronic properties are discussed.

Control of chemical dynamics by lasers: theoretical considerations.

PubMed

Kondorskiy, Alexey; Nanbu, Shinkoh; Teranishi, Yoshiaki; Nakamura, Hiroki

2010-06-03

Theoretical ideas are proposed for laser control of chemical dynamics. There are the following three elementary processes in chemical dynamics: (i) motion of the wave packet on a single adiabatic potential energy surface, (ii) excitation/de-excitation or pump/dump of wave packet, and (iii) nonadiabatic transitions at conical intersections of potential energy surfaces. A variety of chemical dynamics can be controlled, if we can control these three elementary processes as we desire. For (i) we have formulated the semiclassical guided optimal control theory, which can be applied to multidimensional real systems. The quadratic or periodic frequency chirping method can achieve process (ii) with high efficiency close to 100%. Concerning process (iii) mentioned above, the directed momentum method, in which a predetermined momentum vector is given to the initial wave packet, makes it possible to enhance the desired transitions at conical intersections. In addition to these three processes, the intriguing phenomenon of complete reflection in the nonadiabatic-tunneling-type of potential curve crossing can also be used to control a certain class of chemical dynamics. The basic ideas and theoretical formulations are provided for the above-mentioned processes. To demonstrate the effectiveness of these controlling methods, numerical examples are shown by taking the following processes: (a) vibrational photoisomerization of HCN, (b) selective and complete excitation of the fine structure levels of K and Cs atoms, (c) photoconversion of cyclohexadiene to hexatriene, and (d) photodissociation of OHCl to O + HCl.

Phytochrome regulation of plant immunity in vegetation canopies.

PubMed

Moreno, Javier E; Ballaré, Carlos L

2014-07-01

Plant immunity against pathogens and herbivores is a central determinant of plant fitness in nature and crop yield in agroecosystems. Plant immune responses are orchestrated by two key hormones: jasmonic acid (JA) and salicylic acid (SA). Recent work has demonstrated that for plants of shade-intolerant species, which include the majority of those grown as grain crops, light is a major modulator of defense responses. Light signals that indicate proximity of competitors, such as a low red to far-red (R:FR) ratio, down-regulate the expression of JA- and SA-induced immune responses against pests and pathogens. This down-regulation of defense under low R:FR ratios, which is caused by the photoconversion of the photoreceptor phytochrome B (phyB) to an inactive state, is likely to help the plant to efficiently redirect resources to rapid growth when the competition threat posed by neighboring plants is high. This review is focused on the molecular mechanisms that link phyB with defense signaling. In particular, we discuss novel signaling players that are likely to play a role in the repression of defense responses under low R:FR ratios. A better understanding of the molecular connections between photoreceptors and the hormonal regulation of plant immunity will provide a functional framework to understand the mechanisms used by plants to deal with fundamental resource allocation trade-offs under dynamic conditions of biotic stress.

CdS/MoS2 heterojunction-based photoelectrochemical DNA biosensor via enhanced chemiluminescence excitation.

PubMed

Zang, Yang; Lei, Jianping; Hao, Qing; Ju, Huangxian

2016-03-15

This work developed a CdS/MoS2 heterojunction-based photoelectrochemical biosensor for sensitive detection of DNA under the enhanced chemiluminescence excitation of luminol catalyzed by hemin-DNA complex. The CdS/MoS2 photocathode was prepared by the stepwise assembly of MoS2 and CdS quantum dots (QDs) on indium tin oxide (ITO), and achieved about 280% increasing of photocurrent compared to pure CdS QDs electrode due to the formation of heterostructure. High photoconversion efficiency in the photoelectrochemical system was identified to be the rapid spatial charge separation of electron-hole pairs by the extension of electron transport time and electron lifetime. In the presence of target DNA, the catalytic hairpin assembly was triggered, and simultaneously the dual hemin-labeled DNA probe was introduced to capture DNA/CdS/MoS2 modified ITO electrode. Thus the chemiluminescence emission of luminol was enhanced via hemin-induced mimetic catalysis, leading to the physical light-free photoelectrochemical strategy. Under optimized conditions, the resulting photoelectrode was proportional to the logarithm of target DNA concentration in the range from 1 fM to 100 pM with a detection limit of 0.39 fM. Moreover, the cascade amplification biosensor demonstrated high selectivity, desirable stability and good reproducibility, showing great prospect in molecular diagnosis and bioanalysis. Copyright © 2015 Elsevier B.V. All rights reserved.

Photocycle dynamics of the E149A mutant of cryptochrome 3 from Arabidopsis thaliana.

PubMed

Zirak, P; Penzkofer, A; Moldt, J; Pokorny, R; Batschauer, A; Essen, L-O

2009-11-09

The E149A mutant of the cryDASH member cryptochrome 3 (cry3) from Arabidopsis thaliana was characterized in vitro by optical absorption and emission spectroscopic studies. The mutant protein non-covalently binds the chromophore flavin adenine dinucleotide (FAD). In contrast to the wild-type protein it does not bind N5,N10-methenyl-5,6,7,8-tetrahydrofolate (MTHF). Thus, the photo-dynamics caused by FAD is accessible without the intervening coupling with MTHF. In dark adapted cry3-E149A, FAD is present in the oxidized form (FAD(ox)), semiquinone form (FADH(.)), and anionic hydroquinone form (FAD(red)H(-)). Blue-light photo-excitation of previously unexposed cry3-E149A transfers FAD(ox) to the anionic semiquinone form (FAD()(-)) with a quantum efficiency of about 2% and a back recovery time of about 10s (photocycle I). Prolonged photo-excitation leads to an irreversible protein re-conformation with structure modification of the U-shaped FAD and enabling proton transfer. Thus, a change in the photocycle dynamics occurs with photo-conversion of FAD(ox) to FADH(.), FADH(.) to FAD(red)H(-), and thermal back equilibration in the dark (photocycle II). The photocycle dynamics of cry3-E149A is compared with the photocycle behaviour of wild-type cry3 and other photo-sensory cryptochromes.

IR-Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation.

PubMed

Zhang, Zhenyi; Jiang, Xiaoyi; Liu, Benkang; Guo, Lijiao; Lu, Na; Wang, Li; Huang, Jindou; Liu, Kuichao; Dong, Bin

2018-03-01

The ultrafast transfer of plasmon-induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble-metal-semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR-driven transfer of plasmon-induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W 18 O 49 nanowires (as branches) onto TiO 2 electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W 18 O 49 branches to the TiO 2 backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 10 12 to 5.5 × 10 12 s -1 . Upon LSPR excitation by low-energy IR photons, the W 18 O 49 /TiO 2 branched heterostructure exhibits obviously enhanced catalytic H 2 generation from ammonia borane compared with that of W 18 O 49 nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon-enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Three-dimensional scanning near field optical microscopy (3D-SNOM) imaging of random arrays of copper nanoparticles: implications for plasmonic solar cell enhancement.

PubMed

Ezugwu, Sabastine; Ye, Hanyang; Fanchini, Giovanni

2015-01-07

In order to investigate the suitability of random arrays of nanoparticles for plasmonic enhancement in the visible-near infrared range, we introduced three-dimensional scanning near-field optical microscopy (3D-SNOM) imaging as a useful technique to probe the intensity of near-field radiation scattered by random systems of nanoparticles at heights up to several hundred nm from their surface. We demonstrated our technique using random arrays of copper nanoparticles (Cu-NPs) at different particle diameter and concentration. Bright regions in the 3D-SNOM images, corresponding to constructive interference of forward-scattered plasmonic waves, were obtained at heights Δz ≥ 220 nm from the surface for random arrays of Cu-NPs of ∼ 60-100 nm in diameter. These heights are too large to use Cu-NPs in contact of the active layer for light harvesting in thin organic solar cells, which are typically no thicker than 200 nm. Using a 200 nm transparent spacer between the system of Cu-NPs and the solar cell active layer, we demonstrate that forward-scattered light can be conveyed in 200 nm thin film solar cells. This architecture increases the solar cell photoconversion efficiency by a factor of 3. Our 3D-SNOM technique is general enough to be suitable for a large number of other applications in nanoplasmonics.

Femtosecond laser spectroscopy of the rhodopsin photochromic reaction: a concept for ultrafast optical molecular switch creation (ultrafast reversible photoreaction of rhodopsin).

PubMed

Smitienko, Olga; Nadtochenko, Victor; Feldman, Tatiana; Balatskaya, Maria; Shelaev, Ivan; Gostev, Fedor; Sarkisov, Oleg; Ostrovsky, Mikhail

2014-11-11

Ultrafast reverse photoreaction of visual pigment rhodopsin in the femtosecond time range at room temperature is demonstrated. Femtosecond two-pump probe experiments with a time resolution of 25 fs have been performed. The first рump pulse at 500 nm initiated cis-trans photoisomerization of rhodopsin chromophore, 11-cis retinal, which resulted in the formation of the primary ground-state photoproduct within a mere 200 fs. The second pump pulse at 620 nm with a varying delay of 200 to 3750 fs relative to the first рump pulse, initiated the reverse phototransition of the primary photoproduct to rhodopsin. The results of this photoconversion have been observed on the differential spectra obtained after the action of two pump pulses at a time delay of 100 ps. It was found that optical density decreased at 560 nm in the spectral region of bathorhodopsin absorption and increased at 480 nm, where rhodopsin absorbs. Rhodopsin photoswitching efficiency shows oscillations as a function of the time delay between two рump pulses. The quantum yield of reverse photoreaction initiated by the second pump pulse falls within the range 15%±1%. The molecular mechanism of the ultrafast reversible photoreaction of visual pigment rhodopsin may be used as a concept for the development of an ultrafast optical molecular switch.

Analysis and Evaluation of Parameters Determining Maximum Efficiency of Fish Protection

NASA Astrophysics Data System (ADS)

Khetsuriani, E. D.; Kostyukov, V. P.; Khetsuriani, T. E.

2017-11-01

The article is concerned with experimental research findings. The efficiency of fish fry protection from entering water inlets is the main criterion of any fish protection facility or device. The research was aimed to determine an adequate mathematical model E = f(PCT, Vp, α), where PCT, Vp and α are controlled factors influencing the process of fish fry protection. The result of the processing of experimental data was an adequate regression model. We determined the maximum of fish protection Emax=94,21 and the minimum of optimization function Emin=44,41. As a result of the statistical processing of experimental data we obtained adequate dependences for determining an optimal rotational speed of tip and fish protection efficiency. The analysis of fish protection efficiency dependence E% = f(PCT, Vp, α) allowed the authors to recommend the following optimized operating modes for it: the maximum fish protection efficiency is achieved at the process pressure PCT=3 atm, stream velocity Vp=0,42 m/s and nozzle inclination angle α=47°49’. The stream velocity Vp has the most critical influence on fish protection efficiency. The maximum efficiency of fish protection is obtained at the tip rotational speed of 70.92 rpm.

Dual side control for inductive power transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Hunter; Sealy, Kylee; Gilchrist, Aaron

An apparatus for dual side control includes a measurement module that measures a voltage and a current of an IPT system. The voltage includes an output voltage and/or an input voltage and the current includes an output current and/or an input current. The output voltage and the output current are measured at an output of the IPT system and the input voltage and the input current measured at an input of the IPT system. The apparatus includes a max efficiency module that determines a maximum efficiency for the IPT system. The max efficiency module uses parameters of the IPT systemmore » to iterate to a maximum efficiency. The apparatus includes an adjustment module that adjusts one or more parameters in the IPT system consistent with the maximum efficiency calculated by the max efficiency module.« less

Efficiency at Maximum Power Output of a Quantum-Mechanical Brayton Cycle

NASA Astrophysics Data System (ADS)

Yuan, Yuan; He, Ji-Zhou; Gao, Yong; Wang, Jian-Hui

2014-03-01

The performance in finite time of a quantum-mechanical Brayton engine cycle is discussed, without introduction of temperature. The engine model consists of two quantum isoenergetic and two quantum isobaric processes, and works with a single particle in a harmonic trap. Directly employing the finite-time thermodynamics, the efficiency at maximum power output is determined. Extending the harmonic trap to a power-law trap, we find that the efficiency at maximum power is independent of any parameter involved in the model, but depends on the confinement of the trapping potential.

Transparent perovskite light-emitting diodes by employing organic-inorganic multilayer transparent top electrodes

NASA Astrophysics Data System (ADS)

Liang, Junqing; Guo, Xiaoyang; Song, Li; Lin, Jie; Hu, Yongsheng; Zhang, Nan; Liu, Xingyuan

2017-11-01

Perovskite light-emitting diodes (PeLEDs) have attracted much attention in the past two years due to their high photoluminescence quantum efficiencies and wavelength tuneable characteristics. In this work, transparent PeLEDs (TPeLEDs) have been reported with organic-inorganic multilayer transparent top electrodes that have more convenient control of the organic/electrode interface. By optimizing the thickness of the MoO3 layer in the top electrode, the best average transmittance of 47.21% has been obtained in the TPeLED in the wavelength range of 380-780 nm. In addition, the TPeLED exhibits a maximum luminance of 6380 cd/m2, a maximum current efficiency (CE) of 3.50 cd/A, and a maximum external quantum efficiency (EQE) of 0.85% from the bottom side together with a maximum luminance of 3380 cd/m2, a maximum CE of 1.47 cd/A, and a maximum EQE of 0.36% from the top side. The total EQE of the TPeLED is about 86% of that of the reference device, indicating efficient TPeLED achieved in this work, which could have significant contribution to PeLEDs for see-through displays.

Dual-step synthesis of 3-dimensional niobium oxide - Zinc oxide

NASA Astrophysics Data System (ADS)

Rani, Rozina Abdul; Zoolfakar, Ahmad Sabirin; Rusop, M.

2018-05-01

A facile fabrication process for constructing 3-dimensional (3D) structure of Niobium oxide - Zinc oxide (Nb2O5-ZnO) consisting of branched ZnO microrods on top of nanoporous Nb2O5 films was developed based on dual-step synthesis approach. The preliminary procedure was anodization of sputtered niobium metal on Fluorine doped Tin Oxide (FTO) to produce nanoporous Nb2O5, and continued with the growth of branched microrods of ZnO by hydrothermal process. This approach offers insight knowledge on the development of novel 3D metal oxide films via dual-step synthesis process, which might potentially use for multi-functional applications ranging from sensing to photoconversion.

Maximum efficiency of state-space models of nanoscale energy conversion devices

NASA Astrophysics Data System (ADS)

Einax, Mario; Nitzan, Abraham

2016-07-01

The performance of nano-scale energy conversion devices is studied in the framework of state-space models where a device is described by a graph comprising states and transitions between them represented by nodes and links, respectively. Particular segments of this network represent input (driving) and output processes whose properly chosen flux ratio provides the energy conversion efficiency. Simple cyclical graphs yield Carnot efficiency for the maximum conversion yield. We give general proof that opening a link that separate between the two driving segments always leads to reduced efficiency. We illustrate these general result with simple models of a thermoelectric nanodevice and an organic photovoltaic cell. In the latter an intersecting link of the above type corresponds to non-radiative carriers recombination and the reduced maximum efficiency is manifested as a smaller open-circuit voltage.

Maximum efficiency of state-space models of nanoscale energy conversion devices.

PubMed

Einax, Mario; Nitzan, Abraham

2016-07-07

The performance of nano-scale energy conversion devices is studied in the framework of state-space models where a device is described by a graph comprising states and transitions between them represented by nodes and links, respectively. Particular segments of this network represent input (driving) and output processes whose properly chosen flux ratio provides the energy conversion efficiency. Simple cyclical graphs yield Carnot efficiency for the maximum conversion yield. We give general proof that opening a link that separate between the two driving segments always leads to reduced efficiency. We illustrate these general result with simple models of a thermoelectric nanodevice and an organic photovoltaic cell. In the latter an intersecting link of the above type corresponds to non-radiative carriers recombination and the reduced maximum efficiency is manifested as a smaller open-circuit voltage.

Efficiency at maximum power output of quantum heat engines under finite-time operation.

PubMed

Wang, Jianhui; He, Jizhou; Wu, Zhaoqi

2012-03-01

We study the efficiency at maximum power, η(m), of irreversible quantum Carnot engines (QCEs) that perform finite-time cycles between a hot and a cold reservoir at temperatures T(h) and T(c), respectively. For QCEs in the reversible limit (long cycle period, zero dissipation), η(m) becomes identical to the Carnot efficiency η(C)=1-T(c)/T(h). For QCE cycles in which nonadiabatic dissipation and the time spent on two adiabats are included, the efficiency η(m) at maximum power output is bounded from above by η(C)/(2-η(C)) and from below by η(C)/2. In the case of symmetric dissipation, the Curzon-Ahlborn efficiency η(CA)=1-√(T(c)/T(h)) is recovered under the condition that the time allocation between the adiabats and the contact time with the reservoir satisfy a certain relation.

Efficient non-doped phosphorescent orange, blue and white organic light-emitting devices

NASA Astrophysics Data System (ADS)

Yin, Yongming; Yu, Jing; Cao, Hongtao; Zhang, Letian; Sun, Haizhu; Xie, Wenfa

2014-10-01

Efficient phosphorescent orange, blue and white organic light-emitting devices (OLEDs) with non-doped emissive layers were successfully fabricated. Conventional blue phosphorescent emitters bis [4,6-di-fluorophenyl]-pyridinato-N,C2'] picolinate (Firpic) and Bis(2,4-difluorophenylpyridinato) (Fir6) were adopted to fabricate non-doped blue OLEDs, which exhibited maximum current efficiency of 7.6 and 4.6 cd/A for Firpic and Fir6 based devices, respectively. Non-doped orange OLED was fabricated utilizing the newly reported phosphorescent material iridium (III) (pbi)2Ir(biq), of which manifested maximum current and power efficiency of 8.2 cd/A and 7.8 lm/W. The non-doped white OLEDs were achieved by simply combining Firpic or Fir6 with a 2-nm (pbi)2Ir(biq). The maximum current and power efficiency of the Firpic and (pbi)2Ir(biq) based white OLED were 14.8 cd/A and 17.9 lm/W.

Thermal modelling and optimisation of total useful energy rate of Joule-Brayton reheat cogeneration cycle

NASA Astrophysics Data System (ADS)

Dubey, M.; Chandra, H.; Kumar, Anil

2016-02-01

A thermal modelling for the performance evaluation of gas turbine cogeneration system with reheat is presented in this paper. The Joule-Brayton cogeneration reheat cycle is based on the total useful energy rate (TUER) has been optimised and the efficiency at the maximum TUER is determined. The variation of maximum dimensionless TUER and efficiency at maximum TUER with respect to cycle temperature ratio have also been analysed. From the results, it has been found that the dimensionless maximum TUER and the corresponding thermal efficiency decrease with the increase in power to heat ratio. The result also shows that the inclusion of reheat significantly improves the overall performance of the cycle. From the thermodynamic performance point of view, this methodology may be quite useful in the selection and comparison of combined energy production systems.

The tolerance efficiency of Panicum maximum and Helianthus annuus in TNT-contaminated soil and nZVI-contaminated soil.

PubMed

Jiamjitrpanich, Waraporn; Parkpian, Preeda; Polprasert, Chongrak; Laurent, François; Kosanlavit, Rachain

2012-01-01

This study was designed to compare the initial method for phytoremediation involving germination and transplantation. The study was also to determine the tolerance efficiency of Panicum maximum (Purple guinea grass) and Helianthus annuus (Sunflower) in TNT-contaminated soil and nZVI-contaminated soil. It was found that the transplantation of Panicum maximum and Helianthus annuus was more suitable than germination as the initiate method of nano-phytoremediation potting test. The study also showed that Panicum maximum was more tolerance than Helianthus annuus in TNT and nZVI-contaminated soil. Therefore, Panicum maximum in the transplantation method should be selected as a hyperaccumulated plant for nano-phytoremediation potting tests. Maximum tolerance dosage of Panicum maximum to TNT-concentration soil was 320 mg/kg and nZVI-contaminated soil was 1000 mg/kg in the transplantation method.

Schottky junction interfacial properties at high temperature: A case of AgNWs embedded metal oxide/p-Si

NASA Astrophysics Data System (ADS)

Mahala, Pramila; Patel, Malkeshkumar; Gupta, Navneet; Kim, Joondong; Lee, Byung Ha

2018-05-01

Studying the performance limiting parameters of the Schottky device is an urgent issue, which are addressed herein by thermally stable silver nanowire (AgNW) embedded metal oxide/p-Si Schottky device. Temperature and bias dependent junction interfacial properties of AgNW-ITO/Si Schottky photoelectric device are reported. The current-voltage-temperature (I-V-T), capacitance-voltage-temperature (C-V-T) and impedance analysis have been carried out in the high-temperature region. The ideality factor and barrier height of Schottky junction are assessed using I-V-T characteristics and thermionic emission, to reveal the decrease of ideality factor and increase of barrier height by the increasing of temperature. The extracted values of laterally homogeneous Schottky (ϕb) and ideality factor (n) are approximately 0.73 eV and 1.58, respectively. Series resistance (Rs) assessed using Cheung's method and found that it decreases with the increase of temperature. A linear response of Rs of AgNW-ITO/Si Schottky junction is observed with respect to change in forward bias, i.e. dRS/dV from 0 to 0.7 V is in the range of 36.12-36.43 Ω with a rate of 1.44 Ω/V. Impedance spectroscopy is used to study the effect of bias voltage and temperature on intrinsic Schottky properties which are responsible for photoconversion efficiency. These systematic analyses are useful for the AgNWs-embedding Si solar cells or photoelectrochemical cells.

Photothermally Activated Pyroelectric Polymer Films for Harvesting of Solar Heat with a Hybrid Energy Cell Structure.

PubMed

Park, Teahoon; Na, Jongbeom; Kim, Byeonggwan; Kim, Younghoon; Shin, Haijin; Kim, Eunkyoung

2015-12-22

Photothermal effects in poly(3,4-ethylenedioxythiophene)s (PEDOTs) were explored for pyroelectric conversion. A poled ferroelectric film was coated on both sides with PEDOT via solution casting polymerization of EDOT, to give highly conductive and effective photothermal thin films of PEDOT. The PEDOT films not only provided heat source upon light exposure but worked as electrodes for the output energy from the pyroelectric layer in an energy harvester hybridized with a thermoelectric layer. Compared to a bare thermoelectric system under NIR irradiation, the photothermal-pyro-thermoelectric device showed more than 6 times higher thermoelectric output with the additional pyroelectric output. The photothermally driven pyroelectric harvesting film provided a very fast electric output with a high voltage output (Vout) of 15 V. The pyroelectric effect was significant due to the transparent and high photothermal PEDOT film, which could also work as an electrode. A hybrid energy harvester was assembled to enhance photoconversion efficiency (PCE) of a solar cell with a thermoelectric device operated by the photothermally generated heat. The PCE was increased more than 20% under sunlight irradiation (AM 1.5G) utilizing the transmitted light through the photovoltaic cell as a heat source that was converted into pyroelectric and thermoelectric output simultaneously from the high photothermal PEDOT electrodes. Overall, this work provides a dynamic and static hybrid energy cell to harvest solar energy in full spectral range and thermal energy, to allow solar powered switching of an electrochromic display.

Reversible chemical tuning of charge carriers for enhanced photoelectrochemical conversion and probing of living cells.

PubMed

Wang, Yongcheng; Tang, Jing; Zhou, Tong; Da, Peimei; Li, Jun; Kong, Biao; Yang, Zhongqin; Zheng, Gengfeng

2014-12-10

A facile, solution method for reversible tuning of oxygen vacancies inside TiO2 nanowires, in which the reducing treatment of TiO2 by NaBH4 leads to 2.4-fold increase of photocurrent density, compared to pristine TiO2 nanowires, is reported. Subsequent oxidizing treatment using KMnO4 or annealing in air can reset the photocurrent density to the original values. The incident photo-to-current conversion efficiency measurement exhibits that the reduced TiO2 nanowires present both enhanced photoactivity in both UV and visible regions. Density functional theory calculations reveal that the oxygen vacancies in the reduced TiO2 cause defect states in the band structure and result in enhanced carrier density and conductivity. In addition, the enhanced solar energy-driven photoelectrochemical conversion allows real-time, sensitive chemical probing of living cells that are directly grown on the TiO2 nanowire photoanodes. As proofs-of-concept, after functionalized with horseradish peroxidase (HRP) on the surface, the reduced TiO2 NWs demonstrate sensitive, real-time monitoring of the H2O2 levels in several distinctive living cell lines, with the lowest detectable H2O2 concentration of 7.7 nM. This reversible tuning of oxygen vacancies suggests a facile means for transition metal oxides, with enhanced photoconversion activity and electrochemical sensitivity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoreduction of CO2 on TiO2/SrTiO3 Heterojunction Network Film

NASA Astrophysics Data System (ADS)

Bi, Yongsheng; Zong, Lanlan; Li, Chen; Li, Qiuye; Yang, Jianjun

2015-08-01

Nanotube titanic acid (NTA) network film has a porous structure and large BET surface area, which lead them to possessing high utilization of the incident light and strong adsorption ability. We used NTA as the precursor to fabricate a TiO2/ SrTiO3 heterojunction film by the hydrothermal method. In the process of the reaction, part of NTA reacted with SrCl2 to form SrTiO3 nanocubes, and the remainder dehydrated to transform to the rutile TiO2. The ratio of TiO2 and SrTiO3 varied with the hydrothermal reaction time. SEM and TEM images indicated that SrTiO3 nanocubes dispersed uniformly on TiO2 film, and the particle size and crystallinity of SrTiO3 nanocubes increased with the reaction time prolonging. The TiO2/SrTiO3 heterojunction obtained by 1 h showed the best activity for CO2 photoreduction, where the mole ratio of TiO2 and SrTiO3 was 4:1. And the photo-conversion efficiency of CO2 to CH4 improved remarkably after the foreign electron traps of Pt and Pd nanoparticles were loaded. The highest photocatalytic production rate of CH4 reached 20.83 ppm/h cm2. In addition, the selectivity of photoreduction product of CO2 was also increased apparently when Pd acted as the cocatalyst on TiO2/SrTiO3 heterojunction film.

Metal-Halide Perovskites for Gate Dielectrics in Field-Effect Transistors and Photodetectors Enabled by PMMA Lift-Off Process.

PubMed

Daus, Alwin; Roldán-Carmona, Cristina; Domanski, Konrad; Knobelspies, Stefan; Cantarella, Giuseppe; Vogt, Christian; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Tröster, Gerhard

2018-06-01

Metal-halide perovskites have emerged as promising materials for optoelectronics applications, such as photovoltaics, light-emitting diodes, and photodetectors due to their excellent photoconversion efficiencies. However, their instability in aqueous solutions and most organic solvents has complicated their micropatterning procedures, which are needed for dense device integration, for example, in displays or cameras. In this work, a lift-off process based on poly(methyl methacrylate) and deep ultraviolet lithography on flexible plastic foils is presented. This technique comprises simultaneous patterning of the metal-halide perovskite with a top electrode, which results in microscale vertical device architectures with high spatial resolution and alignment properties. Hence, thin-film transistors (TFTs) with methyl-ammonium lead iodide (MAPbI 3 ) gate dielectrics are demonstrated for the first time. The giant dielectric constant of MAPbI 3 (>1000) leads to excellent low-voltage TFT switching capabilities with subthreshold swings ≈80 mV decade -1 over ≈5 orders of drain current magnitude. Furthermore, vertically stacked low-power Au-MAPbI 3 -Au photodetectors with close-to-ideal linear response (R 2 = 0.9997) are created. The mechanical stability down to a tensile radius of 6 mm is demonstrated for the TFTs and photodetectors, simultaneously realized on the same flexible plastic substrate. These results open the way for flexible low-power integrated (opto-)electronic systems based on metal-halide perovskites. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ab Initio Simulation of Charge Transfer at the Semiconductor Quantum Dot/TiO 2 Interface in Quantum Dot-Sensitized Solar Cells

DOE PAGES

Xin, Xukai; Li, Bo; Jung, Jaehan; ...

2014-07-24

Quantum dot-sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next-generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO 2 acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. In order to understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO 2 substrate are simulated using a rigorous ab initio density functional method. Our method capitalizes onmore » localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO 2 occurring via the strong bonding between the conduction bands of QDs and TiO 2 is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO 2 acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO 2 systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO 2 acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.« less

The role of exciton ionization processes in bulk heterojunction organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Zou, Yunlong; Holmes, Russell

2015-03-01

Dissociating photogenerated excitons into their constituent charges is essential for efficient photoconversion in organic semiconductors. Organic photovoltaics cells (OPV) widely adopt a heterojunction architecture where dissociation is facilitated by charge transfer at a donor-acceptor (D-A) interface. Interestingly, recent work on MoOx/C60 Schottky OPVs has demonstrated that excitons in C60 may also undergo bulk-ionization to generate photocurrent, driven by the built-in field at the MoOx/C60 interface. Here, we show that bulk-ionization processes also contribute to the photocurrent in bulk heterojunction (BHJ) OPVs with fullerene-rich compositions. The short-circuit current density (JSC) in a MoOx/C60 Schottky OPVs shows almost no dependence on temperature down to 80 K. This characteristic of bulk-ionization allows the use of temperature-dependent measurements of JSC to distinguish dissociation by bulk-ionization from charge transfer at a D-A interface. For BHJ OPVs constructed using the D-A pairing of boron subphthalocyanine chloride (SubPc)-C60, bulk-ionization is found to contribute >10% of the total photocurrent and >30% of the photocurrent from C60. We further find that fullerene-rich SubPc-C60 BHJ OPVs show a larger open-circuit voltage (VOC) than evenly mixed BHJs due to the presence of bulk-ionization. This talk will examine the dependence of JSC and VOC on the relative fraction of dissociation by charge transfer and bulk-ionization processes.

Photo-reduction of CO2 Using a Rhenium Complex Covalently Supported on a Graphene/TiO2 Composite.

PubMed

Cui, Shi-Cong; Sun, Xue-Zhong; Liu, Jin-Gang

2016-07-07

One of the promising solutions for decreasing atmospheric CO2 is artificial photosynthesis, in which CO2 can be photoconverted into solar fuels. In this study, a rhenium complex Re(PyBn)(CO)3 Cl (PyBn=1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) was covalently grafted onto the surface of reduced graphene oxide (rGO). This was further combined with TiO2 to fabricate a novel catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl for CO2 photo-reduction. This hybrid composite demonstrated high selectivity conversion of CO2 into CO under xenon-lamp irradiation. Compared with the unsupported homogeneous catalyst Re(PyBn)(CO)3 Cl, the covalent immobilized catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl enhanced the turnover number six times and significantly improved catalyst stability. During the process of CO2 photo-reduction, intermediate species with lifetimes longer than hundreds of microseconds were observed and the formation of CO products was revealed using timeresolved infrared spectroscopy. A plausible mechanism for CO2 photo-reduction by the TiO2 -rGO-Re(PyBn)(CO)3 Cl catalyst composite has been suggested. The obtained results have implications for the future design of efficient catalyst composites for CO2 photo-conversion. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic electroluminescent devices and method for improving energy efficiency and optical stability thereof

DOEpatents

Heller, Christian Maria

2004-04-27

An organic electroluminescent device ("OELD") has a controllable brightness, an improved energy efficiency, and stable optical output at low brightness. The OELD is activated with a series of voltage pulses, each of which has a maximum voltage value that corresponds to the maximum power efficiency when the OELD is activated. The frequency of the pulses, or the duty cycle, or both are chosen to provide the desired average brightness.

Classic maximum entropy recovery of the average joint distribution of apparent FRET efficiency and fluorescence photons for single-molecule burst measurements.

PubMed

DeVore, Matthew S; Gull, Stephen F; Johnson, Carey K

2012-04-05

We describe a method for analysis of single-molecule Förster resonance energy transfer (FRET) burst measurements using classic maximum entropy. Classic maximum entropy determines the Bayesian inference for the joint probability describing the total fluorescence photons and the apparent FRET efficiency. The method was tested with simulated data and then with DNA labeled with fluorescent dyes. The most probable joint distribution can be marginalized to obtain both the overall distribution of fluorescence photons and the apparent FRET efficiency distribution. This method proves to be ideal for determining the distance distribution of FRET-labeled biomolecules, and it successfully predicts the shape of the recovered distributions.

Highly efficient continuous-wave Nd:YAG ceramic lasers at 946 nm

NASA Astrophysics Data System (ADS)

Zhu, H. Y.; Xu, C. W.; Zhang, J.; Tang, D. Y.; Luo, D. W.; Duan, Y. M.

2013-07-01

Highly efficient CW operation of diode-end-pumped Nd:YAG ceramic lasers at 946 nm is experimentally demonstrated. When a 5 mm long in-house fabricated Nd:YAG ceramic was used as the gain medium, a maximum output power of 10.5 W was obtained under an incident pump power of 35 W, corresponding to an optical conversion efficiency of 30%, while, when a 3 mm long ceramic sample was used, a maximum output power of 8.7 W was generated with a slope efficiency of 65% with respect to the absorbed pump power. Both the optical conversion efficiency and slope efficiency are the highest results reported so far for the diode-pumped 946 nm lasers.

The Photoconversion of Phytochrome Includes an Unproductive Shunt Reaction Pathway.

PubMed

Buhrke, David; Kuhlmann, Uwe; Michael, Norbert; Hildebrandt, Peter

2018-03-05

Phytochromes are modular bimodal photoswitches that control gene expression for morphogenetic processes in plants. These functions are triggered by photoinduced conversions between the inactive and active states of the photosensory module, denoted as Pr and Pfr, respectively. In the present time-resolved resonance Raman spectroscopic study of bacterial representatives of this photoreceptor family, we demonstrate that these phototransformations do not represent linear processes but include a branching reaction back to the initial state, prior to (de)activation of the output module. Thus, only a fraction of the photoreceptors undergoing the phototransformations can initiate the downstream signaling process, consistent with phytochrome's function as a sensor for more durable changes of light conditions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Proliferation of the Golgi apparatus in tobacco BY-2 cells during cell proliferation after release from the stationary phase of growth.

PubMed

Abiodun, Moses; Matsuoka, Ken

2013-08-01

We have recently developed a new method aimed at mass photo-conversion of photo-convertible fluorescence protein (PFP) fluorescence in transformed tobacco BY-2 cells. Using this method we reported recently that the Golgi apparatus is generated by the de novo formation from ER and the division of pre-existing Golgi stacks with similar extents In this work we report that the proliferation of the Golgi apparatus in tobacco cells that enter the growing cycle from the non-dividing cycle is quite similar to that in rapidly growing cells and that de novo formation from the ER and division of pre-existing stacks seems to contribute almost equally to the proliferation.

Bias and Efficiency in Structural Equation Modeling: Maximum Likelihood versus Robust Methods

ERIC Educational Resources Information Center

Zhong, Xiaoling; Yuan, Ke-Hai

2011-01-01

In the structural equation modeling literature, the normal-distribution-based maximum likelihood (ML) method is most widely used, partly because the resulting estimator is claimed to be asymptotically unbiased and most efficient. However, this may not hold when data deviate from normal distribution. Outlying cases or nonnormally distributed data,…

Finding the quantum thermoelectric with maximal efficiency and minimal entropy production at given power output

NASA Astrophysics Data System (ADS)

Whitney, Robert S.

2015-03-01

We investigate the nonlinear scattering theory for quantum systems with strong Seebeck and Peltier effects, and consider their use as heat engines and refrigerators with finite power outputs. This paper gives detailed derivations of the results summarized in a previous paper [R. S. Whitney, Phys. Rev. Lett. 112, 130601 (2014), 10.1103/PhysRevLett.112.130601]. It shows how to use the scattering theory to find (i) the quantum thermoelectric with maximum possible power output, and (ii) the quantum thermoelectric with maximum efficiency at given power output. The latter corresponds to a minimal entropy production at that power output. These quantities are of quantum origin since they depend on system size over electronic wavelength, and so have no analog in classical thermodynamics. The maximal efficiency coincides with Carnot efficiency at zero power output, but decreases with increasing power output. This gives a fundamental lower bound on entropy production, which means that reversibility (in the thermodynamic sense) is impossible for finite power output. The suppression of efficiency by (nonlinear) phonon and photon effects is addressed in detail; when these effects are strong, maximum efficiency coincides with maximum power. Finally, we show in particular limits (typically without magnetic fields) that relaxation within the quantum system does not allow the system to exceed the bounds derived for relaxation-free systems, however, a general proof of this remains elusive.

Analysis of the aerodynamic interaction between two plunging plates in tandem at low Reynolds number for maximum propulsive efficiency

NASA Astrophysics Data System (ADS)

Ortega-Casanova, Joaquin; Fernandez-Feria, Ramon

2015-11-01

The thrust generated by two heaving plates in tandem is analysed for two particular sets of configurations of interest in forward flight: a plunging leading plate with the trailing plate at rest, and the two plates heaving with the same frequency and amplitude, but varying the phase difference. The thrust efficiency of the leading plate is augmented in relation to a single plate heaving with the same frequency and amplitude in most cases. In the first configuration, we characterize the range of nondimensional heaving frequencies and amplitudes of the leading plate for which the stationary trailing plate contributes positively to the global thrust. The maximum global thrust efficiency, reached for an advance ratio slightly less than unity and a reduced frequency close to 5, is about the same as the maximum efficiency for an isolated plate. But for low frequencies the tandem configuration with the trailing plate at rest is more thrust efficient than the isolated plate. In the second configuration, we find that the maximum thrust efficiency is reached for a phase lag of 180o (counterstroking), particularly for an advance ratio unity and a reduced frequency 4.4, and it is practically the same as in the other configuration and that for a single plate. Supported by the Ministerio de Economía y Competitividad of Spain Grant no. DPI2013-40479-P.

Reconstruction of calmodulin single-molecule FRET states, dye interactions, and CaMKII peptide binding by MultiNest and classic maximum entropy

NASA Astrophysics Data System (ADS)

DeVore, Matthew S.; Gull, Stephen F.; Johnson, Carey K.

2013-08-01

We analyzed single molecule FRET burst measurements using Bayesian nested sampling. The MultiNest algorithm produces accurate FRET efficiency distributions from single-molecule data. FRET efficiency distributions recovered by MultiNest and classic maximum entropy are compared for simulated data and for calmodulin labeled at residues 44 and 117. MultiNest compares favorably with maximum entropy analysis for simulated data, judged by the Bayesian evidence. FRET efficiency distributions recovered for calmodulin labeled with two different FRET dye pairs depended on the dye pair and changed upon Ca2+ binding. We also looked at the FRET efficiency distributions of calmodulin bound to the calcium/calmodulin dependent protein kinase II (CaMKII) binding domain. For both dye pairs, the FRET efficiency distribution collapsed to a single peak in the case of calmodulin bound to the CaMKII peptide. These measurements strongly suggest that consideration of dye-protein interactions is crucial in forming an accurate picture of protein conformations from FRET data.

Reconstruction of Calmodulin Single-Molecule FRET States, Dye-Interactions, and CaMKII Peptide Binding by MultiNest and Classic Maximum Entropy

PubMed Central

DeVore, Matthew S.; Gull, Stephen F.; Johnson, Carey K.

2013-01-01

We analyze single molecule FRET burst measurements using Bayesian nested sampling. The MultiNest algorithm produces accurate FRET efficiency distributions from single-molecule data. FRET efficiency distributions recovered by MultiNest and classic maximum entropy are compared for simulated data and for calmodulin labeled at residues 44 and 117. MultiNest compares favorably with maximum entropy analysis for simulated data, judged by the Bayesian evidence. FRET efficiency distributions recovered for calmodulin labeled with two different FRET dye pairs depended on the dye pair and changed upon Ca2+ binding. We also looked at the FRET efficiency distributions of calmodulin bound to the calcium/calmodulin dependent protein kinase II (CaMKII) binding domain. For both dye pairs, the FRET efficiency distribution collapsed to a single peak in the case of calmodulin bound to the CaMKII peptide. These measurements strongly suggest that consideration of dye-protein interactions is crucial in forming an accurate picture of protein conformations from FRET data. PMID:24223465

Efficient non-doped phosphorescent orange, blue and white organic light-emitting devices.

PubMed

Yin, Yongming; Yu, Jing; Cao, Hongtao; Zhang, Letian; Sun, Haizhu; Xie, Wenfa

2014-10-24

Efficient phosphorescent orange, blue and white organic light-emitting devices (OLEDs) with non-doped emissive layers were successfully fabricated. Conventional blue phosphorescent emitters bis [4,6-di-fluorophenyl]-pyridinato-N,C(2')] picolinate (Firpic) and Bis(2,4-difluorophenylpyridinato) (Fir6) were adopted to fabricate non-doped blue OLEDs, which exhibited maximum current efficiency of 7.6 and 4.6 cd/A for Firpic and Fir6 based devices, respectively. Non-doped orange OLED was fabricated utilizing the newly reported phosphorescent material iridium (III) (pbi)₂Ir(biq), of which manifested maximum current and power efficiency of 8.2 cd/A and 7.8 lm/W. The non-doped white OLEDs were achieved by simply combining Firpic or Fir6 with a 2-nm (pbi)₂Ir(biq). The maximum current and power efficiency of the Firpic and (pbi)₂Ir(biq) based white OLED were 14.8 cd/A and 17.9 lm/W.

Reconstruction of Calmodulin Single-Molecule FRET States, Dye-Interactions, and CaMKII Peptide Binding by MultiNest and Classic Maximum Entropy.

PubMed

Devore, Matthew S; Gull, Stephen F; Johnson, Carey K

2013-08-30

We analyze single molecule FRET burst measurements using Bayesian nested sampling. The MultiNest algorithm produces accurate FRET efficiency distributions from single-molecule data. FRET efficiency distributions recovered by MultiNest and classic maximum entropy are compared for simulated data and for calmodulin labeled at residues 44 and 117. MultiNest compares favorably with maximum entropy analysis for simulated data, judged by the Bayesian evidence. FRET efficiency distributions recovered for calmodulin labeled with two different FRET dye pairs depended on the dye pair and changed upon Ca 2+ binding. We also looked at the FRET efficiency distributions of calmodulin bound to the calcium/calmodulin dependent protein kinase II (CaMKII) binding domain. For both dye pairs, the FRET efficiency distribution collapsed to a single peak in the case of calmodulin bound to the CaMKII peptide. These measurements strongly suggest that consideration of dye-protein interactions is crucial in forming an accurate picture of protein conformations from FRET data.

Solar photovoltaic charging of lithium-ion batteries

NASA Astrophysics Data System (ADS)

Gibson, Thomas L.; Kelly, Nelson A.

Solar photovoltaic (PV) charging of batteries was tested by using high efficiency crystalline and amorphous silicon PV modules to recharge lithium-ion battery modules. This testing was performed as a proof of concept for solar PV charging of batteries for electrically powered vehicles. The iron phosphate type lithium-ion batteries were safely charged to their maximum capacity and the thermal hazards associated with overcharging were avoided by the self-regulating design of the solar charging system. The solar energy to battery charge conversion efficiency reached 14.5%, including a PV system efficiency of nearly 15%, and a battery charging efficiency of approximately 100%. This high system efficiency was achieved by directly charging the battery from the PV system with no intervening electronics, and matching the PV maximum power point voltage to the battery charging voltage at the desired maximum state of charge for the battery. It is envisioned that individual homeowners could charge electric and extended-range electric vehicles from residential, roof-mounted solar arrays, and thus power their daily commuting with clean, renewable solar energy.

Classic Maximum Entropy Recovery of the Average Joint Distribution of Apparent FRET Efficiency and Fluorescence Photons for Single-molecule Burst Measurements

PubMed Central

DeVore, Matthew S.; Gull, Stephen F.; Johnson, Carey K.

2012-01-01

We describe a method for analysis of single-molecule Förster resonance energy transfer (FRET) burst measurements using classic maximum entropy. Classic maximum entropy determines the Bayesian inference for the joint probability describing the total fluorescence photons and the apparent FRET efficiency. The method was tested with simulated data and then with DNA labeled with fluorescent dyes. The most probable joint distribution can be marginalized to obtain both the overall distribution of fluorescence photons and the apparent FRET efficiency distribution. This method proves to be ideal for determining the distance distribution of FRET-labeled biomolecules, and it successfully predicts the shape of the recovered distributions. PMID:22338694

Automotive Stirling Engine Development Program Mod I Stirling engine development

NASA Technical Reports Server (NTRS)

Simetkosky, M. A.

1983-01-01

The development of the Mod I 4-cylinder automotive Stirling engine is discussed and illustrated with drawings, block diagrams, photographs, and graphs and tables of preliminary test data. The engine and its drive, cold-engine, hot-engine, external-heat, air/fuel, power-control, electronic-control, and auxiliary systems are characterized. Performance results from a total of 1900 h of tests on 4 prototype engines include average maximum efficiency (at 2000 rpm) 34.5 percent and maximum output power 54.4 kW. The modifications introduced in an upgraded version of the Mod I are explained; this engine has maximum efficiency 40.4 percent and maximum power output 69.2 kW.

Changes in diffraction efficiency of gratings with high fructose corn syrup by aging

NASA Astrophysics Data System (ADS)

Mejias-Brizuela, Nildia Y.; Olivares-Pérez, Arturo

2017-03-01

High fructose corn syrup was used for preparation of holographic gratings photosensitized with potassium bichromated, for to analyze the behavior of diffraction efficiency to first order. The behavior of diffraction efficiency to first order was analyzed at time intervals different: 24, 48, 72 and 96 hours, because to the recorded gratings showed instability 24 hours after of record. For this reason, we decided to study in the time the evolution of diffraction efficiency parameter for to determine the maximum modulation of material holographic (HFCS-bichromated). The study realized showed that after of 72 hours, the photosensitized material reaches its maximum modulation, with a diffraction efficiency to first order of 4 percent.

[Electricity generation from sweet potato fuel ethanol wastewater using microbial fuel cell technology].

PubMed

Cai, Xiao-Bo; Yang, Yi; Sun, Yan-Ping; Zhang, Liang; Xiao, Yao; Zhao, Hai

2010-10-01

Air cathode microbial fuel cell (MFC) were investigated for electricity production from sweet potato fuel ethanol wastewater containing 5000 mg/L of chemical oxygen demand (COD). Maximum power density of 334.1 mW/m2, coulombic efficiency (CE) of 10.1% and COD removal efficiency of 92.2% were approached. The effect of phosphate buffer solution (PBS) and COD concentration on the performance of MFC was further examined. The addition of PBS from 50 mmol/L to 200 mmol/L increased the maximum power density and CE by 33.4% and 26.0%, respectively. However, the COD removal efficiency was not relative to PBS concentration in the wastewater. When the COD increased from 625 mg/L to 10 000 mg/L, the maximum value of COD removal efficiency and the maximum power density were gained at the wastewater strength of 5 000 mg/L. But the CE ranged from 28.9% to 10.3% with a decreasing trend. These results demonstrate that sweet potato fuel ethanol wastewater can be used for electricity generation in MFC while at the same time achieving wastewater treatment. The increasing of PBS concentration can improve the power generation of MFC. The maximum power density of MFC increases with the rise of COD concentration, but the electricity generation will decrease for the acidification of high wastewater concentration.

Energy Efficient Cluster Based Scheduling Scheme for Wireless Sensor Networks

PubMed Central

Srie Vidhya Janani, E.; Ganesh Kumar, P.

2015-01-01

The energy utilization of sensor nodes in large scale wireless sensor network points out the crucial need for scalable and energy efficient clustering protocols. Since sensor nodes usually operate on batteries, the maximum utility of network is greatly dependent on ideal usage of energy leftover in these sensor nodes. In this paper, we propose an Energy Efficient Cluster Based Scheduling Scheme for wireless sensor networks that balances the sensor network lifetime and energy efficiency. In the first phase of our proposed scheme, cluster topology is discovered and cluster head is chosen based on remaining energy level. The cluster head monitors the network energy threshold value to identify the energy drain rate of all its cluster members. In the second phase, scheduling algorithm is presented to allocate time slots to cluster member data packets. Here congestion occurrence is totally avoided. In the third phase, energy consumption model is proposed to maintain maximum residual energy level across the network. Moreover, we also propose a new packet format which is given to all cluster member nodes. The simulation results prove that the proposed scheme greatly contributes to maximum network lifetime, high energy, reduced overhead, and maximum delivery ratio. PMID:26495417

Irreversible Brownian Heat Engine

NASA Astrophysics Data System (ADS)

Taye, Mesfin Asfaw

2017-10-01

We model a Brownian heat engine as a Brownian particle that hops in a periodic ratchet potential where the ratchet potential is coupled with a linearly decreasing background temperature. We show that the efficiency of such Brownian heat engine approaches the efficiency of endoreversible engine η =1-√{{Tc/Th}} [23]. On the other hand, the maximum power efficiency of the engine approaches η ^{MAX}=1-({Tc/Th})^{1\\over 4}. It is shown that the optimized efficiency always lies between the efficiency at quasistatic limit and the efficiency at maximum power while the efficiency at maximum power is always less than the optimized efficiency since the fast motion of the particle comes at the expense of the energy cost. If the heat exchange at the boundary of the heat baths is included, we show that such a Brownian heat engine has a higher performance when acting as a refrigerator than when operating as a device subjected to a piecewise constant temperature. The role of time on the performance of the motor is also explored via numerical simulations. Our numerical results depict that the time t and the external load dictate the direction of the particle velocity. Moreover, the performance of the heat engine improves with time. At large t (steady state), the velocity, the efficiency and the coefficient of performance of the refrigerator attain their maximum value. Furthermore, we study the effect of temperature by considering a viscous friction that decreases exponentially as the background temperature increases. Our result depicts that the Brownian particle exhibits a fast unidirectional motion when the viscous friction is temperature dependent than that of constant viscous friction. Moreover, the efficiency of this motor is considerably enhanced when the viscous friction is temperature dependent. On the hand, the motor exhibits a higher performance of the refrigerator when the viscous friction is taken to be constant.

Highly efficient maximum power point tracking using DC-DC coupled inductor single-ended primary inductance converter for photovoltaic power systems

NASA Astrophysics Data System (ADS)

Quamruzzaman, M.; Mohammad, Nur; Matin, M. A.; Alam, M. R.

2016-10-01

Solar photovoltaics (PVs) have nonlinear voltage-current characteristics, with a distinct maximum power point (MPP) depending on factors such as solar irradiance and operating temperature. To extract maximum power from the PV array at any environmental condition, DC-DC converters are usually used as MPP trackers. This paper presents the performance analysis of a coupled inductor single-ended primary inductance converter for maximum power point tracking (MPPT) in a PV system. A detailed model of the system has been designed and developed in MATLAB/Simulink. The performance evaluation has been conducted on the basis of stability, current ripple reduction and efficiency at different operating conditions. Simulation results show considerable ripple reduction in the input and output currents of the converter. Both the MPPT and converter efficiencies are significantly improved. The obtained simulation results validate the effectiveness and suitability of the converter model in MPPT and show reasonable agreement with the theoretical analysis.

Femtosecond laser ablation of dentin and enamel: relationship between laser fluence and ablation efficiency.

PubMed

Chen, Hu; Liu, Jing; Li, Hong; Ge, Wenqi; Sun, Yuchun; Wang, Yong; Lü, Peijun

2015-02-01

The objective was to study the relationship between laser fluence and ablation efficiency of a femtosecond laser with a Gaussian-shaped pulse used to ablate dentin and enamel for prosthodontic tooth preparation. A diode-pumped thin-disk femtosecond laser with wavelength of 1025 nm and pulse width of 400 fs was used for the ablation of dentin and enamel. The laser spot was guided in a line on the dentin and enamel surfaces to form a groove-shaped ablation zone under a series of laser pulse energies. The width and volume of the ablated line were measured under a three-dimensional confocal microscope to calculate the ablation efficiency. Ablation efficiency for dentin reached a maximum value of 0.020 mm3∕J when the laser fluence was set at 6.51 J∕cm2. For enamel, the maximum ablation efficiency was 0.009 mm3∕J at a fluence of 7.59 J∕cm2.Ablation efficiency of the femtosecond laser on dentin and enamel is closely related to the laser fluence and may reach a maximum when the laser fluence is set to an appropriate value. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

New stable perfluoroallyl radical from perfluoro-2,4-dimethyl-3-ethylpentene-2 and its photoconversion reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shvedova, M.K.; Allayarov, S.R.; Barkalov, I.M.

1988-05-01

The thermally and chemically stable perfluoroally radical is formed in the radiolysis of perfluoro-2, 4-dimethyl-3-ethylpentene-2. A phototransformation of this radical into other radicals takes place under the action of UV light (/lambda/ < 300 nm) which are thermally unstable. Samples containing up to 90% FMP and 10% of its isomers were placed into ampules made of quartz or SK-4B glass, which gave to EPR signal after irradiation; the ampules were evacuated to a pressure of 0.13 Pa, frozen to 77 K, and irradiated with /sup 60/Co /lambda/-quanta at 77 K with doses up to 200 kGy. Irradiation with UV lightmore » was performed at 77 K with light from a DRSh-1000 lamp.« less

Disc piezoelectric ceramic transformers.

PubMed

Erhart, Jirií; Půlpán, Petr; Doleček, Roman; Psota, Pavel; Lédl, Vít

2013-08-01

In this contribution, we present our study on disc-shaped and homogeneously poled piezoelectric ceramic transformers working in planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, smile, or yin-yang segments. Transformation ratio, efficiency, and input and output impedances were measured for low-power signals. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of 2-segment wedge transformers. Maximum efficiency was reached at optimum impedance, which is in the range from 500 Ω to 10 kΩ, depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency-modulated digital holographic interferometry and by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profiles at higher driving power.

Sun-to-Wheels Exergy Efficiencies for Bio-Ethanol and Photovoltaics.

PubMed

Williams, Eric; Sekar, Ashok; Matteson, Schuyler; Rittmann, Bruce E

2015-06-02

The two main paths to power vehicles with sunlight are to use photosynthesis to grow biomass, converting to a liquid fuel for an internal combustion engine or to generate photovoltaic electricity that powers the battery of an electric vehicle. While the environmental attributes of these two paths have been much analyzed, prior studies consider the current state of technology. Technologies for biofuel and photovoltaic paths are evolving; it is critical to consider how progress might improve environmental performance. We address this challenge by assessing the current and maximum theoretical exergy efficiencies of bioethanol and photovoltaic sun-to-wheels process chains. The maximum theoretical efficiency is an upper bound stipulated by physical laws. The current net efficiency to produce motive power from silicon photovoltaic modules is estimated at 5.4%, much higher than 0.03% efficiency for corn-based ethanol. Flat-plate photovoltaic panels also have a much higher theoretical maximum efficiency than a C4 crop plant, 48% versus 0.19%. Photovoltaic-based power will always be vastly more efficient than a terrestrial crop biofuel. Providing all mobility in the U.S. via crop biofuels would require 130% of arable land with current technology and 20% in the thermodynamic limit. Comparable values for photovoltaic-based power are 0.7% and 0.081%, respectively.

Parametric design criteria of an updated thermoradiative cell operating at optimal states

NASA Astrophysics Data System (ADS)

Zhang, Xin; Peng, Wanli; Lin, Jian; Chen, Xiaohang; Chen, Jincan

2017-11-01

An updated mode of the thermoradiative cell (TRC) with sub-band gap and non-radiative losses is proposed, which can efficiently harvest moderate-temperature heat energy and convert a part of heat into electricity. It is found that when the TRC is operated between the heat source at 800 K and the environment at 300 K , its maximum power output density and efficiency can attain 1490 W m-2 and 27.2 % , respectively. Moreover, the effects of some key parameters including the band gap and voltage output on the performance of the TRC are discussed. The optimally working regions of the power density, efficiency, band gap, and voltage output are determined. The maximum efficiency and power output density of the TRC operated at different temperatures are calculated and compared with those of thermophotovoltaic cells (TPVCs) and thermionic energy converters (TECs), and consequently, it is revealed that the maximum efficiency of the TRC operated at the moderate-temperature range is much higher than that of the TEC or the TPVC and the maximum power output density of the TRC is larger than that of the TEC but smaller than that of the TPVC. Particularly, the TRC is manufactured more easily than the near-field TPVC possessing a nanoscale vacuum gap. The results obtained will be helpful for engineers to choose the semiconductor materials, design and manufacture TRCs, and control operative conditions.

Spherical Harmonic-based Random Fields Based on Real Particle 3D Data: Improved Numerical Algorithm and Quantitative Comparison to Real Particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

X Liu; E Garboczi; m Grigoriu

Many parameters affect the cyclone efficiency, and these parameters can have different effects in different flow regimes. Therefore the maximum-efficiency cyclone length is a function of the specific geometry and operating conditions in use. In this study, we obtained a relationship describing the minimum particle diameter or maximum cyclone efficiency by using a theoretical approach based on cyclone geometry and fluid properties. We have compared the empirical predictions with corresponding literature data and observed good agreement. The results address the importance of fluid properties. Inlet and vortex finder cross-sections, cone-apex diameter, inlet Reynolds number and surface roughness are found tomore » be the other important parameters affecting cyclone height. The surface friction coefficient, on the other hand, is difficult to employ in the calculations.We developed a theoretical approach to find the maximum-efficiency heights for cyclones with tangential inlet and we suggested a relation for this height as a function of cyclone geometry and operating parameters. In order to generalize use of the relation, two dimensionless parameters, namely for geometric and operational variables, we defined and results were presented in graphical form such that one can calculate and enter the values of these dimensionless parameters and then can find the maximum efficiency height of his own specific cyclone.« less

Maximum power point tracking algorithm based on sliding mode and fuzzy logic for photovoltaic sources under variable environmental conditions

NASA Astrophysics Data System (ADS)

Atik, L.; Petit, P.; Sawicki, J. P.; Ternifi, Z. T.; Bachir, G.; Della, M.; Aillerie, M.

2017-02-01

Solar panels have a nonlinear voltage-current characteristic, with a distinct maximum power point (MPP), which depends on the environmental factors, such as temperature and irradiation. In order to continuously harvest maximum power from the solar panels, they have to operate at their MPP despite the inevitable changes in the environment. Various methods for maximum power point tracking (MPPT) were developed and finally implemented in solar power electronic controllers to increase the efficiency in the electricity production originate from renewables. In this paper we compare using Matlab tools Simulink, two different MPP tracking methods, which are, fuzzy logic control (FL) and sliding mode control (SMC), considering their efficiency in solar energy production.

Advanced Power Conditioning System

NASA Technical Reports Server (NTRS)

Johnson, N. L.

1971-01-01

The second portion of the advanced power conditioning system development program is reported. Five 100-watt parallel power stages with majority-vote-logic feedback-regulator were breadboarded and tested to the design goals. The input voltage range was 22.1 to 57.4 volts at loads from zero to 500 watts. The maximum input ripple current was 200 mA pk-pk (not including spikes) at 511 watts load; the output voltage was 56V dc with a maximum change of 0.89 volts for all variations of line, load, and temperature; the maximum output ripple was 320 mV pk-pk at 512 watts load (dependent on filter capacitance value); the maximum efficiency was 93.9% at 212 watts and 50V dc input; the minimum efficiency was 87.2% at 80-watt load and 50V dc input; the efficiency was above 90% from 102 watts to 372 watts; the maximum excursion for an 80-watt load change was 2.1 volts with a recovery time of 7 milliseconds; and the unit performed within regulation limits from -20 C to +85 C. During the test sequence, margin tests and failure mode tests were run with no resulting degradation in performance.

A MATLAB toolbox for the efficient estimation of the psychometric function using the updated maximum-likelihood adaptive procedure.

PubMed

Shen, Yi; Dai, Wei; Richards, Virginia M

2015-03-01

A MATLAB toolbox for the efficient estimation of the threshold, slope, and lapse rate of the psychometric function is described. The toolbox enables the efficient implementation of the updated maximum-likelihood (UML) procedure. The toolbox uses an object-oriented architecture for organizing the experimental variables and computational algorithms, which provides experimenters with flexibility in experimental design and data management. Descriptions of the UML procedure and the UML Toolbox are provided, followed by toolbox use examples. Finally, guidelines and recommendations of parameter configurations are given.

Numerical modelling of high efficiency InAs/GaAs intermediate band solar cell

NASA Astrophysics Data System (ADS)

Imran, Ali; Jiang, Jianliang; Eric, Debora; Yousaf, Muhammad

2018-01-01

Quantum Dots (QDs) intermediate band solar cells (IBSC) are the most attractive candidates for the next generation of photovoltaic applications. In this paper, theoretical model of InAs/GaAs device has been proposed, where we have calculated the effect of variation in the thickness of intrinsic and IB layer on the efficiency of the solar cell using detailed balance theory. IB energies has been optimized for different IB layers thickness. Maximum efficiency 46.6% is calculated for IB material under maximum optical concentration.

Operation regimes of a dielectric laser accelerator

NASA Astrophysics Data System (ADS)

Hanuka, Adi; Schächter, Levi

2018-04-01

We investigate three operation regimes in dielectric laser driven accelerators: maximum efficiency, maximum charge, and maximum loaded gradient. We demonstrate, using a self-consistent approach, that loaded gradients of the order of 1 to 6 [GV/m], efficiencies of 20% to 80%, and electrons flux of 1014 [el/s] are feasible, without significant concerns regarding damage threshold fluence. The latter imposes that the total charge per squared wavelength is constant (a total of 106 per μm2). We conceive this configuration as a zero-order design that should be considered for the road map of future accelerators.

Improving IMRT delivery efficiency using intensity limits during inverse planning.

PubMed

Coselmon, Martha M; Moran, Jean M; Radawski, Jeffrey D; Fraass, Benedick A

2005-05-01

Inverse planned intensity modulated radiotherapy (IMRT) fields can be highly modulated due to the large number of degrees of freedom involved in the inverse planning process. Additional modulation typically results in a more optimal plan, although the clinical rewards may be small or offset by additional delivery complexity and/or increased dose from transmission and leakage. Increasing modulation decreases delivery efficiency, and may lead to plans that are more sensitive to geometrical uncertainties. The purpose of this work is to assess the use of maximum intensity limits in inverse IMRT planning as a simple way to increase delivery efficiency without significantly affecting plan quality. Nine clinical cases (three each for brain, prostate, and head/neck) were used to evaluate advantages and disadvantages of limiting maximum intensity to increase delivery efficiency. IMRT plans were generated using in-house protocol-based constraints and objectives for the brain and head/neck, and RTOG 9406 dose volume objectives in the prostate. Each case was optimized at a series of maximum intensity ratios (the product of the maximum intensity and the number of beams divided by the prescribed dose to the target volume), and evaluated in terms of clinical metrics, dose-volume histograms, monitor units (MU) required per fraction (SMLC and DMLC delivery), and intensity map variation (a measure of the beam modulation). In each site tested, it was possible to reduce total monitor units by constraining the maximum allowed intensity without compromising the clinical acceptability of the plan. Monitor unit reductions up to 38% were observed for SMLC delivery, while reductions up to 29% were achieved for DMLC delivery. In general, complicated geometries saw a smaller reduction in monitor units for both delivery types, although DMLC delivery required significantly more monitor units in all cases. Constraining the maximum intensity in an inverse IMRT plan is a simple way to improve delivery efficiency without compromising plan objectives.

High performance monolithic power management system with dynamic maximum power point tracking for microbial fuel cells.

PubMed

Erbay, Celal; Carreon-Bautista, Salvador; Sanchez-Sinencio, Edgar; Han, Arum

2014-12-02

Microbial fuel cell (MFC) that can directly generate electricity from organic waste or biomass is a promising renewable and clean technology. However, low power and low voltage output of MFCs typically do not allow directly operating most electrical applications, whether it is supplementing electricity to wastewater treatment plants or for powering autonomous wireless sensor networks. Power management systems (PMSs) can overcome this limitation by boosting the MFC output voltage and managing the power for maximum efficiency. We present a monolithic low-power-consuming PMS integrated circuit (IC) chip capable of dynamic maximum power point tracking (MPPT) to maximize the extracted power from MFCs, regardless of the power and voltage fluctuations from MFCs over time. The proposed PMS continuously detects the maximum power point (MPP) of the MFC and matches the load impedance of the PMS for maximum efficiency. The system also operates autonomously by directly drawing power from the MFC itself without any external power. The overall system efficiency, defined as the ratio between input energy from the MFC and output energy stored into the supercapacitor of the PMS, was 30%. As a demonstration, the PMS connected to a 240 mL two-chamber MFC (generating 0.4 V and 512 μW at MPP) successfully powered a wireless temperature sensor that requires a voltage of 2.5 V and consumes power of 85 mW each time it transmit the sensor data, and successfully transmitted a sensor reading every 7.5 min. The PMS also efficiently managed the power output of a lower-power producing MFC, demonstrating that the PMS works efficiently at various MFC power output level.

Dual functional passivating layer of graphene/TiO2 for improved performance of dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Shahid, Muhammad Umair; Mohamed, Norani Muti; Muhsan, Ali Samer; Khatani, Mehboob; Bashiri, Robabeh; Zaine, Siti Nur Azella; Shamsudin, Adel Eskandar

2018-02-01

The FTO/TiO2 interface plays a crucial role in the performance of dye-sensitized solar cells (DSSCs). The uneven microstructure morphology of FTO (fluorine-doped tin oxide) glass surface and high porosity of TiO2 layer produce tiny gaps and voids at the FTO/TiO2 interface that breaks the connectivity, leading to an increase in the recombination process. In the current work, a dual functional passivating layer is introduced by the combination of the graphene/TiO2 compact layer. The excellent mobility and flexibility of graphene is capitalized using its layer to fill the voids in the FTO surface, which can consequently reduce the charge transfer resistance at the interface, while the added TiO2 compact layer avoids direct contact with the electrolyte thus reducing the recombination. Graphene was synthesized by the facile solvent exfoliation method with the assistance of the probe sonication process. The parameters of sonication were optimized to achieve high-quality concentrated graphene inks (0.177-0.51 mg/ml). Raman spectroscopy and transmission electron microscopy (TEM) revealed that the graphene obtained is of a few-layer type. Electrochemical impedance spectroscopy (EIS) analysis indicated that the incorporated compact layer of graphene/TiO2 was capable of accelerating the charge transfer and reducing the recombination process at the FTO/TiO2 interface. Consequently, the photoconversion efficiency (PCE) for the device (1 cm2 active area) with double-coated graphene layer under one sun irradiation (AM 1.5) was found to be 49.49% higher than the conventional one.

Efficiency at maximum power of low-dissipation Carnot engines.

PubMed

Esposito, Massimiliano; Kawai, Ryoichi; Lindenberg, Katja; Van den Broeck, Christian

2010-10-08

We study the efficiency at maximum power, η*, of engines performing finite-time Carnot cycles between a hot and a cold reservoir at temperatures Th and Tc, respectively. For engines reaching Carnot efficiency ηC=1-Tc/Th in the reversible limit (long cycle time, zero dissipation), we find in the limit of low dissipation that η* is bounded from above by ηC/(2-ηC) and from below by ηC/2. These bounds are reached when the ratio of the dissipation during the cold and hot isothermal phases tend, respectively, to zero or infinity. For symmetric dissipation (ratio one) the Curzon-Ahlborn efficiency ηCA=1-√Tc/Th] is recovered.

Red light-induced formation of ubiquitin-phytochrome conjugates: Identification of possible intermediates of phytochrome degradation

PubMed Central

Shanklin, John; Jabben, Merten; Vierstra, Richard D.

1987-01-01

Phytochrome is the photoreceptor that controls red light-mediated morphogenesis in higher plants. It exists in two photointerconvertible forms, a red light-absorbing form, Pr, and a far-red light-absorbing form, Pfr. Because photoconversion of Pr to Pfr by a brief light pulse decreases the in vivo half-life of this chromoprotein by a factor of ≈100, this system offers a unique way to modulate the turnover rate of a specific protein and hence study the mechanisms responsible for selective protein degradation. In etiolated oat [Avena sativa (L.)] seedlings, degradation of phytochrome as Pfr follows zero-order kinetics as measured both spectrally and by ELISA, with 50% of Pfr lost in ≈130 min at 27°C. Immunoblot analysis of the destruction process with anti-oat phytochrome immunoglobulins reveals that degradation involves the loss of the 124-kDa phytochrome monomer and that proteolytic intermediates of apparent molecular mass lower than 124 kDa do not accumulate to detectable levels in vivo (<0.015% of total phytochrome). The latter observation suggests that proteolytic breakdown of the protein is extremely rapid. However, a series of polypeptides with higher apparent molecular mass and recognized by anti-phytochrome immunoglobulins (principally 129 and 134 kDa) appears after photoconversion to Pfr. These polypeptides represent no more than a few percent of the total immunologically detectable phytochrome pool and have incremental differences in apparent molecular mass of 5 kDa. They appear within 5 min after Pfr formation, reach maximal levels between 90 and 180 min, and decline thereafter. These polypeptides and others of apparent molecular mass up to 160 kDa are also detectable with immunoglobulins directed against either oat or human ubiquitin, indicating that they are ubiquitin-phytochrome conjugates. Since ubiquitin conjugation is involved in intracellular protein turnover and since formation and degradation of Pfr-ubiquitin conjugates coincide with the turnover of Pfr, these data suggest that the Pfr form of phytochrome is degraded via a ubiquitin-dependent proteolytic pathway. Images PMID:16593800

Complexin Mutants Reveal Partial Segregation between Recycling Pathways That Drive Evoked and Spontaneous Neurotransmission

PubMed Central

Sabeva, Nadezhda; Cho, Richard W.; Vasin, Alexander; Gonzalez, Agustin; Littleton, J. Troy

2017-01-01

Synaptic vesicles fuse at morphological specializations in the presynaptic terminal termed active zones (AZs). Vesicle fusion can occur spontaneously or in response to an action potential. Following fusion, vesicles are retrieved and recycled within nerve terminals. It is still unclear whether vesicles that fuse spontaneously or following evoked release share similar recycling mechanisms. Genetic deletion of the SNARE-binding protein complexin dramatically increases spontaneous fusion, with the protein serving as the synaptic vesicle fusion clamp at Drosophila synapses. We examined synaptic vesicle recycling pathways at complexin null neuromuscular junctions, where spontaneous release is dramatically enhanced. We combined loading of the lipophilic dye FM1–43 with photoconversion, electron microscopy, and electrophysiology to monitor evoked and spontaneous recycling vesicle pools. We found that the total number of recycling vesicles was equal to those retrieved through spontaneous and evoked pools, suggesting that retrieval following fusion is partially segregated for spontaneous and evoked release. In addition, the kinetics of FM1–43 destaining and synaptic depression measured in the presence of the vesicle-refilling blocker bafilomycin indicated that spontaneous and evoked recycling pools partially intermix during the release process. Finally, FM1–43 photoconversion combined with electron microscopy analysis indicated that spontaneous recycling preferentially involves synaptic vesicles in the vicinity of AZs, whereas vesicles recycled following evoked release involve a larger intraterminal pool. Together, these results suggest that spontaneous and evoked vesicles use separable recycling pathways and then partially intermix during subsequent rounds of fusion. SIGNIFICANCE STATEMENT Neurotransmitter release involves fusion of synaptic vesicles with the plasma membrane in response to an action potential, or spontaneously in the absence of stimulation. Upon fusion, vesicles are retrieved and recycled, and it is unclear whether recycling pathways for evoked and spontaneous vesicles are segregated after fusion. We addressed this question by taking advantage of preparations lacking the synaptic protein complexin, which have elevated spontaneous release that enables reliable tracking of the spontaneous recycling pool. Our results suggest that spontaneous and evoked recycling pathways are segregated during the retrieval process but can partially intermix during stimulation. PMID:28077717

Efficiency analysis of diffusion on T-fractals in the sense of random walks.

PubMed

Peng, Junhao; Xu, Guoai

2014-04-07

Efficiently controlling the diffusion process is crucial in the study of diffusion problem in complex systems. In the sense of random walks with a single trap, mean trapping time (MTT) and mean diffusing time (MDT) are good measures of trapping efficiency and diffusion efficiency, respectively. They both vary with the location of the node. In this paper, we analyze the effects of node's location on trapping efficiency and diffusion efficiency of T-fractals measured by MTT and MDT. First, we provide methods to calculate the MTT for any target node and the MDT for any source node of T-fractals. The methods can also be used to calculate the mean first-passage time between any pair of nodes. Then, using the MTT and the MDT as the measure of trapping efficiency and diffusion efficiency, respectively, we compare the trapping efficiency and diffusion efficiency among all nodes of T-fractal and find the best (or worst) trapping sites and the best (or worst) diffusing sites. Our results show that the hub node of T-fractal is the best trapping site, but it is also the worst diffusing site; and that the three boundary nodes are the worst trapping sites, but they are also the best diffusing sites. Comparing the maximum of MTT and MDT with their minimums, we find that the maximum of MTT is almost 6 times of the minimum of MTT and the maximum of MDT is almost equal to the minimum for MDT. Thus, the location of target node has large effect on the trapping efficiency, but the location of source node almost has no effect on diffusion efficiency. We also simulate random walks on T-fractals, whose results are consistent with the derived results.

Universality of maximum-work efficiency of a cyclic heat engine based on a finite system of ultracold atoms.

PubMed

Ye, Zhuolin; Hu, Yingying; He, Jizhou; Wang, Jianhui

2017-07-24

We study the performance of a cyclic heat engine which uses a small system with a finite number of ultracold atoms as its working substance and works between two heat reservoirs at constant temperatures T h and T c (

Blue phosphorescent organic light-emitting diodes using an exciplex forming co-host with the external quantum efficiency of theoretical limit.

PubMed

Shin, Hyun; Lee, Sunghun; Kim, Kwon-Hyeon; Moon, Chang-Ki; Yoo, Seung-Jun; Lee, Jeong-Hwan; Kim, Jang-Joo

2014-07-16

A high-efficiency blue-emitting organic light-emitting diode (OLED) approaching theoretical efficiency using an exciplex-forming co-host composed of N,N'-dicarbazolyl-3,5-benzene (mCP) and bis-4,6-(3,5-di-3-pyridylphenyl)- 2-methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis[(4,6-difluorophenyl)- pyridinato-N,C2']picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A(-1) ), which is in perfect agreement with the theoretical prediction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficient protocols for Stirling heat engines at the micro-scale

NASA Astrophysics Data System (ADS)

Muratore-Ginanneschi, Paolo; Schwieger, Kay

2015-10-01

We investigate the thermodynamic efficiency of sub-micro-scale Stirling heat engines operating under the conditions described by overdamped stochastic thermodynamics. We show how to construct optimal protocols such that at maximum power the efficiency attains for constant isotropic mobility the universal law η=2 ηC/(4-ηC) , where ηC is the efficiency of an ideal Carnot cycle. We show that these protocols are specified by the solution of an optimal mass transport problem. Such solution can be determined explicitly using well-known Monge-Ampère-Kantorovich reconstruction algorithms. Furthermore, we show that the same law describes the efficiency of heat engines operating at maximum work over short time periods. Finally, we illustrate the straightforward extension of these results to cases when the mobility is anisotropic and temperature dependent.

Achieving Extreme Utilization of Excitons by an Efficient Sandwich-Type Emissive Layer Architecture for Reduced Efficiency Roll-Off and Improved Operational Stability in Organic Light-Emitting Diodes.

PubMed

Wu, Zhongbin; Sun, Ning; Zhu, Liping; Sun, Hengda; Wang, Jiaxiu; Yang, Dezhi; Qiao, Xianfeng; Chen, Jiangshan; Alshehri, Saad M; Ahamad, Tansir; Ma, Dongge

2016-02-10

It has been demonstrated that the efficiency roll-off is generally caused by the accumulation of excitons or charge carriers, which is intimately related to the emissive layer (EML) architecture in organic light-emitting diodes (OLEDs). In this article, an efficient sandwich-type EML structure with a mixed-host EML sandwiched between two single-host EMLs was designed to eliminate this accumulation, thus simultaneously achieving high efficiency, low efficiency roll-off and good operational stability in the resulting OLEDs. The devices show excellent electroluminescence performances, realizing a maximum external quantum efficiency (EQE) of 24.6% with a maximum power efficiency of 105.6 lm W(-1) and a maximum current efficiency of 93.5 cd A(-1). At the high brightness of 5,000 cd m(-2), they still remain as high as 23.3%, 71.1 lm W(-1), and 88.3 cd A(-1), respectively. And, the device lifetime is up to 2000 h at initial luminance of 1000 cd m(-2), which is significantly higher than that of compared devices with conventional EML structures. The improvement mechanism is systematically studied by the dependence of the exciton distribution in EML and the exciton quenching processes. It can be seen that the utilization of the efficient sandwich-type EML broadens the recombination zone width, thus greatly reducing the exciton quenching and increasing the probability of the exciton recombination. It is believed that the design concept provides a new avenue for us to achieve high-performance OLEDs.

Limits on the maximum attainable efficiency for solid-state lighting

NASA Astrophysics Data System (ADS)

Coltrin, Michael E.; Tsao, Jeffrey Y.; Ohno, Yoshi

2008-03-01

Artificial lighting for general illumination purposes accounts for over 8% of global primary energy consumption. However, the traditional lighting technologies in use today, i.e., incandescent, fluorescent, and high-intensity discharge lamps, are not very efficient, with less than about 25% of the input power being converted to useful light. Solid-state lighting is a rapidly evolving, emerging technology whose efficiency of conversion of electricity to visible white light is likely to approach 50% within the next years. This efficiency is significantly higher than that of traditional lighting technologies, with the potential to enable a marked reduction in the rate of world energy consumption. There is no fundamental physical reason why efficiencies well beyond 50% could not be achieved, which could enable even greater world energy savings. The maximum achievable luminous efficacy for a solid-state lighting source depends on many different physical parameters, for example the color rendering quality that is required, the architecture employed to produce the component light colors that are mixed to produce white, and the efficiency of light sources producing each color component. In this article, we discuss in some detail several approaches to solid-state lighting and the maximum luminous efficacy that could be attained, given various constraints such as those listed above.

Highly efficient blue and warm white organic light-emitting diodes with a simplified structure

NASA Astrophysics Data System (ADS)

Li, Xiang-Long; Ouyang, Xinhua; Chen, Dongcheng; Cai, Xinyi; Liu, Ming; Ge, Ziyi; Cao, Yong; Su, Shi-Jian

2016-03-01

Two blue fluorescent emitters were utilized to construct simplified organic light-emitting diodes (OLEDs) and the remarkable difference in device performance was carefully illustrated. A maximum current efficiency of 4.84 cd A-1 (corresponding to a quantum efficiency of 4.29%) with a Commission Internationale de l’Eclairage (CIE) coordinate of (0.144, 0.127) was achieved by using N,N-diphenyl-4″-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1, 1‧:4‧, 1″-terphenyl]-4-amine (BBPI) as a non-doped emission layer of the simplified blue OLEDs without carrier-transport layers. In addition, simplified fluorescent/phosphorescent (F/P) hybrid warm white OLEDs without carrier-transport layers were fabricated by utilizing BBPI as (1) the blue emitter and (2) the host of a complementary yellow phosphorescent emitter (PO-01). A maximum current efficiency of 36.8 cd A-1 and a maximum power efficiency of 38.6 lm W-1 were achieved as a result of efficient energy transfer from the host to the guest and good triplet exciton confinement on the phosphorescent molecules. The blue and white OLEDs are among the most efficient simplified fluorescent blue and F/P hybrid white devices, and their performance is even comparable to that of most previously reported complicated multi-layer devices with carrier-transport layers.

A MATLAB toolbox for the efficient estimation of the psychometric function using the updated maximum-likelihood adaptive procedure

PubMed Central

Richards, V. M.; Dai, W.

2014-01-01

A MATLAB toolbox for the efficient estimation of the threshold, slope, and lapse rate of the psychometric function is described. The toolbox enables the efficient implementation of the updated maximum-likelihood (UML) procedure. The toolbox uses an object-oriented architecture for organizing the experimental variables and computational algorithms, which provides experimenters with flexibility in experimental design and data management. Descriptions of the UML procedure and the UML Toolbox are provided, followed by toolbox use examples. Finally, guidelines and recommendations of parameter configurations are given. PMID:24671826

Enhancing thermoelectric properties through a three-terminal benzene molecule

NASA Astrophysics Data System (ADS)

Sartipi, Z.; Vahedi, J.

2018-05-01

The thermoelectric transport through a benzene molecule with three metallic terminals is discussed. Using general local and non-local transport coefficients, we investigated different conductance and thermopower coefficients within the linear response regime. Based on the Onsager coefficients which depend on the number of terminal efficiencies, efficiency at maximum power is also studied. In the three-terminal setup with tuning temperature differences, a great enhancement of the figure of merit is observed. Results also show that the third terminal model can be useful in improving the efficiency at maximum output power compared to the two-terminal model.

The association between the maximum step length test and the walking efficiency in children with cerebral palsy.

PubMed

Kimoto, Minoru; Okada, Kyoji; Sakamoto, Hitoshi; Kondou, Takanori

2017-05-01

[Purpose] To improve walking efficiency could be useful for reducing fatigue and extending possible period of walking in children with cerebral palsy (CP). For this purpose, current study compared conventional parameters of gross motor performance, step length, and cadence in the evaluation of walking efficiency in children with CP. [Subjects and Methods] Thirty-one children with CP (21 boys, 10 girls; mean age, 12.3 ± 2.7 years) participated. Parameters of gross motor performance, including the maximum step length (MSL), maximum side step length, step number, lateral step up number, and single leg standing time, were measured in both dominant and non-dominant sides. Spatio-temporal parameters of walking, including speed, step length, and cadence, were calculated. Total heart beat index (THBI), a parameter of walking efficiency, was also calculated from heartbeats and walking distance in 10 minutes of walking. To analyze the relationships between these parameters and the THBI, the coefficients of determination were calculated using stepwise analysis. [Results] The MSL of the dominant side best accounted for the THBI (R 2 =0.759). [Conclusion] The MSL of the dominant side was the best explanatory parameter for walking efficiency in children with CP.

Highly Efficient Red and White Organic Light-Emitting Diodes with External Quantum Efficiency beyond 20% by Employing Pyridylimidazole-Based Metallophosphors.

PubMed

Miao, Yanqin; Tao, Peng; Wang, Kexiang; Li, Hongxin; Zhao, Bo; Gao, Long; Wang, Hua; Xu, Bingshe; Zhao, Qiang

2017-11-01

Two highly efficient red neutral iridium(III) complexes, Ir1 and Ir2, were rationally designed and synthesized by selecting two pyridylimidazole derivatives as the ancillary ligands. Both Ir1 and Ir2 show nearly the same photoluminescence emission with the maximum peak at 595 nm (shoulder band at about 638 nm) and achieve high solution quantum yields of up to 0.47 for Ir1 and 0.57 for Ir2. Employing Ir1 and Ir2 as emitters, the fabricated red organic light-emitting diodes (OLEDs) show outstanding performance with the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 20.98%, 33.04 cd/A, and 33.08 lm/W for the Ir1-based device and 22.15%, 36.89 cd/A, and 35.85 lm/W for the Ir2-based device, respectively. Furthermore, using Ir2 as red emitter, a trichromatic hybrid white OLED, showing good warm white emission with low correlated color temperature of <2200 K under the voltage of 4-6 V, was fabricated successfully. The white device also realizes excellent device efficiencies with the maximum EQE, CE, and PE reaching 22.74%, 44.77 cd/A, and 46.89 lm/W, respectively. Such high electroluminescence performance for red and white OLEDs indicates that Ir1 and Ir2 as efficient red phosphors have great potential for future OLED displays and lightings applications.

Power and Efficiency.

ERIC Educational Resources Information Center

Boyd, James N.

1991-01-01

Presents a mathematical problem that, when examined and generalized, develops the relationships between power and efficiency in energy transfer. Offers four examples of simple electrical and mechanical systems to illustrate the principle that maximum power occurs at 50 percent efficiency. (MDH)

Efficiency droop suppression of distance-engineered surface plasmon-coupled photoluminescence in GaN-based quantum well LEDs

NASA Astrophysics Data System (ADS)

Li, Yufeng; Wang, Shuai; Su, Xilin; Tang, Weihan; Li, Qiang; Guo, Maofeng; Zhang, Ye; Zhang, Minyan; Yun, Feng; Hou, Xun

2017-11-01

Ag coated microgroove with extreme large aspect-ratio of 500:1 was fabricated on p-GaN capping layer to investigate the coupling behavior between quantum wells and surface plasmon in highly spatial resolution. Significant photoluminescence enhancement was observed when the distance between Ag film and QWs was reduced from 220 nm to about 20 nm. A maximum enhancement ratio of 18-fold was achieved at the groove bottom where the surface plasmonic coupling was considered the strongest. Such enhancement ratio was found highly affected by the excitation power density. It also shows high correlation to the internal quantum efficiency as a function of coupling effect and a maximum Purcell Factor of 1.75 was estimated at maximum coupling effect, which matches number calculated independently from the time-resolved photoluminescence measurement. With such Purcell Factor, the efficiency was greatly enhanced and the droop was significantly suppressed.

On-line thermal dependence study of the main solar cell electrical photoconversion parameters using low thermal emission lamps.

PubMed

Gallardo, J J; Navas, J; Alcántara, R; Fernández-Lorenzo, C; Aguilar, T; Martín-Calleja, J

2012-06-01

This paper presents a non-conventional methodology and an instrumental system to measure the effect of temperature on the photovoltaic properties of solar cells. The system enables the direct measurement of the evolution of open-circuit voltage and short-circuit current intensity in relation to a continuously decreasing temperature. The system uses a high-intensity white light-emitting diode light source with low emissions of radiation in the infrared region of the electromagnetic spectrum, resulting in a reduced heating of the photovoltaic devices by the irradiation source itself. To check the goodness of the system and the methodology designed, several measurements were performed with monocrystalline silicon solar cells, dye-sensitized solar cells, and thin-film amorphous silicon solar cells, showing similar tendencies to those reported in the literature.

Photoconversion of 4-nitrophenol in the presence of hydrazine with AgNPs-TiO2 nanoparticles prepared by the sol-gel method.

PubMed

Hernández-Gordillo, Agileo; Arroyo, Missael; Zanella, R; Rodríguez-González, V

2014-03-15

The photocatalytic properties of functionalized TiO2 with silver nanoparticles (AgNPs) for the conversion of 4-nitrophenol to 4-aminophenol in the presence of hydrazine were investigated. The TiO2 semiconductor synthesized by the sol-gel method was functionalized with AgNPs at different loadings, and their structural and optical properties were characterized by several techniques. The functionalized TiO2 with 1.5wt% AgNPs presented the highest photocatalytic activity for the conversion of 4-nitrophenol with appropriate hydrazine concentrations (0.5M). The photoefficiency enhancement under UV light irradiation was attributed to the electron transfer from the TiO2 semiconductor surface to the adsorbed acceptor reactant (4-nitrophenol) through the deposited AgNPs. Copyright © 2014 Elsevier B.V. All rights reserved.

UV-biosensor for visual indication of vitamin D synthesis

NASA Astrophysics Data System (ADS)

Orlova, T. N.; Terenetskaya, I. P.

2008-04-01

Excessive UV doses have adverse effects on human health, but proper amount of UV is beneficial for people and is essential in the natural production of vitamin D# in skin. Most of broadband UV-radiometers that have an output in sunburn units are incapable to record correctly the vitamin D synthetic capacity of sunlight because of the difference between the CIE erythema and 'Vitamin D synthesis' action spectra. The liquid-crystalline UV sensor based on provitamin D photoconversions has been developed for direct observation of vitamin D synthesis under UV irradiation. UV-induced transformation of provitamin D in cholesteric liquid-crystalline matrix is accompanied by the change of cholesteric pitch value in the LC cell. The developed UV biosensor makes possible both instrumental and visual monitoring of the vitamin D synthetic capacity of sunlight and/or artificial UV source.

Development of a Highly Efficient Hybrid White Organic-Light-Emitting Diode with a Single Emission Layer by Solution Processing.

PubMed

Wu, Jun-Yi; Chen, Show-An

2018-02-07

We use a mixed host, 2,6-bis[3-(carbazol-9-yl)phenyl]pyridine blended with 20 wt % tris(4-carbazoyl-9-ylphenyl)amine, to lower the hole-injection barrier, along with the bipolar and high-photoluminescence-quantum-yield (Φ p = 84%), blue thermally activated delay fluorescence (TADF) material of 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) as a blue dopant to compose the emission layer for the fabrication of a TADF blue organic-light-emitting diode (BOLED). The device is highly efficient with the following performance parameters: maximum brightness (B max ) = 57586 cd/m 2 , maximum current efficiency (CE max ) = 35.3 cd/A, maximum power efficiency (PE max ) = 21.4 lm/W, maximum external quantum efficiency (EQE max ) = 14.1%, and CIE coordinates (0.18, 0.42). This device has the best performance recorded among the reported solution-processed TADF BOLEDs and has a low efficiency roll-off: at brightness values of 1000 and 5000 cd/m 2 , its CEs are close, being 35.1 and 30.1 cd/A, respectively. Upon further doping of the red phosphor Ir(dpm)PQ 2 (emission peak λ max = 595 nm) into the blue emission layer, we obtained a TADF-phosphor hybrid white organic-light-emitting diode (T-P hybrid WOLED) with high performance: B max = 43594 cd/m 2 , CE max = 28.8 cd/A, PE max = 18.1 lm/W, and CIE coordinates (0.38, 0.44). This B max = 43594 cd/m 2 is better than that of the vacuum-deposited WOLED with a blue TADF emitter, 10000 cd/m 2 . This is also the first report on a T-P hybrid WOLED with a solution-processed emitting layer.

Diode-pumped quasi-three-level CW Nd:CLNGG and Nd:CNGG lasers.

PubMed

He, Kunna; Wei, Zhiyi; Li, Dehua; Zhang, Zhiguo; Zhang, Huaijin; Wang, Jiyang; Gao, Chunqing

2009-10-12

We have demonstrated what is to our knowledge the first quasi-three-level CW Nd:CLNGG laser with simple linear resonator. When the pump power was 18.2 W, a maximum output power of 1.63 W was obtained at the dual-wavelength of 935 nm and 928 nm. The optical-to-optical conversion efficiency was 9.0% and the slope efficiency was 11.5%. Lasing characteristics of a quasi-three-level CW Nd:CNGG laser were also investigated. A maximum output power of 1.87 W was obtained at the single-wavelength of 935 nm with 15.2 W pump power, corresponding to an optical-to-optical conversion efficiency of 12.3% and a slope efficiency of 15.6%.

Fused Methoxynaphthyl Phenanthrimidazole Semiconductors as Functional Layer in High Efficient OLEDs.

PubMed

Jayabharathi, Jayaraman; Ramanathan, Periyasamy; Karunakaran, Chockalingam; Thanikachalam, Venugopal

2016-01-01

Efficient hole transport materials based on novel fused methoxynaphthyl phenanthrimidazole core structure were synthesised and characterized. Their device performances in phosphorescent organic light emitting diodes were investigated. The high thermal stability in combination with the reversible oxidation process made promising candidates as hole-transporting materials for organic light-emitting devices. Highly efficient Alq3-based organic light emitting devices have been developed using phenanthrimidazoles as functional layers between NPB [4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl] and Alq3 [tris(8-hydroxyquinoline)aluminium] layers. Using the device of ITO/NPB/4/Alq3/LiF/Al, a maximum luminous efficiency of 5.99 cd A(-1) was obtained with a maximum brightness of 40,623 cd m(-2) and a power efficiency of 5.25 lm W(-1).

Highly efficient green phosphorescent organic light emitting diodes with improved efficiency roll-off

NASA Astrophysics Data System (ADS)

Thangaraju, K.; Lee, Jonghee; Lee, Jeong-Ik; Chu, Hye Yong; Kim, Yun-Hi; Kwon, Soon-Ki

2015-06-01

A 10-nm thick 4,4',4″-tris(carbazole-9-yl)tri-phenylamine (TcTa) interlayer effectively confines triplet excitons within the emissive layer (EML) of phosphorescent organic light emitting diodes (PHOLEDs) based on green-emitting Ir(ppy)3 dopant and improves the charge balance in the EML of the device, resulting the higher device efficiencies of 61.7 cd/A, 19.7 %, and 43.2 lm/W with the maximum luminance of 75,310 cd/m2 and highly improved efficiency roll-off (22.2% at 20 mA/cm2) when compared to those (61.1 cd/A, 19.6 %, and 47.2 lm/W with a maximum luminance of 38,350 cd/m2) of the standard device with efficiency roll-off of 62.3 % at 20 mA/cm2.

Trellises and Trellis-Based Decoding Algorithms for Linear Block Codes. Part 3; A Recursive Maximum Likelihood Decoding

NASA Technical Reports Server (NTRS)

Lin, Shu; Fossorier, Marc

1998-01-01

The Viterbi algorithm is indeed a very simple and efficient method of implementing the maximum likelihood decoding. However, if we take advantage of the structural properties in a trellis section, other efficient trellis-based decoding algorithms can be devised. Recently, an efficient trellis-based recursive maximum likelihood decoding (RMLD) algorithm for linear block codes has been proposed. This algorithm is more efficient than the conventional Viterbi algorithm in both computation and hardware requirements. Most importantly, the implementation of this algorithm does not require the construction of the entire code trellis, only some special one-section trellises of relatively small state and branch complexities are needed for constructing path (or branch) metric tables recursively. At the end, there is only one table which contains only the most likely code-word and its metric for a given received sequence r = (r(sub 1), r(sub 2),...,r(sub n)). This algorithm basically uses the divide and conquer strategy. Furthermore, it allows parallel/pipeline processing of received sequences to speed up decoding.

Efficient robust doubly adaptive regularized regression with applications.

PubMed

Karunamuni, Rohana J; Kong, Linglong; Tu, Wei

2018-01-01

We consider the problem of estimation and variable selection for general linear regression models. Regularized regression procedures have been widely used for variable selection, but most existing methods perform poorly in the presence of outliers. We construct a new penalized procedure that simultaneously attains full efficiency and maximum robustness. Furthermore, the proposed procedure satisfies the oracle properties. The new procedure is designed to achieve sparse and robust solutions by imposing adaptive weights on both the decision loss and the penalty function. The proposed method of estimation and variable selection attains full efficiency when the model is correct and, at the same time, achieves maximum robustness when outliers are present. We examine the robustness properties using the finite-sample breakdown point and an influence function. We show that the proposed estimator attains the maximum breakdown point. Furthermore, there is no loss in efficiency when there are no outliers or the error distribution is normal. For practical implementation of the proposed method, we present a computational algorithm. We examine the finite-sample and robustness properties using Monte Carlo studies. Two datasets are also analyzed.

Shape optimization for aerodynamic efficiency and low observability

NASA Technical Reports Server (NTRS)

Vinh, Hoang; Van Dam, C. P.; Dwyer, Harry A.

1993-01-01

Field methods based on the finite-difference approximations of the time-domain Maxwell's equations and the potential-flow equation have been developed to solve the multidisciplinary problem of airfoil shaping for aerodynamic efficiency and low radar cross section (RCS). A parametric study and an optimization study employing the two analysis methods are presented to illustrate their combined capabilities. The parametric study shows that for frontal radar illumination, the RCS of an airfoil is independent of the chordwise location of maximum thickness but depends strongly on the maximum thickness, leading-edge radius, and leadingedge shape. In addition, this study shows that the RCS of an airfoil can be reduced without significant effects on its transonic aerodynamic efficiency by reducing the leading-edge radius and/or modifying the shape of the leading edge. The optimization study involves the minimization of wave drag for a non-lifting, symmetrical airfoil with constraints on the airfoil maximum thickness and monostatic RCS. This optimization study shows that the two analysis methods can be used effectively to design aerodynamically efficient airfoils with certain desired RCS characteristics.

Improving a free air breathing proton exchange membrane fuel cell through the Maximum Efficiency Point Tracking method

NASA Astrophysics Data System (ADS)

Higuita Cano, Mauricio; Mousli, Mohamed Islam Aniss; Kelouwani, Sousso; Agbossou, Kodjo; Hammoudi, Mhamed; Dubé, Yves

2017-03-01

This work investigates the design and validation of a fuel cell management system (FCMS) which can perform when the fuel cell is at water freezing temperature. This FCMS is based on a new tracking technique with intelligent prediction, which combined the Maximum Efficiency Point Tracking with variable perturbation-current step and the fuzzy logic technique (MEPT-FL). Unlike conventional fuel cell control systems, our proposed FCMS considers the cold-weather conditions, the reduction of fuel cell set-point oscillations. In addition, the FCMS is built to respond quickly and effectively to the variations of electric load. A temperature controller stage is designed in conjunction with the MEPT-FL in order to operate the FC at low-temperature values whilst tracking at the same time the maximum efficiency point. The simulation results have as well experimental validation suggest that propose approach is effective and can achieve an average efficiency improvement up to 8%. The MEPT-FL is validated using a Proton Exchange Membrane Fuel Cell (PEMFC) of 500 W.

Irreversibilities and efficiency at maximum power of heat engines: the illustrative case of a thermoelectric generator.

PubMed

Apertet, Y; Ouerdane, H; Goupil, C; Lecoeur, Ph

2012-03-01

Energy conversion efficiency at maximum output power, which embodies the essential characteristics of heat engines, is the main focus of the present work. The so-called Curzon and Ahlborn efficiency η(CA) is commonly believed to be an absolute reference for real heat engines; however, a different but general expression for the case of stochastic heat engines, η(SS), was recently found and then extended to low-dissipation engines. The discrepancy between η(CA) and η(SS) is here analyzed considering different irreversibility sources of heat engines, of both internal and external types. To this end, we choose a thermoelectric generator operating in the strong-coupling regime as a physical system to qualitatively and quantitatively study the impact of the nature of irreversibility on the efficiency at maximum output power. In the limit of pure external dissipation, we obtain η(CA), while η(SS) corresponds to the case of pure internal dissipation. A continuous transition between from one extreme to the other, which may be operated by tuning the different sources of irreversibility, also is evidenced.

Time-varying span efficiency through the wingbeat of desert locusts.

PubMed

Henningsson, Per; Bomphrey, Richard J

2012-06-07

The flight performance of animals depends greatly on the efficacy with which they generate aerodynamic forces. Accordingly, maximum range, load-lifting capacity and peak accelerations during manoeuvres are all constrained by the efficiency of momentum transfer to the wake. Here, we use high-speed particle image velocimetry (1 kHz) to record flow velocities in the near wake of desert locusts (Schistocerca gregaria, Forskål). We use the measured flow fields to calculate time-varying span efficiency throughout the wing stroke cycle. The locusts are found to operate at a maximum span efficiency of 79 per cent, typically at a plateau of about 60 per cent for the majority of the downstroke, but at lower values during the upstroke. Moreover, the calculated span efficiencies are highest when the largest lift forces are being generated (90% of the total lift is generated during the plateau of span efficiency) suggesting that the combination of wing kinematics and morphology in locust flight perform most efficiently when doing the most work.

Thermodynamic analysis of steam-injected advanced gas turbine cycles

NASA Astrophysics Data System (ADS)

Pandey, Devendra; Bade, Mukund H.

2017-12-01

This paper deals with thermodynamic analysis of steam-injected gas turbine (STIGT) cycle. To analyse the thermodynamic performance of steam-injected gas turbine (STIGT) cycles, a methodology based on pinch analysis is proposed. This graphical methodology is a systematic approach proposed for a selection of gas turbine with steam injection. The developed graphs are useful for selection of steam-injected gas turbine (STIGT) for optimal operation of it and helps designer to take appropriate decision. The selection of steam-injected gas turbine (STIGT) cycle can be done either at minimum steam ratio (ratio of mass flow rate of steam to air) with maximum efficiency or at maximum steam ratio with maximum net work conditions based on the objective of plants designer. Operating the steam injection based advanced gas turbine plant at minimum steam ratio improves efficiency, resulting in reduction of pollution caused by the emission of flue gases. On the other hand, operating plant at maximum steam ratio can result in maximum work output and hence higher available power.

Possible improvements in gasoline engines

NASA Technical Reports Server (NTRS)

Ziembinski, S

1923-01-01

High-compression engines are investigated with the three main objects being elimination of vibration, increase of maximum efficiency, and conservation of this efficiency at the highest possible speeds.

Emittance Theory for Cylindrical Fiber Selective Emitter

NASA Technical Reports Server (NTRS)

Chubb, Donald L.

1998-01-01

A fibrous rare earth selective emitter is approximated as an infinitely long cylinder. The spectral emittance, epsilon(lambda), is obtained by solving the radiative transfer equations with appropriate boundary conditions and uniform temperature. For optical depths, Kappa(R) = alpha(lambda)R, where alpha(lambda) is the extinction coefficient and R is the cylinder radius, greater than 1 the spectral emittance is nearly at its maximum value. There is an optimum cylinder radius, R(opt), for maximum emitter efficiency, eta(E). Values for R(opt) are strongly dependent on the number of emission bands of the material. The optimum radius decreases slowly with increasing emitter temperature, while the maximum efficiency and useful radiated power increase rapidly with increasing temperature.

Efficiency and its bounds for a quantum Einstein engine at maximum power.

PubMed

Yan, H; Guo, Hao

2012-11-01

We study a quantum thermal engine model for which the heat transfer law is determined by Einstein's theory of radiation. The working substance of the quantum engine is assumed to be a two-level quantum system of which the constituent particles obey Maxwell-Boltzmann (MB), Fermi-Dirac (FD), or Bose-Einstein (BE) distributions, respectively, at equilibrium. The thermal efficiency and its bounds at maximum power of these models are derived and discussed in the long and short thermal contact time limits. The similarity and difference between these models are discussed. We also compare the efficiency bounds of this quantum thermal engine to those of its classical counterpart.

The relationship between the thermoelectric generator efficiency and the device engineering figure of merit Zd,eng. The maximum efficiency 𝜼max

NASA Astrophysics Data System (ADS)

Hapenciuc, C. L.; Borca-Tasciuc, T.; Mihailescu, I. N.

2017-04-01

Thermoelectric materials are used today in thermoelectric devices for heat to electricity(thermoelectric generators-TEG) or electricity to heat(heat pumps) conversion in a large range of applications. In the case of TEGs the final measure of their performance is given by a quantity named the maximum efficiency which shows how much from the heat input is converted into electrical power. Therefore it is of great interest to know correctly how much is the efficiency of a device to can make commercial assessments. The concept of engineering figure of merit, Zeng, and engineering power factor, Peng, were already introduced in the field to quantify the efficiency of a single material under temperature dependent thermoelectric properties, with the mention that the formulas derivation was limited to one leg of the thermoelectric generator. In this paper we propose to extend the concept of engineering figure of merit to a thermoelectric generator by introducing a more general concept of device engineering thermoelectric figure of merit, Zd,eng, which depends on the both TEG materials properties and which shall be the right quantity to be used when we are interested in the evaluation of the efficiency. Also, this work takes into account the electrical contact resistance between the electrodes and thermoelement legs in an attempt to quantify its influence upon the performance of a TEG. Finally, a new formula is proposed for the maximum efficiency of a TEG.

Comparison of the efficiency of rat papillary muscles during afterloaded isotonic contractions and contractions with sinusoidal length changes.

PubMed

Mellors, L J; Gibbs, C L; Barclay, C J

2001-05-01

The results of previous studies suggest that the maximum mechanical efficiency of rat papillary muscles is lower during a contraction protocol involving sinusoidal length changes than during one involving afterloaded isotonic contractions. The aim of this study was to compare directly the efficiency of isolated rat papillary muscle preparations in isotonic and sinusoidal contraction protocols. Experiments were performed in vitro (27 degrees C) using left ventricular papillary muscles from adult rats. Each preparation performed three contraction protocols: (i) low-frequency afterloaded isotonic contractions (10 twitches at 0.2 Hz), (ii) sinusoidal length change contractions with phasic stimulation (40 twitches at 2 Hz) and (iii) high-frequency afterloaded isotonic contractions (40 twitches at 2 Hz). The first two protocols resembled those used in previous studies and the third combined the characteristics of the first two. The parameters for each protocol were adjusted to those that gave maximum efficiency. For the afterloaded isotonic protocols, the afterload was set to 0.3 of the maximum developed force. The sinusoidal length change protocol incorporated a cycle amplitude of +/-5% resting length and a stimulus phase of -10 degrees. Measurements of force output, muscle length change and muscle temperature change were used to calculate the work and heat produced during and after each protocol. Net mechanical efficiency was defined as the proportion of the energy (enthalpy) liberated by the muscle that appeared as work. The efficiency in the low-frequency, isotonic contraction protocol was 21.1+/-1.4% (mean +/- s.e.m., N=6) and that in the sinusoidal protocol was 13.2+/-0.7%, consistent with previous results. This difference was not due to the higher frequency or greater number of twitches because efficiency in the high-frequency, isotonic protocol was 21.5+/-1.0%. Although these results apparently confirm that efficiency is protocol-dependent, additional experiments designed to measure work output unambiguously indicated that the method used to calculate work output in isotonic contractions overestimated actual work output. When net work output, which excludes work done by parallel elastic elements, rather than total work output was used to determine efficiency in afterloaded isotonic contractions, efficiency was similar to that for sinusoidal contractions. The maximum net mechanical efficiency of rat papillary muscles performing afterloaded isotonic or sinusoidal length change contractions was between 10 and 15%.

Study of EHD flow generator's efficiencies utilizing pin to single ring and multi-concentric rings electrodes

NASA Astrophysics Data System (ADS)

Sumariyah; Kusminart; Hermanto, A.; Nuswantoro, P.

2016-11-01

EHD flow or ionic wind yield corona discharge is a stream coming from the ionized gas. EHD is generated by a strong electric field and its direction follows the electric field lines. In this study, the efficiency of the EHD flow generators utilizing pin-multi concentric rings electrodes (P-MRE) and the EHD pin-single ring electrode (P-SRE) have been measured. The comparison of efficiencies two types of the generator has been done. EHD flow was generated by using a high-voltage DC 0-10 KV on the electrode pin with a positive polarity and electrode ring/ multi-concentric rings of negative polarity. The efficiency was calculated by comparison between the mechanical power of flow to the electrical power that consumed. We obtained that the maximum efficiency of EHD flow generator utilizing pin-multi concentric rings electrodes was 0.54% and the maximum efficiency of EHD flow generator utilizing a pin-single ring electrode was 0.23%. Efficiency of EHD with P-MRE 2.34 times Efficiency of EHD with P-SRE

Spectroscopic and laser characterization of Yb,Tm:KLu(WO4)2 crystal

NASA Astrophysics Data System (ADS)

Loiko, P. A.; Serres, J. M.; Mateos, X.; Demesh, M. P.; Yasukevich, A. S.; Yumashev, K. V.; Petrov, V.; Griebner, U.; Aguiló, M.; Díaz, F.

2016-01-01

We report on a comprehensive spectroscopic and laser characterization of monoclinic Yb,Tm:KLu(WO4)2 crystals. Stimulated-emission cross-section spectra corresponding to the 3F4 → 3H6 transition of Tm3+ ions are determined. The radiative lifetime of the 3F4 state of Tm3+ ions is 0.82 ms. The maximum Yb3+ → Tm3+ energy transfer efficiency is 83.9% for 5 at.% Yb - 8 at.% Tm doping. The fractional heat loading for Yb,Tm:KLu(WO4)2 is 0.45 ± 0.05. Using a hemispherical cavity and 5 at.% Yb - 6 at.% Tm doped crystal, a maximum CW power of 227 mW is achieved at 1.983-2.011 μm with a maximum slope efficiency η = 14%. In the microchip laser set-up, the highest slope efficiency is 20% for a 5 at.% Yb- 8 at.% Tm doped crystal with a maximum output power of 201 mW at 1.99-2.007 μm. Operation of Yb,Tm:KLu(WO4)2 as a vibronic laser emitting at 2.081-2.093 μm is also demonstrated.

High efficiency, linearly polarized, directly diode-pumped Er:YAG laser at 1617  nm.

PubMed

Yu, Zhenzhen; Wang, Mingjian; Hou, Xia; Chen, Weibiao

2014-12-01

An efficient, directly diode-pumped Er:YAG laser at 1617 nm was demonstrated. A folding mirror with high reflectivity for the s-polarized light at the laser wavelength was used to achieve a linearly polarized laser. A maximum continuous-wave output power of 7.73 W was yielded under incident pump power of 50.57 W, and the optical conversion efficiency with respect to incident pump power was ∼15.28%, which was the highest optical conversion efficiency with directly diode-pumped Er:YAG lasers up to now; in Q-switched operation, the maximum pulse energy of 7.82 mJ was generated with pulse duration of about 80 ns at a pulse repetition frequency of 500 Hz.

43 CFR 418.13 - Maximum allowable limits.

Code of Federal Regulations, 2012 CFR

2012-10-01

... OF THE INTERIOR OPERATING CRITERIA AND PROCEDURES FOR THE NEWLANDS RECLAMATION PROJECT, NEVADA... 308,319 acre-feet for the 1995 Example. The sample MAD corresponds to a system efficiency for full... Expected Project Distribution System Efficiency shows the target efficiencies which will be used over the...

Summary of high efficiency silicon solar cell meeting held at NASA-Lewis

NASA Technical Reports Server (NTRS)

Bernatowicz, D. T.

1975-01-01

Attempts made to raise the efficiency of solar cells for space use are reported. The Helios, violet, and non-reflective cells were studied and it was concluded that the maximum practical efficiency of silicon solar cells is between 17 and 20%.

43 CFR 418.13 - Maximum allowable limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... OF THE INTERIOR OPERATING CRITERIA AND PROCEDURES FOR THE NEWLANDS RECLAMATION PROJECT, NEVADA... 308,319 acre-feet for the 1995 Example. The sample MAD corresponds to a system efficiency for full... Expected Project Distribution System Efficiency shows the target efficiencies which will be used over the...

Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

NASA Astrophysics Data System (ADS)

Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

2016-10-01

Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment Dipika Sharmaa, Vibha R. Satsangib, Rohit Shrivastava, Umesh V. Waghmarec, Sahab Dassa aDepartment of Chemistry, Dayalbagh Educational Institute, Agra-282 110 (India) bDepartment of Physics and Computer Sciences, Dayalbagh Educational Institute, Agra-282 110 (India) cTheoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560 064 (India) * Phone: +91-9219695960. Fax: +91-562-2801226. E-mail: drsahabdas@gmail.com. Study on photoelectrochemical activity of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction has been carried out using DFT based band offsets and charge carriers effective mass calculations and their experimental verification. The results of DFT calculations show that BaTiO3 and Cu2O have staggered type band alignment after the heterojunction formation and high mobility of electrons in Cu2O as compared to the electrons in BaTiO3. Staggered type band edges alignment and high mobility of electrons and holes improved the separation of photo-generated charge carriers in BaTiO3/Cu2O heterojunction. To validate the theoretical results experiments were carried out on pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction with varying thickness of Cu2O. All samples were characterized by X- Ray Diffractometer, SEM and UV-Vis spectrometry. Nanostructured thin films of pristine BaTiO3, Cu2O and BaTiO3/Cu2O heterojunction were used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.44 mA/cm2 at 0.90 V/SCE was exhibited by 442 nm thick BaTiO3/Cu2O heterojunction photoelectrode Increased photocurrent density and enhanced photoconversion efficiency, exhibited by the heterojunction may be attributed to improved conductivity and enhanced separation of the photogenerated carriers at the BaTiO3/Cu2O interface. The experimental results and first-principles calculations compare well, thus suggesting that such calculations have the potential to be used in screening various metal oxide heterojunction before performing the experiments thereby saving precious chemicals, time and energy. Keywords: Photoelectrochemical, Water splitting, heterojunction, Cu2O, BaTiO3 References: [1] Surbhi Choudhary, et al. Nanostructured bilayered thin films in photoelectrochemical water splitting - A review: International Journal of Hydrogen Energy, (2012). [2] Dipika Sharma, Anuradha Verma, V.R. Satsangi, Rohit shrivastav, Sahab Dass Nanostructured SrTiO3 thin films sensitized by Cu2O for Photoelectrochemical Hydrogen Generation. International journal of Hydrogen Energy;42:,4230-4241, 2014.

Improvement of Transparent Conducting Performance on Oxygen-Activated Fluorine-Doped Tin Oxide Electrodes Formed by Horizontal Ultrasonic Spray Pyrolysis Deposition.

PubMed

Koo, Bon-Ryul; Oh, Dong-Hyeun; Riu, Doh-Hyung; Ahn, Hyo-Jin

2017-12-27

In this study, highly transparent conducting fluorine-doped tin oxide (FTO) electrodes were fabricated using the horizontal ultrasonic spray pyrolysis deposition. In order to improve their transparent conducting performances, we carried out oxygen activation by adjusting the ratio of O 2 /(O 2 +N 2 ) in the carrier gas (0%, 20%, and 50%) used during the deposition process. The oxygen activation on the FTO electrodes accelerated the substitution concentration of F (F O • ) into the oxygen sites in the FTO electrode while the oxygen vacancy (V O • • ) concentration was reduced. In addition, due to growth of pyramid-shaped crystallites with (200) preferred orientations, this oxygen activation caused the formation of a uniform surface structure. As a result, compared to others, the FTO electrode prepared at 50% O 2 showed excellent electrical and optical properties (sheet resistance of ∼4.0 ± 0.14 Ω/□, optical transmittance of ∼85.3%, and figure of merit of ∼5.09 ± 0.19 × 10 -2 Ω -1 ). This led to a superb photoconversion efficiency (∼7.03 ± 0.20%) as a result of the improved short-circuit current density. The photovoltaic performance improvement can be defined by the decreased sheet resistance of FTO used as a transparent conducting electrode in dye-sensitized solar cells (DSSCs), which is due to the combined effect of the high carrier concentration by the improved F O • concentration on the FTO electrodes and the fasted Hall mobility by the formation of a uniform FTO surface structure and distortion relaxation on the FTO lattices resulting from the reduced V O • • • concentration.

Biological applications of an LCoS-based programmable array microscope (PAM)

NASA Astrophysics Data System (ADS)

Hagen, Guy M.; Caarls, Wouter; Thomas, Martin; Hill, Andrew; Lidke, Keith A.; Rieger, Bernd; Fritsch, Cornelia; van Geest, Bert; Jovin, Thomas M.; Arndt-Jovin, Donna J.

2007-02-01

We report on a new generation, commercial prototype of a programmable array optical sectioning fluorescence microscope (PAM) for rapid, light efficient 3D imaging of living specimens. The stand-alone module, including light source(s) and detector(s), features an innovative optical design and a ferroelectric liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM) instead of the DMD used in the original PAM design. The LCoS PAM (developed in collaboration with Cairn Research, Ltd.) can be attached to a port of a(ny) unmodified fluorescence microscope. The prototype system currently operated at the Max Planck Institute incorporates a 6-position high-intensity LED illuminator, modulated laser and lamp light sources, and an Andor iXon emCCD camera. The module is mounted on an Olympus IX71 inverted microscope with 60-150X objectives with a Prior Scientific x,y, and z high resolution scanning stages. Further enhancements recently include: (i) point- and line-wise spectral resolution and (ii) lifetime imaging (FLIM) in the frequency domain. Multiphoton operation and other nonlinear techniques should be feasible. The capabilities of the PAM are illustrated by several examples demonstrating single molecule as well as lifetime imaging in live cells, and the unique capability to perform photoconversion with arbitrary patterns and high spatial resolution. Using quantum dot coupled ligands we show real-time binding and subsequent trafficking of individual ligand-growth factor receptor complexes on and in live cells with a temporal resolution and sensitivity exceeding those of conventional CLSM systems. The combined use of a blue laser and parallel LED or visible laser sources permits photoactivation and rapid kinetic analysis of cellular processes probed by photoswitchable visible fluorescent proteins such as DRONPA.

Identifying barriers to charge-carriers in the bulk and surface regions of Cu2ZnSnS4 nanocrystal films by x-ray absorption fine structures (XAFSs)

NASA Astrophysics Data System (ADS)

Turnbull, Matthew J.; Vaccarello, Daniel; Yiu, Yun Mui; Sham, Tsun-Kong; Ding, Zhifeng

2016-11-01

Solar cell performance is most affected by the quality of the light absorber layer. For thin-film devices, this becomes a two-fold problem of maintaining a low-cost design with well-ordered nanocrystal (NC) structure. The use of Cu2ZnSnS4 (CZTS) NCs as the light absorber films forms an ideal low-cost design, but the quaternary structure makes it difficult to maintain a well-ordered layer without the use of high-temperature treatments. There is little understanding of how CZTS NC structures affect the photoconversion efficiency, the charge-carriers, and therefore the performance of the device manufactured from it. To examine these relationships, the measured photoresponse from the photo-generation of charge-carrier electron-hole pairs was compared against the crystal structure, as short-range and long-range crystal orders for the films. The photoresponse simplifies the electronic properties into three basic steps that can be associated with changes in energy levels within the band structure. These changes result in the formation of barriers to charge-carrier flow. The extent of these barriers was determined using synchrotron-based X-ray absorbance fine structure to probe the individual metal centers in the film, and comparing these to molecular simulations of the ideal extended x-ray absorbance fine structure scattering. This allowed for the quantification of bond lengths, and thus an interpretation of the distortions in the crystal lattice. The various characteristics of the photoresponse were then correlated to the crystallographic order and used to gain physical insight into barriers to charge-carriers in the bulk and surface regions of CZTS films.

Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites.

PubMed

Turkevych, Ivan; Kazaoui, Said; Ito, Eisuke; Urano, Toshiyuki; Yamada, Koji; Tomiyasu, Hiroshi; Yamagishi, Hideo; Kondo, Michio; Aramaki, Shinji

2017-10-09

Hybrid CPbX 3 (C: Cs, CH 3 NH 3 ; X: Br, I) perovskites possess excellent photovoltaic properties but are highly toxic, which hinders their practical application. Unfortunately, all Pb-free alternatives based on Sn and Ge are extremely unstable. Although stable and non-toxic C 2 ABX 6 double perovskites based on alternating corner-shared AX 6 and BX 6 octahedra (A=Ag, Cu; B=Bi, Sb) are possible, they have indirect and wide band gaps of over 2 eV. However, is it necessary to keep the corner-shared perovskite structure to retain good photovoltaic properties? Here, we demonstrate another family of photovoltaic halides based on edge-shared AX 6 and BX 6 octahedra with the general formula A a B b X x (x=a+3 b) such as Ag 3 BiI 6 , Ag 2 BiI 5 , AgBiI 4 , AgBi 2 I 7 . As perovskites were named after their prototype oxide CaTiO 3 discovered by Lev Perovski, we propose to name these new ABX halides as rudorffites after Walter Rüdorff, who discovered their prototype oxide NaVO 2 . We studied structural and optoelectronic properties of several highly stable and promising Ag-Bi-I photovoltaic rudorffites that feature direct band gaps in the range of 1.79-1.83 eV and demonstrated a proof-of-concept FTO/c-m-TiO 2 /Ag 3 BiI 6 /PTAA/Au (FTO: fluorine-doped tin oxide, PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], c: compact, m: mesoporous) solar cell with photoconversion efficiency of 4.3 %. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spatio-Temporal Convergence of Maximum Daily Light-Use Efficiency Based on Radiation Absorption by Canopy Chlorophyll

NASA Astrophysics Data System (ADS)

Zhang, Yao; Xiao, Xiangming; Wolf, Sebastian; Wu, Jin; Wu, Xiaocui; Gioli, Beniamino; Wohlfahrt, Georg; Cescatti, Alessandro; van der Tol, Christiaan; Zhou, Sha; Gough, Christopher M.; Gentine, Pierre; Zhang, Yongguang; Steinbrecher, Rainer; Ardö, Jonas

2018-04-01

Light-use efficiency (LUE), which quantifies the plants' efficiency in utilizing solar radiation for photosynthetic carbon fixation, is an important factor for gross primary production estimation. Here we use satellite-based solar-induced chlorophyll fluorescence as a proxy for photosynthetically active radiation absorbed by chlorophyll (APARchl) and derive an estimation of the fraction of APARchl (fPARchl) from four remotely sensed vegetation indicators. By comparing maximum LUE estimated at different scales from 127 eddy flux sites, we found that the maximum daily LUE based on PAR absorption by canopy chlorophyll (ɛmaxchl), unlike other expressions of LUE, tends to converge across biome types. The photosynthetic seasonality in tropical forests can also be tracked by the change of fPARchl, suggesting the corresponding ɛmaxchl to have less seasonal variation. This spatio-temporal convergence of LUE derived from fPARchl can be used to build simple but robust gross primary production models and to better constrain process-based models.

Optimized operation of dielectric laser accelerators: Single bunch

NASA Astrophysics Data System (ADS)

Hanuka, Adi; Schächter, Levi

2018-05-01

We introduce a general approach to determine the optimal charge, efficiency and gradient for laser driven accelerators in a self-consistent way. We propose a way to enhance the operational gradient of dielectric laser accelerators by leverage of beam-loading effect. While the latter may be detrimental from the perspective of the effective gradient experienced by the particles, it can be beneficial as the effective field experienced by the accelerating structure, is weaker. As a result, the constraint imposed by the damage threshold fluence is accordingly weakened and our self-consistent approach predicts permissible gradients of ˜10 GV /m , one order of magnitude higher than previously reported experimental results—with unbunched pulse of electrons. Our approach leads to maximum efficiency to occur for higher gradients as compared with a scenario in which the beam-loading effect on the material is ignored. In any case, maximum gradient does not occur for the same conditions that maximum efficiency does—a trade-off set of parameters is suggested.

A New Method to Measure Temperature and Burner Pattern Factor Sensing for Active Engine Control

NASA Technical Reports Server (NTRS)

Ng, Daniel

1999-01-01

The determination of the temperatures of extended surfaces which exhibit non-uniform temperature variation is very important for a number of applications including the "Burner Pattern Factor" (BPF) of turbine engines. Exploratory work has shown that use of BPF to control engine functions can result in many benefits, among them reduction in engine weight, reduction in operating cost, increase in engine life, while attaining maximum engine efficiency. Advanced engines are expected to operate at very high temperature to achieve high efficiency. Brief exposure of engine components to higher than design temperatures due to non-uniformity in engine burner pattern can reduce engine life. The engine BPF is a measure of engine temperature uniformity. Attainment of maximum temperature uniformity and high temperatures is key to maximum efficiency and long life. A new approach to determine through the measurement of just one radiation spectrum by a multiwavelength pyrometer is possible. This paper discusses a new temperature sensing approach and its application to determine the BPF.

Universal Expression of Efficiency at Maximum Power: A Quantum-Mechanical Brayton Engine Working with a Single Particle Confined in a Power-Law Trap

NASA Astrophysics Data System (ADS)

Ye, Zhuo-Lin; Li, Wei-Sheng; Lai, Yi-Ming; He, Ji-Zhou; Wang, Jian-Hui

2015-12-01

We propose a quantum-mechanical Brayton engine model that works between two superposed states, employing a single particle confined in an arbitrary power-law trap as the working substance. Applying the superposition principle, we obtain the explicit expressions of the power and efficiency, and find that the efficiency at maximum power is bounded from above by the function: η+ = θ/(θ + 1), with θ being a potential-dependent exponent. Supported by the National Natural Science Foundation of China under Grant Nos. 11505091, 11265010, and 11365015, and the Jiangxi Provincial Natural Science Foundation under Grant No. 20132BAB212009

The Economic Efficiency of Financial Markets

NASA Astrophysics Data System (ADS)

Wang, Yougui

In this paper, we investigate the economic efficiency of markets and specify its applicability to financial markets. The statistical expressions of supply and demand of a market are formulated in terms of willingness prices. By introducing probability of realized exchange, we also formulate the realized market surplus. It can be proved that only when the market is in equilibrium the realized surplus can reach its maximum value. The market efficiency can be measured by the ratio of realized surplus to its maximum value. For a financial market, the market participants are composed of two groups: producers and speculators. The former brings the surplus into the market and the latter provides liquidity to make them realized.

CW and passively Q-switched laser performance of Nd:Lu2SiO5 crystal

NASA Astrophysics Data System (ADS)

Xu, Xiaodong; Di, Juqing; Zhang, Jian; Tang, Dingyuan; Xu, Jun

2016-01-01

We demonstrated an efficient and controllable dual-wavelength continuous-wave (CW) laser of Nd:Lu2SiO5 (Nd:LSO) crystal. The maximum output power was 3.02 W at wavelength of 1075 nm and 1079 nm, and with increasing of absorbed pump power, the ratio of 1079 nm laser rose. The slope efficiency of 65.6% and optical-to-optical conversion efficiency of 63.3% were obtained. The passively Q-switched laser properties of Nd:LSO were investigated for the first time. The shortest pulse, maximum pulse energy and peak power were 11.58 ns, 29.05 μJ and 2.34 kW, respectively.

Performance of J33 turbojet engine with shaft-power extraction III : turbine performance

NASA Technical Reports Server (NTRS)

Huppert, M C; Nettles, J C

1949-01-01

The performance of the turbine component of a J33 turbojet engine was determined over a range of turbine speeds from 8000 to 11,500 rpm.Turbine-inlet temperature was varied from the minimum required to drive the compressor to a maximum of approximately 2000 degrees R at each of several intermediate turbine speeds. Data are presented that show the horsepower developed by the turbine per pound of gas flow. The relation between turbine-inlet stagnation pressure, turbine-outlet stagnation pressure, and turbine-outlet static pressure was established. The turbine-weight-flow parameter varied from 39.2 to 43.6. The maximum turbine efficiency measured was 0.86 at a pressure ratio of 3.5 and a ratio of blade speed to theoretical nozzle velocity of 0.39. A generalized performance map of the turbine-horsepower parameter plotted against the turbine-speed parameter indicated that the best turbine efficiency is obtained when the turbine power is 10 percent greater than the compressor horsepower. The variation of efficiency with the ratio of blade speed to nozzle velocity indicated that the turbine operates at a speed above that for maximum efficiency when the engine is operated normally with the 19-inch-diameter jet nozzle.

Current control of PMSM based on maximum torque control reference frame

NASA Astrophysics Data System (ADS)

Ohnuma, Takumi

2017-07-01

This study presents a new method of current controls of PMSMs (Permanent Magnet Synchronous Motors) based on a maximum torque control reference frame, which is suitable for high-performance controls of the PMSMs. As the issues of environment and energy increase seriously, PMSMs, one of the AC motors, are becoming popular because of their high-efficiency and high-torque density in various applications, such as electric vehicles, trains, industrial machines, and home appliances. To use the PMSMs efficiently, a proper current control of the PMSMs is necessary. In general, a rotational coordinate system synchronizing with the rotor is used for the current control of PMSMs. In the rotating reference frame, the current control is easier because the currents on the rotating reference frame can be expressed as a direct current in the controller. On the other hand, the torque characteristics of PMSMs are non-linear and complex; the PMSMs are efficient and high-density though. Therefore, a complicated control system is required to involve the relation between the torque and the current, even though the rotating reference frame is adopted. The maximum torque control reference frame provides a simpler way to control efficiently the currents taking the torque characteristics of the PMSMs into consideration.

Quantitative measurement of intracellular protein dynamics using photobleaching or photoactivation of fluorescent proteins.

PubMed

Matsuda, Tomoki; Nagai, Takeharu

2014-12-01

Unlike in vitro protein dynamics, intracellular protein dynamics are intricately regulated by protein-protein interactions or interactions between proteins and other cellular components, including nucleic acids, the plasma membrane and the cytoskeleton. Alteration of these dynamics plays a crucial role in physiological phenomena such as gene expression and cell division. Live-cell imaging via microscopy with the inherent properties of fluorescent proteins, i.e. photobleaching and photoconversion, or fluorescence correlation spectroscopy, provides insight into the movement of proteins and their interactions with cellular components. This article reviews techniques based on photo-induced changes in the physicochemical properties of fluorescent proteins to measure protein dynamics inside living cells, and it also discusses the strengths and weaknesses of these techniques. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Revisiting synaptic vesicle pool localization in the Drosophila neuromuscular junction

PubMed Central

Denker, Annette; Kröhnert, Katharina; Rizzoli, Silvio O

2009-01-01

The synaptic vesicles are organized in distinct populations or ‘pools’: the readily releasable pool (the first vesicles released upon stimulation), the recycling pool (which maintains release under moderate stimulation) and the reserve pool (which is called into action only upon strong, often unphysiological stimulation). A major question in the field is whether the pools consist of biochemically different vesicles or whether the pool tag is a spatial one (with the recycling vesicles found next to the release sites, and the reserve ones farther away). A strong and stable spatial segregation has been proposed in the last decade in the Drosophila larval neuromuscular junction – albeit based solely on light microscopy experiments. We have tested here this hypothesis using electron microscopy (EM) photoconversion. We found the recycling and reserve pools to be thoroughly intermixed at the EM level, indicating that spatial location is irrelevant for the functional properties of the vesicle. PMID:19403600

Single-organelle tracking by two-photon conversion

NASA Astrophysics Data System (ADS)

Watanabe, Wataru; Shimada, Tomoko; Matsunaga, Sachihiro; Kurihara, Daisuke; Fukui, Kiichi; Shin-Ichi Arimura, Shin-Ichi; Tsutsumi, Nobuhiro; Isobe, Keisuke; Itoh, Kazuyoshi

2007-03-01

Spatial and temporal information about intracellular objects and their dynamics within a living cell are essential for dynamic analysis of such objects in cell biology. A specific intracellular object can be discriminated by photoactivatable fluorescent proteins that exhibit pronounced light-induced spectral changes. Here, we report on selective labeling and tracking of a single organelle by using two-photon conversion of a photoconvertible fluorescent protein with near-infrared femtosecond laser pulses. We performed selective labeling of a single mitochondrion in a living tobacco BY-2 cell using two-photon photoconversion of Kaede. Using this technique, we demonstrated that, in plants, the directed movement of individual mitochondria along the cytoskeletons was mediated by actin filaments, whereas microtubules were not required for the movement of mitochondria. This single-organelle labeling technique enabled us to track the dynamics of a single organelle, revealing the mechanisms involved in organelle dynamics. The technique has potential application in direct tracking of selective cellular and intracellular structures.

Phytochrome-Mediated Detection of Changes in Reflected Light

PubMed Central

Mancinelli, Alberto L.

1991-01-01

Measurements of phytochrome photoequilibria and photoconversion rates in vivo, in seedlings of Cucurbita pepo L. exposed to light in growth chambers, indicate that significant changes in the state of phytochrome can be brought about by changes in the quality and quantity of the light reflected from the walls of the growth chambers. The changes in reflected light, although large, were small in terms of the total radiation (direct light from the lamps plus wall-reflected light) to which the seedlings were exposed. The conditions used were approximate simulations of direct and reflected sunlight conditions in the natural environment. Keeping in mind the limitations imposed by the approximation of the simulations, the results from this study are consistent with the hypothesis that, in the natural environment, a plant might be capable of detecting the presence of nearby plants, before being shaded by them, through the phytochrome-mediated perception of changes in reflected light. PMID:16667942

Photoswitchable Molecular Rings for Solar-Thermal Energy Storage.

PubMed

Durgun, E; Grossman, Jeffrey C

2013-03-21

Solar-thermal fuels reversibly store solar energy in the chemical bonds of molecules by photoconversion, and can release this stored energy in the form of heat upon activation. Many conventional photoswichable molecules could be considered as solar thermal fuels, although they suffer from low energy density or short lifetime in the photoinduced high-energy metastable state, rendering their practical use unfeasible. We present a new approach to the design of chemistries for solar thermal fuel applications, wherein well-known photoswitchable molecules are connected by different linker agents to form molecular rings. This approach allows for a significant increase in both the amount of stored energy per molecule and the stability of the fuels. Our results suggest a range of possibilities for tuning the energy density and thermal stability as a function of the type of the photoswitchable molecule, the ring size, or the type of linkers.

A Double Decarboxylation in Superfolder Green Fluorescent Protein Leads to High Contrast Photoactivation.

PubMed

Slocum, Joshua D; Webb, Lauren J

2017-07-06

A photoactivatable variant of superfolder green fluorescent protein (GFP) was created by replacing the threonine at position 203 with aspartic acid. Photoactivation by exposure of this mutant to UV light resulted in conversion of the fluorophore from the neutral to the negatively charged form, accompanied by a ∼95-fold increase in fluorescence under 488 nm excitation. Mass spectrometry before and after exposure to UV light revealed a change in mass of 88 Da, attributed to the double decarboxylation of Glu 222 and Asp 203. Kinetics studies and nonlinear power-dependence of the initial rate of photoconversion indicated that the double decarboxylation occurred via a multiphoton absorption process at 254 nm. In addition to providing a photoactivatable GFP with robust folding properties, a detailed mechanistic understanding of this double decarboxylation in GFP will lead to a better understanding of charge transfer in fluorescent proteins.

bicoid mRNA localises to the Drosophila oocyte anterior by random Dynein-mediated transport and anchoring

PubMed Central

Trovisco, Vítor; Belaya, Katsiaryna; Nashchekin, Dmitry; Irion, Uwe; Sirinakis, George; Butler, Richard; Lee, Jack J; Gavis, Elizabeth R; St Johnston, Daniel

2016-01-01

bicoid mRNA localises to the Drosophila oocyte anterior from stage 9 of oogenesis onwards to provide a local source for Bicoid protein for embryonic patterning. Live imaging at stage 9 reveals that bicoid mRNA particles undergo rapid Dynein-dependent movements near the oocyte anterior, but with no directional bias. Furthermore, bicoid mRNA localises normally in shot2A2, which abolishes the polarised microtubule organisation. FRAP and photo-conversion experiments demonstrate that the RNA is stably anchored at the anterior, independently of microtubules. Thus, bicoid mRNA is localised by random active transport and anterior anchoring. Super-resolution imaging reveals that bicoid mRNA forms 110–120 nm particles with variable RNA content, but constant size. These particles appear to be well-defined structures that package the RNA for transport and anchoring. DOI: http://dx.doi.org/10.7554/eLife.17537.001 PMID:27791980

Hydrogen peroxide contributes to the ultraviolet-B (280-315 nm) induced oxidative stress of plant leaves through multiple pathways.

PubMed

Czégény, Gyula; Wu, Min; Dér, András; Eriksson, Leif A; Strid, Åke; Hideg, Éva

2014-06-27

Solar UV-B (280-315 nm) radiation is a developmental signal in plants but may also cause oxidative stress when combined with other environmental factors. Using computer modeling and in solution experiments we show that UV-B is capable of photosensitizing hydroxyl radical production from hydrogen peroxide. We present evidence that the oxidative effect of UV-B in leaves is at least twofold: (i) it increases cellular hydrogen peroxide concentrations, to a larger extent in pyridoxine antioxidant mutant pdx1.3-1 Arabidopsis and; (ii) is capable of a partial photo-conversion of both 'natural' and 'extra' hydrogen peroxide to hydroxyl radicals. As stress conditions other than UV can increase cellular hydrogen peroxide levels, synergistic deleterious effects of various stresses may be expected already under ambient solar UV-B. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Efficiency of a thermodynamic motor at maximum power

NASA Astrophysics Data System (ADS)

Moreau, M.; Gaveau, B.; Schulman, L. S.

2012-02-01

Several recent theories address the efficiency of a macroscopic thermodynamic motor at maximum power and question the so-called Curzon-Ahlborn (CA) efficiency. Considering the entropy exchanges and productions in an n-sources motor, we study the maximization of its power and show that the controversies are partly due to some imprecision in the maximization variables. When power is maximized with respect to the system temperatures, these temperatures are proportional to the square root of the corresponding source temperatures, which leads to the CA formula for a bithermal motor. On the other hand, when power is maximized with respect to the transition durations, the Carnot efficiency of a bithermal motor admits the CA efficiency as a lower bound, which is attained if the duration of the adiabatic transitions can be neglected. Additionally, we compute the energetic efficiency, or “sustainable efficiency,” which can be defined for n sources, and we show that it has no other universal upper bound than 1, but that in certain situations, which are favorable for power production, it does not exceed ½.

Efficiency of a thermodynamic motor at maximum power.

PubMed

Moreau, M; Gaveau, B; Schulman, L S

2012-02-01

Several recent theories address the efficiency of a macroscopic thermodynamic motor at maximum power and question the so-called Curzon-Ahlborn (CA) efficiency. Considering the entropy exchanges and productions in an n-sources motor, we study the maximization of its power and show that the controversies are partly due to some imprecision in the maximization variables. When power is maximized with respect to the system temperatures, these temperatures are proportional to the square root of the corresponding source temperatures, which leads to the CA formula for a bithermal motor. On the other hand, when power is maximized with respect to the transition durations, the Carnot efficiency of a bithermal motor admits the CA efficiency as a lower bound, which is attained if the duration of the adiabatic transitions can be neglected. Additionally, we compute the energetic efficiency, or "sustainable efficiency," which can be defined for n sources, and we show that it has no other universal upper bound than 1, but that in certain situations, which are favorable for power production, it does not exceed ½. © 2012 American Physical Society

Experimental and numerical investigations of heat transfer and thermal efficiency of an infrared gas stove

NASA Astrophysics Data System (ADS)

Charoenlerdchanya, A.; Rattanadecho, P.; Keangin, P.

2018-01-01

An infrared gas stove is a low-pressure gas stove type and it has higher thermal efficiency than the other domestic cooking stoves. This study considers the computationally determine water and air temperature distributions, water and air velocity distributions and thermal efficiency of the infrared gas stove. The goal of this work is to investigate the effect of various pot diameters i.e. 220 mm, 240 mm and 260 mm on the water and air temperature distributions, water and air velocity distributions and thermal efficiency of the infrared gas stove. The time-dependent heat transfer equation involving diffusion and convection coupled with the time-dependent fluid dynamic equation is implemented and is solved by using the finite element method (FEM). The computer simulation study is validated with an experimental study, which is use standard experiment by LPG test for low-pressure gas stove in households (TIS No. 2312-2549). The findings revealed that the water and air temperature distributions increase with greater heating time, which varies with the three different pot diameters (220 mm, 240 mm and 260 mm). Similarly, the greater heating time, the water and air velocity distributions increase that vary by pot diameters (220, 240 and 260 mm). The maximum water temperature in the case of pot diameter of 220 mm is higher than the maximum water velocity in the case of pot diameters of 240 mm and 260 mm, respectively. However, the maximum air temperature in the case of pot diameter of 260 mm is higher than the maximum water velocity in the case of pot diameters of 240 mm and 220 mm, respectively. The obtained results may provide a basis for improving the energy efficiency of infrared gas stoves and other equipment, including helping to reduce energy consumption.

Optimized anion exchange membranes for vanadium redox flow batteries.

PubMed

Chen, Dongyang; Hickner, Michael A; Agar, Ertan; Kumbur, E Caglan

2013-08-14

In order to understand the properties of low vanadium permeability anion exchange membranes for vanadium redox flow batteries (VRFBs), quaternary ammonium functionalized Radel (QA-Radel) membranes with three ion exchange capacities (IECs) from 1.7 to 2.4 mequiv g(-1) were synthesized and 55-60 μm thick membrane samples were evaluated for their transport properties and in-cell battery performance. The ionic conductivity and vanadium permeability of the membranes were investigated and correlated to the battery performance through measurements of Coulombic efficiency, voltage efficiency and energy efficiency in single cell tests, and capacity fade during cycling. Increasing the IEC of the QA-Radel membranes increased both the ionic conductivity and VO(2+) permeability. The 1.7 mequiv g(-1) IEC QA-Radel had the highest Coulombic efficiency and best cycling capacity maintenance in the VRFB, while the cell's voltage efficiency was limited by the membrane's low ionic conductivity. Increasing the IEC resulted in higher voltage efficiency for the 2.0 and 2.4 mequiv g(-1) samples, but the cells with these membranes displayed reduced Coulombic efficiency and faster capacity fade. The QA-Radel with an IEC of 2.0 mequiv g(-1) had the best balance of ionic conductivity and VO(2+) permeability, achieving a maximum power density of 218 mW cm(-2) which was higher than the maximum power density of a VRFB assembled with a Nafion N212 membrane in our system. While anion exchange membranes are under study for a variety of VRFB applications, this work demonstrates that the material parameters must be optimized to obtain the maximum cell performance.

Microprocessor-controlled step-down maximum-power-point tracker for photovoltaic systems

NASA Astrophysics Data System (ADS)

Mazmuder, R. K.; Haidar, S.

1992-12-01

An efficient maximum power point tracker (MPPT) has been developed and can be used with a photovoltaic (PV) array and a load which requires lower voltage than the PV array voltage to be operated. The MPPT makes the PV array to operate at maximum power point (MPP) under all insolation and temperature, which ensures the maximum amount of available PV power to be delivered to the load. The performance of the MPPT has been studied under different insolation levels.

Performance of Single-Stage Turbine of Mark 25 Torpedo Power Plant with Two Special Nozzles. III; Efficiency with Standard Rotor Blades

NASA Technical Reports Server (NTRS)

Schum, Harold J.; Whitney, Warren J.

1949-01-01

A Mark 25 torpedo power plant modified to operate as a single-stage turbine was investigated to determine the performance with two nozzle designs and a standard first-stage rotor having 0.40-inch blades with a 17O met-air angle. Both nozzles had smaller port cross-sectional areas than those nozzles of similar design, which were previously investigated. The performance of the two nozzles was compared on the basis of blade, rotor, and brake efficiencies as a function of blade-jet speed ratio for pressure ratios of 8, 15 (design), and 20. At pressure ratios of 15 and 20, the blade efficiency obtained with the nozzle having circular passages (K) was higher than that obtained with the nozzle having rectangular passages (J). At a pressure ratio of 8, the efficiencies obtained with the two nozzles were comparable for blade-jet speed ratios of less than 0.260. For blade-jet speed ratios exceeding this value, nozzle K yielded slightly higher efficiencies. The maximum blade efficiency of 0.569 was obtained with nozzle K at a pressure ratio of 8 and a blade-jet speed ratio of 0.295. At design speed and pressure ratio, nozzle K yielded a maximum blade efficiency of 0.534, an increase of 0.031 over that obtained with nozzle J. When the blade efficiencies of the two nozzles were compared with those of four other nozzles previously investigated, the maximum difference for the six nozzles with this rotor was 0.050. From, this comparison, no specific effect of nozzles size or shape on over-all performance was discernible.

Molecular machines operating on the nanoscale: from classical to quantum

PubMed Central

2016-01-01

Summary The main physical features and operating principles of isothermal nanomachines in the microworld, common to both classical and quantum machines, are reviewed. Special attention is paid to the dual, constructive role of dissipation and thermal fluctuations, the fluctuation–dissipation theorem, heat losses and free energy transduction, thermodynamic efficiency, and thermodynamic efficiency at maximum power. Several basic models are considered and discussed to highlight generic physical features. This work examines some common fallacies that continue to plague the literature. In particular, the erroneous beliefs that one should minimize friction and lower the temperature for high performance of Brownian machines, and that the thermodynamic efficiency at maximum power cannot exceed one-half are discussed. The emerging topic of anomalous molecular motors operating subdiffusively but very efficiently in the viscoelastic environment of living cells is also discussed. PMID:27335728

Comparison of two temperature control techniques in a forced water heater solar system

NASA Astrophysics Data System (ADS)

Hernández, E.; E Guzmán, R.; Santos, A.; Cordoba, E.

2017-12-01

a study on the performance of a forced solar heating system in which a comparative analysis of two control strategies, including the classic on-off control and PID control is presented. From the experimental results it was found that the two control strategies show a similar behaviour in the solar heating system forced an approximate settling time of 60 min and over-elongation 2°C for the two control strategies. Furthermore, the maximum temperature in the storage tank was 46°C and the maximum efficiency of flat plate collector was 76.7% given that this efficiency is the ratio of the energy of the radiation on the collector and the energy used to heat water. The efficiency obtained is a fact well accepted because the business efficiencies of flat plate collectors are approximately 70%.

Highly Efficient Nondoped Green Organic Light-Emitting Diodes with Combination of High Photoluminescence and High Exciton Utilization.

PubMed

Wang, Chu; Li, Xianglong; Pan, Yuyu; Zhang, Shitong; Yao, Liang; Bai, Qing; Li, Weijun; Lu, Ping; Yang, Bing; Su, Shijian; Ma, Yuguang

2016-02-10

Photoluminescence (PL) efficiency and exciton utilization efficiency are two key parameters to harvest high-efficiency electroluminescence (EL) in organic light-emitting diodes (OLEDs). But it is not easy to simultaneously combine these two characteristics (high PL efficiency and high exciton utilization) into a fluorescent material. In this work, an efficient combination was achieved through two concepts of hybridized local and charge-transfer (CT) state (HLCT) and "hot exciton", in which the former is responsible for high PL efficiency while the latter contributes to high exciton utilization. On the basis of a tiny chemical modification in TPA-BZP, a green-light donor-acceptor molecule, we designed and synthesized CzP-BZP with this efficeient combination of high PL efficiency of η(PL) = 75% in the solid state and maximal exciton utilization efficiency up to 48% (especially, the internal quantum efficiency of η(IQE) = 35% substantially exceed 25% of spin statistics limit) in OLED. The nondoped OLED of CzP-BZP exhibited an excellent performance: a green emission with a CIE coordinate of (0.34, 0.60), a maximum current efficiency of 23.99 cd A(-1), and a maximum external quantum efficiency (EQE, η(EQE)) of 6.95%. This combined HLCT state and "hot exciton" strategy should be a practical way to design next-generation, low-cost, high-efficiency fluorescent OLED materials.

[Foliar water use efficiency of Platycladus orientalis sapling under different soil water contents].

PubMed

Zhang, Yong E; Yu, Xin Xiao; Chen, Li Hua; Jia, Guo Dong; Zhao, Na; Li, Han Zhi; Chang, Xiao Min

2017-07-18

The determination of plant foliar water use efficiency will be of great value to improve our understanding about mechanism of plant water consumption and provide important basis of regional forest ecosystem management and maintenance, thus, laboratory controlled experiments were carried out to obtain Platycladus orientalis sapling foliar water use efficiency under five different soil water contents, including instantaneous water use efficiency (WUE gs ) derived from gas exchange and short-term water use efficiency (WUE cp ) caculated using carbon isotope model. The results showed that, controlled by stomatal conductance (g s ), foliar net photosynthesis rate (P n ) and transpiration rate (T r ) increased as soil water content increased, which both reached maximum va-lues at soil water content of 70%-80% field capacity (FC), while WUE gs reached a maximum of 7.26 mmol·m -2 ·s -1 at the lowest soil water content (35%-45% FC). Both δ 13 C of water-soluble leaf and twig phloem material achieved maximum values at the lowest soil water content (35%-45% FC). Besides, δ 13 C values of leaf water-soluble compounds were significantly greater than that of phloem exudates, indicating that there was depletion in 13 C in twig phloem compared with leaf water-soluble compounds and no obvious fractionation in the process of water-soluble material transportation from leaf to twig. Foliar WUE cp also reached a maximum of 7.26 mmol·m -2 ·s -1 at the lowest soil water content (35%-45% FC). There was some difference between foliar WUE gs and WUE cp under the same condition, and the average difference was 0.52 mmol·m -2 ·s -1 . The WUE gs had great space-time variability, by contrast, WUE cp was more representative. It was concluded that P. orientalis sapling adapted to drought condition by increasing water use efficiency and decreasing physiological activity.

High Performance Organic Materials and Devices

DTIC Science & Technology

2006-03-31

on this material exhibited external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd/A. 15. SUBJECT TERMS 16...International de L’Eclairage coordinate at (0.164, 0.188). The external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd...more than 90% absorption in active layer, and highly balanced carrier transport. 4 5. High efficient blue- electroluminescence device shows maximum

High-efficiency silicon solar-cell design and practical barriers

NASA Technical Reports Server (NTRS)

Mokashi, A.

1985-01-01

A numerical evaluation technique is used to study the impact of practical barriers, such as heavy doping effects (Auger recombination, band gap narrowing), surface recombination, shadowing losses and minority-carrier lifetime (Tau), on a high efficiency silicon solar cell performance. Considering a high Tau of 1 ms, efficiency of a silicon solar cell of the hypothetical case is estimated to be around 29%. This is comparable with (detailed balance limit) maximum efficiency of a p-n junction solar cell of 30%. Value of Tau is varied from 1 second to 20 micro. Heavy doping effects, and realizable values of surface recombination velocities and shadowing, are then considered in succession and their influence on cell efficiency is evaluated and quantified. These practical barriers cause the cell efficiency to reduce from the maximum value of 29% to the experimentally achieved value of about 19%. Improvement in open circuit voltage V sub oc is required to achieve cell efficiency greater than 20%. Increased value of Tau reduces reverse saturation current and, hence, improves V sub oc. Control of surface recombination losses becomes critical at higher V sub oc. Substantial improvement in Tau and considerable reduction in surface recombination velocities is essential to achieve cell efficiencies greater than 20%.

Pyrimidine-based twisted donor-acceptor delayed fluorescence molecules: a new universal platform for highly efficient blue electroluminescence.

PubMed

Park, In Seob; Komiyama, Hideaki; Yasuda, Takuma

2017-02-01

Deep-blue emitters that can harvest both singlet and triplet excited states to give high electron-to-photon conversion efficiencies are highly desired for applications in full-color displays and white lighting devices based on organic light-emitting diodes (OLEDs). Thermally activated delayed fluorescence (TADF) molecules based on highly twisted donor-acceptor (D-A) configurations are promising emitting dopants for the construction of efficient deep-blue OLEDs. In this study, a simple and versatile D-A system combining acridan-based donors and pyrimidine-based acceptors has been developed as a new platform for high-efficiency deep-blue TADF emitters. The designed pre-twisted acridan-pyrimidine D-A molecules exhibit small singlet-triplet energy splitting and high photoluminescence quantum yields, functioning as efficient deep-blue TADF emitters. The OLEDs utilizing these TADF emitters display bright blue electroluminescence with external quantum efficiencies of up to 20.4%, maximum current efficiencies of 41.7 cd A -1 , maximum power efficiencies of 37.2 lm W -1 , and color coordinates of (0.16, 0.23). The design strategy featuring such acridan-pyrimidine D-A motifs can offer great prospects for further developing high-performance deep-blue TADF emitters and TADF-OLEDs.

Swimming Stroke Mechanical Efficiency and Physiological Responses of 100-m Backstroke with and without the use of paddles

PubMed Central

Messinis, Spilios; Beidaris, Nikos; Messinis, Spyros; Soultanakis, Helen; Botonis, Petros; Platanou, Theodoros

2014-01-01

The use of swimming aids during training contributes to greater swimming efficiency by the improvement of the swimming specific power of the athlete. The purpose of this study was to compare the swimming stroke technical characteristics and the physiological responses of swimming 100-m backstroke, with and without the use of paddles at maximum and sub-maximum intensities at the same swimming speed. Eight swimmers competing at the national level participated in this study. The measurements took place at 4 different sessions. At every session, each participant swam individually one 100-m backstroke swimming trial with or without paddles at the same speed and two levels of intensity (100% and 85% of maximum speed). The results revealed lower stroke length, greater stroke number and gliding length without the use of swimming paddles at both intensities. Blood lactate concentration (10.03±2.96 vs. 5.85±2.23 mmol/l) and Rating of Perceived Exertion (17.43±2.07 vs. 12±2.82) were greater without the use of swimming paddles only at 100% of maximum speed. Thus, swimming backstroke with paddles compared to unaided swimming, at a similar speed, showed a greater efficiency at maximal but not at sub-maximal intensity. PMID:25031685

Swimming Stroke Mechanical Efficiency and Physiological Responses of 100-m Backstroke with and without the use of paddles.

PubMed

Messinis, Spilios; Beidaris, Nikos; Messinis, Spyros; Soultanakis, Helen; Botonis, Petros; Platanou, Theodoros

2014-03-27

The use of swimming aids during training contributes to greater swimming efficiency by the improvement of the swimming specific power of the athlete. The purpose of this study was to compare the swimming stroke technical characteristics and the physiological responses of swimming 100-m backstroke, with and without the use of paddles at maximum and sub-maximum intensities at the same swimming speed. Eight swimmers competing at the national level participated in this study. The measurements took place at 4 different sessions. At every session, each participant swam individually one 100-m backstroke swimming trial with or without paddles at the same speed and two levels of intensity (100% and 85% of maximum speed). The results revealed lower stroke length, greater stroke number and gliding length without the use of swimming paddles at both intensities. Blood lactate concentration (10.03±2.96 vs. 5.85±2.23 mmol/l) and Rating of Perceived Exertion (17.43±2.07 vs. 12±2.82) were greater without the use of swimming paddles only at 100% of maximum speed. Thus, swimming backstroke with paddles compared to unaided swimming, at a similar speed, showed a greater efficiency at maximal but not at sub-maximal intensity.

Reynolds number effect on overall performance of a 10.8-centimeter (4.25-inch) sweptback bladed centrifugal compressor

NASA Technical Reports Server (NTRS)

Weigel, C.; Ball, C. L.

1972-01-01

The performance data were taken at 50,000 rpm, using argon gas. As the Reynolds number was reduced from near design value to 30 percent of design, the maximum efficiency decreased about 1.5 percentage points. Reducing the Reynolds number from 30 percent to approximately 10 percent of design caused the maximum efficiency to decrease another 2.5 percentage points. The variation in loss with Reynolds number is compared with inverse power relation of loss with Reynolds number.

THE SOLAR BATTERY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shchekin, V.

1958-01-01

The maximum output capacity of silicon elements is 10 to 12 milliwatts/ cm/sup 2/ of photosensitive surface area. The efficiency of present-day silicon elements is 11 to 13% compared to 1% with other materials and the maximum efficiency of 22%. The Sputnik'' radio was powered from a solar battery of 5 v and fitted with a miniature TsNK-0.4 storage battery. It is calculated that to supply electricity for lighting a small flat or house at 110 v, 3 amp, a solar battery of 2 x 2 m would be sufficient. (W.D.M.)

Study for the optimization of a transport aircraft wing for maximum fuel efficiency. Volume 1: Methodology, criteria, aeroelastic model definition and results

NASA Technical Reports Server (NTRS)

Radovcich, N. A.; Dreim, D.; Okeefe, D. A.; Linner, L.; Pathak, S. K.; Reaser, J. S.; Richardson, D.; Sweers, J.; Conner, F.

1985-01-01

Work performed in the design of a transport aircraft wing for maximum fuel efficiency is documented with emphasis on design criteria, design methodology, and three design configurations. The design database includes complete finite element model description, sizing data, geometry data, loads data, and inertial data. A design process which satisfies the economics and practical aspects of a real design is illustrated. The cooperative study relationship between the contractor and NASA during the course of the contract is also discussed.

Efficiency at maximum power for an isothermal chemical engine with particle exchange at varying chemical potential

NASA Astrophysics Data System (ADS)

Koning, Jesper; Koga, Kenichiro; Indekeu, Joseph. O.

2017-02-01

We calculate the efficiency at maximum power (EMP) of an isothermal chemical cycle in which particle uptake occurs at a fixed chemical potential but particle release takes place at varying chemical potential. We obtain the EMP as a function of Δμ/ kT, where Δμ is the difference between the highest and lowest reservoir chemical potentials and T is the absolute temperature. In the linear response limit, Δμ ≪ kT, the EMP tends to the expected universal value 1/2.

Glottal volume velocity waveform characteristics in subjects with and without vocal training, related to gender, sound intensity, fundamental frequency, and age.

PubMed

Sulter, A M; Wit, H P

1996-11-01

Glottal volume velocity waveform characteristics of 224 subjects, categorized in four groups according to gender and vocal training, were determined, and their relations to sound-pressure level, fundamental frequency, intra-oral pressure, and age were analyzed. Subjects phonated at three intensity conditions. The glottal volume velocity waveforms were obtained by inverse filtering the oral flow. Glottal volume velocity waveforms were parameterized with flow-based (minimum flow, ac flow, average flow, maximum flow declination rate) and time-based parameters (closed quotient, closing quotient, speed quotient), as well as with derived parameters (vocal efficiency and glottal resistance). Higher sound-pressure levels, intra-oral pressures, and flow-parameter values (ac flow, maximum flow declination rate) were observed, when compared with previous investigations. These higher values might be the result of the specific phonation tasks (stressed /ae/ vowel in a word and a sentence) or filtering processes. Few statistically significant (p < 0.01) differences in parameters were found between untrained and trained subjects [the maximum flow declination rate and the closing quotient were higher in trained women (p < 0.001), and the speed quotient was higher in trained men (p < 0.005)]. Several statistically significant parameter differences were found between men and women [minimum flow, ac flow, average flow, maximum flow declination rate, closing quotient, glottal resistance (p < 0.001), and closed quotient (p < 0.005)]. Significant effects of intensity condition were observed on ac flow, maximum flow declination rate, closing quotient, and vocal efficiency in women (p < 0.005), and on minimum flow, ac flow, average flow, maximum flow declination rate, closed quotient, and vocal efficiency in men (p < 0.01).

Emittance Theory for Cylindrical Fiber Selective Emitter

NASA Technical Reports Server (NTRS)

Chubb, Donald L.

1998-01-01

A fibrous rare earth selective emitter is approximated as an infinitely long, cylinder. The spectral emittance, e(sub x), is obtained L- by solving the radiative transfer equations with appropriate boundary conditions and uniform temperature. For optical depth, K(sub R), where alpha(sub lambda), is the extinction coefficient and R is the cylinder radius, greater than 1 the spectral emittance depths, K(sub R) alpha(sub lambda)R, is nearly at its maximum value. There is an optimum cylinder radius, R(sub opt) for maximum emitter efficiency, n(sub E). Values for R(sub opt) are strongly dependent on the number of emission bands of the material. The optimum radius decreases slowly with increasing emitter temperature, while the maximum efficiency and useful radiated power increase rapidly with increasing, temperature.

All‐optical functional synaptic connectivity mapping in acute brain slices using the calcium integrator CaMPARI

PubMed Central

Sha, Fern; Johenning, Friedrich W.; Schreiter, Eric R.; Looger, Loren L.; Larkum, Matthew E.

2016-01-01

Key points The genetically encoded fluorescent calcium integrator calcium‐modulated photoactivatable ratiobetric integrator (CaMPARI) reports calcium influx induced by synaptic and neural activity. Its fluorescence is converted from green to red in the presence of violet light and calcium.The rate of conversion – the sensitivity to activity – is tunable and depends on the intensity of violet light.Synaptic activity and action potentials can independently initiate significant CaMPARI conversion.The level of conversion by subthreshold synaptic inputs is correlated to the strength of input, enabling optical readout of relative synaptic strength.When combined with optogenetic activation of defined presynaptic neurons, CaMPARI provides an all‐optical method to map synaptic connectivity. Abstract The calcium‐modulated photoactivatable ratiometric integrator (CaMPARI) is a genetically encoded calcium integrator that facilitates the study of neural circuits by permanently marking cells active during user‐specified temporal windows. Permanent marking enables measurement of signals from large swathes of tissue and easy correlation of activity with other structural or functional labels. One potential application of CaMPARI is labelling neurons postsynaptic to specific populations targeted for optogenetic stimulation, giving rise to all‐optical functional connectivity mapping. Here, we characterized the response of CaMPARI to several common types of neuronal calcium signals in mouse acute cortical brain slices. Our experiments show that CaMPARI is effectively converted by both action potentials and subthreshold synaptic inputs, and that conversion level is correlated to synaptic strength. Importantly, we found that conversion rate can be tuned: it is linearly related to light intensity. At low photoconversion light levels CaMPARI offers a wide dynamic range due to slower conversion rate; at high light levels conversion is more rapid and more sensitive to activity. Finally, we employed CaMPARI and optogenetics for functional circuit mapping in ex vivo acute brain slices, which preserve in vivo‐like connectivity of axon terminals. With a single light source, we stimulated channelrhodopsin‐2‐expressing long‐range posteromedial (POm) thalamic axon terminals in cortex and induced CaMPARI conversion in recipient cortical neurons. We found that POm stimulation triggers robust photoconversion of layer 5 cortical neurons and weaker conversion of layer 2/3 neurons. Thus, CaMPARI enables network‐wide, tunable, all‐optical functional circuit mapping that captures supra‐ and subthreshold depolarization. PMID:27861906

Efficiency at maximum power of a laser quantum heat engine enhanced by noise-induced coherence

NASA Astrophysics Data System (ADS)

Dorfman, Konstantin E.; Xu, Dazhi; Cao, Jianshu

2018-04-01

Quantum coherence has been demonstrated in various systems including organic solar cells and solid state devices. In this article, we report the lower and upper bounds for the performance of quantum heat engines determined by the efficiency at maximum power. Our prediction based on the canonical three-level Scovil and Schulz-Dubois maser model strongly depends on the ratio of system-bath couplings for the hot and cold baths and recovers the theoretical bounds established previously for the Carnot engine. Further, introducing a fourth level to the maser model can enhance the maximal power and its efficiency, thus demonstrating the importance of quantum coherence in the thermodynamics and operation of the heat engines beyond the classical limit.

Highly Efficient and Fully Solution-Processed Inverted Light-Emitting Diodes with Charge Control Interlayers.

PubMed

Fu, Yan; Jiang, Wei; Kim, Daekyoung; Lee, Woosuk; Chae, Heeyeop

2018-05-23

In this work, we developed a charge control sandwich structure around QD layers for the inverted QLEDs, the performance of which is shown to exceed that of the conventional QLEDs in terms of the external quantum efficiency (EQE) and the current efficiency (CE). The QD light-emitting layer (EML) is sandwiched with two ultrathin interfacial layers: one is a poly(9-vinlycarbazole) (PVK) layer to prevent excess electrons, and the other is a polyethylenimine ethoxylated (PEIE) layer to reduce the hole injection barrier. The sandwich structure resolves the imbalance between injected holes and electrons and brings the level of balanced charge carriers to a maximum. We demonstrated the highly improved performance of 89.8 cd/A of current efficiency, 22.4% of external quantum efficiency, and 72 814 cd m -2 of maximum brightness with the solution-processed inverted QLED. This sandwich structure (PVK/QD/PEIE), as a framework, can be applied to various QLED devices for enhancing performance.

Methodology for the optimal design of an integrated first and second generation ethanol production plant combined with power cogeneration.

PubMed

Bechara, Rami; Gomez, Adrien; Saint-Antonin, Valérie; Schweitzer, Jean-Marc; Maréchal, François

2016-08-01

The application of methodologies for the optimal design of integrated processes has seen increased interest in literature. This article builds on previous works and applies a systematic methodology to an integrated first and second generation ethanol production plant with power cogeneration. The methodology breaks into process simulation, heat integration, thermo-economic evaluation, exergy efficiency vs. capital costs, multi-variable, evolutionary optimization, and process selection via profitability maximization. Optimization generated Pareto solutions with exergy efficiency ranging between 39.2% and 44.4% and capital costs from 210M$ to 390M$. The Net Present Value was positive for only two scenarios and for low efficiency, low hydrolysis points. The minimum cellulosic ethanol selling price was sought to obtain a maximum NPV of zero for high efficiency, high hydrolysis alternatives. The obtained optimal configuration presented maximum exergy efficiency, hydrolyzed bagasse fraction, capital costs and ethanol production rate, and minimum cooling water consumption and power production rate. Copyright © 2016 Elsevier Ltd. All rights reserved.

A Novel Technique for Maximum Power Point Tracking of a Photovoltaic Based on Sensing of Array Current Using Adaptive Neuro-Fuzzy Inference System (ANFIS)

NASA Astrophysics Data System (ADS)

El-Zoghby, Helmy M.; Bendary, Ahmed F.

2016-10-01

Maximum Power Point Tracking (MPPT) is now widely used method in increasing the photovoltaic (PV) efficiency. The conventional MPPT methods have many problems concerning the accuracy, flexibility and efficiency. The MPP depends on the PV temperature and solar irradiation that randomly varied. In this paper an artificial intelligence based controller is presented through implementing of an Adaptive Neuro-Fuzzy Inference System (ANFIS) to obtain maximum power from PV. The ANFIS inputs are the temperature and cell current, and the output is optimal voltage at maximum power. During operation the trained ANFIS senses the PV current using suitable sensor and also senses the temperature to determine the optimal operating voltage that corresponds to the current at MPP. This voltage is used to control the boost converter duty cycle. The MATLAB simulation results shows the effectiveness of the ANFIS with sensing the PV current in obtaining the MPPT from the PV.

A 15 kWe (nominal) solar thermal-electric power conversion concept definition study: Steam Rankin reciprocator system

NASA Technical Reports Server (NTRS)

Wingenback, W.; Carter, J., Jr.

1979-01-01

A conceptual design of a 3600 rpm reciprocation expander was developed for maximum thermal input power of 80 kW. The conceptual design covered two engine configurations; a single cylinder design for simple cycle operation and a two cylinder design for reheat cycle operation. The reheat expander contains a high pressure cylinder and a low pressure cylinder with steam being reheated to the initial inlet temperature after expansion in the high pressure cylinder. Power generation is accomplished with a three-phase induction motor coupled directly to the expander and connected electrically to the public utility power grid. The expander, generator, water pump and control system weigh 297 kg and are dish mounted. The steam condenser, water tank and accessory pumps are ground based. Maximum heat engine efficiency is 33 percent: maximum power conversion efficiency is 30 percent. Total cost is $3,307 or $138 per kW of maximum output power.

Wind tunnel test of a tailless aircraft with a belly-flap control surface used in combination with wing flaps

NASA Astrophysics Data System (ADS)

Dougherty, Daniel A.

A wind tunnel tat of a tailless aircraft configuration that has been quipped with a belly-flap control surface, was conducted with the goal of improving the trimmed maximum-lift coefficient. Tailless aircraft have aerodynamic and structural efficiencies that are superior to those of a traditionally configured wing/body/tail aircraft. However, tailless aircraft have a low maximum-lift coefficient such that; when sized for equivalent takeoff performance, the tailless aircraft suffers a large reduction in aerodynamic and structural efficiencies. A Belly-Flap control surface used in combination with wing trailing edge flaps was tested in a wind tunnel with the goal of achieving a longitudinally trimmed solution at a higher maximum lift coefficient. It was determined that, though the Belly-Flap increases the trimmed lift of the tailless configuration at low angles of attack, the maximum lift coefficient is slightly reduced in relation to the controls neutral configuration.

FORTRAN program for calculating total efficiency - specific speed characteristics of centrifugal compressors

NASA Technical Reports Server (NTRS)

Galvas, M. R.

1972-01-01

A computer program for predicting design point specific speed - efficiency characteristics of centrifugal compressors is presented with instructions for its use. The method permits rapid selection of compressor geometry that yields maximum total efficiency for a particular application. A numerical example is included to demonstrate the selection procedure.

Efficiency and its bounds for thermal engines at maximum power using Newton's law of cooling.

PubMed

Yan, H; Guo, Hao

2012-01-01

We study a thermal engine model for which Newton's cooling law is obeyed during heat transfer processes. The thermal efficiency and its bounds at maximum output power are derived and discussed. This model, though quite simple, can be applied not only to Carnot engines but also to four other types of engines. For the long thermal contact time limit, new bounds, tighter than what were known before, are obtained. In this case, this model can simulate Otto, Joule-Brayton, Diesel, and Atkinson engines. While in the short contact time limit, which corresponds to the Carnot cycle, the same efficiency bounds as that from Esposito et al. [Phys. Rev. Lett. 105, 150603 (2010)] are derived. In both cases, the thermal efficiency decreases as the ratio between the heat capacities of the working medium during heating and cooling stages increases. This might provide instructions for designing real engines. © 2012 American Physical Society

The Next Breakthrough for Organic Photovoltaics?

PubMed

Jackson, Nicholas E; Savoie, Brett M; Marks, Tobin J; Chen, Lin X; Ratner, Mark A

2015-01-02

While the intense focus on energy level tuning in organic photovoltaic materials has afforded large gains in device performance, we argue here that strategies based on microstructural/morphological control are at least as promising in any rational design strategy. In this work, a meta-analysis of ∼150 bulk heterojunction devices fabricated with different materials combinations is performed and reveals strong correlations between power conversion efficiency and morphology-dominated properties (short-circuit current, fill factor) and surprisingly weak correlations between efficiency and energy level positioning (open-circuit voltage, enthalpic offset at the interface, optical gap). While energy level positioning should in principle provide the theoretical maximum efficiency, the optimization landscape that must be navigated to reach this maximum is unforgiving. Thus, research aimed at developing understanding-based strategies for more efficient optimization of an active layer microstructure and morphology are likely to be at least as fruitful.

Efficient laser-diode end-pumped Nd:GGG lasers at 1054 and 1067 nm.

PubMed

Xu, Bin; Xu, Huiying; Cai, Zhiping; Camy, P; Doualan, J L; Moncorgé, R

2014-10-10

Efficient and compact laser-diode end-pumped Nd:GGG simultaneous multiwavelength continuous-wave lasers at ∼1059, ∼1060 and ∼1062  nm were first demonstrated in a free-running 30 mm plano-concave laser cavity. The maximum output power was up to 3.92 W with a slope efficiency of about 53.6% with respect to the absorbed pump power. By inserting a 0.1 mm optical glass plate acting as a Fabry-Pérot etalon, a single-wavelength laser at ∼1067  nm with a maximum output power of 1.95 W and a slope efficiency of 28.5% can be obtained. Multiwavelength lasers, including those at ∼1054 or ∼1067  nm, were also achievable by suitably tilting the glass etalon. These simultaneous multiwavelength lasers provide a potential source for terahertz wave generation.

DEVELOPMENT OF AN ARMY STATIONARY AXLE TEST STAND FOR LUBRICANT EFFICIENCY EVALUATION-PART II

DTIC Science & Technology

2017-01-13

value was estimated based on the engines maximum peak torque output, multiplied by the transmissions 1st gear ratio, high range transfer case ratio...efficiency test stand to allow for laboratory based investigation of Fuel Efficient Gear Oils (FEGO) and their impact on vehicle efficiency. Development...their impact on vehicle efficiency. The test stand was designed and developed with the following goals: • Provide a lower cost alternative for

A maximum power point tracking algorithm for buoy-rope-drum wave energy converters

NASA Astrophysics Data System (ADS)

Wang, J. Q.; Zhang, X. C.; Zhou, Y.; Cui, Z. C.; Zhu, L. S.

2016-08-01

The maximum power point tracking control is the key link to improve the energy conversion efficiency of wave energy converters (WEC). This paper presents a novel variable step size Perturb and Observe maximum power point tracking algorithm with a power classification standard for control of a buoy-rope-drum WEC. The algorithm and simulation model of the buoy-rope-drum WEC are presented in details, as well as simulation experiment results. The results show that the algorithm tracks the maximum power point of the WEC fast and accurately.

A Comparison of Three Multivariate Models for Estimating Test Battery Reliability.

ERIC Educational Resources Information Center

Wood, Terry M.; Safrit, Margaret J.

1987-01-01

A comparison of three multivariate models (canonical reliability model, maximum generalizability model, canonical correlation model) for estimating test battery reliability indicated that the maximum generalizability model showed the least degree of bias, smallest errors in estimation, and the greatest relative efficiency across all experimental…

Numerical Investigation of the Influence of the Input Air Irregularity on the Performance of Turbofan Jet Engine

NASA Astrophysics Data System (ADS)

Novikova, Y.; Zubanov, V.

2018-01-01

The article describes the numerical investigation of the input air irregularity influence of turbofan engine on its characteristics. The investigated fan has a wide-blade, an inlet diameter about 2 meters, a pressure ratio about 1.6 and the bypass ratio about 4.8. The flow irregularity was simulated by the flap input in the fan inlet channel. Input of flap was carried out by an amount of 10 to 22,5% of the input channel diameter with increments of 2,5%. A nonlinear harmonic analysis (NLH-analysis) of NUMECA Fine/Turbo software was used to study the flow irregularity. The behavior of the calculated LPC characteristics repeats the experiment behavior, but there is a quantitative difference: the calculated efficiency and pressure ratio of booster consistent with the experimental data within 3% and 2% respectively, the calculated efficiency and pressure ratio of fan duct - within 4% and 2.5% respectively. An increasing the level of air irregularity in the input stage of the fan reduces the calculated mass flow, maximum pressure ratio and efficiency. With the value of flap input 12.5%, reducing the maximum air flow is 1.44%, lowering the maximum pressure ratio is 2.6%, efficiency decreasing is 3.1%.

Energy Efficiency and Productivity Enhancement of Microbial Electrosynthesis of Acetate

PubMed Central

LaBelle, Edward V.; May, Harold D.

2017-01-01

It was hypothesized that a lack of acetogenic biomass (biocatalyst) at the cathode of a microbial electrosynthesis system, due to electron and nutrient limitations, has prevented further improvement in acetate productivity and efficiency. In order to increase the biomass at the cathode and thereby performance, a bioelectrochemical system with this acetogenic community was operated under galvanostatic control and continuous media flow through a reticulated vitreous carbon (RVC) foam cathode. The combination of galvanostatic control and the high surface area cathode reduced the electron limitation and the continuous flow overcame the nutrient limitation while avoiding the accumulation of products and potential inhibitors. These conditions were set with the intention of operating the biocathode through the production of H2. Biofilm growth occurred on and within the unmodified RVC foam regardless of vigorous H2 generation on the cathode surface. A maximum volumetric rate or space time yield for acetate production of 0.78 g/Lcatholyte/h was achieved with 8 A/Lcatholyte (83.3 A/m2projected surface area of cathode) supplied to the continuous flow/culture bioelectrochemical reactors. The total Coulombic efficiency in H2 and acetate ranged from approximately 80–100%, with a maximum of 35% in acetate. The overall energy efficiency ranged from approximately 35–42% with a maximum to acetate of 12%. PMID:28515713

Energy Efficiency and Productivity Enhancement of Microbial Electrosynthesis of Acetate.

PubMed

LaBelle, Edward V; May, Harold D

2017-01-01

It was hypothesized that a lack of acetogenic biomass (biocatalyst) at the cathode of a microbial electrosynthesis system, due to electron and nutrient limitations, has prevented further improvement in acetate productivity and efficiency. In order to increase the biomass at the cathode and thereby performance, a bioelectrochemical system with this acetogenic community was operated under galvanostatic control and continuous media flow through a reticulated vitreous carbon (RVC) foam cathode. The combination of galvanostatic control and the high surface area cathode reduced the electron limitation and the continuous flow overcame the nutrient limitation while avoiding the accumulation of products and potential inhibitors. These conditions were set with the intention of operating the biocathode through the production of H 2 . Biofilm growth occurred on and within the unmodified RVC foam regardless of vigorous H 2 generation on the cathode surface. A maximum volumetric rate or space time yield for acetate production of 0.78 g/L catholyte /h was achieved with 8 A/L catholyte (83.3 A/m 2 projected surface area of cathode) supplied to the continuous flow/culture bioelectrochemical reactors. The total Coulombic efficiency in H 2 and acetate ranged from approximately 80-100%, with a maximum of 35% in acetate. The overall energy efficiency ranged from approximately 35-42% with a maximum to acetate of 12%.

Spatio-temporal Convergence of Maximum Daily Light-Use Efficiency Based on Radiation Absorption by Canopy Chlorophyll

DOE PAGES

Zhang, Yao; Xiao, Xiangming; Wolf, Sebastian; ...

2018-04-03

Light-use efficiency (LUE), which quantifies the plants’ efficiency in utilizing solar radiation for photosynthetic carbon fixation, is an important factor for gross primary production (GPP) estimation. Here we use satellite-based solar-induced chlorophyll fluorescence (SIF) as a proxy for photosynthetically active radiation absorbed by chlorophyll (APAR chl) and derive an estimation of the fraction of APAR chl (fPAR chl) from four remotely-sensed vegetation indicators. By comparing maximum LUE estimated at different scales from 127 eddy flux sites, we found that the maximum daily LUE based on PAR absorption by canopy chlorophyll (εmore » $$chl\\atop{max}$$), unlike other expressions of LUE, tends to converge across biome types. The photosynthetic seasonality in tropical forests can also be tracked by the change of fPAR chl, suggesting the corresponding (ε$$chl\\atop{max}$$}$) to have less seasonal variation. Finally, this spatio-temporal convergence of LUE derived from fPAR chl can be used to build simple but robust GPP models and to better constrain process-based models.« less

Roles of coercivity and remanent flux density of permanent magnet in interior permanent magnet synchronous motor (IPMSM) performance for electric vehicle applications

NASA Astrophysics Data System (ADS)

Won, Hoyun; Hong, Yang-Ki; Lee, Woncheol; Choi, Minyeong

2018-05-01

We used four rotor topologies of an interior permanent magnet synchronous motor (IPMSM) to investigate the effects of remanent flux density (Br) and coercivity (Hc) of permanent magnet on motor performance. Commercial strontium hexaferrite (SrFe12O19: energy product, (BH)max, of 4.62 MGOe) and Nd-Fe-B ((BH)max of 38.2 MGOe) magnets were used for the rotor designs. The same machine specifications and magnet volume keep constant, while the Hc and Br vary to calculate torque and energy efficiency with the finite-element analysis. A combination of high Hc and low Br more effectively increased maximum torque of IPMSM when the hexaferrite magnet was used. For Nd-Fe-B magnet, the same combination did not affect maximum torque, but increased energy efficiency at high speed. Therefore, the Hc value of a permanent magnet is more effective than the Br in producing high maximum torque for SrM-magnet based IPMSM and high energy efficiency at high speed for Nd-Fe-B magnet based IPMSM.

The modeling of gold recovery from tetrachloroaurate wastewater using a microbial fuel cell.

PubMed

Choi, Chansoo; Hu, Naixu

2013-04-01

In this study, tetrachloroaurate as an electron acceptor of a microbial fuel cell (MFC) has been studied to discover the parameters that affect the cost-effective recovery of gold. The modeling and equations for calculating the maximum actual efficiency and electrochemical impedance spectroscopic internal resistance of the MFC were also developed. The maximum power density (Pmax) of 6.58 W/m(2) with a fill factor of 0.717 was achieved for 60 mL volumes of 2000 ppm Au(III) catholyte and 12.2 mM acetate anolyte, respectively. The Pmax can also be predicted simply by measuring Rint by EIS. Additionally, the maximum actual MFC efficiency of about 57% was achieved, and the recovery efficiency of Au and the remaining concentration reached 99.89±0.00% and 0.22±0.00 ppm, respectively, for an Au(III) concentration of 200 ppm. The anodic concentration polarization quenching of the MFC strongly supports a mediator mechanism for the electron transfer from the microorganism to the anode. Copyright © 2013 Elsevier Ltd. All rights reserved.

Improving maximum power point tracking of partially shaded photovoltaic system by using IPSO-BELBIC

NASA Astrophysics Data System (ADS)

Al-Alim El-Garhy, M. Abd; Mubarak, R. I.; El-Bably, M.

2017-08-01

Solar photovoltaic (PV) arrays in remote applications are often related to the rapid changes in the partial shading pattern. Rapid changes of the partial shading pattern make the tracking of maximum power point (MPP) of the global peak through the local ones too difficult. An essential need to make a fast and efficient algorithm to detect the peaks values which always vary as the sun irradiance changes. This paper presents two algorithms based on the improved particle swarm optimization technique one of them with PID controller (IPSO-PID), and the other one with Brain Emotional Learning Based Intelligent Controller (IPSO-BELBIC). These techniques improve the maximum power point (MPP) tracking capabilities for photovoltaic (PV) system under partial shading circumstances. The main aim of these improved algorithms is to accelerate the velocity of IPSO to reach to (MPP) and increase its efficiency. These algorithms also improve the tracking time under complex irradiance conditions. Based on these conditions, the tracking time of these presented techniques improves to 2 msec, with an efficiency of 100%.

Spatio-temporal Convergence of Maximum Daily Light-Use Efficiency Based on Radiation Absorption by Canopy Chlorophyll

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yao; Xiao, Xiangming; Wolf, Sebastian

Light-use efficiency (LUE), which quantifies the plants’ efficiency in utilizing solar radiation for photosynthetic carbon fixation, is an important factor for gross primary production (GPP) estimation. Here we use satellite-based solar-induced chlorophyll fluorescence (SIF) as a proxy for photosynthetically active radiation absorbed by chlorophyll (APAR chl) and derive an estimation of the fraction of APAR chl (fPAR chl) from four remotely-sensed vegetation indicators. By comparing maximum LUE estimated at different scales from 127 eddy flux sites, we found that the maximum daily LUE based on PAR absorption by canopy chlorophyll (εmore » $$chl\\atop{max}$$), unlike other expressions of LUE, tends to converge across biome types. The photosynthetic seasonality in tropical forests can also be tracked by the change of fPAR chl, suggesting the corresponding (ε$$chl\\atop{max}$$}$) to have less seasonal variation. Finally, this spatio-temporal convergence of LUE derived from fPAR chl can be used to build simple but robust GPP models and to better constrain process-based models.« less

Extraction of manganese from electrolytic manganese residue by bioleaching.

PubMed

Xin, Baoping; Chen, Bing; Duan, Ning; Zhou, Changbo

2011-01-01

Extraction of manganese from electrolytic manganese residues using bioleaching was investigated in this paper. The maximum extraction efficiency of Mn was 93% by sulfur-oxidizing bacteria at 4.0 g/l sulfur after bioleaching of 9days, while the maximum extraction efficiency of Mn was 81% by pyrite-leaching bacteria at 4.0 g/l pyrite. The series bioleaching first by sulfur-oxidizing bacteria and followed by pyrite-leaching bacteria evidently promoted the extraction of manganese, witnessing the maximum extraction efficiency of 98.1%. In the case of sulfur-oxidizing bacteria, the strong dissolution of bio-generated sulfuric acid resulted in extraction of soluble Mn2+, while both the Fe2+ catalyzed reduction of Mn4+ and weak acidic dissolution of Mn2+ accounted for the extraction of manganese with pyrite-leaching bacteria. The chemical simulation of bioleaching process further confirmed that the acid dissolution of Mn2+ and Fe2+ catalyzed reduction of Mn4+ were the bioleaching mechanisms involved for Mn extraction from electrolytic manganese residues. Copyright © 2010 Elsevier Ltd. All rights reserved.

Enhanced bioelectricity harvesting in microbial fuel cells treating food waste leachate produced from biohydrogen fermentation.

PubMed

Choi, Jeongdong; Ahn, Youngho

2015-05-01

Microbial fuel cells (MFCs) treating the food waste leachate produced from biohydrogen fermentation were examined to enhance power generation and energy recovery. In batch mode, the maximum voltage production was 0.56 V and the power density reached 1540 mW/m(2). The maximum Coulombic efficiency (CEmax) and energy efficiency (EE) in the batch mode were calculated to be 88.8% and 18.8%, respectively. When the organic loading rate in sequencing batch mode varied from 0.75 to 6.2 g COD/L-d (under CEmax), the maximum power density reached 769.2 mW/m(2) in OLR of 3.1 g COD/L-d, whereas higher energy recovery (CE=52.6%, 0.346 Wh/g CODrem) was achieved at 1.51 g COD/L-d. The results demonstrate that readily biodegradable substrates in biohydrogen fermentation can be effectively used for the enhanced bioelectricity harvesting of MFCs and a MFC coupled with biohydrogen fermentation is of great benefit on higher electricity generation and energy efficiency. Copyright © 2015 Elsevier Ltd. All rights reserved.

A distributed-memory approximation algorithm for maximum weight perfect bipartite matching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Azad, Ariful; Buluc, Aydin; Li, Xiaoye S.

We design and implement an efficient parallel approximation algorithm for the problem of maximum weight perfect matching in bipartite graphs, i.e. the problem of finding a set of non-adjacent edges that covers all vertices and has maximum weight. This problem differs from the maximum weight matching problem, for which scalable approximation algorithms are known. It is primarily motivated by finding good pivots in scalable sparse direct solvers before factorization where sequential implementations of maximum weight perfect matching algorithms, such as those available in MC64, are widely used due to the lack of scalable alternatives. To overcome this limitation, we proposemore » a fully parallel distributed memory algorithm that first generates a perfect matching and then searches for weightaugmenting cycles of length four in parallel and iteratively augments the matching with a vertex disjoint set of such cycles. For most practical problems the weights of the perfect matchings generated by our algorithm are very close to the optimum. An efficient implementation of the algorithm scales up to 256 nodes (17,408 cores) on a Cray XC40 supercomputer and can solve instances that are too large to be handled by a single node using the sequential algorithm.« less

An experimental study on the design, performance and suitability of evaporative cooling system using different indigenous materials

NASA Astrophysics Data System (ADS)

Alam, Md. Ferdous; Sazidy, Ahmad Sharif; Kabir, Asif; Mridha, Gowtam; Litu, Nazmul Alam; Rahman, Md. Ashiqur

2017-06-01

The present study aimed to evaluate the feasibility of coconut coir pads, jute fiber pads and sackcloth pads as alternative pad materials. Experimental measurements were conducted and the experimental data were quantitative. The experimental work mainly focused on the effects of different types and thicknesses of evaporative cooling pads by using forced draft fan while changing the environmental conditions. Experiments are conducted in a specifically constructed test chamber having dimensions of 12'X8'X8', using a number of cooling pads (36"X26") with a variable thickness parameters of the evaporative cooling pads i.e., 50, 75 and 100 mm. Moreover, the experimental work involved the measurement of environmental parameters such as temperature, relative humidity, air velocity, water mass flow rate and pressure drops at different times during the day. Experiments were conducted at three different water mass flow rates (0.25 kgs-1, 0.40 kgs-1 & 0.55 kgs-1) and three different air velocities (3.6 ms-1, 4.6 ms-1& 5.6 ms-1). There was a significant difference between evaporative cooling pad types and cooling efficiency. The coconut coir pads yielded maximum cooling efficiency of 85%, whereas other pads yielded the following maximum cooling efficiency: jute fiber pads 78% and sackcloth 69% for higher air velocity and minimum mass flow rate. It is found that the maximum reduction in temperature between cooling pad inlet and outlet is 4°C with a considerable increase in humidity. With the increase of pad thickness there was an increment of cooling efficiency. The results obtained for environmental factors, indicated that there was a significant difference between environmental factors and cooling efficiency. In terms of the effect of air velocity on saturation efficiency and pressure drop, higher air velocity decreases saturation efficiency and increases pressure drop across the wetted pad for maximum flow rate. Convective heat transfer co-efficient has an almost linear relationship with air Velocity. Water consumption or evaporation rate increases with the increase in air velocity. Finally, the present study indicated that the coconut coir pads perform better than the other evaporative cooling pads and have higher potential as wetted-pad material. The outcomes of this study can provide an effective and low-cost solution in the form of evaporative cooling system, especially in an agricultural country like Bangladesh.

Efficiency at maximum power output of linear irreversible Carnot-like heat engines.

PubMed

Wang, Yang; Tu, Z C

2012-01-01

The efficiency at maximum power output of linear irreversible Carnot-like heat engines is investigated based on the assumption that the rate of irreversible entropy production of the working substance in each "isothermal" process is a quadratic form of the heat exchange rate between the working substance and the reservoir. It is found that the maximum power output corresponds to minimizing the irreversible entropy production in two isothermal processes of the Carnot-like cycle, and that the efficiency at maximum power output has the form η(mP)=η(C)/(2-γη(C)), where η(C) is the Carnot efficiency, while γ depends on the heat transfer coefficients between the working substance and two reservoirs. The value of η(mP) is bounded between η(-)≡η(C)/2 and η(+)≡η(C)/(2-η(C)). These results are consistent with those obtained by Chen and Yan [J. Chem. Phys. 90, 3740 (1989)] based on the endoreversible assumption, those obtained by Esposito et al. [Phys. Rev. Lett. 105, 150603 (2010)] based on the low-dissipation assumption, and those obtained by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] for stochastic heat engines which in fact also satisfy the low-dissipation assumption. Additionally, we find that the endoreversible assumption happens to hold for Carnot-like heat engines operating at the maximum power output based on our fundamental assumption, and that the Carnot-like heat engines that we focused on do not strictly satisfy the low-dissipation assumption, which implies that the low-dissipation assumption or our fundamental assumption is a sufficient but non-necessary condition for the validity of η(mP)=η(C)/(2-γη(C)) as well as the existence of two bounds, η(-)≡η(C)/2 and η(+)≡η(C)/(2-η(C)). © 2012 American Physical Society

Efficiency at maximum power output of linear irreversible Carnot-like heat engines

NASA Astrophysics Data System (ADS)

Wang, Yang; Tu, Z. C.

2012-01-01

The efficiency at maximum power output of linear irreversible Carnot-like heat engines is investigated based on the assumption that the rate of irreversible entropy production of the working substance in each “isothermal” process is a quadratic form of the heat exchange rate between the working substance and the reservoir. It is found that the maximum power output corresponds to minimizing the irreversible entropy production in two isothermal processes of the Carnot-like cycle, and that the efficiency at maximum power output has the form ηmP=ηC/(2-γηC), where ηC is the Carnot efficiency, while γ depends on the heat transfer coefficients between the working substance and two reservoirs. The value of ηmP is bounded between η-≡ηC/2 and η+≡ηC/(2-ηC). These results are consistent with those obtained by Chen and Yan [J. Chem. Phys.JCPSA60021-960610.1063/1.455832 90, 3740 (1989)] based on the endoreversible assumption, those obtained by Esposito [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.150603 105, 150603 (2010)] based on the low-dissipation assumption, and those obtained by Schmiedl and Seifert [Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/81/20003 81, 20003 (2008)] for stochastic heat engines which in fact also satisfy the low-dissipation assumption. Additionally, we find that the endoreversible assumption happens to hold for Carnot-like heat engines operating at the maximum power output based on our fundamental assumption, and that the Carnot-like heat engines that we focused on do not strictly satisfy the low-dissipation assumption, which implies that the low-dissipation assumption or our fundamental assumption is a sufficient but non-necessary condition for the validity of ηmP=ηC/(2-γηC) as well as the existence of two bounds, η-≡ηC/2 and η+≡ηC/(2-ηC).

A Comparison of Item Selection Techniques for Testlets

ERIC Educational Resources Information Center

Murphy, Daniel L.; Dodd, Barbara G.; Vaughn, Brandon K.

2010-01-01

This study examined the performance of the maximum Fisher's information, the maximum posterior weighted information, and the minimum expected posterior variance methods for selecting items in a computerized adaptive testing system when the items were grouped in testlets. A simulation study compared the efficiency of ability estimation among the…

Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

PubMed

Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

2014-06-11

Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

Charge Efficiency Tests of Lead/Acid Batteries

NASA Technical Reports Server (NTRS)

Rowlette, J. J.

1984-01-01

Current, voltage, and gas evolution measured during charge/discharge cycles. Series of standarized tests for evaluating charging efficiency of lead/acid storage batteries described in report. Purpose of tests to provide information for design of battery charger that allows maximum recharge efficiency for electric-vehicle batteries consistent with other operating parameters, such as range, water loss, and cycle life.

Temperature effects on gallium arsenide 63Ni betavoltaic cell.

PubMed

Butera, S; Lioliou, G; Barnett, A M

2017-07-01

A GaAs 63 Ni radioisotope betavoltaic cell is reported over the temperature range 70°C to -20°C. The temperature effects on the key cell parameters were investigated. The saturation current decreased with decreased temperature; whilst the open circuit voltage, the short circuit current, the maximum power and the internal conversion efficiency values decreased with increased temperature. A maximum output power and an internal conversion efficiency of 1.8pW (corresponding to 0.3μW/Ci) and 7% were observed at -20°C, respectively. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Determination of the performance of the Kaplan hydraulic turbines through simplified procedure

NASA Astrophysics Data System (ADS)

Pădureanu, I.; Jurcu, M.; Campian, C. V.; Haţiegan, C.

2018-01-01

A simplified procedure has been developed, compared to the complex one recommended by IEC 60041 (i.e. index samples), for measurement of the performance of the hydraulic turbines. The simplified procedure determines the minimum and maximum powers, the efficiency at maximum power, the evolution of powers by head and flow and to determine the correct relationship between runner/impeller blade angle and guide vane opening for most efficient operation of double-regulated machines. The simplified procedure can be used for a rapid and partial estimation of the performance of hydraulic turbines for repair and maintenance work.

High-power and highly efficient diode-cladding-pumped holmium-doped fluoride fiber laser operating at 2.94 microm.

PubMed

Jackson, Stuart D

2009-08-01

A high-power diode-cladding-pumped Ho(3+), Pr(3+)-doped fluoride glass fiber laser is demonstrated. The laser produced a maximum output power of 2.5 W at a slope efficiency of 32% using diode lasers emitting at 1,150 nm. The long-emission wavelength of 2.94 microm measured at maximum pump power, which is particularly suited to medical applications, indicates that tailoring of the proportion of Pr(3+) ions can provide specific emission wavelengths while providing sufficient de-excitation of the lower laser level.

A 3D approximate maximum likelihood localization solver

DOE Office of Scientific and Technical Information (OSTI.GOV)

2016-09-23

A robust three-dimensional solver was needed to accurately and efficiently estimate the time sequence of locations of fish tagged with acoustic transmitters and vocalizing marine mammals to describe in sufficient detail the information needed to assess the function of dam-passage design alternatives and support Marine Renewable Energy. An approximate maximum likelihood solver was developed using measurements of time difference of arrival from all hydrophones in receiving arrays on which a transmission was detected. Field experiments demonstrated that the developed solver performed significantly better in tracking efficiency and accuracy than other solvers described in the literature.

On the Minimum Induced Drag of Wings

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2015-01-01

Birds do not require the use of vertical tails. They do not appear to have any mechanism by which to control their yaw. As an example the albatross is notable in this regard. The authors believe this is possible because of a unique adaptation by which there exists a triple-optimal solution that provides the maximum aerodynamic efficiency, the minimum structural weight, and it provides for coordination of control in roll and yaw. Until now, this solution has eluded researchers, and remained unknown. Here it is shown that the correct specification of spanload provides for all three solutions at once, maximum aerodynamic efficiency, minimum structural weight, and coordinated control. The implications of this result has far reaching effects on the design of aircraft, as well as dramatic efficiency improvement.

High discharge efficiency of (Sr, Pb, Bi) TiO3 relaxor ceramics for energy-storage application

NASA Astrophysics Data System (ADS)

Chao, Mingming; Liu, Jingsong; Zeng, Mengshi; Wang, Debin; Yu, Hongtao; Yuan, Ying; Zhang, Shuren

2018-05-01

We report herein on the energy storage and discharge properties of the relaxor ferroelectric ceramic Sr0.8Pb0.1Bi0.1TiO3 (SPBT). This material has a slanted hysteresis loop, and all samples show low remnant polarization and low coercive field, which leads to a high discharge efficiency. The maximum polarization is 10.1 μC/cm2, the minimum coercive field is 0.229 kV/cm, and the maximum efficiency is 94.2%. The discharge current waveforms are sinusoidal, the first discharge period is 140 ns, and the power density is approximately 4.2 × 107 W/kg. The high discharge speed and high discharge power density indicate that SPBT ceramics are very promising materials for energy storage applications.

Efficient 1.5-μm Raman generation in ethane-filled hollow-core fiber

NASA Astrophysics Data System (ADS)

Chen, Yubin; Gu, Bo; Wang, Zefeng; Lu, Qisheng

2016-11-01

We demonstrated for the first time a novel and effective method for obtaining both high peak-power and narrow linewidth 1.5 μm fiber sources through gas Raman effect in hollow core fibers. An Ethane-filled ice-cream antiresonance hollow-core fiber is pumped with a high peak-power pulse 1064 nm microchip laser, generating 1552.7 nm Stokes wave by pure vibrational stimulated Raman scattering of ethane molecules. A maximum peak-power of about 400 kW is achieved with 6 meter fiber length at 2 bar pressure, and the linewidth is about 6.3 GHz. The maximum Raman conversion efficiency of 1064 nm to 1552.7 nm is about 38%, and the corresponding laser slope efficiency is about 61.5%.

Development and characterization of high-efficiency, high-specific impulse xenon Hall thrusters

NASA Astrophysics Data System (ADS)

Hofer, Richard Robert

This dissertation presents research aimed at extending the efficient operation of 1600 s specific impulse Hall thruster technology to the 2000--3000 s range. While recent studies of commercially developed Hall thrusters demonstrated greater than 4000 s specific impulse, maximum efficiency occurred at less than 3000 s. It was hypothesized that the efficiency maximum resulted as a consequence of modern magnetic field designs, optimized for 1600 s, which were unsuitable at high-specific impulse. Motivated by the industry efforts and mission studies, the aim of this research was to develop and characterize xenon Hall thrusters capable of both high-specific impulse and high-efficiency operation. The research divided into development and characterization phases. During the development phase, the laboratory-model NASA-173M Hall thrusters were designed with plasma lens magnetic field topographies and their performance and plasma characteristics were evaluated. Experiments with the NASA-173M version 1 (v1) validated the plasma lens design by showing how changing the magnetic field topography at high-specific impulse improved efficiency. Experiments with the NASA-173M version 2 (v2) showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. Between 300--1000 V, total specific impulse and total efficiency of the NASA-173Mv2 operating at 10 mg/s ranged from 1600--3400 s and 51--61%, respectively. Comparison of the thrusters showed that efficiency can be optimized for specific impulse by varying the plasma lens design. During the characterization phase, additional plasma properties of the NASA-173Mv2 were measured and a performance model was derived accounting for a multiply-charged, partially-ionized plasma. Results from the model based on experimental data showed how efficient operation at high-specific impulse was enabled through regulation of the electron current with the magnetic field. The decrease of efficiency due to multiply-charged ions was minor. Efficiency was largely determined by the current utilization, which suggested maximum Hall thruster efficiency has yet to be reached. The electron Hall parameter was approximately constant with voltage, decreasing from an average of 210 at 300 V to an average of 160 between 400--900 V, which confirmed efficient operation can be realized only over a limited range of Hall parameters.

Quality analysis, miceller behavior, and environmental impact of some laundry detergents available in Bangladesh.

PubMed

Nur-E-Alam, M; Islam, M Monirul; Islam, M Nazrul; Rima, Farhana Rahman; Islam, M Nurul

2016-03-01

The cleansing efficiencies of laundry detergents depend on composition and variation of ingredients such as surfactants, phosphate, and co-builders. Among these ingredients, surfactants and phosphate are considered as hazardous materials. Knowledge on compositions and micellar behavior is very useful for understanding their cleansing efficiencies and environmental impact. With this view, composition, critical micelle concentration, and dissolved oxygen level in aqueous solution of some laundry detergents available in Bangladesh such as keya, Wheel Power White, Tibet, Surf Excel, and Chaka were determined. Surfactant and phosphate were found to be maximum in Surf Excel and Wheel Power White, respectively, while both of the ingredients were found to be minimum in Tibet. The critical micelle concentration decreased with increasing surfactant content. The amount of laundry detergents required for efficient cleansing was found to be minimum for Surf Excel and maximum for Chaka; however, cleansing cost was the highest for Surf Excel and the lowest for Tibet. The maximum amount of surfactants and phosphate was discharged by Surf Excel and Wheel Power White, respectively, while discharges of both of the ingredients were minimum for Tibet. The maximum decrease of dissolved oxygen level was caused by Surf Excel and the minimum by Tibet. Therefore, it can be concluded that Tibet is cost-effective and environment friendly, whereas Surf Excel and Wheel Power White are expensive and pose a threat to water environment.

Nucleation and Crystal Growth in the Formation of Hierarchical Three-Dimensional Nanoarchitecture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xudong

This project is to obtain fundamental understandings of the operation of the Ostwald-Lussac (OL) Law and the oriented attachment (OA) mechanism in nucleation and growth of TiO2 nanorods (NR) via surface-reaction-limited pulsed chemical vapor deposition (SPCVD) process. Three-dimensional (3D) NW networks are a unique type of mesoporous architecture that offers extraordinary surface area density and superior transport properties of electrons, photons, and phonons. It is exceptionally promising for advancing the design and application of functional materials for photovoltaic devices, catalysts beds, hydrogen storage systems, sensors, and battery electrodes. Our group has developed the SPCVD technique by mimicking the mechanism ofmore » atomic layer deposition (ALD), which effectively decoupled the crystal growth from precursor concentration while retaining anisotropic 1D growth. For the first time, this technique realized a 3D NW architecture with ultrahigh density and achieved ~4-5 times enhancement on photo-conversion efficiency. Through the support of our current DOE award, we revealed the governing role of the OL Law in the nucleation stage of SPCVD. The formation of NR morphology in SPCVD was identified following the OA mechanism. We also discovered a unique vapor-phase Kirkendall effect in the evolution of tubular or core-shell NR structures. These understandings opened many new opportunities in designing 3D NW architectures with improved properties or new functionalities. Specifically, our accomplishments from this project include five aspects: (1) Observation of the Ostwald-Lussac Law in high-temperature ALD. (2) Observation of vapor-solid Kirkendall effect in ZnO-to-TiO2 nanostructure conversion. (3) Development of highly-efficient capillary photoelectrochemical (PEC) solar-fuel generation. (4) Development of efficient and stable electrochemical protections for black silicon PEC electrodes. (5) Development of doped polymers with tunable electrical properties. This project brings a new level of transformative knowledge on nucleation and crystal growth in the SPCVD NR growth processes. Specifically, quantification of the activation energy landscape guided by the OL law will allow us to establish a critical knowledge base of nucleation kinetics for SPCVD synthesis of NR branches on different material surfaces. Studying the OA kinetics will establish a transformative knowledge base to support this new crystal growth mechanism that can be applied to many functional material systems. This research will pave the road toward a capable and versatile synthesis technology for creating 3D hierarchical mesoscale structures.« less

Preparation of ultra-thin and high-quality WO{sub 3} compact layers and comparision of WO{sub 3} and TiO{sub 2} compact layer thickness in planar perovskite solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jincheng; Shi, Chengwu, E-mail: shicw506@foxmail.com; Chen, Junjun

2016-06-15

In this paper, the ultra-thin and high-quality WO{sub 3} compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO{sub 3} and TiO{sub 2} compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO{sub 2} compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO{sub 3} and TiO{sub 2} compact layer was 15 nm and 60 nm. The planar perovskite solar cell with 15 nm WO{submore » 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. - Graphical abstract: The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. Display Omitted - Highlights: • Preparation of ultra-thin and high-quality WO{sub 3} compact layers. • Perovskite solar cell with 15 nm-thick WO{sub 3} compact layer achieved PCE of 10.14%. • Perovskite solar cell with 60 nm-thick TiO{sub 2} compact layer achieved PCE of 12.64%.« less

Study of High-Efficiency Motors Using Soft Magnetic Cores

NASA Astrophysics Data System (ADS)

Tokoi, Hirooki; Kawamata, Shoichi; Enomoto, Yuji

We have been developed a small and highly efficient axial gap motor whose stator core is made of a soft magnetic core. First, the loss sensitivities to various motor design parameters were evaluated using magnetic field analysis. It was found that the pole number and core dimensions had low sensitivity (≤ 2.2dB) in terms of the total loss, which is the sum of the copper loss and the iron losses in the stator core and the rotor yoke respectively. From this, we concluded that to improve the motor efficiency, it is essential to reduce the iron loss in the rotor yoke and minimize other losses. With this in mind, a prototype axial gap motor is manufactured and tested. The motor has four poles and six slots. The motor is 123mm in diameter and the axial length is 47mm. The rotor has parallel magnetized magnets and a rotor yoke with magnetic steel sheets. The maximum measured motor efficiency is 93%. This value roughly agrees with the maximum calculated efficiency of 95%.

Performance study of highly efficient 520 W average power long pulse ceramic Nd:YAG rod laser

NASA Astrophysics Data System (ADS)

Choubey, Ambar; Vishwakarma, S. C.; Ali, Sabir; Jain, R. K.; Upadhyaya, B. N.; Oak, S. M.

2013-10-01

We report the performance study of a 2% atomic doped ceramic Nd:YAG rod for long pulse laser operation in the millisecond regime with pulse duration in the range of 0.5-20 ms. A maximum average output power of 520 W with 180 J maximum pulse energy has been achieved with a slope efficiency of 5.4% using a dual rod configuration, which is the highest for typical lamp pumped ceramic Nd:YAG lasers. The laser output characteristics of the ceramic Nd:YAG rod were revealed to be nearly equivalent or superior to those of high-quality single crystal Nd:YAG rod. The laser pump chamber and resonator were designed and optimized to achieve a high efficiency and good beam quality with a beam parameter product of 16 mm mrad (M2˜47). The laser output beam was efficiently coupled through a 400 μm core diameter optical fiber with 90% overall transmission efficiency. This ceramic Nd:YAG laser will be useful for various material processing applications in industry.

Quasi-Maximum Likelihood Estimation of Structural Equation Models with Multiple Interaction and Quadratic Effects

ERIC Educational Resources Information Center

Klein, Andreas G.; Muthen, Bengt O.

2007-01-01

In this article, a nonlinear structural equation model is introduced and a quasi-maximum likelihood method for simultaneous estimation and testing of multiple nonlinear effects is developed. The focus of the new methodology lies on efficiency, robustness, and computational practicability. Monte-Carlo studies indicate that the method is highly…

Applying Bayesian Item Selection Approaches to Adaptive Tests Using Polytomous Items

ERIC Educational Resources Information Center

Penfield, Randall D.

2006-01-01

This study applied the maximum expected information (MEI) and the maximum posterior-weighted information (MPI) approaches of computer adaptive testing item selection to the case of a test using polytomous items following the partial credit model. The MEI and MPI approaches are described. A simulation study compared the efficiency of ability…

A white organic light emitting diode based on anthracene-triphenylamine derivatives

NASA Astrophysics Data System (ADS)

Jiang, Quan; Qu, Jianjun; Yu, Junsheng; Tao, Silu; Gan, Yuanyuan; Jiang, Yadong

2010-10-01

White organic lighting-diode (WOLED) can be used as flat light sources, backlights for liquid crystal displays and full color displays. Recently, a research mainstream of white OLED is to develop the novel materials and optimize the structure of devices. In this work a WOLED with a structure of ITO/NPB/PAA/Alq3: x% rubrene/Alq3/Mg: Ag, was fabricated. The device has two light-emitting layers. NPB is used as a hole transport layer, PAA as a blue emitting layer, Alq3: rubrene host-guest system as a yellow emitting layer, and Alq3 close to the cathode as an electron transport layer. In the experiment, the doping concentration of rubrene was optimized. WOLED 1 with 4% rubrene achieved a maximum luminous efficiency of 1.80 lm/W, a maximum luminance of 3926 cd/m2 and CIE coordinates of (0.374, 0.341) .WOLED 2 with 2% rubrene achieved a maximum luminous efficiency of 0.65 lm/W, a maximum luminance of 7495cd/m2 and CIE coordinates of (0.365,0.365).

Efficient Sky-Blue Perovskite Light-Emitting Devices Based on Ethylammonium Bromide Induced Layered Perovskites.

PubMed

Wang, Qi; Ren, Jie; Peng, Xue-Feng; Ji, Xia-Xia; Yang, Xiao-Hui

2017-09-06

Low-dimensional organometallic halide perovskites are actively studied for the light-emitting applications due to their properties such as solution processability, high luminescence quantum yield, large exciton binding energy, and tunable band gap. Introduction of large-group ammonium halides not only serves as a convenient and versatile method to obtain layered perovskites but also allows the exploitation of the energy-funneling process to achieve a high-efficiency light emission. Herein, we investigate the influence of the addition of ethylammonium bromide on the morphology, crystallite structure, and optical properties of the resultant perovskite materials and report that the phase transition from bulk to layered perovskite occurs in the presence of excess ethylammonium bromide. On the basis of this strategy, we report green perovskite light-emitting devices with the maximum external quantum efficiency of ca. 3% and power efficiency of 9.3 lm/W. Notably, blue layered perovskite light-emitting devices with the Commission Internationale de I'Eclairage coordinates of (0.16, 0.23) exhibit the maximum external quantum efficiency of 2.6% and power efficiency of 1 lm/W at 100 cd/m 2 , representing a large improvement over the previously reported analogous devices.

Realworld maximum power point tracking simulation of PV system based on Fuzzy Logic control

NASA Astrophysics Data System (ADS)

Othman, Ahmed M.; El-arini, Mahdi M. M.; Ghitas, Ahmed; Fathy, Ahmed

2012-12-01

In the recent years, the solar energy becomes one of the most important alternative sources of electric energy, so it is important to improve the efficiency and reliability of the photovoltaic (PV) systems. Maximum power point tracking (MPPT) plays an important role in photovoltaic power systems because it maximize the power output from a PV system for a given set of conditions, and therefore maximize their array efficiency. This paper presents a maximum power point tracker (MPPT) using Fuzzy Logic theory for a PV system. The work is focused on the well known Perturb and Observe (P&O) algorithm and is compared to a designed fuzzy logic controller (FLC). The simulation work dealing with MPPT controller; a DC/DC Ćuk converter feeding a load is achieved. The results showed that the proposed Fuzzy Logic MPPT in the PV system is valid.

Electricity generation from food wastes and microbial community structure in microbial fuel cells.

PubMed

Jia, Jianna; Tang, Yu; Liu, Bingfeng; Wu, Di; Ren, Nanqi; Xing, Defeng

2013-09-01

Microbial fuel cell (MFC) was studied as an alternate and a novel way to dispose food wastes (FWs) in a waste-to-energy form. Different organic loading rate obviously affected the performance of MFCs fed with FWs. The maximum power density of ~18 W/m(3) (~556 mW/m(2)) was obtained at COD of 3200±400 mg/L and the maximum coulombic efficiency (CE) was ~27.0% at COD of 4900±350 mg/L. The maximum removals of COD, total carbohydrate (TC) and total nitrogen (TN) were ~86.4%, ~95.9% and ~16.1%, respectively. Microbial community analysis using 454 pyrosequencing of 16S rRNA gene demonstrated the combination of the dominant genera of the exoelectrogenic Geobacter and fermentative Bacteroides effectively drove highly efficient and reliable MFC systems with functions of organic matters degradation and electricity generation. Copyright © 2013 Elsevier Ltd. All rights reserved.

Efficient laser emission from cladding waveguide inscribed in Nd:GdVO(4) crystal by direct femtosecond laser writing.

PubMed

Liu, Hongliang; Tan, Yang; Vázquez de Aldana, Javier R; Chen, Feng

2014-08-01

We report on the fabrication of depressed cladding waveguides in Nd:GdVO(4) laser crystal by using femtosecond laser inscription. The cross section of the structure is a circular shape with a diameter of 150 μm. Under the optical pump at 808 nm, the continuous wave (cw) as well as pulsed (Q-switched by graphene saturable absorber) waveguide lasing at 1064 nm has been realized, supporting guidance of both TE and TM polarizations. The maximum output power of 0.57 W was obtained in the cw regime, while the maximum pulse energy of the pulsed laser emissions was up to 19 nJ (corresponding to a maximum average output power of 0.33 W, at a resonant frequency of 18 MHz). The slope efficiencies achieved for the cw and pulsed Nd:GdVO(4) waveguide lasers were as high as 68% and 52%, respectively.

Solution processible MoOx-incorporated graphene anode for efficient polymer light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Dongchan; Kim, Donghyuk; Lee, Yonghee; Jeon, Duk Young

2017-06-01

Graphene has attracted great attention owing to its superb properties as an anode of organic or polymer light-emitting diodes (OLEDs or PLEDs). However, there are still barriers for graphene to replace existing indium tin oxide (ITO) due to relatively high sheet resistance and work function mismatch. In this study, PLEDs using molybdenum oxide (MoOx) nanoparticle-doped graphene are demonstrated on a plastic substrate to have a low sheet resistance and high work function. Also, this work shows how the doping amount influences the electronic properties of the graphene anode and the PLED performance. A facile and scalable spin coating process was used for doping graphene with MoOx. After doping, the sheet resistance and the optical transmittance of five-layer graphene were ˜180 Ω sq-1 and ˜88%, respectively. Moreover, the surface roughness of MoOx-doped graphene becomes smoother than that of pristine graphene. Furthermore, a nonlinear relationship was observed between the MoOx doping level and device performance. Therefore, a modified stacking structure of graphene electrode is presented to further enhance device performance. The maximum external quantum efficiency (EQE) and power efficiency of the PLED using the MoOx-doped graphene anode were 4.7% and 13.3 lm W-1, respectively. The MoOx-doped graphene anode showed enhanced device performance (261% for maximum EQE, 255% for maximum power efficiency) compared with the pristine graphene.

The Energy Budget at the Earth’s Surface: Photosynthesis Under Field Condition: Solar Radiation Balance and Photosynthetic Efficiency.

DTIC Science & Technology

40-cm level in corn that is 300 cm high. Calculations indicate maximum thermal efficiency of photosynthesis under the experimental conditions to be 40 percent of the yield obtained from laboratory grown chlorella . (Author)

Significant performance enhancement of inverted organic light-emitting diodes by using ZnIx as a hole-blocking layer

NASA Astrophysics Data System (ADS)

Cheng, Chuan-Hui; Zhang, Bi-Long; Sun, Chao; Li, Ruo-Xuan; Wang, Yuan; Tian, Wen-Ming; Zhao, Chun-Yi; Jin, Sheng-Ye; Liu, Wei-Feng; Luo, Ying-Min; Du, Guo-Tong; Cong, Shu-Lin

2017-06-01

A highly efficient inverted organic light emitting diode using 1.0 nm-thick ZnIx as a hole-blocking layer is developed. We fabricate devices with the configuration ITO/ZnIx (1.0 nm)/Alq3 (50 nm)/NPB (50 nm)/MoO3 (6.0 nm)/Al (100 nm). The deposition of a ZnIx layer increases the maximum luminance by two orders of magnitude from 13.4 to 3566.1 cd/m2. In addition, the maximum current efficiency and power efficiency are increased by three orders of magnitude, and the turn-on voltage to reach 1 cd/m2 decreases from 13 to 8 V. The results suggest that the electron injection efficiency is not improved by introducing a ZnIx layer. Instead, the improved device performance originates from the strong hole-blocking ability of ZnIx. This work indicates that layered materials may lead to novel applications in optoelectronic devices.

[Spectrum simulation based on data derived from red tide].

PubMed

Liu, Zhen-Yu; Cui, Ting-Wei; Yue, Jie; Jiang, Tao; Cao, Wen-Xi; Ma, Yi

2011-11-01

The present paper utilizes the absorption data of red tide water measured during the growing and dying course to retrieve imaginary part of the index of refraction based on Mie theory, carries out the simulation and analysis of average absorption efficiency factors, average backscattering efficiency factors and scattering phase function. The analysis of the simulation shows that Mie theory can be used to reproduce the absorption property of Chaetoceros socialis with an average error of 11%; the average backscattering efficiency factors depend on the value of absorption whose maximum value corresponds to the wavelength range from 400 to 700 nanometer; the average backscattering efficiency factors showed a maximum value on 17th with a low value during the outbreak of red tide and the minimum on 21th; the total scattering, weakly depending on the absorption, is proportional to the size parameters which represent the relative size of cell diameter with respect to the wavelength, while the angle scattering intensity is inversely proportional to wavelength.

High-efficiency electroluminescence and amplified spontaneous emission from a thermally activated delayed fluorescent near-infrared emitter

NASA Astrophysics Data System (ADS)

Kim, Dae-Hyeon; D'Aléo, Anthony; Chen, Xian-Kai; Sandanayaka, Atula D. S.; Yao, Dandan; Zhao, Li; Komino, Takeshi; Zaborova, Elena; Canard, Gabriel; Tsuchiya, Youichi; Choi, Eunyoung; Wu, Jeong Weon; Fages, Frédéric; Brédas, Jean-Luc; Ribierre, Jean-Charles; Adachi, Chihaya

2018-02-01

Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.

Synthesis and properties of 1,3-dioxo-1H-inden-2(3H)-ylidene fragment and (3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl)vinyl fragment containing derivatives of azobenzene for holographic recording materials

NASA Astrophysics Data System (ADS)

Zarins, Elmars; Kokars, Valdis; Ozols, Andris; Augustovs, Peteris

2011-06-01

New glassy 1,3-dioxo-1H-inden-2(3H)-ylidene fragment und (3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl)vinyl fragment containing push-pull type derivatives of azobenzene able to create thin layers have been synthesized. Thin films of synthesized glasses for holographic recording were prepared using spin coating technique from saturated chloroform solution. Holographic grating recording in films of 6a-b, 7 and 12 has been experimentally studied at 633 and 532 nm in both transmission and reflection modes with p-p recording beam polarizations. The film 12 was found to be the most efficient at both wavelengths in transmission mode exhibiting the maximum self-diffraction efficiency of 9.9% at 633 nm, and 15.3% at 532 nm. The film of 6a was the most efficient in reflection mode with the maximum selfdiffraction efficiency of about 3%.

Defective TiO 2 with high photoconductive gain for efficient and stable planar heterojunction perovskite solar cells

DOE PAGES

Li, Yanbo; Cooper, Jason K.; Liu, Wenjun; ...

2016-08-18

Formation of planar heterojunction perovskite solar cells exhibiting both high efficiency and stability under continuous operation remains a challenge. Here, we show this can be achieved by using a defective TiO 2 thin film as the electron transport layer. TiO 2 layers with native defects are deposited by electron beam evaporation in an oxygen-deficient environment. Deep-level hole traps are introduced in the TiO 2 layers and contribute to a high photoconductive gain and reduced photocatalytic activity. The high photoconductivity of the TiO 2 electron transport layer leads to improved efficiency for the fabricated planar devices. A maximum power conversion efficiencymore » of 19.0% and an average PCE of 17.5% are achieved. In addition, the reduced photocatalytic activity of the TiO 2 layer leads to enhanced long-Term stability for the planar devices. Under continuous operation near the maximum power point, an efficiency of over 15.4% is demonstrated for 100 h.« less

On the minimum quantum requirement of photosynthesis.

PubMed

Zeinalov, Yuzeir

2009-01-01

An analysis of the shape of photosynthetic light curves is presented and the existence of the initial non-linear part is shown as a consequence of the operation of the non-cooperative (Kok's) mechanism of oxygen evolution or the effect of dark respiration. The effect of nonlinearity on the quantum efficiency (yield) and quantum requirement is reconsidered. The essential conclusions are: 1) The non-linearity of the light curves cannot be compensated using suspensions of algae or chloroplasts with high (>1.0) optical density or absorbance. 2) The values of the maxima of the quantum efficiency curves or the values of the minima of the quantum requirement curves cannot be used for estimation of the exact value of the maximum quantum efficiency and the minimum quantum requirement. The estimation of the maximum quantum efficiency or the minimum quantum requirement should be performed only after extrapolation of the linear part at higher light intensities of the quantum requirement curves to "0" light intensity.

Efficient logistic regression designs under an imperfect population identifier.

PubMed

Albert, Paul S; Liu, Aiyi; Nansel, Tonja

2014-03-01

Motivated by actual study designs, this article considers efficient logistic regression designs where the population is identified with a binary test that is subject to diagnostic error. We consider the case where the imperfect test is obtained on all participants, while the gold standard test is measured on a small chosen subsample. Under maximum-likelihood estimation, we evaluate the optimal design in terms of sample selection as well as verification. We show that there may be substantial efficiency gains by choosing a small percentage of individuals who test negative on the imperfect test for inclusion in the sample (e.g., verifying 90% test-positive cases). We also show that a two-stage design may be a good practical alternative to a fixed design in some situations. Under optimal and nearly optimal designs, we compare maximum-likelihood and semi-parametric efficient estimators under correct and misspecified models with simulations. The methodology is illustrated with an analysis from a diabetes behavioral intervention trial. © 2013, The International Biometric Society.

Idle efficiency and pollution results for two-row swirl-can combustors having 72 modules

NASA Technical Reports Server (NTRS)

Biaglow, J. A.; Trout, A. M.

1975-01-01

Two 72-swirl-can-module combustors were investigated in a full annular combustor test facility at engine idle conditions typical of a 30:1 pressure-ratio engine. The effects of radial and circumferential fuel scheduling on combustion efficiency and gaseous pollutants levels were determined. Test conditions were inlet-air temperature, 452 K; inlet total pressure, 34.45 newtons per square centimeter; and reference velocity, 19.5 meters per second. A maximum combustion efficiency of 98.1 percent was achieved by radial scheduling of fuel to the inner row of swirl-can modules. Emission index values were 6.9 for unburned hydrocarbons and 50.6 for carbon monoxide at a fuel-air ratio of 0.0119. Circumferential fuel scheduling of two 90 degree sectors of the swirl-can arrays produced a maximum combustion efficiency of 97.3 percent. The emission index values were 12.0 for unburned hydrocarbons and 69.2 for carbon monoxide at a fuel-air ratio of 0.0130.

Effects of nanoscale vacuum gap on photon-enhanced thermionic emission devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuan; Liao, Tianjun; Zhang, Yanchao

2016-01-28

A new model of the photon-enhanced thermionic emission (PETE) device with a nanoscale vacuum gap is established by introducing the quantum tunneling effect and the image force correction. Analytic expressions for both the thermionic emission and tunneling currents are derived. The electron concentration and the temperature of the cathode are determined by the particle conservation and energy balance equations. The effects of the operating voltage on the maximum potential barrier, cathode temperature, electron concentration and equilibrium electron concentration of the conduction band, and efficiency of the PETE device are discussed in detail for different given values of the vacuum gapmore » length. The influence of the band gap of the cathode and flux concentration on the efficiency is further analyzed. The maximum efficiency of the PETE and the corresponding optimum values of the band gap and the operating voltage are determined. The results obtained here show that the efficiency of the PETE device can be significantly improved by employing a nanoscale vacuum gap.« less

Effect of an InxGa1-xAs-GaAs blocking heterocathode metal contact on the GaAs TED operation

NASA Astrophysics Data System (ADS)

Arkusha, Yu. V.; Prokhorov, E. D.; Storozhenko, I. P.

2004-09-01

The frequency dependence of the generation efficiency of an mm- -nn:In:InxGaGa1-1-xAs- As-nn:GaAs-:GaAs-nn++:GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the :GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the nn:In:InxGaGa1-1-xAs cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.As cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.

Maximum Power Game as a Physical and Social Extension of Classical Games

NASA Astrophysics Data System (ADS)

Kim, Pilwon

2017-03-01

We consider an electric circuit in which the players participate as resistors and adjust their resistance in pursuit of individual maximum power. The maximum power game(MPG) becomes very complicated in a circuit which is indecomposable into serial/parallel components, yielding a nontrivial power distribution at equilibrium. Depending on the circuit topology, MPG covers a wide range of phenomena: from a social dilemma in which the whole group loses to a well-coordinated situation in which the individual pursuit of power promotes the collective outcomes. We also investigate a situation where each player in the circuit has an intrinsic heat waste. Interestingly, it is this individual inefficiency which can keep them from the collective failure in power generation. When coping with an efficient opponent with small intrinsic resistance, a rather inefficient player gets more power than efficient one. A circuit with multiple voltage inputs forms the network-based maximum power game. One of our major interests is to figure out, in what kind of the networks the pursuit for private power leads to greater total power. It turns out that the circuits with the scale-free structure is one of the good candidates which generates as much power as close to the possible maximum total.

Fast and Efficient Stochastic Optimization for Analytic Continuation

DOE PAGES

Bao, Feng; Zhang, Guannan; Webster, Clayton G; ...

2016-09-28

In this analytic continuation of imaginary-time quantum Monte Carlo data to extract real-frequency spectra remains a key problem in connecting theory with experiment. Here we present a fast and efficient stochastic optimization method (FESOM) as a more accessible variant of the stochastic optimization method introduced by Mishchenko et al. [Phys. Rev. B 62, 6317 (2000)], and we benchmark the resulting spectra with those obtained by the standard maximum entropy method for three representative test cases, including data taken from studies of the two-dimensional Hubbard model. Genearally, we find that our FESOM approach yields spectra similar to the maximum entropy results.more » In particular, while the maximum entropy method yields superior results when the quality of the data is strong, we find that FESOM is able to resolve fine structure with more detail when the quality of the data is poor. In addition, because of its stochastic nature, the method provides detailed information on the frequency-dependent uncertainty of the resulting spectra, while the maximum entropy method does so only for the spectral weight integrated over a finite frequency region. Therefore, we believe that this variant of the stochastic optimization approach provides a viable alternative to the routinely used maximum entropy method, especially for data of poor quality.« less

Modeling of a resonant heat engine

NASA Astrophysics Data System (ADS)

Preetham, B. S.; Anderson, M.; Richards, C.

2012-12-01

A resonant heat engine in which the piston assembly is replaced by a sealed elastic cavity is modeled and analyzed. A nondimensional lumped-parameter model is derived and used to investigate the factors that control the performance of the engine. The thermal efficiency predicted by the model agrees with that predicted from the relation for the Otto cycle based on compression ratio. The predictions show that for a fixed mechanical load, increasing the heat input results in increased efficiency. The output power and power density are shown to depend on the loading for a given heat input. The loading condition for maximum output power is different from that required for maximum power density.

Single-stage experimental evaluation of tandem-airfoil rotor and stator blading for compressors. Part 2: Data and performance for stage A

NASA Technical Reports Server (NTRS)

Brent, J. A.

1972-01-01

Stage A, comprised of a conventional rotor and stator, was designed and tested to establish a performance baseline for comparison with the results of subsequent tests planned for two tandem-blade stages. The rotor had an inlet hub/tip ratio of 0.8 and a design tip velocity of 757 ft/sec. At design equivalent rotor speed, rotor A achieved a maximum adiabatic efficiency of 85.1 percent at a pressure ratio of 1.29. The stage maximum adiabatic efficiency was 78.6 percent at a pressure ratio of 1.27.

Diode pumped CW and passively Q-switched Nd:LGGG laser at 1062 nm

NASA Astrophysics Data System (ADS)

Yang, H.; Jia, Z. T.; Zhang, B. T.; He, J. L.; Liu, S. D.; Yang, Y.; Tao, X. T.

2012-05-01

We report a Nd:LGGG laser at 1062 nm in the operations of the continuous-wave (CW) and passively Q-switching. The maximum CW output power of 5.62 W was obtained, corresponding to an optical-to-optical conversion efficiency of 49.0% and slope efficiency of 55.9%. By using Cr4+:YAG with initial transmission of 94% as the saturable absorber, for the first time, we got the maximum passively Q-switched output power of 1.21 W, accompanied with a highest pulse repetition rate of 27.1 kHz and a shortest pulse width of 9.1 ns.

Efficient, diode-pumped Tm3+:BaY2F8 vibronic laser

NASA Astrophysics Data System (ADS)

Cornacchia, F.; Parisi, D.; Bernardini, C.; Toncelli, A.; Tonelli, M.

2004-05-01

In this work we report the spectroscopy and laser results of several Thulium doped BaY2F8 single crystals grown using the Czochralski technique. The doping concentration is between 2at.% and 18at.%. We performed room temperature laser experiments pumping the samples with a laser diode at 789 nm obtaining 61% as maximum optical-to-optical efficiency with a maximum output power of 290 mW and a minimum lasing threshold of 26 mW. The lasing wavelength changed with the dopant concentration from 1927 nm up to 2030 nm and the nature of the transition changed from purely electronic to vibronic, accordingly.

Maximum-performance fiber-optic irradiation with nonimaging designs.

PubMed

Fang, Y; Feuermann, D; Gordon, J M

1997-10-01

A range of practical nonimaging designs for optical fiber applications is presented. Rays emerging from a fiber over a restricted angular range (small numerical aperture) are needed to illuminate a small near-field detector at maximum radiative efficiency. These designs range from pure reflector (all-mirror), to pure dielectric (refractive and based on total internal reflection) to lens-mirror combinations. Sample designs are shown for a specific infrared fiber-optic irradiation problem of practical interest. Optical performance is checked with computer three-dimensional ray tracing. Compared with conventional imaging solutions, nonimaging units offer considerable practical advantages in compactness and ease of alignment as well as noticeably superior radiative efficiency.

Development of a liquid tin microjet target for an efficient laser-produced plasma extreme ultraviolet source.

PubMed

Higashiguchi, Takeshi; Hamada, Masaya; Kubodera, Shoichi

2007-03-01

A regenerative tin liquid microjet target was developed for a high average power extreme ultraviolet (EUV) source. The diameter of the target was smaller than 160 microm and good vacuum lower than 0.5 Pa was maintained during the operation. A maximum EUV conversion efficiency of 1.8% at the Nd:yttrium-aluminum-garnet laser intensity of around 2 x 10(11) Wcm(2) with a spot diameter of 175 microm (full width at half maximum) was observed. The angular distribution of the EUV emission remained almost isotropic, whereas suprathermal ions mainly emerged toward the target normal.

Development of a liquid tin microjet target for an efficient laser-produced plasma extreme ultraviolet source

NASA Astrophysics Data System (ADS)

Higashiguchi, Takeshi; Hamada, Masaya; Kubodera, Shoichi

2007-03-01

A regenerative tin liquid microjet target was developed for a high average power extreme ultraviolet (EUV) source. The diameter of the target was smaller than 160 μm and good vacuum lower than 0.5 Pa was maintained during the operation. A maximum EUV conversion efficiency of 1.8% at the Nd:yttrium-aluminum-garnet laser intensity of around 2×1011 W/cm2 with a spot diameter of 175 μm (full width at half maximum) was observed. The angular distribution of the EUV emission remained almost isotropic, whereas suprathermal ions mainly emerged toward the target normal.

Design principles and optimal performance for molecular motors under realistic constraints

NASA Astrophysics Data System (ADS)

Tu, Yuhai; Cao, Yuansheng

2018-02-01

The performance of a molecular motor, characterized by its power output and energy efficiency, is investigated in the motor design space spanned by the stepping rate function and the motor-track interaction potential. Analytic results and simulations show that a gating mechanism that restricts forward stepping in a narrow window in configuration space is needed for generating high power at physiologically relevant loads. By deriving general thermodynamics laws for nonequilibrium motors, we find that the maximum torque (force) at stall is less than its theoretical limit for any realistic motor-track interactions due to speed fluctuations. Our study reveals a tradeoff for the motor-track interaction: while a strong interaction generates a high power output for forward steps, it also leads to a higher probability of wasteful spontaneous back steps. Our analysis and simulations show that this tradeoff sets a fundamental limit to the maximum motor efficiency in the presence of spontaneous back steps, i.e., loose-coupling. Balancing this tradeoff leads to an optimal design of the motor-track interaction for achieving a maximum efficiency close to 1 for realistic motors that are not perfectly coupled with the energy source. Comparison with existing data and suggestions for future experiments are discussed.

Optimizing the wireless power transfer over MIMO Channels

NASA Astrophysics Data System (ADS)

Wiedmann, Karsten; Weber, Tobias

2017-09-01

In this paper, the optimization of the power transfer over wireless channels having multiple-inputs and multiple-outputs (MIMO) is studied. Therefore, the transmitter, the receiver and the MIMO channel are modeled as multiports. The power transfer efficiency is described by a Rayleigh quotient, which is a function of the channel's scattering parameters and the incident waves from both transmitter and receiver side. This way, the power transfer efficiency can be maximized analytically by solving a generalized eigenvalue problem, which is deduced from the Rayleigh quotient. As a result, the maximum power transfer efficiency achievable over a given MIMO channel is obtained. This maximum can be used as a performance bound in order to benchmark wireless power transfer systems. Furthermore, the optimal operating point which achieves this maximum will be obtained. The optimal operating point will be described by the complex amplitudes of the optimal incident and reflected waves of the MIMO channel. This supports the design of the optimal transmitter and receiver multiports. The proposed method applies for arbitrary MIMO channels, taking transmitter-side and/or receiver-side cross-couplings in both near- and farfield scenarios into consideration. Special cases are briefly discussed in this paper in order to illustrate the method.

High efficiency fluorescent white OLEDs based on DOPPP

NASA Astrophysics Data System (ADS)

Zhang, Gang; Chen, Chen; Lang, Jihui; Zhao, Lina; Jiang, Wenlong

2017-08-01

The white organic light-emitting devices (WOLED) with the structures of ITO/m-MTDATA (10 nm)/NPB (30 nm)/Rubrene (0.2 nm)/DOPPP (x nm)/TAz (10 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al and ITO/NPB (30 nm)/DPAVBi:Rubrene (2 wt.%, 20 nm)/ DOPPP (x nm)/TAZ (10 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al (100 nm) have been fabricated by the vacuum thermal evaporation method. The results show that the chroma of the non-doped device is the best and the color coordinates are in the range of white light. The maximum luminance is 12,750 cd/m2 and the maximum current efficiency is 8.55 cd/A. The doped device A has the maximum luminance (16,570 cd/m2), when the thickness of blue layer DOPPP is 25 nm, and the doped device B achieves the highest efficiency (10.47 cd/A), when the thickness of DOPPP is 15 nm. All the performances of the doped devices are better than the non-doped one. The results demonstrate that the doped structures can realize the energy transfer and then improve the performance of the device effectively.

Enhanced photocatalytic activity of nanocellulose supported zinc oxide composite for RhB dye as well as ciprofloxacin drug under sunlight/visible light

NASA Astrophysics Data System (ADS)

Tavker, Neha; Sharma, Manu

2018-05-01

Zinc oxide nanoparticles were synthesised from zinc acetate di-hydrate via co-precipitation method. Nanocellulose was isolated from agrowaste using chemo-mechanical treatments and characterized. Nanocellulose supported zinc oxide composites were prepared through in-situ method by adding different amounts of nanocellulose. The photocatalytic efficiency of pure Zno and nanocellulose supported ZnO was calculated using RhB dye under visible light and sun light. The composites which had nanocellulose in greater ratio showed higher degradation efficiency in sunlight rather than visible light for both; dye and drug. All the composites showed high rate of photodegradation compared to bare ZnO and bare nanocellulose. The enhancement in photocatalytic activity was observed maximum where the amount of cellulose was maximum. The maximum observed rate was 0.025 min-1 using Ciprofloxacin drug due to the increase in lifetime of Z4 sample delaying the electron and hole pair recombination. The degrading efficiency of nanocellulose supported zinc oxide (NC/ZnO) composite for RhB was found to be 35% in visible, 76% in sunlight and 75% for ciprofloxacin under sunlight.

CuTaS 3 : Intermetal d–d Transitions Enable High Solar Absorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heo, Jaeseok; Yu, Liping; Altschul, Emmeline

To realize the fundamental limits of photovoltaic device efficiency, solar absorbers must exhibit strong absorption and abrupt absorption onsets. Ideally, onsets to maximum absorption (a > 105 cm-1) occur over a few tenths of an electronvolt. First-principles calculations predict CuTaS3 represents a potentially new class of materials with such absorption characteristics. Narrow metallic d bands in both the initial and final states present high joint densities of states and, therefore, strong absorption. Specifically, a mixture of metal d (Cu1+, d10) and S p characterizes states near the valence band maximum, and metal d (Ta5+, d0) dominates near the conduction bandmore » minimum. Optical absorption measurements on thin films confirm the abrupt onset to strong absorption a > 105 cm-1 at Eg + 0.4 eV (Eg = 1.0 eV). Theoretical CuTaS3 solar cell efficiency is predicted to be 28% for a 300 nm film based on the metric of spectroscopic limited maximum efficiency, which exceeds that of CuInSe2. This sulfide may offer new opportunities to discover and develop a new class of mixed d-element solar absorbers.« less

Implementation of GAMMON - An efficient load balancing strategy for a local computer system

NASA Technical Reports Server (NTRS)

Baumgartner, Katherine M.; Kling, Ralph M.; Wah, Benjamin W.

1989-01-01

GAMMON (Global Allocation from Maximum to Minimum in cONstant time), an efficient load-balancing algorithm, is described. GAMMON uses the available broadcast capability of multiaccess networks to implement an efficient search technique for finding hosts with maximal and minimal loads. The search technique has an average overhead which is independent of the number of participating stations. The transition from the theoretical concept to a practical, reliable, and efficient implementation is described.

Labeling tetracysteine-tagged proteins with biarsenical dyes for live cell imaging.

PubMed

Gaietta, Guido M; Deerinck, Thomas J; Ellisman, Mark H

2011-01-01

Correlation of real-time or time-lapse light microscopy (LM) with electron microscopy (EM) of cells can be performed with biarsenical dyes. These dyes fluorescently label tetracysteine-tagged proteins so that they can be imaged with LM and, upon fluorescent photoconversion of 3,3'-diaminobenzidine tetrahydrochloride (DAB), with EM as well. In the following protocol, cells expressing tetracysteine-tagged proteins are labeled for 1 h with biarsenical dyes. The volumes indicated are for a single 30-mm culture dish containing 2 mL of labeling medium. Scale the suggested volumes up or down depending upon the size of the culture dish used in the labeling. The same procedure can be adapted for longer labeling times by lowering the amount of dye used to 50-100 nM; however, the amount of the competing dithiol EDT is maintained at 10-20 μM. Longer labeling times often produce higher signal-to-noise ratios and cause less trauma to the treated cells prior to imaging.

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

PubMed Central

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin-ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; Galler, Andreas; Gawelda, Wojciech; Gosztola, David; Haldrup, Kristoffer; Harlang, Tobias; Liu, Yizhu; Møller, Klaus B.; Németh, Zoltán; Nozawa, Shunsuke; Pápai, Mátyás; Sato, Tokushi; Sato, Takahiro; Suarez-Alcantara, Karina; Togashi, Tadashi; Tono, Kensuke; Uhlig, Jens; Vithanage, Dimali A.; Wärnmark, Kenneth; Yabashi, Makina; Zhang, Jianxin; Sundström, Villy; Nielsen, Martin M.

2015-01-01

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined. PMID:25727920

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

DOE PAGES

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; ...

2015-03-02

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances.more » Thus experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.« less

Photo-enhanced performance and photo-tunable degradation in LC ecopolymers

NASA Astrophysics Data System (ADS)

Kaneko, Tatsuo

2007-05-01

Photosensitive, liquid crystalline (LC) polymers were prepared by in-bulk polymerization of phytomonomers such as cinnamic acid derivatives. The p-coumaric acid (4HCA) homopolymer showed a thermotropic LC phase where a photoreaction of [2+2] cycloaddition occurred by ultraviolet irradiation. LC phase was exhibited only in a low molecular weight state but the polymer was too brittle to materialize. Then we copolymerized 4HCA with multifunctional cinnamate, 3,4 dihydroxycinnamic acid (caffeic acid; DHCA), to prepare the hyperbranching architecture. Many branches increased the apparent size of the polymer chain but kept the low number-average molecular weight. P(4HCA-co-DHCA)s showed high performances which may be attained through the entanglement by in-bulk formation of hyperbranching, rigid structures. P(4HCA-co-DHCA)s showed a smooth hydrolysis, an in-soil degradation and a photoreaction cross-linking from conjugated cinnamate esters to aliphatic esters. The change in photoconversion degree tuned the polymer performance and chain hydrolysis.

Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ihly, Rachelle; Mistry, Kevin S.; Ferguson, Andrew J.

2016-04-25

Understanding the kinetics and energetics of interfacial electron transfer in molecular systems is crucial for the development of a broad array of technologies, including photovoltaics, solar fuel systems and energy storage. The Marcus formulation for electron transfer relates the thermodynamic driving force and reorganization energy for charge transfer between a given donor/acceptor pair to the kinetics and yield of electron transfer. Here we investigated the influence of the thermodynamic driving force for photoinduced electron transfer (PET) between single-walled carbon nanotubes (SWCNTs) and fullerene derivatives by employing time-resolved microwave conductivity as a sensitive probe of interfacial exciton dissociation. For the firstmore » time, we observed the Marcus inverted region (in which driving force exceeds reorganization energy) and quantified the reorganization energy for PET for a model SWCNT/acceptor system. The small reorganization energies (about 130 meV, most of which probably arises from the fullerene acceptors) are beneficial in minimizing energy loss in photoconversion schemes.« less

Surface-plasmon enhanced photodetection at communication band based on hot electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Kai; Zhan, Yaohui, E-mail: yhzhan@suda.edu.cn, E-mail: xfli@suda.edu.cn; Wu, Shaolong

2015-08-14

Surface plasmons can squeeze light into a deep-subwavelength space and generate abundant hot electrons in the nearby metallic regions, enabling a new paradigm of photoconversion by the way of hot electron collection. Unlike the visible spectral range concerned in previous literatures, we focus on the communication band and design the infrared hot-electron photodetectors with plasmonic metal-insulator-metal configuration by using full-wave finite-element method. Titanium dioxide-silver Schottky interface is employed to boost the low-energy infrared photodetection. The photodetection sensitivity is strongly improved by enhancing the plasmonic excitation from a rationally engineered metallic grating, which enables a strong unidirectional photocurrent. With a five-stepmore » electrical simulation, the optimized device exhibits an unbiased responsivity of ∼0.1 mA/W and an ultra-narrow response band (FWHM = 4.66 meV), which promises to be a candidate as the compact photodetector operating in communication band.« less

A photoswitchable orange-to-far-red fluorescent protein, PSmOrange.

PubMed

Subach, Oksana M; Patterson, George H; Ting, Li-Min; Wang, Yarong; Condeelis, John S; Verkhusha, Vladislav V

2011-07-31

We report a photoswitchable monomeric Orange (PSmOrange) protein that is initially orange (excitation, 548 nm; emission, 565 nm) but becomes far-red (excitation, 636 nm; emission, 662 nm) after irradiation with blue-green light. Compared to its parental orange proteins, PSmOrange has greater brightness, faster maturation, higher photoconversion contrast and better photostability. The red-shifted spectra of both forms of PSmOrange enable its simultaneous use with cyan-to-green photoswitchable proteins to study four intracellular populations. Photoconverted PSmOrange has, to our knowledge, the most far-red excitation peak of all GFP-like fluorescent proteins, provides diffraction-limited and super-resolution imaging in the far-red light range, is optimally excited with common red lasers, and can be photoconverted subcutaneously in a mouse. PSmOrange photoswitching occurs via a two-step photo-oxidation process, which causes cleavage of the polypeptide backbone. The far-red fluorescence of photoconverted PSmOrange results from a new chromophore containing N-acylimine with a co-planar carbon-oxygen double bond.

Far-red light photoactivatable near-infrared fluorescent proteins engineered from a bacterial phytochrome.

PubMed

Piatkevich, Kiryl D; Subach, Fedor V; Verkhusha, Vladislav V

2013-01-01

The ability to modulate the fluorescence of optical probes can be used to enhance signal-to-noise ratios for imaging within highly autofluorescent environments, such as intact tissues and living organisms. Here, we report two bacteriophytochrome-based photoactivatable near-infrared fluorescent proteins, named PAiRFP1 and PAiRFP2. PAiRFPs utilize haem-derived biliverdin, ubiquitous in mammalian tissues, as the chromophore. Initially weakly fluorescent PAiRFPs undergo photoconversion into a highly fluorescent state with excitation/emission at 690/717 nm following a brief irradiation with far-red light. After photoactivation, PAiRFPs slowly revert back to initial state, enabling multiple photoactivation-relaxation cycles. Low-temperature optical spectroscopy reveals several intermediates involved in PAiRFP photocycles, which all differ from that of the bacteriophytochrome precursor. PAiRFPs can be photoactivated in a spatially selective manner in mouse tissues, and optical modulation of their fluorescence allows for substantial contrast enhancement, making PAiRFPs advantageous over permanently fluorescent probes for in vivo imaging conditions of high autofluorescence and low signal levels.

Fluorescent proteins for FRET microscopy: monitoring protein interactions in living cells.

PubMed

Day, Richard N; Davidson, Michael W

2012-05-01

The discovery and engineering of novel fluorescent proteins (FPs) from diverse organisms is yielding fluorophores with exceptional characteristics for live-cell imaging. In particular, the development of FPs for fluorescence (or Förster) resonance energy transfer (FRET) microscopy is providing important tools for monitoring dynamic protein interactions inside living cells. The increased interest in FRET microscopy has driven the development of many different methods to measure FRET. However, the interpretation of FRET measurements is complicated by several factors including the high fluorescence background, the potential for photoconversion artifacts and the relatively low dynamic range afforded by this technique. Here, we describe the advantages and disadvantages of four methods commonly used in FRET microscopy. We then discuss the selection of FPs for the different FRET methods, identifying the most useful FP candidates for FRET microscopy. The recent success in expanding the FP color palette offers the opportunity to explore new FRET pairs. Copyright © 2012 WILEY Periodicals, Inc.

Indium Gallium Nitride Multijunction Solar Cell Simulation Using Silvaco Atlas

DTIC Science & Technology

2007-06-01

models is of great interest in space applications. By increasing the efficiency of photovoltaics, the number of solar panels is decreased. Therefore...obtained in single-junction solar cells by using Gallium Arsenide. Monocrystalline Gallium Arsenide has a maximum efficiency of approximately 25.1% [10

10 CFR 430.62 - Submission of data.

Code of Federal Regulations, 2010 CFR

2010-01-01

... energy factor expressed in cycles per kilowatt-hour. (vii) Faucets, the maximum water use in gpm (L/min... seasonal energy efficiency ratio and heating seasonal performance factor. For central air conditioning heat pumps whose seasonal energy efficiency ratio and heating seasonal performance factor are based on an...

Dual fuel diesel engine operation using LPG

NASA Astrophysics Data System (ADS)

Mirica, I.; Pana, C.; Negurescu, N.; Cernat, Al; Nutu, N. C.

2016-08-01

Diesel engine fuelling with LPG represents a good solution to reduce the pollutant emissions and to improve its energetic performances. The high autoignition endurance of LPG requires specialized fuelling methods. From all possible LPG fuelling methods the authors chose the diesel-gas method because of the following reasons: is easy to be implemented even at already in use engines; the engine does not need important modifications; the LPG-air mixture has a high homogeneity with favorable influences over the combustion efficiency and over the level of the pollutant emissions, especially on the nitrogen oxides emissions. This paper presents results of the theoretical and experimental investigations on operation of a LPG fuelled heavy duty diesel engine at two operating regimens, 40% and 55%. For 55% engine load is also presented the exhaust gas recirculation influence on the pollutant emission level. Was determined the influence of the diesel fuel with LPG substitution ratio on the combustion parameters (rate of heat released, combustion duration, maximum pressure, maximum pressure rise rate), on the energetic parameters (indicate mean effective pressure, effective efficiency, energetic specific fuel consumption) and on the pollutant emissions level. Therefore with increasing substitute ratio of the diesel fuel with LPG are obtained the following results: the increase of the engine efficiency, the decrease of the specific energetic consumption, the increase of the maximum pressure and of the maximum pressure rise rate (considered as criteria to establish the optimum substitute ratio), the accentuated reduction of the nitrogen oxides emissions level.

Optimizing any-aged management of mixed-species stands: II. effects of decision criteria

Treesearch

Robert G. Haight; Robert A. Monserud

1990-01-01

The effects of maximum present value and maximum volume objectives on the efficiencies of alternative silvicultural systems are determined by solving any-aged management problems for mixed-conifer stands in the Northern Rocky Mountains. Any-aged management problems are formulated with periodic planting and harvesting controls and without constraints on the stand age or...

Removing volatile organic compounds in cooking fume by nano-sized TiO2 photocatalytic reaction combined with ozone oxidation technique.

PubMed

Li, Yu-Hua; Cheng, Su-Wen; Yuan, Chung-Shin; Lai, Tzu-Fan; Hung, Chung-Hsuang

2018-06-05

Chinese cooking fume is one of the sources of volatile organic compounds (VOCs) in the air. An innovative control technology combining photocatalytic degradation and ozone oxidation (UV/TiO 2 +O 3 ) was developed to decompose VOCs in the cooking fume. Fiberglass filter (FGF) coated with TiO 2 was prepared by an impregnation procedure. A continuous-flow reaction system was self-designed by combining photocatalysis with advanced ozone oxidation technique. By passing the simulated cooking fume through the FGF, the VOC decomposition efficiency in the cooking fume could be increased by about 10%. The decomposition efficiency of VOCs in the cooking fume increased and then decreased with the inlet VOC concentration. A maximum VOC decomposition efficiency of 64% was obtained at 100 ppm. Similar trend was observed for reaction temperature with the VOC decomposition efficiencies ranging from 64 to 68%. Moreover, inlet ozone concentration had a positive effect on the decomposition of VOCs in the cooking fume for inlet ozone≤1000 ppm and leveled off for inlet ozone>1000 ppm. 34% of VOC decomposition efficiency was achieved solely by ozone oxidation with or without near-UV irradiation. A maximum of 75% and 94% VOC decomposition efficiency could be achieved by O 3 +UV/TiO 2 and UV/TiO 2 +O 3 techniques, respectively. The maximum decomposition efficiencies of VOCs decreased to 79% for using UV/TiO 2 +O 3 technique with adding water in the oil fume. Comparing the chromatographical species of VOCs in the oil fume before and after the decomposition of VOCs by using UV/TiO 2 +O 3 technique, we found that both TVOC and VOC species in the oil fume were effectively decomposed. Copyright © 2018 Elsevier Ltd. All rights reserved.

Efficiency optimization in a correlation ratchet with asymmetric unbiased fluctuations

NASA Astrophysics Data System (ADS)

Ai, Bao-Quan; Wang, Xian-Ju; Liu, Guo-Tao; Wen, De-Hua; Xie, Hui-Zhang; Chen, Wei; Liu, Liang-Gang

2003-12-01

The efficiency of a Brownian particle moving in a periodic potential in the presence of asymmetric unbiased fluctuations is investigated. We found that even on the quasistatic limit there is a regime where the efficiency can be a peaked function of temperature, which proves that thermal fluctuations facilitate the efficiency of energy transformation, contradicting the earlier findings [H. Kamegawa et al., Phys. Rev. Lett. 80, 5251 (1998)]. It is also found that the mutual interplay between temporal asymmetry and spatial asymmetry may induce optimized efficiency at finite temperatures. The ratchet is not most efficient when it gives maximum current.

Efficient simple sealed-off CO laser at room temperature

NASA Astrophysics Data System (ADS)

Peters, P. J. M.; Witteman, W. J.; Zuidema, R. J.

1980-07-01

The paper reports a simple sealed-off CW CO laser with gold electrodes. A constant long-life output power of more than 29 W/m and a maximum efficiency of 15% at room temperature are reported. No auxiliary features, such as a palladium hydrogen extraction tube, are necessary.

Efficient room-temperature source of polarized single photons

DOEpatents

Lukishova, Svetlana G.; Boyd, Robert W.; Stroud, Carlos R.

2007-08-07

An efficient technique for producing deterministically polarized single photons uses liquid-crystal hosts of either monomeric or oligomeric/polymeric form to preferentially align the single emitters for maximum excitation efficiency. Deterministic molecular alignment also provides deterministically polarized output photons; using planar-aligned cholesteric liquid crystal hosts as 1-D photonic-band-gap microcavities tunable to the emitter fluorescence band to increase source efficiency, using liquid crystal technology to prevent emitter bleaching. Emitters comprise soluble dyes, inorganic nanocrystals or trivalent rare-earth chelates.

Lead-free inverted planar formamidinium tin triiodide perovskite solar cells achieving power conversion efficiencies up to 6.22%

DOE PAGES

Liao, Weiqiang; Zhao, Dewei; Yu, Yue; ...

2016-08-29

Efficient lead (Pb)-free inverted planar formamidinium tin triiodide (FASnI 3) perovskite solar cells (PVSCs) are demonstrated. Our FASnI 3 PVSCs achieved average power conversion efficiencies (PCEs) of 5.41% ± 0.46% and a maximum PCE of 6.22% under forward voltage scan. Here, the PVSCs exhibit small photocurrent–voltage hysteresis and high reproducibility. The champion cell shows a steady-state efficiency of ≈6.00% for over 100 s.

Porous glass membranes for vanadium redox-flow battery application - Effect of pore size on the performance

NASA Astrophysics Data System (ADS)

Mögelin, H.; Yao, G.; Zhong, H.; dos Santos, A. R.; Barascu, A.; Meyer, R.; Krenkel, S.; Wassersleben, S.; Hickmann, T.; Enke, D.; Turek, T.; Kunz, U.

2018-02-01

The improvement of redox-flow batteries requires the development of chemically stable and highly conductive separators. Porous glass membranes can be an attractive alternative to the nowadays most common polymeric membranes. Flat porous glass membranes with a pore size in the range from 2 to 50 nm and a thickness of 300 and 500 μm have been used for that purpose. Maximum values for voltage efficiency of 85.1%, coulombic efficiency of 97.9% and energy efficiency of 76.3% at current densities in the range from 20 to 60 mA cm-2 have been achieved. Furthermore, a maximum power density of 95.2 mW cm-2 at a current density of 140 mA cm-2 was gained. These results can be related to small vanadium crossover, high conductivity and chemical stability, confirming the great potential of porous glass membranes for vanadium redox-flow applications.

High Step-Up DC—DC Converter for AC Photovoltaic Module with MPPT Control

NASA Astrophysics Data System (ADS)

Sundar, Govindasamy; Karthick, Narashiman; Rama Reddy, Sasi

2014-08-01

This paper presents the high gain step-up BOOST converter which is essential to step up the low output voltage from PV panel to the high voltage according to the requirement of the application. In this paper a high gain BOOST converter with coupled inductor technique is proposed with the MPPT control. Without extreme duty ratios and the numerous turns-ratios of a coupled inductor this converter achieves a high step-up voltage-conversion ratio and the leakage energy of the coupled inductor is efficiently recycled to the load. MPPT control used to extract the maximum power from PV panel by controlling the Duty ratio of the converter. The PV panel, BOOST converter and the MPPT are modeled using Sim Power System blocks in MATLAB/SIMULINK environment. The prototype model of the proposed converter has been implemented with the maximum measured efficiency is up to 95.4% and full-load efficiency is 93.1%.

Solar heating system final design package

NASA Technical Reports Server (NTRS)

1979-01-01

The system is composed of a warm air collector, a logic control unit and a universal switching and transport unit. The collector was originally conceived and designed as an integrated roof/wall system and therefore provides a dual function in the structure. The collector serves both as a solar energy conversion system and as a structural weather resistant skin. The control unit provides totally automatic control over the operation of the system. It receives input data from sensor probes in collectors, storage and living space. The logic was designed so as to make maximum use of solar energy and minimize use of conventional energy. The transport and switching unit is a high-efficiency air-handling system equipped with gear motor valves that respond to outputs from the control system. The fan unit was designed for maximum durability and efficiency in operation, and has permanently lubricated ball bearings and excellent air-handling efficiency.

Compact and efficient CW 473nm blue laser with LBO intracavity frequency doubling

NASA Astrophysics Data System (ADS)

Qi, Yan; Wang, Yu; Wang, Yanwei; Zhang, Jing; Yan, Boxia

2016-10-01

With diode end pumped Nd:YAG directly and LBO intracavity frequency doubling, a compact, high efficient continuous wave blue laser at 473nm is realized. When the incident pump power reach 6.2W, 630mW maximum output power of blue laser at 473nm is achieved with 15mm long LBO, the optical-to-optical conversion efficiency is as high as 10.2%.

Highly efficient orange and warm white phosphorescent OLEDs based on a host material with a carbazole-fluorenyl hybrid.

PubMed

Du, Xiaoyang; Huang, Yun; Tao, Silu; Yang, Xiaoxia; Wu, Chuan; Wei, Huaixin; Chan, Mei-Yee; Yam, Vivian Wing-Wah; Lee, Chun-Sing

2014-06-01

A new carbazole-fluorenyl hybrid compound, 3,3'(2,7-di(naphthaline-2-yl)-9H-fluorene-9,9-diyl)bis(9-phenyl-9H-carbazole) (NFBC) was synthesized and characterized. The compound exhibits blue-violet emission both in solution and in film, with peaks centered at 404 and 420 nm. In addition to the application as a blue emitter, NFBC is demonstrated to be a good host for phosphorescent dopants. By doping Ir(2-phq)3 in NFBC, a highly efficient orange organic light-emitting diode (OLED) with a maximum efficiency of 32 cd A(-1) (26.5 Lm W(-1)) was obtained. Unlike most phosphorescent OLEDs, the device prepared in our study shows little efficiency roll-off at high brightness and maintains current efficiencies of 31.9 and 26.8 cd A(-1) at a luminance of 1000 and 10,000 cd m(-2), respectively. By using NFBC simultaneously as a blue fluorescence emitter and as a host for a phosphorescent dopant, a warm white OLED with a maximum efficiency of 22.9 Lm W(-1) (21.9 cd A(-1)) was also obtained. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improved Efficiency and Enhanced Color Quality of Light-Emitting Diodes with Quantum Dot and Organic Hybrid Tandem Structure.

PubMed

Zhang, Heng; Feng, Yuanxiang; Chen, Shuming

2016-10-03

Light-emitting diodes based on organic (OLEDs) and colloidal quantum dot (QLEDs) are widely considered as next-generation display technologies because of their attractive advantages such as self-emitting and flexible form factor. The OLEDs exhibit relatively high efficiency, but their color saturation is quite poor compared with that of QLEDs. In contrast, the QLEDs show very pure color emission, but their efficiency is lower than that of OLEDs currently. To combine the advantages and compensate for the weaknesses of each other, we propose a hybrid tandem structure which integrates both OLED and QLED in a single device architecture. With ZnMgO/Al/HATCN interconnecting layer, hybrid tandem LEDs are successfully fabricated. The demonstrated hybrid tandem devices feature high efficiency and high color saturation simultaneously; for example, the devices exhibit maximum current efficiency and external quantum efficiency of 96.28 cd/A and 25.90%, respectively. Meanwhile, the full width at half-maximum of the emission spectra is remarkably reduced from 68 to 44 nm. With the proposed hybrid tandem structure, the color gamut of the displays can be effectively increased from 81% to 100% NTSC. The results indicate that the advantages of different LED technologies can be combined in a hybrid tandem structure.

Leaching of aluminum and iron from boiler slag generated from a typical Chinese Steel Plant.

PubMed

Li, Jinping; Gan, Jinhua; Li, Xianwang

2009-07-30

This paper presents a new way of recycling aluminum and iron in boiler slag derived from coal combustion plants, which integrates efficient extraction and reuse of the leached pellets together. The boiler slag was pelletized together with washed coal and lime prior to sintering and then was sintered at 800-1200 degrees C for different periods to produce sintered pellets for the leaching test. An elemental analysis of aqueous solutions leached by sulfuric acid was determined by EDTA-Na(2)-ZnCl(2) titration method. The components and microstructures of the samples, sintered pellets and leached residue were examined by means of XRF, XRD and SEM. XRD analysis indicates that predominate minerals such as kaolinite, quartz, calcium silicide, hematate and metakoalin exist in the boiler slag. An aluminum extraction efficiency of 86.50% was achieved. The maximum extraction efficiency of Fe was 94.60% in the same conditions of that for the maximum extraction efficiency of Al. The extraction efficiencies of Al and Fe increased with an increase in temperature, leaching time and acidity. High Al extraction efficiency was obtained for pellets with high CaO content. The final product of alumina would be used directly for the production of metallic aluminum.

Chewing efficiency and maximum bite force with different attachment systems of implant overdentures: a crossover study.

PubMed

Elsyad, Moustafa Abdou; Khairallah, Ahmed Samir

2017-06-01

This crossover study aimed to evaluate and compare chewing efficiency and maximum bite force (MBF) with resilient telescopic and bar attachment systems of implant overdentures in patients with atrophied mandibles. Ten participants with severely resorbed mandibles and persistent denture problems received new maxillary and mandibular conventional dentures (control, CD). After 3 months of adaptation, two implants were inserted in canine region of the mandible. In a quasi-random method, overdentures were connected to the implants with either bar overdentures (BOD) or resilient telescopic overdentures (TOD) attachment systems. Chewing efficiency in terms of unmixed fraction (UF) was measured using chewing gum (after 5, 10, 20, 30 and 50 strokes), and MBF was measured using a bite force transducer. Measurements were performed 3 months after using each of the following prostheses: CD, BOD and TOD. Chewing efficiency and MBF increased significantly with BOD and TOD compared to CD. As the number of chewing cycles increased, the UF decreased. TOD recorded significant higher chewing efficiency and MBF than BOD. Resilient telescopic attachments are associated with increased chewing efficiency and MBF compared bar attachments when used to retain overdentures to the implants in patients with atrophied mandibles. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Understanding the Slow Transient Optoelectronic Response of Hybrid Organic-Inorganic Halide Perovskites

NASA Astrophysics Data System (ADS)

Jacobs, Daniel Louis

Hybrid organic-inorganic halide perovskites, particularly methylammonium lead triiodide (MAPbI3), have emerged within the past decade as an exciting class of photovoltaic materials. In less than ten years, MAPbI3-based photovoltaic devices have seen unprecedented performance growth, with photoconversion efficiency increasing from 3% to over 22%, making it competitive with traditional high-efficiency solar cells. Furthermore, the fabrication of MAPbI3 devices utilize low-temperature solution processing, which could facilitate ultra low cost manufacturing. However, MAPbI3 suffers from significant instabilities under working conditions that have limited their applications outside of the laboratory. The instability of the MAPbI3 material can be generalized as a complex, slow transient optoelectronic response (STOR). The mechanism of the generalized STOR is dependent on the native defects of MAPbI3, but detailed understanding of the material defect properties is complicated by the complex ionic bonding of MAPbI3. Furthermore, characterization of the intrinsic material's response is complicated by the diverse approach to material processing and device architecture across laboratories around the world. In order to understand and mitigate the significant problems of MAPbI3 devices, a new approach focused on the material response, rather than the full device response, must be pursued. This dissertation highlights the work to analyze and mitigate the STOR intrinsic to MAPbI3. An experimental platform was developed based on lateral interdigitated electrode (IDE) arrays capable of monitoring the current and photoluminescence response simultaneously. By correlating the dynamics of the current and photoluminescence (PL) responses, both charge trapping and ion migration mechanisms were identified to contribute to the STOR. Next, a novel fabrication technique is introduced that is capable of reliably depositing MAPbI3 thin films with grain sizes at least an order of magnitude larger than most common techniques. These films were studied with confocal microscopy to give insight into the intra-grain PL dynamics of MAPbI3. Finally, the lateral IDE device platform was used to study the composition and morphology dependent STOR and revealed important correlations between defect formation and the STOR. These results represent an important step toward realizing a deeper understanding of the intrinsic limitations of MAPbI3 needed to progress the technology outside of the laboratory.

Chloroplast Dynamics and Photosynthetic Efficiency: Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, Maureen

This project investigated the mechanism by which chloroplasts position themselves to maximize solar energy utilization, to enhance gas exchange, to minimize environmental stress, and to promote efficient exchange of metabolites with other compartments within the plant cell. Chloroplasts move within leaf cells to optimize light levels, moving toward levels of light useful for photosynthesis while moving away from excess light. Plastids sometimes extend their reach by sending out projections (stromules) that can connect anchor chloroplasts in position within the cell or provide close contacts with plasma membrane, mitochondria, peroxisomes, endoplasmic reticulum, and the nucleus. The intracellular location of chloroplasts inmore » relation to other organelles with which they share biosynthetic pathways, such as peroxisomes and mitochondria in photorespiration, affects metabolite flow. This work contributed to the knowledge of the mechanisms of organelle movement and anchoring in specific locations in plant cells and how proteins traffic within the cell. We identified two domains on 12 of the 13 Arabidopsis myosins that were similar to the vacuole-binding (V) domain characterized in yeast and to the DIL domain characterized in yeast and mouse as required for secretory vesicle or melanosome movement, respectively. Because all of the Arabidopsis regions with homology to the V domain contain the amino acid sequence PAL, we refer to this region as the Arabidopsis PAL domain. We have used the yeast Myo2p tail structural information to model the 12 myosin XI tail domains containing the homologous PAL and DIL domains. Eight YFP::DIL domain fusions labeled peroxisomes; none labeled mitochondria or chloroplasts. Six myosin XI Vacuole domains labeled mitochondria and seven labeled Golgi bodies. The Arabidopsis myosin XI-F PAL domain and the homologous myosin XI-F PAL domain from N. benthamiana labels chloroplasts and stromules in N. benthamiana leaves. Using an Arabidopsis line containing hotoconvertible GFP, we observed transfer of protein from one plastid to another and within a stromule from single plastids. We provided time-lapse movies demonstrating movement of both the photoconvertible GFP and standard GFP between plastids. We previously demonstrated the lack of a plastid network within plant cells. We provided protocols explaining how to use fluorescent protein technology to track plastids and stromules within plant cells. We demonstrated that standard GFP unexpectedly could be photoconverted to a red form under certain conditions, allowing the use of GFP lines for studies that require photoconversion.« less

Theoretical investigations of energy harvesting efficiency from structural vibrations using piezoelectric and electromagnetic oscillators.

PubMed

Harne, Ryan L

2012-07-01

Conversion of ambient vibrational energy into electric power has been the impetus of much modern research. The traditional analysis has focused on absolute electrical power output from the harvesting devices and efficiency defined as the convertibility of an infinite resource of vibration excitation into power. This perspective has limited extensibility when applying resonant harvesters to host resonant structures when the inertial influence of the harvester is more significant. Instead, this work pursues a fundamental understanding of the coupled dynamics of a main mass-spring-damper system to which an electromagnetic or piezoelectric mass-spring-damper is attached. The governing equations are derived, a metric of efficiency is presented, and analysis is undertaken. It is found that electromagnetic energy harvesting efficiency and maximum power output is limited by the strength of the coupling such that no split system resonances are induced for a given mass ratio. For piezoelectric harvesters, only the coupling strength and certain design requirements dictate maximum power and efficiency achievable. Since the harvesting circuitry must "follow" the split resonances as the piezoelectric harvesters become more massive, the optimum design of piezoelectric harvesters appears to be more involved than for electromagnetic devices.

70% efficiency of bistate molecular machines explained by information theory, high dimensional geometry and evolutionary convergence.

PubMed

Schneider, Thomas D

2010-10-01

The relationship between information and energy is key to understanding biological systems. We can display the information in DNA sequences specifically bound by proteins by using sequence logos, and we can measure the corresponding binding energy. These can be compared by noting that one of the forms of the second law of thermodynamics defines the minimum energy dissipation required to gain one bit of information. Under the isothermal conditions that molecular machines function this is [Formula in text] joules per bit (kB is Boltzmann's constant and T is the absolute temperature). Then an efficiency of binding can be computed by dividing the information in a logo by the free energy of binding after it has been converted to bits. The isothermal efficiencies of not only genetic control systems, but also visual pigments are near 70%. From information and coding theory, the theoretical efficiency limit for bistate molecular machines is ln 2=0.6931. Evolutionary convergence to maximum efficiency is limited by the constraint that molecular states must be distinct from each other. The result indicates that natural molecular machines operate close to their information processing maximum (the channel capacity), and implies that nanotechnology can attain this goal.

An analysis of the surface-normal coupling efficiency of a metal grating coupler embedded in a Scotch tape optical waveguide

NASA Astrophysics Data System (ADS)

Barrios, Carlos Angulo; Canalejas-Tejero, Víctor

2017-01-01

The coupling efficiency at normal incidence of recently demonstrated aluminum grating couplers integrated in flexible Scotch tape waveguides has been analyzed theoretically and experimentally. Finite difference time domain (FDTD) and rigorously coupled wave analysis (RCWA) methods have been used to optimize the dimensions (duty cycle and metal thickness) of Scotch tape-embedded 1D Al gratings for maximum coupling at 635 nm wavelength. Good dimension and tape refractive index tolerances are predicted. FDTD simulations reveal the incident beam width and impinging position (alignment) values that avoid rediffraction and thus maximize the coupling efficiency. A 1D Al diffraction grating integrated into a Scotch tape optical waveguide has been fabricated and characterized. The fabrication process, based on pattern transfer, has been optimized to allow complete Al grating transfer onto the Scotch tape waveguide. A maximum coupling efficiency of 20% for TM-polarized normal incidence has been measured, which is in good agreement with the theoretical predictions. The measured coupling efficiency is further increased up to 28% for TM polarization under oblique incidence. Temperature dependence measurements have been also achieved and related to the simulations results and fabrication procedure.

70% efficiency of bistate molecular machines explained by information theory, high dimensional geometry and evolutionary convergence

PubMed Central

Schneider, Thomas D.

2010-01-01

The relationship between information and energy is key to understanding biological systems. We can display the information in DNA sequences specifically bound by proteins by using sequence logos, and we can measure the corresponding binding energy. These can be compared by noting that one of the forms of the second law of thermodynamics defines the minimum energy dissipation required to gain one bit of information. Under the isothermal conditions that molecular machines function this is joules per bit ( is Boltzmann's constant and T is the absolute temperature). Then an efficiency of binding can be computed by dividing the information in a logo by the free energy of binding after it has been converted to bits. The isothermal efficiencies of not only genetic control systems, but also visual pigments are near 70%. From information and coding theory, the theoretical efficiency limit for bistate molecular machines is ln 2 = 0.6931. Evolutionary convergence to maximum efficiency is limited by the constraint that molecular states must be distinct from each other. The result indicates that natural molecular machines operate close to their information processing maximum (the channel capacity), and implies that nanotechnology can attain this goal. PMID:20562221

The efficiency frontier approach to economic evaluation of health-care interventions.

PubMed

Caro, J Jaime; Nord, Erik; Siebert, Uwe; McGuire, Alistair; McGregor, Maurice; Henry, David; de Pouvourville, Gérard; Atella, Vincenzo; Kolominsky-Rabas, Peter

2010-10-01

IQWiG commissioned an international panel of experts to develop methods for the assessment of the relation of benefits to costs in the German statutory health-care system. The panel recommended that IQWiG inform German decision makers of the net costs and value of additional benefits of an intervention in the context of relevant other interventions in that indication. To facilitate guidance regarding maximum reimbursement, this information is presented in an efficiency plot with costs on the horizontal axis and value of benefits on the vertical. The efficiency frontier links the interventions that are not dominated and provides guidance. A technology that places on the frontier or to the left is reasonably efficient, while one falling to the right requires further justification for reimbursement at that price. This information does not automatically give the maximum reimbursement, as other considerations may be relevant. Given that the estimates are for a specific indication, they do not address priority setting across the health-care system. This approach informs decision makers about efficiency of interventions, conforms to the mandate and is consistent with basic economic principles. Empirical testing of its feasibility and usefulness is required.

Carbon and nutrient use efficiencies optimally balance stoichiometric imbalances

NASA Astrophysics Data System (ADS)

Manzoni, Stefano; Čapek, Petr; Lindahl, Björn; Mooshammer, Maria; Richter, Andreas; Šantrůčková, Hana

2016-04-01

Decomposer organisms face large stoichiometric imbalances because their food is generally poor in nutrients compared to the decomposer cellular composition. The presence of excess carbon (C) requires adaptations to utilize nutrients effectively while disposing of or investing excess C. As food composition changes, these adaptations lead to variable C- and nutrient-use efficiencies (defined as the ratios of C and nutrients used for growth over the amounts consumed). For organisms to be ecologically competitive, these changes in efficiencies with resource stoichiometry have to balance advantages and disadvantages in an optimal way. We hypothesize that efficiencies are varied so that community growth rate is optimized along stoichiometric gradients of their resources. Building from previous theories, we predict that maximum growth is achieved when C and nutrients are co-limiting, so that the maximum C-use efficiency is reached, and nutrient release is minimized. This optimality principle is expected to be applicable across terrestrial-aquatic borders, to various elements, and at different trophic levels. While the growth rate maximization hypothesis has been evaluated for consumers and predators, in this contribution we test it for terrestrial and aquatic decomposers degrading resources across wide stoichiometry gradients. The optimality hypothesis predicts constant efficiencies at low substrate C:N and C:P, whereas above a stoichiometric threshold, C-use efficiency declines and nitrogen- and phosphorus-use efficiencies increase up to one. Thus, high resource C:N and C:P lead to low C-use efficiency, but effective retention of nitrogen and phosphorus. Predictions are broadly consistent with efficiency trends in decomposer communities across terrestrial and aquatic ecosystems.

Maximum Work of Free-Piston Stirling Engine Generators

NASA Astrophysics Data System (ADS)

Kojima, Shinji

2017-04-01

Using the method of adjoint equations described in Ref. [1], we have calculated the maximum thermal efficiencies that are theoretically attainable by free-piston Stirling and Carnot engine generators by considering the work loss due to friction and Joule heat. The net work done by the Carnot cycle is negative even when the duration of heat addition is optimized to give the maximum amount of heat addition, which is the same situation for the Brayton cycle described in our previous paper. For the Stirling cycle, the net work done is positive, and the thermal efficiency is greater than that of the Otto cycle described in our previous paper by a factor of about 2.7-1.4 for compression ratios of 5-30. The Stirling cycle is much better than the Otto, Brayton, and Carnot cycles. We have found that the optimized piston trajectories of the isothermal, isobaric, and adiabatic processes are the same when the compression ratio and the maximum volume of the same working fluid of the three processes are the same, which has facilitated the present analysis because the optimized piston trajectories of the Carnot and Stirling cycles are the same as those of the Brayton and Otto cycles, respectively.

Performance analysis of solar-assisted chemical heat-pump dryer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fadhel, M.I.; Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450, Melaka; Sopian, K.

2010-11-15

A solar-assisted chemical heat-pump dryer has been designed, fabricated and tested. The performance of the system has been studied under the meteorological conditions of Malaysia. The system consists of four main components: solar collector (evacuated tubes type), storage tank, solid-gas chemical heat pump unit and dryer chamber. A solid-gas chemical heat pump unit consists of reactor, condenser and evaporator. The reaction used in this study (CaCl2-NH{sub 3}). A simulation has been developed, and the predicted results are compared with those obtained from experiments. The maximum efficiency for evacuated tubes solar collector of 80% has been predicted against the maximum experimentmore » of 74%. The maximum values of solar fraction from the simulation and experiment are 0.795 and 0.713, respectively, whereas the coefficient of performance of chemical heat pump (COP{sup h}) maximum values 2.2 and 2 are obtained from simulation and experiments, respectively. The results show that any reduction of energy at condenser as a result of the decrease in solar radiation will decrease the coefficient of performance of chemical heat pump as well as decrease the efficiency of drying. (author)« less

Design analysis and simulation study of an efficiency enhanced L-band MILO

NASA Astrophysics Data System (ADS)

Dixit, Gargi; Kumar, Arjun; Jain, P. K.

2017-01-01

In this article, an experimental L-band compact magnetically insulated transmission line oscillator (MILO) has been simulated using the 3D PIC simulation code "Particle Studio," and an improvement in the device efficiency has been obtained. The detailed interaction and operating mechanism describing the role of sub-assemblies have been explained. The performance of the device was found to be the function of the distance between the end-surface of the cathode and the beam-dump disk. During simulation, a high power microwave of the TM01 mode is generated with the peak RF-power of 6 GW and the power conversion efficiency of 19.2%, at the operating voltage of ˜600 kV and at the current of 52 kA. For better impedance matching or maximum power transfer, four stubs have been placed at the λg/4 distance from the extractor cavity, which results in the stable RF power output. In this work, an improved L-band MILO along with a new type beam-dump disk is selected for performance improvement with typical design parameters and beam parameters. The total peak power of improved MILO is 7 GW, and the maximum power conversion efficiency is 22.4%. This improvement is achieved due to the formation of the virtual cathode at the load side, which helps in modulating the energy of electrons owing to maximum reflection of electrons from the mesh or foil.

Multi-watt passively Q-switched Yb:YAB/Cr:YAG microchip lasers

NASA Astrophysics Data System (ADS)

Serres, Josep Maria; Loiko, Pavel; Mateos, Xavier; Liu, Junhai; Zhang, Huaijing; Yumashev, Konstantin; Griebner, Uwe; Petrov, Valentin; Aguiló, Magdalena; Díaz, Francesc

2017-02-01

A trigonal 5.6 at.% Yb:YAl3(BO3)4 (Yb:YAB) crystal is employed in continuous-wave (CW) and passively Q-switched microchip lasers pumped by a diode at 978 nm. Using a 3 mm-thick, c-cut Yb:YAB crystal, which has a higher pump absorption efficiency, efficient CW microchip laser operation is demonstrated. This laser generated a maximum output power of 7.18 W at 1041-1044 nm with a slope efficiency η of 67% (with respect to the absorbed pump power) and an almost diffraction-limited beam, M2 x,y < 1.1. Inserting a Cr:YAG saturable absorber, stable passive Q-switching of the Yb:YAB microchip laser was obtained. The maximum average output power from the Yb:YAB/Cr:YAG laser reached 2.82 W at 1042 nm with η = 53% and a conversion efficiency with respect to the CW mode of 65% (when using a 0.7 mm-thick Cr:YAG). The latter corresponded to a pulse duration and energy of 7.1 ns / 47 μJ at a pulse repetition rate (PRR) of 60 kHz. Using a 1.3 mm-thick Cr:YAG, 2.02 W were achieved at 1041 nm corresponding to η = 38%. The pulse characteristics were 4.9 ns / 83 μJ at PRR = 24.3 kHz and the maximum peak power reached 17 kW. Yb:YAB crystals are very promising for compact sub-ns power-scalable microchip lasers.

Ultimate high power operation of 9xx-nm single emitter broad stripe laser diodes

NASA Astrophysics Data System (ADS)

Kaifuchi, Yoshikazu; Yamagata, Yuji; Nogawa, Ryozaburo; Morohashi, Rintaro; Yamada, Yumi; Yamaguchi, Masayuki

2017-02-01

Design optimization of single emitter broad stripe 9xx-nm laser diodes was studied to achieve ultimate high power and high efficiency operation for a use in fiber laser pumping and other industrial applications. We tuned laser vertical layer design and stripe width in terms of optical confinement as well as electrical resistance. As a result, newly designed LDs with 4mm-long cavity and 220 μm-wide stripe successfully demonstrate maximum CW output power as high as 33 W and high efficiency operation of more than 60 % PCE even at 27 W output power. In pulse measurement, the maximum output of 68 W was obtained.

Photorefractive InGaAs/GaAs multiple quantum wells in the Franz{endash}Keldysh geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iwamoto, S.; Kageshima, H.; Yuasa, T.

2001-06-01

We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz{endash}Keldysh geometry at wavelengths of 0.92{endash}0.94 {mu}m. A maximum two-wave mixing gain of 138 cm{sup {minus}1} and a maximum diffraction efficiency of 1.5{times}10{sup {minus}4} are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law. {copyright} 2001 American Institute of Physics.

Experimental Determination of Operating and Maximum Power Transfer Efficiencies at Resonant Frequency in a Wireless Power Transfer System using PP Network Topology with Top Coupling

NASA Astrophysics Data System (ADS)

Ramachandran, Hema; Pillai, K. P. P.; Bindu, G. R.

2017-08-01

A two-port network model for a wireless power transfer system taking into account the distributed capacitances using PP network topology with top coupling is developed in this work. The operating and maximum power transfer efficiencies are determined analytically in terms of S-parameters. The system performance predicted by the model is verified with an experiment consisting of a high power home light load of 230 V, 100 W and is tested for two forced resonant frequencies namely, 600 kHz and 1.2 MHz. The experimental results are in close agreement with the proposed model.

High Output Maximum Efficiency Resonator (HOMER) Laser for NASA's Global Ecosystem Dynamics Investigation (GEDI) Lidar Mission

NASA Technical Reports Server (NTRS)

Stysley, Paul; Coyle, Barry; Clarke, Greg; Poulios, Demetrios; Kay, Richard

2015-01-01

The Global Ecosystems Dynamics Investigation (GEDI) is a planned mission sending a LIDAR instrument to the International Space Station that will employ three NASA laser transmitters. This instrument will produce parallel tracks on the Earth's surface that will provide global 3D vegetation canopy measurements. To meet the mission goals a total of 5 High Output Maximum Efficiency Resonator lasers will to be built (1 ETU + 3 Flight + 1 spare) in-house at NASA-GSFC. This presentation will summarize the HOMER design, the testing the design has completed in the past, and the plans to successfully build the units needed for the GEDI mission.

Performance of Axial-Flow Supersonic Compressor on XJ-55-FF-1 Turbojet Engine. I - Preliminary Performance of Compressor. 1; Preliminary Performance of Compressor

NASA Technical Reports Server (NTRS)

Hartmann, Melvin J.; Graham, Robert C.

1949-01-01

An investigation was conducted to determine the performance characteristics of the axial-flow supersonic compressor of the XJ-55-FF-1 turbo Jet engine. The test unit consisted of a row of inlet guide vanes and a supersonic rotor; the stator vanes after the rotor were omitted. The maximum pressure ratio produced in the single stage was 2.28 at an equivalent tip speed or 1814 feet per second with an adiabatic efficiency of approximately 0.61, equivalent weight flow of 13.4 pounds per second. The maximum efficiency of 0.79 was obtained at an equivalent tip speed of 801 feet per second.

Humanity's unsustainable environmental footprint.

PubMed

Hoekstra, Arjen Y; Wiedmann, Thomas O

2014-06-06

Within the context of Earth's limited natural resources and assimilation capacity, the current environmental footprint of humankind is not sustainable. Assessing land, water, energy, material, and other footprints along supply chains is paramount in understanding the sustainability, efficiency, and equity of resource use from the perspective of producers, consumers, and government. We review current footprints and relate those to maximum sustainable levels, highlighting the need for future work on combining footprints, assessing trade-offs between them, improving computational techniques, estimating maximum sustainable footprint levels, and benchmarking efficiency of resource use. Ultimately, major transformative changes in the global economy are necessary to reduce humanity's environmental footprint to sustainable levels. Copyright © 2014, American Association for the Advancement of Science.

Approximate maximum likelihood decoding of block codes

NASA Technical Reports Server (NTRS)

Greenberger, H. J.

1979-01-01

Approximate maximum likelihood decoding algorithms, based upon selecting a small set of candidate code words with the aid of the estimated probability of error of each received symbol, can give performance close to optimum with a reasonable amount of computation. By combining the best features of various algorithms and taking care to perform each step as efficiently as possible, a decoding scheme was developed which can decode codes which have better performance than those presently in use and yet not require an unreasonable amount of computation. The discussion of the details and tradeoffs of presently known efficient optimum and near optimum decoding algorithms leads, naturally, to the one which embodies the best features of all of them.

Optimal control of population and coherence in three-level Λ systems

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Malinovskaya, Svetlana A.; Malinovsky, Vladimir S.

2011-08-01

Optimal control theory (OCT) implementations for an efficient population transfer and creation of maximum coherence in a three-level system are considered. We demonstrate that the half-stimulated Raman adiabatic passage scheme for creation of the maximum Raman coherence is the optimal solution according to the OCT. We also present a comparative study of several implementations of OCT applied to the complete population transfer and creation of the maximum coherence. Performance of the conjugate gradient method, the Zhu-Rabitz method and the Krotov method has been analysed.

On the optimization of endoreversible processes

NASA Astrophysics Data System (ADS)

Pescetti, D.

2014-03-01

This paper is intended for undergraduates and specialists in thermodynamics and related areas. We consider and discuss the optimization of endoreversible thermodynamic processes under the condition of maximum work production. Explicit thermodynamic analyses of the solutions are carried out for the Novikov and Agrawal processes. It is shown that the efficiencies at maximum work production and maximum power output are not necessarily equal. They are for the Novikov process but not for the Agrawal process. The role of the constraints is put into evidence. The physical aspects are enhanced by the simplicity of the involved mathematics.

Mineral Carbonation Potential of CO2 from Natural and Industrial-based Alkalinity Sources

NASA Astrophysics Data System (ADS)

Wilcox, J.; Kirchofer, A.

2014-12-01

Mineral carbonation is a Carbon Capture and Storage (CSS) technology where gaseous CO2 is reacted with alkaline materials (such as silicate minerals and alkaline industrial wastes) and converted into stable and environmentally benign carbonate minerals (Metz et al., 2005). Here, we present a holistic, transparent life cycle assessment model of aqueous mineral carbonation built using a hybrid process model and economic input-output life cycle assessment approach. We compared the energy efficiency and the net CO2 storage potential of various mineral carbonation processes based on different feedstock material and process schemes on a consistent basis by determining the energy and material balance of each implementation (Kirchofer et al., 2011). In particular, we evaluated the net CO2 storage potential of aqueous mineral carbonation for serpentine, olivine, cement kiln dust, fly ash, and steel slag across a range of reaction conditions and process parameters. A preliminary systematic investigation of the tradeoffs inherent in mineral carbonation processes was conducted and guidelines for the optimization of the life-cycle energy efficiency are provided. The life-cycle assessment of aqueous mineral carbonation suggests that a variety of alkalinity sources and process configurations are capable of net CO2 reductions. The maximum carbonation efficiency, defined as mass percent of CO2 mitigated per CO2 input, was 83% for CKD at ambient temperature and pressure conditions. In order of decreasing efficiency, the maximum carbonation efficiencies for the other alkalinity sources investigated were: olivine, 66%; SS, 64%; FA, 36%; and serpentine, 13%. For natural alkalinity sources, availability is estimated based on U.S. production rates of a) lime (18 Mt/yr) or b) sand and gravel (760 Mt/yr) (USGS, 2011). The low estimate assumes the maximum sequestration efficiency of the alkalinity source obtained in the current work and the high estimate assumes a sequestration efficiency of 85%. The total CO2 storage potential for the alkalinity sources considered in the U.S. ranges from 1.3% to 23.7% of U.S. CO2 emissions, depending on the assumed availability of natural alkalinity sources and efficiency of the mineral carbonation processes.

Alternative Fuels Data Center

Science.gov Websites

AFV special license plate, which are available from the Arizona Department of Transportation (ADOT license plate. ADOT has reached its maximum limit of 10,000 vehicles and the issuance of Energy Efficient Alternative Fuel Vehicle (AFV) and Energy Efficient Plate Programs Dedicated AFVs qualify for an

Improved design of a tangential entry cyclone separator for separation of particles from exhaust gas of diesel engine.

PubMed

Mukhopadhyay, N

2011-01-01

An effective design of cyclone separator with tangential inlet is developed applying an equation derived from the correlation of collection efficiency with maximum pressure drop components of the cyclone, which can efficiently remove the particles around 1microm of the exhaust gas of diesel engine.

Random benzotrithiophene-based donor-acceptor copolymers for efficient organic photovoltaic devices.

PubMed

Nielsen, Christian B; Ashraf, Raja Shahid; Schroeder, Bob C; D'Angelo, Pasquale; Watkins, Scott E; Song, Kigook; Anthopoulos, Thomas D; McCulloch, Iain

2012-06-14

A series of benzotrithiophene-containing random terpolymers for polymer solar cells is reported. Through variations of the two other components in the terpolymers, the absorption profile and the frontier energy levels are optimized and maximum power conversion efficiencies are nearly doubled (5.14%) relative to the parent alternating copolymer.

Partnerships panel: the use of contractors and partnerships in public forest recreation: some considerations

Treesearch

Ben W. Twight

1995-01-01

This paper argues that short term competitive contracting and "partnerships" with low bidders cannot produce the quality or efficiency that highly socialized normatively guided career organizations, both public and private, can produce. High quality maximum efficiency production requires highly socialized primary group types of organizations, guided by a...

Disordered Nd:LuYSiO5 crystal lasers operating on the 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 transitions

NASA Astrophysics Data System (ADS)

Guan, Xiaofeng; Zhou, Zhiyong; Huang, Xiaoxu; Xu, Bin; Xu, Huiying; Cai, Zhiping; Xu, Xiaodong; Xu, Jun

2017-11-01

We report on diode-pumped disordered Nd:LuYSiO5 (Nd:LYSO) crystal lasers operating on the 4F3/2 → 4I11/2 and 4F3/2 → 4I 13/2 transitions. Simultaneous laser operation at 1074 and 1078 nm is achieved with maximum output power of 4.46 W and slope efficiency of 39.6%. Single wavelength laser at 1358 nm with maximum output power of 1.15 W and slope efficiency of 11.8% is also obtained. Moreover, four single-wavelength lasers at 1058, 1107, 1330 and 1386 nm with relatively low gains are achieved with maximum output powers of 2.72, 1.22, 0.52 and 0.42 W, respectively, for the first time to our knowledge. Lasing at non-traditional emission lines was obtained by using output couplers with dielectric coatings for specific wavelength ranges.

Airflow energy harvesting with high wind velocities for industrial applications

NASA Astrophysics Data System (ADS)

Chew, Z. J.; Tuddenham, S. B.; Zhu, M.

2016-11-01

An airflow energy harvester capable of harvesting energy from vortices at high speed is presented in this paper. The airflow energy harvester is implemented using a modified helical Savonius turbine and an electromagnetic generator. A power management module with maximum power point finding capability is used to manage the harvested energy and convert the low voltage magnitude from the generator to a usable level for wireless sensors. The airflow energy harvester is characterized using vortex generated by air hitting a plate in a wind tunnel. By using an aircraft environment with wind speed of 17 m/s as case study, the output power of the airflow energy harvester is measured to be 126 mW. The overall efficiency of the power management module is 45.76 to 61.2%, with maximum power point tracking efficiency of 94.21 to 99.72% for wind speed of 10 to 18 m/s, and has a quiescent current of 790 nA for the maximum power point tracking circuit.

Maximum likelihood decoding of Reed Solomon Codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sudan, M.

We present a randomized algorithm which takes as input n distinct points ((x{sub i}, y{sub i})){sup n}{sub i=1} from F x F (where F is a field) and integer parameters t and d and returns a list of all univariate polynomials f over F in the variable x of degree at most d which agree with the given set of points in at least t places (i.e., y{sub i} = f (x{sub i}) for at least t values of i), provided t = {Omega}({radical}nd). The running time is bounded by a polynomial in n. This immediately provides a maximum likelihoodmore » decoding algorithm for Reed Solomon Codes, which works in a setting with a larger number of errors than any previously known algorithm. To the best of our knowledge, this is the first efficient (i.e., polynomial time bounded) algorithm which provides some maximum likelihood decoding for any efficient (i.e., constant or even polynomial rate) code.« less

Thermoelectric properties of the LaCoO3-LaCrO3 system using a high-throughput combinatorial approach

NASA Astrophysics Data System (ADS)

Talley, K. R.; Barron, S. C.; Nguyen, N.; Wong-Ng, W.; Martin, J.; Zhang, Y. L.; Song, X.

2017-02-01

A combinatorial film of the LaCo1-xCrxO3 system was fabricated using the LaCoO3 and LaCrO3 targets at the NIST Pulsed Laser Deposition (PLD) facility. As the ionic size of Cr3+ is greater than that of Co3+, the unit cell volume of the series increases with increasing x. Using a custom screening tool, the Seebeck coefficient of LaCo1-xCrxO3 approaches a measured maximum of 286 μV/K, near to the cobalt-rich end of the film library (with x ≈ 0.49). The resistivity value increases continuously with increasing x. The measured power factor, PF, of this series, which is related to the efficiency of energy conversion, also exhibits a maximum at the composition of x ≈ 0.49, which corresponds to the maximum value of the Seebeck coefficient. Our results illustrate the efficiency of applying the high-throughput combinatorial technique to study thermoelectric materials.

Electro-Optical Design for Efficient Visual Communication

NASA Technical Reports Server (NTRS)

Huck, Friedrich O.; Fales, Carl L.; Jobson, Daniel J.; Rahman, Zia-Ur

1995-01-01

Visual communication, in the form of telephotography and television, for example, can be regarded as efficient only if the amount of information that it conveys about the scene to the observer approaches the maximum possible and the associated cost approaches the minimum possible. Elsewhere we have addressed the problem of assessing the end to end performance of visual communication systems in terms of their efficiency in this sense by integrating the critical limiting factors that constrain image gathering into classical communications theory. We use this approach to assess the electro-optical design of image gathering devices as a function of the f number and apodization of the objective lens and the aperture size and sampling geometry of the phot-detection mechanism. Results show that an image gathering device that is designed to optimize information capacity performs similarly to the human eye. For both, the performance approaches the maximum possible, in terms of the efficiency with which the acquired information can be transmitted as decorrelated data, and the fidelity, sharpness, and clearity with which fine detail can be restored.

The theoretical limit to plant productivity.

PubMed

DeLucia, Evan H; Gomez-Casanovas, Nuria; Greenberg, Jonathan A; Hudiburg, Tara W; Kantola, Ilsa B; Long, Stephen P; Miller, Adam D; Ort, Donald R; Parton, William J

2014-08-19

Human population and economic growth are accelerating the demand for plant biomass to provide food, fuel, and fiber. The annual increment of biomass to meet these needs is quantified as net primary production (NPP). Here we show that an underlying assumption in some current models may lead to underestimates of the potential production from managed landscapes, particularly of bioenergy crops that have low nitrogen requirements. Using a simple light-use efficiency model and the theoretical maximum efficiency with which plant canopies convert solar radiation to biomass, we provide an upper-envelope NPP unconstrained by resource limitations. This theoretical maximum NPP approached 200 tC ha(-1) yr(-1) at point locations, roughly 2 orders of magnitude higher than most current managed or natural ecosystems. Recalculating the upper envelope estimate of NPP limited by available water reduced it by half or more in 91% of the land area globally. While the high conversion efficiencies observed in some extant plants indicate great potential to increase crop yields without changes to the basic mechanism of photosynthesis, particularly for crops with low nitrogen requirements, realizing such high yields will require improvements in water use efficiency.

Correlation between Thermodynamic Efficiency and Ecological Cyclicity for Thermodynamic Power Cycles

PubMed Central

Layton, Astrid; Reap, John; Bras, Bert; Weissburg, Marc

2012-01-01

A sustainable global community requires the successful integration of environment and engineering. In the public and private sectors, designing cyclical (“closed loop”) resource networks increasingly appears as a strategy employed to improve resource efficiency and reduce environmental impacts. Patterning industrial networks on ecological ones has been shown to provide significant improvements at multiple levels. Here, we apply the biological metric cyclicity to 28 familiar thermodynamic power cycles of increasing complexity. These cycles, composed of turbines and the like, are scientifically very different from natural ecosystems. Despite this difference, the application results in a positive correlation between the maximum thermal efficiency and the cyclic structure of the cycles. The immediate impact of these findings results in a simple method for comparing cycles to one another, higher cyclicity values pointing to those cycles which have the potential for a higher maximum thermal efficiency. Such a strong correlation has the promise of impacting both natural ecology and engineering thermodynamics and provides a clear motivation to look for more fundamental scientific connections between natural and engineered systems. PMID:23251638

Electro-optical design for efficient visual communication

NASA Astrophysics Data System (ADS)

Huck, Friedrich O.; Fales, Carl L.; Jobson, Daniel J.; Rahman, Zia-ur

1995-03-01

Visual communication, in the form of telephotography and television, for example, can be regarded as efficient only if the amount of information that it conveys about the scene to the observer approaches the maximum possible and the associated cost approaches the minimum possible. Elsewhere we have addressed the problem of assessing the end-to-end performance of visual communication systems in terms of their efficiency in this sense by integrating the critical limiting factors that constrain image gathering into classical communication theory. We use this approach to assess the electro-optical design of image-gathering devices as a function of the f number and apodization of the objective lens and the aperture size and sampling geometry of the photodetection mechanism. Results show that an image-gathering device that is designed to optimize information capacity performs similarly to the human eye. For both, the performance approaches the maximum possible, in terms of the efficiency with which the acquired information can be transmitted as decorrelated data, and the fidelity, sharpness, and clarity with which fine detail can be restored.

A novel minimum cost maximum power algorithm for future smart home energy management.

PubMed

Singaravelan, A; Kowsalya, M

2017-11-01

With the latest development of smart grid technology, the energy management system can be efficiently implemented at consumer premises. In this paper, an energy management system with wireless communication and smart meter are designed for scheduling the electric home appliances efficiently with an aim of reducing the cost and peak demand. For an efficient scheduling scheme, the appliances are classified into two types: uninterruptible and interruptible appliances. The problem formulation was constructed based on the practical constraints that make the proposed algorithm cope up with the real-time situation. The formulated problem was identified as Mixed Integer Linear Programming (MILP) problem, so this problem was solved by a step-wise approach. This paper proposes a novel Minimum Cost Maximum Power (MCMP) algorithm to solve the formulated problem. The proposed algorithm was simulated with input data available in the existing method. For validating the proposed MCMP algorithm, results were compared with the existing method. The compared results prove that the proposed algorithm efficiently reduces the consumer electricity consumption cost and peak demand to optimum level with 100% task completion without sacrificing the consumer comfort.

Polyethers containing 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole chromophores as solution processed materials for hole transporting layers of OLEDs

NASA Astrophysics Data System (ADS)

Krucaite, G.; Tavgeniene, D.; Xie, Z.; Lin, X.; Zhang, B.; Grigalevicius, S.

2018-02-01

Two polyethers containing electroactive pendent 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole moieties have been synthesized by the multi-step synthetic route. Full characterization of their structures is presented. The polymers represent derivatives of very high thermal stability with initial thermal degradation temperatures of 425 °C and 431 °C. Glass transition temperatures of the amorphous materials were also very high and reached values of 154 °C and 163 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of 5.84 eV and 5.93 eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting material. An electroluminescent device containing hole-transporting layer (HTL) of the polymer with electroactive 4-carbazolyl-7-phenylbenzo[c]-1,2,5-thiadiazole moieties exhibited turn on voltage of 6.2 V, maximum photometric efficiency of 2.5 cd/A and maximum brightness exceeding 300 cd/m2. The device containing HTL of the polymer with 4-carbazolyl-7-(1-naphtyl)benzo[c]-1,2,5-thiadiazole moieties demonstrated turn on voltage of 5.2 V, maximum photometric efficiency of 1.6 cd/A and maximum brightness exceeding 1500 cd/m2. The efficiencies were about 30-90% higher than that of the device containing widely used hole transporting layers of poly(9-vinylcarbazole).

The efficiency and budgeting of public hospitals: case study of iran.

PubMed

Yusefzadeh, Hasan; Ghaderi, Hossein; Bagherzade, Rafat; Barouni, Mohsen

2013-05-01

Hospitals are the most costly and important components of any health care system, so it is important to know their economic values, pay attention to their efficiency and consider factors affecting them. The aim of this study was to assess the technical scale and economic efficiency of hospitals in the West Azerbaijan province of Iran, for which Data Envelopment Analysis (DEA) was used to propose a model for operational budgeting. This study was a descriptive-analysis that was conducted in 2009 and had three inputs and two outputs. Deap2, 1 software was used for data analysis. Slack and radial movements and surplus of inputs were calculated for selected hospitals. Finally, a model was proposed for performance-based budgeting of hospitals and health sectors using the DEA technique. The average scores of technical efficiency, pure technical efficiency (managerial efficiency) and scale efficiency of hospitals were 0.584, 0.782 and 0.771, respectively. In other words the capacity of efficiency promotion in hospitals without any increase in costs and with the same amount of inputs was about 41.5%. Only four hospitals among all hospitals had the maximum level of technical efficiency. Moreover, surplus production factors were evident in these hospitals. Reduction of surplus production factors through comprehensive planning based on the results of the Data Envelopment Analysis can play a major role in cost reduction of hospitals and health sectors. In hospitals with a technical efficiency score of less than one, the original and projected values of inputs were different; resulting in a surplus. Hence, these hospitals should reduce their values of inputs to achieve maximum efficiency and optimal performance. The results of this method was applied to hospitals a benchmark for making decisions about resource allocation; linking budgets to performance results; and controlling and improving hospitals performance.

Efficient Coding and Energy Efficiency Are Promoted by Balanced Excitatory and Inhibitory Synaptic Currents in Neuronal Network

PubMed Central

Yu, Lianchun; Shen, Zhou; Wang, Chen; Yu, Yuguo

2018-01-01

Selective pressure may drive neural systems to process as much information as possible with the lowest energy cost. Recent experiment evidence revealed that the ratio between synaptic excitation and inhibition (E/I) in local cortex is generally maintained at a certain value which may influence the efficiency of energy consumption and information transmission of neural networks. To understand this issue deeply, we constructed a typical recurrent Hodgkin-Huxley network model and studied the general principles that governs the relationship among the E/I synaptic current ratio, the energy cost and total amount of information transmission. We observed in such a network that there exists an optimal E/I synaptic current ratio in the network by which the information transmission achieves the maximum with relatively low energy cost. The coding energy efficiency which is defined as the mutual information divided by the energy cost, achieved the maximum with the balanced synaptic current. Although background noise degrades information transmission and imposes an additional energy cost, we find an optimal noise intensity that yields the largest information transmission and energy efficiency at this optimal E/I synaptic transmission ratio. The maximization of energy efficiency also requires a certain part of energy cost associated with spontaneous spiking and synaptic activities. We further proved this finding with analytical solution based on the response function of bistable neurons, and demonstrated that optimal net synaptic currents are capable of maximizing both the mutual information and energy efficiency. These results revealed that the development of E/I synaptic current balance could lead a cortical network to operate at a highly efficient information transmission rate at a relatively low energy cost. The generality of neuronal models and the recurrent network configuration used here suggest that the existence of an optimal E/I cell ratio for highly efficient energy costs and information maximization is a potential principle for cortical circuit networks. Summary We conducted numerical simulations and mathematical analysis to examine the energy efficiency of neural information transmission in a recurrent network as a function of the ratio of excitatory and inhibitory synaptic connections. We obtained a general solution showing that there exists an optimal E/I synaptic ratio in a recurrent network at which the information transmission as well as the energy efficiency of this network achieves a global maximum. These results reflect general mechanisms for sensory coding processes, which may give insight into the energy efficiency of neural communication and coding. PMID:29773979

Efficient Coding and Energy Efficiency Are Promoted by Balanced Excitatory and Inhibitory Synaptic Currents in Neuronal Network.

PubMed

Yu, Lianchun; Shen, Zhou; Wang, Chen; Yu, Yuguo

2018-01-01

Selective pressure may drive neural systems to process as much information as possible with the lowest energy cost. Recent experiment evidence revealed that the ratio between synaptic excitation and inhibition (E/I) in local cortex is generally maintained at a certain value which may influence the efficiency of energy consumption and information transmission of neural networks. To understand this issue deeply, we constructed a typical recurrent Hodgkin-Huxley network model and studied the general principles that governs the relationship among the E/I synaptic current ratio, the energy cost and total amount of information transmission. We observed in such a network that there exists an optimal E/I synaptic current ratio in the network by which the information transmission achieves the maximum with relatively low energy cost. The coding energy efficiency which is defined as the mutual information divided by the energy cost, achieved the maximum with the balanced synaptic current. Although background noise degrades information transmission and imposes an additional energy cost, we find an optimal noise intensity that yields the largest information transmission and energy efficiency at this optimal E/I synaptic transmission ratio. The maximization of energy efficiency also requires a certain part of energy cost associated with spontaneous spiking and synaptic activities. We further proved this finding with analytical solution based on the response function of bistable neurons, and demonstrated that optimal net synaptic currents are capable of maximizing both the mutual information and energy efficiency. These results revealed that the development of E/I synaptic current balance could lead a cortical network to operate at a highly efficient information transmission rate at a relatively low energy cost. The generality of neuronal models and the recurrent network configuration used here suggest that the existence of an optimal E/I cell ratio for highly efficient energy costs and information maximization is a potential principle for cortical circuit networks. We conducted numerical simulations and mathematical analysis to examine the energy efficiency of neural information transmission in a recurrent network as a function of the ratio of excitatory and inhibitory synaptic connections. We obtained a general solution showing that there exists an optimal E/I synaptic ratio in a recurrent network at which the information transmission as well as the energy efficiency of this network achieves a global maximum. These results reflect general mechanisms for sensory coding processes, which may give insight into the energy efficiency of neural communication and coding.

Efficient blue and white polymer light emitting diodes based on a well charge balanced, core modified polyfluorene derivative.

PubMed

Das, Dipjyoti; Gopikrishna, Peddaboodi; Singh, Ashish; Dey, Anamika; Iyer, Parameswar Krishnan

2016-03-14

Fabrication of efficient blue and white polymer light-emitting diodes (PLEDs) using a well charge balanced, core modified polyfluorene derivative, poly[2,7-(9,9'-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide (99:01)] (PFONPN01), is presented. The excellent film forming properties as observed from the morphological study and the enhanced electron transport properties due to the inclusion of the NPN unit in the PFO main chain resulted in improved device properties. Bright blue light was observed from single layer PLEDs with PFONPN01 as an emissive layer (EML) as well as from double layer PLEDs using tris-(8-hydroxyquinoline) aluminum (Alq3) as an electron transporting layer (ETL) and LiF/Al as a cathode. The effect of ETL thickness on the device performance was studied by varying the Alq3 thickness (5 nm, 10 nm and 20 nm) and the device with an ETL thickness of 20 nm was found to exhibit the maximum brightness value of 11 662 cd m(-2) with a maximum luminous efficiency of 4.87 cd A(-1). Further, by using this highly electroluminescent blue PFONPN01 as a host and a narrow band gap, yellow emitting small molecule, dithiophene benzothiadiazole (DBT), as a guest at three different concentrations (0.2%, 0.4% and 0.6%), WPLEDs with the ITO/PEDOT:PSS/emissive layer/Alq3(20 nm)/LiF/Al configuration were fabricated and maximum brightness values of 8025 cd m(-2), 9565 cd m(-2) and 10 180 cd m(-2) were achieved respectively. 0.4% DBT in PFONPN01 was found to give white light with Commission International de l'Echairage (CIE) coordinates of (0.31, 0.38), a maximum luminous efficiency of 6.54 cd A(-1) and a color-rendering index (CRI) value of 70.

A self-powered piezoelectric energy harvesting interface circuit with efficiency-enhanced P-SSHI rectifier

NASA Astrophysics Data System (ADS)

Liu, Lianxi; Pang, Yanbo; Yuan, Wenzhi; Zhu, Zhangming; Yang, Yintang

2018-04-01

The key to self-powered technique is initiative to harvest energy from the surrounding environment. Harvesting energy from an ambient vibration source utilizing piezoelectrics emerged as a popular method. Efficient interface circuits become the main limitations of existing energy harvesting techniques. In this paper, an interface circuit for piezoelectric energy harvesting is presented. An active full bridge rectifier is adopted to improve the power efficiency by reducing the conduction loss on the rectifying path. A parallel synchronized switch harvesting on inductor (P-SSHI) technique is used to improve the power extraction capability from piezoelectric harvester, thereby trying to reach the theoretical maximum output power. An intermittent power management unit (IPMU) and an output capacitor-less low drop regulator (LDO) are also introduced. Active diodes (AD) instead of traditional passive ones are used to reduce the voltage loss over the rectifier, which results in a good power efficiency. The IPMU with hysteresis comparator ensures the interface circuit has a large transient output power by limiting the output voltage ranges from 2.2 to 2 V. The design is fabricated in a SMIC 0.18 μm CMOS technology. Simulation results show that the flipping efficiency of the P-SSHI circuit is over 80% with an off-chip inductor value of 820 μH. The output power the proposed rectifier can obtain is 44.4 μW, which is 6.7× improvement compared to the maximum output power of a traditional rectifier. Both the active diodes and the P-SSHI help to improve the output power of the proposed rectifier. LDO outputs a voltage of 1.8 V with the maximum 90% power efficiency. The proposed P-SSHI rectifier interface circuit can be self-powered without the need for additional power supply. Project supported by the National Natural Science Foundation of China (Nos. 61574103, U1709218) and the Key Research and Development Program of Shaanxi Province (No. 2017ZDXM-GY-006).

Reward and Visual Feedback Relative to the Performance and Mechanical Efficiency of High School Girls in the Standing Broad Jump.

ERIC Educational Resources Information Center

Zebas, Carole J.

This study focuses on changes occurring in selected mechanical components of high school girls performing the standing broad jump, and collects data pertaining to the effects of monetary reward and videotape feedback upon the following components: (a) distance jumped, (b) maximum angle of knee flexion, (c) maximum angle of hip flexion, (d) hip…

Lead-Free Inverted Planar Formamidinium Tin Triiodide Perovskite Solar Cells Achieving Power Conversion Efficiencies up to 6.22.

PubMed

Liao, Weiqiang; Zhao, Dewei; Yu, Yue; Grice, Corey R; Wang, Changlei; Cimaroli, Alexander J; Schulz, Philip; Meng, Weiwei; Zhu, Kai; Xiong, Ren-Gen; Yan, Yanfa

2016-11-01

Efficient lead (Pb)-free inverted planar formamidinium tin triiodide (FASnI 3 ) perovskite solar cells (PVSCs) are demonstrated. Our FASnI 3 PVSCs achieved average power conversion efficiencies (PCEs) of 5.41% ± 0.46% and a maximum PCE of 6.22% under forward voltage scan. The PVSCs exhibit small photocurrent-voltage hysteresis and high reproducibility. The champion cell shows a steady-state efficiency of ≈6.00% for over 100 s. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Novel trans-1-(9-Anthryl)-2-phenylethene Derivative Containing a Phenanthroimidazole Unit for Application in Organic Light-Emitting Diodes.

PubMed

Zhou, Nonglin; Wang, Shirong; Xiao, Yin; Li, Xianggao

2018-01-04

Aryl-substituted phenanthroimidazoles (PIs) have attracted tremendous attention in the field of organic light-emitting diodes (OLEDs), because they are simple to synthesize and have excellent thermal properties, high photoluminescence quantum yields (PLQYs), and bipolar properties. Herein, a novel blue-green emitting material, (E)-2-{4'-[2-(anthracen-9-yl)vinyl]-[1,1'-biphenyl]-4-yl}-1-phenyl-1H-phenanthro[9,10-d]imidazole (APE-PPI), containing a t-APE [1-(9-anthryl)-2-phenylethene] core and a PI moiety was designed and synthesized. Owing to the PI skeleton, APE-PPI possesses high thermal stability and a high PLQY, and the compound exhibits bipolar transporting characteristics, which were identified by single-carrier devices. Nondoped blue-green OLEDs with APE-PPI as the emitting layer show emission at λ=508 nm, a full width at half maximum of 82 nm, a maximum brightness of 9042 cd m -2 , a maximum current efficiency of 2.14 cd A -1 , and Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.55). Furthermore, a white OLED (WOLED) was fabricated by employing APE-PPI as the blue-green emitting layer and 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) doped in tris-(8-hydroxyquinolinato)aluminum (Alq 3 ) as the red-green emitting layer. This WOLED exhibited a maximum brightness of 10029 cd m -2 , a maximum current efficiency of 16.05 cd A -1 , CIE coordinates of (0.47, 0.47), and a color rendering index (CRI) of 85. The high performance of APE-PPI-based devices suggests that the t-APE and PI combination can potentially be used to synthesize efficient electroluminescent materials for WOLEDs. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalytic action of β source on x-ray emission from plasma focus

NASA Astrophysics Data System (ADS)

Ahmad, S.; Sadiq, Mehboob; Hussain, S.; Shafiq, M.; Zakaullah, M.; Waheed, A.

2006-01-01

The influence of preionization around the insulator sleeve by a mesh-type β source (Ni6328) for the x-ray emission from a (2.3-3.9 kJ) plasma focus device is investigated. Quantrad Si p-i-n diodes along with suitable filters are employed as time-resolved x-ray detectors and a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray emission in 4π geometry is measured as a function of argon and hydrogen gas filling pressures with and without β source at different charging voltages. It is found that the pressure range for the x-ray emission is broadened, x-ray emission is enhanced, and shot to shot reproducibility is improved with the β source. With argon, the CuKα emission is estimated to be 27.14 J with an efficiency of 0.7% for β source and 21.5 J with an efficiency of 0.55% without β source. The maximum x-ray yield in 4π geometry is found to be about 68.90 J with an efficiency of 1.8% for β source and 54.58 J with an efficiency of 1.4% without β source. With hydrogen, CuKα emission is 11.82 J with an efficiency of 0.32% for β source and 10.07 J with an efficiency of 0.27% without β source. The maximum x-ray yield in 4π geometry is found to be 30.20 J with an efficiency of 0.77% for β source and 25.58 J with an efficiency of 0.6% without β source. The x-ray emission with Pb insert at the anode tip without β source is also investigated and found to be reproducible and significantly high. The maximum x-ray yield is estimated to be 46.6 J in 4π geometry with an efficiency of 1.4% at 23 kV charging voltage. However, degradation of x-ray yield is observed when charging voltage exceeds 23 kV for Pb insert. From pinhole images it is observed that the x-ray emission due to the bombardment of electrons at the anode tip is dominant in both with and without β source.

Optimization of Wireless Transceivers under Processing Energy Constraints

NASA Astrophysics Data System (ADS)

Wang, Gaojian; Ascheid, Gerd; Wang, Yanlu; Hanay, Oner; Negra, Renato; Herrmann, Matthias; Wehn, Norbert

2017-09-01

Focus of the article is on achieving maximum data rates under a processing energy constraint. For a given amount of processing energy per information bit, the overall power consumption increases with the data rate. When targeting data rates beyond 100 Gb/s, the system's overall power consumption soon exceeds the power which can be dissipated without forced cooling. To achieve a maximum data rate under this power constraint, the processing energy per information bit must be minimized. Therefore, in this article, suitable processing efficient transmission schemes together with energy efficient architectures and their implementations are investigated in a true cross-layer approach. Target use cases are short range wireless transmitters working at carrier frequencies around 60 GHz and bandwidths between 1 GHz and 10 GHz.

Solar Panel System for Street Light Using Maximum Power Point Tracking (MPPT) Technique

NASA Astrophysics Data System (ADS)

Wiedjaja, A.; Harta, S.; Josses, L.; Winardi; Rinda, H.

2014-03-01

Solar energy is one form of the renewable energy which is very abundant in regions close to the equator. One application of solar energy is for street light. This research focuses on using the maximum power point tracking technique (MPPT), particularly the perturb and observe (P&O) algorithm, to charge battery for street light system. The proposed charger circuit can achieve 20.73% higher power efficiency compared to that of non-MPPT charger. We also develop the LED driver circuit for the system which can achieve power efficiency up to 91.9% at a current of 1.06 A. The proposed street lightning system can be implemented with a relatively low cost for public areas.

Efficiency optimization of a photovoltaic water pumping system for irrigation in Ouargla, Algeria

NASA Astrophysics Data System (ADS)

Louazene, M. L.; Garcia, M. C. Alonso; Korichi, D.

2017-02-01

This work is technical study to contribute to the optimization of pumping systems powered by solar energy (clean) and used in the field of agriculture. To achieve our goals, we studied the techniques that must be entered on a photovoltaic system for maximum energy from solar panels. Our scientific contribution in this research is the realization of an efficient photovoltaic pumping system for irrigation needs. To achieve this and extract maximum power from the PV generator, two axes have been optimized: 1. Increase in the uptake of solar radiation by choice an optimum tilt angle of the solar panels, and 2. it is necessary to add an adaptation device, MPPT controller with a DC-DC converter, between the source and the load.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sikes, Karen; Blackburn, Julia; Grubbs, Tyler

Despite a steady record of energy efficiency improvements in residential refrigerators and freezers over recent decades, these products still account for 4% of the site energy consumption for the average U.S. household. The Oak Ridge National Laboratory (ORNL) – along with partners Sandia National Laboratories (SNL) and the University of Maryland – are pursuing further efficiency improvements in this market sector by using a novel/prototype rotating heat exchanger (RHX) based on a Sandia Cooler technology as an evaporator in a residential refrigerator-freezer. The purpose of this study is to investigate the market potential of refrigerator-freezer products equipped with RHX evaporatorsmore » in the United States, including projections of maximum annual market share and unit shipments and maximum direct and indirect job creation.« less

CaFe2O4 as a self-sufficient solar energy converter

NASA Astrophysics Data System (ADS)

Tablero, C.

2017-10-01

An ideal solar energy to electricity or fuel converter should work without the use of any external bias potential. An analysis of self-sufficiency when CaFe2O4 is used to absorb the sunlight is carried out based on the CaFe2O4 absorption coefficient. We started to obtain this coefficient theoretically within the experimental bandgap range in order to fix the interval of possible values of photocurrents, maximum absorption efficiencies, and photovoltages and thus that of self-sufficiency considering only the radiative processes. Also for single-gap CaFe2O4, we evaluate an alternative for increasing the photocurrent and maximum absorption efficiency based on inserting an intermediate band using high doping or alloying.

Development and thermal management of 10 kW CW, direct diode laser source

NASA Astrophysics Data System (ADS)

Zhu, Hongbo; Hao, Mingming; Zhang, Jianwei; Ji, Wenyu; Lin, Xingchen; Zhang, Jinsheng; Ning, Yongqiang

2016-01-01

We report on the development of direct diode laser source with high-power and high reliability. The laser source was realized by the polarization and wavelength combination of four diode laser stacks. When at the operating current of 122 A, the source was capable of producing 10,120 W output while maintaining 46% electro-optical conversion efficiency. The maximum temperature on the lens was decreased from 442.2 K to 320 K by utilizing an efficient thermal dissipation structure, and the corresponding maximum von Mises stress was reduced from 75.4 MPa to 14 MPa. In addition, a reliability test demonstrated that our laser source was reliable and potential in the applications of laser cladding and heat treatment.

H. B. Reitlinger and the origins of the efficiency at maximum power formula for heat engines

NASA Astrophysics Data System (ADS)

Vaudrey, Alexandre; Lanzetta, François; Feidt, Michel

2014-12-01

Even if not so ancient, the history of the heat engine efficiency at maximum power expression has been yet turbulent. More than a decade after the publication of the seminal article by Curzon and Ahlborn in 1975, two older works by Chambadal and Novikov were rediscovered, both dating from 1957. Then, some years ago, the name of Yvon arose from a textual reference to this famous relation in a conference article published in 1955. Thanks to a historical study of French-written books not published for a long time, and since never translated into other languages, we bring to light in this paper that this relation was actually first proposed by Henri B. Reitlinger in 1929.

Single-mode oscillation of a diode-pumped Nd:YAG microchip laser at 1835 nm

NASA Astrophysics Data System (ADS)

Lan, Jinglong; Cui, Qin; Wang, Yi; Xu, Bin; Xu, Huiying; Cai, Zhiping

2016-10-01

Single-mode oscillation of a diode-pumped conventional Nd:YAG laser at 1835 nm is demonstrated, for the first time to our knowledge, in the form of microchip configuration. The achieved maximum output power reaches 189 mW with slope efficiency of about 5.5% with respect to absorbed pump power. The laser spectra are measured with linewidth less than 0.08 nm indicating a single longitudinal mode. The output laser beam is also measured to be near diffraction-limited with M2 factors of about 1.2 and 1.5 in x and y directions. Using a mechanical chopper with 50% duty cycle, the maximum output power is improved to 253 mW with slope efficiency of about 9.7%.

Promoting Accountability and Enhancing Efficiency: Using National Education Accounts to Track Expenditure Flows

ERIC Educational Resources Information Center

Chawla, Deepika; Forbes, Phyllis

2010-01-01

Increasing accountability and efficiency in the use of public and out-of-pocket financing in education are critical to realizing the maximum impact of the meager allocations to education in most developing countries. While broad estimates and numbers are routinely collected by most national ministries and state departments of education, the lack…

Energy conservation and air transportation

NASA Technical Reports Server (NTRS)

1973-01-01

Air transportation demand and passenger energy demand are discussed, in relation to energy conservation. Alternatives to air travel are reviewed, along with airline advertising and ticket pricing. Cargo energy demand and airline systems efficiency are also examined, as well as fuel conservation techniques. Maximum efficiency of passenger aircraft, from B-747 to V/STOL to British Concorde, is compared.

808nm high-power high-efficiency GaAsP/GaInP laser bars

NASA Astrophysics Data System (ADS)

Wang, Ye; Yang, Ye; Qin, Li; Wang, Chao; Yao, Di; Liu, Yun; Wang, Lijun

2008-11-01

808nm high power diode lasers, which is rapidly maturing technology technically and commercially since the introduction in 1999 of complete kilowatt-scale diode laser systems, have important applications in the fields of industry and pumping solid-state lasers (DPSSL). High power and high power conversion efficiency are extremely important in diode lasers, and they could lead to new applications where space, weight and electrical power are critical. High efficiency devices generate less waste heat, which means less strain on the cooling system and more tolerance to thermal conductivity variation, a lower junction temperature and longer lifetimes. Diode lasers with Al-free materials have superior power conversion efficiency compared with conventional AlGaAs/GaAs devices because of their lower differential series resistance and higher thermal conductivity. 808nm GaAsP/GaInP broad-waveguide emitting diode laser bars with 1mm cavity length have been fabricated. The peak power can reach to 100.9W at 106.5A at quasicontinuous wave operation (200μs, 1000Hz). The maximum power conversion efficiency is 57.38%. Based on these high power laser bars, we fabricate a 1x3 arrays, the maximum power is 64.3W in continuous wave mode when the current is 25.0A. And the threshold current is 5.9A, the slope efficiency is 3.37 W/A.

Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels.

PubMed

Singh, Meenesh R; Clark, Ezra L; Bell, Alexis T

2015-11-10

Thermodynamic, achievable, and realistic efficiency limits of solar-driven electrochemical conversion of water and carbon dioxide to fuels are investigated as functions of light-absorber composition and configuration, and catalyst composition. The maximum thermodynamic efficiency at 1-sun illumination for adiabatic electrochemical synthesis of various solar fuels is in the range of 32-42%. Single-, double-, and triple-junction light absorbers are found to be optimal for electrochemical load ranges of 0-0.9 V, 0.9-1.95 V, and 1.95-3.5 V, respectively. Achievable solar-to-fuel (STF) efficiencies are determined using ideal double- and triple-junction light absorbers and the electrochemical load curves for CO2 reduction on silver and copper cathodes, and water oxidation kinetics over iridium oxide. The maximum achievable STF efficiencies for synthesis gas (H2 and CO) and Hythane (H2 and CH4) are 18.4% and 20.3%, respectively. Whereas the realistic STF efficiency of photoelectrochemical cells (PECs) can be as low as 0.8%, tandem PECs and photovoltaic (PV)-electrolyzers can operate at 7.2% under identical operating conditions. We show that the composition and energy content of solar fuels can also be adjusted by tuning the band-gaps of triple-junction light absorbers and/or the ratio of catalyst-to-PV area, and that the synthesis of liquid products and C2H4 have high profitability indices.

Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels

NASA Astrophysics Data System (ADS)

Singh, Meenesh R.; Clark, Ezra L.; Bell, Alexis T.

2015-11-01

Thermodynamic, achievable, and realistic efficiency limits of solar-driven electrochemical conversion of water and carbon dioxide to fuels are investigated as functions of light-absorber composition and configuration, and catalyst composition. The maximum thermodynamic efficiency at 1-sun illumination for adiabatic electrochemical synthesis of various solar fuels is in the range of 32-42%. Single-, double-, and triple-junction light absorbers are found to be optimal for electrochemical load ranges of 0-0.9 V, 0.9-1.95 V, and 1.95-3.5 V, respectively. Achievable solar-to-fuel (STF) efficiencies are determined using ideal double- and triple-junction light absorbers and the electrochemical load curves for CO2 reduction on silver and copper cathodes, and water oxidation kinetics over iridium oxide. The maximum achievable STF efficiencies for synthesis gas (H2 and CO) and Hythane (H2 and CH4) are 18.4% and 20.3%, respectively. Whereas the realistic STF efficiency of photoelectrochemical cells (PECs) can be as low as 0.8%, tandem PECs and photovoltaic (PV)-electrolyzers can operate at 7.2% under identical operating conditions. We show that the composition and energy content of solar fuels can also be adjusted by tuning the band-gaps of triple-junction light absorbers and/or the ratio of catalyst-to-PV area, and that the synthesis of liquid products and C2H4 have high profitability indices.

MASTtreedist: visualization of tree space based on maximum agreement subtree.

PubMed

Huang, Hong; Li, Yongji

2013-01-01

Phylogenetic tree construction process might produce many candidate trees as the "best estimates." As the number of constructed phylogenetic trees grows, the need to efficiently compare their topological or physical structures arises. One of the tree comparison's software tools, the Mesquite's Tree Set Viz module, allows the rapid and efficient visualization of the tree comparison distances using multidimensional scaling (MDS). Tree-distance measures, such as Robinson-Foulds (RF), for the topological distance among different trees have been implemented in Tree Set Viz. New and sophisticated measures such as Maximum Agreement Subtree (MAST) can be continuously built upon Tree Set Viz. MAST can detect the common substructures among trees and provide more precise information on the similarity of the trees, but it is NP-hard and difficult to implement. In this article, we present a practical tree-distance metric: MASTtreedist, a MAST-based comparison metric in Mesquite's Tree Set Viz module. In this metric, the efficient optimizations for the maximum weight clique problem are applied. The results suggest that the proposed method can efficiently compute the MAST distances among trees, and such tree topological differences can be translated as a scatter of points in two-dimensional (2D) space. We also provide statistical evaluation of provided measures with respect to RF-using experimental data sets. This new comparison module provides a new tree-tree pairwise comparison metric based on the differences of the number of MAST leaves among constructed phylogenetic trees. Such a new phylogenetic tree comparison metric improves the visualization of taxa differences by discriminating small divergences of subtree structures for phylogenetic tree reconstruction.

MoS2-based passively Q-switched diode-pumped Nd:YAG laser at 946 nm

NASA Astrophysics Data System (ADS)

Lin, Haifeng; Zhu, Wenzhang.; Xiong, Feibing; Cai, Lie

2017-06-01

We demonstrate a passively Q-switched Nd: YAG quasi-three-level laser operating at 946 nm using MoS2 as saturable absorber. A maximum average output power of 210 mW is achieved at an absorbed pump power of 6.67 W with a slope efficiency of about 5.8%. The shortest pulse width and maximum pulse repetition frequency are measured to be 280 ns and 609 kHz, respectively. The maximum pulse energy and maximum pulse peak power are therefore estimated to be about 0.35 μJ and 1.23 W, respectively. This work represents the first MoS2-based Q-switched laser operating at 0.9 μm spectral region.

Measuring and analyzing thermal deformations of the primary reflector of the Tianma radio telescope

NASA Astrophysics Data System (ADS)

Dong, Jian; Fu, Li; Liu, Qinghui; Shen, Zhiqiang

2018-06-01

The primary reflector of the Tianma Radio Telescope (TMRT) distorts due to the varying thermal conditions, which dramatically reduces the aperture efficiency of Q-band observations. To evaluate and overcome the thermal effects, a thermal deformations measurement system has been established based on the extended Out-of-Focus holography (e-OOF). The thermal deformations can be measured in approximately 20 min with an illumination-weighted surface root mean square (RMS) accuracy of approximately 50 μm. We have measured the thermal deformations when the backup and front structure were heated by the sun respectively, and used the active surface system to correct the thermal deformations immediately to confirm the measurements. The thermal deformations when the backup structure is heated are larger than those when the front structure is heated. The values of half power beam width (HPBW) are related to the illumination-weighted surface RMS, and can be used to check the thermal deformations. When the backup structure is heated, the aperture efficiencies can remain above 90% of the maximum efficiency at 40 GHz for approximately two hours after one adjustment. While the front structure is heated, the aperture efficiencies can remain above 90% of the maximum efficiency at 40 GHz, and above 95% after one adjustment in approximately three hours.

Integration of Rotor Aerodynamic Optimization with the Conceptual Design of a Large Civil Tiltrotor

DTIC Science & Technology

2010-01-01

Rotor MCP Maximum Continuous Power MRP Maximum Rated Power (take-off power) NDARC NASA Design and Analysis of Rotorcraft OEI One Engine Inoperative...OGE Out of Ground Effect SFC Specific Fuel Consumption SNI Simultaneous Non-Interfering approach STOL Short Takeoff and Landing VTOL Vertical...that are assembled into a complete aircraft model. NDARC is designed for high computational efficiency. Performance is calculated with physics- based

Potential efficiencies of open- and closed-cycle CO, supersonic, electric-discharge lasers

NASA Technical Reports Server (NTRS)

Monson, D. J.

1976-01-01

Computed open- and closed-cycle system efficiencies (laser power output divided by electrical power input) are presented for a CW carbon monoxide, supersonic, electric-discharge laser. Closed-system results include the compressor power required to overcome stagnation pressure losses due to supersonic heat addition and a supersonic diffuser. The paper shows the effect on the system efficiencies of varying several important parameters. These parameters include: gas mixture, gas temperature, gas total temperature, gas density, total discharge energy loading, discharge efficiency, saturated gain coefficient, optical cavity size and location with respect to the discharge, and supersonic diffuser efficiency. Maximum open-cycle efficiency of 80-90% is predicted; the best closed-cycle result is 60-70%.

Theoretical Evaluation of the Maximum Work of Free-Piston Engine Generators

NASA Astrophysics Data System (ADS)

Kojima, Shinji

2017-01-01

Utilizing the adjoint equations that originate from the calculus of variations, we have calculated the maximum thermal efficiency that is theoretically attainable by free-piston engine generators considering the work loss due to friction and Joule heat. Based on the adjoint equations with seven dimensionless parameters, the trajectory of the piston, the histories of the electric current, the work done, and the two kinds of losses have been derived in analytic forms. Using these we have conducted parametric studies for the optimized Otto and Brayton cycles. The smallness of the pressure ratio of the Brayton cycle makes the net work done negative even when the duration of heat addition is optimized to give the maximum amount of heat addition. For the Otto cycle, the net work done is positive, and both types of losses relative to the gross work done become smaller with the larger compression ratio. Another remarkable feature of the optimized Brayton cycle is that the piston trajectory of the heat addition/disposal process is expressed by the same equation as that of an adiabatic process. The maximum thermal efficiency of any combination of isochoric and isobaric heat addition/disposal processes, such as the Sabathe cycle, may be deduced by applying the methods described here.

Exergy Analyses of Fabricated Compound Parabolic Solar Collector with Evacuated Tubes at Different Operating Conditions: Indore (India)

NASA Astrophysics Data System (ADS)

Geete, Ankur; Dubey, Akash; Sharma, Ankush; Dubey, Anshul

2018-05-01

In this research work, compound parabolic solar collector (CPC) with evacuated tubes is fabricated. Main benefit of CPC is that there is no requirement of solar tracking system. With fabricated CPC; outlet temperatures of flowing fluid, instantaneous efficiencies, useful heat gain rates and inlet exergies (with and without considering Sun's cone angle) are experimentally found. Observations are taken at different time intervals (1200, 1230, 1300, 1330 and 1400 h), mass flow rates (1.15, 0.78, 0.76, 0.86 and 0.89 g/s), ambient temperatures and with various dimensions of solar collector. This research work is concluded as; maximum instantaneous efficiency is 69.87% which was obtained with 0.76 g/s flow rate of water at 1300 h and 42°C is the maximum temperature difference which was also found at same time. Maximum inlet exergies are 139.733 and 139.532 kW with and without considering Sun's cone angle at 1300 h, respectively. Best thermal performance from the fabricated CPC with evacuated tubes is found at 1300 h. Maximum inlet exergy is 141.365 kW which was found at 1300 h with 0.31 m aperture width and 1.72 m absorber pipe length.

Electronic Equipment Proposal to Improve the Photovoltaic Systems Efficiency

NASA Astrophysics Data System (ADS)

Flores-Mena, J. E.; Juárez Morán, L. A.; Díaz Reyes, J.

2011-05-01

This paper reports a new technique proposal to improve the photovoltaic systems. It was made to design and implement an electronic system that will detect, capture, and transfer the maximum power of the photovoltaic (PV) panel to optimize the supplied power of a solar panel. The electronic system works on base technical proposal of electrical sweeping of electric characteristics using capacitive impedance. The maximum power is transformed and the solar panel energy is sent to an automotive battery. This electronic system reduces the energy lost originated when the solar radiation level decreases or the PV panel temperature is increased. This electronic system tracks, captures, and stores the PV module's maximum power into a capacitor. After, a higher voltage level step-up circuit was designed to increase the voltage of the PV module's maximum power and then its current can be sent to a battery. The experimental results show that the developed electronic system has 95% efficiency. The measurement was made to 50 W, the electronic system works rightly with solar radiation rate from 100 to 1,000 W m - 2 and the PV panel temperature rate changed from 1 to 75°C. The main advantage of this electronic system compared with conventional methods is the elimination of microprocessors, computers, and sophisticated numerical approximations, and it does not need any small electrical signals to track the maximum power. The proposed method is simple, fast, and it is also cheaper.

Energetic aspects of skeletal muscle contraction: implications of fiber types.

PubMed

Rall, J A

1985-01-01

In this chapter fundamental energetic properties of skeletal muscles as elucidated from isolated muscle preparations are described. Implications of these intrinsic properties for the energetic characterization of different fiber types and for the understanding of locomotion have been considered. Emphasis was placed on the myriad of physical and chemical techniques that can be employed to understand muscle energetics and on the interrelationship of results from different techniques. The anaerobic initial processes which liberate energy during contraction and relaxation are discussed in detail. The high-energy phosphate (approximately P) utilized during contraction and relaxation can be distributed between actomyosin ATPase or cross-bridge cycling (70%) and the Ca2+ ATPase of the sacroplasmic reticulum (30%). Muscle shortening increases the rate of approximately P hydrolysis, and stretching a muscle during contraction suppresses the rate of approximately P hydrolysis. The economy of an isometric contraction is defined as the ratio of isometric mechanical response to energetic cost and is shown to be a fundamental intrinsic parameter describing muscle energetics. Economy of contraction varies across the animal kingdom by over three orders of magnitude and is different in different mammalian fiber types. In mammalian skeletal muscles differences in economy of contraction can be attributed mainly to differences in the specific actomyosin and Ca2+ ATPase of muscles. Furthermore, there is an inverse relationship between economy of contraction and maximum velocity of muscle shortening (Vmax) and maximum power output. This is a fundamental relationship. Muscles cannot be economical at developing and maintaining force and also exhibit rapid shortening. Interestingly, there appears to be a subtle system of unknown nature that modulates the Vmax and economy of contraction. Efficiency of a work-producing contraction is defined and contrasted to the economy of contraction. Unlike economy, maximum efficiency of work production varies little across the animal kingdom. There are difficulties associated with the measurement of maximum efficiency of contraction, and it has yet to be determined unequivocally if the maximum efficiency of contraction varies in different fiber types. The intrinsic properties of force per cross-sectional area, economy, and Vmax determine the basic energetic properties of skeletal muscles. Nonetheless, the mechanics and energetics of skeletal muscles in the body are profoundly influenced by muscle architecture, attachment of muscles to the skeleton, and motor unit organization.(ABSTRACT TRUNCATED AT 400 WORDS)

Efficient waveform tomography for lithospheric imaging: implications for realistic, two-dimensional acquisition geometries and low-frequency data

NASA Astrophysics Data System (ADS)

Brenders, A. J.; Pratt, R. G.

2007-01-01

We provide a series of numerical experiments designed to test waveform tomography under (i) a reduction in the number of input data frequency components (`efficient' waveform tomography), (ii) sparse spatial subsampling of the input data and (iii) an increase in the minimum data frequency used. These results extend the waveform tomography results of a companion paper, using the same third-party, 2-D, wide-angle, synthetic viscoelastic seismic data, computed in a crustal geology model 250 km long and 40 km deep, with heterogeneous P-velocity, S-velocity, density and Q-factor structure. Accurate velocity models were obtained using efficient waveform tomography and only four carefully selected frequency components of the input data: 0.8, 1.7, 3.6 and 7.0 Hz. This strategy avoids the spectral redundancy present in `full' waveform tomography, and yields results that are comparable with those in the companion paper for an 88 per cent decrease in total computational cost. Because we use acoustic waveform tomography, the results further justify the use of the acoustic wave equation in calculating P-wave velocity models from viscoelastic data. The effect of using sparse survey geometries with efficient waveform tomography were investigated for both increased receiver spacing, and increased source spacing. Sampling theory formally requires spatial sampling at maximum interval of one half-wavelength (2.5 km at 0.8 Hz): For data with receivers every 0.9 km (conforming to this criterion), artefacts in the tomographic images were still minimal when the source spacing was as large as 7.6 km (three times the theoretical maximum). Larger source spacings led to an unacceptable degradation of the results. When increasing the starting frequency, image quality was progressively degraded. Acceptable image quality within the central portion of the model was nevertheless achieved using starting frequencies up to 3.0 Hz. At 3.0 Hz the maximum theoretical sample interval is reduced to 0.67 km due to the decreased wavelengths; the available sources were spaced every 5.0 km (more than seven times the theoretical maximum), and receivers were spaced every 0.9 km (1.3 times the theoretical maximum). Higher starting frequencies than 3.0 Hz again led to unacceptable degradation of the results.

Biological treatment of steroidal drug industrial effluent and electricity generation in the microbial fuel cells.

PubMed

Liu, Ru; Gao, Chongyang; Zhao, Yang-Guo; Wang, Aijie; Lu, Shanshan; Wang, Min; Maqbool, Farhana; Huang, Qing

2012-11-01

The single chamber microbial fuel cells (MFCs) were used to treat steroidal drug production wastewater (SPW) and generate electricity simultaneously. The results indicated that the maximum COD removal efficiency reached 82%, total nitrogen and sulfate removal rate approached 62.47% and 26.46%, respectively. The maximum power density and the Coulombic efficiency reached to 22.3Wm(-3) and 30%, respectively. The scanning electron microscope showed that the dominant microbial populations were remarkably different in morphology on the surface of SPW and acetate-fed anodes. PCR-denaturing gradient gel electrophoresis profiles revealed that the microbial community structure fed with different concentrations of SPW presented a gradual succession and unique bacterial sequences were detected on the SPW and acetate-fed anodes. This research demonstrates that MFCs fed with SPW achieved a high efficiency of power density and simultaneous nutrient removal, and the dominant microorganisms on the anode were related to the types and the concentrations of substrates. Copyright © 2012 Elsevier Ltd. All rights reserved.

Long-term field phytoextraction of zinc/cadmium contaminated soil by Sedum plumbizincicola under different agronomic strategies.

PubMed

Deng, Lin; Li, Zhu; Wang, Jie; Liu, Hongyan; Li, Na; Wu, Longhua; Hu, Pengjie; Luo, Yongming; Christie, Peter

2016-01-01

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment "S. plumbizincicola intercropped with maize" was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha(-1) gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.

Coolant Design System for Liquid Propellant Aerospike Engines

NASA Astrophysics Data System (ADS)

McConnell, Miranda; Branam, Richard

2015-11-01

Liquid propellant rocket engines burn at incredibly high temperatures making it difficult to design an effective coolant system. These particular engines prove to be extremely useful by powering the rocket with a variable thrust that is ideal for space travel. When combined with aerospike engine nozzles, which provide maximum thrust efficiency, this class of rockets offers a promising future for rocketry. In order to troubleshoot the problems that high combustion chamber temperatures pose, this research took a computational approach to heat analysis. Chambers milled into the combustion chamber walls, lined by a copper cover, were tested for their efficiency in cooling the hot copper wall. Various aspect ratios and coolants were explored for the maximum wall temperature by developing our own MATLAB code. The code uses a nodal temperature analysis with conduction and convection equations and assumes no internal heat generation. This heat transfer research will show oxygen is a better coolant than water, and higher aspect ratios are less efficient at cooling. This project funded by NSF REU Grant 1358991.