Numerical simulation analysis of multi-scale computational fluid dynamics on hemodynamic parameters modulated by pulsatile working modes for the centrifugal and axial left ventricular assist devices.

Continuous flow (CF) left ventricular assist devices (LVAD) operate at a constant speed mode, which could result in increased risk of adverse events due to reduced vascular pulsatility. Consequently, pump speed modulation algorithms have been proposed to augment vascular pulsatility. However, the quantitative local hemodynamic effects on the aorta when the pump is operating with speed modulation using different types of CF-LVADs are still under investigation. The computational fluid dynamics (CFD) study was conducted to quantitatively elucidate the hemodynamic effects on a clinical patient-specific aortic model under different speed patterns of CF-LVADs. Pressure distribution, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and velocity were calculated to compare their differences at constant and pulsatile speeds under centrifugal and axial LVAD support. Results showed that pulse pressure on the aorta was significantly larger under pulsatile speed mode than that under constant speed mode for both CF-LVADs, indicating enhanced aorta pulsatility, as well as the higher peak blood flow velocity on some representative slices of aorta. Pulsatile speed modulation enhanced peak WSS compared to constant speed; high TAWSS region appeared near the branch of left common carotid artery and distal aorta regardless of speed modes and CF-LVADs but these regions also had low OSI; RRT was almost the same for all the cases. This study may provide a basis for the scientific and reasonable selection of the pulsatile speed patterns of CF-LVADs for treating heart failure patients.

A sensorless, physiologic feedback control strategy to increase vascular pulsatility for rotary blood pumps.

Continuous flow rotary blood pumps (RBP) operating clinically at constant rotational speeds cannot match cardiac demand during varying physical activities, are susceptible to suction, diminish vascular pulsatility, and have an increased risk of adverse events. A sensorless, physiologic feedback control strategy for RBP was developed to mitigate these limitations. The proposed algorithm used intrinsic pump speed to obtain differential pump speed (ΔRPM). The proposed gain-scheduled proportional-integral controller, switching of setpoints between a higher pump speed differential setpoint (ΔRPM Hr ) and a lower pump speed differential setpoint (ΔRPM Lr ), generated pulsatility and physiologic perfusion, while avoiding suction. The switching between ΔRPM Hr and ΔRPM Lr setpoints occurred when the measured ΔRPM reached the pump differential reference setpoint. In-silico tests were implemented to assess the proposed algorithm during rest, exercise, a rapid 3-fold pulmonary vascular resistance increase, rapid change from exercise to rest, and compared with maintaining a constant pump speed setpoint. The proposed control algorithm augmented aortic pressure pulsatility to over 35 mmHg during rest and around 30 mmHg during exercise. Significantly, ventricular suction was avoided, and adequate cardiac output was maintained under all simulated conditions. The performance of the sensorless algorithm using estimation was similar to the performance of sensor-based method. This study demonstrated that augmentation of vascular pulsatility was feasible while avoiding ventricular suction and providing physiological pump outflows. Augmentation of vascular pulsatility can minimize adverse events that have been associated with diminished pulsatility. Mock circulation and animal studies would be conducted to validate these results.

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells.

In this contribution, we studied the effect of fluorine substitution on photogenerated charge generation, transport, and recombination in polymer solar cells. Two conjugated polymer materials, PBDTTT-E (fluorine free) and PTB7 (one fluorine substitution), were compared thoroughly. Meanwhile, various characterization techniques, including atomic force microscopy, steady-state spectroscopy, transient absorption spectroscopy, spectroelectrochemistry, and electrical measurements, were employed to analyse the correlation between molecular structure and device performance. The results showed that the influence of fluorine substitution on both the exciton binding energy of the polymer and the carrier recombination dynamics in the ultrafast timescale on the polymer was weak. However, we found that the fluorine substitution could enhance the exciton lifetime in neat polymer film, and it also could increase the mobility of photogenerated charge. Moreover, it was found that the SOMO energy level distribution of the donor in a PTB7:PC71BM solar cell could facilitate hole transport from the donor/acceptor interface to the inner of the donor phase, showing a better advantage than the PBDTTT-E:PC71BM solar cell. Therefore, fluorine substitution played a critical role for high-efficiency polymer solar cells.

Divergent oxidative dearomatization coupling reactions to construct polycyclic cyclohexadienones.

Highly selective divergent oxidative dearomatization coupling reactions, in which the chemoselectivity is controlled by catalysts and bases, are reported herein. Three different kinds of polycyclic cyclohexadienones are produced from the same reactants (41 examples, 85-99% yield). Our method marks a novel copper- and palladium-catalyzed C-H oxidative dearomatization of phenolic derivatives.

Effects of a Short-Term Left Ventricular Assist Device on Hemodynamics in a Heart Failure Patient-Specific Aorta Model: A CFD Study.

Patients with heart failure (HF) or undergoing cardiogenic shock and percutaneous coronary intervention require short-term cardiac support. Short-term cardiac support using a left ventricular assist device (LVAD) alters the pressure and flows of the vasculature by enhancing perfusion and improving the hemodynamic performance for the HF patients. However, due to the position of the inflow and outflow of the LVAD, the local hemodynamics within the aorta is altered with the LVAD support. Specifically, blood velocity, wall shear stress, and pressure difference are altered within the aorta. In this study, computational fluid dynamics (CFD) was used to elucidate the effects of a short-term LVAD for hemodynamic performance in a patient-specific aorta model. The three-dimensional (3D) geometric models of a patient-specific aorta and a short-term LVAD, Impella CP, were created. Velocity, wall shear stress, and pressure difference in the patient-specific aorta model with the Impella CP assistance were calculated and compared with the baseline values of the aorta without Impella CP support. Impella CP support augmented cardiac output, blood velocity, wall shear stress, and pressure difference in the aorta. The proposed CFD study could analyze the quantitative changes in the important hemodynamic parameters while considering the effects of Impella CP, and provide a scientific basis for further predicting and assessing the effects of these hemodynamic signals on the aorta.

Spectral characteristics and optical temperature sensing properties of Er3+/Yb3+-co-doped phosphate glasses with GeO2 modification.

Er3+/Yb3+-co-doped phosphate glasses with GeO2 modification (PLAZGs) were successfully prepared by the melt-quenching method. The phenomenological intensity parameters Ωt (t=2, 4, 6) of the PLAZGs have been calculated by the Judd-Ofelt theory. Based on the phenomenological intensity parameters, the spectroscopic parameters of Er3+ and fluorescence intensity ratio (FIR) of green upconversion emissions were estimated. It was observed that, under 980 nm excitation, all samples exhibit green and red upconversion emissions of Er3+. The 10 mol% GeO2 modified phosphate glass has the strongest upconversion emission. Additionally, the fluorescence decays of the 2F5/2→2F7/2 transition of Yb3+ ions were measured to evaluate the energy transfer efficiency from Yb3+ to Er3+ ions. Finally, the optical temperature sensing properties based on upconversion emissions were investigated at temperatures from 150 K to 600 K. The maximum absolute temperature sensitivity S value of 6.0×10-3K-1 at 400 K is obtained, which indicates that the glass is promising for temperature sensing application based on the FIR technology.

Enhanced Charge Transport in Conventional Polymer Solar Cells with a Perovskite-Type LaNiO3 Layer.

In this study, a novel metal oxide, lanthanum nickelate (LNO) with a perovskite structure, was introduced into a polymer solar cell (PSC) device, replacing the PEDOT:PSS hole transport layer (HTL). The results show that the LNO-based PTB7-Th:PC71BM solar cell exhibits a higher circuit current density, power conversion efficiency, and stability compared with a device with PEDOT:PSS HTL. To understand the effect of LNO HTL on the performance of devices, the active layer morphology and charge transport characteristics in PSCs were systematically analyzed. The morphology of active layer was affected by the HTL, which further regulated the generation and transport processes of charge carrier in the PSC device. For the LNO HTL, an appropriate thickness (8 nm) and a small surface roughness (Sq = 0.7 nm) can coordinate the energy-level structure of device and improve the interface contact between the FTO electrode and PTB7-Th:PC71BM active layer, promoting the charge transport performance of device. Therefore, this work provides a new consideration for the preparation of efficient, stable, and low-cost polymer solar cells.

Morphology and carrier non-geminate recombination dynamics regulated by solvent additive in polymer/fullerene solar cells.

In this study, PBDTTT-E (based on benzo [1,2-b:4,5-b'] dithiophene (BDT) and thieno [3,4-b] thiophene (TT)) as a donor and fullerene derivative PC71BM (phenyl-C71-butyric acid methyl ester) as an acceptor with and without 1,8-diiodooctane (DIO)-treated copolymer solar cells were investigated. The device based on PBDTTT-E with treated DIO showed remarkably high current density (J sc), fill factor (FF) and similar open-circuit voltage (V oc). Charge carrier lifetime (τ n ), density (n) and non-geminate recombination rate (k rec) in the photoactive layers were measured by employing transient photovoltage (TPV) and charge extraction (CE) techniques. Based on k rec and n, J-V curves were reconstructed. The DIO optimized the morphology of the active layer and its PBDTTT-E:PC71BM interfaces were increased. Therefore, compared to the device without the treated DIO, the device with the treated DIO showed larger electron mobility, longer carrier lifetime (τ n ) and lower non-geminate recombination rate (k rec), which enhances the carrier transport and restrains the non-geminate recombination, realizing the higher J sc and FF. In addition, that the DIO-treated devices can weaken the role of other factors (such as field dependent geminate recombination) in limiting device performance. The results provide some hints of improved device performance upon DIO as an additive in the D-A type polymer/fullerene solar cells.

Working area effects on the energetic distribution of trap states and charge dynamics of dye-sensitized solar cells.

Measuring the transient photoelectric signals (photovoltage or photocurrent) after optically perturbing dye-sensitized solar cells (DSSCs) can provide information about electron transport and recombination. Herein, the energetic distribution of trap states in different working areas of DSSCs (0.16 cm2 vs. 1 cm2) and their impacts on charge transport and recombination were investigated by means of time-resolved charge extraction (TRCE), transient photovoltage (TPV) and transient photocurrent (TPC) measurements. The results indicated that increasing the working area deepened the energetic distribution of trap states (i.e., increased the mean characteristic energy k B T 0), which hindered the electron transport within the photoanode, accelerated the electron recombination in high voltage regions, and reduced the charge collection efficiency. All abovementioned are the inherent reasons why the J SC in larger working area cells is significantly smaller than that in smaller area cells (11.58 mA cm-2 vs. 17.17 mA cm-2). More importantly, as the investigation of high-efficiency large area solar cells is currently a promising research topic for new solar cells, we describe the importance of photoanode optimization to achieve high-efficiency DSSCs with large working area by improving charge collection efficiency.

Appropriate Donor-Acceptor Phase Separation Structure for the Enhancement of Charge Generation and Transport in Polymer Solar Cells.

The morphology of active layer for polymer solar cells is critical to enhance the performance especially for fill factor of the devices. To investigate the relationship between active layer morphology and performance of polymer solar cells (PSCs), 1,8-diiodooctane (DIO) additive, and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) electron acceptor were used to regulate the aggregation morphology of copolymer poly(thieno[3,4-b]-thiophene/benzodithiophene) (PTB7) electron donor from solution state to solid state. Atom force microscopy (AFM), steady-state absorption (UV-Vis), time-resolved absorption (TA), spectroelectrochemistry (SEC) and current-voltage (J-V) measurements were employed to characterize the morphology, optical and electrical characteristics of active layers and to reveal the relationship among the morphology, photophysical property, and performance of PTB7-based devices. The results show that DIO can refine the aggregation scale of PTB7 during the dissolution process, whereas both the aggregation scale and aggregation behaviors of PTB7 donor are affected by PC71BM acceptor molecules. Furthermore, the bulk heterojunction structure (BHJ) morphology of active layer can be optimized during the DIO evaporation process. TA kinetic data indicate that the population and lifetime of charged species are improved in the DIO-treated BHJ active layer. Moreover, the active layers with DIO treatment have a relative low highest occupied molecular orbital (HOMO) energy level, which makes hole transport more easily in PTB7 donor phase. As a result, the performance of PTB7-based PSCs is enhanced.

Acceptor Side-Chain Effects on the Excited State Dynamics of Two-Dimensional-Like Conjugated Copolymers in Solution.

Excited state dynamics of two-dimensional-like conjugated copolymers PFDCN and PFSDCN based on alternating fluorene and triphenylamine main chains and malononitrile pendant acceptor groups with thiophene as π-bridge, have been investigated by using transient absorption spectroscopy. There is an additional conjugated -C=C- bond in PFDCN, which distinguishes it from PFSDCN. The lowest energy absorption band of each copolymer absorption spectrum is attributed to the π-π* transition with intramolecular charge-transfer, which has a lower fluorescence contribution than those of higher energy absorption bands. The optical excitation of either PFDCN or PFSDCN solution generates polaron pairs that then self-localize and evolve to a bound singlet exciton within a few picoseconds. Due to the additional conjugated -C=C- bond in the acceptor side-chain, PFDCN has a stronger intramolecular charge-transfer characteristic compared with PFSDCN, therefore exhibiting a longer self-localization time (7 ps vs. 3 ps for PFSDCN) and a shorter fluorescence lifetime (1.48 ns vs. 1.60 ns for PFSDCN).

Impacts of side chain and excess energy on the charge photogeneration dynamics of low-bandgap copolymer-fullerene blends.

Primary charge photogeneration dynamics in neat and fullerene-blended films of a pair of alternating benzo[1,2-b:4,5-b(')]dithiophene (BDT) and thieno[3,4-b]thiophene (TT) copolymers are comparatively studied by using near-infrared, time-resolved absorption (TA) spectroscopy under low excitation photon fluence. PBDTTT-E and PBDTTT-C, differed merely in the respective TT-substituents of ester (-E) and carbonyl (-C), show distinctly different charge photogeneration dynamics. The pair of neat PBDTTT films show exciton lifetimes of ∼0.1 ns and fluorescence quantum yields below 0.2%, as well as prominent excess-energy enhanced exciton dissociation. In addition, PBDTTT-C gives rise to >50% higher P(•+) yield than PBDTTT-E does irrespective to the excitation photon energy. Both PBDTTT-E:PC61BM and PBDTTT-C:PC61BM blends show subpicosecond exciton lifetimes and nearly unitary fluorescence quenching efficiency and, with respect to the former blend, the latter one shows substantially higher branching ratio of charge separated (CS) state over interfacial charge transfer (ICT) state, and hence more efficient exciton-to-CS conversion. For PBDTTT-C:PC61BM, the ultrafast charge dynamics clearly show the processes of ICT-CS interconversion and P(•+) migration, which are possibly influenced by the ICT excess energy. However, such processes are relatively indistinctive in the case of PBDTTT-E:PC61BM. The results strongly prove the importance of ICT dissociation in yielding free charges, and are discussed in terms of the film morphology and the precursory solution-phase macromolecular conformation.

Side-chain effects on the solution-phase conformations and charge photogeneration dynamics of low-bandgap copolymers.

Solution-phase conformations and charge photogeneration dynamics of a pair of low-bandgap copolymers based on benzo[1,2-b:4,5-b(')]dithiophene (BDT) and thieno[3,4-b]thiophene (TT), differed by the respective carbonyl (-C) and ester (-E) substituents at the TT units, were comparatively investigated by using near-infrared time-resolved absorption (TA) spectroscopy at 25 °C and 120 °C. Steady-state and TA spectroscopic results corroborated by quantum chemical analyses prove that both PBDTTT-C and PBDTTT-E in chlorobenzene solutions are self-aggregated; however, the former bears a relatively higher packing order. Specifically, PBDTTT-C aggregates with more π-π stacked domains, whereas PBDTTT-E does with more random coils interacting strongly at the chain intersections. At 25 °C, the copolymers exhibit comparable exciton lifetimes (~1 ns) and fluorescence quantum yields (~2%), but distinctly different charge photogeneration dynamics: PBDTTT-C on photoexcitation gives rise to a branching ratio of charge separated (CS) over charge transfer (CT) states more than 20% higher than PBDTTT-E does, correlating with their photovoltaic performance. Temperature and excitation-wavelength dependent exciton∕charge dynamics suggest that the CT states localize at the chain intersections that are survivable up to 120 °C, and that the excitons and the CS states inhabit the stretched strands and the also thermally robust orderly stacked domains. The stable self-aggregation structures and the associated primary charge dynamics of the PBDTTT copolymers in solutions are suggested to impact intimately on the morphologies and the charge photogeneration efficiency of the solid-state photoactive layers.

Subnanosecond charge recombination dynamics in P3HT/PC61BM films.

Ultrafast near-infrared absorption spectroscopy was used to investigate the influence of film morphology and excitation photon energy on the charge recombination (CR) dynamics in the initial nanosecond timescale in the P3HT/PC(61)BM blend films. With reference to the CS(2)-cast films, the solvent vapor annealed (SVA) ones show 2­3-fold improvement in hole mobility and more than 5-fold reduction in the polymer-localized trap states of holes. At Dt = 70 ps, the hole mobility (m(h)) and the bimolecular CR rate (γ(bi)) of the SVA films are µ(h) = 8.7 × 10(−4) cm2 × s(−1) × V(−1) and γ(bi) = 4.5 × 10(−10) cm3 × s(−1), whereas at Δt = 1 ns they drop to 8.7 × 10(−5) cm2 × s(−1) × V(−1) and 4.6 × 10(−11) cm3 × s(−1), respectively. In addition, upon increasing the hole concentration, the hole mobility increases substantially faster under the above-gap photoexcitation than it does under the band-gap photoexcitation, irrespective of the film morphologies. The results point to the importance of utilizing the photogenerated free charges in the early timescales.

Effect of end groups on the raman spectra of lycopene and ß-carotene under high pressure.

The Raman spectra of all-trans-lycopene in n-hexane were measured under high pressure, and the results compared with those of ß-carotene. The different pressure effects on Raman spectra are analyzed taking into account the different structures of lycopene and ß-carotene molecules. It is concluded that: (a) the vibronic coupling between the S1 and S0 states of ß-carotene is stronger than that of lycopene, (b) the diabatic frequency increment of the ν1 mode is more susceptible to pressure than that of the ν2 mode for lycopene, and (c) ß-rings rotation can relieve the pressure effect on the C=C bond length in ß-carotene. This work provides some insights for elucidating the structural and environmental effects on Raman spectra of carotenoids.