| 1. |
- Zhang, Kaicheng, et al.
(författare)
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SN 2014J in M82 : new insights on the spectral diversity of Type Ia supernovae
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 481:1, s. 878-893
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Tidskriftsartikel (refereegranskat)abstract
- We present extensive spectroscopic observations for one of the closest Type Ia supernovae (SNe Ia), SN 2014J discovered in M82, ranging from 10.4 d before to 473.2 d after B-band maximum light. The diffuse interstellar band features detected in a high-resolution spectrum allow an estimate of line-of-sight extinction as A(v) similar to 1.9 +/- 0.6 mag. Spectroscopically, SN 2014J can be put into the high-velocity (HV) subgroup in Wang's classification with a velocity of Si II lambda 6355 at maximum light of upsilon(0) = 1.22 +/- 0.01 x 10(4) km s(-1) but has a low velocity gradient (LVG, following Benetti's classification) of (v) over bar = 41 +/- 2 km s(-1) d(-1), which is inconsistent with the trend that HV SNe Ia generally have larger velocity gradients. We find that the HV SNe Ia with LVGs tend to have relatively stronger Si III (at similar to 4400 angstrom) absorptions in early spectra, larger ratios of S II lambda 5468 to S II lambda 5640, and weaker Si II 5972 absorptions compared to their counterparts with similar velocities but high velocity gradients. This shows that the HV+ LVG subgroup of SNe Ia may have intrinsically higher photospheric temperature, which indicates that their progenitors may experience more complete burning in the explosions relative to the typical HV SNe Ia.
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| 2. |
- Guo, Pengzhi, et al.
(författare)
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Twisted Alkylthiothien-2-yl Flanks and Extended Conjugation Length Synergistically Enhanced Photovoltaic Performance by Boosting Dielectric Constant and Carriers Kinetic Characteristics
- 2021
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Ingår i: Macromolecular Chemistry and Physics. - : Wiley. - 1022-1352 .- 1521-3935. ; 222:12
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Tidskriftsartikel (refereegranskat)abstract
- Alternating conjugated polymers (CPs), derived from 2-ethylhexylthiothiophen-2-yl (TS) or 2-ethylhexylthiophen-2-yl (T) flanked dithieno[3,2-d:3,2-d ']benzo[1,2-b:4,5-b ']dithiophene (DTBDT) and diketopyrrolo-pyrrole (DPP) termed as PDTBDT-TS-DPP and PDTBDT-T-DPP, are prepared and characterized. It is found that the PDTBDT-TS-DPP not only exhibits slightly deepening the highest occupied molecular orbital energy levels, and similar absorption, etc., but also presents higher dielectric constant (epsilon(r)) of 6.7 at 1 kHz in contrast to 3.2 for PDTBDT-T-DPP, which are even higher than those of 4.3 and 3.0 for PBDT-TS-DPP/PBDT-T-DPP generated from TS and T flanked benzo[1,2-b:4,5-bMODIFIER LETTER PRIME]dithiophene and DPP. Beyond that, the power conversion efficiency of 8.17% for the inverted photovoltaic devices from DPP-based CPs, is achieved from PDTBDT-TS-DPP. The alkylthio side chains are used in the DTBDT of the larger twisting angles of TS flanks and longer conjugation length, synergistically contribute to the highest dipole moments, and then lead to the enhancement of epsilon(r), thus devoted the modification exciton dissociation and charge carriers kinetic characteristics. To the authors' knowledge, it is the first time to report that epsilon(r) of the CPs is connected with the twisting angle of flanks and conjugation length of the building blocks, besides the use of functional side chains and atoms.
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| 3. |
- Li, Yaohui, et al.
(författare)
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An n-n Heterojunction Configuration for Efficient Electron Transport in Organic Photovoltaic Devices
- 2023
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 33:9
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Tidskriftsartikel (refereegranskat)abstract
- Selective electron transport and extraction are essential to the operation of photovoltaic devices. Electron transport layer (ETL) is therefore critical to organic photovoltaics (OPV). Herein, an ETL configuration is presented comprising a solution-processed n-n organic heterojunction to enhance electron transport and hole blocking, and boost power conversion efficiency (PCE) in OPV. Specifically, the n-n heterojunction is constructed by stacking a narrow-band n-type conjugated polymer layer (PNDIT-F3N) and a wide-band n-type conjugated molecule layer (Phen-NaDPO). Based on the ultraviolet photoelectron spectroscopy measurement and numerical simulation of current density-voltage characteristics, the formation of the built-in potential is investigated. In three OPVs with different active layers, substantial improvements are observed in performance following the introduction of this ETL configuration. The performance enhancement arises from the combination of selective carrier transport properties and reduced recombination. Another contributing factor is the good film-forming quality of the new ETL configuration, where the surface energies of the related materials are well-matched. The n-n organic heterojunction represents a viable and promising ETL construction strategy for efficient OPV devices.
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| 4. |
- Liu, Jianhua, et al.
(författare)
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Differential space-code modulation for interference suppression
- 2001
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 49:8, s. 1786-1795
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Tidskriftsartikel (refereegranskat)abstract
- Space-time coding has been receiving much attention due to its potentials offered by fully exploiting the spatial and temporal diversities of multiple transmit and receive antennas. A differential space-time modulation (DSTM) scheme was previously proposed for demodulation without channel state information, which is attractive in fast fading channels where accurate channel estimates are difficult to obtain. However, this technique is sensitive to interference and is likely to deteriorate or even break down in a wireless environment, where interference (including intentional and unintentional jamming) signals exist. We propose a new coding and modulation scheme, referred to as the differential space-code modulation (DSCM), which is interference resistant. Our focus is on single-user communications. We show that DSCM outperforms DSTM significantly when interference is present. This advantage is achieved at the cost of a lower data rate or a wider bandwidth or a combination of both. To alleviate this problem, a high-rate DSCM (HR-DSCM) scheme is also presented, which increases the data rate considerably at the cost of a slightly higher bit-error rate (BER), while still maintaining the interference suppression capability.
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| 5. |
- Liu, Jianhua, et al.
(författare)
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High-rate differential space-code modulation for interference suppression
- 2001
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Ingår i: 2001 IEEE Third Workshop on Signal Processing Advances in Wireless Communications (SPAWC'01). Workshop Proceedings. - 0780367200 ; , s. 283-286
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Konferensbidrag (refereegranskat)abstract
- Space-time coding has been receiving much research attention recently due to the potential offered by fully exploiting spatial and temporal diversity. A differential space-time modulation (DSTM) scheme was recently proposed to perform demodulation without channel state information, which is attractive in fast fading channels where accurate channel estimates are difficult to obtain. More recently, a differential space-code modulation (DSCM) scheme, which is an improvement of DSTM for combating interference (including intentional and unintentional jamming) signals, was proposed. DSCM significantly outperforms DSTM when interference is present. This advantage, however, is achieved at the cost of a lower transmission rate, a wider bandwidth, or a combination of both. To alleviate this problem, we extend DSCM to a so-called high-rate DSCM (HR-DSCM) scheme, which increases the data rate considerably at the cost of a slightly higher bit error rate, while still maintaining the interference suppression capability.
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| 6. |
- Mansouri, Kamel, et al.
(författare)
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CoMPARA : Collaborative Modeling Project for Androgen Receptor Activity
- 2020
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Ingår i: Journal of Environmental Health Perspectives. - 0091-6765 .- 1552-9924. ; 128:2, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Endocrine disrupting chemicals (EDCs) are xenobiotics that mimic the interaction of natural hormones and alter synthesis, transport, or metabolic pathways. The prospect of EDCs causing adverse health effects in humans and wildlife has led to the development of scientific and regulatory approaches for evaluating bioactivity. This need is being addressed using high-throughput screening (HTS) in vitro approaches and computational modeling.OBJECTIVES: In support of the Endocrine Disruptor Screening Program, the U.S. Environmental Protection Agency (EPA) led two worldwide consortiums to virtually screen chemicals for their potential estrogenic and androgenic activities. Here, we describe the Collaborative Modeling Project for Androgen Receptor Activity (CoMPARA) efforts, which follows the steps of the Collaborative Estrogen Receptor Activity Prediction Project (CERAPP).METHODS: The CoMPARA list of screened chemicals built on CERAPP's list of 32,464 chemicals to include additional chemicals of interest, as well as simulated ToxCast (TM) metabolites, totaling 55,450 chemical structures. Computational toxicology scientists from 25 international groups contributed 91 predictive models for binding, agonist, and antagonist activity predictions. Models were underpinned by a common training set of 1,746 chemicals compiled from a combined data set of 11 ToxCast (TM)/Tox21 HTS in vitro assays.RESULTS: The resulting models were evaluated using curated literature data extracted from different sources. To overcome the limitations of single-model approaches, CoMPARA predictions were combined into consensus models that provided averaged predictive accuracy of approximately 80% for the evaluation set.DISCUSSION: The strengths and limitations of the consensus predictions were discussed with example chemicals; then, the models were implemented into the free and open-source OPERA application to enable screening of new chemicals with a defined applicability domain and accuracy assessment. This implementation was used to screen the entire EPA DSSTox database of similar to 875,000 chemicals, and their predicted AR activities have been made available on the EPA CompTox Chemicals dashboard and National Toxicology Program's Integrated Chemical Environment.
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| 7. |
- Fu, Yifeng, 1984, et al.
(författare)
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Graphene related materials for thermal management
- 2020
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field.
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| 8. |
- Hongbin, Zhu, et al.
(författare)
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Microstructure and tribological performance of Cr7C3-(Ni,Cr)3(AI,Cr) coating deposited from Cr7C3 in-situ synthesized alloy powder
- 2016
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Ingår i: International Thermal Spray Conference and Exposition, ITSC 2016; Shanghai International Convention CenterShanghai; China; 10 May 2016 through 12 May 2016. - 9781510844001 ; 2, s. 1003-1010
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Konferensbidrag (refereegranskat)abstract
- The work is aimed at developing a new type of Cr7C3-(Ni,Cr)3(AI,Cr) coatings for parts used in heavy-duty diesel engine. The feedstock, in which the stripe shaped Cr7C3 was in-situ synthesized, was firstly prepared by vacuum melting and gas atomization, then it was subjected to high velocity oxy-fuel(HVOF) spraying to deposited coating.The element composition, microstructures and the phase composition of the powder, as well as the sprayed coating were analyzed by chemical analysis, SEM and XRD. The hardness and sliding wear performance of the sprayed coating was also tested and compared to a commercial Cr3C2-NiCr coating used on piston ring.The results showed that the content of carbon in feedstock was almost the same as it was designed, and the volume content of Cr7C3 was increased with the more carbon and chromium added. The phases of the sprayed coating was also mainly the Cr7C3 and the Cr doped Ni3AI, and the ratio of them was almost similar to it in the powder. With the increased content of Cr7C3 in coating, the microhardness at room temprature was firstly increased to about 1000Hv0.3, but then minor decreased. When the temprature rised to 700°C, the microhardness of the coating was almost no changed, which showed its potential application at the high temprature.The coating involved 70vol.% and 77 vol.%Cr7C3 was showed the improved wear resisrance, lower friction coefficient and better compatibility to contourpartthan other Cr7C3-(Ni,Cr)3(AI,Cr) coatings and Cr3C2-NiCr coating.
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| 9. |
- Kovacic, Suzana, et al.
(författare)
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Construction and Characterization of Kilobasepair Densely Labeled Peptide-DNA
- 2014
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 15:11, s. 4065-4072
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Tidskriftsartikel (refereegranskat)abstract
- Directed assembly of biocompatible materials benefits from modular building blocks in which structural organization is independent of introduced functional modifications. For soft materials, such modifications have been limited. Here, long DNA is successfully functionalized with dense decoration by peptides. Following introduction of alkyne-modified nucleotides into kilobasepair DNA, measurements of persistence length show that DNA mechanics are unaltered by the dense incorporation of alkynes (similar to 1 alkyne/2 bp) and after click-chemistry attachment of a tunable density of peptides. Proteolytic cleavage of densely tethered peptides (similar to 1 peptide/3 bp) demonstrates addressability of the functional groups, showing that this accessible approach to creating hybrid structures can maintain orthogonality between backbone mechanics and overlaid function. The synthesis and characterization of these hybrid constructs establishes the groundwork for their implementation in future applications, such as building blocks in modular approaches to a range of problems in synthetic biology.
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| 10. |
- Li, Changle, 1992-
(författare)
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Ab Initio Investigation of Interfacial and Grain Boundary Properties of Metals and Alloys
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phase interface (IF) and grain boundary (GB) are both common yet critical planar defects influencing the mechanical and physical properties of polycrystalline materials. Due to the complex nature of IFs and GBs in terms of structure and chemistry, determining the accurate excess energies associated with these defects is challenging for both experimental measurements and theoretical simulations. In this thesis, using first-principles methods, I make efforts towards establishing an efficient and robust model for predicting the IF and GB properties in elemental metals and complex multi-component alloys including the temperature and composition dependences.First I focus on the temperature dependent interfacial energy (IFE) for Cu-Co alloys. IFE plays a critical role in determining the nucleation and precipitate coarsening thermodynamics and kinetics. I start with assessing the phase diagram of Cu-Co alloys by ab initio calculations, which is used for establishing the composition-temperature relationship of precipitates and matrix. Calculations of the physical and thermodynamic properties for the ferromagnetic (FM) and paramagnetic (PM) $\ce{Cu}_{1-x}\ce{Co}_{x}$ solid solutions are performed using the exact muffin-tin orbital (EMTO) method in combination with the coherent potential approximation (CPA) for dealing chemical and magnetic randomness. This study demonstrates that the equilibrium volumes and magnetic states are crucial for a quantitative description of the thermodynamics of the Cu-Co system at temperatures up to 1400 K. The predicted ab initio Cu-Co phase diagram is in good agreement with the measurements and CALPHAD data. Then, the composition and magnetic dependent IFEs for a coherent $\ce{Cu}_{1-x}\ce{Co}_{x}$/$\ce{Cu}_{x}\ce{Co}_{1-x}$ interface are investigated at various magnetic states including FM, PM, and the mixed PM+FM states to account for the magnetic state change at different temperatures. Then, I translate the composition dependence of the IFE to the temperature dependence. The obtained results are in reasonable agreement with those obtained by experiments and thermodynamic calculations. The first part of the thesis provides an ab initio database for the IFEs in Cu-Co system and emphasizes the importance of understanding and properly describing various physical and thermodynamic quantities in different materials modeling approaches.The second focus of this thesis is on grain boundary energy (GBE). We calculate the GBEs for ten face-centered cubic (fcc) and seven body-centered cubic (bcc) metals. Various types of symmetric tilt GB structures ranging from twin boundary up to $\Sigma$19 coincident site lattice (CSL) boundaries are studied using the Vienna Ab initio Simulation Package (VASP). Ab initio results show a correlation between the GBEs of the same grain boundary structure in different fcc and bcc metals. Importantly, I show that the correlation factor is best determined by the ratio of the low-index surface energy. By using this correlation, the general GBEs of fcc and bcc metals are predicted at 0 K. Furthermore, using the Foiles's method, which assumes that the general GBE has a similar temperature dependence as the elastic modulus $c_{44}$, the general GBEs at elevated temperatures are predicted. The so obtained theoretical results show a good agreement with the available experimental data. Finally, the proposed method for predicting the general GBEs is applied to complex multicomponent alloys (austinite Fe-Cr-Ni and ferritic Fe-Cr alloys), yielding a parameterized prediction of the composition and temperature dependent GBE. After examining two common experimental methods used for determining the general GBEs, it is concluded that the two sets of experimental GBEs for fcc metals agree well with each other, while for bcc metals they correspond to different grain boundary structures and differ by a factor of 2. This part of the thesis introduces an effective and robust model for predicting the general GBEs of metals and alloys, facilitating grain boundary engineering for advanced alloy design. The third focus is on alloying GB segregation in complex alloys. Manganese (Mn) and Nickel (Ni) segregation behaviors at bcc Fe-Cr grain boundaries are investigated. In this segregation study, three GB structures, namely, $\Sigma$3(111), $\Sigma$9(114), and $\Sigma$11(332), are considered. First, a systematic comparison of the theoretical segregation energies for Mn and Ni solutes in pure Fe GBs is conducted between VASP and EMTO calculations. The EMTO results agree reasonably with VASP and previous theoretical data, indicating a reliable potential for capturing the solute segregation behaviors. Next, the Mn and Ni segregation energies at bcc Fe-Cr solid solution GBs are determined at various concentrations of the matrix and at the FM and PM states to account for the temperature effects on the magnetic state using the EMTO-CPA method. Strong magnetic effects on the segregation energy are observed. Particularly, it is found that the magnetic states of Mn atoms depend strongly on local chemical and structural environment, which has a remarkable effect on the segregation energy. It is found that Mn and Ni show different segregation tendencies at FM and PM states. This part of the thesis puts forward an attempt to investigate the solute segregation properties in complex solid solutions as compared to pure metal or dilute alloys, and improves our understanding of GB segregation in engineering alloys, like steels.
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